JP5455723B2 - Sheet skew correction device and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet skew correction device that corrects an inclination of a conveyed sheet or the like with respect to the conveyance direction, so-called skew feeding, and an image forming apparatus such as a copying machine, a facsimile, or a printer that includes the sheet skew correction device.

  A sheet fed from a cassette or the like containing a sheet is fed due to various reasons such as the shape of the conveying roller being tapered or the alignment of the conveying roller being deviated from the image forming unit or transfer unit. , May be skewed during transport.

  Especially when picking up sheets from a cassette or separating sheets so that multiple sheets are not conveyed at the same time, the roller width may be narrow or the sheet may not be sufficiently held against turning. The skew tends to occur.

  Therefore, in order to obtain a good output image, it is necessary to correct the skew of the sheet before the image forming unit transfers the image to the sheet. The correction position is more effective when close to the image forming unit.

  Japanese Patent Application Laid-Open No. 2004-260260 discloses an image forming apparatus configured to abut the front end of a sheet against a shutter biased by a spring or the like toward the upstream side in the conveyance direction. This is because even if a part of the skewed sheet comes into contact with the shutter, the shutter cannot move, so that the entire front end of the sheet comes into contact with the shutter bus. That is, the sheet skew is corrected by following the shutter bus. When the leading edge of the sheet follows the bus line of the shutter, it is possible to rotate the shutter against the spring urging the shutter by the stiffness of the sheet, and the sheet can pass through the shutter portion. .

  Further, Patent Document 2 proposes a configuration in which the spring force that biases the shutter can be made variable. If the urging force of the shutter is constant, the thin sheet without stiffness will buckle the sheet against the urging force of the shutter when it contacts the shutter. On the other hand, with thick paper that is strong, the shutter rotates with a part of the sheet in contact with the shutter, and the leading edge of the sheet does not follow the bus line of the shutter, that is, skew correction is not sufficiently performed. . By making the urging force of the shutter variable according to the type of sheet to be used, these problems can be solved, and skew correction can be performed regardless of the paper type to be used.

JP 09-183539 A Patent 3554145

  However, in the prior art disclosed in Patent Document 2, when the seat to be used is changed, it is necessary for the user to change the hooking position of the spring that biases the shutter and to change the biasing force of the shutter.

  In an electrophotographic image forming apparatus, it is necessary to apply a necessary and sufficient amount of heat to a sheet on which an image has been transferred to ensure fixability. For this reason, in the case of thick paper having a large heat capacity compared to plain paper, in many devices, the sheet conveyance speed (process speed) in the image forming unit is usually set to about half that of plain paper, and the fixing property is set. Secured.

  That is, when using thick paper, the user changes the process speed by setting that the sheet to be used from the operation unit is thick paper, and then changes the hook position of the spring that biases the shutter. There was a need. For this reason, operativity will worsen.

  In addition, when the user does not set the shutter biasing force to an appropriate value according to the type of paper to be used, there is a problem that the sheet is buckled or the skew is not sufficiently corrected.

  The present invention solves these conventional problems. An object of the present invention is to prevent a problem that buckling or skewing is not sufficiently corrected without changing the hooking position of a spring or the like that biases the shutter according to the type of sheet used by the user. A sheet skew correction device and an image forming apparatus including the same are provided.

  In order to achieve the above object, a typical configuration according to the present invention includes a first sheet conveying unit that conveys a sheet and a sheet conveying direction downstream from the first sheet conveying unit, and conveys the sheet. A second sheet conveying means including a pair of sheet conveying rotating bodies and a sheet leading end upstream of the nip portion of the pair of sheet conveying rotating bodies in the sheet conveying direction and in the vicinity of the nip portion. A sheet holding portion that contacts the sheet and locks the leading edge of the sheet, and the sheet locking portion locks the leading edge of the sheet conveyed by the first sheet conveying means; A shutter member swingable to a second posture that can pass through, a biasing unit that biases the shutter member to maintain the first posture, and a second sheet conveying unit that rotates. A motor for driving; Control means for controlling the rotation direction of the motor according to the type of sheet used, a first drive train for drivingly connecting the motor and the second sheet transport means, and a reduction ratio with the first drive train A second drive train that is different from each other, drive train switching means for switching and transmitting the drive force of the motor to the first drive train or the second drive train according to the rotation direction of the motor, Biasing force switching means for switching the biasing force of the biasing means against the shutter member in accordance with the rotation direction.

  According to the present invention, the urging force with respect to the shutter member can be changed by changing the rotation direction of the motor. For this reason, by changing the rotation direction of the motor in accordance with the type of sheet, it is possible to accurately perform skew correction by the shutter member in accordance with the type of sheet. Further, since an actuator such as a solenoid is not used for switching the biasing force of the shutter member, accurate skew correction can be performed at low cost.

