JP2015158602A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to detect potential changes in an exposure section of a photoreceptor due to variability of characteristics of the photoreceptor or an exposure device, more simply, to adjust operation conditions.SOLUTION: An image forming apparatus 100 includes: a photoreceptor 1; charging means 2; exposure means 3; developing means 3; current detection means D for detecting a DC current flowing between the photoreceptor 1 and a conductive member when a bias is applied to the conductive member arranged adjacent to the photoreceptor 1; execution means 151 which forms an exposure section on a surface of the photoreceptor 1 passing through a developing position c when a developer carrier 41 carries no developer, and causes the current detection means D to detect the DC current on the exposure section; and adjustment means 154 which adjusts operation conditions, according to the DC current detected on the exposure section.

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a laser printer, a facsimile, a printing apparatus, or a complex machine of these.

  In an electrophotographic image forming apparatus, the surface of a photosensitive member, which is generally a rotating member, is charged by a charging unit, and the charged photosensitive member is exposed according to image information by an exposing unit, and electrostatic latent image is applied to the photosensitive member. An image (electrostatic image) is formed. The electrostatic latent image formed on the photoconductor is developed by a developing unit using toner as a developer, and a toner image is formed on the photoconductor. The toner image formed on the photosensitive member is transferred to the recording material using, for example, another rotating member (an intermediate transfer member on which the toner image is once transferred or a recording material conveying member that carries and conveys the recording material). The recording material to which the toner image has been transferred is generally heated and pressed to fix the toner image thereon.

  As described above, at the time of image formation and various adjustment controls, the photosensitive member is charged by the charging unit to form a charged potential on the surface of the photosensitive member, and then the photosensitive member is exposed by the exposing unit to be exposed on the surface of the photosensitive member. An exposed portion potential (latent image potential) is formed. Then, in the developing unit where the developing unit and the photoconductor face each other, toner is blown onto the photoconductor using the potential difference between the potential of the developer carrying member provided in the developing unit and the potential of the exposed unit. Therefore, generally, the image density is controlled by changing the potential of the developing means and the potential of the exposed portion.

  However, the sensitivity of the photosensitive member and the amount of light from an exposure apparatus such as a laser scanner as an exposure means have characteristic variations (individual differences) depending on manufacturing reasons.

  For this reason, as a technique for stabilizing the image density, there is a technique in which an exposure part potential formed by exposure is measured by a potential sensor, and a light amount of the exposure apparatus is adjusted to adjust the exposure part potential (see Patent Document 1).

  In addition, the exposure part potential is measured in factory inspection before the image forming apparatus is shipped, and information relating to the measurement result is stored in an exchange unit such as a process cartridge or a memory provided in the main body of the image forming apparatus to form an image. It may be used for controlling the operating conditions of the apparatus.

JP 2009-42432 A

  However, in recent years, in an image forming apparatus aiming at small size and low cost, it may be difficult to dispose a potential sensor in order to detect the surface potential of the photoreceptor in the apparatus main body. Further, it is not desirable that the user needs to perform a complicated operation for adjustment control. Therefore, it is desirable to be able to detect the exposed portion potential of the photoreceptor more easily.

  Note that the adjustment before the shipment of the image forming apparatus as described above may not be effective because the photoconductor and the exposure apparatus may be replaced on the market.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can more easily detect fluctuations in the potential of an exposed portion of a photoconductor due to variations in characteristics of the photoconductor and the exposure apparatus and adjust operating conditions in the image forming apparatus. Is to provide.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a rotatable photoreceptor, charging means for charging the photoreceptor to form a charging portion, and exposing the charging portion of the photoreceptor to form an exposure portion. An exposure means for forming an electrostatic image on the photosensitive member; and a developing means for developing the electrostatic image formed on the photosensitive member with a developer at a developing position, the developer carrying member for carrying and conveying the developer. A current detecting means for detecting a direct current flowing between the photosensitive member and the conductive member when a bias is applied to the conductive member disposed adjacent to the photosensitive member; and the developer carrier. Execution means for forming the exposed portion on the surface of the photoconductor passing through the developing position when the developer is not carried, and executing detection of a direct current by the current detecting means for the exposed portion; and the exposure The result of DC current detection And adjustment means for adjusting the operating conditions Flip an image forming apparatus characterized by having a.

  According to another aspect of the present invention, a rotatable photosensitive member, a charging unit that charges the photosensitive member to form a charged portion, and an exposed portion is formed by exposing the charged portion of the photosensitive member. An exposure unit that forms an electrostatic image on the photoconductor; and a developing unit that develops the electrostatic image formed on the photoconductor with a developer at a developing position, the developer carrying unit carrying and transporting the developer. A current detecting means for detecting a direct current flowing between the photosensitive member and the conductive member when a bias is applied to the conductive member disposed adjacent to the photosensitive member; and the developer carrier. First execution means for forming the exposed portion on the surface of the photosensitive member that passes through the developing position when the developer is not carried and performing detection of a direct current by the current detecting means for the exposed portion. And the dew by the first execution means After the detection of the direct current to the portion, the exposed portion is formed on the surface of the photosensitive member that passes through the developing position when the developer carrying member carries the developer, A second execution unit that executes detection of a direct current by the current detection unit; and after the detection of the direct current to the exposure unit by the second execution unit, the developer carrier carries the developer. A third execution means for forming the exposure portion on the surface of the photosensitive member that passes through the development position during detection, and for detecting a direct current by the current detection means for the exposure portion; Difference detection means for obtaining a difference between a result of detection of direct current to the exposure unit by the execution unit and a result of detection of direct current to the exposure unit by the second execution unit, and the first execution Adjustment for adjusting the operating condition according to the result of detection of direct current to the exposure unit by the stage and the result of subtracting the difference from the result of detection of direct current to the exposure unit by the third execution means And an image forming apparatus.

  According to the present invention, in the image forming apparatus, it is possible to more easily detect a change in the potential of the exposed portion of the photoconductor due to variations in characteristics of the photoconductor and the exposure device, and adjust the operating conditions.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic vertical cross-sectional view of an image forming unit in an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional bright view of an image forming unit in an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram of a control system of an image forming apparatus according to an embodiment of the present invention. It is a flowchart figure of exposure part electric potential correction control at the time of the initial installation operation | movement in one Example of this invention. It is a timing chart figure of exposure part potential correction control at the time of the initial installation operation in one example of the present invention. FIG. 6 is a schematic diagram showing a relationship among a charging potential VD, an exposure portion potential VL, and a detected current amount I for each range divided in the longitudinal direction of the photoreceptor. It is a schematic diagram for demonstrating the difference of the detection electric current amount by the presence or absence of a coat | cover of a developer. It is a graph which shows an example of the relationship between the detection electric current amount I and exposure part electric potential VL. FIG. 6 is a schematic vertical sectional view of an image forming unit in an image forming apparatus according to another embodiment of the present invention. FIG. 6 is a block diagram of a control system of an image forming apparatus according to another embodiment of the present invention. It is a flowchart figure of exposure part electric potential correction control at the time of the initial installation operation | movement in the other Example of this invention. It is a timing chart figure of exposure part potential correction control at the time of initial installation operation in other examples of the present invention. It is a graph which shows an example of the relationship between transfer contrast and detection electric current amount Itr. It is a graph for demonstrating an example of the method of calculating | requiring an exposure part electric potential. It is a graph which shows an example of the relationship between the light quantity of exposure apparatus, and exposure part electric potential. It is a flowchart figure of exposure part electric potential correction | amendment control after a fluctuation | variation. It is a timing chart figure of exposure part electric potential correction control after change. It is a flowchart figure of the initial installation operation | movement in the case of calculating | requiring the offset value of exposure part electric potential. FIG. 6 is a schematic cross-sectional view of a main part of another example of an image forming apparatus to which the present invention can be applied.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. It is not intended that the scope of the present invention be limited to the following embodiments.

Example 1
1. FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention.

  The image forming apparatus 100 according to the present exemplary embodiment is a tandem type full color laser beam printer that employs an intermediate transfer method capable of forming a full color image.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units PY, PM, PC, and PK that form toner images of yellow, magenta, cyan, and black as a plurality of image forming units. Have. These image forming portions PY, PM, PC, and PK are arranged along the moving direction of the image transfer surface of the intermediate transfer member as the transfer target.

  The configurations and operations of the image forming units PY, PM, PC, and PK are substantially the same except that the color of the toner used is different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of the reference numerals indicating elements of any color will be omitted, and the elements will be described collectively.

  The image forming unit P includes a photosensitive drum 1 that is a cylindrical electrophotographic photosensitive member (photosensitive member) as an image carrier. The following means are arranged around the photosensitive drum 1. First, a charging roller 2 that is a roller-type charging member as a charging unit is disposed. Next, an exposure device (laser scanner) 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 that is a roller-type primary transfer member as a primary transfer means is disposed. Next, a photoreceptor cleaner 6 is disposed as a photoreceptor cleaning means. Further, the image forming portion P is provided with a toner replenishing device 7 as a developer replenishing unit for replenishing the developing device 4 with a developer.

  In this embodiment, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the photosensitive cleaner 6 as process means acting on the photosensitive drum 1 are detachably attached to the apparatus main body 110 of the image forming apparatus 100. The process cartridge 111 is unitized. In this embodiment, each process cartridge 111 is detachably connected to each toner replenishing device 7 when attached to the apparatus main body 110.

  Further, an intermediate transfer belt 8 formed of an endless belt member as an intermediate transfer member is disposed so as to come into contact with each photosensitive drum 1. The intermediate transfer belt 8 is wound around a driving roller 81, a secondary transfer counter roller 82, and a tension roller 83 as a plurality of support rollers with a predetermined tension. The intermediate transfer belt 8 is rotationally driven in the direction of arrow R2 in the figure. Further, the primary transfer roller 5 described above is arranged at a position facing the respective photosensitive drums 1 on the inner peripheral surface side of the intermediate transfer belt 8. The primary transfer roller 5 is pressed against the photosensitive drum 1 via the intermediate transfer belt 8 to form a primary transfer portion N1 where the intermediate transfer belt 8 and the photosensitive drum 1 are in contact with each other. A secondary transfer roller 9, which is a roller-type secondary transfer member serving as a secondary transfer unit, is disposed at a position facing the secondary transfer counter roller 82 on the outer peripheral surface side of the intermediate transfer belt 8. The secondary transfer roller 9 is pressed against the secondary transfer counter roller 82 via the intermediate transfer belt 8 to form a secondary transfer portion N2 where the intermediate transfer belt 8 and the secondary transfer roller 9 are in contact with each other. . In addition, a belt cleaner 10 as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 81 on the outer peripheral surface side of the intermediate transfer belt 8.

