Wearable robots that operate with the wearer's intention to augment muscle strength are called “power suits” or “power assists.” They are expected to play important roles in forthcoming aging society. In such robots, force sensitivity is a vital functionality in order to maintain comfort and safety. The objective of this paper is to develop a power assist device for daily use of elderly with comfort, safety, and reliability. We employ a variation of hydraulic system called electro-hydrostatic actuator to realize intrinsic backdrivability and high mechanical strength. The combination of a low impedance controller that actively enhances backdrivability and a sensitivity function maximization controller are used for power augmentation, which does not require unstable biological signal measurement. A power assist device for knee torque augmentation was developed; it is intended to support the large torque requirement, and to prevent knee buckling that leads to serious injuries.
