JPS599052B2 - electrophotographic copying device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a rotatable photoreceptor 3 having an insulating layer 30 on its surface, a full-surface pre-exposure means 1, a primary charging means 4, and an upper part of the shield along the rotation circumference of the photoreceptor. an optically open secondary charging means 5, an image exposure means for exposing an original image onto a photoreceptor through the secondary charging means, and a full surface exposure means 6;
A developing means I, a transfer means, and a cleaning means 9 are arranged,
The gist of this is an electrophotographic copying device that is capable of reproducing multiple-copy images with uniform density when making continuous multiple-copy copies, and which enables multiple copies with uniform density, high contrast, and good resolution. Let be the desired effect.

As the number of times a photosensitive plate is used increases, its surface potential V decreases as shown in curve A in Figure 2, and the image density also decreases accordingly as shown in curve N in Figure 3. was confirmed.

As a result, when a photosensitive plate is used repeatedly, a difference occurs between the density of the first sheet and the density of several sheets, and there is a drawback that it is not possible to obtain an image of a constant density. On the other hand, in electrophotography, if a photosensitive plate is exposed to light before being charged, the surface potential of the photosensitive plate that has been pre-exposed will be lower than the surface potential of the photosensitive plate that has not been pre-exposed, and the image density will not decrease. widely known.

The present invention attempts to achieve the above-mentioned object by utilizing this pre-exposure effect, and is characterized in that the entire surface of the photosensitive plate is subjected to pre-exposure before the charging process during copying.

Furthermore, when a photosensitive plate is repeatedly used while being subjected to strong pre-exposure, the surface potential V of the photosensitive plate decreases as shown by the dotted line B in Figure 2.
Since the image density D also decreases as shown by the dotted line BI in Figure 3,
As the number of repetitions, that is, the number of copies increases, the amount of light for pre-exposure is weakened in conjunction with the degree of fatigue of the photosensitive plate. Alternatively, better results can be obtained by discontinuing the pre-exposure after the fatigue of the photosensitive plate reaches approximately equilibrium, and performing the pre-exposure again when the rest time of the photosensitive plate has passed approximately the fatigue recovery time. can get. As a means for reducing the amount of light for pre-exposure in accordance with the degree of fatigue of the photosensitive plate, for example, one step of resistance is added to the light source circuit each time the photosensitive plate is used repeatedly.

As the light source for pre-exposure, tungsten or a colored fluorescent light, which includes the characteristic absorption wavelength of the photosensitive plate, is suitable. Figure 1 illustrates a case where the amount of light for pre-exposure is weakened according to the degree of fatigue of the photosensitive plate.If a resistor 2 is added one step at a time to the circuit of light source 1 for each copy, the amount of light decreases. As a result, the degree of fatigue of the photosensitive plate due to pre-exposure is reduced, and the surface potential V of the photosensitive plate becomes approximately constant as shown by curve C in FIG. As a result, the image density D becomes uniform as shown in FIG. 3C/curve, and a large number of copied images can be made uniform with a simple configuration. After 4 to 50 repeated uses, the photoreceptor no longer gets fatigued and reaches an equilibrium state, so after that number of times (7 times in the illustrated example), open switch S to disconnect the light source circuit from the power source. However, it is hardly a problem.

Furthermore, if a tired photosensitive plate is given a rest (for example, about 1 minute to 1 hour), it will recover to approximately 90% of its state without being exposed to the previous exposure. Therefore, better results can be obtained by testing in advance the number of times the photosensitive plate used is repeatedly used to reach equilibrium and the rest time required to recover from fatigue, and by automatically controlling the light source for pre-exposure to blink. can get.

FIG. 4 shows an example of an automatic blinking circuit for a pre-exposure light source, in which a micro switch M is turned on momentarily and turned on immediately upon entering the copying operation.

When this micro switch M is closed, the timer T1 is activated, and a timer of, for example, 1 minute is started, and the contacts T1-1, T, -2, T of the timer T are set for this set time.
, -3 are closed, T and -4 are switched to the contact b side, timer T1 is self-maintained, light source 1 is turned on, and timer T is activated.
Capacitor C is charged. Timer T2 is the same T
1, it operates for a set time of 1 minute, for example, and is self-maintained by closing contact T, -1, and timer T,
The contact T, -2, which opens when the microswitch M1 is operated, has no relation to the operation of the microswitch M1.

Microswitch M is closed at the same time as microswitch M or with some delay for each copying operation, and its closing operates relay R1 to reset timer T.

That is, during continuous copying, the light source 1 is turned on by the timer T for the first minute, and the light source 1 is not turned on by the timer T for one minute after the last copy is completed. Furthermore, when the copying operation is completed in one go, the operation ends when the timer T1 elapses for one minute, and the timer contacts T, -
1 to T, -3 are open, and T1-4 is switched to the contact a side.

Then, the discharge of capacitor C activates relay R, and sets timer T. The timer T, operates for one minute from this time, and the light source 1 does not turn on during this time. That is, 1
If the copying operation is performed within minutes, the micro switch M,
With this operation, relay R is activated and timer T is reset. On the other hand, the timer T, does not operate because the contact T, -2 is open, and the light source 1 will not turn on for one minute thereafter. When the copying operation starts after the operation setting time of timer T has elapsed, timer T has already become inactive and returned to its initial state, so micro switch M and contact T, -2 are activated.
The timer T1 is energized through the timer T1, and when the timer T1 is activated, the contact T1-2 is closed and the light source 1 is turned on.

Note that the circuit shown by the dotted line is used when the copying operation is not performed for a long time, so it turns on and off the contact 1-1 at intervals of, for example, 1 minute, and turns on the light source 1 regardless of the timers T1 and T. be.

When timer T, is operating, timer T, does not operate at contact T, -3, which is opened by its operation.

Further, a capacitor charging/discharging circuit or a transistor circuit can be used as the operating circuit for the timers T, , T, , T. The set times of the timers T, , T, , T, can be arbitrarily selected depending on the characteristics of the photosensitive plate used. 1st
The figure shows an example of an apparatus for implementing the present invention, in which 3 is a drum-type photosensitive plate having a three-layer structure in which a support layer 3a, a photoconductive layer 3b, and an insulating layer 3c are stacked, respectively; 4 is a primary charger; 5 is a secondary charger for simultaneous image exposure, 6 is a light source for full-surface exposure, T is a developer,
8 is a transfer material, 9 is a cleaning device, 10 is a projection lens,
Reference numeral 11 indicates a transfer bias electrode, and between the cleaning device 9 and the primary charger 4, a pre-exposure process is applied to the entire surface of the photosensitive plate of the present invention.

Next, examples of the present invention will be described.

Example 1 First time using CdS photosensitive plate 10 0 0 1ux1
An image was created by weakening the light in a linear manner so that the 0th time was 1ux, and it was possible to obtain an image with a single line density.

Example 2 Using the same photosensitive plate as in Example 1, by applying 100 ux of light only the first time and not applying light from the second time onwards, images that were repeatedly copied 10 times had a uniform density. Obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electrophotographic copying apparatus embodying the present invention;
2 and 3 are characteristic diagrams of the photosensitive plate surface potential and image density with respect to the number of repetitions, that is, the number of copies, and FIG. 4 is a circuit diagram for controlling the flickering of the light source that fatigues the photosensitive member.

Claims (1)

[Scope of Claims] 1. A rotatable photoreceptor having an insulating layer on its surface, a full-surface pre-exposure means that causes optical fatigue on the photoreceptor along the circumference of the photoreceptor, a primary charging means, and an optical shield on the upper part of the photoreceptor. A secondary charging means that is opened to the outside, an image exposure means for exposing an original image to the photoreceptor through the secondary charging means, an entire surface exposure means, a developing means, a transfer means, and a cleaning means are arranged, and a large number of continuous charging means are provided. An electrophotographic copying apparatus capable of reproducing a plurality of copies of uniform density images by turning on the entire surface pre-exposure means at least in the first copying process when copying a number of copies. 2. The electrophotographic copying apparatus according to claim 1, wherein the entire surface pre-exposure means includes a light amount variable means that gradually weakens the exposure amount for each copying cycle.