Image formation apparatus

Abstract

To provide an image formation apparatus capable of maintaining an appropriate surface potential by correcting a charging voltage on the basis of the degree of deterioration of a charging member for charging a photosensitive body.SOLUTION: The image formation apparatus includes: an image carrier; a charging device; a developing device; a developing voltage power supply; a charging voltage power supply; a control unit; and a storage unit. The charging device has a charging member for charging the image carrier. The storage unit stores the transition of surface potential with respect to a cumulative driving distance of the image carrier in a state where a volume resistivity of the charging member is fixed to an initial volume resistivity value and the transition of surface potential with respect to the cumulative driving distance in a state where an increase in the volume resistivity due to deterioration of the charging member is taken into account. The control unit calculates the correction value of charging voltage at the cumulative driving distance on the basis of the difference between a first surface potential, which is the surface potential in the state where the volume resistivity is fixed to the initial volume resistivity value, and a second surface potential, which is the surface potential in the state where the increase in the volume resistivity is taken into account.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic image forming apparatus, and more particularly to a method for detecting deterioration of a charging member that charges a photosensitive member serving as an image carrier. [Background technology]

[0002] In conventional electrophotographic image forming apparatuses, an image carrier, such as a photosensitive drum having a photosensitive layer formed on its surface, is charged to a predetermined surface potential by a charging member, such as a charging roller, and then an exposure device scans the image carrier with light to form an electrostatic latent image with the charge attenuated. This electrostatic latent image is then developed by a developing device and visualized as a toner image. In such image forming apparatuses, it is necessary to stabilize the surface potential of the image carrier to prevent image defects such as image fogging.

[0003] Patent Document 1 discloses an electrophotographic device that includes a circuit that forms a pulsed electrostatic potential pattern on a photosensitive member and detects the current that flows when this electrostatic potential pattern is developed, a circuit that obtains the surface potential on the photosensitive member by converting the detected current into a surface potential based on a predetermined relational expression or using a pre-created correlation table, and a circuit that feeds back the obtained surface potential to control the charging of the photosensitive member by a charger. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-295540 Summary of the Invention [Problem to be solved by the invention]

[0005] In the electrophotographic device of Patent Document 1, a pulsed electrostatic potential pattern is formed on a photosensitive member, a bias is applied to a developing roller, and the surface potential on the photosensitive member is obtained by measuring the current flowing from the photosensitive member to the developing roller when the electrostatic potential pattern is developed.

[0006] However, the current monitored in conventional electrophotographic apparatuses has the problem that it is easily affected by the deterioration over time of the photosensitive member, charging member, etc., is unstable, and is prone to contain errors.

[0007] In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of maintaining an appropriate surface potential by correcting the charging voltage based on the degree of deterioration of the charging member that charges the photosensitive member. [Means for solving the problem]

[0008] In order to achieve the above object, a first aspect of the present invention is an image forming apparatus including an image carrier, a charging device, a developing device, a developing voltage power supply, a charging voltage power supply, a control unit, and a memory unit. The image carrier has a photosensitive layer formed on its surface. The charging device has a charging member that charges the surface of the image carrier to a predetermined surface potential. The developing device has a developer carrier that carries a developer containing toner, and forms a toner image by exposing the image carrier charged by the charging device to light, thereby causing the toner to adhere to an electrostatic latent image formed thereon. The developing voltage power supply applies a developing voltage to the developer carrier. The charging voltage power supply applies a charging voltage to the charging member. The control unit controls the developing voltage power supply and the charging voltage power supply. The memory unit stores the transition of the surface potential versus the cumulative driving distance of the image carrier when the volume resistance of the charging member is fixed to an initial volume resistance value, and the transition of the surface potential versus the cumulative driving distance when an increase in the volume resistance due to deterioration of the charging member is taken into account. The control unit calculates a correction value for the charging voltage for a predetermined cumulative driving distance based on the difference between a first surface potential, which is the surface potential when the initial volume resistance value is fixed, and a second surface potential, which is the surface potential when the increase in the volume resistance value is taken into account, for the predetermined cumulative driving distance. [Effects of the Invention]

[0009] According to the first aspect of the present invention, a correction value for the charging voltage applied to the charging member is calculated in accordance with the degree of deterioration of the charging member, thereby suppressing a decrease in the surface potential of the image carrier caused by deterioration of the charging member, thereby effectively suppressing image defects such as image fogging caused by a decrease in the surface potential of the image carrier. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a side cross-sectional view showing the internal configuration of an image forming apparatus 100 according to an embodiment of the present invention. [Figure 2] 1 is a partially enlarged view of the image forming unit Pa and its surroundings, including a control path of the image forming apparatus 100; [Figure 3] A diagram showing the relationship between the DC voltage Vdc of the developing voltage and the developing current [Figure 4] FIG. 10 is a diagram showing the relationship between the cumulative driving distance of the photosensitive drums 1a to 1d and the transition of the surface potential when a constant charging voltage is applied to the charging roller 34. [Figure 5] 1 is a flowchart showing an example of deterioration prediction and charging voltage correction control for the charging roller 34 in the image forming apparatus 100 of the present invention. [Figure 6] 1 is a graph showing the change in surface potential with respect to the cumulative driving distance of the photosensitive drums 1a to 1d when a constant charging voltage is applied to the charging roller 34 in an embodiment. [Figure 7] 1 is a graph comparing the transition of the surface potential when the charging voltage applied to the charging roller 34 is corrected (the present invention) and when the charging voltage is not corrected (comparison example). DETAILED DESCRIPTION OF THE INVENTION

[0011] [1. Configuration of image forming device] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the present invention. Within the main body of the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in this order from the upstream side in the transport direction (left side in Fig. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, magenta, cyan, and black), and sequentially form images of yellow, cyan, magenta, and black through the processes of charging, exposure, development, and transfer, respectively.

[0012] Each of the image forming stations Pa through Pd is provided with photosensitive drums (image carriers) 1a, 1b, 1c, and 1d, which carry visible images (toner images) of each color. An intermediate transfer belt 8, which rotates counterclockwise in FIG. 1 by a belt drive motor (not shown), is provided adjacent to each of the image forming stations Pa through Pd. The toner images formed on the photosensitive drums 1a through 1d are sequentially transferred (primary transfer) onto the intermediate transfer belt 8, which moves while contacting the photosensitive drums 1a through 1d, and superimposed on each other. The toner images primarily transferred onto the intermediate transfer belt 8 are then secondarily transferred onto a transfer sheet P (an example of a recording medium) by a secondary transfer roller 9. The transfer sheet P, onto which the toner images have been secondarily transferred, is then fixed in a fixing unit 13 and ejected from the image forming apparatus 100. While the photosensitive drums 1a through 1d rotate clockwise in FIG. 1, an image formation process is performed on each of the photosensitive drums 1a through 1d.

[0013] The transfer paper P onto which the toner image is secondarily transferred is stored in a paper cassette 16 located at the bottom of the main body of the image forming apparatus 100, and is transported via a paper feed roller 12a and a pair of registration rollers 12b to the nip between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a seamless belt is usually used. In addition, a belt cleaning device 19 is located downstream of the secondary transfer roller 9 to remove toner and other particles remaining on the surface of the intermediate transfer belt 8.

[0014] Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photosensitive drums 1a to 1d, there are provided charging devices 2a, 2b, 2c, and 2d that charge the photosensitive drums 1a to 1d, an exposure device 5 that exposes image information onto each of the photosensitive drums 1a to 1d, developing devices 3a, 3b, 3c, and 3d that form toner images on the photosensitive drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d that remove toner (residual toner) remaining on the photosensitive drums 1a to 1d.

[0015] When image data is input from a host device such as a personal computer, the surfaces of the photosensitive drums 1a-1d are first uniformly charged by the charging devices 2a-2d. Next, the exposure device 5 irradiates light according to the image data, forming electrostatic latent images on the photosensitive drums 1a-1d in accordance with the image data. The developing devices 3a-3d are filled with a predetermined amount of two-component developer containing yellow, magenta, cyan, and black toner, respectively. If the toner content in the two-component developer filled in each developing device 3a-3d falls below a specified value due to the formation of a toner image (described below), toner is replenished from toner containers 4a-4d to each developing device 3a-3d. The toner in the developer is supplied to the photosensitive drums 1a-1d by the developing devices 3a-3d and electrostatically adheres to the photosensitive drums 1a-1d, forming a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5.

