SHEET FEEDING DEVICE AND IMAGE FORMING APPARATUS

Abstract

To reduce an occurrence of a sheet feeding defect in a device that causes floatation of a sheet and feeds the sheet using air.SOLUTION: A sheet feeding device includes a tray that supports a sheet and is movable up and down, and a lifting unit that moves the tray up and down. Further, the sheet feeding device includes: an air blowing unit that blows air to a side edge of the sheet supported by the tray to cause flotation of the sheet; a suction conveyance unit that can execute a feeding operation that suctions and feeds the floated sheet; and a top surface detection unit that detects a downward state where a top surface of the sheet is below a detection position. Then, the lifting unit can execute a mode in which the tray is raised for a second time period that is longer than a first time period during which the downward state is detected.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a sheet feeding device that feeds sheets, an image forming system, and an image forming apparatus. [Background technology]

[0002] For example, image forming apparatuses and image forming systems such as printers and copiers are equipped with sheet feeding devices such as feeding cassettes and feeding decks that feed sheets to an image forming section that forms an image on the sheets. One such sheet feeding device has been proposed that blows air onto a stack of sheets supported on a tray to lift up multiple sheets above, and then adsorbs only one sheet onto an adsorption conveying belt arranged above, and conveys that sheet (see Patent Document 1).

[0003] The sheet feeding device of Patent Document 1 is equipped with a first sheet surface sensor disposed above the tray that detects the top surface of the uppermost sheet, and a second sheet surface sensor disposed upstream in the sheet feeding direction that detects the top surface of the trailing edge of the uppermost sheet. When the top surface of the uppermost sheet in the tray falls below a reference position as a result of feeding the sheet, and the first sheet surface sensor and the second sheet surface sensor detect this, the tray is raised until it reaches the reference position based on the detection of these sensors. This controls the height of the top surface of the sheet to be within an appropriate range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-195588 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the sheet is a low-rigidity sheet such as plain paper, when the sheet is floated by air, the trailing edge of the sheet, which is upstream in the sheet feeding direction, will sag downward. The second sheet surface sensor is set to a reference position taking into account this sagging trailing edge of the sheet. This controls the height of the top surface of the sheet to be within an appropriate range.

[0006] However, if the sheet is a stiff sheet such as cardboard, the trailing edge of the lifted sheet is less likely to droop. This shortens the time during which the second sheet surface sensor detects that the trailing edge of the sheet is below the reference position, which causes the tray to not rise enough and reduces the number of lifted sheets, resulting in poor sheet feeding.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sheet feeding device, an image forming system, and an image forming apparatus that are capable of reducing the occurrence of sheet feeding failures. [Means for solving the problem]

[0008] One aspect of the present invention is a sheet feeding device comprising: a tray that can be raised and lowered to support a sheet; a lifting section that raises and lowers the tray; an air blowing section that blows air against the side edges of the sheet supported on the tray to lift the sheet; an adsorption transport section that can perform a feeding operation to adsorb and feed the lifted sheet; and an upper surface detection section that detects a downward state in which the upper surface of the sheet is below a detection position, and is characterized in that the lifting section can execute a mode in which the tray is raised for a second time that is longer than the first time during which the downward state is detected.

[0009] One aspect of the present invention is a sheet feeding device comprising: a tray that can be raised and lowered to support a sheet; a lifting section that raises and lowers the tray; an air blowing section that blows air against the side edges of the sheet supported on the tray to lift the sheet; an adsorption transport section that can perform a feeding operation to adsorb and feed the lifted sheet; and an upper surface detection section that outputs a signal when the upper surface of the lifted sheet is below a detection position, and is capable of executing a mode in which the lifting section starts lifting the tray in response to the output of the signal, and stops lifting the tray in response to the elapse of a set time that is set in accordance with the thickness of the sheet. [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce the occurrence of sheet feeding failures. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating an image forming system according to an embodiment of the present invention. [Figure 2] 3A and 3B are schematic diagrams illustrating the configuration of each sheet storage unit of the feeding deck and its surroundings according to the present embodiment. [Figure 3] FIG. 2 is a block diagram showing a control system for controlling a feeding deck according to the embodiment. [Figure 4] 1A is a schematic diagram illustrating the floating operation of a sheet on the feeding deck, and FIG. 1B is a schematic diagram illustrating the adsorption operation of a sheet to an adsorption conveying belt on the feeding deck. [Figure 5] 4 is a cross-sectional view showing the configuration of a sheet surface sensor and a trailing end sheet surface sensor according to the embodiment; FIG. [Figure 6] 10 is a flowchart showing a first lift control of the lift-up tray when a sheet with high rigidity is fed according to the present embodiment. [Figure 7] 10 is a flowchart showing a second lift control of the lift-up tray when a sheet with low rigidity is fed according to the present embodiment. [Figure 8](a) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in a state where lifting is permitted in the first lifting control, and lifting of the lift-up tray is completed while the lifting is permitted. (b) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in a state where lifting is permitted in the first lifting control, and lifting is prohibited while the lift-up tray is being lifted. (c) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in a state where lifting is prohibited in the first lifting control, and lifting of the lift-up tray is started after the lifting is permitted. (d) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in a state where lifting is permitted in the first lifting control, and lifting is prohibited after the lifting tray is interrupted and lifting is permitted, and lifting of the lift-up tray is started [Figure 9] (a) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-permitted state in the second lift control and turns OFF while the lift is permitted. (b) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-prohibited state in the second lift control and the lift-up tray is lifted after the lift-up is permitted. (c) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-permitted state in the second lift control and the lift-up tray is lifted after the lift-up is permitted after the lift-up is interrupted. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings.

[0013] <Overall configuration of image forming system> First, a schematic configuration of an image forming system 300 including a feed deck 200 as a sheet feeding device according to this embodiment will be described. FIG. 1 is a schematic configuration diagram of the image forming system. As shown in FIG. 1, the image forming system 300 includes a printer 100 as an image forming device that forms an image on a sheet, and a feed deck 200 as a sheet feeding device that supplies sheets to the printer 100. Note that various sheets can be used as recording media, including paper such as paper and envelopes, glossy paper, plastic films such as sheets for overhead projectors, and cloth.

[0014] [Configuration of image forming device] As shown in FIG. 1, printer 100 has a control unit 9 that controls the overall operation of printer 100 based on image information input from an external PC or image information read from a document. A device body 100A of printer 1 accommodates a feed cassette 51 that stores sheets S, and an image forming engine 513 that forms images on sheets S fed from the feed cassette 51. Image forming engine 513, which is an example of an image forming unit, includes four image forming process units PY, PM, PC, and PK that form yellow, magenta, cyan, and black toner images, respectively, and an intermediate transfer belt 506. Image forming engine 513 forms images on sheets S using a tandem intermediate transfer method. Image forming process units PY to PK are electrophotographic units that include photosensitive drums 1Y, 1M, 1C, and 1K, respectively, which are photosensitive bodies.

