Sensorless torque control of humanoid arm having highly back-drivable joints

In this paper, novel upper body humanoid manipulators are presented. Each manipulator has 8 joints with coupled wrist joints, actually it has 7DOF. Torque-based interaction is our main manipulation strategy. We chose back-drivable mechanism and current control of motor as significant design factors. Shoulder and elbow joints were composed of gear mechanism, and wrist joints were composed of ball-screw mechanism. These mechanisms are experimentally compared with conventional harmonic drive module which widely used in manipulators. All joints are highly back-drivable. Force/torque sensors were not used. We developed local controller board consisted of DSP and EtherCAT communication. For an application of this system, cartesian impedance control using two arms is implemented.