JP2001356559A - Color electrophotographic equipment - Google Patents

Abstract

(57) [Problem] A color electrophotography capable of performing transfer at a low voltage without being affected by fluctuations in impedance of an intermediate transfer belt and absorbing collision energy between a photosensitive drum and an intermediate transfer belt. Providing equipment. SOLUTION: Each image forming unit 12B, 12Y, 12
M, 12C to the intermediate transfer belt 17
The brush-like conductive member 31 is brought into contact with the back surface of the intermediate transfer belt 17, and a voltage having a polarity opposite to that of the toner image on the photosensitive drum 13 is supplied to the conductive member 31.
Collisions between the photosensitive drum 13 and the intermediate transfer belt 17 when the image forming units 12B are rotated are absorbed by deformation of the intermediate transfer belt 17 and elasticity of the conductive member 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color electrophotographic apparatus used for a copying machine, a facsimile, a printer, and the like.

[0002]

2. Description of the Related Art In recent years, with the rapid development of a device for creating a color document image, demand for an output device such as a printer or a copying machine for printing a color image on a receiving paper is rapidly increasing. In particular, the development of a color image output device using an electrophotographic method, which has advantages such as a wide selection range of an image receiving paper and an excellent halftone reproduction, has been developed.

For example, Japanese Patent Application Laid-Open No. 2-183276 discloses that a plurality of color toner images are successively superimposed and transferred on an intermediate transfer belt or an intermediate transfer drum, and the color toner images on the intermediate transfer body are collectively transferred to image receiving paper. An intermediate transfer method to be performed is shown. The intermediate transfer method reduces the size and price of the device body,
It has the advantage of being excellent in maintainability and capable of outputting a high-quality image.

Among the intermediate transfer systems, for example, Japanese Patent Application Laid-Open
As shown in JP-A-36246 or the like, the entire image forming unit group in which a plurality of color image forming units are arranged in an annular shape is rotated, and each image forming unit is moved to one transfer position. There has been proposed a color image output apparatus which sequentially moves and superimposes a toner image on an intermediate transfer belt sequentially. This method has the advantage of the intermediate transfer method, and at the same time, has the advantage of being particularly excellent in maintainability and miniaturization of the apparatus.

On the other hand, Japanese Patent Application No. 6-50257 discloses that
A configuration is shown in which the intermediate transfer belt is separated from the transfer position while the entire image forming unit group is rotating, and the photosensitive drum is brought into contact with the stretching surface of the intermediate transfer belt during image formation. Accordingly, the intermediate transfer belt does not collide with the photosensitive drum when the image forming unit group is rotated or when the intermediate transfer belt is in contact with the intermediate transfer belt. Having.

[0006] Japanese Patent Application Laid-Open No. 7-84430 discloses that
In order to cope with variations in the time required for the movement of the image forming unit, a method of temporarily stopping the driving of the intermediate transfer belt or driving the intermediate transfer belt at a lower speed than at the time of image formation is disclosed. As a result, it is not necessary to increase the circumference of the intermediate transfer belt, and the size of the apparatus can be reduced and the output speed per sheet can be increased.

[0007] However, each of the above-described configurations has the following problems. That is, Japanese Patent Application No. 6-50257.
In such a configuration as shown in Japanese Patent Application Laid-Open No. H10-209, the stretching surface of the intermediate transfer belt is brought into contact with the photosensitive drum and a transfer voltage is applied to the intermediate transfer belt support roller, A transfer current is supplied to the transfer position via the transfer belt. For this reason, when the electric resistance of the intermediate transfer belt serving as the transfer current path is high, the voltage applied to the support roller must be high. On the other hand, when the electric resistance of the intermediate transfer belt is low, a leak occurs on the photosensitive drum and other supporting rollers. Further, when the electrical resistance of the intermediate transfer belt changes due to environmental fluctuations, aging characteristics of the intermediate transfer belt, and the like, the amount of current supplied to the transfer position changes accordingly. As a result, there has been a problem that stable transfer cannot be performed against environmental fluctuations or long-time use.

Further, as shown in Japanese Patent Application Laid-Open No. 7-36246, the whole image forming unit group in which a plurality of color image forming units are arranged in an annular shape is rotated to move to a single transfer position. A method of sequentially moving each image forming unit,
In the method of temporarily stopping the driving of the intermediate transfer belt or driving the intermediate transfer belt at a lower speed than at the time of image formation, as disclosed in Japanese Patent Application Laid-Open No. 7-84430, the photosensitive drum and the intermediate transfer belt are sequentially driven. Each time the separation / contact and the switching of the intermediate transfer belt driving speed are repeated, the driving load of the intermediate transfer belt fluctuates, and the intermediate transfer belt easily slips. For this reason, when multiple transfer of the toner image is performed on the intermediate transfer belt, there has been a problem that the overlay deviation between the toner images of each color tends to occur.

As a means for solving the misregistration between the toner images of the respective colors, for example, JP-A-5-27521 and JP-A-7-92763 detect a mark on an intermediate transfer belt and place the mark on a photosensitive drum. The method of controlling the timing of the electrostatic latent image writing operation of FIG. However, when the intermediate transfer belt slips and starts driving the image formation from a position immediately after the mark has passed the mark detection sensor, the intermediate transfer belt is operated until the operation of writing the electrostatic latent image on the photosensitive drum is started. It is necessary to wait until the transfer belt is rotated by substantially one rotation, and there is a problem that the printing speed is reduced by the waiting time.

Furthermore, if the intermediate transfer belt is left in a stretched state for a long time, a phenomenon occurs in which a region in contact with the roller supporting the intermediate transfer belt is deformed by the curvature of the roller. When the deformed area passes near the roller during driving of the intermediate transfer belt, the running path of the intermediate transfer belt is displaced up and down (or flutters). Since the displacement of the intermediate transfer belt is poor in reproducibility, if the timing of starting the writing of the electrostatic latent image is controlled by detecting the mark on the intermediate transfer belt, the displacement of the intermediate transfer belt causes a shift in the detection timing of each color. Occurs. as a result,
There has been a problem that toner images of each color on the intermediate transfer belt cause image shift.

As a method of preventing such belt deformation, for example, Japanese Patent Application Laid-Open Nos. Sho 61-130972 and 63-188175 disclose a method of relaxing the tension of the intermediate transfer belt when the intermediate transfer belt is not driven. A method for causing this is shown. Japanese Patent Application Laid-Open No. 5-281775 specifies the Young's modulus of the intermediate transfer belt. Further, Japanese Patent Application Laid-Open No. Hei 7-140805 describes a method in which a cleaner mechanism is pressed against the surface of a rotating intermediate transfer belt to promote elimination of belt deformation.

However, if a structure for relaxing the tension of the intermediate transfer belt is used, the structure of the apparatus becomes complicated. Further, when used in combination with the configuration in which the waste toner box of the belt cleaner is installed inside the intermediate transfer belt, there is a problem that the capacity of the waste toner box is reduced by the provision of the belt relaxation mechanism. In addition, when the Young's modulus of the intermediate transfer belt is defined, in terms of electric resistance, surface roughness, and the like,
The material of the intermediate transfer belt is limited. Furthermore, in the method in which the cleaner mechanism is pressed against the intermediate transfer belt, it takes a considerable amount of time before the belt deformation is eliminated, and as a result, the time from when printing is started to when the receiving paper is ejected becomes longer. I will.

On the other hand, in the color image forming apparatus, it is necessary to control the density of each color toner image in order to achieve a color balance of each color. For example, Japanese Patent Application Laid-Open No. 7-36
No. 231, the optical density of a reference toner image formed on a photosensitive drum is read, and based on the read result, a toner supply amount, a developing voltage, a charging voltage of the photosensitive drum, and the like are controlled. A method for stabilizing the color balance of a toner image is known. However, when a plurality of image forming units as described in JP-A-7-36246 are used, the photosensitive drum provided in the image forming unit is limited to a small-diameter drum of about φ20 to φ40. Therefore, there is a problem that there is no space around the photosensitive drum for disposing the optical density reading sensor for the reference toner image. In addition, when the intermediate transfer method is used, even when the toner concentration on the photosensitive drum is constant, control cannot be performed when the transfer efficiency on the intermediate transfer body changes, and as a result, the image is finally transferred to the image receiving paper side. The formed toner image has a problem that the color balance is disturbed.

As a means for solving the above-mentioned problem with respect to the color balance, a method of transferring a reference toner image onto an intermediate transfer member and reading the optical density thereof can be considered. In this method, an optical density reading sensor is arranged around the intermediate transfer body, so that a small-diameter photosensitive drum can be used. Further, since information on the toner image density can be obtained in a process close to the final image, an accurate color balance can be obtained. It has advantages such as easy operation. However, when the reference toner image passes through the second transfer position at which the intermediate transfer member and the transfer member abut, the surface of the transfer member is contaminated with the reference toner image. There is a problem that a so-called back stain phenomenon in which a reference toner image adheres is caused.

In order to avoid this back-stain phenomenon, a means for contacting the transfer member with the intermediate transfer member after the reference toner image has passed through the second transfer position can be considered. However,
If the transfer member abuts while the toner image is being transferred to the first transfer position where the photoconductor drum and the intermediate transfer member are in contact, the vibration propagates to the first transfer position.
As a result, there is a problem that the toner image being transferred from the photosensitive drum is disturbed. Further, if the color balance is to be kept constant while the transfer efficiency on the intermediate transfer member is greatly reduced, the toner density on the photosensitive drum must be excessively increased. Therefore, if the toner density is excessively high, there is a problem that the toner adheres to the non-image portion on the photosensitive drum, that is, a so-called fogging phenomenon occurs.

[0016]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and is not affected by fluctuations in the impedance of the intermediate transfer belt due to environmental fluctuations, aging, etc. The transfer can be performed, and the collision energy between the photosensitive drum and the intermediate transfer belt can be absorbed by bending of the intermediate transfer belt and deformation of the conductive member. It is an object of the present invention to provide a color electrophotographic apparatus capable of preventing the surface of an intermediate transfer belt from being damaged.

[0017]

In order to achieve the above object, a color electrophotographic apparatus according to the present invention comprises a plurality of image forming units for forming toner images of different colors on an electrostatic latent image holding member; At the exposure position, an exposure device that performs image exposure on the surface of the electrostatic latent image holding member, and a moving unit that moves the entire image forming unit and sequentially moves the plurality of image forming units to the image forming position, An intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units; a support for the intermediate transfer belt; and a tension surface of the intermediate transfer belt and the static transfer belt. A plurality of support rollers arranged to contact the electrostatic latent image holding member to form a predetermined transfer position; and a plurality of support rollers arranged on a back surface of a stretched surface of the intermediate transfer belt facing the electrostatic latent image holding member. And at least the static A conductive member having elasticity, which contacts the back surface of the intermediate transfer belt in a state where the latent image holding member is in contact with the stretching surface of the intermediate transfer belt, and a toner image on the electrostatic latent image holding member. And a power supply for supplying a voltage of opposite polarity to the conductive member.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is constituted, for example, as follows. The first color electrophotographic apparatus of the present invention includes (1) a rotating electrostatic latent image holder and a developing member having toners of different colors, respectively. A plurality of image forming units that form toner images of different colors, and (2) image exposure on a surface of the electrostatic latent image holder of one of the plurality of image forming units at a predetermined exposure position. Exposure device, and (3) moving means for moving the entire image forming unit, sequentially moving the plurality of image forming units to the exposure position,
(4) an intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units, and (5) supporting the intermediate transfer belt, Bringing the tension surface and the electrostatic latent image holding member into contact with each other,
A plurality of support rollers arranged to form a predetermined transfer position, and (6) arranged at the back of the stretching surface of the intermediate transfer belt facing the electrostatic latent image holding member, at least the electrostatic latent image An elastic conductive member that contacts the back surface of the intermediate transfer belt in a state where the holding member is in contact with the stretching surface of the intermediate transfer belt, and (7) a toner image on the electrostatic latent image holding member. And a power supply for supplying a voltage of the opposite polarity to the conductive member. Further, a second color electrophotographic apparatus according to the present invention includes (1) a rotating electrostatic latent image holding member and a developing member having toners of different colors, respectively. A plurality of image forming units that form toner images of different colors, respectively, and (2) at a predetermined exposure position, on the surface of the electrostatic latent image holding member of one of the plurality of image forming units. An exposure apparatus for performing image exposure; (3)
A moving unit that moves the entire image forming unit and sequentially moves the plurality of image forming units to the exposure position, and (4) a toner image of each color formed by the plurality of image forming units is obtained by superimposing. Carrying a color image and
An intermediate transfer belt having a surface resistance of from 0 ⁷ to 10 ¹² Ω / cm ² , (5) supporting the intermediate transfer belt, and abutting the stretched surface of the intermediate transfer belt with the electrostatic latent image holder. A plurality of support rollers arranged to form a predetermined transfer position, and (6) arranged on the back surface of the stretching surface of the intermediate transfer belt facing the electrostatic latent image holding member, at least the electrostatic A brush-shaped conductive member that comes into contact with the back surface of the intermediate transfer belt in a state where the latent image holding member is in contact with the stretching surface of the intermediate transfer belt, and (7) toner on the electrostatic latent image holding member A power supply for supplying a voltage having a polarity opposite to that of the image to the conductive member. In the above configuration, it is preferable that the brush-shaped conductive member has a configuration in which loop-shaped conductive fibers are supported by a conductive base material.

Further, a third color electrophotographic apparatus according to the present invention includes: (1) each comprising a rotating electrostatic latent image holder and a developing member having toners of different colors; A plurality of image forming units for forming toner images of different colors on the holding member, and (2) the electrostatic latent image holding member of one of the plurality of image forming units at a predetermined exposure position An exposure apparatus that performs image exposure on the surface of (3) moving means for moving the entire image forming unit and sequentially moving the plurality of image forming units to the exposure position,
(4) an intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units, and (5) supporting the intermediate transfer belt, Bringing the tension surface and the electrostatic latent image holding member into contact with each other,
A plurality of support rollers arranged so as to form a predetermined transfer position; and A charge supply member for supplying a charge having a polarity opposite to that of the toner image on the electrostatic latent image holding member to the back of the transfer belt stretching surface,
(7) a power supply for supplying a voltage having a polarity opposite to that of the toner image on the electrostatic latent image holding member to the charge supply member;

Further, a fourth color electrophotographic apparatus according to the present invention includes: (1) each comprising a rotating electrostatic latent image holder and a developing member having toner of different colors; A plurality of image forming units that form toner images of different colors on the holding member, and (2) at a predetermined exposure position, the electrostatic latent image holding member of one of the plurality of image forming units. An exposure apparatus that performs image exposure on the surface of (3) moving means for moving the entire image forming unit and sequentially moving the plurality of image forming units to the exposure position,
(4) an intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units, and (5) supporting the intermediate transfer belt, Bringing the tension surface and the electrostatic latent image holding member into contact with each other,
A plurality of support rollers arranged to form a predetermined transfer position, (6) at least one of the plurality of support rollers, a drive roller for rotationally driving the intermediate transfer belt, (7) An intermediate transfer belt holding member for holding the intermediate transfer belt, and after an operation of moving a predetermined image forming unit from the image forming position among the plurality of image forming units is started, the next image forming unit Until the operation of moving to the image forming position is completed,
The driving of the driving roller is stopped, and the intermediate transfer belt is stopped by the intermediate transfer belt holding member. In the above configuration, it is preferable that the intermediate transfer belt holding member includes a cleaner for cleaning a surface of the intermediate transfer belt, and a support roller for the intermediate transfer belt facing the cleaner via the intermediate transfer belt.

According to a fifth aspect of the present invention, there is provided a color electrophotographic apparatus comprising: (1) a rotating electrostatic latent image holding member; and (2) a developing member for forming a toner image on the electrostatic latent image holding member. And (3) an intermediate transfer belt that carries a color image in which a plurality of color toner images transferred from the electrostatic latent image holder are superimposed, and (4) a plurality of support rollers that stretch the intermediate transfer belt. (5) driving means for rotating and driving the intermediate transfer belt from the start of driving to the end of driving so that the rotation cycle of the intermediate transfer belt becomes an integral multiple, and (6) a predetermined rotation of the intermediate transfer belt. Mark formed at the position, (7) disposed between two support rollers of the plurality of support rollers, a sensor for detecting the mark, and (8) a signal for detecting the mark with the sensor Timing for starting an electrostatic latent image writing operation on the electrostatic latent image holding member based on the timing Control means for controlling the intermediate transfer at a position other than the two support rollers positioned upstream and downstream of the sensor in the direction of movement of the intermediate transfer belt when the mark passes through the sensor. The mark and the sensor are arranged such that there is a region where the driving of the belt is stopped and the intermediate transfer belt is in contact with the plurality of support rollers.

According to a sixth aspect of the present invention, there is provided a color electrophotographic apparatus comprising: (1) a rotating electrostatic latent image holding member; and (2) a developing member for forming a toner image on the electrostatic latent image holding member. (3) an intermediate transfer belt that carries the toner image transferred from the electrostatic latent image holding member, and (4) a support for the intermediate transfer belt, a tension surface of the intermediate transfer belt and the electrostatic A plurality of support rollers arranged to contact the latent image holding member to form a predetermined transfer position, and (5) driving means for driving the intermediate transfer belt, and the image forming operation is completed. Thereafter, the driving of the intermediate transfer belt is stopped at a position different from the contact surface between the intermediate transfer belt and the support roller in a state where the intermediate transfer belt is left before the driving of the image forming operation is started.

Further, a seventh color electrophotographic apparatus according to the present invention comprises: (1) a rotating electrostatic latent image holding member; and (2) a developing member for forming a toner image on the electrostatic latent image holding member. (3) an intermediate transfer belt that carries a toner image transferred from the electrostatic latent image holding member, and (4) a support surface of the intermediate transfer belt, The image forming apparatus includes: a plurality of support rollers arranged to contact the latent image holding member to form a predetermined transfer position; and (5) driving means for driving the intermediate transfer belt. During this time, the intermediate transfer belt is driven to rotate for a predetermined time, and the drive of the intermediate transfer belt is stopped at a position different from the contact surface between the intermediate transfer belt and the support roller before the start of driving.

An eighth color electrophotographic apparatus according to the present invention comprises: (1) a rotating electrostatic latent image holder; and (2) a toner image formed on the electrostatic latent image holder. A developing member for forming a reference toner image in a non-image area located at a rear end of the toner image on the electrostatic latent image holding member; and (3) a toner image and a reference toner transferred from the electrostatic latent image holding member. An intermediate transfer member that carries an image, (4) a reference toner image density sensor that reads the density of the reference toner image transferred onto the intermediate transfer member, and (5) information obtained by the reference toner image density sensor. An information storage unit for storing; and (6) a control unit for controlling a next image forming step based on the information stored in the information storage unit.

According to a ninth color electrophotographic apparatus of the present invention, there are provided (1) a rotating electrostatic latent image holder, and (2) a toner image and a plurality of reference toners on the electrostatic latent image holder. A developing member for forming an image, (3) an intermediate transfer member that carries the toner image and the plurality of reference toner images transferred from the electrostatic latent image holding member, and (4) a voltage applied to the transfer member. And (5) transferring the toner image from the electrostatic latent image holding member onto the intermediate transfer member, and the plurality of reference toner images on the intermediate transfer member, each of which differs depending on the power source. A transfer member for transferring with a voltage, (6) a reference toner image density sensor for reading the densities of the plurality of reference toner images transferred on the intermediate transfer body, and (7) a plurality of reference toner image density sensors obtained by the reference toner image density sensor. Comparing means for comparing information of the reference toner images, and (8) the comparing means Based on the comparison result by, and a control means for controlling one of said toner image transfer step of the toner image forming step to the electrostatic latent image holding member on to the intermediate transfer member.

Hereinafter, the present invention will be described more specifically with reference to the drawings. (First Embodiment) A first embodiment of a color electrophotographic apparatus according to the present invention.
Embodiment (hereinafter referred to as a first color electrophotographic apparatus)
Will be described with reference to FIG. 1 and FIG. 1 and 2, the first color electrophotographic apparatus includes a rotating electrostatic latent image holding member (photosensitive drum) 13 and a developing member 132 having toners of different colors. A plurality of image forming units 12B, 12Y, 12M, and 12C that form toner images of different colors on the photosensitive drum 13; and a photoconductor drum 13 of one of the plurality of image forming units at a predetermined exposure position. An exposure device 15 that performs image exposure on the surface, and image forming units 12B, 12Y, and 12
A moving mechanism (not shown) for moving the entire M and 12C to sequentially move the plurality of image forming units to the exposure position, and a toner image of each color formed by the plurality of image forming units 12B, 12Y, 12M and 12C. An intermediate transfer belt 17 for carrying a color image obtained by superimposition, and an intermediate transfer belt 17
And a plurality of support rollers 19 a, 19 b, 19 c, 20 arranged to form a predetermined transfer position by bringing the stretched surface of the intermediate transfer belt 17 into contact with the photosensitive drum 13.
Is disposed on the back side of the stretched surface of the intermediate transfer belt 17 facing the photosensitive drum 13, and at least
Is in contact with the back surface of the intermediate transfer belt 17 in a state in which the toner is in contact with the stretching surface of the intermediate transfer belt 17, and the toner image on the photosensitive drum 13 is opposite to the elastic conductive member (conductive roller) 21. A power supply (not shown) for supplying a voltage having a polarity to the conductive member 21.

The image forming units 12B, 12Y, 12M,
Reference numeral 12C denotes image forming units corresponding to four colors of black, yellow, magenta, and cyan, respectively, and includes a photosensitive drum 13, a charging member 131, a developing device 132,
A cleaning device 133 and the like are provided. For example, the photosensitive drum 13 mounted on each of the image forming units 12B, 12Y, 12M, and 12C has a diameter of 30 mm and a thickness of 1 mm.
An organic photoconductive film having a thickness of 20 μm was applied on an aluminum substrate of the above. As the charging member 131, a roller-shaped member was used, and the photosensitive drum 13 was negatively charged while being driven by the photosensitive drum 13. The developing device 132 has a 50% diameter of about 8 μm.
50% diameter is about 60μ
m in a weight ratio of 0.5 to 5 wt. % Two-component developing apparatus was used. In the first color electrophotographic apparatus, the image forming units 12B, 12Y, 12
M, the charging potential of the photosensitive drum 13 in the 12C is -700.
V, the exposure potential is -100 V, and the developing voltage is -500.
V was set, and the toner image was visualized.

The four color image forming unit groups 12B, 12Y,
12M and 12C are configured to be rotatable around the center of rotation of the unit group, and when moved in the counterclockwise direction in FIG. 1, the developing device 132 is at the upper position at the image forming position, and the cleaning device 133 is at the lower position. Located in. The exposure device 15
For example, in the case of FIG. 1, the developing device 13 of the image forming unit 12Y
2 and a substantially parallel slit formed between the cleaning device 133 of the image forming unit 12B, and arranged so that the photosensitive drum 13 of the image forming unit 12B can be exposed through the reflecting mirror 16 near the center of rotation. I have. The reflection mirror 16 is fixed regardless of the rotation of the image forming unit 12.

The intermediate transfer belt 17 includes a photosensitive drum 13
To form a first transfer position. As the intermediate transfer belt 17, a belt obtained by dispersing conductive carbon in a polycarbonate resin and having a volume resistivity of about 10 ⁹ Ω · cm was used. The circumferential length of the intermediate transfer belt 17 is A
37 so that at least one image of 4 plates can be retained
7 mm, and its thickness is about 150 μm.
The surface roughness of the intermediate transfer belt 17 was about 3 to 5 μm in terms of 10-point average roughness after molding and the like. The surface roughness can be freely controlled by an abrasive such as sandpaper or polisher. Further, on the surfaces at both ends in the width direction of the intermediate transfer belt 17, a film thickness of about 75 μm and a width of about 10
mm PET tape (not shown) is attached. Urethane rubber ribs (not shown) having a thickness of about 5 mm and a width of about 5 mm are attached to the back surface at both ends in the width direction of the intermediate transfer belt 17 to prevent meandering.

The intermediate transfer unit 18 is detachable from the apparatus main body, and includes an intermediate transfer belt 17, a support roller 19a,
19b, 19c, and a drive roller 20 for transmitting a driving force to the intermediate transfer belt 17 and driving the intermediate transfer belt 17 to rotate. The intermediate transfer belt 17 is stretched by a support roller 19 and a drive roller 20. Support roller 19 and drive roller 20
Are composed of metal rollers. The outer diameter of each of the support rollers 19a and 19b is φ16,
9c and the outer diameter of the drive roller 20 were set to φ30. here,
If the supporting roller 19 and the driving roller 20 are made of a material having low or no rigidity, such as sponge or rubber, the end of the intermediate transfer belt 17 bites, and as a result, the intermediate transfer belt 1
7 differs in the circumferential direction in the width direction, and belt meandering occurs. Therefore, it is preferable that each of the support roller 19 and the drive roller 20 is formed of a highly rigid member such as a metal roller.

The support roller 19 and the drive roller 20
Are grounded respectively. If the intermediate transfer belt 17 is supported while each roller is in a floating state, the charges supplied during the transfer are accumulated on the back surface of the intermediate transfer belt 17, and the transfer electric field is generated before the intermediate transfer belt 17 and the photosensitive drum come into contact with each other. Are formed between the two. Therefore, there is a possibility that the toner flies before reaching the transfer position and the toner adheres in front of the image area, that is, a so-called forward jump phenomenon may occur. Therefore, the supporting roller 19 and the driving roller 20
Is preferably grounded. If the resistance component from the intermediate transfer belt 17 to the ground via the rollers 19 and 20 is small, the charge supplied to the back of the intermediate transfer belt 17 flows to the ground via the rollers 19 and 20 and
As a result, a large amount of transfer current is required. Therefore, it is preferable that the supporting roller 19 and the driving roller 20 are grounded via a constant voltage generating element such as a resistance element or a varistor.

