Implementation of LPV H∞ Loop-Shaping Control for a Variable Stiffness Actuator

IFAC-PapersOnLine, vol. 53, pp. 10129–10134

Abstract

Compliant actuators have been increasingly used for active joints in lower-limb exoskeletons or orthoses because they help to guarantee a safe human interaction. One example of such compliant motors is the variable stiffness actuator (VSA). The design of a torque controller for such an actuator is a crucial task in order to provide patients with physical gait assistance and overcome the mechanical limitations of the VSA. Our goal is to implement a torque controller for our mechanical-rotary variable impedance actuator (MeRIA) used in future lower-limb exoskeletons. In the torque control design, we derive a gain-scheduled controller for the polytopic linear parameter-varying (LPV) model of the actuator. This controller is based on the classical H∞ loop-shaping approach. Measurements on the hardware-in-the-loop system in time and frequency domain show that the designed controller provides adequate performance over the whole varying stiffness range. Additionally, the controller provides H∞ robustness with respect to coprime factor uncertainty for the polytopic system. Thus, the torque controller fulfills major safety requirements, and can further be used for human-in-the-loop tests and applications with a lower-limb exoskeleton.

Authors 5

1. Lukas Bergmann corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Medical Information Technology, 52074 Aachen, Germany

2. Lin Liu Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Medical Information Technology, 52074 Aachen, Germany

3. Berno J.E. Misgeld Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Medical Information Technology, 52074 Aachen, Germany

4. Steffen K. Leonhardt Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Medical Information Technology, 52074 Aachen, Germany

5. Chuong Ngo Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University, Medical Information Technology, 52074 Aachen, Germany