JP2007192941A - Image forming apparatus and method for controlling the image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain stable image output over a long period even if the wear of a charge-transporting layer in the surface of a photoreceptor progresses with the lapse of time in an image forming apparatus using a multibeam laser for an exposure. <P>SOLUTION: The image forming apparatus is provided with: a photoreceptor drum 11 for carrying an image; a charging device 12 for charging the photoreceptor drum 11; an exposing device 20 having a semiconductor laser (multibeam laser ROS) 21 composed of a plurality of illumination lasers for forming a latent image on the photoreceptor drum 11 formed by the exposing device 20; and a control part 30 grasping the degree of deterioration in the photoreceptor drum 11, increasing the output duty of the semiconductor laser (multibeam laser ROS) 21 based on the grasped degree of deterioration, and subjecting the multibeam to lightening control with binary values. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine, and more particularly to an image forming apparatus that forms an image using a photoreceptor.

  Conventionally, an image forming apparatus combining an electrophotographic method and laser exposure has been widely used. In an image forming apparatus that employs this method, for example, a technique of varying the development density by pulse width modulation (PWM) of a laser is employed. In this pulse width modulation, if the duty is increased, the development density is increased. Conversely, if the duty is decreased, the development density is decreased.

  On the other hand, there is a technique for minimizing the diameter of a light emission spot per beam while using a surface emitting laser (VCSEL) to make the exposure multi-beam for high resolution. In this case, the pulse width modulation of each light emitting spot is not performed, and the gradation of the image can be expressed by binary control of ON / OFF and the number of simultaneous light emitting spots per unit area. The main reason for not performing the pulse width modulation is that the gradation expression can be sufficiently achieved only by turning ON / OFF the simultaneous light emission spots per unit area. In addition, in order to control multi-beams at high speed, it is necessary to increase the video rate, and it is no longer possible to perform pulse width modulation according to the output gradation degree.

  Here, in an electrophotographic image forming apparatus, charging, exposure, development, transfer, and cleaning processes are sequentially repeated around a photoconductor as an image carrier. Among these, in the cleaning process, for example, a plate-like member (cleaning blade) is provided to scrape excess developer from the surface of the photoreceptor. The plate-like member is brought into frictional contact with the surface of the photoconductor, so that the charge transport layer applied on the surface of the photoconductor is worn. The deterioration of the photosensitive member over time due to the wear reduces the sensitivity of the photosensitive member, and consequently deteriorates the image quality.

  The adjustment parameters of the components surrounding the photoconductor include a charging potential of the photoconductor, a developing bias potential, and an exposure potential. These adjustment parameters are initially adjusted in a balanced manner based on the characteristics of the photoreceptor at the time of shipment from the factory. However, when the photoconductor deteriorates with time as described above, the characteristics of the photoconductor change and the desired image quality cannot be obtained. Conventionally, when image quality deteriorates due to a reduction in sensitivity of the photoreceptor, the photoreceptor is immediately replaced. On the other hand, as a problem for reducing the running cost, it is required to use the photoreceptor for as long as possible.

  Here, as a conventional technique described in the publication, there is a technique that adjusts the amount of laser light in accordance with the degree of deterioration of the photoconductor and controls the output image so that a good image can be always maintained (for example, Patent Document 1). reference.). In addition, as a technique described in other publications, there is one that forms a uniform image in the main scanning direction of the photosensitive member by eliminating non-uniform elements such as uneven coating and partial deterioration of the photosensitive member (for example, (See Patent Document 2).

Japanese Patent Laid-Open No. 5-323740 JP 2002-236400 A

  As described above, in exposure using a surface emitting laser that is a multi-beam laser, pulse width modulation of each light emitting spot is not necessary for gradation expression, binary control of ON / OFF and simultaneous light emitting spots per unit area It is possible to express the gradation of an image with a number. On the other hand, separately from the gradation expression, it may be necessary to control the amount of light, for example, to correct density unevenness. In such a case, in the technique using the surface emitting laser, the light amount control is performed by making the output setting reference voltage (VREF) variable, for example.

