Design improvement of a 2-DOF ankle joint actuation mechanism for a humanoid robot

In this article, a novel mechanism to actuate ankle joint of a humanoid robot SURENA III, which has a 3D structure is presented. The proposed mechanism is based on raising center of mass of robots' legs which may lead to lighten the feet and increase speed. To this end, the actuators of the ankle pitch and roll joints are located in the shank link. Then, a combined timing belt-pulley and harmonic drive module are exploited for power transmission of pitch joint. Also, a roller screw mechanism is used to cause rolling movement of the joint. In order to validate the design procedure, the proposed mechanism is simulated on the model of humanoid robot SURENA III, designed and fabricated in CAST. The results reveal that actuating torques of joints and feet-ground interaction components would be decreased. Also, the stability of the robot simulated with new design is investigated by zero moment point criterion.