JP3525711B2 - Image forming device - Google Patents

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, and more particularly to an electrophotographic image forming apparatus such as a copying machine or a laser printer which uses a two-component reversal development method.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine or a laser printer, a two-component reversal developing method using a developer composed of a carrier and a toner is known. FIG. 4 is a schematic diagram showing an example of a color copying machine. In the figure, the toner image formed on the photosensitive drum 1 rotating in the direction of arrow B is transferred onto the recording paper supplied onto the transfer drum 2. Toner images of a plurality of colors are sequentially formed on the photosensitive drum 1 one by one, and the toner images of four colors are superposed on the recording paper on the transfer drum 2. The four-color toner recording paper is supplied via the curler 3 in a state of being bent and wound around the transfer drum 2. The recording paper on which the four color toner images have been transferred is peeled from the transfer drum 2 by the fingers 4 and conveyed to the thermal fixing device 5, where the curl is corrected by the decurler 6 and output.

Around the photosensitive drum 1, a charging device 7, an exposure device 8, a preliminary transfer device 9, a transfer device 10, a preliminary cleaning device 11, and a cleaner device 12 are arranged. Between the exposure position of the exposure device 8 and the preliminary transfer device 9,
A transfer unit 13 including a four-color toner developing device is disposed so as to be able to contact the photosensitive drum 1. Further, a peeling device 14 and transfer drum charge eliminating devices 15 and 16 are arranged around the transfer drum 2. The charging device 7, the preliminary transfer device 9, the transfer device 10, the preliminary cleaning device 11, the peeling device 14, and the transfer drum charge eliminating devices 15 and 16 are formed by corotron devices.

In this color image forming apparatus, for example, yellow (Y), magenta (M), cyan (C), black (K)
A full-color image can be obtained by superimposing the four color toner images on each other, but it is not easy to superimpose the four color toner images without shifting. Therefore, in order to prevent color misregistration, the peripheral lengths of the photosensitive drum 1 and the transfer drum 2 are set to integer ratios, and the gear ratio of the drive system is set so that the peripheral speeds of the photosensitive drum and the transfer drum match. Driving periodically.

A gear having a pitch circle with the same diameter as the photoconductor drum 1 and the transfer drum 2 is provided coaxially with the photoconductor drum 1 and the transfer drum 2 so that the relative position between the photoconductor drum 1 and the transfer drum 2 can be always kept constant. Image forming device. In this image forming apparatus, by engaging the gears,
Color misregistration is prevented by surely matching the cycles of speed fluctuations that can occur on the photoconductor drum 1 and the transfer drum 2 for each color of Y, M, C, and K.

JP-A-8-227200 discloses an electrophotographic apparatus using a combination of a photosensitive belt and a transfer belt, in which the photosensitive belt and the transfer belt are driven by gears and belts with gears. It is disclosed.

[0007]

The above-mentioned image forming apparatus has the following problems. As described above, when the photosensitive drum and the transfer drum are engaged with each other at an integer ratio, when the operation stop position of the transfer drum is fixed, the stop position of the photosensitive drum is also fixed. This is because the operation timing of the image forming apparatus is usually controlled based on the reference point on the transfer drum.

With the above structure, the corotron device and the cleaner device 12 around the photoconductor drum 1 are in a fixed position with respect to the photoconductor 1 when the operation is stopped. As a result, ozone generated from the corotron device stays at the same position on the photoconductor 1 or discharge products adhere to the photoconductor 1 to change the characteristics of the photoconductor 1 over a long period of time, resulting in image defects such as white spots. May be invited. In order to solve this problem, air flow in the image forming apparatus is taken into consideration, but there is a problem that the structure becomes complicated and the manufacturing process becomes complicated.

It is also conceivable to change the distance to the stop after the marking on the transfer drum is detected when the operation is stopped. However, since the time until the detection of the marking is changed at the start of the operation, the first print image is output. However, there is a problem that the time required for the process varies.

