JPH08248729A - Color image forming device - Google Patents

Abstract

PURPOSE: To suppress uneven density caused at the time of transfer and to obtain a good color image by measuring the driving state of an image carrier and deciding a voltage to be impressed on a transfer electrode based on the measurement result. CONSTITUTION: In order to form a toner image, an image forming unit 10 is rotated and moved to the position in contact with the intermediate transfer belt 19. A current required for driving an image carrier driving motor 60 is measured by a measurement circuit 62. A transfer voltage to the intermediate transfer belt 19 is decided by a calculation circuit 64 based on the measurement result. Also the output voltage of an intermediate transfer power supply 32 is adjusted, and a voltage impressed on the intermediate transfer belt 19 is adjusted. And also, the rotating speed of a transfer roller 28 is measured by a rotating speed measuring means 66. An optimum impressed voltage is decided by a control circuit 68 based on the measurement result, the output voltage of the transfer power supply 30 is adjusted, and a voltage to be impressed on the transfer roller 28 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a printer, and more particularly to a color image device.

[0002]

2. Description of the Related Art In recent years, documents have been created and edited using color displays in offices by enhancing the equipment centering on personal computers. However, an output device that prints a created sentence on paper is mainly a monochrome machine. The reason for this is that the existing color output device has major problems in terms of performance and price. The electrophotographic color output device can also print on plain paper.
It has excellent advantages such as excellent halftone reproduction and high printing speed, but since the device is complicated, maintenance is expensive,
The cost is 10 to 50 times higher than that of a black-and-white output device, so that it is not popular enough.

An electrophotographic color output device optically or electrically color-separates an original image, forms a latent image corresponding to each color of yellow, magenta, and cyan, and then charges powder particles (corresponding to each color). The process of visualizing with toner is the same as in a black and white machine. What is most different from the black-and-white machine is the step of superposing each of these colors on the transfer material.

FIG. 3 shows a schematic configuration of a conventional color output device disclosed in JP-A-6-19331 and JP-A-6-19332. In FIG. 3, 70 is a photosensitive drum, 71 is an exposing means, 72 is a developing device provided with a group of rotatable developing devices of yellow (Y), magenta (M), cyan (C), and black (BK), 74 is a corona discharger, 76
Is a transfer drum and is made of a dielectric or resistor film. 78 is a cleaning means, 80 is a conveyor belt, 82
Is a fixing device, and 84 is a paper feed roller. Next, the operation will be described. A color original is read by an image scanner (not shown) to obtain yellow, magenta, cyan, and black information.
These pieces of information are temporarily stored in the memory. To form a color image, color signals are sequentially sent to the illustrated apparatus. First, the exposure unit 71 forms a yellow latent image on the photosensitive drum 70. The latent image formation is similar to that of a normal monochrome output device. The developing device 72 rotates to press the yellow (Y) developing device against the photosensitive drum 70 to visualize the latent image with yellow toner. The image receiving paper is supplied onto the transfer drum 76 by the paper feed roller 84 in synchronization with the image formation, and is attracted by the electrostatic force. The yellow image on the photosensitive drum 70 is transferred onto the image receiving paper by the transfer charger 77. The photosensitive drum 70 after the transfer is cleaned by a cleaning device 78.
The transfer residual toner is removed by, and the toner is charged by the corona discharger 74, and the next latent image is formed. When all the images of the yellow signal are transferred onto the image receiving paper, the magenta (M) image formation is performed similarly to the case of yellow. Following the magenta image formation, cyan and black image formation are sequentially performed. The image receiving paper on the transfer drum 76 is yellow,
Images of magenta, cyan, and black are sequentially superimposed, and at the same time when the formation of the black image is completed, the image receiving paper is peeled off from the transfer drum 76, passes through the transfer belt 80, and reaches the fixing device 82.
It is fixed to obtain an image.

