This information is part of the Modelica Standard Library maintained by the Modelica Association.

Basic model for Coulomb friction that models the stuck phase in a reliable way.

This procedure is implemented in a "clean" way by state events and leads to a mixed continuous/discrete system of equations if friction elements are dynamically coupled which has to be solved by appropriate numerical methods. The method is described in [Otter1999] (see also a short sketch in UsersGuide.ModelingOfFriction).

The parameter w_small is introduced for particular cases where a reinit is triggered at zero velocity. For such – rather rare – cases the friction handling logic is no longer correct. On the other hand, introducing w_small in general leads to problems when more friction elements are connected together. To omit such problems in the most common situations, the parameter has a large value per default, thus eliminating its effect. The user has to set w_small to a small value only when the special case with reinit occurs.

References