  In addition, the image forming apparatus 100 includes a feeding unit 11 as a feeding unit for the recording material S such as recording paper, a fixing device 12 as a fixing unit for fixing the toner image on the recording material S, and the like.

  For example, when forming a full-color image, each photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the drawing. The surface of each rotating photosensitive drum 1 is uniformly charged by each charging roller 2. Each of the charged photosensitive drums 1 is exposed by the exposure device 3 with a light image corresponding to the color-separated yellow, magenta, cyan, and black images. Thereby, an electrostatic latent image (electrostatic image) for each color of yellow, magenta, cyan, and black is formed on each photosensitive drum 1. The electrostatic latent image formed on each photosensitive drum 1 is developed by the developing device 4 using a developer. As a result, yellow, magenta, cyan, and black toner images are formed on the respective photosensitive drums 1.

  Thereafter, with the rotation of each photosensitive drum 1, the toner image is conveyed to each primary transfer portion N1. The toner images on the photosensitive drums 1 are sequentially transferred (primary transfer) onto the moving intermediate transfer belt 8 by the action of the primary transfer rollers 5.

  As described above, in the first, second, third, and fourth image forming units PY, PM, PC, and PK, yellow, magenta, cyan, and black colors on the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. The toner image is formed. Then, the toner images of the respective colors are transferred (primary transfer) to the intermediate transfer belt 8 so as to be sequentially superimposed.

  The four-color toner images for full-color images transferred and superimposed on the intermediate transfer belt 8 are conveyed to the secondary transfer portion N2 as the intermediate transfer belt 8 rotates. The toner image on the intermediate transfer belt 8 is collectively transferred (secondary transfer) to the recording material S conveyed to the secondary transfer portion N2 by the action of the secondary transfer roller 9. The recording material S is taken out from a recording material cassette (not shown) in the feeding unit 11, separated and sent one by one, and then conveyed to the registration roller 11 a. The registration roller 11a sends the recording material P to the secondary transfer portion N2 in synchronization with the toner image on the intermediate transfer belt 8.

  The recording material S to which the toner image has been transferred by the secondary transfer portion N2 is conveyed to the fixing device 12, where the image is fixed on the surface by being heated and pressurized. Thereafter, the recording material P is discharged outside the apparatus main body 110 of the image forming apparatus 100.

2. Image Forming Unit Next, the configuration and operation of the image forming unit P will be described in more detail. FIG. 2 is a schematic cross-sectional view of the image forming unit P in the image forming apparatus 100 of the present embodiment.

  The image forming unit P includes a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a photoconductor cleaner 6 disposed around a photoconductor drum 1 that is a rotatable photoconductor.

  The charging roller 2 is in contact with the photosensitive drum 1 and is driven to rotate. The charging roller 2 is configured by covering the periphery of a cylindrical core member 21 formed of a conductive material such as metal with an elastic layer 22 formed of a conductive elastic material. The charging roller 2 is connected to a charging power source (high voltage power source) E1 as a charging bias applying unit. When the image is formed, a vibration voltage in which a DC voltage (DC component, charging DC bias) and an AC voltage (AC component, charging AC bias) are superimposed is applied as a charging bias to the charging roller 2 from the charging power source E1. Is done. Thus, the charging roller 2 charges the surface of the photosensitive drum 1 to a predetermined charging potential VD having a predetermined polarity (negative polarity in this embodiment). A portion of the surface of the photosensitive drum 1 charged to the charging potential VD by the charging roller 2 is used as a charging unit. Further, a position where the charging roller 2 charges the photosensitive drum 1 in the circumferential direction of the photosensitive drum 1 is defined as a charging position a. Here, in the moving direction of the surface of the photosensitive drum 1, a small gap (gap) between the photosensitive drum 1 and the charging roller 2 is located upstream and downstream of the contact portion between the charging roller 2 and the photosensitive drum 1. ) Is formed. The charging roller 2 charges the photosensitive drum 1 by discharging in either or both of the upstream and downstream gaps. Whether the discharge in the gap is dominant in the charging process of the photosensitive drum 1 depends on the material, size, arrangement, and the like of the charging roller 2 and the photosensitive drum 1. However, there is no problem if the charging position a in the following description is understood to be roughly the center of the contact portion between the charging roller 2 and the photosensitive drum 1 in the moving direction of the surface of the photosensitive drum 1. .

  Here, the charging member such as the charging roller does not necessarily need to be in contact with the surface of the photosensitive member that is a member to be charged. As long as the dischargeable region determined by the gap voltage and the correction Paschen curve is reliably ensured between the charging member and the photosensitive member, for example, the charging member and the photosensitive member are arranged in close contact with each other with a gap (gap) of several tens of μm. Also good. Here, a method in which a charging member is brought into contact with or in proximity to a member to be charged and the member to be charged is charged by discharge generated in a minute gap is referred to as a contact or proximity charging method or simply a contact charging method.

  The charging means is not limited to the contact charging method described above, and an injection charging method that injects a charge from the charging member that contacts the photosensitive member to the surface of the photosensitive member may be used. The contact portion between the charging member and the photosensitive member is the charging position.

  An exposure device (laser scanner) 3 scans a laser beam, which is ON / OFF-modulated in accordance with an image signal obtained by developing an image of a color component corresponding to each image forming unit P, with a rotating mirror, and is a charged photoconductor The drum 1 is irradiated. As a result, the exposure apparatus 3 writes an electrostatic latent image (electrostatic image) of an image of a color component corresponding to each image forming unit P on the photosensitive drum 1. In the exposed portion of the photosensitive drum 1, the charged potential VD is discharged and the absolute value thereof is lowered to become an exposed portion potential (latent image potential) VL. A portion of the surface of the photosensitive drum where the charged potential VD is attenuated by exposure is defined as an exposure portion. Further, the position where the exposure device 3 exposes the photosensitive drum 1 in the circumferential direction of the photosensitive drum 1 is defined as an exposure position b.

  The developing device 4 is of a two-component developing system using a two-component developer mainly containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. In this embodiment, the charging polarity (normal charging polarity) of the toner during development is negative. The developing device 4 includes a developing container (developing device main body) 45 that stores a developer, and an opening 45 a is formed at a position facing the photosensitive drum 1 of the developing container 45. A developing sleeve 41 as a developer carrying member that carries a developer and conveys the developer to a portion facing the photosensitive drum 1 so that a part is exposed from the opening 45 a is rotatable with respect to the developing container 45. Is held in. In the hollow portion of the developing sleeve 41, a magnet roller 46 is disposed as a magnetic field generating means that cannot rotate with respect to the developing sleeve 41. The developing sleeve 41 is connected to a developing power source (high voltage power source) E2 as a developing bias applying unit. The developing sleeve 41 is disposed to face the photosensitive drum 1 with a predetermined interval (gap) therebetween. The rotation axis direction of the developing sleeve 41 and the rotation axis direction of the photosensitive drum 1 are substantially parallel.

  The developer stored in the developing container 45 is carried on the surface of the developing sleeve 41 while being restrained by the magnetic force of the magnet roller 46 in a state where the toner is attached to the carrier. The developer carried on the developing sleeve 41 is transported to the opposite portion between the photosensitive drum 1 and the developing sleeve 41 by being driven to rotate in the direction of the arrow R3 in the drawing of the developing sleeve 41. At the facing portion between the photosensitive drum 1 and the developing sleeve 41, the developer on the developing sleeve 41 forms a magnetic brush (magnetic spike) that is raised by the magnetic force of the magnet roller 46, and this magnetic brush is the photosensitive drum 1. In contact with or close to the surface (in this embodiment, contact). Then, when a developing bias is applied to the developing sleeve 41 from the developing power source E2, toner is transferred from the magnetic brush on the developing sleeve 41 in accordance with the electrostatic latent image formed on the photosensitive drum 1. Transition to 1. As a result, the electrostatic latent image on the photosensitive drum 1 is developed, and a toner image is formed on the photosensitive drum 1.

  In this embodiment, the exposure device 3 exposes an image portion (image portion), and the developing device 4 develops the electrostatic latent image by reversal development. That is, the charged portion (charged potential VD) of the photosensitive drum 1 subjected to the substantially uniform charging process is exposed to the exposed portion (exposure portion potential VL) in which the absolute value of the potential is reduced. The electrostatic latent image is developed by attaching toner charged to the same polarity as the charged polarity. Further, during image formation, the developing sleeve 41 is vibrated with a DC voltage (DC component, developing DC bias) Vdc and an AC voltage (AC component, developing AC bias) Vac as a developing bias from the developing power source E2. A voltage is applied. In the circumferential direction of the photosensitive drum 1, a position where toner is transferred from the developing sleeve 41 to the electrostatic latent image on the photosensitive drum 1 is defined as a developing position c. In this embodiment, the developing position c includes the closest position between the photosensitive drum 1 and the developing sleeve 41.

  FIG. 3 is a cross-sectional view of the developing container 45 of the developing device 4 as viewed from above. In the present embodiment, the developing container 45 of the developing device 4 is a box body having a substantially rectangular cross section along the longitudinal direction (rotational axis direction) of the developing sleeve 41, and the developing container 45 includes a first chamber 43 and A second chamber 44 is provided. A partition wall 47 is provided between the first chamber 43 and the second chamber 44 so as to stand up from the bottom of the developing container 45. The partition wall 47 includes first and second transport openings 47 a and 47 b that allow the developer to pass between the first chamber 43 and the second chamber 44 on both ends in the longitudinal direction of the developing container 45. Is formed. The developing sleeve 41 is disposed in the first chamber 43 of the first chamber 43 and the second chamber 44 that is closer to the photosensitive drum 1. In the first chamber 43 and the second chamber 44, a first screw 48a and a second screw 48b are disposed as developer agitating and conveying members for agitating and conveying the developer, respectively. The first screw 48 a and the second screw 48 b convey the developer in the reverse direction in the longitudinal direction of the developing container 45 as indicated by arrows X 1 and X 2 in the drawing, respectively. The developer accommodated in the developing container 45 is conveyed by the first and second screws 48a and 48b, and from the second chamber 44 to the first chamber 43 through the first conveying opening 47a. In addition, the second chamber 44 is transferred from the first chamber 43 to the second chamber 44 through the second transfer opening 47b. In the first chamber 43, the developer is carried on the developing sleeve 41, conveyed, and supplied to the developer, whereby the toner concentration (T / D ratio) is lowered. Here, the T / D ratio is the ratio of the developer toner to the carrier (T / D ratio = toner weight / (toner weight + carrier weight). The replenishing toner is replenished from the toner replenishing device 7 as a replenishing means, whereby the developer whose toner density is reduced by the development is conveyed from the first chamber 43 to the second chamber 44, and the replenishing toner is replenished. The developer stirred in this manner is conveyed from the second chamber 44 to the first chamber 43. In this embodiment, the developing sleeve 41 and the first and second screws 48a and 48b are driven through a gear train. A driving force from a single developing drive motor M1 (FIG. 4) as a means is transmitted and rotationally driven.

  Here, in this embodiment, before the use of the developing device 4 (the image forming apparatus 100 in which the developing device 4 is mounted or a unit including at least the developing device 4) is started, the space between the first chamber 43 and the second chamber 44 is used. A sealing member for sealing is provided. In this embodiment, as this sealing member, a sealing sheet 49 is provided between the first chamber 43 and the second chamber 44, and the developer is accommodated in the second chamber 44. This suppresses the scattering of the developer toner and the carrier and keeps the temperature and humidity stable during transportation of the developing device 4 (the image forming apparatus 100 equipped with the developing device 4 or a unit including at least the developing device 4). Because. More specifically, in this embodiment, sealing sheets 49 (49a, 49b) for sealing the first and second transport openings 47a, 47b are attached to the partition wall 47 so as to be peelable. . The sealing sheet 49 is removed when the developing device 4 (the image forming apparatus 100 on which the developing device 4 is mounted or a unit including at least the developing device 4) starts to be used. As a result, the developer can enter the first chamber 43 from the second chamber 44 and come into contact with the developing sleeve 41 to be carried thereon.

  In this embodiment, during the initial installation operation (hereinafter simply referred to as “initial installation operation”) when starting to use the developing device 4 (the image forming apparatus 100 in which the developing device 4 is mounted or a unit including at least the developing device 4). Then, the sealing sheet 49 is removed so that the developer spreads over the developing sleeve 41. In particular, in this embodiment, an operation of automatically winding the sealing sheet 49 in conjunction with driving of the developing device 4 is performed during the initial installation operation. Such a sealing member opening means is described in, for example, Japanese Patent Application Laid-Open No. 2012-8457.

  More specifically, in this embodiment, the automatic winding mechanism 50 as the unsealing means includes a winding shaft provided at the upper portion of the developing container 45 so as to be rotatable around a rotation axis along the longitudinal direction of the developing container 45. 51. The take-up shaft 51 receives a driving force from a developing drive motor M1 (FIG. 4) that rotationally drives the developing sleeve 41 and the first and second screws 48a and 48b of the developing device 4, and the developing sleeve 41 and the first The second screw 48a and the second screw 48b are driven to rotate. One end of a sealing sheet 49 (49a, 49b) that seals the first and second transport openings 47a, 47b is connected to the winding shaft 51 at the upper part of the developing container 45. When the winding shaft 51 rotates during the initial installation operation, the sealing sheet 49 is peeled off from the partition wall 47 and wound on the winding shaft 51, and the first and second transport openings 47a and 47b are opened. The developer can enter the first chamber 43 from the second chamber 44. Then, after the sealing sheet 49 is removed, the developing sleeve 41 and the first and second screws 48a and 48b are driven by a predetermined amount, whereby the developing that has entered the first chamber 43 from the second chamber 44 is performed. The agent is sufficiently carried on the developing sleeve 41.

  In this embodiment, the sealing sheet 49 is automatically wound up. However, when the developing device 4 (the image forming apparatus 100 equipped with the developing device 4 or a unit including at least the developing device 4) is started to be used. Alternatively, the sealing sheet 49 may be manually removed.

  The primary transfer roller 5 presses the inner surface of the intermediate transfer belt 8 to form a primary transfer portion N1 between the photosensitive drum 1 and the intermediate transfer belt 8. The primary transfer roller 5 is configured by covering a cylindrical core material 51 formed of a conductive material such as metal with an elastic layer 52 formed of a conductive elastic material. The primary transfer roller 5 is connected to a primary transfer power supply (high voltage power supply) E3 as a primary transfer bias applying unit. At the time of image formation, the primary transfer roller 5 is applied with a primary transfer bias, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner, from the primary transfer power source E3. As a result, the toner image formed of the negative polarity toner on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 8. In this embodiment, the primary transfer current is set to 20 μA. A position where the toner image is transferred from the photosensitive drum 1 onto the intermediate transfer belt 8 in the circumferential direction of the photosensitive drum 1 is defined as a transfer position d. This transfer position d roughly corresponds to the contact portion between the photosensitive drum 1 and the intermediate transfer belt 1.

  The photoreceptor cleaner 6 removes the toner (primary transfer residual toner) remaining on the surface of the photoreceptor drum 1 after the primary transfer by a cleaning blade 61 as a cleaning member in contact with the photoreceptor drum 1, and collects the collected developer container. Is collected in the collected toner container 62. A position where the primary transfer residual toner is removed by the cleaning blade 61 in the circumferential direction of the photosensitive drum 1 is defined as a cleaning position e.

3. Control during Initial Installation Operation Next, control during initial installation operation in the present embodiment will be described.

  As described above, the exposure portion potential of the photoconductor varies due to variations in the characteristics of the photoconductor and the exposure apparatus. Therefore, it is desirable to control the operating conditions of the image forming apparatus in consideration of this. However, there is a case where it is difficult to arrange a potential sensor for detecting the surface potential of the photoreceptor in the main body of the image forming apparatus due to downsizing and cost reduction of the image forming apparatus.

  In particular, when there is unevenness in the exposed portion potential in the longitudinal direction of the photosensitive member due to variations in characteristics of the photosensitive member and the exposure apparatus, in order to detect unevenness in the exposed portion potential in the longitudinal direction of the photosensitive member, It is desirable to arrange a plurality of potential sensors in the longitudinal direction of the body. However, this can be even more difficult.

  Therefore, in this embodiment, in the image forming apparatus, it is possible to more easily detect the fluctuation of the exposed portion potential due to the variation in the characteristics of the photoreceptor and the exposure device, in particular, the unevenness of the exposed portion potential in the longitudinal direction of the photoreceptor. The operating conditions of the image forming apparatus can be adjusted according to the result.

  Further, in this embodiment, even when the photosensitive member or the exposure apparatus is replaced in the market, for example, when the unit including at least the developing device is replaced at the same time or thereafter, the image forming apparatus can be more easily performed. Then, it is possible to detect the fluctuation of the exposure portion potential.

  That is, according to the present exemplary embodiment, the image forming apparatus 100 exposes the rotatable photosensitive member 1, the charging unit 2 that charges the photosensitive member 1 to form a charging portion, and the charging portion of the photosensitive member 1. Exposure means 3 for forming an electrostatic image on the photosensitive member 1 by forming an exposure portion. The image forming apparatus 100 includes a developer carrying member 41 that carries and conveys the developer, and includes a developing unit 4 that develops the electrostatic image formed on the photoreceptor 1 with the developer at the development position c.

  The image forming apparatus 100 includes a current detection unit that detects a direct current that flows between the photosensitive member 1 and the conductive member when a bias is applied to the conductive member disposed adjacent to the photosensitive member 1. Have. Here, the conductive member is disposed adjacent to the photosensitive member when the conductive member is disposed in contact with the photosensitive member or in a non-contact manner so that a direct current can be detected by the current detecting means. This means that they are placed close together. As the conductive member, a special member can be provided for detection of a direct current by the current detection means. However, the use of a member provided for other purposes also simplifies the configuration and reduces the size. It is preferable from the viewpoint of conversion. For example, as the conductive member, a charging unit, a transfer unit that transfers an image formed of the developer on the photosensitive member to the transfer target, a developer charging member that charges the developer on the photosensitive member, or the like can be used. . In particular, in this embodiment, a charging unit is used as the conductive member, and an ammeter D as a current detection unit is connected to the charging roller 2 (FIGS. 2 and 4).

  Further, the image forming apparatus 100 forms an exposed portion on the surface of the photosensitive member 1 that passes through the developing position c when the developer carrying member 41 does not carry the developer, and direct current is applied to the exposed portion by current detection means. It has execution means for executing current detection. When the developer carrying member 41 does not carry the developer, typically, the developer carrying member 41 is not in contact with the developer at all. However, when the developer carrying member 41 does not carry the developer, the developer is carried on the developer carrying member 41 to such an extent that the developer can adhere to the electrostatic image on the photosensitive member 1 at least at the development position c. Including the state of not adhering. In addition, the detection of the direct current by the current detection means for the exposed portion of the photoconductor means that the target exposed portion reaches the adjacent portion with the conductive member, is adjacent (contact or close), and passes through. Detection during the period.

  In addition, the image forming apparatus 100 includes an adjusting unit that adjusts the operating condition of the image forming apparatus 100 according to the result of detection of the direct current with respect to the exposure unit. The operating condition of the image forming apparatus 100 adjusted by the adjusting unit may be any operating condition that can be adjusted in a direction that suppresses the influence of fluctuations in the exposed portion potential of the photosensitive member 1 on the output image. For example, the charging potential of the photosensitive member, the exposure amount of the photosensitive member by the exposure unit, the potential of the developer carrying member, the potential difference (Vback) between the charging potential of the photosensitive member and the potential of the developer carrying member, and the exposed portion potential of the photosensitive member The potential difference (Vcont) from the potential of the developer carrying member can be adjusted. As will be described in detail later, the operation condition of the image forming apparatus 100 is typically the exposure amount of the exposure apparatus 3. According to the control according to the present invention, more accurate information related to the exposed portion potential of the photosensitive member 1 can be acquired, and thus the influence of the fluctuation of the exposed portion potential on the output image is suppressed using the information. Arbitrary operating conditions can be adjusted in the direction.

  As will be described in detail below, in particular, in this embodiment, unevenness of the exposure portion potential in the longitudinal direction (rotation axis direction) of the photoreceptor 1 is detected, and the operating condition of the image forming apparatus 100 is adjusted according to the result. It can be so. Therefore, in this embodiment, the execution unit forms an exposure unit for each range divided into a plurality in the direction of the rotation axis of the photoreceptor 1, and executes detection of a direct current for the exposure unit for each range. Then, the adjusting unit adjusts the operating condition of the image forming apparatus 100 according to the result of detecting the direct current with respect to the exposure unit for each range. Typically, the adjusting means uses the exposure means 3 so as to suppress the difference in image density in the rotation axis direction of the photosensitive member 1 corresponding to the difference in the detection result of the direct current with respect to the exposure unit for each divided range. The exposure amount of the photoreceptor 1 is adjusted.