  However, while pulse width modulation provides spatial variation of exposure energy in the main scanning direction and sub-scanning direction, it is possible to vary (change) the output setting reference voltage in the main scanning direction and sub-scanning direction. The exposure energy itself is variable without having a spatial spread in the scanning direction. For this reason, for example, when it is considered to expand the light amount adjustment range (dynamic range), the method for changing the output setting reference voltage cannot provide a sufficient adjustment range as compared with the pulse width modulation. In particular, when the image forming apparatus is to be operated for a long period from the time of shipment from the factory, if the light amount adjustment range is restricted, it is not possible to sufficiently cope with changes with time. In each of the above patent documents, it is not possible to cope with such problems inherent in the multi-beam laser, and it is difficult to extend the life of the photoconductor in an image forming apparatus using the multi-beam laser for exposure. is there.

The present invention has been made in order to solve the technical problems as described above, and an object of the present invention is to provide an image forming apparatus using a multi-beam laser for exposure, for example, a photoreceptor along with a change with time. It is to obtain a stable image output over a long period of time even when the surface charge transport layer is worn.
Another object is to maintain a constant density reproduction level by securing a light amount adjustment range when a multi-beam laser is used for exposure.

  In order to achieve such an object, an image forming apparatus to which the present invention is applied includes an image carrier that carries an image, a charger that charges the image carrier, and an image carrier that is charged by the charger. An exposure device having a multi-beam laser composed of a plurality of light emitting lasers for forming an image, a developing device for developing a latent image of the image carrier formed by the exposure device, and a degree of deterioration of the image carrier are grasped. And control means for raising the output duty of the multi-beam laser based on the recognized degree of deterioration and controlling the lighting of the multi-beam in binary.

Here, the control means can be characterized in that the output duty is increased stepwise in accordance with the degree of deterioration of the image carrier.
Further, the control means is characterized in that the initial value of the output duty is suppressed to about 50% of the maximum value of the output duty in a state where the deterioration of the image carrier is not progressing, and is increased stepwise from the initial value. It can be.
Further, the control means adjusts the charging potential of the charger and the developing bias potential of the developing device as the output duty of the multi-beam laser is increased. It is excellent in that the decrease in image density can be suppressed.
Furthermore, this control means can grasp the accumulated number of printed sheets and grasp the degree of deterioration of the image carrier from the grasped accumulated number of printed sheets.

  From another point of view, the present invention is a control method for an image forming apparatus that forms an image by charging, exposing, and developing the image carrier, and the image carrier is in an initial state in which the image carrier has not deteriorated. The step of controlling the multi-beam laser to be exposed to light at a first output duty with a binary value, the step of grasping the degree of deterioration of the image carrier, and the degree of degradation of the image carrier to be grasped are determined in advance. A step of determining whether or not the state is advanced from a predetermined state, and a first output duty that is higher than the first output duty when it is determined that the degree of deterioration is advanced from a predetermined state. And controlling lighting of the multi-beam laser in binary with an output duty of 2.

Here, a state having a higher degree of deterioration than the predetermined state is determined in advance, and when it is determined that the degree of deterioration has advanced from this high state, the output duty is higher than the second output duty. The multi-beam laser can be controlled to be turned on in binary with the third output duty.
Further, as the first output duty is raised to increase the second output duty, and further, the second output duty is raised and the lighting control is performed with binary values at the third output duty, the charging potential at the time of charging is increased. And a step of adjusting the development bias potential at the time of development in accordance with the amount of light at each point, it is possible to suppress a decrease in output image density without greatly changing the development performance. Is preferable.
Further, the step of grasping the degree of deterioration of the image carrier grasps the cumulative number of printed sheets by the image forming apparatus, and grasps that the deterioration is advanced when the cumulative number of printed sheets exceeds a predetermined value. It can be characterized by.

