JPH0973221A - Potential control method and toner replenishment control method for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a potential control method and a toner replenishment control method for an image forming device by which potential can be accurately controlled in a short time without increasing toner consumption accompanied with the developing action of a latent image pattern and which is optimum for reproducing an image with respect to the fluctuation of developer. SOLUTION: Plural patch patterns provided with different toner attachment quantity are formed on a photoreceptor drum 103. Then, the potential and the toner attachment quantity of the patch patterns are measured by sensors 211 and 208. Based on the relation of data between the measured potential and the measured toner attachment quantity, the first developing characteristic of a developing device is calculated by a control part 201 so as to decide the various kinds of potential when the image is formed by the image forming device. Besides, a second developing characteristic is calculated based on the relation between the potential and the toner attachment quantity measured on a different measuring cycle from that of the deciding time of the respective potential. Then, the various kinds of potential when the image is formed by the image forming device are decided based on the first and the second developing characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a latent image pattern on an image carrier in an image forming apparatus such as a copying machine, a facsimile, a printer, etc., and measures the developing characteristic from the potential and the toner adhesion amount. The present invention relates to a potential control method in an image forming apparatus that determines various potentials during image formation based on development characteristics.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a facsimile, a printer, etc., an image carrier, which is generally a photosensitive drum, is rotated by a driving means such as a motor and the image carrier is made uniform by a charging device. After charging to
An image is written on the image carrier by image exposure by an exposure device to form an electrostatic latent image, the electrostatic latent image is developed by a developing device, then transferred to a transfer material by a transfer device, and transferred by a fixing device. It is fixed on the material.

In such an electrophotographic image forming apparatus, a pattern of an electrostatic latent image is formed on an image carrier, the electrostatic latent image potential is measured, the pattern is visualized by a developing device, and then the image is developed. A method is known in which the developing characteristic is obtained from the toner adhesion amount, and various potentials such as the developing bias potential and the charging potential of the image carrier are calculated from the developing characteristic. For example, a potential control method in which reference values of the toner adhesion amount corresponding to the number of latent image patterns are prepared in advance, and various electric potentials are determined by comparing these reference values and the toner adhesion amount on each latent image pattern, respectively. There is. Further, as another potential control method, the electrostatic latent image potential of the latent image pattern and the toner adhesion amount after the pattern is visualized are measured using respective measuring means, and the measured data is used to measure the developing device. Development characteristics,
Obtaining the so-called development linear approximation formula by linear approximation,
A method has been presented in which the gradient of the linear approximation formula is used as the development efficiency, and various potentials are obtained from this development efficiency.

[0004]

In the above potential control method, it is difficult to properly set the above reference value, and in particular, when a developer having a large environmental change and a large temporal change is used, the above various potentials are controlled. The algorithm is complicated to avoid the influence of the environmental change and the temporal change of the developer, 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 approximate linear equation, it cannot be said that accuracy is sufficient with respect to fluctuations in the developer and the image carrier, and potential control is unstable. It is easy to become. 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, and in particular, the highlight portion of a full-color image lacks stability.

In addition, it is generally preferable that the visualized latent image pattern has a certain number (gradation) for obtaining the developing characteristics, but it is accompanied by the latent image pattern visualization. Since the toner consumption increases and a problem that it takes much time to form a pattern occurs, it cannot be formed frequently. For this reason, it was not possible to quickly respond to changes in the development characteristics until the next pattern formation.

According to the present invention, the above-mentioned drawbacks are remedied, and the toner consumption amount associated with the visualization of the latent image pattern is not increased.
Optimum for potential control method in image forming apparatus that can perform accurate potential control in a short time and is optimal for image reproduction against variation of developer, and image forming apparatus adopting this type of potential control method Another object of the present invention is to provide a toner replenishment control method for an image forming apparatus.

[0007]

To achieve the above object, the invention according to claim 1 forms an electrostatic latent image on an image carrier and develops the electrostatic latent image by a developing device. A potential control method in a forming apparatus, wherein a plurality of latent image patterns having different potentials from each other are formed on the image carrier, the potentials are measured by a potential measuring means, and the latent image pattern is visualized. The toner adhesion amount is measured by the toner adhesion amount measuring means, the developing characteristic of the developing device is calculated in the first cycle from the relationship between the measured potential and the toner adhesion amount, and further the The development characteristic is calculated in the second cycle in which the development characteristic measurement cycle with respect to the number of times of image formation is short, and the number of the plurality of latent image patterns is reduced, and the development characteristic obtained in the first cycle and the second cycle is calculated. Based on the development potential at the time of image formation A constant.

According to a second aspect of the present invention, there is provided a toner replenishment control method for an image forming apparatus which employs a potential control method for calculating a developing characteristic of the developing apparatus and determining a developing potential at the time of image formation of the image forming apparatus. The latent image pattern for calculating the second developing characteristic is formed for each image formation, and the toner replenishment control is performed by using the toner adhesion amount after the latent image pattern is visualized. It is what

According to a third aspect of the present invention, in the toner replenishment control method for an image forming apparatus according to the second aspect, the toner replenishment control condition is changed based on the development characteristic or the development characteristic and environmental condition. It is characterized by.

According to a fourth aspect of the present invention, in the toner replenishment control method for an image forming apparatus according to the third aspect, the toner replenishment control condition is that the development γ characteristic line has a large inclination.
When the absolute humidity is low, the toner concentration is changed so as to decrease, and conversely, when the inclination of the development γ characteristic line is small and the absolute humidity is high, the toner concentration is changed so as to increase. .

According to a fifth aspect of the present invention, in the toner replenishment control method for an image forming apparatus according to the fourth aspect, the toner replenishment control condition is based on the development characteristics calculated in the first and second measurement cycles. It is characterized in that it is changed based on the development potential at the time of image formation determined by the above.

[0012]

FIG. 2 is a schematic configuration diagram of an image forming apparatus to which the present invention can be applied. This image forming apparatus is an example of an electrophotographic image forming apparatus including a full-color copying machine. This copying machine has a printer unit 101 composed of an electrophotographic color image recording device and a color image reading device (hereinafter referred to as a color scanner) 102.
The color scanner 102 uses a light source 12 including an exposure lamp to expose an original on the original placing table 119 including contact glass.
0, and the reflected light image is reflected by the reflection mirrors 121 to 1
An image is formed on the color sensor 125 via the optical system including the image forming lens 23 and the image forming lens 124, and the color image information of the document is
For example, it is separated into blue, green, and red, read, and converted into an electrical image signal. The color sensor 125 converts the color image information of the original document into, for example, color separation means for each of blue, green, and red, and converts the image information of each color separated by the color separation means into an electric image signal. It is composed of a photoelectric conversion element composed of a CCD, and the same three colors are read. The blue, green, and red color-separated image signals obtained by the color sensor 125 are subjected to color conversion processing by an image processing unit (not shown) based on the intensity level thereof, and black (hereinafter referred to as BK) and cyan. (Hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) color image data.

