Image forming apparatus

Abstract

To provide a configuration that can improve the accuracy of detecting the thickness (film thickness) of a photosensitive layer of a photoconductor drum.SOLUTION: A control unit can execute a film thickness detection mode for applying a plurality of different DC voltages to an electrifying roller from a power supply, and detecting currents flowing in the electrifying roller with a current detection unit to derive the I-V characteristics being the relation between the currents and the voltages. When the inclination of the I-V characteristics is the same in the case where the temperature detected by an environment sensor during the execution of the film thickness detection mode is a first temperature and the case where the temperature is a second temperature higher than the first temperature, the control unit calculates a smaller thickness of the photosensitive layer in the case where the temperature is the first temperature.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having a plurality of functions thereof.

Background Art

[0002] In an image forming apparatus, a photoreceptor such as a photosensitive drum having a photosensitive layer is charged, an electrostatic latent image is formed on its surface, and the electrostatic latent image is further developed with toner to form a toner image. Then, the toner image thus formed is transferred to a recording material. In such a configuration, since the photosensitive layer of the photoreceptor is worn by use, the photoreceptor is replaced when the thickness (film thickness) of the photosensitive layer becomes equal to or less than a predetermined thickness.

[0003] As a technique for detecting such a film thickness, for example, Patent Document 1 discloses a film thickness detection means for detecting based on the direct current component current flowing through a charging member.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Here, in the method of detecting the film thickness based on the direct current flowing through the charging member, it has been clarified by the study of the present inventors that the detection current changes with the change in the temperature of the photoreceptor and the charging member or the ambient temperature in the vicinity at the detection timing of the direct current. Therefore, when the film thickness is detected by the direct current flowing through the charging member without considering the temperature change, it is difficult to sufficiently ensure the detection accuracy of the film thickness.

[0006] An object of the present invention is to provide a configuration capable of improving the detection accuracy of the thickness of the photosensitive layer of the photoreceptor.

Means for Solving the Problem

[0007] One aspect of the present invention includes a photoreceptor having a photosensitive layer, a core bar, and an elastic layer having conductivity around the core bar, a charging roller that contacts the photoreceptor to charge the surface of the photoreceptor, a power source capable of applying a DC voltage to the charging roller, current detection means capable of detecting a current flowing through the charging roller, temperature detection means capable of detecting temperature, an execution unit capable of executing a mode of deriving an I-V characteristic, which is a relationship between current and voltage, by applying a plurality of different DC voltages by the power source and detecting the current by the current detection means respectively, and a calculation unit that calculates the thickness of the photosensitive layer based on the slope of the I-V characteristic derived by the execution of the mode and the detected temperature detected by the temperature detection means without using humidity information. When the slopes of the I-V characteristics are the same, the calculation unit The lower, the better An image forming apparatus characterized by calculating a smaller thickness of the photosensitive layer.

Advantages of the Invention

[0008] According to the present invention, the detection accuracy of the thickness of the photosensitive layer of the photoreceptor can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0010] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 10. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1.

[0011] [Image Forming Apparatus] The image forming apparatus 100 of the present embodiment is a laser beam printer that uses a transfer type electrophotographic process. The image forming apparatus 100 includes a photosensitive drum 2 as an image carrier or a photoreceptor, a charging roller 1 as a charging member, an exposure device 3, a developing device 4, a transfer roller 5 as a transfer member, a cleaning device 6, a pre-exposure device 12, a fixing device 7, and the like.

[0012] The photosensitive drum 2 is rotationally driven in the clockwise direction of arrow a at a process speed (rotational peripheral speed) of 320 mm / sec, for example. The photosensitive drum 2 of the present embodiment is, for example, a drum 2b made of aluminum (conductive drum substrate) with a diameter of 30 mm, on the outer periphery of which a photosensitive layer 2a, which is an OPC (organic photoreceptor) layer, is formed by coating. The photosensitive layer 2a has, for example, a charge transport layer (Carrier Transfer Layer: hereinafter referred to as a CT layer) with a thickness d = 20 μm disposed on the charge generation layer. In the present embodiment, a polycarbonate resin is used as the binder of this CT layer, and with use, the CT layer is gradually shaved and its thickness decreases.

