JPS61281259A - Picture forming device - Google Patents

Abstract

PURPOSE:To control the change of picture density and to prevent the occurrence of fogging even in a photosensitive body such as a-Si in which the effective contrast electric potential is low by changing over the target setting electric potential at an electric potential sensor part in accordance with the dark attenuation of individual photosensitive bodies, and holding constantly the surface electric potential at the developing part. CONSTITUTION:The prescribed target value can be selected and set and the target value is changed over in accordance with the attenuating value of individual photosensitive bodies. The dark part electric potential Vd of the photosensitive body 1 after the primary charging is measured by an electric potential sensor 13, the result and the target collecting value are compared, and thus, the high pressure impressing voltage to a primary charging device 2 is controlled, and controlled so that the Vd can be the target collecting value. Thus, the controlling to hold constantly the surface electric potential at the developing part position, the stabilization of the picture density is executed and the occurrence of the fogging can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus using an electrophotographic photoreceptor having a low effective contrast potential, such as an amorphous silicon (hereinafter referred to as a-Si) photoreceptor. The present invention relates to an image forming apparatus equipped with a control device that maintains a constant potential.

Traditionally, in image forming apparatuses that apply electrophotography, it is necessary to maintain a constant surface potential of the latent image carrier, that is, the electrophotographic photoreceptor, in order to obtain high-quality copies or printed matter. This is important, and various potential control methods have been proposed to maintain the surface potential of the photoreceptor at a predetermined potential.

For example, in order to keep the dark potential Vd constant, the surface of the photoreceptor after primary charging is measured using an electrometer, and depending on the level of the potential, the current amount of the primary charger is increased or decreased. and converged to a predetermined value. The most ideal thing would be to keep the dark potential at the developing area constant, but since it is not possible to measure the potential on the surface of the photoreceptor at the developing area, normally an electrometer is placed just before the developing area. The potential at that position is measured.

However, among electrophotographic photoreceptors, the a-Si photoreceptor has faster dark decay than other photoreceptors such as NP, a-3e, and OPC, and its 1/2 decay time is Therefore, although it varies depending on the speed of the image forming process or the distance between the developer and the electrometer, the dark area potential Vd at the electrometer position and the dark area potential Vd at the developer area position are 50 seconds.
There is a difference of ~200v. Furthermore, the dark decay time differs depending on the individual photoreceptor. For example, if the process speed is 180 m
m/sec, distance between electrometer position and developing section is 40 mm
In the device described above, the variation in dark attenuation from the electrometer position to the developing section is about 50V.

On the other hand, considering that the effective contrast potential of a-3+ thermal exposure is at most 350 to 400 Vl, the above-mentioned dark attenuation variation value of 50 V is by no means small.

Even if the Vd at the electrometer position is held constant in this way, the Vd at the development position is 50% compared to 350 to 400V.
V changes, which causes changes in image density and fog.

Therefore, the present invention eliminates the drawbacks of the prior art as described above, and stabilizes the image density by controlling the surface potential at the developing section position to be kept constant. An object of the present invention is to provide an image forming apparatus that can prevent the occurrence of fog.

The above objects are achieved by an image forming apparatus according to the present invention. To summarize the present invention, a photoreceptor having a low effective contrast potential, such as an a-Si photoreceptor, is used, and the photoreceptor is In an image forming apparatus that detects a surface potential and controls the value to converge to a predetermined value, the predetermined convergence value can be selected and set, and the convergence value is set according to the dark attenuation value of each photoreceptor. The image forming apparatus is characterized in that the image forming apparatus can be switched.

Next, the image forming apparatus according to the present invention will be explained in more detail.

First, an embodiment of the image forming apparatus according to the present invention is shown in FIG. 1, and its overall configuration will be explained. The image forming apparatus has a photoreceptor layer, particularly an a-Si photoreceptor layer, on two surfaces approximately in the center. The formed photoreceptor drum l is placed. It is assumed that the photosensitive drum l rotates in the direction of the arrow. A primary charger 2 is disposed approximately directly above the photoreceptor drum 1, and performs positive charging to form a latent image. An image exposure unit 3 projects an original image onto a photoreceptor l. Image exposure includes image exposure through a lens system, image signal exposure using a laser beam, image signal exposure using a liquid crystal shutter array, and the like. With the above configuration, an electrostatic latent image is formed on the photoreceptor 1, and the latent image is developed and visualized as a toner image by the developing device 4.

Thereafter, the toner image is transferred by a transfer charger 6 to a transfer material conveyed via a guide plate 5, and separated by a separation charger 7. The transfer material carrying the toner image is transferred to the conveyor belt 1
1, the image is conveyed to the fixing device 12 and fixed. In the case of regular development, the transfer charger 6 has a positive polarity, and in the case of 0 reversal development, in which negatively biased AC is often used, the transfer charger 6 has a negative polarity, and the separation charger 7 has a negative polarity. 7, a positively biased AC is often used.

Toner remaining after transfer is neutralized by a pre-cleaning charger 8 and cleaned by a cleaner 9. For the pre-cleaning charger 8, negative polarity DC or AC or negatively biased AC is used in the case of regular development, and positive polarity DC or AC or positively biased AC is used in the case of reversal development. The cleaned surface of the photoreceptor has its charging history erased by uniform exposure lO, and then proceeds to the next image forming process.

In the image forming apparatus configured as described above, the dark potential Vd of the photoconductor l after primary charging is measured by the potential sensor 13, and the result is compared with a target convergence value, thereby increasing the high voltage to the primary charger 2. The applied voltage is controlled so that Vd becomes the target convergence value.

Next, a control system for the photoreceptor surface potential according to the present invention in the developing section will be explained.

FIG. 2 is a block diagram of one embodiment of the potential control system according to the present invention. In this control system, measurement data from potential sensor -13 is compared with data from target value setting section 15 by comparison control section 14 . Target value setting includes a plurality of changeover switches 15a to 15d, and is based on dark decay data of each photoreceptor.

Can be changed depending on the time. The changeover switch can be changed manually according to the value written on the photoreceptor, or code data can be written on the photoreceptor and the code data can be automatically read and changed automatically. It is possible. A high voltage control signal is sent to the high voltage transformer 16 to be compared by the comparison control section 14 and to provide a target convergence value. The high voltage transformer 16
From there, a high voltage output is applied to the primary charger 2, thereby charging the photoreceptor l. Such control is usually repeated two to three times to converge to the target value.

In the above embodiment using an a-Si photoreceptor, Vd in the developing section was 400 V, and bright area potential Vl after image exposure was 50 V.
V, development bias is set to 150V, development contrast is 250V, and fog removal contrast is 10V.
It is set to 0V. The dark attenuation from the sensor 13 to the developing section 4 varies from 5O to 100V depending on the photoreceptor. Therefore, if the target convergence value is set in IOV steps with a margin of 10 V each, it becomes possible to select from 8 stages from 440 to 510 V using a 3-bit changeover switch.

Such a control mode is shown in FIG. The position immediately after the primary charger is a, b is the potential sensor position, and C is the developing unit position. What is the potential of the photoreceptor to obtain the dark area potential Vd=400V in the developing section C?

At point a and point b, there is variation within the area indicated by diagonal lines. Point b 't' is 450V to 500V. The target convergence value at point b is wider by 10V each, ranging from 440V to 510V.
It is considered to be V. This makes it possible to converge photoreceptors with different dark attenuations to 400V in the developing section.

According to another embodiment of the potential control system according to the present invention, ff, 1
By providing another potential sensor between the next charger 2 and the potential sensor 13, the potential of the developing section can be held constant without having to check the dark decay of the photoreceptor in advance. . To explain with reference to FIG. 3, b'
When the second potential sensor is provided at the position, the developing section C is determined from the potential B' there and the potential B of the first potential sensor 13.
This is because the potential at a point is determined by calculation. In other words, the change in potential due to dark decay is expressed as V = A (1 - total e), so if we know the potentials v1 and Vz at two times t1 and tz, we can also enter A using the simultaneous equations, and this This is because the surface potential V3 at time t3 at the developing device position C is determined by this.

Furthermore, a simple linear approximation may be performed.

According to the image forming apparatus according to the present invention, the target potential setting in a part of the potential sensor is changed according to the dark decay of each photoreceptor, and the surface potential in the developing section is kept constant. Therefore, a-5
Even in a photoreceptor having a low effective contrast potential like i, it is possible to control changes in image density and prevent fogging.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of an image forming apparatus of the present invention using an a-Si photoreceptor. FIG. 2 is a block diagram of a potential control system according to the present invention. FIG. 3 is a graph showing changes in dark area potential from immediately after the primary charger to the developing section. 13 Two-potential sensor 14: Comparison control section 15: Target value setting section 16: High voltage transformer

Claims (1)

[Scope of Claims] 1) In an image forming apparatus that detects the surface potential of an electrophotographic photoreceptor and controls the value to converge to a predetermined target value, the predetermined target value can be selected and set; and An image forming apparatus characterized in that the target value is changed according to the dark attenuation value of each photoreceptor. 2) The photoreceptor is an a-Si photoreceptor. Claim 1
Apparatus described in section.