Different from the above-mentioned color image forming method, in consideration of the paper passing property of the image receiving paper, for example, Japanese Patent Laid-Open No. 2-18327.
No. 6 discloses a toner image formed on an image carrier,
A method is disclosed in which four colors are held on an intermediate transfer belt and then collectively transferred to an image receiving paper. This system uses a belt-shaped image bearing member with a long circumference, a developing device is arranged around this image bearing member, and a developing device is pressed against the image bearing member for each color to form a toner image, and then an intermediate transfer is performed. Transfer to the belt. Two
After the color, toner images are superposed on the intermediate transfer belt.
Toner images of a plurality of colors are formed on the intermediate transfer belt and then collectively transferred to the image receiving paper. In addition, JP-A-6-82235.
The publication discloses an image forming apparatus in which image forming units such as an image carrier, a charger, and a developing device are unitized for each color, and toner images of the respective colors are superposed on an intermediate transfer belt. Excellent device proposals have also been made.

[0006]

In the color image forming method described above, the image receiving paper is wound around the transfer drum to form three color images and a black image. For this reason, since the image receiving paper is adsorbed to the transfer drum and is separated from the transfer drum, the image receiving paper path becomes complicated and causes paper jam. In particular, adsorption and peeling using electrostatic force depend on the usage environment and the physical properties of the image receiving paper, and thus lack stability and impair reliability. There are problems such as complicated processing when the image receiving paper is jammed.

In the system in which the toner image is once transferred from the image carrier to the intermediate transfer medium and then re-transferred to the image receiving paper, the path of the image receiving paper is simplified as compared with the above-mentioned method, and therefore, when a jam occurs. However, if the image forming unit is unitized for each color, there is a problem that the image superimposed on the intermediate transfer belt tends to be misaligned due to the mismatch of the drive system for each unit. Was there.

[0008]

In order to solve the above problems, the present invention is a color image forming apparatus having the following constitution.

A plurality of moving image forming units arranged in an annular shape, each of which includes at least an image carrier that rotates, a charging unit that charges the image carrier, and a developing unit that has a developer of a different color. Possible image forming unit group, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the image formation each time the toner image is transferred to the intermediate transfer belt. By moving the unit group around the rotation center, a moving unit that changes the image carrier in contact with the intermediate transfer belt,
A transfer electrode for pressing the intermediate transfer belt against the image carrier, a power source capable of varying a voltage for applying a voltage to the transfer electrode, and the image carrier when the image forming unit is in an image forming position. By measuring the driving state of the body and pressing the image receiving paper against the intermediate transfer belt,
A conductive transfer roller that retransfers the toner image held on the intermediate transfer belt to the image receiving paper, and the voltage applied to the transfer electrode is based on the result measured by the measuring unit. The color image forming apparatus is determined.

Alternatively, a plurality of image forming units each having at least a rotatable image carrier, a charging device for charging the image carrier, and a developing device having a developer having a different color are arranged in an annular shape. Of movable image forming units, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the toner image is transferred to the intermediate transfer belt every time the toner images are transferred to the intermediate transfer belt. By moving the image forming unit group around the center of rotation to change the image carrier in contact with the intermediate transfer belt, and by pressing the image receiving paper against the intermediate transfer belt, A conductive transfer roller that retransfers the held toner image to the image receiving paper, a rotation measuring unit that measures the driving state of the transfer roller, and a voltage is applied to the transfer roller. And a voltage source for changing the voltage for controlling the transfer roller, and the voltage applied to the transfer roller is determined based on the result measured by the rotating unit.

