JPH03278078A - Transfer roller device - Google Patents

Abstract

PURPOSE:To evade that toner is filmed on an intermediate transfer belt by grounding the part of plural cylindrical members, which constitute a back plate roller, corresponding to the length of a direction which is perpendicular to the carrying direction of a paper which is used. CONSTITUTION:The paper is carried so as to make the carrying reference position thereof coincide with the reference position of the back plate roller 32. The roller 32 is divided to the plural cylindrical members 32a - 32f at a position corresponding to the length of the direction which is perpendicular to the carrying directions of the papers of respective size from the carrying reference position on a surface which is perpendicular to the shaft center of the roller 32 under a state that the reference position and the carrying reference position of the paper 30 coincide each other. The parts of the members 32a - 32f corresponding to the length of the direction which is perpendicular to the carrying direction of the paper which is used are grounded. Thus, a voltage is not impressed on an image forming body 23 at a part between a transfer roller 25 and the roller 32 which is not through the paper and the voltage is impressed on the image forming body at the part between the roller 25 and the roller 32 which is through the paper. As the result, the toner is not filmed on the body 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transfer roller device used in an electrophotographic apparatus such as a full-color copying machine.

[Conventional technology]

For example, in the full-color copying machine shown in FIG. 11, when performing full-color copying, the exposure lamp 10 of the optical system 101
2, the color original 103 is scanned three times, and the reflected light from the original 103 in each scan passes through each of the three color filters of red, green, and blue in the filter device 104 and is exposed to light. The body 105 is irradiated, thereby exposing the photoreceptor 105 and forming an electrostatic latent image on the photoreceptor 105. Next, each electrostatic latent image obtained by the above three exposures is individually developed with color toner, which is a developer of three colors of yellow, magenta, and cyan, stored in developing devices 106 to 108. The toner images thus obtained are then sequentially transferred onto the intermediate transfer bell 109 in a superimposed state. Next, the toner image superimposed on the intermediate transfer belt 1O9 is transferred to a sheet of paper (not shown), and this toner image is thermally fixed to the sheet of paper by the fixing device 110, so that a color image is obtained on the sheet of paper. It has become.

The toner image is transferred from the intermediate transfer belt 109 to the paper using a rubber backup roller 111 made of insulating silicone rubber, a driven back electrode roller 112 disposed near the backup roller 111, and an intermediate Backup roller 1 via transfer belt 109
This is performed by a metal transfer roller 113 facing the roller 11.

That is, the backup roller 111 and the back electrode roller 11
2 supports the intermediate transfer belt 109 from the back side,
While feeding the paper so as to overlap the toner image on the intermediate transfer belt 109, the paper is brought into pressure contact with the intermediate transfer belt 109 by the transfer roller 113 and the backup roller 111. Then, in the above state, as shown in FIG.
15 to apply a transfer voltage to the intermediate transfer belt 109.
The upper toner image is transferred to paper 114.

[Problem to be solved by the invention]

However, in the above conventional configuration, the intermediate transfer belt 109
When transferring the above toner image onto the paper 114, the following problems arise.

That is, when the transfer voltage is applied between the transfer roller 113 and the back electrode roller 112 during the above transfer operation, the intermediate transfer belt 109 and the paper 114 between the transfer roller 113 and the back electrode roller 112 As shown in FIG. 13(a), both rollers 1
Due to the presence of the resistance RTX of the intermediate transfer belt 109 and the resistance RP of the paper 114 between 13 and 112, for example, when the transfer applied voltage is 2 kV, a current I of about 50 to 100 μA flows. On the other hand, the intermediate transfer belt 10 between the transfer roller 113 and the back electrode roller 112
As shown in FIG.
By eliminating the resistor R, the total resistance of the circuit decreases, and an overcurrent (2) of approximately 2 mA flows. Therefore, if toner remains on the intermediate transfer belt 109 in the portion between the transfer roller 113 and the back electrode roller 112 where the paper 114 is not interposed, this toner may be generated due to an overcurrent flowing through the intermediate transfer belt 109. This heat causes filming to adhere to the intermediate transfer belt 109, resulting in a reduction in copy quality.

