Adaptive sinusoidal disturbance cancellation for precise pointing of Stewart platforms

This paper combines an adaptive sinusoidal disturbance cancellation scheme with fault tolerant pointing algorithms for Stewart platforms. This results in a fault-tolerant pointing system capable of low-frequency tracking, mid-frequency rejection of large monotone disturbances, and high-frequency passive vibration isolation. Since often the frequency of the monotone sinusoidal disturbance cannot be precisely known, a phase-locked loop (PLL) algorithm is used to catch the frequency and a method for PLL design is developed. Experimental results on the University of Wyoming Stewart platform demonstrate that pointing errors caused by a monotone disturbance decrease 50-fold even in the presence of multiple actuator failures.