JP2781422B2 - Image density control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image density control method for a copying machine.

[Conventional technology]

In recent years, there has been an increasing demand from users for improving the image quality of a copy, whereby the image density control has changed from a method of controlling only the toner density to a method of controlling the amount of toner adhered to the photoconductor (feedback to the toner density). I have.

In a typical method, a detection pattern including a black pattern portion and a white pattern portion (white portion) is formed outside an image area on a contact glass, and the density of the toner image (toner adhesion amount) is determined by a reflection type. Of the so-called P sensor, which is detected by a photo sensor (hereinafter, referred to as a P sensor), and this method is becoming mainstream in recent years.

On the other hand, a surface voltmeter for measuring and controlling the surface potential on the photoreceptor has been mounted on a copying machine in accordance with a demand for improvement in image quality.

[Problems to be solved by the invention]

By the way, although the above detection pattern usually uses a halftone portion having high sensitivity of the P sensor to improve the accuracy of toner density control, this halftone has a low current and is different from a normal image potential. .

Therefore, from the viewpoint of potential control, it is necessary to control charging and exposure by using a value corresponding to the halftone potential separately from the potential control of the normal image portion. However, there is a problem that it is difficult and a deviation from a target occurs (usually, a detection pattern portion is sacrificed).

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image density control method capable of improving the accuracy of toner density control using a detection pattern regardless of potential control.

[Means for solving the problem]

An object of the present invention is to provide an image density control method for controlling the image density by detecting the surface potential on the image carrier and detecting the amount of toner adhering on the image carrier, and detecting the surface potential of the image carrier to which toner adheres. Then, the developing bias is controlled in accordance with the potential, and when the surface potential of the image carrier on which the toner is not adhered is a potential in a range where development is performed by the developing bias, an operation of detecting the amount of adhered toner is performed. This can be achieved by interrupting and changing the toner supply amount.

[Action]

The control of the detection pattern portion is converted from a potential to a developing bias. That is, even if the pattern potential is affected by image control, only the measurement of the potential is performed without any particular control. By controlling the developing bias in accordance with the measured value, the developing potential of the pattern portion is made constant, and it is possible to always control the image density to be constant (because the developing is performed substantially with this potential). ).

The control system only needs to have this potential as a reference, and the development bias has a quick response and the detection pattern is formed in an area other than the image portion, so that there is no effect on the image. Therefore, as the copy quality, the potential of the image is controlled to be constant, and the control of the image density is also stable, so that a stable and high-quality image is always obtained.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a block diagram of a copying machine to which the present invention is applied. 1 is a contact glass, 2 is an illumination lamp, 3 is an automatic document feeder, 4 is a manual document feeder, and 5 is a paper feed unit. . Reference numeral 6 denotes an endless belt-shaped photosensitive member, around which a charger 7, an exposure system 8, a surface voltmeter 9, an eraser 10, a developing unit 11, a P sensor 12, a transfer / separator are arranged in the order of the image forming process.
13, a cleaning device 14 is provided. 15 is a fuser,
Reference numeral 16 denotes a paper discharge tray.

In such a configuration, a copy operation is performed by a well-known process.

FIG. 1 is a flow chart for explaining an embodiment of an image density control method according to the present invention.
2 is repeated when the P sensor 12 is checked (Y at 1-1; usually 5 to 10 fixed intervals), an electrostatic latent image of the detection pattern is created, and its surface potential is measured by a surface voltmeter 9.
(1-3, 1-4).

Next, check the target image density level (this is set by a service person or user according to the user's request).
(1-5 to 1-7), the developing bias (correction bias) required to apply the voltage in accordance with the intended purpose is calculated (1-8 to 1-10). Steps 1-8 to 1-10
, N is a normal potential, L is a light potential, and D is a dark potential.

Further, the correction bias value (the calculated bias value) is compared with the potential of the white pattern portion of the detection pattern (1-11), and when this value A becomes the development start voltage (potential). In other words, if the potential is within the developing range (Y in 1-12), normal pattern density cannot be detected by the P sensor 12, so a small amount of toner (less than the normal toner consumption of the original; The supply is switched to the fixed amount replenishment (usually 2% to 3% replenishment) (1-13), and the runaway of the P sensor 12 is prevented by not detecting the P sensor 12 until the next time.

If the value A does not reach the development start voltage (N in 1-12), a correction bias is applied to the development sleeve (1-1).
4) A toner image of the detection pattern is created, and the pattern density is measured by the P sensor 12 (1-15). as a result,
If the density is low (N in 1-16), replenish the toner (1
-17), if it is dark (Y in 1-16), the toner supply is stopped (1-18). Then, a predetermined number of P sensor checks are completed (1-19), and the process returns.

Note that this replenishment amount is appropriately determined depending on whether the measurement interval is long or short. As a result, a high-quality image can be stably obtained.

FIG. 2 is a control block diagram in which the above control is executed by the CPU 20. Reference numeral 21 denotes a toner supply motor, and reference numeral 22 denotes a developing bias power supply.

〔The invention's effect〕

As described above, according to the present invention, by controlling the developing bias based on the measured potential without controlling the potential of the detection pattern portion, the development potential of the detection pattern portion is always controlled to an arbitrary value, It is possible to provide an image density control method capable of significantly improving the accuracy of density control of a detection pattern and stably performing a target image density irrespective of potential control.

[Brief description of the drawings]

FIG. 1 is a flow chart of an embodiment of an image density control method according to the present invention, FIG. 2 is a control block diagram for executing the flow chart of FIG. 1, and FIG. 3 is a diagram of a copying machine to which the present invention is applied. It is a block diagram. 9: Surface voltmeter, 12: Photosensor, 20: CPU.

Continuation of the front page (56) References JP-A-55-89872 (JP, A) JP-A-57-200052 (JP, A) JP-A-60-142360 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) G03G 15/00 303 G03G 21/00 370-540 G03G 15/08

Claims (1)

(57) [Claims] An image density control method for controlling an image density by detecting a surface potential on an image carrier and detecting an amount of toner adhering on the image carrier. Detecting and controlling the developing bias in accordance with this potential, and detecting the amount of toner adhesion when the surface potential of the image bearing member to which toner is not adhered is a potential within a range developed by the developing bias. And controlling the toner supply amount while changing the toner supply amount.