JPS60133482A - Electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To enable the optimum image to be maintained always stable by detecting the reflected density of a standard visible image formed separately and controlling developing bias voltage. CONSTITUTION:A photosensitive body uniformly electrostatically charged with a charger 2 is exposed with a reflected light from a standard original 4 formed at the end of a contact glass 3 and from an original 5 to form the electrostatic latent images of both original 4, 5 on the surface of the body 1. The electrostatic latent images are developed with a developing zone 15 to form visible images. A photosensor 16 detects the reflected density of the standard image and the detected output is compared with a reference potential 18 through a comparator 17, and a developing power source 20 of bias voltage is subjected to feedback control with a control circuit 19 so as to always equalize the photosensor 16 output to the reference potential and to control the standard visible image density always constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to electrophotographic apparatus such as electrostatic transfer copying machines.

Conventional structure and problems Generally, electronic copying machines use a process in which a photoreceptor is uniformly charged and a toner powder image on the photoreceptor is transferred to transfer paper, but the image quality is always stable. That is essential. For this purpose, it is important that the potential of the surface of the photoreceptor after uniform charging is always constant.

However, as the photoreceptor is used for an extended period of time, it deteriorates and its charging ability decreases, so that a proper image may not be obtained. Furthermore, the charging ability may change due to changes in environmental conditions, and a normal image may not be obtained.

It is also important that the developer and other process conditions are stable, but these also deteriorate or their values fluctuate, making it difficult to maintain an optimal image.

OBJECTS OF THE INVENTION The present invention aims to eliminate the drawbacks of the above-mentioned conventional examples, and provides an electrophotographic copying apparatus equipped with means for constantly maintaining stable and proper images.

DESCRIPTION OF THE INVENTION In order to achieve the above object, the present invention provides at least a charging means, an exposing means, and a developing means around a photoreceptor.

A photo sensor is provided near the photoreceptor and between the developing means and the cleaning means, and a reference developed image is formed separately from the image area on the photoreceptor. The I sensor detects the reflection density of the reference developed image, and the bias voltage of the developing tank is controlled according to the detection output.This makes it possible to maintain a stable and optimal image at all times. can.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The figure is a configuration diagram schematically showing a copying apparatus to which the present invention is applied.

In the figure, 1 is a photoreceptor, 2 is a charger, 3 is a contact glass, 4 is a reference original, 6 is an original, 6 is an illumination lamp, and a plurality of reflective mirrors 7°8, 9. 10.
11. 12. 13 and lens 14 constitute an optical system. 16 is a developing section, 16 is a photosensor, 17 is a comparator, 18 is a reference potential, 19 is a control circuit for a bias voltage power supply for development, 2○ is a bias voltage power supply for development, 21
22゜23.24 are two transfer paper separations, respectively.
It is a charger for static elimination, and 26 is a cleaning section.

The operation of this embodiment configured as above will be described below.

First, the photoreceptor 1, which is uniformly charged by the charger 2, is exposed to light reflected from the reference original 4 and the original 6 provided at the end of the contact glass 3 to form a reference electrostatic latent image on its surface. do. Next, the electrostatic latent image of this document is developed in the developing section 16 to form a visible image.

The developed image formed on the photoreceptor is transferred by a transfer charger 22 onto paper fed from a paper feeding section 21 .

After the paper is separated by the separation charger 23, the electric potential on the photoreceptor is removed by the neutralization charger 24, and finally, the residual toner on the photoreceptor is removed by the cleaning section 25, and one process is completed.

In this series of steps, the photosensor 16, which is provided immediately after the developing section 16 and is equipped with a light emitting circuit (variable circuit) and a light receiving amplification circuit, detects the reflection density of the reference developed image formed on the photoreceptor. To detect. The output detected by the photosensor 16 is compared with a reference potential 18 through a comparator 17, and the developing bias voltage power supply is applied so that the photosensor output is always equal to the reference potential, that is, the reference developed density is always constant. 2O is feedback-controlled by a control circuit 19. Note that the reference potential 19 is set in advance to a value that provides the optimum image density.

According to the above embodiment, when the photosensor detects the reflection density of the reference developed image and controls the developing bias voltage, since the front part of the document has already been developed, the front part of the image to be formed is There is a possibility that the image condition will be different between the front part and the rear part. Therefore, in this embodiment, when only one copy is to be made or before the first copy, a pre-scan is performed so that the irradiation lamp 6 irradiates only the reference original, and the reflection density of the reference image formed at this time is detected and the first copy is made. Controls the bias voltage for developing copies.

Next, the reflection density of the reference developed image formed in the first copy is detected to control the developing bias voltage in the second copy, and the same control is repeated thereafter.

Alternatively, even if a photosensor detects the reflection density of the reference developed image and controls the developing bias voltage, the part of the photoreceptor where the original developed image is formed is in front of the developing unit. The reference original may be provided at various positions.

As described above, according to this embodiment, a photosensor for detecting the reflection density of the reference developed image is provided between the developing means and the cleaning means, and the developing bias voltage is controlled according to this detection output. This makes it possible to always maintain an optimal image.

Effects of the Invention As is clear from the above explanation, the present invention forms a reference developed image on a photoreceptor separately from the image area, detects the reflection density of this reference developed image with a photosensor, and uses this detection output as a reference image. Since the developing bias voltage is controlled accordingly, it is possible to compensate for a decrease in the charged potential of the photoreceptor due to fatigue or the like with the developing bias voltage, and to maintain a proper image at all times.

Unfortunately, in the present invention, the reflection density of the reference developed image is detected after development, so even if image deterioration occurs due to deterioration of the developer or changes in other process conditions, the development bias voltage can be adjusted in the same way. It is possible to control and maintain a proper image.

[Brief explanation of the drawing]

The figure is an explanatory diagram schematically showing an embodiment of the present invention. 1...Photoreceptor, 2...Charger, 3...
...Contact glass, 4...Reference originality 1/, 6...Original, 6...Exposure lamp, 7. 8. 9. 10°11, 12. 13-
-,,,,Reflection mirror, 14-------Lens, 16
■・φ・・Developing section, 16”・0・φ A photo sensor, 17
...Comparator, 18...Reference potential, 19
...Development bias voltage power supply control circuit, 2゜・
...Bias voltage power supply for development, 21...
Paper feed section, 22...Transfer charger, 23...
・Separation charger, 24... Static elimination charger, 26...
...Cleaning department.

Claims (1)

[Claims] At least charging means and exposure means are provided around the photoreceptor. The apparatus comprises a developing means, a transfer means, and a cleaning means, and a photosensor is provided near the photoreceptor and between the developing means and the IJ-ning means, and a reference image is provided separately from the image area on the photoreceptor. An electrophotographic copying apparatus characterized in that the reflection density of the reference developed image is detected by the photosensor, and the bias voltage of a developing reservoir is controlled in accordance with the detected output.