JPS6019177A - Adjusting device of image density - Google Patents

Abstract

PURPOSE:To stabilize always an image density independently of a difference of paper quality or copy condition to improve the image quality, by measuring a leak current from a transfer paper to which an electric charge is given by a transfer charger and controlling a developing bias in accordance with the measured result. CONSTITUTION:An electric charge is given to a transfer paper 18 by a transfer charger 16; and if the transfer paper 18 is humid, the electric charge holding rate is reduced, and the electric charge is leaked to a guide part 17. This leak current is measured by a measuring device 20, and the voltage of a developing bias device 13a of a developing device 13 is varied by a controller 22 to raise the developing density at a development time. Thus, the image density is always held stably to improve the image quality even if the paper quality of the transfer paper 18 or environmental conditions of atmospheric humidity are varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image density adjustment device for stably maintaining the image density of a copied image, for example in a copying machine or the like.

[Technical background of the invention and its problems]

Conventionally, in copying machines, etc., a latent image is formed on a photoreceptor, powder toner is electrostatically attracted to this latent image to develop it, and then this toner image is transferred to transfer paper and further fixed. However, such devices generally have the problem that the image density of the copied image is greatly influenced by the difference in the resistance value of the transfer paper. There is. In other words, the low resistance value of the transfer paper means that the charge retention rate of the transfer paper is low, and the electrical charge on the transfer paper caused by the transfer charger during transfer leaks from the guide part that comes into contact with the transfer paper, and the charge retention rate of the transfer paper is low. As a result, the toner image transfer efficiency is lowered and the image density is lowered. For this reason, even if transfer paper of the same quality is used, if the transfer paper becomes damp or stiff during storage, or if the humidity around the copying machine is high due to weather, This causes a problem in that the resistance value of the transfer paper is lower than its original value, and as a result, the image density is lowered, and the image quality is significantly degraded.

``Purpose of the Invention'' This invention was made based on the above circumstances, and it is an object of the present invention to constantly maintain stable image density and stably improve image quality, regardless of differences in the resistance value of transfer paper, that is, paper quality, or copying conditions. The purpose of the present invention is to provide an image density adjustment device that can perform the following steps.

[Summary of the invention]

This invention measures the leakage current from the transfer paper during transfer, and adjusts any image forming means using a control device according to the measurement results, thereby maintaining a constant image density and improving image quality. This is what we aim to do.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Around the photoreceptor drum 00) which is an image bearing member, there is a voltage of about 2.
A developing device a3) set at 50 [v), a pre-transfer charger α, and a transfer charger αe are provided. In addition, αη is a guide portion that guides the transfer paper to the transfer position, generally having a resistance value of 109 to 1011 (Ω).
A measuring device (20) is connected to measure the leakage current from the transfer paper H. This measuring device (21) is connected to a control device (2) via a comparison circuit Qυ. One is the developing bias device (13) of the developing device 09.
a). In addition, (c) is a peeling charger,
Qa is a cleaning device, (A) is a static eliminator, and (5) is a powder toner image made of toner having negative charging characteristics.

However, with the start of copying, the photoreceptor drum (IQ is
At the same time, each image forming means is operated, and a powder toner image (2'i) is formed on the photosensitive drum roller 0 and reaches the transfer position. At this time, the developing device (13)
The voltage of the developing bias device (13a) is approximately 250 (V).
is set to . On the other hand, the transfer paper θ mark fed from a paper feed unit (not shown) is conveyed to the transfer position, and is charged with a polarity opposite to that of the toner image (27) by the transfer charger Oe, so that the toner image 07) and the photoreceptor drum The toner image (27) is electrostatically attracted against the electrostatic adhesion force between the parts, and transfer is performed. However, during this transfer, if the transfer paper has a high resistance value of about 1~1d1 [Ω],
Due to its high charge retention rate, there is almost no leakage current from the transfer paper (11) to the guide section side, and the transfer paper (marked with 1 has sufficient electrostatic adsorption force for the toner image (27), resulting in high transfer efficiency. However, if the transfer paper Ql is damp, its resistance value and thus the charge retention rate will be significantly reduced, and most of the charge imparted from the transfer charger (11) onto the transfer paper α barrel will be This will cause leakage to the guide section (L7).Therefore, the measurement device (20 is equipped with transfer paper Qa).
Leakage current from is injected and measured. The measurement result of the measuring device (20) is then transmitted to the control device G! via the comparison circuit (2+). When the output is input to the control device (2X!l), the developing bias device (13
The voltage in a) is automatically varied and controlled to increase the developer density during development. Therefore, in the subsequent copying, since the developing density is increased, the amount of toner in the toner image C is increased to compensate for the decrease in transfer efficiency due to the low resistance value of the transfer paper Q81. It will be necessary to cover it.

