JPH09265247A - Image forming device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly converge the controlled variable of image quality on a target value by suppressing an oscillation state, when the control of the image quality becomes the oscillation state, in an image forming device for controlling the image quality, according to a case example. SOLUTION: A control gain adjusting part 109 monitors a control error 108. When both of the control errors at the previous time and this time exceed an allowable error and the signs of the control errors are opposite, a control gain 102 is reduced. Since the control gain is reduced, the oscillation state is suppressed and the controlled variable converges on the target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system,
The present invention relates to an image forming apparatus using various methods such as an ink jet method and a control method therefor, and in particular, enables stable control for always maintaining an image at a predetermined quality.

[0002]

2. Description of the Related Art The applicant of the present invention is
An image forming apparatus has been proposed that follows the change and easily adjusts the control gain (control rule) (Japanese Patent Application No. 7-324441). FIG. 22 shows an outline of an image quality control system of this image forming apparatus. In FIG. 22, a target value 100 relating to image quality, for example, image density is given in advance, and the target value 100 and the actual control amount (measurement image) are given. Density) 101, and the difference and control gain 1
The manipulated variable 103 is determined from 02 and controls the control system 104. The control gain 102 is determined based on the case. In this image quality control, if the error in the image quality, for example, the error in the image density is within the allowable range, the control gain 102 used so far is used as it is. When the image quality error exceeds the allowable range, a control case is sampled and a new control gain 102 is created based on the control case. In this way, a plurality of control gains 102 are prepared. The control gain inference unit 105 infers the optimum control gain 102 based on the operation amount change amount 106, the control amount change amount 107, and the control error 108.

In the above-mentioned structure, once the control gain is calculated by a predetermined number of cases, the control gain is the optimum control gain in that state, and unless the state changes, the subsequent control amount Is usually within tolerance.

However, since the above control is performed discretely, the difference (error) between the control amount and the target value is calculated as a result of calculating the correction amount of the next operation amount with the current control gain with respect to the predetermined error. There is a case where the magnitude of exceeds the allowable error and the sign of the error before and after becomes opposite. Then, such a situation may occur continuously and an oscillation state may occur.

In this case, not only the control does not quickly converge to the target value, but also the control gain is not improved quickly.
Only the case will be acquired in the dark clouds.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and when image quality control is in an oscillating state in an image forming apparatus that controls image quality based on a case. The purpose is to quickly suppress the oscillation state and quickly converge the image quality control amount to the target value.

[0007]

In order to achieve the above object, the present invention uses a control gain calculated based on data of an image forming case to determine a control amount related to image quality as a target. Image formation in which the operation amount is controlled so that the value becomes a value, and when the difference between the control amount and the target value exceeds a predetermined allowable value, data of a new case is collected and a new control gain is calculated. In the apparatus, means for detecting that the magnitude of the difference between the control amount and the target value is a predetermined value or more, and when a difference of the predetermined value or more is detected in a continuous image forming operation, Means for determining whether the sign of the difference is opposite and means for reducing the control gain when it is judged that the sign is opposite are provided.

According to this structure, it is possible to detect the oscillation state, reduce the control gain based on this, and suppress the oscillation so that the control amount converges to the target value. After convergence, control can be performed with normal control gain.

Further, in this configuration, when the data of the new case is collected in order to calculate the new control gain, the control gain is not reduced even if it is determined that the signs are opposite. You can When the state changes and a new case must be sampled and a new control gain must be calculated again, the difference between the controlled variable and the target value increases as the state changes. If the gain is reduced, it becomes difficult to collect the case data correctly, and thus an incorrect control gain will be calculated. Such a problem can be avoided if the control gain is not reduced when the predetermined minimum number of cases for calculating the control gain is not reached.

