Posted by Michael Norman on Fri, Sep 18, 2009 @ 01:59 PM
Your motor has failed and you need to remove it from your machine. You have disconnected all the electrical, dissconnected the coupling, cursed the engineer who designed the machine, and are now ready to remove the motor. There is just one obstacle left however, the motor weighs way more than you can lift by hand.
You decide to use a forklift or ceiling crane to lift the motor out of the machine. You see that the motor has one or two eye-bolts that you can attach slings to. Just connect the motor to the crane and lift right? Almost, but there are a few things you must do to insure your personal safety and the safety of the motor.
Slings are specifically rated for certain loads. These loads vary depending on the manner in which you utilize the sling. These loads should be documented on the sling lable. If the lable is missing or you are using a sub-par sling you should consider throwing it away and investing in proper slings.
Learn the right and wrong ways to attach a sling. Wear-flex has a webpage on the proper use of their slings. Knowing when a sling is being used improperly will reduce the likleyhood of undue strain leading to sling failure.
Always use one sling per eye-blot. Never loop the sling through two eye-bolts. This mistake is common. When the sling loops from one eye-bolt to another it puts force on the bolts at an improper angle that can lead to them bending or breaking. Always lift an eye-bolt straight up from the top of the bolt, and check that the bolt is tight before lifting.
These are some tips on safely lifting your motor out of your machine and putting it back in.
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.