JP2009126603A - Sheet stacking device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet stacking device capable of stacking sheets without impairing productivity and generating a stacking defective, and an image forming device. <P>SOLUTION: When the length of a discharging direction of the discharged sheets is a prescribed length or below, the sheets are discharged to a stacking tray 6 by a sheet discharge roller 5. When the length is the prescribed length or more, the sheets discharged from the sheet discharge roller 5 are transferred to a prescribed position on the sheet stacking part by a transfer means constituted of grippers 7a and 7b and a gripper belt 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sheet stacking apparatus and an image forming apparatus, and more particularly to a sheet stacking sheet discharged from a main body of an image forming apparatus at high speed with high accuracy.

  2. Description of the Related Art In recent years, in image forming apparatuses that form images on sheets, the speed of image formation has been increased due to technological advances, and the discharge of sheets discharged from the main body of the image forming apparatus as the speed of image formation increases. The speed is also increasing. In order to arrange and stack a large number of sheets discharged at such a high speed as described above, a conventional image forming apparatus includes, for example, a large-capacity stacker device as a sheet stacking device (see Patent Document 1). .

  FIG. 6 is a diagram showing the configuration of such a conventional large-capacity stacker apparatus. When a sheet is discharged from an image forming apparatus main body (not shown), the sheet is first carried into the entrance roller 1. Next, when the sheet is conveyed to the upper path by switching the first switching member 2, the sheet passes through the sample tray 9 on the upper part of the stacker or the conveyance path 3 by switching the second switching member 21. Then, the sheet is conveyed to a sheet processing apparatus (not shown) downstream of the exit roller 4.

  When the sheet is conveyed to the lower path by the first switching member 2, the sheet is discharged and stacked horizontally on the stacking tray 6 by the discharge roller 5. Here, the stacking tray 6 is configured to be moved up and down by a driving device (not shown), and the height is controlled by the paper surface detection lever 10 so that the upper surface height of the stacked sheets is always constant.

  By the way, when the sheets are stacked horizontally on the stacking tray 6, especially when the sheet is a small sheet such as thin paper, the leading end of the sheet in the conveyance direction hangs down, and the already stacked sheets P on the stacking tray Contact with. When the sheet comes into contact with the already stacked sheet P in this way, the sheet is damaged or a stacking failure due to buckling occurs.

  Therefore, conventionally, grippers 107a and 107b are provided downstream of the paper discharge roller 5 so as to grip the leading end of the sheet and move the stack tray 6 to the downstream in the sheet conveying direction. The grippers 107 a and 107 b are attached to an endless belt 108 that is suspended on the drive pulley 11 and the driven pulley 12 and is rotatable in the direction of arrow 13. The grippers 107a and 107b are attached at two positions in a direction perpendicular to the sheet conveying direction (hereinafter referred to as a width direction) at a position where the circumferential length of the endless belt 108 is equally divided.

  The leading edge of the sheet discharged by the paper discharge roller 5 is gripped one by one by the grippers 107a and 107b, and the endless belt 108 is held in such a state that the leading edge of the sheet is gripped by the grippers 107a and 107b. Try to rotate. As a result, the sheet moves integrally with the endless belt 108.

  Note that a leading end stopper 114 is provided above the stacking tray 6, and when the sheet is conveyed on the stacking tray while being gripped by the grippers 107 a and 107 b in this way, the sheet eventually hits the leading end stopper 114. When the leading edge of the sheet comes into contact with the leading edge stopper 114 in this way, the grippers 107a and 107b are released from gripping, and the sheets are stacked on the stacking tray.

JP 2006-124051 A

  By the way, in the conventional sheet stacking apparatus (stacker apparatus) and image forming apparatus that grip and convey such discharged sheets one by one with a gripper, the gripper is at a speed equal to the sheet discharging speed for the purpose of conveying the sheet. Need to be driven.

  However, depending on the sheet size, the timing at which the sheet reaches the stacker device becomes earlier, and after the previous sheet is gripped by the gripper, the next gripper grips the sheet until the next sheet is discharged to the stacker device. The position may not be reached. In this case, the next sheet cannot be discharged to the stacker device until the next gripper reaches a position for gripping the sheet, and the productivity of the image forming apparatus is impaired.

