JP2016031471A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that although a nip position of a back-up roller and a secondary transfer roller in a secondary transfer unit is changed to deal with a recording sheet different in a sheet thickness, maintenance such as occurrence of a nip mark in the roller, sheet jam countermeasure, component replacement or the like is cumbersome.SOLUTION: An image formation device includes: a back-up roller 34 that is provided inside an intermediate transfer belt 24 and supports the intermediate transfer belt 24 to be belt-spun; a secondary transfer roller 33 that is arranged to face the back-up roller 34; a bearing 64 that holds a rotary shaft of the secondary transfer roller 33 in a freely rotatable manner; and a secondary transfer roller holding unit 61 that movably loads the bearing 64. The secondary transfer roller holding unit 61 is formed along an arc centering around a shaft center of the back-up roller 34, and has an arc-shape reception face 71 that guides the bearing 64, and a linear reception face 72 that comes out of the arc, extends in a direction separating from the shaft center, and guides the bearing 64.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an intermediate transfer type image forming apparatus, and more particularly to a configuration of a secondary transfer unit that secondary-transfers a developer image onto a medium.

  Conventionally, in this type of medium transport device, when performing transfer to the medium at the nip portion between the backup roller and the transfer roller, there is one that moves the nip position in accordance with the medium thickness, and in this case, The transfer roller is rotatably held by a holding member that rotates coaxially with the backup roller, and the transfer roller is moved in the circumferential direction of the backup roller (see, for example, Patent Document 1).

JP2011-64917A (7th page, FIG. 5)

  However, since the transfer roller and the backup roller cannot be easily separated in the apparatus configured as described above, for example, the unit to which the transfer roller belongs and the unit to which the backup roller belongs cannot be separated and handled individually. There were difficulties in handling and unit replacement. In addition, since the pressure of the transfer roller cannot be reduced when not in use, a nip mark is generated on the soft roller, streaks or the like are generated on the printed image, and there is a problem that causes a decrease in print quality.

An image forming apparatus according to the present invention is an intermediate transfer type image forming apparatus,
An endless intermediate transfer belt that conveys the developer image transferred by primary transfer, a backup roller that supports the intermediate transfer belt that is arranged and stretched inside the intermediate transfer belt, and the intermediate transfer belt The secondary transfer roller that is disposed opposite to the backup roller via the roller and constitutes the secondary transfer unit, the rotary bearing that rotatably holds the rotation shaft of the secondary transfer roller, and the rotary bearing can be moved. And a secondary transfer roller holding part mounted on
The secondary transfer roller holder is
A first mounting portion that is formed along an arc centered on the axial center of the backup roller, guides the rotary bearing, and is disposed adjacent to the first mounting portion, and deviates from the arc. And a second placement portion that extends in a direction away from the shaft center and guides the rotary bearing.

  According to the present invention, it is possible to move the nip position between the backup roller and the secondary transfer roller, to reduce or separate the nip amount, and to freely separate them.

1 is a main part configuration diagram showing a main part configuration of an image forming apparatus according to a first embodiment of the present invention; (A) is an external perspective view showing a state in which the rail unit is pulled out from the main body of the image forming apparatus and the secondary transfer roller unit is removed upward by an operator, and (b) is a diagram in (a) of FIG. It is an external appearance perspective view of the secondary transfer roller unit shown, (c) is an external perspective view of the secondary transfer roller holding part 61 shown to the same figure (a). FIG. 3 is a partial enlarged view of a right end portion of the secondary transfer roller unit shown in FIG. FIG. 3 is a partial enlarged view of a left end portion of a secondary transfer roller unit shown in FIG. FIG. 3 is a partial enlarged view of a right end portion of a secondary transfer roller holding portion shown in FIG. FIG. 3 is a partially enlarged view of a left end portion of a secondary transfer roller holding portion shown in FIG. FIG. 6 is an external perspective view of the vicinity of the right cam gear shown in FIG. 5 as seen from another angle different from FIG. 5 in order to show the configuration of a driving force transmission system for rotationally driving the left and right cam gears. (A) is a block diagram schematically showing the positional relationship of an intermediate transfer belt, a secondary transfer unit, a fixing unit, a conveyance roller pair, and a sheet conveyance path in the vicinity of the secondary transfer unit, and (b) FIG. 4 is a partially enlarged view near a secondary transfer portion. FIG. 6 is an operation explanatory diagram showing the positional relationship between the transfer belt unit, the secondary transfer roller unit, and the secondary transfer roller holding unit when the secondary transfer roller is at the thick paper position P1, the plain paper position P2, and the decompression position P3; (A) shows the state when the secondary transfer roller is located at the thick paper position P1, (b) shows the state when the secondary transfer roller is located at the plain paper position P2, and (c) shows the state when the secondary transfer roller is located at the decompression position P3. Show. FIG. 6 is an external perspective view showing a state when the transfer belt unit is pulled out from the image forming apparatus main body in the direction of arrow E.