[0016] Then, primary transfer rollers 6a-6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a-6d and the photosensitive drums 1a-1d, and the yellow, magenta, cyan, and black toner images on the photosensitive drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed in a predetermined positional relationship for forming a predetermined full-color image. After that, toner and other substances remaining on the surfaces of the photosensitive drums 1a-1d after the primary transfer are removed by cleaning devices 7a-7d in preparation for the subsequent formation of a new electrostatic latent image.

[0017] The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a drive roller 11 on the downstream side. When the intermediate transfer belt 8 starts to rotate counterclockwise as the drive roller 11 is rotated by a belt drive motor (not shown), the transfer paper P is transported from the registration roller pair 12b to a nip portion (secondary transfer nip portion) between the drive roller 11 and the adjacent secondary transfer roller 9 at a predetermined timing, where the toner image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. After the secondary transfer, any toner remaining on the surface of the intermediate transfer belt 8 is removed by a belt cleaner 19. The transfer paper P onto which the toner image has been secondarily transferred is transported to a fixing unit 13.

[0018] The transfer paper P transported to the fixing unit 13 is heated and pressurized by the fixing roller pair 13a, and the toner image is fixed to the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which the full-color image has been formed is then transported in different directions by the branching unit 14, which branches into multiple directions, and is then discharged directly (or after being sent to the double-sided transport path 18 and having images formed on both sides) onto the discharge tray 17 by the discharge roller pair 15.

[0019] [2. Configuration of the image forming unit and its peripherals, including the control path of the image forming device] 2 is a partially enlarged view of the periphery of image forming unit Pa, including the control paths of image forming apparatus 100. In the following explanation, the configuration and control paths of image forming unit Pa will be described, but the configurations and control paths of image forming units Pb to Pd are similar, so their explanation will be omitted.

[0020] The developing device 3a includes a developing roller 30 that carries a two-component developer therein. The developing roller 30 is connected to a developing voltage power supply 43 that generates an oscillating voltage in which a DC voltage Vdc and an AC voltage Vac are superimposed.

[0021] The developing voltage power supply 43 includes an AC constant voltage power supply 43a and a DC constant voltage power supply 43b. During image formation, the developing voltage power supply 43 outputs a developing voltage in which an AC voltage Vac is superimposed on a DC voltage Vdc from the AC constant voltage power supply 43a and the DC constant voltage power supply 43b. The AC constant voltage power supply 43a outputs a sine wave AC voltage Vac generated from a low voltage DC voltage modulated into a pulse shape using a step-up transformer (not shown). The DC constant voltage power supply 43b outputs a DC voltage Vdc obtained by rectifying the sine wave AC voltage Vac generated from a low voltage DC voltage modulated into a pulse shape using a step-up transformer.

[0022] The current detection unit 44 detects the development current flowing between the photosensitive drum 1a and the development roller 30. The development current flowing to the current detection unit 44 may be caused by the movement of toner between the photosensitive drums 1a to 1d and the development roller 30, or may be caused by the movement of electric charge.

[0023] The charging voltage power supply 45 applies a charging voltage consisting of a DC voltage to the charging roller 34 of the charging device 2a. The configuration of the charging voltage power supply 45 is similar to that of the DC constant voltage power supply 43b of the developing voltage power supply 43.

[0024] Transfer voltage power supply 47 applies a primary transfer voltage and a secondary transfer voltage of opposite polarity (negative polarity) to the toner to primary transfer rollers 6a to 6d and secondary transfer roller 9 (see FIG. 1), respectively. In this embodiment, constant current control is used to apply to primary transfer rollers 6a to 6d and secondary transfer roller 9 a transfer voltage that causes a constant current (transfer current) of opposite polarity (negative polarity) to the toner to flow through primary transfer rollers 6a to 6d and secondary transfer roller 9.

