FANUC CNC system has stable performance and low failure rate. However, some problems still appear in the actual production process. The most difficult one is the hardware fault, and the failure rate of the servo part accounts for 90% of the hardware fault.
1. Removable actuator failure
In the servo fault, the most frequently occurring actuators are movable, especially the cables flexed back and forth during the exercise. The motor power cables and encoder cables are the high incidence of faults. The most common ones are caused by the power cables Overcurrent fault and encoder line cause encoder alarm. These alarms are more intuitive, you can quickly find the fault point according to the alarm content, but because of these faults caused by some of the other alarms, because the alarm is not direct, it will interfere with the correct judgment of the fault.
Example 1 A VMC4020 vertical machining center, during the process of 926 alarm (FSSB alarm). Shutdown restart the fault disappears, but in the normal processing, there will be a similar situation. After a series of follow-ups, it was found that every occurrence of an alarm occurred during movement of the Y-axis, the X-axis motor and encoder wires were exchanged with the Y-axis from the amplifier. Trying to find the same problem or the original direction of the move to determine the problem may be in the encoder line, the reason may be due to encoder +5 V power supply short circuit, pulling down the entire power supply caused. Open the inspection and found that the shaft of the encoder wire skin damage, after the insulation later, never found a similar situation.
Amplifier failure
Servo failure, another higher failure rate is the amplifier.
Example 2 A CAK6163 CNC lathe appeared 603 alarm (intelligent power module IPM detected overheating alarm). Maintenance of the module out of the control panel, clean up dust re-installed, the system again a new alarm, can not find the ID number of the module. Open the amplifier check and found that the control board connector has two needles bent, it is estimated that the cleaning process is completed after the completion of the installation of the slot is not aligned, restore the pin shape, the fault still looks up along the pins , Found a 7800A optocoupler integrated block pin to the ground, after the replacement module ID number found, but the machine a move, or there will be 603 alarm. After power off, remove the amplifier and check that the impedance of each pin of IPM (6MBP20RTA060-01) is balanced. Then, the six trigger signals of the module are led to the oscilloscope for measurement, and the mode selection status is set to “Handwheel” and the magnification is set to “0.001 “, Shake the handwheel slowly, observe the waveform of 6 trigger signals, find the signal is complete, and the 6 waveforms are consistent, indicating that the trigger signal is correct. However, the measured output signal does not, so determine the IPM module is damaged, replace the module, the machine back to normal.
3. Amplification board multi-axis fault
Multi-axis amplifier board according to the alarm information can be analyzed to determine the location of the fault point.
Example 3 A XH7160 vertical machining center appears on startup X, Y, Z and spindle 432 alarm CNV.LOWVOLT CON. The device amplifier is FANUC’s integrated module A06B-6134-H303 # A, the common part of only the power supply, so the initial judgment is that the amplifier input power part of the problem. Check the amplifier’s three-phase input power and DC control power are normal, suspected to be a problem with the hardware inside the module. According to the alarm content analysis, the module may not detect the detection part of the appropriate voltage, so check in two parts. The first part is the control part of the DC 24V, after inspection and testing, the module within the voltage of each circuit board are normal, the second part is the main power supply, the incoming terminals R, S and T power supply normal, but found that from this The voltage on the control panel to which the terminal is drawn has no voltage on the R phase of the three phases. After analysis, the measurement point is reached from the R, S and T through 6 series-connected patch elements 2401, respectively. Measurement of the resistance of each patch are normal, but found that the three phases of the 18 resistors around have varying degrees of fever caused by the situation of paint discoloration of the circuit board, and measuring the resistance of the R phase R3 and R4 and R4 and R5 between the printed circuit Board of the line has been blown, re-welding on the machine after troubleshooting.
4. Mechanical and electrical mixing failure
Servo fault, there is a mechanical and electrical hybrid fault, difficult to distinguish, only a comprehensive analysis, from simple to complex step by step to determine the problem as soon as possible.
Example 4 A CKA6163 CNC car during processing, when the workpiece is processed for 2 ~ 3h, the system will appear 366 (built-in pulse encoder count error), 367 (built-pulse encoder pulse error) alarm. According to the alarm, judge the fault may be motor encoder, encoder cable or servo amplifier. According to the principle of repairing convenience, the same alarm appears after replacing the servo amplifier, the motor and the encoder cable one after another. So while the axis alarm monitoring load rate of 15%, fast moving monitoring load rate of about 20%, or the mechanical inspection. The investigation found that the ball screw in the servo motor side of the fixed bearing damage, replace the fault eliminated. Analysis of the reasons for the rotation of the bearing damage caused by motor vibration, resulting in motor encoder count failure.
Example 5 A CAK63135 CNC car also had a similar failure. According to the previous experience, firstly, the bearing on the electric screw side was inspected, no problem was found, the amplifier was replaced, the fault still exists, the motor was replaced, and the fault was eliminated. Inspection found that the motor encoder cover has a gap, suspected dust intrusion into the encoder caused by failure, open the encoder to clean up the dust, try again, troubleshooting.
According to maintenance experience, to quickly solve the problem, we must first clear the failure analysis, especially for hardware failure, it is necessary to carefully analyze the cause of the failure, the time of occurrence, the contents of the fault alarm to determine the direction of maintenance and then start troubleshooting, so that Quickly find out the speed of failure, to avoid misjudgment leading to the expansion of the fault.

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