1 is a schematic cross-sectional view illustrating an entire image forming apparatus according to an embodiment of the present invention. 1 is a perspective view of a sheet skew correction device according to an embodiment of the present invention. Sectional drawing of the sheet | seat skew correction apparatus which concerns on embodiment of this invention 1 is a side view illustrating a drive unit of a sheet skew correction device according to a first embodiment of the invention. 1 is a schematic diagram illustrating a drive unit of a sheet skew correction device according to a first embodiment of the present invention. Explanatory drawing which shows the state immediately after correction | amendment operation start of a sheet | seat skew correction apparatus Explanatory drawing which shows the state at the time of completion | finish of correction | amendment operation | movement of a sheet | seat skew correction apparatus 1 is a flowchart showing an outline of a print job of an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram of an image forming apparatus according to a first embodiment of the present invention. The side view showing the state at the time of plain paper selection of the drive part of the sheet skew feeding correction device concerning a 2nd embodiment of the present invention. The side view showing the state at the time of cardboard selection of the drive part of the sheet skew correction device concerning a 2nd embodiment of the present invention. FIG. 6 is a schematic diagram illustrating a drive unit of a sheet skew correction device according to a second embodiment of the invention.

  Next, a sheet skew correction apparatus and an image forming apparatus using the same according to an embodiment for carrying out the present invention will be described with reference to the drawings.

[First Embodiment]
<Image forming apparatus>
FIG. 1 is a schematic cross-sectional view of an image forming apparatus including a sheet skew correction device according to the first embodiment.

  The image forming apparatus according to this embodiment is an electrophotographic color image forming apparatus in which four image forming units that form yellow, magenta, cyan, and black toner images are arranged in parallel. Each image forming unit has the same configuration except that the color of the toner image to be formed is different.

  In each image forming unit, the photosensitive drums 101a to 101d are uniformly charged by the charging rollers 102a to 102d, and are exposed according to the image signals of the respective colors from the laser scanners 103a to 103d to form electrostatic latent images. Is done. The electrostatic latent images are developed with yellow, magenta, cyan, and black toners by the developing devices 104a to 104d, respectively. The toner developed on each photosensitive drum is sequentially transferred to an endless belt-like intermediate transfer belt 106 by primary transfer rollers 105 a to 105 d, and a full-color toner image is formed on the intermediate transfer belt 106. Transfer residual toner on the photosensitive drum is collected by drum cleaners 107a to 107d.

  On the other hand, in synchronization with the image forming operation, the sheet S is fed from either the feeding cassette 111 or 112 or the manual feeding unit 113. The sheet S is conveyed by a conveying roller 114 and further conveyed toward a registration roller 116 as a second sheet conveying unit by a pre-registration roller 115 as a first sheet conveying unit. The sheet conveyance speed at this time is faster than the peripheral speed (process speed) of the image forming unit, that is, the photosensitive drum or the intermediate transfer belt. In this embodiment, as an example, the process speed for plain paper is 150 mm / s, and the sheet conveyance speed is 200 mm / s.

  When the sheet is conveyed to the registration roller 116, the skew is corrected by the sheet skew correcting device. The configuration and operation for that will be described later.

  The sheet whose skew has been corrected by the sheet skew correcting device passes through the registration roller 116, and then the registration sensor 117 detects the leading edge of the sheet. Then, the sheet conveying speed of the registration roller 116 is set to 150 mm / process speed so that the leading edge of the sheet is aligned with the leading edge of the image formed on the intermediate transfer belt 106 by the secondary transfer unit 118 by the control means. The timing of deceleration to s is calculated.

  The toner image on the intermediate transfer belt 106 is transferred to the sheet S by applying a bias via the secondary transfer outer roller 109, and is fixed on the sheet by heating and pressurizing by the fixing device 110. Thereafter, the sheet is discharged from the discharge unit 119a or 119b to the outside of the apparatus main body. Further, the transfer residual toner on the intermediate transfer belt 106 that has not been transferred in the secondary transfer unit 118 is collected by the intermediate transfer body cleaner 108.

<Sheet skew correction device>
Next, the configuration of the sheet skew correction device for correcting the sheet skew will be described. FIG. 2 is a perspective view of a registration roller 116 portion constituting the sheet skew correction device according to the present embodiment, and FIG. 3 is a sectional view of a portion indicated by BB in FIG.

  As shown in the figure, the registration roller 116 as the second sheet conveying means is a pair of sheet conveying rotating bodies of a lower registration roller 10 and an upper registration roller 20 that are rotatably supported by bearings 11 and 21 near both ends. It is comprised by. The lower registration roller 10 and the upper registration roller 20 are opposed to each other, and springs 12 are hung on the bearings at both ends, and the lower registration roller 10 and the upper registration roller 20 are pressed to form a nip portion. ing. The registration roller 116 is disposed downstream of the pre-registration roller 115 serving as a first sheet conveyance unit and downstream of the secondary transfer unit 118 in the sheet conveyance direction.

  The lower resist roller 10 is formed by integrally forming a plurality of rubber rollers 10b in the longitudinal direction of the metal shaft 10a. Here, the outer diameter of the rubber roller 10b of the present embodiment is φ16.

  The upper resist roller 20 is integrally formed with a polyacetal roller 20b around the metal shaft 20a so as to face the rubber roller 10b formed on the lower resist roller. The outer diameter of the roller 20b of this embodiment is also φ16.

  The registration roller 116 is provided with a shutter arm (shutter member) 30 that can swing around the rotation center of the registration upper roller 20. The shutter arm 30 includes a plurality of (six in this embodiment) semicircular arc-shaped regulating pieces 31 (in this embodiment) along the longitudinal direction of the registration upper and lower rollers 10 and 20 (the width direction of the sheet S perpendicular to the sheet conveying direction). 31a to 31f) are integrally formed.

  A sheet abutting portion (sheet engaging portion) 32 (32a to 32f) where the leading end of the conveyed sheet abuts and locks is formed at the lower end of each regulating piece 31. Each restricting piece 31 is positioned between and adjacent to a plurality of rubber rollers 10 b formed integrally with the resist lower roller 10. That is, each regulating piece 31 is located between and at both ends of a plurality of nip portions formed by the rubber roller 10 b and the roller 20 b in the longitudinal direction of the registration roller 116.

  Further, bearings 33a and 33b are integrally formed on the restricting pieces 31a and 31f at both ends, respectively, and are rotatably supported by the metal shaft 20a of the resist upper roller 20.

  In addition, each regulation piece 31 is arrange | positioned in the symmetrical position with respect to the roller longitudinal direction center of the sheet | seat passage path of the upper and lower rollers 10 and 20. The reason why the plurality of regulating pieces 31 are arranged is to deal with sheets S having various widths.

  Then, the regulating piece 31 is in contact with the leading edge of the sheet to be conveyed in the vicinity of the nip portion, with the sheet abutting portion 32 on the upstream side of the nip portion of the registration roller 116 and in the vicinity of the nip portion. Can be swung between a first posture for engaging the sheet and a second posture for allowing the sheet to pass therethrough.

(Registration roller drive mechanism)
4 is a side view showing a drive mechanism of the registration roller 116, and FIG. 5 is a schematic view of the drive mechanism.

  A registration driving gear 41 is attached to the shaft 10 a of the registration lower roller 10. A motor gear 42 a is attached to the motor 42 for rotationally driving the lower registration roller 10.

  The registration drive gear 41 and the motor gear 42 a are drivingly connected by two gear trains of a first drive train 43 and a second drive train 44. Here, the reduction ratio of the second drive train 44 is set to be twice that of the first drive train 43. Specifically, in the present embodiment, the reduction ratio of the first drive train is 4, and the reduction ratio of the second drive train is 8.

  Drive transmission from the motor gear 42a to the registration drive gear 41 is transmitted by switching the driving force of the motor 42 to the first drive train 43 or the second drive train 44 according to the rotation direction of the motor 42 by the drive train switching means. The

  Here, the configuration of the drive train switching means will be specifically described. A one-way clutch 43b as drive train switching means is disposed on the inner diameter portion of the first gear 43a of the first drive train that meshes with the motor gear 42a. When the motor 42 rotates counterclockwise, as indicated by the broken line arrow in FIG. 4, the one-way clutch 43b is locked, and the rotation is transmitted to the registration drive gear 41 via the shaft 43c and the coaxial gear 43d. . Conversely, when the motor 42 rotates clockwise in FIG. 4, the one-way clutch 43b is in a free state and the first gear 43a is rotated by the motor, but the rotation is not transmitted to the shaft 43c and the coaxial gear 43d. . The gear ratio of the motor gear 42a, the first gear 43a, and the coaxial gear 43d is 1: 2: 1.

  Similarly, a one-way clutch 44b as a drive train switching means is also arranged at the inner diameter portion of the first gear 44a of the second drive train that meshes with the motor gear 42a. When the motor 42 rotates clockwise as indicated by the solid line arrow in FIG. 4, the one-way clutch 44b is locked, and the rotation is transmitted to the shaft 44c and the coaxial gear 44d. Conversely, when the motor 42 rotates counterclockwise in FIG. 4, the one-way clutch 44b is in a free state and the first gear 44a is rotated by the motor, but the rotation is transmitted to the shaft 44c and the coaxial gear 44d. do not do. The gear ratio of the motor gear 42a, the first gear 44a, and the coaxial gear 44d is also 1: 2: 1.

  Further, the one-way clutch 44f is also arranged at the inner diameter portion of the gear 44e that meshes with the registration driving gear 41 at the final stage of the second drive train 44, and the shaft fitted to the inner diameter rotates clockwise in FIG. It becomes free when it is locked to and rotates counterclockwise.

