JPH1090961A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control various potentials in an image formation based on a linear approximate expression by changing the forming condition of the following reference image according to the linear approximate expression calculated on the basis of the measurement data of surface potential and toner adhesion quantity within a section having a high measuring precision of toner adhesion quantity. SOLUTION: The control system of a color copying machine, for example, is formed of a main control part 201 and a plurality of peripheral control parts, and the main control part 201 is formed of CPU 202, ROM 203, RAM 204 and the like. In such an image forming device, the section in which toner adhesion quantity is linearly changed to development potential is calculated on the basis of the measurement data of potential and toner adhesion quantity after development of a plurality of reference latent images formed on a photoreceptor, and a linear approximate expression is calculated on the basis of the data of a section having a high measuring precision of toner adhesion quantity. When the developing characteristic is changed, the optical writing light quantity of the latent image is changed according to the linear approximate expression so that the measurement data of toner adhesion quantity gets into the section having a high measuring precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a plurality of reference latent images on an image carrier in an image forming apparatus such as a copying machine, a facsimile, a printer, etc., the surface potential of the images, and the toner adhesion amount of the developed reference toner image. The present invention relates to an image forming apparatus that employs a potential control method of calculating a linear approximation of the developing characteristic of a developing device based on the measurement data of (1), and determining various potentials during image formation using the linear approximation.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a facsimile, a printer, or the like, generally, an image carrier composed of a photosensitive drum or the like is rotated by a motor and the image carrier is uniformly charged by a charging device. Thereafter, an image is written on the image carrier by image exposure using an exposure device to form an electrostatic latent image, and the electrostatic latent image is developed by a developing device and then transferred to a transfer material by a transfer device. Then, in order to form a color image, a plurality of color toner images are formed on the image carrier by repeating the above image forming process for each color,
A method of batch-transferring the toner onto a transfer material or forming a single-color color toner image on an image carrier in a plurality of times and sequentially transferring the color toner image to the transfer material is adopted.

In such an electrophotographic image forming apparatus, an electrostatic latent image of a patch pattern as a reference latent image is formed on an image carrier, developed by a developing device, and the surface potential and the surface potential of the patch pattern are determined. There is known a potential control method in which development characteristics are measured from the toner adhesion amount and various potentials such as a development bias potential and a charging potential of an image carrier are determined from the development characteristics. For example, there is a potential control method in which reference values are prepared in advance for the number of patch patterns, and various reference potentials are determined by comparing these reference values with the amount of toner adhered on each patch pattern. Further, as another potential control method, the surface potential of the patch pattern and the toner adhesion amount are measured by a sensor, and the developing characteristics of the developing device are linearly approximated from the measured data. Methods for obtaining various potentials from the development efficiency have been proposed.

In the above-described potential control method, it is difficult to correctly determine a reference value. In particular, when a developer having a large environmental change and a large variation over time is used, an algorithm for controlling the above-mentioned various potentials uses an environmental variation of the developer. However, it becomes complicated to avoid the influence of aging, and it takes a very long time to obtain a stable potential. Further, in the above potential control method, since various potentials are determined only from the slope of the linear approximation formula, it cannot be said that the accuracy is sufficient with respect to the fluctuation of the developer and the image carrier, and the potential control is unstable. Easily. In particular, when applied to a full-color copying machine that is easily affected by potential fluctuations, color fluctuations are likely to occur due to potential changes,
Particularly, the stability of the highlight portion of the full-color image is lacking.

Accordingly, the present applicant has improved the above-mentioned drawbacks,
As a potential control method that can perform accurate potential control in a short time and avoid the influence on the image reproduction due to environmental fluctuations of the developer and aging, a plurality of patch patterns formed on the image carrier are used. Is measured, and based on the measured data of the plurality of sets of potentials and the amount of toner adhesion, a section where the relationship between the potential and the amount of toner adhesion changes linearly is calculated. A linear approximation is obtained by linearly approximating the development characteristics from the measured data of the potential and the amount of toner adhered, and using this linear approximation to determine various potentials during image formation has been proposed (Japanese Patent Application No. Hei 6-275869). reference). Further, in the above-mentioned Japanese Patent Application No. 6-275869, the present applicant uses an optical reflection type image density sensor having no sensitivity in a multi-adhesion portion having a large amount of toner adhesion, and uses the image reflection sensor in an area where the image density sensor has sensitivity. It is proposed to calculate the toner adhesion amount of the multi-adhesion portion from a linear approximation formula obtained from the relationship between the measured potential and the measurement data of the toner adhesion amount, and to determine the various potentials during the image formation from this relationship. doing. In this case, even if an optical reflection type image density sensor is used as the toner adhesion amount measuring means, accurate potential control can be performed without being affected by the saturation characteristics of the image density sensor.

In addition, the above-mentioned potential control method and the above-mentioned Japanese Patent Application No.
In the potential control method proposed in US Pat. No. 2,275,869, it is common to use an optical reflection type image density sensor as a toner adhesion amount measuring means. The measurement accuracy tends to change depending on the amount of adherence. For example, there is a feature that the measurement accuracy gradually decreases because the amount of reflected light decreases as the amount of toner adhesion increases. The decrease in the accuracy of the image density sensor is caused by the fact that the measurement data of the toner adhesion amount changes linearly with respect to the section where the sensitivity of the sensor to the toner adhesion amount has not decreased, that is, the measurement data of the surface potential of the patch pattern. May also occur on the side with a large amount of adhesion in a section where there is. Since the measurement data of the image density sensor having the reduced measurement accuracy has a measurement error, when the linear approximation expression of the development characteristic is calculated using the measurement data, the accuracy of the linear approximation expression of the development characteristic is calculated. And the potential control is likely to be unstable.

Further, a section in which the measurement data of the toner adhesion amount linearly changes with respect to the development potential is calculated, and a plurality of sets of the surface potential and the toner adhesion amount measurement data in the interval are used to perform development. When calculating a linear approximation of the development characteristics of the apparatus, the latent image of the patch pattern is formed such that the intervals between the surface potentials of the patch pattern are equal as shown in Japanese Patent Application No. 6-275869. It is common to do. However, as described above, all of the measurement data is not always within the linearly changing section, and is not necessarily measured with a predetermined measurement accuracy. There is a possibility that effective measurement data is insufficient for accurately calculating the approximate expression.

Accordingly, the applicant of the present invention has proposed that the toner adhering amount data in a section where the toner adhering amount data changes linearly with respect to the developing potential calculated based on the plurality of sets of potential and toner adhering amount measurement data. The interval of the measurement data of the toner adhesion amount in the section where the measurement accuracy is high is made denser than the interval of the measurement data of the toner adhesion amount in the section where the measurement accuracy is low, and the surface potential in the section where the measurement accuracy is high is high. A potential control method for obtaining various linear potentials at the time of image formation using the linear approximation formula of the developing characteristic based on the measured data of toner adhesion amount was proposed (Japanese Patent Application No. Hei 7-233398). ). According to this, under the condition that the number of patch patterns formed is the same, the number of measurement data in the section used for calculating the linear approximation expression of the development characteristic is increased as compared with the case where the measurement data intervals are equal. be able to.

[0009]

However, in implementing the potential control method of Japanese Patent Application No. 7-233398, when the conditions for forming the patch pattern are fixed,
In particular, when the environment of the developer and the photoconductor as an image holding member and the fluctuation with time are large, the development characteristics change, and there is a possibility that the measurement data in the section used for calculating the linear approximation formula of the development characteristics becomes insufficient. .

If the conditions for forming the patch pattern are fixed in advance as initial settings, the initial settings are not appropriate due to individual differences between the developing device and the developer. There is a possibility that the measurement data in the section to be used is insufficient. This is because, depending on the developing device, development conditions such as the amount of developer pumped up to the developing sleeve as a developer carrier and the gap between the developing sleeve and the photoreceptor are different, and depending on the developer, the amount of charge and the standing time until use of the agent are different. This is because the development characteristics also change due to these differences.

When the measurement data in the above section is insufficient, the accuracy of the linear approximation of the developing characteristic is reduced, and various potential settings such as the developing bias potential and the charging potential of the image carrier deviate from appropriate values. Causes excess or deficiency. In particular, in the above-described full-color copying machine, not only is the image density excessive or insufficient, but also
Changes in color tone are likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the object of being based on the aging of the developer and the image carrier, environmental fluctuation, or individual differences between the developing device and the developer. It is an object of the present invention to provide an image forming apparatus capable of accurately calculating a linear approximation expression of a developing characteristic of a developing device and stably controlling various potentials during image formation based on the linear approximation expression. .

[0013]

According to a first aspect of the present invention, a plurality of reference latent images are formed on an image carrier, and the surface potential of the reference latent image is measured. Are developed with different developing potentials to form a plurality of reference toner images, the toner adhesion amount of the reference toner image is measured, and the plurality of sets of surface potential and toner adhesion amount measurement data are used. A section in which the measurement data of the toner adhesion amount linearly changes with respect to the development potential is calculated, and a linear approximation expression of the developing characteristic is obtained based on the plurality of sets of surface potential and toner adhesion amount measurement data in the section. In the image forming apparatus which calculates various potentials at the time of image formation using the linear approximation formula, the surface potential and the toner adhesion amount are measured in a section of the section where the toner adhesion amount measurement accuracy is high. Based on data Calculating the linear approximation formula, and changing the next formation condition of the plurality of reference latent images in accordance with the linear approximation formula so that the measurement data of the toner adhesion amount is included in a section where the measurement accuracy is high. It is characterized by the following.

In this image forming apparatus, a plurality of reference latent images are formed on an image carrier, and the potential of the plurality of reference latent images is measured based on the potential of the reference latent image and the toner adhesion amount of the developed reference toner image. The section in which the measurement data of the amount linearly changes is calculated, and a plurality of sets of the surface potential and the measurement data of the toner adhesion in the section where the measurement accuracy of the toner adhesion is high in the section are used for the developing device. A linear approximation of the development characteristic is calculated, and various potentials during image formation are determined using the linear approximation. Then, even if the developing characteristics change due to the aging of the developer and the image carrier, environmental changes, or individual differences between the developing device and the developer, the next plurality of reference latents are calculated according to the calculated linear approximation formula. By changing the image forming conditions, the measurement data of the toner adhesion amount is included in the section where the measurement accuracy is high. Therefore, there is no shortage of measurement data in the section used for calculating the linear approximation expression of the development characteristic.

According to a second aspect of the present invention, a plurality of reference latent images are formed on an image carrier, a surface potential of the reference latent images is measured, and the plurality of reference latent images are developed with different developing potentials. Forming a plurality of reference toner images, measuring a toner adhesion amount of the reference toner image, and measuring the toner adhesion amount with respect to the development potential based on the plurality of sets of surface potential and toner adhesion amount measurement data; Is calculated linearly, and a linear approximation of development characteristics is calculated based on a plurality of sets of surface potential and toner adhesion amount measurement data within the interval, and image formation is performed using the linear approximation. In the image forming apparatus that determines the various potentials at the time, the linear approximation formula is calculated based on the surface potential and the toner adhesion amount measurement data in the section where the measurement accuracy of the toner adhesion amount is high in the section. Toner adhesion amount The measured data is compared with a preset reference value, and according to the result of the comparison, the plurality of reference latent images for the next time are set such that the measured data of the toner adhesion amount is included in a section where the measurement accuracy is high. Is characterized by changing the formation conditions.

