JP2010001091A - Paper feeder and image forming device provided with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper feeder capable of suppressing generation of double feed and rubbing sound of a paper by variation of a paper feeding position and performing stable paper feeding action, and an image forming device provided with it. <P>SOLUTION: When a printing signal is received, a lift plate drive motor 61 is rotated/driven by a control signal transmitted from a control part 75 and a lift plate 45 is ascended. Nextly, when a detection signal from an upper surface detection sensor 50 is transmitted, the control part 75 transmits a control signal to the lift plate drive motor 61 to stop rotation and a time from detection timing by the upper surface detection sensor 50 to motor stop timing is simultaneously measured by a timer 81. Since the lift plate 45 is excessively ascended by the measured time, the lift plate 45 is descended to a reference paper feeding position by reversely rotating the lift plate drive motor 61 by a predetermined amount. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheet feeding device that separates and feeds sheets one by one from a sheet bundle, such as a sheet feeding cassette or a document conveying device mounted in an image forming apparatus such as a digital copying machine or a laser printer. .

  2. Description of the Related Art Conventionally, in an image reading apparatus mounted on a copying machine using an electrophotographic process, a document is conveyed so that a sheet-like document is sequentially sent to a document placing table and discharged from the document placing table after reading. Some have a device (Automatic Document Feeder). In such an image reading apparatus, a sheet-through method in which a document is automatically conveyed and read by a document conveying device while the document press is closed, and the document press is opened and closed each time reading is performed on a document placement table (contact glass). Two types of reading methods are possible: a document fixing method that replaces each original document one by one. In the former sheet-through method, the optical system in the image reading apparatus is scanned and moved while being held at a predetermined image reading position. On the other hand, in the latter document fixing method, A reading operation is performed while the optical system scans and moves.

  In the sheet-through type reading, a configuration in which the uppermost surface of a stacked document bundle is conveyed while being pressed against a pickup roller is generally used. As a method of pressing the uppermost surface of the document bundle against the pickup roller, a method of raising and lowering the pickup roller with respect to the document bundle was used. However, noise and vibration are generated by the impact when the pickup roller falls on the upper surface of the paper. There was a bug to do.

In order to prevent such problems, a configuration has been proposed in which a lift plate is provided at the downstream end of the document feed tray on which documents are stacked, and the lift plate is raised and lowered to raise the uppermost surface of the document bundle to the feed position. Yes. For example, Patent Document 1 discloses an automatic document feeder that achieves noise reduction by transmitting a driving force to a movable plate via a cam when the movable plate is moved up and down by a step clutch or a motor. Patent Document 2 discloses that the number of originals loaded on the paper feed tray is not changed without changing the height position of the paper feed tray by raising and lowering the discharge outlet of the document discharge tray by the same amount as the document feed tray is raised and lowered. A document feeder having an increased number is disclosed.
JP-A-6-255806 JP 2005-8283 A

  In Patent Document 2, a stepping motor is used as a drive source for raising and lowering the paper feed tray, and the driving of the motor is stopped based on the output timing of the detection signal from the document contact sensor (upper surface detection sensor) or the document presence / absence sensor. . At this time, as shown in FIG. 10, the rotation speed of the stepping motor is gradually accelerated from the start of driving until t1, and then rotates at a constant speed s1, and further, the motor gradually decelerates from t2 when the detection signal is transmitted. So-called through-up / through-down control that stops at t3 is performed. For this reason, when the stepping motor is used at a high speed, a time lag (t3-t2) occurs between the output timing of the detection signal and the stop timing of the motor, and the paper feed tray is placed after the original contact sensor detects the upper surface of the original. It stops at a position that has been raised by a fixed amount (shaded area in the figure).

