Analytical modeling method for joint friction in harmonic drive robot

Traditional methods for characterizing friction in mechanical systems can be challenging, and the fitting accuracy often proves unsatisfactory. In contrast to conventional friction identification and numerical fitting approaches, we explore friction by analytically determining the normal forces emerging at contact surfaces. The associated joints are modeled as dual-mass systems with elastic transmission elements, which account for the effects of viscous damping and friction. When a joint experiences a constraint, the corresponding constraint force is computed as the solution to the Udwadia-Kalaba (U-K) equation. Employing a normal force, a closed-form expression for the friction torque is derived using the Stribeck friction model. This expression encompasses the magnitude at any instant of time without the need for auxiliary variables. A comparison between experimental and simulation results demonstrates that the friction analysis method proposed offers a reasonable and effective description.