JPS63169672A - Potential control method for electrophotographic equipment - Google Patents

Abstract

PURPOSE:To accurately control the potential of a photosensitive body by controlling the discharging current of a primary electrostatic charger and the quantity of exposure of an exposure device and making the detection potential of a detection sensor larger than 1st and 2nd target potentials by 1st and 2nd correcting target potentials. CONSTITUTION:A potential sensor 4 detects the dark part potential VD of a photosensitive body 1 charged electrostatically by the electrostatic charging of a primary charger and a potential signal is inputted to a microcomputer (MC) 16 through a potential measuring circuit 14 and an A/D converter 15. The MC 16 finds variation DELTAI of the discharging current of an electrostatic charger 2 for obtaining the 1st correcting target potential which is larger by a 1st correcting potential than the 1st target potential stored in a storage circuit 17 by using VD, and sends it to a control circuit 20 through a D/A converter 18 to obtain the detection potential VD as the 1st correcting target potential through a high-voltage transformer 23. Then an exposure lamp 11 is turned on and a sensor 4 detects a light part potential VL. Similarly, the CM 16 finds variation of the voltage of the lamp 11 for setting the 2nd target potential as the 2nd correcting target potential and sets the potential VL as the 2nd correcting target potential through a control circuit 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a potential control method for an electrophotographic apparatus, and more particularly to a potential control method for controlling the potential of an image carrier (photoreceptor) to a predetermined potential.

[Prior Art] In an electrophotographic apparatus, the potential of an electrostatic latent image formed on a photoreceptor (image carrier) by exposure to light changes due to environmental fluctuations such as temperature and humidity, deterioration of the photoreceptor, long periods of rest, etc. Since the amount of toner that adheres to the electrostatic latent image varies depending on various conditions, the amount of toner that adheres to the electrostatic latent image during development using a developing device becomes unstable, resulting in uneven image quality of the copied image. Therefore, in order to maintain a constant image quality, it is necessary to keep the potential of the electrostatic latent image constant. Conventionally, this has been achieved by using a potential sensor to detect the potential of the photoreceptor charged by the discharge of the primary charger. This detected potential is set in advance at the first
Control 1i is used to control the discharge current of the primary charger so that the target potential is reached, and then a model electrostatic latent image is formed on the photoreceptor by exposure of the exposure device. A method has been implemented in which a potential is detected by a potential sensor, and the exposure of an exposure device is controlled by the control device so that the detected model potential becomes a preset second target potential.

[Problem to be solved by the invention] However, due to the structure of the electrophotographic apparatus, it is difficult to install the above-mentioned potential sensor at the same level as the developing device. It is installed near the axial end of the photoreceptor.

By the way, since the carrier mobility of the photoreceptor is small, due to variations in discharge current, etc., the potential at the end of the photoreceptor in the axial direction, where the potential sensor is installed, and the potential of the photoreceptor, which corresponds to the installation position of the developing device, may differ. If the potentials are not the same, therefore, the potential detected by the potential sensor is different from the potential of the photoconductor corresponding to the installation position of the developing device, and the carrier mobility of the photoconductor is less than 10-'V am'/see, the original When an electrostatic latent image corresponding to the dark part of the document is formed and when an electrostatic latent image corresponding to the bright part of the document is formed, the potential detected by the potential sensor and the photosensitive area at the position corresponding to the developing device are determined. As shown in Table 1, the magnitude of the difference with the body potential differs from IOV in the dark area to 30V in the light area.
It has been reported that it is difficult to accurately control the potential of the photoreceptor at a position corresponding to the developer.

Table 1 [Purpose] This invention was made in view of the above problems, and an object thereof is to provide a potential control method that can accurately control the potential of a photoreceptor at a position corresponding to a developing device. do.

[l of invention! [Summary] In order to achieve the above object, the present invention detects the potential of an image carrier charged by discharge of a primary charger, and controls the discharge current of the primary charger using the detected potential. A first correction target potential is set by increasing a first target potential set in advance by a first correction potential, and then a model electrostatic latent image corresponding to a white background portion of the document is formed on the image carrier by exposure of an exposure device. and detecting the model potential, and increasing the detected model potential by a second correction potential larger than the first correction potential from a preset second target potential by controlling the exposure amount of the exposure device. It was made to be a corrected target potential.

[Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows a schematic configuration diagram of an electrophotographic apparatus that implements the method of the present invention. A primary charger 2 for uniformly charging the photoreceptor is installed above the body l, and an original exposure lamp (first exposure device ff1) 1 for exposing the original lO is further above the primary charger 2.
1 is installed, and reflected light from the exposure of the document exposure lamp 11 is guided to the photoreceptor l by a mirror 12.13, so that an electrostatic latent image is formed on the photoreceptor l. 3. Blank exposure amount M (second exposure device) along the circumferential surface of the photoreceptor l on the downstream side of the primary charger 2. A developing sleeve 5 of a developing device (not shown) that develops the electrostatic latent image formed on the photoreceptor 1 to form a toner image is provided. In order to detect the potential of the photoreceptor 1, a potential sensor 4 is installed near the end of the circumferential surface of the photoreceptor 1 between the blank exposure lamp 3 and the developing sleeve 5. Further, below the photoreceptor l, there is a transfer charger (secondary charger) 6 that transfers the toner image to a transfer paper (not shown), and a transfer paper that comes into contact with the photoreceptor l from the photoreceptor l. A separation charger 7 for separation is provided. A cleaner 8 for removing toner adhering to the photoconductor l is installed downstream of the separation charger 7, and a pre-exposure lamp 9 for removing static from the photoconductor l is further downstream of the cleaner 8.
or installed. In addition, the device main body includes a potential measuring circuit (amplifier circuit) that receives the potential signal output from the potential sensor 4.
A control device 31 is provided which receives input via 14;
This control device 31 controls the exposure of the original exposure lamp 11, the discharge current of the primary charger 2, The discharge current of the transfer charger 6, the discharge current of the separation charger 7, and the potential of the developing sleeve 5 are controlled accordingly.

The control device 31 includes an A/D converter 15 that converts a potential signal input via the potential measuring circuit 14 into a digital quantity, and this A/D converter! A microcomputer 16 performs calculations necessary for each control based on the digital signals outputted from the microcomputer 16, and outputs control signals based on the calculations. Memory circuit 1 for storing data etc.
7, a D/A converter 18 that converts the control signal output from the microcomputer 16 into an analog quantity, and controls the lamp regulator 22 based on the analog signal output from the D/A converter 18. A light amount control circuit 19, a primary high voltage control circuit 20 that controls the primary high voltage transformer 23, a transfer control circuit 25 that controls the transfer high voltage transformer 27, and a separation control circuit 26 that controls the separation high voltage transformer 28. and a DC developing bias control circuit 21 that applies a DC voltage to the developing sleeve 5.

Next, a method for controlling the potential charged on the photoreceptor will be explained with reference to the flowchart shown in FIG.

When a main switch (not shown) is turned on, the photoreceptor l rotates and the primary charger 2 is discharged to charge the photoreceptor l. Then, in step l, the potential sensor 4 detects the potential VD of the charged photoreceptor l (corresponding to the dark part of the document: dark part potential) and outputs a potential signal according to the dark part potential VD.

This potential signal is transmitted to the potential measurement circuit 14 and the A/D converter 1.
5 to the microcomputer 16, and the microcomputer 16 calculates the dark potential VD from the input potential signal (end of measurement of the dark potential VD). In step 2, the dark potential VD and the memory circuit 17 are input to the microcomputer 16. The difference ΔV between the first target potential stored in advance and the first corrected target potential lowered by the first corrected potential (typically 10 V)
D, and from this difference ΔVD, the potential vO detected by the potential sensor 4 is set to the first correction target potential, that is, the developing sleeve 5
The amount of change ΔI in the discharge current of the primary charger 2 that makes the potential of the photoreceptor 1 corresponding to the position the first target potential is determined from the following equation (1).

ΔI=αΔVD −(1) However, α is a control coefficient.

Next, in step 3-, the microcomputer 16 outputs a signal of the calculated discharge current change Δ■, the D/A converter 18 converts the signal into an analog signal, and this analog signal is sent to the primary high voltage control circuit. Enter 20. This primary high voltage control circuit 20 controls the discharge current of the primary charger 2 via the primary high voltage transformer 23 based on the analog signal, and sets the potential VD detected by the potential sensor 4 to the first corrected target potential. . That is, the potential of the photoreceptor l corresponding to the position of the developing sleeve 5 is set to the first target potential. Then, in step 4, the number of times the above routine has passed is counted by a counter (not shown) in the microcomputer 16, and in step 5
It is determined whether the counted number is greater than or equal to N1, and if it is less than N1, the process returns to step 1, and the dark potential VD is measured again, and the above control is performed. If the number of zero passes is N or more, the model potential is detected. Proceed to step 6.

