JPH1063120A - Transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the speed fluctuation of the surface of a transfer roller coincide with that of the surface of an image carrier at a nip between the image carrier and the transfer roller by constituting a power transmission roller of a material whose contact frictional coefficient with the surface of the image carrier is high and whose hardness is higher than that of the surface of the transfer roller. SOLUTION: The power transmission roller 21 is provided with an outside diameter being smaller than that of the transfer roller 8 and larger than that of a tracking roller 20 and constituted of the material whose contact frictional coefficient with the surface of the image carrier K is high and whose hardness is larger than that of the roller 8. Therefore, the circumferential speed of the surface of the roller 21 is almost equal to that of the surface of the carrier K on a contact surface between the carrier K. At this time, since the rotational radius of the roller 21 fixed to a transfer roller shaft 18 and the rotational radius of the contact surface of the roller 8 fixed to the shaft 18 with the carrier K coincide with each other because the contact surface is recessed, the circumferential speed of the roller 8 at the nip with the carrier K becomes equal to that of the carrier K.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a developing device for developing an electrostatic latent image formed on the surface of an image carrier into a toner image, transferring the toner image on the image carrier to a sheet, and fixing the toner image on the sheet to a fixing device. The present invention relates to a transfer device used for transferring a toner image formed on the image carrier to a sheet in an image forming apparatus fixed by the method, and particularly to a transfer device which is in pressure contact with the image carrier and between the image carrier. The present invention relates to a transfer device using a transfer roller to which a bias is applied.

[0002]

2. Description of the Related Art A transfer roller pressing means such as a spring acting on a bearing of a transfer roller shaft applies a pressure load of about 500 gf to 4 kgf on one side of the transfer roller. The transfer roller, which is an elastic body, is compressed in the pressure contact area with the image carrier by the pressure load, and forms a nip that conveys the sheet between the image carrier and the image carrier. In the nip, since the outer diameter of the transfer roller is reduced by the compression, the peripheral speed of that portion is lower than the peripheral speed of the surface of the non-compressed portion. Therefore, when the outer peripheral speeds of the image carrier and the transfer roller are set to be the same, there is a problem that the speed of the sheet becomes smaller than the peripheral speed of the image carrier surface.

[0003]

Conventionally, in order to solve the above-mentioned problems, an image carrier is driven by driving a transfer gear provided at an end of a transfer roller shaft by a drive source such as a motor. , The peripheral speed of the transfer roller is increased by 3 to 10%. However, in the method using the drive gear, since the speed fluctuation caused by the gear meshing error is transmitted to the paper speed, the speed fluctuation of the image carrier and the speed of the paper on which the toner image on the image carrier is transferred are described. The fluctuation does not match. As a result, even if a system in which the speed fluctuation of the image carrier surface is reduced is used, since the image carrier surface and the paper speed do not match, the toner image on the image carrier can be faithfully transferred onto the paper. Can not.

The present invention has been made in view of the above circumstances, and has the following (O0
The contents described in 1) shall be the subject. (O01) Nip between image carrier and transfer roller (pressure contact area)
The speed fluctuation on the surface of the transfer roller in step (c) coincides with the speed fluctuation on the surface of the image carrier.

[0005]

Next, the present invention devised to solve the above-mentioned problems will be described. Elements of the present invention are used to facilitate correspondence with elements of the embodiments described later. , The reference numerals of the elements of the embodiment are enclosed in parentheses. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described below is to facilitate understanding of the present invention and not to limit the scope of the present invention to the embodiments.

(1st invention) In order to solve the aforementioned problem,
The transfer device of the first invention of the present application has the following requirements: (A01) a transfer roller shaft (18) disposed parallel to the rotation axis of the image carrier (K) and rotatably supported; (A
02) a transfer roller (8) fixed to the axial center of the transfer roller shaft (18) and forming a nip for nipping and transporting the sheet (P) in a pressure contact area with the image carrier (K);
(A03) Each of the transfer roller shafts (18) is rotatably supported at both outer ends thereof, and comes into contact with the outer peripheral surface of the image carrier (K) outside the paper passage area to contact the image carrier (K). Tracking rollers (20, 20) for maintaining a constant distance between the rotating shaft and the transfer roller shaft (18); (A04) the transfer roller (8) fixed to the outer end of the transfer roller shaft (18); An outer diameter smaller than the outer diameter of the tracking roller (20, 20), a higher coefficient of contact friction with the surface of the image carrier (K), and higher than that of the transfer roller (8). Power transmission roller (21) made of a material having high hardness, and (A05) the transfer roller shaft (1).
8) toward the rotation axis of the image carrier (K),
A transfer roller shaft urging means (24) for pressing the transfer roller (8), the power transmission roller (21), and the tracking rollers (20, 20) against the image carrier (K);

(Second Invention) A transfer device according to a second invention of the present application has the following requirements. (B01) The transfer device is disposed parallel to the rotation axis of the image carrier (K) and is rotatable. Supported transfer roller shafts (18), (B02) are fixed to the axial center of the transfer roller shaft (18), and convey the paper (P) in a pressure contact area with the image carrier (K). Transfer rollers (8) and (B03) which form a nip to be formed are rotatably supported on both outer ends of the transfer roller shaft (18), and are provided on the outer peripheral surface of the image carrier (K) outside the paper passage area. Tracking rollers (20, 20) for keeping the distance between the rotation axis of the image carrier (K) and the transfer roller shaft (18) constant, and (B04) the transfer roller shaft (1).
(B05) a power transmission roller (21) fixed to the outer end of the transfer roller (8) and having an outer diameter smaller than the outer diameter of the transfer roller (8) and the tracking roller (20, 20); ) Is urged toward the rotation axis of the image carrier (K) to press the transfer roller (8) and the tracking rollers (20, 20) against the image carrier (K). (24), (B06) Rotating force relay rollers (31, 32, 3) for transmitting the rotating force of the image carrier (K) to the power transmitting roller (21) on the transfer roller shaft.
3).

[0008]

[Action]

(Operation of the First Invention) Next, the operation of the present invention having the above-described features will be described. In the transfer device of the first invention of the present application having the above-described features, the transfer roller shaft (18) arranged parallel to the rotation axis of the image carrier (K) is rotatably supported. The transfer roller shaft urging means (24) urges the transfer roller shaft (18) toward the rotation axis of the image carrier (K), thereby transferring the transfer roller (8) and the power transmission roller (21). Then, the tracking rollers (20, 20) are pressed against the image carrier (K). Due to this pressure contact, the transfer roller moves the paper into a pressure contact area with the image carrier (K).
A nip for nipping and conveying (P) is formed. Further, the tracking rollers (20, 20) abutting on the outer peripheral surface of the image carrier (K) outside the paper passage area are free-rotating at both outer ends of the transfer roller shaft (18), respectively. The distance between the rotation axis of the body (K) and the transfer roller axis (18) is kept constant.

The power transmission roller (21) has an outer diameter smaller than the transfer roller (8) and an outer diameter larger than the outer diameter of the tracking rollers (20, 20).
The transfer roller (8) is made of a material having a high coefficient of contact friction with the surface of the image carrier (K) and a hardness higher than that of the transfer roller (8). At the contact surface, it is substantially equal to the peripheral speed of the surface of the image carrier (K). At this time, the rotational radius of the power transmission roller (21) fixed on the transfer roller shaft (18) and the rotational radius of the contact surface of the transfer roller (8) with the image carrier (K) are the contact surfaces. Are recessed, the peripheral speed of the transfer roller at the nip with the image carrier (K) is equal to the peripheral speed of the image carrier (K). Therefore, when the peripheral speed of the image carrier (K) changes, the change is transmitted to the transfer roller (8) via the power transmission roller (21), so that the transport speed of the sheet (P) in the nip also changes. Thereby, the peripheral speed of the surface of the image carrier (K) and the paper (P)
Are the same, the toner image on the image carrier (K) is faithfully transferred onto the sheet (P).

(Operation of the Second Invention) In the transfer device of the second invention of the present application, a transfer roller shaft (18) arranged parallel to the rotation axis of the image carrier (K) is rotatably supported. Is done. The transfer roller shaft (18) urging means urges the transfer roller shaft (18) toward the rotation axis of the image carrier (K), whereby the transfer roller (8) and the tracking rollers (20, 20) are urged. ) Is pressed against the image carrier (K). By this pressure contact, the transfer roller forms a nip for nipping and transporting the sheet (P) in a pressure contact area with the image carrier (K). Further, a tracking roller (20, 20) abutting on the outer peripheral surface of the image carrier (K) outside the paper passage area.
20) maintains the distance between the rotation axis of the image carrier (K) and the transfer roller shaft (18) constant while freely rotating at both outer ends of the transfer roller shaft (18).
The power transmission roller (21) includes a rotational force relay roller (3).
1, 32, 33) transmit the rotational force of the image carrier (K).

As a result, if the peripheral speed of the image carrier (K) changes, the rotational force relay rollers (31, 32, 33)
The change is transmitted to the transfer roller (8) via a power transmission roller (21) fixed on the transfer roller shaft (18) and integrally rotating with the transfer roller (8), so that the paper (P) is transported in the nip. Speed also changes. Therefore,
Since the peripheral speed of the surface of the image carrier (K) matches the transport speed of the sheet (P), the toner image on the image carrier (K) is
(P) Transferred faithfully on

(Embodiment) Next, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment. In order to facilitate understanding of the following description, arrows X, Y,
The orthogonal coordinate axes X axis, Y axis, and Z axis are defined in the Z direction, and the arrow X direction is forward, the arrow Y direction is left, and the arrow Z direction is upward. In this case, the direction opposite to the X direction (front) (−X direction) is backward, the direction opposite to the Y direction (left) (−Y direction) is right, and the direction Z (upward) is opposite (−Z direction). Is below. Also referred to as the front-rear direction or the X-axis direction including the front (X direction) and the rear (-X direction), and the left-right direction or the Y-axis direction including the left (Y direction) and the right (-Y direction). Good,
It is referred to as a vertical direction or a Z-axis direction including the upper part (Z direction) and the lower part (-Z direction). Furthermore, in the figure, those with "•" in "○" mean arrows pointing from the back of the paper to the front, and those with "x" in "○" are from the table on the paper. It shall mean an arrow pointing to the back.

(Embodiment 1) FIG. 1 is an overall explanatory view of an image forming apparatus provided with a transfer apparatus according to Embodiment 1 of the present invention. FIG.
1, the image forming apparatus U has a laser writing device U1. The laser writing device U1 includes a semiconductor laser oscillator 1 as a laser light source, a collimating lens 2 for condensing a laser beam L from the semiconductor laser oscillator 1 and collimating the laser beam L, and scanning the beam from the collimating lens 2 in the scanning direction. The polygon mirror 3 includes a polygon mirror 3 for deflecting the laser beam L, a convex lens 4 for forming and irradiating the deflected laser beam L onto the image carrier K, and a cylindrical mirror 5 for correcting a tilt of the polygon mirror 3. The laser writing device U1 is connected to an image processing device (not shown) for sending an image information signal to the semiconductor laser oscillator 1.

A charger (charging roller) 6 for uniformly charging the surface of the image carrier K is provided around the image carrier K. An electrostatic latent image is written on the surface of the image carrier K charged by the charger 6 at the latent image writing position Q1 by the laser writing device U1.
The image carrier K is formed by depositing an amorphous silicon film on the surface of a cylindrical aluminum member to form a photosensitive layer. Around the image carrier K, a developing device 7 containing a pressure fixing toner and a developing roll 7a are arranged in order from the latent image writing position Q1 in the drum rotation direction. A transfer device T having a transfer roller for transferring a toner image Ia formed on K to a sheet (transfer material) P, and a cleaner having a blade 9a for scraping off toner to remove residual toner on the image carrier K 9 and a static eliminator (static elimination roller) 10 for removing the residual charge on the image carrier K are provided, respectively. The transfer roller 8 and the transfer device T will be described later in detail.

The paper P stored in the paper feed tray 11 which can be pulled out and inserted inward is shot by a paper feed roller 12 in synchronism with the operation of the laser writing device U1. From the member 13 to the transfer roller 8
The image carrier K is conveyed to a transfer area Q2 formed by a press-contact area (nip) of the image carrier K. When passing through the transfer area Q2, the toner image Ia on the image carrier K is transferred onto the sheet P. The sheet P on which the toner image has been transferred is fixed to the fixing device 1.
4, the toner image is fixed, and then discharged to the discharge tray H by the discharge roller 16.