[0025] The cleaning device 7a includes a collection roller 31 that temporarily holds the residual toner remaining on the surface of the photosensitive drum 1a. The collection roller 31 is connected to a cleaning voltage power supply 48 that generates a DC voltage. The cleaning voltage power supply 48 applies a voltage of the same polarity (positive polarity) as that of the toner and a voltage of the opposite polarity (negative polarity) to the collection roller 31. The configuration of the cleaning voltage power supply 48 is similar to that of the DC constant voltage power supply 43b.

[0026] Next, the control system of image forming apparatus 100 will be described with reference to Fig. 2. Image forming apparatus 100 is provided with a main control unit 80 constituted by a CPU and the like. Main control unit 80 is connected to a storage unit 70 constituted by a ROM, RAM and the like. Main control unit 80 controls each unit of image forming apparatus 100 (charging devices 2a-2d, developing devices 3a-3d, exposure device 5, primary transfer rollers 6a-6d, cleaning devices 7a-7d, secondary transfer roller 9, fixing unit 13, developing voltage power supply 43, charging voltage power supply 45, transfer voltage power supply 47, cleaning voltage power supply 48, voltage control unit 50, etc.) based on the control program and control data stored in storage unit 70.

[0027] Based on control signals sent from the main control unit 80, the voltage control unit 50 controls a development voltage power supply 43 that applies a development voltage to the development roller 30, a charging voltage power supply 45 that applies a charging voltage to the charging roller 34, a transfer voltage power supply 47 that applies a transfer voltage to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, and a cleaning voltage power supply 48 that applies a voltage to the collection roller 31. The voltage control unit 50 may be configured by a control program stored in the storage unit 70.

[0028] The internal temperature and humidity sensor 60 constantly detects the temperature and relative humidity inside the image forming apparatus 100, specifically in the vicinity of the image forming units Pa to Pd. The detected temperature and humidity are sent to the main control unit 80.

[0029] The main control unit 80 is connected to a liquid crystal display unit 90 and a transmission / reception unit 91. The liquid crystal display unit 90 functions as a touch panel for the user to make various settings for the image forming apparatus 100, and also displays the status of the image forming apparatus 100, the image formation status, the number of printed pages, etc. The transmission / reception unit 91 communicates with the outside world using a telephone line or an internet line. The transmission / reception unit 91 functions as an input unit that receives print commands and image data from a higher-level device such as a personal computer.

[0030] [3. Predicting deterioration of charging rollers] The following describes a method for predicting deterioration of the charging roller 34, which is a characteristic feature of the present invention, and a procedure for correcting the charging voltage based on the method. First, we will explain a method for estimating the surface potential used to predict deterioration of the charging roller 34. Figure 3 is a graph showing the relationship between the DC voltage Vdc of the developing voltage and the developing current.

[0031] 3, when no DC voltage (0 [V]) is applied to the developing roller 30 and the charging roller 34, the current detection unit 44 detects an uncharged developing current, which is the sum of the current that flows when toner moves from the developing roller 30 to the photosensitive drums 1a-1d and the current that flows to the photosensitive drums 1a-1d via the magnetic brush formed on the developing roller 30. This uncharged developing current is defined as the reference current Cs (Vdc=0 [V], surface potential=0 [V]).

[0032] Then, with a predetermined charging voltage applied to the charging roller 34 to charge the photosensitive drums 1a to 1d to a predetermined surface potential V0, the DC voltage Vdc is gradually changed (increased) from an initial value smaller than the surface potential V0, and the progress of the development current detected by the current detection unit 44 is measured.

[0033] When the DC voltage Vdc becomes equal to the surface potential V0 of the photosensitive drums 1a to 1d (ΔV=V0-Vdc=0 [V]), only the uncharged developing current (reference current Cs) flows between the developing roller 30 and the photosensitive drums 1a to 1d. That is, the DC voltage Vdc1 at point P where the curve L representing the change in the developing current intersects with the reference current Cs becomes equal to the surface potential V0 of the photosensitive drums 1a to 1d, and therefore the surface potential V0 can be estimated as Vdc1.

[0034] Fig. 4 is a diagram showing the relationship between the cumulative driving distance of the photosensitive drums 1a to 1d and the change in surface potential when a constant charging voltage is applied to the charging roller 34. In Fig. 4, the solid line shows the change in surface potential (first surface potential) when only the effect of the decrease in the thickness of the photosensitive layer of the photosensitive drums 1a to 1d is considered and the volume resistance of the charging roller 34 is fixed at its initial resistance value. The dashed line shows the change in surface potential (second surface potential) when the effect of the deterioration of the charging roller 34 (increase in volume resistance) is taken into account in addition to the decrease in the thickness of the photosensitive layer.

