JP6529270B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to an apparatus that adsorbs a sheet to an endless belt and conveys the sheet.

  2. Description of the Related Art Conventionally, there have been image forming apparatuses such as copying machines, facsimiles, laser printers, etc., in which an image is formed on a sheet by an electrophotographic method. In such an image forming apparatus, when forming an image on a sheet, first, the photosensitive drum is exposed according to the image information to form an electrostatic latent image on the photosensitive drum. Next, the electrostatic latent image is developed with a toner in a developing device to make it visible as a toner image, and the toner image is transferred to a sheet supplied from a paper feeding unit in a transfer unit. Thereafter, the sheet is conveyed to a fixing nip between a fixing roller provided in a fixing unit and a pressure roller, and the toner image is fixed on the sheet as a permanent image.

  By the way, in recent years, image forming apparatuses are required to stably form high-quality images on a wide variety of sheets from thin paper to thick paper, from plain paper to coated paper. And, in order to meet such a demand, it is necessary to stably convey, for example, a small postcard size to a wide size sheet of A3 full size or more for light printing and design.

  Therefore, in the conventional image forming apparatus, for example, an endless conveyance belt is provided in the conveyance path between the transfer unit and the fixing unit, and the conveyance belt is moved while the sheet is placed on the belt surface. There is one provided with a pre-fixing conveyance unit for conveying a sheet. When the sheet is transported by the transport belt in contact with the non-image surface side of the sheet as described above, the sheet does not damage the image surface before fixing as compared to the case where the sheet is transported using the transport roller. Can be transported.

  As such a pre-fixing conveyance unit, there is one that conveys a sheet by adsorbing the sheet to the conveyance belt by the suction force of air. However, when the sheet is attracted to the transport belt as described above, the transport power of the transport belt is insufficient unless the magnitude of the adsorption force is sufficient. If the conveying force is insufficient, after the sheet reaches a guide for guiding the sheet to the fixing unit, the frictional force with the guide prevents the sheet from being conveyed to the fixing unit at a predetermined timing. Unfed sheets may occur.

  Here, if the suction power of air is increased, occurrence of non-feeding of the sheet can be prevented, but if the suction power of air is increased, in the case of light and thin sheets, a large restraint force is applied to the sheets during conveyance. Working may cause wrinkles and image defects.

  Therefore, conventionally, by controlling the applied voltage applied to a fan for sucking air, the negative pressure generated by sucking air is changed, and the suction force for adsorbing the sheet is switched according to the characteristics (material) of the sheet. There is one that has been made (see Patent Document 1). Further, there is one in which the transport angle of the sheet with respect to the guide guided to the fixing unit is switched according to the characteristics of the sheet by controlling the angle of the transport belt (see Patent Document 2).

Unexamined-Japanese-Patent No. 2003-54783 Unexamined-Japanese-Patent No. 2010-85976

  However, in the conveyance unit before fixing, which is an example of such a conventional sheet conveyance apparatus, in the case where control of the suction force acting on the sheet is controlled by the voltage applied to the fan, it is necessary to adsorb the sheet having high rigidity. , Need more powerful fans, cost more. In addition, when controlling the angle of the transport belt to switch the transport angle of the sheet with respect to the guide, a drive source for changing the transport belt angle is required separately from the drive source for driving the transport belt, which causes cost It takes.

  Therefore, the present invention has been made in view of such a present situation, and an object thereof is to provide a sheet conveying apparatus and an image forming apparatus capable of stably conveying a sheet at low cost. is there.

The present invention provides a sheet conveying device, the conveying belts endless plurality of suction holes are formed to transport by adsorbing sheet over preparative, wound around the conveyor belt, belt drive for driving the conveyor belt A rotating body, a belt driven rotating body wound around the transport belt and driven to rotate by the transport belt, an elevating unit for moving up and down the belt drive rotating body and the belt driven rotating body, and one generating driving force A motor, a first drive means for transmitting a driving force of the motor to the belt drive rotating body only when the motor rotates in a first direction, and a second direction opposite to the first direction of the motor only when rotated in a second driving means for transmitting driving force of the motor to the elevating unit, comprising a, it is characterized in.

According to the present invention , the sheet can be stably transported at low cost.

