A forearm pronation/supination assessment method integrated into Haptic Knob for stroke rehabilitation

The Haptic Knob (HK) is a robotic device that enables subjects to open or close their hands, or rotate their forearms for stroke rehabilitation. The present HK uses force sensors to measure the force applied by the subject, which provides an indirect force measurement with high development cost. In this paper, we propose a novel method to detect the grasping force applied directly on the haptic knob by measuring the current of the driving motor instead of the rotating torque applied. The same method can also be used to detect the pronation or supination torque applied by the subject by measuring the current of the driving motor. Experiments are performed using weights to apply known torque through a cylindrical disc calibration structure on the haptic knob to establish the relationship between the current of driving motor and the applied torque. The results show a near-linear relationship between the applied torque and the current of the driving motor which demonstrated the feasibility of inferring the applied torque from a subject in performing pronation or supination on the haptic knob from the current of the driving motor. This demonstrated the feasibility of inferring both the applied grasping force of a stroke subject as well as the applied pronation or supination torque on the haptic knob from the current of the driving motor.