DETERMINING THE EFFECTS OF COULOMB-FRICTION ON THE DYNAMICS OF BEARINGS AND TRANSMISSIONS IN ROBOT MECHANISMS

In order to accurately model robots for precision applications where d ynamics are significant, it is important to include the effects of Cou lomb friction in the bearings and transmissions. The general guideline s for analyzing friction at the joints will be discussed. It will be s hown that friction can be related to the joint coordinates and their f irst and second time derivatives. The resulting extended robot dynamic s formulation will be investigated as it applies to the inverse and fo rward robot dynamics problems. The analytical dependency of Coulomb fr iction on joint interactions is explicitly examined. As an illustratio n of friction effects in transmissions, we elaborate on the friction i n harmonic drives and develop a method for its evaluation. The effect of friction in the bearings on the dynamics is also considered and a q uantitative characterization of several specific cases is provided. Th is study is significant to understanding the design and control issues as they relate to achieving high speed precision robot motion.