Further, according to the present invention, in order to achieve the above object, a means for setting the target value in an image forming apparatus for controlling the operation amount so that the control amount relating to the image quality becomes the target value. , A means for measuring the control amount, and an operation amount actually added in a series of image forming processes,
One or a plurality of parameters (control gain) of the function of the operation amount and the control amount, which are determined based on the control amount actually measured when the operation amount is applied, are stored as a control rule. A storage unit, a state transition determining unit that determines a state transition of the image forming apparatus main body, and an actual measurement value of the operation amount and the control amount in a series of image forming processes according to the determination output of the state transition determining unit. Means for deciding a new parameter of the function from the above and storing it as a control rule in the storage means, and an applied control rule applied for calculating the operation amount based on the control amount, by the parameter of the function of the above-mentioned 1 Or combining at least some of the parameters of the above functions,
Applied control rule calculation means for calculating, the applied control rule, means for changing the operation amount based on the error of the control amount with respect to the target value, and the magnitude of the error of the control amount with respect to the target value. Means for detecting that the value is equal to or greater than a predetermined value, means for determining whether or not the sign is reversed when an error equal to or greater than the predetermined value is detected in a continuous image forming operation, and the sign A means is provided for reducing the degree of change in the operation amount when it is determined that they are opposite.

Also in this configuration, it is possible to perform control so that the change in the manipulated variable is promptly reduced when the oscillation state is entered, so that the controlled variable quickly converges to the target value.

Further, according to the present invention, in order to achieve the above-mentioned object, the control method of the image forming apparatus which controls the operation amount so that the control amount relating to the image quality becomes the target value is actually added. A step of generating one or a plurality of control rules in an initial state based on an operation amount and a control amount measured when the operation amount is added; and calculating the operation amount based on the control amount. According to the step of generating an application control rule applied to the above one or more control rules, the step of determining the state transition of the image forming apparatus main body, and the step of determining the state transition.
A step of generating a new control rule from an operation amount and a control amount at the time of image formation, a step of changing the applied control rule in consideration of the new control rule, and a magnitude of an error with respect to the target value of the control amount. Is greater than or equal to a predetermined value, and when an error greater than or equal to the predetermined value is detected in a continuous image forming operation, it is determined whether or not the sign is opposite, When it is determined that the signs are opposite, the step of reducing the degree of change in the operation amount is executed.

Also in this configuration, when the oscillation state is entered, the control is promptly performed so as to reduce the change in the manipulated variable, so that the controlled variable quickly converges to the target value.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. [First Embodiment] First, a first embodiment showing the principle configuration of the present invention will be described.

FIG. 1 shows this embodiment as a whole, and in FIG. 1, parts corresponding to those in FIG. 20 are designated by corresponding reference numerals and detailed description thereof will be omitted. In FIG. 1, a control gain inference unit 10 based on conventional case-based inference is used.
5, a control gain adjusting unit 109 is provided. The control gain adjusting unit 109 monitors the difference (control error) 108 between the target value 100 and the controlled variable 101 and adjusts the gain. This control gain adjusting unit 109 is provided when the control system 104 does not converge due to the gain based on the inference result based on the case.
By supplementing this, a predetermined operation is added to the control gain so that the control amount 101 converges to the target value 100. This operation is an operation that reduces the control gain by case-based reasoning.

Specifically, when an actual controlled object is operated with a predetermined operation amount 103, as a result, the control amount 101 of the control system is measured and output. The control amount 101 is compared with the target value 100, and the error 108 thereof is calculated. The control gain calculation unit 105 multiplies the gain inferred and updated for each print by the error 108 to calculate the correction amount of the operation amount 103 for the error. Then, when the control amount does not converge to the target value, the control gain adjusting unit 109 adjusts the gain.

FIG. 2 explains the operation of gain adjustment. The operation of FIG. 2 is as follows. Step S1: An image is formed and the image quality at that time, for example, the image density is measured. Step S2: Determine whether the control error is within the allowable range. Step S3: It is determined whether or not it is a mode in which a case is acquired to create a new control rule (control gain). Step S4: It is determined whether or not the control error at the time of the previous image formation exceeds the allowable range and, as a result, is stored. Step S5: It is determined whether or not the sign of the control error exceeding the allowable range of the previous time and the current time is opposite. Step S6: The control gain is reduced. Step S7: Decrease E1 / (E0 + E1). The control gain at the time of image formation is reduced by using this reduction count. However, E0 is the absolute value of the previous control error, and E1 is the absolute value of the current control error. Step S8: It is determined whether the mode is the gain reduction mode. Step S9: The gain reduction count is returned to 1. Step S10: Store the current control error data. Step S11: The current control error is set as the previous control error in preparation for the next process.