FIG. 1 is a view showing a schematic configuration of a color laser printer as an example of an image forming apparatus provided with a sheet conveying apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view of a pre-fixing conveyance device which is an example of the sheet conveyance device. The top view of the conveyance apparatus before the above-mentioned fixation. FIG. 6 is a view for explaining the operation of a lifting unit provided in the pre-fixing conveyance device. FIG. 6 is a view for explaining the configuration of a drive unit of an elevating mechanism provided in the pre-fixing conveyance device. The figure explaining the drive row of the drive part of the said raising / lowering mechanism. FIG. 5 is a control block diagram of the conveyance device before fixing. The figure explaining the drive row which drives the conveyance belt by the drive part of the said raising / lowering mechanism. The figure explaining the raising / lowering mechanism of the said raising / lowering mechanism. FIG. 2 is a schematic cross-sectional view of the pre-fixing conveyance device. The figure explaining the drive row which raises / lowers the raising / lowering part by the drive part of the said raising / lowering mechanism.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view showing a schematic configuration of a color laser printer which is an example of an image forming apparatus provided with a sheet conveying apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a color laser printer, and 1A denotes a color laser printer main body (hereinafter referred to as a printer main body). The printer body 1A is provided with an image forming unit 1B that forms an image on a sheet S, an intermediate transfer unit 1C, a fixing device 5, and a sheet feeding device 1D that feeds the sheet S to the image forming unit 1B. There is. The color laser printer 1 can form an image on the back side of the sheet, so the sheet S on which the image is formed on the front side (first side) is reversed to form an image again. A re-conveying unit 1E is provided for conveying to the unit 1B.

  The image forming unit 1B is disposed substantially in the horizontal direction, and four process stations 2 (2Y, 2Y, 2Y, 2Y, 2M, and 4K) that form toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. 2M, 2C, 2K). The process station 2 carries four color toner images of yellow, magenta, cyan and black, and is a photosensitive drum 11 (11Y, 11M, 12C, 11K) which is an image carrier driven by a stepping motor (not shown). ).

  Further, charging devices 12 (12Y, 12M, 12C, 12K) for charging the surface of the photosensitive drum uniformly are provided. Furthermore, an exposure device 13 (13Y, 13M, 13C, 13K) is provided which forms an electrostatic latent image on a photosensitive drum rotating at a constant speed by irradiating a laser beam based on image information. In addition, a developing device 14 (14Y, 14M, 14C, 14K) is provided which makes toners of yellow, magenta, cyan and black adhere to the electrostatic latent image formed on the photosensitive drum to make it visible as a toner image. There is. The charging device 12, the exposure device 13, the developing device 14 and the like are disposed around the photosensitive drum 11 along the rotational direction.

  The sheet feeding apparatus 1D is provided at a lower portion of the printer main body, and includes sheet feeding cassettes 61 to 64 as sheet storage units for storing sheets S, and a pickup roller 71 for feeding the sheets S stacked and stored in the sheet feeding cassettes 61 to 64 And 74 are provided. Then, when the image forming operation is started, the sheets S are separated and fed one by one from the sheet feeding cassettes 61 to 64 by the pickup rollers 71 to 74, and thereafter, the sheet S passes through the conveyance vertical path 81. Transported to

  The intermediate transfer portion 1C includes an intermediate transfer belt 31 which is rotationally driven in synchronization with the outer peripheral speed of the photosensitive drum 11 along the arrangement direction of the process stations 2 indicated by the arrows. Here, the intermediate transfer belt 31 applies appropriate tension to the intermediate transfer belt 31 by the urging force of a driving roller 33, a driven roller 32 forming a secondary transfer area with the intermediate transfer belt 31 interposed therebetween, and a spring (not shown). The tension roller 34 is stretched. The intermediate transfer belt 31 holds four intermediate transfer belts 31 together with the photosensitive drums 11 on the inner side, and primary transfer rollers 35 (35Y, 35M, 35C, 35K) constituting a primary transfer portion are disposed. ing.

  Further, the secondary transfer roller 41 is disposed to face the driven roller 32. The secondary transfer roller 41 contacts the lowermost surface of the intermediate transfer belt 31 to form a secondary transfer portion T, and nips and conveys the sheet S conveyed by the registration roller 76 together with the intermediate transfer belt 31. . Then, when the sheet S passes through the nip portion between the secondary transfer roller 41 and the intermediate transfer belt 31, a bias is applied to the secondary transfer roller 41 so that the toner image on the intermediate transfer belt on the sheet S is secondary. Transcribed.

  The fixing device 5 constituting the fixing unit fixes the toner image formed on the sheet to the sheet S via the intermediate transfer belt 31, and the sheet S holding the toner image passes through the fixing device 5. At the same time, heat and pressure are applied to fix the toner image. In FIG. 1, a control unit 200 is a control unit that controls the image forming operation of the image forming unit 1B, the sheet feeding operation of the sheet feeding device 1D, and the sheet conveying operation of the pre-fixing conveying device 42 described later. is there.

  Next, an image forming operation of the color laser printer 1 configured as described above will be described. When the image forming operation is started, first, the photosensitive drum 11Y is irradiated with laser light by the exposure device 13Y at the process station 2Y located at the most upstream in the rotational direction of the intermediate transfer belt 31, and yellow on the photosensitive drum. Form a latent image of Thereafter, the latent image is developed with yellow toner by the developing device 14Y to form a yellow toner image. Next, the yellow toner image thus formed on the photosensitive drum 11Y is primarily transferred to the intermediate transfer belt 31 in the primary transfer area by the primary transfer roller 35Y to which a high voltage is applied.

  Next, the toner image is constituted by the photosensitive drum 11M and the primary transfer roller 35M of the next process station 2M where the image is formed with a delay of the time when the toner image is conveyed with the intermediate transfer belt 31 more than the process station 2Y. Transported to the primary transfer area. Then, the leading end of the image is aligned on the yellow toner image on the intermediate transfer belt, and the next magenta toner image is transferred. Thereafter, the same process is repeated, and as a result, toner images of four colors are primarily transferred on the intermediate transfer belt 31, and a full-color image is formed on the intermediate transfer belt. Incidentally, the transfer residual toner slightly remaining on the photosensitive drum is collected by the photosensitive cleaner 15 (15Y, 15M, 15C, 15K) to prepare for the next image formation again.

  Further, in parallel with the toner image forming operation, for example, the sheets S accommodated in the sheet feeding cassettes 61 to 64 are separated and fed one by one by the pickup rollers 71 to 74 and then conveyed to the registration roller 76 Ru. At this time, the registration roller 76 is stopped, and the sheet S is abutted against the registration roller 76 in the stopped state, whereby the skew of the sheet S is corrected.

  Further, after the skew feeding is corrected, the sheet S is rotated by the registration roller 76, which starts rotating at the timing when the leading end of the sheet and the toner image formed on the intermediate transfer belt 31 coincide with each other. The sheet is conveyed to the nip with the transfer belt 31. The sheet is nipped and conveyed by the secondary transfer roller 41 and the intermediate transfer belt 31, and a sheet applied by the bias applied to the secondary transfer roller 41 when passing through the nip portion between the secondary transfer roller 41 and the intermediate transfer belt 31. The toner image on the intermediate transfer belt is secondarily transferred to S.

  Next, the sheet S on which the toner image has been secondarily transferred is an example of a sheet conveying device provided in the sheet conveying path R between the secondary transfer portion T and the fixing device 5. Is conveyed to the fixing device 5. Then, the toner image is melted and fixed on the sheet S by being pressurized and heated in the fixing device 5. Here, the color laser printer 1 has a face-up mode in which the sheet on which the image is formed is discharged on the sheet discharge tray with the image forming surface up, an automatic duplex mode in which the image is formed on both sides of the sheet, Have. A switching member (not shown) is provided to convey the sheet S having the fixed image to the discharge conveyance path 82 in the face-up mode, and to convey the sheet S having the fixed image to the pull-in path 83 in the automatic duplex mode. Path selection is performed.

  Here, in the case of the face up mode, the sheet S having the fixed image passes the sheet discharge conveyance path 82 and is discharged to the sheet discharge tray 65 by the sheet discharge roller 77. Further, in the case of the automatic duplex mode, the sheet S is drawn into the switchback path 84 by the first reverse roller pair 78 and the second reverse roller pair 79 through the pull-in path 83. Thereafter, by performing a switchback operation of reversing the second reverse roller pair 79 from normal rotation to reverse rotation, the sheet is transported to the duplex conveying path 85 by replacing the front and rear ends. Thereafter, the sheet is sent to the secondary transfer portion T through the registration roller 76, and an image is formed on the second side.

  FIG. 2 is a perspective view of the pre-fixing transport device 42, and FIG. 3 is a top view of the pre-fixing transport device 42. As shown in FIG. As shown in FIG. 2, the pre-fixing transport device 42 transports the endless transport belt 101 provided with a large number of suction holes 101a and the central portion in the width direction orthogonal to the sheet transport direction of the area through which the sheet passes. And a suction duct 106 around which the belt 101 is wound. Here, the transport belt 101 is stretched around the drive pulley 102 and the driven pulley 103, and rotates in the sheet transport direction as the drive pulley 102 rotates.

  The suction duct 106 guides the sheet S on which the toner image has been secondarily transferred to the fixing device 5 and is inserted into the inside of the conveyance belt 101 and is shown in FIG. 3 for sucking air to a position facing the conveyance belt 101. A duct opening 112 is provided. And as shown in FIG. 2, it has the adsorption | suction path | pass 109 which is an air path through which the air (air) attracted | sucked from this duct opening part 112 flows.

  Further, as shown in FIG. 3, the pre-fixing conveyance device 42 includes a fixed duct 104 communicating with the suction duct 106 and a suction fan 105. Then, when the suction fan 105 is driven to rotate, air is sucked and a negative pressure is generated at the duct opening 112 via the fixed duct 104 and the suction duct 106. When a negative pressure is generated as described above, air is sucked through the duct opening 112 and the plurality of suction holes 101 a of the conveyance belt 101 to generate a flow of air, whereby the sheet S is attracted to the conveyance belt 101.

