Sheet stacking device and image forming apparatus

Abstract

To provide a sheet loading apparatus with improved sheet transport speed.SOLUTION: A sheet loading apparatus (1) includes a tray (50) that can load a plurality of sheets (M), a transport portion (27) that is located above the tray (50) and transports the sheets (M) in a transport direction, a tip guide portion (40) that is disposed above the tray (50) and on a downstream side of the transport direction with respect to the transport portion (27) to guide the sheets (M) to the tray (50) by accommodating an end portion of the sheet (M) transported by the transport portion (27) at an accommodation position on the downstream side of the transport direction and separating the end portion at a separation position on the downstream side in the transport direction with respect to the accommodation position, and an air discharge portion (60) that discharges air on an upper surface of the sheet (M) loaded on the tray (50) to an upstream side in the transportation direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sheet stacking device and an image forming apparatus. [Background technology]

[0002] Conventionally, image forming apparatuses have been known that include a conveying section that conveys sheets, an image forming section that forms an image on the sheets conveyed by the conveying section, and a tray that stacks the sheets on which the images have been formed by the image forming section.

[0003] Such an image forming apparatus has a problem in that the leading edge of a sheet floats up just before it is stacked on the tray. To address this problem, some image forming apparatuses are provided with a gripping unit that is located above the tray and grips the leading edge of a sheet conveyed by a conveying unit at a gripping position and releases the sheet at a release position downstream of the gripping position in the conveying direction (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0004] However, in this type of image forming apparatus, the air above the sheets stacked on the tray creates resistance, making it take time for the sheets to free fall after being released from the gripping section. Therefore, if the interval between sheets free falling after passing through the conveying section is short, the sheets may come into contact with each other and not be properly stacked on the tray. As a result, when forming images on multiple sheets consecutively, a new issue arises: the sheet conveying speed is limited.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a technique for improving the sheet conveying speed in a sheet stacking device that allows sheets to freely fall toward a tray. [Means for solving the problem]

[0006] In order to solve the above technical problems, one aspect of the present invention is a sheet transport device including a tray capable of stacking a plurality of sheets, a transport section disposed above the tray and downstream of the transport section in the transport direction, a leading edge guide section disposed above the tray and downstream of the transport section in the transport direction, for guiding the sheet to the tray by storing an end portion of the sheet transported by the transport section in the downstream direction in the transport direction at a storing position and releasing the end portion at a releasing position downstream of the storing position in the transport direction, and a discharge section for discharging air from above the surface of the sheets stacked on the tray to the upstream side in the transport direction. having an opening and an air exhaust section. The opening is disposed at a position facing the upper surface of the sheet stacked on the tray, and is larger than the thickness of the sheet in the vertical direction and larger than the maximum width of the sheet in the width direction of the sheet perpendicular to the conveying direction. It is characterized by: [Effects of the Invention]

[0007] According to the present invention, in a sheet stacking device that allows sheets to freely fall toward a tray, the sheet transport speed can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating an internal structure of an image forming apparatus. [Figure 2] FIG. 4 is a diagram showing the sheet stacking device when the guide member is located at the storage position. [Figure 3] FIG. 10 is a diagram showing the sheet stacking device when the guide member is located at the detached position. [Figure 4] FIG. 4 is a schematic diagram of a lifting mechanism that lifts and lowers the paper output tray. [Figure 5] FIG. [Figure 6] FIG. 2 is a diagram showing the hardware configuration of an image forming apparatus. [Figure 7] 10 is a flowchart of an air volume determination process. [Figure 8] 10 is a flowchart of a tray lifting / lowering process. DETAILED DESCRIPTION OF THE INVENTION

[0009] An image forming apparatus 1 according to an embodiment will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the internal structure of the image forming apparatus 1. The image forming apparatus 1 forms images continuously on a plurality of sheets M. The sheets M as a sheet-like medium include, for example, paper (paper), overhead projector sheets, thread, fiber, fabric, leather, metal, and plastic. As shown in FIG. 1, the image forming apparatus 1 mainly includes a paper feed tray 10, a conveying unit 20, an image forming unit 30, a leading edge guide unit 40, a paper discharge tray 50 (tray), and an air exhaust unit 60.

