JP2019184769A - Image forming apparatus - Google Patents

Abstract

To easily make visible on a test chart an image defect due to cleaning means.SOLUTION: A photoreceptor drum 11 and an intermediate transfer belt 31 are rotating bodies. Each station of YMCBk forms a toner image. A primary transfer device 17 and a secondary transfer device 27 transfer the toner image formed on the rotating body to a predetermined member. A drum cleaner 15 and a belt cleaner 35 clean a toner which is not transferred to the predetermined member and remains on the rotating body. A CPU 60 forms the toner image on a predetermined area of the rotating body at n rotating times of the rotating body, and causes cleaning means to clean the toner image. The CPU 60 forms a test chart 701 for identifying a replacement component by not forming the toner image on the predetermined area of the rotating body at n+1 rotating times of the rotating body.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  An electrophotographic image forming apparatus has various replaceable parts such as a charging unit, an exposure unit, and a developing unit. A user or a service person determines which replacement part should be replaced by viewing the output image, but this determination is difficult. If it takes a long time to identify the replacement part, the time during which the user cannot form an image (so-called down time) will become longer.

  According to Patent Document 1, there is a test chart that can specify which one of the charging unit and the developing unit should be replaced by forming two types of toner images formed without exposure using different charging potentials. Proposed. A test chart is a sheet on which a test image is formed.

JP 2017-194573 A

  In Patent Document 1, it is further proposed to determine whether the belt cleaner or the drum cleaner should be replaced based on whether or not there is a streak on a white background where no toner image is formed on the test chart. When the cleaner is consumed, the toner cannot be sufficiently cleaned, and the remaining toner is transferred to the sheet. In Patent Document 1, this principle is used to determine the replacement of the cleaner. However, when sufficient toner is not supplied to the cleaner, streaks are not transferred to the sheet in the first place.

  In view of the above, an object of the present invention is to make an image defect caused by a cleaning means easily manifest on a test chart.

  In order to solve the above problems, an image forming apparatus according to claim 1 conveys a sheet, an image carrier that is rotationally driven, an image forming unit that forms an image on the image carrier using a developer, and a sheet. A transfer unit that transfers the image formed on the image carrier to the sheet; and a development that remains on the image carrier without being transferred from the image carrier to the sheet in the transfer unit. An image forming apparatus comprising a removing member for removing the agent and a control unit, wherein the control unit executes a process of creating a test chart used for detecting an abnormal portion of the image forming apparatus, When the processing is performed, the control unit rotates the image carrier so that the image forming unit forms a pattern image and the pattern image is removed by the removing member through the transfer unit. And controlling the conveying means so that a period in which the region of the image carrier including the position where the pattern image is transferred passes through the transfer unit again overlaps a period in which the sheet passes through the transfer unit. It is characterized by that.

  In order to solve the above-described problem, an image forming apparatus according to another claim includes an image forming unit that includes a photosensitive member that is rotationally driven and forms an image on the photosensitive member using a developer; A primary transfer nip portion where the image formed on the photosensitive member is transferred to the transfer member, and a developer remaining on the photosensitive member without being transferred from the photosensitive member to the transfer member in the primary transfer nip portion is removed. An image forming apparatus comprising: a removing member to be conveyed; a conveying unit that conveys a sheet; a secondary transfer nip portion to which the image transferred to the transfer body is transferred to the sheet; and a control unit. The control unit executes a process of creating a test chart used for detecting an abnormal portion of the image forming apparatus. When the process is executed, the control unit forms a pattern image by the image forming unit. The The primary transfer nip portion is controlled to a first transfer condition, and the photoconductor is rotated so that the pattern image is removed by the removing member through the primary transfer nip portion, and the pattern image is formed. The primary transfer nip portion is controlled to a second transfer condition different from the first transfer condition during a period in which the first region of the photoconductor including the position passes through the primary transfer nip portion again. The period in which the second region of the transfer body in contact with the first region of the photoreceptor passes through the secondary transfer nip portion and the period in which the sheet passes through the secondary transfer nip portion overlap. The conveyance means is controlled.

  According to the present invention, image defects caused by the cleaning means are easily manifested on the test chart.

1 is a diagram illustrating an image forming apparatus. The figure which shows a control system. FIG. 3 is a diagram showing a test chart in the first embodiment. The figure which shows the relationship between the charging voltage of a charger and the charging potential of a photosensitive drum. The figure which shows the relationship between a stripe, a charging potential, and development potential. The figure which shows the toner patch for making cleaner defect manifest. The figure which shows the toner patch for revealing the cleaner defect The figure which shows the toner patch for making cleaner defect manifest. The figure which shows the relationship between the kind of streak and replacement parts. The figure which shows the defect of a development coat. The figure which shows the relationship between a stripe, a charging potential, and development potential. The figure which shows exposure failure and plastic deformation. The figure which shows the relationship between a stripe, a charging potential, and development potential. The figure which shows the relationship between the cleaning defect of a photosensitive drum, and a stripe. The figure which shows the relationship between a stripe, a charging potential, and development potential. The figure which shows the generation | occurrence | production mechanism of the image defect resulting from a cleaner. The flowchart which shows the preparation process of a test chart, and the identification process of replacement parts. The figure which shows an example of the message which shows replacement parts. The flowchart which shows the specific process of replacement parts. FIG. 10 is a diagram illustrating a method for specifying a replacement part in the second embodiment. The flowchart which shows the specific process of replacement parts. FIG. 10 is a diagram showing the characteristics of a test chart in Example 3.

[Image forming apparatus]
FIG. 1 is a cross-sectional view showing the image forming apparatus 1. The image forming apparatus 1 has an image reader 2 and a printer 3. The image reader 2 is a reading unit that reads a document, a test chart, and the like. The light source 23 irradiates light on the document 21 placed on the document table glass 22. The optical system 24 guides reflected light from the document 21 to the CCD sensor 25 to form an image. CCD is an abbreviation for charge-coupled device. The CCD sensor 25 has red, green, and blue line sensors, and generates red, green, and blue color component signals. The image processing unit 28 performs image processing (for example, shading correction) on the image data obtained by the CCD sensor 25 and outputs the image data to the printer control unit 29 of the printer 3.

  The image forming unit 10 of the printer 3 is an electrophotographic image forming engine that forms a toner image corresponding to image information on a sheet P. The image forming unit 10 has four stations for forming toner images of respective colors of Y (yellow), M (magenta), C (cyan), and Bk (black). The present invention can also be applied to a monochrome printer that forms a single color image. As shown in FIG. 1, the image forming unit 10 includes four photosensitive drums 11 corresponding to the colors Y, M, C, and Bk in order from the left side. Around each photosensitive drum 11, a roller-shaped charger 12, an exposure device 13, a developing device 14, a primary transfer device 17, a drum cleaner 15, and the like are arranged. Here, the photosensitive drum 11, the charger 12, and the drum cleaner 15 are integrated as a process cartridge 50. The process cartridge 50 is detachable from the image forming apparatus 1. The image forming apparatus 1 also includes an intermediate transfer belt 31 on which a toner image is formed, a secondary transfer unit 27 that transfers the toner image on the intermediate transfer belt 31 to the sheet P, and a fixing unit 40 that fixes the toner image on the sheet P. Is provided. The intermediate transfer belt 31 is wound around three rollers 34, 36, and 37, and rotates in a predetermined direction when the roller 37 rotates in the arrow direction. A belt cleaner 35 is provided on the intermediate transfer belt 31.

  Here, the configuration of each unit of the image forming apparatus 1 will be described. The photosensitive drum 11 is an aluminum cylinder having a photosensitive layer formed on the surface. The photosensitive drum 11 functions as a photosensitive member. The charger 12 includes, for example, a metal wire to which a charging voltage is supplied, a charging roller, or a charging brush. The configuration of the exposure device 13 may include a light source that emits laser light and a rotary polygon mirror that deflects the laser light from the light source, or a plurality of light sources that emit laser light are arranged in the axial direction of the photosensitive drum 11. The structure arranged side by side may be sufficient. The axial direction is a direction parallel to the rotation axis of the photosensitive drum 11. The axial direction is hereinafter simply referred to as the X direction. Laser light from the exposure device 13 scans the photosensitive drum 11. The developing device 14 contains a developer. The developing device 14 has a developing roller for supplying a developer to the photosensitive drum 11. A magnet 141 provided inside the developing roller supports the developer on the surface of the developing roller. Note that the developer described in this embodiment is a two-component developer including a non-magnetic toner and a magnetic carrier. The developer may be, for example, a one-component developer composed of magnetic toner. The primary transfer device 17 is, for example, a transfer roller or a transfer blade to which a primary transfer voltage is supplied. When the primary transfer unit 17 presses the intermediate transfer belt 31 against the photosensitive drum 11, a nip portion (primary transfer nip portion N <b> 1) is formed between the photosensitive drum 11 and the intermediate transfer belt 31. The drum cleaner 15 is, for example, a cleaning blade made of an elastic material that contacts the surface of the photosensitive drum 11 or a fur brush that contacts the surface of the photosensitive drum 11 and collects toner. The secondary transfer unit 27 is, for example, a transfer roller to which a secondary transfer voltage is supplied or a transfer belt wound around a plurality of rollers. When the secondary transfer device 27 presses the intermediate transfer belt 31, a nip portion (secondary transfer nip portion N <b> 2) is formed between the intermediate transfer belt 31 and the secondary transfer device 27. The belt cleaner 35 is, for example, a cleaning blade that contacts the surface of the intermediate transfer belt 31 or a fur brush that contacts the surface of the intermediate transfer belt 31.

  A procedure for forming a black toner image representing the four colors will be described below. The procedure for forming the other color toner image is the same as the procedure for forming the black toner image, and the detailed description thereof is omitted. When image formation is started, the photosensitive drum 11 is rotationally driven in a predetermined direction (arrow direction). The charger 12 uniformly charges the surface of the photosensitive drum 11. The exposure device 13 exposes the surface of the photosensitive drum 11 in accordance with image information output from the printer control unit 29 to form an electrostatic latent image. The developing device 14 attaches toner to the electrostatic latent image and develops it to form a toner image. The primary transfer unit 17 primarily transfers the toner image carried on the photosensitive drum 11 to the intermediate transfer belt 31. The drum cleaner 15 removes toner remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 31 at the primary transfer nip portion N1.

  The feeding cassette 20 accommodates the sheet P. A sheet P is placed on the multi-feed tray 30. The sheet P fed from the feeding cassette 20 or the multi-feed tray 30 is conveyed toward the registration roller pair 26. The registration roller pair 26 temporarily stops the sheet P fed from the feeding cassette 20 or the multi-feed tray 30 so that the toner image on the intermediate transfer belt 31 is transferred to a desired position on the sheet P. The sheet P is conveyed to the secondary transfer nip portion N2. A secondary transfer voltage is applied to the secondary transfer unit 27 while the sheet P passes through the secondary transfer nip N2. As a result, the secondary transfer unit 27 secondarily transfers the toner image on the intermediate transfer belt 31 to the sheet P. The belt cleaner 35 removes the toner remaining on the intermediate transfer belt 31 without being transferred to the sheet P at the secondary transfer nip portion N2. The sheet P on which the toner image is transferred is conveyed to the fixing device 40. The fixing device 40 fixes the toner image on the sheet P.

[Charging method]
Generally, there are two types of charging methods for the charger 12: a non-contact charging method and a contact charging method. The non-contact charging method is a method of charging the photosensitive drum 11 by corona discharge generated from the charging member by applying a high voltage to the charging member (metal wire) that is not in contact with the photosensitive drum 11. However, the corona discharge generates discharge products such as ozone and nitrogen oxide (NOx), which causes deterioration of the photosensitive drum 11 and image blurring. Further, when the discharge product adheres to the charging member (metal wire), non-uniform discharge occurs, and the image may be poorly charged. For this reason, the cleaning member which cleans a charging member (metal wire) is required. The contact charging method is a method of charging the photosensitive drum 11 by bringing the charging member (charging roller) of the charger 12 into contact with the photosensitive drum 11. In general, the contact charging method has a lower applied voltage than the non-contact charging method and generates very little discharge products such as ozone and nitrogen oxide (NOx). However, if the toner that has passed through the drum cleaner 15 or the external additive of the toner adheres to the charging member (charging roller) or is fused, a charging failure may occur.

[Replacement parts]
In the image forming apparatus 1 described in this embodiment, the photosensitive drum 11, the charger 12, and the drum cleaner 15 are integrated into one process cartridge 50. By replacing the process cartridge 50, the photosensitive drum 11, the charger 12, and the drum cleaner 15 can be quickly replaced. In the image forming apparatus 1, the developing device 14 can also be attached to and detached from the image forming apparatus 1. Further, in the image forming apparatus 1, the primary transfer unit 17 and the intermediate transfer belt 31 form a transfer unit. The transfer unit is also detachable from the image forming apparatus 1. By exchanging the transfer unit, the primary transfer unit 17 and the intermediate transfer belt 31 can be quickly replaced. Further, the belt cleaner 35 can be attached to and detached from the image forming apparatus 1. In this way, by using the process cartridge 50, the developing device 14, the transfer unit, and the belt cleaner 35 as replacement parts, the maintenance by the user and the service person can be simplified and the maintenance time can be shortened.

[Control system]
FIG. 2 shows a control system of the image forming apparatus 1. The image forming apparatus 1 is connected to network devices such as a PC 124 and a server 128 via a network 123. PC is an abbreviation for personal computer. The server 128 is, for example, a computer of a service company in charge of maintenance of the image forming apparatus 1 or a mail server. The printer control unit 29 is a controller that controls the image reader 2 and the printer 3. The printer control unit 29 may be divided into a printer controller in charge of image processing and the like, and an engine control unit that controls the image forming unit 10 and the like. The communication IF 55 is a communication circuit that receives print data from the PC 124 or transmits information to the PC 124 or the server 128 from the image forming apparatus 1. IF is an abbreviation for interface. The CPU 60 is a control circuit or arithmetic circuit that controls each part of the image forming apparatus 1 in an integrated manner. The CPU 60 realizes various functions by executing a control program stored in the storage device 63. Note that some or all of the functions of the CPU 60 may be realized by hardware such as an ASIC or FPGA. ASIC is an abbreviation for application specific integrated circuit. FPGA is an abbreviation for field programmable gate array. The display device 61 includes a liquid crystal screen that displays various information. The input device 62 includes buttons and numeric keys for inputting commands. The storage device 63 includes a memory such as a ROM and a RAM, and a mass storage device such as a hard disk drive. The CPU 60 converts the image data transferred from the image reader 2 or the like into image data that can be printed by the printer 3. The CPU 60 further performs gradation correction. Tone correction is a process of converting an image signal value included in image data based on a lookup table so that the tone characteristic of an image to be formed by a printer engine becomes an ideal tone characteristic. . Next, the CPU 60 generates a laser control signal for controlling the laser light emitted from the exposure unit 13 based on the image data on which the gradation correction has been performed, and outputs the laser control signal to the exposure unit 13.

  The CPU 60 implements various functions. Here, representative functions will be described. The chart generation unit 64 controls the printer 3 so as to form a test image for specifying a replacement part (abnormal part) on the sheet P. The test image itself or the sheet P on which the test image is formed is called a test chart. The charging controller 65 controls the charging voltage applied from the charging power source 68 to the charger 12. The development controller 66 controls the development voltage applied to the developing device 14 from the development power source 69. The transfer controller 70 controls the primary transfer voltage applied from the primary transfer power supply 71 to the primary transfer device 17 and the secondary transfer voltage applied from the secondary transfer power supply 72 to the secondary transfer device 27. The diagnosis unit 67 acquires a test chart reading result (read data) from the image reader 2 or a reading device connected to the image forming apparatus 1 and selects a replacement part based on the read data. Further, the image forming apparatus 1 may be configured such that the read data of the test chart read by the image reader 2 is transferred to the server 128 by the communication IF 55 and the replacement part (abnormal part) is determined in the server 128. In this configuration, the diagnosis unit 67 may be omitted. Note that the diagnosis unit 67 may also be omitted when a user or service person identifies a replacement part (abnormal part) by visually checking the test chart.

[Test chart]
When the replacement part arrives at the replacement time, vertical streaks appear in the output image. Alternatively, when an abnormality occurs in the replacement part, a vertical stripe is generated in the output image. The vertical stripe is a linear image extending in parallel with the conveyance direction of the sheet P. When an abnormality occurs in the belt cleaner 35, the toner to be removed by the belt cleaner 35 passes through the abnormal portion of the belt cleaner 35 and is transferred to the sheet P at the secondary transfer nip portion N2. As a result, vertical stripes appear on the sheet P. Similarly, when an abnormality occurs in the drum cleaner 15, the toner to be removed by the drum cleaner 15 passes through the abnormal portion of the drum cleaner 15, is transferred to the sheet P, and vertical stripes appear on the sheet P. However, when the cause of the vertical streak is an abnormality in the belt cleaner 35 or the drum cleaner 15, the vertical streak does not always occur every time the output image is formed on the sheet P. Unless a large amount of toner is collected in the belt cleaner 35 or the drum cleaner 15, the amount of toner passing through the belt cleaner 35 or the drum cleaner 15 is very small. Therefore, vertical streaks occur only in the output image for several pages after a detection image that is not transferred to the sheet P is formed, or after a high-density image that consumes a large amount of toner is formed. Therefore, even if the cause of the vertical stripe is in the belt cleaner 35 or the drum cleaner 15, the vertical stripe does not appear on the test chart unless sufficient toner is supplied to the belt cleaner 35 or the drum cleaner 15. Therefore, a control method of the image forming apparatus 1 for determining whether or not the belt cleaner 35 or the drum cleaner 15 should be replaced is proposed. In particular, the image forming apparatus 1 is controlled so that vertical stripes caused by the belt cleaner 35 or the drum cleaner 15 are easily manifested on the test chart. A replacement part (abnormal part) is specified by visually observing the test chart or by causing the image reader 2 to read the test chart.

  In addition, the test chart may include a plurality of pattern images (hereinafter referred to as analog patterns) that are formed with different charging potentials of the image carrier and without applying exposure. Thereby, it is possible to determine whether not only the belt cleaner 35 or the drum cleaner 15 but also the exposure device 13, the developing device 14, and the charging device 12 should be replaced.

  A4 size (width direction length 297 mm, transport direction length 210 mm) is adopted as the size of the test chart, but this is only an example. When the maximum size that allows paper to pass through the image forming apparatus 1 is selected, for example, streaks generated at the end in the X direction in the charger 12 and the developing device 14 may be detected. As described above, if a sheet of the maximum size that can be printed by the image forming apparatus 1 is employed, it is possible to accurately specify the replacement equipment. Note that the number of test charts may be one or plural. In this embodiment, various types of test charts are illustrated, but not all of them are always required. That is, the number of test charts increases or decreases depending on the type of replacement part that the user or maintenance person wants to specify.

  FIG. 3 shows exemplary test charts 701-704. An arrow Y indicates the toner image conveyance direction (Y direction). The arrow Y is also the conveyance direction of the sheet P. An arrow X indicates a direction (X direction) orthogonal to the transport direction. Each size of the test charts 701 to 704 is A4 size. The test chart 701 is a test chart used for determining the necessity of replacing the belt cleaner 35 or the drum cleaner 15. The test chart 701 includes white background portions WD and WT where a pattern image is not formed. The white background portion WD is a region where a streak for determining the necessity of replacing the drum cleaner 15 can occur. The CPU 60 forms the toner patch PD by the printer 3 so that the streaks appear in the white background WD when the drum cleaner 15 should be replaced. The CPU 60 uses the registration roller pair 26 so that the timing at which the toner patch PD that has passed through the drum cleaner 15 passes through the secondary transfer nip portion N2 and the timing at which the test chart 701 passes through the secondary transfer nip portion N2 overlap. The conveyance of the test chart 701 is controlled. For example, the CPU 60 controls the timing at which the registration roller pair 26 starts to transport the test chart 701 to the secondary transfer nip N2 so that the above-described timings overlap. Further, for example, the CPU 60 controls the conveyance speed of the test chart 701 by the registration roller pair 26 so that the above-described timings overlap. The formation position of the toner patch PD is, for example, separated from the position where the white background portion WD of the test chart 701 is in contact with the intermediate transfer belt 31 in the secondary transfer nip portion N2 by the circumference Ld of the photosensitive drum 11. The photosensitive drum 11 conveys the toner image by rotating in the arrow direction shown in FIG. Therefore, the toner patch PD is formed on the photosensitive drum 11 in the n-th turn of the photosensitive drum 11, and no toner image is formed in the area on the photosensitive drum 11 corresponding to the white background portion WD in the n + first turn. That is, on the photosensitive drum 11, the position of the toner patch PD and the position of the white background portion WD coincide with each other.

  The white background portion WT is a region where a streak for determining the necessity of replacing the belt cleaner 35 can occur. The CPU 60 forms a toner patch PT by the printer 3 so that a streak appears in the white background portion WT when the belt cleaner 35 should be replaced. The CPU 60 uses the registration roller pair 26 so that the timing at which the toner patch PT that has passed through the belt cleaner 35 passes through the secondary transfer nip portion N2 and the timing at which the test chart 701 passes through the secondary transfer nip portion N2 overlap. The conveyance of the test chart 701 is controlled. For example, the CPU 60 controls the timing at which the registration roller pair 26 starts to transport the test chart 701 to the secondary transfer nip N2 so that the above-described timings overlap. Further, for example, the CPU 60 controls the conveyance speed of the test chart 701 by the registration roller pair 26 so that the above-described timings overlap. The formation position of the toner patch PT is, for example, separated from the position where the white background portion WT of the test chart 701 is in contact with the intermediate transfer belt 31 in the secondary transfer nip portion N2 by the circumference Lb of the intermediate transfer belt 31. The intermediate transfer belt 31 conveys the toner image by rotating in the direction of the arrow shown in FIG. Accordingly, the toner patch PT is formed on the intermediate transfer belt 31 by the n′th rotation of the intermediate transfer belt 31, and the toner image is formed on the region on the intermediate transfer belt 31 corresponding to the white background portion WT by the n ′ + first rotation. Is not formed. That is, on the intermediate transfer belt 31, the position of the toner patch PT and the position of the white background portion WT coincide with each other. When determining abnormality of the drum cleaner 15 and the belt cleaner 35 using one test chart 701, the relationship between the formation position of the toner pattern PT and the formation position of the toner pattern TD is as shown in FIG. It becomes. In FIG. 3, the X direction indicates a direction orthogonal to the sheet conveying direction, and the Y direction indicates the sheet conveying direction.

  In the drawing, each character of YMCBk given at the end of the reference numeral indicates the color of the toner used to form the toner patch PD used for determining the replacement of the drum cleaner 15. Here, the color of the toner used when forming the toner patch PD is a single color (any one of YMCBk). This is to identify in which color station the part to be replaced is present. For example, if yellow streaks are formed in the white background portion WDY, it is found that the drum cleaner 15 needs to be replaced in the yellow station.

  The length of the toner patch PT and each color toner patch PD in the transport direction is, for example, 10 mm. If the length in the transport direction is 10 mm or more, vertical stripes can be detected in the white background. The outer diameter of the photosensitive drum 11 is 30 mm, and the outer periphery (peripheral length) is about 94.2 mm. If the length of the toner patch in the transport direction is too long, the toner patches PD (white background portion WD) for four colors of YMCBk overlap on the test chart 701. For example, if the white background portion WDY overlaps with the white background portion WDM, the yellow vertical stripe and the magenta vertical stripe overlap, making it difficult to determine which color of the drum cleaner 15 should be replaced at first glance. sell. Therefore, the lengths and formation positions of the toner patches PD for the four colors may be determined so that the white background portions WD for the four colors of YMCBk do not overlap.

  The white background portion WT and the white background portion WD may not be a white background portion where a pattern image is not formed. That is, pattern images may be formed on the white background portion WT and the white background portion WD. However, when the pattern image is formed on the white background portion WT and the white background portion WD, the luminance difference between the background and the vertical stripe becomes small, and the stripe detection performance may be lowered. Therefore, if the pattern image is not formed on the white background portion WT and the white background portion WD, the streak detection performance will be good. Also, toner consumption will be reduced.

  The length of the white background portion WT (toner patch PT) and the white background portion WD (toner patch PD) in the X direction may be the maximum length of the toner image that can be formed by the image forming apparatus 1. However, in this embodiment, an image forming method common to the digital pattern D is used to form the toner patches PT and PD. Therefore, the length of the toner patches PT and PD in the X direction is the same as the length of the digital pattern D in the X direction. The white background portion WT and the white background portion WD do not need to be formed on the same sheet. Further, it is not always necessary to form both the white background portion WT and the white background portion WD. For example, when it is desired to know whether or not to replace the belt cleaner 35, the white background portion WT may be formed on the test chart 701. In order to know whether or not to replace the drum cleaner 15 for yellow toner, the white background portion WDY may be formed on the test chart 701.

  Next, in this embodiment, test charts 702 to 704 for specifying replacement parts other than the belt cleaner 35 or the drum cleaner 15 will be described. The test charts 702 to 704 include a digital pattern D and analog patterns A1 and A2. The digital pattern D is a toner image formed by applying exposure. The analog pattern A1 is a toner image formed by applying the first charging potential and applying no exposure. The analog pattern A2 is a toner image formed by applying a second charging potential different from the first charging potential and applying no exposure. A white background W is also formed in the test charts 702 to 704. YMCBk given at the end of the reference symbol indicates the color of toner used to form each pattern. The color of the toner used when each pattern is formed is a single color and any one of YMCBk. This is to identify in which color station the part to be replaced is present. For example, if a yellow streak is found, a part related to yellow is identified as a replacement part (abnormal part). The length of each pattern in the conveyance direction is, for example, 30 mm. This is because if the pattern length is 30 mm or more, it is possible to detect vertical stripes in the area where the pattern image is formed.

  The length of the digital pattern D in the X direction is slightly shorter than the entire length that can be formed by the image forming apparatus 1, and blank areas are provided at both ends of the digital pattern D in the X direction. On the other hand, the length in the X direction of the analog pattern A1 and the analog pattern A2 is the same as the length in the X direction of the sheet P, and no margin is formed.

  Four digital patterns D shown in FIG. 3 are exposure images (toner images) formed by exposure by the exposure device 13. The analog pattern A1 is a non-exposed image (toner image) formed by performing exposure by the exposure device 13 and setting the charging potential of the photosensitive drum 11 by the charger 12 to the first charging potential. The analog pattern A2 is not exposed by the exposure device 13, and is a non-exposed image formed by setting the charging potential of the photosensitive drum 11 by the charger 12 to a second charging potential sufficiently lower than the first charging potential ( Toner image). The second charging potential may be approximately 0 [V]. Here, the terms “high” and “low” mean high and low in the potential in absolute value. The appearance of the streak caused by the charging device 12 and the streak caused by the developing device 14 differs between the analog pattern A1 and the analog pattern A2. That is, by comparing the streaks generated in the analog pattern A1 and the streaks generated in the analog pattern A2, it is possible to determine whether the streaks are caused by the charger 12 or the developing device 14.

  Here, a method of forming an image without performing the charging process by the charger 12 will be described with reference to FIG. FIG. 4 shows the relationship between the applied voltage Vin and the charging potential Vd of the photosensitive drum 11 in the contact charging method. When the applied voltage Vin applied to the charging member of the charger 12 by the charging controller 65 is set to be equal to or lower than the discharge start voltage Vth, the charging potential Vd of the photosensitive drum 11 becomes substantially 0 [V]. Thus, by setting the applied voltage Vin to a voltage (for example, 0 [V]) that is equal to or lower than the discharge start voltage Vth (for example, 400 [V]), the charging potential of the photosensitive drum 11 is controlled to approximately 0 [V]. Is done.

  In order to further reduce the influence of the charger 12 on the analog pattern A2, the charge on the surface of the photosensitive drum 11 may be removed. For example, the surface of the photosensitive drum 11 cleaned by the drum cleaner 15 may be irradiated with light for charge removal from the pre-exposure light source. When the non-contact charging method is used, the charging process may not be applied to the photosensitive drum 11 by controlling the charging power source 68 so that the charging control unit 65 does not flow current through the metal wire.

  FIG. 5A shows the potential at the position in the X direction on the photosensitive drum 11 charged by the charger 12 when the digital pattern D is formed. FIG. 5B shows the density dD of the digital pattern D and the density d0 of the white background portion W formed on the sheet P. The density d0 is the optical density of the background (white background) of the sheet P.

  The charging control unit 65 controls the charging power source 68 so that the charging potential on the surface of the photosensitive drum 11 becomes Vd_D, and causes the charger 12 to charge the photosensitive drum 11. The exposure device 13 exposes the surface of the photosensitive drum 11 according to the image data generated by the chart generation unit 64. As a result, the potential of the exposed portion of the surface of the photosensitive drum 11 changes to Vl_D. The development controller 66 controls the development power source 69 so that the potential of the developing sleeve of the developing device 14 becomes a DC potential Vdc_D that is a developing bias. Vdc_D is set between the charging potential Vd_D and the exposure portion potential Vl_D. The margin m provided at both ends of the digital pattern D is not exposed. Therefore, the potential of the margin m is maintained at Vd_D. Thus, the fog removal voltage Vb is formed in the margin m which is a non-exposed portion. The fog removal voltage Vb prevents the toner from adhering to the margin m. The image signal value of the digital pattern D is set to 50%. This corresponds to an image having an optical density of 0.6 (that is, dD = 0.6). Such a halftone pattern increases the detection accuracy of vertical stripes as compared to a solid pattern.

  FIG. 5C shows the potential at the position in the X direction on the photosensitive drum 11 charged by the charger 12 when the first analog pattern A1 is formed. FIG. 5D shows the density dA1 of the analog pattern A1 formed on the sheet P. In order to form the analog pattern A1, the charging control unit 65 controls the charging power source 68 in accordance with an instruction from the chart generation unit 64, and the surface potential of the photosensitive drum 11 is adjusted to the charging potential Vd_A1. The development control unit 66 controls the development power source 69 in accordance with the instruction from the chart generation unit 64, and adjusts the potential of the development sleeve of the development unit 14 to the development bias Vdc_A1. The development bias Vdc_A1 is a development potential higher than the charging potential Vd_A1. The chart generation unit 64 does not cause the exposure device 13 to irradiate laser light. As a result, a developing voltage Vc_A1 is generated as a potential difference between the photosensitive drum 11 and the developing sleeve. That is, an electrostatic latent image corresponding to the analog pattern A1 is formed, and a toner image is formed on the photosensitive drum 11 by the toner supplied from the developing device 14. As shown in FIG. 5C, in the analog pattern A1, since exposure is not applied, a constant development voltage Vc_A1 is formed regardless of the position in the X direction. Therefore, no margin is formed at both ends of the analog pattern A1. Also, since no exposure is applied, halftone processing cannot be performed. Therefore, in this embodiment, the development control unit 66 controls the development power source 69 to adjust the development voltage Vc_A1 so that the optical density of each color of the analog pattern A1 becomes 0.6. As shown in FIG. 5D, an analog pattern A1 having an optical density dA1 (= 0.6) is formed on the sheet P.

  FIG. 5E shows the potential at the position in the X direction on the photosensitive drum 11 charged by the charger 12 when forming the second analog pattern A2. FIG. 5F shows the density d1 of the analog pattern A2 formed on the sheet P. In order to form the analog pattern A2, the charging control unit 65 controls the charging power source 68 in accordance with an instruction from the chart generation unit 64. As a result, the surface potential of the photosensitive drum 11 is adjusted to the charging potential Vd_A2 (for example, approximately 0 [V]). The development control unit 66 controls the development power source 69 in accordance with an instruction from the chart generation unit 64. As a result, the potential of the developing sleeve of the developing device 14 is adjusted to the developing bias Vdc_A2. The development bias Vdc_A2 is higher than the charging potential Vd_A2. The chart generation unit 64 does not cause the exposure device 13 to irradiate laser light. As a result, a developing voltage Vc_A2 is formed between the photosensitive drum 11 and the developing sleeve. That is, an electrostatic latent image corresponding to the analog pattern A2 is formed, and a toner image is formed on the photosensitive drum 11 by the toner supplied from the developing device 14. As shown in FIG. 5E, in the analog pattern A2, since no exposure is applied, a constant development voltage Vc_A2 is formed regardless of the position in the X direction. Therefore, no margin is formed at both ends of the analog pattern A2. Also, since no exposure is applied, halftone processing cannot be performed. Therefore, in this embodiment, the development control unit 66 controls the development power supply 69 to adjust the development voltage Vc_A2 so that the optical density of each color of the analog pattern A2 becomes 0.6. As shown in FIG. 5F, an analog pattern A2 having an optical density dA2 (= 0.6) is formed on the sheet P.

  Here, the second charging potential Vd_A2 (for example, approximately 0 [V]) for forming the analog pattern A2 is set lower than the charging potential Vd_A1 for forming the analog pattern A1 (| Vd_A1 |>). | Vd_A2 |). As a result, the contribution rate of the charger 12 to the image defect is reduced in the analog pattern A2 as compared with the analog pattern A1. The development control unit 66 controls the development power source 69 to adjust the development voltage Vc_A2 so as to be the same as the development voltage Vc_A1. As a result, the optical density of each color of the analog pattern A2 becomes 0.6.

  In this embodiment, the development voltage Vc_A1 of the analog pattern A1 and the development voltage Vc_A2 of the analog pattern A2 are adjusted to be equal to each other. As a result, the optical density of the analog pattern A1 is equal to the optical density of the analog pattern A2. However, the development voltage Vc_A1 of the analog pattern A1 and the development voltage Vc_A2 of the analog pattern A2 may be different.

  When the non-contact charging method is used, the charging potential of the photosensitive drum 11 is adjusted by changing the amount of current that the charging power supply 68 passes through the metal wire. Thereby, the analog pattern A1 and the analog pattern A2 are formed even in the non-contact charging method.

  As an example, the case where the optical density of the digital pattern D matches the optical density of the two types of analog patterns A1 and A2 (dD = dA1 = dA2) has been described. However, it is not necessary to match the optical density of the digital pattern D with the optical densities of the two types of analog patterns A1 and A2. If these densities are not matched, it is necessary to correct the difference in density for the stripes having different densities and compare the degree of the stripes.

