JP2011143995A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably conveying a sheet, even when the sheet is thin. <P>SOLUTION: A sheet is held by rubber rollers 103a and 103b provided to move in the axial direction of a shaft 101, together with rollers 107a and 107b, of a drive roller 100A of a first conveyance roller pair 100 and is moved by bending at the center of the axial direction of the shaft 101 with the rotation of the shaft 101. When the sheet reaches a second conveyance roller pair 200, the sheet is reciprocated so that the sheet returns to the initial position before moving with reduced bending. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly, to a sheet on which an image is formed with a waist to be conveyed.

  2. Description of the Related Art Conventionally, some image forming apparatuses such as printing machines, copiers, fax machines, and printers form an image on a sheet by an electrophotographic method. In such an image forming apparatus, when an image is formed on a sheet, first, the photosensitive drum is exposed in accordance with image information to form an electrostatic latent image on the photosensitive drum. Next, the electrostatic latent image is developed with toner in a developing unit to be visualized as a toner image, and the toner image is transferred to a sheet fed from a paper feeding unit in a transfer unit. Yes. Thereafter, the sheet is conveyed to a fixing nip between a fixing roller and a pressure roller provided in the fixing unit, and the toner image is fixed on the sheet as a permanent image.

  In the conventional image forming apparatus, a sheet feeding cassette as a sheet storage unit is detachably attached to the image forming apparatus main body. At the time of image formation, the sheet stored in the sheet feeding cassette is sent out by a sheet feeding roller and then transported to an image forming unit by a sheet transporting device.

By the way, in recent years, the above-described image forming apparatus has been provided for the printing market with a small number of copies, taking advantage of not making a plate. In the light printing market, it is required to support various sheets. In particular, thin sheets having a basis weight of 60 g / m ² or less are particularly frequently used due to the unit price per sheet and the cost merit at the time of delivery. However, the sheet is conveyed by the conveyance roller while being guided by the conveyance guide. However, when the sheet is conveyed, the sheet may stick to the guide due to a minute frictional resistance with the guide or a minute static electricity. In particular, since a thin sheet has low rigidity (rigidity), even if it is slightly attached to a guide, buckling may occur and jam may occur.

  On the other hand, if the sheet is conveyed only by the conveyance roller without providing the conveyance guide, the stiffness of the thin sheet is small, so that the leading edge of the sheet bends downward during conveyance. For this reason, when a thin sheet is conveyed, the intervals between the conveying rollers must be arranged such that the thin paper does not buckle. Normally, the interval between the conveying rollers is slightly shorter than the length of the minimum size sheet, but in an apparatus that conveys a thin sheet, the conveying rollers must be arranged at intervals shorter than usual. The number will increase.

  Therefore, conventionally, when a thin sheet is conveyed, the sheet is bent in the width direction perpendicular to the sheet conveying direction, thereby increasing the substantial rigidity of the sheet (with a seat) and conveying the sheet. Has been devised. As such an apparatus, for example, a roller and a roller provided with flange portions on both sides of the body portion are provided, and when the sheet is sandwiched and conveyed by the roller and the roller, the sheet is moved in the width direction by the flange portion. Bend (see Patent Document 1).

  Moreover, in order to respond | correspond to various materials, there exist some which comprise the seating part for raising the substantial rigidity of a sheet | seat with an elastic body. As such a configuration, for example, a seating roller protrudes from one end of the roller body in the axial direction along the circumferential direction, and the seating roller is formed of a flexible material. (See Patent Document 2).

Japanese Patent Laid-Open No. 9-110260 JP-A-2005-272111

  However, in a conventional image forming apparatus that is seated and conveyed by bending the sheet, the sheet may be slightly bent due to bending at the flange portion when the sheet is conveyed. Note that even when the flange part and the waist roller are made of an elastic body and the bending is light, the pressure is always applied to the same position in the width direction of the sheet, so the image is transferred even if the sheet is not folded. When a subsequent sheet is conveyed, streaky gloss unevenness may occur on the image.

  In addition, as a cause of gloss unevenness, there is a rubbing trace due to a difference in peripheral speed between the roller portion and the flange portion. Further, in a state where the toner is not completely hardened after fixing, the surface roughness of the image surface varies even with a slight difference in pressure, so that it is visually recognized as uneven gloss.

  Further, when the sheet is bent and conveyed in a wave shape, the sheet reaches the conveyance roller disposed downstream in the wave shape. However, since the wave shape during conveyance is not stable, when the sheet reaches the conveyance roller and then the sheet is nipped by the conveyance roller, the leading edge of the sheet may be bent.

  12A shows a state in which the sheet S starts to be clamped by the seating roller 801, and FIG. 12B shows an example in which the leading edge wave shape of the sheet S is not stable during conveyance. is there. FIG. 12C is a diagram showing a state where the wave shape of the front end of the sheet is unstable and has reached the downstream conveying roller. At this time, the sheet is wavy and the back side is in contact with the upper roller 802. However, the front side is guided to the roller nip while being in contact with the conveying roller 803. When sandwiched in such a state, since the approach behavior of the sheet S differs between the back side and the near side of the roller nip, the leading end of the sheet may be folded.

  Accordingly, the present invention has been made in view of such a current situation, and an object of the present invention is to provide an image forming apparatus capable of stably conveying a sheet even when the rigidity of the sheet is low. is there.

  The present invention provides an image forming apparatus including a pair of conveyance rollers that conveys a sheet and a pair of downstream conveyance rollers provided on the downstream side of the conveyance roller pair in the sheet conveyance direction. A drive roller portion having at least one of the plurality of drive rollers provided to be movable in the axial direction of the roller shaft; a driven roller that is in pressure contact with each of the plurality of drive rollers; A reciprocating mechanism that reciprocates the driving roller in the axial direction of the roller shaft, and the reciprocating mechanism is configured such that the sheet is sandwiched between the driving roller and the driven roller from the initial position in the axial direction of the roller shaft. When the sheet reaches the pair of downstream-side conveyance rollers, the roller is reciprocated so as to reduce the bending formed on the sheet. It is characterized in that characterized in that to create.

  As in the present invention, the drive roller is moved while bending the sheet, and when the sheet reaches the downstream conveying roller pair, the sheet is returned to a state in which the bending of the sheet is reduced. Can be stably conveyed.

1 is a diagram illustrating a schematic configuration of a color image forming apparatus which is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a perspective view of a first roller unit provided in a duplex conveying device of the color image forming apparatus. Sectional drawing explaining the structure of the 1st conveyance roller pair which comprises the said 1st roller unit. FIG. 3 is a control block diagram of the color image forming apparatus. FIG. 6 is a first diagram illustrating sheet conveying operation of the first roller unit. FIG. 10 is a second diagram illustrating the sheet conveying operation of the first roller unit. FIG. 6 is a diagram illustrating a relationship between a sheet leading end position and a movement amount (= sheet bending amount) of a rubber roller of the first conveyance roller in a thrust direction. FIG. 10 is a third diagram illustrating the sheet conveying operation of the first roller unit. The figure explaining the state when conveying the thick sheet | seat of the said 1st roller unit. FIG. 6 is a perspective view illustrating a configuration of a roller unit provided in an image forming apparatus according to a second embodiment of the present invention. The top view explaining the structure of the said roller unit. FIG. 10 is a diagram illustrating a sheet conveying operation of a conventional image forming apparatus.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a color image forming apparatus which is an example of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a color image forming apparatus, and 1A denotes a color image forming apparatus main body (hereinafter referred to as apparatus main body).

  In the apparatus main body 1A, the toner image formed by the image forming unit 1B, the sheet feeding unit 1C that conveys the sheet S, and the image forming unit 1B is transferred to the sheet S fed by the sheet feeding unit 1C. A transfer unit 1D is provided. Further, the apparatus main body 1A is provided with a sheet conveying apparatus 1E for conveying a sheet. The image forming unit 1B includes a yellow (Y), a magenta (M), a cyan (C), and a photosensitive drum 91, an exposure device 93, a developing device 92, a primary transfer device 45, a charging unit 99, a cleaner 95, and the like. Black (Bk) image forming units 90 and 96 to 98 are provided. Note that the colors formed by the image forming units 90 and 96 to 98 are not limited to these four colors, and the color arrangement order is not limited to this.

  The sheet feeding unit 1 </ b> C includes a sheet storage unit 10 that stores sheets S stacked on the lift-up device 11, and a sheet feeding unit 12 that sends out the sheets S stored in the sheet storage unit 10. Yes. Examples of the sheet feeding unit 12 include a method using frictional separation by a paper feed roller and the like, a method using air separation and adsorption, and the like. In the present embodiment, a paper feeding method using air is used. An example is given. The transfer unit 1D is provided with an intermediate transfer belt 40 that is stretched by rollers such as a driving roller 42, a tension roller 41, and a secondary transfer inner roller 43, and is conveyed and driven in the direction of arrow B in the drawing. . Here, the toner image formed on the photosensitive drum is transferred to the intermediate transfer belt 40 by a predetermined pressure and an electrostatic load bias given by the primary transfer device 45. Further, the intermediate transfer belt 40 provides a predetermined pressing force and an electrostatic load bias at the secondary transfer portion formed by the substantially opposed secondary transfer inner roller 43 and secondary transfer outer roller 44, thereby reducing the sheet S. The non-fixed image is adsorbed to the head.