Next, the transfer paper 08) is renewed, and if its resistance value is the usual 1 (1' to 1011 [Ω]), the measuring device (
20) Measured that there was no leakage current from the transfer paper ← ladle,
The control device (2) automatically returns the voltage of the developing bias device (13a) to its normal value.

With this configuration, even if the transfer paper α8) is damp or the surrounding area is high humidity, the resistance value of the transfer paper a barrel and thus the transfer efficiency may be reduced, even if it is not developed. Since the density can be covered by automatically increasing the density, the image density of the copied image is kept constant, and regardless of the type of transfer paper or the difference in conditions, a high quality copy image can always be obtained. .

It should be noted that the present invention is not limited to the above-mentioned embodiments and can be modified in various ways. For example, the type of transfer paper is not limited, and the normal voltage value of the developing bias device can be changed as desired. Further, the transformer of the pre-transfer charger or the transfer charger may be made variable, and the applied voltage may be controlled by varying the transformer of each charger by a control device according to the measurement result of the measuring device. Furthermore, as in the other modified example shown in FIG. Depending on the measurement result of the device (20), all applied voltages may be controlled simultaneously by the control device (2) to compensate for the decrease in transfer efficiency.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of charge leaked from the transfer paper during transfer is measured, the measurement result is fed back to the image forming means, and the image forming means is automatically adjusted by the control device. Additionally, even if the transfer paper has a low resistance value and poor transfer efficiency, the decrease in transfer efficiency can be compensated for by other image forming means, and the image density of the copied image can be stably maintained. Regardless of the type of transfer paper or environmental conditions such as storage, it is possible to consistently improve image quality.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention, FIG. 1 is a schematic sectional view showing the image forming process, FIG. 2 is a block diagram showing the control of the developing bias, and FIG. 3 is the invention. It is a block diagram showing another modification of . 10... Photosensitive drum, 11... Charger,
11a... Charging transformer, 12... Exposure device, 13
...Developing device, 13a...Developing bias device, I4
. . . Pre-transfer charger, 14a . . . Pre-transfer transformer, 16 . 21... Comparison circuit, 22-
・Control device, 27...Powder toner image agent Patent attorney
Inoue - Male 5 Figure 1 Figure 2 Figure 3 Figure 7

Claims (1)

[Scope of Claims] 1. In an electrophotographic apparatus that forms a toner image on an image carrier using an image forming means and transfers this toner image onto a transfer paper to obtain a copy image, a part of the image forming means a measuring device for measuring the leakage current from the transfer paper charged by the transfer charger; and a control device for controlling the image forming means based on the measurement results of the measuring device; An image θ degree adjusting device characterized in that the density of a copied image is kept constant regardless of leakage current. 2. Image density nl'4 according to claim 1, wherein both image forming means have a developing device as a part thereof, and a control device controls the developing bias of the developing device.
*Device. 3. The image density adjusting device according to claim 1, wherein the control device controls the voltage applied to the transfer charger. 4. The image density adjusting device according to claim 1, wherein the image forming means includes a pre-transfer charger as a part thereof, and a control device controls the voltage applied to the pre-transfer charger. 5. The image forming means has a charging charger in a part thereof,
2. The image density adjusting device according to claim 1, wherein the control device controls the voltage applied to the charger.