JP2020086286A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that makes a charging current or a charging voltage appropriate according to the surface nature of a charging member to be used.SOLUTION: An image forming apparatus including a charging member 311 brought into pressure contact with a surface of a photoreceptor 300 comprises: surface detection means 326 that detects the surface nature of the charging member 311; and width changing means 322, 324, 325 that change a contact width between the surface of the photoreceptor 300 and the charging member 311 in the direction of movement of the surface. The image forming apparatus is further provided with width control means that controls the width changing means according to a result of detection performed by the surface detection means 326.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, there is known an image forming apparatus including a charging member that is brought into pressure contact with the surface of a photoconductor. For example, in Patent Document 1, an image forming apparatus having a contact pressure control means for controlling the contact pressure between a charging roller, which is a charging member, and a photoconductor to match the contact pressure determined according to the material of the charging roller. Is listed. According to this, it is described that the impedance change at the contact surface between the charging roller and the photoconductor can be prevented, and the charge output voltage charged on the photoconductor can be maintained constant.

However, in the image forming apparatus of Patent Document 1, even if the same material is used, the charging current or the charging voltage may become incorrect when the surface properties such as surface roughness differ depending on the charging member.

In order to solve the above-mentioned problems, the present invention provides a surface detection means for detecting the surface shape of the charging member, and a movement of the surface in an image forming apparatus provided with a charging member that is brought into pressure contact with the surface of the photosensitive member. A width changing means for changing a contact width between the surface of the photoconductor and the charging member in a direction, and a width control means for controlling the contact width changing means according to a detection result of the detecting means. To do.

According to the present invention, an appropriate charging current or charging voltage can be set according to the surface property of the charging member used.

FIG. 3 is a schematic configuration diagram of an internal mechanism of the color printer 1. 3 is a block diagram showing a main part of power supply control of the charging device of the image forming unit 100. FIG. FIG. 3 is an explanatory diagram of a charging device 310 that charges the photoconductor 300 of the image forming unit 100. 6 is a graph showing a change in surface roughness (Rz [μm]) according to the traveling distance of the charging roller 311. 6 is a graph showing the relationship between the lower limit value of Vpp for preventing the occurrence of an abnormal image called charging spot and the pressing force of the charging roller.

An embodiment in which the present invention is applied to an electrophotographic color printer which is an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of an internal mechanism of the color printer 1. The color printer 1 is a four-tandem tandem type image forming apparatus equipped with four image forming units. The color printer 1 forms a color image using toner of each color of yellow (Y), magenta (M), cyan (C), and black (K). The color printer 1 has a paper feed unit 10 in which paper feed cassettes 11 and 12 for accommodating paper sheets as recording media are arranged below the color printer 1. The image forming unit 20 and the transfer unit 30 are arranged above the image forming unit 20.

The image forming unit 20 includes four photoconductor drums 110Y, 110M, 110C, and 110K (hereinafter, the other photoconductor drums 110 are the same unless otherwise specified) which are image carriers. Image forming units 100Y, 100M, 100C and 100K. Each image forming unit 100 is provided with a charging device, a developing device, and a cleaning device. By forming a process cartridge that includes a photoconductor and at least one of a charging device, a developing device, and a photoconductor cleaning device and can be attached to and detached from the main body of the device, the image forming unit is integrated to improve the settability and maintenance. Well, and also improve the photoconductor position system.

The transfer unit 30 includes an intermediate transfer belt 34 as an intermediate transfer member configured by a flexible endless belt wound around a plurality of rollers 31, 32, 33, and the photosensitive drums 110Y, 110M, 110C, 110K. An optical writing unit 40 that is a latent image forming device that forms a latent image, a fixing device 50 that fixes a toner image on a sheet, and the like are arranged. Further, a transport path 60 for transporting a sheet is formed between the sheet cassettes 11 and 12 and the fixing device 50.

The intermediate transfer belt 34 is provided with a secondary transfer roller 35, which serves as a secondary transfer device, facing the roller 32 at a portion facing the roller 32, and a belt cleaning device that cleans the belt surface at a portion facing the roller 31. 37 are installed.