The conductive roller 21 is a sponge roller having a conductive sponge provided on a metal shaft. As the material of the conductive sponge, a material obtained by adding an ion conductive material of a lithium salt to polyurethane is used.
It is 50 ° or less on the IS A scale. Conductive roller 2
Reference numeral 1 is arranged so that the photosensitive drum 13 contacts the back surface of the intermediate transfer belt 17 when the intermediate transfer belt 17 is urged. The metal shaft of the conductive roller 21 is connected to the grounded photosensitive drum 13 and the intermediate transfer belt 17.
Is connected to a primary transfer power supply (not shown) for supplying a DC voltage in order to apply a transfer voltage between the two. +300 V for the first color as the applied voltage during transfer by the primary transfer power supply
DC voltage was applied.

The secondary transfer roller 23 is used for the intermediate transfer belt 1
7 and contacts the drive roller 20 to form a second transfer position. As the secondary transfer roller 23, the conductive roller 2
A member having the same configuration and material as in Example 1 was used. Also, the outer diameter ratio of the drive roller 20 to the secondary transfer roller 23 (the value obtained by dividing the outer diameter of the secondary transfer roller 23 by the outer diameter of the drive roller 20)
Was set to 0.6 or less. If the outer diameter ratio exceeds 0.6, the color toner on the intermediate transfer belt 17 flies toward the image receiving paper 22 before the intermediate transfer belt 17 comes into contact with the photosensitive drum 13. As a result, the periphery of the image portion becomes a blurred image. Further, the secondary transfer roller 23 is connected to the intermediate transfer belt 17.
It is connected to a secondary transfer power supply (not shown) for forming a retransfer voltage between the image forming apparatus and the image receiving paper 22. The applied voltage at the time of transfer by the secondary transfer power supply was + 700V.

The metal paper receiving member neutralizing member 24 is arranged so that the electric charge supplied to the back of the image receiving paper 22 at the second transfer position is self-discharged toward the image receiving paper neutralizing member 24, and is grounded. . Thereby, the winding of the image receiving paper 22 around the intermediate transfer belt 17 due to the electrostatic force is prevented, and the image receiving paper 22 is separated from the intermediate transfer belt 17. The cleaning device 25 is for removing waste toner remaining on the intermediate transfer belt 17 after the transfer from the intermediate transfer belt 17 to the image receiving paper 22 is completed, and contacts the surface of the intermediate transfer belt 17 to remove the waste toner. The cleaning device 25 includes a rubber blade for scraping and an entrance seal on the film for preventing waste toner from spilling from the cleaning device 25.

The paper feed roller 26 conveys the image receiving paper 22 one by one from a paper feed tray. The pair of timing rollers 27 feeds the fed image receiving paper 22 to the second transfer position in accordance with the image signal. The timing roller 27 includes
A scraper or a pad (neither is shown) is brought into contact with the scraper or a pad to remove paper dust attached on the timing roller 27. The fixing device 28 fixes the toner image on the image receiving paper 22 after the transfer. After the fixing step, the image receiving paper 22 is discharged out of the apparatus. In the first color electrophotographic apparatus, the photosensitive drums 13 of the image forming units 12B, 12Y, 12M, and 12C were rotated at a speed of 33 mm / s. The speed difference between the photosensitive drum 13 of each of the image forming units 12B, 12Y, 12M, and 12C and the intermediate transfer belt 17 is about 1 to 5%.
Is appropriate. Secondary transfer roller 23 and intermediate transfer belt 1
7 was also rotated at substantially the same speed difference.

Next, a color image forming operation will be described with reference to FIG. When printing a color image, images are formed in the order of black, cyan, magenta, and yellow. First, the photosensitive drum 1 of the black image forming unit 12B
The entire image forming unit group rotates so that the three surfaces can be exposed. In the black image forming unit 12B,
As in the case of a normal black and white printer, a toner image is formed through charging, latent image formation, and development steps. This black toner image is transferred onto the intermediate transfer belt 17 by the transfer voltage supplied to the conductive roller 21 from the primary transfer power supply.
During a series of operations for transferring a toner image to the intermediate transfer belt 17, the cleaning blade and the entrance seal attached to the cleaning device 25 are separated from the surface of the intermediate transfer belt 17.

When the transfer of the black toner image from the photosensitive drum 13 in the black image forming unit 12B to the intermediate transfer belt 17 is completed and the rotation of the intermediate transfer belt 17 is stopped, the image forming unit groups 12B, 12Y, and 12M. , 1
2C rotates, the next cyan image forming unit 12C moves to the image forming position, and performs the same visualization process as the previous black toner image. The cyan toner image is transferred to the cyan image forming unit 12
At the same time that the intermediate transfer belt 17 is formed on the photosensitive drum 13 in C, the intermediate transfer belt 17 resumes its rotation with its position aligned with the leading end of the black toner image on the intermediate transfer belt 17. Simultaneously with this rotation, a transfer voltage is applied from the primary transfer power supply to the conductive roller 21, and the cyan toner image is transferred onto the black toner image carried on the intermediate transfer belt 17 in a superimposed manner.

As in the above series of operations, the magenta toner image is transferred onto the black and cyan toner images carried on the intermediate transfer belt 17 in a superimposed manner. Then 4
A yellow toner image is formed on the photoreceptor drum 13 in the yellow image forming unit 12Y, a transfer voltage is applied to the conductive roller 21, and transfer of the yellow toner image to the intermediate transfer belt 17 is started. . The cleaning blade and the entrance seal attached to the secondary transfer roller 23 and the cleaning device 25 come into contact with the area on the intermediate transfer belt 17 where the toner image does not exist at a proper timing. A transfer voltage is applied to the secondary transfer roller 23 at the same time as the contact with the intermediate transfer belt 17.

On the other hand, the image receiving paper 22 is transported between a pair of timing rollers 27 by a paper feed roller 26. Thereafter, the intermediate transfer belt 17 is driven by the timing roller 27.
Conveying of the image receiving paper 22 is started in synchronization with the leading edge of the upper image. The intermediate transfer belt 1 is placed on the image receiving paper 22.
The toner image on the intermediate transfer belt 17 is transferred at the same time as it passes through the transfer area where the secondary transfer roller 7 and the secondary transfer roller 23 are in contact. Thereafter, the toner is fixed on the image receiving paper 22 by the fixing device 28, and the image receiving paper 22 is discharged out of the apparatus. A color image is obtained by the above operation.

After the above steps, the secondary transfer roller 23 is separated from the intermediate transfer belt 17 again, and the transfer voltage supplied to the secondary transfer roller 23 is also turned off. On the other hand, the cleaning blade attached to the cleaning device 25 and the entrance seal are kept in contact with the intermediate transfer belt 17. Further, the image forming unit groups 12B, 12Y, 12
M and 12C rotate and stop in a state of non-contact with the intermediate transfer belt 17. During the period when the first color electrophotographic apparatus main body is not operating, the intermediate transfer belt 17 and the image forming unit 1
2 and between the intermediate transfer belts 17 and 2
By maintaining a state of non-contact with the next transfer roller 23, deformation of the intermediate transfer belt 17 and contamination of the non-contact member by additives contained in the contact member are prevented.

Next, the image forming units 12B, 12Y, 1
The operation near the first transfer position at the time of replacement of 2M and 12C will be described with reference to FIG. 2 showing the configuration near the first transfer position. As shown in FIG. 2, both ends of the shaft of the conductive roller 21 are supported by support springs 29. The end of the support spring 29 opposite to the conductive roller 21 side is fixed. The intermediate transfer belt 1 is driven by the conductive roller 21.
The spring constant of the support spring 29 is appropriately adjusted so as not to urge. In the first color electrophotographic apparatus, a spring having a spring constant of about 200 gf / mm is used, and the conductive roller 21 is slightly moved to the intermediate transfer belt 17.
Contacted.

The arcs shown by the dotted lines in FIG. 2 indicate the image forming units 12B, 12Y, 12M, 12M when the image forming unit groups 12B, 12Y, 12M, 12C are rotating.
C is the trajectory of the tip of the photosensitive drum 13 in C. FIG.
A straight line indicated by a dashed line in the drawing indicates a stretched surface of the intermediate transfer belt 17 in a state where the photosensitive drum 13 is not in contact with the drum.

After the step of forming a toner image of a predetermined color is completed,
The entire four image forming unit groups 12B, 12Y, 12M, and 12C rotate to move to the next color toner image forming process. Image forming unit group 12B, 12Y, 12M, 12C
During the rotation of, the tip of the photosensitive drum 13 contacts the intermediate transfer belt 17 at a point A where the dotted arc and the dashed line intersect. Since the members other than the intermediate transfer belt 17 among the members constituting the intermediate transfer unit 18 do not exist inside the circular arc shown by the dotted line, the photosensitive drum 13 reaches the point A until the end thereof reaches the point A. During this time, it does not collide with other members.

After passing through the point A, the tip of the photosensitive drum 13 moves to the point B facing the conductive roller 21 while applying a load inward on the stretching surface of the intermediate transfer belt 17. By this load application, the stretched surface of the intermediate transfer belt 17 is urged inward, and at the same time, the supporting spring 29
Is compressed. When the tip of the photosensitive drum 13 reaches the point B, the image forming unit groups 12B, 12Y, 12M, 12
The rotation of C stops. At this time, the photosensitive drum 13
It comes into contact with the conductive roller 21 via the intermediate transfer belt 17. The sponge layer of the conductive roller 21 is
It is distorted by the pressing force from 3. This distorted area D becomes the first transfer position. Then, the photosensitive drum 1
The intermediate transfer belt 3 and the intermediate transfer belt 17 are driven to rotate in a direction indicated by an arrow in FIG. 2 to start a process of forming a toner image on the intermediate transfer belt 17. After the toner image is transferred to the intermediate transfer belt 17, the photosensitive drum 13 and the intermediate transfer belt 17
Means that the rotational drive is stopped. Thereafter, in order to proceed to the next color toner image forming process, the four-color image forming unit group 12 is formed.
B, 12Y, 12M, and 12C rotate again. At this time, the tip of the photosensitive drum 13 moves in the direction of the intersection C between the dotted arc and the dashed line, and separates from the intermediate transfer belt 17 at the position of the point C.

As described above, the image forming units 12B, 1
The surface of the photosensitive drum 13 exposed to the outside from 2Y, 12M, and 12C contacts only the easily deformable member such as the surface of the intermediate transfer belt 17 and the conductive roller 21 via the intermediate transfer belt 17. Further, the load applied to the intermediate transfer belt 17 is absorbed by the support spring 29 abutting on the conductive roller 21. Thereby, the photosensitive drum 13
Since no impact is applied to the surface or the surface of the intermediate transfer belt 17, the problem of damage to the surface of the photosensitive drum 13 and the surface of the intermediate transfer belt 17 can be avoided.

In the first color electrophotographic apparatus, a conductive roller 21 having a conductive sponge provided on a metal shaft is used as the conductive member 21. Instead, a metal roller supported by a spring is used. May be used. However, in order to avoid collision with the photosensitive drum 13, the spring constant for supporting the metal roller needs to be set lower than the value described in the above description.

(Second Embodiment) A second embodiment of the color electrophotographic apparatus of the present invention (hereinafter referred to as a second color electrophotographic apparatus) will be described with reference to FIGS. The second color electrophotographic apparatus uses a brush-shaped conductive member 31 instead of the conductive roller 21 in the first color electrophotographic apparatus. Therefore, portions common to those of the first color electrophotographic apparatus shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The second color electrophotographic apparatus, like the first color electrophotographic apparatus shown in FIG. 1, uses a rotating electrostatic latent image holder (photosensitive drum) 13 and a toner of different colors. And a developing member 132 having the photosensitive drum 1
And a plurality of image forming units 12B, 12Y, 12M, and 12C for forming toner images of different colors on the photosensitive drum 13 of one of the plurality of image forming units at a predetermined exposure position. An exposure device 15 for performing image exposure on the surface, and image forming units 12B, 12Y, and 12
A moving mechanism (not shown) that moves the entire M and 12C and sequentially moves a plurality of image forming units to the exposure position.
And a plurality of image forming units 12B, 12Y, 12M, 1
An intermediate transfer belt 17 that carries a color image obtained by superimposing toner images of respective colors formed in 2C and has a surface resistance of 10 ⁷ to 10 ¹² Ω / cm ² ;
And a plurality of support rollers 19 a, 19 b, 19 c, 20 arranged to form a predetermined transfer position by bringing the stretched surface of the intermediate transfer belt 17 into contact with the photosensitive drum 13.
Is disposed on the back side of the stretched surface of the intermediate transfer belt 17 facing the photosensitive drum 13, and at least
Is in contact with the back surface of the intermediate transfer belt 17 in a state where the brush-like conductive member 31 is in contact with the stretched surface of the intermediate transfer belt 17, and a voltage having a polarity opposite to that of the toner image on the photosensitive drum 13 is applied to the brush-like conductive member 31. And a power supply (not shown) for supplying to the conductive member 31.

