Design of Robust Two-Degree-of-Freedom Controllers for Position Servos Using H-Infinity Theory

Linear feedback controllers for position servos are designed using the structured singular value optimization (Doyle's μ-synthesis) method. The method produces a two-degree-of-freedom controller, including both the feedback and the prefilter, which is ‘performance robust’, in the sense that the closed-loop system is guaranteed to meet performance specifications in the presence of unmodelled dynamics. A detailed design of a low-order controller for a hydraulic position servo, including numerical non-linear simulation results, is presented.