JPH0756414A - Method for correcting sensitivity of potential sensor - Google Patents

Abstract

PURPOSE:To make possible the simpler correction of a change in the detection sensitivity of a potential sensor which measures the potential electrostatically charged on the surface of a photosensitive drum by utilizing the change in the difference between the detected values of the potential sensor to be caused by an environmental change. CONSTITUTION:The difference DELTAVS between the detected values S VS1, VS2 of the potential sensor is proportional to a change in the sensitivity of the potential sensor if two grid voltages VG1, VG2 are respectively assumed to be -300(V), -700(V) and the difference DELTAV0 between the potentials V01, V02 electrostatically charged on the surface of the photosensitive drum is assumed to be a specified value. The difference DELTAV'S between the detected values of the potential sensor for the two grid voltages VG1=-300(V), VG2=-700(V) is detected and the ratio to the difference DELTAVS of the detected value under the ideal environmental conditions is determined. This ratio is determined as the correction factor A of the detected values of the potential sensor. The correction quantity DELTAVG of the grid voltages is thereafter determined by using this correction factor A and the max. light quantity of the laser beam outputted from a semiconductor laser is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for stabilizing an image in a digital color copying machine.

[0002]

2. Description of the Related Art In an electrophotographic digital color copying machine that performs color printing using density data of an original image read by an image scanner, it is an important issue to improve reproducibility of halftone images such as photographs. Has become.

One of the major factors affecting the density of reproduced images to be printed is the characteristics of the photoconductor and toner. The characteristics of the photoconductor and toner change due to environmental changes such as temperature and humidity inside the copying machine, and the amount of toner attached to the photoconductor changes during development. Generally, in an environment of high temperature and high humidity, the amount of toner adhered to the photosensitive member increases, the gradient of the gradation characteristic becomes large in the low density portion, and the reproduced image becomes dark. Further, in an environment of low temperature and low humidity, the amount of toner adhered to the photoconductor is reduced, the gradient of the gradation characteristics is reduced in the low density portion, and the reproduced image becomes thin.

In order to solve the problem that the density of the image reproduced on the copy paper changes due to changes in the environment and stabilize the density of the reproduced image, a general electrophotographic copying machine warms up when the power is turned on. After completion, an image stabilization process is performed to keep the maximum density level of the printed image constant. Image stabilization processing is performed in a digital color copying machine with four colors (C: cyan, M: magenta, Y: yellow,
K: black), that is, it is necessary to execute four times.

A general image stabilizing process will be briefly described below. Prior to laser exposure, a negative surface voltage V _O is applied to the photosensitive drum by a charging charger. The surface voltage V _O is measured by a potential sensor provided near the photosensitive drum. Next, an electrostatic latent image is formed without irradiating the photosensitive drum 41 with the laser beam having the maximum exposure amount set. Next, the electrostatic latent image is developed by the developing device set to the developing bias voltage V _B , and the reference toner image is formed. The toner adhesion amount of this toner image is detected by the AIDC sensor. If the voltage V _O and the developing device voltage V _B are changed according to the detected value of the toner adhering material, the maximum value of the toner adhering amount can be kept constant. Such image stabilization processing is called automatic density control (AIDC).

[0006]

In order to execute the above-mentioned image stabilization processing, it is necessary to form a reference toner image under a certain condition. Therefore, before the image stabilization processing is executed, the surface of the photosensitive drum 41 is formed. An appropriate condition is set by measuring the value of the potential V _O of the above with a potential sensor. For this image stabilization process, it is essential to maintain the detection accuracy of the potential sensor. As this potential sensor, there is a non-feedback type potential sensor shown in FIG. This potential sensor detects electric charges induced in the electrodes by periodically interrupting (chopping) the electric field on the surface of the photoconductor drum, amplifies this, detects the potential from the amplified waveform, and detects it. The value V _S
Is output. For example, if the surface potential of the photoconductor is constant,
It is desirable that the value of the voltage V _S detected by the potential sensor is always a constant value. However, the detection accuracy of this potential sensor depends on the amplitude of the chopper (voltage tuning fork) that periodically interrupts the electric field. The amplitude of this tuning fork changes with changes in the environment such as temperature and humidity. In this potential sensor, it becomes difficult to maintain the detection accuracy of the potential sensor when the change in the amplitude of the tuning fork portion becomes large.

FIG. 2 shows the output characteristics of the potential sensor when the environment changes with time. The solid line represents the output characteristics of the potential sensor under ideal environmental conditions (appropriate temperature and humidity). Also, the output characteristics when the environment such as temperature and humidity changes are shown by the dotted line. As shown, the sensitivity of the potential sensor 44 changes with changes in the environment over time.
That is, since the slope of the graph of the output characteristic changes with time with a certain width, even if the potential difference on the surface of the photoconductor drum is constant, the output value of the potential sensor may vary depending on the environmental conditions at the time of measurement. The difference ΔV _S ′ is smaller than ΔV _S when the potential sensor is under ideal environmental conditions. Of course, the reverse relationship may be established.

