Dual mode control of a system with friction

The stick-slip friction system is known to exhibit very different macro and microscopic behaviors. For large movements, the system exhibits the familiar stick-slip friction characteristics; and for very fine movements, the elastic deformation seems to prevail. While there have been tremendous efforts to understand the stick-slip friction mechanism, most people would agree that the complexity of the friction characteristics prevents the establishment of a simple mathematical model. Thus, the controller design cannot be solely dependent on a friction model. In this paper, a robust controller is developed so that it achieves ultimate boundedness in both the macro and micro motion regions. As a result, the controller is capable of controlling the system across the macro movement range and achieves precision positioning in the micro motion resolution. Comparisons with the existing controllers also show that the proposed controller easily achieves a better performance.