JPH11174862A - Transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the blurring of an image formed on a paper sheet by eliminating the difference between the circumferential speed of image carriers and that of a transfer device with simple structure. SOLUTION: This transfer device is provided with photoreceptor drums 14a, 14b, 14c and 14d circulated in such a manner that toner images are formed on the peripheries of these drums, transfer rollers 16a, 16b, 16c, and 16d arranged to face the drums 14a, 14b, 14c and 14d, a transfer belt 21 for holding the paper between the belt 21 and the peripheries of the drums 14a, 14b, 14c and 14d rotationally driven by a driving roller 22, to carry the paper and a torque limiter 25 for controlling the turning on/off the transmission of driving force from a driving system to the driving roller 22 based on the difference between the circumferential speed of the drums 14a, 14b, 14c and 14d and that of the belt 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device, and more particularly, to a transfer device for transferring a toner image formed on a peripheral surface of an image carrier in an image forming apparatus to a sheet to be conveyed. It is.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer or a facsimile machine, a photosensitive drum as an image carrier on which a toner image is formed on a peripheral surface, and a transfer charger or a photosensitive drum arranged opposite to the photosensitive drum. Generally, a transfer device including a transfer roller is provided, and a toner image formed on the peripheral surface of the photosensitive drum is transferred to a sheet conveyed between the photosensitive drum and the transfer device.

In such an image forming apparatus, when a color image is formed on a sheet, black, yellow,
Four photoconductor drums are formed on the peripheral surface of which toner images are formed in four colors of cyan and magenta, and transfer rollers are provided corresponding to these photoconductor drums. There is known a so-called tandem-type image forming unit provided with a transfer belt for conveying the image. In such an apparatus, the transfer belt is stretched between a driving roller connected to driving means such as a motor, and a driven roller spaced apart from the driving roller. The driving roller is driven so as to be substantially the same as the moving speed of the peripheral surface of the photosensitive drum.

The paper conveyed between the photoconductive drum and the transfer roller is conveyed while being sandwiched between the photoconductive drum and the transfer belt, and the toner images of each color are transferred to the surface. At this time, the toner image formed on the surface of the paper is transported by the photosensitive drum and the transfer belt,
The image is transferred from each photosensitive drum.

[0005]

In the above-described apparatus, when the transport speed of the paper is uneven when reaching the photosensitive drums, the toner image transferred to the paper is shifted. Normal image formation cannot be performed. It is easy to control the rotation speed of the photosensitive drum by a sensor or the like, and it is easy to synchronize a plurality of photosensitive drums. However, the driving roller on which the transfer belt is stretched often uses rubber having a high coefficient of thermal expansion, and may be deformed by the heat of the fixing device arranged adjacently. Further, as the sheet passes through the sheet, the surface heat is taken away, and the diameter of the drive roller changes. As a result, the moving speed of the peripheral surface of the transfer belt stretched over the drive roller changes, and the transfer speed of the sheet conveyed by the transfer belt also changes. For this reason, there is a disadvantage that the toner image formed on the paper is displaced and an appropriate image cannot be formed.

In order to solve such a problem, it is conceivable to provide a sensor on the transfer belt, monitor the moving speed of the peripheral surface, and control the moving speed to be equal to the moving speed of the peripheral surface of the photosensitive drum. Can be It is also conceivable to use a high-precision driving means for driving the transfer belt and maintain the speed of the peripheral surface of the transfer belt with high accuracy in order to maintain the sheet conveyance speed with high accuracy.

However, in order to maintain the speed of the peripheral surface of the transfer belt with high accuracy, a complicated and expensive mechanism is required, and it is difficult to reduce the cost and reduce the size. Even with such a high-precision mechanism, it is impossible to completely match the speed of the peripheral surface of the photosensitive drum with the speed of the peripheral surface of the transfer belt. Will occur.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate a difference in speed between the peripheral surfaces of an image carrier and a transfer device with a simple structure, and to eliminate a displacement of an image formed on a sheet.