  According to the present invention configured as described above, in an image forming apparatus using a multi-beam laser for exposure, for example, even if wear of the charge transport layer on the surface of the photoreceptor progresses with time, a stable image over a long period of time. Output can be obtained.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a basic configuration of an image forming apparatus to which the exemplary embodiment is applied. This image forming apparatus is an image forming apparatus that employs a so-called electrophotographic system, and an image forming unit 10 that forms an image includes a photosensitive drum (photosensitive member) 11 that is an image carrier at the center thereof. . Further, around the photosensitive drum 11 in the image forming unit 10, a charger 12 that charges the photosensitive drum 11 and an exposure device 20 that exposes the photosensitive drum 11 to form an electrostatic latent image are provided. Yes. Further, the developing unit 13 that develops the formed electrostatic latent image with toner to form a toner image, and scrapes the residual toner on the photosensitive drum 11 after the toner image is transferred to a sheet by a transfer unit (not shown). A cleaning blade 14 is provided.

  Here, the exposure device 20 includes a semiconductor laser (multi-beam laser ROS) 21 that emits laser light, and a collimator lens 22 and an aperture 23 for converting the emitted laser light into parallel light. Further, a polygon mirror (rotating polygon mirror) 24 for scanning the laser beam converted into parallel light in the main scanning direction is provided. Further, an imaging lens (fθ lens) 25 that corrects optical distortion such as surface tilt of the polygon mirror 24 and a cylindrical mirror that irradiates the photosensitive drum 11 by reflecting the laser beam corrected by the imaging lens 25. 26. The semiconductor laser 21 is a surface-emitting multi-beam laser as described later, and has, for example, 32 light emitting sources in one device.

  On the other hand, the control system (control means) of the image forming apparatus includes a control unit 30 that controls the entire image forming apparatus, a charge control unit 31 that controls the charge amount and timing of charging of the charger 12, and a developing device. And a developing bias control unit 32 for controlling the developing device 13 such as control of the developing bias voltage (potential) of 13. Further, as a feature point of the present embodiment, a laser emission duty control unit 33 that controls the emission duty of the semiconductor laser 21 and a laser drive unit 34 that drives the semiconductor laser 21 are provided.

Next, the operation of the image forming apparatus shown in FIG. 1 will be described.
The semiconductor laser 21 emits light based on the output signal of the laser drive unit 34 controlled by the control unit 30. As will be described later in detail, the semiconductor laser 21 is provided with a total of 32 laser diodes (LDs) as one light source. In the exposure unit 20, the 32 beams emitted from the 32 laser diodes are collimated by the collimating lens 22, and then deflected and scanned by the polygon mirror 24 through the aperture 23, thereby forming the imaging lens 25 and the cylindrical mirror. 26 is used to form an image on the photosensitive drum 11. In this way, 32 lines can be simultaneously scanned on the photosensitive drum 11. This rotary polygon mirror (polygon mirror) is rotationally driven with high rotational accuracy by a DC motor (scan motor). The photosensitive drum 11 is rotationally driven by a driving means (not shown), and the photosensitive drum 11 whose surface is charged by the charger 12 by the exposure device 20 is rotated in a direction orthogonal to the laser scanning (main scanning) (rotational driving). Direction, sub-scanning direction), and a two-dimensional electrostatic latent image can be formed. The electrostatic latent image formed on the photosensitive drum 11 is developed by the developing device 13 under the control of the developing bias control unit 32, and the formed toner image is transferred to a sheet by a transfer unit (not shown), The sheet is heated and fixed on a sheet by a fixing device (not shown). Thus, a print image is formed on the paper. On the other hand, residual toner (excess developer) remaining without being transferred exists on the photosensitive drum 11 after transfer. This residual toner is cleaned by the cleaning blade 14.

Next, description will be given of gradation expression by performing binary lighting control on the semiconductor laser 21 which is a surface emitting multi-beam laser.
FIGS. 2A to 2C are diagrams for explaining gradation expression using a multi-beam laser. FIG. 2A shows an example of an image formed in the main scanning direction (FS) and the sub scanning direction (SS). The area of D11 to D14... Is shown in one block row, D21 to D24... FIG. 2B shows an enlarged block area of D11 and D12. One block area is formed with a total of 32 dots, 4 dots in the sub-scanning direction and 8 dots in the main scanning direction. FIG. 2C shows a surface emitting multi-beam laser constituting the semiconductor laser 21. This surface-emitting multi-beam laser is provided with a total of 32 laser diodes (LDs) LD1 to LD32 in a 4 × 8 array (arrangement shape) as a light source in one device. The 32 laser diodes can simultaneously scan 32 lines with 32 beams.

