Design and control of a wearable and force-controllable hand exoskeleton system

In this paper, a wearable and force-controllable hand exoskeleton system is proposed. In order to apply force feedback to the fingertip while allowing natural finger motions, the exoskeleton linkage structure with three degrees of freedom (DOFs) was designed, which was inspired by the muscular skeletal structure of the finger. Kinematic performance of the proposed linkage structure was verified by comparing with functional range of motion (ROM) which is required for activities in daily living. As an actuating system, a series elastic actuator (SEA) mechanism, which consisted of a small linear motor, a manually designed motor driver, a spring and potentiometers, was applied. Friction of the motor was identified and compensated to obtain a linearized model of the actuating system. Using a linear quadratic (LQ) tuned proportional-derivative (PD) controller and a disturbance observer (DOB), the proposed actuator module could generate the desired force accurately even with arbitrary finger movement. The performance of force transmission through linkage structure was verified by simulation and experiments. The proposed exoskeleton structure, actuator modules and control algorithms were integrated as a wearable and force-controllable hand exoskeleton system that could deliver force to the fingertips for flexion/extension motions.