Derive the transfer function of ac servo motor?
go through slides 21-25 for exact derivation
The shaft inertia is an integration time constant, which levels off after a while, and becomes a first-order TF. The time constant of the winding can be disregarded, i.e., assumed small, relative to the inertia TC, but it also is a first-order TF, with an estimated TC of 0.1 sec. Then, there is a viscous friction TC, which can also be disregarded, unless some sort of braking is involved. Therefore, in short: rpm (s) / power-in (s) = 1 / 1 + s T s: Laplace operator T: shaft inertia time constant, in time units, = moment-of-inertia / nominal (nameplate) power The moment of inertia must include the motor shaft PLUS the inertia of the load driven by it. To determine the inertia, you?ll have to do a test, measuring the acceleration under a certain force. .
