JPH0854767A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To remove load on a cleaner and to prevent wasteful use of toner by preventing toner from being developed on a photoreceptor when potential on the photoreceptor is controlled. CONSTITUTION:A photoreceptor 1 is uniformly electrified by an electrifier 2 and forms potentials of three grades by means of a laser beam emitted from an optical system 9. A high-potential part allows the regular development of toner whose polarity is opposite to that of the photoreceptor 1, by means of a first developing device 4. At this time, a bias voltage is applied to the development roll of the first developing device 4, thereby preventing toner development in the intermediate-potential part and the low-potential part. The low-potential part allows the reversal development of toner whose polarity is the same as that of the photoreceptor 1, by means of a second developing device 5. At this time, a bias voltage is applied to the developing roll of the second developing device 5, toner development is not carried out in the intermediate-potential part and the high-potential part. Therefore, load is not applied on the cleaner and wasteful use of toner is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus, and in particular, it forms a three-step potential consisting of a high potential part, an intermediate potential part and a low potential part on a uniformly charged photoreceptor. The present invention relates to an electrophotographic apparatus that forms toner images of two colors while a photoreceptor rotates once.

[0002]

2. Description of the Related Art A high potential portion on a uniformly charged photoreceptor,
An electrophotographic process in which a three-step potential composed of an intermediate potential part and a low potential part is formed, and a two-color toner image is formed during one rotation of the photoconductor is also called a tri-level method. It is known from US Pat. No. 4,078,929 and the like. This method uses a high-potential portion (V
H), the intermediate potential part (VM) formed by irradiating the photosensitive member with a laser light amount of about a half exposure amount, and the photosensitive member is irradiated with a laser light amount of about 3 to 4 times the half exposure amount. To form a three-stage potential consisting of a low potential portion (VL), and then the first developing means causes the high potential portion (VH) to normally develop the toner charged to the opposite polarity to the photoconductor. The second developing means reversely develops the toner charged to the same potential as the photoconductor on the low potential portion (VL), and the intermediate potential portion (VM) is not developed and becomes the background portion (blank sheet portion). At this time, the bias voltage (VBH) between the high potential portion (VH) and the intermediate potential portion (VM) is applied to the first developing means for performing regular development, and the second phenomenon means for performing reversal development. Has a low potential part (VL) and an intermediate potential part (VM)
Bias voltage (VBL) between and is applied. After the development, the toners having different polarities on the photoconductor are made to have the same polarity by the pre-transfer charger and transferred to the paper at once, and then the toner is fixed on the paper by the fixing device.

[0003]

The advantage of the tri-level method is that since two color toner images can be formed by one optical system, it is inexpensive and high speed can be secured, and the printing position is accurate. . However, the disadvantage of the tri-level system is that since a three-step potential is formed, the difference between the developing section potential and the background section potential is higher than that of an apparatus using a two-step potential.
The so-called potential contrast is reduced. Generally, in an apparatus using a two-step potential, the potential contrast is increased to some extent in consideration of potential variations due to photoconductor manufacturing lot differences, light fatigue, environment, etc., to prevent deterioration of print quality due to potential variations of the photoconductor. ing. If the potential contrast is low, the potential of the photosensitive member fluctuates, so that a print quality problem such as a decrease in print density or occurrence of fog is likely to occur. Therefore, in order to secure and maintain high print quality by the tri-level method, it is important to reduce the potential fluctuation of the photoconductor.

An object of the present invention is to provide an electrophotographic apparatus of high print quality by improving the tri-level system.

[0005]

The above-mentioned object is to provide a charging means for uniformly charging a photoconductor and a three-step potential composed of a high potential part, an intermediate potential part and a low potential part on the uniformly charged photoconductor. An exposing means for forming a toner, a developing means for supplying a toner having a polarity opposite to that of the photoconductor to a high potential portion among the three-stage potentials using the contact magnetic brush developing method, and a contact magnetic brush developing method for the developing means. In an electrophotographic apparatus provided with a developing unit that supplies toner having the same polarity as that of the photoconductor to the low potential portion of the three-stage potential, between the exposure process position by the exposure unit and the development process position by the developing unit. It is achieved by providing a surface potential detecting means on the surface of the photosensitive member and bringing the developer into a non-contact state when measuring the high potential portion, the intermediate potential portion and the low potential portion by the surface potential detecting means.

[0006]

In the electrophotographic apparatus constructed as described above, the toner is not developed on the photoconductor even when the high-potential portion and the low-potential portion pass through the developing device, so that there is no load on the cleaning device and waste of toner. Use is prevented.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the outline of an embodiment of the present invention. The photoconductor 1 is arranged so as to be rotatable at a constant speed in a direction of an arrow, and a charger 2, a surface potential sensor 3, a first developing device 4, a second developing device 5, a pre-transfer charger 6, a transfer member are arranged around the photoconductor 1. A container 7 and a cleaning device 8 are arranged. Further, the surface potential sensor 3 installed between the exposure position of the optical system 9 and the first developing device 4 is the surface potential detecting device 11.
Driven to measure the potential on the photoconductor 1. Based on this measured value, a charge amount control device 13 that controls the voltage or current applied to the high voltage power supply 12, a light amount control device 10 that controls the laser light amount, and a bias high voltage that applies a bias voltage to the developing roll of the first developing device 4. A bias voltage control device 15 for controlling the power supply 14 and a bias voltage control device 17 for controlling a bias high-voltage power supply 16 for applying a bias voltage to the developing roll of the second developing device 5. Next, the printing process of this apparatus will be described. The photoconductor 1 is uniformly charged by the charger 2, and a laser beam emitted from the optical system 9 forms a three-step potential. High potential part (VH)
Is normally developed by the first developing device 4 with toner having a polarity opposite to that of the photoconductor 1. At this time, the bias voltage (VBH) is applied to the developing roller of the first developing device 4, and the toner is not developed on the intermediate potential portion (VM) and the low potential portion (VL). Next, in the low potential portion (VL), the toner having the same polarity as that of the photoconductor 1 is reversely developed by the second developing device 5. At this time, the bias voltage (VBL) is applied to the developing roll of the second developing device 5, and the toner is not developed in the intermediate potential portion (VM) and the high potential portion (VH). Needless to say, the same effect can be obtained even if the first developing device 4 performs the reversal development and the second developing device 5 performs the regular development. After the development, the toners having different polarities on the photoconductor 1 are made to have the same polarity by the pre-transcharger 6 and are transferred to the paper 18 by the transfer device 7.
Is transferred to The untransferred toner remaining on the photoconductor 1 is cleaned by the cleaning device 8 and the above process is repeated. Further, the toner transferred onto the paper 18 is fixed on the paper by being heated and pressed by a fixing device (not shown).

Next, the potential control operation according to the present invention will be specifically described in the case where the photoconductor 1 is negatively charged. The potential control operation is started by turning on the power of the apparatus, restarting after the apparatus such as job end, paper end, toner empty, etc., the specified number of pages to be used, and the operation by the operator. First, by rotating the motor driving the developing roll in the opposite direction to that during normal use for several seconds, the developer existing between the photoconductor 1 and the developing roll is returned to the developing device to remove the photoconductor 1 and the developer. No contact. Another method is to move the developing device in a direction away from the photoconductor 1 so that the photoconductor and the developer are not in contact with each other. Next, rotate the photoconductor 1,
The charger 2 uniformly charges the surface. The high potential portion (VH) formed by not emitting laser light is measured by the surface potential sensor 3, and the applied voltage or current of the charger 2 is adjusted by the charge amount control device 13 so that the value becomes −900 ± 20V. Adjust. The adjusted value is stored in the storage circuit in the surface potential detecting device. Here, it is assumed that the high potential part (VH) is -900V. Next, the low potential portion (VL) formed by irradiating the laser light amount (PH) is measured by the surface potential sensor 3 and similarly stored in the storage circuit. Here, it is assumed that the low potential portion (VL) is −80V. The intermediate potential part (VM) is VM = (VH + VL)
/ 2 = (− 900−80) / 2 = −490V, and the laser light amount (PM) is adjusted by the exposure amount control device 10 so that the intermediate potential portion (VM) becomes −490 ± 10V.

