JP5382409B2 - Image forming apparatus - Google Patents

Description

  The present invention forms an electrostatic latent image on an image carrier, develops it into a toner image, and transfers the image directly or indirectly via an intermediate transfer member to a so-called electrophotographic image formation Regarding the apparatus, it can be used in a printer, a facsimile, a copying machine, and the like.

JP 2001-222149 A Japanese Patent Application Laid-Open No. 2007-79378.

  A charger having a casing, a grid, and a discharge electrode is widely used. In a high-speed image forming apparatus, a charging device having a plurality of discharge electrodes is also used to ensure a necessary discharge current. In addition, an image forming apparatus having a plurality of image forming speeds (linear speed: moving speed of the image carrier) has been put into practical use in order to ensure fixing performance of cardboard and to enable high-resolution output. Yes. Scorotron, which is a charger equipped with wires and grid electrodes, can control the charged charge of the photoconductor, which is an image carrier, with a grid bias applied to the grid electrodes. It is used. In addition, scorotrons having two or more wires have been put into practical use in order to obtain a discharge current that can cope with a high linear velocity.

  Patent Document 1 discloses a charging device that can individually set voltages of two wires in order to easily correct a potential deviation in a longitudinal direction. Patent Document 2 discloses a charging device in which two chargers are arranged in order to compensate for a delay in charge rising of a photoreceptor.

  Conventionally, since a plurality of wires are supplied with power from a single high-voltage power source, the discharge of each wire cannot be individually controlled. In an image forming apparatus having a plurality of linear velocities (moving speed of the photosensitive member), the same is applied. Even when the grid bias is applied, there is a problem that the charging potential varies depending on the linear velocity.

  In the image forming apparatus having two chargers as in Patent Document 2, it is possible to operate each charger individually, but two high-voltage power supplies for wires and two grids are required respectively. There is a problem that it is difficult to reduce the size of the apparatus because an insulating partition plate is required between the two chargers, which is costly.

  In view of such a situation, the present invention has a first object to provide an image forming apparatus that is excellent in controllability of a charged potential regardless of the linear velocity of an image carrier, and that can be reduced in size and cost. A second object is to maintain a stable charging function over a long period of time.

(1) Image carrier (40);
A casing (71), a grid (75), a plurality of discharge electrodes (73, 74), and a plurality of high-voltage power sources (76, 77) that individually output / stop high voltages, each of the plurality of discharge electrodes A charging device for charging the image carrier (FIG. 3; 70, 76, 77) connected to each of the plurality of high-voltage power supplies;
Exposure means (21) for irradiating the charged surface of the image carrier with light to form an electrostatic latent image;
Developing means (60) for developing the electrostatic latent image to form a toner image;
Transfer means (10, 11, 22) for transferring the toner image onto a sheet; and
If the high-speed / low-speed designation data is low-speed designation, a small number of high-voltage power supplies specified by the wire designation data among the plurality of high-voltage power supplies are specified, and if the high-speed / low-speed designation data is high-speed designation, the wire designation data is involved. specifies the number of high-voltage power supply often without performing high pressure output to the discharge electrodes of the high-voltage power supply running set number of sheets image formation, to identify the high-voltage power supply of the small number in accordance slow specified imaging identified If so, control means (90, FIG. 4) for changing the wire instruction data to specify a small number of other high voltage power supplies next time ;
An image forming apparatus comprising:

  In addition, in order to make an understanding easy, the code | symbol of the corresponding element or the corresponding matter of the Example which is shown in drawing and mentions later in a parenthesis was added as an example for reference. The same applies to the following.

Since the number of discharge electrodes to be used is switched according to the moving speed of the image carrier, that is, the image forming speed, the image carrier can be charged to an appropriate charging potential without being affected by the image forming speed, and unnecessary discharge is possible. Product generation can also be prevented. When a low speed is specified, only some of the discharge electrodes are used for charging for image formation, but since the discharge electrodes to be used are switched using the wire instruction data, the frequency of use of the plurality of discharge electrodes is almost the same and specified. Degradation of only the discharge electrode is reduced.

( 2 ) The casing has a shielding wall (72) that shields between adjacent discharge electrodes; The image forming apparatus according to ( 1) above. By shielding between adjacent discharge electrodes, interference between the discharge electrodes can be prevented, and discharge can be stabilized when only some of the discharge electrodes are used.

( 3 ) The image carrier has a roller shape, and the grid has a curved surface forming a part of a circumference concentric with the image carrier, and has an aperture ratio of 75 to 85%; The image forming apparatus according to 1) or (2) . By making the grid a curved surface concentric with the image carrier and setting the aperture ratio to 75 to 85%, the controllability of the charging potential is improved.

( 4 ) The image forming apparatus according to any one of (1) to ( 3 ), wherein the discharge electrode is a wire having a diameter of 25 to 55 μm. By reducing the wire diameter to φ25 to 55 μm, the generation amount of discharge products can be reduced.

( 5 ) The image forming apparatus according to ( 4 ), wherein the wire has a surface coating of a noble metal having a thickness of 1 to 4 μm. By covering the surface of the wire with a noble metal, the wire can be made difficult to get dirty, and good charging characteristics can be maintained over a long period of time.

( 6 ) The image forming apparatus according to ( 4 ) or ( 5 ), wherein the high-voltage power supply supplies a discharge current of 9 to 18 μA / cm per length of the wire. By setting the discharge current per length of the wire within the above range, the discharge state is good and the generation of excessive discharge products can be prevented.

(7) easily in a process cartridge detachably mountable (18) with respect to the image forming apparatus main body, the image bearing member and the casing of the charging device, equipped with a grid and a plurality of discharge electrodes; (1) to (6 The image forming apparatus according to any one of the above. By integrating the charger (70) consisting of a casing, grid and multiple discharge electrodes into the process cartridge, the distance between the image carrier and the grid can be maintained well, so the image carrier can be charged uniformly. It becomes possible to do.

( 8 ) The image forming apparatus according to ( 7 ), wherein the process cartridge is also equipped with the developing unit and a unit for cleaning the surface of the image carrier after the transfer.

  Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

  FIG. 1 shows an outline of the mechanism of a copying machine equipped with an embodiment of the present invention. The copier includes an image forming mechanism including a printer 100 and a paper feeding unit 200, a scanner 300, and an ADF (automatic document feeder) 400. The scanner 300 is attached on the printer 100, and the ADF 400 is attached on the scanner 300. The scanner 300 reads image information of a document placed on the contact glass 32 by a reading sensor (CCD in this example) 36, and reads the read image information by an engine control (not shown) (Image Processing Processor; hereinafter simply referred to as “Image Processing Processor”). To IPP). The engine control is based on the image information received from the scanner 300, and controls a laser, LED, and the like (not shown) disposed in the exposure device 21 of the printer 100 to form four drum-shaped photoconductors 40 as image carriers. Laser writing light is irradiated toward (K, Y, M, C). By this irradiation, an electrostatic latent image is formed on the surface of the photoreceptor 40 (K, Y, M, C), and this latent image is generated by the image forming mechanism of the process cartridge 18 (K, Y, M, C). The toner image is developed through a predetermined development process. Note that the subscripts K, Y, M, and C added after the reference numerals indicate specifications for black, yellow, magenta, and cyan.

  The printer 100 includes an exposure device 21 as an exposure means, a primary transfer roller 11 (K, Y, M, C) as a transfer means, a secondary transfer device 22, a fixing device 25, a paper discharge device, and a toner (not shown). A supply device, a toner disposal device, and the like are also provided. The paper feeding unit 200 includes an automatic paper feeding unit disposed below the printer 100 and a manual feeding unit disposed on a side surface of the printer 100. The automatic paper feeding unit separates the three paper feed cassettes 44 arranged in multiple stages in the paper bank 43, the paper feed roller 42 that feeds transfer paper as paper from the paper feed cassette, and the fed transfer paper. A separation roller 45 and the like are sent to the paper feed path 46. Further, it also includes a transport roller 47 that transports the transfer paper to the paper feed path 48 of the printer 100. On the other hand, the manual feed section includes a manual feed tray 51 and a separation roller 52 that separates the transfer paper on the manual feed tray 51 one by one toward the manual feed path 53.

  A registration roller pair 49 is disposed near the end of the paper feed path 48 of the printer 100. The registration roller pair 49 is formed between the intermediate transfer belt 10 serving as an intermediate transfer body and the secondary transfer device 22 at a predetermined timing after receiving the transfer paper sent from the paper feed cassette 44 or the manual feed tray 51. To the secondary transfer nip.

  In this copying machine, an operator sets a document on the document table 30 of the ADF 400 when copying a color image. Alternatively, after the ADF 400 is opened and a document is set on the contact glass 32 of the scanner 300, the ADF 400 is closed and the document is pressed. Then, a start switch (not shown) is pressed. Then, when a document is set on the ADF 400, the scanner 300 starts driving immediately after the document is conveyed on the contact glass 32 and then when the document is set on the contact glass 32. Then, the first carriage 33 and the second carriage 34 travel, and the light emitted from the light source of the first carriage 33 is reflected by the document surface and then travels toward the second carriage 34. Further, after being reflected by the mirror of the second carriage 34, it reaches the reading sensor 36 via the imaging lens 35 and is read as image information.

  When the image information is read in this way, the printer 100 rotates the other two support rollers while rotating one of the support rollers 14, 15, and 16 with a drive motor (not shown). Then, the intermediate transfer belt 10 that is an intermediate transfer member stretched around these rollers is moved endlessly. Further, laser writing as described above and a development process described later are performed. Then, while rotating the photoreceptors 40 (K, Y, M, C), black, yellow, magenta, and cyan monochrome images are formed on them. These are electrostatically transferred in four colors at the primary transfer nips for K, Y, M, and C where the photosensitive member 40 (K, Y, M, and C) and the intermediate transfer belt 10 come into contact with each other, and are four colors. A superimposed toner image is obtained. A toner image is formed on the photoreceptor 40 (K, Y, M, C).

  On the other hand, the paper feed unit 200 operates one of the three paper feed rollers to feed transfer paper of a size corresponding to the image information, and feeds the transfer paper to the paper feed path 48 of the printer 100. Lead to. The transfer sheet, which is a sheet of paper that has entered the paper feed path 48, is sandwiched between the registration roller pair 49 and temporarily stops. Then, the intermediate transfer belt 10 and the secondary transfer roller 23 of the secondary transfer device 22 are matched in time. To the secondary transfer nip which is a contact portion. Then, in the secondary transfer nip, the four-color superimposed toner image on the intermediate transfer belt 10 and the transfer paper are brought into close contact in synchronization. Then, the four-color superimposed toner image is secondarily transferred onto the transfer paper due to the influence of the transfer electric field formed at the nip, the nip pressure, etc., and becomes a full color image combined with the white color of the paper.

  The transfer paper that has passed through the secondary transfer nip is fed into the fixing device 25 by the endless movement of the transport belt 24 of the secondary transfer device 22. Then, after the full color image is fixed by the action of the pressure applied by the pressure roller 27 of the fixing device 25 and the heating by the heating belt, the paper is discharged onto the discharge tray 57 provided on the side surface of the printer 100 via the discharge roller 56. To be discharged.

  This copying machine has a plurality of photosensitive member linear speeds, and operates at 352 mm / sec when passing plain paper and at 176 mm / sec when passing thick paper.

  FIG. 2 shows one configuration of the process cartridge 18 shown in FIG. The other three configurations are the same or similar. The case of the process cartridge 18 is provided with an opening for allowing the exposure light 76 to pass from the laser exposure device 21 to the photoconductor 40 that is an image carrier. Around the photoconductor 40 inside the process cartridge 18, a scorotron charger 70 that uniformly charges the photoconductor 40, a potential sensor 81 that detects the potential of the photoconductor 40, and an electrostatic latent image formed on the photoconductor 40 A developing device 60 for developing the toner, a neutralizing lamp 72 for neutralizing the surface of the photoreceptor 40 after the toner image is transferred, and a brush roller 83 and a cleaning blade 85 as a cleaning device for cleaning the residual toner. Yes. The toner scraped off from the photoreceptor 40 by the brush roller 83 or the cleaning blade 85 made of polyurethane rubber is collected by the toner transport coil 89 and transported to a waste toner storage unit (not shown).

  In this example, the photoconductor 40 that has been discharged after the transfer is configured to be cleaned, but the photoconductor that has been cleaned after the transfer may be configured to be discharged.

  A lubricant supply device including the brush roller 84, the solid lubricant 88, and the lubricant supply blade 80 is disposed downstream of the cleaning devices (83, 85). The brush roller 84 scrapes the solid lubricant 88 and supplies it to the photoconductor 40, and the lubricant supplied to the photoconductor 40 is uniformly stretched on the photoconductor 40 by the lubricant supply blade 80. Examples of solid lubricants 88 include zinc stearate, barium stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, magnesium stearate, zinc oleate, oleic acid Fatty acid metal salts such as cobalt, magnesium oleate, and zinc palmitate, natural waxes such as carnauba wax, and fluorine-based resins such as polytetrafluoroethylene can be used. As shown in FIG. 2, by arranging a dedicated lubricant supply device downstream of the cleaning device (83, 85), it is not affected by changes in the amount of residual transfer toner or reverse transfer toner depending on the image area to be formed. A lubricant can be stably supplied to the photoreceptor 40 which is an image carrier.

  The developing device 60 of each process cartridge 18 has the same configuration, and is a two-component developing type developing device that differs only in the color of the toner to be used, and each color developing device 60 comprises toner and a carrier. Contains a two-component developer. The developing device 60 includes a developing roller 61 facing the photoreceptor 40, screws 62 and 63 for conveying and stirring the developer, a toner concentration sensor 64, and the like. The developing roller 61 is composed of an outer rotatable sleeve and an inner magnet. In accordance with the output of the toner density sensor 64, a necessary amount of toner is supplied from a toner supply device (not shown).

  The toner includes a binder resin, a colorant, and a charge control agent as main components, and other additives are added as necessary. Specific examples of the binder resin include polystyrene, styrene-acrylic acid ester copolymer, polyester resin, and the like. As coloring materials (for example, yellow, magenta, cyan and black) used for the toner, those known for toners are used.

  The carrier is a core material itself or a core layer provided with a coating layer. The core material of the resin-coated carrier is ferrite or magnetite. The core material has a particle size of about 20 to 60 μm. Examples of the material used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. The coating layer is obtained by applying a resin to the surface of the carrier core particle by a spraying method or a dipping method.

  The charger 70 shown in FIG. 2 is a double-wire scorotron, and the casing 71 is made of stainless steel and has a shielding wall 72 that shields between the two wires 73 and 74. The grid 75 is made of stainless steel and manufactured by etching, has an aperture ratio of 82%, and is arranged concentrically with the photoconductor at a distance of 2 mm from the surface of the photoconductor 40 having a diameter of 60 mm. The grid 75 has a cylindrical curved surface concentric with the photoreceptor 40.

  The wires 73 and 74 are obtained by applying a gold plating with a thickness of 1.5 μm on a tungsten wire with a diameter of 40 μm, and are disposed at a distance of 6 mm from the surface of the photoreceptor. The two wires 73 and 74 are connected to separate high-voltage power sources (76 and 77 in FIG. 3). The grid 75 is connected to a grid high-voltage power supply (78 in FIG. 3), and the casing 71 is connected to the same potential as the grid 75 by a power supply circuit (79 in FIG. 3).

  Since the casing 71 includes a shielding wall 72 that shields between the two wires 73 and 74, when the two wires 73 and 74 are also used, interference of the electric field between the wires can be prevented. Even when only one wire is used, the electric field is not disturbed and stable corona discharge can be generated.

  If the wire current is small, the discharge state is not stable, and uneven charging is likely to occur. If the wire current is too large, leakage to the casing is likely to occur, and the amount of discharge products such as ozone increases. Therefore, it is desirable to set the discharge current per unit length of the wires 73 and 74 in the range of 9 to 18 μA / cm. It is known that the smaller the diameter of the wire used, corona discharge occurs at a lower voltage and less generation of discharge products such as ozone. Considering the strength of the wire and ease of handling, the diameter of the wires 73 and 74 is preferably 25 to 55 μm. Tungsten is used as the wire material because of its mechanical strength.

  By covering the surface of the wire with a noble metal such as gold or platinum by a treatment such as plating, deterioration such as oxidation hardly occurs, and the wire can be easily removed. If the thickness of the noble metal coating is too thin, the durability is poor, and if it is too thick, the cost is increased.

  Further, by making the grid 75 a circumferential curved surface concentric with the photoconductor 40, the controllability of the photoconductor potential by the grid 75 is improved. The controllability of the potential is improved when the aperture ratio of the grid 75 is low, but if it is too low, the wire current for obtaining the necessary charging potential becomes large. Therefore, the aperture ratio of the grid 75 is preferably 75 to 85%. .

  In the scorotron, if there is a longitudinal deviation in the distance between the grid and the surface of the photoconductor, a deviation also occurs in the charging potential of the photoconductor. Therefore, it is necessary to maintain this distance with high accuracy. The photosensitive member and the charger 70 are integrated into the process cartridge 18 so that the distance between the photosensitive member surface and the grid can be maintained in the process cartridge. Accordingly, even the user can easily replace the process cartridge 18 as a unit, and the charged potential deviation hardly occurs.

  Although the above embodiment uses two wires, the present invention can be similarly applied even when there are three or more wires. Further, although the case where the discharge electrode is a wire has been described, the present invention can also be implemented using a charger having a plurality of sawtooth-shaped metal electrodes instead of a wire.

  FIG. 3 shows an outline of a power supply circuit that applies a charging voltage to the charger 70 shown in FIG. The charger 70 is a scorotron composed of a metal casing 71, a first wire 73 made of a thin metal wire, a second wire 74, and a metal grid 75. The first wire 73 is connected to the first high-voltage power supply circuit 76. The second wire 74 is connected to the second high-voltage power supply circuit, and the grid 75 is connected to the grid power supply circuit 78. The casing 71 is grounded or has the same potential as the grid by a casing power supply circuit 79. An engine control process controller 90 (not shown) controls or sets output on / off of the power supply circuits 76 to 79, grid voltage, and wire current. That is, the process controller 90 controls the power supply circuits 76 to 79 to apply a high voltage to the wires 73 and 74 of the charger 70 to generate corona discharge, and the voltage applied to the grid 75, that is, the grid bias, The charging potential of the body 40 is controlled.

  The process controller 90 shown in FIG. 3 mainly includes an input / output interface, an MPU (microcomputer), and an image forming process control ASIC, and an image forming command for executing an image processing job designated by a user from a system controller (not shown). In response, the image forming process is set and executed.

  In the charger 70 which is a scorotron, it is necessary to increase the wire current in order to sufficiently charge the photosensitive member 40 as the photosensitive member linear velocity, that is, the moving speed of the photosensitive member surface increases. If is too large, the voltage applied to the wire becomes too high, and there is a risk of leakage to the casing 71. Therefore, a high-speed image forming apparatus includes two or more wires to reduce the discharge current per wire. Conventionally, since a plurality of wires are collectively connected to one high-voltage power source, the wire current cannot be lowered even in the low-speed mode, and the same wire current as that in the normal mode is set in the low-speed mode. This is because if the wire current is too low, stable corona discharge cannot be maintained and charging unevenness occurs. Since excessive wire current is set in the low-speed mode, there is a difference in charge potential controllability between the high-speed mode, which is the normal mode, and the low-speed mode. There was a bug that it was different.

  In the present embodiment, each of the plurality of wires 73 and 74 is connected to each of a plurality of high-voltage power sources 76 and 77 that individually output / stop high voltages, and the number of wires to be used is switched according to the line speed. Then, an appropriate wire current can be set in both the high speed mode and the low speed mode. If the grid bias is the same, the charging potential can be made the same regardless of the high speed / low speed mode.