Embodiment 1 FIG.
FIG. 1 is a main part configuration diagram showing the main part configuration of the image forming apparatus according to the first embodiment of the present invention.

  The image forming apparatus 1 is an intermediate transfer color electrophotographic printer capable of printing five colors of transparent (T), black (K), yellow (Y), cyan (C), and magenta (M) as special colors. It has the composition of. The paper tray 11 is detachably attached to the image forming apparatus 1 and accommodates recording paper 12 as recording media stacked therein, and a paper feeding unit 13 that feeds out the recording paper 12 one by one on its feeding side. Is arranged. A pickup roller 14 that feeds the recording paper 12 that rises to a certain height in the paper tray 11 and presses it toward the conveyance path, and the fed recording paper 12 are separated and sent to the paper feed unit 13 one by one. A feed roller 15 and a retard roller 16 are provided.

  The recording sheets 12 separated one by one are transported through the medium transport path 17 by transport roller pairs 19, 20, and 21 and reach the secondary transfer unit 18. During this time, the recording paper 12 is corrected in skew, and further conveyed to the secondary transfer unit 18 at a predetermined timing.

  The development forming unit 22 includes a toner image forming unit 23T that forms a transparent (T) toner image, a toner image forming unit 23Y that forms a yellow (Y) toner image, and a toner image that forms a magenta (M) toner image. A forming unit 23M, a toner image forming unit 23C that forms a cyan (C) toner image, and a toner image forming unit 23K that forms a black (K) toner image. , And five LED heads 28T to 28K (facing 28 when there is no need to distinguish).

  The five toner image forming units 23T to 23K are sequentially arranged from the upstream side along the moving direction (arrow B direction) in which an intermediate transfer belt 24 of the transfer belt unit 30 described later moves on the upper portion of the transfer belt unit 30. As will be described later, the five LED heads 28T to 28K are opposed to the toner image forming units 23T to 23K in order to irradiate a predetermined portion of the photosensitive drum 26 provided in the toner image forming unit 23. Are arranged.

  Since the toner image forming units 23T to 23K have the same internal configuration, the internal configuration will be described by taking the black (K) toner image forming unit 23K as an example.

  In the toner image forming portion 23K, a photosensitive drum 26 is disposed so as to be rotatable in the direction of the arrow (counterclockwise), and around the photosensitive drum 26, the photosensitive drum 26 is sequentially arranged from the upstream side in the rotation direction. A charging roller 27 that supplies a negative charge to the surface, an LED head 28K that forms an electrostatic latent image by selectively irradiating light on the surface of the charged photosensitive drum 26, and an electrostatic latent image is formed. A developing roller 29 is disposed on the surface of the photosensitive drum 26 for development by attaching toner as a black (K) developer by frictional charging.

  The drum or roller used in each toner image forming unit 23 is rotated by power transmitted from a driving source (not shown) via a gear or the like, and the developing roller 29 of each toner image forming unit 23 Corresponding color toners are supplied from toner cartridges arranged correspondingly above the toner image forming unit 23 via a predetermined path and supply means.

  The transfer belt unit 30 is disposed opposite to a drive roller 31 that is rotationally driven by a drive source (not shown), a tension roller 32 that applies tension to the intermediate transfer belt 24, and a secondary transfer roller 33, and the secondary transfer unit 18. , The intermediate transfer belt 24 stretched around these rollers and moved in the direction of arrow B (clockwise), and the support roller disposed upstream of the backup roller 34 in the moving direction of the intermediate transfer belt 24 35.

  Further, the transfer belt unit 30 includes five primary transfer rollers 36T to 36K (distinguishable) disposed inside the intermediate transfer belt 24 and in pressure contact with the photosensitive drums 26 of the corresponding toner image forming units 23T to 23K. When not necessary, each primary transfer roller 36 is provided with a predetermined number for primary transfer of each toner image formed on the corresponding photosensitive drum 26 onto the intermediate transfer belt 24. Is added. These five primary transfer rollers 36T to 36K form a primary transfer portion 25.

  Further, an upper guide member 37 and a lower guide member 38 for guiding the recording paper 12 to the secondary transfer unit 18 are provided between the transport roller pair 21 and the secondary transfer unit 18. Between the roller pair 21, a paper thickness sensor 39 is provided as a medium thickness detector that detects the paper thickness information of the recording paper 12 being conveyed.