[Method of forming a toner patch for revealing streaks caused by a cleaner]
As shown in FIG. 6, the distance between the toner patch PD and the white background WD matches the circumference Ld of the photosensitive drum 11. The toner patch PD is formed on the photosensitive drum 11 at a timing that is a predetermined time later than the timing of forming the white background portion WD. The predetermined time is a time required for the photosensitive drum 11 to make one rotation. The toner patch PD may be a digital pattern formed by setting the image signal value to 100%. The image signal value is a signal for determining the optical density of the toner image. When the image signal value is set to 100%, the optical density of the toner image becomes the maximum value. The maximum value is the maximum value in the optical density range of the toner image that can be formed by the image forming apparatus 1. As a result, the largest amount of toner is supplied to the drum cleaner 15, and streaks are likely to appear. As described above, the larger the amount of toner supplied to the drum cleaner 15 by the toner patch PD, the more advantageous it is to detect a defect of the drum cleaner 15. However, if the toner patch PD is excessively supplied, an excessive load is applied to the drum cleaner 15. In addition, minor defects that should be overlooked are also detected. Therefore, the image signal value for forming the toner patch PD may be lower than 100%.

  In the sequence shown in FIG. 6, time t <b> 1 is the timing at which the region where the toner patch PD is formed passes through the primary transfer unit 17 for the first time. That is, time t1 is the timing when the toner patch PD passes through the primary transfer nip portion N1. By adjusting the primary transfer voltage 1Tr_PD at this time, the amount of toner supplied to the drum cleaner 15 by the toner patch PD is controlled.

  FIG. 7A shows the relationship between the amount of toner supplied to the drum cleaner 15 by the toner patch PD and the primary transfer voltage 1Tr. In the case of the primary transfer voltage 1Tr_D [V] indicated by the one-dot chain line in FIG. 6, the amount of toner is small. The primary transfer voltage 1Tr_D is a primary transfer voltage used in normal image formation. The primary transfer voltage indicated by the solid line in FIG. 6 is 0 [V], but the amount of toner increases at this time. 0 [V] is a primary transfer voltage used in the jam processing. In the case of the primary transfer voltage 1Tr_PD [V] indicated by the dotted line in FIG. 6, the toner amount TnPD supplied to the drum cleaner 15 is a value between TnD and Tn0.

  Therefore, the primary transfer voltage when the toner patch PD passes through the primary transfer nip portion N1 for the first time is controlled to 0 [V] which is the first primary transfer voltage. As a result, the toner patch PD is not transferred to the intermediate transfer belt 31 but remains on the photosensitive drum 11 and is conveyed to the drum cleaner 15.

  The primary transfer voltage when the toner patch PD passes through the primary transfer nip N1 for the second time is controlled to 1Tr_D which is the second primary transfer voltage. As a result, among the toner patches PD remaining on the photosensitive drum 11, streaky toner that has not been removed by the drum cleaner 15 is transferred to the intermediate transfer belt 31.

  As described above, when the toner patch PD passes through the primary transfer nip portion N1 for the first time, the first voltage that suppresses the transfer of the toner patch PD from the photosensitive drum 11 to the intermediate transfer belt 31 is the primary transfer. Set as voltage. In addition, when the toner patch PD passes through the primary transfer nip portion N1 for the second time, the primary transfer voltage is set to a second voltage at which a streak caused by defective drum cleaning is transferred from the photosensitive drum 11 to the intermediate transfer belt 31. Is set. In this embodiment, when an area corresponding to the test chart 701 on the photosensitive drum 11 passes through the primary transfer unit 17, the transfer control unit 70 sets the primary transfer voltage to 1Tr_D. As a result, the vertical stripes are easily transferred to the white background WD of the test chart 701 via the intermediate transfer belt 31.

  As shown in FIG. 8, the distance between the toner patch PT and the white background WT matches the circumference Lb of the intermediate transfer belt 31. The toner patch PT is formed on the photosensitive drum 11 at a timing that is a predetermined time later than the timing at which the white background portion WT is formed. The predetermined time is a time required for the intermediate transfer belt 31 to make one rotation. The color of the toner patch PT is a multi-color (mixed color). That is, the toner patch PT is formed by mixing two or more of the YMCBk toner colors. The chart generation unit 64 selects an image signal value corresponding to the maximum value of the toner amount of the multi-order color, and forms the toner patch PT as a digital pattern. In the present embodiment, the chart generating unit 64 sets the yellow image signal value to 100% and sets the magenta image signal value to 100%. As a result, a red toner patch PT is formed on the intermediate transfer belt 31. The larger the amount of toner supplied to the belt cleaner 35 by the toner patch PT, the more advantageous it is to detect a defect of the belt cleaner 35. However, if the toner is excessively supplied to the belt cleaner 35, an excessive load is applied to the belt cleaner 35. In addition, minor defects that should be overlooked are also detected. Therefore, the image signal value of each toner color for forming the toner patch PT may be lower than 100%.

  In FIG. 8, the amount of toner supplied to the belt cleaner 35 by the toner patch PT can be controlled depending on the secondary transfer voltage at time t <b> 1 ′ when the toner patch PT passes through the secondary transfer device 27. Time t1 'is the timing at which a predetermined area on the intermediate transfer belt 31 on which the toner patch PT is formed passes through the secondary transfer device 27 for the first time. That is, the time t1 'is the timing at which the toner patch PT passes through the secondary transfer nip portion N2 for the first time. The white background WT is formed on the sheet P at the timing when the predetermined area (toner patch PT) passes through the secondary transfer device 27 for the second time.

  FIG. 7B shows the relationship between the toner amount of the toner patch PT supplied to the belt cleaner 35 and the secondary transfer voltage 2Tr. In the case where the secondary transfer voltage is set to 2Tr_D [V] as indicated by the one-dot chain line in FIG. 8, the amount of toner decreases. 2Tr_D is a secondary transfer voltage used for normal image formation. As indicated by the solid line in FIG. 8, the secondary transfer voltage may be set to 2Tr_PT [V]. In this case, the amount of toner supplied to the belt cleaner 35 increases. 2Tr_PT is a secondary transfer voltage used in the jam processing.

  The secondary transfer voltage when the toner patch PT passes through the secondary transfer nip N2 for the first time is controlled to 2Tr_PT which is the first secondary transfer voltage. As a result, the toner patch PT does not easily adhere to the secondary transfer unit 27 and remains on the intermediate transfer belt 31.

  The secondary transfer voltage when the toner patch PT passes through the secondary transfer nip portion N2 for the second time is controlled to 2Tr_PT which is the second secondary transfer voltage. As a result, the toner that cannot be removed by the belt cleaner 35 becomes a streaky toner image and is transferred to the sheet.

  Thus, when the toner patch PT passes through the secondary transfer nip portion N2 for the first time, the first secondary transfer voltage (2Tr_PT) is set as the secondary transfer voltage. The first secondary transfer voltage (2Tr_PT) is a voltage that suppresses transfer of the toner patch PT from the intermediate transfer belt 31 to the sheet. When the toner patch PT passes through the secondary transfer nip N2 for the second time, the second secondary transfer voltage (2Tr_D) is set as the secondary transfer voltage. The second secondary transfer voltage (2Tr_D) is a voltage at which streaks caused by poor belt cleaning are transferred from the intermediate transfer belt 31 to the sheet. That is, the vertical stripe is easily transferred to the white background portion WT of the test chart 701. The secondary transfer portion is a nip portion (secondary transfer nip portion N2) between the secondary transfer device 27 and the intermediate transfer belt 31.

[Vertical stripes]
A vertical stripe, which is one of image errors that occur in the image forming apparatus 1 of this embodiment, will be described with reference to FIG. FIG. 9 shows the types of vertical stripes, replacement parts or coping methods, the state of the white background, and the color of the pattern in which the stripes are generated. Further, FIG. 9 shows the presence / absence of streaks in each of the digital pattern and the analog pattern, and no streaks due to defective charging in the analog pattern A2 formed without applying the charging process. A streak whose density is lower than that of a normal part where no streak exists is called a white streak. A streak whose density is higher than the normal part is called a black streak.

Lines due to defective development coat The development coating defect stripes shown in FIG. 9 are vertical stripes generated due to insufficient development coating. FIG. 10A and FIG. 10B are diagrams showing factors that cause streaks due to defective development coating. The term “develop coat” means that the developer is adhered to the surface of the developing sleeve 142 with a uniform thickness. Inside the developing sleeve 142, a magnet 141 that functions as a developer carrier is provided. The developing sleeve 142 is rotatably supported by the developing container 143. The closest portion 145 is a portion where the distance between the developing sleeve 142 and the photosensitive drum 11 is the shortest. A regulating blade 146 is provided upstream of the closest portion 145 in the rotation direction of the developing sleeve 142. The regulating blade 146 is disposed so that the distance to the developing sleeve 142 is constant, and regulates the amount of the two-component developer supplied to the closest portion 145.

  As shown in FIG. 10B, foreign matter 148 such as dust or hair may become clogged between the developing sleeve 142 and the regulating blade 146. In this case, the foreign matter 148 hinders the flow of the developer. As shown in FIG. 10C, an uncoated region 151 where the developer is not carried is generated on the developing sleeve 142. There is no developer in the uncoated region 151. Therefore, the developer is not supplied to the portion of the surface of the photosensitive drum 11 that faces the non-coated region 151. Therefore, a straight continuous vertical line 152 is generated on the surface of the photosensitive drum 11. As shown in FIG. 9A, the developing unit 14 is a unit to be replaced in order to eliminate such a development coating defect streak.

  Further, with reference to FIG. 9, the characteristics of white stripes generated due to defective development coat will be described. First, the development coat defect stripe (white stripe) does not occur in the white background portions W, WD, and WT where the pattern image is not formed. Then, the developing device 14 in which the development coat defect is generated is identified from the color of the pattern in which the development coat defect stripe is detected.

  FIG. 11A shows the potential at the position in the X direction of the photosensitive drum 11 when the digital pattern D is formed. FIG. 11B shows the optical density at the position in the X direction of the sheet P when the digital pattern D is formed. FIG. 11C shows the potential at the position in the X direction of the photosensitive drum 11 when the analog pattern A1 is formed. FIG. 11D shows the optical density at the position in the X direction of the sheet P when the analog pattern A1 is formed. FIG. 11E shows the potential at the position in the X direction of the photosensitive drum 11 when the analog pattern A2 is formed. FIG. 11F shows the optical density at the position in the X direction of the sheet P when the analog pattern A2 is formed. As indicated by these, the development coat defect streaks are caused by the fact that the developer is not supplied onto the development sleeve 142. Accordingly, vertical stripes are generated in all of the digital pattern D, the analog pattern A1, and the analog pattern A2. Furthermore, there is no difference between the density of streaks occurring in the analog pattern A1 and the density of streaks occurring in the analog pattern A2.

Next, the white stripe resulting from the exposure failure shown in FIG. 9 will be described. FIG. 12A is a diagram illustrating a generation mechanism of white stripes due to exposure failure. A dustproof glass 132 is provided in the optical path through which the laser beam output from the exposure device 13 passes. If foreign matter 135 such as hair or toner adheres to a part of the dust-proof glass 132, the laser beam applied to the surface of the photosensitive drum 11 is blocked. That is, the potential of the electrostatic latent image in the portion of the surface of the photosensitive drum 11 where the laser beam is not irradiated by the foreign matter 135 is lowered, and vertical stripes are generated. This vertical streak is caused by a decrease in the amount of toner attached, and thus becomes a white streak. A countermeasure for reducing white stripes due to exposure failure is to clean the dustproof glass 132 or replace the exposure unit 13.

