AAS 97-721
COMMAND SHAPING FOR NONLINEAR TRACKING CONTROL OF A TWO-LINK FLEXIBLE MANIPULATOR
A.K. Banerjee - Lockheed Martin Research Laboratory, W.E. Singhose - MIT
Abstract
Tracking of a commanded trajectory by a multibody sensor system has become a necessary feature in several recent spacecraft projects. This task is often split up as the design of two parts: a feedforward command generator and a feedback controller. When the multibody system has flexible components, control-structure interaction makes the tracking task quite difficult. This paper considers the basic problem in the simple context of end-point tracking control a planar two-link flexible robot .
The model consists of an order-n formulation for two beams connected by revolute joints. The control task chosen is for the end point of the flexible manipulator to track a prescribed rectangle in minimum time. A nonlinear control law employing feedback linearization based on a rigid body model of the two-link manipulator is used for reference. Convolution of the original bang-bang commands with an impulse sequence aimed at suppressing the control-excited vibration is then used as the shaped command. Simulation results show the effectiveness of this approach. The interaction of the closed-loop controller and the command shaper is examined. Comparison is made with a simple linear controller with input shaping, and robustness of the controller with command shaping is studied.