Robust servo design with applications

An optimal multivariable proportional-integral (PI) controller with preassigned eigenspectrum is designed so that the system output would track constant reference inputs in spite of constant but unknown plant disturbances. A sequential strategy for modal servomechanism design is given for the above problem. In addition, since the proposed PI controller is of state feedback type, an observer capable of estimating the unmeasurable state variables in spite of the presence of unknown disturbances is introduced, thus resulting in a suboptimal overall system. The separation property for the overall servo/observer system is illustrated. The design strategy is successfully used for position control of a brushless DC motor, and in a regulator mode for controlling a headbox which is an integral part of the modern paper machines used in the pulp and paper industry.