Examples of the material of the brush fibers of the brush-like conductive member 31 include metals such as tungsten, aluminum, copper, and stainless steel, synthetic fibers in which carbon or carbon fibers are dispersed or laminated, and high crystallinity. Instead of a material, an amorphous metal fiber such as an amorphous metal fiber such as cobalt or a non-metallic amorphous fiber such as amorphous carbon can be used. Further, a combination or knitting of these materials may be used. The electric resistance of the brush fibers of the brush-like conductive member 31 is set to 10 ¹⁰ Ω ·
cm or less is preferred. The mounting angle of the brush-like conductive member 31 from the back of the intermediate transfer belt 17 is set so that the contact area between the intermediate transfer belt 17 and the brush fibers is large and the intermediate transfer belt 17 is not greatly deformed. The angle is preferably 45 degrees or less with respect to the 17th surface. In the second color electrophotographic apparatus, an amorphous cobalt fiber having a wire diameter of about 15 μm was used in a brush shape. further,
The brush fibers had a free length of about 10 mm, and were arranged such that the length of the brush fibers in contact with the intermediate transfer belt 17 was about 5 mm. The mounting angle was set to about 30 degrees. Also, the photosensitive drum 1 is attached to the brush-shaped conductive member 31.
A power supply (not shown) for supplying a voltage having a polarity opposite to that of the toner image on No. 3 was connected, and a constant voltage of +300 V was applied during transfer.

The other structure shown in FIG. 3 is the same as that of the first color electrophotographic apparatus shown in FIG. By using the above configuration, the same effect as that of the first color electrophotographic apparatus can be obtained. That is, the surface of the photosensitive drum 13 exposed from the image forming units 12B, 12Y, 12M, and 12C is the surface of the intermediate transfer belt 17 and the brush-like conductive member 3 via the intermediate transfer belt 17.
Contact only with easily deformable members such as 1. Therefore, the load applied to the intermediate transfer belt 17 is absorbed by the deformation of these members. Thereby, since no impact is applied to the surfaces of the photosensitive drum 13 and the intermediate transfer belt 17, the problem of damage to the surfaces of the photosensitive drum 13 and the intermediate transfer belt 17 can be avoided. Furthermore, first, the brush-shaped conductive member 31 is inexpensive compared to the conductive roller 21 of the electrophotographic apparatus, so that a low-cost color image forming apparatus can be provided.

In the second color electrophotographic apparatus, the intermediate transfer belt 17 used in this embodiment is
A belt having a surface resistance of ⁷ to 10 ¹² Ω / cm ² was used. When an intermediate transfer belt showing a surface resistance value higher than the above range was used, in some places in the toner image after transfer,
A sweep-like image noise to which the toner was not transferred occurred. The cause of such a phenomenon is that the brush-like conductive member 3
This is because the transfer charge was not sufficiently supplied to the area between the one brush fibers. Therefore, in order to realize uniform transfer without generation of a sweep-like image noise, the intermediate transfer belt 17 is set to be lower than the upper limit of the above range so that the transfer charge is transferred between the brush fibers on the back surface of the intermediate transfer belt 17. It is necessary to set the surface resistance.

On the other hand, when an intermediate transfer belt having a surface resistance lower than the above range was used,
There is a problem that the transfer charge flows into the support rollers 19a, 19b, and 19c supporting the image transfer. For this reason, the electric field intensity required for transfer is weakened, and the transfer efficiency is reduced. Therefore, it is necessary to set the surface resistance of the intermediate transfer belt 17 to a value not lower than the lower limit of the above range.

Further, when the brush-shaped conductive member 31 is used continuously, there is a problem that the brush fibers come off, and the above-mentioned sweep-like image noise is generated. In order to avoid such bristle of the brush fiber, it is preferable to use a brush-like conductive member in which the brush fiber is formed in a loop as shown in FIG. In FIG. 4, the brush fibers 32 are supported by a conductive brush fiber supporting substrate 33, and the brush fibers 32 and the brush fiber supporting substrate 33 are bonded by a conductive adhesive. Further, the loops of the brush fibers 32 are arranged so as to overlap each other. Further, as shown by the area A in FIG. 4, the loop fibers 32 abut on the back surface of the intermediate transfer belt in the overlapping area. As described above, by forming the brush fibers 32 in a loop shape, both ends of the brush fibers 32 are fixed, and the occurrence of hair loss is suppressed. Further, since the brush fibers 32 are in contact with the back surface of the intermediate transfer belt in the area A, the brush fibers 32 exist in the entire width direction of the intermediate transfer belt. As a result, a sweep phenomenon caused by insufficient supply of transfer charges in the region between the brush fibers is prevented, and uniform transfer can be performed.

Third Embodiment Next, a third embodiment of the color electrophotographic apparatus of the present invention (hereinafter, referred to as a third color electrophotographic apparatus) will be described with reference to FIG. Third
This color electrophotographic apparatus uses a corona charger 34 instead of the conductive roller 21 used in the first color electrophotographic apparatus. Therefore, portions common to those of the first color electrophotographic apparatus shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The third color electrophotographic apparatus includes a rotating electrostatic latent image holding member (photosensitive drum) 13 and a developing member 132 having toners of different colors. A plurality of image forming units 12B, 12Y, 12M, and 12C that form toner images of different colors
An exposure device 15 for performing image exposure on the surface of the photosensitive drum 13 of one of the plurality of image forming units at a predetermined exposure position; and image forming units 12B and 12
A moving mechanism (not shown) for moving the entire Y, 12M, 12C to sequentially move the plurality of image forming units to the exposure position, and a plurality of image forming units 12B, 12Y, 12
M, 12C, an intermediate transfer belt 17 that carries a color image obtained by superimposing the toner images of the respective colors, an intermediate transfer belt 17 is supported, and a stretched surface of the intermediate transfer belt 17 and the photosensitive drum 13 And a plurality of support rollers 19a and 19B arranged to form a predetermined transfer position.
19C and 20 are disposed in a non-contact state on the back surface of the stretched surface of the intermediate transfer belt 17 facing the photosensitive drum 13;
A charge supply member (corona charger) 34 for supplying a charge having a polarity opposite to that of the toner image on the photosensitive drum 13 to the back surface of the intermediate transfer belt stretching surface; A power supply (not shown) for supplying a voltage to the corona charger 34.

As shown in FIG. 5, the corona charger 34 is composed of a metal wire and a grounded conductive shield. The shield of the corona charger 34 is a metal case having a height of 10 mm and a width of 15 mm, and has a substantially U shape.
The open portion faces the intermediate transfer belt 17. As the metal wire, a tungsten wire of 80 μm is arranged at a substantially central portion of the shield case, and is approximately 1 mm away from the back surface of the intermediate transfer belt 17.
At a position of 0 mm, a power supply (not shown) for supplying a voltage having a polarity opposite to that of the toner image on the photosensitive drum 13 is connected. In the third color electrophotographic apparatus, a constant voltage of +4 kV was applied to the metal wire of the corona charger.

The other structure shown in FIG. 5 is the same as that of the first color electrophotographic apparatus shown in FIG. By using the above configuration, the same effect as that of the first color electrophotographic apparatus can be obtained. That is, since the corona charger 34 does not contact the intermediate transfer belt 17, the surface of the photosensitive drum 13 exposed from the image forming units 12B, 12Y, 12M, and 12C is
7 Contact only the surface. Therefore, the load applied to the intermediate transfer belt 17 due to the bending of the intermediate transfer belt 17 is absorbed, and no impact is applied to the surfaces of the photosensitive drum 13 and the intermediate transfer belt 17. The problem of surface damage can be avoided.

Further, in the third color electrophotographic apparatus,
Compared with the configuration of the first and second color electrophotographic apparatuses, since a member for pressing the photosensitive drum 13 via the intermediate transfer belt 17 is not used, the photosensitive drum 1 during transfer is not used.
The load applied to the toner image on No. 3 becomes the smallest. As a result, the mechanical adhesion between the surface of the photoconductor drum 13 and the toner particles is strengthened, and the so-called hollow phenomenon, in which the central portion of the line drawing is not transferred, is suppressed.

(Fourth Embodiment) Next, a fourth embodiment (hereinafter, referred to as a fourth color electrophotographic apparatus) of a color electrophotographic apparatus of the present invention will be described with reference to FIG. FIG.
FIG. 9 is a perspective view showing a configuration near a first transfer position in a fourth color electrophotographic apparatus. In addition, the first shown in FIG.
The members denoted by the same reference numerals as those of the color electrophotographic apparatus are substantially the same, and the description thereof will be omitted.

The fourth color electrophotographic apparatus includes a rotating electrostatic latent image holding member (photosensitive belt) 13 and a developing member 132 having toners of different colors. A plurality of image forming units 12B, 12Y, 12M, 12C for forming toner images of different colors
An exposure device 15 for performing image exposure on the surface of the photosensitive drum 13 of one of the plurality of image forming units at a predetermined exposure position; and image forming units 12B and 12
A moving mechanism (not shown) for moving the entire Y, 12M, 12C to sequentially move the plurality of image forming units to the exposure position, and a plurality of image forming units 12B, 12Y, 12
M, 12C, an intermediate transfer belt 17 that carries a color image obtained by superimposing the toner images of the respective colors, an intermediate transfer belt 17 is supported, and a stretched surface of the intermediate transfer belt 17 and the photosensitive drum 13 And a plurality of support rollers 19a, 19b arranged so as to form a predetermined transfer position.
19c, 20 and a plurality of support rollers 19a, 19b, 1
9c and 20, each of which includes a driving roller 20 that rotationally drives the intermediate transfer belt 17 and an intermediate transfer belt holding member (cam 36) that holds the intermediate transfer belt 17; Forming units 12B, 12
From the start of the operation of moving a predetermined image forming unit of the Y, 12M, and 12C from the image forming position to the completion of the operation of moving the next image forming unit to the image forming position, the driving roller 20 Is stopped, and the intermediate transfer belt 17 is stopped by the intermediate transfer belt holding member 36.

As shown in FIG. 6, a reinforcing tape 38 is provided near both ends of the intermediate transfer belt 17 to reinforce the ends of the intermediate transfer belt 17. The cam 36 is eccentrically attached to the cam support shaft 37, and has a rubber layer on the surface. By rotating the cam support shaft 37 in the direction of arrow A in FIG.
The support roller 19b is pressed into contact with the intermediate transfer belt 7 to hold the intermediate transfer belt 17 therebetween. The cam 36 is connected to the intermediate transfer belt 17.
Are provided so as to oppose only near both ends of the reinforcing tape 38, and are pressed against only the reinforcing tape 38. As a result, the toner image carried on the intermediate transfer belt 17 is not disturbed, and the cam 36 is not stained with the toner.

A slit-like detection hole 39 provided on the intermediate transfer belt 17 is provided. Here, when tension is applied to the intermediate transfer belt 17, stress is concentrated on each corner of the detection hole 39, and a crack is generated. For this reason, it is preferable to cut the side of the detection hole 39 parallel to the moving direction of the intermediate transfer belt 17 to avoid stress concentration. A sensor 40 including an LED and a light receiving element is provided near one end of the intermediate transfer belt 17 and has a detection hole 3.
9 is detected. When the detection hole 39 is detected by the sensor 40, the start timing of writing the electrostatic latent image on the photosensitive drum 13 is controlled based on the signal to that effect.

Next, referring to FIG. 6, the image forming unit 12 will be described.
The operation at the time of moving (exchanging) B, 12Y, 12M, and 12C will be described. After the completion of the toner image forming process of the predetermined color, first, the driving of the intermediate transfer belt 17 is stopped. After the driving of the intermediate transfer belt 17 is stopped, the cam support shaft 37 is stopped.
Rotate along the arrow A, and the cam 36 moves to the position shown by the solid line in FIG. As a result, the intermediate transfer belt 17 is held between the cam 36 and the support roller 19b. At this time, the detection hole 39 on the intermediate transfer belt is stopped before the sensor 40.

To proceed to the next color toner image forming step,
Image forming unit groups 12B, 12Y, 12M, 12C
The whole rotates in the direction of arrow B. During the rotation of the image forming unit, the photosensitive drum 13 moves while contacting the surface of the intermediate transfer belt 17 until it reaches the position shown by the solid line in FIG. At this time, a load is applied to the intermediate transfer belt in the direction of arrow C. However, since the intermediate transfer belt 17 is sandwiched between the cam 36 and the support roller 19b, the intermediate transfer belt 17 remains stationary.

Next, the photosensitive drum 13 reaches the position indicated by the solid line in FIG.
When the rotation of Y, 12M, and 12C stops, the cam support shaft 3
7 rotates in the direction of arrow A, and the cam 36 moves to the position shown by the dotted line in FIG. Thereafter, the photosensitive drum 13 and the intermediate transfer belt 17 start rotating and driving, and the formation of the next color toner image on the intermediate transfer belt 17 is started.

After the toner image is transferred to the intermediate transfer belt 17, the rotation of the photosensitive drum 13 and the intermediate transfer belt 17 is stopped. After the driving of the intermediate transfer belt 17 is stopped, the cam support shaft 37 rotates again along the arrow A, and the cam 36 moves to the position shown by the solid line in FIG.

As described above, the image forming units 12B, 1
In the movement (replacement) process of the 2Y, 12M, and 12C, the photosensitive drum 13 and the intermediate transfer belt 17 come into contact with each other, and a load for generating a slip is applied. However, the intermediate transfer belt 17 is moved in advance by the cam 36 and the support roller 19b. By sandwiching, the slip of the intermediate transfer belt 17 can be avoided. As a result, the detection hole 39 on the intermediate transfer belt 17 is reliably stopped before the sensor 40, so that it is possible to quickly proceed to the next color toner image forming step.