[0035] When a constant charging voltage is applied to the charging roller 34, the amount of charge that can be supplied to the photosensitive drums 1a-1d remains the same, so as the thickness of the photosensitive layer decreases, the surface potential decreases, as shown by the solid line in Figure 4. When the surface potential decreases, toner (fogging toner) moves from the developing roller 30 to the white areas of the photosensitive drums 1a-1d, causing a developing current to flow. Therefore, as the cumulative driving distance increases, the developing current detected by the current detection unit 44 when a predetermined charging voltage is applied increases.

[0036] Furthermore, if the volume resistance of the charging roller 34 increases in addition to the decrease in the thickness of the photosensitive layer, the amount of charge that can be supplied decreases even when the same charging voltage is applied. Therefore, compared to when only the decrease in the thickness of the photosensitive layer is taken into consideration, the surface potential decreases more, the amount of fogging toner increases, and the development current detected by the current detection unit 44 increases. In other words, the difference between the first surface potential and the second surface potential is the decrease in surface potential caused by deterioration of the charging roller 34.

[0037] Because the decrease in the thickness of the photosensitive layer correlates with the cumulative driving distance of the photosensitive drums 1a-1d, the change in the first surface potential can be predicted. A table or the like that stores the correlation between the cumulative driving distance and the change in the first surface potential can be stored in the memory unit 70. The change in the second surface potential can be measured using the method shown in FIG. 3 from the development current detected by the current detection unit 44. Then, by comparing the changes in the first surface potential and the second surface potential, it is possible to estimate the degree of deterioration of the charging roller 34.

[0038] Then, a correction value for the charging voltage is determined based on the estimated degree of deterioration of the charging roller 34, and the determined correction value is used to correct the default charging voltage, thereby setting the surface potential at which fogging toner does not develop. Furthermore, if the difference between the first surface potential and the second surface potential is equal to or greater than a certain level, the surface potential may not be maintained by correcting the charging voltage, and replacement of the charging roller 34 may be recommended.

[0039] The timing for predicting deterioration of the charging roller 34 may be when the cumulative number of printed sheets since the charging roller 34 began to be used or when the cumulative number of printed sheets since the previous deterioration prediction reaches a predetermined number.

[0040] 5 is a flowchart showing an example of deterioration prediction and charge voltage correction control for the charging roller 34 in the image forming apparatus 100 of the present invention. The deterioration prediction and charge voltage correction procedure for the charging roller 34 will be described along the steps of FIG. 5, with reference to FIGS. 1 to 4 as needed.

[0041] First, the main control unit 80 determines whether it is time to predict deterioration of the charging roller 34 (step S1). If it is not time to predict deterioration of the charging roller 34 (No in step S1), the process ends without predicting deterioration of the charging roller 34 or correcting the charging voltage.

[0042] When it is time to predict deterioration of the charging roller 34 (Yes in step S1), such as when the cumulative number of printed sheets since the start of use of the charging roller 34 or the cumulative number of printed sheets since the previous deterioration prediction reaches a predetermined number, the second surface potential V02 is measured (step S2). Specifically, a constant charging voltage is applied to the charging roller 34, and the surface potentials of the photosensitive drums 1a to 1d are measured. The surface potential is measured using the relationship between the DC voltage Vdc of the developing voltage and the developing current shown in FIG.

[0043] Next, the main control unit 80 compares the measured second surface potential V02 with the first surface potential V01 stored in the storage unit 70 in advance (step S3), and determines whether V01 - V02 is less than a predetermined value A (step S4). If V01 - V02 < A (Yes in step S4), since it is predicted that the deterioration of the charging roller 34 has not advanced to the level where replacement is necessary, in order to charge the photosensitive drums 1a to 1d to a desired surface potential, a correction value to be added to the predetermined charging voltage is determined based on V01 - V02 (step S5). Then, the charging voltage is corrected using the determined correction value (step S6).

