Measurement of the Cable-Pulley Coulomb and Viscous Friction for a Cable-Driven Surgical Robotic System

In this paper we present experimentally obtained cable-pulley Coulomb and viscous friction for cable-driven surgical robotic systems including the RAVEN II surgical robotic research platform. In the study of controlling cabledriven systems a simple mathematical model which does not capture physical behavior well is often employed. Even though control of such systems is achievable without an accurate model, fully understanding the behavior of the system will potentially realize more robust control. A surgical robot is one of the systems that often relies on cables as an actuation method as well as pulleys to guide them. Systems with such structure encounter frictional force related to conditions of cable and pulley such as cable velocity, tension, type and number of pulley, and angle of cable wrapping around pulley. Using a couple of test platforms that incorporate cable, pulleys, and other experimental conditions corresponding to the RAVEN II system, it is shown that cable-pulley friction is function of tension, wrap angle, and number of pulleys and not of magnitude of cable velocity.