Design And Control Of Rotatable Stage For Multi-station Precision Operation

Precision positioning and operation technology is one of the key technologies in the fields of cell manipulation,ultra-precision machining,precision optics,and so on.With the deepening of research in the above fields,people have gradually begun to put forward higher requirements for work efficiency,which has promoted the emergence and development of multi-station precision operation methods.Multi-station precision operation simplifies the complexity of multiple positioning operations by rotating the positioning method,greatly improving work efficiency.Rotary positioning technology also puts more functional requirements on the stage.One is that unlike the traditional stage,which has only linear freedom,the rotary positioning technology relies more on the rotation degree of the z-direction of the stage.The second is that the motion accuracy of the station puts higher requirements.The traditional driving method has been gradually eliminated,and the piezoelectric driving technology is widely used due to its advantages of high precision,fast response,and compact structure.However,the small stroke of the piezoelectric actuator restricts its application in the field of rotational positioning.In view of the above requirements and current technical problems,this paper carries out the following work to design and control the high-motion precision and large-stroke rotating stage.(1)Structural design and simulation analysis of the rotating stage.Combining the principle of the Inchworm movement with the piezoelectric drive technology,the design principle of the ’clamp-drive-clamp’ movement of the Inchworm movement is realized by the design of the double-layer structure.The design keeps the high-precision output of the piezoelectric drive while retaining the high-precision output of the piezoelectric drive.The problem that the piezoelectric drive with small displacement is solved.In order to ensure that the designed structure is reasonable and reliable,it can run smoothly under normal working conditions.This paper uses ABAQUS finite element analysis software to carry out static analysis and modal analysis.The static analysis results show that under the maximum displacement load,the maximum stress of the fixed part is concentrated at the flexible hinge.The maximum stress of the moving part is concentrated at the flexible hinge of the bridge amplifying mechanism.The maximum stress of the fixed part is 28.96MPa.The maximum stress of 69.25MPa is less than the yield strength of the material,and there is no plastic deformation that affects the performance of the rotating stage;The modal analysis results show that the resonant frequency of the fixed part and the minimum resonant frequency of the moving part are far greater than the normal working frequency of the stage.During normal working,it will not generate resonance due to working at the resonant frequency.(2)Modeling and control of hysteresis characteristics of the rotating stage drive unit.Because piezoelectric material as a ferroelectric material has its own nonlinear hysteresis characteristics,this paper studies and controls the hysteresis characteristics of the driving unit to ensure the output accuracy of the designed rotating stage.Firstly,aiming at the asymmetry of the hysteresis characteristic,this paper improves the classical Prandtl-Ishlinskii(PI)model,then introduces a polynomial model to construct a composite model based on the improved PI model to improve the modeling accuracy,and finally uses the model to drive.The hysteresis data of the unit is identified,and the result shows that the identification error is 1.9%.In order to reduce the influence of this hysteresis on the output accuracy of the rotating stage,this paper designs a compound control strategy combining feedforward control and feedback control.The feedforward controller is obtained by constructing an inverse model based on the above positive model;the feedback controller adopts a PID controller.The experimental results show that the nonlinearity of the input and output curves of the compound control is 2.21%,which has obvious linearization compensation effect on the hysteresis nonlinear characteristics.(3)Weak signal processing.Aiming at the problem that the amplitude of the feedback signal is small and the signal-to-noise ratio is reduced due to the interference in the transmission process,which affects the control effect,a weak signal processing scheme of the analog filter plus the digital filter is proposed to improve the SNR of the feedback signal.In this scheme,the analog filter is implemented using a fourth-order Butterworth low-pass filter,and the digital filter is implemented by an improved Variable Step Size Least Mean Square(VLMS)filter.The Multisim software is used to verify the cutoff frequency and passband amplification of the analog filter circuit.The improved VLMS filter is used to process the noisy signal with-10dB,and the fixed step size LMS algorithm and the traditional VLMS algorithm.For comparison,the signal-to-noise ratio of the improved VLMS algorithm is increased to 4.1774dB.Compared with the other two schemes,the improvement effect is obvious.(4)Experimental test.Based on the above work,the prototype of the rotating stage is processed and the experimental test platform is built to test the performance of the stage.The resolution is 10.76μrad,the maximum load is 20N,the repetitive motion error is less than 2%,and the reciprocating motion error is less than 5%.The design specifications are feasible.Finally,the research work of the thesis is summarized,and the research work on the key technologies of the rotating stage and its control is prospected.