Distributed torque estimation toward low-latency variable stiffness control for gear-driven torque sensorless humanoid

Abstract

This paper explains low-latency joint torque feedback control based on torque estimation on each joint for gear-driven humanoid robots with harmonic drives. Force control of gear-driven robots has an advantage in its fully variable stiffness in comparison with elastic robots. However, feedback latency makes gear-driven robots vulnerable to impact rising in several milliseconds. It would be resolved by low-latency torque feedback loop in a single joint, but torque sensors are too large for life-sized humanoid robots. We estimate joint torque from motor current and rotation observed in each joint, and give artificial elasticity to joints using compliance control and shock absorption control. Our controller performance is demonstrated by landing experiments.