JPH0511310B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention detects the current value generated when toner particles are transferred from the developing roll to the photoreceptor during development, and controls the amount of toner replenishment according to the obtained current value. The present invention relates to an automatic image density control method for a copying machine.

Conventional technology In conventional electronic copying machines that use a dry two-component developer, the toner in the developer is consumed during copying, so in order to keep the density of the copied image constant, the amount of toner in the developer must be detected. If the amount is less than the specified amount, it will be necessary to replenish it.

Furthermore, various methods have been proposed for detecting the amount of toner in the developer.

For example, a patch-like development area that forms another latent image is provided close to the photoreceptor or development roll, and this development area is developed and the reflection density of that area is optically detected. There is a method of controlling the amount of toner replenishment so that the reflection density is always a constant value, and a method of detecting the magnetic permeability of the developer by installing a detector inside the developer to detect the magnetic permeability. Generally, a method is adopted in which the amount of toner replenishment is controlled to be constant. Another method is to change the surface potential of the photoreceptor, change the amount of light in the optical system,
A method of detecting the background density of copied paper and controlling the amount of toner replenishment based on the detected value in combination with a discharge current is also adopted in some high-end copying machines.

Problems to be Solved by the Invention However, since none of the above methods detects the amount of toner actually consumed during development, the amount of toner replenishment may be excessive or insufficient relative to the amount of toner consumed, resulting in poor accuracy. In addition, there were problems in that high image density control could not be obtained, and the detection means was complicated and expensive.

This invention was made for the purpose of improving the above-mentioned problems.

Method for solving the problem When developing an electrostatic latent image formed on the surface of a photoconductor using a developing roll to which a developing bias is applied,
The current generated when the toner is transferred from the developing roll to the photoreceptor is detected by a current detection circuit provided in the developing bias application circuit, and an amount of toner commensurate with the consumed amount is supplied to the developing device according to the obtained current value. At the same time, if the current value detected by the current detection circuit exceeds the preset toner replenishment amount range, the amount of toner that exceeds this range is stored in the memory, and the next copy with less toner consumption is used. By adding up the shortage and replenishing it to the developing device,
1 even when copying an original with a large image area
An automatic image density control method for a copying machine that prevents a large amount of toner from being replenished at the same time.

Embodiment An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a copying machine in which the method of the present invention is implemented. Reference numeral 3 indicates an optical system such as a self-cleaning lens that forms an electrostatic latent image on the surface of the photoreceptor 1. The electrostatic latent image formed on the surface of the photoreceptor 1 is developed by the developing device 4, and then transferred to a paper 6 fed by a paper feeding device (not shown) in the transfer device 5, and the transferred paper 6 is The toner image on the paper 6 is sent to the fixing device (not shown) by the conveying means 7 and fixed on the surface of the paper 6, and the untransferred toner remaining on the surface of the photoreceptor 1 is removed from the surface of the photoreceptor 1 by the cleaning device 8. removed.

On the other hand, the developing device 4 has a photoreceptor 1 inside the housing 4a.
A developing roll 10 is provided adjacent to. As shown in FIG. 2, the developing roll 10 has a structure in which a sleeve 10b that rotates in the direction of the arrow is provided around a magnetic roll 10a in which magnetic poles are arranged. After the agent is trimmed by a trimming bar 11 so that the spike height is constant, the agent reaches the photoreceptor 1 and develops an electrostatic latent image on the surface of the photoreceptor 1. Further, the developer scraped off from the sleeve 10b is mixed with the developer stored in the housing 4a, and the housing 4a is newly replenished from the toner bottle 12 via the toner supply auger 13. A mixing roll 14 is provided for mixing the toner and the developer in the housing 4a, and a toner bottle 12 is provided.
The toner supply auger 13 for replenishing the toner inside the housing 4a is connected to a driving motor 13a such as a stepping motor, and the amount of toner replenishment is controlled as follows.

Next, the method will be described. A developing bias power source 15 applies a developing bias to the developing roll 10 that develops the electrostatic latent image formed on the surface of the photoreceptor 1. A current detection circuit 17 is provided in the middle of the line 16 connecting the developing roll 10 during development.
The current value generated when the toner is transferred to the photoreceptor 1 is detected. That is, there is usually a distance of 1.0 to 1.5 mm between the photoreceptor 1 and the developing roll 10, as shown in FIG.
During development, this gap is filled with a developer consisting of a sufficiently insulating carrier and a sufficiently insulating toner that is electrostatically attracted to the carrier by frictional charging. filled in by At this time, the toner and the carrier, which have a certain charge due to frictional charging, are electrically balanced, but when they come into contact with the surface of the photoreceptor 1 on which the electrostatic latent image is formed, the electrostatic latent image has Toner in the developer is transferred to the photoreceptor 1 side in an amount corresponding to the amount of charge. As a result, the charge that the toner particles were charged with disappears from the developing roll 10, and in order to replenish this, a current flows from the developing bias power supply 15 to the developing roll 10, and this current is transmitted to the current detection circuit 1.
Detected at 7.

