Determining the Effects of Coulomb Friction on the Dynamics of Bearings and Transmissions in Robot Mechanisms

Abstract

In order to accurately model robots for precision applications where dynamics are significant, it is important to include the effects of Coulomb friction in the bearings and transmissions. The general guidelines for analyzing friction at the joints will be discussed. It will be shown that friction can be related to the joint coordinates and their first and second time derivatives. The resulting extended robot dynamics formulation will be investigated as it applies to the inverse and forward robot dynamics problems. The analytical dependency of Coulomb friction on joint interactions is explicitly examined. As an illustration of friction effects in transmissions, we elaborate on the friction in harmonic drives and develop a method for its evaluation. The effect of friction in the bearings on the dynamics is also considered and a quantitative characterization of several specific cases is provided. This study is significant to understanding the design and control issues as they relate to achieving high speed precision robot motion.