Should I compare the natural frequency to RPM of motor? or is it related to cogging torque? How do I know if my motor remains stable & won't vibrate at natural frequencies?
Hello Usman Khan ,
One of the modes of vibration of an electric motor is torsional vibration, which depends on the moment of inertia of the motor's armature, the torsional stiffness of the drive shaft, and the moment of inertia of the load, see, for example, Research Mechanical Resonance in Closed Loop Servo System
Regards,
Thomas Cuff
Hi, Thomas Cuff & thank you for referencing this detailed paper. Like you mentioned, one of the vibration modes is torsional vibration, I completely agreed as I am getting this mode in my FEA analysis. But how do you define your Natural frequency as 'Safe range' considering different operating frequencies which are unknow? How can we calculate those operating vibrations/frequencies? is there any formulation?
Hi Usman Khan ,
Because you are really talking about the subject of fatigue testing, I would recommend, for example, the book by Harris and Crede [1]. You can only really define a safe operating range via experimental testing of the actual motor under the applicable loads and control conditions. FEA is okay for simple linear systems, but it cannot tell you about nonlinear behaviors, or material tolerances. You simply cannot model a mechanical system in enough detail to give your analysis verisimilitude (trueness to life).
[1] Cyril M. Harris, Charles E. Crede (editors); Shock and Vibration Handbook, Second Edition; McGraw-Hill Book Company; 1976; pp. 25-1 - 5-26, Chapter 25 - Vibration Testing Machines.
Regards,
Thomas Cuff