JPH02259676A - Method for controlling concentration of toner contained in developer for image forming device - Google Patents

Abstract

PURPOSE:To evade an unnecessary drop in picture density by utilizing the amount of toner attaching to an image carrier for the control of toner concentration sensors only when the detection timing comes at a specific image forming speed and conversely not controlling the toner concentration sensors based on a change in the amount of toner adhering to the image carrier at other image forming speeds. CONSTITUTION:The image forming device has several image forming speeds such as a specific speed and operation is carried out by switching them, for instance, two- staged switching from a low speed to a high speed and vice versa. In this case, only when a black/while developed image is formed at the high speed, which operation is frequently carried out if the detection timing determined by a toner adhering detecting signal comes, toner concentration is detected to control the toner concentration sensors 31 to 34. Conversely, at speeds other than the specific one, that is, low speed image formation, the action of the toner concentration detecting means is inhibited, or detected data is not utilized for the control of the toner concentration sensors 31 to 34 even when the toner adherence detection timing comes. Consequently, the concentration of toner for an image on the image carrier 2 can be prevented from falling more than expected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the toner concentration of a developer in an image forming apparatus capable of developing with a plurality of types of developers.

[Prior art]

In a color copying machine, which is one of the conventional image forming devices, it is possible to switch between a color image mode in which at least three types of toner images such as cyan, magenta, and yellow are superimposed and transferred, and a black image mode in which black toner is used alone. It is known to do.

In copying machines, efforts are being made to increase the image forming speed because it is desired that the speed be as high as possible, but in color image mode where development is performed using multiple color developers, there are many problems with document illumination devices, fixing devices, etc. Because it requires electricity,
In contrast to the image forming speed, for example, the copying linear speed, in the case of a black image mode in which only black is developed, in the case of color image formation, the copying linear speed is lowered to save labor.

In order to maintain good image quality in copying machines, the toner concentration of each color developer is detected by a toner concentration detection means, and when the toner concentration of each developer decreases, toner is replenished to maintain a constant toner concentration. things are being done.

Even if the toner concentration in the developer of the developing device is maintained constant,
The image bearing member may deteriorate due to changes over time or environmental conditions, and the toner adhesion ability may change.

When an image bearing member, for example a photosensitive drum, deteriorates, the amount of toner adhesion decreases, so in order to ensure a predetermined density, it is necessary to increase the toner density of the developer in the developing device.

When the image forming speed is switched depending on the image mode, the amount of toner adhering to the photosensitive drum, which is an image carrier, during development changes depending on the image forming speed. Even with the same development potential of the photoreceptor drum, the image forming speed is
For example, if the linear speed of the photoreceptor drum and developing device is low, the amount of toner adhesion will be large, and the detected value by the toner adhesion amount detection means tends to evaluate that the amount of toner adhesion is large if the image detection speed is low. . Therefore, even if a sufficient toner density is obtained at a low speed, a sufficient amount of toner adhesion cannot be obtained at a high image forming speed.

Therefore, when controlling the target value of the toner density sensor of the developing unit based on the output of the toner adhesion amount detection means of the image bearing member, it is difficult to control the target value of the toner concentration sensor of the developing unit based on the output of the toner adhesion amount detection means of the image bearing member. If the toner adhesion amount detection timing happens to be during low-speed image formation when there is a lot of image formation and there is little low-speed image formation, such as in color image mode, the image carrier may actually deteriorate.
Even if it is necessary to correct the toner concentration of the developer in the developing device, the toner adhesion amount detection means outputs a signal indicating that the toner concentration is sufficient, and toner concentration control is performed accurately. The problem was that there was no.

[Problem to be solved by the invention]

The present invention solves the above-mentioned conventional problems, and even when the image forming speed is changed, the amount of toner adhering to the image bearing member is maintained without decreasing more than necessary, and image formation is possible that ensures good image quality. An object of the present invention is to provide a method for controlling the toner concentration of a developer in an apparatus.

