Design, Optimization And Experiment Study Of A Bridge-type Mechanism-based Compliant Micro-positioning Stage

Ultrahigh precision positioning and motion tracking technology in the micro/nano-scales is one of the key enabling technologies for modern precision industries, such as precision manufacturing, semiconductor production, data storage, as well as biomedical engineering. Due to the advantages of ultra-high precision and fast response, piezoelectric actuator-driven compliant micro-positioning stage has been studied with significant research efforts. However, the limited stroke of the piezoelectric actuator restricts its application in those fields. To address such challenges, this dissertation designs a bridge-type mechanism-based compliant micro-positioning stage. The output displacement of the piezoelectric actuator is amplified by the bridge-type mechanism such that the positioning stage enables a large motion stroke. Reserch efforts have been made in the mechanical design, theoretical modeling, finite element simulation analysis (FEA), parameters optimization and experimental verification. The detailed research work is as follows:A compliant micro-positioning stage is designed based on bridge-type amplification mechanism. Thanks to the superior amplification capability and compact size, a bridge-type mechanism is used, and a four-bar symmetrical guiding mechanism is used for its good decoupling capability to actuator’s assembling error, the proposed compliant stage achieves a large workspace with high positioning accuracy. A more accurate static and dynamic model is established. Taking account of the effect of external load, the static model of the corner-filleted flexure hinge-based bridge-type mechanism is established according to the Castigliano’s theorem and strain energy theory. Through the Euler-Bernoulli beam theory, the static model of the compliant links-based guiding mechanism is built. On this basis, the static model of the positioning stage is obtained by combining the models of the two parts. The dynamic model is also established by Lagrange equation. A comparison between the results of this thesis and the existing literatures demonstrate the accuracy of the proposed model.The finite element method is utilized to verify the theoretical models including the displacement amplification ratio of the bridge-type mechanism, the stiffness characters of the motion guiding mechanism, as well as the static and dynamic models and the parasitic motion rejection capability of the positioning stage. A multi-objective optimization method is proposed to optimize the structure parameters by balancing the static and dynamic performance. Based on the accurate mathematical model, the relationships between the structure parameters and performance targets including the displacement amplification ratio and nature frequency are obtained. Considering the inevitable tradeoffs among the static and dynamic performance, we establish the multi-objective optimization model of the positioning stage through linear weighted method, such that the structure parameters are optimized.The experimental study of compliant miro-positioning stage is performed. A prototype of the proposed stage is fabricated and an experimental apparatus is established. Firstly, some open loop experiments are carried out to verify the design, where the results agree well with the theoretical and FEA analyses. Secondly, a Prandtl-Ishlinskii (PI) inverse model-based feed-forward control strategy is adopted to compensate the hysteresis nonlinear effect. However, this method depends on the accurate system model parameter, which usually leads to significant errors in real applications. To handle the compensation error and the system uncertainties, as well as the environmental disturbances, we introduce a robust H∞ controller on top of the feed-forward compensation structure. The closed-loop experimental results demonstrate excellent positioning and tracking performance of the proposed control method.