Pretension Analysis for Piezoelectric Stack Actuator in Nano-Positioning Stage

Taking advantages of high stiffness, fast response, high-bandwidth as well as large pushing force capability, piezoelectric stack actuators have been widely used in the fields of high speed nano-positioning stages and precision systems. An inevitable disadvantage of piezoelectric actuators is that they are highly intolerant to shear and tensile forces. During high speed scanning operations, the inertial forces due to the effective mass of the stage may cause the actuators to withstand excessive shear or tension forces. To protect the actuators, preload is often applied to compensate for these forces. Flexures have been used to supply preload to the piezoelectric stack actuators in many high-speed nano-positioning stages. Nevertheless, for nano-positioning stages with stiff flexures, it is a difficult job to displace the flexures and slide the actuators in place to preload them. This paper proposed a novel preloading nano-positioning stage which allows the piezoelectric stack actuator to be preloaded and mounted easily without obviously reducing the stiffness and speed of the nano-positioning stage. A preloading nano-positioning stage is designed and the flexible hinge and piezoelectric stack actuator of the stage are analyzed. The stiffness and resonance frequency of flexible hinge and optimal preload for the proposed stage is obtained by kinetics analysis. In order to verify the effectiveness of preloading nano-positioning stage, an online test system is established. The system mainly composed by a force sensor module, a capacitive sensor module and the preloading nano-positioning stage. A force sensor is applied between piezoelectric actuator and flexible hinge which can directly measure the preload in real time. The displacement of the flexible hinge is measured by a capacitive sensor to evaluate the positioning accuracy. Experiments are conducted, and the results demonstrate the effectiveness of the proposed approach.