Media loading device and image forming system

Abstract

To provide a medium loading device capable of suppressing buckling of a medium even when slidability of the medium deteriorates below a level assumed from a recording density, and suppressing deterioration of productivity when the slidability of the medium does not deteriorate to such a degree as to be assumed from the recording density.SOLUTION: A medium loading device 11 comprises: a side end aligning member which is located at a standby position WP when a medium is discharged and aligns the side end of the medium; and a control unit. The control unit specifies a first position WP1 which overlaps with a medium M1 to be discharged this time in a width direction X as the standby position WP when a value based on the first information relating to a recording density of at least one medium of the medium M1 to be discharged this time and a medium discharged last time is equal to or larger than a threshold value, and specifies a second position WP2 which does not overlap with the medium M1 to be discharged this time in the width direction X as the standby position WP when the value based on the first information is less than the threshold value. The control unit adjusts the threshold value based on second information relating to at least one medium of the media recorded until the discharge of this time.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a medium loading device that loads printed media, and an image forming system that includes the medium loading device. [Background technology]

[0002] The sheet stacking device described in Patent Document 1 includes a discharge means for discharging sheets on which an image has been formed, a first stacking section on which the discharged sheets are stacked, and an alignment member that is provided below the discharge means and is movable in a width direction perpendicular to the sheet conveying direction by the discharge means. The alignment member aligns the sheets by contacting side edges in the width direction of the discharged sheets. The sheets are an example of a medium, the discharge means is an example of a discharge section, the first stacking section is an example of a processing tray, and the alignment member is an example of a side edge alignment section.

[0003] Immediately after an image is formed on a medium using the inkjet method, the medium is wet with ink. The wetter the medium, the lower the slidability of the medium. More specifically, the greater the amount of ink used to form an image on the medium surface, the greater the water content of the medium surface, so the higher the image ratio of the medium, the lower the slidability of the medium. Therefore, when the image ratio of a medium is high, the medium being discharged may buckle due to the sliding resistance with the medium surface of the medium already loaded, and may not be discharged normally. The image ratio is an example of a recording density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-090376 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the medium loading device described in Patent Document 1, when the recording density of the medium is equal to or greater than a threshold value, the side edge alignment section moves inward from the side edge of the medium discharged by the discharge section when the discharge section discharges the medium. Then, after the medium is discharged by the discharge section, the side edge alignment section moves outward from the side edge of the medium discharged by the discharge section and then contacts the side edge of the discharged medium to align the medium. In other words, when the recording density of the medium is equal to or greater than the threshold value, more processing time is required for alignment compared to when the recording density of the medium is less than the threshold value, which reduces the productivity of the medium loading device.

[0006] Even if the recording density is the same, the slidability of the medium when it is discharged from the discharge section is not necessarily the same. For example, when the leading edge of the medium discharged from the discharge section is curled downward, the angle at which the media surface of the leading edge of the medium hits the media surface that is already loaded is an obtuse angle, and the slidability of the medium is reduced. In addition, the moisture content of the media surface also changes depending on the time from when an image is formed on the medium until the medium is discharged and the environmental conditions. That is, even if the recording density is the same, the slidability of the medium when it is discharged from the discharge section changes due to other factors. Therefore, if the side end alignment section is not moved inward from the side end of the medium discharged by the discharge section when the slidability of the medium is reduced more than expected from the recording density of the medium, there is a risk of the medium buckling. In addition, if the side end alignment section is moved inward from the side end of the medium discharged by the discharge section even though the slidability of the medium is not reduced as much as expected from the recording density due to other factors, there is a risk of the productivity of the medium loading device being reduced. [Means for solving the problem]

[0007] A medium loading device that solves the above problem includes an ejection unit that repeatedly ejects media recorded on by a recording unit that ejects liquid to perform recording, a processing tray that loads the media in the order they are ejected by the ejection unit, a side end alignment member that is positioned below the medium currently ejected and is positioned at a standby position when the medium is ejected, and then moves in a width direction perpendicular to the ejection direction of the medium to align the side end of the medium with the side end of the medium loaded on the processing tray, and a control unit that controls the side end alignment member, wherein if a value based on first information related to the recording density of at least one of the medium currently ejected and the medium previously ejected is equal to or greater than a threshold value, the control unit specifies a first position that overlaps with the medium currently ejected in the width direction as the standby position, and if the value based on the first information is less than the threshold value, specifies a second position that does not overlap with the medium currently ejected in the width direction as the standby position, and the control unit adjusts the threshold value based on second information related to at least one of the media recorded up to the current ejection.

[0008] A medium loading device that solves the above problem includes a discharge unit that repeatedly discharges media recorded by a recording unit that performs recording by ejecting liquid, a processing tray that loads the media in the order in which they are discharged by the discharge unit, a side edge alignment member that is disposed below the medium currently discharged, that is positioned at a standby position when the medium is discharged, and then moves in a width direction perpendicular to the discharge direction of the medium to align a side edge of the medium with a side edge of the medium loaded on the processing tray, and a control unit that controls the side edge alignment member, and the control unit determines whether or not the side edge alignment member is aligned based on first information related to the recording density of at least one of the medium currently discharged and the medium previously discharged. If the value based on the first information is equal to or greater than a threshold value, a first position that overlaps with the medium currently being discharged in the width direction is specified as the standby position, and if the value based on the first information is less than the threshold value, a second position that does not overlap with the medium currently being discharged in the width direction is specified as the standby position, and the control unit determines a control parameter for controlling at least one of the position in the width direction of the first position and the time that the side end alignment member waits at the first position based on second information related to at least one of the media recorded up to the current discharge, and controls the side end alignment member with the control parameter determined based on the second information.

[0009] An image forming system that solves the above problem includes a recording unit that ejects liquid onto a medium to record, a discharge unit that repeatedly discharges the medium recorded on by the recording unit, a processing tray that loads the medium in the order they are discharged by the discharge unit, a side end alignment member that is positioned below the medium currently discharged and is positioned at a standby position when the medium is discharged, and then moves in a width direction perpendicular to the discharge direction of the medium to align the side end of the medium with the side end of the medium loaded on the processing tray, and a control unit that controls the side end alignment member, wherein if a value based on first information related to the recording density of at least one of the medium currently discharged and the medium previously discharged is equal to or greater than a threshold value, the control unit specifies a first position that overlaps with the medium currently discharged in the width direction as the standby position, and if the value based on the first information is less than the threshold value, specifies a second position that does not overlap with the medium currently discharged in the width direction as the standby position, and the control unit adjusts the threshold value based on second information related to at least one of the media recorded up to the current discharge.

[0010] An image forming system that solves the above problem includes a recording unit that performs recording by ejecting liquid onto a medium, a discharge unit that repeatedly discharges the medium recorded on by the recording unit, a processing tray that stacks the media in the order they are discharged by the discharge unit, a side edge alignment member that is disposed below the medium currently discharged and is positioned at a standby position when the medium is discharged, and then moves in a width direction perpendicular to the discharge direction of the medium to align a side edge of the medium with a side edge of the medium stacked on the processing tray, and a control unit that controls the side edge alignment member, and the control unit is configured to perform a first determination related to the recording density of at least one of the medium currently discharged and the medium previously discharged. If the value based on one piece of information is greater than or equal to a threshold value, a first position that overlaps with the medium being currently discharged in the width direction is identified as the waiting position, and if the value based on the first information is less than the threshold value, a second position that does not overlap with the medium being currently discharged in the width direction is identified as the waiting position.The control unit determines a control parameter that controls at least one of the position of the first position in the width direction and the time that the side end alignment member waits at the first position based on second information related to at least one of the media recorded up to the current discharge, and controls the side end alignment member with the control parameter determined based on the second information. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a medium loading device and an image forming system. [Diagram 2] FIG. 2 is a side cross-sectional view showing a loading section of the medium loading device. [Diagram 3] FIG. 4 is a schematic side view showing the state of the medium when it is ejected. [Figure 4] 4 is a plan view showing the positional relationship between the first side edge guide member, the second side edge guide member, and the medium. FIG. [Diagram 5] 5 is a schematic diagram showing a state of the medium when the first side edge guide member is located at a first position. FIG. [Figure 6] 6 is a schematic diagram showing a state of the medium when the first side edge guide member is located at a second position. FIG. [Figure 7]6 is a schematic diagram showing a state of the medium when the second side edge guide member is located at a first position. FIG. [Figure 8] 11 is a schematic diagram showing a state of the medium when the second side edge guide member is located at a second position. FIG. [Figure 9] FIG. 2 is a block diagram showing the configuration of a medium loading device and an image forming system. [Figure 10] 5 is a flowchart showing a control method of a medium alignment operation in the first embodiment. [Figure 11] 5 is a flowchart showing a threshold adjustment process in the first embodiment. [Figure 12] 11 is a flowchart showing a control parameter determination process. [Figure 13] 13 is a flowchart showing a medium alignment operation. [Figure 14] 11 is a flowchart showing a side edge aligning operation. [Figure 15] 10 is a flowchart showing a control method of a medium alignment operation in the second embodiment. [Figure 16] 10 is a flowchart showing a threshold adjustment process in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a medium loading device and an image forming system including the medium loading device according to the first and second embodiments will be described with reference to the drawings. The image forming system performs an image forming process in which ink, which is an example of a liquid, is discharged onto a medium such as paper, and characters and images are recorded onto the medium, and the recorded medium is loaded and a predetermined post-processing is performed.

[0013] In the drawings, the direction of gravity is indicated by the Z axis, assuming that the medium loading device and the image forming system including the medium loading device are placed on a horizontal plane, and the directions along the horizontal plane are indicated by the X and Y axes. The X, Y, and Z axes are perpendicular to one another. In the following description, the direction along the X axis is also referred to as the width direction X, the direction along the Y axis is also referred to as the depth direction Y, and the direction along the Z axis is also referred to as the gravity direction Z.

[0014] The length of the medium in the transport direction is referred to as the length direction Y1. The length of the medium in the direction perpendicular to the transport direction is the same as the width direction X in the image forming system. Therefore, the length of the medium in the direction perpendicular to the transport direction is also referred to as the width direction X. The length of the medium in the direction perpendicular to the transport direction is referred to as the medium width A, and the length of the medium in the transport direction is referred to as the medium length B.

[0015] (First embodiment) <Overview of image forming system> 1, image forming system 200 includes a recording device 111 that records on medium M, and a medium loading device 11 that loads medium M in units of copies and discharges it as a media stack. Recording device 111 records on medium M using a recording unit 160 that performs recording by ejecting liquid. Recording device 111 is, for example, an inkjet printer that ejects ink onto medium M to print characters and images. After media M recorded by recording device 111 are loaded into medium loading device 11 to form a media stack, post-processing such as stapling to bind the media stack may be performed.

[0016] The image forming system 200 may include a transport device 210 that transports the medium M recorded by the recording device 111 and discharged from the recording device 111 to the medium loading device 11. That is, the recording device 111 and the medium loading device 11 may be directly connected, or the recording device 111 and the medium loading device 11 may be connected via the transport device 210.

[0017] The image forming system 200 may include one or more processing devices separate from the medium loading device 11. For example, a folding device 220 that performs folding processing on the medium M transported to the medium loading device 11 or the media bundle loaded in the medium loading device 11 may be connected to the medium loading device 11.

[0018] Recording device 111 includes one or more medium storage units 112 capable of storing medium M, and a main body unit 113 having a recording unit 160 that records on medium M. Recording device 111 may also include a first discharge tray 114 to which medium M is discharged, and an operation unit 115 such as a touch panel for operating recording device 111. Recording device 111 may also include an image reading unit 116 that reads an image of a document, and an automatic feed unit 117 that sends the document to image reading unit 116.

[0019] The medium loading device 11 includes a second discharge tray 12 onto which the medium M is discharged, and a stacker tray 13 capable of stacking a large amount of the medium M. The medium M is discharged onto the first discharge tray 114 of the recording device 111 with the recorded side facing downward. The medium M is discharged onto the second discharge tray 12 of the medium loading device 11 with the recorded side facing upward.

[0020] <Configuration of the media loading device and media loading process flow> 2, the medium loading device 11 includes a transport section 70 that transports the medium M, and a loading section 20 that loads the medium M in units of copies and discharges it as a media bundle. The transport section 70 has an input path 76 that loads the medium M from the recording device 111, a first transport path 78, a second transport path 79, and a branching section 77 that branches the input path 76 into the first transport path 78 and the second transport path 79. The loading section 20 includes a processing tray 21 that loads the medium M and performs a shift process or the like that moves the discharge position of the medium M in the width direction X in units of copies, and a bundle discharge section 51 that discharges the medium M loaded on the processing tray 21 as a media bundle onto the stacker tray 13.

[0021] The medium M is carried in from an inlet section (not shown) of the medium loading device 11, and is transported upward by the inlet path 76. The branching section 77 is configured to be able to switch whether the medium M transported on the inlet path 76 is transported to the first transport path 78 side or the second transport path 79 side. When the medium M is transported to the first transport path 78 side by the branching section 77, the medium M is transported by the first transport path 78 and then discharged to the second discharge tray 12 located above the medium loading device 11. When the medium M is transported to the second transport path 79 side by the branching section 77, the medium M is transported by the second transport path 79 to the stacking section 20 and then discharged to the processing tray 21 located inside the medium loading device 11.

[0022] The transport unit 70 has a discharge unit 71 that discharges the medium M transported on the second transport path 79 onto the processing tray 21. The discharge unit 71 is configured as a discharge roller pair 72 including a discharge drive roller 72a that is driven to rotate by a transport motor (not shown) and a discharge driven roller 72b that is nipped with the discharge drive roller 72a and rotates in a driven manner. The discharge unit 71 repeatedly discharges the medium M recorded by the recording unit 160 shown in FIG. 1 that performs recording by ejecting liquid. The processing tray 21 stacks the medium M in the order in which they were discharged by the discharge unit 71.

[0023] The end of the medium M that is first discharged from the discharge section 71 is referred to as the leading end, and the end that is last discharged from the discharge section 71 is referred to as the trailing end. In other words, the ends of the medium M in the length direction Y1 are the leading end and the trailing end. Also, the ends of the medium M in the width direction X are referred to as the side ends.

[0024] When medium M is discharged by discharge section 71, a medium discharge operation is performed in processing tray 21, and when the rear end of medium M is discharged from discharge section 71, a medium alignment operation is performed in processing tray 21. In the medium alignment operation, first, a rear end alignment operation is performed to align the rear end of medium M, and then a side end alignment operation is performed to align the side ends of medium M. Details of the medium discharge operation, rear end alignment operation, and side end alignment operation will be described later.

[0025] Each time media M is discharged, the media M is loaded on the processing tray 21, and each time media M is loaded, the media M is aligned on the processing tray 21. Therefore, an aligned bundle of media is formed on the processing tray 21. Then, the position of the bundle of media in the width direction X when it is discharged onto the stacker tray 13 is shifted in the width direction X relative to the bundle of media discharged onto the stacker tray 13 immediately before this bundle of media. In this manner, the shift process is performed on the processing tray 21. Details of the shift process will be described later.

[0026] The bundle discharge section 51 is configured as a bundle discharge roller pair 52 including a bundle discharge drive roller 52a that is driven to rotate by a bundle discharge motor (not shown) and a bundle discharge driven roller 52b that is nipped with the bundle discharge drive roller 52a and rotates in a driven manner. The bundle discharge drive roller 52a is located at the end on the stacker tray 13 side on the processing tray 21. The bundle discharge driven roller 52b is configured to be able to switch its position between a nip position shown by a two-dot chain line in FIG. 2 where it is nipped with the bundle discharge drive roller 52a, and a separated position shown by a solid line in FIG. 2 where it is separated from the bundle discharge drive roller 52a and located above the bundle discharge drive roller 52a.

[0027] When the discharge section 71 discharges the medium M onto the processing tray 21, the bundle discharge driven roller 52b is located at the separated position shown by the solid line in Fig. 2. By positioning the bundle discharge driven roller 52b away from the bundle discharge drive roller 52a, a space is formed between the bundle discharge driven roller 52b and the bundle discharge drive roller 52a. This allows the medium M to be discharged onto the processing tray 21 without coming into contact with the bundle discharge driven roller 52b. Then, the medium alignment operation allows the medium M to be aligned on the processing tray 21.

[0028] When a media bundle aligned by the media alignment operation is formed on the processing tray 21 and the media bundle is discharged to the stacker tray 13, the bundle discharge driven roller 52b moves down from the separated position shown by the solid line in Fig. 2 to position at the nip position shown by the two-dot chain line in Fig. 2. Then, the bundle discharge drive roller 52a is rotationally driven by a bundle discharge motor (not shown), whereby the media bundle is discharged from the processing tray 21 to the stacker tray 13.

[0029] <About media ejection> 3, the discharge unit 71 discharges the currently discharged medium M1 onto the processing tray 21. When no medium M is loaded onto the processing tray 21, the currently discharged medium M1 is discharged directly onto the processing tray 21. That is, when the currently discharged medium M1 is the first medium M in the set of copies, the discharge unit 71 discharges the currently discharged medium M1 directly onto the processing tray 21. When the processing tray 21 is loaded with medium M, the currently discharged medium M1 is discharged onto the medium Ms loaded onto the processing tray 21. That is, when the currently discharged medium M1 is not the first medium M in the set of copies, the discharge unit 71 discharges the currently discharged medium M1 onto the previously discharged medium M2.

[0030] When the discharge unit 71 discharges the medium M1 to be discharged this time, the medium M1 to be discharged this time is discharged onto the processing tray 21 starting from the leading end portion M1a of the medium M1 to be discharged this time. When the leading end portion M1a of the medium M1 to be discharged this time is discharged from the discharge unit 71, the lower surface of the leading end portion M1a comes into contact with the upper surface of the previously discharged medium M2. As the leading end portion M1a is discharged, the currently discharged medium M1 is discharged while the lower surface of the leading end portion M1a rubs against the upper surface of the previously discharged medium M2. Depending on conditions such as the medium length B of the currently discharged medium M1, the curl direction of the leading end portion M1a, and the number of media Ms loaded on the processing tray 21, the lower surface of the leading end portion M1a of the currently discharged medium M1 may not come into contact with the upper surface of the previously discharged medium M2.

[0031] When the lower surface of the medium M1 discharged this time comes into contact with the upper surface of the medium M2 discharged last time, a frictional force F1 is generated between the lower surface of the medium M1 discharged this time and the upper surface of the medium M2 discharged last time. In the following description, the "frictional force F1 between the lower surface of the medium M1 discharged this time and the upper surface of the medium M2 discharged last time" is simply referred to as the "frictional force F1". When the frictional force F1 is large, when the medium M1 discharged this time is discharged, the medium M1 discharged this time may buckle. Note that according to the bending strength of the medium M1 discharged this time, a resistance force F2 that resists buckling is generated in the medium M1 discharged this time. In the following description, the "resistance force F2 that resists buckling generated in the medium M1 discharged this time" is simply referred to as the "resistance force F2". When the resistance force F2 is larger than the frictional force F1, the medium M1 discharged this time is less likely to buckle. More specifically, when F1 > F2, the medium M1 discharged this time is likely to buckle, and when F1 < F2, the medium M1 discharged this time is less likely to buckle. That is, the ease of buckling of the medium M1 discharged this time is caused by the frictional force F1 and the resistance force F2.

[0032] As shown in FIG. 4, the loading portion 20 has a first side end guiding member 41 that is disposed below one side in the width direction X of the medium M1 discharged this time and moves in the width direction X. The side ends of the medium M1 discharged this time are the first side end M1c and the second side end M1d. One side is the first side end M1c side, which is the -X direction side in the width direction X. The other side is the second side end M1d side, which is the +X direction side in the width direction X.

[0033] When the medium M1 discharged this time is discharged, the first side end guiding member 41 is located at one of the standby positions WP, namely the first position WP1 and the second position WP2. The first position WP1 is a position that overlaps the medium M1 discharged this time in the width direction X, and the second position WP2 is a position that does not overlap the medium M1 discharged this time in the width direction X.

[0034] The first side end guide member 41 has an alignment surface 41a that abuts against the first side end M1c of the currently discharged medium M1 to align the currently discharged medium M1. The alignment surface 41a is a surface perpendicular to the width direction X. In the width direction X, the position of the first side end guide member 41 when the alignment surface 41a overlaps with the expected first side end M1c of the currently discharged medium M1 when the currently discharged medium M1 is discharged from the discharge section 71 is referred to as the reference position RP. When the first side end guide member 41 is located on the +X direction side of the reference position RP, it is assumed that the first side end guide member 41 overlaps with the currently discharged medium M1 in the width direction X, and therefore the first side end guide member 41 is said to be located at the first position WP1. Furthermore, when the first side end guide member 41 is located on the -X direction side of the reference position RP, it is assumed that the first side end guide member 41 does not overlap with the currently discharged medium M1 in the width direction X, and therefore the first side end guide member 41 is said to be located at the second position WP2. Note that "expected to overlap" may be expressed as "overlaps" and "expected not to overlap" may be expressed as "does not overlap".

[0035] When the standby position WP of the first side end guide member 41 is the second position WP2, the first side end guide member 41 does not overlap with the currently discharged medium M1 in the width direction X. Therefore, as soon as the currently discharged medium M1 starts to be discharged, the bottom surface of the leading end portion M1a of the currently discharged medium M1, shown by the solid line in FIG. 3, comes into contact with the top surface of the previously discharged medium M2, at least on the first side end M1c side.

[0036] When the standby position WP of the first side end guide member 41 is the first position WP1, the first side end guide member 41 overlaps with the medium M1 to be discharged this time in the width direction X. Therefore, for a while after the medium M1 to be discharged this time starts to be discharged, the lower surface of the leading end portion M1a of the medium M1 to be discharged this time, indicated by the two-dot chain line in FIG. 3, does not come into contact with the upper surface of the medium M2 discharged last time, on the first side end M1c side. That is, on the first side end M1c side, the first side end guide member 41 suppresses contact between the leading end portion M1a of the medium M1 to be discharged this time and the medium M2 discharged last time. Therefore, it is possible to delay the timing at which the lower surface of the leading end portion M1a of the medium M1 to be discharged this time comes into contact with the upper surface of the medium M2 discharged last time. Then, even after the lower surface of the leading end portion M1a of the medium M1 to be discharged this time comes into contact with the upper surface of the medium M2 discharged last time, the first side end guide member 41 can continue to suppress contact between the medium M1 to be discharged this time and the medium M2 discharged last time.

[0037] When the first side end guide member 41 is located at the first position WP1, the alignment surface 41a of the first side end guide member 41 overlaps with the currently discharged medium M1 in the width direction X, and a portion moving in the width direction X together with the first side end guide member 41 may overlap with the medium M1. In other words, on the first side end M1c side, a member moving together with the first side end guide member 41 may prevent contact between the tip portion M1a of the currently discharged medium M1 and the previously discharged medium M2.

[0038] The stacking unit 20 has a second side end guide member 42 that is disposed below the other side in the width direction X of the medium M1 currently being discharged and moves in the width direction X. The other side is the second side end M1d side, which is the +X direction side in the width direction X. In this embodiment, the second side end guide member 42 is configured symmetrically to the first side end guide member 41 in the width direction X.

[0039] When the currently discharged medium M1 is discharged, the second side end guide member 42 is located at a standby position WP, which is either the first position WP1 or the second position WP2. The first position WP1 is a position where the second side end guide member 42 overlaps with the currently discharged medium M1 in the width direction X, and the second position WP2 is a position where the second side end guide member 42 does not overlap with the currently discharged medium M1 in the width direction X.

[0040] The second side end guide member 42 has an alignment surface 42a that abuts against the second side end M1d of the currently discharged medium M1 to align the currently discharged medium M1. The alignment surface 41a is a surface perpendicular to the width direction X. In the width direction X, the position of the second side end guide member 42 when the alignment surface 42a overlaps with the expected second side end M1d of the currently discharged medium M1 when the currently discharged medium M1 is discharged from the discharge section 71 is referred to as the reference position RP. When the second side end guide member 42 is located on the -X direction side of the reference position RP, it is assumed that the second side end guide member 42 overlaps with the currently discharged medium M1 in the width direction X, and therefore the second side end guide member 42 is referred to as being located at the first position WP1. In addition, when the second side end guide member 42 is positioned on the +X side of the reference position RP, it is assumed that the second side end guide member 42 does not overlap with the medium M1 being discharged currently in the width direction X, and therefore the second side end guide member 42 is said to be positioned at the second position WP2.

[0041] When the waiting position WP of the second side end guide member 42 is the second position WP2, as soon as the currently discharged medium M1 begins to be discharged, the underside of the tip portion M1a of the currently discharged medium M1, shown by the solid line in Figure 3, comes into contact with the upper surface of the previously discharged medium M2, at least on the second side end M1d side.

[0042] When the standby position WP of the second side end guide member 42 is the first position WP1, for a while after the medium M1 to be discharged this time starts to be discharged, the lower surface of the leading end portion M1a of the medium M1 to be discharged this time does not contact the upper surface of the previously discharged medium M2 on the second side end M1d side. That is, on the second side end M1d side, the second side end guide member 42 suppresses contact between the leading end portion M1a of the medium M1 to be discharged this time and the previously discharged medium M2, as shown by the two-dot chain line in FIG. 3. Therefore, it is possible to delay the timing at which the lower surface of the leading end portion M1a of the medium M1 to be discharged this time contacts the upper surface of the previously discharged medium M2. Then, even after the lower surface of the leading end portion M1a of the medium M1 to be discharged this time contacts the upper surface of the previously discharged medium M2, the second side end guide member 42 can continue to suppress contact between the medium M1 to be discharged this time and the previously discharged medium M2.

[0043] When the second side end guide member 42 is located at the first position WP1, the alignment surface 42a of the second side end guide member 42 overlaps with the currently discharged medium M1 in the width direction X, and a portion moving in the width direction X together with the second side end guide member 42 may overlap with the medium M1. In other words, on the second side end M1d side, a member moving together with the second side end guide member 42 may prevent contact between the tip portion M1a of the currently discharged medium M1 and the previously discharged medium M2.

[0044] <Regarding rear end alignment operation> 3, the stacking unit 20 has a rear end alignment member 31 that is disposed below the discharge unit 71 and above the processing tray 21 and rotates in an alignment direction W1, and a rear end reference surface 32 that serves as a reference surface on the rear end side when aligning the rear end of the currently discharged medium M1. The rear end alignment member 31 is formed of a material such as a rubber material with a large coefficient of friction, and has multiple blade-shaped portions 31a on its outer periphery.

[0045] When the discharge section 71 discharges the currently discharged medium M1, the rear end portion M1b of the currently discharged medium M1 is finally discharged to the processing tray 21. When the rear end portion M1b of the currently discharged medium M1 is discharged, the three blade-shaped portions 31a of the rear end alignment member 31 rotating in the alignment direction W1 sequentially contact the upper surface of the rear end portion M1b of the currently discharged medium M1, and pull the currently discharged medium M1 toward the rear end reference surface 32. Then, the rear end of the currently discharged medium M1 abuts against the rear end reference surface 32.

[0046] Since the coefficient of friction of the blade-shaped portion 31a is large, the rear end alignment member 31 can easily draw the medium M1 to be discharged this time toward the rear end reference surface 32. Furthermore, the blade-shaped portion 31a intermittently contacts the upper surface of the medium M1 to be discharged this time. That is, the blade-shaped portion 31a intermittently draws the medium M1 to be discharged this time. Therefore, it is possible to suppress the medium M1 to be discharged this time from being drawn further toward the rear end reference surface 32 than the state in which the rear end of the medium M1 to be discharged this time abuts against the rear end reference surface 32. As a result, the state in which the rear end of the medium M1 to be discharged this time abuts against the rear end reference surface 32 can be maintained. Note that, in order to prevent the medium M1 to be discharged this time from buckling between the rear end alignment member 31 and the rear end reference surface 32, it is desirable that the position of the rear end alignment member 31 be close to the rear end reference surface 32.

[0047] The trailing end alignment member 31 may rotate constantly, or may rotate for a fixed period of time when the trailing end of the medium M1 currently discharged is discharged by the discharge section 71. The trailing end alignment member 31 may be any member capable of attracting the currently discharged medium M1. The trailing end alignment member 31 may be, for example, a knurled belt, a brush, a sponge roller, or the like.

[0048] 3, the processing tray 21 on which the media M are loaded is disposed at an angle of approximately 30 degrees with respect to the horizontal plane. Gravity acting on the currently discharged media M1 acts to move the currently discharged media M1 toward the rear end reference surface 32 on the processing tray 21, and even after the rear end of the currently discharged media M1 abuts against the rear end reference surface 32, a force acts to maintain that state. This makes it easier to align the currently discharged media M1 toward the rear end reference surface 32, and also makes it possible to prevent the loading state of the currently discharged media M1 from becoming disarrayed after alignment. The angle that the processing tray 21 makes with respect to the horizontal plane may be set to an appropriate value.

[0049] <Side edge alignment operation> 4, in the side edge alignment operation, one of the first side edge guide member 41 and the second side edge guide member 42 is specified as the side edge alignment member, and the guide member specified as the side edge alignment member is controlled as the side edge alignment member. During the side edge alignment operation, the position of the guide member not specified as the side edge alignment member is fixed, and the alignment surface of that guide member becomes the reference surface when aligning the side edges M1c, M1d of the currently discharged medium M1. When the currently discharged medium M1 is discharged, the side edge alignment member is located at a standby position WP, which is either the first position WP1 or the second position WP2.

[0050] First, a side edge aligning operation when the first side edge guide member 41 is controlled as a side edge aligning member and the standby position WP of the first side edge guide member 41 is the first position WP1 will be described. As shown in FIG. 5, when the first side edge guide member 41 is controlled as a side edge alignment member, the position of the second side edge guide member 42 is fixed at the second position WP2, and the alignment surface 42a of the second side edge guide member 42 becomes the reference surface. When the medium M1 to be discharged this time is discharged, the first side edge guide member 41 is located at the first position WP1 as the standby position WP. Then, the first side edge guide member 41 moves in the width direction X perpendicular to the discharge direction of the medium M1 to be discharged this time to perform the side edge alignment operation. More specifically, the first side edge guide member 41 moves away from the first position WP1 to the second position WP2 side, and then moves to the first position WP1 which is the side edge alignment position, and aligns the first side edge M1c of the medium M1 to be discharged this time with the first side edge Msc of the medium Ms loaded on the processing tray 21. In the example shown in FIG. 5, the side edge alignment position is the first position WP1, but the side edge alignment position and the first position WP1 do not have to be the same position. For example, the first position WP1 as the waiting position WP may be located inside the reference position RP and outside the side edge alignment position.

[0051] In other words, the first side edge guide member 41 is configured as a side edge alignment member so as to be located at the standby position WP when the currently discharged medium M1 is discharged, and then be capable of aligning the first side edge M1c of the currently discharged medium M1 with the first side edge Msc of the medium Ms loaded on the processing tray 21. The standby position WP at this time is set to the first position WP1.

[0052] When the standby position WP of the first side end guide member 41 is the first position WP1, when the currently discharged medium M1 is discharged by the discharge section 71, the second side end guide member 42 is located at the second position WP2, and the first side end guide member 41 is located at the first position WP1. Therefore, the first side end guide member 41 located at the first position WP1 overlaps with the currently discharged medium M1 in the width direction X. As a result, on the side of the first side end M1c, the first side end guide member 41 suppresses contact between the currently discharged medium M1 and the previously discharged medium M2.

[0053] At the set timing, the first side end guide member 41 leaves the first position WP1 and starts moving toward the second position WP2. If this timing is early, the side end alignment operation can start at the same time as the trailing end of the currently discharged medium M1 is discharged from the discharge section 71. If this timing is late, contact between the currently discharged medium M1 and the previously discharged medium M2 can be suppressed for a while after the trailing end of the currently discharged medium M1 is discharged from the discharge section 71.

[0054] The distance in the width direction X between the alignment surface 41a of the first side end guide member 41 at the first position WP1 and the first side end M1c of the medium M1 to be discharged this time when it is discharged from the discharge section 71 is referred to as the overlap amount L1. The first side end guide member 41 at the first position WP1 and the medium M1 to be discharged this time are assumed to overlap by the overlap amount L1 in the width direction X on the side of the first side end M1c of the medium M1 to be discharged this time. In the following description, the "distance in the width direction X between the alignment surface 41a of the first side end guide member 41 at the first position WP1 and the first side end M1c of the medium M1 to be discharged this time when it is discharged from the discharge section 71" is simply referred to as the "overlap amount L1". The overlap amount L1 can be increased by setting the first position WP1 of the first side end guide member 41 and the second position WP2 of the second side end guide member 42 further toward the +X direction side. When the overlap amount L1 is large, contact between the currently discharged medium M1 and the previously discharged medium M2 can be further suppressed. When the overlap amount L1 is small, even if the timing at which the first side end guide member 41 leaves the first position WP1 and starts moving toward the second position WP2 is the same, the movement distance to the second position WP2 is small. Therefore, it is possible to shorten the time from when the rear end of the currently discharged medium M1 is discharged from the discharge section 71 until the first side end M1c of the currently discharged medium M1 is aligned with the first side end Msc of the medium Ms loaded on the processing tray 21.

[0055] The first side edge guide member 41 located at the second position WP2 does not overlap with the currently discharged medium M1 in the width direction X. Therefore, when the first side edge guide member 41 moves from the second position WP2 to the first position WP1, the alignment surface 41a of the first side edge guide member 41 can be brought into contact with the first side edge M1c of the currently discharged medium M1. The first side edge guide member 41, as a side edge alignment member, moves in the width direction X perpendicular to the discharge direction of the currently discharged medium M to perform a side edge alignment operation in which the first side edge M1c of the currently discharged medium M is aligned with the first side edge Msc of the medium Ms loaded on the processing tray 21. The first side edge guide member 41 moves from the second position WP2 to the first position WP1 as the side edge alignment position, whereby the first side edge M1c of the currently discharged medium M1 is aligned.

[0056] In order to align the side ends of the medium M, it is desirable that the distance between the first position WP1 of the first side end guide member 41 and the second position WP2 of the second side end guide member 42 when aligning the side ends of the medium M currently being discharged is set equal to the medium width A.

[0057] While the first side end guide member 41 remains positioned at the first position WP1 as the side end alignment position, the discharge section 71 discharges the next medium M. This makes it possible to prevent contact between the currently discharged medium M1 and the previously discharged medium M2 in the next medium M as well.

[0058] Next, a side edge aligning operation performed by the side edge aligning member when the first side edge guiding member 41 is controlled as the side edge aligning member and the standby position WP of the first side edge guiding member 41 is the second position WP2 will be described.

[0059] As shown in FIG. 6, when the first side edge guide member 41 is controlled as a side edge alignment member, the position of the second side edge guide member 42 is fixed at the second position WP2, and the alignment surface 42a of the second side edge guide member 42 becomes a reference surface. When the currently discharged medium M1 is discharged, the first side edge guide member 41 is located at the second position WP2 as a standby position WP. Then, the first side edge guide member 41 moves in the width direction X perpendicular to the discharge direction of the currently discharged medium M1 to perform a side edge alignment operation. More specifically, the first side edge guide member 41 moves from the second position WP2 to the first position WP1, which is the side edge alignment position, and aligns the first side edge M1c of the currently discharged medium M1 with the first side edge Msc of the medium Ms loaded on the processing tray 21.

[0060] In other words, the first side edge guide member 41 is configured as a side edge alignment member so as to be located at the standby position WP when the currently discharged medium M1 is discharged, and then be capable of aligning the first side edge M1c of the currently discharged medium M1 with the first side edge Msc of the medium Ms loaded on the processing tray 21. The standby position WP at this time is set to the second position WP2.

[0061] When the standby position WP of the first side end guide member 41 is the second position WP2, the second side end guide member 42 is located at the second position WP2 and the first side end guide member 41 is located at the second position WP2 when the currently discharged medium M1 is discharged by the discharge section 71. Therefore, the first side end guide member 41 located at the second position WP2 does not overlap with the currently discharged medium M1 in the width direction X.

[0062] When the standby position WP of the first side end guide member 41 is the second position WP2, in the side end aligning operation, the first side end guide member 41 does not need to perform an additional operation of moving from the second position WP2 side to the outside in the width direction X. Therefore, it is possible to shorten the time from when the rear end of the currently discharged medium M1 is discharged from the discharge section 71 to when the first side end M1c of the currently discharged medium M1 is aligned with the first side end Msc of the medium Ms loaded on the processing tray 21.

[0063] Next, a side edge aligning operation performed by the side edge aligning member when the second side edge guiding member 42 is controlled as a side edge aligning member and the standby position WP of the second side edge guiding member 42 is the first position WP1 will be described. Note that in this embodiment, the second side edge guiding member 42 is symmetrical to the first side edge guiding member 41 in terms of configuration and side edge aligning operation in the width direction X, so a common description will be omitted.

[0064] As shown in FIG. 7, when the second side edge guide member 42 is controlled as a side edge alignment member, the position of the first side edge guide member 41 is fixed at the second position WP2, and the alignment surface 41a of the first side edge guide member 41 becomes the reference surface. When the medium M1 to be discharged this time is discharged, the second side edge guide member 42 is located at the first position WP1 as the standby position WP. Then, the second side edge guide member 42 moves in the width direction X perpendicular to the discharge direction of the medium M1 to be discharged this time to perform the side edge alignment operation. More specifically, the second side edge guide member 42 moves away from the first position WP1 to the second position WP2 side, and then moves to the first position WP1, which is the side edge alignment position, to align the second side edge M1d of the medium M1 to be discharged this time with the second side edge Msd of the medium Ms loaded on the processing tray 21. In the example shown in FIG. 7, the side edge alignment position is the first position WP1, but the side edge alignment position and the first position WP1 do not have to be the same position. For example, the first position WP1 as the waiting position WP may be located inside the reference position RP and outside the side edge alignment position.

[0065] In other words, the second side edge guide member 42 is configured as a side edge alignment member so as to be located at the standby position WP when the currently discharged medium M1 is discharged, and then be capable of aligning the second side edge M1d of the currently discharged medium M1 with the second side edge Msd of the medium Ms loaded on the processing tray 21. The standby position WP at this time is set to the first position WP1.

[0066] When the standby position WP of the second side end guide member 42 is the first position WP1, when the currently discharged medium M1 is discharged by the discharge section 71, the first side end guide member 41 is located at the second position WP2, and the second side end guide member 42 is located at the first position WP1. Therefore, the second side end guide member 42 located at the first position WP1 overlaps with the currently discharged medium M1 in the width direction X. As a result, on the side of the second side end M1d, the second side end guide member 42 suppresses contact between the currently discharged medium M1 and the previously discharged medium M2.

[0067] The distance in the width direction X between the alignment surface 42a of the second side end guiding member 42 at the first position WP1 and the expected second side end M1d of the currently discharged medium M1 when it is discharged from the discharge section 71 is referred to as the overlap amount L2. The second side end guiding member 42 at the first position WP1 and the currently discharged medium M1 overlap in the width direction X on the side of the second side end M1d of the currently discharged medium M1. In the following description, "the distance in the width direction X between the alignment surface 42a of the second side end guiding member 42 at the first position WP1 and the expected second side end M1d of the currently discharged medium M1 when it is discharged from the discharge section 71" will simply be referred to as "overlap amount L2."

[0068] The second side edge guide member 42, as a side edge alignment member, moves in the width direction X perpendicular to the discharge direction of the currently discharged medium M to perform a side edge alignment operation of aligning a first side edge M1c of the currently discharged medium M with a first side edge Msc of the medium Ms loaded on the processing tray 21. The second side edge guide member 42 moves from the second position WP2 to the first position WP1 as the side edge alignment position, thereby aligning the second side edge M1d of the currently discharged medium M.

[0069] Next, a side edge aligning operation performed by the side edge aligning member when the second side edge guiding member 42 is controlled as a side edge aligning member and the standby position WP of the second side edge guiding member 42 is the second position WP2 will be described. Note that in this embodiment, the second side edge guiding member 42 is symmetrical to the first side edge guiding member 41 in terms of configuration and side edge aligning operation in the width direction X, so a common description will be omitted.

[0070] As shown in FIG. 8, when the second side edge guide member 42 is controlled as a side edge alignment member, the position of the first side edge guide member 41 is fixed at the second position WP2, and the alignment surface 41a of the first side edge guide member 41 becomes a reference surface. When the currently discharged medium M1 is discharged, the second side edge guide member 42 is located at the second position WP2 as a standby position WP. Then, the second side edge guide member 42 moves in the width direction X perpendicular to the discharge direction of the currently discharged medium M1 to perform a side edge alignment operation. More specifically, the second side edge guide member 42 moves from the second position WP2 to the first position WP1, which is the side edge alignment position, and aligns the second side edge M1d of the currently discharged medium M1 with the second side edge Msd of the medium Ms loaded on the processing tray 21.

[0071] In other words, the second side edge guide member 42 is configured as a side edge alignment member so as to be located at the standby position WP when the currently discharged medium M1 is discharged, and then be capable of aligning the second side edge M1d of the currently discharged medium M1 with the second side edge Msd of the medium Ms loaded on the processing tray 21. The standby position WP at this time is set to the second position WP2.

[0072] When the standby position WP of the second side end guide member 42 is the second position WP2, the first side end guide member 41 is located at the second position WP2 and the second side end guide member 42 is located at the second position WP2 when the currently discharged medium M1 is discharged by the discharge section 71. Therefore, the first side end guide member 41 located at the second position WP2 does not overlap with the currently discharged medium M1 in the width direction X.

[0073] <About shift processing> Before the media bundle with its rear end and side ends aligned is discharged to the stacker tray 13, a shift process is performed on the processing tray 21. After the side end alignment operation, the position of the media bundle in the width direction X is shifted on the processing tray 21 while it is still a media bundle, and the position of the media bundle in the width direction X when it is discharged to the stacker tray 13 is changed.

[0074] When the side edge alignment operation is completed, the alignment surface 41a is in contact with the first side edge Msc of the medium Ms loaded on the processing tray 21, and the alignment surface 42a is in contact with the second side edge Msd of the medium Ms loaded on the processing tray 21. Then, before the medium Ms loaded on the processing tray 21 is discharged to the stacker tray 13, the first side edge guide member 41 and the second side edge guide member 42 are moved at the same speed, at the same timing, and by the same distance in the same direction in the width direction X. This makes it possible to change the position in the width direction X of the medium Ms loaded on the processing tray 21.

[0075] The position of the reference surface when the side ends M1c, M1d of the medium M1 discharged this time are aligned may be changed for each copy unit. For example, the position of the alignment surface 42a serving as the reference surface may be 10 mm away from the reference position RP in the +X direction in the first medium bundle, and 20 mm away from the reference position RP in the +X direction in the next medium bundle. In other words, by changing the position of the reference surface when the side ends M1c, M1d are aligned for each copy unit, the position in the width direction X of the medium Ms loaded on the processing tray 21 when the side ends M1c, M1d are aligned may be changed for each copy unit. For example, the alignment surface 41a may be the reference surface for the first medium bundle, and the alignment surface 42a may be the reference surface for the next medium bundle. In other words, by changing the alignment surface that serves as the reference surface when the side ends M1c, M1d are aligned for each unit of copies, the position in the width direction X of the medium Ms loaded on the processing tray 21 when the side ends M1c, M1d are aligned may be changed for each unit of copies.

[0076] <Image forming system configuration> 9, the recording device 111 includes a recording unit 160 that ejects liquid to perform recording on a medium M, a second transport unit 170 that transports the medium M recorded by the recording unit 160 to the medium loading device 11, and a second control unit 190 that controls the recording device 111. The second control unit 190 has a second storage unit 191 that stores information. In the recording device 111 and medium loading device 11 shown in FIG. 9, components that are not related to loading of the medium M are omitted.

[0077] The recording device 111 may be connected to an external network and receive a recording command from a server, computer, etc. connected to the network. The recording command may include information related to the medium M to be recorded, such as the size of the medium M, the basis weight of the medium M, the type of medium M, the number of pages to be recorded and the recording data for each page, designation of single-sided or double-sided recording, the number of copies to be recorded, the type of post-processing, etc.

[0078] For example, the second storage unit 191 of the recording device 111 stores information such as the size, basis weight, and type of the medium M contained in the recording device 111. When the recording device 111 receives a recording command, the second control unit 190 checks whether the recording device 111 contains a medium M that satisfies the size, basis weight, and type of the medium M contained in the recording command. When the recording device 111 determines that the medium M specified in the recording command is contained in the recording device 111, it accepts the recording command. Then, the second control unit 190 controls the operation of the recording unit 160 and the second conveying unit 170 in response to the recording command to record on the medium M. The recording device 111 may record in response to a recording command from the operation unit 115 shown in FIG. 1.

[0079] The medium loading device 11 includes a loading section 20, a conveying section 70 having a discharge section 71, and a control section 90 that controls the medium loading device 11. The loading section 20 includes a trailing edge alignment section 30 that aligns the trailing edge of the medium M, a side edge alignment section 40 that moves a side edge alignment member to align the side edges of the medium M, and a bundle discharge section 51 that discharges the aligned bundle of media. The control section 90 includes a storage section 91 that stores information. The movement of the side edge alignment member is controlled by the control section 90. Information is exchanged between the control section 90 and the second control section 190 by wired or wireless communication. The medium loading device 11 may include a post-processing section 60 that performs post-processing on a medium sheet unit or on a number of copies unit. The post-processing on a medium sheet unit is, for example, a punching process. The post-processing on a number of copies unit is, for example, a stapling process. The post-processing on a number of copies unit may be a punching process.

[0080] The medium loading device 11 may include a temperature and humidity measuring unit 80. The temperature and humidity measuring unit 80 measures the temperature and humidity of the environment in which the image forming system 200 is installed. The temperature and humidity measuring unit 80 is intended to measure the temperature and humidity of the environment in which the medium M is recorded by the recording unit 160. Therefore, the recording device 111 equipped with the recording unit 160 may also include the temperature and humidity measuring unit 80.

[0081] <Information about media> As shown in FIG. 9, when the medium M recorded by the recording unit 160 is discharged from the recording device 111 to the medium loading device 11, the second control unit 190 notifies the control unit 90 of information related to the medium M1 to be discharged this time. When the medium M1 to be discharged this time is the last medium in the number of copies, information indicating that the medium M1 is the last medium in the number of copies is notified in addition to the information related to the medium M1 to be discharged this time. Note that the medium M1 to be discharged this time from the recording device 111 to the medium loading device 11 is the medium M1 to be discharged this time to the processing tray 21 by the discharge unit 71. The information related to the medium M1 to be discharged this time is stored in the storage unit 91 as information related to the medium recorded up until this discharge, and is stored in the storage unit 91 at least until the processing in the number of copies is completed in the medium loading device 11. Note that there is a time lag corresponding to the transport time required for transport between the medium M1 discharged this time from the recording device 111 to the medium loading device 11 and the medium M1 to be discharged this time to the processing tray 21 by the discharge unit 71.

[0082] The information related to the currently discharged medium M1 is information necessary for the medium loading device 11 to load the currently discharged medium M recorded by the recording device 111 and discharge it as a media stack. For example, the size of the medium M is information necessary when a media alignment operation is performed. By being notified of the medium width A and the medium length B, the medium loading device 11 can align the currently discharged medium M1 with the notified size of the medium M when loading the currently discharged medium M1.

[0083] The tendency of the currently discharged medium M1 to buckle during the medium discharge operation is due to frictional force F1 and resistance force F2. That is, information related to frictional force F1 and information related to resistance force F2 are information on factors of the tendency of buckling. Therefore, information related to the currently discharged medium M1 includes information related to frictional force F1 and information related to resistance force F2.

[0084] The information related to the currently discharged medium M1 includes the recording density on the bottom surface of the currently discharged medium M1 and the recording density on the top surface of the currently discharged medium M1. In the following description, the "recording density on the bottom surface of the currently discharged medium M1" is simply referred to as the "first bottom surface recording density," and the "recording density on the top surface of the currently discharged medium M1" is simply referred to as the "first top surface recording density."

[0085] The print density refers to the amount of liquid ejected per area of ​​the medium M. The print density is indicated as 0 to 100%. For example, the print density is the ratio of the number of dots that the printing unit 160 can eject onto the medium M to the number of dots that have actually been ejected.

[0086] The print density may also be the print ratio of the medium M. The print ratio of the medium M is the ratio of the print area to the area of ​​the medium M. Furthermore, the print density may be given by the product of the liquid ejection amount per area of ​​the medium M and the print ratio of the medium M.

[0087] The higher the recording density, the wetter the medium surface is with ink. The wetter the medium M is, the lower the slidability of the medium M is, and the greater the friction force F1 is. Therefore, the first lower-surface recording density and the first upper-surface recording density are information related to the friction force F1.

[0088] If there is a difference in recording density between the upper surface and the lower surface of the medium M, the end of the medium M curls toward the side with the lower recording density. More specifically, when the fibers of the medium M absorb moisture and expand, if there is a difference in recording density between the upper surface and the lower surface of the medium M, the expansion rate of the fibers is different. Therefore, the end of the medium M curls toward the side with the lower expansion rate. That is, the curl state of the medium M can be estimated from the difference in recording density between the upper surface and the lower surface of the medium M. For example, when the tip portion M1a of the medium M1 to be discharged this time is not curled, the angle at which the tip portion M1a of the medium M1 to be discharged this time contacts the medium M2 discharged last time is an acute angle. On the other hand, for example, if the tip of the medium M1 to be discharged this time curls downward, the angle at which the tip portion M1a of the medium M1 to be discharged this time contacts the medium M2 discharged last time is an obtuse angle. This increases the frictional force F1, thereby reducing the slidability. That is, the subtraction value obtained by subtracting the first lower-surface recording density from the first upper-surface recording density is a value that substitutes for the curl amount of the medium M1 to be discharged this time. In the following description, the "subtraction value obtained by subtracting the first lower-surface recording density from the first upper-surface recording density" will be simply referred to as the "subtraction value." The second control unit 190 may notify the control unit 90 of the subtraction value as information related to the medium M1 to be discharged this time.

[0089] The information related to the medium M1 currently being discharged may include the actual curl amount of the medium M1 currently being discharged. For example, the recording device 111 may be equipped with a curl sensor (not shown) that measures the curl amount of the medium M1 currently being discharged, and the second control unit 190 may notify the control unit 90 of the measured curl amount as information related to the medium M1 currently being discharged. In addition, if the curl amount of the medium M1 currently being discharged can be estimated from the image pattern to be recorded, the second control unit 190 may notify the control unit 90 of the estimated curl amount as information related to the medium M1 currently being discharged. Note that the value that substitutes for the curl amount of the medium M1 currently being discharged, including the curl amount and the subtraction value, is information related to the friction force F1.

[0090] The information related to the medium M1 being discharged this time may include a recording density distribution in the width direction X of the bottom surface of the medium M1 being discharged this time, or may include a recording density distribution in the width direction X of the top surface of the medium M1 being discharged this time. In the following description, the "recording density distribution in the width direction X of the bottom surface of the medium M1 being discharged this time" will be simply referred to as the "first bottom surface width direction recording density distribution." Also, the "recording density distribution in the width direction X of the top surface of the medium M1 being discharged this time" will be simply referred to as the "first top surface width direction recording density distribution." Also, the "recording density distribution in the width direction X of the top surface of the medium M2 discharged last time" will be simply referred to as the "second top surface width direction recording density distribution."

[0091] For example, the lower medium surface of the currently ejected medium M1 is divided into two in the width direction X, the medium surface on the first side end M1c side and the medium surface on the second side end M1d side. The first lower surface width direction recording density distribution is composed of two pieces of information: the recording density of the lower medium surface on the first side end M1c side and the recording density of the lower medium surface on the second side end M1d side. The number of divisions may be three or more.

[0092] The first lower surface width direction recording density distribution and the first upper surface width direction recording density distribution are information related to the friction force F1. For example, the control unit 90 can determine which of the friction forces F1 is larger, the friction force F1 of the medium surface on the first side end M1c side or the friction force F1 of the medium surface on the second side end M1d side, on the lower surface of the medium M1 to be discharged this time, based on the first lower surface width direction recording density distribution. For example, the control unit 90 can determine which of the friction forces F1 is larger, the friction force F1 of the medium surface on the first side end M1c side or the friction force F1 of the medium surface on the second side end M1d side, on the upper surface of the medium M1 to be discharged this time, based on the first upper surface width direction recording density distribution.

[0093] The information related to the medium M1 being discharged this time may include a recording density distribution in the length direction Y1 of the bottom surface of the medium M1 being discharged this time, or may include a recording density distribution in the length direction Y1 of the top surface of the medium M1 being discharged this time. In the following description, the "recording density distribution in the length direction Y1 of the bottom surface of the medium M1 being discharged this time" will be simply referred to as the "first bottom surface length direction recording density distribution." Also, the "recording density distribution in the length direction Y1 of the top surface of the medium M1 being discharged this time" will be simply referred to as the "first top surface length direction recording density distribution."

[0094] The first lower surface length direction record density distribution and the first upper surface length direction record density distribution are information related to the friction force F1. The currently discharged medium M1 is discharged while the lower surface of the leading end portion M1a of the currently discharged medium M1 rubs against the upper surface of the previously discharged medium M2. The first lower surface length direction record density distribution and the first upper surface length direction record density distribution notified to the control unit 90 allow the record density of the portion where the medium M rubs to be grasped, and the magnitude of the friction force F1 of the portion where the medium M rubs to be determined more accurately.

[0095] The information related to the medium M1 currently being discharged includes the size of the medium M1 currently being discharged. The size of the medium M1 currently being discharged is information required when a medium alignment operation is performed in the medium loading device 11. Since a medium M with a long medium length B or a medium M with a short medium width A has a small bending strength, the size of the medium M1 currently being discharged is also information related to the resistance force F2.

[0096] The information related to the currently discharged medium M1 may include the basis weight of the currently discharged medium M1. The basis weight of the currently discharged medium M1 is the weight per unit area of ​​the currently discharged medium M1, and the smaller the basis weight, the smaller the bending strength of the medium M, so the basis weight of the currently discharged medium M1 is information related to the resistance force F2.

[0097] The information related to the medium M1 currently being discharged may include the type of medium M1 currently being discharged. The type of medium M1 currently being discharged is, for example, the brand and grain direction of the medium M1 currently being discharged. Because the bending strength may differ depending on the brand of the medium M1 currently being discharged, the brand of the medium M1 currently being discharged is information related to the resistance force F2. In addition, because the bending strength is smaller when the grain direction is the width direction X compared to when the grain direction is the length direction Y1, the grain direction is information related to the resistance force F2.

[0098] When the recording device 111 includes the temperature and humidity measuring unit 80, the information related to the medium M1 to be discharged this time may include the temperature and humidity of the environment in which the medium M1 to be discharged this time was recorded. For example, when the medium M recorded by the recording unit 160 is discharged from the recording device 111 to the medium loading device 11, the second control unit 190 may notify the control unit 90 of the value measured by the temperature and humidity measuring unit 80 as information related to the medium M1 to be discharged this time. For example, when the humidity of the environment in which the medium M1 to be discharged this time was recorded is high, it takes a long time for the medium surface to dry, so the humidity of the environment in which the medium M1 to be discharged this time was recorded is information related to the frictional force F1. In addition, when the temperature of the environment in which the medium M1 to be discharged this time was recorded is low, the moisture content is not improved by the drying process, and it takes a long time for the medium surface to dry, so the temperature of the environment in which the medium M1 to be discharged this time was recorded is information related to the frictional force F1. Note that the effect of temperature is smaller than the effect of humidity.

[0099] The information related to the medium M1 to be discharged this time may include the time when the medium M1 to be discharged this time was recorded. The control unit 90 subtracts the time when the medium M1 to be discharged this time from the time when the medium M1 to be discharged this time is discharged. In this way, the control unit 90 can calculate the elapsed time from when the medium M1 to be discharged this time was recorded to when it is discharged. In the following description, the "elapsed time from when the medium M1 to be discharged this time was recorded to when it is discharged" is simply referred to as the "first elapsed time". The control unit 90 may use the first elapsed time to control the side edge alignment operation. If the first elapsed time is short, the medium surface is not yet dry, so the time when the medium M1 to be discharged this time was recorded is information related to the friction force F1. The second control unit 190 may notify the control unit 90 of the elapsed time from when the medium M1 to be discharged this time was recorded to when the medium M1 to be discharged this time is discharged from the recording device 111 to the medium loading device 11 as information related to the medium M1 to be discharged this time.

[0100] Information such as the transport speed of the medium M in the recording device 111, the resolution at the time of recording, and the processing content of the medium M may be used as a substitute for the first elapsed time. In other words, information related to the medium M1 currently discharged may include information that can be used as a substitute for the first elapsed time, such as the transport speed of the medium M1 currently discharged in the recording device 111, the resolution at the time of recording, and the processing content of the medium M1 currently discharged. If the transport speed of the medium M is slow, the first elapsed time will be long. If the resolution at the time of recording is high, the recording time will be long, and therefore the first elapsed time will be long. The first elapsed time will be long depending on the processing content of the medium M. For example, if a reverse discharge process or a double-sided recording process is performed on the medium M, the first elapsed time will be long.

[0101] Information related to the medium M1 to be discharged this time may be input by a user. For example, the user may input information related to the medium M1 to be discharged this time using operation unit 115 shown in FIG. 1 that is provided in recording device 111. Alternatively, medium loading device 11 may be provided with an operation unit (not shown) that allows input by the user, and the user may input information related to the medium M1 to be discharged this time using that operation unit. For example, the user may input the temperature and humidity of the environment in which medium M1 to be discharged this time was recorded.

[0102] <Regarding Information 1 and Information 2> The information used to control the medium alignment operation includes information related to the recording density of at least one of the medium M1 being ejected this time and the medium M2 ejected last time, and information related to at least one of the media on which recording has been performed up until this ejection. In the following description, "information related to the recording density of at least one of the medium M1 being ejected this time and the medium M2 ejected last time" is simply referred to as "first information," and "information related to at least one of the media on which recording has been performed up until this ejection" is simply referred to as "second information." There may be multiple pieces of second information.

[0103] Each time the medium M recorded by the recording unit 160 is discharged from the recording device 111 to the medium loading device 11, information related to the currently discharged medium M1 is stored in the memory unit 91. That is, the memory unit 91 stores information related to the medium recorded up until the currently discharged medium.

[0104] The information related to the medium recorded up to the current ejection includes information related to the previously ejected medium M2 and information related to the medium M1 to be ejected this time. The information related to the medium recorded up to the current ejection includes information related to the recording density of the medium recorded up to the current ejection. The control unit 90 uses necessary information from the information related to the currently ejected medium M1 and the information stored in the memory unit 91 as first information and second information for controlling the medium alignment operation.

[0105] The storage unit 91, which stores information related to the medium recorded up to the current ejection, stores the recording density on the top surface of the previously ejected medium M2 and the recording density on the bottom surface of the previously ejected medium M2. In the following description, the "recording density on the top surface of the previously ejected medium M2" will simply be referred to as the "second top surface recording density."

[0106] Since the current medium M1 is discharged while the bottom surface of the leading end portion M1a of the current medium M1 rubs against the top surface of the previously discharged medium M2, a friction force F1 is generated between the bottom surface of the current medium M1 and the top surface of the previously discharged medium M2. The friction force F1 depends on the recording density of at least one of the current medium M1 and the previously discharged medium M2.

[0107] More specifically, if the recording density of the bottom surface of the medium M1 to be discharged this time is high, the moisture content of the bottom surface of the medium M1 to be discharged this time is high. This leads to poor sliding properties of the medium surface, so the frictional force F1 increases and the medium is more likely to buckle. If the recording density of the top surface of the medium M2 discharged last time is high, the moisture content of the top surface of the medium M2 to be discharged last time is high. This leads to poor sliding properties of the medium surface, so the frictional force F1 increases and the medium is more likely to buckle. If the recording density of the top surface of the medium M1 to be discharged this time is higher than the recording density of its bottom surface, the difference in moisture content due to the difference in recording density between the top and bottom surfaces increases, so the tip of the medium M1 to be discharged this time curls downward. This leads to strong contact between the bottom surface of the medium M1 to be discharged this time and the top surface of the medium M2 discharged last time, so the frictional force F1 increases and the medium is more likely to buckle. If the recording density of the bottom surface of the medium M2 to be discharged last time is higher than the recording density of its top surface, the difference in moisture content due to the difference in recording density between the top and bottom surfaces increases, so the tip of the medium M2 to be discharged last time curls upward. As a result, the bottom surface of the medium M1 being discharged this time and the top surface of the medium M2 being discharged last time come into strong contact with each other, and the frictional force F1 increases, making the medium more likely to buckle. In other words, the first information related to the recording density of at least one of the medium M1 being discharged this time and the medium M2 being discharged last time is information related to the frictional force F1 and is a factor of the frictional force F1. Therefore, the first information related to the recording density of at least one of the medium M1 being discharged this time and the medium M2 being discharged last time is used in controlling the medium alignment operation as a factor of the susceptibility of the medium M1 being discharged this time to buckling.

[0108] In this embodiment, the first information is the first bottom-side recording density and the second top-side recording density. The value based on the first information is the total value of the first bottom-side recording density and the second top-side recording density, and is a value based on information related to the recording density of both the medium M1 being discharged this time and the medium M2 discharged last time. The control unit 90 calculates the total value of the first bottom-side recording density and the second top-side recording density, and uses the total value to control the side edge alignment operation. In the following description, the "total value of the first bottom-side recording density and the second top-side recording density" is simply referred to as the "total value." In addition, the "threshold value" used in the following description is a threshold value for the value based on the first information, and in this embodiment, is a threshold value for the total value.

[0109] The currently discharged medium M1 is discharged while the lower surface of the leading end portion M1a of the currently discharged medium M1 rubs against the upper surface of the previously discharged medium M2. The larger the total value, the wetter the medium surfaces slide against each other. That is, the larger the total value, the lower the sliding property between the currently discharged medium M1 and the previously discharged medium M2, so that the frictional force F1 increases and buckling becomes more likely. The total value as a value based on the first information is information related to the frictional force F1 and is a factor of the frictional force F1. Therefore, in this embodiment, the total value is used to control the medium alignment operation as a factor of the ease of buckling in the currently discharged medium M1.

[0110] More specifically, when the sum is greater than the threshold, the standby position WP of the side end alignment member is set to the first position WP1, and the side end alignment member prevents contact between the currently discharged medium M1 and the previously discharged medium M2. This prevents buckling of the currently discharged medium M1. When the sum is less than the threshold, the standby position WP of the side end alignment member is set to the second position WP2, and the time required to align the currently discharged medium M1 can be shortened compared to when the standby position WP is the first position WP1.

[0111] The second control unit 190 may calculate the total value. Then, when the currently discharged medium M1 is discharged from the recording device 111 to the medium stacking device 11, the second control unit 190 may notify the control unit 90 of the total value as information related to the currently discharged medium M1.

[0112] There are other factors that affect the ease of buckling besides the first information. The ease of buckling of the medium M1 being discharged this time is due to the frictional force F1 and the resistance force F2, which is a force that resists the frictional force F1. When the frictional force F1 is greater than the resistance force F2, if the second position WP2 where the medium M1 being discharged this time does not overlap with the side end alignment member is specified as the standby position WP, the medium M1 being discharged this time is likely to buckle. Also, when the frictional force F1 is smaller than the resistance force F2, the medium M1 being discharged this time is less likely to buckle, so there is no need to specify the first position WP1 where the medium M1 being discharged this time overlaps with the side end alignment member as the standby position WP. Moreover, if the first position WP1 is specified as the standby position WP, the media alignment operation takes time, which reduces the productivity of the medium loading device 11. In addition to the first information related to the recording density of at least one of the medium M1 being discharged this time and the medium M2 discharged last time, the information related to the medium includes information related to the frictional force F1. The medium-related information may also include information related to the drag force F2. In other words, if the determination of the standby position WP is controlled only by the value based on the first information, the performance of the medium stacking device 11 may be degraded.

[0113] When the actual frictional force F1 is smaller than the frictional force F1 estimated from the total value, the control unit 90 may adjust the threshold value based on the second information, or may determine the control parameters when the side end alignment member is made to wait at the first position WP1 based on the second information. Then, when the control unit 90 identifies the first position WP1 as the waiting position WP, the control unit 90 may control the side end alignment member to be made to wait at the first position WP1 with the control parameters determined based on the second information. Both the adjustment of the threshold value and the control with the determined control parameters may be performed, or only one of them may be performed. More specifically, the control parameters when the side end alignment member is made to wait at the first position WP1 are control parameters that control at least one of the position of the first position WP1 in the width direction X and the time the side end alignment member waits at the first position WP1. In the following description, the "control parameters when the side end alignment member is made to wait at the first position WP1" will be simply referred to as "control parameters". The position of the first position WP1 in the width direction X and the time that the side edge alignment member waits at the first position WP1 are changed within a range that has little effect on buckling. This makes it possible to suppress a decrease in productivity of the medium stacking device 11 while suppressing buckling of the medium M1 being discharged this time.

[0114] When the actual frictional force F1 is greater than the frictional force F1 estimated from the total value, the control unit 90 may adjust the threshold value based on the second information, or the control unit 90 may determine the control parameters based on the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member to be placed on standby at the first position WP1 with the control parameters determined based on the second information. Both the adjustment of the threshold value and the control with the determined control parameters may be performed, or only one of them may be performed. The position of the first position WP1 in the width direction X and the time for which the side end alignment member waits at the first position WP1 are changed within a range that has little effect on productivity. This makes it possible to suppress buckling under recording conditions in which buckling could not be suppressed.

[0115] The control parameters include overlap amounts L1, L2, which are the distances in the width direction X between the alignment surfaces 41a, 42a of the side end alignment member at the first position WP1 and the expected side edges M1c, M1d of the currently discharged medium M1 when it is discharged from the discharge section 71. The overlap amounts L1, L2 are control parameters that control the position of the first position WP1 in the width direction X. When the side end alignment member is the first side end guiding member 41, the overlap amount L1 is the distance in the width direction X between the alignment surface 41a of the first side end guiding member 41 at the first position WP1 and the expected first side edge M1c of the currently discharged medium M1 when it is discharged from the discharge section 71. When the side edge alignment member is the second side edge guide member 42, the overlap amount L2 is the distance in the width direction X between the alignment surface 42a of the second side edge guide member 42 at the first position WP1 and the second side edge M1d of the medium M1 to be discharged this time when it is discharged from the discharge section 71. The control unit 90 determines the overlap amounts L1 and L2 based on the second information, and when the first position WP1 is identified as the standby position WP, controls the side edge alignment member to be placed on standby at the first position WP1 with the overlap amounts L1 and L2 determined based on the second information. When the overlap amounts L1 and L2 are reduced, the productivity of the medium loading device 11 can be prevented from decreasing. When the overlap amounts L1 and L2 are increased, buckling can be prevented under recording conditions where buckling could not be prevented.

[0116] The control parameters include the timing at which the side edge alignment members move from the first position WP1. The timing is a control parameter that controls the time that the side edge alignment members wait at the first position WP1. The control unit 90 determines the timing based on the second information, and when the first position WP1 is identified as the wait position WP, controls the side edge alignment members to wait at the first position WP1 at the timing determined based on the second information. If the timing is made earlier, a decrease in productivity of the medium stacking device 11 can be suppressed. If the timing is made later, buckling can be suppressed under recording conditions where buckling could not be suppressed.

[0117] The control parameters include a selection by the control unit 90 to specify either the first side end guide member 41 or the second side end guide member 42 as the side end alignment member. The selection is a control parameter that controls the position of the first position WP1 in the width direction X. The control unit 90 determines the selection based on the second information, and when the first position WP1 is specified as the standby position WP, controls the side end alignment member to be standby at the first position WP1 with the selection determined based on the second information. When the frictional force F1 on the first side end M1c side is greater than the frictional force F1 on the second side end M1d side, the control unit 90 controls the first side end guide member 41 as the side end alignment member, thereby suppressing contact on the first side end M1c side, and thus more effectively suppressing buckling. When the first side end guide member 41 is selected to specify the first side end guide member 41 as the side end alignment member, for example, the selected value is 1. At this time, the position of the first position WP1 in the width direction X is closer to the first side end M1c than the second side end M1d. When the frictional force F1 on the second side end M1d side is greater than the frictional force F1 on the first side end M1c side, the control unit 90 controls the second side end guide member 42 as the side end alignment member, thereby suppressing contact on the second side end M1d side, and thus more effectively suppressing buckling. When the second side end guide member 42 is selected to specify the second side end guide member 42 as the side end alignment member, for example, the selected value is 2. At this time, the position of the first position WP1 in the width direction X is closer to the second side end M1d than the first side end M1c.

[0118] The second information may include a subtraction value obtained by subtracting the first lower surface recording density from the first upper surface recording density. The control unit 90 may calculate the subtraction value that is the second information, and adjust the threshold value based on the subtraction value. The control unit 90 may determine a control parameter based on the subtraction value that is the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member that is made to wait at the first position WP1 with the control parameter. The subtraction value is information related to the friction force F1, and is a factor of the friction force F1. Since the friction force F1 increases as the subtraction value increases, the control unit 90 may lower the threshold value when the subtraction value is equal to or greater than a predetermined value.

[0119] The second control unit 190 may calculate the subtraction value, which becomes the second information. Then, when the currently ejected medium M1 is ejected from the recording device 111 to the medium loading device 11, the second control unit 190 may notify the control unit 90 of the subtraction value as information related to the currently ejected medium M1.

[0120] The second information may include at least one of the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time. The control unit 90 may adjust the threshold value based on at least one of the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time, which are the second information. The control unit 90 may also determine a control parameter based on at least one of the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time, which are the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, it may control the side end alignment member to be standby at the first position WP1 with the control parameter. The size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time are information related to the drag force F2 and are factors of the drag force F2.

[0121] The size of the medium M is the medium length B and the medium width A. The longer the medium length B of the medium M1 being discharged this time, the smaller the bending strength, and therefore the smaller the resistance F2, making the medium M1 being discharged this time more likely to buckle. The shorter the medium length B of the medium M1 being discharged this time, the more likely the medium M1 being discharged this time will be to buckle, as discharging ends before the medium length of the medium M1 being discharged from the discharge section 71 becomes long. The shorter the medium width A of the medium M1 being discharged this time, the smaller the bending strength, and therefore the smaller the resistance F2, making the medium M1 being discharged this time more likely to buckle. The longer the medium width A of the medium M1 being discharged this time, the greater the bending strength, and therefore the larger the resistance F2, making the medium M1 being discharged this time more likely to buckle.

[0122] When the basis weight of the currently discharged medium M1 is small, the bending strength is small, so the resistance F2 is small and the currently discharged medium M1 is more likely to buckle. When the basis weight of the currently discharged medium M1 is large, the bending strength is large, so the resistance F2 is large and the currently discharged medium M1 is less likely to buckle.

[0123] Depending on the type of medium M1 being discharged this time, the bending strength may be small, so the resistance F2 may be small and the medium M1 being discharged this time may be more likely to buckle. Depending on the type of medium M1 being discharged this time, the bending strength may be large, so the resistance F2 may be large and the medium M1 being discharged this time may be less likely to buckle.

[0124] The second information may include at least one of the temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded. The control unit 90 may adjust the threshold value based on at least one of the temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded, which serves as the second information. The control unit 90 may also determine a control parameter based on at least one of the temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded, which serves as the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member to standby at the first position WP1 with the control parameter determined based on the second information. The temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded are information related to the frictional force F1 and are factors of the frictional force F1.

[0125] The second information may include the number of media Ms stacked on the processing tray 21 when the currently discharged medium M1 is discharged. The control unit 90 may adjust the threshold value based on the number of media Ms stacked on the processing tray 21, which is the second information. The control unit 90 may also determine the control parameters based on the number of media Ms stacked on the processing tray 21, which is the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member to wait at the first position WP1 with the control parameters determined based on the number of media Ms stacked on the processing tray 21. The storage unit 91 stores information related to the media recorded up to the current discharge, so that the control unit 90 can calculate the number of media Ms stacked on the processing tray 21 when the currently discharged medium M1 is discharged. When the number of media Ms loaded on the processing tray 21 is large, the distance between the top surface of the previously discharged medium M2 and the bottom surface of the currently discharged medium M1 is close, so the frictional force F1 is large. On the other hand, when the number of media Ms loaded on the processing tray 21 is small, the distance between the top surface of the previously discharged medium M2 and the bottom surface of the currently discharged medium M1 is far, so the frictional force F1 is small. In other words, the number of media Ms loaded on the processing tray 21 is information related to the frictional force F1 and is a factor of the frictional force F1.

[0126] The second information may include the first elapsed time. The control unit 90 may calculate the first elapsed time, which is the second information, and adjust the threshold value based on the first elapsed time. The control unit 90 may also calculate the first elapsed time, which is the second information, and determine the control parameters based on the first elapsed time, which is the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member that is made to wait at the first position WP1 with the control parameters determined based on the first elapsed time. If the first elapsed time is short, the media surface of the medium M1 to be discharged this time is not yet dry, so the first elapsed time is information related to the frictional force F1 and is a factor of the frictional force F1.

[0127] The control unit 90 subtracts the time when the previously ejected medium M2 was recorded from the time when the currently ejected medium M1 is ejected. This allows the control unit 90 to calculate the elapsed time from when the previously ejected medium M2 was recorded to when the currently ejected medium M1 is ejected. In the following explanation, the "elapsed time from when the previously ejected medium M2 was recorded to when the currently ejected medium M1 is ejected" is simply referred to as the "second elapsed time."

[0128] The second information may include the second elapsed time. The control unit 90 may calculate the second elapsed time as the second information and adjust the threshold value based on the second elapsed time. The control unit 90 may also calculate the second elapsed time as the second information and determine the control parameters based on the second elapsed time as the second information. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member to be standby at the first position WP1 with the control parameters determined based on the second elapsed time. If the second elapsed time is short, the media surface of the previously discharged media M2 is not yet dry, so the second elapsed time is information related to the frictional force F1 and is a factor of the frictional force F1.

[0129] The information related to the medium M1 to be discharged this time may include the first lower surface width direction recording density distribution, or the first upper surface width direction recording density distribution. The second upper surface width direction recording density distribution is stored in the storage unit 91 that stores the information related to the medium recorded up to the current discharge.

[0130] The second information may include a first lower surface width direction recording density distribution in the width direction X of the lower surface of the medium M1 to be discharged this time. The control unit 90 calculates a side end density difference of the medium M1 to be discharged this time, which is obtained by subtracting the recording density of the medium surface of the lower surface on the second side end M1d side from the recording density of the medium surface of the lower surface on the first side end M1c side in the first lower surface width direction recording density distribution. Then, the control unit 90 may adjust a threshold value based on the side end density difference, which is the second information. Furthermore, the control unit 90 may determine a control parameter based on the side end density difference. Then, when the control unit 90 specifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member to be made to wait at the first position WP1 with the control parameter determined based on the side end density difference. In the following description, the "side end density difference of the medium M1 to be discharged this time, which is obtained by subtracting the recording density of the medium surface of the lower surface on the second side end M1d side from the recording density of the medium surface of the lower surface on the first side end M1c side" is simply referred to as the "first side end density difference."

[0131] The larger the first side end concentration difference, the larger the friction force F1 between the medium surfaces on the first side end M1c side becomes compared to the friction force F1 between the medium surfaces on the second side end M1d side. Also, the smaller the first side end concentration difference, the larger the friction force F1 between the medium surfaces on the second side end M1d side becomes compared to the friction force F1 between the medium surfaces on the first side end M1c side. In other words, the first side end concentration difference is information related to the friction force F1 and is a factor of the friction force F1.

[0132] The second information may include a second upper surface width direction recording density distribution in the width direction X of the upper surface of the medium M1 to be discharged this time. The control unit 90 calculates a side end density difference of the previously discharged medium M2 obtained by subtracting the recording density of the upper surface medium surface on the second side end M1d side from the recording density of the upper surface medium surface on the first side end M1c side in the second upper surface width direction recording density distribution. Then, the control unit 90 may adjust a threshold value based on the side end density difference, which is the second information. The control unit 90 may also determine a control parameter based on the side end density difference. Then, when the control unit 90 specifies the first position WP1 as the standby position WP, the control unit 90 may control the side end alignment member to be made to wait at the first position WP1 with the control parameter determined based on the side end density difference. In the following description, the "side end density difference of the previously discharged medium M1 obtained by subtracting the recording density of the upper surface medium surface on the second side end M1d side from the recording density of the upper surface medium surface on the first side end M1c side" is simply referred to as the "second side end density difference."

[0133] The larger the second side end concentration difference, the larger the friction force F1 between the medium surfaces on the first side end M1c side becomes compared to the friction force F1 between the medium surfaces on the second side end M1d side. Also, the smaller the second side end concentration difference, the smaller the friction force F1 between the medium surfaces on the first side end M1c side becomes compared to the friction force F1 between the medium surfaces on the second side end M1d side. In other words, the second side end concentration difference is information related to the friction force F1 and is a factor of the friction force F1.

[0134] <Control method of media alignment operation> First, an overview of the control method of the media alignment operation will be described, and then the flow of the control method of the media alignment operation will be described in order of the control executed by the control unit 90 in each step. After that, the subroutines executed in the flow of the control method of the media alignment operation, that is, the threshold adjustment process subroutine, the control parameter determination process subroutine, the media alignment operation subroutine, and the side edge alignment operation subroutine, will be described in order.

[0135] As shown in FIG. 10, first, an outline of a method for controlling the medium alignment operation will be described. In steps S301 to S307, when the medium M1 to be discharged this time is discharged from the discharge unit 71, the control unit 90 acquires information related to the medium M1 to be discharged this time from the recording device 111 and stores it in the storage unit 91. Then, the control unit 90 selects a plurality of pieces of information to be used for controlling the medium alignment operation from the information related to the medium M1 to be discharged this time and the information related to the previously discharged medium stored in the storage unit 91. A calculated value may be calculated based on one or more pieces of information among the plurality of pieces of information, and the calculated value may be used as information to be used for controlling the medium alignment operation. Note that the previously discharged medium includes the medium Ms that is stacked on the processing tray 21 when the medium M1 to be discharged this time is discharged from the discharge unit 71. That is, in steps S301 to S307, the first information and the second information to be used for controlling the medium alignment operation are prepared.

[0136] In steps S400 to S500, the control unit 90 adjusts the threshold value based on the second information. Then, the control unit 90 determines the control parameters for making the side edge alignment member wait at the first position WP1 based on the second information. The threshold value is a threshold value when the wait position WP is specified by a value based on the first information in steps S308a to S309.

[0137] In steps S308a to S309, the control unit 90 determines whether the value based on the first information is equal to or greater than a threshold value. Then, the control unit 90 specifies either the first side edge guide member 41 or the second side edge guide member 42 as the side edge alignment member. If the value based on the first information is equal to or greater than the threshold value, the control unit 90 specifies a first position WP1 that overlaps with the currently discharged medium M1 in the width direction X as the standby position WP for the side edge alignment member. If the value based on the first information is less than the threshold value, the control unit 90 specifies a second position WP2 that does not overlap with the currently discharged medium M1 in the width direction X as the standby position WP for the side edge alignment member.

[0138] In step S600, the control unit 90 executes a medium alignment operation. When the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 controls the side edge alignment member to be placed on standby at the first position WP1 with the control parameters determined based on the second information. When the medium alignment operation ends, this flow ends.

[0139] 10, the flow of the control method for the medium alignment operation will be described below in order of the control executed by the control unit 90 in each step. When the currently discharged medium M1 recorded by the recording unit 160 is discharged from the recording device 111 to the medium loading device 11, the second control unit 190 notifies the control unit 90 of information related to the currently discharged medium M1, and this flow is started.

[0140] In step S301, the control unit 90 obtains information related to the medium M1 to be discharged currently from the recording device 111 and stores it in the memory unit 91. In step S302, the control unit 90 calculates a total value. In step S303, the control unit 90 calculates a subtraction value. In step S304, the control unit 90 calculates the number of media Ms stacked on the processing tray 21. In step S305, the control unit 90 calculates a first elapsed time. In step S306, the control unit 90 calculates a second elapsed time. In step S307, the control unit 90 calculates a first side end density difference.

[0141] In step S400, the control unit 90 executes a threshold adjustment process subroutine. The threshold adjustment process subroutine will be described later. After the threshold adjustment process subroutine ends, in step S500, the control unit 90 executes a control parameter determination process subroutine. The control parameter determination process subroutine will be described later.

[0142] When the control parameter determination process subroutine ends, in step S308a, the control unit 90 determines whether the total value is equal to or greater than the threshold value. If the total value is equal to or greater than the threshold value, step S308a becomes YES, and the control unit 90 transitions to step S309.

[0143] In step S309, the control unit 90 specifies the first position WP1 as the standby position WP for the side edge alignment member. Whether the side edge alignment member is the first side edge guide member 41 or the second side edge guide member 42 is specified in step S509, which will be described later. If the sum is less than the threshold, step S308a becomes NO, and the control unit 90 proceeds to step S310. Then, in step S310, the control unit 90 specifies the second position WP2 as the standby position WP for the side edge alignment member.

[0144] For example, when the first lower surface recording density is 60% and the second upper surface recording density is 60%, the value of the first lower surface recording density is 60, and the value of the second upper surface recording density is 60. In this case, (total value)=(first lower surface recording density)+(second upper surface recording density)=60+60=120. When the threshold value is 100, (total value)≧(threshold value), so the control unit 90 determines that the total value is equal to or greater than the threshold value. The higher the recording density, the wetter the medium surface is, and the lower the slidability of the medium surface of the medium M is. Since the medium M1 is discharged this time while the lower surface of the medium M1 to be discharged this time rubs against the upper surface of the medium M2 discharged last time, the larger the total value, the larger the frictional force F1 is. Therefore, when the total value is equal to or greater than the threshold value, the control unit 90 specifies the first position WP1 as the standby position WP of the side end alignment member. The first position WP1 is a standby position WP where the side edge alignment member overlaps with the currently discharged medium M1 in the width direction X, making it difficult for the top surface of the previously discharged medium M2 and the bottom surface of the currently discharged medium M1 to come into contact with each other.

[0145] The first lower surface recording density and the second upper surface recording density may be recording densities of the entire medium surface or of a part of the medium surface. For example, the second upper surface recording density may be the recording density of the leading end portion M1a of the lower surface of the currently ejected medium M1 that first comes into contact with the upper surface of the previously ejected medium M2 when the lower surface of the currently ejected medium M1 comes into contact with the upper surface of the previously ejected medium M2.

[0146] The first lower surface recording density and the second upper surface recording density may be weighted and added. The medium M1 being discharged this time has been recorded for a shorter period of time than the previously discharged medium M2, so its contribution to the frictional force F1 is greater. Therefore, the total value may be calculated weighted so that the contribution of the first lower surface recording density is greater. For example, the first lower surface recording density may be weighted twice and added, such as (total value)=2×(first lower surface recording density)+(second upper surface recording density). Also, when the time interval between media M being loaded is very long, the upper surface of the previously discharged medium M2 may already be dry when the currently discharged medium M1 is discharged. In such a case, the second upper surface recording density may be weighted and added so that its contribution is eliminated. For example, the total value may be calculated with the weighting coefficient set to "zero," such as (total value)=(first lower surface recording density)+0×(second upper surface recording density).

[0147] In step S600, the control unit 90 executes a medium matching operation subroutine, which will be described later. When the medium matching operation subroutine ends, this flow ends.

[0148] <About the threshold adjustment processing subroutine> As shown in FIG. 11, the flow of the threshold adjustment process subroutine will be described in order of the control executed by the control unit 90 in each step.

[0149] In step S401a, the control unit 90 judges whether the subtraction value is equal to or greater than a predetermined value. If the subtraction value is equal to or greater than the predetermined value, step S401a becomes YES, and the control unit 90 shifts the process to step S402. Then, in step S402, the control unit 90 lowers the threshold by one step and shifts the process to step S403. If the subtraction value is less than the predetermined value, step S401a becomes NO, and the control unit 90 shifts the process to step S403.

[0150] For example, when the first upper surface recording density is 100 and the first lower surface recording density is 10, the value of the first upper surface recording density is 100 and the value of the first lower surface recording density is 10. In this case, (subtraction value)=(first upper surface recording density)-(first lower surface recording density)=100-10=90. When the predetermined value is 50, (subtraction value)≧(predetermined value), so the control unit 90 determines that the subtraction value is equal to or greater than the predetermined value. The more the leading edge of the medium M1 to be discharged this time curls downward, the more obtuse the angle at which the leading edge portion M1a of the medium M1 to be discharged this time contacts the previously discharged medium M2 becomes. In other words, the larger the subtraction value, the stronger the bottom surface of the medium M1 to be discharged this time rubs against the top surface of the previously discharged medium M2 when it is loaded. This increases the frictional force F1, thereby decreasing the slidability. Therefore, when the subtraction value is equal to or greater than the predetermined value, the control unit 90 reduces the threshold value for specifying the first position WP1 as the standby position WP of the side end aligning member by one step.

[0151] A second predetermined value greater than the predetermined value is set, and when the subtraction value is equal to or greater than the second predetermined value, the control unit 90 may lower the threshold by two steps, or may set even more predetermined values. Furthermore, the control unit 90 may raise the threshold when the subtraction value is less than the predetermined value. If the leading edge of the medium M1 to be discharged this time curls upward, the angle at which the leading edge portion M1a of the medium M1 to be discharged this time contacts the previously discharged medium M2 becomes acute. This reduces the frictional force F1, making it less likely for the medium M1 to be discharged this time to buckle.

[0152] In step S403, the control unit 90 determines whether the medium length B of the medium M1 to be discharged this time is equal to or greater than a predetermined value. If the medium length B of the medium M1 to be discharged this time is equal to or greater than the predetermined value, step S403 becomes YES, and the control unit 90 transitions the process to step S404. Then, in step S404, the control unit 90 lowers the threshold by one step and transitions the process to step S405. If the medium length B of the medium M1 to be discharged this time is less than the predetermined value, step S403 becomes NO, and the control unit 90 transitions the process to step S405.

[0153] For example, when the medium M1 currently being discharged is an A3-sized medium M, the medium length B is 420 mm, and the value of the medium length B is 420. When the predetermined value is 350, (medium length B) ≧ (predetermined value), so the control unit 90 determines that the medium length B of the medium M1 currently being discharged is equal to or greater than the predetermined value. The longer the medium length B of the medium M1 currently being discharged, the smaller the bending strength, and therefore the more likely the medium M1 currently being discharged will buckle. Therefore, when the medium length B of the medium M1 currently being discharged is equal to or greater than the predetermined value, the control unit 90 lowers by one step the threshold value for identifying the first position WP1 as the standby position WP of the side end alignment member.

[0154] A predetermined value may be set for the width of the medium M1 currently being discharged. The shorter the width of the medium M1 currently being discharged, the smaller the bending strength, and therefore the more likely the medium M1 currently being discharged will buckle. Therefore, when the width of the medium M1 currently being discharged is equal to or smaller than the predetermined value, the control unit 90 may lower the threshold value for identifying the first position WP1 as the standby position WP of the side end alignment member.

[0155] A predetermined value may be set for the basis weight of the medium M or the type of the medium M. For example, when the basis weight of the medium M1 discharged this time is small, the bending strength is small, so the medium M1 discharged this time is more likely to buckle. Therefore, when the basis weight of the medium M1 discharged this time is small, the control unit 90 may lower the threshold value for specifying the first position WP1 as the standby position WP of the side end alignment member. For example, if the medium M1 discharged this time is cross-grained, the bending strength is small, so the medium M1 discharged this time is more likely to buckle. Therefore, when the medium M1 discharged this time is cross-grained, the control unit 90 may lower the threshold value for specifying the first position WP1 as the standby position WP of the side end alignment member. Furthermore, a predetermined value may be set for other factors that affect the bending strength of the medium M.

[0156] In step S405, the control unit 90 determines whether the number of media M on the processing tray 21 is equal to or greater than a predetermined value. If the number of media Ms stacked on the processing tray 21 is equal to or greater than the predetermined value, step S405 becomes YES, and the control unit 90 transitions to step S406. Then, in step S406, the control unit 90 lowers the threshold by one step and transitions to step S407. If the number of media Ms stacked on the processing tray 21 is less than the predetermined value, step S405 becomes NO, and the control unit 90 transitions to step S407.

[0157] For example, when the number of media Ms loaded on the processing tray 21 is 40, the value of the number of media Ms loaded on the processing tray 21 is 40. When the predetermined value is 10, (the number of media Ms loaded on the processing tray 21) ≧ (predetermined value). Therefore, the control unit 90 determines that the number of media Ms loaded on the processing tray 21 is equal to or greater than the predetermined value. The greater the number of media Ms loaded on the processing tray 21, the closer the distance between the top surface of the previously discharged medium M2 and the bottom surface of the currently discharged medium M1 is, and the greater the frictional force F1 is, so that the currently discharged medium M1 is more likely to buckle. Therefore, when the number of media Ms loaded on the processing tray 21 is equal to or greater than the predetermined value, the control unit 90 lowers the threshold value for identifying the first position WP1 as the standby position WP of the side end alignment member by one step.

[0158] The predetermined value may be changed according to the basis weight of the medium Ms loaded on the processing tray 21. The greater the basis weight of the medium Ms loaded on the processing tray 21, the higher the stacking height becomes, and the closer the distance between the top surface of the previously discharged medium M2 and the bottom surface of the currently discharged medium M1 becomes. As a result, the currently discharged medium M1 becomes more likely to buckle. The predetermined value may also be changed according to the type and recording density of the medium Ms loaded on the processing tray 21. Depending on the type and recording density of the medium Ms loaded on the processing tray 21, waviness or curling may occur on the medium surface, causing the stacking height to increase.

[0159] In step S407, the control unit 90 determines whether the humidity of the environment in which the medium M1 to be discharged this time was recorded is equal to or higher than a predetermined value. If the humidity is equal to or higher than the predetermined value, step S407 becomes YES, and the control unit 90 transitions the process to step S408. Then, in step S408, the control unit 90 lowers the threshold by one step and transitions the process to step S409. If the humidity is less than the predetermined value, step S407 becomes NO, and the control unit 90 transitions the process to step S409.

[0160] In step S409, the control unit 90 judges whether the first predetermined time is equal to or greater than a predetermined value. If the first predetermined time is equal to or greater than the predetermined value, step S409 becomes YES, and the control unit 90 transitions the process to step S410. Then, in step S410, the control unit 90 increases the threshold by one step and transitions the process to step S411. If the first predetermined time is less than the predetermined value, step S409 becomes NO, and the control unit 90 transitions the process to step S411.

[0161] In step S411, the control unit 90 judges whether the second predetermined time is equal to or greater than a predetermined value. If the second predetermined time is equal to or greater than the predetermined value, step S411 becomes YES, and the control unit 90 proceeds to step S412. Then, in step S412, the control unit 90 increases the threshold by one step and ends the threshold adjustment process subroutine. If the second predetermined time is less than the predetermined value, step S411 becomes NO, and the control unit 90 ends the threshold adjustment process subroutine.

[0162] <Control parameter determination subroutine> As shown in FIG. 12, the control executed by the control unit 90 in each step of the flow of the control parameter determination process subroutine will be described in order.

[0163] In step S501, the control unit 90 determines whether the medium length B of the medium M1 to be discharged this time is equal to or greater than a predetermined value. If the medium length B of the medium M1 to be discharged this time is equal to or greater than the predetermined value, step S501 becomes YES, and the control unit 90 transitions the process to step S502. Then, in step S502, the control unit 90 increases the overlap amounts L1 and L2 by one step, and transitions the process to step S503. If the medium length B of the medium M1 to be discharged this time is less than the predetermined value, step S501 becomes NO, and the control unit 90 transitions the process to step S502.

[0164] In step S503, the control unit 90 determines whether the humidity of the environment in which the medium M1 to be discharged this time was recorded is equal to or higher than a predetermined value. If the humidity is equal to or higher than the predetermined value, step S503 becomes YES, and the control unit 90 transitions the process to step S504. Then, in step S504, the control unit 90 increases the overlap amounts L1 and L2 by one step, and transitions the process to step S505. If the humidity is less than the predetermined value, step S503 becomes NO, and the control unit 90 transitions the process to step S505.

[0165] In step S505, the control unit 90 determines whether the first predetermined time is equal to or greater than a predetermined value. If the first predetermined time is equal to or greater than the predetermined value, step S505 becomes YES, and the control unit 90 transitions the process to step S506. Then, in step S506, the control unit 90 advances the timing at which the side edge alignment member leaves the first position WP1 by one step, and transitions the process to step S507. If the first predetermined time is less than the predetermined value, step S505 becomes NO, and the control unit 90 transitions the process to step S507.

[0166] In step S507, the control unit 90 determines whether the second predetermined time is equal to or greater than a predetermined value. If the second predetermined time is equal to or greater than the predetermined value, step S507 becomes YES, and the control unit 90 transitions the process to step S508. Then, in step S508, the control unit 90 advances the timing at which the side edge alignment member leaves the first position WP1 by one step, and transitions the process to step S509. If the first predetermined time is less than the predetermined value, step S507 becomes NO, and the control unit 90 transitions the process to step S509.

[0167] In step S509, the control unit 90 determines whether the first side end density difference is equal to or greater than a predetermined value. If the first side end density difference is equal to or greater than the predetermined value, step S509 becomes YES, and the control unit 90 proceeds to step S510. Then, in step S510, the control unit 90 identifies the first side end guide member 41 as the side end alignment member, and ends the control parameter determination process subroutine. If the first side end density difference is less than the predetermined value, step S509 becomes NO, and the control unit 90 proceeds to step S511. Then, in step S511, the control unit 90 identifies the second side end guide member 42 as the side end alignment member, and ends the control parameter determination process subroutine.

[0168] For example, when the predetermined value is "zero" and the first side end density difference is equal to or greater than the predetermined value, the recording density on the first side end M1c side of the medium M1 being discharged this time is greater than the recording density on the second side end M1d side, so the medium surface on the first side end M1c side is wetter than the medium surface on the second side end M1d side. Therefore, the first side end guide member 41 is specified as the side end alignment member. Then, the first side end guide member 41 prevents the medium surfaces on the first side end M1c side, which is the wet side, from coming into contact with each other.

[0169] Also, two predetermined values ​​may be provided with "zero" between them. For example, the control unit 90 may specify the first side end guide member 41 as the side end alignment member when the first side end density difference is equal to or greater than the first predetermined value, and may specify the second side end guide member 42 as the side end alignment member when the first side end density difference is less than the second predetermined value. Then, when the first side end density difference is less than the first predetermined value and equal to or greater than the second predetermined value, the control unit 90 may specify the guide member with higher productivity as the side end alignment member. That is, when the first side end density difference is close to "zero", there is little difference in suppression of buckling regardless of which guide member is specified as the side end alignment member, so the control unit 90 specifies the guide member with higher productivity as the side end alignment member. For example, if the side end alignment member is not changed from the first side end guide member 41 to the second side end guide member 42 during processing in units of copies, there is no need to change the position of the media Ms loaded on the processing tray 21 for side end alignment of the next media M, and therefore productivity is increased. For example, if the side edge alignment member is changed from the first side edge guide member 41 to the second side edge guide member 42 when processing the first media M in a set, the shift process performed before discharging the media bundle is not required for that media bundle, thereby increasing productivity. In other words, when the friction force F1 is nearly uniform, the control unit 90 can improve the productivity of the media stacking device 11 by selectively using the first side edge guide member 41 as the side edge alignment member and the second side edge guide member 42 as the side edge alignment member depending on the situation.

[0170] The control unit 90 may determine whether the second side end density difference is equal to or greater than a predetermined value, or may determine whether both the first side end density difference and the second side end density difference are equal to or greater than a predetermined value. Note that when the control unit 90 determines whether both the first side end density difference and the second side end density difference are equal to or greater than a predetermined value and both are equal to or greater than a predetermined value, the control unit 90 may, for example, determine which of the first side end density difference and the second side end density difference is the larger density difference.

[0171] <Regarding the media alignment operation subroutine> As shown in FIG. 13, the flow of the medium alignment operation subroutine will be described in order of the control executed by the control unit 90 in each step.

[0172] In step S601, the control unit 90 determines whether or not it is necessary to change the position of the medium Ms stacked on the processing tray 21 before the currently ejected medium M1 is ejected. If a position change is necessary, step S601 becomes YES, and the control unit 90 transitions the process to step S602. Then, in step S602, the control unit 90 moves the position of the medium Ms stacked on the processing tray 21, and transitions the process to step S603. If a position change is not necessary, step S601 becomes NO, and the control unit 90 transitions the process to step S603.

[0173] When the side edge alignment operation of the previously discharged medium M2 is completed, the alignment surface 41a of the first side edge guide member 41 abuts against the first side edge Msc, and the alignment surface 42a of the second side edge guide member 42 abuts against the second side edge Msd. In this state, if the overlap amounts L1, L2 when the currently discharged medium M1 is discharged differ from the overlap amounts L1, L2 set when the flow chart shown in FIG. 12 is completed, the control unit 90 moves the position of the medium Ms stacked on the processing tray 21. That is, a shift process is performed. More specifically, the first side edge guide member 41 and the second side edge guide member 42 are moved at the same speed, at the same timing, and by the same distance in the same direction in the width direction X. This allows the overlap amounts L1, L2 when the currently discharged medium M1 is discharged to be the overlap amounts L1, L2 set when the flow chart shown in FIG. 12 is completed.

[0174] In step S603, the control unit 90 moves the first side edge guide member 41 and the second side edge guide member 42 to the standby position WP. Then, in step S604, the control unit 90 starts the medium discharge operation. That is, the leading end portion M1a of the medium M1 to be discharged this time is discharged from the discharge unit 71, and the discharge operation starts. Then, in step S605, the control unit 90 judges whether it is time for the side edge alignment member to leave the first position WP1. More specifically, the side edge alignment member does not move until the side edge alignment member leaves the first position WP1. The side edge alignment member leaves the first position WP1 at the timing set when the flowchart shown in FIG. 12 ends. When it is time for the side edge alignment member to leave the first position WP1, step S606 becomes YES, and the control unit 90 transitions the process to step S606.

[0175] In step S606, the control unit 90 determines whether the standby position WP of the side edge alignment member is the first position WP1. If the standby position WP of the side edge alignment member is the first position WP1, step S606 becomes YES, and the control unit 90 transitions the process to step S607. Then, in step S607, the control unit 90 moves the side edge alignment member to the second position WP2, and transitions the process to step S608. If the standby position WP of the side edge alignment member is the second position WP2, step S606 becomes NO, and the control unit 90 transitions the process to step S608.

[0176] In step S608, the control unit 90 determines whether or not the medium ejection operation is completed. More specifically, the control unit 90 determines whether or not the rear end of the medium M1 to be ejected this time has been ejected from the ejection unit 71. When the medium ejection operation is completed, step S608 becomes YES, and the control unit 90 transitions to step S609.

[0177] In step S609, the control unit 90 performs a trailing edge alignment operation. When the trailing edge alignment operation is completed, in step S700, the control unit 90 executes a side edge alignment operation subroutine. The side edge alignment operation subroutine will be described later. When the side edge alignment operation subroutine is completed, the control unit 90 ends the medium alignment operation subroutine.

[0178] As shown in FIG. 14, the flow of the side edge aligning operation subroutine performed in step S700 in FIG. 13 will be described in order of control executed by the control unit 90 in each step.

[0179] In step S701, the control unit 90 determines whether the position of the side edge alignment member is the first position WP1. If the position of the side edge alignment member is the first position WP1, step S701 becomes YES, and the control unit 90 transitions the process to step S702. Then, in step S702, the control unit 90 moves the side edge alignment member to the second position WP2, and transitions the process to step S703. If the position of the side edge alignment member is the second position WP2, step S701 becomes NO, and the control unit 90 transitions the process to step S703.

[0180] If the medium M1 being discharged this time is prone to buckling, the side edge alignment member may be located at the first position WP1 until the medium discharge operation is completed. In other words, the position of the side edge alignment member when the medium discharge operation is completed may be the first position WP1. At this time, the control unit 90 temporarily moves the side edge alignment member to the second position WP2.

[0181] In step S703, the control unit 90 moves the side edge alignment member from the second position WP2 to the first position WP1. This aligns the side edges M1c, M1d of the medium M1 to be discharged this time. More specifically, when the first side edge guide member 41 is specified as the side edge alignment member, the first side edge guide member 41 aligns the first side edge M1c of the medium M1 to be discharged this time with the first side edge Msc of the medium Ms loaded on the processing tray 21. When the second side edge guide member 42 is specified as the side edge alignment member, the second side edge guide member 42 aligns the second side edge M1d of the medium M1 to be discharged this time with the second side edge Msd of the medium Ms loaded on the processing tray 21. When the side edge alignment member moves from the second position WP2 to the first position WP1, the control unit 90 ends the side edge alignment operation subroutine.

[0182] <Operation of the embodiment> The operation of this embodiment will be described. In this embodiment, the largest total value at which buckling does not occur under standard recording conditions is set as the threshold value. The largest total value at which buckling does not occur is determined, for example, by experiment. Note that the standard recording conditions may be average recording conditions or the most frequently used recording conditions. There is no limitation on the method of determining the standard recording conditions.

[0183] An example of standard recording conditions is described below. For medium M, A4 size, 80 gsm, long grain paper is used in vertical feeding. Standard resolution images are recorded on both sides of medium M, and there is no difference in recording density in the width direction X. The same image is recorded on each medium M. The temperature and humidity of the environment in which medium M is recorded are 22 degrees and 65%. When medium M is discharged, the number of media Ms loaded on the processing tray 21 is 5. When the above conditions are standard recording conditions, if the largest total value that does not cause buckling is 80, the total value threshold is set to 80. In other words, the threshold value before being adjusted based on the second information is 80. Note that "gsm" is the unit of basis weight of medium M. There are long grain and short grain in the paper grain direction, and the paper grain direction is an example of a type of medium M. Also, vertical feeding refers to a feeding direction in which the long side of the paper is parallel to the transport direction.

[0184] An example of actual recording conditions is described below. For medium M, A3 size, 80 gsm, long grain paper is used with vertical feeding. High resolution images are recorded on both sides of medium M, with the top surface recording density being 50% and the bottom surface recording density being 20%. There is a difference in recording density in the width direction X, with the first side end density difference being 20. The same image is recorded on each medium M. The temperature and humidity of the environment in which medium M is recorded are 22 degrees and 85%. The number of media Ms loaded on the processing tray 21 when medium M is discharged is 20. When the above conditions are the actual recording conditions, the total value based on the first information is (total value) = (first bottom surface recording density) + (second top surface recording density) = 20 + 50 = 70.

[0185] The sum is 70, and the threshold of the sum before being adjusted based on the second information is 80. That is, when the threshold is not adjusted based on the second information, (sum)<(threshold). Since the sum is less than the threshold, when the threshold is not adjusted based on the second information, the second position WP2 is identified as the standby position WP.

[0186] The threshold is adjusted based on the second information. In this embodiment, the threshold is adjusted when the value based on the second information is equal to or greater than a predetermined value. The threshold may be adjusted when the value based on the second information is equal to or less than a predetermined value. That is, the threshold is adjusted when the value based on the second information is outside a predetermined range. When the value based on the second information is outside the predetermined range, the frictional force F1 under standard recording conditions assumed from the value based on the first information is largely different from the frictional force F1 under the actual recording conditions. Or, the resistance force F2 under standard recording conditions is largely different from the resistance force F2 under the actual recording conditions. Therefore, the control unit 90 adjusts the threshold when the value based on the second information is outside the predetermined range, thereby changing the control to one suitable for the actual recording conditions.

[0187] When the control unit 90 calculates a subtraction value by subtracting the first lower-surface recording density from the first upper-surface recording density, the result is (subtraction value)=(first upper-surface recording density)-(first lower-surface recording density)=50-20=30. For example, when the predetermined value of the subtraction value as the second information is 25, if the subtraction value exceeds 25, the deviation between the frictional force F1 under the standard recording conditions assumed from the value based on the first information and the frictional force F1 under the actual recording conditions is large, so the threshold is adjusted. Since (subtraction value)≧(predetermined value), the control unit 90 lowers the threshold by one step. When the value of one step of the threshold is 15, the result is (threshold value)=80-15=65. There is no limitation on how to determine the value of one step.

[0188] The value of the medium length B of the medium M1 currently discharged as the second information is 420. If the predetermined value for the medium length B of the medium M1 currently discharged is 350, then (medium length B) ≧ (predetermined value), so the control unit 90 lowers the threshold by one step. When the value of one step of the threshold is 15, (threshold) = 65 - 15 = 50. The control unit 90 may adjust the threshold based on the type of the medium M1 currently discharged as the second information and the basis weight of the medium M1 currently discharged as the second information.

[0189] The value of the number of media Ms loaded on the processing tray 21, which is the second information, is 20. If the predetermined value for the number of media Ms loaded on the processing tray 21 is 10, then (the number of media Ms loaded on the processing tray 21) ≧ (predetermined value), so the control unit 90 lowers the threshold by one step. When the value of one step of the threshold is 15, (threshold) = 50 - 15 = 35.

[0190] The humidity value of the environment in which the medium M1 currently being ejected as the second information was recorded is 85. If the predetermined value for the humidity of the environment in which the medium M was recorded is 75, then (humidity of the environment in which the medium M1 currently being ejected was recorded) ≧ (predetermined value), so the control unit 90 lowers the threshold by one step. When the value of one step of the threshold is 15, (threshold) = 35 - 15 = 20. The control unit 90 may adjust the threshold based on the temperature of the environment in which the medium M was recorded as the second information.

[0191] Since the recording time is long when a high-resolution image is recorded on both sides, the first elapsed time as the second information from when the medium M1 to be discharged this time is recorded to when it is discharged is longer than the first elapsed time under the standard recording conditions, and satisfies (first elapsed time) ≧ (predetermined value). The control unit 90 increases the threshold by one step. When the value of one step of the threshold is 15, (threshold) = 20 + 15 = 35.

[0192] Since high resolution images are recorded on both sides, the second elapsed time as the second information from when the previously discharged medium M2 was recorded until the currently discharged medium M1 is discharged is longer than the second elapsed time under the standard recording conditions, and satisfies (second elapsed time) ≧ (predetermined value). The control unit 90 increases the threshold by one step. When the value of one step of the threshold is 15, (threshold) = 35 + 15 = 50.

[0193] In this way, the threshold is adjusted based on the second information. The sum as a value based on the first information is 70, and the threshold after adjustment based on the second information is 50. That is, after the threshold is adjusted based on the second information, (sum)>(threshold). Since the sum is greater than or equal to the threshold, when the threshold is adjusted based on the second information, the first position WP1 is identified as the standby position WP. In this example, when the threshold is not adjusted based on the second information, the second position WP2 is identified as the standby position WP, and when the threshold is adjusted based on the second information, the first position WP1 is identified as the standby position WP.

[0194] The sum value as a value based on the first information is information related to the friction force F1 and is a factor of the friction force F1. Therefore, the sum value is used in controlling the medium alignment operation as a factor of the tendency of the medium M1 to buckle this time being discharged. However, there are other factors of the tendency of buckling besides the sum value. The tendency of the medium M1 to buckle this time being discharged is caused by the friction force F1 and the resistance force F2. Therefore, by using information related to the friction force F1 other than the first information and information related to the resistance force F2 as second information in controlling the medium alignment operation, a more appropriate waiting position WP can be selected.

[0195] The control parameter is determined based on the second information. In this embodiment, the control parameter is changed from the reference value when the value based on the second information is equal to or greater than a predetermined value. The control parameter may be changed from the reference value when the value based on the second information is equal to or less than a predetermined value. That is, the control parameter is changed from the reference value when the value based on the second information is out of a predetermined range. When the value based on the second information is out of a predetermined range, the frictional force F1 under the standard recording conditions assumed from the value based on the first information is largely different from the frictional force F1 under the actual recording conditions. Or, the resistance force F2 under the standard recording conditions is largely different from the resistance force F2 under the actual recording conditions. Therefore, the control unit 90 changes the control parameter to be suitable for the actual recording conditions by changing the control parameter when the value based on the second information is out of a predetermined range.

[0196] Since (medium length B)≧(predetermined value), the control unit 90 increases the overlap amounts L1 and L2, which are control parameters, by one step based on the medium length B of the medium M1 currently discharged as the second information. That is, the control unit 90 controls the medium M1 currently discharged and the side edge alignment member at the first position WP1 so that they overlap more. The control unit 90 may change the timing at which the side edge alignment member leaves the first position WP1 based on the medium length B of the medium M1 currently discharged. The control unit 90 may also change the overlap amounts L1 and L2 or change the timing at which the side edge alignment member leaves the first position WP1 based on the type of the medium M1 currently discharged as the second information and the basis weight of the medium M1 currently discharged as the second information.

[0197] Since (humidity of environment)≧(predetermined value), the control unit 90 further increases the overlap amounts L1 and L2, which are control parameters, by one step based on the humidity of the environment in which the medium M1 to be discharged this time was recorded as the second information. That is, the control unit 90 controls the medium M1 to be discharged this time and the side end alignment member at the first position WP1 to further overlap. The control unit 90 may change the timing at which the side end alignment member leaves the first position WP1 based on the humidity of the environment in which the medium M1 to be discharged this time was recorded. The control unit 90 may also change the overlap amounts L1 and L2 or change the timing at which the side end alignment member leaves the first position WP1 based on the temperature of the environment in which the medium M1 to be discharged this time was recorded as the second information.

[0198] It is assumed that (first elapsed time)≧(predetermined value) is satisfied. The control unit 90 advances the timing at which the side edge alignment member leaves the first position WP1 by one step based on the first elapsed time as the second information. In other words, the control unit 90 changes the control so that the side edge alignment operation ends earlier. The control unit 90 may change the overlap amounts L1, L2 based on the first elapsed time.

[0199] It is assumed that (second elapsed time)≧(predetermined value) is satisfied. The control unit 90 advances the timing at which the side edge alignment member leaves the first position WP1 by one step based on the second elapsed time as the second information. In other words, the control unit 90 changes the control so that the side edge alignment operation ends even earlier. The control unit 90 may change the overlap amounts L1, L2 based on the second elapsed time.

[0200] The control unit 90 may determine the control parameters based on the subtraction value as the second information. The control unit 90 may also determine the control parameters based on the number of media Ms stacked on the processing tray 21 as the second information.

[0201] In this embodiment, the control parameter "selection of identifying either the first side end guide member 41 or the second side end guide member 42 as the side end alignment member" is determined based on the first side end density difference as the second information. The first side end density difference as the second information is 20. If the predetermined value of the first side end density difference is "zero", (first side end density difference) ≧ (predetermined value), so the control unit 90 identifies the first side end guide member 41 as the side end alignment member. That is, the control unit 90 identifies the alignment member on the side end side where the currently discharged medium M1 is wet as the side end alignment member, and performs control so that the currently discharged medium M1 and the side end alignment member at the first position WP1 on the side end side where the currently discharged medium M1 is wet overlap. In addition, the "selection of identifying either the first side end guide member 41 or the second side end guide member 42 as the side end alignment member" may be determined based on the second side end density difference as the second information, or may be determined based on both the first side end density difference and the second side end density difference.

[0202] <Effects of the embodiment> The effects of this embodiment will be described. The medium stacking device 11 and image forming system 200 of this embodiment provide the following advantages.

[0203] (1) When the deviation between the frictional force F1 under standard recording conditions, which is assumed based on the value based on the first information, and the frictional force F1 under actual recording conditions is large, the control unit 90 adjusts the threshold value based on the second information. Also, when the deviation between the drag force F2 under standard recording conditions and the drag force F2 under actual recording conditions is large, the control unit 90 adjusts the threshold value based on the second information. By adjusting the threshold value based on the second information, the first position WP1 is more likely to be identified as the standby position WP when buckling of the medium M is likely to occur, compared to when the threshold value is not adjusted. Also, when buckling of the medium M is unlikely to occur, the first position WP1 is less likely to be identified as the standby position WP. In other words, even when the slidability of the medium M is lower than that assumed based on the recording density, buckling of the medium M can be suppressed. Also, when the slidability of the medium M is not lowered as much as that assumed based on the recording density, a decrease in productivity of the medium loading device 11 can be suppressed. In other words, compared to when the control unit 90 controls the side end alignment member using only the first information related to the recording density of at least one of the medium M1 being discharged this time and the medium M2 discharged last time, it is possible to improve the productivity of the medium loading device 11 while suppressing buckling of the medium M.

[0204] (2) When the difference between the frictional force F1 under the standard recording conditions, which is assumed from the value based on the first information, and the frictional force F1 under the actual recording conditions is large, the control unit 90 determines the control parameters for making the side end alignment member wait at the first position WP1 based on the second information. Then, when the control unit 90 specifies the first position WP1 as the waiting position WP, it controls the side end alignment member to wait at the first position WP1 with the control parameters. Also, when the difference between the drag force F2 under the standard recording conditions and the drag force F2 under the actual recording conditions is large, the control unit 90 determines the control parameters for making the side end alignment member wait at the first position WP1 based on the second information. Then, when the control unit 90 specifies the first position WP1 as the waiting position WP, it controls the side end alignment member to wait at the first position WP1 with the control parameters. More specifically, the position of the first position WP1 in the width direction X and the time for which the side end alignment member waits at the first position WP1 are changed within a range that has little effect on buckling and productivity. This increases or increases the necessary movement of the side edge alignment member when the first position WP1 is specified as the standby position WP. Also, the unnecessary movement of the side edge alignment member when the first position WP1 is specified as the standby position WP is eliminated or reduced. In other words, buckling of the medium M can be suppressed even when the slidability of the medium M is lower than expected from the recording density. Also, it is possible to suppress a decrease in the productivity of the medium loading device 11 when the slidability of the medium M is not lower than expected from the recording density. In other words, it is possible to improve the productivity of the medium loading device 11 while suppressing buckling of the medium M, compared to when the control unit 90 controls the side edge alignment member only with the first information related to the recording density of at least one of the medium M1 to be discharged this time and the medium M2 discharged last time.

[0205] (3) The second information includes a subtraction value obtained by subtracting the first lower surface recording density from the first upper surface recording density. The larger the subtraction value, the more the leading end portion M1a of the medium M1 to be discharged this time curls downward due to the difference in moisture content between the upper surface and the lower surface of the medium M1 to be discharged this time. In other words, the larger the subtraction value, the more obtuse the angle at which the leading end portion M1a of the medium M1 to be discharged this time contacts the previously discharged medium M2, so that the lower surface of the medium M1 to be discharged this time and the upper surface of the previously discharged medium M2 come into strong contact with each other. This increases the frictional force F1, so that the slidability decreases. When the subtraction value is equal to or greater than a predetermined value, the control unit 90 sets the threshold lower than when the subtraction value is less than the predetermined value. When the subtraction value is less than the predetermined value, the control unit 90 may set the threshold higher than when the subtraction value is equal to or greater than the predetermined value. When the angle at which the leading end portion M1a of the medium M1 to be discharged this time contacts the previously discharged medium M2 is an obtuse angle and the frictional force F1 is large, buckling of the medium M1 to be discharged this time can be suppressed. Also, when the angle at which the leading end portion M1a of the medium M1 to be discharged this time contacts the previously discharged medium M2 is an acute angle and the frictional force F1 is small, a decrease in productivity of the medium loading device 11 can be suppressed.

[0206] (4) The second information includes at least one of the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time. The resistance F2 against buckling of the medium M1 to be discharged this time varies depending on the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time. That is, depending on the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time, there may be a large deviation between the resistance F2 of the standard medium M and the resistance F2 of the medium M1 to be discharged this time. The control unit 90 may adjust the threshold value based on at least one of the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time. The control unit 90 may determine the control parameter when the side end alignment member is made to wait at the first position WP1 based on at least one of the size of the medium M1 to be discharged this time, the basis weight of the medium M1 to be discharged this time, and the type of the medium M1 to be discharged this time. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side edge alignment member to be standby at the first position WP1 with the control parameters. This can prevent the medium M1 being discharged this time from buckling when the resistance F2 is small. Also, when the resistance F2 of the medium M1 being discharged this time is sufficiently larger than the friction force F1, it can prevent the productivity of the medium stacking device 11 from decreasing.

[0207] (5) The second information includes at least one of the temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded. When the humidity of the environment in which the medium M1 to be discharged this time is recorded is high, it takes a long time for the medium surface to dry, and when the humidity of the environment in which the medium M1 to be discharged this time is recorded is low, it takes a long time for the medium surface to dry. Also, when the temperature of the environment in which the medium M1 to be discharged this time is recorded is low, it takes a long time for the medium surface to dry because the moisture content is not improved by the drying process, and when the temperature of the environment in which the medium M1 to be discharged this time is recorded is high, it takes a short time for the medium surface to dry. The control unit 90 may adjust the threshold value based on at least one of the temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded. The control unit 90 may determine the control parameter when the side end alignment member is made to wait at the first position WP1 based on at least one of the temperature and humidity of the environment in which the medium M1 to be discharged this time is recorded. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may control the side edge alignment member to be standby at the first position WP1 with the control parameters. This can prevent the medium M1 to be discharged this time from buckling when the medium M1 to be discharged this time and the medium M2 discharged last time are not yet dried. Also, when the medium M1 to be discharged this time and the medium M2 discharged last time are dried and have a sufficiently small moisture content, it can prevent a decrease in productivity of the medium loading device 11.

[0208] (6) The second information includes the number of media Ms stacked on the processing tray 21 when the currently discharged medium M1 is discharged. When the number of media Ms stacked on the processing tray 21 is large, the distance between the upper surface of the previously discharged medium M2 and the lower surface of the currently discharged medium M1 is small, and the frictional force F1 is large. When the number of media Ms stacked on the processing tray 21 is small, the distance between the upper surface of the previously discharged medium M2 and the lower surface of the currently discharged medium M1 is large, and the frictional force F1 is small. The control unit 90 may adjust the threshold value based on the number of media Ms stacked on the processing tray 21 when the currently discharged medium M1 is discharged. The control unit 90 may determine the control parameters for causing the side edge alignment member to wait at the first position WP1 based on the number of media Ms stacked on the processing tray 21 when the currently discharged medium M1 is discharged. Then, when the control unit 90 identifies the first position WP1 as the standby position WP, the control unit 90 may use the control parameters to control the side edge alignment member that is placed on standby at the first position WP1. This can prevent the medium M1 being discharged this time from buckling when the frictional force F1 is large due to the large number of media Ms loaded on the processing tray 21. Also, when the frictional force F1 is small due to the small number of media Ms loaded on the processing tray 21, a decrease in productivity of the medium loading device 11 can be prevented.

[0209] (7) The second information includes a first elapsed time from when the medium M1 to be discharged this time is recorded to when it is discharged. If the first elapsed time is short, the drying of the medium surface of the medium M1 to be discharged this time is not progressing. If the first elapsed time is long, the drying of the medium surface of the medium M1 to be discharged this time is progressing. The control unit 90 may adjust the threshold value based on the first elapsed time. The control unit 90 may determine a control parameter for making the side end alignment member wait at the first position WP1 based on the first elapsed time. Then, when the control unit 90 identifies the first position WP1 as the waiting position WP, it may control the side end alignment member to wait at the first position WP1 with the control parameter. This makes it possible to suppress buckling of the medium M1 to be discharged this time when the drying of the medium M1 to be discharged this time is not progressing. In addition, it is possible to suppress a decrease in productivity of the medium loading device 11 when the drying of the medium M1 to be discharged this time is progressing and the moisture content is sufficiently small.

[0210] (8) The second information includes a second elapsed time from when the previously discharged medium M2 was recorded until the currently discharged medium M1 is discharged. If the second elapsed time is short, the drying of the medium surface of the previously discharged medium M2 has not progressed. If the second elapsed time is long, the drying of the medium surface of the previously discharged medium M2 has progressed. The control unit 90 may adjust the threshold value based on the second elapsed time. The control unit 90 may determine a control parameter for causing the side end alignment member to wait at the first position WP1 based on the second elapsed time. Then, when the control unit 90 identifies the first position WP1 as the waiting position WP, it may control the side end alignment member to wait at the first position WP1 with the control parameter. This makes it possible to suppress buckling of the currently discharged medium M1 when the previously discharged medium M2 has not progressed in drying. In addition, it is possible to suppress a decrease in productivity of the medium loading device 11 when the previously discharged medium M2 has progressed in drying and has a sufficiently small moisture content.

[0211] (9) When the first position WP1 is identified as the standby position WP, the control parameters for causing the side edge alignment member to wait at the first position WP1 include the overlap amounts L1 and L2. When the overlap amounts L1 and L2 are increased, contact between the medium M1 to be discharged this time and the medium M2 discharged last time can be more effectively prevented. That is, the control unit 90 determines the overlap amounts L1 and L2 based on the second information, and when the first position WP1 is identified as the standby position WP, the control unit 90 controls the side edge alignment member with the overlap amounts L1 and L2, thereby more effectively preventing the medium M1 to be discharged this time from buckling. Furthermore, when the overlap amounts L1 and L2 are decreased, the movement distance to the second position WP2 is reduced even if the timing at which the side edge alignment member leaves the first position WP1 and starts moving toward the second position WP2 is the same. This makes it possible to shorten the time from when the rear end of the currently discharged medium M1 is discharged from the discharge section 71 until the first side end M1c of the currently discharged medium M1 is aligned with the first side end Msc of the medium Ms loaded on the processing tray 21. That is, the control section 90 determines the overlap amounts L1, L2 based on the second information, and when the first position WP1 is identified as the standby position WP, controls the side end alignment members according to the overlap amounts L1, L2, thereby preventing a decrease in productivity of the medium loading device 11.

