JP2542684B2 - Method of preventing erroneous output of digital controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital control device such as a programmable logic controller, and more particularly to a digital control device at the time of restart of the programmable logic controller after repairing an abnormality. Erroneous output prevention method.

[Conventional technology]

Generally, programmable logic controllers (below
The basic configuration of the PLC) is composed of a processor unit and an input / output unit, and the processor unit stores a sequence program for controlling the machine or equipment to be controlled in a preset order. It is operated to output the arithmetic processing result by checking the on / off state of the input / output signal and reading and decoding it sequentially from the input signal from the input device such as limit switch and push button and electromagnetic switching. It has a function as an interface that performs mutual conversion between an output signal to an output device such as a container, a lamp, and a solenoid valve, and a signal transferred in the processor unit. In addition to this, a power supply unit is provided, and a DC stabilized power supply is used for this power supply unit because the processor unit is composed of a semiconductor circuit.

The PLC configured in this way further determines whether the power supply voltage is being applied to the PLC to determine whether it is normal or not. It is usually equipped with a self-diagnosis function that can determine the normality of the processing unit. With this self-diagnosis function, the PLC itself constantly monitors the normal operating state of each part of the PLC, and when an abnormality occurs, the digital control output is forcibly turned off to operate in a safe direction for the controlled object. Next, at the time of restarting after the abnormality is repaired, the hardware is reset to cancel the forced off operation of the digital control output by the self-diagnosis function and restore the PLC to normal operation.

[Problems to be Solved by the Invention]

However, according to the above-mentioned PLC, there is a possibility that an erroneous output may be output at the time of restarting after the abnormality is repaired. In other words, the restart is performed by resetting the hardware and releasing the forced OFF operation of the control output by the self-diagnosis function of the PLC. However, there is a problem that an erroneous output is output after the PLC starts the output of the control output and before it detects the abnormality again by the self-diagnosis function and forcibly turns off the control output.

This is because the self-diagnostic functions such as the watchdog timer and read-after-write check are functions that can be detected after the PLC has started, so the control output of the PLC will not be output until the abnormality is detected after restarting. Even if it is abnormal, it is output as it is.

Therefore, an object of the present invention is to achieve a safe control operation that does not cause an erroneous output with a simple configuration and reliably when restarting a PLC after repairing an abnormality, even if the abnormality is not completely repaired. It is an object of the present invention to provide a method of preventing an erroneous output of a digital control device that can be performed.

[Means for solving the problem]

An erroneous output prevention method for a digital control device according to the present invention includes a digital input / output unit and a control calculation unit, performs sequence control of a control target according to an input program, and outputs a control output to the control target when an abnormality occurs. In a digital control device with a self-diagnosis function that forcibly turns off, a self-diagnosis unit with a self-diagnosis function equipped with a reset switch is provided for the control calculation unit, and the output signal of this self-diagnosis unit is input. An erroneous output prevention circuit that outputs a set and reset signal is provided, and when the control output is forcibly turned off by the self-diagnosis function of the self-diagnosis unit, the hardware is reset when the abnormality is corrected and the output is performed again. The erroneous output prevention circuit maintains the output of the set signal and turns off the control output within a certain period of initial operation. In this state, the control output is output to the controlled object by a manual closing operation of the reset switch provided in the erroneous output prevention circuit after a certain period of time.

[Action]

According to the erroneous output prevention method of the digital controller according to the present invention, when restarting after the abnormality is repaired, it is regarded as a system abnormality within a certain time period of the initial operation, and the control output of the digital controller is forcibly turned off. To do. As a result, it is possible to effectively prevent erroneous output that may have been output by the conventional method after the initial operation and before the self-diagnosis function is restored. Furthermore, even if a certain time has passed after the initial operation, the control output of the digital control device is not output to the external device unless the reset switch of the external protection circuit is manually turned on. It is possible to reliably prevent an erroneous output in a normal state.

〔Example〕

Next, an embodiment of an erroneous output prevention method for a digital controller according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a main part system diagram showing an embodiment of a PLC system equipped with an erroneous output prevention circuit according to the method of the present invention. In FIG. 1, reference numeral 10 is a PLC, and the PLC 10 includes a digital input unit 12, a processor unit 14 and a digital output unit.
It consists of 16. The digital input unit 12 inputs signals from the multiple input contacts 40 via the photocouplers 28, respectively, and thereby transmits the signals to the processor unit 14 in an electrically insulated state. The digital input unit 12 also performs a level shift operation for adjusting the external signal level to the signal level of the control calculation unit 18 and the like inside the PLC. The processor unit 14 is
It is mainly composed of a control calculation unit 18 for performing sequential calculation processing according to a sequence program, a start unit 20 for instructing the start of control calculation, a stop unit 22 for turning off the control calculation output, and a self-diagnosis unit 26. Start section 20 and self-diagnosis section
26, the reset switch 24 can restart the control calculation and the self-diagnosis operation. Self-diagnosis unit 26
The output signal of is sent to the stop unit 22 and also to the erroneous output prevention circuit 60 outside the PLC 10.

The digital output unit 16 is configured to output a load output relay 42 and a solenoid valve (not shown) based on the output of the control calculation result.
And the like, each of the transistors 30 has a collector connected to an external positive power supply line P via a contact 44 and an output relay 42, and an emitter connected to a ground line or a negative power supply line N. To do. Therefore, as the transistor 30 of the digital output section 16, one having a withstand voltage according to the external power supply voltage is used.

