Designing replacements for human limbs

Prosthetic designers face a fascinating range of issues when designing devices that simulate normal walking. In this episode Vince and Allison review how designers control the proportional loads from walking by capturing and harnessing the ground strike forces.

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Transcript For This Video

Allison: Hi, welcome to the product design show. I¦m Allison Topperwein. Most people take the commonplace act of walking for granted.

Vince: And I¦m Vince penman. For prosthetic designers, controlling the proportional load response required to simulate natural walking might be one of the most difficult design challenges we¦ve seen.

Allison: Image your own walking motion. A lot of force is created the moment your heel strikes the ground. As the action continues, you spring forward and allow the ball of your foot to propel you into your next step.

Vince: In a previous episode, we showed how designers at College Park Industries developed a unique method for controlling the setup and alignment of prosthesis with their ipecs lab device. However, with prosthetics, as in most designs, more than one issue must be addressed to fully solve the problem.

Allison: One of the major complications in designing a dynamic prosthetic that moves with extreme precision is capturing and harnessing the rebound forces created when the foot hits the floor. An average Male Human exerts 16 PSI of force onto the ground with each step.

Vince: While that may seem small, consider this: an M-1 Abrams tank exerts 15 PSI on the ground at any given timea I guess that brings a whole new meaning to the phrase (That guy¦s a tank÷!

Allison: Now imagine having to control and compensate for that force rapidly and repeatedly. We spoke to Mike Leydet, designer at College Park Industries, about how they created a system of springs that act in series to properly control these forces.

Vince: But how did they design the series of springs to move with such precision and fluidity that the wearer feels as if they have a natural gait? The solution comes from the careful tuning of the contraction and release of each spring. If a spring isn¦t tuned correctly, it unloads it¦s force at the wrong moment, which leads to a jerking or bouncing walking motion.

Allison: To avoid these issues, the College Park engineers conducted rigorous analysis of the mechanics of foot fall and gait with CAD and simulation software. By determining the stress on each spring as it was engaged, the designers were able to accurately time the reaction of each spring, and create a system that works in a fluid and natural motion.

Vince: With the precision designed into these prosthetics most patients can participate in a wide range of activities that make up an active lifestyle. And honestly, this guy on the mountain bike would probably leave me sucking dust on the trails.

Allison: Designers at college park used Creo Parametric and Mathmatica software for the design and analysis of their integrated spring technology. You can see Creo parametric in action at

Vince: If you like the show please give it a like on facebook, subscribe on youtube or give us a rating on itunes. And make sure To join us next week for more great design engineering.