Research On Characterization Of Target Surface Roughness Based On Laser Speckle

Surface roughness is a common indicator in determining the micro-roughness of a target surface,and its impact on practical applications cannot be underestimated.The size of surface roughness has a direct effect on the performance of instrument parts such as fatigue strength,wear resistance,sealing,and corrosion resistance.Therefore,accurately measuring surface roughness has become a critical topic in research.There are two common methods for measuring surface roughness,contact measurement,and non-contact measurement.Non-contact measurement has become more popular as it does not damage the measured parts.Among non-contact measurement methods,the speckle method has become the main means of measuring surface roughness due to its low error and ease of operation.Initially,speckle method was used to eliminate noise,but researchers have discovered that the information carried in speckles can be used for surface roughness measurement.After long-term research,it has been found that the formation of speckles is random,and statistical methods need to be used to study speckle characteristics and achieve surface roughness measurement by utilizing the statistical properties of speckles.The main research objectives of this project are as follows:(1)Firstly,the relevant theories of laser speckle and surface roughness are studied.Secondly,to classify the methods for measuring surface roughness according to whether they contact the target surface and analyze the working principles and shortcomings of the scattering method,interference method,and light-cutting method in non-contact measurement methods.On this basis,it is necessary to propose using the speckle method to characterize surface roughness.(2)The construction of the surface roughness measurement model obtains the relationship between the target surface height and phase by introducing the complex amplitude characteristics of speckle,then uses the autocorrelation function to obtain the calculation formula of the correlation area of the scattered wave,and then uses the diaphragm function to calculate the equivalent area of the distinguishable speckle,uses the ratio between the equivalent area of the distinguishable speckle and the correlation area of the scattered wave to calculate the average number of speckles,and finally derives the speckle contrast and speckle contrast through the statistical characteristics of speckle and surface scattering theory.The mathematical relationship between the average number of speckles and the target surface roughness,and the theoretical curve is obtained by simulating the relationship between the three by MATLAB,so that the experimental curve can be compared with the theoretical curve.(3)To construct an experimental platform and conduct error analysis.The experimental optical path is constructed by selecting an appropriate optical instrument,and multiple sets of scatter contrast and average speckle number scatter diagrams are obtained by changing the pupil size and replacing the measured target.Then,the obtained scatter diagrams are fitted using MATLAB software,and the least squares method is used to analyze the error results to achieve surface roughness measurement.This paper utilizes the statistical properties of speckles to obtain the relationship between speckle contrast,average speckle number,and surface roughness of the target.An appropriate optical instrument is selected to construct the experimental platform,and the experimental results are processed using image algorithm technology to achieve surface roughness measurement.These results will help to realize the measurement of surface roughness of industrial parts and promote the development of the industry.