JP2010204370A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of easily detecting life of an image carrier. <P>SOLUTION: The image forming apparatus 10 includes: a transformer 42 which applies charged voltage in which AC voltage with a predetermined frequency is superposed on DC voltage to an electrifying roller 14 which electrifies a photoreceptor drum 12; a voltage detection circuit 44 which detects the voltage value of the electrified voltage to be applied to the electrifying roller 14 by the transformer 42; and a main control part 46 which controls a driving circuit 40 which makes the transformer 42 induce the electrostatically charged voltage so that the current value of current based on the electrostatically charged voltage becomes a current value specified by a constant current instruction signal I1, calculates the capacity value of a capacity component of a surface layer of the photoreceptor drum 12 on the basis of the voltage value detected by the voltage detection circuit 44, the current value specified by the constant current instruction signal I1, and the predetermined frequency of the AC voltage, and outputs a signal indicating that the life of the photoreceptor drum 12 runs out when the calculated capacity value exceeds a value indicating the limit of thickness of the surface layer of the photoreceptor drum 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  Conventionally, in a so-called electrophotographic image forming apparatus, a photosensitive member is charged by a charger, and an electrostatic latent image corresponding to the image is formed on the photosensitive member by irradiating the charged photosensitive member with light corresponding to the image. Then, this is developed with toner by a developing device, and transferred and fixed on a recording sheet to form an image.

  As such an image forming apparatus, for example, Patent Document 1 detects the amount of electric charge of a discharge generated between a charging device that applies a bias voltage in which an AC voltage is superimposed on a DC voltage and charges the photosensitive member. An image forming apparatus is described that controls the voltage applied to the photosensitive member so that the detected discharge charge amount falls within a predetermined range including a singular point in the change of the discharge charge amount.

  Japanese Patent Laid-Open No. 2004-228561 stores, as table data, a wear amount per predetermined rotation time of the photoconductor for each paper type, and calculates a wear amount corresponding to the rotation time of the photoconductor based on the table data. Thus, an image forming apparatus that reports the life of the photoreceptor is described.

JP 2007-192993 A JP 2005-326696 A

  The present invention provides an image forming apparatus capable of easily detecting the life of an image carrier as compared with the case of detecting the life of an image carrier without calculating the capacitance value of the capacitive component of the surface layer of the image carrier. The purpose is to do.

  In order to achieve the above object, an image forming apparatus according to the first aspect of the present invention is configured such that an AC voltage having a predetermined frequency is applied to a charging unit for charging an image carrier on which an image corresponding to an image is carried. Voltage application means for applying the superimposed charging voltage, voltage detection means for detecting the voltage value of the charging voltage applied to the charging means by the voltage application means, and the current value of the current based on the charging voltage are predetermined. A value representing the thickness of the surface layer of the image carrier based on the voltage value detected by the voltage detector and a control means for controlling the voltage applying means so as to obtain a current value. Output means for outputting a signal indicating that the image carrier is at the end of its life when a value indicating the limit of the layer thickness is exceeded.

  According to a second aspect of the present invention, the surface layer of the image carrier is based on the voltage value detected by the voltage detecting means, the predetermined current value, and the predetermined frequency of the AC voltage. A calculation unit that calculates a capacitance value of a capacitance component; and the output unit calculates when the capacitance value calculated by the calculation unit exceeds a value indicating a limit of a thickness of the surface layer of the image carrier. A signal indicating that the image carrier is at the end of its life is output.

  According to a third aspect of the present invention, there is provided a voltage applying means for applying a charging voltage in which an alternating voltage having a predetermined frequency is superimposed on a direct current voltage to a charging means for charging an image carrier on which an image corresponding to an image is carried. Current detecting means for detecting a current value of a current based on a charging voltage applied to the charging means by the voltage applying means; and the voltage applying means so that the voltage value of the charging voltage becomes a predetermined voltage value. When the value representing the thickness of the surface layer of the image carrier based on the current value detected by the control means for controlling and the current detector exceeds the value indicating the limit of the thickness of the surface layer of the image carrier And an output means for outputting a signal indicating that the image carrier is at the end of its life.

  According to a fourth aspect of the present invention, the surface layer of the image carrier is based on the current value detected by the current detection means, the predetermined voltage value, and the predetermined frequency of the AC voltage. A calculation unit that calculates a capacitance value of a capacitance component; and the output unit calculates when the capacitance value calculated by the calculation unit exceeds a value indicating a limit of a thickness of the surface layer of the image carrier. A signal indicating that the image carrier is at the end of its life is output.

  The invention according to claim 5 further comprises storage means for storing a value representing the thickness of the surface layer of the image carrier at a predetermined time when the image carrier is unused. The value representing the thickness of the surface layer of the image carrier calculated by the calculating means exceeds a predetermined threshold value than the value capacity value representing the thickness of the surface layer of the image carrier stored in the storage means. In this case, a signal indicating that the image carrier is at the end of its life is output.

  According to a sixth aspect of the present invention, the charging means is a contact charging roll that charges the image carrier while rotating in contact with the image carrier.

  According to the first aspect of the present invention, the life of the image carrier can be easily detected as compared with the case where the life of the image carrier is detected without calculating the capacitance value of the capacitive component of the surface layer of the image carrier. It has the effect of being able to.

  According to the second aspect of the present invention, it is possible to accurately detect the life of the image carrier even when the frequency of the AC voltage is changed, compared with the case where the present configuration is not provided.

  According to the third aspect of the present invention, the life of the image carrier is easily detected as compared with the case where the life of the image carrier is detected without calculating the capacitance value of the capacitive component of the surface layer of the image carrier. It has the effect of being able to.

  According to the fourth aspect of the present invention, it is possible to accurately detect the life of the image carrier even when the frequency of the AC voltage is changed, compared with the case where the present configuration is not provided.

  According to the fifth aspect of the present invention, there is an effect that the life of the image carrier can be detected with higher accuracy than in the case where the present configuration is not provided.

  According to the sixth aspect of the present invention, it is possible to accurately detect the degree of wear of the surface layer of the image carrier by the contact charging roll, compared to the case without this configuration.

1 is a schematic configuration diagram of a main part of an image forming apparatus according to a first embodiment. 1 is a schematic configuration diagram of a high-voltage power supply according to a first embodiment. It is a figure for demonstrating the capacitive component which each part, such as a high voltage cord which connects a high voltage power supply and a charging roller, has. It is a flowchart of the process performed with the high voltage power supply which concerns on 1st Embodiment. It is a schematic block diagram of the high voltage power supply which concerns on 2nd Embodiment. It is a flowchart of the process performed with the high voltage power supply which concerns on 2nd Embodiment.

(First embodiment)
Hereinafter, embodiments of the present invention will be described.

  FIG. 1 schematically shows a configuration of a main part of an image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 includes a photosensitive drum 12 that rotates in the direction of arrow A at a predetermined speed.

  Around the photosensitive drum 12, a charging roller 14, an exposure unit 16, a developing device 18, a transfer roller 20, and a cleaning blade 22 are provided in this order along the arrow A direction.

  The charging roller 14 is rotatably provided while being in contact with the peripheral surface of the photosensitive drum 12. The charging roller 14 is applied with a charging voltage of a predetermined potential by a high-voltage power supply 24 and is rotated by a driving device (not shown) to charge the peripheral surface of the photosensitive drum 12.

  The high-voltage power supply 24 includes a direct-current power supply 26 and an alternating-current power supply 28. The charging roller 14 applies a voltage obtained by superimposing a direct-current voltage output from the direct-current power supply 26 to an alternating-current voltage output from the alternating-current power supply 28. Apply to.

  The exposure unit 16 is an optical scanning device configured to include, for example, a light source (not shown), an optical system including various lenses, a rotary polygon mirror, and the like, and scans and exposes a light beam corresponding to image data on the photosensitive drum 12. As a result, an electrostatic latent image corresponding to the image is formed on the photosensitive drum 12. The exposure unit 16 is not limited to the optical scanning device as described above, and may be an LED head configured by including a plurality of light emitting diodes (LEDs).

  The developing unit 18 develops the electrostatic latent image formed on the photosensitive drum 12 by charging the toner to a predetermined potential by the power source 30 and attaching the toner to the photosensitive drum 12. As a result, a toner image corresponding to the image is formed on the photosensitive drum 12.

  The power source 30 includes a DC power source 32 and an AC power source 34, and a voltage obtained by superimposing a DC voltage output from the DC power source 32 on an AC voltage of a predetermined frequency output from the AC power source 34 is provided in the developing device 18. Applied to the toner contained in the toner.

  The transfer roller 20 is provided so as to sandwich and transport the paper P as a recording medium transported in the direction of arrow B in FIG. 1 with the photosensitive drum 12. A voltage is applied to the paper P.

  The toner on each photosensitive drum 12 is attracted to the transfer roller 20 side and transferred to the paper P at a transfer position facing the transfer roller 20.

  The toner image formed on the photosensitive drum 12 is transferred to the paper P fed between the photosensitive drum 12 and the transfer roller 20.

  The paper P on which the toner image has been transferred is subjected to a fixing process for melting and pressurizing the toner onto the paper P by a fixing device (not shown), and then discharged out of the image forming apparatus 10.

  Further, the toner remaining on the photosensitive drum 12 without being transferred onto the paper P is removed from the photosensitive drum 12 by the cleaning blade 22.

  FIG. 2 is a schematic block diagram of a high-voltage power supply 24 that applies a charging voltage to the charging roller 14. As shown in the figure, the high-voltage power supply 24 includes a control circuit 38, a drive circuit 40, a boosting transformer 42, and a voltage detection circuit 44.

  The drive circuit 40 includes a switching element (not shown) and the like, and this switching element is switching-controlled by the control circuit 38. When the switching element of the drive circuit 40 is switching-controlled by the control circuit 38, a charging voltage applied to the charging roller 14, that is, a charging voltage in which an AC voltage having a predetermined frequency is superimposed on the DC voltage is induced in the transformer 42.

  The voltage detection circuit 44 detects the voltage level of the charging voltage induced in the transformer 42 and outputs the voltage level to the control circuit 38 as a voltage detection signal V1. Further, the control circuit 38 has a function of stopping the power supply when the voltage level indicated by the voltage detection signal V1 is abnormal, and is usually a function originally provided in the high-voltage power supply 24. As described above, the image forming apparatus 10 determines the life of the photosensitive drum, which will be described later, using the voltage detection circuit originally provided.

  The control circuit 38 is connected to a main control unit 46 that controls each part of the image forming apparatus 10, and the main control unit 46 supplies a current having a predetermined current value to the charging roller 14. A constant current instruction signal I1 for instructing is input.

  The control circuit 38 performs constant current control so that a current having a current value instructed by the constant current instruction signal I 1 is supplied to the charging roller 14. The main control unit 46 also includes a memory 46A for storing various parameters, processing programs, and the like.

  As shown in FIG. 3, the high-voltage power supply 24 and the charging roller 14 are connected by a high-voltage cord 48, and the high-voltage cord 48 is wired around the inside of the image forming apparatus 10. For this reason, the high-voltage cord 48 has a capacitance component 50 that is a stray capacitance.

  Further, when a charging voltage is applied to the charging roller 14, the charging roller 14 is supplied to a metallic rotating shaft that rotates the charging roller 14. A capacitance component 52 is provided depending on the distance between the rotating shaft and the photosensitive drum 12.

