JP2799009B2 - Programmable controller - Google Patents

Description

The present invention relates to a programmable controller, and more particularly, to a programmable controller.
The present invention relates to a programmable controller suitable for executing a sequence control program having a PID control program therein.

[Prior Art] FIG. 8 is a configuration diagram of a conventional programmable controller. Conventional programmable controllers use a CPU
Unit 1 and an input / output unit 2, and a control program created by a user using a programming device 3 provided outside
The control program is executed by being read by the U unit 1, and the sequence control target 5 is controlled via the input / output unit 2. The CPU unit 1 includes an MPU 11 and a system ROM / RAM 1
2, a peripheral device interface 13 connected to the programming device 3 and the like, a user memory 15 storing a control program, and a system bus 14 interconnecting these. The input / output unit 2 has a digital signal input port 21
, A digital signal output port 22, an analog signal input port 23, and an analog signal output port 24, which are connected to the system bus 14.

The control program stored in the user memory 15 is divided into a normal scan program unit 40 and a fixed-cycle scan program unit 41 that is interrupted at a constant period during execution of the normal scan program unit 40. The normal scan program section 40 performs a cyclic operation from the beginning of the program section 40 to the END instruction, and the fixed scan program section 41 executes the RTI instruction from the INT instruction (label indicating the start position of the fixed scan program). (Instructions for returning from the periodic scan program to the normal scan program) are interrupted.

The above-described control program is written from the programming device 3 to the user memory 15 via the peripheral device interface 13, and the MPU 11 sequentially reads each instruction of the control program, performs arithmetic processing on data read from the input / output unit 2, The control of the control target 5 is performed.

In the conventional programmable controller, as described above, the control program is stored in the normal scan program section.
The reason for dividing into 40 and the periodic scan program section 41 is as follows. The processing time of the normal scan program unit 40 becomes longer in proportion to the program amount of the user. Therefore,
When there is a control part that requires a short response time in the control target, control of a control part that should respond in a short time becomes impossible if the program amount is large. Therefore, the periodic scan program section 41 is included in the control program.
Is provided, and the control that requires a short-time response is performed by the fixed-period scan program unit 41, so that the short-time response control is performed at a fixed time so that the user can form a large program. I have.

As related to the conventional programmable controller, for example, "Hitachi Review" issued in July 1989 (UD
C.658.527.7'132) There are those described on pages 43 to 48.

[Problems to be Solved by the Invention] The control target of the programmable controller has conventionally been limited to one that performs sequence control, but in recent years, there has been a tendency to apply it to process control.
However, PID (proportional, integral,
Differential) control. However, the conventional programmable controller does not consider PID control, and has a problem that the following problem occurs.

(1) In performing the PID calculation, it is necessary to sample the measurement data to be controlled and take it into the controller, but this sampling must be performed at regular intervals. However, since the processing time varies depending on the size of the user program, the sampling period cannot be fixed, and therefore, there is a problem that the PID constant cannot be uniquely set.

(2) The problem (1) can be dealt with by programming the PID operation in the periodic scan program unit 41. However, when the number of PID loops to be controlled increases, the execution of the periodic scan is performed. The time gets longer,
There is a problem that the scan program is almost never executed.

(3) The sequence operation instruction usually has only four arithmetic operations. However, since the PID operation includes the integration and the differential operation, the program length is longer in the PID control program.
Also, the programming requires a great deal of effort.

An object of the present invention is to be able to set a PID constant regardless of the size of a user program, to execute a normal scan program reliably even when the number of PID loops is large, and to easily create a PID control program. To provide a programmable controller capable of performing such operations.

[Means for solving the problem]

The purpose of the above is to use multiple loop PIDs in the fixed-cycle arithmetic processing program that exists in the sequence arithmetic processing program.
In a programmable controller having a control program and having a processor for executing and executing these programs, the processor executes only one loop of the PID control program at the time of execution of the fixed-cycle operation processing program, and executes the next fixed-cycle operation processing program. This is achieved by providing means for executing another one-loop PID control program at the time of execution, and means for setting an execution interval of an arbitrary loop in the multiple-loop PID control program at an arbitrary multiple of the number of loops. You.

By periodically executing the PID control program, the data to be controlled can be periodically taken in regardless of the size of the user program, and the PID constant can be determined. Furthermore, even if there are a large number of PID loops for performing PID control on a regular basis, it is possible to avoid a situation in which the execution of the normal scan program is not performed, and to set the execution interval of the PID control at an arbitrary multiple. Because it is possible, the execution of the normal scan program can be ensured.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

FIG. 1 is a configuration diagram of a programmable controller according to one embodiment of the present invention. The present programmable controller and the conventional programmable controller shown in FIG.
The other configuration is the same except that the D control target 6 is connected to the analog signal input / output ports 23 and 24. Hereinafter, the contents of the periodic scan program unit 41 and the operation performed by the MPU 11 according to the contents will be described.

The periodic scan program unit 41 in the present embodiment includes:
It is read out and executed every 20 milliseconds during the execution processing of the normal scan program unit 40. The program configuration starts with an INT instruction which is a label indicating a start position, and then there is an instruction PID “C” for performing loop management. Hereinafter, PID “1” to PID “n” which are actual PID operation instructions (In each instruction, the measured value Xn of the PID control target 6 is taken from the analog signal input port 23 and the corresponding target value Wn
From the system ROM / RAM12 and using both values Xn and Wn
The PID calculation is performed, and the result is output to the PID control target 6 from the analog signal output port 24 as the manipulated variable Yn. Finally, there is an instruction RTI that returns to the normal scan program.

The loop management instruction PID “C” is a PID operation instruction PID “1” to PID
PID operation start flag R provided in software for "n"
“1” to R “n” are converted by the fixed-cycle scan program unit 41.
Each time it is read by the MPU 11 and interrupted, it is turned on one by one. In other words, if the flag R “i” at the time when the periodic scan program unit 41 is read and interrupted at a certain cycle is on, the PID “ Only the “i” instruction is executed, and in the execution of the fixed-cycle scan program unit 41 after the next 20 milliseconds, the PID “i + 1” instruction is executed because the flag R “i + 1” is on. That is,
In one execution of the fixed-cycle scan program unit 41, only one loop of the PID operation instruction is executed. In the present embodiment, such a program configuration is performed, as described above, when the PID control is continuously performed, the processing time of the PID control becomes longer, and the normal scan program to be executed between the interrupt processes is performed. This is to avoid running out of the execution time of the unit 40. Therefore, if a high-speed processor is used and the execution time of the normal scan program is always ensured between each interrupt processing, that is, the execution of the normal scan program and the execution of the fixed-cycle scan program alternately at the time interval order of the interrupt processing. If the parallel processing is performed in parallel, the PID calculation instruction of a plurality of loops such as two loops or three loops may be continuously executed by one execution of the fixed-cycle scan program unit 41. Absent.

FIG. 2 is an explanatory diagram of creating a PID control program.
The subroutine instructions FUN (0), FUN (1),..., FUN described on the left side of FIG. 2 are stored in the system ROM / RAM 12 of FIG.
(N) is the PID operation instruction PID (0), PID (1), ..., PID
(N) It is created in advance so that the user does not need to create the entire subroutine instruction FUN (i), and the parameters Tz, K used in each subroutine instruction FUN (i) are not required.
You only need to set p, KI, etc. These parameters are stored in the data areas WR000, 001,..., But it is inconvenient for the user to set the parameters while specifying the address of the data area. Draw the drawing on CRI,
Here, it can be performed by designating Tz = 20 mm s or the like.

In this way, the user sets each parameter and
When U11 refers to the flag described above and activates the i-th subroutine instruction FUN (i), the MPU 11
A parameter necessary for executing FUN (i) is searched by searching the data area, and a PID operation is executed to control the PID control target (i).

FIG. 3 is a system configuration diagram of the programmable controller in the present embodiment. Peripheral device interface
The sequence control program and the PID control program programmed in the user memory MEM via the CPU 13 are executed by the CPU. A detection signal and a control signal are transmitted and received between the CPU and the machine to be sequence-controlled through a digital input DI and a digital output DO, and an analog signal is transmitted between the CPU and an analog control target (in this embodiment, a process control target). A detection signal and a control signal are transmitted and received via the input AI and the analog output AO. Thereby, the sequence control target is subjected to sequence control, and the process control target is subjected to PID control.

FIG. 4 is a system configuration diagram when there are a plurality of PID loops. In this embodiment, a basic unit 3 having a CPU
The extension units 31, 32, and 33 having no CPU are connected to 0, and the extension units 34 and 35 are connected to the basic unit 30 at remote positions via a remote line. Each unit is modularized. In the illustrated example, AI indicates an analog input module, and AO indicates an analog output module. In this example, the PID control target is 3
The first is connected to the AI and AO modules provided in the basic unit 30, and the second is the AI and AO
Connected to the module, the third is AI, A of the extension unit 35
Connected to O module. Each PID control target is controlled by the CPU of the basic unit 30. As described above, the first control target is controlled in the first interrupt processing, and the second control target is controlled in the second interrupt processing. The control target is controlled, the third control target is controlled in the third interrupt processing, and the first control target is controlled again in the fourth interrupt processing.

FIG. 5 is a chart showing control timing when the PID control loop is two loops. CP in this embodiment
U has four operation modes, and C in each mode
The PU operation is as follows.

System periodic scan process: This is a process executed by the CPU every 10 milliseconds. (In FIG. 5, two processes are collectively expressed to make the figure easier to read, so that the process is executed every 20 milliseconds. Actually, after processing of 3 ms, processing of 4 ms is performed, then processing of 3 ms is performed, and then again (10 ms after the beginning), processing of 3 ms is performed. In FIG. 5, each of the above processes is omitted by writing a line segment at the center of 6 milliseconds of the process.), And updating of the elapsed value of the timer in the sequence program ·self-diagnosis·
Perform peripheral services.

Periodic scan processing every 20 milliseconds: Processing that the CPU always executes every 20 milliseconds. Processing a, b, c, d
Consists of In the process a, the periodic scan start instruction INT of the PID loop 1 is executed, and in the process b, the loop management instruction P
The ID “C” is executed, then the PID operation instruction is executed in the process c, and finally the periodic scan end process (return to the process) is executed in the process d.

Scan end processing: Processing that is executed at the end of the normal scan processing.
It is started by the “END” instruction of the normal scan program, and executes processing to return the value of the program counter indicating the address of the execution instruction to the head of the normal scan program, and to perform diagnostic processing of a computing unit in the MPU.

Normal scan processing: The normal scan program written in the user memory is cyclically executed from the beginning to the “END” instruction.

In the periodic scan processing shown in FIG. 5, the PID calculation is performed in the processing c of the processing, but in the first periodic scan processing, the PID loop 1 is performed, and in the second periodic scan processing, the PID calculation is performed. Execute the operation of loop 2 and execute 3
The PID loop 1 is executed at the fourth time, the PID loop 2 is executed at the fourth time, and so on.
Execute alternately every 20 milliseconds. Therefore, the processing of one PID loop is executed once every 40 milliseconds at a constant period, and each PID loop is surely executed at a constant sampling period.

FIG. 6 is a timing chart when the number of PID control loops is three. In the periodic scan process, each loop is executed one by one without overlapping. In this example, loop 1 is processed every 60 milliseconds (the minimum sampling time when executing three loops), loop 2 is processed every 120 milliseconds, and loop 3 is processed every 240 milliseconds. Therefore, each loop is always executed at a fixed cycle,
The PID loop is not executed every time in the periodic scan processing every 20 milliseconds, and at the timing indicated by the arrow ↓ in FIG. 6, there is room for executing the normal scan program.
Usually, the processing of the scan program can be increased. FIG. 7 shows an example of the specifications of the PID calculation function.

The PID control is performed, for example, when the temperature is controlled to a constant temperature. When the temperature changes rapidly, a shorter sampling interval enables more accurate control. However, after the temperature has reached a steady state near a certain temperature, the control accuracy does not decrease so much even if the sampling interval is lengthened. Therefore, after the control target is controlled to the vicinity of the target value and the control amount is stabilized, the sampling cycle is extended,
By dividing that amount into the execution of a normal scan program,
Smooth control can be performed.

According to the present embodiment, regardless of the size of the user program (sequence control program portion), PI
D operation can be executed, so sequence control and PID control
Even if executed by one CPU, it can be executed without changing the sampling interval of PID control, and complicated processing such as adjusting the PID constant in accordance with the sampling time is unnecessary. Further, since only one CPU is required, the cost of the control device of the system can be reduced by adjusting the combination of the sequence operation and the PID operation. Furthermore, the ratio of the operation load of PID control and sequence control can be adjusted by specifying the execution cycle of each PID loop, and the response time of sequence control can be adjusted.

According to the present invention, the sequence control target and P
ID control targets can be controlled in parallel, and even if there are multiple PID control targets, the PID control cycle can be extended and the execution interval can be set arbitrarily. The control can be executed more reliably. Further, the user can easily create the PID control program.

[Brief description of the drawings]

FIG. 1 is a block diagram of a programmable controller according to one embodiment of the present invention, and FIG. 2 is a PID according to one embodiment of the present invention.
FIG. 3 is an explanatory diagram of a control program creating method, FIG. 3 is a system configuration diagram in the case of performing one-loop PID control with the programmable controller of FIG. 1, and FIG. 4 is three-loop PID control with the programmable controller shown in FIG. FIG. 5 is a timing chart according to an example when performing two-loop PID control, FIG. 6 is a timing chart according to an example when performing three-loop PID control, FIG. Is a diagram for explaining one specification of a PID calculation function, and FIG. 8 is a block diagram of a conventional programmable controller. 1 ... CPU unit, 2 ... input / output unit, 3 ... programming device, 5 ... sequence control target, 6 ... PID control target, 11 ... MPU, 12 ... system ROM / RAM, 13 ... peripheral Device interface, 14: system bus, 15: user memory, 40: normal scan program unit, 41: fixed-cycle scan program unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-220001 (JP, A) JP-A-1-116705 (JP, A) JP-A-62-248002 (JP, A) 72202 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G05B 19/00-19/05

Claims (2)

(57) [Claims] 1. A programmable controller comprising a plurality of loops of PID control programs in a fixed cycle calculation processing program existing in a sequence calculation processing program and including a processor for executing and executing these programs. Means for executing only one loop PID control program when executing the periodic calculation processing program, and executing another one loop PID control program when executing the next fixed cycle calculation processing program; Means for setting an execution interval of an arbitrary loop at an arbitrary multiple of the number of loops. 2. The apparatus according to claim 1, further comprising means for programming a subroutine instruction by having a PID operation subroutine instruction as one of the sequence operation instructions and setting a parameter of the PID in the subroutine instruction. Features a programmable controller.