$H\sb \infty$ and mu controller design for an actuator

Robust linear controllers for a rotary electro-mechanical actuator are designed by H/sub infinity /-optimization and mu -synthesis. Meeting the tracking specifications in the presence of input saturation, persistent load disturbances, and Coulomb friction appears difficult: only for the system without saturation, the closed-loop response is satisfactory. The reason for this is believed to be threefold. First, some of the specifications are physically infeasible. Second, accounting for saturation and Coulomb friction in linear controller design is not straightforward. Third, the time domain specifications are not easily translated into the frequency domain. An elaborate trial-and-error procedure may improve the design, but is taxing for the designer