[0010] The paper feed tray 10 accommodates stacked sheets M before images are formed on them. The conveying unit 20 discharges the sheets M accommodated in the paper feed tray 10 to a paper discharge tray 50 via a position facing the image forming unit 30. The conveying unit 20 includes a paper feed roller 21 and multiple roller pairs 22, 23, 24, 25, 26, and 27.

[0011] The paper feed roller 21 rotates while contacting the topmost sheet M in the paper feed tray 10, thereby supplying the sheet M to the conveyance path. A plurality of roller pairs 22 to 27 are arranged at predetermined intervals along the conveyance path. The roller pairs 22 to 27 convey the sheet M by rotating while holding the sheet M between them. The conveyance path indicated by the dashed line in FIG. 1 is a space that runs from the paper feed tray 10 to the discharge tray 50, passing through a position facing the image forming unit 30.

[0012] The conveying directions of the sheet M by the roller pairs 22 to 27 are different from each other. Of the roller pairs 22 to 27, the conveying direction of the sheet M by the roller pair 27, which is closest to the paper discharge tray 50, is the horizontal direction (direction from right to left in FIG. 1). In this specification, when the term "conveying direction" is simply written, it refers to the conveying direction by the roller pair 27.

[0013] The image forming unit 30 employs an inkjet method for forming an image on the sheet M by ejecting ink onto the sheet M. The image forming unit 30 includes a plurality of head modules for ejecting ink of each color: cyan, magenta, yellow, and black. An image is formed on the sheet M facing the image forming unit 30 by ejecting ink from each head module at a predetermined timing. However, the image forming unit 30 may employ an electrophotographic method for forming an image by fixing toner on the sheet M.

[0014] Among the components of the image forming apparatus 1 shown in FIG. 1, the roller pair 27 (conveying section), the leading edge guide section 40, the paper discharge tray 50, and the air discharge section 60 constitute an example of a sheet stacking device that stacks multiple sheets M.

[0015] The leading edge guide section 40 is disposed downstream in the conveying direction from the roller pair 27. The roller pair 27 and the leading edge guide section 40 are disposed above the paper discharge tray 50. The leading edge guide section 40 guides the leading edge of the sheet M conveyed by the roller pair 27 downstream in the conveying direction, thereby preventing the leading edge of the sheet M, which is falling freely toward the paper discharge tray 50, from floating up.

[0016] Fig. 2 is a view showing the sheet stacking device when the guide member 44 is located at the storage position. Fig. 3 is a view showing the sheet stacking device when the guide member 44 is located at the release position. As shown in Figs. 1 to 3, the leading edge guide section 40 is made up of a drive roller 41, a driven roller 42, an endless circular belt 43, and a plurality of guide members 44, 45.

[0017] The drive roller 41 and the driven roller 42 are rotatably supported on the housing of the image forming apparatus 1 at positions spaced apart in the conveyance direction. The endless circular belt 43 is stretched over the drive roller 41 and the driven roller 42. When the driving force of the motor is transmitted to rotate the drive roller 41, the endless circular belt 43 rotates between the drive roller 41 and the driven roller 42. The endless circular belt 43 rotates clockwise in FIGS. 2 and 3. In other words, the endless circular belt 43 rotates in a direction in which the lower surface moves in the conveyance direction and the upper surface moves in the opposite direction to the conveyance direction.

[0018] The guide members 44, 45 are attached at equal intervals to the outer peripheral surface of the endless circular belt 43. Therefore, as the endless circular belt 43 rotates, the guide members 44, 45 move in the conveying direction on the lower surface side of the endless circular belt 43 and move in the opposite direction to the conveying direction on the upper surface side of the endless circular belt 43. The number of guide members 44, 45 is not limited to two.