[0013] The charging roller 1 constitutes a charging device 13 together with a power source 8 and a current detection unit 27 as current detection means. The charging roller 1 of the present embodiment includes a core metal 1a, a conductive rubber layer 1b as an elastic layer having conductivity formed around the core metal 1a, and a high-resistance layer 1c formed on the outer periphery thereof.

[0014] Both ends of the core metal 1a of the charging roller 1 are rotatably supported by bearings on a frame (not shown), and the charging roller 1 is arranged such that the rotational axis directions of the charging roller 1 and the photosensitive drum 2 are substantially parallel. Then, the outer peripheral surface of the charging roller 1 is brought into contact with the outer peripheral surface of the photosensitive drum 2 so as to press against it. In the case of the present embodiment, the charging roller 1 rotates in a driven manner as the photosensitive drum 2 rotates.

[0015] The power source 8 is a power source that applies a charging bias to the charging roller 1. When a predetermined charging bias is applied to the charging roller 1 via the core metal 1a by the power source 8, the surface of the rotating photosensitive drum 2 is charged. Specifically, the outer peripheral surface of the photosensitive layer 2a is subjected to contact charging treatment to a predetermined polarity and potential.

[0016] The high-resistance layer 1c on the outer periphery of the charging roller 1 serves to prevent the charging current from concentrating in this part when there are low withstand voltage defect parts such as pinholes in the photosensitive layer 2a, causing the potential on the surface of the charging roller to drop and resulting in horizontal stripe-like charging defects.

[0017] The current detection unit 27 is an ammeter and can detect the current flowing from the power source 8 to the charging roller 1. The power source 8 is controlled by a control unit 25 and can apply a predetermined voltage to the charging roller 1 according to a command from the control unit 25. Also, the current value (output value) detected by the current detection unit 27 is sent to the control unit 25. The configuration and the like of the control unit 25 will be described later.

[0018] The exposure device 3 is a laser beam scanner that irradiates a laser beam L based on image information input from an external terminal such as a document reading device or a personal computer. That is, the exposure device 3 performs scanning exposure on the charged surface of the rotating photosensitive drum 2 with the laser beam L (a laser beam intensity-modulated according to the time-series electrical digital pixel signals of the target image information). As a result, the exposed portion on the surface of the photosensitive drum 2 is discharged, and an electrostatic latent image of the image information is formed on the surface of the photosensitive drum 2.

[0019] The developing device 4 contains a developer including toner and carrier, develops the electrostatic latent image formed on the surface of the photosensitive drum 2 with toner, and visualizes it as a toner image. As a result, a toner image is formed on the surface of the photosensitive drum 2.

[0020] The toner image thus formed on the surface of the photosensitive drum 2 is transferred to the surface of a recording material 9 such as paper fed at a predetermined timing to the pressure contact nip portion (transfer portion) between the photosensitive drum 2 and the transfer roller 5 from a feeding mechanism (not shown) at the position of the transfer roller 5. In this embodiment, a transfer bias of 3 kV is applied to the transfer roller 5 by a transfer bias application power source 10 to transfer the toner image from the photosensitive drum 2 to the recording material 9. Examples of the recording material include sheets such as paper and plastic sheets.

[0021] The recording material 9 that has passed through the transfer portion is separated from the surface of the photosensitive drum 2 and sent to the fixing device 7. Then, by being pressurized and heated in the fixing device 7, the toner image is fixed to the recording material 9 and output as an image formation.

[0022] After the transfer of the toner image to the recording material 9, the surface of the photosensitive drum 2 is cleaned by scraping off and removing adhering contaminants such as residual transferred toner and paper dust with a cleaning blade of the cleaning device 6 (in this embodiment, a counter blade made of urethane rubber). And it is prepared for the next image formation.

[0023] The image forming apparatus 100 according to this embodiment has a cartridge detachment method in which three process devices, namely a photosensitive drum 2, a charging roller 1, and a cleaning device 6, are integrated into a drum cartridge 11 that can be detachably exchanged all at once with respect to the apparatus main body of the image forming apparatus 100. Note that the developing device 4 may also be an integrally detachable process cartridge.

