JP3254380B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color image forming apparatus used for a digital color printer, a digital color copying machine, a color facsimile and the like, and an image forming apparatus applicable to an electrophotographic color image processing apparatus. The present invention relates to an image forming apparatus that forms an output image from input image data, and more particularly, to calibration of an image forming apparatus that forms a multi-tone image.

[0002]

2. Description of the Related Art Conventionally, in a digital color copying machine or the like, four colors of one color are provided on a paper transport belt to correct a color tone variation affected by a change in environment (temperature and humidity).
It is known that a two-tone patch is formed, the density is monitored, and the color tone is automatically corrected so that the tint does not change (FUJI XEROX Co., Ltd., full-color copying machine, DocuColor 4040). However, in this method, since 12 patches are created between sheets, a load is applied to the cleaner unit.

Further, in an image reproducing apparatus for performing gradation correction on an input color signal and forming a color image on a recording medium in accordance with the color signal after the gradation correction, an image density sensor or a potential sensor is used. A device that changes gradation correction information is known (Japanese Patent Publication No. 2-34509). However, since the image density sensor has no sensitivity in the high-density portion, the gradation correction information cannot be correctly changed. Further, when changing the gradation correction information by detecting the potential with the potential sensor, the gradation correction information cannot be changed correctly because the toner charge amount changes due to toner density fluctuation and environmental fluctuation.

[0004]

Problems to be solved by the image forming apparatus for forming an output image from input image data and forming a multi-tone image include the following. (1) FIG. 26 shows the aging characteristics of the photoconductor surface potential, and FIG. 27 shows the charging potential characteristics of the photoconductor surface potential. The characteristics of the photoconductor change with temperature and aging, and the charging grid potential of the photoconductor is changed. The image is not stable because the charge potential characteristic of the photoconductor changes due to a change in the image quality. (2) FIG. 28 shows how the relationship between the written value and the amount of toner attached changes depending on the toner density (TC), and FIG. 29 shows how the relationship between the written value and the amount of toner attached changes depending on the toner charge amount. The image is not stable because the amount of toner attached changes due to a change in toner charge amount due to a density change or humidity change. (3) In order to solve the above problems (1) and (2), a patch for gradation correction is formed between sheets of a photoconductor or an intermediate transfer member for gradation correction, and the density of the patch is monitored. Although correction is performed, if many patches are created between sheets for gradation correction, a load is applied to the cleaner unit, and the life of the component is shortened.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and solves the above-mentioned problems. Therefore, it is possible to set optimum gradation correction information (γ correction value) in real time (for each sheet). An object of the present invention is to provide an image forming apparatus capable of forming a stable image even at the time of copying (printing). It is another object of the present invention to provide an image forming apparatus capable of finely controlling image forming conditions by fuzzy inference and further reducing the load on a cleaner unit and extending the life of components.

Further, the optimum gradation correction information (γ correction value) can be set from the image density (toner adhesion amount) output from the image density sensor and the surface potential output from the potential sensor. It is an object of the present invention to provide an image forming apparatus capable of achieving stability.

[0007]

According to another aspect of the present invention, an image forming apparatus includes: an image forming condition determining unit that determines an image forming condition; and a tone correction unit that corrects a tone of an image signal. Means, a gradation pattern generating means for changing a pattern signal of the gradation pattern for each image formation to generate a gradation pattern in a non-image area, and a gradation correction means or a gradation pattern generation means based on an output signal of the gradation pattern generation means. Latent image forming means for forming a latent image on the image carrier, surface potential detecting means for detecting the surface potential of the latent image of the gradation pattern, developing means for visualizing the latent image, Or, a light irradiating unit for irradiating a visible image on a transfer body with light, and an image density detecting unit for detecting an image density by detecting an amount of reflected light obtained by irradiating the visible image with the light by the light irradiating unit with an optical detection element And in the region where the sensitivity of the optical sensing element is reduced And the image density estimating means for estimating the image density in the serial image density detecting means and the surface potential detecting means,
The image processing apparatus further includes a tone correction information changing unit that estimates the image density of the tone pattern by the image density estimating unit and changes the correction amount of the tone correcting unit so that the target image density is obtained. .

Here, in the image forming apparatus according to the first aspect, in the image density estimating means, when the output of the image density detecting means is equal to or less than a threshold, the area / sensitivity where the sensitivity of the optical sensing element is reduced is good. Is determined (claim 5).

In the image forming apparatus according to the present invention, in the image density estimating means, a relation between a surface potential (Vs) and an image density (ID) in the gradation pattern is as follows: ID = a × Vs + b (where a , B are constants) or as the DC component VDC of the developing bias, ID = a × (Vs−VDC) + b (where a and b are constants). Further, the relational expression between the surface potential and the image density is obtained by the least square method.

In the image forming apparatus according to the present invention, the image density estimating means estimates the surface potential of the high density gradation pattern from the surface potential of the low density portion.

In the image forming apparatus according to the first aspect, the gradation correction means is a look-up table (LUT).

In the image forming apparatus according to the present invention, in the gradation correction information changing means, a target image density can be set from an external device.

In the image forming apparatus according to the first aspect, in the gradation correction information changing means, if the image density is not close to the target image density even after the correction based on the gradation correction information, the image forming condition is changed or It indicates that it is impossible (claim 11).

In the image forming apparatus according to the present invention, the image forming condition determining means determines an image forming condition from at least one of a temperature, a humidity, a toner density, and a cumulative number of formed images of the apparatus. ).

2. The image forming apparatus according to claim 1, wherein said image forming condition determining means detects at least one of temperature, humidity, toner density, and the number of accumulated images formed by the apparatus, A rule storage unit storing at least one rule relating the amount and the control amount of the imaging condition; and a plurality of membership functions expressed by a plurality of fuzzy sets with respect to the state amount and the control amount of the imaging condition. The stored function storage means, and how much the state quantity is included in which fuzzy set by the plurality of membership functions, and using the obtained result, the most likely image formation according to each rule Fuzzy inference means for fuzzy inference of the control amount of the condition.
3).

2. The image forming apparatus according to claim 1, wherein said image forming condition determining means detects at least one of temperature, humidity, toner density, and the number of accumulated images formed by said apparatus, and said state quantity detecting means. State change amount detection means for detecting an amount of change in the amount (state change amount); rule storage means for storing at least one rule relating the state amount, the state change amount and the control amount of the imaging condition; Function storage means for storing a plurality of membership functions each represented by a plurality of fuzzy sets with respect to a state amount, a state change amount and a change amount of an image forming condition; and the state amount and the state change amount are the plurality of membership functions. Fuzzy set to determine how much is included in which fuzzy set, and using the obtained result, fuzzy inference of the control amount of the most probable image forming condition in accordance with each rule. And a inference means (claim 1
4).

In the image forming apparatus according to the first aspect, the image forming condition is at least one of a charging potential, a developing bias, an exposure amount, and a transfer bias.
5).

Next, an image forming apparatus according to a second aspect of the present invention generates an image forming condition determining means for determining an image forming condition, a tone correcting means for correcting a tone of an image signal, and a tone pattern signal. And a latent image forming a latent image on an image carrier in accordance with an output signal of the tone correction unit or an output signal of the tone pattern generating unit. Forming means, surface potential detecting means for detecting the surface potential of the latent image of the gradation pattern, developing means for visualizing the latent image, and light irradiating means for irradiating the visible image on the image carrier with light An image density detecting means for detecting an image density by detecting an amount of reflected light, which is obtained by irradiating a visible image with light by the light irradiating means, with an optical detecting element; a surface potential which is an output of the surface potential detecting means; From the image density, which is the output of the detection means, to the surface potential Image density estimating means 1 for estimating image density, latent image characteristic estimating means for estimating a latent image characteristic from the gradation pattern signal and a surface potential output from the surface potential detecting means, and the latent image characteristic estimating means Density estimating means 2 for estimating the relationship between the gradation pattern signal and the image density from the image density estimating means 1, target image density storing means for storing the target image density, the image density estimating means 2 and the target image And a gradation correction information changing unit for changing a correction amount of the gradation correcting unit from the density storage unit so as to obtain a target image density.

According to a third aspect of the present invention, there is provided an image forming apparatus comprising: an image forming condition determining unit for determining an image forming condition; a gradation correcting unit for correcting a gradation of an image signal; Tone pattern generating means for generating a tone pattern in an area, selecting means for selecting an output signal of the tone correcting means and an output signal of the tone pattern generating means, and performing halftone processing on the output signal of the selecting means Halftone processing means, a latent image forming means for forming a latent image on an image carrier according to an output of the halftone processing means, and a surface potential detecting means for detecting a surface potential of the latent image of the gradation pattern Developing means for visualizing the latent image, light irradiating means for irradiating the visible image on the image carrier with light, and the amount of light reflected by irradiating the visible image with the light irradiating means with an optical detection element Image density detecting means for detecting and detecting image density; An image density estimating means for estimating an image density with respect to a surface potential from a surface potential output from a potential detecting means and an image density output from the image density detecting means; A latent image characteristic estimating means for estimating a latent image characteristic from an output surface potential, and an image density estimating means for estimating a relationship between a gradation pattern signal and an image density from the latent image characteristic estimating means and the image density estimating means 1 2, a target image density storage unit for storing a target image density, and a floor for changing a correction amount of the gradation correction unit so as to obtain a target image density from the image density estimation unit 2 and the target image density storage unit. It is characterized by having tone correction information changing means.

