A novel hand strength assessment method integrated into haptic knob for stroke rehabilitation

Haptic knob is a robotic assistive tool that allows subjects to open or close their hands, or rotate their arms so as to improve their motor functions after stroke. Current haptic knob uses force sensors to measure the force applied by the subject, which provides an indirect force with high development cost. This paper proposes a method to detect the force applied directly on the haptic knob by measuring the current of the driving motor. An experiment is performed whereby weights are used to apply known forces on the haptic knob in order to establish the relationship between the current of driving motor and the applied force of the subject. The experiment results showed a linear relationship between the applied force and the current of the driving motor. This demonstrated the feasibility of inferring the applied force of a stroke subject on the haptic knob from the current of the driving motor.