JPH07319237A - Surface potential measuring instrument - Google Patents

Abstract

PURPOSE:To exactly calculate the output linear expression of a potential measuring means in spite of residual potential on a photoreceptor. CONSTITUTION:This instrument is provided with the potential measuring means 13 measuring the surface potential of the photoreceptor 11 by applying known voltage on the photoreceptor 11 from a high voltage power source 19, and a correction means 22 correcting the measured value of the measuring means 13 by detecting the secular offset value of the measuring means 13; and the surface potential of the photoreceptor 11 destaticized just before the known voltage is applied is used as an input factor when the correction means 22 calculates the corrected value of the measuring means 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface potential measuring device used in an image forming apparatus for electrophotographic processes such as copying machines and laser printers.

[0002]

2. Description of the Related Art An electrostatic latent image is formed by charging a photoreceptor and exposing it to an image, and the electrostatic latent image is developed into a visible image. In an image forming apparatus such as a copying machine or a laser printer, which performs an electrophotographic process of removing residual toner after transfer of a visible image on the body, paper dust by transfer paper, etc., and removing electricity by light irradiation, etc. It has already been attempted to obtain a good image by measuring the surface potential and controlling the amount of charge, the amount of exposure and the amount of development based on the results to control the surface potential and image density of the photoreceptor.

In an image forming apparatus which performs an electrophotographic process, a surface electrometer for measuring the surface potential of a photoconductor has a zero point and a gain variation due to environmental changes such as distance between a probe and the photoconductor and humidity and toner adhesion. It is likely to occur, and the surface potential of the photoconductor may not be accurately detected. Therefore, in an image forming apparatus that performs an electrophotographic process, a correction unit that corrects the output of the surface electrometer before measuring the surface potential of the photoconductor is provided, and a voltage known as the image forming apparatus is applied to the photoconductor by the correction unit. The surface potential of the photoconductor is measured with a surface electrometer, and the output value is used to calculate the correction value of the surface electrometer, which is used to measure the surface potential of the surface electrometer. There is used a surface potential measuring device for accurately determining the surface potential of the photoreceptor.

This surface potential measuring device applies _two different kinds of known voltages (y ₁ , y ₂ ) to the photoconductor at different timings, and the output value of the surface electrometer (x ₁ , X ₂ ) is used to calculate an output linear equation of the surface electrometer, and when the surface potential of the surface electrometer is measured by this output linear equation, an accurate photoconductor surface potential (y) is obtained from the measured value (x). There is an example. In this embodiment, the linear output equation of the surface electrometer is y = (y ₁ −y ₂ ) / (x ₁ −x ₂ ) · x + (x ₁ y ₂ −x ₂
y ₁₎ / become (x ₁ -x _2).

Various other methods for measuring the surface potential of the photosensitive member and calibrating it are disclosed in Japanese Patent Laid-Open No. 1-1.
07179, JP-A-56-95255, JP-A-58-21169, and JP-A-60-1033.
65, JP-A-60-103365, JP-A-61-56372, JP-A-62-44755, JP-A-63-133164, JP-A-4-17.
It is known from Japanese Patent No. 4871, Japanese Utility Model Laid-Open No. 4-31153, and the like.

[0006]

In an image forming apparatus for carrying out an electrophotographic process, an electrostatic latent image is formed by charging and imagewise exposing a photoconductor, and the electrostatic latent image is developed into a visible image. The visible image is transferred onto a recording paper and fixed, and the residual toner after transfer of the visible image on the photoconductor, paper dust by the transfer paper, etc. are cleaned and light is erased by light irradiation or the like. However,
Due to fatigue over time and film scratches on the charge transport layer, the photoconductor remains in a potential even after static elimination. This potential is called the residual potential, and the residual potential rises with time.

In the above-mentioned surface potential measuring device, when an output linear equation of the surface potential meter is to be obtained with the residual potential remaining on the photoconductor, the known voltages (y ₁ , y ₂ ) applied to the photoconductor are respectively calculated. The residual potential V _R of the photoconductor is added, and the actual potential of the photoconductor becomes (y ₁ + V _R , y ₂ + V _R ), and the output value of the surface electrometer shifts by the residual potential V _R. Is output.

