JP2018017868A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus capable of detecting a maximum scraped amount of a photosensitive layer in a direction along the rotation axis of an image carrier with high accuracy and setting adequate charging conditions.SOLUTION: The image formation apparatus includes an image carrier, a charging device, a developing device, a transfer member, a charge bias power source, a transfer bias power source and a control unit. The control unit can execute such a charge bias correction control by: calculating a maximum scraped amount Smax of the photosensitive layer in a direction along the rotation axis of the image carrier from an expression Smax=α*Ta+β*Tb+γ*Tc using scraped amounts α, β, γ of the photosensitive layer per unit drive amount of the image carrier and cumulative drive amounts Ta, Tb, Tc of the image carrier; and correcting a charge bias based on the calculated maximum scraped amount Smax.SELECTED DRAWING: Figure 6

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, the surface potential of an image carrier when a recording medium having a size smaller than the maximum width is used. It is related with the method of suppressing the fluctuation | variation.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, etc., a powdery developer (toner) is mainly used, and a photosensitive layer on the surface of a photosensitive drum (image carrier) is predetermined by a charging device. After charging to a surface potential (same polarity as the charging polarity of the toner), an electrostatic latent image is formed on the photosensitive drum by the exposure device. Then, the formed electrostatic latent image is visualized with toner in the developing device, and the toner image is recorded on a recording medium that passes through a nip portion (transfer nip portion) between the photosensitive drum and a transfer member that contacts the photosensitive drum. Generally, a process of performing a fixing process after the image is transferred to the sheet. At this time, the transfer process of the toner image to the recording medium is performed in a state where a transfer voltage or a transfer current having a polarity opposite to the toner charging polarity is applied to the transfer member.

  By the way, in the case of a photosensitive drum having an organic photosensitive layer (OPC), the photosensitive layer may be worn and thinned due to durability, and the surface potential may be lowered. Specifically, the photosensitive layer is scraped and thinned by friction between the photosensitive drum and a member such as a cleaning blade that contacts the photosensitive drum. When the surface potential of the photosensitive drum decreases, problems such as fogging occur.

  In order to avoid problems due to the thinning of the photosensitive layer, it is common to correct the charging condition by detecting the number of printed sheets, the cumulative driving time or the cumulative rotational speed of the photosensitive drum. As a correction method for reducing the thickness of the photosensitive layer, a charging condition for ensuring a predetermined surface potential according to the layer thickness of the photosensitive layer is set, and the amount of the photosensitive layer that has been scraped in advance corresponding to the number of printed sheets and the driving time is set in advance. I ask you to. Then, in the durability test, the photosensitive layer thickness at a predetermined cumulative driving time is calculated, and the charging output setting is changed according to the calculated photosensitive layer thickness. As a parameter for changing the charging output, it is common to control the charging application current and grid voltage in the scorotron charging method, and to control the applying voltage or charging current in the contact charging method using a charging roller or the like.

  In recent years, the life of photoconductor units has been extended, and a photoconductive drum having an organic photoconductive layer having a durable life of 100,000 sheets or more has been developed. In order to extend the lifetime, the wear resistance of the organic photosensitive layer is being improved, but studies are being made to use it until the photosensitive layer becomes thinner than before. When used in a range where the amount of abrasion of the photosensitive layer is large, prediction of uneven wear of the photosensitive layer becomes a problem as well as improvement in accuracy of prediction of the amount of abrasion of the photosensitive layer.

  Factors that cause uneven wear of the photosensitive layer include variations in the rotation axis direction of the photosensitive drum, print image pattern such as presence or absence of solid (solid) area, ratio of large size paper to small size paper, continuous printing and intermittent printing Although there are printing patterns such as a ratio, uneven wear becomes more prominent when a large number of small-size sheets are printed. Conventionally, charging conditions corresponding to film removal of the photosensitive layer have been changed based on the amount of scraping of the maximum size paper, but an increasing number of users use small size paper from the viewpoint of resource saving and cost reduction. As a result, uneven wear on small-size paper is not negligible for long-life design.

  Therefore, for example, in Patent Document 1, a charging unit and an exposure unit are used to charge a sheet passing portion of a photosensitive drum to a first potential before image formation, and a non-sheet passing portion is potential difference from a potential before exposure. An image forming apparatus is disclosed in which a difference in wear rate between a sheet passing portion and a non-sheet passing portion is reduced by charging to a second potential whose absolute value is greater than the first potential.

JP 2012-173382 A

  However, in the method disclosed in Patent Document 1, it is necessary to charge the sheet passing portion and the non-sheet passing portion of the photosensitive drum to different potentials before image formation, which makes it difficult to control the charging unit and the exposure unit. There was a problem.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of accurately detecting uneven wear of a photosensitive layer in the rotation axis direction of an image carrier and setting appropriate charging conditions.

In order to achieve the above object, a first configuration of the present invention includes an image carrier, a charging device, a developing device, a transfer member, a charging bias power source, a transfer bias power source, and a control unit. An image forming apparatus. A photosensitive layer is formed on the surface of the image carrier. The charging device charges the surface of the image carrier with the same polarity as the charging polarity of the toner. The exposure device exposes and scans the surface of the image carrier uniformly charged by the charging device to form an electrostatic latent image on the image carrier. The developing device is disposed on the downstream side of the charging device with respect to the rotation direction of the image carrier, and forms a toner image on the image carrier by attaching toner to the electrostatic latent image. The transfer member is disposed on the downstream side of the developing device with respect to the rotation direction of the image carrier so as to contact the image carrier to form a transfer nip portion, and transfers the toner image to a recording medium passing through the transfer nip portion. . The charging bias power source applies a charging bias to the charging device. The transfer bias power source applies a transfer bias having a polarity opposite to the charging polarity of the toner or a transfer reverse bias having the same polarity as the charging polarity of the toner to the transfer member. The control unit controls the charging bias power source and the transfer bias power source. The control unit calculates the maximum scraping amount Smax of the photosensitive layer in the rotation axis direction of the image carrier by the following formula (1), and also corrects the charging bias based on the calculated maximum scraping amount Smax. Can be executed.
Smax = α * Ta + β * Tb + γ * Tc (1)
However,
α: Abrasion amount of the photosensitive layer per unit driving amount of the image carrier when the recording medium of the maximum size passes through the transfer nip portion β: Image in a state where the recording medium does not pass through the transfer nip portion Photosensitive layer abrasion amount γ per unit drive amount of the carrier: Photosensitive layer abrasion amount Ta per unit drive amount of the image carrier when a recording medium other than the maximum size passes through the transfer nip portion: maximum Cumulative driving amount Tb of the image carrier when the recording medium of size passes through the transfer nip portion: Cumulative driving amount Tc of the image carrier when the recording medium does not pass through the transfer nip portion: maximum size This is the cumulative driving amount of the image carrier in a state where the recording medium other than is passing through the transfer nip portion.

  According to the first configuration of the present invention, the maximum abrasion amount of the photosensitive layer in the direction of the rotation axis of the image carrier can be accurately calculated regardless of the size ratio of the recording medium passing through the transfer nip portion. The charging bias can be appropriately corrected based on the maximum scraped amount. Therefore, the surface potential unevenness in the rotation axis direction of the image bearing member is eliminated, and density image quality and edge fogging can be suppressed to maintain high quality image quality.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention. Partial enlarged view of the image forming unit 9 in FIG. A block diagram showing an example of a control path used in the image forming apparatus 100 The graph which shows transition of the layer thickness of the photosensitive layer 1b in the rotating shaft direction of the photosensitive drum 1 at the time of passing small size paper The graph which shows transition of the layer thickness of the photosensitive layer 1b in the paper passing area | region of the photosensitive drum 1, and a non-paper passing area | region. 7 is a flowchart illustrating an example of charging bias correction control based on the maximum amount of shaving Smax of the photosensitive layer in the image forming apparatus 100 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view around an image forming unit P in FIG. In the main body of the image forming apparatus (for example, a monochrome printer) 100, an image forming portion P that forms a monochrome image by each process of charging, exposure, development, and transfer is disposed.