  In this embodiment, the execution means is realized by a CPU 151 that is provided in the control unit of the apparatus main body 110 and operates according to a program stored in the ROM 152 (FIG. 4). In the present embodiment, the adjustment means is realized by the CPU 151 and a shading correction unit 154 (described later) that operates under the control of the CPU 151 (FIG. 4).

  In this embodiment, the execution unit executes detection of a direct current for the exposure unit until the developer is carried on the developer carrier 41 when the development unit 4 is started to be used. In particular, in this embodiment, the developing means 4 includes a first chamber 43 in which the developer carrier 41 is disposed and a second chamber 44 in which the developer is accommodated before the developing means 4 is started to be used. Have. Then, when the developing means 4 is started to be used, the sealing member 49 that has sealed the space between the first chamber 43 and the second chamber 44 is opened, so that it was accommodated in the second chamber 44. The developer can enter the first chamber 43 and be carried on the developer carrier 41. In this embodiment, the image forming apparatus 100 includes an opening unit 50 that opens the sealing member 49 in a state where the developing unit 4 is disposed at a predetermined position where the developing operation can be performed.

  FIG. 4 is a block diagram of a control unit provided in the apparatus main body 110 of the image forming apparatus 100 according to the present exemplary embodiment. FIG. 5 shows a control flow during the initial installation operation in the present embodiment. In the present embodiment, correction control of the exposure portion potential of the photosensitive drum 1 is also performed during the initial installation operation. FIG. 6 is a control timing chart during the initial installation operation. In FIG. 6, in particular, charging DC bias applied to the charging roller 2, exposure on / off by the exposure device 3, presence / absence of developer coating on the developing sleeve 41, and current detection by the ammeter D at the charging position a are shown. Indicates timing.

  The power switch 155 of the image forming apparatus 100 is turned on (S101). The CPU 151 receives information (new / old detection signal) indicating whether or not the developing device 4 (the process cartridge 111 including the developing device 4 in this embodiment) is new from the ROM 152, and determines whether or not the developing device 4 is new. Judgment is made (S102).

  In this embodiment, information indicating whether or not the developing device 4 is new is stored in the ROM 152 of the control unit of the apparatus main body 110, but the present invention is not limited to this. For example, this information may be stored in this memory when the developing device 4 (in this embodiment, the process cartridge 111 including the developing device 4) has a memory as a storage unit. Alternatively, when the initial installation operation is started by pressing a predetermined button or switch on the operation unit 156 of the apparatus main body 110, the CPU 151 may determine that the developing device 4 is new.

  If it is determined in S102 that the developing device 4 is new, the CPU 151 starts correction control of the exposure portion potential of the photosensitive drum 1.

  First, the charging potential VD of the photosensitive drum 1 is raised (S103). That is, the CPU 151 starts to rotate the photosensitive drum 1 and applies a charging bias to the charging roller 2 from the charging power source E1. At this time, an oscillating voltage in which a charging DC bias of −800 V and a predetermined charging AC bias are superimposed is applied to the charging roller 2 from the charging power source E1 as a charging bias. In this embodiment, the charging DC bias at the time of image formation is −605V. Further, the CPU 151 turns on the developing drive motor M1 simultaneously with the rise of the charging potential VD of the photosensitive drum 1. As a result, in conjunction with the start of rotational driving of the developing sleeve 41 and the first and second screws 48a and 48b, winding of the sealing sheet 49 by the automatic winding mechanism 50 is also started.

  Here, the peak-to-peak voltage Vpp of the charging AC bias is set to at least twice the discharge start point (discharge threshold, discharge start voltage) when a DC voltage is applied to the charging roller 2. Thereby, the surface potential of the photosensitive drum 1 immediately after the AC discharge is generated and passes through the charging position a converges to the charging potential VD corresponding to the charging DC bias (substantially the same as the value of the charging DC bias). The discharge starting point is a direct current that flows through the charging roller 2 when a discharge starts to occur when only the DC voltage is applied to the charging roller 2 and the absolute value of the applied DC voltage is increased. This is the DC voltage value at the point at which increases rapidly.

  Second, exposure by the exposure device 3 is started at the timing when the leading portion of the charging portion of the photosensitive drum 1 formed as described above comes to the exposure position b, and the photosensitive drum 1 is exposed for one round. An exposed portion is formed on the entire surface of the image forming area of the body drum 1 (S104). In the present embodiment, the light amount of the exposure device 3 at this time is the same as that at the time of forming an exposure portion for detecting a current described later. The same timing as the exposure start timing on the surface of the photosensitive drum 1 is indicated by a broken line A in FIG.

  Third, at the timing when the head of the exposed portion of the photosensitive drum 1 formed as described above comes to the charging position a after one revolution of the photosensitive drum 1 (broken line B in FIG. 6), the ammeter D Detection of the current flowing between the photosensitive drum 1 and the charging roller 2 is started (S105). At this time, as will be described in detail later, the CPU 151 sequentially detects the current by the ammeter D with respect to the exposure portion potential VL for each of a plurality of ranges in the longitudinal direction of the photosensitive drum 1.

  In this embodiment, the charging roller 2 is used as a conductive member for detecting current by the ammeter D. In this case, in order to reduce the influence on the surface potential of the photosensitive drum 1, it is preferable that the primary transfer roller 5 (further, the intermediate transfer belt 8 in this embodiment) is separated from the photosensitive drum 1. The primary transfer roller 5 (further, the intermediate transfer belt 8 in this embodiment) is separated from the photosensitive drum 1 at least while a portion on the photosensitive drum 1 for detecting current passes through the primary transfer position d. Is preferred. For example, any available means such as a mechanism for separating the intermediate transfer belt 8 from the photosensitive drum 1 by releasing the pressing of the primary transfer roller 5 to the photosensitive drum 1 can be used.

  In the present embodiment, areas (hereinafter also referred to as “longitudinal areas”) 1 to 5 in which the longitudinal direction of the photosensitive drum 1 is equally divided into five are set. The longitudinal regions 1 to 5 are obtained by dividing the image forming region in the longitudinal direction of the photosensitive drum 1. Here, the longitudinal regions 1 to 5 are sequentially arranged from one end side to the other end side in the longitudinal direction. And Then, the exposure part potential VL is sequentially formed in the longitudinal regions 1 to 5 in time series, and the current detection by the ammeter D is sequentially performed in time series on the exposure part potential VL in the longitudinal areas 1 to 5. In this embodiment, the charged portion of the photosensitive drum 1 is exposed with a predetermined light amount LP = 3.0 μW (current amount X applied to the laser of the exposure apparatus 3 = 20 μA) to form an exposed portion. Then, the amount of current (DC current amount, DC current value) I flowing according to the potential difference between the exposed portion potential VL of the photosensitive drum 1 and the charging potential VD is detected. That is, the charging roller 2 to which a predetermined charging DC bias is applied at the charging position a is charged according to the exposure portion potential VL when charging the surface of the photosensitive drum 1 to a predetermined charging potential VD corresponding to the charging DC bias. Current amount I is detected.

  FIG. 7 schematically shows the relationship between the surface potential of the photosensitive drum 1 and the detected current amount I for the longitudinal region 1 and the longitudinal region 5. As shown in FIG. 7A, when the current amount I for the longitudinal region 1 is detected, the exposed portion potential VL is formed only in the longitudinal region 1, and the exposed portion potential VL is formed in the longitudinal regions 2 to 5. do not do. In this state, when the current is detected by the ammeter D through the charging roller 2 at the charging position a after the exposure portion potential VL is formed and the photosensitive drum 1 makes one round, for example, the current amount I of the longitudinal region 1 is The average value is 8.5 μA.

  Similarly, the current amount I is sequentially detected in the time series for the longitudinal regions 2 to 5. As shown in FIG. 7B, when the current amount I for the longitudinal region 5 is detected, the exposed portion potential VL is formed only in the longitudinal region 5, and the exposed portion potential VL is formed in the longitudinal regions 1 to 4. do not do. In this state, when the current is detected by the ammeter D through the charging roller 2 at the charging position a after the exposure portion potential VL is formed and the photosensitive drum 1 makes one round, for example, the current amount I of the longitudinal region 1 is The average value is 7.9 μA.

  The number of divisions in the longitudinal direction of the photosensitive drum 1 can be determined as necessary. If the number of divisions is increased, the unevenness of the exposed portion potential in the longitudinal direction of the photosensitive drum 1 can be detected more finely. However, when the number of divisions is increased, the detected current amount I decreases. When increasing the number of divisions, the absolute value of the charging DC bias is increased so that the current flows easily, the potential difference Vcnt between the charging potential VD and the exposure portion potential VL is increased, and the current measurement time is increased. Is effective. The number of divisions can be set to an arbitrary number less than or equal to the resolution of the image in the longitudinal direction of the photosensitive drum 1, for example, 10 or less is appropriate from the viewpoint of the detected current amount I and the complexity of control. is there. Note that the measurement time in each longitudinal region (the range of the exposed portion in the circumferential direction of the photosensitive drum 1) is arbitrarily set within a range in which sufficient current detection accuracy can be obtained in accordance with the number of divisions and the charging DC bias. can do. In order to average the detected current amount I and suppress the influence of uneven sensitivity in the circumferential direction of the photosensitive drum 1, an exposed portion is formed for at least one round of the photosensitive drum 1 for each longitudinal region. It is preferable. However, for example, when the unevenness of the sensitivity in the circumferential direction of the photosensitive drum 1 is sufficiently small, or when the influence of the sensitivity on the current detection accuracy can be ignored, a plurality of different times during one rotation of the photosensitive drum 1 are obtained. An exposed portion may be formed in the longitudinal region.

  For ease of explanation, the average value of the current amount I detected in each longitudinal region is also simply referred to as “current amount I”.

  In this embodiment, as a result of the current detection as described above, the current amounts I for the longitudinal regions 1 to 5 are 8.5 μA, 10.2 μA, 10.0 μA, 8.3 μA, and 7.9 μA, respectively, in this order. It shall be. Since the charging potential VD is constant in the longitudinal regions 1 to 5, the difference in the detection result of the current amount I is in accordance with the difference in the exposure portion potential VL.