  As described above, the transfer belt unit 30 primary-transfers the toner images of the respective colors formed by the development forming unit 22 sequentially on the intermediate transfer belt 24 as described later, and further performs the primary transfer toner. The image is conveyed to the secondary transfer unit 18. In the secondary transfer unit 18, the toner image transferred to the intermediate transfer belt 24 is secondarily transferred to the recording paper 12 supplied from the paper tray 11 by the secondary transfer roller 33. The transfer belt unit 30 in the present embodiment is detachably attached to the main body of the image forming apparatus 1 as will be described later.

  The fixing unit 40 includes an upper roller 42 that is rotationally driven in a direction indicated by an arrow (clockwise) by a drive source (not shown), a heater 41 that serves as a heat source for heating, and a pressure lower roller 43 that is driven to rotate in pressure contact with the upper roller 42. The recording paper 12 fed from the secondary transfer unit 18 is nipped and conveyed at the nip, and in the conveyance process, heat and pressure are applied to the toner image transferred onto the recording paper 12 to melt it. Then, the melted toner image is fixed.

  The discharge roller pairs 44 to 48 convey the recording sheet 12 discharged from the fixing unit 40 along a predetermined conveyance path, and discharge the printed recording sheet 12 to the stacker unit 49.

  In FIG. 1, the X, Y, and Z axes take the X axis in the transport direction (arrow B direction) when the intermediate transfer belt 24 passes through the toner image forming unit 23, and the photosensitive drum 26 rotates. The Y-axis is taken in the axial direction, and the Z-axis is taken in a direction perpendicular to both the axes. Moreover, when each axis | shaft of X, Y, and Z is shown in the other figure mentioned later, these axial directions shall show a common direction. That is, the XYZ axes in each figure indicate the arrangement direction when the depicted portion of each figure constitutes the image forming apparatus 1 shown in FIG. Here, it is assumed that the Z-axis is arranged in a substantially vertical direction.

  Next, the configuration around the secondary transfer unit 18 will be further described. Note that the image forming apparatus 1 shown in FIG. 1 may be identified with respect to the left and right directions of the image forming apparatus 1 when viewed from the direction of the arrow A (the positive direction of the X axis).

  2A is an external perspective view showing a state in which the rail unit 62 is pulled out from the main body of the image forming apparatus 1 and the secondary transfer roller unit 60 is removed upward by the operator, and FIG. FIG. 5A is an external perspective view of a portion surrounded by an encircled ellipse 101 in FIG. 10A, that is, an external perspective view of the secondary transfer roller unit 60. FIG. 10C is enclosed by an enclosed ellipse 102 in FIG. FIG. 5 is an external perspective view of a secondary transfer roller holding portion 61 disposed in a portion, that is, a rail unit 62. The rail unit 62 corresponds to a portion surrounded by a dotted line in FIG.

  3 is an enlarged view of a portion surrounded by a circle 103 in FIG. 2B, that is, a partial enlarged view of a right end portion of the secondary transfer roller unit 60, and FIG. 4 is a view in FIG. FIG. 5 is a partially enlarged view of a portion surrounded by a surrounding circle 104, that is, a left end portion of the secondary transfer roller unit 60. FIG. 5 is a portion surrounded by a surrounding circle 105 in FIG. FIG. 6 is a partially enlarged view of the right end portion of the transfer roller holding portion 61. FIG. 6 is a portion surrounded by a circle 106 in FIG. 2C, that is, a left end portion of the secondary transfer roller holding portion 61. It is an enlarged view.

  As shown in FIG. 1, the rail unit 62 is disposed between the paper tray 11 and the transfer belt unit 30 in the image forming apparatus 1, and in the conveyance direction of the recording paper 12, as shown in FIG. It is held so that it can be pulled out in a certain arrow C direction (minus X-axis direction). The rail unit 62 includes a secondary transfer roller holding portion 61 that extends in the axial direction of the photosensitive drum 26 and holds the secondary transfer roller unit 60 slidably and detachably as will be described later. It has been.

  As shown in FIG. 2C, the secondary transfer roller holding portion 61 includes a bottom plate 69a, a sheet metal frame 69 having left and right side plates 69L and 69R connected thereto, and a lower plate disposed on the sheet metal frame 69. The secondary transfer roller unit 60 includes a resin sheet guide 70 that also serves as a side guide member 38. As shown in FIG. 2B, the secondary transfer roller unit 60 connects the secondary transfer roller 33 and the secondary transfer roller 33 to the left and right side walls. A secondary transfer roller holding frame 63 that is rotatably held by the portions 63L and 63R and also serves as a paper travel guide.

  In the secondary transfer roller unit 60, the right side wall 63R of the secondary transfer roller holding frame 63 is a rotary bearing that rotatably holds one end of the rotary shaft of the secondary transfer roller 33, as shown in FIG. The right side bearing 64R is formed in the right side bearing house 90R, protrudes outward in parallel with the rotation axis of the secondary transfer roller 33, and engages with a secondary transfer roller holding portion 61 described later, and a vertical slide post 65R. First and second right regulating walls 66R and 67R are formed as engaging portions that extend in opposition to each other and have surfaces parallel to the rotation axis of the secondary transfer roller 33.

  Similarly, in the secondary transfer roller unit 60, the other end of the rotating shaft of the secondary transfer roller 33 is rotatably held on the left wall 63L of the secondary transfer roller holding frame 63 as shown in FIG. The left bearing 64L (not shown) is formed in the left bearing house 90L, and the left sliding post 65L and the first and second left regulating walls 66L and 67L (not shown) are formed. In this case, the left and right side wall parts 63L and 63R are configured to be symmetrical with respect to a virtual center plane (perpendicular to the rotation axis of the secondary transfer roller 33) between the left and right side wall parts 63L and 63R. As shown in FIG. 4, a light shielding plate 68 that blocks light from an optical sensor, which will be described later, is formed in a lower portion near the left side wall portion 63 </ b> L.

  In the secondary transfer roller holding portion 61, a cylindrical outer ring (cap) of the right bearing 64R (FIG. 3) of the secondary transfer roller unit 60 is formed on the upper edge portion of the right plate 69R of the sheet metal frame 69 as shown in FIG. ), And a linear receiving surface 72R as a second mounting portion formed adjacent to the arcuate receiving surface 71R as a first mounting portion is formed. A right post receiving portion 73R as a post receiving portion that slidably receives the right sliding post 65R (FIG. 3) of the secondary transfer roller unit 60 is formed. Each of the arc-shaped receiving surface 71R, the linear receiving surface 72R, and the right post receiving portion 73R is formed into a surface by bending a part of the right plate 69R inward by sheet metal processing. Further, the arcuate receiving surface 71R and the linear receiving surface 72R may be formed continuously or may be formed through a slit.

  Further, the right side plate 69R supports, on the inner side, a rotation shaft that rotatably holds a right cam gear 75R having a right eccentric cam 74R formed integrally with the rotation shaft of the secondary transfer roller 33 to be mounted. doing.

  Similarly, in the secondary transfer roller holding portion 61, an outer periphery of the left bearing 64 </ b> L (not shown) of the secondary transfer roller unit 60 is formed on the upper edge portion of the left plate 69 </ b> L of the sheet metal frame 69 as shown in FIG. 6. An arc-shaped receiving surface 71L and a linear receiving surface 72L on which the surface is placed are formed, and a left-side post receiving portion 73L that slidably receives the left-side sliding post 65L (FIG. 4) of the secondary transfer roller unit 60. Is formed. Further, the left side plate 69L supports, on the inner side, a rotation shaft that rotatably holds a left cam gear 75L having a left eccentric cam 74L that is integrally formed in parallel with the rotation axis of the secondary transfer roller 33 to be mounted. doing.

  Here, the left and right side plates 69L and 69R and the cam gears 75L and 75R are on a virtual center plane (perpendicular to the rotation axis of the mounted secondary transfer roller 33) between the left and right side plates 69L and 69R. On the other hand, it is symmetrical. As shown in FIG. 6, an optical sensor 76 that is shielded by the light shielding plate 68 (FIG. 4) is disposed on the inner bottom near the left side plate 69L. The light shielding plate 68 and the optical sensor 76 correspond to a position detection device.

  FIG. 7 is an external perspective view of the vicinity of the right cam gear 75R shown in FIG. 5 viewed from another angle different from FIG. 5 in order to show the configuration of the driving force transmission system for rotationally driving the left and right cam gears 75L and 75R. . In FIG. 7, the right side plate 69R is omitted to show the internal configuration.

  7, a right transmission gear 84R meshing with the right cam gear 75R is disposed below the right cam gear 75R, and a left transmission gear 84L meshing with the left cam gear 75L is disposed below the left cam gear 75L, as shown in FIG. Has been placed. These left and right transmission gears 84L and 84R are coaxially and integrally fixed to a connecting shaft 83 whose both ends are rotatably held by left and right side plates 69L and 69R below the left and right cam gears 75L and 75R. .

  Further, an intermediate gear 82 is coaxially fixed to the connecting shaft 83 in the vicinity of the right transmission gear 84R, and the rotation of the drive motor 80 is transmitted to the intermediate gear 82 via a transmission system including a reduction gear 81. Communicated. Therefore, the left and right cam gears 75L and 75R are configured to rotate in the same direction when the drive motor 80 rotates in a predetermined direction.

