JP5537483B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus using a plurality of photosensitive drums, such as a tandem color printer and a color copying machine.

  In an electrophotographic image forming apparatus using a plurality of photosensitive drums, first, an electrostatic latent image is formed by irradiating the surface of a first photosensitive drum charged by a charger with laser light of an output image. . The developing device forms a toner image by attaching toner of a certain color to the electrostatic latent image. The toner image is transferred to a copy sheet or an intermediate transfer belt by a transfer roller provided on the photosensitive drum in a one-to-one relationship. A voltage having a polarity opposite to that of the toner is applied to the transfer roller. The formation and transfer of the toner image are repeated by the number of photosensitive drums.

  Conventionally, one constant voltage source is provided for one transfer roller. In order to reduce the size of the apparatus, it is conceivable to use a parallel circuit to unite the power sources. For example, Patent Document 1 below is a case where a single constant voltage source is used, a change in toner density due to environmental / endurance fluctuations is detected, and a resistance element (having an environment dependency by switching a switch based on the result) ( A color image forming apparatus is described in which the primary transfer voltage is reduced by adding a circuit (not a circuit). Further, in Patent Document 2 below, a series circuit in which a plurality of transfer units are interposed with variable resistors is connected to one constant voltage source, a transfer current value is detected, and each transfer roller is detected based on the detected value. An image forming apparatus is described in which each variable resistance value is adjusted so as to compensate for a resistance value variation, and a transfer voltage applied to each transfer roller is made constant.

JP 2006-337816 A JP 2003-57917 A

  It is known that the resistance value of the surface of the photosensitive drum decreases as the usage time increases and becomes a different value for each photosensitive drum. The devices described in Patent Documents 1 and 2 cannot cope with such a change in resistance value for each photosensitive drum.

  The present invention provides an image capable of performing stable image formation over a long period of time in an image forming apparatus including a plurality of photosensitive drums, a plurality of transfer rollers corresponding to the plurality of photosensitive drums, and one constant voltage source. An object is to provide a forming apparatus.

The image forming apparatus according to claim 1, wherein a plurality of photosensitive drums whose resistance value decreases according to a use time, a plurality of transfer roller units corresponding to the photosensitive drums on a one-to-one basis, and each transfer roller unit And a constant voltage source connected in parallel to a plurality of closed circuits for applying a transfer voltage, wherein each closed circuit has a resistance value connected in series to a transfer roller unit. An adjustment circuit, the resistance adjustment circuit including a rod shaft, an urging means, and a variable resistance portion, wherein the rod shaft is provided on a drive shaft shaft of the photosensitive drum, Alternatively, it is electrically insulating, and the biasing means presses the variable resistance portion against the rod shaft, and the variable resistance portion includes an integrated resistance portion and a wear portion , In series with each transfer roller unit in each closed circuit Are continued, the wear part is at a position to be pressed against the rod axis, made of a material that is cut by the friction caused by the rotation of the rod axis, wherein the variable resistor unit includes a resistor portion and the wear portion It is an integrated conductive resin, the resistance value is increased in accordance with the reduction in the cross-sectional area of the conductive resin caused by scraping the wear part , and the voltage applied to the transfer roller unit is reduced, thereby The transfer current is made uniform by compensating for a decrease in the resistance value of each photosensitive drum.

According to a second aspect of the present invention, there is provided an image forming apparatus including: a plurality of photosensitive drums each having a resistance value that decreases according to a use time; a plurality of transfer roller units that correspond one-to-one to the photosensitive drum; And a constant voltage source connected in parallel to a plurality of closed circuits for applying a transfer voltage, wherein each closed circuit has a resistance value connected in series to a transfer roller unit. An adjustment circuit, the resistance adjustment circuit including a rod shaft, an urging means, and a variable resistance portion, wherein the rod shaft is provided on a drive shaft shaft of the photosensitive drum, Alternatively, the biasing means presses the variable resistance portion against the rod shaft, and the variable resistance portion includes an integrated or separate resistance portion and a wear portion. A transfer roller unit in each closed circuit. Tsu are serially connected to the preparative, the wear part is at a position to be pressed against the rod axis, made of a material that is cut by the friction caused by the rotation of the rod axis, wherein the resistance portion deforms under pressure This is a pressure-sensitive conductive elastic body with a reduced resistance value, and the pressing force against the resistance portion decreases and the resistance value increases according to the position change in the rod axis direction caused by the wear portion being shaved. The voltage applied to the transfer roller unit is lowered to compensate for a decrease in the resistance value of each of the photosensitive drums, thereby making the transfer current uniform.

The image forming apparatus according to claim 1 or 2 is configured so that the individual transfer currents are uniform according to the usage time of each photosensitive drum, so that one constant voltage source is used. However, a stable transfer current can always be supplied. Accordingly, stable image formation can be performed for a long time without replacing all the photosensitive drums at once.

In the image forming apparatus according to claim 1, wherein, by using the conductive resin as variable resistance unit, a simple configuration of a small number of parts, can supply a stable transfer current to the photosensitive drum. Accordingly, stable image formation can be performed for a long time without replacing all the photosensitive drums at once.

In the image forming apparatus according to claim 2 , a pressure-sensitive conductive elastic body is used for the resistance portion. However, since the resistance portion is not cut by this, there is no change in the resistance value due to the state of the surface to be cut by wear. A stable transfer current can be supplied by each photosensitive drum. Accordingly, stable image formation can be performed for a long time without replacing all the photosensitive drums at once.

1 is a cross-sectional view of an image forming apparatus. It is a block diagram of a constant voltage supply circuit. It is a figure which shows the structure in a photoconductor drum unit. It is a figure which shows the structure of the resistance value adjustment circuit in 1st Embodiment. It is a graph which shows the reduction | decrease of the resistance value of the photosensitive drum with respect to actual working time, and the increase of the resistance value of a resistance value adjustment circuit. It is a figure which shows the structure of the resistance value adjustment circuit in 2nd Embodiment.

  FIG. 1 is a cross-sectional view of an electrophotographic digital color image forming apparatus 1. The image forming apparatus 1 forms toner images of different colors (C, M, Y, Bk) on the four photosensitive drums 21a, 21b, 21c, and 21d, and the formed toner images are arranged in one direction. It is a tandem type that performs primary transfer sequentially to the moving intermediate transfer body 8.

  The charging / exposure devices 1a, 1b, 1c, and 1d charge the surfaces of the photosensitive drums 21a, 21b, 21c, and 21d, and form an electrostatic latent image by irradiating the output image with laser light. The developing devices 3a, 3b, 3c, and 3d form toner images by attaching cyan, magenta, yellow, and black toners to the electrostatic latent image, respectively. The primary transfer roller units 6a, 6b, 6c, and 6d provided on the photosensitive drums 21a, 21b, 21c, and 21d on a one-to-one basis transfer the toner image to the intermediate transfer belt 8 by the transfer roller. A voltage having a polarity opposite to that of the toner is applied to the transfer roller in accordance with a transfer voltage input to the unit. The formation and transfer of the toner image are repeated by the number of photosensitive drums.

  The full-color image formed by transferring the toner image of each color to the intermediate transfer belt 8 is transferred onto the copy paper supplied from the paper feed cassette 10 through the conveyance path 11 by the transfer roller of the secondary transfer roller unit 9. Transcribed. The copy sheet is discharged to the discharge tray 12 after being fixed.

  FIG. 2 is a configuration diagram of a constant voltage supply circuit. The circuit is connected to one constant voltage source 100 and the constant voltage source 100 in parallel, and four closed circuits (C1, C2) for supplying a transfer voltage equal to the transfer roller units 6a, 6b, 6c, 6d. , C3, C4). Each circuit (C1, C2, C3, C4) includes resistance value adjusting circuits 50a, 50b, 50c, 50d connected in series to the primary transfer roller units 6a, 6b, 6c, 6d in the circuit. ing.

  Each resistance value adjusting circuit has the same configuration. Hereinafter, the configuration of the resistance value adjusting circuit 50a will be described as an example. The resistance value adjusting circuit 50a is provided in the photosensitive drum unit 2a shown in FIG. The photosensitive drum unit 2 a has a frame, and the frame fixes the drive shaft 22 a of the photosensitive drum 21 a and the resistance value adjustment circuit 50 a at a predetermined position in the image forming apparatus 1.

  The resistance adjustment circuit 50a is attached to the drive shaft 22a and the frame of the unit 2a, and includes a rod shaft 52, an urging means 54, and a cylindrical variable resistance portion 53.

  The rod shaft 52 is of high resistance or electrical insulation provided on the drive shaft 22a axis.

  The biasing means 54 is an elastic body such as a spring, and lifts the variable resistance portion 53 upward in the drawing so as to press the variable resistance portion 53 against the rod shaft 52 with the frame of the photoreceptor drive unit 2 as a base.

  A more detailed configuration of the resistance value adjusting circuit 50a will be described below. FIG. 4 is a cross-sectional view showing a configuration of the resistance value adjusting circuit 50a in the first embodiment. FIG. 4A shows a state in the initial use. FIG. 4B shows a state after the elapse of time.

  The variable resistance portion 53 includes a resistance portion / abrasion portion 55 integrally formed therein. Both ends 56 and 57 of the resistance portion / wear portion 55 are connected in series between the transfer roller unit 6 a and the low voltage source 100 in the parallel connection circuit C <b> 1 of the constant voltage source 100. The resistance portion / wear portion 55 is in a position where it is pressed against the rod shaft 52, and is made of a material, such as resin, that is scraped by friction caused by the rotation of the rod shaft 52. When the resistance portion / wear portion 55 is cut, the cross-sectional area of the portion is reduced, and the resistance value increases in accordance with the position change in the direction of the rod shaft 52 as a result. As a matter of setting, for example, an electrically insulating sheet 58 made of rubber is provided between the variable resistance portion 53 and the resistance portion / wear portion 55.

  By adopting the above configuration, the resistance value adjusting circuit 50a becomes high resistance as the total number of rotations of the photosensitive drum increases, and the voltage applied to the transfer roller unit 6a connected in series in the circuit C1. make low.

  FIG. 5 is a graph conceptually showing a decrease in the resistance value of the photosensitive drum 21a with respect to use time (a graph indicated by an arrow 210) and an increase in the resistance value of the resistance value adjusting circuit 50a (a graph indicated by an arrow 500). It is. In an experiment using a certain color image forming apparatus and mounting a photosensitive drum in an initial state and a photosensitive drum printed with 100,000 sheets, respectively, the relationship between the primary transfer current and the transfer voltage was measured. Therefore, it was predicted that the resistance value of the photosensitive drum after printing 100,000 sheets was considerably lowered. From further experiments, it has been found that when a resistance of about 25 MΩ is applied to the photosensitive drum printed with 100,000 sheets, the current-voltage characteristics of the primary transfer of the photosensitive drum in the initial state are substantially equal. Along with other findings, it is predicted that the resistance value of the photosensitive drum decreases almost in proportion to the usage time. Therefore, the speed at which the resistance portion / wear portion 55 is scraped, that is, the rate of increase in the resistance value, compensates for the decrease in the resistance value of each photosensitive drum according to the rate of decrease in the resistance value of the photosensitive drum 21a. To make the transfer current uniform. By adopting this configuration, it is possible to realize stable operation of the image forming apparatus over a long period of time without replacing all the photosensitive drums at once.

  FIG. 6 is a diagram illustrating a configuration of the resistance value adjusting circuit 60a according to the second embodiment. FIG. 6A shows an initial use state. FIG. 6B shows a state after a predetermined actual working time has elapsed. In the figure, the same components as those of the resistance value adjusting circuit 50a are denoted by the same reference numerals, and redundant description is omitted. The circuits 60b, 60c, and 60d having the same configuration as the circuit 60a are attached to the photosensitive drums 21b, 21c, and 21d.

  The resistance value adjustment circuit 60 a includes a rod shaft 52, an urging means 54, and a cylindrical variable resistance portion 63. The variable resistance portion 63 includes a resistance portion 61 and a wear portion 62 inside. The resistance portion 61 is a pressure-sensitive conductive elastic body whose resistance value in the pressurizing direction is reduced by pressurizing and deforming, and two action points where resistance changes are connected in series to the parallel circuit C1. Is done. Examples of the pressure-sensitive conductive elastic body having the above characteristics include Inastomer (registered trademark) manufactured by Inaba Rubber Co., Ltd.

  The wear portion 62 is in a position where it is pressed against the rod shaft 52 and is made of a material, for example, resin, that is scraped by friction accompanying the rotation of the rod shaft 52. The wear part 62 pressurizes and deforms the resistance part 61 in the initial state. The wear part 62 reduces the pressure applied to the resistance part 61 according to the change in position in the direction of the rod axis 52 due to cutting, and as a result, increases the resistance value of the resistance part 61.

  By adopting the above configuration, the resistance value adjustment circuit 60a becomes high resistance as the total number of rotations of the photosensitive drum 21a increases, and the voltage applied to the transfer roller unit 6a connected in series in the circuit C1. Lower. The setting of the increasing rate of the resistance value of the resistance value adjusting circuit 60a is the same as that of the resistance value adjusting circuit 50a.

  The image forming apparatus according to the present invention is not limited to the tandem type, and includes a plurality of photosensitive drums whose resistance value decreases according to actual working time, a plurality of transfer roller units corresponding to the photosensitive drum one-to-one, and a photosensitive drum. A digital color printer or copier including a constant voltage source configured with a parallel connection circuit so as to apply a voltage for transferring a toner image attached to the surface of the body drum to each transfer roller unit It can be used for an image forming apparatus.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2a-2d Photosensitive drum unit 3a-3d Developer 6a-6d Primary transfer roller unit 8 Intermediate transfer belt 9 Secondary transfer roller unit 10 Paper feed cassette 11 Conveyance path 12 Paper discharge tray 50a-50d Resistance value adjustment Circuit 60a Modification of resistance adjustment circuit

Claims (2)

Parallel to a plurality of photosensitive drums whose resistance value decreases according to usage time, a plurality of transfer roller units corresponding to the photosensitive drums on a one-to-one basis, and a plurality of closed circuits for applying a transfer voltage to each transfer roller unit An image forming apparatus including one connected constant voltage source,
Each closed circuit includes a resistance value adjusting circuit connected in series to the transfer roller unit,
The resistance value adjusting circuit includes a rod shaft, an urging means, and a variable resistance portion,
The rod axis is provided on the drive shaft axis of the photosensitive drum, and has a high resistance or electrical insulation,
The urging means presses the variable resistance portion against the rod shaft,
The variable resistance portion includes an integrated resistance portion and a wear portion, and is connected in series to the transfer roller unit in each closed circuit,
The wear part is at a position pressed against the rod shaft, and is made of a material that is scraped by friction accompanying rotation of the rod shaft,
The variable resistance portion is a conductive resin in which the resistance portion and the wear portion are integrated, and the resistance value is increased in accordance with a decrease in the cross-sectional area of the conductive resin caused by the wear portion being shaved. By reducing the voltage applied to the roller unit, the transfer current is made uniform by compensating for the decrease in the resistance value of each photosensitive drum.
An image forming apparatus. Parallel to a plurality of photosensitive drums whose resistance value decreases according to usage time, a plurality of transfer roller units corresponding to the photosensitive drums on a one-to-one basis, and a plurality of closed circuits for applying a transfer voltage to each transfer roller unit An image forming apparatus including one connected constant voltage source,
Each closed circuit includes a resistance value adjusting circuit connected in series to the transfer roller unit,
The resistance value adjusting circuit includes a rod shaft, an urging means, and a variable resistance portion,
The rod axis is provided on the drive shaft axis of the photosensitive drum, and has a high resistance or electrical insulation,
The urging means presses the variable resistance portion against the rod shaft,
The variable resistance portion includes an integrated or separate resistance portion and a wear portion, and is connected in series to the transfer roller unit in each closed circuit,
The wear part is at a position pressed against the rod shaft, and is made of a material that is scraped by friction accompanying rotation of the rod shaft,
The resistance portion is a pressure-sensitive conductive elastic body whose resistance value is reduced by being deformed under pressure, and the pressing force against the resistance portion according to a change in position in the rod axis direction caused by the wear portion being shaved. Decreases , increases the resistance value, and lowers the voltage applied to the transfer roller unit, thereby compensating for the decrease in the resistance value of each of the photosensitive drums to make the transfer current uniform.
An image forming apparatus.

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