JP5852704B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus.

  In an image forming apparatus such as a copying machine that forms an image on a sheet, image accuracy with respect to the sheet is an important element of image quality. When the sheet is skewed, the image accuracy deteriorates. In view of this, a skew feeding correcting means for correcting the skew feeding of the sheet is provided in a sheet transporting device that transports the sheet to the image forming unit. This corrects the skew of the sheet to improve the image accuracy.

  As an example of such skew correction means, a registration shutter system is adopted. In the resist shutter system, a sheet is abutted against a sheet abutting member positioned perpendicular to the sheet conveying direction, and the skew of the sheet is corrected by causing the leading end of the sheet to follow the abutting surface of the sheet abutting member. In such a configuration, a drive control system is not required for the skew correction, so that the cost merit is high.

  In the skew correction unit of the registration shutter system, for example, the sheet front end is placed against the registration shutter that is disposed upstream of the image forming unit in the sheet conveyance direction and applied with a predetermined biasing force, and the sheet front end is bent (looped). ). This corrects the skew of the sheet. Thereafter, when the pressing force of the sheet against the registration shutter becomes equal to or greater than the urging force, the registration shutter is pressed by the sheet and rotated toward the downstream side in the sheet conveying direction, whereby the sheet whose skew has been corrected becomes the image forming unit. It is conveyed toward.

  On the other hand, there is also a stop registration type skew correction means for correcting the skew of the sheet by stopping the rotation of the registration roller, butting the sheet against the nip portion of the registration roller and causing the leading edge of the sheet to follow the registration roller. It has been adopted. Compared with the stop resist system, the resist shutter system has the advantage that it can be conveyed with a smaller sheet interval and the productivity of the product is easy to increase.

  However, in the resist shutter system, the type of sheet that can pass through the resist shutter is limited because a loop is formed in the sheet by the biasing force of the resist shutter and the pressing force of the sheet, and the resist shutter is opened and closed. For example, if the sheet is thin paper with low rigidity (strength), even if a loop is formed, the resist shutter cannot be rotated thereafter, and a paper jam may occur. In addition, there is a similar problem because the apparent waist strength of the sheet decreases in a high humidity environment.

  Furthermore, when the biasing force of the resist shutter is set in accordance with the thin paper side, there is a problem that the skew feeding correction capability is deteriorated on thick paper having high rigidity (stretch strength).

  Further, the sheet whose skew has been corrected by the skew correction unit of the registration roller is conveyed toward the image forming unit on the downstream side of the registration roller. At this time, the sheet is conveyed downstream of the registration roller while the loop difference in the sheet width direction formed at the time of skew correction by the registration roller remains. Therefore, a slip difference occurs in the width direction in the roller nip between the sheets sandwiched between the nips of the registration rollers.

  For this reason, as the sheet whose skew has been corrected by the registration roller is conveyed to the downstream side of the registration roller, it reaches the image forming unit while gradually returning to the original skew state. In general, the sheet conveyance speed of the registration rollers is set to be faster than the sheet conveyance speed of the image forming unit.

  At this time, when the sheet is transported to the image forming unit in a state where the sheet is skewed from the registration roller, a loop difference occurs in the width direction of the sheet, and on the sheet end side where the loop amount is relatively small, There is a problem that an image transfer defect due to the sheet posture occurs.

  For this reason, there is a demand for a sheet conveying apparatus capable of correcting skew feeding of sheets without limiting the types of sheets while improving the productivity of the deliverables.

  In order to solve such a problem, in Patent Document 1, a pair of conveying rollers is provided between a transfer paper separating device including a feeding roller and the like and a registration roller. Then, the transfer paper is skewed, and one of the leading ends first hits the registration roller, and the transfer paper cannot further advance. Then, the planetary gear starts to rotate, and the rotation of the input gear is transmitted only to the opposite conveyance roller, and the rotation speed of the left and right conveyance rollers is adjusted until both ends of the transfer paper abut against the registration rollers, thereby skewing the transfer paper. A paper feeding device for correction has been proposed.

Japanese Patent Laid-Open No. 9-290936

  However, in Patent Document 1, the rotation speed of the left and right conveying rollers is adjusted until one end of the skewed sheet first hits the registration roller and then both ends of the transfer paper hit the registration roller. Then, an operation for correcting the skew of the transfer paper at a certain time is required. For this reason, since the stop time of the registration roller cannot be shortened, the sheet cannot be conveyed at a small sheet interval, and the product productivity is likely to be limited.

  SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and an object of the present invention is to obtain a good skew correction capability regardless of the sheet rigidity (waist strength) and to produce a product with a small sheet interval. It is an object of the present invention to provide a sheet conveying apparatus capable of improving the performance.

A typical configuration of a sheet conveying apparatus according to the present invention for achieving the object includes a first conveying unit that conveys a sheet, and a downstream side of the first conveying unit in the sheet conveying direction. a second conveying means for conveying the sheet conveyed by the first conveying means further disposed on the downstream side in the sheet conveyance direction than the second conveying means, conveying the sheet conveyed by said second conveying means further A second conveying unit that corrects skew of the sheet by abutting the leading end of the sheet conveyed by the first conveying unit against the second conveying unit. The conveying means is respectively rotated by a rotary differential gear that generates a differential rotation due to a difference in sheet bending tension generated in the sheet width direction due to sheet skew between the second conveying means and the third conveying means. Driving Is, has first, second driving rotary body disposed on the same axis, the rotation differential gear, a first side gear drivingly connected to said first drive rotor, the second A second side gear drivingly connected to the drive rotor, a pinion gear meshed with the first and second side gears, the first and second side gears and the pinion gear rotatably supported, and A rotating shaft of the first and second side gears arranged on the same axis, a case provided rotatably with the rotating shaft on the same axis of the first and second side gears as a revolution axis, and the first and second side gears; Differential locking means for engaging and releasing the case with the case, drive means for rotationally driving the case, and operating means for operating engagement and release of the differential locking means. To do.

  According to the above configuration, the skew correction can be performed during the sheet conveyance by the rotational differential of the plurality of driving rotating bodies due to the difference in the sheet bending tension due to the skew in the sheet width direction. As a result, it is possible to obtain a good skew correction capability regardless of the sheet rigidity (waist strength) and to improve the productivity of the product with a small sheet interval.