  Further, the gripper needs to be disposed on the endless belt corresponding to the leading edge of the sheet that is continuously conveyed. Here, in order to deal with large-size sheets such as A3 and B4, for example, as shown in FIG. 6, two grippers are arranged on an endless belt. On the other hand, when transporting half-size sheets such as A4 and B5 sizes, for example, four grippers are arranged on the endless belt because the transport distance is short and the timing at which the sheet reaches the stacker device is early. Like that.

  However, when four grippers are arranged in this way, when carrying and stacking large sized sheets, the gripper immediately after the gripper that grips the leading edge of the sheet does not grip the sheet, and between the endless belt and the sheet. Will come to be located. When the gripper immediately after this comes into contact with the sheet surface, the image is damaged, stress is applied to the gripped sheet, and problems such as a grip disengagement at the front end of the sheet are caused.

  For this reason, it is necessary to arrange, for example, two grippers of the endless belt in accordance with the conveying position of the large size sheet. However, when the gripper is arranged in accordance with the large size sheet as described above, when the half size sheet is conveyed, it is necessary to wait for the sheet according to the movement timing of the gripper, which impairs the productivity of the image forming apparatus. Become.

  Even when the number of grippers is two, in order not to reduce the productivity, at the time of transporting the half-size sheet, the endless belt is transported from the time when the previous sheet is transported onto the stacking tray and released from the gripper. There is a method of shortening the processing time by accelerating the rotation speed.

  However, in this method, after the rotational speed of the endless belt is accelerated, the rotational speed of the endless belt is controlled so as to be the same as the transport speed of the next sheet until the next sheet is gripped. There is a need. For this reason, the rotational speed control of the endless belt becomes complicated, and there is a limit to improving the productivity.

  Accordingly, the present invention has been made in view of such a current situation, and provides a sheet stacking apparatus and an image forming apparatus that can stack sheets without impairing productivity and causing stacking defects. It is intended to do.

  The present invention comprises a sheet stacking unit for stacking sheets, a sheet discharge unit for discharging sheets, and a transfer unit for transferring the sheet discharged from the sheet discharge unit to the sheet stacking unit, and a sheet discharge direction When the length of the sheet is less than a predetermined length, the sheet discharge unit discharges the sheet to the sheet stacking unit. When the length of the sheet in the discharge direction is equal to or longer than the predetermined length, the sheet is discharged by the transfer unit. The sheet is transferred to the sheet stacking unit.

  As in the present invention, by discharging the sheet by the sheet discharge unit according to the length of the sheet or by transferring it to the sheet stacking unit by the transfer unit, productivity is not impaired and a stacking defect is caused. Sheets can be stacked.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of an image forming apparatus including a sheet stacking apparatus according to an embodiment of the present invention.

  In FIG. 1, reference numeral 900 denotes an image forming apparatus, and reference numeral 901 denotes an image forming apparatus main body. The image forming apparatus main body 901 is provided with an image reading apparatus 951 including a scanner unit 955 and an image sensor 954, an image forming unit 902 that forms an image on a sheet, a double-sided device 953, a platen glass 952, and the like. A document feeder 950 for feeding a document to the platen glass 952 is provided on the upper surface of the image forming apparatus main body 901.

  The image forming unit 902 includes a cylindrical photosensitive drum 906, a charger 907, a developing unit 909, a cleaning device 913, and the like. Further, a fixing device 912 and a discharge roller pair are provided on the downstream side of the image forming unit 902. 914 etc. are arranged. Further, the image forming apparatus main body 901 is connected to a stacker 100 which is a sheet stacking apparatus for stacking sheets on which image formation has been performed after image formation from the image forming apparatus main body 901. Reference numeral 960 denotes a control unit that controls the image forming apparatus main body 901 and the stacker 100.

  Next, an image forming operation of the image forming apparatus main body 901 having such a configuration will be described.

  When an image forming signal is output from the control unit 960, a document is first placed on the platen glass 952 by the document feeder 950, and the document image is read by the image reading device 951. The read digital data is exposed. Input to means 908. The exposure unit 908 irradiates the photosensitive drum 906 with light corresponding to the digital data.

  At this time, the surface of the photosensitive drum 906 is uniformly charged by the charger 907. When light is irradiated in this manner, an electrostatic latent image is formed on the surface of the photosensitive drum, and the electrostatic latent image is developed. By developing with the device 909, a toner image is formed on the surface of the photosensitive drum.

  On the other hand, when a paper feed signal is output from the control unit 960, the sheet P set in the cassettes 902a to 902e is first transported to the registration roller 910 by the paper feed rollers 903a to 903e and the transport roller pair 904.

