JPS5815788B2 - Development electrode control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing electrode control device for an electrophotographic copying machine.

Electrophotographic copying machines use an automatic bias device that detects the residual potential of the photoconductor, that is, the surface potential of the exposed bright area of the photoconductor, and applies the optimal bias voltage to the developing electrode according to the output. I have something prepared.

This automatic bias device has been put to practical use, that is, the optimum bias voltage has been set, on the premise of copying general originals, that is, originals with information on a relatively dull background, such as white.

For example, line contrast ratio RL, area contrast ratio RA
However, it has been proposed that: I) rt: information reflection density of the original Dr2: reflection density of the white background of the original.

Furthermore, human visual sense tends to gain information by comparing with the background.

Therefore, in order to make better copies, it is more desirable to obtain information without the background than to increase the density of the information, that is, to copy only the information without the background.

However, in addition to general manuscripts, there are special manuscripts, which are (Al) A manuscript with light information on a light background (B) A manuscript with dark information on a dark background (q) A manuscript with information on a colored background ■ A manuscript with high density background It is classified as a manuscript with low concentration of information.

(The originals of q are often actively used to classify documents by color, and the originals of (A) to (q) have a small reflection density ratio between the background and the information.

When copying these special originals, the bias voltage described above is either too high or too low, making it difficult to make good copies.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks and provide a developing electrode control device that makes it possible to copy not only general originals but also special originals.

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, in an electrophotographic copying machine, a photoreceptor 11 is formed in the shape of a drum and is driven by a driving device at a constant speed in the direction of the arrow shown in the figure.

As this photoreceptor 11 rotates, it is sequentially charged by a charging device 12, an optical image from a document is exposed by an exposure device 13 to form an electrostatic latent image, which is developed by a developing device 14, and transferred to a transfer sheet by a transfer device 15. 16 and cleaned by a cleaning device 17.

After the transfer, the transfer paper 16 is fixed by a fixing device and discharged outside the machine as a copy.

The developing device 14 is equipped with a developing electrode 18, and the developing electrode 18 is made of an electrode plate placed facing the photoreceptor 11.

The developer 20 in the developer tank 19 is supplied by a pump between the photoreceptor 11, the developing electrode 18, and the detector 21, and develops the photoreceptor 11.

The detector 21 has a plurality of electrodes 21, -2 as shown in FIG.
13, each of which detects the surface potential of the photoreceptor 11.

The plurality of electrodes 211 to 213 are each connected to a diode 2.
21-223 to the voltage follower 230 input terminal, and the minimum of the output voltages of each electrode 211-213 is connected to the diode 22. ~223 and is applied to the voltage follower 23 as a residual potential detection force.

The voltage follower 23 is an amplifier with a small input current and high input impedance, and has an output terminal connected to a non-inverting input terminal of an operational amplifier 24 and an inverting input terminal of an operational amplifier 26 via an integrating circuit 25. It is connected to a negative power supply (-Vcc) via constant voltage diodes 27, 28 and a resistor 29 in series.

Also, the switch 30 is a constant voltage diode. An adjustment circuit 31 is connected in parallel with the voltage regulator 27 and the voltage regulator diodes 27 and 28, a resistor 29, and a switch 30.

The output terminals of the operational amplifiers 24 and 260 are connected to the displays 32 and 33, and the voltages Vref1°vref2 corresponding to the upper and lower limits of the optimum bias voltage range when copying a general original are inverted by the operational amplifier 240. input terminal and the non-inverting input terminal of operational amplifier 26.

Further, a connection point between the constant voltage diode 28 and the resistor 29 is connected to each fixed terminal of the switch 34 via constant voltage diodes 35 to 37, and is also connected to the developing electrode 18.

A movable contact piece of the switch 34 is grounded, and a limiter 38 is configured by the constant voltage diodes 35 to 37 and the switch 32.

The output of the voltage follower 23 is adjusted to an optimal bias voltage by an adjustment circuit 31 and applied to the developing electrode 18 through a limiter 38.

Therefore, toner adheres only to the portions of the photoreceptor 11 where the surface potential is higher than the bias voltage of the developing electrode 18, and the portions corresponding to the dark portions of the document are visualized.

Normally, the switch 30 is open and the adjustment circuit 31 adjusts the output of the voltage follower 23 to a bias voltage optimal for copying a typical original.

Therefore, general originals can be copied well.

Further, the operational amplifier 24 does not output an output when the output voltage of the voltage follower 23 is lower than the reference voltage Vrefl, that is, when copying a general original or the original (A) mentioned above.
The display 32 does not display any information.

However, when the output of the voltage follower 23 becomes higher than the reference voltage ref1, the operational amplifier 24 operates as described in (B).
When the originals of ~(D) are copied, the display 32 is driven to display (
B) Give a warning that it is a copy of the original manuscript.

If the original (D) is to be copied, the output of the adjustment circuit 31 is limited to the upper limit value by the limiter 38 and applied to the developing electrode 18, so that the n original is successfully copied.

Note that the constant voltage diodes 35 to 37 have different constant voltage values, and the upper limit value can be changed by the switch 34.

Furthermore, if the original is copied in (B) or (C), a good copy will not be automatically made.

Then, when the switch 30 is closed, the regulation circuit 31 regulates the voltage follower 23 to a lower voltage, (B) or (
C) The original is successfully copied.

Further, the output of the operational amplifier 23 is integrated by an integrating circuit 25,
When the output is higher than the reference voltage Vref2, that is, when copying the originals (B) to (D) or a general original, the display 33 outputted from the operational amplifier 26 does not display anything.

However, the output of the integrating circuit 25 is the reference voltage Vref2.
When the value is lower, that is, when copying the original (A), the operational amplifier 26 drives the display 33 to warn that the original (A) is being copied.

Therefore, the shutter member 39 in the exposure device 13 is operated to reduce the amount of exposure.

The photoreceptor 11 has a light attenuation characteristic as shown in FIG. 3, and the relationship between the size of the dark part of the document and the surface potential changes depending on the amount of exposure as shown in FIG. 4.

That is, when the exposure amount is reduced, the sensitivity of the photoreceptor 11 increases, and the surface potential of the photoreceptor 11 becomes higher, especially for dark areas of the document.

Therefore, the electrostatic latent image on the photoreceptor 11 has a greater contrast than the original, so that the original (A) can be copied well.

In this case, although the residual voltage of the photoreceptor 11 increases, the bias voltage of the developing electrode 18 also increases accordingly, and a copied image without the background can still be obtained.

Although the present invention has been described with reference to embodiments in which warnings and bias voltages are corrected for the manuscripts (A) to (D), one of (A) to p may be used if there is no practical problem. Warnings and corrections may be made only for such cases.

As described above, according to the present invention, in an electrophotographic copying machine, the bias voltage is corrected when it deviates from a predetermined range, so that even special originals can be copied optimally.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram of an example of an electrophotographic copying machine to which the present invention is applied, FIG. 2 is a circuit diagram of the same electrophotographic copying machine, and FIGS. 3 and 4 are for explaining the above electrophotographic copying machine. FIG. 11...Photoreceptor, 18...Development electrode,
21°21, ~213...Detector, 31...
...Adjustment circuit, 32.33...Display device, 38
...Limiter, 39...Shutter member.

Claims (1)

[Claims] 1. In an electrophotographic copying machine, an automatic bias device that detects the potential on a photoreceptor and applies a bias voltage to a developing electrode according to the output thereof, and a device that corrects the bias voltage when the bias voltage is out of a predetermined range. A developing electrode control device comprising: