JP2005154073A - Sheet conveying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet conveying device capable of improving the tilt correcting capacity and front-edge detecting accuracy of the sheet even when the tilt of the sheet is corrected by a front-edge detecting means, and to provide an image forming device having this. <P>SOLUTION: The front-edge of the sheet P is detected by detecting means 46 and 45a based on a turn of an abutting member 45 that is energized in the opposite direction to the sheet conveying direction, abuts on the conveyed sheet P, pressed by the sheet P, and turns against the energizing force. An abutting section 45b abutting on the sheet is disposed on the abutting member 45, a predetermined angle is formed between an upstream-side sheet conveying passage R1 disposed on the upstream side in the sheet conveying direction of the abutting section 45b and a conveying direction of the sheet P conveyed with the abutting member 45 pressed. Thus, when the sheet P travels through the upstream-side sheet conveying passage R1 and when the abutting member 45 pressed by the sheet P turns to a sheet front-edge detecting position by the detecting means 46 and 45a, the sheet P abuts on the abutting section 45b substantially rectangularly. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to an apparatus in which skew feeding of a sheet is corrected by a leading edge detecting unit that detects the leading edge of the sheet.

  Conventional image forming apparatuses such as printers, facsimiles, and copiers include a sheet conveying device that conveys a sheet to an image forming unit. Such a sheet conveying device is provided before conveying a sheet to the image forming unit. Skew correction means for correcting the skew of the sheet is provided. As the skew correction means, there is a configuration in which a shutter is provided between the conveying rollers, and the skew of the sheet is corrected by resistance when the leading edge of the sheet is brought into contact with the shutter and the shutter is rotated (for example, , See Patent Document 1).

  Further, in such a sheet conveying apparatus, the sheet leading end is abutted against the abutting surface of the abutting member that constitutes the leading end detecting unit that detects the leading end of the sheet and is perpendicular to the sheet conveying direction. In some cases, the skew of the sheet is corrected by the leading edge detection means by correcting the skew of the sheet along the contact surface.

  FIG. 9 is a diagram for explaining the configuration of the leading edge detecting means of such a sheet conveying apparatus, in which 103 is a conveying roller attached to the roller shaft 103a, and 102 is attached to the roller shaft 102a. 103 is a roller in contact with 103. The sheet P is conveyed while being sandwiched between the conveying roller 103 and the roller 102.

  Reference numeral 100 denotes a contact member rotatably attached to the roller shaft 102a. The contact member 100 protrudes upstream in the sheet conveyance direction of the nip portion between the conveyance roller 103 and the roller 102. It has. The contact member 100 is urged to rotate in a direction opposite to the sheet conveying direction by a spring (not shown) attached to the roller shaft 102a.

  Reference numeral 105 denotes a sensor flag integrally provided at one end of the abutting member 100. Reference numeral 104 denotes a photosensor. When the abutting member 100 is at the position shown in FIG. The light is shielded by 105. The photo sensor 104 and the contact member 100 constitute a tip detection means.

  Here, in the conventional sheet conveying apparatus provided with such a leading edge detecting means, when the sheet P is conveyed and the sheet P hits the contact portion 100a, first, when the sheet P is skewed, The sheet P follows the abutting portion 100a of the abutting member 100 that is biased so as to rotate in the direction opposite to the sheet conveying direction, thereby correcting skew.

  After the skew is corrected in this way, when the conveying force of the sheet P exceeds the urging force of the spring, the sheet P is pressed and the contact member 100 rotates in the direction opposite to the urging direction of the spring. . As a result, the leading edge of the sheet reaches the nip portion between the conveying roller 103 and the roller 102a, and then the sheet P is nipped and conveyed by the conveying roller 103 and the roller 102.

  On the other hand, when the contact member 100 rotates in the direction opposite to the spring biasing direction in this way, the light shielding by the sensor flag 105 is released, and thus the photosensor 104 can detect the leading end position of the sheet P, As a result, a control unit (not shown) can measure the timing of outputting the image data and can detect the size of the sheet.

JP 09-183539 A

  However, in the conventional sheet conveying apparatus provided with the leading edge detecting means that also functions as the skew correction mechanism as described above, for example, as shown in FIG. When detecting the leading edge of the sheet, the abutting portion 100a has an angle with respect to the normal direction of the sheet conveying direction, and the leading edge detection position of the sheet depends on the rigidity or type of the sheet. There was a problem of variation.

  For example, in FIG. 11, when the contact member 100 is rotated to a position where the front end of the sheet P is detected by the photosensor 104, the contact portion 100 a is moved in the conveyance direction of the sheet P by an angle d that the contact member 100 is rotated. In this case, if the length of the contact portion 100a in the vertical direction is x, the leading edge detection position of the sheet P varies by a maximum of x · sind.

  In order to solve this problem, if the abutting portion 100a is configured to abut against the sheet P at a right angle when detecting the leading edge of the sheet, the abutting portion 100a is in the sheet conveyance direction during skew correction. The sheet abuts against the sheet P while being inclined to the upstream side in the sheet conveying direction by an angle d with respect to the normal direction, and the skew correction ability is reduced. That is, when the leading edge detection unit also serves as a skew correction mechanism, there is a problem that it is difficult to achieve both the skew correction capability and the sheet leading edge detection accuracy.

  Accordingly, the present invention has been made in view of such a current situation, and even when correcting the skew of the sheet by the leading edge detection means, the sheet can improve the skew correction ability and the leading edge detection accuracy of the sheet. It is an object of the present invention to provide a transport device and an image forming apparatus including the transport device.

  The present invention provides an abutting member that is urged in a direction opposite to a sheet conveying direction and abuts on the conveyed sheet, and that is pressed by the sheet and rotates while resisting the urging force, and the abutting member A leading edge detecting means having a detecting means for detecting the leading edge of the sheet based on the rotation; a contact portion provided on the contact member and contacting the sheet; and an upstream side in the sheet conveying direction of the contact portion An upstream sheet conveying path through which the sheet passes, and a contact member pressed by the sheet when the sheet passes through the upstream sheet conveying path and a sheet leading edge by the detection means When the sheet is rotated to the detection position, the upstream sheet conveyance path and the conveyance direction of the sheet conveyed while pressing the abutting member form a predetermined angle so that the sheet abuts on the abutting portion at a substantially right angle. Like The one in which the features.

  According to the present invention, a predetermined angle is formed between the upstream sheet conveyance path provided on the upstream side in the sheet conveyance direction of the contact portion and the conveyance direction of the sheet that moves while pressing the contact member. When the sheet passes through the sheet conveyance path, and when the contact member pressed by the sheet is rotated to the sheet leading edge detection position by the detection means, the sheet is brought into contact with the contact portion at a substantially right angle, Even when the skew of the sheet is corrected by the leading edge detection means, the skew correction capability and the accuracy of detecting the leading edge of the sheet can be improved.

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

  FIG. 8 is a diagram showing a schematic configuration of a color laser printer which is an example of an image forming apparatus provided with the sheet conveying apparatus according to the first embodiment of the present invention.

  In the figure, A is a color laser printer, and B is a color laser printer main body (hereinafter referred to as a printer main body). The printer main body B includes an image forming unit C for forming an image on a sheet P and an image forming unit C. A sheet conveying device D that conveys the sheet P and a fixing unit 50 are provided.

  Here, the image forming unit C is arranged in the vertical direction, and includes process stations C1 to C4 that form toner images of four colors of yellow (Y), magenta (M), cyan (S), and black (Bk), respectively. I have. The process stations C1 to C4 include a photosensitive drum 21 (21Y, 21M, 21C, and 21Bk) that is an image carrier that carries toner images of four colors of yellow, magenta, cyan, and black, and a photosensitive drum. A charging roller 23 (23Y, 23M, 23C, 23Bk), which is arranged around the rotation direction 21 and uniformly charges the surface of the photosensitive drum, and a constant speed by irradiating a laser beam based on image information The scanner 1 (1Y, 1M, 1C, 1Bk) for forming an electrostatic latent image on the photosensitive drum rotating in Step 1, yellow, magenta, cyan and black toners are applied to the electrostatic latent image formed on the photosensitive drum. A developing unit 2 (2Y, 2M, 2C, 2Bk) and the like that are attached and visualized as a toner image are provided.

