JPH01285966A - Developing device - Google Patents

Abstract

PURPOSE:To form the natural color image of the color tones faithful to the color tones of an original without having fogging and carrier sticking by controlling the differences between the potentials in the image exposing parts in the developing regions of respective developing devices and the DC bias voltages of respective developing sleeves in such a manner that the same differences are maintained through the respective developing devices. CONSTITUTION:The surface potentials of the non-exposing part of an image forming body 1 near the developing regions are measured by using surface potential sensors 9-1-9-4 and the developing sleeve bias voltages of the developing devices 5-8 are so controlled by using control circuits 10-1-10-4 that the specified differences from the surface potentials measured by the surface potential sensors are maintained. The specified differences between the potentials in the image exposing section on the image forming body 1 in the developing regions and the DC bias voltages of the developing sleeves are maintained in such a manner. The developing electric field sin the respective developing regions are, therefore, maintained at the same levels and the toner depositions of the respective colors are uniformized even if the developing devices housing the toners of difference colors such as with a natural color image forming device are disposed in the positions differing in the arrival time from the positions of an electrostatic charger. The natural color images of the color tones faithful to the original image are thereby formed without having the fogging and carrier sticking.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a developing device for an image forming apparatus, and in particular, to a developing device for controlling a DC bias voltage of a developing sleeve according to a surface potential near a developing area of an image forming member. This invention relates to improvements that maintain appropriate toner adhesion and improve image quality.

(Background of the Invention) FIG. 2 is a diagram illustrating the steps of charging, image exposure, and development in an image forming apparatus.

In the first step of image formation, the surface of the image forming body is charged to a predetermined potential by the charger 2 while the image forming body 1 is rotated in the direction of the arrow. When the charged portion moves to a location where it is irradiated with image exposure light 4 from image exposure device 3, image exposure is performed and a latent image is formed. The image forming body 1 continues to rotate, and when the latent image forming area reaches the development area of the toner developing device corresponding to the latent image, the toner adheres to the exposed area of the latent image. The amount of toner attached depends on the potential difference between the surface potential of the exposed area of the image forming member 1 in the developing area and the DC bias voltage applied to the developing sleeve, and the amount of adhered toner depends on the potential difference between the surface potential of the exposed part of the image forming member 1 in the developing area and the DC bias voltage applied to the developing sleeve. In order to obtain an image with high density and clear edges, it is necessary to set the above potential difference within an appropriate range.For this reason, it is necessary to set the potential difference immediately after charging the image forming body 1 to a predetermined value (for example, -730V). In some cases, the DC bias voltage of the developing sleeve is set higher than the surface potential by a certain value (for example, 100 V). (For example, if the charged potential is 1730 V in the above example, the surface potential of the image-exposed area will be approximately 160 V.) Ift is the potential of the exposed area, keeping the difference from the charged potential constant This is because the difference between This is done in the same way even when utensils are used.

(Problems to be Solved by the Invention) However, the above-mentioned technique has problems as in the case of natural color image forming apparatuses.

Even if the image forming body 1 is charged by the charger 2 and reaches a predetermined potential, the absolute value of the surface potential decreases over time due to dark decay of the image forming body 1 and the like. The natural color image forming apparatus includes three developing devices: a yellow developing device 5, a magenta developing device 6, a cyan developing device 7, and in some cases a black developing device 8.
A total of 3 to 4 developing devices, including 1, are arranged along the periphery of the image forming body 1 as shown in FIG.

The time required for the area charged by the slant charger 2 to reach the development area of each developer is the shortest for the yellow developer, and becomes longer in the order of magenta, cyan, and black. That is, the time from being charged by the charger 2 to being developed differs depending on the developing device. As a result, the degree of dark decay will be different, and the surface potential of the image forming member will also be different when it reaches the developing area of each developing device.

- To give an example, the potential under the charger 2 is 1730V, but when it reaches the yellow development area, it becomes 1690V, and in the same way, for magenta it is 1680V, and for cyan it is 16V.
For 50V and black, the absolute value becomes smaller, such as -645■. The potentials of the exposed portions will also differ accordingly. Therefore, even if the DC bias voltage of the developing sleeve of each developing device is set to a voltage that is a certain difference from the surface potential of the image forming member immediately after charging (for example, 100 V difference - 630 V), the image in the developing area of each developing device is The difference between the potential of the formed body I@exposed area and the developing sleeve bias voltage differs for each developing device. As a result, the amount of henna applied varies depending on the developing device, and the potential of the non-exposed areas of the image forming body also changes, resulting in image fogging and making it difficult to obtain natural color images with tones that are faithful to the original. The problem is that there is no.

In view of the problem described in item 1, an object of the present invention is to create a non-exposed area in advance in addition to image information when forming a latent image, and to create an image forming body (non-exposed area) in the vicinity of the development area for each developing device. of)
By measuring the surface potential and controlling the bias voltage of the developing sleeve of the developing device so that it has a constant difference from the measured potential, the potential of the image-exposed portion of the image forming member in each developing area and the developing sleeve DC bias voltage can be determined. To provide a developing device capable of forming a natural color image with a tone faithful to an original by adjusting the difference to an appropriate constant value, thereby making the amount of toner 14 applied to each developing device appropriate.

(Means for Solving the Problems) The present invention has the following means configuration to achieve the above object.

That is, the developing device of the present invention is a developing device that reversely develops an electrostatic latent image formed by performing charged image exposure on an image forming body, and includes a DC bias power supply that supplies a DC bias voltage to a developing sleeve. and a surface potential sensor for measuring the surface potential of an unexposed part of the image forming body near the current part: a difference between the DC bias voltage and the surface potential of the image forming body is set in advance based on an output signal of the surface potential sensor. The present invention is characterized by comprising: a control circuit that controls the value so that the value is set to a specified value;

(Function) Hereinafter, the function of the developing device of the present invention having the above means configuration will be explained.

