JPH04110970A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of the sticking of a carrier by changing the limit value of the variable range of a developing bias voltage on an adjustment image density with a value detected by means of a toner concentration sensor. CONSTITUTION:The photoelectric conversion output of the toner concentration sensor 13 is inputted into a concentration detecting circuit 15 and detected as a concentration signal corresponding to an input level. Then, the detected concentration signal of the concentration detecting circuit 15 is inputted into a control circuit 16, and it sets a developing bias supplying voltage from a power source supplying circuit 17 to a developing unit 9 based on the detection density of a pattern image, at this time. Thus, for instance, when a detection that the toner concentration is low is carried out, an upper limit value within the variable range of the developing bias voltage is set lower, so that the occurrence of the sticking of the toner can be prevented even if the developing bias voltage is set higher by the misoperation, etc., of an user.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus equipped with a two-component developing device, such as a copying machine or a printer.

[Prior art]

An image forming apparatus that forms an electrostatic latent image on a photoreceptor, visualizes the latent image using a developer, transfers the visualized image to a transfer material, and fixes it to form an image. widely known.

In conventional electrophotographic copying machines, an image density adjustment device (button, lever, etc.) is generally installed on the operation panel so that the user can select an arbitrary image density. With this image density adjustment mechanism, in order to increase the image density, the exposure lamp voltage is controlled to lower the lamp voltage, or the developing bias voltage is controlled to lower the developing bias voltage. .

The above-mentioned image density adjustment can always be carried out regardless of the level of toner concentration of the developer in the developing device.

By the way, in an electrophotographic copying machine using a two-component developer, there is a phenomenon in which the carrier of the developer is developed and adheres to the transfer agent.

Particularly, when the toner concentration is low and the developing bias voltage is high, a reverse electric field is generated between the developing roller and the photoreceptor, which tends to cause carrier adhesion. When carrier adhesion occurs, it not only causes transfer and fixing failure due to poor adhesion between the photoreceptor and the transfer material, but also has an adverse effect on the photoreceptor, fixing roller, cleaning blade, etc., such as the occurrence of scratches.

By switching the developing roller bias voltage for the non-image area between images on the photoreceptor so that it is lower than the value for the image area on the photoreceptor, carrier adhesion to the non-image area and toner to the image background area can be reduced. It is known, for example, from Japanese Unexamined Patent Publication No. 1-6966, to prevent the adhesion of carriers, but the problem of carrier adhesion due to changes in toner concentration is not considered.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned conventional problems and provide an image forming apparatus that does not cause carrier adhesion even when the toner concentration decreases.

[Means to solve the problem]

The present invention solves the above problem by forming an electrostatic latent image on a photoreceptor, making the latent image visible using a developer, and transferring the visualized image to a transfer material and fixing it. An image forming apparatus that performs image formation includes a toner density sensor that detects the toner density of a developer and a control unit that controls a developing bias voltage, and adjusts the adjusted image density based on the detected value detected by the toner density sensor. The problem was solved by an image forming apparatus characterized by changing the limit value of the variable range of the developing bias voltage.

[Operation] According to the present invention, the toner concentration of the developer is detected by the toner concentration sensor, and the variable range of the developing bias voltage is set based on the detected value. For example, when it is detected that the toner density is low, by setting the upper limit value within the variable range of the developing bias voltage low, the image density adjustment may be set to "bright", that is, the developing bias voltage may be set to a high value due to user error. Prevent carrier adhesion from occurring.

〔Example〕

The details of the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 conceptually shows the structure of an electrophotographic copying machine equipped with a toner concentration sensor and a developing bias voltage control device according to the present invention. A detection pattern 3 is provided. The toner density detection pattern 3 is illuminated by a light source lamp 4 that illuminates the original.

First, as a preliminary step for copying, the original to be copied for the first day has been placed on the platen glass 1, and when a copy cycle operation command is issued, the light source lamp 4 is turned on, and the original is placed under the platen support 2. The arranged toner density detection pattern (hereinafter referred to as pattern) 3 is scanned.

This pattern 3 consists of a reflector having a standard density,
The scanning light passes through an optical system of a mirror 5, a lens 6, and a mirror 7 to a photoreceptor 8 charged by a charging member 10.
forming an electrostatic latent image thereon. The electrostatic latent image of the pattern 3 is then developed by the developing device 9 to become a pattern image with toner of a predetermined density adsorbed, which is transferred as the photoreceptor 8 rotates, and is transferred onto the toner density sensor 13 during separation charging 12. Pass sequentially.