An external device 50 such as a device or a production facility that is a control target of this PLC system is connected to each output relay 42, and the external device 50 is controlled by an on / off operation of the output relay 42.

The erroneous output prevention circuit 60 has an AND element 68 that receives the signal from the self-diagnosis unit 26 as one input and the series circuit of the NOT element 64 and the timer element 66 and that receives the signal from the reset switch 62 as the other input. The output of the AND element 68 serves as a reset input and the RS flip-flop 70 receives the signal from the self-diagnosis unit 26 as a set input. The output signal of the erroneous output prevention circuit 60 controls the on / off operation of the contact point 44.

Next, an erroneous output prevention method of the PLC system configured as above will be described.

First, when the PLC 10 detects an abnormality by the self-diagnosis unit 26 during operation, the self-diagnosis unit 26 sends a signal to the stop unit 22 to force the safety side to forcibly turn off the output of the control calculation result. Operate. In addition, the erroneous output prevention circuit 60 receives the RS flip-flop 70 according to the input signal from the self-diagnosis unit 26.
Is in the set state, the output in response to this controls the contact point 44 to the off state.

When the cause of the abnormality is removed and the restart is performed after the abnormality is repaired, the reset switch 24 resets the hardware to start the control calculation. At the same time, the self-diagnosis unit 26 also starts to operate, but among the self-diagnosis functions, the watchdog timer and read-after-write check are functions that can be detected after the PLC is operating. 16 may generate erroneous output. However, since the erroneous output prevention circuit 60 operates so as to maintain the compulsory OFF state of the contact 44 within the fixed period of initial operation even after restarting, the external device 50 is not controlled by erroneous output. . That is,
Even if the input signal from the self-diagnosis unit 26 to the erroneous output prevention circuit 60 changes at the time of restart, the signal input to the AND element 68 by the timer element 66 remains in the previous state within a certain time.
Even if the reset switch 62 is pressed, the output of the AND element 68 does not change and the reset input to the RS flip-flop 70 is not performed. Therefore, the contact 44 can maintain the off state. it can.

When a certain period of time has passed after the operation of the PLC, that is, after the time set by the timer element 66 has elapsed, the output of the AND element 68 to the RS flip-flop 70 is reset switch 6
It will depend on the signal from 2. That is, R-S
The reset permission for enabling the reset input to the flip-flop 70 is established.

Therefore, after confirming the surroundings of the PLC system and finding that the abnormality has been completely repaired, the erroneous output prevention circuit
When the reset switch 62 of 60 is manually turned on, the reset input to the RS flip-flop 70 is performed, and the output in response to this makes the contact 44 in the ON state, whereby the digital output section 16 of the PLC is turned on. Since an operation command or the like is output to the external device 50, erroneous output can be reliably prevented. Here, it is clear that the fixed time set by the timer element 66 may be set to a time at which the self-diagnosis function such as the watchdog timer and the read-after-write check can sufficiently operate.

〔The invention's effect〕

As is apparent from the above-described embodiment, according to the present invention, in a digital control device such as a PLC, the digital control output is forced even if the reset switch is pressed within a certain period of initial operation at restart after abnormality recovery. By configuring the erroneous output prevention circuit so that it is turned off automatically, the abnormality detection time of the self-diagnosis function is secured, and even if the abnormality repair is incomplete, the external device is erroneously output due to erroneous output during this period. Is never controlled. further,
After the lapse of a certain period of initial operation, the error output prevention circuit was configured so that the operation command etc. to the external device is output only by the operation of manually turning on the reset switch. The digital control output can be restarted after confirmation, and the erroneous output prevention can be achieved easily and surely, which contributes sufficiently to the improvement of safety.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and it is needless to say that various design changes can be made without departing from the spirit of the present invention.

[Brief description of drawings]

FIG. 1 is a system diagram of a main part of a PLC system that implements the erroneous output prevention method according to the present invention. 10 …… Programmable logic controller (PLC) 12 …… Digital input section, 14 …… Processor section 16 …… Digital output section, 18 …… Control calculation section 20 …… Start section, 22 …… Stop section 24 …… Reset switch , 26 …… Self-diagnosis part 28 …… Photo coupler, 30 …… Transistor 40 …… Input contact, 42 …… Output relay 44 …… Contact, 50 …… External device 60 …… False output prevention circuit 62 …… Reset switch , 64 …… NOT element 66 …… Timer element, 68 …… AND element 70 …… RS flip-flop

Claims (1)

(57) [Claims] 1. A self-diagnosis system comprising a digital input / output unit and a control operation unit, performing sequence control of a controlled object according to an inputted program and forcibly turning off a control output to the controlled object when an abnormality occurs. In a digital control device having a function, a self-diagnosis unit having a self-diagnosis function having a reset switch is provided for the control calculation unit, and the output signal of the self-diagnosis unit is input and an erroneous output for outputting a set and reset signal A preventive circuit is provided, and when the control output is forcibly turned off by the self-diagnosis function of the self-diagnosis unit and the output is corrected again and the re-output operation is performed, within the fixed time of the initial operation accompanying the reset of the hardware, The erroneous output prevention circuit keeps the set signal output and keeps the control output in the off state, An erroneous output prevention method for a digital control device, characterized in that a control output is output to a controlled object by manually turning on a reset switch provided in the erroneous output prevention circuit.