JP2008176149A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve more stable control of an intermediate transfer belt by enabling control of the surface speed of a secondary transfer roller so as to restrain influence on the drive of the transfer belt. <P>SOLUTION: A secondary transfer rotated roller 15 rotated with the secondary transfer roller 8 is arranged, and a rotational speed detection device 16 is provided on the rotary shaft of the secondary transfer rotated roller 15 so as to detect the speed of the surface of the secondary transfer roller 8. Then the rotational speed of the secondary transfer roller 8 is controlled based on the speed information of the rotational speed detection device 16. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that transfers a toner image created on a photoreceptor using an intermediate transfer belt onto a recording sheet at a secondary transfer roller unit.

In recent years, in order to improve image quality in an electrophotographic image forming apparatus, a technique for controlling the speed of an intermediate transfer belt to reduce color misregistration and banding has been used.
For example, the moving amount or moving speed of the intermediate transfer belt that is rotationally driven by a driving device such as a motor is detected by an encoder attached to a pulley or the like that stretches the intermediate transfer belt, and the position and speed information is also obtained. In addition, high-precision speed control is realized by controlling the rotation speed of the intermediate transfer belt.

Further, in Patent Document 1, in a belt conveyance device that spans an intermediate transfer belt between a drive roller and a pulley and drives the intermediate transfer belt by driving the drive roller, a roller that presses against the intermediate transfer belt, A first encoder disposed on the same axis; a second encoder disposed on the shaft of the drive roller; and a detection unit configured to detect a belt traveling speed of the intermediate transfer belt based on rotation information of the first encoder. By detecting the slip of the roller pressed against the intermediate transfer belt from the output ratio of the encoder to the second encoder and correcting the output of the first encoder with the output of the second encoder, the belt running speed A technique for maintaining a constant value is disclosed.
In general, in an image forming apparatus, a toner image formed on a photosensitive member is once superimposed on an intermediate transfer belt, and a secondary transfer roller is attached to the intermediate transfer belt to transfer the toner image on the intermediate transfer belt to a recording sheet. The transfer is realized by pressing the portion where the secondary transfer roller is in contact with the recording paper. Therefore, the secondary transfer roller is driven by a driving device separately from the intermediate transfer belt for conveying the recording paper.

Since the secondary transfer roller is also driven in contact with the intermediate transfer belt in this way, when the rotational speed of the secondary transfer roller varies or when there is a speed difference with the moving speed of the intermediate transfer belt. Or the like affects the rotational speed of the intermediate transfer belt and causes speed fluctuation.
In order to improve this state, it is necessary to rotationally drive the secondary transfer roller at the same speed as the speed of the intermediate transfer belt or a constant speed difference. As a technique for controlling the rotational drive of the secondary transfer roller, Patent Document 2 discloses a secondary drive that is driven by a motor that is in contact with the intermediate transfer belt and that is in contact with the intermediate transfer belt and that is separate from the drive motor for the intermediate transfer belt. In a conveyor belt apparatus including a transfer roller, a speed detection pattern formed on the intermediate transfer belt is detected by a speed detection pattern, and a rotation of the secondary transfer roller is synchronized with the rotation speed fluctuation. Controlling speed is described.
JP 2006-78906 A JP 2004-4573 A

However, the recording paper is conveyed at the surface speed of the secondary transfer driving roller. However, when the secondary transfer driving roller is decentered or the surface of the secondary transfer driving roller is deformed, When the surface speed fluctuates and the rotation speed is detected on the shaft of the secondary transfer roller, the fluctuation cannot be detected.
Therefore, in the present invention, a secondary transfer follower roller that is brought along with the secondary transfer roller is provided, and a rotational speed detection device such as an encoder is provided on the rotation shaft of the secondary transfer follower roller. The surface speed of the secondary transfer roller can be controlled by controlling the rotational speed of the secondary transfer roller based on the speed information of the rotational speed detection device, and the influence on the drive of the transfer belt can be controlled. An object of the present invention is to realize a more stable control of the intermediate transfer belt.
Depending on the material of the secondary transfer roller, the roller diameter expands and contracts due to a temperature change, and the surface speed of the secondary transfer roller changes. An object of the present invention is to minimize the influence of changes in the roller diameter of the secondary transfer roller by changing the material and diameter of the roller, and to keep the surface speed of the secondary transfer roller constant.