[0015] The image forming process units PY to PK share a common configuration except for the different colors of toner used for development. Here, the configuration of the image forming engine 513 and the toner image formation process will be described using the yellow image forming process unit PY as an example. In addition to the photosensitive drum 1Y, the image forming process unit PY also includes an exposure device 511, a development device 510, and a drum cleaner 509. The photosensitive drum 1Y is a drum-shaped photosensitive body having a photosensitive layer on its outer periphery, and rotates in a direction (arrow A in FIG. 1 ) that is parallel to the rotation direction of the intermediate transfer belt 506 (arrow B in FIG. 1 ). The surface of the photosensitive drum 1Y is charged by receiving electrical charge from a charging unit such as a charging roller. The exposure device 511 irradiates the photosensitive drum 1Y with laser light modulated according to image information, and scans the photosensitive drum 1Y using an optical system including a reflection device 512, thereby drawing an electrostatic latent image on the surface of the photosensitive drum 1Y. The developing device 510 contains a developer containing toner, and supplies the toner to the photosensitive drum 1Y to visualize the electrostatic latent image as a toner image. The toner image formed on the photosensitive drum 1Y is primarily transferred to the intermediate transfer belt 506 at a primary transfer portion, which is a nip portion between the primary transfer roller 507 and the intermediate transfer belt 506. Residual toner remaining on the photosensitive drum 1Y after transfer is removed by a drum cleaner 509.

[0016] Intermediate transfer belt 506 is wound around drive roller 504, driven roller 505, inner secondary transfer roller 503, and primary transfer roller 507, and is driven to rotate in the clockwise direction (arrow B) in FIG. 1 by drive roller 504. The image formation process described above is carried out in parallel in each image forming process unit PY to PK, and four color toner images are transferred in a superimposed manner to form a full-color toner image on intermediate transfer belt 506. This toner image is transported to secondary transfer unit 100C while still supported by intermediate transfer belt 506. Secondary transfer unit 100C is configured as a nip between secondary transfer roller 56 and inner secondary transfer roller 503, which serve as transfer means. A bias voltage of a polarity opposite to the charge polarity of the toner is applied to secondary transfer roller 56, thereby secondarily transferring the toner image to sheet S. Residual toner remaining on intermediate transfer belt 506 after transfer is removed by belt cleaner 508.

[0017] The sheet S onto which the toner image has been transferred is delivered to a fixing unit 58 by a pre-fixing conveyance section 57. The fixing unit 58 has a pair of fixing rollers that sandwich and convey the sheet S, and a heat source such as a halogen heater, and applies pressure and heat to the toner image carried on the sheet S. This melts and fixes the toner particles to the sheet S.

[0018] Next, a sheet transport process for transporting a sheet will be described. A sheet transport system 100D as a sheet transport device in this embodiment transports a sheet S fed from a sheet feeding unit 100B as a sheet feeding device or a feed deck 200 (described later), and discharges the sheet S on which an image has been formed to the outside of the apparatus main body 100A. The sheet transport system 100D includes a sheet transport section 54, a sheet detection and transport section 50, a skew correction section 55, a pre-fixing transport section 57, a branch transport section 59, a reversing transport section 550, a retraction section 501, and a duplex transport section 502.

[0019] A feed cassette 51 provided in the sheet feeding unit 100B is removably attached to the apparatus main body 100A, and stores sheets S stacked and supported on a liftable tray 52 that can be raised and lowered. The sheets S are fed one by one by a sheet feeding section 53. Examples of the sheet feeding section 53 include a belt type in which a suction fan attracts and conveys the sheet S to a belt member, and a friction separation type using rollers or pads. The sheet S fed from the sheet feeding section 53 is conveyed along a feed path 54a by a pair of conveying rollers in a sheet conveying section 54, and after the sheet is detected by a sheet detection sensor 5 in a sheet detecting and conveying section 50, the sheet is delivered to a skew correction section 55. Note that a sheet S fed from a feed deck 200, which will be described in detail later, is conveyed along a feed path 54c, and then similarly, after the sheet is detected by a sheet detection sensor 5 in a sheet detecting and conveying section 50, the sheet is delivered to a skew correction section 55.

[0020] The sheet S handed over to the skew correction unit 55 is subjected to skew correction and timing correction, and then conveyed toward the secondary transfer unit 100C. At this time, the registration roller pair 7 of the skew correction unit 55 sends the sheet S to the secondary transfer unit 100C at a timing that matches the progress of the image formation process by the image forming process units PY to PK, based on the timing of sheet detection by the sheet detection sensor 5. The sheet S, on which the toner image has been transferred in the secondary transfer unit 100C and the image has been fixed by the fixing unit 58, is conveyed to a branch conveyance unit 59 that branches off from the conveyance path of the sheet S. When the image formation on the sheet S has been completed, the sheet S is discharged by a discharge roller pair to a discharge tray 500 arranged outside the apparatus main body 100A.

[0021] On the other hand, when an image is formed on the back side of the sheet S, the sheet S is delivered to the duplex conveying unit 502 via the reversing conveying unit 550. The reversing conveying unit 550 has a pair of reversing rollers that can rotate forward and backward, and reverses the sheet by a switchback method that reverses the front and back sides of the sheet S. That is, the reversing conveying unit 550 retracts the leading edge of the sheet to the retracting unit 501, then reverses the conveying direction to reverse the front and back sides of the sheet, and delivers the sheet to the duplex conveying unit 502. The duplex conveying unit 502 again conveys the sheet S via the feeding path 54b of the sheet conveying unit 54 toward the sheet detection and conveying unit 50 and the skew correction unit 55. Then, after an image is formed on the back side of the sheet S, the sheet S is discharged to the discharge tray 500.

[0022] [Feed deck configuration] Next, the configuration of a feed deck 200 as a sheet feeding device will be described with reference to Figures 1 and 2. Figure 2 is a schematic diagram showing the configuration of each sheet storage section of the feed deck and its surroundings according to this embodiment. As shown in Figure 1, the feed deck 200 has three sheet storage sections 11 provided inside the device main body 200A, and in each sheet storage section 11, sheets are stacked and supported on a lift-up tray 12.

[0023] 2, each sheet storage unit 11 is provided with a liftable tray 12, a trailing edge regulating plate 13, a leading edge regulating plate 17, and a side edge regulating plate 14. The leading edge regulating plate 17 abuts against the leading edge of the sheet S stacked on the liftable tray 12, which is the downstream edge in the sheet feeding direction, to regulate its position. The trailing edge regulating plate 13 is arranged to be movable in the sheet feeding direction, and while sandwiching the sheet S stacked on the liftable tray 12 between itself and the leading edge regulating plate 17, abuts against the trailing edge of the sheet S, which is the upstream edge in the sheet feeding direction, to regulate its position. Meanwhile, the side edge regulating plate 14 is arranged to be movable in the width direction perpendicular to the sheet feeding direction, and abuts against the widthwise edge of the sheet S to regulate its position. In other words, the positions of the trailing edge regulating plate 13 and the side edge regulating plate 14 can be arbitrarily changed depending on the size of the sheets to be stored. Further, the rear end regulating plate 13 is provided with a rear end upper surface regulating portion 18 that is movable up and down to regulate the height position of the rear end, which is the upstream end in the sheet feeding direction, of the uppermost sheet Sa.

