JP2007098681A - Electrophotographic image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming a high quality image without variation in electric charge by performing laser-scanning by controlling a light quantity for removing the electric charge by considering variation in sensitivity of a photoreceptor. <P>SOLUTION: This electrophotographic image forming apparatus comprises a first laser light source (not shown in the figure) for forming an electrostatic latent image on the photoreceptor on a photosensitive drum 11, a second laser light source (not shown in the figure) for removing a residual potential on the photoreceptor after the forming of the electrostatic latent image, and a polygon mirror 8 for reflecting laser lights 12, 13 from the first and second laser light sources. A reflection face of the polygon mirror 8 on which the laser light 12 from the first laser light source is incident and a reflection face thereof on which the laser light 13 from the second laser light source are identical to each other, and the laser lights 12, 13 are incident on the reflection face of the polygon mirror 8 at different angles. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an electrophotographic image forming apparatus capable of correcting charging unevenness due to a difference in sensitivity of a photoreceptor and printing with high image quality.

  2. Description of the Related Art Conventionally, an image forming method using an electrophotographic method has been widely used in image forming apparatuses such as copying machines, printers, and fax machines. In such an image forming apparatus, the surface of the photoconductor is neutralized with a light emitting element such as an LED and charged uniformly in the dark, and then charged by exposing the photoconductor by irradiating a laser beam with an exposure device. A desired electrostatic latent image is formed on the photosensitive member, and an electrostatic latent image is developed by supplying a developer from a developing device in correspondence with the formed electrostatic latent image, thereby forming an image. . That is, the image is formed by transferring the toner image onto the transfer paper and fixing it by such steps.

  In the above-described electrophotographic process, a light source for charge removal used for light charge removal is usually one in which LED elements are arranged at a predetermined interval. However, light emitting elements such as LED elements have a Gaussian distribution of light quantity, and thus the light quantity is inevitably uneven in the longitudinal direction of the photoreceptor. If the distance between the elements is narrowed, the unevenness in the amount of light is reduced, but in this case, the number of elements is increased and the cost is increased.

  Therefore, in the image forming apparatus disclosed in Patent Document 1, the first reflecting surface and the second reflecting surface having different surface tilt amounts are formed on the polygon mirror that deflects the laser light from the semiconductor laser. The laser beam is selectively incident on one of the first and second positions of the photoconductor as the polygon mirror rotates. At the first position, an electrostatic latent image is formed, while at the second position, it is located between the transfer means and the charging means, and the residual potential of the photoreceptor is removed by laser light.

Japanese Patent Laid-Open No. 11-119618 (FIG. 1, paragraph 0007)

  However, in Patent Document 1, since exposure and static elimination are alternately performed by the adjacent reflecting surfaces of the polygon mirror, the rotation speed of the polygon mirror has to be doubled as usual, which causes a problem of noise and a problem of heat generation of the motor. Will occur. In addition, for these problems, the polygon mirror is sealed and noise countermeasures are taken, or a heat radiation plate is attached to the motor to take heat countermeasures, but this causes a considerable cost increase. . Therefore, such a configuration is not desirable nowadays when the number of printed sheets of the printer is increased.

  In Patent Document 1, since the light path for neutralization directly uses the reflected light of the polygon mirror, the scan speed differs between the center of the image and the edge of the image, strictly speaking, there is a difference in the amount of light, and the light neutralization is performed uniformly. I can't.

  Also, when there is a variation in the film thickness of the photoconductor, it is easy to be charged when the film is thin, and it is difficult to charge when the film is thick. .

  SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality image forming apparatus free from uneven charging by performing laser scanning while controlling the amount of charge removed in consideration of variations in the sensitivity of the photosensitive member.

A first means for solving the above-described problem is a first laser light source for forming an electrostatic latent image on the photoconductor and a first potential for removing the residual potential of the photoconductor after forming the electrostatic latent image. Two laser light sources;
A polygon mirror for scanning the laser light from the first and second laser light sources, and the laser beam from the second laser light source is incident on the reflection surface of the polygon mirror on which the laser light from the first laser light source is incident. The electrophotographic image forming apparatus is characterized in that the laser beam from the first and second laser light sources is incident on the reflecting surface of the polygon mirror at different angles, which is the same as the reflecting surface of the polygon mirror. It is.

  As a result, it is possible to simultaneously perform static elimination (residual potential removal) and exposure (formation of an electrostatic latent image) by laser scanning, eliminating the need for a static elimination dedicated device, and realizing space saving. Further, by using a plurality of laser light sources, scanning can be performed without doubling the number of rotations of the optical deflector, and noise and heat generation can be suppressed.

