JP2017142330A - Image carrier unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image carrier unit and an image forming apparatus in which the image forming apparatus can acquire information on an accurate initial value of the film thickness of a photoreceptor film included in the image carrier even when the image forming apparatus does not include a static eliminating part.SOLUTION: There is provided a drum cartridge 57 that can be attached to an apparatus body of an image forming apparatus, the drum cartridge comprising a photoreceptor drum 51 that includes a photoreceptor film 51b capable of carrying an electrostatic image on its surface layer, and storage means that stores a measurement related to information on the film thickness of the photoreceptor film 51b and measured before the attachment to the apparatus body.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image carrier unit and an image forming apparatus used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus has been widely applied as a copying machine, a printer, a facsimile, and a multifunction machine having a plurality of these functions. In such an image forming apparatus, a photosensitive film formed on the surface layer of a photosensitive drum as an image carrier is charged by a charging unit such as a charging roller, and is exposed by a laser scanner to form an electrostatic latent image. Further, the electrostatic latent image on the surface of the photosensitive drum is developed as a toner image using a toner by a developing device, transferred onto a sheet, and visualized.

  As an image forming apparatus employing such a process, in order to continuously form a good image, a photosensitive drum, a charging roller, and the like are accommodated in an image carrier unit (for example, a drum cartridge) and attached to and detached from the apparatus main body. What has become possible to exchange by doing so is popular. As this image carrier unit, there is one that houses a photosensitive drum in which the thickness of the photosensitive film is varied according to the number of sheets to be printed. That is, for example, an image carrier unit containing a photosensitive drum having a thick photosensitive film is assumed when printing a large number of sheets, and a photosensitive drum having a thin photosensitive film is accommodated when printing a small number of sheets is assumed. The image carrier unit. As a result, the user can select an image carrier unit suitable for the desired number of printed sheets and mount it on the apparatus main body, ensuring an appropriate life of the photosensitive drum and forming a good image. .

  When the film thickness of the photoconductor drum is different, in order to charge the surface of the photoconductor drum to an appropriate potential, it is necessary to adjust the charging bias output from the charging unit according to the film thickness of the photoconductor film. . For this reason, an image carrier unit having a storage means for storing an initial set value of the thickness of the photosensitive film has been developed (see Patent Document 1). The image forming apparatus to which the image carrier unit is mounted reads the initial setting value of the photosensitive film thickness from the storage means of the image carrier unit, and adjusts the charging bias output from the charging means according to the film thickness. By doing so, the charging potential on the surface of the photosensitive drum is optimized.

  On the other hand, an image forming apparatus capable of detecting the film thickness of the photosensitive film on the photosensitive drum after being mounted on the apparatus main body has been developed (see Patent Document 2). In this image forming apparatus, the film thickness of the photoreceptor film can be detected based on the relationship between the charging voltage applied to the charging unit and the charging current in the charging unit. In this image forming apparatus, since the film thickness of the photosensitive film can be detected even after the photosensitive drum is mounted on the apparatus main body, the photosensitive drum is adjusted by adjusting the charging bias output from the charging unit according to the film thickness. It is possible to optimize the charging potential of the surface. When detecting the film thickness of the photoreceptor film by this method, it is necessary to apply the charging voltage after setting the surface potential of the photosensitive drum to a predetermined value.

  In this image forming apparatus, the surface potential of the photosensitive drum can be converged to 0 V if the AC charging method is used, but when the film thickness is detected by the DC charging method, the surface potential cannot be converged to 0 V as in the case of AC charging. For this reason, a charge removal unit such as a pre-exposure device or a charge removal device is used. In addition, in an image forming apparatus that has a DC charging method and does not have a charge eliminating unit such as a pre-exposure apparatus or a charge eliminating apparatus, the surface potential of the photosensitive drum is set to 0 V by, for example, exposure means, thereby detecting the film thickness of the photosensitive film. be able to.

JP-A-10-133545 JP-A-5-223513

  However, in the above-described image forming apparatus disclosed in Patent Document 1, the film thickness stored in the storage unit is an initial setting value based on the design value of the product, so that an error occurs in the film thickness of the photosensitive film during actual manufacturing. Therefore, there is a possibility that the initial set value is different from the actual film thickness. When the initial setting value is different from the actual film thickness, the image forming apparatus sets the charging bias according to the erroneous initial setting value, and thus the charging potential on the surface of the photosensitive drum cannot be optimized. There is a possibility that the formation of a good image is hindered.

  Further, in the image forming apparatus disclosed in Patent Document 2 described above, when the surface of the photosensitive drum is neutralized by using a DC charging method and without a neutralization unit such as a pre-exposure apparatus or a neutralization apparatus and using an exposure unit, the photosensitive drum Passes through the developing device before reaching the charging roller from the exposure means. That is, the portion of the photosensitive drum that has been neutralized by the exposure means passes through the developing device before reaching the charging roller. For this reason, in the case of the two-component development method, the magnetic carrier carried on the developing sleeve may mechanically adhere to the surface of the photosensitive drum, which may adversely affect the photosensitive drum. For this reason, when there is no charge eliminating portion in the DC charging method, it is not preferable to detect the film thickness of the photosensitive drum in the image apparatus, and the charging bias is set according to an inaccurate initial setting value. The charge potential on the drum surface cannot be optimized. That is, in the case of the DC charging method, the surface potential of the photosensitive drum changes due to the change of the discharge start voltage depending on the thickness of the photosensitive film. In particular, in an image forming apparatus using a magnetic carrier such as dry two-component development, an appropriate range of surface potential that does not cause fogging or carrier adhesion is narrowed. As a result, image defects such as fogging and carrier adhesion are likely to occur, and formation of a good image may be hindered.

  The present invention provides an image carrier unit and an image forming apparatus capable of acquiring information on an accurate initial value of the film thickness of a photoconductor film of an image carrier even when the static eliminator is not provided. With the goal.

  An image carrier unit of the present invention is an image carrier unit that can be mounted on the main body of an image forming apparatus, and has an image carrier that has an electrostatic image carrier on its surface, and the photosensitive film. And storage means for storing measurement values measured before being attached to the apparatus main body.

  According to the present invention, before the image carrier unit is mounted on the apparatus main body, information relating to the film thickness of the photosensitive film of the image carrier is measured, and the measured value is stored in the storage means. For this reason, the control unit of the image forming apparatus can read the measurement value from the storage unit of the image carrier unit mounted on the apparatus main body, and control a control target such as a charging unit based on the measurement value. . As a result, even when the surface of the image carrier is not provided with a charge eliminating unit, the image forming apparatus can acquire information on the accurate initial value of the film thickness of the photosensitive film of the image carrier. .

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. 1 is a cross-sectional view illustrating a schematic configuration of an image forming unit according to an embodiment. It is sectional drawing which shows schematic structure of the drum cartridge which concerns on embodiment. It is a block diagram which shows schematic structure of the control system which concerns on embodiment. It is a flowchart which shows the procedure of the film thickness measurement of the photoreceptor film | membrane of the drum cartridge which concerns on embodiment. 6 is a timing chart for measuring the film thickness of the photosensitive film of the drum cartridge according to the embodiment. 3 is a flowchart illustrating a procedure for reading a measured value by mounting a drum cartridge in the image forming apparatus according to the embodiment. It is a graph which shows the relationship between the travel distance of the photosensitive drum which concerns on embodiment, and the variation | change_quantity of a discharge start voltage.

  Hereinafter, an image carrier unit according to an embodiment of the present invention will be described in detail with reference to FIGS. In this embodiment, the case where the image carrier unit is applied to a tandem type full color printer as an example of an image forming apparatus is described. However, the present invention is not limited to the image carrier unit of the tandem type image forming apparatus, but may be an image carrier unit of another type of image forming apparatus, and is not limited to a full-color image. Or a mono color. Alternatively, it can be implemented in various applications such as a printer, various printing machines, a copying machine, a FAX, and a multifunction machine by adding necessary equipment, equipment, and a housing structure. In the present embodiment, the image forming apparatus 1 includes the intermediate transfer belt 44b. After the primary transfer of the toner images of each color from the photosensitive drum 51 to the intermediate transfer belt 44b, the composite toner image of each color is applied to the sheet S. It is a system that performs secondary transfer in a batch. However, the present invention is not limited to this, and a method of directly transferring from the photosensitive drum to the sheet conveyed by the sheet conveying belt may be employed.

  As shown in FIG. 1, the image forming apparatus 1 includes an apparatus main body 10, a sheet feeding unit 30, an image forming unit 40, a sheet conveying unit and a sheet discharging unit (not shown), and a control unit 20. Yes. Note that the sheet S as a recording material is formed with a toner image, and specific examples include plain paper, a synthetic resin sheet that is a substitute for plain paper, cardboard, and an overhead projector sheet.

  The apparatus main body 10 is a housing that houses the sheet feeding unit 30, the image forming unit 40, the control unit 20, and the like. For example, a door (not shown) that can be opened and closed is provided on the front side surface. By opening this door, a drum cartridge 57 described later can be attached to and detached from the apparatus main body 10. Further, the apparatus main body 10 is provided with a door sensor (not shown) that detects opening and closing of the door.

  The sheet feeding unit 30 is disposed in the lower part of the apparatus main body 10, and includes a sheet cassette 31 that stacks and stores sheets S and a feeding roller 32, and feeds the sheet S to the image forming unit 40. .

  The image forming unit 40 includes image forming units 50y, 50m, 50c, and 50k, a toner bottle (not shown), exposure devices 42y, 42m, 42c, and 42k, an intermediate transfer unit 44, a secondary transfer unit 45, and a fixing unit. Part 46. The image forming unit 40 can form an image on the sheet S based on the image information. The image forming apparatus 1 according to the present embodiment is compatible with full color, and the image forming units 50y, 50m, 50c, and 50k are yellow (y), magenta (m), cyan (c), black ( Each of the four colors k) is provided separately with the same configuration. For this reason, in FIG. 1, each of the four color components is shown with the same symbol followed by a color identifier, but in FIG. 2, FIG. 3 and the specification, only the symbol is described without adding the color identifier. In some cases.

  In this embodiment, a two-component developer that is a mixture of a non-magnetic toner and a magnetic carrier is used as the developer. The toner is produced by pulverization or polymerization by encapsulating a colorant, a wax component or the like in a resin such as polyester or styrene. The carrier is generated by applying a resin coat to the surface layer of the core made of resin particles kneaded with ferrite particles or magnetic powder.

  The image forming unit 50 includes four image forming units 50y, 50m, 50c, and 50k for forming toner images of four colors. As shown in FIG. 2, each image forming unit 50 includes a photosensitive drum (image carrier) 51 that forms a toner image, a charging device (charging means) 52, a developing device 53, and a cleaning device 54. Yes. Note that the image forming unit 50 according to the present embodiment does not have a static eliminating unit that neutralizes the surface of the photosensitive drum 51.

  The photosensitive drum 51 includes an organic photosensitive support 51a having a cylindrical conductive support 51a and a photosensitive film 51b having a photosensitive layer of an organic material and a surface protective layer sequentially stacked on the outer peripheral surface of the conductive support 51a. It consists of a body and can carry an electrostatic image on its surface. That is, the photosensitive drum 51 has a photosensitive film 51b capable of carrying an electrostatic image on the surface layer. The photosensitive layer is formed by applying a thin film of organic photoconductor (OPC) having a negative charge polarity. The surface protective layer contains fluororesin fine particles. In the present embodiment, an aluminum cylinder having a thickness of 1 mm is used as the conductive support 51a, and a photosensitive film 51b having a thickness of 20 μm is formed on the outer peripheral surface of the conductive support 51a. A photosensitive drum 51 having a diameter of 30 mm is configured. The photosensitive drum 51 rotates in the arrow direction at a predetermined process speed (circumferential speed). Note that the image forming apparatus 1 according to the present embodiment does not have a film thickness detecting unit for detecting the film thickness of the photosensitive film 51b of the photosensitive drum 51.

  The charging device 52 includes a charging roller 55 and a power source 56, and can charge the surface by applying a charging voltage to the surface of the photosensitive film 51 b of the photosensitive drum 51. The charging roller 55 is disposed in contact with the photosensitive drum 51 and uniformly charges the surface of the photosensitive drum 51 to a predetermined potential. Both ends of the charging roller 55 in the longitudinal direction are supported by being urged toward the photosensitive drum 51 with a predetermined pressure by a pressure mechanism (not shown). For this reason, the charging roller 55 rotates following the rotation of the photosensitive drum 51. The driving method of the charging roller 55 is not limited to the driven rotation to the photosensitive drum 51, and may be driving using an electric motor, for example.

  The charging roller 55 has a conductive core bar 55a that is a shaft portion and serves as a base, and an elastic layer 55b provided around the conductive core bar 55a. The conductive metal core 55a is made of, for example, a metal material such as iron, copper, stainless steel, or aluminum, and is made of aluminum in the present embodiment. In addition, if it is a range which does not lose electroconductivity, in order to provide rust prevention property and scratch resistance, you may perform the plating process to the electroconductive core metal 55a.

The elastic layer 55b is formed by dispersing carbon black as a conductive agent in rubber (EPDM (ethylene-propylene-diene rubber)) as an elastic material. In the present embodiment, the elastic layer 55b is subjected to resistance adjustment processing to be less than 10 ¹⁰ Ωcm by the dispersion of carbon black, and has conductivity. In the present embodiment, the diameter of the conductive metal core 55a is 8 mm, the resistance of the elastic layer 55b is 1 × 10 ⁶ Ωcm, and the outer diameter of the charging roller 55 is 14 mm. As the elastic material, natural rubber, SBR, silicone rubber, urethane rubber, epichlorohydrin rubber, synthetic rubber such as IR, BR, NBR and CR, polyamide resin, polyurethane resin, silicone resin, etc. may be used. . In addition, as the conductive agent, an electronic conductive material such as graphite or conductive metal oxide, or an ionic conductive material such as an alkali metal salt may be used.

