| Summary: | 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. === Applied Science, Faculty of === Electrical and Computer Engineering, Department of === Graduate
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