  FIG. 4 shows an outline of the wire number switching function by the process controller 90. When a system controller (not shown) gives a copy or print command (hereinafter collectively referred to as image formation or image formation) to the process controller 90 in response to a user's start instruction, the process controller 90 An image forming condition for the image mechanism is set, and image forming under the set image forming condition is executed for the set number of sheets included in the image forming condition.

In setting the image forming condition, the process controller 90 executes “determination of charger wire to be used” WSP shown in FIG. First, high-speed / low-speed designation data (linear velocity data) is read from the system controller, and wire instruction data Wf is read from the nonvolatile memory (S1).

  Next, in response to the contents of the high-speed / low-speed designation data and the wire designation data Wf, when the low-speed designation (176 mm / sec in this embodiment) is designated, when the wire designation data Wf is “0”, the charger Only the wire 73 is determined to be used in the charging process for the current set number of image formation (S2, S3), and the wire designation data Wf is changed to “1” so that the next designation is the wire 74. (S4). However, when the wire instruction data Wf is “1”, only the charger wire 74 is determined to be used in the charging process for image formation of the current set number (S2, S5), and the next designation is the wire 73. Therefore, the wire instruction data Wf is changed to “0” (S6).

  When the high speed (352 mm / sec in this embodiment) is designated, the charger wires 73 and 74 are determined to be used in the charging process (S2, S7). The wire instruction data Wf is not operated.

  Thereafter, the process controller 60 starts image formation for the set number of sheets and supplies power to the charger wires 73, 74 or 73 and 74 set to be used in S3, S5 or S7 in the charging process for image formation for each page. The high-voltage power supply circuits 76, 77 or 76 and 77 to be turned on are turned on (charge voltage output on).

  In the case of low speed designation, the wire designation data Wf changes from “0” (wire 73 designation) to “1” (wire 74 designation) each time the set number of images are formed in response to the start instruction. On the other hand, since it is changed (S4, S6), over a long period of time, the usage frequency of the charger wires 73 and 74 in the case of low speed designation is substantially the same. That is, the usage frequency is equalized. As a result, deterioration of only one wire does not progress and image formation quality is not deteriorated at an early stage. That is, high-quality image formation is highly stable.

  In addition to the above, in the aspect of equalizing the usage frequency of each of the charger wires 73 and 74, in addition to the above, a count register for the wire 73 and 74 is defined in the nonvolatile memory, and the data of each count register is stored in the count register. Is incremented by 1 each time the wire (73 or 74) to which is assigned is used (for the set number of times of one image formation), the wire (73 or 74) to which a register having a small count value is assigned is counted. There is also an aspect defined for use in the charging process. There is also a mode of counting up each time a one-page image is created.

Comparative Example The copying machine of FIG. 1 is a comparative example in which a charging voltage is simultaneously applied to two wires 73 and 74 of a charger 70 from a conventional high-voltage power supply circuit as in the conventional case. This comparative example also has a plurality of photosensitive member linear velocities, and operates at 352 mm / sec when passing plain paper and 176 mm / sec when passing thick paper. Table 1 shows the measurement results of the photosensitive member charging potential when the grid bias Vg and the wire current Ic are changed at the respective linear velocities. FIG. 6 is a graph showing the measurement results when Vg = −700 V in Table 1. Due to the linear velocity, a difference occurs in the charging potential even with the same grid bias Vg, and this difference cannot be eliminated even if the wire current is changed within a range in which proper discharge can be maintained.

Embodiment of the Present Invention As shown in FIG. 3, a separate high voltage power supply circuit 76 and 77 is connected to each of two wires 73 and 74 of a charger 70, and a high voltage from each power supply circuit to each wire is connected. The copying machine of FIG. 1 in which the output is individually turned on and off is taken as an embodiment of the present invention. The other configuration is the same as that of the comparative example. Table 2 shows the measurement results of the photosensitive member charging potential when the grid bias Vg and the wire current Ic are changed at the photosensitive member linear velocity of 352 mm / sec and 176 mm / sec. FIG. 5 is a graph showing the measurement results when Vg = −700 V in Table 2. Here, the wire current at a linear velocity of 352 mm / sec is a current value per wire, and the two wires are set to the same current. Therefore, the wire current of the entire scorotron (charger) is twice that of FIG. At a linear speed of 176 mm / sec, only the wire 73 positioned upstream in the photoconductor rotation direction is discharged, and no high voltage is applied to the downstream wire 74. By switching the number of wires according to the linear velocity, the charging potential can be made substantially the same if the grid bias is the same.

1 is a longitudinal sectional view of a copying machine according to an embodiment of the present invention. FIG. 2 is an enlarged view of one process cartridge 18 of the copying machine shown in FIG. 1. It is a block diagram which shows the combination of the charger 70 shown in FIG. 2, and the power supply circuit which supplies electric power to it. It is a flowchart which shows the logic which determines the wire used in the charging process of the process controller 90 shown in FIG. 4 is a graph showing a charging potential of the photoreceptor 40 when a charging voltage is applied only to one wire 73 of the charger 70 shown in FIG. 3. 4 is a graph showing a charging potential of the photosensitive member 40 when power is simultaneously supplied to two wires 73 and 74 of the charger 70 shown in FIG.

10: Intermediate transfer belt 11: Primary transfer rollers 14-16: Support roller 17: Intermediate transfer member cleaning device 18: Process cartridge 20: Image forming device 21: Laser exposure device 22: Secondary transfer roller 23: Roller 24: Conveyance Belt 25: fixing device 26: fixing belt 27: pressure roller 28: sheet reversing device 32: contact glass 33: first carriage 34: second carriage 35: imaging lens 36: CCD
40: photosensitive drum 42: paper feed roller 43: paper bank 44: paper feed cassette 45: separation roller 46: paper feed path 47: transport roller 48: paper feed path 49: registration roller 50: paper feed roller 51: manual feed tray 55: switching claw 56: discharge roller 57: discharge tray 60: developing device 61: developing roller 62, 63: screw 70: scorotron charger 71: casing 72: shielding wall 73, 74: wire 75: grid 80: lubricant Supply blade 81: Potential sensor 82: Static elimination lamp 83, 84: Brush roller 85: Cleaning blade

Claims (7)

An image carrier;
The image carrier including a casing, a grid, a plurality of discharge electrodes, and a plurality of high-voltage power supplies that individually output / stop a high voltage, wherein each of the plurality of discharge electrodes is connected to each of the plurality of high-voltage power supplies Charging device for charging
Exposure means for irradiating the charging surface of the image carrier with light to form an electrostatic latent image;
Developing means for developing the electrostatic latent image to form a toner image;
Transfer means for transferring the toner image onto a sheet; and
If the high-speed / low-speed designation data is low-speed designation, a small number of high-voltage power supplies specified by the wire designation data among the plurality of high-voltage power supplies are specified, and if the high-speed / low-speed designation data is high-speed designation, the wire designation data is involved. specifies the number of high-voltage power supply often without performing high pressure output to the discharge electrodes of the high-voltage power supply running set number of sheets image formation, to identify the high-voltage power supply of the small number in accordance slow specified imaging identified Control means for changing the wire instruction data to specify a small number of other high-voltage power supplies next time ;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the casing has a shielding wall that shields between adjacent discharge electrodes. Said image bearing member is a roller-shaped, the grid is a curved surface forming a part of the circumference of said image bearing member concentric with, the aperture ratio is 75 to 85%; claim 1 or 2 The image forming apparatus described in 1. The discharge electrodes may have a diameter are wires 25～55Myuemu: image forming apparatus according to any one of claims 1 to 3. The image forming apparatus according to claim 4 , wherein the wire has a surface coating of a noble metal having a thickness of 1 to 4 μm. The high voltage power supply to power the discharge current length per 9~18μA / cm of the wire; image forming apparatus according to claim 4 or 5. Easily removable process cartridge to the image forming apparatus main body, the image bearing member and the casing of the charging device, equipped with a grid and a plurality of discharge electrodes; according to any one of claims 1 to 6 Image forming apparatus.

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