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High-performance prostheses and orthoses (i.e., exoskeletons) could significantly improve the quality of life for nearly a million American lower-limb amputees and even more stroke survivors, whose ambulation is slower, less stable, and requires more energy than that of able-bodied individuals. Although recent motorized prostheses have the potential to restore mobility in impaired populations, critical barriers in control technology still limit their clinical viability. These systems discretize the gait cycle into multiple distinct control models, each tracking reference joint torques, kinematics (angles/velocities), or impedances (stiffness/viscosity) that resemble human behavior. These increasingly complex designs are difficult to tune to individuals and generalize to different tasks, and their sequential controllers are not necessarily robust to external perturbations that push joint kinematics forward or backward in the gait cycle. However, recent bipedal robots can stably walk, run, and climb stairs with one control model that drives joint patterns as functions of a mechanical variable, which continuously represents the robot’s progression through the gait cycle, i.e., a sense of “phase.”
These breakthroughs in robot control theory present an emerging opportunity to address a key roadblock in prosthetic and orthotic control technology, which will be the topic of this talk. I will offer evidence that the Center of Pressure (COP) in the plantar sole serves as a biomechanical phase variable, potentially addressing a fundamental gap in knowledge about how the human neuromuscular system represents the phase of the gait cycle. A prosthesis controller will then be designed to enforce a biomimetic virtual constraint between the COP and joint angles, known as the “effective shape.” Ongoing experiments will be previewed and future directions will be discussed, including neural feedback for subconscious control adaptation and haptic devices that enhance sensory feedback during impaired locomotion.
Robert D. Gregg received the B.S. degree in electrical engineering and computer sciences from the University of California, Berkeley in 2006 and the M.S. and Ph.D. degrees in electrical and computer engineering from the University of Illinois at Urbana-Champaign in 2007 and 2010, respectively. Dr. Gregg is a Research Scientist in the Center for Bionic Medicine at the Rehabilitation Institute of Chicago and an Engineering into Medicine Fellow in the Department of Mechanical Engineering at Northwestern University. His research concerns the control mechanisms of bipedal locomotion with application to both autonomous and wearable robots. In June 2013 Dr. Gregg will join the faculty of the Departments of Mechanical Engineering and Bioengineering at the University of Texas, Dallas.
Dr. Gregg holds a Career Award at the Scientific Interface from the Burroughs Wellcome Fund. He also received the Best Technical Paper Award of the 2011 International Conference on Climbing and Walking Robots, the 2009 O. Hugo Schuck Award from the IFAC American Automatic Control Council, and the Best Student Paper Award of the 2008 American Control Conference. Dr. Gregg is a member of the IEEE Control Systems Society and the IEEE Robotics & Automation Society. http://lims.mech.northwestern.edu/postdocs/rgregg/
PLEASE JOIN US FOR COOKIES AND COFFEE PRIOR TO THE SEMINAR
IN ROOM 154 CSL AT 2:30PM