[0024] [Detection of the thickness (film thickness) of the photosensitive layer] FIG. 2 shows the relationship between the applied voltage and the surface potential of the surface to be charged in a charging method (hereinafter referred to as DC charging) in which the voltage applied to the charging roller 1 is only a DC voltage (DC voltage) and the surface to be charged (for example, the surface of the photosensitive drum 2) is charged. Since the contact charging is performed by the discharge from the charging roller 1 to the surface to be charged, the charging of the surface to be charged is started by applying a DC voltage equal to or higher than a certain threshold voltage to the charging roller 1.

[0025] As a specific example, when the charging roller 1 is brought into pressure contact with the surface of the photosensitive drum 2 having a photosensitive layer 2a with a thickness of 20 μm as the surface to be charged, if a DC voltage of about 560 V or more is applied to the charging roller 1 as shown in FIG. 2, the surface potential of the photosensitive drum 2 starts to rise. After that, the surface potential of the photosensitive drum 2 increases linearly with a slope of 1 with respect to the applied voltage. The applied DC voltage value of about 560 V at which the surface potential of the photosensitive drum 2 starts to rise is the charging start voltage Vth for the photosensitive drum 2.

[0026] That is, when a DC voltage is applied to the charging roller 1, the charging of the photosensitive drum 2 starts when the applied voltage is equal to or higher than the charging start voltage Vth, and after that, the surface potential of the photosensitive drum 2 rises linearly at the same rate as the increase ΔV of the applied voltage (ΔVd). Here, for the sake of argument, the region where the applied voltage V is less than Vth is called the A region, and the region where V is equal to or higher than Vth is called the B region. Among these, in the A region, since the voltage at which the applied voltage is low and the air layer is divided cannot exceed the breakdown voltage based on Paschen's law, charging is not performed, so this region is irrelevant to this control.

[0027] On the other hand, with respect to the B region, actual discharge is performed from the charging roller 1 to the photosensitive drum 2. The applied voltage V and the surface potential Vd of the photosensitive drum 2 increase linearly with a slope of 1 regardless of the film thickness of the photosensitive drum 2 or the environment, so ΔV = ΔVd. In contrast, as shown in FIG. 3, the graph representing the relationship between the applied voltage V and the charging current I is the same regarding non-charging in the A region, but in the B region, the slope changes depending on the thickness of the photosensitive layer 2a of the photosensitive drum 2, that is, the film thickness D. This indicates that the charging current I required to charge up to the same Vd differs depending on the film thickness D.

[0028] Therefore, in the present embodiment, the charging roller 1 as the primary charging member of the photosensitive drum 2 is also used as the electrode member for detecting the film thickness of the photosensitive layer 2a. In the present embodiment, the control unit 25 as the execution unit applies a plurality of different DC voltages by the power supply 8, and the current detection unit 27 as the current detection means detects the current to derive the I-V characteristic, which is the relationship between the current and the voltage (film thickness detection mode). Then, the control unit 25 which is also the calculation unit calculates the film thickness from the I-V characteristic.

[0029] Specifically, in the B region, the applied voltage V to the charging roller 1 and the charging current I flowing at that time are measured at four points, and from this relationship, the slope of the straight line of the I-V characteristic (with the horizontal axis being the DC current I and the vertical axis being the applied voltage V) is calculated to detect the thickness of the photosensitive layer 2a. In the present embodiment, since the photosensitive layer 2a with an initial film thickness of 20 μm is used, the initial Vth is 560 V, and as the photosensitive layer 2a is worn away, Vth decreases, so if the applied voltage is 560 V or more, it can be regarded as the B region.

[0030] It should be noted that it is also possible to detect the film thickness in the same way by measuring I and Vd. However, for the measurement of Vd, it is necessary to separately provide a measuring instrument for measuring the surface potential of the photosensitive drum on the apparatus main body of the image forming apparatus, or additional hardware such as another power supply.

[0031] When performing the above control, the potential of the photosensitive drum 2 during measurement must be a certain fixed value; otherwise, the relationship between the charging potential and the charging current cannot be clarified. Therefore, the measurement is performed with the surface potential of the photosensitive drum 2 discharged by the pre-exposure device 12. Also, the time for applying each voltage is set to one rotation of the photosensitive drum 2 in order to remove the influence of noise, etc., and the current measured during this time is averaged. Further, the film thickness measurement of the photosensitive layer 2a by this control is performed during the post-rotation after the completion of image formation, and the sequence is such that it does not adversely affect image formation.

