JP6035212B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet.

  Conventionally, an image forming apparatus that forms an image on a sheet includes a photosensitive drum, a charging device, an exposure device, a developing device, a transfer device, and a fixing device. An electrostatic latent image is formed by the exposure device on the photosensitive drum charged by the charging device, and the electrostatic latent image is made visible as a toner image by the developing device. A transfer nip is formed between the photosensitive drum and the transfer device. Then, the toner image on the photosensitive drum is transferred to the sheet at the transfer nip portion. The sheet on which the toner image is transferred is subjected to a fixing process by a fixing device and then discharged.

  Patent Document 1 discloses a technique in which an amorphous silicon photoconductor is used as the photoconductor drum.

JP 2009-8828 A

  As described above, in the technique using the amorphous silicon photoconductor, the one in which the durable life of the main body of the apparatus achieves 500,000 or more printed sheets due to the long life characteristics of the photoconductor is the mainstream. On the other hand, when an abnormality occurs in the charging device or the developing device for some reason, toner fog occurs on the image. The cause of such toner fog is difficult to determine at the site where the image forming apparatus is installed. Therefore, in order to eliminate the occurrence of the toner fog, the maintenance worker often replaces both the charging device and the photosensitive unit including the photosensitive drum, and the developing device with new ones. As a result, there is a problem that the repair time of the image forming apparatus becomes longer and the service cost required for the repair increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that can quickly determine a unit that is the cause of occurrence of an image defect.

An image forming apparatus according to an aspect of the present invention includes an apparatus main body, a photosensitive drum that is driven to rotate, forms an electrostatic latent image on a peripheral surface, and carries a toner image, and the peripheral surface is made of amorphous silicon. A charging device disposed in contact with or in proximity to the peripheral surface of the photoconductive drum and charging the peripheral surface; and disposed so as to face the photoconductive drum, and rotated and driven to rotate the peripheral surface of the photoconductive drum. A developing unit that includes a developing roller that supplies toner to the surface, and is detachable from the apparatus main body; and a transfer unit that is disposed in the apparatus main body and transfers the toner image carried on the photosensitive drum onto a sheet. A static eliminator that performs a static elimination operation for neutralizing the peripheral surface of the photosensitive drum after the toner image has been transferred; and the photosensitive drum and the charger are integrally supported; A detachable drum unit, a charging bias in which an AC voltage is superimposed on a DC voltage, is applied to the charger, and a developing bias including at least a DC voltage is applied to the developing roller. A bias control unit for controlling the charging bias to be applied and the developing bias applied to the developing roller; an image forming control unit for controlling an image forming operation for forming the toner image on the sheet; and the photoreceptor. A mode control unit that executes a service mode for determining which of the developing unit and the drum unit is the cause of the image defect when an image defect occurs on the peripheral surface of the drum or the sheet; And the image forming control unit rotates the photosensitive drum during the image forming operation, In the state where the static elimination operation is performed, the bias control unit is controlled to apply the charging bias to the charger, thereby setting the surface potential of the photosensitive drum to a predetermined target potential, A mode control unit controls the bias applying unit in a state in which the photosensitive drum is rotated and the static elimination operation of the static eliminator is stopped when the service mode is executed, so that the absolute value is larger than the charging bias. Is applied to the charger to set the surface potential of the photosensitive drum to the target potential, and when the service mode is executed, the circumference of the photosensitive drum is set. On the surface, toner that has been charged by applying the determination bias to the charger and that has adhered to a region that has passed through a facing position where the developing roller faces is sealed. It is characterized in that it is transferred to the head.

According to this configuration, during the image forming operation, the image forming control unit rotates the photosensitive drum and controls the bias control unit in a state in which the static eliminator performs the static eliminating operation, so that the charging bias is charged. By applying the voltage to the photoconductor, the surface potential of the photosensitive drum is set to a predetermined target potential. As a result, the potential of the background portion of the photosensitive drum is set. When the charging performance of the charger is lowered, the actual potential of the background portion is lowered regardless of the setting of the potential by the image formation control unit. As a result, an image defect such as a toner fog in which the toner moves from the developing roller to the background portion occurs. On the other hand, when the charging performance of the toner in the developing unit decreases, image defects such as toner fog similarly occur. In this case, it is difficult for a maintenance operator of the image forming apparatus to determine which of the developing unit and the drum unit should be repaired or replaced. Even in such a case, according to the above configuration, the mode control unit rotates the photosensitive drum and stops the neutralization operation of the static eliminator when the service mode is executed. The surface potential of the photosensitive drum is set to the target potential by controlling and applying a bias for determination to the charger. For this reason, the surface potential of the photosensitive drum is directly set to the target potential regardless of a decrease in charging performance of the charger. As a result, when image quality defects such as toner fog still remain, the maintenance worker can determine that there is a high possibility that the development unit has a cause. When the image quality defect is eliminated, it can be determined that there is a high possibility that the drum unit has a cause. Therefore, it is possible to determine the unit causing the image defect at an early stage. Further, according to this configuration, it is possible to confirm on the sheet whether or not image defects remain with the execution of the service mode.