  FIG. 11 is a graph showing a change in the height of the document feeding position when 100 documents are set on the document feeding tray and the lift plate provided at the downstream end of the tray is raised to feed the document. is there. As shown in FIG. 11, in the conventional through-up / through-down control, when the first original is fed, the upper face is detected at the original feeding position by the time lag from the detection of the upper face of the original to the stop of the lift plate. About 2.2 mm from the position. Thereafter, control by the upper surface detection sensor is not performed until the 20th sheet (after about 15 seconds), and the documents are sequentially fed with the lift plate stopped. Along with this, the pickup roller is lowered by its own weight, and the document feeding position gradually approaches the upper surface detection position. Since the document feeding position is lower than the upper surface detection position after the 20th sheet, control by the upper surface detection sensor is entered again, and the lift plate is raised and stopped at the upper surface detection position. Is slightly smaller than the first document, so there is no overrun phenomenon when the lift plate stops. Up to the 100th document, the height of the lift plate is stable within the range from the top surface detection position to 0.5 mm. It is controlled.

  That is, immediately after the document is set, the stop position of the lift plate is not stably controlled, and is raised to a position higher than the upper surface detection position (reference feed position). When the lift plate is lifted from the reference sheet feeding position, the pressure contact force between the upper surface of the document and the pickup roller is increased, and there is a problem that double feed of the document and rubbing noise are generated. Although an example of a document conveying apparatus that automatically conveys a sheet document has been described here, the situation is the same in other sheet feeding apparatuses such as a sheet feeding cassette and a manual tray that feed sheets as a recording medium. there were.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a paper feeding device capable of suppressing the occurrence of paper double feed and rubbing noise due to fluctuations in the paper feeding position and capable of stable paper feeding operation, and an image forming apparatus including the paper feeding device. The purpose is to provide.

  In order to achieve the above object, the present invention is configured to press and contact a paper stacking plate that can be moved up and down and a top surface of the paper stacked on the paper stacking plate to move the press contact surface in a predetermined direction. A sheet feeding unit that sequentially feeds sheets, a lifting unit that lifts and lowers the sheet stacking plate, a control unit that controls driving of the lifting unit, and a top surface detection that detects the top surface of the sheets stacked on the sheet stacking plate. The control means is configured to detect when the upper surface detection means detects the upper surface of the paper when the elevation means raises the paper stacking plate to a reference paper feed position, and the elevation means. The amount of deviation from the reference sheet feeding position is calculated based on the timing at which the sheet stops, and the sheet stacking plate is lowered by the calculated amount of deviation.

  According to the present invention, in the paper feeding device having the above-described configuration, a time measuring unit that measures a time from when the upper surface detecting unit detects the upper surface of the sheet to when the lifting unit stops is provided.

  According to the present invention, in the paper feeding device having the above-described configuration, a pulse motor is used as a driving source of the lifting / lowering unit, and the number of pulses from when the upper surface detecting unit detects the upper surface of the paper until the lifting / lowering unit stops is determined. It is characterized by providing a counting means for counting.

  Further, the present invention is an image forming apparatus equipped with the sheet feeding device having the above-described configuration.

  According to the first configuration of the present invention, the shift amount of the sheet stacking plate from the reference sheet feeding position due to the time lag from the detection timing of the upper surface detection unit to the stop of the lifting unit is calculated, and the sheet stacking plate is shifted. It can be lowered by an amount and put into standby at the reference paper feed position. Accordingly, it is possible to perform a stable paper feeding operation by suppressing the double feeding of paper and the generation of rubbing noise due to the fluctuation of the paper feeding position.

  Further, according to the second configuration of the present invention, in the paper feeding device of the first configuration, the time measuring unit that measures the time from when the upper surface detection unit detects the upper surface of the paper until the lifting unit stops is provided. By providing, it is possible to easily calculate the amount of deviation of the sheet stacking plate from the reference sheet feeding position based on the time from when the upper surface of the sheet is detected to when the elevating means stops.

  According to the third configuration of the present invention, in the paper feeding device having the above first configuration, the pulse motor is used as a driving source for the elevating means, and the elevating means is detected after the upper surface detecting means detects the upper surface of the paper. By providing a counting means for counting the number of pulses until stopping, the sheet stacking plate is easily and accurately placed on standby at the reference sheet feeding position by simply rotating the pulse motor in the reverse direction by the number of pulses counted by the counting means. be able to.

  According to the fourth configuration of the present invention, when the sheet feeding device having any one of the first to third configurations is mounted, the sheet or document can be conveyed from the sheet feeding cassette or the document conveying device. An image forming apparatus capable of effectively preventing troubles such as double feeding and performing a stable conveying operation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus provided with a document conveying device of the present invention. In FIG. 1, in an image forming apparatus 100 (here, a digital multi-function peripheral is shown as an example), when performing a copying operation, an image reading apparatus 6 converts image data of a document into a read image signal. On the other hand, in the image forming unit 3 in the MFP main body 2, the photosensitive drum 5 rotating in the direction A in the figure is uniformly charged by the charging unit 4, and is based on the document image data read by the image reading device 6. An electrostatic latent image is formed on the photosensitive drum 5 by a laser beam from an exposure unit (laser scanning unit or the like) 7, and a developer (hereinafter referred to as toner) is attached to the electrostatic latent image by the developing unit 8. An image is formed. The toner is supplied to the developing unit 8 from the toner container 9.

  The sheet is conveyed from the sheet feeding mechanism 10 to the image forming unit 3 via the sheet conveying path 11 and the registration roller pair 12 toward the photosensitive drum 5 on which the toner image is formed as described above. 3, the toner image on the surface of the photosensitive drum 5 is transferred to the sheet by the transfer roller 13 (image transfer unit). The sheet onto which the toner image has been transferred is separated from the photosensitive drum 5 and conveyed to a fixing unit 14 having a fixing roller pair 14a to fix the toner image. The sheet that has passed through the fixing unit 14 is sent to a sheet conveyance path 15 branched in a plurality of directions, and is conveyed in a conveyance direction by path switching mechanisms 21 and 22 having a plurality of path switching guides provided at branch points of the sheet conveyance path 15. Are distributed as they are (or after being sent to the paper conveyance path 16 and double-sided copying), and discharged to the paper discharge section including the first discharge tray 17a and the second discharge tray 17b.

  Although not shown, a static elimination device that removes residual charges on the surface of the photosensitive drum 5 is provided on the downstream side of the cleaning device 18. Further, the paper feed mechanism 10 is detachably attached to the multifunction machine main body 2 and includes a plurality of paper feed cassettes 10a and 10b for storing paper and a stack bypass (manual feed tray) 10c provided above the paper feed cassettes 10a and 10b. These are connected to the image forming unit 3 including the photosensitive drum 5 and the developing unit 8 by the paper transport path 11. A platen (original presser) 24 that presses and holds a document placed on the contact glass 25 (see FIG. 2) of the image reading device 6 is provided on the upper surface of the apparatus body so as to be openable and closable. A document conveying device 27 is attached.

  Specifically, the sheet conveyance path 15 first branches into a left and right fork on the downstream side of the fixing roller pair 14a, and one path (a path branching rightward in FIG. 1) communicates with the first discharge tray 17a. It is configured as follows. The other path (the path that branches in the left direction in FIG. 1) branches into the upper and lower forks via the conveying roller pair 19, and the other path (the path that branches in the upper direction in FIG. 1) is the second discharge tray. It is comprised so that it may communicate with 17b. On the other hand, the other path (the path that branches downward in FIG. 1) is configured to communicate with the sheet conveyance path 16.

  FIG. 2 is a side sectional view showing the internal structure of the document conveying device. The document transport device 27 includes a document feed tray 29 provided with a document guide 29 a for aligning and stacking a plurality of documents, and a reversing tray 30 provided below the document feed tray 29. Each member of the paper tray 29 and the reverse tray 30 is attached to the frame of the document conveying device 27. Further, a cover member 31 is supported so as to be openable and closable with one end (lower left in the figure) as a rotation fulcrum with respect to the frame of the document conveying device 27, and a document discharge tray 32 is disposed on the side of the cover member 31. It is formed directly on a part of the upper surface. A document transport path d from the document feed tray 29 to the document discharge tray 32 is formed in the cover member 31. By opening the cover member 31, the document transport path d is opened, and jamming can be performed. ing.

  In the cover member 31, a pickup roller 33, a paper feed belt 34 and a separation roller 35, a registration roller pair 36, a conveyance roller pair 37, 38, 39, and 40, a CIS roller 41, a reverse roller along the document conveyance path d. Document conveying means including a pair 42, a discharge roller pair 43 and the like is provided. The paper feed belt 34 is wound around a driving roller 44a and a driven roller 44b, and a separation roller 35 is in contact with the roller at a predetermined pressure from below. The separation roller 35 has a built-in torque limiter, which rotates in the opposite direction to the paper feed belt 34 only when the rotational load is lower than a predetermined torque, and is driven to rotate with the paper feed belt 34 when the rotational load exceeds a predetermined torque. It is supposed to be. Above the pickup roller 33, an upper surface detection sensor 50 for detecting the upper surface position of the document is disposed.

  The contact glass 25 includes a manually placed original glass 25a and an automatic reading glass 25b. A shading correction white reference plate disposed opposite to the automatic reading glass 25b (image reading position), and a white reference plate. There is provided a document pressing portion (none of which is shown) for pressing the white reference plate toward the manually placed document glass 25a. The document conveyance path d is curved so as to be reversed between the registration roller pair 36 and the automatic reading glass 25b. A plurality of paper detection sensors including a paper feed sensor S1 and a discharge sensor S2 for detecting the presence / absence or passage of a document are provided at appropriate positions on the document conveyance path d.

  Next, a sheet-through type document conveyance operation using the document conveyance unit 27 will be described. In the sheet-through method, after a plurality of documents are set on the document feed tray 29 with the image surface facing upward, when the copy start button on the operation panel of the image forming apparatus 100 is turned on, an elevating mechanism (FIG. 4, FIG. 4). The lift plate 45 lifted by (see FIG. 5) pushes up the pickup roller 33 through the document, and the weight of the frame 53 (see FIG. 3) including the pickup roller 33 is added to the lift plate 45. It is pressed against the pickup roller 33 with a predetermined pressure (paper feed pressure). Here, the driving roller 44a is rotated by the roller driving motor 77 (see FIG. 8), and the pickup roller 33 and the paper feeding belt 34 are rotationally driven.

  The document set on the document feed tray 29 is usually fed to the nip portion between the feed belt 34 and the separation roller 35 by a pickup roller 33. Only the uppermost one of the plurality of documents is separated by the separation roller 35 and conveyed toward the registration roller pair 36. At that time, after the leading edge of the original is detected by the paper feed sensor S 1, the original is conveyed by a predetermined distance, and then the rotation of the pickup roller 33 and the paper feed belt 34 is stopped by the operation of the roller drive motor 77 being stopped. Primary feeding ends. The document that has been primarily fed is stopped in a state in which the leading end is pressed against the nip portion of the registration roller pair 36 and the leading end is bent.

  Secondary feeding is started after a predetermined time has elapsed since the completion of primary feeding. That is, the registration roller pair 36 is rotationally driven by the operation of a secondary paper feed drive motor (not shown). The original is conveyed toward the discharge roller pair 43 through the automatic reading glass 25b by the registration roller pair 36, the conveyance roller pairs 37 to 39, and the CIS roller 41, and finally the original is discharged by the discharge roller pair 43. It is discharged onto the tray 32. At this time, the completion of image reading of one original is detected by detecting passage of the rear end of the original by the discharge sensor S2.

  Here, the discharge sensor S2 has a count function for counting the number of documents every time the document conveyance is completed. If the paper feed sensor S1 detects a subsequent document, the second and subsequent document conveyance is performed as described above. Will continue as well. The original is conveyed while being lightly pressed toward the automatic reading glass 25b when passing through the automatic reading glass 25b, and the image of the original is read through the automatic reading glass 25b (see FIG. 1). It can be read by.

  When reading a double-sided document, a contact image sensor 51 provided opposite to the CIS roller 41 reads an image on the back side of the document, and an automatic reading glass 25b reads an image on the surface of the document. After the image on the surface of the document is read by the reading glass 25b, the document is distributed to the reversing tray 30 by the branching claws 47a, 47b, and 47c, the reversing roller pair 42 is reversed, and the back surface of the document is turned up again. There is a two-stage reading method in which the image is conveyed to the upstream side of the registration roller pair 36 and the image on the back side of the document is read by the automatic reading glass 25b.

  Reading by the contact image sensor 51 can shorten the reading time, but is inferior in image quality as compared with reading by the automatic reading glass 25b. For this reason, a one-step reading method using the contact image sensor 51 is used for text originals, and a two-step reading method using the reverse tray 31 is used when high-quality and high-definition reading is required for photo originals. It is preferable.

  When the two-stage reading method is used, when the original after reading is sequentially discharged to the original discharge tray 32 as it is, the discharged original is stacked with the reverse side of the state set on the original feed tray 29. It will be. Therefore, after the image on the back side of the document is read by the automatic reading glass 25 b, the branching claws 47 a to 47 c are swung to introduce the document again onto the reversing tray 31, via the conveying roller pair 40 and the discharge roller pair 43. The document is discharged to the document discharge tray 32. As a result, the front and back of each document are reversed again before being discharged, so that they can be stacked on the document discharge tray 32 while maintaining the state of being set on the document feed tray 29.

  FIG. 3 is a perspective view of the periphery of the paper feed mechanism of the document conveying device. The lift plate 45 is supported so as to be rotatable up and down around a fulcrum 52. The pickup roller 33, the paper feed belt 34, the drive roller 44 a, and the driven roller 44 b are unitized in the frame 53, and the drive force of the drive roller 44 a is transmitted to the pickup roller 33 via the drive transmission belt 48. . The frame 53 is supported so as to be rotatable up and down around the rotation axis of the drive roller 44a.

  An upper surface detection sensor 50 that detects the position of the upper surface of the document by detecting the height of the pickup roller 33 is disposed above the side surface of the frame 53. The upper surface detection sensor 50 is a PI (photo interrupter) sensor in which a detection unit including a light emitting unit and a light receiving unit is provided on the opposed inner surfaces of a U-shape in plan view. When the light-shielding plate 54 protruding from the side surface of the frame 53 passes through the detection unit and blocks or opens the optical path, the light-receiving signal level of the detection unit is switched to LOW or HIGH, and the height of the pickup roller 33 is changed. That is, the upper surface position of the document can be detected.

  4 and 5 are perspective views of the lift plate lifting mechanism as seen from the outside and inside of the apparatus. A protrusion 55 is provided on the side surface of the lift plate 45, and a swinging end of an arm member 57 whose one end is rotatably supported is in contact with the upper surface of the protrusion 55. An eccentric cam 60 is in contact with the upper surface of the arm member 57. The lift plate drive motor 61 transmits drive force to the eccentric cam 60 via the drive output gear 63, idle gears 65 and 66, drive input gear 67 and drive input shaft 68. As the lift plate drive motor 61, a pulse motor such as a stepping motor capable of accurately controlling the rotation amount by the number of drive pulses is used.

  Above the drive input gear 67, a lower limit detection sensor 71 for detecting the lower limit position of the lift plate 45 is disposed. The lower limit detection sensor 71 is a PI sensor similar to the upper surface detection sensor 50, and the light path of the detection unit is blocked by a flag 70 protruding from a part of the outer peripheral surface of the drive input gear 67, and the light reception signal of the lower limit detection sensor 71. When LOW becomes LOW, it is possible to detect a state in which the large diameter portion of the eccentric cam 60 contacts the arm member 57 and the lift plate is lowered to the lower limit position. In addition, as the upper surface detection sensor 50 and the lower limit detection sensor 71, a sensor other than the PI sensor may be used.

