Motion support of upper extremity with agonist alone under negative admittance control

In this paper, different from the conventional admittance control, an originally negative admittance control, in which two virtual parameters, virtual damping coefficient and virtual moment of inertia, are negative, is developed to support the movement of human's upper extremity only by agonist's EMG signals. First, we empirically determine two agonists, biceps brachii and clavicular part of deltoid to get their EMGs respectively as the control signals for elbow joint and shoulder joint. Then a negative admittance control is developed to support the movement of human's upper extremity for holding up, keeping and holding down a load only by agonist's EMG signals. The experiments demonstrate that seamless movements of holding up, keeping and holding down a heavy load is successfully realized. The experimental results show that the performance of the negative admittance control can be arbitrarily adjusted by control parameters and user's “load feeling” can be arbitrarily reduced.