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 (DOF) structure. A procedure based on a novel variation of l₁-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 the control system for a single joint illustrate the approach. It was found that it gave good performance over varying conditions. We conclude that the trade-off between good command tracking and reasonable plant inputs can be improved by using the proposed approach