Self-Tuning Control of a Two-Link Manipulator With a Flexible Forearm

Abstract

The control of the motion of a two-link manipulator with a flex ible forearm is studied. The first link is rigid, and the second link has a flexible part as an extension of a rigid part. The motion of the manipulator takes place on a horizontal plane. The dynamics of the two-link manipulator with a flexible fore arm are determined in Lagrange's formulation. The positions of specified points on the flexible forearm are obtained from the strain gauge measurements and the positions of the joint vari ables. The inputs are applied to the actuators of the revolute first joint and the prismatic link. For the controller design, a time series multivariate model of the autoregressive exogenous (ARX) type is used to describe the input/output relation. The discounted least squares method is used to estimate the parameters of the time series model. A self-tuning controller is so designed that the positions of the specified points on the flexible forearm track the given trajectory points. The controller operates on the Cartesian coordinates, which specify the positions of the chosen points on the flexible forearm. Simulation results as well as laboratory experiments on a Stanford/JPL arm controlled by a self-tuning controller are presented to illustrate the approach.