FIG. 4 is a cross-sectional explanatory diagram illustrating a configuration of an image forming apparatus including a sheet conveying device according to the present invention. It is a perspective explanatory drawing which shows the structure of a 2nd conveyance means. FIG. 5 is a perspective explanatory view showing a configuration in which a rotary differential gear and first and second drive rotators are drivingly connected. FIG. 4 is a partially enlarged view of FIG. 3. FIG. 10 is an explanatory plan view illustrating a state where a skewed sheet enters a nip portion of a second conveying unit while being bent. It is a figure which shows an example of the torque value given with respect to a 1st, 2nd drive rotary body by the bending of the sheet | seat conveyed diagonally between the 2nd conveying means and the 3rd conveying means. (A) is a perspective explanatory view showing the operation of the rotary differential gear when the torque resistances of the first and second drive rotors are equal, and (b) is the difference between the torque resistances of the first and second drive rotors. It is a perspective explanatory view showing the operation of the rotary differential gear in the case of occurrence of. The conveying operation of the second conveying unit is started at the timing when the leading end position of the central portion in the width direction of the sheet reaches the nip portion of the second conveying unit. In this case, the skew correction rate when the input skew of a sheet made of paper having a basis weight of 64 g is 5 mm is calculated by simulation, and this embodiment is compared with a comparative example. It is a block diagram which shows the structure of the control system of a 2nd conveyance means. (A) is sectional explanatory drawing which showed an example of the cancellation | release state of a differential lock | rock means. (B) is sectional explanatory drawing which showed an example of the engagement state of the differential lock | rock means. FIG. 10 is an explanatory plan view illustrating a state in which a skewed sheet enters a nip portion of a third conveying unit while being bent.

  An embodiment of a sheet conveying apparatus according to the present invention and an image forming apparatus having the same will be described in detail with reference to the drawings.

<Image forming apparatus>
An image forming apparatus 4 shown in FIG. 1 is an example of a digital color copying machine. The image forming apparatus 4 includes an image forming unit 1 serving as an image forming unit that forms an image on a sheet P, an image reading unit 2 disposed above the image forming unit 1, and an image reading unit 2. And a document conveying unit 3 to be placed.

  The document transport unit 3 feeds the documents D set upward on the document tray 301 one by one in order from the first page, and passes them over the platen glass 201 of the image reading unit 2 through a curved transport path. After that, it is discharged to the discharge tray 302.

  The image reading unit 2 performs an image reading process by the scanner unit 202 held at a predetermined position when the document D conveyed by the document conveying unit 3 passes from the left to the right in FIG. 1 on the platen glass 201. . Specifically, the reading surface of the document D is irradiated with the light of the lamp 203 of the scanner unit 202, and the reflected light from the document D is guided to the lens 207 via the mirrors 204 to 206. The light passing through the lens 207 is imaged on the imaging surface of the image sensor 208, converted into an electrical digital signal, and transmitted.

  Further, the image reading unit 2 lifts the document conveying unit 3 without using the document conveying unit 3 and sets the document D directly on the platen glass 201, and moves the scanner unit 202 from the left to the right in FIG. The image reading process can also be performed by scanning. That is, the image reading unit 2 does not necessarily have to be equipped with the document conveying unit 3 and may be provided with a document pressing member (not shown) that presses the document D set on the platen glass 201.

  The image forming unit 1 includes an image forming unit 10 for each color of yellow Y, magenta M, cyan C, and black Bk. The photosensitive drum 11 serving as an image carrier is uniformly charged on the surface by a charging roller 12 serving as a charging unit, and then exposed by a laser scanner 13 serving as an exposure unit that is driven based on the transmitted image information signal. Thus, an electrostatic latent image is formed. The electrostatic latent image formed on the surface of the photosensitive drum 11 is supplied with toner by a developing device 14 serving as a developing unit, and is visualized as a toner image.

  The toner image formed on the surface of the photosensitive drum 11 is given a predetermined pressure and an electrostatic load bias voltage by a primary transfer roller 17 serving as a primary transfer unit, thereby being applied to an intermediate transfer belt 31 serving as an image carrier. Sequentially transferred. After the transfer, the toner remaining on the surface of the photosensitive drum 11 is removed and collected by the photosensitive drum cleaner 15 serving as a cleaning unit, and is again prepared for the next image formation.

<Sheet conveying device>
On the other hand, the sheets P accommodated in the feeding cassette 20 are fed from the feeding cassette 20 by the feeding roller 5, separated by a separating means (not shown), and fed one by one. Then, the sheet P is nipped and conveyed by the pre-registration roller pair 22 serving as a first conveying means for conveying the sheet P. After that, the skew is skewed by a registration roller pair 23 that is disposed downstream of the pre-registration roller pair 22 in the sheet conveyance direction a and serves as a second conveyance means for further conveying the sheet P sandwiched and conveyed by the pre-registration roller pair 22. Corrected and transported.

  The leading end portion of the sheet P nipped and conveyed by the pre-registration roller pair 22 abuts on the nip portion N1 of the registration roller pair 23 of the registration unit 21 and forms a loop on the sheet P following the nip portion N1. P skew is corrected. Thereafter, the registration roller pair 23 is rotationally driven and is nipped and conveyed by the registration roller pair 23.

  Thereafter, the registration roller pair 23 conveys the sheet P between the intermediate transfer belt 31 and the secondary transfer outer roller 35 serving as a secondary transfer unit in synchronization with the toner image on the outer peripheral surface of the intermediate transfer belt 31. . The color toner images on the outer peripheral surface of the intermediate transfer belt 31 are arranged on the inner peripheral surface side of the intermediate transfer belt 31 so as to face the secondary transfer outer roller 35 and the secondary transfer outer roller 35 and the secondary transfer outer roller 35. A predetermined pressure and an electrostatic load bias voltage are applied to the nip portion N2. As a result, the toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the sheet P.

  The secondary transfer inner roller 34 and the secondary transfer outer roller 35 serving as the third transport unit are disposed downstream of the registration roller pair 23 in the sheet transport direction a, and the sheet P is nipped and transported by the registration roller pair 23. Is further conveyed downstream.

  After the toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the sheet P, the toner remaining on the outer peripheral surface of the intermediate transfer belt 31 is removed and collected by a belt cleaner 36 serving as a cleaning unit. Prepare for image formation. The toner image transferred onto the sheet P is fixed by being heated and pressed by a fixing device 40 serving as a fixing unit, and is discharged onto a discharge tray 50 by a discharge roller pair 41.

<Skewing correction operation>
Next, the skew correction operation of the sheet P performed by the registration unit 21 when the sheet P nipped and conveyed by the pre-registration roller pair 22 is conveyed obliquely will be described with reference to FIGS. FIG. 5 is a plan view showing a state where the skewed sheet P sandwiched and conveyed by the pre-registration roller pair 22 has entered the nip portion N1 of the registration roller pair 23 while being bent.

  In the sheet conveyance path shown in FIG. 1, the sheet P is detected by a sheet detection sensor 71 serving as a sheet detection unit disposed between the pre-registration roller pair 22 and the registration roller pair 23. Based on a detection signal obtained by detecting the sheet P by the sheet detection sensor 71, the control unit 80 serving as a control unit shown in FIG. 9 controls a motor 64 serving as a drive unit provided in the registration unit 21. The motor 64 serving as the driving means rotates the case 24e of the rotary differential gear 24 via a drive transmission means (not shown).

  In the case 24e of the present embodiment, as shown in FIGS. 10A and 10B, the rotation shafts 6a and 6b to which the first and second side gears 24a and 24b are respectively fixed are centered on the rotation shaft 24i. 10 (a) and 10 (b) are configured to be movable symmetrically in the left-right direction. The rotating shafts 6a and 6b are moved in the direction of arrow P3 in FIG. 10A by moving means (not shown) driven by the electromagnetic solenoid 101. As a result, the back surfaces of the first and second side gears 24a and 24b are separated from the engagement surface 24j provided on the case 24e, so that the braking force does not act on the first and second side gears 24a and 24b.

