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2. Review of jigs and ®xtures design
2.1. The classical theory of jigs and ®xtures design
Jigs and ®xtures design is highly experienced-based and skill-oriented. The design theories have been fully developed since the last century. In this sense, we may call them the classical jigs and ®xtures design. Utilization of the classical theory to solve design problems can be found in Colvin and Stanley (1948), Hoffman (1962) and Kempster (1969), which give an in-depth review of the design in conventional methods. A lot of important issues associated with jigs and ®xtures design have been discussed, such as the cutting tools, process planning, location and clamping.
2.2. Expert systems in jigs and ®xtures design
Application of arti®cial intelligence (AI) in jigs and ®xtures design started along with the advances of computer-aided design. The most recent development available about automated ®xture design indicated that expert systems played a prominent role in this ®eld. D.T. Pham and A. de Sam Lazaro presented the knowledge-based, interactive design aid ``Jigs and Fixtures Designer's Assistant'' and an automated system ``AutoFix'' (Pham, 1991). The Jigs and Fixtures Designer's Assistant is an expert system shell, which is implemented via XI Plus. The system consists of four different modules for ®xture planning, location, clamp and support. A knowledge base governing all ®xture planning principles forms the brains of the system. The interactive modules provide the guidelines for the user to implement the design. Actually the Jigs and Fixtures Designer's Assistant is an advisory program; designers make the ®nal design decisions. The rule-based language OPS5 and the I-Deas CAD package has bean used by the automated ®xture design system AutoFix. AutoFix program has four sections, the input stage, the knowledge-base, satellite programs and output stage. In the input stage, the part geometry is retrieved from the CAD system and converted to a language readable by the knowledgebased system. Additional questions are asked by the system to de®ne the problem more accurately. The knowledge base consists of facts, meta-rules and knowledge rules necessary to arrive at a decision and
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a ®xture con®guration. In the system, nine satellite programs have been adopted for handling the symbolic language OPS5. The programs enable the user to monitor the data fed into the system. The ®nal stage is the output stage which shows the design results with the selected ®xture components. Englert and Wright (1986) present the development of an expert system ``Expert Machinist'' which takes ®ve major stages: identi®cation, conceptualization, formalization, implementation and testing. The boundary conditions and the assumptions for a given design problem are appropriately de®ned in the identi®cation stage. In conceptualization, conventional machining and manufacturing practices and rules are retrieved and used in the control strategy of the expert system. In the formalization stage, the expert system development language is used to represent the derived concepts, which could be added to the knowledge base as a design rule for the future application. In the implementation stage, the strategies and heuristics are transformed into rules and control structures used by the expert systems. The above mentioned expert systems for jigs and ®xtures design suffered from the same obstacles as they did in mechanical design automation (Bardasz, 1991). No information can be found in the ®eld of jigs and ®xtures design using UMJFS.
3. Introduction to universal modular jigs and ®xtures system (UMJFS)
Jigs and ®xtures are designed for manufacturing processes. They are also called ``tooling''. They are the tools needed to hold a workpiece in an assigned position, where a variety of tasks may be performed such as turning, milling, drilling, and grinding. Generally speaking, approximately thirty percent of the manufacturing cost is for tooling, based on medium quantity production. The features of ®xtures are countless. They include the type of the ®xture (milling, drilling), the shape of the workpiece (rectangular, cylindrical), the size and weight of the workpiece (the housing overall dimensions, the appropriate weight), and the workpiece material (high carbon steel, bronze, plastic and any other synthetic material). Other important features are tolerance analysis, and stress and strain analysis either for the workpiece or the ®xture itself. Tolerance analysis is used for quality