Independent joint control using two-degrees-of-freedom control structures

This paper presents an innovative approach to independent joint control in robotic systems. The proposed approach uses a robust compensator implemented with a full two-degrees-of-freedom (2-DoF) structure. A procedure based on a novel variation of l(1)-optimal control theory is applied to design the second or "open loop" DoF. It is shown that this design may be carried out completely independently of the first or "closed-loop" DoF, provided an appropriate factorization of the feedback controller is used. The design and evaluation of a control system for a single joint illustrate the approach. It was found that it gave good performance over varying conditions. We conclude that the tradeoff between good command tracking and reasonable plant inputs can be improved by the use of the proposed approach.