JPH08251366A - Digital image forming device - Google Patents

Abstract

PURPOSE: To attain optimum gamma correction at all times without the use of a memory of a large capacity. CONSTITUTION: A printer control section 201 conducts prescribed arithmetic processing based on a toner deposition density sensed by an AIDC sensor 214 and a surface potential of a photoreceptor 6 sensed by a V sensor 207 and a luminance intensity of a light source 216 is corrected to generate gamma correction luminescent characteristics data to obtain an optimum image. A gamma correction section 219 uses the gamma correction luminescent characteristics data obtained through the arithmetic operation to obtain an image signal outputted from an image signal processing section 4 and the light source 216 is lighted based on the corrected data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image forming apparatus, and more particularly, to a digital image forming apparatus for correcting an emission intensity of a light source based on γ correction emission data to form an image.

[0002]

2. Description of the Related Art A laser printer which drives a light source based on image data converted into digital values to form an image,
Various digital image forming apparatuses such as digital copying machines have been put into practical use, and various digital image forming apparatuses for faithfully reproducing so-called halftone images such as photographs have been proposed.

As a digital image forming apparatus of this type,
Known are an area gradation method using a dither matrix, a multi-value laser exposure method which expresses gradation for one dot to be printed by changing a laser pulse width or emission intensity and changing a laser light amount. Further, a digital image forming apparatus using a multi-valued dither method in which dither and a pulse width modulation method or an intensity modulation method are combined is also known.

By the way, according to the gradation method of this kind, it should be possible in principle to reproduce the image density having the gradation corresponding to the gradation of the image data to be reproduced. However, in reality, various factors such as the photosensitivity of the photoconductor, the properties of the toner, and the use environment are intricately entangled with each other, and the document density to be reproduced and the reproduced image density are not exactly proportional to each other. Such characteristics are generally called γ characteristics. FIG. 47 shows
It is a figure which shows a (gamma) characteristic diagrammatically. As shown in FIG. 47,
A characteristic such as a characteristic B deviated from the proportional characteristic A that should be originally obtained is shown. This γ characteristic is a major factor that reduces the fidelity of the reproduced image, especially for halftone originals.

Therefore, in order to improve the fidelity of the reproduced image, the density of the read original is converted by using a conversion table which stores predetermined γ correction light emission data, and a digital image is formed based on the converted original density. By doing
So-called γ correction is performed so that the document density and the image density satisfy a linear relationship (characteristic A shown in FIG. 47). As a result, by applying γ correction,
The image can be faithfully reproduced according to the document density.

In a conventional digital image forming apparatus for performing the above-mentioned γ correction, at least one of the surface potential of the photosensitive member before the exposure by the exposure device and the developing bias potential applied in advance to the developing device is changed, Density control is performed, and γ
A digital image forming apparatus for compensating for gradation variation is selected by selecting a predetermined conversion table from a plurality of γ correction conversion tables in which correction light emission data is stored and performing non-linear control of the light amount of the exposure device. Proposed.

[0007]

In the conventional digital image forming apparatus as described above, γ correction is performed by using a predetermined number of γ-correction conversion tables created in advance, so that it is possible to prevent environmental changes. There is a problem in that it is not possible to carry out a finely tuned correction in accordance therewith, and it is not always possible to carry out an optimum γ correction.

Further, the γ-correction conversion table used must store the γ-correction conversion table corresponding to an enormous combination pattern when a plurality of factors that cause the fluctuation of the γ-curve change. It was necessary to use a large-capacity memory for storing the γ correction conversion table. This is because the fixed type full-color copying machine has a different developing position for each color, and the combination pattern is more complicated than a monochrome copying machine or an elevator-type full-color copying machine. Here, the elevator-type full-color copying machine includes a developing unit in which developing devices of respective colors are vertically arranged and accommodated, and one of the developing devices is selectively opposed to the photoconductor by moving the developing unit up and down. It is to be developed. Therefore, the developing position is the same regardless of which color is developed. A fixed-type full-color copying machine is one in which developing devices for each color are sequentially arranged along the periphery of the photoconductor so as to face the photoconductor, and the developing device is selectively operated to develop each color. It is something to do. Therefore, the developing position is different for each color.

As described above, using a large-capacity memory for storing the γ-correction conversion table corresponding to these enormous combination patterns not only increases the cost of the apparatus, but also experiments each combination pattern. However, it is necessary to create a γ-correction conversion table corresponding to each combination pattern, which results in an enormous number of experimental man-hours, which makes it impossible to perform efficient development.

An object of the present invention is to solve the above problems, and it is an object of the present invention to provide a digital image forming apparatus which can always perform optimum γ correction without using a large capacity memory. .

[0011]

According to a first aspect of the present invention, there is provided a digital image forming apparatus for correcting an emission intensity of a light source on the basis of γ correction data to form an image. An image carrier on which a predetermined latent image is formed by modulating the intensity of the generated light, a developing means for developing the latent image with a predetermined toner, and an adhesion amount detection for detecting the toner adhesion amount on the image carrier. Means, the sensitivity specifying means for specifying the sensitivity characteristic of the image carrier, and the development of the developing means based on the sensitivity characteristic of the image carrier specified by the sensitivity specifying means and the toner adhesion amount detected by the adhesion amount detecting means. A predicting unit that predicts characteristics, a parameter determining unit that determines an optimum image forming parameter based on the developing characteristic of the developing unit predicted by the predicting unit, and an image forming parameter that is determined by the parameter determining unit. And a calculating means for calculating a correction data γ to obtain the desired gradation characteristics.

According to a second aspect of the present invention, there is provided a digital image forming apparatus.
In addition to the configuration of the digital image forming apparatus according to claim 1, when forming an image, the digital image forming apparatus updates the γ correction data for each image forming operation, and the digital image forming apparatus further performs the γ correction. Comparing means for comparing the first data used to calculate the emission data for use with at least one of the second data previously used as the first data and the third data having a predetermined value, and a comparing means. When the comparison result of 1 indicates that the first data is an abnormal value, the correction means for correcting the first data to one of the second and third data is included.

According to another aspect of the digital image forming apparatus of the present invention,
In addition to the configuration of the digital image forming apparatus according to claim 2, further, when the comparison result by the comparison means indicates that the first data is an abnormal value, the value of the first data has a predetermined threshold value. A warning unit is included to warn that the device is abnormal when the value exceeds the threshold value and the value of the first data continuously exceeds the threshold value a predetermined number of times.

According to another aspect of the digital image forming apparatus of the present invention,
In addition to the configuration of the digital image forming apparatus according to claim 2, further comprising surface potential detecting means for detecting the surface potential of the image carrier, the image carrier, the developer contained in the developing means, and the adhesion amount detection. The means and the surface potential detecting means are detachably provided from the apparatus main body, and the digital image forming apparatus further includes the image carrier, the developer, the adhesion amount detecting means, and the surface potential detecting means. It includes an initialization means for initializing at least one of the second data and the third data when exchanging at least one of them.

According to a fifth aspect of the digital image forming apparatus,
In addition to the configuration of the digital image forming apparatus according to claim 1, the light source emits light in first and second modes with different light emission ratios, and the arithmetic means is for first gamma correction corresponding to the light emission ratio in the first mode. The data and the second γ correction data corresponding to the light emission ratio in the second mode are calculated.

[0016]

In the digital image forming apparatus according to the present invention, the sensitivity characteristic of the image bearing member is specified, and the developing characteristic of the developing means is predicted based on this sensitivity characteristic and the amount of toner attached to the image bearing member. Then, the optimum image forming parameter is determined based on this developing characteristic, and the γ correction data for obtaining the desired gradation characteristic is calculated according to this image forming parameter. That is, since the γ correction data for finally obtaining the desired gradation characteristics can be calculated based on the amount of toner attached to the image carrier, it is always optimal even if the environment changes. The γ correction data can be calculated, and it is not necessary to store a plurality of γ correction data in advance.

In the digital image forming apparatus according to the second aspect, in addition to the operation of the digital image forming apparatus according to the first aspect, when the first data used for calculating the γ correction data is an abnormal value, Since the first data can be corrected to at least one of the second data used last time and the third data having a predetermined value, there is no need to calculate the γ correction data using the abnormal value as it is.

In the digital image forming apparatus according to the third aspect, in addition to the operation of the digital image forming apparatus according to the second aspect, when the value of the first data exceeds a predetermined threshold value,
Since it is possible to warn that the device is abnormal in at least one of the case where the value of the first data exceeds the threshold value continuously for a predetermined number of times, it is possible to notify the user of the abnormality of the device. You can

In the digital image forming apparatus according to the fourth aspect, in addition to the operation of the digital image forming apparatus according to the second aspect, at least one of an image carrier, a developer, an adhesion amount detecting means, and a surface potential detecting means is provided. When exchanged, at least one of the second and third data can be initialized. Therefore, the γ correction data can be obtained by using the second data and the third data that match the characteristics of each means before the exchange. There is no calculation.

In the digital image forming apparatus according to the fifth aspect, since the first and second γ correction data corresponding to the first and second modes having different light emission ratios are calculated, the optimum γ for each light emission ratio is obtained. It becomes possible to calculate the correction data.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a digital copying machine which is a digital image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. Although a digital copying machine will be described as an example in the following description, the present invention can be similarly applied to other digital image forming apparatuses such as a laser printer.

FIG. 1 is a sectional view showing the overall construction of a digital copying machine according to an embodiment of the present invention. Referring to FIG. 1, the digital copying machine includes an image reader unit 100 and a copying unit 20.
Contains 0. The image reader unit 100 includes a document table 1, CC
A D (Charge Coupled Device) sensor 2, an optical unit 3, and an image signal processing unit 4 are included. The copying unit 200 includes a print head unit 5, a photoconductor 6, an eraser lamp 7, a charging charger 8, developing devices 9y, 9m, 9c and 9k, a paper feeding device 10,
A transfer drum 11, a transport device 12, a fixing device 13, and a paper discharge tray 14 are included.

As described above, the digital copying machine of the present embodiment is divided into the image reader section 100 for reading the original image and the copying section 200 for reproducing the read image. In the image reader unit 100, first, the document placed on the document table 1 is illuminated, and the reflected light is exposed by the reading optical unit 3 including the contact type CCD sensor 2. In the optical unit 3, each pixel is converted into a multi-valued electric signal of three colors of R, G and B, and the image of the original is read. Read R, G, B
The multi-valued electric signal of 8 bits of each color of yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), and black (hereinafter referred to as K) is processed by the digital signal processing unit 4. Converted to gradation data.

Next, in the copying section 200, the print head section 5 has a level corresponding to the sensitivity characteristics of the photoconductor 6 and the developing characteristics of the developing devices 9y, 9m, 9c and 9k with respect to the input gradation data. After performing key adjustment, that is, γ correction,
A light source 216 (see FIG. 2) made of a semiconductor laser is caused to emit light based on the corrected image data. Print head 5
The laser light emitted from exposes the photoconductor 6 which is rotationally driven. The photoconductor 6 is irradiated by the eraser lamp 7 before being exposed and is uniformly charged by the charging charger 8 in each copying operation. By being exposed in this state, the image reader unit 100 is formed on the surface of the photoconductor 6.
An electrostatic latent image of the document read by is formed.

Each of the developing devices 9y, 9m, 9c and 9k contains a two-component type developer consisting of toner and carrier, and the electrostatic latent image formed on the photoconductor 6 can be toner of a corresponding color. Visualize. The developing devices 9y, 9m, 9c,
9k corresponds to the toner of each color of Y, M, C, and K, respectively.

The transfer sheets are fed one by one from the sheet feeding device 10 and wound around the outer periphery of the transfer drum 11. On the other hand, the toner images on the photoconductor 6 are sequentially transferred to the transfer paper from the created ones based on the discharge of the transfer charger provided on the transfer drum 11, and finally a full-color toner image is created on the transfer paper. It The transfer paper on which the full-color toner image is formed is separated from the transfer drum 11, and is conveyed to the fixing device 13 by the conveying device 12, the fixing device 13 heat-fixes the toner image on the transfer paper, and finally the paper ejection tray 14 Is discharged to.

Next, the printer control system of the digital copying machine shown in FIG. 1 will be described. FIG. 2 is a block diagram showing the configuration of the printer control system of the digital copying machine shown in FIG.

Referring to FIG. 2, the digital copying machine further includes a printer controller 201 and a control ROM (Read Only Me).
mory) 202, data ROM 203, RAM (Random A
ccess Memory) 204, operation panel 205 including reset button 206, V sensor (surface potential sensor) 207,
Photoconductor drive counter 208, environment sensor 209, developing device drive counter 210, developing device drive circuit 211, toner replenishment drive device 212, Vb generation unit 213, AI
DC sensor (density sensor) 214, light source 216, light source drive unit 217, D / A conversion circuit 218, γ correction unit 219,
It includes a light emission signal generation circuit 220 and a Vg generation unit 221.

The printer control unit 201 includes a control ROM 2
02, a data ROM 203, and a RAM 204 are connected to each other. Various programs for control are stored in the control ROM 202. The data ROM 203 stores various data necessary for automatic density control and γ correction control described later. The printer controller 201 controls the control RO
The printing operation is controlled by various data stored in the M202, the data ROM 203, and the RAM 204, and the automatic density control and the γ correction control, which will be described later, are performed.

An operation panel 205, a photoconductor drive counter 208, and an environment sensor 209 are also connected to the printer control unit 201. Printer control unit 20
1, the AIDC sensor 214, the developing device drive counter 210, and the V sensor 207 are further connected. Various operation commands are input to the printer control unit 201 from the operation panel 205, a reset signal is input from the reset button 206, and the photosensor 6 is input from the V sensor 207.
The detection signal of the surface potential of the AIDC sensor 21 is input.
4, a detection signal obtained by optically detecting the amount of toner attached to the surface of the photoconductor 6 is input, a signal indicating the number of times the photoconductor 6 has been driven is input from the photoconductor drive counter 208, and the environment sensor 209 is input. A signal indicating environmental characteristics such as temperature and humidity is input, and a signal indicating the number of driving times of the developing devices 9y, 9m, 9c, 9k is input from the developing device drive counter 210.

The printer control unit 201 performs automatic density control and γ correction control, which will be described later, based on the above-mentioned various input information. Therefore, the Vg generating unit 221 for generating the grid potential Vg of the charger 8 and each developing device 9y,
V for generating the developing bias potential Vb of 9m, 9c, 9k
Control the b generation unit 213. Further, the printer control unit 201 outputs the γ correction light emission data calculated by a predetermined process described later to the γ correction unit 219. The γ correction unit 219 performs γ correction on the 8-bit image data output from the image signal processing unit 4 based on the input γ correction emission data, and the corrected image data is the D / A conversion circuit. It is converted into an analog signal by 218 and is output to the light source drive section 217. The light source drive unit 217 causes the light source 216 to emit light in accordance with the input analog signal under the control of the light emission signal generation circuit 220 controlled by the printer control unit 201.

The digital copying machine of the present embodiment is configured as described above, and performs γ correction control (image density stabilization control) by constantly calculating γ correction emission data used for γ correction of image data inside the device. Are doing. Further, in the present embodiment, sensing is performed by multi-point input of the V sensor and the AIDC sensor, and the γ correction emission data is calculated and created for each image forming operation. Hereinafter, the gamma correction control of this embodiment will be described in detail with reference to a flowchart.

FIG. 3 is a main flowchart of the printer control system of the digital copying machine shown in FIG. Referring to FIG. 3, when the power of the digital copying machine is turned on, first, the AIDC calibration process is executed in step S1.

The output characteristics of the AIDC sensor 214 fluctuate due to dirt due to toner dust or the like and variations in sensor mounting. Figure 4 shows AID with and without dirt
It is a figure which shows the output characteristic of C sensor. The output characteristics shown in FIG. 4 show the output characteristics for the C, M, and Y toners, the solid line shows the case where the AIDC sensor is not contaminated, and the broken line shows the case where the AIDC sensor is contaminated.

For example, when the output characteristics fluctuate from the case where there is no dirt to the case where there is dirt (when it changes from the solid line to the broken line), even if the toner adhesion amount on the photoconductor 6 is the same, the AIDC sensor 214 Since the output characteristics fluctuate, it is not possible to accurately detect the toner adhesion amount. Therefore, in step S1, a test toner image is created, and the AIDC sensor 214 outputs an AI
The relationship between the output of the DC sensor 214 and the toner adhesion amount is standardized, and the standardized output characteristic is set as the output characteristic of the AIDC sensor 214.

Since the amount of reflected light differs between the color toner and the black toner, the output characteristics for the color toner and the black toner are created respectively. The output characteristics of the AIDC sensor produced by the above processing are as shown in FIG. 5 for color toner (cyan toner) and as shown in FIG. 6 for black toner, for example.

Next, the above AIDC calibration process will be described in more detail. FIG. 7 is a flow chart for explaining the AIDC calibration process.

Referring to FIG. 7, first in step S21, the AID at the solid level at which the toner adhesion amount becomes maximum.
A grid potential Vg for obtaining the output Vab of the C sensor,
The maximum outputs of the developing bias potential Vb and the exposure amount LD are set.

Next, in step S22, the photoconductor background level and solid level detection processing is executed. First, a test toner image is created under the conditions set in step S21,
The output Vab of the AIDC sensor at this time is detected. In addition, the AI at the background level of the photoconductor without the toner image
The output Van of the DC sensor is detected. Next, based on this, the relationship between the output of the sensor and the toner adhesion amount (the output characteristic of the AIDC sensor) is standardized and stored in the RAM 204. Regarding the output Vab of the solid level AIDC sensor, as described above, there are two types of sensor output characteristics of the cyan toner image for color toner and the black toner image, for example, the sensor output characteristics shown in FIGS. 5 and 6. Is standardized and stored.

Next, the process of step S22 shown in FIG. 7 will be described in more detail. FIG. 8 is a flow chart for explaining the photoconductor background level and solid level detection processing.

Referring to FIG. 8, first in step S31, the photoconductor background level and solid level detection processing is performed as described above. Next, in step S32,
Subtract the previous data or a preset comparison value from the output Van of the AIDC sensor at the background level,
It is determined whether or not the absolute value is less than or equal to a predetermined threshold value X. If larger than the predetermined threshold value X, step S
38, and in the following cases, the process proceeds to step S33.