In order to solve this problem, as shown in FIG. 1B, a feedback type potential sensor for inputting a detection signal to a high voltage generator to generate a high voltage and feeding it back to a probe body of the potential sensor is provided. is there. This potential sensor makes the potential of the probe the same as the surface of the photosensitive drum,
By dividing this and outputting a detection value, an increase in detection error due to a change in environment is suppressed. However, since this potential sensor requires a high voltage generator, the cost is about three times as high as that of the non-feedback type potential sensor shown in FIG. Applicable only to

Further, there have been proposed some methods of correcting the sensitivity of the potential sensor by using a non-feedback type potential sensor.
For example, JP-A-60-103364 and JP-A-60-1
The method disclosed in 03364 includes means for switching the photosensitive drum to the grounded or non-grounded state, and applies a predetermined DC voltage to the non-grounded state to correct the sensitivity of the potential sensor.
In addition, in the method disclosed in Japanese Patent Laid-Open No. 1-107179,
The potential of the surface of the photoconductor drum is switched between the grounded state and the charged state of the low bias potential, and the sensitivity of the potential sensor is corrected.

However, these methods require a bias applying power source in addition to the components of the copying machine in order to perform the sensitivity correction of the potential sensor. Further, even if this power source is shared with an external power source, a device for switching the photosensitive drum to the grounded / non-grounded state is required. Therefore, the structure of the copying machine becomes complicated and the cost becomes high.

An object of the present invention is to provide a method for more easily correcting a change in detection sensitivity of a potential sensor due to a change in environmental conditions with time.

[0012]

According to a first aspect of the present invention, there is provided a method for correcting a sensitivity of a potential sensor, which is a digital color copying machine in which a potential sensor detects a surface potential of a photoconductor charged by the charger. By setting the grid voltage to V _G1 and detecting the surface potential of the charged photoconductor with a potential sensor, the detected value is taken as V _S1, and the grid voltage of the charger is V _G2 (where V _G1 <V _G2 by setting the a) the surface potential of the charged photoreceptor detected by the potential sensor, and the detected value as V _S2, the V _S1
Absolute value ΔV _S of the difference between V _S2 and V _S2 and the absolute value Δ of the difference between V _S1 'and V _S2 ' detected under ideal environmental conditions.
The sensitivity of the potential sensor is corrected based on V _S '.

According to a second aspect of the present invention, there is provided a method for correcting a sensitivity of a potential sensor according to the first aspect of the present invention, which is a semiconductor for exposing a photosensitive member when detecting V _S1 and V _S2. It is characterized in that the driving of the laser is stopped.

According to a third aspect of the present invention, there is provided a method for correcting the sensitivity of a potential sensor according to the first aspect, wherein the absolute value of the difference between V _S1 and V _S2 is ΔV _S.
V _S1 'and V _S2 ' detected under ideal environmental conditions
Difference in absolute value [Delta] V _S between 'on the basis of a, when correcting the sensitivity of the potential sensor, [Delta] V _S for [Delta] V _S' and a ratio of the potential sensor based on the change amount of the temperature and humidity around the potential sensor It is characterized in that a coefficient for correcting the sensitivity is obtained, and the sensitivity of the potential sensor is corrected by the obtained coefficient.

The sensitivity correction method of the potential sensor according to claim 4 is the sensitivity correction method of the potential sensor according to claim 3, the ratio of [Delta] V _S 'with respect to the [Delta] V _S, the temperature around the potential sensor and When the coefficient calculated based on the amount of change in humidity exceeds a predetermined range, a warning is given to the user.

According to a fifth aspect of the present invention, in the method of correcting the sensitivity of the potential sensor, the surface potential V _O of the photoconductor charged by the charging charger is measured by the potential sensor, and the reference toner image is formed based on the measurement result. In a digital color copying machine for setting conditions, the potential sensor detects the surface potential of the photoconductor when the grid voltage of the charger is set to V _G1 , and the detected value is set to V _S1, and the grid voltage of the charger is set to V _{S1. The} potential sensor detects the surface potential of the photoconductor when _G2 (however, V _G1 <V _G2 ) is set,
The detected value is V _S2, and the absolute value ΔV of the difference between V _S1 and V _{S2
Based on S} and the absolute value ΔV _S ′ of the difference between V _S1 'and V _S2 ' obtained under ideal environmental conditions, a coefficient for correcting the sensitivity of the potential sensor is calculated, and the potential sensor is calculated using the calculated coefficient. The sensitivity of is corrected, and the image forming condition of the reference toner image is corrected.

[0017]

According to the sensitivity correction method of the electric potential sensor described in claim 1, the difference ΔV _G between the values of the two grid voltages V _G1 and V _G2.
Is constant, the difference ΔV _O between the actual potentials V _O1 and V _O2 charged on the surface of the photoconductor drum is constant regardless of changes in the environment, but the potential charged on the surface of the photoconductor drum is constant. Difference ΔV _S between the detected values V _S1 and V _S2 of the potential sensor for measuring
Takes advantage of changes in the environment. First, the surface voltage when the grid voltages V _G1 and V _G2 are set is detected by the potential sensor, and the detected values are set to V _S1 and V _S2 . Then V _S1
Based on the absolute value [Delta] V _S 'of the difference between V _S1' and V _S2 'in the absolute value [Delta] V _S and an ideal environmental conditions of the difference between V _S2 and corrects the sensitivity of the potential sensor.

