A comparison of parallel- and series elastic elements in an actuator for mimicking human ankle joint in walking and running

Elastic elements in prosthetic devices can help to reduce peak power (PP) and energy requirements (ER) for the actuators. Calculations showed that it is impossible with current commercial motor technology to mimic human ankle behavior in detail for higher walking and running speeds with single motor solutions using a Serial Elastic Actuator (SEA). Concerning this result we checked the requirements of a parallel elastic actuator (PEA) and a combination of serial and parallel (SE+PEA) springs. We found that a PEA can reduce PP additionally in comparison to the SEA by pre-loading the spring in the flight phase. This reduces also peak torque. But this loading needs additional energy so that the ER increase in comparison to the SEA. The SE+PEA concept can further decrease PP. With that, the ER are less than the PEA but higher than for the SEA. The results show less benefit for the PEA and the SE+PEA when a constant stiffness and a fixed parallel spring slack length is used for both gaits and all speeds. All concepts show that mimicking human ankle joint behavior in running and walking at higher speeds is still challenging for single motor devices.

[1]  Hugh M. Herr,et al.  Powered Ankle--Foot Prosthesis Improves Walking Metabolic Economy , 2009, IEEE Transactions on Robotics.

[2]  Stefano Stramigioli,et al.  Conceptual design of an energy efficient transfemoral prosthesis , 2010, 2010 IEEE/RSJ International Conference on Intelligent Robots and Systems.

[3]  Michael Goldfarb,et al.  Self-contained powered knee and ankle prosthesis: Initial evaluation on a transfemoral amputee , 2009, 2009 IEEE International Conference on Rehabilitation Robotics.

[4]  Hartmut Geyer,et al.  Control of a Powered Ankle–Foot Prosthesis Based on a Neuromuscular Model , 2010, IEEE Transactions on Neural Systems and Rehabilitation Engineering.

[5]  Michael Günther,et al.  DEALING WITH SKIN MOTION AND WOBBLING MASSES IN INVERSE DYNAMICS , 2003 .

[6]  Philip D. Gollnick,et al.  Human soleus muscle: A comparison of fiber composition and enzyme activities with other leg muscles , 1974, Pflügers Archiv.

[7]  Jonathon W. Sensinger,et al.  Exterior vs. interior rotors in robotic brushless motors , 2011, 2011 IEEE International Conference on Robotics and Automation.

[8]  André Seyfarth,et al.  Stiffness adjustment of a Series Elastic Actuator in an ankle-foot prosthesis for walking and running: The trade-off between energy and peak power optimization , 2011, 2011 IEEE International Conference on Robotics and Automation.

[9]  Thomas G. Sugar,et al.  Bionic Running for Unilateral Transtibial Military Amputees , 2010 .

[10]  Alena M. Grabowski,et al.  Bionic ankle–foot prosthesis normalizes walking gait for persons with leg amputation , 2012, Proceedings of the Royal Society B: Biological Sciences.

[11]  Taija Finni,et al.  In vivo estimation and repeatability of force–length relationship and stiffness of the human achilles tendon using phase contrast MRI , 2008, Journal of magnetic resonance imaging : JMRI.

[12]  Thomas G. Sugar,et al.  An Active Foot-Ankle Prosthesis With Biomechanical Energy Regeneration , 2010 .

[13]  R. M. Alexander,et al.  Exploring Biomechanics: Animals in Motion , 1992 .