Practical and robust control for precision positioning systems

This paper presents a practical and improved practical controller for enhancing precision motion performance. For practical use, high motion control performance, ease of design and controller adjustment are desired. A nominal characteristic trajectory following (NCTF) control has been studied to realize high performance and ease of application. The NCTF controller consists of a nominal characteristic trajectory (NCT) which is the reference motion of a control system and determined from experimental open-loop time responses of the mechanism and a compensator which makes the motion of the controlled object to follow NCT. The controller parameters can be determined easily, without any given model parameters. In the present paper, the Acceleration-Reference - Continuous Motion (AR-CM) NCTF controller has been proposed and implemented. The AR-CM NCTF considers the acceleration reference for object motion as additional controller elements besides the velocity reference. The AR-CM NCTF controller provides the advantage of high overshoot reduction and disturbance reduction characteristics. This paper then highlights how robustness the controller in the precision positioning systems. The issues considered include (i) variation of mass object; (ii) variation of disturbance force such as coulomb and viscosity frictions. The design procedure of the AR-CM NCTF controller remains easy, practical and is independent of friction characteristics. Validation and implementation of the AR-CM NCTF controller with a mechanism with friction are carried out in order to confirm its effectiveness. The robustness of the AR-CM NCTF controller is examined by comparing its motion performance with the PDDO (PD + disturbance observer) controllers. The comparative experimental results illustrate the achievable performance of the AR-CM NCTF controller in positioning and tracking control and the higher robustness to plant parameter variations, as compared to the PDDO controllers.