Design of Robust High-Speed Motion Controller for a Plant With Actuator Saturation

A robust high-speed motion controller is proposed. The proposed controller consists of the proximate time optimal servomechanisms (PTOS) for high-speed motion, disturbance observer (DOB) for robustness, friction compensator, and saturation handling element. In the proposed controller, DOB basically provides the chance to apply PTOS to nondouble integrator systems by drastically reducing disturbances as well as unwanted signals due to difference between real system and the double integrator model. But, in DOB-based systems, if control input is saturated due to control input of PTOS and/or DOB, overall system stability cannot be guaranteed, which is first found and analyzed in this paper. To solve this problem, robust stability and internal stability conditions of DOB-based system are derived. It is also shown that DOB could violate the internal stability, when the control input is saturated. Eventually, a simple saturation handling element is inserted to maintain internal stability of overall system. Also, we explain that our two saturation handling methods, i.e., Additional Saturation Element (ASE) and Self Adjusting Saturation (SAS) are the equivalent solutions of saturation problem to maintain internal stability. The stability and performances of the proposed controller are verified through numerical simulations and experiments using a precision linear motor system. [S0022-0434(00)01103-5]