  The photosensitive drum 21 is configured by applying an organic photoconductive layer on the outer side of an aluminum cylinder, and is rotated counterclockwise in accordance with an image forming operation by a drive motor (not shown). Further, the developing unit 2 is adjacent to the toner storage container 24 (24Y, 24M, 24C, 24Bk) that stores toners of black, cyan, magenta, and yellow, respectively, and the surface of the photosensitive drum, and is driven by a drive unit (not shown). It comprises a developing sleeve 22 (22Y, 22M, 22C, 22Bk) that is driven to rotate in the direction opposite to that of the photosensitive drum 21 and that develops with each color toner by applying a developing bias voltage from a developing bias power source (not shown). Is done.

  The photosensitive drum 21 is rotatably supported by the toner storage container 24 of the developing unit 2. Further, the developing unit 2 is detachably attached to the printer main body B so that it can be easily replaced according to the life of the photosensitive drum 21.

  The sheet conveying device D is provided at the lower part of the printer main body, and includes a sheet feeding cassette 7 that stores a plurality of sheets P, a sheet feeding roller 41 that sends out the sheets P stacked and stored in the sheet feeding cassette 7, and a sheet feeding roller. A separation pad 42 for separating the sheet P fed from 41, a paper feed guide 43, a registration roller pair 44, and the like are provided.

  When the image forming operation is started, the sheet P is separated and fed one by one from the sheet feeding cassette 7 by the sheet feeding roller 41 and the separation pad 42, and conveyed to the registration roller pair 44 along the sheet feeding guide 43. Further, it is conveyed to the image forming portion C by the registration roller pair 44.

  In the figure, reference numeral 35 denotes an intermediate transfer member that is stretched around the drive roller 31, the secondary transfer counter roller 32 and the tension roller 33, and is driven to rotate in the direction of the arrow in synchronization with the outer peripheral speed of the photosensitive drum 21. The intermediate transfer belt 35 is moved along the arrangement direction of the process stations C1 to C4, and has four intermediate transfer belts 35 sandwiched with the respective photosensitive drums 21 inside. A primary transfer roller 34 (34Y, 34M, 34C, 34Bk) constituting the primary transfer portion T1 (T1Y, T1M, T1C, T1Bk) is disposed.

  These primary transfer rollers 34 are connected to a power supply for transfer bias (not shown). By applying a transfer bias from the primary transfer roller 34 to the intermediate transfer belt 35, the respective color toner images on the photosensitive drums are sequentially formed. Multiple transfer is performed on the intermediate transfer belt 35, and a full color image is formed on the intermediate transfer belt 35.

  Here, in the present embodiment, the intermediate transfer belt 35 is formed of a seamless resin belt having a circumferential length of about 620 mm. Further, both ends of the tension roller 33 are held by springs, so that even if the peripheral length of the intermediate transfer belt 35 changes due to changes in temperature, humidity, and time in the printer body, the amount of change can be absorbed. ing.

  Reference numeral 51 denotes a secondary transfer roller disposed so as to face the secondary transfer counter roller 32. The secondary transfer roller 51 abuts on the lowermost surface of the intermediate transfer belt 35 and is registered by the registration roller pair 44. The conveyed sheet P is nipped and conveyed together with the intermediate transfer belt 35.

