JPS61159663A - Automatic image density control method of copying machine - Google Patents

Abstract

PURPOSE:To supply toner whose amount is suitable to consumption and to take a copy with constant image density by calculating a current value based upon toner which is consumed during development and controlling the supply amount of toner with the obtained current value. CONSTITUTION:A developing roll 10 which develops an electrostatic latent image formed on the surface of a photosensitive body 1 is applied with a developing bias from a developing bias power source 15. A current detecting circuit 17 detects the value of a current generated when toner is transferred from the developing roll 10 to the photosensitive body 1 during development. This current value is converted by a voltage converting circuit 18 into a voltage value, which is sent to an arithmetic circuit 19. This arithmetic circuit 19 calculates the value of a current generated by the toner consumed during the development and a toner supply amount control circuit 20 drives a driving motor 13a to supply toner.

Description

[Detailed Description of the Invention] Industrial Application Field This invention detects the current value generated when toner particles are transferred from a developing roll to a photoreceptor during development, and controls the amount of toner replenishment according to the obtained current value. This 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 the amount of toner in the developer is detected in order to maintain a constant density per copy. 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, and the detected value is obtained. 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 installing a detector to detect magnetic permeability in the developer to detect the magnetic permeability of the developer, and detecting the magnetic permeability from the obtained detector. Generally, a method is adopted in which the amount of toner replenishment is controlled so that the amount of toner is kept constant.

Another method is to detect changes in the surface potential of the photoreceptor, changes in the optical system's view, and the background density of the copied paper2, and control the amount of toner replenishment using the obtained detected values in combination with the discharge current. It is used in some high-end copiers.

Problems to be Solved by the Invention However, since none of the above methods detects the amount of toner that is to be dissipated during development, the amount of toner replenishment may be excessive or insufficient relative to the amount of toner consumed. However, there have been disadvantages in that highly accurate image density control cannot be obtained, and the detection means is complex 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 The leakage current that occurs is detected by the current detection circuit installed in the development bias application circuit, and the value obtained is set to the reference value and 1 for automatic zero adjustment. Next, when developing the image area of the photoreceptor, the photoreceptor is removed from the developing roll. The leakage current caused by the transfer of toner to the body is detected by the current detection circuit, and the true toner consumption is detected as a current value by subtracting the reference value from the detected value. An automatic image density control method for a copying machine comprising controlling the amount of toner supplied to a developing device.

Embodiment One embodiment of the present invention will be described in detail with reference to the drawings.
The figure shows a copying machine that implements the method of the present invention, in which 1 is a photoconductor, 2 is a charger that charges the surface of the photoconductor 1, and 3 is a cell that forms an electrostatic latent image on the surface of the photoconductor 1. Shows an optical system such as a hook lens. The electrostatic latent image formed on the surface of the photoreceptor 10 is developed by the developing device 4, and then transferred to the paper 6 fed by a paper feeding device (not shown) in the transfer device 5, and the transferred paper 6 is transported. The toner image on the paper 6 is sent to a fixing device (not shown) by the 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 I by the cleaning device 8. be done. 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. 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 magnet roll IOa on which a grinding pole is arranged. The developer is trimmed by a trimmer 11 so that the height thereof is constant, and then reaches the photoreceptor 1 to develop the electrostatic latent image on the surface of the photoreceptor 1. Further, the developer scraped off from the sleeve IOA is stored in the housing 4a.
It mixes with the developer stored in the α, and also the toner bottle)
A mixing roll 14 is provided for mixing the toner newly replenished from 2 through the toner supply auger 13 with the developer in the housing 4a, and a toner roll 14 for replenishing the toner in the toner bottle 12 into the housing 4a. A driving motor 13σ such as a stepping motor is connected to the supply auger 13, and the amount of toner replenishment is controlled as follows.

Next, the method will be explained with reference to the flowchart shown in FIG. A current detection circuit 17 is provided in the middle of the line !6 that connects 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. That is, a gap of about 1.0 to 1.5 mm is usually provided between the photoreceptor and the developing roll 10, as shown in FIG. The developer is filled with a developer consisting of a carrier having a certain amount of charge and a sufficiently insulating toner that is electrostatically attracted to the carrier due to frictional charging between the carrier and the toner that has a certain charge due to frictional charging. Although it is electrically balanced, when it comes into contact with the surface of the photoconductor 1 on which an electrostatic latent image is formed, the toner in the developer is transferred to the photoconductor by an amount corresponding to the amount of charge that the electrostatic latent image has. As a result, the amount of charge that the toner particles were carrying disappears from the developing roll 10, and a current flows from the developing bias power supply 15 to the developing roll 10 to replenish this, and this current becomes a current. It is detected by the detection circuit 17.

Normally, a developing bias of 200 to 500 V is applied to the developing roll 10, and the photoreceptor 1 and the developing roll 10
During this period, contact is made with a developer having sufficient drowsiness resistance (usually 109 to 100 or more), so the leak 1fE current when a developing bias is applied is about 0.2 to 0.05 μA.

However, even when the photoreceptor 1 is not developed with a developer, there may be a potential difference between the residual potential or background potential of the photoreceptor 1 and the developing bias, or there may be a difference in potential between the rotation axis of the photoreceptor 1 and the electrode portion of the developing roll 10. Due to the combined resistance of specific resistance and developer specific resistance (usually several hundred to several thousand MΩ),
A small current flows from 0 to the photoreceptor i side, and this I current is changed by V 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.

Copying is now started. When the start button is pressed, the drive system for the photoreceptor 1 etc. starts operating in step (2), and the non-image area is charged and optically neutralized in step (2). Thereafter, in step (2), the developing device 4 starts operating, and an on signal of the developing device 1114 is output to the current detection circuit 17.
Current detection circuit 17 enters an idle link state.

On the other hand, when the non-image area enters the development area in step (2), the current detection circuit 17 detects a minute leakage voltage caused by the potential difference between the residual potential on the surface of the photoconductor 1 after photostatic discharge and the development bias potential applied to the development roll 10. is detected and automatically zero-adjusted so that this value becomes the base $ value.

Thereafter, the setting of the reference value is completed in step O) in which 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 in step (3). After detection and voltage conversion by the voltage conversion circuit 18, the voltage 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 nine toners consumed during development, and the toner supply amount is controlled. Output to circuit 20. 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 I2 to the developing device 4, thereby causing the drive motor 13ff to supply toner. The auger 13 is rotated to replenish the developing device 1It4 with an amount of toner corresponding to 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. The signal is output to the toner supply amount control circuit 20, and the rotation of the drive motor 13a of the toner supply auger 13 is controlled.

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 (2) and at the same time a reset signal is output to the current detection circuit 17, which resets the current circuit 17. At the same time, in the case of continuous copying, the process returns to step (3) 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 the ears, and a predetermined non-image area on the photoreceptor 1 is adjusted to the developing roll io. The leakage current is detected when the current is reached, zero adjustment is performed using this as a reference value, and then the developing roll 10 rotates (it may rotate at the same time or immediately before) to develop the image area. Detect the leakage current again 1,
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 a speed of about 5 to 1 Q rpm, and the amount of toner supplied by the drive motor 13a is 1.
The toner is fed 10 to 100 times per second of rotation, but in consideration of the start-up of the rotation of the drive motor 131 and variations in the amount of toner replenishment, it is desirable that the toner be approximately 5 Q and rrtf of 7 kc.

Effects of the Invention As described in detail above, this invention uses the current value detected from the non-image area of the photoconductor as a reference value, and subtracts the reference value from the current value detected during development to determine the amount of toner consumed during development. Since the current value is calculated and the toner replenishment amount is controlled based on the obtained t current value, even if the developing bias is changed, the reference value is 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, toner can be replenished according to the consumed amount without being affected by changes in the developing bias, so that copies with constant image density can be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and 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. . 1 is a photoreceptor, 10 is a developing roll, and 17 is a current detection circuit.

Claims (1)

[Claims] Before the electrostatic latent image formed on the surface of the photoreceptor 1 in the exposure process is developed by the developing roll 10 to which a developing bias power source 15 is applied, a gap between the non-image area of the photoreceptor 1 and the developing roll 10 is created. A current detection circuit 17 provided in the developing bias application circuit detects the leakage current generated in the development bias application circuit and uses this as a reference value.Next, the leakage current generated when the image area of the photoconductor 1 is developed by the development roll 10 is detected by the current detection circuit 17 provided in the developing bias application circuit. An automatic image of a copying machine in which the true amount of toner consumption is detected as a current value by subtracting the reference value from the current value detected by the detection circuit 17, and the amount of toner replenishment is controlled based on this current value. Concentration control method.