A Fast Searching Method For Precision Parts Mating Based Upon Fuzzy Logic Approach

Abstract

The difficulties in devising reliable assembly strategies result from tlie complexity and the uncertainties of the assembly process and its environments such as imperfect knowledge of the parts being assembled as well as the limitations of the assembly devices performing the assembly. To cope with these problems, we presented a new fuzzy rulebased assembly algorithm for precision parts mating(l7). However, the previous method has limitation in mating precision parts because the parameters in the fuzzy control algorithm were fixed, resulting in rather slow search time. To cope with such limitation, this paper presents a technique which can significantly reduce the search time. The presented technique is based upon the fact that adjustable factors in fuzzy algorithm largely influence the assembly performance. Especially, this investigation focuses on the effect of the output scaling factor. Experimental results show that the proper selection of scaling factors can effectively improve the assembly vagueness associated with actual assembly phenomena. Also, the linguistic fiizzy rules desc.ribed by IF-THEN not only can overcome the diffficulties caused by analytic models but also can effectively construct human thinking and knowledge. However, the previous presented technique had a critical limitation in that the technique requires too much searchin effort for the case of corrective motion generated from the fuzzy rules. Moreover, although control performance was lar ely affected by some fuzzy partitioning and the shape of membership function for a primary fuzzy set, the effect of these parameters was not considered. This pa,per, therefore, investigates the effect of scaling factors on assembly performance arid presents a fast searching technique for large initial error based upon the fuzzy rules. This technique consists of two modes: The one is a fine compensation mode whicli is activated in case of small error, while the other is a coarse compensation mode which is activated in case of large error. The above two modes are switched by heuristically adjusting the output scaling factors depending on the magnitude of errors. The performance of the presented method is evaluated through a series of experiments for chamferless peg-in-hole tasks. large initial error(above lmm) because