The printer unit 101 forms visible images of BK, C, M and Y based on the color image data from the image processing unit to form a final color copy. Where BK,
Color scanner 1 for obtaining C, M, Y image data
Reference numeral 02 designates the operation of the printer unit 102 and a predetermined timing to move the exposure lamp 120 and the optical systems 121 to 123 to the left to scan the original document on the original document table 119, and to scan the original document every time the original document is scanned. Obtain image data for one color. By the color scanner 102 repeating such an operation four times in total, the image processing unit sequentially operates as BK, C,
Image data of four colors of M and Y are obtained. Then, every time image data of each color is obtained, the printer unit 102 sequentially forms a visible image by the image data and superposes them to form a four-color full-color image.

In the printer section 101, the image bearing member 103 composed of the photosensitive drum is stopped during non-image formation (during copy standby). Further, the photosensitive drum 103 is
During image formation (during copying), the main motor rotates and is uniformly charged by the charging unit 104 including a charging charger, and then black and cyan are generated by laser light irradiation by the exposing unit 105 including a laser optical system for each rotation. By sequentially performing image exposure of the color components of magenta, yellow, and yellow, electrostatic latent images of the color components are sequentially formed.

The laser optical system 105 converts the color image data from the image processing section into an optical signal and converts the color image data into an optical signal.
An electrostatic latent image is formed by performing optical writing corresponding to the image on the original document 3. The laser optical system 105 includes a laser, a light emission drive control unit that controls light emission drive of the laser, a polygon mirror, a motor that rotates the polygon mirror, an f / θ lens, a reflection mirror, and the like. It is driven by image data and emits light. The optical signal from this laser is deflected by a polygon mirror and then f / θ lens,
The photoconductor drum 103 is irradiated with the light via a reflection mirror.

The photosensitive drum 103 rotates counterclockwise as shown by the arrow in the figure. Around the photoconductor drum 103, a photoconductor cleaning device 112, a discharge lamp 113, a charging charger 104, and a BK developing device 1
06, a C developing device 107, an M developing device 108, a Y developing device 109, an optical reflection density sensor 208, an intermediate transfer belt 110, and the like are arranged. Each developing device 106-
Reference numeral 109 denotes developing sleeves 106a, 107a, 108 that rotate by bringing the brush of the developer into contact with the surface of the photosensitive drum 103 to develop the electrostatic latent image on the photosensitive drum 103.
a, 109a and developing paddles 106b, 107b, 108 that rotate to pump up and stir the developer inside
b, 109b and toner concentration sensors 106c, 107c, 108c, 109c for detecting the toner concentration of the developer.
It is composed of 4 developing devices 1 in the standby state
All of 06 to 109 are the developing sleeves 106a and 107.
The developer on a, 108a, and 109a is in the state of cutting off (development inoperative) state, and the order of each developing operation of the developing devices 106 to 109 (the order of forming each image of BK, C, M, and Y).
Is the order of developing the electrostatic latent image in the order of BK, C, M and Y. However, the order of image formation for each color is not limited to this, and may be any order.

At the start of the copying operation, the photosensitive drum 10
3 rotates and is uniformly charged by the charging charger 104. Then, the color scanner 102 starts the reading for obtaining the BK image data at a predetermined timing, the image processing unit obtains the BK image data from the image data from the color scanner 102, and the laser optical is obtained based on the BK image data. The system 105 performs optical writing on the photosensitive drum 103 with laser light to form a latent image. Hereinafter, the electrostatic latent image based on this BK image data is referred to as a BK latent image. C,
Similarly, the electrostatic latent image based on the M and Y image data is the C latent image,
These are called M latent image and Y latent image. In order to make this BK latent image developable from its tip, the developing sleeve 106a starts to rotate before the tip of the latent image reaches the developing position of the BK developing device 106, and the BK of the developer is raised. Develop the latent image with BK toner. After that, the developing operation of the BK latent image area on the photosensitive drum 103 is continued, but when the trailing edge of the latent image passes the BK developing position, the BK developing position is quickly changed to the developer chain on the developing sleeve 106a of 106. Cut off to make development inoperative. This is completed at least before the leading edge of the C latent image by the next C image data arrives. In addition,
The cutting of the developer in the direction of rotation of the developing sleeve 106a
It is performed by switching in the opposite direction to that during the developing operation. This time,
The other developing devices 107 to 109 remain in the non-developing state.

The BK toner image on the photosensitive drum 103 is
The image is transferred onto the surface of the intermediate transfer belt 110 that is driven at the same speed as the photosensitive drum 103 (hereinafter, the photosensitive drum 1
A toner image transfer from 03 to the intermediate transfer belt 110 is referred to as belt transfer). The belt transfer is performed by applying a predetermined bias voltage to the electrode 111 including the transfer bias roller that is in contact with the intermediate transfer belt 110 while the photosensitive drum 103 and the intermediate transfer belt 110 are in contact with each other. After the BK toner image is transferred, the photoconductor drum 103 is cleaned by the photoconductor cleaning device 112, discharged by the discharge lamp 113, and charged again by the charging charger 104. The intermediate transfer belt 110 is formed on the photosensitive drum 103 in the order of B
By sequentially aligning and transferring the K, C, M, and Y toner images on the same surface to form a belt transfer image of four colors, the belt transfer image is transferred to a transfer material as described later. Are collectively transferred to the transfer paper.

By the way, on the photosensitive drum 103 side, BK
After the image forming process, the process proceeds to the C image forming process. In this C image forming process, the color scanner 103 starts reading for obtaining C image data at a predetermined timing, and the color scanner 103
The image processing unit obtains C image data from the image data from the above, and based on the C image data, the laser optical system 105 performs optical writing on the photosensitive drum 103 with laser light to form a C latent image.

With respect to the developing position of the C developing device 107, the developing sleeve 107a starts rotating after the rear end of the previous BK latent image has passed and before the leading end of the C latent image arrives, and the developing agent is developed. The C latent image is developed with C toner. After that, the C developing device 107 continues to develop the C latent image area on the photosensitive drum 103, but when the rear end portion of the C latent image passes, the C developing sleeve is the same as in the case of the BK developing device 106. The ear of the developer on 107a is cut off. This is also completed before the next M latent image front end arrives.

The C toner image on the photosensitive drum 103 is transferred onto the surface of the intermediate transfer belt 110 which is driven at the same speed as the photosensitive drum 103. The photoconductor drum 110 is C
After the toner image is transferred, it is cleaned by the photoconductor cleaning device 112, discharged by the discharge lamp 113, and charged again by the charging charger 104.

On the side of the photosensitive drum 103, the C image forming process is followed by the M image forming process. In this M image forming process, the color scanner 103 starts reading for obtaining M image data at a predetermined timing, and the color scanner 103 The image processing unit obtains M image data from the image data from 102, and based on this M image data, the laser optical system 105 causes the photosensitive drum 1 to move.
An optical latent image is formed on the optical disc 03 by laser light writing.

