JPH0785182B2 - Surface potential control device for photoconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a photoconductor used in, for example, an electrophotographic copying machine, which can uniformly charge the photoconductor so that its surface potential becomes a preset value. The present invention relates to a surface potential control device.

(Prior Art) A photoconductor used in an electrophotographic copying machine is usually arranged on the outer peripheral surface of a cylindrical drum. In such a copying machine, while the drum is rotated and the drum is rotated once, the photoreceptor is charged and exposed, and the electrostatic latent image formed on the surface of the photoreceptor by the exposure is toner-developed. The developed toner image is transferred onto recording paper.

Generally, a corotron or a scorotron is used to charge the photoconductor. Since the corotron charges the linear photoconductor with a corona wire to which a high voltage is applied, rapid charging is possible. However, since the charging stability is poor, it is difficult to uniformly charge the surface potential of the photoconductor to a set value. On the other hand, in the scorotron, a control grid is arranged between the corona wire and the photoconductor, and the corona current is controlled by the voltage applied to the control grid. In the scorotron, when the surface potential of the photoconductor becomes large, the electric field between the photoconductor surface and the control grid becomes weak, and as a result, the acceleration of ions to the photoconductor surface decreases, and the charge amount of the photoconductor decreases. . Therefore, by controlling the potential of the grid, the surface potential of the photoconductor can be set to the set value. In other words, when the surface potential of the photoconductor reaches the set value, the photoconductor is not further charged, and the surface potential of the photoconductor becomes the set value, so that excessive charging of the photoconductor is prevented.

However, it takes time to charge to a desired surface potential using a scorotron. For this reason, scorotrons are generally used to prevent uneven charging, rather than as chargers. However, it has been proposed to control the surface potential based on the fact that the response sensitivity of the control grid current to the surface potential of the photoconductor of the scorotron is very good (for example, JP-A-59-201075).

In recent years, the peripheral speed of the photosensitive drum has increased with the increase in copying speed. In addition, development of high-sensitivity photoconductors such as a-Si and As ₂ Se ₃ has progressed, but on the other hand, the problem that the surface potential is not stable when used at high speed due to environmental conditions has been addressed.

Further, when a conventional corotron is used for high-speed charging, if the applied voltage is increased to secure the surface potential of a predetermined photoconductor, the photoconductor is overcharged, and if the surface potential becomes too high, pinholes or the like may occur. Destruction occurs. If the applied voltage is kept as it is, the surface potential may be below a predetermined value or may not be uniform, resulting in deterioration of the quality of the copied image.

However, as described above, when the photoconductor rotates at a high speed, it is difficult to charge the photoconductor so that the surface potential of the photoconductor becomes a set value even by using a scorotron. Since the charging characteristic of the photoconductor changes when the surface temperature of the photoconductor changes, it is not easy to uniformly control the surface potential of the photoconductor to the set value.

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to make a photoreceptor moving at a high speed so that its surface potential becomes a set value. An object is to provide a surface potential control device for a photoconductor that can be charged.

(Means for Solving Problems) A surface potential control device for a photoconductor according to the present invention includes a corona wire arranged to face the surface of the photoconductor, and a corona line arranged between the corona line and the surface of the photoconductor. And a controlled grid,
A scorotron that charges the photoconductor by a corona current flowing from the corona wire to the photoconductor via a control grid,
The charging device is provided downstream of the scorotron in the moving direction of the photoconductor and charges the photoconductor. Further, the surface potential control device of the photoconductor responds to a difference voltage between a reference potential corresponding to a preset surface potential of the photoconductor and a potential obtained based on a corona current flowing from the corona wire into the control grid. Then, a control unit is provided to control the amount of charge of the photoconductor by the charging device so that the surface potential of the photoconductor becomes a preset potential.

In this invention, preferably, the charging device has a corona wire arranged to face the surface of the photoreceptor.
A corotron for charging the photoconductor by a corona current flowing from the corona line to the photoconductor, wherein the control means controls the voltage applied to the corona line of the corotron,
The charge amount of the photoconductor is controlled.

In the present invention, preferably, the charging device has a corona wire arranged to face the surface of the photoconductor, and a control grid arranged between the corona line and the surface of the photoconductor. And a second scorotron that charges the photoconductor by a corona current flowing from the to the photoconductor through the control grid, and the control means controls the voltage applied to the control grid of the second scorotron. The charge amount of the photoconductor is controlled.

(Operation) In the present invention, a scorotron that charges the photoconductor by a corona current flowing from the corona wire to the photoconductor via the control grid, and a photoconductor disposed downstream of the scorotron in the moving direction of the photoconductor. A charging device for charging the body is provided, and a reference potential corresponding to a preset surface potential of the photoreceptor and a potential difference obtained between the potential obtained based on the corona current flowing from the corona line to the control grid,
Since the charging amount of the photoconductor by the charging device is controlled so that the surface potential of the photoconductor becomes a preset potential, the control is performed from the corona line of the scorotron according to the charging amount of the photoconductor. When the corona current flowing into the grid changes, the charge amount of the photoconductor by the charging device becomes a potential difference between a potential obtained based on the grid current and a reference potential corresponding to a preset surface potential of the photoconductor. It will be controlled to be smaller. As a result, the photoconductor that moves at high speed can be charged so that the surface potential thereof becomes a set value.