According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: an image forming condition determining unit for determining an image forming condition; a halftone processing unit for performing halftone processing on an image signal; Tone correcting means for correcting, a tone pattern generating means for generating a tone pattern in a non-image area by generating a tone pattern signal, an output signal of the tone correcting means and an output signal of the tone pattern generating means A latent image forming means for forming a latent image on an image carrier according to an output signal of the selecting means, and a surface potential detecting means for detecting a surface potential of the latent image of the gradation pattern. Developing means for visualizing the latent image, light irradiating means for irradiating the visible image on the image carrier with light, and the amount of light reflected by irradiating the visible image with the light irradiating means with an optical detection element Image density detecting means for detecting and detecting image density; Image density estimating unit 1 for estimating the image density image density and a relative surface potential which is the output of the output is the surface potential is the image density detecting means electric potential detecting means
Latent image characteristic estimating means for estimating a latent image characteristic from the gradation pattern signal and the surface potential output from the surface potential detecting means; the latent image characteristic estimating means and the image density estimating means 1
Image density estimating means 2 for estimating the relationship between the gradation pattern signal and the image density from the target, target image density storing means for storing the target image density, and a target image density estimating means 2 and the target image density storing means. The image processing apparatus further includes a gradation correction information change unit that changes a correction amount of the gradation correction unit so as to obtain an image density.

Here, in the image forming apparatus according to any one of claims 2, 3 and 4, the gradation pattern generating means changes the gradation pattern signal every time an image is formed.

More specifically, the gradation pattern generating means may be configured to perform each gradation of yellow (Y), magenta (M), cyan (C), and black (K) before or during image formation. Forming a patch (example: image formation → forming a YMCK patch of 0/256 gradations → forming an image forming forming a YMCK patch of 1/256 gradation → image formation →...) (Claim 17); Before or during image formation, patches of all gradations of yellow (Y), magenta (M), cyan (C), and black (K) are formed (example: image formation → Y patch of 0 to 255 gradations) Formation → image formation → M patch of 0-255 gradation → image formation → ...) (Claim 18), Before or during image formation, yellow (Y), magenta (M), cyan (C), some patches of all gradations of black (K) are formed (example: image formation → YM of gradation
CK patch formation → image formation → 50 gradation YMCK patch formation → image formation → 100 gradation YMCK patch → image formation → ...) (claim 19), before image formation or image formation During the formation, some patches are formed among the respective gradations of yellow (Y), magenta (M), cyan (C), and black (K) (eg, image formation → 0, 5
Form Y patches of 0, 100, and 150 gradations → image formation →
The gradation pattern signal is changed for each image formation as described in any one of the following: formation of M patches of 0, 50, 100, and 150 gradations → image formation →...

In the image forming apparatus according to the third or fourth aspect, the halftone processing means is dither processing means.

In the image forming apparatus according to the third or fourth aspect, the halftone processing means is a multi-level error diffusion means.

In the image forming apparatus according to any one of claims 2, 3 and 4, the image density estimating means 1 includes a surface potential (Vs) and an image density (ID) in the gradation pattern.
ID = a × Vs + b (where a and b are constants) or ID = a × (Vs−VDC) + b (where a and b are constants) as the DC component VDC of the developing bias. Is approximated by a broken line that is formed from
3). The relational expression between the surface potential and the image density is obtained by the least square method.

In the image forming apparatus according to the second, third or fourth aspect, in the image density estimating means 1, in a region where the sensitivity of the optical detection element is reduced, the image density is estimated by a straight line having a maximum inclination of a broken line ( Claim 25). In the image density estimating means 1, the straight line having the maximum inclination of the broken line has the image density or the surface potential equal to or more than a certain threshold value.

In the image forming apparatus according to the present invention, the relationship between the gradation pattern signal and the image density is approximated by calculation in the image density estimating means 2 (claim 27). In addition, the approximation is performed by a broken line (claim 28). Alternatively, the approximation is a least squares method, a spline, or a Bezier curve (claim 29).

In the image forming apparatus according to the present invention, the target image density can be set by communication from an external device in the target image density storage means.

In the image forming apparatus according to the second, third or fourth aspect, the gradation correction information changing means changes the image forming condition if the density is not close to the target image density even if the correction is made based on the gradation correction information. (Claim 31). Further, the image density estimating means 1 corrects the relationship between the surface potential and the image density after the image forming condition is changed by the ratio of the charged potential before and after the image forming condition is changed. Alternatively, the image density estimating means 1 corrects the relationship between the surface potential after the image forming condition is changed and the image density by the ratio of the surface potential before and after the image forming condition is changed.

In the image forming apparatus according to the second, third or fourth aspect, if the gradation correction information changing means does not approach the target image density even if the correction is made based on the gradation correction information, the image cannot be formed. It displays certain information or transmits it by communicating with an external device (claim 34).

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, an embodiment of the image forming apparatus according to the present invention will be described. FIG. 1 is an explanatory view showing the overall configuration of an image forming apparatus according to the present invention, in which an electrophotographic color image forming section and an image forming control system are shown together. The section shows a configuration example of the printer section of the digital color copying machine. First, the configuration and operation of the digital color copying machine according to the present invention will be described.

The digital color copying machine comprises a color image reading section (hereinafter, referred to as a color scanner) and a color image forming section (hereinafter, referred to as a color printer). Although not shown, the color scanner forms an image of the document on a color sensor via an illumination lamp, a mirror group, and a lens, and converts color image information of the document into, for example, blue (B), green ( G) and red (R) are read for each color separation light and converted into an electric image signal. The color sensor
Here, it is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD, and reads the three colors.
In FIG. 1, the color sensor is shown as a CCD.

An image signal from the color sensor (CCD) is A / D converted and sent to an image processing unit, where B, G, R
The color conversion processing is performed by the image processing unit based on the color separation image signal intensity levels of yellow (hereinafter, referred to as Y), magenta (same, M), cyan (same, C), and black (same, same). K) color image data is obtained. The color image data is corrected by a YMCK gamma correction unit, which is a gradation correction unit, and then sent to an exposure control unit of a color printer. The exposure control unit controls a writing optical unit (not shown). , M, C, and K, each process of forming a latent image on the photosensitive drum 1 as an image carrier, visualizing the image by the developing unit 4, and transferring the image to the intermediate transfer belt 7 is performed on the intermediate point belt. A color image is formed thereon, and this is collectively transferred to transfer paper to form a final color copy.

The operation system of the color scanner for obtaining the image data of Y, M, C, and K is such that the original is scanned in response to a scanner start signal that is timed with the operation of the color printer, and the scanning is performed once each time. , Image data of one color each of Y, M, C, and K is obtained. By repeating this operation a total of four times, sequential four-color image data is obtained. And
Each time, while a latent image is sequentially formed and visualized by a color printer, the latent image is superimposed on an intermediate transfer belt to form a four-color full-color image.

Next, an outline of the color printer shown in FIG. 1 will be described. The exposure control unit converts the color image data from the color scanner into an optical signal, controls a writing optical unit (not shown) to perform optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 1. Form an image. This writing optical unit includes a known laser light source and its light emission drive control unit, an optical deflector such as a polygon mirror, and an optical system such as an fθ lens and a reflection mirror. Further, instead of the above configuration, a writing optical unit using a light emitting diode (LED) array light source, an equal-magnification imaging element array, or the like can be used.

The photosensitive drum 1 rotates in a counterclockwise direction as indicated by an arrow. Around the charger, the charger 2, the optical writing unit, the surface voltmeter 3, and the Y
Developing unit 4Y, M developing unit 4M, C developing unit 4C, K developing unit 4
An image density sensor (P sensor) comprising a light irradiating means 6a such as K or LED and an optical detecting element 6b such as a phototransistor.
6, intermediate transfer belt 7, photoreceptor cleaner 8, static eliminator 9
And so on.

Each of the developing units 4Y, 4M, 4C, 4 of the developing unit 4
K is a developing sleeve that rotates by contacting the ears of the developer with the surface of the photosensitive drum 1 to develop the electrostatic latent image; a stirring roller that rotates to pump and agitate the developer;
The developing unit includes a replenishing clutch for replenishing the replenishing toner from the toner replenishing unit into the developing unit, a toner concentration sensor (T sensor) 5 for detecting the toner concentration of the developer in the developing unit, and the like. In the standby state, all of the four developing devices are in a state of cutting off the developer on the developing sleeve (development is not activated).

Next, the image forming operation will be described. Here, the order of the developing operation (color image forming order) is K, C,
An example of M and Y will be described (however, the order of image formation is not limited to this, and may be in the order of Y, M, C, K, etc.).

When the copying operation is started, reading of the K image data is started at a predetermined timing by the color scanner, and based on the image data, light writing to the photosensitive drum 1 by a laser beam and formation of a latent image are performed. (Hereinafter, the electrostatic latent image based on the K image data is referred to as a K latent image, and the same applies to C, M, and Y). In order to enable development from the leading end of the K latent image, before the leading end of the latent image reaches the developing position of the K developing unit 4K of the developing unit 4, the developing sleeve of the K developing unit 4K is started to rotate, and The K latent image is developed with the K toner by applying a predetermined bias voltage to the developing sleeve by the developing bias control unit.

Thereafter, the developing operation of the K latent image area is continued, but when the rear end of the latent image has passed the K developing position, the cutting of the material on the K developing sleeve is immediately performed, and the developing operation is stopped. I do. This is completed at least before the leading end of the C latent image based on the next C image data arrives. The ear cutting is performed by switching the rotation direction of the developing sleeve to a direction opposite to that during the developing operation.

The K toner image formed on the photosensitive drum 1 is transferred onto the surface of the intermediate transfer belt 7 driven at the same speed as the photosensitive drum 1 (hereinafter, the transfer from the photosensitive drum to the intermediate transfer belt). The toner image transfer is referred to as a belt transfer).
This belt transfer is performed by the photosensitive drum 1 and the intermediate transfer belt 7.
Is performed in a contact state by applying a predetermined bias voltage to the transfer bias roller 7a by the intermediate transfer control unit.

On the intermediate transfer belt 7, the toner images of K, C, M, and Y sequentially formed on the photosensitive drum 1 are sequentially aligned on the same surface, and a four-color superimposed belt transfer image is formed. Then, batch transfer is performed on transfer paper.

On the photosensitive drum 1 side, the process proceeds to the C image process after the K image process. At a predetermined timing, C image data reading by a color scanner starts.
The C latent image is formed by laser light writing based on the image data.

The C developing device 4C starts rotating the developing sleeve after the trailing end of the preceding latent image has passed and before the leading end of the C latent image has arrived at the developing position, so that the developer is spiked. The C latent image is developed with the C toner by applying a predetermined bias voltage to the developing sleeve by the developing bias control unit. Thereafter, the development of the C latent image area is continued, but when the trailing end of the latent image passes, the cutting of the agent on the C developing sleeve is performed in the same manner as in the case of the K developing device. This is also completed before the leading end of the next M latent image arrives.

Note that the operations of M and Y are the same as those of the above K and C, since the operations of reading image data, forming a latent image, and developing are the same as those in the above-described steps.

The intermediate transfer belt 7 is stretched around a drive roller 7b, a belt transfer bias roller 7a, and a driven roller group, and is driven and controlled by a drive motor (not shown). The intermediate transfer belt 7 has a belt cleaner 13.
The belt cleaner 13 includes a cleaning member such as a brush roller and a rubber blade, and a mechanism (not shown) for contacting and separating from the belt. The belt cleaner 13 transfers the K image of the first color to the belt. While the second, third, and fourth colors are being transferred to the belt, they are separated from the belt surface by a contact / separation mechanism.

A transfer charger (or transfer bias roller) is provided in the paper transfer section 10 of the intermediate transfer belt 7, and the transfer bias of the transfer charger is controlled by paper transfer control. When the four-color superimposed image formed above is transferred collectively to transfer paper,
A predetermined transfer bias is applied to perform transfer to paper. Further, a separation unit 11 composed of a separation charger or the like is provided downstream of the transfer unit 10, and separates the transfer paper after transfer from the intermediate transfer belt 7 and conveys the transfer paper toward the fixing roller.
The transfer paper is transferred to the transfer unit 10 by a feed roller or a registration roller (not shown) in accordance with the timing at which the leading end of the four-color superimposed image on the intermediate transfer belt surface reaches the paper transfer position.
Paper.

The manner of movement of the intermediate transfer belt 7 is defined as an operation system after the belt transfer of the K toner image of the first color is completed to the rear end portion. Continue to move), skip forward movement method (when the transfer of the first color is completed, skip the high speed in the forward direction away from the photoconductor surface, return to the initial constant speed after moving a predetermined amount, and contact the photoconductor surface again) Reciprocating (quick return) method (when the transfer of the first color is completed, it is separated from the photoreceptor surface, returns at a high speed in the reverse direction, temporarily stops, and contacts the photoreceptor surface again in time with the leading end of the image of the second color) , Starting in the forward movement direction) are known. One of these methods or an efficient combination of methods (such as in terms of copy speed) according to the copy size is operated.
The C, M, and Y toner images are sequentially superimposed on the K toner image on the intermediate transfer belt 7 to transfer the belt, and a four-color superimposed belt transfer image is obtained. Then, following the belt transfer process of the Y toner image of the fourth color, the four-color superimposed toner image on the surface of the intermediate transfer belt 7 is collectively transferred onto transfer paper by the respective operation methods.

The transfer paper on which the four-color superimposed toner image has been collectively transferred from the intermediate transfer belt 7 by the transfer unit 10 is separated by the separation unit 11 and conveyed to the fixing device, where the fixing control unit controls the temperature to a predetermined temperature. After the toner image is fused and fixed by the roller 12, it is carried out to a copy tray (not shown) to obtain a full-color copy.

The surface of the photoreceptor drum 1 after the belt transfer is cleaned by a photoreceptor cleaner 8 (consisting of a pre-cleaning static eliminator, a brush roller, a rubber blade, etc.). Static electricity is removed. Further, the surface of the intermediate transfer belt 7 after the transfer of the toner image onto the transfer paper is cleaned by bringing the belt cleaner 13 into contact with the belt surface by a contact / separation mechanism (not shown).

At the time of repeat copying, the operation of the color scanner and the formation of an image on the photosensitive drum 1 are performed at a predetermined timing following the first Y (fourth color) image process. (1st color) Proceed to the image process. In the case of the intermediate transfer belt 7, the surface of the intermediate transfer belt 7 is transferred to the belt cleaner 1 following the batch transfer process of the first four-color superimposed image onto transfer paper.
The second K toner image is transferred to the belt cleaned area in step 3. After that, the operation is the same as that of the first sheet.

The copy mode for obtaining four full colors has been described above. In the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated number of times of the colors. become. In the case of the single-color copying mode, only the developing device of that color is set in a developing operation (springing) until the predetermined number of sheets is completed, and the intermediate transfer belt 7 contacts the surface of the photosensitive drum 1. The copy operation is performed while the belt cleaner 13 is driven at a constant speed in the forward movement direction and the belt cleaner 13 is still in contact with the intermediate transfer belt 7.

Next, detection means of the image forming control system relating to image formation of this apparatus will be described. First, the surface potential meter 3 as a surface potential detecting means detects the surface potential of the photosensitive drum 1. The toner density sensor (T sensor) 5 detects the toner density in the developing units 4Y, 4M, 4C, and 4K for each color. Image density sensor 6 as image density detecting means
Detects the density of the visible image (developed image) on the photoconductor. Further, a fixing thermistor or the like is disposed in contact with the surface of the fixing roller (not shown) as a temperature detecting means of the fixing roller, and detects the surface temperature of the fixing roller. In addition, a temperature sensor, a humidity sensor, and the like for detecting the temperature and humidity in the copying machine are provided.

The detection output of each detection means is output to a well-known CPU, memory (ROM, RAM), interface, I / O
The image forming condition control unit includes a port, various control circuits, and the like. The image forming condition control unit determines image forming conditions based on the input information, and controls each of the control units (a charging control unit, a developing bias control unit, Exposure controller, intermediate transfer controller, paper transfer controller, etc.)
To output control information.

By the way, in the digital color copying machine having the above configuration and operation, an output image is formed from input image data, and more specifically, a multi-color image of color is formed. In the forming apparatus, the characteristics of the photoreceptor change with temperature and time, and the charging potential characteristics of the photoreceptor change due to a change in the charging grid potential of the photoreceptor, so that the image is not stable (see FIGS. 26 and 27). The image is not stable because the toner adhesion amount changes due to a change in toner charge amount due to a change in toner density or a change in humidity (FIG. 2).
8 and 29). For this reason, it has been practiced to form a patch for gradation correction between papers of a photoreceptor or an intermediate transfer member for gradation correction, and monitor and correct the density thereof. If a large number of patches are created between sheets, a load is applied to the cleaner unit, and there is a problem that the life of the parts is shortened. The present invention solves the problem in such an image forming apparatus, and can set the optimal gradation correction information (γ correction value) in real time (each sheet), so that the image is stable even during continuous copying (printing). Can be formed.

In the image forming apparatus according to the present invention, FIG.
As shown in the figure, an imaging condition control unit that determines the imaging condition,
A YMCKγ correction unit for correcting the gradation of the image signal, a gradation pattern control unit for changing the pattern signal of the gradation pattern for each image formation to generate a gradation pattern in the non-image area, An exposure control unit for forming a latent image on the photosensitive drum 1 based on an output signal of the tone pattern control unit, a surface voltmeter 3 for detecting a surface potential of the latent image of the gradation pattern, and visualizing the latent image And a light irradiating unit (LE) for irradiating a visible image on the photosensitive drum 1 with light.
D) 6a, and the amount of reflected light obtained by irradiating the visible image with the light irradiating means 6a is used as an optical detection element (phototransistor, etc.) 6
and an image density sensor 6 for detecting the image density by detecting the image density in step b. The image density sensor 6 detects the image density of the gradation pattern and changes the correction amount of the YMCKγ correction unit so that the target image density is obtained. It has a configuration having tone correction information changing means.

In FIG. 1, the YMCKγ correction section is a look-up table (hereinafter, referred to as LUT). The gradation pattern control unit is connected to an external personal computer (hereinafter, referred to as an external personal computer).
And the like, so that the target image density and the like can be set from outside (not shown).

Here, generation of a gradation pattern in a non-image area will be described. FIG. 3 shows a non-image area between papers on the photosensitive drum 1. In an image area (not shown), a latent image is formed by exposing a laser beam by controlling a writing optical unit by an exposure control unit based on color image data obtained by performing image processing on an image signal read by a CCD of the color scanner described above. I do. On the other hand, in the non-image region, the exposure control unit controls the writing optical unit according to the gradation pattern signal from the gradation pattern control unit to expose the gradation pattern. In the exposure of this gradation pattern, a gradation pattern can be created for each image formation by creating a gradation pattern for each sheet, that is, between sheets. Further, the gradation pattern can be generated by changing the density of the gradation pattern every time an image is formed. The thus formed gradation pattern is irradiated with light from an LED or the like as light irradiating means 6a, and the reflected light is detected by a phototransistor as an optical detection element 6b of the image density sensor 6, The gradation correction is performed by detecting the image density of the gradation pattern.

Although the non-image area between papers has been described with reference to FIG. 3, in the case of a large photosensitive drum, a non-image area can be created at the end of the drum. That is, it is also possible to generate a plurality of gradation patterns by changing the density at the end of the photosensitive drum each time an image is formed.

Next, a gradation correction method will be described. FIG. 5 shows an example of gradation correction by the image density sensor. This is an example in which ten patches are created in a non-image area on a photoconductor by changing a write value of a tone pattern, and these are detected by an image density sensor to perform tone correction. It should be noted that in the figure, the toner adhesion amount is converted by the image density sensor.

FIG. 5 shows the relationship between the laser writing value (LD writing value) and the toner adhesion amount on the photosensitive member in the first quadrant. In the figure,
Is a relationship between the LD writing value and the actual toner adhesion amount. The actual toner adhesion amount is a value obtained by measuring the toner on the photoconductor with a balance. In addition, the relationship between the output of the image density sensor and the actual amount of toner adhesion is determined in advance for the black toner and the color toner (see FIG. 4), and the black toner and the color toner are stored separately in the adhesion amount table. deep.
Is a graph obtained by measuring black toner with an image density sensor and converting the black toner adhesion amount table. Is a graph obtained by measuring a color toner with an image density sensor and converting the color toner adhesion amount table. Also,
The graph in the second quadrant in FIG. 5 shows the target toner adhesion amount (target image density) on the photoconductor with respect to the write value, which can be set from an external personal computer.