At the developing position of the M developing device 108, the developing sleeve 108a starts to rotate after the rear end of the previous C latent image has passed and before the front end of the M latent image arrives, and the developing agent The M latent image is developed with M toner.
After that, the M developing device 108 continues to develop the M latent image area on the photoconductor drum 103, but at the time when the rear end portion of the M latent image passes, the M developing image is the same as the case of the C developing device 107. The developer is cut off from the sleeve 108a. This is also completed before the arrival of the leading edge of the next Y latent image. The M toner image on the photosensitive drum 103 is transferred to the surface of the intermediate transfer belt 110 that is driven at the same speed as the photosensitive drum 103. After the transfer of the M toner image, the photoconductor drum 103 is cleaned by the photoconductor cleaning device 112 and discharged by the charge removal lamp 113, and the charger 1
It is uniformly charged by 04.

On the side of the photosensitive drum 103, the M image forming process is followed by the Y image forming process. In this Y image forming process, the color scanner 102 starts reading for obtaining Y image data at a predetermined timing, and the color scanner The image processing unit obtains Y image data from the image data from 102, and based on the Y image data, the laser optical system 105 causes the photosensitive drum 1 to move.
Optical writing is performed by using a laser beam on 03 to form a Y latent image.

In the Y developing device 109, the developing sleeve 109a starts rotating after the rear end portion of the previous M latent image has passed and before the leading end of the Y latent image arrives at the developing position, so that the developer is developed. And the Y latent image is developed with Y toner.
After that, at the Y developing position 109, the development of the Y latent image area on the photosensitive drum 103 is continued, but at the time when the rear end of the Y latent image passes, the Y visible image is developed as in the case of the M developing device 108. The ear of the developer on the sleeve 109a is cut off. This is also completed before the trailing edge of the Y latent image arrives. The Y toner image on the photoconductor drum 103 is transferred onto the surface of the intermediate transfer belt 110 that is driven at the same speed as the photoconductor drum 103.

The intermediate transfer belt 110 is stretched around a driving roller 131, a belt transfer bias roller 111, and driven rollers 132 and 133, and a transfer bias voltage is applied from a power supply circuit via the belt transfer bias roller 111. Drive roller 13 driven by drive motor
1 is driven to rotate the intermediate transfer belt 110. The belt cleaning device 115 includes a rubber blade, a contact / separation mechanism for the intermediate transfer belt 110, and the like.
When the C image, the M image, and the Y image are transferred by the belt after transferring the BK image of the first color, the rubber blade is separated from the intermediate transfer belt 110 by the contact / separation mechanism.

The paper transfer bias roller 114 is usually separated from the intermediate transfer belt 110, and the intermediate transfer belt 1
When the four-color superposed images formed on the transfer sheet 10 are collectively transferred to the transfer sheet, they are pressed by the contact / separation mechanism at a certain timing to come into contact with the intermediate transfer belt 110, and a predetermined bias voltage is applied to the sheet transfer bias roller 114. Is applied from the power supply circuit to transfer the four-color superimposed image on the intermediate transfer belt 110 to the transfer paper passing between the paper transfer bias roller 114 and the intermediate transfer belt 110. (Below margin)

In this case, the transfer paper is fed from the paper feed device 134 consisting of the transfer paper cassette to the registration roller 136 by the paper feed roller 135, and the registration roller 136 transfers the transfer paper onto the intermediate transfer belt 110 with a four-color superimposed image. Paper is fed at the timing when the leading edge of the sheet arrives at the sheet transfer position.

The transfer paper on which the four-color superposed toner images are collectively transferred from the intermediate transfer belt 110 is conveyed to the fixing device 117 by a conveying device including a conveying belt, and the fixing device 1
Fixing roller 1 controlled to a predetermined temperature of 17
The toner image is fixed by heating / pressurizing by 17a and the pressing roller 117b, and is carried out to the paper discharge tray 118 as a full-color copy. The surface of the photoconductor drum 103 after the belt transfer is cleaned by the photoconductor cleaning device 112. At the time of repeat copying in which copying is continuously performed, the operation of the color scanner 102 and the image formation on the photosensitive drum 103 are started following the Y (fourth color) image forming process for the first sheet, and the second sheet is formed at a predetermined timing. B
Proceed to the K (first color) image formation process. In addition, the intermediate transfer belt 1
In step 10, the surface is cleaned by the cleaning device 115 following the step of transferring the four-color superimposed image to the first transfer sheet all at once, and the second BK toner image is belt-transferred thereto. Thereafter, the same operation as that of the first sheet is performed, and thereafter, the same operation is performed for each sheet.

FIG. 1 shows a control system incorporated in this copying machine. This control system is composed of a main control unit 201 and a plurality of peripheral control units. The main control unit 201 stores a main CPU 202, a ROM 203 storing control programs and various data, and various data temporarily as a work area. The RAM 204 and the I / O interface unit 205 for inputting / outputting data to / from each peripheral control unit and the like.

The main control unit 201 also controls the laser optical system control unit 20 via the I / O interface unit 205.
6, a power supply circuit 207, a reflection density sensor 208, toner density sensors 106c, 107c, 108c and 109c, an environment sensor 210, a surface potential sensor 211, a toner replenishing circuit 212, an intermediate transfer belt drive unit 213, etc. are connected. The laser optical system control unit 206 is the main CPU 202.
Control the laser optical system 105 based on the instruction from the main CPU 202, and the power supply circuit 207 applies a high voltage to the charging charger 104 based on the instruction from the main CPU 202 to apply the transfer bias voltage to the transfer bias roller 111 and the paper transfer bias roller 114. And developing rollers 106a, 10
A developing bias potential is applied to each of 7a, 108a, and 109a. The reflection density sensor 208 is the photosensitive drum 10.
The reflection density of the toner image on No. 3 is optically detected between the yellow developing device 109 and the intermediate transfer belt 110, and the environment sensor 210 detects temperature and humidity. Surface potential sensor 2
Reference numeral 11 detects the surface potential of the photosensitive drum 103 between the charging charger 104 and the black developing device 106.

The toner supply circuit 212 is the main CPU 20.
2 supplies magenta toner from the magenta toner replenishing section to the magenta developing device 108. Similarly, a plurality of toner replenishing circuits (not shown) are respectively provided in the main C
Based on an instruction from the PU 202, the black toner supply unit, the cyan toner supply unit, the yellow toner supply unit, the black developing device 106, the cyan developing device 107, and the yellow developing device 10
9 is replenished with black toner, cyan toner, and yellow toner. The intermediate transfer belt drive unit 213 drives the drive roller 131 based on an instruction from the CPU 202 to rotate the intermediate transfer belt 110.

FIGS. 3A and 3B show the main controller 20.
The electric potential control routine of 1 is shown. The potential control by the potential control routine of the present embodiment includes potential control a and potential control b. In the potential control a routine of the main control unit 201, in order to distinguish the power-on state from the time of abnormal processing such as jamming, an input signal from the fixing temperature sensor that detects the fixing temperature of the fixing device 117 in step 501 is input. Based on this, it is determined whether or not the fixing temperature of the fixing device 117 exceeds 100 ° C. If the fixing temperature of the fixing device 117 exceeds 100 ° C., it is determined to be abnormal and the potential control a is not performed. On the other hand, the potential control b is performed every time an image is formed. In the present embodiment, the potential control a is basically performed at the time of starting the apparatus, but it may be performed every time a predetermined number of copies is made or every fixed time.

