Joint Torque Estimation toward Dynamic and Compliant Control for Gear-Driven Torque Sensorless Quadruped Robot

This paper investigates dynamic and compliant control based on joint output torque estimation for electrically actuated quadruped robots with large-reduction-ratio harmonic gear. Compared with position control, force control exhibits better performance of dynamics and compliance for the robot's interactions with complex environments. However, force control without direct feedbacks from torque sensors may come with poor tracking performance of joint compliance when the robot equipped with gears of high reduction. To solve this problem, we propose a new method to estimate joint torque from motor current and rotation velocity detected on each joint, using a more precise friction model of the harmonic gear. We also introduce a pre-stance phase to the whole cycle of leg alternating swing/stance based on hybrid force and position control to dynamically absorb feet impacts on the ground. Our controller performance is validated by standing experiment and walking experiment.