  Next, the sheet P is conveyed by a registration roller 910 to a transfer unit including a charger 905 at a timing such that the leading edge of the sheet and the leading edge of the toner image on the photosensitive drum 906 are aligned. In this transfer portion, a transfer bias is applied to the sheet P by the charger 905, whereby the toner image on the photosensitive drum 906 is transferred to the sheet side.

  Next, the sheet P on which the toner image is transferred is conveyed to the fixing device 912 by the conveying belt 911, and then the toner image is heat-fixed when nipped and conveyed between the heating roller and the pressure roller of the fixing device 912. The At this time, foreign matters such as residual toner that are not transferred to the sheet on the photosensitive drum 906 are scraped off by the blade of the cleaning device 913. As a result, the surface of the photosensitive drum 906 becomes clear, and the next It can prepare for image formation.

  The fixed sheet is conveyed as it is to the stacker 100 which is a sheet stacking device by the discharge roller pair 914 or is conveyed to the double-sided device 953 by the flapper 915, and the image forming surface is reversed and image formation is performed again. It will be.

  FIG. 2 is a block diagram illustrating a configuration of the control unit 960. The control unit 960 includes a CPU circuit unit 150, and the CPU circuit unit 150 incorporates a CPU, a ROM 151, and a RAM 152 (not shown). Then, according to the control program stored in the ROM 151, the document feed control unit 101, the operation unit 102, the image reader control unit 201, the image signal control unit 202, the printer control unit 301, the stacker control unit 401, and the sheet processing apparatus control unit. 501 is collectively controlled.

  The sheet processing apparatus control unit 501 controls a sheet processing apparatus (not shown) connected to the stacker 100. In FIG. 2, reference numeral 203 denotes an external I / F that is an interface between the image forming apparatus 900 and an external computer 204. The print data from the computer 204 is expanded into a bitmap image, and an image signal control unit as image data To 202.

  The RAM 152 temporarily stores control data and is used as a work area for arithmetic processing associated with control. The document feeding control unit 101 controls driving of the document feeding device 950 based on an instruction from the CPU circuit unit 150. The image reader control unit 201 performs drive control on the scanner unit 955 and the image sensor 954 provided in the image reading device 951 and transfers an analog image signal output from the image sensor 954 to the image signal control unit 202. is there.

  The image signal control unit 202 converts each analog image signal from the image sensor 954 into a digital signal, performs each process, converts the digital signal into a video signal, and outputs the video signal to the printer control unit 301. The digital image signal input from the computer 204 via the external I / F 203 is subjected to various processes, and the digital image signal is converted into a video signal and output to the printer control unit 301. The processing operation by the image signal control unit 202 is controlled by the CPU circuit unit 150.

  The printer control unit 301 drives the exposure unit 908 via an exposure control unit (not shown) based on the input video signal. The operation unit 102 includes a plurality of keys for setting various functions relating to image formation, a display unit for displaying information indicating a setting state, and the like. A key signal corresponding to the operation of each key is output to the CPU circuit unit 150, and corresponding information is displayed on the display unit based on the signal from the CPU circuit unit 150.

  The user can input sheet size information, for example, whether the sheet is a large size such as A3 or B4, or a half size sheet such as A4 or B5 size, from the operation unit 102 serving as an input unit.

  The CPU circuit unit 150 controls the stacking operation of the stacker 100 via the stacker control unit 401 based on the sheet size information (the length information in the sheet discharge direction) input from the operation unit 102. . When the image forming apparatus 900 is controlled by the external computer 204, the sheet size information is input from the external computer 204, not from the operation unit 102.

  The stacker control unit 401 is mounted on the stacker 100 and performs overall drive control of the stacker such as driving of the gripper belt motor 601 by exchanging information with the CPU circuit unit 150. This control content will be described later. Note that the stacker control unit 401 may be integrated into the CPU circuit unit 150 on the image forming apparatus main body 901 side so as to control the stacker 100 directly from the image forming apparatus main body 901.

  FIG. 3 is a diagram illustrating a configuration of the stacker 100 connected to the image forming apparatus main body 901. In FIG. 3, reference numeral 8 denotes a gripper belt. The gripper belt 8 is suspended from the drive pulley 11 and the driven pulley 12 and is rotationally driven by the gear transmission of the drive of the gripper belt motor 601 so as to have the same speed as the sheet conveying speed. Rotate in the direction of arrow 13.

