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1、Analysis of automated modular fixture configuration design systemRONG Yi ming，LI Jie，MA Wei-dong（Worcester Polytechnic institute，MA 01609，U. S. A）Abstract To counter the fixture planning of computer-aided fixture design (CAFD) an automated modular fixture configuration design system is developed. Ha
2、ving fixture surface accessibility analysis as the core, the optimum selection of fixturing surfaces and points on workpiece is fullfilled. Firstly, several basic criteria for evaluating the eligibility of a surface being a preliminary candidate fixturing surface are discussed. Secondly, by applying
3、 a discretization technique, an accessibility model of fixturing surfaces is established based on an overall evaluation of the accessibility of discrete points on the surface. Finally, the implementation issue and an analysis/design example are presented.Key words computer-aided fixture design; fixt
4、ure planning; fixturing surface1 INTRODUCTIONImportant manufacturing activity in the production cycle. Computer-aided fixture design (CAFD) technique has been developed and become part CAD/CAM integration. The development of CAFD contributes to the reduction manufacturing lead time, optimization of
5、manufacturing operations, and verification of manufacturing process designs. CAFD plays an important role in flexible manufacturing system(FMS) and computer-integrated manufacturing system (CIMS) Figure one outlines the activities of fixture design in manufacturing systems which basically include th
6、ree major aspects: setup planning, fixture planning, and fixture configuration design. The objective of setup planning is to determine the number of setups needed, the position and orientation of workpiece in each setup, and the machining surfaces in each setup. Fixture planning is to determine the
7、locating, supporting, and clamping points on workpiece surfaces. The tasks of fixture configuration design is to select fixture components and place them into a final configuration to fulfill the functions of locating and clamping the workpiece. An automated modular fixture configuration design syst
8、em has been developed where when fixturing surfaces and points are selected on the workpiece model fixture units are automatically generated and placed into position with the assistant of fixture component assembly relationships. In the development of automated fixture planning, it is desired that t
9、he fixturing surfaces and positions on workpiece be selected automatically. As shown in Figure2, several factors which attribute influences on fixture planning should be taken in- to consideration, ie., workpiece geometric information and operational information need to be extracted and retrieved， a
10、ccuracy relationships and surface accessibility of workpiece need to be analyzed, fixturing stability and easiness of workpiece loading/unloading operation need to be verified. In this paper, the research focus is on resolving the problem of fixturing surface accessibility analysis.2 BASIC REQUIREME
11、NTS ON FIXTURING SURFACESFixturing surfaces are the surfaces on workpiece used to locate and clamp the workpiece where functional fixture components (locators and clamps) are in contact with these surface. As the focus of this research is on analyzing the accessibility of fixturing surface on workpi
12、ece, first of all, the study is started with the discussion on the basic requirements for a surface on workpiece to be eligible as a preliminary candidate fixturing surface. In automated fixture planning, once the primary locating direction is determined in setup planning, the accessibility property
13、 of each candidate fixturing surface should be assessed so as to help the fixture planning fulfill the optimum selection of fixturing surfaces and point distributions. In this research, the accessibility analysis is investigated briefly on the basis of pure geometric information of the workpiece and
14、 its surfaces which can be extracted from the CAD solid model. Other information such as surface finish and tolerance are excluded from concern because they are the factors considered in the accuracy analysis of fixture planning.On a complex workpiece, some surfaces might be obviously ineligible to
15、be the candidate fixturing surfaces and should be filtered out at first. In our current research, only the surfaces which satisfy the following basic requirements can be selected as preliminary candidate fixture surfaces, imachining surfaces,planar surfaces,surfaces with accessible normal directions
16、, and surfaces which are large enough. The main purpose of identifying these requirements is to filtez out those obviously ineligible surfaces on workpiece and assume all re-maining surfaces as preliminary candidate .fixturing surfaces.2.1 Non-machining SurfacesIn a real fixture design, it is well known that the surfaces to be machined at one setup should not be used as fixturing surfaces and hence are definitely inaccessible to any fixture component Therefore a
