Stability and convergence of integrated adaptive control for space manipulators

Abstract

Robot manipulators carrying out autonomous extra-vehicular operations in space will have to handle payloads with imperfectly known mechanical properties, as well as to cope with the manipulator parameter and structural uncertainties. On-line estimation of those parameters will be required to ensure the quality of the maneuvers. In order to achieve this objective, recourse is taken to indirect adaptive control methods: the system parameters used in control law are adjusted on-line, during execution of the desired maneuver. This paper focuses on the analysis of the stability and convergence aspects of the multiple degree-of-freedom case of the integrated adaptive control of a multi-body space manipulator. In the integrated adaptive control the generalized parameter matrices and vectors, which represent the integrated, time-varying effect of all the unknown as well as known parameters, are directly estimated and tracked. This is achieved by reinterpreting the system dynamic equation as a linear time-varying measurement equation, where those generalized parameters are state variables. The generalized parameters, in the case of space manipulator operations, vary slowly with time. For the purposes of establishing stability and convergence of the integrated adaptive control these generalized parameters will be assumed to remain constant. The motivation and the theoretical development are briefly covered. The system equations of motion, control and estimation are presented, and a formal solution is given. The parameter estimation process and the control law are separately analyzed. It is shown that the control system output error is globally asymptotically stable, and that the parameter error will also converge to zero if the external command input satisfies a certain sufficient excitation condition.