  Further, the surface layer of the photosensitive drum 12 is formed of a semiconductive member (not shown), for example, a polymer organic photoconductive material, and electrically becomes a capacitive component 54.

  Of these three capacitive components, the capacitive component 50 of the high-voltage cord 24 and the capacitive component 52 of the charging roller 14 do not change over time.

  On the other hand, the surface layer of the photosensitive drum 12 is worn according to the frequency of use due to the influence of contact with the charging roller 14, the cleaning blade 22, and the like.

  By the way, in general, the capacitance value C of a capacitor is expressed by C = ε × (S / d) where ε is a dielectric constant, S is an electrode area, and d is a distance between the electrodes, and the electrode area S And inversely proportional to the distance d between the electrodes.

  In this embodiment, the capacitance value C corresponds to the capacitance value of the capacitance component 54, the electrode area S corresponds to the area of the surface layer of the photosensitive drum 12, and the distance d between the electrodes corresponds to the photosensitive drum 12. It corresponds to the thickness of the surface layer. Since the dielectric constant ε is a constant, and the area S of the surface layer of the photosensitive drum 12 may be substantially the same regardless of the change in thickness, the capacitance value C of the capacitive component 54 is equal to that of the surface layer of the photosensitive drum 12. It is inversely proportional to the thickness d. Therefore, when the capacitance value of the capacitance component 54 is obtained, the thickness d of the surface layer of the photosensitive drum 12 can be determined, and the degree of wear of the surface layer can be determined.

  Therefore, the main control unit 46 applies the current value indicated by the constant current instruction signal I1 instructed to the control circuit 38, the voltage value indicated by the voltage detection signal V1 input from the voltage detection circuit 44, and the charging roller 14 to the application. The capacitance value C of the capacitance component 54 is obtained based on the frequency of the alternating voltage of the charging voltage to be applied. The capacitance value C is obtained by the following equation.

C = I _rms / (2 × π × Freq × V _rms ) (1)
Here, _Irms is an effective value of the current supplied to the charging roller 14, and is determined in advance. Freq is the frequency of the alternating voltage of the charging voltage applied to the charging roller 14, and is determined in advance. Further, V _rms is an effective value of the voltage supplied to the charging roller 14, and when the voltage detection signal V1 is represented by a maximum voltage value V _pp (peak to peak), V _pp is 1 / 2√2. Obtained by multiplication.

The main control unit 46 obtains the capacitance value C of the capacitance component 54 by the above equation (1), and determines the life of the photosensitive drum 12 based on the obtained capacitance value C. Specifically, the voltage V when a constant current having a predetermined current value is supplied to the charging roller 14 at a predetermined time when the photosensitive drum 12 is not in use, for example, when the image forming apparatus 10 is manufactured. By measuring _pp , the capacitance value C is obtained by the above equation (1), and this is stored in the memory 46A as the initial capacitance value C1.

  Then, the capacity value C2 of the capacity component 54 obtained by the above equation (1) when the image forming apparatus 10 is operated is compared with the initial capacity value C1, and the capacity value C2 is higher than the initial capacity value C1 by a predetermined threshold or more. If it is determined that the photosensitive drum 12 has reached the end of its life.

  The threshold value is set to a value that determines that the degree of wear of the surface layer of the photosensitive drum 12 is outside the allowable range when the difference between the capacitance value C2 and the initial capacitance value C1 is equal to or greater than this value.

  According to the test by the present inventor, the difference between the thickness of the surface layer of the new photoconductor drum and the thickness of the surface layer of the photoconductor drum of the lifetime was about 15%. That is, the thickness of the surface layer of the photoconductor drum having a lifetime increased by about 15% from the thickness of the surface layer of the new photoconductor drum. Therefore, for example, when the capacity value C2 increases by 15% or more from the initial capacity value C1, it is determined that the life of the photosensitive drum 12 is reached.

  When the main control unit 46 determines that the lifetime is reached, the main control unit 46 notifies the display unit (not shown) of a message or the like indicating that the photosensitive drum 12 has a lifetime.

  Next, the life determination control of the photosensitive drum executed by the main control unit 46 will be described with reference to the flowchart shown in FIG.

  The main control unit 46 controls the switching element of the drive circuit 40 so that the constant current having the current value indicated by the constant current instruction signal I1 instructed to the control circuit 38 is supplied to the charging roller 14. In addition to the above-mentioned instruction, control for determining the life of the photosensitive drum as shown in FIG. 4 is executed.

  First, in step 100, the voltage detection signal V1 output from the voltage detection circuit 44 is input.

  In step 102, the current value indicated by the constant current instruction signal I1 instructed to the control circuit 38, the voltage value indicated by the voltage detection signal V1 input from the voltage detection circuit 44, and the charging voltage applied to the charging roller 14 are determined. Based on the predetermined frequency Freq of the AC voltage, the capacitance value C2 of the capacitance component 54 is obtained from the above equation (1).

  In step 104, it is determined whether or not the obtained capacity value C2 is higher than the initial capacity value C1 stored in the memory 46A by a predetermined threshold or more. If the capacity value C2 is higher than the initial capacity value C1 by a predetermined threshold or more, it is determined that the photosensitive drum 12 is at the end of its life, and the routine proceeds to step 106.

  On the other hand, if the capacity value C2 is not higher than the initial capacity value C1 by a predetermined threshold or more, it is determined that the photosensitive drum 12 is not at the end of life, and the process returns to step 100 to perform the same processing as described above.

  In step 106, the main control unit 46 notifies the display unit (not shown) of a message indicating that the photosensitive drum 12 has reached the end of its life. Further, the application of the charging voltage to the charging roller 14 may be stopped.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the present embodiment, another form of the high-voltage power supply will be described. In addition, the same code | symbol is attached | subjected about the same part as 1st Embodiment, and the detailed description is abbreviate | omitted.

  FIG. 5 shows a schematic block diagram of a high-voltage power supply 24A according to this embodiment. The high-voltage power supply 24A according to this embodiment is different from the high-voltage power supply 24 shown in FIG. 2 in that a current detection circuit 44A is provided instead of the voltage detection circuit 44, and the constant current instruction signal I1 from the main control unit 46. Is a point that the constant voltage instruction signal V2 is input.

  The current detection circuit 44A detects the current level of the current supplied to the charging roller 14, and outputs it to the control circuit 38 as a current detection signal I2. Further, the control circuit 38 has a function of stopping power supply when the current level indicated by the current detection signal I2 is abnormal.

  The control circuit 38 receives a constant voltage instruction signal V2 for instructing that a voltage having a predetermined voltage value is supplied from the main control unit 46 to the charging roller 14, and the main control unit 46 receives the constant voltage. The capacitance component 54 is based on the voltage value indicated by the instruction signal V2, the current value indicated by the current detection signal I2 input from the current detection circuit 44A, and the frequency of the alternating voltage of the charging voltage applied to the charging roller 14. Is obtained. The method for obtaining the capacitance value C2 is the same as in the first embodiment.

  The main control unit 46 determines the life of the photosensitive drum 12 based on the obtained capacitance value C2. Specifically, when the image forming apparatus 10 is manufactured, for example, when the constant voltage is supplied to the charging roller 14, the current value is measured to obtain the capacitance value C by the above equation (1), and this is stored in the memory 46A. Stored as the initial capacitance value C1. Then, the capacity value C2 of the capacity component 54 obtained by the above equation (1) when the image forming apparatus 10 is operated is compared with the initial capacity value C1, and the capacity value C2 is higher than the initial capacity value C1 by a predetermined threshold or more. If it is determined that the photosensitive drum 12 has reached the end of its life.

  Next, the photosensitive drum life determination control executed by the main control unit 46 will be described with reference to the flowchart shown in FIG.

