JPH06230642A - Potential controller for photosensitive body - Google Patents

Abstract

PURPOSE:To set target dark potential or light potential even when the electrostatic charging characteristic of a photosensitive body is changed with the laps of time or humidity, and to secure the stable light potential even when the surface temperature of the photosensitive body is changed in the midst of forming an image. CONSTITUTION:In an image forming device provided with an electro-static charging amount varying device 27 varying the dark potential of the photosensitive body 17, a light quantity varying device 28 varying the light potential of the photosensitive body 17, an electrometer 19 detecting the potential of the photosensitive body 17, and a temperature sensor 22 detecting the surface temperature of the photosensitive body 17; an arithmetic device 26 is provided, which sets the dark potential of the photosensitive body 17 to a target value before forming the image, and obtains optimum light quantity to get the target light potential after obtaining the target light potential of the photosensitive body 17 in accordance with the surface temperature of the photosensitive body, and corrects the optimum light quantity according to the surface temperature of the photosensitive body at the time of forming the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for stabilizing the potential of a photoconductor in an image forming apparatus such as a copying machine, a facsimile and a printer which uses electrophotography.

[0002]

2. Description of the Related Art In electrophotography, the surface of a rotating photoconductor is uniformly charged, and image information is recorded on the charged photoconductor by exposure to form an electrostatic latent image. Toner is attached to the image for development, the developed image is transferred onto a transfer material, and then fixed.

By the way, a change in the ambient temperature in the machine or a contact between the photosensitive member and the transfer material causes a temperature change of the photosensitive member. As a result, the bright potential changes even though the exposure light amount is constant, so that the exposure light amount is constant. It is known that the image density of 1 cannot be obtained. Therefore, conventionally, as a control method for keeping the bright potential constant, by detecting the surface temperature of the photoconductor, for example, when the temperature is low, the sensitivity is deteriorated so that the exposure light amount is increased. Conversely, when the temperature is high, the sensitivity is increased. Therefore, in order to reduce the exposure light amount, the bright potential is kept constant by outputting the exposure light amount according to the temperature by the table of the relationship between the surface temperature of the photosensitive member and the exposure light amount set in advance. (For example, JP-A-3-163574 and JP-A-4-60661).

[0004]

However, in the above-mentioned conventional method, since the relationship between the surface temperature of the photoconductor and the exposure light amount is very well matched, the fluctuation itself of the bright potential during image formation should be stabilized. However, the shift amount of the target potential itself of the bright potential could not be corrected because the charge amount and the sensitivity of the photoconductor changed with time or humidity.

On the other hand, as a means for correcting the shift amount of the target potential, a method of detecting the humidity in the vicinity of the photoconductor and feeding it back to the potential forming means has been considered (Japanese Patent Publication No. 2-53790, Japanese Patent Publication No. 53790/1990). However, this method has a problem that the relationship between humidity and charging characteristics / sensitivity does not always match well, and correction with time cannot be performed.

According to the present invention, the target dark potential and bright potential can be set even if the charging characteristic of the photoconductor changes with time or humidity, and the photoconductor surface temperature changes during image formation. Another object of the present invention is to provide a photoconductor potential control device that can secure a stable bright potential.

[0007]

To this end, a photoconductor potential control device of the present invention comprises a charge amount varying device for varying the dark potential of the photoconductor, and a light amount varying device for varying the bright potential of the photoconductor. In an image forming apparatus including an electrometer for detecting the potential of the photoconductor and a temperature sensor for detecting the surface temperature of the photoconductor, the dark potential of the photoconductor is set to a target value prior to image formation, and the surface of the photoconductor is also set. After calculating the target bright potential of the photoconductor in accordance with the temperature, the optimum light amount for obtaining the target bright potential is calculated, and at the time of image formation, a computing device is provided for correcting the optimum light amount based on the photoconductor surface temperature. It is characterized by

In the arithmetic unit, the dark potential and the bright potential of the photoconductor are set to target values prior to image formation, the optimum light amount for obtaining the target bright potential is obtained, and the surface of the photoconductor at that time is determined. The temperature may be stored, and at the time of image formation, the optimum light amount may be corrected based on the detected value of the surface temperature of the photoconductor and the stored value.

[0009]

In the present invention, the desired dark potential and bright potential are set up, and a stable bright potential is secured even in the image forming operation.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a photoconductor potential control device of the present invention, which is applied to an electrophotographic copying machine.

The electrophotographic copying machine comprises an image input section 1, an image output section 2, and an image forming section 3. A document 5 placed on a document glass is exposed by a CCD line sensor 7 by an exposure lamp 6.
And the read image signal is exposed to the amplifier 8, A
After being converted into a digital signal through the D / D converter 9, it is sent to the image processing unit 10, where various data processing is performed to convert it into a gradation toner signal, and the D / A converter 11 converts it into a level signal. It is converted and sent to the image output unit 2. In the image output unit 2, the laser 13 is turned on by the laser driving circuit 12, the polygon mirror 14, the fθ lens 1
5, the photoconductor 17 is exposed through the reflection mirror 16.

Around the photoconductor 17, a charging device 18, an electrometer 19, a developing device 20, a transfer device 21, and a temperature sensor 2.
2, a cleaning device 23, and a discharge lamp 24 are provided. The photoconductor 17 rotates as shown by an arrow in the figure, is uniformly charged by the charging device 18, and an electrostatic latent image is formed by the above-mentioned exposure, and the electrostatic latent image is developed into a toner image by the developing device 20. This toner image is transferred onto the transfer material 25 conveyed by the transfer device 21, and is conveyed and fixed by a fixing device (not shown). In addition, the photoconductor 17 after transfer
After being cleaned by the cleaning device 23, the charge is removed by the charge removing lamp 24, and the above-described series of copy cycles are repeated.

In the present invention, the detection signals of the electrometer 19 and the temperature sensor 22 are sent to the arithmetic unit 26, the arithmetic processing described later is performed here, and the result is obtained by the charge amount varying unit 27.
And the laser light amount varying device 28 to control the charging device 18 and the laser driving circuit 12, respectively, so that the dark potential and the bright potential of the photoconductor 17 can be controlled.

Next, the photoconductor potential control of the present invention will be described. 2 is a diagram showing the flow of processing for explaining the control method, FIG. 3 is a diagram showing the relationship between the dark potential and the grid voltage, and FIG. 4 is a diagram showing the relationship between the bright potential and the laser light amount.

In steps S1 to S6 of FIG. 2, when the power of the copying machine is turned on or when a certain period of time elapses prior to the image forming operation, the means for correcting the change in the charge amount and the means for correcting the sensitivity of the photosensitive member are used. A method for obtaining the target dark potential and the target bright potential of the photoconductor is shown.

First, as a dark potential setup, FIG.
As shown in FIG.
Of the grid voltage VG is changed to VG1, VG2 and VG3, and the dark potentials VH1, VH2 and VH3 at that time are measured by the electrometer 19, and the arithmetic unit 26 obtains the relation between the grid voltage VG and the dark potential VH. Target dark potential VH * (eg −
Find the grid voltage VG * which will be 650V).

Next, the grid voltage VG * is output, and the target bright potential VL * is obtained with the target dark potential VH *. As the method, the temperature sensor 22
Then, the surface temperature of the photoconductor is measured according to Table 1, and the target bright potential VL * is obtained according to Table 1. Table 1 is stored in advance in the ROM of the arithmetic unit 26 as a table based on the experimental results. When the surface temperature of the photoconductor is 32 ° C., the bright potential is set to −200 V, and when the temperature is low, the sensitivity deteriorates. The exposure light amount is increased, and conversely, the sensitivity is improved when the temperature is high, so that the exposure light amount is decreased.

[0018]

[Table 1] Next, as shown in FIG. 4, the laser light amount varying device 28 changes the laser light amount L from L1 to L5 so that the target bright potential VL * obtained as described above is obtained. VL1 to VL5 are measured by the electrometer 19, the relationship between the light amount L and the bright potential VL is obtained by the arithmetic unit 26, and the optimum light amount L * that becomes the target bright potential VL * is obtained from the graph,
It is output to the laser light amount varying device 28.

Steps S7 to S9 of FIG. 2 show a method for correcting the fluctuation of the bright potential due to the temperature fluctuation of the photoconductor during the image forming operation. The temperature sensor 22 detects the surface temperature of the photoconductor for each image formation. The amount of light is corrected so that the bright potential becomes the target -200 V by the relational table (experimentally obtained) between the surface temperature of the photoconductor and the amount of exposure light as shown in Table 2. The correction method is step S
According to Table 2, the optimum light amount L * obtained in step 5 is multiplied by a correction coefficient for the temperature to obtain the value.