If the threshold value is less than or equal to X, in step S33, as in step S32, the solid level AID is set.
It is determined whether the absolute value of the value obtained by subtracting the previous data or the comparison value from the output Vab of the C sensor is less than or equal to a predetermined threshold value Y. If it is larger than the threshold value Y, step S
34, and in the following cases, in S44, AID
The output characteristics of the C sensor are standardized and stored, and step S2 is performed.
The process proceeds to 3 and the subsequent processing is continued.

If it is determined in step S33 that the threshold value Y is greater than the threshold value Y, it is determined in step S34 whether the number N _{2 of} times the threshold value Y is exceeded is equal to or less than the predetermined number n ₂ . If n ₂ or less, in step S35, the number N ₂ of times the threshold value is exceeded is incremented. Next, in step S36, the current data is canceled, the process proceeds to step S33, and the subsequent processing is continued.

On the other hand, if the number N _{2 of} times the threshold value is exceeded is greater than n ₂ in step S34, step S3
7, the service call processing (processing for instructing the user to call a service person, for example, displaying a predetermined warning screen on the operation panel) is executed, and step S4
At 3 the device is stopped.

When it is determined in step S32 that the threshold value X is greater than the threshold value X, it is determined in step S38 whether the number N _{1 of} times the threshold value X is exceeded is equal to or less than the predetermined number n _1. It If n ₁ or less, step S
39, the number N ₁ of times the threshold value X is exceeded is incremented, the process proceeds to step S40, the current data is cancelled, and the process proceeds to step S33 to continue the subsequent processing.

On the other hand, if it is larger than n ₁ , step S4
1, the service call process is executed, and the process proceeds to step S43 to stop the device.

Referring again to FIG. 7, next, step S2
In 3, the five types of test toner images are created for each color, that is, two colors by the predetermined grid potential Vg and the development bias potential Vb and five different exposure amount levels. The exposure dose level at this time is shown in FIG.
Of the two exposure amount steps, 1 (32 gradation levels), 3 (64 gradation levels), 5 (96 gradation levels),
A test toner image is created with 5 gradations of 9 (160 gradation levels) and 10 (192 gradation levels).

Next, in step S24, the output Vab of the AIDC sensor for the test toner image created for each color is detected, and the detected output Vab and the output Van of the AIDC sensor at the background level are compared with step S2.
The toner adhesion amount is obtained from the relationship between the sensor output created in 2 and the adhesion amount.

Next, in step S25, based on the amount of adhered toner obtained at step S24, the amount of adhered three exposure in 0.05mg / cm ² ~0.5mg / cm ² in the region for each color The quantity level is selected from FIG. 9 and stored.

The exposure amount level is selected so that the toner adhesion amount falls within the above range for the following reason. As the toner adhesion amount increases, the specular reflection light amount component on the surface of the photoconductor 6 decreases, so that the output of the AIDC sensor 214 decreases. Therefore, the detection sensitivity of the sensor also decreases, and when the toner adhesion exceeds a certain amount, the AIDC sensor 21
The output of 4 is completely saturated. As a result, in order to improve the detection accuracy of the sensor, in the case of this embodiment, the toner adhesion amount is about 0.05 mg / cm ^{2 to} 0.5 mg.
It is preferable to use a region of / cm ² .

Referring again to FIG. 3, after the AIDC calibration process, the AIDC detection process is executed in step S2. This processing is a subroutine for obtaining the toner adhesion amount using the AIDC sensor 214.

First, 12 kinds of test toner images of three levels of exposure amount level × 4 colors are formed under a predetermined grid potential Vg and developing bias potential Vb. The three exposure dose levels are the three exposure dose levels selected in step S25. The AIDC sensor 214 detects the toner adhesion amount of each of the created test toner images.
That is, the toner adhesion amount corresponding to the output of the AIDC sensor 214 is obtained by using the output characteristic of the AIDC sensor obtained in step S22.

The above AIDC detection process will be described in more detail below. FIG. 10 is a flowchart for explaining the AIDC detection process.

Referring to FIG. 10, first, step S51.
Under the conditions of a predetermined grid potential Vg (the same potential as in step S23), a development bias potential Vb (a potential that is switched by each color based on the predicted dark decay rate), and the exposure level of three stages selected in step S25. ,
Three test toner images (a low-density side test toner image M1 and an intermediate density level test toner image M are formed on the photoconductor 6).
2. A test toner M3) on the high density side is prepared for each color.

Next, the process of step S51 will be described in more detail. 11 to 13 are first to third flowcharts for explaining the three-level test toner image forming process shown in step S51.

First, referring to FIG. 11, step S61
At, a three level test toner image is created using cyan toner. Next, in step S62, 3
It is determined whether or not the level is almost completely developed. If it has not been developed, the process proceeds to step S63, and if it has been developed, the process proceeds to step S81 shown in FIG.

Next, if almost no development has been performed, it is determined in step S63 that the output during cyan development is abnormal. Next, in step S64, a black toner is used to create a three-level test toner image. Next, in step S65, it is determined whether or not all three levels have been developed. If it has not been developed, the process proceeds to step S66, and if it has been developed, the process proceeds to step S69.

Next, if almost no image has been developed, it is determined in step S66 that the output during black development is abnormal. Next, in step S67, service call processing is executed. Next, in step S68, the apparatus is stopped.

On the other hand, if it is determined in step S65 that the image has been developed, then in step S69, 3
It is determined whether or not the levels are almost solid outputs. If it is a solid output, the process proceeds to step S66 to continue the subsequent processing, and if it is not a solid output, step S70.
Move to.

Next, in step S70, it is determined that the output during black development is normal. Next, step S7
In No. 1, only the black copy process using the black toner is permitted. Next, in step S70, the service call process is executed, and the process proceeds to step S52 shown in FIG.

On the other hand, if it is determined in step S62 that the image has been developed, step S81 shown in FIG.
In, it is determined whether or not the three levels using cyan toner are almost solid outputs. If it is a solid output, the process proceeds to step S82, and otherwise, the process proceeds to step S101 shown in FIG.

If the output is solid, it is determined in step S82 that the output during cyan development is abnormal.
Since steps S83 to S91 are the same as steps S64 to S72 described above, the description thereof will be omitted below.

On the other hand, if it is determined in step S81 that the output is not solid, step S101 shown in FIG.
In, it is determined that the output during cyan development is normal. Next, in step S102, a three-level test toner image using black toner is created. Next, in step S103, it is determined whether or not most of the three levels have been developed. If almost not developed, the process proceeds to step S104, and if developed, the process proceeds to step S107.

Next, when almost no image has been developed, it is determined in step S104 that the output during black development is abnormal. Next, in step S105, service call processing is executed. Next, step S106.
At, the device is stopped.

If it is determined in step S103 that the image has been developed, it is determined in step S107 whether all three levels are solid outputs. If it is a solid output, the process proceeds to step S104 and the subsequent processing is continued. If it is not a solid output, the process proceeds to step S108.

If it is not a solid output, it is determined in step S108 that the output during black development is normal. Next, in step S109, a three-level test toner image is created using yellow toner. Next, in step S110, it is determined whether or not most of the three levels are developed. If almost not developed, the process proceeds to step S111, and if developed, the process proceeds to step S114.

Next, when almost no development has been performed, it is determined in step S111 that the output during yellow development is abnormal. Next, in step S112, a process of permitting only black copy is performed. next,
In step S113, the service call process is executed, and the process proceeds to step S52.

On the other hand, if it is determined in step S110 that the image has been developed, in step S114
It is determined whether or not the 3 levels are almost solid outputs. If it is solid output, the process proceeds to step S111 and the subsequent processing is continued. If it is not solid output, step S111 is performed.
Transition to 115. If not solid output, step S1
At 15, it is determined that the output during yellow development is normal.

Next, in step S116, a three-level test toner image is created using magenta toner. Next, in step S117, it is determined whether or not most of the three levels are developed. If almost no development has been performed, the process proceeds to step S118, and it is determined that the output during magenta development is abnormal, and step S1 is performed.
Move to 12. On the other hand, in the case of being developed, it is determined in step S119 whether or not the 3rd level is almost a solid output. If it is almost solid output, the process proceeds to step S118 and the subsequent processing is continued. If it is not solid output, the process proceeds to step S120, it is determined that the output during magenta development is normal, and the process proceeds to step S52.

By the above processing, when the cyan output is normal, the black output is normal, and either one of yellow and magenta is abnormal, only the black copy is permitted and the color copy cannot be performed. If it is normal, full color copying is permitted, and if black output is abnormal, the device is stopped.

Referring again to FIG. 10, next, step S
At 52, the density of the test toner image is detected by the AIDC sensor 214 provided near the photoconductor 6. The output value Va detected for each color is processed in the same manner as in step S1, the output characteristic of the AIDC sensor stored in step S22 is read from the RAM 204, and the output Va of the AIDC sensor is used as the toner adhesion amount using this output characteristic. Convert.

Next, in step S53, based on the result of step S52, the next exposure amount level of the test toner image is determined and updated. That is, from the next time, the three exposure amount levels of the test toner image created in step S51 will be
It is determined by the data set and updated in 93. Therefore, as will be described later, step S1 is always performed after the copy is completed.
Instead of returning to the AIDC calibration process, the process returns to the AIDC detection process of step S2 to determine the next three exposure amount levels when the normal test toner is detected in step S2.

