Identification of a friction model for MoS2 solid-lubricated bearings in the context of friction compensation

The system performance of a mechanical system is frequently expressed in terms of the positioning or tracking error. Friction, which is often encountered in these mechanical systems, can induce unwanted effects, such as steady-state errors or limit cycling, deteriorating the systems performance. Prediction and evaluation of these unwanted effects can be realized when friction is described accurately in a friction model. TNO TPD proposed a design of a telescope, in which a scan-mirror is supported by solid-lubricated bearings to reflect the light of a star on a spectrometer, to determine the local composition of the earths atmosphere. The friction in these bearings can impose restrictions on the attainable positioning and tracking accuracy of the mirror. Subject of this research is the identification of a friction model to investigate possible unwanted effects of friction. This identification is performed in the context of application of the friction model in a friction compensation algorithm, to diminish or eliminate these unwanted effects. In order to be able to evaluate the friction phenomena of the solid-lubricated bearings and to identify a friction model, an experimental setup is designed and constructed. With this setup, various friction identification experiments, such as constant velocity, break-away and pyramid input experiments, are performed. Based on the results of these experiments, a friction model is chosen and its parameters are identified. Validation experiments are performed to verify the predictive quality of the friction model. Next, the system performance is analyzed on both a simulation level and an experimental level. Hereto, a third order point-to-point reference profile is used together with a feedback controller, tuned on Frequency Response Function measurements of the experimental system. Finally, friction compensation is applied in a feedforward (using the desired values of the friction model states) and feedback (utilizing estimates of the actual friction states) manner, to investigate whether the system performance is improved.