Research On Visual Precision Measurement Methods For Micro Displacement/deformation Based On Scanning Electron Microscope

Precision measurement technology based on micro-vision is widely used in researches such as micro-nano operation,MEMS component performance evaluation,and full-field stress-strain measurement.Currently,it is one of the research hotspots in the field of precision engineering.In response to the urgently needed of high-precision micro-displacement/deformation measurement requirements in the design,model verification and performance evaluation of micro-compliant micro-nano operating tools,this paper uses the Scanning Electron Microscope(SEM)as an imaging tool to carry out research on related visual precision measurement methods.The main research contents are as follows:(1)Aiming at the problems of image blur and measurement accuracy degradation caused by astigmatism in SEM imaging,a single image astigmatism quantitative evaluation and correction method based on Fourier transform and ellipse fitting is proposed.In this method,the Fourier transform is performed on the SEM image containing the spherical target first,and the image is transformed from the time domain space to the frequency domain space.Then,the minimum envelope ellipse is performed on the transformed image feature area,and judge the astigmatism state according to the azimuth of the main axis of the fitted ellipse.Finally,the astigmatism of each axis is corrected sequentially by the sequence method.The experimental results show that the proposed astigmatism correction method can effectively quantify and evaluate the degree of astigmatism under a single SEM image,thereby realizing the correction of SEM astigmatism,and providing a high-quality image source for subsequent precision measurements.(2)In order to realize the effective measurement of in-plane angle/linear coupling micro-displacements,a robust visual micro-motion detection algorithm based on enhanced gradient template matching is proposed.Firstly,use edge extraction combined with adaptive threshold segmentation to process the template image to establish an effective template model under noise interference.Secondly,to achieve the effective matching of micro displacement under angle/line coupling,a local deformation robust enhancement based on gradient template matching operator is adopted,and a detailed analysis on how to improve the calculation efficiency is also conducted.Then,to further optimize the matching results,an interpolation optimization strategy based on the gradient direction angle and a three-degree-of-freedom micro-motion estimation method based on image moments are developed.Finally,the effectiveness of the proposed method was verified through a series of experiments.The results show that the algorithm can achieve precise measurement of the micro-displacement of the plane coupling three degrees of freedom under low contrast,large gray scale fluctuations and strong noise interference(the characteristics of SEM imaging).(3)Aiming at the complex measurement problem of composite micro-motion measurement under the superposition of elastic body micro-deformation and displacement,an active profile measurement method based on single-phase phase is proposed.First,the single-stage phase analysis strategy is used to extract the edge of the SEM image target to solve the problem that the traditional edge extraction method is easily interfered by noise and brightness fluctuation.Then,the robust vector field convolution(VFC)active contour method is used to track and measure the target contours.Finally,a 12-direction-based contour structure centering scheme is proposed to track and measure the elastic deformation and in-plane displacement of the measurement target.Simulation and experimental results show that the proposed algorithm has a faster convergence speed and better robustness,and can effectively achieve the complex measurement requirements of micro-displacement/deformation of elastomers under SEM.(4)Based on the application of force-displacement measurement of straight beam compliant hinge(micro-cantilever beam),the experimental research on the precision measurement method of micro-displacement/deformation mentioned above is carried out.Firstly,a micro cantilever force-displacement measurement experimental system including a force sensor,a precision positioning platform,etc.was built in the SEM cavity.Then,based on the Euler-Bernoulli beam theory and the visual precision measurement method described above,an image-based force-displacement measurement mapping relationship is established.Finally,the eigen-parameter calibration experiment of the micro cantilever based on SEM vision and the micro-force measurement experiment based on SEM vision were carried out in the established experimental environment,which verified the effectiveness of the proposed method.Finally,the research content of the full text is summarized,and the future research is prospected.