The motion of a human walking gait was observed and recorded by analyzing videos. From these videos, three periodic joint angle functions were documented at the hip, knee, and ankle, which are shown in the figures below.
A Stephenson II function generator was designed to replicate each of these joint angle functions. Information on designing Stephenson function generators is found here and in . The mechanism generated functions appear in the figures above as well. The three linkages appear here:
These function generators were designed into the assembly of a machine that replicates the human’s walking gait. All three function generators were packaged into a compact motor-drive unit. The function generator motions are passed to the distal joints by parallelogram linkages.
The dynamic simulation below propels the body forward by friction forces at the foot. The hip assembly was permitted to bob up and down, but fore-aft and lateral rotations were artificially constrained so that the machine does not tip over. A spring was added at the end of the foot to allow toe flex. The machine shows promise for walking with low-powered controls systems, perhaps integrating onto the human body in order to take advantage of the human being’s balance and control while providing powered locomotion.
 M. Plecnik and J. M. McCarthy, 2015. “Computational Design of Stephenson II Function Generators for 11 Accuracy Points,” Accepted for publication in the Journal of Mechanisms and Robotics, May 2015.