  Thereafter, the developing sleeve 41 starts to be coated with the developer at a predetermined timing after at least the exposed portion of the photosensitive drum 1 (the exposed portion of the longitudinal region in which the current is finally detected) passes the developing position c. . The same timing as the timing at which the developer starts to be carried on the developing sleeve 41 on the surface of the photosensitive drum 1 is indicated by a broken line C in FIG. The timing at which the developer sleeve 41 starts to hold the developer, that is, the time from when the developing device 4 is started to when the developer is carried on the developer sleeve 41 can be adjusted as follows. is there. For example, it is possible to adjust the time until the sealing sheet 49 is removed due to the length of the sealing sheet 49 (for example, the winding length until opening is started). Further, for example, it is possible to adjust by the rotation speed of the development drive motor M1 (that is, the developer conveyance speed by the rotation speeds of the first and second screws 48a and 48b). Further, it is possible to make adjustments by actively changing the rotation speed of the developing drive motor M1 during the initial installation operation or by stopping it with respect to the time of image formation. In this way, a sufficient time for correction control of the exposure portion potential can be provided.

  Referring again to FIG. 5, fourthly, the detection result of the current amount I for the longitudinal regions 1 to 5 obtained as described above is used to suppress unevenness in the exposed portion potential VL in the longitudinal direction of the photosensitive drum 1. In this manner, feedback is made to control of the operating conditions of the image forming apparatus 100 (S106). The difference in the current amount I corresponds to the unevenness of the exposed portion potential VL in the longitudinal direction of the photosensitive drum 1. Therefore, controlling the operating conditions of the image forming apparatus 100 so as to suppress the difference in the current amount I substantially corresponds to correcting the unevenness of the exposed portion potential VL in the longitudinal direction of the photosensitive drum 1. . In this embodiment, the detection result of the current amount I is fed back to the light amount unevenness correction (shading correction) of the exposure device 3 in the longitudinal direction of the photosensitive drum 1. This point will be described later in detail.

  Note that the fluctuation of the exposure portion potential is largely caused by variations in characteristics of the photosensitive drum 1 and variations in characteristics of the exposure apparatus. In some cases, inspection prior to shipment alone may not be able to cope with, for example, a combination of the photosensitive drum 1 that is a consumable item and the replaceable exposure device 3. Therefore, as in this embodiment, it is effective to detect fluctuations in the exposure portion potential at the time of initial installation or at least at the replacement timing of consumables including replacement of the developing device 4.

4). Effect of Developer on Developing Sleeve on Current Detection Accuracy Here, the current detection accuracy when the developing sleeve 41 is coated with the developer when the exposed portion of the photosensitive drum 1 passes through the developing position c. The effect will be described.

  FIG. 8A shows the charging potential VD and exposure portion potential VL of the photosensitive drum 1, the potential (developing DC bias) Vdc of the developing sleeve 41, and the charging position a when the developing sleeve 41 is not coated with the developer. The relationship of the detected electric current amount I is shown. On the other hand, FIG. 8B shows the same relationship when the developing sleeve 41 is coated with a developer.

  According to the present embodiment, as described above, when the exposed portion of the photosensitive drum 1 passes through the developing position c, the developer is not carried on the developing sleeve 41, so that the exposed portion adheres to the toner. And pass through the development position c without causing carrier adhesion. Then, as shown in FIG. 8A, for this exposure unit, a current amount I = 8.5 μA flowing according to the potential difference Vcnt between the charging potential VD and the exposure unit potential VL is detected at the charging position a. . In general, the potential difference (VD−Vdc) between the charging potential VD at the time of image formation and the development DC bias Vdc has an allowable range in order to prevent toner adhesion and carrier adhesion. In this embodiment, VD-Vdc at the time of image formation needs to be -130 to -200V. However, as described above, since the developer is not carried on the developing sleeve 41 when the exposure unit passes the developing position c, and toner adhesion and carrier adhesion do not occur, a current is more applied at the charging position a. The voltage can be set freely so that it can be easily detected.

  However, as shown in FIG. 8B, if the developer is carried on the developing sleeve 41 when the exposed portion of the photosensitive drum 1 passes through the developing position c, the exposed portion potential is exposed to the exposed portion. The toner adheres due to the potential difference between VL and the development DC bias. In this exposed portion, since there is a lot of toner, the electrical resistance increases, and at the charging position a, the detected current amount I = 1.2 μA, and almost no current flows. In addition, since it is not known how much toner amount is on the exposed portion, even if the setting is made to reduce the toner amount, there is an effect. This influence is in the direction in which the amount of current at the charging position a decreases, so that the detection accuracy of the exposure portion potential VL is greatly reduced. Further, since the developer is carried on the developing sleeve 41, if VD−Vdc is increased, the carrier is scattered to the photosensitive drum 1 or current is exchanged through the carrier to increase the exposure portion potential VL. It will be affected.

  As described above, it is important that the developer is not carried on the developing sleeve 41 when the exposure portion of the photosensitive drum 1 for detecting the current passes the developing position b.

  It should be noted that the process of S103 to S106 in FIG. 5 is performed without driving the development drive motor M1 during the initial installation operation except for the sealing sheet 49 manually, and thereafter the operation of the development drive motor M1 is started. Good.

  Here, there is a configuration in which the developing device is separated from the photosensitive member. However, it may be difficult to provide such a configuration in order to reduce the size and cost of the image forming apparatus. Therefore, with the configuration of this embodiment, in the image forming apparatus, it is possible to more easily detect fluctuations in the exposed portion potential, particularly unevenness in the exposed portion potential in the longitudinal direction of the photoreceptor.

5. Feedback to shading correction of exposure portion potential According to the present embodiment, it is possible to confirm the unevenness of the current amount I in the longitudinal direction of the photosensitive drum 1 as described above. As described above, the unevenness of the current amount I corresponds to the unevenness of the exposed portion potential VL in the longitudinal direction of the photosensitive drum 1. The detection result of the current amount I can be used as it is in the processing, or is used as the detection result of the exposure portion potential VL based on the relationship between the current amount I obtained in advance and the exposure portion potential VL (see FIG. 9). You can also. In this specification, the detection result of the current amount I and the exposure portion potential VL obtained from the detection result may be described as the detection result of the exposure portion potential VL of the photosensitive drum 1.

  Next, a method of feeding back the unevenness detection result of the exposure portion potential VL in the longitudinal direction of the photosensitive drum 1 in this embodiment to the light amount unevenness correction (shading correction) of the exposure device 3 in the longitudinal direction of the photosensitive drum 1 will be described. explain.

  In this embodiment, the shading correction unit 154 (FIG. 4) changes the current amount X applied to the laser of the exposure apparatus 3 for each of the longitudinal regions 1 to 5 divided in the longitudinal direction of the photosensitive drum 1. As a result, shading correction is performed for unevenness of the exposure portion potential VL in the longitudinal direction of the photosensitive drum 1 due to unevenness of the laser light amount of the exposure device 3 in the longitudinal direction of the photosensitive drum 1.

  The outline of the shading correction in this embodiment will be described below. However, if the unevenness of the exposure portion potential VL in the longitudinal direction of the photosensitive drum 1 can be detected, a specific shading correction method itself is the same as that of this embodiment. It is not limited to. Any available general shading correction can be applied arbitrarily.

  Here, as described above, the current amounts I detected for the longitudinal regions 1 to 5 were 8.5 μA, 10.2 μA, 10.0 μA, 8.3 μA, and 7.9 μA, respectively, in this order. To do. In this case, it can be seen that the average value (average detected current amount) of the current amount I in the entire longitudinal regions 1 to 5 is 9 μA. When the detected current amount I is large, it can be seen that the light amount of the exposure apparatus 3 is large, and the absolute value of the exposure portion potential VL is reduced to be close to zero. Since the amount of current I is determined from the potential difference between the exposed portion potential VL and the charging potential VD, the amount of current I increases as the exposed portion potential VL approaches zero.

  Therefore, in the shading correction, the set value of the current amount X applied to the laser of the exposure apparatus 3 is changed so that the detected current amount I becomes 9.0 μA of the average detected current amount for each longitudinal region. Here, for each of the longitudinal regions 1 to 5, the current amount X applied to the laser of the exposure apparatus 3 is changed from 20 μA to 21.1 μA, 17.3 μA, 17.7 μA, 21.5 μA, when the current amount I is detected. Adjust to 22.4 μA. The correction amount of the current amount X applied to the laser of the exposure apparatus 3 with respect to the difference in the current amount I in each longitudinal region with respect to the average detected current amount (that is, the difference in the exposure portion potential in each longitudinal region with respect to the average exposure portion potential) is Can be obtained in advance. As a result, the unevenness of the exposure portion potential VL in the longitudinal direction of the photosensitive drum 1 due to the unevenness of the laser light amount of the exposure device 3 in the longitudinal direction of the photosensitive drum 1 can be corrected. Note that even when there is uneven sensitivity in the longitudinal direction of the photosensitive drum 1, the unevenness of sensitivity can be corrected by the above-described shading correction.

  When such correction is not performed, the in-plane density difference in the solid portion measured using a reflection densitometer (X-Rite) is about ΔD = 0.2, and the image density unevenness in a uniform halftone image or the like. Has come out prominently. Such image density unevenness is caused by a combination of the exposure device 3 and the sensitivity of the photosensitive drum 1, and is difficult to predict and suppress in advance.

  On the other hand, when the charging potential VL of the photosensitive drum 1 is corrected according to the present embodiment, the in-plane density difference at the solid portion measured using a reflection densitometer (X-Rite) is ΔD = 0. To 0.03.

  As described above, according to the present exemplary embodiment, in the image forming apparatus 100, the photosensitive drum 1 can be simply used during the initial installation operation and when the unit (process cartridge 111) including the developing device 4 is replaced by the user. It is possible to correct the exposure portion potential. For this reason, it is possible to stabilize the image density over a long period of time.

  As described above, according to the present embodiment, the exposure is stable with a simpler configuration and not affected by variations in the characteristics of the photoconductor and the exposure apparatus in consideration of unevenness in the potential of the exposed portion in the longitudinal direction of the photoconductor. The partial potential can be controlled. Accordingly, stable image density control can be performed in consideration of unevenness of the exposed portion potential in the longitudinal direction of the photoreceptor.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In the present embodiment, the control during the initial installation operation is different from that in the first embodiment.

