JPH06258923A - Developing bias controller - Google Patents

Abstract

PURPOSE:To prevent fogging on a ground part when image procesing to give gradation to copying density is executed, to prevent the generation of BCO in developer and to stabillize highlight density by providing a means correcting the drift of measureed back ground potential accompanying image processing. CONSTITUTION:The potential difference between the back ground potential V of a photosensitive body 18 subjected to image processing and the back ground potential V of the photosensitive body 18 not subjected to image processing is previously obtained and the potential difference becomes the drift correcting quantity DELTAVHSET of the measured back ground potential. Then, the corrected back ground potential is obtained by adding the drift correcting quantity DELTAVHSET to the back ground potential V subjected to image processing while copying cycle is executed at measurement mode. Developing bias is controlled so that the difference between the developing bias potential VBIAS and the corrected back ground potential is held constant at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, and more particularly to bias control in a developing process of an electrophotographic apparatus.

[0002]

2. Description of the Related Art Generally, in a developing process of an electrophotographic apparatus, the development start threshold potential is changed in response to fluctuations in the background potential of a photoconductor to reproduce a low-density character original without background stains. The developing bias control is performed as.

Conventionally, as a method for detecting a characteristic change by a sensor and automatically controlling a developing bias, for example, as disclosed in Japanese Patent Publication No. 3-5583 and Japanese Patent Publication No. 3-68388, a photosensitive member is disclosed. Of controlling the potential difference between the bright part potential and the bias potential of the
As disclosed in Japanese Patent Publication No. 943, the maximum surface potential of the non-image area of the photosensitive member is detected in order to correct the characteristic deterioration of the photosensitive member due to the reduction of the film thickness of the photosensitive material, and the image is detected according to the maximum surface potential. It is known to correct the process condition correction amount. Further, generally, the potential difference V between the background potential V _H and the bias potential V _BIAS in the non-image area of the photoconductor is
_{By controlling CLEANING FIELD} (= V _H -V _BIAS ) at a constant level, it is possible to prevent fog on the background and to prevent BCO (Beads).
It is also known to prevent the occurrence of carryover and stabilize the highlight density.

[0004]

However, the above-mentioned conventional developing bias control is applied to an analog copying apparatus or a digital copying apparatus having no gradation image processing (analog screen generator, hereinafter referred to as ASG processing) with respect to copy density. However, the conventional developing bias control cannot be applied to the digital copying apparatus that performs this ASG processing. Here, the ASG process will be described. As shown in FIG. 4, the reproduction density characteristic with respect to the original density in the conventional analog copying apparatus or digital apparatus is as shown in FIG. 4, and the density change of the reproduced density D _OUT reproduced with respect to the density change of the original on the highlight side where the original density C _IN is low. Reproduction density D that is reproduced with respect to the density change of the document on the high density side where the document density C _IN is high.
The density change of _OUT tends to be large and reproduced too much. Therefore, it is necessary to give gradation characteristics as shown by a broken line in FIG. 5 to the reproduction density characteristics with respect to the original density so that the highlight side is easy to reproduce and the high density side is low in reproducibility.
The reproduction density characteristic with respect to the original density cannot be changed by the xerography in which the laser light for image writing is adjusted in 256 steps from OO level to FF level as shown in FIG. Therefore, the ASG process is a means for changing the gradation characteristic. As shown in FIG. 7, this ASG process is performed so that the high-concentration side does not turn on what is originally turned on by the laser.
The development potential is suppressed by inputting the G processing signal, and conversely, by inserting the ASG processing signal so that the laser on the highlight side is originally turned off, but the part is turned on, the development is facilitated and shown by the dotted line in FIG. Realizes gradation characteristics.

When the ASG process is performed in the copy mode, the resolution in the laser irradiation area is 200 or 400 dpi (dot per inc) as shown in FIG.
h) and since the average potential in the measurement area of about φ10 mm is used as the detection value in a normal potential detector, when the background potential is to be detected, the measurement value detected by the potential detector is essentially necessary. It is detected at a level lower than the background potential V _H, which is a portion not irradiated by the laser light. This potential state will be described with reference to the potential diagram of the background potential and the bias potential in FIG. When the background potential V _H is used as a reference, the bias potential V _BIAS is controlled so that the potential difference between the background potential V _{H and the} background potential V _H becomes a constant V _{CLEANING FIELD} and becomes the potential indicated by the broken line (FIG. 8). (A)). In contrast, the measured value V of the background potential detected by the potential detector 12 in the ASG process
_{When 00} is used as a reference, the bias potential V _BIAS is controlled so that the potential difference becomes a constant V _{CLEANING FIELD} with respect to the measured value V ₀₀ of the background potential, but the measured value V ₀₀ of the background potential is Background potential V _H
Since it is detected at a lower level, the bias potential V _BIAS has a potential difference V V with respect to the background potential V _H.
It cannot be a _{CLEANING FIELD} ((b) in Fig. 8).

Therefore, in the digital copying apparatus which performs the AGS process, since the background potential V _H includes an error, the conventional developing bias control for controlling the potential difference between the background potential V _H and the bias potential V _BIAS to be constant is performed. It cannot be applied. Therefore, the present invention eliminates the above-mentioned problems and prevents the fog on the background portion when the image processing (ASG processing) for imparting the gradation to the copy density is introduced, and the BCO of the developer. It is an object of the present invention to provide a developing bias control device that prevents generation and stabilizes highlight density.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is an image processing for controlling the potential of a photoconductor in order to reproduce the density of an original, which control is performed by the background potential and the development. In a digital copying apparatus that changes the developing bias so that the difference from the bias becomes constant, the developing bias control apparatus has means for correcting drift of the measured background potential due to image processing. Then, the drift correction means obtains a potential difference between a background potential when the image processing is performed and a background potential when the image processing is not performed, and determines the potential difference as a background potential during the image processing during the copying cycle. It is to be added to the electric potential. Further, the correction value by the drift correction means can be obtained in a mode other than the copy mode.

[0008]

According to the developing bias control device of the present invention, the potential difference between the background potential of the photoconductor when the image processing is passed and the background potential of the photoconductor when the image processing is not passed is previously obtained, and The potential difference is used as the drift correction amount of the measured background potential, and the corrected background potential is calculated by adding the drift correction amount to the background potential when the image processing is performed during the copy cycle in the copy mode. The developing bias is controlled so that the difference from the developing bias is always kept constant with respect to the generated background potential.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a developing bias controller of the present invention. Referring to FIG. 1, a developing bias control device according to the present invention includes a scanner unit A and an image processing unit B.
And an ROS optical section C and an image forming section D, the image signal read by the scanner section A is processed by an image processing section B, and then a laser beam is driven in the ROS optical section C to expose a photoconductor. , Development in the image forming section D,
Processing such as transfer is performed.

[Scanner Unit A] The scanner unit A reads the image of the original 1 illuminated by the exposure lamp 2 with the CCD 3 and amplifies the image signal thereof, converts it into a digital signal with an A / D converter, and then converts the density. Obtain the concentration signal. [Image processing unit B] The image processing unit B is the scanner unit A.
The color conversion and gradation correction processing are performed on the digital density signal from. The signal is converted to an analog signal by an A / D converter and then input to a comparator for ASG processing. An ASG processed signal from the ASG triangular wave generator is input to the other input terminal of the comparator. [ROS Optical Unit C] The ROS optical unit C irradiates the laser light emitted from the laser 7 onto the photoconductor of the image forming unit D via the optical system such as the polygon lens 8, the lens system 9 and the reflection mirror 10. This laser 7 is driven by the laser drive circuit 5 which receives the signal from the image processing unit B as an input signal. Further, the light amount of the laser driving circuit 5 is a laser light amount varying device 6 which receives a signal from the image forming section D as an input signal.
Adjusted by. [Image Forming Section D] The image forming section D includes a charging device 11, a potential device 12, a developing device 13, a transfer device 14, a temperature sensor 15, and a cleaner device 1, which are sequentially installed around the photoconductor 18.
6 and a charge eliminating lamp 17, a computing device 19, and a charge amount varying device 20. The photoconductor 18 is charged by the charging device 11, and then a latent image is formed by an exposure process based on an image signal by the laser light from the ROS optical section C. Next, toner is attached to the latent image in the developing device 13, and is transferred and fixed on the paper 21 in the transfer device 14. Thereafter, the cleaner 18 removes the toner from the photoconductor 18 and the charge removal lamp 17 removes the electric charge. Here, the arithmetic unit 19 includes the electrometer 12 and the temperature sensor 1.
The measurement signal from 5 is used as an input signal, the charge amount of the charging device 11 is adjusted through the charge amount varying device 20, and the bias potential V _BIAS of the developing device 13 is set.

Next, the setting of the bias potential V _BIAS of the developing bias controller of the present invention will be described with reference to the flow chart of FIG. 2 and FIG. Step S1: In the developing bias control, a method of controlling the difference ΔV _H between the background potential V _H and the developing bias V _BIAS to be constant is selected. Step S2: First, the background potential V _H is set to the photoconductor 18 by the charging device 11 to, for example, 650V. Step S3: In a state in which the ASG process is not performed, the background potential V _H set in the step S2 is measured by the electrometer 12 to obtain a measured background potential V _H1 when the ASG is not passed. In this measurement, for example, the average value of the background potential of the drum of the photoconductor 18 in one round can be used. This potential state is shown in the background potential diagram of FIG.

Step S4: Next, the process is switched to the ASG process. Step S5: In the state where the ASG process is performed, the background potential V set in the step S2.
_H is measured by the electrometer 12 to obtain the measured background potential V ₀₀ when passing through ASG. In this measurement, for example, the average value of the background potential of the drum of the photoconductor 18 in one round can be used. This potential state is shown in the background potential diagram of FIG. Step S6: From the measured background potential V _H1 when the ASG is not passed and the measured background potential V ₀₀ when the ASG is passed, obtained by the steps S4 and S5, the drift amount ΔV _{HSET of the} background potential due to the ASG. Ask for. This drift amount ΔV _HSET
Is calculated by the following equation. ΔV _HSET = V _H1 −V ₀₀ Step S7: Drift amount Δ found in step S6 in order to calculate the developing bias potential in the copy mode.
_Remember V _HSET . Step S8: Background potential V in copy mode
Detects ₀₀ (copy mode). In the copy mode, since the ASG process is normally performed, the background potential measured by the electrometer 12 becomes the measured background potential V ₀₀ when the ASG is passed, and this is referred to as the background potential V ₀₀ (copy mode).

Step S9: A corrected background potential V _H2 is obtained based on the measured background potential V ₀₀ (copy mode) obtained in step S8.
This background potential V _H2 is a drift amount Δ to the measured background potential V ₀₀ (copy mode) as shown in the following equation.
It is _determined by adding V _HSET . V _H2 = V ₀₀ (copy mode) + ΔV _HSET This potential state is shown in the background potential diagram of FIG. 3 (b). Step S10: A corrected developing bias potential V _BIAS is obtained based on the corrected background potential V _H2 obtained in the step S9. This developing bias potential V _BIAS is always stable by changing V _BIAS = V _{H2 −fixed} value (for example, 150 V) = V ₀₀ (copy mode) −V _{CLEANING FIELD} + ΔV _{HSET.
CLEANING FIELD} = _VH - _VBIAS is obtained.

Next, the steps S2 to S7
The time for _obtaining ΔV _{HSET of} is described. ΔV
_{Since HSET} needs to measure the background potential V _H when ASG is not passed, the time required in advance can be, for example, the setup cycle immediately after the power is turned on, or when the setup cycle is forcibly selected. , And can be performed at regular intervals using a timer. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0015]

As described above, according to the present invention,
In the case where the image processing that gives the gradation to the copy density is introduced, it is possible to obtain the effect of preventing the fog on the background, preventing the generation of BCO of the developer, and stabilizing the highlight density. You can

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a developing bias control device of the present invention.

FIG. 2 is a flowchart for setting a bias potential of the developing bias control device of the present invention.

FIG. 3 is a background potential diagram of the present invention.

FIG. 4 is a reproduction density characteristic diagram with respect to document density.

FIG. 5 is a reproduction density characteristic diagram with respect to document density.

FIG. 6 is a laser lighting range diagram.

FIG. 7 is an ASG processed signal diagram.

FIG. 8 is a potential diagram of a background potential and a bias potential.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Original document, 2 ... Exposure lamp, 3 ... CCD, 5 ... Laser drive circuit, 6 ... Laser light amount varying device, 7 ... Laser, 8 ... Polygon lens, 9 ... Lens system, 10 ... Reflection mirror, 11
... Charging device, 12 ... Potential device, 13 ... Developing device, 14 ...
Transfer device, 15 ... Temperature sensor, 16 ... Cleaner device, 1
7 ... Static elimination lamp, 18 ... Photoconductor, 19 ... Arithmetic unit, 20
Charge amount varying device, A ... Scanner unit, B ... Image processing unit, C ... ROS optical unit, D ... Image forming unit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location G03G 15/00 303 H04N 1/29 Z 9186-5C (72) Inventor Shunichiro Shishikura Hongo, Ebina, Kanagawa 2274 In Fuji Xerox Co., Ltd. (72) Inventor Satoshi Tomita 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Toru Yoshida 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A digital copying apparatus for image processing for controlling a potential of a photoconductor to reproduce an original density, wherein the control changes a developing bias so that a difference between a background potential and a developing bias becomes constant. 2. The developing bias control device according to claim 1, further comprising a unit that corrects a drift of the measurement background potential that accompanies the image processing. 2. The drift correction means previously obtains a potential difference between a background potential when the image processing is performed and a background potential when the image processing is not performed, and the potential difference is the image in a copying cycle. A method for adding to a background potential which has been processed.
The developing bias control device described. 3. The correction value by the drift correction means is
3. The method according to claim 1 or 2, further comprising means for determining in a mode other than the copy mode.
The developing bias control device described.