Next, the exposure amount level determining and updating process in step S53 will be described in detail. FIG. 14 is a flowchart for explaining the determination update process of the exposure amount level. In this embodiment, as described above, the toner adhesion amount is 0.05mg / cm ² ~0.5mg / cm at ² in the region from exposure levels shown in Figure 9 of the three test patterns exposure level (Exposure amount step STP1
~ STP3) is selected by the following process for each color.

Referring to FIG. 14, first, step S131.
, The test toner image M1 on the low-density side detected in step S52 is tested for each color.
It is determined whether or not the toner adhesion amount is 0.05 mg / cm ² or more. If the toner adhesion amount of the test toner image M1 is not 0.05 mg / cm ² or more, step S142.
Then, the exposure amount step STP1 on the low density side is increased by one step in accordance with FIG. 9, and the process proceeds to step S134.

On the other hand, when the toner adhesion amount of the test toner image M1 is 0.05 mg / cm ² or more, step S2
Then, the process proceeds to 32, and it is determined whether the toner adhesion amount of the test toner image M1 is 0.1 mg / cm ² or less. The toner adhesion amount of the test toner image M1 is 0.1 mg / cm ²
If not, the process proceeds to step S239, the exposure amount step STP1 is reduced by one step according to FIG. 9, and is set as the exposure amount level on the low density side at the time of the next test toner image formation, and stored in the RAM 204.

On the other hand, when the toner adhesion amount of the test toner image M1 is 0.1 mg / cm ² or less, the exposure amount step STP1 is not changed in step S133 and the exposure amount level is not changed as it is when the test toner image is formed next time. The exposure amount step STP1 is set and stored in the RAM 204.

Next, in step S134, it is determined whether or not the toner adhesion amount of the test toner image M2 having the intermediate density level detected in step S52 is 0.25 mg / cm ² or more. When the toner adhesion amount of the test toner image M2 is not 0.25 mg / cm ² or more, step S1
Step 40, exposure step ST of intermediate density level
P2 is increased by one step according to FIG.

On the other hand, when the toner adhesion amount of the test toner image M2 is 0.25 mg / cm ² or more, the process proceeds to step S135, the exposure amount step STP2 is decreased by one step, and the exposure amount level at the time of creating the next test toner image. And is stored in the RAM 204.

Next, in step S136, it is determined whether or not the toner adhesion amount of the high density test toner image M3 detected in step S52 is 0.4 mg / cm ² or more. Toner adhesion amount of the test toner image M3 is 0.4 m
If it is not more than g / cm ² , the process proceeds to step S143, and the exposure amount step STP3 on the high density side is set to 1 according to FIG.
It is stepped up, set as the exposure amount level at the time of creating the high-density test toner next time, and stored in the RAM 204.

On the other hand, when the toner adhesion amount of the test toner image M3 is 0.4 mg / cm ² or more, step S13
7, the toner adhesion amount of the test toner image M3 is 0.
It is judged whether it is 5 mg / cm ² or less. When the toner adhesion amount of the test toner image M3 is not 0.5 mg / cm ² or less, the process proceeds to step S141, the exposure amount step STP3 is decreased by one step, and the exposure amount level at the time of creating the test toner image on the high density side next time Set and RA
Store in M204.

On the other hand, when the toner adhesion amount of the test toner image M3 is 0.5 mg / cm ² or less, step S13
In step 8, the exposure amount step STP3 is not changed and is set as it is as the exposure amount level when the test toner image on the high density side is formed next time, and is stored in the RAM 204. With the above processing, the toner adhesion amount is always 0.05 mg for each color.
/ Cm ^{2 to} 0.5 mg / cm ² within the range,
The exposure area level (exposure area steps STP1 to STP3) when three test toner images are formed is set and updated. Therefore, at the next test toner image creation, R
Light intensity steps STP1 to ST stored in AM204
P3 is read out for each color, and the exposure amount level is set as described above based on FIG. As a result, a test toner image can always be formed in a region where the AIDC sensor has a high detection sensitivity, and it becomes possible to calculate γ correction emission data described later with high accuracy.

Referring again to FIG. 3, in step S3, V (photoconductor surface potential) detection processing is performed. The V detection process is a process of detecting the surface potential of the photoconductor 6 using the V sensor 207. Specifically, a latent image pattern (test pattern) is created at 10 levels of exposure amount (different from the exposure amount step shown in FIG. 9) under the conditions of a predetermined exposure amount and grid potential Vg, and the V sensor is used. The surface potential of each latent image pattern formed on the photoconductor 6 is detected by 207. Further, in order to improve the detection accuracy of the surface potential, when the power is turned on, the exposure amount and the grid potential Vg are switched in three steps, and in each step, a latent image pattern is formed at an exposure level of 10 steps, and 3 × 10 3 Detect the surface potential of a point. When the power is turned on, after the surface potential of 3 × 10 points is detected, the surface of the photoconductor is erased by the eraser lamp 7, and the surface potential Vr after the erase is detected. In other cases, after the surface potential of 10 points is detected. , The erased photoreceptor surface potential Vr is detected. In this process, the V sensor 207 is used to detect the surface potential, but the surface potential may be directly predicted by a predetermined calculation instead of being directly detected.

Next, the above V detection processing will be described in more detail. FIG. 15 is a flow chart for explaining the V detection process. First, in step S151, the V detection process described above is executed. Next, in step S152, it is determined whether the outputs of all the V sensors 207 are the same output. If the outputs are the same, the process proceeds to step S153, and if they are different, the process proceeds to step S156.

When the outputs of all the V sensors are the same, it is determined in step S153 that the outputs of the V sensors are abnormal. Then, in step S154,
Perform service call processing. Next, step S15
At 5, the device is stopped.

On the other hand, when it is determined that the output of the V sensor is different, it is determined in step S156 that the output of the V sensor 207 is normal, and the process proceeds to step S4.
By the above processing, it is possible to detect an abnormality in the output data of the V sensor 207 and stop the device.

The detection operation is completed by the steps S1 to S3 described above, and thereafter the arithmetic processing is executed.

Next, the photosensitive member sensitivity characteristic calculation processing of step S4 shown in FIG. 31 will be described in detail. 16
6 is a flowchart for explaining a photosensitive member sensitivity characteristic calculation process. Referring to FIG. 16, first, step S161
In, the process for creating the approximate sensitivity formula of the photoconductor is performed. Next, in step S162, a charging efficiency calculation process is executed. Next, in step S163, a process of predicting each position of the photoconductor sensitivity characteristic is executed, and the process proceeds to step S5.

Next, the above-mentioned photosensitive member sensitivity characteristic approximation formula preparation processing will be described in more detail. FIG. 17 is a flowchart for explaining the photosensitive member sensitivity characteristic approximate expression creation processing.

First, in step S171, the sensitivity characteristic of the photoconductor 6 is calculated. Specifically, the light decay curve of the photoconductor is approximated by using the data of the surface potential of the photoconductor 6 for the 10-level latent image pattern detected in step S3. Since the photoconductor light decay curve has a simple decay characteristic, it can be approximated in the form of V × e ^{a * x + b} ,
Obtain each coefficient by the method of least squares.

Next, a method of creating an approximate expression for the photoconductor light decay curve will be described below. Step S as above
Based on the surface potential V of the photoconductor detected by the detection data of 3, the approximation is made in a form including the ripple of the exposure so that the effective developing potential can be calculated. That is, what can be detected by the electrometer is considered to be the average potential due to the ripple of exposure, and here, the coefficient of the approximate expression shown below is obtained by the method of least squares in the form of the average potential of the maximum value and the minimum value of the ripple.

V = (Vbi−Vr) × (e ^{(−B * E (n) * D / Ks)} + e ^{(−A * E (n) * D / Ks)} ) / 2 + Vr (1) B = 2 −A + 0.18 × (A−1) ³ (2) where Vbi: surface potential under bias exposure (≠
V ₀ ), Vr: residual potential, E (n): bias exposure amount subtracted from average exposure amount (modulated exposure amount at each gradation), A: maximum value (coefficient) under average exposure, B: under average exposure Minimum value (coefficient), Ks: sensitivity coefficient of photoconductor, D: exposure lighting ratio with respect to modulation time, n: gradation for test pattern (n = 1 to 10), and "*" in the exponent part is " Multiplication ”
Indicates. In this embodiment, a semiconductor laser (laser diode) is used as a light source for image writing. To improve the responsiveness of laser diode emission,
A bias current is applied and the laser diode spontaneously emits light. Therefore, the above Vbi
Indicates the photoconductor surface potential under the exposure of this spontaneous emission.

In the above approximate expression, the surface potential Vbi under bias exposure is used as the initial value of attenuation for ease of detection and reliability. By using the coefficient obtained by the above approximate expression, the surface potential V of the photoconductor at an arbitrary grid potential Vg and an exposure amount can be calculated under the actual use environment.

Next, in order to obtain each coefficient A, B, Ks of the above approximation formula by using the least squares method, it is necessary to first determine the initial value. The initial value Ks0 of Ks is determined by the following equation.

[0094]

[Equation 1] Here, Vs (n): average surface potential (detection potential of each gradation), m: grid potential Vg of the charging charger,
The initial value of A is 1.4.

By the above processing, when the power is turned on, the exposure amount and the grid potential Vg are switched three times to detect the surface potential of the photoconductor, so that the light decay curves of the three photoconductors, that is, the sensitivity of the photoconductor. A characteristic curve is created. FIG.
FIG. 4 is a diagram showing sensitivity characteristics of a photoconductor when power is turned on. Further, since the surface potential is detected only once except when the power is turned on, a sensitivity characteristic curve for one photoconductor is created.
Note that Ks and A obtained by the above process are V
Since it is a coefficient for obtaining the surface potential of the photoconductor at the position of the sensor, it will be referred to as Ksv and Av in the following description.

Referring again to FIG. 17, next, in step S172, the coefficient A calculation process is executed as described above. Next, in step S173, it is determined whether or not there is a coefficient A between the predetermined maximum value Amax and the minimum value Amin. If the coefficient A is between Amin and Amax, the process proceeds to step S174, and otherwise, the process proceeds to step S176. Next, in step S176, the coefficient A is changed to a predetermined value As. As As, the coefficient A calculated last time or a predetermined set value is used.

Next, in step S174, the calculation process of the coefficient Ks is executed as described above. Next, in step S175, a predetermined minimum value Ksm determined in advance.
It is determined whether or not there is a coefficient Ks between in and the maximum value Ksmax. If the coefficient Ks is within the above range, the process proceeds to step S162, otherwise, step S177.
Move to. Next, in step S177, the coefficient K
Change s to a predetermined value Kss. As Kss, the previously calculated coefficient Ks or a predetermined set value is used.

As described above, the previous calculation result or the initial set value is compared, and when the difference or ratio exceeds the set threshold value, the value is regarded as irregular and the previous value is set. It is also possible to adopt the calculation result of or the initial set value and proceed to the next stage. Further, when the irregular calculation result continues for the set threshold value a predetermined number of times or more, it is displayed that any one of the photoconductor 6, the charger 8, the Vg generation unit 221, and the V sensor 207 is defective. You may Further, the above calculation result shows the photoconductor 6, the developer, the AIDC sensor 21.
4, the V sensor 207 or the like may be replaced to reset automatically or by the reset button 206.

Next, the above charging efficiency calculation processing will be described in detail. FIG. 19 is a flowchart for explaining the charging efficiency calculation process. First, step S181
In, the charging efficiency calculation process is executed. That is,
The charging efficiency of the photoconductor 6 is calculated using the surface potential detected in step S3. The charging efficiency is used to calculate a grid potential Vg for obtaining a desired surface potential described later. To calculate the charging efficiency, the relationship between the grid potential Vg and the surface potential Vbi is obtained as a linear expression. This linear function is originally a function having no intercept or a function having the erased potential Vr as an intercept, but is approximated by the following equation in a form with an intercept in order to improve accuracy in the vicinity of actual use.

Vbi = α × Vg + β (4) Here, α is the charging efficiency and β is the intercept. From the above equation, for example, the relationship between the surface potential and the grid potential shown in FIG. 20 can be obtained. Α and β obtained by the above equation
Is a coefficient at the position of the V sensor 207, and is referred to as αv and βv in the following description.

Again referring to FIG. 19, in step S182, it is determined whether or not the calculated charging efficiency α is larger than a preset minimum value αmin and smaller than a maximum value αmax. When this condition is satisfied, the process proceeds to step S186, it is determined that the charging efficiency α is a normal value, and the process proceeds to step S163.

On the other hand, if the above conditions are not satisfied, the process proceeds to step S183, and it is determined that charging or laser emission is abnormal. Then, the process proceeds to step S184, and the service call process is executed. Next, step S185.
At, the device is stopped.

By the above processing, if the data used for creating the γ correction emission characteristic data such as the coefficients A, Ks, the charging efficiency α, etc. is abnormal, the data can be changed to the predetermined data and the maintenance can be performed. It is possible to warn the user that is needed and to shut down the device. As a result, the user can always use the device in a good condition without using the device in an abnormal condition.

Also, the previous calculation result or the initial set value is compared, and if the difference or ratio exceeds the set threshold value, the value is regarded as irregular and the previous calculation result is obtained. Alternatively, the initial set value may be adopted to advance to the next stage. Further, when the irregular calculation result continues for the set threshold value a predetermined number of times or more, it is displayed that any one of the photoconductor 6, the charger 8, the Vg generation unit 221, and the V sensor 207 is defective. You may Further, the calculation result may be reset automatically by the replacement of the photoconductor 6, the developer, the AIDC sensor 214, the V sensor 207 or the like or by the reset button 206.

Referring again to FIG. 16, next, in step S163, the photosensitive characteristic curve of the photosensitive member 6 at each developing position of the developing devices 9y, 9m, 9c and 9k is predicted. Each coefficient obtained by the above processing is a coefficient at the position of the V sensor. Therefore, the coefficient at each developing position is calculated by proportional calculation with respect to the coefficient of the V sensor position. The calculation of the photosensitive characteristic of the photoconductor at each developing position cannot be directly calculated only in a series of γ correction control, and therefore the calculation is performed using the empirical rule described below.

Regarding the rule of thumb, an analysis of variance was performed by experiments with the environment, film thickness, paper passing mode, pause mode, beam diameter and the like as control factors. As a result, the contribution rate is high (5%
(About the above), the influence is stored in the data ROM 203 as a look-up table for each control factor as predetermined data, and the Av of the position of the V sensor 207,
It is possible to obtain the respective ratios of the respective developing positions with respect to Ksv, αv and βv.

As a concrete example, the relationship between the temperature and the ratio of Ks at the position of each developing device is shown in FIG. 21, the relationship between the temperature and the ratio of α is shown in FIG. 22, and the relationship between the number of printed sheets and the ratio of α is shown. 23 is shown in FIG. 23, and the relationship between the number of prints and the ratio of A is shown in FIG. Further, the circles in FIGS. 21 to 24 indicate the developing device 9y.
Is data regarding the developing position of the developing device 9m, Δ is data regarding the developing position of the developing device 9c, and □ is data regarding the developing device 9k. Each of these data is stored in the data ROM 203 in advance as a lookup table.
Therefore, the sensitivity characteristic of the photoconductor at each developing position can be obtained based on the stored data of the lookup table.

Further, in the case where the photosensitive member has a rotation speed switching function, the prediction at the developing position is performed by selecting the correction coefficient of the position corresponding to the arrival time according to the increase / decrease in speed due to the speed switching. It is possible to calculate the sensitivity characteristic of the photoconductor. In addition, print density (resolution)
When the switching function is provided, the correction coefficient may be selected in accordance with the print density, as described above.

FIG. 25 is a diagram showing the sensitivity characteristic of the photoconductor at each developing position obtained by the above calculation. In FIG. 25, the uppermost curve is the curve showing the sensitivity characteristic of the photoconductor at the position of the V sensor 207, and the developing device 9
Curves showing the sensitivity characteristics of the photoconductor at the developing positions of y, 9m, 9c, and 9k are sequentially shown. By the above processing,
It is possible to obtain each coefficient at each developing position by using each coefficient at the position of the V sensor 207, and finally obtain the sensitivity characteristic of the photoconductor at each developing position.

Referring again to FIG. 3, next, step S
In 5, the LD power light amount (maximum exposure amount during image formation) is optimized. The amount of LD power light is uniquely determined by the conditions of the photoconductor regardless of the development conditions. The LD power light amount Pmax (i) is determined to be a value about 2.5 times the half-light amount Eh (i) at each developing position based on the predicted sensitivity characteristic of the photoconductor at each developing position. The above-mentioned half-light amount Eh (i) is obtained by exposing a photoconductor charged at a certain potential at an exposure position, and then, when the photoconductor reaches each developing position,
The exposure amount is such that the potential of the photosensitive member is halved.

The following formula was used to calculate the LD power light amount. V = (Vbi-Vr) x (e ^{(-B (i) * Eh (i) * D / Ks (i))} + e ^{(-A (i) * Eh (i) * D / Ks (i))} ) /2+Vr...(5) V = (Vbi-Vr) / 2 + Vr ... (6) V = (Vbi-Vr) * (e ^{(-A (i) * Eha (i) * D / Ks (i))} ) + Vr (7) V = (Vbi-Vr) * (e ^{(-B (i) * Ehb (i) * D / Ks (i))} ) + Vr ... (8) V = (Vbi-Vr) / 2 + Vr ... ( 9) Here, i = 1 to 4 (where i = 1 is the yellow developing device 9y, i = 2 is the magenta developing device 9m, and i = 3).
Indicates a cyan developing device 9c, i = 4 indicates a black developing device 9k, Eh (1) to Eh (4) indicate half-light amounts at the yellow, magenta, cyan, and black developing positions, respectively. A (1) to A (4), B (1)
.About.B (4) and Ks (1) to Ks (4) represent respective coefficients at respective developing positions. ). The LD power light amount may be calculated by obtaining Eh (i) which is the equation (6) of the equation (5), but Eha (i) and Ehb which are the equations (7) and (8) of the equation (9). (I) was obtained, and the average of these was taken as Eh (i), and the product of 2.5 times was taken as Pmax (i). That is, Pmax (i) was calculated by the following equation.