  In the above-described configuration, it is preferable that an operation unit is provided in the apparatus main body, to which a predetermined image forming operation condition is input, and an execution instruction for the service mode can be input from the operation unit.

  According to this configuration, the maintenance worker can instruct execution of the service mode from the operation unit. Therefore, it is possible to determine the unit that is the cause of the image defect early with a simple operation.

  In the above configuration, the toner has a positively charged polarity, the target potential is a predetermined positive polarity potential, and the DC voltage of the developing bias is a positive polarity potential smaller than the target potential. It is desirable to be.

  According to this configuration, the positively charged toner moves from the developing roller to the background portion of the photosensitive drum, thereby causing an image defect. Then, the unit that is the cause of the occurrence of the image defect can be determined at an early stage.

  In the above configuration, it is preferable that the static eliminator neutralizes the peripheral surface of the photosensitive drum with light.

  According to this configuration, during the image forming operation, the peripheral surface of the photosensitive drum is stably neutralized by the light emitted from the static eliminator. On the other hand, when the service mode is executed, the surface charge potential of the photosensitive drum can be set to the same potential as the determination bias applied to the charger by stopping the neutralization operation by light.

  In the above configuration, it is preferable that the mode control unit executes the service mode in order to determine a unit that is a cause of the toner fog generated on the peripheral surface of the photosensitive drum or the sheet.

  According to this configuration, it is possible to determine early the unit that is the cause of occurrence of toner fog.

  According to the present invention, there is provided an image forming apparatus capable of early determining a unit that is the cause of occurrence of an image defect.

1 is a cross-sectional view schematically showing an internal structure of an image forming apparatus according to an embodiment of the present invention. 2 is a schematic cross-sectional view of the periphery of an image forming unit according to an embodiment of the present invention. FIG. 1 is an electrical block diagram of an image forming apparatus according to an embodiment of the present invention. In the image forming apparatus according to an embodiment of the present invention, FIG. 5 is a flowchart of an operation including a service mode according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an internal structure of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a part of the image forming unit 32 of the image forming apparatus 1. Note that FIG. 2 shows the image upside down and left and right reversed in FIG. FIG. 2 illustrates one of the units 32Y to 32Bk of the image forming unit 32 described later arranged corresponding to a plurality of colors. Here, the image forming apparatus 1 is exemplified by a color multifunction machine having a printer function and a copying function. However, the image forming apparatus may be a printer, a copying machine, a facsimile machine, or a monochrome machine. Good. Note that the terms used in the following description, such as “up”, “down”, “front”, “rear”, “left” and “right”, are merely for the purpose of clarifying the description. There is no limitation on the principle of the image forming apparatus.

<Description of Image Forming Apparatus>
The image forming apparatus 1 includes an apparatus main body 10 having a substantially rectangular parallelepiped housing structure, and an automatic document feeder 20 disposed on the apparatus main body 10. In the apparatus main body 10, a reading unit 25 that optically reads a document image to be copied, an image forming unit 30 that forms a toner image on a sheet, a fixing unit 60 that fixes the toner image on a sheet, and image formation A sheet feeding unit 40 for storing sheets conveyed to the unit 30, and a conveyance path 50 for conveying the sheet from the sheet feeding unit 40 or the sheet feeding tray 46 to the sheet discharge port 10E via the image forming unit 30 and the fixing unit 60. And a conveyance unit 55 having therein a sheet conveyance path constituting a part of the conveyance path 50 is accommodated.

  An automatic document feeder (ADF) 20 is rotatably attached to the upper surface of the apparatus body 10. The ADF 20 automatically feeds a document sheet to be copied toward a predetermined document reading position in the apparatus main body 10. On the other hand, when the user manually places the document sheet on a predetermined document reading position, the ADF 20 is opened upward. The ADF 20 includes a document tray 21 on which a document sheet is placed, a document transport unit 22 that transports a document sheet via an automatic document reading position, and a document discharge tray 23 that discharges a document sheet after reading. .

  The reading unit 25 optically reads an image of a document sheet automatically fed from the ADF 20 on the upper surface of the apparatus main body 10 or a manually placed document sheet. In the reading unit 25, a scanning mechanism including a light source, a movable carriage, a reflection mirror, and the like, and an image sensor are accommodated (not shown). The scanning mechanism irradiates the original sheet with light and guides the reflected light to the image sensor. The image sensor photoelectrically converts the reflected light into an analog electric signal. The analog electric signal is converted into a digital electric signal by an A / D conversion circuit and then input to the image forming unit 30.

