For control applications involving small displacements and velocities, friction modeling and compensation can be very important. In particular, the modeling of presliding displacement (motion prior to fully developed slip) can play a pivotal role. In this note, it is shown that existing single-state friction models exhibit a nonphysical drift phenomenon which results from modeling presliding as a combination of elastic and plastic displacement. A new class of single state models is defined in which presliding is elastoplastic: under loading, frictional displacement is first purely elastic and then transitions to plastic. The new model class is demonstrated to substantially reduce drift while preserving the favorable properties of existing models (e.g., dissipativity) and to provide a comparable match to experimental data.

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igh performance position control of drives with friction is one of t h e requirements in machine-tool applications. A gradient method based algorithm is proposed in this article for t h e auto-tuning of feedforward friction compensation. T h e method presented guarantees robust stability for all states of the system which is of great importance for industrial applications. Theoretical considerations a r e illustrated with experimental d a t a collected from t h e drive of a vertical axis used for electro-discharge machining.

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