Experimental adaptive control of a hydraulic robot

Abstract

An adaptive position controller is investigated to compensate for the effects of both the actuator and linkage dynamics in a four axis hydraulic robot. A simulation study was done, prior to the experimental implementation, in order to compare and contrast different adaptive control algorithms for this system. The dynamics of the linkage were developed using Lagrangian techniques. The equations of motion of the robot were generated with a computer program which uses symbolic manipulation. The equations describing the dynamics of the hydraulic actuator were developed using a lumped parameter, control volume analysis. Implicit and explicit deterministic autoregressive moving average (DARMA) model based adaptive control algorithms were first simulated for a single axis hy­ draulic servo system. Least-squares identification algorithms with or without covariance resetting or forgetting factors were combined with model reference, pole assignment, and weighted one-step-ahead control algorithms. The model reference adaptive controller which offered an advantage in the design process was then applied to the entire four axis model. Simulation results indicated a satisfactory response for this multiple-input, multiple-output system. The results of this discrete-time, model-reference adaptive controller (MRAC) were compared with Craig's continuous-time, statevariable-based, adaptive con-