Minimizing the Physical Stress by Virtual Impedance of Exoskeletal Robot in Swinging Motion with Power Assist System for Lower Limb

The objective in this paper is to suggest the method to examine the relationship between impedance of exoskeletal robot and physical stress of the operator in order to minimize the operator's physical stress in swinging motion. The exoskeletal robot, “HAL-3” which we developed for assisting the motor function of lower limb was used for experiments in this research. To accomplish the objective, first, the physical parameters around joint of HAL 3 were identified, secondly, the relationships between virtual impedance values and physical stress of operator were examined through experiments for swinging motions. The physical stress was evaluated with myoelectricity, joint torque, and operator's feelings during the experimental motion. As the results, we found the physical stress tended to decline with the decrease of virtual inertia and coulomb friction, and to increase slightly with the decrease of gravitational torque. The decrease of virtual viscous friction coefficient made the physical stress increase gradually after it declined to trough at the positive virtual viscous friction. We could establish the criteria to adjust the virtual impedances for minimizing the operator's physical stress in swinging motion based on these examined results.