In the fourth color electrophotographic apparatus, the cam 36 is used as a member for holding the intermediate transfer belt 17. However, a cleaning blade (not shown) for cleaning the surface of the intermediate transfer belt 17 holds the intermediate transfer belt 17. It may be used also as a member. In this case, the number of parts can be reduced by using the cleaning blade, and an inexpensive color electrophotographic apparatus can be provided. However, when the intermediate transfer belt 17 is nipped by the cleaning blade, the contact position between the intermediate transfer belt 17 and the cleaning blade must be in a non-image area.

In the fourth color electrophotographic apparatus, the detection hole 39 is provided in the intermediate transfer belt 17 in order to detect the position of the intermediate transfer belt 17. As described above, the detection hole 39 is cracked. Therefore, there is a possibility that the life of the intermediate transfer belt 17 is shortened. For this reason, for example, a detection method in which the stress acting on the belt tension is not concentrated, such as attaching a seal having a different light reflectance to the surface of the intermediate transfer belt 17 and detecting a change in the reflectance, may be used.

(Fifth Embodiment) Next, a fifth embodiment of a color electrophotographic apparatus according to the present invention (hereinafter referred to as a fifth color electrophotographic apparatus) will be described with reference to FIGS. 7 and 8. I do. FIG. 7 is a diagram showing a configuration around the intermediate transfer belt 17 of the fifth color electrophotographic apparatus.
(B) and (c) are diagrams for explaining the deformation phenomenon of the intermediate transfer belt 17. In addition, the first shown in FIG.
The members denoted by the same reference numerals as those of the color electrophotographic apparatus are substantially the same, and the description thereof will be omitted.

The fifth color electrophotographic apparatus comprises a rotating electrostatic latent image holder (photosensitive drum) 13 and a photosensitive drum 1
A developing member for forming a toner image on the photosensitive drum 1;
An intermediate transfer belt 17 that carries a color image in which a plurality of color toner images transferred from above are superimposed;
7, a plurality of support rollers 19a, 19b, 19
c, 20; a drive mechanism (20, 44) for rotating the intermediate transfer belt from the start to the end of the drive so that the rotation cycle of the intermediate transfer belt 17 becomes an integral multiple; Mark 39 formed at a predetermined position
And two support rollers 19b among the plurality of support rollers,
20 and a sensor 40 for detecting the mark 39
And a signal detected by the sensor 40 to detect the mark,
A control circuit 41 for controlling a timing of starting an electrostatic latent image writing operation on the photosensitive drum 13, wherein when the mark 39 passes through the sensor 40, At a position other than the two support rollers 19b and 20 located on the downstream side, the intermediate transfer belt 1 is driven in a state where the driving of the intermediate transfer belt 17 is stopped.
The mark 39 and the sensor 40 are arranged so that there is an area that has been in contact with the plurality of support rollers 19a, 19b, 19c, and 20.

As shown in FIG. 7, the exposure apparatus control circuit 41
Includes a timer 42, an image formation start signal transmitter 43, a counter 46, a motor stop signal generator 47, and the like. The timer 42 is set by an input signal from the sensor 40. After the time set by the timer 42 has elapsed, a time-up signal is output to the image formation start signal transmitter 43. The rotation phase signal of the polygon mirror provided in the exposure device 15 is output from the exposure device 15 to the image formation start signal transmitter 43. The image formation start signal transmitter 43 to which the time-up signal and the polygon mirror rotation phase signal have been input is adjusted in phase with the polygon mirror.
An exposure light beam for image formation is irradiated onto the photosensitive drum 13 to start forming an electrostatic latent image.

The driving roller 20 of the intermediate transfer belt 17
Drive control is performed by the exposure apparatus control circuit 41 via a motor 44 and an encoder 45. The number of pulse signals from the encoder 45 is set in the counter 46 so that the number of rotations of the intermediate transfer belt 17 during the image forming period is an integral multiple of the period of the intermediate transfer belt 17. Further, a motor stop signal transmitter 47 is connected to the counter 46. The motor stop signal transmitter 47 outputs a stop signal to the motor 44 at the same time as the count-up signal from the counter 46 is input, and stops the rotation of the drive roller 20.

Next, the operation when the intermediate transfer belt 17 is driven to rotate will be described. FIG. 8 shows the intermediate transfer belt 1.
7 is a cross-sectional view of a traveling path, where (a) is at a stop, (b) is at the start of rotational driving, and (c) is a state when a detection hole 39 of the intermediate transfer belt 17 has been conveyed to a sensor 40 position. Are respectively shown. In FIG. 8A, the detection hole 39 is disposed substantially at the center between the two support rollers 19a and 19b. Further, the sensor 40 is connected to the support roller 19.
It is disposed substantially at the center between b and the drive roller 20. At this time, compared with the belt travel distance between the support rollers 19a and 19b,
Each roller is disposed so that the belt traveling distance to the belt becomes long. As shown in FIG. 8A, the intermediate transfer belt 17
Is left for a long time while applying tension to the intermediate transfer belt 17 in the areas A1, A2, A3, and A4 of the intermediate transfer belt 17 that are wound around each roller.
And the intermediate transfer belt 17 is deformed according to the curvature of each roller. In particular, the areas A1 and A1 wound around the support rollers 19a and 19b having a small outer diameter.
2, the amount of belt deformation increases.

As shown in FIG. 8B, when the image forming operation is started, the deformed areas A1, A2, A3, and A4 move with the rotation of the intermediate transfer belt 17.
For example, when the deformation area A1 passes through the support roller 19b, the support position of the intermediate transfer belt 17 at the support roller 19b changes. As a result, a phenomenon occurs in which the original traveling path of the intermediate transfer belt 17 shown by the solid line in FIG. At this time, the detection hole 39 is located before the sensor 40.
When the intermediate transfer belt 17 further travels and the deformation area A1 has passed through the support roller 19b, the intermediate transfer belt 17
Runs stably.

Further, the intermediate transfer belt 17 travels, and FIG.
It is assumed that the detection hole 39 has reached the position of the sensor 40 as shown in FIG. At this time, the deformation area A2 is
Since it has not reached 0, the detection hole 39 is detected before the displacement (flapping) of the belt running path occurs again. When a detection signal of the detection hole 39 is input from the sensor 40 to the exposure device control circuit 41, the exposure device 15 starts an electrostatic latent image writing operation on the photosensitive drum 13 at a predetermined timing. After the transfer of the toner image onto the intermediate transfer belt 17 is completed, the intermediate transfer belt 17 starts from the start of the image forming operation.
The drive of the intermediate transfer belt 17 is stopped when the rotation speed of the intermediate transfer belt 17 becomes an integral multiple of the period of the intermediate transfer belt 17. As a result, each deformation area A1, A2, A of the intermediate transfer belt 17
3, A4 stops at the fixed position shown in FIG.

As described above, the deformation areas A1, A2, A3, and A4 of the intermediate transfer belt 17 correspond to the respective support rollers 19a and 1a.
When passing over the belts 9b, 19c and 20, a displacement (fluttering) phenomenon of the belt running path occurs. If the detection hole 39 is detected while the belt traveling path is being displaced, the surface of the intermediate transfer belt 17 moves up and down, and the sensor 40
Since the running distance to the vehicle varies, the detection timing may be different for each color. As a result, the timing of starting the formation of the electrostatic latent image changes for each color, causing an image shift between the toner images of each color.

On the other hand, in the fifth color electrophotographic apparatus, the rotation speed of the intermediate transfer belt 17 is
Since the intermediate transfer belt 17 is driven so as to be an integral multiple of the period, the belt deformation areas A1, A2, A3, and A4 are always located at fixed positions. Therefore, displacement (fluttering) of the belt traveling path is prevented, and a stable belt traveling path is secured. Further, when the detection hole 39 passes through the position of the sensor 40, since the belt deformation areas A1, A2, A3, and A4 are not on the respective support rollers 19a, 19b, 19c, and 20, there is no displacement (flapping) phenomenon. The detection hole 39 can be detected on the belt running surface thus set. Thereby, the timing of starting the electrostatic latent image of each color can be made the same,
A color toner image without image shift can be obtained.

(Sixth and Seventh Embodiments) Next, the sixth and seventh embodiments of the color electrophotographic apparatus of the present invention (hereinafter referred to as sixth and seventh color electrophotographic apparatuses) will be described. This will be described with reference to FIGS. FIG. 9 shows the sixth
10A and 10B are diagrams illustrating a configuration around the intermediate transfer belt 17 in the seventh color electrophotographic apparatus, and FIGS. 10A and 10B are diagrams illustrating a stop position of the intermediate transfer belt 17. Note that the members denoted by the same reference numerals as those of the first color electrophotographic apparatus shown in FIG. 1 are substantially the same, and the description thereof will be omitted.

The sixth color electrophotographic apparatus comprises a rotating electrostatic latent image holder (photosensitive drum) 13 and a photosensitive drum 1
A developing member for forming a toner image on the photosensitive drum 1;
3, an intermediate transfer belt 17 carrying the toner image transferred from above, the intermediate transfer belt 17 is supported, and a stretched surface of the intermediate transfer belt 17 is brought into contact with the photosensitive drum 13 to form a predetermined transfer position. Support rollers 1 arranged to be
9A, 19B, 19C, and 20; and a drive mechanism (20, 44) for driving the intermediate transfer belt 17. In a state where the image forming operation is completed and left unattended before starting the image forming operation. The drive of the intermediate transfer belt 17 is stopped at a position different from the contact surface between the intermediate transfer belt 17 and the support rollers 19a, 19B, 19C, 20.

The seventh color electrophotographic apparatus comprises a rotating electrostatic latent image holder (photosensitive drum) 13, a developing member for forming a toner image on the photosensitive drum 13, and a photosensitive drum 13. An intermediate transfer belt 17 that carries the toner image transferred from above, and supports the intermediate transfer belt 17, and a stretched surface of the intermediate transfer belt 17 is brought into contact with the photosensitive drum 13;
The image forming apparatus includes a plurality of support rollers 19a, 19B, 19C, and 20 arranged to form a predetermined transfer position, and a driving mechanism (20, 44) for driving the intermediate transfer belt 17, and performs an image forming operation. During this period, the intermediate transfer belt 17 is driven to rotate for a predetermined time, and the drive of the intermediate transfer belt 17 is stopped at a position different from the contact surface between the intermediate transfer belt 17 and the support rollers 19a, 19B, 19C, 20 before the start of driving. It is configured to be.

As described above, the sixth color electrophotographic apparatus and the seventh color electrophotographic apparatus have the same basic configuration, but different control methods for driving the rotation of the intermediate transfer belt 17. As shown in FIG. 9, the rotation speed of the drive roller 20 of the intermediate transfer belt 17 is controlled by a rotation speed control circuit 48 via a motor 44 and an encoder 45. The rotation speed control circuit 48 includes a counter 46, a CPU 4
9, a random number generator 50, a count number table 51, a motor stop signal transmitter 47 and the like.

A random number generator 50 and a count table 51 are connected to the CPU 49. The count number table 51 is configured by a ROM in which a plurality of count number data corresponding to random numbers output from the random number generator 50 are stored. The CPU 49 is connected to a motor stop signal transmitter 47 via a counter 46. CPU
49 reads out the count number data corresponding to the random number output from the random number generator 50 from the count number table 51,
The count is set in the counter 46. Counter 46
Is connected to a motor stop signal transmitter 47. The motor stop signal transmitter 47 outputs a stop signal to the motor 44 at the same time as the count-up signal from the counter 46 is input, and stops the rotation of the drive roller 20.

Next, the operation of the intermediate transfer belt 20 connected to the rotation speed control circuit 48 will be described. FIGS. 10A and 10B are diagrams showing a state of the intermediate transfer belt 17 in the sixth and seventh color electrophotographic apparatuses, wherein FIG. 10A shows a state before the start of the rotation drive, and FIG. 10B shows a state after the end of the rotation drive.
As shown in FIG. 10A, it is assumed that the intermediate transfer belt 17 is left with tension applied. At this time, the rollers 19a, 19b, 19
c, A1, A2, A3, the area wrapped around 20
A4. When the intermediate transfer belt 17 stops, a timer (not shown) is set. When the predetermined time elapses and the timer expires, the rotational drive of the intermediate transfer belt 17 is started. At this time, the photosensitive drum 13 is brought into contact with the intermediate transfer belt 17, and the respective areas A1 and A
2. Press A3 and A4. Also, the intermediate transfer belt 17
The cleaning device 25, which has been in contact with, presses the areas A1, A2, A3, and A4 while maintaining that state.

On the other hand, in the rotation number control circuit 48, the count number based on the random number from the random number generator 50 in FIG. The counting of the pulse signal is started. When the counter 46 counts up, the drive of the motor 44 is stopped by the motor stop signal transmitter 47 and the intermediate transfer belt 17 is stopped.
Stops in the state shown in FIG. 10B, for example. During the rotation driving period of the intermediate transfer belt 17, the random number generator 5
0, the intermediate transfer belt 17 does not always stop at a fixed position. Therefore, in FIG.
The areas A1, A2, A3, and A4 that have been in contact with the respective support rollers 19a, 19b, 19c, and 20 are the intermediate transfer belt 1
7 moves to a position different from the position before the start of the rotation drive. After the driving of the intermediate transfer belt 17 is stopped, a timer (not shown) is set again, and the above steps are repeated. In addition, the same control as described above is performed at the end of the image forming operation.

