JPH0245186B2 - DENSHIFUKUSHAKINOTAIDENDENRYUSEIGYOSOCHI - Google Patents

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.

An electronic copying machine charges the surface of a photoreceptor drum to a certain potential using a charger, irradiates and exposes it with imagewise light to form an electrostatic latent image on the surface of the photoreceptor drum, and transfers this to toner. A copy is obtained by developing and fixing the image.

In this case, the image density and background density of the obtained copy are determined by the surface potential of the photosensitive drum at the time of development, so in order to obtain a good copy of the desired quality, the surface potential of the developing section of the photosensitive drum must be It is necessary to control the value 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 vary greatly depending on temperature, humidity, usage time, changes over time, etc., so even if the high-voltage power supply for charging is made constant voltage or constant current, the photoreceptor drum in the developing section It is difficult to maintain the surface potential at a predetermined value.

In order to improve this, currently, the surface potential of the photoreceptor is controlled to a constant value 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.

Incidentally, in an electronic copying machine, the surface potential that is also related to the copy image obtained is the surface potential at the position where development is performed. The photoreceptor has charge discharge development called dark decay, and its dark decay characteristics (speed) are determined by the material of the photoreceptor,
It varies depending on the deposition method, temperature, usage time, etc.

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 density of the obtained copy image is not constant.

An object of the present invention is to improve the above-mentioned drawbacks of the prior art, to always maintain the surface potential of a photoreceptor at a development position at a desired value regardless of changes in dark decay characteristics (speed), and to suppress its fluctuations. The object of the present invention is to provide a charging 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 second sensor position). By detecting the amount of decrease in surface potential while the photoreceptor moves to the sensor position, the dark decay characteristic (speed) is approximately estimated, and the charging current is controlled based on this. .

The present invention will be explained 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 photosensitive drum, 2 is a charger, 3 is a first surface potential sensor, 3A is a second surface potential sensor, 4 is an exposure section, 4A is an imagewise 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
95 is a comparator, 95 is a control calculation section, 96 is a D/A converter, and 10 is a high voltage power source for charging. Further, an arrow R indicates the rotation direction 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 volts), the electric potential V at a certain point on the photoreceptor drum 1 is When we actually measure how the value decreases as time 8 passes, we find that the second
A dark decay characteristic line as shown in the figure is obtained.

In the figure, the horizontal axis is time t, and the vertical axis is surface potential V. Further, at t ₁ , t ₂ and t ₃ , one point on the photoreceptor drum 1 is the first point from below the charger 2, respectively.
This is the time required to move below the surface potential sensor 3, the second surface potential sensor 3A, and the developing device 5.

As can be seen from the above, the dark decay characteristic changes as shown by the curve shown by the dotted line depending on the material of the photoreceptor, its formation method, temperature, humidity, usage time, and the like.

In the present invention, first, the dark decay characteristic curve described above is approximated by a predetermined functional expression. Next, the unknown coefficients of the functional expression are calculated using the output of a surface potential sensor installed along the moving path of the photoreceptor (i.e., the surface potential at times t ₁ and t ₂ in FIG. 2, for example). and estimate the dark decay characteristic curve.

Next, the photoreceptor surface potential at the development position is estimated and calculated according to the dark decay characteristic, the obtained estimated value is compared with the target value, and the charging current of the charger is adjusted so that the two match. Control.

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 charger 2. At this time, the detected values by the surface potential sensors 3 and 3A are respectively
Let V ₁ and V ₂ be. Here, as shown in Figure 3, it is assumed that the dark decay characteristic is expressed by a straight line, that is, the equation (1) V = at + b ... (1), so the following (2) and (3)
The formula holds true.

V ₁ = at ₁ + b ... (2) V ₂ = at ₂ + b ... (3) Here, since V ₁ , V ₂ , t ₁ , and t ₂ are all known, the above (1), ( 2) By calculating the equations simultaneously, the coefficients a and b can be obtained. That is, the coefficients a and b are expressed by the following equations (4) and (5).

a = (V ₁ - V ₂ ) / t ₁ - t ₂ ... (4) b = V ₂ - at ₂ = V ₂ t ₁ - V ₁ t ₂ / t ₁ - _{t 2} ... (5) Above ( 4) The calculation of equation (5) is performed by converting the detection outputs V ₁ and V ₂ of the surface potential sensors 3 and 3A into A/
By inputting each to the arithmetic unit 92 via the D converter 91, the arithmetic unit 92 can execute them.