[0032] In order to perform this control, it is necessary to previously measure the relationship between the slope of the I-V characteristic and the film thickness D of the photosensitive layer 2a. Therefore, measurements were performed using photosensitive drums 2 with film thicknesses D of 18 μm, 20 μm, 22 μm, and 24 μm for the photosensitive layer 2a, respectively. FIG. 4 shows the I-V characteristics in the cases where the film thickness D of the photosensitive layer 2a is 18 μm, 20 μm, and 22 μm as representative examples thereof. Also, FIG. 5 shows a graph of the relationship between the film thickness D and the slope of the I-V characteristic based on the slopes of the I-V characteristics for the above four film thicknesses.

[0033] Furthermore, as a result of the inventors' intensive studies, it was found that in the method of detecting the film thickness from the relationship between the film thickness D and the slope of the I-V characteristic, the temperature of the photosensitive layer 2a and the charging roller 1 at the detection timing or the ambient temperature in the vicinity thereof significantly contributes to the slope of the I-V characteristic. Also, it was found that the detection accuracy is remarkably improved by detecting the film thickness based on the correlation with the detection temperature from the environmental sensor 30 (FIG. 8 to be described later) without using humidity information.

[0034] Therefore, in this embodiment, the temperature can be detected by the environmental sensor 30 as the temperature detection means during the execution of the film thickness detection mode. And when the detected temperature is the first temperature and when it is the second temperature higher than the first temperature, and the slope of the I-V characteristic is the same, the control unit 25 calculates that the thickness (film thickness) of the photosensitive layer 2a is smaller when it is the first temperature.

[0035] FIG. 6 is a graph showing the relationship between the film thickness D and the slope of the I-V characteristics when the ambient temperatures in the vicinity of the photosensitive layer 2a and the charging roller 1 are 2.5 °C, 15 °C, 23 °C, and 30 °C, respectively, for the photosensitive layer 2a with a thickness of 20 μm.

[0036] It can be seen from FIG. 6 that even when the change amount of the film thickness D is equal, the change amount of the slope of the I-V characteristics is smaller as the ambient temperature is higher. Therefore, from FIG. 6, it can be understood that when the slopes of the I-V characteristics are the same, the film thickness D is smaller at a lower temperature. For example, when the first temperature is 2.5 °C and the second temperature is 30 °C, the film thickness when the slope of the I-V characteristics is 9 is smaller at 2.5 °C.

[0037] Furthermore, it has been found that the change amount of the film thickness D (slope) with respect to the change amount of the slope of the I-V characteristics and the intercept have a high correlation with the ambient temperature T, and the film thickness D can be calculated by the following formula 1. D = (a×T + b)×A_iv+(c×T + d) ···(Formula 1) D: Film thickness A_iv: Slope of the I-V characteristics at the time of detecting the body film thickness T: Internal temperature (°C) at the start of the film thickness detection mode a, b, c, d: Constants calculated from the correlation between the I-V characteristic slope, the film thickness D characteristic, and the temperature T

[0038] That is, in Formula 1, “a×T + b” is the slope of the graph in FIG. 6, and “c×T + d” is the intercept. These constants a, b, c, d are set, for example, at the time of shipment from the factory and are predetermined values depending on the device. In the image forming apparatus 100 of the present embodiment, the constants a, b, c, d are a = 0.017, b = 2.128, c = -0.064, and d = 1.5574, respectively.

[0039] As described above, in the present embodiment, the control unit 25 calculates the slope of the I-V characteristics based on the applied voltage applied to the charging roller 1 and the charging current flowing therethrough. Then, the film thickness D of the photosensitive drum 2 is calculated from the temperature of the photosensitive drum 2 and the charging roller 1 at the detection timing or the ambient temperature in the vicinity thereof.

