Willem F. Bronsvoort

Semantic feature modelling

Abstract Almost all current feature modelling systems are parametric, history-based modelling systems. These systems suffer from a number of shortcomings with regard to the modelling process. In particular, they lack a complete specification of feature semantics, and therefore fail to maintain the meaning of the features during modelling. Also, modelling operations sometimes are hampered by the model history, and occasionally even have ill-defined semantics. In the semantic feature modelling approach presented here, the semantics of features is well defined and maintained during all modelling operations. The result of these operations is independent of the order of feature creation, and is well defined. The specification of feature classes, the structure and functionality of the feature model, in particular the Cellular Model, and the model validity maintenance scheme are described. The advantages and disadvantages of the approach, compared to current feature modelling approaches, are pointed out.

Assembly Features in Modelling and Planning

Abstract In recent years, features have been introduced in modeling and planning for manufacturing of parts. Such features combine geometric and functional information. Here it is shown that the feature concept is also useful in assembly modeling and planning. For modeling and planning of both single parts and assemblies, an integrated object-oriented product model is introduced. For specific assembly-related information, assembly features are used. Handling features contain information for handling components, connection features information on connections between components. A prototype modeling environment has been developed. The product model has been successfully verified within several analyses and planning modules, in particular stability analyses, grip planning, motion planning and assembly sequence planning. Altogether, feature-based product models for assembly can considerably help in both assembly modeling and planning, on the one hand by integrating single-part and assembly modeling, and on the other hand by integrating modeling and planning.

Representation and management of feature information in a cellular model

Many limitations in current feature modelling systems are inherited from the geometric representation they use for the product model. Both a very rigid and a very extensive representation are unsuitable for feature applications, at least if no convenient support is provided to manage the data. This paper describes a cellular representation for feature models that contains all the relevant information to effectively solve a variety of current problems in feature modelling. Much benefit is gained from a coherent integration between shapes of a feature model and cells in the cellular model. Every feature shape has an explicit volumetric representation in terms of cells. Specific subsets of its boundary are also distinguished in terms of cell faces and edges. Feature interactions are maintained in attributes of cells, cell faces and cell edges. Methods for modifying and querying the cellular model are presented, and their application is illustrated for feature validity maintenance, feature interaction management, feature conversion between multiple views, and feature visualization.

Feature modelling and conversion: key concepts to concurrent engineering

Abstract Feature modelling is a relatively new development in CAD/ CAM. Whereas in solid modelling only information about the geometry of products is stored, in feature modelling also functional information is stored in the product model. One aim of this article is to give an overview of the main concepts in feature modelling, another is to indicate the issues in feature modelling that are relevant for further research. There is much confusion about what features actually are, and therefore definitions, classifications and examples of features are first given. Because feature modelling builds on solid modelling, an overview of advanced solid modelling is given, with emphasis on the concepts of parametric and constraint-based modelling. Attention is next focused on representation of features. The two most important ways to define features in a product model, feature recognition from a geometric model and design by features, are then discussed. Design by features is illustrated by the GeoNode system. One of the main themes in this article is that for different applications, different features are required, and that therefore there is a need for automatic conversion between features. Such conversion is of particular importance for the support of concurrent engineering, in which several engineers from different disciplines work simultaneously on the design of a product.

Multiple-view feature modelling for integral product development

Abstract To allow a designer to focus on the information that is relevant for a particular product development phase, is an important aspect of integral product development. Unlike current modelling systems, multiple-view feature modelling can adequately support this, by providing an own view on a product for each phase. Each view contains a feature model of the product specific for the corresponding phase. An approach to multiple-view feature modelling is presented that supports conceptual design, assembly design, part detail design and part manufacturing planning. It does not only provide views with form features to model single parts, as previous approaches to multiple-view feature modelling did, but also a view with conceptual features, to model the product configuration with functional components and interfaces between these components, and a view with assembly features, to model the connections between components. The general concept of this multiple-view feature modelling approach, the functionality of the four views, and the way the views are kept consistent, are described.