  Further, the rotating shafts 6a and 6b are moved in the direction of arrow P4 in FIG. 10B by moving means (not shown) driven by the electromagnetic solenoid 101. As a result, the back surfaces of the first and second side gears 24a and 24b come into contact with the engagement surface 24j provided on the case 24e, and a braking force acts on the first and second side gears 24a and 24b.

  FIG. 9 is a block diagram of the control system of this embodiment. The motor 64 of this embodiment employs a stepping motor. The motor 64 transmits the rotational driving force to the drive transmission gear 24f of the rotary differential gear 24 shown in FIG. 4 via a drive transmission means (not shown). Thus, the case 24e of the rotary differential gear 24 is rotationally driven around the revolution shaft 24h by the motor 64 serving as a driving means.

  The rotary differential gear 24 is provided with an electromagnetic solenoid 101 as an example of an operating means that allows the first and second side gears 24a, 24b and the case 24e to be freely engaged and released by the control unit 80 serving as a control means. The differential lock part 100 used as the differential lock means is provided. As shown in FIGS. 4 and 7, the first side gear 24a is drivingly connected to a driving roller 25a serving as a first driving rotating body via gears 24c1 and 24c2.

  The second side gear 24b is drivingly connected to a driving roller 25b serving as a second driving rotating body via gears 24d1 and 24d2. The electromagnetic solenoid 101 as the operation means is engaged by contact between the back surfaces of the first and second side gears 24a and 24b and the engagement surface 24j provided on the case 24e by the differential lock unit 100 as the differential lock means. And release by separation. Reference numeral 90 shown in FIG. 9 denotes a power source, which is a power source for the control unit 80, the sheet detection sensor 71, the motor 64, and the like.

  In FIG. 1, the sheets P are separated and fed one by one from the feeding cassette 20 and conveyed from the pre-registration roller pair 22 to the registration roller pair 23. When the leading end of the sheet P is conveyed from the pre-registration roller pair 22 to the registration roller pair 23, the rotation of the registration roller pair 23 is stopped. Further, the sheet detection sensor 71 provided in the section between the pre-registration roller pair 22 and the registration roller pair 23 detects the timing at which the central portion in the sheet width direction of the leading end portion of the sheet P passes.

  As the sheet detection sensor 71, a non-contact type sensor that detects the passage of the sheet P by directly irradiating the sheet P with light and detecting reflected light reflected on the sheet P is generally used. In addition, the leading edge of the sheet P tilts the flag provided in the sheet conveyance path, and the light shielding part integrally provided in the flag blocks the optical path between the light emitting part and the light receiving part, thereby allowing the sheet P to pass. A photo interrupter type sensor for detecting In the present embodiment, the type of the sheet detection sensor 71 is not particularly limited.

  When the sheet P sandwiched and conveyed by the pre-registration roller pair 22 is conveyed obliquely, as shown in FIG. 5, the leading edge of the sheet P that is conveyed in advance at the leading edge of the sheet P (see FIG. 5). 5 (Left end portion) Pa enters the nip portion N1 of the registration roller pair 23 first.

  At this time, the rotation of the registration roller pair 23 is stopped. For this reason, the sheet P having the leading end Pa on the side that has been conveyed in advance first entered the nip portion N1 of the registration roller pair 23 comes into contact with and is locked by the nip portion N1 of the registration roller pair 23. The above will not proceed.

  Further, when the pre-registration roller pair 22 transports the sheet P, the side (the left side in FIG. 5) on which the sheet P is transported in advance in the section between the pre-registration roller pair 22 and the registration roller pair 23 bends. . In the leading end portion of the sheet P, the leading end portion (the leading end portion on the right side in FIG. 5) Pb that is conveyed with delay is the leading end portion on the side that is transported in advance (the leading end on the left side in FIG. 5). Part) Keep up with Pa. As a result, the skew of the sheet P is corrected.

  As described above, in the configuration in which the skew feeding of the sheet P is corrected by the stop registration method, the leading end portion of the sheet P is abutted against the nip portion N1 of the registration roller pair 23 whose rotation is stopped. Further, the sheet P is nipped and conveyed by the pre-registration roller pair 22 so that both sides of the front end portion of the sheet P follow the nip portion N1 of the registration roller pair 23, thereby correcting the skew of the sheet P.

  In the present embodiment, the sheet detection sensor 71 provided in the section between the pre-registration roller pair 22 and the registration roller pair 23 detects the timing at which the central portion in the sheet width direction of the leading end portion of the sheet P passes. Based on the detected information, the control unit 80 shown in FIG. The timing to reach the nip portion N1 with 27 is calculated.

<Differential lock means>
The rotational differential gear 24 of the registration roller pair 23 is on standby in a state where driving is stopped. At this time, since the first and second side gears 24a and 24b are rotatable with respect to the case 24e that is stopped, the driving rollers 25a and 25b that are the driving rotating bodies of the registration roller pair 23 are also provided. It is in a rotatable state.

  In this state, when the leading edge of the skewed sheet P is abutted against the nip portion N1 of the registration roller pair 23, the following occurs. Since the sheet P cannot contact and be locked to the nip portion N1 of the registration roller pair 23, the sheet P is transported in advance in a section between the pre-registration roller pair 22 and the registration roller pair 23 (left side in FIG. 5). ) Can not be bent.

  For this reason, the rotation differential gear 24 of the registration roller pair 23 is as follows in a state where the drive is stopped. 10 (a) and 10 (b), the differential lock portion 100 serving as the differential lock means makes contact between the back surfaces of the first and second side gears 24a and 24b and the engagement surface 24j of the case 24e. Combine. Thereby, it is made to stand by in the state which controlled rotation of drive rollers 25a and 25b.

  That is, while the differential lock unit 100 is functioning, the rotational differential between the drive rollers 25a and 25b is not functioning. The differential lock unit 100 abuts the back surfaces of the first and second side gears 24a and 24b and the engagement surface 24j of the case 24e by the control unit 80 shown in FIG. 9 and the electromagnetic solenoid 101 as an operation means. Alternatively, the engagement and release are performed separately. As a result, it is possible to select whether or not there is rotational differential between the drive rollers 25a and 25b.

  FIG. 10A is a cross-sectional explanatory view showing a released state of the differential lock portion 100, and FIG. 10B is a cross-sectional explanatory view showing an engaged state of the differential lock portion 100. As shown in FIGS. 10 (a) and 10 (b), the differential lock portion 100 is engaged and separated by contact between the back surfaces of the first and second side gears 24a and 24b and the engagement surface 24j of the case 24e. Release by.

  The operation means presses and separates the back surfaces of the first and second side gears 24a and 24b and the engagement surface 24j of the case 24e in a conical clutch shape by the operation of the electromagnetic solenoid 101.

