JPH0287176A - Control method for surface potential of photosensitive body - Google Patents

Abstract

PURPOSE:To control the surface potential of a photosensitive body constantly and appropriately by previously obtaining the degree of a secular change in the photosensitive body from the relation between grid potential and the surface potential of the photosensitive body and altering the grid potential according to the degree of the secular change. CONSTITUTION:An electrifier 2 is made of scorotron. By altering the grid potential VG impressed on a grid 2b, a current flowing into the photosensitive body 1 from the electrifier 2 can be controlled. A grid potential correction amount calculating means 9 is connected to a high voltage generating circuit 8, and a voltage applied to the grid 2b of the electrifier 2 is controlled according to the difference between the output of a photosensitive surface potential VPR detected by a potential sensor 3 and a target voltage VPET. Namely, the degree of the secular change in the photosensitive body 1 is obtained from the relation between the grid potential VG and the photosensitive body surface potential VPR, and the grid potential of scorotron is altered according to the degree of the secular change. Thus, not only the variance of the photosensitive body but also the secular change can be corrected.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to image output devices such as copying machines and printers,
In particular, the present invention relates to a method of controlling the surface potential of a photoreceptor for forming a latent image.

[Conventional technology]

For example, in a copying machine, a photoreceptor is charged in advance by a charger, and then the photoreceptor is exposed to light reflected from a document to form an electrostatic latent image. This electrostatic latent image is then developed with toner or the like and further transferred onto paper to obtain a copy image.

In this case, the surface potential of the photoreceptor must be maintained at a predetermined constant potential because it has a large effect on the density, latitude, etc. of the copied image.

For this reason, efforts have been made to stabilize the surface potential of the photoreceptor.

For example, it is known to use a scorotron as a charger and control the current flowing into the photoreceptor by changing the bias applied to its grid. It is also known to detect the surface potential of the photoreceptor after being charged and to change the operating parameters of the charger depending on the difference from the target value.

Furthermore, in order to perform more stable control, a combination of the two is also being practiced.

FIG. 3(a) shows the photoreceptor inflow current I. and photoreceptor surface potential V
The relationship between Pl and the grid potential V is shown in the same figure.

FIG. 2C shows the relationship between the grid potential VG and the photoconductor surface potential VP.

As can be seen from these graphs, the surface potential of the photoreceptor can be controlled by changing the grid potential v0 of the scorotron. Therefore, even if there are variations in the characteristics of each photoconductor used in a copying machine, the variations in each photoconductor can be corrected by changing the control characteristics for each photoconductor.

A conventional method for controlling the surface potential of a photoreceptor will be described below.

(i) The surface potential of the photoreceptor after being charged is read by a potential sensor.

(11) Detect the difference between the read value (detected value) and the target value, and calculate the grid potential correction amount based on the following formula (see FIG. 4).

ΔVP1 = ΔVx α However, ΔV: Difference between detected value and target value ΔVG = Grid potential change ΔVpi: Photoconductor surface potential change α: Correction coefficient Note that the correction coefficient α may vary slightly between each photoconductor. However, the vicinity of the target value of the photoreceptor surface potential VPI can be represented by approximately one type of slope.

(iii) The calculated grid potential correction amount is added or subtracted from the current grid potential Vc and applied to the grid.

In this way, by controlling the grid potential V0 according to the read photoconductor surface potential VPI, the photoconductor surface potential can be set to a predetermined value regardless of variations in the charging characteristics of each photoconductor.

[Problem to be solved by the invention]

However, the charging characteristics of the photoreceptor are not constant;
There is a change over time. In other words, the initial characteristics of the photoreceptor are
As shown by the broken line in Figure (a), it is represented by a linear straight line passing approximately through the origin, but when the photoreceptor is used for a long period of time, the characteristics of the photoreceptor change to those shown by the solid line. That is, the relationship between the grid potential v6 and the photoconductor inflow current I0 is only slightly shifted in parallel to the positive side of the photoconductor inflow current I, as shown in FIG. 11b), but the relationship between the photoconductor inflow current In and the photoconductor inflow current I The relationship between the surface potential VPI is as shown by the solid line in FIG.
The maximum value of p m decreases, and furthermore, the photoreceptor surface potential VPI
start-up becomes slower. Therefore, the grid potential V
The relationship between a and the photoreceptor surface potential V□ is shown in FIG.

As mentioned above, as the usage period of the photoreceptor becomes longer, the slope, that is, the correction coefficient indicating the change in the grid potential VG with respect to the photoreceptor surface potential Vpλ, becomes α as shown in FIG.
to α′.

An example of actually measuring changes in the charging characteristics of a photoreceptor over time is shown in Section 7.
As shown in the figure. Figure (a) shows the relationship between the photoconductor inflow current 1° and the photoconductor surface potential VPl, Figure 2 (a) shows the relationship between the grid potential Va and the photoconductor inflow current I0, and figure (a) shows the relationship between the grid potential Va and the photoconductor inflow current I0.
C) shows the relationship between the grid potential v0 and the photoreceptor surface potential VPR. Further, in each figure, characteristic A indicates the initial characteristic of the photoreceptor, characteristic B indicates the characteristic after approximately 100,000 copies, and characteristic C indicates the characteristic after approximately 300,000 copies.

As mentioned above, in the conventional photoreceptor surface potential control method, the grid potential correction amount is calculated by ΔVxα;
Even if the correction coefficient changes from α to α′ due to changes over time, it is calculated with a constant α, so the correction is performed with a smaller correction amount than the actually required grid potential correction amount, and the photoreceptor surface potential There is a problem that it is not possible to match the target value with the target value, or that the convergence to the target value is delayed.

The present invention has been devised to solve the above-mentioned δ self problem, and an object of the present invention is to always perform optimal control of the surface potential of a photoreceptor even when the charging characteristics of the photoreceptor change over time.

[Means to solve the problem]

In order to achieve the above object, the photoreceptor surface potential control method of the present invention charges the photoreceptor with a scorotron, detects the photoreceptor surface potential after charging with a potential sensor, and combines the detected photoreceptor surface potential with a target value. In the photoconductor surface potential control method, the photoconductor surface potential is made constant by comparing the grid potential of the scorotron and changing the grid potential of the scorotron based on the comparative output, Determining the degree of change over time of the photoreceptor,
The method is characterized in that the grid potential is changed depending on the degree of the change over time.

The degree of the change over time can be determined from the value of the grid potential when the target value of the photoreceptor surface potential is obtained, or from the value of the photoreceptor surface potential when a predetermined grid potential is applied.

[Effect]

The change characteristics of the photoreceptor surface potential with respect to the grid potential on the photoreceptor charged by the scorotron change over time. Therefore, in the present invention, the degree of change over time of the photoconductor is determined in advance from the relationship between the grid potential and the photoconductor surface potential, and the degree of change over time of the photoconductor is determined in advance.
The grid potential of the scorotron is also changed depending on the degree of this change over time. This corrects not only variations in the photoreceptor but also changes over time.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 1 is an explanatory diagram schematically showing a configuration example of a copying machine to which the photoreceptor potential control method of the present invention is applied.

In the figure, reference numeral 1 indicates a drum-shaped photoreceptor, and after the photoreceptor 1 is charged by a charger 2 made of a scorotron, a potential sensor 3 detects the surface potential of the photoreceptor.

Next, the photoreceptor 1 is exposed to light reflected from the original or light from an exposure means (not shown) such as a light emitting diode or laser modulated by the video signal, and an electrostatic latent image is formed.

This electrostatic latent image is developed by a developing device 4 to form a toner image, and this toner image is transferred by a transfer device 6 onto a sheet of paper 5 that has been conveyed in synchronization with the rotation of the photoreceptor 1. Furthermore, the toner remaining on the photoconductor 1 after the transfer is removed by the cleaning device 7, and then the photoconductor 1 is charged again by the charger 2.

The charger 2 includes a discharge electrode 2a and a grid 2b, to which predetermined voltages are applied from a high voltage generation circuit 8, respectively. Since this charger 2 is a scorotron, by changing the grid potential V applied to the grid 2b, the photoreceptor inflow current I flows from the charger 2 to the photoreceptor 1.
You can control ゎ. A grid potential correction amount calculation means 9 is connected to the high voltage generation circuit 8, and the charger 2 is adjusted according to the difference between the output of the photoreceptor surface potential Vpm detected by the potential sensor 3 and the target value V□7. The voltage applied to grid 2b is controlled.

Further, the grid potential correction amount calculation means 9 is supplied with a correction coefficient α for adjusting the correction amount for the high voltage generation circuit 8 from the correction coefficient setting means 10. This correction coefficient α is
It is changed according to the grid potential vG.

Next, a photoreceptor potential control method according to the present invention will be explained.

(i) The surface of the photoreceptor 1 is charged by the charger 2.

(ii) The grid potential 3 is set by the correction coefficient setting means lO.
A correction coefficient α is set according to a.

(iii) The surface potential of the photoreceptor after being charged is read by the potential sensor 3 and sent to the grid potential correction amount calculation means 9.

(iv) Detect the difference between the read value (detected value) and the target value and calculate the grid potential correction amount based on the following formula.

Grid potential correction amount=ΔvXα In this embodiment, the correction coefficient α is not a constant value, but is determined by the correction coefficient setting means 10 based on the level of the absolute value of the grid potential V0.

As shown in FIG. 5(C), the photoconductor surface potential V Grid potential V. This makes identification possible.

To explain in more detail, the relationship between the grid potential Vc and the photoreceptor surface potential VPI is shown in characteristics P and Q in FIG.

As shown by R, it changes over time in the direction of the arrow. therefore,
The degree of change over time can be detected by determining the level of grid potential v0゜+Vc++ VO2 corresponding to the target value VPIa of photoreceptor surface potential V□, and the correction coefficient α1゜ is determined based on the degree of change over time. α2. α3
can be set. Table 1 shows the grid potential V0
An example of the relationship between the correction coefficient α and the correction coefficient α is shown below.

Table 1 (v) The calculated grid potential correction amount is added or subtracted from the previous grid potential Va to obtain a new grid potential vG. is applied to grid 2b.

As a result, optimal photoconductor potential control can be performed at all times regardless of variations in the charging characteristics of the photoconductor 1 and changes over time.

In the explanatory diagram shown in FIG. 1, the grid potential correction base calculation hand 9 and the correction coefficient setting means 10 are shown as independent structures in order to facilitate understanding, but the setting of the correction coefficient α and The grid potential correction amount can also be calculated using software using a microcomputer.

Moreover, instead of directly detecting the grid potential vr,
The correction coefficient α may be determined by reading data corresponding to this grid potential Va from within the circuit.

Furthermore, as mentioned earlier, this correction coefficient α indicates the degree of change over time of the photoreceptor 1, so from another perspective, the correction coefficient α indicates the lifespan of the photoreceptor 1. become. Therefore, the correction coefficient α can also be used as a guideline for maintenance work.

Note that in the embodiment shown in FIG. 1, the grid potential v
Although the correction coefficient α is changed according to G, the correction coefficient α is not limited to this;
may be changed.

That is, as shown in FIG.
The photoreceptor surface potential VPl at G II t F is
Vpi+, V□2+VP13 depending on the degree of change over time
Based on this change in the photoreceptor surface potential, the correction coefficient α1. α2. α3 can be set.

In order to obtain this correction coefficient α, for example, a mode is provided in which a predetermined grid potential v6□ is applied to the grid 2b of the charger 2 after the copying machine is powered on and before the first copy is made. The photoreceptor surface potential V□ at this time may be detected, and the correction coefficient α may be set stepwise or linearly in accordance with this value.

Table 2 shows the predetermined grid potential V c l ! An example of the relationship between the photoreceptor surface potential vP and the correction coefficient α at F is shown.

Table 2 Note that in Table 2, the photoreceptor surface potential VP11 and the correction coefficient α are shown as discontinuous values, but Vp*+,
VP12. Other than Vp*s (D M Light body surface 'R
The correction coefficient α for the position L can be obtained by approximate calculation using an interpolation method.

〔Effect of the invention〕

As described above, according to the present invention, the surface potential of the photoreceptor is controlled not only by detecting the surface potential of the photoreceptor (but also by detecting changes over time in the charging characteristics of the photoreceptor). ,
The optimum surface potential of the photoreceptor can always be maintained regardless of variations in the photoreceptor or changes over time. Furthermore, since the decrease in control sensitivity due to changes over time is corrected, the photoreceptor surface potential converges to the target value accurately and in a short time.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram schematically showing a configuration example of a copying machine to which the photoreceptor potential control method of the present invention is applied, FIG. 2 is a graph showing changes over time in photoreceptor surface potential with respect to grid potential, and FIG.
Figures (a), (b), and (C) show the photoreceptor surface potential in the case where changes over time are not considered. A graph showing the relationship between photoreceptor inflow current and grid potential,
Figure 4 is an enlarged graph of the main part of Figure 3 (C), and Figures 5 (a), (b), and (C) are the surface potential of the photoreceptor when considering changes over time, and the photoreceptor surface potential of the photoreceptor. A graph showing the relationship between inflow current and grid potential, Fig. 6 is a graph showing changes in the correction coefficient based on changes over time, Fig. 7 (a),
(b) and (C) are graphs showing actual measurement examples of changes over time in photoreceptor surface potential, photoreceptor inflow current, and grid potential in the photoreceptor. 1: Photoreceptor 2: Charger 2a: Discharge electrode 2b Nigelid 3: Potential sensor 4: Developing device 5: Paper 6: Transfer device 7: Cleaning device 8: High pressure generation circuit 9 Nigellid potential correction amount calculation means 10: Correction coefficient setting means

Claims (1)

[Claims] 1. Charge the photoconductor with a scorotron, detect the surface potential of the photoconductor after charging with a potential sensor, compare the detected photoconductor surface potential with a target value, and adjust the scorotron based on the comparison output. In the method for controlling the surface potential of the photoreceptor in which the surface potential of the photoreceptor is made constant by changing the grid potential of the photoreceptor, the degree of change over time of the photoreceptor is determined in advance from the relationship between the grid potential and the surface potential of the photoreceptor. . A photoconductor surface potential control method, comprising changing the grid potential according to the degree of the change over time. 2. The photoconductor surface potential control method according to claim 1, wherein the degree of change over time of the photoconductor is determined from the value of the grid potential when the photoconductor surface potential of the target value is obtained. 3. The photoconductor surface potential control method according to claim 1, wherein the degree of change over time of the photoconductor is determined from the value of the photoconductor surface potential when a predetermined grid potential is applied.