JP3481708B2 - Potential sensor calibration method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a potential sensor calibration method for calibrating the output of a potential sensor in an image forming 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 image forming apparatus such as a copying machine, a facsimile machine, a printer or the like has potential fluctuations due to changes in its charging characteristics, sensitivity, etc. due to environmental changes and aging. 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 is a distance-correction type potential sensor in which the distance between the probe housing and the measurement target is adjusted to the same potential as that of the measurement target to eliminate the dependency on the distance to the measurement target.
There is a potential sensor that does not perform distance correction. 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 from the power source 12 to the measurement target 11 and the detection electrode 14 in the sensor case 13 is driven by the piezoelectric tuning fork to vibrate, whereby the measurement target 11 and the detection electrode 14 are separated from each other. Capacity C between
Change. At this time, a current flows from the detection electrode 14 to the ground via the resistor 15 and the potential of the measurement target 11 is measured by utilizing 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 the piezoelectric tuning fork to vibrate, whereby the measuring object 11 and the sensor case are oscillated. 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.

A potential sensor that does not perform distance correction is shown in FIG.
When the distance l between the potential sensor 10 and the object to be measured 11 changes as shown in FIG. 8B, the distance l between the potential sensor 10 and the object to be measured 11 is changed as shown in FIG. 8A. As a result, the output Vm of the potential sensor 10 fluctuates. In addition, FIG.
When the angle θ between the potential sensor 10 and the DUT 11 changes as shown in (b), the potential sensor 1 changes according to the angle θ between the potential sensor 10 and the DUT 11 as shown in FIG. 9A.
The output Vm of 0 fluctuates. Further, as shown in FIG. 10, the relationship (inclination and intercept) between the DUT 11 and the output Vm of the potential sensor 10 changes due to the variation in the inclination of the potential sensor 10. Therefore, the output of the potential sensor must be calibrated for each unit.

To calibrate the output of the potential sensor, for example, a voltage of 800 V or 100 V is applied to the photoconductor when the photoconductor is stationary,
When the output voltage of the potential sensor when 800 V is applied to the photoconductor is V ₈₀₀ , and the output voltage of the potential sensor when 100 V is applied to the photoconductor is V ₁₀₀ , y = {(800V-100V) / (V _{800 -V 100)} x + {800V} -V 800 · (800V-100V) / ( potential sensor calibration method of calibrating at V ₈₀₀ -V _100)} becomes calibration equation the output x of the potential sensor to y is adopted . The calibration formula is generally represented by y = ax + b (a, b: coefficient).

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

Further, Japanese Patent Laid-Open No. 56-95255 discloses an image forming apparatus equipped with a surface electrometer for measuring the electric potential of the surface of a recording medium, and a high-voltage power source and a surface for calibrating the surface electrometer. An image forming apparatus is described which has a built-in display for displaying a potential measurement value by an electrometer.

Japanese Unexamined Patent Publication No. 80772/1992 discloses a photoconductor, a charging means for uniformly charging the photoconductor, a means for exposing the charged photoconductor, and an electrostatic latent image formed on the photoconductor by the exposure. In the image forming apparatus, a potential detecting unit that detects a surface potential of the photoconductor and generates a potential signal indicating the potential, and a control unit that controls an image forming condition according to the potential signal. Means for charging the photoconductor with different amounts of charge, and the potential signal detected by the potential detection means when the photoconductor is charged with different amounts of charge correlates the potential signal with the surface potential of the photoconductor of the potential detection means. And an input / output characteristic detecting means for calculating the surface potential of the photoconductor corresponding to the potential signal generated by the potential detecting means according to the correlation calculated by the input / output characteristic detecting means. Control means for determining the corresponding image forming conditions: characterized in that it comprises a image forming apparatus using the photoreceptor is described.

Japanese Unexamined Patent Publication No. 4-174871 discloses an image forming apparatus equipped with a surface potential meter for measuring the surface potential of a photoconductor, using the potential of the photoconductor surface during non-image formation as a reference value. A method for calibrating a surface electrometer is described, which comprises calibrating the surface electrometer.

Japanese Unexamined Patent Publication No. 4-181267 discloses an image forming apparatus equipped with a recording medium for performing an image forming process by electrophotography and a surface potential sensor for measuring the surface potential of the recording medium. A high-voltage power supply for calibrating the potential sensor, and a base material of the recording body is electrically connected to an output end of the high-voltage power supply when the surface potential sensor is calibrated, and the base material of the recording body is a device except during calibration. An electrophotographic image forming apparatus is described, which is provided with a switching unit that switches to electrically connect to a housing.

Japanese Unexamined Patent Publication (Kokai) No. 4-181268 discloses an image forming apparatus equipped with a recording medium for performing an image forming process by electrophotography and a surface potential sensor for measuring the surface potential of the recording medium. Connection switching means for switching between a state in which the base material of the body is electrically connected to the output end of the high-voltage power supply and a state in which the base material of the body is electrically connected to the device housing, and the base material of the recording body is connected to the high-voltage power supply by the means. Means for storing each output value of the surface potential sensor while stepping up the voltage applied to the base material of the recording medium by a predetermined value in a state of being electrically connected to the output terminal of the recording medium, and the connection switching means. By comparing the output value of the surface potential sensor with each value stored by the storage means in a state where the base material of the recording body is electrically connected to the apparatus housing by the actual surface of the recording body. An electrophotographic image forming apparatus, characterized in that a means for detecting the position are described.

[0013]

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. In other potential sensors that do not perform distance correction, the output of the potential sensor is calibrated by the above potential sensor calibration method. However, as shown in FIG. 13, the residual potential of the photoconductor is the rest of the measured object (photoconductor). If the residual potential remains on the photoconductor due to changes with time or the photoconductor temperature, the potential sensor cannot be calibrated.

Further, in the photoconductor surface electrometer calibration device for an electrostatic recording device described in the above-mentioned Japanese Patent Laid-Open No. 4-58266, the residual potential increase amount and the potential sensor offset amount are simultaneously measured by using the distance correction type potential sensor. However, this cannot be applied to a potential sensor that is not a distance correction type, 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 output of a potential sensor that is not a distance correction type is calibrated with four reference voltages, but when the residual potential remains on the photoconductor, the voltage applied to the photoconductor is used. Since the residual potential is added to, the output of the potential sensor cannot be calibrated.

Further, as shown in FIG. 12, when a charged substance such as toner adheres to the potential sensor as dirt over time, the coefficients a and b of the calibration formula change. Also,
In the distance correction type potential sensor, the distance between two points (see FIG. 6 and FIG.
Since the permittivity (between the DUT 11 and the electrode 14 as shown in Fig. 4) changes depending on the environment, the output of the potential sensor changes due to the change of environment, for example, the ambient temperature of the potential sensor as shown in Fig. 14. (The slope of the output characteristic of the potential sensor changes). As described above, since the output of the potential sensor fluctuates due to various factors in the coefficients a and b of the calibration formula, the output of the potential sensor cannot be calibrated accurately.

Further, the voltage used when calibrating the output of the potential sensor is set to have a wide range because it is considered that the accuracy of the output of the potential sensor is improved as the distance between the two points is increased when the coefficient a is normally calculated. However, there is no consideration for the linearity of the input / output characteristic which is the characteristic of the potential sensor. In order to be able to use the distance correction type potential sensor, the linear region of the input / output characteristic as shown in FIG.
1 is 200 V or more) and the non-linear region of input / output characteristics (200 V or less in FIG. 11), and a voltage between two points is applied in the linear region of input / output characteristics to calculate a calibration formula of y = ax + b. Otherwise, a precise calibration formula cannot be obtained.
As for the voltage between two points, if the voltage from the developing bias power supply is used at the time of calibration and this voltage is set to a voltage higher than the applied voltage at the time of image formation, leakage to the main body occurs and an appropriate calibration formula cannot be obtained. It also causes noise to the electrical control system of the main body.

According to the present invention, the above problems are improved, the output of the potential sensor can be accurately calibrated, and the output of the potential sensor can be calibrated even when the residual potential remains on the photoconductor, and the distance is low. An object of the present invention is to provide a potential sensor calibration method capable of accurately calibrating the output of a potential sensor even with a correction type potential sensor.

[0018]

In order to achieve the above object, the invention according to claim 1 is an image forming apparatus equipped with a potential sensor for measuring the surface potential of a photoconductor, and a reference voltage is applied to a conductive portion of the photoconductor. In the potential sensor calibration method for calibrating the output of the potential sensor with a predetermined arithmetic expression on the basis of the output obtained by applying the potential sensor, the coefficients of different combinations in the plurality of coefficients of the arithmetic expression are respectively different. A plurality of calibrating means for calibrating the output of the potential sensor by the arithmetic expression using the calculated coefficient are provided, and the output of the potential sensor is calibrated by switching the plurality of calibrating means.

