JPS60260071A - Controlling method of electrophotography - Google Patents

Abstract

PURPOSE:To always obtain a stable image by detecting a density of a test developed image which is different in potential difference between an electrostatic latent image and a developing means, comparing a variation rate calculated from said density with a standard variation rate set in advance, calculating the correct quantity of an image exposure, and executing the image exposure to a photosensitive body by its calculated exposure quantity. CONSTITUTION:A V-D curve in a state that an electrophotographic device is operated, namely, a V-D curve of a test image is derived. When an image of a test original picture 19a and 19b is formed in accordance with a sequence of a conventional method, a test image 17a and 17b whose density is different from each other are formed in a non-image part 16 provided on the way of the outside peripheral surface on a drum 1. An image density of the test image 17a and 17b is read by a sensor 18a and 18b, respectively, brought to digital conversion by an A/D22a and 22b, respectively, and read in a microcomputer 20. Subsequently, this density difference is derived, a variation rate M of the V-D curve is derived, and this variation rate M is compared with a reference variation rate stored in advance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to, for example, an electronic copying machine or a plain paper non-printing machine. This is an indication. In the figure, a drum l, which is a photoreceptor, is uniformly and primarily charged by a charger 2 while rotating in the direction of the arrow. The image of the document 0 on the document table 9 illuminated by the light source 4 is exposed by a moving optical system consisting of a first mirror 11, a lens 12, and a second mirror 13, and an electrostatic latent image is formed. This electrostatic latent image becomes a visible image with the developer supplied from the developing unit 5 by the developing sleeve 7 to which a bias voltage is applied. The visible image is transferred onto a transfer material P such as paper by a transfer charger 6. The transferred image is fixed on the transfer material P by a fixing device (not shown), and then the transfer material P is discharged outside the machine. In addition,
Toner remaining on the photosensitive drum l without being transferred is cleaned by a cleaning blade 8.

The density (D) of a developed image in such electrophotography is the surface potential (electrostatic latent image potential) on the photosensitive drum Vx The relationship between the development potential difference and the image density after development is as shown in Figure 2. The higher the potential difference (v) is, the higher the image density (D) becomes, resulting in a curve sloping upward to the right (hereinafter, a curve showing this relationship will be referred to as a V-0 curve).

By the way, the V-0 curve is from the standard curve p,
It changes like the curve q or r due to developer deterioration, environmental changes, etc. As a result, the density of a halftone image (halftone, for example, a gray area in an image) does not appear constant. There is an inconvenience that the change in the shape of the V-0 curve changes the reproducibility of originals including halftones such as photographs. Furthermore, so-called laser beam printers and the like that record images on electrophotography using a laser or the like that emits light based on a time-series modulated digital signal of the image also have inconveniences.

When an image is scratched with laser beam dots, the midtones of each dot are not expressed and are either white or black. However, the actual light intensity distribution of a laser beam has a Ligaussian distribution.

Therefore, it is also affected by the midtone part of the V-0 curve,
As the V-D polarity changes, the dot size and image density after development change.

[Object of the Invention] An object of the present invention is to provide an electrophotographic control method that eliminates the inconvenience that image reproducibility deteriorates due to changes in the shape of the V-0 curve and that allows stable images to be obtained at all times. It is something to do.

[Structure of the invention]

The present invention achieves this object by exposing a charged photosensitive member imagewise to form an electrostatic latent image, and developing the electrostatic latent image by a developing means to which a developing bias voltage is applied to obtain a visible image. In photography, the density of a test microscope image with a different potential difference between the electrostatic latent image and the developing means is detected, the rate of change in the density is calculated, and the calculated rate of change is compared with a standard rate of change set in advance. This control method is characterized in that an appropriate amount of image exposure is calculated, and the photoreceptor is exposed imagewise with the calculated exposure amount.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, each part that has already been explained will not be explained again. In the figure, there are the following parts in addition to the above. Original table 9
Test original pattern patterns 19a and 19b for forming a test image are arranged on the top in the width direction (in the paper depth direction in the figure).
is formed. Patterns 19a and 19b are both halftones, but are original images with different densities. Image density detection sensors 18a and 18b are arranged in the longitudinal direction of the photosensitive drum l (also in the depth direction of the paper).

As the sensors 18a and 18b, the original pattern 19a-
The test image 17a which was visualized on the drum surface of 19b.
'17b (see FIG. 5) is used. Preferably, the performance characteristics of sensors 18a and 18b are balanced. The surface voltmeter 27 is installed facing the surface of the drum 1 on the upstream side of the developing device 5 in the rotational direction of the drum, and measures the surface potential of the latent image. The central control system 14 includes a variable power source driver 2 for the light s4.
5. A drum clock 21 for controlling the control timing of the central control system 14 is connected.

A block diagram of the configuration around the control system 14 is shown in FIG. In the figure, the central control system 14 includes a microcomputer 20 and analog/digital converters (A/D) 22a-22.
b-24, and a digital-to-analog converter (D/A) 23. In addition to this, a circuit for sequence control of the electrophotographic apparatus is also incorporated, but since it is well known, a description thereof will be omitted.

A clock 21 generates clock pulses corresponding to the rotation of the photosensitive drum, and sends a synchronization signal to the microcomputer 20. The A/Ds 22a and 22b convert the detection signals of the image density sensors 18a and 18b, respectively, into digital signals and input them to the microcomputer 20. A/D 2
4 digitally converts the surface potential measured by the surface voltmeter 27 and inputs it to the microcomputer 20. D/A2
3 converts the digital output signal of the microcomputer 20 into an analog signal and drives the variable power supply driver 25.