  The sheet transport apparatus 1E includes a transport unit 20, a skew correction device 30, a pre-fixing sheet transport unit 51, a branch transport device 60, a reverse transport device 70, a double-side transport device 80, and the like. The pre-fixing sheet conveyance unit 51 conveys the sheet onto which the toner image has been transferred by the secondary transfer unit to the fixing nip of the fixing device 50.

  In the color image forming apparatus 1 having such a configuration, when forming an image, first, the photosensitive drum 91 is rotated in the direction of the arrow in the drawing, and the surface of the photosensitive drum is uniformly made by the charging means 99 in advance. To charge. Thereafter, the exposure device 93 emits light to the rotating photosensitive drum 91 based on the transmitted image information signal, and this light is irradiated through the reflecting means 94 and the like as appropriate, whereby the photosensitive drum 91 is irradiated. A latent image is formed on top.

  Next, toner development is performed by the developing device 92 on the electrostatic latent image formed on the photosensitive drum 91 in this manner, and a toner image is formed on the photosensitive drum. Thereafter, a predetermined pressure and electrostatic load bias are applied by the primary transfer device 45, and the toner image is transferred onto the intermediate transfer belt 40. Note that image formation by the image forming units 90, 96 to 98 in the Y, M, C, and Bk image forming units of the image forming unit 1B is performed at a timing when the toner image is superimposed on 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 40. Note that the transfer residual toner slightly remaining on the photosensitive drum 91 is collected by the cleaner 99 to prepare for the next image formation again.

  Further, the sheet S is sent out by the sheet feeding unit 12 in accordance with the image forming timing of the image forming unit 1B. Thereafter, the sheet S passes through a transport path 20 a provided in the transport unit 20 and is transported to a skew correction device 30 for correcting the positional deviation and skew of the sheet being transported. Then, after the positional deviation and the skew feeding are corrected by the skew feeding correction device 30, the sheet S is conveyed to the secondary transfer portion formed by the secondary transfer inner roller 43 and the secondary transfer outer roller 44, and the second sheet S is conveyed. In the next transfer portion, the full-color toner image on the intermediate transfer belt 40 is secondarily transferred. Note that the transfer residual toner slightly remaining on the intermediate transfer belt 401 is collected by the cleaner 46 to prepare for the next image formation again.

  Next, the sheet S on which the toner image is secondarily transferred in this way is conveyed to the fixing device 50 by the pre-fixing conveyance unit 51. In the fixing device 50, the toner on the sheet S is melted and fixed on the sheet S by applying a predetermined pressing force and generally a heating effect by a heat source such as a heater. Next, the sheet S having the fixed image obtained in this way is discharged as it is onto the paper discharge tray 61 by the branch conveyance device 60. In addition, when forming an image on both surfaces of the sheet S, the sheet S is then conveyed to the reverse conveying device 70 by switching a switching member (not shown).

  Here, when the sheet S is conveyed to the reversing conveyance device 70 in this way, the leading and trailing ends are switched by performing a switchback operation, and the sheet S is conveyed to the re-conveyance path R provided in the double-sided conveyance device 80. Thereafter, the sheet is fed from the sheet re-feeding path 20b of the sheet conveying apparatus 20 in synchronism with the sheet of the subsequent job conveyed from the sheet feeding unit 1C, and similarly sent to the secondary transfer unit. Since the image forming process is the same as that of the first side, it is omitted.

  By the way, in the present embodiment, for example, two roller units 80A and 80B having the same configuration are continuously arranged in the double-sided conveyance device 80. Here, as shown in FIG. 2, the first roller unit 80 </ b> A includes a first conveyance roller pair 100, which is a conveyance roller pair, and a downstream conveyance roller provided on the downstream side in the sheet conveyance direction of the first conveyance roller pair 100. A pair of second transport rollers 200 is provided.

  The first conveying roller pair 100 includes a driving roller unit 100A and a driven roller 100B. The drive roller unit 100A includes a shaft 101, cam flanges 102a and 102b that are movable with respect to the shaft 101 in a thrust direction (axial direction), and rubber rollers 103a and 103b to which the cam flanges 102a and 102b are fixed. I have. The rollers 107a and 107b constituting the driven roller 100B are in pressure contact with the rubber rollers 103a and 103b which are driving rollers of the driving roller portion 100A.

  The cam flanges 102a and 102b are urged toward both ends of the shaft 101 by springs 104a and 104b, which are urging members. A stepping motor 106, which is the same drive source as the second transport roller pair 200, is connected to the end of the shaft 101. When the stepping motor 106 is rotated, the rubber rollers 103a and 103b are rotated together with the shaft 101, and the sheet S is conveyed by a clamping force between the rollers 107a and 107b disposed opposite to the rubber rollers 103a and 103b.

  As shown in FIG. 3, pins 105a and 105b are press-fitted into the shaft 101, and grooves 1020a and 1020b into which the pins 105a and 105b are fitted are formed in the cam flanges 102a and 102b. . By fitting the pins 105a and 105b of the shaft 101 into the grooves 1020a and 1020b of the cam flanges 102a and 102b, the cam flanges 102a and 102b rotate together with the shaft 101 and can move in the thrust direction.

  Here, as shown in FIG. 2, the cam flanges 102a and 102b, which are cams, are formed with cam surfaces 102c having a shape obtained by obliquely cutting a cylinder on the side surfaces in the direction orthogonal to the axial direction of the shaft 101. ing. Further, leaf springs 114a and 114b, which are elastic bodies, are provided on a frame (not shown) of the double-sided conveyance device 80 (device main body). The abutting members 113a and 113b, which are abutting portions that abut against the cam surfaces 102c of the cam flanges 102a and 102b biased by the springs 104a and 104b, are elastically applied to the plate springs 114a and 114b that are the supporting portions. It is supported.

  When the cam surface 102c of the cam flanges 102a and 102b abuts against the abutting members 113a and 113b, when the shaft 101 rotates, the rubber rollers 103a and 103b move integrally with the cam flanges 102a and 102b in the thrust direction. The cam phases of the two cam flanges 102a and 102b coincide with each other by matching the phases of the pins 105a and 105b.

  The second conveying roller pair 200 includes a driving roller unit 200A and a driven roller 200B. The drive roller unit 200A includes a shaft 201, cam flanges 202a and 202b that are movable with respect to the shaft 201 in the thrust direction, and rubber rollers 203a and 203b that are drive rollers to which the cam flanges 202a and 202b are fixed. ing. The cam flanges 202a and 202b are urged toward both ends of the shaft 201 by springs 204a and 204b, respectively. Further, the abutting members 113a and 113b elastically supported by the leaf springs 114a and 114b abut against the cam surfaces 202c of the cam flanges 202a and 202b.

  Here, a stepping motor 106 is connected to the shaft 201 via pulleys 108 and 208 and a timing belt 109. When the stepping motor 106 rotates, the shaft 201 is also rotationally driven. When the shaft 201 rotates, the rubber rollers 203a and 203b move in the thrust direction integrally with the cam flanges 202a and 202b.

  When the shaft 201 is rotated, the rubber rollers 203a and 203b are rotated together with the shaft 201, and the sheet S is conveyed by a clamping force between the rollers 207a and 207b disposed opposite to the rubber rollers 203a and 203b. Since the two pulleys 108 and 208 are the same component, the phase of the first and second transport roller pairs 100 and 200 and the cam phase of the cam flanges 202 and 202 can be made the same.

  In FIG. 2, reference numeral 110 denotes a slit plate fixed to the shaft 101. The slit plate 110 has a detection hole 110h. Reference numeral 111 denotes a home position sensor. By detecting the detection hole 110h of the slit plate 110 by the home position sensor 111, the phase of the first transport roller pair 100 is determined by the controller 500 in the apparatus main body shown in FIG. To do.

  Reference numeral 112 denotes a sheet detection sensor that is provided upstream of the first conveyance roller pair 100 in the sheet conveyance direction and detects the presence or absence of a sheet. The controller 500 is conveyed to the first roller unit 80A by the sheet detection sensor 112. The presence or absence of a sheet is judged. A guide (not shown) for guiding the sheet is disposed between the pair of transport rollers 100 and 200 so as to sandwich the sheet S.