1. Control during Initial Installation Operation FIG. 10 is a schematic cross-sectional view of the image forming unit P in the image forming apparatus 100 of the present embodiment. FIG. 11 is a block diagram of a control unit provided in the apparatus main body 110 of the image forming apparatus 100 according to the present exemplary embodiment. FIG. 12 shows a control flow during the initial installation operation in the present embodiment. In the present embodiment, correction control of the exposure portion potential of the photosensitive drum 1 is also performed during the initial installation operation. FIG. 13 is a control timing chart during the initial installation operation. In FIG. 13, in particular, the charging DC bias is applied to the charging roller 2, the exposure device 3 is turned on / off, the developer sleeve 41 is coated with developer, and the current is detected by the ammeter D at the primary transfer position d. Each timing is shown.

  In this embodiment, as a conductive member used for current detection by the current detection means, the position where the exposed portion of the photoreceptor reaches in the shortest possible time after passing the development position (as close as possible to the development position). A member arranged at (position) is used. In particular, in this embodiment, the primary transfer unit 5 is used as a conductive member, and an ammeter D as a current detection unit is connected to the primary transfer roller 5.

  The power switch 155 of the image forming apparatus 100 is turned on (S201). The CPU 151 receives information (new / old detection signal) indicating whether or not the developing device 4 (the process cartridge 111 including the developing device 4 in this embodiment) is new from the ROM 152, and determines whether or not the developing device 4 is new. Judgment is made (S202).

  As in the case of the first embodiment, for example, information indicating whether or not the developing device 4 is new is stored in the memory on the developing device 4 (process cartridge 111 including the developing device 4 in this embodiment) side. May be stored in this memory. Alternatively, when the initial installation operation is started by pressing a predetermined button or switch on the operation unit 156 of the apparatus main body 110, the CPU 151 may determine that the developing device 4 is new.

  If it is determined in S202 that the developing device 4 is new, the CPU 151 starts correction control of the exposure portion potential of the photosensitive drum 1.

  First, the charging potential VD of the photosensitive drum 1 is raised (S203). That is, the CPU 151 starts to rotate the photosensitive drum 1 and applies a charging bias to the charging roller 2 from the charging power source E1. Further, the CPU 151 turns on the developing drive motor M1 simultaneously with the rise of the charging potential VD of the photosensitive drum 1. As a result, in conjunction with the start of rotational driving of the developing sleeve 41 and the first and second screws 48a and 48b, winding of the sealing sheet 49 by the automatic winding mechanism 50 is also started.

  At this time, an oscillating voltage in which a charging DC bias of −605 V, which is the same as that at the time of image formation, and a predetermined charging AC bias are superimposed is applied from the charging power source E1 to the charging roller 2. The surface potential of the charging portion of the photosensitive drum 1 charged by the charging roller 2 is −600 V at the development position c because of dark decay. Further, the surface potential of the charging portion of the photosensitive drum 1 is similarly −555 V at the primary transfer position d because of dark decay.

  Secondly, it flows between the photosensitive drum 1 by the ammeter D and the primary transfer roller 5 at the timing when the head of the charging portion of the photosensitive drum 1 formed as described above comes to the primary transfer position d. Current detection is started (S204). The same timing as the current detection start timing on the surface of the photosensitive drum 1 is indicated by a broken line A in FIG. In this embodiment, at this time, the current amount (DC current amount, DC current value) Itr is detected by the ammeter D over the entire circumference of the photosensitive drum 1.

  In this embodiment, in order to make the influence of the dark decay of the surface potential of the photosensitive drum 1 most difficult, the current is passed at the primary transfer position d which is the nearest position after passing through the exposure position b and the development position d. The current is detected by the meter D. That is, in this embodiment, the primary transfer roller 5 is used as a conductive member for detecting current by the ammeter D. However, for example, as in the case of the first embodiment, the charging roller 2 can be used as a conductive member for detecting the current by the ammeter D. In this case, as in the first embodiment, the primary transfer roller 5 (further, the intermediate transfer belt 8 in this embodiment) is separated from the photosensitive drum 1 in order to reduce the influence on the surface potential of the photosensitive drum 1. It is preferable to be configured.

  At this time, a primary transfer bias (DC voltage) Vtr of +500 V is applied to the primary transfer roller 5 from the primary transfer power supply E3. The absolute value of the primary transfer bias Vtr is increased, or the absolute value of the charging bias VD is increased by increasing the absolute value of the charging bias, whereby the transfer contrast Vtrcnt = (Vtr−VD) is increased and detected. The amount of current that can be increased. Thereby, detection accuracy can be improved. In the present embodiment, it is assumed that the current amount Itr detected at this time is 30.5 μA. The value of the current amount is recorded in the RAM 153.

  In S <b> 204, the CPU 151 changes the charging DC bias to change the charging potential VD by a total of three points, obtains the relationship between the transfer contrast Vtrcnt and the detected current amount Itr, and records this relationship in the RAM 153. For each charging potential VD, the current amount Itr is detected over one revolution of the photosensitive drum 1, and the average value is stored.

  FIG. 14 shows an example of a measurement result of the relationship between the transfer contrast Vtrcnt and the detected current amount Itr. In this embodiment, the primary transfer roller 5 is applied with a primary transfer bias Vtr that becomes Vtrcnt that is equal to or higher than the discharge start point, and current is detected. Here, the discharge start point is that when only the DC voltage is applied to the primary transfer roller 5 and the absolute value of the applied DC voltage is increased, the discharge starts to occur in the primary transfer roller 5. This is the DC voltage value at which the flowing DC current increases rapidly. In this embodiment, the CPU 151 causes the arithmetic control unit 157 to complement each other by linearly connecting each point of Vtrcnt and Itr, obtains a relational expression between Vtrcnt and Itr, and stores the relational expression in the RAM 153. .

  Thirdly, the exposure by the exposure device 3 is started at the timing when the surface of the photosensitive drum 1 at the timing when the detection of the current with respect to the charging potential VD ends as described above comes to the exposure position b, and the photosensitive drum An exposed portion is formed on the surface of 1. At this time, in this embodiment, the charged portion of the photosensitive drum 1 is exposed with a predetermined light amount LP = 2.0 μW to form an exposed portion. Then, the current flowing between the photosensitive drum 1 and the primary transfer roller 5 by the ammeter D at the timing when the head of the exposed portion of the photosensitive drum 1 formed in this way immediately comes to the primary transfer position d. Detection is started (S205). At this time, in this embodiment, the exposed portion is formed on the entire surface of the image forming area of the photosensitive drum 1 over one rotation of the photosensitive drum 1. As a result, in this embodiment, it is assumed that the average value of the detected current amount Itr is 20 μA. A broken line B in FIG. 13 indicates the same timing as the timing at which the current detection for the charging potential VD on the surface of the photosensitive drum 1 is completed.

  In this embodiment, it is assumed that the exposure part is formed in the entire image forming area in the longitudinal direction of the photosensitive drum 1 when the current is detected in the exposure part. However, in the same manner as in the first embodiment, an exposure unit is sequentially formed for each of a plurality of ranges divided in the longitudinal direction of the photosensitive drum 1, and a current detection result for each exposure unit in each range is used for each range. The potential VL may be detected. Further, as described in the first embodiment, the range in which the exposed portion in the circumferential direction of the photosensitive drum 1 is formed is not limited to one round of the photosensitive drum 1, and the current is sufficiently accurate. Can be changed as appropriate so that can be detected.

  Fourth, the CPU 151 obtains the exposure part potential VL at the development position c in consideration of the dark attenuation more accurately by the calculation by the calculation control part 157 from the current detection result for the exposure part (S206). . That is, first, a relational expression between Vtrcnt (= Vtr−VD) and Itr is obtained, and the relational expression is stored in the RAM 153. For example, as the VD in this relational expression, the charging potential VD is used in the development at the development position c in consideration of dark decay from the charging position a to the development position c. Further, the primary transfer bias Vtr applied to the primary transfer roller 5 at the time of detecting the current with respect to the charging potential VD is constant. Accordingly, as shown in FIG. 15A, the relationship (relational expression) between the current detection result at the primary transfer position d and the charging potential VD at the development position c can be obtained. This relationship shows the relationship between the surface potential of the photosensitive drum 1 at the development position c and the current detection result at the primary transfer position d. Accordingly, as shown in FIG. 15B, this is used as a relationship (relational expression) indicating the detection result of the exposure portion potential VL of the photosensitive drum 1 at the development position c and the current at the primary transfer position d. And the exposure part electric potential VL in the image development position c can be calculated | required from the detection result of the electric current about the exposure part acquired as mentioned above. As a result, in this embodiment, it is calculated that the exposed portion potential VL at the development position c is −250V.

  Thereafter, at least a predetermined timing after the exposed portion of the photosensitive drum 1 has passed the developing position c, the developing sleeve 41 starts to be coated with the developer. The same timing as the timing at which the developer starts to be carried on the developing sleeve 41 on the surface of the photosensitive drum 1 is indicated by a broken line C in FIG. The timing at which the developing sleeve 41 starts to hold the developer, that is, the time from when the developing device 4 starts to be carried on the developing sleeve 41 is adjusted in the same manner as in the first embodiment. It is possible.

  Note that the fluctuation of the exposure portion potential is largely caused by variations in characteristics of the photosensitive drum 1 and variations in characteristics of the exposure apparatus. In some cases, inspection prior to shipment alone may not be able to cope with, for example, a combination of the photosensitive drum 1 that is a consumable item and the replaceable exposure device 3. Therefore, as in this embodiment, it is effective to detect fluctuations in the exposure portion potential at the time of initial installation or at least at the replacement timing of consumables including replacement of the developing device 4.

2. Effect of developer on developing sleeve on current detection accuracy Even when primary transfer roller 5 is used as a conductive member, developer sleeve 41 is coated with developer for the same reason as described in the first embodiment. In this case, the current detection accuracy is affected.

  That is, if the developer is carried on the developing sleeve 41 when the exposed portion of the photosensitive drum 1 passes through the developing position c, the toner adheres to the exposed portion and the electrical resistance increases, and at the primary transfer position d. Almost no current flows. As a result, the detection accuracy of the exposed portion potential VL is significantly reduced. Further, since the developer is carried on the developing sleeve 41, VD−Vdc cannot be increased.

  Therefore, even when the primary transfer roller 5 is used as the conductive member, as in the first embodiment, when the exposed portion of the photosensitive drum 1 for detecting the current passes the developing position b, It is important that no developer is carried.

  As in the case of the first embodiment, the sealing sheet 49 is manually removed, and the processing of S201 to S206 in FIG. 12 is performed without driving the development drive motor M1 during the initial installation operation, and then the development drive motor is performed. A sequence for starting the operation of M1 may be used.

3. According to the present embodiment, the exposure portion potential VL at the development position c can be detected with higher accuracy. Therefore, the operation conditions of the image forming apparatus can be adjusted with higher accuracy according to the detection result.

  For example, the detection result of the exposure portion potential of the photosensitive drum 1 can be fed back to the adjustment of the exposure amount of the exposure apparatus 3 as in the first embodiment. In general, when the absolute value of the exposure part potential is larger than the reference value, the exposure amount of the exposure apparatus 3 is adjusted to be larger. When the absolute value of the exposure part potential is smaller than the reference value, the exposure amount of the exposure apparatus 3 is adjusted. Make it smaller.

  As described above, in this embodiment, in order to make the understanding of the detection method of the exposure portion potential VL easier, the current for the exposure portion formed in the entire image forming area in the longitudinal direction of the photosensitive drum 1 is determined. And the potential of the exposed portion is detected. However, as in the first embodiment, the current in each of the exposure portions formed for each of a plurality of ranges divided in the longitudinal direction of the photosensitive drum 1 is detected, and the exposure portion potential in each range is detected. May be. Then, the detection result of the exposure potential according to the present embodiment can be fed back to the light amount unevenness correction (shading correction) of the exposure device 3 in the longitudinal direction of the photosensitive drum 1 as in the first embodiment.

  As described above, according to the present embodiment, the exposure potential of the photoconductor can be more accurately changed with a simpler configuration and without being influenced by variations in characteristics of the photoconductor and the exposure apparatus, and taking dark attenuation into consideration. It is possible to detect and control the exposure portion potential more stably. Thereby, more stable image density control can be performed.

Example 3
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, as in the second embodiment, in order to make it easier to understand the detection method of the exposure portion potential VL, the exposure portion formed in the entire image forming area in the longitudinal direction of the photosensitive drum 1 is described. , And the exposed portion potential is detected.

  As a method for controlling the image density, detection with a patch detection sensor composed of a reflective optical sensor or the like as an image density detection means in combination with a method for adjusting the T / D ratio of the developer in the developing device 4 There is a method for determining the optimum exposure amount of the exposure apparatus 3 according to the result.

  On the other hand, if the exposure amount of the exposure device 3 is increased too much, the surface potential of the photosensitive drum 1 where the exposed portion potential VL is formed cannot be leveled by the charging roller 2, and the potential is one cycle after the photosensitive drum 1. As a memory, image defects may occur. For this reason, it is preferable to control the exposure amount of the exposure apparatus 3 to be a predetermined value or less. That is, it is preferable to control the absolute value of the exposure portion potential VL so as to be a predetermined value or more.

  However, if there is a variation in sensitivity of the photosensitive drum 1 or a variation in the amount of light in the exposure device 3, the characteristics of the charging potential VL with respect to the amount of light cannot be accurately grasped. It can be difficult.

  Therefore, in this embodiment, the CPU 151 forms an exposure unit by changing the light amount of the exposure apparatus 3 between S204 and S205 during the initial installation operation shown in FIG. A process for obtaining the potential VL is performed. The method itself for obtaining the exposure portion potential VL for each light quantity can be the same as that described as the processing of S205 in the second embodiment.

  For example, in this embodiment, the amount of light of the exposure apparatus 3 is changed by five points, 0.5 μW, 1.0 μW, 1.5 μW, 2.0 μW, and 2.5 μW, and the current detection for each exposed portion is primarily transferred. Performed at position d. As a result, the amount of current Itr detected for each exposed portion was −22 μA, −17.6 μA, −12 μA, −7.2 μA, and −4.8 μA, respectively. From the detection result of the current amount Itr, the exposed portion potential VL of each exposed portion was obtained in the same manner as in Example 2. FIG. 16 shows the relationship between the obtained light quantity and the charging potential VL. It is known that a potential memory is generated when the upper limit of the charging potential VL indicated by a broken line in the figure is exceeded.

  Therefore, the CPU 151 can determine that the maximum value (upper limit) of the light amount of the exposure apparatus 3 is 2.2 μW from the relationship between the obtained light amount and the charging potential VL. In the subsequent operations, the image density is controlled to an appropriate range by, for example, setting the developing DC bias or setting the charging DC bias while operating the exposure apparatus 3 in the light amount range below the maximum value. This makes it possible to control the image density stably without generating a defective image due to the potential memory.

  As in the case of the second embodiment, in the present embodiment, as in the first embodiment, the current for each of the exposure portions formed for each of the plurality of ranges divided in the longitudinal direction of the photosensitive drum 1 is detected. Thus, the present invention can also be applied to the case where the exposure portion potential in each range is detected. In this case, the maximum value (upper limit) of the light amount of the exposure device 3 can be determined for each range in the longitudinal direction of the photosensitive drum 1.

Example 4
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, as in the second embodiment, in order to make it easier to understand the detection method of the exposure portion potential VL, the exposure portion formed in the entire image forming area in the longitudinal direction of the photosensitive drum 1 is described. , And the exposed portion potential is detected.

  When the same photosensitive drum 1 is used over a long period of time, the sensitivity of the photosensitive drum 1 may be changed by the current from the charging roller 2 depending on the number of sheets used. Normally, when the number of used sheets increases, the photosensitive drum 1 deteriorates and sensitivity decreases.

  Therefore, in this embodiment, similarly to the second embodiment, the exposure portion potential VL is measured more accurately during the initial setting operation. Then, for each predetermined number of used sheets (about 10k in this embodiment), a fluctuation part (difference) in the sensitivity of the photosensitive drum 1 due to the increase in the number of used sheets is obtained, and the potential of the exposed portion that has fluctuated due to the increase in the number of used sheets is obtained. Perform correction control. The corrected exposure portion potential is fed back to subsequent image density control and various controls.

  FIG. 17 is a flowchart of exposure part potential correction control (hereinafter referred to as “post-change exposure part potential correction control”) that fluctuates as the number of sheets used increases. FIG. 18 is a control timing chart of post-fluctuation exposed portion potential correction control. In FIG. 18, in particular, the charging DC bias is applied to the charging roller 2, the on / off of exposure by the exposure device 3, the presence or absence of the developer coating on the developing sleeve 41, and the current detection by the ammeter D at the primary transfer position d Each timing is shown.

  First, when the post-fluctuation exposure unit potential correction control is started, the CPU 151 sets the charging bias (superimposed bias of charging DC bias and charging AC bias) and the developing bias (superimposing bias of developing DC bias and developing AC bias). Start up (S301). At this time, the developing sleeve 41 is assumed to be driven. Unlike the initial installation operation described in the second embodiment, the developing sleeve 41 is already coated with the developer during the post-fluctuation exposure portion potential correction control. In this state, it is desirable to keep VD-Vdc constant in order to prevent carrier adhesion. Therefore, first, the CPU 151 gradually raises the charging DC bias of the charging bias and the developing DC bias of the developing bias.

  Secondly, the CPU 151 forms an exposure part on the photosensitive drum 1 and detects a current for the exposure part (S302). First, exposure by the exposure device 3 is started at the timing when the top of the charging potential VD of the photosensitive drum 1 that has risen to a predetermined value comes to the exposure position b, and an exposure portion is formed on the photosensitive drum 1. Further, the developing drive motor M1 is stopped and the developing sleeve 41 is stopped before the head of the exposure unit reaches the developing position c. The same timing as the timing of starting exposure on the surface of the photosensitive drum 1 is indicated by a broken line A in FIG.

  In order to reduce toner adhesion to the exposed portion of the photosensitive drum 1 as much as possible, when a development bias is applied for a long time with the development drive motor M1 stopped, the following may occur. That is, the toner charge at the contact portion (development nip portion) between the developer coated on the developing sleeve 41 and the photosensitive drum 1 may become abnormal, leading to a defective image. Therefore, it is preferable that the stop time of the developing sleeve 41 be as short as possible. Therefore, in this embodiment, the developing sleeve 41 is stopped in accordance with the timing when the exposure unit reaches the developing position c.

  In addition, it waits for the timing when the surface potential of the photosensitive drum 1 immediately after the start of the formation of the exposure portion passes the primary transfer position d. This is because the developing drive motor M1 is stopped, but the toner in the developing nip portion is discharged to the exposure portion of the photosensitive drum 1, and thus the discharged toner temporarily waits for passing through the primary transfer position d. This is because (the timing of the broken line B in FIG. 18).

  Thereafter, current detection for the exposed portion is performed. Further, the driving of the developing drive motor M1 is started at the timing (broken line C in FIG. 18) when the exposure is finished (the rear end of the exposed portion) passes the developing position c.

  Thirdly, the CPU 151 confirms information related to the exposure portion potential VL detected under the same conditions (that is, a state where the developing sleeve 41 is coated with the developer) during the initial installation operation.

  Here, in the present embodiment, as shown in FIG. 19, following the sequence shown in FIG. 13 in the second embodiment, a sequence for detecting the exposure portion potential in a state where the developer is carried on the developing sleeve 41 is executed. . In the present embodiment, when the developer is not carried on the developing sleeve 41, the detected exposure portion potential VL was −250V. On the other hand, under the condition that the toner is difficult to fly but the developer is carried on the developing sleeve 41, the detected exposure portion potential VL was −280V. For this reason, during the initial installation operation, the CPU 151 records 30 V, which is the difference between these exposure portion potentials, as an offset value in the ROM 152. This offset value is a value determined in accordance with the toner fog amount which varies depending on the distance between the developing sleeve 41 and the photosensitive drum 1 and the toner state.

  Fourthly, the CPU 151 obtains the exposed portion potential after fluctuation (S304). That is, it is assumed that the exposure part potential VL is −300 V from the detected current. The CPU 151 calculates an exposed portion potential VL-270V after fluctuation obtained by subtracting the offset value obtained during the initial installation operation from the exposed portion potential VL obtained from the detected current by calculation in the arithmetic control unit 157. Then, the CPU 151 feeds back the obtained exposure portion potential VL to the image density control, for example, in the same manner as in the second embodiment.

  As described above, the detection accuracy of the exposure portion potential VL as an absolute value is lowered due to the influence of the toner and the carrier. Can be sought. As a result, it is possible to easily correct the variation from the exposure portion potential obtained more accurately during the initial installation operation. Therefore, it is possible to effectively correct the sensitivity variation of the photosensitive drum 1 when the photosensitive drum 1 is used over a long period of time.

  That is, in this embodiment, the image forming apparatus 100 forms an exposed portion on the surface of the photosensitive member 1 that passes through the developing position c when the developer carrying member 41 does not carry the developer, and First execution means for executing detection of direct current by the current detection means D is provided. Further, after the detection by the first execution unit, the image forming apparatus forms an exposure portion on the surface of the photoreceptor 1 that passes through the development position c when the developer carrier 41 carries the developer, A second execution unit configured to execute detection of a direct current by the current detection unit for the exposure unit; Further, after the detection by the second execution unit, the image forming apparatus forms an exposed portion on the surface of the photosensitive member 1 that passes the developing position when the developer carrying member 41 carries the developer, There is provided third execution means for executing detection of a direct current by the current detection means D for the exposure unit. Further, the image forming apparatus 100 detects difference (offset value) between a result of detection of direct current to the exposure unit by the first execution unit and a result of detection of direct current to the exposure unit by the second execution unit. Have means. In this embodiment, the adjustment unit subtracts the difference from the result of detection of the direct current for the exposure unit by the first execution unit and the result of detection of the direct current for the exposure unit by the third execution unit. The operating conditions are adjusted according to the above. In the present embodiment, the first, second, and third execution means and the difference detection means are realized by the CPU 151 that operates according to the program stored in the ROM 152.

  In particular, in the present embodiment, the adjustment means is the result of detecting the direct current for the exposure unit by the first execution unit as a result of subtracting the difference from the result of detection of the direct current for the exposure unit by the third execution unit. The operating conditions are adjusted according to the amount of change from. Further, the first execution unit causes the exposure unit to detect a direct current until the developer is carried on the developer carrier 41 when the development unit 4 is started to be used. Further, the second execution unit causes the exposure unit to detect a direct current before forming the first image when the developing unit 4 starts to be used. On the other hand, the third execution unit causes the exposure unit to detect a direct current after a predetermined period of time has elapsed after the development unit 4 is started and the first image is formed. Typically, the third execution unit executes detection of direct current to the exposure unit every time a predetermined period elapses. Preferably, the second and third execution units stop the developer carrier 41 while the exposure unit passes the development position c.

  As described above, according to the present embodiment, a stable exposure unit with a simpler configuration and not affected by variations in characteristics of the photoconductor and the exposure apparatus, taking into account sensitivity fluctuations due to an increase in the amount of use of the photoconductor. The potential can be controlled.

Others The conductive member used for current detection by the current detection unit is not limited to the charging unit and the primary transfer unit, and can also be used in an image forming apparatus having a charging auxiliary member. That is, for example, the image forming apparatus adopting a so-called cleaner-less method that does not have the photoreceptor cleaner in the image forming apparatus of the above-described embodiment and collects the transfer residual toner on the photoreceptor after being charged by the developing device. There is a device. In this case, the charging auxiliary member 60 is provided as a developer charging member for charging the transfer residual toner on the photoreceptor for the purpose of suppressing the transfer residual toner from adhering to the charging means such as a charging roller. (FIG. 20). The auxiliary charging member 60 is provided downstream of the transfer position and upstream of the charging position in the movement direction of the surface of the photoreceptor. The auxiliary charging member is a fixed brush-like member or a roller-like brush member having a brush fiber portion formed of a conductive material. The charging auxiliary member is typically configured to be able to apply a bias having the same polarity as the normal charging polarity of the toner from the power supply E4. Therefore, this charging auxiliary member can be used as a conductive member used for current detection by an ammeter D as current detection means.

  In the above-described embodiments, the developing device uses a two-component developer as a developer. However, the present invention can be equally applied to a case where a one-component developer is used, and similar effects can be obtained. Can be obtained.

  In the above-described embodiment, the oscillating voltage in which the charging DC bias and the charging AC bias are superimposed as the charging bias is applied to the charging unit. However, the present invention is not limited to this. At least one of the charging DC bias (DC voltage, DC component) may be applied to the charging unit as the charging bias at least one of the time of image formation and the current detection by the current detection unit. The DC voltage in this case is a DC voltage that is equal to or higher than the discharge start point.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure apparatus 4 Developing apparatus 5 Primary transfer roller 49 Sealing sheet 92
D Ammeter

Claims (17)

A rotatable photoreceptor,
Charging means for charging the photoreceptor to form a charging portion;
Exposure means for forming an electrostatic image on the photosensitive member by exposing the charging portion of the photosensitive member to form an exposed portion;
A developing unit that includes a developer carrying member that carries and conveys the developer, and develops the electrostatic image formed on the photosensitive member with the developer at a developing position;
Current detection means for detecting a direct current flowing between the photosensitive member and the conductive member when a bias is applied to the conductive member disposed adjacent to the photosensitive member;
When the developer carrying member is not carrying a developer, the exposed portion is formed on the surface of the photosensitive member that passes through the developing position, and a DC current is detected by the current detecting means for the exposed portion. Execution means;
Adjusting means for adjusting operating conditions according to the result of detection of direct current to the exposure unit;
An image forming apparatus comprising: The execution means causes the exposure unit to be formed for each of the ranges divided into a plurality in the rotational axis direction of the photoconductor, and causes the exposure unit to detect a direct current for each range,
The image forming apparatus according to claim 1, wherein the adjustment unit adjusts an operation condition according to a result of detection of a direct current with respect to the exposure unit for each range.   The adjusting unit is configured to suppress the difference in image density in the rotation axis direction of the photoconductor corresponding to a difference in detection result of a direct current with respect to the exposure unit for each of the divided ranges. The image forming apparatus according to claim 2, wherein the exposure amount of the body is adjusted.   The adjusting unit adjusts the charging potential of the photosensitive member, the exposure amount of the photosensitive member by the exposing unit, and the potential of the developer carrying member. Image forming apparatus.   The execution unit is configured to execute detection of a direct current to the exposure unit until the developer is carried on the developer carrier when the developing unit is used. Item 5. The image forming apparatus according to any one of Items 1 to 4.   The developing means has a first chamber in which the developer carrying member is disposed, and a second chamber in which a developer is accommodated before the developing means is used, and the developing means starts using When the sealing member sealing the space between the first chamber and the second chamber is opened, the developer contained in the second chamber enters the first chamber. The image forming apparatus according to claim 5, wherein the image forming apparatus can be carried on the developer carrying member.   The image forming apparatus according to claim 6, further comprising an opening unit that opens the sealing member in a state where the developing unit is disposed at a predetermined position where the developing operation can be performed.   As the conductive member, the charging unit, a transfer unit that transfers an image formed of the developer on the photosensitive member to the transfer target, or a developer charging member that charges the developer on the photosensitive member is used. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The execution means further forms a plurality of the charging portions having different potentials on the photosensitive member, and causes the current detection means to execute detection of a direct current with respect to each of the charging portions,
The adjusting means applies the surface potential of the photoreceptor and the conductive member from the detection result of the direct current to each charging unit and the bias applied to the conductive member when the detection result is acquired. A relationship between a direct current detected by the current detection means with respect to a difference from a bias to be obtained is obtained, and a potential of the exposure unit is obtained from a detection result of the direct current with respect to the exposure unit and the relationship. The image forming apparatus according to claim 1.   The image according to claim 1, wherein a unit including at least the photosensitive member and the developing unit is detachably attached to the apparatus main body of the image forming apparatus. Forming equipment. A rotatable photoreceptor,
Charging means for charging the photoreceptor to form a charging portion;
Exposure means for forming an electrostatic image on the photosensitive member by exposing the charging portion of the photosensitive member to form an exposed portion;
A developing unit that includes a developer carrying member that carries and conveys the developer, and develops the electrostatic image formed on the photosensitive member with the developer at a developing position;
Current detection means for detecting a direct current flowing between the photosensitive member and the conductive member when a bias is applied to the conductive member disposed adjacent to the photosensitive member;
When the developer carrying member is not carrying a developer, the exposed portion is formed on the surface of the photosensitive member that passes through the developing position, and a DC current is detected by the current detecting means for the exposed portion. First execution means;
After the detection of the direct current to the exposure unit by the first execution means is performed, the exposure is performed on the surface of the photoconductor that passes through the development position when the developer carrier carries the developer. A second execution means for forming a part and executing detection of a direct current by the current detection means for the exposure part;
After the detection of the direct current to the exposure unit by the second execution unit is performed, the exposure is performed on the surface of the photoconductor that passes through the development position when the developer carrying member carries the developer. A third execution means for forming a part and executing detection of a direct current by the current detection means for the exposure part;
Difference detection means for obtaining a difference between a result of detection of direct current to the exposure unit by the first execution unit and a result of detection of direct current to the exposure unit by the second execution unit;
The operation according to the result of detecting the direct current to the exposure unit by the first execution unit and the result of subtracting the difference from the result of detection of the direct current to the exposure unit by the third execution unit Adjusting means for adjusting the conditions;
An image forming apparatus comprising:   The adjustment means is obtained by subtracting the difference from the result of detection of the direct current for the exposure unit by the third execution unit, from the result of detection of the direct current for the exposure unit by the first execution unit. The image forming apparatus according to claim 11, wherein the operation condition is adjusted according to the amount of change. The first execution unit executes detection of a direct current to the exposure unit until the developer is carried on the developer carrier when the development unit is started to be used.
The second execution unit executes detection of a direct current to the exposure unit before forming the first image when the development unit is started to be used,
The third execution unit causes the exposure unit to detect a direct current after a predetermined period has elapsed after the development unit is started to use and an initial image is formed. The image forming apparatus according to 11 or 12.   The image forming apparatus according to claim 13, wherein the third execution unit causes the exposure unit to detect a direct current every time a predetermined period elapses.   The image according to claim 11, wherein a unit including at least the photosensitive member and the developing unit is detachably attached to the apparatus main body of the image forming apparatus. Forming equipment.   The said 2nd, 3rd execution means stops the said developer carrier, respectively, while the said exposure part passes the said development position, It is any one of Claims 11-15 characterized by the above-mentioned. Image forming apparatus. The first, second, and third execution units each form the exposure unit for each of a plurality of ranges divided in the rotation axis direction of the photoconductor, and detect a direct current for the exposure unit for each range. And execute
The image forming apparatus according to claim 11, wherein the adjustment unit adjusts an operation condition according to a result of detection of a direct current for the exposure unit for each range.

Images