Among those placed on the passing position of this pattern image,
The toner concentration sensor 13 includes, for example, a light emitting element that irradiates the surface of the photoreceptor 8 with a predetermined amount of light, and a light receiving element that receives the reflected light, and converts the light received by the light receiving element into the received light amount. It converts into a corresponding electrical signal and outputs it. The photoelectric conversion output of the toner density sensor 13 is input to a density detection circuit 15, and detected as a density signal according to the input level. Therefore, the detection value of the density detection circuit 15 indicates the density of the pattern image. Next, the detected density signal of the density detection circuit 15 is input to the control circuit 16, and the control circuit 16 sets the developing bias supply voltage from the power supply circuit 17 to the developing device 9 based on the detected density of the pattern image. On the other hand, the pattern image that has passed on the toner density sensor 13 is completely erased from the photosensitive body 8 by the cleaning 14 that passes thereafter. The photoreceptor 8 that has been subjected to such treatment is continuously driven and begins to rotate for the next copy cycle, and as the first operation of this copy cycle, a charging process is performed on the surface of the photoreceptor 8. At the start of this copy cycle, the scanning optical system exposes the photoreceptor 8 that has undergone the charging process through the mirror 5, lens 6, and mirror 7. The electrostatic latent image formed on the photoreceptor 8 by the exposure is then developed by a developing device 9 to form a toner image. At this timing, the control circuit 16 starts controlling the supply from the power supply circuit 17 to the developing roller of the developing device 9 based on a preset voltage value according to the density of the pattern image, Apply developing bias voltage.

- In the above-mentioned developing process, the toner particles (+) on the surface of the developing roller are electrostatically attracted to the photoconductor 8 due to the potential difference between the surface potential of the photoconductor 8 and the developing bias voltage applied to the developing roller. However, as the toner concentration of the developer decreases, when a high developing bias voltage is applied, a reverse electric field is generated in the gap between the non-image area of the photoreceptor 8 and the developing roller, and the carrier particles (-) are It is electrostatically attracted to the photoreceptor 8.

Therefore, in this embodiment, the developing bias voltage is set in accordance with the toner density as follows.

When the toner density is at the normal control level, the image density adjustment device on the operation panel shown in Figure 2! Select the desired density on the density step display scale 21 by operating the button 20, and then set the exposure lamp voltage and development current voltage as shown in Tables 1 and 3.
As shown in the figure and FIG. 4, settings are made according to the density so that an arbitrary image density can be obtained.

Table 1 In FIG. 3, the horizontal axis shows the notch, and the vertical axis shows the bias voltage, and in FIG. 4, the horizontal axis shows the notch, and the vertical axis shows the lamp voltage.

When toner near-end or toner end (low toner density) is detected, turn the notch 6.7 as shown in Table 2 and Figure 5.
In the diagram, the horizontal axis shows the notch and the vertical axis shows the bias voltage.

Table 2 In Fig. 5, the dashed line indicates the developing bias voltage when a≦v, , <b, and the solid line indicates the developing bias voltage when b<v, eV! F indicates the output of the toner concentration sensor.

The developing bias voltages of the notches 6 and 7 are set to a voltage lower than the normal voltage shown in FIG. 3 to prevent carrier adhesion. FIG. 6 shows the relationship between toner concentration, toner concentration sensor output, and developing bias voltage. When the toner concentration decreases, the developing bias voltage is changed from 240 V to -200 V for notch 6, for example, from 240 V to -200 V for notch 7, and It decreases from -280■ to -1240■ and further to -1200■. The embodiment shown here relates to an electrophotographic copying machine in which a photoreceptor is charged (-).

Some models already have a means for detecting the density of the pattern image during the dead cycle immediately after the start of the copy cycle as a component such as a sensor that controls toner density by detecting the magnetic permeability of the developer. By using the same function, the configuration can be simplified.

〔effect〕

According to the present invention, in an image forming apparatus, the range that can be varied by the image density adjustment device of the bias voltage applied to the developing roller during development is regulated according to the toner density of the developer. For example, carrier adhesion that occurs when a high bias voltage is applied at a low toner concentration can be prevented.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an image forming apparatus according to the present invention, and FIG.
The figure is a schematic diagram showing the image density adjustment device on the operation panel.
The depression shows the variable range of the developing bias voltage when adjusting the image density, Figure 4 shows the variable range of the exposure lamp voltage, and Figure 5 shows the change in the limit value of the variable range of the developing bias voltage when the density decreases. FIG. 6 is a diagram showing the relationship between toner density and developing bias voltage. ]...Contact glass 3...Toner density detection pattern 4...Light source lamp 9...Developer 13...Toner density sensor 15...Toner density detection circuit 3rd

Claims (1)

[Claims] In an image forming apparatus that forms an electrostatic latent image on a photoreceptor, visualizes the latent image with a developer, transfers the visualized image to a transfer material, and fixes it to form an image. ,
It includes a toner density sensor that detects the toner density of the developer and a control means that controls a developing bias voltage, and the limit of the variable range of the developing bias voltage regarding the adjusted image density is determined based on the detected value detected by the toner density sensor. An image forming device characterized by changing values.