The design of nonlinear controllers for mechanical systems has been an
ex- tremely active area of research in the last two decades. From a
theoretical point of view, this attention can be attributed to their
interesting dynamic behavior, which makes them suitable benchmarks for
nonlinear control the- oreticians. On the other hand, recent
technological advances have produced many real-world engineering
applications that require the automatic con- trol of mechanical systems.
the mechanism for de- Often, Lyapunov-based techniques are utilized as
veloping different nonlinear control structures for mechanical systems.
The allure of the Lyapunov-based framework for mechanical system control
de- sign can most likely be assigned to the fact that Lyapunov function
candi- dates can often be crafted from physical insight into the
mechanics of the system. That is, despite the nonlinearities, couplings,
and/or the flexible effects associated with the system, Lyapunov-based
techniques can often be used to analyze the stability of the closed-loop
system by using an energy- like function as the Lyapunov function
candidate. In practice, the design procedure often tends to be an
iterative process that results in the death of many trees. That is, the
controller and energy-like function are often constructed in concert to
foster an advantageous stability property and/or robustness property.
Fortunately, over the last 15 years, many system the- ory and control
researchers have labored in this area to produce various design tools
that can be applied in a variety of situations.