  In FIG. 2, reference numeral 42 a denotes a sheet conveyance unit which is a sheet conveyance unit including the suction duct 106 and the conveyance belt 101, and the sheet conveyance unit 42 a is provided to be movable up and down with respect to the fixed unit 42 b. As shown in FIG. 3, the fixed duct 104 and the suction duct 106 are connected by the sealing material 110 which is a sponge-like sealing member attached to the suction duct 106, and the suction duct 106 is thereby lifted. Also, air does not leak from the suction path 109.

  In FIG. 4A, the sheet S is a nip portion between the secondary transfer roller 41 and the intermediate transfer belt 31 (hereinafter referred to as a transfer nip portion) N1 to a nip portion of the heating roller 5a and the pressure roller 5b of the fixing device 5. A state where the sheet is conveyed to the fixing nip portion (hereinafter referred to as a fixing nip portion) N2 is shown. In FIG. 4, reference numeral 43 denotes a transfer passage guide which is a first passage member forming the sheet conveyance passage R shown in FIG. 1 described above, and reference numeral 52 denotes a predetermined interval downstream of the transfer passage guide 43 in the sheet conveyance direction. It is a fixing entrance guide which is a second passage member arranged in a manner.

  Here, the fixing device 5 is constituted by the heating roller 5a and the pressure roller 5b, but the sheet conveying speed of the fixing device 5 changes due to the thermal expansion of the heating roller 5a. Then, when the sheet conveyance speed changes in this manner, the sheet S is pulled between the transfer nip N1 and the fixing nip N2 (hereinafter referred to as a fixing nip) of the heating roller 5a and the pressure roller 5b. The resulting toner image is disturbed.

  Therefore, even when the sheet conveyance speed changes in this manner, the sheet conveyance speed of the fixing device 5 is set so that the sheet S bends downward between the transfer nip N1 and the fixing nip N2 so that the sheets S do not pull each other. It is set. Further, the conveyance belt 101 is positioned below the transfer nip N1 and the fixing nip N2 between the transfer exit guide 43 and the fixing entrance guide 52 so that the sheet can be bent downward. .

  Here, in the case of a normal sheet with a small size such that the sheet S is not simultaneously nipped by the transfer nip portion N1 and the fixing nip portion N2, the sheet S is downward between the transfer exit guide 43 and the fixing entrance guide 52. Flex. Thus, the sheet S is transported while being attracted by the transport belt 101.

  However, in the case of a small size but high rigidity sheet such as thick paper, when the leading end of the sheet S reaches the fixing entrance guide 52 with the sheet rear end on the transfer exit guide 43, the sheet S or A part of the sheet S may be separated from the transport belt 101. That is, when conveying a sheet whose rigidity is larger than a predetermined size, the sheet S or the sheet S may be separated from the conveying belt 101 by overcoming the suction force of the conveying belt 101 due to the rigidity of the sheet. Then, when the sheet S or a part of the sheet S separates from the conveying belt 101 as described above, the conveying force is insufficient, and the non-feed of the sheet and jamming occur.

  Therefore, in the present embodiment, in the case of a sheet with high rigidity, as shown in FIG. 4B, the sheet conveying portion 42a is raised to bring the conveying belt 101 closer to the sheet S. For example, in the case of a sheet having a basis weight of 129 gsm or more and a length in the sheet conveying direction of 210 mm or less, the position of the sheet conveying portion 42a is raised by 4 mm. As a result, the adsorptive power to the sheet can be increased, and even a highly rigid sheet can be stably transported.

  As described above, as shown in FIG. 2, the driving mechanism 142 is provided below the sheet conveying unit 42 a in order to raise and lower the sheet conveying unit 42 a as described above. In the present embodiment, the conveyance belt 101 is driven by the drive mechanism 142 to convey a sheet. That is, in the present embodiment, the sheet conveying portion 42 a is moved up and down by the driving mechanism 142, and the conveying belt 101 is driven.

  The drive mechanism 142 includes a drive unit 142a shown in FIGS. 5 and 6 in order to apply a drive force for moving the sheet transport unit 42a up and down and a drive force for rotating the transport belt 101. The drive portion 142a is provided in the fixed portion 42b and can be a motor 122 capable of rotating in the positive and reverse directions, a pinion gear 123 provided in the motor 122, a step gear 124 engaged with the pinion gear 123, and a step gear 124. And an idler gear 125 engaged with the gear.

  In addition, the drive portion 142a meshes with the idler gear 125, and includes a conveyance one-way gear 126, which is a first drive transmission gear, having a first one-way clutch 126b shown in FIG. 8 described later. The drive unit 142 a further includes a transport idler gear 127 that is a second drive transmission gear that meshes with the transport one-way gear 126. Furthermore, the drive portion 142a meshes with the idler gear 125 on the opposite side to the conveyance one-way gear 126, and includes an elevation one-way gear 128 which is a third drive transmission gear having a second one-way clutch 129a shown in FIG. There is.