  The main control unit 46 controls the switching element of the drive circuit 40 so that the constant voltage having the voltage value indicated by the constant voltage instruction signal V <b> 2 instructed to the control circuit 38 is supplied to the charging roller 14. In addition to the above-described instruction, control for determining the life of the photosensitive drum as shown in FIG. 6 is executed.

  First, in step 200, the current detection signal I2 output from the current detection circuit 44A is input.

  In step 202, the voltage value indicated by the constant voltage instruction signal V2 instructed to the control circuit 38, the current value indicated by the current detection signal I2 input from the current detection circuit 44A, and the charging voltage applied to the charging roller 14 are determined. Based on the predetermined frequency Freq of the AC voltage, the capacitance value C2 of the capacitance component 54 is obtained from the above equation (1).

  In step 204, it is determined whether or not the obtained capacity value C2 is higher than a predetermined threshold value by a predetermined threshold value than the initial capacity value C1 stored in the memory 46A. If the capacitance value C2 is higher than the initial capacitance value C1 by a predetermined threshold or more, it is determined that the photosensitive drum 12 is at the end of its life, and the routine proceeds to step 206.

  On the other hand, when the capacity value C2 is not higher than the initial capacity value C1 by a predetermined threshold or more, it is determined that the photosensitive drum 12 is not at the end of life, and the process returns to step 200 to perform the same processing as described above.

  In step 206, the main control unit 46 notifies a message or the like indicating that the photosensitive drum 12 is at the end of life on a display unit (not shown).

In each of the above embodiments, the case where the charging roller 14 that is charged while contacting the photosensitive drum 12 is used as a means for charging the photosensitive drum 12 is described. However, the present invention is not limited to this, and a corotron wire or the like is used. A conventional charger may be used.
In each of the above embodiments, the case where the main controller 46 determines the life of the photosensitive drum 12 has been described. However, the control circuit 38 in the high-voltage power supply 24 may determine the life of the photosensitive drum 12. Good.

  In addition, when the capacitance value C2 of the capacitance component 54 becomes higher than the initial capacitance value C1 by a second threshold value (eg, 13%) that is slightly smaller than a predetermined threshold value (eg, 15%), “life is soon” Such a notice message may be displayed.

  Incidentally, the frequency of the charging voltage applied to the charging roller 14 is generally proportional to the operation speed (process speed) of the image forming apparatus 10. That is, a device having a high process speed (a device having high productivity) has a high frequency. For example, in the case of an image forming apparatus having a process speed of 200 mm / s, 1500 Hz is used as the frequency of the charging voltage applied to the charging roller 14, and in the case of an image forming apparatus having a process speed of 100 mm / s, the frequency is 750 Hz. Is used.

  In this way, when the frequency of the charging voltage is fixed by the image forming apparatus, the voltage value detected by the voltage detection circuit 44 or the current value detected by the current detection circuit 44A is the surface layer of the photosensitive drum 12. Corresponds to the thickness.

  Therefore, when the frequency of the AC voltage of the charging voltage is fixed, the life of the photosensitive drum 12 is determined based on the voltage value detected by the voltage detection circuit 44 without obtaining the capacitance value by the above equation (1). It may be. In this case, when the detected voltage value becomes a value equal to or less than a predetermined threshold value, it is determined that the lifetime is reached. Further, the life of the photosensitive drum 12 may be determined based on the current value detected by the current detection circuit 44A. In this case, when the detected current value is equal to or greater than a predetermined threshold value, it is determined as the life.

  Further, a high-function image forming apparatus may have a plurality of operation speeds. Also in this case, since the frequency of the charging voltage is determined by the operation speed of the image forming apparatus, the life of the photosensitive drum 12 is detected by the voltage value detected by the voltage detection circuit 44 or the current detection circuit 44A. The determination may be made based on the current value. For example, when there are three types of image forming modes, such as a monochrome mode, a color mode, and a high image quality mode, for example, the monochrome mode is 300 mm / s, the color mode is 200 mm / s, and the high image quality mode is 100 mm / s. It is assumed to be operating speed. When the operator presses a predetermined operation button of the image forming apparatus, the operation mode is determined, and thereby the frequency of the charging voltage is also determined. Therefore, a threshold value for determining the life of the photosensitive drum 12 may be set for each frequency. Note that the threshold value may not be set in all modes, but may be set to a mode with a high normal use frequency.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photosensitive drum (Image carrier)
14 Charging roller (charging means)
16 Exposure unit (exposure means)
18 Developer (Developer)
20 Transfer roller (transfer means)
22 Cleaning blade 24, 24A High voltage power supply 26, 32, 36 DC power supply 28, 34 AC power supply 30 Power supply 38 Control circuit (calculation means, output means)
46A memory 40 drive circuit (voltage applying means)
42 transformer (voltage application means)
44 Voltage detection circuit (voltage detection means)
44A Current detection circuit (current detection means)
46 Main control unit (control means)
48 High voltage cord 50, 52, 54 Capacitance component V1 Voltage detection signal I1 Constant current instruction signal I2 Current detection signal V2 Constant voltage instruction signal

Claims (6)

Voltage applying means for applying a charging voltage in which an alternating voltage having a predetermined frequency is superimposed on a direct current voltage to charging means for charging an image carrier on which an image corresponding to an image is carried;
Voltage detecting means for detecting a voltage value of a charging voltage applied to the charging means by the voltage applying means;
Control means for controlling the voltage application means so that the current value of the current based on the charging voltage becomes a predetermined current value;
When the value representing the thickness of the surface layer of the image carrier based on the voltage value detected by the voltage detector exceeds the value indicating the limit of the thickness of the surface layer of the image carrier, the image carrier Output means for outputting a signal indicating that is a lifetime,
An image forming apparatus. Based on the voltage value detected by the voltage detection means, the predetermined current value, and the predetermined frequency of the AC voltage, the capacitance value of the capacitance component of the surface layer of the image carrier is calculated. A calculation means,
The output means outputs a signal indicating that the image carrier is at the end of its life when the capacitance value calculated by the calculation means exceeds a value indicating the limit of the thickness of the surface layer of the image carrier. The image forming apparatus according to claim 1, which outputs the image forming apparatus. Voltage applying means for applying a charging voltage in which an alternating voltage having a predetermined frequency is superimposed on a direct current voltage to charging means for charging an image carrier on which an image corresponding to an image is carried;
Current detection means for detecting a current value of a current based on a charging voltage applied to the charging means by the voltage applying means;
Control means for controlling the voltage application means so that the voltage value of the charging voltage becomes a predetermined voltage value;
When the value representing the thickness of the surface layer of the image carrier based on the current value detected by the current detection means exceeds the value indicating the limit of the thickness of the surface layer of the image carrier, the image carrier Output means for outputting a signal indicating that is a lifetime,
An image forming apparatus. Based on the current value detected by the current detection means, the predetermined voltage value, and the predetermined frequency of the AC voltage, the capacitance value of the capacitance component of the surface layer of the image carrier is calculated. A calculation means,
The output means outputs a signal indicating that the image carrier is at the end of its life when the capacitance value calculated by the calculation means exceeds a value indicating the limit of the thickness of the surface layer of the image carrier. The image forming apparatus according to claim 3. Storage means for storing a value representing the thickness of the surface layer of the image carrier at a predetermined time when the image carrier is unused;
The output means determines in advance that the value representing the thickness of the surface layer of the image carrier calculated by the calculating means is greater than the value representing the thickness of the surface layer of the image carrier stored in the storage means. The image forming apparatus according to claim 1, wherein when the threshold value is exceeded, a signal indicating that the image carrier is at the end of its life is output. The image forming apparatus according to claim 1, wherein the charging unit is a contact charging roll that charges the image carrier while rotating in contact with the image carrier.

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