The image forming unit 20 is arranged so as to face the lower belt running side of the intermediate transfer belt 34 of the intermediate transfer belt 34, which is arranged between the roller 31 and the roller 32. In each of the image forming units 100Y, 100M, 100C and 100K, the photoconductor drums 110Y, 110M, 110C and 110K are arranged so as to be in contact with the intermediate transfer belt 34. Inside the intermediate transfer belt 34 at the position where each of the photoconductor drums 110Y, 110M, 110C and 110K is in contact with the intermediate transfer belt 34, a transfer roller as a transfer device for performing primary transfer is provided. It should be noted that reference numerals 70Y, 70M, 70C, and 70K in the drawings denote toner bottles that store replenishment toner.

In this color printer 1, after the photoconductor drums 110Y, 110M, 110C and 110K of the image forming units 100Y, 100M, 100C and 100K are charged by a charging device, they are exposed by a predetermined pattern by an optical writing unit 40 to form photoconductors. The drums 110Y, 110M, 110C and 110K are developed by the developing device. In response to this, the transfer sheet conveyed from the sheet feeding cassettes 11 and 12 is conveyed to the image forming unit 20, and the transfer unit 30 sequentially transfers the toner from the photoconductor drums 110Y, 110M, 110C, and 110K and fixes the toner. It is fixed by the device 50 and discharged.

FIG. 2 is a block diagram showing a main part of power supply control of the charging device of the image forming unit 100.
The control unit 200 is provided as a control unit that controls the entire color printer. The control unit 200 includes a CPU 201 as a calculation unit, a system OS, various control programs required for a printer process, and a PDL (Page Description Language) of the printer. It is composed of a ROM 202 storing a processing system, system initial setting values, and the like, a RAM 203 for work memory, and the like. The control unit 200 also includes a display unit configured by a liquid crystal display or the like for displaying character information and the like, and an operation unit 204 as an operation receiving unit that receives input information from an operator through a ten-key pad or the like and sends it to the control unit 200. It is connected. Then, as a charging member of the charging device, a charging output power source 205 for the charging roller, a motor drive circuit 206 for the cam of the contact width changing means, which will be described later, and the surface property of the charging roller are detected. A circuit 207 of a reflection type optical sensor that receives reflected light from is also connected.

FIG. 3 is an explanatory diagram of the charging device 310 that charges the photoconductor 300 of the image forming unit 100. The following is used as the photoconductor 300. The photosensitive drum has a diameter of 30 mm, and a high-hardness protective layer containing inorganic fine particles (for example, aluminum oxide fine particles) and hardened by a cross-linking resin (for example, polycarbonate) is provided on the surface of the photosensitive drum.

As the charging roller 311, a contact AC charging roller in which a DC voltage is superposed with an AC voltage is used in order to reduce the ozone generation amount and stabilize the charging potential. In the charging roller 311, a resistance adjusting layer made of a conductive elastic body is formed on the outer periphery of the shaft body, and a protective layer (surface layer resin) is formed on the outer periphery by a coating film. This surface layer is made of a material containing a resin such as a polyamide resin, a fluorine resin, an acrylic resin, or a urethane resin as a main component and a conductive agent. For example, an elastic layer made of hydrin rubber having a diameter of 2 mm is provided on a metal core having a diameter of 8 mm. A surface layer of about 5 μm is provided on the surface of the elastic rubber layer to prevent the contamination of the photoreceptor due to the exudation of the contaminant components. The surface layer is made of a cross-linked resin containing fine particles (for example, acrylic fine particles), and unevenness due to the fine particles appears on the surface.

A voltage related to charging is applied to the charging roller 311 by the charging output power source 205. The charging output power supply 205 outputs a charging output voltage obtained by superimposing the AC voltage from the AC power supply circuit and the DC voltage from the DC power supply circuit by constant current control. Both ends of a shaft 320 of the charging roller 311 are rotatably attached to the slider 321. Each slider 321 is guided by a charging roller holder 322 as a holding member and is movable in a contacting/separating direction with respect to the photoconductor 300. The charging roller holder 322 holds the spring 323 as a biasing means between the slider facing surface of the charging roller holder 322 and the slider 321. The force of this spring 323 presses the charging roller 311 against the photoconductor 300 via the slider 321.

In the charging device 310 according to the present exemplary embodiment, the charging roller holder 322 is guided by the guide 324 so as to be movable in the contacting/separating direction with respect to the photoconductor, and the cam member 325 resists the biasing force of the spring 323 to charge the charging roller holder. The movement of 322 in the direction away from the photoconductor is regulated. It can be said that the cam member 325 regulates the position of the end of the spring 323 opposite to the charging roller 311. In order to fix the charging roller 311 against the force of the spring, an elliptical cam member 325 that comes into contact with the charging roller holder 322 is installed, and the cam is rotated to push up the charging roller holder 322. Mechanism. The cam member 325 has, for example, an elliptical shape, and is rotationally driven by a cam motor such as a stepping motor capable of controlling the rotational position via a gear or the like.

FIG. 3A shows a state in which the charging roller holder 322 is regulated at a location relatively large in distance from the rotation axis of the cam member 325, and FIG. 3B shows a state in which the charging roller holder 322 is regulated at a relatively small distance. Indicates. In the former case, the charging roller holder 322 is restricted to a position relatively close to the photoconductor 300, and the charging roller 311 is pressed against the photoconductor 300 with a relatively large pressing force. As a result, as for the width of the charging nip in the movement direction of the photosensitive member surface (hereinafter referred to as the charging nip width) due to the deformation of the charging roller 311, the width Na in FIG. 3A is larger than the width Nb in FIG. 3B. growing. The nip length can be changed without affecting the modules other than the charging roller 311 that are in contact with the photoconductor 300, such as changing the configuration and adding a spring function.

The movable charging roller holder 322, the guide 324, and the cam member 325 constitute a mechanism portion of a contact width changing unit. This cam motor is driven by the motor drive circuit 206. An optical sensor 326 for detecting the surface property facing the surface of the charging roller 311 is also arranged. Instead of optically detecting the surface property, the surface property (surface roughness) may be mechanically detected.

FIG. 4 is a graph showing changes in surface roughness (Rz [μm]) according to the traveling distance of the charging roller 311. The surface roughness becomes smaller as the charging roller 311 of the present embodiment is used and the traveling distance becomes longer. Reference numerals A, B, and C show graphs of the charging rollers having different initial surface roughnesses. Among the three, A, B, and C are in the descending order of the initial surface roughness. Such a difference in the initial surface roughness is due to manufacturing variations of the charging roller. Reducing the variation (strictly setting the Rz crossing) causes an increase in manufacturing cost, and thus the variation must be allowed to some extent.

From the beginning, the difference in surface roughness becomes smaller as the mileage becomes longer. At about 150KM, there is almost no difference. The reason why the surface roughness becomes smaller as the traveling distance increases is that the surface of the fine particles forming the unevenness of the surface layer is scraped off due to abrasion or comes off and the surface becomes smooth. ..

FIG. 5 shows the relationship between the lower limit value of the peak-to-peak [Vpp] of the DC/AC superimposed charging voltage and the pressing force of the charging roller to prevent the occurrence of an abnormal image called charging spot, and the surface roughness of the charging roller ( It is the graph which displayed side by side for every A, B, and C). The charging spot is an abnormal image that is halftone and easily noticeable with spot-shaped white spots of several hundred μm. It is caused by local over discharge. Since this abnormal image can be eliminated by increasing the peak-to-peak, there is a peak-to-peak lower limit that can prevent the occurrence of the abnormal image. The vertical axis shows this lower limit (charging potential).

This lower limit depends on the surface roughness of the charging roller. Specifically, the lower the surface roughness (the smaller A, B, and C), the larger the lower limit peak-to-peak. As a result, a charging roller having a smaller surface roughness requires a larger peak-to-peak value so as not to generate a charging petit. The magnitude of the surface roughness is caused by the manufacturing variation as described above, or is caused by the change with time as shown in FIG.

It is sufficient to use a sufficiently large peak-to-peak value in order to reliably prevent the occurrence of charging spots regardless of the surface roughness, but in this case, another abnormal image called photoconductor medaka or photoconductor An abnormal image may be generated due to filming, or the photoreceptor may be damaged due to excessive discharge to shorten the life of the photoreceptor.

The photoconductor medaka means that silica, which is a toner additive, and calcium carbonate contained in paper adheres to and is immobilized on the surface of the photoconductor 3, and the potential is less likely to drop even by optical writing at the place where these are immobilized. White spots appear on the image. These adherences and fixations occur in a streamlined shape extending in the sub-scanning direction, and a plurality of medaka fish are gathered together in a group. As a result, the white spots on the image also occur in the form of a plurality of streamlined shapes, and the medaka appears to form a swarm, which is called a photoconductor medaka.

As shown in FIG. 5 by various experiments, the inventors of the present invention have shown that as shown in FIG. 5, the peak to prevent the abnormal image of the charging spot from being generated as the pressing force of the charging roller is increased at any surface roughness. It was discovered that the peak can be made smaller (the rise can be suppressed). The larger the pressing force, the larger the charging nip width. As a result, it is considered that the chances of exchanging charges by the alternating current component of the DC and AC superimposed charging voltage are increased, and the difference in the electric charges between the local excessive discharge location and the surrounding area, which is the cause of the charging pot, is alleviated.

Based on the above findings, the surface property (specifically, the surface roughness Rz) of the charging roller 311 is detected based on the output of the optical sensor 326 shown in FIG. Then, based on this result, the pressing force changing control is performed by switching the rotational position of the cam member 325 of the width changing mechanism. Specifically, the relationship between the surface roughness of the charging roller and the rotational position of the cam corresponding to the surface roughness is experimentally obtained in advance and stored in a storage unit such as the ROM 202. The rotational position of the cam corresponds to the charging roller pressing force corresponding to the lower limit of the peak-to-peak that prevents the occurrence of an abnormal image of the charging pot when the surface is rough. Then, the rotational position of the cam corresponding to the surface roughness detected by using the optical sensor 326 is stored and determined from the relationship, and when the rotational position of the cam needs to be changed, it is controlled so as to be changed.

As described above, according to the present embodiment, Vpp can be set low without being disadvantageous to an abnormal image due to Rz variation of the charging roller 311. Further, since it is not necessary to strictly set the Re intersection of the charging roller 311, it is possible to avoid cost increase.

Instead of the feedback control as in the above embodiment, the following control can be adopted. That is, first, as shown in FIG. 4, the surface of the charging roller is abraded over time, and Rz changes, and the relationship between the traveling distance and the change amount of Rz is previously obtained by an experiment and a storage unit such as the ROM 202 is used. To remember. As can be seen from FIG. 4, Rz of the charging roller decreases with time, so that Rz can be predicted at the traveling distance determined based on the experimental data.

Then, the Rz of the charging roller 311 is measured at the stage of assembling the machine, and the value is input using the operation unit 204 or the like in the initial setting when the machine is operating (initial use of the image forming apparatus). After that, the relationship between the traveling distance and the change amount of Rz for each initial surface roughness as shown in FIG. 4 stored in the storage unit such as the ROM 202, and the surface roughness used in the previous embodiment. The rotation amount of the cam is determined based on the relationship with the rotational position of the cam corresponding to the height, and the cam is rotated as necessary to determine the pressurization amount. This makes it possible to set how to change the width thereafter according to the input initial setting value when the machine is operating. This control can be operated without extra control such as control based on detection using an optical sensor during image formation. The traveling distance of the charging roller 311 can be grasped by using the number of image formed sheets as an alternative characteristic. The number of formed images can be counted by a number counter as a usage amount grasping means.

As described above, in Patent Document 1, a cam is used to prevent charging of the charging roller and the photosensitive member in order to prevent image quality from being deteriorated or beat noise due to a change in impedance value at a contact surface between the charging roller and the photosensitive member. There is disclosed a configuration in which the impedance (and accordingly the charging output voltage) is changed by changing the contact pressure of the body.

It is similar to the embodiment of the present invention in that the cam is used to control the pressing of the charging roller. However, since the charging output voltage setting is not suitable for the surface roughness Rz, a roller having a large Rz at the time of manufacturing the charging roller has a short life due to excessive discharge, and a roller having a small Rz has a small value. Cannot solve the problem of being disadvantageous to abnormal images.

Unlike the prior art, in the present embodiment, the nip length can be set only in accordance with the surface roughness Rz that is sensitive to abnormal images such as charging spots, and Vpp can be set lower, resulting in a longer life of the photoconductor. It can be extended (as Rz becomes large, it becomes advantageous for the charging pot, and as a result, the pressing force of the charging roller rises (the nip becomes longer in the circumferential direction), which is advantageous for the charging pot). Furthermore, if the amount of pressurization is determined by the initial setting when the machine is operating, it can be operated without extra control during image formation.

1: Color printer 10: Paper feeding unit 11: Paper feeding cassette 12: Paper feeding cassette 20: Image forming unit 30: Transfer unit 31: Roller 32: Roller 33: Roller 34: Intermediate transfer belt 35: Secondary transfer roller 37: Belt cleaning device 40: Optical writing unit 50: Fixing device 60: Conveying path 100: Image forming unit 110: Photosensitive drum 200: Control unit 201: CPU
202: ROM
203: RAM
204: Operation unit 205: Charging output power source 206: Motor driving circuit 207: Circuit 300: Photoconductor 310: Charging device 311: Charging roller 320: Shaft 321, Slider 322: Charging roller holder 323: Spring 324: Guide 325: Cam member 326: Optical sensor

JP-A-9-297455

Claims (10)

In an image forming apparatus equipped with a charging member that presses against the surface of the photoconductor,
Surface detection means for detecting the surface property of the charging member,
Width changing means for changing the contact width between the surface of the photoconductor and the charging member in the moving direction of the surface,
An image forming apparatus comprising: a width control unit that controls the width changing unit according to a detection result of the front surface detecting unit. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the surface property detected by the surface detecting means is surface roughness. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the surface detection unit detects the surface property from reflected light of light incident on the charging member. In an image forming apparatus equipped with a charging member that presses against the surface of the photoconductor,
Use the one whose surface roughness becomes smaller by using as the charging member,
Usage amount grasping means for grasping the usage amount of the charging member,
Width changing means for changing the contact width between the surface of the photoconductor and the charging member in the moving direction of the surface of the photoconductor,
An image forming apparatus comprising: a width control unit that controls the width changing unit according to a grasped result of the usage amount grasping unit. The image forming apparatus according to any one of claims 1 to 4,
The image forming apparatus according to claim 1, wherein the charging member has a surface layer made of a crosslinked resin containing fine particles, and a surface layer on the surface of which irregularities are formed by the fine particles. The image forming apparatus according to any one of claims 1 to 5,
The image forming apparatus, wherein the charging member is a rotatable roller. The image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus, wherein the width changing unit changes the pressure applied to the surface of the photoconductor by the charging member. The image forming apparatus according to claim 7,
The width changing means includes a holding member that holds the charging member so as to be movable toward and away from the photoconductor, and a biasing means that biases the charging member in a direction to press the surface of the photoconductor. And a cam member that regulates the position of the end of the biasing unit opposite to the charging member against the biasing force of the biasing unit. The image forming apparatus according to any one of claims 1 to 8,
The image forming apparatus, wherein the width changing unit can set a width changing method at an initial stage of use of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 9,
An image forming apparatus comprising a process cartridge that includes the photoconductor, includes at least one of a charging device, a developing device, and a photoconductor cleaning device, and is removable from the apparatus main body.

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