  The second means is that in the first means, the laser light from the first laser light source is perpendicularly incident on the reflection surface of the polygon mirror.

  Thus, since the two optical paths are transmitted through the fθ lens, the scanning speed of the neutralizing beam can be kept constant, and the amount of neutralizing light can be made uniform. In addition, the optical path adjustment of the laser light from the first laser light source becomes easy.

  The third means further comprises a charging means for uniformly charging the photoconductor in the first means or the second means, and a memory for storing a charging potential distribution of uniform charging in the laser beam scanning direction. Based on this, the laser light from the second laser light source is modulated to remove the residual potential.

  Thereby, it is possible to perform photostatic discharge based on the sensitivity distribution for each photoconductor.

  The fourth means is a third means for modulating the laser light intensity at a photosensitive member position where the charging potential is low and increasing the laser light intensity at a photosensitive member position where the charging potential is high. Is to do.

  As a result, the second laser light source refers to the charging potential information in the longitudinal direction of the photoconductor stored in the memory, and reduces the laser output when the charging potential is low and increases the laser output when the charging potential is high. The charging means information obtained due to the variation in the film thickness of the photosensitive member is acquired, and the second charging means that can remove the charging unevenness that occurs even if the amount of static elimination light is made constant by correcting the laser output. Since the optical path is transmitted through the fθ lens, the scanning speed of the neutralizing beam can be kept constant, and the amount of neutralizing light can be made uniform.

  According to the present invention, it is possible to provide a high-quality image forming apparatus free from uneven charging by performing laser scanning while controlling the amount of charge removed in consideration of variations in sensitivity of the photosensitive member.

  Embodiments of the present invention will be described below with reference to the drawings. However, even if there are specific descriptions in the dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment, the present invention is not intended to be limited thereto.

  FIG. 1 is a cross-sectional view of the electrophotographic image forming apparatus of this embodiment.

  In this apparatus, a charger 1, a developing device 3, a transfer roller 5, and a cleaning blade 6 are arranged in this order around a photosensitive drum 11 that rotates clockwise in the drawing. The charger 1 uniformly charges the photosensitive member on the photosensitive drum 11 to a predetermined potential having a predetermined polarity. After uniform charging, the photosensitive member is exposed with the laser beam 12, and the potential of the portion exposed with the laser beam is changed to form an electrostatic latent image. The electrostatic latent image is developed as a toner image on the photosensitive member by the developing device 3. Then, a sheet (not shown) is conveyed between the photosensitive drum 11 and the transfer roller 5, and a toner image is transferred onto the sheet by applying a voltage having a polarity opposite to the charging polarity of the toner and attracting the toner to the sheet side. The Thereafter, the toner is fixed on the paper by a fixing device (not shown) to complete the image forming process. The cleaning blade 6 scrapes off the toner remaining on the photoconductor in the image forming process, cleans the surface of the photoconductor and prepares for the next image formation. The reason why the laser beam 13 is irradiated between the cleaning blade 6 and the charger 1 is to erase the potential remaining on the photosensitive member.

  Next, each part of the electrophotographic image forming apparatus will be described.

The photosensitive drum 11 is preferably a laminate in which a carrier blocking layer, a photosensitive layer, and a surface protective layer formed thereon are laminated in this order on a conductive substrate. For example, an organic photosensitive agent or amorphous silicon can be used as the photosensitive layer. In particular, inorganic materials such as a-Si, a-SiC, a-SiO, and a-SiON can be exemplified as preferred materials for amorph. Among these materials, a-SiC has a particularly high resistance, and more excellent charging ability, wear resistance, and environmental resistance can be obtained. Moreover, it is preferable to use a specific ratio of Si and C (carbon) in a-SiC. As such a-SiC, a-Si _(1-x) C _x (X value is less than 0.3 to 1) is more preferable, and X value is more preferably 0.5 to 0.95. It is as follows. This is because such a-SiC has a particularly high resistance of 10 < ¹² > to 10 < ¹³ > [Omega] cm, there is little flow of the latent image in the surface direction of the photoreceptor, and the electrostatic latent image maintaining ability and moisture resistance are reduced. It is because it is also excellent.

  As the charger 1, for example, a corotron that is not in contact with the photosensitive drum 11 can be used.

  The laser beam 12 is exposure light for forming an electrostatic latent image, is output from a first laser light source (not shown), and is modulated by a modulator (not shown) according to an image signal.

  In the developing device 3, a developing roller is disposed in the developing container, and a part of the developing roller is exposed from the developing container and is brought close to the photosensitive drum 11 with a predetermined gap. Therefore, in order to develop the electrostatic latent image on the photoreceptor, toner is caused to fly from the toner thin layer on the developing roller toward the photoreceptor (one-component jumping development). At the time of development, a DC superimposed AC voltage is applied to the developing roller, and the toner is caused to fly using electric force. When a magnetic one-component toner is used as the toner, a thin toner layer is formed on the developing roller by a magnet disposed inside the developing roller.

  The transfer roller 5 pressurizes and conveys paper between the photosensitive drum 11 and transfers the toner image on the photosensitive drum 11 to the paper side. At the time of transfer, a voltage having a polarity opposite to the charging polarity of the toner is applied to attract the toner to the paper side.

  The cleaning blade 6 scrapes off the toner remaining on the photosensitive drum 11 after the transfer. Thereby, the surface of the photoreceptor is cleaned and prepared for the next image forming step.

  Further, the laser beam 13 is exposed at a position between the cleaning blade 6 and the charger 1, thereby removing the remaining potential due to the electrostatic latent image formation. The laser beam 13 is output from a second laser light source (not shown) and modulated by a modulator based on a charged potential distribution stored in a memory (not shown).

  FIG. 2 is an optical path cross-sectional view of the laser light after being reflected by the polygon mirror 8. The laser beam 12 is incident perpendicularly on the reflecting surface of the polygon mirror 8, is focused by the fθ lenses 9 and 10, is reflected by the mirror M 2, and forms an image on the photosensitive drum 11. On the other hand, the laser beam 13 is incident obliquely on the reflection surface of the polygon mirror 8, is focused by the fθ lenses 9 and 10, is reflected by the mirror M 1, and forms an image at another position on the photosensitive drum 11.

  FIG. 3 is a top view of the laser scanning unit.

  The first laser light 12 from the first laser light source LD1 is converted into parallel light by the collimator lens C1, and reflected by the mirror M3 toward the polygon mirror. A cylindrical lens CL is disposed between the mirror M3 and the polygon mirror 8, and the laser beam 12 is linearly imaged on the reflection surface of the polygon mirror 8, so that the photosensitive drum can be used regardless of the surface tilt of the reflection surface. The scanning line on the 11th axis can be a straight line.

  Although the second laser beam 13 is shown slightly apart for the sake of illustration, in actuality, it is more advantageous to adjust the optical axis if they are matched.

  The second laser light 13 from the second laser light source LD2 is converted into parallel light by the collimator lens C2, the optical axis is shifted by the mirrors M4 and M5, and the light is reflected toward the polygon mirror by M3. A cylindrical lens CL is disposed between the mirror M3 and the polygon mirror 8, and the laser beam 13 is linearly imaged on the reflection surface of the polygon mirror 8, so that the photosensitive drum is irrelevant regardless of the tilt of the reflection surface. The scanning line on the 11th axis can be a straight line.

  The first laser beam 12 deflected at the angle by the polygon mirror 8 is reflected downward toward the photosensitive drum 11 by the mirror M2, and exposes the photosensitive drum 11 at a position between the charger 1 and the developing unit 3. . The second laser beam 13 deflected at the angle by the polygon mirror 8 is reflected downward toward the photosensitive drum 11 by the mirror M 1, and at the position between the cleaning blade 6 and the charger 1, the photosensitive drum 11. To expose.

  The first laser beam 12 and the second laser beam 13 reflected by the polygon mirror are imaged on a minute spot on the photosensitive drum 11 by the lenses 9 and 10 constituting the fθ lens. This combination lens includes a spherical lens 10 and a toric lens 9, and scans two laser beams 12 and 13 linearly (at a constant speed) with respect to a scanning angle (deflection angle) θ in the axial direction of the photosensitive drum 11. Further, the scanning trajectories of the two laser beams 12 and 13 imaged linearly on the reflecting surface of the polygon mirror 8 are made linear.

  A first laser light source (not shown) is used to form an electrostatic latent image on the photosensitive member of the photosensitive drum 11, and a second laser light source is used to remove the residual potential of the photosensitive member after forming the electrostatic latent image. It is done. The wavelength of the laser light is preferably 600 to 900 nm if the photoreceptor is, for example, amorphous silicon or an organic photosensitive material.

