JPS5990871A - Controlling method of potential of electrophotographic sensitive body - Google Patents

Abstract

PURPOSE:To maintain the copying density in a black part even if a photosensitive body changes by forming beforehand the potential corresponding to a throughly non-exposed part and the potential corresponding to a part drawn with a pencil, etc. on the photosensitive body and controlling these potentials so as to attain target values. CONSTITUTION:Blank exposing light 12 is flickered to form the potential (potential in a dark part) V1 corresponding to a throughly non-exposed part and the potential V2 corresponding to an intermediate gradation part, such as writing with a pencil, on a drum 4. The potentials V1, V2 are measured with a potential sensor 8 and the current values of the primary electrostatic charge by a primary electrostatic charger 5 and the secondary electrostatic charge by a secondary electrostatic charger 6 are controlled to approximate the potentials to target values. A developing bias voltage is thereafter applied on a developer 9 so that the toner sticks more than substantially on the part of the intermediate gradation part having the target surface potential. A satisfactorily high copying density is provided to the dark part such as printing and typewritten characters and the copying density higher than a considerable level is provided to a gray part, such as characters drawn with a pencil, as well. As a result, the same copying density is maintained without decrease even if the photosensitive body is variously changed and the gray part is copied sharply, too.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for automatically controlling the potential of an electrostatic latent image on an electrophotographic photoreceptor in order to always obtain a stable image in electrophotography.

In electrophotography, in order to stabilize the image quality of the copied image, before the copying operation, a normal latent image formation cycle is used to create a model potential on the photoreceptor in completely unexposed areas (7th place in Dark City) and completely exposed areas. (bright area potential), these potentials are detected by a potential sensor, and after calculation based on these detection signals, the amount of charge on the photoreceptor is changed to obtain dark area %1 and bright area t4.
There is a known method for controlling the positions so that they approach their respective target values.

However, if the dark area %, level and bright area potential are controlled to predetermined values in this way, various exposure amount-potential curves (E=V curves) can be obtained depending on the sensitivity characteristics of the photoreceptor as shown in Figure 1. .

Therefore, the image quality of the intermediate gradation (gray part) differs for each.

In a photoreceptor potential control method for obtaining a stable 1IIIll image, the present invention particularly stabilizes the dark area potential corresponding to commonly used printing and type originals, and the potential corresponding to the intermediate gradation area of pencil originals. The characteristics of the photoconductor potential control method of the present invention are as follows.
In the photoreceptor method, which forms an electrostatic latent image by a process consisting of secondary charging, secondary charging, simultaneous image exposure, and full-surface exposure, the potential that builds up in completely unexposed areas before the start of the copying operation ( dark area potential) and intermediate gradation areas such as pencil-drawn areas (
A potential corresponding to a reflection density of 0.3 to 0.5) is formed on the photoreceptor as a model potential, and these potentials are detected by a potential sensor, and primary charging and secondary charging currents are applied so as to approach each target value. It is about controlling the value.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 is a schematic cross-sectional view of an electrophotographic copying machine embodying the present invention, in which conductive layers 1. On the photosensitive drum 4 consisting of the photosensitive layer 22 and the surface insulating layer 3, as it rotates in the direction of the arrow, -.
Secondary charger 5, secondary charging simultaneous flasher 6, full exposure lamp 7
This forms an electrostatic latent image. After the entire surface exposure run f7, a potential sensor 8 is provided to detect the potential of the photoreceptor after the entire surface is fogged. Reference numeral 9 indicates a display section, 1o indicates a transfer section, and 11 indicates a cleaning section. 12 is light for blank exposure.

Before the copying operation, the drum 4 is rotated in advance, a blank brightness lamp (not shown) is blinked, and the blank exposure light 12 is blinked, and a potential corresponding to a completely non-exposed area (dark area potential) V+ is set.
and intermediate gradation areas such as pencil writing (reflection density 0.3 to 0.
A potential V2 corresponding to 5) is created on the drum 4, measured by the potential sensor 8, and the primary charger 5 performs primary charging and secondary charger 7 in order to bring the obtained potentials V, V2 closer to their respective target values. 6 controls the current value of secondary charging.

When performing such a control operation, the potential V can be effectively adjusted by controlling the current value for primary charging, and the potential V2 can be effectively adjusted by controlling the current value for secondary charging.

After completing such control, a developing bias voltage is applied to the developing device 9 such that a considerable amount of toner adheres to the target surface potential portion of the intermediate gradation area. This makes it possible to achieve a sufficient copy density for dark areas such as printed and typed characters, and a considerably higher copy density for gray areas such as pencil-written characters.

In the above example, the target value of the dark potential V is set to +450v.
, there is still an intermediate gradation part potential V2 (equivalent to reflection density 0.3)
When I set it to +200■, set the lighting voltage to the blank exposure lamp to 17V, blinked it, and performed the above potential control, the copy density did not decrease even when the photoreceptor was changed to different types. , even gray areas could be clearly copied.

Note that the model potential V! on the photoreceptor is and v2, instead of blinking the blank exposure lamp, a gray area may be provided in the non-document area of the document table of the electrophotographic copying machine, and the document illumination rung may be made to blink. A black portion and a gray portion may be provided in the non-document portion of the document, and the document illumination lamp may be turned on to scan these black portions and gray portions.

As explained above, in the present invention, a potential corresponding to a completely unexposed area and a potential corresponding to a pencil-written area, etc. are formed as model potentials on the photoreceptor before the start of copying operation, and these potentials are respectively set as model potentials. By controlling the image density to match the target value, even if the photoconductor changes, the image density of the black part of the copy will be maintained sufficiently, and the gray part will also be reproduced with considerable density, making it possible to obtain clear copies. effective.

[Brief explanation of the drawing]

FIG. 1 is a sensitivity curve diagram of an electrophotographic photoreceptor, and FIG. 2 is a schematic sectional view showing an example of an electrophotographic copying machine implementing the method of the present invention. 4: Photoreceptor, 5: Secondary charger, 6: Secondary charging simultaneous image exposure device, 7: Full-surface exposure lamp, 8: Potential sensor, 9: Developing section, IO: Transfer section, 11: Cleaning section, 12 Ni blank light for exposure.

Claims (1)

[Claims] In an electrophotographic method in which an electrostatic latent image is formed by performing primary charging, secondary charging, simultaneous image exposure, and full-surface exposure on a photoreceptor, a completely neutralized potential is set as the model potential on the photoreceptor after full-surface exposure before the start of copying operation. A potential corresponding to an exposed area and a potential corresponding to an intermediate gradation area such as a pencil-written area are formed on the photoreceptor through the above process, and each of the model potentials described above is detected by a potential sensor and brought closer to each target value. A photoreceptor potential control method characterized by controlling the current values of secondary charging and secondary charging, respectively.