[0020]

[Table 2] As described above, the desired dark potential and bright potential are set up, and a stable bright potential is secured even during the image forming operation.

Next, another embodiment of the present invention will be described with reference to FIG. The setting of the dark potential in steps S1 and S2 is the same as that in the embodiment of FIG. 2, but in this embodiment, the target bright potential according to the surface temperature of the photoconductor according to Table 1 is not obtained and immediately as shown in FIG. , Laser light intensity variable device 2
8, the laser light amount L is changed from L1 to L5, and the bright potentials VL1 to VL5 at that time are measured by the electrometer 19 to obtain the light amount L.
And the bright potential VL are calculated by the arithmetic unit 26, and the optimum light quantity L * that becomes the target bright potential VL * (in this case, a predetermined value, for example, -200 V) is obtained from the graph,
In addition, the surface temperature of the photoconductor at this time is stored and output to the laser light amount varying device 28.

Steps S7 to S9 in FIG. 5 show a method for correcting the fluctuation of the bright potential due to the temperature fluctuation of the photosensitive member during the image forming operation, and the surface temperature of the photosensitive member is detected by the temperature sensor 22 for each image formation. The optimum light amount is corrected based on the detected value and the stored value of the surface temperature of the photoconductor by the relation table (experimentally obtained) between the photoconductor surface temperature and the exposure light amount as shown in Table 2. . The correction method is obtained by multiplying the optimum light amount obtained in step S4 by (correction coefficient corresponding to detection value / correction coefficient corresponding to stored value).

[0023]

As is apparent from the above description, according to the present invention, the target dark potential and bright potential can be set up even if the charging characteristic of the photoconductor changes with time or humidity, and the image forming operation is performed. Since a stable bright potential can be secured even if the paper comes into contact with the photoconductor and the surface temperature of the photoconductor drops, stable reproduction density and reproduction gradation can always be obtained. Further, when forming an image, a patch for detecting a bright potential is not required, and a gap (inter image) between images can be shortened. Further, in the exposed portion developing method, the bright potential detecting patch is not developed, so that the cleaning device is not burdened.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a photoconductor potential control device of the present invention and applied to an electrophotographic copying machine.

FIG. 2 is a diagram showing a flow of processing for explaining a control method according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between dark potential and grid voltage.

FIG. 4 is a diagram showing a relationship between a bright potential and a laser light amount.

FIG. 5 is a diagram showing a flow of processing for explaining a control method according to another embodiment of the present invention.

[Explanation of symbols]

12 ... Laser drive circuit, 17 ... Photoconductor, 18 ... Charging device, 19 ... Potentiometer 20 ... Developing device, 21 ... Transfer device, 22 ... Temperature sensor,
26 ... Arithmetic device 27 ... Charge amount varying device, 28 ... Light amount varying device

Claims (2)

[Claims] 1. A charge amount varying device for varying the dark potential of a photoconductor, a light amount varying device for varying the bright potential of a photoconductor, an electrometer for detecting the potential of the photoconductor, and a surface temperature of the photoconductor. In the image forming apparatus having a temperature sensor for detecting the, while setting the dark potential of the photoconductor to a target value prior to image formation, after obtaining the target bright potential of the photoconductor according to the photoconductor surface temperature, A photoconductor potential control device comprising: an arithmetic unit that obtains an optimum light amount for obtaining a target bright potential, and corrects the optimum light amount based on the photoconductor surface temperature during image formation. 2. A charge amount varying device for varying the dark potential of the photoconductor, a light amount varying device for varying the bright potential of the photoconductor, an electrometer for detecting the potential of the photoconductor, and a surface temperature of the photoconductor. In an image forming apparatus equipped with a temperature sensor for detecting, a dark potential and a bright potential of the photoconductor are set to target values prior to image formation, and an optimum light amount for obtaining the target bright potential is obtained, and A photoconductor potential control device comprising: an arithmetic unit that stores a photoconductor surface temperature and corrects the optimum light amount based on a detected value and a stored value of the photoconductor surface temperature during image formation.