[Means to solve the problem]

The present invention solves the above problems by being able to develop a latent image formed on an image carrier with a plurality of developers, by switching the image forming speed depending on the type of developer used for development, and by making it possible to develop a latent image formed on an image carrier using a plurality of developers. In a method for controlling toner concentration of a developer in an image forming apparatus, which forms a latent image on an image carrier, detects the amount of toner adhesion after development, and corrects and controls the toner density of a developing device based on information on the amount of toner adhesion. , performs correction control based on the detection of the toner adhesion amount of the specific pattern by the toner adhesion amount detection means only in the case of one image forming speed specified in advance, and performs correction control based on the detection of the toner adhesion amount of the specific pattern in the case of other image forming speeds. The problem has been solved by a method for controlling the toner concentration of a developer in an image forming apparatus, which is characterized by prohibiting correction control based on the above-described method.

[Effect]

According to the present invention, when the image forming speed is switched and used, only when forming an image at a predetermined specific speed,
For example, in the case of two-stage switching between high and low speeds, the toner concentration sensor is controlled by detecting when the detection timing based on the toner adhesion amount detection signal on the image bearing member arrives only during high-speed image formation for black development that uses high carbon usage. When forming an image at a speed other than a specific speed, for example, at a low speed, the operation of the toner adhesion amount detection means is prohibited even when the toner adhesion amount detection timing comes, or the detected data is not used to control the toner density sensor.

According to the present invention, even if the amount of toner adhering to the image carrier changes due to speed switching, it is determined that the amount of toner adhering is large, that is, the toner density is high, and the amount of toner adhering during image formation is detected by the speed at which the amount of toner adhering is likely to be determined or its detection. Since the correction control of the toner density sensor is prohibited, the toner density of the image on the image carrier is prevented from decreasing more than necessary.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

To explain an example of a color copying machine as an example of an image forming apparatus to which the present invention is applied, as shown in FIG. Around the drum 2, there is a charging stage -3 for initially charging the surface of the photosensitive drum 2, and an electrostatic latent image formed by exposing the light image of the document on the --like charged surface of the photosensitive drum 2. an exposure optical system 4 for forming an electrostatic latent image, a black developer 5 for supplying toner of each color to the electrostatic latent image, and developing it to obtain a toner image for each color;
A developing device having two color developing units 6,7,8, a transfer drum 9 that winds and holds a recording paper and sequentially transfers a toner image of each color onto the recording paper, and a transfer section in the transfer drum 9. Arranged to face the! A transfer charger 10 to be transferred, a cleaning device 11 for removing toner remaining on the surface of the photoreceptor drum 2 after transfer, and an eraser 12 for removing charges remaining on the surface of the photoreceptor drum 2 after transfer, etc. are sequentially installed. Arranged. Further, the transfer drum 9 is provided with a separation charger 13 and a separation claw 14 for separating the recording paper from the transfer drum 9 after the transfer has been completed.

A fixing device 16 is disposed at the exit side end of the conveyor belt 15 that conveys the recording paper peeled off from the transfer drum 9, and fixes the toner image by heating and applying pressure.
A paper discharge tray 17 is attached to the exit portion of the fixing device 16 .

Further, the exposure optical system 4 includes a contact glass 18 as a developing stage installed and placed on the upper part of the copying machine main body 1;
An exposure lamp 19 that irradiates scanning light onto the original on the contact glass 18, a reflection mirror 21 and an imaging lens 2 that image the reflected light from the original onto the surface of the photoreceptor drum 2.
2. A color separation filter 23 and the like are provided to separate the light image into complementary colors.

In the area between the developing unit 8 and the transfer charger 10 of the photosensitive drum 2, a toner adhesion amount detection means (P (hereinafter referred to as sensor) 30
For example, the P sensor 30 detects a toner image obtained by developing a latent image on the photosensitive drum 2 formed by exposing a standard pattern formed outside the document placement area of the contact glass 18. Then, the amount of toner adhering to the image area of the standard pattern and the amount of toner adhering to the background area of the standard pattern are detected for each toner of each developing device.

The developing device 5 includes, for example, a magnetic permeability sensor 31 that detects toner concentration based on changes in magnetic permeability of the developer, similarly, the developing device 6 includes a magnetic permeability sensor 32, and the developing device 7 includes a magnetic permeability sensor 33. A magnetic permeability sensor 34 is arranged in the developing device 8 .

There is a second difference between the output V of the toner concentration sensor composed of magnetic permeability sensors 3132, 33, and 34 and the toner concentration wt%.
A relationship as shown by straight line A in the figure is obtained.

