In this paper, we present an online adaptive robust control framework for
underactuated brachiating robots traversing flexible cables. Since the dynamic
model of a flexible body is unknown in practice, we propose an indirect
adaptive estimation scheme to approximate the unknown dynamic effects of the
flexible cable as an external force with parametric uncertainties. A boundary
layer-based sliding mode control is then designed to compensate for the
residual unmodeled dynamics and time-varying disturbances, in which the control
gain is updated by an auxiliary direct adaptive control mechanism. Stability
analysis and derivation of adaptation laws are carried out through a Lyapunov
approach, which formally guarantees the stability and tracking performance of
the robot-cable system. Simulation experiments and comparison with a baseline
controller show that the combined direct-indirect adaptive robust control
framework achieves reliable tracking performance and adaptive system
identification, enabling the robot to traverse flexible cables in the presence
of unmodeled dynamics, parametric uncertainties and unstructured disturbances.Comment: 8 pages, 8 figures, 2020 IEEE Conference on Decision and Control
(CDC