  FIG. 4 is a control block diagram of the image forming apparatus 1. In FIG. 4, reference numeral 500 denotes a controller that is a control unit that controls the entire image reading apparatus. The controller 500 includes a CPU 501, a program storage ROM 503, a temporary data storage RAM 502, and a communication I / O 504. . The CPU 501 operates according to a control program stored in the ROM 503. Further, the CPU 501 recognizes signals from the home position sensor 111 and the sheet detection sensor 112 via the AD conversion unit 505, and controls the rotation operation of the stepping motor 106 via the driver 506.

  Next, the sheet conveying operation of the first roller unit 80A will be described. FIG. 5 is a diagram illustrating a state immediately before the sheet S reaches the first conveying roller pair 100. Here, the thin sheet S is conveyed from the reverse conveying device 70 to the first conveying roller pair 100. At this time, the first conveying roller pair 100 is stopped.

  At this time, as shown in FIGS. 5A and 5B, the rubber rollers 103a and 103b integrated with the cam flanges 102a and 102b are in a state where the distance between them is the largest. Note that the home position sensor 111 can detect the thrust position of the rubber rollers 103a and 103b, which is the initial position where the distance between the two is opened. Accordingly, the CPU 501 stops the stepping motor 106 based on the detection signal from the home position sensor 111, so that the rubber rollers 103a and 103b can be in a state where the distance between them is most widened in advance.

  Next, when the sheet detection sensor 112 detects the leading edge of the sheet S, the CPU 501 rotates the stepping motor 106 in accordance with the timing when the sheet reaches the first conveying roller pair 100. Accordingly, the cam flanges 102a and 102b rotate together with the rubber rollers 103a and 103b while abutting against the abutting members 113a and 113b.

  As a result, the rubber rollers 103a and 103b are moved toward the center in the width direction of the shaft 101 as shown by the arrows in FIG. 6 according to the shape of the cam surface 102c of the cam flanges 102a and 102b while resisting the springs 104a and 104b. Moving. When the rubber rollers 103a and 103b move in this way, the portions of the sheet S that are in contact with the rubber rollers 103a and 103b move to the center side of the shaft 101 due to friction between the rubber rollers 103a and 103b. Thereby, the sheet S bends (curves) in the width direction.

  FIG. 7 is a diagram illustrating the relationship between the sheet leading edge position and the amount of movement of the rubber rollers 103a and 103b in the thrust direction (= the amount of curvature of the sheet). In FIG. 7, the interval between the first conveying roller pair 100 and the second conveying roller pair 200 indicated by the horizontal axis is set to the circumferential length of the rubber rollers 103a and 103b. Therefore, as indicated by the solid line, when the leading edge of the sheet is at an intermediate point between the first conveying roller pair 100 and the second conveying roller pair 200, the rubber rollers 103a and 103b move to the maximum and come closest to each other, and the bending amount of the sheet S (Bending amount) also increases.

  On the other hand, when the leading edge of the sheet reaches the second conveying roller pair 200, the rubber rollers 103a and 103b return to the home position according to the shape of the cam surface 102c of the cam flanges 102a and 102b. Thereby, the curved state (deflection state) decreases or disappears, and the sheet S is flattened. In this case, the curved state may not disappear due to slippage between the roller and the sheet, but the friction coefficient of the rubber roller may be set so as not to leave a curve large enough to break the leading edge of the sheet. In the present exemplary embodiment, an example in which the curve is the largest at the intermediate point between the first conveyance roller pair 100 and the second conveyance roller pair 200 has been described. However, the curved state of the sheet S is preferably the second conveyance roller pair 200. It is advantageous for the buckling of the sheet S to be maintained until just before reaching. For this reason, the shape of the cam surface 102c of the cam flanges 102a and 102b may be formed so that the maximum curve position approaches the conveying roller pair 200 as indicated by a dotted line.

  Next, as shown in FIGS. 8A and 8B, the leading edge of the sheet S once flattened reaches the second conveying roller pair 200, and thereafter conveyed by the second conveying roller pair 200. Is done. When the sheet S reaches the second conveying roller pair 200, the leading edge of the sheet S is flattened, so that the sheet S does not get caught by the second conveying roller pair 200 and the nip portion of the second conveying roller pair 200. Then, it is nipped and conveyed by the second conveying roller pair 200. Further, when the sheet S is conveyed, the rubber rollers 203a and 203b integrated with the cam flanges 202a and 202b of the second conveying roller pair 200 are in a state where the distance between them is the largest.

