ABSTRACT
In this text, a compact introduction into analysis and compensation of kinetic friction in 1DOF drives, commonly used in the mechatronic and robotic systems, is provided. Despite a long and rich history of studying the frictional effects in the machines and mechanisms, different aspects of cause and effect of the friction forces remain almost always in focus of the system and control engineering. This is not surprising since the phenomena of friction manifest themselves on the weakly specified contact interfaces of the moving bodies. As a logical consequence, frictional effects usually have a spatially distributed, nonlinear, and often time-varying nature and behavioral appearance. This renders the kinetic friction to a challenging disturbance in the drive systems, although it is often matched with the available and used control forces. In addition to the basic assumptions that we made for modeling the viscous and Coulomb friction forces, we have pursued the simplified point-contact and single DOF approximations in our developments. We considered the friction terms of the system dynamics also from the energy dissipation point of view and discussed how the non-conservative friction forces can be integrated into the standard Lagrangian framework of a dynamic system modeling. In addition to a well-understood frictional behavior at steady-state motion, we paid also a particular attention to the non-trivial transients at the beginning and stop and also reversals of relative motion. From a viewpoint of position control, these challenging to analyze phases of relative motion have been in our special focus. In the last part of the text, we discussed a possible control-oriented mitigation of the disturbing friction effects and highlighted both the output-based feedback and observer-based feedforward friction compensation methods. At large, the present text aims to master the basics of modeling and compensation of kinetic friction and to motivate and prepare interested students and engineers for further appealing challenges of friction phenomena.
