A Comparison between PI and I-P Velocity Controls in a Position Control System that Considers Oscillatory Mechanisms

Abstract

In this closed-loop position control system, the mechanism's oscillatory characteristics were considered in the design of the control loop. Using the usual P and PI modes for position and velocity controls, the oscillations become unstable as the control gain was set larger. For (P, I-P) controls, on the other hand, those characteristics become more stable as the gain increased. For this reason, the latter can be set at higher gain for faster response. For this oscillatory mechanism having a 40 Hz natural frequency and a 0.15 damping ratio, the maximum gains were 147 s-1 using (P, I-P) and 62 s-1 in (P, PI). A stable response was obtained in (P, I-P) at a gain of 60 s but severe oscillations were observed in (P, PI) at the same gain. An experiment using an X-Y table resulted in seven-times higher gain using (P, I-P) over (P, PI), and ±0.2μm contouring error using (P, I-P) as opposed to from +3.0 to 0.5μm using (P, PI) for 10 mm-radius-circle generations at a speed of 100 mm/min. © 1988, The Japan Society for Precision Engineering. All rights reserved.