Nonlinear tracking control for dual-stage actuator systems

This paper presents a nonlinear control method for dual-stage actuator (DSA) systems to track a step command input fast and accurately. Conventional tracking controllers for DSA systems were generally designed to enable the primary actuator to approach the setpoint without overshoot. However, we observe that this strategy is unable to achieve the minimal settling time when the setpoints are beyond the secondary actuator travel limit. To further reduce the settling time, we design the primary actuator controller to yield a closedloop system with a small damping ratio for a fast rise time and certain allowable overshoot. Then, a composite nonlinear control law is designed for the secondary actuator to reduce the overshoot caused by the primary actuator as the system output approaches the setpoint. The proposed control method was applied to an actual DSA positioning system, which consists of a linear motor and a piezo actuator. Experimental results demonstrate that it can further reduce the settling time significantly compared with the conventional control.