2DOF control-based fast and precise positioning using disturbance observer

The paper presents a practical compensator design approach for the fast-response and high-precision positioning using a two degrees-of-freedom (2DOF) controller. In the controller design for mechatronic positioning devices, effects of resonant vibrations and nonlinear friction on the positioning performance are especially paid attention: A feedforward control based on a coprime factorization description successfully suppresses the mechanical vibrations and provides the fast response. A feedback control with a disturbance observer, on the other hand, allows the plant system to behave a nominal one with robust stability, and compensates for effects of nonlinear friction on the positioning performance. The disturbance observer is especially designed in order to improve the servo characteristic in positioning, where an initial value compensation based on a rolling friction model is adopted at the starting motion. The proposed positioning controller has been verified by experiments using a prototype which simulates the vibratory mechanism with the nonlinear friction and the dead time components.