Feature recognition within a truth maintained process planning system

Abstract

A major problem for computer aided process planning (CAPP) is the difference in data representation between the design and planning stages. Computer aided design (CAD) uses a data representation which is suited to solid modelling but is impractical for process planning. A partial solution to the non-unique nature of the set-theoretic solid model is detailed.A method of feature recognition for the set-theoretic solid model, together with its implementation in a process planning system is described. It is essentially a rule-based conversion of the CSG string into a set of manufacturing features. One or more alternative ways of viewing the component in terms of features are produced, and user interaction may be required to determine the best set of features to process plan with.

Feature technology: an overview

“…A part model may be represented by an arbitrary CSG tree (depending on different designers), requiring an unlimited number of shape grammars or templates to match the trees. To solve this problem, Lee and Fu (1987), Herbert et al (1990) and Hinde et al (1990) re-construct the arbitrary CSG tree to form a unique and computer understandable tree, then the nodes (primitives) of the re-constructed tree can be identified by a recognizer. Li and Yu (1990) and Perng et al (1990) converted the CSG tree into a DSG (Destructive Solid Modelling) tree, then features are recognized from the DSG model.…”

“…Some definitions are related to the representation and recognition methodology such as Henderson's: "Features are defined as geometric and topological patterns of interest in a part model and which represent high level entities useful in part analysis" (Henderson et al, 1990). Herbert et al (1990) define a feature as a group of geometric entities with some meaning for the particular activity to be performed with them. Choi et al (1984) relate features to the manufacturing methods and define a feature as a portion of the workpiece generated by a certain mode of metal cutting.…”

Symbolic representation of three-dimensional objects to aid local and global shape analysis for defect prediction of casting design

“…However, in Brep, an object is represented by topological and geometric information about its surfaces, hence it is very difficult and complex to build a general procedure to extract complete feature information. Some feature extraction has also been carried out based on a CSG tree structure [12,13]. Since CSG provides a compact and concise data structure, it would seem to be useful for building a general feature extraction algorithm.…”

Using a design by features CAD system for process capability modelling

“…Replacing the human intelligence (in the grouping of geometric entities) by intelligent computer techniques overcomes this reservation. This approach is known as 'feature recognition' and is described in more detail elsewhere [6][7][8][9][10] . Feature recognition techniques could be said to emphasise rather than remove the traditional functional differences that exist in engineering design and manufacture, i.e.…”