JPH0511629B2 - - 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 electronic copying machines that conventionally use a dry two-component developer, the toner in the developer is consumed during copying, so the amount of toner in the developer is detected in order to keep the density of the copied image constant. 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 photoconductor 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 of the developer. Generally, a method is adopted in which the amount of toner replenishment is controlled to be constant.

Another method is to detect changes in the surface potential of the photoreceptor, changes in the amount of light in the optical system, and the background density of the copied paper, and control the amount of toner replenishment using the detected values in combination with the discharge current. It is used in high-end copying machines in the department.

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 Before the electrostatic latent image formed on the surface of the photoreceptor is developed by a developing roll to which a developing bias is applied, a gap between the non-image area of the photoreceptor and the developing roll is Automatic zero adjustment is performed using the value obtained by detecting the generated leakage current with a current detection circuit installed in the development bias application circuit as a reference value, and then the electrostatic latent image is developed with a development roll to which a development bias power supply is applied. At this time, the current generated when the toner in the developer is transferred from the developing roll to the electrostatic latent image on the photoreceptor is detected by a current detection circuit installed in the developing bias application circuit, and the detected value is determined based on the above standard. An automatic image density control method for a copying machine, in which the true amount of toner consumption is detected as a current value by subtracting the value, and the amount of toner replenished to a developing device is controlled based on this current value.

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, in the developing device 4, a developing roll 10 is provided in a housing 4a and close to the photoreceptor 1. The above developing roll 1
0 is a sleeve 1 that rotates in the direction of the arrow around a magnet roll 10a on which magnetic poles are arranged as shown in FIG.
0b, the developer adhering to the surface of the sleeve 10b due to the magnetic action of the magnet roll 10a is trimmed by the trimming bar 11 so that the spike height is constant, and then reaches the photoconductor 1, and the developer is removed from the photoconductor 1. The electrostatic latent image on one surface is developed. Further, the developer scraped off from the sleeve 10b is stored in the housing 4a.
A mixing roll 14 is provided which mixes the developer contained in the housing 4a and the toner newly replenished from the toner bottle 12 via the toner supply auger 13 with the developer in the housing 4a. , a toner supply auger 13 that replenishes the toner in the toner bottle 12 into the housing 4a.
is a driving motor 13 such as a stepping motor.
a is connected, and the amount of toner replenishment is controlled as follows.

Next, the method will be explained with reference to the flow chart shown in FIG. A current detection circuit 17 is provided in the middle of a line 16 connecting the developing bias power supply 15 and the developing roll 10, and detects the current value generated when toner is transferred from the developing roll 10 to the photoreceptor 1 during development. do.
That is, there is a second
As shown in the figure, a gap of about 1.0 to 1.5 mm is usually provided, and during development, this gap is filled with enough material that is electrostatically attracted to the carrier due to the frictional electrification between the carrier and the carrier. The area is filled with a developer consisting of toner having insulating properties.
At this time, the toner and the carrier, which have a certain charge due to triboelectric 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 on the developing roll 10 corresponding to the charge on the toner particles disappears, and a current flows from the developing bias power supply 15 to the developing roll 10 to replenish this charge, and this current is detected by the current detection circuit 17. Ru.

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 applying the developing bias is about 0.2 to 0.05 μA. However, even when the photoreceptor 1 is not developed with a developer, there is a potential difference between the residual potential or background potential of the photoreceptor 1 and the developing bias, and the photoreceptor 1
A minute current flows from the developing roll 10 to the photoreceptor 1 side due to the combined resistance of the resistivity of the photosensitive layer and the resistivity of the developer (usually several hundred to several thousand M) between the rotating shaft of the developing roll 10 and the electrode portion of the developing roll 10. This leakage current changes by changing the developing bias.
Furthermore, since the leakage current is detected by the current detection circuit 17 along with the leakage current caused by the developer, it is necessary to subtract this leakage current in order to detect only the amount of consumed toner.

When the start button is pressed to start copying, the drive system for the photoreceptor 1 etc. starts operating in step, and the non-image area is charged and optically neutralized in step. Thereafter, the step developing device 4 starts operating, and an on signal of the developing device 4 is output to the current detection circuit 17, and the current detection circuit 17 enters an idling state.

On the other hand, when the non-image area enters the development area in step, the current detection circuit 17 detects a minute leakage voltage caused by the potential difference between the residual potential on the surface of the photoreceptor 1 after photostatic discharge and the development bias potential applied to the development roll 10. Detected and automatically zero-adjusted so that this value becomes the reference value.