[0024] This sheet storage section 11 can be pulled out from the device main body 200A by slide rails 15, and when the sheet storage section 11 is pulled out from the device main body 200A, the lifting tray 12 descends to a predetermined position, allowing sheets to be replenished or replaced, etc. The lifting tray 12 is raised and lowered by a lifter mechanism (not shown) that includes a lifter motor 12M (see FIG. 3) as a lifting section such as a stepping motor or a DC servo motor.

[0025] An air-feeding sheet feeding section (hereinafter referred to as air feeding section 150) for separating and feeding sheets one by one is disposed above sheet storage section 11. Air feeding section 150 includes a suction conveying section 20 for suction-conveying sheets S stacked on lift-up tray 12, and an air blowing section 30 for lifting up the upper portions of multiple sheets S on lift-up tray 12, separating the sheets S one by one.

[0026] The suction conveying section 20 includes an suction conveying belt 21 that is stretched over a belt drive roller 22 and that attracts and feeds the sheet S to the right in the drawing, and an suction fan 27 that generates negative pressure to attract the sheet S to the suction conveying belt 21. The suction conveying section 20 also includes an suction duct 25 that is disposed inside the suction conveying belt 21 and that sucks air through suction holes (not shown) formed in the suction conveying belt 21. The suction conveying section 20 also includes an suction shutter 26 that is disposed between the suction fan 27 and the suction duct 25 and that turns on / off the suction operation of the suction conveying belt 21. This allows for the execution of a feeding operation in which the floated sheet is attracted and fed. In this embodiment, a plurality of suction conveying belts 21 are disposed at predetermined intervals in the width direction.

[0027] The air blowing unit 30 also includes a separating nozzle 33 and a separating nozzle 34 for blowing air onto the upper front sides of the stored sheets S, a separating / separating fan 31, and a separation duct 32 for sending air from the separating / separating fan 31 to the nozzles 33, 34. Some of the air sucked in by the separating / separating fan 31 in the direction of arrow c passes through the separation duct 32 and is blown in the direction of arrow a by the separating nozzle 33, causing several upper sheets of the sheets S stacked on the lift-up tray 12 to float up. Other air is blown in the direction of arrow b by the separation nozzle 34, which separates the floated sheets one by one by the separating nozzle 33. The separated uppermost sheet Sa is attracted to the suction conveying belt 21 and fed one by one by the suction conveying belt 21, and feeding from the sheet storage unit 11 begins by a pair of drawing rollers 29 consisting of a drive roller 29a and a driven roller 29b.

[0028] The sheet S that has started to be fed from the sheet storage unit 11 in this way is fed to the feeding path 24 shown in Fig. 1 and is detected by the sheet detection sensor 241 that detects the leading edge of the sheet S. The sheet S whose leading edge is detected by the sheet detection sensor 241 is temporarily stopped in the feeding path 24. Then, feeding of the sheet S is started in synchronization with the image formation timing of the printer 100, and the sheet is sent out to the feeding path 24a of the printer 100. This makes it possible to correct variations in the transport timing that occur in the air feeding unit 150.

[0029] [Seat surface sensor and rear end seat surface sensor] Next, the sheet surface sensor 41 that detects the top surface of the uppermost sheet of the sheet stack supported in the sheet storage unit 11 and the trailing end sheet surface sensor 42 that detects the top surface of the trailing end of the sheet that is upstream in the feeding direction of the uppermost sheet will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view showing the configurations of the sheet surface sensor and the trailing end sheet surface sensor according to this embodiment.

[0030] 5, a sheet surface detection mechanism 45 is disposed above the lift-up tray 12 of the sheet storage unit 11 so as to face the uppermost sheet Sa of the sheet stack. The sheet surface detection mechanism 45 has two rotating levers 46 and 47 whose tips move up and down when rotated, and an abutment plate 48 that is supported by the rotating levers 46 and 47 and abuts against the top surface of the uppermost sheet Sa. In other words, the sheet surface detection mechanism 45 constitutes a link mechanism that allows the abutment plate 48 to move up and down while maintaining the horizontal state.

[0031] The sheet surface sensor 41, which serves as an upper surface detection unit or first upper surface sensor, is configured with an optical sensor or the like that detects the presence or absence of the flag portion 46F of the rotating lever 46. That is, the sheet surface sensor 41 is turned ON (detects the downward state) when the contact plate 48 that contacts the sheet Sa is lower than the reference position as the detection position (first detection position) and the rotation angle of the rotating lever 46 exceeds the detection angle. Conversely, the sheet surface sensor 41 is turned OFF when the contact plate 48 that contacts the sheet Sa is higher than the reference position and the rotation angle of the rotating lever 46 is smaller than the detection angle. This enables the sheet surface sensor 41 to detect whether the vertical position of the floated sheet Sa is lower than the reference position. The ON and OFF signal outputs may be reversed, as long as a signal indicating whether the contact plate 48 is lower than the reference position is output.

[0032] Meanwhile, a rear end upper surface regulating portion 18 is disposed on the rear end regulating plate 13. The rear end upper surface regulating portion 18 comes into contact with the upper surface of the rear end of the uppermost sheet Sa supported on the lift-up tray 12 and regulates the lifting of the rear end of the sheet Sa. The rear end upper surface regulating portion 18 is supported along the rear end regulating plate 13 so as to come into contact with the rear end of the uppermost sheet Sa of the sheet stack supported on the lift-up tray 12 from above and to be able to move up and down integrally with the sheet Sa. This allows the rear end upper surface regulating portion 18 to follow the movement of the uppermost sheet Sa.

[0033] The trailing-end upper surface restricting portion 18 is provided with a flag portion 18F, and a trailing-end sheet surface sensor 42 serving as an upper surface detecting portion or second upper surface sensor is configured with an optical sensor or the like that detects the presence or absence of the flag portion 18F. Similarly, the trailing-end sheet surface sensor 42 is turned ON (detects the downward state) when the trailing-end upper surface restricting portion 18, which abuts against the trailing end of the sheet Sa, is lower than the reference position serving as the detection position (second detection position). Conversely, the trailing-end sheet surface sensor 42 is turned OFF when the trailing-end upper surface restricting portion 18, which abuts against the trailing end of the sheet Sa, is higher than the reference position. This enables the trailing-end sheet surface sensor 42 to detect whether the vertical position of the trailing end of the floated sheet Sa is lower than the reference position. Similarly, the ON and OFF signal outputs may be reversed, as long as a signal indicating whether the trailing-end upper surface restricting portion 18 is lower than the reference position is output.

[0034] [Control system configuration] Next, the configuration of a control system that controls the feed deck 200 will be described with reference to FIG. 3. FIG. 3 is a block diagram showing the control system that controls the feed deck according to this embodiment. In this embodiment, the control unit 9 is described as being provided in the printer 100 as shown in FIG. 1, but this is not limiting and the control unit 9 may be provided in the feed deck 200. Furthermore, the control unit 9 may be located in any device, including a case where a processing device or the like is provided downstream of the printer 100 in the sheet conveying direction. In other words, the control unit 9 may be located anywhere inside the image forming system 300 as long as it is capable of communicating with the feed deck 200.

[0035] The control unit 9 is connected to the sheet surface sensor 41 and the trailing edge sheet surface sensor 42, and receives ON / OFF signals from them. Also connected to the control unit 9 are a belt drive motor 21M that drives the suction conveyor belt 21, a lifter motor 12M that raises and lowers the lift tray 12, and a suction shutter solenoid 26SL that rotates the suction shutter 26. Also connected to the control unit 9 are a separation fan 31 that is provided in the air blowing unit 30 and blows air onto the sheets, a suction fan 27 that generates negative pressure to attract the lifted sheets to the suction conveyor belt 21, and a monitor 301, not shown in FIG. 1.

[0036] [Feeding operation] Next, the feeding operation of the feeding deck 200 controlled by the control unit 9 will be described with reference to Fig. 4. Fig. 4(a) is a schematic diagram illustrating the floating operation of the sheet on the feeding deck. Fig. 4(b) is a schematic diagram illustrating the adsorption operation of the sheet to the adsorption conveying belt on the feeding deck.

[0037] First, the user pulls out the sheet storage unit 11 and sets the sheets S (a stack of sheets), and then stores the sheet storage unit 11 inside the apparatus main body 200A. A sensor (not shown) detects that the sheet storage unit 11 has been stored. Then, the control unit 9 drives the lifter motor 12M to raise the lift tray 12. When the lift tray 12 reaches a position where the distance between the supported sheet and the suction conveyor belt 21 is a distance at which feeding is possible, the control unit 9 stops raising the lift tray 12 at this position. Then, the control unit 9 waits until a command to start feeding is generated.

[0038] Thereafter, when a command to start an image forming job is issued by operation input from an operation unit (not shown) provided on the monitor 301 (see FIG. 3) or a signal from an external computer, a sheet feeding signal is generated, and in response, the control unit 9 starts the sheet feeding operation. Then, as shown in FIG. 4(a), the control unit 9 activates the separation fan 31 to suck air in the direction of arrow c. The air is then blown out of the separation nozzle 33 and the separation nozzle 34 via the separation duct 32 and onto the sheets as shown by the arrows a and b. This causes the top several sheets S of the stack of multiple sheets to float. The control unit 9 also activates the suction fan 27 to blow air in the direction F in the figure. At this time, the suction shutter 26 is still closed.

[0039] Next, when a predetermined time has elapsed since the start of the sheet feeding operation (since the sheet feeding signal is received), the floating of the uppermost sheet in the sheet stack stabilizes. At this timing, the control unit 9 drives the suction shutter solenoid 26SL (see FIG. 3) to rotate the suction shutter 26 in the direction of arrow G, as shown in FIG. 4(b). As a result, air is sucked in the direction of arrow H from suction holes provided in the suction conveyor belt 21, generating a suction force for the sheets. Then, while only the uppermost sheet Sa is separated by separation air from the separation nozzle 34, this suction force causes the uppermost sheet Sa to be sucked to the suction conveyor belt 21.

[0040] Then, the control unit 9 drives the belt drive motor 21M (see FIG. 3) to rotate the belt drive roller 22 in the direction of the arrow J. As a result, the uppermost sheet Sa is fed in the direction of the arrow K while being attracted to the attraction conveying belt 21. The sheet Sa is fed to the feeding path 24 (see FIG. 1) by the pair of pull-out rollers 29, which is composed of a drive roller 29a driven in the direction of the arrow L and a driven roller 29b driven in the direction of the arrow M, and then fed to the image forming engine 513.

[0041] [Controlling the lifting tray] Next, the lift control of the lift-up tray 12 according to this embodiment will be described with reference to FIGS.

[0042] The lift control of the lift tray 12 according to this embodiment includes first lift control and second lift control, which can be selectively executed. The first lift control is executed when feeding a first sheet having a second stiffness, such as cardboard, which has a higher stiffness. The second lift control is executed when feeding a second sheet having a first stiffness, such as plain paper, which has a lower stiffness than the first sheet. The control unit 9 selectively executes either the first lift control or the second lift control based on the type of sheet set on an operation unit (not shown) provided on the monitor 301 or the type of sheet set by an external computer. That is, the control unit 9 selects the first lift control when the sheet set in the sheet storage unit 11 is a sheet type having a preset high stiffness, and selects the second lift control when the sheet type has a preset low stiffness.

[0043] <Second climb control (second mode)> First, the second lift control as the second mode when a sheet with low stiffness, such as plain paper, is supported on the lift tray 12 will be described with reference to Fig. 7. Fig. 7 is a flowchart showing the second lift control of the lift tray when a sheet with low stiffness is fed according to this embodiment.

[0044] As described above, when the control unit 9 starts the second lift control and starts the sheet feeding operation (receives a sheet feeding signal), it rotates the separation fan 31 to start blowing air, thereby floating the sheet. In this state, as shown in FIG. 7, it determines whether the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 are ON (S9). If these sensors are OFF (N in S9), the process proceeds directly to step S12. It then determines whether the image formation job has ended (S12). If the image formation job has not ended (N in S12) and further sheet feeding is required, the process returns to step S9. If the image formation job has ended (Y in S12), the second lift control ends.

[0045] On the other hand, if the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 turn ON (Y in S9) during the second lift control and detect that the height of the uppermost sheet Sa is lower than the reference position before the image formation job is completed (N in S12), the process proceeds to step S10. In step S10, it is determined whether the suction shutter 26 is open and the belt drive motor 21M is ON. That is, if the lift tray 12 is lifted while the suction shutter 26 is open and the suction conveyance belt 21 is driven, i.e., while the uppermost sheet Sa is being fed, the floating state of the next sheet will be disturbed. Therefore, if the suction shutter 26 is open and the belt drive motor 21M is ON (Y in S10), the lift tray 12 is prohibited from lifting, and the process proceeds to step S12 without lifting the lift tray 12. That is, the lift tray 12 is prohibited from lifting while the suction conveyance unit 20 is performing the sheet feeding operation. Similarly, if the image forming job is not completed (N in S12) and sheet feeding is required, the process returns to step S9. If the image forming job is completed (Y in S12), the second lift control is terminated.

[0046] On the other hand, if the suction shutter 26 is not open and the belt drive motor 21M is OFF (N in S10), that is, the uppermost sheet Sa is not being fed, so the lift tray 12 is permitted to be lifted, and the lift tray 12 is lifted (S11). In other words, the lift tray 12 is permitted to be lifted while the sheet feeding operation by the suction conveyance unit 20 is stopped. While the lift tray 12 is being lifted in this manner, if the position of the uppermost sheet Sa rises and the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 turn OFF (N in S9), the lift tray 12 stops lifting and proceeds to step S12. Similarly, if the image formation job is not finished (N in S12) and sheet feeding is required, the process returns to step S9. If the image formation job is finished (Y in S12), the second lift control is terminated.