[0011]

In the method of temporarily transferring the toner image from the image carrier to the intermediate transfer medium and then re-transferring it to the image receiving paper, the path of the image receiving paper is simplified as compared with the above-described method, so that a jam occurs. Will be better handled. Further, if the image forming unit is unitized for each color, the replacement work that occurs when the toner is consumed becomes easy. However, since each unit has its own drive transmission system, the unit at the image forming position obtains power from the drive source to form a toner image, which is transferred to the intermediate transfer belt and superposed on each other. Due to the torque fluctuation of the intrinsic transmission system, the image is shaded for each color and an unpleasant image is formed. For example, when the torque of the image carrier becomes larger than the reference value, the number of rotations of the image carrier decreases, and the exposure of the laser scanning in the direction perpendicular to the surface moving direction of the image carrier overlaps, resulting in overexposure. The surface potential of the carrier is lower than the standard value, and the amount of adhered toner increases. Conversely, when the torque of the image carrier becomes smaller than the reference value, the number of rotations increases and the toner adhesion amount decreases. In this way, the toner image formed on the image carrier cannot be corrected and causes image jitter. In the first aspect of the invention, the difference in the toner adhesion amount that occurs is corrected when the toner is transferred to the intermediate transfer belt. That is, when the rotation speed of the image carrier is lower than the reference value, the transfer voltage is lowered and the amount of toner to be transferred is reduced, and when the rotation speed is higher than the reference value, the transfer voltage is increased and the transfer voltage is increased. Correction is performed by increasing the amount of toner to be used. The second aspect of the invention is to correct the same image density that occurs when the image is transferred from the intermediate transfer belt to the image receiving paper. The image receiving paper is pressed against the intermediate transfer belt, the transfer roller drive for transferring the toner image on the intermediate transfer belt is received from the intermediate transfer belt, and the rotational speed of this transfer roller is applied to the transfer roller by comparing it with a reference value. Determine the voltage. Alternatively, the surface moving speed of the intermediate transfer belt may be detected to determine the voltage applied to the transfer roller. The basic idea of control is to reduce the voltage applied to the transfer roller when the rotational speed of the transfer roller is lower than the reference value or when the surface moving speed of the intermediate transfer belt is lower than the reference value.

By the above control, the shading of the image is corrected and a good image can be obtained.

[0013]

【Example】

(Embodiment 1) FIG. 1 is a schematic view of the configuration of a color image forming apparatus according to the first embodiment of the present invention. In FIG. 1, reference numeral 10 denotes an image forming unit, which has four colors of yellow, magenta, cyan, and black, and each has an image carrier 12 (diameter 30 mm), a charging roller 14, a developing device 16, and a cleaning blade 17.
It has. The image forming unit 10 is composed of two blocks: a developing section in which an image carrier 12 and a developing device 16 are combined, and a toner collecting section in which a charging roller 14 and a cleaning blade 17 are combined. The unit group of four colors can be rotated around the center of movement rotation of the unit group by the unit moving device 18. The image forming unit group is
When it is moved counterclockwise, the developing section is located at the bottom and the toner collecting section is located at the top at the image forming position. Reference numeral 20 denotes an exposure unit, which allows one unit in the image forming unit 10 to be exposed through a substantially parallel slit between the developing unit and the toner collecting unit of the image forming unit 10 and a reflecting mirror 21 near the center of rotation. Are arranged as follows. Reflection mirror 2
1 is fixed without rotating with the rotation of the image forming unit 10. Reference numeral 19 is an intermediate transfer belt having a circumference of 377 mm so that at least one A4 size image can be held.
Is. The intermediate transfer belt 19 is used by kneading a conductive filler in an insulating resin and forming a film with an extruder. In this embodiment, a polycarbonate resin (for example, Iupilon Z300 manufactured by Mitsubishi Gas Chemical Co., Inc.) 9 is used as the insulating resin.
5 parts of conductive carbon (for example, Ketjen black) was added to form a film. The thickness of the film was about 150 μm. An antioxidant, a dispersion aid, a release member and the like may be mixed in the resin.

The surface roughness of the intermediate transfer belt 19 was about 3 to 5 μm as a 10-point average roughness after molding and the like. This surface roughness can be freely controlled by an abrasive such as sandpaper or polisher. Electric resistance is 10 ⁵ to 10 ¹¹ Ω
The cm range is effective. When it is less than 10 ⁵ Ω · cm, electric discharge occurs to the image carrier and a conductive roller that transfers an image to an image receiving paper described later. On the other hand, when it exceeds 10 ¹¹ Ω · cm, there arises inconveniences such as an increase in the resin ratio of the conductive portion forming the intermediate transfer belt 19, an increase in applied voltage, and a large environmental change. The intermediate transfer belt 19 is not limited to the configuration described above, and may be, for example, an insulating base material coated with a conductive layer. In this case, polyethylene terephthalate (PET), polyimide, polyamide, polyurethane or the like is used as the insulating substrate. As described above, the conductive layer is provided by dispersing a conductive filler in an insulating resin and spraying or dipping. The intermediate transfer belt 19 is stretched around a pressing roller 24, a stretching roller 26, and a driving roller 27. The pressure roller 24 has a diameter of 1
A foam sponge is provided on a 0 mm metal shaft, and the hardness is 30 ° or less on the JIS A scale. The conductive foam sponge layer is made by dispersing a conductive filler such as carbon in a rubber material such as polyurethane or EPDM or containing an ionic conductive material. The pressing roller 24 is connected to an intermediate transfer power supply 32 for electrostatically transferring the toner image on the image carrier 12 to the intermediate transfer belt 19. The intermediate transfer power source 32 is capable of applying a voltage having the same polarity as that of the toner and having a reverse polarity, and is capable of applying a desired voltage value after control described later. The diameter of the pressing roller 24 most affects the image quality when the toner image is transferred from the image carrier 12 onto the intermediate transfer belt 19. In the case of this embodiment, the diameter of the image carrier 12 is 30 mm.
And the diameter of the pressing roller 24 is the diameter ratio (transfer roller 2
4 divided by the diameter of the image bearing member) was set to 0.6 or less. This is because if the diameter ratio of the pressing roller 24 exceeds 0.6, the toner scattering increases around the characters transferred on the intermediate transfer belt 19 and the image quality deteriorates.

The intermediate transfer belt is pressed by the pressing roller 2 by the separating / contacting device while the image forming unit 10 is moving for color exchange.
4 is moved so as to be brought into contact with or separated from the image carrier 12 of the image forming unit 10, or the image forming unit 10 is located at a position where there is no toner image on the intermediate transfer belt 19.
Prevents damage to the toner image due to replacement of the toner.

28 is a transfer roller, which is an intermediate transfer belt 19
When the upper toner image is retransferred to the image receiving paper 37, the image receiving paper 37
Is a backup roller for pressing the intermediate transfer belt 19 to transfer the toner image. Transfer roller 28 is φ1
Elastic rubber made by adding conductive fillers such as lithium salt and carbon to polyurethane rubber on a 0 mm metal shaft,
Alternatively, it is made of a metal material integrally with the shaft. Outer diameter is φ
It is 19 mm. A roller made of a rubber material on a metal shaft has a resistance of about 10 ⁷ to 10 ⁹ Ω · cm.
The transfer roller 28 is transferring the toner image onto the intermediate transfer belt 19 while the toner image is being transferred from the image carrier.
Are separated from each other by a separating / contacting device (not shown), and when transferring to the image receiving paper 37, they contact the intermediate transfer belt 19 and a voltage having a polarity opposite to that of the toner is applied from the transfer power supply 30. The transfer power source 30 is a power source that can output a voltage that can be controlled, which will be described later.

Reference numeral 26 denotes a tension roller, which has a diameter of 10 mm and is made of a metal roller. Reference numeral 27 denotes a drive roller for rotating the intermediate transfer belt 19, which is made of a metal roller and has a diameter of 16 mm and is grounded.

Reference numeral 34 denotes an image receiving paper 37 from the intermediate transfer belt 19.
This is a cleaning device for removing the unnecessary toner remaining on the surface after the transfer to the. Cleaning device 3
4 is a cleaning roller 3 similar to the transfer roller 28.
5 is brought into contact with the intermediate transfer belt 19 and a voltage having a polarity opposite to the charging polarity of the toner is applied to remove the toner on the intermediate transfer belt 19. The cleaning roller 35 may be made of a metal material, or a conductive rubber material may be provided on the metal shaft. The toner attached to the surface of the cleaning roller 35 is scraped off by a scraper and collected in a toner reservoir in the cleaning device 34. However, in the sequence, the reverse polarity voltage is applied after the transfer of the toner image on the intermediate transfer belt 19 to the image receiving paper 37 is completed, and in other cases, that is, color superimposition is performed on the intermediate transfer belt 19. During that time, a voltage having the same polarity as the toner is applied to the cleaning roller 35 so that the toner is not collected. Alternatively, a device may be provided that separates and contacts the entire cleaning device 34 from the intermediate transfer belt 19 and may be separated and contacted when cleaning is unnecessary.

Reference numeral 44 is a paper feed roller for feeding the image receiving paper 37 one by one from the cassette tray. The manual paper feed roller 50 is a roller for feeding paper that is not set in the cassette. A timing roller 42 is a roller that is in contact with the metal roller 43 and sends out the fed image receiving paper 37 to the transfer portion according to the image signal. A scraper for removing paper dust is attached to the metal roller 43. A fixing device 52 fixes the toner image on the image receiving paper 37 that has been transferred. After the fixing process, the image receiving paper 37 is ejected outside the machine. Image carrier 1 of each unit
2 rotates at a speed of 33 mm / s. The appropriate speed difference between the image carrier 12 and the intermediate transfer belt 19 is about 1 to 5%. The transfer roller 28 and the intermediate transfer belt 19 also rotate at almost the same speed difference.

The intermediate transfer belt 19, the pressing roller 24, the tension roller 26, the driving roller 27, and the cleaning device 34.
Shall be an integral unit configuration. As shown in FIG. 1, the pressure roller 24 side is set to a length that makes it easier for the entire unit to be taken in and out than the length between the stretching roller 26 and the drive roller 27, and the manual feed roller shown in the dotted line on the right side in FIG. Fifty,
Timing roller 42, metal roller 43, transfer roller 2
8. When the fixing device 52 is attached to the opening / closing lid of the color image forming apparatus and put together, the unit can be easily pulled out to the transfer roller 28 side. When this unit is pulled out to the side of the opening / closing lid (front side of the apparatus) and when it is pulled out in the axial direction of the image carrier 12, it is easy to design a positioning mechanism and an avoidance mechanism for preventing damage to devices such as the image carrier 12, and at the same time. Maintainability is greatly improved.

The operation will be described with reference to FIG. The process of printing a color image will be described. When printing a color image, images are formed in the order of yellow (Y), magenta (M), cyan (C), and black (BK). First, when a yellow image signal is sent, the image forming unit 10 rotates and rotates until the yellow image forming unit 10 contacts the intermediate transfer belt 19 at a horizontal position. The intermediate transfer belt 19 contacts the image carrier 12 in synchronization with the movement of the yellow image forming unit 10 to the image forming position. The exposure device 20 emits a laser beam corresponding to a yellow image signal, and charges the same as a normal black-and-white printer.
The latent image is formed and developed, and then visualized. In this embodiment, the image carrier 12 is negatively charged, and the toner is also negatively charged. The yellow toner image is transferred onto the intermediate transfer belt 19 to which a voltage is applied by the intermediate transfer power supply 32 via the pressing roller 24. The applied voltage at this time was + 200V. The transfer roller 28 keeps a state in which no voltage is applied so as not to disturb the toner image on the intermediate transfer belt 19 and separates from the intermediate transfer belt 19.

