JPH07140736A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To precisely calibrate a potential sensor even if a charge remains on a photoreceptor. CONSTITUTION:A potential sensor calibrating means calibrating the output (x) of the potential sensor 31 to (y) by a calibration expression that y= ax+b, a=(VMAX-VMIN)/(Vmax-Vmin) and (b) is an intercept, when the outputs of the potential sensor 31 at the time of applying voltages VMAX and VMIN to the photoreceptor 21 are defined as Vmax and Vmin respectively is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as a copying machine, a facsimile or a printer having a potential sensor for measuring the potential of a photoconductor.

[0002]

2. Description of the Related Art A photoconductor used in an electrophotographic apparatus has potential fluctuations due to changes in its charging characteristics, sensitivity, etc. due to environmental changes and changes over time. Therefore, in the electrophotographic apparatus, in order to suppress the potential fluctuation of the photoconductor and maintain a high-quality image, the potential pattern formed on the photoconductor is detected by the potential sensor, and the output of the charger is determined based on the detected potential pattern. The exposure amount and the like are controlled.

The potential sensor includes a distance-correction type potential sensor in which the distance between the probe housing and the measurement object is corrected to eliminate the dependency on the distance to the measurement object, and a potential sensor in which the distance correction is not performed. There is. As potential sensors that do not perform distance correction, there are a vibration capacitance type potential sensor as shown in FIG. 6 and a chopper type potential sensor as shown in FIG. In the vibration capacitance type potential sensor, a voltage is applied to the measurement target 11 from the power source 12, and the detection electrode 14 in the sensor case 13 is driven by the piezoelectric tuning fork to vibrate, thereby measuring the measurement target 11 and the detection electrode 1.
The capacitance C between 4 and 4 is changed. At this time, the detection electrode 1
A current flows from 4 to the ground via the resistor 15 and the potential of the measurement target 11 is measured by utilizing the fact that the AC voltage generated in the detection electrode 14 depends on the potential of the measurement target 11.

Further, in the chopper type potential sensor, a voltage is applied to the measuring object 11 from the power source 12 and the chopper 16 in the sensor case 13 is driven by a piezoelectric tuning fork to vibrate, thereby measuring the measuring object 11 and the sensor case. The capacitance C between the detection electrode 14 in 13 and the detection electrode 14 is changed. At this time, a current flows from the detection electrode 14 to the ground via the resistor 15, and the AC voltage generated at the detection electrode 14 is measured.
The potential of the measurement target 11 is measured by utilizing the dependence on the potential of.

In the potential sensor that does not perform the distance correction, the potential sensor 10 and the object to be measured 11 as shown in FIG.
When the distance l between the potential sensor 10 and the measurement object 11 changes, the output Vm of the potential sensor 10 varies according to the distance 1 between the potential sensor 10 and the object to be measured 11, as shown in FIG. When the angle θ between the potential sensor 10 and the object to be measured 11 changes as shown in FIG. 9B, the angle θ between the potential sensor 10 and the object to be measured 11 changes according to the angle θ as shown in FIG. 9A. As a result, the output Vm of the potential sensor 10 fluctuates. Further, as shown in FIG. 10, the DUT 11 and the potential sensor 1 are
The relationship (slope and intercept) with the output Vm of 0 is the potential sensor 1
It changes due to the variation of the inclination of 0. Therefore, each potential sensor must be calibrated.

The potential sensor is calibrated by, for example, applying a voltage of 800 V and 100 V to the photosensitive member when the photosensitive member is stationary, and applying an output voltage of V ₈₀₀ and 100 V to the photosensitive member when applying ₈₀₀ V to the photosensitive member. When the output voltage of the potential sensor at that time is V ₁₀₀ , y = (800V-100V) / (V ₈₀₀ −V ₁₀₀ ) x +
{800V-V ₈₀₀・ (800V-100V) / (V ₈₀₀
The potential sensor calibration method of calibrating the output x of the potential sensor to y by the calibration formula of −V ₁₀₀ ) is adopted.

