Study On Non-contact Measurement Method Of Micro-tilt And Flexural Deformation Of The Objects

Laser Speckle measurement technique is a modern optical measurement mechanics developing on the basis of characteristics of laser speckle. It has the advantages of full-field, non-contact, high precision and efficiency, real-time processing, simple and flexible, low environment factors requirements, and so on. With the rapid development of digital image technology and optoelectronic technology, Laser speckle image measurement technology develops along the direction of faster speed, smaller equipment, newer methods. It is being gradually applied to various areas such as displacement measurement, vibration detection, strain gauge, medical diagnosis, etc.Micro tilt and flexural deformation measurement has important value in the mechanics performance testing of engineering specimen and the health detection of engineering field objects. Based on the research of digital speckle image displacement measurement methods and the characteristic of the laser speckle image, laser speckle measurement method of micro-tilt and flexural deformation of the objects has been proposed and researched, with the theoretical analysis, numerical simulation and experimental tests. The main contents of this thesis are as follows:(1) The mechanism of laser speckle, type, and mathematical description were expounded. The statistical characteristics of speckle field were analyzed from probability and statistics. The basic optical principle of laser speckle being used to measure micro tilt and flexural deformation was deduced.(2) Laser speckle image displacement analysis method with high efficiency, precision and robustness was studied. A fast and non-interpolating method for sub-pixel displacement analysis of digital speckle images using phase shifts of spatial frequency spectra (SSPSM) was presented. The edge effect of DFT was well restrained by introducing the window function and the iteration method. At the same time a method to generate speckle simulation based on physical scene was proposed. It came true to generate speckle images with arbitrary displacement, quantization, resolution and SNR. The the calculation accuracy and efficiency of the algorithm were analyzed in MATLAB simulation. The result showed that the SSPSM algorithm had high accuracy, efficiency and good robustness.(3) The experiment research of objects’ micro-tilt non-contact measurement was done. First of all, the micro tilt measuring light path has been set in the laboratory. The tilt angle of specimen was controlled by the RSP60-L rotating platform. Using CCD camera was used to gather the speckle images before and after tilt. The SSPSM algorithm based on MATLAB was used to calculate these speckle images. The result verified the feasibility and accuracy of the measurement method. It also verified the good robustness of the SSPSM algorithm.(4) The experiment research of steel beam model flexure deformation based on analysis of laser speckle image displacement also was done. The deflection under positive pressure loading of steel beam model was measured. Electro-hydraulic servo structure test load system was using to control the flexural deflection of steel beam model. Different parts of the steel beam model were vertically illuminated by laser. CCD camera using to record speckle images under different pressure load. The displacements of speckle images were calculated through SSPSM algorithms.Then the deflection angles of steel beam model with different parts were obtained. The result verified the feasibility of non-contact measurement method of micro-tilt and flexural deformation of the objects based on analysis of displacement of speckle images. Finally the factors of affecting measurement precision were qualitative analyzed. Corresponding suppression measures were also presented.