In this image forming apparatus, a plurality of reference latent images are formed on an image carrier, and the potential of the plurality of reference latent images and the toner adhesion amount of the developed reference toner image are measured based on measurement data of the amount of toner adhesion. The section in which the measurement data of the amount linearly changes is calculated, and a plurality of sets of the surface potential and the measurement data of the toner adhesion in the section where the measurement accuracy of the toner adhesion is high in the section are used for the developing device. A linear approximation of the development characteristic is calculated, and various potentials during image formation are determined using the linear approximation. Then, even if the developing characteristics change due to the aging of the developer and the image carrier, environmental fluctuations, or individual differences between the developing device and the developer, the measured data of the toner adhesion amount and the preset reference value By changing the formation conditions of the next plurality of reference toner images according to the result of the comparison, the measurement data of the toner adhesion amount is included in the section where the measurement accuracy is high. Therefore, there is no shortage of measurement data in the section used for calculating the linear approximation expression of the development characteristic. Here, as a specific mode of comparison between the measurement data of the toner adhesion amount and the reference value, comparison of the number of measurement data deviating from the section with high measurement accuracy or the deviation amount of individual measurement data may be mentioned. . Also, when calculating the toner adhesion amount from the measurement data of the reflection density of the reference toner image,
Instead of comparing the measured toner adhesion data with the reference value,
The measurement data of the reflection density may be compared with a preset reference value.

In the first or second aspect of the present invention, in order to form a plurality of reference toner images by developing the plurality of reference latent images with different developing potentials, for example, It is formed to have different surface potentials. Further, for example, the plurality of reference latent images are formed so as to have a constant surface potential, and the reference latent images are developed using different developing bias voltages to form a reference toner image. Further, for example, both the surface potential of the reference latent image and the developing bias voltage may be changed. Therefore, when changing the formation condition of the reference toner image, the surface potential of the reference latent image is changed,
The development bias voltage may be changed, or both the surface potential of the reference latent image and the development bias voltage may be changed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an image forming apparatus will be described below. FIG. 2 is a schematic diagram of a full-color copying machine (hereinafter, referred to as a color copying machine) as an image forming apparatus to which the present invention is applied, and FIG. 3 is an enlarged view around a photosensitive drum and an intermediate transfer belt of the color copying machine. is there. In FIG. 2, the color copying apparatus includes a color image reading device (hereinafter, referred to as a color scanner) 1 and a color image recording device (hereinafter, referred to as a color printer) 2.
It is composed of

First, the color scanner 1 forms an image of an original 3 on a color sensor 7 via an illumination lamp 4, a mirror group 5, and a lens 6, and converts color image information of the original into, for example, blue (Blue, It is read out for each color separation light of green (hereinafter, referred to as B), green (hereinafter, referred to as G), and red (Red, hereinafter, referred to as R) and converted into an electric image signal. And B, G, obtained by this color scanner 1,
Based on the color separation image signal intensity level of R, a color conversion process is performed in an image processing unit (not shown), and black (hereinafter, referred to as Bk), cyan (Cyan, hereinafter referred to as C),
Magenta (hereinafter referred to as M), yellow (Yel
low, hereinafter referred to as Y).

Next, in the color printer 2, the laser optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and performs photosensitive writing as an image carrier. Body drum 9
To form an electrostatic latent image. The photosensitive drum 9 rotates counterclockwise as shown by the arrow, and around the photosensitive drum 9, a photosensitive member cleaning unit (including a pre-cleaning static eliminator) 1 is provided.
0, static elimination lamp 11, charging device 12, surface potential sensor 13 as surface potential measuring means, Bk developing device 14, C developing device 15, M developing device 16, Y developing device 17, image density measurement for detecting development density pattern A light reflection type optical sensor 18 and an intermediate transfer belt 19 as means are arranged. Each developing device has a developing sleeve (14a, 15a, 16a, 17a) that rotates by bringing a spike of developer into contact with the surface of the photosensitive drum 9 to develop an electrostatic latent image, and draws and agitates the developer. Developing paddle (14b, 1
5b, 16b, 17b) and toner concentration sensors (14c, 15c, 16c, 17c) as toner concentration measuring means for measuring the toner concentration of the developer.

Hereinafter, the outline of the copying operation will be described with an example in which the order of the developing operation (color toner image forming order) is Bk, C, M, and Y (however, the image forming order is not limited to this). ). When the copying operation is started, reading of the Bk image data is started at a predetermined timing by the color scanner 1, and light writing by a laser beam and formation of a latent image are started based on the image data (hereinafter, electrostatic image formation by the Bk image data). The latent image is called a Bk latent image, C, M, Y.
Are referred to as C latent image, M latent image and Y latent image, respectively).
Before the front end of the latent image reaches the developing position of the Bk developing device 14 so as to enable development from the front end of the Bk latent image, the rotation of the developing sleeve 14a is started to develop the Bk latent image with Bk toner. Thereafter, the developing operation of the Bk latent image area is continued,
When the rear end of the latent image passes the Bk developing position, the developer on the developing sleeve 14a is promptly cut off, and the developing operation is stopped. The developer is cut off by the developing sleeve 14.
This is performed by switching the rotation direction of “a” to a direction opposite to that during the developing operation. The switching of the Bk developing device 14 to the development inoperative state is completed at least before the leading end of the C latent image based on the next C image data arrives.

Next, the Bk toner image formed on the photosensitive drum 9 is transferred onto the surface of the intermediate transfer belt 19 driven at the same speed as the photosensitive drum 9 (hereinafter referred to as the photosensitive drum 9).
(Transfer of the toner image from the belt to the intermediate transfer belt 19 is referred to as belt transfer.) This belt transfer is performed by applying a predetermined bias voltage to the transfer bias roller 20a in a state where the photosensitive drum 9 and the intermediate transfer belt 19 are in contact with each other.

In the same operation, C and C are sequentially placed on the photosensitive drum 9.
M, Y toner images are formed (the order of Bk, C, M, Y is not limited to this), and the four-color superimposed belt transfer image is sequentially and accurately aligned on the intermediate transfer belt 19. And then transfer paper 24 by paper transfer unit 23
The paper transfer is performed collectively.

In the above-described intermediate transfer belt unit, the intermediate transfer belt 19 includes the driving roller 21 and the transfer bias roller 2.
0 and a group of driven rollers, and is driven and controlled by a drive motor (not shown). At a predetermined position facing the surface of the intermediate transfer belt 19, a belt cleaning unit 22 is provided.
Are the inlet seal 22a, the cleaning blade 22b,
And a contact / separation mechanism 22c from the intermediate transfer belt 19. When cleaning is not required, the contact / separation mechanism 22c
Seal 22a and cleaning blade 2
2b is separated from the belt surface.

A paper transfer unit 23 is provided so as to face the portion of the intermediate transfer belt 19 wound around the drive roller 21. This unit 23
Paper transfer bias roller 23a, roller cleaning blade 23b, and mechanism 2 for contacting and separating from intermediate transfer belt 19
3c and the like. Although the paper transfer bias roller 23a is normally separated from the intermediate transfer belt 19, the four-color superimposed image formed on the belt 19 is
At the time of collective transfer to the transfer paper 24, the transfer is performed by the contact / separation mechanism 23c at a timing, and a predetermined bias voltage is applied to the roller 23a to transfer the image onto the transfer paper 24.

The transfer paper 24 is fed by a feed roller 25 and a registration roller 26 at the timing when the leading end of the four-color superimposed image on the surface of the intermediate transfer belt 19 reaches the paper transfer position. Then, the transfer paper 24 on which the four-color superimposed toner image is collectively transferred from the surface of the intermediate transfer belt 19 is conveyed to a fixing device 28 by a paper conveyance unit 27, and the fixing roller 28a and the pressure roller 2 are controlled to a predetermined temperature.
In step 8b, the toner image is fused and fixed, and is carried out to the copy tray 29 to obtain a full-color copy.

The photosensitive drum 9 after the belt transfer is
Photoconductor cleaning unit 10 (pre-cleaning static eliminator 10a, brush roller 10b, rubber blade 10c)
Then, the surface is cleaned, and the charge is uniformly removed by the charge removing lamp 11. After the transfer of the toner image onto the transfer paper 24, the surface of the intermediate transfer belt 19 is cleaned by pressing the cleaning unit 22 again by the contact / separation mechanism 22c.

The transfer paper cassettes 30, 31, 32,
Reference numeral 33 stores transfer papers of various sizes, which are fed and conveyed in the direction of the registration rollers 26 from the storage cassette of the size paper designated by the operation panel (not shown) at a certain timing. Reference numeral 34 denotes a manual paper feed tray for feeding OHP paper, thick paper, or the like.

The above is a description of the copy mode for obtaining four full colors. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. become. Further, in the case of the single color copy mode, only the developing device of the color is set in the developing operation (spring) until the predetermined number of sheets is completed, and the intermediate transfer belt 19 reciprocates while being in contact with the photosensitive drum 9. Direction, and the belt cleaning unit 22 performs a copying operation while keeping the belt cleaning unit 22 in contact with the intermediate transfer belt 19.

FIG. 1 shows an example of a control system of the color copying machine. This control system includes a main control unit 201 and a plurality of peripheral control units.
U202, a ROM 203 storing a control program and various data, a RAM 204 temporarily storing various data as a work area, and an I / O interface unit 205 for inputting / outputting to / from each peripheral control unit. ing.

The main control unit 201 is provided with an I / O
Via an interface unit 205, a laser optical system control unit 206, a power supply circuit 207, an optical sensor 18, toner concentration sensors 14c, 15c, 16c, 17c, a toner supply circuit 212, an intermediate transfer belt drive circuit 213, a surface potential sensor 13, and the like. It is connected. The laser optical system control unit 206 controls the laser optical unit 8 based on a command from the main CPU 202, and the power supply circuit 207 applies a high voltage to the charger 12 based on a command from the main CPU 202, and also controls the developing sleeve 14a. , 15
a, 16a and 17a are applied with a developing bias voltage, respectively. The optical sensor 18 optically detects the reflection density of the toner image on the photosensitive drum 9. The surface potential sensor 13 detects the surface potential of the photosensitive drum 9. The toner supply circuit 212 controls a toner supply motor of each toner supply unit based on a command from the main CPU 202 to supply toner of each color to each developing device.

FIG. 4 is a flowchart of a potential control routine by the main control unit 201. The potential control by the potential control routine is basically performed when the apparatus (copying machine) is started, but may be performed as needed, for example, every predetermined number of copies or every certain time. In the potential control routine of FIG. 4, the main control unit 201 first receives a signal from a fixing temperature sensor (not shown) that detects the fixing temperature of the fixing device 28 in order to distinguish the power-on state from the abnormality processing such as a jam. Fixing temperature is 100 ° C based on input signal
It is determined whether or not this is the case (step 501). Here, when the fixing temperature exceeds 100 ° C., it is determined that there is an abnormality, and the potential control is not performed. On the other hand, when the fixing temperature is 100
If the temperature is lower than ° C, the power supply circuit 207 supplies the photosensitive drum 9
The reference voltage is applied to the surface potential sensor 13 to calibrate the surface potential sensor 13 (step 502). This calibration value is used in subsequent potential calculations. Next, the main control unit 201 fetches the output value Vsg for the background portion of the photosensitive drum 9 from the optical sensor 18 so that the reflected light of the light emitted from the optical sensor 18 to the background portion of the photosensitive drum 9 becomes a constant value. Then, the light emission amount of the optical sensor 18 is adjusted (step 503).

Next, as shown in FIG. 5, electrostatic latent images 301, 302, 303,... Of a patch pattern, which are reference images having N gradation densities, are provided at the center of the photosensitive drum 9 in the width direction.
Are created at predetermined intervals along the rotation direction of the photosensitive drum 9 (step 504). For example, the electrostatic latent images 301, 302,... 314 of a rectangular patch pattern having 14 different gradation densities and each side being 40 mm are 10 m long.
It is created at intervals of m. Hereinafter, a case where an electrostatic latent image of 14 patch patterns is created will be described. The output values of the surface potential sensor 13 corresponding to the potentials of the electrostatic latent images 301, 302,... 314 are read and converted into surface voltage values by using the above calibration values.
(Step 505). In this case, the main control unit 201 controls the electrostatic latent image 301 of the 14 patch patterns,
.. 314 for four colors Bk, C, M, and Y are sequentially formed on the photosensitive drum 9 at predetermined intervals.

Next, the main controller 201 controls the electrostatic latent images 301 and 3 of the patch pattern for four colors on the photosensitive drum 9.
, 314 are developed for each color by a Bk developing unit 14, a C developing unit 15, an M developing unit 16, and a Y developing unit 17 to form a toner image of each color. The output value of the optical sensor 18 for the toner image is set to Vpi for each color.
It is stored in the RAM 204 as (i = 1 to 14) (step 506).

The main control unit 201 uniformly charges the photosensitive drum 9 by the charger 12 and changes the output of the laser optical unit 8 via the laser optical system control unit 206 to change the electrostatic latent image of the patch pattern. 301, 302, ...
.. 314 may be created, but the toner image of each patch pattern may be created by switching the developing bias voltage of each of the developing units 14 to 17 without operating the laser optical unit 8.

Next, the main control unit 201
The output value of the optical sensor 18 stored in the storage unit 4 is converted into a toner adhesion amount per unit area with reference to a table stored in the ROM 203 and stored in the RAM 204 (step 507).

FIG. 6 is a diagram in which the relationship between the measured data of the surface potential obtained in the above step 505 and the measured data of the amount of applied toner obtained in the above step 507 in each patch pattern is plotted on the XY plane. And the developing potential (the difference between the developing bias voltage Vb at the time of creating the patch pattern and the surface potential Vs of the photosensitive drum 9: V
b-Vs: unit (V)), and the toner adhesion amount per unit area (mg / cm ² ) is allocated on the Y axis. Normal,
As shown in FIG. 6, the infrared light reflection type sensor used as the optical sensor 18 shows a saturation characteristic in a large amount of toner attached to a large amount of toner, and the sensitivity in the large amount of toner is low. The measurement accuracy of the toner adhesion amount is also poor. Therefore, in order to accurately calculate a linear approximation formula (Y = a * X + b) that linearly approximates the true developing characteristic of the developing device, a high sensitivity section (high precision section) of the optical sensor 18 as shown in FIG. And measurement data of the development potential obtained from the output value of the surface potential sensor 13 and the optical sensor 1
The linear approximation formula is calculated using only the measured data points in the section where the relationship with the toner adhesion amount obtained from the output value of No. 8 is a straight line (hereinafter referred to as a calculation range) (step 508). The calculation accuracy of the approximate expression has been improved. Further, the light amount data used by the laser optical unit 8 when each patch pattern stored in the ROM 203 is created is set to a desired value so that the measurement data points in this section are denser than those in other sections. Under the same condition where the total number of measurement data is the same, the number of measurement data used for calculating the linear approximation formula is increased as compared with the case where the measurement data intervals are equal, and the calculation accuracy of the linear approximation formula is further increased. Is increasing.

When the toner image of each patch pattern is formed by changing the developing bias voltage without operating the laser optical unit 8 as described above, the measured data points in the above-mentioned section are smaller than those in other areas. The data of the developing bias voltage stored in advance in the ROM 203 and applied when creating each patch pattern is set to a desired value so as to be dense.

As described above, if the environment of the developer and the photoreceptor and the time-dependent fluctuation are large, the development characteristics may change and the measurement data in the section used for calculating the linear approximation of the development characteristics may be insufficient. There is. Therefore, in the present embodiment, in order to accurately calculate a linear approximation expression of the development characteristic and stably control various potentials at the time of image formation based on the linear approximation expression, the environment of the developer and the photoreceptor, The patch pattern forming conditions are changed so that the measurement data of the toner adhesion amount falls within the above-mentioned calculation range regardless of aging. The change of the condition for forming the patch pattern will be described later in detail.

To select the measurement data of the section from all the measurement data in step 508, for example, focusing on the measurement data of the toner adhesion amount calculated in step 507, 0.15 to 0.45 mg / cm ^What is necessary is to select a set of measurement data of the toner adhesion amount and the development potential between the ^two .

Next, a smoothing process is performed only on the effective measurement data selected in the above step 508 using a plurality of formulas shown in Expression 1 (step 509), and smoothing is performed on the measurement data having a large measurement error. The linear approximation formula can be calculated with high accuracy without causing a deviation in the approximate straight line calculation as in the case where the process is used to calculate the linear approximation formula. Here, i ≦ n ≦ j, and the smoothing process is not performed on the measurement data at the end of the section.
Also, “′” is added to the measurement data after the smoothing process.

X '(n) = X (n-1) * 0.25 + X (n) * 0.5 + X (n + 1) Y' (n) = Y (n-1) * 0.25 + Y (n ) * 0.5 + Y (n + 1) X '(i) = X (i) X' (j) = X (j) Y '(i) = Y (i) Y' (j) = Y (j)

By applying the least squares method to the measured data obtained in this way after the smoothing processing, the linear approximation of the developing characteristic of each of the developing units 14 to 17 is performed, and the linear approximation formula of the developing characteristic is obtained. Is obtained for each color (step 510). Various control potentials are calculated for each color based on the linear approximation formula. For the calculation of the least squares method, a plurality of equations shown in the following Expression 2 were used. Here, “′” indicating the measurement data after the smoothing process is omitted for convenience. K indicates the number of measurement data used for the calculation.

Xave = ΣXn / k Yave = ΣXn / k Sx = Σ (Xn-Xave) * (Xn-Xave) Sy = Σ (Yn-Yave) * (Yn-Yave) Sxy = Σ (Xn-Xave) * (Yn-Yave)

Then, a linear approximation formula calculated from the measured data of the surface potential of the patch pattern and the toner adhesion amount obtained from the surface potential sensor 13 and the optical sensor 18 is represented by Y =
Assuming that a * X + b, the coefficients a and b are expressed by the following equation 3 using the variables of the above equation 2.

## EQU3 ## a = Sxy / Sx b = Yave-a * Xave

The coefficient a may be determined by the following method. That is, since a plurality of continuous (for example, four) data sets are obtained from a plurality of sets of measurement data in the selected section, a linear regression is performed on each of the data sets, and among them, a linear regression is performed. It is also possible to select a value having a large value, a value in which the value of the gradient a is close to the average value, or a value having the largest correlation coefficient of the linear regression equation.

Next, the main control unit 201 uses the linear approximation formula calculated for each color in step 510 to set each control potential so that the value of Y becomes the required maximum toner adhesion amount Mmax. It is determined (step 511). As shown in FIG. 7, an image is obtained from the developing electric field (Vgp) necessary for obtaining the above Mmax and Vk (= -b / a: development start voltage) which is the X intercept of the calculated linear approximation. Vkp (developing potential: reference potential for setting various potentials during formation)
Vb−Vs) is determined by the following equation (4).

Vgp = Mmax / a Vkp = Vgp + Vk

Next, from the value of the developing electric field Vgp, R
Referring to the potential table as shown in FIG. 8 stored in the OM 203 (step 512), the charging potential (Vd)
The developing bias voltage (Vb) and the maximum exposure potential (Vl) are determined as target potentials (step 513). Then, the power supply circuit 207 is adjusted so that the charging potential of the photosensitive drum 9 by the charger 12 becomes the target potential Vd, and the amount of laser light emission (light emission power) by the laser optical system 8 becomes the target potential Vl. Adjustment, and each color developing device 13-1
7 are adjusted so that each of the developing bias voltages becomes the target voltage Vb (step 514).

As described above, according to the present embodiment, the interval between the measurement data of the toner adhesion amount within the above calculation range is made narrower than the interval between the measurement data of the toner adhesion amount outside the calculation range, and the measurement accuracy is improved. A linear approximation of the development characteristics is calculated based on the measured data of the surface potential and the amount of toner attached within a high calculation range. Therefore, under the condition that the number of formed patch patterns is the same, the number of measurement data used for calculating the linear approximation formula can be increased as compared with the case where the measurement data intervals are equal, and the linear approximation can be performed more accurately. Equations can be calculated.

In the present embodiment, the smoothing process is performed only on the measurement data of the surface potential and the amount of toner adhered in the above calculation range, and the linear approximation expression of the developing characteristic is calculated using the measurement data after the smoothing process. I do. Therefore, compared to the case where the measurement data having a large measurement error is subjected to the smoothing process and used for calculating the linear approximation formula, the deviation of the approximate straight line calculation is less likely to occur, and the linear approximation formula is calculated with higher accuracy. Can be.

Next, a method of changing the patch pattern forming conditions according to the linear approximation formula of the developing characteristic will be described in detail. FIG. 9 is a graph showing the relationship between the development potential and the amount of toner adhering per unit area in each patch pattern. Note that the approximate straight line P is an initial profile before the development characteristics change, the approximate straight line Q is a profile when the developing capability is high, and the straight line R is a profile when the developing capability is low. The measurement data within the above calculation range is indicated by a black circle, and the measurement data outside the calculation range is indicated by a white circle.

When the developer exhibiting the developing characteristics represented by the approximate straight line Q as the initial profile deteriorates due to the temporal change,
The specific charge amount Q / M of the toner decreases, and the development characteristics change as indicated by the approximate straight line Q. As a result, the number of measurement data within the calculation range is reduced from six at the beginning to two. For example, the measurement data point i is within the calculation range even if shifted in the direction of arrow A, but the measurement data point j is shifted out of the calculation range in direction B. As a result, the number of valid measurement data within the calculation range becomes insufficient, and it becomes impossible to accurately calculate the linear approximation expression of the development characteristics. In general, the phenomenon that the developing ability increases as indicated by the approximate straight line Q occurs even in a high-temperature environment in addition to the deterioration due to the aging of the developer.

On the other hand, in a low-temperature environment, the specific charge amount Q / M of the toner increases, and the developing characteristic changes as indicated by an approximate straight line R. As a result, the number of measurement data within the calculation range is reduced from six at the beginning to four. For example, the measurement data points i and j are shifted in the directions of arrows C and D, respectively, and fall outside the calculation range. As a result, there is a shortage of valid measurement data within the calculation range, and it becomes impossible to accurately calculate a linear approximation expression of the development characteristics.

Further, when the photosensitive member deteriorates due to aging, the latent image potential changes, and similarly, effective measurement data within the calculation range becomes insufficient, and it becomes impossible to calculate a linear approximation expression of development characteristics with high accuracy. Specifically, in FIG. 9, on the curve S connecting the measurement data points at the initial stage, the measurement data points corresponding to the patch patterns of the same light writing light amount are indicated by arrows according to the change in the photoconductor potential due to the deterioration. It shifts in the direction a or the direction of the arrow b.

Here, the position on the X axis of the plurality of patch patterns is determined by the potential of the patch patterns, that is, the writing light amount. Therefore, when the developing characteristics change due to the aging of the developer and the photoconductor and environmental changes, the number of measurement data within the calculation range can be reduced by changing the writing light amount of the next patch pattern according to the linear approximation formula of the developing characteristics. Can be secured. (Hereinafter, margin)

In FIG. 10, Y = pX0 + bp (p is a slope, bp is a Y intercept) of the approximate line P of the developing characteristic at the initial stage, and Y = pX0 + bp (Y is the intercept of bp). When qX1 + bq (q is the slope, bq
In order to translate only the X component of the measured data point in parallel after the development characteristic changes, as indicated by the arrow in the figure, the following equation 5 only needs to be satisfied.

## EQU5 ## pX0 + bp = qX1 + bq

When the above equation (5) is solved for X1, the following equation (6) is obtained.
Can lead to a relationship.

X1 = 1 / q (pX0 + bp-bq) X1 = (p / q) X0 + 1 / q (bp-bq)

Therefore, each measured data is represented by (p / q) X0 +
By performing the calculation of 1 / q (bp−bq) and resetting the measurement data points, the measurement data points can be shifted in a direction falling within the calculation range even after the development characteristics change. Specifically, in order to shift the development potential to the value of Xi, assuming that the surface potential Vxi and the development bias value at the time of forming the patch pattern are Vb, the surface potential Vxi is changed so as to satisfy the following Expression 7. The light writing light amount of the patch pattern is changed as needed.

Xi = Vxi-Vb

The constants q and bq in Equation 6 are the slope and Y intercept of the approximate straight line Q calculated from the measurement data within the calculation range under the conditions before the shift of the measurement data points. Since the development characteristics do not change so rapidly in the next measurement due to the aging of the photoreceptor and environmental changes, there is substantially no problem. Further, by repeating the change and measurement of the measurement data points, the shift amount for shifting the measurement data points in a direction falling within the calculation range can be accurately obtained as compared with the case where the measurement data points are not changed. In addition, the calculation accuracy of the linear approximation of the developing capacity is improved.

Further, the change of the measurement data point may be performed only when the amount of change in the inclination is determined and the amount of change becomes larger than a predetermined amount of change. When the difference bp−bq between the Y intercepts is small, the term of 1 / q (bp−bq) in the above equation (6) may be ignored.

When the developing characteristics change due to the aging of the developer and the photosensitive member and environmental changes, the measured data of the amount of toner adhering is compared with a preset reference value, and the next time, according to the comparison result, May be changed.

FIG. 11 is a graph showing the relationship between the development potential and the amount of applied toner per unit area in each patch pattern. Note that the approximate straight line P is an initial profile before the development characteristics change, and the approximate straight line Q is a profile when the developing ability is increased. The measurement data points within the calculation range at the time of calculating the approximate straight line P are set to P1, P2,.

When the developer deteriorates due to a change over time and the developing characteristics change as indicated by an approximate straight line Q, the first, second,.
.. .6 measurement data points P1, P2,..., P6 are shifted in the direction of the arrow, and three measurement data points P4, P5, P6 are sequentially calculated from the measurement data points in descending order of toner adhesion amount. Exceeds the upper limit. When the developing characteristic changes as indicated by an approximate straight line R shown in FIG. 9, two measurement data points P are sequentially measured from the measurement data points having the smaller toner adhesion amount.
1, P2 is below the lower limit of the calculation range. Therefore, by examining which measured data point has deviated from the upper limit or the lower limit of the calculation range, the profile of the development characteristic can be identified.

In this case, in order to secure the number of measurement data within the calculation range, for example, when only the sixth measurement data P6 exceeds the upper limit of the calculation range, the coefficient A is increased, and the fifth and sixth measurement data P5, If P6 exceeds the upper limit of the calculation range, the coefficient B
(0 <B <A <1) is converted to each measurement data P1, P2,.
Shift the measured data point into the calculation range by multiplying P6. When the first measurement data P1 falls below the lower limit of the calculation range, the measurement data point is shifted into the calculation range by multiplying by the coefficient F (1 <F). Note that the coefficients A, B, and F may be obtained in advance by experiments or may be calculated according to the amount of deviation from the upper or lower limit of the calculation range. When the measurement data point is shifted within the calculation range according to the shift amount, for example, in FIG. 11, the upper limit of the calculation range is Ymax, the lower limit is Ymin, and the measurement data point with the largest amount of toner to be included in the calculation range, that is, , Sixth
Assuming that the toner adhesion amount at the measurement data point P6 is Yupper, the potential of the patch pattern is reduced by the amount of deviation (Ymax−Ymin) / (Yupper−Ymin). However, the value of the measured data point on the lower limit side of the calculation range is the lower limit Ymi of the calculation range.
If there is a risk of falling below n, the first measurement data point P1 is fixed, and the second, third,.
3... P6 and the difference in toner adhesion amount between the first measurement data point P1 and the difference (Ymax−Ymin) / (Yupper
-Ymin).

As described above, in the present embodiment, the comparison between the measured data of the amount of toner adhered and the upper and lower limits of the calculation range, which is a preset reference value, is performed in accordance with the calculated linear approximation formula. By changing the formation conditions of the next plurality of reference toner images in accordance with the result, the measurement data of the toner adhesion amount falls within the above calculation range regardless of the aging of the developer and the image carrier and environmental fluctuation. I do. Therefore, since there is no shortage of measurement data for calculating the linear approximation expression of the development characteristics within the calculation range, the linear approximation expression can be accurately calculated, and various potentials during image formation based on the linear approximation expression can be calculated. Control can be performed stably. As a result, it is possible to prevent the image density from being excessive or insufficient and to prevent the color tone from changing in the full-color copying machine.

In the present embodiment, the case where the developing characteristics change due to the aging of the developer and the image carrier and the environmental change has been described. Even if the number of pieces of measurement data within the calculation range is insufficient due to individual differences between the developing device and the developer when the conditions are set in advance, similarly, by changing the patch pattern formation conditions, the next measurement data point Can be shifted into the calculation range.

[0065]

According to the first or second aspect of the present invention, even if the developing characteristics change due to the aging of the developer and the image carrier, environmental fluctuations, or individual differences between the developing device and the developer, the present invention is not limited thereto. Since there is no shortage of measurement data in the section used for calculating the linear approximation expression of the development characteristic, the linear approximation expression of the development characteristic can be accurately calculated. Therefore, there is an excellent effect that various potentials can be stably controlled during image formation based on the linear approximation formula. As a result, it is possible to prevent the image density from being excessive or insufficient and to prevent the color tone from changing in the full-color copying machine.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a control system of a color copying machine to which the present invention is applied.

FIG. 2 is a schematic configuration diagram of the entire color copying machine.

FIG. 3 is an enlarged view around a photosensitive drum and an intermediate transfer belt of the color copying machine.

FIG. 4 is a flowchart of a potential control routine in the color copying machine.

FIG. 5 is an explanatory diagram of a patch pattern on a photosensitive drum in the color copying machine.

FIG. 6 is a characteristic diagram showing a relationship between a development potential and a toner adhesion amount during the patch pattern development and an approximate straight line of development characteristics.

FIG. 7 is an explanatory diagram showing a relationship between the approximation straight line and a development electric field (Vgp) and a development potential Vkp corresponding to a maximum toner adhesion amount Mmax.

FIG. 8 is a diagram showing a potential table used to determine various potentials during image formation from a development potential Vkp corresponding to a maximum toner adhesion amount Mmax.

FIG. 9 is a characteristic diagram showing a relationship between a development potential and a toner adhesion amount during the patch pattern development and an approximate straight line of development characteristics.

FIG. 10 is an explanatory diagram of a measurement data point changing method based on an approximate straight line of development characteristics.

FIG. 11 is an explanatory diagram of a measurement data point changing method based on the measurement data of the toner adhesion amount.

[Description of Signs] 9 Photoconductor drum 13 Surface potential sensor 14 Bk developing device 14c Toner density sensor 15 C developing device 15c Toner density sensor 16 M developing device 16c Toner density sensor 17 Y developing device 17c Toner density sensor 18 Optical sensor 201 Main Control unit

Claims (2)

[Claims] A plurality of reference latent images are formed on an image carrier, surface potentials of the reference latent images are measured, and the plurality of reference latent images are developed with different developing potentials to form a plurality of reference toner images. Is formed, the toner adhesion amount of the reference toner image is measured, and the toner adhesion amount measurement data linearly changes with respect to the development potential based on the plurality of sets of surface potential and toner adhesion amount measurement data. Calculate a section to be performed, calculate a linear approximation of development characteristics based on measurement data of a plurality of sets of surface potential and toner adhesion amount in the section, and use the linear approximation to calculate various potentials during image formation. In the image forming apparatus to be determined, the linear approximation formula is calculated based on the surface potential and the toner adhesion amount measurement data in the section where the toner adhesion amount measurement accuracy is high in the section, and the measurement accuracy is high. Part of the tona An image forming apparatus for changing the formation conditions of the next plurality of reference latent images in accordance with the linear approximation formula so that measurement data of the adhesion amount is included; 2. A plurality of reference latent images are formed on an image carrier, surface potentials of the reference latent images are measured, and the plurality of reference latent images are developed with different developing potentials to form a plurality of reference toner images. Is formed, the toner adhesion amount of the reference toner image is measured, and the toner adhesion amount measurement data linearly changes with respect to the development potential based on the plurality of sets of surface potential and toner adhesion amount measurement data. Calculate a section to be performed, calculate a linear approximation of development characteristics based on measurement data of a plurality of sets of surface potential and toner adhesion amount in the section, and use the linear approximation to calculate various potentials during image formation. In the image forming apparatus to be determined, the linear approximation formula is calculated based on surface potential and toner adhesion amount measurement data in a section of the section where the toner adhesion amount measurement accuracy is high, and the toner adhesion amount is measured. Data and advance The set reference value is compared with the set reference value, and according to the result of the comparison, the formation condition of the next plurality of reference latent images is changed so that the measurement data of the toner adhesion amount is included in the section where the measurement accuracy is high. An image forming apparatus characterized by changing.