On the control of magnetically levitated robot wrists

Abstract

The author deals with the problem of controlling six-degrees-of-freedom magnetically levitated robot wrists. This control problem is greatly simplified by the use of the Euler quaternion representation of rotation. It is shown that both the approximate and exact linearizations of the equations of motion are fully decoupled second-order systems, and therefore simple scalar PD/PID (proportional-derivative/proportional-integral-derivative) compensators can be used for their control. The author presents a novel nonlinear angular velocity or angular momentum observer and shows that it has global and eventually exponential convergence. He presents simulation results and discusses some implementation issues and experimental results. The simulations, using the magic wrist parameters, showed that these controllers perform well.