Input-Observer-Based Estimation of the External Torque for Single-Link Flexible-Joint Robots

To enable safe interaction between a robot and its environment, it is necessary to monitor in real-time the external torque that acts on the robot. This paper proposes a strategy that exploits solely encoder and current data to estimate the external torque acting on the single-link flexible-joint robot driven by a variable stiffness actuator in the antagonistic setup. The strategy comprises two steps: first, the elastic torques generated by motors within a variable stiffness actuator are reconstructed, then the external torque is estimated leveraging the data on the previously reconstructed elastic torques and robot dynamic model. The effectiveness of the estimator is tested in the simulation environment with respect to the time-varying external torque.