  The secondary transfer roller unit 60 is placed on the secondary transfer roller holding portion 61 so that the secondary transfer roller 33 is accommodated in the roller accommodating portion 77 (FIG. 6) of the secondary transfer roller holding portion 61. At that time, the outer peripheral surface of the right bearing 64R is placed on either the arc-shaped receiving surface 71R or the linear receiving surface 72R of the right plate 69R, and the right sliding post 65R is placed on the right post receiving portion 73R. Similarly, the outer peripheral surface of the left bearing 64L is placed on either the arcuate receiving surface 71L or the linear receiving surface 72L of the left plate 69L, and the left sliding post 65L is placed on the left post receiving portion 73L. Like that. Further, at this time, the right eccentric cam 74R of the right cam gear 75R is configured to fit between the first and second right regulating walls 66R and 67R of the secondary transfer roller unit 60. The left side is similarly configured.

  In the above configuration, first, the printing operation of the entire image forming apparatus 1 will be described with reference mainly to FIG.

  The recording sheets 12 stacked inside the sheet tray 11 are fed out to the nip portion of the roller pair of the feed roller 15 and the retard roller 16 by a pickup roller 14 driven by a drive motor (not shown) and separated one by one. The The recording paper 12 fed to the medium transport path 17 by one sheet by the paper feed unit 13 is transported to the secondary transfer unit 18 by transport roller pairs 19, 20, and 21. The skew is corrected during the conveyance here, the conveyance timing is measured, and the paper thickness sensor 39 detects the paper thickness.

  During this time, in the development forming unit 22, each color toner image forming unit 23 forms a corresponding color toner image on the surface of the photoconductive drum 26, and in the transfer belt unit 30, the color formed on each photoconductive drum 26. The toner images of the respective colors are primarily transferred to the intermediate transfer belt 24 by the primary transfer roller 36 of the primary transfer unit 25 arranged correspondingly. The photosensitive drum 26 of each toner image forming unit 23 and the intermediate transfer belt 24 of the transfer belt unit 30 are driven in synchronization, and the toner images of the respective colors formed on the respective photosensitive drums 26 are sequentially superimposed on the intermediate transfer belt 24. Is transcribed.

  The toner image primarily transferred onto the intermediate transfer belt 24 is transported to the secondary transfer unit 18, and in synchronization therewith, the toner image is transferred to a predetermined position on the recording surface of the recording paper 12 transported to the secondary transfer unit 18. Next is transferred. Therefore, in the secondary transfer unit 18, a predetermined electric field is generated between the secondary transfer roller 33 and the backup roller 34 connected to the frame ground at the nip portion between the secondary transfer roller 33 and the backup roller 34. A voltage is applied to the next transfer roller 33 by a power supply device (not shown).

  The recording paper 12 on which the toner image is secondarily transferred by the secondary transfer unit 18 is sent out to the fixing unit 40. In the fixing unit 40, heat and pressure are applied to the recording paper 12 on which the toner image is secondarily transferred, and the toner image is melted and fixed on the recording paper 12. Thereafter, the recording paper 12 subjected to the fixing process is discharged to the stacker unit 49 by the discharge roller pairs 44 to 48.

  In the image forming apparatus 1 according to the present embodiment, the secondary transfer unit 18 changes the arrangement position of the secondary transfer roller 33 with respect to the backup roller 34 in accordance with the thickness and use state of the recording paper 12 to be used. A medium transport mechanism is provided. The configuration and operation of the medium transport mechanism will be described below.

  Here, the left and right side wall portions 63L and 63R of the secondary transfer roller unit 60 (FIG. 2B), the left and right side plates 69L and 69R of the secondary transfer roller holding portion 61 (FIG. 2C), and Since the cam gears 75L and 75R (FIGS. 5 and 6) are formed symmetrically with respect to a predetermined center plane as described above, only the components on the right side are shown in FIGS. I will explain.

  FIG. 8A is a configuration diagram schematically showing the positional relationship of the intermediate transfer belt 24, the secondary transfer unit 18, the fixing unit 40, the conveyance roller pair 21, and the sheet conveyance path in the vicinity of the secondary transfer unit 18. FIG. 4B is a partially enlarged view in the vicinity of the secondary transfer portion 18.

  8B, for ease of explanation, the right side bearing 64R that holds the rotation shaft of the secondary transfer roller 33 and the secondary transfer roller 33 of the secondary transfer roller unit 60 (FIG. 2B), the right side. Only the contours of the arcuate receiving surface 71R and the linear receiving surface 72R of the secondary transfer roller holding portion 61 (FIG. 2C) on which the bearing 64R is placed are shown.