[0019] The guide member 44 has an internal space that accommodates a portion of the leading edge (the downstream end in the conveying direction) of the sheet M. More specifically, the guide member 44 is composed of an opening 44a, a middle portion 44b, and a deep portion 44c. The guide member 45, like the guide member 44, is composed of an opening 45a, a middle portion 45b, and a deep portion 45c. The structure of the guide member 44 will be described below.

[0020] The opening 44a opens upstream in the conveying direction (i.e., the side facing the roller pair 27) when the guide member 44 is located below the endless circular belt 43. The middle portion 44b is located downstream in the conveying direction from the opening 44a when the guide member 44 is located below the endless circular belt 43. The middle portion 44b has a smaller vertical gap than the opening 44a and the innermost portion 44c. The innermost portion 44c is located downstream in the conveying direction from the middle portion 44b when the guide member 44 is located below the endless circular belt 43. The innermost portion 44c is the portion that comes into contact with the leading edge of the sheet M that has entered the guide member 44 through the opening 44a.

[0021] The vertical gaps between the opening 44a, the middle portion 44b, and the rear portion 44c are set larger than the thickness of the sheet M that can be conveyed by the roller pair 27. In other words, the guide member 44 supports the sheet M to an extent that does not interfere with the forward and backward movement of the sheet M without sandwiching the sheet M between its upper and lower walls. This prevents the sheet M from being damaged as it moves forward and backward relative to the guide member 44. However, the vertical gap of the middle portion 44b is not limited to being smaller than those of the opening 44a and the rear portion 44c, and the vertical gaps of the opening 44a, the middle portion 44b, and the rear portion 44c may be the same. Furthermore, the vertical gap of the rear portion 44c may be smaller than that of the middle portion 44b.

[0022] Furthermore, when the guide member 44 is positioned below the endless circular belt 43, the upper surface of the lower wall of the opening 44a is inclined upward toward the middle portion 44b. The surface of the opening 44a that can come into contact with the sheet M is a smooth surface without any protrusions formed thereon. This reduces the resistance when the sheet M enters the internal space of the guide member 44. Furthermore, by constructing the portion of the guide member 44 that can come into contact with the sheet M from a highly smooth material such as metal or resin, the sheet M can enter even more smoothly.

[0023] The guide member 44 is stopped at the storage position shown in Fig. 2. The storage position is a position on the lower surface side of the endless circular belt 43 where the opening 44a faces the roller pair 27. In other words, the storage position is a position where the leading edge of the sheet M that has passed through the roller pair 27 can be stored. That is, the leading edge of the sheet M conveyed by the roller pair 27 enters the internal space of the guide member 44 through the opening 44a and reaches the inner portion 44c.

[0024] When the leading edge of the sheet M enters the internal space of the guide member 44, the endless circular belt 43 starts to rotate and stops again when the guide member 45 reaches the storage position. At this time, the speed (maximum speed) of the guide member 44 moving downstream in the transport direction is set faster than the transport speed of the sheet M by the roller pair 27. Therefore, the leading edge of the sheet M stored in the guide member 44 separates from the guide member 44 when the guide member 44 reaches the separation position shown in FIG. 3 due to the speed difference between the transport speed of the sheet M by the roller pair 27 and the moving speed of the guide member 45.

[0025] The release position is a position on the lower surface of the endless circular belt 43, downstream of the storage position in the conveying direction. When the leading edge of the sheet M releases from the guide member 44, the trailing edge (the upstream edge in the conveying direction) of the sheet M is still held by the pair of rollers 27. That is, the leading edge guide section 40 releases the leading edge of the sheet M before the trailing edge of the sheet M passes through the pair of rollers 27. In other words, the trailing edge of the sheet M passes through the pair of rollers 27 after the leading edge releases from the leading edge guide section 40.

[0026] As a result, the sheet M falls freely toward the discharge tray 50. More specifically, the leading edge of the sheet M starts to fall freely at the release position, and then the trailing edge of the sheet M starts to fall freely after passing through the roller pair 27. That is, the leading edge guide unit 40 plays a role in guiding the sheet M to the discharge tray 50 by storing the leading edge of the sheet M conveyed by the roller pair 27 in the guide members 44, 45 at the storage position and separating the leading edge from the guide members 44, 45 at the release position. Then, by intermittently rotating the endless circular belt 43, multiple sheets M can be discharged onto the discharge tray 50.

[0027] The endless circular belt 43 may start rotating when the leading edge of the sheet M abuts against the innermost portion 44c of the guide member 44, or may start rotating just before the leading edge of the sheet M abuts against the innermost portion 44c of the guide member 44. By preventing the sheet M from abutting against the innermost portion 44c, it is possible to prevent the leading edge of the sheet M from being folded. The position of the leading edge of the sheet M conveyed by the roller pair 27 can be identified by a well-known position sensor (for example, an optical sensor, a rotary encoder, or a combination thereof).

[0028] The paper discharge tray 50 accommodates a plurality of sheets M in a stacked state after images have been formed by the image forming unit 30. The paper discharge tray 50 is disposed downstream of the roller pair 27 in the conveyance direction and below the roller pair 27 and the leading edge guide unit 40. In other words, the paper discharge tray 50 is disposed at the destination of the free fall of the sheet M conveyed by the roller pair 27 and having its leading edge guided by the leading edge guide unit 40.

[0029] 4 is a schematic diagram of a lifting mechanism 51 that lifts and lowers the paper output tray 50. The paper output tray 50 is configured to be able to be raised and lowered in the vertical direction by the lifting mechanism 51. The lifting mechanism 51 mainly includes a pair of pulleys 52a, 52b, a pair of chains 53a, 53b, a pair of weights 54a, 54b, an upper surface detection sensor 55, and a full-state detection sensor 56. However, the specific structure of the lifting mechanism 51 is not limited to the example shown in FIG. 4.

[0030] The pair of pulleys 52a, 52b are rotatably supported on the housing of the image forming apparatus 1 at positions above the paper discharge tray 50 and spaced apart from each other in the conveyance direction. The pair of chains 53a, 53b are stretched over the corresponding pulleys 52a, 52b. One end of each of the pair of chains 53a, 53b is connected to the paper discharge tray 50, and the other end is connected to the corresponding weights 54a, 54b.

[0031] When the pulleys 52a and 52b rotate in a first direction (in FIG. 4, the pulley 52a rotates clockwise and the pulley 52b rotates counterclockwise), the paper output tray 50 rises and the weights 54a and 54b fall. On the other hand, when the pulleys 52a and 52b rotate in a second direction opposite to the first direction (in FIG. 4, the pulley 52a rotates counterclockwise and the pulley 52b rotates clockwise), the paper output tray 50 falls and the weights 54a and 54b rise.

[0032] The top surface detection sensor 55 is a sensor that detects the position of the top sheet M stacked on the paper discharge tray 50. The top surface detection sensor 55 is disposed above the paper discharge tray 50 (for example, at a position facing the duct 61 or slightly above the duct 61 in the vertical direction). The top surface detection sensor 55 is, for example, a reflective optical sensor that includes a light-emitting unit that outputs light and a light-receiving unit that receives light that is output from the light-emitting unit and reflected by the sheet M.

[0033] The top surface detection sensor 55 outputs a detection signal to the controller 100 (see FIG. 6), which will be described later, when a sheet M is present on the optical path (i.e., when a sheet M stacked on the paper discharge tray 50 is detected). On the other hand, the top surface detection sensor 55 stops outputting the detection signal when a sheet M is not present on the optical path. However, the top surface detection sensor 55 is not limited to a reflective optical sensor, and may be a transmissive optical sensor.

