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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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FIGURE 1.14 The system architecture of the tolerance synthesis system.<br />

Implementation and Case Study<br />

Implementation<br />

The TSS for automatic allocation of tolerances on components has been implemented using the CM<br />

software package on a SUN SPARC workstation. 26 The IMSL math library and the CLIPS expert system<br />

shell are also used in the implementation of the TSS. The high-level system architecture of the system<br />

is shown in Figure 1.14. In addition to different computational modules (as shown in Figure 1.14), a<br />

number of other routines have been developed using the CLOS language for performing different<br />

utility functions. The TSS has been built in a modular fashion such that each one of the modules could<br />

be modified without affecting the rest of the system. At present, the TSS consists of about 11 modules<br />

that are built around the CM package. The 11 modules are<br />

• Pre-processing module: In this module, the user specifications (such as geometry, part functions,<br />

material description, surface finish, and assembly graph) are represented as attribute values in the<br />

product model of the part. The information is distributed along three hierarchical levels of the<br />

part product model. These functions are performed in conjunction with the product model<br />

templates and the solid modeler in the CM system.<br />

• Solid modeler: The solid modeler (SHAPES) is used for creating the geometric model (hybrid<br />

CSG/B-Rep based) of the part. The geometric attributes of the part (solid, surface, edge, and<br />

vertex information) can be attached as information attributes to the product model templates of<br />

the part.<br />

• Function decomposition module: In this module, the component functions as specified by the user<br />

are decomposed into equivalent functional specifications (PFM) on the individual surfaces of the<br />

part. This is done by using the PFM algorithm16 in conjunction with the geometric reasoning<br />

module.<br />

• Geometric reasoning module: This module (AGM function-based) is an independent module that<br />

provides geometric reasoning support for a number of other modules within the TSM module. It<br />

© 2001 by CRC Press LLC

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