However, since the photoconductor applied voltage calculation value when obtaining the output linear equation remains the fixed value (y ₁ , y ₂ ), the output linear equation is deviated from the true output linear equation, which is incorrect. The surface potential measurement value is output. This allows
Accurate control of the amount of charge, the amount of exposure and the amount of development may not be possible, and a good image may not be obtained. This point will be described in detail below.

Now, it is assumed that the output value x of the surface electrometer and the surface potential y of the photosensitive member have a relation of y = ax + b (1) a, b: constants.

When two different known voltages (y ₁ , y ₂ ) are applied to the photoconductor at different timings, the output voltage (x ₁ , x ₂ ) of the surface electrometer is expressed by the equation (1) as x ₁ = ( _{y 1 + V R -b) /} a ··· (2) is expressed by _{x 2 = (y 2 + V} R -b) / a ··· (3).

The slope α and the intercept β of the output linear equation to be obtained now can be obtained by solving the following simultaneous equations. y ₁ = αx ₁ + β (4) y ₂ = αx ₂ + β (5) Substituting equations (2) and (3) into equations (4) and (5), α and β
Solving each for, α = a β = b- V R becomes, but the slope alpha of the output linear equation by the residual potential V _R is not deviated from the true value, intercept beta deviates only residual potential V _R min. As a result, the charge amount, the exposure amount, and the development amount cannot be accurately controlled, and a good image may not be obtained.

According to the present invention, the output linear equation of the potential measuring means for measuring the surface potential of the photoconductor can be accurately calculated even if there is a residual potential on the photoconductor, and the surface potential of the photoconductor at the time of image formation can be calculated. It is an object of the present invention to provide a surface potential measuring device that can be accurately detected and can stably obtain good image quality.

[0013]

In order to achieve the above object, the invention according to claim 1 forms an image by measuring the surface potential of a photoreceptor and controlling the surface potential of the photoreceptor based on the result. In the apparatus, a potential measuring means for measuring a surface potential of the photoconductor by applying a known voltage to the photoconductor from a high voltage power supply, and a potential offset of the potential measuring means by detecting an offset amount of the potential measuring means over time. In a surface potential measuring device having a correction means for correcting a measured value, the charge-removed photoreceptor immediately before applying a known voltage as an input factor when the correction means calculates a correction value of the potential measuring means. The surface potential of is used.

According to a second aspect of the present invention, there is provided an image forming apparatus for measuring the surface potential of a photoconductor and controlling the surface potential of the photoconductor based on the result, which is a voltage known to the photoconductor from a high voltage power source. Surface potential measurement having potential measuring means for applying a voltage to measure the surface potential of the photoconductor and correcting means for detecting a time-dependent offset amount of the potential measuring means and correcting the measured value of the potential measuring means. In the apparatus, the correction means varies the known voltage applied to the photoconductor by using the surface potential measurement value of the photoconductor that has been neutralized.

[0015]

According to the present invention, the potential measuring means measures the surface potential of the photoconductor by applying a known voltage to the photoconductor from the high voltage power source. The correcting means detects the time-dependent offset amount of the potential measuring means, and corrects the measured value of the potential measuring means using the surface potential of the photoconductor that has been neutralized immediately before applying a known voltage.

According to the second aspect of the invention, the potential measuring means applies a known voltage from the high voltage power source to the photoconductor to measure the surface potential of the photoconductor. The correcting unit varies the known voltage applied to the photoconductor by using the surface potential measurement value of the photoconductor that has been neutralized, corrects the measured value of the potential measurement unit by detecting the offset amount of the potential measurement unit over time. To do.