If the reference toner density is , then the output (target value) for that density is ■. The output V of the toner density sensor is ■. If it becomes larger, the toner concentration has decreased, so control is performed to replenish toner and increase the toner concentration. However, when the photoreceptor drum deteriorates, the amount of toner adhesion tends to decrease, so it is necessary to increase the toner concentration in the developing device compared to the normal state. In this case, to increase the toner concentration, set the target value of the toner concentration sensor ■. For example, correction control is performed so that the toner density is shifted by -ΔV, and the toner density is maintained constant at the shifted target value. When the amount of toner adhering to the photoreceptor drum tends to increase due to environmental conditions or the like, correction control is performed to shift the target value of the toner density sensor by +Δ■.

Output ■ by the P sensor (toner adhesion amount detection sensor) 30 and toner adhesion amount ■ / +111 on the photosensitive drum 2
In FIG. 3, the upper half of the vertical axis represents the toner adhesion amount detection sensor output, and the horizontal axis represents the toner adhesion amount.

Image forming speed (process speed), for example, when the linear speed of the photoreceptor drum and developing roller is switched depending on the image mode, the development potential of the photoreceptor drum ■ and the amount of toner adhesion ■
/ CI'', the image forming speed is high speed S+,
For example, in the case of 226 tm/sec, the image forming speed is as shown by straight line C in FIG. 3, and the image forming speed is low speed S! For example, in the case of 113 .mu./sec, the lower half of the vertical axis in FIG.

High speed S at the same development potential of the photoreceptor drum
In the case of 1, the output of the toner adhesion amount detecting means (P sensor) of the amount of toner adhesion on the image portion of the standard pattern is vo, and in the case of low speed S2, it is V'SP. The output V of the P sensor for the background portion of the standard pattern is hardly affected by changes in the image forming speed.

Toner concentration control is performed according to the flow shown in FIG. 4, for example. When copying is started by pressing the main switch ONL, it is checked whether it is the timing to detect the amount of toner adhesion. If NO, the process returns to copy start and waits.

When it is the toner adhesion amount detection timing, it is checked whether the process speed, that is, the image forming speed is the specified speed S1, and if it is not the specified speed Sl but S2 and No, the toner density sensor target value remains unchanged. and prohibits the operation of the toner adhesion detection means.

When YES, a reference pattern is created on the image carrier, and the P sensor 9 selects VIP and ■. The value of the ratio vsr/V
S. Detects and checks whether Vsr/V□〉A,
If YES, the amount of toner adhesion has decreased, so the target value of the toner concentration sensor is shifted by -ΔV, and correction control is performed so that the toner concentration becomes higher. V when NO
sr/Vs. <Check whether it is A, and if YES, shift the toner concentration sensor target value by +ΔV, and
If it is O, the toner density sensor target value is left as is.

〔effect〕

According to the present invention, the amount of toner adhering to the image carrier is used for toner density sensor control only when the detection timing occurs at a specific image forming speed, and at other image forming speeds, the toner density sensor is used to control the toner density sensor. Since control is not performed based on changes in the amount of toner adhering to the body, toner density can be controlled in a stable state, and image density is prevented from lowering more than necessary.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an image forming apparatus using the present invention;
Figure 2 is a diagram showing the relationship between toner density sensor output and toner concentration, Figure 3 is a diagram showing the relationship between toner adhesion amount, development potential, and toner adhesion amount detection sensor output, and Figure 4 is a diagram showing the relationship between toner adhesion amount detection sensor output and toner adhesion amount detection sensor output.
The figure is a control flowchart. 2...Image carrier 5.6.7.8...Developer 30...P sensor 31.32.33.34...Toner concentration sensor S1

Claims (1)

[Claims] The latent image formed on the image carrier can be developed using multiple developers, and the image forming speed can be switched depending on the type of developer used for development, and a latent image of a specific pattern can be formed on the image carrier. In a toner concentration control method of a developer of an image forming apparatus, which detects the amount of toner adhering after development and corrects and controls the toner density of the developing device based on the information on the amount of toner adhering, one image forming speed specified in advance is used. The present invention is characterized in that the correction control is performed based on the detection of the toner adhesion amount of the specific pattern by the toner adhesion amount detecting means only in the case of , and the correction control based on the detection of the toner adhesion amount of the specific pattern is prohibited in the case of other image forming speeds. A method for controlling toner concentration of a developer in an image forming apparatus.