Question

A machine tool in a manufacturing cell is driven by a 3-phase a.c. motor controlled by an inverter. Before the inverter receives a RUN signal from a PLC, the following conditions must be met:

(a) The workpiece is to be in its initial position in the chuck. (WPI)

(b) Lubrication pressure is to be 5 bar or above. (LUB)

(c) No movement is to have been detected in the cell for 1 minute. (SAFE)

(d) The pre-start inverter self-test routine is to be satisfactory. (TEST)

(e) The motor must be stationary, i.e. the motor speed signal is to be zero. (RPM0)

(f) The manufacturing cell door is to be shut. (DOOR)

If the above conditions are met the PLC is to output a RUN signal to the inverter. The output is to be from a rung dedicated to outputs. The memory element on this rung is to be activated by memory cell MC1. The output rung is also to control an output to the manufacturing cell door bolt solenoid.

The memory cell MC1 is to remain on until one of the following occurs:

(a) Motor speed exceeds 1000 rpm. (RPM1000)

(b) The emergency stop button is pressed. (EMER)

(c) Lubrication pressure falls below 5 bar. (LUB)

(d) A signal indicating the end of machining is received. (END)

When memory cell MC1 goes high, the following are to occur:

(a) MC1 is to receive a hold in supply.

(b) The inverter is to receive a RUN signal. (RUN)

(c) The manufacturing cell door is to be locked by a solenoid-operated bolt. (LOCK)

Draw a ladder diagram to represent the software program that should be installed in the program memory of the PLC. Identify the elements on the rungs by the abbreviations given.

Answer 1

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