Discussion on the maintenance method of emergency stop failure of CNC machine tools

During the operation of the CNC machine tool, the grid voltage is normal, which generally does not cause parameter loss. The preliminary judgment is that the absolute encoder interface is bad, the wiring is bad, or the encoder itself is bad. After inspection, it was found that the absolute encoder feedback signal interface on the servo unit was loose. Treatment method: Plug the absolute encoder feedback signal interface; set the system parameter 1320 to 99999999, and set the parameter 1321 to -99999999 to invalidate the soft limit detection; set the system parameter 1815#5#4 to "0", the system is set to the incremental encoder mode, and the actual position of the machine tool is inconsistent with the detection position; power off and then power on the system; manually control the X axis to the reference point position of the machine tool; clear the mechanical coordinate value, set the system parameter 1240 to 0; then set the parameter 1815#5#4 to "1", the system is set to the absolute encoder mode, and the actual position of the machine tool is consistent with the detection position; power off and then power on the system, press the RESET key; reset the soft limit. The machine tool returns to normal. The possible reasons for the emergency stop failure caused by the loss of absolute position of the CNC machine tool are: insufficient battery voltage of the absolute encoder; repair of servo motor or servo amplifier failure; disassembly and assembly of encoder signal line; disassembly and repair of mechanical failure; system parameter overwriting and initialization operation; poor encoder interface, poor wiring and poor encoder itself.

Emergency stop caused by bad system parameters

Fault phenomenon:

When a FANUC-0iMC system CNC milling machine was transmitting data through the RS-232 interface, 101#, 1013#, 417#, 750# and "EMG" alarms suddenly appeared. The program could not be transmitted any further and the machine tool could not move.

Fault analysis and processing:

101# alarm means power failure during program transmission; 1013# alarm means each axis needs to return to the reference point; 417# alarm means incorrect servo parameter setting; 750# alarm means incorrect serial spindle parameter setting; "EMG" is an emergency stop alarm. Check the system parameters and find that many parameters are lost or changed. Clear all system parameters and then restore data through the memory card; perform the return to reference point operation and issue a 506# positive overtravel alarm; reset the soft limit, perform reverse clearance compensation and pitch error compensation, and the machine tool returns to normal.

Emergency stop caused by damage to the zero return deceleration switch

Fault phenomenon:

For a CNC machine tool with a FANUC-0iMC system, each time the Z and Y axes return to zero, they move normally, that is, they first move quickly toward the reference point, then start to decelerate after hitting the deceleration switch, and stop accurately at the reference point. The X axis continues to move toward the reference point at the zero return speed until an overtravel alarm is issued and an emergency stop is made.

Fault analysis and processing:

Cancel the soft limit, adjust the ratio to 50%, and perform the return to reference point operation again. The fault phenomenon still exists, and the parameter is not good. Check whether the signal of the machine tool is normal when returning to zero through the system PMC status monitoring screen. It is found that the deceleration switch signal X9.0 does not change, while the X9.1 and X9.2 signals change. It is determined that the deceleration switch is bad. Remove the deceleration switch and find that the switch is damaged. Repair the deceleration switch, install and adjust it, the emergency stop disappears, and the machine tool returns to normal.

Relay damage causes emergency stop

Fault phenomenon:

A CNC machine tool with a FANUC-0iMB system has been in an emergency stop state after startup and cannot be reset. The contactors of the spindle and servo main circuits do not energize, and a "SPINDLEOFF, SERVOOFF" alarm is issued, accompanied by an emergency stop.

Fault analysis and processing:

After checking the emergency stop circuit, it was found that the relay was not energized, and it was determined that the fault might be caused by a circuit breaker in the emergency stop circuit. The entire emergency stop circuit was checked with a multimeter, and the normally closed contacts, overtravel limit switch, and electrical wiring of the emergency stop button were all normal. It was found that the relay was damaged. After replacing a new relay, the machine tool returned to normal.

Emergency stop caused by emergency stop button

Fault phenomenon:

A vertical machining center with a FANUC-0iMC system displays "NOTREADY" when it is turned on, the servo power cannot be connected, and an emergency stop alarm occurs.

Fault analysis and processing:

FANUC-0iMC system caused "NOTREADY" and emergency stop: The possible reason is that the enabling circuit is blocked, that is, the emergency stop signal "*ESP" of the CNC system is input. Through the PMC status display function, it was found that the emergency stop input signal of the I/O module was "0". It was found that the relay in the emergency stop circuit was not energized. It can be judged that the fault is caused by the emergency stop circuit being broken. The whole emergency stop circuit was checked with a multimeter, and it was found that the emergency stop button on the machine tool operation panel was broken. Rewire, reset the emergency stop button, and the machine tool returned to normal.

Inverter alarm causes emergency stop

Fault phenomenon:

A CNC milling machine of a Huazhong CNC Century Star HNC-22M system was equipped with a Yaskawa inverter VS616GG7. When the system was powered on, a spindle fault input alarm occurred accompanied by an "emergency stop".

Fault analysis and processing:

When the inverter detects a fault, it stops the inverter output and puts the system in emergency stop state through the inverter output terminal MB-MC. After inspection, it is determined that the inverter operation panel is damaged. After replacing the new inverter operation panel and resetting the parameters, the machine tool returns to normal.

Servo unit failure causes emergency stop

Fault phenomenon:

A machining center equipped with FANUC7M system, when turned on, the system CRT displayed the alarms "the system is in 'emergency stop' state" and "the servo drive system is not ready".

Fault analysis and processing:

In the FANUC7M system, the common causes of the above two alarms are the loss of machine tool parameters of the CNC system or the failure of the servo drive system. The machine tool parameters were checked and found to be normal; but the alarm indicators on the speed control unit were not on, indicating that the servo drive system was not ready and the cause of the failure was in the speed control unit. Further inspection revealed that the 30A (thyristor main circuit) and 1.5A (control circuit) fuses on the Z-axis servo drive had blown, indicating that there was a short circuit in the main circuit of the Z-axis drive. After replacing the thyristor, the drive returned to normal.

Spindle overheat alarm causes emergency stop

Fault phenomenon:

A GS-928TC system CNC lathe suddenly stopped while working. The system displayed an alarm of over-high spindle temperature, accompanied by an "emergency stop".

Fault analysis and processing:

The possible causes of the failure include excessive spindle temperature rise, defective temperature sensor itself and poor wiring. After inspection and measurement, it was found that the spindle temperature did not exceed the allowable range, and it was determined that the fault occurred on the temperature instrument. After adjusting the circuit, the alarm disappeared, and the machine tool returned to normal after replacing the new instrument.

Conclusion

Fault diagnosis and maintenance of CNC machine tools is a highly technical and complex task, and many faults are often accompanied by emergency stops. Maintenance personnel must be familiar with the structure, working principle, ladder diagram of the control system, and the setting of system parameters of the entire machine tool. When a problem occurs, first determine whether it is a mechanical problem or an electrical problem, a strong current problem or a system problem, a system parameter problem or a PMC program problem, be good at grasping their commonalities, and constantly learn and accumulate experience in practice, and gradually improve the ability to judge and troubleshoot emergency stop faults.