  Reference numerals 7a and 7b denote grippers for gripping (clamping) the sheet discharged from the sheet discharge roller 5 serving as a sheet discharge unit. The grippers 7a and 7b are attached to the gripper belt 8 and integrated with the gripper belt 8. It moves in the direction of arrow 13 at the same speed as the sheet conveyance speed. Then, by being gripped by the grippers 7a and 7b, the sheet is transferred (conveyed) to a predetermined position along the sheet discharge direction above the stacking tray 6 which is a sheet stacking unit.

  That is, in the present embodiment, the transfer means for transferring the sheet discharged from the paper discharge roller 5 to a predetermined position on the stacking tray includes grippers 7a and 7b which are a plurality of holding means for holding (holding) the sheets, And a gripper belt 8.

  Reference numeral 14 denotes a front end stopper which is a butting portion that contacts the front end of the sheet and positions the sheet. The front end stopper 14 includes a slope 14a on which the sheet held by the grippers 7a and 7b abuts, and a sheet as a drawing means. And retracting means 16.

  Here, when the grippers 7 a and 7 b move in the direction of the leading end stopper 14 by the rotation of the gripper belt 8, the leading end of the sheet gripped by the grippers 7 a and 7 b eventually comes into contact with the inclined surface 14 a of the leading end stopper 14. Then, the sheet is released from the grippers 7a and 7b by the front end contacting the inclined surface 14a in this way.

  Further, after being released from the grippers 7a and 7b, the sheet is discharged toward the sheet retracting means 16, and then the sheet retracting means 16 causes the leading edge of the sheet to abut against the abutting surface 14b of the leading end stopper 14, The leading edge of the sheet is positioned.

  By the way, the leading end stopper 14 is movable above the stacking tray 6 along the sheet discharging direction. For example, when a large size sheet is stacked on the stacking tray 6, the leading end stopper 14 is transferred to a predetermined position on the sheet stacking portion shown in FIG. 3 by the transfer means (grippers 7a and 7b and the gripper belt 8). To a position corresponding to the length of the sheet in the conveyance direction. On the other hand, when a half-size sheet is stacked on the stacking tray 6, the leading end stopper 14 moves to a position corresponding to the length in the conveyance direction of the sheet discharged from the discharge roller 5 shown in FIG.

  Next, the operation of the stacker 100 when a large-size sheet whose length in the sheet discharge direction is a predetermined length or more is stacked on the stacking tray 6 will be described with reference to FIG.

  When the sheet is discharged from the image forming apparatus main body 901, the sheet is carried into the entrance roller 1, and then the path is switched and conveyed by the first switching member 2 in accordance with a selection instruction from the operation unit 102 or the like. Further, for example, when the user designates the sheet stacking position for the sample tray 9 on the upper surface of the stacker, the sheet is directed to the sample tray 9 by switching the second switching member 21 thereafter. When conveyance to a sheet processing apparatus (not shown) connected downstream is specified, the sheet passes through the conveyance path 3 by the upward rotation of the second switching member 21, and is discharged from the exit roller 4 to the sheet processing apparatus. It is conveyed to.

  When the user designates the sheet stacking position on the stacking tray 6, the sheet is guided to the sheet discharge roller 5 by switching the first switching member 2 when being conveyed by the entrance roller 1. Thereafter, the sheet is gripped by one of the two grippers 7 a and 7 b and is transported on the stacking tray while being gripped by the gripper 7 a and the paper discharge roller 5.

  Next, the sheet transported in this way is released from the gripper 7a by coming into contact with the inclined surface 14a of the leading end stopper 14 at the position shown in FIG. 3, and the sheet retracting means 16 provided integrally with the leading end stopper 14 is provided. It is discharged toward.

  Here, the distance between the sheet drawing means 16 and the sheet discharge roller 5 is set to be shorter than the length of the discharged sheet. Therefore, after that, the sheet is guided to the contact surface 14 b of the front end stopper 14 by the sheet drawing means 16, so that the front end position is regulated and the rear end is separated from the paper discharge roller 5. Thus, the sheets are stacked on the stacking tray 6 in a state where the leading end position is regulated. After that, the next sheet discharged from the paper discharge roller 5 is conveyed and stacked on the stacking tray while the leading edge is gripped by the next gripper 7b.

  Next, the operation of the stacker 100 when stacking half-size sheets whose length in the sheet discharge direction is a predetermined length or less on the stacking tray 6 will be described with reference to FIG.