Next, the transfer device T of the image forming apparatus U will be described in detail. FIG. 2 shows the transfer device T and the image carrier K in the first embodiment to the right (-Y direction).
FIG. FIG. 3 is a view showing a state where the paper P passes through the nip between the transfer roller and the image carrier K shown in FIG. FIG. 4 is a perspective view of a main part of the transfer device T. FIG. 5 is a perspective view showing a state in which the paper P passes through the nip between the image carrier K and the transfer roller 8. FIG. 6 shows the image carrier K
FIG. 4 is a cross-sectional view illustrating a state in which a sheet P passes through a nip of a transfer roller 8. 2 and 3, the transfer roller 8
Is fixed to the center of the transfer roller shaft 18. The tracking roller 2 is provided at both ends of the transfer roller shaft 18.
0 and 20 are rotatably supported. A power transmission roller 21 is fixed to the rear end of the transfer roller shaft 18 between the transfer roller 8 and the tracking roller 20.

The front and rear ends of the transfer roller shaft 18 are swingable arms 23, 23 swingable about a swing shaft 22, respectively.
It is rotatably supported by. The tip of the swing arm 23 is pulled upward by a tension spring (that is, transfer roller shaft urging means) 24 provided between the swing arm 23 and the frame of the image forming apparatus U. By the tension spring 24,
The transfer roller shaft 18 is urged toward the rotation axis of the image carrier K, and the transfer roller 8, the power transmission roller 21, and the tracking rollers 20, 20 are pressed against the image carrier K.

The transfer roller 8 is made of a urethane roll (volume resistivity 10 ⁸ Ωcm, hardness 30 °: Asuka C) by a foaming method. Tracking roller 2
Reference numerals 0 and 20 are made of a POM (polyoxymethylene) material. The power transmission roller 21 is formed of a silicon roll (volume resistivity 10 ¹¹ Ωcm, hardness 45 °: Asuka C). Then, the rollers 8, 20,
The hardness of No. 21 is as follows when arranged in ascending order. Low hardness ... Transfer roller 8 ... Power transmission roller 21 ... Tracking rollers 20, 20 ... High hardness The size of the outer diameter is set as follows. Transfer roller 8 outer diameter> power transmission roller 21 outer diameter> tracking rollers 20,20 outer diameter

2 and 3, the power transmission roller 21
The tracking rollers 20 and 20 are disposed axially outside the area where the sheet P passes. Since the tracking rollers 20, 20 having the smallest outer diameter are pressed against the image carrier K, the transfer roller 8 having the largest outer diameter is pressed largely in a nip with the image carrier K and pressed. The power transmission roller 21 having a smaller outer diameter is slightly recessed and pressed. Since the surface of the power transmission roller 21 is formed of a material having a high friction coefficient,
The peripheral speed of the surface of the image carrier K is transmitted to the surface of the power transmission roller 21.

(Operation of the First Embodiment) The transfer roller shaft 18
Is urged by the tension spring 24 in the direction of the rotation axis of the image carrier K. Tracking rollers 20 and 2 rotatably supported by the outer end of the transfer roller shaft 18.
0 is pressed against the image carrier K. At this time, the transfer roller 8 and the power transmission roller 21 having outer diameters larger than those of the tracking rollers 20 and 20 are pressed against the surface of the image carrier K in a state where their surfaces are compressed and deformed. Since the power transmission roller 21 has a smaller diameter than the transfer roller 8, the amount of compressive deformation is small. The power transmission roller 21 includes:
Since the transfer roller 8 is harder than the transfer roller 8 and has a higher surface friction coefficient, the peripheral speed of the surface of the power transmission roller 21 rotated by the rotational force transmitted from the surface of the image carrier K is less than that of the contact surface with the image carrier K. If there is no slip, it is equal to the peripheral speed of the surface of the image carrier K. In this case, the radius of rotation of the contact surface of the transfer roller 8 that rotates integrally with the power transmission roller 21 and the image carrier K is the same as the radius of rotation of the power transmission roller 21. The peripheral speed at the nip with the carrier K is equal to the peripheral speed of the image carrier K.

