JP4449554B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these.

Some image forming apparatuses include a photosensitive drum and a developing device as a set of image forming units, and a plurality of sets thereof are arranged in tandem. Such a tandem type image forming apparatus includes a photosensitive drum of each image forming unit. An electrostatic latent image is formed by exposing each of the body drums, and the electrostatic latent image is developed by a developing device to form a toner image of a predetermined color for each image forming unit. IBT (Intermediate Belt Transfer) After each toner image is primarily transferred to the belt of the module, the toner image is secondarily transferred to a sheet by a secondary transfer unit and fixed by a fixing device to form a color image.
For example, when removing paper jammed inside the image forming apparatus main body due to a jam or when performing regular maintenance, it is necessary to retract the IBT module from each image forming unit and the secondary transfer unit.

  Conventionally, various systems have been proposed as a structure in which the IBT module and the image forming unit are separated from each other and the IBT module and the secondary transfer unit are separated from each other (see, for example, Patent Document 1).

The technology disclosed in Patent Document 1 is a first retracting means for retracting the intermediate transfer member (IBT module) downward so that the belt of the intermediate transfer member (IBT module) is separated from all the image carriers (image forming units). And a second retracting means for retracting the secondary transfer module that supports the secondary transfer member (secondary transfer unit) so as to be swingable downward, and the secondary transfer module is intermediately transferred by the second retracting means. After being retracted from the body (IBT module), the intermediate transfer body (IBT module) can be retracted away from all the image carriers (image forming units) by the first retracting means. .
The secondary transfer module is retracted by the swinging motion by the second retracting means, and the image forming position or the retracting position is selected by the swinging. The secondary transfer module further includes a secondary transfer position where the supported secondary transfer member (secondary transfer unit) is pressed against the intermediate transfer member (IBT module), and a supported secondary transfer member (secondary transfer). One of the standby positions where the unit) is brought close to the intermediate transfer member (IBT module) without being pressed against the intermediate transfer member (IBT module) can be selected by a swinging operation. The timing for setting the standby position is a standby time between jobs or the like, thereby preventing bleed or deformation of the belt in the intermediate transfer member (IBT module).

JP 2001-154507 A (page 4, FIG. 1)

  However, the swing center by the second retracting means of the secondary transfer module is provided separately from the central axis on which the secondary transfer module supports the secondary transfer member (secondary transfer unit) so as to be swingable. A shaft, a stud, and a bearing are required, so that a simple configuration cannot be taken, and it is difficult to reduce the size and cost of the apparatus.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of easily configuring a structure for swinging a secondary transfer unit. There is to do.

For this purpose, an image forming apparatus to which the present invention is applied includes a carrier on which a toner image is carried, a transfer belt for transferring the toner image carried on the carrier to a recording material, and a transfer belt. A drive unit for driving, a first frame for holding the transfer belt and the drive unit, a second frame for holding the first frame, and the transfer belt moving away from the carrier to a standby position. A swinging means for swinging the first frame with respect to the second frame, and an image provided on the image forming apparatus main body side so that the transfer belt is separated to a retracted position further away from the standby position with respect to the carrier. A retracting means for swinging the second frame with respect to the forming apparatus main body, and a swing shaft for swinging the first frame and a swing shaft for swinging the second frame are: Also characterized by being provided coaxially It is.
The swinging shaft of the transfer belt may be provided at a position farthest from the transfer belt in the second frame. Further, the swing axis of the transfer belt can be characterized in that the transfer belt is located downstream in the transport direction of the recording material from the position where the toner image carried on the carrier is transferred to the recording material. .
Further, the driving force from the driving unit can be transmitted to the transfer belt via a torque limiter. In addition, the first frame may include a cleaning device that cleans the transfer belt and a drive source that drives the cleaning device. Further, the swinging means abuts against the urging means for urging the first frame in a direction in which the transfer belt is pressed against the carrier, and a highly rigid portion of the first frame, and resists urging by the urging means. And a cam mechanism that swings the first frame in a direction in which the transfer belt is retracted from the carrier.

  According to the present invention, since the transfer belt and the swinging means are provided with the retracting means for swinging coaxially with the swing shaft of the transfer belt, the structure for swinging the secondary transfer unit can be simply configured. Is possible.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus shown in FIG. 1 is a so-called tandem type image forming apparatus, for example, a plurality of image forming units 10 (10Y, 10M, 10C, 10K) in which toner images of respective color components are formed by electrophotography. An intermediate transfer belt (toner image carrier) 15 for sequentially transferring (primary transfer) and holding each color component toner image formed by each image forming unit 10, and an overlap transferred on the intermediate transfer belt 15 A secondary transfer device 20 that batch-transfers (secondary transfer) images to a sheet P as a transfer material, and a fixing device 30 that fixes the secondary-transferred image on the sheet P are provided. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  In the present embodiment, each of the image forming units 10 (10Y, 10M, 10C, and 10K) includes a charger 12 around the photosensitive drum 11 that rotates in the direction of arrow A, and a charger 12 that charges the photosensitive drum 11. A laser exposure unit 13 (an exposure beam is indicated by a symbol Bm in the drawing) in which an electrostatic latent image is written on the photosensitive drum 11 and each color component toner is accommodated to generate an electrostatic latent image on the photosensitive drum 11. The developing device 14 that visualizes the toner image, the primary transfer roll 16 that transfers the color component toner images formed on the photosensitive drum 11 to the intermediate transfer belt 15, and the residual toner on the photosensitive drum 11 are removed. Electrophotographic devices such as a drum cleaner 17 are sequentially disposed. These image forming units 10 are arranged in the order of yellow (Y color), magenta (M color), cyan (C color), and black (K color) from the upstream side of the intermediate transfer belt 15.

The intermediate transfer belt 15 that is an intermediate transfer member is made of a resin such as polyimide or polyamide containing an appropriate amount of a conductive agent such as carbon black, and has a volume resistivity of 10 ⁶ to 10 ¹⁴ Ω · cm. The thickness of the endless belt is, for example, about 0.1 mm. The intermediate transfer belt 15 is configured to be circulated and driven (rotated) at a predetermined speed in the direction B shown in the drawing by various rolls. As these various rolls, there are provided a drive roll 31 that is driven by a motor (not shown) to rotate the intermediate transfer belt 15 and a function of giving a constant tension to the intermediate transfer belt 15 and preventing meandering of the intermediate transfer belt 15. The tension roll 32, a tension roll 35 that functions as a correction roll that applies a constant tension to the intermediate transfer belt 15 and prevents the intermediate transfer belt 15 from meandering, and a backup roll 28 provided in a secondary transfer portion. And have.

  In the IBT module 18 provided facing each photoconductor drum 11, a voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roll 16 provided inside the intermediate transfer belt 15 extending substantially linearly. It has come to be. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15, and a superimposed toner image is formed on the intermediate transfer belt 15.

  The secondary transfer device 20 includes a secondary transfer conveyance belt (transfer belt) 21 disposed on the toner image carrying surface side of the intermediate transfer belt 15. The backup roll 28 as an opposing roll is a tube of EPDM and NBR blend rubber with carbon dispersed on the surface, and the inside is made of EPDM rubber, the surface resistivity is 7 to 10 logΩ / □, and the roll diameter is 28 mm. The hardness is set to 70 degrees (Asker C), for example. The backup roll 28 is disposed on the back surface side of the intermediate transfer belt 15 to form a counter electrode of the secondary transfer conveyance belt 21, and a metal power supply roll 29 for stably applying a secondary transfer bias is disposed in contact therewith. Has been.

On the other hand, the secondary transfer conveyance belt (secondary transfer belt) 21 is stretched by a drive roll (transfer roll) 22 made of metal, for example SUS, and a driven roll 23 made of, for example, a rubber roll. ^It is a semiconductive endless annular belt of ⁶ to 10 ¹⁰ Ω · cm, and a material having a 100% elongation modulus of 3.8 MPa is used. The secondary transfer transport belt 21 is transported at a predetermined speed by the drive roll 22, and a predetermined tension is applied by the drive roll 22 and the driven roll 23.

  The drive roll 22 is disposed in pressure contact with the backup roll 28 with the secondary transfer conveyance belt 21 and the intermediate transfer belt 15 interposed therebetween, and performs secondary transfer on the paper P conveyed on the secondary transfer conveyance belt 21. It functions as a secondary transfer roll. In addition, the contact state of the secondary transfer member can be changed by changing the pressure state between the backup roll 28 and the drive roll 22, and alignment adjustment and image parallelism adjustment can be performed. The diameter of the driven roll 23 is small enough not to be wound around the secondary transfer conveyance belt 21 even when thin paper coated paper or the like is conveyed. Further, the secondary transfer conveyance belt 21 is provided with conductive fur brushes 24 and 25 for removing dirt adhering to the secondary transfer conveyance belt 21 in the vicinity of the upstream side of the secondary transfer portion in contact with the intermediate transfer belt 15. Arranged in contact. Collection rollers 26 and 27 are arranged adjacent to the fur brushes 24 and 25.

  Further, on the downstream side of the backup roll 28, a belt cleaner 41 that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15 is provided so as to be contactable and separable. ing. On the other hand, on the upstream side of the yellow image forming unit 10Y, a reference sensor (home position sensor) 43 that generates a reference signal serving as a reference for taking an image forming timing in each image forming unit 10 is disposed. The reference sensor 43 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 to generate a reference signal, and each image forming unit 10 receives the instruction from the control unit 40 based on the recognition of the reference signal. It is configured to start image formation. Further, an image density sensor 42 for adjusting image quality is disposed on the downstream side of the black image forming unit 10K.

  Furthermore, in the present embodiment, as a paper transport system, a paper tray 50 that stores the paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup roll 51. , A transport roll 52 that transports the paper P fed out by the transport roller 52, a transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer position by the secondary transfer device 20, and the paper P after the secondary transfer Are provided with conveying belts 54 and 55 for conveying the paper P to the fixing device 30, and a chute 56 for guiding the paper P between the conveying belts 54 and 55.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. Image data output from an image reading device (IIT) (not shown), a personal computer (PC) (not shown), or the like is input to the image forming apparatus shown in FIG. In the image forming apparatus, after predetermined image processing is performed by an image processing apparatus (IPS) (not shown), an image forming operation is performed by the image forming unit 10 or the like. In the image processing apparatus (IPS), the input reflectance data is subjected to image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and movement editing. . The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and is output to the laser exposure unit 13. .

  The laser exposure unit 13 irradiates each photosensitive drum 11 of the image forming units 10Y, 10M, 10C, and 10K with, for example, an exposure beam Bm emitted from a semiconductor laser according to the input color material gradation data. Yes. In the photosensitive drum 11 of the image forming units 10Y, 10M, 10C, and 10K, the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image. The formed electrostatic latent image is developed as a toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) in each of the image forming units 10Y, 10M, 10C, and 10K. Is done.

  The toner images formed on the photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K are transferred onto the intermediate transfer belt 15 at a primary transfer portion where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Transcribed. More specifically, in the primary transfer portion, the primary transfer roll 16 applies a voltage having a polarity opposite to the charged polarity of the toner to the base material of the intermediate transfer belt 15, and the unfixed toner image is transferred to the surface of the intermediate transfer belt 15. Are sequentially superposed on each other to perform primary transfer. The unfixed toner image primarily transferred in this way is conveyed to the secondary transfer device 20 as the intermediate transfer belt 15 rotates.

  On the other hand, in the paper transport system, the pickup roll 51 rotates in synchronization with the image formation timing, and the paper P of a predetermined size is supplied from the paper tray 50. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer device 20 via the transport chute 53. Before reaching the secondary transfer device 20, the conveyance chute 53 rises in conjunction with the ascending operation (advance operation) of the secondary transfer conveyance belt 21 to form a conveyance path to the secondary transfer device 20. Yes. The sheet P is temporarily stopped, and the registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 carrying the toner image as described above, whereby the position of the sheet P and the position of the toner image are detected. And alignment.

  In the secondary transfer device 20, the drive roll 22 is connected to the backup roll 28 in a state where the semiconductive secondary transfer conveyance belt 21 and the intermediate transfer belt 15 are sandwiched between them in accordance with the timing of the secondary transfer onto the paper P. Pressed. At this time, the sheet P transported at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer transport belt 21. At this time, when a voltage (normal transfer bias) having the same polarity as the toner charging polarity is applied to the power supply roll 29, a transfer electric field is formed on the secondary transfer conveyance belt 21 as a counter electrode, and the drive roll 22 and the backup roll 22 are backed up. The unfixed toner image carried on the intermediate transfer belt 15 is electrostatically transferred onto the paper P at the secondary transfer position pressed by the roll 28.

  Thereafter, the sheet P on which the toner image has been electrostatically transferred is conveyed as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer conveyance belt 21 and is provided downstream of the secondary transfer conveyance belt 21 in the sheet conveyance direction. It is conveyed at a constant speed to the conveyor belt 54. The paper P transported to the end of the transport belt 54 is transferred to the transport belt 55 via the chute 56. The conveyance belt 55 changes the speed according to the optimum conveyance speed in the fixing device 30 and conveys the paper P to the fixing device 30. The unfixed toner image on the paper P is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 30, and the paper P on which the fixed image is formed is provided by a discharge roll (not shown). Is discharged outside. On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and is removed from the intermediate transfer belt 15 by the belt cleaner 41. Removed.

Next, the structure of the secondary transfer device 20 in the present embodiment will be described.
FIG. 2A is a schematic view showing a state where the secondary transfer device 20 is in an image forming position with respect to the IBT module 18, and FIG. 2B is a partially enlarged view of the IIb portion of FIG. 3 is a perspective view of the secondary transfer device 20 as seen from the downstream side in the paper conveyance direction on the IN side (back side, rear side), and FIG. 4 shows a state in which only the secondary transfer unit 60 is separated. FIG. 5 is an exploded perspective view of the secondary transfer device 20 as viewed from the OUT side (front side, front side) downstream in the sheet conveyance direction, and FIG. 5 is an IN side for explaining a drive system of the secondary transfer unit 60 FIG.

  The secondary transfer device 20 shown in FIG. 2 can swing with respect to the IBT module 18 around a shaft 72 that is a swing shaft. 2 to 4, the secondary transfer device 20 includes a secondary transfer unit 60, a base frame (second frame) 70, and a mounting frame (first frame) 80.

  The secondary transfer unit 60 includes a secondary transfer conveyance belt 21, a drive roll 22, a driven roll 23, fur brushes 24 and 25, collection rollers 26 and 27, and a conveyance chute 53 shown in FIG. 1. Also, as shown in FIG. 3 or FIG. 4, the secondary transfer unit 60 has a groove portion 61 into which positioning pins 19 (see FIG. 2) that can be adjusted on both sides of the IN / OUT of the IBT module 18 are inserted. Have Bearings 62 are provided at both ends of the rotation shaft of the drive roll 22 included in the secondary transfer unit 60. Further, as shown in FIG. 3 or FIG. 5, a drive gear 63 connected to the drive roll 22 is provided at the IN side end of the secondary transfer unit 60, and as shown in FIG. At the end are the fur brushes 24, 25 and the drive gear 64 connected to the collection rollers 26, 27.

As shown in FIG. 2 or 3, the secondary transfer device 20 includes a single shaft 72 attached to the base frame body 71 of the base frame 70 so as to extend in the IN / OUT direction, and an upper end on the base frame body 71. And a tension coil spring 73 having a lower end attached to the mounting frame 80. Thus, the base frame 70, mounting frame 80 is attached. That is, the mounting frame 80 is swingably connected to the base frame main body 71 by the shaft 72 at the end downstream in the paper transport direction (the right side in FIG. 2 and the left side in FIG. 3), and the upstream end in the paper transport direction Then, the coil frame 73 is suspended and held by the base frame main body 71.
As shown in FIG. 4, the base frame main body 71 includes a retract cam 74 that is an eccentric cam provided at both ends of IN / OUT and swings the mounting frame 80, and retract cams 74 at both ends of IN / OUT. A shaft 75 coupled so as to be able to rotate at the same time, a retract cam 74 and a retract motor 76 (see FIG. 3) for generating a driving force for rotationally driving the shaft 75, and a retracting force 74 for the retracting motor 74. A drive transmission gear 77 for transmitting to the motor and an encoder (not shown) for detecting the reference position and rotation amount of the retract cam 74 are attached.

As shown in FIG. 4, the mounting frame 80 on which the secondary transfer unit 60 is mounted has swing arms 81 and 82 that are provided at both ends of IN / OUT and connected to the shaft 72, and an upward biasing force of the coil spring 73. The secondary transfer unit receives the cam pressing member 83 that contacts the lower part of the retract cam 74 of the base frame 70 and is pressed downward by the retract cam 74 and the bearings 62 of the secondary transfer unit 60 provided at both ends of the IN / OUT. A U-shaped groove portion 84 that holds 60, a stopper 85 that opens and closes the bearing 62 of the secondary transfer unit 60 held in the U-shaped groove portion 84, and a cam pressing member 83. The secondary transfer unit 60 extending in the / OUT direction and held by the U-shaped groove 84 is positioned with respect to the mounting frame 80. And a positioning shaft 86 that.
A drive motor 87 for generating a driving force for rotationally driving the driving roll 22 of the secondary transfer unit 60 and a drive transmission gear 88 (for transmitting the driving force of the drive motor 87) are connected to the IN swing arm 81. 5), a torque limiter 89 (see FIG. 5) that slips when a torque exceeding a predetermined value is applied, and a drive that meshes with the drive gear 63 of the drive roll 22 of the secondary transfer unit 60 mounted on the mounting frame 80. A gear 90 is attached.
The OUT swing arm 82 includes a drive motor 91 for driving the fur brushes 24 and 25 (see FIG. 1) and the collection rollers 26 and 27 (see FIG. 1) of the secondary transfer unit 60, and a drive motor. A drive transmission gear 92 (see FIG. 5) for transmitting the driving force 91 is meshed with the fur brushes 24 and 25 of the secondary transfer unit 60 mounted on the mounting frame 80 and the drive gear 64 of the collection rollers 26 and 27. A drive gear 93 (see FIG. 5) is attached.
The mounting frame 80 is provided with a flange portion 96 (see FIG. 3) having a mounting hole 95 for mounting a frame (not shown) of the transport roller 54.

Next, a state where the secondary transfer unit 60 is mounted on the mounting frame 80 will be described.
When the bearing 62 of the secondary transfer unit 60 shown in FIG. 4 is inserted into the U-shaped groove 84 of the mounting frame 80, the hook 65 provided on the secondary transfer unit 60 on the positioning shaft 86 of the mounting frame 80, and the illustrated figure. The leaf spring that does not engage is engaged. Thereafter, when the bearing 62 of the secondary transfer unit 60 is fixed by the stopper 85, the secondary transfer unit 60 is positioned and attached to the mounting frame 80. Since the stopper 85 is screwed to the swinging arms 81 and 82 of the mounting frame 80, the secondary transfer unit 60 is detachable, facilitating maintenance.

When the secondary transfer unit 60 is positioned with respect to the mounting frame 80, the drive gear 63 of the secondary transfer unit 60 and the drive gear 90 of the mounting frame 80 shown in FIG. The drive gear 64 and the drive gear 93 (see FIG. 5) of the mounting frame 80 mesh with each other. Therefore, as shown in FIG. 5, the drive force of the drive motor 87 is transmitted from the drive gear 90 to the drive gear 63 of the secondary transfer unit 60 via the drive transmission gear 88 and the torque limiter 89, and secondly by the drive roll 22. The next transfer conveyance belt 21 is driven. As shown in FIG. 5, the driving force of the drive motor 91 is transmitted from the driving gear 93 to the driving gear 64 of the secondary transfer unit 60 via the driving transmission gear 92, and the fur brushes 24, 25 and the collection roller 26. , 27 (see FIG. 1) are driven.
As described above, since all the drive transmission systems such as the drive motor 87 for driving the intermediate transfer belt 15 are mounted on the mounting frame 80, it is not necessary to use a so-called swing gear as the drive transmission system. Therefore, the secondary transfer unit 60 can be easily attached and detached, the gear drive is stabilized, and the reliability can be improved.
Similarly, a drive transmission system such as a drive motor 91 for driving the fur brushes 24 and 25 and the collection rollers 26 and 27 is also mounted on the mounting frame 80. That is, since the drive transmission system swings along with the mounting frame 80, stable drive performance can be ensured.

Next, the positional relationship between the secondary transfer unit 60 mounted on the mounting frame 80 and the IBT module 18 will be described.
The position of the positioning pin 19 of the IBT module 18 inserted into the groove 61 of the secondary transfer unit 60 can be adjusted by a displacement cam 66 shown in FIG. By changing the position of the positioning pin 19, the position of the secondary transfer unit 60 with respect to the IBT module 18 can be changed. That is, by moving the secondary transfer unit 60 up and down, it is possible to adjust the nip width (the amount of bite and the amount of pressure contact) according to the types of sheets having different thicknesses. The secondary transfer position is directly below the positioning pin 19 of the IBT module 18.
Here, as shown in FIG. 2B, the swing arm 82 of the mounting frame 80 is provided with a long hole 94 whose long axis extends in the paper transport direction, and the mounting frame 80 passes through the long hole 94. The shaft 72 is swingably held. The other swing arm 81 (see FIG. 3) is also provided with a similar slot (not shown) and is held swingably with the shaft 72. That is, the mounting frame 80 has a degree of freedom in the paper transport direction with respect to the shaft 72. The positioning of the secondary transfer unit 60 with respect to the IBT module 18 is performed by the positioning pin 19 closest to the secondary transfer position, so that the accuracy of the secondary transfer can be improved.

Next, an operation in which the mounting frame 80 retracts with respect to the base frame 70 will be described.
As shown in FIG. 2, in a state in which the mounting frame 80 is suspended from the base frame 70 by the tension coil spring 73, the retract motor 76 shown in FIG. 3 operates and the retract cam 74 and the shaft 75 shown in FIG. When rotating, the retract cam 74 shown in FIG. 4 pushes down the cam pressing member 83 shown in FIG. 4 of the mounting frame 80. By this pressing operation, the mounting frame 80 retracts with respect to the base frame 70. When the retract cam 74 returns to the original position, it moves upward by the urging force of the tension coil spring 73 shown in FIG.
Here, as shown in FIG. 2, the shaft 72, which is the swing center of the mounting frame 80, is located at the downstream end in the conveying direction far from the groove 61 (see FIG. 3) that receives the positioning pin 19. In the portion where 61 is provided, the movement accompanying the swing is close to a straight line, and the positioning pin 19 can easily enter the groove 61. Further, as shown in FIG. 4, the cam pressing member 83 has an upper end connected to the positioning shaft 86 to enhance rigidity. For this reason, the deflection | deviation at the time of pushing down by the retract cam 74 decreases, and the stable retract can be performed.

  The base frame 70, together with the mounting frame 80, is configured to be swingable about the shaft 72 with respect to the image forming apparatus main body by rotating a lever (not shown) provided on the image forming apparatus main body side. When the lever is rotated, the secondary transfer unit 60 moves about 30 mm, for example.

Next, the position that the secondary transfer apparatus 20 according to the present embodiment takes with respect to the IBT module 18 will be described.
6A is a front view showing the state in which the secondary transfer device 20 is retracted with respect to the IBT module 18 corresponding to FIG. 2, and FIG. 6B is the secondary view in the retracted state. FIG. 8 is a schematic configuration diagram showing a change in position of the transfer conveyance belt 21 corresponding to FIG. 1. FIG. 7A shows a state in which the secondary transfer device 20 is separated from the IBT module 18 in FIG. FIG. 6B is a schematic front view showing the position change of the secondary transfer conveyance belt 21 in the retracted state corresponding to FIG. Note that the two-dot chain line in FIG. 6B indicates the image forming position, and the solid line indicates the standby position. Further, a two-dot chain line in FIG. 7B indicates an image forming position, and a solid line indicates a retracted position.

In the state shown in FIG. 2 in which the secondary transfer device 20 is in contact with the IBT module 18, the secondary transfer conveyance belt 21 presses the intermediate transfer belt 15 by the driving roll 22, thereby forming an image on the paper P. (Image forming position).
For example, when the job is over and no image is formed, the secondary transfer device 20 retracts downward as shown in FIG. In this retracting operation, only the mounting frame 80 swings around the shaft 72. In this way, the secondary transfer conveyance belt 21 is separated from the intermediate transfer belt 15 by, for example, about 7 mm (standby position). When returning from the standby position to the image forming position, it swings upward about the shaft 72 and is positioned by the positioning pins 19 of the IBT module 18.
Further, when performing maintenance such as pulling out the secondary transfer device 20 from the image forming apparatus main body, the secondary transfer device 20 swings around the shaft 72 by rotating a lever (not shown), and the IBT module 18. And completely separated (retracted position).

  Here, the drive roll 22 that drives the secondary transfer conveyance belt 21 is disposed upstream of the driven roll 23 in the sheet conveyance direction. This arrangement is based on the results of experiments on motion quality (MQ) when the drive roll 22 is arranged on the downstream side with respect to the driven roll 23 and when the drive roll 22 is arranged on the upstream side. The MQ characteristics as a result of the experiment are as follows. The MQ characteristic affects the image quality. The relative speed is relative to the IBT (%), and the speed difference between the intermediate transfer belt (IBT) 15 and the secondary transfer conveyance belt 21 is determined as the intermediate transfer. The value divided by the speed of the belt 15, that is, the relative speed ratio.

As is apparent from the table, good results could be obtained when the drive roll 22 was arranged on the upstream side. It is considered that the sag of the secondary transfer conveyance belt 21 in the secondary transfer device 20 is larger than the case where the secondary transfer conveyance belt 21 is arranged on the downstream side, and the poor MQ is difficult to be transmitted to the intermediate transfer belt 15 and the like.
Note that it is not preferable to dispose the drive roll 22 on the downstream side from the viewpoint of positional deviation of the photoconductor. Among them, a higher speed is not preferable as a result, and it is not preferable as a result, although it is not shown in the table but a torque limiter value is small.

  Examples of use of the present invention include use in a developing device that forms an image with a developer and an image forming device such as a printer or a copying machine.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. It is the schematic which shows the state which has a secondary transfer apparatus in an image formation position with respect to an IBT module. FIG. 7 is a perspective view of the secondary transfer device as viewed from the downstream side in the sheet conveyance direction on the IN side. FIG. 6 is an exploded perspective view of the secondary transfer device when only the secondary transfer unit is separated as viewed from the downstream side in the paper conveyance direction on the OUT side. FIG. 6 is a perspective view seen from the downstream side in the sheet conveyance direction on the IN side for explaining the drive system of the secondary transfer unit. It is explanatory drawing which shows the state which the secondary transfer apparatus is retracting with respect to an IBT module. It is explanatory drawing which shows the state which the secondary transfer apparatus is spaced apart with respect to the IBT module.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 15 ... Intermediate transfer belt, 19 ... Positioning pin, 20 ... Secondary transfer device, 21 ... Secondary transfer conveyance belt, 22 ... Drive roll, 23 ... Driven roll, 60 ... Secondary transfer unit, 61 ... Groove, 62 ... Bearing 63, 64, 90, 93 ... drive gear, 65 ... hook, 66 ... displacement cam, 70 ... base frame, 71 ... base frame body, 72, 75 ... shaft, 73 ... coil spring, 74 ... retract cam, 76 ... Retract motor, 77, 88, 92 ... drive transmission gear, 80 ... mounting frame, 81, 82 ... swing arm, 83 ... cam pressing member, 84 ... U-shaped groove, 85 ... stopper, 86 ... positioning shaft, 87, 91 ... Drive motor, 89 ... Torque limiter, 94 ... Long hole

Claims (6)

A carrier on which a toner image is carried;
A transfer belt for transferring a toner image carried on the carrier to a recording material;
A drive unit for driving the transfer belt;
A first frame that holds the transfer belt and the drive unit;
A second frame holding the first frame;
Rocking means for rocking the first frame with respect to the second frame so that the transfer belt moves away from the carrier and moves to a standby position;
Provided on the image forming apparatus main body side, and swinging the second frame relative to the image forming apparatus main body so that the transfer belt is separated to a retracted position further away from the standby position with respect to the carrier. Evacuation means;
Have
An image forming apparatus , wherein a swing shaft for swinging the first frame and a swing shaft for swinging the second frame are provided coaxially . The image forming apparatus according to claim 1, wherein the swing shaft is provided at a position farthest from the transfer belt in the second frame.   2. The rocking shaft is located on the downstream side in the conveyance direction of the recording material from the position where the transfer belt transfers the toner image carried on the carrier to the recording material. Image forming apparatus. The image forming apparatus according to claim 1 , wherein a driving force from the driving unit is transmitted to the transfer belt via a torque limiter. The image forming apparatus according to claim 1 , wherein the first frame includes a cleaning device that cleans the transfer belt, and a drive source that drives the cleaning device. Said swinging means includes a biasing means for biasing the first frame in a direction for pressing the transfer belt to the carrier, the high rigidity portion and the contact in the first frame, due to the urging means the image forming according to the transfer belt against the bias to claim 1, characterized in that it is configured to include a cam mechanism for swinging the first frame in a direction to retract from the carrier apparatus.

Images