This paper addresses the problem of adaptive trajectory control of space manipulators that exhibit elastic vibrations in their joints and that are subject to parametric uncertainties and modeling errors. First, it presents a comprehensive study of rigid and linear flexible-joint stiffness models, to propose a dynamic formulation that includes nonlinear effects such as soft-windup and time-varying joint stiffness. Second, it develops an adaptive composite control scheme for tracking the end effector of a two-link flexible-joint manipulator. The control scheme consists of a direct model reference adaptive system designed to stabilize the rigid dynamics and a linear correction term to improve damping of vibrations at the joints. Numerical simulations compare the performance of the adaptive controller with its nonadaptive version in the context of a 12:6 12:6 m square trajectory tracking. Results obtained with the adaptive control strategy show an increased robustness to modeling errors and uncertainties in joint stiffness coefficients, and greatly improved tracking performance, compared with the nonadaptive strategy.

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