Mechanism and Control of Knee Power Augmenting Device with Backdrivable Electro-Hydrostatic Actuator

Wearable robots that assist human mobility are actuated according to human intention. The estimation of the intention is difficult that the direct measurement is not possible. Especially the force control of the robot require quick response and highly non-repeatable. Biological signals such as electromyography are often used but they lack stability. Sensitivity function gain maximization is yet another approach, but high backdrivability is necessary to realize comfort, which was difficult in conventional gear driven actuators. In this paper, we apply backdrivable electro-hydrostatic actuator to realize intrinsic backdrivability, which is then enhanced with low-impedance controller consisting of inertia scaling and disturbance observer based friction compensation. Power augmenting controller was realized with sensitivity function gain maximization. Numeric analysis and evaluation tests on actual prototype were carried out.