Design, implementation and evaluation of stable bilateral teleoperation control architectures for enhanced telepresence
Creators: name: Hashtrudi-Zaad, Keyvan
Publisher: name: University of British Columbia
Year: 2009

description: Teleoperation systems are designed to project the human sensing and manipulation ability at different scales to remote locations or to virtual worlds. The goal of any bilateral teleoperation controller design is to maintain stability in all circumstances while achieving desired performance, known as "transparency". Among a variety of proposed bilateral controllers, in theory, four-channel control architectures that incorporate master and slave position and force information exchange can provide stable perfect transparency. However, in practice, the need for stability robustness to communication-channel time-delays and dynamic uncertainties of unstructured environments limits performance severely. This thesis is concerned with the analysis of stability robustness and transparency of teleoperation systems, and performance optimization through the development and incorporation of new fixed-parameter and adaptive bilateral controllers. The stability and performance of teleoperation systems are analyzed by first providing a better understanding of the technical definition of transparency. In addition, the common interpretation of four-channel control architecture is extended to teleoperation systems with different master and slave manipulator structures. The stability and performance robustness of a number of well-known control architectures are analyzed and evaluated using network theory analysis tools such as the passivitybased Llewellyn's absolute stability criterion and the minima and dynamic ranges of the transmitted impedances. The analysis results provide clear guidelines on how to choose the control parameters in trading off stability robustness versus performance. The new fixed-parameter bilateral controllers which are developed for performance enhancement are simple in structure and easy to implement. The first group of controllers that benefit from the proper use of local feedback loops, is the class of transparency-optimized three-channel control architectures that can provide perfect transparency under ideal conditions. The robustness of the proposed architecture to delays is analytically investigated. The second group of controllers in which the priority is given to force control at one side and to position control at the other side, considerably reduces the force and position tracking errors. Spatial stability and performance of the proposed bilateral parallel force/position controller are analyzed. In support of the theoretical work, both fixed-parameter control schemes are tested on a master-slave experimental set-up. The new adaptive bilateral controllers are designed for increased robustness to delays and environment uncertainties. Using a novel geometric approach to impedance control, the four-channel bilateral variable impedance controller, featuring dual adjustment of the master and slave impedances based on the environment mechanical contact properties, is proposed. Experimental results on a remote excavation test-bed show stable contact and satisfactory force and position tracking. The second category of adaptive controllers rely on identification and reflection of the operator and environment mechanical impedances to the slave and master. It is shown that these control schemes can provide transparency in the presence of timedelays. A nonlinear least squares stiffness identification methodology for estimation of the environment contact location and impedance is also developed.