[0009]

A transfer device according to the present invention includes an image carrier, a first drive unit, a transfer device, an auxiliary transport unit, a second drive unit, and a transport speed control unit. ing. The image carrier circulates with a toner image formed on the peripheral surface. The first driving unit drives the image carrier to rotate. The transfer device is opposed to the image carrier, and transfers the toner image formed on the peripheral surface of the image carrier to the conveyed paper. The auxiliary conveyance unit conveys the paper conveyed between the image carrier and the transfer device while nipping the paper between the image carrier and the peripheral surface of the image carrier. The second drive unit drives the auxiliary transport unit in the paper transport direction. The conveying speed control means turns on / off the transmission of the driving force from the second driving means to the auxiliary conveying means based on a difference between the speed of the peripheral surface of the image carrier and the speed of the peripheral surface of the auxiliary conveying means.
The off control is performed to make the paper transport speed dependent on the peripheral speed of the image carrier.

In the transfer apparatus according to the present invention, the sheet is conveyed by sandwiching the sheet between the image carrier and the auxiliary conveying means, and the toner image formed on the peripheral surface of the image carrier is transferred onto the sheet. Is transferred to At this time, when there is a speed difference between the peripheral surface of the image carrier and the peripheral surface of the auxiliary transport unit, the transmission of the driving force from the second drive unit to the auxiliary transport unit by the transport speed control unit is turned off. The paper transport speed can be made dependent on the peripheral surface speed of the image carrier. Therefore, the sheet is transported according to the speed of the peripheral surface of the image carrier, and a toner image is formed on the surface at this speed.

Here, as an auxiliary conveying means, a driving roller driven by the second driving means, a driven roller spaced apart from the driving roller, and an image stretched between the driving roller and the driven roller. A transfer belt that circulates between the carrier and the transfer device may be provided. In this case, even if the speed of the peripheral surface of the transfer belt is uneven due to the thermal deformation of the drive roller or the transfer belt, the paper conveyance speed can be made dependent on the speed of the peripheral surface of the photosensitive drum. The displacement of the image formed on the image is eliminated.

The image carrier may include a plurality of photosensitive drums, and the transfer device may include a plurality of transfer rollers corresponding to the plurality of photosensitive drums. The plurality of photoconductor drums may be four photoconductor drums corresponding to the toner images of black, yellow, cyan, and magenta, and in this case, four photoconductor drums may correspond to each photoconductor drum. One transfer roller can be provided.

In such a transfer device, since the paper transport speed depends on the peripheral surface speed of the photosensitive drum,
By synchronizing the speeds of the peripheral surfaces of the respective photoconductor drums, regardless of the rotation unevenness of the transfer belt and the driving roller, the image formed on the paper is not shifted, and a normal color image can be obtained. . Further, a transfer roller pressed against the photosensitive drum via a transfer belt can be used. In this case, it is easy to make the peripheral surface speed of the transfer belt coincide with the peripheral surface speed of the photosensitive drum.

The transport speed control means is provided on the drive roller, and when there is a speed difference between the peripheral surface of the photosensitive drum and the peripheral surface of the transfer belt, the drive force of the second drive means is controlled by the drive roller. May be configured to include a torque limiter configured to prevent transmission to the motor. Further, the speed of the peripheral surface of the transfer belt is set to be lower than the speed of the peripheral surface of the photoconductor drum, and the conveying speed control means determines that the speed of the peripheral surface of the photoconductor drum is higher than the speed of the peripheral surface of the transfer belt. A configuration may be adopted that includes a one-way clutch configured to prevent the driving force of the second driving unit from being transmitted to the driving roller when the speed is delayed.

The transport speed control means is configured not to transmit the driving force of the second drive means to the drive roller when there is a speed difference between the peripheral surface of the photosensitive drum and the peripheral surface of the transfer belt. It is possible to adopt a configuration including a clutch that has been set. In any case using the torque limiter, the one-way clutch, and the clutch as described above, the speed of the peripheral surface of the transfer belt as the auxiliary transport unit is made to match the speed of the peripheral surface of the photosensitive drum as the image carrier. In addition, it is possible to make the conveyance speed of the conveyed paper dependent on the speed of the peripheral surface of the photosensitive drum, and to eliminate the deviation of the toner image formed on the paper.

[0016]

FIG. 1 shows a copying machine to which an embodiment of the present invention is applied.
An original mounting table 2 on which an original is mounted is disposed on an upper surface of the copying machine main body 1. An automatic document feeder 3 for automatically feeding a document to the document table 2 is provided on the upper surface of the document table 2.
Are provided to be freely opened and closed. A paper feed unit 4 is mounted on the bottom of the copying machine body 1. On the left side of the copying machine body 1 in the figure, a paper discharge tray 5 for stacking the discharged paper is mounted. Further, on the right side of the figure, a paper feed tray 6 for manual paper feed is mounted so as to be freely opened and closed.