When the image formation for one screen is completed, the intermediate transfer belt 19 is temporarily stopped at the position where the portion not holding the toner image comes into contact with the image carrier 12. The stop position on the intermediate transfer belt 19 is about 80 mm between the leading edge and the rear end when the A4 size image is fed vertically, and the distance from the charging position of the image forming unit 10 to the transfer position is considered. To set. During the series of operations for transferring the toner image to the intermediate transfer belt 19, the cleaning roller 35 of the cleaning device 34 is applied with the same polarity and voltage as the transfer roller 28, and the toner on the intermediate transfer belt 19 is applied to the cleaning device 34. The image is never recovered. When the intermediate transfer belt 19 stops, the group of image forming units 10 rotates and moves to a position where the next magenta image forming unit 10 can contact the intermediate transfer belt 19. When the rotational movement of the unit is completed, a magenta toner image is formed on the image carrier 12 through the same process as the yellow image formation, and the intermediate transfer belt 19 is aligned with the front end of the yellow image and the intermediate transfer is performed. The belt 19 starts to rotate again,
A voltage of about +300 V is applied to the pressing roller 24 from the intermediate transfer power source 30, and the magenta toner image is transferred onto the yellow toner image on the intermediate transfer belt 19 in an overlapping manner. The transfer roller 28 remains separated from the intermediate transfer belt 19 as in the transfer of yellow. Since a voltage higher than that at the time of yellow transfer is applied to the intermediate transfer belt 19, the yellow toner previously transferred to the image carrier 12 of the magenta image forming unit 10 does not reversely transfer. Similarly, a cyan image of +350 V is applied to the intermediate transfer belt 19 to transfer the cyan image over the yellow and magenta toner images. The transfer roller 28 remains separated as in the case of yellow and magenta. When the black toner image of the fourth color is transferred by applying a voltage of +460 V to the intermediate transfer belt 19, the transfer roller 28 shifts the timing to a portion of the intermediate transfer belt 19 where there is no toner image (slightly before the leading edge of the image portion). Together, they contact the intermediate transfer belt 19. +1 which is almost the same as the contact and opposite to the charging polarity of the toner
000V is applied. During transfer of the black image of the fourth color from the image carrier 12 onto the intermediate transfer belt 19, the image receiving paper 37
Re-transcription to After the image receiving paper 37 is fed by the paper feed roller 44 or the manual paper feed roller 50, the timing roller 42 aligns the timing with the leading edge of the image on the intermediate transfer belt 19. Intermediate transfer belt 19
When all the above toner images are retransferred to the image receiving paper 37, the transfer roller 28 comes in contact with the intermediate transfer belt 19 again. At this time, +400 V applied during the transfer of the black image remains applied to the intermediate transfer belt 19. The image receiving paper 37 on which the four-color toner images are placed has the toner fixed by the fixing device 52 and is discharged to the outside of the machine.

While the toner images of the respective colors are superposed and transferred onto the intermediate transfer belt 19, the cleaning device 34 remains in contact with the intermediate transfer belt 19, but a voltage of about -300 V is applied to the cleaning roller 35. By doing so, the toner image on the intermediate transfer belt 19 can be held without being disturbed. However, since the toner remaining on the intermediate transfer belt 19 without being retransferred to the image receiving paper 37 and the toner adhering to the outside of the width of the image receiving paper 37 remain, the cleaning device 3
A voltage of about + 1000V is applied to the cleaning roller 35 of No. 4 because it has a positive polarity which is the opposite polarity to the charging polarity of the toner
The toner remaining on the intermediate transfer belt 19 is cleaned at least while the intermediate transfer belt 19 makes one round. After this cleaning operation, the unit was changed from the black image forming unit 10 to the yellow image forming unit 10,
At the same time, the voltage applied to the transfer belt 19 is switched from the transfer voltage of the black toner image + 400V to the transfer voltage of the yellow image + 200V, the image carrier 12 of the yellow image forming unit 10 contacts the intermediate transfer belt 19, and the same operation is performed. A new image is formed by.

The transfer voltage applied to the transfer roller 28 is
The state of the image receiving paper 37, for example, low in a high temperature and high humidity environment,
Further, it may be set higher in a low temperature and low humidity environment so that optimum retransfer can be obtained. This is because the resistance fluctuation of the resistance layer of the transfer roller 28 is absorbed. Similarly, from the image carrier 12 of the image forming unit 10 to the intermediate transfer belt 19
The voltage applied to the intermediate transfer power supply 32 at the time of transferring the toner image may be adjusted according to the environment. For these adjustments, a humidity sensor and a temperature sensor may be arranged in the machine, and after the reading, the adjustment may be performed according to a predetermined program.

Next, an embodiment of image density control will be described with reference to the drawings. FIG. 2 is a block diagram of density unevenness correction when the toner image formed on the image carrier 12 of the unit 10 is transferred to the intermediate transfer belt 19, and the image on the intermediate transfer belt 19 is retransferred to the image receiving paper 37. A block diagram for performing density correction when performing is shown. In FIG. 2, reference numeral 60 denotes a drive motor for driving the image carrier 12 when the image carrier 12 is at the image forming position (position where it can contact the intermediate transfer belt 19). Reference numeral 62 is a measuring circuit for calculating the driving torque from the current when the driving motor 60 is driven. Reference numeral 64 is an arithmetic circuit that compares the result of the measurement circuit 62 with the reference torque of the drive motor 60 to determine an appropriate voltage value. On the other hand, 6
Reference numeral 6 denotes a rotation speed measuring means for measuring the rotation speed of the transfer roller 28 driven by the intermediate transfer belt 19,
It can be measured by an optical method. Reference numeral 68 denotes a control circuit for comparing the result obtained by the rotation speed measuring means with a reference rotation speed to determine an appropriate voltage applied to the transfer roller 28. Next, the operation will be described with reference to FIG. Imaging unit 1
0 rotates to a position where it contacts the intermediate transfer belt 19 to form a toner image. At this position, the image bearing member 12 is connected to the driving motor 60 to rotate the image bearing member 12 to start image formation.
An image signal is sent to form an electrostatic latent image on the image carrier 12 and the electrostatic latent image is visualized by the developing device. At the same time, the measuring circuit 62 measures the current required to drive the driving motor 60.
Next, the transfer voltage to the intermediate transfer belt 19 is determined by the arithmetic circuit 64 based on the measurement result. Voltage drive motor 60
DC motor is used for the drive current is about 175mA
In case of, 160 ± 10 with proper drive current as reference current
If it is mA, the current drive current exceeds the reference value,
The driving torque increases and the rotation of the image carrier 12 is slow. In the above operation example, the transfer voltage for the first color is + 200V
Therefore, the transfer voltage lower than the initially set +200 V is calculated from the previously prepared comparison table of the drive current and the proper transfer voltage, and the output voltage of the intermediate transfer power source 32 is adjusted.
As described above, the voltage applied to the intermediate transfer belt 19 can be sequentially adjusted so that the unevenness of the image density does not occur.

To control the transfer voltage to the transfer roller 28, first, the rotation speed of the transfer roller 28 is measured by the rotation speed measuring means 66. Next, the control circuit determines an appropriate applied voltage based on the measurement result. For example, the reference speed is 120 ± 3
In the case of rpm, if the measurement result is 128 rpm, it turns out that the rotation is faster than the reference frequency, and control is performed to increase the transfer voltage from the comparison table of the rotation speed and the appropriate transfer voltage prepared in advance. The density unevenness that occurs during transfer onto the image receiving paper 37 is suppressed.

As described above, it is possible to obtain a good image by suppressing unevenness in density that occurs during transfer from the image carrier to the intermediate transfer belt and from the intermediate transfer belt to the image receiving paper.

[0028]

INDUSTRIAL APPLICABILITY As described above, the present invention forms an image with an image carrier that rotates at least, a charging unit that charges the image carrier, and a developing unit that has developers of different colors. A plurality of movable image forming unit groups in which the units are arranged in an annular shape, and a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group,
Each time the toner image is transferred to the intermediate transfer belt, the image forming unit group is rotated about the center of rotation to move the image carrier in contact with the intermediate transfer belt, and the intermediate transfer belt is used as the image carrier. A transfer electrode for pressing, a power supply capable of varying the voltage for applying a voltage to the transfer electrode, a measuring unit for measuring the driving state of the image carrier when the image forming unit is in the image forming position, and an intermediate transfer The belt is provided with a conductive transfer roller that retransfers the toner image held on the intermediate transfer belt to the image receiving paper by pressing the image receiving paper against the belt, and the voltage applied to the transfer electrode is measured by the measuring means. In a color image forming apparatus or a similar image forming apparatus characterized by being determined based on the result, a rotation measuring unit for measuring the driving state of the transfer roller, and a transfer roller. A power source capable of varying the voltage for applying a voltage to the transfer roller, and the voltage applied to the transfer roller is determined based on the result measured by the rotating unit. A good color image without unevenness can be obtained.

As described above, when the image forming unit is configured for each color, the handling such as maintenance becomes good. Furthermore, unevenness in density that occurs due to each unit having its own power transmission system is avoided by detecting the drive state of the motor that drives the image carrier of each unit and applying an appropriate transfer voltage. Get the image. Similarly, when transferring the toner image on the intermediate transfer belt to the image receiving paper,
It is possible to obtain a good color image by controlling the transfer voltage by detecting the surface moving speed of the intermediate transfer belt or the driving state of the transfer roller for pressing the image receiving paper against the intermediate transfer belt.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram for controlling image density unevenness of a color image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a conventional color output device.

[Explanation of symbols]

 10 image forming unit 12 image carrier 14 charging roller 16 developing device 17 cleaning blade 19 intermediate transfer belt 20 exposure means 24 pressing roller 28 transfer roller 30 transfer power supply 32 intermediate transfer power supply 34 cleaning device 35 cleaning roller 37 image receiving paper 44 paper feed roller 60 Driving Motor 62 Measuring Circuit 64 Arithmetic Circuit 66 Rotation Speed Measuring Means 68 Control Circuit

Claims (2)

[Claims] 1. A plurality of annularly arranged image forming units each including at least a rotatable image bearing member, a charging unit for charging the image bearing member, and a developing unit having a developer of a different color. A movable image forming unit group, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the toner image is transferred to the intermediate transfer belt each time the toner image is transferred. Moving means for changing the image carrier in contact with the intermediate transfer belt by rotating and moving the image forming unit group around the center of rotation; transfer electrodes for pressing the intermediate transfer belt against the image carrier; A power source capable of varying a voltage for applying a voltage to the transfer electrode; a measuring unit that measures the driving state of the image carrier when the image forming unit is in the image forming position; and the intermediate transfer unit. A conductive transfer roller for retransferring the toner image held on the intermediate transfer belt to the image receiving paper by pressing the image receiving paper against the image transfer belt, and the voltage applied to the transfer electrode is A color image forming apparatus, which is determined based on a result measured by a measuring unit. 2. A plurality of annularly arranged image forming units each including at least a rotatable image bearing member, a charging unit for charging the image bearing member, and a developing unit having a developer of a different color. A movable image forming unit group, a conductive intermediate transfer belt that conveys toner images of a plurality of colors formed by the image forming unit group, and the toner image is transferred to the intermediate transfer belt each time the toner image is transferred. By moving the image forming unit group around the rotation center to change the image carrier in contact with the intermediate transfer belt, and by pressing the image receiving paper against the intermediate transfer belt, A conductive transfer roller that retransfers the held toner image to the image receiving paper, a rotation measuring unit that measures a driving state of the transfer roller, and a voltage is applied to the transfer roller. Comprising a power supply voltage of the eye can be changed, the voltage applied to the transfer roller, the color image forming apparatus characterized in that it is determined based on results measured by said rotating means.