Motion control of a 2-DOF decoupled compliant mechanism using H∞ synthesis

A decoupled piezo-driven compliant mechanism has been designed and manufactured to track 2-DOF trajectories. Although it features decoupled characteristics, the small cross axis coupling can result in poor tracking performance in 2-DOF trajectories. For such structures, the damping ratio is so small that the modal vibrations are likely to be excited, which greatly degrade its positioning accuracy. In this paper, an H∞ controller is designed to make the closed-loop system match a well-damped second order system. The H∞ controller effectively suppresses the modal vibrations and further reduces the cross axis coupling motions. Experimental results show that the mechanism's tracking performance in 2-DOF trajectories is significantly improved.