Reliable chattering-free simulation of friction torque in joints presenting high stiction.

The simulation of static friction, and especially the effect of stiction, is cumbersome to perform in discrete-time due to its discontinuity at zero velocity and its switching behavior. However, it is essential to achieve reliable simulations of friction to develop compliant torque control algorithms, as they are much disturbed by this phenomenon. This paper takes as a base an elastoplastic model approach for friction, which is free from chattering and drift. It proposes two closed-form solutions that can be used to reliably simulate the effect of stiction consistently with the physics-based Stribeck model. These solutions consider the nonlinearity and velocity dependency, which are main characteristics of lubricated joints. One is directly inspired by the Stribeck nonlinear terms, and the other is a simplified rational approximation. The reliability of this simulation method is shown in simulation, where the consistency and stability are assessed. We also demonstrate the accuracy of these methods by comparing them to experimental data obtained from a robot joint equipped with a high gear reduction harmonic drive.