JPS58120270A - Charge current controller for electronic copying machine - Google Patents

Abstract

PURPOSE:To hold the surface potential of a photoreceptor in a desired value to suppress its variance, by estimating approximately a dark decay characteristic by outputs of plural surface potential sensors provided along the moving course of the photoreceptor and controlling a charge current on a basis of this dark decay characteristic. CONSTITUTION:First, the dark decay characteristic curve is approximated by a prescribed functional expression. Outputs V1 and V2 of surface potential sensors 3 and 3A provided along the moving course of the photoreceptor are used to obtain unknown coefficients of this functional expression in a circuit 9 by operation, and said dark decay characteristic curve is estimated. Next, a surface potential V3 in the current position is estimated and operated in accordance with this dark decay characteristic. The charge current of a charger 2 is so controlled that the comparison between the estimated and operated surface potential V3 and a target value V0 from a target potential setter 93 results in coincidence. Thus, the surface potential of the photoreceptor in the development position is always held in a desired value independently of the change of the dark decay characteristic, and its variance is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a charging current control device for maintaining the surface potential of a photoreceptor at a constant value in an electronic copying machine.

The electronic copying machine charges the surface of the photosensitive drum to a certain potential using a charging device, and irradiates and exposes the surface of the photosensitive drum to the photosensitive drum 11! A copy is obtained by forming an electrostatic latent image on the rain, applying it with toner, etc., and fixing it.

In this case, the image density and background density of the obtained copy are determined by the surface potential of the photosensitive drum in the special development program, so in order to obtain a good copy of the desired quality,
It is necessary to control the position of Table 1fi]llL in the m image area of the photosensitive drum to a desired value.

In order to maintain good image quality of copies, conventionally, a charging high-voltage power source that supplies a charging current to a charger has a constant voltage or constant current.

However, in general, the specific resistance and sensitivity of a photoreceptor are affected by temperature, humidity,
Since the potential changes greatly depending on usage time, changes over time, etc., it is difficult to maintain the surface potential of the photoreceptor drum at a predetermined value even if the charging high-voltage power source is made constant voltage or constant current.

In order to improve this, it is currently possible to control the surface potential of the photoreceptor at a constant level by measuring the surface potential of the photoreceptor and adjusting the voltage applied to the charger based on the measurement result. is widely practiced.

However, as is clear, what can be controlled to be constant using such conventional methods is the surface potential at the point where the surface potential is being measured.

By the way, in an electronic copying machine, the surface potential that is related to the copy image obtained is the surface potential at the position where 'kj4yl is performed. Photoreceptors have a charge discharge phenomenon called dark decay, and the dark decay characteristics (speed) vary depending on the material of the photoreceptor, vapor deposition method, humidity, usage time, and the like.

Therefore, when the surface potential of the photoreceptor is controlled using the conventional method, the surface potential at the surface potential detection position is held constant, but the surface potential at the development position is not necessarily constant. Therefore, there is a drawback that the number of copy images obtained is not constant.

An object of the present invention is to improve the above-mentioned drawbacks of the prior art, and to always maintain the surface potential of a photoreceptor at a development position at a desired value of 11, regardless of changes in dark decay characteristics (speed), and to suppress variations thereof. The object of the present invention is to provide a normal current control device that can perform the following functions.

In order to achieve the above object, in the present invention, a plurality of surface potential sensors are provided along the moving path of the photoreceptor, and the output of each potential sensor is used (i.e., from the first sensor position to the first sensor position). (by detecting the amount of decrease in surface potential while the photoreceptor moves to the sensor position 2)
The dimming *lF# property (ship) is estimated approximately, and the charging current is controlled based on this.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

In the figure, 1 is a photoreceptor drum, 2 is a charger, 3 is a first surface potential sensor, 3A is a second surface potential sensor, 4 is an exposure section, 4 people are exposed to light, 5 is a developer, and 9 is a calculation unit. control@device,
91 is an A/D converter, 92 is an arithmetic unit, 93 is a target potential setter, 94 is a comparator, 95 is a control controller, 96i
2D/A:l:#(-1, 10 are high-voltage power supplies for charging. Also, arrow R indicates the direction of rotational force of the photoreceptor drum 1.

Now, when the photoreceptor drum 1 is charged by the charger 2 so that the surface potential of the photoreceptor drum 1 is constant (for example, 1000 ports), the potential ■ at a certain point on the photoreceptor drum 1 changes over time. By actually measuring how T decreases over time, a dark decay characteristic curve as shown in FIG. 2 is obtained.

In the figure, the horizontal axis is time t, and the vertical axis is surface potential V. In addition, tl+J and t$ are calculated when a point on the photosensitive drum 1 moves from below the surface 1[&2 to below the first surface position sensor 3, second surface potential sensor 3A, and developer 5, respectively. It's time to take in the scenery.

As can be seen from the above, the dark decay characteristic is
It changes as shown by the curve indicated by the dots, depending on the material of the photoreceptor, the formation method, the humidity, the usage time, etc.

In the present invention, first, the dark decay characteristic curve described above is approximated by a predetermined functional expression. Next, the unknown coefficient of the function equation is calculated from the output of a surface potential sensor installed along the moving path of the photoreceptor (i.e., for example, at time jl*Lg in FIG. 2).
It is obtained by calculation using the surface potential at
Estimate the memorization decay characteristic curve.

Next, the photoreceptor interface potential at the development position is estimated and calculated according to the darkening tear characteristics, and the obtained estimated value is used as the eye 4M.
The charging current of the 11L device is controlled so that the values match.

In the following, in order to simplify the explanation, a case will be described in which the dark decay characteristic curve is approximated by a linear equation, but it goes without saying that the present invention is not limited to this.

In the apparatus shown in FIG. 1, it is assumed that the photosensitive drum 1 is charged to a constant surface potential (this itself may be unknown) by the charging 62. At this time, the surface potential sensor 3, 3A
Let the detected value by Vl be one round, respectively. Here the third
As shown in the figure, it is assumed that the dark decay characteristic is expressed by a straight line - that is, equation (1) (%), so the following (2) (
Equation 31 holds true.

V1=aLl+b・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
(2) Vl-at! 10b ”・；・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
... (3) Here, Vl + v寞 + jl +
t, are all known, so (1), (
Coefficients a and b can be obtained by calculating equations 21 simultaneously. In other words, ti &.

b is expressed by the following formula (4) (51).

b=Vgat2 The above (41(51) calculation is performed by converting the detection output vt l Vl of the surface potential sensors 3 and 3A into A/
By inputting each to the calculation unit 92 via the D converter 91, it can be executed in the operation 11892.

In the manner described above, the dark fItc decay characteristic curve is released from the mold. On the other hand, the time required for the point on the photoreceptor drum 1 to move from directly below the sensor 2 to directly below the current G# device 5 is 1. Since Vsit is also known, the surface potential Vsit of the photosensitive drum 1 under the developing device 5 can be determined by the following equation (6).

Va-aLl + b・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
... (6) Here, equation (6) is the above +41
(By substituting equation 51, it can be written as the following equation (7).

Therefore, the surface potential v8 under the current gI device 5 can be obtained by directly performing Rinshun equation (7) in the calculation unit 92. $ is comparison g1
194. On the other hand, compare! 94, the setting device 9
3, the surface potential directly under the developing unit 5 is all 1m.
Since Vo is supplied, the ratio IIR device 94 softens both ratios and outputs the deviation ΔV from the surface potential v Hatake's eye III value Vo.

The deviation ΔV is added to the control calculation section 95, and the control lid is determined by an appropriate method (for example, proportional calculation, proportional integral calculation, etc.). The control ii is converted into an analog value by the D//A converter 96, and the output of the charging high-voltage power supply 10 is controlled accordingly.

That is, when the deviation ΔV is positive, the voltage or current applied to the charger 2 from the charging high-voltage power source IQ is decreased, and on the other hand, when the deviation ΔV is negative, the voltage or current is increased.

