JP2002108154A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic device capable of stably obtaining satisfactory image quality. SOLUTION: In the electrophotographic device using a contact type electrifying device 2 controlled at constant current, a pre-electrifying device 16 having a developing bias power 14 for applying developing bias to a developing device 4 as its power is disposed on the upper stream side in the rotational direction of a photosensitive body 1 to an electrostatic charge removing device 7 for removing residual electrostatic charge of the photosensitive body 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus such as a copying machine, a printer, a facsimile and the like using an electrophotographic process, and more particularly to an electrophotographic apparatus using a contact type charging device controlled at a constant current.

[0002]

2. Description of the Related Art An electrophotographic apparatus using a charging device of a photosensitive member contact type such as a charging roller is disclosed in Japanese Patent Application Laid-Open Nos. 4-161963 and 4-186261.

[0003] When a negative / positive developing method is used in an electrophotographic process, the polarity applied at the transfer portion is opposite to the charging polarity. In this method, the exposed portion on the photoreceptor is charged to a polarity opposite to the charging potential at the transfer portion after the transfer. Normally, the photoreceptor does not have photoconductivity with respect to the charging of the opposite polarity, so that even if the photoreceptor passes through the charge removing step by exposure, it is not exposed and reaches the charging step while being charged to plus several hundred volts.

[0004]

The function in the charging step of the electrophotographic process is to uniformly charge the photosensitive member to a set voltage, but the constant current control system supplies a constant charge to the photosensitive member. As described above, when the photoconductor surface potential is charged to a polarity opposite to the charging polarity after the transfer, as described above,
When the potential before charging fluctuates as in the case where the residual potential of the photoconductor rises, there is a problem that the charging potential fluctuates accordingly.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrophotographic apparatus capable of stably obtaining good image quality.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic apparatus using a contact-type charging device which is controlled by a constant current, in the rotation direction of the photosensitive member on the upstream side with respect to the static eliminator for removing the residual charge of the photosensitive member. This is achieved by arranging a pre-charging device using a developing bias power supply for applying a developing bias to the developing device as a power source.

[0007]

In the above means, even if the surface potential of the photoreceptor becomes reverse to the charging polarity after passing through the transfer step, the pre-charging device is charged by using the developing bias power supply as a power source, so that the potential before charging is always substantially equal. 0 V, and the charging potential becomes constant.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the outline of the electrophotographic process. In the figure, a charging unit (charging roller) 2, an optical writing unit 3,
A developing unit 4, a transfer unit 5, a cleaning unit 6, and a charge removing unit (light charge removing unit) 7 are arranged. Reference numeral 8 denotes cut paper, 9 denotes a feed roller, 10 denotes a registration roller, 11 denotes a fixing unit, 1
Reference numeral 2 denotes a paper discharge unit.

The surface of the photoreceptor 1 rotating counterclockwise is uniformly charged by the charging unit 2, the charged portion moves with the rotation of the photoreceptor 1, is exposed by the optical writing unit 3, and a latent image is formed. It is formed. This latent image reaches the developing unit 4 by rotation, and is developed by toner. The toner image is synchronized with the paper feed roller 9 and the registration roller 10 at a certain timing.
The paper comes into contact with the cut sheet 8 fed from the transfer section 5 and is transferred onto the cut sheet 8. The cut sheet 8 to which the toner is transferred and adhered is fixed by the fixing unit 11, discharged from the sheet discharging unit 12 to the outside of the apparatus, and formed into a hard copy. on the other hand,
The toner that has not been transferred after passing through the transfer unit is collected by the cleaning unit 6, the surface potential of the photoconductor is set to approximately 0 V by the charge removal unit 7, and this portion returns to the charging unit 2 again. These series of operations are repeated to continuously form a hard copy.

FIG. 2 is a configuration diagram around a photosensitive member of an electrophotographic apparatus according to an embodiment of the present invention. In the figure, reference numeral 13 denotes a constant current negative charging power source, 14 denotes a constant voltage negative developing bias power source, and 15 denotes a constant current positive transfer power source. Also,
A pre-charging device 16 in which, for example, a conductive cloth is brought into contact with the photoconductor 1 is provided downstream of the transfer unit 5 and upstream of the charge removing unit 7 in the rotation direction of the photoconductor 1. This pre-charging device 16
Uses a developing bias power supply 14 as a power supply. The developing bias is usually of the same polarity as the photoconductor charging potential. Photoconductor 1
Is positively charged in the transfer process, the pre-charging device 16
As a result, the photoconductor 1 is negatively charged. The charge potential in this case may be negative since it is before the charge removal step. The negatively charged photoreceptor 1 is pre-charged, and the charged potential on the photoreceptor 1 is always constant because the charge is removed to approximately 0 V in the next charge removal step. Since the developing bias power supply 14 is used as the power supply of the pre-charging device 16, the problem can be solved without increasing the cost. FIG. 3 shows the relationship between the post-transfer potential and the charging potential.

FIG. 4 is a system block diagram of the electrophotographic apparatus. In the figure, 22 is a CPU, 23 is an image input unit, 24 is an image processing unit, 25 is a memory, 26 is an operation unit,
27 is a recording unit (printer engine), 28 is a page memory, 29 is a communication control unit for communicating with an external host,
These units are connected via a system bus 30 to exchange data.

[0013]

According to the first aspect of the present invention, even if the surface potential of the photoreceptor becomes reverse to the charging polarity after passing through the transfer step, the photoreceptor is charged by the pre-charging device. Since the voltage is approximately 0 V, the charging potential is constant, and a good image can be stably obtained. At that time, since a developing bias power supply is used as a power supply for the pre-charging device, the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an outline of an electrophotographic process.

FIG. 2 is a configuration diagram around a photosensitive member of the electrophotographic apparatus according to the embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a post-transfer potential and a charged potential.

FIG. 4 is a system block diagram of the electrophotographic apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging part (charging device) 4 Developing part (developing device) 7 Static elimination part (static elimination device) 13 Charging power source 14 Development bias power source 16 Pre-charging device 22 CPU (control means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H035 AA08 AA14 AA20 AB03 AB06 AZ01 AZ03 BA01 2H073 AA01 BA02 BA13 BA41 BA45 CA01 2H200 FA16 GA14 GA23 GA33 GA44 GB12 GB41 HA02 HB12 HB14 HB41 HB48 JA02 JB10 LA12 NA13 NA13

Claims (1)

[Claims] 1. An electrophotographic apparatus using a contact-type charging device controlled by a constant current, wherein a developing device is developed upstream of a photoconductor in a rotation direction of the photoconductor and a developing device is removed from the developing device. An electrophotographic apparatus, comprising a pre-charging device using a developing bias power source for applying a bias as a power source.