APPLICATION OF H_∞ ROBUST CONTROL TO PARAPLEGIC STANDING

摘要

The aim of this work was to design and test robust H_∞ feedback control systems for the control of the upright posture of paraplegic persons standing. While the subject stands in a special apparatus, stabilising torque at the ankle joint is generated by electrical stimulation of the paralyzed calf muscle of both legs using surface electrodes. This allows the subject to stand without the need to hold on to external supports for stability: we call this "unsupported standing". Sensors in the apparatus allow measurement of ankle moments and the inclination angle. A nested loop structure for control of standing is implemented where an inner loop provides control of the total ankle moment while the controller in the outer loop regulates the inclination angle. A difficulty in using electrically-stimulated muscles as actuators in this setup is the very significant degree of nonlinearity in the muscle response. We therefore focus here on robust H_∞-control design for the angle control loop. The design approach is verified in experiments with a paraplegic subject.