  6 is a side view of the paper feed mechanism showing a state where the lift plate is lowered or raised, FIG. 7 is a side view of the lift plate drive mechanism when the lift plate is lowered or raised, and FIG. FIG. 9 is a flowchart showing a document conveyance control procedure in the document conveyance device of the present invention. Lifting control of the lift plate will be described according to the steps in FIG. 9 with reference to FIGS.

  First, when a predetermined number of documents are set on the document feed tray 29 and a print start signal is received by the control unit 75 by a user operation (step S1), the lower limit detection sensor 71 as shown in FIG. Check that the lift plate 45 is in the lower limit position. At this time, as shown in FIG. 7 (a), the arm member 57 is in contact with the large diameter portion of the eccentric cam 60, and the flag 70 shields the detection portion of the lower limit detection sensor 71 so that the light reception signal becomes the LOW level. It has become.

  Next, the lift plate drive motor 61 is rotationally driven by the control signal transmitted from the control unit 75, and the eccentric cam 60 rotates counterclockwise from the state of FIG. 7A, as shown in FIG. 7B. The small diameter portion of the eccentric cam 60 contacts the arm member 57. As a result, as shown in FIG. 6B, the lift plate 45 is rotated upward about the fulcrum 52 by the biasing force of the spring 73 (step S2).

  Next, it is determined whether or not the ON state of the upper surface detection sensor 50 has been detected (step S3). When the upper surface of the document pushes up the pickup roller 33 as the lift plate 45 is raised, the frame 53 is also raised by a predetermined amount, and the light shielding plate 54 that has shielded the detection portion of the upper surface detection sensor 50 moves upward to open the optical path. To do. At this time, the light reception signal of the upper surface detection sensor 50 is switched from LOW to HIGH level (sensor ON state).

  When the detection signal from the upper surface detection sensor 50 is transmitted, the control unit 75 transmits a control signal to the lift plate drive motor 61 to stop the rotation (step S4). At the same time, the timer 81 measures the time from the detection timing by the upper surface detection sensor 50 to the motor stop timing (step S5). Here, since the lift plate 45 has been lifted excessively by the measured time, the lift plate drive motor 61 is reversed by a predetermined amount to lower the lift plate 45 to the reference paper feed position (step S6). The lowering amount of the lift plate 45 (the reverse rotation amount of the lift plate drive motor 61) based on the time from the detection by the upper surface detection sensor 50 to the motor stop is determined by a through-down table stored in the storage unit 80 in advance.

  Next, a control signal is transmitted from the controller 75 to the roller drive motor 77, and the pickup roller 33 and the paper feed belt 34 are rotated clockwise in FIG. 6 via the drive roller 44a to convey the document (step S7). ). Then, a predetermined time elapses after the leading edge of the document passes the paper feed sensor S1 (see FIG. 2), that is, the timing when the leading edge of the document is pressed against the nip portion of the registration roller pair 36 and the leading edge is bent. Thus, a control signal is transmitted to the roller drive motor 77, and the rotation of the pickup roller 33 and the paper feed belt 34 is stopped (step S8). In the case of single-side reading, the original stopped by the registration roller pair 36 is conveyed to the automatic reading glass 25b by the conveyance roller pairs 37 to 39 and the CIS roller 41, and the image is read. To be discharged.

  Thereafter, it is determined whether or not the reading of the document set on the document feeding tray 29 has been completed (step S9). When all the documents have been read, the lift plate 45 is lowered to the lower limit position. The process is terminated as it is. On the other hand, if the reading operation continues, the process returns to step S7, and the same procedure is repeated thereafter (steps S7 to S9).

