JPH04153671A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To obtain stable image quality by keeping a transfer electric field constant at the time of transferring an image on a transfer sheet by a transfer means after developing the image by an image developing means. CONSTITUTION:When environmental humidity changes, the resistance of a paper changes, and the transfer electric field changes. There is an interrelationship between the detection of the resistance of the transfer sheet and the detection of the transfer electric field, and the output of a resistance measurement circuit 15 is detected based on measurement data on the resistance value so as to control the potential of the transfer sheet 12 which forms the transfer electric field, and then, the output is inputted in a control circuit 18, and then, it is compared with an optional threshold value set by a setting means 19 by the control circuit 18, and in the case that the output of the resistance measurement circuit 15 does not exceed the threshold value, that means, in the case that the environmental humidity is high, a changeover switch 17 is turned off, on the contrary, in the case that the output of the resistance measurement circuit 15 exceeds the threshold value, that means, in the case that the humidity is normal, the changeover switch 17 is turned on and a transfer sheet guide 16 is grounded so as to obtain a constant transfer electric field. Thus, the transfer image whose density is stable can be obtained.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an electrophotographic apparatus using the so-called Carlson process, in which a latent image formed on an image carrier is visualized and transferred to transfer paper to obtain an image. It is.

Conventional technology Conventionally, in electrophotographic equipment, a photoconductor whose upper surface is uniformly charged is exposed to light to form an electrostatic latent image, and a developer charged to a desired polarity is attached to the electrostatic latent image. A transfer charger applies a charge of opposite polarity to the developer from the back side of the transfer paper, and the developed image on the photoconductor is electrostatically transferred onto the transfer paper to obtain an image ( For example, "Fundamentals and Applications of Electrophotography Technology" published by Corona Publishing, Electrophotography Society & i, page 66).Furthermore, the transfer paper is pre-charged at a position upstream of the transfer charger, the amount of charge is detected by a potential sensor, and the amount of charge is applied to the transfer charger. A method of controlling the voltage has also been proposed (
JP 1-142583).

Problems to be Solved by the Invention In the above conventional electrophotographic apparatus, when used in a high humidity environment, the electrical resistance of the transfer paper decreases, and the transfer electric field changes due to the transfer charger, resulting in a decrease in transfer density. The present invention provides an endless image carrier having photoconductivity for forming a latent image, and a method for imparting a uniform charge to the surface of the image carrier. a charging device, an exposure device for selectively forming a latent image as image information on the uniformly charged surface of the image carrier, and a developing device for visualizing the latent image. a transfer means for transferring the developed image onto the transfer paper; a means for detecting the surface electrical resistance of the transfer paper at a position upstream of the transfer means on the path of the transfer paper; and a means for applying an electric charge to the transfer paper. a paper charging means, a transfer paper guide member that guides the transfer paper to the transfer means at an upstream position of the transfer means and is held insulated and separated from the electrophotographic apparatus main body; and a transfer paper guide member and the electrophotographic apparatus main body. When the output value of the surface electrical resistance detecting means exceeds an arbitrary threshold value, the transfer paper guide member is grounded, and the output value of the surface electrical resistance detecting means exceeds the threshold value. If the transfer paper guide member is not exceeded, a changeover switch member for maintaining the transfer paper guide member insulated and separated from the main body of the electrophotographic apparatus, and a changeover switch member for determining switching of the changeover switch member from the a force result of the surface electric resistance detection means. The electrophotographic apparatus is equipped with a control means that can set the threshold value arbitrarily from the outside. Image information is written on the body as an electrostatic latent image.The surface is developed by the visualization means.The image is transferred to the transfer paper by the transfer means.During this transfer, the transfer charger of the transfer paper is used to write the image on the development transfer surface side. The surface potential changes depending on the thickness of the transfer paper, and the amount of developer transferred from the photoconductor changes, which lowers the transfer density and degrades the quality of the image. There is a change in the transfer electric field due to the transfer charger, which causes the transfer density to decrease.In order to achieve stable image quality by keeping the transfer electric field constant, there is a change in the transfer electric field due to the transfer charger. It detects the surface electrical resistance of the transfer paper at the position and determines whether or not the resistance value exceeds an arbitrarily set threshold value.
If the threshold value is exceeded, the transfer paper guide member is connected to the grounding part of the electrophotographic device.If the threshold value is not exceeded, the transfer paper guide member is insulated and separated from the electrophotographic device body. Dea
EXAMPLE An electrophotographic apparatus according to a first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is formed in the shape of a drum, rotates at a constant speed in the direction of arrow A, and emits light onto its surface. A conductive photoreceptor 2 is a charger for uniformly charging the surface of the photoreceptor 1 using corona discharge, and is disposed close to the photoreceptor 1. An exposure unit 4 consisting of a semiconductor laser, an imaging optical system, etc., is disposed close to the photoreceptor 1 to develop the electrostatic latent image, in order to form an electrostatic latent image thereon as image information. A developed image 7 containing a charged developer 5 and supplied to the photoreceptor 1 by a developing roller 6
is a belt for conveying the transfer paper 12 in the direction of arrow B in synchronization with the rotation of the photoreceptor 1; the belt 7 is a conveyance roller 9;
With tension being applied by 10 and 11,
13 is a transfer charger that uses corona discharge to transfer the developer 5 electrostatically attached to the surface of the photoreceptor 1 onto the transfer paper 12; 14 is the transfer paper 1;
15 is a resistance measuring circuit for measuring resistance; 16 is a transfer paper guide for guiding the transfer paper 12 when conveying the transfer paper 12 onto the belt 7; 17 is a transfer paper guide Grounding force for 16＼ Selector switch for switching between insulation and isolation, 18
The control circuit 19 is composed of a microcomputer or the like for controlling the selector switch 17 according to the output of the resistance measuring circuit 15, and the control circuit 19 is composed of a digital switch or ROM for inputting a threshold value to the control circuit 18. Next, the operation of this embodiment will be explained.While the photoreceptor 1 is being rotated at a constant speed in the direction of arrow A by a drive source (not shown), the charger 2 to which a high voltage of volts is applied is applied. Even if the surface is charged to several hundred volts of positive polarity, the light beam 18 is irradiated onto the photosensitive zone 1 from the exposure unit 3. At this time, a rotating polygon mirror (not shown) and an imaging optical system, etc. Achieves exposure scanning. Image information is formed on the photosensitive belt 1 as an electrostatic latent image due to the difference in brightness and darkness of the beam light 18. Even though the static electricity is removed from the selectively exposed position, the photosensitive member l on which the electrostatic latent image is formed remains on the developing roller. The surface of the developing roller 6 is in contact with the surface of the photoreceptor 1 and is biased with a low voltage, and an electric field is formed between the developing roller 6 and the photoreceptor 1, which causes it to be positively charged. Even though the developer 5 attached thereto adheres to the uncharged portion of the photoreceptor 1 and the electrostatic latent image is visualized, the photoreceptor 1 further rotates in the direction of arrow A.