  The characteristics of white stripes resulting from exposure failure will be described with reference to FIG. First, the poorly exposed white stripe does not occur in the white background portion W where the pattern image is not formed. Then, from the color of the digital pattern D in which the exposure poor white stripe is detected, the exposure device 13 that has caused the exposure failure is specified.

  FIG. 13A shows the potential at the position in the X direction of the photosensitive drum 11 when the digital pattern D is formed. FIG. 13B shows the optical density at the position in the X direction of the sheet P when the digital pattern D is formed. FIG. 13C shows the potential at the position in the X direction of the photosensitive drum 11 when the analog pattern A1 is formed. FIG. 13D shows the optical density at the position in the X direction of the sheet P when the analog pattern A1 is formed. FIG. 13E shows the potential at the position in the X direction of the photosensitive drum 11 when the analog pattern A2 is formed. FIG. 13F shows the optical density at the position in the X direction of the sheet P when the analog pattern A2 is formed.

  As shown in FIG. 13A and FIG. 13B, white streaks are generated due to poor exposure (reducing the amount of exposure light). In the digital pattern D, the surface potential becomes higher than Vl_D at a part of the position of the photosensitive drum 11 in the X direction, thereby causing an exposure failure white streak. On the other hand, as shown in FIG. 13C to FIG. 13F, the analog patterns A1 and A2 are formed without exposure, so that no exposure white stripes are generated.

Streaks due to poor charging The charger 12 of this embodiment employs a contact charging method in which charging is performed by bringing a charging member into contact with the photosensitive drum 11. In the contact charging method, cleaning becomes insufficient at a certain position in the X direction on the surface of the photosensitive drum 11, so that an external additive such as silicon can adhere to the charging member. FIG. 14A shows the surface potential (charging potential) of the photosensitive drum 11. FIG. 14B shows the relationship between the image signal and the optical density. As shown in FIG. 14A, the resistance of the charging member increases at a part of the surface of the photosensitive drum 11 in the X direction, and the charging potential at that position increases. A region in the X direction where the resistance is increased is called a high resistance portion. When the charging potential increases, as shown in FIG. 14B, even if the position of the photosensitive drum 11 in the X direction is exposed using the same image signal, the density of the high resistance portion is lower than the density of the normal portion. And white streaks occur.

  On the other hand, if a cleaning failure occurs at a part of the surface of the photosensitive drum 11 in the X direction, the toner may adhere to the charging member. The resistance of the surface of the charging member where the toner is attached becomes small. Although the charging member gradually increases in resistance due to durability, the resistance of the charging member is partially reduced by peeling off the surface layer of the charging member. As a result, as shown in FIG. 14A, the resistance of the charging member partially decreases in a partial region in the X direction, and the charging potential decreases. This portion is called a low resistance portion. When the charging potential is lowered, as shown in FIG. 14B, even if the position of the photosensitive drum 11 in the X direction is exposed using the same image signal, the density of the low resistance portion is higher than the density of the normal portion. And black streaks occur.

  The characteristics of the defective charging stripe will be described with reference to FIG. First, defective charging lines do not occur in the white background W where the pattern image is not formed. Then, the charger 12 in which the charging failure has occurred is identified from the color of the pattern in which the exposure failure stripe is detected.

  FIG. 15A shows the potential at the position in the X direction on the photosensitive drum 11 when the digital pattern D is formed. FIG. 15B shows the optical density at the position in the X direction of the sheet P when the digital pattern D is formed. FIG. 15C shows the potential at the position in the X direction of the photosensitive drum 11 when the analog pattern A1 is formed. FIG. 15D shows the optical density at the position in the X direction of the sheet P when the analog pattern A1 is formed. FIG. 15E shows the potential at the position in the X direction on the photosensitive drum 11 when the analog pattern A2 is formed. FIG. 15F shows the optical density at the position in the X direction of the sheet P when the analog pattern A2 is formed.

  As shown in FIGS. 15A and 15B, in the digital pattern D, the charged potential at a part of the position of the photosensitive drum 11 exposed in the X direction is different from Vl_D. Black streaks occur at positions where the charging potential is lower than Vl_D, and white streaks occur at positions where the charging potential is higher than Vl_D. As shown in FIG. 15C and FIG. 15D, even in the analog pattern A1, since the charging potential is different from Vd_A1 in a part in the X direction, black stripes and white stripes are generated. Since the charging failure occurs due to the difference in resistance of the charging member, the charging failure is reduced by lowering the charging potential of the charger 12. As shown in FIG. 15E and FIG. 15F, the analog pattern A2 is formed without applying the charging process, and therefore streaks due to charging failure do not occur.

Next, streaks due to plastic deformation of the intermediate transfer belt 31 shown in FIG. 9 will be described. Due to long-term use, the inner surface of the intermediate transfer belt 31 may be scraped to generate powder. Some parts constituting the transfer unit may adhere to the surfaces of the rollers 36 and 37. As shown in FIG. 12B, a part of the intermediate transfer belt 31 is plastically deformed into a convex shape. This portion is called a convex portion 311. When the convex portion 311 is generated on the intermediate transfer belt 31 in this way, both sides of the convex portion 311 are less likely to come into contact with the photosensitive drum 11 and the sheet P. Therefore, it is difficult for the both side portions to secondarily transfer the toner image to the sheet P, and white stripes are generated. Since the convex portion 311 secondarily transfers a large amount of toner to the sheet P, black streaks are generated. Therefore, a part to be replaced in order to eliminate streaks due to plastic deformation of the intermediate transfer belt 31 is an intermediate transfer unit. The white streaks are not white streaks but light streaks whose density is light (toner is reduced). Further, the black stripe is a dark stripe having a high density (increasing toner).

  The feature of streaks resulting from plastic deformation will be described with reference to FIG. Streaks due to plastic deformation do not occur in the white background W where the pattern image is not formed. Streaks due to plastic deformation can occur in all color patterns. This is because streaks due to plastic deformation occur at the secondary transfer portion. Further, since there is no relation to the presence or absence of exposure and the charged potential, streaks occur not only in the digital pattern D but also in the analog patterns A1 and A2.

• Streaks due to poor cleaning of the photosensitive drum The streaks due to poor cleaning of the photosensitive drum 11 are black streaks. In some rare cases, the drum cleaner 15 may lose a part of the blade that rubs against the photosensitive drum 11. When a part of the blade as the removing member is lost, the lost part cannot scrape off the toner remaining on the photosensitive drum 11. This causes black streaks. Therefore, the drum cleaner 15 in which the cleaning failure has occurred is identified from the color of the black stripe. For example, when a cleaning failure occurs in the drum cleaner 15 of the yellow station, yellow black streaks are generated. Further, black streaks due to poor cleaning are generated as substantially straight lines on the white background WD. Therefore, the process cartridge 50 is a part to be replaced in order to reduce black streaks due to poor cleaning of the photosensitive drum 11. Thus, the assembly unit including the drum cleaner 15 becomes a replacement part.

  The feature of streaks due to defective drum cleaning will be described with reference to FIG. Since streaks occur due to poor drum cleaning, streaks also occur in the white background WD where the pattern image is not formed. The streak color generated in the white background WD is the same color as the toner color accumulated in the drum cleaner 15. Therefore, this streak becomes a single color streak. Since streaks occur even in colors that do not form an image, they occur in all color patterns of yellow, magenta, cyan, and black. For example, when the drum cleaner 15 in the yellow station is lost, yellow stripes are generated over the entire area in the conveyance direction of the sheet P.

  However, even if part of the blade is missing, streaks may not occur. FIG. 16A shows that toner is not supplied to the drum cleaner 15 in which a part of the blade is missing. In this case, since there is almost no toner passing through the missing part, no streak occurs in the test chart.

  On the other hand, as shown in FIG. 16B, in this embodiment, toner is supplied to the drum cleaner 15 by the toner patch PD. Therefore, the toner passes through the blade defect portion of the drum cleaner 15 and the streak-shaped image X is conveyed again to the primary transfer nip portion N1. The streak-shaped image X is transferred from the photosensitive drum 11 to the intermediate transfer belt 31 at the primary transfer nip N1, and is transferred from the intermediate transfer belt 31 to the white background WD of the test chart 701 at the secondary transfer nip N2. Therefore, streaks appear in the white background portion WD. Even if there is a defect in the fur brush, streaks become apparent.

A streak resulting from poor cleaning of the intermediate transfer belt A black streak caused by poor cleaning of the intermediate transfer belt 31 will be described with reference to FIG. In some rare cases, the belt cleaner 35 may have a part of a blade as a removing member that rubs the intermediate transfer belt 31. When a part of the blade of the belt cleaner 35 is lost, the lost part cannot scrape off the toner remaining on the intermediate transfer belt 31. This causes black streaks. The color of this type of stripe can be a color (mixed color) in which yellow, magenta, cyan, and black toners are mixed. A unit to be replaced in order to reduce black streaks caused by poor cleaning of the intermediate transfer belt 31 is a belt cleaner 35.

  The characteristics of the streaks resulting from the poor cleaning of the intermediate transfer belt 31 will be described with reference to FIG. Due to the belt cleaning failure, streaks also occur in the white background portions W and WT where the pattern image is not formed. Since the streaks generated in the white background portions W and WT are caused by the toner accumulated in the belt cleaner 35, the color of the streaks can be a mixed color of yellow, magenta, cyan, and black.

  However, even if a part of the blade of the belt cleaner 35 is missing, streaks may not occur. FIG. 16C shows that no toner is supplied to the belt cleaner 35 in which a part of the blade is missing. In this case, since there is almost no toner passing through the missing part, no streak occurs in the test chart.

  On the other hand, as shown in FIG. 16D, in this embodiment, toner is supplied to the belt cleaner 35 by the toner patch PT. Therefore, the toner passes through the blade defect portion of the belt cleaner 35, and the streak-shaped image X is conveyed again to the secondary transfer nip portion N2. The streak-shaped image X is transferred from the intermediate transfer belt 31 to the white background portion WT of the test chart 701 at the secondary transfer nip portion N2. Therefore, streaks appear in the white background portion WT. Even if there is a defect in the fur brush, streaks become apparent. In this embodiment, as shown in FIG. 16D, a pattern is formed to make a streak-like image appear on the test chart. This pattern supplies toner to the belt cleaner 35. If the belt cleaner 35 is defective, streaks due to poor cleaning of the intermediate transfer belt 31 are generated on the test chart.

[Identification of replacement parts]
The creation process of the test charts 701 to 704 and the replacement part specifying process for specifying the replacement part will be described with reference to FIG. When an instruction for specifying a replacement part or an instruction for creating test charts 701 to 704 is input from the input device 62, the CPU 60 executes the following processing.

  In S101, the CPU 60 (chart generating unit 64) controls the printer 3 to create test charts 701 to 704.

● Test chart 701
In the test chart 701, the streak-like image that has passed through the missing portion of the drum cleaner 15 and the streak-like image that has passed through the missing portion of the belt cleaner 35 need to be transferred to one sheet. However, the time for which the photosensitive drum 11 rotates once is shorter than the time for which the intermediate transfer belt 31 rotates once. Accordingly, in the process of creating the test chart 701, first, the toner patch PT is formed before the toner patch PD.

