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Friday, July 30, 2021

A New Era for Mechanical CAD

Considerable piece.   We actively worked with computer aided design, and used sketchpad too.  Had always thought there would be better models for 'assistance' for its use.  Early on we examined automated efficiency of design measures.    And a means to more readily integrate designs with existing contexts and uses.  Technical. 

A New Era for Mechanical CAD

Time to move forward from decades-old design

Jessie Frazelle  in Queue.acm.org

CAD (computer-aided design) has been around since the 1950s. The first graphical CAD program, called Sketchpad, came out of MIT [designworldonline.com]. Since then, CAD has become essential to designing and manufacturing hardware products. Today, there are multiple types of CAD. This column focuses on mechanical CAD, used for mechanical engineering.

Digging into the history of computer graphics reveals some interesting connections between the most ambitious and notorious engineers. Ivan Sutherland, who won the Turing Award for Sketchpad in 1988, had Edwin Catmull as a student. Catmull and Pat Hanrahan won the Turing award for their contributions to computer graphics in 2019. This included their work at Pixar building RenderMan [pixar.com], which was licensed to other filmmakers. This led to innovations in hardware, software, and GPUs. Without these innovators, there would be no mechanical CAD, nor would animated films be as sophisticated as they are today. There wouldn't even be GPUs.

Modeling geometries has evolved greatly over time. Solids were first modeled as wireframes by representing the object by its edges, line curves, and vertices. This evolved into surface representation using faces, surfaces, edges, and vertices. Surface representation is valuable in robot path planning as well. Wireframe and surface representation contains only geometrical data. Today, modeling includes topological information to describe how the object is bounded and connected, and to describe its neighborhood. (A neighborhood of a point consists of a set of points containing that point where one can move some distance in any direction away from that point without leaving the set.)

OpenCascade, Parasolid, and ACIS are all boundary-representation (B-rep) kernels. A B-rep model is composed of geometry and topology information. The topology information differs depending on the program used. B-rep file formats include STEP (Standard for the Exchange of Product Model Data), IGES (Initial Graphics Exchange Specification), NX's prt, Solid Edge's par and asm, Creo's prt and asm, SolidWorks' sldprt and sldasm, Inventor's ipt and iam, and AutoCAD's dwg.

Visual representation (vis-rep) models tend to be much smaller in data size than B-rep models. This is because they do not contain as much structural or product management information. Vis-rep models are approximations of geometry and are composed of a mass of flat polygons. Vis-rep file formats include obj, STL, 3D XML, 3D PDF, COLLADA, and PLY.

CAD programs tend to use B-rep models, while animation, game development, augmented reality, and virtual reality tend to use vis-rep models. However, the two are interchanged frequently. For example, if you were using a B-rep model for manufacturing but wanted to load it into Apple's ARKit for some animations, you would first convert it to COLLADA, a vis-rep file format. The file should already be a bit smaller from dropping all the CAD data, but if you wanted to make it even smaller, you could tweak the polygon counts on each of the meshes for the various parts.

The tools used to build with today are supported on the shoulders of giants, but a lot could be done to make them even better. At some point, mechanical CAD lost some of its roots of innovation. Let's dive into a few of the problems with the CAD programs that exist today and see how to make them better. .... ' 

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