As described above, the dark decay characteristic curve is estimated. On the other hand, since the time t ₃ required for the point on the photosensitive drum 1 to move from directly below the charger 2 to directly below the developing device 5 is also known, the surface of the photosensitive drum 1 below the developing device 5 is known. The potential V ₃ is determined by the following equation (6).

V ₃ =at ₃ +b...(6) Here, equation (6) can be changed to the following by substituting equations (4) and (5) above.
It can be written as equation (7).

V ₃ =V ₁ −V ₂ /t ₁ −t ₂・t ₃ +V ₂ t ₁ −V ₁ t ₂ /t ₁ −t ₂ ……(7
) Therefore, the calculation section 92 directly calculates the equation (7), and calculates the surface potential V ₃ under the developing unit 5.
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The surface potential V ₃ calculated in this manner is supplied to a comparator 94 . On the other hand, the comparator 94 is supplied with the target value V ₀ of the surface potential directly below the developing unit 5 from the setting device 93, so the comparator 94 compares the two and sets the target value V ₃ of the surface potential V 3 Outputs the deviation ΔV from ₀ .

The deviation ΔV is added to the control calculation section 95, and the control amount is determined by an appropriate method (eg, proportional calculation, proportional integral calculation, etc.). The control amount is converted into an analog amount by a D/A converter 96, and the output of the charging high voltage power source 10 is controlled accordingly.

That is, when the deviation ΔV is positive, the voltage or current applied from the charging high-voltage power source 10 to the charger 2 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 V ₃ of the surface of the photosensitive drum directly below the developing device 5 is
The target value _V0 will always be maintained. Note that, as is clear, the above-described surface potential control can be continuously performed at all times even during the copying operation.

FIG. 4 shows how the second surface potential sensor 3A is connected to the exposure section 4.
This is another embodiment of the present invention arranged after (downstream side).

In this case, the distance between the first surface potential sensor 3 and the second surface potential sensor 3A can be made longer than in the case of FIG. Since it can be arranged, the accuracy of estimating the surface potential V ₃ directly under the developing device 5 can be improved.

However, in this case, the second surface potential sensor 3
At position A, since an electrostatic latent image is formed on the photosensitive drum 1, it is extremely difficult to accurately measure the surface potential. Therefore, it is not possible to control the charging current by controlling the charging high-voltage power supply 10 during normal copying operations.

That is, in order to realize the embodiment shown in FIG. 4, the charging current is controlled only in a special mode such as immediately after the power is turned on, or an area is provided on the photosensitive drum 1 where no electrostatic latent image is formed. It is necessary to take measures such as arranging a second surface potential sensor in that area.

In the above explanation, two surface potential sensors were used along the moving path of the photoconductor in order to directly approximate the dark decay characteristic (linear equation), but instead, other functions (hyperbolic, quadratic) were used. It will be easily understood that in the case of using a function (e.g., an exponent, a logarithm, etc.), the number of surface potential sensors may be selected depending on the number of constants (coefficients) in these functions.

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

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure shows an example of the dark decay characteristic of a photoreceptor, FIG. 3 is a diagram for explaining the method for estimating the surface potential of the developing section according to the present invention, and FIG. 4 is a block diagram of another embodiment of the present invention. be. DESCRIPTION OF SYMBOLS 1... Photosensitive drum, 2... Charger, 3, 3A... Surface potential sensor, 4... Exposure section, 5... Developing device, 9... Arithmetic control device, 91... A/D converter, 92... Arithmetic unit, 93... Target Potential setting device, 94... Comparator, 9
5... Control calculation section, 96... D/A converter, 10
...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 charging device, a plurality of surface potential sensors, a developing device, etc. arranged in order along the movement path of a photoreceptor, and connected to the charging device. a high-voltage power supply for supplying a charging current to the photoreceptor, 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 surface potentials. Means is supplied with the output of the 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 photoreceptor surface potential is compared with its target value, and includes means for determining 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. Charging current control device for electronic copying machines. 2. The charging current control device for an electronic copying machine according to claim 1, wherein 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. A charging current control device for an electronic copying machine according to claim 1.