JP2963676B2 - Programmable controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a programmable controller, and more particularly to a programmable controller suitable for executing a sequence control program having a plurality of loop PID control programs therein.

[0002]

2. Description of the Related Art FIG. 8 is a block diagram of a conventional programmable controller. The conventional programmable controller includes a CPU unit 1 and an input / output unit 2. The CPU 1 reads a control program created by a user using a programming device 3 provided externally and executes the control program. Sequence control target 5 via output unit 2
Is controlled.

[0003] The CPU unit 1 includes an MPU 11 and a system R.
It comprises an OM / RAM 12, 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 includes a digital signal input port 21 and a digital signal output port 2.
2, an analog signal input port 23, and an analog signal output port 24, which are connected to the system bus 14.

[0006] The control program stored in the user memory 15 is divided into a normal scan program section 40 and a fixed cycle scan program section 41 which is interrupted at a fixed cycle during execution of the normal scan program section 40. . In the normal scan program unit 40, the operation from the top of the program unit 40 to the END instruction is cyclically processed. In the fixed scan program unit 41, the INT command (label indicating the start position of the fixed scan program) is used. Interrupt processing is performed up to an RTI instruction (an instruction for returning from the fixed scan program to the normal scan program).

The above-mentioned control program is written into the user memory 15 from the programming device 3 via the peripheral device interface 13, and the MPU 11 sequentially reads out each instruction of this control program and calculates read data from the input / output unit 2. Then, the sequence control target 5 is controlled.

In the conventional programmable controller, as described above, the control program is divided into the normal scan program section 40 and the fixed-cycle scan program section 41 for the following reasons. That is, 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 target portion in the sequence control target 5 that requires response control within a short period of time, the response control within a short period of time for the control target portion increases as the program amount increases. It becomes impossible. Therefore, a fixed-cycle scan program unit 41 is provided in the control program, and required short-term response control is performed in the fixed-cycle scan program unit 4.
In step 1, the program is executed at regular intervals, and at the same time, a large program can be created by the user.

[0007] Incidentally, as a related to the conventional programmable controller, for example, "Hitachi Review" (1989)
Published in July, 2000 (UDC 658.527.7'13
2) P43 to P48).

[0008]

Conventionally, the control target of the programmable controller has been limited exclusively to those that perform sequence control, but in recent years there has been a tendency to apply it to process control. I have.
However, although PID (proportional / integral / differential) control must be performed in order to perform process control, PID control has not been taken into account in any of the conventional programmable controllers. Is caused.

(1) In performing the PID calculation, it is necessary to sample the measurement data to be controlled and take it into the controller. 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 into the fixed-period scan program unit 41. However, if the number of PID loops to be controlled increases, the fixed-period scan program unit 41 must be controlled. A problem arises that the scan execution time becomes longer and the normal scan program is hardly executed.

An object of the present invention is to set a PID constant regardless of the size of a user program.
An object of the present invention is to provide a programmable controller that can surely execute a normal scan program even when the number of loops increases.

[0012]

An object of the present invention is to transmit and receive data between a sequence control program and a user memory storing a PID control program of n (n: an arbitrary integer of 2 or more) loops and a sequence control target. A digital signal input / output port for transmitting and receiving data to and from a PID control target; and a system setting for periodically executing timer elapsed value updating, self-diagnosis, and peripheral services in a sequence control program. A process executed at the end of the periodic scan process or the normal scan process, and a process of returning the value of the program counter indicating the address of the execution instruction to the beginning of the normal scan program. A scan end process for executing a diagnostic process of a computing unit in the MPU. While executing the sequence control program as the normal scan process, While the through Ijitaru signal input and output ports are sequence controls the sequence control object, from among the PID control program of the n loops,
By selectively selecting only one of the PID control programs periodically in accordance with a predetermined selective update order and performing an interrupt process as a periodic scan process, the PID control program is performed via the analog signal input / output port. And a processor for performing PID control of the object.

By executing the PID control program at a fixed period, data to be controlled can be periodically taken in regardless of the size of the user program, and a PID constant can be determined. In addition, when PID control is performed at a fixed period, one loop of PID
If only the calculation is performed, even if there are a large number of PID loops, it is possible to avoid a situation in which the execution of the normal scan program is not performed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
7 will be described with reference to FIG. FIG. 1 is a configuration diagram of a programmable controller according to an embodiment of the present invention. This programmable controller is different from the conventional programmable controller shown in FIG. 8 only in the content of the fixed-cycle scan program unit 41 and in that the PID control target 6 is connected to the analog signal input / output ports 23 and 24. The other configuration is the same. 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 is read out and executed every 20 milliseconds during the execution process of the normal scan program unit 40. The program configuration includes a label indicating the start position, IN
Instruction PID that starts with T instruction and then performs loop management
There is “C”, and hereafter, PI which is an actual PID operation instruction
An instruction group of n loops of D “1” to PID “n” is arranged (in each instruction, the measured value Xn of the PID control target 6 is fetched from the analog signal input port 23 and the corresponding target value Wn is stored in the system ROM / RAM 12 And performs a PID operation using both values Xn and Wn, and outputs the result as an operation amount Yn from the analog signal output port 24 to the PID control target 6). Finally, there is an instruction RTI for returning to the normal scan program. .

The loop management instruction PID “C” includes PID operation start flags R “1” to R “n” provided in software corresponding to the PID operation instructions PID “1” to PID “n”.
Each time the periodic scan program unit 41 is read by the MPU 11 and interrupted, only one of them is sequentially turned on. That is, when the fixed-cycle scan program unit 41 is read and interrupted at a certain cycle, when only the flag R “i” is turned on, the execution of the fixed-cycle scan program unit 41 is not performed. Only the PID “i” instruction is executed. Next 2
In the execution of the fixed-cycle scan program unit 41 after 0 millisecond, only the flag R “i + 1” is turned on, so that only the PID “i + 1” instruction is executed. That is, in one execution of the fixed-period scan program unit 41, only one loop of the PID operation instruction is executed. The reason why such a program configuration is adopted in the present embodiment is that, as described above, if the PID control is executed continuously, the processing time of the PID control becomes longer,
This is to avoid running out of the execution time of the normal scan program unit 40 to be executed between each interruption process. Therefore, if the execution time of the normal scan program is always ensured between each interrupt process using a high-speed processor, that is, the execution of the normal scan program and the periodic scan program can be performed at the time interval order of the interrupt process. If the parallel processing is performed alternately, a plurality of loops, such as two loops and three loops, may be continuously executed by one execution of the periodic scan program unit 41. is there.

FIG. 2 is an explanatory diagram for creating a PID control program. The system ROM / RAM 12 shown in FIG. 1 has subroutine instructions FUN (0),
FUN (1),..., FUN (n) are PID operation instructions PI
D (0), PID (1),..., PID (n).
(I) It is not necessary to create the whole, and the parameters Tz, Kp, KI used in each subroutine instruction FUN (i)
And so on. These parameters are stored in the data area WR000,001,..., But it is inconvenient for the user to set the parameters while specifying the address of the data area. Draw on the CRT so that the value of Tz can be specified specifically.

In this way, when the user sets each parameter and the MPU 11 activates the i-th subroutine instruction FUN (i) with reference to the aforementioned flag, the MPU 11
Numeral 11 searches the data area for parameters necessary for executing the subroutine instruction FUN (i), executes PID calculation, and controls the PID control target (i).

FIG. 3 is a system configuration diagram of the programmable controller according to the present embodiment. The sequence control program and the PID control program programmed in the user memory MEM via the peripheral device interface 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 via the digital input DI and the digital output DO, and an analog signal is transmitted between the CPU and the analog control target (the process control target in the present embodiment). 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.
FIG. 2 is a system configuration diagram when there are a plurality of ID loops. In this embodiment, the basic unit 30 including the CPU has C
Extension units 31, 32, 33 having no PU are connected, and extension units 34, 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, there are three PID control targets, and the first is connected to the AI and AO modules provided in the basic unit 30,
The third is connected to the AI and AO modules of the extension unit 33, and the third is connected to the AI and AO modules of the extension unit 35. 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 the control timing when the PID control loop is two loops. The CPU in this embodiment has four types of operation modes, and the CPU operation in each mode 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 represented for easy viewing, In practice, the processing of 3 ms is followed by the processing of 4 ms, then the processing of 3 ms, and again (after 10 ms from the beginning). In FIG. 5, each of the above processes is omitted by drawing a line segment at the center of 6 milliseconds in the process), and the elapsed value of the timer in the sequence program Perform update, self-diagnosis, and peripheral services.

Periodic scan processing every 20 milliseconds: Processing that is always executed by the CPU every 20 milliseconds.
b, c, d. 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 PID “C” is executed, and then P
An ID calculation instruction is executed, and finally, a periodic scan end process is performed in process d.

Scan end processing: This processing is executed at the end of the normal scan processing, is started by the "END" instruction of the normal scan program, and returns the value of the program counter indicating the address of the execution instruction to the top of the normal scan program. It performs processing and diagnostic processing of the arithmetic unit in the MPU.

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

In the periodic scan process shown in FIG. 5, the PID calculation is performed in process c. However, in the first periodic scan process, the operation of the PID loop 1 is performed, and in the second periodic scan process, the PID calculation is performed. Perform the operation of loop 2,
The PID loop 1 is executed at the third time, the PID loop 2 is executed at the fourth time, and the processes of the PID loop 1 and the PID loop 2 are alternately executed 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 three PID control loops are provided. In the periodic scan process, each loop is executed one by one without overlapping.
In this example, loop 1 is processed every 60 milliseconds (minimum sampling time when executing three loops), loop 2 is processed every 120 milliseconds, and loop 3 is processed every 240 milliseconds. Therefore, although each loop is always executed at a fixed period, the PID loop is not executed every time in the fixed period scan processing every 20 milliseconds.
At the timing indicated by the mark, there is a margin for executing the normal scan program, and the processing of the normal scan program can be increased. FIG. 7 shows an example of the specifications of the PID calculation function.

Note that 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 object is controlled to be close to the target value and the control amount is stabilized, the sampling period is extended and the control period is divided into the execution of the normal scan program, whereby smoother control can be performed.

According to the present embodiment, the PID operation can be executed at a predetermined cycle regardless of the size of the user program (sequence control program portion). Therefore, even if the sequence control and the PID control are executed by one CPU, PI
The D control can be performed without changing the sampling interval, 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.

[0029]

According to the programmable controller of the present invention, the PID is independent of the size of the user program.
A constant can be set, and even if the number of PID loops increases, the normal scan program can be executed without fail.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a programmable controller according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a PID control program creation method according to an embodiment of the present invention.

FIG. 3 is a system configuration diagram in a case where one loop of PID control is performed by the programmable controller of FIG. 1;

FIG. 4 is a system configuration diagram in the case where three-loop PID control is performed by the programmable controller shown in FIG. 1;

FIG. 5 is a timing chart according to an example of a case where two-loop PID control is performed;

FIG. 6 is a timing chart according to an example of a case where PID control of three loops is performed.

FIG. 7 is an explanatory diagram of one specification of a PID calculation function.

FIG. 8 is a configuration diagram of a conventional programmable controller.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CPU part, 2 ... input / output part, 3 ... programming device, 5 ... sequence control object, 6 ... PID control object, 1
DESCRIPTION OF SYMBOLS 1 ... MPU, 12 ... System ROM / RAM, 13 ... Peripheral device interface, 14 ... System bus, 15 ... User memory, 40 ... Normal scan program part, 41 ...
Fixed scan program section.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-72202 (JP, A) JP-A-61-220001 (JP, A) JP-A-1-140301 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G05B 19/05

Claims (1)

(57) [Claims] A sequence control program and n (n: 2
(Arbitrary integer above) Stores PID control program for loop
Data between the user memory and the sequence control target
Digital signal input / output port for transmitting and receiving
Analog signal input / output for sending / receiving data to / from the control target
Output port and timer in sequence control program
System that periodically executes value update, self-diagnosis, and peripheral services
At the end of the regular scan process or the regular scan process
A program that shows the address of the execution instruction after being executed
Returning the counter value to the beginning of the normal scan program
Scan and execute diagnostic processing of the arithmetic and logic units in the MPU
While executing the normal scan process,
The sequence control program is executed to execute the digital
The sequence control target is switched via the signal input / output port.
During the sequence control, the PID control of the n loop is performed.
Pre-determined optional updates from your program
According to the order, only one PID control program
After selecting periodically, interrupt processing as periodic scan processing
The analog signal input / output port
A processor for performing PID control on the PID control target via
A programmable controller comprising: