JP2005316320A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where the influence of vibration on an intermediate transfer body due to the thickness of a recording member is eliminated. <P>SOLUTION: Respective eccentric cams 103a and 103b arranged in IN/OUT of an apparatus are fixed on a rotating shaft 104 so as to have the same phase. A motor 105 connected to the shaft 104 is controlled by a control part 40. When the motor 105 is rotated by instructions from the control part 40, frames 101a and 101b are depressed, then, a secondary transfer device is moved downward via respective positioning pins 102a and 102b of the frames 101a and 101b. Then, a nip width defined by the contact of the intermediate transfer belt in an IBT module with the secondary transfer carrying belt of the secondary transfer device is reduced. In the case of secondarily transferring a toner image to a cardboard, prior to the transfer process, the nip width is decreased, and occurrence of the vibration is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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.

  In recent years, so-called full-color tandem machines have been proposed in image forming apparatuses such as printers, copiers, and facsimile machines for the purpose of forming color images at high speed and high image quality. As a typical tandem machine, four image forming units of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in parallel with each other, and each of these image forming units. The toner images of yellow, magenta, cyan, and black that are sequentially formed in step 1 are transferred once (multiple transfer) onto the intermediate transfer belt, which is an intermediate transfer member, and then the recording material (from the intermediate transfer belt). For example, a full-color or black-and-white (monochrome) image can be formed by collectively transferring (secondary transfer) onto a sheet of paper and fixing the toner image formed on the recording material.

  Here, in an image forming apparatus using an intermediate transfer body, when a plurality of differently transferred toner images and the like transferred onto the intermediate transfer body are collectively transferred onto a recording material, the intermediate transfer body Is supported by a backup roll from the inside, and a secondary transfer roll is brought into contact with the surface side of the intermediate transfer member to employ a backup roll type transfer device that supplies a voltage to the backup roll. However, since the nip state between the intermediate transfer member supported by the backup roll and the secondary transfer roll can only be adjusted at one end position of the backup roll, recording can be performed even if the alignment of the intermediate transfer member can be adjusted. When the type of material is different, the nip state between the backup roll and the secondary transfer roll will change, and the recording material with the higher nip pressure will be transported first and transferred to the recording material. There is a problem that the image is inclined. Therefore, a nip width adjusting unit that adjusts the nip width of the secondary transfer roll with respect to the backup roll according to the type of the recording material conveyed to the secondary transfer unit is provided to adjust the inclination of the image at the secondary transfer unit. In other words, a technique has been proposed that can compensate for a portion that cannot be adjusted at the same time, can increase the adjustment range, and can always adjust the inclination of an image even when the type of recording material is different (for example, patents). Reference 1).

  Further, in Patent Document 1, since the adjustment of the nip width of the secondary transfer roll is limited to a range that does not cause a transfer failure, the correction range of the skew amount of the recording material is limited to about ± 0.3 mm. Focusing on the fact that the improvement effect may not be sufficient, while maintaining the state where the intermediate transfer body is sandwiched between the backup roll and the secondary transfer roll, at least the backup roll in the direction perpendicular to the traveling direction of the intermediate transfer body There has also been proposed a technique capable of adjusting a displacement of an image transferred onto a recording material to substantially zero without providing a displacing means for displacing the transfer performance without affecting transfer performance (for example, Patent Document 2). reference).

JP 2002-328771 (pages 5-6, FIG. 1) Japanese Patent Laying-Open No. 2003-186318 (pages 6-7, FIG. 20)

  However, the technique according to the above-mentioned patent document aimed at adjusting the image parallelism has no effect on the influence of vibration on the intermediate transfer member due to the thickness of the recording material. Therefore, the thicker the recording material, the greater the influence of vibration on the intermediate transfer member, and there is a concern that the vibration affects image formation and causes a streak-like image quality defect called banding.

  The present invention has been made to solve the technical problems as described above, and an object thereof is to form an image that can eliminate the influence of vibration on the intermediate transfer member due to the thickness of the recording material. To provide an apparatus.