According to a second aspect of the present invention, an image forming apparatus is provided with a potential sensor for measuring the surface potential of the photoconductor, and a plurality of reference voltages are applied to the conductive portions of the photoconductor to obtain the potential from the potential sensor. From the output, the output x of the potential sensor is y =
In the potential sensor calibration method for calibrating to y with the arithmetic expression ax + b, a first calibration means for obtaining the coefficients a and b and a second calibration means for obtaining only the coefficient a and using the previous coefficient b are used. , The first calibration means is normally used,
Alternatively, when it is detected that the cumulative operating time of the potential sensor or the cumulative operating time of the photoconductor exceeds a predetermined time, it is used from the relationship between the rest time of the photoconductor and the previous residual potential of the photoconductor, The second calibration means detects the environment around the potential sensor and uses it when the environment exceeds a predetermined range.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the potential sensor calibration method described above, the application of the reference voltage is performed by a developing bias power source of the image forming apparatus,
The reference voltage is within a range of a voltage applied by the developing bias power source during image formation by the image forming apparatus and within a range where the linearity of the potential sensor is obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a first image forming apparatus to which the present invention is applied.
For example: The first example is an example in which the inventions of claims 1 and 2 are applied to an electrophotographic image forming apparatus. In the first example, for example, the photoconductor drum 21 is used as the image carrier made of the photoconductor. The photoconductor drum 21 is rotationally driven by a driving unit and uniformly charged by a charging charger 22 as a charging unit, and then subjected to image exposure by an exposing unit to form an electrostatic latent image, and an eraser 23 eliminates unnecessary areas. Then, the electrostatic latent image is developed into a toner image by the developing device 24 having the developing roller 24a as a developing means. A transfer sheet is fed between the photoconductor drum 21 and the transfer device 25 from the paper feeding device in synchronization with the toner image on the photoconductor drum 21, and the transfer sheet is transferred to the photoconductor by the transfer charger 25 as a transfer unit. Drum 2
The toner image on 1 is transferred and separated from the photoconductor drum 21 by a separation charger 26 as a separating means.

Further, the transfer sheet is conveyed by the conveying device 27, the toner image is fixed by the fixing device 28 having the fixing roller 28a and the pressure roller 28b as the fixing means, and the toner image is discharged to the outside. Further, the photosensitive drum 21 is
Cleaning is performed by a cleaning device 29 having a cleaning brush 29a and a cleaning blade 29b as a cleaning unit to remove residual toner, and the charge is removed by a charge removal lamp 30 as a charge removal unit to enable reuse.

The exposure means 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)
The V _L and the residual potential (potential of the portion removed by the eraser 23) V _R are measured.

A microcomputer comprising a CPU 32, a ROM 32 and a RAM 33 constitutes a control section. CP
U32 is the photoconductor drum 21 measured by the potential sensor 31.
The charge potential V _0, potential after exposure V _L, the output signal of the A / D converter 35 for the residual potential _{V R (V 0, V L} , a V _R A / D
The converted signal) is fetched and stored in the RAM 34 to be used for necessary calculation. A power pack (not shown) drives the charging charger 22 and the exposure lamp of the exposure device, and the CPU 32 forms a development bias power pack which constitutes a development bias power source via the PWM circuit 38 based on the measurement value of the potential sensor 31 stored in the RAM 34. (Hereinafter simply referred to as a power pack) 37 is controlled to control the developing bias voltage from the power pack 37 to the developing roller 24a, and a power pack (not shown) is controlled to control the output of the charger 22 and the exposure lamp voltage. This controls the amount of exposure.

The changeover switch 40 does not operate, and the photosensitive drum 21 has a photoconductive layer formed on a conductive portion made of a conductive substrate.
It remains grounded through. The above is the configuration and operation of the image forming apparatus. In addition, the photosensitive drum 21
The cumulative operating time of rotation of the photoconductor drum 2 is counted (measured) by the photoconductor cumulative operating time measuring means.
The stopped pause time of 1 is counted (measured) by the photoconductor pause time measuring means, and the accumulated operation time of the potential sensor 31 is counted (measured) by the potential sensor accumulated operation time measuring means.

Next, the potential sensor calibration means in the first example will be described. When calibrating the output of the potential sensor 31, the switch 40 is switched to operate. When the output of the potential sensor 31 is calibrated, the photosensitive drum 2
1 is stopped, and the thermistor 39 detects the temperature around the potential sensor 31 and the temperature of the photosensitive drum 21. The CPU 32 receives the temperature detection signal from the thermistor 39 after being A / D converted by the A / D converter 36 and input, and also has a compulsory execution signal from a switch (not shown) and a photosensitive member cumulative operation time measuring means. The photosensitive member cumulative operating time count value, the photosensitive member resting time count value from the photosensitive member resting time measuring means, and the potential sensor cumulative operating time count value from the potential sensor cumulative operating time measuring means are input,
ROM comparing these signals with the data in RAM 34
The output of the potential sensor 31 is calibrated according to the data from 33.

At this time, the CPU 32 sends the predetermined data to the PW.
The power pack 37 is output via the M circuit 38 to control the power pack 37, and the reference voltage is applied from the power pack 37 to the conductive substrate of the photoconductor drum 21 through the switch 40. Further, the CPU 32 takes in the output signal from the potential sensor 31 through the A / D converter 35 after applying the reference voltage to the conductive substrate of the photoconductor drum 21, and the A / D
Calibration formula data is calculated from the digital signal from the converter 35 and stored in the RAM 34.

2 and 3 show the processing flow of the potential sensor calibration of the CPU 32. In the first example, a predetermined reference voltage V _MAX , for example, 60 is applied to the conductive substrate of the photosensitive drum 21.
When the output of the potential sensor 31 when 0 V is applied is V _max, and when the output of the potential sensor 31 when another predetermined reference voltage V _MIN , for example, 200 V is applied to the photoconductor drum 21 is V _min , a _{= (V mAX -V mIN) /} (V max -V min): slope _{··· (1) b = V mAX} -V max × {(V mAX -V mIN) / (V max -V min)}: Intercept ... (2) The slope and the intercept of the calibration formula are obtained by the formula, and the calibration formula y = a
The output x of the potential sensor 31 is calibrated to y from x + b.

In order to turn on the calibration mode for calibrating the output of the potential sensor 31, the changeover switch (not shown) is turned on, and the accumulated operating time when the power of the potential sensor 31 is turned on exceeds a predetermined time. It is determined whether or not the temperature around the potential sensor 31 is equal to or more than a predetermined temperature difference from the previous calibration mode ON, and when the photosensitive drum 21 is operating (rotating). It is necessary to judge whether or not it is in the calibration mode. Further, when noise or the like is mixed in the output of the potential sensor 31 while the photosensitive drum 21 is operating, an accurate calibration formula may not be obtained. Therefore, in this example, the output of the potential sensor 31 is calibrated only when the stop of the photosensitive drum 21 is detected.

Here, the change-over switch (not shown) can be manually turned on when the photosensitive drum 21 or the potential sensor 31 is changed, and the change-over switch (not shown) is manually forced. Is turned on to generate a forced execution signal. Therefore, the changeover switch (not shown) constitutes a forced execution signal generating means. Further, in this example, a manual switch for selecting a coefficient for selecting different combinations of the coefficients a and b in the calibration formula y = ax + b, that is, for selecting either a and b or only a. Is provided, and an appropriate calibration formula is obtained by obtaining the selected coefficient.

The cumulative operating time of the potential sensor 31 is for detecting deterioration of the potential sensor 31 with time, and the potential sensor 31 is detected by detecting the operating time of the photosensitive drum 21.
The above may be substituted as long as it can substitute the elapsed time. Here, since the deterioration of the potential sensor 31 is short, the cumulative operation time of the potential sensor 31 is a predetermined time, for example, 20.
It is assumed that the calibration of the potential sensor 31 is executed after the lapse of 0 hours.

However, at this time, unless the residual potential of the photosensitive drum 21 is taken into consideration, the accuracy of calibration of the output of the potential sensor 31 is lacking, so that the photosensitive drum 21 before entering the calibration mode as shown in FIG. An outline of the residual potential during operation and the temperature of the photosensitive drum 21 detected by the thermistor 39;
From the relationship with the time during which the photoconductor drum 21 was stopped before entering the calibration mode, it is determined whether or not the residual potential of the photoconductor drum 21 can change the calibration formula (sufficiently low). However, when the residual potential of the photosensitive drum 21 is such that the calibration formula should not be changed, the cumulative operation time of the potential sensor 31 is counted up and the potential sensor 31 is counted.
The calibration is finished without executing.

The output sensitivity (inclination) of the potential sensor 31 changes due to changes in the dielectric constant in the air due to the temperature, humidity, atmospheric pressure, etc. around the potential sensor 31, but humidity changes depending on the correlation with temperature, and Since it was experimentally confirmed as shown in Fig. 14 that the value can be used as a substitute for the environmental change by detecting the temperature, the difference between this temperature and the temperature when the previous calibration formula was obtained For 6 minutes or more continuously for 2 minutes or more, and if the difference continues for 6 minutes or more for 2 minutes or more, confirm that the photosensitive drum 21 is stopped and execute the calibration mode. to go into. However, at this time, since the output sensitivity of the potential sensor 31 only changes, only the slope (coefficient a) is changed and the intercept (coefficient b) is changed so as not to be affected by the residual potential of the photosensitive drum 21. I am trying to use the previous data without changing it.

That is, as shown in FIG.
In the potential sensor calibration processing flow, it is determined in step S1 whether or not a changeover switch (not shown) is turned on. If the changeover switch is off, the cumulative operating time of the potential sensor 31 is determined in step S2. It is determined whether or not time has passed, for example, 200 hours. CPU32
When the accumulated operating time of the potential sensor 31 has not passed 200 hours, the output signal of the thermistor 39 is taken in through the A / D converter 36 in step S3, and the digital value from the A / D converter 36 and The ambient temperature of the potential sensor 31 detected by the thermistor 39 at the time of this calibration and the previous calibration formula are calculated based on the value acquired from the thermistor 39 via the A / D converter 36 when the calibration formula was obtained last time and stored in the RAM 34. When it was obtained, it was judged whether or not the difference from the ambient temperature of the potential sensor 31 detected by the thermistor 39 continued for 6 minutes or more and continued for 2 minutes or more, and the difference continued for 6 minutes or more and continued for 2 minutes or more. In this case, the flag n is set to 0 in step S3 '.
However, if not so, the potential sensor calibration process flow ends.

When the accumulated operation time of the potential sensor 31 has passed 200 hours, the CPU 32 sets the flag n to 1 in step S4, fetches the input signal from the photoconductor rest time measuring means in step S5, and The output signal of the sensor 31 is taken in via the A / D converter 35 to obtain the rest time and residual potential of the photosensitive drum 21, and in step S6 the rest time and residual potential of the photosensitive drum 21 and the thermistor 39 to A / D converter 36
With the input signal taken in through, the residual potential during operation of the photoconductor drum 21 before entering the calibration mode as shown in FIG. 13, the outline of the temperature of the photoconductor drum 21 detected by the thermistor 39, and the calibration mode. It is determined whether the residual potential of the photoconductor drum 21 is sufficient to change the calibration formula (sufficiently low) from the relationship with the time during which the photoconductor drum 21 was stopped before entering.

The CPU 32 may change the calibration formula for the residual potential of the photosensitive drum 21 (sufficiently low).
If it is determined to be, the process proceeds to step S7. If not, the flag n is cleared to 0 in step S8, and then the process proceeds to step S. When the changeover switch is turned on, the CPU 32 checks the input signal from the coefficient selecting manual switch (manual SW) in step S9 to determine whether only the coefficient a is selected. If it is selected, the process proceeds to step S7. If the coefficients a and b are selected, the flag n is set to 1 in step S10, and then the process proceeds to step S7.

The CPU 32 determines in step S7 whether or not the photosensitive drum 21 is stopped, and the photosensitive drum 2 is stopped.
When 1 is not stopped, the potential sensor calibration processing flow ends. Further, the CPU 32 controls the photoconductor drum 21.
Is stopped, the flag n is set to 0 in step S11.
If the flag n is 0, the output signal of the thermistor (temperature sensor) 39 is fetched via the A / D converter 36 and stored in the RAM 34 in step S13, and step S14 and thereafter. Move on to the calculation of calibration mode. When the flag n is not 0, the CPU 32 clears the data fetched from the potential sensor cumulative operation time measuring means and stored in the RAM 34 in step S12, and then proceeds to step S13.

Next, the calculation of the calibration mode will be described. In step S14, the CPU 32 turns on the switch 40 to apply the same voltage as the developing bias voltage to the developing roller 24a to the conductive substrate of the photosensitive drum 21 from the power pack 37 through the switch 40 as a reference voltage. This is because the developing bias power source including the power pack 37 is driven at a constant voltage, the accuracy of the power pack 37 is high within ± 1%, and the developing device 24 is not used during the calibration.

Further, when the voltage is applied from the power pack 37 to the conductive substrate of the photosensitive drum 21, the power pack 37 applies the voltage to the conductive substrate of the photosensitive drum 21 and to the developing roller 24a when the output of the potential sensor 31 is calibrated. Is also used to apply the voltage of the photoconductor drum 21 and the developing roller 24.
This is because the potential of “a” is set to the same potential to prevent the leak from the photoconductor drum 21 to the developing device 24 and to simplify the switch 40.

Next, the CPU 32 executes the measurement routine in step S15. In this measurement routine, as shown in FIG.
As shown in FIG.
To control the conductive substrate of the photosensitive drum 21 to, for example, 200
A reference voltage V _MIN of V is applied, the measured value V _min of the potential sensor 31 is captured via the A / D converter 35, and V _MIN and V _min are stored in the RAM 34. Similarly, CPU
The reference numeral 32 controls the power pack 37 by switching the data from the PWM circuit 38 to the power pack 37 so that the reference voltage V _MAX applied to the conductive substrate of the photosensitive drum 21 becomes, for example, 600 V, and the measured value V of the potential sensor 31. _max is captured via the A / D converter 35 to obtain V _{M AX} and V _max.
Are stored in the RAM 34.

Here, the CPU 32 actually applies the voltages V _MIN and V _MAX to the conductive substrate of the photosensitive drum 21 as shown in FIG. 5 in order to avoid the rise of the potential sensor 31 (5 msec) and the noise of the output. Measured value V of the potential sensor 31 after 5 msec has passed from each time of application
_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, the CPU 32 judges whether or not the flag n is set to 1 in step S16, and if the flag n is set to 1, R is read in step S17.
The following calculation formula previously stored in the OM 33: b = V _MAX −V _max × {(V _MAX −V _MIN ) / (V _max −V _min )}: The above V _MAX and V _MIN stored in the RAM 34 by the intercept. , V
_The intercept b is obtained based on the _max and V _min data, and the intercept b is stored in the RAM 34 in step S18, and is stored in step S18.
Proceed to 19.

When the flag n is cleared to 0, the CPU 32 proceeds from step S16 to step S1.
Fly to 9. The CPU 32 causes the ROM 3 in step S19.
The following pre-stored in the 3 equation _{a = (V MAX -V MIN)} / (V max -V min): slope by said V _MAX was stored in RAM 34, V _MIN, V
_The inclination a is obtained based on the _max and V _min data, and the inclination a is stored in the RAM 34 in step S20.

Next, the CPU 32 corrects the previous a, b data or b data only with the new a, b data or b data currently obtained in step S21 to obtain the arithmetic expression y = ax + b. After correction, the flag n is cleared in step S22 and the potential sensor calibration processing flow ends.

After the calibration of the potential sensor output is completed, the CPU
32 is the photoconductor drum 21 measured by the potential sensor 31.
Of the charge potential V ₀ , the post-exposure potential V _L , and the residual potential V _R of the output signal of the A / D converter 35 are stored in the RAM 34, and the measured value of the potential sensor 31 stored in the RAM 34 is stored as a coefficient in the RAM 34. The potential sensor measurement value is corrected by calibrating with the formula y = ax + b in the ROM 33 by a and b, and the power pack 37 is provided via the PWM circuit 38 so as to maintain the image of high quality based on the corrected value. To control the developing bias voltage, and to control the output of the charger 22 and the exposure lamp voltage by controlling a power pack (not shown) to control the charging potential and the exposure amount of the photosensitive drum 2.

The first example is an example of an image forming apparatus to which the invention described in claim 1 is applied, and includes a CPU 32 and a ROM.
The control unit composed of 32 and the RAM 33 has an arithmetic expression y = ax +
A plurality of calibrating means for calibrating the output of the potential sensor 31 by the arithmetic expression y = ax + b by using only the different combinations a and b of the plurality of coefficients a and b of b and b, respectively. The plurality of calibration means are switched by a coefficient selection manual switch to change the potential sensor 3
Since the output of No. 1 is calibrated, even if the coefficient fluctuates due to various fluctuation factors, the output of the potential sensor 31 can be calibrated accurately by switching the calibration means according to the fluctuation factors. For example, even when the output of the potential sensor 31 is calibrated when a high residual potential remains on the photoconductor drum 21, if there is a defect by checking the cause of the defect during the calibration, a processing flow for obtaining a coefficient that fluctuates due to the defect Is skipped by switching the calibration means, the output of the potential sensor 31 is calibrated, the defect is checked again during the subsequent calibration, and when there is no defect, the coefficient that fluctuates due to the defect is obtained without skipping the processing flow. By calibrating the output of the potential sensor 31, it is possible to always ensure accurate calibration of the output of the potential sensor 31 without the accuracy of the calibration of the output of the potential sensor 31 deteriorating.

Further, the intercept (coefficient b) of the equation (2) can be always measured and determined for each machine. Since the intercept is the intercept possessed by each potential sensor 31 itself, there will always be variations unless actually measured for each unit, but by always measuring and determining for each machine as in the first example. Variations can be suppressed and the potential sensor output can be calibrated with high accuracy.

The replacement of the photoconductor drum 21 includes the factory shipment, and the output of the potential sensor 31 can be calibrated using the aluminum drum or the like at the factory shipment. A potential sensor 3 each time the photosensitive drum 21 is replaced.
When the output of No. 1 is calibrated, the inclination of linearity of the potential sensor 31 and the deviation of the intercept (for example, stain by toner)
Is also excellent in that it can be calibrated.

The first example is an example of an image forming apparatus to which the invention described in claim 2 is applied, and includes a CPU 32, RO
The control unit composed of the M32 and the RAM 33 serves both as a first calibrating means for obtaining the coefficients a and b, and as a second calibrating means for obtaining only the coefficient a and using the last one as the coefficient b.
The calibration means is normally used, or when it is detected that the accumulated operating time of the potential sensor 31 or the accumulated operating time of the photosensitive drum 21 exceeds a predetermined time, the rest time of the photosensitive drum and the previous photosensitive body. The second calibration means detects the environment around the potential sensor 31 and is used when this environment exceeds a predetermined range. Therefore, even if the coefficient fluctuates due to various fluctuation factors. The output of the potential sensor 31 can be accurately calibrated by switching the calibration means according to the variation factor, and the output of the potential sensor 31 can be calibrated even when the residual potential remains on the photosensitive drum 21.