[Means to solve the problem]

In order to solve the above problem, the transfer roller device of the invention according to claim 1 is provided with a transfer roller provided on the front side of a belt-shaped image forming body, and a transfer roller provided on the back side of the image forming body. A backup roller facing the image forming body is provided, and a back electrode roller that is in sliding contact with the image forming body at a predetermined distance from the backup roller is provided, and the paper fed between the transfer roller and the image forming body is backed up with the transfer roller. In a transfer roller device that transfers an image made of a developer on the surface of an image forming body to a sheet of paper by applying a transfer voltage between a back electrode roller and a transfer roller while pressing the image forming body with a roller, The following measures have been taken:

That is, the paper is transported so that its transport reference position coincides with the reference position of the back electrode roller, and the back electrode roller is transported by a surface perpendicular to the axis of the back electrode roller.
With the reference position of the back electrode roller and the paper transport reference position matching, the paper is divided into a plurality of cylindrical members at positions corresponding to the length in the direction orthogonal to the transport direction from the transport reference position for each size of paper. , these cylindrical members are grounded at a portion corresponding to the length in the direction orthogonal to the conveying direction of the paper used.

In order to solve the above problem, the transfer roller device of the invention according to claim 2 is provided with a transfer roller provided on the front side of a belt-shaped image forming body, and a transfer roller provided on the back side of the image forming body. A backup roller facing the image forming body is provided, and a back electrode roller that is in sliding contact with the image forming body at a predetermined distance from the backup roller is provided, and the paper fed between the transfer roller and the image forming body is backed up with the transfer roller. In a transfer roller device that transfers an image made of a developer on the surface of an image forming body to a sheet of paper by applying a transfer voltage between a back electrode roller and a transfer roller while pressing the image forming body with a roller, The following measures have been taken:

That is, the paper is transported so that its transport reference position coincides with the reference position of the back electrode roller, and the back electrode roller is transported by a surface perpendicular to the axis of the back electrode roller.
With the reference position of the back electrode roller and the paper transport reference position matching, the paper is divided into a plurality of cylindrical members at positions corresponding to the length in the direction orthogonal to the transport direction from the transport reference position for each size of paper. , a paper size detection means for detecting the size of the paper used, a switching means for selectively grounding the cylindrical member of the back electrode roller, and a length in a direction perpendicular to the conveyance direction of the paper detected by the paper size detection means. and a switching control means for controlling the switching operation of the switching means so that a portion of the cylindrical member corresponding to the position of the cylindrical member is grounded.

[For production]

According to the structure of claim 1, since the back electrode roller is grounded only at a portion corresponding to the size of the paper used, the portion between the transfer roller and the back electrode roller that does not have the paper in between is grounded. No voltage is applied to the image forming body, and voltage is applied only to the portion of the image forming body where the paper is interposed between the transfer roller and the back electrode roller. Therefore, no current flows to the image forming body in the area where the paper is not interposed, and it is possible to avoid generation of heat due to overcurrent.As a result, the toner is Even if toner remains, the toner will not be filmed on the image forming member.

According to the structure of claim 2, the switching control means controls the switching means so that a portion of the cylindrical member corresponding to the length in the direction orthogonal to the conveying direction of the paper detected by the paper size detection means is grounded. Since the switching operation of the cylindrical member that is in contact with the ground is automatically controlled depending on the paper size of each used.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 10. In this embodiment, a case where the transfer roller device is applied to a full-color copying machine is exemplified.

As shown in FIG. 7, the pull color copying machine is provided with a document table 10 on top of a main body 8 on which a document 9 is placed. Below the document table 10 are a copy lamp 12 and a mirror 1.
5..., an optical system section that includes a lens 13 and a filter device 14 having blue, red, and green filters, and scans and exposes the original 9 to form an electrostatic latent image on the photoreceptor belt 1, which will be described later. 1
1 is provided.

Below the optical system section 11 is an organic photoreceptor (OPC photoreceptor).
A photoreceptor belt 1 is provided. This photoreceptor belt 1 is passed between a driving roller 2 and a driven roller 3 which are arranged in parallel at a constant interval. Further, around the photoreceptor belt 1, a charging charger 16, developing bags W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W4, W5, W6, a cleaning device 18, and a static elimination lamp 17 are provided, facing the photoreceptor belt 1, respectively. In the developer bags W4, W5, and W6, an intermediate transfer device 19 is provided near the drive roller 2, which stores yellow, cyan, and magenta developers, respectively.

The intermediate transfer device 19 has a drive roller 20, a driven roller 21, and a backup function for the transfer roller 25 during transfer. Transfer charger 24, transfer roller 25, back electrode roller 3
2, a cleaner 33, and a peeling plate 34.

The intermediate transfer belt 23 is wound around a drive roller 20, a driven roller 21, and a backup roller 22, and the portion of the intermediate transfer belt 23 between the drive roller 20 and the driven roller 21 is The drive roller 2 side of the photoreceptor belt 1 is pressed against the drive roller 2 side.

In order to transfer the monochromatic toner image formed on the photoreceptor belt 1 onto the intermediate transfer belt 23, the intermediate transfer charger 24 is connected to the back side of the intermediate transfer belt 23 to which the driving roller 2 side of the photoreceptor belt l is pressed. It is located in The cleaner 33 is disposed near the drive roller 20 in order to remove toner remaining on the intermediate transfer belt 23. The peeling plate 34 is connected to the backup roller 22 in order to peel the paper 30 from the intermediate transfer belt 23.
and the transfer roller 25.

The transfer roller 25 is disposed below the backup roller 22, as shown in FIG.
B.

When moving forward in the direction, it comes into contact with the backup roller 22 at a contact point A via a paper 30 and an intermediate transfer belt 23, which will be described later, and is made of a conductive material such as metal, for example. A transfer voltage is applied from a power source 7.

The back electrode roller 32 is in sliding contact with the back side of the intermediate transfer belt 23 at a portion of the intermediate transfer belt 23 between the backup roller 22 and the second driven roller,
In addition, from the contact point A between the backup roller 22 and the transfer roller 25 to the direction in which the driven roller 21 is arranged, there is a length l2.
(=about 10-18 ribs), and are arranged at distant positions.

Further, the back electrode roller 32 is as shown in FIGS. 1(a) and (b).
As shown in FIG. 2, the intermediate transfer belt 23 is made of stainless steel and has a diameter of about 8 mm, and extends over the entire width of the intermediate transfer belt 23. In this embodiment, 11 cylindrical members It is divided into 32a to 32f. These cylindrical members 32a to 32f have the same axial length and are arranged symmetrically around the cylindrical member 32a, with the central cylindrical member 32a having a length of 100 mm, and the outer cylindrical members 32b to 32f sequentially 41kaku/14a
n.23IIIi.20++II.22 mm, and the back electrode roller 32 with a total length of 340aI11 is configured. That is, the back electrode roller 32 is provided so that the center, or reference position, of a cylindrical member 32a disposed at the center coincides with the transport center, or transport reference position, of the paper 30, and each of the cylindrical members 32a to 32e is arranged as described below. The length of the paper 30 of each size shown in Table 1 in the direction perpendicular to the transport direction, that is, the width of the paper 30 of each size in the transport direction, and the cylindrical member 32a, or the left and right sides of this cylindrical member 32a. A plurality of cylindrical members 32a to 32e lined up
are arranged so that the length including the Each cylindrical member 32a to 32e is connected to the paper 3 to be used.
A portion corresponding to the width of 0 in the conveying direction is grounded. The structure of this back electrode roller 32 for grounding is shown in FIG. That is, each cylindrical member 3 is placed inside the back electrode roller 32.
Sliding conductors 38 . Furthermore, this wiring board 39 is connected to a switching section 52 in a cylindrical member switching device 48, which will be described later, which grounds wiring 39a on the wiring board 39.

On the paper feeding side of the intermediate transfer device 19 shown in FIG. 7, paper cassettes 26 and 27 containing paper 30 are installed vertically as shown in FIG.
A manual paper feed tray 40 is provided above. In this embodiment, the above-mentioned paper cassettes 26 and 27 are used to store postcards and OH paper among the papers 30 shown in Table 1.
P (over head projector)
It is possible to feed paper 30 other than OHP sheets (hereinafter referred to as OHP sheets), and the manual paper feed tray 40
This makes it possible to feed postcards and OHP sheets. A paper feed roller 2 is provided between each paper cassette 26, 27, manual paper feed tray 40, and intermediate transfer device 19.
8, 29, 41, transport rollers 42, 43, and paper 30
A timing roller 31 is provided for sending out at a predetermined timing. A manual paper detection switch 47 is provided between the manual paper feed tray 40 and the paper feed roller 41 to detect the manual paper inserted from the manual paper feed tray 40.
1, an OHP sensor 44 including a light emitting element 44a and a light receiving element 44b is provided, which detects whether or not the paper 30 being conveyed is an OHP sheet.

The above paper cassettes 26 and 27 installed in the copying machine body
As shown in FIG.
- Paper size detection sections 45a to 45f are formed to indicate the size of the paper 30 housed in the paper 27.