Usually, a developing bias of 200 to 500 V is applied to the developing roll 10, and the contact between the photoreceptor 1 and the developing roll 10 is made by a developer having sufficient electrical resistance (usually ^{109 to} 10 Ω or more). Therefore, the leakage current when a developing bias is applied is about 0.2 to 0.05 μA, and with this as a reference value, the current value exceeding this reference value is transferred from the developing roll 10 to the photoreceptor 1 during development, and leaks from the developer. The current detection circuit 17 detects the amount of toner consumed. Further, the current detection circuit 17 performs zero adjustment so that the reference value becomes zero for each copy, and outputs only current values exceeding this reference value as detected current values. Specifically, the rotation of the developing roll 10 is stopped for each copy, and the charge in a certain area where the non-image area of the photoreceptor 1 reaches the developing roll 10 is detected and zero adjustment is performed.
At this time, a predetermined developing bias is applied to the developing roll 10, and before development, the charge in the area is detected and zero adjustment is performed, and then the current in the image area is detected.

On the other hand, the current value detected by the current detection circuit 17 is integrated by an integrator 18 and then transferred to the A-D converter 1.
A drive motor 13a that drives the toner supply auger 13
is input to. As a result, the drive motor 13a
is rotated, and the toner in the toner bottle 12 is supplied to the developing device 4 by the toner supply auger 13. The toner supplied to the developing device 4 is mixed with the developer in the housing 4a and used for development. However, when copying a document with a large image area, the amount of toner consumed per copy increases. Because of this, a large amount of toner is replenished at one time, causing the following problems. If a large amount of toner is replenished into the housing 4a at one time, the carrier in the developer and the newly replenished toner are used for development before they are sufficiently charged by friction, and more toner than necessary is left on the static surface of the photoreceptor 1. It transfers to the latent image and causes fogging and dirt on the background.

Therefore, in the method of the present invention, the amount of toner replenished for each copy is limited to a certain value, for example in the range of 20 mg to 200 mg, and the current detection circuit 17 detects when an amount of toner exceeding this is consumed during development. In this case, this information is stored in a memory provided in the current detection circuit 17. The contents stored in this memory are then added to the drive motor 1 the next time a document with a small image area is copied.
By outputting toner toner 3a and replenishing the shortage that occurs when copying a document with a large image area, the developing device is always supplied with an amount of toner commensurate with consumption.

Effects of the Invention As described in detail above, when an electrostatic latent image formed on the surface of a photoreceptor is developed by a developing device, the current value generated when toner is transferred from the developing roll to the photoreceptor is used for developing. It is detected by the current detection circuit installed in the bias circuit, and the amount of toner commensurate with the consumption is replenished into the developing device according to the obtained current value. If the amount of toner exceeding this range is exceeded, the amount of toner exceeding this range is stored in memory, and the insufficient amount is added and refilled to the developing device the next time the toner consumption is low. Even when copying, a large amount of toner is not replenished at one time, and as a result, good copies without background fog or stains can always be obtained.

[Brief explanation of the drawing]

The drawings show one embodiment of this explanation, and FIG. 1 is an overall configuration diagram, and FIG. 2 is an explanatory diagram showing a developing device and a control system for controlling it. 1 is a photoreceptor, 4 is a developing device, 10 is a developing roll, and 17 is a current detection circuit.

Claims (1)

[Claims] 1. When the electrostatic latent image formed on the surface of the photoconductor 1 in the exposure process is developed with the development roll 10 to which the development bias power supply 15 is applied, the electrostatic latent image on the photoconductor 1 is transferred from the development roll 10 into the electrostatic latent image on the photoconductor 1 in the developer. The current generated when the toner is transferred is detected by the current detection circuit 17 provided in the developing bias application circuit, and according to the detected value, the amount of toner commensurate with the consumption is replenished into the developing device 4. , the above current detection circuit 1
If the current value detected in step 7 exceeds the preset toner replenishment amount range, the amount of toner that exceeds this range is stored in memory, and the insufficient amount is added at the next copying with low toner consumption. An automatic image density control method for a copying machine, characterized in that the image density is replenished to the developing device 4 using