  The transfer roller 51 has a configuration in which a metal shaft is wound with a medium resistance foamed elastic body, and is moved to an upper position by a cam member (not shown) in accordance with the timing of transferring a color image to the sheet P. The intermediate transfer belt 35 is pressed against the intermediate transfer belt 35 through P. When pressed against the intermediate transfer belt 35 in this way, a transfer bias is applied to the transfer roller 51, whereby the toner image on the intermediate transfer belt 35 is transferred to the sheet P. Since the intermediate transfer belt 35 and the transfer roller 51 are respectively driven, the sheet P sandwiched between the two is conveyed toward the fixing unit 50 at a predetermined speed at the same time as the transfer process is performed. .

  The fixing unit 50 fixes the toner image formed on the sheet P via the intermediate transfer belt 35 to the sheet P. The fixing sleeve 63 for applying heat to the sheet P and the sheet P are attached to the fixing sleeve 63. And a pressure roller 62 for press contact. The sheet P holding the toner image is conveyed by the fixing sleeve 61 and the pressure roller 62 and is applied with heat and pressure, whereby the toner image is fixed to the sheet P.

  Next, an image forming operation of the color laser printer configured as described above will be described.

  When the image forming operation is started, first, the sheet P stored in the paper feed cassette 7 is separated and fed one by one by the paper feed roller 41 and the separation pad 42, and a pair of registration rollers is fed along the paper feed guide 43. 44. Then, as will be described later, the sheet P is corrected for skewing and the leading edge position is detected by a leading edge detection unit also serving as a skew feeding correction mechanism provided in the registration roller pair 44.

  Then, when the leading edge of the sheet is detected by the leading edge detecting means in this manner, a control unit (not shown) first irradiates the yellow image with the laser by the scanner 1Y to form a yellow latent image on the photosensitive drum, Simultaneously with the formation of the latent image, the developing sleeve 22Y is driven, and a yellow voltage is applied by applying a voltage having the same polarity as the charging polarity of the photosensitive drum 21Y so that the yellow toner adheres to the latent image on the photosensitive drum. I do. Thereafter, at the first transfer position T1Y, a voltage having a reverse characteristic to that of yellow toner is applied to the intermediate transfer belt 35 by the primary transfer roller 34Y so that the yellow toner image on the photosensitive drum is placed on the outer periphery of the intermediate transfer belt 35. Primary transfer.

  Next, the laser irradiation of the magenta image is started by the scanner 1M so that the leading edge of the yellow image on the outer periphery of the intermediate transfer belt 35 coincides, and the magenta toner image is formed on the latent image on the photosensitive drum 21M in the same manner as yellow. The developed magenta toner image on the photosensitive drum 21M is transferred onto the intermediate transfer belt 35 at the first transfer position T1M.

  Next, laser irradiation of the cyan image is started by the scanner 1C so that the yellow on the outer periphery of the intermediate transfer belt 35 and the leading edge of the magenta image coincide with each other, and cyan toner is applied to the latent image on the photosensitive drum 21C in the same manner as magenta. The image is developed, and the cyan toner image on the photosensitive drum 21C is transferred onto the intermediate transfer belt 35 so as to overlap the yellow and magenta toner images at the first transfer position T1C.

  Next, laser irradiation of the black image is started by the scanner 1K so that the leading edges of the yellow / magenta / cyan images on the outer periphery of the intermediate transfer belt 35 coincide with each other, and the latent image on the photosensitive drum 21K is formed in the same manner as cyan. The black toner image is developed, and the black toner image on the photosensitive drum 21K is further transferred onto the intermediate transfer belt 35 at the first transfer position T1K. As a result, a full color image is formed on the intermediate transfer belt 35.

  The full-color image formed on the intermediate transfer belt 35 in this way is the sheet P conveyed to the nip portion (secondary transfer portion 2T) between the secondary transfer roller 51 and the intermediate transfer belt 35 by the registration roller 44. When passing through the nip portion between the secondary transfer roller 51 and the intermediate transfer belt, the image is secondarily transferred to the sheet P by a transfer bias applied to the secondary transfer roller 51.

  Next, the sheet P onto which the toner image has been transferred in this manner is nipped and conveyed by the secondary transfer roller 51 and the intermediate transfer belt 35 and then conveyed to the fixing device 50 by the conveying belt 52. By being pressurized, the toner image is fixed. Note that after the image is fixed in this manner, the sheet P is discharged to a discharge tray 56 outside the printer main body by the discharge rollers 53 to 55.

