JP3179936B2 - Image density control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control device for controlling an image density in an electrophotographic process.

[0002]

2. Description of the Related Art With the rapid progress of OA, there is a strong demand for a copying machine, a printer, and a facsimile capable of obtaining high-quality image quality. Under such demands, the density of the copied image has been measured and compared with a preset reference density signal to control the image density so that an image with a constant density is always realized. ing. For example, JP-A-4-
No. 85602 has a high density reference density patch and a low density reference density patch. First, these reference density patches are projected onto a charged photoconductor to form a latent image of the reference density patch. Is made a visible image by a developing means and its density is detected. Then, the control input change direction is determined by using a qualitative model of the electrophotographic process by comparing with a preset reference density signal, and the control is repeatedly performed until the detected density becomes equal to the reference density signal. As a result, an image having a constant density was always obtained.

[0003]

However, in such a conventional image density control device, only a qualitative control input change direction is determined, and a quantitative control input change amount is given at regular intervals. Therefore, when this method is implemented, there is a problem that it takes a large number of times to repeat the control until the output density becomes equal to the reference density signal.

An object of the present invention is to provide an image density control apparatus capable of obtaining an image of a constant density with a small number of control repetitions in view of the above-mentioned conventional problems.

[0005]

An image density control apparatus according to the present invention comprises a charging means for charging a photosensitive member of an electrophotographic process to a predetermined charging voltage, and a method for projecting a document on a document table with a predetermined exposure amount. Exposure means for forming a latent image on the photoreceptor, developing means for developing the latent image with a developer set to a predetermined developing bias voltage to produce a visible image, and at least one reference provided on a platen A density patch, density detection means for charging, exposing and developing the reference density patch to detect the output density of a visible image created on the photoreceptor; and an output density of the density detection means and a preset target density. Error calculating means for calculating an error, charging voltage by multiplying the output of the error calculating means by a change amount conversion function to calculate a change amount of the exposure amount, and a change amount calculating means for calculating the change amount of the exposure amount; Change amount and change amount of exposure amount A set value updating unit for adding to the electric voltage and the exposure amount; and a function updating unit for updating the change amount conversion function according to the updated charging voltage and the exposure amount after the set value updating unit updates the charging voltage and the exposure amount. , The function updating means, by experiment, charging voltage, charging voltage according to the exposure amount,
It is provided with storage means for a change amount conversion function set in advance by obtaining the relationship between the change amount of the exposure amount and the change amount of the output density, and means for selecting the change amount conversion function according to the updated charging voltage and exposure amount. It is characterized by having.

The function updating means includes a storage means for storing a reference change amount conversion function represented by at least one preset parameter, and a charging voltage based on the updated charging voltage, exposure amount and developing bias voltage. Change rate calculating means for calculating a change rate of the change amount of the output density with respect to the change amount of the exposure amount and the change amount of the exposure amount, and calculating a change rate of the parameter based on the change rate of the change amount; A change amount conversion function calculating means for calculating a change amount conversion function based on an output of the rate calculating means.

[0007]

According to the present invention, the quantitative change amount of the control input is determined from the output of the error calculating means by the change amount conversion function, and after the updating by the function updating means according to the characteristic fluctuation of the electrophotographic process. Based on the charging voltage and the exposure amount, a change amount conversion function according to the current characteristic fluctuation is selected, or the characteristic fluctuation of the process is estimated based on the updated charging voltage and the exposure amount, and the characteristic fluctuation is estimated. The change rate of the change amount conversion function is calculated, the change amount conversion function is calculated based on the change rate and the reference change rate conversion function, or the output of the error sign detection means for detecting the sign of the output of the error calculation means. By using the history to correct the change amount conversion function so as to approach the optimum change amount conversion function, even if the characteristics of the electrophotographic process fluctuate due to environmental changes, the output density can be reduced with a small number of control repetitions. Standard It can be equal to the degree signal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image density control apparatus according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of an image density control device according to a first embodiment of the present invention. In FIG. 1, 100 is a charging corotron, 102 is an exposure subsystem, 104 is a development subsystem, 106 is a photoreceptor, 108 is toner, 11
0 is a document, 112 is a density detector, 114 is a high density reference density patch, 116 is a low density reference density patch, 118
Are the toner images for the high density reference density patch 114;
Reference numeral 20 denotes a toner image corresponding to the low-density reference density patch 116, and reference numeral 122 denotes a document table.

Reference numeral 200 denotes an image control unit, 202 denotes an error detector, 204 denotes a control end inspection unit, 206 denotes a change amount calculator,
208 is a control input update unit, 210 is a control input generation unit, 2
12 is a change amount conversion function storage unit, 214 is a change amount conversion function selection unit, and 216 is a change amount conversion function update unit.

Next, the operation will be described. First, the operation of the electrophotographic process will be described. The photoreceptor 106 receives the inflow current Id by the charging corotron 100 and is charged to the initial surface potential V0. Next, an image of the document 110 is formed on the photoreceptor 106 via the illumination and imaging optical system in the exposure subsystem 102. The effective light energy E _IM corresponding to the image density D _IM in this case the image portion, the effective light energy E _BG corresponding to the density in the background portion (the background portion) D _BG is applied respectively to the photoreceptor 106. The surface potential of the photoreceptor 106, which was uniformly V0 before exposure, is attenuated by receiving the effective light energy corresponding to the document density, and reaches V _IM ,
It is _{VBG in the} background. Toner concentration T _C such a developing device of various configuration parameters of the toner 108 (sleeve rotational speed, the sleeve and the distance between the photosensitive member 106, magnetization pattern, a bias such as a voltage V _BIAS) photoreceptor from 106
The toner amount corresponding to the surface potential of the photosensitive member 10 is developed.
6 adheres to the surface. At the same time, a toner image 118 is formed on the high density reference density patch 114,
For the low density reference density patch 116, the toner image 12
0 is formed.

Next, a density detector 112 detects the densities of the toner images of the high-density and low-density reference density patches, and an error detector 202 sets the detected values to a reference high density signal and a reference low density signal, respectively. The high density error signal and the low density error signal are calculated by comparing with the density signal. The change amount calculator 206 calculates the change amount of the charging voltage and the exposure amount such that the error signal becomes 0 based on the high density error signal and the low density error signal and the change amount conversion function of the change amount conversion function update unit 216. The control voltage updating unit 208 adds the charging voltage and the amount of change in the exposure amount calculated by the change amount calculator 206 to the charging voltage and the amount of exposure, which are the previous control inputs, respectively. Update the exposure. Then, the control input generation unit 210 generates inputs of the charging corotron and the exposure subsystem based on the charging voltage and the exposure amount updated by the control input updating unit 208.

The change amount conversion function storage unit 212 stores a plurality of preset change amount conversion functions, and the change amount conversion function selection unit 214 stores the change amount conversion function storage unit 21.
Control input update unit 20 from the plurality of change amount conversion functions
The optimum change amount conversion function is selected based on the charging voltage and the exposure amount updated in step 8. The change amount conversion function update unit 216 updates the change amount conversion function with the change amount conversion function selected by the change amount conversion function selection unit 214.

The above operation realizes an image having a density equal to the reference density. A control end inspection unit 204 is provided between the error detection unit 202 and the change amount calculator 206, and the high density error signal and the low density error signal output from the error detection unit 202 are approximately zero. In some cases, it is determined that a desired image has been obtained, and the control operation is terminated.

The basic operation up to the development of the electrophotographic process will be described below in detail. In the electrophotographic process, a toner image is formed on the photoconductor 106 through three sub-processes, a charging sub-process, an exposure sub-process, and a developing sub-process. Assuming that the image density of the original 110 is the input image density D _IM and the corresponding density D _S of the toner image on the photoconductor 106 is the output image density, the relationship between the two is as follows when the input image is a solid image. Can be expressed.

[0016]

(Equation 1)

[0017]

(Equation 2)

[0018]

(Equation 3)

Here, S is the sensitivity of the photoreceptor 106,
γ _S is a constant determined by each parameter of the development sub-process 104, the physical property and the degree of deterioration of the toner 108, the film thickness and the dielectric constant of the photoconductor 106, and V _BIAS is a development bias voltage. Further, the photosensitive member surface potential V _DDP, the effective light energy E _BG is an adjustable parameter, it is possible to adjust the value of the output image density D _S with respect to the input image density D _IM By adjusting these . Although the photoconductor surface potential V _DDP cannot be directly operated, it can be indirectly operated by manipulating the inflow current Id from the charging corotron 100.

The relationship between the input image density D _IM and the output image density D _S, from Equation 1 through (3),

[0021]

(Equation 4)

## EQU2 ## The equation is obtained as shown in the measured density characteristic curve shown in FIG. The purpose of the image control is to match this measured density characteristic curve with the desired target density characteristic curve.

