The most important problems which should be considered in designing servo controllers are resonance effects and nonlinear frictions. These problems exist in almost all the servo systems, especially for the robotic manipulators and numerical control sy...
The most important problems which should be considered in designing servo controllers are resonance effects and nonlinear frictions. These problems exist in almost all the servo systems, especially for the robotic manipulators and numerical control systems and cause difficulties in designing controllers. In this paper, controller design procedure which employs H∞ control theory is proposed for the servo systems with these problems. In order to design a controller which is capable of compensating frictions and ensures no steady state error, the original system is augmented with an integrator and H∞ controller design method is applied. Sometimes, for these systems, there is a possibility of limit cycles due to the interaction between the nonlinear friction and integrator. To check the possibility of limit cycles, describing function method is used.