The application of an indirect (self-tuning) adaptive controller to an electro-hydraulic positioning system is described. The underlying control method is pole placement, with the addition of a demand filter to allow noise effects to be reduced without degrading closed-loop performance. Recursive least squares is used to estimate the plant parameters, but the data is pre-filtered to reduce bias. A novel covariance trace limiting algorithm provides estimator reliability despite periods of insufficient excitation. Off-line system identification is employed to help controller design for the electro-hydraulic servosystem. The resulting controller performs well, and adapts rapidly to changes in load stiffness and supply pressure.