  In the image forming portion P, along the rotation direction of the photosensitive drum 1 (counterclockwise direction in FIG. 1), the charging device 2, the exposure device 3, the developing device 4, the transfer roller 5, the cleaning device 6, and the charge eliminating device. 7 is disposed. In the image forming unit P, the image forming process for the photosensitive drum 1 is executed while rotating the photosensitive drum 1 in the counterclockwise direction in FIG.

  The photosensitive drum 1 is formed by laminating a photosensitive layer 1b on an outer peripheral surface of, for example, an aluminum drum base tube 1a, and the charging device 2 charges the photosensitive layer 1b. Then, an electrostatic latent image in which charging is attenuated is formed on the surface of the photosensitive layer 1b that has received a light beam from the exposure apparatus 3 described later. In the present embodiment, an organic photosensitive layer (OPC) that generates a high-resolution image with little generation of ozone during charging is used as the photosensitive layer 1b.

  The charging device 2 uniformly charges the surface of the photosensitive drum 1. In the present embodiment, a scorotron charging type charging device that includes a grid between the corona wire and the photosensitive drum 1 and discharges by applying a high voltage to the grid is used. The exposure device 3 irradiates the photosensitive drum 1 with a light beam based on the image data, and forms an electrostatic latent image on the surface of the photosensitive drum 1.

  The transfer roller 5 transfers the toner image formed on the surface of the photosensitive drum 1 onto the sheet conveyed through the sheet conveyance path 11. The cleaning device 6 includes a cleaning blade 20 that makes line contact with the longitudinal direction of the photosensitive drum 1, and a recovery spiral 21 that discharges waste toner scraped off from the surface of the photosensitive drum 1 by the cleaning blade 20. After the image is transferred to the paper, residual toner on the surface of the photosensitive drum 1 is removed. The static eliminator 7 irradiates the surface of the photosensitive drum 1 with static elimination light to remove residual charges.

  When a printing operation is performed, image data transmitted from a host device such as a personal computer is converted into an image signal. On the other hand, in the image forming unit P, the photosensitive drum 1 that rotates counterclockwise in the drawing is uniformly charged by the charging device 2, and the exposure device 3 emits a light beam onto the photosensitive drum 1 based on the image signal. By irradiating, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 1. Thereafter, the toner carried on the developing roller 4a of the developing device 4 is attached to the electrostatic latent image to form a toner image. The toner is supplied to the developing device 4 from the toner container 8.

  A sheet is conveyed at a predetermined timing from the sheet storage unit 10 via the sheet conveyance path 11 and the resist roller pair 13 toward the image forming unit P on which the toner image is formed as described above. The toner image on the surface of the photosensitive drum 1 is transferred onto a sheet at a transfer nip N with the transfer roller 5. The sheet on which the toner image has been transferred is separated from the photosensitive drum 1, conveyed to the fixing unit 9, and heated and pressed to fix the toner image on the sheet. The paper that has passed through the fixing unit 9 is sorted in the transport direction by the transport guide member 16 disposed in the branching section of the paper transport path 11, and is sent as it is (or after being sent to the reverse transport path 17 and copied on both sides). The paper is discharged to the paper discharge unit 15 via the discharge roller pair 14.

  FIG. 3 is a block diagram illustrating an example of a control path used in the image forming apparatus 100. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The bias control circuit 51 is connected to the charging bias power source 52, the developing bias power source 53, and the transfer bias power source 54, and operates these power sources 52 to 54 according to output signals from the control unit 90. To 54 apply a predetermined bias to the charging device 2, the developing roller 4 a, and the transfer roller 5 in accordance with a control signal from the bias control circuit 51.

  The bias application to the transfer roller 5 will be described in detail. When a toner image is transferred from the photosensitive drum 1 to a sheet, a constant current (forward transfer constant current) that causes the transfer roller 5 to have a polarity (negative polarity) opposite to that of the toner. ) Flows so that a transfer bias is applied. By adopting constant current control for the transfer bias, there is almost no influence of impedance change between the photosensitive drum 1 and the transfer roller 5 that varies depending on the durability and the environment, and there is no effect between the photosensitive drum 1 and the transfer roller 5. The transfer electric field with respect to the air gap can be stabilized.

  On the other hand, when there is no sheet in the transfer nip N (between sheets), constant voltage control is performed in which a constant voltage (transfer reverse bias) having the same polarity (positive polarity) as the toner is applied to the transfer roller 5. As a result, contamination of the transfer roller 5 due to toner adhering from the photosensitive drum 1 to the transfer roller 5 can be prevented, and unnecessary current flow into the photosensitive drum 1 can be suppressed.

  The operation unit 70 is provided with a liquid crystal display unit 71 and LEDs 72 that indicate various states, and displays the state of the image forming apparatus 100 and displays the image forming status and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a readable / writable storage unit, A plurality of (two in this case) I's for temporarily transmitting control signals to the temporary storage unit 94 for storing image data and the like, and for receiving input signals from the operation unit 70. / F (interface) 95 is provided at least. In addition, the control unit 90 can be arranged at any location inside the main body of the image forming apparatus 100.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 95. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 95. Examples of each part and device controlled by the control unit 90 include the charging device 2 of the image forming unit P, the transfer roller 5, the bias control circuit 51, and the operation unit 70.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. Further, the ROM 92 (or RAM 93) stores the scraping rates α, β, γ used when calculating the maximum scraping amount Smax of the photosensitive layer 1b of the photosensitive drum 1 and the maximum scraping amount Smax and the maximum scraping as will be described later. A charging bias correction table that correlates an appropriate charging bias according to the amount Smax is also stored. The timer 94 accumulates and measures the rotation time of the photosensitive drum 1 at the time of transfer to the paper by the transfer roller 5 and at the time of non-transfer (paper interval).

  Next, a method for calculating the abrasion amount of the photosensitive layer 1b of the photosensitive drum 1 in the image forming apparatus 100 of the present invention will be described in detail. FIG. 4 is a graph showing the transition of the layer thickness of the photosensitive layer 1b in the direction of the rotation axis of the photosensitive drum 1 when a small-size sheet is passed, and FIG. It is a graph which shows transition of the layer thickness of the photosensitive layer 1b in a paper passing area | region.

  In FIG. 4, the rotation when passing 5K (5,000) sheets, passing 25K (25,000) sheets, passing 43K (43,000) sheets, and passing 68K (68,000) sheets. The layer thickness of the photosensitive layer 1b in the axial direction is indicated by a solid line, a broken line, an alternate long and short dash line, and a dotted line, respectively. The A5 paper width, transfer roller width, and cleaning blade width are indicated by arrows in FIG. In FIG. 5, the transition of the layer thickness of the photosensitive layer 1b at the center of the photosensitive drum 14 in the rotation axis direction (left and right direction in FIG. 4) is shown in the data series of ● and the left and right ends. The transition of the layer thickness of the photosensitive layer 1b is shown by the data series of ▲ and ×, respectively.

  When a sheet whose width direction size is smaller than the dimension in the rotation axis direction of the photosensitive drum 1 (here, A5 sheet) passes through the photosensitive drum 1, the center in the rotation axis direction of the photosensitive drum 14 (left and right direction in FIG. 4). Only the portion (center) becomes a region (sheet passing region) R1 through which the sheet passes, and a region (non-sheet passing region) R2 through which the sheet does not pass occurs at both ends (left, right). As shown in FIGS. 4 and 5, the amount of abrasion of the photosensitive layer 1b in the non-contact area R2 is greatly increased as the number of sheets to be passed or the number of drum rotations is increased as compared with the amount of abrasion of the photosensitive layer 1b in the contact area R1. It has increased.

  Here, the relationship between the abrasion amount of the photosensitive layer 1b and the bias application pattern in the transfer nip portion N will be examined. Table 1 shows an application pattern of the transfer bias or the transfer reverse bias in the transfer nip portion N when passing a small size sheet.