  The elastic layer 55b has a so-called crown shape in which a central portion in the longitudinal direction is thicker than both end portions in the longitudinal direction. In the present embodiment, the elastic layer 55b is formed in a crown shape by polishing the surface of the elastic layer 55b. As described above, both ends of the charging roller 55 in the longitudinal direction are supported by being urged toward the photosensitive drum 51 with a predetermined pressure by the pressurizing mechanism, so that the charging roller 55 may be slightly bent. For this reason, the contact pressure on the photosensitive drum 51 at the center in the longitudinal direction of the charging roller 55 tends to be smaller than that at both ends. However, by forming the elastic layer 55b in a crown shape, the length of the charging roller 55 is increased. The contact pressure is uniform regardless of the position in the direction.

  The power source 56 is connected to the conductive mandrel 55a and can apply a charging bias. In the present embodiment, the charging bias is a DC voltage of −1400V. In the case where the DC charging method is adopted, the discharge start voltage is lowered because the film thickness of the photoconductor film 51b is worn by long-time use. For this reason, when a constant voltage is continuously applied to the photoconductor film 51b, the surface potential increases as the film thickness of the photoconductor film 51b decreases, and thus the film thickness of the photoconductor film 51b. It is desirable to perform control to reduce the applied voltage in accordance with the decrease in the voltage.

  The developing device 53 includes a developing container 53a, conveying screws 53b and 53c, and a developing sleeve 53d. The developing container 53a is supplied with toner from a toner bottle filled with toner. The conveying screws 53b and 53c agitate the developer inside the developing container 53a and supply it to the developing sleeve 53d. The developing sleeve 53d is provided to face the photosensitive drum 51, and develops the electrostatic image formed on the photosensitive drum 51 with toner stored in the developing container 53a.

  As a result, the charging roller 55 comes into contact with the surface of the photosensitive drum 51 and charges the surface of the photosensitive film 51b to, for example, a uniform negative polarity dark portion potential. On the surface of the photosensitive drum 51, after charging, an electrostatic image is formed by the exposure device 42 based on the image information. The photosensitive drum 51 carries the formed electrostatic image, moves around, and is developed with toner by the developing device 53. The developed toner image is primarily transferred to an intermediate transfer belt 44b described later. The cleaning device 54 is disposed in contact with the surface of the photosensitive drum 51 with the blade 54a, and cleans residues such as transfer residual toner remaining on the surface of the photosensitive drum 51 after the primary transfer.

  In the present embodiment, as shown in FIG. 3, the photosensitive drum 51, the charging roller 55, and the cleaning device 54 are provided in a drum cartridge (image carrier unit) 57 and unitized. The drum cartridge 57 is detachable (attachable) to the apparatus main body 10 and constitutes the image forming unit 50 together with the developing device 53 and the like by the attachment. As shown in FIG. 4, the drum cartridges 57y, 57m, 57c, and 57k are separately provided with the same configuration for each of the four colors, and can be attached to and detached from the apparatus main body 10 (see FIG. 1).

  Each drum cartridge 57y, 57m, 57c, 57k has memory tags (storage means) 58y, 58m, 58c, 58k. Each of the memory tags 58y, 58m, 58c, and 58k includes, for example, a non-volatile memory, and stores measurement values measured before mounting on the apparatus main body 10 with respect to information on the film thickness of the photosensitive film 51b of each photosensitive drum 51. Yes. In the present embodiment, each memory tag 58 uses the discharge start voltage on the surface of the photosensitive film 51 b of each photosensitive drum 51 as information on the film thickness of the photosensitive film 51 b of each photosensitive drum 51 to the apparatus main body 10. The measured value measured before wearing is stored.

  As shown in FIG. 1, the intermediate transfer unit 44 is disposed below the image forming units 50y, 50m, 50c, and 50k. The intermediate transfer unit 44 includes a plurality of rollers such as a driving roller 44a, a driven roller 44d, and primary transfer rollers 43y, 43m, 43c, and 43k, and an intermediate transfer belt 44b wound around these rollers. Each primary transfer roller 43 is disposed opposite to the photosensitive drum 51 and abuts against the intermediate transfer belt 44b.

  By applying a positive transfer bias from the power supply 47 connected to each primary transfer roller 43 via each primary transfer roller 43, each negative polarity on each of the photosensitive drums 51y, 51m, 51c, 51k is changed. The toner images possessed are sequentially transferred to the intermediate transfer belt 44b in a multiple manner. Thus, the intermediate transfer belt 44b moves by transferring the toner image obtained by developing the electrostatic image on the surface of the photosensitive drum 51.

  The secondary transfer unit 45 includes a secondary transfer inner roller 45a and a secondary transfer outer roller 45b. A full color image formed on the intermediate transfer belt 44b is transferred to the sheet S by applying a positive secondary transfer bias to the secondary transfer outer roller 45b. The fixing unit 46 includes a fixing roller 46a and a pressure roller 46b. When the sheet S is nipped and conveyed between the fixing roller 46a and the pressure roller 46b, the toner image transferred to the sheet S is heated and pressurized and fixed to the sheet S. The sheet S formed with the toner image is conveyed by a sheet conveyance unit (not shown) and discharged from a sheet discharge unit (not shown).

  As shown in FIG. 4, the control unit 20 is configured by a computer. For example, a CPU 21, a ROM 22 that stores a program for controlling each unit, a RAM 23 that temporarily stores data, and an input / output that inputs and outputs signals to and from the outside. Circuit (I / F) 24. The CPU 21 is a microprocessor that controls the entire control of the image forming apparatus 1 and is the main body of the system controller. The CPU 21 is connected to the sheet feeding unit 30, the image forming unit 40, the sheet conveying unit, the sheet discharging unit, and the operation unit via the input / output circuit 24, and exchanges signals with each unit and controls the operation. The CPU 21 also connects the memory tags 58y, 58m, 58c, and 58k of the drum cartridges 57y, 57m, 57c, and 57k, and the power sources 56y, 56m, and 56c of the charging rollers 55y, 55m, 55c, and 55k via the input / output circuit 24. , 56k. The control unit 20 performs control using the measurement values stored in the memory tags 58y, 58m, 58c, and 58k, and in particular, controls the power sources 56y, 56m, 56c, and 56k based on the measurement values, thereby controlling the charging voltage. Control. Furthermore, a door sensor that detects opening and closing of the door of the apparatus main body 10 is connected to the control unit 20.

  Next, an image forming operation in the image forming apparatus 1 configured as described above will be described.

  As shown in FIG. 1, when the image forming operation is started, the photosensitive drum 51 rotates and the surface is charged by the charging roller 55. Then, laser light is emitted from the exposure device 42 to the photosensitive drum 51 based on the image information, and an electrostatic latent image is formed on the surface of the photosensitive drum 51. When toner adheres to the electrostatic latent image, it is developed and visualized as a toner image, and transferred to the intermediate transfer belt 44b.

  On the other hand, the feeding roller 32 rotates in parallel with the toner image forming operation and feeds the uppermost sheet S of the sheet cassette 31 while separating it. Then, the sheet S is conveyed to the secondary transfer unit 45 via the conveyance path in synchronization with the toner image on the intermediate transfer belt 44b. Further, the image is transferred from the intermediate transfer belt 44b to the sheet S, and the sheet S is conveyed to the fixing unit 46, where the unfixed toner image is heated and pressed to be fixed on the surface of the sheet S, and the sheet discharging unit. Discharged from.

  Next, a procedure for detecting the discharge start voltage Vth of the photosensitive film 51b of the photosensitive drum 51 and writing it to the memory tags 58y, 58m, 58c, and 58k will be described with reference to the flowchart of FIG. 5 and the time chart of FIG. To do.

  An assembled drum cartridge 57 and a detection device for detecting the discharge start voltage Vth of the photosensitive drum 51 accommodated therein are prepared in advance. Examples of the detection device include a drive unit that can drive the photosensitive drum 51, a voltage application unit that can apply a DC voltage to the charging roller 55, and a surface potential vd at a position corresponding to the development region of the photosensitive drum 51. It is assumed that a potential measuring unit capable of measuring the voltage and a charge eliminating unit are provided. The neutralization unit is, for example, an AC voltage application unit, a neutralization member, or the like, and is disposed in a neutralization area downstream of the developing area of the photosensitive drum 51 in the drum rotation direction and upstream of the charging roller 55 in the drum rotation direction. The surface of the drum 51 can be neutralized. In the present embodiment, the detection device includes a static elimination unit. However, the present invention is not limited to this, and the static elimination unit may be omitted. Further, the detection device is not limited to a configuration including only such a drive unit, a voltage application unit, a potential measurement unit, and a charge removal unit, and for example, an image forming apparatus modified for detection may be used. .

Here, the principle of detecting the discharge start voltage Vth of the photoreceptor film 51b by this detection device will be described. In the case of the DC charging method, the electrostatic capacity of the photosensitive film 51b of the photosensitive drum 51 is C1, and the electrostatic capacity of the air layer between the gaps in the discharge area between the charging roller 55 and the photosensitive drum 51 is C2. The charging phenomenon of the photosensitive drum 51 by 55 can be expressed by an electrical equivalent circuit. In a steady environment, the resistance of the charging roller 55 is small compared to the photosensitive drum 51 and the air layer and can be ignored. When a DC voltage V is applied to this equivalent circuit, the voltage is proportionally distributed to the impedance of each capacitor, and the voltage Va applied to the air layer is calculated by the following formula (1).
Va = C1 / (C1 + C2) × V (1)