  The other configuration is as follows when the leading end portion of the sheet P skewed at the nip portion N1 of the registration roller pair 23 is abutted. It is only necessary that the driving rollers 25a and 25b serving as the driving rotators of the registration roller pair 23 have a rotation restricting holding force capable of bending the leading end portion of the sheet P against the pressing force of the leading end portion of the sheet P. For this reason, the engagement surface 24j of the case 24e of the differential lock portion 100 may be formed of a high friction body, and in this embodiment, the type of the differential lock portion 100 is not particularly limited.

  9 performs drive control of the motor 64 of the registration unit 21 at the timing when the central portion in the sheet width direction of the leading end portion of the sheet P reaches the nip portion N1 of the registration roller pair 23. Then, the rotary differential gear 24 from the motor 64 through the drive transmission means (not shown) transmits the drive in a state where the first and second side gears 24a, 24b and the case 24e are engaged by the differential lock unit 100. The rotational driving force is transmitted to the gear 24f. Then, the case 24e fixed to the drive transmission gear 24f is rotationally driven around the revolution shaft 24h.

  Then, the drive rollers 25a and 25b serving as the first and second drive rotators disposed on the same axis as a plurality of drive rotators are rotationally driven via the rotary differential gear 24. Then, the sheet P is started to be conveyed by being sandwiched by a driven roller 27 that is a driven rotating body that is pressed against and driven by the driving rollers 25a and 25b.

  In the present embodiment, as shown in FIG. 5, the leading end portion (the leading end portion on the right side in FIG. 5) Pb of the sheet P that is conveyed with a delay is the leading end portion (the leading end portion on the right side in FIG. 5). The rotation of the registration roller pair 23 is started in a state where it has not completely caught up with Pa on the left end portion in FIG. For this reason, the sheet P is conveyed downstream of the registration roller pair 23 in the sheet conveying direction a in a state where the skew correction of the leading end is incomplete.

  Therefore, in the present embodiment, the time during which the registration roller pair 23 is stopped can be shortened. As a result, it is possible to reduce the conveyance interval (the separation interval between the preceding sheet P and the subsequent sheet P) of the sheet P that feeds the sheet P from the feeding cassette 20 one by one. Productivity can be improved.

  In the present embodiment, a rotation differential gear 24 is provided on the registration roller pair 23 serving as the second conveying means. The rotational differential gear 24 conveys the sheet P downstream of the registration roller pair 23 in the sheet conveying direction, and the leading edge of the sheet P is the secondary transfer inner roller 34 and the secondary transfer outer roller 35 shown in FIG. The skew correction means is configured when the nip portion N2 is reached.

  The rotary differential gear 24 includes a pair of registration rollers 23 serving as a second transport unit and a skew feeding of the sheet P between a secondary transfer inner roller 34 and a secondary transfer outer roller 35 serving as a third transport unit. Thus, a rotational differential is generated due to a difference in sheet deflection tension generated in the sheet width direction.

  As shown in FIGS. 4 and 7, the registration roller pair 23 serving as the second conveying means shown in FIG. 2 includes a driving roller 25a serving as a plurality of driving rotating bodies that are respectively driven to rotate by the rotary differential gear 24. , 25b are provided.

  In this embodiment, the sheet conveying apparatus is configured to include at least the nip portion N2 of the pre-registration roller pair 22, the registration roller pair 23, the rotation differential gear 24, the secondary transfer inner roller 34, and the secondary transfer outer roller 35. The The registration roller pair 23 is driven to rotate by the rotary differential gear 24 and has drive rollers 25a and 25b serving as first and second drive rotating bodies arranged on the same axis. As shown in FIG. 7B, the rotation differential gear 24 differentially rotates the drive rollers 25a and 25b.

  In general, when an image is transferred to the sheet P, it is desired to make the sheet P follow the transfer belt surface of the intermediate transfer belt 31 immediately adjacent to the nip portion N2 of the secondary transfer inner roller 34 and the secondary transfer outer roller 35. For this reason, the conveyance speed V1 of the registration roller pair 23 of the sheet P is set faster than the conveyance speed V2 of the intermediate transfer belt 31 (V1> V2).

  Therefore, between the nip portion N1 of the registration roller pair 23 and the nip portion N2 of the secondary transfer inner roller 34 and the secondary transfer outer roller 35, the sheet P is gradually bent (looped) as the sheet P is conveyed. ) Will be formed.

  FIG. 11 shows a state in which the leading edge portion Pa on the side of the skewed sheet P that is nipped and conveyed by the registration roller pair 23 serving as the second conveying means enters the nip portion N2. At this time, the front end portion Pa of the sheet P enters the nip portion N2 while being in contact with the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35 serving as the third conveying means in a stopped state. To do.

  At this time, the registration roller pair 23 is rotationally driven by the motor 64 via the rotary differential gear 24 and sandwiches and conveys the sheet P. Further, the skew correction can be performed by the rotational differential action of the rotational differential gear 24 in which rotational differential is generated by the difference in sheet deflection tension generated in the sheet width direction by the skew of the sheet P.

  Further, the secondary transfer inner roller 34 and the secondary transfer outer roller 35 are stopped at the leading end Pa on the side of the sheet P that is sandwiched and conveyed obliquely by the pair of registration rollers 23. It contacts the nip portion N2. Then, the control unit 80 calculates the timing at which the difference in tension of the sheet deflection occurring in the sheet width direction of the sheet P occurs.

  The control unit 80 operates the electromagnetic solenoid 101 serving as the operation means at the calculated timing to release the differential lock unit 100 of the rotary differential gear 24 provided in the registration roller pair 23. The rotary differential gear 24 from which the differential lock unit 100 is released differentially rotates the drive rollers 25a and 25b.

  The controller 80 calculates the following timings based on the detection information detected by the sheet detection sensor 71. The timing at which the central portion in the sheet width direction of the leading end of the sheet P reaches the nip portion N1 between the driving rollers 25a and 25b serving as the driving rotating bodies of the registration roller pair 23 and the driven roller 27 serving as the driven rotating body is calculated. Alternatively, the timing at which the central portion of the sheet P in the sheet width direction reaches the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35 is calculated.

  Then, the motor 64 is rotationally driven at the timing calculated by the control unit 80 to rotationally drive the case 24e of the rotational differential gear 24. Further, the electromagnetic solenoid 101 is operated at the timing calculated by the control unit 80 to engage and release the differential lock unit 100.

  As shown in FIG. 4, in the rotation differential gear 24, a driving roller 25a serving as a first driving rotating body is fixed to a rotating shaft 26a. A gear 24c2 that meshes with a gear 24c1 fixed to the end of the rotating shaft 26a is fixed to the rotating shaft 6a. The first side gear 24a is fixed to the rotary shaft 6a and is drivingly connected to the driving roller 25a.

  Further, a second side gear 24b fixed to the rotating shaft 6b fixed to the rotating shaft 6b and connected to the driving roller 25b is connected to the gear 24d1 fixed to the end of the rotating shaft 26b to which the driving roller 25b is fixed. Have. The rotary shafts 6a and 6b of the first and second side gears 24a and 24b are arranged on the same axis, and the first and second side gears 24a and 24b are arranged facing each other.

  Further, a pair of pinion gears 24g functioning as planetary gears are meshed with each other with the first and second side gears 24a, 24b arranged facing each other. The rotation shafts 24i of the pair of pinion gears 24g are disposed on the same axis, and the pair of pinion gears 24g are disposed to face each other. The rotation shaft 24i of the pair of pinion gears 24g and the rotation shafts 6a and 6b (revolution shafts 24h) of the first and second side gears 24a and 24b are arranged orthogonal to each other.

  The first and second side gears 24a and 24b and the pair of pinion gears 24g are supported by a bearing member (not shown) with respect to the apparatus frame 60 so as to be rotatable in the sheet conveying direction a around the revolution shaft 24h. It is rotatably supported inside. In the case 24e, the rotation shafts 6a and 6b of the first and second side gears 24a and 24b are arranged on the same axis, and the rotation shafts 6a and 6b on the same axis of the first and second side gears 24a and 24b are revolved. 24h is provided rotatably.

  2 is a perspective explanatory view showing the configuration of the registration unit 21, and FIG. 3 is a perspective explanatory view showing the configuration of the drive rollers 25a, 25b and the rotary differential gear 24 of the registration unit 21. As shown in FIG. As shown in FIG. 2, the registration unit 21 has a plurality of drive rollers 25a and 25b fixed to the rotation shafts 26a and 26b, respectively. Furthermore, it has the some driven roller 27 fixed to the rotating shaft 28 and press-contacted to this some driving roller 25a, 25b. The driving rollers 25a and 25b and the driven roller 27 are pressed against each other by an urging means (not shown) to form a registration roller pair 23.

  The registration roller pair 23 includes rotating shafts 26a and 26b of driving rollers 25a and 25b provided on the same axis, and a rotary differential gear that rotationally differentially drives the driving rollers 25a and 25b by being connected to the rotating shafts 26a and 26b. Has 24.

  FIG. 4 is a partially enlarged view of FIG. 3 showing the configuration of a gear train that drives and connects the rotary differential gear 24 and the rotary shafts 26a and 26b of the drive rollers 25a and 25b. In FIG. 4, the case 24e of the rotary differential gear 24 has a device frame of the image forming apparatus 4 by a bearing member (not shown) so as to be rotatable in the sheet conveying direction a about the revolution shaft 24h of the pair of pinion gears 24g. Attached to 60.

  Further, the rotation shafts 26a and 26b of the drive rollers 25a and 25b are attached to the apparatus frame 60 of the image forming apparatus 4 by bearing members (not shown) so as to be rotatable in the sheet conveyance direction a. The rotation shafts 26a and 26b of the drive rollers 25a and 25b and the rotary differential gear 24 are set to the following separation distances. That is, the gears 24c1 and 24d1 fixed to the ends of the rotary shafts 26a and 26b and the rotary shafts 6a and 6b of the first and second side gears 24a and 24b rotatably supported with respect to the case 24e are fixed. The separation distance is set so that the gears 24c2 and 24d2 mesh with each other.

  A rotational driving force is transmitted to the drive transmission gear 24f of the rotational differential gear 24 from a motor 64 shown in FIG. The drive transmission gear 24f is fixed to the case 24e, and the case 24e rotates around the revolution shaft 24h of the pair of pinion gears 24g integrally with the drive transmission gear 24f.

  As shown in FIG. 10, the rotary differential gear 24 is engaged with the first and second side gears 24a, 24b and the case 24e when waiting while the drive is stopped, and the drive roller A differential lock unit 100 is provided that waits in a state where the rotations of 25a and 25b are restricted.

<Operation of rotating differential gear during sheet conveyance>
The case 24e rotates around the revolution shaft 24h by the rotational driving force transmitted from the motor 64 to the drive transmission gear 24f. When the case 24e rotates around the revolution shaft 24h, the load applied from the driving rollers 25a and 25b to the first and second side gears 24a and 24b via the gears 24c1, 24d1, 24c2, and 24d2 may be equal. In that case, the pair of pinion gears 24g as planetary gears revolves around the revolving shaft 24h integrally with the case 24e while maintaining a stationary state.

  The rotational force of the case 24e is transmitted to the first and second side gears 24a and 24b through the stopped pinion gear 24g. Accordingly, the first and second side gears 24a and 24b rotate in the same direction as the case 24e around the rotation shafts 6a and 6b disposed on the same axis as the revolution shaft 24h.

  The gears 24c2, 24d2 fixed to the rotary shafts 6a, 6b of the first and second side gears 24a, 24b mesh with the gears 24c1, 24d1 fixed to the rotary shafts 26a, 26b of the drive rollers 25a, 25b. ing. As a result, the drive rollers 25a and 25b are rotationally driven in the direction in which the sheet P is conveyed. The sheet P is conveyed while being sandwiched between the driving rollers 25a and 25b and the driven roller 27 pressed against the driving rollers 25a and 25b.

  When different loads are applied to the drive rollers 25a and 25b, the pinion gear 24g serving as the planetary gear rotates according to the difference in rotational speed between the first and second side gears 24a and 24b. That is, the rotational driving force transmitted from the motor 64 to the drive transmission gear 24f is separated in the rotational differential gear 24 via the pinion gear 24g serving as a planetary gear, and the left and right first and second left and right in FIG. It is transmitted to the side gears 24a and 24b.

  A case 24e is fixed to the drive transmission gear 24f. In the case 24e, the first and second side gears 24a, 24b made of bevel gears in which the rotation shaft 24i and the rotation shafts 6a, 6b are arranged orthogonally with each other and the pair of pinion gears 24g mesh with each other. It is rotatably supported with respect to 24e.

  The first and second side gears 24a and 24b are integrated with the gears 24c2 and 24d2 via the rotation shafts 6a and 6b, respectively. The pair of pinion gears 24g are attached to the case 24e so as to be rotatable about the revolution shaft 24h. A pair of pinion gears 24g is provided above and below the case 24e shown in FIG. 4, and is attached to the case 24e so as to be rotatable around the rotation shaft 24i of the pinion gear 24g.

  The drive transmission gear 24f fixed to the case 24e of the rotary differential gear 24 is rotated by the rotational drive of the motor 64 shown in FIG. Then, the pair of pinion gears 24g revolves around the revolving shaft 24h integrally with the case 24e. Different rotational load resistances are generated in the left and right first and second side gears 24a and 24b shown in FIG.

  Then, the pair of pinion gears 24g mesh with the left and right first and second side gears 24a and 24b, respectively. Then, according to the difference in rotational speed between the first and second side gears 24a, 24b, the pair of pinion gears 24g revolve around the revolution shaft 24h while rotating around the rotation shaft 24i.

  The rotational drive of the first side gear 24a is transmitted to the gear 24c2 via the rotational shaft 6a, and the rotational drive of the second side gear 24b is transmitted to the gear 24d2 via the rotational shaft 6b. Thus, the rotational driving force transmitted from the motor 64 to the drive transmission gear 24f is shown in FIG. 4 via the case 24e, the pair of pinion gears 24g, the first and second side gears 24a and 24b, and the rotary shafts 6a and 6b. They are distributed to the left and right gears 24c2, 24d2.

