“…Models of a dynamically evolving friction force are traceable from Dahl [13] through various developments to, for example, the LuGre model [7,4,37] where a friction force F = ksz + csż + cv evolves according to the deflection z of bristles on the surface, with stiffness ks and damping cs, including a viscous friction coefficient c, and Stribeck velocity vstr below which speed dependence is seen; bristle models capture the key effects of friction and yield a smooth force law, and have inspired many variations on the model, usually bringing with them more coefficients connected with nonlinearities, giving dependence on acceleration or forming alternative models of asperities. For example in [50] it was proposed to switch the contact force between accelerative, decelerative, and static modes, requiring several quantifiers of effects including compliance or friction memory and hysteresis, Stribeck velocity dependence, dwell times in stick-slip transition, and static friction.…”