JPS60209753A - Copying machine - Google Patents

Abstract

PURPOSE:To keep the surface potential of the circumference of a photosensitive drum constant and to obtain a copied image always stable in density by detecting the surface temp. of an image bearing body and changing the exposure amt. of an preexposure device. CONSTITUTION:The whole surface of a photosensitive body 2a is preexposed with a preexposing light source prior to electrostatic charging, and a controller (b) controls a voltage converter (c) in accordance with a program prescribed in advance in response to a signal sent from a temp. detector (a) for detecting the surface temp. of the photosensitive drum 2 with a temp. sensor 40 to control voltage to be applied to the light source 20. The surface temp. of the drum 2 changed by repeating an image forming cycle of the same original is always detected, and when the body 2a is low (high) in temp., high (low) voltage is applied to the preexposure source 20 to enhance (lower) illuminance, and the amt. of exposure to the body 2 is increased to suppress (enhance) the charging potential of the body 2a. As a result, although the temp. of the photosensitive body changes between the initial stage and the final stage in the repeated copying, the potential of the developing zone of the drum 2 is kept constant, and occurrence of differences in image density can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a copying machine which has been improved so that the exposure amount of a pre-exposure device for an image carrier in an electrophotographic copying plate can be made variable.

[Prior art]

The surface potential charged on the circumferential surface of an image bearing member, that is, a photosensitive drum of an electrophotographic duplicating machine has a characteristic that it gradually decreases as the photosensitive member is repeatedly used.

Such fluctuations in surface potential are due to a decrease in the receptive potential caused by repeated use of the photoreceptor, and as a result, the amount of toner supplied during development decreases and the density of the copied image on recording paper decreases. For example, this may cause insufficient density in thin lines or characters, or in dark areas, resulting in a noticeably low F of the image quality.

In addition, especially in the case of a 5e-Te type photoreceptor drum, when the photoreceptor is in a high temperature state, the amount of fading increases and the receptive potential tends to decrease. In some cases, it may not be possible to continuously obtain images of a constant density from the same original.

As a means of compensating for the decrease in the surface potential of the photoreceptor drum caused by darkening, the density of the toner image formed on the circumferential surface of the photoreceptor drum is constantly optically detected and the density of the toner is increased or decreased as necessary to improve the image quality. A so-called toner control method has been proposed to keep the density constant, but this method is undesirable because it increases the proportion of toner in the developer and promotes dirt in the peripheral device. There is also a method of detecting the rotation speed and increasing the charging current to the photoconductor in response to the rotation speed, thereby increasing the amount of toner adhering to the photoreceptor, but the increase in current value may generate more harmful ozone and This method has drawbacks such as staining the charging electrode wire.

In addition, if strict standards are set for the repeatability and temperature characteristics of the photoreceptor in order to minimize fluctuations in the surface potential of the photoreceptor drum, the quality of the photoreceptor drum production will drop steadily and the copying machine itself will suffer. This will make it expensive.

On the other hand, it is well known that the surface potential of the photoreceptor drum is suppressed and averaged by a uniform full-surface exposure, so-called 110 exposure, performed prior to charging. With such light sources, it is difficult to control the applied voltage corresponding to the amount of exposure, and these light sources also have the disadvantage of emitting high heat and increasing the temperature inside the copying machine, making them impractical.

[Object of the Invention] The present invention aims to provide a copying distance (Jl) that can always obtain a copied image with a stable density by keeping the surface potential on the circumferential surface of a photosensitive drum constant. This is what I did.

[Structure of the invention]

The present invention uses, for example, a light-emitting device as a light source for an exposure device for a photoreceptor drum. ) The luminance of the light emitting diode is changed according to the temperature of the photoreceptor in the photoreceptor drum 111, thereby keeping the surface potential of the photoreceptor 111 constant. Support: After forming this image and transferring the +'+ii image, image formation l'l! j: This is achieved by a copying machine characterized by detecting the temperature of the surface of the image hole 1 (11i) and changing the exposure amount of the pre-exposure device during the copying process in which the j1j exposure is applied to the two image carriers.

〔Example〕

An embodiment according to the present invention is shown in FIGS. 1 and 2.

FIG. 1 shows a light source 2 of a pre-exposure device in a copying machine 1 of the present invention.
This figure shows the arrangement of image carriers (9 bodies, that is, around the photoconductor 2a on the circumferential surface of the photoconductor drum 2, a charging electrode 3, a developing device 5, transfer/separation electrodes 6 and 7, and Electrode 8
, a pre-exposure light source 20 according to the present invention is disposed between each image forming means of the cleaning device 9 and between the charging electrode 3 and the cleaning device 9.

That is, by each of these image forming means, the photoreceptor 2a changes in charge as it rotates clockwise. The image forming process such as power-saving recording of the image on the original paper, toner image formation, and transfer of the recording paper/＼ is achieved, and after that, the residual toner is removed by the cleaning device 9, and the image forming cycle is repeated again using the same original paper. Here, the entire surface of the photoreceptor 2a is subjected to pre-exposure by the pre-exposure light source 20 according to the present invention prior to charging.

In this embodiment, the pre-exposure light source 20 has a wavelength of 570n.
The pre-exposure light source 20 is compact and does not require space, and despite its low price, it has an extremely long life and is excellent in economic efficiency, and the amount of exposure, that is, the brightness of the light emitting diode. can be controlled by forward current. Furthermore, the cold light source has the advantage of not increasing the internal rAa degree by 1-J.

The second part is the leakage of the present invention.
j HI, ζ A method of controlling the seedness of the light source 20>i';
Then, the surface temperature of the photoreceptor drum 2 was set to 2 (U).
In response to the signal from the temperature sensor 40 detected by the temperature sensor 40, the voltage converter is activated according to a program determined by the control unit 1.
j) to control the applied voltage according to the exposure light source 20)
・It is configured so that it can be rolled.

That is, the surface temperature of the drum 2 is detected at 1; By applying a high voltage to 10, its brightness is increased and the amount of exposure to the photoreceptor 2u is greatly reduced.
The charging potential of the photoreceptor 2a is suppressed, and as the temperature of the photoreceptor 2a rises, the exposure light 1! The applied voltage to r'A 20 is lowered to eliminate its brightness, and the amount of exposure applied to the photoreceptor 2a is reduced to eliminate the 1 degrees lower charge potential, resulting in the initial and final stages of repeated copying. It is possible to maintain the potential of the developing portion of the photosensitive drum 2 constant despite the temperature change of the photosensitive wood 2a, and to control the image density so that there is no difference in image density.

Expressing this in a graph, as shown in FIG. However, for the photoconductor 2a having such temperature characteristics, the pre-exposure light source 2 due to the temperature change of the photoconductor 2a as described above
0, that is, when the brightness of the light emitting diode is corrected by varying the applied voltage (indicated by a solid line) as shown in FIG. 2(a), the surface temperature of the photoreceptor drum 2 changes as shown in FIG. 3(c). Regardless of this, it is possible to maintain the potential of the developing portion of the photoreceptor 2a at a substantially constant level.

〔Effect of the invention〕

According to the present invention, the potential of the developing section of the photosensitive drum is kept constant regardless of the temperature of the photosensitive member, and a copying machine capable of always recording high quality images with stable density is provided. It became a thing.

Figure 1 is a sectional view of a copying machine equipped with a pre-exposure device. Figure 2 is a control circuit diagram of a copying machine according to the present invention. Figure 3 has been renamed according to the present invention: δ tram 2...Photoreceptor drum 2a...Photoreceptor 3...4j
'j electrode lj...(shi'v 7L) Ni1j' system 5
Developing device 9 Cleaning device 20 Exposure light source 40 Temperature sensor agent Patent attorney Field 1) Parent-in-law Figure 1 Figure 2 Figure 3 Call S, Sui Thursday Mu! &good

Claims (1)

[Claims] an image carrier, an image is formed on the image carrier, and the image is completely
A copying machine that applies pre-exposure to an image carrier after copying and before image formation, wherein the temperature of the surface of the image carrier is detected to change the exposure amount of a +if exposure device.