[0034] The full detection sensor 56 is a sensor that detects when the maximum amount of sheets M has been stacked on the discharge tray 50. The full detection sensor 56 is disposed, for example, at a position facing the weight 54b when the discharge tray 50 is full. The full detection sensor 56 is, for example, a reflective optical sensor that includes a light-emitting unit that emits light and a light-receiving unit that receives light that is output from the light-emitting unit and reflected by the weight 54b.

[0035] The full detection sensor 56 outputs a detection signal to the controller 100 when the weight 54b is present on the optical path (i.e., when the paper output tray 50 is full). On the other hand, the full detection sensor 56 stops outputting the detection signal when the weight 54b is not present on the optical path. However, the full detection sensor 56 is not limited to a reflective optical sensor, and may be a transmissive optical sensor.

[0036] The air discharge unit 60 discharges, upstream in the transport direction, residual air 70 on the top surface of the top sheet M stacked on the paper discharge tray 50. More specifically, as shown in Fig. 3, the air discharge unit 60 discharges, upstream in the transport direction, residual air 70 between the top sheet M stacked on the paper discharge tray 50 and a new sheet M freely falling toward the paper discharge tray 50.

[0037] The air discharge section 60 is disposed below the roller pair 27 and the leading edge guide section 40 and above the sheet discharge tray 50. The air discharge section 60 is disposed upstream of the sheet discharge tray 50 in the conveyance direction. FIG. 5 is a plan view of the sheet discharge tray 50 and the air discharge section 60. As shown in FIGS. 1 and 5, the air discharge section 60 is disposed at a position facing the uppermost sheet M stacked on the sheet discharge tray 50 in the vertical direction (FIG. 1) and in the width direction of the sheets M (FIG. 5). The air discharge section 60 mainly includes a duct 61 and a fan 62.

[0038] The duct 61 constitutes an air passage that discharges residual air 70 on the upper surfaces of the sheets M stacked on the paper discharge tray 50 to the outside of the image forming apparatus 1. The duct 61 is disposed upstream of the paper discharge tray 50 in the transport direction and at a position facing the upper surfaces of the sheets M stacked on the paper discharge tray 50. One end of the duct 61 faces the upper surfaces of the sheets M stacked on the paper discharge tray 50, upstream of the paper discharge tray 50 in the transport direction. The other end of the duct 61 is open to the outside of the image forming apparatus 1. The opening of the duct 61 facing the upper surfaces of the sheets M stacked on the paper discharge tray 50 is set to be sufficiently larger than the thickness of the sheets M in the vertical direction and larger than the maximum width of the sheets M in the width direction of the sheets M.

[0039] The fan 62 generates an air flow toward the upstream side in the transport direction inside the duct 61. That is, the air discharge unit 60 sucks the residual air 70 on the upper surface of the sheets M stacked on the paper discharge tray 50 toward the upstream side in the transport direction. The fan 62 is configured to be able to change (increase or decrease) at least one of the flow path and the flow rate of the generated air flow. Note that the means for generating the air flow toward the upstream side in the transport direction is not limited to the fan 62, and well-known means such as a blower can be used.

[0040] 6 is a diagram showing the hardware configuration of image forming apparatus 1. Image forming apparatus 1 includes a CPU (Central Processing Unit) 101 as a control unit, a RAM (Random Access Memory) 102 as a storage unit, a ROM (Read Only Memory) 103 as a storage unit, a HDD (Hard Disk Drive) 104 as a storage unit, and an I / F 105 as an interface, all of which are connected via a common bus 109 as a communication unit. The CPU 101, RAM 102, ROM 103, and HDD 104 are examples of a controller 100.

[0041] The CPU 101 is a computing unit that controls the overall operation of the image forming apparatus 1. The RAM 102 is a volatile storage medium that can read and write information at high speed, and is used as a work area when the CPU 101 processes information. The ROM 103 is a read-only nonvolatile storage medium that stores programs such as firmware. The HDD 104 is a nonvolatile storage medium that can read and write information and has a large storage capacity, and stores an OS (Operating System), various control programs, application programs, etc.

