Pneumatic Control of Robots for Rehabilitation

Pneumatic actuators are attractive for robotic rehabilitation applications because they are lightweight, powerful, and compliant, but their control has historically been difficult, limiting their use. In this paper we present the pneumatic control system developed for Pneu-WREX: a pneumatically actuated, upper extremity orthosis for rehabilitation after stroke. The developed pneumatic control system combines several novel components to make the entire system stable, reliable, and backdrivable. These components, which are described in this paper, include: (1) a unique two-valve force control subsystem that keeps chamber pressure low (to reduce friction and energy consumption) and adaptively compensates for leakage (2) a new servovalve characterization approach that uses experimentally measured data in a combined non-linear and least-squares regression to obtain a linear relationship between mass flow and valve voltage and (3) a new approach to state estimation using accelerometers and a Kalman filter to obtain clean signals for use in a non-linear adaptive feedback conThe International Journal of Robotics Research Vol. 29, No. 1, January 2010, pp. 23–38 DOI: 10.1177/0278364909103787 c The Author(s), 2010. Reprints and permissions: http://www.sagepub.co.uk/journalsPermissions.nav Figures 1, 5, 6, 8–10, 12–15, 17 appear in color online: http://ijr.sagepub.com trol law. Experimental testing of the device demonstrates the efficacy of the developed pneumatic control system. KEY WORDS—neurorehabilitation, kalman filter, state estimation, Lyapunov’s direct method, nonlinear control, force control, pneumatic control, compliance, movement training, servovalve characterization, radial basis functions, impairment modeling