In this embodiment, it is judged whether the error of the print (N-1st sheet) at that time is within the error range in which the control gain adjustment is necessary, and if the control gain adjustment is necessary, the next print is performed. The state and the error are stored up to (Nth print). Then, in the next print (Nth sheet), the error is similarly monitored, and it is determined whether or not the error range requires the control gain adjustment. If the control gain adjustment is in a required range, it is determined whether the sign is an inverse number.

Here, it is assumed that the control error has to be adjusted within a control error range and the sign thereof is reversed (oscillation state). This state, as it is, means that it is difficult to converge the control amount to the target value with the control gains deduced so far. This is because, if the gain deduced so far is adapted, the error of the control amount in the next print (Nth print) should theoretically be zero if the first error occurs.

Therefore, when this state is detected, the control gain adjusting section 109 is operated to perform a predetermined calculation to reduce the control gain as in this embodiment. This calculation is performed by, for example, the error (E
1) is the error (E0) of the N-1th print stored
Value divided by the sum of the error of N and the Nth print (E1 / (E0 +
Calculate E1)). This calculation result is used as the reduction coefficient in this state. Therefore, the product of this reduction coefficient and the gain at this time is multiplied by the error (E1) of the Nth print and set as the correction amount of the operation amount of the next print. The result of such control gain adjustment is shown in FIG.

The reduction coefficient can be obtained by a method other than the proportional calculation as described above. As mentioned above, the oscillation state is
Since the control error exceeds the permissible error and the sign changes across the target value of the development density, the adjustment amount having the highest probability may be set as the reduction coefficient. For example, the control gain can be easily adjusted by uniquely adjusting the control gain with 1/2 as the reduction coefficient.

Further, important when creating a control rule,
When acquiring a case immediately after a state change, the difference between the target value and the control amount naturally deviates from the allowable error range. At this time, if the control gain is adjusted, not only the case cannot be correctly acquired, but also an erroneous control rule may be created. In this embodiment, in order to avoid such a problem, the control gain is not adjusted when the number of cases is counted and the number is less than or equal to the number for which the control rule can be calculated.

In the conventional example, as shown in FIG. 3, the control amount (measured concentration) deviates from the permissible error range with the target concentration as a boundary, and the state where the control amount does not converge to the target concentration (after 7 prints) is conventional. However, according to this embodiment, it is possible to detect that such a state continues, and it is possible to avoid the situation where the convergence does not occur as shown in FIG.

Further, when the value is close to the first acquired case (that exceeds the allowable error), the above situation may occur, and the control does not converge to the target value, and only the case is acquired and added to the dark clouds. It In this embodiment, such a situation can be avoided.

Further, as shown in FIG. 5, in this embodiment, when the number of cases in which the control rule can be calculated is less than or equal to the number of cases, it is possible to prevent the control gain from being adjusted. Despite that, it is not necessary to store the control rule calculated based on the case where the gain adjustment is performed.

[Second Embodiment] Next, a second embodiment showing a more detailed structure of the present invention will be described. This example is
After uniformly charging the photoconductor surface with a scorotron charger, an electrostatic latent image is formed by laser beam irradiation, and this electrostatic latent image is developed with toner. The invention is applied. In this embodiment, the control amount is the image density (two types of solid density and highlight density), and the operation amount is the grid potential of the scorotron charger and the output of the laser beam output unit.

(1) Configuration of Image Forming Apparatus First, the image output section IOT of the image forming apparatus of this embodiment.
Figure 6 shows the outline of (Image Output Terminal). Note that the image reading unit and the image processing unit are omitted in FIG. That is, only the image output unit IOT based on the electrophotographic method is shown.

The image forming procedure will be described with reference to FIG.
First, an image processing unit (not shown) applies an original image signal obtained by reading an original by an image reading unit (not shown) or created by an external computer (not shown). Process. The input image signal thus obtained is input to the laser output unit 1 and modulates the laser beam R. Thus, the laser beam R modulated by the input image signal is irradiated onto the photoconductor 2 in a raster manner.

On the other hand, when the photoconductor 2 is uniformly charged by the scorotron charger 3 and is irradiated with the laser beam R,
An electrostatic latent image corresponding to the input image signal is formed on the surface. Next, the electrostatic latent image is developed with toner by the developing device 6, the developing toner is transferred onto a sheet (not shown) by the transfer device 7, and is fixed by the fixing device 8. Thereafter, the photoreceptor 2 is cleaned by the cleaner 11, and one image forming operation is completed. A development density sensor 10 detects the density of a development patch (described later) formed outside the image area.

