What to Consider When Your Motor Has a Bad Bearing Fit
Posted by Michael Norman on Fri, Sep 04, 2009 @ 07:45 AM
Your motor has a strong vibration or knocking sound. You send it somewhere for repair and you are told that the bearing fit is no good. You get a quote to change the bearings and repair the bearing fit. Problem solved you say.... Then your servo is returned and fails again. What is so difficult about fixing a bearing fit?
Failure of a bearing fit is a common problem with all electric motors. Bearing fits fail when the fit is not the correct bore, the bearing was incorrectly installed, or the bearing seized. If a bearing fit fails this can lead to many other problems with your servo motor.
-Feedback devices are very sensitive and are damaged easily by oscillation. Encoders often have glass scales that shatter and resolvers have windings that are damaged when their axis of rotation is not perfectly central.
-Rotor shafts can bend or break. Servos need to run true and broken shafts can occur under the armature where they are often missed until the motor is under load in your machine.
-Stator Laminations can be damaged resulting in rubs and grounded power leads. The air gap between rotor and stator is small, so when there is an oscillation in the rotor it will bang into the stator laminations. Bending the laminations can cause high spots that rub and also cause the lamination to pinch the coil under it shorting the motor windings to ground.
When your servo motor has a failed bearing fit be cautious where you have it repaired. Regular motor shops will not be capable of evaluating or repairing the feedback on your servo. Most places will see a failed fit and look no further. Being aware of the side effects of a bad fit will improve the likelihood that your servo gets properly repaired the first time.