In the present invention, a surface potential sensor is used to measure the surface potential of the non-exposed part of the image forming member near the developing area, and based on the measured value signal, the control circuit adjusts the DC bias voltage of the developing sleeve to the surface potential of the image forming member. The difference is controlled to be a predetermined constant value.

As a result, the difference between the potential of the exposed portion of the image forming member and the DC bias voltage of the developing sleeve in the developing region also becomes a predetermined constant value, and the amount of toner adhesion becomes constant.

In the present invention, as described above, the bias voltage is determined based on the surface potential of the image forming member in the developing area, so the f111 time differs due to the difference in the distance from the charger to the developer, and the degree of dark decay. Even if the surface potential of the unexposed area is different due to the difference in the surface potential of the unexposed area, the difference between the image exposed area and the bias voltage will be the same.

Furthermore, even if the dark decay characteristics of the image forming body change due to changes over time or the charging characteristics of the image forming body change, the difference between the potential of the image exposed area and the bias voltage in the development area can be kept constant. Therefore, even if three or four developing units are arranged sequentially around the image forming body as in a natural color image forming apparatus, the surface potential of the unexposed area of the image forming body in the development area of each developing unit is used as a reference. Since the bias voltage is controlled by the developer, the difference between the potential of the image exposed portion in the development area of each developer and the DC bias voltage of each developer sleeve can be made the same throughout each developer.

As a result, the amount of toner deposited on each developing device can be made uniform, and a natural color image with a tone faithful to the original can be formed without fog or carrier deposition.

(Example) Hereinafter, an example of the developing device of the present invention will be explained with reference to the drawings. 6 Figure 1 shows a natural image forming apparatus having four developing units of yellow, magenta, cyan, and black, similar to Figure 2. This is an example in which the developing device of the present invention is applied to a color image forming apparatus. 9-1 to 9- in the figure
Reference numeral 4 denotes a surface potential sensor, which is provided near each development area of a yellow developer 5, a magenta developer 6, a cyan developer 7, and a black developer 8, respectively. 10-1~1
Reference numeral 0-4 denotes a control circuit corresponding to each developing device, which receives measurement signals from surface potential sensors 9-1 to 9-4 and outputs a voltage control signal. 11-1 to 11-4 are DC bias power supplies for the developing sleeve, and each control circuit 10-1
- A bias voltage controlled by a voltage control signal from 10-4 is supplied to each corresponding developing sleeve.

Table 1 In this example, when a latent image is formed, a non-exposed area is placed in front of the image area, and the surface potential of the above area of the image forming body is measured using a surface potential sensor near the developing area of each developing device. ,
The bias voltage of the developing sleeve of the developing device is controlled to be 100 V smaller in absolute value than the surface potential of the non-exposed area.

Table 1 shows the potential relationship when the charging potential directly below the charger is 1730V.

Other conditions are as follows.

Image forming body (photoreceptor) composition LICL/vinyl chloride Vinyl acetate/maleic acid copolymer 0.1 μm CGL: Disazo compound II/polycarbonate-2/1
Approx. 0.25 μm CTL Nistyril Triphenyl amine compound/polycarbonate = 2/1 Approx. 20 μm Photoreceptor diameter 1
80 degrees Photoreceptor linear speed 140 degrees/S Developing sleeve Diameter 20 degrees Magnetic poles 12 poles (30 degrees apart) Fixed developer Carrier (...ner) 2 components (effects of the invention) As explained above, the development of the present invention The apparatus used a surface potential sensor to measure the surface potential of a non-exposed area of the image forming body near the development area, and used a control circuit to measure the DC bias voltage of the developing sleeve of the developing device using the surface potential sensor. By controlling the difference between the surface potential and the surface potential to be constant, the difference between the potential of the image-exposed area on the image forming member in the developing area and the developing sleeve DC bias voltage is kept constant. Even if developing devices containing toner of different colors, such as a forming device, are placed at positions with different arrival times from the position of the charger, the developing electric field (potential of the image exposed area) in each developing area It has the advantage that it can maintain the same amount of toner (the electric field created by the DC bias voltage of the developing sleeve) and the amount of toner adhesion for each color can be made uniform, and that it can form a natural color image with a tone that is faithful to the original image without fogging or carrier adhesion.

Another advantage is that even if the charging characteristics and dark decay characteristics of the image forming body change, the amount of toner adhesion does not change.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment in which four developing devices of the present invention are applied to a natural color image forming apparatus, and FIG. 2 is a diagram showing the configuration of a natural color image forming device having four developing devices. . 1... Image forming body (photoreceptor), 2... Charger, 3... Image exposure device, 4... Image exposure light, 5...... Yellow developer, 5'...
・Yellow developing sleeve, 6...Magenta developing device, 6'...Magenta developing sleeve, 7...
Cyan developer, 7′・Cyan developer sleeve, 8・
...Black developer, 8'...Black developer sleeve,
9-1 to 9-4 ・Surface potential sensor, 10-1 to 10
-4...control circuit, 11-1 to 11-4...
・DC bias power supply. Agent Patent Attorney Yoshihiro Hachiman

Claims (1)

[Claims] A developing device that reversely develops an electrostatic latent image formed by charging and imagewise exposure on an image forming body; a DC bias power source that supplies a DC bias voltage to a developing sleeve; a surface potential sensor that measures the surface potential of the exposed portion; a control circuit that controls the difference between the DC bias voltage and the surface potential of the image forming member to a preset value based on the output signal of the surface potential sensor; A developing device comprising: