JPH0318183B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an electrophotographic method that incorporates potential control by controlling the amount of discharge of a corona discharger to the photoreceptor in order to form a latent image on the photoreceptor at a predetermined potential. It is related to. Furthermore, it relates to potential control when changing the rotational speed of the photoreceptor, that is, when reducing the speed for reduction and increasing it for enlargement.

In the conventional potential control method, in order to form a latent image of a predetermined potential on the photoreceptor, first a latent image with a bright and dark pattern is formed on the photoreceptor. The latent image potential of the bright and dark pattern thus formed is measured by a potential sensor, and the amount of corona discharge to the photoreceptor is varied until a desired potential is reached. This change in the amount of corona discharge is controlled so that the latent image of the bright and dark pattern converges to a predetermined potential. For this reason, the conventional potential control method repeats the process (trial latent image formation → potential detection → changing the applied current of the discharger) multiple times, and when the condition is established, this condition is held. is being carried out.
In addition, the potential control method in conventional electrophotography is
It is applied to converge the potential to one predetermined target value.

Next, a case will be described in which the speed of the photoreceptor, that is, the process speed is changed by variable-magnification copying or the like. Note that here, the process speed is changed by a magnification.

Conventionally, for example, the constants required for potential control (target potential, initial value, control system number, etc.) were fixed for the case of equal magnification (1:1), and they were also fixed when the process speed had to be changed when changing the magnification. It was controlled using constants. Even with such a control method, potential control is possible because the potential contrast is controlled to be constant regardless of process speed in either case of equal magnification or variable magnification.
However, in reality, if the initial value is fixed and the process speed changes, the initial charge amount will change, so it will take more time to reach the predetermined potential than when it is the same. In addition, conditions such as the bias voltage value on the developing means side and the rotation speed of the developing sleeve are generally fixed, and as a result, even if the contrast of the latent image is constant due to changes in process speed, the developing results may vary. There will be a difference. For example, when shrinking, the process speed will decrease from the standard value, and the amount of charge will actually increase. Therefore, if the initial amount of charge is set constant, the standard process speed will decrease by the amount of increase in the initial charge amount.
Compared to speed, it takes a longer time to complete potential control and achieve a constant contrast. Also, when a certain contrast is reached with the process speed reduced,
When the development conditions are constant, the amount of development is increased as the speed is reduced, resulting in an image quality that is darker and more prone to background fog than at standard speed. On the other hand, in the case of expansion, the process speed increases, so the initial charge amount decreases compared to the standard time. Similarly to the above, this increases the time required to complete potential control. Furthermore, when the potential of the photoreceptor reaches a predetermined constant contrast, if the developing conditions are constant, the image quality will generally be thin and have intermediate colors easily skipped because the speed has decreased. For this reason, it is inconvenient to keep the control constant fixed when the process speed is variable.

An object of the present invention is to enable potential control to maintain the latent image potential of the photoreceptor at a predetermined value before forming a latent image corresponding to the original image on the photoreceptor even if the speed of the photoreceptor changes due to a change in process speed. This provides a latent image forming method that can be performed in a short time.

In order to achieve the above object, the present invention moves a photoreceptor charged by a discharge means at a first speed and a second speed greater than the first speed, and forms a latent image corresponding to an original image on the photoreceptor. In the latent image forming method, before forming a latent image corresponding to the original image on the photoreceptor, forming an initial latent image on a trial basis by applying an initial value (current or voltage) to the discharge means, Based on the potential of this initial latent image, the applied value (current or voltage) applied to the discharging means is corrected so that the potential of the latent image formed on the photoreceptor becomes a predetermined value, and this corrected applied value is applied to the discharging means. By applying voltage to the means, the potential of the latent image formed on the photoreceptor according to the original image is set to a predetermined value, and when the above initial value is applied, the amount of discharge discharged by the discharge means is set to a predetermined value. is larger when moving at the second speed than when moving at the first speed.

The present invention will be explained in more detail below with reference to Examples.

FIG. 1 shows a sectional view of the main parts of an electrophotographic copying apparatus to which the present invention is applied. In the figure, 1 is a drum-shaped photoreceptor that rotates in the direction of the arrow. This photoreceptor 1 has a conductive base, a photoconductive layer thereon, and a surface insulating layer.
This is disclosed in Japanese Patent No. 23910, and detailed explanation will be omitted here. A latent image corresponding to the original image is formed on the photoreceptor 1 by irradiating the original image with the DC corona from the first corona discharger 2 and the AC corona from the second corona discharger 3, and by further irradiating the entire surface with the lamp 4. It is formed. The latent image on the photoreceptor is then developed with toner by a developer 5, and the developed image is transferred to a transfer material 6 under the electric field of a discharger 7. The transfer material 6 is separated from the photoreceptor by a separation roller 8 and reaches a fixing device (not shown), where the toner is fixed and a copy is completed.
On the other hand, residual toner on the photoreceptor 1 is removed by a cleaning device 9, and the photoreceptor 1 is reused.

In the above apparatus, a potential sensor 10 located downstream of the corona discharger 3 detects the latent image potential on the photoreceptor 1. This potential sensor 10 detects the latent image potential of the photoreceptor when the original exposure lamp is turned off.
V _D and the potential V _L of the latent image corresponding to a white original are measured, and the measured values are fed back to the control section 11 in order to form a latent image with a preset potential on the photoreceptor. That is, the control unit 11 changes the amount of current applied to the first and second dischargers 2 and 3 based on the measured values, thereby adjusting the V _D and V _L described above.
and become the target value. And V _D and V _L
If the original image is exposed on the photoreceptor to form a latent image when the value reaches the target value, a latent image having a predetermined potential can be formed on the photoreceptor. The above discharger 2・
The voltage applied to 3 is controlled by the control unit 11 by changing the output of the high voltage transformer. Further, as a method for forming a light and dark pattern on the photoreceptor, the unexposed state is formed as a dark region (black original), and the blank exposure is formed as a bright region (white original). In this device, the voltages applied to the first and second dischargers 2 and 3 are changed until the measured value by the sensor 10 reaches a predetermined value, and when a latent image of a predetermined potential is obtained, the actual document is The image is exposed onto a photoreceptor 1 to form a latent image for making copies.

By applying the above control method, it is possible to form a latent image at a predetermined potential even if the state of the atmosphere changes or the sensitivity characteristics of the photoreceptor change. Regarding this control method, a patent application filed in 1983 by the applicant
No. 103041 discloses this, and detailed explanation will be omitted here.

Hereinafter, the potential control method in the present invention will be explained in more detail. As an example, a case will be described in which the variable magnification a is obtained. In this case, before copying, start by pressing the selection button to obtain the scaling factor a.

When obtaining the above magnification ratio a, potential target values for dark and bright areas are set in advance to V _D0a and V _L0a . and,
Before actually exposing the original image, the first and second dischargers 2 and 3 are used to form dark and bright latent images on the photoreceptor.
Apply current to. In order to bring this initial current as close to the target value as possible, especially the first and second
The specified outputs I _p1a and I _s1a are used for the discharger. If the potentials of the dark and bright areas become V _D1a and V _L1a , respectively, with this output, the subsequent control is set to V _D0a .
The high-voltage output current to the first and second dischargers 2 and 3 is changed so that the difference from V _D1a and the difference between V _L0a and V _L1a converge to zero. Then, when the output current values of the first and second dischargers for this second time are I _p2a and I _s2a , the control formula for determining this I _p2a and I _s2a is I _p2a = α _1a (V _D0a −V _D1a )+α _2a (V _L
0a −V _L1a ) + I _p1a I _s2a = β _1a (V _D0a −V _D1a ) + β _2a (V _L
0a −V _L1a )+I _s1a . In addition, in the above formula, the coefficient α _1a・α _2a・
β _1a and β _2a are control coefficients determined by the characteristics of the photoreceptor used. Furthermore, the general formula when potential control is performed n times is as follows.

I _p(o+1)a = α _1a (V _D0a −V _Doa ) + α _2a
(V _L0a −V _Loa ) + I _poa I _s(o+1)a = β _1a (V _D0a −V _Doa ) + β _2a
(V _L0a −V _Loa +I _soa . Then, by repeating the above potential control, it is possible to obtain the potential of the target value.

By the way, in the above control method, the magnification ratios are b and c.
When selecting , a in the above method may be replaced with b or c. Here, b is the standard, a is the reduction side, and c is the enlargement side. That is, the magnification ratio is a<b
<c, and the rotational speed of the photoreceptor at that time is Sa,
If Sb and Sc are used, the rotational speed becomes Sc>Sb>Sa.

Therefore, I _p1a < I _p1b < I _p1c I _s1a < I _s1b < I _s1c . The developing ability of the developing means can be increased as the rotational speed of the photoreceptor increases, for example by changing the developing bias, or by changing the amount of toner applied, or by changing one of the potential target values, e.g.
It is better to set V _D0 to V _D0a < V _D0b < V _D0c . Furthermore, correction coefficients α ₁ , α ₂ , β ₁ , β ₂
It is sufficient to select appropriate values for the magnification ratios a, b, and c based on the correlation with the photoreceptor and constants other than these. The potential curves at variable magnifications a, b, and c are
It is shown in the figure. The output currents I _p(o+1) and I _s(o+1) at each magnification ratio a, b, and c are held for a certain period of time or longer and are used as the initial output values for the next control. It becomes possible to improve accuracy.

Without applying the configuration of the present invention, one type of I _p1 , I _s1 , α ₁ , α ₂ ,
When controlling the potential using β ₁ and β ₂ , V _D0 and V _L0 differ depending on each magnification ratio, so a long time is required from the initial latent image formation to obtaining the target value, and prompt and accurate control is difficult. I can't hope.

FIG. 3 shows a block diagram for explaining the operation of the embodiment of the present invention.

When the operator who operates the copying machine according to the magnification ratio selects the curve a shown in FIG. 2, he first presses the switch 12a of the switches 12 labeled "a". switch a
By selecting the initial current setting circuit 13, the initial current setting circuit 13 is also set to obtain an output corresponding to the switch a. Therefore, the initial current is determined to be I _p for the first discharger 2 or I _s for the second discharger 3, _{and the} latent image in the bright and dark areas is is formed.

The latent image pattern formed on the photoreceptor 1 in this way is detected by the sensor 10 and has a potential of V _D1a ,
V _L1a is detected, and based on this measured value, the potential on the photoreceptor 1 is set to the target value in the arithmetic circuit 14.
The output of the high voltage transformer 15 is controlled so that V _D0a and V _L0a are achieved. When the target values are reached, the output currents from the high voltage transformer become I _p2a and I _s2a , and these current values are maintained by the hold circuit 16 and are used as the output during the copy operation and at the same time as the initial current for the next control. used.

In the device shown in FIG. 3, when the magnification is a, pressing the button 12a yields a curve a, but when the magnification is b or c, curve b or c is obtained, respectively.
By pressing the button you can get curve b or c. In the examples, a photoreceptor with a three-layer structure is illustrated as a photoreceptor; however, a photoreceptor with a two-layer structure consisting of a conductive layer and a photoconductive layer, or other photoreceptors may also be used. A similar effect can be obtained by controlling the amount of charge.

As described above, according to the present invention, even if the speed of the photoreceptor changes due to a change in process speed,
By applying the initial value, the amount of discharge discharged by the discharge means changes according to the speed of the photoreceptor, so potential control to bring the latent image potential of the photoreceptor to a predetermined value can be performed in a short time. As a result, the time required for the copying process for making copies can be shortened, and work efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts of a copying apparatus to which the present invention is applied, FIG. 2 is a graph showing the relationship between electric potential and amount of light, and FIG. 3 is a block diagram of a circuit configuration for driving the apparatus. In the figure, 1 is a photoreceptor, 2 is a first discharger, 3 is a second discharger, 10 is a potential sensor, 11 is a control unit, 13 is an initial current setting circuit, 1
4 represents an arithmetic circuit, and 16 represents a hold circuit.

Claims (1)

[Claims] 1. A photoreceptor charged by a discharging means is moved at a first speed and a second speed greater than the first speed, and a latent image corresponding to an original image is formed on the photoreceptor. In the image forming method, before forming a latent image corresponding to the original image on the photoreceptor,
An initial latent image is formed on a trial basis by applying an initial value (current or voltage) to the discharge means, and the applied value (current or voltage) to be applied to the discharge means is applied to the photoreceptor based on the potential of this initial latent image. By correcting the potential of the latent image formed on the photoreceptor so that it becomes a predetermined value, and applying this corrected applied value to the discharge means, the potential of the latent image formed on the photoconductor according to the original image is adjusted to the predetermined value. This means that by applying the above initial value, the amount of discharge discharged by the discharge means is larger when the photoreceptor is moved at the second speed than when it is moved at the first speed. Characteristic latent image formation method.