For this purpose, the image forming apparatus to which the present invention is applied has means capable of reducing the nip width of the transfer portion more than usual when transferring a toner image onto a thick recording material. That is, a carrier on which a toner image is carried, a transfer belt that conveys the recording material and contacts the carrier, and transfers the toner image carried on the carrier to the recording material, and the carrier and the transfer belt The nip width changing means for changing the nip width defined by the contact with the nip width in the direction orthogonal to the nip width and the information of the recording material onto which the toner image is transferred are input, and according to the information of the recording material Control means for controlling the nip width changing means to change the nip width.
Here, the control means can control the nip width changing means so that the nip width change is completed before the recording material of the input information is conveyed by the transfer belt.
The nip width changing means has a first nip width value and a second nip width value smaller than the first nip width value as the nip width, and the control means transfers the toner based on the inputted information. When the recording material is determined to be plain paper, the nip width is set to the first nip width value, and when the recording material is determined to be thick paper, the nip width is set to the second nip width value. . Further, the nip width changing means can change the nip width by moving the transfer belt relative to the carrier.
The nip width changing unit may further include a transfer voltage changing unit that changes the transfer voltage according to information on the recording material when the nip width is changed.

From another point of view, an image forming apparatus to which the present invention is applied has a carrier on which a toner image is carried, and a toner image carried on the carrier by conveying the recording material and contacting the carrier. A transfer belt for transferring to the recording material, a judging means for judging whether the recording material onto which the toner image is transferred is thicker than a predetermined value, and when the judging means judges that the recording material is thick paper In addition, nip pressure changing means for reducing nip pressure due to contact between the transfer belt and the carrier at both ends in the width direction of the transfer belt is included.
Here, the apparatus further comprises a plurality of trays for storing the recording materials, and a recording material information input means for inputting information of the recording materials stored in each tray, and the judging means includes the information of the recording material information input means. It can be characterized that a determination is made based on this. Further, the determination means can be characterized in that the determination is performed when the tray for storing the recording material to be conveyed is changed.

  According to the present invention, the influence of vibration on the intermediate transfer member due to the thickness of the recording material can be eliminated. For example, recording materials having different thicknesses (basis weights) are supplied from a plurality of trays in one print job. In this case, it is possible to form images on recording materials having different thicknesses without switching the productivity by switching the transfer nip amount.

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 that is an intermediate transfer member that sequentially transfers (primary transfer) and holds each color component toner image formed by each image forming unit 10; A secondary transfer device 20 that collectively transfers (secondary transfer) the superimposed image transferred to the paper P as a transfer material, and a fixing device 30 that fixes the secondary transferred image on the paper P. . 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 substantially linearly 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. .

Further, the intermediate transfer belt 15 is made of a resin such as polyimide or polyamide containing a suitable amount of a conductive agent such as carbon black, and is formed so that its volume resistivity is 10 ⁶ to 10 ¹⁴ Ω · cm. The thickness of the endless belt is, for example, about 0.08 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, a drive roll 31 that is driven by a motor (not shown) to rotate the intermediate transfer belt 15, an idler roll 35 for maintaining the flatness of the intermediate transfer belt with respect to a sensor 42 described later, and an intermediate transfer belt 15 includes a tension roll 32 that functions as a correction roll that applies a constant tension to the belt 15 and prevents the intermediate transfer belt 15 from meandering, and a backup roll 28 having a diameter of, for example, 28 mm provided at a secondary transfer portion. ing.

  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 the opposite 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 10 ⁷ to 10 ¹⁰ Ω / □, and the roll diameter is It is formed to be 28 mm, and 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. A secondary transfer voltage having the same polarity as the charging polarity of the toner is applied to the power supply roll 29 by the secondary transfer power supply 44. In the secondary transfer power supply 44, the secondary transfer voltage is controlled by the control unit 40.

On the other hand, the secondary transfer conveyance belt 21 is stretched by a drive roll (transfer roll) 22 having a hardness of 20 degrees (Asker C) and a diameter of, for example, 28 mm, and a metal driven roll 23 made of, for example, SUS. A semiconductive endless annular belt having a volume resistivity of 10 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.

A belt cleaner 41 is provided on the downstream side of the backup roll 28 to remove residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and clean the surface of the intermediate transfer belt 15. 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.
A reference sensor (home position sensor) (not shown) that generates a reference signal serving as a reference for taking the image forming timing in each image forming unit 10 is also arranged on the upstream side of the backup roll 28. An image density sensor (not shown) for adjusting image quality and a sensor 42 for controlling meandering of the intermediate transfer belt 15 are arranged side by side on the downstream side of the black image forming unit 10K.

  Furthermore, in the present embodiment, as a paper transport system, paper trays 50 and 57 that store paper P, and pick-up rolls 51 that take out and transport the paper P accumulated in the paper trays 50 and 57 at a predetermined timing. 58, a transport roll 52 that transports the paper P fed by the pick-up rolls 51 and 58, and the paper P transported by the transport roll 52 are temporarily stopped and the paper P is transferred to the secondary transfer section at a predetermined timing. A registration roller 59 to be conveyed, a conveyance chute 53 for feeding the sheet P conveyed by the registration roller 59 to a secondary transfer position by the secondary transfer device 20, and a sheet P after the secondary transfer to the fixing device 30. Conveying belts 54 and 55 and a chute 56 for guiding the paper P between the conveying belts 54 and 55 are provided. The paper P collected on the paper tray 50 and the paper P collected on the paper tray 57 have different thicknesses.

  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, 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 pick-up rolls 51 and 58 rotate in accordance with the timing of image formation, and the paper P of a predetermined size is supplied from the paper trays 50 and 57. For example, the paper P supplied by the pickup roll 51 is transported by the transport roll 52, and reaches the secondary transfer device 20 through 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 secondary transfer 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 The unfixed toner image carried on the intermediate transfer belt 15 is electrostatically transferred to the paper P at the secondary transfer position pressed by the backup roller 22 and the backup 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 discharged by a discharge roll (not shown). Is discharged outside. On the other hand, after the transfer onto 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 viewed from the downstream side in the sheet conveyance direction on the IN side (back side, rear side) of the device, and FIG. 4 shows only the secondary transfer unit 60 separated. FIG. 5 is an exploded perspective view of the secondary transfer apparatus 20 as viewed from the downstream side in the sheet conveyance direction on the OUT side (front side, front side) of the apparatus, and FIG. 5 illustrates a drive system of the secondary transfer unit 60. FIG. 6 is a perspective view as viewed from the downstream side in the paper conveyance direction on the IN side.

  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. Further, as shown in FIG. 3 or FIG. 4, the secondary transfer unit 60 is inserted with positioning pins 102a and 102b (see FIG. 8) that can be adjusted on the IN / OUT sides of the IBT module 18. The groove portion 61 is provided. 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.

2 or 3, the base frame 70 has a base frame main body 71, a single shaft 72 attached to the base frame main body 71 so as to extend in the IN / OUT direction, and an upper end on the base frame main body 71. And a tension coil spring 73 having a lower end attached to the mounting frame 80. The mounting frame 80 is attached to the base frame 70 configured as described above. 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 an attachment hole 95 for attaching a frame (not shown) of the conveyor belt 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 driving force of the drive motor 87 is transmitted from the driving gear 90 to the driving gear 63 of the secondary transfer unit 60 via the driving transmission gear 88 and the torque limiter 89 and is then transmitted by the driving roll 22. The next transfer conveyance belt 21 is driven. Further, as shown in FIG. 5, the drive force of the drive motor 91 is transmitted from the drive gear 93 to the drive gear 64 of the secondary transfer unit 60 via the drive transmission gear 92, and the fur brushes 24 and 25 and the recovery 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 positioning pins 102a and 102b of the IBT module 18 inserted into the groove 61 of the secondary transfer unit 60 can be adjusted by the eccentric cam 103 of the shaft unit 100 shown in FIG. 2 or FIG. By changing the positions of the positioning pins 102a and 102b, the position of the secondary transfer unit 60 relative to the IBT module 18 can be changed relatively. That is, by moving the secondary transfer unit 60 up and down, it is possible to adjust the nip width (nip pressure, biting amount, and pressure contact amount) according to the types of sheets having different thicknesses. Directly below the positioning pins 102a and 102b of the IBT module 18 is the secondary transfer position. The nip width referred to here indicates the length in the conveyance direction of the contact area between the backup roll 28 and the drive roll 22 with the intermediate transfer belt 15 and the secondary transfer conveyance belt 21 interposed therebetween. It can be adjusted as appropriate depending on the strength of the pressing force.
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 pins 102a and 102b closest to the secondary transfer position, so that the accuracy of the secondary transfer can be improved.

Next, operations of the mounting frame 80 and the base frame 70 for the secondary transfer device 20 to retract the IBT module 18 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 moves downward in FIG. 2 with respect to the base frame 70, and the secondary transfer device 20 can be retracted with respect to the IBT module 18.
When the retract cam 74 returns to the original position, the mounting frame 80 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 away from the groove 61 (see FIG. 3) that receives the positioning pins 102a and 102b. In the portion where the groove portion 61 is provided, the movement accompanying the swing is close to a straight line, so that the positioning pins 102 a and 102 b can easily enter the groove portion 61. 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 102a and 102b (see FIG. 8) 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).

