This paper describes an experimental study of power assist systems based on harmonization of human operators, actuators and mechanical elastic elements. This power assist system proposed by the authors simultaneously realizes amplification of operator's torque and optimization of stiffness of a mechanical elastic element. The optimization in the proposed power assist system means that the minimum torque from the actuator can generate periodical motions even if the parameters of the operator's periodic torque are not known. The amplification and the optimization were mathematically proven in our previous papers. In this paper, effectiveness of the proposed power assist system is experimentally investigated by using a mechanical device with a stiffness adjustable mechanism. Next, another type power assist system of a mechanical structure with better backdrivability is proposed and effectiveness of the new structure is also verified through simulation and experimental results.
