Larry G. Richards
University of Virginia
School of Engineering and Applied Science
Charlottesville, VA 22903
E-mail: lgr@virginia.edu
Many experiments are underway to revise the initial stages of engineering education. Our first year courses are an opportunity to attract students to engineering, or to drive them away. We must insure that students about to commit to a career choice have accurate information about that career. One function of the first year experience is to give students an appreciation of what engineers do and how they do it. Another is to emphasize design as a fundamental aspect of engineering.
The first year should include an introduction to the technical tools of engineering, as well as the content and methods of the various disciplines. Computer tools are essential and pervasive in modern industry. The CAD/CAE/CAM revolution, which started in the major aerospace and automotive companies, has now changed industrial practice in fundamental ways. CAD has come to mean computer aided design, not merely drafting or documentation. In industry, design and documentation of product ideas involves a product model data base. This database captures the three-dimensional nature of an object or assembly. Engineering drawings are a result of the 3D product model: they are generated from it, and changes in the model are easily reflected in updated drawings [1].
The elimination of traditional courses on engineering graphics at many schools should cause us to ask what content from those courses is still relevant to modern practice. How can we insure that the necessary knowledge and skills are retained in the new curriculum? Two types of cognitive skills were emphasized in such courses:
We deal with real 3D objects in everyday life. Thinking and talking about 3D objects is natural. Even if we don't know the technical terms for a shape or object we can usually describe it well enough for someone else to understand what we mean. Students learn about the geometry of real world objects by manipulating them; they learn about 3D computer models in the same way. Creating 2D pictures of models or objects is more difficult. We find that as students work with a CAD system they learn how objects map into views. There is some evidence that working with a 3D graphics system improves visualization skills [2]. This evidence is limited; it does match our experience but systematic research is needed to really establish this result.
The third key element in engineering graphics was learning the symbols and conventions used in engineering drawings, including conventions for dimensions, tolerances, and notes. Thus, students learned how to create and read blueprints. ``Reading'' and understanding engineering symbols and conventional representations is an essential skill for any engineer. However, much of it is discipline-specific; the conventions for mechanical or civil engineering differ from those for electrical or chemical engineering. A general course can introduce common (standard) conventions and notations, but many of the details of documentation must be left to the separate engineering disciplines.
The time spent learning to make perfect drawings manually is no longer necessary. Computers make better and more precise drawings, and they permit easy changes and updates. The drudgery has been eliminated from engineering graphics, and few of us will miss it.
Increasing enrollments and decreasing resources demand new approaches to delivering computer lab instruction. At Virginia, the facility available for our first year students contains 120 personal computers networked for access to all the resources of the university (and beyond). An instructor can guide all these students through coordinated lab activities, or each student can work at their own pace on assigned problems. In either case, a cadre of graduate teaching assistants is available to answer questions, provide help, and guide individual students.
The geometric modeling program we use for our first year classes is SilverScreen from Schroff Development Corporation [3]. It provides all the 3D modeling capabilities we require, and is extremely easy to learn. SilverScreen is a menu driven package. The menu is organized around the basic modeling, drawing, and rendering functions. Once the students see the capabilities of the program, most are readily able to use it.
Our fundamental goal is to enable students to capture their design ideas using a geometric modeling system. Since most products are 3D objects or assemblies, students should learn 3D representation from the start. Thus, during our first lab, every student creates, views, and renders a 3D model of a simple object (a rectangular block with two holes through it). They then create a model of their own choosing. Both models are constructed using the linear sweep technique; the student creates a profile in a x-y plane which is then swept along the z axis to provide depth.
This simple exercise accomplishes a great deal pedagogically. First and most important, it reinforces the basic concept of modeling. The user provides the computer the minimum amount of information needed to specify the model for the object; in this case, a profile and a path along which the profile is swept. Second, the student then views the model by accessing a four-way split screen containing three orthogonal and one oblique view of the model. The views follow from the model; they are the result of modeling-not the basis for it. When we then ask student to generate 6 and 9 way split screens, we drive home the message that views are arbitrary.
Next, we guide the students to the rendering menu (presentation) and show them how to obtain colored, shaded views of their model. They may also display a picture of it with hidden lines removed or dotted (semi-hidden). This reinforces the fact that they are working with true solid models, not merely wireframe representations. This first lesson also emphasizes that modeling, viewing, and rendering are three distinct processes.
In the second lesson, we introduce circular sweep to create volumes of revolution and the use of both 2D and 3D Boolean Operations. Sitting at a computer watching the effects of the union, intersection, and difference operations gives our students understanding well beyond what we can achieve with Venn Diagrams on blackboards. Venn diagrams are graphic representations of sets and their relationships. They are used to illustrate the effects of various set operations. At the computer, students will experiment with a variety of shapes and solids, and quickly learn to intuitively predict the results of these operations.
The third lesson introduces working in multiple spaces and some ways to edit and modify drawings and models. To create an assembly, we must model a set of parts and then position those parts in the correct relationships to each other. Each part can be created in the appropriate construction space and then positioned by locating it in world space. Most of our students require substantial practice to master working simultaneously with two coordinate systems. Once they understand this concept, they have a powerful modeling tool.
Lesson four focuses on additional modeling techniques (path sweeps, ruled surfaces, and how to sweep and join separate profiles), and on the use of the Command History as a means of editing a model. At this point, the student has a powerful collection of techniques for constructing and modifying models of objects and assemblies.
Lesson 5 covers techniques for Annotation and accurate drawing and modeling, including inputing metric dimensions and exact spatial coordinates, and drawing to a grid. We also introduce the data structure of SilverScreen, and show how to use this data structure to modify the model.
The basic lessons cover essential concepts and modeling techniques, but to truly master CAD skills requires practice. We assign a series of problems designed to bring the students to a minimal level of competence with this program and then assign a major project. Each student must submit an entry for a class competition. Thus, each student must generate a design idea and produce a model of it. The models may be of real objects or imaginary ones. The figures accompanying this paper show some recent results achieved by our first year students.
The techniques for viewing and rendering a model are described and demonstrated in lecture, reinforced in workshops, and mastered in lab. We now include a sixth SilverScreen lesson-by popular demand-rendering techniques. Our students were intrigued by how the many SilverScreen demonstration files were created. They wanted to work with color, texture, shading, light sources, etc. We now show them how. In lecture, we also discuss the representation techniques of artists, the principles of visual perception, and the developing field of scientific visualization [4].
Each of the lessons described above is covered in 50 minutes during a lab session. Thus, our students receive less than 6 hours of formal instruction on how to use this software. That is enough! We believe in minimalist training [5]. We give the students the essentials and turn them loose to discover the capabilities and limitations of these tools. All achieve mastery of this software; some become real experts.
The excitement of working with a true solids modeling system is tremendously motivating for our students. We are now able to teach them things which were only available to graduate students a decade ago. First year engineering students are working with software that reflects the capabilities of systems used by industry. Many of the teaching techniques and modeling exercises developed for an industry CAD system are available to our students in a PC environment. They gain understanding of engineering design and the role of computer tools in modern industry.
The skills learned in this class carry over to other courses. This is the kind of knowledge our students can actually use throughout their education. Its relevance to engineering design is obvious and direct. We also find that our students use CAD to prepare presentations and assignments for other classes.