Since the change in the peripheral speed of the image carrier K is also directly transmitted to the surface of the power transmission roller 21, the peripheral speed of the power transmission roller 21 is changed according to the change in the peripheral speed of the image carrier K. Change. For this reason, the peripheral speed of the transfer roller 8 fixed to the transfer roller shaft 18 that rotates integrally with the power transmission roller 21 also changes according to the change in the peripheral speed of the image carrier K.
A change in the transport speed of the sheet P onto which the toner image on the image carrier K is transferred when passing through the nip between the image carrier K and the transfer roller 8 is caused by a change in the speed of the image carrier K and the transfer roller 8. Will change accordingly. Therefore, the peripheral speed of the surface K of the image carrier is equal to the transport speed of the sheet, so that the toner image on the image carrier is faithfully transferred onto the sheet.

(Embodiment 2) FIG. 7 is an explanatory view of a transfer apparatus T according to a second embodiment of the present invention, corresponding to FIG. 2 of the first embodiment. In the second embodiment, the outer diameter of the power transmission roller 21 is set to be substantially the same as or slightly smaller than the outer diameter of the tracking rollers 20, 20. The outer diameter of the outer peripheral portion is set to be the same as or slightly larger than the portion that rotates in contact with the tracking rollers 20,20. In this case, since the rotation radius of the contact portion of the transfer roller 8 that rotates integrally with the power transmission roller 21 and the image carrier K is larger than the rotation radius of the power transmission roller 21,
The peripheral speed is higher than the peripheral speed of the power transmission roller 21. In the second embodiment, when there is a slight slip between the image carrier K and the power transmission roller 21 to which the rotational force is transmitted,
Due to the slip, the peripheral speed of the power transmission roller 21 is reduced by the image carrier K.
Can be compensated for slightly lower than the peripheral speed.

(Embodiment 3) FIG. 8 is an explanatory view of Embodiment 3 of the transfer apparatus T of the present invention, and corresponds to FIG. 6 of Embodiment 1 described above. In the third embodiment, the outer diameter of the power transmission roller 21 is set smaller than the outer diameter of the tracking rollers 20,20. The transmission of the rotational force to the power transmission roller 21 is performed by the first relay roller 31 that is pressed against the image carrier K.
And the second relay roller 32 pressed against the first relay roller 31 and the power transmission roller 21. In the third embodiment, the image carrier K, the first relay roller 31,
When there is no slippage between the second relay roller 32 and the power transmission roller 21, their peripheral speeds are the same. In this case, the contact portion of the transfer roller 8 that rotates integrally with the power transmission roller 21 and the image carrier K has a rotation radius larger than the rotation radius of the power transmission roller 21. It becomes higher than the peripheral speed of the power transmission roller 21 and the like. However, generally, there is a slight slip between the image carrier K, the first relay roller 31, the second relay roller 32, and the power transmission roller 21, so that the peripheral speed of the power transmission roller 21 It is slightly smaller than the peripheral speed of the carrier K. In the third embodiment, the transfer roller 8 that rotates integrally with the power transmission roller 21 has a slightly larger radius of contact with the image carrier K than the power transmission roller 21. Slightly higher than the peripheral speed of Accordingly, the peripheral speed can be made substantially the same as that of the image carrier K and the portion of the transfer roller 8 which comes into contact with the image carrier K.

(Embodiment 4) FIG. 9 is an explanatory view of Embodiment 4 of the transfer apparatus T of the present invention. The fourth embodiment has the same configuration as that of the third embodiment except for the following points. In FIG. 9, a third relay roller 33 is fixed to a rotation shaft of the second relay roller 32 so as to rotate integrally with the second relay roller 32. The outer diameter of the third relay roller is set to be slightly smaller than the outer diameter of the second relay roller 32. The transmission of the rotational force to the power transmission roller 21 is performed by a first relay roller 31 pressed against the image carrier K, a second relay roller 32 pressed against the first relay roller 31, and the second relay roller. 32
This is performed by a third relay roller 33 that rotates integrally with the power transmission roller 21 and that is pressed against the power transmission roller 21. In the fourth embodiment, the second relay roller 32 and the third relay roller 33
By adjusting the ratio of the outer diameters of the power transmission rollers 21
The peripheral speed transmitted to the motor can be adjusted. In this case, the peripheral speed of the transfer roller 8 at the portion in contact with the image carrier K can be adjusted so that the peripheral speeds of the image carrier K and the transfer roller 8 at the nip can be the same.