According to a second aspect of the present invention, there is provided a method of correcting the sensitivity of a potential sensor according to the first aspect of the present invention, wherein the sensitivity of the potential sensor is corrected by detecting the V _S1 and V _S2. The driving of the laser is stopped to prevent the surface potential from changing due to the irradiation of the semiconductor laser.

According to a third aspect of the present invention, there is provided a method for correcting the sensitivity of a potential sensor according to the first aspect, which further comprises the absolute value ΔV of the difference between V _S1 and V _S2.
Calculated and compared with the [Delta] V _S 'detected in _S and ideal environmental conditions, the coefficient for correcting the sensitivity of the potential sensor based on the change amount of the temperature and humidity around the potential sensor, the coefficient calculated potential Correct the sensor sensitivity.

According to a fourth aspect of the present invention, there is provided a method for correcting the sensitivity of a potential sensor according to the third aspect, wherein the absolute value ΔV _S of the difference between V _S1 and V _S2 is ideal. If the coefficient determined based on the comparison with ΔV _S 'detected under various environmental conditions and the amount of change in temperature and humidity around the potential sensor exceeds a predetermined range, for example, Warning is given using the display panel.

In the potential correction method according to the fifth aspect, first, the surface voltage when the grid voltages V _G1 and V _G2 are set is detected by the potential sensor, and the detected values are set to V _S1 and V _S2 . Then based on the absolute value [Delta] V _S 'of the difference between V _S1' and V _S2 'in the absolute value [Delta] V _S and an ideal environmental conditions of the difference between V _S1 and V _S2, corrects the sensitivity of the potential sensor The sensitivity of the potential sensor is corrected by the calculated coefficient, and the image forming conditions of the reference toner image such as the grid voltage V _G of the charging charger and the maximum light amount of the semiconductor laser that exposes the photosensitive member are corrected.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of detecting and correcting a potential sensor according to the present invention is the actual potential V _O1 charged on the surface of the photosensitive drum when the difference ΔV _G between the two grid voltages V _G1 and V _G2 is constant.
And the difference ΔV _O between V _O2 and V _O2 is constant irrespective of changes in the environment, but the difference ΔV _S between the detection values V _S1 and V _S2 of the potential sensor for measuring the potential charged on the surface of the photosensitive drum is It takes advantage of the fact that it changes in proportion to changes in the environment. In other words, there is 2
The difference ΔV _S between the detected values V _S1 and V _S2 of the potential sensor when the photosensitive drum is charged with two grid voltages V _G1 and V _G2 is the difference between the detected values (reference values) of the potential sensor under ideal environmental conditions. Then, the correction coefficient of the detection value is calculated by comparing with, and the detection value by the potential sensor is corrected based on the calculated correction coefficient. Less than,
A method of detecting and correcting a potential sensor will be described in the following order with reference to the accompanying drawings. (1) Configuration of copying machine (2) Image stabilization processing (3) Potential sensor sensitivity correction <3-1> First embodiment <3-2> Second embodiment

(1) Configuration of Copier FIG. 3 is a diagram showing the overall configuration of a digital color copier. The digital color copying machine is roughly divided into an image reader unit 100 that reads a document image and a copying unit 200 that reproduces the image data read by the image reader unit 100. In the image reader unit 100, the scanner 10 includes an exposure lamp 12 that irradiates a document, a rod lens array 13 that collects reflected light from the document, and a contact-type CCD color that converts the collected light into an electric signal. The image sensor 14 is provided. When reading a document image, the scanner 10 is driven by the motor 11 and moves in the direction of the arrow (sub-scanning direction) to scan the document placed on the platen 15. The image on the document surface illuminated by the exposure lamp 12 is photoelectrically converted by the image sensor 14. 3 of R, G, B obtained by the image sensor 14
The multi-valued electrical signal of color is processed by the read signal processing unit 20 to be yellow (Y), magenta (M), cyan (C), black (K).
Is converted into 8-bit gradation data and stored in the synchronization buffer memory 30.

Next, in the copying section 200, the printer head section 31 performs gradation correction (γ correction) on the input gradation data according to the gradation characteristics of the photoconductor, and then after the correction. The image data is D / A converted to generate a semiconductor laser drive signal, and the semiconductor laser is caused to emit light by this drive signal. This semiconductor laser is always in a weak light emitting state in order to improve the rising response at the time of light emission. The weak light emitted by the semiconductor laser at this time is called bias light.

The printer head unit 3 corresponding to the gradation data
The laser beam emitted from the laser beam No. 1 exposes the photosensitive drum 41, which is rotationally driven, via the reflecting mirror 37. The photosensitive drum 41 is irradiated by the eraser lamp 42 before being exposed for each copy, and is uniformly charged by the charging charger 43. When exposed in this state, an electrostatic latent image of the original is formed on the photosensitive drum 41. cyan,
Magenta, yellow, and black toner developing devices 45a to 45d
Only one of them is selected and the photosensitive drum 41
Develop the electrostatic latent image on top. The developed toner image is transferred by the transfer charger 46 onto the copy paper wound around the transfer drum 51.

Further, the non-feedback type potential sensor 44 according to the present invention is set at a position about 3 mm from the photosensitive drum 41 at the illustrated position. Further, when the toner adhesion amount is detected, the light from the pre-transfer eraser 55 is emitted from the AIDC sensor 21.
The pre-transfer eraser 55 is turned off to prevent the light from entering the zero light receiving portion.

Here, the rotational position of the transfer drum 51 is detected by a detector and a detection sensor (not shown) provided inside. The copying operation is controlled starting from this. Further, the photosensitive drum 41 and the transfer drum 51 are configured such that the diameters of the drums are an integer ratio (2: 1), and are connected and driven.
The photosensitive drum 41 and the transfer drum 51 are always in contact with each other at the same position. This eliminates the deviation when the toners are superposed.

The above printing process is repeated for four colors of yellow (Y), magenta (M), cyan (C) and black (K). At this time, the photosensitive drum 41,
The scanner 10 repeats the scanning operation in synchronization with the operation of the transfer drum 51. Thereafter, the copy paper is separated from the transfer drum 51 by operating the separation claw 7, and the toner image is fixed through the fixing device 48, and then the paper discharge tray 49.
Is ejected. The copy paper is fed from the paper cassette 50, and the chucking mechanism 52 on the transfer drum 51 chucks the front end of the copy paper to prevent misalignment during transfer.

Next, FIG. 4 shows an overall block diagram of a control system of the digital color copying machine according to the embodiment. The image reader unit 100 is controlled by the image reader control unit 101. The image reader control unit 101 uses the platen 15
The exposure lamp 12 is controlled via the drive I / O 103 by the position signal from the position detection switch 102 indicating the position of the upper original, and the scan motor driver 1 is controlled via the drive I / O 103 and the parallel I / O 104.
Control 05. The scan motor 11 is driven by the scan motor driver 105.

On the other hand, the image reader control unit 101 is connected to the image control unit 106 by a bus. The image control unit 106 is connected to each of the CCD color image sensor 14 and the image signal processing unit 20 by a bus.
The image signal from the image sensor 14 is input to the image signal processing unit 20 and processed.

The copying unit 200 is provided with a printer control unit 201 which controls general copying operations. A printer control unit 201 including a CPU includes a control ROM 202 storing a control program and various data (AID
The data ROM 203 in which the C table and the γ correction table are stored is connected. Printer control unit 201
Controls the printing operation based on the data in these ROMs.

The printer control unit 201 includes a potential sensor 4 for detecting the surface voltage of the photosensitive drum 41 and an AIDC sensor 210 for chemically detecting the toner adhesion amount of the reference toner image adhered to the surface of the photosensitive drum 41. , Developing device 45a
Analog signals from various sensors such as the ATDC sensor 211, the temperature sensor 212, and the humidity sensor 213 that detect the toner concentration within 45 d are input.

The printer control unit 201 includes a potential sensor 4
4, and other sensors 210 to 213, operation panel 2
21 and the data from the data ROM 203,
The copy control unit 231 and the display panel 232 are controlled according to the contents of the control ROM 202. Further, the printer control unit 2
01 is automatically operated by the AIDC sensor 210 at the time of image stabilization processing, or is operated by the user.
Concentration control is performed by inputting to 1. As a result, the printer control unit 201 causes the high voltage unit for generating V _G 24 that generates the grid voltage V _G of the charger 43 via the parallel I / O 241 and the drive I / O 242.
3, and the developing bias voltage V _B of the developing devices 45a to 45d
The high voltage unit 244 for generating V _{B is} generated.

The printer control unit 201 is also connected to the image signal processing unit 200 of the image reader unit 100 via an image data bus, and stores a γ correction table based on an image density signal transmitted via the image data bus. The semiconductor laser driver 263 is controlled via the drive I / O 261 and the parallel I / O 262 with reference to the data ROM 203 that is stored. Light emission of the semiconductor laser 264 is driven by the semiconductor laser driver 263. The gradation expression is executed by modulating the emission intensity of the semiconductor laser 264.

(2) Image Stabilization Process FIG. 5 shows the charging charger 43 around the photosensitive drum 41.
And the arrangement of the developing device (for example, 45r) is schematically shown. The photoconductor drum 41 has a charging charger 4 with a discharge voltage V _C.
3 are installed facing each other. A negative grid voltage V _G is applied to the grid of the charging charger 43 by the grid voltage generation unit 243. The surface voltage V _O is detected by a potential sensor 44 which is a surface electrometer. The capacitance C changes as the distance d between the potential sensor 44 and the measured surface of the photoconductor changes. Also, (the capacitance C is
It is proportional to the reciprocal of the distance d. ) The change in the distance d is also caused by a shake due to eccentricity when the photosensitive drum 41 rotates,
A large error occurs in the detection of the surface potential. Therefore, in the present embodiment, when the potential before image formation is detected, the potential of one rotation of the photosensitive drum is detected and the detected values are averaged to eliminate the influence of the shake of the photosensitive drum 41.

Before the laser exposure, the charging charger 4
3 causes the photosensitive drum 41 to have a negative surface voltage V
_O , and a negative bias voltage V _B satisfying the relationship of | V _B | <| V _O | is given to the roller of the developing device 45r by the developing bias generating unit 244. Therefore, the voltage on the sleeve surface of the developing device 45r is V _B.

By irradiating the laser beam with the maximum exposure amount, the surface voltage V _{O at} the laser beam irradiation position on the photoconductor drum 41.
The absolute value of is attenuated to zero and transits to the attenuation voltage V _i of the electrostatic latent image. The absolute value of the attenuation voltage V _i becomes a value close to zero in proportion to the increase in the exposure amount of the irradiated laser light. When the absolute value of the attenuation voltage V _i becomes lower than the absolute value of the developing bias voltage V _B , the toner (having a negative charge) carried to the sleeve surface of the developing device 45r adheres to the photosensitive drum 41. The difference between | V _O | and | V _B | is neither too large nor too small. In addition, the toner adhesion amount is the development voltage Δ
The larger V = | V _B −V _i |, the larger. On the other hand, the attenuation voltage V _i changes with the change of the surface voltage V _O even with the same exposure amount. Therefore, while maintaining the difference between V _O and V _B within a certain range, for example, while a difference in constant, if changing the surface voltage V _O and the developing device voltage V _B, V _B due to this and V
_Since the difference from _i changes, the toner adhesion amount on the photosensitive drum 41 can be changed, and the print density can be controlled.

Specifically, first, a reference toner image serving as a reference for density control is formed on the photoconductor drum 41, and the AIDC sensor 210 provided near the photoconductor drum 41 specularly reflects the reference toner image. Light and scattered reflected light are detected. Each detection signal detected by the AIDC sensor 210 is input to the printer control unit 201, where the toner adhesion amount is obtained from the difference between the two detection signals.
By changing the values of V _O and V _{B in accordance} with this detected value, the toner adhesion amount at the maximum density level can be kept constant. Therefore, the amount of adhered toner changes due to environmental changes such as humidity and temperature inside the main body of the copying machine, but by changing the values of V _O and V _B , the photosensitive drum 4 can be changed.
It is possible to keep the maximum amount of toner adhered onto the sheet 1, that is, the maximum density level printed on the copy paper constant. In this embodiment, one grid voltage V _{B is set} to one bias voltage V _B.
G a (≒ V _O) is associated, keeping the difference constant. The printer control unit 201 selects the value of (V _G , V _B ) from the AIDC table stored in the data ROM 203 based on the detection value of the AIDC sensor 210, and selects (V _G , V _B ).
_The γ correction table No. corresponding to the values of _G , V _B ) is specified. The printer control unit 201 reads the specified No. γ correction data from the γ correction table stored in the data ROM 203, and executes the γ correction based on this.

The following "Table 1" shows an example of the AIDC table stored in the data ROM 203. 0 shown in the leftmost column
The levels of ˜15 are determined based on the detection value of the AIDC sensor 210. The value of the bias voltage V _B varies from −220V to 40V in units of 40V corresponding to each level, and reaches −820V at maximum. The value of the grid voltage V _G is 1 than V _B
It is kept at a small value of 80V. Therefore, the grid voltage V _G
Changes from -400V to -1000V in 40V units. The amount of change in the value of (V _G , V _B ) is not limited to the above case, and may be determined according to the control accuracy.

[Table 1]

(3) Potential sensor sensitivity correction As described above, toner density detection by automatic density control is performed.
And control is based on the reference grid potential V_G, Development bias voltage
Rank V_BAnd the reference formed on the photoconductor by the exposure amount
Detects the toner adhesion amount of the toner image and responds to the detected value.
(V_G, V_B) Is changed to control the amount of toner adhesion.
Nau. At this time, the reference grid voltage V_GSurface charge against
The value of Vo is the sensitivity change or charging due to the environment of the photoconductor
It changes due to dirt on the charger. Therefore, the same V
_G, V_BAnd even if the exposure amount is given, ΔV = | V_B−
V_iSince | differs, the adhesion amount changes. Well
V _iIs the sensitivity change of the photoconductor due to the influence of environment, durability, etc.
It also changes from the change. Therefore, the same V_G, V_BAnd exposure
Even if the amount is given, | V_B-V_iBecause | is different
The amount of adhesion changes. Naturally, the surface potential Vo and the decay voltage
Rank V_iHowever, when both change, | V_B-V_i
| And the amount of adhered toner changes. These phenomena
Therefore, before the toner adhesion amount is detected by the image stabilization process,
Proposed condition: constant | V_B-V_iThe amount of adherence can be detected at
Absent. As a result, the accuracy of automatic density control at the maximum density level
Will be low.

For these reasons, in order to accurately perform the image stabilizing process by the automatic density control, it is necessary to make Vo and V _i constant when forming the reference toner image under any condition. Therefore, in this embodiment, the sensitivity of the potential sensor 44 is corrected prior to the image stabilization process. As a result, the surface potential Vo and the decay potential V _i are detected, the grid potential V _G and the maximum light amount are corrected, and the accuracy of the image stabilization process by the AIDC sensor 210 can be improved.

As described in the conventional example, FIG. 2 shows an example of changes in the output characteristics of the potential sensor 44 with respect to changes in the environment over time. The solid line represents the output characteristic of the potential sensor 44 under ideal environmental conditions (ideal temperature and humidity). In addition, the output characteristic when the environment changes is indicated by a dotted line. The sensitivity of the potential sensor 44 changes as the environment changes over time. As shown in the figure, since the slope of the output characteristic graph changes with time, the difference ΔV between the surface potentials V _O1 and V _O2 of the photoconductor is ΔV.
_O even when constant, the difference between the output value of the potential sensor 44, a different [Delta] V _S 'and [Delta] V _S of the reference characteristics of the potential sensor 44.

FIG. 6 shows an example of a modification of the charging characteristics of the photosensitive drum, which changes with the deterioration of the environment over time. The solid line represents the charging characteristics of the photoconductor under ideal environmental conditions, and the dotted line represents the charging characteristics when the environment changes. As shown in the figure, the charging characteristic of the photosensitive drum changes with time. That is, even if the grid voltage V _G of a constant value is applied, the surface potential V _O of the photosensitive drum becomes a low value due to deterioration over time.
However, as shown in the figure, the value of the electric potential charged on the surface deteriorates as a whole over time, and therefore the surface potential at the start of use with respect to the same difference ΔV _G between the grid electric potentials V _G1 and V _G2. Difference ΔV _O and the potential difference ΔV _O ′ at the time of deterioration are the same.

As described above, as understood from FIG. 2, when the difference ΔV _G between the two grid voltages V _G1 and V _G2 is a constant value,
The difference ΔV _O between the potentials V _O1 and V _O2 charged on the surface of the photoconductor drum is a constant value regardless of the degree of deterioration of the photoconductor drum. As understood from FIG. 6, when the difference ΔV _O between the potentials V _O1 and V _O2 charged on the surface of the photoconductor is a constant value, the difference ΔV between the detection values V _S1 and V _S2 of the potential sensor.
_S is proportional to the change in the sensitivity of the potential sensor 44. Therefore, the correction coefficient of the detected value is obtained by comparing with the difference between the detected values of the potential sensor 44 under the ideal environmental conditions with respect to the two grid voltages V _G1 and V _G2, and the potential sensor 44 is operated based on the obtained correction coefficient. The detected value can be corrected. The difference ΔV _G between the two grid voltages V _G1 and V _G2
The larger the value of, the smaller the error and the higher the accuracy.
Therefore, it is preferably set to 400V or higher. In this embodiment, the grid voltages V _G1 and V _G2 are each -300.
(V), -700 (V).

<3-1> First Example FIG. 7 shows the charging characteristics of the photosensitive drum. Typical V _G −
The V _O characteristic is shown by the solid line A. In addition, broken lines B and C indicate characteristic ranges due to variations such as machine differences and photoconductor differences. As shown in the figure, the slope of the characteristic straight line of the surface voltage V _O with respect to the grid voltage V _G does not change significantly depending on the change in the environment. Therefore, the following relationship of "Equation 1" is established.

[Equation 1] Further, as described above, when the difference ΔV _O between the potentials V _O1 and V _O2 charged on the surface of the photosensitive drum is a constant value, the difference ΔV _S between the detection values V _S1 and V _S2 of the potential sensor is It is proportional to the change in the sensitivity of the potential sensor 44. Therefore, in the first embodiment, the difference ΔV _S ′ between the detected values of the potential sensor 44 with respect to the two grid voltages V _G1 = −300 (V) and V _G2 = −700 (V) is detected, and ideal environmental conditions are detected. The ratio of the lower detection value to the difference ΔV _S is calculated and used as the correction coefficient A for the detection value of the potential sensor 44. Thereafter, the correction amount A is used to calculate the grid voltage correction amount ΔV _G, and the maximum amount of laser light output from the semiconductor laser 264 is corrected.

FIG. 8 shows the printer controller 20 of the first embodiment.
1 shows a processing flowchart of 1. First, when the user presses a print key (not shown) on the operation panel 221 (YES in step S100), the temperature and humidity at that time are determined by the temperature sensor 212 and the humidity sensor 213.
And the value detected when the copying operation was performed last time (step S101). If the temperature and humidity values detected this time are within the permissible range, the sensitivity correction process of the potential sensor 44 is not executed, and the image forming process of steps S119 and S120 is executed as it is.
In the present embodiment, the change in temperature and humidity within the above-mentioned allowable range means that the temperature is ± 5 ° C. and the humidity is approximately ± 10% RH. However, the above range changes depending on the performance of the potential sensor 44 and the like. If the detected values of temperature and humidity exceed the permissible range (YES in step S102),
The sensitivity correction process of the potential sensor 44 in steps S103 to S118 is executed. The semiconductor laser 264 is always in a weak light emitting state in order to improve the rising response at the time of light emission. The weak light emitted by the semiconductor laser 264 at this time is called bias light. When correcting the sensitivity of the potential sensor 44, the bias light is turned off in order to eliminate the influence of the sensitivity of the photoconductor (step S103). Next, V _G1 = −300 (V) and V _G2 = −700 (V) are set (step S104). Next, the P / C motor is turned on to rotate the photosensitive drum (step S105).
Next, the grid voltage V _G1 is applied, and the average value of the detection values detected by the potential sensor 44 during one rotation of the photosensitive drum is set as V _O1 . Further, the grid voltage V _G2 is applied to obtain the average value of the detection values detected by the potential sensor 44 while the photosensitive drum makes one rotation, and this is set as V _O2 (step S10).
6). The difference between V _O1 and V _O2 detected in step S106 is obtained, and this is defined as ΔV _S ′. Here, the potential sensor 4
4 detected under ideal environmental conditions V _O1 and V _O2
A value obtained by dividing the difference ΔV _O of the above by ΔV _O ′ is obtained as the correction coefficient A (step S107). Next, the above step S1
The bias light turned off in 03 is emitted (step S108).