  In the present embodiment, as shown in FIG. 1, the registration roller pair 44, which is a pair of conveyance rollers, is attached to the conveyance roller 44b attached to the roller shaft 44c and the roller shaft 44d, and contacts the conveyance roller 103. The sheet P is conveyed while being held between the conveying roller 44b and the roller 44a.

  In the figure, reference numeral 45 denotes a registration shutter which is a contact member rotatably attached to the roller shaft 44d. The registration shutter 45 is upstream of the sheet conveyance direction of the nip portion between the conveyance roller 44b and the roller 44a. The contact part 45b which protrudes in is provided. The registration shutter 45 is urged to rotate in a direction opposite to the sheet conveying direction by a spring (not shown) attached to the roller shaft 44d.

  Reference numeral 45a denotes a sensor flag integrally provided at one end of the registration shutter 45. Reference numeral 46 denotes a photosensor that constitutes a detection unit together with the sensor flag 45a. The sensor flag 45a and the photosensor 46 constitute the detection unit. The registration shutter 45 constitutes a tip detection means.

  The photo sensor 46 is configured such that the sheet P conveyed along the paper feed guide 43 from the position shown in FIG. 7 abuts (contacts) the contact portion 45b of the registration shutter 45. Until the sheet P is pressed against the urging force of a spring (not shown) and rotated by an angle d1 as shown in FIG. 2, the sensor flag 45a shields the light. Reference numeral 49 denotes a conveyance guide provided downstream of the registration roller pair 44.

  In the registration shutter 45 configured as described above, when the conveyed sheet P hits the contact portion 45b, first, when the sheet P is skewed, the sheet P is in a direction opposite to the sheet conveying direction. It follows the abutting portion 45b of the registration shutter 45 that is biased to rotate in the direction, thereby correcting the skew.

  After the skew is corrected in this way, when the conveying force of the sheet P exceeds the urging force, the registration shutter 45 rotates in the direction opposite to the urging direction. As a result, the leading edge of the sheet reaches the nip portion between the conveyance roller 44b and the roller 44a, and thereafter, is nipped and conveyed by the conveyance roller 44b and the roller 44a.

  On the other hand, when the registration shutter 45 rotates in the direction opposite to the biasing direction in this way, the sensor flag 45a also moves, and eventually the light shielding by the sensor flag 45a is released as shown in FIG. As a result, the photo sensor 46 can detect the leading end position of the sheet P, and as a result, a control unit (not shown) can measure the timing of outputting image data and can detect the size of the sheet. .

  In addition, after detecting the leading edge position of the sheet by the rotation of the registration shutter 45 as described above, the registration shutter 45 is further rotated in the same direction by the conveying force of the sheet P, and the state shown in FIG. Thereafter, when the sheet P passes through the registration roller pair 44, the registration shutter 45 is rotated in the direction of arrow F opposite to the conveyance direction of the sheet P by a spring (not shown) to return to the standby position.

  In FIG. 1 to FIG. 3, R1 is an upstream sheet conveyance path provided on the upstream side of the contact portion 45b of the registration shutter 45 and formed by a conveyance guide 43 through which the sheet P passes. The conveyance direction of the sheet P conveyed while pressing the conveyance path R1 and the registration shutter 45, that is, the tangential direction of the registration roller pair 44 forms a predetermined angle.

  In the present embodiment, the upstream sheet conveying path R1 is inclined toward the downstream, and the tangential direction of the registration roller pair 44 that is substantially horizontal is an angle d2 as shown in FIG. Is made. In this way, the upstream sheet conveyance path R1 is inclined toward the downstream, so that the sheet P that has passed through the upstream sheet conveyance path R1 comes into contact with the contact portion 45b obliquely from above. At this time, the registration shutter 45 is held by a stopper (not shown) at a standby position where the contact portion 45b comes into contact with the sheet P that strikes obliquely from above at a right angle.