  For example, the block region of D11 shown in FIG. 2B is exposed by scanning four laser diodes LD1 to LD4 with the polygon mirror 24 in the main scanning direction. Similarly, the block region of D21 is exposed by four laser diodes LD5 to LD8. For example, in the block region of D11 shown in FIG. 2B, each of 4 × 8 total 32 dots obtained by multiplying four laser diodes LD1 to LD4 in binary and multiplying by 8 pixels in the main scanning direction. By controlling ON / OFF of dots, a plurality of gradations can be expressed using one area.

  FIG. 3 is a diagram for explaining the relationship between the light emission duty of the laser and the amount of light on the photosensitive drum (photosensitive member) 11. FIG. 3 shows an example in which light is emitted with ON / OFF at a duty of 100%, an example in which light is emitted with ON / OFF at a duty of 75%, and an example in which light is emitted with ON / OFF at a duty of 50%. Yes. Each ON time is a light emission unit. FIG. 3 shows the amount of light on the photosensitive member generated by the ON / OFF light emission timing. The amount of light on the photoconductor is indicated by the movement of the light emitting spot in the main scanning direction on the horizontal axis, and the amount of light on the photoconductor is indicated on the vertical axis. The amount of light obtained is a Gaussian distribution (see FIG. 3). Normal distribution). When the duty is changed from 100% to 75%, the light emission unit appearing in the pulse width is about 75%, but the amount of light on the photoconductor does not reach 75% and is greatly reduced. When the duty is from 100% to 50%, the light emission unit is about 50%, but the amount of light on the photoconductor is much less than 50%. Therefore, for example, when the multi-beam method is employed, which can express gradation only by binary lighting control of ON / OFF of the light emission spot, the duty is generally close to 100% for the most efficient state for exposure. The amount of light is obtained. However, in the present embodiment, as will be described later, the duty of the initial value of the multi-beam laser is reduced to, for example, about 50%, and the output duty is increased stepwise in accordance with the deterioration state of the photosensitive drum 11, so The life of the drum 11 is extended.

  FIGS. 4A and 4B are views for explaining the laminated structure of the photosensitive drum (photosensitive member) 11 and the wear state of the surface of the photosensitive member. As shown in FIG. 4A, the photosensitive drum 11 has a laminated structure having an undercoat layer, a charge generation layer, and a charge transport layer on a conductive support. In the electrophotographic process, when light is irradiated while the photosensitive drum 11 is charged, positive and negative charge carriers are generated in the charge generation layer. As the charge generation layer, a material having photoconductivity and generating carriers with high efficiency is used. The charge transport layer is a layer for transporting carriers generated in the charge generation layer, and a material having high charge mobility is used. The undercoat layer is used to prevent electric charges from being injected from the substrate when not irradiated with light, and serves as a blocking layer. The conductive support is a base material and is generally a cylindrical aluminum pipe, but there is also a belt-like one.

  FIG. 4B shows how the cleaning blade 14 wears the surface of the photosensitive drum 11 in the cleaning process. Wear progresses in proportion to the cumulative number of rotations of the photosensitive drum 11. This cumulative rotational speed is also proportional to the cumulative number of printed sheets as the image forming apparatus. In the laminated structure shown in FIG. 4A, the charge transport layer is scraped off by wear. When the thickness of this layer decreases, the charge mobility deteriorates, so that the sensitivity as a so-called photoreceptor is lowered. That is, even if the same amount of light is given, a desired output image density tends not to be obtained after the wear compared to before the wear.

  FIG. 5 is a diagram for explaining the relationship between the degree of wear of the photosensitive drum (photosensitive member) 11 and the output image density. In FIG. 5, the horizontal axis represents the degree of wear of the photosensitive member, and the vertical axis represents the output image density. As shown in FIG. 5, when the degree of wear of the photosensitive member increases, the output image density decreases. Therefore, for example, when the photosensitive drum 11 is worn due to a phenomenon as shown in FIG. 4B, a desired output image density cannot be obtained even when the same amount of light is applied, unlike before the wear.

  FIG. 6 is a diagram for explaining the relationship between laser exposure energy and output image density. In FIG. 6, the horizontal axis indicates the laser exposure energy amount, and the vertical axis indicates the output image density. As shown in FIG. 6, when the laser exposure energy amount is increased, the output image density is also increased. Further, according to FIG. 6, when the adjustment range of the laser exposure energy amount can be widened, the touch range of the output image density can be increased, and when the adjustment range of the laser exposure energy amount cannot be widened. It can be understood that the touch width of the output image density cannot be increased.

  Here, FIG. 7 is a diagram showing the relationship between the magnitude of the output setting reference voltage VREF and the amount of light on the photosensitive drum 11. Here, a case where the light emission duty is fixed to 100%, for example, is shown. In the current technology using the multi-beam laser ROS, gradation is realized by fixing the duty at, for example, 100% and controlling each laser diode ON / OFF. In addition, the output setting reference voltage VREF has been adjusted in accordance with environmental conditions such as the ambient temperature of the apparatus, conditions when the apparatus is first turned on, and the like. That is, the light emission duty is fixed, and exposure is performed by ON / OFF control and adjustment of the output setting reference voltage VREF.

  FIG. 8 is a diagram showing the relationship between the magnitude of the output setting reference voltage VREF and the amount of light on the photosensitive drum 11 when the light emission duty is variable. As described with reference to FIG. 7, at present, the light emission duty is fixed, and exposure is performed by ON / OFF control and adjustment of the output setting reference voltage VREF. However, in this case, the range of adjustment is very narrow, and it has been difficult to perform extremely fine control. Further, as described with reference to FIGS. 4A and 4B, when the sensitivity of the photosensitive member is lowered due to deterioration with time such as wear of the photosensitive drum 11, a desired output image density is obtained with the current control. The photoconductor replacement time was accelerated.

  Here, since the laser exposure energy is considered to be proportional to the integral value of the Gaussian distribution graph as shown in FIG. 8, that is, the area of the graph, the area ratio is more variable when the light emission duty is fixed than when the light emission duty is fixed. Can be taken big. That is, by making the light emission duty variable, the laser exposure energy adjustment range (dynamic range) can be increased. Therefore, in the present embodiment, for example, the light emission duty is set to about 50% in the initial state, and the light emission duty is increased stepwise when it is considered that the sensitivity of the photoconductor on the photoconductor drum 11 is lowered. I did it.

  That is, in this embodiment, first, the light emission duty of the multi-beam laser ROS that is controlled to perform binary lighting and records a latent image at a high resolution on the photosensitive drum (photosensitive member) 11 is set to 50% of the maximum value. This is the initial value at the time of factory shipment. Then, the level of the charging potential and the developing bias potential of the photoconductor is adjusted so as to obtain a necessary and sufficient developing density in accordance with the amount of light in this state. After that, when the photoconductor is thinned with time (the thickness of the charge transport layer is reduced) and the sensitivity is lowered, resulting in a decrease in the output image density, it is suppressed to 50%. The output duty of the multi-beam laser ROS is increased stepwise, for example, 75% or 100%, depending on the degree of deterioration of the photoreceptor. At this time, the charging potential and the developing bias potential of the photoconductor are also automatically adjusted according to the light quantity in each. With this configuration, the output image density is prevented from decreasing. Even in the case of a multi-beam laser ROS with a high video rate, it is possible to vary the light emission duty in several discrete steps as long as the resolution is not high enough to express gradation.