The inverse transformation of the graph is obtained in advance. However, in the case of color toner, an area where the image density sensor has sensitivity, that is, the toner adhesion amount is set to a threshold th1 or less.

As shown in FIG. 5, as the gradation correction value for the black maximum writing value, a black maximum writing value correction value can be obtained as shown by the arrow in the figure. Similarly, for the maximum color writing value, the maximum color writing value correction value can be obtained as indicated by the arrow in the figure. Then, by changing the correction amount of the YMCKγ correction unit by the gradation correction information changing means based on the correction value thus obtained, gradation correction can be performed satisfactorily and the image density is stabilized.

However, in the above method, since the sensitivity of the image density sensor is insensitive at the high toner adhesion portion (see FIG. 4), an error occurs between the actual toner adhesion amount and the toner adhesion amount calculated from the image density sensor. However, the accuracy of correction of the high density portion is not good.

Therefore, as shown in FIG. 2, in the image forming apparatus according to the first aspect of the present invention, in addition to the configuration of the control system of FIG. 1, an area where the sensitivity of the optical sensing element (phototransistor or the like) 6b is reduced. In the (high toner adhesion portion), the image density sensor 6
And an image density estimating means for estimating the image density with the surface voltmeter 3. The gradation correction information changing means estimates the image density of the gradation pattern by the image density estimating means and performs YMCKγ correction so that the image density becomes the target image density. The correction amount of the section is changed.

FIG. 6 shows an example of gradation correction by the configuration of claim 1 (image density estimation). That is, ten patches are created in the non-image area on the photoreceptor by changing the writing value of the gradation pattern, and the image density of the gradation pattern is determined based on the detection values of the image density sensor 6 and the surface voltmeter 3. This is an example in which the gradation estimation is performed by the density estimating means so as to achieve the target image density. still,
In the figure, the amount is shown by the toner adhesion amount converted by the image density sensor. The graph of FIG. 6 shows the relationship between the potential (the difference between the surface potential of the gradation pattern and the developing bias) and the amount of toner adhesion (measured value) when the gradation pattern is created. Is a graph obtained by converting the output of the image density sensor when the black toner and the color toner are measured by the image density sensor using the above-described toner adhesion amount table. In the high toner adhesion amount portion, there is an error from the actual adhesion amount. If the toner adhesion amount is equal to or larger than the threshold value th_H, an error occurs with the toner adhesion amount calculated from the image density sensor. If the toner adhesion amount is equal to or smaller than the threshold value th_L, the relationship between the potential and the toner adhesion amount is not linear. Therefore, the area enclosed by the frame in the figure (the area used in the estimation of the amount of adhesion)
The straight line area of the graph is determined by the least squares method or the like based on the portion. The area surrounded by this frame is the toner adhesion amount th
It is also possible to determine from the image density output corresponding to _H or more.

Here, the toner adhesion amount on the photoreceptor is expressed as MA
MA = a × Vs + b (where a and b are constants) (1) Alternatively, assuming that the DC component of the developing bias is VDC, = A × (Vs−VDC) + b (where a and b are constants) (2)

The relationship between the laser writing value (LD writing value) and the amount of toner adhering on the photoreceptor (graph in FIG. 6) can be obtained from the relationship of the above expression (1) or (2). Yes, the inverse transform is required. The graph shows the relationship between the writing value and the target toner adhesion amount on the photoconductor. This relationship can also be set by an external personal computer (not shown). The gradation correction value for the maximum write value is
As shown by the arrow in the figure, it can be obtained by the inverse transformation.

Since the high adhesion portion is estimated using the linear region of the graph and the potential information of the gradation pattern, it is not necessary to develop the gradation pattern of the high adhesion amount portion. Therefore, since the gradation correction can be performed without wasteful toner consumption, the load on the cleaning unit of the image forming apparatus can be reduced. Further, the surface potential V on the photosensitive member when the writing value W in the high density portion is V1 is the surface potential when the writing value W1 is in the low density portion, and V2 is the surface potential when the writing value W2 is in the low density portion. Then (W1 ≠ W2), V = (V2−V1) / (W2−W1) W (3) That is, if the surface potential of the high-density gradation pattern is estimated from the surface potential of the low-density part, a patch of the high-density part is not created.
The number of patches can be reduced.

In the above gradation correction example, the gradation correction unit (YM
The CKγ correction unit) is an LUT and is configured to set the gradation correction information in the LUT by the gradation correction information changing unit. However, a plurality of curves (without generating a pseudo contour) are prepared in advance and the gradation is corrected. A curve closest to the correction information may be selected.

If the target toner adhesion amount (target image density) does not reach the target toner adhesion amount even if the correction is performed using the gradation correction information obtained in the above-described gradation correction example, the image forming conditions are changed. After the image forming conditions are changed, if the new gradation correction information cannot be corrected, the image forming conditions are changed again. If the target toner adhesion amount is not reached even after the change of the image forming condition is repeated up to a predetermined number of times, a display indicating that image formation is impossible is displayed on the display panel of the operation unit to inform the user. Alternatively, it is also possible to notify an external personal computer to display a warning (not shown). The image forming conditions can be changed by selecting the potential table shown in FIG. In FIG. 8, VD is a charging potential, and VB is a developing bias.

Next, a method of obtaining the control amount of the image forming condition by fuzzy inference will be described. FIG. 7 shows an example of the image forming condition determining means for obtaining the control amount of the image forming condition by fuzzy inference. The image forming condition determining means includes a state quantity detecting means for detecting at least one of a temperature, a humidity, a toner density, and a cumulative number of image forming sheets (copy counter) of the apparatus, and a change amount of the state quantity (state change amount). State change amount detection means for detecting, rule storage means storing at least one rule relating the state amount (and / or the state change amount) and the control amount of the imaging condition, and the state amount (and / or Function storage means for storing a plurality of membership functions each represented by a plurality of fuzzy sets with respect to the state change amount) and the image formation condition change amount, and the state amount (and / or the state change amount) being the plurality of members A fuzzy set is determined by a ship function to what extent, and the obtained result is used to determine a control amount of an image forming condition most likely according to each rule. And a fuzzy inference means for logical.

The above-mentioned control amount is a number for selecting the potential table shown in FIG. If the control amount is between the first table and the second table as in 1.6, a table that is simply close may be selected. Further, the first table and the second table may be obtained by interpolation. Hereinafter, a specific example of fuzzy inference will be described.

(Fuzzy Inference Example 1) FIG. 9 shows a fuzzy inference example 1. This is an example in which a fuzzy inference unit selects a potential table number from toner concentration and humidity. FIG. 10 is a diagram showing fuzzy rules stored in the rule storage means of the fuzzy inference means of FIG. 9, and FIGS.
(F) is a diagram showing the membership function stored in the function storage means of the fuzzy inference means of FIG.

Hereinafter, the following four fuzzy rules are used for explanation. (Rule 1) if toner concentration = NB and humidity = NM then table number = NB. (Rule 2) if toner concentration = NM and humidity = NM then table number = NM. (Rule 3) if toner concentration = NB and humidity = NS then table number = NM. (Rule 4) if toner concentration = NM and humidity = NS then table number = ZO.

As described above, the fuzzy rules are set as needed. Note that NB, NM, NS, Z in FIGS.
O, PS, PM, and PB represent fuzzy sets.

FIGS. 11A to 11F show examples of calculating a table number by fuzzy inference using rules 1 to 4. FIG. The horizontal axis of (a) is 1 to 25
It has been normalized to 6. (A) is a membership function of the toner density, and (c) is a membership function of the humidity.

As an example, consider the case where toner density = x and humidity = y. First, according to rule 1, the toner density membership function is included in the set of NB (part 1 in FIG. 11B) and the humidity membership function is included in the set of NB (part 1 in FIG. 11D). Furthermore, the minimum value (MIN-OP
ERATION) is obtained as a part 1 in FIG. Perform rules 2 to 4 as described above,
When the AX-OPERATION is performed, 1 to 1 in FIG.
A hatched area of 4 is obtained. By calculating the defuzzification of this area by the centroid method, the table number (the control amount of the imaging condition) can be obtained.

(Fuzzy Inference Example 2) FIG. 12 shows a fuzzy inference example 2. This is an example in which a fuzzy inference unit selects a potential table number from a toner density and a toner density change amount. FIG. 13 is a diagram showing fuzzy rules stored in the rule storage means of the fuzzy inference means in FIG. 12,
FIGS. 14A to 14F are diagrams showing membership functions stored in function storage means of the fuzzy inference means of FIG. In this example, similarly to the fuzzy inference example 1, it is possible to determine the potential table (the control amount of the imaging condition) by using the fuzzy rules of FIG. 13 and the membership functions of FIGS. .

(Fuzzy Inference Example 3) FIGS. 15 and 18 show a fuzzy inference example 3. FIG. This is because the fuzzy inference means shown in FIG.
This is an example in which a potential table number (a control amount of image forming conditions) is determined by fuzzy inference in FIG. 18 based on the GAIN and the temperature. By making the fuzzy inference two stages, the former stage and the latter stage, it is possible to easily create the fuzzy rule and the membership function. FIG. 16 is a diagram showing the fuzzy rules stored in the rule storage means of the fuzzy inference means of FIG. 15, and FIGS. 17 (a) to 17 (f) are stored in the function storage means of the fuzzy inference means of FIG. FIG. 4 is a diagram illustrating a membership function.
FIG. 19 is a diagram showing the fuzzy rules stored in the rule storage means of the fuzzy inference means of FIG. 18, and FIGS. 20 (a) to (f) are stored in the function storage means of the fuzzy inference means of FIG. FIG. 4 is a diagram illustrating a membership function.

