Safety Circuit Design - Mitsubishi Electric MELSEC Q Series User Manual

3 DESIGN

3.2.2 Safety circuit design

(1) Concept of safety circuits
When the PLC system is powered on and off, normal control output may not be
done momentarily due to a delay or a startup time difference between the PLC
power supply and the external power supply (DC in particular) for the control
target.
Also, an abnormal operation may be performed if an external power supply fault
or positioning module failure takes place.
To prevent any of these abnormal operations from leading to the abnormal
operation of the whole system and in a fail-safe viewpoint, areas which can
result in machine breakdown and accidents due to abnormal operations (e.g.
emergency stop, protective and interlock circuits) should be constructed outside
the PLC system.
(2) Emergency stop circuit
The circuit should be constructed outside of the PLC system or servo amplifier.
Shut off the power supply to the external servo amplifier by this circuit, make the
electromagnetic brakes of the servomotor operated.
(3) Forced stop circuit
(a) The forced stop of all servo amplifiers is possible in a lump by using the EMI
forced stop input by external 24VDC of QD74MH. After forced stop, the
forced stop factor is removed and the forced stop canceled.
(The servo error detection signal does not turn on with the forced stop.)
The forced stop input can be selected "valid/invalid" in the parameter
setting.
Make the forced stop input cable within 30m(98.43ft.).
The wiring example for the forced stop input of QD74MH is shown below.
Q61P PLC CPU
<Positioning module>
QD74MH
Forced stop
EMI
24VDC
EMI.COM
(Note-1)
24VDC
EMI.COM
EMI
R
Forced stop
(Note): The forced stop input can be selected "valid/invalid" in the
parameter settings.
(Note-1): Both of positive common and negative common can be used.
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MELSEC-Q