That is, when forming a color image,
The number of rotations of the intermediate transfer belt 17 is controlled by the number of rotations control circuit 48 from the start of the formation of the final toner image to the time when the fixed image receiving paper is discharged to the outside and stopped. Further, during the formation of a single-color toner image, the rotation speed of the intermediate transfer belt 17 is controlled by the rotation speed control circuit 48 from the start of driving. As a result, the area A in contact with each of the support rollers 19a, 19b, 19c, 20 before the start of the image forming operation.
1, A2, A3, and A4 are moved to different positions after the image forming operation is stopped.

As described above, the rotation of the intermediate transfer belt 17 after the lapse of the predetermined time allows the support rollers 1 to rotate.
No load due to belt tension is accumulated in the areas A1, A2, A3, and A4 of the intermediate transfer belt 17 that are in contact with 9a, 19b, 19c, and 20. Further, since the rotation speed of the intermediate transfer belt 17 is set at random, the areas A1, A2, A3, and A4 of the intermediate transfer belt 17 that are in contact with the support rollers 19a, 19b, 19c, and 20 during the idle period are changed as needed. . Thereby, the intermediate transfer belt 17 is not subjected to a load at the same position for a long time, so that the deformation of the intermediate transfer belt 17 is suppressed. Further, by bringing the photosensitive drum 13 and the cleaning device 25 into contact with the intermediate transfer belt 17 during the rotation of the intermediate transfer belt 17, even if the intermediate transfer belt 17 is deformed, the belt deformation is eliminated. It is needless to say that the control method is not limited to the method described above as long as the control method is such that the rotation speed of the intermediate transfer belt 17 is set at random.

(Eighth Embodiment) Next, an eighth embodiment of the color electrophotographic apparatus of the present invention (hereinafter referred to as an eighth color electrophotographic apparatus) will be described with reference to FIG. FIG. 11 is a diagram showing a configuration around the intermediate transfer belt 17 in the eighth color electrophotographic apparatus. Note that the members denoted by the same reference numerals as those of the first color electrophotographic apparatus shown in FIG. 1 are substantially the same, and the description thereof will be omitted.

The eighth color electrophotographic apparatus comprises a rotating electrostatic latent image holder (photosensitive drum) 13 and a photosensitive drum 1
A developing member 14 that forms a toner image on the photosensitive drum 3 and forms a reference toner image in a non-image area located at the rear end of the toner image on the photosensitive drum 13; Intermediate transfer member 17 carrying reference toner image
A reference toner image density sensor 52 for reading the density of the reference toner image transferred onto the intermediate transfer body 17; an information storage medium (memory) 56 for storing information obtained by the reference toner image density sensor 52; A control circuit 53 for controlling the next image forming process based on the information stored in 56
And

In FIG. 11, for example, the developing unit 14B of the black image forming unit 12B is connected to a developing voltage power supply 54 for supplying a developing voltage. A density sensor 52 for reading the optical density of the reference toner image of each color formed on the intermediate transfer belt 17 is provided substantially at the center of the support roller 19b and the drive roller 20 of the intermediate transfer belt 17. The developing voltage control circuit 53 is connected to the density sensor 52 and the developing voltage power supply 54.

The developing voltage control circuit 53 includes a density sensor 52
A / D converter 55 to which an analog signal from
It comprises a volatile memory 56 for storing digital signals from the / D converter 55, a data table 57, a CPU 49, a developing voltage setting device 58, and the like. Further, a volatile memory 56 and a data table 57 are connected to the CPU 49. The data table 57 is constituted by a ROM or the like in which a plurality of development voltage data corresponding to the signals stored in the volatile memory 56 are stored. The CPU 49 is connected to the developing voltage setting device 58. The CPU 49 reads development voltage data corresponding to the signal stored in the volatile memory 56 from the data table 57, performs a predetermined calculation, and outputs development voltage correction data to the development voltage setter 58. A plurality of development voltage setting values are stored in the development voltage setter 58, and a development voltage corresponding to the correction data from the CPU 49 is set. Apply.

Next, the operation of the eighth color electrophotographic apparatus to which the developing voltage control circuit 53 is connected will be described. First, in the black image forming unit 12B, a toner image is formed through charging, an electrostatic latent image forming, and a developing process as in a normal black and white printer. During this process, an electrostatic latent image for forming a reference toner image is formed at the rear end of the image portion, and the developing device 14 forms a reference toner image. The black toner image and the black reference toner image are transferred onto the intermediate transfer belt 17. In addition, during a series of operations for transferring the toner image to the intermediate transfer belt 17, the cleaning blade and the entrance seal attached to the cleaning device 25 and the secondary transfer roller 23 are separated from the surface of the intermediate transfer belt 17. Next, the cyan image forming unit 12C moves to form a cyan toner image and a cyan reference toner image located at the rear end, as before. At this time, the cyan reference toner image is formed at a position that does not overlap the black reference toner image.

The cyan toner image on the photosensitive drum 13 is
The black toner image is transferred onto the black toner image so as to be aligned with the leading end of the black toner image on the intermediate transfer belt 17.
At the same time, a cyan reference toner image is transferred to a position different from the black reference toner image on the intermediate transfer belt 17. The magenta toner image and the magenta reference toner image are transferred onto the intermediate transfer belt 17 in the same manner as the above series of operations. Subsequently, formation of a yellow toner image and a yellow reference toner image on the photosensitive drum 13 in the yellow image forming unit 12Y is started. At this time, the secondary transfer roller 23, the cleaning blade attached to the cleaning device 25, and the entrance seal are brought into contact with the area on the intermediate transfer belt 17 where the toner image does not exist in a timely manner.

Thereafter, the leading end of the toner image on the intermediate transfer belt 17 is conveyed to the first transfer position where the photosensitive drum 13 and the intermediate transfer belt 17 are in contact, and the transfer of the yellow toner image and the reference toner image starts. Is done. The intermediate transfer belt 1 is synchronized with the toner image on the intermediate transfer belt 17.
The image receiving paper 22 is conveyed to a second transfer position where the transfer roller 7 and the secondary transfer roller 23 are in contact with each other, and the color toner image on the intermediate transfer belt 17 is transferred to the image receiving paper 22 side. After the transfer, the toner remaining on the intermediate transfer belt 17 is
5 removed. Immediately before the reference toner image of each color formed at the rear end of the color toner image passes through the second transfer position, the secondary transfer roller 23 is again moved to the intermediate transfer belt 1.
Separated from 7. Thereafter, the reference toner image on the intermediate transfer belt 17 is removed from the intermediate transfer belt 17 by the cleaning device 25. Cleaning device 2
The density sensor 52 reads the density of the reference toner of each color on the intermediate transfer belt 18 before the reference toner image is removed from the intermediate transfer belt 17 at 5. The density signal of each color read by the density sensor 52 is stored in the volatile memory 56 through the A / D converter 55.

When the second color image forming process is started, the density signals of the respective colors stored in the volatile memory 56 are sent to the CPU.
49, and outputs the development voltage correction data to the development voltage setter 58. The developing voltage setting device 58 is connected to the CP
The developing voltage of each color corresponding to the correction data from U49 is set. Then, in the image forming operation for the second sheet, the corrected developing voltage is applied to the developing device 14 of each color via the developing voltage power supply 54.

As described above, the reference toner image formed on the photosensitive drum 13 is read by the density sensor 52 while being transferred onto the intermediate transfer belt 17, so that a toner image close to the final image is referred to. Thus, the adjustment of the color balance can be reflected on the color toner image on the image receiving paper 22. In addition, before the transfer of the toner image is started at the first transfer position, the secondary transfer roller 23 and the cleaning device 25 are brought into contact with the intermediate transfer belt 17. The first transfer is performed without causing toner disturbance. Further, before the reference toner image passes through the second transfer position, the image receiving paper 22
Since the toner transfer to the secondary transfer roller 23 has been completed, the secondary transfer roller 23 can be separated from the intermediate transfer belt 17 when the reference toner image passes, so that toner contamination of the secondary transfer roller 23 by the reference toner image is avoided. You.

In the above operation, the developing voltage control circuit 5
3 is applied during the image forming operation for the second and subsequent sheets, so that there is a problem that the control of the developing voltage is not performed at the time of forming the first sheet. However, regarding this problem, an initialization operation performed immediately after the power supply to the apparatus main body is turned on, an apparatus adjustment operation during a period when the image forming operation is stopped, and the like are performed, and a reference toner image is formed during these operations. By storing the density signal in the volatile memory 56, this can be avoided.

In the eighth color electrophotographic apparatus, the developing voltage was adjusted as a means for controlling the color balance. However, the charging voltage of the photosensitive drum 13 and the exposure device 15 were adjusted.
It goes without saying that the above configuration and operation may be applied to the toner image forming process such as the amount of exposure from.

Ninth Embodiment Next, a ninth embodiment of the color electrophotographic apparatus of the present invention (hereinafter, referred to as a ninth color electrophotographic apparatus) will be described with reference to FIG. FIG. 12 is a diagram showing a configuration around the intermediate transfer belt 17 in the ninth color electrophotographic apparatus. Note that the members denoted by the same reference numerals as those of the first color electrophotographic apparatus shown in FIG. 1 are substantially the same, and the description thereof will be omitted.

The ninth color electrophotographic apparatus comprises a rotating electrostatic latent image holder (photosensitive drum) 13 and a photosensitive drum 1
A developing member 14 for forming a toner image and a plurality of reference toner images on the photosensitive drum 3; an intermediate transfer belt 17 for carrying the toner image and the plurality of reference toner images transferred from the photosensitive drum 13; A power supply for supplying voltage to the
A transfer roller (conductive roller) 21 for transferring a toner image from the photosensitive drum 13 onto the intermediate transfer belt 17 and transferring a plurality of reference toner images onto the intermediate transfer belt at different voltages by a power supply; A reference toner image density sensor 52 for reading the densities of the plurality of reference toner images transferred onto the belt 17;
A comparison means (CPU) 49 for comparing information of the plurality of reference toner images obtained by the above-mentioned steps, and a step of forming a toner image on the photosensitive drum 13 and a step of And a control circuit 60 for controlling any one of the toner image transfer processes.

The exposure device 15 shown in FIG. 12 forms a toner image and an electrostatic latent image corresponding to two reference toner images on the photosensitive drum 13. The developing device 14 includes the photosensitive drum 13
A toner image and two reference toner images are formed thereon. The developing voltage power supply 54 is connected to the developing device 14 and supplies a developing voltage. The transfer voltage power supply 59 supplies a transfer voltage to the conductive roller 21 to transfer the two reference toner images on the photosensitive drum 13 onto the intermediate transfer belt 17 at different transfer voltages. The density sensor 52 sequentially reads the optical densities of two reference toner images formed on the intermediate transfer belt 17 at different transfer voltages, and sequentially converts the respective reference toner image densities into electric signals as a first signal and a second signal. I do. The development / transfer control circuit 60 is connected to the density sensor 52, the development voltage power supply 54, and the transfer voltage power supply 59, and controls them.

The development / transfer control circuit 60 includes the density sensor 5
A / D to which the first signal and the second signal are sequentially input from
Converter 55, volatile memory 5 for storing the first signal and the second signal converted into digital signals by A / D converter 55
6, a data table 57a of the development voltage and the transfer voltage, a reference data table 57b of the first signal and the second signal, C
It comprises a PU 49, a developing voltage setting device 58, a transfer voltage setting device 61 and the like. The CPU 49 has a volatile memory 5
6, data tables 57a, 57b, developing voltage setting device 5
8, a transfer voltage setting device 61 and the like are connected. The data table 57a is configured by a ROM or the like in which a data matrix of a development voltage and a transfer voltage is stored.
The data table 57b is configured by a ROM or the like in which a reference difference value between the first signal and the second signal is stored. The reference data difference value is stored as data when the transfer voltage is constant in a steady state.

First, the CPU 49 reads the first signal stored in the volatile memory 56 and refers to the data matrix in the data table. Next, the second signal is read, and a density difference value between both the first signal and the second signal is calculated. As a result, the correction data is output to one or both of the developing voltage setting device 58 and the transfer voltage setting device 61. A plurality of development voltage setting values are stored in the development voltage setter 58, and a development voltage corresponding to the correction data from the CPU 49 is set. Apply. Similarly, the transfer voltage setting unit 61 applies the corrected transfer voltage to the conductive roller 21 via the transfer voltage power supply 59.

Next, the operation of the ninth color electrophotographic apparatus to which the developing / transfer control copying circuit 60 is connected will be described. The steps from the black toner image forming step to the magenta toner image forming step are performed in the same manner as in the case of the eighth color electrophotographic apparatus. Subsequently, formation of a yellow toner image and two reference yellow toner images on the photosensitive drum 13 in the yellow image forming unit 12Y is started. At this time, the two reference yellow toner images are formed at the same developing voltage. At the same time, the secondary transfer roller 23 and the cleaning device 2
The cleaning blade and entrance seal attached to 5,
The intermediate transfer belt 17 is brought into contact with a region where a toner image does not exist in a timely manner.

