Comments on "A new model for control of systems with friction"

This paper provides a complete stability proof of Theorem 1 of the above-mentioned paper (Canudas-de-Wit et al., 1995) for the tracking and the regulation case. In the paper, the proof presented for Theorem 1 only holds for the regulation case where the LaSalle's invariant principle may be invoked. In the tracking case, the closed-loop system becomes a nonautonomous one, and arguments other than the LaSalle's invariant principle should be used. Here we present these arguments and show that Theorem 1 holds for both cases.