  A polygon mirror 8 is used to scan the laser beam 13 from the second laser light source. The reflection surface of the polygon mirror 8 on which the laser beam 12 from the first laser light source is incident is the same as the reflection surface of the polygon mirror on which the laser beam 13 from the second laser light source is incident, and from the first and second laser light sources. The laser beams 12 and 13 are incident on the reflecting surface of the polygon mirror 8 at different angles. Specifically, as shown in FIG. 2, the laser light 12 from the first laser light source may be incident perpendicularly on the reflection surface of the polygon mirror.

  Further, the photosensitive member on the surface of the photosensitive drum 11 is uniformly charged by the charger 1, and the charged potential distribution on the shaft of the photosensitive drum 11 at that time is measured and stored in a memory (not shown) in advance. Then, based on the charged potential distribution, the laser beam 13 from the second laser light source is modulated to perform photostatic elimination (removal of residual potential).

  Specifically, modulation is performed to decrease the intensity of the laser beam 13 at a photosensitive member position with a low charging potential, and modulation is performed to increase the laser beam intensity at a photosensitive member position with a high charging potential. Here, the laser beam 13 is continuous light. However, the laser beam 13 may be modulated by a signal obtained by inverting the image forming signal, and light neutralization may be performed for each minute spot where the charged potential remains.

  FIG. 4 is an example of the charge potential distribution of the photoreceptor, and shows charge potential unevenness. Both ends of the photoconductor are thin and easily charged, and the charging potential is likely to rise. The charging potential was 270 V at both ends of the short side of the A4 sheet. In addition, the film thickness was thick in the vicinity of the center, so that it was difficult to charge and the charging potential was difficult to rise. Therefore, even if static elimination is performed with a uniform amount of light, the charged potential is affected by variations in the photoreceptor itself.

  This charging unevenness information is stored in the memory chip of the drum unit. Data stored in the memory chip is read when the printer is turned on.

  FIG. 5 shows the intensity distribution on the drum axis of the laser beam 13 of the second laser light source. The experimental conditions are: the linear velocity of the photosensitive drum 11 is 210 mm / sec, the standard static elimination laser power (the laser beam 13 power at the center position of the A4 paper short side) is 0.4 mW, and the standard exposure laser power (the center position of the A4 paper short side). Laser power at 12) was 0.4 mW, and the standard charging potential (charging potential at the center position of the A4 paper short side) was 260V.

Based on the read data, the laser power was reduced where the charged potential was low (about 0.40 mW at the center position of the A4 paper short side). Further, the laser power was increased where the charging potential was high (about 0.45 mW at both ends of the A4 paper short side).
Implementation was performed under the above conditions. As a result, the residual potential distribution within the A4 paper short side width was flat.

  The present invention can be used in electrophotographic image forming apparatuses such as laser printers, laser facsimiles, and laser copying machines.

It is a conceptual diagram of an electrophotographic image generation device. It is an optical path figure of the laser beam scanned with a polygon mirror. It is a top view of a laser operation part. The intensity distribution on the photosensitive drum axis It is intensity distribution on the photosensitive drum axis of the laser beam from the second laser light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charging device 3 Developing device 5 Transfer roller 6 Cleaning blade 8 Polygon mirror 9, 10 Lens constituting fθ lens Photosensitive drum 12 Laser beam from first laser light source 13 Laser beam LD1 from second laser light source First laser Light source LD2 Second laser light source C1, C2 Collimator lens CL Cylindrical lenses M1, M2, M3 Mirror

Claims (4)

A first laser light source for forming an electrostatic latent image on the photoreceptor;
A second laser light source for removing a residual potential of the photoconductor after forming the electrostatic latent image;
A polygon mirror for scanning laser light from the first and second laser light sources,
The reflective surface of the polygon mirror on which the laser light from the first laser light source is incident is the same as the reflective surface of the polygon mirror on which the laser light from the second laser light source is incident,
2. The electrophotographic image forming apparatus according to claim 1, wherein the laser beams from the first and second laser light sources are incident on the reflecting surface of the polygon mirror at different angles.   2. The electrophotographic image forming apparatus according to claim 1, wherein the laser light from the first laser light source is perpendicularly incident on a reflection surface of the polygon mirror. Charging means for uniformly charging the photoreceptor;
A memory for storing the uniformly charged charge potential distribution in the laser beam scanning direction;
3. The electrophotographic image forming apparatus according to claim 1, wherein the residual potential is removed by modulating laser light from the second laser light source based on the charged potential distribution.   2. The method according to claim 1, wherein in the charging potential distribution, modulation is performed to lower the laser beam intensity at a photosensitive member position having a low charging potential, and modulation is performed to increase the laser beam intensity at a photosensitive member position having a high charging potential. 3. The image forming apparatus according to 3.

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