JPH0535104A - Method for controlling toner concentration - Google Patents

Abstract

PURPOSE:To provide the method for controlling a toner concn. which can well control the toner concn. without fluctuating the weight ratio (T/C) of the toner and developer by a deviation in an initial value by controlling the toner image having a reference concn. so as to attain the prescribed concn. CONSTITUTION:The toner image formed on a photosensitive body 4 is used at the time of storing the reference concn. The toner image is so controlled as to be outputted in accordance with electrostatic charging, exposing and developing conditions corrected by detecting the concn. of the gradation pattern image of the toner formed on the photosensitive body 4 by using the measurement of a reflected light quantity to obtain a concn. gradation pattern, then comparing this pattern with a predetermined concn. gradation pattern and correcting the concn. The reading in of the reference concn. is constant regardless of the developing capacity of the toner in this way and the stabler T/C is maintained. The good control is thus possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for an electrophotographic apparatus, and more particularly to a method for controlling the toner density of a two-component developer.

[0002]

2. Description of the Related Art Conventionally, it has been used in an electrophotographic apparatus.
An inductance control method, a patch detection method, a light detection method, and the like are known and widely used for controlling the toner concentration of the component developer.

[0003]

The above-mentioned inductance control method controls the toner concentration based on the fact that the magnetic permeability of the developer, which is a mixture of toner and carrier composed of a magnetic substance, changes depending on the toner concentration. The degree of compression of the developer,
Variations occur due to toner resistance and the like, and it is difficult to control with high accuracy.

The light detection method utilizes a difference in the amount of reflected light of a toner made of resin and a carrier made of a magnetic material with respect to light of a specific wavelength, and derives the toner concentration from the fluctuation of the amount of reflected light for control. , Again, not only the measured value changes due to the compression of the agent on the light-irradiated surface, but also detection becomes impossible when a substance having a light-absorbing / reflecting ability equivalent to a carrier such as carbon is used in the toner. ..

Further, in the patch detection method, a toner image is formed in a patch shape on a photosensitive member according to predetermined charging, exposure, and developing conditions, and the density is irradiated with light from a light source such as an LED to reflect the reflected light. It is intended to detect the concentration according to the intensity of. According to this method, when the density of the patch toner image becomes low, the toner is replenished to the developer (mixture of toner and carrier), and when the patch density becomes high, the replenishment is stopped and the By waiting for the toner concentration to decrease, it becomes possible to keep the T / C ratio (weight ratio of toner and developer) constant. Also, if T /
Even if the C ratio is out of order, the density of the image can be kept constant by observing the density of the toner image on the photoconductor from time to time.

However, even in this patch detection, there is a problem that the T / C ratio cannot be controlled with sufficient accuracy by the method of inputting the initial value for comparing the densities of the toner images.

For example, the amount of light reflected by a patch-shaped toner image formed using an unused developer whose T / C ratio is known in advance by a light-reflecting patch density detector installed near the photoconductor. When this amount of light is used as the reference density, the toner used, especially the tribo value, cannot be constant for all operating environments of the copying machine, resulting in a difference in toner development capability. However, the reference density may vary.

There is also a method of using the reference density plate instead of the toner image when storing the reference density.

However, this method also cannot read in the same optical system path as the actual toner image, and there is a possibility that there will be a difference from the actually measured value, and in the case of using the same optical system. , The non-image portion of the photoconductor has no choice but to reflect the actual image data.

The present invention is intended to solve the above problems. That is, the present invention provides a toner density control method in which a toner image serving as a reference density has a predetermined density so that the T / C ratio does not fluctuate due to a shift in an initial value and good control is possible. The purpose is to do.

[0011]

In order to achieve the above object, the present invention forms a toner image of a predetermined pattern on a rotatably movable photoconductor, and the toner image of the formed pattern has a specific wavelength. Toner density in the developer by detecting the density of the toner image by detecting the light quantity of the reflected light and comparing the detected density with a reference density stored in advance. In the toner density control method of replenishing the toner so as to keep constant, the toner image formed on the photoconductor is used at the time of storing the reference density, and the toner image is formed on the photoconductor. The density of the gradation pattern image of the toner is detected using the above reflected light amount measurement to form a density gradation pattern, which is then corrected by comparing with a predetermined density gradation pattern. And to be output based on.

[0012]

According to the present invention, the reference density has a predetermined gradation pattern formed on the photoconductor in advance, the gradation pattern is read by the patch inspection, and the output value by this reading and the predetermined gradation pattern are read. The toner image serving as the reference density is read from the patch toner image output after the predetermined gradation pattern is corrected based on the correspondence relationship of the above. No matter how different it is from the main body of the copier, the T / C ratio does not fluctuate due to the deviation of the initial value because it has a predetermined density.
Good control is possible.