  In order to solve the above-described problems, the invention described in claim 1 includes an intermediate transfer belt that superimposes toner images formed on a plurality of photoconductors, an abutting contact with the intermediate transfer belt, and the intermediate transfer belt. A secondary transfer roller that transfers the toner image superimposed on the recording paper to a recording paper, a secondary transfer rotation roller that rotates in contact with the secondary transfer roller, and the secondary transfer roller Speed detecting means for detecting the angular speed of the rotating shaft on the rotating shaft of the follower roller; and speed control means for controlling the rotating speed of the secondary transfer roller based on the angular speed detected by the speed detecting means. The image forming apparatus is provided.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the follower roller has a smaller diameter than the secondary transfer roller.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the secondary transfer rotation roller is formed of a material having a smaller thermal expansion coefficient than the secondary transfer roller. Features the device.

  By detecting the rotation of the secondary transfer follower roller that rotates with the secondary transfer roller, it is possible to detect surface speed fluctuations due to the distortion and eccentricity of the secondary transfer roller. By controlling the rotational speed of the secondary transfer roller, the surface speed can be controlled to be constant.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a main part of an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 1 drives the photoreceptors 2-1 to 4 corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (B), the intermediate transfer belt 3, and the intermediate transfer belt 3. The intermediate transfer belt drive roller 4 for carrying out the operation, pulleys 5 and 6 for stretching the intermediate transfer belt 3, and a tension pulley 7 for applying a tension to the intermediate transfer belt 3 to keep the tension constant.
Here, the intermediate transfer belt 3 is driven by the intermediate transfer belt drive roller 4 being rotationally driven by a drive mechanism (not shown).
Further, a secondary transfer roller 8 is further arranged so as to contact the intermediate transfer belt 3 at a position corresponding to the pulley 6.

  When image formation is performed in the image forming apparatus according to the present exemplary embodiment, in the configuration illustrated in FIG. 1, image information based on charges called a latent image by a laser beam (not illustrated) or the like on the photoreceptors 2-1 to 4 corresponding to each color. And a toner image is formed on the photoreceptors 2-1 to 4 by adsorbing the toner to the charge by a developing device (not shown). Thereafter, the toner image on the photosensitive member is transferred to the intermediate transfer belt 3. In particular, when color printing is performed, each color toner image created on each photoconductor is transferred onto the intermediate transfer belt 3 and superimposed to form a color image. The color image formed on the intermediate transfer belt 3 is transferred onto the recording paper P conveyed from the right hand direction to the left hand direction in FIG. The image forming apparatus is configured to form a print image on the recording paper P that is fixed by being heated and pressed by a fixing device including a heating roller and a pressure roller (not shown).

FIG. 2 is a diagram illustrating a configuration when an encoder is provided on the secondary transfer roller.
In FIG. 2, the encoder 10 is connected to the secondary transfer roller 8 and the number of edges of pulses output from the encoder 10 is counted to measure the amount of rotation when the secondary transfer roller 8 is rotationally driven. Do it. Based on the number of pulses obtained from the encoder 10, the secondary transfer drive control device 11 performs speed control calculation so that the rotation shaft of the secondary transfer drive motor 13 has a constant rotational speed, and the motor drive is performed based on the result. The command value is output to the secondary transfer drive motor driver 12. The secondary transfer drive motor driver 12 generates a drive signal that matches the motor, such as a drive current for driving the secondary transfer drive motor 13 and PWM output, and the number of pulse edges obtained from the encoder output for the secondary transfer drive motor 13 Rotational drive control is performed so as to be equal per unit time. By performing such processing, the secondary transfer roller 8 is rotationally driven at a constant speed.

3A and 3B are diagrams showing changes in the state of the secondary transfer roller 8, respectively. FIG. 3A shows a normal state where the drive shaft 14 is not decentered and the roller diameter is distorted, and FIG. 3B shows the roller diameter. The state where the drive shaft 14 is decentered even if there is no distortion, (c) is a diagram showing a state where the drive shaft 14 is not decentered but the roller diameter is distorted.
According to the configuration of FIG. 2, the angular velocity of the drive shaft 14 of the secondary transfer roller 8 can be kept constant, but the drive shaft 14 and the roller diameter are normal as shown in FIG. When the drive shaft 14 of the transfer roller 8 is not eccentric and the roller is not distorted, the speed converted from the position / angular speed measured by the encoder 10 attached to the drive shaft 14 and the speed of the surface of the secondary transfer roller 8 are It will be the same.

However, when the drive shaft 14 of the secondary transfer roller 8 is eccentric as shown in FIGS. 3B and 3C, or when the roller diameter is distorted, the drive of the secondary transfer roller 8 is performed. Even if the drive shaft 14 is rotationally driven at an equiangular speed using pulses from the encoder 10 provided on the shaft 14, the speed of the roller surface of the secondary transfer roller 8 differs (varies) according to the distance from the shaft center. Will occur.
As described above, since the fluctuation of the surface speed of the secondary transfer roller 8 cannot be detected by the encoder 10 on the drive shaft 14, the intermediate transfer belt 3 and the secondary transfer roller are rotated when the intermediate transfer belt 3 is rotating at a constant speed. 8 changes the speed of the surface 8 and changes the conveyance speed of the recording paper, and also causes a load fluctuation in driving the intermediate transfer belt 3, which causes the fluctuation of the speed of the intermediate transfer belt 3.

FIG. 4 is a diagram showing the configuration of the secondary transfer roller of the present invention.
FIG. 4A is a schematic configuration diagram showing the secondary transfer roller 8 and a secondary transfer rotation roller that rotates around the secondary transfer roller 8, and FIG. 4B is a side view thereof.
As shown in FIGS. 4 (a) and 4 (b), a secondary transfer follower roller 15 is provided that contacts and drives the secondary transfer roller 8, and an encoder 16 (speed detecting means) is provided on the rotating shaft. Arranged. The secondary transfer rotation roller 15 is configured to be pressed in a direction (D) orthogonal to the drive shaft 14 of the secondary transfer roller 8 and rotate with the rotation of the secondary transfer roller 8. ing. Unlike the configuration shown in FIG. 2, the encoder 16 is provided at the axial center of the secondary transfer roller 15.

FIG. 5 is a diagram showing a drive control configuration of the secondary transfer roller 8 in the case of FIG.
In FIG. 5, an encoder 16 is connected to the secondary transfer follower roller 15 and the number of edges of pulses output from the encoder 16 is counted to rotate when the secondary transfer follower roller 15 is rotationally driven. Measure quantity. Based on the number of pulses obtained from the encoder 16, the secondary transfer drive control device 18 (speed control means) performs a speed control calculation so that the rotation shaft of the secondary transfer drive motor 13 has a constant rotational speed. From the result, the motor drive command value is output to the secondary transfer drive motor driver 19. The secondary transfer drive motor driver 19 creates a drive signal that matches the motor, such as a drive current for driving the secondary transfer drive motor 17 and PWM output, and the number of pulse edges obtained from the encoder output for the secondary transfer drive motor 17 Rotational drive control is performed so as to be the same per unit time. By performing such processing, the secondary transfer roller 8 is rotationally driven at a constant speed.

As shown in FIG. 4, the secondary transfer rotation roller 15 is moved to the secondary transfer rotation roller 15 by rotating the rotation axis of the secondary transfer rotation roller 15 to detect the position and speed. Since it is driven to rotate at the surface speed of the transfer roller 8, the secondary transfer roller 15 can measure the surface speed of the secondary transfer roller 8 including fluctuations due to eccentricity and deformation of the secondary transfer roller 8. Become.
In other words, by detecting the rotation of the secondary transfer roller 15 that rotates with the secondary transfer roller 8, it is possible to detect surface speed fluctuations due to the influence of the distortion or eccentricity of the secondary transfer roller 8, and this speed information is Originally, the surface speed can be controlled to a constant speed by controlling the speed of the secondary transfer roller 8.

By the way, when the temperature environment is changed, expansion and contraction occur in the diameter of the secondary transfer roller 8. Accordingly, in the conventional method of detecting the speed with the drive shaft 14 of the secondary transfer roller 8, the surface speed of the secondary transfer roller 8 increases when the diameter of the secondary transfer roller 8 expands, and the surface when it contracts. There is a problem that the speed becomes slow.
That is, when the secondary transfer roller 8 expands, if the angular speed of the drive shaft 14 of the secondary transfer roller 8 is constant, the speed varies according to the amount of change in the circumferential length of the secondary transfer roller 8. Become.

4 and 5, a secondary transfer follower roller 15 is arranged so as to follow the secondary transfer roller 8, and the thermal expansion coefficient of the secondary transfer roller 8 is set to β1,2 and the heat of the secondary transfer follower roller. Β1> β2 when the expansion coefficient is β2.
It is composed of materials that satisfy the following formula.
By doing so, the change in the surface linear velocity is such that the surface linear velocity of the secondary transfer driving roller 8 is v1, and the surface linear velocity of the secondary rolling roller 15 is v2, the amount of speed fluctuation of v1. The ratio vr of the speed fluctuation amount between v2 and v2 is vr = √ (β1 / β2)
Thus, the larger this ratio, the smaller the influence on v2 even when the speed fluctuation of v1 is large.
That is, by satisfying the above equation, speed fluctuation due to temperature change of the secondary transfer roller 8 is reduced.

Further, when the diameter of the secondary transfer roller 8 is L1, and the diameter of the secondary transfer rotation roller 15 is L2, the secondary transfer rotation roller 15 is compared with the case where the encoder 10 is mounted on the secondary transfer roller 8 axis. In the case where the encoder 16 is mounted on the shaft, even if an encoder having the same resolution is used, the resolution with respect to the feed amount of the same recording paper or intermediate transfer belt is increased, and the effect of improving the position detection system can be obtained. Furthermore, the smaller the diameter in machining, the smaller the variation of the eccentric outer shape in machining can be suppressed. Therefore, the relationship between the diameters L1 and L2 is L1> L2.
It is preferable that

1 is a diagram illustrating a configuration of a main part of an image forming apparatus according to an embodiment of the present invention. The figure explaining the structure at the time of providing an encoder in a secondary transfer roller. The figure which shows each state change of a secondary transfer roller. The figure which shows the structure of the secondary transfer roller of this invention. The figure which shows the structure of the drive control of the secondary transfer roller of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 2-1-4 Photoconductor, 3 Intermediate transfer belt, 4 Intermediate transfer belt drive roller, 5, 6 Pulley, 7 Tension pulley, 8 Secondary transfer roller, 9 Recording paper conveyance roller, 10 Encoder, 11 Secondary transfer drive motor controller, 12 Secondary transfer drive motor driver, 13 Secondary transfer drive motor, 14 Drive shaft, 15 Secondary transfer rotation roller, 16 Encoder, 17 Secondary transfer drive motor, 18 Secondary transfer drive Motor controller, 19 Secondary transfer drive motor driver

Claims (3)

An intermediate transfer belt that superimposes toner images formed on a plurality of photoconductors, and a secondary transfer roller that contacts the intermediate transfer belt and transfers the toner images superimposed on the intermediate transfer belt to a recording sheet; In an image forming apparatus comprising:
A secondary transfer rotating roller that rotates in contact with the secondary transfer roller, a speed detection unit that detects an angular velocity of the rotation shaft on a rotation shaft of the secondary transfer rotation roller, and a detection by the speed detection unit An image forming apparatus comprising: a speed control unit configured to control a rotation speed of the secondary transfer roller based on the angular speed.   The image forming apparatus according to claim 1, wherein the follower roller has a diameter smaller than that of the secondary transfer roller.   3. The image forming apparatus according to claim 1, wherein the secondary transfer rotation roller is made of a material having a smaller coefficient of thermal expansion than the secondary transfer roller.

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