JP7674806B2 - Control device and control method - Google Patents

Description

The present invention relates to a control device and a control method for controlling physical quantities such as temperature, flow rate, humidity, and pressure of a controlled object, such as an electric furnace, a flow rate system, or a chemical reaction system, to target values.

For example, in electric furnaces, regulators are commonly known as control devices that compare the furnace temperature with a target value and perform calculations based on the deviation to control heating means such as heaters.

Digital controllers are equipped with an auto-tuning function that automatically calculates and sets the PID constants according to the controlled object. This auto-tuning function employs the limit cycle method, in which the controller is temporarily used as an on-off controller, and the on/off operation alternately outputs 100% and 0% manipulated variable to calculate the PID constants from the period and amplitude of the hunting that occurs in the controlled object.

As an example of the limit cycle method described above, the present applicant has proposed a control device that determines the manipulated variable by finding a PID constant from a cycling (limit cycle) waveform near a set value, as disclosed in the following Patent Document 1.

Japanese Patent Application Publication No. 7-13608

However, in the limit cycle method described above, if the PID constants are not determined appropriately, a phenomenon called overshooting occurs, in which the controlled variable exceeds the target value. When this overshooting occurs, excessive stress is placed on the controlled object (e.g., the manufactured product), causing a problem of reduced yield, and so there is a need to suppress the overshooting.

The present invention was made in consideration of the above problems, and aims to provide a control device and control method that can suppress overshoot.

In order to achieve the above object, a control device according to a first aspect of the present invention is a control device that changes a control amount of a controlled object according to an operation amount, and causes the control amount to coincide with a target value,
a first control means for performing PID control at least twice in order of increasing intermediate target values so that the controlled variable reaches at least two intermediate target values that are set smaller than the target value, and for continuing the PID control for a first predetermined time until the controlled variable becomes stable after reaching the intermediate target values;
a first calculation means for calculating an average manipulated variable as an average manipulated variable within the first predetermined time after the controlled variable for each of the PID control by the first control means has reached the intermediate target value;
a second calculation means for calculating a manipulation amount corresponding to the target value on an approximation line of a function equation created from an average manipulation amount for each of the PID control calculated by the first calculation means, as an estimated manipulation amount when the controlled amount reaches the target value;
A second control means for performing control using the estimated manipulated variable;
a third control means for finely adjusting the manipulated variable so that the controlled variable coincides with the target value after the second control means has performed control for a second predetermined time;
The present invention is characterized by comprising:

The control device according to claim 2 is the control device according to claim 1 ,
The fine adjustment control is characterized in that it is integral control.

A control method according to claim 3 is a control method for changing a control amount of a controlled object based on an operation amount to make the control amount coincide with a target value, comprising the steps of:
performing PID control at least twice in order of increasing intermediate target values so that the controlled variable reaches at least two intermediate target values that are set smaller than the target value, and continuing the PID control for a first predetermined time until the controlled variable is stabilized after reaching the intermediate target values;
calculating an average value of an operation amount within the first predetermined time after the control amount for each of the PID control has reached the intermediate target value as an average operation amount;
calculating a manipulated variable corresponding to the target value on an approximation line of a function equation created from the average manipulated variable for each of the PID control as an estimated manipulated variable when the controlled variable reaches the target value;
performing control using the estimated manipulated variable;
a step of performing control for a second predetermined time with a manipulated variable corresponding to the target value on the approximation line, and then fine-tuning the manipulated variable so that the controlled variable coincides with the target value;
The present invention is characterized by comprising:

The control method according to claim 4 is the control method according to claim 3 , further comprising:
The fine adjustment control is characterized in that it is integral control.

According to the present invention, after calculating and controlling an estimated manipulated variable corresponding to a target value, overshooting can be suppressed by fine-tuning the manipulated variable so that the controlled variable coincides with the target value.

1 is a block diagram showing a schematic configuration of a control device according to the present invention; FIG. 2 is a diagram showing an example of a timing chart of tuning and control by the control device and control method according to the present invention.

The following describes in detail the embodiment of the present invention with reference to the attached drawings.

As shown in FIG. 1, the control device 1 of this embodiment is a regulator that uses physical quantities such as temperature, flow rate, humidity, and pressure of a controlled object such as an electric furnace, flow rate system, or chemical reaction system as control quantities, and changes the control quantities according to the manipulated variables to match the control quantities with target values, and is generally configured with an operation and display unit 2, a memory unit 3, and a control unit 4 as components for performing tuning and control.

As shown in FIG. 1, the control target is an electric furnace 13 having a heating means 11 such as a heater and a temperature sensor 12 installed inside the furnace, and the heating means 11 is controlled by driving an actuator (not shown) with a manipulated variable MV so that the furnace temperature detected by the temperature sensor 12 (controlled variable PV) coincides with a target temperature (target value SV).

The operation and display unit 2 is equipped with various keys provided on the front of the device, and displays such as LCD and LED. The operation and display unit 2 issues an instruction to start tuning, sets the PID constant at the start of tuning, the target value SV, multiple intermediate target values (for example, an intermediate target value SV1 with a load rate of 60% and an intermediate target value SV2 with a load rate of 80% relative to the target value SV), and the predetermined times T1, T2, and T3 described below. In addition to displaying the setting screen, the operation and display unit 2 also displays the target value SV and the controlled variable PV, various data such as program patterns, and various monitor displays such as bar graphs and trends.

The memory unit 3 stores various information related to the control of the temperature inside the electric furnace 13, including the set values (PID constants, target value SV, intermediate target values SV1, SV2, and predetermined times T1, T2, and T3) set by operating the operation display unit 2, the estimated operation amount MV3 described below, and the approximation line according to formula (1).

The control unit 4 controls the control device 1 based on the set values set by the operation of the operation display unit 2, various information stored in the memory unit 3, and the temperature inside the electric furnace detected by the temperature sensor 12 of the electric furnace 13. The control unit 4 includes a first control means 4a, a first calculation means 4b, and a second calculation means 4c as a configuration for performing tuning, and includes a second control means 4d and a third control means 4e as a configuration for performing control to adjust the control amount PV so that it coincides with the target value SV.

The first control means 4a drives the actuator with the operation amount MV in the order of increasing intermediate target values to control the heating means 11 so that the control amount PV reaches the multiple intermediate target values set by the operation of the operation display unit 2.

Specifically, for example, when an intermediate target value SV1 with a load rate of 60% and an intermediate target value SV2 with a load rate of 80% are set for the target value SV, the first control means 4a first drives the actuator with the manipulated variable MV to PID-control the heating means 11 so that the temperature (controlled variable PV) of the temperature sensor 12 of the electric furnace 13 reaches the intermediate target value SV1 with a load rate of 60%. After that, the first control means 4a drives the actuator with the manipulated variable MV to PID-control the heating means 11 so that the temperature (controlled variable PV) of the temperature sensor 12 of the electric furnace 13 reaches the intermediate target value SV2 with a load rate of 80%. Note that the control of the heating means 11 by driving the actuator is not limited to PID control.

The first calculation means 4b calculates the average operation amount as the average operation amount, which is the average value of the operation amount MV within a predetermined time after the control amount PV reaches each intermediate target value by the first control means 4a.

Specifically, for example, if an intermediate target value SV1 with a load rate of 60% and an intermediate target value SV2 with a load rate of 80% are set for the target value SV, the first calculation means 4b calculates as the average operation amount MV1 the average value of the operation amount MV within a predetermined time T1 after the control amount PV reaches the intermediate target value SV1 with a load rate of 60% for the target value SV. The first calculation means 4b also calculates as the average operation amount MV2 the average value of the operation amount MV within a predetermined time T2 after the control amount PV reaches the intermediate target value SV2 with a load rate of 80% for the target value SV.

The predetermined time T1 is set to the time until the controlled variable PV reaches an intermediate target value SV1 with a load rate of 60% relative to the target value SV and stabilizes. The predetermined time T2 is set to the time until the controlled variable PV reaches an intermediate target value SV2 with a load rate of 80% relative to the target value SV and stabilizes.

The second calculation means 4c calculates the operation amount MV corresponding to the target value SV on the approximation line based on the average operation amount calculated by the first calculation means 4b as an estimated operation amount when the control amount PV reaches the target value SV.

Specifically, for example, when an intermediate target value SV1 with a load factor of 60% and an intermediate target value SV2 with a load factor of 80% are set for the target value SV, the second calculation means 4c creates a linear function formula (1): y = 5 (MV2-MV1) x + MV2-4 (MV2-MV1) from the two average operation amounts MV1 and MV2 calculated by the first calculation means 4b. This linear function formula (1) is created by substituting a = 5 (MV2-MV1) and b = MV2-4 (MV2-MV1) into y = ax + b when the two average operation amounts MV1 = 0.6 x a + b and MV2 = 0.8 x a + b. Then, the operation amount MV corresponding to the target value SV on the approximation line according to this linear function formula (1) is calculated as the estimated operation amount MV3 when the control amount PV reaches the target value SV.

The above-mentioned approximation line is represented by equation (1), which is a linear function created from the two average operation amounts MV1 and MV2, but is not limited to equation (1), which is a linear function. For example, when three or more intermediate target values are set, the accuracy can be further improved by using an approximation line represented by an equation, which is a quadratic function created from these three or more intermediate target values.

The second control means 4d drives the actuator with the estimated operation amount MV3 based on the fixed value calculated by the second calculation means 4c to control the heating means 11.

After the second control means 4d controls the heating means 11 with the estimated operation amount MV3 for a predetermined time T3, the third control means 4e fine-tunes the operation amount MV by integral control in addition to the estimated operation amount MV3 so that the control amount PV coincides with the target value SV, and drives the actuator to control the heating means 11.

Next, the tuning and control method using the control device 1 configured as described above will be explained with reference to Figure 2.

First, the PID constants are set arbitrarily by operating the operation display unit 2, and the target value SV, the operation amount MV, and the intermediate target value are set. Here, the intermediate target values are set as follows: a load factor of 60% of the target value SV is set as intermediate target value SV1, and a load factor of 80% of the target value SV is set as intermediate target value SV2.

After completing the above settings, when tuning is started by operating the operation display unit 2, the first control means 4a of the control unit 4 drives the actuator with the manipulated variable MV to PID-control the heating means 11 so that the temperature inside the electric furnace 13 reaches an intermediate target value SV1 = 0.6 x SV [%] with a load factor of 60% of the target value SV, as shown in section (a) of Figure 2. This PID control sets the manipulated variable MV according to the controlled variable PV, and continues for a predetermined time T1 after the controlled variable PV reaches the intermediate target value SV1.

Then, the first calculation means 4b of the control unit 4 calculates the average value of the operation amount MV within a predetermined time T1 after the control amount PV reaches the intermediate target value SV1 as the average operation amount MV1. Specifically, if the number of samples in the predetermined time T1 is n1, the average operation amount MV1 is calculated as Σ(MVn1)/n1 [%].

Next, the first control means 4a of the control unit 4 drives the actuator with the manipulated variable MV to PID-control the heating means 11 so that the temperature inside the electric furnace 13 reaches an intermediate target value SV2 = 0.8 x SV [%], which is a load factor of 80% of the target value SV, as shown in section (b) of Figure 2. This PID control sets the manipulated variable MV based on the controlled variable PV, and continues for a predetermined time T2 after the controlled variable PV reaches the intermediate target value SV2.

Then, the first calculation means 4b of the control unit 4 calculates the average value of the operation amount MV within a predetermined time T2 after the control amount PV reaches the intermediate target value SV2 as the average operation amount MV2. Specifically, if the number of samples in the predetermined time T2 is n2, the average operation amount MV2 is calculated as Σ(MVn2)/n2 [%].

Next, the second calculation means 4c of the control unit 4 creates an approximation line of a linear function from the average operation amounts MV1 and MV2. Specifically, if MV1 = 0.6 x a + b and MV2 = 0.8 x a + b, then a = 5 (MV2 - MV1) and b = MV2 - 4 (MV2 - MV1). These a and b are substituted into y = ax + b, and an approximation line is created using the linear function equation (1) consisting of y = 5 (MV2 - MV1) x + MV2 - 4 (MV2 - MV1).

Then, the second calculation means 4c of the control unit 4 calculates the operation amount MV corresponding to the target value SV on the approximation line according to the created linear function equation (1) as the estimated operation amount MV3 when the control amount PV reaches the target value SV. That is, according to the linear function equation (1), the estimated operation amount MV3 = 5 (MV2 - MV1) + MV2 - 4 (MV2 - MV1) [%] is obtained, and the average operation amounts MV1 and MV2 calculated by the first calculation means 4b are substituted to calculate the estimated operation amount MV3.

Then, as shown in section (c) of FIG. 2, the second control means 4d of the control unit 4 continues to output the operation amount MV as the estimated operation amount MV3 for a predetermined time T3, and drives the actuator with the estimated operation amount MV3 to control the heating means 11.

Furthermore, as shown in section (d) of FIG. 2, when the control based on the estimated operation amount MV3 has elapsed for a predetermined time T3, the third control means 4e of the control unit 4 starts integral control in addition to the estimated operation amount MV3, thereby fine-tuning the operation amount MV. As a result, control is performed so that the control amount PV coincides with the target value SV while suppressing overshooting.

In the above-described embodiment, the tuning and control of a control device that controls the temperature inside the electric furnace 13 to a target value SV has been described as an example of a control target, but the present invention is not limited to this. For example, the present invention can also be used as tuning and control of a control device that controls physical quantities such as flow rate, humidity, and pressure in a flow rate system or chemical reaction system to target values.

In this way, according to this embodiment, after the estimated manipulated variable corresponding to the target value is calculated and controlled through tuning and control, the manipulated variable is fine-tuned so that the controlled variable matches the target value, so that overshooting is suppressed and tuning and control can be performed without the controlled variable exceeding the target value.

The above describes the best mode for the control device and control method according to the present invention, but the present invention is not limited to the description and drawings of this mode. In other words, it goes without saying that all other modes, examples, and operational techniques that are made by those skilled in the art based on this mode are included in the scope of the present invention.

REFERENCE SIGNS LIST 1 Control device 2 Operation display unit 3 Memory unit 4 Control unit 4a First control means 4b First calculation means 4c Second calculation means 4d Second control means 4e Third control means 11 Heating means 12 Temperature sensor 13 Electric furnace (controlled object)

Claims (4)

A control device that changes a control amount of a control target according to an operation amount to make the control amount coincide with a target value,
a first control means for performing PID control at least twice in order of increasing intermediate target values so that the controlled variable reaches at least two intermediate target values that are set smaller than the target value, and for continuing the PID control for a first predetermined time until the controlled variable becomes stable after reaching the intermediate target values;
a first calculation means for calculating an average manipulated variable as an average manipulated variable within the first predetermined time after the controlled variable for each of the PID control by the first control means has reached the intermediate target value;
a second calculation means for calculating a manipulation amount corresponding to the target value on an approximation line of a function equation created from an average manipulation amount for each of the PID control calculated by the first calculation means, as an estimated manipulation amount when the controlled amount reaches the target value;
A second control means for performing control using the estimated manipulated variable;
a third control means for finely adjusting the manipulated variable so that the controlled variable coincides with the target value after the second control means has performed control for a second predetermined time;
A control device comprising: The control device according to claim 1, characterized in that the fine adjustment control is integral control. A control method for changing a control amount of a control target based on an operation amount to make the control amount coincide with a target value, comprising the steps of:
performing PID control at least twice in order of increasing intermediate target values so that the controlled variable reaches at least two intermediate target values that are set smaller than the target value, and continuing the PID control for a first predetermined time until the controlled variable is stabilized after reaching the intermediate target values;
calculating an average value of an operation amount within the first predetermined time after the control amount for each of the PID control has reached the intermediate target value as an average operation amount;
calculating a manipulated variable corresponding to the target value on an approximation line of a function equation created from the average manipulated variable for each of the PID control as an estimated manipulated variable when the controlled variable reaches the target value;
performing control using the estimated manipulated variable;
a step of performing control for a second predetermined time with a manipulated variable corresponding to the target value on the approximation line, and then fine-tuning the manipulated variable so that the controlled variable coincides with the target value;
A control method comprising: The control method according to claim 3, characterized in that the fine adjustment control is integral control.

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