  Accordingly, when the motor 42 is rotated counterclockwise by the control means 50, the lower registration roller 10 is driven by the first drive train 43, and when the motor 42 is rotated clockwise. The registration lower roller 10 is driven by the second drive train 44.

  Further, a gear train 60 as an urging force switching means is connected to the second drive train 44 on the downstream side in the drive transmission direction from the one-way clutch 44b and on the upstream side in the drive transmission direction from the one-way clutch 44f.

  An urging force switching arm 62 having a torque limiter 61 attached to the inner diameter portion is arranged coaxially with the most downstream gear of the gear train 60. The amount of rotational movement of the urging force switching arm 62 is regulated by stoppers 63a and 63b provided in the image forming apparatus main body.

(Biasing configuration of shutter member)
The shutter arm 30 is urged by urging means so as to maintain the first posture. Next, the biasing configuration of the shutter arm 30 will be described.

  As shown in FIGS. 2 and 4, a spring hook 34 and a stopper 35 are formed on one end side in the longitudinal direction of the shutter arm 30, and there is a gap between the spring hook 34 and the biasing force switching arm 62. A tension coil spring 64 as a biasing means is hooked.

  The shutter arm 30 is urged counterclockwise (arrow B direction) in FIG. 4 by the spring force of the tension coil spring 64. Thus, in a state where the sheet is not conveyed by the registration roller 116, the stopper portion 35 of the shutter arm 30 is in contact with the protruding piece 36 (see FIG. 2) provided in the image forming apparatus main body. The sheet abutting portion 32 of each regulating piece 31 is configured to be positioned slightly upstream from the nip portion of the registration roller 116 in a state perpendicular to the sheet passing path (FIG. 3). The first posture of the shutter member shown in FIG.

(Skew correction operation)
Next, sheet skew correction by the shutter member will be described. First, the basic skew correction operation of the sheet will be described.

  6 and 7 are views of the sheet S conveyed to the registration roller 116 by the pre-registration roller 115 as viewed from the upper side of the conveyance path. 6 and 7, the rubber roller 10b of the lower registration roller 10 and the roller 20b of the upper registration roller 20 are omitted for explanation. Although the drive parts of the registration roller 116 and the pre-registration roller 115 are omitted, they are driven by the same motor.

  The sheet conveyance speed of the pre-registration roller 115 and the registration roller 116 is set so that the pre-registration roller 115 is about 1% faster. This is to prevent the sheet conveyance speed of the registration roller 116 from becoming slower than the sheet conveyance speed of the pre-registration roller 115 due to component tolerances. Ideally, the two rollers have the same conveyance speed. good.

  As shown in FIG. 6, when the sheet S is conveyed with the sheet S skewed in the sheet width direction (a direction orthogonal to the sheet conveying direction A) with respect to the registration roller 116, first, the restriction on the right side of FIG. The leading end of the sheet S on the right side in the width direction contacts the sheet contact portion 32f of the piece 31f.

  At this time, since the tension coil spring 64 is hung on the shutter arm 30 holding the regulation piece 31 f, the sheet S rotates the regulation piece 31 and the shutter arm 30 against the urging force of the tension coil spring 64. It is not possible. Accordingly, in this state, the sheet S is prevented from advancing at the portion in contact with the restricting piece 31f, thereby forming a loop.

  On the other hand, since the sheet S is skewed at this time, the sheet S does not come into contact with the sheet contact portion 32a of the left regulation piece 31a in FIG.

  Accordingly, one side (left side in the drawing) of the sheet S that is not in contact with the regulating piece 31a can be continuously conveyed by the pre-registration roller 115 as the first sheet conveying means. As a result, as shown in FIG. 7, the sheet S comes into contact with the sheet contact portion 32 a of the left regulation piece 31 a that is not in contact with the sheet S.

  In this state, the sheet abutting portions 32 a and 32 f of the regulating pieces 31 a and 31 f provided in the vicinity of both ends of the sheet S both abut on the sheet S. Then, when the pressing force by the sheet S overcomes the urging force of the tension coil spring 64, all the regulating pieces 31 are pushed. Only in this state, the restricting piece 31 and the shutter arm 30 rotate about the shaft 20a of the registration upper roller 20 that is the rotation center of the shutter arm (second posture of the shutter member).

  In this state, the leading edge position of the sheet S is in a state where both ends in the sheet width direction are in contact with the sheet contact portion 32 of each regulating piece 31, and thus the same position with respect to the sheet conveyance direction, that is, a state where skew is corrected It is. When the restricting piece 31 and the shutter arm 30 are rotated, the sheet S is transported again because there are no obstacles, and the roller roller 20b of the lower resist roller and the roller 20b of the upper resist roller immediately after the skew is corrected. Enter the nip part of.