Freeform feature modelling: concepts and prospects

Abstract Much research has already been done on regular-shaped features, but more complicated, freeform features are now demanded by product designers. Freeform shapes are mostly represented by low-level representations, such as Bezier, B-Spline and NURBS patches. Freeform features provide a high-level interface to these low-level representations. The purpose of freeform features is faster and more intuitive modelling with more guarantees for a high-quality design. In contrast to the traditional ways of modelling with freeform surfaces, where low-level entities such as control points and weights are used to interact with a freeform surface, the user is offered a set of freeform features whose basic shape is fully defined by intuitive parameters. The design-by-features approach offers good opportunities for validity maintenance, by which only models that satisfy certain pre-defined validity conditions can be created. In this paper, the most important concepts in design by freeform features are surveyed, and issues such as classification and parameterisation of freeform features and freeform feature recognition are described. Wherever appropriate, promising research prospects are indicated.

A Collaborative Feature Modeling System

Collaborative systems are distributed multiple-user systems that are both concurrent and synchronized. An interesting research challenge is to develop a collaborative modeling system that offers all facilities of advanced modeling systems to its users, while at the same time providing them with the necessary coordination mechanisms that guarantee effective collaboration. To achieve this, a web-based collaborative feature modeling system, webSpiff, has been developed. It has a client-server architecture, with an advanced feature modeling system as a basis for the server, providing feature validation, multiple views and sophisticated visualization facilities. A careful distribution of the functionality between the server and the clients has resulted in a well-balanced system. On the one hand, the server offers all the functionality of the original feature modeling system. On the other hand, all desirable interactive modeling functionality is offered by the clients, ranging from display of feature model images to interactive model specification facilities. The architecture of webSpiff, the distribution of model data, the functionality of the server and the clients, and the communication mechanisms are described. It is shown that a good compromise between interactivity and network load has been achieved, and that indeed advanced feature modeling with a collaborative system is feasible. @DOI: 10.1115/1.1521435#

Maintaining multiple views in feature modeling

A new feature modeling concept and its implementation are presented. In the multiple-view modeling concept, a set of open feature views of a product is maintained. The implementation does not rely on the existence of certain views, but instead is generic since generic view specifications are used. Views are maintained using feature conversion techniques, including constraint techniques. For adding a view to the set of open views, an open view function has been developed. This function uses the specified view properties, including its feature definitions. It derives a meaningful feature interpretation for the opened view. Geometric constraint solving is used to propagate feature parameter changes between views, and a priority mechanism is used in case of conflicting constraints. In case of a conflict, a new incremental version of the open view function is invoked, which updates the feature model of the reopened view efficiently.

Integrating part and assembly modelling

Current modelling systems adequately support either modelling of parts or modelling of assemblies, whereas ideal modelling systems should adequately support both. To achieve this, a new modelling system has been developed, which uses enhanced multiple-view feature modelling. This advanced modelling approach provides specialised interpretations of a product for different development phases, by means of so-called feature views, and ways to keep these interpretations consistent, i.e. to make sure that they all represent the same product. The paper concentrates on the views that support detail design of parts and assembly design of the whole product, and the way these views are related and kept consistent. It describes the features and the tools that can be used to build and maintain the feature models of the views. An example modelling session is given to illustrate the benefits of such integrated modelling.

Developments in Feature Modelling

AbstractFeature modelling is nowadays the predominant way of product modelling, in which geometric and functional information is stored in a single product model. The basic concepts of feature modelling in general, and the state of the art in commercial feature modelling systems, will be presented first. This will be followed by an overview of four major developments that solve shortcomings in such systems. First, in semantic feature modelling, it is possible to more adequately specify and maintain the meaning of features. Second, in multiple-view feature modelling, there is a specific feature model for each product development phase. Third, in collaborative feature modelling, teams of users can collaborate on the development of a product with full feature modeling functionality. Fourth, in freeform feature modelling, features with freeform shapes are made available. Some other developments are mentioned as well.