[ASME ASME 2007 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - Las Vegas, Nevada, USA (September 4–7, 2007)] Volume 5: 6th International Conference on Multibody Systems, Nonlinear Dynamics, and Control, Parts A, B, and C - The SPARKy (Spring Ankle With Regenerative Kinetics) Project: Design and Analysis of a Robotic Transtibial Prosthesis With Regenerative Kinetics