By repeating the above calculation and correction control, the potential on the surface of the photosensitive drum directly below the developing device 5 is always maintained at the target value VO. Note that, as is clear, the above-described surface potential control can be carried out at all times, even when copying operations are being performed.

FIG. 4 shows another embodiment of the present invention in which the second surface potential sensor 3 is arranged after (downstream) the Al exposure section 4.

In this case, the distance between the first front surface potential sensor 3 and the second front surface potential sensor 3A can be made longer than in the case of FIG. Since consideration can be given to the vicinity of , it is possible to improve the accuracy of estimating the surface potential v in mF of the developing device 5.

However, in this case, since an electrostatic latent image is formed on the photosensitive drum 1 at the position where the second front potential sensor is lying, it is extremely difficult to accurately determine the surface potential -j. Therefore, it is not possible to control the charging current by controlling the charging island pressure power source 10 during normal copying operations.

That is, in order to realize the embodiment shown in FIG. 4, it is necessary to control the charging current only in a special mode such as after the power is turned on, or to provide an area on the photoreceptor drum 1 in which no electrostatic latent image is formed. , it is necessary to take measures such as arranging a table 2 potential sensor in that area.

In addition, in the above explanation, the dark decay characteristic is directly referred to. (−the following formula)
We used two surface potential sensors along the moving path of the photoreceptor in order to approximate it with
It will be easily understood that the number of surface potential sensors may be selected depending on the number of constants (coefficients) in the Jia number.

As is clear from the above description, according to the present invention, a functional formula that produces a predetermined dark decay characteristic curve is estimated by the outputs of a plurality of surface potential sensors provided along the moving path of the photoreceptor. Based on this, the surface potential of the photoreceptor directly under the developing unit is estimated and calculated, thereby suppressing potential variations at the developing position due to changes in the dark decay characteristics of the photoreceptor, and preventing variations in copy quality such as copy density. and variations can be reduced.

[Brief Description of the Drawings] Fig. 1 is a block diagram of one implementation of the present invention, Fig. 2 is a diagram showing an example of the dark decay characteristics of a photoreceptor, and Fig. 3 is a surface of the present part in the present invention. FIG. 4, which is a diagram for explaining potential estimation assistance, is a block diagram of another embodiment of the present invention. l...Photosensitive drum, 2...Charger, 3,3A...
・Surface potential sensor, 4...Exposure section, 5...Developer, 9
... Arithmetic control device, 91 ... A/D converter, 9
2... Performance X section, 93... Target potential setting device, 94...
・Comparison-, 95...Control calculation section, 96...D/
A: 17 parts, 10...Michihito Hiraki, patent attorney representing high-voltage power supply for charging

Claims (1)

[Scope of Claims] +1) A charging current control device for an electronic copying machine, which includes a charger, a plurality of surface potential sensors, a developer, etc. arranged in order along the moving meridian of a photoreceptor, the charger having a high-voltage power supply connected to supply a charging current to the high-voltage power supply, means for generating a control voltage for controlling the output of the high-voltage power supply, means for storing a function that approximates the dark decay characteristic of the photoreceptor, and the plurality of surfaces. Means is supplied with the output of the potential sensor, calculates the unknown coefficient of the function to determine the function, and estimates the photoreceptor surface potential directly below the developing device based on the determined function; The method further comprises: means for comparing the photoreceptor surface potential with a target value to obtain a deviation of the photoreceptor surface potential from the target value; and means for controlling the output of the high voltage power supply based on the deviation. Characteristic charging current control device for electronic copying machines. (2) A charging current control device for an electronic copying machine according to claim 1II, characterized in that two surface potential sensors are arranged, both of which are located between the charger and the exposure section. (3) Two surface potential sensors are arranged, one surface potential sensor is located between the charger and the exposure section, and the other surface potential sensor is located between the exposure section and the developer. The charging current control device for an electronic copying machine according to item 1, wherein the range of %fFi1'Il is determined.