Research On Compliant Displacement-reducing Mechanisms With Large Reduction Ratio

The compliant transmission mechanisms for displacement reduction and amplification have the characteristics of no friction and no gap,and have attracted much attention in the field of precision positioning.Among them,the compliant displacement-amplifying mechanisms solve the problem of the small output stroke of the piezoelectric drivers,but lose the motion accuracy and are difficult to meet the needs of precision equipment such as lithography machines for nano-positioning accuracy.And displacement reduction is an effective way to solve the problem.However,due to space constraints,it is challenging to obtain a displacement-reducing mechanism with a large reduction ratio and a small reduction ratio variation.Therefore,this thesis proposes a displacement reduction design idea of differential superposition formed by two-way motion transmission,and conducts research on configuration synthesis,modeling analysis,optimization design and experimental testing of compliant displacement-reducing mechanisms with large reduction ratio.2Based on the design idea of differential superposition,the configuration synthesis of the differential displacement-reducing mechanisms is realized by using graph theory representation and enumeration combination method.The method first uses matrices to characterize the design elements,then enumerates all element combinations,uses the design premises and other conditions to filter,and then organically combines the elements according to the necessary conditions for the formation of differential motion,and finally generates 8mechanisms.According to the form of motion output,two typical configurations of lever-bridge mechanism with the same input and output direction and the bridge-SR mechanism with orthogonal input and output are selected from the 8 compliant differential displacement-reducing mechanisms.The kinetostatic models of two new mechanisms are established,and the accuracy of the models are verified by comparing with the finite element simulation results.Under the same design premises,the performance of the two new mechanisms is calculated,and the leverbridge mechanism has more obvious advantages in reduction ratio and stiffness ratio.The characteristics of the two new mechanisms are analyzed.The structure of bridge-SR mechanism is more compact,and the design flexibility of lever-bridge mechanism is higher.The lever-bridge mechanism overcomes the limitation that the actuator of the bridge-SR mechanism needs to move together with the mechanism,and is not affected by the motion of the actuator when used in the XY precision platform,so it is further optimized.The parameters of the mechanism are optimized by using fmincon function,the relative variation of the reduction ratio is reduced from 1.62% to 0.0316%,and the error between the average reduction ratio and the ideal value is close to zero.According to the optimization results,a lever-bridge mechanism prototype with a reduction ratio of 194 is designed.After testing,the motion resolution of the prototype is better than 2 nm,and the errors between the theoretical value and the reduction ratios under various input signals are less than 11.8%.The new compliant displacement-reducing mechanisms proposed in this thesis achieve the goals of large reduction ratio and small reduction ratio variation,which provides a new idea for the design of XY precision positioning platform.