[0040] More specifically, first, the control unit 25 causes the pre-exposure device 12 to reduce the surface potential of the photosensitive drum 2 to a predetermined potential (here, 80 V). This is because when the surface potential of the photosensitive drum 2 varies from the predetermined potential, the relationship between the charging voltage and the charging current becomes unclear. After setting the surface potential of the photosensitive drum 2 to 80 V, as shown in FIG. 7, four DC voltages DC1, DC2, DC3, and DC4 equal to or higher than the charging start voltage (discharge start voltage) Vth (here, 560 V) are applied to the charging roller 1. Then, the currents Idc1, Idc2, Idc3, and Idc4 flowing through each are measured. From the I-V characteristics obtained as shown in FIG. 7, the slope A_iv is represented by the following Equation 2 [Number] ···(Equation 2)

[0041] In the above Equation 2, the control unit 25 calculates the slope A_iv from the I-V characteristics. That is, the control unit 25 measures the voltage applied to the charging roller 1 and the current flowing therethrough, and calculates the slope A_iv of the I-V characteristics necessary for calculating the film thickness D of the photosensitive drum 2. Therefore, it is not necessary to provide a measuring instrument or the like for measuring the surface potential of the photosensitive drum 2 in the image forming apparatus 100, and the number of parts can be reduced and the apparatus can be downsized.

[0042] Further, the control unit 25 calculates the film thickness D of the photosensitive drum 2 from this slope A_iv and the ambient temperature in the vicinity of the photosensitive drum 2 and the charging roller 1 detected by the environmental sensor 30 in the main body according to the above Equation 1.

[0043] More specifically, as shown in FIG. 8, the control unit 25 includes, for example, a CPU (Central Processing Unit) 26, a ROM (Read Only Memory) 23, and a RAM (Random Access Memory) 24. The CPU 26 is a microprocessor that controls the overall operation of the image forming apparatus and is the main body of the system controller. The ROM 23 stores programs for controlling each part. The RAM 24 temporarily stores data. Further, the control unit 25 includes an input / output circuit (I / F) 22 for inputting and outputting signals to and from the outside.

[0044] The CPU 26 is connected via the input / output circuit 22 to a feeding unit that feeds the recording material from the cassette, an image forming unit that forms an image on the recording material, a conveying unit that conveys the recording material, a discharging unit that discharges the recording material outside the apparatus, and an operation unit 31 for operating the apparatus. Then, it exchanges signals with each part and controls the operations. Also, the CPU 26 is connected via the input / output circuit 22 to an environmental sensor 30 installed inside the apparatus main body of the image forming apparatus 100, a power supply 8 for the charging roller 1, and a current detection unit 27.

[0045] The operation unit 31 is arranged, for example, on the front surface of the apparatus main body and has a display unit 32 such as a liquid crystal panel. Various information can be displayed on the display unit 32. For example, the display unit 32, which is also a notification means, notifies information regarding the replacement of the photosensitive drum 2 when the thickness (film thickness) of the photosensitive layer 2a calculated by the control unit 25 as described above becomes equal to or less than a predetermined thickness. For example, when the film thickness D becomes 18 μm or less as the predetermined thickness, a display indicating that the drum cartridge 11 should be replaced is made. Note that the notification means may be a light emitting unit such as an LED. In this case, the light emitting unit is lit so as to correspond to the replacement of the photosensitive drum 2.

[0046] Next, the procedure for calculating the film thickness D of the photosensitive layer 2a according to the above-described film thickness detection mode will be described with reference to the flowchart of FIG. 9 and the time chart of FIG. 10. Briefly, first, the slope A_iv of the I-V characteristic is calculated by measuring the current value flowing from the power supply 8 to the charging roller 1 when a voltage is applied to the photosensitive drum 2 and the charging roller 1. Further, the film thickness D of the photosensitive drum 2 is calculated from the ambient temperature in the vicinity of the photosensitive drum 2 and the charging roller 1 detected by the environment sensor 30 at the measurement timing.

[0047] This will be described with reference to FIGS. 9 and 10. First, when executing the film thickness detection mode, the driving of the photosensitive drum 2 is started (S1 in FIG. 9, t1 in FIG. 10). If the photosensitive drum 2 is already rotating, such as during reverse rotation, the rotation is continued. Next, the pre-exposure device (charge removal unit) 12 starts charge removal of the photosensitive drum 2 (S2 in FIG. 9, t1 in FIG. 10). Then, the environment sensor 30 detects the ambient temperature T in the vicinity of the photosensitive drum 2 and the charging roller 1 (S3 in FIG. 9, t1 in FIG. 10).