The potential control (a) will be described below. When the fixing temperature of the fixing device 117 does not exceed 100 ° C., the main control unit 201 applies the reference potential as the developing bias potential to the developing roller 106a by the power supply circuit 207 in step 502 to apply the surface potential sensor 21.
The calibration value of 1 is performed, and the calibration value is used in the potential calculation thereafter. Next, the main control unit 201 determines V in step 503.
In the sg adjustment, from the reflection density sensor 208 to the photosensitive drum 1
The output value for the background portion of 03 is taken in and the reflection density sensor 208 adjusts the reflected light of the light emitted from the reflection density sensor 208 to the background portion of the photoconductor drum 103 to a constant value.
Adjust the light emission amount of.

Next, the main controller 201 forms a latent image pattern on the photosensitive drum 103 (step 50).
4). As shown in FIG. 4, electrostatic latent images (N electrostatic latent image patterns) 301, 302, 303, ... Rectangular latent image patterns 301, 302, 303 ... Which are formed at a predetermined interval along the rotation direction of the drum 103 and have, for example, 10 different gradation densities and 40 mm on each side.
Are formed at intervals of 10 mm, and in step 505 the output value of the surface potential sensor 211 with respect to the potentials of these electrostatic latent images 301, 302, 303 ...
Store in M204. Then, the main control unit 201
0 latent image patterns 301, 302, 303, ... are visualized on the photosensitive drum 103 in order at a predetermined interval for four colors of black, cyan, magenta, and yellow.

Next, the main controller 201 proceeds to step 5
In the P sensor detection of 06, the black developing device 106, the cyan developing device 107, the magenta developing device 108, and the yellow of the four color latent image patterns 301, 302, 303, ... The toner image of each color is developed by the developing device 109 and visualized, and the output value of the reflection density sensor 208 for the toner image of each color is stored in the RAM 204 as Vpi (i = 1 to N) for each color.

The main control unit 201 uniformly charges the photoconductor drum 103 by the charging charger 104 and changes the output of the laser optical system 105 via the laser optical system control unit 206 to change the latent image patterns 301, 302 ,. 303 ...
. Is formed to visualize the pattern, but the method is not limited to such a method, and the latent image pattern is visualized by switching the developing bias potentials of the developing devices 106 to 109 without operating the laser optical system 105. You may make it image.

Next, the main controller 201 proceeds to step 5
In the adhesion amount calculation step of 07, the RAM 204
The output value of the reflection density sensor 208 stored in the ROM 20 is stored in the ROM 20.
3 is referred to and converted into a toner adhesion amount per unit area and stored in the RAM 204. Then, steps 508 to 510 are executed. Hereinafter, these steps will be described in detail.

FIG. 5 is a plot of the relationship between the potential data obtained in step 505 and the toner adhesion amount data obtained in step 507 in each latent image pattern on the xy plane. The x-axis represents the potential potential (the difference between the developing bias potential V _B and the surface potential V _D of the photosensitive drum 103: V _B −V _D ) (unit V), and the y-axis represents the toner adhesion amount (mg) per unit area. / cm ² ) is shown. An infrared light reflection type sensor such as the optical reflection density sensor 208 of the present embodiment generally exhibits a saturation characteristic in a multi-adhesion portion having a large toner adhesion amount as shown in FIG. The value does not correspond to the actual toner adhesion amount. Therefore, if the toner adhesion amount is calculated using the detection value of the reflection density sensor 208 obtained at the multi-adhesion portion as it is, an adhesion amount different from the actual adhesion amount is obtained, and this toner adhesion amount is obtained. The toner replenishment control based on the amount cannot be accurately performed. Therefore, the main control unit 201 of the present embodiment determines, for each latent image pattern of each color, the potential of the latent image pattern obtained from the surface potential sensor 211 and the reflection density sensor 208 and the toner adhesion amount after the visualization. As will be described later, the data is selected only in the linear section of the relationship between the potential data Xn (n = 1 to 10) and the toner adhesion amount data Yn (development γ characteristic of the developing device), and the minimum value is selected for the data in this section. By applying the multiplication method, each developing device 106-1
The linear approximation of the development characteristic of No. 09 is performed by the method described later to obtain the approximate linear equation (E) of the development characteristic for each color, and the control potential is calculated for each color by the approximate linear equation (E). There is.

The following equation is used for the calculation of the least squares method. Xave = ΣXn / k (1) Yave = ΣYn / k (2) Sx = Σ (Xn-Xave) * (Xn-Xave) (3) Sy = Σ (Yn-Yave) * (Yn-Yave) ... (4) Sxy = Σ (Xn-Xave) * (Yn-Yave) ... (5) The potential of the latent image pattern obtained from the surface potential sensor 211 and the reflection density sensor 208. , The approximate linear equation (E) obtained from the data of the toner adhesion amount after visualization is Y = A1 * X +
When B1 is used, the coefficients A1 and B1 can be expressed as A1 = Sxy / Sx ... (6) B1 = Yave−A1 * Xave.

The correlation coefficient R of the approximate linear equation (E)
Can be expressed as R * R = (Sxy * Sxy) / (Sx * Sy) ... (8). In the present embodiment, the main control unit 201 is
In step 508, the surface potential sensor 21 is set for each color.
1 and the latent image pattern potential data Xn obtained from the reflection density sensor 208 and the toner adhesion amount data Y after visualization.
Five data sets (X1 to X5, Y from the youngest n value)
1 to Y5), (X2 to X6, Y2 to Y6), (X3 to X7, Y3
~ Y7), (X4 ~ X8, Y4 ~ Y8), (X5 ~ X9, Y5 ~
Y9), (X6 to X10, Y6 to Y10) are taken out, linear approximation calculation is performed according to the above-mentioned equations (1) to (8), and the correlation coefficient R is calculated to obtain the following six sets of approximate straight lines. Obtain equations and correlation coefficients (9)-(14).

Y11 = A11 * X + B11; R11 ... (9) Y12 = A12 * X + B12; R12 ... (10) Y13 = A13 * X + B13; R13 ... (11) Y14 = A14 * X + B14; R14. .. (12) Y15 = A15 * X + B15; R15 ... (13) Y16 = A16 * X + B16; R16 ... (14) The main control unit 201 calculates the phase from the obtained six sets of approximate linear equations. Approximate linear equation (E) is a set of approximate linear equations corresponding to the maximum value among relational numbers R11 to R16.
To choose as.

Next, the main controller 201 proceeds to step 5
09, the above-mentioned approximate linear equation (E) selected for each color
6, the value of X when the value of Y reaches the required maximum toner adhesion amount Mmax, that is, the value Vmax of the development potential is calculated. The developing bias potentials V _{B of the} black developing device 106, the cyan developing device 107, the magenta developing device 108, and the yellow developing device 109, and the photosensitive drum 1.
03 surface potential (exposure potential) V due to image exposure of each color
The _L given by the following equation from the above equation (15) (16), Vmax = (Mmax-B1) / A1 ··· (15) V B -V L = Vmax = (Mmax-B1) / A1 (16) The relationship between V _B and V _L can be expressed using the coefficient of the approximate linear method (E). Therefore, the equation (16) becomes Mmax = A1 * Vmax + B1 (17).

Here, the relationship between the charge potential V _D of the photosensitive drum 103 before exposure and the developing bias potential V _B is a linear equation as shown in FIG. 6, that is, Y = A2 * X + B2 ... (18) From the x-coordinate V _K (developing start voltage of the developing device) and the experimentally obtained background stain voltage V α, V _D −V _B = V _K + V α (19) Given.

[0045] Therefore, Vmax, V _D, V _B, the relationship of V _L is determined by (16) (19). In this example Vma
Using x as a reference value, the relationship between this and the control voltages V _D , V _B , and V _L is previously obtained by experiments or the like, and tabulated as shown in FIG. And
In step 510, the main control unit 201 selects the table having the Vmax closest to the calculated Vmax for each color, and sets the control voltages V _B , V _D , and _VL corresponding to the selected table as the target potentials. To do.

Next, the main controller 201 proceeds to step 5
At 11, the laser emission power of the laser optical system 105 is controlled via the laser optical system control unit 206 so that the maximum light amount is obtained, and the output value of the surface potential sensor 211 is taken in to detect the residual potential of the photosensitive drum 103. To do. Then, at step 512, when the residual potential is not 0, the target potentials V _B , V _D and _VL determined by the above table are corrected by the residual potential to obtain the target potential.
Finally, in step 513, the power supply circuit 207 is adjusted so that the charging potential by the charger 104 of the photosensitive drum 103 becomes the target potential V _D , and the laser in the laser optical system 105 is controlled via the laser optical system controller 206. The light emission power is adjusted so that the exposure potential of the photosensitive drum 103 becomes the target potential V _L , and the black developing device 106,
The power supply circuit 207 is adjusted so that the developing bias voltages of the cyan developing device 107, the magenta developing device 108, and the yellow developing device 109 respectively become the target potential V _B. Next, with respect to a predetermined number of potentials in the table centering on the target potentials of V _D and V _L (in this embodiment, two potentials obtained from the upper and lower tables centering on the target potential of interest) The remaining target potential is corrected to obtain the final target potential. Then, the charging charger grid voltage V _G applied to the charging charger 104 is changed so that the target potential of V _D is achieved, and adjustment is performed so that V _D becomes the target potential. Next, when V _D is obtained, the laser power is adjusted so as to achieve the target potential of V _L. Then, the charging charger grid voltage V _G and the adjustment value of the laser power obtained for a predetermined potential are stored in the RAM 204. This value is used in the next potential control b. Note that step 512 of FIG. 3A is a step for toner replenishment control according to an embodiment described later.

Next, the main controller 2 which is a feature of the present invention
The potential control b of 01 will be described with reference to FIG. In the latent image pattern formation in step 601, the photosensitive drum 103 as shown in FIG.
Of the electrostatic latent image patterns (N latent image patterns) 301, 302, 303 ...
Are formed along the rotation direction of the photosensitive drum 103 at predetermined intervals. In the potential control b of the present embodiment, three rectangular latent image patterns 301, 302, 303 having 40 mm on each side having different gradation densities are formed at intervals of 10 mm, and at step 602, these are formed. Latent image pattern 30
Surface potential sensor 21 for the potentials of 1, 302, 303
The output value of 1 is read and stored in the RAM 204. Then, the main control unit 201 causes the three latent image patterns 301,
302, 303 for black, cyan, magenta, and yellow 4
The color components are visualized on the photosensitive drum 103 sequentially at predetermined intervals.

What is important here is the potential (laser power) when forming a latent image pattern. This potential is a latent value obtained by appropriately dividing a linear section determined by the upper and lower limits of the potential data and the toner adhesion amount data used when the approximate linear equation was obtained from the development characteristics (see FIG. 5) obtained by the potential control a. It is desirable to set three potentials that form an image pattern, and this is a point to reduce the number of patches. Here, if it is difficult to calculate the straight line section, the target toner adhesion amount on the latent image pattern may be determined in advance by experiments after allowing some accuracy reduction.

Next, in the P sensor detection (detection by the reflection density sensor 208) in step 603, the photosensitive drum 1
03 latent image patterns 301, 302, 303 for four colors
The black developing device 106 and the cyan developing device 10 for each color.
7, magenta developing device 108, yellow developing device 109
To develop the image into a toner image of each color, and the reflection density sensor 208 for the toner image of each color
RAM2 with the output values of Vpi (i = 1 to N) for each color
04.

Next, in the toner adhesion amount detection in step 604, the output value of the reflection density sensor 208 stored in the RAM 204 in step 603 is referred to, and the toner adhesion amount M per unit area is referred to by referring to the table stored in the ROM 203. / A (mg / cm ² ) and then stored in the RAM 204.

FIG. 8 is a plot of the data in each patch of the potential data obtained in step 602 and the adhesion amount data obtained in step 604, plotted on the xy plane. The x-axis of FIG. 8 shows the potential, that is, the difference between the developing bias and the surface potential of the photosensitive drum 103: Vb-Vd (V), and the y-axis shows the toner adhesion amount M / A (mg) per unit area. / cm ² ) is shown.

In this potential control b, the pattern data obtained from the surface potential sensor 211 and the reflection density sensor 208 is in a substantially straight line section as shown in FIG. In step 605, a linear equation is obtained, and in step 606, the value of X at the required maximum toner adhesion amount Mmax, that is, the potential Vmax is calculated. In the potential control b of this embodiment, two points are selected from the three points of data and the following three linear equations are obtained. Y21 = A21 * X + B21 ... (20) Y22 = A22 * X + B22 ... (21) Y23 = A23 * X + B23 ... (22) X = Vmax = (Mmax-B1) / A1 ... (15) The processing of the potential control b of this embodiment is performed from the standpoint of correction of the potential control a, and the obtained value of Vmax may differ greatly from the value of Vmax obtained by the processing of the potential control a. , Vmax obtained by the potential control b is the potential control a
A straight line that has a value closest to Vmax obtained in step 3 is selected. Thus, for example, when a rapid change occurs due to a temporary image detection error or the like, it is possible to prevent the detection result at this time from being used as it is to obtain Vmax.

Here, in the potential control b of this embodiment, 3
Although the linear equation is calculated by selecting two points from the points, the method is not limited to such a method, and it is of course possible to calculate an approximate straight line or increase the number of patterns as described above. However, if the number is increased too much, a large amount of toner will be consumed in addition to the original image formation. Therefore, it is desirable to obtain the linear equation with as little data as possible.

Next, in step 607, the relationship between V _D , V _B , and V _L is stored in the ROM 203 in the form of a data table as shown in FIG. select a table having the closest Vmax to the calculated Vmax, determined control voltage V _B by the selected table, V _D, the V _L as the target potential.