In step 6, the original exposure lamp 11 turns on and the original 1 is exposed.
A standard white plate (not shown) provided in advance outside the image area of 0 is exposed to light, and the reflected light generated by this exposure is reflected by mirror 12.
13 to the photoreceptor 1, and a model electrostatic latent image corresponding to the standard white plate is formed on the photoreceptor 1. Then, the potential sensor 4 detects the model potential VLI (light area potential) of the model electrostatic latent image and outputs a potential signal corresponding to the bright area potential VL, and this potential signal is transmitted to the potential measurement circuit 14 and the A /D
The bright area potential VL is input to the microcomputer 16 via the converter 15, and the microcomputer 16 determines the bright area potential VL from the input potential signal (end of measurement of the bright area potential VL). In step 7, the microcomputer 16 calculates the bright area potential VL determined above.

Then, from the second target potential stored in advance in the storage circuit 17, a second correction potential (typically 30V
) The difference ΔVL from the second corrected target potential which has been increased by a large amount is determined, and from this difference ΔVL, the potential VL detected by the potential sensor 4,
to the second target potential, that is, the voltage change ΔVll of the document exposure lamp 11 that brings the bright area potential VL of the electrostatic latent image formed at the position corresponding to the developing sleeve 5 to the second corrected target potential.
is obtained from the following equation (2).

AVII = J3AVL - (2) However, β
is the control coefficient.

Next, in step 8, the microcomputer 16 outputs a signal corresponding to the obtained voltage change of the document exposure lamp 11, and
The /A converter 18 converts the signal into an analog signal, and this analog signal is input to the light amount control circuit 19. This light amount control circuit 19 controls the lighting voltage (exposure amount) of the original exposure lamp 11 via the lamp regulator 22 based on the analog signal, and the potential VL detected by the potential sensor 4
, is set to the first corrected target potential, that is, the bright area potential VL of the electrostatic latent image formed at the position corresponding to the developing sleeve 5 is set to the second corrected target potential.
Set to target potential. Microcomputer 1 in step 9
A counter (not shown) in 6 counts the number of times the control is performed, and in step 10 it is determined whether the counted number is greater than or equal to N2.If it is less than or equal to N2, the process returns to step 6 and the model potential is measured again to perform the above control. If the number of times of control is N2 or more, the process proceeds to step 11 in which the bright area potential VL is measured.

In step 11, the microcomputer 16 or N2
The bright area potential VL2 of the electrostatic latent image formed by the controlled original exposure lamp 11 is measured in the same manner as in step 6, and further, in step 12, the microcomputer 16 sets this measured bright area potential VL2 to a predetermined potential. VBD(20
~300V) is added to the development bias potential VDc.
Calculate. This completes the series of routines. Then, after the I)C development bias control circuit 21 sets the potential of the development sleeve 5 to the calculated development bias potential VDc,
Electrophotographic devices perform conventional copying.

[Effects of the Invention] As explained above, the present invention detects the potential of the image bearing member charged by the discharge of the primary charger, and uses the detected potential to control the discharge current of the primary charger. A first correction target potential is set by lowering the first target potential set in advance by a first correction potential, and then a model electrostatic latent image corresponding to a white background portion of the document is formed on the image carrier by exposure of an exposure device. and detecting the model potential, and increasing the detected model potential by a second correction potential larger than the first correction potential from a preset second target potential by controlling the exposure amount of the exposure device. Since the correction target potential is set to the first potential which is set in advance by controlling the discharge current of the W control device or the primary charger and the exposure amount of the exposure device, the potential detected by the potential sensor 4 is set in advance. from the second target potential to the first
．． The first correction potential was increased by the second correction potential. Since the second correction target potential is set, the potential of the photoreceptor l at the position corresponding to the developing device is accurately adjusted to the first correction target potential. This has the effect that the second target potential can be set.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an electrophotographic apparatus that implements the method of the present invention, and FIG. 2 is a flow diagram showing the processing process of a microcomputer. l...Photoreceptor, 3...Blank exposure lamp, 4...
・Potential sensor, 11-... Original exposure lamp, 16...
Microcomputer, 31--control device.

Claims (1)

[Claims] The potential of the image carrier charged by the discharge of the primary charger is detected, and the detected potential is increased by a first correction potential from a preset first target potential by controlling the discharge current of the primary charger. After that, a model electrostatic latent image corresponding to the blank area of the document is formed on the image carrier by exposure of the exposure device, and the model potential is detected. Electrophotography, characterized in that by controlling the exposure amount of the exposure device, a second correction target potential is increased from a preset second target potential by a second correction potential that is larger than the first correction potential. Device potential control method.