JP6099947B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that uses an electrophotographic recording system such as a laser printer, a copying machine, and a facsimile.

  Conventionally, an image forming apparatus such as a copying machine or a laser printer using an electrophotographic system is known. In recent years, such an image forming apparatus is required to be reduced in size and cost for use in a small office such as a personal office. On the other hand, further improvement in image quality is also demanded.

  Under such circumstances, for example, Patent Document 1 discloses a configuration in which a plurality of charging power sources are shared and a plurality of transfer power sources are shared in order to achieve downsizing of the apparatus. In order to improve the image quality, for example, Patent Document 2 discloses a configuration in which a non-image portion in the entire printable area is finely exposed by an exposure unit. Hereinafter, such an exposure method is referred to as non-image area fine exposure. Therefore, as a configuration that achieves both the downsizing of the device and the improvement of the image quality, the power source is shared as in the configuration disclosed in Patent Document 1, and the configuration disclosed in Patent Document 2 is not common. It is possible to propose a color image forming apparatus that performs fine image portion exposure.

US Pat. No. 7,228,085 JP 2003-312050 A

  However, the color image forming apparatus combining the configuration of Patent Document 1 and the configuration of Patent Document 2 has a problem that the image density and the line width change due to the sensitivity deterioration of the photosensitive drum. Specifically, as the exposure amount of the photosensitive drum increases, the photosensitive layer deteriorates and the sensitivity change increases. In particular, in a photosensitive drum having a late life, the surface potential of the photosensitive drum may not be brought to a desired potential by exposure due to sensitivity change. In some cases, the development contrast, which is the potential difference between the development potential and the surface potential of the exposed photosensitive drum, becomes smaller than the optimum value. As a result, a phenomenon such as a decrease in image density and a narrowing of the line width occurs as compared with a case where a photosensitive drum that is less used is used.

  The present invention has been made under such circumstances, and an object thereof is to reduce the deterioration of the photosensitive drum and the deterioration of the image quality.

  In order to solve the above-described problems, the present invention has the following configuration.

(1) a sense performs an optical member, a charging means for charging the pre-Symbol feeling light body, the exposure in the first exposure to the image portion to adhere the toner onto the photosensitive member during image formation, before the time of the image forming serial sense of rows intends exposure means exposure with the second exposure amount smaller than the first exposure amount in the non-image area which does not adhere to the toner on the optical member to form a toner image by adhering toner to the image portion a developing means, and a transfer means for transferring to a transfer member the toner image formed on the front Symbol feeling light body on by being applied a transfer voltage to said transfer means when performing the images formed and control means for performing transfer voltage control for determining the applied transfer voltage Ru, an image forming apparatus provided with the control hand stage is less than the second exposure amount at the time of the image formed by the exposure means third intends row the transfer voltage control I line exposure with an exposure amount Or, an image forming apparatus which is characterized in that said transfer voltage control is not performed exposure by the exposing unit.

  According to the present invention, it is possible to reduce the deterioration of the photosensitive drum and the deterioration of the image quality.

The figure which shows the outline of the cross section of the color image forming apparatus of Examples 1-4, The figure which shows the cross section of the photosensitive drum of Examples 1-4 FIG. 4 is a diagram illustrating sensitivity characteristics of photosensitive drums according to first to fourth embodiments, and FIG. The figure which shows the charging high voltage power supply and transfer high voltage power supply of Examples 1-4 The figure which shows the exposure apparatus provided with the micro exposure function of Examples 1-4. The figure which shows the relationship between the charging voltage of Examples 1-4, the charging potential of a photosensitive drum, and a primary transfer potential. 7 is a flowchart illustrating fine exposure and normal exposure parameter setting processing, image formation processing, and photosensitive drum usage status update processing according to the first to fourth embodiments. FIG. 10 is a diagram illustrating a potential relationship during primary transfer voltage control and image formation according to the first embodiment. The figure which shows the relationship between the integral rotation speed of the photosensitive drum of Example 1, and exposure amount. The figure which shows the relationship between the charging voltage of Example 3, and a photosensitive drum electric potential.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

  First, the configuration of a color image forming apparatus (hereinafter simply referred to as an image forming apparatus) will be described with reference to FIGS. 1 to 3, and then the control operation related to microexposure will be described with reference to FIGS. 4 to 6. Further, the control operation related to the primary transfer voltage control will be described, and finally the effects of the embodiment will be described with reference to FIGS.

(Schematic of cross section of image forming apparatus)
FIG. 1A is a diagram showing an outline of a cross section of the image forming apparatus. The configuration and operation of the image forming apparatus of this embodiment will be described with reference to FIG. First, the image forming apparatus includes first to fourth image forming stations a to d. Here, the first is yellow (hereinafter referred to as Y), the second is magenta (hereinafter referred to as M), the third is cyan (hereinafter referred to as C), and the fourth is black (hereinafter referred to as Bk). Hereinafter, the image forming station a may be referred to as a yellow station a, the image forming station b as a magenta station b, the image forming station c as a cyan station c, and the image forming station d as a black station d. Each of the image forming stations a to d includes a storage member (not shown) (memory tag 32-2 to be described later) that stores the accumulated number of rotations of the photosensitive drums 1a to 1d as information on the life of the photosensitive drum as a photosensitive member. ing. Here, the life of the photosensitive drum 1 means that the charge transport layer of the photosensitive drum 1 described later is gradually scraped by continuously using the unused photosensitive drum (which is also an initial photosensitive drum) 1. As a result, the use time has passed so that an image defect occurs. The symbols a to d are omitted as appropriate unless it is necessary to explain each color. Each image forming station can be exchanged for the image forming apparatus main body. Each image forming station only needs to include at least the photosensitive drum 1, and up to which member can be included in the image forming station and exchangeable is not particularly limited.

  In the following, the operation of the first image forming station (yellow station) a will be described as an example as a representative of each image forming station. The image forming station a includes a photosensitive drum 1a as a photosensitive member, and the photosensitive drum 1a is rotationally driven in a direction of an arrow (counterclockwise direction) at a predetermined peripheral speed (process speed). In this rotation process, the photosensitive drum 1a is uniformly charged to a charging potential having a predetermined polarity by a charging roller 2a serving as a charging unit. Next, the surface of the photosensitive drum 1a corresponding to the image portion is exposed by a laser beam 6a scanned by an exposure device 31a which is an exposure unit based on image data (image signal) input from the outside, and the charge is discharged. An exposure potential Vl is formed on the surface of the photosensitive drum 1a. Subsequently, the toner is developed in the exposure potential Vl portion which is the image portion by the potential difference between the development potential Vdc applied to the developing roller 43a of the developing device (yellow developing device) 4a which is the developing means and the exposure potential Vl. A toner image is visualized. The image forming apparatus according to the present exemplary embodiment is a reversal developing type image forming apparatus in which image exposure is performed by the exposure device 31a and toner is developed on the exposure unit.

  The intermediate transfer belt 10 as a transfer target is stretched by stretching members 11, 12, and 13 and is in contact with the photosensitive drum 1 a. The intermediate transfer belt 10 is rotationally driven at the contact position in the same direction as the photosensitive drum 1a (clockwise as the rotational direction) and at substantially the same peripheral speed. The yellow toner image formed on the photosensitive drum 1a (on the photosensitive member) is transferred as follows. That is, the yellow toner image is transferred onto the intermediate transfer belt 10 in the process of passing through a contact portion (hereinafter referred to as a primary transfer nip portion) between the photosensitive drum 1 a and the intermediate transfer belt 10. That is, a current flows between the photosensitive drum 1a and the primary transfer roller 14a by the primary transfer voltage applied from the primary transfer power supply 15 to the primary transfer roller 14a, which is a transfer unit, and thus on the photosensitive drum 1a. The yellow toner image formed on the toner image is transferred (moved) onto the intermediate transfer belt 10. Hereinafter, this transfer is referred to as primary transfer. Toner remaining on the surface of the photosensitive drum 1a (hereinafter referred to as primary transfer residual toner) is cleaned and removed by a drum cleaner 5a serving as a cleaning unit. Thereafter, the above-described image forming process after charging is repeated for each color. In this manner, the second color magenta toner image (M), the third color cyan toner image (C), and the fourth color black toner image (Bk) are formed, and are sequentially transferred onto the intermediate transfer belt 10. As a result, a composite color image is obtained.

  In the process in which the four color toner images on the intermediate transfer belt 10 pass through a contact portion (hereinafter referred to as a secondary transfer nip portion) between the intermediate transfer belt 10 and the secondary transfer roller 20, the secondary transfer power source 221 A secondary transfer voltage is applied to the secondary transfer roller 20. As a result, the four color toner images on the intermediate transfer belt 10 are collectively transferred onto the surface of the recording material P fed from the paper feed roller 50. Thereafter, the recording material P carrying the four color toner images is introduced into the fixing device 30 and heated and pressurized by the fixing device 30, and the four color toners are melted and mixed to be fixed to the recording material P. With the above operation, a full-color toner image is formed on the recording material P. Further, toner remaining on the surface of the intermediate transfer belt 10 (hereinafter referred to as secondary transfer residual toner) is cleaned and removed by the intermediate transfer belt cleaning device 16.

  In FIG. 1A, the image forming apparatus having the intermediate transfer belt 10 has been described as an example, but the present invention is not limited to such an image forming apparatus. For example, a recording material conveyance belt (recording material carrier) is provided, and a toner image developed on the photosensitive drum 1 is directly transferred to a recording material P as a transfer medium conveyed by the recording material conveyance belt. The image forming apparatus may also be used. Hereinafter, an image forming apparatus having the intermediate transfer belt 10 will be described as an example.

(Photosensitive drum cross section)
FIG. 1B shows an example of a cross section of the photosensitive drum 1a. In the photosensitive drum 1a, a charge generation layer 223a and a charge transport layer 224a are stacked on a conductive support substrate 222a. The conductive support base 222a is, for example, an aluminum cylinder having an outer diameter of 30 mm and a thickness of 1 mm. The charge generation layer 223a is a phthalocyanine pigment having a thickness of 0.2 μm, for example. The charge transport layer 224a has, for example, a thickness of 20 μm, uses polycarbonate as a binder resin, and blends an amine compound as a charge transport material. FIG. 1B is an example of the photosensitive drum 1a, and dimensions and materials are not limited to those described here.

(Sensitivity characteristics of photosensitive drum)
FIG. 2A is an example of an EV curve showing the photosensitive characteristics of the photosensitive drum 1. In the graph of FIG. 2A, the horizontal axis represents the exposure amount E (μJ / cm ² ) (hereinafter simply referred to as the exposure amount) of the laser beam 6 a irradiated from the exposure device 31 a, and the vertical axis represents the surface of the photosensitive drum 1. Potential (hereinafter also referred to as photosensitive drum potential) (V) is shown. Vcdc is a charging voltage, and the numerical value on the vertical axis in FIG. 2A is the photosensitive drum potential when −1100 V (Vcdc = −1100 V) is applied to the charging roller 2 as the charging voltage Vcdc. FIG. 2A shows the photosensitive drum 1 whose surface is charged to V by the charging roller 2 with a laser beam 6 so that the exposure amount is E (μJ / cm ² ) on the surface of the photosensitive drum. It shows the potential decay when exposed. This EV curve shows that a larger potential attenuation can be obtained by increasing the exposure amount E. In addition, since a high potential portion (for example, a potential portion having a large absolute value such as −600 V) is an environment with a strong electric field, recombination of charge carriers (electron-hole pairs) generated by exposure hardly occurs and is small. It shows a large potential decay even at the exposure amount. On the other hand, in the low potential portion (for example, a potential portion having a small absolute value such as −200 V), the generated carriers are easily recombined. In FIG. 2A, the EV curve (solid line) of the photosensitive drum 1 at the initial stage when it is used and the photosensitive drum when it is used and reaching the end of its life (hereinafter simply referred to as the end of its life). 1 EV curves (broken lines) are respectively shown.

As the photosensitive drum 1 is used, the surface tends to be charged even when the same charging voltage Vcdc is applied by the charging roller 2. Further, even when the same exposure dose is irradiated, the potential attenuation tends to be small. For this reason, as shown in FIG. 2A, the initial photosensitive drum 1 has a charging voltage Vcdc of −1100 V, a surface potential of −600 V, and an exposure amount E for setting the surface potential to −500 V is 0. It can be seen that 03 μJ / cm ^{2 is} necessary. On the other hand, when the photosensitive drum 1 reaches the end of its life, the charging voltage Vcdc is −1100 V, the surface potential is −700 V, and the exposure amount E for setting the surface potential to −500 V needs to be 0.12 μJ / cm ^2. Recognize. It can also be seen that the initial photosensitive drum 1 requires an exposure amount E of 0.25 μJ / cm ² to bring the surface potential to −150V. On the other hand, in the case of the photosensitive drum 1 at the end of its life, the surface cannot be attenuated to −150 V even if the exposure amount E is increased due to sensitivity deterioration of the photosensitive drum 1 due to exposure, and the exposure amount E is 0.40 μJ. / cm ² even only up to -200V it can be seen that does not decay. Note that the sensitivity characteristic of the photosensitive drum 1 shown in FIG. 2A is an example, and application of a photosensitive drum having various EV curves is assumed in this embodiment.

