A Novel Force Oscillations Reduction Method Based on Nonlinear Tracking Differentiator for Robot Contact Transition Process

Impedance control is an effective force tracking approach for robot contact operation tasks such as grinding/polishing, deburring, assembly and dexterous hand manipulations, etc. Within the impedance control framework, when the robot begins to contact with the environment, however, force oscillations may occur even if the optimal approach velocity is adopted, which may increase the settling time of the system, result in serious damage to the parts, and even make the otherwise stable controller unstable. To this end, based on the real-time adjustment of the desired force by the nonlinear tracking differentiator (NTD) strategy, a novel force oscillations reduction method for robot contact tasks is proposed in this article, which can reduce the force oscillations in a feed-forward style. To the best of our knowledge, this is the first time that the NTD is used to reduce the force oscillations. The performance of the proposed method is evaluated by simulations and experiments, and the results demonstrate that the proposed method can effectively reduce the force oscillations, which provides a simple and useful solution for practical robot contact applications.