“Translational Control Design for Lower-Limb Prosthetics and Orthotics:
Lessons from Robot Locomotion”
Dr. Robert Gregg, Department of Mechanical Engineering, Northwestern University
Powered lower-limb prostheses and orthoses (i.e., exoskeletons) are currently designed for biomimetic behavior at the cost of simplicity. Most control strategies 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 analyze for stability, tune to individuals, and generalize to different tasks, and their time-varying controllers are not necessarily robust to external perturbations that push joint kinematics forward or backward in the gait cycle. However, recent work on autonomous walking robots has produced time-invariant, provably stabilizing strategies from feedback control theory.
Using neuromechanical principles in the context of control theory, this talk will develop simple control strategies for a powered ankle-foot orthosis and a powered prosthetic leg. This work attempts to address a fundamental gap in knowledge about how the human nervous system knows its location in the gait cycle (i.e., a biomechanical sense of phase), suggesting that the Center of Pressure (COP) in the plantar sole drives the progression of joint patterns. A prosthesis controller is then designed to enforce a biomimetic constraint between the COP and joint angles, known as the “effective shape.” Future directions will also be discussed, including neural feedback for subconscious control adaptation, wearable biomechanical sensors for real-time feedback control, and haptic devices that enhance sensory feedback during impaired locomotion.
Robert D. Gregg received the B.S. in Electrical Engineering and Computer Sciences from the University of California, Berkeley in 2006. He received the M.S. in 2007 and Ph.D. in 2010 from the department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign. Dr. Gregg is an Engineering into Medicine Postdoctoral Fellow in the Department of Mechanical Engineering, Northwestern University and the Center for Bionic Medicine, Rehabilitation Institute of Chicago. His research is in the control mechanisms of bipedal locomotion with application to both autonomous and wearable robots, and his current work concerns the translation of robot control theories into biomimetic strategies for powered prosthetic legs. Dr. Gregg 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 Robotics & Automation Society, and he was co-chair of the 2010 Symposium on Control and Modeling of Biomedical Systems.