Precision Motion Control for a Piezoelectric Micro-positioning Stage via Integrating Iterative Learning and Disturbance Observer

For the commonly used repetitive trajectory in motion systems, the iterative learning control (ILC) method is still quite sensitive to non-repetitive disturbance, although it can eliminate repetitive errors effectively via iterations. In order to achieve precision motion with non-repetitive disturbance for piezoelectric micro-positioning stages, a control strategy integrating ILC with disturbance observer (DOB) is proposed. Firstly, the hysteresis nonlinearity is treated as repetitive input disturbance during the iterative process to avoid complex hysteresis modeling. Then, to ensure the stability of the proposed strategy, the convergence condition is deduced and the suppression of non-repetitive disturbance is analyzed to minimize convergence error. Finally, comparative experiments are performed on a piezoelectric micro-positioning stage. Results show that the proposed strategy can compensate hysteresis nonlinearity effectively without hysteresis modeling. The root-mean-square values of tracking errors are within 0.4% of the stroke for tracking of 5Hz,10Hz and 20Hz triangular waves under ideal environment. While for the environment with non-repetitive disturbance, the proposed strategy can achieve root-mean-square value of tracking error at 10.24nm, that is reduced by 98.73%, 98.67% and 88.24% respectively compared with the built-in controller, the stand-alone feedback controller and ILC. Besides, the proposed control strategy can accelerate the convergence speed of ILC. Experimental results validate the effectiveness of the proposed strategy sufficiently, and the precision motion of the piezoelectric micro-positioning stage can be realized.