[0013]

【Example】

(First Embodiment) FIG. 1 is a sectional view showing the outline of a color printer suitable for carrying out the first embodiment of the method of the present invention.

In this embodiment, an image signal is converted into a laser beam through a laser driver and a laser light source (neither shown), the laser beam is reflected by the polygon mirror 1 and the mirror 2, and the photosensitive drum 4 is formed. Irradiated on. The photosensitive drum 4 on which a latent image has been formed by scanning with laser light rotates in the direction of the arrow shown in the figure. Then, development is performed for each color by the rotary developing device 3 (FIG. 1 shows development with yellow toner).

On the other hand, the transfer paper 6 is wound around the transfer drum 5 and rotated once in the order of Y (yellow), M (magenta), C (cyan) and B (black), for a total of four rotations. Then the transfer is completed.

When the transfer is completed, the transfer paper 6 is separated from the transfer drum 5 and is fixed by a pair of fixing rollers 7 to complete a color image print.

Reference numeral 8 is a light source, and 9 is a light receiving element, which is used for reading a gradation pattern, which will be described in detail later, and is also used for controlling the T / C ratio from the toner density.

FIG. 2 is a block diagram showing an example of a process of reproducing a gradation image for creating a reference density patch according to this embodiment.

An image brightness signal is obtained at the CCD input 21, and the brightness signal is converted into a digital brightness signal by the A / D converter 22.

The obtained luminance signal passes through a shading circuit 23 which corrects the sensitivity variations of individual CCD elements.

A LOG transform 24 is passed through to convert the modified luminance signal into a density signal.

The obtained density signal is converted by the LUT 25 in order to correct the γ characteristic of the printer at the initial setting so that the original image density and the output image density match.

The LUT 25 is adapted to be corrected by the LUT correction table 28 formed from the calculation result described later.

After being converted by the LUT 25, the signal is converted into a signal corresponding to the dot width by the pulse width conversion 26 and sent to the laser driver 27.

With the above digital signal processing, a laser scan is performed to form a latent image having gradation characteristics on the photosensitive drum 4 due to a change in dot area. Images have been obtained.

In the above-mentioned image forming apparatus, a test pattern generator for changing the density signal level and changing the density signal level by several steps is built in on the photosensitive drum 4.

In the present embodiment, the density signal level has 8 bits, that is, 256 gradations, and 00 _H , 40 _H , 80 _H , CO by the test pattern generator.
Gradation patterns were formed on the photosensitive drum 4 for five levels of _H and FF _H. The formed gradation pattern is
By synchronizing the timing, by the light source 8 and the light receiving element 9,
The output corresponding to each toner optical density of the gradation pattern was detected.

Here, as the light source 8, an LED having a main wavelength of about 950 nm is used.

In this embodiment, the photosensitive drum 4 has 950n.
An OPC photoconductor having a reflectance of about 20% at m was used, while a toner containing a styrene-based copolymer resin having a reflectance of 90% or more at 950 nm as a main component was used.

FIG. 3 shows an example of the relationship between the output image density of each color and the output of the light receiving element 9.

FIG. 4 is a block diagram for processing the signal read by the light receiving element 9 to create the LUT correction table 28.

The signal read by the light receiving element 9 is converted into a digital signal by the A / D converter 41, and converted into a density signal by the density conversion circuit. The density for each density level of the gradation pattern is set by the LUT 25 so as to be the line C in FIG. 5 showing the relationship between the density level and the density at the initial setting.

However, the development characteristics and the like change due to changes in the toner environment, and change from the set C line in FIG. 5 to the A line and B line.

If the density obtained from the light receiving element 9 is higher than the setting as shown by the line A, a correction value to be lowered from the setting by the increased amount as shown by the line A'in FIG. 6 is calculated.

If the density obtained from the light receiving element 9 is lower than the setting as shown by the line B, a correction value to be increased from the setting by the lowered amount is calculated as shown by the line B'in FIG.

A correction value calculation circuit 43 for calculating the correction value as described above from the density calculated by the density conversion circuit 42.
A table 28 for correcting the LUT 25 is created via the.

Based on this LUT correction table 28, LU
By correcting T25, it is possible to obtain printer gradation characteristics that do not depend on environmental characteristics and machine differences.

Next, the toner density control utilizing this correction will be described. In particular, the Bk toner will be described in detail. Normally, for toner density control, a plurality of gradation patch toner images are not output as described above, but a patch toner image having a specific level of density is output. For example, 80 _H in FIG.
An image of the density level of is output on the photoconductor as a toner image, and this density is read by the patch detector P of FIG. 1, and if it is lower than the density stored in advance, it is assumed that the T / C ratio is lowered. Add toner. The reading of the reference density will be described next. 80 selected according to C of FIG. 5 optimized by the LUT correction table 28 described above.
_{When the H} image signal is input to the printer of FIG. 1, the photosensitive member pre-charged to a predetermined level according to the image signal is scanned by the exposure of a laser or the like at the predetermined level with a predetermined patch size, and electrostatically charged. Form a latent image. Next, this latent image is developed by the Bk developing device of the rotary developing device 3 and becomes a toner image.

This toner image moves to the front surface of the patch detection P by the rotation of the photoconductor 4, is irradiated with the light of the light source 8, and the reflected light is taken into the photosensor 9 such as a photodiode, and the patch toner density is changed. It is output in the form of current or voltage.

The output value is converted into a digital signal by an A / D converter (not shown) and stored in the storage element.

Next, the T / C ratio control is performed during the above-described image output. For example, in the case of Bk, the patch similar to the above is used before and after the latent image output corresponding to the original image is performed, preferably afterward. Is output, the density is read by the patch detection P, the density is compared with the reference value and converted into the density during development of the toner, and replenishment control is performed. The replenishment control is performed using a table that directly converts the toner replenishment amount using the difference in density.

Here, the reference density is stored as the level 0 in FIG. In this embodiment, the T / C ratio can be kept constant. However, if the correction of the present invention is not performed, the environmental characteristics of the copying machine main body and the developer do not match, and the developing ability of the developer is low. , D on the lines B and B are initially taken in, and the reference density is at a low level, so that T / C is lowered and the maximum density D _max is also lowered when the developer has environmental characteristics. On the other hand, in the case of the line A, the T / C is high, so that the inside of the machine is contaminated such as the toner scattering.

(Second Embodiment) In the first embodiment, the patch density output from the corrected LUT is stored as a reference value. In this case, the LUT correction is performed at any time according to the environmental fluctuation. There is a need. On the other hand, a standard LUT corrected in advance in accordance with environmental changes is stored in the main body of the copying machine, and the correction LUT is output when the reference density is output.
And the standard LUT are output, the density difference is stored, and the toner replenishment control is performed by the patch output using the standard LUT.

(Third Embodiment) After reading the reference density, after changing the primary charging condition of the latent image forming conditions so that the patch density of the standard LUT image of the second embodiment approaches the reference density, In this method, an image is formed, a patch image for T / C ratio control is created in the standard table under the above conditions, and toner density control is performed.

[0045]

As described above, according to the present invention,
Toner density control is performed by using a light reflection type density detector to compare the optical density of a patch-shaped toner image formed on a photoconductor with a predetermined image signal with a light-reflective density detector, and compare it with a prestored reference density. Since the toner density control method is to perform the replenishment operation of T, since the reading of the reference density is constant regardless of the developing ability of the toner, T / T
C ratio can be kept stable. Further, since the appropriate density is used as the reference value, the image density does not change so much and good control can be performed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an outline of a color printer suitable for carrying out a first embodiment of the method of the present invention.

FIG. 2 is an explanatory diagram showing the operation of the printer of FIG. 1 in a block diagram.

FIG. 3 is an explanatory diagram showing a relationship between a light receiving element output and image density.

FIG. 4 is an explanatory diagram showing a block diagram from a light receiving element to a LUT correction table.

FIG. 5 is an explanatory diagram showing printer gradation characteristics.

FIG. 6 is an explanatory diagram showing LUT correction values.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Polygon mirror 2 ... Mirror 3 ... Rotational developing device 4 ... Photosensitive drum 5 ... Transfer drum 6 ... Transfer paper 7 ... Fixing roller 8 ... Light source 9 ... Light receiving element

Claims (1)

Claim: What is claimed is: 1. A toner image having a predetermined pattern is formed on a rotatably movable photoconductor, and the toner image of the formed pattern is irradiated with light of a specific wavelength. The density of the toner image is detected by detecting the amount of light, and the detected density is compared with a reference density stored in advance to replenish the toner so that the toner density in the developer becomes constant. In the method of controlling toner density, the toner image formed on the photoconductor is used for storing the reference density, and the toner image is reflected by the gradation pattern image of the toner formed on the photoconductor. After detecting the density using the light intensity measurement and making it a density gradation pattern, it is output based on the corrected charging, exposure, and development conditions by comparing with a predetermined density gradation pattern. Toner density control method comprising and.