JPH05127477A - Image density controller - Google Patents

Abstract

PURPOSE:To compensate for a density change in a transfer process by adjusting an exposure lamp voltage, an electrification unit voltage, a developing bias voltage, and a transfer electrification voltage so that the output image density after the transfer approximates to the target image density. CONSTITUTION:The image density controller is provided with an input change vector determination circuit 310 which determines an input change vector, an input vector renewal circuit 311 which renews the input vector inputted to a copying machine based on the output of the input change vector determination circuit 310, an output sign detecting circuit 313 which detects the signs of the change directions of the output (the fixed direction is determined as positive or negative) from the output of an output vector calculator 113, a qualitative model correction circuit 312, and an error sign detection circuit 308. Toner concentration after the transfer is detected on a transfer belt. Based on the qualitative relationship of the copying machine including the transfer process set by a qualitative calculation circuit 303, the exposure lamp voltage, electrification unit voltage, developing bias voltage and transfer electrification unit voltage are adjusted so that the output image density after the transfer matches the target image density.

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 a copying machine having an electrophotographic process.

[0002]

2. Description of the Related Art The applicant of the present application has already applied for an image density control device capable of making an output image density match a target image density in a copying machine having an electrophotographic process shown in FIG. (Japanese Patent Application No. 2-202180) An image density control device proposed by the present applicant will be described below with reference to the drawings. FIG. 7 is a perspective view of a copying machine having an electrophotographic process, which is a control target of the image density control device proposed by the present applicant. In FIG. 7, 101 is a photoconductor, 102 is a charger, 103 is an exposure lamp, and 105.
Is a developing device, 120 is a transfer belt, 121 is a transfer charger,
Reference numeral 106 is a copy original, and 107 is a first reference density plate (density =
D _{IN · H} ), 108 is a second reference density plate (density = D _{IN L} ,
Also, D _{IN · H} > D _{IN · L.} ), 109B is the photoconductor 10
No. 1 is a first toner image (image density = D _{IM · H} ) on the first reference density plate, and 110B is a second toner image (image density = D _{IM · H} ) on the photoconductor 101.
D _{IM / L} ), 112B is the first formed on the photoconductor 101
Is a density sensor that detects the densities of the toner image 109B and the second toner image 110B.

In the image density control device, the density sensor 112 is used.
Calculate the density difference from the density detected in B and the reference density,
The toner image 109B on the photoconductor 101 is adjusted by adjusting the exposure lamp voltage u ₁ , the charger voltage u ₂ and the developing bias voltage u ₃ based on the preset qualitative relational expression of the copying machine. It is possible to match the respective densities of 1 and 110B with the target density.

[0004]

However, the image density control device proposed by the applicant of the present invention has a problem that it is not possible to compensate the density fluctuation in the transfer process. That is, since the density of the toner image formed on the photoconductor is detected, it cannot be detected even if the density changes due to changes in temperature and humidity or changes with time in the subsequent transfer process. Further detection,
Since a qualitative relational expression between the transfer charger voltage and the toner density after transfer has not been obtained, there is a problem that the density cannot be controlled because it is not known how to adjust the transfer charger voltage.

Therefore, it is an object of the present invention to provide an image density control system capable of compensating for density fluctuations in the transfer process.

[0006]

In order to achieve this object, the present invention has the following constitution. That is, charging means for charging the photosensitive member to a predetermined charging voltage,
Exposure means for projecting a document on a document table at a predetermined exposure voltage to create a latent image on the photoconductor, and developing for developing the latent image with a developer having a predetermined developing bias voltage. And a transfer unit for transferring the visible image onto a transfer belt set to a predetermined transfer voltage, wherein the reference density patch on the document table is charged, exposed, developed and transferred by the transfer belt. A density detecting means for detecting the output density of the image formed above, a means for generating a plurality of input change vectors ΔU _i for changing the charging voltage, the exposure voltage, the developing bias voltage, and the transfer voltage, and the input change vector ΔU _i , a qualitative model calculation means for performing calculation based on the qualitative model of the copying machine and outputting the prediction code data;
The input change vector ΔU based on the error code detection means for detecting the sign of the difference value between the output density of the density detection means and the target density, and the output [e] of the error code detection means and the predicted code data. An input change vector selecting circuit for selecting _i , an output code detecting means for detecting a predetermined code indicating a change in output value of the copying machine, and an input change vector selected by the input vector selecting circuit for the copying machine. Input vector updating means for adding to the charging voltage, exposure voltage, developing bias voltage, and transfer voltage, and qualitative model correcting means for correcting the qualitative model based on the input of the copying machine and the detection output of the output code detecting means. An image density control device comprising:

[0007]

According to the present invention, the toner density after transfer is detected on the transfer belt, and the qualitative relationship of the copying machine including the transfer process is adjusted so that the output image density after transfer coincides with the target image density. Based on the formula, the exposure lamp voltage, the charger voltage,
Since the developing bias voltage and the transfer charger voltage are adjusted, it is possible to compensate the density fluctuation in the transfer process.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a copying machine having an electrophotographic process according to the first embodiment of the present invention. In FIG. 1, 101 is a photoconductor, 102 is a charger, 103 is an exposure lamp, 105 is a developing device, 120 is a transfer belt, and 12
1 is a transfer charger, 106 is a copy original, 107 is a first reference density plate (density = D _{IN · H} ), 108 is a second reference density plate (density = D _{IN · L} , and D _{IN · H} > D _{IN ・ L.} ), 10
9B is the first with respect to the first reference density plate on the photoconductor 101.
Toner image (image density = D _{IM · H} ), 110B is photoconductor 1
Second toner image with respect to a second reference density board 01 (image density = D _{IM · L),} 109A is the first toner image with respect to a first reference density plate on the transfer belt 120 (image density = D
_{OUT · H} ), 110A is the second toner image (image density =
D _{OUT · L} ), 111 is a copying machine having an electrophotographic process composed of the above-mentioned elements, and 112 A is a density sensor.

Next, the operation of the electrophotographic process thus constructed will be described. First, by inputting the charger voltage u ₂ to the charger 102, the surface of the photoconductor 101 is charged to the initial potential corresponding to u ₂ . Next, the exposure lamp 103 irradiates the copy original 106, the first reference density plate 107, and the second reference density plate 108 with light according to the exposure lamp voltage u ₁ . This light is imaged on the photoconductor 101, and the surface potential of the photoconductor 101, which was uniform before the exposure, is attenuated by receiving the light energy corresponding to each density, and the potential distribution on the photoconductor 101 is reduced. To form an image.
Further, the developing device 10 set to the developing bias voltage u ₃
5, the toner amount according to the surface potential of the photoconductor 101 adheres to the surface of the photoconductor 101, and the first toner image 109
B and the second toner image 110B are formed. further,
With the transfer charger 121 set to the transfer voltage u ₄ ,
Toner images 109B and 110B are transferred to transfer belt 120 to form toner images 109A and 110A.

The quantitative relationship in the operation described above is expressed by the following equation. (See, for example, "Basics and Applications of Electrophotographic Technology," edited by The Institute of Electrophotography, Corona Publishing Co.)

[0011]

[Equation 1]

Where D _IN is the input density (D _{IN · H} or D _{IN
IN / L} ) and D _OUT are the output densities on the transfer belt (D _{OUT / H} or D _{OUT / L} ), D _IM is the density on the photoconductor (D _{IM / H} or D)
_{IM ・ L} ), E is the light energy corresponding to the input density D _IN , V
Is the surface potential on the photoconductor 101 attenuated by the light energy E, p ₁ is a positive parameter determined by the characteristics of the exposure lamp 103, p ₂ is a positive parameter determined by the natural discharge characteristics of the photoconductor 101, and p ₃ is the photoconductor 101 is a positive parameter determined by the sensitivity and the transmittance of the optical system, p ₄ is a positive parameter determined by the toner density of the developing device 105 and the dielectric constant of the photoconductor 101, and p ₅ is the transfer charging device 121 and the transfer belt 120. It is a positive parameter determined by the characteristics.

At this time, it is determined by (Equation 1) to (Equation 4)
Input density D_INAnd output density D _OUTRelationship is general
The characteristic curve is as shown in FIG. This characteristic curve is simplified
For the sake of representation only, the two outputs y given by₁, Y₂
think of.

[0014]

[Equation 2]

That is, y ₁ represents the midpoint in the straight line portion of the characteristic curve of FIG. 2, and y ₂ represents the slope of the straight line portion.

Returning to FIG. 1 again, the density sensor 112A controls the density D _{OUT · H} of each of the first toner image 109A and the second toner image 110A formed on the transfer belt.
And D _{OUT · L} are detected, and then output vector operation circuit 1
13 (described later) calculates _two outputs of the copying machine 111, the intermediate density y ₁ and the density gradient y ₂ , based on (Equation 5) to (Equation 6). By rearranging (Equation 1) to (Equation 6), the input vector U = [u ₁ , u ₂ ,
The relationship between u ₃ , u ₄ ] ^T and the output vector Y = [y ₁ , y ₂ ] ^T can be expressed using the following equation.

[0017]

[Equation 3]

Where g ₁ and g ₂ are positive parameters p
It is a function including _{1 to} p ₅ . If the functions g ₁ and g ₂ can be accurately obtained, (Equation 7A), (Equation 7B)
By solving, the input vector U for the output vector Y to match the target output vector Y _d can be obtained. However, the parameters p _{1 to} p ₅ included in g ₁ and g ₂ depend on various characteristic parameters of the copying machine 111 as described above, and also fluctuate depending on the temperature and humidity of the environment. It is actually extremely difficult to ask for. The purpose of image density control is to match y ₁ with the target intermediate density y _{1 — d} and with y ₂ with the target density gradient y _{2 — d} . y 1 _{_d} and y 2 _{_d} are respectively (equation 7
C), as shown in (Equation 7D), the first reference concentration plate 10
It can be determined from the target density D _{T · H} for the density D _{IN · H} of 7 and the target density D _{T · L} for the density D _{IN · L} of the second reference density plate 108.

[0019]

[Equation 4]

FIG. 3 is a block diagram of an image density control apparatus according to the first embodiment of the present invention. In FIG. 3, an input change vector determination circuit 31 that determines an input change vector
0, the input vector update circuit 311 for updating the input vector input to the copying machine based on the output of the input change vector determination circuit 310, the sign of the change direction of the output from the output of the output vector calculator 113. It has an output code detection circuit 313, which detects positive or negative), a qualitative model correction circuit 312, and an error code detection circuit 308.

