Three-phase AC servo motors are widely used, but after long-term operation, various faults may occur. Timely identification of the cause of the fault and corresponding handling are important tasks to prevent the fault from spreading and to ensure the normal operation of the equipment.
The main faults and their analysis are as follows:
1. Motor encoder alarm
2. Motor shaft breakage
3. The motor's no-load current is unbalanced, with a large difference between the three phases.
4. The motor makes abnormal noises or unusual sounds when running.
5. The motor is difficult to start; under rated load, the motor speed is significantly lower than the rated speed.
6. After being powered on, the motor does not rotate, but there is no abnormal noise, odor, or smoke.
7. The motor vibrates significantly during operation.
8. The motor does not turn on after being powered on, but makes a humming sound.
9. Bearing overheating
10. The electric motor overheats or even smokes.
I. Motor encoder alarm
1. Cause of the malfunction:
① Wiring error
② Electromagnetic interference
③ Encoder hardware damage caused by mechanical vibration
④ Pollution caused by the on-site environment
2. Troubleshooting:
① Check the wiring and rule out any errors.
② Check if the shielding is in place, check if the wiring is reasonable and address any issues, and add filters if necessary to improve the situation.
③ Inspect the mechanical structure and make improvements.
④ Check if the encoder's interior is contaminated or corroded (dust, oil, etc.), and strengthen protection accordingly.
3. Device and wiring standards:
Use original cables whenever possible
Keep cables as far away as possible from contaminated wiring, especially high-contamination wiring.
Use internal power whenever possible. If using a switching power supply, a filter should be used to ensure the power supply meets cleanliness standards.
Always ground the common terminal
Insulate the encoder housing from the machine structure and connect it to the cable shield.
If the encoder cannot be insulated, the cable shield can be connected to the ground (or a dedicated terminal) on the encoder housing and driver frame.
II. Motor shaft breakage
1. Cause of the malfunction:
① Unreasonable mechanical design leads to excessive radial load force
② Load-side freeze or severe instantaneous overload
③ The motor and reducer are not concentric during installation.
2. Troubleshooting:
① Verify the maximum radial load force that the motor sample can withstand and improve the mechanical design.
② Inspect the operating status of the load end, acknowledge the practical process requirements, and make improvements.
③ Check whether the load operates stably and whether there is any vibration, and improve the mechanical installation accuracy accordingly.
3. The motor's no-load current is unbalanced, with a large difference between the three phases.
1. Cause of the malfunction
① The start and end terminals of the winding are connected incorrectly;
② Unbalanced power supply voltage;
③ The winding has faults such as inter-turn short circuit and coil reverse connection.
2. Troubleshooting
① Review and correct;
② Measure the power supply voltage and try to eliminate the imbalance;
③ Eliminate winding faults.
IV. Abnormal noises or unusual sounds during motor operation
1. Cause of the malfunction
① The bearing is worn or there are foreign objects such as sand particles in the oil;
② The rotor core is loose;
③ The bearing is short of oil;
④ The power supply voltage is too high or unbalanced.
2. Troubleshooting
① Replace or clean the bearing;
②Inspect the rotor core;
③ Keep going;
④ Check and adjust the power supply voltage.
5. The motor is difficult to start; under rated load, the motor speed is significantly lower than the rated speed.
1. Cause of the malfunction
① The power supply voltage is too low;
② Misconnection of the motor using the surface connection method;
③ The rotor is either unwelded or cracked;
④ The rotor coils are incorrectly connected or reversed;
⑤ Too many turns were added when correcting the motor windings;
⑥ Motor overload.
2. Troubleshooting
① Measure the power supply voltage and find ways to improve it;
② Correct the connection method;
③Inspect and correct any open welds and breaks;
④ Identify and correct any incorrect connections;
⑤ Restore the correct number of turns;
⑥ Reduce load.
6. After power is applied, the motor does not rotate, but there is no abnormal noise, odor, or smoke.
1. Cause of the malfunction
① Power is not connected (at least two phases are not connected);
② The fuse blows (at least two phases are blown);
③ The overcurrent relay setting is too low;
④ Incorrect wiring of the control equipment.
2. Troubleshooting
① Check the power circuit switch, fuses, and junction box for any breaks, and correct them;
② Check the fuse type and cause of failure, and replace the fuse with a new one;
③ Adjust the relay setting value in conjunction with the motor;
④ Correct the wiring.
7. The motor vibrates significantly during operation.
1. Cause of the malfunction
① Because the bearing clearance is too large due to wear;
② Uneven air gap;
③ Rotor imbalance;
④ The pivot is bent;
⑤ The coaxiality of the coupling (pulley) is too low.
2. Troubleshooting
① Inspect the bearings and replace them if necessary;
② Adjust the air gap to make it uniform;
③ Check the rotor dynamic balance;
④ Straighten the shaft;
⑤ Proofread from the beginning to make it conform to the rules.
8. The motor does not turn on after being powered on, but makes a buzzing sound.
1. Cause of the malfunction
① The rotor winding has an open circuit (one phase is disconnected) or one phase of the power supply is lost;
② The beginning and end of the winding leads are connected incorrectly or the internal winding connections are reversed;
③ The power circuit contacts are loose, resulting in high resistance when touched;
④ The motor is overloaded or the rotor is stuck;
⑤ The power supply voltage is too low;
⑥ The small electric motor is installed too tightly or the grease in the bearing is too hard;
⑦ The bearing is stuck.
2. Troubleshooting
① Identify the breakpoints and correct them;
② Check the winding polarity; determine if the winding ends correctly;
③ Tighten any loose wiring screws, use a multimeter to check if any connectors are faulty, and correct them accordingly;
④ Reduce the load or identify and eliminate mechanical faults.
⑤ Check if the standard wiring method has been incorrectly applied; check if the voltage drop is too large due to the power supply wire being too thin, and correct any errors.
⑥ Reinstall from scratch to ensure flexibility; replace with qualified grease;
⑦ Correct the bearing.
9. Bearing overheating
1. Cause of the malfunction
① Too much or too little grease;
② The oil quality is poor and contains impurities;
③ The bearing is not properly fitted to the journal or end cap (too loose or too tight);
④ The bearing bore is eccentric and rubs against the shaft;
⑤ The motor end cover or bearing cover is not installed flat;
⑥ The coupling between the motor and the load is not aligned, or the belt is too tight;
⑦ The bearing clearance is too large or too small;
⑧ The motor shaft is bent.
2. Troubleshooting
① Add grease according to the rules (1/3-2/3 of the volume);
② Replace with clean, smooth grease;
③ If it is too loose, it can be corrected with adhesive; if it is too tight, it should be machined, and the journal or end cap inner hole should be ground to make it fit properly.
④ Repair the bearing cap and eliminate the rubbing points;
⑤ Install from scratch;
⑥ Recalibrate from scratch and adjust the belt tension;
⑦ Replace with a new bearing;
⑧ Check the motor shaft or replace the rotor.
10. Overheating or even smoking of the electric motor
1. Cause of the malfunction:
① The power supply voltage is too high;
② The power supply voltage is too low, and the motor is running under rated load, resulting in excessive current and overheating of the windings;
③ When repairing or removing the windings, the hot disassembly method is not appropriate and may burn the iron core;
④ Motor overload or frequent starting;
⑤ The motor is operating with two phases running when one phase is missing;
⑥ The varnish impregnation of the fixed winding was insufficient after rewinding;
⑦ High ambient temperature, excessive dust on the motor exterior, or blocked ventilation ducts;
2. Troubleshooting:
① Reduce the power supply voltage (e.g., adjust the tap of the power supply transformer);
②Increase the power supply voltage or replace the power supply wire with a thicker one;
③ Inspect the iron core and troubleshoot the fault;
④ Reduce load; control the start-up according to the prescribed number of times;
⑤ Restore three-phase operation;
⑥ Select two-stage impregnation and vacuum impregnation processes;
⑦ Clean the motor, improve the ambient temperature, and select cooling methods.
