JP2015030571A - Sheet oblique motion correction device and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct oblique motion whatever bias weight a conveyed sheet has without setting energizing force of a sheet restriction member in advance.SOLUTION: A guide member 21 on a sheet conveyance upstream side of a sheet restriction member 12 is moved by utilizing stiffness of a sheet. When the sheet is not stiff enough, the guide member 21 guides the sheet so that the front end of the sheet abuts on a side (first position) 12b farther away from the center of rotation of the sheet restriction member 12. When the sheet is stiff enough, the guide member 21 guides the sheet so that the front end of the sheet abuts on a side (second position) 12c close to the center of rotation of the sheet restriction member 12.

Description

  The present invention relates to a sheet skew correction device that corrects skew of a conveyed sheet and an image forming apparatus using the same.

  In general, in an image forming apparatus such as a printer, a copier, a facsimile machine, or a complex machine thereof, sheets separated one by one from a cassette containing sheets are conveyed, and the skew of the sheet is corrected during the conveyance, thereby An image is formed by the forming unit.

  As a conventional sheet skew correction apparatus, a sheet skew correction apparatus including a shutter (sheet restriction member) biased in a direction opposite to the sheet conveying direction has been proposed. The sheet is conveyed toward the sheet skew correction device by a conveyance roller provided upstream, and the conveyed sheet forms a loop on the sheet while the leading edge abuts the shutter and the pushing force of the sheet is lower than the shutter biasing force. To go. At this time, the leading edge of the sheet is uniformly pressed against the shutter, and the skew of the leading edge of the sheet is corrected by forming a loop on the sheet. When the sheet is further pushed in, the pushing force of the sheet exceeds the shutter urging force. At that time, the shutter is opened and transferred to a registration roller provided immediately after the shutter and conveyed downstream (see Patent Document 1). .

  Here, the pushing force of the sheet varies depending on the basis weight of the sheet. Generally, the pushing force is low when the basis weight is low, and the pushing force is high when the basis weight is high. Is different. Therefore, a method has been devised in which a shutter urging force is generated using a spring, a hooking portion of the shutter urging spring is selected stepwise to change the pulling length, and the shutter urging force is switched (see Patent Document 2). ). If this method is used, it is possible to switch the shutter urging force in advance according to the basis weight of the sheet to be used.

  In Patent Document 2, the hooking portion of the shutter urging spring is manually switched. As an alternative, the basis weight of the sheet is input from the operation unit or the changeover switch, and the control unit makes a judgment based on the input signal to operate the actuator, and switches the hooking portion of the shutter biasing spring. It is also possible to switch power.

JP 09-183539 A JP-A-11-011745

  In the shutter configuration in which the urging force is generated by the spring, the shutter urging force gradually increases as the shutter is opened and the sheet is conveyed downstream. Therefore, if the amount of increase in the urging force is large, there is a concern that depending on the sheet, scratches such as dents may occur at the leading edge, and the skew feeding may not be corrected because the sheet is not reliably conveyed to the registration roller nip. Therefore, it is desirable to set the spring multiplier of the spring that generates the shutter biasing force as low as possible so that the shutter biasing force is not increased as much as possible when the sheet is conveyed downstream.

  However, in the case of the method of switching the shutter urging force according to the pulling length of the shutter urging spring as in Patent Document 2, if the spring multiplier of the spring being used is set low, it is necessary to widen the interval between the spring hooks. is there. Therefore, it is necessary to secure a space for that purpose. On the other hand, if the space is to be minimized, the spring multiplier needs to be set high, and there is a possibility that the amount of increase in the shutter urging force becomes large as described above.

  Furthermore, when the shutter biasing force is switched in advance according to the basis weight of the sheet to be used, the pushing force of the sheet is not uniform even with the same basis weight, and the optimum shutter biasing force is obtained depending on the basis weight of the sheet. It may not be possible to set.

  Accordingly, the present invention provides a sheet skew correction device and image formation capable of correcting skew feeding regardless of the basis weight of any sheet without using a method of switching the biasing force by changing the tension length of the spring. An object is to provide an apparatus.

  In order to solve the above-described problem, a sheet skew correcting device according to the present invention includes a first sheet conveying unit and a second sheet conveying unit disposed upstream of the first sheet conveying unit in the sheet conveying direction. And the first sheet conveying unit disposed in the vicinity of the first sheet conveying unit and locking the leading end of the sheet conveyed by the second sheet conveying unit upstream of the first sheet conveying unit in the sheet conveying direction. A sheet restricting member rotatably held in a second attitude that allows the sheet to pass through, and a holding means that holds the sheet restricting member in the first attitude with a biasing force; A guide member that guides the sheet conveyed by the second sheet conveying unit to the sheet regulating member, and the guide member has a front end that is forward when the sheet is guided to the sheet regulating member. First position distant from the rotation center of the sheet regulating member, and wherein the movably supported so as to abut between the second position close to the center of rotation of the sheet regulating member.

  According to the present invention, no matter what basis weight sheet is conveyed, the position where the sheet hits the sheet regulating member is changed, and the force necessary for the sheet to push the sheet regulating member is changed to the strength of the waist of the sheet. By changing accordingly, it is possible to correct the skew of the sheet. Further, since the configuration for switching the pulling length of the spring is not required, the configuration can be simplified and the cost can be reduced.

1 is an overall schematic front view showing an image forming apparatus to which the present invention is applied. (A) is the perspective view which shows the sheet | seat skew correction | amendment apparatus, (b) is the right view. 1 is a cross-sectional view illustrating a sheet skew correction device according to a first embodiment of the present invention. In the sheet skew correction device according to the first embodiment of the present invention, (a), (b), (c), (d) and (e) are cross-sectional views showing different states of skew correction. In the sheet skew correction device according to the first embodiment of the present invention, (a) and (b) are right side views showing different states of skew correction. 4A and 4B are cross-sectional views illustrating a state in which the leading end of the sheet is in contact with a different position of a shutter (sheet regulating member) in the sheet skew correction device according to the first embodiment of the present invention. In the sheet skew correction apparatus according to the second embodiment of the present invention, (a), (b), (c), (d) are cross-sectional views showing different states of skew correction. The perspective view of the sheet | seat skew correction apparatus which concerns on the 3rd Embodiment of this invention. In sheet skew correction device concerning a 3rd embodiment of the present invention, (a), (b), (c), and (d) are sectional views showing a state from which skew correction differs, respectively. FIGS. 9A and 9B are cross-sectional views illustrating different states of skew correction in a sheet skew correction apparatus according to a third embodiment of the present invention. FIGS. FIG. 10 is a cam curve diagram illustrating a cam height of an urging cam with respect to a shutter rotation angle in a sheet skew correction device according to a third embodiment of the present invention.

  Hereinafter, an example of an image forming apparatus including the sheet skew correction device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus provided with a sheet skew correcting device employing the present invention. First, the cassette 111 is provided so as to be able to be pulled out in the front direction in FIG. On the other hand, image information transmitted from an external connection cable (not shown) is processed by a controller (not shown). Further, a laser beam is emitted from the laser scanner unit 142 by a signal based on the processing result, and an electrostatic latent image is formed on the photosensitive drum 141. The electrostatic latent image on the photosensitive drum is developed by the developing unit 143, and a toner image is formed on the photosensitive member. Thereafter, a predetermined pressure and an electrostatic load bias are applied by the primary transfer device 144, and the toner image is transferred onto the intermediate transfer belt 145. In the case of FIG. 1, the image forming unit 140 described above includes four sets of yellow Y, magenta M, cyan C, and black Bk.

  Next, the intermediate transfer belt 145 will be described. The intermediate transfer belt 145 is conveyed and driven in the direction of arrow A in FIG. Accordingly, the Y, M, C, and Bk image forming units 140 described above perform parallel processing. The image forming process for each color is performed at a timing of superimposing the upstream toner image primarily transferred onto the intermediate transfer belt. As a result, a full-color toner image is finally formed on the intermediate transfer belt 145 and conveyed to the secondary transfer unit 130.

  On the other hand, the sheets S such as paper and OHT stacked and stored in the cassette 111 are separated and fed one by one by the paper feeding unit 110. The fed sheet S is transferred to the second conveying roller pair (second conveying means) 120, and the sheet skew correction is arranged on the downstream side in the sheet conveying direction (hereinafter simply referred to as “downstream side”). The sheet is conveyed toward the apparatus 10 and the skew of the sheet S is corrected. Thereafter, the sheet S transferred to the first conveying roller pair (first conveying means) 30 arranged further downstream is conveyed to the secondary transfer unit 130 by the first conveying roller pair 30. .

  As described above, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 130 by the conveyance process and the image forming process described above. Thereafter, the sheet S is conveyed to the fixing device 150. The fixing device 150 melts and fixes the toner on the sheet S by applying a predetermined pressurizing force by a substantially opposed roller or belt and generally a heating effect by a heat source such as a heater. The sheet S having a fixed image obtained in this way passes through the post-fixing conveyance section 160 and is discharged as it is onto the paper discharge tray 170 by the paper discharge roller 161. When double-sided image formation is required, the image is conveyed to the reverse conveying device 180 through the switching flapper 162.

  Next, a first embodiment of the sheet skew correction device 10 that is a feature of the present invention will be described in detail with reference to FIGS. As shown in FIG. 2, the first transport roller pair (first transport means) 30 is composed of a transport roller 31 and a transport roller 32. The conveyance roller 31 is divided into a plurality of parts in a direction orthogonal to the sheet conveyance direction, and rotates integrally with the rotation shaft 31a. The transport roller 32 is divided into a plurality of parts facing the positions corresponding to the plurality of transport rollers 31 and is rotatably supported by a fixed shaft (support shaft) 33 fixed to the frame 34. .

  A shutter 11 in which the seat regulating member 12 and the bearing portion 14 are integrally connected to the connecting member 13 is rotatably supported on the fixed shaft 33 by the bearing portion 14. Here, the sheet regulating member 12 is disposed between the conveyance rollers 32 divided into a plurality of parts, and the bearing portions 14 are disposed at both ends of the connecting member 13.

  As shown in FIG. 3, the shutter 11 is urged by a shutter urging spring (holding means, urging portion) 15 in the direction of the arrow 15 a around the fixed shaft 33. By abutting the stopper surface 14b of the shutter 11 and the stopper surface 34b of the frame 34, the rotation of the shutter 11 in the direction of the arrow 15a is restricted, and the shutter 11 is held in the initial posture (first posture).

  Further, in the state where the shutter 11 is held in the first posture (initial posture), the abutting surface 12a of the sheet regulating member 12 is the nip portion of the first conveying roller pair 30 as shown in FIG. It is arranged so as to be positioned upstream of the sheet conveying direction (hereinafter simply referred to as “upstream side”). Further, when the leading edge of the sheet comes into contact with the abutting surface 12a of each sheet regulating member 12 and the sheet is conveyed by the first conveying roller pair (first conveying means) 30 in this state, each sheet regulating member 12 is Then, the sheet rotates to the second posture (retracted posture) in which the sheet has passed the nip portion against the biasing force of the shutter biasing spring 15. In other words, the sheet regulating member 12 is disposed in the vicinity of the first sheet conveying roller pair (conveying means) and is rotatably held between the first posture and the second posture. Specifically, the sheet regulating member 12 is rotatable about the support shaft (fixed shaft) 33, and has a first posture located on the upstream side of conveyance of the nip portion and a second position located on the downstream side of conveyance of the nip portion. It is rotated to the posture. The shutter urging spring 15 is an urging portion that urges the sheet regulating member 12 toward the first posture, and a holding unit that holds the sheet regulating member in the first posture with a predetermined urging force. It is.

  A guide member 21 is provided on the upstream side of the shutter 11 to guide the sheet S conveyed by the second conveying roller pair (second conveying means) 120 to the shutter 11 and the first conveying roller pair 30. ing. The guide member 21 is movable (swingable) with the upstream side in the sheet conveying direction as a fulcrum by pivotal portions 21a provided at both ends in the width direction at the upstream end in the sheet conveying direction being pivotally supported by the frame 34. It is supported by. The guide member 21 is urged by the guide urging spring 22 in the direction of the arrow 22a. By abutting the stopper surface 21c of the guide member 21 and the stopper surface 34d of the frame 34, the swinging of the guide member 21 in the direction of the arrow 22a is restricted, and the guide member 21 is held in the initial posture. The guide member 21 has a curved portion such that the upstream side in the sheet conveying direction faces the biasing direction of the guide biasing spring (biasing means) 22 (the direction of the arrow 22a). That is, in the guide member 21, the upstream side in the sheet conveyance direction is biased in the biasing direction of the guide biasing spring 22 with respect to the downstream side. Accordingly, the guide member 21 rotates about the rotating portion 21a against the urging force of the guide urging spring 22 by the waist of the seat, and the downstream end position of the guide member 21 moves.

  Next, the skew correction operation of the sheet S by the sheet skew correction device 10 will be described with reference to FIGS. When the sheet S is conveyed downstream by the second conveying roller pair 120, the sheet S is guided to the sheet regulating member 12 of the shutter 11 by the guide member 21. When the sheet S is skewed and conveyed as shown in FIG. 5A, the leading end S <b> 2 on the preceding side (right side in the figure) of the sheet S comes into contact with the abutting surface 12 a of the sheet regulating member 12. At this time, the leading end S3 on the subsequent side (left side in the figure) of the sheet S is not in contact with the sheet regulating member 12, and the pushing force of the sheet S cannot exceed the urging force generated by the shutter urging spring 15. The shutter 11 cannot be pushed and rotated.

  When the sheet S is further conveyed by the second conveying roller pair 120, the leading end S2 on the preceding side is engaged with the abutting surface 12a of the sheet regulating member 12 as shown in FIG. The leading end S3 on the subsequent side is sequentially brought into contact with the abutting surface 12a of the sheet regulating member 12 and locked. When the sheet S is further conveyed, the sheet S forms a loop as shown in FIG. 4B, and the entire leading edge of the sheet S is brought into contact with the abutting surface 12 a of the sheet regulating member 12 by the strength of the waist of the sheet S itself. The skew of the sheet S is corrected.

  When the sheet S forms a predetermined loop, the pushing force of the sheet S exceeds the urging force generated by the shutter urging spring 15, and the shutter 11 rotates in the direction of the arrow 15b. When the sheet regulating member 12 is retracted, the leading edge of the sheet S is nipped by the first conveying roller pair 30, and the leading edge of the sheet S is conveyed downstream with the skew correction corrected.

  When the sheet S is conveyed downstream by the first conveying roller pair 30, the abutting surface 12a of the sheet regulating member 12 and the leading edge of the sheet S are separated from each other, and the sheet regulating member 12 is moved as shown in FIG. 2 posture. Then, the sheet regulating member 12 is rotated in the opposite direction by the urging force of the shutter urging spring (the urging portion) 15 in a state where the rear end of the sheet has passed the abutting surface 12a in the second posture. The first posture is maintained.

  As described above, when the basis weight of the sheet S is low (when the waist of the sheet is weak), even if the sheet S is conveyed obliquely as described above, the entire leading edge of the sheet S is transferred to the sheet regulating member 12. At the end, a loop can be formed to correct skew. However, when the basis weight of the sheet S is high and the sheet S is strong, when the sheet S is conveyed obliquely, a part of the leading edge of the sheet S comes into contact with the abutting surface 12a of the sheet regulating member 12 Therefore, the urging force generated in the shutter 11 by the shutter urging spring 15 may be exceeded, and the sheet S may be nipped by the first conveying roller pair 30 and conveyed downstream without correcting skew.

  Therefore, in the present embodiment, the guide member 21 provided upstream of the shutter 11 is urged by the guide urging spring 22 and is arranged so as to be able to swing, so that even when the basis weight of the sheet S is high, the skew is reliably performed. Is corrected.

  The sheet S conveyed by the second conveying roller pair 120 is guided to the shutter 11 while abutting and sliding on the guide member 21. When the leading edge of the sheet S reaches the guide member 21, the relationship between the force Fg that causes the sheet S to swing the guide member and the biasing force F22 of the guide biasing spring 22 that biases the guide member 21 causes the guide member 21 to move. The position is determined.

As shown in FIG. 4A, when the basis weight of the sheet S is low and the relationship between the force Fg that causes the sheet S to swing the sheet guide and the biasing force F22 generated by the guide biasing spring 22 is Fg <F22. The guide member 21 is held in the initial posture. Then, the leading end 21b of the guide member 21 guides the sheet S toward the leading end side of the abutting surface 12a of the sheet regulating member 12 (the side far from the rotation center 33 of the sheet regulating member 12; referred to as the first position). 4B, the sheet S reaches the leading end side (first position) 12b of the abutting surface 12a. Here, as shown in FIG. 6A, the distance between the abutting surface front end side 12 b reached by the sheet S and the center of the fixed shaft 33 that is the rotation center of the sheet regulating member 12 is Rs, and the sheet S abuts. When the moment applied to the shutter 11 generated at the center of the fixed shaft 33 by the force Fs applied to the shutter on the front surface side 12b is Ms, and the moment of the shutter 11 by the shutter urging spring 15 with respect to the fixed shaft 33 is M15, the shutter 11 When starting to rotate in the direction of arrow 15b,
M15 = Ms = Fs × Rs... C1
The relationship holds.

  If a sheet having a high basis weight is conveyed in a configuration in which the guide member 21 does not swing, the leading edge of the preceding side of the sheet S is conveyed when the leading edge of the sheet S is conveyed obliquely because the sheet S is stiff. When the portion S2 reaches the abutting surface 12a, a pressing force Fs sufficient to satisfy the expression C1 and rotate the shutter 11 is obtained, and the skew of the sheet S is conveyed downstream without being corrected. It will be.

However, in this embodiment, since the guide member 21 is configured to be swingable, skew correction can be performed even when the basis weight of the sheet S is high as follows. Here, when the sheet S ′ having a high basis weight is conveyed, the relationship between the force Fg ′ that causes the sheet S ′ to swing the guide member 21 and the urging force F22 generated by the guide urging spring 22 satisfies Fg ′> F22. In this case, as shown in FIG. 4 (d), the guide member 21 rotates from the initial posture in the direction of the arrow 22b and assumes a retracted posture. In this state, the leading end 21b of the guide member 21 faces the sheet S ′ toward the base side (side closer to the rotation center of the sheet regulating member 12; the second position) of the abutting surface 12a of the sheet regulating member 12. As shown in FIG. 4E, the sheet S ′ reaches the base side (second position) 12c of the abutting surface 12a. Here, as shown in FIG. 6B, the distance between the abutting surface base side 12c reached by the sheet S and the center of the fixed shaft 33, which is the rotation center of the shutter 11, is Rs 'and the sheet S' abuts. Assuming that the moment applied to the shutter 11 at the center of the fixed shaft 33 by the force Fs ′ applied to the shutter on the surface base side 12c is Ms ′, and the moment of the shutter 11 by the shutter urging spring 15 with respect to the fixed shaft 33 is M15. When 11 starts to rotate in the direction of arrow 15b,
M15 = Ms ′ = Fs ′ × Rs ′... C2
The relationship holds.

  From the above, when the relationship between the formula C1 and the formula C2 is arranged, the point (first position) 12b where the sheet S having a low basis weight reaches the sheet regulating member 12 is far from the rotation center of the sheet regulating member 12, and Since the point (second position) 12c at which the sheet S ′ having a high basis weight reaches the sheet regulating member is close to the rotation center of the sheet regulating member 12, the relationship of Rs> Rs ′ is established. As a result, the relationship of Fs <Fs ′ is clear from the equations C1 and C2. That is, when the basis weight of the sheet S is high, the guide member 21 can be swung from the initial posture in the direction of the arrow 22b. (Second position) 12c. As a result, the force Fs necessary for the sheet S to push the shutter 11 can be increased, so that the leading end of the sheet S is in the width direction with respect to the sheet regulating member 12 of the shutter 11 as shown in FIG. It is possible to form an abutting loop as a whole, and it is possible to correct skew even when the basis weight of the sheet S is high.

  If the configuration described above is used, the moment that the sheet S gives to the shutter 11 can be made substantially constant regardless of the basis weight of the sheet S being conveyed. Accordingly, the sheet S pushes the shutter 11 by changing the distances Rs and Rs ′ from the rotation center of the sheet regulating member 12 at the position where the sheet S hits the sheet regulating member 12 without adjusting the urging force of the shutter 11 in advance. By optimizing the force necessary for the sheet S according to the waist strength of the sheet S, it is possible to provide a sheet skew correction device capable of correcting skew in any basis weight of the sheet S.

  Next, a second embodiment of the present invention will be described with reference to FIG. In the first embodiment described above, the guide member 21 is swingably supported and biased using the biasing spring 22, whereby the guide member 21 utilizes the force by which the sheet S swings the guide member 21. The direction in which the tip 21 b of 21 guides the sheet regulating member 12 of the shutter 11 is determined. In the second embodiment, a flexible guide member 23 is used instead of the guide member 21.

  The flexible guide member 23 is fixed to a guide base 24 fixed to the frame 34 with a double-sided tape or the like. As a result, the guide member 23 has a force F23 for maintaining the initial posture in the natural state as shown in FIG. When the basis weight of the sheet S is low, F23 is larger than the force Fg that the sheet S applies to the guide member 21, and the guide member 23 maintains the initial posture as shown in FIG. It is guided to the leading end side (the side far from the rotation center 33 of the sheet regulating member 12; the first position) 12b with respect to the abutting surface 12a of the regulating member 12. On the other hand, in the case of the sheet S ′ having a high basis weight, the initial posture is maintained until the sheet S ′ reaches the guide member 23, but when the sheet S ′ reaches the guide member 23 as shown in FIG. Since the biasing force F23 due to flexibility is smaller than the force Fg ′ applied to the guide member 21 by the sheet S ′, the guide member 23 bends in the direction of the arrow 22b, and as shown in FIG. It is guided to the base side (side closer to the rotation center of the sheet regulating member 12; second position) 12 c with respect to the abutting surface 12 a of the sheet regulating member 12.

  As described above, the lower the basis weight of the sheet S, the more the leading end of the sheet S is guided toward the leading end side with respect to the sheet abutting surface 12a of the sheet regulating member 12 of the shutter 11, and the higher the basis weight of the sheet S, the more the sheet Since the leading end of S is guided toward the base side with respect to the sheet abutting surface 12a of the sheet regulating member 12, the relationship of the formula C1 and the formula C2 is established as in the first embodiment, and the basis weight of the sheet S is determined. It is possible to correct skewing regardless.

  Next, a third embodiment of the present invention will be described with reference to FIGS. In the first and second embodiments, the sheet regulating member 12 of the shutter 11 has one abutting surface 12a, and the abutting surface 12a is upstream of the first conveying roller pair 30 in the sheet conveying direction. In the third embodiment, the sheet regulating member 12 ′ is used to reciprocate between the first posture that locks the leading end of the sheet on the side and the second posture that allows the sheet to pass therethrough. Uses a rotary shutter 11 ′ having a plurality of (for example, three) butting surfaces 12 ′ a and rotating in one direction.

  As shown in FIGS. 8 and 9, in the shutter 11 ′, a sheet regulating member 12 ′, an urging cam (cam member) 43, and a shutter shaft (support shaft) 44 are integrally connected. The frame 34 is rotatably supported. The sheet regulating member 12 ′ is disposed between the plurality of divided conveyance rollers 32, and the conveyance rollers 32 are rotatably supported by the shutter shaft 44. A plurality of sheet regulating members 12 ′ are provided in the circumferential direction, and each includes a plurality (three) of abutting surfaces 12 ′ a against which the leading edge of the sheet S abuts. The urging cam (cam member) 43 corresponds to the sheet regulating member 12 'and includes a bottom portion 43a and a vertex portion 43b. The urging cam 43 and the tip of the urging arm 46 that is rotatably supported by the frame 34 and is urged by an arm urging spring (elastic member) 45 are in rolling contact via frictional contact or rollers. . Normally, the urging arm 46 is stopped with the tip end of the urging arm 46 and the bottom portion 43a of the urging cam being matched. The urging cam 43, the urging arm 46 and the arm urging spring 45 constitute a positioning means, and the sheet regulating member 12 'is positioned and held in a stopped state where the deformation amount of the arm urging spring 45 which is a resilient member is the smallest. Is done. At this time, the abutting surface 12 ′ a of the sheet regulating member 12 ′ is arranged in a first posture positioned upstream of the first conveying roller pair 30 as shown in FIG.

  When the sheet S is conveyed by the second conveying roller pair 120 and guided to the shutter 11 ′ by the guide member 21, as shown in FIG. 9B, the leading edge of the sheet S is the sheet as in the first embodiment. A butting loop is formed on the butting surface 12'a of the regulating member 12 '. When the pushing force of the sheet S exceeds the urging force generated on the shutter 11 ′ by the urging arm, the shutter 11 ′ rotates in the direction of the arrow 11 ′ and the sheet regulating member 12 ′ is retracted. As a result, the sheet S is nipped by the first conveying roller pair 30, and the leading edge of the sheet S is conveyed downstream with the skew correction corrected. When the sheet S is further conveyed, the shutter 11 ′ is further rotated, and the tip of the urging arm 46 gets over the apex portion 43 b of the urging cam 43 as shown in FIG. It rotates in the direction of the arrow 11a and is held in the second posture waiting for the sheet S to pass as shown in FIG.

Here, the distance rb from the rotation center of the sheet regulating member 12 ′ to the abutting surface 12b shown in FIG. 10A and the abutting surface from the rotation center of the sheet regulating member 12 ′ shown in FIG. 10B. The distance rc to 12c is
rb> rc (1)
Are in a relationship. Further, the abutting surface 12b when the sheet S abuts against the abutting surface (the side rb distant from the rotation center of the sheet regulating member 12 ′; first position) 12b shown in FIG. The rotation angle θb when rotating from the posture (standby position) to the nip position, and the abutting surface (side rc near the rotation center of the sheet regulating member 12 ′; second position) 12c shown in FIG. The rotation angle θc when the abutting surface 12c when the sheet S comes into contact with the sheet S rotates from the first posture (standby position) to the nip position is:
θc> θb (2)
It is set to be the relationship.

Here, a case where the leading edge of the sheet S abuts against the abutting surface (first position) 12b and a case where the leading edge of the sheet S abuts against the abutting surface (second position) 12c will be described. The cam height hb at the sheet passing position when the sheet S abuts against the abutting surface (first position) 12b of the sheet regulating member 12 'and the abutting surface (second position) 12c of the sheet regulating member 12'. As shown in FIG. 11, the cam height hc at the sheet passing position when the sheet S comes into contact with
hc> hb (3)
It becomes the relationship. The amount of change from the cam height h0 in the first posture (standby position) is shown in FIG.
hc−h0> hb−h0 (4)
It becomes the relationship. From Equation (4), the amount of cam height variation is greater when the sheet S abuts against the abutting surface (second position) 12c of the sheet regulating member 12 '(first abutting surface (first). The position S is larger than the case where the sheet S comes into contact with 12b. Further, since the shutter pressure is represented by the product of the cam height variation and the biasing spring constant, the shutter pressure F1 at the nip position when the sheet S abuts against the abutting surface (first position) 12b and The shutter pressure F2 at the nip position when the sheet S abuts against the abutting surface (second position) 12c is:
F2> F1 (5)
It becomes the relationship.

  When the waist of the sheet S is weak, the sheet S is brought into contact with the abutting surface (first position) 12b of the sheet regulating member 12 ′ to correct the skew of the sheet S. On the other hand, when the sheet S is strong, the sheet S is brought into contact with the abutting surface (second position) 12c of the sheet regulating member 12 ′ to correct the skew of the sheet S.

  If the rotary shutter 11 ′ is provided as described above and the biased and swingable guide member 21 described above is used, it is possible to correct skewing regardless of the basis weight of the sheet S.

  By providing the rotary shutter 11 ′ as described above, if the rotatable guide member 21 that is biased similarly to the first and second embodiments is used, the sheet S is skewed regardless of the basis weight. Can be corrected. The third embodiment has been described by applying the guide member 21 used in the first embodiment supported by the guide member so as to be swingable and biased by a guide biasing spring. Of course, the flexible guide member 23 according to the second embodiment may be applied.

10. Sheet skew correcting device 11, 11 '... Shutter 12, 12' ... Sheet regulating members 12a, 12a '... Abutting surfaces 12b, 12b' ... First position (butting Abutting surface tip side)
12c, 12c '... 2nd position (butting surface base side)
15. Holding means, biasing portion (shutter biasing spring)
21, 23 ... Guide member 22 ... Biasing means (guide biasing spring)
30: First conveying means (roller pair)
31 ... Conveying roller 31a ... Rotating shaft 32 ... Conveying rollers 33, 44 ... Support shaft (fixed shaft, shutter shaft)
43, 45, 46 ... holding means, positioning means [cam member (biasing cam), elastic member (arm biasing spring), biasing arm]
120... Second conveying means (roller pair)

Claims (8)

First sheet conveying means;
A second sheet conveying means disposed upstream of the first sheet conveying means in the sheet conveying direction;
A first posture that is disposed in the vicinity of the first sheet conveying unit and that locks the leading end of the sheet conveyed by the second sheet conveying unit on the upstream side in the sheet conveying direction from the first sheet conveying unit. And a sheet regulating member that is rotatably held in a second posture that allows the sheet to pass therethrough,
Holding means for holding the sheet regulating member in the first posture with a biasing force;
A guide member for guiding the sheet conveyed by the second sheet conveying means to the sheet regulating member,
When guiding the sheet to the sheet restricting member, the guide member has a first position where the leading end of the sheet is far from the rotation center of the sheet restricting member and a second position close to the rotation center of the sheet restricting member. Movably supported so as to be in contact with the position of
A sheet skew correction device characterized by that. The guide member is swingably supported between an initial posture for guiding the sheet leading end to the first position and a retreating posture for guiding the sheet leading end to the second position with the upstream side in the sheet conveying direction as a fulcrum. ,
Biasing means for biasing the guide member toward the initial posture;
The guide member rotates toward the retracted posture against the urging force of the urging means by the waist of the seat.
The sheet skew correcting device according to claim 1. The guide member has flexibility and is in an initial posture to guide the sheet front end toward the first position in a natural state, and the sheet front end is guided to the second position by the waist of the sheet. Deforms toward the retracted posture,
The sheet skew correcting device according to claim 1. The first sheet conveying means includes a conveying roller fixed to a rotating shaft and integrally rotating, and a conveying roller rotatably supported by a support shaft, and the sheet includes the conveying roller and the conveying roller. Is transported by being sandwiched between
The sheet restricting member is rotatably supported by the support shaft, and is positioned on the upstream side of the nip portion in the sheet conveyance direction, and on the downstream side of the nip portion in the sheet conveyance direction. Rotated to the second position,
The sheet skew correction device according to any one of claims 1 to 3. The sheet regulating member has one abutting surface that can abut the sheet tip,
The holding means biases the sheet regulating member toward the first posture,
The sheet regulating member is moved from the first position to the second position against the urging force of the holding unit by the second sheet conveying unit in a state where the sheet leading end is in contact with the abutting surface. When the rear end of the sheet passes through the sheet regulating member in the second posture, the sheet is rotated in the opposite direction by the urging force of the holding means and held in the first posture.
The sheet skew correcting device according to claim 4. The sheet regulating member has a plurality of abutting surfaces that can come into contact with the front end of the sheet,
The holding means is a positioning means for positioning the sheet regulating member so that the respective abutting surfaces are in the first posture;
As the sheet is conveyed in a state where the leading end of the sheet is in contact with the abutting surface, the sheet rotates from the first position to the second position, and the rear end of the sheet is in the second position. When passing through the sheet regulating member, the positioning means is positioned so that the different abutting surfaces are rotated in the same direction to be in the first posture.
The sheet skew correcting device according to claim 4. The positioning means includes a cam member that rotates integrally with the sheet regulating member, and an elastic member that is deformed by the rotation of the cam member,
In the sheet regulating member, the rotation angle from the first posture to the nip portion at the second position is larger than the rotation angle from the first posture to the nip portion at the first position. Set to be large,
The amount of deformation of the elastic member by the cam member at the rotation angle of the second position is greater than the amount of deformation of the elastic member by the cam member at the rotation angle of the first position.
The sheet skew correction device according to claim 6. The sheet skew correction device according to any one of claims 1 to 7,
An image forming unit that forms an image on a sheet whose skew has been corrected by the skew correction device,
An image forming apparatus characterized by that.

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