Here, when the capacity or voltage of the high-voltage power supply 12 for controlling the high potential part (VH) reaches a limit value, the high potential part (VH) formed at the limit value is set as a set value. Here, it is assumed that the high potential part (VH) is -850V. It is assumed that the low potential portion (VL) was measured in the same manner as above and that the low potential portion (VL) was -50V. In this case, the intermediate potential part (VM) is VM = (− 850
−50) / 2 = −450V, and the intermediate potential part (VH) becomes −
The laser light amount (PM) is adjusted by the exposure amount control device 10 so as to be 450 ± 10V. Next, the bias voltage is adjusted so as to secure a constant potential difference (ΔVB = −100V) with respect to the intermediate potential section (VM). That is, the intermediate potential part (VM) =-4
When the voltage is 90V, the bias voltage (VBH) applied to the first developing device 4 for normal development is VBH = -490-100 =-
The bias voltage (VBL) applied to the second developing device 5 for reversal development is 590V, and VBL = -490 + 100.
= -390V. Here, when VM = −450V, VBH = −550V and VBL = −350V.

[0010]

As described above, according to the present invention, the toner is prevented from being developed on the photoconductor during the potential control on the photoconductor, so that the cleaning device is not overloaded and the toner is prevented from being wasted. it can. Further, by controlling the potential of the photoconductor, it is possible to stabilize the print density and eliminate the unevenness of the print density in the high-potential portion and the low-potential portion. Further, the life of the photoconductor can be extended and the fog can be prevented by controlling the bias voltage.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a light attenuation curve of a photoconductor.

FIG. 3 is an explanatory diagram showing a potential distribution on a photoconductor.

[Explanation of symbols]

3 ... Surface potential sensor, 10 ... Light quantity control device, 11 ...
Surface potential detection device, 13 ... Charge amount control device, 15 ... Bias voltage control device, 17 ... Bias voltage control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Takahashi 1060 Takeda, Katsuta-shi, Ibaraki Hitachi Koki Co., Ltd. (72) Inventor Yoshihiko Sano 1060 Takeda, Katsuta-shi, Ibaraki Hitachi Koki Co., Ltd. (72 ) Inventor Kazutoshi Ohara 1060 Takeda, Katsuta City, Ibaraki Hitachi Koki Co., Ltd.

Claims (4)

[Claims] 1. A charging means for uniformly charging a photoconductor, and an exposing means for forming a three-step potential composed of a high potential part, an intermediate potential part and a low potential part on the uniformly charged photoconductor.
Among the three potentials using the contact magnetic brush development method, a developing unit that supplies toner having a polarity opposite to that of the photoconductor to the high potential portion, and among the three potentials using the contact magnetic brush development method, In an electrophotographic apparatus provided with a developing unit for supplying toner having the same polarity as that of a photoconductor to a low potential portion, a surface potential detecting unit is provided between an exposing process position by the exposing unit and a developing process position by the developing unit. An electrophotographic apparatus, wherein the developer is brought into a non-contact state with the photoconductor when the high potential portion, the intermediate potential portion and the low potential portion are measured by the surface potential detecting means. 2. A charge amount control means for controlling an applied voltage or a current to the charging means based on an output of the surface potential detecting means, and a light quantity control means for controlling a light quantity of the exposing means. The high potential part (VH), the low potential part (VL) and the intermediate potential part (VM) are controlled by a means and a light amount control means so as to satisfy the relationship of the following formula (1): 1. The electrophotographic apparatus according to 1. VM = (VH + VL) / 2 ... Formula (1) 3. When the control range of the charge amount control means reaches a limit value, the high potential portion (V
3. The electrophotographic apparatus according to claim 2, wherein the light quantity control means controls the light quantity of the exposure means so that the intermediate potential portion (VM) satisfies the relationship of the equation (1) based on (H). . 4. A bias voltage control means for controlling a bias voltage applied to said developing means based on an output of said surface potential detecting means, wherein the bias voltage applied to said developing means is applied to said intermediate potential portion (VM). 2. The electrophotographic apparatus according to claim 1, wherein the electrophotographic apparatus is controlled so that a constant potential difference is maintained.