[0042] Image forming apparatus 1 processes a control program stored in ROM 103, an information processing program (application program) loaded into RAM 102 from a storage medium such as HDD 104, and the like using the arithmetic functions of CPU 101. This processing constitutes a software control unit including various functional modules of image forming apparatus 1. The combination of the software control unit thus constituted and the hardware resources installed in image forming apparatus 1 constitutes a functional block that realizes the functions of image forming apparatus 1.

[0043] The I / F 105 is an interface that connects the conveying unit 20, the image forming unit 30, the leading edge guide unit 40, the lifting mechanism 51, and the air exhaust unit 60 to the common bus 109. That is, the controller 100 controls the operations of the conveying unit 20, the image forming unit 30, the leading edge guide unit 40, the lifting mechanism 51, and the air exhaust unit 60 through the I / F 105.

[0044] 7 is a flowchart of the air volume determination process. The air volume determination process is a process for determining the volume of air discharged by the air discharge unit 60 (the flow rate of air generated by the fan 62 per unit time). The controller 100 executes the air volume determination process shown in FIG. 7 in response to, for example, receiving an image formation instruction for forming images successively on a plurality of sheets M.

[0045] The image formation instruction includes, for example, image data indicating an image to be formed on a sheet M, the number of sheets M (number of copies) on which the image is to be formed, and the size S of the sheets M on which the image is to be formed (in other words, the size S of the sheets M contained in the paper feed tray 10). The size S of the sheet M refers to the area of ​​the surface on which the image of the sheet M is recorded (e.g., A4, B5, etc.). The controller 100 may receive the image formation instruction from a user via an operation panel, or may receive the image formation instruction from an external device via a communication interface.

[0046] First, the controller 100 compares the size S of the sheet M included in the image formation instruction with a predetermined first threshold value Th1 and a predetermined second threshold value Th2 (S701, S702). The second threshold value Th2 is set to a value greater than the first threshold value Th1. However, the number of threshold values ​​compared with the size S in the air volume determination process is not limited to two. The controller 100 then increases the air volume of the air discharge unit 60 as the size S of the sheet M increases (S703 to S705). Note that the numerical values ​​shown in steps S703 to S705 indicate the percentage of the air volume when the maximum air volume that can be generated by the fan 62 is 100%. However, the numerical values ​​in steps S703 to S705 are merely examples and are not limited to these.

[0047] More specifically, if the size S of the sheet M is less than the first threshold value Th1 (S701: Yes), the controller 100 determines the air volume of the air discharge unit 60 to be 20% (S703). Furthermore, if the size S of the sheet M is equal to or greater than the first threshold value Th1 and less than the second threshold value Th2 (S701: No & S702: Yes), the controller 100 determines the air volume of the air discharge unit 60 to be 50% (S704). Furthermore, if the size S of the sheet M is equal to or greater than the second threshold value Th2 (S701: No & S702: No), the controller 100 determines the air volume of the air discharge unit 60 to be 80% (S705).

[0048] Next, the controller 100 drives the air discharge unit 60 (more specifically, the fan 62) at the air volume determined in steps S703 to S705 (S706). Then, after the driving of the fan 62 has stabilized, the controller 100 starts the process of forming an image on the sheet M in accordance with the image formation instruction (S707). More specifically, the controller 100 causes the conveying unit 20 to convey the multiple sheets M in order, causes the image forming unit 30 to form an image on the sheet M conveyed by the conveying unit 20, and operates the leading edge guide unit 40 in accordance with the timing of the conveyance of the sheet M by the roller pair 27.

[0049] 8 is a flowchart of the tray lifting / lowering process. The tray lifting / lowering process is a process for lifting / lowering the discharge tray 50 so that the topmost sheet M supported on the discharge tray 50 faces the air discharge section 60 while images are being continuously formed on multiple sheets M by the image forming apparatus 1. The controller 100 executes the tray lifting / lowering process, for example, every time a predetermined time has elapsed (or a predetermined number of sheets M have been stacked on the discharge tray 50) while images are being continuously formed on multiple sheets M by the image forming apparatus 1.

[0050] First, the controller 100 determines whether the sheet M has been detected by the upper surface detection sensor 55 (in other words, whether a detection signal has been output from the upper surface detection sensor 55) (S801). Then, when the controller 100 determines that the sheet M has been detected by the upper surface detection sensor 55 (S801: Yes), the controller 100 drives the lifting mechanism 51 to lower the paper discharge tray 50 by a predetermined amount (S802).

[0051] As a result, the top surface of the top sheet M stacked on the paper discharge tray 50 faces the air discharge unit 60. Note that, for example, in step S802, the controller 100 may lower the paper discharge tray 50 by a predetermined fixed value (for example, 5 mm), or may lower the paper discharge tray 50 until the output of the detection signal from the upper surface detection sensor 55 stops.

[0052] Next, the controller 100 determines whether the fullness detection sensor 56 has detected that the paper discharge tray 50 is full (in other words, whether a detection signal has been output from the fullness detection sensor 56) (S803). If the controller 100 determines that the paper discharge tray 50 is full (S803: Yes), the controller 100 suspends image formation by the image forming apparatus 1 (S804). That is, the controller 100 stops the operations of the conveying unit 20, the image forming unit 30, and the leading edge guiding unit 40. Furthermore, the controller 100 notifies the user, via an operation panel or the like, that the sheets M stacked on the paper discharge tray 50 should be removed. Then, in response to the removal of the sheets M from the paper discharge tray 50, the controller 100 resumes image formation by the image forming apparatus 1.

[0053] On the other hand, if the upper surface detection sensor 55 does not detect the sheet M (S801: No), the controller 100 ends the tray lifting / lowering process without executing the processes in steps S802 and onward. Also, if the controller 100 determines that the paper discharge tray 50 is not full (S803: No), the controller 100 ends the tray lifting / lowering process without executing the process in step S804. Then, by repeatedly executing the tray lifting / lowering process, images are formed successively on the multiple sheets M with the upper surface of the topmost sheet M stacked on the paper discharge tray 50 facing the air discharge section 60.

[0054] According to the above embodiment, for example, the following advantageous effects are achieved.

[0055] According to the above embodiment, the residual air 70 between the top sheet M stacked on the discharge tray 50 and the new sheet M freely falling toward the discharge tray 50 is removed, thereby reducing the resistance to the free fall of the sheet M. As a result, even if the conveying speed of the sheet M by the roller pair 27 is increased (in other words, even if the interval between the sheets M passing through the roller pair 27 is shortened), it is possible to prevent the sheets from contacting each other. In other words, the throughput of the image forming apparatus 1 is improved.

[0056] Note that the leading edge guide section 40 according to the above embodiment does not clamp the leading edge of the sheet M. Also, in the above embodiment, the leading edge of the sheet M separates from the guide members 44, 45 before the trailing edge of the sheet M passes through the roller pair 27. As a result, as shown in FIG. 2, the trailing edge of the freely falling sheet M is positioned higher than the leading edge. Therefore, it is desirable that the air discharge section 60 according to the above embodiment discharges the residual air 70 upstream in the conveyance direction in order to increase the falling speed of the trailing edge of the sheet M.

[0057] Furthermore, according to the above embodiment, the tray lifting / lowering process controls the vertical position of the paper discharge tray 50 so that the top sheet M stacked on the paper discharge tray 50 faces the duct 61. This makes it possible to always discharge the residual air 70 from an appropriate position when images are continuously formed on multiple sheets M. Note that, although the above embodiment describes an example in which the paper discharge tray 50 is lifted / lowered, the air discharge unit 60 may also be lifted / lowered. In other words, the air discharge unit 60 may be configured to be liftable / lowerable in the vertical direction so that the duct 61 faces the top surface of the top sheet M stacked on the paper discharge tray 50.