Therefore, if the functions (Equation 1) to (Equation 3) representing the characteristics of the electrophotographic process can be quantitatively determined by experiments or the like, the adjustable parameters V _DDP and E _BG satisfying the purpose can be determined. it can.

However, the photoreceptor sensitivity S in (Equation 2) is a parameter that changes depending on the environmental temperature, humidity, deterioration degree, and the like, and the development constant γ _{S in} (Equation 3) also indicates the environmental temperature, humidity, physical properties and deterioration of the toner. It is a parameter that changes depending on the degree, the thickness of the photoconductor, and the dielectric constant.

Therefore, in the method of performing control based on a function representing input / output characteristics in which an adjustable parameter of an electrophotographic process obtained by an experiment or the like in an initial environment and an initial process state is obtained as an input and an output image density is output, the environment and the method are controlled. Good control performance can be obtained when the process state does not change from the beginning, but when the input and output characteristics change due to changes in the photoconductor sensitivity S and development constant γs due to changes in the environment and the process state, the control performance is improved. Deteriorates.

Therefore, a plurality of environments and process states are set in advance, and a function representing the input / output characteristics for each environment is obtained by an experiment or the like. Is selected, and control is performed based on the selected value, so that good control performance can always be maintained.

Hereinafter, the operation of the image control unit 200 will be described in detail.

Now, the control input generation unit 210 controls the input composed of the photosensitive member surface potential V _DDP and the effective light energy E _BG which are the inputs to the electrophotographic process.

[0029]

(Equation 5)

Assume that the k-th trial is performed based on The electrophotographic process is performed by the density detector 1 by the control input X (k).
12 by the output consists of a concentration D _S _l concentration D _S _h the low concentration portion of the high density portion detected

[0031]

(Equation 6)

It is assumed that the above is realized. At this time, the control input update unit 208 stores the control input X (k) input to the electrophotographic process by the control input generation unit 210 in the k-th trial as the reference control input Xold. Before the first trial (initial state), the initial control input Xini is given to the reference control input Xold and stored.

The change amount conversion function storage unit 212 sets a plurality of environments and process states and obtains a change amount conversion function corresponding to each environment and process state obtained by experiments and the like.
Control inputs for matching the output image density to the reference image density in each environment are stored. Here, the environment and the process state to be set are set so that the control input for matching the output image density to the reference density changes variously. The details will be described below. For setting a plurality of environments and process states, each environment and process state is denoted by i (i = 1, 2,
3 ...).

Now, an environment and a process state represented by i are set, and an amount of change in output with respect to a change in input in the environment of i.

[0035]

(Equation 7)

Is obtained by an experiment, and then the inverse function of the output change amount with respect to the input change is obtained, whereby the change amount conversion function is obtained as follows.

[0037]

(Equation 8)

The values ai, bi, ci, and di in (Expression 8) vary depending on the output density. ai and ci are empirical formulas:

[0039]

(Equation 9)

[0040]

(Equation 10)

Is a function of high density. And bi and di are

[0042]

[Equation 11]

[0043]

(Equation 12)

Is a function of the low density. Also, the environment of i,
Control input to match high and low density output to target output in process state

[0045]

(Equation 13)

Is stored. The environment and the process state i are variously changed and set, and an experiment is performed to match many high-density and low-density outputs to the target output (Equation 1).
A change amount conversion function represented by (Equation 8) corresponding to the control input of 3) is obtained.

Next, in the change amount conversion function selection unit 214,
The control input X (k) input to the electrophotographic process by the control input generation unit 210 and the density output in a plurality of i environments and process states stored in the change amount conversion function storage unit 212 are matched with the target output (number 13) the control input Xi represented by

[0048]

[Equation 14]

Based on the comparison. In (Equation 14), E
_BGMIN , E _BGMAX , V _DDPMIN , and V _DDPMAX are respectively a preset lower limit of exposure amount, an upper limit of exposure amount, a lower limit of charging voltage, and an upper limit of charging voltage. Since the control input Xi that minimizes the evaluation function (Equation 14) is close to the control input X (k), the change amount conversion function in the i environment corresponding to the control input Xi is calculated as the change at the k-th control. Select as a quantity conversion function.

The change amount conversion function update unit 216 updates the change amount conversion function with the change amount conversion function selected by the change amount conversion function selection unit 214.

Next, the error detector 202, an output vector Y, and the reference high density signal D _S _hd a desired value of the two concentrations, the reference comprised a reference output from the at low concentration signal D _S _ld _Yd and the error signal

[0052]

(Equation 15)

Is output.

Next, in the change amount calculator 206, e (k), which is the output of the error detector 202, and the change amount conversion function updating unit 2
Change amount conversion function which is the output of 16

[0055]

(Equation 16)

By multiplying by (Equation 17), the control input change amount

[0057]

[Equation 17]

Is output.

Then, the control input updating unit 208 adds the input change △ X (k + 1) to the reference input vector Xold, and
k + 1th control input

[0060]

(Equation 18)

The control input generation unit 210 creates
This input is given to the electrophotographic process and the same operation is repeated.

The error detector 202 and the change amount calculator 2
Between 06, the control end checker 204 is installed,
If the output of the error detector 202 is approximately 0, it is determined that a desired image has been obtained, and the learning operation ends.

As a result, even when the environment and the process state change, and the input / output characteristics change, the environment and the process state are set in advance so that the control input for matching the output image density to the reference density changes variously. Maintains good control performance by selecting the optimal change conversion function based on the control input and the evaluation function from among the multiple change conversion functions corresponding to the environment and process state obtained by experiments be able to.

Next, if the second embodiment as with changes in environmental and process conditions (Equation 1) through (3) change in photoconductor sensitivity S and developing constant gamma _S of the present invention occurs, electrophotographic process by estimating the function representing the characteristics (number 1) to the photoconductor sensitivity S and based (number 3) changes in developing constant gamma _S, we obtain the change in the function representing the input-output characteristics, obtained by experiments or the like initially Provided is an image density control device capable of always maintaining good control performance by performing control based on a function representing input / output characteristics and a change in a function representing input / output characteristics.

Hereinafter, an image density control apparatus according to a second embodiment of the present invention will be described with reference to FIG.

In FIG. 3, reference numeral 100 denotes a charged corotron;
102 is an exposure subsystem, 104 is a development subsystem, 106 is a photoconductor, 108 is toner, 110 is a document,
114 is a high density reference density patch, 116 is a low density reference density patch, and 118 is a high density reference density patch 114
Image 120 is a low density reference density patch 1
Reference numeral 16 denotes a toner image, 122 denotes a document table, 126 denotes a high density detector, 128 denotes a low density detector, 300 denotes an image control unit, 202 denotes an error detector, and 204 denotes a control end inspection unit.
06 is a change amount calculator, 208 is a control input update unit, 210
Denotes a control input generation unit, 302 denotes a reference change amount conversion function storage unit, 304 denotes a change rate calculation unit, 306 denotes a change amount conversion function calculation unit, and 216 denotes a change amount conversion function update unit. Components that perform the same operations as in the first embodiment are given the same reference numerals as in the first embodiment.

Next, the operation of the image density control device having the above configuration will be described. First, the operation of the electrophotographic process is the same as that of the first embodiment. However, in this embodiment, the image control unit 200 is replaced by the image control unit 300, and the control input generation unit 210 and the change amount conversion function update are accordingly performed. A change rate calculation unit 304 is provided between the units 216, and a reference change amount conversion unit that stores one reference change amount conversion function instead of the change amount conversion function storage unit 212 that stores a plurality of change amount conversion functions. A function storage unit 302 is provided, and a change amount conversion function calculation unit 306 is provided instead of the change amount conversion function selection unit 214.

Hereinafter, only the points different from the first embodiment will be described. The reference change amount conversion function storage unit 302 stores one reference change amount conversion function obtained by an experiment or the like in an initial state as a matrix. Output change with respect to input change

[0069]

[Equation 19]

Is obtained by experiments or the like, and then the inverse function of the amount of change in output with respect to the change in input is obtained, whereby the reference change amount conversion function is obtained experimentally as follows.

[0071]

(Equation 20)

A ₀ , b ₀ , c ₀ , and d ₀ in (Equation 20) are:
It changes depending on the output density. a ₀ and c ₀ are

[0073]

(Equation 21)

[0074]

(Equation 22)

As described above, it becomes a function of the output of high density. Also, b ₀ and d ₀ are

[0076]

(Equation 23)

[0077]

(Equation 24)

As described above, it becomes a function of the output of low density. Then, a control input to match the high and low density outputs to the target output in the initial state

[0079]

(Equation 25)

Is stored.

Next, in the change rate calculating section 304, the control input X input by the control input generating section 210 to the electrophotographic process is output.
From (k) and the density Ds_h of the high-density part and the density Ds_l of the low-density part detected by the density detector 112, the change of the change amount conversion function from the reference change amount conversion function in the initial state is calculated.

Hereinafter, the operation of the change rate calculating section 304 will be described in detail. The control inputs E _BG0 and V _DDP0 that match the high-density and low-density outputs to the target output in the initial state stored in the reference change amount conversion function storage unit 302 and the density D _{IM — l} of the low-density reference density patch 114 and each relationship reference value D _S _ld and D _S _hd corresponding output image density to the density D _IM _h high density of the reference density patch 116 from equation (1) through (3),

[0083]

(Equation 26)

[0084]

[Equation 27]

## EQU10 ## From (Equation 26) and (Equation 27), the estimated value of the photoconductor sensitivity in the initial state

[0086]

[Equation 28]

The estimated value of the development constant in the initial state is obtained from (Equation 26), (Equation 27) and (Equation 28).

[0088]

(Equation 29)

Is required. By the way, each element of the matrix of the output change amount with respect to the input change expressed by (Equation 19) is obtained by partially differentiating (Equation 26) and (Equation 27) with E _BG or V _DDP as follows. Is represented by

By partially differentiating (Equation 26) with E _BG ,

[0091]

[Equation 30]

By partially differentiating ( _Equation 26) with V _DDP ,

[0093]

(Equation 31)

Similarly, by partially differentiating (Equation 27) with E _BG ,

[0095]

(Equation 32)

Similarly, by partially differentiating ( _Equation 27) with V _DDP ,

[0097]

[Equation 33]

Is obtained. Here, (Equation 28), (Equation 29)
Photoconductor sensitivity estimate of the initial state S and ₀ _ _E and developing a constant estimated value gamma] s ₀ _ _E obtained, the control input E _BG0 and V
By substituting _DDP0 by equation (29) (number 30) (number 31) (number 32) (number 33), the estimated value A ₀ _ _E of change in the output relative to change in the input in the initial state is determined , The inverse function, the estimated value of the initial state change amount conversion function

[0099]

(Equation 34)

Is obtained.

On the other hand, the control input (Equation 5) input to the electrophotographic process by the control input generation unit 210 and the density detector 11
The relation of the output (Equation 6) detected by Equation (2) is (Equation 1)
~ (Equation 3)

[0102]

(Equation 35)

[0103]

[Equation 36]

Is obtained. From (Equation 35) and (Equation 36), k
Estimated value of photoconductor sensitivity at the time of the second control

[0105]

(37)

The estimated value of the development constant at the time of the k-th control is obtained from (Equation 35), (Equation 36) and (Equation 37).

[0107]

(38)

Is obtained. (Equation 37) The estimated value of the photoconductor sensitivity and the estimated value of the development constant at the k-th control obtained by (Equation 37) and (Equation 29) (Equation 30) (Equation 31) (Equation 3)
By 2) (number 33), the estimated value of the variation of the output to a change in k-th control time of the input A_ _E (k) is determined, by determining the inverse function of the change amount conversion function at the time of a k-th control Estimate

[0109]

[Equation 39]

Is obtained. From (Equation 34) and (Equation 39), the rate of change of the initial state of the change amount conversion function during the k-th control from the reference change amount conversion function

[0111]

(Equation 40)

Is obtained.

Next, the change amount conversion function calculation unit 306
The rate of change (equation 40) of the change amount conversion function at the time of the k-th control calculated by the change rate calculation unit 304 from the reference change amount conversion function in the initial state, and the reference change amount conversion function (equation 20) in the initial state ) To the change amount conversion function at the time of the k-th control based on (Equation 41).

[0114]

[Equation 41]

Is calculated.

As a result, a function (Equation 1) representing the characteristics of the electrophotographic process according to changes in the environment and the process state
~ Photoconductor sensitivity S and developing constant gamma _S is changed in the equation (3), even if the input-output characteristics change, and adapt to changes to update the change amount conversion function, always good by performing control based thereon Control performance can be maintained. In addition, since only one reference change amount conversion function as a reference is obtained in the initial state, it is unnecessary to perform many experiments.

Next, an image density control apparatus according to a third embodiment of the present invention will be described. The purpose of the third embodiment is to improve the control performance by modifying the change amount conversion function at the time of the k-th control using the history information when the output density does not match the reference density in the control before the k-th control. It is to improve.

Hereinafter, an image density control apparatus according to a third embodiment of the present invention will be described with reference to FIG. 4, reference numeral 100 denotes a charging corotron; 102, an exposure subsystem; 104, a development subsystem;
08 is a toner, 110 is a document, 114 is a high density reference density patch, 116 is a low density reference density patch, 118 is a toner image for the high density reference density patch 114, 12
0 is the toner image for the low density reference density patch 116,
122 is a document table, 126 is a high density detector, 128 is a low density detector, 400 is an image control unit, 202 is an error detector,
204 is a control end inspection unit, 206 is a change amount calculator, 20
8 is a control input update unit, 210 is a control input generation unit, 302
Denotes a reference change amount conversion function storage unit, 402 denotes an error code detector, 404 denotes an error code history storage unit, 406 denotes a correction code calculation unit, 408 denotes a change amount conversion function correction unit, and 216 denotes a change amount conversion function update unit. . Here, components performing the same operations as in the first embodiment are given the same reference numerals as in the first embodiment.

Next, the operation of the image density control device having the above configuration will be described. First, the operation of the electrophotographic process is the same as that of the second embodiment. However, in this embodiment, the image control unit 300 is replaced by the image control unit 400, and accordingly, the error checker 202 and the change amount conversion function update unit An error code checker 402, an error code history storage unit 404, a correction code calculation unit 406, and a change amount conversion function correction unit 408 are provided between 216.

Hereinafter, only points different from the first embodiment of the image control section 400 will be described.

The error code detector 402 outputs qualitative values [e ₁ (k)] and [e ₂ (k)] of the output signal e (k) of the error detector 202 expressed by (Equation 15). . here,
[] Indicates a value focused on only the sign of the variable, and outputs +1 when positive, 0 when 0, and -1 when negative.
However, a variable of 0 means that the variable is approximately 0. The error code history storage unit 404 stores a qualitative value [e ₁ (k)], which is an output of the error code detector 402,
[E ₂ (k)] is stored.

In the modified code arithmetic unit 406, when the number of times of control k is the second or more, the k-th qualitative values [e ₁ (k)] and [e] stored in the error code history storage unit 404.
₂ (k)] and the qualitative value of the (k-1) th time [e ₁ (k-1)],
Based on [e ₂ (k−1)], a parameter a relating to the amount of change in the charging voltage of the change amount conversion function represented by (Equation 20)
And a code representing a direction in which the parameters b and b are corrected, and a code representing a direction in which the parameters c and d relating to the exposure amount of the change amount conversion function are corrected.

The operation of the modified code calculator 406 will be described below in detail. From the equation (17) for calculating the change amount of the charging voltage and the change amount of the exposure amount, among the parameters of the change amount conversion function expressed by (Equation 20), the parameters regarding the calculation of the change amount of the charging voltage are a and b. There are parameters c and d relating to the calculation of the change amount of the exposure amount. From the results obtained by experiments etc., between the values of the parameters related to charging,

[0124]

(Equation 42)

Between the values of the parameters related to exposure,

[0126]

[Equation 43]

There is a relationship of magnitude. (Equation 42), (Equation 4)
In 3), | | represents the absolute value of a variable. That is,
From (Equation 17), e (k) is used to determine the amount of change in the charging voltage.
It can be seen that e ₁ (k) is dominant among them, and e ₂ (k) is dominant among e (k) in determining the amount of change in exposure. It is assumed that the change is related to the change amount of the charging voltage and e ₁ (k), and the change amount of the exposure amount is related to e ₂ (k). When the change amount △ X (k) is determined and controlled according to (Equation 17), if the change amount conversion function is optimally set, the error e (k) of the output density after control becomes 0. . However, if the change amount conversion function is not optimal, a non-zero error e (k) occurs.

Focusing on the signs of the k-th qualitative value [e ₁ (k)] and the (k−1) -th qualitative value [e ₁ (k−1)] stored in the error code history storage unit 404, for example, [E ₁
(K)] = − and [e ₁ (k−1)] = −, the change amount of the given charging voltage was found to be too small.
The parameters a and b of the change amount conversion function for determining the change amount of the charging voltage in the direction of increasing the change amount of the charging voltage are corrected. [E ₁ (k)] = −, and [e ₁ (k−1)] =
In the case of +, it is found that the given amount of change in the charging voltage is excessive, and the parameters a and b of the change amount conversion function that determines the amount of change in the charging voltage in a direction to decrease the amount of change in the charging voltage are corrected. I do. Based on this concept, the correction directions of the parameters are summarized as shown in (Table 1).

[0129]

[Table 1]

Parameters c and d relating to change in exposure amount
Similarly,

[0131]

[Table 2]

[Δa], [δb], [δ] in Table 1
c] and [δd] represent the sign of the change of the parameter of the change amount conversion function represented by (Equation 8), for example, [δa] = +
Means that the parameter a of the change amount conversion function is corrected to increase, and [δa] = − means that the parameter a of the change amount conversion function is corrected to decrease, and [δa] = 0 is the parameter a of the change amount conversion function.
Does not change.

The change amount conversion function correction unit 408 calculates [δa], [δb], and [δ] calculated by the correction code calculator 406.
c] and [δd], the corresponding correction coefficients ηa, ηb, ηc and ηd are calculated based on (Equation 44) to (Equation 47).

[0134]

[Equation 44]

[0135]

[Equation 45]

[0136]

[Equation 46]

[0137]

[Equation 47]

In (Equation 44) to (Equation 47), δ is a positive minute amount, and δ = about 0.05 is set. Calculated ηa,
The values of ηb, ηc, and ηd are stored and used in the next calculation. Before performing the first trial (initial state), 1 is given to ηa, ηb, ηc, and ηd and stored. Next, the change amount conversion function is calculated based on the reference change amount conversion function (Equation 20) and ηa, ηb, ηc, and ηd stored in the reference change amount conversion function storage unit 302 (Equation 4).
Determined by 8).

[0139]

[Equation 48]

The change amount conversion function updating unit 216 updates the change amount conversion function with the change amount conversion function selected by the change amount conversion function correction unit 408.

Thus, even if the preset change amount conversion function is not optimal, it can be approximated to the optimum change amount conversion function by correcting using the control history.
Good control performance can be obtained.

[0142]

According to the present invention, as described above, the quantitative change amount of the control input is determined from the output of the error calculating means by the change amount converting function, and the charging voltage after updating by the function updating means is determined. Based on the exposure amount, select a change amount conversion function according to the current characteristic change, or estimate the process characteristic change based on the updated charging voltage and the exposure amount, and convert the change amount according to the characteristic change. Calculate the change rate of the function, calculate the change amount conversion function based on the change rate and the reference change rate conversion function, or use the output history of the error code detection means to detect the sign of the output of the error calculation means. , By modifying the change conversion function so that it approaches the optimal change conversion function,
Even when the characteristics of the electrophotographic process change due to environmental changes, etc., it is possible to determine the quantitative control input change amount based on the change amount conversion function adapted to the characteristic change, and output with a small number of control repetitions. An image density control device capable of generating a high-quality image whose density is equal to the reference density signal can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image density control device according to a first embodiment of the present invention.

Figure 2 is a concentration characteristic diagram illustrating the relationship between the input image density D _IM and the output image density D _S.

FIG. 3 is a configuration diagram of an image density control device according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of an image density control device according to a third embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 charged corotron 102 exposure subsystem 104 development subsystem 106 photoreceptor 108 toner 110 document 112 density detector 114 high density reference density patch 116 low density reference density patch 118 toner image for high density reference density patch 120 low density Toner image for reference density patch 122 Platen plate 200 Image control unit 202 Error detector 204 Control end check unit 206 Change amount calculator 208 Control input update unit 210 Control input generation unit 212 Change amount conversion function storage unit 214 Change amount conversion function selection Unit 216 Change amount conversion function update unit 300 Image control unit 302 Reference change amount conversion function storage unit 304 Change rate calculation unit 306 Change amount conversion function operation unit 400 Image control unit 402 Error code detector 404 Error code history storage unit 406 Correction code Arithmetic unit 408 Change amount conversion function correction unit

Continuation of front page (56) References JP-A-4-186255 (JP, A) JP-A-5-72859 (JP, A) JP-A-5-127477 (JP, A) JP-A-4-55866 (JP) , A) JP-A-4-361278 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/00 G03G 21/00

Claims (5)

(57) [Claims] A charging unit configured to charge a photoconductor of an electrophotographic process to a predetermined charging voltage; an exposure unit configured to project a document on a document table with a predetermined exposure amount to form a latent image on the photoconductor;
Developing means for developing the latent image with a developer set to a predetermined developing bias voltage to form a visible image, at least one reference density patch provided on a document table, and charging, exposing, and concentration detection means for detecting an output density of the visible image was created and developed to on the photoreceptor, an error calculation means for calculating an error between the output density and a predetermined target density of the density detection means, error calculation A change amount calculating means for calculating the change amount of the charging voltage and the exposure amount by multiplying the output of the means by a change amount conversion function; includes a setting value updating means for adding the amount of exposure set value updating means charging voltage, the charging voltage of the updated after updating the exposure amount, and a function updating means for updating the variation conversion function in accordance with the exposure amount, the Function update means More charging voltage, response to exposure
Of output density with respect to the amount of charge voltage and exposure
The amount of change set in advance by determining the relationship with the amount
The storage means for the conversion function and the updated charging voltage and exposure amount
Images concentration controller comprising the means for selecting a change amount conversion function I. 2. A predetermined charge of a photosensitive member in an electrophotographic process.
Charging means for charging to a voltage; and
Exposure means for projecting at an exposure amount to create a latent image on the photoconductor,
The latent image is developed by a developer set at a predetermined developing bias voltage.
Developing means for developing a visible image by developing it on a platen
At least one reference density patch
Image formed on the photoconductor by charging, exposing and developing the switch
Density detecting means for detecting the output density of the
Calculate the error between the output density and the preset target density
Error calculation means, and a change amount conversion function in the output of the error calculation means
Multiplication to calculate the change in the charging voltage and exposure amount.
Of the charging voltage calculated by the calculating means and the change amount calculating means.
The amount of change in the amount of exposure and the amount of exposure to the charging voltage and the amount of exposure
The setting value updating means, and the setting value updating means includes a charging voltage and an exposure amount.
After updating, changes according to the updated charging voltage and exposure amount
Function updating means for updating the quantity conversion function, wherein the function updating means comprises at least one of
Storage means for a reference change amount conversion function represented by a parameter
And the updated charging voltage, exposure amount and developing bias voltage
Output for change of charging voltage and change of exposure based on
Calculate the rate of change of the density and calculate the rate of change based on the rate of change of the density.
Rate change means for calculating the rate of change of the parameter
Based on the reference change amount conversion function and the output of the change rate calculation means
Images concentration controller you characterized in that a change amount conversion function calculating means for calculating a change amount conversion function. 3. The function updating means according to claim 1, further comprising:
Change conversion function only when force density matches target density
Characterized by being adapted to update the claims 1 or 2
The image density control device as described in the above. 4. A predetermined charge of a photosensitive member in an electrophotographic process.
Charging means for charging to a voltage; and
Exposure means for projecting at an exposure amount to create a latent image on the photoconductor,
The latent image is developed by a developer set at a predetermined developing bias voltage.
Developing means for developing a visible image by developing it on a platen
At least one reference density patch
Image formed on the photoconductor by charging, exposing and developing the switch
Density detecting means for detecting the output density of the
Calculate the error between the output density and the preset target density
Error calculation means, and a change amount conversion function in the output of the error calculation means
Multiplication to calculate the change in the charging voltage and exposure amount.
Of the charging voltage calculated by the calculating means and the change amount calculating means.
The amount of change in the amount of exposure and the amount of exposure to the charging voltage and the amount of exposure
The setting value updating means, and the setting value updating means includes a charging voltage and an exposure amount.
After updating, changes according to the updated charging voltage and exposure amount
Function updating means for updating the quantity conversion function, wherein the function updating means comprises at least one of
Storage means for a reference change amount conversion function represented by a parameter
Sign detection for detecting the sign of the output of the error calculation means
Means and a reference change according to the history of the output of the error code detecting means.
Change conversion function to modify the parameter of conversion function
Images concentration controller characterized in that a positive means. 5. Two reference density patches of high density and low density
And set the high and low output densities to their respective target densities.
And degree, the variation amount converting function correcting means, the error sign-detecting means
The previous value of the low-density error code history, which is the output of
When the current value is negative and when the previous value is negative and the current value is positive
When, the change amount is converted in the direction to reduce the change amount of the exposure amount.
Modify the function parameters so that the previous value is negative and the current value is
When negative and previous value is positive and current value is positive
When the change amount conversion function is
Correct the parameter and set the high
The previous value of the density error sign history is positive and the current value is negative.
At certain times and when the previous value is negative and the current value is positive
Is the parameter of the change amount conversion function in the direction to reduce the change amount of the charging voltage.
Correct the parameter so that the previous value is negative and the current value is negative
When and when the previous value is positive and the current value is positive,
Parameter of the change amount conversion function in the direction to increase the change amount of the voltage
Wherein the data is modified.
5. The image density control device according to 4 .