These paper size detection sections 45a to 45f are capable of selectively forming recesses, like the paper size detection section 45a. On the other hand, as shown in FIG. 5, portions of the copying machine body corresponding to the paper size detection sections 45a to 45f are provided with detection switches (not shown) corresponding to the paper size detection sections 45a to 45f. A size detection switch section 46 is provided. Therefore, when the paper cassettes 26 and 27 are installed in the copying machine main body, the paper size detection section 45a of the paper cassettes 26 and 27
Any one of ~45f is a recess, and corresponds to this recess,
When the detection switch of the paper size detection switch unit 46 is turned on by the recess, the paper cassettes 26 and 27
The size of the paper 30 inside can be detected.

Note that the paper 30 stored in the paper cassettes 26 and 27
Paper size detection section 45a which has a concave portion with the size of
The relationship with 45f is as shown in Table 1.

Furthermore, a conveyor belt 35 , a fixing device 36 , and a paper discharge section 37 are provided on the paper discharge side with respect to the intermediate transfer device 19 .

The present transfer roller device also includes a cylindrical member switching device 48 shown in FIG. This cylindrical member switching device 48
The paper size detection sections 45a to 45f, the paper size detection switch section 46, the manual paper detection switch 47,
An OHP sensor 44, an input key 49 for selecting the paper cassette 26 and 27 to be used, and a document 9 provided below the document table 10 and arranged on the document table 10.
a document size sensor 50 that detects the size of the document, a switching control section 51 as a switching control means configured by a microcomputer, and a switching control section 51 that selectively selects the cylindrical members 32a to 32e of the back electrode roller 32. A switching section 52 is provided as a switching means for grounding.

The switching unit 52 can be configured by a known technique such as an electric one using a switch having contacts such as a relay, or an electronic circuit using a switching element. Then, the paper size detection section 45
a to 45f, paper size detection switch section 46, manual paper detection switch 47, OHP sensor 44, input key 49
, the document size sensor 50, and the switching control section 51 constitute a paper size detection means.

The switching control section 51 described above is based on the output of the document size sensor 50 and the output of the paper size detection switch section 46.
When it is detected that paper corresponding to the original size is stored in one of the paper cassettes 26 and 27, the input key 4 is
When it is detected that manual paper is being fed by turning on the manual paper detection switch 47 in accordance with or in priority to the paper 30 stored in the paper cassette 26 or 27 specified by 9. , OHP
Postcards or OH detected by the output of the sensor 44
Depending on the P sheet, as shown in Table 1, the switching unit 52 is set so that one of the cylindrical members 32a to 32e of the back electrode roller 32 corresponding to the width in the conveying direction of the paper 30 to be used is grounded. is designed to be controlled. In addition, in the same table, "'[F]" is added to the end of size 1 of r paper.
” indicates vertical feeding of paper 30, and “[F]”
Those without a mark indicate horizontal feeding of the paper 30.

(The following is a margin.) In the above-mentioned configuration of the table, the full-color copying process in the full-color copying machine is as follows.

The copy lamp 12 and mirrors 15 of the optical system section 11 shown in FIG. 7 scan the original 9 by reciprocating the lower surface of the original platen 10 in the directions of arrows C and D. The reflected light of the light irradiated onto the original 9 from the copy lamp 12 passes through mirrors 15 . . . is transmitted and reaches the surface of the photoreceptor belt 1 which is uniformly charged by the charger 16, and an electrostatic latent image corresponding to yellow is formed on the photoreceptor heald 1. This electrostatic latent image is developed by adsorbing the charged yellow toner in the developing device 4, and the obtained yellow toner image is transferred to the intermediate transfer device 19 by further movement of the photoreceptor belt 1. The image is transferred onto the intermediate transfer belt 23 by the transfer charger 24 . The photoreceptor belt 1 continues to move, and the yellow toner remaining on its surface is scraped off by the blade of the cleaning device 18, and then removed.
The static electricity is eliminated by the static elimination lamp 17. Thereafter, the same operation as above is repeated for cyan and magenta developers, and through this series of operations, toner of each color is transferred onto the intermediate transfer belt 23 in a superimposed manner, forming a full-color toner image. be done.

On the other hand, the sheets 30 and 30 stored in the paper cassettes 26 and 27 are
... are fed one by one to timing rollers 31 and 31 by paper feed rollers 28 and 29, and
・31 is the above paper 3 in synchronization with the intermediate transfer belt 23.
0 is conveyed between the intermediate transfer belt 23 and the transfer roller 25. After the toner image on the intermediate transfer belt 23 is transferred to the paper 30, the paper 30 is peeled off from the intermediate transfer belt 23 by a peeling plate 34. Then, the paper 30 on which the toner image has been transferred is guided to a fixing device 36 by a conveyor belt 35 and fixed by heating and pressure.
7 is discharged to the outside.