  The sheet S entering the nip portion between the rubber roller 10b of the lower registration roller 10 and the roller 20b of the upper registration roller 20 is conveyed to the secondary transfer unit while maintaining the skew correction state. In order to allow the skew-corrected sheet to be conveyed by the registration roller 116 in that state, when the shutter member is in the first posture, the sheet contact portion 32 with which the leading end of the sheet contacts is the registration roller 116. It is preferable to arrange so as to be located in the vicinity of the nip portion.

(Description of print job and shutter urging force switching operation)
Next, switching of the urging force of the shutter member in accordance with the type of sheet (hereinafter “paper type”) will be described.

  As described above, since the operation of rotating the regulating piece 31 and the shutter arm 30 by the sheet S is performed by the stiffness of the sheet S, the behavior of the sheets S having different basis weights is different.

  That is, in the thin paper sheet S having a small basis weight, the force for rotating the regulating piece 31 and the shutter arm 30 is relatively small. Therefore, if the urging force of the shutter arm 30 is too strong, the sheet may buckle or bend at a corner. Therefore, in the case of a thin paper sheet, the urging force of the shutter arm 30 is preferably set to about 2 to 3N.

  On the other hand, in the thick paper sheet S having a large basis weight, the force for rotating the regulating piece 31 and the shutter arm 30 is relatively large. Therefore, if the urging force of the shutter arm 30 is too weak, the regulation piece 31 and the shutter arm 30 are rotated only by a part of the skewed sheet coming into contact with the regulation piece, and the skew correction is sufficient. May not be possible. Therefore, in the case of a thick sheet, the urging force of the shutter arm 30 is preferably larger than that in the case of a thin sheet and is preferably set to about 4 to 5N.

  FIG. 8 is a flowchart showing an outline of a print job of the image forming apparatus according to this embodiment, and FIG. 9 is a block diagram. The operation of the image forming apparatus will be described with reference to FIGS.

  As described above, in this image forming apparatus, the process speed when the sheet is plain paper is 150 mm / s, and the sheet conveyance speed until the process speed is reduced to 200 mm / s before the secondary transfer unit is 200 mm / s. is there. In addition, the process speed when the sheet is thick paper and the sheet conveyance speed until the process speed is reduced to the process speed before the secondary transfer portion are ½ times that of plain paper, 75 mm / s and 100 mm / s, respectively. is there.

  In the image forming apparatus, the paper type set in advance by the user using the operation unit 51 or the like is registered.

For example, the upper cassette 111 and lower cassette 112 of Figure 1 basis weight are plain paper set of 80 g / m ^2, the manual feeding unit 113 basis weight is set cardboard 209 g / m ² Suppose that

  A print job is executed directly from the image forming apparatus or from a computer 52 connected via a network. At this time, the sheet to be used is selected from the upper cassette 111, the lower cassette 112, and the manual feed unit 113, together with the number of copies to be printed (S1).

  The image forming apparatus determines whether the paper type set in the feeding unit such as the selected cassette is plain paper or thick paper based on previously registered information (S2).

  When the paper type to be used is plain paper, the control means 50 instructs the motor 42 to rotate counterclockwise in FIG. 4 (S3), and when it is thick paper, the motor 42 rotates clockwise. (S5). Note that the rotation speed of the motor 42 of this embodiment is 15.9 rps.

(In the case of plain paper)
When the feeding unit on which plain paper is set is selected, the motor 42 rotates counterclockwise in FIG. For this reason, the one-way clutch 43 b in the first drive train 43 is locked, and the rotation is transmitted to the registration drive gear 41 by the first drive train 43. On the other hand, for the second drive train 44, the first gear 44a rotates at 15.9 / 2 = 7.95 rps due to the gear ratio with the motor gear. However, since the one-way clutch 44b is not locked, the rotation is not transmitted from the motor 42 downstream from the one-way clutch 44b. At this time, the rotation speed of the registration drive gear 41 is a value obtained by dividing the rotation speed of the motor 42 by the reduction ratio of the first drive train 43, that is, 15.9 / 4 = 3.975 rps. Since the diameter of the rubber roller 10b is φ16, the peripheral speed of the registration roller 116 is 3.975 × 16π = 200 mm / s.

  Incidentally, the final stage gear 44e of the second drive train 44 is engaged with the registration drive gear 41. For this reason, the gear 44e is rotated clockwise in FIG. 4 by the rotation of the registration drive gear 41 by the drive transmission from the first drive train 43. However, the one-way clutch 44f disposed in the inner diameter portion of the final gear 44e is locked when the shaft fitted to the inner diameter rotates clockwise as described above. Therefore, when the gear 44e is rotated clockwise, the shaft fitted to the inner diameter rotates relatively counterclockwise, and becomes free. For this reason, rotation is not transmitted from the one-way clutch 44f to the motor side of the second drive train.

  At this time, the urging force switching arm 62 is pulled by the tension coil spring 64 and is in contact with the stopper 63a (solid line state in FIG. 4).