Thereafter, the setting of the reference value is completed at the step when the image area enters the development area, and the reference value (zero level) is set in the arithmetic circuit 19, and the current detection circuit 17 detects the current in the image area at the step. After the voltage is converted by the voltage conversion circuit 18, it is sent to the arithmetic circuit 19, and the value obtained by subtracting the reference value from the detected value is calculated as the current value generated by the toner consumed during development, and sent to the toner supply amount control circuit 20. Output. The toner replenishment amount control circuit 20 outputs a control signal to the drive motor 13a so that the toner corresponding to the input current value is replenished from the toner bottle 12 to the developing device 4.
3a rotates the toner supply auger 13 to supply the developing device 4 with an amount of toner commensurate with the toner consumed during development. In addition, when the developing bias is changed, zero adjustment is performed so that the leakage current generated by the changed developing bias becomes the reference value, and the value obtained by subtracting this reference value from the current value detected during development is calculated from the arithmetic circuit 19. Toner supply amount control circuit 2
0, and the rotation of the drive motor 13a of the toner supply auger 13 is controlled.

On the other hand, when the image area of the photoreceptor 1 passes through the developing area of the developing device 4, the developing device 4 is stopped in step and at the same time a reset signal is output to the current detection circuit 17, thereby resetting the current circuit 17 and In the case of continuous copying, the process returns to the step and the above operation is repeated again.

That is, the reference value is adjusted for each copy, and in the embodiment, the developing roll 10 is temporarily stopped between each copy, and a predetermined non-image area on the photoreceptor 1 is adjusted to the developing roll 10. When the leakage current is reached, the leakage current is detected and zero adjustment is performed using this as a reference value.Then, the developing roll 10 rotates (it may rotate at the same time or immediately before), and when the image area is being developed. Detect leakage current again,
The value obtained by subtracting the reference value from the detected current during development is calculated as the current value that occurs when toner is consumed during development. Further, the drive motor 13a that drives the toner supply auger 13 is designed to rotate at a speed of 5 to 20 rpm, but preferably rotates at about 5 to 10 rpm, and the amount of toner replenishment is determined while the drive motor 13a rotates for 1 second. 10~
100 mg is sent, but considering the startup of rotation of the drive motor 13a and variations in the amount of toner replenishment, etc.
Approximately 50mg/sec is desirable.

Effects of the Invention As described in detail above, the present invention develops the electrostatic latent image formed on the surface of the photoreceptor 1 through the exposure process using the developing roll 10 to which the developing bias power source 15 is applied. The leakage current generated between the non-image area of the photoreceptor 1 and the developing roll 10 is detected by the current detection circuit 17 provided in the developing bias application circuit, and this is used as a reference value. When developing with a developing roll to which is applied, the current generated when the toner in the developer is transferred from the developing roll to the electrostatic latent image on the photoreceptor is detected by a current detection circuit provided in the developing bias application circuit,
The true amount of toner consumption is detected as a current value by subtracting the above reference value from the obtained current value, and the amount of toner replenishment is controlled using this current value, so even if the developing bias is changed. Since the reference value is also corrected each time according to the change, the true amount of toner consumed by development can always be detected as a current value. As a result, an amount of toner commensurate with the consumed amount can be replenished without being affected by changes in the developing bias, etc., so that copies with constant image density can be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is an overall configuration diagram, FIG. 2 is an explanatory diagram showing a developing device and a control system for controlling it, and FIG. 3 is a flowchart showing the operation. be. 1 is a photoreceptor, 10 is a developing roll, and 17 is a current detection circuit.

Claims (1)

[Claims] 1. Prior to developing the electrostatic latent image formed on the surface of the photoconductor 1 in the exposure process with the development roll 10 to which the development bias power supply 15 is applied, the non-image area of the photoconductor 1 and the development roll 10 are A current detection circuit 17 provided in the development bias application circuit detects the leakage current generated between the two and uses this as a reference value.Next, when the electrostatic latent image is developed with a development roll to which a development bias power supply is applied, the development roll The current generated when the toner in the developer is transferred to the electrostatic latent image on the photoreceptor is detected by a current detection circuit provided in the development bias application circuit, and the above reference value is subtracted from the obtained current value. An automatic image density control method for a copying machine in which the true amount of toner consumption is detected as a current value, and the amount of toner replenishment is controlled based on this current value.