Adaptive robust control for bilateral teleoperated robotic manipulators with arbitrary time delays

Abstract

Bilateral teleoperation systems have been extensively developed over decades. Communication delay is one of the most challenging control design problems. Additionally, nonlinearity, parameter variation, and uncertainty in the environment dynamics and robot model are also challenging issues that should be taken into account for excellent control performance. In our work, we propose a globally stable non-linear adaptive robust control structure is proposed, dealing with the following problems. Firstly, this new control structure can tolerate arbitrary, long, and time-varying delays. Secondly, a nonlinear adaptive robust control scheme is proposed to stabilize the system under nonlinearities, unknown parameters, modeling errors and uncertainties in the system, in order to ensure excellent tracking performance on both sides. Thirdly, an environmental torque estimator is designed to estimate immeasurable torques by a least square adaptive law. Moreover, a novel structure of communication block is developed. The master trajectory is sent to the slave side. However, from the slave side to the master side, estimated parameters of the environmental torque are transmitted back. This structure is designed to enhance the control performance of the adaptive robust controller. To ensure the desired transparency performance, an impedance control structure is developed on the master side. The proposed approach can guarantee robust stability, excellent transparency and synchronization under arbitrary time-varying delays. In simulation, two 2-DoF robotic manipulators are considered to verify the effectiveness of the control design.