Analysis and treatment of several common faults in nc machine PLC

Analysis and treatment of several common faults in nc machine PLC

Wed Jun 29 10:42:19 CST 2022

Analysis and treatment of several common faults in nc machine PLC

CNC machine tool PLC in the operation process of the following several common faults, in the work of the project to take the following corresponding measures to solve the fault, the normal operation of the equipment.

Power grid fluctuation too large PLC does not work

Performance for PLC no output.First check the input signal (power signal, interference signal, instruction signal and feedback signal).For example, SINUMERIK 3g-4b system CNC lathe, its built-in PLC can not work.USES the method of observation, use oscilloscope to check power grid voltage waveform, first find the grid voltage fluctuation is too big, under voltage noise jump duration is more than 1 s, because the machine is in debugging stage, unit in the system to form a fault shall be excluded, the internal measures of power network disturbance (filtering, isolation, voltage regulator), conventional power systems have been unable to cut or filter the continuous time is too long power grid voltage noise, this is due to insufficiency of grid resistance measures (internal), led to the PLC can't work normally.

An ac regulator is added to the system power input, and the PLC works normally.

Electromagnetic interference

Electromagnetic interference fault often occurs in the new machine tool debugging phase machine frequently shut down, but can work, you can rule out parameter confusion and components caused by internal factors, may be caused by electrical network or environmental electromagnetic interference, resulting in system instability, its external cause is the frequency conversion inductive interference source.This is because the capacity of the selected components is too small and the power grid interference pulse is too large, making the internal inductance of the filter magnetic saturation, unable to filter the high-frequency interference pulse.

A 2.2mf capacitor is connected in parallel between the system power input lines, which means an absorption network is added for troubleshooting.

PLC-MD parameter fault

The fault occurs in the debugging stage and can only move along the negative direction of the coordinate axis during the zero return operation.For example, when a processing center of FANUC 0M system is energized to return to the reference point (zero return operation), the superrange alarm will appear after the feed axis moves forward for a certain distance, and the travel switch is not actually touched."Reset method" cannot eliminate alarm.After power failure, the failure is still the same, indicating that the essence of the alarm is soft overrange.As the machine is in the debugging stage, the possibility of false overpass caused by hardware fault can be eliminated.

First, check the parameter setting table for disorder, then use the parameter modification method.Method 1. Close (OFF) the soft alarm key, and restore the soft alarm key ON after zero operation;Method 2. Temporarily modify the soft limit parameter (143) to +999999, and restore the original parameter value after zero operation.Both methods can be rebooted after troubleshooting.

Note: in the actual return to zero operation, the collision of the trip switch and produce an over - range alarm, at this time is not allowed to use the "reset method", in case of another collision and damage to the accuracy of the machine.

Four.PLC input board failure

PLC input board failure often occurs in automatic processing, CRT display alarm, the machine can not work.For example, when the CNC machine tool of FANUC 3t-a system is automatically processed, the CRT shows "NOT READY", the machine tool cannot work normally, and the alarm shows that the main control board, whether the CNC or the main body of the PLC is good, there is no specific alarm content.Suspect a fault in the servo amplifier or PLC.However, if there is a fault with the servo amplifier, the alarm should be given when starting the self-diagnosis.Therefore, the fault can be located as the I/O interface board of PLC. This fault belongs to the hardware fault, and the main cause should be the circuit hardware fault of the previous link corresponding to the output "NOT READY".

Troubleshooting after replacement of parts.