(Examples) Examples of the present invention will be described below.

As shown in FIG. 1, the apparatus of the present invention has a scorotron 20 and a corotron 30 which are charging devices arranged around the photosensitive drum 10, and a control means 40 for the corotron 30.

In this embodiment, the grid current from the upstream scorotron 20 used for detecting the surface potential is used as the input signal of the control means 40, and the output signal of the control means 40 is used as the voltage. The output signal controls the downstream corotron 30 used for correction of the surface potential.

The photoconductor drum 10 has, for example, a photoconductor 12 of amorphous silicon laminated on the outer peripheral surface of a cylindrical drum 11.
It is arranged to be rotatable in the direction of the arrow.

The scorotron 20 and the corotron 30 are the photosensitive drum 10
Are arranged side by side in the rotation direction, and the scorotron 20 is located on the upstream side in the rotation direction. Scorotron 20 is corona line 21
And a control grid 22. A predetermined high voltage is applied to the corona wire 21, a corona current is generated from the corona wire 21 by the application of the voltage, and the photoconductor 12 is charged by the corona current. Scorotron 20 control grid 22
The grid current flowing through is input to the control means 40.
The increase in the grid current is proportional to the increase in the surface potential of the photoconductor 12, and the grid current also increases as the surface potential increases. Therefore, the surface potential of the photoconductor 12 is measured from the grid current.

The output of the transformer 50 controlled by the control means 40 described later is given to the corona wire 31 of the corotron 30 located on the downstream side, and the voltage applied to the corona wire 31 by the output of the control means 40. Is changed.

The control means 40 has a differential amplifier 41 and an amplifier 42. The input end of the differential amplifier 41 is connected to the control grid 22 of the scorotron 20 through a varistor, and the grid flowing through the control grid 22 is connected to the control grid 22. The current is converted into a potential corresponding to this. Here, the varistor holds the control grid of the scorotron 22 at a constant potential, whereby the grid current that changes according to the charge amount of the photoconductor linearly corresponds to the charge amount of the photoconductor. Becomes Further, the differential amplifier 41 has a photosensitive member finally required by charging the scorotron 20 and the corotron 30.
The potentials corresponding to the 12 surface potentials are also set and input. The differential amplifier 41 calculates the difference between the two, and the calculation result is amplified by the amplifier 42. That is, the differential amplifier 41 is
An amplifier that outputs a signal corresponding to the difference between the preset final required surface potential of the photoconductor 12 and the actual surface potential of the photoconductor 12 charged by the upstream scorotron 20 is output.
42 amplifies the signal.

The output of amplifier 42 is provided to transformer 50. The transformer 50 is interposed between the corona wire 31 of the downstream corotron 30 and the high-voltage power supply, and the voltage applied to the corona wire 31 is changed according to the output of the amplifier 42. , The corona wire 31 is applied with a voltage that gives a charge amount necessary to eliminate the difference between the final required surface potential of the photoconductor 12 and the surface potential of the photoconductor 12 that is actually charged. It

The device of the present invention having such a configuration operates as follows.
The photoconductor drum 10 is rotated in the direction of the arrow in FIG. 1, and during the rotation of the photoconductor drum 10, the photoconductor 12 is charged by the scorotron 20 on the upstream side, and the surface potential thereof is increased. At this time, a current corresponding to the surface potential of the photoconductor 12 flows through the control grid 22 of the scorotron 20. Then, the difference between the surface potential of the photoconductor 12 and the preset potential at this time is calculated by the differential amplifier 41 in the control device 40, and the output corresponding to the difference is given to the amplifier 42. The signal amplified by the amplifier 42 is given to the transformer 50.
The transformer 50 is the final set surface potential of the photoconductor 12 and the photoconductor actually charged by the scorotron 20 on the upstream side.
The voltage required to eliminate the difference from the surface potential of 12 is applied to the corona wire 31 of the corotron 30 on the downstream side. The corona wire 31 of the corotron 30 to which such a voltage is applied further charges the photoconductor 12, and the surface potential of the photoconductor 12 is set to a preset value. The charged photoconductor 12 is subjected to a predetermined copying process such as development and transfer.

FIG. 2 shows a surface potential control device for a photoconductor according to another embodiment of the present invention, in which the grid current from the upstream scorotron 20 used for detecting the surface potential is used as an input signal of the control means 70. The output signal of the control means 70 is a current. The output signal controls the grid current of the scorotron 60 on the downstream side. In this embodiment, the photosensitive drum
A scorotron 60 is used as a charging device located on the downstream side in the rotational direction of 10. The control means 70 has a differential amplifier 71 and an amplifier 72.

