e-Profiles, Spring 2002: Pro/ANATOMY--Modeling Body Parts in Pro/ENGINEER®

Pro/ANATOMY
Modeling Body Parts In Pro/ENGINEER®

Why in the world would I want to model body parts in Pro/ENGINEER®? This question really has two parts—why body parts and why Pro/ENGINEER.

When a customer approached me with a need for a surface model of an anatomical nature, I had a pretty good answer to the first question. The surface model had to be not only anatomically accurate and aesthetically pleasing, but also highly adaptive so it could be easily manipulated to populate a large product family. It is this requirement that led me to pursue the assignment using Pro/ENGINEER. As the premier parametric associative solid modeling tool, it works well with rectilinear geometry. Wouldn’t it be a good test to see how well it works on amorphous geometry?

Yea verily, it can be done. And in doing so, I’ve discovered a few things that could help you in your complex surface modeling.

Applications for Anatomical Modeling

There are really two types of design applications using anatomical models—direct and indirect. Indirect applications require an anatomical reference to aid in the design or presentation of another object. This could be anything from a hand model for a joystick or a head model for a headset. In this case, models must satisfy requirements for anatomical correctness and have an attractive appearance. Other indirect applications —such as shoes, gloves, or furniture— may just require a generic size or shape reference. Models used primarily for design presentations are more concerned with aesthetics than accuracy.

In direct applications, however, the anatomical model is the primary object or product. Examples include toys, action figures, medical training aids, orthotics and prosthetics. These products demand the highest level of modeling capability in order to be dimensionally controlled, anatomically accurate, aesthetically pleasing, and highly adaptive to support size and shape manipulation. My introduction into this arena was through prosthetics.

Changing Approaches

The master geometry for direct applications such as prosthetics is traditionally a physical object. This could be in the form of a handsculpted model or a plaster cast replication. It can also be a digitized copy of the subject, which has characteristics similar to a physical object in that you can view it on the computer screen, take measurements, check relationships to other computer models, and interface directly with fabrication equipment.

Problems with this traditional approach can, however, arise when you need to have precise dimensional control of the design, make a design change, or create a new variation of a design. In these cases, starting from a physical object can require a lot of tedious measuring and scaling, creating new plaster castings, hand sculpting changes directly to the original masters, or obtaining new digitized copies. Each one of these tasks introduces significant time, continuity, and repeatability factors that can directly delay delivery of the product.



	Figure 1.

Today’s computer design tools are able to create the same level of detail as the traditional approach. The skilled 3D designer can use curves, points, and surfaces to work a model on the screen, just like an sculptor does with clay. Alternatively, a designer can use digitized copies of existing designs as a reference for creating a more sophisticated CAD model. While many tools exist for creating 3D surface models (Fig 1), not all of them offer the dimensional control, parametric associativity, and level of detail necessary to create convincing anatomical models. Pro/ENGINEER has just the necessary tools.