Robust μ-design of a disk drive servo system

In this paper we show the application of the SLICOT routines, for robust control system analysis and design, in a disk drive servo control system design. An uncertainty model of the system plant is first derived which contains eleven uncertain parameters including four resonance frequencies, four damping coefficients and three rigid body model parameters. The μ-synthesis and analysis method is applied in the design. With the designed controller the closed-loop system achieves robust stability and practically achieves robust performance. A detailed analysis of the frequency domain and time domain characteristics of the closed-loop system is conducted. Further, model reduction routines have been applied to find a reasonably low order controller based on the μ-synthesis design. This reduced order controller maintains the robust stability and robust performance of the closed-loop system. Simulations of the nonlinear sampled-data servo system with the low order controller have been included as well, which confirms the practical applicability of the controller obtained.