(2) Developing Patch Creating Mechanism and Monitoring Mechanism Thereof The developing patch and its monitoring mechanism in this embodiment will be described. The development patch is for monitoring the output image density, and as shown in FIG. 7, two types of patches are a solid (100% dot coverage) density patch PA1 and a highlight (20% dot coverage) density patch PA2. Has been adopted. Then, these density patches P
As shown in FIG. 7, each of the A1 and the highlight density patch PA2 is set to a size of about 2 to 3 cm square and is formed outside the image area of the photoconductor 2.
That is, as shown in FIG. 8, after the latent image is formed in the image area 2a, the evening density patch PA1 and the highlight density patch PA2 are sequentially formed in the empty area 2b.

The density sensor 10 is composed of an LED irradiation unit for irradiating the surface of the photoconductor 2 with light, and a photosensor for receiving specularly reflected light or diffused light from the surface of the photoconductor 2. A line L1 shown in FIG. 7 is a detection line of the developer liquid level sensor 10. Therefore, the solid density patch PA1 and the highlight density patch PA2 are formed on the detection line L1, and sequentially pass near the development density sensor 10.

Here, FIG. 9 is a diagram showing an example of the output signal of the developing density sensor 10. As shown in the drawing, first, a density detection signal corresponding to the image of the document is obtained, and then each density detection signal of the solid density patch PA1 and the highlight density patch PA2 is obtained. Since the solid density patch PA1 and the highlight density patch PA2 are formed outside the image area, they are not transferred to the paper and are erased when passing through the cleaner 11.

In this embodiment, the density of the developing patch is detected because it has a high correlation with the density (final image density) of the fixed image that the user holds and can be removed by the cleaner 11. Is. Further, the development patch may be formed in the image area at a timing other than the time of image formation. Further, as the development patch, a patch having another halftone dot coverage may be used.

(3) Configuration of Control Unit Next, FIG. 10 is a block diagram showing the configuration of the control unit 20 for controlling the scorotron charger 3 and the laser output unit 1. In the figure, 21 is a density adjustment dial,
The operator sets a value according to the desired density. The set value of the density adjustment dial 21 is converted by the converter 22 into a value converted into the output of the developing density sensor 10 (a value between “0” and “255” in this embodiment). Converter 2
2 is held in the control amount memory 23. In this case, the control amount memory 23 also stores the allowable error amount.

On the other hand, the output signal of the developing density sensor 10 and the output signal of the memory 23 are compared in the density comparator 24. In this comparison, the allowable error amount stored in the memory 23 is referred to. The output signal of the development density sensor 10 is supplied to the applicable control rule calculator 30 if the difference between the two is within the allowable value, and is supplied to the control case memory 25 if the difference is equal to or more than the allowable value.

The control case memory 25 is a memory for storing control cases, and stores three kinds of quantities of state quantity (representative value), operation quantity and control quantity as one set. In this embodiment, the control cases are stored in order to perform various controls based on control cases stored in the past.

Here, the state quantity stored in the control case memory 25 refers to temperature, humidity, or the amount of deterioration over time that dominates the electrophotographic process, and there are these state quantities. Since it can be regarded as almost constant within a limited time, in the case of this embodiment, the occurrence time (date and hour / minute / second) of the case and the number of formed images are used instead. If the occurrence time is within a predetermined time unit (a predetermined time unit such as 3 minutes, 5 minutes or 10 minutes), the states of the image output units IOT are handled as being equal. This is the case where the occurrence times are close to each other,
This is because both are under substantially the same temperature and humidity, and the degree of deterioration over time can be expected to be the same. The time data indicating the time of occurrence is supplied from the clock timer 40 shown in FIG. 6 in this embodiment. Next, the operation amount refers to an adjustment amount of a parameter that changes the output value of the controlled object. In the case of this embodiment, the scorotron charger is used. Grid voltage setting value of 3 (0 to 255, hereinafter abbreviated as scoro setting value)
And laser power setting values (0 to 255, hereinafter abbreviated as LP setting values). The two amounts were set as the manipulated variables because the final image density to be controlled is two points of a solid density part and a highlight density part, and the scoro set value and the LP set value are the solid density and the high density. This is because the light density has a high correlation.

Further, the scoro setting value and the LP setting value are
Each value is stored in the manipulated variable memory 32, and the value corresponding to the output signal of the manipulated variable correction calculator 31 is read out as appropriate. Then, the scoro set value read from the operation amount memory 32 is supplied to the grid power supply 15, whereby the grid power supply 15 applies a voltage corresponding to the scoro set value to the scorotron charger 3. Further, the LP setting value read from the operation amount memory 32 is supplied to the light amount controller 16, whereby the light amount controller 1
Numeral 6 gives a laser power corresponding to the LP set value to the laser output unit 1.

Next, the control amount supplied to the control case memory 25 is an output signal of the developing density sensor 10, and as a result of the above, the control case shown in FIG. 11 is stored in the control memory 25. To be done. In this table, for example, in the case 1 of cluster 1, the state quantity (occurrence time) is 12:00:00 on December 1, 1995, and the LP setting value is “83”.
The scoro set value is "130", the control amount (sensor output value) is "185" for the solid portion, and "23" for the highlighted portion. In case 1 of cluster 2, the state amount 199
At 9:05:00 on December 2, 5th, the LP setting value was "14
8 ", the scoring set value is" 115 ", and the control amount is" 185 "for the solid portion and" 30 "for the highlight portion. As described later, a control rule is created for each cluster of control cases.

Next, the state quantity comparator 2 shown in FIG.
6. Cluster memory 27 and control rule calculator 28
Has a function of extracting a control rule with reference to a control case stored in the control case memory 25. The operation of these blocks will be described in detail later.

The control rule memory 29 is a memory for storing a plurality of control rules calculated by the control rule arithmetic unit 28. When a request is issued from the applied control rule arithmetic unit 30, a control rule corresponding to the request is returned. To do. In this case, the applied control rule calculator 30 determines that the density comparator 2
The control rule memory 29 is requested to provide a control rule corresponding to the density difference supplied from No. 4 and the operation amount supplied from the operation amount memory 32 (that is, the LP set value and the scoro set value). The control rule memory 29 is shown in FIG.
As shown in 2, the control rule coefficient (gain) is stored. The control case memory 25 described above stores a case for creating a control rule, but basically does not use any case other than the latest control rule. Reset cluster data.

Next, the manipulated variable correction value calculator 31 obtains the correction value of the manipulated variable using the control rule retrieved by the applied control rule calculator 30, and stores the obtained correction value in the manipulated variable memory 32. Supply. When it is desired to clearly express a control rule applied for obtaining a correction value of the operation amount (or the operation amount itself), this is referred to as an application control rule. As a result, the operation amount memory 32 supplies the operation amount corresponding to the operation amount correction value, that is, the LP setting value and the scoro setting value to the grid power supply 15 and the light amount controller 16, respectively.

On the other hand, the reference patch signal generator 42 is a circuit for instructing the creation of the solid density patch PA1 and the highlight density patch PA2, and outputs the calibration reference patch signal to the image output unit IOT at the patch creation timing.
As a result, the solid density patch PA1 and the highlight density patch PA2 shown in FIG. 7 are created.

In this case, the operation timing of the reference patch signal generator 42 is controlled by the I / O adjusting section 41.
The I / O adjusting unit 41 monitors the time signal output from the clock timer 40, and outputs an operation timing signal to the reference patch signal generator 42 so that the solid density patch P1 and the highlight density patch P2 are formed at predetermined positions. To supply.

Further, in this embodiment, the correction calculation adjustment unit 43
Is provided to control the operation of the operation amount correction calculation unit 31. The correction calculation control unit 43 detects the oscillation state and reduces the correction amount of the operation amount at the time of detection.

(4) Initial Setting Operation Next, the operation of this embodiment having the above configuration will be described. First, the initial setting process (so-called function start-up process) will be described mainly with reference to FIG. First, the technician appropriately sets the scoro set value and the LP set value selected as the control parameters (S11). Then, the control unit 20 creates a solid density patch PA1 and a highlight density patch PA2 (S12), measures the respective optical densities by the development density sensor 10 (S13), and uses the contents as a control case as a control case memory 25. (S14). As a result, the control case memory 25 stores the first control case (control case 1).

Similarly, while changing the scoro setting value and the LP setting value respectively, two more control cases are stored in the control case memory. That is, the engineer creates a total of three sets of control cases when the control device is started (within the time when the state quantities are equal) and stores them in the control case memory 25 (S15).

As described above, when three sets of control cases at the time of initialization are stored in the control case memory 26, the stored contents are the state quantity comparator 26 and the cluster memory 2.
7 is supplied to the control rule calculator 28 via
Control rules are required. The control rule in this case is extracted as a control case plane as shown in FIG. 14 (S1).
6). Note that three independent control cases are required to determine the control case plane of FIG. Of course, four or more control cases may be used. In this case, an optimal control case plane is determined using a mean square error method or the like.

In FIG. 14, P1, P2, and P3 are points indicating the combination of the square setting value and the LP setting value for the three sets of control cases in the initial setting. Here, points indicating highlight densities (detection densities of highlight density patches) corresponding to the points P1, P2, and P3 are represented by H1, H2, and H3.
Similarly, points indicating the base density (detection density of the base density patch) corresponding to the points P1, P2, and P3 are denoted by B1, B2, and
B3. A plane passing through the points B1, B2, and B3 is defined as a solid case plane BP, and a plane passing through the points H1, H2, and H3 is defined as a highlight case plane HP. Here, in the case where the state quantity does not change, all points indicating the base density obtained when the scoro set value and the LP set value are appropriately changed fall within the solid case plane BP. Similarly, when the state quantity does not change, all points indicating the highlight density obtained when the scoro set value and the LP set value are appropriately changed fall within the highlight case plane HP. As described above, the solid case plane BP and the highlight case plane HP show all cases where the state quantity does not change. In other words, these planes have a solid density and a highlight density at the time of initializing. This shows the control rules for With the above processing, the initial setting processing in this embodiment ends.

By using the control rule thus obtained, the scoro setting value and the LP setting value can be uniquely determined for a predetermined target density. That is, when a desired density instruction value is input from the user, a solid density (solid target density) and a highlight density (highlight target density) are calculated according to the instruction values. As shown in FIG. 15, in the solid case plane BP and the highlight case plane HP, a plane having a solid target density (solid target density plane BTP) and a plane having a highlight target density (highlight target density plane HT) are obtained.
P). The intersection line BTL of the solid case plane BP and the solid target plane BTP is a set of points that satisfy a control rule regarding solid density and take a solid target density. The intersection line HTL between the highlight case plane HP and the highlight target density plane HTP is a set of points that satisfy the control rule regarding highlight density and take the highlight target density. Then, a set of a scoro set value and an LP set value that satisfies both the intersection lines BTL and HTL is obtained. The set of the scoro set value and the LP set value is the intersection of the projections of the intersection lines BTL and HTL onto the plane formed by the coordinate axis of the scoro set value and the coordinate axis of the LP set value.

If it is shown using a mathematical expression, it becomes as follows.
The control rule for solid density and the control rule for highlight density are D100 = a1.LP + a2.SC + a3 D20 = b1.LP + b2.SC + b3, respectively. Here, D100 is a solid density, D20 is a highlight density, LP is an LP set value, and SC is a scoro set value. A1, a2, a3, b1, b2, and b3 are coefficients. This formula can be used as the SCoro setting value SC and LP setting value LP
Solving for, SC = (b1 · D100−a1 · D20−a3 · b1 +
a1 ・ b3) / (a2 ・ b1-a1 ・ b2) LP = (b2 ・ D100-a2 ・ D20-a3 ・ b2 +
a2 · b3) / (a1 · b2-a2 · b1). By substituting the solid target density and the highlight target density for D100 and D20 in this equation, LP and S
C is determined.

When the solid density and the highlight density of the case satisfying the control rule are measured in advance, the scoro setting value and the LP setting value can be obtained from the solid density and the highlight density. That is, ΔD100 = a1 · ΔLP + a2 · ΔSC ΔD20 = b1 · ΔLP + b2 · ΔSC where ΔD100 is the difference between the case solid density and the target solid density, ΔD20 is the difference between the case highlight density and the target solid density, and ΔLP is the case LP. The difference between the set value and the next LP set value, ΔSC is the difference between the case scoro set value and the next scoro set value. This equation is solved for the difference ΔSC of the scoro setting value and the difference ΔLP of the LP setting value, and ΔSC = (b1ΔD100−a1ΔD20) / (a2b
1-a1b2) ΔLP = (b2ΔD100−a2ΔD20) / (a1b
2-a2b1) is obtained. By substituting ΔD100 and ΔD20 into this equation, ΔLP and ΔSC can be determined, and the next scoro setting value and LP setting value can be obtained.

The control rules are coefficients a1, a2, a3, b
1, b2, b3 and the coefficients a1, a2, b1, b
2 can be represented.

In this structure, the solid patch and the highlight patch are used as the density measuring patch (density difference 80%), but various density patches can be used as the measuring patch. . However, it is desirable that the density difference between the two patches be at least 30% apart. When the density difference is 30% or more, as shown in FIGS.
The target realization line LH of the case plane SH obtained from the high-density patch and the target realization line LL of the case plane SL obtained from the low-density patch are obtained, as shown in FIG. The projections of LH and LL are
The solution (LPx, SCx) can be obtained in an appropriate range of the scoro set value and the LP set value by intersecting on the plane formed by the coordinate axes of the scoro set value and the LP set value. However, when the density difference between the high density patch and the low density patch is less than 30%, as shown in FIG. 194, the target realization line LH of the high density patch case plane and the low density patch case plane target are obtained. Since the realization line LL is almost parallel to the realization line LL, a solution may not be obtained with appropriate LP setting value and scoro setting value, as shown in FIG. For example, when the operable range of the LP set value and the scoro set value is both set to 0 to 511, a solution (LPy, SCy) is obtained in a region outside this range, and appropriate control cannot be performed.

Therefore, it is important that the patch density difference is 30% or more.

(5) Operation after Initial Setting After the initial setting, the image density can be controlled by obtaining the correction amount of the operation amount using the following equation.

ΔSC = (b1ΔD100−a1ΔD2
0) / (a2b1-a1b2) ΔLP = (b2ΔD100−a2ΔD20) / (a1b
2-a2b1) When the state changes, it is detected and a new control rule is generated. Further, a plurality of control rules can be combined to obtain an appropriate control rule to control the image density.

In this case, the control rule (correction amount of operation amount)
To avoid the above-mentioned oscillation state. The operation of adjusting the control rule is shown in FIG. In FIG. 21, FIG.
Corresponding reference numerals are given to portions corresponding to and detailed description thereof will be omitted. In FIG. 21, the control rule adjustment mode is set in step S32, and accordingly step S33 is set.
At, the correction calculation adjustment unit 43 adjusts the control rule. For example, the above-mentioned ΔSC and ΔLP are respectively E1 /
Multiply by (E0 + E1). Alternatively, ΔSC and ΔLP are multiplied by 1/2. This prevents the manipulated variable from being excessively corrected in the next control, and creates an opportunity for the controlled variable to converge to the target value.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, the image quality such as the image density may not be measured for each image formation, but may be measured for each predetermined number of sheets or when an event occurs. In this case, the oscillation state may be detected and the oscillation state may be suppressed for measuring the image quality such as successive image densities.

[0060]

As described above, according to the present invention, in the image forming apparatus which controls the image quality based on the case, when the control of the image quality becomes the oscillation state, this oscillation state is detected and the control gain is obtained. Alternatively, since the control rule is adjusted to quickly suppress the oscillation state, the image quality control amount can be quickly converged to the target value.

[Brief description of drawings]

FIG. 1 is a first embodiment embodying the principle of the present invention.
FIG.

FIG. 2 is a flowchart illustrating the operation of the above-described embodiment.

FIG. 3 is a diagram illustrating an oscillation state that occurs in a conventional control system.

FIG. 4 is a diagram illustrating that the oscillation state is suppressed by the above-described embodiment.

FIG. 5 is a diagram illustrating a relationship between suppression of an oscillation state and acquisition of a gain calculation case according to the above-described embodiment.

FIG. 6 is a block diagram showing a configuration of an image output unit IOT according to a second embodiment in which the present invention is applied to an electrophotographic image forming apparatus.

FIG. 7 is a diagram illustrating generation of patches for density detection according to the second embodiment.

FIG. 8 is a diagram illustrating a patch and an image forming timing of an input signal in the second embodiment.

FIG. 9 is a diagram illustrating the density of an image formed in the second embodiment.

FIG. 10 is a block diagram showing a configuration of a control unit 20 according to the second embodiment.

11 is a diagram illustrating case data stored in a control case memory 25 of FIG.

12 is a diagram illustrating control rules stored in a control rule memory 29 of FIG.

FIG. 13 is a flowchart illustrating an operation at the time of initial setting according to the second embodiment.

FIG. 14 is a diagram for explaining the operation of FIG. 13;

FIG. 15 is a diagram for explaining the operation of FIG.

16 is a diagram for explaining the operation of FIG.

FIG. 17 is a diagram for explaining the operation of FIG. 13.

FIG. 18 is a diagram for explaining the operation of FIG. 13.

FIG. 19 is a diagram for explaining the operation of FIG. 13.

FIG. 20 is a diagram for explaining the operation of FIG. 13.

FIG. 21 is a flowchart illustrating adjustment of control rules according to the second embodiment.

FIG. 22 is a diagram illustrating a conventional control system.

[Explanation of symbols]

 100 target value 101 control amount 102 control gain 103 operation amount 104 control system 105 control gain inference unit 106 change amount of operation amount 107 change amount of control amount 108 difference between target value and control amount (control error) 109 control gain adjusting unit

Claims (4)

[Claims] 1. A control gain calculated based on image forming case data is used to control an operation amount such that a control amount relating to image quality reaches a target value, and the control amount and the target value are controlled. In the image forming apparatus that collects data of a new case and calculates a new control gain when the difference between the control amounts exceeds a predetermined allowable value, the magnitude of the difference between the control amount and the target value is a predetermined value. A value that is greater than or equal to a value, a means that determines whether the sign of the difference is opposite when a difference greater than or equal to the predetermined value is detected in a continuous image forming operation, and the sign is An image forming apparatus comprising: a unit that reduces the control gain when it is determined that they are opposite. 2. When the data of the new case is collected to calculate the new control gain, the control gain is not reduced even if it is determined that the signs are opposite. The image forming apparatus according to item 1. 3. An image forming apparatus for controlling an operation amount so that a control amount relating to image quality becomes a target value, a means for setting the target value, a means for measuring the control amount, and a series of image formations. One or more parameters of the manipulated variable and the function of the controlled variable, which are determined based on the manipulated variable actually applied in the process and the controlled variable actually measured when the manipulated variable is applied. Individually, a storage unit that stores the control rule, a state transition determination unit that determines a state transition of the image forming apparatus main body, and an operation amount in a series of image forming processes according to the determination output of the state transition determination unit. Means for determining a new parameter of the function from the measured value of the control amount, storing the control rule in the storage means, and calculating the operation amount based on the control amount An application control rule to be applied in order to calculate the application control rule from the parameter of the function 1 or by combining at least a part of the parameters of the plurality of functions; the application control rule; Means for changing the operation amount based on an error of the control amount with respect to the target value, a means for detecting that the magnitude of the error of the control amount with respect to the target value is a predetermined value or more, and continuous image formation. When an error greater than or equal to the predetermined value is detected during operation, a means for determining whether or not the sign is reversed, and a change in the operation amount when it is determined that the sign is opposite. An image forming apparatus having means for reducing the degree. 4. A control method for an image forming apparatus, which controls an operation amount such that a control amount relating to image quality reaches a target value, wherein an operation amount actually applied and a value measured when the operation amount is applied. The step of generating one or a plurality of control rules in the initial state based on the control amount, and the applied control rule applied to calculate the manipulated variable based on the control amount. And a step of determining a state transition of the image forming apparatus main body, a step of generating a new control rule from an operation amount and a control amount at the time of image formation according to the determination of the state transition. A step of changing the applied control rule in consideration of the new control rule, and detecting that the magnitude of the error of the control amount with respect to the target value is a predetermined value or more. The step of issuing, the step of determining whether or not the sign is opposite when an error of the predetermined value or more is detected in the continuous image forming operation, and the above sign is determined to be opposite. Sometimes, a step of reducing the degree of change in the operation amount is included.