Tuning P-PI and PI-PI controllers for electrical servos

Abstract

Tuning rules for position and velocity controllers in P-PI and PI-PI electrical servomechanisms are developed using the root locus design method. P-PI controller is equivalent to PID controller with a set-point filter. PI-PI servo provides zero steady-state error for linear disturbances, which may be important for some tracking tasks. Three design data are needed to calculate the tunings, i.e. drive gain, settling time and control cycle. The development begins with continuous controllers for better understanding. Closed-loop transfer functions involve real multiple poles, so the responses are smooth, without overshoot. Upper limits on control cycles as fractions of settling times are given. Some experimental results are presented.