GLOBAL TRACKING CONTROLLERS FOR FLEXIBLE-JOINT MANIPULATORS - A COMPARATIVE-STUDY

Several new controller design techniques for global stabilization of nonlinear systems have recently been reported. Typically, these methodologies provide the designer with various degrees of freedom; consequently, their application in specific examples;leads to the definition of various control schemes. One question of interest is the relationship between these schemes, or whether one contains the other. Further, since these schemes will, in general, exhibit different transients and possess different robustness properties, another challenging research problem is to establish some common framework to compare their robustness and performance properties. In this paper we investigate these questions for three different controller design techniques as applied to the problem of global tracking of robots with flexible joints. The connection between the various controllers are investigated. Further, they are compared using the following performance indicators: continuity properties vis-a-vis the joint stiffness, availability of adaptive implementations when the robot parameters are unknown, and robustness to 'energy-preserving' (i.e. passive) unmodelled effects. Complete stability proofs of all the resulting controllers are given.