[0017]

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 invention described in claim 1 is applied, and the photoconductor 11 is, for example, a photoconductor drum. Around the photosensitive drum 11, a potential measuring unit 1 including a charging device 12, an exposure device, and a surface electrometer.
3, a developing device 14, a transfer device 15, a separating device 16, a cleaning device 17, and a static eliminator 18 are arranged. High-voltage power supply 19 for applying a voltage to the back side of the photoconductor drum 11.
And the ground 21 by the switch 20 to the photosensitive drum 11
Is switched and connected to the back side of. The high-voltage power source 19 may be shared with a developing bias applying power source that applies a developing bias to the developing device 14, a charging device power source that drives the charging device 12, and the like.

At the time of image formation, the photosensitive drum 11 is connected to the ground 21 by the switch 20 and is rotationally driven by the driving unit, and is uniformly charged by the charging device 12, and then an electrostatic latent image is formed by image exposure by the exposure device. It is formed. The electrostatic latent image on the photosensitive drum 11 is developed by the developing device 14 into a visible image, which is transferred by the transfer device 15 to the recording paper fed from the paper feeding device to separate the recording paper by the separating device 16. Is separated from the photoconductor drum 11. A visible image is fixed on the recording paper by a fixing device, and the recording paper is discharged to the outside.

After the recording paper is separated, the photosensitive drum 11 is cleaned by the cleaning device 17 to remove residual toner, paper dust and the like due to the transfer paper, and the static eliminator 18 removes the charge to complete the image forming operation. The control unit 22 controls each unit of this example to start the above-mentioned image forming operation by a start command from the operation display device as shown in FIG. 2 and to continuously repeat the set number of sheets.

The surface potential meter 13 measures the surface potential of the photosensitive drum 11 between the charging device 12 and the developing device 14, and the control section 22 determines the surface potential value of the surface potential meter 13 during the image forming operation. It is corrected by the output linear formula y = αx + β of the electrometer 13, and at least one of the charging device power source, the exposure amount control unit, and the developing bias application power source is controlled according to the corrected surface potential measurement value. Surface after correcting at least one of the amount of charge of the photoconductor drum 11 by the charging device 12, the amount of exposure of the photoconductor drum 11 by the exposure device, and the amount of development (toner adhesion amount) of the photoconductor drum 11 by the developing device 14 Control according to the measured potential. In this case, α and β are values obtained in the surface electrometer correction mode, and the control unit 22 constitutes a correction means for correcting the surface potential measurement value of the surface electrometer 13.

After the image forming operation is completed, the control unit 22 starts a surface electrometer correction mode for calculating the output linear expression of the surface electrometer 13, and first turns on the static eliminator 18 to drive the photoconductor drum 11. When the photoconductor drum 11 is rotated, the photoconductor drum 11 is discharged by the static eliminator 18.
Measurement V _R of the surface potential (residual potential) was allowed to measure the surface potential meter 13 as temporal offset of the electrometer 13 surface electrometer 13 of the photosensitive drum 11 while but one rotation
Read.

Next, the control unit 22 switches the switch 20 to the high voltage power source 19 side and controls the high voltage power source 19 to transfer two different known voltages (y ₁ , y ₂ ) from the high voltage power source 19 to the photosensitive drum 11. One of the above voltages y ₁ is applied to the photosensitive drum 11. The surface potential meter 13 measures the surface potential of the photosensitive drum 11 to which the known voltage y ₁ is applied, and the control unit 22 controls the photosensitive drum 11 to which the known voltage y ₁ is applied.
The measured value v ₁ of the surface electrometer 13 for the surface potential of ₁ is read.

Next, the control unit 22 controls the high voltage power source 19 to supply the other voltage y ₂ of the _two different known voltages (y ₁ , y ₂ ) from the high voltage power source 19 to the photosensitive drum 11. It is applied to the photoconductor drum 11. The surface potential meter 13 measures the surface potential of the photosensitive drum 11 to which the known voltage y ₂ is applied, and the control unit 22 measures the surface potential of the surface potential of the photosensitive drum 11 to which the known voltage y ₂ is applied. The measured value v _{2 of} is read.

Next, the controller 22 controls the photoconductor drum 11
Applied voltage calculation value (y ₁ , y ₂ ) to the surface electrometer 13
Surface potential measurement values (x ₁ , x ₂ ) and residual potential measurement value V _R
Determined by solving the simultaneous equations of the slope α and intercept of the output linear equation of the surface electrometer _{13 β, y 1 -V R =} αx 1 + β y 2 -V R = αx 2 + β as operators. Next, the control unit 22 stops the photoconductor drum 11 to turn off the static eliminator 18, and ends the surface electrometer correction mode.

In this first example, the control unit 22 controls the correction value of the surface electrometer 13 (the inclination α of the output linear equation of the surface electrometer 13).
And the intercept β), the surface potential V _R of the photoconductor drum 11 that has been neutralized immediately before the known voltage (y ₁ , y ₂ ) is applied is used as the input factor. The difference between the voltage applied to the photosensitive drum 11 when correcting the potential measurement value and the applied voltage calculation value (y ₁ , y ₂ ) when obtaining the output linear equation of the surface electrometer 13 (photosensitive drum 11
Difference due to residual potential) can be eliminated, the surface potential of the photosensitive drum 11 at the time of image formation can be accurately detected, and good image quality can be obtained.

FIG. 3 shows an operation flow of the second example of the image forming apparatus to which the present invention is applied. The second example is an example to which the invention described in claim 2 is applied. In the second example, in the first example, the control unit 22 controls each unit of the second example to operate as shown in FIG.
That is, the control unit 22 starts the surface electrometer correction mode in which the output linear expression of the surface electrometer 13 is calculated after the image forming operation is completed, and first, the static eliminator 18 is turned on to rotate the photosensitive drum 11 to the drive unit. When the photosensitive drum 11 is driven, the static eliminator 18 eliminates the charge.
Surface potential (residual potential) of the photoconductor drum 11 during rotation
Is measured by the surface electrometer 13 as an offset amount of the surface electrometer 13, and the measured value V _R of the surface electrometer 13 is read.

Next, the control unit 22 switches the switch 20 to the high voltage power source 19 side and controls the high voltage power source 19 so that the high voltage power source 19 transfers two different known voltages (y ₁ , y ₂ ) to the photosensitive drum 11. ) One of the voltages y ₁ and the measured value V _R
And the difference (y ₁ −V _R ) from that is applied to the photosensitive drum 11.
The surface potential meter 13 measures the surface potential of the photosensitive drum 11 to which the voltage (y ₁ −V _R ) is applied, and the control unit 22 controls the voltage (y
₁ -V _R) reads the surface electrometer 13 readings v ₁ 'of relative surface potential of the photosensitive drum 11 applied.

Next, the control unit 22 controls the high-voltage power supply 19 so that the other voltage y _{2 of the two} different known voltages (y ₁ , y ₂ ) is supplied from the high-voltage power supply 19 to the photosensitive drum 11. The difference (y ₂ −V _R ) from the measured value V _R is applied to the photoconductor drum 11. The surface potential meter 13 measures the surface potential of the photosensitive drum 11 to which the voltage (y ₂ −V _R ) is applied, and the control unit 2
2 reads the measured value v ₂ ′ of the surface electrometer 13 with respect to the surface potential of the photosensitive drum 11 to which the voltage (y ₂ −V _R ) is applied.

Next, the control unit 22 measures the applied voltage to the photosensitive drum 11 (y ₁ , y ₂ ), the surface potential measurement value (x ₁ ', x ₂ ') of the surface potential meter 13, and the residual potential measurement. Value V
Output _R of surface electrometer 13 with _R as operator
And the intercept β are obtained by solving a simultaneous equation of y ₁ = αx ₁ ′ + β y ₂ = αx ₂ ′ + β. Next, the control unit 22 stops the photoconductor drum 11 to turn off the static eliminator 18, and ends the surface electrometer correction mode.

In this second example, the control unit 22 uses the surface potential measurement value V _R of the photosensitive drum 11 that has been neutralized when the output linear expression of the surface electrometer 13 is obtained, and
Known voltage (y ₁ , y ₂ ) to be applied to (y ₁ −
V _R ), (y ₂ −V _R ), so when calculating the voltage applied to the photosensitive drum 11 when correcting the surface potential measurement value of the surface electrometer 13 and the output linear expression of the surface electrometer 13 Can be eliminated (difference due to the residual potential of the photoconductor drum 11) and the applied voltage calculation value (y ₁ , y ₂ ) of the photoconductor drum 11, and the surface potential of the photoconductor drum 11 at the time of image formation can be accurately detected. As a result, good image quality can be obtained. The present invention is not limited to the above-described example, and can be similarly applied to a surface potential measuring device used in an image forming apparatus that performs an electrophotographic process such as a laser printer.

[0031]

As described above, according to the first aspect of the invention, an image forming apparatus for measuring the surface potential of a photoconductor and controlling the surface potential of the photoconductor based on the result is used as a high voltage power source. Potential measuring means for applying a known voltage to the photoconductor to measure the surface potential of the photoconductor, and detecting the offset amount with time of the potential measuring means to correct the measured value of the potential measuring means. In a surface potential measuring device having a correcting means, the surface potential of the discharged photoreceptor immediately before applying a known voltage is used as an input factor when the correcting means calculates a correction value of the potential measuring means. Therefore, the difference between the voltage applied to the photoconductor when correcting the surface potential measurement value of the potential measurement means and the applied voltage calculation value when obtaining the output linear expression of the potential measurement means (difference due to the residual potential of the photoconductor) Can be eliminated The surface potential of the photosensitive member during image formation to be able to accurately detect it is possible to obtain an excellent image quality.

According to a second aspect of the invention, an image forming apparatus for measuring the surface potential of a photoconductor and controlling the surface potential of the photoconductor based on the result is known from the high voltage power source to the photoconductor. A surface having potential measuring means for applying the voltage of 1 to measure the surface potential of the photoconductor and correcting means for detecting the time-dependent offset amount of the potential measuring means and correcting the measured value of the potential measuring means. In the potential measuring device, since the correcting means varies the known voltage applied to the photoconductor by using the surface potential measurement value of the photoconductor that has been neutralized,
Difference between the voltage applied to the photoconductor when correcting the surface potential measurement value of the potential measurement means and the applied voltage calculation value when obtaining the output linear expression of the potential measurement means (difference due to the residual potential of the photoconductor)
Can be eliminated, the surface potential of the photoconductor at the time of image formation can be accurately detected, and good image quality can be obtained.

[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 an operation flow of the first example.

FIG. 3 is a flowchart showing an operation flow of a second example of the image forming apparatus to which the invention is applied.

[Explanation of symbols]

 11 Photoreceptor 13 Surface Potential Meter 18 Static Eliminator 19 High Voltage Power Supply 20 Switch 21 Earth 22 Control Section

Claims (2)

[Claims] 1. An image forming apparatus for measuring the surface potential of a photoconductor and controlling the surface potential of the photoconductor based on the result, wherein a known voltage is applied to the photoconductor from a high-voltage power source. A surface potential measuring device having potential measuring means for measuring a surface potential of a body and correcting means for detecting a time-dependent offset amount of the potential measuring means to correct a measured value of the potential measuring means, Is used as an input factor when calculating a correction value of the potential measuring means, the surface potential of the photoconductor that has been neutralized immediately before applying a known voltage is used. 2. An image forming apparatus for measuring the surface potential of a photoconductor and controlling the surface potential of the photoconductor based on the result, wherein a known voltage is applied to the photoconductor from a high-voltage power source. A surface potential measuring device having potential measuring means for measuring a surface potential of a body and correcting means for detecting a time-dependent offset amount of the potential measuring means to correct a measured value of the potential measuring means, However, the known voltage applied to the photoconductor is changed by using the measured value of the surface potential of the photoconductor that has been neutralized.