To transfer the full color toner image from the intermediate transfer belt 23 to the paper 30, the transfer roller 25 is driven in the B1 direction and moves forward, and the paper 30 is transferred to the backup roller 22.
Intermediate transfer belt 23 at contact point A by transfer roller 25 and
The cylindrical member 3 of the back electrode roller 32 is in pressure contact with the
2a to 32e are postcards, 0I (P@, B5, B50,
It is grounded according to the size of the paper 30 to be used among A4, A40, B4, and A3, so that the transfer from the power supply 7 is performed between the transfer roller 25 and the grounded cylindrical members 32a to 32e. This is done by applying an applied voltage. The grounding of each cylindrical member 32a to 32e is performed by the paper size detection switch section 46, manual paper detection switch 47, OHP sensor 44, input key 49, as described above.
The switching operation is automatically performed by the switching control unit 51 controlling the switching operation of the switching unit 52 based on the human power from the document size sensor 50.

Here, when a transfer voltage is applied between the transfer roller 25 and the back electrode roller 32 during the transfer operation, the intermediate transfer belt 23 and the paper 30 between the transfer roller 25 and the back electrode roller 32 The part through which the 9th
As shown in Figure (a), due to the presence of the resistance RTX of the intermediate transfer belt 23 and the resistance RP of the paper 30 between the rollers 25 and 32, for example, under the condition that the transfer applied voltage is 2 kV, the A current It of 100 μA flows. This is the same as the case of FIG. 13(a) described above.

On the other hand, between the transfer roller 25 and the back electrode roller 32, a portion where only the intermediate transfer belt 23 is interposed, that is, a portion where the paper 30 is not interposed, is provided with cylindrical members 32a to 32.
Since the part corresponding to this part in e is not grounded, as shown in FIG. 9(b), no transfer voltage is applied and the intermediate transfer belt 23 between the rollers 25 and 32
No current flows through. This is as shown in Figure 1O.
When the paper 30 is a postcard, for example, the current density in the portion 23a of the intermediate transfer belt 23 corresponding to the grounded cylindrical member 32a is high, and overcurrent in the portion of the intermediate transfer belt 23 not facing the postcard is avoided. This is due to the fact that As a result, toner filming does not occur even if toner adheres to a portion of the intermediate transfer belt 23 that does not face the postcard.

〔Effect of the invention〕

As described above, in the transfer roller device of the invention as claimed in claim 1, the paper is transported so that its transport reference position coincides with the reference position of the back electrode roller, and the back electrode roller is carefully aligned with the back electrode roller. When the reference position of the back electrode roller and the paper transport reference position coincide with each other due to the plane perpendicular to the paper transport direction, The cylindrical member is divided into a plurality of cylindrical members, and a portion of each cylindrical member corresponding to a length in a direction orthogonal to the conveyance direction of the paper used is grounded.

This makes it possible to prevent heat generation due to overcurrent in the intermediate transfer belt in the portion between the transfer roller and the back electrode roller where the paper is not interposed. As a result, even if toner on the developing side remains on the intermediate transfer belt in a portion not passing through the paper, it is possible to avoid a situation in which the toner is filmed on the intermediate transfer belt. Therefore, in a copying machine equipped with the present transfer roller device, it is possible to obtain high-quality copies.

As described above, in the transfer roller device of the invention as claimed in claim 2, the paper is transported so that its transport reference position coincides with the reference position of the front electrode roller, and the back electrode roller is aligned with the axis of the back electrode roller. With the plane orthogonal to A paper size detection means for detecting the size of the paper that is divided into a plurality of cylinders at corresponding positions; a switching means for selectively grounding the circular negative member of the back electrode roller; and a switching control means for controlling the switching operation of the switching means so that the striking force of the cylindrical portion of the portion corresponding to the length in the direction orthogonal to the conveying direction of the paper detected by the noise detection means is grounded. It is.

As a result, in addition to the same advantages as the configuration of claim 1, there is an effect that the cylindrical member that is in contact with the ground can be automatically switched in accordance with each size of paper used.

[Brief explanation of drawings]

1 to 10 show an embodiment of the present invention. FIG. 1(a) is a front view showing a back electrode roller made up of a plurality of cylindrical members. FIG. 1(b) is a side view of the same. FIG. 2 is a schematic perspective view showing the structure around the back electrode roller in the transfer roller device. FIG. 3 is a schematic perspective view showing a structure for grounding the back electrode roller. FIG. 4 is a schematic configuration diagram showing the transfer roller device. FIG. 5 is an explanatory diagram showing the structure of the vicinity of the paper feeding cassette/sheet loading section in a full-color copying machine. FIG. 6 is a perspective view of a main part showing a paper size detection section of the paper feed cassette shown in FIG. 5. FIG. FIG. 7 is an overall configuration diagram of a full-color copying machine. FIG. 8 is a block diagram showing the configuration of a cylindrical member switching device included in the transfer roller device. FIG. 9(a) is a diagram showing an equivalent circuit at the time of transfer between the transfer roller and the back electrode roller in a portion where paper is interposed. FIG. 9(b) is a diagram showing an equivalent circuit during transfer between the transfer roller and the back electrode roller in a portion where no paper is present. FIG. 1O is an explanatory diagram of the current density during transfer when the cylindrical member of the back electrode roller is grounded. 11 to 13 show conventional examples. FIG. 11 is an overall configuration diagram of a full-color copying machine. FIG. 12 is a schematic configuration diagram showing the transfer roller device. FIG. 13 (Ca) is a diagram showing an equivalent circuit during transfer between the transfer roller and the back electrode roller in a portion where paper is interposed. FIG. 13(b) is a diagram showing an equivalent circuit during transfer between the transfer roller and the back electrode roller in a portion where no paper is present. 7 is a power supply, 22 is a backup roller, 23 is an intermediate transfer belt (image forming body), 25 is a transfer roller, 30 is paper,
32 is a back electrode roller, 32a to 32f are cylindrical members, 4
4 is an OHP sensor (paper size detection means), 45a-4
5f is a paper size detection unit (paper size detection means), 46
is the paper size detection switch section (paper size detection means),
47 is a manual paper detection switch (paper size detection means)
48 is a cylindrical member switching device, 49 is an input key (paper size detection means), 50 is a document size sensor (paper size detection means), 51 is a switching control section (switching control means, paper size detection means), and 52 is a switching device. (switching means).

Claims (1)

[Claims] 1. A transfer roller is provided on the front side of the belt-shaped image forming body, and a backup roller facing the above-mentioned transfer roller is provided on the back side of the image forming body, and a predetermined distance from the backup roller. A back electrode roller is provided which is in sliding contact with the image forming body, and the paper fed between the transfer roller and the image forming body is brought into pressure contact with the image forming body by the transfer roller and the backup roller. In a transfer roller device that transfers an image made of developer on the surface of an image forming body onto paper by applying a transfer voltage between the transfer roller and the transfer roller, the above-mentioned paper has its conveyance reference position set to the reference position of the back electrode roller. The back electrode roller is conveyed to each size with the reference position of the back electrode roller and the paper transport reference position matching, due to the plane orthogonal to the axis of the back electrode roller. The paper is divided into multiple cylindrical members at positions corresponding to the length in the direction perpendicular to the transport direction from the paper transport reference position, and these cylindrical members correspond to the length in the direction perpendicular to the transport direction of the paper to be used. A transfer roller device characterized in that a part of the transfer roller device is grounded. 2. A transfer roller is provided on the front side of the belt-shaped image forming body, and a backup roller facing the above-mentioned transfer roller is provided on the back side of the image forming body, and a predetermined interval from this backup roller is provided, and the image forming body A back electrode roller that is in sliding contact with the transfer roller is provided, and the paper sent between the transfer roller and the image forming body is pressed against the image forming body by the transfer roller and the backup roller, and a back electrode roller that is in sliding contact with the image forming body is provided. In a transfer roller device that transfers an image made of developer on the surface of an image forming body onto paper by applying a transfer voltage to The back electrode roller moves from the paper transport reference position for each size of paper in a state where the reference position of the back electrode roller and the paper transport reference position match due to the plane orthogonal to the axis of the back electrode roller. Paper size detection means that is divided into a plurality of cylindrical members at positions corresponding to the length in the direction perpendicular to the conveying direction and that detects the size of the paper used, and the cylindrical member of the back electrode roller are selectively grounded. A switching means, and a switching control means for controlling the switching operation of the switching means so that a portion of the cylindrical member corresponding to the length of the paper detected by the paper size detection means in a direction orthogonal to the conveyance direction is grounded. A transfer roller device characterized by: