Design And Experimental Study Of Parallel Chromatic Confocal Measurement System Based On Optical Fiber Bundle

Chromatic confocal technology is one of the optical measurement technologies.Due to its measurement characteristics with no axial scanning,fast measurement speed and high accuracy,it is widely used in industrial measurement fields,such as threedimensional reconstruction,thickness measurement of transparent specimens and so on.However,on the one hand,the traditional chromatic confocal technology is generally a coaxial illumination optical path structure,and the light energy utilization rate and signal-to-noise ratio are low.Therefore,in order to measure the thickness of thin transparent specimens,a chromatic confocal system with non-coaxial illumination is proposed in this paper.The corresponding thickness calculation formula of transparent specimens is derived.On the other hand,the horizontal scanning time of single-point detection is long.Therefore,in order to improve the measurement efficiency,the optical fiber bundle is used as an optical beam splitter in our system combined with line scanning to achieve full-field measurement.And the existing threedimensional reconstruction algorithm is also improved.Finally,according to the noncoaxial illumination technology and the characteristics of the optical fiber bundle,a non-coaxial illumination chromatic confocal detection system based on the optical fiber bundle is established,which not only improves the light energy utilization rate but also improves the detection speed.The experimental results show that the measurement accuracy of the above systems can reach the micron level,and the repeatability is within0.9 μm.The main research contents of this paper are as follows:(1)In order to overcome the low light energy utilization rate and signal-to-noise ratio of the traditional coaxial illumination,a chromatic confocal measurement system with non-coaxial illumination is designed.By changing the angle of the incident light,it is verified that the non-coaxial illumination can effectively solve the problem of signal overlapping.Through the establishment of the transparent specimen thickness measurement model and the derivation of the thickness calculation formula,the light energy utilization rate and signal-to-noise ratio are improved.(2)In further research,the problem of low measurement efficiency of the traditional single-point system is solved by the parallel coaxial illumination optical path structure.It is found by comparison that the horizontal scanning time of the above structure is shortened due to the usage of the optical fiber bundle.Finally,a chromatic confocal measurement system with parallel non-coaxial illumination is constructed by combining non-coaxial illumination and optical fiber bundle.The system has the advantages of high efficiency and high signal-to-noise ratio.(3)Based on the color conversion algorithm,the three-dimensional reconstruction algorithm for existing parallel chromatic confocal technology is improved.The improved algorithm uses the Open CV library to achieve image-stitching and combines the regionprops function of MATLAB to extract centroid and centroid connected areas.Finally,the three-dimensional reconstruction of the “N” character on the back of the one-yuan coin has been carried out,which verifies the high-efficiency and highprecision three-dimensional topography reconstruction capability of the system.