  According to the above control procedure, it is possible to correct an excessive increase (overrun) of the lift plate 45 caused by a time lag from the detection timing of the upper surface detection sensor 50 until the lift plate drive motor 61 stops. Therefore, even in a high-speed machine that uses the lift plate drive motor 61 at a high rotation, the lift plate 45 can be accurately arranged at the reference paper feed position, and it is possible to effectively generate rubbing noise between documents and double feed of documents. Can be suppressed.

  Since the reference paper feed position for stopping the lift plate 45 is determined by the detection result of the upper surface detection sensor 50, the pressure contact force of the pickup roller 33 is maintained even when the amount of originals loaded on the original paper feed tray 29 increases or decreases. There is no risk of change.

  The lower limit position of the lift plate 45 may be set as appropriate according to the document size and thickness, or the specifications of the paper feed mechanism. For example, it may be a position where the pressure contact force of the pickup roller 33 is alleviated without lowering to a position where the upper surface of the document and the pickup roller 33 are completely separated. However, if the upper surface of the document and the pickup roller 33 are in contact with each other, there is a possibility that paper will be double fed due to friction. Therefore, it is preferable to lower the lift plate 45 to a position where the upper surface of the document and the pickup roller 33 are completely separated from each other.

  In the above control example, the lowering amount of the lift plate 45 is determined based on the time from the detection timing of the upper surface detection sensor 50 measured by the timer 81 to the motor stop timing, but the upper surface detection sensor is determined by the pulse counter 82. The number of drive pulses of the lift plate drive motor 61 from the detection timing by 50 to the motor stop timing may be counted, and the lift plate drive motor 61 may be reversely rotated by the counted number of pulses.

  In the above embodiment, the lower limit position of the lift plate 45 is determined based on the detection result of the lower limit detection sensor 71. However, the lowering position of the lift plate 45 is a position where the upper surface of the document and the pickup roller 33 are separated from each other. It is sufficient that the control is not strictly required as compared with the paper feed position. For example, the control may be performed by the drive amount (rotation speed) of the lift plate drive motor 61.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, a unit in which the pickup roller 33 and the paper feeding belt 34 are unitized is used, but the pickup roller 33 may be provided separately from the paper feeding belt 34. A configuration in which a paper feed roller is disposed in place of the paper feed belt 34 and a configuration in which a separation pad is disposed in place of the separation roller 35 are also possible.

  In the above embodiment, the lift plate 45 is moved up and down by the lift plate drive motor 61, the drive input gear 63, the idle gears 65 and 66, the drive output gear 67, the eccentric cam 60, the arm member 57, and the spring 73. The lift mechanism that lifts and lowers the lift plate 45 may have another configuration. For example, a drive coupling mechanism may be provided at the rotation fulcrum 52 of the lift plate 45 and the lift plate 45 may be directly connected to the motor and lifted. Further, the document feed tray 29 itself may be lifted and lowered so that the upper surface of the document is pressed against the pickup roller 33 without providing the lift plate 45.

  In the above-described embodiment, the document conveying apparatus that sequentially conveys a plurality of sheet documents has been described as an example. However, the sheet feeding apparatus of the present invention is a sheet feeding cassette 10a illustrated in FIG. 1 used as a sheet supply source. Of course, the present invention can also be applied to the inserter 10b, the manual feed tray 10c, and the inserter device disposed as a reduction in the supply of slip sheets between the image forming apparatus and the sheet post-processing apparatus.

  According to the present invention, a paper stacking plate that can be moved up and down on which the paper is stacked and a top surface of the paper stacked on the paper stacking plate are pressed against each other, and the press contact surface is moved in a predetermined direction to sequentially send the paper. Means, elevating means for elevating and lowering the paper stacking plate, control means for controlling the driving of the elevating means, and upper surface detecting means for detecting the upper surface of the paper stacked on the paper stacking plate. When the stacking plate is raised to the reference sheet feeding position, the deviation amount from the reference sheet feeding position is calculated based on the timing when the upper surface detection unit detects the upper surface of the sheet by the control unit and the timing when the lifting unit stops. This is a paper feeding device that lowers the paper stacking plate by the amount of misalignment.

  As a result, even in high-speed machines, the paper stacking plate can be accurately placed at the reference paper feed position, and it is possible to effectively generate paper double feed and friction between paper due to fluctuations in the paper feed position. A sheet feeding device capable of being suppressed can be provided. When calculating the amount of deviation from the reference paper feed position, a time measuring unit that measures the time from when the upper surface detecting unit detects the upper surface of the paper until the lifting unit stops, or a pulse motor as a drive source for the lifting unit Can be performed by using a counting unit that counts the number of pulses from when the upper surface detecting unit detects the upper surface of the sheet to when the lifting unit stops.

  In addition, when the paper feeding device of the present invention is installed, an image forming apparatus that effectively suppresses the occurrence of double feeding and rubbing noise when transporting paper and originals and performs a stable paper feeding operation and original transportation operation is provided. It becomes possible.

FIG. 2 is a side sectional view showing the overall configuration of the image forming apparatus on which the document conveying device of the present invention is mounted. These are side sectional views showing the internal structure of the document conveying device of the present invention. FIG. 4 is a perspective view of the periphery of a paper feed mechanism of the document conveying device. These are the perspective views which looked at the raising / lowering mechanism of the lift board from the apparatus outer side. These are the perspective views which looked at the raising / lowering mechanism of the lift board from the apparatus inner side. These are side views of the paper feed mechanism showing a state in which the lift plate is lowered or raised. These are side views of the lift plate drive mechanism when the lift plate is lowered or raised. FIG. 5 is a block diagram illustrating a control path of a paper feed mechanism. These are the flowcharts which show the document conveyance control procedure by the document conveyance device of the present invention. These are graphs showing conventional through-up / through-down control in which a motor is driven and stopped based on a detection signal. Changes the height of the document feed position when 100 documents are set on the document feed tray in a conventional document feeder and the lift plate provided at the downstream end of the tray is raised to feed the document. It is a graph which shows.

Explanation of symbols

27 Document feeder (paper feeder)
29 Document feed tray 30 Reverse tray 32 Document discharge tray 33 Pickup roller (sending means)
34 Paper feed belt 35 Separating roller 45 Lift plate (paper stacking plate)
50 Upper surface detection sensor (upper surface detection means)
53 Frame 57 Arm member 60 Eccentric cam 61 Lift plate drive motor (lifting means)
71 Lower limit detection sensor 73 Spring (lifting means)
75 Control unit (control means)
77 Roller drive motor 81 Timer (time measuring means)
82 Pulse counter (counting means)
100 Image forming apparatus

Claims (4)

A paper stacking plate that can be moved up and down to load paper;
A sending means which is pressed against the upper surface of the paper stacked on the paper stacking plate, and sequentially sends the paper by moving the press contact surface in a predetermined direction;
Elevating means for elevating and lowering the paper stacking plate;
Control means for controlling the drive of the lifting means;
Upper surface detection means for detecting the upper surface of the paper stacked on the paper stacking plate;
In a paper feeder provided with
The control means, when raising and lowering the paper stacking plate to the reference paper feeding position by the lifting and lowering means, is based on the timing when the upper surface detecting means detects the upper surface of the paper and the timing when the lifting and lowering means stops. A sheet feeding device characterized by calculating a deviation amount from the sheet and lowering the sheet stacking plate by the calculated deviation amount.   2. The sheet feeding device according to claim 1, further comprising a time measuring unit that measures a time from when the upper surface detecting unit detects the upper surface of the paper until the lifting unit stops.   A pulse motor is used as a driving source for the lifting and lowering means, and a counting means for counting the number of pulses from when the upper surface detecting means detects the upper surface of the paper until the lifting and lowering means stops is provided. Item 2. The sheet feeding device according to Item 1.   An image forming apparatus comprising the sheet feeding device according to claim 1.

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