[0212] (10) The control parameters for making the side edge alignment member wait at the first position WP1 when the first position WP1 is specified as the standby position WP include the timing at which the side edge alignment member moves from the first position WP1. If this timing is advanced, the side edge alignment operation can be started at the same time as the trailing end of the currently discharged medium M1 is discharged from the discharge section 71. That is, the control unit 90 determines this timing based on the second information and controls the side edge alignment member at that timing when the first position WP1 is specified as the standby position WP, thereby preventing a decrease in productivity of the medium stacking device 11. If this timing is delayed, contact between the currently discharged medium M1 and the previously discharged medium M2 can be prevented until the trailing end of the currently discharged medium M1 is discharged from the discharge section 71. That is, the control unit 90 determines this timing based on the second information and controls the side edge alignment member at that timing when the first position WP1 is specified as the standby position WP, thereby further preventing buckling of the currently discharged medium M1.

[0213] (11) The second information includes at least one of the first lower surface width direction recording density distribution and the second upper surface width direction recording density distribution. The control parameters for making the side edge alignment member wait at the first position WP1 when the first position WP1 is specified as the standby position WP include a selection for specifying either the first side edge guide member 41 or the second side edge guide member 42 as the side edge alignment member. The control unit 90 can determine which of the frictional forces F1 of the medium surface on the first side edge M1c side and the medium surface on the second side edge M1d side is larger on the lower surface of the medium M1 to be discharged this time, based on the first lower surface width direction recording density distribution as the second information. The control unit 90 can also determine which of the frictional forces F1 of the medium surface on the first side edge M1c side and the medium surface on the second side edge M1d side is larger on the upper surface of the medium M1 to be discharged this time, based on the first upper surface width direction recording density distribution as the second information. The control unit 90 then identifies the side edge guide member on the side with the larger frictional force F1 as the side edge alignment member, and controls the side edge guide member on the side with the larger frictional force F1 as the side edge alignment member. This suppresses contact of the medium surface on the side edge side with the larger frictional force F1, and more effectively suppresses buckling of the medium M1 being discharged this time. Furthermore, when the frictional forces F1 are nearly uniform, the control unit 90 selectively uses the first side edge guide member 41 as the side edge alignment member and the second side edge guide member 42 as the side edge alignment member depending on the situation, thereby improving the productivity of the medium stacking device 11.

[0214] Second embodiment The second embodiment will be described below with reference to the drawings. Since the second embodiment is substantially the same as the first embodiment, the same components are denoted by the same reference numerals and the duplicated description will be omitted.

[0215] <Regarding Information 1 and Information 2> In this embodiment, the first information is the first top-side recording density and the first bottom-side recording density. The value based on the first information is a subtraction value obtained by subtracting the first bottom-side recording density from the first top-side recording density, and is a value based on information related to the recording density of the medium M1 currently being ejected. The control unit 90 calculates the subtraction value obtained by subtracting the first bottom-side recording density from the first top-side recording density, and uses this subtraction value to control the side edge alignment operation. Note that in this embodiment, the "threshold value" is a threshold value for the subtraction value.

[0216] The medium M1 is discharged while the lower surface of the leading end portion M1a of the medium M1 to be discharged this time rubs against the upper surface of the previously discharged medium M2. The larger the subtraction value, the more the leading end portion M1a of the medium M1 to be discharged this time curls downward. The subtraction value is information indicating the ease of the medium M1 to curl downward. That is, the larger the subtraction value, the more obtuse the angle at which the leading end portion M1a of the medium M1 to be discharged this time contacts the previously discharged medium M2, so that the lower surface of the medium M1 to be discharged this time and the upper surface of the previously discharged medium M2 come into strong contact with each other. This increases the frictional force F1, making it easier for the medium M1 to buckle. The subtraction value as a value based on the first information is information related to the frictional force F1 and is a factor of the frictional force F1. Therefore, in this embodiment, the subtraction value is used to control the medium alignment operation as a factor of the ease of buckling in the medium M1 to be discharged this time.

[0217] The second control unit 190 may calculate the subtraction value. Then, when the currently ejected medium M1 is ejected from the recording device 111 to the medium stacking device 11, the second control unit 190 may notify the control unit 90 of the subtraction value as information related to the currently ejected medium M1.

[0218] The second information may include a total value obtained by adding up the first lower surface recording density and the second upper surface recording density. The control unit 90 may calculate the total value that is the second information, and adjust the threshold value based on the total value. The control unit 90 may also determine a control parameter for making the side end alignment member wait at the first position WP1 based on the total value that is the second information. Then, when the control unit 90 identifies the first position WP1 as the waiting position WP, the control unit 90 may control the side end alignment member that is made to wait at the first position WP1 with the control parameter determined based on the total value. The total value is information related to the friction force F1, and is a factor of the friction force F1. Since the friction force F1 increases as the total value increases, the control unit 90 may lower the threshold value when the total value is equal to or greater than a predetermined value.

[0219] The second control unit 190 may calculate the total value that becomes the second information. Then, when the currently discharged medium M1 is discharged from the recording device 111 to the medium stacking device 11, the second control unit 190 may notify the control unit 90 of the total value as information related to the currently discharged medium M1.

[0220] <Control method of media alignment operation> As shown in Fig. 15, the flow of the control method for the medium alignment operation will be described with reference to the control executed by the control unit 90 in each step. Note that since this flow is almost the same as that of the first embodiment, the same steps are denoted by the same reference numerals and the description of the duplicated steps will be omitted.

[0221] When the control parameter determination process subroutine ends, in step S308b, the control unit 90 determines whether the subtraction value is equal to or greater than the threshold value. If the subtraction value is equal to or greater than the threshold value, step S308a becomes YES, and the control unit 90 transitions the process to step S309.

[0222] In step S309, the control unit 90 specifies the first position WP1 as the standby position WP for the side edge alignment members. It is specified in step S509 whether the side edge alignment member is the first side edge guide member 41 or the second side edge guide member 42. If the subtracted value is less than the threshold value, step S308b becomes NO, and the control unit 90 proceeds to step S310. Then, in step S310, the control unit 90 specifies the second position WP2 as the standby position WP for the side edge alignment members.

[0223] The first upper surface recording density and the first lower surface recording density may be the recording density of the entire medium surface or may be the recording density of a part of the medium surface. For example, the first upper surface recording density and the first lower surface recording density may be the recording density of the leading end portion M1a of the medium M1 to be discharged this time. The control unit 90 can estimate the curl state of the leading end portion M1a of the medium M1 to be discharged this time.

[0224] <About the threshold adjustment processing subroutine> 16, the flow of the threshold adjustment process subroutine will be described with reference to the control executed by the control unit 90 in each step. Note that since this flow is almost the same as that of the first embodiment, the same steps are denoted by the same reference numerals and the description of the duplicated steps will be omitted.

[0225] In step S401b, the control unit 90 judges whether the total value is equal to or greater than a predetermined value. If the total value is equal to or greater than the predetermined value, step S401b becomes YES, and the control unit 90 shifts the process to step S402. Then, in step S402, the control unit 90 lowers the threshold by one step and shifts the process to step S403. If the total value is less than the predetermined value, step S401b becomes NO, and the control unit 90 shifts the process to step S403.

[0226] <Operation of the embodiment> The operation of this embodiment will be described. Since the second embodiment is almost the same as the first embodiment, the duplicated explanation of the operation will be omitted.

[0227] In this embodiment, the largest subtraction value at which buckling does not occur under standard recording conditions is set as the threshold value. The largest subtraction value at which buckling does not occur is determined, for example, by experiment. Note that the standard recording conditions may be average recording conditions or the most frequently used recording conditions. There is no limitation on the method of determining the standard recording conditions.

[0228] An example of standard recording conditions is described below. For medium M, A4 size, 80 gsm, long grain paper is used with vertical feeding. A standard resolution image is recorded on both sides of medium M, and there is no difference in recording density in the width direction X. The same image is recorded on each medium M. The temperature and humidity of the environment in which medium M is recorded are 22 degrees and 65%. When medium M is discharged, the number of media Ms loaded on the processing tray 21 is five. When the above conditions are standard recording conditions, if the largest subtraction value at which buckling does not occur is 25, the subtraction value threshold is set to 25. In other words, the threshold value before being adjusted based on the second information is 25.

[0229] An example of actual recording conditions is described below. For medium M, A3 size, 80 gsm, long grain paper is used with vertical feeding. High resolution images are recorded on both sides of medium M, with the top surface recording density being 50% and the bottom surface recording density being 35%. There is a difference in recording density in the width direction X, with the first side end density difference being 20. The same image is recorded on each medium M. The temperature and humidity of the environment in which medium M is recorded are 22 degrees and 85%. The number of media Ms loaded on the processing tray 21 when medium M is discharged is 20. When the above conditions are the actual recording conditions, the subtraction value based on the first information is (subtraction value) = (first top surface recording density) - (first bottom surface recording density) = 50 - 35 = 15.

[0230] The subtraction value is 15, and the threshold of the subtraction value before being adjusted based on the second information is 25. That is, when the threshold of the subtraction value is not adjusted based on the second information, (subtraction value)<(threshold). Since the sum is less than the threshold, when the threshold is not adjusted based on the second information, the second position WP2 is identified as the waiting position WP.

[0231] The threshold value is adjusted based on the second information. When the control unit 90 calculates a total value by adding up the first lower surface recording density and the second upper surface recording density, (total value) = (first lower surface recording density) + (second upper surface recording density) = 50 + 35 = 85. If the predetermined value for the total value as the second information is 80, (total value) ≧ (predetermined value), so the control unit 90 lowers the threshold value by one step. When the value of one step of the threshold value is 15, (threshold value) = 25 - 15 = 10.

[0232] The following explanation of the operation of the second embodiment will be omitted since it is the same as the operation of the first embodiment, although the numerical values ​​used in the explanation are different. <Effects of the embodiment> The effects of this embodiment will be described.

[0233] In the medium stacking device 11 and image forming system 200 of this embodiment, the same advantages as those (1), (2), and (4) to (11) in the first embodiment can be obtained. (12) The second information includes a total value obtained by adding up the first lower surface recording density and the second upper surface recording density. The larger the total value, the wetter the medium surfaces slide against each other. That is, the larger the total value, the lower the sliding property between the medium M1 to be discharged this time and the medium M2 discharged last time, and therefore the larger the friction force F1. When the total value is equal to or greater than a predetermined value, the control unit 90 sets the threshold lower than when the total value is less than the predetermined value. When the total value is less than the predetermined value, the control unit 90 may set the threshold higher than when the total value is equal to or greater than a predetermined value. When the sliding property between the leading end portion M1a of the medium M1 to be discharged this time and the medium M2 discharged last time is reduced, and the friction force F1 is increased, the medium M1 to be discharged this time can be prevented from buckling. In addition, when the sliding property between the leading end portion M1a of the medium M1 to be discharged this time and the medium M2 discharged last time is not reduced, the productivity of the medium loading device 11 can be prevented from decreasing.

[0234] <Modifications of the embodiment> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

[0235] In the first embodiment, when the previously ejected medium M2 was recorded only on its bottom surface and the currently ejected medium M1 is also recorded only on its bottom surface, the top surface of the previously ejected medium M2 is not wet, and the bottom surface of the currently ejected medium M1 is wet. In such a case, the first bottom surface recording density may be set as the first information, and the value may be set as a value based on the first information. That is, the control unit 90 may determine whether the value based on the first information relating to the recording density of only the currently ejected medium M1 is equal to or greater than a threshold value.

[0236] In the first embodiment, when the previously ejected medium M2 was recorded only on its top surface and the currently ejected medium M1 is also recorded only on its top surface, the top surface of the previously ejected medium M2 is wet and the bottom surface of the currently ejected medium M1 is not wet. In such a case, the second top surface recording density may be set as the first information, and the value may be set as a value based on the first information. That is, the control unit 90 may determine whether the value based on the first information relating to the recording density of only the previously ejected medium M2 is equal to or greater than a threshold value.

[0237] The first information may be the second upper surface recording density and the second lower surface recording density. The value based on the first information may be a subtraction value obtained by subtracting the second upper surface recording density from the second lower surface recording density, and may be a value based on information related to the recording density of the previously discharged medium M2. The currently discharged medium M1 is discharged while the leading end portion M1a of the lower surface of the currently discharged medium M1 rubs against the upper surface of the previously discharged medium M2. The larger the subtraction value, the more the leading end portion of the previously discharged medium M2 curls and rises upward, so that the angle at which the leading end portion M1a of the lower surface of the currently discharged medium M1 contacts the upper surface of the previously discharged medium M2 becomes obtuse. This increases the frictional force F1, making it easier for the currently discharged medium M1 to buckle. The subtraction value obtained by subtracting the second upper surface recording density from the second lower surface recording density as a value based on the first information is information related to the frictional force F1 and is a factor of the frictional force F1. Therefore, the difference obtained by subtracting the second upper surface recording density from the second lower surface recording density may be used to control the medium alignment operation as a factor of the likelihood of buckling in the currently ejected medium M1.

[0238] The first information may be a first top-surface recording density, a first bottom-surface recording density, a second top-surface recording density, and a second bottom-surface recording density.The value based on the first information may be a value substituting the frictional force F1 calculated based on four factors: the moisture content of the bottom surface of the currently discharged medium M1, the moisture content of the top surface of the currently discharged medium M1, the curl state of the currently discharged medium M1, and the curl state of the previously discharged medium M2.

[0239] <Technical ideas and effects understood from the embodiments and modified examples> The technical ideas and effects obtained from the above-described embodiment and modified examples will be described below.

[0240] (A) A medium loading device includes an ejection unit that repeatedly ejects media recorded on by a recording unit that ejects liquid to perform recording; a processing tray that loads the media in the order they are ejected by the ejection unit; a side end alignment member that is positioned below the medium currently ejected, moves to a standby position when the medium is ejected, and then moves in a width direction perpendicular to the ejection direction of the medium to align a side end of the medium with a side end of the medium loaded on the processing tray; and a control unit that controls the side end alignment member, wherein if a value based on first information related to the recording density of at least one of the medium currently ejected and the medium previously ejected is equal to or greater than a threshold value, the control unit specifies as the standby position a first position that overlaps with the medium currently ejected in the width direction, and if the value based on the first information is less than the threshold value, the control unit specifies as the standby position a second position that does not overlap with the medium currently ejected in the width direction, and the control unit adjusts the threshold value based on second information related to at least one of the media recorded up to the current ejection.

[0241] According to this configuration, the threshold is adjusted based on the second information related to at least one of the media recorded up to the current ejection. When the value based on the first information related to the recording density of at least one of the media ejected this time and the media ejected last time is equal to or greater than the threshold, the first position overlapping the medium ejected this time in the width direction is specified as the standby position. When the value based on the first information is less than the threshold, the second position not overlapping the medium ejected this time in the width direction is specified as the standby position. By adjusting the threshold based on the second information, the first position is more likely to be specified as the standby position when buckling of the medium is likely to occur than when the threshold is not adjusted. Also, the first position is less likely to be specified as the standby position when buckling of the medium is unlikely to occur. In other words, buckling of the medium can be suppressed even when the slidability of the medium is lower than expected from the recording density. Also, it is possible to suppress a decrease in productivity of the medium loading device when the slidability of the medium is not lower than expected from the recording density. In other words, the productivity of the media loading device can be improved while suppressing buckling of the media, compared to when the control unit controls the side end alignment member using only the first information related to the recording density of at least one of the media being discharged this time and the media discharged last time.

[0242] (B) The medium loading device includes a discharge unit that repeatedly discharges media recorded on by a recording unit that discharges liquid to perform recording, a processing tray that loads the media in the order discharged by the discharge unit, a side edge alignment member that is disposed below the medium currently discharged, that is positioned at a standby position when the medium is discharged, and then moves in a width direction perpendicular to the discharge direction of the medium to align a side edge of the medium with a side edge of the medium loaded on the processing tray, and a control unit that controls the side edge alignment member, and the control unit determines a value based on first information related to the recording density of at least one of the medium currently discharged and the medium previously discharged. is equal to or greater than a threshold value, a first position that overlaps with the medium currently being discharged in the width direction is identified as the standby position, and if a value based on the first information is less than the threshold value, a second position that does not overlap with the medium currently being discharged in the width direction is identified as the standby position, and the control unit determines a control parameter that controls at least one of the position of the first position in the width direction and the time that the side end alignment member waits at the first position based on second information related to at least one of the media recorded up to the current discharge, and controls the side end alignment member with the control parameter determined based on the second information.

[0243] According to this configuration, the control parameters are determined based on the second information related to at least one of the media recorded up to the current ejection. Based on the first information related to the recording density among the information related to the media, whether the standby position is the first position or the second position is specified. In addition, based on the control parameters determined based on the second information, which is information other than the first information among the information related to the media, the movement of the side end alignment member when the first position is specified as the standby position is controlled. More specifically, the position in the width direction of the first position and the time for which the side end alignment member waits at the first position are changed within a range that has little effect on buckling and productivity. Therefore, the necessary movement in the movement of the side end alignment member when the first position is specified as the standby position increases or increases. In addition, unnecessary movement in the movement of the side end alignment member when the first position is specified as the standby position is eliminated or reduced. In other words, buckling of the medium can be suppressed even when the slidability of the medium is lower than expected from the recording density. In addition, it is possible to suppress a decrease in the productivity of the medium loading device when the slidability of the medium is not lowered as much as expected from the recording density. In other words, the productivity of the media loading device can be improved while suppressing buckling of the media, compared to when the control unit controls the side end alignment member using only the first information related to the recording density of at least one of the media being discharged this time and the media discharged last time.

[0244] (C) In the above-mentioned medium loading device, the value based on the first information may be a total value obtained by adding together a first bottom surface recording density, which is the recording density on the bottom surface of the medium currently being ejected, and a second top surface recording density, which is the recording density on the top surface of the medium previously ejected.

[0245] According to this configuration, the larger the total value, the wetter the medium surfaces slide against each other, and the smaller the total value, the drier the medium surfaces slide against each other. That is, the larger the total value, the lower the sliding property between the medium being discharged this time and the medium discharged last time, so the frictional force increases and the medium is more likely to buckle. Also, the smaller the total value, the lower the sliding property between the medium being discharged this time and the medium discharged last time, so the frictional force decreases and the medium is less likely to buckle. Since the total value is a factor of the susceptibility of the medium being discharged this time to buckling, buckling of the medium being discharged this time can be suppressed by using the total value as a value based on the first information in controlling the medium alignment operation.

[0246] (D) In ​​the above-mentioned medium loading device, the second information includes a subtraction value obtained by subtracting the first bottom-surface recording density from a first top-surface recording density, which is the recording density on the top surface of the medium currently being ejected, and the control unit may lower the threshold value when the subtraction value is equal to or greater than a predetermined value compared to when the subtraction value is less than the predetermined value.

[0247] According to this configuration, the greater the subtraction value, the more the leading edge of the medium being discharged this time curls downward due to the difference in moisture content between the upper and lower surfaces of the medium. In other words, the greater the subtraction value, the more obtuse the angle at which the leading edge of the medium being discharged this time comes into contact with the previously discharged medium, so that the lower surface of the medium being discharged this time comes into contact with the upper surface of the previously discharged medium more strongly. This increases the frictional force, so that sliding properties decrease. When the subtraction value is equal to or greater than a predetermined value, the control unit lowers the threshold value compared to when the subtraction value is less than the predetermined value. When the frictional force is large due to the angle at which the leading edge of the medium being discharged this time comes into contact with the previously discharged medium being obtuse, it is possible to suppress buckling of the medium being discharged this time.

[0248] (E) In the above-mentioned medium loading device, the value based on the first information may be a subtraction value obtained by subtracting a first lower surface recording density, which is the recording density on the lower surface of the medium currently being ejected, from a first upper surface recording density, which is the recording density on the upper surface of the medium currently being ejected.

[0249] According to this configuration, the larger the subtraction value, the more the leading edge of the medium to be discharged this time curls downward due to the difference in moisture content between the upper and lower surfaces of the medium. That is, the larger the subtraction value, the more obtuse the angle at which the leading edge of the medium to be discharged this time contacts the previously discharged medium, so that the lower surface of the medium to be discharged this time and the upper surface of the previously discharged medium come into strong contact. Then, the frictional force increases, so that the medium is more likely to buckle. Also, the smaller the subtraction value, the more the leading edge of the medium to be discharged this time curls upward due to the difference in moisture content between the upper and lower surfaces of the medium. That is, the smaller the subtraction value, the more acute the angle at which the leading edge of the medium to be discharged this time contacts the previously discharged medium, so that the lower surface of the medium to be discharged this time and the upper surface of the previously discharged medium come into weak contact. This reduces the frictional force, so that the medium is less likely to buckle. Since the subtraction value is a factor of how easily the medium to be discharged this time buckles, by using the subtraction value as a value based on the first information in controlling the medium alignment operation, buckling of the medium to be discharged this time can be suppressed.