The air layer has a breakdown voltage in accordance with Paschen's law. If the thickness of the air layer is d [μm], discharge occurs when the voltage Va applied to the air layer exceeds 312 + 6.2 d [V]. Is done. The voltage at which discharge occurs for the first time is when the quadratic equation relating to d when the voltage Va in equation (1) is equal to 312 + 6.2d has a multiple solution (capacitance C2 is also a function of d). Voltage Va corresponds to the discharge start voltage Vth. That is, the discharge start voltage Vth is calculated by the following mathematical formula (2).
Vth = 312 + 6.2 × 10 ⁶ × t / ε + (7736.7 × 10 ⁶ × t / ε) ^0.5
(Where ε: dielectric constant of photosensitive layer, t: thickness of photosensitive layer) (2)

  Therefore, when the film thickness t of the photosensitive film 51b of the photosensitive drum 51 decreases, the electrostatic capacitance C1 of the photosensitive film 51b of the photosensitive drum 51 increases and the discharge start voltage Vth decreases. For example, in the present embodiment, the photosensitive film 51b has a film thickness of 20 μm, the discharge start voltage Vth of the photosensitive drum 51 is about 580 V, and the change amount of the discharge start voltage Vth per film thickness of 1 μm is about 8 V. is there. Therefore, the film thickness of the photoreceptor film 51b can be calculated by measuring the discharge start voltage Vth.

  When detecting the discharge start voltage Vth of the photosensitive film 51b of the photosensitive drum 51, the drum cartridge 57 is installed in the detection device, and the driving of the detection device starts the driving of the photosensitive drum 51 (step S1, FIG. 6). t1). Then, the neutralization unit of the detection device starts neutralization of the photosensitive drum 51 (step S2, t1 in FIG. 6). If the detection device does not have a charge removal unit, step S2 is not executed.

  A first charging voltage V1 (for example, 1200 V) is applied by the voltage application unit via the charging roller 55 while the rotation speed of the photosensitive drum 51 is stable (step S3, t2 to t4 in FIG. 6). After the first charging voltage V1 is applied, the surface potential vd1 of the photosensitive drum 51 is measured by the potential measuring unit in the developing region of the photosensitive drum 51 (step S4, t3 in FIG. 6). The measurement result here is assumed to be 620 V, for example. Note that the measurement of the first surface potential vd1 and second and third surface potentials vd2 and vd3 described later by the potential measuring unit includes potential fluctuations in the circumferential direction of the photosensitive drum 51 and the charging roller 55. It is preferable to measure more than one revolution of the drum 51. Of course, this is not restrictive.

  Next, a second charging voltage V2 (for example, 1400 V) is applied through the charging roller 55 by the voltage application unit (step S5, t5 to t7 in FIG. 6). After the second charging voltage V2 is applied, the second surface potential vd2 of the photosensitive drum 51 is measured by the potential measuring unit in the development region of the photosensitive drum 51 (step S6, t6 in FIG. 6). The measurement result here is assumed to be 820 V, for example.

  Further, a third charging voltage V3 (for example, 1600 V) is applied through the charging roller 55 by the voltage application unit (step S7, t8 to t10 in FIG. 6). After the third charging voltage V3 is applied, the third surface potential vd3 of the photosensitive drum 51 is measured by the potential measuring unit in the developing region of the photosensitive drum 51 (step S8, t9 in FIG. 6). The measurement result here is assumed to be 1020 V, for example.

After three measurements by the potential measurement unit, the charge removal is stopped by the charge removal unit (step S9, t11 in FIG. 6), and the drive of the photosensitive drum 51 by the drive unit is stopped (step S10, t11 in FIG. 6). ). Note that if the detection device does not have a charge removal unit, step S9 is not executed. Then, the discharge start voltage Vth is calculated based on the average of three differences between the charging voltages V1 to V3 and the surface potentials vd1 to vd3 at that time (step S11). That is, the discharge start voltage Vth can be calculated by the following mathematical formula (3).
Vth = ((V1-vd1) + (V2-vd2) + (V3-vd3)) / 3 (3)
The calculated discharge start voltage Vth is stored in the memory tag 58 provided in the drum cartridge 57 as a measured value of the discharge start voltage Vth (step S12). For example, in this embodiment, as shown in FIG. 6, Vth = 580 [V].

  Next, FIG. 7 shows a procedure in which the image forming apparatus 1 reads the measured value of the discharge start voltage Vth after the drum cartridge 57 having the memory tag 58 in which the discharge start voltage Vth is written is attached to the image forming apparatus 1. It demonstrates along the flowchart shown.

