JPS62191867A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To stabilize a temperature stress to a photosensitive body and the variation of a characteristic of the photosensitive body to a developer, by providing an outside air temperature sensor, in addition to a drum temperature sensor for measuring the temperature of the photosensitive drum. CONSTITUTION:A comparator COMP compares voltages of a point (a) and a point (b). At the time the voltage of the point (a) exceeds the voltage of the point (b), a voltage of a point (c) of an output is set to 'H'. On the con trary, at the time of the voltage of the point (a) becomes below the voltage of the point (b), the voltage of the point (c) is set to 'L'. A heater driving circuit 4 turns on a heater 2, in case the voltage of the point (c) is 'H'. In this way, a control of the heater 2 is executed so that the voltages of the points (a), (b) become equal. A variable resistance VR executes a control so that the voltages of the points (a), (b) become the same, at the time of a temperature of a photosensitive drum is higher than an outside air temperature, and a differ ence of both of them is, for instance, within a range of 10-15 deg.C.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to an electrophotographic method for compensating for deterioration of image quality due to changes in ambient temperature in electrophotographic copying machines, etc. <Prior art and its disadvantages> If this is repeated, the process of charging and exposing the photoreceptor will be repeated. By repeating this operation, the surface of the photoreceptor may be oxidized by 03 generated by corona discharge or corona products (No.

HNC)+) may adhere. These oxidized layers and corona products are generally highly hygroscopic and thus absorb moisture from the air in high-temperature environments, gradually deteriorating the properties of the photoreceptor. For this reason, the photoreceptor is no longer able to hold the electrostatic latent image, causing image blurring. Conventionally, in order to solve this problem, a heater is provided to heat the photoreceptor drum to keep the temperature of the photoreceptor high and prevent moisture absorption.

There is a method to prevent moisture absorption on the surface of the photoreceptor (one method is to control the temperature of the photoreceptor so that it is always at a constant temperature). When a photoreceptor is exposed to high temperatures, i.e., used at high temperatures, image blurring occurs due to crystallization in selenium-based photoreceptors, and other photoreceptors, including organic photoreceptors, In this method, micro defects in the photoreceptor tend to appear in images, such as white spots, etc.In addition, the temperature of the photoreceptor is not controlled to a constant temperature, and the temperature of the photoreceptor is A system in which the output of the charger is controlled to keep the surface potential constant has also been put into practical use.However, with this method, the output of the charger must be increased at high temperatures, and the charging There were disadvantages such as a large amount of 03 generated from the device, increased stress on micro defects in the photoresist film, causing image blurring due to surface oxidation and crystallization, and further promoting the appearance of white spots.

Furthermore, when the temperature of the photoreceptor increases, its charging characteristics deteriorate and its photosensitivity increases, so that when copying is performed, the resulting copy image may be bright and have low density. Furthermore, as the temperature decreases, the residual potential increases, resulting in a copy image with so-called ground blur.

<Object of the Invention> The object of the present invention is to eliminate the above-mentioned drawbacks by providing an outside temperature sensor in addition to the drum temperature sensor that measures the photoreceptor drum temperature, and to alleviate temperature stress on the photoreceptor and stress on the developer. Another object of the present invention is to provide an electrophotographic apparatus that can stabilize changes in photoreceptor characteristics due to changes in the temperature of the photoreceptor.

<Configuration and Effects of the Invention> The present invention includes an outside temperature sensor that measures outside temperature, and the photoreceptor drum temperature is several degrees Celsius lower than the outside temperature measured by this sensor.
The heater that heats the photoreceptor drum is controlled so that the temperature rises to a temperature in the +ix range of ~20-odd degrees Celsius, and the developer tank that develops the electrostatic latent image formed on the surface of the photoreceptor is controlled according to the temperature of the photoreceptor. The bias is changed.

With this configuration, when the air temperature is low, the drum temperature is also low, so the charger output can be kept low. This makes it possible to reduce the stress on the photoreceptor especially in the ISt charging process, and since the occurrence of white spots due to pinholes and the occurrence of 03 is reduced, it is possible to suppress the production of oxide films. In addition, when the air temperature is low, the drum temperature is lower, which alleviates the temperature stress on the developer and cleaner blade, which has the effect of extending their lifespan. Furthermore, the photosensitivity of the photoreceptor can be lowered when the temperature of the photoreceptor is high, and the photosensitivity of the photoreceptor can be increased when the temperature is low, which has the effect of stabilizing changes in image density due to the temperature of the photoreceptor. be.