  The image forming unit 30 performs a process of generating a full-color toner image and transferring it onto a sheet. Yellow (Y), magenta (M), cyan (C), and black (Bk) arranged in tandem. An image forming unit 32 including four units 32Y, 32M, 32C, and 32Bk for forming the respective toner images, an intermediate transfer unit 33 disposed adjacent to the image forming unit 32, and an intermediate transfer unit 33. And a toner replenishing section 34 disposed in the.

  Each of the units 32Y to 32Bk of the image forming unit 32 includes a photosensitive drum 321 (image carrier), a charger 322, an exposure device 323, a developing device 324, a cleaning device 326, and a static eliminator 328 (FIG. 3). ). In each unit, the photosensitive drum 321, the charger 322, the cleaning device 326, and the charge eliminator 328 can be integrally attached to and detached from the apparatus main body 10 as a drum unit 321 </ b> H (FIG. 2). The In other words, the drum unit 321H integrally supports at least the photosensitive drum 321 and the charger 322, and is detachable from the apparatus main body 10.

  The photosensitive drum 321 has a cylindrical shape. The photosensitive drum 321 has an electrostatic latent image formed on its peripheral surface, and carries a toner image (developer image) corresponding to the electrostatic latent image on the peripheral surface. The photosensitive drum 321 is disposed to face the intermediate transfer belt 331. In FIG. 2, the intermediate transfer belt 331 is not shown. The photoconductor drum 321 is a photoconductor whose peripheral surface is made of amorphous silicon. The photosensitive drum 321 is rotationally driven in a predetermined rotational direction (the arrow direction in FIG. 2) by the drive unit 83 described later.

  The charger 322 is applied with a predetermined voltage and charges the peripheral surface of the photosensitive drum 321 substantially uniformly. In this embodiment, the charger 322 is a charging roller that contacts the circumferential surface of the photosensitive drum 321 and rotates following the photosensitive drum 321. The charger 322 is formed by arranging an elastic roller around a metal shaft (not shown). A charging bias is applied to the charger 322 from a bias applying unit 80 described later. In other embodiments, the charger 322 may be disposed close to the peripheral surface of the photosensitive drum 321.

  The exposure device 323 irradiates the peripheral surface of the photosensitive drum 321 charged by the charger 322 with laser light. The laser light is emitted in accordance with image data output from an external device (not shown) such as a personal computer that is communicably connected to the image forming apparatus 1. As a result, an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 321.

  The developing device 324 (developing unit) develops the electrostatic latent image formed on the peripheral surface of the photosensitive drum 321. When the developing device 324 supplies toner to the photosensitive drum 321, the electrostatic latent image formed on the peripheral surface of the photosensitive drum 321 is developed (visualized). As a result, a toner image (developer image) is formed on the peripheral surface of the photosensitive drum 321. The developing device 324 is detachable from the apparatus main body 10. The developing device 324 includes a developing roller 324A (FIG. 2). The developing roller 324A is disposed to face the photosensitive drum 321 and is rotationally driven by a driving unit 83 described later. The developing roller 324A supplies toner to the peripheral surface of the photosensitive drum 321 on which the electrostatic latent image is formed. Specifically, a developing bias is applied to the developing roller 324A by a bias applying unit 80 described later. The toner is moved from the developing roller 324A to the photosensitive drum 321 by the potential difference between the developing roller 324A and the electrostatic latent image formed on the peripheral surface of the photosensitive drum 321. The developing device 324 contains a one-component developer made of magnetic toner. In this embodiment, the toner has a characteristic of being charged to a positive polarity. In another embodiment, the developing device 324 may contain a one-component developer made of a nonmagnetic toner or a two-component developer made of a nonmagnetic toner and a magnetic carrier.

  The cleaning device 326 removes the toner remaining on the peripheral surface of the photosensitive drum 321 after the toner image is transferred to the sheet S1. The cleaning device 326 includes a plate-shaped cleaning blade (FIG. 2). The toner remaining on the photosensitive drum 321 is scraped off by the cleaning blade. As shown in FIG. 1, the cleaning device 326 may be provided with a cleaning roller instead of the cleaning blade. The peripheral surface of the photosensitive drum 321 cleaned by the cleaning device 326 passes under the charger 322 again and is uniformly charged. Thereafter, the above-described toner image is newly formed.

  The static eliminator 328 (FIG. 2) is disposed between the primary transfer roller 325 and the cleaning device 326 described later in the rotation direction of the photosensitive drum 321. The static eliminator 328 performs a static elimination operation for neutralizing charges on the peripheral surface of the photosensitive drum 321 after the toner image is transferred to the intermediate transfer belt 331. In the present embodiment, the static eliminator 328 irradiates the peripheral surface of the photosensitive drum 321 with static elimination light (light). The charge on the photosensitive drum 321 is neutralized by the neutralizing light. The static elimination operation of the static eliminator 328 is controlled by a check mode control unit 94 and an image formation control unit 95 described later.

  The intermediate transfer unit 33 includes an intermediate transfer belt 331, a driving roller 332, a driven roller 333, and a primary transfer roller 325. The intermediate transfer belt 331 is an endless belt that is stretched around a driving roller 332 and a driven roller 333, and toner images from a plurality of photosensitive drums 321 are superimposed on the same portion on the outer peripheral surface of the intermediate transfer belt 331. Is transcribed. The intermediate transfer belt 331 is rotated counterclockwise in FIG.

  The primary transfer roller 325 forms a nip portion with the photosensitive drum 321 across the intermediate transfer belt 331 of the intermediate transfer unit 33, and primarily transfers the toner image on the photosensitive drum 321 onto the intermediate transfer belt 331. .

  A secondary transfer roller 35 is disposed to face the peripheral surface of the drive roller 332. The nip portion between the driving roller 332 and the secondary transfer roller 35 becomes a secondary transfer portion that transfers the full-color toner image overcoated on the intermediate transfer belt 331 to the sheet S1. A secondary transfer bias potential having a polarity opposite to that of the toner image is applied to the driving roller 332, and the secondary transfer roller 35 is grounded. In addition, the density sensor 35 </ b> A is disposed opposite to the circumferential surface of the intermediate transfer belt 331 at a position upstream of the drive roller 332 in the rotation direction of the intermediate transfer belt 331. The density sensor 35A outputs an electrical signal corresponding to the density of the image formed on the intermediate transfer belt 331. The intermediate transfer unit 33 and the secondary transfer roller 35 function as a transfer unit of the present embodiment. The transfer unit is disposed in the apparatus main body 10 and transfers the toner image carried on the photosensitive drum 321 to the sheet S1.

  The toner supply unit 34 includes a yellow toner container 34Y, a magenta toner container 34M, a cyan toner container 34C, and a black toner container 34Bk. These toner containers 34Y, 34C, 34M, and 34Bk store toners of the respective colors, and are supplied to the developing devices 324 of the units 32Y, 32M, 32C, and 32Bk corresponding to the respective colors of YMCBk through supply paths (not shown). Supply toner.

  The paper feed unit 40 includes two-stage paper feed cassettes 40A and 40B that accommodate sheets S1 on which image forming processing is performed. These paper feed cassettes 40A and 40B can be pulled out from the front of the apparatus body 10 toward the front.

  The fixing unit 60 is an induction heating type fixing device that performs a fixing process for fixing the toner image on the sheet S <b> 1, and includes a heating roller 61, a fixing roller 62, a pressure roller 63, a fixing belt 64, and an induction heating unit 65. . A pressure roller 63 is pressed against the fixing roller 62 to form a fixing nip portion. The heating roller 61 and the fixing belt 64 are induction-heated by an induction heating unit 65, and give the heat to the fixing nip portion. As the sheet S1 passes through the fixing nip portion, the toner image transferred to the sheet S1 is fixed to the sheet S1.

  Next, the electrical configuration of the image forming apparatus 1 will be described. FIG. 3 is an electrical block diagram of the image forming apparatus 1.

  The image forming apparatus 1 includes a control unit 90 that controls the operation of each unit disposed inside the apparatus main body 10. The control unit 90 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a control program, a RAM (Random Access Memory) that is used as a work area of the CPU, and the like. The control unit 90 includes a drive control unit 91, an applied voltage control unit 92, a storage unit 93, a check mode control unit 94, and an image formation control unit 95 by causing the CPU to execute a control program stored in the ROM. To function. In addition to the photosensitive drums 321, the charger 322, the developing device 324, and the charge eliminator 328 of each color of the image forming unit 32, the bias applying unit 80 and the driving unit 83 are electrically connected to the control unit 90. ing.

  The bias applying unit 80 applies a charging bias in which an AC voltage is superimposed on a DC voltage to the charger 322. The bias applying unit 80 applies a developing bias in which an alternating voltage is superimposed on a direct current voltage to the developing roller 324A. In another embodiment, the bias applying unit 80 may apply a developing bias consisting of only a DC voltage to the developing roller 324A. The bias applying unit 80 includes an AC constant voltage power supply 81 and a DC constant voltage power supply 82. As described above, the bias applying unit 80 includes a high-voltage power source that can apply a direct current and an alternating voltage. The bias applying unit 80 is controlled by an applied voltage control unit 92 described later.

  The drive unit 83 drives each member inside the image forming apparatus 1. The driving unit 83 is a motor that rotationally drives the photosensitive drums 321 of the respective colors of the image forming unit 32, the developing roller 324A of the developing device 324, and the like.

