Dissipation mechanisms and dissipative forces play a pivotal role in the operations and performance of human-machine interfaces and particularly in haptic systems. Dissipation is a very difficult phenomenon to model. Coulomb friction in general can be the most influential element in systems involving multiple direct contact connections such as joints with transmissions or mechanically guided components. Coulomb friction includes non-smooth discontinuity and can induce complex dynamic behaviours. Very little attention has been paid to the analysis of the effects of Coulomb friction in haptic devices. In this paper we illustrate, by experiment, analysis and simulation, the nature of the dynamic behaviour caused by Coulomb friction in haptic sampled-data systems. We demonstrate that a simple model can represent this behaviour, and show the effects of the haptic system parameters on this dynamics.

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