Common Servo Motor Issues & Possible Causes
Even with a strict regimen of upkeep and preventative maintenance, a servo motor failure can (and will) happen during operation. Here's a list of common problems & some tips on troubleshooting your servo motor.
Issue: No Rotation
- The motor connections are loose or open.
- Foreign matter is lodged in the motor.
- The motor load is excessive.
- The bearings are worn.
- The rotor is partially demagnetizing causing excessive motor current.
- Motor voltage is exceeding the maximum value.
- The duty cycle is excessive.
Issue: Abnormal Noise
- Loose parts are present in the motor.
- Through bolts are loose.
- The bearings are worn.
- GAIN setting is too high.
Issue: Erratic Operation (motor locks into position, runs without control or with reduced torque)
- Phases A & B, A & C or B & C reversed
- Sine, Cosine or Rotor leads reversed
- Sine, Cosine, Rotor lead sets reversed
- Combinations of above three
.7 Common Reasons for a Servo Motor Breakdown
A servo motor can be one of the most susceptible parts on your CNC machine or robot that may breakdown and require repair or replacement. The environment in which it is placed can be violent and extremely dirty. A servo is a very complex mechanism that needs all of its parts to work in unison for the whole to be successful. Here is a guide to help you know what to look for when your machine will not run and your servo motor may be the culprit:
1. Contamination. Errant oil, coolant, cutting fluid can have a devastating effect on your entire machine, including the drives and electronics, even in a cabinet. But it really harms a servo in several ways, since it is on the battlefront of machines’ main objectives. This type of constant contamination can negatively affect the bearings, the encoder, the electrical of the motor, and the integrity of the windings.
2. Bad Bearings. A very common occurrence, but over time, bearings wear out, as simple as that. Moreover, if there is a lack of PM (Preventative Maintenance) the life-span of the bearing will be much shorter. Checking the motors consistently and removing excess contamination and changing bearings when you start to hear them scream will help to eliminate bigger problems with your servo motor. Always send your servo to a trusted repair facility for a quick bearing change and rebuild.
3. Electrical Degradation. Over time, aging electrical components breakdown: capacitors, diodes, resistors, etc. This is also true of the electrical in a servo motor, such as the feedback device- encoder, resolver, etc.
4. Improper Installation. Believe it or not, this happens more often than one would think. Sometimes, a servo is installed in a hurry and belts are too tight, or positioning is off. Other improper techniques involve coupling it to a gear box or ball screw that is worn-out or bad.
5. Bad Drive or Power Supply. There are times where the issue is not with the motor, rather it’s with the drive or power supply. A bad drive or power supply can lead to a ‘spike’ or improper voltage going to the servo, causing damage. Improper voltage can single phase a winding and will need to be rewound.
6. Damaged Cable. Bad Cables are common to a servo failure. A shorted cable can also ‘spike’ voltage and knock out the motor. Testing your cables should be included when troubleshooting.
7. Machine Overload or Overworked. The harder you run – the shorter the servo motor will last. If your machine is properly maintained on a regularly-scheduled basis, it will greatly reduce the chances of your motor prematurely failing.
In short, if proper maintenance is performed along with correct usage, your servo motor will last longer. If you suspect a bearing going bad due to a loud noise, it is best to send in to a professional repair facility for service and bearing change. If you wait too long, a more catastrophic repair will surely result, causing longer machine downtime and higher costs.