Further, Japanese Patent Laid-Open No. 4-58266 discloses that
Using a distance correction type potential sensor (residual potential increase +
There is described a photoreceptor surface potential meter calibration device for an electrostatic recording device that simultaneously measures the potential sensor offset amount). Japanese Patent Laid-Open No. 5-196672 describes a method of calibrating a potential sensor that is not a distance correction type with four calibration potentials and performing an abnormality determination when the calibration formula is not within a predetermined range. Further, Japanese Patent Application Laid-Open No. 62-44755 describes a method of correcting the offset component and the residual potential component of the potential sensor at the same time as in the device described in Japanese Patent Application Laid-Open No. 4-58266.

[0008]

In the above-mentioned potential sensor of the distance correction type, the output is stable with respect to the distance and the angle with respect to the measuring object, but it is expensive. Also, with other potential sensors that do not perform distance correction, the potential sensor is calibrated by the potential sensor calibration method described above, but since the potential sensor is calibrated by resting the photoconductor, the output of the potential sensor is different from that during machine operation. There will be some deviation. For example, if the photoconductor has a drum shape and the deflection during machine operation is 0.1 mm,
0.1V when 800V is applied to the photoconductor from (a)
Detection error occurs. This is about 20 in terms of the potential of the photoconductor
It becomes an error of V. In addition, the potential sensor cannot be calibrated if residual potential remains on the photoreceptor.

Further, in the above-mentioned photoconductor surface potential meter calibration device for an electrostatic recording device disclosed in Japanese Patent Laid-Open No. 4-58266, a distance correction type potential sensor is used to calculate (residual potential increase + potential sensor offset). Although measured at the same time, this is not applicable to non-distance compensated potential sensors and cannot be used unless the linearity of the potential sensor is calibrated in the first place. Further, in the method described in JP-A-5-196672, the calibration of the potential sensor which is not the distance correction type is performed with four calibration potentials, but when the residual potential remains on the photosensitive member, the residual voltage remains on the photosensitive member applied voltage. The potential is added and the potential sensor cannot be calibrated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrophotographic apparatus which is capable of remedying the above-mentioned drawbacks, calibrating a potential sensor with high accuracy, and performing it even when a residual potential remains on a photoconductor. .

[0011]

In order to achieve the above object, the invention according to claim 1 has a potential sensor for measuring the potential of a photoconductor, and applies the voltage to the photoconductor to set the potential sensor. In the electrophotographic apparatus to be calibrated, the output of the potential sensor when the voltage V _MAX is applied to the photoconductor is V _max, and the output of the potential sensor when the voltage V _MIN is applied to the photoconductor is V _min . Then, y = ax + ba = (V _MAX −V _MIN ) / (V _max −V _min ) b: A potential sensor calibration means for calibrating the output x of the potential sensor to y by a calibration formula is there.

According to a second aspect of the invention, in the electrophotographic apparatus according to the first aspect, the potential sensor calibrating means calibrates the potential sensor at the time of exchanging the photoconductor to determine the section b. According to a third aspect of the invention, in the electrophotographic apparatus according to the second aspect, the photoconductor is stationary during calibration of the potential sensor that determines the section b.

According to a fourth aspect of the present invention, in the electrophotographic apparatus according to the first aspect, the photosensitive member is rotated at the time of calibration of the potential sensor that determines the section b. According to a fifth aspect of the present invention, in the electrophotographic apparatus according to the fourth aspect, the potential sensor is calibrated at at least four locations on the entire circumference of the photoconductor, and an average value thereof is used as a calibration value of the potential sensor. It is a thing.

[0014]

[Action] In the first aspect of the present invention, the potential sensor calibration means y = ax + b a = ( V MAX -V MIN) / (V max -V min) b: the output x of the potential sensor in sections made-calibrating y Calibrate to. According to a second aspect of the invention, in the electrophotographic apparatus according to the first aspect, the potential sensor calibrating means calibrates the potential sensor at the time of exchanging the photoconductor to determine the section b.

According to a third aspect of the invention, in the electrophotographic apparatus according to the second aspect, the photoconductor is stationary during calibration of the potential sensor that determines the section b. According to a fourth aspect of the invention, in the electrophotographic apparatus according to the first aspect, the photoconductor is rotated when the potential sensor for determining the section b is calibrated. According to a fifth aspect of the present invention, in the electrophotographic apparatus according to the fourth aspect, the potential sensor is calibrated at at least four locations on the entire circumference of the photoconductor, and the average value is used as the calibration value of the potential sensor.

[0016]

FIG. 1 shows a first embodiment of the present invention. This first
The embodiment is an embodiment of the invention described in claims 1, 2 and 3.
The photoconductor drum 21 is rotationally driven by a driving unit and uniformly charged by a charging charger 22 and then imagewise exposed by an exposure device to form an electrostatic latent image.
The unnecessary area is neutralized by 3, and the electrostatic latent image is developed on the developing roller 2.
The toner image is developed by the developing device 24 having 4a. A transfer paper is sent between the photoconductor drum 21 and the transfer device 25 from the paper feeding device in time with the toner image on the photoconductor drum 21, and the transfer paper is transferred to the transfer device 2.
The toner image on the photosensitive drum 21 is transferred by 5 and separated from the photosensitive drum 21 by the separating device 26.

Further, the transfer sheet is conveyed by the conveying device 27, and the toner image is fixed by the fixing device 28 having the fixing roller 28a and the pressure roller 28b and is discharged to the outside. Further, the photoconductor drum 21 is cleaned by a cleaning device 29 having a cleaning brush 29a and a cleaning blade 29b to remove residual toner, and is neutralized by a static elimination lamp 30 to be reused.

The exposure device forms an electrostatic latent image on the photosensitive drum 21 by illuminating the original with an exposure lamp and irradiating the photosensitive drum 21 with the reflected light. The potential sensor 31 is disposed between the eraser 23 and the developing device 24, and the surface potential of the photosensitive drum 21, that is,
Charging potential V ₀ , potential after exposure (potential of exposed portion)
_VL and the residual potential (potential of the portion removed by the eraser 23) V _R are measured, and the thermistor 28c detects the fixing roller 2
The surface temperature is detected by contacting the surface of 8a.

A microcomputer including a CPU 32, a ROM 32 and a RAM 33 constitutes a control unit. The output signal of the potential sensor 31 and the detection signal of the thermistor 28c are converted into digital signals by the A / D converters 35 and 36, respectively, and the CPU 32 measures the charging potential V ₀ of the photosensitive drum 21 measured by the potential sensor 31 and potential V _L, and the output signal of the a / D converter 35 for the residual potential V _R, takes in the output signal of the a / D converter 36 to the surface temperature of the fixing roller 28a which is detected by the thermistor 28c R
Stored in AM34 and used for necessary calculations. The drive circuit 37 including a power pack applies a voltage corresponding to the pulse width modulation signal from the PWM circuit 38 to the photoconductor drum 21, and PW
The M circuit 38 applies to the power pack 37 a pulse width modulation signal having a duty ratio according to the control signal from the CPU 32.

A power pack (not shown) drives the charger 22 and the exposure lamp of the exposure device, and the CPU 32 reads R
The power pack 37 is controlled via the PWM circuit 38 based on the measured value of the potential sensor 31 stored in the AM 34 or the detected temperature of the thermistor 28c, or the power pack (not shown) is controlled to output the charger 22 or the exposure lamp. The amount of exposure is controlled by controlling the voltage.