[0250] (F) In the medium loading device, the second information includes a total value obtained by adding up the first lower-surface recording density and a second upper-surface recording density, which is a recording density on the upper surface of the medium previously ejected, The control unit may set the threshold lower when the total value is equal to or greater than a predetermined value than when the total value is less than the predetermined value.

[0251] According to this configuration, the larger the total value, the wetter the medium surfaces slide against each other. In other words, the larger the total value, the lower the sliding property between the medium to be discharged this time and the medium discharged last time, and the greater the frictional force. When the total value is equal to or greater than a predetermined value, the control unit sets the threshold lower than when the total value is less than the predetermined value. When the frictional force is greater due to the lower sliding property between the medium to be discharged this time and the medium discharged last time, the control unit can suppress buckling of the medium to be discharged this time.

[0252] (G) In the medium loading device, the second information may include at least one of the size of the medium currently ejected, the basis weight of the medium currently ejected, and the type of the medium currently ejected.

[0253] According to this configuration, the resistance force against buckling of the currently discharged medium changes depending on the size, basis weight, and type of the currently discharged medium. That is, depending on the size, basis weight, and type of the currently discharged medium, the difference between the resistance force of a standard medium and the resistance force of the currently discharged medium may be large. The control unit may adjust the threshold value based on at least one of the size, basis weight, and type of the currently discharged medium. The control unit may determine a control parameter for causing the side edge alignment member to wait at the first position based on at least one of the size, basis weight, and type of the currently discharged medium. Then, when the control unit identifies the first position as the wait position, the control unit may control the side edge alignment member to wait at the first position with the control parameter. This makes it possible to suppress buckling of the currently discharged medium when the resistance force is small. In addition, when the resistance force of the currently discharged medium is sufficiently larger than the friction force, it is possible to suppress a decrease in productivity of the medium loading device.

[0254] (H) In the medium loading device, the second information may include at least one of the temperature and humidity of the environment in which the medium currently being ejected was recorded. According to this configuration, when the humidity of the environment in which the medium to be discharged this time is recorded is high, it takes a long time for the medium surface to dry, and when the humidity of the environment in which the medium to be discharged this time is recorded is low, it takes a long time for the medium surface to dry. Also, when the temperature of the environment in which the medium to be discharged this time is recorded is low, the moisture content state is not improved by the drying process, and it takes a long time for the medium surface to dry, and when the temperature of the environment in which the medium to be discharged this time is recorded is high, it takes a short time for the medium surface to dry. The control unit may adjust the threshold value based on at least one of the temperature and humidity of the environment in which the medium to be discharged this time is recorded. The control unit may determine a control parameter for causing the side edge alignment member to wait at the first position based on at least one of the temperature and humidity of the environment in which the medium to be discharged this time is recorded. Then, when the control unit identifies the first position as the waiting position, it may control the side edge alignment member to wait at the first position with the control parameter. This makes it possible to suppress buckling of the medium to be discharged this time when the drying of the medium to be discharged this time and the medium discharged last time is not progressing. In addition, when the medium to be discharged this time and the previously discharged medium have been dried to a sufficiently low moisture content, a decrease in productivity of the medium loading device can be suppressed.

[0255] (I) In the medium loading device, the second information may include the number of the media loaded on the processing tray when the medium to be currently ejected is ejected. According to this configuration, when the number of media loaded on the processing tray is large, the distance between the top surface of the previously discharged medium and the bottom surface of the currently discharged medium is small, and the frictional force is large. Also, when the number of media loaded on the processing tray is small, the distance between the top surface of the previously discharged medium and the bottom surface of the currently discharged medium is large, and the frictional force is small. The control unit may adjust the threshold value based on the number of media loaded on the processing tray when the currently discharged medium is discharged. The control unit may determine a control parameter for causing the side end alignment member to wait at the first position based on the number of media loaded on the processing tray when the currently discharged medium is discharged. Then, when the control unit identifies the first position as the waiting position, the control unit may control the side end alignment member to wait at the first position with the control parameter. This makes it possible to suppress buckling of the currently discharged medium when the frictional force is large due to the large number of media loaded on the processing tray. In addition, when the number of media loaded on the processing tray is reduced and the frictional force is small, a decrease in productivity of the medium loading device can be suppressed.

[0256] (J) In the medium loading device, the second information may include a first elapsed time from when the medium currently being ejected is recorded to when the medium is ejected. According to this configuration, when the first elapsed time is short, the drying of the medium surface of the medium discharged this time is not progressing. When the first elapsed time is long, the drying of the medium surface of the medium discharged this time is progressing. The control unit may adjust the threshold value based on the first elapsed time. The control unit may determine a control parameter for causing the side edge alignment member to wait at the first position based on the first elapsed time. Then, when the control unit identifies the first position as the waiting position, the control unit may control the side edge alignment member to wait at the first position with the control parameter. This makes it possible to suppress buckling of the medium discharged this time when the drying of the medium discharged this time is not progressing. Also, when the drying of the medium discharged this time is progressing and the moisture content is sufficiently small, it is possible to suppress a decrease in productivity of the medium loading device.

[0257] (K) In the medium loading device, the second information may include a second elapsed time from when the previously ejected medium was recorded to when the currently ejected medium is ejected. According to this configuration, when the second elapsed time is short, the drying of the medium surface of the previously discharged medium is not progressing. When the second elapsed time is long, the drying of the medium surface of the previously discharged medium is progressing. The control unit may adjust the threshold value based on the second elapsed time. The control unit may determine a control parameter for causing the side edge alignment member to wait at the first position based on the second elapsed time. Then, when the control unit identifies the first position as the waiting position, the control unit may control the side edge alignment member to wait at the first position with the control parameter. This makes it possible to suppress buckling of the currently discharged medium when the drying of the currently discharged medium is not progressing. Also, when the drying of the currently discharged medium is progressing and the moisture content is sufficiently small, it is possible to suppress a decrease in productivity of the medium loading device.

[0258] (L) In the above-mentioned media loading device, the distance in the width direction between the alignment surface of the side end alignment member at the first position and the expected side end of the medium when it is discharged from the discharge section is specified by an overlap amount, and the control section may determine the overlap amount based on second information relating to at least one of the media recorded up to the current discharge, and control the side end alignment member with the overlap amount determined based on the second information.

[0259] According to this configuration, when the overlap amount is increased, contact between the medium to be discharged this time and the medium discharged last time can be more effectively prevented. That is, the control unit determines the overlap amount based on the second information, and when the first position is identified as the standby position, controls the side edge alignment member based on the overlap amount, thereby more effectively preventing the medium to be discharged this time from buckling. Furthermore, when the overlap amount is reduced, even if the timing at which the side edge alignment member leaves the first position and starts moving toward the second position is the same, the movement distance to the second position is reduced. Therefore, it is possible to shorten the time from when the rear end of the medium to be discharged this time is discharged from the discharge unit until the first side edge of the medium to be discharged this time is aligned with the first side edge of the medium loaded on the processing tray. That is, the control unit determines the overlap amount based on the second information, and when the first position is identified as the standby position, controls the side edge alignment member based on the overlap amount, thereby preventing a decrease in productivity of the medium loading device.

[0260] (M) In the above-mentioned media loading device, when the side end alignment member moves to the first position when the medium to be currently discharged is discharged, it moves away from the first position toward the second position, and then aligns the side end of the medium to be currently discharged with the side end of the medium loaded on the processing tray, and the control unit may determine the timing for the side end alignment member to move from the first position based on second information relating to at least one of the media recorded up to the current discharge, and control the side end alignment member at the timing determined based on the second information.

[0261] According to this configuration, by advancing this timing, the side edge alignment operation can be started at the same time as the trailing end of the currently discharged medium is discharged from the discharge section. That is, the control unit determines this timing based on the second information, and controls the side edge alignment member at that timing when the first position is identified as the standby position, thereby preventing a decrease in productivity of the medium loading device. By delaying this timing, contact between the currently discharged medium and the previously discharged medium can be prevented until the trailing end of the currently discharged medium is discharged from the discharge section. That is, by the control unit determines this timing based on the second information, and controls the side edge alignment member at that timing when the first position is identified as the standby position, it is possible to further prevent buckling of the currently discharged medium.

[0262] (N) The above-mentioned medium loading device includes a first side edge guide member that is arranged below one side in the width direction of the medium currently being discharged and moves in the width direction, and a second side edge guide member that is arranged below the other side in the width direction of the medium currently being discharged and moves in the width direction, the first side edge guide member being configured as the side edge alignment member to be located at the standby position when the medium currently being discharged is discharged, and then aligning a first side edge of one side of the medium with a first side edge of one side of the medium loaded on the processing tray, and the second side edge guide member being configured as the side edge alignment member to be located at the standby position when the medium currently being discharged is discharged, and then aligning a second side edge of the other side of the medium with a first side edge of one side of the medium loaded on the processing tray. the second information includes at least one of a first lower surface widthwise recording density distribution which is a recording density distribution in the width direction of the lower surface of the medium currently ejected, and a second upper surface widthwise recording density distribution which is a recording density distribution in the width direction of the upper surface of the medium previously ejected, the control unit may identify either the first side edge guide member or the second side edge guide member as the side edge alignment member, and the control unit may determine the selection of which one to identify based on second information relating to at least one of the media recorded up to the current ejection, and control the side edge alignment member with the selection determined based on the second information.

[0263] According to this configuration, the control unit can determine which of the frictional forces of the medium surface on the first side edge side and the medium surface on the second side edge side is greater, based on the first lower surface width direction recording density distribution as the second information, on the lower surface of the medium currently being ejected. The control unit can also determine which of the frictional forces of the medium surface on the first side edge side and the medium surface on the second side edge side is greater, based on the first upper surface width direction recording density distribution as the second information, on the upper surface of the medium currently being ejected. Then, the control unit specifies the side edge guide member on the side with the greater frictional force as the side edge alignment member, and controls the side edge guide member on the side with the greater frictional force as the side edge alignment member. This suppresses contact of the medium surface on the side edge side with the greater frictional force, and more effectively suppresses buckling of the medium currently being ejected. In addition, when there is little bias in the recording density, i.e., when the frictional force is nearly uniform, the control unit can improve the productivity of the medium loading device by selectively using the first side end guide member as a side end alignment member and the second side end guide member as a side end alignment member depending on the situation.

[0264] (O) An image forming system includes a recording unit that ejects liquid onto a medium to perform recording, a discharge unit that repeatedly discharges the medium recorded on by the recording unit, a processing tray that loads the medium in the order in which they are discharged by the discharge unit, a side end alignment member that is positioned below the medium currently discharged and moves to a standby position when the medium is discharged and then moves in a width direction perpendicular to the discharge direction of the medium to align a side end of the medium with a side end of the medium loaded on the processing tray, and a control unit that controls the side end alignment member, wherein if a value based on first information related to the recording density of at least one of the medium currently discharged and the medium previously discharged is equal to or greater than a threshold value, the control unit specifies a first position that overlaps with the medium currently discharged in the width direction as the standby position, and if the value based on the first information is less than the threshold value, specifies a second position that does not overlap with the medium currently discharged in the width direction as the standby position, and the control unit adjusts the threshold value based on second information related to at least one of the media recorded up to the current discharge.

[0265] According to this configuration, the same effect as (A) can be obtained in the image forming system. (P) An image forming system includes a recording unit that performs recording by ejecting liquid onto a medium, a discharge unit that repeatedly discharges the medium recorded on by the recording unit, a processing tray that stacks the media in the order discharged by the discharge unit, a side edge alignment member that is disposed below the medium currently discharged, that is positioned at a standby position when the medium is discharged, and then moves in a width direction perpendicular to the discharge direction of the medium to align a side edge of the medium with a side edge of the medium stacked on the processing tray, and a control unit that controls the side edge alignment member, and the control unit is configured to: If the value based on the first information is equal to or greater than a threshold value, a first position that overlaps with the medium currently being discharged in the width direction is identified as the standby position, and if the value based on the first information is less than the threshold value, a second position that does not overlap with the medium currently being discharged in the width direction is identified as the standby position, and the control unit determines a control parameter for controlling at least one of the position in the width direction of the first position and the time that the side end alignment member waits at the first position based on second information related to at least one of the media recorded up to the current discharge, and controls the side end alignment member with the control parameter determined based on the second information.

[0266] According to this configuration, the same effect as (B) can be obtained in the image forming system. [Explanation of symbols]

[0267] 11...medium stacking device, 12...second discharge tray, 13...stacker tray, 20...loading section, 21...processing tray, 30...rear end alignment section, 31...rear end alignment member, 32...rear end reference surface, 40...side end alignment section, 41...first side end guide member as side end alignment member, 41a...alignment surface, 42...second side end guide member as side end alignment member, 42a...alignment surface, 51...bundle discharge section, 52...bundle discharge roller pair, 52a...bundle discharge drive roller, 52b...bundle discharge driven roller, 60...post-processing section, 70...conveyance section, 71...discharge section, 72...discharge roller pair, 72a...discharge drive roller, 72b...discharge driven roller, 76...entry path, 77...branch section, 78...first transport path, 79...second transport path, 80...temperature and humidity measuring section, 90...control section, 111...recording device, 112...medium Storage section, 113...main body section, 114...first discharge tray, 115...operation section, 116...image reading section, 117...automatic feed section, 160...recording section, 170...second conveying section, 190...second control section, 191...second storage section, 200...image forming system, F1...friction force, A...medium width, B...medium length, F2...resistance force, L1...overlap amount, L2...overlap amount, M...medium, M1...currently discharged Media, M1a...leading end portion, M1b...rear end portion, M1c...first side end, M1d...second side end, M2...previously ejected media, Ms...media loaded on processing tray, Msc...first side end, Msd...second side end, RP...reference position, W1...alignment direction, WP...waiting position, WP1...first position, WP2...second position, X...width direction, Y...depth direction, Y1...length direction, Z...height direction.

Claims

1. a discharge unit that repeatedly discharges the medium recorded by the recording unit that performs recording by discharging liquid; a processing tray that stacks the media in the order in which they are discharged by the discharge unit; a side edge alignment member that is disposed below the medium to be discharged, that is positioned at a standby position when the medium is discharged, and that then moves in a width direction perpendicular to the direction in which the medium is discharged to align a side edge of the medium with a side edge of the medium loaded on the processing tray; a control unit for controlling the side edge alignment member, when a value based on first information relating to the recording density of at least one of the medium being discharged this time and the medium discharged last time is equal to or greater than a threshold value, the control unit specifies a first position that overlaps with the medium being discharged this time in the width direction as the standby position, and when the value based on the first information is less than the threshold value, specifies a second position that does not overlap with the medium being discharged this time in the width direction as the standby position; The medium loading device, wherein the control unit adjusts the threshold value based on second information relating to at least one medium among the media recorded up until the current ejection.

2. The media loading device described in Claim 1, characterized in that the control unit determines a control parameter that controls at least one of the position in the width direction of the first position and the time that the side end alignment member waits at the first position based on second information relating to at least one of the media recorded up to the current ejection, and controls the side end alignment member with the control parameter determined based on the second information.

3. A medium loading device as described in claim 1 or claim 2, characterized in that the value based on the first information is a total value obtained by adding together a first bottom surface recording density, which is the recording density on the bottom surface of the medium being ejected this time, and a second top surface recording density, which is the recording density on the top surface of the medium ejected last time.

4. the second information includes a subtraction value obtained by subtracting the first lower-surface recording density from a first upper-surface recording density, which is a recording density on the upper surface of the medium currently being ejected; 4. The medium stacking device according to claim 3, wherein the control unit sets the threshold lower when the subtraction value is equal to or greater than a predetermined value than when the subtraction value is less than the predetermined value.

5. A medium loading device as described in claim 1 or claim 2, characterized in that the value based on the first information is a subtraction value obtained by subtracting a first lower surface recording density, which is the recording density on the lower surface of the medium being currently ejected, from a first upper surface recording density, which is the recording density on the upper surface of the medium being currently ejected.

6. the second information includes a total value obtained by adding up the first lower-surface recording density and a second upper-surface recording density, which is a recording density on the upper surface of the medium that was previously ejected; The medium stacking device according to claim 5 , wherein the control unit sets the threshold lower when the total value is equal to or greater than a predetermined value than when the total value is less than the predetermined value.

7. A medium loading device as described in any one of claims 1 to 6, characterized in that the second information includes at least one of the size of the medium currently being ejected, the basis weight of the medium currently being ejected, and the type of the medium currently being ejected.

8. 8. The medium loading device according to claim 1, wherein the second information includes at least one of a temperature and a humidity of an environment in which the medium to be discharged is recorded.

9. 9. The medium stacking device according to claim 1, wherein the second information includes a number of the media stacked on the processing tray when the medium to be currently discharged is discharged.

10. 10. The medium stacking device according to claim 1, wherein the second information includes a first elapsed time from when the medium to be discharged is recorded to when the medium is discharged.

11. 11. The medium loading device according to claim 1, wherein the second information includes a second elapsed time from when the previously ejected medium was recorded to when the currently ejected medium is ejected.

12. a distance in the width direction between an alignment surface of the side edge alignment member at the first position and an expected side edge of the medium when the medium is discharged from the discharge portion, the distance being defined by an overlap amount; A media loading device as described in any one of claims 1 to 11, characterized in that the control unit determines the amount of overlap based on second information relating to at least one of the media recorded up to the current ejection, and controls the side edge alignment member with the amount of overlap determined based on the second information.

13. when the side edge alignment member moves to the first position when the medium to be discharged this time is discharged, the side edge alignment member moves from the first position toward the second position and then aligns the side edge of the medium to be discharged this time with the side edge of the medium loaded on the processing tray; A media loading device as described in any one of claims 1 to 12, characterized in that the control unit determines the timing at which the side end alignment member moves from the first position based on second information relating to at least one of the media recorded up to the current ejection, and controls the side end alignment member at the timing determined based on the second information.

14. a first side end guide member that is disposed below one side in the width direction of the medium to be discharged and moves in the width direction; a second side end guide member that is disposed below the other side in the width direction of the medium currently being discharged and moves in the width direction, the first side edge guide member is configured as the side edge alignment member to be positioned at the standby position when the medium to be discharged this time is discharged, and then to be capable of aligning a first side edge of one side of the medium with a first side edge of one side of the medium loaded on the processing tray; the second side edge guide member is configured as the side edge alignment member to be positioned at the standby position when the medium to be discharged this time is discharged, and then to be capable of aligning the second side edge of the other side of the medium with the second side edge of the other side of the medium loaded on the processing tray; the second information includes at least one of a first lower surface width direction recording density distribution which is a recording density distribution in the width direction of a lower surface of the medium currently ejected, and a second upper surface width direction recording density distribution which is a recording density distribution in the width direction of an upper surface of the medium previously ejected, the control unit specifies one of the first side edge guide member and the second side edge guide member as the side edge alignment member, The control unit determines the selection to specify one of the two media based on second information relating to at least one of the media recorded up to the current ejection, and controls the side edge alignment member based on the selection determined based on the second information.

15. a recording unit that performs recording by ejecting liquid onto a medium; a discharge unit that repeatedly discharges the medium recorded by the recording unit; a processing tray that stacks the media in the order in which they are discharged by the discharge unit; a side edge alignment member that is disposed below the medium to be discharged, that is positioned at a standby position when the medium is discharged, and that then moves in a width direction perpendicular to the direction in which the medium is discharged to align a side edge of the medium with a side edge of the medium loaded on the processing tray; a control unit for controlling the side edge alignment member, when a value based on first information relating to the recording density of at least one of the medium being discharged this time and the medium discharged last time is equal to or greater than a threshold value, the control unit specifies a first position that overlaps with the medium being discharged this time in the width direction as the standby position, and when the value based on the first information is less than the threshold value, specifies a second position that does not overlap with the medium being discharged this time in the width direction as the standby position; The control unit adjusts the threshold value based on second information relating to at least one medium among the media recorded up to the current ejection.

16. The control unit determines a control parameter that controls at least one of the widthwise position of the first position and the time that the side end alignment member waits at the first position based on second information relating to at least one of the media recorded up to this ejection, and controls the side end alignment member with the control parameter determined based on the second information.

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