Limited degree-of-freedom (DOF) parallel kinematic mechanisms (PKM) are capable of high bandwidth tracking and disturbance rejection with smaller actuators than are required for serial machines. A high performance Nyquist-stable (NS) controller with nonlinear dynamic compensation (NDC) applied to a new PKM is presented. The Popov criterion is used to show absolute stability (AS) of the closed loop system and experimental evidence of closed loop performance is provided. This novel approach to PKM control provides 38 dB of disturbance rejection below 10 Hz, an order of magnitude more that what is achieved by implementing an absolutely stable fixed gain (ASFG) controller.
Carruthers, Dustin J. and O'Brien, John F. (2011). "Two Degree-of-Freedom Parallel Mechanisms for High Bandwidth Vibration Suppression and Tracking." Active and Passive Smart Structures and Integrated Systems 7977, 797708-1-797708-11.