Next, the value of the grid voltage V _G is corrected based on the detected value of the potential sensor 44 whose sensitivity has deteriorated. First, the grid voltage V _G3 = -800 is set (step S109). The potential V _O3 on the surface of the photosensitive drum to which the grid voltage V _G3 is applied is detected by the potential sensor 44 (step S110). Next, the detected potential V _O3 is multiplied by the correction coefficient A obtained in step S107 to obtain the actual surface potential V _O3 '(step S111). The correction amount ΔV _G of the grid voltage V _G corresponding to the actual surface potential V _O3 'is selected from the following "Table 2" (step S112),
It is added to the grid voltage V _G3 (step S113).

[Table 2]

Subsequently, the maximum light amount of the semiconductor laser 264 is corrected. First, the table No. in the following "Table 3".
5 is selected and the maximum light amount (1.15 mw / cm ² ) is set (step S114). Next, the semiconductor laser 264 is pressed to make it emit light (step S115). The potential sensor 44 detects the attenuation potential of the electrostatic latent image formed on the surface of the photosensitive drum by the irradiation of the laser light, and the average value of the detected values for one rotation of the photosensitive drum is set to V _i (step S116).
This detected value V _i is multiplied by the correction coefficient A obtained in step S107 to obtain the actual attenuation potential V _i ′ (step S117). From the actual value of the attenuation voltage V _i ', the optimum light amount is selected from the V _i correction table shown in "Table 3", and this light amount is set (step S118). The image forming process including the above-described image stabilizing process is executed with the grid voltage and the light emission amount of the semiconductor laser corrected by the above process (steps S119 and 120). By the above processing, the sensitivity of the potential sensor 44 is corrected without adding a dedicated power supply for bias application as in the conventional example, and the grid voltage and the correction conditions of the reference toner image of the maximum light amount of the semiconductor laser are corrected. It can be performed. As a result, the accuracy of the image stabilization process can be improved.

[Table 3]

<3-2> Second Embodiment The charging characteristic of the photosensitive drum shown in FIG. 7 is established under a constant environment (constant temperature and humidity). Charging characteristics of the actual photosensitive drum, as shown in FIG. 9, the slope of V _G -V _O linear changes in proportion to the increase of the humidity. Therefore,
In the second embodiment, after the sensitivity correction of the potential sensor 44 is executed by using the charging characteristic of the photosensitive drum 41 shown in FIG. 7, the detection error of the potential sensor 44 due to the humidity change is further based on this correction value. To correct. Semiconductor laser 264
Is always in a weak light emitting state in order to improve the rising response at the time of light emission. The weak light emitted by the semiconductor laser at this time is called bias light. FIG. 10 shows a processing flowchart of the printer control unit 201 of the second embodiment. When the print key on the operation panel (not shown) is pressed by the user (YES in step S200),
The bias light is turned off. (Step S20
0). Next, V _G1 = -300 (V), V _G2 = -700
It is set to (V) (step S202). Then P / C
The motor is turned on to rotate the photosensitive drum (step S203). Next, the grid voltage V _G1 is applied, and the average value of the detection values detected by the potential sensor 44 during one rotation of the photosensitive drum is set as V _O1 . The reason for obtaining the average value is to cope with the change in the detected value due to the change in the distance between the photosensitive drum and the potential sensor, as described above.
Further, the grid voltage V _G2 is applied, the average value of the detection values detected by the potential sensor 44 during one rotation of the photosensitive drum is obtained, and this is set as V _O2 (step S204). The difference between V _O1 and V _O2 detected in step S204 is obtained, and this is defined as ΔV _S ′. Here, a value obtained by dividing the difference ΔV _O between V _O1 and V _O2 detected by the potential sensor 44 under ideal environmental conditions by the above ΔV _O ′ is obtained as the correction coefficient A (step S205). The humidity around the photoconductor drum is calculated by the humidity sensor 213 (FIG. 4), and the correction coefficient B corresponding to the calculated humidity is selected with reference to the following "Table 4" (step S).
206). Note that the temperature sensor 21 is used to set the correction coefficient B.
The temperature determined by 2 (FIG. 4) may also be taken into account.

[Table 4]

Next, the correction coefficients A and B are multiplied, and the multiplied coefficient is set as the correction coefficient C (step S20).
7). When the absolute value of the correction coefficient C is 1.10 or more (YES in step S208), it is determined that the potential sensor 44 is abnormal, and a warning is displayed on the display panel 232 (FIG. 4). When the absolute value of the correction coefficient C is 1.10 or less (NO in step S208), or after the warning of the abnormality of the potential sensor 44 in step S209, the correction coefficient C is applied to V _O2 detected in step S204. The result of the combination and the multiplication is used as the actual surface potential V _O (step S210). From the “Table 2” shown above, the correction amount ΔV _G of the grid voltage V _G corresponding to the actual surface potential V _O
Is selected and added to the grid voltage V _G to correct the grid voltage (step S212).

Subsequently, the maximum light amount of the semiconductor laser is corrected. First, the table No. of "Table 3" shown above.
5 is selected and the maximum light amount (1.15 mw / cm ² ) is set (step S212). Next, the semiconductor laser is turned on to emit light (step S213). The potential sensor 44 detects the attenuation potential V _i of the electrostatic latent image formed on the surface of the photosensitive drum by the irradiation of the laser light (step S21).
4). The detected value V _i is multiplied by the correction coefficient C obtained in step S207 to obtain the actual attenuation potential V _i ′ (step S216). From this actual value of the attenuation voltage V _i ', the optimum light amount is selected from the V _i correction table shown in "Table 3", and this light amount is set (step S21).
7). The image forming process including the image stabilizing process described above is executed with the grid voltage corrected by the above process and the light emission amount of the semiconductor laser (steps S218 and S21).
9). By the above processing, it is possible to perform sensitivity correction of the potential sensor 44 in consideration of changes in the environment of temperature and humidity without adding a dedicated bias applying power source or the like as in the conventional example. This makes it possible to correct the grid voltage and the image forming conditions of the reference toner image of the maximum light amount of the semiconductor laser.

[0052]

The method of correcting the sensitivity of the potential sensor of the present invention is
The detection accuracy of the potential sensor 44 due to environmental conditions, dirt, and deterioration over time is corrected only by the functional parts of the copying machine body without using a special power source. Therefore, it is possible to inexpensively and accurately perform the sensitivity correction of the potential sensor without requiring a device dedicated to the sensitivity correction of the potential sensor.

[Brief description of drawings]

FIG. 1A shows the configuration of a non-feedback type potential sensor, and FIG. 1B shows the configuration of a feedback type potential sensor.

FIG. 2 is a diagram showing output characteristics of a potential sensor.

FIG. 3 is a diagram showing a configuration cross section of a digital color copying machine.

FIG. 4 is a diagram showing a control block of the copying machine shown in FIG.

FIG. 5 is a diagram showing a configuration around a photosensitive drum 41.

FIG. 6 is a diagram showing charging characteristics of a photoconductor.

FIG. 7 is a diagram showing charging characteristics of a photosensitive drum 41.

FIG. 8 is a diagram showing a processing flowchart of sensitivity correction of the potential sensor of the first embodiment.

FIG. 9 is a diagram showing charging characteristics of a photosensitive drum 41 due to a change in humidity.

FIG. 10 is a diagram showing a processing flowchart of sensitivity correction of the potential sensor of the second embodiment.

[Explanation of symbols]

44 ... the potential sensor 201 ... printer control unit 212 ... temperature sensor 213 ... humidity sensor 232 ... display panel 243 ... V _G generation unit 264 ... semiconductor laser

Claims (5)

[Claims] 1. A digital color copying machine in which a surface potential of a photoconductor charged by a charging charger is detected by a potential sensor, and a grid voltage of the charging charger is set to V _G1 to measure a surface potential of the charged photoconductor as a potential sensor. And the detected value is V _S1, and the grid voltage of the charger is V _G2 (where V _G1 <V
The surface potential of the charged set to have) the relationship between _G2 photoreceptor detected by the potential sensor, the detected value and V _S2, the absolute value [Delta] V _S of the difference between the V _S1 and V _S2, the ideal A sensitivity correction method for a potential sensor, characterized in that the sensitivity of the potential sensor is corrected based on the absolute value ΔV _S ′ of the difference between V _S1 'and V _S2 ' detected under typical environmental conditions. 2. The potential sensor sensitivity correction method according to claim 1, wherein when the V _S1 and V _S2 are detected, the driving of the semiconductor laser that exposes the photoconductor is stopped. Sensitivity correction method. 3. The method of correcting the sensitivity of a potential sensor according to claim 1, wherein the absolute value ΔV _S of the difference between V _S1 and V _S2 and V _S1 ′ and V detected under ideal environmental conditions. _S2, based on the 'absolute value [Delta] V _S of the difference between', when correcting the sensitivity of the potential sensor, the ratio of [Delta] V _S 'for [Delta] V _S, based on the amount of change in temperature and humidity around the potential sensor potential A method of correcting the sensitivity of a potential sensor, characterized in that a coefficient for correcting the sensitivity of the sensor is obtained, and the sensitivity of the potential sensor is corrected by the obtained coefficient. 4. A sensitivity correction method of the potential sensor according to claim 3, the ratio of [Delta] V _S 'with respect to the [Delta] V _S, the coefficients obtained on the basis of the amount of change in temperature and humidity around the potential sensor prescribed A method for correcting the sensitivity of a potential sensor, which warns the user when the value exceeds the range. 5. The surface potential V _O of charged photoreceptor measured by the potential sensor by a charger, the digital color copying machine to set the image forming condition of the reference toner image based on the measurement result, the electric charger The grid voltage is set to V _G1 and the surface potential of the charged photoconductor is detected by a potential sensor, the detected value is set to V _S1, and the grid voltage of the charging charger is set to V _G2 (where V _G1 <V
The surface potential of the set to have) the relationship between _G2 charged photoreceptor detected by the potential sensor, the detected value and V _S2, the absolute value [Delta] V _S of the difference between V _S1 and V _S2, ideal Absolute value Δ of the difference between V _S1 'and V _S2 ' determined under environmental conditions
Based on V _S ', a coefficient for correcting the sensitivity of the potential sensor is obtained, and the sensitivity of the potential sensor is corrected by the obtained coefficient,
A potential correction method characterized by correcting the image forming conditions of a reference toner image.