Thereafter, the leading end of the toner image on the intermediate transfer belt 17 is transported to the first transfer position where the photosensitive drum 13 and the intermediate transfer belt 17 are in contact, and the transfer of the yellow toner image and the reference toner image is started. Is done. At this time, the two reference yellow toner images are sequentially transferred at different transfer voltages. The intermediate transfer belt 17 and the secondary transfer roller 23 are synchronized with the toner image on the intermediate transfer belt 17.
The image receiving paper 22 is conveyed to a second transfer position where
The color toner image on the intermediate transfer belt 17 is transferred to the image receiving paper 22 side. After the transfer, the toner remaining on the intermediate transfer belt 17 is removed by the cleaning device 25. Further, immediately before the two reference toner images pass through the second transfer position, the secondary transfer roller 23 is separated from the intermediate transfer belt 17 again. Thereafter, the reference toner image on the intermediate transfer belt 17 is removed from the intermediate transfer belt 17 by the cleaning device 25.

When the two reference yellow toner images pass the position of the density sensor 52, the density sensors 52 read the respective toner densities. The density signals of the two reference yellow toner images are stored in the volatile memory 56 through the A / D converter 55. On the other hand, each reference toner image is removed from the surface of the intermediate transfer belt 17 by the cleaning device.

When the second color image forming process is started, the density signal of each color stored in the volatile memory
49, and outputs the correction data to one or both of the developing voltage setting device 58 and the transfer voltage setting device 61. In the image forming operation for the second sheet, the yellow developing device 14 is
The corrected transfer voltage is applied to the conductive roller 21 via the transfer voltage power supply 61 or the corrected transfer voltage.
For the developing units other than yellow, correction is performed in the manner described for the eighth color electrophotographic apparatus.

Next, the control procedure in the development / transfer control circuit 60 will be described with reference to Table 1 below. Table 1
Is a data matrix of the development voltage and the transfer voltage stored in the data table 57a constituting the development / transfer control circuit 60. In Table 1, Vb1, Vb2, and Vb3 are development voltages, and the voltage values increase in the order of Vb1, Vb2, and Vb3.
Vt1, Vt2, and Vt3 are transfer voltages, and Vt1, Vt
2, the voltage value increases in the order of Vt3. The numbers in the matrix indicate toner density data, and the toner density increases in ascending order from 1 to 5, and the developing voltages Vb2 and Vb2
The value obtained at t2 is determined as normal concentration data. Also,
The two reference toner images are transferred using transfer voltages Vt1 and Vt2.

[0109]

[Table 1]

First, the first density data of the reference toner image obtained by applying the transfer voltage Vt2 is referred to the data matrix. At this time, if the first density data is 1, the developing voltage and the transfer voltage are set to Vb1 and Vt1, respectively. When the density data is 5, the developing voltage and the transfer voltage are set to Vb3 and Vt3, respectively. For example, when the first density data is 2, the second density data based on the reference toner image obtained by continuously applying the transfer voltage Vt1 is read, and both the first and second density data are differentiated.
If the difference value at this time is equal to the reference difference value stored in the data table 57b, the transfer voltage is determined to be normal, and the developing voltage is adjusted so that the density data becomes 3.
If the difference value is different from the difference value in the steady state, the transfer voltage is determined to be abnormal, and the transfer voltage is adjusted so that the density data becomes 3. The same adjustment is performed even when the first density data is 3 or 4.

As described above, one or both of the developing voltage and the transfer voltage are controlled by using the two reference toner images formed on the intermediate transfer belt 17 with different transfer voltages. There is no burden in controlling the developing voltage. As a result, control that does not affect image quality can be performed.

In the ninth color electrophotographic apparatus, two reference toner images are formed using yellow toner, but other color toners or all color toners may be used. However, since the color of the intermediate transfer belt 17 is generally black, the contrast is higher than that of the surface of the intermediate transfer belt 17 and the final color in the four-color overlapping process.
Considering that the reference toner density can be read for a long period of time and that the consumption amount is smaller than that of the toners of other colors, it is preferable to form the reference toner image using the yellow toner.

Further, as the photosensitive drum 13 in each of the above electrophotographic apparatuses, zinc oxide, selenium, cadmium sulfide, amorphous silicon, or the like can be used in addition to the organic photosensitive member. Further, as shown in FIG. 1, a roller-shaped charging member 131 was used as a charger, but the present invention is not limited to this, and a photoreceptor such as a corotron charger, a scorotron charger, and a fur brush charger may be used. Any member that charges the surface of the drum 13 may be used.

The volume resistivity of the intermediate transfer belt 17 is preferably 10 ⁶ to 10 ¹² Ω · cm.
Preferably those of the 0 ⁸ ~10 ¹⁰ Ω · cm. If the resistance is lower than the above range, the transfer current flows along the surface of the intermediate transfer belt to the grounded member that is in contact with the intermediate transfer belt, and the transfer voltage drops, thereby lowering the transfer efficiency. In addition, if an intermediate transfer belt having a higher resistance than the above range is used, the neutralization of the intermediate transfer belt cannot be sufficiently performed, and if continuous transfer is performed, the intermediate transfer belt will be charged up, resulting in a decrease in transfer efficiency and This causes toner scattering.

The structure of the intermediate transfer belt 17 is not limited to the structure used in each of the above electrophotographic apparatuses. Good. Further, a conductive layer may be applied on an insulating base material. In this case, polyethylene terephthalate (PET), polyimide, polyamide, polyurethane, or the like is used as the insulating substrate. The conductive layer is formed by dispersing a conductive filler in an insulating resin and spraying or dipping as described above.

Although a DC voltage power supply for supplying a constant voltage is used as the primary transfer power supply, a constant current power supply may be used. However, in the case of a constant current power supply, if there is a region where the toner layer is thick and a region where the toner layer does not exist when viewed in the longitudinal direction of the intermediate transfer belt 17, a region where the impedance component in the transfer region is large, that is, the toner layer thickness There is a possibility that the transfer current concentrates on the region where the thickness is thick, and the overall transfer voltage drops. Further, when each roller stretching the intermediate transfer belt 17 is conductive and grounded,
The transfer current may leak along the surface of the intermediate transfer belt 17. In order to solve these problems caused by using a DC constant current power supply, the volume resistivity of the intermediate transfer belt 17 may be set high.

The transfer voltage applied to the secondary transfer roller 23 is low in the state of the image receiving paper 22, for example, in a high temperature and high humidity environment, and is high in a low temperature and low humidity environment so that optimum transfer can be obtained. It may be. This is to absorb the resistance fluctuation of the resistance layer of the transfer roller 23. Similarly, the voltage applied to the conductive roller 21 may be adjusted according to the environment. With respect to these adjustments, a humidity and temperature sensor are arranged in the machine, and after reading, the adjustment is performed according to a predetermined program. Further, during a period in which image formation is not performed, a constant voltage or a constant current having the same polarity as that of the toner is applied to the secondary transfer roller 23, and the toner adhered to the secondary transfer roller 23 is reversely transferred to the intermediate transfer belt side to receive an image. A cleaning mode for reducing the back stain on the paper may be provided.

According to the above embodiment of the present invention, the following effects can be obtained. The first color electrophotographic apparatus of the present invention includes (1) a rotating electrostatic latent image holder and a developing member having toners of different colors, respectively. A plurality of image forming units that form toner images of different colors, and (2) image exposure on a surface of the electrostatic latent image holder of one of the plurality of image forming units at a predetermined exposure position. Exposure device, and (3) moving means for moving the entire image forming unit, sequentially moving the plurality of image forming units to the exposure position,
(4) an intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units, and (5) supporting the intermediate transfer belt, Bringing the tension surface and the electrostatic latent image holding member into contact with each other,
A plurality of support rollers arranged to form a predetermined transfer position, and (6) arranged at the back of the stretching surface of the intermediate transfer belt facing the electrostatic latent image holding member, at least the electrostatic latent image An elastic conductive member that contacts the back surface of the intermediate transfer belt in a state where the holding member is in contact with the stretching surface of the intermediate transfer belt, and (7) a toner image on the electrostatic latent image holding member. And a power supply for supplying a voltage of the opposite polarity to the conductive member. Therefore, a transfer voltage is applied by the transfer member close to the photosensitive drum, and the impedance component of the intermediate transfer belt, which is a transfer current path from the transfer member to the transfer position, can be reduced. Thus, the transfer can be performed at a low voltage without being affected by the impedance change of the intermediate transfer belt due to environmental change, temporal change, or the like. At the same time, since an elastic member is used as the conductive member, the collision energy between the photosensitive drum and the intermediate transfer belt can be absorbed by bending of the intermediate transfer belt and deformation of the conductive member. Thus, it is possible to prevent the surface of the photosensitive drum and the surface of the intermediate transfer belt from being damaged when the image forming unit is moved or replaced.

Further, the second color electrophotographic apparatus of the present invention (1) includes a rotating electrostatic latent image holding member and a developing member having toners of different colors, respectively. A plurality of image forming units for forming toner images of different colors on the holding member, and (2) at a predetermined exposure position, the electrostatic latent image holding member of one of the plurality of image forming units. An exposure apparatus that performs image exposure on the surface of (3) moving means for moving the entire image forming unit and sequentially moving the plurality of image forming units to the exposure position,
(4) the plurality of respective colors formed by the image forming unit a color image obtained by superimposing the toner images bearing, and 10 ⁷
An intermediate transfer belt having a surface resistance of 10 to 10 ¹² Ω / cm ² , (5) supporting the intermediate transfer belt, and bringing the stretched surface of the intermediate transfer belt into contact with the electrostatic latent image holding member; A plurality of support rollers arranged to form a predetermined transfer position, and (6) arranged at the back of the stretching surface of the intermediate transfer belt facing the electrostatic latent image holding member, at least the electrostatic latent image A brush-shaped conductive member that contacts the back surface of the intermediate transfer belt in a state where the holding member is in contact with the stretching surface of the intermediate transfer belt, and (7) a toner image on the electrostatic latent image holding member. Comprises a power supply for supplying a voltage of opposite polarity to the conductive member. Therefore, a transfer voltage is applied by the transfer member close to the photosensitive drum, and the impedance component of the intermediate transfer belt, which is a transfer current path from the transfer member to the transfer position, can be reduced. Thus, the transfer can be performed at a low voltage without being affected by the impedance change of the intermediate transfer belt due to environmental change, temporal change, or the like. At the same time, since a brush-like member is used as the conductive member, the collision energy between the photosensitive drum and the intermediate transfer belt can be absorbed by bending of the intermediate transfer belt and deformation of the conductive member. This allows
When the image forming unit is moved or replaced, damage to the surfaces of the photosensitive drum and the intermediate transfer belt can be prevented. Further, the brush-shaped conductive member is configured such that the loop-shaped conductive fiber is supported on the conductive base material, so that the conductive member can be easily deformed and restored.

Further, the third color electrophotographic apparatus of the present invention includes (1) a rotating electrostatic latent image holding member and a developing member having toners of different colors, respectively. A plurality of image forming units that form toner images of different colors on the holding member, and (2) at a predetermined exposure position, the electrostatic latent image holding member of one of the plurality of image forming units. An exposure apparatus that performs image exposure on the surface of (3) moving means for moving the entire image forming unit and sequentially moving the plurality of image forming units to the exposure position,
(4) an intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units, and (5) supporting the intermediate transfer belt, Bringing the tension surface and the electrostatic latent image holding member into contact with each other,
A plurality of support rollers arranged so as to form a predetermined transfer position; and A charge supply member for supplying a charge having a polarity opposite to that of the toner image on the electrostatic latent image holding member to the back of the transfer belt stretching surface,
(7) a power supply for supplying a voltage having a polarity opposite to that of the toner image on the electrostatic latent image holding member to the charge supply member; Therefore, a transfer voltage is applied by the transfer member close to the photosensitive drum, and the impedance component of the intermediate transfer belt, which is a transfer current path from the transfer member to the transfer position, can be reduced. Thus, the transfer can be performed at a low voltage without being affected by the impedance change of the intermediate transfer belt due to environmental change, temporal change, or the like. At the same time, since the non-contact member is used as the conductive member, the collision energy between the photosensitive drum and the intermediate transfer belt can be absorbed by the bending of the intermediate transfer belt. Thus, it is possible to prevent the surface of the photosensitive drum and the surface of the intermediate transfer belt from being damaged when the image forming unit is moved or replaced.

Further, the fourth color electrophotographic apparatus of the present invention includes (1) a rotating electrostatic latent image holding member and a developing member having toners of different colors, respectively. A plurality of image forming units that form toner images of different colors on the holding member, and (2) at a predetermined exposure position, the electrostatic latent image holding member of one of the plurality of image forming units. An exposure apparatus that performs image exposure on the surface of (3) moving means for moving the entire image forming unit and sequentially moving the plurality of image forming units to the exposure position,
(4) an intermediate transfer belt that carries a color image obtained by superimposing toner images of respective colors formed by the plurality of image forming units, and (5) supporting the intermediate transfer belt, Bringing the tension surface and the electrostatic latent image holding member into contact with each other,
A plurality of support rollers arranged to form a predetermined transfer position, (6) at least one of the plurality of support rollers, a drive roller for rotationally driving the intermediate transfer belt, (7) An intermediate transfer belt holding member for holding the intermediate transfer belt, and after an operation of moving a predetermined image forming unit from the image forming position among the plurality of image forming units is started, the next image forming unit Until the operation of moving to the image forming position is completed,
The driving of the driving roller is stopped, and the intermediate transfer belt is stopped by the intermediate transfer belt holding member. Therefore, even when a force for driving the intermediate transfer belt acts upon replacement of the image forming unit, the slip of the intermediate transfer belt can be suppressed by the intermediate transfer belt holding member. Further, the intermediate transfer belt can be stopped at a predetermined position before and after the image forming unit replacement operation. As a result, slippage of the intermediate transfer belt does not occur, and it is possible to quickly shift to the next color toner image forming step. Further, the intermediate transfer belt holding member includes a cleaner for cleaning a surface of the intermediate transfer belt, and a support roller for the intermediate transfer belt facing the cleaner via the intermediate transfer belt. , And the surface of the intermediate transfer belt can be cleaned at the same time.

The fifth color electrophotographic apparatus according to the present invention comprises: (1) a rotating electrostatic latent image holding member; and (2) a developing member for forming a toner image on the electrostatic latent image holding member. (3) an intermediate transfer belt that carries a color image in which a plurality of color toner images transferred from the electrostatic latent image holding member are superimposed, and (4) a plurality of support rollers that stretch the intermediate transfer belt. (5) driving means for rotating and driving the intermediate transfer belt from the start of driving to the end of driving so that the rotation cycle of the intermediate transfer belt becomes an integral multiple, and (6) a predetermined rotation of the intermediate transfer belt. Mark formed at the position, (7) disposed between two support rollers of the plurality of support rollers, a sensor for detecting the mark, and (8) a signal for detecting the mark with the sensor Timing for starting an electrostatic latent image writing operation on the electrostatic latent image holding member based on the timing Control means for controlling the intermediate transfer at a position other than the two support rollers located upstream and downstream of the sensor in the direction of movement of the intermediate transfer belt when the mark passes through the sensor. The mark and the sensor are arranged such that there is a region where the driving of the belt is stopped and the intermediate transfer belt is in contact with the plurality of support rollers. Therefore, by driving the intermediate transfer belt by an integral multiple of the rotation cycle of the intermediate transfer belt, the area of the intermediate transfer belt that is deformed by contact with the support roller can be fixed at a predetermined position. Accordingly, it is possible to specify a time zone in which the predetermined position where the belt is deformed does not pass through the support roller, that is, a time zone in which the smooth movement of the intermediate transfer belt is performed. Further, since the mark on the intermediate transfer belt is detected in that time zone, it is possible to avoid a shift in the detection time of each color due to the vibration (fluttering) of the intermediate transfer belt. As a result, the timing of starting the formation of the electrostatic latent image on the photosensitive drum can be made constant for each color, and an image of excellent print quality without image deviation between toner images of each color can be obtained.

The sixth color electrophotographic apparatus according to the present invention comprises: (1) a rotating electrostatic latent image holding member; and (2) a developing member for forming a toner image on the electrostatic latent image holding member. (3) an intermediate transfer belt that carries the toner image transferred from the electrostatic latent image holding member, and (4) a support for the intermediate transfer belt, a tension surface of the intermediate transfer belt and the electrostatic A plurality of support rollers arranged to contact the latent image holding member to form a predetermined transfer position, and (5) driving means for driving the intermediate transfer belt, and the image forming operation is completed. Thereafter, the driving of the intermediate transfer belt is stopped at a position different from the contact surface between the intermediate transfer belt and the support roller in a state where the intermediate transfer belt is left before the driving of the image forming operation is started. Therefore, in addition to the effect of the fifth color electrophotographic apparatus, a region where a load is applied in the circumferential direction of the intermediate transfer belt in a stopped state can be changed at any time, and deformation of the belt can be suppressed.

Further, the seventh color electrophotographic apparatus of the present invention comprises: (1) a rotating electrostatic latent image holding member; and (2) a developing member for forming a toner image on the electrostatic latent image holding member. (3) an intermediate transfer belt that carries a toner image transferred from the electrostatic latent image holding member, and (4) a support surface of the intermediate transfer belt, The image forming apparatus includes: a plurality of support rollers arranged to contact the latent image holding member to form a predetermined transfer position; and (5) driving means for driving the intermediate transfer belt. During this time, the intermediate transfer belt is driven to rotate for a predetermined time, and the drive of the intermediate transfer belt is stopped at a position different from the contact surface between the intermediate transfer belt and the support roller before the start of driving. Therefore, similarly to the sixth color electrophotographic apparatus, in addition to the effects of the fifth color electrophotographic apparatus, a region where a load is applied in the circumferential direction of the intermediate transfer belt in a stopped state can be changed as needed. The deformation of the belt can be suppressed.

An eighth color electrophotographic apparatus according to the present invention comprises: (1) a rotating electrostatic latent image carrier; and (2) a toner image formed on the electrostatic latent image carrier. A developing member for forming a reference toner image in a non-image area located at a rear end of the toner image on the electrostatic latent image holding member; and (3) a toner image and a reference toner transferred from the electrostatic latent image holding member. An intermediate transfer member that carries an image, (4) a reference toner image density sensor that reads the density of the reference toner image transferred on the intermediate transfer member, and (5) information obtained by the reference toner image density sensor. An information storage unit for storing; and (6) a control unit for controlling a next image forming step based on the information stored in the information storage unit. Therefore, since the reference toner image is formed on the intermediate transfer member, the density reading sensor for the reference toner image can be disposed around the intermediate transfer member. This allows
It is not necessary to use a large-diameter photosensitive drum, and the color balance can be adjusted at a position close to the final image. Since the reference toner image is formed at the rear end of the image portion, the transfer member is brought into contact with the intermediate transfer belt before the transfer to the image receiving paper is completed and before the transfer of the toner image is started at the first transfer position. Can be done. Thus, the first transfer can be performed without causing toner disturbance due to vibration caused by contact of the transfer member with the intermediate transfer member. As a result, even when an image forming unit using a small-diameter photosensitive drum is used, adjustment of the toner image forming process becomes easy. At the same time, vibration of the secondary transfer roller and the cleaner is not applied during the transfer, and toner contamination of the secondary transfer roller can be avoided.

The ninth color electrophotographic apparatus according to the present invention comprises: (1) a rotating electrostatic latent image holding member; and (2) a toner image and a plurality of reference toners on the electrostatic latent image holding member. A developing member for forming an image, (3) an intermediate transfer member that carries the toner image and the plurality of reference toner images transferred from the electrostatic latent image holding member, and (4) a voltage applied to the transfer member. And (5) transferring the toner image from the electrostatic latent image holding member onto the intermediate transfer member, and the plurality of reference toner images on the intermediate transfer member, each of which differs depending on the power source. A transfer member for transferring with a voltage, (6) a reference toner image density sensor for reading the densities of the plurality of reference toner images transferred on the intermediate transfer body, and (7) a plurality of reference toner image density sensors obtained by the reference toner image density sensor. Comparing means for comparing information of the reference toner images of (8) and (8) the comparing means Based on the comparison result by, and a control means for controlling one of said toner image transfer step of the toner image forming step to the electrostatic latent image holding member on to the intermediate transfer member. Therefore, a plurality of reference toner images can be transferred onto the intermediate transfer body at different transfer voltages. By subtracting the optical densities obtained from these reference toner images, it is possible to obtain a linear transfer characteristic while image formation is in progress. Further, by comparing the transfer characteristics during normal operation with the transfer characteristics obtained during the progress of image formation, it is possible to determine whether the transfer onto the intermediate transfer body is normal in the ongoing image forming process. . If the transfer characteristics are abnormal, adjust the transfer voltage applied to the intermediate transfer belt.If the transfer characteristics are normal but the predetermined reference toner image density is not obtained, the charging voltage of the photoconductor is adjusted. By adjusting the toner image forming process such as the developing voltage of the developing member and the developing member, the image can be adjusted from two directions, and the control margin of the color balance can be reduced without burdening the control in only one process. Can be expanded.

[0127]

As is apparent from the above description, according to the present invention, the transfer can be performed at a low voltage without being affected by the fluctuation of the impedance of the intermediate transfer belt due to environmental fluctuation or aging. The collision energy between the drum and the intermediate transfer belt can be absorbed by the bending of the intermediate transfer belt and the deformation of the conductive member, and the surface of the photosensitive drum and the intermediate transfer belt can be damaged when the image forming unit is moved or replaced. Thus, a color electrophotographic apparatus which can be prevented can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the overall configuration of a first color electrophotographic apparatus according to the present invention.

FIG. 2 is a cross-sectional view showing a configuration near a first transfer position in FIG.

FIG. 3 is a diagram illustrating a configuration near a first transfer position in a second color electrophotographic apparatus according to the present invention.

FIG. 4 is a perspective view showing a configuration of a brush-like conductive member in a second color electrophotographic apparatus of the present invention.

FIG. 5 is a diagram showing a configuration near a first transfer position in a third color electrophotographic apparatus of the present invention.

FIG. 6 is a perspective view showing a configuration around an intermediate transfer belt in a fourth color electrophotographic apparatus of the present invention.

FIG. 7 is a diagram showing a configuration around an intermediate transfer belt in a fifth color electrophotographic apparatus of the present invention.

FIG. 8 is a diagram showing a traveling path of an intermediate transfer belt in a fifth color electrophotographic apparatus according to the present invention.

FIG. 9 is a diagram showing a configuration around an intermediate transfer belt in the sixth and seventh color electrophotographic apparatuses of the present invention.

FIG. 10 is a diagram showing a state of an intermediate transfer belt in the sixth and seventh color electrophotographic apparatuses of the present invention.

FIG. 11 is a diagram showing a configuration around an intermediate transfer belt in an eighth color electrophotographic apparatus of the present invention.

FIG. 12 is a diagram showing a configuration around an intermediate transfer belt in a ninth color electrophotographic apparatus of the present invention.

[Explanation of symbols]

 12B, 12Y, 12M, 12C Image forming unit 13 Photoconductor drum 14 Developing device 15 Exposure device 16 Reflection mirror 17 Intermediate transfer belt 18 Intermediate transfer unit 19a, 19b, 19C Support roller 20 Drive roller 21 Conductive roller 22 Image receiving paper 23 2 Next transfer roller 24 Image receiving paper charge removing member 25 Cleaning device 26 Paper feed roller 27 Timing roller 28 Fixing device 29 Support spring 31 Brush-like conductive member 32 Brush fiber 33 Brush fiber support base material 34 Corona charger 35 Nipping roller 36 Cam 37 Cam support Shaft 38 Reinforcement tape 39 Detection hole 40 Sensor 41 Control circuit 42 Timer 43 Image formation start signal transmitter 44 Motor 45 Encoder 46 Counter 47 Motor stop signal transmitter 48 Rotation speed control circuit 49 CPU 50 Random number generator 5 1 Count number table 52 Density sensor 53 Developing voltage control circuit 54 Developing voltage power supply 55 A / D converter 56 Volatile memory 57 Data table 58 Developing voltage setting device 59 Transfer voltage power supply 60 Developing / transfer control circuit 61 Transfer voltage setting device 131 Charging Device 132 developing device 133 cleaning device

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2H030 AB02 BB02 BB34 BB36 BB42 BB54 BB56 BB63 2H200 FA02 FA09 GA12 GA14 GA16 GA23 GA34 GA45 GA47 GA49 GA56 GA59 GB11 HA02 HA12 HA28 HB03 HB12 HB26 HB43 HB45 HB47 JA28 JA02 JC03 JC07 JC10 JC12 JC13 JC15 JC16 JC17 JC18 JC20 KA01 KA06 LA01 LA18 LA19 LA24 LA25 LA38 LB02 LB13 MA04 MA11 MA14 MA20 MB04 MB05 MC02 MC06 NA15 PB39 PB18 PB39

Claims (1)

[Claims] A plurality of image forming units for forming toner images of different colors on an electrostatic latent image holding member; and an exposure device for performing image exposure on a surface of the electrostatic latent image holding member at a predetermined exposure position. An apparatus, a moving unit that moves the entire image forming unit and sequentially moves the plurality of image forming units to an image forming position, and a toner image of each color formed by the plurality of image forming units, which is obtained by superimposing. An intermediate transfer belt that carries the color image, and an intermediate transfer belt that supports the intermediate transfer belt, and is arranged so that a stretched surface of the intermediate transfer belt and the electrostatic latent image holding member are in contact with each other to form a predetermined transfer position. And a plurality of support rollers, which are arranged on the back surface of the stretching surface of the intermediate transfer belt facing the electrostatic latent image holding member, and at least the electrostatic latent image holding member is disposed on the stretching surface of the intermediate transfer belt. In contact with the above A conductive member having elasticity, which is in contact with the back surface of the transfer belt, and a power supply for supplying a voltage having a polarity opposite to that of the toner image on the electrostatic latent image holding member to the conductive member. Color electrophotographic apparatus.