An original reading device 7 for reading image information of an original placed on the original placing table 2, an image forming unit 8 disposed below the original reading device 7, A sheet feeding device 9 arranged below the image forming unit 8 and a fixing device 10 arranged on the left side of the image forming unit 8 in the figure are provided. In the paper feed unit 4,
A plurality of paper cassettes 4a detachably mounted on the apparatus,
4b and 4c are arranged. The paper feeder 9 is provided with a paper feed path for feeding paper from the paper feed cassettes 4a, 4b, 4c or the paper feed tray 6 to the image forming unit 8 side, and each paper feed cassette 4a, 4b, 4c is provided. Alternatively, the paper is selectively conveyed from the paper feed tray 6 to the image forming unit 8.

The document reading device 7 includes a reading unit 11 for reading image information of a document on the document table 2 and a laser unit 12 for forming an electrostatic latent image on a photosensitive drum described later. . The reading unit 11 is provided with a CCD element, is driven in the horizontal direction in the figure, scans an original image placed on the original placing table 2, and converts image information read by the CCD element into an electrical signal. Is configured. The image information read by the reading unit 11 is
The signal is converted into an electric signal and transmitted to the laser unit 12.

The image forming unit 8 includes four developing units 13a, 13b, 13c and 13d corresponding to four colors of black, yellow, cyan and magenta. The developing unit 13a includes a photosensitive drum 14a having an electrostatic latent image formed on the surface thereof, and a developing device 15a for visualizing the electrostatic latent image formed on the peripheral surface of the photosensitive drum 14a with a corresponding color toner. A transfer roller 16a disposed opposite to the photoconductor drum 14a and transferring a toner image formed on the surface of the photoconductor drum 14a to a conveyed sheet;
It includes a cleaning device 17a and the like. Developing device 1
5a, as shown in FIG. 2, a toner hopper 18a for accommodating toner, and a developing roller disposed opposite to the photosensitive drum 14a to visualize an electrostatic latent image formed on the photosensitive drum 14a with toner. 19a and a developing roller 19a
And a supply roller 20a for supplying toner to the printer. Similarly, the other developing units 13b, 13c, and 13d also have photosensitive drums 14b, 14c, and 14d, developing devices 15b, 15c, and 15d, and transfer rollers 16b and 1, respectively.
6c, 16d, cleaning devices 17b, 17c, 17
d. Each of the developing devices 15b, 15c, 1
5d are toner hoppers 18b, 18c, 18 respectively.
d, developing rollers 19b, 19c and 19d and supply rollers 20b, 20c and 20d.

Each of the photosensitive drums 14a, 14b, 14c,
A transfer belt 21 is disposed below 14d.
The transfer belt 21 includes a driving roller 22 that is rotationally driven by a driving unit such as a motor (not shown).
The tension roller 24 is provided with a predetermined tension by a tension roller 24. The driving roller 22 has at least a peripheral surface made of a material having a high friction coefficient such as rubber, and when the driving force of the driving unit is transmitted, the transfer belt 21 is driven.
Is driven to circulate between the driven rollers.

A torque limiter 25 is provided between the drive roller 22 and the drive system so as not to transmit the drive force of the drive system to the drive roller 22 when a torque greater than a predetermined value is applied. Have been. Each transfer roller 16
a, 16b, 16c, and 16d are respectively transferred to the photosensitive drums 14a, 14b, 14c, and 14 via the transfer belt 21.
The transfer belt 21 is urged so as to press against the photosensitive drums 14a, 14b, 14c, and 14d.
14d.

In the fixing device 10, a heating roller 26 and a pair of conveying rollers 27 and 28 are arranged. A fixing belt 29 is stretched between the heating roller 26 and the transport roller 27. When the sheet on which the toner image is formed on the surface by the image forming unit 8 is conveyed to the fixing device 10, the sheet is conveyed to the sheet discharge tray 5 side by conveying rollers 27 and 28, and is heated by the heating roller 26. The fixing belt 29 heats and fixes the toner image on the sheet.

In the copying machine to which the embodiment of the present invention is applied, image information of an original placed on the original placing table 2 is read by the reading unit 11, and the photosensitive unit of the image forming unit 8 is read by the laser unit 12. Body drums 14a, 14
An electrostatic latent image corresponding to each color is formed on the peripheral surfaces of b, 14c, and 14d. At the same time, the paper feeder 9 selects the paper feed cassettes 4a, 4b, 4c or the paper feed tray 6, and supplies the paper to the image forming unit 8 from any one of them.