  When the registration shutter 45 is in such a standby position, the registration shutter 45 extends from the angle when the leading edge of the sheet P shown in FIG. 1 comes into contact with the photo sensor 46 shown in FIG. The relationship d1 = d2 is established between the rotation angle d1 and the angle d2 formed between the upstream sheet conveyance path R1 and the tangential direction of the substantially horizontal registration roller pair 44.

  By configuring the registration shutter 45 and the upstream sheet conveyance path R1 in this way, when the sheet P is conveyed from obliquely upward toward the registration shutter 45, the sheet P is first contacted as shown in FIG. When the sheet P is in a skewed contact with the right angle 45b and the sheet P is skewed, the skew is corrected by the registration shutter 45.

  Then, after the skew is corrected in this way, the registration shutter 45 is rotated by being pressed by the sheet P, and finally the light shielding of the photosensor 46 by the sensor flag 45a is released, and the state shown in FIG. Detects the tip position of the sheet P.

  At this time, the contact between the sheet P and the registration shutter 45 is detected also when the front end position of the sheet P is detected in the same manner as the moment when the front end of the sheet P contacts the registration shutter 45 due to the relationship of d1 = d2. As shown in FIG. 2, the contact portion 45b can contact at a perpendicular angle with respect to the sheet conveying direction.

  Thus, a predetermined angle (d2) is formed between the upstream sheet conveyance path R1 and the tangential direction of the registration roller pair 44, and the sheet P is pressed when the sheet P passes through the upstream sheet conveyance path R1 and by the sheet P. When the registered shutter 45 is rotated to the sheet leading edge detection position by the photosensor 46, the skew correction is performed by causing the sheet P to contact the contact portion 45b of the registration shutter 45 at a substantially right angle. In both the state and the state of FIG. 2 in which the leading edge position is detected, the skew feeding correction and the leading edge position detection can be stably performed, and the skew feeding correction capability and the sheet leading edge detection accuracy can be improved.

  In this embodiment, the position of the contact portion 45b when the registration shutter 45 detects the sheet leading edge position is closer to the downstream side of the nip portion of the registration roller pair 44 and closer to the nip portion. It is difficult to be affected by the curl of P and the stiffness and variation of the sheet P. For this reason, for example, the position of the contact portion 45b when detecting the tip position is preferably 0 to 3 mm from the nip portion of the registration roller pair 44 as shown in FIG.

  Next, a second embodiment of the present invention will be described.

  FIG. 4 is a diagram illustrating the configuration of the sheet conveying apparatus according to the present embodiment. In the figure, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  In the figure, reference numeral 45A denotes a registration shutter which is a contact member, and this registration shutter 45A includes a first contact part 45c and a second contact part 45d as contact parts as shown in FIG. Yes. That is, the registration shutter 45A has two contact portions 45c and 45d.

  Here, of the two contact portions, the first contact portion 45c is similar to the first embodiment described above in that the sheet P that has passed through the upstream sheet transport path R1 is obliquely registered from above. When the sheet P is conveyed toward 45, as shown in FIG. 4, the sheet P abuts at a right angle.

  On the other hand, after the skew is corrected, the second contact portion 45d is pressed by the sheet P, and the registration shutter 45A rotates in the direction opposite to the urging direction, and the photosensor 46 is shielded by the sensor flag 45a. When the release position is reached, that is, when the registration shutter 45A reaches the position where the leading edge of the sheet is detected, the sheet P abuts at a right angle as shown in FIG. In other words, in the present embodiment, when the leading edge of the sheet P is detected, the leading edge of the sheet comes into contact with the second contact portion 45d from the first contact portion 45c.

  By configuring the registration shutter 45A in this manner, the conveyed sheet P first strikes the first contact portion 45c. Here, when the sheet P is skewed, the sheet P follows the first contact portion 45c of the registration shutter 45A that is biased to rotate in the direction opposite to the sheet conveying direction. This corrects the skew.