  In this case, first, the leading end stopper 14 is moved in the direction of the arrow 15 and positioned at a position corresponding to the length in the sheet discharge direction shown in FIG. Further, the gripper belt 8 is rotated, and the grippers 7a and 7b are moved to a position where they do not come into contact with the discharged sheet, that is, a position where the conveyance of the sheet is not hindered.

  Here, by stopping the grippers 7a and 7b at positions that do not hinder the conveyance of the sheet, the grippers 7a and 7b damage the image on the sheet or prevent the sheet conveyance when the sheet is discharged. Can be prevented.

  Next, after the sheet stacking position is designated as the stacking tray 6 and guided to the sheet discharge roller 5 by switching the first switching member 2, the sheet is discharged toward the leading end stopper 14 by the sheet discharge roller 5.

  The sheet discharged toward the leading end stopper 14 in this way is discharged toward the sheet retracting means 16 by contacting the inclined surface 14 a of the leading end stopper 14. In this case as well, the distance between the sheet retracting means 16 and the paper discharge roller 5 is set shorter than the length of the discharged sheet.

  Therefore, after that, the sheet is guided by the sheet drawing means 16 to the contact surface 14b of the leading end stopper 14, whereby the leading end position is regulated, and the stacking tray 6 with the leading end position regulated in this way is regulated. Loaded on top. After that, the next sheet discharged from the sheet discharge roller 5 is stacked on the stacking tray 6 after the leading end abuts against the leading end stopper 14.

  Thus, in the present embodiment, the sheet stacking operation on the stacking tray 6 is changed according to the sheet size. Next, a sheet stacking operation on the stacking tray 6 according to the sheet size will be described with reference to a flowchart shown in FIG.

  First, the stacker control unit 401 determines whether or not to stack sheets in accordance with an instruction from the CPU circuit unit 150 on the image forming apparatus main body 901 side or an instruction from the operation unit 102 (S100). Here, when it is determined that the sheets are stacked on the stacking tray, that is, stacked on the stacking tray (Y in S100), the stacker control unit 410 next inputs the sheet information from the operation unit 102 or the like (S101). ). If it is determined that the sheets are not stacked (N in S100), the process proceeds to another process (S102).

  Next, it is determined from the sheet information whether the sheet to be processed is a large size sheet (S103). When it is determined that the sheet to be processed is a large size sheet (Y in S103), the grippers 7a and 7b are used for stacking the sheets as described above (S104). Further, the leading end stopper 14 is positioned at a position corresponding to the length in the discharge direction of the large size sheet shown in FIG. Thereafter, the sheets are stacked on the stacking tray using the grippers 7a and 7b (S110).

  On the other hand, when it is determined that the sheet to be processed is a half-size sheet (N in S103), the grippers 7a and 7b are not used as described above (S105). Along with this, the gripper belt 8 is rotated, and the grippers 7a and 7b are moved to a retracted position that does not hinder sheet conveyance (S106). Further, the front end stopper 14 is positioned at a position corresponding to the length in the discharge direction of the half size sheet shown in FIG. Thereafter, the sheet is stacked on the stacking tray by the discharge roller 5 (S110).

  As described above, in the case of a large-sized sheet, the sheet is buckled even when stacking sheets such as thin paper that is weak, by gripping the sheet by the grippers 7a and 7b and transferring the sheet on the stacking tray. High-precision loading is possible without any problems. In the case of a half-size sheet, the sheet is directly discharged onto the stacking tray by the paper discharge roller 5 without using the grippers 7a and 7b, thereby eliminating the productivity restriction due to the positions of the grippers 7a and 7b. Can do.

  In this way, by discharging the sheet by the discharge roller 5 according to the length of the sheet or by transferring the sheet to a predetermined position on the sheet stacking unit by the transfer unit, the productivity is not impaired and the stacking is performed. Sheets can be stacked without causing defects.

  In the above description, the grippers 7a and 7b grip and convey the leading edge of the sheet in order to prevent buckling and conveyance failure of the thin sheet, but it is not always necessary to grasp the leading edge of the sheet. Instead, the side end portion in the vicinity of the leading end of the sheet may be held.

  In the description so far, the gripper (gripper member) is taken as an example of the holding means for holding the sheet, but the present invention is not limited to this. For example, even when the holding means uses a structure that can adsorb the sheet by air, a structure that adsorbs the sheet by static electricity, or the like that can transfer while holding the leading end of the sheet, An effect can be obtained.