In the image forming unit 8, the photosensitive drum 1
4a, 14b, 14c, and 14d are rotationally driven by driving means, respectively, and transfer rollers 16a, 16b,
16c and 16d, the photosensitive drums 14a, 14b, 1
The sheet conveyed together with the transfer belt 21 pressed against 4c and 14d is nipped and conveyed to the left in the figure. At this time, the electrostatic latent images formed on the peripheral surfaces of the photosensitive drums 14a, 14b, 14c,
a, 19b, 19c, and 19d are visualized by corresponding color toners. The visualized toner images are transferred to transfer rollers 16a, 16b, 16c, 1 respectively.
By 6d, the images are sequentially transferred onto the conveyed paper to form a full-color image. When the sheet is conveyed to the fixing device 10, the toner image formed on the surface of the sheet is heated and fixed, and is conveyed to the sheet discharge tray 5 side.

In the image forming unit 8, the rotation of each of the photosensitive drums 14a, 14b, 14c and 14d is controlled by a sensor, and when an image of each color toner is superimposed on the conveyed paper, Synchronization is performed so as to form a full-color image. The driving roller 22 is configured such that the peripheral surface of the transfer belt 21 is
It is rotationally driven by driving means (not shown) so as to be at the same speed as the peripheral surfaces of a, b, c and d. Therefore, the photosensitive drums 14a, 14b, 14
c and 14d and the paper conveyed while being nipped by the transfer belt 21 are photosensitive drums 14a, 14b, 14c and 1
It is moved at the same speed as the moving speed of the peripheral surface of 4d.

Here, the photosensitive drums 14a, 14b, 1
Consider a case where there is a difference between the peripheral surface speeds of 4c and 14d and the peripheral surface speed of the transfer belt. This speed difference occurs when, for example, the transfer speed of the peripheral surface of the transfer belt 21 fluctuates due to deformation of the transfer belt 21 or the drive roller 22 due to temperature fluctuations.
It is conceivable that a driving force fluctuates in the driving system of b, 14c, 14d or the driving system of the driving roller 22.

The photosensitive drums 14a, 14b, 14c, 1
When the speed of the peripheral surface of 4d is lower than the speed of the peripheral surface of the transfer belt 21, each of the photosensitive drums 14a, 14b,
14c, 14d and each transfer roller 16a, 16b, 16
A force in the direction opposite to the circulation direction is applied to the transfer belt 21 between c and 16d. As a result, a force acts on the transfer belt 21 to rotate the drive roller 22 in a direction opposite to the drive direction of the drive system. Here, a difference between the driving force from the driving system and the force from the transfer belt 21 acting via the driving roller 22 acts on the torque limiter 25 as torque. The torque limiter 25 is set so as to cause a slip when a predetermined torque is applied, and the difference between the driving force from the driving system and the force from the transfer belt 21 acting via the driving roller 22 is set to a predetermined value. Slip occurs when a torque is generated, and the driving force from the driving system is not transmitted to the driving roller 22.

Similarly, the photosensitive drums 14a, 14b, 1
When the speed of the peripheral surface of 4c, 14d becomes faster than the speed of the peripheral surface of the transfer belt 21, the transfer belt 21 receives more force from the photosensitive drums 14a, 14b, 14c, 14d in the circulation direction. Become. As a result, a force acts on the drive roller 22 from the transfer belt 21 to further rotate the drive roller 22 in the drive direction. Again,
The difference between the driving force from the driving system and the force from the transfer belt 21 via the driving roller 22 is used as a torque as a torque limiter 25.
Will work. The torque limiter 25 is configured to receive a predetermined torque in the reverse direction as described above, and to slip in this case.
Will not be transmitted.

Here, the paper and the photosensitive drums 14a, 14
B, the frictional resistance between the paper and the transfer belt 21 is B, the frictional resistance between the transfer belt 21 and the drive roller 22 is C, the torque limiter 2
Assuming that the frictional resistance at which the slip of No. 5 occurs is D, the relationship of B> C, A> D holds.