The input change vector determination circuit 310 is shown below.
It has a circuit. (1) Input change vector memory 301: predetermined
81 input change vectors ΔU₁,…, ΔU₈₁But
It is stored in memory. Input change vector ΔU_iIs 3^Four
= 81, "3" is the number of code types of each element,
Corresponds to three "+", "-" or "0"
The number “4” is the input change vector ΔU_iCorresponds to the degree of
It Input change vector ΔU_iIs four data (Δu₁, Δ
u₂, Δu₃, Δu_Four), Each data is a positive value,
It is either a negative value or zero. For example (Δu₁, 0,0,-
Δu_Four), (0, -Δu₂, Δu₃, 0). Positive values are
Represents an increase in a fixed direction, negative values decrease
Is represented. Zero means no change. Each device
Data (Δu₁, Δu ₂, Δu₃, Δu_Four) Is the exposure lamp voltage
u₁, Charger voltage u₂, Development bias voltage u₃, Transfer charging
Unit voltage u_FourIs a small amount of voltage applied to, for example, 0.
A minute value such as 5v is set. All data are the same
It does not have to be the same voltage value.
Good (eg 0.5v, -0.7v, 0.1v, -0.1
v). (2) Switch 305A: input change vector memory 30
When inputting 1 data to the code vector detector 302
To be closed. (3) Code vector detector 302: input vector memory
Input change vector ΔU input from 301_iBased on
The code vector representing the code (+,-, 0) of each data.
Tol [ΔU_i] Is output. (Subsequently put in []
The character is the sign "+", "-",
Rui indicates “0”. ) For example, the input change vector ΔU_i
= (0, -Δu₂, Δu₃, Δu_Four) Is entered, the sign
Cuttle [ΔU_i] = (0,-, +, +) is output. (4) Qualitative model arithmetic circuit 303: code vector detector
A code vector [ΔU output from 302_i] Based on
Output y of the output vector calculator 113₁, Y₂Sign of
Has an arithmetic circuit that predicts (corresponding to the output change direction)
To do. Computation follows a preset qualitative model
Resulting predictive code data done

[0022]

[Equation 5]

Is output. Hereinafter, the hat "^" above the character represents the predicted data of the data represented by the character. Each element of the prediction code data (Equation 5) represents a code indicating the direction of change of the outputs y ₁ and y ₂ , and the increase prediction is “+”, the decrease prediction is “−”, the no change is “0”, the prediction is Impossible has any data of "?". For example,

[0024]

[Equation 6]

It has the following values. (5) Switch 305B: Closed when the output data of the qualitative model arithmetic circuit 303 is input to the memory 304. (6) Memory 304: The predictive code data (Equation 5) output from the qualitative model arithmetic circuit 303 is stored in the memory 304 via the switch 305B. Normally 81 prediction code data

[0026]

[Equation 7]

Is stored in memory. (7) Input change vector selection circuit 309: memory 304
Predicted code data (Equation 7) and input change vector ΔU
_i is input, and one of the prediction code data (Equation 7), whose code matches the code [e] of the error value input from the error code detection circuit 308 described later, respectively.

[0028]

[Equation 8]

Is selected, and the qualitative model correction circuit 312 is selected.
Is applied. This image density control device further includes the following circuit.
I have it. The error code detection circuit 308 outputs the output vector.
Output value calculated by the calculator 113 Y = (y₁, Y₂) And goals
Value Y _d= (Y_{d_1}, Y_{d_2}) Error calculation circuit to find the difference between
A code detection circuit 307 including an error e of a calculation result.
To enter. In the code detection circuit 307, the error e
Input change vector selection circuit 3 that detects the sign [e] of the value
Enter in 09. Sign [e] is "+", "-", "0"
It has data representing any one of the above. Ie the mark
No. [e] changes output Y to target output Y_dOutput to get closer to
Increase or decrease Y, or keep the current value
Have information on what to do.

The input vector update circuit 311 performs an addition operation on the input change vector ΔU _j output from the input change vector selection circuit 309 and the current input U and outputs a new updated input U. The switch 316 is open during the above addition operation.

The exposure lamp voltage u ₁ and the prediction code data (Equation 8) are input to the qualitative model correction circuit 312. Further, when the output code detection circuit 313 detects a code change vector [ΔY] representing the output change direction, the switch 3
14 is closed (steps 1 and 2 in the flowchart of FIG. 4), and the sign change vector [ΔY] is input to the qualitative model correction circuit 312 (step 3).

In the qualitative model correction circuit 312, the code change vector [ΔY] and the predicted code data (Equation 8) are compared (step 4). If they are not equal, the switch 315 is closed and the corrected output Q is qualitative model. Arithmetic circuit 30
3 is input (steps 5 and 6).

The qualitative model will be described below. The qualitative relationship is obtained by partially differentiating the functions g ₁ and g ₂ of (Expression 8A) and (Expression 8B) with u ₁ , u ₂ , u ₃ and u ₄ .

The functions g ₁ and g ₂ are

[0035]

[Equation 9]

Therefore, each expression after partial differentiation is

[0037]

[Equation 10]

[0038] Here, V _H and V _L are surface potentials formed on the photoconductor 101 after the exposure and charging processes, and correspond to the first reference density plate 107 and the second reference density plate 108, respectively. Since the result of partial differentiation is always negative in (Equation 9), if the input u ₁ is increased,
It shows a qualitative relationship that the output y ₁ decreases,
The direction of change of the output y ₁ with respect to the change of the input u ₁ can be predicted. Therefore, from (Equation 9) to (Equation 16), the predicted value of the output

[0039]

[Equation 11]

Input [ΔU] = ([Δu ₁ ], [ΔU]
The relationship of u ₂ ], [Δu ₃ ], [Δu ₄ ]) is obtained as in the following equation.

[0041]

[Equation 12]

Here, Q is a value obtained by setting 0 in {} of (Equation 13), and is a boundary parameter represented by (Equation 19).

[0043]

[Equation 13]

Table 1 is a summary of (Equation 17) to (Equation 18).

[0045]

[Table 1]

In Table 1, the area numbers (1 to 3) are classified according to the sign of the difference between the input U = (u ₁ , u ₂ , u ₃ , u ₄ ) given to the copying machine and the boundary parameter Q. It shows the area to be filled. The region is divided into three types according to the sign of the difference value between the input value u ₁ and the boundary parameter Q in (Equation 18). Output values y ₁ and y ₂ in each region
The function for finding is different.

The sign of the value of the boundary function is obtained as follows. For example, in the area number (1), since the boundary function code [u ₁ -Q] is u ₁ -Q> 0, the code of the value is "+". Similarly, in area number (2),
Since u ₁ -Q = 0, the value is “0”.

In Table 1, predicted code data

[0049]

[Equation 14]

Is calculated as follows. For example, in the case of the area number (1), the code vector [ΔU _i ] =
For (+, 0,-,-), the prediction code data (Equation 5)
Becomes (-,-).

In the case of the area number (2), for example, for the code vector [ΔU _i ] = (-, +,-, +), the prediction code data (Equation 5) becomes (+, +). ..

[0052]

[Equation 15]

For example, the code vector [ΔU _i ] =
For (+, +,-, +), a fixed value cannot be obtained for the prediction code data (Equation 5).

[0054]

[Equation 16]

The output of the qualitative model correction circuit 312 is (equation 1
As shown in 6), a positive parameter p ₁ determined by the characteristics of the exposure lamp 103, a positive parameter p ₂ determined by the natural discharge characteristics of the photoconductor 101, a positive parameter determined by the sensitivity of the photoconductor 101 and the transmittance of the optical system. It includes the boundary parameter Q determined by the parameter p ₃ of.
These parameters p ₁ , p ₂ , p ₃ are difficult to measure data and cannot be predicted, and therefore the boundary parameter Q containing them cannot be predicted accurately, and the prediction of (Table 1) is correct. Not necessarily. If this prediction is not correct, the code data [Δy] of the actual output value detected by the output code detection circuit 313 and the prediction code data output from the input vector selection circuit 309 (Equation 8)
Do not match. In such a case, the qualitative model used in the qualitative model calculation circuit 303 is considered to be inappropriate, so the boundary parameter Q of the qualitative model is changed.

An example of the correction operation in which actual numerical values are applied is shown below. The input to the copier is Ui = (u ₁ , u ₂ , u ₃ , u
₄ ) = (65v, 700v, 400v, 2000v), and if Q = 70v, then [u ₁ −Q] = [65−70] = [− 5] = “−” (Table 1) Area number (3) is selected.

At this time, for example, the following data is input as the input change vector. _{△ Ui = (+ △ u 1} , 0, + △ u 3) = (+ 0.5v, 0
v, + 0.5v, 0v) In this case, the prediction code data (Equation 14) is calculated from (Table 1) as follows.

[0058]

[Equation 17]

Next, the copying machine given the above input change vector outputs the output code data [ΔY] after the end of the process operation.
If is (-,-), it is expected that the selection of the area number is wrong. Therefore, in (Table 1), the area number where the prediction code data (Equation 8) becomes (-,-) is searched for. As a result, it can be seen that the matching area number is (1). Therefore, a boundary parameter Q that fits the boundary function of the area number (1) is obtained.

[U ₁ −Q ′] = [65−Q ′] = “+”> 0 In order for the above expression to hold, the value of Q ′ may be set as follows.

Q '= 65-ε where "ε" is a positive real number.

On the other hand, the code data [ΔY] is “(−, +)”
In Case of,

[0063]

[Equation 18]

Therefore, the prediction code data and the code data match. Therefore, the boundary parameter Q is not modified.

When the exposure lamp voltage u ₁ is much smaller than the boundary parameter Q, that is, [u 1 -Q]
When only the area of "=" exists, the boundary parameter is not corrected. As a result, the qualitative model correction circuit 31
2, output change code detection circuit 313 and switch 314,
The circuit of FIG. 4 without 315 can be used.

Although a sufficient accuracy cannot be obtained, as a simple method, it is also possible to compensate for the density fluctuation in the transfer without adjusting the transfer voltage. In that case, the second embodiment is used. The circuit shown in FIG. 6 is obtained.

[0067]

As described above, according to the present invention, the toner density on the transfer belt is detected by the density sensor, and the transfer is performed from the qualitative relational expression of the copying machine including the transfer process set by the qualitative model calculation circuit 303. Since the exposure lamp voltage, charger voltage, developing bias voltage, and transfer charger voltage are adjusted so that the output image density afterwards can be made closer to the target image density, it is possible to compensate for density fluctuations in the transfer process. it can. Further, in the image density control device proposed by the applicant of the present invention, only the exposure lamp voltage, the charger voltage, and the developing bias voltage are adjusted, whereas the transfer charger voltage can be adjusted. It also has the effect of controlling various concentrations. For example, when the exposure lamp voltage, the charger voltage, and the developing bias voltage have reached their respective limit values, but it is still necessary to control the overall output density, what was previously uncontrollable is: In the present invention, this can be dealt with by adjusting the transfer charger voltage.

[Brief description of drawings]

FIG. 1 is a perspective view of a copying machine having an electrophotographic process according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between an input image density and an output image density of the copying machine having the electrophotographic process according to the first embodiment of the present invention.

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

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

FIG. 5 is a flowchart showing the operations of the qualitative model correction circuit and the output code detection circuit in the image density control apparatus according to the first embodiment of the present invention.

FIG. 6 is a block diagram of an image density control device according to a second embodiment of the present invention.

FIG. 7 is a perspective view of a copying machine having an electrophotographic process according to the first embodiment already proposed by the present applicant.

[Explanation of symbols]

101 Photoreceptor 102 Charger 103 Exposure Lamp 105 Developer 106 Copying Document 107 First Reference Density Plate 108 Second Reference Density Plate 109A, 109B First Toner Image for the First Reference Density Plate 110A, 110B Second Second toner image for the reference density plate 112A Density sensor 120 Transfer belt 121 Transfer charger 111 Copier 308 Error code detection circuit 310 Input change vector determination circuit 311 Input vector update circuit 312 Qualitative model correction circuit 313 Output code detection circuit 113 output Vector calculator 314, 315 switch

Claims (5)

[Claims] 1. A charging means for charging a photoconductor to a predetermined charging voltage, an exposure means for projecting a document on a document table at a predetermined exposure voltage to form a latent image on the photoconductor, and the latent image. A developing means for forming a visible image with a developer set to a predetermined developing bias voltage; and a transfer means for transferring the visible image onto a transfer belt set to a predetermined transfer voltage, the original table The reference density patch above is charged, exposed,
A density detecting means for detecting the output density of the image formed on the transfer belt by the developing and transferring means, and a plurality of input change vectors ΔU _i for changing the charging voltage, the exposure voltage, the developing bias voltage, and the transfer voltage are generated. Means, a qualitative model calculation means for performing a calculation on the input change vector ΔU _i based on a qualitative model of the copying machine, and outputting predicted code data, and a sign of a difference value between the output density and the target density of the density detecting means. Of the output of the copying machine, an error code detecting means for detecting the error code, an input change vector selecting circuit for selecting the input change vector ΔU _i based on the output [e] of the error code detecting means and the predicted code data. An output sign detecting means for detecting a predetermined sign indicating a change in the value, and an input change vector selected by the input vector selecting circuit are supplied to the charging device of the copying machine. , An input vector updating means for adding to the exposure voltage, the developing bias voltage and the transfer voltage, and a qualitative model correcting means for correcting the qualitative model based on the input of the copying machine and the detection output of the output code detecting means. And an image density control device for matching the output density of the copying machine with a target density by repeating the above series of operations. 2. A charging means for charging a photoconductor to a predetermined charging voltage, an exposure means for projecting a document on a document table with a predetermined exposure voltage to form a latent image on the photoconductor, and the latent image. A developing means for forming a visible image with a developer set to a predetermined developing bias voltage; and a transfer means for transferring the visible image onto a transfer belt set to a predetermined transfer voltage,
Density detecting means for detecting the output density of the image formed on the transfer belt by the charging, exposing, developing and transferring means for the reference density patch on the original table, and the charging voltage, exposure voltage, developing bias voltage, transfer Means for generating a plurality of input change vectors ΔU _i for changing the voltage; qualitative model operation means for performing an operation on the input change vectors ΔU _i based on a qualitative model of the copying machine to output predictive code data; The input change vector ΔU _i is selected on the basis of the error code detection means for detecting the sign of the value of the difference between the output density of the means and the target density, and the output [e] of the error code detection means and the predicted code data. An input change vector selecting circuit, and an input change vector selected by the input vector selecting circuit, the charging voltage of the copying machine,
An image density control device configured to have an input vector updating means for adding to an exposure voltage, a developing bias voltage, and a transfer voltage, and making the output density of the copying machine match a target density by repeating the above series of operations. 3. A charging means for charging a photoconductor to a predetermined charging voltage, an exposure means for projecting a document on a platen at a predetermined exposure voltage to form a latent image on the photoconductor, and the latent image. A developing means for forming a visible image with a developer set to a predetermined developing bias voltage; and a transfer means for transferring the visible image onto a transfer belt set to a predetermined transfer voltage,
Density detecting means for detecting the output density of the image formed on the transfer belt by the charging, exposing, developing, and transferring means of the reference density patch on the original table, and the charging voltage, the exposure voltage, and the developing bias voltage are changed. Means for generating a plurality of input change vectors ΔU _i , qualitative model calculation means for performing a calculation on the input change vectors ΔU _i based on a qualitative model of the copying machine, and outputting predicted code data, and an output of the density detecting means. Error code detection means for detecting the sign of the difference value between the density and the target density, and an input change for selecting the input change vector ΔU _i based on the output [e] of the error code detection means and the predicted code data. A vector selection circuit, an output code detection means for detecting a predetermined code indicating a change in the output value of the copying machine, and an input selected by the input vector selection circuit. Input vector updating means for adding a charge vector to the charging voltage, exposure voltage, and developing bias voltage of the copying machine, and qualitative correction of the qualitative model based on the input of the copying machine and the detection output of the output code detecting means. An image density control device configured to include a model correction means and making the output density of the copying machine match a target density by repeating the series of operations described above. 4. The image density control device according to claim 1, wherein the reference density patch has two types of high density and low density. 5. The image density control device according to claim 1, wherein the reference density patch is in a non-image portion.