A second example of the image forming apparatus to which the invention of claim 3 is applied is an example of the image forming apparatus to which the invention of claim 3 is applied. In the first example, the photosensitive drum 21 is used. The reference voltage to be applied to the conductive substrate is defined. FIG. 11 shows the outline of the input / output characteristics of the potential sensor. The distance correction type potential sensor used as the potential sensor 31 cannot obtain linearity in the entire region of the input / output characteristics as shown in FIG. 11, and the voltage applied to the photosensitive drum 21 is also the developing device 24 and the cleaning device 28. A stable calibration equation y = ax + b with no defects can be obtained by matching not only the power supply voltage of the above, but also the voltage of the unit in contact with the photosensitive drum 21.

Here, at the time of calibration for calibrating the output of the potential sensor 31, the reference voltage applied from the power pack 37 to the conductive substrate of the photoconductor drum 21 through the switch 40 is 2.
When the input voltage of the potential sensor 31 has a linearity of ± 1% when the voltage is 00V or more, and when the reference voltage applied from the power pack 37 to the conductive substrate of the photoconductor drum 21 through the switch 40 is 200V or less. Potential sensor 3
The linearity of the input / output characteristic of 1 is ± 2.5%, and the photoconductor drum 2 from the power pack 37 through the switch 40.
Since the input / output characteristics of the potential sensor 31 are unstable even when the reference voltage applied to the conductive substrate 1 is 0 V or less, the CPU 32 controls the power pack 37 via the PWM circuit 38 during calibration. The reference voltage V _MIN is set within the range in which the linearity of the input / output characteristics of the potential sensor 31 is obtained. For example, the CPU 32 controls the power pack 37 via the PWM circuit 38 during calibration, and sets the reference voltage V _MIN applied from the power pack 37 to the conductive substrate of the photoconductor drum 21 through the switch 40 to 200V.

Further, the CPU 32 controls the power pack 37 via the PWM circuit 38 at the time of calibration so that the reference voltage V _MAX applied to the conductive substrate of the photoconductor drum 21 from the power pack 37 to the image forming apparatus main body via the switch 40. Problems or leaks to the cleaning device 29 that leaks or is in contact with the photosensitive drum 21 (for example, the photosensitive drum 21).
Scratches and cleaning brush 29a with reference voltage V _MAX
Is set to 600 V, which is within the range of the developing bias voltage applied to the developing roller 24a by the power pack 37 at the time of image formation by the image forming apparatus.

The second example is an example of the image forming apparatus to which the invention according to claim 3 is applied, and is the photosensitive drum 21.
The developing bias power supply 37 applies the reference voltage to the developing bias power supply 37, and the reference voltage is within the range of the voltage applied to the developing device 24 by the developing bias power supply 37 at the time of image formation of the image forming apparatus and the linearity of the potential sensor 31 is obtained. Since the voltage is within the range, the voltage applied to the photoconductor drum 21 matches the power supply voltage of the developing device 24, the cleaning device 28, and the like, as well as the photoconductor drum 21 within the range where the linearity is obtained as the input / output characteristic of the potential sensor. A stable calibration formula y = ax + b with good accuracy can be obtained because it can be matched with the voltage of the unit in contact with the unit, and the output of the potential sensor can be accurately measured even with a low-cost distance correction type potential sensor. Can calibrate.

[0054]

As described above, according to the first aspect of the invention, in the image forming apparatus equipped with the potential sensor for measuring the surface potential of the photoconductor, the reference voltage is applied to the conductive portion of the photoconductor, and In a potential sensor calibration method in which the output of the potential sensor is calibrated with a predetermined arithmetic expression on the basis of the output obtained from the potential sensor, coefficients of different combinations in a plurality of coefficients of the arithmetic expression are respectively obtained, and this is obtained. Since a plurality of calibrating means for calibrating the output of the potential sensor by using the coefficient is provided by using the coefficient and the output of the potential sensor is calibrated by switching the plurality of calibrating means, the coefficient fluctuates due to various fluctuation factors. However, the output of the potential sensor can be calibrated with high accuracy by switching the calibrating means according to the variation factor. Even when the output of the potential sensor is calibrated when a high residual potential remains on the photoconductor, the cause of the defect is checked during calibration, and if there is a defect, the output of the potential sensor is calculated without obtaining the coefficient that fluctuates due to the defect. When the calibration is performed, the defect is checked again at the time of the subsequent calibration, and when there is no defect, the coefficient of output of the potential sensor is calibrated by obtaining the coefficient that fluctuates due to the defect. It is possible to always ensure accurate calibration of the output of the potential sensor.

