JPH08314284A - Image forming device - Google Patents

Abstract

PURPOSE: To precisely always keep a primary transfer current constant, by detecting the current quantity allowed to flow to a grounded electrode held in contact with an intermediate transfer body, and controlling the current quantity supplied to the intermediate transfer body based on the detected current quantity. CONSTITUTION: The primary transfer current is supplied by the primary transfer power source 40, to the primary transfer roller 28 of the intermediate transfer body unit. The current flowing in the direction to the photoreceptor 10 is allowed to flow from the photoreceptor 10 to the ground through the transfer belt 20 and the toner image T. While, the current flowing to the secondary transfer counter roller 23, transmitted through the transfer belt 20, is allowed to flow to the ground through a transfer current control device 41. The transfer current control device 41, provided in-between the secondary counter roller 23 and the ground, is allowed to measure the current flowing from the secondary transfer counter roller 23 to the ground. The primary transfer power source 40 is controlled based on the current quantity detected by the transfer current control device 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which forms a toner image using an intermediate transfer member.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus for forming a toner image by using an intermediate transfer member such as an intermediate transfer belt or an intermediate transfer drum has been used. For example, a color image forming method is known in which toner images of respective colors formed on a photoconductor are primarily transferred onto an intermediate transfer member to perform color superimposition, and then secondarily transferred onto a transfer material. By using the intermediate transfer member, the transfer material conveyance path of the image forming apparatus can be simplified, and the configuration of the image forming apparatus itself can be made small and simple.

Generally, in the primary transfer, a constant voltage system in which a constant voltage is applied is used in order to transfer the toner image on the photosensitive member to the intermediate transfer member. However, according to the constant voltage method, the voltage applied to the toner fluctuates due to manufacturing variations of the intermediate transfer member and characteristic changes due to long-term use, and the transfer efficiency becomes unstable.

On the other hand, according to Japanese Patent Laid-Open No. 4-128857, the transfer current of the primary transfer is estimated and controlled from the amount of charge applied to the transfer material from the secondary transfer means measured in the secondary transfer. A method of doing so is disclosed. Also, JP-A-4-
128858 discloses a method of estimating and controlling the primary transfer current by the secondary transfer current.

[0005]

However, in any of the control methods disclosed in JP-A-4-128857 and JP-A-4-128858, the transfer current of the primary transfer is estimated from the measurement result of the secondary transfer. It is a method of controlling. Therefore, there is a problem in that the change in the primary transfer current cannot be constantly measured, the measurement accuracy is low, and the primary transfer current cannot always be made constant.

[0006]

In order to solve this problem, an image forming apparatus of the present invention comprises a photoconductor, an image forming device for forming a toner image on the photoconductor, an intermediate transfer member, and an intermediate transfer member. A transfer device that transfers a toner image on a photoconductor onto an intermediate transfer body by applying a current to the transfer body, a ground electrode that contacts the intermediate transfer body, and a current amount detection that detects the amount of current flowing through the ground electrode. An apparatus and a controller for controlling the amount of current applied to the intermediate transfer member based on the amount of current detected by the current amount detector.

[0007]

The amount of current flowing through the ground electrode contacting the intermediate transfer member changes in accordance with the change in the primary transfer current. Therefore,
The change in the primary transfer current can be constantly measured by detecting the amount of current flowing through the ground electrode that is in contact with the intermediate transfer member by the current amount detection device. Further, the current amount of the primary transfer current measured in this way is more accurate than the value estimated from the current amount of the secondary transfer current. By controlling the amount of primary transfer device current applied to the intermediate transfer member based on this measured value, the primary transfer current can be accurately kept constant at all times.

[0008]

1 is a sectional view of an electrophotographic image forming apparatus 100 according to the present invention.

The electrophotographic image forming apparatus 100 is an electrophotographic printer that receives data from a host computer (not shown) to form an image.
It is composed of an intermediate transfer body unit 2, a print head 3, a developing unit 4, a paper feed cassette 5, a copy paper transport unit 6, and a fixing device 7.

The photoconductor unit contains the photoconductor 10 and an image forming element (not shown) such as a charging device and a cleaner disposed around the photoconductor 10, and the photoconductor 10 is provided.
Is cleaned by a cleaner and then uniformly charged by a charging device.

The print head 3 contains a laser diode, a scanning optical system, etc., and controls the laser diode based on the data from the host computer.
An electrostatic latent image is formed on the photoconductor 10 that is uniformly charged.

The developing unit 4 is rotatably provided around the developing unit shaft 11. Also, the developing unit 4
The developing devices 4Y, 4M, 4C, and 4K are housed in the developing device 4, and the selected developing device faces the photoconductor 10 by the rotation of the developing unit 4. The developing device facing the photoconductor 10 develops the electrostatic latent image formed on the photoconductor 10 to form a toner image T.

The paper feed cassette 5 feeds the print paper P stored therein at a predetermined timing and conveys it to the facing portion of the timing rollers 30 and 31.

Next, the detailed structure of the intermediate transfer body unit 2 will be described. FIG. 2 is a cross-sectional view showing the structure of the intermediate transfer body unit 2.

The intermediate transfer body unit 2 is mainly composed of an intermediate transfer belt 20, a driving roller 21 and a biasing roller 22 and 2.
Next transfer counter roller 23, intermediate transfer belt cleaner 2
5, a primary pre-transfer roller 27, and a primary transfer roller 28. The intermediate transfer belt 20 has a circumference of 370.
mm, width 250 mm, endless belt made of polycarbonate. As for the size of the intermediate transfer belt 20, when the maximum size of A4 size paper is used as the print paper P,
50 mm or more in both sub-scanning directions, preferably 1
Use one that is larger than 00 mm.

The intermediate transfer belt 20 is a drive roller-2.
1, energizing roller 22, secondary transfer opposing roller 23, 1
The pre-transfer roller 27 and the primary transfer roller 28 are stretched and suspended.
Is in contact with The surface of the drive roller 21 is made of a rubber material, and the drive is transmitted from the main motor 15 via a drive transmission device (not shown) such as a gear and a timing belt. Rotate in the direction of. Drive low
The rotation of the LA-21 is transmitted to the intermediate transfer belt 20, and the intermediate transfer belt 20 is conveyed in the counterclockwise direction at substantially the same speed as the rotation speed of the photoconductor 10. Also, the energizing roller-22
Is urged in the direction of arrow a, and the intermediate transfer belt 2
It is stretched so that 0 is not loose between the rollers. For this reason, the rotation of the drive roller -21 is caused by the rotation of the intermediate transfer belt 20.
Be efficiently transmitted to.

Further, a belt position detecting mark (not shown) is provided at a side end portion of the intermediate transfer belt 20. Belt position detection sensor (not shown)
The position of the intermediate transfer belt 20 can be detected by detecting the position. The belt position detection mark is provided by a method such as making a hole in the intermediate transfer belt 20, providing unevenness, or providing areas having different reflectances. As the belt position detection sensor, either a reflection type optical sensor or a transmission type optical sensor is used depending on the form of the belt position detection mark.

The primary transfer roller 28 is obtained by winding an elastic resistor such as silicon rubber or sponge around a core metal such as aluminum or stainless steel. The intermediate transfer belt 20 and the photoconductor 10 are connected to each other. It is biased in the direction of arrow b to bring it into contact. In addition, the primary transfer roller 28 has
A primary transfer current is applied by the primary transfer power supply 40. The primary transfer power supply 40 can change the amount of current,
The amount of current applied to the primary transfer roller 24 can be changed. The toner image T formed on the photoconductor 10 is 1
It is transferred to the intermediate transfer belt 20 by the primary transfer current applied to the next transfer roller 28, and is superposed on the intermediate transfer belt 20 by the required number of color components. The overlapping positions of the toner images T are made coincident with each other by timing with an intermediate transfer belt position detection sensor (not shown). When forming a single-color image, only one color toner image T is transferred onto the intermediate transfer belt 20, and the repeating process is not performed.

The toner image T transferred onto the intermediate transfer belt 20 is conveyed to a portion facing the secondary transfer roller 24 while being attached to the intermediate transfer belt 20. A secondary transfer counter roller 23 is provided at a portion of the intermediate transfer belt 20 facing the secondary transfer roller 24.

The secondary transfer roller 24 is made by winding an elastic resistor such as silicon rubber or sponge around a core metal such as aluminum or stainless steel. A secondary transfer current is applied to the secondary transfer roller 24. or,
The secondary transfer roller 24 can be pressed against and separated from the intermediate transfer belt 20. The drive of the secondary transfer roller 24 is transmitted from a drive motor 16 provided separately from the main motor 15 via a drive transmission device (not shown) such as a gear, a pulley and a timing belt. And rotates in the direction of the arrow in the figure.

The secondary transfer counter roller 23 includes a silicon rubber, a silicon rubber, a core metal such as aluminum and stainless steel.
An elastic resistor such as a sponge is wound, and is grounded via the transfer current control device 41. The transfer current control device 41 detects the amount of current flowing from the secondary transfer counter roller 23 to the ground. The transfer current control device 41 will be described in detail later.

The secondary transfer roller 24 is a printing paper P.
The pressure contact separation is performed in association with the conveyance of the sheet, and at the time of the pressure contact, the print sheet P and the intermediate transfer belt 20 are brought into contact with the secondary transfer counter roller 23. At this time, the toner image T on the intermediate transfer belt 20 is applied to the secondary transfer roller 24.
The secondary transfer current causes secondary transfer to the print paper P.
In this way, the superimposed toner image T is formed on the print paper P.

The toner image T secondarily transferred onto the print paper P is fixed by the copying paper transport unit 6 to the fixing device 7.
Be transported to. The fixing device 7 fixes the toner image T on the print paper P, discharges it to the outside of the machine, and finishes the image formation.

The intermediate transfer belt cleaner 25 has a cleaning blade 26 which can be brought into contact with and separated from the intermediate transfer belt 20. The cleaning blade 26 is made of an elastic member such as silicon rubber, and is pressed against the intermediate transfer belt 20 with a total contact force of 200 g during pressing to remove residual toner on the intermediate transfer belt 20.

FIG. 3 shows an image forming apparatus 10 according to the present invention.
It is a block diagram of the control circuit of 0. The CPU 32 controls each element such as the main motor, the print head 3, the intermediate transfer belt cleaner 25, the timing rollers 30, 31 based on the input from the host computer, the operation panel, the intermediate transfer belt position detection sensor and the like. .

FIG. 4 is a circuit diagram showing an equivalent circuit of the primary transfer portion.

The current (I
t) is a current (Ipc) flowing in the direction of the photoconductor 10,
The current (I
g). Current flowing in the direction of the photoconductor 10 (Ip
c) flows from the photoconductor 10 to the ground via the transfer belt 20 and the toner image T. On the other hand, the current (Ig) flowing to the secondary transfer counter roller 23 is transmitted through the transfer belt 20 and flows from the secondary transfer counter roller 23 to the ground. The transfer current control device 41 includes a secondary transfer facing roller 2
It is provided between No. 3 and the ground, and measures the current (Ig) flowing from the secondary transfer counter roller 23 to the ground.

Actually, the current used to transfer the toner image T is the current (Ipc) flowing toward the photoconductor 10.
Is. However, since there is an electric current flowing into the photoconductor 10 from the charging charger (not shown), the photoconductor 1
The current (Ipc) flowing in the 0 direction cannot be detected. Therefore, in the present invention, as described above, the transfer current control device 41 controls the secondary transfer counter roller 23.
The current (Ig) flowing into the is measured. As can be seen from this equivalent circuit, the current (I
pc) and the current (I
g) has a relation of It = Ig + Ipc, and by measuring the current (Ig) flowing into the secondary transfer counter roller 23, the same effect as that obtained by directly measuring the current (Ipc) flowing in the photoconductor 10 direction can be obtained. It is possible to raise.

That is, the current (Ig) flowing into the secondary transfer counter roller 23 is detected by the transfer current control device 41, and a current having a value obtained by adding a predetermined current amount (Ipc) to the current amount Ig is passed. As described above, the primary transfer power supply 40 is controlled. This control is always performed during the operation of the primary transfer power supply 40. Therefore, the equilibrium state represented by the formula It = Ig + Ipc is always maintained.

FIG. 5 is a graph showing the relationship between the primary transfer current applied by the primary transfer power supply 40, the transfer efficiency, and the core metal voltage of the primary transfer roller 28. The case where the resistance value and the resistance value of the primary transfer roller 28 are changed is shown.

In practice, the resistance value of the intermediate transfer belt is 1 due to variations in manufacturing and deterioration due to long-term use.
The resistance value of the digit and the primary transfer roller may change within a width of about two digits.

As can be seen from these figures, when the primary transfer current value is set to 3 μA to 5 μA, particularly 4 μA, the transfer efficiency is stable regardless of the resistance values of the intermediate transfer belt and the primary transfer roller. To 90% or more.

On the contrary, when the voltage applied to the core metal of the primary transfer roller is controlled to a constant voltage, if the resistance values of the intermediate transfer belt and the primary transfer roller change, the value of the primary transfer current changes, and Efficiency is not stable.

For example, when constant voltage control is performed at 1.04 kV,
In the case of a standard intermediate transfer belt (surface resistance 10 9 Ω / sq) and a standard primary transfer roller (resistance 10 3 Ω), the primary transfer current is 4 μA and a transfer efficiency of 90% or more is obtained. However, the surface resistance of the intermediate transfer belt is 10 7 Ω /
When it fluctuates to sq, the primary transfer current becomes 5.9 μA,
The transfer efficiency is 90% or less. Similarly, when the resistance of the primary transfer roller fluctuates to 10 5 Ω, the primary transfer current becomes 2.6 μA and the transfer efficiency becomes 90% or less.

In the present invention, since the current amount of the primary transfer current is directly detected and the current amount of the primary transfer power source 40 is controlled, the transfer efficiency becomes stable.

FIG. 6 shows another embodiment of the present invention. In this embodiment, the primary pre-transfer roller 27 is grounded, and the current flowing into the ground via the primary pre-transfer roller 27 is detected. In this way, the primary pre-transfer roller 2
7 is provided between the facing portion of the primary transfer roller 28 and the facing portion of the secondary transfer roller 24 of the intermediate transfer belt 20 in contact with the intermediate transfer belt 20. Acts as. The guard electrode means an electrode that is provided between the primary transfer portion and the secondary transfer portion and that prevents current from flowing from the primary transfer portion to the secondary transfer portion. The guard electrode is not limited to the pre-primary transfer roller 27,
Any roller or electrode that contacts the intermediate transfer belt may be used. When a plurality of images are continuously output, the guard electrode can prevent current from flowing from the primary transfer portion to the secondary transfer portion during the secondary transfer of the previous image.
This makes it possible to perform the primary transfer of the next image while the secondary transfer of the previous image is performed.

FIG. 7 is a graph showing the relationship between the primary transfer current and transfer efficiency when the pre-primary transfer roller 27 is grounded and when it is floated, and the voltage applied to the core metal of the primary transfer roller 28. Is. From this graph, it is understood that the transfer efficiency is better when the pre-primary transfer roller 27 is grounded and used as a guard electrode.

The ground electrode connecting the transfer current control device 41 may be in contact with the intermediate transfer belt so that the current flowing from the intermediate transfer belt to the ground can be detected. It is not limited to
Further, the present invention can be used in an image forming apparatus using another intermediate transfer member such as an intermediate transfer film, an intermediate transfer drum, or a transfer roller instead of the intermediate transfer belt.

[0039]

By using the present invention, the change in the primary transfer current can be constantly measured, and the primary transfer device current amount applied to the intermediate transfer member can be controlled based on the measured current amount. It is possible to keep the primary transfer current constant with high accuracy. As a result, even if the intermediate transfer member fluctuates or fluctuates due to deterioration, the current used to actually transfer the toner is controlled to be constant, so that stable transfer efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an electrophotographic image forming apparatus according to the present invention.

FIG. 2 is a cross-sectional view showing a configuration of an intermediate transfer member unit according to the present invention.

FIG. 3 is a block diagram of a control circuit of the image forming apparatus according to the present invention.

FIG. 4 is a circuit diagram showing an equivalent circuit of the image forming apparatus according to the present invention.

FIG. 5 is a graph of primary transfer current, transfer efficiency, and primary transfer roller core metal voltage.

FIG. 6 is a sectional view showing a configuration of an intermediate transfer member unit according to another embodiment of the present invention.

FIG. 7 is a graph showing a case where a roller before primary transfer is grounded and a case where it is floated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor unit 2 Intermediate transfer body unit 3 Print head 4 Developing unit 5 Paper feed cassette 6 Copy paper transport unit 7 Fixing device 10 Photoconductor 15 Main motor 16 Drive motor 20 Intermediate transfer belt 21 Drive roller 22 Energizing Roller 23 Secondary Transfer Opposing Roller 24 Secondary Transfer Roller 25 Intermediate Transfer Belt Cleaner 27 Pre-Primary Transfer Roller 26 Cleaning Blade 28 Primary Transfer Roller 30 Timing Roller 31 Timing roller 32 CPU 40 Primary transfer power supply 41 Transfer current control device 100 Electrophotographic image forming device P Print paper T Toner image

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuo Tanaka 2-3-3 Azuchicho, Chuo-ku, Osaka Osaka International Building Minolta Co., Ltd.

Claims (1)

[Claims] 1. A photosensitive member, an image forming device for forming a toner image on the photosensitive member, an intermediate transfer member, and a toner image on the photosensitive member by applying a current to the intermediate transfer member. A transfer device that transfers the image onto the intermediate transfer member, a ground electrode that contacts the intermediate transfer member, a current amount detection device that detects the amount of current flowing through the ground electrode, and an application to the intermediate transfer member based on the current amount detected by the current amount detection device An image forming apparatus having a control device for controlling the amount of current to be applied.