Sensorless External Torque Sensing for Collision Detection in Collaborative Robots

The measurement of external forces in Collaborative Robots (Cobots) is commonly realized by dedicated sensors in the joints. Since the use of these sensors is cost-intensive and reduces the stiffness of the manipulator, alternative approaches are needed. This paper presents a sensing principle for measuring external forces acting on a robot arm using a generalized momentum observer. The proposed approach does not require dedicated force/torque sensors and relies on measurements available in standard robot joints. The presented method estimates the external forces based on motor current measurement and joint torsion measurement. Both measurements are implemented and compared against a dynamometer in terms of accuracy. Depending on the joint, an RMS error within 2% to 4% of the dynamometer measurement can be achieved.