  As described above, in the present embodiment, the output light quantity of the multi-beam laser ROS is combined with the variable of the output setting reference voltage (VREF) and the variable of the light emission duty, so that even in the case of binary lighting control, the multi-beam is controlled. The dynamic range of the light quantity of the laser ROS can be expanded. If the dynamic range of the light quantity of the multi-beam laser ROS can be expanded, the set touch width of the charging potential and the developing bias potential of the photosensitive member can be increased. As a result, it becomes possible to continue to use the photoconductor with a reduced film thickness, and as a result, it is possible to extend the life of the photoconductor.

  FIG. 9 is a block diagram for explaining in detail the functions of the control means including the control unit 30 in the image forming apparatus shown in FIG. The laser drive unit 34 includes an image output data generation circuit 41 and a multi-beam laser ROS drive circuit 42. The image output data generation circuit 41 executes various processes such as edge enhancement processing, gradation correction, screen processing, registration, and light amount correction. The multi-beam laser ROS drive circuit 42 executes ON / OFF control of the semiconductor laser (multi-beam laser ROS) 21, setting control of the output setting reference voltage VREF, and the like.

In the control unit 30, for example, the number of printed sheets on the image forming apparatus is accumulated and stored in a predetermined memory (not shown). This memory is preferably constituted by, for example, a non-volatile memory so that the accumulated count value does not disappear even when the power of the image forming apparatus is shut down, and this non-volatile memory holds the accumulated count value. For example, the degree of wear of the photosensitive drum 11 is determined based on the cumulative number. The determination result of the degree of wear is output to the laser emission duty control unit 33 and the image output data generation circuit 41. The laser emission duty control unit 33 determines the emission duty according to the acquired degree of wear and outputs it to the multi-beam laser ROS drive circuit 42. On the other hand, the image output data generation circuit 41 acquires setting information from the laser emission duty control unit 33 and sets the output setting reference voltage VREF and the light amount correction signal according to the degree of wear determined by the control unit 30. And output to the multi-beam laser ROS driving circuit 42. The image output data generation circuit 41 acquires a timing signal from the multi-beam laser ROS driving circuit 42, and outputs a multi-beam ON / OFF signal corresponding to the input image signal in accordance with the acquired timing signal. Yes. Further, the control unit 30 outputs information on the determined wear level to the charge control unit 31 and the development bias control unit 32, and the charge control unit 31 and the development bias control unit 32 charge the charge potential V _H according to the wear level. And the developing bias potential V _BIAS is controlled.

FIG. 10 is a diagram showing the relationship _among the charging potential V _H , the developing bias potential V _BIAS , the exposure potential V _L , and the developing potential V _DAVE . Now, the difference between the charge potential _{V H} and the developing bias potential _{V BIAS} and _{V CLN,} also development potential _{V DEVE,} the relationship between the developing bias potential _{V BIAS} and the exposure potential _{V L} is as defined in the following.
V _CLN = V _H -V _BIAS
V _DAVE = V _{BIAS- VL}
At this time,
When V _DVE / V _CLN , that is, (V _BIAS −V _L ) / (V _H −V _BIAS ) is kept constant, the developing performance remains unchanged. Since the exposure potential V _L is proportional to the laser exposure energy, the exposure potential V _L is also proportional to the laser emission duty and the output setting reference voltage VREF shown in FIG. Therefore, by adjusting the laser emission duty, the output setting reference voltage VREF, the charging potential V _H, and the developing bias potential V _BIAS to keep the above formula constant, development can be performed even when the photosensitive drum 11 is deteriorated with time. Performance can be maintained.

FIG. 11 is a flowchart for explaining an image forming processing method accompanying the photoreceptor deterioration. The control unit 30 acquires, for example, the cumulative number of printed sheets as an index of deterioration of the photosensitive drum 11 (step 101). Then, the control unit 30 determines whether or not the acquired cumulative number of printed sheets exceeds a predetermined reference value A (step 102). This reference value A is determined in accordance with the characteristics of the photosensitive drum 11 provided in the image forming apparatus. More specifically, the reference value A for the cumulative number of sheets is determined as the first reference wear degree obtained from the relationship between the wear degree of the photoconductor and the output image density as shown in FIG. If the reference value A is not exceeded, the initially set parameters are maintained. That is, for example, the light emission duty output from the laser light emission duty controller 33 is 50% (first output duty), the charging potential controlled by the charging controller 31 is V _H1 , and the developing bias controller 32 controls the charging potential. The development bias potential is set to V _BIAS1 (step 103), and the process returns to the process for obtaining the cumulative number of printed sheets in step 101.

If the cumulative number of printed sheets exceeds the reference value A in step 102, it is determined whether or not the acquired cumulative number of printed sheets has exceeded a predetermined reference value B (step 104). Similar to the reference value A, the reference value B is determined from the cumulative number of printed sheets employed as a determination index for the degree of wear that the wear of the photosensitive drum 11 has further progressed beyond a certain level from the state of the reference value A. Is set as the second reference wear degree. When the reference value B is not exceeded, the light emission duty output from the laser light emission duty control unit 33 is changed to 75% (second output duty), for example, as a state exceeding the reference value A, The charging potential controlled by the charging controller 31 is adjusted as V _H2 and the developing bias potential controlled by the developing bias controller 32 is adjusted as V _BIAS2 (step 105). Thereafter, the process returns to the process for acquiring the cumulative number of printed sheets in step 101.

If the accumulated number of printed sheets exceeds the reference value B in step 104, it is determined whether or not the acquired accumulated number of printed sheets has exceeded a predetermined reference value C (step 106). The reference value C is a third reference in which the wear of the photosensitive drum 11 is determined to have progressed by a certain amount or more from the cumulative number of prints employed as a determination index for the degree of wear in the same way as the reference value A and the reference value B. Set as the degree of wear. When the reference value C is not exceeded, the light emission duty output from the laser light emission duty control unit 33 is changed to 100% (third output duty), for example, as the state exceeding the reference value B, The charging potential controlled by the charging control unit 31 is adjusted to V _H3 and the developing bias potential controlled by the developing bias control unit 32 is adjusted to V _BIAS3 (step 107). Thereafter, the process returns to the process of acquiring the cumulative number of printed sheets in step 101. . If the reference value C is exceeded in step 106, a message prompting the replacement of the photosensitive drum 11 is displayed (step 108), and a series of processes accompanying the deterioration of the photosensitive member is completed. Further, instead of the cumulative number of printed sheets described above, the cumulative rotational speed of the photosensitive drum 11 may be used.

  As described above, in the processing shown in FIG. 11, a predetermined reference value is provided for the cumulative number of printed sheets, and the combination of the VREF limiter setting value, the charging potential, and the developing bias potential level is switched by comparison with the reference value. . Each combination is considered so as to maintain the relationship shown in FIG. In the process shown in FIG. 11, the cumulative number of printed sheets is adopted as the reference value determination. However, for example, the cumulative number of revolutions of the photosensitive drum 11 may be employed instead of the cumulative number of printed sheets. Further, if there is another index for recognizing the degree of deterioration of the photosensitive drum 11, it is also possible to adopt it. Further, in the processing shown in FIG. 11, three reference values A, B, and C are used for determination, and three light emission duties are 50%, 75%, and 100%. However, the present invention is not limited to this.

  As described above, in the present embodiment, the output light quantity of the multi-beam laser ROS is combined with the variable of the output setting reference voltage (VREF) and the variable of the light emission duty, so that even in the binary lighting control, the multi-beam laser ROS. It is possible to expand the dynamic range of the amount of light. By expanding the dynamic range of the light quantity of the multi-beam laser ROS, it is possible to increase the set touch width of the charging potential and the developing bias potential of the photoconductor. As a result, it is possible to continue to use the photoconductor with a reduced film thickness, and as a result, it is possible to extend the life of the photoconductor.

1 is a diagram illustrating a basic configuration of an image forming apparatus to which the exemplary embodiment is applied. (A)-(c) is a figure for demonstrating the gradation expression using a multi-beam laser. It is a figure for demonstrating the relationship between the light emission duty of a laser, and the light quantity on a photosensitive drum. (A), (b) is a figure for demonstrating the laminated structure of a photoconductor drum (photoconductor), and the abrasion state of the photoconductor surface. It is a figure for demonstrating the relationship between the abrasion degree of a photoconductive drum, and output image density. It is a figure for demonstrating the relationship between laser exposure energy and an output image density. It is a figure which shows the relationship between the magnitude of the output setting reference voltage VREF, and the light quantity on a photosensitive drum. It is a figure which shows the relationship between the magnitude of the output setting reference voltage VREF at the time of making a light emission duty variable, and the light quantity on a photosensitive drum. FIG. 2 is a block diagram for explaining in detail the function of a control unit in the image forming apparatus shown in FIG. 1. FIG. 5 is a diagram illustrating a relationship _among a charging potential V _H , a developing bias potential V _BIAS , an exposure potential V _L , and a developing potential V _DAVE . 6 is a flowchart for explaining an image forming processing method accompanying photoreceptor deterioration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image formation part, 11 ... Photosensitive drum, 12 ... Charger, 13 ... Developing device, 14 ... Cleaning blade, 20 ... Exposure device, 21 ... Semiconductor laser (multi-beam laser ROS), 30 ... Control part, 31 ... Charge control unit, 32... Development bias control unit, 33... Laser emission duty control unit, 34.

Claims (10)

An image carrier for carrying an image;
A charger for charging the image carrier;
An exposure device having a multi-beam laser composed of a plurality of light emitting lasers for forming a latent image on the image carrier charged by the charger;
A developing unit for developing a latent image of the image carrier formed by the exposure unit;
An image forming apparatus comprising: a control unit that grasps a degree of deterioration of the image carrier, raises an output duty of the multi-beam laser based on the grasped degree of deterioration, and controls lighting of the multi-beam in binary.   The image forming apparatus according to claim 1, wherein the control unit increases the output duty in a stepwise manner in accordance with a degree of deterioration of the image carrier.   The control means controls the initial value of the output duty by suppressing it to about 50% of the maximum value of the output duty in a state where the deterioration of the image carrier is not progressing, and gradually increases the initial value from the initial value. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 1, wherein the control unit adjusts a charging potential of the charger and a developing bias potential of the developing device as the output duty of the multi-beam laser is increased.   The image forming apparatus according to claim 1, wherein the control unit grasps a cumulative number of printed sheets, and grasps a degree of deterioration of the image carrier from the grasped cumulative number of printed sheets. A method for controlling an image forming apparatus for forming an image by charging, exposing and developing an image carrier,
Controlling the lighting of the multi-beam laser that performs the exposure with a binary value at a first output duty in an initial state in which the deterioration of the image carrier has not progressed;
Grasping the degree of deterioration of the image carrier;
Determining whether or not the degree of deterioration of the image carrier to be grasped is more advanced than a predetermined state;
When it is determined that the degree of deterioration is more advanced than the predetermined state, the multi-beam laser is lit in binary with a second output duty that is higher than the first output duty. And a control method for the image forming apparatus.   A step of adjusting the charging potential at the time of charging and the developing bias potential at the time of developing together with increasing the first output duty and performing lighting control with binary values at the second output duty. The method of controlling an image forming apparatus according to claim 6, further comprising:   When a state having a higher degree of deterioration than the predetermined state is determined in advance and it is determined that the degree of deterioration has progressed more than the high state, the third output duty is higher than the second output duty. 7. The method of controlling an image forming apparatus according to claim 6, wherein the multi-beam laser is controlled to be turned on with a binary value at an output duty.   A step of adjusting the charging potential at the time of charging and the developing bias potential at the time of developing together with increasing the second output duty and performing lighting control with a binary value at the third output duty. The method of controlling an image forming apparatus according to claim 8, further comprising:   The step of grasping the degree of deterioration of the image carrier comprises grasping the cumulative number of printed sheets or the cumulative number of revolutions of the image carrier by the image forming apparatus, and the cumulative number of printed sheets or cumulative number of revolutions being a predetermined value set in advance. 7. The method of controlling an image forming apparatus according to claim 6, further comprising grasping that the deterioration has progressed when the value exceeds.

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