The configuration and operation of the differential amplifier 71 are the same as those in the above-mentioned embodiment. A constant high voltage is applied to the corona wire 61 of the scorotron 60. Based on the signal from the differential amplifier 71,
An amplifier 72 controls the current flowing in the control grid 62 of the scorotron 60. Since the other components denoted by the same reference numerals are the same as those in the above-described embodiment, their description will be omitted.

In this embodiment, the photoconductor charged by the scorotron 20.
Based on the difference between the surface potential of 12 and the set surface potential, the grid current of the control grid 62 of the downstream side scorotron 60 is controlled, and the set surface potential of the photoconductor 12 and the upstream side scorotron 20.
The surface potential of the photoconductor 12 is increased by charging the scorotron 60 on the downstream side by the difference from the surface potential actually charged at.

It should be noted that it is clear in implementing the present invention that the input signal to the control means may be current or voltage, and similarly, the output signal from the control means may be either. That is.

Fig. 3 shows the relationship between the surface potential of the photoconductor and the surface temperature.
B shows the charging result by the device of the present invention, and B shows the charging result by the conventional device. As is clear from this figure, according to the device of the present invention, the variation of the surface potential due to the displacement of the surface temperature is reduced.

As described above, in each of the above-described embodiments, the charging of the photoconductor is performed twice in the moving direction of the photoconductor, and the charge amount of the photoconductor is grasped by the scorotron 20 on the upstream side. Since the scorotron 60 controls the charge amount of the photoconductor so that the surface potential of the photoconductor becomes a preset potential, the photoconductor moves at high speed, such as during continuous copying in a copying machine. Also in this case, the surface potential of the photoconductor has a preset value, and there is no fear of excessive charging, insufficient charging, or uneven charging.

In particular, since the scorotron on the upstream side is charged to a certain extent and the shortage is charged by a charging device such as a corotron on the downstream side, there is no risk of control hunting. Further, even if the surface temperature of the photoconductor changes, such as environmental changes, there is little variation in the surface potential, and control can be performed with high accuracy.

(Effects of the Invention) As described above, according to the surface potential control device for a photoconductor according to the present invention, a scorotron that charges the photoconductor by a corona current flowing from the corona wire to the photoconductor via a control grid, and the scorotron. And a charging device that is disposed on the downstream side in the moving direction of the photoconductor and charges the photoconductor,
Depending on the difference voltage between the reference potential corresponding to the preset surface potential of the photoconductor and the potential obtained based on the corona current flowing from the corona line to the control grid, the charge amount of the photoconductor by the charging device is changed. Since the surface potential of the photoconductor is controlled so as to be a preset potential, the photoconductor is charged in two steps along the moving direction of the photoconductor, and further, the charging device on the downstream side is charged. Thus, the charge amount of the photoconductor is adjusted. As a result, the photoreceptor moving at high speed can be charged so that the surface potential of the photoreceptor becomes a set value. For example, even when the photoconductor moves at a high speed as in the case of continuous copying in a copying machine, the surface potential of the photoconductor has a preset value, and there is no fear of excessive charging, insufficient charging, or uneven charging. In particular, because the scorotron on the upstream side is charged to a certain extent and the shortage is charged by the charging device on the downstream side, there is no risk of control hunting. Further, even if the surface temperature of the photoconductor changes, such as environmental changes, there is little variation in the surface potential and control can be performed with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of the device of the present invention, FIG. 2 is a schematic diagram showing another embodiment of the device of the present invention, and FIG. 3 is a graph showing the effect of the device of the present invention. 10 ... Photosensitive drum, 12 ... Photosensitive body, 20, 60 ... Scorotron, 30 ... Corotron, 40 ... Control means.

Claims (3)

[Claims] 1. A corona wire arranged so as to face the surface of the photoconductor, and a control grid arranged between the corona line and the surface of the photoconductor. A scorotron that charges the photoconductor by a corona current flowing to the photoconductor, a charging device that is disposed downstream of the scorotron in the moving direction of the photoconductor and charges the photoconductor, and a surface of the photoconductor set in advance According to the difference voltage between the reference potential corresponding to the potential and the potential obtained based on the corona current flowing from the corona wire to the control grid, the charge amount of the photoconductor by the charging device is changed to the surface potential of the photoconductor. A surface potential control device for a photoconductor, comprising: a control unit that controls the potential to be a preset potential. 2. The corotron, wherein the charging device has a corona wire arranged to face the surface of the photoconductor, and charges the photoconductor by a corona current flowing from the corona line to the photoconductor. 2. The surface potential control device for a photoconductor according to claim 1, wherein the control means controls the charge amount of the photoconductor by controlling the voltage applied to the corona wire of the corotron. 3. The charging device has a corona line arranged to face the surface of the photoconductor and a control grid arranged between the corona line and the surface of the photoconductor. Is a second scorotron for charging the photoconductor by a corona current flowing from the photocoil to the photoconductor via the control grid, wherein the control means controls the voltage applied to the control grid of the second scorotron to control the photosensitivity of the photoconductor. The surface potential control device for a photoconductor according to claim 1, which controls the amount of electrostatic charge on the body.