Next, the shaft unit 100 for changing the positions of the positioning pins 102a and 102b with respect to the image forming apparatus main body will be described. The shaft unit 100 constitutes a nip width changing unit or a part of the nip width changing unit.
FIG. 8 is a perspective view for explaining the mechanism of the shaft unit 100. As shown in the figure, the shaft unit 100 is provided at both ends of the IN / OUT of the apparatus, and is provided on the frames 101a and 101b that move up and down at the same phase, and the IN / OUT frames 101a and 101b. The positioning pins 102a and 102b that engage with the grooves 61 of the next transfer unit 60 and the IN / OUT frames 101a and 101b provided on each of the IN / OUTs are moved up and down to adjust the nip width or nip pressure by IN / OUT. The eccentric cams 103a and 103b, the rotating shaft 104 that rotates the eccentric cams 103a and 103b, the motor 105 that is the driving source, and the driving gear of the motor 105 are engaged with each other to transmit the driving force to the rotating shaft 104. And the frames 101a and 101 with respect to the eccentric cams 103a and 103b at both ends thereof. A coil spring 107 for urging the, and an encoder 108 for detecting the eccentric cam 103a, the reference position and the rotation amount of 103b.
The shaft unit 100 is configured to control the rotation amount of the motor 105 by the control unit 40 as a control unit according to the type of the paper P, the environment such as temperature and humidity. The control unit 40 appropriately sets the control amount based on storage means (not shown) made of NVM or the like in which a correction table is stored in advance.

  The eccentric cams 103a and 103b provided at the IN / OUT are fixed to the rotating shaft 104 so that the phases are the same, and the nip width can be changed depending on the rotation angle of the rotating shaft 104. It is configured. That is, in the image forming apparatus to which the exemplary embodiment is applied, the positioning pin 102a that engages with the groove portion 61 of the secondary transfer unit 60 by controlling the rotation angle of the rotation shaft 104 based on an instruction of the control unit 40. , 102b move by the same distance to change its position. As a result, the position of the secondary transfer unit 60 with respect to the IBT module 18 changes. The backup roll 28 is fixed to the IBT module 18 regardless of such a moving mechanism.

With the above configuration, in the image forming apparatus according to this embodiment, even in the case where the thickness of the paper P is different in the image forming apparatus using the intermediate transfer member as described below, It is possible to prevent banding from occurring (keep the same level).
That is, by controlling the rotation angle of the eccentric cams 103 a and 103 b of the shaft unit 100, the push amount of the drive roll 22 in the secondary transfer unit 60 is adjusted. As a result, the nip width between the drive roll 22 and the backup roll 28 can be adjusted with the intermediate transfer belt 15 and the secondary transfer conveyance belt 21 interposed therebetween. In this way, the length of the short side can be adjusted while the nip width is rectangular.
Specifically, when the positioning pins 102a and 102b are moved downward, the secondary transfer conveyance belt 21 and the drive roll 22 are similarly moved downward, while the positions of the intermediate transfer belt 15 and the backup roll 28 remain unchanged. Therefore, the nip width is reduced. For this reason, when the paper P to be transported to the secondary transfer unit is a thick paper, the control unit 40 operates the motor 105 to reduce the nip width before the paper P is transported to the secondary transfer unit. Since the paper P is received by the width, banding at the secondary transfer portion can be prevented. When the paper P is thin paper (plain paper), the original nip width is restored.
The influence of vibration on the secondary transfer conveyance belt 21 at the secondary transfer portion that occurs when the paper P enters / exits the secondary transfer portion changes according to the thickness of the paper P, and the thick paper is the plain paper The influence of vibration is greater than that. However, by reducing the nip width during running of thick paper, the influence of vibration during running of thick paper can be made the same as in the case of plain paper. For this reason, even when sheets having different thicknesses are conveyed from the plurality of sheet trays 50 and 57 in one print job, the nip width is switched to continuously reduce the productivity. An image can be formed. It is also conceivable to set a plurality of stepwise values in advance as the nip width.

  Here, Table 1 shows the experimental results of changing the nip width with different paper types.

Experiments were performed on plain paper and coated paper having basis weights of 187 to 220 gsm and 221 to 300 gsm while changing the nip width under three different conditions.
Three different conditions are zone B, zone MNA and zone MNC. Zone B has a temperature of 22 degrees and a humidity of 55%. Zone MNA has a temperature of 27 degrees and a humidity of 80%. Zone MNC has a temperature of 15 degrees and a humidity of 20%.
As the nip width, experiments were conducted on 0.9 mm, 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm, and 0 mm.
As each experimental result, banding and a transferred image are evaluated.

  For paper with a small basis weight, i.e. thin paper, a larger nip width is better, while for paper with a larger basis weight, i.e. thick paper, a smaller nip width is better.

Here, in the image forming apparatus according to the present embodiment, the type of paper stored in each of the paper trays 50 and 57 shown in FIG. 1 can be selected in advance. That is, each paper tray 50, 57 is provided with a button (recording material information input means) (not shown) corresponding to the paper thickness and paper type, and the content of the selected button is output to the control unit 40 shown in FIG. .
If the example is shown, as paper thickness, basic weight is either 60-80gsm, 81-105gsm, 106-135gsm, 136-186gsm, 187-220gsm, or 221-300gsm, and as a paper type, Plain paper or coated paper. Furthermore, it is conceivable that an overhead projector sheet (OHP) can be selected with a button.

The control unit 40 shown in FIG. 8 changes the nip width by operating the motor 105 of the shaft unit 100 based on the paper type selected in the paper trays 50 and 57 of the paper P conveyed to the secondary transfer unit. . The values shown in Table 2 can be adopted as the nip width in that case. That is, 0.9 mm (first nip width value) used for plain paper, 0.3 mm (second nip width value) used for thick paper, and 0 mm used for OHP. 5 mm.
Here, it is preferable that the cam position after initialization corresponds to plain paper, and thereafter the nip width is reduced according to the paper thickness or paper type. This is because the rate at which plain paper is conveyed is greater than the rate at which cardboard and OHP are conveyed.
Further, when the paper tray for storing the paper P to be transported is switched from one of the paper trays 50 and 57 to the other, the change information is input to the control unit 40 shown in FIG. For example, the change information can be dealt with.

The nip width adopts the value in the same table as an initial value, but is configured to be able to be changed to an arbitrary value between plain paper 0 and thick paper 0.9 mm by a user interface (UI) (not shown). Also good.
When the nip width is changed, correspondingly, the voltage of the secondary transfer power supply 44 shown in FIG. It is also conceivable to configure to control the voltage. That is, as the paper P becomes thicker, the resistance increases and the secondary transfer voltage is increased.

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, in which 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. It is a perspective view for demonstrating the mechanism of a shaft unit.

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, 28 ... Backup 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 ... Slot, 100 ... Shaft unit, 101 ... Frame, 02a, 102b ... positioning pins, 103 ... eccentric cam, 104 ... rotary shaft, 105 ... motor, 106 ... gear, 107 ... coil spring, 108 ... encoder

Claims (8)

A carrier on which a toner image is carried;
A transfer belt that conveys the recording material and contacts the carrier, and transfers the toner image carried on the carrier to the recording material;
A nip width changing means for changing the nip width defined by the contact between the carrier and the transfer belt over substantially the same amount in a direction orthogonal to the nip width;
An image forming apparatus comprising: a control unit that inputs information on a recording material onto which a toner image is transferred and controls the nip width changing unit so as to change the nip width according to the information on the recording material.   2. The control unit according to claim 1, wherein the control unit controls the nip width changing unit so that the nip width change is finished before the recording material of the input information is conveyed by the transfer belt. Image forming apparatus. The nip width changing means has a first nip width value and a second nip width value smaller than the first nip width value as the nip width,
The control means sets the first nip width value as the nip width when the recording material to which the toner is transferred is determined to be plain paper based on the input information, and sets the nip width when the recording material is determined to be thick paper. The image forming apparatus according to claim 1, wherein the second nip width value is set.   The image forming apparatus according to claim 1, wherein the nip width changing unit changes the nip width by moving the transfer belt relative to the carrier.   The image forming apparatus according to claim 1, further comprising a transfer voltage changing unit that changes the transfer voltage to a transfer voltage corresponding to information on the recording material when the nip width changing unit changes the nip width. A carrier on which a toner image is carried;
A transfer belt that conveys the recording material and contacts the carrier, and transfers the toner image carried on the carrier to the recording material;
Determining means for determining whether the recording material onto which the toner image is transferred is thick paper thicker than a predetermined value;
A nip pressure changing unit that reduces a nip pressure due to contact between the transfer belt and the carrier at both ends in the width direction of the transfer belt when the determination unit determines that the recording material is thick paper. Forming equipment. A plurality of trays for storing recording materials; and a recording material information input means for inputting information of the recording materials stored in each tray;
The image forming apparatus according to claim 6, wherein the determination unit makes a determination based on information from the recording material information input unit.   The image forming apparatus according to claim 7, wherein the determination unit makes a determination when a tray that accommodates a recording material to be conveyed is changed.

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