Top 10 Failure Analysis of Servo Motors

Servo motors are widely used, but after a long period of operation, a variety of faults will occur. Timely judgment of the cause of the failure, the corresponding treatment, is to prevent the expansion of the failure, to ensure the normal operation of the equipment is an important work.

I: Motor encoder alarm

Causes of failure

• Wiring error;
• Electromagnetic interference;
• Encoder hardware damage caused by mechanical vibration;
• Pollution caused by the site environment;

Troubleshooting

• Check the wiring and eliminate errors;
• Check whether the shielding is in place, check whether the wiring is reasonable and solve it, and improve it by adding filters if necessary;
• Check the mechanical structure and improve it;
• Check the inside of the encoder for contamination and corrosion (dust, oil, etc.) and strengthen protection;

Installation and wiring standards

• Use original cables as much as possible;
• Separate cables to keep them as far away as possible from contaminated wiring, especially highly contaminated wiring;
• Whenever possible, always use internal power supplies. If a switching power supply is used, a filter should be used to ensure that the power supply is clean;
• Always ground the common terminal;
• Keep the encoder housing insulated from the machine structure and connect it to the cable shield;
• If it is not possible to insulate the encoder, the cable shield can be connected to ground (or a dedicated terminal) on the encoder housing and drive frame.

II: Motor broken shaft

Causes of failure

• Inadequate mechanical design leads to excessive radial loading force;
• Stuck at the load side or severe momentary overload;
• The motor and reducer are not concentric when assembled.

Troubleshooting

• Check the maximum radial load force that can be withstood in the motor samples and improve the mechanical design;
• Check the operation of the load side, confirm the actual process requirements and improve them;
• Check whether the load operation is stable and there is no vibration, and improve the precision of mechanical assembly.

Ⅲ: motor no-load current imbalance, three-phase difference is large

Causes of failure

• The first and last ends of the winding are connected incorrectly;
• The power supply voltage is unbalanced;
• The winding has a turn-to-turn short circuit, reverse coil connection and other faults.

Troubleshooting

• Check and correct;
• Measure the power supply voltage and try to eliminate the imbalance;
• Eliminate winding faults.

Ⅳ: motor operation ringing abnormal noise with strange

Causes of failure

• Worn bearings or foreign matter such as sand in the oil;
• Loose rotor core;
• Bearings are out of oil;
• The power supply voltage is too high or unbalanced.

Troubleshooting

• Replace or clean the bearings;
• Overhaul the rotor core;
• Go for it;
• Check and adjust the power supply voltage

Ⅴ: Difficulty in starting the motor, when the rated load, the motor speed is lower than the rated speed of the more

Causes of failure

• The power supply voltage is too low;
• Face connection method motor misconnection;
• Rotor open weld or fracture;
• The rotor local coil is misconnected or reversed;
• Increase the number of turns too much when repairing the motor winding;
• Motor overload.

Troubleshooting

• Measure the power supply voltage and try to improve it;
• Correct the connection;
• Check for open welds and breaks and repair them;
• Identify misconnections and correct them;
• Restore the correct number of turns;
• Load shedding.

Ⅵ: The motor does not rotate after being energized, but there is no noise, odor or smoke

Causes of failure

• The power supply is not turned on (at least two phases are not turned on);
• Fuse is blown (at least two phases are blown);
• The overcurrent relay is set too small;
• The control equipment is wired incorrectly.

Troubleshooting

• Check the power circuit switch, fuse, and junction box for breakage and repair;
• Check the fuse type, the reason for melting, and replace the fuse with a new one;
• Adjust the relay setting value to match the motor;
• Correct the wiring.

Ⅶ: High motor vibration during operation

Causes of failure

• due to wear bearing clearance is too large;
• Uneven air gap;
• Rotor imbalance;
• The rotating shaft is bent;
• Coupling (pulley) coaxiality is too low.

Troubleshooting

• Overhaul the bearings and replace them if necessary;
• Adjust the air gap to make it even;
• Correct the rotor dynamic balance;
• Straighten the rotor shaft;
• Recalibrate to bring it into compliance.

Ⅷ: Motor doesn't rotate after power on with humming sound

Causes of failure

• rotor winding has a broken circuit (a phase of broken wire) or power supply a phase of the loss of power;
• The beginning and end of the winding lead wire are connected incorrectly or the internal connection of the winding is reversed;
• Loose power circuit contacts and high contact resistance;
• The motor is overloaded or the rotor is stuck;
• The power supply voltage is too low;
• Small motor assembly is too tight or grease in bearings is too hard;
• The bearing is stuck.

Troubleshooting

• identify the breakpoint to be repaired;
• Check the polarity of the winding; determine if the winding ends are correct;
• Tighten the loose wiring screws, and use a multimeter to determine whether each connector is falsely connected, and repair it;
• Reduce loads or identify and eliminate mechanical problems;
• Check whether the specified face connection is connected by mistake; whether the voltage drop is too large due to the thin power supply lead, and correct it;
• Reassemble to make it flexible; replace with qualified grease;
• Repair the bearing.

Ⅸ: Bearings overheating

Causes of failure

• too much or too little grease;
• Bad oil contains impurities;
• Improper fit (too loose or too tight) between bearing and journal or end cap;
• The bearing bore is eccentric and rubs against the shaft;
• Motor end caps or bearing caps are not mounted flat;
• The coupling between the motor and the load is not calibrated, or the belt is too tight;
• The bearing clearance is too large or too small;
• The motor shaft is bent.

Troubleshooting

• Add grease (1/3-2/3 of volume) as required;
• Replace clean lubricating grease;
• Too loose can be repaired with bonding agent, too tight should be turned, grinding journal or end cap bore to make it fit;
• Repair the bearing cap to eliminate rubbing points;
• Reassemble;
• Recalibrate and adjust the belt tension;
• Replace the bearing with a new one;
• Correct the motor shaft or replace the rotor.

Ⅹ: Motor overheating or even smoking

Causes of failure

• power supply voltage is too high;
• power supply voltage is too low, the motor is running with the rated load, the current is too high for the winding to heat up;
• When repairing and removing the winding, the hot dismantling method is used improperly, which burns the iron core;
• Motor overload or frequent starting;
• Motor is out of phase and running in two phases;
• Inadequate dipping of the fixed winding after rewinding;
• High ambient temperature motor surface dirt, or blockage of the ventilation channel.

Troubleshooting

• Reduce the power supply voltage (such as adjusting the power supply transformer tap);
• Increase the power supply voltage or change the supply wire to a thicker one;
• Overhaul the iron core to eliminate the problem;
• Load shedding; controlled starting for a specified number of times;
• Restore three-phase operation;
• Adopt secondary dipping paint and vacuum dipping paint process;
• Clean the motor, improve the ambient temperature, and use cooling measures.