JPH0442181A - Toner concentration control method - Google Patents

Abstract

PURPOSE:To enable invariably stable and highly reliable toner concentration control by not setting an initial set value when a toner concentration target value is an upper-limit or lower-limit value at the time of the toner concentration control. CONSTITUTION:With a developer concentration signal obtained by detecting the toner concentration in a developing unit, the toner concentration is controlled to the target value between the specific upper-limit value and lower-limit value, and the target value is corrected with a pattern image density signal obtained by detecting the density of a reference pattern image formed on a photosensitive body. In this toner density control method, the pattern image density signal is generated by comparing the ratio of the detected value of the density of the reference pattern image and the detected value of the density of a ground part with the initial set value and when the target value is equal to the upper- limit or lower-limit value, setting operation for the initial set value is not performed. Consequently, abnormal image density due to improper initial value setting under the toner concentration control can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for controlling toner density in an electrophotographic apparatus, and particularly to a method for controlling toner density in an electrophotographic apparatus, and particularly to a method for controlling a toner density on a photoreceptor. The present invention relates to a toner concentration control method characterized in that seismic intensity detection and toner concentration detection in a developing device are used together.

[Conventional technology]

FIG. 3 shows a configuration diagram of an image forming system of an electrophotographic apparatus, which is the premise of the present invention.

This electrophotographic apparatus is a part of a transfer drum type full-color copying machine, and 1 is a developing unit 4 for each color (4Y,
4M, 4C, 4B), and detects the developer concentration (toner concentration) in the developing device 4. Developer concentration sensor (hereinafter referred to as TS sensor), 2 is a paddle provided in each developing device 4. , 3 is a developing sleeve, 9 is a toner hopper, 10 is an agitator, 5 is a photoreceptor drum, 6 is a charger, 7 is an exposure area on the photoreceptor, 8 is a transfer paper wrapped around the transfer charger 11. The transfer drum 12 transfers the image on the photoreceptor drum 5 under the action of the photoreceptor drum 5, and 12 is an optical density sensor (hereinafter referred to as P sensor) that reads the amount of toner adhering to the background portion of the photoreceptor drum 5 and the reference pattern image, and detects the toner density. , I3 is a cleaning section. The operation of this electrophotographic apparatus is performed according to a well-known electrophotographic process, and therefore a description thereof will be omitted.

By the way, as the developer in the developing device in such an electrophotographic apparatus, a two-component developer consisting of a mixture of toner and carrier is usually used. The weight mixing ratio of toner and carrier in this developer greatly affects the development effect of the developer.

That is, if the toner density of the developer is lower than the appropriate value, the density of the developed image will be low. On the other hand, if the toner density becomes too high, the density of the developed image will become too high and fog will increase. Therefore, there is a drawback that the recorded image on the transfer paper 8 becomes inappropriate.

Therefore, in order to always obtain images with a desirable density, it is necessary to bring the toner density of the developer to an appropriate level and to maintain the appropriate level at a constant level during development.

As a means of controlling such toner density to a constant level,
The following was proposed.

For example, there are devices that control the amount of toner replenishment by detecting changes in the magnetic permeability or dielectric constant of the developer, and devices that control the amount of toner replenishment by detecting changes in the magnetic permeability or dielectric constant of the developer. Some devices detect changes in the amount of toner and limit the amount of toner replenishment.

Toner concentration control by the TS sensor 1 will be explained with reference to FIG. The output of the TS sensor 1 exhibits a characteristic that as the toner concentration decreases, the output of the TS sensor 1 increases as shown in FIG. 4. When the TS sensor 1 detects the toner concentration in the developing device 4 and outputs an output value ■, a control means (not shown) controls this output value V and the target potential Vc.
o, , are compared, and by controlling on/off of toner supply, the toner concentration can be controlled to the target concentration.

In addition, the target potential ■ゎ is used to prevent runaway toner concentration control. Upper and lower limit values VMAX + Vl'lIN are provided at ゎ.

However, this control method is easily affected by spent toner, which exists in the developer but does not contribute to actual development, and it is difficult to maintain an appropriate level of toner concentration over a long period of time. .

Furthermore, since the density of the actually developed image is not directly detected, even if the potential on the photoreceptor where the image is formed changes over time and the actual image density deviates from the appropriate value,
There is a drawback that the image density cannot be compensated by feeding back the toner density and changing the toner density.

Therefore, in order to maintain the development effect stably and appropriately for a long period of time in an electrophotographic device, the toner concentration of the developer is detected, and the
It has been proposed to variably control the level at which the previous toner density is detected.

First, the toner concentration control operation by the P sensor 12 will be described with reference to FIG. 5, which shows the output of the P sensor 12 in comparison with the threshold voltage. A reference pattern image is formed on the photosensitive drum 5, and the P sensor 12 detects the background potential VSG and the reference pattern image potential V3. Read V Sr/V s
, and calculate the preset initial setting value (V SP/
Vsc). Compare with. And VSP/VSG>
(VsP/VSG) (+ means low concentration, Vsp/Vsc-
(Vsp/Vsc) If o, the concentration is appropriate, V Sr/V
sc<(V sr/V sc). If so, a controller (not shown) determines that the temperature is high.

In this way, the P sensor 12 reads the reference pattern image potential, and if it is determined that the potential is high, the toner density is lowered.
The technology for correcting the target potential of the TS sensor to increase the toner concentration if it is determined to be low is disclosed in Japanese Patent Application Laid-Open No. 57-1366.
This is disclosed in Publication No. 67 and the like.

FIG. 6 is a control flowchart using a combination of two P sensors and a TS sensor.

Here, if the background potential V3G is larger than the threshold voltage (Y in Sl) and the reference pattern image potential VSP is smaller than V (Y in S2), then the ratio V Sr/
V sc is the initial setting value (V sP/V sc) o
It is determined whether it is larger or smaller (S3, s4), and if it is larger (Y in S3), the target potential of the TS sensor 1 ■. . 7
is shifted to the negative side (S5), and if it is small, (S
4 (Y), and shift to the plus side (S6). If the skin potential VSC is smaller than ■ (N at Sl), ■oO
, , are left as they are. Also, ■. 7 to the negative side, if it becomes smaller than the lower limit value V M I N (Y in S8), V C61'l is changed to V M
IN fake) (SIO), also V. . 7 to the plus side, if V C0fi becomes larger than the upper limit value VMAX, V co, , becomes the upper limit value V MAX
(Sll).

By the way, the above-mentioned initial setting value (Vsp/VsG) at the time of detection by the P sensor 12. Registration in the memory is performed when the machine is delivered, when the developer is replaced, when the sensor is replaced, and when the photoreceptor is replaced. Of these, it is clear that initial settings are required during the first three periods, but it is also necessary when replacing the photoreceptor, since when the latent image characteristics of the photoreceptor change, the latent image of the reference pattern image also changes, and the This is because the amount of toner adhesion changes.

C Problems to be Solved by the Invention] In the above-mentioned conventional technology, when the photoreceptors are intersected, the characteristics of the developer change over time, and naturally, in order to compensate for this,
The target potential ■3°7 is often shifted either upward or downward from the center value.

and target potential ■. . In the case of our upper limit or lower limit, a satisfactory image density on the photoreceptor is not obtained, but it is unavoidably controlled by the developing side density. At this time, if the initial setting mode of the P sensor 12, that is, the mode in which initial setting values are registered, is executed, the image density will be controlled at that density even though it is not appropriate. In other words, there is a problem in that an image density that is too high or too low is obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a toner concentration control method that is always stable and highly reliable by appropriately performing the initial setting mode of the P sensor.

[Means to solve the problem]

The above purpose is to control the toner concentration to a target value between a predetermined upper limit value and a predetermined lower limit value based on a developer concentration signal that detects the toner concentration in the developing device, and to In a toner density control method in which the target value is corrected using a pattern image density signal obtained by detecting the density of a pattern image, the pattern image density signal includes a detection value obtained by detecting the density of the reference pattern image and a detection value obtained by detecting the density of the background portion. The ratio of the values is compared with its initial setting value, and when the target value is the upper limit value or the lower limit value, it is achieved by not performing the setting operation of the initial setting value. .

In addition to the above, the above object can also be achieved by displaying a prohibition of the setting operation of the initial setting value when the target value is the upper limit value or the lower limit value.

[Effect]

During toner density control, if the toner density target value is the upper limit or lower limit, do not set the initial setting value or
Or display prohibition of initial setting operation.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a flowchart regarding the initial setting mode of the P sensor 12 of the control method according to the first embodiment.

In the initial setting mode, first create a latent image and a developed image of the reference pattern image (S20.521), and set the reference pattern image potential V.
The SF and skin potential VSG are read by the P sensor 12 (S
22), this ratio is the initial setting value (VSF/Vsc). However, in this initial setting mode,
Target potential ■ controlled by TS sensor I2. If o7 is the upper limit value or the lower limit value (Y in S23), the initial setting value data is not adopted (S24). If it is not the upper limit value or the lower limit value (N in S23), the initial setting value data is stored in the memory (525), and the initial setting mode is ended.

FIG. 6 is a flowchart in the initial setting mode according to another embodiment.

Similarly to the above, in the initial setting mode, if the target potential V con is the upper limit value VMAX or the lower limit value VMIN (S3
0 (Y), the initial setting mode is prohibited (S31), and a display to that effect (not shown) is displayed (S32).

The target potential V e6 is the upper limit value VMAX or the lower limit value V
If there is no KIN (S30), the same processing as steps S20 to S22 and S25 described in the first embodiment is performed (833 to 836).

〔Effect of the invention〕

As explained above, according to the invention described in the present application, when initializing the pattern image density signal based on the detection value of the P sensor, T
When the toner concentration target value of the S sensor is at the upper or lower limit, the initial setting value is not set or a display prohibiting the initial setting operation is displayed to prevent images caused by inappropriate initial value setting of toner density control. Abnormal concentration can be prevented.

[Brief explanation of the drawing]

1 and 2 are flowcharts of an image density control method according to each embodiment of the present invention, FIG. 3 is a configuration diagram of an image forming system of an electrophotographic apparatus, FIG. 4 is a characteristic diagram of a TS sensor, and FIG. The figure is a characteristic diagram of the P sensor, and FIG. 6 is a flowchart of a conventional image density control method. ■...Developer concentration sensor, 4...Developer, 8...
Photosensitive drum, 12... optical density sensor. Figure 3 Figure 4 Rod Figure 5

Claims (2)

[Claims] (1) Based on a developer concentration signal that detects the toner concentration in the developing device, the toner concentration is controlled to a target value between a predetermined upper limit value and lower limit value, and a reference pattern is formed on the photoreceptor. In a toner density control method in which the target value is corrected using a pattern image density signal obtained by detecting the density of an image, the pattern image density signal includes a detected value obtained by detecting the density of the reference pattern image and a detected value obtained by detecting the density of the background part. The ratio of
The toner density control method for an electrophotographic apparatus is compared with the initial setting value, and when the target value is the upper limit value or the lower limit value, the setting operation of the initial setting value is not performed. . (2) A toner density control method for an electrophotographic apparatus according to claim 1, characterized in that when the target value is the upper limit value or the lower limit value, a prohibition of the setting operation of the initial setting value is displayed. .