  In the paper passing area R1 through which the paper passes, there are a pattern A state and a pattern B state. Specifically, while the paper is passing through the transfer nip N, the transfer bias is such that a transfer current (forward transfer constant current) that causes the toner to move from the photosensitive drum 1 to the paper (transfer roller 5) flows. Is applied to pattern A. Further, when the sheet does not pass through the transfer nip N, the application of the transfer bias is stopped, and a transfer reverse bias (reverse transfer constant voltage) for preventing the toner from adhering to the transfer roller 5 is applied, so that the pattern B It becomes.

  In the non-sheet passing region R2 where the sheet does not pass, there are a pattern B state and a pattern C state. Specifically, the transfer bias is applied so that the forward transfer constant current flows while the sheet is passing through the transfer nip N, but the pattern C is formed because the sheet does not pass in the non-sheet passing region R2. Further, when the sheet does not pass through the transfer nip N, the application of the transfer bias is stopped, and a transfer reverse bias that prevents the toner from adhering to the transfer roller 5 is applied, so that the pattern B is obtained.

  Since the time in the state of the pattern B is the same in the paper passing area R1 and the non-paper passing area R2, the difference in the scraping amount of the photosensitive layer 1b shown in FIGS. 4 and 5 is the state of the pattern A and the state of the pattern C. This is caused by the difference in the amount of shaving. Pattern C is a state in which a transfer bias is applied without a sheet interposed between the photosensitive drum 1 and the transfer roller 5, and a transfer current flows directly from the transfer roller 5 to the photosensitive drum 1. That is, it is considered that the phenomenon in which the transfer current directly flows into the photosensitive drum 1 promotes the abrasion of the photosensitive layer 1b.

  Therefore, in this embodiment, the abrasion rate (the amount of abrasion of the photosensitive layer 1b per unit driving amount of the photosensitive drum 1) is obtained by experiment for each application pattern of the transfer bias or the transfer reverse bias in the transfer nip portion N. Based on the cumulative driving amount and the scraping rate of each applied pattern, the scraping amount of the photosensitive layer 1b in the non-sheet-passing region R2 where the scraping amount of the photosensitive layer 1b is maximum in the rotation axis direction of the photosensitive drum 1 is calculated. . Then, a charging bias application condition to the charging device 2 is set according to the calculated amount of wear.

When the scraping rate of the photosensitive layer 1b in the patterns A, B, and C is α, β, and γ, and the cumulative driving amount of the photosensitive drum 1 in the patterns A, B, and C is Ta, Tb, and Tc, non-sheet passing The maximum scraping amount Smax in the region R2 is expressed by the following equation (1).
Smax = α * Ta + β * Tb + γ * Tc (1)

  The accumulated drive amounts Ta, Tb, and Tc can be obtained by measuring and accumulating the rotation time of the photosensitive drum 1 in each of the patterns A to C. The pattern A in the non-sheet passing region R2 is a case where the maximum size paper is passed through the transfer nip portion. Therefore, the cumulative driving amount Ta in the pattern A is the cumulative value of the transfer time to the maximum size paper. It is. In addition, since the pattern C in the non-sheet passing region R2 is a case where a sheet other than the maximum size is passed, the accumulated driving amount Tc in the pattern C is an accumulated value of the transfer time to a sheet other than the maximum size. It is. The cumulative drive amount Tb in the pattern B is a cumulative value of the non-transfer time (inter-paper time) for all size sheets.

  In the image forming apparatus 100 in which the process speed is switched between two stages according to the thickness and type of the conveyed paper and the type of output image, the photosensitive drum 1 also rotates at two stages of linear speed. In this case, even if the rotation time (driving time) of the photosensitive drum 1 is the same, the driving amount of the photosensitive drum 1 varies depending on the linear velocity. Therefore, the cumulative driving amounts Ta to Tc are calculated as the rotational speed of the photosensitive drum 1 or the movement distance of the outer peripheral surface (rotational speed × drum outer peripheral length), thereby accumulating the photosensitive drum 1 rotating at different linear speeds. The driving amount can be calculated appropriately. In this case, the shaving rates α, β, and γ also use the shaving amount per unit rotation number (or unit movement distance) of the photosensitive drum 1.

  FIG. 6 is a flowchart showing an example of charging bias control based on the maximum scraping amount Smax of the photosensitive layer 1b. With reference to FIGS. 1 to 5, the setting procedure of the charging bias applied to the charging device 2 will be described in detail along the steps of FIG. 6.

  When a printing command is input from a personal computer or the like and printing is started (step S1), the control unit 90 counts the cumulative number of printed sheets Σn since the previous charging bias correction (or when the image forming apparatus 100 starts to be used). (Step S2). Further, the control unit 90 also starts measuring the cumulative drive times Ta, Tb, and Tc of the photosensitive drum 1 in the patterns A, B, and C (step S3).

  Next, the control unit 90 determines whether or not printing has been completed (step S4). If printing continues (No in step S4), the process returns to step S2, and the counting of the cumulative number of printed sheets Σn and the measurement of the cumulative driving times Ta, Tb, and Tc are continued. If printing has ended (Yes in step S4), it is determined whether or not the cumulative number of printed sheets Σn has reached a predetermined number n1 (for example, 5,000) or more (step S5).

  When Σn ≧ n1 (Yes in step S5), the scraping rates α, β, γ of the photosensitive layer 1b in the patterns A, B, C are read from the ROM 92 (or RAM 93), and the cumulative drive times Ta, Tb, Tc And the scraping rates α, β and γ are used to calculate the maximum scraping amount Smax of the photosensitive layer 1b by the above formula (1) (step S6).

  Then, the charging bias applied to the charging device 2 is corrected based on the calculated maximum shaving amount Smax (step S7). Specifically, the surface potential of the photosensitive drum 1 when a constant charging bias is applied becomes lower as the layer thickness of the photosensitive layer 1b becomes thinner. Therefore, the photosensitive layer 1b obtained by subtracting Smax from the initial layer thickness of the photosensitive layer 1b. And the charging bias is increased so that a predetermined surface potential can be obtained at the minimum layer thickness. On the other hand, if Σn <n1 in step S5 (No in step S5), the process returns to step S1, and the process of steps S1 to S7 is repeated when the next print command is input.

  According to the above control, the maximum abrasion amount of the photosensitive layer 1b from the abrasion rates α, β, γ of the photosensitive layer 1b and the cumulative driving times Ta, Tb, Tc of the photosensitive drum 1 in the patterns A, B, C. Since Smax is calculated, the maximum scraping amount Smax of the photosensitive layer 1b in the rotation axis direction of the photosensitive drum 1 can be accurately calculated regardless of the ratio of the large size paper to the small size paper, and the calculated maximum The charging bias can be appropriately corrected based on the scraping amount Smax. Therefore, since the surface potential unevenness in the rotation axis direction of the photosensitive drum 1 is eliminated, it is possible to maintain high-quality image quality by suppressing the density step and the edge fog regardless of the width direction size of the paper to be used. it can.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the control shown in FIG. 6, the maximum shaving amount Smax is calculated and the charging bias is corrected when the number of printed sheets reaches a predetermined number. However, the control in FIG. The maximum scraping amount Smax may be calculated every time a sheet is passed, and correction may be performed when the maximum scraping amount Smax has increased by a certain amount from the previous correction of the charging bias.

  In the above-described embodiment, the transfer roller 5 is used as a transfer member that is disposed so as to be in contact with the photosensitive drum 1 and forms the transfer nip portion N. However, an endless transfer belt is used instead of the transfer roller 5. Can be brought into contact with the photosensitive drum 1 to form a transfer nip portion. Further, instead of the scorotron charging type charging device 2 having a corona wire and a grid as shown in FIG. 2, a corotron charging type charging device without a grid or a contact charging type charging using a charging roller is used. An apparatus can also be used.

  Furthermore, the image forming apparatus of the present invention is not limited to the monochrome printer as shown in FIG. 1, and may be other image forming apparatuses such as monochrome and color copiers, digital multifunction peripherals, color printers, and facsimiles. .

  The present invention is used in an image forming apparatus including an image carrier such as a photosensitive drum, a charging device that charges the image carrier, and a transfer member that transfers a toner image formed on the image carrier to a recording medium. Is possible. By utilizing the present invention, it is possible to provide an image forming apparatus capable of accurately calculating the maximum amount of shaving of the photosensitive layer in the rotation axis direction of the image carrier and setting appropriate charging conditions.

1 Photosensitive drum (image carrier)
2 Charging device 3 Exposure device 4 Developing device 4a Developing roller 5 Transfer roller (transfer member)
6 Cleaning Device 20 Cleaning Blade 51 Bias Control Circuit 52 Charging Bias Power Supply 54 Transfer Bias Power Supply 90 Control Unit 100 Image Forming Device N Transfer Nip Portion

Claims (7)

An image carrier having a photosensitive layer formed on the surface;
A charging device that charges the surface of the image carrier to the same polarity as the charging polarity of the toner;
An exposure device that exposes and scans the surface of the image carrier uniformly charged by the charging device to form an electrostatic latent image on the image carrier;
A developing device that is disposed downstream of the charging device with respect to the rotation direction of the image carrier, and forms a toner image on the image carrier by attaching toner to the electrostatic latent image;
A transfer nip portion is formed on the downstream side of the developing device with respect to the rotation direction of the image carrier to form the transfer nip portion, and the toner image is transferred to a recording medium passing through the transfer nip portion. A transfer member;
A charging bias power source for applying a charging bias to the charging device;
A transfer bias power source for applying a transfer bias having a reverse polarity to the charging polarity of the toner or a transfer reverse bias having the same polarity as the charging polarity of the toner,
A controller for controlling the charging bias power source and the transfer bias power source;
In an image forming apparatus comprising:
The control unit calculates the maximum amount of scraping Smax of the photosensitive layer in the rotational axis direction of the image carrier by the following formula (1), and corrects the charging bias based on the calculated maximum amount of scraping Smax. An image forming apparatus capable of executing charging bias correction control.
Smax = α * Ta + β * Tb + γ * Tc (1)
However,
α: Abrasion amount of the photosensitive layer per unit driving amount of the image carrier in a state where a recording medium of the maximum size passes through the transfer nip portion β: The recording medium does not pass through the transfer nip portion Abrasion amount γ of the photosensitive layer per unit driving amount of the image carrier in a state: per unit driving amount of the image carrier in a state where a recording medium other than the maximum size passes through the transfer nip portion. Abrasion amount Ta of the photosensitive layer: Cumulative driving amount Tb of the image carrier in a state in which the recording medium of the maximum size passes through the transfer nip portion: In a state in which the recording medium does not pass through the transfer nip portion The cumulative driving amount Tc of the image carrier is the cumulative driving amount of the image carrier in a state where a recording medium other than the maximum size passes through the transfer nip portion.   The image forming apparatus according to claim 1, wherein the cumulative driving amount of the image carrier is a cumulative value of a rotation time of the image carrier.   The accumulated driving amount of the image carrier is either a cumulative value of the rotation speed of the image carrier or a cumulative value of a movement distance of the outer peripheral surface of the image carrier. Image forming apparatus.   2. The control unit according to claim 1, wherein the controller corrects the charging bias so that a predetermined surface potential is obtained at a minimum layer thickness obtained by subtracting the maximum scraping amount Smax from an initial layer thickness of the photosensitive layer. Item 4. The image forming apparatus according to Item 3.   5. The image forming apparatus according to claim 1, wherein the charging bias correction control is executed when the number of printed sheets from the previous correction reaches a predetermined number.   6. The control unit according to claim 1, wherein the controller applies the transfer bias to the transfer member by constant current control, and applies the transfer reverse bias to the transfer member by constant voltage control. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the image carrier is an organic photoreceptor having an organic photosensitive layer formed on a surface thereof.