  Further, in the description so far, in the case of a half-size sheet, the case where the sheet is stacked on the stacking tray by the discharge roller 5 as it is has been described, but the present invention is not limited to this. For example, in the case of an extremely thin sheet whose rigidity is smaller than a predetermined rigidity, even in the case of a half-size sheet, the leading end of the sheet in the conveyance direction hangs down and comes into contact with the already stacked sheets P on the stacking tray. .

  For this reason, when discharging such a sheet, the leading end stopper 14 is moved to the first position, and an extremely thin sheet is transferred by the gripper, so that the sheet can be removed without causing a stacking failure. Can be loaded. That is, even when the sheet size is a half size, the sheets can be stacked without causing a stacking failure by selectively transferring the sheets by the gripper according to the information on the rigidity of the sheet.

1 is a diagram illustrating a configuration of an image forming apparatus including a sheet stacking apparatus according to an embodiment of the present invention. FIG. 3 is a control block diagram of a control unit provided in the image forming apparatus. FIG. 3 is a diagram illustrating a configuration of a stacker connected to an image forming apparatus main body of the image forming apparatus. FIG. 4 is a diagram illustrating a sheet stacking operation in the stacker. The flowchart explaining the control in the said stacker. The figure which shows the structure of the conventional large capacity | capacitance stacker apparatus.

Explanation of symbols

5 Paper discharge roller 6 Stack trays 7a, 7b Gripper 8 Gripper belt 14 End stopper 100 Stacker 102 Operation unit 150 CPU circuit unit 401 Stacker control unit 900 Image forming apparatus 901 Image forming apparatus main body 902 Image forming part P Sheet

Claims (11)

A sheet stacking unit for stacking sheets;
Sheet discharge means for discharging the sheet;
A transfer means for transferring the sheet discharged from the sheet discharge means to the sheet stacking unit,
When the length of the sheet in the discharge direction is not more than a predetermined length, the sheet discharging means discharges the sheet to the sheet stacking unit, and when the length of the sheet in the discharge direction is not less than the predetermined length, the transfer is performed. A sheet stacking apparatus for transferring a sheet to the sheet stacking unit by means. Abutting portions that abut against one of the sheet transferred by the transfer means and the sheet discharged by the sheet discharge means are provided to be movable along the sheet stacking portion,
2. The abutting portion is moved to a position corresponding to a length in a discharge direction of a sheet transferred by the transfer unit and a length in a discharge direction of a sheet discharged by the sheet discharge unit. 1. The sheet stacking apparatus according to 1. Provide input means to input length information in the sheet discharge direction,
One of the positions corresponding to the length in the discharge direction of the sheet transferred by the transfer means and the length in the discharge direction of the sheet discharged by the sheet discharge means based on the information from the input means The sheet stacking apparatus according to claim 2, wherein the sheet stacking apparatus is moved to a position.   4. The apparatus according to claim 1, further comprising: a pulling unit that presses the sheet against the butting portion, wherein a distance between the pulling unit and the sheet discharging unit is shorter than a length in a discharging direction of the discharged sheet. The sheet stacking apparatus according to claim 1.   5. The sheet stacking apparatus according to claim 1, wherein the transfer unit includes a plurality of holding units that hold sheets to be transferred. 6.   6. The sheet stacking apparatus according to claim 5, wherein when the sheets are discharged by the sheet discharge means, the plurality of holding means are moved to a position where they do not contact the discharged sheets.   7. The sheet stacking apparatus according to claim 5, wherein the holding unit of the transfer unit is a gripper member that holds a sheet.   7. The sheet stacking apparatus according to claim 5, wherein the holding unit of the transfer unit is configured to adsorb sheets by static electricity.   7. The sheet stacking apparatus according to claim 5, wherein the holding means of the transfer means is configured to adsorb sheets by air.   Even when the length of the sheet in the discharge direction is equal to or less than a predetermined length, if the rigidity of the sheet is smaller than the predetermined rigidity, the length of the sheet in the discharge direction of the sheet transferred by the transfer means is the abutting portion. 3. The sheet stacking apparatus according to claim 2, wherein the sheet is moved to a position corresponding to the position and the sheet is transferred by the transfer means.   An image forming unit that forms an image on a sheet, and a sheet stacking device according to any one of claims 1 to 10, further comprising a sheet stacking unit that stacks sheets discharged after image formation. A featured image forming apparatus.

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