  Then, after the skew is corrected in this way, when the conveying force of the sheet P exceeds the urging force, the registration shutter 45A rotates in the direction opposite to the urging direction. As a result, the leading edge of the sheet reaches the nip portion between the conveyance roller 44b and the roller 44a, and thereafter, is nipped and conveyed by the conveyance roller 44b and the roller 44a.

  On the other hand, when the registration shutter 45 rotates in the direction opposite to the urging direction in this way, the sensor flag 45a also moves, and eventually the light shielding by the sensor flag 45a is released as shown in FIG. As a result, the photosensor 46 can detect the leading end position of the sheet P, and as a result, a control unit (not shown) can measure the timing of outputting image data and can detect the size of the sheet.

  In addition, after detecting the leading end position of the sheet by the rotation of the registration shutter 45A in this way, the registration shutter 45A is further rotated in the same direction by the conveying force of the sheet P, and the state shown in FIG. Thereafter, when the sheet P passes through the registration roller pair 44, the registration shutter 45A is rotated in the direction of arrow F opposite to the conveyance direction of the sheet P by a spring (not shown) to return to the standby position.

  Incidentally, in the present embodiment, the first contact portion 45c and the second contact portion 45d of the registration shutter 45 are formed to form an angle d3 which is a predetermined angle as shown in FIG. The angle d3 is the rotation angle d1 from the position where the registration shutter 45A shown in FIG. 4 is in contact with the leading edge of the sheet P to the position where the registration shutter 44A shown in FIG. The following relationship exists between the above-described angle d2 between the upstream sheet conveyance path R1 and the tangential direction of the registration roller pair 44.

  d3 = d1-d2

  By configuring the registration shutter 45A and the upstream sheet conveyance path R1 in this way, when the sheet P is conveyed from obliquely upward toward the registration shutter 45, first, the sheet P is first as shown in FIG. When the sheet P is skewed, the skew is corrected by the registration shutter 45.

  Then, after the skew is corrected in this way, the registration shutter 45A is rotated by being pressed by the sheet P, and the shading of the photosensor 46 by the sensor flag 45a is released, and the state shown in FIG. Detects the tip position of the sheet P.

  Here, at the same time as the moment when the leading edge of the sheet P comes into contact with the registration shutter 45 due to the relationship d3 = d1−d2 described above, the sheet P and the second are also detected when the sheet leading edge position is detected. As shown in FIG. 6, the abutting portion 45d can abut at an angle perpendicular to the sheet conveying direction.

  In this way, when the sheet P passes through the upstream sheet conveyance path R1, and when the registration shutter 45A pressed by the sheet P is rotated to the sheet leading edge detection position by the photosensor 46, the sheet P is moved to the registration shutter 45A. By making contact with the contact portion 45b at a substantially right angle, the skew correction and the tip position detection can be performed stably both in the state of FIG. 4 in which the skew correction is performed and in the state of FIG. 6 in which the tip position is detected. It is possible to improve the skew correction capability and the sheet leading edge detection accuracy.

  In the present embodiment, the position of the second contact portion 45d when the registration shutter 45A detects the sheet leading edge position is not easily affected by the curl of the sheet P, the stiffness or variation of the sheet P. It is preferable that the position is on the downstream side of the nip portion of the registration roller pair 44 and closer to the nip portion.

  Further, even when the leading edge of the sheet P is in contact with the second abutting part 45d from the first abutting part 45c of the registration shutter 45A at the moment when the leading edge of the sheet P is detected, before the leading edge of the sheet P is detected. However, there is no problem with this function.

FIG. 3 is a diagram illustrating a configuration near a registration roller of the sheet conveying device according to the first embodiment of the present invention. FIG. 4 is a diagram illustrating a state when a position detection unit provided in the sheet conveying apparatus detects a leading end position of a sheet. The figure which shows a state when the sheet | seat front end position detection of the said position detection means is complete | finished. The figure explaining the structure of the registration roller vicinity of the sheet conveying apparatus which concerns on the 2nd Embodiment of this invention. FIG. 3 is a perspective view of a registration shutter that constitutes a position detection unit provided in the sheet conveying apparatus. FIG. 4 is a diagram illustrating a state when a position detection unit provided in the sheet conveying apparatus detects a leading end position of a sheet. The figure which shows a state when the sheet | seat front end position detection of the said position detection means is complete | finished. 1 is a diagram illustrating a schematic configuration of a color laser printer which is an example of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. The figure explaining the structure of the front-end | tip detection means of the conventional sheet conveying apparatus. FIG. 10 is a diagram illustrating a skew correction operation of a conventional sheet conveying apparatus. FIG. 10 is a diagram illustrating a sheet leading edge position detection operation of a conventional sheet conveying apparatus.

Explanation of symbols

43 conveyance guide 44 registration roller pair 45 registration shutter 45A registration shutter 45a sensor flag 46 photo sensor 45b (registration shutter) contact portion 45c first contact portion 45d second contact portion A color laser printer
B Printer main body C Image forming unit D Sheet conveying device R1 Upstream sheet conveying path P Sheet

Claims (9)

A contact member that is urged in a direction opposite to the sheet conveyance direction and abuts on the conveyed sheet and then rotates while resisting the urging force by being pressed by the sheet, and based on the rotation of the contact member Leading edge detecting means having detecting means for detecting the leading edge of the sheet;
A contact portion provided on the contact member and contacting the sheet;
An upstream sheet conveying path provided on the upstream side of the contact portion in the sheet conveying direction, through which the sheet passes;
With
When the sheet passes through the upstream sheet conveyance path, and when the contact member pressed by the sheet rotates to the sheet leading edge detection position by the detection means, the sheet is substantially perpendicular to the contact portion. A sheet conveying apparatus, wherein the upstream sheet conveying path and the conveying direction of a sheet conveyed while pressing the abutting member make a predetermined angle so as to contact each other.   A pair of conveyance rollers for conveying the sheet is provided, and the abutting member can be rotated about the axis of the conveyance roller pair, and the abutting portion is attached so as to protrude upstream in the sheet conveyance direction of the conveyance roller pair. The sheet conveying apparatus according to claim 1, wherein   The abutting portion abuts the sheet at a substantially right angle upstream of the pair of conveying rollers, and is substantially the same as the sheet obtained by rotating the abutting member to a sheet leading edge detecting position by the detecting means downstream of the conveying roller pair. The sheet conveying device according to claim 2, wherein the sheet conveying device abuts at a right angle.   The predetermined angle formed by the upstream sheet conveyance path and the conveyance direction of the sheet conveyed while pressing the contact member is determined by the detection unit after the sheet contacts the contact member. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is substantially equal to a rotation angle until the sheet leading edge detection position is reached. The abutment portion forms a predetermined angle with a first abutment portion that abuts the sheet at a substantially right angle upstream of the conveyance roller pair, and at the downstream of the conveyance roller pair. 4. The sheet conveying apparatus according to claim 3, further comprising a second contact portion that contacts the sheet rotated substantially to the sheet leading edge detection position by the detection means. .   The predetermined angle formed by the first contact portion and the second contact portion is a rotation angle from when the sheet contacts the contact member to when the corresponding contact member reaches the sheet leading edge detection position by the detection means. 6. The sheet conveying apparatus according to claim 5, wherein the sheet conveying apparatus is substantially equal to a difference between a moving angle and a predetermined angle formed by the upstream sheet conveying path and a conveying direction of a sheet conveyed while pressing the contact member. .   The sheet conveying apparatus according to claim 1, wherein the detection unit includes a photo sensor and a sensor flag provided on the contact member.   The sheet conveying apparatus according to claim 7, wherein a sheet leading edge position detected by the photosensor is located at a nip portion formed by the conveying roller pair or downstream of the nip portion in the sheet conveying direction. An image forming apparatus comprising: an image forming unit; and the sheet conveying device according to claim 1 that conveys a sheet to the image forming unit.

Images