Rule-based systems approach to fixture design

Jigs and fixtures are indispensable tools in the metal removal process. They position the workpiece with respect to the cutting tool and rigidly hold the workpiece throughout the cutting operation. These work holding devices require a considerable amount of time, money and effort to design, fabricate and test. Fixture design has been more of an art than a science and the factors influencing the automated design process have not been studied. With the development of CAD/CAM, modern manufacturing technology is rapidly changing. However, technological development in the area of work holding devices has been minimal. This research is a study of automating the design process of fixtures for machining.; The objective of this dissertation was to develop and test a methodology that can shorten or automate the fixture design process. Shortening the time required for fixture design will enable a manufacturer to react more rapidly to market demands and engineering changes.; One primary research issue is the development of a methodology by which a computer system can recognize a workpiece such that an acceptable fixture will be designed. A second research issue is to determine those factors that influence the automation of the fixture design process. A rule based system was used as a research vehicle to identify and incorporate the many kinds of problem solving techniques needed for fixture design.; The developed system named PBFIXS stands for pattern based fixture design system. The workpiece is represented by the summation of cuboids. Different seating patterns are applied to the workpiece to emulate human recognition of the workpiece. The application of a seating pattern is based on the combinations of the relative positions of four factors; they are: the centers of volume, material removed, shape of the workpiece, and the major thrust force generated by drilling. Other fixture design requirements are also incorporated in the developed system. A number of fixture designs for imaginary and actual workpieces by two experts were compared with the designs by PBFIXS. The results indicate that pattern matching to be a viable approach to fixture design.