  As shown in FIG. 8B, the secondary transfer roller 33 has a right bearing 64 </ b> R that holds the rotating shaft thereof in an arcuate shape formed on the right plate 69 </ b> R (FIG. 5) of the secondary transfer roller holding unit 61. The rotational axis center is placed on the surface 71R or the linear receiving surface 72R, and the center of the rotation axis is the thick paper position P1 as the first position, the plain paper position P2 as the second position, and the third position. Each of the slide positions of the decompression position P3 is configured to be able to take. In FIG. 8B, in order to avoid complication, the positions of the secondary transfer roller 33 at the thick paper position P1 and the decompression position P3 are indicated only by dotted lines indicating the outer shape of the right bearing 64R at each position.

Here, the cross section of the arcuate receiving surface 71R (cut by a plane perpendicular to the rotation axis of the secondary transfer roller 33) is formed on an arc having a radius L1 centering on the rotation axis center 34a of the backup roller 34. Yes. Accordingly, the nip amount between the backup roller 34 and the secondary transfer roller 33 does not change at the thick paper position P1 and the plain paper position P2 where the outer peripheral surface of the right bearing 64R is set at a position in contact with the arcuate receiving surface 71R. The distance L2 to the rotation axis center 34a of the backup roller 34 is L2> L1
At the pressure reducing position P3 provided at a position in contact with the linear receiving surface 72R, the nip amount between the backup roller 34 and the secondary transfer roller 33 is reduced and the pressure is reduced, or the backup roller 34 and the secondary transfer roller 33 Are separated from each other.

  9 shows the positional relationship between the transfer belt unit 30, the secondary transfer roller unit 60, and the secondary transfer roller holding portion 61 when the secondary transfer roller 33 is at the thick paper position P1, the plain paper position P2, and the pressure reducing position P3. FIG. 4A shows the secondary transfer roller 33 at the thick paper position P1, FIG. 2B shows the secondary transfer roller 33 at the plain paper position P2, and FIG. A state when the next transfer roller 33 is positioned at the pressure reducing position P3 is shown.

  As shown in FIG. 9A, the transfer belt unit 30 is provided with a backup roller 34 that constitutes the secondary transfer portion 18, and an intermediate transfer belt 24 is suspended. As shown in FIG. 9B, the secondary transfer roller unit 60 includes a secondary bearing roller 33, a right bearing 64 </ b> R that holds the rotation shaft of the secondary transfer roller 33, a right sliding post 65 </ b> R, and a first right regulation. A wall 66R, a second right regulating wall 67R, and a light shielding plate 68 are disposed.

  Then, as shown in FIG. 9C, the secondary transfer roller holding portion 61 receives the outer peripheral surface of the right bearing 64R and places an arcuate receiving surface 71R and a linear receiving surface 72R on which the outer peripheral surface is placed. A right post receiving portion 73R on which the post 65R is placed, a right eccentric cam 74R interposed between and abutting between the first and second right regulating walls 66R and 67R, and a right cam gear formed integrally with the right eccentric cam 74R 75R is disposed, and the right cam gear 75R is rotationally driven in the direction of arrow D by the drive motor 80 (FIG. 7). The center 79R of the right eccentric cam 74R is eccentric with respect to the rotation shaft center 78R of the right cam gear 75R. Further, FIG. 8C shows a light detection point 76a of the light sensor 76 (FIG. 6) disposed on the secondary transfer roller holding portion 61. FIG.

  Here, an example of a moving method for moving the secondary transfer roller 33 between the three positions of the thick paper position P1, the plain paper position P2, and the decompression position P3 will be described.

  First, the right cam gear 75R is rotated in the direction of the arrow R, and the light shielding plate 68 detects the light shielding that blocks the light detection point 76a of the optical sensor 76, and this light shielding position is set as the reference position of the right cam gear 75R. The reference position here corresponds to the decompression position P3 shown in FIG. 9C where the secondary transfer roller 33 is located. Accordingly, here, the light shielding plate 68 is configured to block the light detection point 76a of the light sensor 76 when the secondary transfer roller 33 is located at the pressure reducing position P3.

  Accordingly, the secondary transfer roller 33 is moved to the thick paper position P1 by rotating the right cam gear 75R from the reference position by 180 degrees in the direction of the arrow D, and the secondary transfer roller 33 is moved to the plain paper position by further rotating by 90 degrees. You can move to P2.

  Here, the drive motor 80 rotationally drives the right cam gear 75R in one direction of the arrow D by one-way rotational driving. However, the rotational speed of the right cam gear 75R is corrected by performing the reference position correction every time light is detected. With this increase, the error of the stop position of the secondary transfer roller 33 due to the rotation error is not accumulated and the position accuracy is not lowered.

  Here, the amount of eccentricity of the center 79R of the right eccentric cam 74R with respect to the rotation shaft center 78R of the right cam gear 75R is 3 mm, the distance between the thick paper position P1 and the plain paper position P2, and the normal paper position P2 and the decompression position P3. The distance is also about 3 mm. Further, the play of the right eccentric cam 74R with respect to the first and second right regulating walls 66R and 67R at each position P1 to P3 is provided about 0.2 mm.

