NONLINEAR ADAPTIVE ROBUST CONTROL FOR BILATERAL TELEOPERATED ROBOTIC MANIPULATORS WITH ARBITRARY TIME DELAYS

Abstract

Bilateral teleoperation systems have been extensively developed over decades. The communication delay can cause instability and 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 need to be considered in order to achieve excellent control performance. This thesis aims to develop a globally stable nonlinear adaptive robust control structure, dealing with the following problems. Firstly, this new control structure can tolerate arbitrary, long, and time-varying delays. Secondly, in order to ensure excellent tracking performance on both sides, a nonlinear adaptive robust control algorithm is proposed. Lyapunov method is used with stability proof. Thirdly, an environmental torque estimator is designed to estimate unmeasurable torques by a least square adaptive law. Moreover, a novel structure of communication block is developed. From the master side to the slave side, the position signal of the master manipulator is being transmitted. However, from the slave side backwards, only the estimated parameters of the environmental torque are sent 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. Simulations are carried out to verify the robust stability, excellent transparency and synchronization of the proposed design under arbitrary time-varying delays. Simulation studies on the control gain tuning and model mismatches are carried out in order to verify the effectiveness of the design under different circumstances. Two different control algorithms are also presented to compare with the proposed method. In the last chapter, conclusions and the possible future work are presented.