Robust Wide-Range Controller Using Multirate Estimation and Control for Velocity Regulation and Tracking

A method for velocity estimation and control for systems with only incremental position measurements (e.g. motor / encoder systems) is presented that is appropriate for a wide velocity range. In order to maintain good performance at very low velocities, where Coulomb friction becomes more significant, a multirate estimation and control scheme, which incorporates sliding mode control, is proposed. The method will be compared to and further combined with other schemes such as one for high velocities based on counting encoder pulses between sampling instants and one for low velocities based on measuring time between encoder pulses. Superior velocity tracking control over a wide operating range is demonstrated through implementation of the algorithm on the capstan motor of a digital tape drive. Since the algorithm relies significantly on the system model, the algorithm is shown to be robust to parameter uncertainty with the inclusion of an adaptive element.