  The drive control unit 91 controls the drive unit 83 according to the image forming operation of the image forming apparatus 1 to rotationally drive each member inside the image forming apparatus 1.

  The applied voltage control unit 92 (bias control unit) controls the bias applied to each member inside the image forming apparatus 1. In particular, the applied voltage control unit 92 controls the bias application unit 80 to control the charging bias applied to the charger 322 in order to form an electrostatic latent image on the photosensitive drum 321. Further, the bias applying unit 80 controls the developing bias applied to the developing roller 324A in order to develop the electrostatic latent image.

  The storage unit 93 stores drive timing information of each member referred to by the drive control unit 91. In addition, the storage unit 93 stores setting values for the charging bias and the developing bias referred to by the applied voltage control unit 92.

  The check mode control unit 94 (mode control unit) executes a maintenance check mode (service mode) described later. Specifically, the check mode control unit 94 determines whether the image defect is caused by the developing device 324 or the drum unit 321H when an image defect occurs on the peripheral surface of the photosensitive drum 321 or the sheet S1. Execute the maintenance check mode for At this time, when executing the maintenance check mode, the check mode control unit 94 controls the applied voltage control unit 92 in a state where the photosensitive drum 321 is rotated and the charge removal operation of the charge eliminator 328 is stopped. By applying a later-described determination bias VC to the device 322, the surface potential of the photosensitive drum 321 is set to a predetermined target potential VB1 (= VC).

  The image forming control unit 95 controls an image forming operation in which a toner image is formed on the sheet S <b> 1 in the image forming apparatus 1. The image formation control unit 95 rotates the photosensitive drum 321 during the image formation operation, and controls the applied voltage control unit 92 in a state where the charge removal unit 328 performs the charge removal operation, so that the charging bias is supplied to the charger 322. To set the surface potential of the photosensitive drum 321 to the predetermined target potential VB1. The target potential VB1 will be described in detail later.

  Next, an image forming operation executed in the image forming apparatus 1 will be described. FIG. 4 is a schematic diagram illustrating the relationship between the surface potential of the photosensitive drum 321 of the image forming apparatus 1 and the DC component VD of the developing bias applied to the developing roller 324A. FIG. 4A shows a relationship in a normal image forming operation.

  When the image forming operation is started in the image forming apparatus 1, the image forming control unit 95 described above rotates the photosensitive drum 321 and the intermediate transfer belt 331, and applies the voltage in a state where the static eliminator 328 executes the static eliminating operation. By controlling the voltage control unit 92 to apply the charging bias to the charger 322, the surface potential of the photosensitive drum 321 is set to the target potential VB1. In the present embodiment, the target potential VB1 is set to 300 V having a positive polarity. At this time, a charging bias in which an AC voltage of 1200 V (peak-to-peak voltage) is superimposed on a DC voltage of 450 V is applied from the bias applying unit 80 to the charger 322.

  Further, the applied voltage control unit 92 controls the bias applying unit 80 to apply a developing bias VD having a DC voltage of +150 V to the developing roller 324A. That is, the DC voltage of the developing bias VD is a positive polarity potential smaller than the target potential VB1. The target potential VB1 corresponds to the potential of the background portion of the electrostatic latent image formed on the photosensitive drum 321. When the image portion is exposed by the exposure device 323, the potential of the image portion is set to an image portion potential VI1 that is smaller than the developing bias VD (FIG. 4A).

  The toner moves from the developing roller 324A to the photosensitive drum 321 by the potential difference between the developing bias VD and the image portion potential VI1. On the other hand, the background portion of the photosensitive drum 321 is set to a larger potential (target potential VB1) with a potential difference of 150 V than the developing bias VD. For this reason, the occurrence of toner fog in which the toner moves from the developing roller 324A to the background portion of the photosensitive drum 321 is prevented. The toner image formed on the photosensitive drum 321 by supplying toner from the developing roller 324A is transferred to the intermediate transfer belt 331 by the primary transfer roller 325 (FIG. 1), and then the sheet is transferred by the secondary transfer roller 35. Transferred to S1. The peripheral surface of the photosensitive drum 321 after the toner image is transferred to the intermediate transfer belt 331 is neutralized by the static eliminator 328. Further, the toner remaining on the peripheral surface of the photosensitive drum 321 is removed by the cleaning device 326. Thereafter, the peripheral surface of the photosensitive drum 321 is charged again by the charger 322, and the same image forming operation as described above is repeated.

  As described above, in this embodiment, an amorphous silicon photoconductor is used as the photoconductor drum 321. In this embodiment, the durable life of the image forming apparatus 1 is set to 500,000 or more printed sheets due to the long life characteristics of the amorphous silicon photoconductor. However, as the image forming apparatus 1 is used, the above-described toner fog may occur on the image formed on the sheet S1. The toner fog is an image defect in which the toner adheres to the background portion of the sheet S1 and is lightly colored. As a cause of the toner fog, defects such as the photosensitive drum 321, the charger 322, the developing device 324, the primary transfer roller 325, and the like can be considered, but defects in the charger 322 and the developing device 324 are often caused.