According to the second aspect of the invention, in the image forming apparatus equipped with the potential sensor for measuring the surface potential of the photoconductor, a plurality of reference voltages are applied to the conductive portion of the photoconductor to obtain from the potential sensor. The output of the potential sensor from the obtained output x
In a potential sensor calibration method for calibrating y to y by an arithmetic expression of y = ax + b, a first calibration means for obtaining coefficients a and b, and a second calibration means for obtaining only coefficient a and using the previous coefficient b And the first calibration means is used at a normal time, or when the accumulated operation time of the potential sensor or the accumulated operation time of the photoconductor is detected to exceed a predetermined time, the rest time of the photoconductor And the previous residual potential of the photoconductor, the second calibrating means detects the environment around the potential sensor and uses it when the environment exceeds a predetermined range. Even if it fluctuates due to a fluctuating factor, the output of the potential sensor can be calibrated accurately by switching the calibration means according to the fluctuating factor. Even when the output of the potential sensor is calibrated when a high residual potential remains on the photoconductor, the cause of the defect is checked during calibration, and if there is a defect, the output of the potential sensor is calculated without obtaining the coefficient that fluctuates due to the defect. When the calibration is performed, the defect is checked again at the time of the subsequent calibration, and when there is no defect, the coefficient of output of the potential sensor is calibrated by obtaining the coefficient that fluctuates due to the defect. It is possible to always ensure accurate calibration of the output of the potential sensor.

According to a third aspect of the invention, in the potential sensor calibration method according to the first or second aspect, the reference voltage is applied by a developing bias power source of the image forming apparatus, and the reference voltage is used for the image formation. Since the voltage is applied within the range of the voltage applied by the developing bias power source when the image is formed in the apparatus and within the range where the linearity of the potential sensor is obtained, the photosensitivity is set within the range where the input / output characteristic of the potential sensor is linear. The voltage applied to the body can be matched not only with the power supply voltage of each part, but also with the voltage of the unit in contact with the photoconductor, and a stable and accurate calibration formula can be obtained without any problems. The output of the potential sensor can be accurately calibrated even with a cost-effective distance correction type potential sensor.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a first example of an image forming apparatus to which the present invention has been applied.

FIG. 2 is a flowchart showing a part of a potential sensor calibration processing flow of the CPU in the first example.

FIG. 3 is a flowchart showing another part of the potential sensor calibration processing flow of the CPU in the first example.

FIG. 4 is a flowchart showing in detail a part of a potential sensor calibration processing flow of the CPU in the first example.

FIG. 5 is a timing chart showing the operation timing when calibrating the potential sensor that determines the slope and intercept of the calibration formula used in the first example.

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

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

FIG. 8 is a diagram showing a relationship between a distance to 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 and an angle of a potential sensor, which is not subjected to distance correction, with respect to a measured object.

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

FIG. 11 is a diagram showing how the input / output characteristics of the potential sensor without distance correction change when the distance (gap) to the object to be measured is changed.

FIG. 12 is a diagram showing how the input / output characteristics of the potential sensor change over time.

FIG. 13 is a diagram showing how the residual potential of the photoconductor decays due to the rest time, together with the decay due to the effect of the photoconductor temperature.

FIG. 14 is a diagram showing how the output value of the potential sensor changes depending on environmental conditions.

[Explanation of symbols]

21 photoconductor drum 24 Developing device 29 Cleaning device 31 Potential sensor 32 CPU 33 ROM 34 RAM 35,36 A / D converter 37 Power Pack 38 PWM circuit 39 Thermistor 40 switch

Claims (3)

(57) [Claims] 1. An image forming apparatus equipped with a potential sensor for measuring a surface potential of a photoconductor, wherein a reference voltage is applied to a conductive portion of the photoconductor and an output of the potential sensor is used as a reference. In a potential sensor calibration method for calibrating an output with a predetermined arithmetic expression, coefficients of different combinations in a plurality of coefficients of the arithmetic expression are respectively obtained, and the obtained coefficient is used to calculate the output of the electric potential sensor by the arithmetic expression. A method for calibrating a potential sensor, characterized in that a plurality of calibrating means for calibrating are provided, and the output of the potential sensor is calibrated by switching the plurality of calibrating means. 2. An image forming apparatus equipped with a potential sensor for measuring a surface potential of a photoconductor, wherein a plurality of reference voltages are applied to a conductive portion of the photoconductor, and an output obtained from the potential sensor is used to detect the potential sensor. The output x is expressed as y = ax + b in the formula y
In the potential sensor calibration method for calibrating according to step 1, there is provided a first calibration means for obtaining the coefficients a and b, and a second calibration means for obtaining only the coefficient a and using the previous coefficient b.
The calibrating means is normally used, or when the accumulated operation time of the potential sensor or the accumulated operation time of the photoconductor is detected to exceed a predetermined time, the rest time of the photoconductor and the previous photoconductor A method for calibrating a potential sensor, characterized in that the second calibrating means detects the environment around the potential sensor and uses it when the environment exceeds a predetermined range, based on the relationship with the residual potential. 3. The potential sensor calibration method according to claim 1, wherein the reference voltage is applied by a developing bias power source of the image forming apparatus, and the reference voltage is the developing bias when an image is formed by the image forming apparatus. A method of calibrating a potential sensor, characterized in that it is within a range of a voltage applied by a power source and within a range where linearity of the potential sensor is obtained.