Systematic strategy for choosing optimal membership function and
fuzzy rulebase based on fuzzy entropy for intelligent control of robotic part
assembly tasks
Affiliations: Department of Electronic Engineering, DanKook
University, South Korea 330-714. E-mail: cmson@dankook.ac.kr
Abstract: Using the control of robotic part assembly tasks, consisting of a
macro and a micro-assembly, as an example, a systematic way, not a heuristic
one, that can determine an optimal membership function and rulebase among
feasible fuzzy membership functions and rulebases which can execute the part
assembly tasks successfully, based on a fuzzy entropy is introduced. In a
macro-assembly, a part is brought from an initial position to an assembly hole
or a receptacle (target or destination) for a purpose of a part mating in a
partially unstructured environment that includes unknown obstacles. Then, in a
micro-assembly, the part is placed at a position that is ready to mate
successfully with the target without jamming. An entropy function, which is a
useful measure of the variability and the information in terms of uncertainty,
is introduced to measure its overall performance of a task execution related to
the part assembly tasks. Three different types of membership functions are
applied to two different sets of fuzzy rulebases for a macro and a
micro-assembly to show a robustness. The membership function that generates the
lowest degree of uncertainty in the part assembly procedure is chosen as an
optimal one. The same criterion is applied to determine an optimal fuzzy
rulebase. In order to address the uncertainty associated with the part assembly
procedure, a fuzzy theory, that is well-suited to the management of
uncertainty, is introduced. The degree of uncertainty associated with the part
assembly procedure is used as an optimality criterion, or cost function, e.g.
minimum fuzzy entropy, for a specific task execution. The results show the
effectiveness of the proposed approach. The proposed methodology is not only a
useful tool in choosing an optimal membership function and fuzzy rulebase but
applicable to a wide range of robotic tasks including controlling of mobile
based robots around obstacles, and a part mating and pick and place
operations.
Keywords: Systematic methodology, optimal membership function/fuzzy rulebase, part macro/micro-assembly (part-bringing/mating), robustness, fuzzy entropy, uncertainty (= fuzziness), machine reasoning, inferencing, and decision-making, and vision sensor
