Hybrid position/force control of an upper-limb exoskeleton for assisted drilling

Abstract

Exoskeletons are wearable robotic systems to assist the human body concerning power and accuracy. In this work, an upper limb exoskeleton with seven degrees of freedom provides haptic guidance to the user enhancing accuracy of the target position and constant thrust force during drilling tasks. Therefore, an inverse kinematics algorithm is introduced using selective damping, depending on joint velocities to minimize the end effector position error for redundant systems. Additionally, the method recognizes user intention with structurally integrated torque sensors for null space optimization. An implicit, hybrid force-position controller is implemented to perform position controlled drilling tasks with constant thrust force. The performance evaluation with the exoskeleton shows a maximum position error of 1.27 mm and steady-state thrust force response with a maximum overshoot of 1N.