JPH0452467B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a control device for the charging potential of a photoreceptor in a copying machine.

(Prior Art) Conventionally, the following devices are known as this type of charging potential control device.

One is a constant current corona discharge device, but this has the disadvantage that the potential is not constant due to variations in the photoreceptor, temperature characteristics, etc.

In addition, the scorotron charger device has the disadvantage that it is not practical as a copying machine because it takes too much time, although the charging potential becomes constant if it takes a sufficient amount of time to charge to a voltage determined by the grid potential. Note that this device is usually not used as described above, but is used to prevent uneven charging, so it is insufficient for controlling potential.

Furthermore, a method is also known in which an electrometer is used and the output of the electrometer is used to control the high-voltage power supply, exposure, development bias, etc., so that the quality of the copied image remains constant even if the potential changes. However, this method has drawbacks such as the electrometer is expensive, the electrometer is easily contaminated by bias voltage and induced voltage, and the high input impedance circuit is easily affected by electrical noise and atmosphere. Additionally, some systems have mechanical vibrating parts such as choppers, which have the disadvantage of shortening lifespan and reliability.

(Purpose) The present invention has been made in view of the above-mentioned drawbacks of the conventional examples, and it is possible to control charging potential without using a special device such as an electrometer and without being affected by variations in photoreceptors. The purpose is to provide a device.

(Structure) Hereinafter, the structure of the present invention will be explained based on an illustrated embodiment.

FIG. 1 is a functional diagram of a control device according to an embodiment. The charger 1 has the same structure as what is called a scorotron, and consists of a coronode 2, a shield 3, and a grid 4. In this embodiment, the grid 4 acts as a detection electrode for detecting the surface potential of the photoreceptor. The coronode 2 is connected to the output of the high voltage power supply 5. Shield 3 is grounded. The charger 1 is placed opposite the photoreceptor 6 and charges the photoreceptor 6. The back electrode of the photoconductor 6 is grounded, and when charging the photoconductor 6, a current I _p is applied to charge the photoconductor 6.
flows. The photoreceptor 6 rotates in the direction of the arrow, and the entire surface is sequentially charged by the charger 1. The detection electrode 4 is made up of a plurality of conductor wires, which are electrically connected to each other. The detection electrode 4 is a constant voltage element 7
The other end of the constant voltage element 7 is connected to the constant voltage element 7.
It is grounded via a current detection resistor 8 for detecting the current flowing through it. The voltage appearing on the current detection resistor 8 is made to be sufficiently low compared to the voltage of the constant voltage element 7, which is approximately several hundred to one thousand volts. By selecting the resistance value in this way, it is possible to avoid deterioration of constant voltage characteristics caused by inserting a series resistor.
The voltage generated across this current detection resistor 8 is proportional to the current flowing through the constant voltage element 7. This detected signal is input to the comparison circuit 9 of the high voltage power supply 5. The current flowing due to corona discharge contains an alternating current component, so
In actuality, the circuit averages the signal and converts it to direct current, which is then input to the comparator circuit 9. In order to provide a reference for the comparator circuit 9, a reference voltage is input to the comparator circuit 9 from a block 10 labeled "Current Setting" in the figure. Reference from “Current setting” and current detection resistor 8
The voltages generated are compared, a difference signal is extracted, and the output of the high voltage power supply 5 is controlled by the difference signal. Such control is performed by the pulse width control circuit 11 and DC-DC converter 12 shown in the figure.
In other words, a feedback control system is configured to keep the current flowing through the constant voltage element 7 connected to the detection electrode 4 constant.

Next, the relationship between keeping the current flowing through the constant voltage element 7 constant and keeping the charging potential of the photoreceptor 6 constant will be explained. As a basis for explanation, the function of a known scorotron charger will first be explained with reference to FIG. Note that the reference numeral 13 is a grid bias power source. The scorotron charger applies electric charge to the photoreceptor 6 by corona discharge of the coronode 2 by the high-voltage power supply 5 while applying a constant potential to the grid 4. grid 4
An equipotential surface is formed along the grid 4 by the voltage applied to the grid. When corona discharge occurs in the coronode 2, ions are generated near the coronode 2.
The generated ions are accelerated by the electric fields formed between the coronode 2 and the shield 3, between the coronode 2 and the photoconductor 6, and between the coronode 2 and the grid 4, and move toward each direction.This causes a current to flow and move toward the photoconductor 6. Charging is performed. However, as the potential of the photoreceptor 6 increases, the electric field between the photoreceptors 6 and the grid 4 becomes weaker. When it becomes weak, grid 4 and photoconductor 6
Since the degree of acceleration of ions is reduced between the two, the number of ions reaching the photoreceptor 6 is reduced, and the charging current of the photoreceptor 6 is reduced. A reduced current flows through grid 4. While the charging current flows, the potential of the photoconductor 6 increases (here, for the sake of simplicity, it is assumed that the decrease in potential due to leakage of the photoconductor 6 can be ignored). When the potential of the photoconductor 6 becomes equal to the potential of the grid 4 due to an increase in potential, ions are no longer accelerated between the grid 4 and the photoconductor 6. Even at this time, some of the ions reach the photoreceptor 6 due to the initial velocity when the ions reach the equal voltage surface formed by the grid 4. When the voltage of the photoreceptor 6 further increases, the electric field between the grid 4 and the photoreceptor 6 becomes of opposite polarity, and the ions accelerated between the coronode 2 and the grid 4 are accelerated in the opposite direction, and the charge on the photoreceptor 6 is becomes unreachable. When the charge no longer increases, the voltage of the photoreceptor 6 becomes constant. This is the control of the charging potential of the photoreceptor 6 by the scorotron charger. However, controlling the charging by the potential applied to the grid 4 takes too much time and is not very practical in an electrostatic copying machine in which the photoreceptor 6 is charged while being moved. Generally, a scorotron charger is used in an electrostatic copying machine for the purpose of uniformly charging the photoreceptor 6. As can be seen from the above explanation, when uneven charging occurs, a large current flows in areas with low potential due to the large potential difference between the grid 4 and photoreceptor 6, and the current in areas with high potential is suppressed. This is because it has the effect of alleviating unevenness. Next, the relationship between the above-mentioned constant voltage element and the photoreceptor will be explained based on FIG. 3.

Figure 3 shows the characteristic graph in Figure 1, that is, a constant voltage element (1.0 kV) is attached to the grid 4, a plate to which an external bias is applied is placed in place of the photoreceptor 6, and the plate current I _p is determined. A measurement of the current I _v flowing through the voltage element 7 is shown. As can be seen from the figure, a large amount of I _p flows when the plate voltage V _p is low, and I _p decreases as V _p rises. On the contrary, I _v
increases as V _p increases. This shows that I _v is determined by the potential of the photoreceptor 6 if the structure of the charger 1 and the positional relationship with the photoreceptor 6 and the characteristics of the constant voltage element 7 are constant. Therefore, the first
Keeping _Iv constant with the configuration shown in the figure has the same effect as detecting the charged potential of the photoreceptor 6 and controlling it to be constant.

Next, the meaning of using the constant voltage element 7 in the grid 4 will be explained as a supplement to the previous explanation. In FIG. 2, the region indicated by a of the characteristics showing the V, I characteristics of a constant voltage element has a small current and does not show constant voltage characteristics. In general, it can be approximated as a resistor with a high resistance value. b is a region where current flows and exhibits constant voltage characteristics. Here, when approximated by a straight line, the resistance value indicated by that straight line is low. This is called the operating resistance of the constant voltage element 7. The fact that this resistance is low means that a nearly constant voltage is applied even if the current changes. This makes the sensitivity of the current increase to a rise in the potential of the photoreceptor 6 extremely high. The high sensitivity of the detection section is also very advantageous in the design of a control system, and a stable control system can be constructed with a simple circuit. If the operating resistance is high, even if I _v increases due to an increase in the potential of the photoreceptor 6, this will cause the constant voltage element 7 to
The voltage also increases, canceling out the change due to the increase in the potential of the photoreceptor 6, resulting in a decrease in sensitivity. Therefore, it is desirable to lower the operating resistance.

(Effects) As described above, according to the present invention, since no special device such as an electrometer is used, there are no restrictions on implementation, the potential can be detected and controlled within the mounting range of the charger, and the detection part is a simple conductor. Therefore, the cost is low and it is not easily affected by dirt.

Furthermore, since it is not a high impedance circuit, it is possible to create a device that is less affected by electrical noise and atmosphere.

[Brief explanation of drawings]

FIG. 1 is a functional explanatory diagram of a device according to an embodiment of the present invention, FIG. 2 is a V, I characteristic diagram of a constant voltage element, and FIG.
The figure is a characteristic diagram showing the relationship between the plate current and the detected current according to an embodiment of the present invention, and FIG. 4 is a simplified diagram showing the scorotron charge which is the premise of the present invention. 1...Chargeer, 2...Coronode, 4...
...Detection electrode, 5...High voltage power supply, 6...Photoreceptor, 7
... Constant voltage element, 9 ... Comparison circuit, 11 ... Pulse width control circuit, 12 ... DC-DC converter.

Claims (1)

[Scope of Claims] 1. A charger facing the photoreceptor, a detection electrode provided between the coronode of the charger and the photoreceptor, and a constant voltage element provided between the detection electrode and ground. a means for detecting a current flowing through the constant voltage element; and a means for controlling the output of a high voltage power supply for charging based on the detection result of the current to maintain a constant current flowing through the constant voltage element. A charging potential control device for a photoreceptor, characterized by comprising: