Control of nonlinear teleoperation systems subject to disturbances and variable time delays

Instability and poor performance are two wellknown problems encountered in bilateral teleoperation over a communication channel with variable time delays, where force feedback from the slave side is provided to the master side. When unknown disturbances or external forces act on the master and/or the slave manipulators, the teleoperation system will be even more prone to stability and performance degradation. By adopting a Lyapunov approach, we present a novel nonlinear disturbance observer based control scheme for teleoperation systems that are subject to variable time delays and disturbances. Lumping the effects of dynamic uncertainties, unknown forces/torques exerted by the human operator and the remote environment, and external disturbances into a single disturbance term enables us to use a disturbance observer and suppress these disturbances in order to alleviate their adverse effects on the teleoperation system stability and performance. The proposed disturbance observer based control laws guarantee asymptotic disturbance tracking, asymptotic position tracking, and stability of teleoperation system in both constrained and free motions. Experimental results are presented to verify the effectiveness of the proposed approach.