[0044] On the other hand, if V01 - V02 ≥ A in step S4 (No in step S4), since it is predicted that the deterioration of the charging roller 34 has advanced to the level where replacement is necessary, a notification prompting the replacement of the charging roller 34 is issued (step S7). Specifically, a message prompting the replacement of the charging roller 34, such as "Please replace the charging roller", is displayed on the liquid crystal display unit 90.

[0045] According to the control example shown in FIG. 5, by correcting the charging voltage applied to the charging roller 34 according to the degree of deterioration of the charging roller 34, it is possible to suppress a decrease in the surface potential of the photosensitive drums 1a to 1d caused by the deterioration of the charging roller 34. Therefore, it is possible to effectively suppress image defects such as image fogging caused by a decrease in the surface potential of the photosensitive drums 1a to 1d.

[0046] Also, by detecting the developing current flowing between the photosensitive drum 1a and the developing roller 30 and estimating the surface potential based on the detected developing current, the surface potential can be accurately measured. In addition, since a dedicated potential measuring device for measuring the surface potential is not required, it also contributes to cost reduction of the image forming apparatus 100.

[0047] Furthermore, if the degree of deterioration of the charging roller 34 has progressed to the point where replacement is necessary, the user is notified of this fact using the liquid crystal display unit 90, so there is no risk of continuing printing operations with the charging roller 34 in an advanced state of deterioration or forgetting to replace the charging roller 34.

[0048] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, a color printer as shown in FIG. 1 was used as an example of image forming apparatus 100, but the present invention is not limited to color printers, and may be other image forming apparatuses that charge photosensitive drums 1a-1d using a charging member such as charging roller 34, such as color copiers, digital multifunction peripherals, and facsimiles. The effects of the present invention will be described more specifically below using examples. [Example]

[0049] [Relationship between the presence or absence of charge voltage correction based on deterioration of the charge roller and the change in the surface potential of the photosensitive drum] The transition of the surface potential of the photosensitive drum when the charging voltage is corrected based on the degree of deterioration of the charging roller 34 was evaluated.

[0050] The image formation conditions were a printing speed (process speed) of 55 sheets per minute, and the developing roller 30 used a developing sleeve 31 with an outer diameter of 20 mm, the outer surface of which was knurled (80 rows circumferentially) and blasted. The regulating blade 27 used a magnetic blade made of stainless steel (SUS430) with a thickness of 1.5 mm. A developing voltage was applied to the developing roller 30, which was a DC voltage Vdc superimposed with a square-wave AC voltage of 1200 V peak-to-peak (Vpp), 50% duty, and 8 kHz frequency.

[0051] The photosensitive drums 1a to 1d were positively charged organic photosensitive drums (OPC: Organic Photo Conductors) with a 32 μm-thick organic photosensitive layer formed as the photosensitive layer, the peripheral speed ratio of the developing roller 30 to the photosensitive drums 1a to 1d was 1.8 (trail rotation at the opposing position), and the distance between the photosensitive drums 1a to 1d and the developing roller 30 (DS distance) was 0.30 mm. The charging roller 34 was a rubber roller with a conductive rubber layer 3 mm thick and a volume resistivity of 6.0 [LogΩ] laminated on the outer surface of a core metal with an outer diameter of 6 mm, and a charging voltage consisting only of a DC voltage was applied.

[0052] The toner used was a positively charged toner with an average particle diameter of 6.8 μm, and the carrier used was a ferrite-resin coated carrier with an average particle diameter of 38 μm. The initial toner concentration in the developer (weight ratio of toner to carrier) was 6%.

[0053] The test method first measured the change in surface potential over time relative to the cumulative driving distance of the photosensitive drums 1a-1d when a constant charging voltage was applied to the charging roller 34. Figure 6 is a graph showing the change in surface potential over time relative to the cumulative driving distance of the photosensitive drums 1a-1d when a constant charging voltage was applied to the charging roller 34. As is clear from Figure 6, when wear on the photosensitive layers of the photosensitive drums 1a-1d and deterioration of the charging roller 34 were accelerated by durability printing (second surface potential, data series indicated by black circles), the decrease in surface potential was greater as the cumulative driving distance increased compared to when only the photosensitive layers of the photosensitive drums 1a-1d were worn and a constant resistance charging roller 34 was used (first surface potential, data series indicated by open circles). The difference in surface potential was used to determine the correction value for the charging voltage relative to the cumulative driving distance.