Embodiment FIG. 1 is a block diagram of a control device for controlling the temperature of a photosensitive drum and the bias voltage of a developing tank in an electrophotographic apparatus according to an embodiment of the present invention. A heater 2 is provided concentrically inside the photosensitive drum 1 so as to be substantially in contact with the inner surface thereof.

A first thermistor 3 for measuring the surface temperature of the photoreceptor drum 1 is disposed in a partially cut-out portion of the heater 2 . This first thermistor 3 is a drum temperature sensor. Both terminals of the heater 2 are connected to output terminals of a heater drive circuit 4, and the heater drive circuit 4 receives the output of the temperature control circuit 5. The temperature control circuit 5 also receives signals from the first thermistor 3 and a second thermistor 6 that measures the outside temperature.

The temperature control circuit 5 sends a signal to the heater drive circuit 4 to drive the heater 2 so that the temperatures measured by the thermistors 3 and 6 differ by about 10°C. The variable resistor 7 is used to set this temperature difference. In addition, 8 in the figure
1 is a 1st charger, 9 is a developer tank, and 10 is a drum rotating shaft. Further, a second thermistor 6 for measuring the outside temperature is placed at an appropriate location on the main body where the photosensitive drum 1 is installed.

A developing bias transformer 15 applies a bias voltage to the developing tank 9. The developer tank 9 deposits toner in an amount corresponding to the potential of the electrostatic latent image formed on the surface of the photoreceptor drum 1 in accordance with the bias voltage.

CPtJl 2 is connected to the first
The temperature of the photosensitive drum detected by the thermistor 3 is read. Data for determining the value of the bias voltage and tenon value to be applied to the developer tank 9 in accordance with the temperature of the photoreceptor drum is written in the memory 13 in advance. CI)
U 12 outputs optimal bias voltage data to the D/A converter 14 based on the output data of the A/D converter 11 and the data stored in the memory 13 .

In this way, an optimum bias voltage is applied to the developer tank 9 according to the temperature of the photoreceptor drum.

FIG. 2 is a schematic circuit diagram of the temperature control circuit 5. As shown in FIG. The thermistor Rtl corresponds to the first thermistor 3 that measures the temperature of the surface of the photoreceptor. Thermistor RL2 corresponds to the second thermistor 6 that measures the outside temperature. The variable resistor VR is a resistor that adjusts the temperature difference. The comparator COMP compares the voltage at point a and the voltage at point b. When the voltage at point a becomes higher than the voltage at point b, the output voltage at point 0 is set to "H". When the voltage at point a becomes lower than the voltage at point b, the voltage at point 0 is set to “L”.
Set to . The heater drive circuit 4 turns on the heater 2 when the voltage at the 0 point is "H". With such control, a
The heater 2 is controlled so that the voltage at point b is equal to the voltage at point b. Variable resistance VR is used when the temperature of the photoreceptor drum is higher than the outside temperature and the difference between the two is 10°C-15°.
It has a resistance value that can be controlled so that the voltage at point a and the voltage at point b are the same when in the range C. If the value of the variable resistor VR is minimized, the voltage at the 0 point becomes "L" when the temperature difference exceeds 10°C. Also, if the value of the variable resistor VR is maximized, the voltage at the 0 point becomes "L" when the temperature difference exceeds 15°C.
become. In this way, by adjusting the variable resistor VR, the difference in temperature between the outside air temperature and the photoreceptor drum can be set within the range of 10°C to 15°C.

Figure 3 shows that the difference between the photoreceptor drum temperature and the outside temperature is 5"C, 1
The copy results for each case at 0°C, 25°C, and 35°C are shown. As shown in the figure, when the difference between the photoreceptor drum temperature and the outside temperature exceeds 35° C., white spots and toner clumps occur, resulting in poor copy quality and a sharp decrease in the number of sheets to be printed. Note that when the temperature difference is 5° C., the copy quality deteriorates somewhat in terms of ground blur, but all other image quality conditions are favorable.

Therefore, good copy quality can be obtained when the temperature difference is in the range of several degrees Celsius to several tens of degrees Celsius. As a result,
For example, if the temperature difference is set to 10℃, the outside temperature is 10℃.
When the temperature is very low, around .degree. C., the photoreceptor drum temperature is controlled to 20.degree. -Finally, in the control method that keeps the photoreceptor temperature constant, the photoreceptor temperature is maintained at a progeny temperature of around 40'C, so it can be seen that the temperature is very low compared to this. Therefore, since the drum temperature is low, the output of the charger can be kept low, and stress on the photoreceptor can be reduced. Furthermore, since the temperature of the photoreceptor drum is low, temperature stress on the developer and the cleaner blade is alleviated, and the life of the drum can be extended.

General electrophotographic photoreceptors include Se-based, ASz S
e, system, inorganic photoreceptor such as amorphous Si, CdS,
A resin-dispersed photoreceptor such as ZnO, an OPC system, etc. are used. All of these materials have the necessary temperature characteristics as semiconductors. The important temperature characteristics in electrophotography are:
These are temperature characteristics such as charging ability and photosensitivity.

For example, using an amorphous Si photoreceptor, 2
When a component-based developer is used, as shown in FIG. 5, as the temperature rises, the image density decreases as the surface potential decreases. On the other hand, the relationship between the image density I8 and the bias voltage V applied to the developer tank is expressed as shown in FIG. Therefore, the image density I0 can be kept constant by applying the bias voltage (2) to be applied to the developing tank with respect to the temperature T of the photoreceptor as shown in FIG.

In the memory 13 shown in FIG. 1, the relationship between the photoreceptor temperature and the developing bias voltage shown in FIG. 7 is stored in advance as an arithmetic expression or a table. Based on such data, it is possible to determine the optimum bias voltage to be applied to the developer tank depending on the temperature of the photoreceptor drum. Note that only the data representing the relationship between the photoreceptor temperature and image density shown in Figure 5 and the relationship between the developing bias voltage and image density shown in Figure 6 are stored in advance, and the optimum developing bias for the photoreceptor temperature is determined. You can also find the voltage.

FIG. 4 shows another embodiment of the invention.

In this embodiment, thermocouples T and C are used in place of the first thermistor Rtt shown in FIG. 2, and the reference junction is kept at room temperature. According to such a configuration, it is not necessary to use two thermistors as shown in FIG. 2, and only one thermocouple is sufficient. The amplifier OP amplifies the thermocouple output signal, and the comparator COMP compares the voltage at point a and the voltage at point b, similar to the circuit shown in FIG. A variable resistor VR2 sets the difference between the outside temperature and the photoreceptor drum temperature.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a control device for controlling the temperature of a photosensitive drum and bias voltage of a developer tank in an electrophotographic apparatus according to an embodiment of the present invention, FIG. 2 is a schematic block diagram of a temperature control circuit, and FIG. 3 is a diagram of an external device. FIG. 4 is a diagram showing copying results for the difference between air temperature and photoreceptor drum temperature; FIG. 4 is a diagram showing another embodiment of the present invention; FIG.
The figure shows the relationship between photoreceptor temperature and image density, Figure 6 shows the relationship between developing bias voltage and image density, and Figure 7 shows the relationship between optimum developing bias voltage and photoreceptor temperature. . 1-Photoconductor drum, 2-Heater, 3-Thermistor for measuring photoconductor drum temperature, 6-Thermistor for measuring outside temperature, 9-Developing tank, 11-A/D converter, 12-CPtJ. 13-Memory, 14-D/A converter, 15-Development high-speed transformer.

Claims (1)

[Claims] (1) A charger and a developer tank are arranged around the photoreceptor drum, a heater for heating the photoreceptor drum, a drum temperature sensor for measuring the temperature of the photoreceptor drum, and the developer tank for adjusting image density. In the electrophotographic method, which is equipped with a bias voltage application means for applying a bias voltage to means for controlling the heater so as to increase the temperature of the heater; an optimum bias extraction means for obtaining an optimum bias voltage to be applied to the developing tank according to the temperature of the photoreceptor drum; An electrophotographic apparatus comprising: bias voltage control means for controlling an application means.