Failure Analysis of Servo Motor

Motor encoder alarm
1. Cause of failure
① Wiring error;
② Electromagnetic interference;
③ Encoder hardware damage caused by mechanical vibration;
④ Pollution caused by the site environment;
2. Troubleshooting
① Check the wiring and eliminate errors;
② Check whether the shielding is in place, check whether the wiring is reasonable and solve it, and add filters to improve it if necessary;
③ Check and improve the mechanical structure;
④ Check whether the encoder interior is polluted and corroded (dust, oil, etc.), and strengthen the protection;
3. Installation and wiring standards
① Try to use original cables;
② Separate cables to keep them away from polluted wiring, especially highly polluted wiring;
③ Always use an internal power source whenever possible. If switching power supply is used, filter shall be used to ensure that the power supply reaches the cleanliness level;
④ Always ground the common terminal;
⑤ Keep the encoder housing insulated from the machine structure and connect it to the cable shielding layer;
⑥ If it is not possible to insulate the encoder, connect the cable shield to the ground (or special terminal) on the encoder housing and drive frame.

Motor shaft broken
1. Cause of failure
① Unreasonable mechanical design leads to excessive radial load force;
② The load end is stuck or severely overloaded in a moment;
③ The motor and reducer are not concentric during assembly;
2. Troubleshooting
① Check the maximum radial load force that can be borne in the motor sample, and improve the mechanical design;
② Check the operation of the load end, confirm the actual process requirements and make improvements;
③ Check whether the load operates stably and vibrates, and improve the mechanical assembly accuracy.

The motor no-load current is unbalanced, and the three-phase difference is large
1. Cause of failure
① Wrong connection of winding head and tail;
② The power supply voltage is unbalanced;
③ The winding has inter turn short circuit, coil reverse connection and other faults.
2. Troubleshooting
① Check and correct;
② Measure the power supply voltage and try to eliminate the imbalance;
③ Eliminate winding faults.

Abnormal noise during motor operation
1. Cause of failure
① The bearing is worn or there are sand particles and other foreign matters in the oil;
② Loose rotor core;
③ The bearing is short of oil;
④ The supply voltage is too high or unbalanced.
2. Troubleshooting
① Replace or clean the bearing;
② Overhaul the rotor core;
③ Refueling;
④ Check and adjust the power supply voltage.

It is difficult to start the motor, and the motor speed is much lower than the rated speed under the rated load
1. Cause of failure
① The power supply voltage is too low;
② The motor of surface connection method is wrongly connected;
③ The rotor is cracked or broken;
④ The local coils of the rotor are wrongly connected or inversely connected;
③ Too many turns are added when repairing the motor winding;
⑤ Motor overload.
2. Troubleshooting
① Measure the power supply voltage and try to improve it;
② Correct connection;
③ Check the open weld and broken point and repair them;
④ Correct the wrong connection;
⑤ Restore the correct number of turns;
⑥ Load shedding.

After power on, the motor cannot rotate, but there is no abnormal noise, odor and smoke?
1. Cause of failure
① Power supply is not connected (at least two phases are not connected);
② Fuse fusing (at least two phase fusing);
③ The over-current relay is too small;
④ The control equipment is wired incorrectly.
2. Troubleshooting
① Check whether there are breakpoints at the power circuit switch, fuse and junction box, and repair them;
② Check the fuse model, cause of fusing and replace it with a new one;
③ Adjust the relay setting value to match with the motor;
④ Correct the wiring.

The motor vibrates greatly during operation
1. Cause of failure
① Excessive bearing clearance due to wear;
② Uneven air gap;
③ Rotor unbalance;
④ Bent shaft;
⑤ Coaxiality of coupling (pulley) is too low.
2. Troubleshooting
① Maintain the bearing and replace it if necessary;
② Adjust the air gap to make it uniform;
③ Correct rotor dynamic balance;
④ Straighten the shaft;
⑤ Recalibrate to make it meet the requirements.

The motor does not rotate and hums after power on
1. Cause of failure
① The rotor winding has open circuit (one phase is broken) or one phase of the power supply loses power;
② The beginning and end of the winding outgoing line are wrongly connected or the winding is reversely connected internally;
③ The contact of power circuit is loose and the contact resistance is large;
④ The motor is overloaded or the rotor is stuck;
⑤ The power supply voltage is too low;
⑥ Small motors are assembled too tightly or grease in bearings is too hard;
⑦ The bearing is stuck.

2. Troubleshooting
① Find out the fault point and repair it;
② Check the winding polarity; Judge whether the winding end is correct;
③ Fasten the loose wiring screws, use a multimeter to judge whether each connector is falsely connected, and repair it;
④ Reduce load or find out and eliminate mechanical faults;
⑤ Check whether the specified surface connection method is wrongly connected; If the voltage drop is too large due to too thin power wire, correct it;
⑥ Reassemble to make it flexible; Replace qualified grease;
⑦ Repair the bearing.

Bearing overheating
1. Cause of failure
① Too much or too little grease;
② Poor oil quality contains impurities;
③ Improper matching of bearing and journal or end cover (too loose or tight);
④ The bearing bore is eccentric and rubs against the shaft;
⑤ Motor end cover or bearing cover is not installed flat;
⑥ The coupling between the motor and the load is not corrected, 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 lubricating grease (1/3-2/3 of the volume) as required;
② Replace the clean lubricating grease;
③ If it is too loose, it can be repaired with adhesive. If it is too tight, it should be turned. Grind the inner hole of journal or end cover to make it suitable;
④ Repair the bearing cover and eliminate the friction points; For more highlights, please pay attention to the WeChat technical training;
⑤ Reassemble;
⑥ Recalibrate and adjust the belt tension;
⑦ Replace with a new bearing;
⑧ Correct the motor shaft or replace the rotor.

The motor is overheated and even smokes
1. Cause of failure
① The power supply voltage is too high;
② If the power supply voltage is too low, the motor will run with rated load, and excessive current will cause winding heating;
③ When repairing and removing the winding, the hot removal method is improper, which burns the iron core;
④ Motor overload or frequent starting;
⑤ Motor phase loss, two-phase operation;
⑥ After rewinding, the winding is not fully dipped in paint;
⑦ There is much dirt on the surface of the motor when the ambient temperature is high, or the ventilation duct is blocked.

2. Troubleshooting
① Reduce the power supply voltage (such as adjusting the tap of the power supply transformer);
② Increase the power supply voltage or replace the thick power supply wire;
③ Repair the iron core and remove the fault;
④ Load reduction; Control the starting according to the specified times;
⑤ Restore three-phase operation;
⑥ The secondary impregnation and vacuum impregnation processes are adopted;
⑦ Clean the motor, improve the ambient temperature and take cooling measures.