  In order to form the toner patch PT, the chart generation unit 64 sets the charging potential Vd_D to the chargers 12 of the yellow station and the magenta station, and sets the developing potential Vdc_D to the developer 14 of the yellow station and the magenta station. The chart generator 64 sets 1Tr_D as the primary transfer voltage by the transfer controller 70. Then, the chart generation unit 64 outputs an image signal for forming the toner patch PT to the exposure unit 13 of the yellow station and the magenta station. As a result, a toner patch PT in which yellow toner and magenta toner are mixed is formed on the intermediate transfer belt 31. The chart generation unit 64 sets the secondary transfer voltage to 2Tr_PT by the transfer control unit 70. Thus, the toner patch PT passes through the secondary transfer nip portion N2 and is conveyed to the belt cleaner 35. Then, toner is supplied to the belt cleaner 35. If there is a defective portion in the belt cleaner 35, even if the region where the toner patch PT is formed passes through the cleaning position of the belt cleaner 35, a streak-like image remains in the region. The chart generation unit 64 controls the secondary transfer voltage to 2Tr_D by the transfer control unit 70 after the toner patch PT passes through the secondary transfer nip N2. As a result, when the above-mentioned region passes through the secondary transfer nip portion N2 again, a streak-like image caused by belt cleaning failure is transferred from the intermediate transfer belt 31 to the sheet P (test chart 701).

  Further, the chart generation unit 64 sets a charging potential Vd_D in the yellow station charger 12 and a developing potential Vdc_D in the yellow station developer 14 in order to form the toner patch PDY. The chart generator 64 sets the primary transfer voltage to 0 by the transfer controller 70. Then, the chart generation unit 64 outputs an image signal for forming the toner patch PDY to the yellow station exposure device 13. As a result, the yellow station forms the toner patch PDY. Similarly, toner patches PDM, PDC, and PDBk are also formed. The toner patches PDY, PDM, PDC, and PDBk pass through the primary transfer nip portion N1 and are conveyed to the drum cleaner 15. As a result, toner is supplied to the drum cleaner 15. If the drum cleaner 15 has a defective portion, even if the region where the toner patches PDY, PDM, PDC, and PDBk are formed passes through the cleaning position of the drum cleaner 15, a streak-like image remains in the region. The chart generation unit 64 controls the primary transfer voltage to 1Tr_D by the transfer control unit 70 after the toner patches PDY, PDM, PDC, and PDBk pass through the primary transfer nip N1. As a result, when the above-mentioned area again passes through the primary transfer nip portion N <b> 1, the stripe-shaped image in the area is transferred to the intermediate transfer belt 31. Then, the chart generation unit 64 controls the secondary transfer voltage to 2Tr_D by the transfer control unit 70. As a result, a streak-shaped image caused by defective drum cleaning is transferred from the intermediate transfer belt 31 to the white background WD of the sheet P (test chart 701).

Test chart 702
The chart generator 64 sets a charging potential Vd_D in the charger 12 of the yellow station in order to form the digital pattern DY. In addition, the chart generation unit 64 sets the development potential Vdc_D in the developing device 14 of the yellow station. Further, the chart generator 64 outputs an image signal for forming the digital pattern DY to the yellow station exposure unit 13. Thereby, the digital pattern DY is formed. Similarly, digital patterns DM, DC, and DBk are formed.

● Test chart 703
Next, the CPU 60 sets the charging potential Vd_A1 in the charger 12 of each color station in order to form the analog pattern A1Y. In addition, the chart generation unit 64 sets a development potential Vdc_A1 in the developing device 14 of each color station. Thereby, analog patterns A1Y, A1M, A1C, and A1Bk are formed.

Test chart 704
Next, in order to form the analog pattern A2Y, the CPU 60 sets a charging potential Vd_A2 in the charger 12 of each color station. In addition, the chart generation unit 64 sets a development potential Vdc_A2 in the developing device 14 of each color station. Thereby, analog patterns A2Y, A2M, A2C, and A2Bk are formed. Thus, test charts 701 to 704 are formed and discharged to the discharge tray of the image forming apparatus 1. In addition, when a user or a service person specifies a replacement part by visual inspection of the test charts 701 to 704, the following processing is omitted.

  In S102, the CPU 60 (diagnosis unit 67) controls the image reader 2 and reads the test charts 701 to 704. The diagnosis unit 67 may display guidance on the display device 61 urging the operator to place the test charts 701 to 704 and press the reading start button. The reading results of the test charts 701 to 704 are stored in the storage device 63.

  In S103, the CPU 60 (diagnosis unit 67) detects streaks from the reading results of the test charts 701 to 704. For example, the diagnosis unit 67 may analyze image data that is a read result and acquire a feature amount for detecting streaks. The read result includes RGB luminance values, and the diagnosis unit 67 divides the read result into an R image, a G image, and a B image, and performs analysis for each color individually. That is, the diagnosis unit 67 detects vertical stripes for each image data of the R image, the G image, and the B image. The diagnosis unit 67 may detect vertical stripes for each color after converting the R image, the G image, and the B image into a Y image, an M image, a C image, and a K image. The diagnosis unit 67 calculates an average value of luminance values of a plurality of pixels arranged in the vertical direction of the image data (the conveyance direction of the test charts 701 to 704 and the scan direction of the image reader 2). This is to reduce electrical noise superimposed by the image reader 2.

  In the present embodiment, since the width of the white background portions WD and WT (the length in the transport direction) is 10 mm, the averaging is applied to a plurality of pixels corresponding to 10 mm. On the other hand, in the digital pattern D and the analog patterns A1 and A2, since the width (length in the short direction) of each color pattern is 30 mm, averaging is applied to a plurality of pixels corresponding to 30 mm. The diagnosis unit 67 performs an inclination correction process for correcting the inclination of the luminance value (average value in the vertical direction) along the longitudinal direction of the pattern. Thereby, the influence of the density unevenness of the image reader 2 and the pattern image is reduced. The diagnosis unit 67 detects a pixel group (region) having a difference in luminance value with respect to a uniform portion (normal portion) in the luminance value of the pattern. For example, the diagnosis unit 67 calculates a difference (luminance difference) between the average luminance value of the pattern in the longitudinal direction and the luminance value (luminance value whose inclination is corrected) at each position of the pattern in the longitudinal direction. The diagnosis unit 67 detects a pixel group whose luminance difference exceeds a predetermined threshold (eg, 20% of the average value) as a vertical stripe. The diagnosis unit 67 may determine a streak whose brightness is lower (higher density) than that of a normal part as a black streak, and conversely, a streak with higher brightness (lower density) may be determined as a white streak. The diagnosis unit 67 stores the position in the X direction and the position in the Y direction where the streak is detected, the color of the streak, the luminance difference, and the like in the storage device 63 as a streak feature amount. The streak position indicates where the streak occurs in the white background portions W, WT, WD, the digital pattern D, and the analog patterns A1 and A2. The streak color helps identify the replacement part. The luminance difference for the streaks in the analog pattern A1 and the luminance difference for the streaks in the analog pattern A2 are useful for determining whether the streaks are improved.

  In S <b> 104, the CPU 60 (diagnosis unit 67) identifies the cause of the stripe and the replacement part (or coping method) based on the reading results (the detection result of the stripe) of the test charts 701 to 704. For example, the diagnosis unit 67 determines the presence / absence of a streak and the color of a streak (single color (YMCBk) / mixed color) for each of the white background portions W, WT, WD, and YMCBk patterns based on the streak feature amount stored in the storage device 63. . The diagnosis unit 67 identifies the cause and the replacement part by comparing the determination result with a specific condition for identifying the cause and the replacement part. The diagnosis unit 67 functions as a detection unit that detects an abnormal part of the image forming apparatus 1.

  In S <b> 105, the CPU 60 (diagnosis unit 67) displays a message indicating a replacement part and a coping method on the display device 61, or transmits the message to the PC 124 or server 128 via the communication IF 55.

  FIG. 18 shows an example of a message indicating a replacement part and a coping method. In this example, the test charts 701 to 704 contain information such as vertical streaks (streaks extending in the transport direction), codes indicating the cause, and names of replacement parts. Users and service personnel can easily understand the cause of streaks and replacement parts by referring to the message. If no vertical stripe is detected, the diagnosis unit 67 displays a message on the display device 61 indicating that the image forming apparatus 1 is normal. As described above, since the occurrence of the vertical stripe and the replacement part can be known from the specific information, the user and the service person can easily understand the replacement part.

[Details of identifying replacement parts]
FIG. 19 is a flowchart showing details of processing for specifying a replacement part and a coping method. The CPU 60 (diagnosis unit 67) detects vertical stripes at each position in the X direction (eg, every 1 mm). For this reason, vertical stripes may be detected at a plurality of positions in the X direction. In addition, the causes of the plurality of vertical stripes may be different. Therefore, the CPU 60 (diagnosis unit 67) identifies the cause and the replacement part for each stripe. The replacement part may be specified by specifying the cause of the streak. Each determination process shown in FIG. 19 is also an aggregate of specific conditions for specifying replacement parts and causes.

  In S200, the CPU 60 (diagnosis unit 67) reads the feature amount from the storage device 63, and determines whether or not there are any streaks in any of the white background portions W, WD, and WT. The coordinates of the white background portions W, WD, and WT in the test charts 701 to 704 are known. The CPU 60 determines the presence or absence of streaks in the white background portions W, WD, and WT by comparing the position of the streaks and the coordinates of the white background portions W, WD, and WT. If there is a streak in any of the white background portions W, WD, and WT, the CPU 60 proceeds to S201.

  In S201, the CPU 60 (diagnosis unit 67) determines whether or not the streak color is a mixed color. If the streak color is a mixed color, the CPU 60 proceeds to S202. In S <b> 202, the CPU 60 (diagnosis unit 67) determines that the cause of streaks is a cleaning failure of the intermediate transfer belt 31, and specifies the belt cleaner 35 as a replacement part. On the other hand, if the streak color is any one of YMCBk, the CPU 60 proceeds to S203. In S203, the CPU 60 (diagnosis unit 67) determines that the cause of the streak is a defective cleaning of the photosensitive drum 11, and specifies the process cartridge 50 corresponding to the streak color as a replacement part. If no streak is detected in the white background portions W, WD, and WT in S200, the CPU 60 proceeds to S204.

  In S204, the CPU 60 (diagnosis unit 67) reads the feature amount from the storage device 63, and determines whether or not streaks exist in the digital patterns DY to DBk. The coordinates of the digital patterns DY to DBk in the test charts 701 to 704 are known. The CPU 60 determines the presence or absence of streaks in the digital patterns DY to DBk by comparing the positions of the streaks and the coordinates of the digital patterns DY to DBk. If there is no streak in any of the digital patterns DY to DBk, the CPU 60 proceeds to S205. In S205, the CPU 60 (diagnosis unit 67) specifies that there is no replacement part (normal). On the other hand, when the CPU 60 detects a streak in any of the digital patterns DY to DBk, the process proceeds to S206.

  In S206, the CPU 60 (diagnosis unit 67) reads the feature amount from the storage device 63 and determines whether or not a streak is generated in a specific color. This is the same as determining whether streaks occur in all colors (all of the digital patterns DY to DBk). If streaks have occurred in all colors, the CPU 60 proceeds to S207. In S207, the CPU 60 (diagnosis unit 67) determines that the cause of the streaks is plastic deformation of the intermediate transfer belt 31, and specifies the transfer unit including the intermediate transfer belt 31 as a replacement part. On the other hand, if the streak occurs only in the specific color, the CPU 60 proceeds to S208.

  In S208, the CPU 60 (diagnosis unit 67) determines whether or not a streak has occurred in the analog pattern A1 having the same color as the color of the digital pattern D in which the streak has occurred. If there is no streak in the analog pattern A1, the CPU 60 proceeds to S209. In S209, the CPU 60 (diagnosis unit 67) determines that the cause of the streak is an exposure failure and identifies the exposure unit 13 corresponding to the streak color as a replacement part. The CPU 60 may specify cleaning of the exposure device 13 corresponding to the streak color as a countermeasure method. If a stripe has occurred in the analog pattern A1 having the same color as the color of the digital pattern D in which the stripe has occurred, the CPU 60 proceeds to S210.

  In S210, the CPU 60 (diagnosis unit 67) reads the feature amount from the storage device 63, and determines whether the analog pattern A2 has a streak. If there is a streak in the analog pattern A2, the CPU 60 proceeds to S211. In S <b> 211, the CPU 60 (diagnosis unit 67) identifies the developing device corresponding to the stripe color as a replacement part. If there is no streak in the analog pattern A2, the CPU 60 proceeds to S212. In S212, the CPU 60 (diagnosis unit 67) identifies the charging failure as the cause of the streak, and identifies the process cartridge 50 including the charger 12 as a replacement part. The replacement part is a replacement part corresponding to the stripe color. For example, if the yellow analog pattern A1 has a streak but the yellow analog pattern A2 does not have a streak, the process cartridge 50 in charge of yellow is specified as a replacement part.

  As described above, the CPU 60 creates the test charts 701 to 704 and analyzes the streaks generated in the test charts 701 to 704 to identify the cause of the streaks and the replacement parts. Further, the CPU 60 may output a message indicating the cause of the streak or the replacement part to the display device 61 or the like. As a result, the user and the service person can easily recognize the cause of the stripe and the replacement part. Therefore, the work time (downtime) required for maintenance will be greatly reduced. Also, since the parts involved in the streak are identified, parts that are not involved in the streak will not be replaced. Therefore, maintenance costs will be reduced in addition to maintenance time. A message indicating the cause of a streak or a replacement part may be transmitted to the service person's server 128 via the network. Since the service person can grasp the replacement part in advance, the replacement part can be reliably carried and maintained. The process of identifying the cause of the streak, the replacement part, and the like shown in FIG. 19 may be executed by the user or service person viewing the test charts 701 to 704. Here, a color printer is used as an example, but the present embodiment may be applied to a monochrome printer.

  The test charts 701 to 704 shown in FIG. 3 are merely examples. The order of the white background portions W and WD, the white background portion WT, the digital pattern D, and the analog patterns A1 and A2 in the test charts 701 to 704 may be other orders. It suffices if the test chart has the white background portion WD or the white background portion WT, and the white background portion W, the digital pattern D, and the analog patterns A1 and A2 may be omitted from the test chart. In other words, a test chart including a pattern related to a replacement part that the operator wants to determine the necessity of replacement out of the white background portions W, WD, WT, the digital pattern D, and the analog patterns A1 and A2 may be created.

  Examples of image errors other than vertical streaks include horizontal streaks that occur in accordance with the rotation period of the rotating parts in the direction orthogonal to the conveyance direction of the sheet P and image flaws that occur due to scratches on the rotating parts. When the length of the test chart 701 in the conveying direction is equal to or longer than the length of the rotating component that causes horizontal stripes and image scratches, horizontal stripes and image scratches can be detected. The storage device 63 may store a specific condition in which the feature of the horizontal stripe or the image flaw is associated with the component corresponding to the feature. In this case, the CPU 60 identifies the replacement part by comparing the characteristic of the detected horizontal streak or image scratch with the specific condition.

[Example 2]
In the first embodiment, it is determined which cleaner should be replaced depending on the color of the stripe generated in the white background portion W. That is, if the streak is a single color, the diagnosis unit 67 determines that the cause of the streak is in the drum cleaner 15 that matches the streak color. The diagnosis unit 67 determines that the belt cleaner 35 has a cause of the streak if the streak color is a mixed color.

  However, when the level of the streak is small, the luminance value of the detected streak is small, and it is difficult to determine whether it is a single color or a mixed color. In addition, the diagnosis unit 67 cannot distinguish between black single-color streaks and black streaks formed by mixing toner with streak detection values.

  Therefore, in the second embodiment, the CPU 60 determines which one of the drum cleaner 15 and the belt cleaner 35 should be replaced and which toner color is to be replaced based on the detected position. To do. As described above, even when the color of the stripe generated in the white background portions W, WD, and WT cannot be recognized, the replacement part can be specified. In addition, Example 2 is the same as Example 1 except S201-S203 of Example 1 of FIG. Therefore, the parts already described are omitted.

[Identification processing of replacement part based on position where streak is detected in white background portion W]
FIG. 20 shows the relationship between replacement parts and streak detection positions. This relationship may be stored in the storage device 63 and referred to by the CPU 60. FIG. 21 is a flowchart showing the replacement part specifying process. S201 to S203 in FIG. 19 are replaced with S2101 to S2103 in FIG.
In S2101, the CPU 60 (diagnosis unit 67) determines whether the position where the streak is detected is the white background portion WT. If the streak is detected at the white background WT, the CPU 60 proceeds to S2102.
In S2102, the CPU 60 (diagnosis unit 67) specifies the belt cleaner 35 as a replacement part as shown in FIG. On the other hand, when the streak is not detected in the white background portion WT, the CPU 60 proceeds to S2103.
In S2103, the CPU 60 (diagnostic unit 67) identifies the cartridge corresponding to the streak detection position as a replacement part. As shown in FIG. 20, when a streak is detected in the white background WDY, the diagnosis unit 67 specifies the drum cleaner 15 for yellow toner as a replacement part. When a streak is detected in the white background WDM, the diagnosis unit 67 specifies the magenta toner drum cleaner 15 as a replacement part. When streaks are detected in the white background portion WDC, the diagnosis unit 67 identifies the drum cleaner 15 for cyan toner as a replacement part. When streaks are detected in the white background portion WDBk, the diagnosis unit 67 specifies the drum cleaner 15 for black toner as a replacement part.

  In this way, the diagnosis unit 67 can identify the replacement part based on the streak detection position. Therefore, even if the color of the stripe cannot be recognized, the replacement part can be specified.

[Example 3]
In the second embodiment, it is determined which color of the drum cleaner 15 should be replaced and whether the belt cleaner 35 should be replaced, depending on which white background portion the stripe has been detected. As shown in FIG. 22A, the length of the streak caused by the cleaner becomes longer as the degree of wear and loss of the cleaner increases. In this example, the test chart 701 shows that the yellow drum cleaner 15 has three different defects. The degree of the three defects is different. The streak St1 is a streak caused by a large defect. The streak St2 is a streak caused by a medium defect. The streak St3 is a streak caused by a small defect. In the transport direction of the test chart 701, the length of the streak St1 is the longest and the length of the streak St3 is the shortest. The length of the stripe in the conveyance direction of the test chart 701 may be shorter than the length of the patch PD. The generation position of the streak St3 is a position (a rear position) delayed from the generation positions of the streaks St1 and St2.

  The reason that the length of the streak is different from the length of the patch PD or that the streak generation position is different from the position corresponding to the patch PD is that the toner constituting the patch PD is blocked by the blade of the drum cleaner 15. This is because the drum cleaner 15 gradually passes. This phenomenon also occurs in the belt cleaner 35.

  In the second embodiment, the replacement part is specified based on the streak position. When this specifying method is strictly applied, both the yellow drum cleaner 15 and the magenta drum cleaner 15 are specified as replacement parts by the streak St1. Further, the magenta drum cleaner 15 is specified as the replacement part by the streak St3.

  FIG. 22B shows a test chart 701 and a replacement part specifying method according to the third embodiment. As the white background portion for the patch PD, the wide-width type white background WideWD is employed. The length of the widened white background WideWD is longer than the length of the patch PD in the test chart 701. For example, the streaks St1 to St3 caused by the yellow photosensitive drum 11 are all located in the wide-width type white background WideWDY. Therefore, the CPU 60 can correctly specify the yellow photosensitive drum 11 as a replacement part based on the streaks St1 to St3.

  In addition, if each wide-width type white background WideWD of YMCBk overlaps with another adjacent wide-width type white background WideWD, it is difficult to accurately identify the replacement part based on the streak position. Therefore, the chart generation unit 64 shifts the formation start positions of the patches PDM, PDC, and PDBk according to the formation start positions of the wide-width white background portions WideWDM, WideWDC, and WideWDBk, respectively. However, the distance between the patch PD and the widened white background WideWD is maintained at the circumferential length Ld of the photosensitive drum 11.

  As described above, in the third embodiment, the replacement part can be specified more accurately than in the second embodiment by devising the formation position of the patch PD in the test chart 701 and the position and length of the wide-width white background portion WideWD. It should be noted that the widened white background can be similarly used for the white background WT corresponding to the patch PT.

[Example 4]
The fourth embodiment is a higher technical idea derived from the first to third embodiments. The photosensitive drum 11 and the intermediate transfer belt 31 are an example of a rotating body. In particular, the photosensitive drum 11 is an example of a photosensitive member that is rotationally driven. The intermediate transfer belt 31 is an example of an image carrier. Each station of YMCBk is an example of an image forming unit that forms a toner image. That is, the station is an example of an image forming unit that forms an image on the image carrier or the photosensitive member using a developer. The registration roller pair 26 is an example of a conveying unit that conveys a sheet. The primary transfer unit 17 and the secondary transfer unit 27 are an example of a transfer unit that transfers a toner image formed on a rotating body to a predetermined member (for example, the intermediate transfer belt 31 and the sheet P). In particular, the secondary transfer nip portion N2 is an example of a transfer portion to which an image formed on the image carrier is transferred to a sheet. The drum cleaner 15 and the belt cleaner 35 are examples of a cleaning unit that cleans toner remaining on the rotating body without being transferred to a predetermined member. The belt cleaner 35 is an example of a removing member that removes the developer remaining on the image carrier without being transferred from the image carrier to the sheet in the transfer unit. The CPU 60 is an example of a control unit that controls the image forming unit and the transfer unit. As described with reference to FIG. 3 and the like, the CPU 60 controls the image forming unit at the nth rotation of the rotating body to form a toner image in a predetermined area of the rotating body, and causes the cleaning unit to clean the toner image. Further, the CPU 60 controls the image forming means at the (n + 1) th rotation of the rotating body to form a test chart (for example, test chart 701) for specifying replacement parts by not forming a toner image in a predetermined area of the rotating body. . That is, the CPU 60 is a control unit that executes a process of creating a test chart used for detecting an abnormal portion of the image forming apparatus. When this process is executed, the CPU 60 causes the image forming unit to form a pattern image, and rotates the image carrier so that the pattern image is removed by the removing member through the transfer unit. Further, the CPU 60 controls the conveying unit so that the period in which the region on the image carrier including the position where the pattern image is transferred passes through the transfer unit again overlaps the period in which the sheet passes through the transfer unit. As described above, the toner image is formed on the rotating body in advance before the test chart is formed, and the cleaning unit cleans the toner image, so that the image defect due to the cleaning unit is easily manifested on the test chart. That is, the toner image formed in the predetermined area of the rotator at the n-th rotation is a toner image for revealing an image defect.

  As shown in FIG. 16, the image forming unit does not form a toner image at the n + 1th rotation in a predetermined area where the toner image is formed on the rotating body at the nth rotation, thereby causing a streak-like image on the test chart. Detection areas (eg, white background portions WD, WT) are formed. The CPU 60 forms the white background portion WD at the timing when the photosensitive drum 11 rotates once from the timing when the patch PD for making the vertical stripes appear. That is, the time difference between the formation start time of the patch PD and the formation start time of the white background WD is the time required for one rotation of the photosensitive drum 11. The patch PD is formed at a time before a time required for one rotation of the photosensitive drum 11 from the formation start time of the white background portion WD.

  Similarly, the CPU 60 forms the white background portion WT at the timing when the intermediate transfer belt 31 rotates once from the timing at which the patch PT for making the vertical stripes appear. That is, the time difference between the formation start time of the patch PT and the formation start time of the white background portion WT is the time required for one rotation of the intermediate transfer belt 31. The patch PT is formed at a time before the formation start time of the white background portion WT by the time required for one rotation of the intermediate transfer belt 31.

  The diagnosis unit 67 of the CPU 60 is an example of a specifying unit that specifies a replacement part based on the detection result of the streak-like image generated in the detection area in the test chart. The test chart 701 may be read by the image reader 2 and used by the diagnosis unit 67, but a human may identify the replacement part by viewing the test chart 701.

  As described in the first embodiment, the diagnosis unit 67 may identify the replacement part based on the color of the streak-like image generated in the detection area in the test chart 701. As described in the second and third embodiments, the diagnosis unit 67 may identify the replacement part based on the generation position of the streak-like image generated on the test chart. As described with reference to FIG. 3, the length of the toner image (eg, patch PD, PT) in the rotating direction of the rotating body and the length of the detection region (eg, white background portion WD, WT) in the rotating direction of the rotating body. May be basically the same.

  As shown in FIG. 22B, the length of the detection region in the rotating direction of the rotating body may be longer than the length of the toner image in the rotating direction of the rotating body. Thereby, even if a difference in streak length or a streak delay occurs, the diagnosis unit 67 can appropriately specify the replacement part.

  The test chart 703 may have a first non-exposure image that is a toner image that is formed with the first charging potential applied and no exposure applied. The test chart 704 may include a second non-exposed image that is a toner image formed by applying a second charging potential different from the first charging potential and applying no exposure.

  The toner image formed on the image carrier at the nth rotation of the image carrier is a single color toner image, but the toner image formed on the intermediate transfer member at the mth rotation of the intermediate transfer member is a mixture of a plurality of toner colors. It may be a toner image. This makes it easier for the diagnosis unit 67 to identify which of the drum cleaner 15 and the belt cleaner 35 has a problem.

  The transfer control unit 70 performs primary operation when a toner image formed in a predetermined region of the image carrier passes through a nip portion (primary transfer nip portion N1) between the image carrier and the primary transfer unit at the n-th rotation of the image carrier. The transfer condition may be set to a condition that makes the toner image difficult to adhere to the intermediate transfer member. As a result, it becomes easy to supply the toner for making the vertical stripes visible to the drum cleaner 15. Further, the intermediate transfer belt 31 will not be easily soiled. The transfer control unit 70 sets the primary transfer condition when the predetermined region of the image carrier passes through the nip portion (primary transfer nip portion N1) between the image carrier and the primary transfer means to the predetermined region at the (n + 1) th rotation of the image carrier. Of the formed toner images, a condition is set such that toner that cannot be completely cleaned by the first cleaning means is easily transferred to the intermediate transfer member. As a result, streaks are easily revealed on the test chart.

  When the toner image formed in a predetermined region of the intermediate transfer member passes through the nip portion (secondary transfer nip portion N2) between the intermediate transfer member and the secondary transfer unit at the m-th rotation of the intermediate transfer member. These secondary transfer conditions are set to conditions that make it difficult for the toner image to adhere to the secondary transfer means. As a result, it becomes easy to supply the toner for making the vertical stripes visible to the belt cleaner 35. Also, the secondary transfer device 27 will not be easily soiled. The transfer control unit 70 determines the secondary transfer conditions when a predetermined region of the intermediate transfer member passes through the nip portion (secondary transfer nip portion N2) between the intermediate transfer member and the secondary transfer unit at the (m + 1) th rotation of the intermediate transfer member. A condition is set such that toner that has not been completely cleaned by the second cleaning unit among the toner images formed in the predetermined area is easily transferred to a sheet serving as a test chart. As a result, streaks are easily revealed on the test chart.

  The diagnosis unit 67 is an example of a detection unit that detects an abnormal part of the image forming apparatus based on the read data regarding the test chart acquired from the reading apparatus. The diagnosis unit 67 detects a streak-like image from the test chart based on the read data, and detects an abnormal part of the image forming apparatus based on the detection result of the streak-like image. When a streak-like image is detected from the test chart based on the read data, the diagnosis unit 67 detects an abnormality of the removal member. When the pattern image passes through the transfer portion, the CPU 60 controls the transfer portion based on the first transfer condition. When the pattern image region passes through the transfer portion again, the CPU 60 controls the transfer portion to a second transfer condition different from the first transfer condition. The secondary transfer power source 72 is an example of a supply unit that supplies a transfer voltage to the transfer unit. When the pattern image passes through the transfer portion, the CPU 60 supplies the first transfer voltage from the supply means to the transfer portion so that the developer on the image carrier is not transferred to the sheet. The CPU 60 supplies the second transfer voltage from the supply means to the transfer unit so that the developer on the image carrier is transferred to the sheet when the pattern image region passes through the transfer unit again.

  The primary transfer nip portion N1 is an example of a primary transfer nip portion where an image formed on the photosensitive member is transferred to the transfer member. The drum cleaner 15 is an example of a removing member that removes the developer remaining on the photosensitive member without being transferred from the photosensitive member to the transfer member in the primary transfer nip portion. The secondary transfer nip portion N2 is an example of a secondary transfer nip portion where an image transferred to a transfer body is transferred to a sheet. The CPU 60 executes processing for creating a test chart used for detecting an abnormal part of the image forming apparatus. When this process is executed, the CPU 60 causes the image forming unit to form a pattern image, controls the primary transfer nip portion to the first transfer condition, and the pattern image is removed by the removal member through the primary transfer nip portion. Rotate the photoreceptor so that The CPU 60 controls the primary transfer nip portion to a second transfer condition different from the first transfer condition during a period in which the first region of the photoreceptor including the position where the pattern image is formed passes through the primary transfer nip portion again. Further, the period in which the second region of the transfer member that has contacted the first region of the photosensitive member in the primary transfer nip portion passes through the secondary transfer nip portion overlaps the period in which the sheet passes through the secondary transfer nip portion. In this way, the conveying means is controlled.

  The diagnosis unit 67 is an example of a detection unit that detects an abnormal part of the image forming apparatus based on the read data regarding the test chart acquired from the reading apparatus. The diagnosis unit 67 detects a streak-like image from the test chart based on the read data, and detects an abnormal part of the image forming apparatus based on the detection result of the streak-like image. The diagnosis unit 67 is characterized by detecting an abnormality of the removal member when a streak-like image is detected from the test chart based on the read data. The primary transfer power supply 71 is an example of a supply unit that supplies a transfer voltage to the primary transfer nip portion. The CPU 60 supplies the first transfer voltage from the supply unit to the primary transfer nip portion based on the first transfer condition. Further, the CPU 60 supplies a second transfer voltage such that the amount of developer transferred from the supply unit to the primary transfer nip portion is larger than the first transfer voltage based on the second transfer condition.

Claims (12)

A rotationally driven image carrier;
Image forming means for forming an image on the image carrier using a developer;
Conveying means for conveying the sheet;
A transfer portion where the image formed on the image carrier is transferred to the sheet;
A removing member that removes the developer remaining on the image carrier without being transferred from the image carrier to the sheet in the transfer unit;
An image forming apparatus comprising a control unit,
The control means executes a process of creating a test chart used for detecting an abnormal portion of the image forming apparatus,
When the processing is executed, the control unit causes the image forming unit to form a pattern image, and rotates the image carrier so that the pattern image is removed by the removing member through the transfer unit. Controlling the conveying means so that a period in which the region of the image carrier including the position where the pattern image is transferred passes through the transfer unit again overlaps a period in which the sheet passes through the transfer unit. An image forming apparatus.   The image forming apparatus according to claim 1, further comprising a detecting unit configured to detect an abnormal portion of the image forming apparatus based on read data relating to the test chart acquired from the reading apparatus.   The detection unit detects a streak-like image from the test chart based on the read data, and detects an abnormal portion of the image forming apparatus based on a detection result of the streak-like image. Item 3. The image forming apparatus according to Item 2.   The image forming apparatus according to claim 2, wherein the detection unit detects an abnormality of the removal member when a streak-like image is detected from the test chart based on the read data. The control unit controls the transfer unit based on a first transfer condition when the pattern image passes through the transfer unit;
2. The image formation according to claim 1, wherein when the region passes through the transfer portion again, the control unit controls the transfer portion to a second transfer condition different from the first transfer condition. apparatus. A supply unit for supplying a transfer voltage to the transfer unit;
The control unit supplies a first transfer voltage from the supply unit to the transfer unit so that the developer of the image carrier is not transferred to the sheet when the pattern image passes through the transfer unit,
The control unit supplies a second transfer voltage from the supply unit to the transfer unit so that the developer of the image carrier is transferred to the sheet when the region passes through the transfer unit again. The image forming apparatus according to claim 1. A supply unit for supplying a transfer voltage to the transfer unit;
The control unit supplies a first transfer voltage from the supply unit to the transfer unit when the pattern image passes through the transfer unit;
The control unit supplies a second transfer voltage that increases the amount of developer transferred from the supply unit to the transfer unit than the first transfer voltage when the region passes through the transfer unit again. The image forming apparatus according to claim 1. An image forming unit having a photosensitive member that is rotationally driven and forming an image on the photosensitive member using a developer;
A primary transfer nip portion to which the image formed on the photoreceptor is transferred to a transfer body;
A removal member that removes the developer remaining on the photoconductor without being transferred from the photoconductor to the transfer body in the primary transfer nip portion;
Conveying means for conveying the sheet;
A secondary transfer nip portion to which the image transferred to the transfer body is transferred to the sheet;
An image forming apparatus comprising a control unit,
The control means executes a process of creating a test chart used for detecting an abnormal portion of the image forming apparatus,
When the processing is executed, the control unit causes the image forming unit to form a pattern image, controls the primary transfer nip portion to a first transfer condition, and the pattern image passes through the primary transfer nip portion. The primary transfer nip portion is rotated during a period in which the first region of the photoconductor including the position where the pattern image is formed passes through the primary transfer nip portion again by rotating the photoconductor to be removed by the removal member. Is controlled to a second transfer condition different from the first transfer condition, and the second region of the transfer member that is in contact with the first region of the photosensitive member in the primary transfer nip portion passes through the secondary transfer nip portion. The image forming apparatus, wherein the conveying unit is controlled such that a period overlaps with a period during which the sheet passes through the secondary transfer nip portion.   The image forming apparatus according to claim 8, further comprising a detection unit configured to detect an abnormal portion of the image forming apparatus based on read data regarding the test chart acquired from the reading apparatus.   The detection unit detects a streak-like image from the test chart based on the read data, and detects an abnormal portion of the image forming apparatus based on a detection result of the streak-like image. Item 10. The image forming apparatus according to Item 9.   The image forming apparatus according to claim 9, wherein the detection unit detects an abnormality of the removal member when a streak-like image is detected from the test chart based on the read data. A supply means for supplying a transfer voltage to the primary transfer nip portion;
The control unit supplies a first transfer voltage from the supply unit to the primary transfer nip portion based on the first transfer condition,
The control unit supplies a second transfer voltage such that an amount of developer transferred from the supply unit to the primary transfer nip portion is larger than the first transfer voltage based on the second transfer condition. Item 9. The image forming apparatus according to Item 8.

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