FIG. 2 shows a section calculation flow for the potential sensor calibration of the CPU 32. In the first embodiment, the output of the potential sensor 31 when a predetermined voltage V _MAX , for example 800 V, is applied to the photosensitive drum 21 is V _max, and another predetermined voltage V _MIN , for example 100 V, is applied to the photosensitive drum 21. when the output of the voltage sensor 31 at the time of applying to the _{V m in, y = ax +} b ··· (1) a = (V mAX -V mIN) / (V max -V min) b: in sections made-calibrating The output x of the potential sensor 31 is calibrated to y.

When replacing the photosensitive drum 21, V
Utilizing the fact that _R ≈ 0V, the intercept b of the potential sensor 31 itself is obtained as shown in FIG. That is, CP
U32 checks the input signal from the potential sensor initial calibration switch (SW) at the time of replacement of the photosensitive drum 21, and when the potential sensor initial calibration switch is pressed, the U32 keeps the photosensitive drum 21 stationary and sets the PWM circuit 38. The power pack 37 is controlled via the
The voltage V _MIN of 0 V is applied, the measured value V _min of the potential sensor 31 is taken in through the A / D converter 35, and the RAM is obtained.
It is stored in 34.

Next, the CPU 32 controls the power pack 37 via the PWM circuit 38 so that the photoconductor drum 21 receives the power.
The voltage V _MAX of 00 V is applied, and the measured value V _max of the potential sensor 31 is taken in via the A / D converter 35 and RA
Store in M34. Here, in order to avoid the rise of the potential sensor 31 (5 msec) and the noise of the output, the CPU 32 actually applies the respective voltages V _MIN and V _MAX to the photosensitive drum 21 as shown in FIG. Measured value V of the potential sensor 31 after 5 msec has passed
_min, V _max was 50 points at a time sampled by the A / D converter 35, respectively, V _min Searching for the respective average value, V
_It is stored in the RAM 34 as _max .

Next, CPU 32 has the following formula stored in advance in ROM33 (2) b = 800V- V max × a (800V-100V) / (V max -V min) ··· (2) The calculation is performed based on V _min and V _max stored in the RAM 34 to obtain the intercept b, and the intercept b is stored in the RAM 34. After that, the CPU 32 determines the charging potential V ₀ of the photoconductor drum 21 measured by the potential sensor 31, the post-exposure potential V _L ,
The output signal of the A / D converter 35 with respect to the residual potential V _R is captured and stored in the RAM 34, and the measured value of the potential sensor 31 stored in this RAM 34 is calibrated by the equation (1) by the intercept b in the RAM 34 to obtain the potential. The power pack 3 is calibrated through the PWM circuit 38 so as to calibrate the sensor and maintain a high quality image based on the calibrated measurement values.
7 or by controlling a power pack (not shown) to control the output of the charging charger 22 and the exposure lamp voltage to control the charging potential and the exposure amount of the photosensitive drum 2.

In the first embodiment, the intercept b of the equation (1) can always be measured and determined for each machine. Intercept b is
Since each potential sensor 31 itself has a segment, there will always be variations unless actually measured for each unit, but variations are suppressed by always measuring and determining each machine as in the first embodiment. Therefore, the potential sensor can be accurately calibrated.

The replacement of the photoconductor drum 21 includes the factory shipment, and the potential sensor 31 can be calibrated using the aluminum drum or the like at the factory shipment.
If the potential sensor 31 is calibrated every time the photosensitive drum 21 is replaced, it is advantageous in that the linearity deviation of the potential sensor 31 over time (for example, stain due to toner) can be calibrated.

Further, the potential sensor 31 is provided by using the photoconductor drum 21 in which the residual potential remains even when the photoconductor drum 21 is stationary.
When performing the calibration, it is necessary to suppress the variation in the intercept b. However, since the intercept b is obtained and the potential sensor 31 is calibrated by utilizing the fact that V _R ≈0 V in the initial stage of the photoconductor drum 21, the calibration is performed. However, there is no need to calibrate the potential sensor even when the residual potential remains on the photoconductor.

FIG. 4 shows a CPU according to the second embodiment of the present invention.
32 shows a potential sensor calibration formula calculation flow of 32. This second
The embodiment is an embodiment of the invention described in claims 1, 4 and 5, and in the above embodiment, the CPU 32 executes the potential sensor calibration formula calculation flow shown in FIG.

In the second embodiment, the potential sensor is constantly calibrated when the main switch is turned on after waiting for a long time. That is, CP
U32 is the thermistor 28c after the main switch is turned on.
The input signal taken in from the A / D converter 36 is checked to check the fixing temperature of the fixing device 28 (fixing roller 28a
Surface temperature) is 100 ° C. or lower, and if the fixing temperature is not 100 ° C. or lower, it is determined that the standby time was short without performing the image forming operation, and the processing is directly performed. Over.

The CPU 32 has a fixing temperature of 100.degree.
In the case of the following, the input signal fetched from the thermistor 28c via the A / D converter 36 is repeatedly checked and waited until the fixing temperature reaches 200 ° C.
When the temperature reaches 00 ° C., the drive unit is controlled to rotate the photosensitive drum 21. Next, the CPU 32 causes the PWM circuit 3
8 to control the power pack 37 to control the photosensitive drum 2
1 is applied with a voltage V _MIN of 100 V, and the potential sensor 31
A large number of points are sampled through the A / D converter 35, the respective average values are obtained and stored in the RAM 34 as V _min 1.

Next, the CPU 32 samples a large number of measurement values of the potential sensor 31 through the A / D converter 35 when the photosensitive drum 21 is rotated by 90 °, and obtains each average value to obtain V. _It is stored in the RAM 34 as _min 2.
Similarly, the CPU 32 then detects that the photosensitive drum 21 is 9
The measured value of the potential sensor 31 is sampled through the A / D converter 35 at a position rotated by 0 °, and an average value thereof is obtained and stored in the RAM 34 as V _min 3. Furthermore, C
The PU 32 then samples the measured value of the potential sensor 31 at a plurality of points through the A / D converter 35 when the photosensitive drum 21 rotates by 90 °, obtains each average value, and obtains V
_It is stored in the RAM 34 as _min 4. Therefore RAM
The 34 will store the measurements V _min 1 to V _min 4 of potential sensor 31 for four positions spaced substantially equidistantly in the direction of rotation the entire circumference of the photosensitive drum 21.

Next, the CPU 32 controls the power pack 37 via the PWM circuit 38 so that the photosensitive drum 21 can be controlled.
A voltage V _MAX of 00 V is applied, and the measured value of the potential sensor 31 is sampled at multiple points via the A / D converter 35.
The respective average values are obtained and stored in the RAM 34 as V _max 1. Next, the CPU 32 samples a large number of measurement values of the potential sensor 31 through the A / D converter 35 when the photosensitive drum 21 is rotated by 90 °, and obtains each average value thereof as V _max 2. It is stored in the RAM 34.

Similarly, the CPU 32 samples a large number of measured values of the potential sensor 31 through the A / D converter 35 when the photosensitive drum 21 is rotated by 90 °, and obtains each average value to obtain V. _It is stored in the RAM 34 as _max 3. Further, the CPU 32 then detects the photosensitive drum 21.
A / D the measured value of the potential sensor 31 at the place rotated by 90 °.
A large number of points are sampled through the converter 35, the respective average values are obtained, and stored in the RAM 34 as V _max 4. Therefore, the storing measured values V _{ma x} 1 to V _max 4 potential sensor 31 for four positions spaced substantially equidistantly in the direction of rotation the entire circumference of the photosensitive drum 21 to the RAM 34.

Here, the CPU 32 applies the voltage V to the photosensitive drum 21 in order to avoid the rise of the potential sensor 31 (5 msec) and the noise of the output, as in the first embodiment.
Measured values V _min 1 and V _max 1 of the potential sensor 31 after 5 msec have passed from the respective times when _MIN and V _MAX were applied
Are sampled at a large number of points via the A / D converters 35, and their average values are calculated and stored in the RAM 34 as V _min 1 and V _max 1.

Next, the CPU 32 controls the power pack 37 via the PWM circuit 38 to end the voltage application to the photoconductor drum 21, and controls the drive unit to stop the photoconductor drum 21. Then, the CPU 32 uses the RAM 34.
V _min 1~V _min 4 stored in, V _max 1 to V _max 4 was used to calculate the calibration equation of voltage sensor 31 (1), _{i.e., y = (V MAX -V MIN} ) / {(V max _{1 + V max 2 + V max} 3 + V max 4) - (V min 1+ V min 2 + V min 3 + V min 4)} x + b = 700V / {(V max 1 + V max 2 + V max 3 + V max 4) - (V min 1 + V min 2+ V min 3 + V min 4 )} x + b b = 800V- (V max 1 + V max 2 + V max 3 + V max 4) × (800V-100V) / {(V max 1 + V max 2 + V max 3 + V max 4) - (V min 1 + V min 2 + V min 3 + V min 4 )} Is calculated and this calibration formula (1) is stored in the RAM 34.

After that, the CPU 32 fetches the output signals of the A / D converter 35 for the charging potential V ₀ of the photosensitive drum 21, the post-exposure potential V _L , and the residual potential V _R measured by the potential sensor 31, and stores them in the RAM 34. The potential sensor is stored in the RAM 34, and the measured value of the potential sensor 31 is calibrated by the equation (1) in the RAM 34 to calibrate the potential sensor, and the image is maintained in high quality based on the calibrated measured value. Further, by controlling the power pack 37 via the PWM circuit 38 or controlling the power pack (not shown) to control the output of the charging charger 22 and the exposure lamp voltage, the charging potential and the exposure amount of the photosensitive drum 2 can be controlled. Control.

In the second embodiment, since the potential sensor 31 is calibrated on the average in the circumferential direction of the photosensitive drum 21 while rotating the photosensitive drum 21, the potential sensor is very close to the operating state of the actual machine. 31 can be calibrated, for example, the deviation from the perfect circle of the photoconductor drum 21 can be absorbed, and the potential of the photoconductor drum 21 can be controlled with high accuracy.

In the second embodiment, the potential sensor 31 is calibrated at four locations on the entire circumference of the photosensitive drum 21 and the average value thereof is used as the calibration value of the potential sensor.
For example, while rotating 1, the measurement value of the potential sensor 31 may be sampled over the entire circumference of the photosensitive drum 21 and the potential sensor may be calibrated by the average value.

Further, in the above embodiment, even if the potential sensor is calibrated only by the calibration formula (1) stored in advance in the memory without calculating the intercept b or the calibration formula (1), If it is possible to suppress the variation of b (the variation that each potential sensor has), the potential sensor can be calibrated while the residual potential remains on the photosensitive drum 21. Further, in the above-described embodiment, the calibration voltage applied to the photoconductor drum 21 is set to two points V _MAX and V _MIN , but a voltage of three or more points is applied to the photoconductor drum 21 and the potential sensor 31 for those voltages is applied. Of course, it does not matter if the potential sensor is calibrated based on the measured value.

[0040]

As described above, according to the first aspect of the invention, the electrophotographic apparatus has the potential sensor for measuring the potential of the photoconductor and calibrates the potential sensor by applying the voltage to the photoconductor. In the above, when the output of the potential sensor when the voltage V _MAX is applied to the photoconductor is V _max and the output of the potential sensor when the voltage V _MIN is applied to the photoconductor is V _min , y = _{ax + b a = (V mAX} -V mIN) / (V max -V min) b: since the output x of the potential sensor in sections made-calibrating with a potential sensor calibration means for calibrating the y, the calibration of the voltage sensor It can be performed with high accuracy and even when the residual potential remains on the photoconductor.

According to the second aspect of the invention, in the electrophotographic apparatus of the first aspect, the potential sensor calibrating means calibrates the potential sensor and replaces the intercept b when the photoconductor is replaced. Deviations in sensor linearity over time can also be calibrated.

According to the third aspect of the invention, in the electrophotographic apparatus according to the second aspect, since the photoconductor is stationary during the calibration of the potential sensor that determines the intercept b, the residual potential of the photoconductor is initially set. It is possible to calibrate the potential sensor with high accuracy by utilizing the fact that is almost 0, and also when the residual potential remains on the photoconductor.

According to the invention described in claim 4, in the electrophotographic apparatus according to claim 1, the photoconductor is rotated at the time of calibration of the potential sensor for determining the intercept b. Therefore, the output of the potential sensor is at the time of calibration of the potential sensor. There is almost no deviation from the time of machine operation, and the potential sensor can be calibrated with high accuracy.

According to a fifth aspect of the present invention, in the electrophotographic apparatus according to the fourth aspect, the potential sensor is calibrated at at least four locations along the entire circumference of the photosensitive member, and the average value thereof is used as the potential sensor. Since the calibration value is set to, the output of the potential sensor does not deviate from the mechanical operation when the potential sensor is calibrated, and the potential sensor can be calibrated with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic view showing a first embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of calculating a potential sensor calibration intercept of the CPU in the first embodiment.

FIG. 3 is a timing chart showing the operation timing when calibrating the potential sensor that determines the intercept b in the first embodiment.

FIG. 4 is a flowchart showing a potential sensor calibration formula calculation flow of a CPU according to a second embodiment of the present invention.

FIG. 5 is a timing chart showing the operation timing at the time of calibration of the potential sensor for obtaining the calibration formula of the second embodiment.

FIG. 6 is a schematic view showing a conventional vibrating capacitance type potential sensor.

FIG. 7 is a schematic view showing a conventional chopper type potential sensor.

FIG. 8 is a diagram showing a relationship between a distance from an object to be measured and an output of the potential sensor without distance correction.

FIG. 9 is a diagram showing a relationship between an output of an electric potential sensor that is not subjected to distance correction and an object to be measured and an output.

FIG. 10 is a diagram showing variations in linearity of a potential sensor without distance correction.

[Explanation of symbols]

 21 Photoreceptor Drum 31 Potential Sensor 32 CPU 37 Power Pack 38 PWM Circuit

Claims (5)

[Claims] 1. A has a potential sensor for measuring the potential of the photosensitive member, wherein the photosensitive member by applying a voltage to the electrophotographic apparatus to calibrate the voltage sensor, the voltage V _MAX on the photosensitive member
When the output of the potential sensor when V is applied is V _max and the output of the potential sensor when the voltage V _MIN is applied to the photoconductor is V _min , y = ax + ba = (V _MAX −V _MIN ) / (V _max -V _min ) b: An electrophotographic apparatus comprising a potential sensor calibration means for calibrating the output x of the potential sensor to y by a calibration formula of intercept. 2. The electrophotographic apparatus according to claim 1, wherein the potential sensor calibrating means calibrates the potential sensor to determine the section b when the photoconductor is replaced. 3. The electrophotographic apparatus according to claim 2, wherein the photoconductor is stationary during calibration of a potential sensor that determines the section b. 4. The electrophotographic apparatus according to claim 1, wherein the photosensitive member is rotated when a potential sensor that determines the section b is calibrated. 5. The electrophotographic apparatus according to claim 4, wherein the potential sensor is calibrated at at least four locations around the entire circumference of the photoconductor, and an average value thereof is used as a calibration value of the potential sensor. And an electrophotographic device.