  When the secondary transfer roller 33 moves in the thick paper position P1, the plain paper position P2, and the decompression position P3, the right sliding post 65R is guided by the right post receiving portion 73R and moves on the mounting surface. The mounting surface of the right post receiving portion 73R is formed so as to maintain the posture (inclination) of the secondary transfer roller unit 60 when the secondary transfer roller 33 moves between the positions P1 to P3 in a desired state. However, here, it is formed substantially horizontally (X-axis direction).

  As described with reference to FIG. 8B, the linear receiving surface 72R of the secondary transfer roller holding unit 61 is formed so as to satisfy L2> L1, but here, it is substantially horizontal (X-axis direction). Is formed.

  The drive motor 80 is rotationally controlled by a control unit (not shown). As a control method in that case, for example, when the recording paper 12 is in a non-sheet-passing state before passing through the paper thickness sensor 39 (FIG. 1), When the cam gear 75R is stopped at the reference position and the secondary transfer roller 33 is maintained at the pressure-reducing position P3, and the thickness of the recording paper 12 detected by the paper thickness sensor 39 when passing is greater than or equal to a predetermined thickness, The drive motor 80 is rapidly rotated until the transfer roller 33 moves to the thick paper position P1, and if the thickness is less than the predetermined thickness, the drive motor 80 is promptly moved until the secondary transfer roller 33 moves to the plain paper position P2. Can be controlled to repeat the operation of rotating the right cam gear 75R to the reference position again when the sheet passing is completed.

  As described above, here, the configuration and operation of the medium transport mechanism on the right side of the apparatus have been described with reference to FIGS. 8 and 9, but the same operation is performed on the left side of the similarly configured medium transport mechanism. Therefore, although the explanation of the operation is omitted here, the secondary transfer roller 33 can move each position while maintaining the parallel state with the backup roller 34 at all times.

  At the thick paper position P1, the recording paper 12 enters the nip portion between the backup roller 34 and the secondary transfer roller 33, and the tangential direction of the intermediate transfer belt 24 at the position where the winding around the backup roller 34 starts. Since the angle can be increased, even if the recording paper 12 is a heavy thick paper, it is possible to suppress the trailing edge from hitting the intermediate transfer belt 24 and disturbing the toner image. At the plain paper position P2, the angle between the advance direction of the recording paper 12 from the nip portion and the tangential direction of the intermediate transfer belt 24 at the position where the winding to the backup roller 34 is completed can be increased. Even if the paper is weak, it is possible to prevent the leading edge of the paper from being conveyed while being attached to the intermediate transfer belt 24.

  Here, the relationship between the rail unit 62 and the transfer belt unit 30 shown in FIG. 1 will be described.

  The backup roller 34 and the intermediate transfer belt 24 constituting the secondary transfer unit 18 belong to the transfer belt unit 30 which is one constituent unit, and the secondary transfer roller 33 constituting the secondary transfer unit 18 is attached to the rail unit 62. The secondary transfer roller holder 61 is arranged so as to be movable in the axial direction. Further, the backup roller 34 and the secondary transfer roller 33 are arranged so as to be in pressure contact with each other so as to form a nip portion, but are not mechanically connected, and thus can be separated without limitation in direction, distance, or the like. .

  Therefore, here, for example, as shown in FIG. 2A, the rail unit 62 to which the secondary transfer roller 33 belongs can be pulled out in the direction of arrow C (the negative direction of the X axis) by a guide mechanism (not shown). For example, as shown in FIG. 10, the transfer belt unit 30 to which the backup roller 34 and the intermediate transfer belt 24 belong has a configuration that can be pulled out in the direction of arrow E (the negative direction of the Y axis) by a guide mechanism (not shown).

  In the present embodiment, the right eccentric cam 74R has an oval shape and the right cam gear 75R is rotated by 90 degrees to drive the position of the secondary transfer roller 33. However, the present invention is not limited to this. Instead, for example, the right eccentric cam 74R has a circular cross section, and the eccentric amount and the rotation angle of the right cam gear 75R are set appropriately, thereby reducing the distance between the thick paper position P1 and the plain paper position P2, and the normal paper position P2 and the decompression. Each distance from the position P3 can be set freely. In this manner, the secondary transfer roller 33 may be further moved away from the plain paper position P2 than the decompression position P3 to move to a separation position that is separated from the backup roller 34. To get.

  As described above, according to the image forming apparatus of the first embodiment, the position of the secondary transfer roller 33 is set to a plurality of positions such as the thick paper position P1 and the plain paper position P2 without changing the nip amount with the backup roller 34. In addition to being able to move to other positions, it is possible to move to a decompression position P3 with a reduced nip amount or a separation position where the nip amount becomes zero, etc. This can contribute to extending the life of the backup roller 34 and the secondary transfer roller 33.

  Further, since the secondary transfer roller 33 and the backup roller 34 can be freely separated, the rail unit 62 to which the secondary transfer roller 33 belongs and the transfer belt unit 30 to which the backup roller 34 belongs are individually or in the same direction or different directions from the apparatus main body. Therefore, it is effective for maintenance such as replacement of parts and removal of jammed recording paper.

  In this embodiment, the color printer is used as the image forming apparatus. However, the present invention can be applied to a single color printer, a copying machine, a FAX, and a complex machine in which these are combined.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 11 Paper tray, 12 Recording paper, 13 Paper feed part, 14 Pickup roller, 15 Feed roller, 16 Retard roller, 17 Medium conveyance path, 18 Secondary transfer part, 19 Conveyance roller pair, 20 Conveyance roller pair , 21 Conveying roller pair, 22 Development forming section, 23 Toner image forming section, 24 Intermediate transfer belt, 25 Primary transfer section, 26 Photosensitive drum, 27 Charging roller, 28 LED head, 29 Developing roller, 30 Transfer belt unit, Reference Signs List 31 drive roller, 32 tension roller, 33 secondary transfer roller, 34 backup roller, 34a rotational axis center, 35 support roller, 36 primary transfer roller, 37 upper guide member, 38 lower guide member, 39 paper thickness sensor, 40 Fixing section, 41 heater, 42 upper roller, 43 b Roller, 44 to 48 discharge roller pair, 49 stacker unit, 60 secondary transfer roller unit, 61 secondary transfer roller holding unit, 62 rail unit, 63 secondary transfer roller holding frame, 63L left side wall, 63R right side wall, 64L left bearing, 64R right bearing, 65L left sliding post, 65R right sliding post, 66L first left regulating wall, 66R first right regulating wall, 67L second left regulating wall, 67R second right regulation Wall, 68 light shielding plate, 69 sheet metal frame, 69a bottom plate, 69L left side plate, 69R right side plate, 70 resin paper guide, 71L arc-shaped receiving surface, 71R arc-shaped receiving surface, 72L linear receiving surface, 72R linear receiving surface, 73L Left post receiving part, 73R Right post receiving part, 74L Left eccentric cam, 74R Right eccentric 75L left cam gear, 75R right cam gear, 76 light sensor, 76a light detection point, 77 roller housing, 78R rotation shaft center, 79R center, 80 drive motor, 81 reduction gear, 82 intermediate gear, 83 connection shaft, 84L left transmission Gear, 84R Right transmission gear, 90L Left bearing house, 90R Right bearing house.

Claims (8)

In an intermediate transfer type image forming apparatus,
An endless intermediate transfer belt for conveying a developer image transferred by primary transfer;
A backup roller that supports the intermediate transfer belt disposed and stretched inside the intermediate transfer belt;
A secondary transfer roller disposed opposite to the backup roller via the intermediate transfer belt and constituting a secondary transfer portion;
A rotary bearing for rotatably holding a rotary shaft of the secondary transfer roller;
A secondary transfer roller holding portion for movably mounting the rotary bearing,
The secondary transfer roller holder is
A first mounting portion that is formed along an arc centered on the axial center of the backup roller and guides the rotary bearing;
And a second placement portion that is arranged adjacent to the first placement portion and extends in a direction away from the arc and away from the center of the shaft to guide the rotary bearing. Image forming apparatus. A secondary transfer roller unit including the rotary bearing and the sliding post;
The image forming apparatus according to claim 1, wherein the secondary transfer roller holding portion includes a post receiving portion that guides the sliding post.   3. The image forming apparatus according to claim 2, further comprising positioning means for positioning the rotary bearing at a plurality of positions of the first mounting section and at one or a plurality of positions of the second mounting section. . The positioning means includes
A cam gear provided with an eccentric cam and rotatably provided in the secondary rotating roller holding portion;
The image forming apparatus according to claim 3, further comprising an engaging portion that is provided in a secondary transfer roller unit and engages with the eccentric cam.   The positioning means includes a first position where the rotary bearing is placed on the first placement portion, a second position closer to the second placement portion than the first position, and the rotation. 5. The image forming apparatus according to claim 3, wherein the bearing is positioned at a third position where the bearing is placed on the second placement portion.   The image forming apparatus according to claim 2, further comprising a position detection device that detects a movement position of the secondary transfer roller unit.   The image forming apparatus according to claim 1, wherein the rotary bearing is a bearing having a cylindrical outer ring. The image forming apparatus according to claim 1, further comprising a medium thickness detector that detects a thickness of a recording medium onto which the developer image is transferred in the secondary transfer unit.

Images