[0058] Furthermore, according to the above embodiment, the air volume is adjusted according to the size S of the sheet M, so that the falling speed of the sheet M can be appropriately controlled. Note that the controller 100 may adjust the air velocity (the flow velocity of the air generated by the fan 62) instead of the air volume, or may adjust both the air volume and the air velocity. That is, the controller 100 may increase at least one of the flow velocity and the flow rate of the air generated by the fan 62 as the size of the sheet M transported by the roller pair 27 increases.

[0059] The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the technical gist thereof. The present invention covers all technical matters included in the technical ideas described in the claims. The above-described embodiments are preferred examples, but a person skilled in the art can realize various modifications from the disclosed content. Such modifications are also included in the technical scope described in the claims. [Explanation of symbols]

[0060] 1: Image forming device 10: Paper feed tray 20: Transport unit 21: Paper feed roller 22, 23, 24, 25, 26, 27: Laura vs. 30: Image forming unit 40:Tip guide part 41: Drive roller 42: Driven roller 43: Endless circular belt 44, 45: Guide member 44a, 45a: Opening 44b,45b: Middle part 44c, 45c: Back 50: Paper output tray 51: Lifting mechanism 52a, 52b: Pulley 53a, 53b: Chain 54a, 54b: Weight 55: Top detection sensor 56: Full detection sensor 60: Air exhaust section 61: Duct 62: Fan 70: Residual air 100: Controller 101: CPU 102: RAM 103:ROM 104: HDD 105: Interface 109: Common bus [Prior art documents] [Patent documents]

[0061] [Patent Document 1] Japanese Patent Application Publication No. 2019-182655

Claims

1. A tray that can hold multiple sheets, a conveying section disposed above the tray and configured to convey the sheet in a conveying direction; a leading edge guide unit that is disposed above the tray and downstream of the conveying unit in the conveying direction, and that guides the sheet to the tray by storing an end portion of the sheet conveyed by the conveying unit on the downstream side in the conveying direction at a storing position and releasing the end portion at a releasing position downstream of the storing position in the conveying direction; an air discharge unit having an opening for discharging air from an upper surface of the sheets stacked on the tray to an upstream side in the conveying direction, A sheet stacking device characterized in that the opening is positioned facing the upper surface of the sheets stacked on the tray, is larger than the thickness of the sheets in the vertical direction, and is larger than the maximum width of the sheets in the width direction of the sheets perpendicular to the conveying direction.

2. The air exhaust section a duct having the opening at a position upstream of the tray in the conveying direction and facing an upper surface of the sheets stacked on the tray; 2. The sheet stacking device according to claim 1, further comprising a fan or blower that generates an air flow in the duct toward the upstream side in the conveying direction.

3. 3. The sheet stacking device according to claim 2, wherein the air discharge section is configured to be movable up and down so that the duct faces the upper surface of the sheets stacked on the tray.

4. 4. The sheet stacking device according to claim 2, wherein the air discharge section is configured to be able to change at least one of the flow velocity and the flow rate of the air generated by the fan or the blower.

5. 5. The sheet stacking device according to claim 4, further comprising a controller that increases at least one of the flow velocity and the flow rate of the air generated by the fan or the blower as the size of the sheet transported by the transport unit increases.

6. 3. The sheet stacking device according to claim 2, further comprising a lifting mechanism that lifts the tray up and down so that the upper surfaces of the sheets stacked on the tray face the duct.

7. an image forming unit that forms an image on a sheet; 7. An image forming apparatus comprising: a sheet stacking device according to claim 1, which stacks, on the tray, sheets on which images have been formed by the image forming section.

Images