The humanoid robot SURENA III is composed of 12 DOF in its lower-body and 19 DOF in its upper-body. This robot has 6 DOF in each leg, 7 DOF in each arm, 1 DOF in each hand (a simple gripper), one DOF in torso and 2 DOF in neck. The sensory layout includes incremental and absolute encoders mounted on the motor output and gearbox output, six axes force/torque sensors embedded to the ankles, an IMU mounted on the upper-body, and contact switches embedded to each sole.
Design of the legs of a humanoid robot is certainly the most challenging part in the design procedure. The 6 DOF leg structure allows the foot to have dexterous motion with respect to the pelvis. The lower-body joints are actuated by EC motors and a combined timing belt-pulley and harmonic drive module is exploited for power transmission. Rigid and light-weight structure may greatly enhance performance of a position controlled walking machine. In order to alleviate the vibration of the joints which may be existed due to flexibility of harmonic drive or the cross modules (in ankle and hip), by employing high resolution absolute encoders at the joints output, the cascade position control loop has been exploited which decreased the vibration of the joints. In order to increase rigidity of the links, while keeping the robot’s weight low as much as possible, aluminum plates have been used for the shanks and thighs.
The upper body joints of SURENA III are driven by servomotor packages which include motor, gearbox and driver. One DOF in waist enlarges the workspace of the arms for gripping and whole body motions. Two DOFs in neck give the head capability of having pan and tilt motions. Furthermore, inspired from human beings, each arm of the robot has 7 DOF (three in shoulder, 1 in elbow, 3 in wrist), in which the actuators have been connected via fiberglass plates to reduce the weight. This redundant structure gives the robot arms capability of dexterous manipulation. Finally, a mechanism has been employed in hands to enable it to grip the objects. Using this mechanism, all 5 fingers of each hand may move simultaneously, and realize the gripping.