  Thereafter, the rubber rollers 203a and 203b rotate, and the cam surfaces 202c of the cam flanges 202a and 202b rotate while abutting against the abutting members 113a and 113b together with the rubber rollers 203a and 203b. Thereby, the rubber rollers 203a and 203b move to the center side of the shaft 201 while resisting the springs 204a and 204b. When the rubber rollers 203a and 203b move to the center side of the shaft 201, the portions of the sheet S that are in contact with the rubber rollers 203a and 203b move to the center side of the shaft 201 due to friction with the rubber rollers 203a and 203b. Thereby, the sheet S is curved in the width direction.

  At this time, the rubber rollers 103a and 103b of the first conveying roller pair 100 also operate in synchronization with the rubber rollers 203a and 203b of the second conveying roller pair 200. Thus, when the sheet S is nipped and conveyed by the first conveyance roller pair 100 and the second conveyance roller pair 200, the sheet S is positioned at the same position in the width direction by the first conveyance roller pair 100 and the second conveyance roller pair 200. Curve in the width direction by the same size.

  Next, the leading edge of the sheet S once flattened reaches the second roller unit 80B (see FIG. 1) on the downstream side in the sheet conveying direction, and is then conveyed by the second roller unit 80B. After that, the sheet S is repeatedly curved and flattened by the second roller unit 80B, and eventually reaches the transport roller pair 20A of the transport unit 20 which is the downstream transport roller pair in a state where the leading end is flattened.

  On the other hand, when the leading edge of the sheet reaches the second roller unit 80B, the trailing edge of the sheet S then passes through the first conveying roller pair 100 of the first roller unit 80A. When the detection signal from the sheet detection sensor 112 detects that the trailing edge of the sheet S has passed through the first conveyance roller pair 100, the CPU 501 enters a stop operation of the stepping motor 106.

  Here, when the trailing edge of the sheet S passes through the first conveying roller pair 100, depending on the size of the sheet, the first conveying roller pair 100 is at a home position for preparing the next sheet having the largest rubber roller interval. It may not stop. In this case, since the rubber rollers 103a and 103b are located on the axial center side from the initial position, when the first conveying roller pair 100 is rotated thereafter, the curve shown in FIG.

  In this case, the sheet reaches the second conveying roller pair 200 without the curvature disappearing. Therefore, when the CPU 501 detects that the trailing edge of the sheet has passed through the first conveying roller pair 100, the CPU 501 stops the stepping motor 106 based on a signal from the home position sensor 111 serving as a detection unit. Thereby, before the sheet reaches the first conveying roller pair 100, the circumferential phase of the shaft 101 can be adjusted to a phase in which the circumferential phase of the rubber rollers 103a and 103b is stopped at the initial position. As a result, the first transport roller pair 100 can be stopped at the home position. At this time, the same phase alignment is also performed in the second conveying roller pair 200.

  By the way, since a thick sheet has high rigidity (rigidity), it is not necessary to bend the sheet when conveying the thick sheet. Conversely, when the sheet is bent, a very large force is required and the driving load increases. This increases the cost of the drive source and transmission mechanism. In addition, when bent, the curved portion may come into contact with a conveyance guide (not shown). In this case, a large rubbing force is generated between the conveyance guide and the sheet is damaged or jammed. Sometimes.

  For this reason, when a thick sheet is conveyed, it is necessary to configure so that the sheet is not curved. Therefore, in the present embodiment, as described above, the abutting members 113a and 113b are supported by the leaf springs 114a and 114b, and the spring force of the leaf springs 114a and 114b is set to be weaker than the stiffness of the cardboard. ing. As a result, as shown in FIG. 9, when a thick sheet is conveyed, the rubber rollers 103a, 114b are pressed by the cam surfaces 102c, 202c and the leaf springs 114a, 114b are deformed to both ends in the axial direction of the shafts 101, 201, respectively. 103b, 203a and 203b do not move.

  Thus, even if the cam flanges 102a, 102b, 202a, 202b rotate, the rubber rollers 103a, 103b, 203a, 203b may not move due to the rigidity of the sheet S. In this case, the abutting members 113a and 113b move together with the leaf springs 114a and 114b toward the end portion in the axial direction. With this configuration, when a thick sheet is conveyed, the thick sheet can be prevented from being bent.

  As described above, in this embodiment, when the sheet is conveyed, the rubber rollers 103a, 103b, 203a, and 203b are moved while the sheet is bent. Further, when the sheet reaches the second conveying roller pair 200 or the conveying roller pair 20A of the conveying unit 20, the sheet is bent back and forth so that it returns to the initial position before movement in a state where the bending of the sheet is reduced or eliminated. Yes.

