JPH11109688A - Potential control method for photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive potential control method of a photoreceptor by which a proper electrifying potential is always maintained. SOLUTION: This device is provided with an electrifier 11 providing an electrifying power source 18 varying an electrifying potential, a thermistor 17 being a temperature measurement means measuring the temperature of a photoreceptor, a surface potential sensor 16 being a surface potential measurement means measuring the surface potential of the photoreceptor at a gap between an electrifying position and a developing position and a control part 60 correcting the electrifying potential based on the temperature and the surface potential of the photoreceptor so that the potential of the photoreceptor is controlled. In this case, when the output of the sensor 16 is different from a reference value, the correction coefficient of the electrifying potential is corrected based on a difference between the temperature and the electrifying potential of the photoreceptor and the reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoconductor potential control method for controlling a voltage value of a charger for applying a charge to a photoconductor surface potential of an image forming apparatus using an electrophotographic technique.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus,
Maintaining a constant charge potential of the photoconductor is important for stably obtaining good image quality. Therefore, the charging potential before and after the developing position of the photoreceptor is measured by a surface potential sensor, and if the charging potential is shifted, the voltage value of the charger is corrected and controlled so as to be maintained at an appropriate charging potential. However, the photoreceptor has a temperature-dependent dark decay characteristic,
Since the surface potential measurement position is different from the development position, it has been difficult to maintain a constant surface potential at the development position. Therefore, a method of installing an electrometer at two locations and measuring the potential difference between the two points as the amount of dark attenuation is disclosed in Japanese Utility Model Laid-Open Publication No. Sho 62-195154. In addition, a method has been proposed in which individual photoconductors are classified according to rank in accordance with the magnitude of the temperature dependence, and the deviation of the charged potential due to the temperature dependence is accurately corrected.

[0003]

However, in the above-mentioned method, the number of steps required before shipping increases and the cost increases due to sorting by rank. Due to the large fatigue characteristics, there is a problem that the temperature dependency cannot be completely corrected even if the ranking is performed.

An object of the present invention is to solve the above-mentioned problems and to provide a method for controlling the potential of a photosensitive member which always maintains an appropriate charging potential at low cost.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a charging device having a charging power supply for varying a charging voltage, a temperature measuring device for measuring a temperature of a photoconductor, and a photoconductor between a charging position and a developing position. Surface potential measuring means for measuring surface potential,
An electrophotographic apparatus for controlling the surface potential of the photoconductor, comprising a control unit for correcting the charging potential from the photoconductor temperature and the photoconductor surface potential, wherein the output of the surface potential measurement unit is different from a reference value In this case, it is achieved by a photoconductor potential control method, wherein a correction coefficient of a charging voltage is corrected based on the temperature of the photoconductor and a difference between the reference value and the charging potential.

In a preferred embodiment of the present invention, the photosensitive member is made of amorphous silicon (a-Si) and the reference value is classified.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the present invention, an embodiment common to image forming apparatuses to which the present invention is applied will be described. The present invention is not limited to the embodiments described below.

FIG. 1 is a sectional view showing the structure of an example of an image forming apparatus to which the present invention is applied. This image forming apparatus includes an image signal processing unit S, a laser writing unit K, a control unit 60, and an image forming unit 100.

The image forming unit 100 includes a photosensitive drum 10 formed by applying a photosensitive member such as amorphous silicon (a-Si) or an organic semiconductor to the surface of a drum-shaped substrate made of a metal material such as aluminum. Photoconductor drum 1
0, a charger 11 as a charging unit, an image exposure unit 12 of a laser writing unit K as an image exposure unit, and a developing device 1
3. Transfer device 14, separator 15, and cleaning device 19
Are arranged in this order. Further, the image exposure unit 12
A surface potential sensor 16 serving as a surface potential measuring means for detecting the surface potential of the photosensitive drum 10 provided by the scorotron charger 11 between the developing device 13 and the rotation of the photosensitive drum 10 of the developing device 13 A thermistor 17, which is a temperature measuring means for measuring the temperature of the photoconductor, is disposed on the downstream side. The base of the photoconductor drum 10 is grounded and rotated clockwise by a photoconductor drive motor (not shown).

In an image reading apparatus separate from the present apparatus, image data of a document image read by an image pickup element or image data of an image edited by a computer is processed in an image signal processing section S, and the image data is processed. The signal is temporarily stored in a built-in memory.