  When the motor 122 rotates in the CW direction (first direction), the transport one-way gear 126 rotates by receiving the drive of the idler gear 125 by the action of the one-way clutch. In addition, when the motor 122 rotates in the CCW direction (second direction) opposite to the CW direction, the elevation one-way gear 128 receives the drive of the idler gear 125 and rotates by the action of the one-way clutch.

  FIG. 7 is a control block diagram of the pre-fixing conveyance device 42 according to the present embodiment, and as shown in FIG. 7, the control unit 200 receives an operation unit 201 for inputting sheet rigidity information and a motor 122. Is connected. Then, when the rigidity of the sheet is larger than a predetermined size based on the rigidity information of the sheet input by the operation unit 201, the control unit 200 rotates the motor 122 in the CCW direction so as to be described later. Raise 42a. Thereafter, the motor 122 is rotated in the CW direction to rotate the transport belt 101 to transport the sheet.

  Next, an operation of driving the conveyance belt 101 by the drive unit 142a having such a configuration will be described. When driving the transport belt 101, the motor 122 is rotated in the CW direction shown in FIG. 5 to rotate the pinion gear 123 in the CW direction. The CW direction rotation of the pinion gear 123 is decelerated and transmitted to the conveying one-way gear 126 via the step gear 124 and the idler gear 125. Then, the rotation of the conveyance one-way gear 126 is transmitted to the conveyance idler gear 127.

  Here, as shown in FIG. 8, the transport idler gear 127 meshes with a gear portion 102 a which is a first drive gear provided integrally with the drive pulley 102 which is a drive rotating body. Thus, when the transport idler gear 127 rotates, the drive pulley 102 rotates integrally with the gear portion 102a, and the transport belt 101 rotates in the sheet transport direction indicated by arrow A in FIG. In FIG. 5, reference numeral 143 denotes a first drive transmission unit that transmits the rotation of the motor 122 in the CW direction to the conveyance belt 101. The first drive transmission means 143 includes a pinion gear 123, a step gear 124, an idler gear 125, a conveyance one-way gear 126 and a conveyance idler gear 127 provided between the motor 122 and the conveyance belt 101.

  In FIG. 9, reference numeral 142 b denotes an elevating mechanism which is an elevating means for raising and lowering the sheet conveying unit 42 a by driving of the driving unit 142 a of the driving mechanism 142. The lifting mechanism 142b includes a lifting drive shaft 138, and a lifting input gear 133 which is a second drive gear for rotating the lifting drive shaft 138 by driving from the drive unit 142a. The elevating mechanism 142 b further includes elevating output gears 139 provided on both sides of the elevating drive shaft 138 and elevating cam gears 135 meshing with the elevating output gear 139.

  The elevating drive shaft 138 and the elevating cam gear 135 are rotatably attached to a frame 106 a provided opposite to both ends in the width direction of the bottom surface of the suction duct 106. Further, a driven elevating cam gear 1351 is rotatably mounted at the same height position as the elevating cam gear 135 at a position about 60 mm apart upstream of the frame 106a in the sheet conveying direction.

  The raising and lowering cam gear 135 and the driven raising and lowering cam gear 1351 have a cam portion 135a on one side surface and a pulley portion 135b on the other side surface as shown in FIG. 10, and drive transmission attached to the pulley portion 135b. It rotates in conjunction with the belt 137. Further, the lift cam gear 135 and the cam portion 135 a of the driven lift cam gear 1351 that can be interlockedly rotated with the lift cam gear 135 are in contact with the cam holding member 136 from above. The cam holding member 136 is provided on the frame 111 shown in FIG. 2 described above.

  As a result, when the lift drive shaft 138, which is a cam rotation shaft, rotates and the lift output gear 139 rotates, the lift cam gear 135 and the driven lift cam gear 1351 rotate. When the lift cam gear 135 and the driven lift cam gear 1351 rotate half, the cam portion 135a of the lift cam gear 135 and the cam portion 135a of the driven lift cam gear 1351 which is a driven cam rotate half. As a result, the lift cam gear 135 and the driven lift cam gear 1351 move up with the cam holding member 136 as a fulcrum, and the sheet conveying portion 42a moves up.

  The raising and lowering cam gear 135 and the following raising and lowering cam gear 1351 are rotatably attached in the same phase to the frame 106a provided opposite to each other, and at the same timing. Further, when the lift cam gear 135 and the driven lift cam gear 1351 rotate half, the cam portion 135 a rotates half, the lift cam gear 135 and the driven lift cam gear 1351 move downward, and the sheet conveying unit 42 a returns to the original position.

  Here, as described above, the lift cam gear 135 and the driven lift cam gear 1351 are provided at the same height position and rotate at the same timing. Therefore, when the lift cam gear 135 and the driven lift cam gear 1351 rotate, the sheet conveying unit 42a moves up and down (moves) in a horizontal state without changing the angle as shown in FIG. 4B described above. As a result, the adsorption force for adsorbing the sheet becomes constant, and the sheet having passed the transfer exit guide 43 can be stably placed on the transport belt 101, and can be stably delivered to the fixing entrance guide 52. .

  As shown in FIG. 10, the drive pulley 102 is provided coaxially with the elevation drive shaft 138, but since the bearing 140 is provided between the drive pulley 102 and the elevation drive shaft 138, the elevation drive shaft is provided. The rotation of 138 is not transmitted to the drive pulley 102. That is, in the present embodiment, the drive pulley 102 is rotatably supported by the elevation drive shaft 138, and is rotated by the rotation of the motor 122 in the CW direction.

  Next, an operation of moving up and down the sheet conveying unit 42a by the elevating mechanism 142b and the drive unit 142a configured as described above will be described. When raising and lowering the sheet conveying unit 42a, the motor 122 is rotated in the CCW direction shown in FIG. 5 to rotate the pinion gear 123 in the CCW direction. Then, the rotation in the CCW direction of the pinion gear 123 is decelerated and transmitted to the elevating one-way gear 128 via the step gear 124 and the idler gear 125.

  The rotation of the elevating one-way gear 128 is transmitted to an elevating idler gear 129 which is a fourth drive transmission gear shown in FIG. 11, and the rotation of the elevating idler gear 129 is transmitted to an elevating input gear 133 provided on the elevating drive shaft 138. As a result, when the lift drive shaft 138 rotates in the B direction and the lift drive shaft 138 rotates in the B direction, as shown in FIG. 9 described above, the lift output gear 139 rotates and the lift cam gear 135 and the driven lift cam gear 1351 rotates. As a result, the sheet conveying unit 42a moves up or down.

  In FIG. 5, reference numeral 144 denotes a second drive transmission unit that transmits the rotation of the motor 122 in the CCW direction to the lifting and lowering mechanism 142 b. The second drive transmission means 144 includes a pinion gear 123, a step gear 124, an idler gear 125, an elevation one-way gear 128 and an elevation idler gear 129 shown in FIG. .

  Here, when information indicating that the sheet is a small-sized sheet with high rigidity is input from the operation unit 201, the control unit 200 CCW rotates the motor 122 to half-rotate the cam unit 135a, and the sheet conveyance unit Raise 42a. After that, the motor 122 is CW-rotated in a state in which the sheet conveying unit 42a is raised, and the conveying belt 101 is rotated to convey the sheet. Thus, the sheet is conveyed in a state in which the sheet is reliably placed on the conveyance belt 101. Incidentally, even if the motor 122 is CW-rotated in this manner, the elevating one-way gear 128 is not reversely rotated by the action of the one-way clutch, and therefore, the sheet conveying portion 42a is not lowered.

  Further, after this, when information that the sheet is a small size and a normal sheet is input from the operation unit 201, the motor 122 is CCW-rotated to rotate the cam portion 135a half-turn to lower the sheet conveying portion 42a. . Thereafter, the motor 122 is CW rotated to convey the sheet. After that, when the normal sheet is conveyed in a small size, the motor 122 is CW-rotated to convey the sheet without being CCW-rotated.

  By the way, since the driving pulley 102 is also raised when the sheet conveying portion 42a is raised, the interaxial distance between the conveying idler gear 127 provided on the fixed portion 42b and the driving pulley 102 is deviated. In this case, the rotation of the transport idler gear 127 can not be transmitted to the drive pulley 102, and the transport belt 101 can not be rotated. Therefore, in the present embodiment, the rotation of the conveyance idler gear 127 can be transmitted to the drive pulley 102 even if the sheet conveyance unit 42a is raised as described above.

  Next, such a configuration will be described. In the present embodiment, as shown in FIG. 5, a swinging conveying gear support plate 130, which is a first holding member, is rotatably provided with a shaft 126a of the transfer one-way gear 126 as a fulcrum. A transport idler gear 127 is provided at 130. Thus, the transport idler gear 127 can rotate while maintaining the distance between the transport one-way gear 126 and the shaft while meshing with the transport one-way gear 126.

  Further, as shown in FIG. 8, the swing conveyance gear support plate 130 is biased by the swing spring 132 as the first biasing means so that the transfer idler gear 127 is directed to the gear portion 102 a of the drive pulley 102. . Thus, even if the drive pulley 102 moves up and down, the transport idler gear 127 can follow the drive pulley 102 and can transmit the drive to the gear portion 102 a.

