JPH0248899B2 - KANKOTAINOTAIDENSEIGYOSOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charge control device for a photoreceptor in a copying machine.

A conventional device of this type will be explained with reference to FIG. Light emitted from a light source 1 hits a platen 2, and the reflected light passes through an optical system consisting of mirrors 3a, 3b, 3d and a lens 3c, and forms an image on a photoreceptor 4. Around the photoreceptor 4, corotrons and developing machines 5 used for charging, transfer, separation, static elimination, etc. are arranged. An electrostatic potential sensor 7 for detecting the charging of the photoreceptor 4 is provided after the corona discharger such as the charging corotron 6, that is, at a rear position with respect to the rotational direction of the photoreceptor 4.

8 is a switch for detecting the start of forward movement of the optical system during copying, and 9 is a switch for detecting the end of forward movement of the optical system.

In an electrophotographic copying machine having such components, the photoreceptor 4 is generally charged by applying a high voltage (about 5 to 8 KV) to a corona discharger to cause corona discharge. The level of this charge fluctuates depending on the environment and deterioration of the corona discharger over time. Therefore, the potential of the photoconductor 4 is detected by an electrostatic level sensor 7 installed after the corona discharger, and the photoconductor 4 is charged by feedback control to a high-voltage power source for discharging (not shown). The practice is to keep the position constant.

However, electrostatic position sensors are sensitive to the distance between the sensor and the object to be measured (in this case, the photoreceptor). Furthermore, since the copying device has a driving section, it constantly vibrates, and the vibrations are particularly large when the optical system is reciprocating. As a result, the distance between the sensor and the photoreceptor also oscillates due to the shaking of the copying machine body, and the output of the sensor is not flat as shown in FIG.

Note that FIG. 2a shows time in the horizontal direction and sensor output in the vertical direction. Also, b in the same figure shows the second
In the enlarged view of a part of Figure A, t ₀ is the time required for one copy (i.e., one copy cycle), t ₁ is the time required for the optical system to move forward, and t ₂ is the time required for the optical system to move backward. show.

As is clear from the above, the fluctuation of the sensor output during one copying cycle is large, so if this output is used to feedback-control the high-voltage power supply for discharging, the photoreceptor potential will also fluctuate following the vibration of the copying machine. There was a drawback. Furthermore, when attempting to remove the vibration component using a filter, there is a drawback that tracking of actual charge level fluctuations is delayed.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-described drawbacks of the prior art and to correctly control the photoreceptor potential by eliminating error components caused by vibrations in the potential sensor output due to mechanical vibrations.

First, the principle of the present invention will be explained. Analysis of FIG. 2b shows that the largest output vibration of the electrostatic potential sensor during one copying cycle t ₀ occurs when the optical system changes back and forth. In addition, in copying machines, in order to prevent disturbance of the latent image formed on the photoreceptor, care is generally taken to minimize mechanical vibration during forward movement of the optical system _t1 .
It can be seen that the output vibration of the potential sensor is small. Therefore, if the potential sensor output is sampled only when the optical system is moving forward, and the high-voltage power supply of the photoreceptor charging corona discharger is controlled based on this data, the potential can be controlled correctly and stably.

The present invention has been made in accordance with such a principle, and one embodiment of the present invention will be explained with reference to FIG.

The output of an electrostatic potential sensor 7 placed after the charging corotron is sent to a buffer 10. The buffer 10 performs impedance matching and the like, and the output of the buffer 10 is sent to the switch 11.

On the other hand, a forward movement start signal detected by the switch 8 (see FIG. 1) which detects the start of the forward movement of the optical system is input to the copying machine sequence controller 12. A timer device 12a is provided in the copying machine sequence controller 12, and upon receiving a forward movement start signal from the switch 8, the timer device 12a outputs, for example, a high level output for a certain period of time after a certain period of time. Therefore, after receiving the forward movement start signal, the timer device 12a outputs a high-level signal after a certain period of time when the forward movement of the optical system is stable, and then the forward movement of the optical system starts. If the switch 11 is designed so that it falls to a low level shortly before the timer ends, and the switch 11 is controlled by the output signal of the timer device 12a, it is possible to pick up only the stable sensor output when the optical system is moving forward.

The stable and correct sensor outputs selected in this manner enter the sample and hold circuit 13 and are held. This held value is input to the copying machine sequence controller 12, and the difference from the previously input target value is calculated by the subtraction circuit 12b.
It is calculated by The value calculated by the subtraction circuit 12b,
That is, the output of the subtraction circuit 12b becomes a control signal for the high voltage power supply 14.

In the high voltage power supply 14, the difference between the high voltage partial voltage fed back by the differential amplifier 14a and the control signal is amplified, and this difference signal is input to the negative side of the comparator 14b. A triangular wave is output from the oscillator 14c and input to the plus side of the comparator 14b. The comparator 14b outputs a signal having a high level period according to the magnitude of the difference signal to the transistor 14d. This controls the period during which the transistor 14d is on.

Now, if the output of the sensor 7 increases and the control signal output from the copying machine sequence controller 12 decreases, the output of the differential amplifier 14a changes in the direction of increasing, and the negative input signal of the comparator 14b becomes larger. Therefore, the high level period of the signal output from the comparator 14b changes to become shorter, and the transistor 14d
The conduction period becomes shorter. Therefore, the high voltage obtained on the secondary side of the high voltage transformer 14e changes in the direction of decreasing. Therefore, the voltage applied to the charging corotron 6 becomes lower, and the amount of charge charged on the photoreceptor decreases.

On the other hand, when the amount of charge on the photoreceptor decreases and the output of the sensor 8 becomes smaller, the operation opposite to the above case is performed, and the conduction period of the transistor 14d in the high voltage power supply 14 becomes longer. controlled by.
As a result, the voltage output from the high-voltage power supply 14 increases, the amount of discharge from the charging corotron 6 increases, and the amount of charge on the photoreceptor increases.

Note that the initial setting value before correction by the first sampling is set by the second switch 15.
given through. In this case, a preset reference value may be given from the reference power supply 16 as the initial setting value. Alternatively, the final data of the previous copying operation may be used.

In the above description of the embodiment, control of the amount of charge on the photoreceptor of a charging corotron was taken as an example, but the present invention is not limited to this, and can also be used to control the amount of charge removed by a charge removal corotron. Further, the charge amount control device according to the present invention can be applied not only to copying machines but also to electrophotographic facsimile machines, laser beam printers, and the like.

As described above, according to the present invention, the amount of charge on the photoreceptor can be controlled using only the electrostatic potential sensor output during a stable fixed period of time during the forward movement of the optical system, so that vibrations in the copying machine can be controlled. This has a great effect in that the amount of charge on the photoreceptor can be accurately controlled without being affected by errors in sensor output power due to seams of the photoreceptor.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main parts of a conventional copying machine, FIG. 2 is a waveform diagram of the output of an electrostatic potential sensor, and FIG. 3 is a circuit diagram of an embodiment of the present invention. 6... Charged corotron, 7... Electrostatic potential sensor, 8
...Optical system forward movement start detection switch, 12...Copy machine sequence controller, 13...Sample hold circuit, 14...High voltage power supply.

Claims (1)

[Claims] 1. A photoreceptor, a corona discharger provided around the photoreceptor, and a potential sensor provided at a position downstream of the corona discharger, the output of the potential sensor being applied to the corona discharger. In an electrophotographic copying apparatus of a type that controls the high voltage applied to the machine, a sampling and hold circuit samples the output of the potential sensor only during a certain period of time in which the output of the potential sensor is synchronized with the operating cycle of the machine and the forward movement of the optical system is made uniform. The data held by the sampling and holding circuit includes means for comparing the output signal of the sampling and holding circuit with a preset target value and outputting a control signal, and a high voltage power source whose output voltage is controlled by the control signal. A charge control device for a photoreceptor, characterized in that it also controls a non-sampling period.