Alternatives in precise load motion control of two-mass servomechanisms

Load motion control in high precision elastic servo systems is addressed. It is assumed that only the motor position measurement is available to close control loops. Four controllers are compared: a conventional PID; a state space plus feedforward controller with integral action on the motor position measure; a second state space plus feedforward controller with integral action on the estimate of the load position; and a pole assignment controller designed based on input-output models. The essential elements for the design of the controllers are given. Detailed simulation analysis is used to compare the controllers from several points of view (set-point tracking, robustness, disturbance rejection, friction induced limit cycles). Experiments performed on a prototype servo are also discussed