Decentralized Resilient Control Algorithms for Cooperative Robotic Walking with Application to Powered Prosthetic Legs
We are on the verge of a new revolution in robotic legged locomotion. Important medical applications of legged locomotion research include lower-limb prostheses, exoskeletons, and devices for the rehabilitation of walking and balance after injury. While rapidly advancing technologies enable the design of increasingly sophisticated (and more humanlike) legged robots, the nonlinear feedback control laws currently used to achieve stable dynamic walking cannot scale with the increasing dimensionality of these robots. The centralized nature of state-of-the-art control algorithms prevents their transfer into local controllers for wearable robots like prostheses and orthoses. A substantial body of research in neurophysiology also suggests that there is a great deal of locality structured in the control of mammalian locomotion. In this talk, we present a systematic design framework for decentralized feedback controllers that coordinate low-dimensional subsystems to achieve robust legged locomotion, overcoming the curse of dimensionality in legged robots and enabling cooperative human-machine walking with powered prosthetic legs. Our approach provides a computationally attractive solution to tuning the parameters for a general form of decentralized controllers so as to achieve exponential stability as well as H2 and H∞ robustness. We investigate nonlinear stability tools for hybrid dynamical systems to formulate the problem of designing resilient nonlinear controllers as an iterative optimization problem involving matrix inequalities. The power of the algorithm is finally demonstrated in designing robust stabilizing controllers for walking of ATRIAS, a highly underactuated autonomous bipedal robot. It is also illustrated in designing a set of robust stabilizing decentralized controllers for a model of amputee locomotion with a decentralization scheme motivated by a transpelvic prosthetic leg.
Dr. Kaveh Akbari Hamed is currently an assistant professor in the Mechanical Engineering Department at San Diego State University. He received his Ph.D. in Electrical Engineering with specialization in Robotics and Controls from Sharif University of Technology in June 2011. As an assistant professor, he has been actively working on a number of different problems and approaches related to robotics, control theory, biomedical engineering, and cyber-physical systems. His research is interdisciplinary and well positioned to transform state-of-the-art methods for the control of a class of cyber-physical systems.