Servo Stability Heavy Stuff

Posted by Bill Beatty at 04/26/2001 1:27 AM EST

Other on team #71, Team Hammond, from Team Hammond.

We have been building machines that servo position very heavy masses at high speeds for 40 years. Paul can correct me, but it is my understanding that the rule of thumb inertia ratios actually come from the ratio of available torque output of the motor in relation to the WR2 of the rotor of the motor. Over the years servo motors have greatly improved as they have much higher output torques and small diameter rotors. This feature, as well as others allows for higher ratios of reflected to motor inertia.

Another huge factor in servo stability is internal servo loop lost motion ie. backlash. Mounting the position feedback device as close to the motor as possible (directly on the motor shaft is best) greatly improves the overall servo stability. Unfortunately, it is difficult to do with the components from FIRST and any lost motion results in error of location/repeatability.

BTW. We have used a number of GE/Fanuc controls and their AC servo drives. Good stuff.

Posted by Paul Copioli at 04/26/2001 8:41 AM EST

Engineer on team #217, Team Macomb - Royal Fusion, from Utica Schools, Fraser Schools, Warren Cons. School and Ford Motor Company.

In Reply to: Servo Stability Heavy Stuff
Posted by Bill Beatty on 04/26/2001 1:27 AM EST:


You are absolutely correct. See my follow up to Dr. Joe’s post.