Research on human upper limb endpoint mechanical impedance with multi-task environment

Abstract

This paper analyzes the influence of different task environment on the endpoint impedance of human upper limb. Two different task environment which combine non-contact environment in free space and constrained contact environment are selected. In non-contact environment, the task is to perform an approximate uniform linear motion along a straight way in a horizontal plane by holding a tool. In contact environment, the task is to perform manual surface polishing on a relatively flat steel plate by holding a tool. A 7-DOF (degree of freedom) robot arm is employed to make the perturbation to the human upper limb and compensated the external force. An experimental platform includes robot arm, force/torque sensor, accelerometer and motion tracking system is set up for impedance measurement. A set of 5 subjects perform 9 repetitions of both non-contact task and contact task. The result shows that compared with contact task, the stiffness values of non-contact task decrease by 32.7% averagely in direction perpendicular to the motion trajectory. Therefore, the human impedance measurement should be combined with a specific task environment. This result provides some guidance and advice for human impedance measurement. In addition, it is beneficial for robot system programming and mapping human operation skills to industrial robots.