[0054] The changes in surface potential were compared between the case where the charging voltage applied to the charging roller 34 was corrected using the determined correction value (the present invention) and the case where the charging voltage was not corrected (a comparative example). The results are shown in Figure 7.

[0055] As is clear from Figure 7, when the charging voltage is corrected (data series marked with triangles), the surface potential remains almost constant even as the cumulative driving distance of the photosensitive drums 1a to 1d increases. In contrast, when the charging voltage is not corrected (data series marked with circles), the surface potential decreases as the cumulative driving distance of the photosensitive drums 1a to 1d increases.

[0056] From the above results, it was confirmed that by correcting the charging voltage based on the degree of deterioration of the charging roller 34, the surface potential can be maintained constant even if the cumulative driving distance of the photosensitive drums 1a to 1d becomes long, and the generation of fogging toner can be suppressed. [Industrial Applicability]

[0057] The present invention can be applied to an image forming apparatus that uses a charging member to charge a photosensitive member, and can provide an image forming apparatus that can accurately correct the charging voltage based on the degree of deterioration of the charging member and maintain an appropriate surface potential. [Explanation of symbols]

[0058] 1a to 1d Photosensitive drum (image carrier) 2a~2d Charging device 3a~3d developing device 5 Exposure equipment 6a~6d Primary transfer rollers 8 Intermediate transfer belt 9 Secondary transfer roller 19 Belt cleaner 30 Developing roller (developer carrier) 34 Charging roller (charging member) 43 Development voltage power supply 44 Current detection unit 45 Charge voltage power supply 47 Transfer voltage power supply 48 Cleaning voltage power supply 50 Voltage control section 70 Storage section 80 Main control unit (control unit) 90 Liquid crystal display unit (notification unit) 100 image forming device

Claims

1. an image carrier having a photosensitive layer formed on its surface; a charging device having a charging member for charging the surface of the image bearing member to a predetermined surface potential; a developing device having a developer carrier that carries a developer containing toner, and that forms a toner image by adhering the toner to an electrostatic latent image formed by exposing the image carrier that has been charged by the charging device; a developing voltage power source that applies a developing voltage to the developer carrier; a charging voltage power source that applies a charging voltage to the charging member; a control unit that controls the developing voltage power supply and the charging voltage power supply; In an image forming apparatus comprising: a storage unit that stores a transition of the surface potential with respect to the cumulative driving distance of the image carrier in a state where the volume resistance value of the charging member is fixed to an initial volume resistance value, and a transition of the surface potential with respect to the cumulative driving distance in a state where an increase in the volume resistance value due to deterioration of the charging member is taken into consideration; The control unit an image forming apparatus, characterized in that a correction value of the charging voltage for a predetermined cumulative driving distance is calculated based on the difference between a first surface potential, which is the surface potential when the initial volume resistance value is fixed, and a second surface potential, which is the surface potential when an increase in the volume resistance value is taken into account, for the predetermined cumulative driving distance.

2. a notification unit that notifies the status of each unit of the image forming apparatus, including a deterioration state of the charging member; 2. The image forming apparatus according to claim 1, wherein the control unit uses the notification unit to issue a notification urging replacement of the charging member when the difference between the first surface potential and the second surface potential is equal to or greater than a predetermined value.

3. a current detection unit that detects a development current flowing between the image carrier and the developer carrier; the developing voltage power supply applies the developing voltage including a DC voltage to the developer carrier; The control unit the developing current when the developing voltage and the charging voltage are not applied to the developer carrier and the charging member, respectively, is measured and used as a reference current; a predetermined charging voltage is applied to the charging member to charge the image carrier to a predetermined surface potential, and the DC voltage of the developing voltage is increased stepwise from an initial value that is smaller than the surface potential, and the transition of the developing current detected by the current detecting unit is measured; 3. The image forming apparatus according to claim 1, wherein the DC voltage at a point where the curve representing the change in the development current intersects with the reference current is estimated as the surface potential of the image carrier.

Images