Geometric and Feature modelling

Feature Conversion for Concurrent Engineering

Summary

Today's development of industrial products faces high demands. The market demands products to be marketed earlier than those of the competitors. Customers demand products that meet their functional requirements at a low price. Thus, products must be developed fast, and must be of good quality.
For product developers, this implies integration of traditionally separated product development phases, i.e. concurrent engineering. Various product properties, such as manufacturability and maintainability, may be checked and improved already during design of the product. Furthermore, production planning activities may be started early. Since different engineering disciplines are considered simultaneously, computer support is required to manage the huge amount of complex product data.
For such concurrent engineering, functional product information is required. Whereas geometric modeling only deals with geometric product information, feature modeling embeds both geometric and functional information in features. Design by features enables to model a product with functional product properties. Using feature validation, the intended functional product properties are maintained under model modifications.
Hence, the ideal product development environment integrates concurrent engineering and feature modeling. Because each engineering discipline has its own vocabulary, it has its own set of features. Therefore, each engineering discipline is represented by a so-called view. Communication between engineers from different disciplines, or between views, requires feature conversion. Such feature conversion translates modifications to a feature model from one view to another.

For concurrent engineering using feature modeling, a product model has been developed. It consists of a central geometry and constraint representation, and a feature model for each view. The central product representation is shared between the views. In this way, each constraint is reflected in all views. The product geometry representation is a cellular data structure, which has a quasi nonmanifold topology. Generic features embed geometry and constraints. Each feature model consists of instances of generic features and of generic constraints. Feature instances refer to geometry stored in the cellular model.
Two types of feature conversion have been developed that propagate feature model geometry and topology changes between views. Geometry changes are propagated using automatically derived geometric constraints, and geometric constraint solving techniques. Topology changes are propagated using generic view specifications, the cellular model, and a newly developed feature recognition technique.
This new feature recognition technique is a generic and hierarchical technique which is called top-down feature recognition. At the top level, it prescribes feature classes in a specified order, which ensures that a meaningful feature interpretation is found for the view. At the lower level, instances of a feature class are recognized, which uses generic feature specifications and is based on geometric reasoning; it has the advantage that it can handle intersecting features. Where possible, top-down feature recognition uses incremental techniques. In this way, top-down feature recognition is capable of efficiently generating multiple feature interpretations of one product.

The product model has been incorporated in a prototype feature modeling system called Spiff. It has been used to validate the developed feature conversion techniques. Spiff implements declarative feature modeling using object-oriented techniques. It has a generic graphical user interface and provides several feature visualization facilities.

It is concluded that multiple-view feature modeling can support concurrent engineering. A central product model with different feature models provides a shared product representation that contains functional product information. Such a product model enables communication between the different engineering disciplines through propagation of feature model changes.

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de Kraker KJ (1998), Feature Conversion for Concurrent Engineering, PhD Thesis, Delft University of Technology, ISBN 90-9011280-4.