Vibration Analysis And Optimization Design Of Displacement System Of Metrological Scanning Electron Microscope

Metrological scanning electron microscope(M-SEM)is a device for measuring nanometer size.The length measurement of micro and nano scale is realized by combining scanning electron microscope(SEM)with micro-nano displacement platform and laser interferometer.In the M-SEM,the micro-nano displacement platform is one of the key components,which carries the measured samples.During the fast reciprocating scanning movement,vibration and large inertia are generated,and it is difficult to accurately scan.Therefore,in order to obtain accurate measurement,must have a good micro-nano displacement platform.For the M-SEM involved in this paper,the micro-nano displacement platform includes the mechanical displacement platform and the flexible hinge displacement platform.In order to improve the stability and measurement accuracy of the M-SEM,a model was established according to the operating conditions of the mechanical displacement platform,and the static and modal analysis was performed using the finite element method to obtain the vibration parameters of the mechanical platform.Based on the modal analysis,a harmonic response analysis was performed to obtain the relationship between the excitation frequency and the stress,strain,deformation and acceleration in the upper plane of the mechanical platform.The optimal load position of the mechanical platform and the influence of the material properties on its frequency were obtained through simulation.The results show that the static stiffness of the mechanical displacement platform is 6.634×105 N/mm,and the coupling ratios of the horizontal X and Z movements are 15.22% and 17.63%,respectively.According to the response curve of the upper plane vibration parameters to the frequency,the dangerous frequency is approximately 7750 Hz(i.e.,the frequency under the eighth natural mode).In order to reduce the coupling vibration of the flexible hinge displacement platform,its mathematical model was established and the coupling vibration mechanism was analyzed.On this basis,combined with the PID control algorithm,a feed-forward and feed-back control and a BP neural network PID control were designed respectively.The feed-forward and feed-back control was verified by simulation.The feed-forward and feed-back control can effectively reduce the image distortion by correcting the displacement points in the image acquisition process.At the same time,the displacement step jump response under the BP neural network PID control and the single PID control was simulated.The results show that the BP neural network PID control can quickly make the control system stable and has a small overshoot,and the steady-state error is close to zero.Figure 52;Table 8;Reference 81...