Pmax (i) = 2.5 × (−Ks (i)) × ln (1/2) × (1 / A (i) + 1 / B (i)) / 2 (10) The above calculation Therefore, the LD power light amount Pmax (i) is about 2.5 times the half-light amount at each developing position (i = 1 to 4).
To decide.

Further, for example, when the system speed at the time of detection is different from that at the time of image formation, such as increasing the system speed only during monocolor copying, the integrated light quantity per time unit becomes equivalent to the light quantity obtained under the above conditions. Thus, the LD power light amount is determined.

Next, the developing efficiency calculation process shown in step S6 of FIG. 3 will be described in detail. FIG. 26 is a flowchart for explaining the developing efficiency calculation process. First, in step S191, an effective developing potential calculation process is executed.

Specifically, the effective developing potential of the test pattern of 3 gradations × 4 colors (hereinafter referred to as AIDC pattern) created in step S2 is obtained. Here, it is calculated by inputting the condition at the time of pattern formation using the sensitivity characteristic of the photoconductor predicted at each developing position.

First, the average developing potential Ve (i, n) is calculated by the following equation. Ve (i, n) = (Vbi (i) -Vr) * (Ks (i)) / {(B (i) -A (i)) * E (n)} * (e ^{(-B (i)) * E (n) * D / Ks (i))-} e ^{(-A (i) * E (n) * D / Ks (i))} ) + Vr (11) Next, each development position during uniform exposure V (C) = Vb + V at
The light amount C (i), which becomes mg, is obtained by the following equation.

C (i) = Ks (i) × ln {(Vbi (i) −Vr) / (Vb (i) + Vmg (i) −Vr)} (12) where Vmg is the fog start potential ( Development start potential) correction coefficient, and the initial value is 0.

Next, the effective developing potential ΔVe (i, n) of the AIDC pattern is calculated. In the calculation, when the exposure ripple is sufficiently larger than the developing bias potential Vb,
It is divided into three cases, that is, when the voltage is across the developing bias potential Vb or when it is sufficiently small.

First, (C (i) / B (i)) <E (n)
In the case of × D (when the ripple is sufficiently larger than Vb), it is calculated by the following formula.

ΔVe (i, n) = Vb (i) + Vmg (i) −Ve (i, n) (13) Next, (C (i) / A (i)) <E (n) × D <(C
In the case of (i) / B (i)) (when it straddles Vb), it is calculated by the following formula.

ΔVe (i, n) = [− 1 / {(A (i) −B (i)) × E (n) × D}] × {Ks (i) × (Vbi (i) −Vr) Xe ^{(-A (i) * E (n) * D / Ks (i))} + (A ^{(i) * E (n) *} DC (i) -Ks (i)) * (Vb (i ) + Vmg (i) -Vr)} (14) Finally, when (C (i) / A (i))> E (n) × D (when it is sufficiently smaller than Vb), it is calculated by the following formula.

ΔVe (i, n) = 0 (15) Referring again to FIG. 26, next, in step S192, the developing efficiency calculation process is executed for each color, and the process proceeds to step S7.

Next, the developing efficiency calculation processing for each color will be described in detail. FIG. 27 is a flowchart for explaining the developing efficiency calculation process for each color. First, in step S201, a developing efficiency calculation process for each color is executed.

Specifically, the developing efficiency is obtained from the amount of adhered toner obtained in step S2 and the effective developing potential obtained by calculating the effective developing potential. The relationship between the adhesion amount and the effective developing potential is approximated by a linear expression, and the slope and intercept are obtained. The inclination at this time is defined as the development efficiency. Originally, the intercept of the linear equation should be 0, but since it does not always start to fog from the level of the developing bias potential Vb,
It will have some value. Therefore, the intercept is used as the fog-out potential correction coefficient Vmg.

The actual fog-out potential correction coefficient Vmg is calculated from the slope (developing efficiency η (i)) and the intercept (ν (i)). FIG. 28 is a diagram showing the relationship between the surface potential and the adhered amount. As shown in FIG. 28, the fog-out potential correction coefficient Vmg (i) can be obtained by Vmg (i) = ν (i) / η (i) (16) Vmg calculated here
By recalculating the above-described calculation process of the effective developing potential using (i), it is possible to calculate the developing efficiency in a form without intercept (ν (i) = 0).

Further, the operation panel 205 may be provided with an adjustment key for manually adjusting the fog start potential. In this case, the service person can manually correct the fog potential.

Referring again to FIG. 27, next, in step S202, the calculated developing efficiency η (i) is larger than the minimum value ηmin (i) set for each color and is larger than the maximum value ηmax (i). It is determined whether or not it is small. If this condition is satisfied, the process proceeds to step S203, and if not, the process proceeds to step S205. If it falls within the above range, it is determined in step S203 that the developing device and the like are normal, and the process proceeds to step S7.

On the other hand, when the condition of step S202 is not satisfied, the developing efficiency η (i) is determined in step S205.
Is changed to a predetermined value ηs (i), and the process proceeds to step S7. Here, ηs (i) used is
It is a value calculated last time or a preset predetermined value.

Further, when compared with the previous calculation result or the set value of the initial value, and when the difference or ratio exceeds the set threshold value, the value is regarded as irregular and the previous calculation result or the initial value is set. The set value of may be adopted and the process may proceed to the next process. Furthermore, when the irregularity calculation result of the set threshold value is repeated a predetermined number of times or more and the calculated coefficients of the photoconductor are normal, the Vb generation unit 213 and the developing device 9
It may be displayed that any one of y, 9m, 9c, 9k and the AIDC sensor 214 is defective. Further, the calculation result may be reset automatically by the replacement of the photoconductor 6, the developer, the AIDC sensor 214, the V sensor 207 or the like or by the reset button 206.

Referring again to FIG. 3, next, step S
7, the effective developing potential ΔV required for each color
Calculate e. First, the development characteristic curve is approximated. The development characteristics should be a straight line (a linear relationship between the potential and the adhesion amount), but it is not always linear at high adhesion such as low temperature and low humidity, low T / C (when the toner content in the carrier is low). It may not be possible. Therefore, here, the development characteristic curve of each color is approximated by using the development efficiency obtained by the calculation processing of the development efficiency of each color, with the high adhesion side being slightly blunted. FIG. 29 is a diagram showing an example of the developing characteristic curve obtained by the above processing.

Next, the required effective development potential ΔVe for each color to obtain the desired maximum adhesion amount (maximum density) is calculated from the LD power light amount obtained in step S5 and the development characteristic curve obtained by the above processing. calculate. First, the transfer characteristics are predicted and calculated in order to set the desired maximum adhesion amount on the transfer material. Here, the transfer characteristics are predicted by the data RO
Humidity information input from the environment sensor 209, transfer material information input from the operation panel 205, and the developing device drive counter 210 using a predetermined coefficient previously stored in M203.
Correction is performed by using at least one or more pieces of counter information input from. FIG. 30 is a diagram showing the relationship between the amount of toner transferred to a transfer sheet and the amount of toner remaining on the photoconductor that has not been transferred, and FIG. 31 is a diagram showing coefficients with respect to absolute temperature. FIG. 32 is a diagram showing coefficients for paper types, and FIG. 33 is a diagram showing coefficients for durable sheets. For the correction process, for example, FIG.
At least one or more of each information shown in 0 to 33 is used.

In this embodiment, the target amount of adhesion on paper is 0.7 mg / cm ² . The remaining toner amount (R _0.7 ) on the photoconductor 6 when the toner adhesion amount on the photoconductor 6 is 0.7 mg / cm ² is read from FIG. 30, and the environmental information input from the environment sensor 209 at that time is read. Based on the transfer material information input from the operation panel 205 and the counter information input from the photoconductor drive counter 210, for example, the transfer efficiency coefficients d1, d2, d3 for each information shown in FIGS. 31 to 33 are read. Next, the effective developing potential ΔVe ₍₂₅₅₎ required for each color is calculated using the following formula.

ΔVe ₍₂₅₅₎ = (0.7 + R _0.7 × d1 × d2 × d3) / η (i) (17) Next, in step S8, the grid potential Vg and the developing bias potential Vb which are image forming parameters are set. decide. Specifically, first, step S163 shown in FIG.
The approximate expression of the photosensitivity characteristic at each developing position obtained in 1 is calculated back to calculate the developing bias potential Vb for each color to satisfy the required effective developing potential ΔVe for each color obtained in the above process. At this time, the fog-out potential correction coefficient obtained in the developing efficiency calculation process is also considered.

Next, the surface potential Vbi of each color is obtained by adding the set fog margin to the obtained developing bias potential Vb.
Then, the grid potential Vg for obtaining this Vbi is calculated using the charging efficiency obtained in step S181. At this time,
If either of the settable grid potential Vg or the development bias potential Vb exceeds the settable range, the closest value is set, and the other is recalculated according to the set value (Vb +
Fogging margin or Vbi-fogging margin).

Next, in step S9, the correction potential for multi-copy is obtained. That is, the potential for correcting the sensitivity change during multi-copy is obtained. If the charging efficiency does not change significantly during multi-copying, it is considered that the change in the latent image forming system is due to the change in the sensitivity of the photoconductor 6.
Since the LD power light amount is determined by the sensitivity of the photoconductor, it is considered that the LD power light amount can be corrected by normalizing the exposure amount and the potential. When geometrically standardizing, the maximum value or the minimum value may be used. However, since the halftone portion with high sensitivity has a larger impact on the image, standardization is performed in the vicinity of the half-light amount or with a certain gradation. Make a change. That is, L is set so that the potential of that gradation is always constant.
Feedback is applied to the D power light amount. However, since the actual detection is performed by the V sensor 207, the V sensor 20
If the potential at the position 7 can be corrected, the potential at the developing position can be corrected.

