Design Of A Rigid-flexible Coupling Motion Stage Driven By Ball Screw

Electronics manufacturing is a pillar industry in China.As electronic integration enters the sub-micron and nano era,high-end electronic manufacturing equipments gradually face the real problem of operating accuracy lagging behind the process requirements.The motion stage is the core component of high-end equipments to achieve point-to-point motion,and its positioning accuracy is the key to equipment accuracy.Therefore,the common demand of high-end equipment is to improve the positioning accuracy of the motion platform.Linear motion stages powered by ball screws are widely used in engineering with the advantages of high cost-effectiveness and high reliability.However,due to the uneven elastic deformation and the difficulty in compensating the frictional dead zone,the existing ball screw motion stages are unable to meet the requirements of the next generation of high-end equipments in terms of positioning accuracy,which stops at the micron level.To address these two pain points,this thesis proposes a new rigid-flexible coupling ball screw motion stage based on the idea of "anti-disturbance",so that the deformation generated by the driving force of the stage is concentrated at the flexible hinge and the consistency of the stage displacement is improved.In the positioning process,the flexure hinge deformation is used to achieve micro-displacement output and compensate for frictional dead zones.This thesis completes the design work of the whole motion stage and investigates its working principal,structural fatigue and positioning performance,mainly as follows:（1）Firstly,this thesis proposes a new rigid-flexible coupling structure for ball screw motion stages inspired by the idea of using expanded state quantities to describe the "total disturbance" in active disturbance reject control.Through the analysis of the motion process of the stage,the principle to solve the uneven deformation and frictional dead zone compensation of the motion stage is introduced.The design of the flexure hinge and the selection of ball screws are also presented.In order to further reflect the design idea,a multi-flexible ball screw dynamics model was established.It was found that the flexible vibration of the system is concentrated on the structure with the lowest stiffness.This conclusion is used to reduce the order of the dynamics model and the equivalent dynamics model of the rigid-flexible coupling ball screw motion stage is established（2）Secondly,a finite element analysis model of the rigid-flexible coupling motion stage and the conventional rigid motion stage were developed.The equivalent stiffness and the inherent frequency of the designed stage were solved,and the error is 0.8% compared with the theoretical value,which verifies the accuracy of the finite element model.On the basis of this,the simulation verifies the feasibility of the rigid-flexible motion stage in solving the uneven elastic deformation problem by comparing the force deformation of the above two motion stages.（3）Then,to address the problem of fatigue life of 7075 Al straight beam type flexible hinges,this thesis introduces spring plate flexible hinges at both ends of the motion stage to form a sandwich type flexible hinge structure.Through fatigue life analysis of the two structures of flexible hinges,the fatigue cycle life was found to be 1183 times and 5254000 times respectively,verifying that the sandwich type flexible hinges can effectively solve the fatigue problem of aluminium alloy flexible hinges.（4）Finally,the experimental stage was built and the experiments were realized based on the fully closed-loop position control.Experiment one measures the deformation of two sandwich-type flexural hinges and the error is only 0.024 μm,which is 99.1% more uniform than that of the rigid stage,verifying the effectiveness of the experimental stage in solving the problem of uneven elastic deformation.Experiment two compares the positioning accuracy of the motion stage under different accelerations and strokes.The results show that the experimental stage can achieve a positioning accuracy of nearly 0.05μm with grating feedback,which proves the effectiveness of the flexure hinge deformation to compensate for the friction dead zone.The thesis concludes with simulations to test the dynamic tracking accuracy of the PID control and "self-anti-disturbance" control.Reasonable recommendations are given to further improve the stage performance.