[0047] Furthermore, in step S11, after the lifting of the lift-up tray 12 starts, the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 may remain ON (before they turn OFF) (Y in S9), resulting in the prohibited state (Y in S10). In this case, the process proceeds to step S12, where the lifting of the lift-up tray 12 (S11) is interrupted and stopped. This prevents the floating state of the next sheet from being disturbed. If the image formation job is not yet completed (N in S12) and sheet feeding is required, the process returns to step S9. Thereafter, if the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 remain ON (Y in S9) and the permitted state is reached (N in S10), the lifting of the lift-up tray 12 is resumed. In other words, if the prohibited state is reached, the lifting of the lift-up tray 12 is interrupted and put on hold, and the suspended lifting of the lift-up tray 12 is resumed once the permitted state is reached. Then, when the position of the top sheet Sa rises and the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 turn OFF (N in S9), the lifting of the lifting tray 12 ends and the process proceeds to step S12. Similarly, if the image forming job is not finished (N in S12) and further sheet feeding is required, the process returns to step S9. Also, if the image forming job is finished (Y in S12), the second lifting control ends.

[0048] <Example of operation using the second climb control (second mode)> Next, an example of operation by the second lift control will be described with reference to Fig. 9. Fig. 9(a) is a time chart showing a case where the trailing edge sheet surface sensor is turned ON when lift is permitted in the second lift control, and the trailing edge sheet surface sensor is turned OFF while the lift is permitted. Fig. 9(b) is a time chart showing a case where the trailing edge sheet surface sensor is turned ON when lift is prohibited in the second lift control, and the lift tray is lifted after the lift is permitted. Fig. 9(c) is a time chart showing a case where the trailing edge sheet surface sensor is turned ON when lift is permitted in the second lift control, and the lift tray is lifted after the lift is permitted after the lift is interrupted.

[0049] In the explanation of this operation example, since the trailing end sheet surface sensor 42 turns ON before the sheet surface sensor 41 in most cases due to the trailing end of the sheet drooping when the sheet floats, only the ON / OFF of the trailing end sheet surface sensor 42 will be explained. Also, as described above, when the suction shutter 26 is open and the belt drive motor 21M is ON, this is a lift-prohibited state that prohibits the lifting tray 12 from rising, and this is simply referred to as the "prohibited state." Conversely, when the suction shutter 26 is closed and the belt drive motor 21M is OFF, this is a lift-permitted state that permits the lifting tray 12 to rise, and this is simply referred to as the "permitted state."

[0050] 9(a), when the trailing edge sheet surface sensor 42 is turned ON (see Y in S9), if the lifting tray 12 is permitted (see N in S10), the lifter motor 12M is immediately turned ON (driven) to start lifting the liftable tray 12 (see S11). Then, while the lifting tray 12 is permitted, if the trailing edge sheet surface sensor 42 is turned ON and the detection time T3 has elapsed since the trailing edge sheet surface sensor 42 was turned ON, the lifter motor 12M is turned OFF to stop lifting the liftable tray 12.

[0051] In this case, for a sheet with low stiffness, such as plain paper, the trailing edge of the lifted sheet hangs down. Then, after the trailing edge of the sheet is lower than the reference position and the trailing edge sheet surface sensor 42 turns ON, the trailing edge sheet surface sensor 42 turns OFF when the lift tray 12 is raised by, for example, about 0.09 mm, which is the thickness of one sheet of plain paper. Therefore, at the lifting speed of the lift tray 12 in this embodiment, the detection time T3 is, for example, about 15 ms.

[0052] 9(b), if the trailing edge sheet surface sensor 42 is turned ON (see Y in S9), and if the state is prohibited (see Y in S10), the system waits until the state becomes permitted (see N in S12 and Y in S9), i.e., the lifting of the liftable tray 12 is suspended. After that, when the state changes from prohibited to permitted (see N in S10), the lifter motor 12M is turned ON (driven) to start lifting the liftable tray 12 (see S11). Then, when the state becomes permitted and the trailing edge sheet surface sensor 42 is turned ON and the detection time T3 has elapsed since the trailing edge sheet surface sensor 42 was turned OFF (see N in S9), the lifter motor 12M is turned OFF, and the lifting of the liftable tray 12 is stopped.

[0053] 9(c), when the trailing edge sheet surface sensor 42 is turned ON (see Y in S9), if the tray is in the permitted state (see N in S10), the lifter motor 12M is immediately turned ON (driven) to start lifting the liftable tray 12 (see S11). If the tray changes from the permitted state to the prohibited state after the detection time T3' while the tray 12 is being lifted, the lifter motor 12 waits until the tray changes to the permitted state (see N in S12 and Y in S9), that is, the lifting of the tray 12 is suspended and put on hold. After that, when the tray changes from the prohibited state to the permitted state (see N in S10), the lifter motor 12M is turned ON (driven) to resume lifting the tray 12 (see S11). Then, when the tray is in the permitted state and the trailing edge sheet surface sensor 42 is turned ON, the lifter motor 12M is turned OFF after the detection time T3' has elapsed (see N in S9), and the lifter motor 12M is turned OFF to stop lifting the tray 12.

[0054] Here, the total of detection time T3' and detection time T3" is the same as detection time T3, for example, for one sheet of plain paper. However, in the prohibited state, the topmost sheet Sa is fed, so there is one less sheet than when the trailing end sheet surface sensor 42 is turned ON in the permitted state. In other words, the top surface position of the trailing end of the sheet detected by the trailing end sheet surface sensor 42 is lower, for example, by the amount of two sheets of plain paper. Therefore, the total detection time of detection time T3' and detection time T3" is, for example, the amount of two sheets of plain paper, and is twice the detection time T3 (for example, about 30 ms).

[0055] As described above, in the second lift control (second mode), the lift tray 12 starts to rise when the trailing end sheet surface sensor 42 is ON in the permitted state, and stops to rise when the trailing end sheet surface sensor 42 is OFF in the permitted state. Also, in the prohibited state, the lift tray 12 stops or is interrupted to rise. When a sheet with low rigidity that causes the trailing end of the sheet to droop is set on the lift tray 12, the trailing end sheet surface sensor 42 is turned ON / OFF according to the thickness of the sheet, so that the lift tray 12 can be lifted with good precision.

[0056] <First climb control (first mode)> Next, the first lift control as the first mode when a stiff sheet such as cardboard is supported on the lift tray 12 will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the first lift control of the lift tray when feeding a stiff sheet according to this embodiment. Note that the cardboard used in this embodiment has a basis weight of 350 gsm or more and a thickness of about 0.35 to 0.5 mm, which is about 4 to 5.5 times the thickness of the plain paper, but is not limited to such cardboard.

[0057] As described above, when the control unit 9 starts the first lift control and starts the sheet feeding operation (receives a sheet feeding signal), it rotates the separation fan 31 to start blowing air, thereby floating the sheet. In this state, as shown in FIG. 6, it determines whether the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 are ON (S1). If these sensors are OFF (N in S1), the process proceeds directly to step S8. It then determines whether the image formation job has ended (S8). If the image formation job has not ended (N in S8) and further sheet feeding is required, the process returns to step S1. If the image formation job has ended (Y in S8), the first lift control ends.

[0058] On the other hand, if the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 are turned ON (Y in S1) before the image formation job is completed (N in S8) during the first lift control, that is, if it is detected that the height of the uppermost sheet Sa is lower than the reference position, the process proceeds to step S2. In step S2, it is determined whether the suction shutter 26 is open and the belt drive motor 21M is ON. That is, if the lift tray 12 is lifted while the suction shutter 26 is open and the suction conveyance belt 21 is driven, that is, while the uppermost sheet Sa is being fed, the floating state of the next sheet will be disturbed. Therefore, if the suction shutter 26 is open and the belt drive motor 21M is ON (Y in S2), the lift tray 12 is prohibited from lifting, and the process proceeds to step S3 without lifting the lift tray 12. That is, the prohibition state is in effect while the suction conveyance unit 20 is performing the sheet feeding operation. Similarly, if the image forming job is not completed (N in S3) and sheet feeding is required, the process returns to step S1. If the image forming job is completed (Y in S3), the first lift control is terminated.

[0059] On the other hand, if the suction shutter 26 is not open and the belt drive motor 21M is OFF (N in S2), that is, the uppermost sheet Sa is not being fed, so the state is set to the permitted state, which allows the lift tray 12 to rise, and the lift tray 12 starts to rise (S4). In other words, the permitted state is maintained while the sheet feeding operation by the suction conveyance unit 20 is stopped. Next, it is determined whether the second time T2 has elapsed since the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 turned ON (in other words, since the lift tray 12 started to rise) (S5). Until the second time T2 has elapsed (N in S5), it is determined whether the suction shutter 26 is open and the belt drive motor 21M is ON (S6), that is, whether the state is permitted or prohibited. Here, if the state is permitted (N in S6), the lift tray 12 continues to rise (S4). Then, when the second time T2 has elapsed since the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 turned ON (Y in S5), the lifting of the lift tray 12 is stopped (S7), and the process proceeds to step S8. If the image forming job has not ended (N in S8) and sheet feeding is required, the process returns to step S1. If the image forming job has ended (Y in S8), the first lifting control is terminated.

[0060] Furthermore, after the lifting of the lift-up tray 12 starts in step S4, the prohibited state may occur (Y in S6) before the second time T2 has elapsed (N in S5). In this case, the lifting of the lift-up tray 12 (S7) is interrupted and stopped. This prevents the floating state of the next sheet from being disturbed. If the image formation job is not completed (N in S8) and sheet feeding is required, the process returns to step S1. Thereafter, if the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 remain ON (Y in S1) and the permitted state is reached (N in S2), the lifting of the lift-up tray 12 is resumed (S4). In other words, if the prohibited state occurs, the lifting of the lift-up tray 12 is interrupted and put on hold, and once the permitted state is reached, the suspended lifting of the lift-up tray 12 is resumed. Then, after the second time T2 has elapsed (Y in S5), the lifting of the lift-up tray 12 is completed (S7) and the process proceeds to step S8. Similarly, if the image forming job is not completed (N in S8) and sheet feeding is required, the process returns to step S1. If the image forming job is completed (Y in S8), the first lift control is terminated.

[0061] <Example of operation using first ascent control (first mode)> Next, an example of operation by the first lift control will be described with reference to FIG. 8. FIG. 8(a) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-permitted state in the first lift control, and the lifting of the lift-up tray is completed while the lift-up state is permitted. FIG. 8(b) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-permitted state in the first lift control, and the lift-up tray is prohibited from rising while it is rising. FIG. 8(c) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-prohibited state in the first lift control, and the lift-up tray is lifted after the lift-up state is permitted. FIG. 8(d) is a time chart showing a case where the trailing edge sheet surface sensor turns ON in the lift-permitted state in the first lift control, and the lift-up tray is prohibited from rising after the lift-up tray is interrupted, and the lift-up tray is lifted after the lift-up state is permitted.

[0062] In addition, in explaining this operation example, since the trailing end sheet surface sensor 42 turns ON before the sheet surface sensor 41 in most cases due to the trailing end of the sheet drooping when the sheet floats up, only the ON / OFF of the trailing end sheet surface sensor 42 will be explained.

[0063] 8(a), when the trailing edge sheet surface sensor 42 turns ON (see Y in S1), if the state is permitted (see N in S2), the lifter motor 12M is immediately turned ON (driven) to start lifting the lift-up tray 12 (see S4). Then, while the state remains permitted, the trailing edge sheet surface sensor 42 turns OFF after a first time T1 (i.e., the detection time for thick paper) has elapsed since the trailing edge sheet surface sensor 42 turned ON, but the lifter motor 12M remains ON to continue lifting the lift-up tray 12. Then, when a second time T2 has elapsed (see Y in S5), the lifter motor 12M is turned OFF to stop lifting the lift-up tray 12 (see S7).

[0064] Here, for a sheet such as cardboard, which has a stiffness higher than that of plain paper, the trailing end of the lifted sheet is less likely to sag. Therefore, once the trailing end of the sheet is lower than the reference position and the trailing end sheet surface sensor 42 turns ON, the trailing end sheet surface sensor 42 turns OFF when the lift tray 12 is raised to a certain extent. Specifically, for example, cardboard is about 4 to 5.5 times thicker than plain paper, as described above. Therefore, if the trailing end of the sheet were to sag in the same way as plain paper, the time during which the trailing end sheet surface sensor 42 remains ON would be about 4 to 5.5 times longer, which would be the same time as the second time T2. However, because the trailing end of the sheet is less likely to sag, the trailing end sheet surface sensor 42 turns OFF immediately after the first time T1 when the lift tray 12 begins to rise. Therefore, if the lifting tray 12 is stopped from rising in response to the trailing edge sheet surface sensor 42 being turned OFF, the lifting tray 12 will not rise enough, and the number of floating sheets will decrease, resulting in poor sheet feeding.

[0065] Therefore, in this first lift control, the lift tray 12 is lifted until the second time T2 (for example, about 60 ms to 82.5 ms) has elapsed since the trailing edge sheet surface sensor 42 turned ON, that is, a lift time according to the thickness of the cardboard is secured. This ensures that the lift tray 12 is lifted an appropriate lift distance, preventing the lift tray 12 from being lifted insufficiently and reducing the occurrence of sheet feeding failures.

[0066] 8(b), when the trailing edge sheet surface sensor 42 turns ON (see Y in S1), if the state is permitted (see N in S2), the lifter motor 12M is immediately turned ON (driven) to start lifting the lift-up tray 12 (see S4). Then, while the state remains permitted, the trailing edge sheet surface sensor 42 turns OFF after a first time T1 (i.e., the detection time for thick paper) has elapsed since the trailing edge sheet surface sensor 42 turned ON, but the lifter motor 12M continues to turn ON to continue lifting the lift-up tray 12. Then, if the trailing edge sheet surface sensor 42 turns OFF and the state is prohibited before the second time T2 has elapsed (see N in S5 and Y in S6), the lifter motor 12M is turned OFF to stop lifting the lift-up tray 12 (see S7).

