Volume: 23 Issue: 1 (January 2000)
More, Better Views
Dutch researchers are developing a feature-based modeling system that will enhance collaboration by letting engineers across a variety of disciplines simultaneously view different aspects of the same CAD model.
In the manufacturing world, enhancing the efficiency of new product development has been the driving force behind much of the CAD research in recent years. And many of these efforts have focused on ways to support and encourage full collaboration among the various parties involved in getting a new product to market, such as design, manufacturing, distribution, and service. One of the most significant trends in this arena has been the push toward techniques that enable simultaneous, cross-functional involvement early in the product-development cycle. In an effort to push the envelope on this front, researchers at the Technical University of Delft are developing an enhanced feature-based modeling system that provides different disciplines their own unique view of a product that includes only those features relevant to that discipline. To be useful to all phases of the product-development process, the system supports geometry that hasn't been completely specified.
The system, which is being developed as an extension to a program the researchers have been working on for more than five years, utilizes a feature-modeling paradigm, in which functional shape information for each object is stored along with the object's geometric definition. This means that the system knows not only the geometry of an object, but also aspects of the product that have significance for some application, such as its function and ways that it can be manufactured. These types of systems use advanced geometric-modeling techniques, such as parametric and constraint-based modeling, to build models using form features. These features represent specific shape attributes that are functionally significant to some aspect of the product life cycle. In mechanical engineering, features include things like holes, slots, and protrusions.
|The interface of the Spiff multiple-view feature modeling system shows a modeling session involving the part-design view (left) and the part-manufacturing planning view (right). It displays the panels of both views, and incorporates cameras showing the ge|
Called Spiff, the feature-modeling system is a multiple-view program through which different feature views of the same product can be accessed and manipulated by users to whom the respective features are relevant. For example, says project director Willem Bronsvoort, "A 'design' view might show general features that remove or add material from or to the model [holes and protrusions], whereas a 'manufacturing-planning' view might show only holes and slots, features that remove material from the model." The latter view would contain only subtractive features because the manufacturing planners are only interested in determining how to mill the product from a stock of raw material.
One disadvantage of this and other feature-modeling systems is that they require the user to completely specify the form and function of a model at the outset, making them of little value to the early, conceptual-design phase of the engineering process, in which the geometry has not been finalized. Thus, the Delft researchers are developing the enhanced multiple-view system to support incompletely specified geometry. In addition, the system allows users to model the relevant assembly information for products that have several parts.
|Two views of the same product provide different information. The model for the part-detail design phase (left) is built from features that add material to the model, such as the yellow rib at the back of the model and features that remove material from th|
The enhanced system will support five views, says Bronsvoort. The first is a conceptual-design view, including features on components (a hole of a certain radius, for instance) and interface features between components, such as a fixed connection. An assembly-design view will display connection features between parts of the product, such as a pen-hole connection. A part-detail design view will show the form features in a part, which may correspond to component features. This view might display such information as a hole with a certain radius at fixed distances from given faces.
The part-manufacturing view will include the form features in a part that correspond to specific machining operations. Finally, an assembly-planning view will depict the handling features on a part, such as the faces that can be used by a gripper to grasp the part.
The hierarchy graph of the feature model for the assembly design view of a door-latch assembly shows how the product is structured with compound components. The top node shows the final assembly, the middle nodes show the compound components that are used to structure the model, and the bottom nodes show the single components from which the product is built. The structure of the product depends on the view of the product. For example, the assembly-design view can be structured to manage the design of the assembly, while the assembly-planning view can be structured to specify a particular assembly sequence.
To maintain consistency among the multiple views, the system employs various feature-conversion techniques. The general feature-modeling system uses conversion processes through which new views can automatically be derived from existing views, and changes made in one view are automatically propagated to the other views.
To achieve similar results with enhanced feature models, the conversion process is less straightforward. This is because enhanced feature models of different views do not have a common denominator, such as the product geometry that is common among different views of form-feature models. Each enhanced feature model contains only information that is relevant to the specific application for which the view is intended. For example, the assembly-design view contains only information on aspects relevant to the assembly of parts. The detail-design view contains information on the part geometry, but not on the assembly of the parts.
In addition, the data for some of the enhanced views, such as the conceptual-design view, is not complete. Consequently, says Bronsvoort, "when deriving a part-design view from a conceptual-design view, the user has to specify more details of the model, so this conversion will not be fully automatic." However, he notes, properties of the part-detail design will be automatically checked against constraints specified in the conceptual-design view. For example, the system will automatically check whether a hole in the part-detail design view has a radius within a range specified in the conceptual design view.
The relations graph of the feature model for the door-latch assembly design view shows how the components of the assembly, represented by large nodes, are related by connection features, which are represented by the small nodes.
The researchers use a combination of conversion methods to deal with the unique nature of enhanced feature models. These include techniques for linking, mapping, and recognizing features.
Linking features involves the creation of links between feature elements of different views representing the same aspect of the model. The links are constrained so that different views specify corresponding model aspects in the same way. Mapping features entails match ing feature de finitions of the new view with the feature models of the existing view to make the two consistent. As a result, the system generates a new feature model based on the feature information of the existing model. Feature recognition involves adding features to a new view to make it consistent with existing views, thus building a new feature model from the geometry of the features and the interactions between them.
Once the enhanced multiple-view modeling system is complete, it will offer a number of benefits over traditional modeling systems, not only for mechanical design applications, but also for electrical, civil, and industrial design applications, says Bronsvoort. "Having multiple feature views on a product is very advantageous in engineering. Each engineer can have his or her own view of a product, with features relevant for his application. This translates to a view much closer to the engineer's way of thinking than that provided in traditional systems in which all views remain consistent." And the enhanced system extends this benefit across the product-development cycle, to include conceptual design and assembly planning.
As noted, the development of the enhanced multiple-view feature modeling system is ongoing. "This is a major research and implementation challenge. We've been working on it for more than five years and will continue for another two." The research ers currently have no plans to commercialize the system. More information about the modeling system can be found on the project Web site located at www.cg.its.tudelft.nl/ wwwcc/.
Diana Phillips Mahoney is chief technology editor of Computer Graphics World.
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