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Title: Towards better uncertainty handling based on zSlices and general type-2 fuzzy logic systems
Author: Wagner, Christian
ISNI:       0000 0004 5358 2358
Awarding Body: University of Essex
Current Institution: University of Essex
Date of Award: 2015
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This thesis presents an investigation towards better uncertainty handling using zSlices and general type-2 fuzzy systems. Uncertainty as a concept is investigated and its perception through history is reviewed, together with the several theories such as probability and possibility based theories which have been proposed to address uncertainty. The field of fuzzy logic, its roots and its complementing nature when considering probability and fuzzy logic is detailed, while progressing to focus on recent developments in uncertainty handling in the field of fuzzy logic, in particular the application of interval type-2 fuzzy logic systems and an emerging interest in general type-2 fuzzy systems. As a first step towards better uncertainty handling, the combination of stochastic search techniques such as genetic algorithms and interval type-2 fuzzy logic systems is investigated both from a conceptual and an experimental point of view. Several interesting results, in particular in terms of the uncertainty representation of interval type-2 fuzzy sets, which cannot account for potentially complex distributions of uncertainty, introduce the specific focus on general type-2 fuzzy systems. While general type-2 fuzzy systems have been largely avoided because of their significant complexity, the complex three-dimensional representation of uncertainty associated with general type-2 fuzzy sets promises significant improvements in accurate uncertainty handling. This thesis presents the framework of zSlices based general type-2 fuzzy systems which allows for the implementation and application of general type-2 fuzzy systems while avoiding most of the complexity (in terms of computation, implementation and interpretability) of standard general type-2 fuzzy logic systems. The complete theoretical framework of zSlices based general type-2 fuzzy systems is presented, including proofs and examples of all major operations Goin, meet, centroid and type-reduction) required in the design of fuzzy logic controllers. Furthermore, a complete zSlices based general type-2 fuzzy logic controller implementing an edge-following behaviour of a two-wheeled mobile robot has been implemented and its performance investigated. In particular, the zSlices based general type-2 fuzzy logic controllers have been compared to corresponding type-l and interval type-2 fuzzy logic controllers which has allowed to identify potential shortcomings in simplified representation of uncertainty (such as in interval type-2 fuzzy systems) which can be addressed using general type-2 fuzzy systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available