(For cardboard)
Next, when the feeding unit on which thick paper is set is selected, the motor 42 rotates clockwise in FIG. 4 as opposed to the case of plain paper. Therefore, the one-way clutch 44 b in the second drive train 44 is locked, and the rotation is transmitted to the registration drive gear 41 by the second drive train 44. On the other hand, with respect to the first drive train 43, the first gear 43a rotates at 15.9 / 2 = 7.95 rps due to the gear ratio with the motor gear, but the one-way clutch 43b is not locked, so it is downstream from the one-way clutch 43b. The side is not transmitted rotation from the motor. At this time, the rotation speed of the registration drive gear 41 is a value obtained by dividing the rotation speed of the motor gear 42a by the reduction ratio of the second drive train 44, that is, 15.9 / 8 = 1.875 rps. As described above, since the diameter of the rubber roller 10b is φ16, the peripheral speed of the registration roller 116 is 1.9875 × 16π = 100 mm / s, which is half the speed of plain paper.

  By the way, the gear 43d coaxial with the first gear 43a of the first drive train 43 is also meshed with the registration drive gear 41. For this reason, the gear 43d rotates in the clockwise direction of FIG. 4 by the rotation of the registration drive gear 41 by the drive transmission from the second drive train 44. The rotation speed of the gear 43d is 1.9875 rps of the registration drive gear 41. Of the reduction ratio 4 of the first drive train 43, the reduction ratio is 2 by the gear ratio 1: 2 of the motor gear 42a and the first gear 43a. Rotate clockwise at a rate of 1.9875 × 2 = 3.975 rps, multiplied by a reduction ratio of 2 excluding.

  On the other hand, as described above, the first stage gear 43a meshes with the motor gear 42a, so that it rotates counterclockwise at 7.95 rps by the motor 42 rotating clockwise. From a relative viewpoint, the first gear 43a is rotating counterclockwise at 7.95 + 3.975 = 11.925 rps. For this reason, the torque limiter is in a free state, the first stage gear 43a and the coaxial gear 43d can rotate at their respective speeds, and no contradiction occurs.

  The control means 50 determines the rotation direction of the registration motor 42, and at the same time, determines the speed of each motor 53 that drives the image forming unit such as the photosensitive drum, the intermediate transfer belt, and the developing sleeve, and their peripheral speed is a predetermined process speed. (S4, S6). That is, in this embodiment, when the feeding unit on which plain paper is set is selected, the image forming unit such as the photosensitive drum, the intermediate transfer belt, and the developing sleeve is driven at a peripheral speed of 150 mm / s (S4). ). On the other hand, when the feeding unit on which thick paper is set is selected, these image forming units are driven at a peripheral speed of 75 mm / s, which is half the speed of plain paper (S6).

  The urging force of the tension coil spring 64 against the shutter arm 30 can be switched by the urging force switching means according to the rotation direction of the motor 42. This will be specifically described.

  When the feeding unit on which plain paper is set is selected and the registration motor 42 rotates counterclockwise in FIG. 4, the one-way clutches 44b and 44f of the second drive train do not lock together as described above. The gear train 60 as the power switching means does not rotate. Therefore, since the urging force switching arm 62 is pulled by the tension coil spring 64 as described above, it comes into contact with the stopper 63a. At this time, since the operating length of the tension coil spring 64 becomes relatively short, the urging force of the shutter arm 30 is set to be about 2 to 3 N, which is appropriate for correcting the skew of the plain paper.

  On the other hand, when the feeding unit on which the thick paper is set is selected and the registration motor 42 rotates clockwise in FIG. 4, the one-way clutch 44b of the second drive train is locked as described above. For this reason, the gear train 60 as the urging force switching means is driven by the second drive train 44 and rotates. Then, the urging force switching arm 62 rotates counterclockwise in FIG. 4 and comes into contact with the stopper 63b. Even if the gear train 60 continues to rotate while the urging force switching arm 62 is in contact with the stopper 63b, the torque limiter 61 provided on the urging force switching arm 62 slips, and the urging force switching arm 62 is moved to the stopper 63b. Continue to abut on. At this time, since the operating length of the tension coil spring 64 becomes relatively long, the urging force of the shutter arm 30 becomes stronger than that of plain paper. The urging force at this time is set to be about 4 to 5N, which is appropriate for correcting skew feeding of the thick paper.

  In this way, the speeds of the registration motor 42 and the motor for driving the image forming unit are set, the operating length of the tension coil spring 64 is changed corresponding to the paper type, and the urging force of the shutter arm 30 is appropriate for the paper type. The image forming operation is started (S7).

  In addition, the feeding motor 54 starts to be driven at a predetermined timing so that the toner image on the intermediate transfer belt and the leading end position of the sheet to be transferred are matched in the secondary transfer unit, and the selected feeding unit Sheet feeding is started (S8).

  After feeding the sheet, the sheet is conveyed at a conveyance speed faster than the image forming unit (200 mm / s for plain paper, 100 mm / s for thick paper).

  When the sheet reaches the shutter member, the skew that occurred during conveyance by the above-described operation is corrected (S9). At this time, since the urging force by the tension coil spring 64 has an appropriate value corresponding to the paper type, the skew of the sheet is reliably corrected.

  The leading edge of the sheet conveyed by the registration roller in a state where the skew is corrected (S10) is detected by the registration sensor 117 (S11). Then, the control means 50 calculates the timing at which the sheet speed is reduced from the conveyance speed to the process speed so that the leading edge of the toner image on the intermediate transfer belt coincides with the leading edge of the sheet at the secondary transfer portion (S12). The registration motor 42 is decelerated at that timing (S13). That is, when the sheet reaches the registration sensor 117 with a delay, the deceleration timing is delayed. On the contrary, when the sheet reaches the registration sensor 117 earlier, the deceleration timing is advanced so that the front end of the toner image on the intermediate transfer belt is aligned with the secondary transfer unit.

  Thereafter, the toner image on the intermediate transfer belt is transferred to the sheet in the secondary transfer unit (S14), the toner image is fixed on the sheet by heat and pressure in the fixing device 110 (S15), and selected by the discharge unit switching means 55. Is discharged from the discharged discharge unit (S16), and the print job ends.

  As described above, the user only selects the feeding unit in which the paper type to be used is set, and the image forming speed necessary for fixing the paper type is selected, and the skew of the paper type is selected. An appropriate biasing force of the shutter arm is automatically selected to correct the above. Therefore, the user operability can be significantly improved.

  Further, since the actuator is not used for switching the urging force of the shutter arm 30, this function can be realized at low cost.

  In the present embodiment, as illustrated in FIG. 6, the case where the sheet S is skewed in the left direction in the sheet width direction has been described, but the sheet S is in the opposite direction (right direction) to the present embodiment. Obviously, the skew correction can be similarly performed for the case where the skew is performed.

  Further, in the present embodiment, the description has been made with specific values such as the process speed of plain paper and cardboard, the urging force of the shutter arm 30 and the reduction ratio of the drive train of the registration rollers. It is clear that is not limited to these values.

  In addition, the electrophotographic image forming apparatus has been described as an example, but it is apparent that the skew correction operation can be similarly performed in other image forming apparatuses such as an ink jet system.

[Second Embodiment]
Next, an image forming apparatus according to the second embodiment will be described. Note that the basic configuration of the apparatus of this embodiment is the same as that of the above-described embodiment, and thus a duplicate description is omitted. Here, a configuration that is a feature of this embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  In the present embodiment, the configuration of the drive mechanism of the lower registration roller 10 is different from that of the first embodiment. The drive mechanism will be described with reference to FIGS. 10 and 11 are side views showing a driving mechanism of a registration roller constituting the skew feeding correcting apparatus according to the second embodiment, and FIG. 12 is a schematic diagram of the driving mechanism.

  A registration driving gear 41 is attached to the registration lower roller 10. A first drive train 70 and a second drive train 71 are disposed between the motor gear 42 a attached to the motor 42 and the registration drive gear 41. Here, the speed reduction ratio of the second drive train 71 is set to twice the speed reduction ratio of the first drive train 70.

  The motor gear 42a meshes with a swing center gear 72 as an input side gear. The swing center gear 72 meshes with a swing gear 74 as an output side gear, which is rotatably supported by a swing arm 73 as a support member. Here, the swing arm 73 is rotatable about the same axis as the swing center gear 72 as a fulcrum.

  The rocking gear 74 is configured so that a predetermined frictional force acts between the rocking gear 74 and the bearing. Thus, when the swing center gear 72 rotates, the swing center gear 72 and the swing gear 74 are engaged with each other, and the swing arm 73 swings in the rotation direction of the swing center gear 72 by the friction force. It is supposed to be. The swinging gear 74 swings against the frictional force because the swinging arm 73 is prevented from swinging after meshing with the gear of the first drive train 70 or the second drive train 71. The rotational force of the center gear 72 is transmitted to rotate.

  Accordingly, in FIG. 10, when the motor 42 rotates counterclockwise, the swing center gear 72 rotates clockwise. Then, the swing arm 73 swings clockwise by the force received from the swing center gear 72, and the swing gear 74 supported thereby constitutes the first drive train 70, as shown in FIG. Engage with the gear.

  On the contrary, when the motor 42 rotates clockwise, the swing center gear 72 rotates counterclockwise, so that the swing arm 73 swings counterclockwise by the force received from the swing center gear 72. As a result, the swing gear 74 supported by the swing arm 73 meshes with the gear constituting the second drive train 71, as shown in FIG.

  That is, when the motor is rotated counterclockwise by the control means 50, the driving of the registration lower roller 10 is transmitted by the first drive train 70 as shown in FIG. On the other hand, when the motor 42 is rotated clockwise, the lower registration roller 10 is driven by the second drive train 71 as shown in FIG.

  Further, a tension coil spring 64 as an urging means is hung between the swing arm 73 and the shutter arm 30. Therefore, the operating length of the tension coil spring 64 changes depending on the position of the swing arm 73, that is, the urging force of the shutter arm 30 changes.

  When the feeding unit on which plain paper is set is selected, the control unit 50 rotates the registration motor 42 counterclockwise. Then, as described above, the swing arm 73 is in the state shown in FIG. 10, the operating length of the tension coil spring 64 that biases the shutter arm 30 becomes relatively short, and the biasing force of the shutter arm 30 is corrected for the skew of plain paper. It is set to be about 2 to 3 N, which is appropriate for the above.

  On the other hand, when the feeding unit on which the thick paper is set is selected, the control unit 50 rotates the registration motor 42 clockwise. Then, the swing arm 73 is in the state shown in FIG. 11, the operating length of the tension coil spring 64 that biases the shutter arm 30 becomes relatively long, and the biasing force of the shutter arm 30 is appropriate for correcting skew feeding of the cardboard. , About 4-5N.

  As described above, also in this embodiment, the user only selects the feeding unit in which the paper type to be used is set, and the image forming speed necessary for fixing the paper type is selected. An appropriate biasing force of the shutter arm is automatically selected to correct the skew of the paper type. Therefore, the user operability can be remarkably improved.

  Further, since the actuator is not used for switching the urging force of the shutter arm, this function can be realized at low cost.

  Further, as compared with the case of the first embodiment, since the one-way clutch and the torque limiter are not required, this function can be realized at a lower cost.

S ... Sheet 10 ... Registration lower roller 20 ... Registration upper roller 30 ... Shutter arm 31 ... Restriction piece 32 ... Sheet contact portion 36 ... Projection piece 41 ... Registration drive gear 42 ... Motor 43 ... First drive train 44 ... Second Drive train 50 ... control means 51 ... operating section 60 ... gear train 62 ... biasing force switching arm 64 ... tension coil spring 70 ... first drive train 71 ... second drive train 72 ... swing center gear 73 ... swing arm 74: Swing gear 115 ... Pre-registration roller 116 ... Registration roller

Claims (7)

First sheet conveying means for conveying a sheet;
A second sheet conveying means disposed on the downstream side in the sheet conveying direction from the first sheet conveying means and including a pair of sheet conveying rotating bodies for conveying the sheet;
A sheet locking portion that is upstream of the nip portion of the pair of sheet conveyance rotating bodies in the sheet conveyance direction and in the vicinity of the nip portion, and abuts against the sheet leading edge to lock the sheet leading edge; A shutter member that is swingable between a first posture in which the sheet locking portion locks the leading edge of the sheet conveyed by the first sheet conveying means and a second posture in which the sheet can pass;
Biasing means for biasing the shutter member so as to maintain the first posture;
A motor for rotationally driving the second sheet conveying means;
Control means for controlling the rotation direction of the motor according to the type of sheet to be used;
A first drive train for drivingly connecting the motor and the second sheet conveying means, and a second drive train having a reduction ratio different from that of the first drive train;
Drive train switching means for switching and transmitting the driving force of the motor to the first drive train or the second drive train according to the rotation direction of the motor;
An urging force switching means for switching an urging force of the urging means against the shutter member according to a rotation direction of the motor;
A sheet skew correction device comprising:   The urging force switching means operates so that the urging force of the shutter member is increased when a drive train having a larger reduction ratio is selected from the first drive train or the second drive train. The sheet skew correcting device according to claim 1, wherein:   The sheet skew correcting device according to claim 1, wherein the urging unit includes a spring, and the urging force switching unit changes an operating length of the spring.   4. The seat skew according to claim 1, wherein the drive train switching means is a one-way clutch disposed in the first drive train and the second drive train. 5. Line correction device. The first drive train and the second drive train are constituted by gear trains,
The drive train switching means includes, on a support member, an input side gear that receives a drive force from the motor, and an output side gear that transmits the drive force to the first drive train or the second drive train. ,
The support member is swingable about a rotation center of the input side gear, and swings in a rotation direction of the input side gear so that the output side gear is the first drive train or the second drive. The sheet skew correction device according to any one of claims 1 to 3, wherein the sheet skew correction gear meshes with a row of gears.   6. The shutter according to claim 1, wherein the shutter member is swingable about a rotation center of one of the pair of sheet transport rotators. Sheet skew correction device. A sheet skew correction device according to any one of claims 1 to 6, comprising:
An image forming apparatus comprising: an image forming unit configured to form an image on a conveyed sheet whose skew is corrected by the sheet skew correcting device.

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