  After the discharge start voltage Vth is stored in the memory tag 58 (step S21, step S12 in FIG. 5), the drum cartridge 57 is sealed and packaged and shipped as a product (step S22). When using a new drum cartridge 57, for example, a user or the like of the image forming apparatus 1 unpacks the drum cartridge 57 and attaches it to the image forming apparatus 1 (step S23). The control unit 20 determines whether or not the main body power of the image forming apparatus 1 is on (step S24). If the main body power is on, the front side door of the main body 10 is closed. Is determined based on the detection result of the door sensor (step S25). If the control unit 20 determines that the door of the apparatus main body 10 is closed, it is assumed that the drum cartridge 57 is mounted and an image can be formed, and the discharge start voltage Vth from the memory tag 58 of the drum cartridge 57 is assumed. The measured value is read (step S26). If the control unit 20 determines that the main body power supply is not turned on or determines that the door of the apparatus main body 10 is not closed, the image forming apparatus 1 is accessed again without accessing the memory tag 58. It is determined whether or not the main body power supply is on (step S24).

  In step S26, when the control unit 20 cannot read the information of the memory tag 58, or when the read value exceeds the allowable range, the change amount of the discharge start voltage Vth is set to be small. That is, in the table of FIG. 8 to be described later, control is performed so that the reduction lower limit value 64 side. As a result, the occurrence of carrier adhesion can be more reliably suppressed, and deterioration of the photosensitive drum 51 due to carrier adhesion can be prevented.

  The control unit 20 writes the discharge start voltage Vth read from the memory tag 58 in, for example, the RAM 23 as an offset value of the charging DC voltage applied during image formation. Here, the ROM 22 stores in advance a discharge start voltage table corresponding to the travel distance of the photosensitive drum 51 and a discharge start voltage table corresponding to the operating environment of the main body, and the control unit 20 performs charging applied during image formation. The DC voltage is determined from the travel distance and the main body operating environment. The control unit 20 adds the offset value obtained from the memory tag 58 to the determined charging DC voltage and performs actual control.

  FIG. 8 shows the transition of the allowable range (latitude) for fogging or carrier adhesion with respect to the change amount of the discharge start voltage Vth. As described above, the discharge start voltage Vth decreases as the film thickness of the photosensitive film 51b of the photosensitive drum 51 decreases according to the travel distance of the photosensitive drum 51. When a constant voltage is continuously applied, the surface potential increases as the film thickness decreases, so that it is necessary to perform applied voltage control according to the film thickness of the photoreceptor film 51b. It is widely known that the decrease in the film thickness of the photoconductor film 51b is affected by the usage status, usage environment, charging DC current amount, contact pressure of the cleaning device 54, and the like of the image forming apparatus 1. In the present embodiment, since the image forming apparatus 1 does not have a film thickness detection unit, as shown in FIG. 8, the relationship between the travel distance of the photosensitive drum 51 and the amount of change in the discharge start voltage Vth is obtained in advance. Obtained as a table.

  In this table, when the film thickness of the photosensitive film 51b is greatly reduced from the allowable range and the discharge start voltage Vth is greatly reduced from the allowable range, the carrier adhesion limit value 61 is set on the assumption that carrier adhesion occurs. ing. A region where the discharge start voltage Vth exceeds the carrier adhesion limit value 61 is defined as a carrier adhesion region R2 where carrier adhesion occurs. Further, in this table, when the film thickness of the photosensitive film 51b is reduced below the allowable range and the discharge start voltage Vth is reduced below the allowable range, the fogging limit value 62 is set on the assumption that fogging occurs. ing. A region where the discharge start voltage Vth exceeds the fog limit value 62 is defined as a fog region R3 where fog occurs. Therefore, the center value 60 of the discharge start voltage Vth is set at the center of these limit values 61 and 62 in the allowable region R1 between the carrier adhesion limit value 61 and the fogging limit value 62 so as to avoid carrier adhesion and fogging as much as possible. It is set to be near.

  With respect to the upper and lower limits of the variation of the variation with respect to the center value 60, it is preferable to design with a tolerance for carrier adhesion and fogging. For this reason, the reduction upper limit value 63 and the reduction lower limit value 64 corresponding to the travel distance of the photosensitive drum 51 are set with the center value 60 as the center, and neither of them reaches the limit values 61 and 62. .

  However, when the initial value of the film thickness of the photosensitive film 51b is different from the actual film thickness, the center value 60 and the actual value are shifted. For this reason, for example, when the initial value of the film thickness is thinner than the actual film thickness by an error and reaches the reduction upper limit 63, the actual decrease upper limit obtained by adding the film thickness error to the reduction upper limit 63. It becomes the relationship of the value 65. In this case, when the traveling distance of the photosensitive drum 51 is increased, the actual reduction upper limit value 65 exceeds the carrier adhesion limit value 61, and therefore, there is a possibility that carrier adhesion may occur when used for a long time. For example, when the initial value of the film thickness is thicker than the actual film thickness by an error and reaches the reduction lower limit value 64, the actual decrease lower limit 66 is obtained by subtracting the film thickness error from the decrease lower limit 64. It becomes a relationship. In this case, when the traveling distance of the photosensitive drum 51 is increased, the actual reduction lower limit 66 exceeds the fogging limit 62, and thus there is a possibility that fogging may occur when used for a long time.