(Modifications) Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, but falls within the scope of the present invention described in the appended claims. Thus, various changes can be made. Modified embodiments of the present invention will be exemplified below. (H01) The power transmission roll can be used even if a high hardness urethane rubber surface layer is formed on an inner layer of an insulating resin such as a POM material. (H02) In the present embodiment, the case where the present invention is used in the pressure roll system is exemplified, but the present invention can also be used in other fixing systems such as the pressure belt system. (H03) A release agent supply roll may be used as the relay roll used in the above embodiment.

[0026]

The transfer device of the present invention described above has the following effects. (E01) The speed fluctuation on the surface of the transfer roller at the nip between the image carrier and the transfer roller can be matched with the speed fluctuation on the surface of the image carrier.

[Brief description of the drawings]

FIG. 1 is an overall explanatory diagram of an image forming apparatus including a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the transfer device T according to the first embodiment.
FIG. 3 is a diagram of the image carrier K viewed from the right (−Y direction).

FIG. 3 is a diagram showing a state in which a sheet P passes through a nip between the transfer roller and the image carrier K shown in FIG. 2;

FIG. 4 is a perspective view of a main part of the transfer device T.

FIG. 5 is a perspective view showing a state in which a sheet P passes through a nip between the image carrier K and the transfer roller 8;

FIG. 6 is a cross-sectional view illustrating a state in which a sheet P passes through a nip between the image carrier K and the transfer roller 8;

FIG. 7 is an explanatory view of a transfer apparatus T according to a second embodiment of the present invention, and corresponds to FIG. 2 of the first embodiment.

FIG. 8 is an explanatory view of a transfer apparatus T according to a third embodiment of the present invention, and corresponds to FIG. 6 of the first embodiment.

FIG. 9 is an explanatory view of a transfer apparatus T according to a fourth embodiment of the present invention.

[Explanation of symbols]

K: image carrier, P: paper 8: transfer roller, 18: transfer roller shaft, (20, 20)
... Tracking roller, 21 ... Power transmission roller, 24 ...
Transfer roller shaft urging means, (31, 32, 33): rotational force relay roller

Claims (2)

[Claims] 1. A transfer device having the following requirements: (A01)
(A02) a transfer roller shaft arranged in parallel with the rotation axis of the image carrier and rotatably supported, (A02) fixed to the axial center portion of the transfer roller shaft, and holding a sheet in a pressure contact area with the image carrier; Transfer roller forming a nip to be transported
03) The distance between the rotation axis of the image carrier and the axis of the transfer roller shaft rotatably supported at both outer ends of the transfer roller shaft and abutting against the outer peripheral surface of the image carrier outside the paper passage area. Tracking roller that keeps constant (A04)
Fixed to the outer end of the transfer roller shaft, having an outer diameter smaller than the transfer roller and larger than the outer diameter of the tracking roller, having a high coefficient of contact friction with the surface of the image carrier; (A05) a power transmission roller made of a material having a higher hardness than the transfer roller; (A05) a transfer roller, a power transmission roller, and a tracking roller which urge the transfer roller shaft toward a rotation axis of the image carrier; Transfer roller shaft urging means for pressing the image bearing member against the image carrier, 2. A transfer device having the following requirements: (B01)
(B02) a transfer roller shaft disposed in parallel with the rotation axis of the image carrier and rotatably supported, and (B02) fixed to the axial center of the transfer roller shaft, and sandwiching a sheet in a pressure contact area with the image carrier Transfer roller forming a nip to be transported
03) The distance between the rotation axis of the image carrier and the axis of the transfer roller shaft rotatably supported at both outer ends of the transfer roller shaft and abutting against the outer peripheral surface of the image carrier outside the paper passage area. A tracking roller that keeps constant, (B04)
A power transmission roller fixed to the outer end of the transfer roller shaft and having an outer diameter smaller than the outer diameters of the transfer roller and the tracking roller; and (B05) the transfer roller shaft facing the rotation shaft of the image carrier. A transfer roller shaft urging means for urging the transfer roller and the tracking roller into pressure contact with the image carrier; (B06) a rotational force for transmitting a rotational force of the image carrier to a power transmission roller on the transfer roller shaft; Relay roller.