Many amputees seem to show a clear preference for walking with these devices, but the function of the devices during gait and the influence on the resulting pattern of walking is unclear. The purpose of this investigation is to perform mechanical analyses of commercially available vertical shock pylons to gain a better understanding of their function during walking. Static and dynamic testing of these devices, using a specially designed testing apparatus with attached mass will permit calculation of the damped natural frequencies, spring constants, damping coefficients, damping ratios, and indicate their abilities to store and return energy.
Static testing allows the force versus deflection characteristic of each device to be determined.
Creep rate is also measured. The dynamic testing involves step loading and unloading the vertical shock pylons while measuring the resulting axial displacement. The Re-Flex Vertical Shock Pylon consists of graphite telescoping tubes in parallel with a carbon fiber compression spring for shock absorption and energy return. There are a total of nine spring stiffnesses available from Flex Foot, accommodating subjects weighing anywhere from 100 lbs to 325 lbs. We are testing five of the nine spring stiffnesses available, evenly distributed across the range of stiffness values.