(Image forming system diagram)
FIG. 2B is a block diagram of an image forming system including the external device 101, the video controller 103, and the printer engine 105. The printer engine 105 includes an engine control unit 104 and an engine mechanism unit 106 which are control means. Each will be described below.

<Video controller 103>
First, the video controller 103 will be described. The CPU 44 controls the entire video controller 103. The non-volatile storage unit 45 stores various control codes executed by the CPU 44. The nonvolatile storage unit 45 corresponds to a ROM, an EEPROM, a hard disk, or the like. The RAM 46 functions as a main memory, work area, and the like for the CPU 44, and is a storage means for temporary storage. A host interface unit (hereinafter referred to as host I / F) 7 is an input / output unit for printing data and control data with an external device 101 such as a host computer. Print data received by the host I / F 7 is stored in the RAM 46. The DMA control unit 9 transfers the image data in the RAM 46 to an engine interface unit (hereinafter referred to as engine I / F) 11 in accordance with an instruction from the CPU 44. A panel interface unit (hereinafter referred to as a panel I / F) 10 receives various settings and instructions from an operator from a panel unit (not shown) provided in the printer body. Next, the engine I / F 11 is a signal input / output unit for the printer engine 105, and transmits a data signal from an output buffer register (not shown) and controls communication with the printer engine 105. The system bus 12 has an address bus and a data bus. The above-described components are connected to the system bus 12 and are accessible to each other.

<Printer engine 105>
Next, the printer engine 105 will be described. The printer engine 105 is roughly divided into an engine control unit 104 and an engine mechanism unit 106 (broken line frame). The engine mechanism unit 106 is a part that operates according to various instructions from the engine control unit 104, and is a generic name for the mechanisms related to image formation described with reference to FIG. The laser / scanner system 31 (corresponding to the exposure apparatus 31 described with reference to FIG. 1A) functions as an exposure unit, and includes a laser light emitting element, a laser driver circuit, a scanner motor, a rotary polygon mirror, a scanner driver, and the like. The laser / scanner system 31 forms a latent image on the photosensitive drum 1 by exposing and scanning the photosensitive drum 1 with the laser beam 6 according to the image data sent from the video controller 103.

  The image forming system 32 is a central part of the image forming apparatus, and forms a toner image based on the latent image formed on the photosensitive drum 1 on the recording material P. The image forming system 32 includes process cartridges 32-1, an intermediate transfer belt 10, and a fixing device 30 that form an image forming station, and a high-voltage power supply circuit that generates various high voltages for image formation. Consists of.

  The process cartridge 32-1 includes at least the photosensitive drum 1, and in this embodiment, further includes a static eliminator (not shown), a charging roller 2, a developing device 4, and the like. The process cartridge 32-1 constitutes at least a part of the image forming station. Further, the process cartridge 32-1 is provided with a memory tag 32-2 which is a nonvolatile storage unit. In this embodiment, each of the image forming stations a to d includes a nonvolatile memory tag 32-2. The CPU 21 or the ASIC 22 in the engine control unit 104 executes saving (storing) or reading of various information in the memory tag 32-2.

  The paper feed / conveyance system 33 is a part that feeds and conveys the recording material P, and includes various conveyance system motors, a paper supply / discharge tray, various conveyance rollers, and the like. The sensor system 34 is a sensor group for collecting information necessary for the CPU 21 and the ASIC 22 to control the laser / scanner system 31, the image forming system 32, and the paper feed / conveyance system 33. The sensor system 34 includes at least various types of sensors already known, such as a temperature sensor for the fixing device 30, a toner remaining amount detection sensor, a density sensor for detecting image density, a paper size sensor, a paper leading edge detection sensor, and a paper conveyance detection sensor. included. Information detected by these various sensors is acquired by the CPU 21 and reflected in various operations of the image forming system 32 and print sequence control. Although the sensor system in the figure is described separately as the laser / scanner system 31, the image forming system 32, and the paper feed / conveyance system 33, it may be considered to be included in any mechanism.

  Next, the engine control unit 104 will be described. The CPU 21 uses the RAM 23 as a main memory and a work area, and controls the engine mechanism unit 106 according to various control programs stored in the nonvolatile storage unit 24. More specifically, the CPU 21 drives the laser / scanner system 31 based on a print control command and image data input from the video controller 103 via the engine I / F 11 and the engine I / F 25. Further, the CPU 21 controls various print sequences by controlling the image forming system 32 and the paper feed / conveyance system 33. The CPU 21 acquires information necessary for controlling the image forming system 32 and the paper feed / conveyance system 33 by driving the sensor system 34. On the other hand, the ASIC 22 performs control of each motor and control of a high voltage power source such as a development voltage in executing various print sequences in accordance with instructions from the CPU 21.

  Note that part or all of the functions of the CPU 21 may be performed by the ASIC 22, and conversely, part or all of the functions of the ASIC 22 may be performed by the CPU 21 instead. Further, a part of the functions of the CPU 21 and the ASIC 22 may be provided with separate dedicated hardware so that the dedicated hardware can perform the function. The system bus 26 is the same as the system bus 12.

(Charging high-voltage power supply 52 and transfer high-voltage power supply 120)
Next, the charging high-voltage power supply 52 and the transfer high-voltage power supply 120 will be described with reference to FIG. The transfer high-voltage power supply 120 corresponds to the primary transfer power supply 15 described with reference to FIG. FIG. 3A is an example of the charging high-voltage power supply 52 and the transfer high-voltage power supply 120. First, the charging high-voltage power supply 52 will be described. In FIG. 3A, charging rollers 2a to 2d corresponding to each of a plurality of colors are connected to a charging high-voltage power supply 52 as one charging voltage applying means. The charging high-voltage power supply 52 applies the charging voltage Vcdc (power supply voltage) output from the negative transformer 53 to the charging rollers 2a to 2d. In the configuration of FIG. 3A, the charging voltage Vcdc applied to the charging rollers 2a to 2d from the charging high-voltage power supply 52 can be collectively adjusted while maintaining a predetermined relationship. However, in the configuration of FIG. 3A, independent adjustment (individual control) between colors cannot be performed on the charging voltage Vcdc applied to the charging rollers 2a to 2d from the charging high-voltage power supply 52.

  Here, the resistance elements R1 and R2 may be configured by any of a fixed resistance, a semi-fixed resistance, and a variable resistance. In FIG. 3A, the voltage itself output from the transformer 53 is directly applied to the charging rollers 2a to 2d. However, this is merely an example, and the present invention is not limited to such a voltage application mode. Various forms of voltage application to individual rollers (charging means and developing means) are assumed. For example, instead of the configuration in which the output from the transformer 53 is applied, a converted voltage (voltage after conversion) obtained by DC-DC conversion of the output from the transformer 53 by a converter may be applied to the charging rollers 2a to 2d. Alternatively, a voltage obtained by dividing and / or stepping down the power supply voltage or the conversion voltage by an electronic element having a fixed voltage drop characteristic may be applied to the charging rollers 2a to 2d. Here, examples of the electronic element having a fixed voltage drop characteristic include a resistance element and a Zener diode. The converter also includes a variable regulator. Note that the voltage division and / or step-down by the electronic element includes, for example, a case where the divided voltage is further stepped down and vice versa.

  The engine control unit 104 performs the following control in order to control the charging voltage Vcdc to be substantially constant. That is, the engine control unit 104 offsets the negative voltage obtained by stepping down the charging voltage Vcdc by R2 / (R1 + R2) to the positive voltage by the reference voltage Vrgv to obtain the monitor voltage Vref, and performs feedback control so that it becomes a constant value. It is carried out. Specifically, the control voltage Vc preset by the engine control unit 104 (CPU 21) is input to the positive terminal of the operational amplifier 54, and the monitor voltage Vref is input to the negative terminal of the operational amplifier 54. The engine control unit 104 changes the control voltage Vc as appropriate depending on the situation. The output value of the operational amplifier 54 performs feedback control of the control / drive system of the transformer 53 so that the monitor voltage Vref becomes equal to the control voltage Vc. As a result, the charging voltage Vcdc output from the transformer 53 is controlled to a target value. As for the output control of the transformer 53, the output of the operational amplifier 54 may be input to the CPU 21, and the calculation result by the CPU 21 may be reflected in the control / drive system of the transformer 53. In this embodiment, control is performed so that the charging voltage Vcdc is −1100V. Under this control, the charging rollers 2a to 2d charge the surfaces of the photosensitive drums 1a to 1d so as to have the charging potential Vd.

  Next, the transfer high-voltage power supply 120 will be described. A transfer high-voltage power supply 120 serving as a transfer voltage applying unit is connected to primary transfer rollers 14a to 14d corresponding to a plurality of colors. A power supply voltage from the transfer high-voltage power supply 120 or a converted voltage obtained by converting the power supply voltage with a DC-DC converter may be input to the transfer rollers 14a to 14d. Further, a voltage obtained by dividing and / or stepping down the power supply voltage or the conversion voltage by an electronic element having a fixed voltage drop characteristic may be input. In the case of FIG. 3A, the same voltage is distributed and supplied from the transfer high-voltage power supply 120 to the transfer rollers 14a to 14d, and the ratio cannot be changed. The transfer high-voltage power supply 120 includes a transformer 121, a transformer drive / control system, and a transfer current detection circuit 122. In addition, the same code | symbol is attached | subjected to the same structure as the structure demonstrated in Fig.1 (a), and description here is abbreviate | omitted. In the transfer high-voltage power supply 120, the output value of the operational amplifier 56 feedback-controls the control / drive system of the transformer 121 so that the monitor voltage Vref becomes equal to the control voltage Vc.

  FIG. 3B shows another example of a charging high-voltage power supply and a transfer high-voltage power supply. The same members as those in FIG. 3A are denoted by the same reference numerals, and description thereof is omitted. In FIG. 3B, the charging high voltage power source is divided into a YMC color common charging high voltage power source 52 and a Bk color charging high voltage power source 52d, and the transfer high voltage power source 120 is shared by YMCBk as in FIG. 3A. . In the case of FIG. 3B, when image formation is performed in the full color mode, the charging high-voltage power supplies 52 and 52d are operated (turned on). On the other hand, when image formation is performed in the mono-color mode, the charging high-voltage power supply 52 for the YMC color image forming station is not operated (turned off), while the charging high voltage for the Bk image forming station is set. The power supply 52d is operated (turned on). In the case of FIG. 3B, since the charging high-voltage power supply 52 is shared for the YMC color image forming station, the same can be said for the charging high-voltage power supply 52 of FIG. Note that the transfer high-voltage power supply 120 is operating (turned on) in both full-color mode image formation and mono-color mode image formation.

  As described above, according to the charging high-voltage power supply 52 and the transfer high-voltage power supply 120 shown in FIGS. 3A and 3B, the high-voltage power supply is shared by the plurality of charging rollers 2a to 2d and the transfer rollers 14a to 14d. Therefore, further downsizing of the apparatus can be realized. Further, it is possible to reduce costs by providing a high-voltage power supply in common as compared with the case where a transformer with variable output voltage is provided for each color and the voltage applied to each charging roller 2a is individually controlled. In addition, a DC-DC converter (variable regulator) is provided for each of the charging rollers 2a to 2d so that the output from one transformer is individually controlled for each of the charging rollers 2a to 2d. The cost can be reduced. The same applies to the transfer rollers 14a to 14d.

  This completes the description of the configuration of the image forming apparatus. In the following, with reference to FIGS. 4 to 6, each exposure device 31 is allowed to perform minute exposure on a non-image portion that is a portion where the toner images on the photosensitive drums 1 a to 1 d are not visualized (no toner is attached). explain. In addition, for the image portion that is a place where the toner images on the photosensitive drums 1a to 1d are visualized (attached toner), in addition to the light amount of minute exposure, the normal exposure in which the light amount based on the image forming image data is further added. Is also described for causing each exposure apparatus 31 to perform the above. In the following description, the configuration and operation of the exposure apparatus 31a in the image forming station a will be described mainly. However, the exposure apparatuses 31b to 31d in the second to fourth image forming stations b to d are also described. It is assumed that the same configuration and operation are performed.

(Regarding normal exposure and fine exposure operation)
The exposure control of the laser beam 6a by the exposure device 31a in the non-image area fine exposure region of the photosensitive drum 1a will be described with reference to FIG. Here, the non-image portion microexposure means that the non-image portion in the entire printable area is finely exposed by the exposure device 31a to the extent that the toner is not developed in order to improve the image quality. The area on the photosensitive drum 1a where the non-image area fine exposure is performed is referred to as a non-image area fine exposure area. Further, the non-image area microexposure may be simply referred to as microexposure. It should be noted that the non-image portion fine exposure control in the photosensitive drums 1b to 1d is assumed to have the same configuration as in FIG. 4, and detailed description thereof will be omitted.

First, the operation of the engine control unit 104 will be described. The engine control unit 104, exposure to form an electrostatic latent image on the photosensitive drum 1a, that is, in the exposure at the time of image formation by the exposure amount E ₀ of the non-image area for the minute exposure minute exposure signal 68a (shown by arrows) Control. The engine control unit 104 normally controlled by a pulse width signal 60a exposure amount E _x for exposure (shown by arrows) used for the exposure of the image area (image area). The control by the minute exposure signal 68a and the pulse width signal 60a is specifically light emission time control. Here, an OR circuit is built in the laser driver 62a, and the OR circuit performs an OR process on the pulse signal based on the minute exposure signal 68a and the pulse signal based on the pulse width signal 60a for normal exposure. The laser driver 62a drives the laser diode 63a to emit light by outputting an OR-processed pulse signal to the laser diode 63a. Further, the engine control unit 104 controls the emission intensity of the laser driver 62a by the luminance signal 61a.

Here, the exposure amount is the exposure amount of the laser light emitted from the laser diode 63a, and is a unit of μJ / cm ² as described above. That is, this is the light energy converted per unit area on the surface of the photosensitive drum 1 when the laser diode 63a continuously emits light in a certain area at a certain emission intensity for a certain time. The non-image portion microexposure is not uniform in the entire region, and light irradiation of the laser diode 63a is intermittently performed. Therefore, the exposure amount may be substantially regarded as the average light energy (μJ) per unit area. Also in the exposure of the image area, when the light irradiation of the laser diode 63a is intermittently performed in a non-uniform manner in the entire area, the exposure amount may be substantially regarded as the average light energy (μJ) per unit area. .

Also, depending on the response characteristics of the laser diode 63a, if the pulse driving time is short, the peak value of the light pulse decreases, and the light emission intensity is substantially controlled. This factor also affects the average light energy (μJ). Come on. For example, the substantial exposure amount (μJ / cm ² ) can be adjusted and controlled by changing the pulse width (hereinafter referred to as PW _MIN ) in the non-image area fine exposure and the emission intensity of the laser diode 63a. Further, in the actual exposure amount, the characteristics of the correction optical system 67a affect the direction in which the exposure amount E is reduced. In this embodiment, the light emission conditions of the laser diode 63a with respect to the exposure amount are set including this point. However, regardless of the degree of influence of the characteristics of the correction optical system 67a, the exposure amount E can be varied depending on the light emission time and intensity of the laser diode 63a.

Here, the pulse width signal 60a will be described in detail. The pulse width signal 60a is represented by, for example, 8-bit (= 256 gradations) image data of a multilevel signal (0 to 255), and is a signal for determining the emission time of the laser beam. The pulse width when the image data is 0 (also referred to as the background portion) is PW _MIN (for example, 12.0% for one pixel), which is determined by the minute exposure signal 68a. When the image data is 255, the pulse width is one pixel (PW ₂₅₅ ) at full exposure. For image data having a value of 1 to 254, a pulse width (PW _x ) proportional to the gradation value is generated between PW _MIN and PW ₂₅₅ , for example. This will be described in detail in Equation (1) described later. The image data for controlling the laser diode 63a is 8 bits (= 256 gradations), which is an example. For example, the image data is converted into 4 bits (= 16 gradations) or 2 bits (half gradation processing). (4 gradations) multi-value signal. Further, the image data after halftone processing may be a binarized signal.

On the other hand, the engine control unit 104 changes the minute exposure signal 68a, the pulse width signal 60a, and the luminance signal 61a in conjunction with the remaining life of the photosensitive drum 1a (remaining time and remaining number until the end of the life). Then, the engine control unit 104 controls the non-image portion minute exposure amount E ₀ and the image region exposure amount _Ex to appropriate values. The width of the pulse signal output in response to the instruction by the minute exposure signal 68a of the engine control unit 104 is the pulse width PW _MIN (for example, 12.0% for one pixel) when the image data is 0 (background portion). Basically they match. However, the back-calculated exposure amount E ₀ (pulse width) when the image data (density) is 0, which is calculated backward from the exposure amount (pulse width) of image data other than 0, is not necessarily the value when the image data is 0. It does not have to coincide with the minute exposure amount (pulse width PW _MIN ). If the average surface potential per pixel does not fall below the development potential when fine exposure is performed and the charge uniformity can be realized, values approximated to each other are set for the calculated exposure amount E ₀ and the minute exposure amount. Can achieve a certain effect.

In the case of the EV curve illustrated in FIG. 2A, the engine control unit 104 outputs the pulse width PW _MIN corresponding to the minute exposure amount E ₀ at 12.0% of PW ₂₅₅ for one pixel. By doing so, the engine control unit 104 sets the initial exposure dose E ₀ of the photosensitive drum 1a to 0.03 μJ / cm ² , and a background potential attenuation of 100 V (potential attenuation from −600 V to −500 V). Have gained. Further, the engine control unit 104 sets the maximum exposure amount E _{255 at} the time of full exposure with the pulse width PW ₂₅₅ so that the EV curve in FIG. The exposure amount in the near region is 0.25 μJ / cm ² .

Further, when the EV curve of the photosensitive drum 1a during exemplified life end of in FIG. 2 (a) (dashed line), the non-image portion small exposure amount _{E 0} and 0.12μJ / cm ^2, the background portion potential attenuation 200V ( (Potential decay from −700 V to −500 V). Further, the engine control unit 104 sets the maximum exposure amount E _{255 at} the time of full exposure for exposure with the pulse width PW ₂₅₅ to 0.40 μJ / cm ² .

  Then, the laser driver 62a uses the luminance signal 61a input from the engine control unit 104, the pulse width signal 60a based on the image data, and the minute exposure signal 68a to emit light from the laser diode 63a (laser light emission intensity) and light emission time. To control. Further, the laser driver 62a executes automatic light quantity control, and controls the current supplied to the laser diode 63a so that the laser light emitted from the laser diode 63a has a target light emission luminance (mW). The emission luminance can be controlled by adjusting the current supplied from the laser driver 62a to the laser diode 63a. Further, the laser light emitted from the laser diode 63a is optically scanned, and irradiated to the photosensitive drum 1a as the laser light 6a through the correction optical system 67a including the polygon mirror 64a, the lens 65a, and the folding mirror 66a.

As described above, in the initial photosensitive drum 1a, the surface potential (hereinafter referred to as a post-microexposure charging potential) Vd_bg of the photosensitive drum 1a after the non-image portion microexposure is performed is the charging potential Vd = − before correction. It drops from 600V to -500V. On the other hand, in the photosensitive drum 1 at the end of its life, the post-microexposure charging potential Vd_bg decreases from the pre-correction charging potential Vd = −700V to −500V. Here, the exposure potential Vl of the image portion is changed from the charged potential Vd = −600 V to Vl = −150 V by performing exposure of 0.25 μJ / cm ² by the full light emission of the laser diode 63a in the initial photosensitive drum 1. Become. Further, the exposure potential Vl of the image portion is such that the photosensitive drum 1 at the end of its life reaches 0.40 μJ / cm ² by full light emission of the laser diode 63a, so that the charging potential Vd = −700V to Vl = −200V. become. The same is performed by the laser diodes 63b to 63d in the image forming stations b to d.

  In FIG. 4, the system in which exposure is performed by the laser diode 63 a has been described as an example, but the present invention is not limited thereto. For example, the present invention can also be implemented in a system including an LED array as exposure means. Specifically, the signal described with reference to FIG. 4 may be input to a driver that drives each LED light emitting element, and the processing of the flowchart of FIG. Hereinafter, an exposure system using the laser diode 63a will be described as an example.

(Necessity for correction of minute exposure)
A problem relating to the difference in film thickness of the photosensitive drum 1 (hereinafter also referred to as drum film thickness) will be described with reference to FIG. As the use of the photosensitive drum 1 progresses, the surface of the photosensitive drum 1 is scraped by discharge by the charging roller 2, exposure by the exposure device 31 or by rubbing against the drum cleaner 5, and the film thickness of the photosensitive drum 1 decreases. . At this time, if photosensitive drums having different usage conditions (for example, cumulative rotation speed) are mixed, the film thicknesses of the photosensitive drums 1a to 1d vary. In this state, when a constant charging voltage Vcdc is applied to the plurality of photosensitive drums 1a to 1d by the common charging high voltage power supply 52 as illustrated in FIG. 3, the following occurs. That is, since the potential difference generated in the air gap between the charging roller 2 and the photosensitive drum 1 is different, the charging potential Vd varies depending on the photosensitive drums 1a to 1d. Specifically, the photosensitive drum 1 with a small number of image formations (also the cumulative number of rotations) has a large film thickness and a small potential difference generated in the air gap between the charging roller 2 and the photosensitive drum 1, and therefore the absolute value of the charging potential Vd. Becomes smaller. On the other hand, the photosensitive drum 1 having a large cumulative number of rotations is thin, and the potential difference generated in the air gap between the charging roller 2 and the photosensitive drum 1 is large, so that the absolute value of the charging potential Vd is large.

  In such a situation, for example, the transfer potential Vtr and the charging potential Vd are set so that the transfer contrast Vtrcont (= Vtr−Vd) is in a desired state on the thick photosensitive drum 1. Here, the transfer contrast Vtrcont is a potential difference (contrast) (= Vtr−Vd) between the transfer potential Vtr which is the surface potential of the primary transfer roller 14 and the charging potential Vd. Then, in the image forming station having the photosensitive drum 1 having a thin film thickness, the absolute value of the charging potential Vd is large as described above (shown as VdUP in the figure), so that the transfer is performed with respect to the same transfer potential Vtr. The contrast Vtrcont becomes large. FIG. 5A shows this state. When the transfer contrast Vtrcont increases, the transfer voltage obtained as a result of the primary transfer voltage control deviates from a desired value as will be described later, which causes problems such as transfer failure and retransfer. Hereinafter, the primary transfer voltage control will be described.

(Primary transfer voltage control)
The primary transfer voltage control adjusts the setting of the primary transfer voltage for appropriately primary transferring the toner image formed on the photosensitive drum 1 onto the intermediate transfer belt 10. The primary transfer voltage is determined so that the transfer current flows.

  The engine control unit 104 detects the impedance obtained by adding the transfer rollers 14a to 14d and the intermediate transfer belt 10 in a preparatory operation (hereinafter referred to as pre-rotation) before the image forming operation, for example. In the image forming apparatus according to the present exemplary embodiment, the pre-rotation is performed for each print job. Based on the detected impedance, the engine control unit 104 calculates the voltage of the transformer 121 such that the detection current Itr detected by the transfer current detection circuit 122 becomes a predetermined value Itr0. Then, the same processing is repeated, and the voltage of the transformer 121 is calculated a plurality of times so that the detection current Itr becomes the predetermined value Itr0, and the average voltage of the plurality of voltages is calculated.

  In addition to the impedance detection method, there is the following primary transfer voltage control method. First, the engine control unit 104 sets an initial transfer voltage, detects the current at that time, resets the transfer voltage higher if the detected current value is lower than the target value, and conversely if lower, the transfer voltage. Reset to lower. Then, the current is detected again with the transfer voltage reset by the engine control unit 104, the detected current value is compared with the target current value, and the transfer voltage is reset. The engine control unit 104 sets an appropriate transfer voltage by repeating this process several times. Even with such a method, appropriate primary transfer voltage control can be executed.

  In the image forming operation for visualizing the toner image on the photosensitive drum 1 after executing the primary transfer voltage control by the engine control unit 104, non-image part exposure and image part exposure are performed based on the above-described image data. Then, after developing the toner images on the photosensitive drums 1a to 1d, the engine control unit 104 applies the transfer voltage calculated by detecting the impedance of the pre-rotation to the primary transfer rollers 14a to 14d by the transfer high-voltage power source 120. .

  The above is the primary transfer voltage control. In this embodiment, as described with reference to FIG. 3, the high-voltage power supply for applying a voltage to the primary transfer rollers 14 a to 14 d is shared as the transfer high-voltage power supply 120. ing. For this reason, when the engine control unit 104 performs the primary transfer voltage control, the average of the total current flowing through the four image forming stations is regarded as the current flowing through each station, and the average current becomes a desired current. A primary transfer voltage is determined. FIG. 5B is an example of the transfer contrast Vtrcont in each of the four image forming stations a to d when the photosensitive drums 1 a to 1 d having different sensitivity characteristics coexist. FIG. 5B shows a current value corresponding to the transfer contrast Vtrcont. As shown in FIG. 5B, when the photosensitive drums 1a to 1d having different film thicknesses are mixed, the primary transfer current is different for each image forming station.

  In the example of FIG. 5B, when the target current value of the primary transfer current is 8 μA, the yellow station a has 10 μA, the magenta station b has 6 μA, the cyan station c has 7 μA, and the black station d has 9 μA. Flowing. For this reason, in the magenta station b and the cyan station c, the primary transfer voltage is lower than the voltage corresponding to the target value of 8 μA, so that a part of the toner on the photosensitive drums 1 b and 1 c is transferred onto the intermediate transfer belt 10. A transfer defect that does not occur is generated. Further, at the yellow station a and the black station d, the primary transfer voltage is set higher than the voltage corresponding to the target value of 8 μA, so that discharge occurs between the photosensitive drums 1 a and 1 d and the intermediate transfer belt 10. The polarity of the toner on the photosensitive drums 1a and 1d is partially lost. For this reason, a part of the toner whose polarity is lost is not transferred to the intermediate transfer belt 10 and remains on the photosensitive drums 1a and 1d. From the above, it is necessary to make the surface potential of the photosensitive drum 1 the same value in all the image forming stations a to d.

  In this embodiment, even when the power supply configuration illustrated in FIG. 3 is used, the surface potential of the photosensitive drum when the primary transfer voltage control is performed can be made uniform in all image forming stations with a simple configuration.

(Processing related to a series of image formation)
Hereinafter, using the flowchart shown in FIG. 6, the minute exposure amount E ₀ of each of the laser diodes 63a to 63d in a series of image processes is corrected in relation to the integrated rotation speed of the photosensitive drums 1a to 1d, in other words, the remaining life. Processing to be performed will be described.

  In step (hereinafter referred to as “S”) 101, the engine control unit 104 reads the photosensitive drums 1 a to 1 as information relating to the remaining lifetime of the photosensitive drums 1 a to 1 d from the memory tags 32-2 of the image forming stations a to d. The information of the accumulated rotational speed of 1d is read. Here, the storage unit that stores information relating to the remaining life of each photosensitive drum 1 is not limited to the memory tag 32-2 of each image forming station a to d. For example, the information read from the memory tag 32-2 of each image forming station a to d is temporarily stored in another storage unit, and the information stored in the other storage unit is subsequently read and updated. Also good. In this case, when the power of the image forming apparatus main body is turned off or when the print job is finished, the information in another storage unit is reflected in the memory tags 32-2 of the image forming stations a to d.

  In addition, the information related to the remaining life of the photosensitive drum 1 can be paraphrased as information related to how much the photosensitive drum 1 has been rotated (for example, the accumulated number of rotations) or how it has been used (for example, the usage time). In addition, as described with reference to FIG. 2A, the information can be paraphrased as information related to the photosensitive characteristic (EV curve characteristic) of the photosensitive drum 1. Both mean the same thing. Other examples of information relating to the remaining life of the photosensitive drum 1 include other information correlated with the film thickness of the charge transport layer 224a of the photosensitive drum 1. For example, information on the number of prints taking into account the number of rotations of the intermediate transfer belt 10, the number of rotations of the charging roller 2, the paper size of the recording material P (for example, the total number of recording materials on which image formation has been performed), and the like. it can. Further, means for directly detecting the film thickness of the photosensitive drum 1 may be provided in each photosensitive drum 1, and the detection result may be used as information relating to the remaining life of each photosensitive drum 1. That is, the information related to the remaining life of the photosensitive drum 1 may be any information that includes at least one piece of information.

  In S102, the engine control unit 104 defines a correspondence relationship between the integrated rotation speed (photosensitive drum usage status) of each photosensitive drum 1 read from the memory tag 32-2 in S101 and parameters related to normal exposure, which will be described later. Refer to the table shown in Table 1 or Table 2. Here, the information related to the accumulated rotational speed of the photosensitive drums 1a to 1d read by the engine control unit 104 from the memory tag 32-2 in S101 may be different for each of the photosensitive drums 1a to 1d. That is, as described above, there are cases where the photosensitive drums 1a to 1d having different integrated rotational speeds are mixed. Therefore, the engine control unit 104 refers to the table in Table 1 or Table 2 for each photosensitive drum 1. Details of Tables 1 and 2 will be described later.

  Then, the engine control unit 104 sets the exposure parameters of the normal exposure amounts of the laser diodes 63a to 63d based on the information on the accumulated rotational speed read in S101. Note that the tables shown in Tables 1 and 2 are stored in storage means that can be referred to by the engine control unit 104. By the processing of S102, the engine control unit 104 causes the exposure potential Vl of each photosensitive drum 1 to be within the allowable target potential range regardless of the sensitivity characteristic (EV curve characteristic) of each photosensitive drum 1. Laser light emission can be set. Then, the engine control unit 104 substantially exposes the laser diodes 63a to 63d with the parameters set from the table of Table 1 or Table 2 in the process of S102, thereby substantially reducing the exposure potential Vl of each of the plurality of photosensitive drums 1. Can be the same. In some cases, the setting of the exposure potential Vl is not the same, and may be set for each photosensitive drum 1 individually.

The operation performed by the engine control unit 104 in S102 will be described in more detail. The engine control unit 104 sets light emission luminance values (mW (milliwatts)) corresponding to the integrated information of the photosensitive drums 1a to 1d read from the memory tag 32-2 in the luminance signals 61a to 61d. Although Table 1 and Table 2 show the light emission luminance value (mW) for the sake of explanation, the engine control unit 104 actually uses the voltage value corresponding to this light emission luminance value as the luminance signals 61a to 61d. Set. Further, the engine control unit 104 sets the% (PWM) value of normal exposure (density 0%) in Tables 1 and 2 to PW _MIN, and sets the% (PWM) value of normal exposure (density 100%) to PW _MIN. Set to ₂₅₅ . Then, the engine control unit 104 sets a pulse width PWd for image data of an arbitrary gradation value (also a density value) d (= 0 to 255) by the following equation (1).
PWd = d × (PW ₂₅₅ −PW _MIN ) / 255 + PW _MIN formula (1)
According to Equation (1), PW ₀ = PW _MIN when d = 0, and PW ₂₅₅ when d = 255. Thereafter, when the engine control unit 104 is instructed from the outside to emit light by image data having an arbitrary gradation value (density value) d, the voltage corresponding to the corresponding pulse width (PWd) set here. The value is set as the pulse width signal 60a. The same applies to the pulse width signals 60b to 60d. Further, although the expression (1) assumes an 8-bit multilevel signal, as described with reference to FIG. 4, in the case of an arbitrary m bit such as 4 bits, 2 bits, or 1 bit (binary). Can be done as follows. That is, the pulse width at PW _MIN may be assigned when the image data is 0, and the pulse width at PW ₂₅₅ may be assigned to the gradation value (2 ^m −1).

In S103 of FIG. 6, the engine control unit 104 sets a parameter (table) related to the laser light emission amount (micro exposure amount E ₀ ) of micro exposure based on the integrated rotation number of each photosensitive drum 1 read from the memory tag 32-2. 1 or% (PWM) value of minute exposure in Table 2) is set. Even in S <b> 103, the engine control unit 104 refers to the table in Table 1 or Table 2 for each photosensitive drum 1. More specifically, the engine control unit 104 sets, for each photosensitive drum 1, a minute exposure% (PWM) value corresponding to the information of the accumulated rotational speed of the photosensitive drum 1 read in S101, and the voltage corresponding to each. The value is set to the minute exposure signals 68a to 68d. Through the processing of S103, the engine control unit 104 sets the charged potential Vd of each photosensitive drum 1 to an allowable target potential (value of the post-microexposure charging potential Vd_bg) regardless of the sensitivity characteristic (EV curve) of the photosensitive drum 1. ) Can be set. The engine control unit 104 can at least reduce the variation in the charged potential after correction of the plurality of photosensitive drums 1 by causing the laser diodes 63a to 63d to emit a small amount of light using the set parameters. In some cases, the setting of the charged potential after correction is not the same, and may be set individually for each photosensitive drum 1.

As described above, by the processing of S102 and S103, the engine control unit 104 can appropriately set the fine exposure and the normal exposure in relation to the cumulative number of rotations, in other words, the remaining life for each photosensitive drum 1. Become. In S102 and S103, the engine control unit 104 has been described as referring to the tables in Table 1 and Table 2, but the present invention is not necessarily limited to this form. For example, a desired set value (normal exposure parameter and minute exposure parameter) may be obtained from a parameter relating to the remaining life of the photosensitive drum 1 (for example, the total number of revolutions of the photosensitive drum 1) by calculation based on a calculation formula of the CPU 21. Good. Further, all the values calculated by the equation (1) may be stored and held in advance in a table, and the engine control unit 104 may refer to the table each time. The nonvolatile storage unit 24 may store and hold a plurality of EV curves corresponding to the respective usage states of the photosensitive drum 1 as shown in FIG. Then, the engine control unit 104 calculates the exposure amount (μJ / cm ² ) necessary for the desired photosensitive drum potential (V) from the EV curve corresponding to the acquired information on the usage state of the photosensitive drum 1. Also good. In this case, the engine control unit 104 calculates the light emission luminance, the pulse width at the time of fine exposure, and the pulse width at the time of normal exposure from the exposure amount (μJ / cm ² ) obtained each time, and the result Are set as parameters corresponding to S102 and S103.

  In S104 of FIG. 6, the engine control unit 104 performs primary transfer voltage control in a state where the post-microexposure charging potentials Vd_bg of the plurality of photosensitive drums 1 are aligned by the microexposure set in S103. For this reason, the primary transfer voltage at the time of image formation is set appropriately. In step S105, the engine control unit 104 executes the series of image forming operations and controls described with reference to FIG. Details of the primary transfer voltage control performed by the engine control unit 104 in S104 will be described later.

  In S106, the engine control unit measures the number of rotations of the photosensitive drums 1a to 1d rotated in the series of image forming operations performed in S106. This measurement process may use a known method for measuring the number of rotations of the rotating body. Further, the rotation speeds of the photosensitive drums 1 a to 1 d are measured in order to update the usage status of the photosensitive drum 1. Further, the process of S106 is actually performed in parallel with the processes of S104 and S105.

  In S107, the engine control unit 104 determines whether or not the image forming operation has ended. If it is determined that the image forming operation has not ended, the process returns to S104. On the other hand, if the engine control unit 104 determines in S107 that the image forming operation has been completed, the process proceeds to S108. In S108, the engine control unit 104 adds the measurement result of each photosensitive drum 1 measured in S106 to the accumulated rotational speed corresponding to each photosensitive drum 1 read in S101 (it can be said that the accumulated rotational speed has been updated). ). In S109, the engine control unit 104 stores the updated integrated rotation number added in S108 in the memory tag 32-2 of each image forming station. In the process of S109, information relating to the remaining life of the photosensitive drums 1a to 1d is updated. Note that the storage destination here may be a storage unit different from the memory tag 32-2, as described in S101.

(Explanation of correction table)
Tables 1 and 2 show that the engine control unit 104 refers to information relating to the remaining life of the photosensitive drum 1 that is referred to in S102 and S103 in FIG. 6 (the number of rotations in the drawing), and light emission control during microexposure and normal exposure. It is the table | surface which showed the detail of the table with which the setting was matched. For example, the information in Table 1 and Table 2 is stored in the nonvolatile storage unit 24 in FIG. In both Table 1 and Table 2, the exposure dose for microexposure (μJ / cm ² ) and the exposure dose for normal exposure (μJ / cm ² ) are the target photosensitivity as exemplified in FIG. It is assumed that it is preset based on the photosensitive characteristic (EV curve) of the drum 1. The engine control unit 104 refers to the tables shown in Tables 1 and 2 so that the surface potential variations of the background portions in the charged photosensitive drums 1a to 1d can be made substantially the same. For this reason, in the primary transfer voltage control performed by the engine control unit 104, the voltage for the primary transfer current can be set appropriately. Further, the variation in the exposure potential Vl in each of the plurality of photosensitive drums 1 after the normal exposure can be made substantially the same. Table 1 is a table in the case where the photosensitive drum 1 has such a characteristic that the exposure potential Vl can be attenuated to −150 V even if the light emission luminance remains constant from the initial stage to the end of its life. . On the other hand, Table 2 is a table in the case where the exposure potential Vl cannot be attenuated to −150 V if the light emission luminance remains constant from the beginning to the end of the lifetime, and is described with reference to FIG. Corresponding to such a case.

First, Table 2 will be described with reference to the EV curve in FIG. In the following description, the photosensitive drum 1a of the yellow station a will be described, but the same applies to the photosensitive drums 1b to 1d. When the film thickness of the charge transport layer 224a of the photosensitive drum 1a in the initial state is 20 μm, it is necessary to set the exposure amount at the time of background portion exposure to 0.03 μJ / cm ² . On the other hand, the dashed curve in FIG. 2 (a) shows the EV curve in the photosensitive drum 1a when the life is reached (the integrated rotation number of the photosensitive drum 1a is 150,000 rotations or more). In the photosensitive drum 1a at the end of its life, since the film thickness of the charge transport layer 224a is reduced to 10 μm, the charging potential Vd is increased as described with reference to FIG. Further, in FIG. 2A, with respect to the charged potential Vd, in order to keep the surface potential of the photosensitive drum 1a at the end of its life at the same background potential of −500 V as that of the initial photosensitive drum 1a, the exposure amount is set. It is necessary to set to 0.12 μJ / cm ² .

<Table 1>
Since the wear amount of the charge transport layer 224a of the photosensitive drum 1a is promoted by discharge erosion and exposure at the drum cleaner 5a and the charging portion that are in contact with each other, the wear amount of the photosensitive drum 1a is substantially proportional to the integrated rotational speed. In Table 1, when the two-sheet intermittent printing is performed, the relationship between the total number of rotations and the film thickness of the charge transport layer 224a is based on the preliminary experiment result that the charge transport layer 224a is worn by 1 μm at 15000 revolutions (equivalent to 1000 pages). Has been done. In other words, in Table 1, the exposure amount E ₀ for microexposure is increased by 0.003 μJ / cm ² by increasing PW _MIN every 15,000 integrated rotations. Then, from the initial subjected during the life end of usage of the photosensitive drum 1a, it is set by linearly changes the exposure amount _{E 0} for small exposure from 0.03μJ / cm ² to 0.06μJ / cm ^2. With this control, the engine control unit 104 keeps the background portion potential substantially constant at -500 V regardless of the film thickness of the photosensitive drum 1a.

  Further, in Table 1, the correspondence between the light emission luminance (mW) of normal exposure to the portion where the toner image is visualized and the integrated rotation speed of the photosensitive drum 1 is also set. Regardless of the total number of revolutions), a constant light emission luminance (mW) is set. This is because the characteristic of the photosensitive drum 1 assumed in Table 1 corresponds to the case where the exposure potential Vl can be lowered to −150 V throughout the lifetime with the setting and it is considered that there is no problem.

<Table 2>
On the other hand, in the table illustrated in Table 2, both the pulse width PW _{MIN at} the minute exposure and the light emission luminance (mW) at the normal exposure are changed. By referring to the table in Table 2, the engine control unit 104 can appropriately set not only the fine exposure but also the normal exposure in conjunction with the cumulative rotation speed of the photosensitive drum 1. The table in Table 2 corresponds to the case where the exposure potential Vl cannot be lowered to −150 V with the light emission luminance kept constant, that is, the case described with reference to FIG. Such deterioration of the exposure sensitivity of the photosensitive drum 1a tends to appear as the exposure amount to the photosensitive drum 1a increases. In the example of the EV curve in FIG. 2A, even when the photosensitive drum 1a at the end of its life is irradiated with laser light at an exposure amount of 0.40 μJ / cm ² , the exposure potential Vl is attenuated only to −200V. I can't let you. Hereinafter, an increase in the absolute value of the exposure potential Vl due to deterioration of the photosensitive drum 1 is referred to as an increase in the exposure potential Vl. When the exposure potential Vl cannot be lowered to a desired potential, the development contrast, which is a potential difference between the development voltage Vdc and the exposure potential Vl, is reduced. For this reason, there is a possibility that problems such as a decrease in density and a thin line image may occur. In order to solve such a problem, it is necessary to reduce the deterioration of the photosensitive drum 1 as much as possible. For this purpose, it is necessary to reduce the exposure amount of the laser beam applied to the photosensitive drum 1.

  In Tables 1 and 2, the light emission control setting at the time of minute exposure or normal light emission is shown for a certain range of the integrated rotation number of the photosensitive drum 1, but it may be set more finely. For example, the CPU 21 of the engine control unit 104 estimates and calculates an appropriate light emission control setting value for any rotation number of the photosensitive drum 1 from the relationship between the drum rotation speed in the table and each light emission control setting value. Also good. The same applies to normal exposure. By so doing, it is possible to further improve the accuracy of the amount of light emitted by the laser diode 63a at the time of fine exposure or normal exposure. Further, in the tables of Tables 1 and 2, the case where both the minute exposure amount and the normal exposure amount are linearly increased according to the integrated rotation number of the photosensitive drum 1 has been described. However, it is not limited to this. In view of the characteristics of the photosensitive drum 1, a table that increases non-linearly according to the integrated rotation speed of the photosensitive drum 1 may be provided.

  As described so far, by adjusting the exposure amount in accordance with the cumulative number of rotations of the photosensitive drum 1, the charged potentials of the plurality of photosensitive drums 1 can be made uniform, so that an appropriate primary transfer voltage is set. Can do. In the primary transfer voltage setting, the charging potential at the time of primary transfer voltage control may be different from that at the time of image formation as long as the charging potential of the photosensitive drum 1 is uniform.

(Characteristics of Example 1)
This embodiment is characterized in that the fine exposure control is performed with a smaller exposure amount than the fine exposure control during image formation during the primary transfer voltage control. Specifically, primary transfer voltage control is performed with reference to −600 V which is the initial charging potential of the photosensitive drum 1. FIG. 7 shows the relationship between the transfer potential Vtr and the surface potential of the photosensitive drum 1a during primary transfer voltage control (FIG. 7A) and image formation (FIG. 7B). In this embodiment, the primary transfer voltage control is performed by setting the surface potential of the photosensitive drum 1 to −600V. Since the surface potential of the non-image area of the initial photosensitive drum 1 at the time of image formation is −500 V (= charge potential after micro exposure Vd_bg) shifted by 100 V due to micro exposure, the voltage set by the primary transfer voltage control is also There is a deviation of 100 V from the desired voltage during image formation. Therefore, the primary transfer voltage at the time of image formation is expressed by the following equation (2), where Vt1 is the primary transfer voltage at the time of image formation and V0 is a voltage that is a set value set by the primary transfer voltage control. become. That is, as shown in Expression (2), it is necessary to apply a value that is offset by 100 V from the voltage V0 set by the primary transfer voltage control.
Vt1 = V0 + 100 (V) Formula (2)
As shown in Expression (2), the engine control unit 104 uses the primary transfer voltage (V0) determined with respect to the surface potential of the photosensitive drum 1 to −600 V during the primary transfer voltage control, and 100 V during image formation. Reset to the offset value. The engine control unit 104 applies the optimum primary transfer voltage Vt1 to the transfer roller 14 at the time of image formation by the transfer high-voltage power supply 120.

尚、以下の実施例における１次転写電圧制御と区別するため、露光量Ｅ_転写制御の添え字に「・実施例１」を付加しており、その他の実施例においても同様の表記とする。また、実施例中の説明では、「・実施例１」等の表記は省略して説明する。式（３）の中で、ｎは１次転写電圧制御中に回転した感光ドラム１ａの回転数であり、Ｅ（ｎ）は、感光ドラム１ａの１次転写電圧制御中の回転数がｎのときの露光量を表している。以下ｎを転写電圧制御積算回転数という。式（３）は、本実施例の露光量Ｅ（ｎ）を、回転数０から回転数ｎまで、転写電圧制御回転数ｎにより積分した値である露光量Ｅ_転写制御を求めている。即ち、露光量Ｅ_転写制御は、１次転写電圧制御を行った際に、感光ドラム１に照射されたレーザ光の露光量を累積した量といえる。また、プリント時間をＴ_{Ｔｏｔａｌ}、１次転写電圧制御時間をＴ_転写制御とすると、感光ドラム１ａの積算回転数ｒに対して転写制御積算回転数ｎは、式（４）の関係から求められる。尚、プリント時間Ｔ_{Ｔｏｔａｌ}とは、図６で説明した処理の開始から終了までに必要な時間をいう。
ｎ＝ｒ×（Ｔ_転写制御／Ｔ_{Ｔｏｔａｌ}） 式（４） Expression (3) is exposure amount E _{transfer control} of the laser light 6 irradiated from the laser diode 63a to the photosensitive drum 1a during the primary transfer voltage control.

In addition, in order to distinguish from the primary transfer voltage control in the following embodiments, “• Example 1” is added to the subscript of the exposure amount E _{transfer control} , and the same notation is used in the other embodiments. Further, in the description of the embodiment, the description such as “• Example 1” is omitted. In equation (3), n is the number of rotations of the photosensitive drum 1a rotated during primary transfer voltage control, and E (n) is the number of rotations of the photosensitive drum 1a during control of the primary transfer voltage n. Represents the amount of exposure. Hereinafter, n is referred to as a transfer voltage control integrated rotation speed. Expression (3) obtains exposure amount E _{transfer control} , which is a value obtained by integrating the exposure amount E (n) of this embodiment from the rotational speed 0 to the rotational speed n by the transfer voltage control rotational speed n. That is, the exposure amount E _{transfer control} can be said to be an amount obtained by accumulating the exposure amount of the laser light applied to the photosensitive drum 1 when the primary transfer voltage control is performed. Also, assuming that the printing time is T _Total and the primary transfer voltage control time is T _{transfer control} , the transfer control integrated rotational speed n is obtained from the relationship of the equation (4) with respect to the integrated rotational speed r of the photosensitive drum 1a. Note that the print time T _Total is the time required from the start to the end of the processing described with reference to FIG.
n = r × (T _{transcription control} / T _Total ) Formula (4)

Table 3 is a table in which the fine exposure amount control at the time of the primary transfer voltage control in this embodiment is summarized with respect to the total number of rotations r of the photosensitive drum 1. The microexposure control is also shown collectively. In this embodiment, the fine exposure amount at the time of primary transfer voltage control (left column in the table) is different from the fine exposure amount at the time of image formation other than the primary transfer voltage control (right column in the table). It is said. In this embodiment, since the initial charging potential Vd of the photosensitive drum 1 is −600 V, the primary transfer voltage control is performed when the accumulated rotational speed r of the photosensitive drum 1 a is 0 ≦ r <37500. Sometimes it is not necessary to perform micro exposure (see FIG. 2A). That is, the initial exposure amount for the photosensitive drum 1 is 0.000 μJ / cm ² . On the other hand, when the accumulated rotational speed r of the photosensitive drum 1 is, for example, 112500 ≦ r <150,000, in order to set the charging potential Vd of the photosensitive drum 1 to −600 V, at the time of primary transfer voltage control, 0.035 μJ / cm. ² minute exposure is performed.

Note that the value of normal microexposure other than the primary transfer voltage control shown in Table 3 is the microexposure amount (μJ / cm ² ) described in Table 2. For example, in the case of the initial photosensitive drum 1 (0 ≦ r <37500), the normal fine exposure amount other than the primary transfer voltage control is 0.030 μJ / cm ² . On the other hand, the fine exposure amount at the time of controlling the primary transfer voltage in this embodiment is 0.000 μJ / cm ² smaller than 0.030 μJ / cm ² , that is, no exposure is performed. As described above, when the values of the accumulated rotation speed r of the photosensitive drum 1 are compared, the fine exposure amount during the primary transfer voltage control is smaller than the fine exposure amount other than the primary transfer voltage control.

  In Expression (3), the exposure amount E (n) when the rotational speed of the photosensitive drum 1 is n is smaller than the exposure amount at the primary transfer voltage control compared to the exposure amount other than the primary transfer voltage control. Therefore, the exposure amount calculated from the equation (3) becomes small.

また、画像形成中の積算回転数ｍと、１次転写電圧制御と画像形成以外の積算回転数ｌは、積算回転数ｒに対して式（７）と式（８）の関係を満たす。
ｍ＝ｒ×（Ｔ_画像形成／Ｔ_{Ｔｏｔａｌ}） 式（７）
ｌ＝ｒ×（Ｔ_その他／Ｔ_{Ｔｏｔａｌ}） 式（８） In addition to the primary transfer voltage control, the exposure amount of the laser light applied to the photosensitive drum 1 includes the following. For example, the printing time T _Total is divided into three parts: primary transfer voltage control time T _{transfer control} , image formation time T _{image formation} , primary transfer voltage control and time T _other than image formation, and others. In this case, 1 the primary transfer voltage exposure amount irradiated to other than the control, and the exposure amount E _imaging irradiated in the image formation time T _imaging, the primary transfer voltage control and the image forming addition to the time T _Others there are _other exposure E to be irradiated in the. Therefore, the sum of E _{transfer control / Embodiment 1} , E _{image formation} , E, and _others is the total exposure amount with which the photosensitive drum 1a is irradiated in this embodiment. During image formation, from Table 2, normal exposure corresponding to the image density (d) is performed, and normal fine voltage control other than primary transfer voltage control and image formation (for example, between sheets during continuous printing). Exposure is performed. If the cumulative rotational speed during image formation is m, and the cumulative rotational speed other than primary transfer voltage control and image formation is l, E _{image formation} and E and _others can be expressed by equations (5) and (6).

The accumulated rotational speed m during image formation, the primary rotational voltage control and the accumulated rotational speed 1 other than image formation satisfy the relationship of Expressions (7) and (8) with respect to the accumulated rotational speed r.
m = r × (T _{image formation} / T _Total ) Equation (7)
l = r × (T _other / T _Total ) Formula (8)

(Description of action / effect)
In this embodiment, the exposure amount irradiated onto the photosensitive drum 1a can be reduced by the amount of the minute exposure amount at the time of controlling the primary transfer voltage. In this embodiment, in order to make the exposure amount at the time of primary transfer voltage control smaller than the minute exposure amount during image formation, primary transfer voltage control is performed based on the initial charging voltage of the photosensitive drum 1a. As a result, the E _{transfer control / Embodiment 1} expressed by the above-described equation (3) can be reduced, and as a result, the sensitivity deterioration of the photosensitive drum 1a can be reduced. The deterioration of the photosensitive drum 1a means that positive charges generated in the charge generation layer 223a of the photosensitive drum 1a by exposure are combined with the binder resin in the charge transport layer 224a and remain. The amount of positive charges remaining on the charge transport layer 224a increases as the exposure amount on the photosensitive drum 1a increases. As the positive charge remaining in the charge transport layer 224a increases, the number of positive charges reaching the surface of the photosensitive drum 1a decreases. For this reason, the negative charge applied to the photosensitive drum 1a by the charging roller 2a cannot be sufficiently canceled, and the exposure potential Vl is increased. The larger the amount of increase in the exposure potential Vl, the smaller the development contrast, which is the potential difference between the development voltage Vdc and the exposure potential Vl. Therefore, the amount of toner supplied from the development roller 43a to the photosensitive drum 1a is reduced. Decrease in density, narrowing of line width, etc. occur.

  On the other hand, if the exposure amount to the photosensitive drum 1a is reduced as in this embodiment, the amount of remaining positive charge is reduced by the reduced amount, and thus the amount of increase in the exposure potential Vl is reduced. As a result, the amount of toner developed on the photosensitive drum 1a from the developing roller 43a becomes close to an appropriate amount, and the decrease in image density is reduced. Also, when forming a line image, toner close to a desired amount can be developed on the photosensitive drum 1a, so that line width narrowing in the latter half of the life can be reduced. The same applies to the other photosensitive drums 1b to 1d.

  As described above, in this embodiment, in a color image forming apparatus that performs microexposure on a non-image portion, an initial photosensitive drum is used to make the microexposure amount during primary transfer voltage control smaller than the microexposure amount during image formation. The primary transfer voltage control is performed with the charging potential of 1 as a reference. Thereby, since the exposure amount with which the photosensitive drum 1 is irradiated can be reduced, the sensitivity deterioration of the photosensitive drum 1 can be suppressed, and the use time of the photosensitive drum 1 (hereinafter also referred to as durability) is accompanied. Reduces image density and line width.

  Hereinafter, an evaluation result when the exposure control of this embodiment is performed will be described.

(Evaluation of Example 1)
In the evaluation of this example, the exposure amount at the time of primary transfer voltage control follows the values shown in Table 3 for microexposure (primary transfer voltage control). The exposure amount in processes other than the primary transfer voltage control follows the values shown in Table 2 for microexposure and normal exposure.

  In order to confirm the effect of the present embodiment, a durability test was performed from the initial stage to 150,000 revolutions when the service life was reached, using a color image forming apparatus having a process speed of 100 mm / sec. Then, the amount of increase in the exposure potential Vl at the end of the life of this example and the comparative example described below was confirmed and image evaluation was performed. In the endurance test, two print jobs were intermittently performed, and the number of image gradations (density) during the endurance test was d = 20. Further, as a comparative example, an evaluation was performed in the same color image forming apparatus as in the present example in the case where the minute exposure amount at the time of primary transfer voltage control and image formation was not changed.

Table 4 is a table showing information related to the printing operation performed in the durability test in this example and the comparative example. Specifically, the total printing time T _Total is divided into three parts: primary transfer voltage control time T _{transfer control} , image formation time T _{image formation} , primary transfer voltage control and time T _other than image formation and other times. It is the table | surface which showed each time. As described above, since the primary transfer voltage control is performed during the pre-rotation, it can be said that the primary transfer voltage control time is the pre-rotation time. The units of time are all seconds (sec). Table 4 also shows the ratio of the primary transfer voltage control time to the printing time T _{transfer control} / T _Total , the ratio of image formation time T _{image formation} / T _Total , and the ratio of _other time T _other / T _Total. ing. Table 4 shows the intermittent number of sheets, from the top, one sheet per second, two sheets per second, and three sheets per second. In the case of two sheets per second, that is, in the case of intermittent two sheets, it takes 24 seconds for the entire print, of which 6 seconds are required for transfer control, 12 seconds for image formation, and 6 seconds for others. In the case of such two-sheet intermittent printing, T _{transfer control} / T _Total is 0.25, T _{image formation} / T _Total is 0.5, and T _other / T _Total is 0.25.

となる。 In the evaluation in this example, the exposure amount E _{transfer control} irradiated in the primary transfer voltage _{control / Example 1} is expressed by the following equations (3) and (4).

It becomes.

FIG. 8A is a graph showing the minute exposure amount at the time of primary transfer voltage control with respect to the transfer control integrated rotation speed n. The horizontal axis represents the transfer control integrated rotation speed n (ie, r × T _{transfer control} / T _Total from equation (4)), and the vertical axis represents the rotation speed of the photosensitive drum 1 during the primary transfer voltage control shown in Table 3. The exposure amount (μJ / cm ² ) corresponding to E _{transfer control / Example 1} calculated from the equation (3) by the end of the life of the photosensitive drum 1a corresponds to the area of FIG. 8A, and E _{transfer control / Example 1} = 666 μJ / cm ^2. It becomes. In the present embodiment, the time when the accumulated rotational speed r of the photosensitive drum 1a reaches 150,000 is regarded as the end of the service life. In this embodiment, the engine control unit 104 sets the micro exposure amount for the primary transfer voltage control shown in Table 3, so that the micro exposure is not performed until the transfer control integrated rotation speed n reaches n1, and becomes n1. Sometimes 0.012 μJ / cm ² . Furthermore, the engine control unit 104, when the transfer control cumulative revolution speed n becomes n2 is the 0.024μJ / cm ^2, when it becomes n3 are the 0.035μJ / cm ^2.

となり、それぞれ図８（ｂ）、図８（ｃ）の面積に相当する。尚、図８（ｂ）のグラフの横軸は、画像形成積算回転数ｍ（即ち、式（７）よりｒ×Ｔ_画像形成／Ｔ_{Ｔｏｔａｌ}）、縦軸は表２に示した通常露光における濃度（濃度階調）ｄ＝２０の場合の感光ドラム１の回転数に応じた露光量（μＪ／ｃｍ^２）を示す。また、図８（ｃ）のグラフの横軸は、その他積算回転数ｌ（即ち、式（８）よりｒ×Ｔ_その他／Ｔ_{Ｔｏｔａｌ}）、縦軸は表２に示した微小露光の感光ドラム１の回転数に応じた露光量（μＪ／ｃｍ^２）を示す。 In addition, when E _{image formation} and E and _others are similarly calculated,

These correspond to the areas of FIGS. 8B and 8C, respectively. The horizontal axis of the graph of FIG. 8B is the image formation cumulative rotation speed m (that is, r × T _{image formation} / T _Total from equation (7)), and the vertical axis is the density in normal exposure shown in Table 2. (Density gradation) The exposure amount (μJ / cm ² ) corresponding to the rotational speed of the photosensitive drum 1 when d = 20 is shown. Further, the horizontal axis of the graph of FIG. 8C is the other integrated rotational speed l (that is, r × T _other / T _Total from equation (8)), and the vertical axis is the micro-exposure photosensitive drum 1 shown in Table 2. The exposure amount (μJ / cm ² ) corresponding to the number of rotations of is shown.

In this embodiment, the total exposure amount E _{Total of the} laser light irradiated from the laser diode 63a until the photosensitive drum 1a reaches the end of its life,
E _{Total-Example 1} = E _{Pre-rotation-Example 1} + E _{Image formation} + E _Others
= 8935 μJ / cm ²
It becomes.

  In this embodiment, the engine control unit 104 sets parameters corresponding to the accumulated rotational speed r of the photosensitive drum 1 read in S101 before performing the primary transfer voltage control in S104 described in FIG. Is set from the minute exposure amount at the time of primary transfer voltage control. Further, the engine control unit 104 sets a parameter corresponding to the integrated rotation speed r of the photosensitive drum 1 read in S101 from the minute exposure amounts shown in Table 2 before image formation in S105.

(Comparative example)
FIG. 8D is a graph showing the fine exposure control during the primary transfer voltage control in the comparative example with respect to the transfer control integrated rotation speed n. The horizontal axis of the graph of FIG. 8D is the transfer control integrated rotation speed n, and the vertical axis is the exposure amount (μJ / cm ² ) corresponding to the rotation speed of the photosensitive drum 1 for microexposure shown in Table 2. Show. In the comparative example, the exposure amount of minute exposure at the time of image formation shown in Table 2 is used even during the primary transfer voltage control. In the comparative example, the exposure amount E _{transfer control / comparative example} irradiated during the primary transfer voltage control corresponds to the area of FIG.
E _{transfer control and comparison} = 2231 μJ / cm ²

The photosensitive drum 1a is, the exposure amount E are illuminated in addition to the exposure E _{image formation} and the primary transfer voltage control and imaging irradiated during imaging _Others are the same as the embodiment described above. From the above, in the comparative example, the total exposure amount E _{Total of the} laser light irradiated from the laser diode 63a until the photosensitive drum 1a reaches the end of its life _{, the comparative example} is
E _{Total / Comparative Example} = E _{Transfer Control / Comparative Example} + E _{Image Formation} + E _Others
= 10500 μJ / cm ²
It becomes. That is, in the comparative example, it can be seen that the total exposure amount ETotal _{· comparative example} is larger than the present embodiment (ETotal _{· comparative example} (= 10500 μJ / cm ² )> E _{Total · example 1} (= 8935 μJ / cm ² )).

  Table 5 is a table summarizing the evaluation results of the present example and the comparative example. The comparison result for the amount of increase in the exposure potential Vl, the optical density value (OD) (hereinafter simply referred to as image density). The comparison result and the comparison result of the formed line width (μm) are shown. The image density is the result of reading the recording material on which image formation was performed with d = 255 by the density detection means.

First, in this embodiment and the comparative example, the exposure amount of the laser beam irradiated from the laser diode 63a to the photosensitive drum 1a is compared. As described above, the exposure amount E _Total irradiated in the present example is 8935 μJ / cm ² , and the exposure amount E _Total irradiated in the _{comparative example} is 10500 μJ / cm ^{2 as the} _{comparative example} . Reduced by about 15%. In this embodiment, as a result of reducing the exposure amount, the increase amount of the exposure potential Vl can be suppressed to 42.2 V. Therefore, the image density can be reduced to 1.29 and the line width can be reduced to about 149 μm. On the other hand, in the comparative example, the amount of increase in the exposure potential Vl is 50V, which is larger than 42.2V in this embodiment. In the comparative example, the image density is 1.20, which is lower than 1.29 in this embodiment. Furthermore, the line width is 140 μm in the comparative example, which is thinner than 149 μm in the present example. As described above, in the comparative example, the deterioration in image quality is larger than that in the present embodiment.

  As described above, in this embodiment, the primary transfer voltage control is performed based on the initial charged potential of the photosensitive drum. Thereby, compared with the comparative example in which the exposure amount during the primary transfer voltage control and the image formation is the same, the total exposure amount of the laser light irradiated until the photosensitive drum reaches the end of its life can be reduced by about 15%. As a result, in this embodiment, since the increase amount of the exposure potential Vl can be suppressed, even when the usage time of the photosensitive drum 1 is long, the deterioration of the photosensitive drum is reduced and the deterioration of the image quality is reduced. be able to.

(Characteristics of Example 2)
Embodiment 2 is a color image forming apparatus characterized in that primary transfer voltage control is performed with a smaller minute exposure amount in order to further reduce the exposure amount. In this embodiment, the photosensitive drum 1a will be described as an example. Except for the control of the exposure amount, the configuration of the color image forming apparatus in the present embodiment is the same as that in the first embodiment, and the same members as those in the first embodiment are denoted by the same reference numerals. Omitted.

  In the present embodiment, specifically, the primary transfer voltage control is performed based on the charging potential of the photosensitive drum having the smallest integrated rotation number among the plurality of photosensitive drums 1a to 1d. That is, the surface potentials of the other photosensitive drums (hereinafter simply referred to as other photosensitive drums) excluding the photosensitive drum having the smallest accumulated rotational speed are matched with the surface potential of the photosensitive drum having the smallest accumulated rotational speed. In other words, among the plurality of photosensitive drums 1a to 1d, the information on the life of the photosensitive drum is based on the photosensitive drum closest to the information on the life of the initial photosensitive drum. In this embodiment, the other photosensitive drums are finely exposed so as to have the same potential as the charging potential of the photosensitive drum having the smallest cumulative number of rotations. For this reason, the photosensitive drum with the smallest cumulative number of rotations is not subjected to minute exposure and is not irradiated with laser light during the primary transfer voltage control.

In this embodiment, since the surface potential of the photosensitive drum at the time of primary transfer voltage control changes according to the integrated rotation speed, the primary transfer voltage at the time of image formation needs to be corrected according to the integrated rotation speed. Specifically, the primary transfer voltage at the time of image formation is Vt2, the primary transfer voltage control setting value is V02, the accumulated rotation speed is X, and the increase amount of the charged potential absolute value due to the accumulated rotation speed X is αX. In this embodiment, the primary transfer voltage control is performed in a state where the surface potential of the photosensitive drum 1 is shifted by αX + 100 (V) as compared with the time of image formation. For this reason, it is necessary to apply a value offset from the voltage set by the primary transfer voltage control as the primary transfer voltage at the time of image formation as in the following formula (9). This is different from the formula (2) in the first embodiment.
Vt2 = V02 + αX + 100 (V) Formula (9)

  As shown in Expression (9), the engine control unit 104 determines the primary transfer voltage Vt2 during image formation from the primary transfer voltage determined with respect to the surface potential of the photosensitive drum 1 during the primary transfer voltage control. , (ΑX + 100) V is reset to the offset value. The engine control unit 104 applies the optimum primary transfer voltage Vt2 during image formation to the transfer roller 14 from the transfer high-voltage power source 120.

尚、Ｅ_画像形成とＥ_その他については、実施例１と同様であるため、１次転写電圧制御時に削減できる露光量が、本実施例の構成により削減できる露光量となる。 Hereinafter, the case where any one of the other photosensitive drums 1b to 1d other than the photosensitive drum 1a is exchanged for the photosensitive drum 1a until the transfer control integrated rotation speed of the photosensitive drum 1a becomes 0 to n will be described. . Note that the photosensitive drums 1b to 1d to be replaced are not specified and the reference numerals are also omitted. Here, the transfer control integrated rotation speed of the photosensitive drum 1a when the first other photosensitive drum is exchanged is represented by na, and the transfer control integration of the photosensitive drum 1a when the second other photosensitive drum is exchanged. The rotation speed is nb (> na). Further, the transfer control integrated rotation speed of the photosensitive drum 1a when the other photosensitive drums are replaced after the third time is set to nc (> nb), nd (> nc),. Then, in this embodiment, the exposure amount E _{transfer control} during the primary transfer voltage control of the laser beam irradiated to the photosensitive drum 1a from the laser driver 62a. Can be deployed for each exchange.

Since E _{image formation} , E, and _others are the same as those in the first embodiment, the exposure amount that can be reduced during the primary transfer voltage control is the exposure amount that can be reduced by the configuration of the present embodiment.

は、感光ドラム１ａの積算回転数が最も少ないためゼロとなる。具体的には、感光ドラム１ａの転写制御積算回転数ｎは、０≦ｎ＜ｎａであり、他の感光ドラムの転写制御積算回転数と同じ、又は他の感光ドラムの転写制御積算回転数よりも少ない状態となっている。このため、本実施例では、最も積算回転数の少ない感光ドラムである感光ドラム１ａの帯電電位を基準として１次転写電圧制御を行う。即ち、感光ドラム１ｂ〜１ｄの表面電位が、感光ドラム１ａの表面電位と同じ電位となるように、感光ドラム１ｂ〜１ｄに微小露光を行う。上述したように、感光ドラム１ａは、基準となる感光ドラムであるため、微小露光は行われない。 (Description of action / effect)
This is the first term of the formula developed for each exchange of another photosensitive drum in Formula (10).

Is zero because the integrated rotational speed of the photosensitive drum 1a is the smallest. Specifically, the transfer control integrated rotation speed n of the photosensitive drum 1a is 0 ≦ n <na, which is the same as the transfer control integrated rotation speed of the other photosensitive drums or from the transfer control integrated rotation speed of the other photosensitive drums. There are few states. For this reason, in this embodiment, the primary transfer voltage control is performed based on the charging potential of the photosensitive drum 1a, which is the photosensitive drum having the smallest integrated rotation speed. That is, the photosensitive drums 1b to 1d are finely exposed so that the surface potential of the photosensitive drums 1b to 1d is the same as the surface potential of the photosensitive drum 1a. As described above, since the photosensitive drum 1a is a reference photosensitive drum, fine exposure is not performed.

  When the transfer control integrated rotation speed n of the photosensitive drum 1a is na ≦ n <nb, the other photosensitive drums have been replaced, and the integrated rotation speed of the replaced photosensitive drum is the integrated rotation speed of the photosensitive drum 1a. It is less than the number of revolutions. In this case, the primary transfer voltage control is performed based on the charging potential of another replaced photosensitive drum having a lower integrated rotational speed than that of the photosensitive drum 1a. That is, the photosensitive drum 1a is finely exposed so that the surface potential of the photosensitive drum 1a is the same as the surface potential of the replaced photosensitive drum. Since the surface potential of the photosensitive drum 1a changes according to the accumulated rotational speed X, the minute exposure amount on the surface of the photosensitive drum 1a is determined according to the accumulated rotational speed X of the photosensitive drum 1a. The same applies to other photosensitive drums that have not been replaced. Since the replaced photosensitive drum is a reference photosensitive drum, fine exposure is not performed. The same applies to the case where the photosensitive drum is replaced after the second time.

The E _{Example 2} (n) after the second term of the equation (10) varies depending on the integrated rotational speed X of the photosensitive drum 1a when the photosensitive drum is replaced. The absolute value of Vd_bg increases as the usage time increases. For this reason, it becomes a small value compared with the case where the same expansion | deployment is performed by Formula (3) of Example 1. FIG.

  In this embodiment, if the other photosensitive drum has not been exchanged by the end of the life of the photosensitive drum 1a, the photosensitive drum 1a continues to be the reference, and therefore the primary transfer to the photosensitive drum 1a is performed. Microexposure during voltage control is not performed. In addition, when the photosensitive drum is replaced once, the photosensitive drum is charged to a new photosensitive drum, and when the photosensitive drum is replaced a second time, the photosensitive drum is charged to the new photosensitive drum. The minute exposure amount on the drum 1a is readjusted. As the photosensitive drum is replaced, the amount of minute exposure to the photosensitive drum 1a during the primary transfer voltage control increases. Therefore, the effect of this embodiment decreases as the number of replacements of the photosensitive drum decreases. In this embodiment, the reference photosensitive drum (the photosensitive drum having the smallest cumulative number of revolutions) is not subjected to minute exposure, and therefore the exposure amount that can be reduced in this embodiment is larger than that in the first embodiment. For this reason, the increase amount of the exposure potential Vl can be more effectively suppressed, and the decrease in image density and the narrowing of the line width can be reduced more effectively.

  As described above, in this embodiment, the primary transfer voltage control is performed based on the charging potential of the photosensitive drum having the smallest integrated rotation speed among the plurality of photosensitive drums. As a result, in this embodiment, the total exposure amount irradiated before the photosensitive drum reaches the end of its life can be reduced more than in the first embodiment. As a result, in this embodiment, compared to the comparative example of Embodiment 1 in which the exposure amount during the primary transfer voltage control and the image formation is the same, the total exposure amount irradiated until the photosensitive drum reaches the end of its life is obtained. It can be reduced by about 15% or more, and the increase amount of the exposure potential Vl can be suppressed. Thereby, according to the present embodiment, the deterioration of the photosensitive drum can be reduced, and the deterioration of the image quality can be reduced.

(Characteristics of Example 3)
The third embodiment is a color image forming apparatus characterized in that an exposure amount reduction effect substantially equivalent to that of the first embodiment can be obtained by adjusting the charging voltage Vcdc during the primary transfer voltage control. In this embodiment, the photosensitive drum 1a will be described as an example. Except for the control of the exposure amount, the configuration of the color image forming apparatus in the present embodiment is the same as that in the first embodiment, and the same members as those in the first embodiment are denoted by the same reference numerals. Omitted.

  Specifically, the primary transfer voltage control is performed with the charging voltage Vcdc so that the initial charging potential of the photosensitive drum 1 becomes −500 V which is the post-microexposure charging potential Vd_bg at the time of image formation. FIG. 9 shows the surface potential of the photosensitive drum 1 (photosensitive drum potential V) with respect to the charging voltage Vcdc (V). FIG. 9 shows that when the photosensitive drum 1 is in the initial stage (indicated by a solid line in the figure), the charging voltage Vcdc may be set to −1000 V (predetermined voltage) in order to set the charging potential Vd to −500 V. Show. 9 shows that when half of the time until the end of the life of the photosensitive drum 1 has been reached (half of the end of life, indicated by a one-dot chain line in FIG. 9), the charging voltage Vd is set to −500V. It shows that Vcdc should be about -950V. Furthermore, when the life of the photosensitive drum 1a is reached (indicated by a broken line in FIG. 9), in order to set the charging potential Vd to −500V, the charging voltage Vcdc must be set to about −900V.

  As shown in FIG. 9, when the photosensitive drum 1a is in the initial stage (shown by a solid line in the figure), the charging voltage Vcdc is set to -1000V to be applied to the charging roller 2a in order to set the charging potential Vd to -500V. That's fine. In this embodiment, the charging voltage Vcdc at the time of controlling the primary transfer voltage is set to −1000 V, and minute exposure is performed according to the integrated rotation speed of the photosensitive drum 1a. In other words, even when the life of the photosensitive drum 1a reaches half or when the life of the photosensitive drum 1a is reached, the charging voltage Vcdc is set to -1000V, and is set to -500V by performing minute exposure. As described above, in this embodiment, the surface potential is adjusted to −500 V by minute exposure as the usage time of the photosensitive drum 1 a elapses. In this embodiment, since the surface potential of the photosensitive drum 1a at the time of primary transfer voltage control is the same as that at the time of image formation, an offset of the primary transfer voltage at the time of image formation becomes unnecessary.

であり、Ｅ_実施例３（ｎ）は、感光ドラム１ａの転写制御積算回転数ｎに応じて、感光ドラム電位を−５００Ｖにするために必要な露光量を示す。 In this embodiment, the exposure amount E _{transfer control} during the primary transfer voltage control of the laser beam irradiated to the photosensitive drum 1a from the laser diode 63a, and the _{third embodiment} ,

E _{Example 3} (n) shows an exposure amount necessary for setting the photosensitive drum potential to −500 V in accordance with the transfer control integrated rotation speed n of the photosensitive drum 1a.

(Description of action / effect)
In this embodiment, the charging voltage Vcdc at the time of primary transfer voltage control is set to -1000V. For this reason, the microexposure E _{Example 3} (n) for attenuating the surface potential of the photosensitive drum 1a to -500V (hereinafter also referred to as lowering) may be less than the case where the charging voltage Vcdc is -1100V. On the other hand, the charging potential Vd of the photosensitive drum 1a is proportional to the charging voltage Vcdc. In Example 1, the charging potential Vd_bg after microexposure according to microexposure E _{Example 1} (n) was set to −600 V while the charging voltage Vcdc was −1100V. On the other hand, in this embodiment, the charging potential Vd_bg after microexposure by microexposure E _{Example 3} (n) is set to −500 V with respect to the charging voltage Vcdc of −1000V. The potential difference between the charging voltage Vcdc and the post-microexposure charging potential Vd_bg is the same between the present embodiment and the first embodiment. For this reason, in the primary transfer voltage control, the potential to be lowered by the minute exposure is also equal between the present embodiment and the first embodiment. In addition, since the surface potential of the photosensitive drum 1a when performing microexposure is an environment of a strong electric field having a large absolute value, recombination of charge carriers (electron-hole pairs) generated by exposure hardly occurs and is small. It shows a large potential decay even at the exposure amount. For this reason, if the potential to be lowered by the microexposure is the same, E _{Example 1} (n) and E _{Example 3} (n) may be regarded as approximately equivalent. Since the E _{image formation} , E, and _others are the same as those in the first embodiment, the exposure amount that can be reduced during the primary transfer voltage control is the exposure amount that can be reduced in the present embodiment. For this reason, the reduction of the exposure amount in the present embodiment is substantially the same as that in the first embodiment, and it can be expected that the amount of increase in the exposure potential Vl as in the first embodiment is suppressed.

  As described above, in this embodiment, the primary transfer voltage control is performed with the charging voltage Vcdc so that the initial charging potential of the photosensitive drum is −500 V, which is the potential after microexposure during image formation. . Thereby, as a result of reducing the total exposure amount substantially the same as that of the first embodiment, the increase amount of the exposure potential Vl can be suppressed. Thereby, according to the present embodiment, the deterioration of the photosensitive drum can be reduced, and the deterioration of the image quality can be reduced.

  The color image forming apparatus according to the fourth embodiment is characterized in that by adjusting the charging voltage Vcdc during the primary transfer voltage control, an exposure amount reduction effect substantially equal to that of the second embodiment can be obtained. In this embodiment, the photosensitive drum 1a will be described as an example. Except for the control of the exposure amount, the configuration of the color image forming apparatus in the present embodiment is the same as that in the first embodiment, and the same members as those in the first embodiment are denoted by the same reference numerals. Omitted.

Specifically, among the plurality of photosensitive drums, the charging voltage Vcdc is adjusted so that the charging potential Vcdc of the photosensitive drum having the smallest cumulative number of rotations becomes −500 V, which is the charging potential Vd_bg after minute exposure at the time of image formation. Thus, primary transfer voltage control is performed. The other photosensitive drums except the photosensitive drum having the smallest cumulative rotation number are charged by the charging voltage Vcdc adjusted according to the photosensitive drum having the smallest cumulative rotation number. The other photosensitive drums are adjusted so that the surface potential of the other photosensitive drums becomes −500 V by performing micro exposure on the charged potential Vd obtained by the charging voltage Vcdc. A charging voltage Vcdc (predetermined voltage) necessary for setting the charging potential of the photosensitive drum to −500 V is proportional to the integrated rotational speed r, and in this embodiment, follows the equation (11).
Vcdc = − {(1/1500) × r + 1000} (11)

  In this embodiment, the offset of the primary transfer voltage at the time of image formation becomes unnecessary.

  In this embodiment, the expression (11) is applied to the photosensitive drum having the smallest cumulative number of rotations, and the charging voltage Vcdc to be applied during the primary transfer voltage control is determined. For example, when the integrated rotation number of the photosensitive drum 1a is the smallest, the charging voltage Vcdc according to the equation (11) is applied to the integrated rotation number of the photosensitive drum 1a. However, when another photosensitive drum is replaced once by the end of the life of the photosensitive drum 1a, the charging voltage Vcdc adapted to the expression (11) is applied to the accumulated number of revolutions of the replaced new photosensitive drum. To do. Further, when the photosensitive drum is replaced for the second time, a charging voltage adapted to the equation (11) is applied to the accumulated rotational speed of the photosensitive drum replaced for the second time. Thus, since the charged photosensitive drum V becomes −500 V by applying the charging voltage Vcdc corresponding to the accumulated rotational speed r according to the equation (11), the replaced photosensitive drum is changed to that of the photosensitive drum that has not been replaced. Thus, it is not adjusted by minute exposure. That is, the exchanged photosensitive drum is not subjected to minute exposure during the primary transfer voltage control. On the other hand, the photosensitive drum that has not been replaced, for example, the photosensitive drum 1a, is charged by the charging voltage Vcdc determined from the equation (11) in accordance with the accumulated rotational speed of the replaced photosensitive drum. However, the charging potential Vd of the photosensitive drum 1a does not become −500 V depending on the charging voltage Vcdc adjusted to match the replaced photosensitive drum. For this reason, the photosensitive drum 1a that has not been replaced is subjected to minute exposure so that the surface potential is further −500V.

式（１２）中のＥ_実施例４（ｎ，Ｖｃｄｃ（ｎ））は、感光ドラム１ａの表面電位を−５００Ｖにするために必要な露光量を示す。本実施例では、転写制御積算回転数ｎによって帯電電圧Ｖｃｄｃが変わる（Ｖｃｄｃ（ｎ））ため、Ｅ_実施例４（ｎ，Ｖｃｄｃ（ｎ））は、転写制御積算回転数ｎと帯電電圧Ｖｃｄｃで決まる。 Further, the minute exposure amount at the time of controlling the primary transfer voltage varies depending on the number of times the photosensitive drum is replaced and the total number of rotations. Here, the transfer control cumulative rotation speed of the photosensitive drum 1a when the first photosensitive drum replacement is performed is represented by na, and the transfer control cumulative rotation speed of the photosensitive drum 1a when the second photosensitive drum replacement is performed is performed by nb. And Further, let nc, nd... Be the transfer control integrated rotation speed of the photosensitive drum 1a when the photosensitive drum is replaced after the third time. Then, in this embodiment, the exposure amount E _{transfer control} during the primary transfer voltage control of the laser light emitted from the laser diode 63a to the photosensitive drum 1a is _performed every time the photosensitive drum is replaced as shown in Expression (12). Expressions can be expanded into

E _{Example 4} (n, Vcdc (n)) in the equation (12) indicates an exposure amount necessary for setting the surface potential of the photosensitive drum 1a to −500V. In the present embodiment, since the charging voltage Vcdc varies depending on the transfer control integrated rotation speed n (Vcdc (n)), the E _{embodiment 4} (n, Vcdc (n)) is based on the transfer control integrated rotation speed n and the charging voltage Vcdc. Determined.

(Description of action / effect)
In the equation (12), the first term of the equation developed every time the photosensitive drum is replaced represents the exposure amount when the cumulative rotation number of the photosensitive drum 1a is the smallest. Since the charging voltage Vcdc is applied so that the charging potential Vd of the photosensitive drum 1a is −500 V, the minute exposure amount E _{example 4} (n, Vcdc (n)) becomes zero. In the second and subsequent terms, E _{Example 4} (n, Vcdc (n)) varies depending on the total number of revolutions of the photosensitive drum 1a when another photosensitive drum is replaced. In this embodiment, when the photosensitive drum is replaced once, the photosensitive drum 1a is subjected to minute exposure so that the surface potential of the photosensitive drum 1a becomes −500V. In this embodiment, since the absolute value of the charging voltage Vcdc is reduced in proportion to the cumulative number of rotations of the photosensitive drum having the smallest cumulative number of rotations, the magnitude of the potential that is reduced to −500 V by microexposure is It doesn't change while the exchange is not taking place. On the other hand, in Example 2, the microexposure is performed so that the charging potential Vd of the photosensitive drum having the smallest cumulative number of revolutions is obtained. In this case as well, the potential to be lowered by the microexposure is reduced while the photosensitive drum is not replaced. The size does not change. If the magnitude of the potential to be lowered does not change, the magnitudes of E _{Example 4} (n, Vcdc (n)) and E _{Example 3} (n) do not change, and therefore the photosensitive drum is replaced at the same integrated rotational speed. In this embodiment, the amount of exposure with which the photosensitive drum 1a is irradiated is substantially the same as that in the second embodiment.

Since E _{image formation} , E, and _others are the same as those in the first embodiment, the exposure amount that can be reduced during the primary transfer voltage control is the exposure amount that can be reduced in the present embodiment. For this reason, this embodiment can be expected to suppress the increase in exposure potential Vl equivalent to that in the second embodiment.

  As described above, in this embodiment, among the plurality of photosensitive drums, the charging potential of the photosensitive drum having the smallest cumulative number of rotations is −500 V, which is the post-microexposure charging potential Vd_bg at the time of image formation. The primary transfer voltage control is performed by adjusting the charging voltage Vcdc. For other photosensitive drums, primary transfer voltage control is performed by adjusting the surface potential to −500 V by microexposure with respect to the charged potential Vd obtained by the adjusted charging voltage Vcdc. As a result, it is possible to reduce the total exposure amount substantially the same as that of the second embodiment. As a result, the increase amount of the exposure potential Vl can be suppressed, so that the deterioration of the photosensitive drum can be reduced and the deterioration of the image quality can be reduced. .

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 14 Transfer roller 31 Exposure apparatus 104 Engine control part

Claims (14)

And feeling light body,
A charging means for charging the previous Symbol feeling light body,
Subjected to exposure in the first exposure to the image portion to deposit toner on said photosensitive member during image formation, the first exposure to the non-image area which does not adhere to the toner before Symbol feeling light body on during the image forming a row intends exposure means exposure with the second exposure amount smaller than,
Developing means for attaching toner to the image portion to form a toner image;
Anda transfer means for transferring to a transfer member the toner image formed on the front Symbol feeling light body on by being applied a transfer voltage,
And control means for performing transfer voltage control for determining the applied transfer voltage Ru to the transfer means when performing the images formed,
An image forming apparatus comprising:
The control hand stage, cormorants line the transfer voltage control I the second row of the exposure in the third exposure amount less than an exposure amount at the time of the image formed by the exposure means, or, exposure by the exposing unit An image forming apparatus that performs the transfer voltage control without performing the step. Wherein, when performing the transfer voltage control, surface potential before Symbol feeling light body, so as to have the same potential as the charge potential of the initial photoreceptor, dew before Symbol feeling light body by said exposure means The image forming apparatus according to claim 1, wherein the image forming apparatus performs light. The image forming apparatus according to claim 2, wherein the control unit determines the third exposure amount at the time of performing the transfer voltage control according to information on a life of the photoconductor. A plurality of the photoreceptor, the charging unit, the transfer unit, and the exposure unit;
Said control means, said when performing the transfer voltage control, other photoreceptor information about the life of the photosensitive member excluding the nearest photoreceptor information on the life of the initial photoreceptors among a plurality of pre-Symbol feeling light body the surface potential of, to be the same potential as the charge potential of the closest photoreceptor, an image forming apparatus according to claim 1, characterized in that the exposure light to the other photosensitive bodies by said exposure means. 5. The image forming apparatus according to claim 4, wherein the control unit determines the third exposure amount when performing the transfer voltage control according to information on a life of the other photoconductor. A plurality of the photoreceptor, the charging unit, the transfer unit, and the exposure unit;
One charging voltage application means for applying a charging voltage to the plurality of charging means,
Wherein, when performing the transfer voltage control, the surface potential of the plurality of pre-Symbol feeling light body, early photoreceptor of the initial photoreceptor upon application of a predetermined voltage by the charging voltage applying means so that the same potential as the surface potential, an image forming apparatus according to claim 1, characterized in that the exposure light to the plurality of photosensitive member by the exposure means. The image forming apparatus according to claim 6, wherein the control unit determines the third exposure amount when performing the transfer voltage control in accordance with information relating to a life of the photoconductor. A plurality of the photoreceptor, the charging unit, the transfer unit, and the exposure unit;
One charging voltage application means for applying a charging voltage to the plurality of charging means,
Said control means, said when performing the transfer voltage control, other photoreceptor information about the life of the photosensitive member excluding the nearest photoreceptor information on the life of the initial photoreceptors among a plurality of pre-Symbol feeling light body the surface potential, the so that the same potential as the surface potential of the closest photoreceptor at the time of applying a predetermined voltage to the nearest photoreceptor by the charging voltage applying means, to the other photosensitive bodies by said exposure means the image forming apparatus according to claim 1, characterized in that the exposure light.   The image forming apparatus according to claim 8, wherein the control unit determines the predetermined voltage according to information on a life of the nearest photoconductor. 10. The image formation according to claim 8, wherein the control unit determines the third exposure amount when performing the transfer voltage control according to information on a lifetime of the other photoconductor. apparatus.   The image forming apparatus according to claim 1, further comprising a non-volatile storage unit that stores information relating to a lifetime of the photoconductor.   The information relating to the life of the photoconductor includes at least one information among an accumulated rotation speed of the photoconductor, a usage time of the photoconductor, and an accumulated number of recording materials on which image formation has been performed. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the control unit performs the transfer voltage control before forming an image on a recording material. 14. The image according to claim 1, wherein the control unit determines the second exposure amount at the time of image formation based on information relating to a lifetime of the photoconductor. Forming equipment.

Images