If the fuzzy inference example 3 described above is used as the image forming conditions in addition to the charging potential and the developing bias, the control amounts of the exposure amount, the intermediate transfer bias, and the paper transfer bias can be easily determined. Although the example in which the control amount of the image forming condition is obtained from the toner density, the humidity, and the temperature has been described, similarly, the control amount of the image forming condition can be obtained from the cumulative number of image formation sheets (copy counter) of the apparatus. It is.

Next, an embodiment of the image forming apparatus according to the second, third, and fourth aspects will be described.

FIG. 21 is a diagram showing a configuration of an image forming control system of the image forming apparatus according to the third aspect, and FIG. 22 is a view showing a configuration of an image forming control system of the image forming apparatus according to the fourth aspect. FIG.
23 is a diagram illustrating a configuration example of a portion of an image forming control unit in FIG. 21 or FIG. 22. FIG. 24 is a diagram illustrating a configuration example of a color image forming unit of an image forming apparatus including the image forming control system of FIG. 21 or FIG. Note that the color image forming section shown in FIG. 24 has the same configuration as the color image forming section of the image forming apparatus shown in FIGS. 1 and 2, and its configuration and operation are as described above. Is omitted.

The image forming apparatus having the configuration shown in FIGS. 21, 23, and 24 has an image forming condition control section for determining image forming conditions, a YMCKγ correction section for correcting the gradation of an image signal, and generates a gradation pattern signal. And a selector for selecting an output signal of the YMCKγ correction unit and an output signal of the gradation pattern generation unit, and a halftone output signal of the selector. A halftone processing unit for processing, an exposure control unit for forming a latent image on the photosensitive drum 1 according to an output of the halftone processing unit, and a surface voltmeter for detecting a surface potential of the latent image of the gradation pattern 3, a developing unit 4 for visualizing the latent image, a light irradiating means (LED or the like) 6a for irradiating the visible image on the photosensitive drum 1 with light, and a light for irradiating the visible image with the light irradiating means 6a. The amount of reflected light illuminated is measured by an optical sensor (phototransistor). An image density sensor 6 for detecting the image density by detecting the image density at 6b; and a surface potential as an output of the surface voltmeter 3 and an image density as an output of the image density sensor 6 to determine an image density with respect to the surface potential. An image density estimating means for estimating, a latent image characteristic estimating means for estimating a latent image characteristic from the gradation pattern signal and a surface potential output from the surface voltmeter 3; An image density estimating means for estimating a relationship between a gradation pattern signal and an image density from the estimating means, a target image density storing means for storing a target image density, the image density estimating means and the target image density storing means; And the tone correction information changing means for changing the correction amount of the YMCKγ correction unit so as to achieve the target image density.

The image forming apparatus having the structure shown in FIGS. 22, 23 and 24 has an image forming condition control section for determining image forming conditions, a halftone processing section for performing halftone processing on an image signal, and the halftone processing section. Correction unit for correcting the gradation of the output of the unit, a gradation pattern generation unit for generating a gradation pattern signal to generate a gradation pattern in a non-image area, an output signal of the YMCK γ correction unit and a gradation pattern A selector for selecting an output signal of the generation unit, an exposure control unit for forming a latent image on the photosensitive drum 1 according to the output signal of the selector, and a surface for detecting a surface potential of the latent image of the gradation pattern An electrometer 3, a developing unit 4 for visualizing the latent image, a light irradiating unit (such as an LED) 6a for irradiating the visible image on the photosensitive drum 1 with light, and a visible image by the light irradiating unit 6a. The amount of reflected light illuminated is determined by the optical detection element (photo And an image density sensor 6 for detecting the image density by detecting the image density with an image density sensor 6b, and a surface potential output from the surface electrometer 3 and an image density output from the image density sensor 6. An image density estimating means for estimating, a latent image characteristic estimating means for estimating a latent image characteristic from the gradation pattern signal and a surface potential output from the surface voltmeter 3; An image density estimating means for estimating a relationship between a gradation pattern signal and an image density from the estimating means, a target image density storing means for storing a target image density, the image density estimating means and the target image density storing means; And the tone correction information changing means for changing the correction amount of the YMCKγ correction unit so as to achieve the target image density.

The combination of FIGS. 21, 23, and 24 shows the structure of the image forming apparatus according to claim 3, and FIGS.
The combination of Nos. 4 shows the configuration of the image forming apparatus of the fourth aspect, but the configuration of FIG. 21 or FIG. 22 from which the halftone processing unit is omitted is the configuration of the image forming apparatus of the second aspect. FIG.
The first image forming apparatus has a configuration in which an output signal of a selector is subjected to halftone processing by an intermediate processing unit and a latent image is formed on the photosensitive drum 1 according to the output of the halftone processing unit. The image forming apparatus has a configuration in which an image signal is subjected to halftone processing by a halftone processing unit, and the gradation of the output of the halftone processing unit is corrected by a YMCKγ correction unit. The operation (gradation correction operation) is the same.

Hereinafter, a gradation correction operation by the image forming apparatus will be described.

In the image forming apparatus of FIG. 21 or FIG.
The YMCKγ correction unit uses a look-up table (hereinafter, LU
T). Dither processing or multi-level error diffusion can be used for the intermediate processing unit. Further, by using the multi-level error diffusion, the bit width of the signal after the multi-level error diffusion can be reduced, so that the hardware can be reduced. Incidentally, FIG.
With the configuration described above, the effect of reducing hardware is greater.

Next, generation of a gradation pattern in a non-image area will be described. As shown in FIG. 3, a gradation pattern is formed in the non-image area between the papers on the photosensitive drum 1.
In an image area (not shown), a latent image is formed by exposing a laser beam by controlling a writing optical unit by an exposure control unit based on color image data obtained by performing image processing on an image signal read by a CCD of the color scanner described above. I do. On the other hand, in the non-image area, the exposure control unit controls the writing optical unit by the gradation pattern signal from the gradation pattern generation unit to expose the gradation pattern. In the exposure of this gradation pattern, a gradation pattern can be created for each image formation by creating a gradation pattern for each sheet, that is, between sheets.
Further, the gradation pattern can be generated by changing the density of the gradation pattern every time an image is formed.

As a specific method of forming a gradation pattern, a patch of each gradation of yellow (Y), magenta (M), cyan (C), and black (K) is formed before or during image formation. (Example: image formation → formation of a Y / MCK patch of 0/256 gradations → formation of a YMCK patch of 1/256 gradation → image formation →...) Before or during image formation. A patch of all gradations of yellow (Y), magenta (M), cyan (C), and black (K) is formed (example: image formation → Y patch of 0 to 255 gradations → image formation → 0 Formation of M patches of 255 gradations → image formation →...), Before or during image formation, for all gradations of yellow (Y), magenta (M), cyan (C), and black (K) Some patches are formed (example: image formation → YM of 0 gradation)
CK patch formation → image formation → 50 gradation YMCK patch formation → image formation → 100 gradation YMCK patch formation → image formation →), yellow before or during image formation (Y), magenta (M), cyan (C), and black (K), each of which forms some patches (eg, image formation → 0, 5)
Form Y patches of 0, 100, and 150 gradations → image formation →
(Formation of M patches of 0, 50, 100, and 150 gradations → image formation →...).

Although the non-image area between the sheets has been described with reference to FIG. 3, a non-image area can be created at the end of the drum in the case of a large photosensitive drum. That is, it is also possible to generate a plurality of gradation patterns by changing the density at the end of the photosensitive drum each time an image is formed.

The surface potential and the image density of the gradation pattern formed as described above are detected by the surface voltmeter 3 and the image density sensor 6, and gradation correction information is created by the image forming control unit shown in FIG. FIG. 23 is a block diagram showing the configuration of the image forming control unit, and the flow of information is indicated by arrows.

In FIG. 23, the gradation correction information changing means and the target image density storage means can be connected to an external device (a personal computer, an operation unit of a copying machine, a display panel, or the like) by an external interface. Is a cable or a network. By connecting to an external device in this way, a target image density (standard image density) and the like can be set from the external device. An example of the target image density is shown in the second quadrant of FIG. Further, information such as the fact that gradation correction is not possible or that image forming conditions are changed can be transmitted to an external device and displayed. The standard image density is a value that is linear in lightness or a value that is linear in density with respect to the written value, and is a value that is balanced in gray.

Next, a method of estimating image density and a method of creating gradation correction information will be described with reference to FIG. FIG. 25 shows an example in which the writing value of the gradation pattern is changed to a non-image area on the photosensitive member.
In this example, zero patches are created, and this is detected by an image density sensor and a surface voltmeter to perform tone correction.
It should be noted that in the figure, the toner adhesion amount is converted by the image density sensor. First, the relationship between the potential (the difference between the surface potential of the gradation pattern and the developing bias) and the toner adhesion amount (measured value) on the photoconductor is determined. In this case, the relationship between the output of the image density sensor and the amount of toner adhered on the photoconductor is obtained in advance and is tabulated. The graph in the first quadrant of FIG. 25 shows the relationship between the potential when a gradation pattern is created and the amount of toner adhered to the photoconductor (development characteristics).

The relationship between the potential Vs and the toner adhesion amount MA (corresponding to the image density ID) is as follows: MA = a × Vs + b (where a and b are constants) (1) As VDC, MA = a × (Vs−VDC) + b (where a and b are constants) (2) It is also possible to reduce the measurement error by approximation by the least square method.

However, FIG. 4 (characteristic diagram of the image density sensor)
As shown in (2), the image density sensor has no sensitivity at the high adhesion portion. Therefore, the least-squares method is applied to the relationship between the potential in the graph in the first quadrant of FIG. 25 and the toner adhesion amount (a value obtained by converting the output from the image density sensor using the adhesion amount table). In other words, the first approximation by the least squares method is applied to adjacent N points, and a straight line having the maximum slope is selected, thereby estimating the relationship between the potential and the amount of adhesion in the high adhesion portion. An experiment has shown that the estimation error can be reduced by selecting the maximum inclination when the potential or the toner adhesion amount is equal to or larger than a certain threshold. N is 3
Or 4 is practical. In the low / medium adhesion amount portion, adjacent points are linearly approximated. Alternatively, a linear approximation may be performed using a linear expression obtained by the least square method.

Next, the relationship between the third and fourth quadrants in the graph of FIG. 25, that is, the relationship between the written value (gradation pattern signal) and the potential (latent image characteristic) is obtained. This can also be obtained by using the patch used when obtaining the relationship in the first quadrant. It is also possible to create and obtain another patch.

Next, the relationship between the written value and the toner adhesion amount is determined from the development characteristics and the latent image characteristics. By tracing as shown by the arrows (solid lines) in the third and fourth quadrants → first quadrant in FIG.
The toner adhesion amount with respect to the written value can be obtained. Further, by approximating the obtained points by a method such as a least square method, a spline, or a Bezier curve, it is possible to obtain the relationship (printer gamma (development gamma)) of the toner adhesion amount to all the written values.

Next, gradation correction information can be obtained from the target toner adhesion amount (target image density) in the second quadrant in FIG. 25 and the printer gamma obtained in accordance with the arrow (dashed line) in FIG. Become. Then, the obtained gradation correction information is converted into a YMCKγ correction unit (L
UT) enables gradation correction. Alternatively, a plurality of curves (for which no false contour occurs) may be prepared in advance, and the curve closest to the gradation correction information may be selected.

As described above, image density can be stabilized by performing gradation correction based on the development characteristics and the latent image characteristics.
Further, if the residual potential of the photosensitive member 1 is detected by the surface voltmeter 3 and the latent image characteristic is corrected by the latent image characteristic estimating means of the image forming control unit shown in FIG. Image density can be stabilized.

Next, in the gradation correction information changing means, if the target toner adhesion amount (target image density) does not reach the target toner adhesion amount even if the correction amount of the YMCKγ correction section is corrected by the gradation correction information, the image forming condition is changed. I do. When the image forming conditions are changed, the image density changes. Therefore, the tone correction information may be newly created by the same method as described above. Alternatively, if the image density estimating means 1 estimates the relationship between the surface potential and the image density after changing the image forming conditions from the state before changing the image forming conditions, it is only necessary to create a gradation pattern for obtaining a latent image characteristic. The gradation correction information can be determined. In this case, since a development patch is not created, there is an advantage that wasteful toner consumption is prevented.

Here, the estimation of the image density after changing the image forming conditions is described below. VS [i], MA [i] (i = 0 to VS [i], MA [i]) where the potential at the time of gradation pattern creation and the toner adhesion amount (the value obtained by converting the output from the image density sensor using the adhesion amount table).
9), and a first-order approximation by the least squares method is applied to four adjacent points. Assuming that the charging potential before the image forming condition change is VD1 and the charging potential after the change is VD2, the above (1) or (2)
The slope a of the equation is as follows: a → (VD2 / VD1) × a (where VD1> VD2) a → (VD1 / VD2) × a (where VD1 <VD2). Further, b is obtained by using the corrected a, and b = (MA [i-1] + MA [i]) / 2−a × (VS [i−1] + VS
[i]) / 2.

Further, assuming that the surface potential after charging before changing the imaging conditions is V1 and the surface potential after charging after changing is V2, the slope a is a → (V2 / V1) × a (where V1> V2 A) (V1 / V2) × a (where V1 <V2).

After the image forming conditions are changed, if new gradation correction information cannot be corrected, the image forming conditions are changed again. If the target toner adhesion amount does not reach the target toner adhesion amount even if the change of the image forming conditions is repeated up to a predetermined number of times, an image indicating that image formation is impossible is displayed on the operation panel of the image forming apparatus to inform the user. Alternatively, the information can be transmitted to an external host computer or the like by the above-described communication means such as a network (not shown). The image forming conditions are a charging potential and a developing bias. Further, the writing exposure amount may be set as the image forming condition.

[0106]

As described above, in the image forming apparatus according to the first aspect of the present invention, the tone pattern is formed in the non-image area (such as between sheets) by changing the tone signal of the tone pattern every time an image is formed. Since the image density (toner adhesion amount) of the gradation pattern is detected by the image density detection unit and the correction amount of the gradation correction unit is changed so as to reach the target image density (target toner adhesion amount), the optimum gradation is obtained. The correction information (γ correction value) can be set in real time (for each sheet), and the image density can be stabilized against environmental conditions (temperature, humidity) and changes over time. Further, in an area where the sensitivity of the optical detection element is reduced, the image density of the gradation pattern is estimated from the detection values of the image density detection means and the surface potential detection means, and the correction amount of the gradation correction means is adjusted so as to reach the target image density. Is changed, the image density is stabilized even in the high density portion. Also, since the number of patches to be created in a non-image area such as a sheet interval can be reduced, the load on the cleaner unit can be reduced,
The life of components can be extended.

Further, in addition to the structure of the first aspect, by determining the area where the image density detecting means has sensitivity with a threshold value (claim 5), it is possible to stably obtain the relationship between the potential and the toner adhesion amount. And the image density is stabilized.

In addition to the configuration of the first aspect, by linearly approximating the relationship between the potential and the toner adhesion amount (claim 6), the estimation of the toner adhesion amount is improved, and the image density is stabilized. Further, by determining the relationship between the potential and the toner adhesion amount by the least square method (claim 7), the measurement error can be reduced, and the image density is stabilized.

In addition to the configuration of the first aspect, the surface potential of the high-density gradation pattern is estimated from the surface potential of the low-density portion (claim 8), so that gradation correction information is set with a small number of patches. And the image density is stabilized.

In addition to the structure of the first aspect, by using a look-up table (LUT) as the gradation correcting means (claim 9), the gradation correction information can be easily changed, and the copy speed is reduced. Without this, the image density can be stabilized.

In addition to the structure of claim 1, the target image density can be set from an external device (claim 1).
0), the target of gray balance can be set, and the image density can be stabilized.

In addition to the structure of the first aspect, the target image density is output by changing the image forming conditions if the image density is not close to the target image density even if corrected by the gradation correction information (claim 11). , The image density is stabilized.
Further, by displaying that the image cannot be formed, the user is prevented from making useless copies.

In addition to the structure of the first aspect, the image forming condition determining means determines the image forming condition from at least one of temperature, humidity, toner density, and the number of cumulative image formations of the apparatus. Thus, the image density is stabilized.

In addition to the configuration of the first aspect, the image forming condition determining means determines the image forming condition by fuzzy inference from at least one of temperature, humidity, toner density, and the number of accumulated images formed by the apparatus. (13) Fine control is possible, and the image density is stabilized.

In addition to the configuration of the first aspect, the image forming condition determining means detects a state quantity from at least one of temperature, humidity, toner density, and the cumulative number of image formations of the apparatus, and further detects a change amount of the state quantity. Is detected, and the image forming conditions are determined by fuzzy inference from the state amount and the state change amount, thereby enabling fine-grained control and stabilizing the image density.

In addition to the configuration of claim 1, by controlling at least one of a charging potential, a developing bias, an exposure amount, and a transfer bias as image forming conditions.
5) The image density is stabilized.

In the image forming apparatus according to the present invention, a gradation pattern signal is generated to form a gradation pattern in a non-image area (e.g., between sheets), and the surface potential and image density (toner adhesion) of the gradation pattern are generated. Amount) is detected by the surface potential detecting means and the image density detecting means, and the relationship (development characteristic) of the image density (toner adhesion amount) to the surface potential is estimated from the surface potential and the image density. And the relationship between the gradation pattern signal and the image density (toner adhesion amount) is estimated from the development characteristics and the latent image characteristics, and the estimated gradation pattern signal and the image density (toner adhesion amount) are estimated. ) And the previously stored target image density (target toner adhesion amount)
From this, the correction amount of the tone correction means is changed so as to achieve the target image density, that is, the toner adhesion amount on the image carrier is obtained from the development characteristics and the latent image characteristics, and the tone correction is performed from the target image density. Therefore, the image density is stabilized.

In the image forming apparatus according to the third aspect, a gradation pattern signal is generated, and a gradation pattern is formed in a non-image area (a sheet interval or the like) by an output signal obtained by intermediately processing the gradation pattern signal. The surface potential and the image density (toner adhesion amount) of the gradation pattern after the intermediate processing are detected by the surface potential detection means and the image density detection means, and the image density (toner adhesion amount) with respect to the surface potential is determined from the surface potential and the image density. The relationship (development characteristics) is estimated, the latent image characteristics are estimated from the gradation pattern signal and the surface potential, and the gradation pattern signal and image density (toner adhesion amount) are estimated from the development characteristics and the latent image characteristics after the intermediate processing. Is estimated, and from the relationship between the estimated gradation pattern signal and the image density (toner adhesion amount) and the previously stored target image density (target toner adhesion amount), the gradation is adjusted to the target image density. Correction means Changing the Seiryo, i.e., determine the amount of toner deposited on the image bearing member and a developing characteristic and the latent image characteristics after intermediate processing, since the tone correction from the target image density, image density is stabilized.

In the image forming apparatus according to the present invention, a gradation pattern signal is generated to form a gradation pattern in a non-image area (e.g., between sheets), and the surface potential and the image density (toner adhesion) of the gradation pattern are generated. Amount) is detected by the surface potential detecting means and the image density detecting means, and the relationship (development characteristic) of the image density (toner adhesion amount) to the surface potential is estimated from the surface potential and the image density. And the relationship between the gradation pattern signal and the image density (toner adhesion amount) is estimated from the development characteristics and the latent image characteristics, and the estimated gradation pattern signal and the image density (toner adhesion amount) are estimated. ) And the previously stored target image density (target toner adhesion amount)
From the above, the correction amount of the gradation correction means for correcting the gradation of the image signal after the intermediate processing is changed so as to achieve the target image density, that is, the toner on the image carrier is determined based on the development characteristics and the latent image characteristics. Since the adhesion amount is obtained and the gradation correction of the image signal after the intermediate processing is performed from the target image density, the image density is stabilized.

Further, in addition to the constitution of claim 2, 3 or 4, the gradation pattern generating means changes the gradation pattern signal for each image formation (claim 16). The gradation pattern generating means forms patches of each gradation of yellow (Y), magenta (M), cyan (C), and black (K) before or during image formation (claim 17). Before or during image formation, patches of all gradations of yellow (Y), magenta (M), cyan (C), and black (K) are formed (claim 18). , Yellow (Y), magenta (M), cyan (C), and black (K) to form some patches (claim 19). Before or during image formation, yellow is formed. (Y), magenta (M), cyan (C), and black (K) floors By changing the gradation pattern signal for each image formation, any of the patches formed in the non-image area such as a sheet interval is formed as described in any one of the following. Since the number can be reduced, the load on the cleaner portion is not applied, and the life of the component can be extended. Further, since the tone pattern signal is changed every time an image is formed and the toner adhesion amount on the image carrier is obtained and tone correction is performed, the image density is stabilized.

In addition to the structure of claim 3 or 4, the halftone processing means is a dither processing means (claim 2).
1) Since the number of bits of the signal after dither processing can be reduced, hardware can be reduced.

In addition to the configuration of claim 3 or 4, the halftone processing means is multi-level error diffusion means (claim 22), so that the number of bits of the signal after multi-level error diffusion can be reduced. Wear can be reduced.

In addition to the constitution of claim 2, 3 or 4, the image density estimating means 1 estimates the relationship between the surface potential and the image density in the gradation pattern by linear approximation (claim 23). The concentration can be stabilized. Further, by approximating the relationship between the surface potential and the image density by the least square method (claim 24), the measurement error can be reduced and the image density can be stabilized.

In addition to the configuration of the second, third or fourth aspect, the image density estimating means 1 estimates in a region where the sensitivity of the optical sensing element is reduced by a straight line having the maximum inclination of the broken line. 25) The image in the high density portion can be estimated, and the image density is stabilized. Image density estimating means 1
In (2), when the straight line having the maximum inclination of the fold line is determined that the image density or the surface potential is equal to or more than a certain threshold value (claim 26), the image of the high density portion can be estimated, and the image density is stabilized.

In addition to the structure of the second, third or fourth aspect, the image density estimating means 2 approximates the relationship between the gradation pattern signal and the image density by calculation.
7) Since the image density for all the written values can be estimated, the image density is stabilized. Further, the approximation can be made by a broken line (claim 28), so that the image density for all the written values can be estimated, so that the image density is stabilized. Alternatively, the approximation is performed by using a least squares method, a spline, or a Bezier curve.
9) Since the image density for all the written values can be estimated, the image density is stabilized.

In addition to the configuration of claim 2, 3 or 4, the target image density storage means can set the target image density by communication from an external device.
0), the image density can be set externally. Further, a target of gray balance can be set, and image density can be stabilized.

In addition to the constitution of the second, third or fourth aspect, the tone correction information changing means changes the image forming condition if the density is not close to the target image density even if the correction is made by the tone correction information. (31) Since the target image density can be output, the image density is stabilized. Further, an image density estimating means 1 for correcting the relationship between the surface potential after the image forming condition is changed and the image density by the ratio of the charged potential before and after the image forming condition is changed.
(Claim 32) Alternatively, the image density estimating means 1 corrects the relationship between the surface potential after the image forming condition is changed and the image density by the ratio of the surface potential before and after the image forming condition is changed (Claim 3).
3) Thus, after the image forming condition is changed, it is sufficient to generate a gradation pattern for estimating the latent image characteristics, so that wasteful toner consumption can be avoided, and the load on the cleaner unit can be reduced. .

In addition to the constitution of the second, third or fourth aspect, the gradation correction information changing means removes the information that cannot be formed unless the density is close to the target image density even if the correction is made by the gradation correction information. By displaying or communicating with an external device (claim 34), it is possible to inform the user that image formation is impossible, and to prevent the user from making useless copies.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing the overall configuration of an image forming apparatus according to the present invention.

FIG. 2 is a view showing an embodiment of the present invention, and is an explanatory view showing the entire structure of the image forming apparatus according to the first embodiment.

FIG. 3 is an explanatory diagram of a method of generating a gradation pattern on a non-image area of a photosensitive drum and an image density detection unit.

FIG. 4 is a diagram illustrating characteristics of the image density sensor (sensor output with respect to toner adhesion amount).

FIG. 5 is an explanatory diagram of a method of detecting a toner adhesion amount (image density) of a gradation pattern by an image density sensor and performing gradation correction so as to reach a target toner adhesion amount (target image density).

FIG. 6 illustrates a method of estimating a toner adhesion amount (image density) of a gradation pattern from detection values of an image density sensor and a surface electrometer and performing gradation correction so as to reach a target toner adhesion amount (target image density). FIG.

FIG. 7 is a diagram illustrating an example of an image forming condition determining unit that obtains a control amount of an image forming condition by fuzzy inference.

FIG. 8 is a diagram illustrating an example of a potential table which is one of image forming conditions.

FIG. 9 is a diagram showing an example of fuzzy inference by fuzzy inference means.

FIG. 10 is a diagram showing fuzzy rules stored in a rule storage means of the fuzzy inference means of FIG. 9;

11 is a diagram showing membership functions stored in function storage means of the fuzzy inference means of FIG. 9;

FIG. 12 is a diagram showing another example of fuzzy inference by fuzzy inference means.

FIG. 13 is a diagram showing fuzzy rules stored in rule storage means of the fuzzy inference means of FIG.

FIG. 14 is a diagram showing membership functions stored in a function storage unit of the fuzzy inference unit of FIG.

FIG. 15 is a diagram showing an example of a fuzzy inference means at a preceding stage in a case where fuzzy inference means is configured in two stages to perform fuzzy inference.

FIG. 16 is a diagram showing fuzzy rules stored in rule storage means of the fuzzy inference means of FIG.

FIG. 17 is a diagram showing membership functions stored in function storage means of the fuzzy inference means of FIG.

FIG. 18 is a diagram illustrating an example of a fuzzy inference unit at a subsequent stage following the fuzzy inference unit in FIG. 15;

FIG. 19 is a diagram showing fuzzy rules stored in rule storage means of the fuzzy inference means of FIG. 18;

20 is a diagram showing membership functions stored in function storage means of the fuzzy inference means of FIG.

FIG. 21 is a diagram showing an embodiment of the present invention, and FIG.
FIG. 2 is a block diagram illustrating a configuration of an image forming control system of the image forming apparatus described above.

FIG. 22 is a diagram showing an embodiment of the present invention, and FIG.
FIG. 2 is a block diagram illustrating a configuration of an image forming control system of the image forming apparatus described above.

FIG. 23 is a block diagram illustrating a configuration of an image forming control unit of the image forming control system illustrated in FIG. 21 or FIG. 22;

24 is a configuration explanatory view showing a configuration of an image forming unit of an image forming apparatus provided with the image forming control system shown in FIG. 21 or FIG.

FIG. 25 shows a relationship between a potential (surface potential) of a gradation pattern and an image density (toner adhesion amount) (development characteristics) and a relationship between a writing value (gradation pattern signal) and a potential (latent image characteristics). FIG. 9 is an explanatory diagram of a method of estimating the above toner adhesion amount and performing gradation correction so as to reach a target toner adhesion amount (target image density).

FIG. 26 is a diagram showing a temporal characteristic of a photoconductor surface potential.

FIG. 27 is a diagram showing a charging potential characteristic of a photoconductor surface potential.

FIG. 28 is a diagram illustrating a relationship in which a relationship between a value written on a photoconductor and a toner adhesion amount changes depending on a toner density (TC).

FIG. 29 is a diagram illustrating a relationship in which a relationship between a writing value and a toner adhesion amount changes according to a toner charge amount (Q / M).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 2 charger 3 surface electrometer 4 developing unit 4Y yellow (Y) developing device 4M magenta (M) developing device 4C cyan (C) developing device 4K black (K) developing device 5 toner density sensor 6 image density sensor 6a Light irradiation means (LED etc.) 6b Optical detection element (phototransistor etc.) 7 Intermediate transfer belt 8 Photoconductor cleaner 9 Static eliminator 10 Transfer unit 11 Separation unit 12 Fixing roller 13 Belt cleaner

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/52 B41J 29/46 H04N 1/407

Claims (34)