[0067] In this case, when the lift-up tray 12 is lifted for a time T2' that is shorter than the second time T2, the prohibition state is entered and the lift-up of the lift-up tray 12 is interrupted, but because the trailing edge sheet surface sensor 42 is OFF (see N in S1), the lift-up of the lift-up tray 12 ends. In other words, the amount of lift of the lift-up tray 12 may be slightly less than the thickness of one sheet of cardboard, but this does not pose a problem because the timing when the next trailing edge sheet surface sensor 42 turns ON should be earlier by that amount.

[0068] Next, as shown in FIG. 8(c), if the trailing edge sheet surface sensor 42 is turned ON (see Y in S1), and if the state is prohibited (see Y in S2), the system waits until the state is permitted (see N in S3 and Y in S2), i.e., the lift of the lift-up tray 12 is suspended. Thereafter, when the state changes from the prohibited state to the permitted state (see N in S2), the lifter motor 12M is turned ON (driven) to start lifting the lift-up tray 12 (see S4). Then, after the first time T1 (i.e., the detection time for thick paper) has elapsed since the state became permitted, the trailing edge sheet surface sensor 42 is turned OFF, but the lifter motor 12M is still turned ON to continue lifting the lift-up tray 12. Then, after the second time T2 has elapsed since the state became permitted and the trailing edge sheet surface sensor 42 was turned ON (see Y in S5), the lifter motor 12M is turned OFF to stop lifting the lift-up tray 12 (see S7).

[0069] As described above, if the lift tray 12 is raised while the uppermost sheet Sa is being fed in the prohibited state, the floating state of the next sheet may be disturbed. However, by waiting for the lift tray 12 to rise until the permitted state is reached, the floating state of the sheet is not disturbed and the lift tray 12 can be raised by an appropriate distance for the thickness of one sheet of cardboard.

[0070] Finally, as shown in FIG. 8(d), when the trailing edge sheet surface sensor 42 is turned ON (see Y in S1), if the state is permitted (see N in S2), the lifter motor 12M is immediately turned ON (driven) to start lifting the liftable tray 12 (see S4). During this lifting of the liftable tray 12, if the state changes from permitted to prohibited at detection time T1", that is, after lifting time T2", the lifting of the liftable tray 12 is interrupted and stopped (see S7). Then, the system waits until the state becomes permitted (see N in S8, Y in S1, Y in S2, and N in S3), that is, the lifting of the liftable tray 12 is interrupted and put on hold. Thereafter, when the state changes from prohibited to permitted (see N in S2), the lifter motor 12M is turned ON to resume lifting the liftable tray 12 (see S4). Then, after the detection time T1" has elapsed since the permitted state was established, the trailing edge sheet surface sensor 42 turns OFF, but the lifter motor 12M is still turned ON to continue lifting the liftable tray 12. Then, after the permitted state was established and the trailing edge sheet surface sensor 42 turned ON, when the second time T2 has elapsed (see Y in S5), the lifter motor 12M is turned OFF to stop lifting the liftable tray 12 (see S7).

[0071] In this case, the lift-up tray 12 is lifted at time T2'', but because the uppermost sheet Sa is fed in the prohibited state, there is one less sheet than when the trailing end sheet surface sensor 42 is turned ON in the permitted state. In other words, there is no problem even if the lift-up tray 12 is lifted by the amount of, for example, two sheets of cardboard. Also, there is a possibility that the amount of lift of the lift-up tray 12 is slightly less than the thickness of two sheets of cardboard, but this does not cause a problem because the timing when the next trailing end sheet surface sensor 42 is turned ON should be earlier by that amount.

[0072] As described above, in the first lift control (first mode), the lift tray 12 starts to rise when the trailing end sheet surface sensor 42 turns ON in the permitted state, and stops rising when the second time T2 has elapsed in the permitted state. Also, in the prohibited state, the lift tray 12 stops or is interrupted. If a highly rigid sheet whose trailing end does not easily droop is set on the lift tray 12, there is a risk that the trailing end sheet surface sensor 42 will turn ON and then immediately turn OFF, but the lift tray 12 can be lifted an appropriate distance for the thickness of, for example, cardboard.

[0073] [Possibilities for other embodiments] In the first lift control according to the present embodiment, the lift tray 12 is lifted until the second time T2 has elapsed after the sheet surface sensor 41 and the trailing end sheet surface sensor 42 are turned ON. However, the present invention is not limited to this, and the lift tray 12 may be lifted until a set time has elapsed after the sheet surface sensor 41 and the trailing end sheet surface sensor 42 are turned ON and then turned OFF.

[0074] In the present embodiment, the control unit 9 selects either the first rise control or the second rise control depending on the type of sheet. However, this is not limiting, and the rise control may be selected depending on parameters such as the thickness, basis weight, and stiffness of the sheet. Furthermore, the second time T2 in the first rise control may be configured to be changed depending on these parameters.

[0075] Furthermore, in the present embodiment, the prohibited state is established when the suction shutter 26 is open and the belt drive motor 21M is ON, and conversely, the permitted state is established when the suction shutter 26 is closed and the belt drive motor 21M is OFF. However, this is not limiting, and the prohibited state may be established when either the suction shutter 26 is open or the belt drive motor 21M is ON. Conversely, the permitted state may be established when either the suction shutter 26 is closed or the belt drive motor 21M is OFF. In other words, the conditions for establishing the prohibited state and the permitted state may be any conditions as long as the position of the floated sheet is not disturbed.

[0076] In addition, in the present embodiment, the condition for starting to lift the lift-up tray 12 is when both the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 are ON. However, because the trailing edge of the sheet is likely to droop, the condition for starting to lift the lift-up tray 12 may be only when the trailing edge sheet surface sensor 42 is ON. Furthermore, the ON and OFF states of these sensors simply detect a change in signal, and they may be OFF when they are below the reference position.

[0077] In the present embodiment, the reference positions at which the signals from the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 change are set to correspond to a sheet with low stiffness, such as plain paper. However, this is not limiting. The reference positions at which the signals from the sheet surface sensor 41 and the trailing edge sheet surface sensor 42 change may also be set to correspond to a sheet with high stiffness, such as cardboard. In this case, the trailing edge of a sheet with low stiffness, such as plain paper, sags earlier than the trailing edge of a sheet with high stiffness, such as cardboard. In other words, the timing of the change in the signal from the trailing edge sheet surface sensor 42 is earlier. Therefore, the second lift control is performed when a sheet with high stiffness, such as cardboard, is set, and the first lift control is performed when a sheet with low stiffness, such as plain paper, is set. It is conceivable to set the second time T2 shorter than the first time T1 (shorter than the detection time for plain paper, etc.). In other words, it is conceivable to start lifting the lift-up tray 12 when the trailing edge sheet surface sensor 42 outputs an ON signal and stop lifting the lift-up tray when a set time, set according to the thickness of the sheet, has elapsed.

[0078] In the present embodiment, the image forming system 300 is described as being provided with the feed deck 200 as a sheet feeding device. However, the present invention is not limited to this, and the sheet feeding device may be the sheet feeding unit 100B provided in the printer 100. The control unit 9 is not limited to being provided in the printer 100, but may be provided in the feed deck 200, or each may have its own control unit. In particular, it is sufficient that the control unit is provided in any part of the image forming system 300.

[0079] The present disclosure can also be realized by providing a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0080] [Summary of this embodiment] [Configuration 1] a tray that can be raised and lowered to support the sheet; a lifting unit that lifts and lowers the tray; an air blowing unit that blows air onto the side edges of the sheets supported on the tray to lift the sheets; a suction conveyance unit capable of performing a feeding operation of suctioning and feeding the floated sheet; an upper surface detection unit that detects a downward state in which the upper surface of the seat is lower than the detection position, A mode in which the tray is raised by the lifting unit for a second time period longer than a first time period during which the lowered state is detected can be executed. A sheet feeding device characterized by: [Configuration 2] a prohibition state in which the lifting unit prohibits the tray from being lifted, and an permission state in which the lifting unit permits the tray to be lifted, are set; When the upper surface detection unit detects the lowered state in the prohibited state during execution of the mode, the tray is raised for the second period of time after the permitted state is entered. 2. The sheet feeding device according to configuration 1, [Configuration 3] If the state is shifted from the permitted state to the prohibited state while the tray is being raised during execution of the mode, the raising of the tray is stopped. 3. The sheet feeding device according to configuration 2. [Configuration 4] the prohibited state is when the feeding operation is being performed by the suction conveyance unit, The permitted state is a state in which the feeding operation by the suction conveyance unit is stopped. 4. The sheet feeding device according to configuration 2 or 3. [Configuration 5] the mode is a first mode, a second mode in which the lifting unit lifts the tray during the first time period; 5. The sheet feeding device according to any one of configurations 1 to 4. [Configuration 6] The first mode is executed when the stiffness of the sheet supported on the tray is a second stiffness higher than the first stiffness; the second mode is executed when the stiffness of the sheet supported on the tray is the first stiffness. 6. The sheet feeding device according to configuration 5, [Configuration 7] The upper surface detection unit a first upper surface sensor disposed above the tray and configured to detect an upper surface of the floated sheet; a second upper surface sensor disposed upstream of the first upper surface sensor in the sheet feeding direction and configured to detect the upper surface of the floated sheet; When the first upper surface sensor detects that the upper surface of the floated sheet is below a first detection position and the second upper surface sensor detects that the upper surface of the floated sheet is below a second detection position, the sheet is detected as being in the lower state. 7. The sheet feeding device according to any one of configurations 1 to 6, wherein: [Configuration 8] The sheet feeding device according to any one of configurations 1 to 7, an image forming apparatus including an image forming unit that forms an image on a sheet fed from the sheet feeding device, and a control unit that controls the lifting unit and the suction conveying unit; An image forming system comprising: [Configuration 9] The sheet feeding device according to any one of configurations 1 to 7, an image forming unit that forms an image on the sheet fed from the sheet feeding device; a control unit that controls the lifting unit and the suction conveying unit, An image forming apparatus characterized by: [Configuration 10] a tray that can be raised and lowered to support the sheet; a lifting unit that lifts and lowers the tray; an air blowing unit that blows air onto the side edges of the sheets supported on the tray to lift the sheets; a suction conveyance unit capable of performing a feeding operation of suctioning and feeding the floated sheet; an upper surface detection unit that outputs a signal when the upper surface of the floated sheet is below a detection position; The lifting unit can execute a mode in which the lifting of the tray starts in response to the output of the signal, and the lifting of the tray stops in response to the lapse of a set time period set in accordance with the thickness of the sheet. A sheet feeding device characterized by: [Explanation of symbols]

[0081] 9...control unit / 12...lifting tray (tray) / 12M...lifter motor (lifting unit) / 20...suction transport unit / 30...air blowing unit / 41...sheet surface sensor (upper surface detection unit, first upper surface sensor) / 42...rear end sheet surface sensor (upper surface detection unit, second upper surface sensor) / 100...printer (image forming apparatus) / 200...feed deck (sheet feeding device) / 300...image forming system / 513...image forming engine (image forming unit) / S...sheet / T1...first time / T2...second time

Claims

1. a liftable tray for supporting the sheet; A lifting unit that lifts and lowers the tray; an air blowing unit that blows air against a side edge of the sheet supported by the tray to lift the sheet; a suction conveying unit capable of performing a feeding operation of suctioning and feeding the levitated sheet; an upper surface detection unit that detects a downward state in which the upper surface of the sheet is lower than a detection position; a control unit that controls the lifting unit and the suction transport unit, The control unit is capable of executing a mode in which the tray is lifted by the lift unit for a second time period longer than a first time period during which the lowered state is detected. A sheet feeding device comprising:

2. A prohibited state in which the lifting unit is prohibited from lifting the tray and an allowed state in which the lifting unit is allowed to lift the tray are set, When the upper surface detection unit detects the lowered state in the prohibited state during execution of the mode, the tray is raised for the second period of time after the permitted state is entered.

2. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus comprises:

3. When the state is changed from the permitted state to the prohibited state while the tray is being raised during execution of the mode, the raising of the tray is stopped.

3. The sheet feeding apparatus according to claim 2, wherein the sheet feeding apparatus comprises:

4. the prohibited state is a state in which the feeding operation is being performed by the suction transport unit, the permitted state is a state in which the feeding operation by the suction conveying unit is stopped; 3. The sheet feeding apparatus according to claim 2, wherein the sheet feeding apparatus comprises:

5. the mode is a first mode, a second mode in which the lifting unit lifts the tray during the first period of time; 2. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus comprises:

6. executing the first mode when the stiffness of the sheet supported on the tray is a second stiffness higher than the first stiffness; and executing the second mode when the stiffness of the sheet supported by the tray is the first stiffness.

6. The sheet feeding apparatus according to claim 5,

7. The upper surface detection unit is disposed upstream of the air blowing unit in a sheet feeding direction.

2. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus comprises:

8. The upper surface detection unit is a first upper surface sensor disposed above the tray and configured to detect an upper surface of the floated sheet; a second upper surface sensor disposed upstream of the first upper surface sensor in a sheet feeding direction and configured to detect an upper surface of the floated sheet; when the first upper surface sensor detects that the upper surface of the floated sheet is below a first detection position and the second upper surface sensor detects that the upper surface of the floated sheet is below a second detection position, the sheet is detected as being in the lower state.

2. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus comprises:

9. The sheet feeding device according to claim 1 ; an image forming unit that forms an image on the sheet fed from the sheet feeding device, 1. An image forming apparatus comprising:

10. a liftable tray for supporting the sheet; A lifting unit that lifts and lowers the tray; an air blowing unit that blows air against a side edge of the sheet supported by the tray to lift the sheet; a suction conveying unit capable of performing a feeding operation of suctioning and feeding the levitated sheet; an upper surface detection unit that outputs a signal when the upper surface of the floated sheet is below a detection position; a control unit that controls the lifting unit and the suction transport unit, The control unit is capable of executing a mode in which the control unit starts lifting the tray in response to the output of the signal, and stops lifting the tray in response to the lapse of a set time period that is set in accordance with a thickness of the sheet. A sheet feeding device comprising:

Images