-X The transfer paper 12 is guided along the transfer paper guide 16 to the belt 7, and the photoreceptor 1 is moved by the belt 7, which moves in the direction of arrow B due to the rotational force of the conveyance rollers 9, 10, and 11.
The transfer charger 13 is inserted between the transfer charger 13 and the transfer charger 13, and a negative high voltage of several volts is applied to the transfer charger 13, causing a corona discharge L.
The developer J9 on the surface of the M light body 1 is negatively charged, and the transfer paper 1 is
The transfer paper 12 is then conveyed to a fixing device (not shown) by the rotational force of the belt 7, and the developed image is fixed to form an electrophotographic image. Although it is generally known that the surface resistance changes depending on the amount of As is clear from the relationship between transfer performance and transfer paper resistance, stable transfer performance can be obtained by keeping the transfer electric field constant at an arbitrary value regardless of transfer paper resistance.
Here, transfer performance generally refers to transfer efficiency.When the environmental humidity changes, the resistance of the paper changes and the transfer electric field changes.Detecting the transfer paper resistance means detecting the transfer electric field. The control circuit 18 detects the 8 forces of the resistance measurement circuit 15 in order to control the potential of the transfer paper 12 forming the transfer electric field based on the measurement data of the resistance value.
The control circuit 18 compares it with an arbitrary threshold value set by the setting means 19 and determines the resistance measurement circuit 1.
If the output of 5 does not exceed the threshold value,
In other words, if the environmental humidity is high, turn the changeover switch 17 to the OFF side, and if the output of the resistance measurement circuit 15 exceeds the threshold value, that is, if the humidity is normal, turn the changeover switch 17 to the ON side and transfer. paper guide 1
By grounding 6, a constant transfer electric field is obtained, and a transferred image with stable density can be obtained.Here, the control circuit 18 is constituted by a microcomputer as described above, and the setting Means 19 can be realized by a so-called hardware configuration such as a digital switch,
Also, the same effect can be obtained by reading the threshold value written in the ROM using the control circuit 18, and the threshold value can be set programmably.

Effects of the Invention Since the present invention is configured as explained above, it has the following effects, and can prevent concentration fluctuations caused by changes in the usage environment.
The purpose is to realize an electrophotographic device that can always obtain transferred images of good quality.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of the main parts of an electrophotographic apparatus according to an embodiment of the present invention.
The figure is a diagram showing the relationship between humidity, surface resistance transfer performance of transfer paper, and value of transfer paper resistance in Examples. Photoconductor 12 Transfer paper 13 Transfer charged edge 15...・Resistance measurement mouth wide 16...Transfer paper guide,
17... Selector switch, 18... Control port 1
9... Name of the designated agent Patent attorney Akira Okaji and 2 others I regret it;

Claims (1)

[Claims] (1) An endless image bearing member having photoconductivity for forming a latent image, a charging means for applying a uniform charge to the surface of the image bearing member, and a charging means for applying a uniform charge to the surface of the image bearing member; an exposure means for selectively forming a latent image as image information on the surface of the image carrier; a developing means for making the latent image visible; and a developing means for transferring the developed image onto transfer paper. a transfer means;
means for detecting the surface electrical resistance of the transfer paper at a position upstream of the transfer means on the transfer paper path; paper charging means for applying electric charge to the transfer paper; a transfer paper guide member that guides the transfer paper to the transfer means and is held insulated and separated from the electrophotographic apparatus main body; and the surface electrical resistance detection means that is provided between the transfer paper guide member and a grounding portion of the electrophotographic apparatus main body. When the output value of the surface electrical resistance detection means exceeds a certain threshold value, the transfer paper guide member is grounded, and when the output value of the surface electrical resistance detection means does not exceed the threshold value, the transfer paper guide member is connected to the electrophotographic apparatus. a changeover switch member for maintaining an insulated state separated from the main body; and a control means capable of externally setting the threshold value for determining switching of the changeover switch member based on the output result of the surface electric resistance detection means. An electrophotographic device characterized by comprising: