JPS62191866A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To stabilize a variation of a characteristic of a photosensitive body, caused by the temperature variation of the photosensitive body, by providing an outside air temperature sensor, in addition to a drum temperature sensor for measuring the temperature of a photosensitive drum. CONSTITUTION:A comparator COMP compares a voltage of a point (a) and a voltage of a point (b), and 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 contrary, in case voltage of the point (a) is below the voltage of the point (b), the voltage of the point (c) is set to 'L'. Also a heater driving circuit 4 turns on a heater 2, in case the voltage of the point (c) is 'H'. A variable resistance VR executes a control so that the voltages of both 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 temperature of both of them is, for instance, within a range of 10-15 deg.C.

Description

[Detailed Description of the Invention] Technical Field> This invention relates to a W using a photoreceptor drum such as an electrophotographic copying machine.
In particular, the present invention relates to an electrophotographic apparatus that obtains stable image quality regardless of outside temperature.

<Prior Art and Its Disadvantages> When a copying process is repeated in an electrophotographic copying machine or the like, the steps of charging and exposing a photoreceptor are repeated. By repeating this operation, the surface of the photoreceptor may be oxidized by O3 generated by corona discharge or corona products (NoX).

HNO:l) 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.

One method for preventing moisture absorption on the surface of a photoreceptor is to control the temperature of the photoreceptor so that it always remains at a constant temperature. However, according to this method, the photoreceptor and parts (toner, cleaner blade) that are in contact with or near the photoreceptor are constantly exposed to high temperatures. When a photoreceptor is exposed to high temperatures, that is, used at high temperatures, image blurring occurs due to crystallization in selenium-based photoreceptors, and in other photoreceptors, including organic photoreceptors, minute defects in the photoresist film cause images to blur. In other words, problems such as white spots tend to occur. In addition, a device that does not control the temperature of the photoreceptor to a constant temperature, but controls the output of the charger so that the surface potential of the photoreceptor is always kept constant according to the temperature of the photoreceptor, has been put into practical use. There is. However, with this method, the output of the charger must be increased at high temperatures, which increases the amount of 03 generated from the charger, increases stress on micro defects in the photosensitive film, and causes image blurring due to surface oxidation and crystallization. This also has the disadvantage of further promoting the appearance of white spots.

In addition, when the temperature of the photoreceptor becomes high, its charging characteristics deteriorate and the photosensitivity increases, resulting in a bright and low-seismic copied image when copying.
When the temperature decreases, the residual potential increases, which has the disadvantage of resulting in a so-called blurred copy image.

<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 tram 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 to a temperature of ~20-odd degrees Celsius, and the exposure amount is controlled so that an appropriate amount of exposure is obtained according to the temperature of the photoreceptor drum. It is.

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 1st charging step, and since the occurrence of white spots due to pinholes and even 03 is reduced, it is possible to suppress the formation of an oxide film. 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, since the exposure amount is optimized according to the sensitivity of the photoreceptor, which changes depending on the temperature, images with appropriate density can always be obtained regardless of the outside temperature.

Embodiment FIG. 1 is a block diagram of a temperature and exposure control device for a photosensitive drum in an electrophotographic apparatus according to an embodiment of the present invention. A heater 2 is provided concentrically inside the photoreceptor tram 1 so as to be substantially in contact with its inner surface. 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 these thermistors 3.6 differ by about 10°C. The variable resistor 7 is used to set this temperature difference. In the figure, 8 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.

Reference numeral 17 denotes a document table, and a copy lamp 16 for illuminating the document is arranged below the document table. The original image is mirror 18.1
The image is formed on the photoreceptor tram 1 via the lens 9 and the lens 20.

The voltage control circuit 15 is the output 1 of the D'/A converter 14.
Is the voltage applied to the copy lamp 16 controlled according to No. 3? 1
tl L, controls the amount of irradiation light.

The CPU 12 reads the temperature of the photosensitive drum detected by the first thermistor 3 via the A/D converter 11 . Data for controlling the voltage to be applied to the copy lamp 16 in accordance with the temperature of the photosensitive drum 16 or data for determining the value thereof are written in advance in the memory 13. C
The PU 12 outputs appropriate 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 manner, an appropriate voltage is applied to the copy lamp 16 in accordance with 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 Rt2 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 equal to or higher than the voltage at point b, the output voltage at point 0 is set to "'H".

If the voltage at point a becomes less than the voltage at point b, the voltage at point 0 becomes “
The heater drive circuit 4 turns on the heater 2 when the voltage is at the 0 point or when the voltage is "L".
The heater 2 is controlled by n so that the voltage at point a and the voltage at point b are equal. With variable grinding (VR), the temperature of the photoreceptor drum is higher than the outside temperature, and the difference between the two is 1
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 the temperature is in the range of 0°C to 15°C. If the variable resistance VRO value is minimized, the voltage at the 0 point becomes "L" when the temperature difference exceeds 10°C. Also variable resistance VR
If you maximize the value of
The voltage at the point becomes "L". In this way, the variable resistance V
By adjusting R, the temperature difference between the outside temperature and the photoreceptor drum is reduced to 10°C.
It can be set in the range of ~15°C.

Figure 3 shows that the difference between the photoreceptor drum temperature and the outside temperature is 5'c, 1
The copy results are shown for each case of 0°C, 125°C, and 235°C. 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. Incidentally, 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 dozen degrees Celsius.

As a result, for example, if the temperature difference is set to 10°C and the outside temperature is very low, around 10°C, the photoreceptor drum temperature will be controlled to 20°C. Generally, in a control method that keeps the photoreceptor temperature constant, the photoreceptor temperature is maintained at a high temperature of around 40° C., so it can be seen that the temperature is extremely 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 tram is low, temperature stress on the developer and cleaner blade is alleviated, thereby extending the life of the photoreceptor.

Common electrophotographic photoreceptors include 3e series and A! 3z
Inorganic photoreceptor such as Se, amorphous Si, CdS
, a resin-dispersed photoreceptor such as Zn○, an OPC system, etc. may be used. All of these materials have the necessary temperature characteristics as semiconductors. Important temperature characteristics in electrophotography include charging ability, photosensitivity, and the like.

For example, using an amorphous Si photoreceptor, 2
When a component-based developer is used, the temperature characteristics of the photoreceptor are such that as the temperature rises, the photosensitivity increases, and the brightness of the image changes accordingly. FIG. 5 is a diagram showing this relationship. In other words, when the photoconductor temperature is 30"C, proper exposure can be obtained when the exposure dial is set to 3, but if the photoconductor temperature changes, the exposure dial that provides the proper exposure changes, making manual adjustment of the exposure amount complicated. This also causes problems when using automatic exposure.

Therefore, the photoreceptor temperature T is set in advance. Accordingly, the change range of the applied voltage of the copy lamp is determined such that the value of the exposure dial 3 or the automatic exposure amount always gives an appropriate exposure amount, and the sensitivity change of the photoreceptor with respect to the photoreceptor temperature is compensated for. Specifically, as shown in FIG. 6, the exposure amount corresponding to the exposure dial is biased according to the photoreceptor temperature T.

The amount by which the exposure amount should be adjusted with respect to the photoreceptor temperature is written in the memory in advance as a calculation formula or a table, as described above.

FIG. 4 shows another embodiment of the invention.

In this embodiment, thermocouples T and C are used in place of the first thermistor Rtl 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.

As described above, the temperature of the Miyakota tram can be adjusted to a few degrees Celsius higher than the outside temperature.
It is possible to set the temperature within a range of 20-odd degrees Celsius, and to optimize the exposure amount according to the temperature of the photoreceptor drum.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a control device that controls the temperature and exposure amount of a photoreceptor drum of an electrophotographic apparatus according to an embodiment of the present invention, Fig. 2 is a schematic circuit diagram of a temperature control circuit, and Fig. 3 is an outside temperature. FIG. 4 shows the copying results for the difference in temperature between
The figure shows another embodiment of the present invention, Figure 5 is a diagram showing the relationship between the photoreceptor drum temperature and the appropriate exposure dial, and Figure 6 shows the appropriate exposure amount for the exposure dial according to the photoreceptor drum temperature. FIG. 1-Photoconductor drum, 2-Heater, 3-Thermistor for measuring photoconductor drum temperature, 6-Thermistor for measuring outside temperature, 15-Voltage control circuit, 16-Copy lamp. @2 Figure 3 Figure 4 Figure 5 Otori round stock drum temperature L T. 67th

Claims (1)

[Claims] (1) A charger, a developer tank, etc. are arranged around the photoreceptor drum, and a heater that heats the photoreceptor drum, a drum temperature sensor that measures the temperature of the photoreceptor drum, and a drum temperature sensor that measures the exposure amount of the photoreceptor drum. In an electrophotographic apparatus equipped with an exposure amount adjusting means for adjusting an outside temperature, an outside temperature sensor for measuring outside temperature, and a temperature of a photoreceptor drum that is higher than the outside temperature measured by this sensor in the range of several degrees Celsius to several tens of degrees Celsius. means for controlling the heater in such a manner; appropriate exposure amount extraction means for determining an exposure amount according to the temperature of the photoreceptor drum; and exposure amount for controlling the exposure amount adjustment means using a signal obtained by the appropriate exposure amount extraction means. An electrophotographic apparatus comprising: an optimization control means; and an electrophotographic apparatus.