Load-dependent Friction Laws of Three Models of Harmonic Drive Gearboxes Identified by Using a Force Transfer Diagram

Abstract

Industrial robotics and aerospace engineering widely use harmonic drive gearboxes for their reliability, high accuracy with zero backlash and high ratio torque transmission However, they present known problematic behaviors that affect their performance. The article deals with the first step towards the improvement of torque control of collaborative robots. We designed and developed two experimental setups to study three types of Harmonic Drive gearboxes. We identify the friction laws by using Force Transfer Diagrams. The results exhibit a new parabolic law of friction torque as a function of the transmitted torque.

Electro-mechanical modeling and identification of the UR5 e-series robot

“…The friction model can be arbitrarily simplified, as much as describing it only by means of the viscous and Coulomb terms without any major modeling error [28]. Nonetheless, a higher accuracy seems to be achievable by considering also the dependence to load [35,36] and temperature [37]. Some extensive studies by Madsen et al offer a rather complete characterization of friction for the UR5e robot by means of a nonlinear model [38][39][40], which also takes into consideration joint stiffness.…”