Similarity Assessment and Retrieval of CAD Models
With rapid globalization and highly competitive markets, mechanical design reuse has been recognized as an effective way for manufacturing enterprises to survive by revitalizing existing designs instead of creating new ones. However, existing 3D content-based retrieval algorithms and systems, which have only focused on geometrical representations (i.e., meshed or surface models), can hardly retrieve reusable results for reuse. An effective similarity assessment and retrieval mechanism for CAD model reuse, which also takes the mechanical reusability into account, has not been defined. Therefore, this research aims to develop a reuse-oriented retrieval mechanism to locate reusable CAD models effectively. A semantics-based feature directed acyclic graph (FDAG) representation has been developed to capture complicated modeling interdependency knowledge among feature constitutes of a CAD model. Based on modeling expertise captured by FDAG representation, complicated and implicit design precedence semantics are organized as a partially ordered set (POSET). Two knowledge-driven FDAG partitioning schemes have been proposed to extract reusable CAD components. With these partitionings applied on existing CAD models, the CAD model similarity is no longer assessed on rigid 3D shapes. Instead, details of models are progressively simplified by using the proposed horizontal FDAG partitioning; therefore, assessment on essential similarity becomes possible. On the other hand, reusable sub-parts are extracted from complete models by using the vertical FDAG partitioning. An essential shape matching (ESM) method supporting CAD model retrieval based on their essential shape similarities has been presented. In ESM, complete CAD models are simplified, and their essential shapes are preserved for comparison. An essential shape aggregation (ESA) descriptor has been defined for comparing only essential shapes of CAD models while effectively tolerating trivial details. A partial shape matching (PSM) method has also been proposed to address the reuse-oriented retrieval of CAD partial components. In the PSM method, the vertical partitioning has been applied to find out disjointed sub-graph from the FDAG representation, by examining the reachability of a POSET data. The found disjointed sub-graphs are equivalent to reusable CAD partial components, which are further compared by the partial shape aggregation (PSA) descriptor. A prototype system has been implemented to demonstrate the feasibility of the proposed reuse-oriented retrieval method. The effectiveness has also been evaluated on more than six hundred realistic CAD models and multiple case studies. The proposed method brings more advantages: (1) it offers ease of reuse on retrieved results as the reusability is taken into account in the retrieval; thus, inflexibility to reuse can be greatly avoided, and (2) it maximally preserves design intelligence to reused parts. The prototype provides users the access to original modeling expertise embedded in existing models when reusing. As a result, design intelligence including parametric constraints will be inherently transferred to new designs and future reuse.
CAD model retrieval, design reuse, feature-based modeling, essential shape matching, partial shape matching
Networked Digital Library of Theses and Dissertations