  On the other hand, according to the drum cartridge 57 of the present embodiment, the film thickness of the photosensitive film 51b is measured before the drum cartridge 57 is mounted on the apparatus main body 10, and the control unit 20 measures the film thickness during image formation. The value is used. Therefore, the relationship between the travel distance of the photosensitive drum 51 and the change amount of the discharge start voltage Vth can be corrected so as to approach the center value 60. Therefore, the amount of change in the discharge start voltage Vth can be controlled so as not to cause carrier adhesion and fogging.

  As described above, according to the drum cartridge 57 of the present embodiment, before the drum cartridge 57 is mounted on the apparatus main body 10, the discharge start voltage Vth of the photosensitive film 51b of the photosensitive drum 51 is measured, and the measured value is Stored in the memory tag 58. For this reason, the control unit 20 can read the measurement value from the memory tag 58 of the drum cartridge 57 attached to the apparatus main body 10 and control, for example, the charging device 52 based on the measurement value. As a result, even when the surface of the photosensitive drum 51 is not provided with a charge removal unit, the image forming apparatus 1 can acquire information regarding the accurate initial value of the film thickness of the photosensitive film 51b of the photosensitive drum 51. It becomes. As a result, even in the image forming apparatus 1 that employs the two-component development method without the charge eliminating portion by the DC charging method, it is possible to provide a good image that is stable for a longer period of time.

  Further, according to the image forming apparatus 1 of the present embodiment, the discharge start voltage Vth of the photoconductor film 51b is applied as information regarding the film thickness of the photoconductor film 51b. For this reason, when the control unit 20 controls the charging voltage applied to the charging roller 55, the control unit 20 uses the amount of change in the discharge start voltage Vth read from the table (see FIG. 8) as the discharge start voltage Vth read from the memory tag 58. It can be easily corrected using the measured value. For this reason, simplification of control can be achieved.

  In the image forming apparatus 1 of the above-described embodiment, the case where the discharge start voltage Vth of the photoconductor film 51b is applied as the information regarding the film thickness of the photoconductor film 51b has been described, but the present invention is not limited thereto. The information regarding the film thickness of the photoconductor film 51b may be, for example, the film thickness of the photoconductor film 51b or the charging direct current of the photoconductor film 51b. Also in these cases, the control unit 20 can read the measurement value from the memory tag 58 of the drum cartridge 57 attached to the apparatus main body 10 and control, for example, the charging device 52 based on the measurement value.

  In addition, when the information regarding the film thickness of the photoreceptor film 51b is the film thickness of the photoreceptor film 51b, the film thickness can be calculated as follows. In this embodiment, as described above, the discharge start voltage Vth in the photoconductor film 51b with a film thickness of 20 μm is 580 [V], and the amount of change in the discharge start voltage Vth per 1 μm film thickness of the photoconductor film 51b. Is about 8V. Therefore, when the calculated discharge start voltage Vth is, for example, 572 [V], the film thickness of the photoreceptor film 51b can be calculated as 19 um.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Main part of apparatus, 20 ... Control part, 51, 51c, 51k, 51m, 51y ... Photosensitive drum (image carrier), 51b ... Photoconductor film | membrane, 52, 52c, 52k, 52m, 52y ... Charging device (charging means), 57, 57c, 57k, 57m, 57y ... drum cartridge (image carrier unit), 58, 58c, 58k, 58m, 58y ... memory tag (storage means).

Claims (5)

An image carrier unit that can be attached to the main body of an image forming apparatus,
An image carrier having, on the surface, a photoreceptor film capable of carrying an electrostatic image;
With respect to information relating to the film thickness of the photoreceptor film, a storage unit that stores measurement values measured before mounting on the apparatus main body is provided.
An image carrier unit characterized by that. Information on the film thickness of the photoreceptor film is a discharge start voltage in the photoreceptor film.
The image carrier unit according to claim 1, wherein: Information on the film thickness of the photoreceptor film is the film thickness of the photoreceptor film.
The image carrier unit according to claim 1, wherein: The image carrier unit according to any one of claims 1 to 3,
A control unit that executes control using the measurement value stored in the storage unit,
An image forming apparatus. A charging means capable of charging the surface by applying a charging voltage to the surface of the photoreceptor film;
The controller controls the charging voltage based on the measured value;
The image forming apparatus according to claim 4.

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