[0048] With the rotation speed of the photosensitive drum 2 stabilized, the first charging voltage DC1 (e.g., 760V) is applied via the charging roller 1 by the power supply (voltage application unit) 8 (S4 in FIG. 9, t2 - t4 in FIG. 10). After applying the first charging voltage DC1, the charging current Idc1 is measured by the current detection unit 27 in a state where the voltage is stable (S5 in FIG. 9, t3 - t4 in FIG. 10). Assume that the measurement result here is, for example, 19.5 μA.

[0049] Note that for the measurement of the first charging current Idc1 and the second, third, and fourth charging currents Idc2, Idc3, Idc4 described later, since there are current fluctuations in the circumferential direction of the photosensitive drum 2 and the charging roller 1, it is preferable to measure for at least one full rotation of the photosensitive drum 2. However, it goes without saying that this is not limited thereto.

[0050] Next, a second charging voltage DC2 (e.g., 910 V) is applied by the power supply 8 via the charging roller 1 (S6 in FIG. 9, t4 to t6 in FIG. 10). After applying the second charging voltage DC2, the charging current Idc2 is measured by the current detection unit 27 in a state where the voltage is stable (S7 in FIG. 9, t5 to t6 in FIG. 10). Assume that the measurement result here is, for example, 34.3 μA.

[0051] Next, a third charging voltage DC3 (e.g., 1110 V) is applied by the power supply 8 via the charging roller 1 (S8 in FIG. 9, t6 to t8 in FIG. 10). After applying the third charging voltage DC3, the charging current Idc3 is measured by the current detection unit 27 in a state where the voltage is stable (S9 in FIG. 9, t7 to t8 in FIG. 10). Assume that the measurement result here is, for example, 54.0 μA.

[0052] Furthermore, a fourth charging voltage DC4 (e.g., 1310 V) is applied by the power supply 8 via the charging roller 1 (S10 in FIG. 9, t8 to t10 in FIG. 10). After applying the fourth charging voltage DC4, the charging current Idc4 is measured by the current detection unit 27 in a state where the voltage is stable (S11 in FIG. 9, t8 to t10 in FIG. 10). Assume that the measurement result here is, for example, 73.7 μA.

[0053] After four current measurements, the surface of the photosensitive drum 2 is discharged by the pre-exposure device 12 and then the discharging is stopped (S12 in FIG. 9, t11 in FIG. 10), and the driving of the photosensitive drum 2 by the driving unit (e.g., a motor) is stopped (S13 in FIG. 9, t11 in FIG. 10). Then, the control unit 25 calculates the slope A_iv of the I-V characteristic from each of the charging voltages DC1 to DC4 and the corresponding charging currents Idc1 to Idc4 at that time in the above formula 2 (S14 in FIG. 9).

[0054] Next, the control unit 25 reads out the constants a, b, c, and d stored in the ROM 23 obtained by the preliminary experiment represented by the above formula (1). Then, from the slope A_iv of the I-V characteristic and the ambient temperature T in the vicinity of the photosensitive drum 2 and the charging roller 1 at the time of control activation, the film thickness D of the photosensitive layer 2a is calculated using formula (1) (S15 in FIG. 9). As described above, in the present embodiment, the constants a, b, c, and d are a = 0.017, b = 2.128, c = -0.064, and d = 1.5574, respectively.

[0055] In this embodiment, the relationship among the film thickness D in FIG. 6, the slope A_iv of the I-V characteristic, and the ambient temperature T in the vicinity of the photosensitive drum 2 and the charging roller 1 at the time of control activation is stored in the ROM 23 of the control unit 25. And it is configured such that the film thickness D of the photosensitive layer 2a can be calculated from the obtained slope A_iv of the I-V characteristic and the detected temperature T.

[0056] For example, when the slope A_iv of the I-V characteristic is lower than 7.14 V / μm corresponding to the lower limit of the film thickness D at which good images can be obtained in an environment where the detected temperature T is 23°C, the display unit 32 lights up a display indicating that the life has reached. By this life display, the operator recognizes that the photosensitive drum 2 has reached the end of its life, and in the case of this embodiment, the operator replaces the new and old of the drum cartridge 11.

[0057] Thus, in the present embodiment, by using the temperature detected by the environmental sensor 30, the detection accuracy of the thickness of the photosensitive layer 2a can be improved. As a result, the life of the photosensitive drum 2 can be accurately detected, and for example, it is possible to prevent the occurrence of charging defects and image defects caused by the photosensitive layer 2a being used even though it has reached the usage limit.

[0058] Actually, a test was conducted in an environment where the temperature and humidity were 23°C and 50% respectively, and this control was performed when 200,000 sheets of images were formed. In this case, the slope A_iv of the I-V characteristic became 7.14 V / μm, and since it was lower than the preset value, the display unit 32 displayed that the life had reached. At this time, when the film thickness D of the photosensitive layer 2a was measured, it was about 17.7 μm, which proved that this control was appropriate.

[0059] Thus, in this embodiment, the slope A_iv of the I-V characteristic is measured by measuring the voltage V applied to the charging roller 1 and the charging current I flowing at this time, and at the same time, the ambient temperature T in the vicinity of the photosensitive drum 2 and the charging roller 1 at the time of control activation is measured. Then, the film thickness D of the photosensitive layer 2a is detected using the above-described formula 1. As a result, the detection of the film thickness (life) of the photosensitive layer 2a can be accurately performed with a simple device and circuit configuration without newly using a special device configuration or the like.

[0060] <Second Embodiment> The second embodiment will be described. In the above-described first embodiment, the film thickness detection mode is executed at a predetermined timing, and when the film thickness D calculated at that time becomes equal to or less than a predetermined thickness, it is determined that the life of the photosensitive drum 2 has expired. In contrast, in this embodiment, the life of the photosensitive drum 2 is determined based on the variation amount from the detection result of the film thickness D by the film thickness detection mode performed at each predetermined timing, with the film thickness D detected at a timing shortly after replacement as a reference. Since the configuration of each part is the same as that of the first embodiment, the same components are denoted by the same reference numerals, and the following description will focus on the differences from the first embodiment.

[0061] In this embodiment, the relationship between the film thickness D, the slope A_iv of the I-V characteristic, and the ambient temperature T in the vicinity of the photosensitive drum 2 and the charging roller 1 at the time of control activation shown in FIG. 6 is stored in the ROM 23 of the control unit 25. And it is configured such that the initial film thickness D_int of the photosensitive drum 2 can be calculated from the slope A_iv of the I-V characteristic and the detected temperature T obtained at a timing shortly after the drum cartridge 11 is replaced. Then, when the difference between the thickness of the photosensitive layer 2a calculated by the control unit 25 and the initial thickness of the photosensitive layer 2a exceeds a predetermined value, the display unit 32 notifies information regarding the replacement of the photosensitive drum 2 in the same manner as in the first embodiment.

[0062] For example, when measuring the initial film thickness D_int of the photosensitive layer 2a in an environment where the detected temperature T is 15°C, the slope A_iv of the I-V characteristics is 8.16 V / μA, and the initial film thickness D_int of the photosensitive layer 2a calculated from Equation 1 is 20 μm. Subsequently, when testing was performed in an environment of 23°C and 50%, and this control was carried out when image formation was performed on 200,000 sheets, the slope A_iv became 7.14 V / μA, and the film thickness D_end of the photosensitive layer 2a after use calculated from Equation 1 was calculated to be 18 μm.

[0063] At this time, the amount of change ΔD in the film thickness D of the photosensitive layer 2a from the initial value is represented by the following Equation 3. ΔD = D_end - D_int ···(Equation 3) ΔD: Amount of film thickness change from the initial value D_end: Film thickness after use D_int: Initial film thickness

[0064] In this embodiment, when the amount of change (difference) in the film thickness D from the initial value exceeds 2 μm (predetermined value), which is the amount of change at which a good image can be obtained, a display indicating that the life has reached is lit on the display unit 32. With this life display, the operator recognizes that the photosensitive drum 2 has reached the end of its life, and in this example, the drum cartridge 11 is replaced with a new one.

[0065] Also, the ratio LF (%) of the current film thickness change amount ΔD to the film thickness change amount at the usage limit (predetermined value) ΔDlimit is represented by the following Equation 4. LF (%) = ΔD / ΔDlimit × 100 ···(Equation 4) LF (%): Ratio of the current film thickness change amount ΔD ΔD: Amount of film thickness change from the initial value ΔDlimit: Film thickness change amount at the usage limit

[0066] In this example, since the film thickness change amount ΔDlimit at the usage limit is set to 2 μm, when a durability test of 200,000 sheets was performed in an environment of 23°C and 50%, ΔD became 2 μm, and LF (%) reached 100%.

[0067] Thus, in this embodiment, the life of the drum cartridge 11 is determined based on the initial film thickness D detected at a timing shortly after replacement, and then based on the amount of variation from the detection result of the film thickness D in the film thickness detection mode performed at predetermined timings. As a result, similar to the first embodiment, the film thickness (life) of the photosensitive layer 2a can be accurately detected with a simple device and circuit configuration without newly using a special device configuration or the like.

[0068] <Other Embodiments> The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the gist thereof. For example, although the voltage applied to the charging roller 1 during film thickness detection is a DC voltage, a charging bias in which an AC voltage is superimposed on the DC voltage may be used at timings other than during film thickness detection including during image formation. That is, the power supply 8 can apply a superimposed voltage in which an AC voltage is superimposed on a DC voltage to the charging roller 1. Then, only a DC voltage is applied to the charging roller 1 during execution of the film thickness detection mode, and the superimposed voltage is applied to the charging roller 1 during image formation.

[0069] Further, the photosensitive member may be, for example, an endless belt having a photosensitive layer, i.e., a photosensitive belt, other than the photosensitive drum. Also, in the above-described embodiment, the direct transfer method of directly transferring the toner image on the photosensitive drum to the recording material has been described. However, the present invention is also applicable to an intermediate transfer method in which the toner image on the photosensitive drum is first transferred to an intermediate transfer member such as an intermediate transfer belt, and then secondarily transferred from the intermediate transfer member to the recording material. Also, in a configuration in which there are a plurality of image forming units including a photosensitive drum, a charging roller, etc. and forming a toner image on the photosensitive drum, the film thickness of the photosensitive drum of each image forming unit may be detected as described above. Furthermore, the present invention is applicable not only to printers but also to copiers, facsimiles, multifunction devices, etc.

Description of Reference Numerals

[0070] 1 ··· Charging roller (charging member) 1a ··· Core bar 1b ··· Conductive rubber layer (elastic layer) 2···Photoconductive drum (photoreceptor) 2a··Photoconductive layer 8···Power supply 25···Control unit (execution unit, calculation unit) 27···Current detection unit (current detection means) 30···Environmental sensor (temperature detection means) 32···Display unit (notification means) 100···Image forming apparatus

Claims

1. A photoreceptor having a photosensitive layer, a charging roller having a core bar and an elastic layer having conductivity around the core bar, and contacting the photoreceptor to charge the surface of the photoreceptor, a power source capable of applying a DC voltage to the charging roller, current detection means capable of detecting a current flowing through the charging roller, temperature detection means capable of detecting temperature, an execution unit capable of executing a mode of deriving an I-V characteristic, which is a relationship between current and voltage, by applying a plurality of different DC voltages by the power source and detecting currents by the current detection means respectively, a calculation unit for calculating the thickness of the photosensitive layer based on the slope of the I-V characteristic derived by the execution of the mode and the detected temperature detected by the temperature detection means during the execution of the mode without using humidity information, The image forming apparatus according to claim 1, wherein the calculation unit calculates the thickness of the photosensitive layer to be smaller as the detected temperature is lower when the slopes of the I-V characteristics are the same.

2. The image forming apparatus according to claim 1, further comprising notification means for notifying information regarding replacement of the photoreceptor when the thickness of the photosensitive layer calculated by the calculation unit becomes equal to or less than a predetermined thickness.

3. The image forming apparatus according to claim 1, further comprising notification means for notifying information regarding replacement of the photoreceptor when a difference between the thickness of the photosensitive layer calculated by the calculation unit and the thickness of the initial photosensitive layer exceeds a predetermined value.

4. The image forming apparatus according to any one of claims 1 to 3, wherein the plurality of DC voltages applied during the execution of the mode are equal to or higher than a charging start voltage.

5. The image forming apparatus according to any one of claims 1 to 4, wherein the power source applies a DC voltage to the charging roller also during the execution of the mode and during image formation.

6. The image forming apparatus according to any one of claims 1 to 4, wherein the power source is capable of applying a superimposed voltage obtained by superimposing an AC voltage on a DC voltage to the charging roller, applies only a DC voltage to the charging roller during the execution of the mode, and applies the superimposed voltage to the charging roller during image formation.

Images