Specifically, in this processing, the potential V1 at the irradiation of the exposure amount E1 is calculated by the following equation.

V1 = (Vbi−Vr) × (e ^{(−Bv * E1 * D / Ksv)} + e ^{(−Av * E1 * D / Ksv} ) / 2 + Vr (18) This is the exposure when creating the γ correction curve. It becomes the electric potential at the time of irradiation of the amount E1.

Next, in step S10, the γ characteristic during linear light emission is predicted. First, the light quantity divided into 255 from the bias light quantity to the set LD power light quantity is obtained.
Here, for example, the relationship between the emission data and the emission intensity as shown in FIG. 34 is obtained.

Next, for each light quantity, the approximate expression of the photosensitive member sensitivity characteristic at each developing position obtained in step S4 and the set grid potential Vg, developing bias potential Vb and fog-out potential correction coefficient are used. Thus, the effective developing potential ΔVe for the above 256 gradations is obtained. The relationship between the exposure amount and the effective developing potential ΔVe obtained here is shown in FIG.
As shown in FIG.

Next, with respect to each effective developing potential ΔVe, the developing efficiency is used to determine the toner adhesion amount on the photosensitive member. The relationship between the effective developing potential ΔVe obtained here and the toner adhesion amount on the photoconductor is as shown in FIG. 36, for example.

Next, the predicted transfer remaining amount is subtracted from the toner adhesion amount on each photoconductor to obtain the paper adhesion amount. Here, the estimated transfer residual amount is stored in advance in the look-up table and is fed back by the information of the environment sensor 209. Assuming that the adhered amount on paper is PT (n, i) and the adhered toner amount on the photoconductor is PA (n, i), the adhered amount on paper is represented by the following formula.

PT (n, i) = PA (n, i) -R (n) × d1 × d2 × d3 (19) Next, the relationship between the amount of toner adhered on the paper and the density according to the characteristics of the toner is obtained. In this process, the characteristics measured in advance are stored in a lookup table. For example, the relationship between the adhered amount on paper and the density shown in FIG. 37 is stored in advance. Therefore, the density for 256 gradations can be calculated by obtaining the density on the paper using this lookup table. As a result, for example, a γ characteristic curve as shown in FIG. 38 can be obtained.

Next, in step S11, the γ-correction emission characteristic data is created using the γ-characteristic curve created by the above processing. In this calculation method, when the γ characteristic curve has a linear characteristic, the γ correction emission characteristic data to be calculated can be calculated by the XY axis conversion of the γ characteristic curve.

First, the target concentration (concentration of target adhesion amount) and level 0 of the γ characteristic curve obtained in step S10 are set.
And 8 bits are standardized. At this time, when the maximum density of the γ characteristic curve does not reach the target density, the standardization gain is adjusted according to the shortage. As a result, for example, density data and light emission data as shown in FIG. 39 are obtained.

Next, the 8-bit data is converted into 10-bit data (4 times), and the XY axes are converted. After that, the data loss is linearly complemented. As a result, the data shown in FIG. 40 is obtained.

Finally, the data obtained by using the moving average filter is smoothed. As a result, γ correction emission characteristic data for linearly converting the γ characteristic curve created in step S10 is created.

Further, in this embodiment, it is possible to create a plurality of γ-correction emission characteristic data. For example, when a plurality of gradation reproduction methods with different light emission ratios are used, γ is set so that a predetermined gradation characteristic can be obtained in any gradation reproduction method.
It is necessary to create correction emission characteristic data. Therefore, in this embodiment, as a gradation reproduction method with different light emission ratios, for example, a light emission ratio of 100% (mode A)
41 for 100% or less (mode B).
It is possible to create two types of γ-correction emission characteristic data as shown in FIG.

A method for creating two types of γ correction emission characteristic data will be described below. 42 to 44
FIG. 6 is a flowchart for explaining first to third methods for creating a plurality of γ correction emission characteristic data.

First, the first method will be described with reference to FIG. First, when the print key is turned on in step S211, a copy operation is performed in step S212. Next, in step S213, it is determined whether or not the previous detection mode is the mode A. If the previous detection mode is mode A, the process proceeds to step S214, and image formation is performed in mode B. on the other hand,
If it is not the mode A, the process proceeds to step S218, and image formation is performed in the mode A.

Then, similarly to the above steps S2 and S3, the detection processing of each data is performed. Next, step S2
In 16, the γ correction emission characteristic data is created based on the detected data. Next, in step S217, a wait process is executed.

Next, the second method will be described with reference to FIG. First, in step S221, the print key is turned on. Next, in step S222, an image forming process is executed. Next, in step S223, the image forming process is executed in the mode B. Next, in step S224, detection processing of each data is executed. Next, in step S225, the image forming process is executed in the mode A. Then, in step S226,
Detection processing of each data is executed. Next, step S2
In 27, the emission characteristic data for γ correction for modes A and B are created, respectively. Finally step S228
In, the weight process is executed.

Next, the third method will be described with reference to FIG. First, in step S231, the print key is turned on. Next, in step S232, a copy operation is executed. Next, step S233.
In, the image forming process is executed in the mode B. Next, in step S234, detection processing of each data is executed. Next, in step S235, the gamma correction emission characteristic data for mode B is created. Next, in step S236, the γ correction emission characteristic data for mode B created in step S235 is used to determine γ for mode A.
The correction emission characteristic data is created. Finally, step S
At 237, wait processing is performed.

By each of the above-mentioned methods, it is possible to prepare the γ-correction emission characteristic data suitable for each mode A, B, that is, the emission ratio, and it is possible to obtain the desired gradation characteristic according to the gradation reproduction method. Becomes Moreover, in the first method, the detection process (step S215) is simplified once. Further, in the second method, since the γ-correction emission characteristic data is created for each mode, the γ-correction emission characteristic data can be created with higher accuracy. Furthermore, in the third method, since the γ-correction emission characteristic data created for one mode is used to create the other γ-correction emission characteristic data, the process is simplified.

Further, depending on the pixel signal output from the image signal processing section 4, the γ correction section 219 can switch a plurality of γ correction emission characteristic data to obtain a desired gradation characteristic. In this case, since each γ-correction emission characteristic data has already been calculated and stored, it is possible to switch at high speed, for example, even during copying of one sheet.

Referring again to FIG. 3, the print key is input in step S12. Next, step S
At 13, it is determined whether the print switch is turned on. If the print switch is turned on, the process proceeds to step S14, and if not turned on, step S12 is repeated.

Next, in step S14, image forming processing for each color is executed. Next, in step S15,
It is confirmed whether or not the copying is completed. If the copying is not completed, the process proceeds to step S14, and if the copying is completed, the process proceeds to step S2 and the subsequent processes are repeated.

Next, the above steps S13 to S15 will be described more specifically. FIG. 45 is a flowchart for specifically explaining the processing of steps S13 to S14 shown in FIG.

Referring to FIG. 45, first, step S24.
In step 1, when the print key is turned on, step S
At 242, the V1 point is detected. Next, in step S243, a process of correcting the LD power light amount (Pmax) is performed.

Next, in step S244, an image forming process is executed using C toner. Next, step S2
At 45, an image forming process is executed using M toner. Next, in step S246, an image forming process is executed using Y toner. Next, in step S247, a V1 point detection process is executed. Next, in step S248, the toner adhesion amount of Bk is detected.
Next, in step S249, the LD power light amount (P
max) correction processing is executed.

FIG. 46 is a flow chart for explaining the LD power light amount (Pmax) correction processing shown in FIG. Referring to FIG. 46, first, in step S261, the LD light emission process is executed. Next, step S
At 262, V detection processing is performed. Next, in step S263, the half-light amount E2 during actual operation is calculated. Next, in step S264, P'max
Calculate (i). Next, in step S265,
Set the calculated P'max (i).

The above LD power light amount correction processing is specifically performed as follows. That is, step S9
The potential V2 at the time of E1 exposure obtained in step 1 is actually measured, and the half-light amount E2 in the real image is obtained from the value by using the following equation.

E2 = (E1) ⁻² / [Ks × ln {V1−Vr) / (V2−Vr)} + E1] (20) As a result, P′max (i) during multi-copy is expressed by the following equation. It is represented by.

P′max (i) = Pmax (i) × (E2 / E1) (21) From the above equation, the final color VG is detected, and Pma is used for the next copy.
Change x (i) to P'max (i). As a result, it is possible to detect the electric potential during continuous copying and change the image forming parameter based on the result to obtain an optimum image.

Referring again to FIG. 45, step S250
In, the image forming process is executed using K toner. Next, in step S251, it is determined whether copying has been completed. If the copy is not completed, the process proceeds to step S244 to continue the multi-copy process, and if the copy is completed, the process proceeds to step S2 shown in FIG. 3 and the subsequent processes are continued.

With the above processing, the optimum image forming parameters and the γ correction emission characteristic data can always be calculated, and a good image can be formed.

[0166]

In the digital image forming apparatus according to the first aspect of the present invention, since the γ correction data for obtaining the desired gradation characteristic is obtained by calculation, it is always possible to optimize the γ correction data without using a large capacity memory. It becomes possible to perform γ correction.

In the digital image forming apparatus according to the second aspect, in addition to the effect of the digital image forming apparatus according to the first aspect, since the γ correction data is not calculated using the abnormal data, the abnormal data Even if occurs, it is possible to always perform good γ correction.

In the digital image forming apparatus according to the third aspect, in addition to the effect of the digital image forming apparatus according to the second aspect, when the data used for the calculation has an abnormal value, a warning that the apparatus is abnormal is issued. Therefore, the user does not use the device in an abnormal state, which facilitates maintenance of the device.

In the digital image forming apparatus according to the fourth aspect, in addition to the effect of the digital image forming apparatus according to the second aspect, at least one of the image carrier, the developer, the adhesion amount detecting means, and the surface potential detecting means. When replacing one, the first
At least one of the third and third data is initialized, so that the second and third data are matched to the characteristics of each means before the replacement.
Without using the data to calculate the γ correction data,
It is possible to obtain normal γ correction data.

In the digital image forming apparatus according to the fifth aspect, since the γ correction data corresponding to the light emission ratio can be calculated, even if a plurality of gradation reproduction methods with different light emission ratios are used, it is always optimum. It is possible to perform a γ correction.

[Brief description of drawings]

FIG. 1 is a sectional view showing an overall configuration of a digital copying machine according to an embodiment of the present invention.

2 is a block diagram showing a configuration of a printer control system of the digital copying machine shown in FIG.

FIG. 3 is a main flowchart of a printer control system of the digital copying machine shown in FIG.

FIG. 4 is a diagram showing output characteristics of an AIDC sensor with and without dirt.

FIG. 5 is a diagram showing standardized output characteristics of an AIDC sensor for color toner.

FIG. 6 is a diagram showing standardized output characteristics of a black toner AIDC sensor.

FIG. 7 is a flowchart illustrating an AIDC calibration process.

FIG. 8 is a flowchart for explaining a photoconductor background level and solid level detection process.

FIG. 9 is a diagram showing a relationship between an exposure amount step and an exposure amount level.

FIG. 10 is a flowchart illustrating an AIDC detection process.

FIG. 11 is a first flowchart for explaining a three-level test toner image forming process for each color.

FIG. 12 is a second flowchart for explaining a three-level test toner image forming process for each color.

FIG. 13 is a third flowchart for explaining a three-level test toner image forming process for each color.

FIG. 14 is a flowchart illustrating an exposure amount level determination / update process.

FIG. 15 is a flowchart for explaining V detection processing.

FIG. 16 is a flowchart for explaining a photosensitive member sensitivity characteristic calculation process.

FIG. 17 is a flowchart for explaining a process of creating an approximate expression of a photosensitive member sensitivity characteristic.

FIG. 18 is a diagram showing the sensitivity characteristics of the photoconductor when the power is turned on.

FIG. 19 is a flowchart illustrating a charging efficiency calculation process.

FIG. 20 is a diagram showing a relationship between a surface potential and a grid potential.

FIG. 21 is a diagram showing the relationship between the temperature and the ratio of Ks at the position of each developing device.

FIG. 22 is a diagram showing the relationship between the temperature and the ratio of α at the position of each developing device.

FIG. 23 is the number of prints and α at the position of each developing device
It is a figure which shows the relationship with the ratio of.

FIG. 24 is the number of prints and A at the position of each developing device.
It is a figure which shows the relationship with the ratio of.

FIG. 25 is a diagram showing the sensitivity characteristic of the photoconductor at each developing position.

FIG. 26 is a flowchart illustrating a developing efficiency calculation process.

FIG. 27 is a flowchart for explaining a developing efficiency calculation process for each color.

FIG. 28 is a diagram showing a relationship between a surface potential and an adhesion amount.

FIG. 29 is a diagram showing an example of a curve of developing characteristics.

FIG. 30 is a diagram showing the relationship between the amount of toner transferred to a transfer sheet and the remaining amount of toner remaining on the photoconductor without being transferred.

FIG. 31 is a diagram showing a transfer efficiency coefficient with respect to absolute humidity.

FIG. 32 is a diagram showing transfer efficiency coefficients for paper types.

FIG. 33 is a diagram showing a transfer efficiency coefficient with respect to the number of durable sheets.

FIG. 34 is a diagram showing a relationship between emission data and emission intensity.

FIG. 35 is a diagram showing a relationship between an exposure amount and an effective developing potential.

FIG. 36 is a diagram showing the relationship between the amount of adhesion on the photoconductor and the effective developing potential.

FIG. 37 is a diagram showing the relationship between the amount of adhesion on paper and the density.

FIG. 38 is a diagram showing a γ correction characteristic curve.

FIG. 39 is a diagram showing a relationship between density data and light emission data.

FIG. 40 is a diagram showing data that has undergone XY axis conversion.

FIG. 41 is a diagram showing data obtained by XY axis conversion for two modes.

FIG. 42 is a flow chart for explaining a first method for creating a plurality of γ correction emission characteristic data.

FIG. 43 is a flowchart for explaining a second method for creating a plurality of γ-correction emission characteristic data.

FIG. 44 is a flowchart for explaining a third method for creating a plurality of γ-correction light emission characteristic data.

45 is a flowchart for specifically explaining the processing of steps S13 to S14 shown in FIG.

FIG. 46 is a flowchart for explaining LD light amount correction processing.

FIG. 47 is a diagram schematically showing γ correction.

[Explanation of symbols]

 1 developing table 2 CCD sensor 3 optical part 4 image signal processing part 5 print head part 6 photoconductor 7 eraser lamp 8 charging charger 9y, 9m, 9c, 9k developing device 10 paper feeding device 11 transfer drum 12 transport device 13 fixing device 14 Paper ejection tray 201 Printer control unit 202 Control ROM 203 Data ROM 204 RAM 205 Operation panel 206 Reset button 207 V sensor 208 Photoconductor drive counter 209 Environment sensor 210 Development device drive counter 211 Development device drive circuit 212 Toner supply drive device 213 Vb generation Unit 214 AIDC sensor 216 Light source 217 Light source drive unit 218 D / A conversion circuit 219 γ correction unit 220 Light emission signal generation circuit 221 Vg generation unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihiko Okuno 2-3-3 Azuchi-cho, Chuo-ku, Osaka, Minato, Osaka International Building (72) Inventor Masaki Tanaka 2-chome, Azuchi-cho, Chuo-ku, Osaka No. 13 Osaka International Building Minolta Co., Ltd. (72) Inventor Hironobu Nakata 2-3-3 Azuchi-cho, Chuo-ku, Osaka City Osaka International Building Minolta Co. (72) Inventor Katsuyuki Hirata Chuo-ku, Osaka City 2-3-3 Azuchicho Osaka International Building Minolta Co., Ltd.

Claims (5)

[Claims] 1. A digital image forming apparatus for forming an image by correcting the emission intensity of a light source based on γ correction data, wherein a predetermined latent image is formed by modulating the intensity of light emitted from the light source. An image carrier to be formed, a developing unit that develops the latent image with a predetermined toner, an adhesion amount detection unit that detects an amount of toner adhered to the image carrier, and a sensitivity characteristic of the image carrier is specified. And a predicting means for predicting the developing characteristic of the developing means based on the sensitivity characteristic of the image carrier specified by the sensitivity specifying means and the toner adhesion amount detected by the adhesion amount detecting means. A parameter determining unit that determines an optimum image forming parameter based on the developing characteristics of the developing unit predicted by the predicting unit, and an image forming parameter determined by the parameter determining unit. A digital image forming apparatus including: a calculating unit that calculates the γ correction data for obtaining a desired gradation characteristic. 2. The digital image forming apparatus updates the γ correction data for each image forming operation when forming the image, and the digital image forming apparatus further calculates the γ correction data. Comparing the first data used for the first data with at least one of the second data previously used as the first data and the third data having a predetermined value, and the comparison result by the comparing means, If the first data indicates an abnormal value, the first data is replaced by the second data.
The digital image forming apparatus according to claim 1, further comprising: a correction unit that corrects one of the third data. 3. The digital image forming apparatus, further, when the comparison result by the comparing unit indicates that the first data is an abnormal value, the value of the first data is a predetermined threshold value. And a warning unit that warns that the device is abnormal when the value of the first data exceeds the threshold value continuously for a predetermined number of times. The described digital image forming apparatus. 4. The digital image forming apparatus further includes a surface potential detecting unit that detects a surface potential of the image carrier, the image carrier, a developer included in the developing unit, and the adhesion amount detecting unit. , And the surface potential detecting means are provided detachably from the apparatus main body, and the digital image forming apparatus further includes: the image carrier, the developer, the adhesion amount detecting means, and the surface potential detecting means. The digital image forming apparatus according to claim 2, further comprising an initialization unit that initializes at least one of the second data and the third data when replacing at least one of them. 5. The light source emits light in first and second modes having different emission ratios, and the arithmetic means emits data for the first γ correction corresponding to the emission ratio in the first mode and emission in the second mode. The digital image forming apparatus according to claim 1, wherein the second γ correction data corresponding to the ratio is calculated.