As described above, the photosensitive drums 14a,
When the rotation speed of the peripheral surface of the transfer belt 21 is different from the rotation speed of the peripheral surface of the transfer belt 21, the torque limiter 25 slips, and the drive system is driven by the drive roller 22.
Is not transmitted. As a result, the paper transport speed in the image forming unit 8 depends on the peripheral speed of the photosensitive drums 14a, 14b, 14c, and 14d. Therefore, each photosensitive drum 14a,
The toner images formed by 14b, 14c and 14d are transferred onto the paper without displacement.

FIG. 3 shows the current waveform of the motor for driving the drive roller 22. FIG. 3A shows the current waveform of the drive motor when the drive roller 22 is not provided with the torque limiter 25 when a peripheral speed difference of 0.16% is provided between the peripheral speed of the photosensitive member and the peripheral speed of the transfer belt. Is shown. Further, FIG.
The current waveform of the drive motor when the belt drive roller 22 is provided with a torque limiter 25 of 1.8 kgf · cm with a peripheral speed difference provided under the same conditions as in FIG.

As described above, when the torque limiter 25 is not provided, the current value of the drive motor fluctuates greatly, and a difference in speed between the peripheral surfaces of the photosensitive drum and the transfer belt occurs depending on the operating condition. Thus, it can be recognized that the torque is generated in the drive system. When the torque limiter 25 is provided as in the embodiment of the present invention, the speed difference between the peripheral surfaces of the photosensitive drum and the transfer belt is determined by the torque limiter 25.
Is absorbed, no extra torque is generated in the drive system, and the current waveform of the drive motor is substantially constant.

[Other Embodiments] (A) In the above embodiment, a one-way clutch can be used instead of the torque limiter 25.
In this case, the peripheral surface of the transfer belt 21 is
The drive system is set so as to be slightly slower than the peripheral surfaces of a, 14b, 14c, and 14d, and the one-way clutch idles when the drive roller 22 receives a force in a direction opposite to the drive direction of the drive system. Set as follows.

In this case, at the time of image formation, the photosensitive drums 14a, 14b, 14c, 14d and the transfer belt 21
Transports the paper while holding the paper on its peripheral surface and transferring the toner image onto the paper. At this time, the transfer belt 2
1 is the speed of the photosensitive drums 14a, 14b, 14
so that it is slightly slower than the peripheral speed of c, 14d
A drive system for driving the drive roller 22 is set. For this reason, the transfer belt 21 circulates so that the peripheral surface thereof has the same speed as the peripheral surfaces of the photosensitive drums 14a, 14b, 14c and 14, and accordingly, the drive roller 22 is also slightly smaller than the rotation of the drive system. To rotate at high speed. At this time, a slight slip occurs between the drive roller 22 and the transfer belt 21.

Here, the photosensitive drums 14a, 14b, 1
When the speed of the peripheral surface of 4c and 14d is lower than the speed of the peripheral surface of the transfer belt 21, a force in the direction opposite to the driving direction acts on the driving roller 22 from the transfer belt 21.
The drive roller 22 receives a force in the direction opposite to the drive force received from the drive system, and the one-way clutch idles.

Therefore, regardless of the driving force of the driving system driving the driving roller 22, the speed of the peripheral surface of the transfer belt 21 becomes the same as the speed of the peripheral surface of the photosensitive drums 14a, 14b, 14c, 14d. The conveying speed of the sheet passing through the image forming unit 8 is determined by the photosensitive drums 14a, 14b, 1
It depends on the speed of the peripheral surface of 4c and 14d. Thus, a normal full-color image can be obtained without causing a shift in the toner image formed on the sheet. (B) In the above embodiment, a clutch can be used instead of the torque limiter 25. in this case,
The driving force transmitted from the driving system to the driving roller 22 is turned on.
Provide a clutch to turn off. Photoconductor drum 14
a, 14b, 14c, and 14d and transfer belt 2
1 is detected by a sensor or the like, and when a predetermined speed occurs between the speed of the peripheral surface of the photosensitive drums 14a, 14b, 14c, and 14d and the speed of the peripheral surface of the transfer belt 21, the clutch is activated. The control is performed so that the drive roller 22 is turned off, and the drive force from the drive system is not transmitted to the drive roller 22.

In this case, the photosensitive drum 14
When a speed difference occurs between the transfer belt 21 and the transfer belt 21, the clutch is disengaged. As a result, the driving roller 22 is in a free state in the rotation direction, and the transfer belt 21 has its peripheral surface on the photosensitive drum 14a,
It circulates at the same speed as the speed of the peripheral surface of 14b, 14c, 14d.

The photosensitive drums 14a, 14b, 14c, 1
If the speed difference between the peripheral surface of 4d and the peripheral surface of the transfer belt 21 is within a predetermined range, the clutch is turned on to transmit the driving force of the driving system to the driving roller 22. In this embodiment,
The speed of the peripheral surface of the transfer belt 22 is controlled by the photosensitive drums 14a, 1
4b, 14c, and 14d are formed on the paper in accordance with the speed of the peripheral surface of the photosensitive drums 14a, 14b, 14c, and 14d so that the transport speed of the paper passing through the image forming unit 8 depends on the speed of the peripheral surface. Of the displayed image can be eliminated. (C) A transfer charger can be used instead of the transfer roller. (D) The present invention is not limited to a full-color copying machine, but can be applied to a single-color, two-color, and multi-color copying machine. (E) The present invention is not limited to a copying machine but can be applied to a facsimile apparatus, a printer, and the like.

[0039]

In the transfer apparatus according to the present invention, the transfer speed of the paper depends on the speed of the peripheral surface of the image carrier, so that the toner image formed on the image carrier is transferred to the paper when the image is transferred. , And appropriate image formation can be performed. For example, in the case of an apparatus such as a full-color copying machine that forms an image by superimposing toner images on a plurality of image carriers, it is only necessary to synchronize the rotation of each image carrier, The deviation of the transferred toner image can be eliminated, and an appropriate full-color image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a copier employing a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part thereof.

FIG. 3 is a current waveform diagram of a drive motor that drives a drive roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copier main body 8 Image forming unit 13 Developing unit 14 Photoreceptor drum 16 Transfer roller 21 Transfer belt 22 Drive roller 23 Follower roller 25 Torque limiter

Claims (8)

[Claims] An image carrier that circulates with a toner image formed on a peripheral surface thereof; a first driving unit that rotationally drives the image carrier; and an image carrier that faces the image carrier and faces the image carrier. A transfer device that transfers the toner image formed on the peripheral surface of the paper to the conveyed paper; and a transfer device that transfers the paper conveyed between the image carrier and the transfer device to the peripheral surface of the image carrier. An auxiliary transporting means for nipping and transporting the auxiliary transporting means, a second driving means for driving the auxiliary transporting means in a paper transporting direction, and a difference between a speed of a peripheral surface of the image carrier and a speed of a peripheral surface of the auxiliary transporting means. Transport speed control means for controlling the transmission of the driving force from the second drive means to the auxiliary transport means on / off based on the control so that the transport speed of the paper depends on the peripheral surface speed of the image carrier. And a transfer device comprising: 2. The auxiliary transport means includes a drive roller driven by the second drive means, a driven roller spaced apart from the drive roller, and a tension member between the drive roller and the driven roller. The transfer device according to claim 1, further comprising a transfer belt that is circulated through the image carrier and the transfer device. 3. The transfer device according to claim 1, wherein the image carrier includes a plurality of photosensitive drums, and the transfer device includes a plurality of transfer rollers corresponding to the plurality of photosensitive drums. 4. The image bearing member includes four photosensitive drums on which toner images of black, yellow, cyan, and magenta are formed, and the transfer device includes four photosensitive drums corresponding to the four photosensitive drums. It is provided with two transfer rollers, and forms a color image on the conveyed paper,
The transfer device according to claim 3. 5. The transfer device according to claim 3, wherein the transfer roller is pressed against the photosensitive drum via the transfer belt. 6. The transfer speed control means provided on the drive roller, wherein when there is a speed difference between the peripheral surface of the photosensitive drum and the peripheral surface of the transfer belt, the transfer speed control means of the second drive means is provided. The transfer device according to claim 3, further comprising a torque limiter configured to not transmit a driving force to the driving roller. 7. The transfer belt according to claim 6, wherein the speed of the peripheral surface of the transfer belt is set to be lower than the speed of the peripheral surface of the photosensitive drum. 4. A one-way clutch configured to not transmit the driving force of the second driving means to the drive roller when the speed of the belt becomes lower than the speed of the peripheral surface of the belt.
6. The transfer device according to any one of 5. 8. The transfer speed control means, when there is a speed difference between the peripheral surface of the photosensitive drum and the peripheral surface of the transfer belt, applies the drive force of the second drive unit to the drive roller. 4. A clutch, comprising: a clutch configured to prevent transmission.
The transfer device according to any one of claims 1 to 5,