Abstract:
Many control problems are based on control objectives easily quantified and
consequently realisable by standard control synthesis methods. When an unmanned
aircraft navigates, it moves inside a complex environment due to interactions with its
surrounding and time varying environmental conditions. Several causes of perturbations
have been identified as for example gusts and corrupted information of position. The
characteristics of possible missions carried out by the un manned aircraft leads to the
desire to construct navigation control systems which when operated in perturbed
environments combine the advantages of smooth control with accurate navigation. Rule
based, and adaptive controllers have favourable properties for such systems.
This thesis investigates the use of a rule based navigation controller for a particular
unmanned aircraft, the XRAEl aircraft. To achieve this objective several different types
of fuzzy logic controllers are analysed as for example conventional and direct and
indirect adaptive fuzzy controllers. They are designed by employing simple control
engineering knowledge and subsequently validated using a stability method. For this
purpose diverse stability methods are described and a new technique presented, the
fuzzy root locus method, which is also based on the introduction of a new concept for
fuzzy logic controllers, the fuzzy cell.
The realisation of this work has been achieved by a series of simulation tests employing
different processes and a simulation model of the XRAEl aircraft. The conclusions
drawn from the results of the experiments consider in general that a rule based controller
can improve the quality of navigation when compared to conventional controllers.
