Friction compensation techniques for tendon-driven robotic hands

In this paper, novel methods for friction compensation in tendon-driven robotic hands are presented and discussed. The results of the proposed techniques have been experimentally validated on the DEXMART robotic hand, where the adoption of joints based on sliding pairs (to reduce the complexity of the mechanism and to ease the assembly procedure) introduces as a side effect a non-negligible joint friction. These friction phenomena have been modeled by means of a specialized version of the LuGre model in which the friction coefficients vary with the normal force. After an experimental validation on a specific laboratory setup, a simplified friction model has been derived and used in the joint position control loop of the DEXMART hand to compute a feed-forward term for reducing the position error. A comparison of this approach with other model and non-model based friction compensation techniques is also presented and discussed.