(57) [Claims] An image forming condition determining means for determining an image forming condition;
Gradation correction means for correcting the gradation of an image signal, gradation pattern generation means for changing a pattern signal of the gradation pattern for each image formation to generate a gradation pattern in a non-image area, and the gradation correction means A latent image forming unit for forming a latent image on an image carrier based on an output signal of the gradation pattern generating unit; a surface potential detecting unit for detecting a surface potential of the latent image of the gradation pattern; Developing means for visualizing the image, light irradiating means for irradiating the visible image on the image carrier or the transfer body with light, and detecting the amount of reflected light obtained by irradiating the visible image with the light irradiating means with the optical detection element Image density detecting means for detecting the image density, and in an area where the sensitivity of the optical sensing element is reduced, image density estimating means for estimating the image density by the image density detecting means and the surface potential detecting means, and a gradation pattern. The image density of Image forming apparatus characterized by having a gradation correction information changing means for changing a correction amount of the gradation correcting means such that the target image density is estimated at a constant means. 2. An image forming condition determining means for determining an image forming condition;
Tone correction means for correcting the tone of an image signal, tone pattern generation means for generating a tone pattern signal to generate a tone pattern in a non-image area, and an output signal or tone of the tone correction means Latent image forming means for forming a latent image on the image carrier in accordance with an output signal of the pattern generating means; surface potential detecting means for detecting the surface potential of the latent image of the gradation pattern; and visualizing the latent image Developing means, light irradiating means for irradiating a visible image on the image carrier with light, and detecting an image density by detecting an amount of reflected light which irradiates the visible image with the light irradiating means with an optical detection element. Image density detecting means, image density estimating means 1 for estimating an image density with respect to a surface potential from a surface potential output from the surface potential detecting means and an image density output from the image density detecting means, and the gradation pattern signal And the surface potential detecting means A latent image characteristic estimating means for estimating a latent image characteristic from an output surface potential, and an image density estimating means for estimating a relationship between a gradation pattern signal and an image density from the latent image characteristic estimating means and the image density estimating means 1 2, a target image density storage unit for storing a target image density, and a floor for changing a correction amount of the gradation correction unit so as to obtain a target image density from the image density estimation unit 2 and the target image density storage unit. An image forming apparatus comprising: tone correction information changing means. 3. An image forming condition determining means for determining an image forming condition;
Gradation correction means for correcting the gradation of an image signal, gradation pattern generation means for generating a gradation pattern signal to generate a gradation pattern in a non-image area, and an output signal and gradation of the gradation correction means Selecting means for selecting an output signal of the pattern generating means, halftone processing means for performing halftone processing on the output signal of the selecting means, and forming a latent image on the image carrier in accordance with an output of the halftone processing means Latent image forming means, surface potential detecting means for detecting the surface potential of the latent image of the gradation pattern, developing means for visualizing the latent image, and light for irradiating the visible image on the image carrier with light. Irradiating means, an image density detecting means for detecting an image density by detecting an amount of reflected light irradiating a visible image with the light irradiating means with an optical detecting element, and a surface potential which is an output of the surface potential detecting means. An image density which is an output of the image density detecting means; An image density estimating means 1 for estimating an image density with respect to a surface potential, a latent image characteristic estimating means for estimating a latent image characteristic from the gradation pattern signal and a surface potential output from the surface potential detecting means, Image density estimating means 2 for estimating the relationship between a gradation pattern signal and image density from image characteristic estimating means and image density estimating means 1; target image density storing means for storing a target image density; An image forming apparatus comprising: a gradation correction information changing unit configured to change a correction amount of the gradation correcting unit so as to obtain a target image density from the target image density storing unit and the target image density storing unit. 4. An image forming condition determining means for determining an image forming condition;
Halftone processing means for performing halftone processing on the image signal, tone correction means for correcting the tone of the output of the halftone processing means, and generating a tone pattern signal to generate a tone pattern in a non-image area. Gradation pattern generating means, selecting means for selecting an output signal of the gradation correcting means and an output signal of the gradation pattern generating means, and forming a latent image on the image carrier in accordance with the output signal of the selecting means Latent image forming means, surface potential detecting means for detecting the surface potential of the latent image of the gradation pattern, developing means for visualizing the latent image, and light for irradiating the visible image on the image carrier with light. Irradiating means, an image density detecting means for detecting an image density by detecting an amount of reflected light irradiating a visible image with the light irradiating means with an optical detecting element, and a surface potential which is an output of the surface potential detecting means. An image density which is an output of the image density detecting means; An image density estimating means 1 for estimating an image density with respect to a surface potential, a latent image characteristic estimating means for estimating a latent image characteristic from the gradation pattern signal and a surface potential output from the surface potential detecting means, Image density estimating means 2 for estimating the relationship between a gradation pattern signal and image density from image characteristic estimating means and image density estimating means 1; target image density storing means for storing a target image density; An image forming apparatus comprising: a gradation correction information changing unit configured to change a correction amount of the gradation correcting unit so as to obtain a target image density from the target image density storing unit and the target image density storing unit. 5. The image density estimating means, when the output of the image density detecting means is equal to or less than a threshold value, judges an area where the sensitivity of the optical detecting element is reduced / an area where the sensitivity is good. 2. The image forming apparatus according to 1. 6. The image density estimating means, wherein a surface potential (Vs) and an image density (ID) in the gradation pattern are provided.
ID = a × Vs + b (where a and b are constants) or ID = a × (Vs−VDC) + b (where a and b are constants) as the DC component VDC of the developing bias. The image forming apparatus according to claim 1, wherein 7. The image forming apparatus according to claim 1, wherein the relational expression between the surface potential and the image density is obtained by a least square method. 8. The image forming apparatus according to claim 1, wherein said image density estimating means estimates a surface potential of a high density gradation pattern from a surface potential of a low density portion. 9. An image forming apparatus according to claim 1, wherein said gradation correcting means is a look-up table (LUT). 10. An image forming apparatus according to claim 1, wherein said gradation correction information changing means can set a target image density from an external device. 11. The image forming apparatus according to claim 1, wherein said gradation correction information changing means changes the image forming condition if the image density is not close to the target image density even if corrected by the gradation correction information, or indicates that the image cannot be formed. The image forming apparatus according to claim 1, wherein: 12. The image forming condition determining means includes a temperature, a humidity,
2. The image forming apparatus according to claim 1, wherein the image forming condition is determined based on at least one of a toner density and a cumulative number of images formed by the apparatus. 13. An image forming condition determining means, comprising:
State quantity detection means for detecting at least one of the toner density and the cumulative number of images formed by the apparatus; rule storage means for storing at least one rule relating the state quantity to the control amount of the image forming condition; Function storage means for storing a plurality of membership functions each represented by a plurality of fuzzy sets with respect to the amount and the control amount of the image forming condition; and how much the state quantity is included in any of the fuzzy sets by the plurality of membership functions. 2. An image forming apparatus according to claim 1, further comprising: fuzzy inference means for fuzzy inferring a control amount of an image forming condition most likely according to each rule using the obtained result. apparatus. 14. An image forming condition determining means, comprising:
State quantity detecting means for detecting at least one of the toner density and the cumulative number of images formed by the apparatus; state change quantity detecting means for detecting a change amount of the state quantity (state change quantity); A rule storing means for storing at least one rule for associating the state quantity, the control amount of the image forming condition, and a plurality of members expressed by a plurality of fuzzy sets with respect to the state amount, the state change amount and the change amount of the image forming condition, respectively. Function storage means storing a ship function, the state amount, the state change amount is determined by what kind of fuzzy set is included in the plurality of membership functions by the plurality of membership functions, using the obtained result, according to each of the rules 2. An image forming apparatus according to claim 1, further comprising fuzzy inference means for fuzzy inferring a control amount of an image forming condition having the highest possibility. 15. The image forming apparatus according to claim 1, wherein the image forming condition is at least one of a charging potential, a developing bias, an exposure amount, and a transfer bias. 16. An image forming apparatus according to claim 2, wherein said gradation pattern generating means changes a gradation pattern signal every time an image is formed. 17. The gradation pattern generating means forms a patch of each gradation of yellow (Y), magenta (M), cyan (C), and black (K) before or during image formation. 17. An image forming method according to claim 16, wherein: image forming → forming a YMCK patch of 0/256 gradations → forming a YMCK patch of 1/256 gradation forming → image forming →... apparatus. 18. The gradation pattern generating means forms patches of all gradations of yellow (Y), magenta (M), cyan (C), and black (K) before or during image formation. (Example: Image formation → Y patch of 0 to 255 gradations → Image formation → M patch of 0 to 255 gradations → Image formation →
The image forming apparatus according to claim 16, wherein: 19. The image processing apparatus according to claim 1, wherein said gradation pattern generating means includes a part of all gradations of yellow (Y), magenta (M), cyan (C), and black (K) before or during image formation. (Example: Image formation → YMCK of 0 gradation)
17. An image forming method according to claim 16, wherein: a patch of YMCK of 50 gradations is formed → an image is formed → a patch of YMCK of 100 gradations is formed → image forming →. apparatus. 20. The image processing apparatus according to claim 19, wherein: before or during the image formation, the gradation pattern generation means selects some of the gradations of yellow (Y), magenta (M), cyan (C), and black (K). (Eg, image formation → 0, 5)
Form Y patches of 0, 100, and 150 gradations → image formation →
17. The image forming apparatus according to claim 16, wherein M patches of 0, 50, 100, and 150 gradations are formed → image formation →. 21. An image forming apparatus according to claim 3, wherein said halftone processing means is dither processing means. 22. An image forming apparatus according to claim 3, wherein said halftone processing means is a multilevel error diffusion means. 23. In the image density estimating means 1, a surface potential (Vs) and an image density (I
The relationship of D) is as follows: ID = a × Vs + b (where a and b are constants) or ID = a × (Vs−VDC) + b (where a and b are constants) as the DC component VDC of the developing bias. 5. The image forming apparatus according to claim 2, wherein the image is approximated by a broken line obtained from the relational expression. 24. The image forming apparatus according to claim 23, wherein the relational expression between the surface potential and the image density is obtained by a least square method. 25. The image density estimating means 1 estimates in a region where the sensitivity of the optical detection element is reduced, a straight line having a maximum inclination of a broken line.
5. The image forming apparatus according to 3 or 4. 26. In the image density estimating means 1, the straight line having the maximum inclination of the broken line has an image density or a surface potential equal to or higher than a certain threshold value.
Or the image forming apparatus according to 25. 27. An image forming apparatus according to claim 2, wherein said image density estimating means 2 approximates the relationship between the gradation pattern signal and the image density by calculation. 28. An image forming apparatus according to claim 27, wherein said approximation is approximated by a broken line. 29. The method according to claim 2, wherein the approximation is a least squares method, a spline, or a Bezier curve.
8. The image forming apparatus according to 7. 30. An image forming apparatus according to claim 2, wherein said target image density storage means can set a target image density by communication from an external device. 31. An apparatus according to claim 2, wherein said tone correction information changing means changes the image forming condition if the density is not close to the target image density even when the correction is made based on the tone correction information.
5. The image forming apparatus according to 3 or 4. 32. The image density estimating means 1 according to claim 31, wherein said image density estimating means 1 corrects the relationship between the surface potential after image forming condition change and image density by the ratio of charged potential before and after image condition change. Image forming device. 33. The image density estimating means 1 according to claim 31, wherein said image density estimating means 1 corrects the relationship between the surface potential after image forming condition change and image density by the ratio of surface potential before and after image condition change. Image forming device. 34. If the tone correction information changing means does not approach the target image density even after the correction with the tone correction information, the information indicating that the image cannot be formed is displayed or communicated with an external device. The image forming apparatus according to claim 2, 3 or 4, wherein