  When the occurrence of the toner fog is caused by the charger 322, it is possible that a predetermined charging potential cannot be obtained on the photosensitive drum 321 due to adhesion of discharge products or the like on the surface of the charger 322. . FIG. 4B is a schematic diagram showing the relationship between the surface potential VB2 of the photosensitive drum 321 and the DC component of the developing bias VD when the charging performance of the charger 322 is lowered. The applied voltage control unit 92 refers to a predetermined set value for obtaining the above-described target potential VB1 from the storage unit 93, and controls the bias applying unit 80. However, if the surface resistance of the charger 322 is increased, even if a charging bias based on the set value is applied to the charger 322, the surface potential of the photosensitive drum 321 is lower than the target potential VB1. Is charged. For example, the surface potential VB2 is + 250V. Note that the potential of the image portion of the photosensitive drum 321 decreases to VI2, which is lower than VI1. Then, when the surface potential of the background portion of the photosensitive drum 321 is closer to the developing bias VD than the target potential VB1 (arrow D51 in FIG. 4B), toner is transferred from the developing roller 324A to the surface of the photosensitive drum 321. It moves (arrow D52 in FIG. 4B). That is, a toner fog is generated in which toner adheres to the photosensitive drum 321 with respect to the background portion of the electrostatic latent image on the photosensitive drum 321. In this case, the toner fog is eliminated by replacing the drum unit 321H including the charger 322.

  On the other hand, when the occurrence of toner fog is caused by the developing device 324, it may be caused by a decrease in chargeability of the toner in the developing device 324 or a defective application of the developing bias to the developing roller 324A. In this case, the toner fog is eliminated by replacing the developing device 324.

  As described above, when the toner fog occurs in the image forming apparatus 1, the toner fog is often eliminated by replacing the drum unit 321H or the developing device 324. However, it is difficult to determine the cause of such toner fog at the site where the image forming apparatus 1 is installed. Therefore, in order to eliminate the occurrence of the toner fog, the maintenance worker often replaces both the drum unit 321H including the charger 322 and the photosensitive drum 321 and the developing device 324 with new ones. As a result, there is a problem that the repair time of the image forming apparatus 1 becomes longer and a service cost required for the repair increases due to an erroneous replacement of a unit having no problem.

  In order to solve the above-described problem, in the present exemplary embodiment, the maintenance check mode is executed in the image forming apparatus 1 so that the unit that causes the toner fog can be determined. In the present embodiment, the maintenance check mode is executed by paying attention to whether the cause of toner fog is the charger 322 or not.

  As described above, in a normal image forming operation, the peripheral surface of the photosensitive drum 321 is charged by the charger 322 in a state in which the static elimination operation of the static eliminator 328 is performed. When the static eliminator 328 irradiates the peripheral surface of the photosensitive drum 321 with static elimination light, charge carriers are generated in the amorphous silicon layer on the peripheral surface of the photosensitive drum 321. The generation of the charge carriers partially inhibits charging of the photosensitive drum 321 by the charger 322. For this reason, the target potential VB 1 of the photosensitive drum 321 does not match the DC voltage of the charging bias applied to the charger 322. That is, in order to set the surface potential of the photosensitive drum 321 to the target potential VB1, it is necessary to apply a charging bias including a DC voltage (450 V) higher than the target potential VB1 to the charger 322 as described above. .

  On the other hand, in the state where the static elimination operation of the static eliminator 328 is stopped, the generation of charge carriers as described above is suppressed. In this case, when a charging bias is applied to the charger 322 while the photosensitive drum 321 is rotated for several rotations, the DC voltage of the charging bias and the surface potential of the photosensitive drum 321 substantially coincide. Therefore, the surface potential of the photosensitive drum 321 can be reliably set to a desired potential without being affected by the resistance change of the charger 322. In the present embodiment, in the maintenance check mode to be described later, a determination bias VC including a DC voltage smaller than the charging bias during the image forming operation is applied to the charger 322 in a state where the neutralization operation of the neutralizer 328 is stopped. Is done. When the static elimination operation of the static eliminator 328 is stopped, the charging of the photosensitive drum 321 by the charger 322 is not easily inhibited. Therefore, although the absolute value of the DC voltage of the determination bias VC is smaller than the absolute value of the DC voltage of the charging bias during the image forming operation, the surface potential of the photosensitive drum 321 is caused by the determination bias VC. The target potential VB1 is set.

  Next, the restoration operation of the image forming apparatus 1 including the maintenance check mode (service mode) in the present embodiment will be described. FIG. 5 is a flowchart showing a flow until the maintenance check mode is executed and the developing device 324 or the drum unit 321H is replaced in the image forming apparatus 1. Hereinafter, with reference to FIG. 5, a restoration operation in a unit corresponding to one color of the image forming units 32 will be described.

  When the occurrence of toner fog is confirmed in the image forming apparatus 1, a maintenance operator of the image forming apparatus 1 inputs an instruction to execute a maintenance check mode from an operation unit (not shown) provided in the image forming apparatus 1. Upon receipt of the execution instruction, the check mode control unit 94 (FIG. 3) stops the static elimination operation of the static eliminator 328 (step # 1 in FIG. 5). Next, the check mode control unit 94 controls the driving unit 83 to rotate the photosensitive drum 321 (step # 2 in FIG. 5). At this time, the intermediate transfer belt 311 is also rotated at the same time. Further, the check mode control unit 94 controls the bias applying unit 80 to turn on the charging bias applied to the charger 322 and the developing bias applied to the developing roller 324A (step # 3 in FIG. 5). As a result, a determination bias VC composed of a DC voltage and an AC voltage is applied to the charger 322. The DC voltage of the determination bias VC corresponds to a DC voltage having the same bias value as the target potential VB1 in the image forming operation. FIG. 4C is a schematic diagram showing the relationship between the surface potential of the photosensitive drum 321 and the developing bias VD at this time. As described above, in the state in which the static elimination operation of the static eliminator 328 is stopped in Step # 1, the relationship of determination bias VC applied to the charger 322 = surface potential of the photosensitive drum 321 is substantially satisfied. Therefore, the surface potential of the photosensitive drum 321 is set to the target potential VB1 by the charger 322 to which the determination bias VC is applied. In this case, as described above, it is difficult for the toner to move from the developing roller 324A to the photosensitive drum 321 and the occurrence of toner fog is suppressed.

  With the bias applied to the charger 322 and the developing roller 324A, the photosensitive drum 321 is rotated and rotated three times. In this state, it is confirmed by a maintenance worker whether toner fog is generated on the peripheral surface of the photosensitive drum 321 (step # 4 in FIG. 5). Alternatively, the check mode control unit 94 is charged by applying the determination bias VC to the charger 322 on the peripheral surface of the photosensitive drum 321, and the developing roller 324 </ b> A faces the photosensitive drum 321. The toner adhering to the region that has passed the facing position is transferred to the sheet S1 via the intermediate transfer belt 331. As a result, it is confirmed by the maintenance worker whether toner fogging has occurred on the sheet S1 (step # 4 in FIG. 5). Note that when the toner does not adhere to the peripheral surface of the photosensitive drum 321, the sheet S <b> 1 is discharged as white paper. As a result, with the execution of the maintenance check mode, it can be confirmed on the sheet S1 whether or not the toner fog remains.

  In step # 4, if toner fog has occurred on the peripheral surface of the photosensitive drum 321 or the sheet S1 (YES in step # 4), the maintenance worker may indicate that the cause of toner fog is in the developing device 324. Is determined by As a result, the developing device 324 is replaced by the maintenance worker (step # 5 in FIG. 5). Note that a defective portion of the developing device 324 may be repaired by a maintenance worker.

  On the other hand, if no toner fog occurs on the peripheral surface of the photosensitive drum 321 or the sheet S1 in step # 4 (NO in step # 4), the cause of the toner fog is caused by the drum unit 321H including the charger 322. It is determined that there is a maintenance worker. As a result, the drum unit 321H is replaced by the maintenance worker (step # 6 in FIG. 5). Note that a defective portion of the drum unit 321H may be repaired by a maintenance worker.

  As described above, according to the present embodiment, it is possible to quickly determine a unit that causes toner fog among the developing device 324 and the drum unit 321H. As a result, the repair time of the image forming apparatus 1 is shortened and an increase in service cost required for the repair is prevented. Further, the maintenance worker can instruct execution of the maintenance check mode from an operation unit (not shown). Therefore, it is possible to determine the unit that is the cause of the image defect early with a simple operation.

  Further, in this embodiment, during the image forming operation, the peripheral surface of the photosensitive drum 321 is stably discharged by the discharging light emitted from the discharging device 328. On the other hand, when the maintenance check mode is executed, the surface potential of the photosensitive drum 321 can be set to the same potential as the determination bias VC applied to the charger 322 by stopping the neutralization operation by the neutralization light. .

  Note that when a plurality of image forming units 32Y to 32Bk are arranged in the apparatus main body 10 of the image forming apparatus 1 as in the present embodiment, the cause of occurrence of toner fog as described above is identified and repaired. A lot of time is required. Even in such a case, the cause of occurrence of toner fog is identified early by executing the maintenance check mode. Note that the maintenance check mode described above may be executed simultaneously for each color unit 32Y to 32Bk. Even in this case, the unit (developing device 324 or drum unit 321H) to be repaired in each of the color units 32Y to 32Bk can be specified based on the presence or absence of the toner fog of each color on one sheet S1.

  The image forming apparatus 1 (image forming apparatus) according to the embodiment of the present invention has been described above. However, the present invention is not limited to this, and for example, the following modified embodiment can be taken.

  (1) In the above embodiment, the description has been given using the toner fog as the image defect generated in the toner image on the sheet S1, but the present invention is not limited to this. When the surface potential of the photosensitive drum 321 becomes unstable due to the charger 322, even if another image defect occurs in the toner image on the sheet S1, the same maintenance check mode is used. May be executed.

  (2) In the above-described embodiment, the configuration in which the static eliminator 328 is supported by the drum unit 321H has been described, but the present invention is not limited to this. The static eliminator 328 may be fixed to the apparatus main body 10 side.

  (3) In the above-described embodiment, the intermediate transfer unit 33 including the intermediate transfer belt 331 has been described. However, the present invention is not limited to this. The toner image may be directly transferred from the photosensitive drum 321 to the sheet S1. In this case, a transfer roller (not shown) disposed to face the photosensitive drum 321 functions as a transfer unit.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Apparatus main body 30 Image forming part 32 Image forming unit 33 Intermediate transfer unit (transfer part)
35 Secondary transfer roller (transfer section)
DESCRIPTION OF SYMBOLS 80 Bias application part 81 AC constant voltage power supply 82 DC constant voltage power supply 83 Drive part 90 Control part 91 Drive control part 92 Applied voltage control part (bias control part)
93 Storage Unit 94 Check Mode Control Unit (Mode Control Unit)
95 Image Formation Control Unit 321 Photosensitive Drum 321H Drum Unit 322 Charger 323 Exposure Device 324 Development Device (Development Unit)
325 Primary transfer roller 326 Cleaning device 328 Static eliminator

Claims (5)

The device body;
A photosensitive drum that is driven to rotate and forms an electrostatic latent image on the peripheral surface and carries a toner image, and the peripheral surface is made of amorphous silicon;
A charger that is disposed in contact with or close to the peripheral surface of the photosensitive drum and charges the peripheral surface;
A developing unit that is disposed opposite to the photosensitive drum and that is rotationally driven to supply toner to the peripheral surface of the photosensitive drum;
A transfer unit disposed in the apparatus main body and configured to transfer the toner image carried on the photosensitive drum to a sheet;
A static eliminator for performing a static elimination operation for neutralizing the peripheral surface of the photosensitive drum after the toner image is transferred;
A drum unit that integrally supports the photosensitive drum and the charger and is detachable from the apparatus main body;
A bias applying unit that applies a charging bias in which an AC voltage is superimposed on a DC voltage to the charger, and applies a developing bias including at least a DC voltage to the developing roller;
A bias controller for controlling the charging bias applied to the charger and the developing bias applied to the developing roller;
An image forming control unit for controlling an image forming operation in which the toner image is formed on the sheet;
Mode control for executing a service mode for determining which of the developing unit and the drum unit is the cause of the image defect when an image defect occurs on the peripheral surface or the sheet of the photosensitive drum And
The image forming control unit rotates the photosensitive drum during the image forming operation, and controls the bias control unit in a state in which the static eliminator performs the static eliminating operation, thereby charging the charging bias with the charging bias. The surface potential of the photosensitive drum is set to a predetermined target potential
The mode control unit controls the bias applying unit in a state where the photosensitive drum is rotated and the static elimination operation of the static eliminator is stopped when the service mode is executed, and is more absolute than the charging bias. By applying a bias for determination including a DC voltage having a small value to the charger, the surface potential of the photosensitive drum is set to the target potential, and further, when the service mode is executed, the surface of the photosensitive drum is The toner charged on the peripheral surface when the bias for determination is applied to the charger and attached to a region passing through a facing position where the developing roller faces is transferred to a sheet. Image forming apparatus. An operation unit disposed in the apparatus main body, to which a predetermined image forming operation condition is input;
The image forming apparatus according to claim 1, wherein an instruction to execute the service mode can be input from the operation unit. The toner has a positively charged polarity,
The target potential is a predetermined potential having a positive polarity,
Wherein the DC voltage of the developing bias, an image forming apparatus according to claim 1 or 2, characterized in that than the target potential is the potential of small positive polarity. The discharger, an image forming apparatus according to any one of claims 1 to 3, characterized in that to neutralize the circumferential surface of the photosensitive drum by light. The mode control unit, to determine the which is the circumferential surface or cause toner fog generated on the sheet of the photosensitive drum unit, according to claim 1, wherein performing said service mode The image forming apparatus according to any one of the above.

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