Abstract/Summary

Performance degradation in most mechanical systems with friction which are not easily eliminated through design mechanisms can be greatly reduced within acceptable limits through the process of friction compensation. Generally friction compensators are used to improve system performance in terms of error reduction, transient response, thereby countering the effects of friction. Model-based techniques for friction compensation require an accurate model of the system friction. This is very important for high precision mechanical systems where excellent positioning and motion tracking, especially in the low velocities, is critical. This thesis proposes a new integrated friction model structure capable of modelling known friction dynamics. The new friction model incorporates a pre-sliding friction function with non-local hysteretic features. Analysis of the model shows the model to possess dissipative, boundedness, passivity and uniqueness properties. Results of sensitivity and robustness analysis indicate the new friction model is robust to parameter variations. A friction characterisation test-bed was designed and constructed for the purposes of friction identification, compensation and control. A set of experiments were designed and implemented on the test rig/bed to demonstrate friction dynamics. The input- output results of the experiments were used for parameter estimation of the proposed new friction model and some other relevant friction model structures. The performance of the new friction model for position and velocity control was studied using the experimental friction test-bed and simulations. The result of such analysis underscores the advantage of integrating a friction observer in the system control loop. The new friction model provided better position and velocity control of the experimental friction test-rig when compared with other well known models of friction.