  The rotational differential gear 24 of the present embodiment is an example including a pair of pinion gears 24g and bevel gears (bevel gears) as an example of the first and second side gears 24a and 24b. However, it can also be configured with a helical gear or the like. The shape and material of the gear need not be limited to the configuration of this embodiment. Further, in the present embodiment, the two pinion gears 24g are provided, but a similar function can be exhibited even with one pinion gear 24g.

  As shown in FIG. 11, the sheet P is nipped and conveyed by the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. The sheet P is made of paper having a basis weight of 256 g. Consider a case where the sheet P is conveyed obliquely in a section between the registration roller pair 23 and the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35.

  In that case, the sheet P bends while the leading end of the sheet P is conveyed to the nip N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. FIG. 6 shows the rotational torque applied to the left and right drive rollers 25a and 25b shown in FIG. 11 by the waist force of the sheet P generated thereby.

<Still time of registration roller pair>
In this embodiment, the stationary time during which the leading end of the sheet P abuts against the nip N1 of the registration roller pair 23 and the rotation of the registration roller pair 23 is stopped is as follows. First, the sheet detection sensor 71 detects the timing t1 at which the central portion in the sheet width direction of the leading end portion of the sheet P passes. On the other hand, a CPU (Central Processing Unit) provided in the control unit 80 calculates the following transport time Tt as shown in the following Equation 1.

  That is, the control unit 80 uses the separation distance L on the sheet conveyance path between the sheet detection sensor 71 and the nip N1 of the registration roller pair 23 stored in advance in the memory 7 serving as a storage unit. Further, the conveyance speed V of the sheet P nipped and conveyed by the pair of pre-registration rollers 22 stored in advance in the memory 7 is used. Then, the conveyance time Tt until the sheet P reaches the nip portion N1 of the registration roller pair 23 from the sheet detection sensor 71 is calculated by the following equation (1).

[Equation 1]
Tt = L / V

  Then, the control unit 80 calculates a timing t2 at which the central portion in the sheet width direction of the leading end portion of the sheet P reaches the nip portion N1 of the registration roller pair 23 by the following equation (2). In the following Expression 2, the timing t1 at which the center portion in the sheet width direction of the leading end portion of the sheet P detected by the sheet detection sensor 71 passes is used. Further, the transport time Tt until the sheet P calculated by the control unit 80 reaches the nip portion N1 of the registration roller pair 23 from the sheet detection sensor 71 is used.

[Equation 2]
t2 = t1 + Tt

  Then, the control unit 80 drives the motor 64 at the timing t2 when the central portion in the sheet width direction of the leading end portion of the sheet P reaches the nip portion N1 of the registration roller pair 23. Then, the rotational force is transmitted to the drive transmission gear 24 f shown in FIG. 4, and the registration roller pair 23 that is stationary via the rotational differential gear 24 is rotationally driven to start the conveyance of the sheet P.

  As described above, the stationary time Tr during which the rotation of the registration roller pair 23 is stopped is calculated by the following equation (3). A timing t1 at which the sheet width direction central portion of the leading end portion of the sheet P passes by the sheet detection sensor 71 and a timing t2 at which the sheet width direction central portion of the leading end portion of the sheet P reaches the nip portion N1 of the registration roller pair 23. Use.

[Equation 3]
Tr = t2-t1

  As a result, the stationary time Tr during which the rotation of the registration roller pair 23 is stopped becomes substantially constant regardless of the skew amount of the leading edge of the sheet P.

  As shown in FIG. 11, the sheet P is conveyed obliquely in a section between the nip portion N1 of the registration roller pair 23 and the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. Is done. In that case, the amount of deflection (loop) of the sheet P is larger than the side of the sheet P which is conveyed on the left side in FIG. The amount is larger.

  For this reason, as the leading edge skew amount Δx1 of the sheet P shown in FIG. Note that the leading edge skew amount Δx1 of the sheet P shown in FIG. 11 is the leading edge portion Pa on the preceding sheet conveyance path in the sheet conveyance direction and the leading edge portion on the side conveyed with delay. This is the separation distance from Pb.

  For this reason, the sheet P gives a rotational torque in the direction opposite to the sheet conveying direction a according to the difference in the amount of bending at both ends in the width direction of the sheet P with respect to the left and right drive rollers 25a and 25b in FIG. .

  For example, consider the case of a sheet P made of paper having a basis weight of 256 g. In this case, when the skew amount Δx1 of the leading edge of the sheet P shown in FIG. 11 is 4 mm, the rotational torque difference corresponding to the difference in the deflection amount at both ends in the width direction of the sheet P with respect to the left and right drive rollers 25a and 25b in FIG. This produces a resistance difference of about 800 gf (7.84 N).

  Here, the resistance difference means that the left and right drive rollers 25a and 25b in FIG. 11 that sandwich and convey the sheet P are between the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. The sheet P is pushed by the strength of the waist when it is bent. As a result, a force (back tension) that tries to resist the force that the driving rollers 25a and 25b try to rotate in the sheet conveying direction a is originally applied. This is the difference between the forward direction and the reverse direction.

  As shown in FIG. 11, in the registration roller pair 23, the sheet P is nipped and conveyed by the driving rollers 25a and 25b and the driven roller 27 that is a driven rotating body that rotates following the rotation of the driving rollers 25a and 25b. The leading end of the sheet P abuts on the nip N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35.

  Further, the state in which the differential lock portion 100 of the rotary differential gear 24 of the registration roller pair 23 is released is as follows. The left and right drive rollers 25a and 25b shown in FIG. 7A are pushed by the deflection of the sheet P due to the strength of the waist of the sheet P generated by the deflection of the sheet P, so as to reversely rotate in the sheet conveyance direction a. To do.

  As shown in FIG. 7 (a), the left and right drive rollers 25a and 25b are pushed by the deflection of the sheet P, and counter the rotational torque that tries to reversely rotate in the sheet conveyance direction a. Resistance forces (back tension) f1 and f2 indicated by broken lines are generated. FIG. 7A is an explanatory perspective view showing the operation of the pinion gear 24g and the first and second side gears 24a and 24b of the rotary differential gear 24 when the resistance forces f1 and f2 are equal.

  When the resistance forces f1 and f2 shown in FIG. 7A are equal, the pair of pinion gears 24g revolves integrally with the case 24e around the revolution shaft 24h while meshing with the first and second side gears 24a and 24b. However, it does not rotate around the rotation axis 24i.

  The motor 64 is driven and the sheet P is conveyed via the rotary differential gear 24 while the left and right drive rollers 25a and 25b shown in FIG. As shown in FIG. 11, the leading end of the sheet P nipped and conveyed by the registration roller pair 23 comes into contact with the nip N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. In the registration roller pair 23 in which the conveyance of the sheet P is started, the sheet P is nipped and conveyed by the driving rollers 25a and 25b and the driven roller 27.

  The state in which the differential lock part 100 of the rotary differential gear 24 is released is as follows. A rotational differential is generated by the difference in sheet bending tension generated between the left and right drive rollers 25a and 25b in the sheet width direction of the sheet P due to the waist strength of the sheet P generated by the bending of the sheet P. As a result, rotational torque is applied to rotate in the reverse direction with respect to the sheet conveying direction a.

  Resistive forces f1 and f2 are generated in the driving rollers 25a and 25b that sandwich and convey the sheet P, which are counteracted by rotational torque that is pushed by the bending of the sheet P to rotate in the reverse direction with respect to the sheet conveying direction a. . The resistance forces f1 and f2 differ depending on the difference in the amount of deflection at both ends in the width direction of the sheet P with respect to the left and right drive rollers 25a and 25b in FIG. FIG. 7B is an explanatory perspective view showing the operations of the pinion gear 24g and the first and second side gears 24a and 24b of the rotary differential gear 24 when there is a difference between the resistance forces f1 and f2.

  For example, as shown in FIG. 11, a sheet conveyed in a skewed manner while being sandwiched by a pair of registration rollers 23 at a nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35 on the left side of FIG. The front end portion Pa1 on the side of P that is transported in advance is brought into contact. Then, the loop on the left side of FIG. 11 grows according to the speed difference between the conveyance speed V1 by the registration roller pair 23 and the conveyance speed by the secondary transfer inner roller 34 and the secondary transfer outer roller 35.

  In the registration roller pair 23, the sheet P is nipped and conveyed by the drive rollers 25a and 25b and the driven roller 27, and the differential lock portion 100 of the rotary differential gear 24 is released. Then, in addition to the rotational driving torque transmitted from the motor 64 to the driving roller 25a, a resistance force (back tension) of the bending (loop) of the sheet P shown in FIG. 11 acts on the driving roller 25a. For this reason, the rotational differential gear 24 moves the drive roller 25b shown in FIG. 11 relative to the rotational speed of the drive roller 25a so as to eliminate the bias of the loop in the width direction of the sheet P in the sheet conveyance direction a. Thus, a rotational differential is generated which is intended to rotate rapidly.

  As shown in FIG. 11, the sheet P being conveyed obliquely in the section between the nip portion N1 of the registration roller pair 23 and the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. The amount of deflection is as follows. Compared to the side that is transported with delay shown on the right side of FIG. 11, the side that is transported in advance shown on the left side of FIG. 11 is larger.

  The leading edge Pa on the side of the sheet P that is nipped and conveyed by the registration roller pair 23 is in contact with the nip N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. Then, the left and right drive rollers 25a and 25b shown in FIG. 7B are pushed by the deflection (loop) of the sheet P by the strength of the waist of the sheet P generated by the deflection (loop) of the sheet P. The magnitude relationship between the resistance forces (back tensions) f1 and f2 with respect to the rotational torque to be rotated in the reverse direction with respect to the sheet conveyance direction a is as shown in the following equation (4).

[Equation 4]
f1> f2

  As described above, the driving roller 25a on the side on which the skewed sheet P is transported in advance is pushed by the bending (loop) of the sheet P, and the rotational torque to reversely rotate in the sheet transport direction a. The resistance force f1 to becomes larger.

  The motor 64 is driven and controlled. As a result, the following force acts on the driving rollers 25a and 25b in a state where the sheet P is nipped and conveyed via the rotary differential gear 24. The driving rollers 25a and 25b are pushed in the direction opposite to the sheet conveyance direction a by the strength of the waist of the sheet P which is bent in contact with the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. . Resistive forces f1 and f2 to resist it are generated in the registration roller pair 23.

  The sheet P is nipped and conveyed by the driving rollers 25a and 25b and the driven roller 27, and the differential lock portion 100 of the rotary differential gear 24 is released. Then, the drive rollers 25a and 25b are transmitted to the rotary shafts 26a and 26b, the gears 24c1, 24d1, 24c2, and 24d2, and the first and second side gears 24a and 24b, and the resistance forces f1 and f2 are transmitted to the first and second side gears 24a. , 24b. Thereafter, when the motor 64 is rotationally driven, the resistance forces f1 and f2 held in the first and second side gears 24a and 24b act on the rotational operation of the rotary differential gear 24.

  Then, the rotational force of the motor 64 is transmitted to the case 24e via the drive transmission gear 24f, and the pair of pinion gears 24g revolves integrally with the case 24e around the revolution shaft 24h. At this time, the resistance forces f1 and f2 applied to the drive rollers 25a and 25b are transferred to the left and right first and second side gears in FIG. 7B via the rotary shafts 26a and 26b and the gears 24c1, 24d1, 24c2, and 24d2. It is transmitted to 24a and 24b, respectively. Since the resistance force f1 applied to the left driving roller 25a in FIG. 7B is large, the pinion gear 24g rotates around the rotation shaft 24i along the teeth of the left first side gear 24a in FIG. 7B. Then, the second side gear 24b on the right side of FIG.

  At this time, the first and second side gears 24a and 24b rotate integrally with the gears 24c2 and 24d2 via the rotating shafts 6a and 6b, respectively, and with respect to the driving roller 25a on the left side of FIG. The right driving roller 25b in FIG. 7B is rotated excessively. When the rotation amount of the left drive roller 25a in FIG. 7B is r1, and the rotation amount of the right drive roller 25b in FIG. 7B is r2, the following equation (5) is obtained.

[Equation 5]
r1 <r2

  Thus, the rotational differential r1 between the rotation amount r1 of the drive roller 25a on the side where the skewed sheet P is conveyed in advance and the rotation amount r2 of the drive roller 25b on the side conveyed with a delay are rotational differential. Will occur.

  As shown in FIG. 7B, the pair of registration rollers 23 that sandwich and convey the skewed sheet P is relatively on the side on which the skewed sheet P shown on the left side of FIG. The rotation amount r1 of the drive roller 25a is small. Further, the rotation amount r2 of the drive roller 25b on the side where the skewed sheet P shown on the right side of FIG. Therefore, the skew of the sheet P is corrected while being nipped and conveyed by the registration roller pair 23.

  Further, the skew of the sheet P is corrected. Then, the difference in resistance force (back tension) pressed by the left and right drive rollers 25a and 25b of the registration roller pair 23 shown in FIG. Then, the magnitude relationship between the resistance forces f1 and f2 that oppose the rotational torque to be rotated in the reverse direction with respect to the sheet conveying direction a approaches {f1≈f2}. And finally, it converges in the direction in which the rotational differential between the left and right drive rollers 25a and 25b in FIG. The rotation amount r1 of the left drive roller 25a in FIG. 7B and the rotation amount r2 of the right drive roller 25b in FIG. 7B converge to {r1≈r2}.

  The operation of nipping and conveying the sheet P by the registration roller pair 23 is started at a timing t2 when the leading end position of the central portion in the width direction of the sheet P reaches the nip portion N of the registration roller pair 23. FIG. 8 shows, by simulation, the skew correction rate when the leading skew amount Δx shown in FIG. 5 of the sheet P made of paper of A3 size and basis weight of 64 g is 5 mm (input skew amount). FIG. 6 is a view comparing with a conventional configuration that does not have the rotary differential gear 24.

  As shown in FIG. 8, in the conventional configuration, the leading end position of the sheet P shown in FIG. 5 where the leading edge skew amount Δx is 5 mm (input skew amount) is in the center in the width direction is the nip portion of the registration roller pair 23. Consider the timing t2 to reach N1. At the timing t2, the operation of nipping and conveying the sheet P by the registration roller pair 23 is started. In that case, the skew amount Δx of the leading edge of the sheet P after skew correction is corrected to an output skew amount of about 2.2 mm (2.17 mm) and conveyed downstream of the registration roller pair 23.

  It is assumed that there is no skew return of the sheet P while the registration roller pair 23 is conveyed from the nip portion N1 to the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. At this time, the output skew amount from the nip portion N1 of the registration roller pair 23 becomes substantially equal to the output skew amount from the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35.

  On the other hand, in the present embodiment, in addition to the skew correction in the conventional configuration, the following is performed. Further, the right and left shown in FIG. 7B are caused by the difference in tension of the sheet P between the nip portion N1 of the registration roller pair 23 and the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. Rotational differential is generated in the drive rollers 25a and 25b.

  During the sheet conveyance between the nip portion N1 of the registration roller pair 23 and the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35, the skewed sheet P is further transferred to the sheet P. Skew is corrected. For this reason, in the present embodiment, as shown in FIG. 8, the skew amount Δx1 of the leading edge of the sheet P after skew correction is corrected to an output skew amount of about 1.2 mm (1.16 mm) while It is conveyed downstream of the nip portion N2 between the next transfer inner roller 34 and the secondary transfer outer roller 35.

  In this case, the skew correction rate (%) is converted from the simulation value of the input skew amount and the output skew amount of the sheet P. The skew correction rate (%) is obtained by the following equation (6).

[Equation 6]
Skew correction rate (%) = {(input skew amount) − (output skew amount)} / (input skew amount) × 100

  The skew correction rate of the conventional configuration is, based on Equation 6, the skew correction rate (%) = {(5 mm) − (2.17 mm)} / (5 mm) × 100 = 56.6%, which is about 57%. (56.6%).

  On the other hand, the skew correction rate of the present embodiment is calculated based on the equation (6) as follows: skew correction rate (%) = {(5 mm) − (1.16 mm)} / (5 mm) × 100 = 76.8 %, Approximately 77% (76.8%). Therefore, the skew correction rate was improved by about 20% (= 77% −57%).

  The rotation shaft 28 of the driven roller 27 of the registration roller pair 23 shown in FIG. 2 is arranged in parallel to the rotation shafts of the secondary transfer inner roller 34 and the secondary transfer outer roller 35 shown in FIG. The sheet P that has been skew-corrected by the rotation differential gear 24 so as to be parallel to the rotation shaft 28 of the driven roller 27 of the registration roller pair 23 does not substantially skew. In this state, the intermediate transfer belt 31 and the secondary transfer outer roller 35 are conveyed to a secondary transfer portion formed by a nip portion, and stable image accuracy can be obtained.

  In this way, the skew is provided with the rotary differential gear 24 for making the left and right rotations differential with respect to the center between the ends of the rotary shafts 26a and 26b of the left and right drive rollers 25a and 25b shown in FIG. It has a correction means. Thus, skew correction can be performed during sheet conveyance of the sheet P that is nipped and conveyed by the registration roller pair 23.

  The sheet P is nipped and conveyed between the nip portion N1 of the registration roller pair 23 and the nip portion N2 between the secondary transfer inner roller 34 and the secondary transfer outer roller 35. In the meantime, a rotational differential is generated in the left and right drive rollers 25a and 25b shown in FIG. 7B due to a difference in flexural tension of the sheet P due to skew in the sheet width direction, and skew correction can be performed during sheet conveyance. .

  That is, according to the present embodiment, skew correction can be performed during sheet conveyance by the rotational differential of the plurality of drive rollers 25a and 25b due to the difference in sheet deflection tension due to skew in the sheet width direction. As a result, regardless of the rigidity (waist strength) of the sheet P, a good skew correction capability is obtained, the sheet P is sent out at a predetermined timing, and the product productivity is improved by a small sheet interval. Both stability of accuracy can be achieved.

  In the present embodiment, as shown in FIG. 1, the specific operation when the registration unit 21 is applied to one conveyance path has been described. However, a plurality of registration units 21 are arranged on the sheet conveyance path. Also good.

P ... Sheet N1 ... Nip part N2 of registration roller pair ... Nip part between secondary transfer inner roller and secondary transfer outer roller
22… Roller pair before registration (first transport means)
23… Registration roller pair (second conveying means)
24… Rotating differential gear
25a, 25b ... driving roller (first and second driving rotating bodies)
34… Secondary transfer inner roller (third transport means)
35 ... Secondary transfer outer roller (third transport means)

Claims (4)

First conveying means for conveying a sheet;
A second conveying unit disposed further downstream in the sheet conveying direction than the first conveying unit and further conveying the sheet conveyed by the first conveying unit;
A third conveying unit disposed further downstream in the sheet conveying direction than the second conveying unit and further conveying the sheet conveyed by the second conveying unit;
Have
In the sheet conveying apparatus in which the leading end portion of the sheet conveyed by the first conveying unit abuts on the second conveying unit to correct the skew of the sheet,
The second conveying means is a rotary differential gear that generates a rotational differential due to a difference in sheet bending tension generated in the sheet width direction due to sheet skew between the second conveying means and the third conveying means. , Each of which is driven to rotate and has first and second driving rotating bodies arranged on the same axis ,
The rotational differential gear is
A first side gear that is drivingly connected to the first driving rotating body ;
A second side gear drivingly connected to the second drive rotating body ;
A pinion gear meshed with the first and second side gears ;
The first and second side gears and the pinion gear are rotatably supported, and the rotation shafts of the first and second side gears are arranged on the same axis, and the first and second side gears are on the same axis. A case rotatably provided with a rotating shaft as a revolution shaft ;
Differential locking means for engaging and releasing the first and second side gears and the case ;
Drive means for rotationally driving the case ;
Operating means for operating engagement and release of the differential locking means ;
A sheet conveying apparatus comprising: A sheet detecting means provided between the first conveying means and the second conveying means in the sheet conveying path;
Control means for calculating the timing at which the central portion in the sheet width direction of the leading edge of the sheet reaches the nip portion between the driving rotating body and the driven rotating body of the second conveying means based on the detection information detected by the sheet detecting means. When,
The sheet conveying apparatus according to claim 1 , wherein the case is rotated by driving the driving unit at the timing calculated by the control unit. A sheet detecting means provided between the first conveying means and the second conveying means in the sheet conveying path;
Control means for calculating the timing at which the central portion in the sheet width direction of the leading edge of the sheet reaches the nip portion between the driving rotating body and the driven rotating body of the third conveying means based on the detection information detected by the sheet detecting means. When,
Sheet conveying apparatus according to claim 1, characterized in that to perform engagement of the differential lock means by operating said operating means in said timing computed by the control unit, the release. The sheet conveying device according to any one of claims 1 to 3 ,
Image forming means for forming an image on a sheet;
An image forming apparatus comprising:

Images