  Thereby, even when the sheet is thin and the rigidity is low, the sheet can be stably conveyed without breaking the leading end of the sheet. In addition, since it is not necessary to narrow the distance between the upstream and downstream transport rollers, the number of transport rollers can be reduced and the cost increase can be suppressed. Furthermore, since it is not the structure which seats on a sheet | seat using a flange, the bending | flexion in a flange part does not generate | occur | produce at the time of sheet conveyance. For this reason, image defects such as gloss streaks due to the seating of the sheet can be reduced, and various materials can be handled.

  In the present embodiment, the rubber rollers 103a and 103b and the rubber rollers 203a and 203b are set to reach the second conveying roller pair 200 and the conveying roller pair 20A of the conveying unit 20 when the rubber rollers 103a and 203b return to the home position. However, as long as the leading edge of the sheet is not bent, the rubber roller is brought to the home position so as to reach the second conveying roller pair 200 and the conveying roller pair 20A of the conveying unit 20 in a state where the sheet is slightly bent. The return timing may be shifted.

  Next, a second embodiment of the present invention will be described. FIG. 10 is a diagram illustrating the configuration of the roller unit provided in the image forming apparatus according to the present embodiment. 10, the same reference numerals as those in FIG. 2 described above denote the same or corresponding parts, and detailed description thereof will be omitted.

  In FIG. 10, 301 a and 301 b are small bevel gears that are first bevel gears fixed to positions near the rubber rollers 103 a and 103 b of the shaft 101 of the first conveying roller pair 100. Reference numerals 302 a and 302 b denote large bevel gears that are provided on a frame (not shown) of the double-sided conveyance device 80 and are second bevel gears that mesh with the small bevel gears 301 a and 301 b and rotate in parallel with the shaft 101. Reference numerals 304a and 304b denote roller flanges fixed to the side surfaces of the rubber rollers 103a and 103b.

  In addition, eccentric cams 303a and 303b are integrally formed on the upper surfaces of the bevel gears 302a and 302b as shown in FIG. The roller flanges 304a and 304b of the rubber rollers 103a and 103b are pressed against the eccentric cams 303a and 303b by the springs 104a and 104b. The second transport roller pair 200 has the same configuration.

  Here, in the present embodiment, the gear (number of teeth) ratio between the small bevel gears 301a and 301b and the large bevel gears 302a and 302b is 1: 2. Accordingly, when the first conveying roller pair 100 rotates twice, the large bevel gears 302a and 302b rotate once due to the gear ratio between the small bevel gears 301a and 301b and the large bevel gears 302a and 302b. When the bevel gears 302a and 302b rotate once in this way, the rubber rollers 103a and 103b reciprocate once in the axial direction of the shaft 101, which is a roller shaft, by the action of the eccentric cams 303a and 303b.

  As described above, in this embodiment, the reciprocating mechanism for reciprocating the rubber rollers 103a and 103b includes the small bevel gears 301a and 301b, the large bevel gears 302a and 302b, the eccentric cams 303a and 303b, and the springs 104a and 104b. . Further, by this reciprocating mechanism, the first conveying roller pair 100 rotates twice, so that the rubber rollers 103 a and 103 b reciprocate once in the axial direction of the shaft 101. That is, in the present embodiment, when the shaft 101 is rotated twice (multiple rotations) by the small bevel gears 301a and 301b and the large bevel gears 302a and 302b, the drive transmission unit in which the eccentric cams 303a and 303b rotate once is provided. Composed.

  Here, in the first embodiment described above, the circumferential length of the rubber roller 103 and the distance between the first transport roller pair 100 and the second transport roller pair 200 are the same. In this case, when it is desired to increase the distance between the rollers, it is necessary to increase the roller diameter. However, when the first conveyance 100 rotates twice as in the present embodiment, the rubber rollers 103a and 103b are configured to move once, so that the conveyance roller interval can be doubled even with the same roller diameter. . In addition, by making the number of teeth of the large bevel gears 302a and 302b an integral multiple of the number of teeth of the small bevel gears 301a and 301b, the interval between the conveying rollers can be expanded to an integral multiple.

  As described above, this embodiment also has the same functions and effects as those of the first embodiment described above. Even when the sheet is thin and the rigidity is low, the sheet is stabilized without breaking the sheet tip. Can be transported.

  By the way, in the first and second embodiments described so far, both the rubber rollers are moved. However, it is only necessary to reciprocate at least one rubber roller, and the number of rubber rollers needs to be limited to two. There is no. In the above description, the cam mechanism is described as an example of the reciprocating mechanism for reciprocating the rubber roller. However, the present invention is not limited to this. As a reciprocating mechanism, for example, a rubber roller may be moved using a dedicated actuator such as a motor or a solenoid. Furthermore, the amount of curvature of the sheet can be finely adjusted by controlling the amount of movement of the rubber roller by the dedicated actuator by means for detecting the rigidity such as the thickness of the sheet.

  In the above description, the example in which the present invention is applied to the pair of conveyance rollers provided in the double-sided conveyance device 80 has been described. However, the present invention is also applied to a pair of conveyance rollers provided in a place with relatively little bending. Is possible. Further, the example in which the present invention is applied to an image forming apparatus using an electrophotographic method has been described so far. However, the present invention is applied to an image forming apparatus of another image forming method such as an ink jet method or a thermal transfer method. May be.

DESCRIPTION OF SYMBOLS 1 ... Color image forming apparatus, 1A ... Color image forming apparatus main body, 1B ... Image forming part, 1E ... Sheet conveying apparatus, 20A ... Pair of conveying rollers, 80 ... Double-sided conveying apparatus, 80A, 80B ... Roller unit, 100 ... First Conveying roller pair, 100A: Driving roller unit, 100B: Driven roller, 101 ... Shaft, 102a, 102b ... Cam flange, 102c ... Cam surface, 103a, 103b ... Rubber roller, 104a, 104b ... Spring, 106 ... Stepping motor, 107a, 107b ... roller 111 ... home position sensor 113a, 113b ... butting member 114a, 114b ... plate spring 200 ... second conveying roller pair 200A ... driving roller unit 200B ... driven roller 201 ... shaft 202a 202b ... cam flange, 202c ... cam surface, 203a 203b ... rubber roller, 204a, 204b ... spring, 301a, 301b ... small bevel gears, 302a, 302b ... large bevel gear, 303a, 303b ... eccentric cam, 304a, 304b ... roller flange 500 ... controller, S ... Sheet

Claims (8)

In an image forming apparatus comprising a pair of conveyance rollers for conveying a sheet, and a pair of downstream conveyance rollers provided on the downstream side in the sheet conveyance direction of the conveyance roller pair,
The conveying roller pair is
A drive roller portion having a plurality of drive rollers, wherein at least one of the plurality of drive rollers is movably provided in the axial direction of the roller shaft;
A driven roller in pressure contact with each of the plurality of drive rollers;
A reciprocating mechanism for reciprocating the movable drive roller in the axial direction of the roller shaft;
With
The reciprocating mechanism bends the sheet to be conveyed by moving the driving roller in the axial direction of the roller shaft from the initial position in a state where the sheet is sandwiched by the driven roller, and the sheet reaches the pair of downstream conveying rollers. An image forming apparatus, wherein the roller is reciprocated so as to reduce the bending formed on the sheet.   The reciprocating mechanism is provided on the movable drive roller, and rotates with the roller shaft, a contact portion provided on the apparatus main body, which contacts the cam, and presses the cam against the contact portion. The image forming apparatus according to claim 1, further comprising: an urging member that urges in such a manner.   When the movable driving roller is moved from the initial position to the maximum shape, the leading edge of the sheet is more in the sheet conveying direction than the middle between the conveying roller pair and the downstream conveying roller pair. The image forming apparatus according to claim 2, wherein the image forming apparatus has a shape that forms a downstream side. A support portion for elastically supporting the contact portion;
Even if the cam rotates, if the movable drive roller does not move due to the stiffness of the sheet, the abutting portion is moved toward the axial end of the roller shaft by being pressed by the cam. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   5. The image forming apparatus according to claim 2, wherein a circumferential length of the cam is an integral multiple of a distance between the pair of conveying rollers and the pair of downstream conveying rollers.   The reciprocating mechanism includes a first bevel gear that rotates together with the roller shaft, a second bevel gear that is provided in the apparatus main body and meshes with the first bevel gear and rotates parallel to the roller shaft, and the second bevel gear. 2. A cam provided on a gear and abutting the movable drive roller, and a biasing member biasing the movable drive roller so as to press the cam. Image forming apparatus.   The image forming apparatus according to claim 6, wherein the number of teeth of the second bevel gear is an integral multiple of the number of teeth of the first bevel gear. A detector for detecting a circumferential phase of the roller shaft;
Based on a signal from the detection unit, the circumferential phase of the roller shaft is adjusted so that the movable drive roller is stopped at the initial position before the sheet reaches the downstream conveying roller pair. The image forming apparatus according to claim 1.

Images