CNC machine tool PLC (programmable logic controller) has the following common faults in the operation process, and the following corresponding solutions are taken for the faults in the work engineering to make the equipment operate normally.
1. The power grid fluctuates too much, and the PLC does not work
It is manifested as no output of the PLC. Check the input signals (power signal, interference signal, command signal, and feedback signal) first. For example, a CNC lathe with SINUMERIK 3G-4B system does not work with its built-in PLC. Using the observation method, first use the oscilloscope to check the grid voltage waveform, found that the power grid voltage fluctuation is too large, the undervoltage noise jump duration is greater than 1s, because the machine tool is in the debugging stage, the unit system assembly fault should be excluded, by the internal power grid interference measures (filtering, isolation, voltage stabilization) can be seen, the conventional power supply system has been unable to cut or filter out the power grid undervoltage noise that lasts too long, which is caused by insufficient anti-grid measures (internal cause), resulting in PLC can not work normally.
Solution: Add an AC voltage regulator to the power input of the system, and the PLC works normally.
2. Electromagnetic interference
Electromagnetic interference faults often occur in the new machine tool debugging stage of the machine tool frequent shutdown, but can work, Gu Ke can rule out the parameters of confusion and components caused by internal factors, may be caused by the power grid or environmental electromagnetic interference, resulting in system instability, the external cause is the frequency conversion inductive interference source. This is because the capacity of the selected components is too small, and the grid interference pulse is too large, so that the inductive elements inside the filter are magnetically saturated and cannot filter out the high-frequency interference pulses.
Solution: Connect a 2.2mF capacitor in parallel between the system power input lines, i.e., add an absorption network, troubleshooting.
3. PLC-MD parameter failure
This fault occurs in the debugging stage, and can only move in the negative direction of the coordinate axis during the zeroing operation, and the overtravel alarm will appear when moving normally. For example, in a machining center of FANUC 0M system, when the return reference point (return to zero operation) is done after power-on, the overtravel alarm will appear after the feed axis moves forward for a certain distance, but the travel switch is not actually touched. The "reset method" does not eliminate the alarm. After the power failure, the power is re-energized, and the fault is still there, indicating that the alarm is essentially a soft overtravel. Since the machine is in the commissioning phase, false overtravel due to hardware failures can be ruled out.
Solution: Check whether the parameter setting table is out of order, and then use the parameter modification method. Method 1: Turn off (OFF) the alarm soft key, and restore the alarm soft key ON after the zero return operation; Method 2: Temporarily modify the soft limit parameter (143) to +999999, and restore the original parameter value after the zero return operation. Both treatment methods can be used to eliminate the fault after rebooting.
Note: If the overtravel alarm is generated by hitting the travel switch in the actual zero-return operation, it is not allowed to use the "reset method" to prevent the accuracy of the machine tool from being damaged by hitting it again.
4. PLC input board failure
PLC input board failure often occurs during automatic processing, the CRT displays an alarm, and the machine tool cannot work. For example, when the FANUC 3T-A system CNC machine tool is automatically processed, the CRT displays "NOT READY", the machine tool cannot work normally, and the alarm shows that the main control board is good, regardless of the main body of CNC or PLC, and there is no specific content of the alarm. A fault in the servo amplifier or PLC is suspected. However, if the servo amplifier is faulty, it should be alarmed when the self-diagnosis is started. Therefore, the fault can be located as the I/O interface board of the PLC, which is a hardware failure, and the main cause should be the hardware failure of the circuit in the front link of the corresponding output "NOT READY".
Solution: Eliminate the fault after replacing the parts.
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