Next, in step 608, step 60
The target potential obtained in 7 is set. Here, unlike the potential control a, the potential control b is performed every time an image is formed, so it is difficult in time to perform feedback control so that V _D and V _L reach the target values. Therefore, V for the three tables previously obtained by the processing of potential control a
_The adjustment value is determined by calculation from a linear approximation of the relationship between _{G 1} and the adjustment value of the laser power. In addition,
Step 608 of FIG. 3B is a step for toner replenishment control according to an embodiment described later. (Hereinafter, margin)

As described above, according to the potential control method of the present invention, a plurality of latent image patterns having different toner adhering amounts are formed on the photosensitive drum 103 and the potentials thereof are measured by the surface potential sensor 21.
1, the latent image pattern is visualized, and the toner adhesion amount is measured by the reflection density sensor 208. From the relationship between the measured potential and the toner adhesion amount, the developing characteristic of the developing device at the time of starting the device is the potential. It is calculated by control a.
Further, in the potential control b, the developing characteristic is calculated by reducing the number of the plurality of latent image patterns each time the image is formed after the apparatus is activated. Then, based on the development characteristics obtained by the potential control a and the potential control b, various potentials V _B , V _D , and _VL for determining the development potential at the time of image formation of the image forming apparatus including the copying machine are determined. The photoconductor drum 10
Since a smaller number of latent image patterns than the latent image patterns formed when the potential control a is calculated are formed on the surface 3, the number of latent image patterns formed by the potential control b is the same as that formed by the potential control a. Thus, the pattern formation time can be shortened, and the toner consumption associated with the pattern formation can be reduced as much as possible to accurately grasp the developing characteristics.

Moreover, the potential control b of this embodiment is performed from the standpoint of correcting the potential control a, and Vma obtained by the potential control a is calculated.
The value closest to the value of x is adopted. Thus, even if the detection result obtained by the potential control b changes abruptly due to a temporary image detection error or the like, erroneous potential control based on such a detection error can be prevented. Therefore, the developing characteristics can be accurately grasped, and the optimum image can be reproduced from the obtained developing characteristics.

In particular, in this embodiment, a plurality of sets of potential and toner adhesion amount data are obtained in the above measurement, and a section in which the relationship between the plurality of sets of potential and toner adhesion amount changes linearly is calculated. An approximate linear equation is obtained by linearly approximating the developing characteristic from the data of the measured electric potential and toner adhesion amount in the above, and this approximate linear equation is used as the developing characteristic. Therefore, the reflection density sensor 20 has a simple structure.
Even if the detection characteristic of 8 has nonlinearity, accurate potential control can be performed without being affected by this nonlinearity,
Optimal for image reproduction against changes in developer.

Also, assuming that A and B are coefficients, an approximate linear equation in the linear portion of the developing characteristic is Y = A * X + B, measured potential data is X, toner adhesion amount data is Y, and developing bias potential of the developing device. V _B, since the _{Mmax = a * Vmax + B V} B -V L = Vmax the relationship between the exposure potential V _L and the potential Vmax of the maximum amount of adhered toner Mmax is obtained in the potential control of the photosensitive drum 103, a developing bias potential V _B , photoconductor drum 10
The exposure potential V _L of 3 can be controlled with high accuracy.

Further, M (M ≦ N) is selected from the data of the potential and the toner adhesion amount of the N combinations obtained in the above measurement.
The correlation coefficient of each straight line is calculated with respect to the K straight lines obtained by applying the least squares method to the data of the set, and the section of the combination of the data in which the maximum value of the correlation function is obtained is the above section. Therefore, more accurate potential control can be performed.

Next, as in the above potential control method, it is applied to an image forming apparatus that employs a potential control method that calculates the developing characteristics of the developing device and determines various potentials during image formation in the image forming apparatus. An embodiment of the invention relating to the optimum toner replenishment control method will be described. In the potential control method according to the above-described embodiment, a plurality of latent image patterns having different toner adhesion amounts are formed, the potentials of the latent image patterns and the toner adhesion amount after the visualization are measured, and this measurement is performed. From the relationship between the potential and the data of the toner adhesion amount, the actual (at that time) developing characteristics of the developing device are calculated. Then, the power supply circuit 2 of the charger 104 is provided so that a desired maximum toner adhesion amount Mmax can be obtained and a desired background contamination margin voltage can be secured on the basis of the calculated developing characteristics.
07, the laser emission power of the laser optical system 105, the developing bias potential of each developing device, and the like are adjusted to control various potentials at the time of image formation. This development characteristic includes
Since the influence of the fluctuation of the developer, for example, the fluctuation of the charge amount (Q / M) of the developer (each of the carrier and the toner) is reflected, the charge amount of the developer approaches Even in the case of decreasing, a desired maximum toner adhesion amount Mmax can be obtained, and a good image can be formed in which a desired background stain margin voltage can be secured.

For example, the vertical axis represents the toner adhesion amount on the photoconductor drum 103 and the horizontal axis represents the potential on the photoconductor drum 103, and the approximate linear equation Y obtained in the first patch pattern formation is obtained. = A1 * X + B1, the second similar approximation linear equation shows Y = A2 * X + B2, and the third similar approximation linear equation shows Y = A3 * X + B3, so that the developing characteristic changes with time. When the developer approaches the end of its life, the charge amount of the developer decreases, and as a result, for example, the slope of the approximate linear equation gradually increases. Along with this, according to the approximated linear equation corresponding to the calculated developing characteristics, the desired maximum toner adhesion amount Mmax can be obtained, and the desired background stain margin voltage can be secured so that V _D ,
Since V _B and V _L are adjusted, for example, a desired image can be formed even under the developing characteristics in which the slope of the approximate linear equation is large.

However, as a toner replenishment control method in an image forming apparatus adopting such a potential control method,
A problem may occur if the conventional toner replenishment control method using a latent image pattern after visualization is used together. That is, in the conventionally known toner replenishment control method using a latent image pattern, a latent image pattern for detecting the toner adhesion amount is formed on the photosensitive drum 103, and the toner image is adhered when the pattern is visualized. The toner replenishment amount is controlled by judging the toner adhesion amount based on the magnitude of the reflection density. Potential potential that forms this latent image pattern (difference between the patch potential on the photosensitive drum 103 and the developing bias potential)
Is always kept constant. Therefore, as mentioned above,
When the developer is approaching the end of life and the charge amount (Q / M) of both the toner and the carrier decreases, and the developing characteristics change such that the slope of the approximate linear equation becomes large, the actual developer Even if the toner concentration is considerably low, a certain amount of toner adhesion can be obtained on the latent image pattern after visualization. Therefore, the amount of toner supplied according to the magnitude of the reflection density of the pattern after the visualization becomes smaller than the actual toner density, and the toner density decreases. This reduces the amount of toner attached to the carrier,
Direct contact of the carrier with the surface of the photoconductor drum 103 causes transfer to the photoconductor drum 103 side, which causes problems such as carrier adhesion.

Therefore, in the toner replenishment control method of the present embodiment, the toner replenishment condition is determined according to the developing characteristics calculated in the above potential control a and b.
A problem in toner replenishment control due to a change in developer is prevented. Hereinafter, the toner replenishment control method of this embodiment applied to the image forming apparatus adopting the potential control method shown in FIGS. 3A and 3B will be described.

When the image forming operation is started, the latent image pattern for the potential control b is formed at a constant interval from the rear end of the image on the photosensitive drum 103 under a predetermined image forming condition after the image formation. The surface potential sensor 21 is formed in the image area.
1, the surface potential Vp of the latent image pattern portion is measured, and Vp
A developing bias is applied during the development of the latent image pattern so that the development potential of the latent image pattern becomes constant based on the measurement result of 1. Then, the reflection density sensor 208 measures the reference reflection density Vsg of the background portion of the photosensitive drum 103 and the reflection density Vsp of the detection pattern portion. Note that the reference reflection density Vsg of the background portion is adjusted when the potential control a is executed in a state where there is no toner on the photosensitive drum 103 (in this embodiment, around 4V). Further, toner replenishment is performed based on the measurement result of the latent image pattern used for the potential control b. FIG. 9 shows an example of output characteristics of the reflection density sensor 208 applied to the apparatus of this embodiment. Characteristic line a indicates black toner, and characteristic line b indicates
The color toner is shown. This reflection density sensor 208
In the output characteristic of, the amount of reflected light increases and the output of the sensor 208, that is, the value of Vsp increases when the developing ability (toner density) is low and the toner adhesion amount on the pattern after visualization is small. On the contrary, when the developing ability is high and the toner adhesion amount on the pattern after visualization is large, the reflected light amount decreases and the value of Vsp also decreases. However, in the case of the color toner shown by the characteristic line b, when the toner adhesion amount becomes a predetermined amount or more, the reflected light from the toner surface increases and the characteristic gradually increases again.

Therefore, the preferable control level, that is, the specified value of the toner adhesion amount is roughly determined according to the output characteristic of the reflection density sensor 208. In this embodiment, the specified value of the black toner adhesion amount is 0.4 mg / cm ² , and the specified value of the amount of adhered color toner is 0.3 mg / cm ² . Therefore, from the development characteristics obtained by the potential control a, the black toner adhesion amount is 0.4 mg / cm ² , and the color toner adhesion amount is 0.3 mg / cm ² .
The latent image pattern of the development potential of / cm ² is included in one of the latent image patterns of the potential control b. For example, in the case of black toner, when the developing characteristic obtained by the potential control a is as shown in FIG. 5, the determination of the linear region and the developing potential of the three points of the latent image pattern when the toner adhesion amount becomes the above specified value. To decide. Black toner: V _0.4 = (0.4-B1) / A1 Color toner: V _0.3 = (0.3-B1) / A1 Then, for example, the toner adhesion amount is a specified value (0.3,0.
4, 0.5), the three development potential points that give such an adhesion amount are calculated by the approximate linear equation used in the potential control a process.
It becomes 10,142 (V). The above specified value is
The determination is not limited to the three points (0.3, 0.4, 0.5) and may be determined according to the following criteria. That is, the reflection density sensor 208
Is a range showing linearity, and includes a specified value of the adhesion amount of black toner and a specified value of the adhesion amount of color toner for determining the development potential, and more preferably 3 points are M / A. It may be determined so that the intervals are equal.

In the present embodiment, following the above-mentioned replenishment potential calculation, the Vb thus determined is applied to the developing sleeve to develop the patch pattern. The reflected light for the toner image on the developed patch pattern is detected by the reflection density sensor 208, and this potential is set to Vsp. The amount of reflected light in the toner non-developing area is obtained in advance as Vsg, and the toner replenishment amount is determined based on the ratio of Vsp and Vsg. Toner supply control is 0.4 mg / cm for black toner
² (0.3 mg / cm ^{2 for} color toner) based on the output of the reflection density sensor 208 when the latent image pattern when the development potential is 110 (V) is visualized Replenish toner. The replenishment amount at this time is determined by the ROM 20 based on the output of the reflection density sensor 208.
It is obtained as follows by referring to the data table stored in 3. Vsp / Vsg <A1 ---> Tona1 (mg) A1 <Vsp / Vsg <A2 ---> Tona2 (mg) A2 <Vsp / Vsg ---> Tona3 (mg) Actual toner replenishment time X (sec) Is the calculated toner supply amount Tadd (mg), and the toner supply motor supply capacity is K (mg / s
ec), X = Tadd / K, and Tona1 to 3 under the above conditions correspond to the calculated toner replenishment amount Tadd.

As a result, the pattern density after visualization, which is used for toner replenishment, is maintained within the range in which toner replenishment follows, but the developing capacity may differ even with the same toner concentration due to environmental changes over time. It is conceivable that the toner concentration gradually rises or falls outside the preferable concentration range (for example, 4 to 7 wt%).

In general, the inclination of the developing characteristic line has a property that it increases as the toner concentration increases and decreases as the absolute humidity decreases.

Therefore, in the present invention, in consideration of this property, from the development characteristics and the environmental characteristics so that the toner density is within a predetermined range, the inclination of the development characteristic line is large, and preferably, when the absolute humidity is low, Change the toner density so that the toner density increases, and if the slope of the development characteristic line is small and the absolute humidity is high, change the development potential of the latent image pattern used for toner replenishment control so that the toner density increases. To do. For example, as a result of the potential control a, when it is determined that the slope of the development characteristic line is large, and it is desirable that the absolute humidity is low, 0.4 mg of the potential control b is set according to the degree so that the toner concentration decreases. The development potential of the target latent image pattern is increased by several tens of volts. As a result, the toner adhesion amount on the latent image pattern increases, so that the toner replenishment amount is suppressed and the toner density decreases.

If the reflection density sensor 208 has the same sensitivity from the low adhesion amount region of the toner to the high adhesion amount region of the toner, it is based on the detected value even if the humidity sensor is not provided. Toner density and image density can be controlled. However, in general, the reflection density sensor has low sensitivity in the high adhesion amount region of the toner, so that the adhesion amount in the high adhesion amount region is predicted based on the detection value detected in the medium adhesion amount region. There is. Further, if there is a large change in environment such as temperature and humidity, especially a large change in humidity, it affects the charge amount (Q / M) of the toner, and the toner adhesion amount on the patch pattern portion changes.
This makes it difficult to predict. For this reason, it is preferable to use a sensor such as a humidity sensor that can detect environmental fluctuations in order to detect the toner adhesion amount in consideration of the absolute humidity condition, and it is advantageous to control the toner density and the image density. Often.

Here, when the environmental change cannot be detected because there is no sensor for detecting the environmental change,
The slope of the development characteristic line resulting from the potential control a, that is,
Depending on the selected potential control table number, when the slope of the development characteristic line is larger or smaller than a predetermined slope, the development potential of the latent image pattern used for the toner replenishment control of the potential control b is similarly set. When the slope of the development characteristic line is large, it is large, and when it is small, it is small. According to this, although the toner density fluctuation amount is slightly increased as compared with the case where the environmental fluctuation can be considered, it is possible to suppress the toner density range to some extent.

As described above, according to the toner replenishment control method of the present embodiment, when such control is normally performed, if the toner density changes until the next measurement of the developing characteristic, the image also changes only by the potential control a. On the other hand, since each potential is controlled by the potential control b that controls the potential every time an image is formed, it is possible to obtain a stable image by following a short range change such as a toner density change.

Particularly, in the toner replenishment control method of this embodiment, since the developing characteristics are directly detected in the apparatus,
The optimum image potential can be obtained, and the optimum toner density control condition can be determined. This can guarantee the best image at that time.
Further, as the developing characteristic, since the linear characteristic in the region where the relationship between the latent image potential on the photosensitive drum 103 and the toner adhesion amount shows the linear characteristic is used as the developing characteristic, stability of calculation accuracy can be obtained. In addition to being possible, the control routine can be simply constructed. Further, a reflection density sensor 20 for detecting the toner adhesion amount on the photoconductor drum 103.
Since 8 can be used for both calculation of developing characteristics and toner replenishment, the number of sensors can be minimized. This simplifies the structure and is very advantageous in terms of cost. In particular, when the full color system is configured, it is not necessary to provide a sensor for controlling the toner density for each color of the toner density control, which is very advantageous.

In the toner replenishment control method of this embodiment, the developing bias at the time of forming the latent image pattern is calculated as the developing characteristic (affected by the characteristic variation of the developer).
On the assumption, 0.4 mg / cm ² in the case of black toner, because in the case of color toner to correct such amount of deposition of 0.3 mg / cm ² is obtained, the toner concentration back to the lower limit of the allowable range Even when it approaches, a certain amount of toner adhesion to the pattern is obtained. For this reason, the toner replenishment amount becomes small in spite of the actual toner concentration, and the toner concentration may be excessively lowered. However, such a fear may be caused by various known techniques for securing an optimum toner replenishment amount, for example, predicting the toner consumption amount by using image data, and referencing the predicted toner consumption amount when setting the toner replenishment amount. It can be eliminated by using the same technology. Needless to say, such a technique is also used in the device of this embodiment. (Hereinafter, margin)

[0076]

According to the invention described in claim 1, there is provided a potential control method in an image forming apparatus for forming an electrostatic latent image on an image carrier and developing the electrostatic latent image by a developing device.
A plurality of latent image patterns having different potentials are formed on the image carrier, the potentials are measured by the potential measuring means, and the latent image patterns are visualized to measure the toner adhesion amount by the toner adhesion amount measuring means. Then, the developing characteristic of the developing device is calculated in the first cycle from the relationship between the measured potential and the toner adhesion amount, and the developing characteristic measuring cycle with respect to the number of image forming times is shorter than the first cycle. Of the plurality of latent image pattern formation times, the development characteristics are calculated, and the development potential at the time of image formation is determined based on the development characteristics obtained in the first cycle and the second cycle. There is. Therefore, since a latent image pattern smaller in number than the latent image patterns formed in the first cycle is formed on the image carrier, the latent image formed in the first cycle in the second cycle is formed. The pattern formation time can be shortened as compared with the case where the same number of patterns as the number of patterns are formed, and the toner consumption due to pattern visualization can be minimized to accurately grasp the developing characteristics. . Therefore, it is possible to accurately control various potentials, and it is most suitable for image reproduction against the fluctuation of the developer.

In particular, according to the second aspect of the invention, the image forming method according to the second aspect employs a potential control method for calculating the developing characteristic of the developing device to determine the developing potential of the image forming device during image formation. In a toner replenishment control method for an apparatus, toner replenishment control is performed based on data of toner adhesion amount after visualization of a latent image pattern formed for each image forming operation in order to calculate development characteristics in the second measurement cycle. Therefore, it is possible to obtain the optimum image potential by following the change in the developing characteristic due to the change in the toner density, and by determining the optimum toner density control condition,
The best image at that time can be guaranteed.

According to the third aspect of the invention, in the toner replenishment control method for the image forming apparatus according to the second aspect, the toner replenishment control condition is based on the developing characteristic or the developing characteristic and environmental condition. Since the change is made, even if the environmental change of the developer occurs, the toner replenishment control is performed following the change, and a stable image can be obtained.

In particular, according to the invention described in claim 4, in the toner replenishment control method in the image forming apparatus according to claim 3, the toner replenishment control condition is that the slope of the development γ characteristic line is large and the absolute humidity is low. Sometimes, the toner concentration is changed so as to decrease, and conversely, when the inclination of the development γ characteristic line is small and the absolute humidity is high, the toner concentration is changed so as to increase, so that the toner concentration is kept within a desired concentration range. It is possible to always obtain a stable image.

In particular, according to the invention described in claim 5, in the toner replenishment control method in the image forming apparatus according to claim 4, as the toner replenishment control condition, the development obtained in the first and second measurement cycles is performed. Since the development potential at the time of image formation determined based on the characteristics is used, for example, the development bias voltage, which is relatively easy to control, can be controlled, so that the toner replenishment control condition can be easily changed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus to which the present invention can be applied.

FIG. 2 is a cross-sectional view showing a mechanism portion of the same example.

FIG. 3 is a flowchart showing a flow of potential control (a) and (b) of the same example.

FIG. 4 is a developed view showing a photosensitive drum and a patch pattern of the same example.

FIG. 5 is a characteristic diagram showing the relationship between the surface potential of the photosensitive drum and the toner adhesion amount in the same example.

FIG. 6 is a diagram showing a relationship between an approximate straight line and a control potential in the same example.

FIG. 7 is a diagram showing a table of the same example.

FIG. 8 is an explanatory diagram of toner supply control in potential control (b) of the same example.

FIG. 9 is an output characteristic diagram of the reflection density sensor of the same example.

[Explanation of symbols]

 103 Photoreceptor Drum 108 Developing Device 201 Main Control Unit 208 Optical Reflection Density Sensor 211 Surface Potential Sensor

Claims (5)

[Claims] 1. A potential control method in an image forming apparatus, wherein an electrostatic latent image is formed on an image carrier, and the electrostatic latent image is developed by a developing device. A plurality of different latent image patterns are formed, the potentials thereof are measured by the potential measuring means, the latent image patterns are visualized, and the toner adhesion amount is measured by the toner adhesion amount measuring means. The developing characteristic of the developing device is calculated from the relationship with the toner adhesion amount in the first cycle, and the developing characteristic measuring cycle with respect to the number of image formation is shorter than the first cycle in the second cycle, and The image forming apparatus is characterized in that the developing characteristic is calculated by reducing the number of latent image patterns of the image forming apparatus, and the developing potential at the time of image formation is determined based on the developing characteristic obtained in the first cycle and the second cycle. Potential control method in. 2. A toner replenishment control method for an image forming apparatus, which employs the potential control method for an image forming apparatus according to claim 1, wherein a latent image pattern for calculating the second developing characteristic is formed for each image formation. A toner replenishment control method for an image forming apparatus, wherein the toner replenishment control is performed by using the toner adhesion amount after the latent image pattern is visualized. 3. The toner replenishment control method for an image forming apparatus according to claim 2, wherein the toner replenishment control condition is changed based on the developing characteristic or the developing characteristic and environmental condition. 4. The toner replenishment control condition is changed so that the toner density decreases when the slope of the development γ characteristic line is large and the absolute humidity is low, and conversely, the slope of the development γ characteristic line is small and the absolute humidity is low. 4. The toner replenishment control method for an image forming apparatus according to claim 3, wherein the toner density is changed to increase when is high. 5. The toner replenishment control condition is changed based on the development potential at the time of image formation, which is determined based on the development characteristics calculated in the first and second measurement cycles. Item 4. A toner supply control method for an image forming apparatus according to item 4.