The image forming section 10 is started by the start of image recording.
The photoconductor drive motor 0 rotates to rotate the photoconductor drum 10 clockwise, and at the same time, a charging voltage suitable for the temperature of the photoconductor drum 10 specified by the control of the control unit 60 is a variable voltage charging power supply. The application of a predetermined potential to the photosensitive drum 10 is started by the scorotron charger 11 operating via 18.

Next, the image signal is input from the memory to the laser writing section K via the laser drive circuit 28.

In the image forming unit 100, the image signal from the memory of the image signal processing unit S is controlled by the control unit 60.
Drive motor 21, polygon mirror 22, semiconductor laser 23, collimator 24, fθ via laser drive circuit 28
When input to the laser writing unit K composed of the lens 25 and the correction lenses 26 and 27, the image recording operation is started.

That is, with the rotation of the photosensitive drum 10, a scorotron charger (hereinafter simply referred to as a charger) 11 is provided.
And the surface potential of the photoreceptor is set to a predetermined potential. An electrostatic latent image corresponding to image data is formed on the uniformly charged photoconductor drum 10 by the laser beam L from the laser writing unit K. This electrostatic latent image is subjected to reversal development in a contact state by a magnetic brush of a two-component developer carried by a developing sleeve 130 which is a developer carrying member to which a developing bias voltage of the developing device 13 is applied, and a visible toner It becomes an image.

On the other hand, a paper supply unit (not shown) carries out the transfer papers P one by one from a loaded paper supply cassette by a carry-out roller, and feeds the paper toward an image transfer unit via a carry-out path and a carry-out roller. The fed transfer paper P is transferred to the photosensitive drum 1
Registration roller 44 which operates in synchronization with the toner image on
To the photosensitive drum 10. The toner image on the photoconductor drum 10 is transferred to the transfer paper P by the operation of the transfer device 14, and is separated from the photoconductor drum 10 by the charge removing operation of the separator 15.
5, is fed to the fixing device 50, and is fused and fixed by the heating roller 51 and the pressure roller 52.
Is discharged to a tray outside the apparatus.

The photoreceptor drum 10 continues to rotate, and the toner remaining on the surface thereof without being transferred is removed and cleaned by a cleaning blade 19A which is pressed against the surface of the photoreceptor drum 19, and then charged again by the charger 11. Then, the image forming process is started.

Under the control of the control unit 60, the surface potential sensor 16 measures the surface potential of the non-image portion between the toner images on the photosensitive drum 10 and sends the data to the control unit 60. The surface potential of the photosensitive drum 10 that is not affected by the laser beam L from the laser writing unit K can be detected.

Here, the reference value of the surface potential will be described. FIG. 3 is a graph showing a dark decay curve of the photoconductor. As can be seen from the figure, the surface potential decreases at a constant rate over time after the photoconductor is charged. In this embodiment, since the scorotron charging is employed, the surface potential of the photoconductor at the charging position is always constant. Therefore,
If the target surface potential at the developing position is set, the surface potential at the setting position of the surface potential sensor 16 necessary for achieving the target surface potential can be obtained. The obtained surface potential is used as a reference value. This reference value differs depending on the setting position of the surface potential sensor 16. For example, when the target surface potential at the development position is V0, the reference value of the surface potential at the position of the surface voltmeter from line A is V
A is required. Therefore, the setting position of the surface potential sensor 16 only needs to be between the charging position and the developing position, and the reference value of the surface potential differs depending on the setting position.

The dark decay curve based on the temperature change of the photoreceptor varies as shown by D, E and F in FIG. In the image forming apparatus of the present embodiment, the photosensitive drum 10
The dark decay curve based on the temperature change of the photoreceptor is measured in advance, and is ranked, for example, as shown in d, e, and f of FIG.
R in which several tables of the appropriate correction coefficient of the charging voltage and the reference value corresponding to the temperature of the photoconductor are recorded for each rank
An OM 60a is prepared. The control unit 60 has a built-in ROM 60a selected according to the rank of the dark decay characteristic of the photosensitive member of the photosensitive drum 10 attached to the image forming apparatus.

In this image forming apparatus, the table is read out from the ROM 60a at the time of the first image formation, and R
Transferred to AM60b. The controller 60 controls the charger 1 based on the surface potential and the temperature of the photoreceptor from the thermistor 17.
An appropriate charging voltage correction coefficient of 1 is selected from the table of the RAM 60b, the charging voltage is determined, and a signal is sent to the charging power supply 18. The charging power supply 18 adjusts a charging voltage applied to the charger 11 or controls on / off of the voltage in response to a signal from the control unit 60.

The photosensitive member is preferably made of amorphous silicon (a-Si) because of environmental problems.
In this case, it is preferable to perform the ranking of the reference values because the reference values vary.

Hereinafter, referring to the flowchart,
The operation of the present embodiment will be described.

FIG. 2 is a flowchart showing a method for controlling the charged potential of the photosensitive member in the image forming apparatus of the present embodiment. In the following description, S1, S2,... Indicate the numbers of the processing procedures (steps).

First, when image formation (copy) is started, a counter A for counting the number of copies is incremented by 1 in S1. Next, in S2, a correction coefficient of the charging voltage suitable for the temperature of the photosensitive drum 10 in the table called from the RAM 60b is selected, and a voltage based on the correction coefficient is applied to the charger 11 via the charging power supply 18. As a result, the photoconductor surface of the photoconductor drum 10 is charged to a uniform potential. In S3, the surface potential measured at the position of the surface potential sensor 16 and the temperature of the photosensitive drum 10 are input to the control unit 60. In S4, the control unit 60 determines whether the measured surface potential matches a reference value suitable for the photoconductor temperature. If they match, the process proceeds to S7 to perform image formation. In S8, it is determined whether or not the count number of the counter A has exceeded a preset count number M. If not, the routine returns and the next copy is continuously performed. If the counted number exceeds M, the counters A and B are cleared (S9) and the process ends. That is, the previously selected correction coefficient and reference value are maintained as they are.

If the surface potential does not match the reference value in S4, the process proceeds to S5, where the counter B is incremented by 1 and S
The program proceeds to 6, where it is determined whether the count of the counter B exceeds a preset count N. If not, the process proceeds to S7 to perform the above-described image formation.
If so, the process proceeds to S10, where the counters A and B are cleared and the process proceeds to S11, where the control unit 60 calculates the potential difference between the measured surface potential and the reference value. Next, in S12, the correction coefficient of the charging voltage and the reference value are corrected based on the potential difference, and after rewriting the table called from the RAM 60b, the process proceeds to S7 to perform image formation. The rewritten table is used for the subsequent image formation (copy).

As described above, the reference value is corrected only when the mismatch of the measured surface potential with the reference value occurs N times during M copies, so that the a-
Excessive correction can be prevented for a photoconductor such as Si.

[0027]

According to the present invention, the surface potential of the photoreceptor is constantly measured during use of the image forming apparatus, and the reference value and the charging potential of the photoreceptor are corrected based on the result, and the surface potential at the developing position is corrected. Is maintained at an appropriate and constant value, so that a stable image can always be formed. In addition, only one surface potential sensor needs to be used, and the measurement and ranking of the dark decay characteristics of the photosensitive member in advance can be simplified, and the characteristic change due to fatigue during use can be corrected. Therefore, it is possible to provide an excellent method for controlling the potential of the photosensitive member, which always maintains an appropriate charging potential at low cost.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a configuration of an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a flowchart showing an operation of the embodiment.

FIG. 3 is a graph showing a dark decay curve of a photoreceptor.

FIG. 4 is a graph showing a relationship between a temperature of a photoconductor and a dark decay curve.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger (charging unit) 12 image exposure unit 13 developing device 14 transfer unit 15 separator 16 surface potential sensor (surface potential measuring unit) 17 thermistor (temperature measuring unit) 18 charging power supply (variable) 19 cleaning Apparatus 60 Control unit 100 Image forming unit K Laser writing unit P Transfer paper S Image signal processing unit

Claims (2)

[Claims] 1. A charging device having a charging power supply for varying a charging voltage, a temperature measuring device for measuring a temperature of a photoconductor, and a surface potential measurement for measuring a surface potential of a photoconductor between a charging position and a developing position. An electrophotographic apparatus for controlling the surface potential of the photoconductor, comprising: a control unit that corrects the charging potential from the photoconductor temperature and the photoconductor surface potential. When the value is different from the value, a correction coefficient of a charging voltage is corrected based on a difference between the photoconductor temperature and the reference value and the charging potential. 2. The method according to claim 1, wherein the photosensitive member is made of amorphous silicon, and a reference value is ranked.