An object of the present invention is to solve the above problems,
An object of the present invention is to provide an image forming apparatus capable of preventing the characteristic deterioration of the photoconductor due to ozone and discharge products.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems and to achieve the object, a plurality of toner images formed on a photoconductor in a plurality of steps are sequentially formed on an intermediate transfer member. In the image forming apparatus configured to obtain the output image by performing the secondary transfer on the recording medium after the secondary transfer, the ratio of the peripheral length of the photosensitive member and the peripheral length of the intermediate transfer member is deviated from the integer ratio. There are features. According to the above characteristics, the relative positional relationship between the photoconductor and the intermediate transfer body is constantly changing. Therefore, for example, even when the intermediate transfer body is stopped at a fixed position, the stop position of the photoconductor can be changed.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a main part configuration diagram of a full-color printer which is an example of an image forming apparatus according to an embodiment of the present invention, and the same reference numerals as those in FIG. 4 denote the same or equivalent portions. Figure 1
In FIG. 1, a photosensitive drum (hereinafter, simply referred to as “photosensitive member”) 1 as an image bearing member is provided so as to be rotatable in the direction of arrow A by a motor (not shown). Around the photoreceptor 1, a charging device, that is, a charging corotron 7, an exposure device (R
OS) 8, a developing unit 13, a transfer device, that is, a transfer corotron 10, and a cleaner device 12. A cleaning corotron 11 is arranged in front of the cleaner device 12.

The developing unit 13 includes four developing devices 13Y, 13M, 13C and 13K for full color development.
Consists of. Developing devices 13Y, 13M, 13C, 13K
Develops the latent image on the photoconductor 1 with Y, M, C, and K toners, respectively. When developing the toner of each color, the developing unit 13 is rotated in the direction of arrow R by a motor (not shown), and the developing device of the color is aligned so as to contact the photoconductor 1.

The toner image of each color developed on the photoconductor 1 is transferred by the transfer device 10 to the belt 2 as an intermediate transfer member.
The toner images of four colors are superposed on each other.
The belt 2 is stretched around rolls 17, 18, 19, 20. Of these, the roll 17 functions as a drive roll that drives the belt 2 by being coupled to a drive source (not shown), the roll 18 functions as a tension roll that adjusts the tension of the belt 2, and the roll 19 functions as a secondary transfer device. Function as a backup roll for the transfer roll 21. A belt cleaner 22 is provided at a position facing the roll 20 with the belt 2 sandwiched therebetween, and residual toner on the belt 2 is scraped off by a blade.

The recording paper pulled out from the recording paper cassettes 23 and 24 to the conveying path by the drawing rolls 25 and 26 is a nip portion by the roll pairs 27, 28 and 29, that is, a contact portion between the secondary transfer device 21 and the belt 2. Be delivered to. Belt 2
The toner image formed above is transferred onto the recording paper at this nip portion, thermally fixed by the fixing device 5, and discharged onto the tray 30 or the tray 31 (upper surface of the main body).

Developing devices 13Y, 13M, 13C, 13K
Is a replaceable toner cartridge and a developing magnet roll (hereinafter referred to as "developing roll") that gives a developing bias.
)) And a toner supply device for supplying toner to the developing roll and a conveying device. The toner supply device has a motor as an independent drive unit in order to secure a desired supply amount according to a command from a control device described later.

In the color printer having the above structure, an image is formed as follows. First, a voltage is applied to the charging device 7 to uniformly negatively charge the surface of the photoconductor 1 at a predetermined charging portion potential (for example, −650 V). Subsequently, a latent image is formed by performing exposure with the ROS 8 so that the charged image portion on the photosensitive member 1 has a predetermined exposure portion potential (for example, -200 V). The ROS 8 is turned on / off based on an image signal to form a latent image corresponding to the image.

A developing bias preset for each color is applied to the developing roll of the developing device 13Y or the like, and the latent image is developed with toner when passing through the position of the developing roll and visualized as a toner image. . The toner image is transferred onto the belt 2 by the transfer device 10, further transferred onto the recording paper by the secondary transfer device 21, and then sent to the fixing device 5. During full-color printing, four color toners are superposed on the belt and then transferred onto the recording paper. The toner remaining on the photoconductor 1 is charged and cleaned by a preliminary cleaning device, and is removed and collected by the cleaner device 12. Finally, the photoconductor 1 is uniformly discharged by the static eliminator A near 0 volt. The charge is removed until the next image forming cycle.

The image forming timing of the color printer is controlled with reference to a predetermined position on the belt 2. FIG. 2 is an enlarged view of a main part showing a sensing device and its arrangement for obtaining the reference signal TR0. In the figure, the drive roll 11 is supported by a side frame 32 constituting a belt unit via a shaft 33. Also,
The tension roll 14 is supported by a shaft 34 on a bracket 35 pivotally supported by the side frame 32. The belt 2 is wound around rolls including the drive roll 11, the tension roll 14, the idle roll 20 and the backup roll 19,
A predetermined tension is applied by the tension roll 14.

Drive roll 11 and tension roll 1
A reflection type sensor 36 for detecting the reference position is arranged between the four positions. The reflective sensor 36 is a side frame 3
It is directly fixed to the belt 2 so that the distance SD from the belt 2 does not change. Further, a sensor backing 37 is arranged on the back side of the belt 2, that is, on the inner peripheral surface side, at a position facing the reflective sensor 36. The reflection type sensor 36 detects a marking on a reflection tape or the like provided on the end portion of the outer peripheral surface of the belt 2 and outputs a TR0 signal.

The outer peripheral length of the photoreceptor 1 and the peripheral length of the belt 2 are slightly deviated from the integer ratio. For example, the ratio P of the peripheral lengths of the photoconductor 1 and the belt 2 is 1: 1.998.
≦ P <1: 2.000 or 1: 2.000 <P ≦ 1:
Set in the range of 2.002.

The range of the ratio P is set so that the positional deviation of each color, that is, the color deviation, which occurs during the image formation of one page, for example, when the belt 2 rotates four times, is within a predetermined reference range. ing.

As described above, since the ratio of the peripheral lengths of the photoconductor 1 and the belt 2 is deviated from the integer, the photoconductor 1 and the belt 2 are not completely synchronized. Therefore, the color shift of the image occurs within one page. However, this color misregistration is negligible and does not affect the evaluation of image quality. On the other hand, as the number of printed sheets is increased, the deviation of the relative position between the photoconductor 1 and the belt 2 is accumulated. Therefore, when the operation of the image forming apparatus is stopped based on the reference signal TR0, the belt 2 always stops at the same position and waits for the next operation start, but the photoconductor 1 stops at the stop position each time the operation is stopped. Has changed, and the relative positions of the charging device 7, the transfer device 10, and the preliminary cleaning device 11 arranged around it have changed.

FIG. 3 is a diagram showing the rotational fluctuation of the photoconductor 1, in which the vertical axis represents the fluctuation amount of the peripheral speed of the photoconductor 1 and the horizontal axis represents the passage of time. This figure is a measurement drawing in which the fluctuation of the peripheral speed of the photoconductor 1 for each color is recorded by a recorder, for the sake of easy understanding. The width of the line at the same time indicates the magnitude of the color shift, and as can be understood from the figure, the magnitude of the color shift increases with the passage of time. However, it can be seen that the color misregistration during the superimposition of the four colors, that is, during the four rotations of the belt 2 has almost no effect on the image quality.

Although the present embodiment has been described with reference to an example in which the toner image is primarily transferred from the photoconductor 1 to the belt 2 as an intermediate transfer member, the present invention uses a transfer drum as the intermediate transfer member. The same can be applied to the case. That is, the ratio of the peripheral lengths of the photoconductor 1 and the transfer drum 2 in FIG. 4 is shifted from the integer ratio. However, the driving device is deformed so that the peripheral speeds of the photoconductor 1 and the transfer drum 2 become equal.

[0026]

As is apparent from the above description, according to the present invention, the stop position of the photoconductor can be changed even when the intermediate transfer member is stopped at a fixed position. Therefore, the surface of the photoreceptor around which the ozone generator faces the photoreceptor gradually moves, and the same portion of the photoreceptor surface is less likely to be affected by ozone, resulting in a change in characteristics. Can be prevented.

[Brief description of drawings]

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

FIG. 2 is an enlarged view of a main part showing the configuration of an intermediate transfer member.

FIG. 3 is a diagram showing speed fluctuations of a photoconductor.

FIG. 4 is a schematic diagram showing a configuration of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Intermediate transfer body (belt), 8 ... Exposure device, 7 ... Charging device, 10 ... Transfer device, 11 ... Precleaning device, 13 ... Development unit

Claims (3)

(57) [Claims] 1. A structure in which a plurality of toner images formed on a photosensitive member in a plurality of steps are sequentially primary-transferred onto an intermediate transfer member and then secondary-transferred onto a recording medium to obtain an output image. and an image forming apparatus, a circumferential length ratio of the circumferential length and the intermediate transfer member of the photosensitive member, before
The intermediate transfer member generated during a predetermined number of rotations of the photosensitive member;
The misregistration of the image allows the deviation of the preset primary transfer image.
The image forming apparatus according to claim 1 , wherein the integer ratio is shifted so as to be within a certain range . Wherein said intermediate transfer member, the image forming apparatus according to claim 1, characterized in that it consists of an endless belt. 3. A sensor means for detecting a reference position on the intermediate transfer member is provided, and the operation timing of each part is controlled based on a reference position detection signal output from the sensor means. the image forming apparatus according to claim 1 or 2 wherein.