Prosthesis Device for paraplegic people Jorge J Corujo

Prosthesis Device for paraplegic people Jorge J. Corujo Javier Cruz Irvin De La Paz Francisco Torres

Design and usage: ¡ Prosthesis Device for paraplegic people to use for running l l Unlike normal prosthesis, which allow for its user to accomplish normal basic movement, this one allows the user to participate in sporting events, such as running. A similar device was use by paralympic’s athlete Tony Volpentest

Design and usage:

A little bit of History: ¡ 1981 - The Seattle foot revolutionizes sport prosthetics with the introduction of key elements: l l New stronger and light materials (Derlin, carbon fibers) energy storing prosthetic foot (ESPF)

Why choose this design? ¡ ¡ This design provided us with the opportunity to design and analyze an atypical product, which although simple in design it encompasses many engineering aspects, and proved to be a challenge Our concentration will be the lower component; the flexed toe.

Important engineering considerations: Design Process: ¡ Determine target runner: l l ¡ Max. weight of runner –> F=200 lbs. Person with transtibial amputation (above the foot but below the knee) Determine acting forces (static & dynamic) l Dynamic model ¡ Alternates from: F to -3 F

Important engineering considerations: Attachment to socket and runner Applied force by runner Direction of runner Ground reaction Critical point for Bending Friction force

Important engineering considerations:

Important engineering considerations: Bending l l l Find critical point Determine actual maximum (absolute) magnitude during the cycle. This is the first parameter for choosing the material.

Important engineering considerations: Stress due to bending in a curved beam M = The internal moment, determined from the method of sections and the equations of equilibrium and computed about the neutral axis for the cross section. A = the cross-sectional area of the member R= the distance measured from the center of curvature to the neutral axis r (bar) = the distance measured from the center of curvature to the centroid of the cross-sectional area r = the distance measured from the center of curvature to the point where the stress is to be determined

Important engineering considerations: For a rectangular cross-sectional area:

Important engineering considerations: ¡ Fatigue l l For the desired part we want an infinite life. Determine all stress concentrators ¡ l Ksize, Ktemp=1, Kload, Kreliability (99. 99%), Ksurf This is the second parameter for choosing the material.

Important engineering considerations: ¡ Material selection l We need a material that is: ¡ l Utilize both previously determined parameters: ¡ l Strong and Light Max. Bending and Desired Fatigue Endurance With each candidate the resulting deflection has to be considered. ¡ Some deflection (spring action) is desired for absorbing impact and giving extra boost.

Important engineering considerations: Deflection for curved beams:

Important engineering considerations: ¡ Static analysis: V=-5. 28 lb Normal=-813. 54 lb

Chosen material: Deutsche Titan® Tikrutan RT 18 Pd Low -Alloyed Titanium ¡ For the Purpose of this design, cost was not considered. l ¡ Provides a lightweight design l ¡ Price can be improved with available polymers, but all the needed information for a proper analysis wasn’t reliably available. 1. 28 lbs. per spring toe ¡ for the weight of the whole design add weight of socket Safety factor of n=2. 04 (Goodman)

Design challenges and weaknesses ¡ Our main challenges appeared at the moment of material selection. Finding (information for) a lightweight material with the required strength really limited our options. ¡ The main weak spot is at the center of curvature. However, as long as design parameters are followed the user is within acceptable safety limits (n=2. 04)

What did we learn? ¡ ¡ Simple design ≠ simple calculations Differences in analyzing curved and linear beams. l l ¡ ¡ Moments Deflection Small, apparently insignificant, material property changes can amount to huge problems (and consequences) in the design as a total. Material sciences have become part of the forefront in engineering design.

Questions? Thanks for your attention and your time