Online estimation of friction constraints for multi-contact whole body control

This paper proposes a technique for experimentally approximating surface friction coefficients at contacttime in multi-contact applications. Unlike other multi-contact formulations, our approach does not assume a standard friction coefficient, and instead induces slip in a multi-contact oriented humanoid to estimate available friction force. Incrementally increased tangential force, measured with ankle-mounted force-torque sensors, is used as the basis for slip detection and friction coefficient estimation at the hand. This technique is validated in simulation on a simple three-link model and extended to the humanoid robot platform ESCHER. Approximated friction values are utilized by the robot's whole body controller to prevent multi-contact end effector slip.