The functions of the microcomputer 20 are as follows. ■Count the drum clock. - Outputs an output increase/decrease signal for the driver 25. ■Read the image density. (2) Calculate the rate of change of the V-0 curve from the image density. (2) Compare the rate of change with the rate of change of a standard V-0 curve stored in advance.

The program procedure for each of the above functions is shown in the flowchart of FIG. The operation of the control system 14 will be explained below according to this flowchart.

First, the -D curve in the operating state of the electrophotographic apparatus, that is, the V-0 curve of the test image is determined. Test original images 19a and 19b are created according to the usual sequence (not shown).
form an image. Then, test images 17a and 17b having different densities are formed in a non-image area 16 provided halfway along the outer peripheral surface of the drum 1, as shown in FIG. During this image formation, the timing is determined by reading the signal of the drum clock 21 at 101. The image densities of the test images 17a and 17b are read by sensors 18a and 1, 8b, respectively, converted into digital data by A/Ds 22a and 22b, and read into the microcomputer 20 at 102 (
PD1=a, PD2=b) - Next, calculate this concentration difference in 103 and calculate the rate of change of the V-0 curve (M=PD1-PO2
). This change rate M is compared with a reference change rate stored in advance. If it is greater than the first reference rate of change SM1 (M≧SMI) in step 104, a signal is issued to lower the voltage of the driver 25 in step 105. That is, the slope of the V-0 curve of the test microscope image is
If it is larger than the standard value (a trend like q in Figure 2),
It is determined that the image density in the area where the development potential difference is low is lowered due to toner deterioration or environmental changes, so the amount of light from the light source 4 is decreased to increase the development potential difference. Then, the second
It approaches the trend shown at p in the figure.

The situation during this time will be explained using FIGS. 6 and 7. 6th
The figure is a graph showing the relationship between the exposure amount E to the photoreceptor and the surface potential Vx. When the light intensity of the original exposure light source 4 is reduced,
The amount of exposure due to the light reflected from the bright portion of the document decreases from EL to EL', and the amount of exposure due to the halftone portion decreases from EM to EM'. Since the reflectance of dark areas is originally very low, the exposure amount ED hardly changes even if the amount of light from the light source decreases. As a result, the surface potential in the bright area goes from VL to VL, and the surface potential in the intermediate tone area goes from VM to VL.
to VM. As shown in FIG. 7, the development potential difference V increases from 2 to KI in bright areas and from 2 to 2 in intermediate/tone areas. 3 does not change the development potential difference in the dark area.

As a result, in Fig. 2, the image density Dl at 1 for the development potential difference is
changes to an image density D1' when the development potential difference is high,
The image density D2 at a development potential difference of 2 changes to an image density D2' at a development potential difference of 2rc. Since the V-0 curve has a steep slope at intermediate brightness, the density difference before and after the development potential difference is also large at intermediate brightness. Therefore, the shape of the V-0 curve is corrected and becomes like the curve p, which approaches the original V-D curve p.

If M<SM in the flowchart 104 of FIG. 4, then 106
If the second reference concentration is higher than 3M2 (M≦5M2), a signal to increase the voltage of the driver 25 is issued in step 107. In other words, when the slope of the V-0 curve of the test microscope image is smaller than the standard value (a trend like q in Figure 2)
, it is determined that the image density is high in the area where the development potential difference is low,
The amount of light from the light source 4 is increased and the development potential difference is controlled to decrease. Then, the trend approaches that shown in Figure 2 p.

When the target value of the rate of change M is SMo, the value of the development potential difference PVn due to the n-th control is PVn=PVn-
Apply feedback such that 1+a (M-3M□) (a: constant) and repeat until the calculated value of M becomes SM,>M>3M2.

When the rate of change M is a standard value (SMl>M>, 5M2), the amount of light from the light source 4 is not changed because the exposure amount is appropriate.

In the above embodiment, the density of the test image was detected on the photoreceptor, but the density may be detected in the test image before or after being transferred onto the transfer material and fixed. In that case, by forming a test image for detection on the edge of the transfer material, the present invention can be carried out without any problem to the recorded image.

Furthermore, the present invention is applicable not only to electronic copying machines but also to various applied equipment for electrophotography. For example, when applied to a laser beam printer, the developing potential difference can be adjusted by controlling the laser output. I can do it.

〔effect〕

As explained above, in electrophotography to which the control method of the present invention is applied, stable, high-quality printed images with good reproducibility are always obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an electrophotographic apparatus suitable for carrying out the present invention, Fig. 2 is a diagram explaining changes in the V-0 curve, and Fig. 3 is a schematic diagram of a control system suitable for carrying out the present invention. FIG. 4 is a flowchart showing the operating procedure, FIG. 5 is a perspective view of an example of a test image, and FIGS. 6 and 7 are diagrams explaining changes in surface potential. 1 is a photoreceptor, 2 is a charger, 4 is a light source, 7 is a developing sleeve, 14 is a control system, 17a-1'7b is a test microscope image, 1
8a1118b is an image density sensor, 20 is a microcomputer, 25 is a variable power driver, and 27 is a surface voltmeter.

Claims (1)

[Claims] (1) In electrophotography, a charged photoreceptor is imagewise exposed to form an electrostatic latent image, and the electrostatic latent image is developed by a developing means to which a developing bias voltage is applied to obtain a visible image. The density of a test microscope image with a different potential difference between the electrostatic latent image and the developing means is detected, the rate of change in density is calculated, and the calculated rate of change is compared with a preset standard rate of change to determine the image exposure. A control method characterized by calculating an appropriate amount of light and exposing the photoreceptor to image light using the calculated exposure amount.