  The oscillating and conveying gear support plate 130 has an abutting portion 130 a having a circular arc shape coaxial with the conveying idler gear 127, and is provided with an abutting member 134 and an abutting portion provided coaxially with the elevation drive shaft 138. 130a contacts. Here, in the present embodiment, the sum of the radius of the abutment portion 130 a and the radius of the abutment member 134 is substantially equal to the sum of the pitch circle radius of the transport idler gear 127 and the pitch circle radius of the drive pulley 102. There is. As a result, the distance between the conveying idler gear 127 and the drive pulley 102 can be kept constant.

  In addition, when the sheet conveying unit 42 a is lifted, the distance between the elevating idler gear 129 and the elevating input gear 133 is shifted, and the rotation of the elevating idler gear 129 can not be transmitted to the elevating input gear 133. Therefore, in the present embodiment, even if the sheet conveying portion 42a is raised as described above, the rotation of the elevation idler gear 129 can be transmitted to the elevation input gear 133.

  Next, such a configuration will be described. In the present embodiment, as shown in FIG. 5, a swing elevating gear support plate 131 serving as a second holding member is rotatably provided with a shaft (not shown) of the lift one-way gear 128 as a fulcrum. A lifting idler gear 129 is provided on the plate 131. Thus, the elevating idler gear 129 can rotate while maintaining the distance between the elevating one-way gear 128 and the shaft, that is, meshing with the elevating one-way gear 128.

  Further, as shown in FIG. 11, the swing elevating gear support plate 131 is biased by the swing spring 132 so that the elevating idler gear 129 is directed to the elevating input gear 133. As a result, even if the sheet conveying unit 42a is lifted, the elevation idler gear 129 can follow the elevation input gear 133 to transmit the drive. Here, in the present embodiment, as the second biasing means for biasing the swing elevating gear support plate 131, the swing spring 132 for biasing the swing conveyance gear support plate 130 is used. The spring of may be used.

  The rocking elevating gear support plate 131 has an abutting portion 131a having a circular arc shape coaxial with the elevating idler gear 129, and the abutting portion 131a and the abutting member 134 are in contact with each other. Here, in the present embodiment, the sum of the radius of the butting portion 131a and the radius of the butting member 134 is substantially equal to the sum of the radius of the elevation idler gear 129 and the pitch radius of the elevation input gear 133. There is. As a result, the distance between the elevating idler gear 129 and the elevating input gear 133 can be kept constant.

  As described above, in the present embodiment, when the stiffness of the sheet is larger than the predetermined stiffness, the transport belt 101 is driven in a state in which the sheet transport unit 42a is raised. Further, the conveyance belt 101 is driven by the rotation of the motor 122 in the CW direction, and the sheet conveyance unit 42 a is moved up and down by the rotation of the motor 122 in the CCW direction. As a result, the drive of the conveyance belt 101 and the elevation of the sheet conveyance unit 42a can be performed by the common motor 122, and the sheet can be stably conveyed at low cost.

  In the above description, the sheet conveying unit 42a is moved up and down by interlockingly rotating the elevating cam gear 135 and the driven elevating cam gear 1351, but the present invention is not limited to this. If the sheet conveying unit 42a can be moved up and down horizontally, the sheet conveying unit 42a may be moved up and down only by the raising and lowering cam gear 135.

DESCRIPTION OF SYMBOLS 1 ... color laser printer, 1A ... color laser printer main body, 1B ... image formation part, 5 ... fixing device, 42 ... conveyance apparatus before fixation, 42a ... sheet conveyance part, 43 ... transfer exit guide, 52 ... fixing entrance guide, 101 ... Transport belt, 102 ... Drive pulley, 102a ... Gear section, 105 ... Suction fan, 106 ... Suction duct, 109 ... Suction path, 112 ... Duct opening, 122 ... Motor, 126 ... Transport one way gear, 126b ... 1st One-way clutch, 127: Transport idler gear, 128: Lifting one-way gear, 129: Lifting idler gear, 129a: Second one-way clutch, 130: Swing transport gear support plate, 131: Swing lift gear support plate, 132: Swing spring 135: lifting cam gear, 135a: cam portion, 1351: driven lifting cam gear, 138: lifting drive , 139: elevating output gear 142: driving mechanism 142a: driving unit 142b elevating mechanism 143: first driving transmission means 144: second driving transmission means 200: control section R: sheet conveying path S ... sheet, T ... secondary transfer unit

Claims (13)

