JPS60215210A - Pid controller - Google Patents

Abstract

PURPOSE:To not execute the step response method if a present value approximates a set value, by executing the step response method and the threshold sensitivity method selectively in accordance with the state of a control object. CONSTITUTION:First, a set value and a set time are written by a key input part 2 before turning. When the operation is started, detected temperature data is read into a RAM9 from a temperature detecting part 5 through a control part 6. Next, the present process state is detected to check whether the step response method is required or not. If the present process state obtained from the temperature detecting part 5 at a power-on time and after application of a reset input is <=1/2 of the set value and a proportional band of a proportional constant in a PID constant calculated at the preceding tuning execution time is <=1%, the step response method is executed; but otherwise, the threshold sensitivity method is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a PID control device that temporally controls a controlled object, and in particular to a PID control device that is characterized by tuning of PID constants.
This relates to an ID control device.

Background of the Invention Various control devices, such as temperature control devices, have a control device or a program function that controls the temperature to a single set temperature, and program control that controls the temperature over time according to a predetermined control pattern. There is a device. These control devices require a PID constant to be determined in advance in order to perform PID control on a controlled object. Furthermore, if the controlled object is different, it is necessary to change the PID constant to suit the object, and a tuning operation is required to determine the constant. As this tuning method, a step response method and a limit sensitivity method (frequency response method) are used.

As shown in Figure 1, the step response method is 100% when the current value, for example, the current temperature, is sufficiently lower than the set temperature s1.
When the controlled object is controlled by the manipulated variable of The PID constant is calculated from the values of R and L according to a predetermined formula. According to this step response method, it is possible to easily obtain a PID constant in a short time simply by controlling the controlled object with a 100% manipulated variable. However, in order to obtain the response speed R, which is the maximum slope, a certain amount of difference is required between the set value and the current value.
If there was not much difference, it was necessary to lower the temperature and then perform a step response. Furthermore, there is a problem in that the controlled object is controlled in advance and the PID constant varies depending on various conditions such as whether there is residual heat or not.

On the other hand, the limit sensitivity method calculates the PID constant from the limit sensitivity Kc, which is the limit proportional gain that oscillates steadily at a set value, and its period Tc in the response curve of the controlled object shown in FIG. According to this method, the PID near the set value s1
It is possible to set a constant, and since the PID constant can be tuned during control, highly accurate tuning is possible.

However, when controlling a controlled object for the first time, it is unclear what level of gain is required to cause steady oscillation, and it requires skill to set the sensitivity to the limit and operate until steady oscillation is reached as shown in the figure. Another problem is that tuning takes a long time. In addition, the presence or absence of steady oscillation is confirmed by detecting the controlled object with a sensor and based on the data, but it is difficult to detect the oscillation state especially when the oscillation is small, and it is difficult to find the oscillation state before obtaining the PID constant. There was a problem that it took a long time.

OBJECT OF THE INVENTION The present invention has been made in view of the problems encountered when tuning the PID constants of conventional PID control devices. PID constant can be set by selecting one of the tuning methods depending on the target and its condition.
The present invention provides an ID control device.

Structure and Effects of the Invention The present invention provides a detection means for detecting measured information in a controlled object, an output means for performing a control operation on the controlled object, and a PID control device for performing PID control on the controlled object based on a set value. a selection means for selecting a condition in which a step response is possible based on the current measured information and a set value; and an output means for operating an output means when the step response is selected by the selection means to adjust the response speed according to the step response of the controlled object. Step response means for measuring dead time and determining a PID constant; and frequency response means for measuring limit sensitivity and vibration period from the frequency response of the controlled object and determining a PID constant when step response is not selected by the selection means. It is characterized by comprising the following.

According to the present invention having such characteristics, conditions are selected that allow calculation of a PID constant by step response, and based on the conditions, the PID constant is calculated by either the step response method or the frequency response method. . Therefore, it is possible to perform tuning according to the state of the controlled object, and if the current value is close to the set value, the step response is not executed, so that the influence on the controlled object can be reduced. In particular, since the step response method is selected when the power is turned on, it is possible to execute the step response immediately after the power is turned on, and to immediately execute PIDilJ control using the PID constant obtained from the step response.

DESCRIPTION OF EMBODIMENTS FIG. 3 is an overall configuration diagram of a programmable temperature control device showing an embodiment of the present invention. In this figure, a temperature control device 1 is provided with a key manual part 2 for setting temperature control steps, requesting tuning, etc., a display part 3 for displaying the step number, set temperature, and current temperature, and a control object 4. A temperature detection unit 5 having a sensor that detects the temperature of the sensor and an A/D converter that converts the data obtained from the sensor into a digital value.
, a control unit 6 that controls the controlled object 4 according to a predetermined processing procedure based on data obtained from the temperature detection unit 5, and an output unit 7 that is connected to the control unit 6 and directly controls the controlled object 4, which is made up of a heater, a motor, etc. is provided. The control unit 6 consists of a central processing unit (hereinafter referred to as CPU), and is connected to a read-only memory (hereinafter referred to as ROM) 8 and a random access memory (hereinafter referred to as RAM) 9 as storage devices.

The ROM 8 stores the arithmetic processing procedures of the control section 6, and the RAM 9 has an area for storing various control data given from the key manual section 2 and data used during tuning.

FIG. 4 is a memory map showing storage areas used when tuning the RAM 9. In this figure, the RAM 9 is provided with an area for storing set values, a measured data area for storing current measured information obtained from the temperature detection section 5, a tuning flag set during tuning, and a response obtained by step response. Area for storing speed R and dead time, limit sensitivity Kc by limit sensitivity method, period T
C and the proportionality constant K obtained by these tuning methods
p, an integral constant Ki, and a differential constant Kd. It is preferable that the storage area used for tuning the RAM 9 be a memory back-amplified by a battery or the like so that the data can be stored even after the power is turned off.

FIG. 5 shows the front panel surface of the program temperature control device used in the key input section 2 and display section 3. As shown in FIG. rRUNJ, rATj, rTIME on the top of the panel surface
J is an operation display lamp, an auto tuning lamp, and a time value display lamp, rBJ is a bank display, and rs
TEPJ is a display section for step display, rPVJ is a display section for displaying current values, and rSVJ is a display section for displaying set values. The rcONTROLJ switch at the bottom is an output operation switch that switches between the normal operation mode and a stop mode that stops time progression and stops control output.
DE" switch is a switch that is selected according to the type of change when setting or changing various program contents, rENDJ
The switch is a switch to cancel the operation and return to the current value display mode, rPROGRAMJ switch is a switch that enables and prohibits program writing, r
The ATJ switch is a switch that is pressed when performing tuning during control, ``↑'' and ``↓.''

The "←" and "→" switches increase the value of the parameter, respectively.
It is a numerical control switch that lowers, raises and lowers two digits,
The rwRrTE/NEXTJ switch is a switch that sets display data, stores it in the RAM 9, and moves the setting operation to the next step.

Next, the PID constant calculation operation of the program temperature control device of this embodiment will be explained with reference to a flowchart.

In the flowchart of FIG. 6, numbers indicated using leader lines indicate processing routines or operation steps of the control section 6. First, before tuning, set values and set times are written from the key manual section 2. This is rPROG
After setting the RAMJ key to the cent position and setting the MODEJ key to the program setting, set the value corresponding to the setting step to "↑
", "↓J, r-J, r-J numerically controlled switches are used to input, and the rWRI TE/NEXTJ key is used to write.If the program control device is used, a series of Write setting data.Here, it is assumed that each control step and a series of setting values corresponding thereto have been written in advance in the step area of the RAM 9.

Now, when starting the operation in Fig. 6, first step 21
Read the setting value. Then, in step 22, the detected temperature data is read from the temperature detection section 5 into the measured data area of the RAM 9 via the control section 6. Then, the process proceeds to step 23, where it is checked whether the tuning flag is set by pressing the rATJ key. If this button has been pressed, the process advances to step 24 to detect the current process state. The process then proceeds to step 25 to check whether step response is possible. Conditions under which the step response is possible include, for example, when the memory is cleared after power is turned on, when the current process state obtained from the temperature detection unit 5 is less than the set value A at the time of power is turned on and after a recent input is applied. and the proportional band P at the proportional constant Kp among the PID constants calculated during the previous tuning execution.
is 1% or less. In these cases, step response is performed, and in other cases, frequency response is selected. This is because the current temperature and the set value are usually considered to be sufficiently far apart when the power is turned on, and the current temperature is 2 times the set value.
This is because a step response in which the operation amount of the output section 7 is set to 100% is advantageous in the following cases as well, since it can quickly approach the set value. Also, when the proportional band P is 1% or less, the proportional gain is extremely high, so it is difficult to detect vibrations even if the gain of the temperature control device is increased further. This is because it is necessary to carry out the law. After thus starting the execution of either the step response method or the limit sensitivity method in step 26.27,
The process advances to step 28 to wait for the completion of sampling, and then returns to step 21. Then, the same process is repeated, and in step 23, it is checked whether or not tuning has been input. In this case, since tuning has started, the process advances to step 29 and the tuning flag is checked. Since tuning has not yet been completed, the program proceeds to step 30 and checks whether the step response method has already been started. If the step response method is used, the process proceeds to step 31 and the step response is executed as is. If the limit sensitivity method is used, the limit sensitivity method is executed in step 32, and the process proceeds to step 33 to check whether the tuning is completed. To check. If the tuning has not been completed, the process waits for the sampling to be completed, returns to step 21, and repeats the same process.

The control equation of the idealized analog PID control device is given by the following equation.

τ = Kp en +Ki ΣeQ + K d (e ne nJ −−−−−−−411
Here, Mn: manipulated variable, en: deviation (Ts - Tn) (
T: set temperature, Tn: measured temperature) Kp: proportionality constant + Ki: integral constant, Kd: differential constant, τ: sampling period. The dead time obtained by the step response, the response speed R, the proportional constant of PID, the integral time, the differential time Kp, Ti, and Td have the following relationship.

1-2L Td = 0.5L -------(21 Therefore, by the step response method, PID constants Kp, Ki, Kd
can be used. Also, in the limit sensitivity method, a PID constant is calculated.

In Figure 2, the proportional band at the limit sensitivity Kc is PC (%
), then Kc and Pc are inversely proportional, and from the proportional band Pc (%) obtained there, the following formula % formula % (31) is established, and the proportionality constant Kp is calculated by the following formula K p = A / P --- ---(4) (A is a constant determined by the characteristics of the control device). Furthermore, from the oscillation period Tc, Ti = 0.5Tc Td = 0.125Tc --- (51) determines the PID constant. If this tuning operation is not completed, step 33 to step 28
Proceed to and wait for sampling to complete. In the control device, the temperature detection unit 5 detects the temperature from the controlled object 4 at a predetermined A/D conversion cycle, and when the sampling is completed, the process returns from step 28 to step 21, reads the set value and temperature input, and performs tuning. The same process is repeated by checking whether the rATJ switch has been pressed and whether tuning is in progress. When the tuning is completed by either method, the process proceeds from step 33 to step 34, and the PID constant obtained from equation (2) or equations (3) to (5) is stored in a predetermined area of the RAM 9 shown in FIG. The program then proceeds to step 35 to reset the tuning flag. Then, the process advances to step 28 and waits for the completion of sampling. When the sampling is completed, the process goes to steps 21 and 22 again, where the set value and temperature input are read, and the process goes to step 29 via step 23. In this case, since tuning has already been completed, jump to step 36 and read the PID constant held in RAM9.
In step 37, the controlled object 4 is PID-controlled via the output section 7 based on the value and maintained at the set temperature.

As described above, in the present invention, the tuning operation is performed by selectively implementing either the step response method or the limit sensitivity method depending on the state of the controlled object. Therefore, PID control can be performed immediately after power is turned on, and if the tuning key is pressed as necessary during PID control after determining the PID constant using the step response method, the current temperature state and set value can be checked. Since they are considered to be almost the same, the limit sensitivity method is carried out and it becomes possible to determine a more precise PID constant.

Although this embodiment describes a program temperature control device, the present invention is not limited to this and can be applied to a single setting type PID control device, and the present invention can also be applied to various PID control devices other than temperature control devices. It is also possible.

[Brief explanation of the drawing]

Figure 1 is a graph showing the process values that follow the operation when determining the PID constant using the step response method, Figure 2 is a graph showing the relationship between set values and process values using the limit sensitivity method, and Figure 3 is the invention of the present invention. FIG. 4 is a memory map showing the contents of the memory used for tuning operations, and FIG. 5 is a diagram showing the front panel of the setting section 2 and display section 3. , FIG. 6 is a flowchart showing the operation of the program temperature control device according to this embodiment. 1-...Temperature control device 2--Key human power section 3--11--Display section 4-----1 Controlled object 5.--11-- 1 Temperature detection part 6------
One control part? ---------1 output part 8-----RO
M 9-・-1-RAM Patent Applicant Tateishi Electric Co., Ltd. Agent Patent Attorney Kanki Okamoto (1 person) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) In a detection means for detecting measured information on a controlled object, an output means for performing control operations on the controlled object, and a PID control device that performs PID control on the controlled object based on a set value, the current measured information and a selection means for selecting a condition in which step response is possible based on a set value; and when step response is selected by the selection means, the output means is operated to measure response speed and dead time based on the step response of the controlled object. A step response means for determining a PID constant; and a frequency response means for determining a PID constant by measuring a limit sensitivity and a vibration period from a frequency response of a controlled object when the step response is not selected by the selection means. A PID control device characterized by: (2) The selection means selects the step response when the power is turned on, when the difference between the set value and the current measured information is more than a predetermined value, and when the proportionality constant of the PID that has already been executed is less than a predetermined value. A PID control device according to claim 1, wherein the PID control device is a PID control device. (3) The PID control device according to claim 1, wherein the PID control device is a program temperature cave device.
D control device.