Traditional computer-aided design (CAD) education in mechanical engineering still remains a major challenge today both in industrial settings and in academia. As in many other CAD-related engineering disciplines, there are several shortcomings to be surmounted in the dissemination and development of procedural knowledge and skills in the form of know-how related to the operation of CAD systems. Unfortunately, current educational philosophy does not offer a pedagogy providing sufficient strategic knowledge and understanding to enable students to use CAD systems as intended -that is as knowledge-intensive design and communication tools to properly develop and convey design intent. However, apart from knowing what to do, there is another important aspect to strategic knowledge which is frequently over-looked and ignored in research today, and that is knowing how to avoid serious mistakes. This is a central quality of professional expertise, which is commonly referred to in the literature as negative knowledge. Research presented and discussed in this paper is aimed at providing a framework for negative knowledge and domain knowledge related model evaluation concepts that allow for direct translation of this approach into practice, with the goal of improving learning behavior, skill acquisition and competency building for CAD education in mechanical engineering.
A mixture of general-use and of some custom-designed plastic parts, fabricated on inexpensive layered manufacturing machines, is used to construct a variety of sculptural maquettes. This article describes the design and fabrication of a set of modular parts that permit the assembly of tubular sculptures as well as constructivist realizations of mathematical knots and links.
One basic intent of feature-based modeling is to provide objects and operators which support the implementation of a complete and consistent description of a part in terms of its shape and related functional and technological information. Although feature-based methodology has matured to the point that results are being incorporated into commercial CAD systems, several problems still remain open. A key problem in feature-based modeling is how to maintain the consistent correspondence between the geometrical description of a feature and its related functional meaning (semantics) during the entire modeling process.Uncontrolled feature shape modification due to geometrical operations among aggregated features can affect the correct functionality of a modeled part. Within described work we propose to approach the problem of controlling feature semantics by using what we call self validation features: an entity concept developed to implement feature specifications replenished with self validation capabilities, Along with this new approach the traditional feature definition is extended in order to include a set of rules that allows for feature instances to control the consistency of their shape in respect to functionality associated. A feature-based modeling operation is then executed by computing within three steps as follows: feature instantiation, feature location and validated feature aggregation. A prototype testbed based on a self validation entity concept has been implemented integrating an in house developed feature system with a commercially available geometric modeling kernel, In order to realize a tight integration between feature semantics and shape representation an interfacing mechanism, based on an entity monitor, has been studied. Its lunctionality is partly supported by the attribute handling system of the integrated geometric modeling kernel. In the example section of the reported experimental work a selection of validation rules peculiar to some semantics aspects are evaluated and discussed.
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