An endless conveying belt having a plurality of suction holes formed thereon for adsorbing and conveying sheets;
A belt drive rotating body wound around the transport belt and driving the transport belt;
A belt driven rotating body wound around the transport belt and driven to rotate by the transport belt;
An elevation unit for raising and lowering the belt drive rotating body and the belt driven rotating body;
One motor that generates driving force,
First driving means for transmitting the driving force of the motor to the belt drive rotating body only when the motor rotates in the first direction;
And second driving means for transmitting the driving force of the motor to the elevating unit only when the motor rotates in a second direction opposite to the first direction.
Sheet conveying apparatus characterized in that. The belt drive rotating body is disposed downstream of the belt driven rotating body in the sheet conveying direction.
The sheet conveying apparatus according to claim 1, The transport belt moves in parallel in the vertical direction when it is moved up and down by the lifting and lowering unit via the belt drive rotating body and the belt driven rotating body.
The sheet conveying apparatus according to claim 1 or 2, wherein A frame unit for supporting the motor;
A driving force of the motor is transmitted to the first drive means, and a first drive transmission gear rotatably supported by the frame unit and a rotation shaft of the first drive transmission gear are swingably supported. a first holding member, wherein is rotatably supported by the first holding member, a second transmission gear driven by the first drive transmission gear, the belt drive rotates with being driven by the second drive transmitting gear It drives the body, a first drive gear for vertically integrally with the belt drive rotary member, wherein as the second transmission gear regardless of the position of the first driving gear is meshed with the first driving gear first 1) first biasing means for biasing the holding member ;
The second drive means is swingably supported by a third drive transmission gear which is rotatably supported by the frame unit to which the drive force of the motor is transmitted, and a rotation shaft of the third drive transmission gear. a second holding member is rotatably supported by the second holding member, and the fourth transmission gear driven by said third drive transmission gears, the lifting unit with driven by the fourth transmission gear driven, and the second drive gear for vertically integrally with the belt drive rotor, said second regardless of the position of the drive gear and the fourth transmission gear is the second holding to mesh with the second drive gear And second biasing means for biasing the member .
The sheet conveying apparatus according to any one of claims 1 to 3, wherein The elevating unit has a rotating shaft supporting the belt drive rotating body so as to be able to relatively rotate,
The first drive gear is integrally provided on the belt drive rotating body and rotates around the rotation axis,
The second drive gear is non-rotatably fixed to the rotation shaft.
The sheet conveying apparatus according to claim 4, The lifting and lowering unit lifts and lowers the lifting and lowering frame by the driving force of the rotating shaft, and the lifting and lowering frame for rotatably supporting the rotating shaft and the following shaft. And a lifting unit,
The elevating unit includes an abutting member provided on the frame unit, and an eccentric cam rotatably supported by the elevating frame and rotated by a driving force of the rotating shaft.
The eccentric cam rotates and presses the contact member to raise and lower the elevating frame.
The sheet conveying apparatus according to claim 5, wherein The eccentric cam is a first eccentric cam,
The contact member is a first contact member,
The elevating unit is disposed at a position different from the first eccentric cam in the sheet conveying direction and is interlocked with the first eccentric cam, provided on the frame unit, and pressed by the second eccentric cam. And a second contact member
The sheet conveying apparatus according to claim 6, wherein The elevating unit is provided on both the one side and the other side across the transport belt in the axial direction of the rotation shaft.
The sheet conveying apparatus according to claim 6 or 7, wherein A suction duct which is inserted into the inside of the transport belt and provided with an opening for sucking air at a position facing the transport belt;
A fixed duct provided in the frame unit and connected to the suction duct;
Suction means for suctioning air through the openings of the suction duct and the plurality of suction holes of the transport belt to cause the transport belt to adsorb a sheet;
A sealing member for sealing a connecting portion between the suction duct and the fixed duct even if the suction duct moves up and down together with the transport belt;
The sheet conveying apparatus according to any one of claims 4 to 8, characterized in that: The first drive means has a first one-way clutch that transmits a driving force only when the motor rotates in the first direction,
The second driving means has a second one-way clutch that transmits a driving force only when the motor rotates in the second direction.
The sheet conveying apparatus according to any one of claims 1 to 9, wherein The elevating unit is capable of elevating the transport belt to a first position and a second position above the first position,
The motor is rotated in the first direction with the conveyor belt positioned at the first position, and the conveyor belt is positioned at the second position in a first mode in which the conveyor belt is driven. A control unit capable of executing a second mode of rotating the motor in the first direction and driving the conveyance belt;
The sheet conveying apparatus according to any one of claims 1 to 10, wherein The control means executes the first mode when the rigidity of the sheet to be conveyed is the first rigidity, and the rigidity of the sheet to be conveyed is the second rigidity larger than the first rigidity. Execute the second mode,
The sheet conveying apparatus according to claim 11, wherein An image forming unit for forming a toner image, a transfer unit for transferring the toner image onto a sheet, a fixing unit for fixing the toner image transferred onto the sheet by the transfer unit, and a position between the transfer unit and the fixing unit A sheet conveying apparatus according to any one of claims 1 to 12 provided.
An image forming apparatus characterized by

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