| Chromatic confocal technique is a kind of confocal spectral sensing technology based on chromatic aberration coding.It was widely applied to measurement of displacement,thickness,surface topographyand sub-millimeter depth biological tissue as it has the advantages of non-contact,high measurement accuracy,fast detection speed,high resolution and simple system.Chromatic confocal technique uses multi wavelength dispersion take place of axial scanning of traditional monochromatic laser confocal measurement,which has natural advantages for dynamic monitoring of objects with continuous changes in height or thickness.However,in the process of measuring thickness and surface topography using chromatic confocal technique,there are still many problems,such as the design and optimization of measurement systems,thickness measurement errors,and surface topography measurement errors.To address these issues,this paper discussed the design and construction process of a fiber optic chromatic confocal measurement system,providing guidance for system design and optimization.The established system was used to monitor the evaporation of a sessile water droplet evaporating in different environments,and a spherical cap model was proposed to correct the thickness measurement error caused by the lensing effect of sessile water droplet,providing a method for solving the problem of thickness measurement error.Based on the sessile water droplet evaporation monitoring system,a two-dimensional electronic control scanning module is added to measure surface topography.The measurement errors such as optical artifacts,surface tilt,and height measurement errors in surface topography measurement have been studied and analyzed,and algorithms were proposed to to correct them,providing strategies for solving the problem of surface topography measurement errors.These research are of great significance for expanding the application of chromatic confocal technique,developing new dynamic monitoring techniques for thickness,and developing high-precision surface topography measurement techniques.The main works and achievements of this thesis are explained as following:1.Aiming at the problem of device parameter selection in chromatic confocal measurement system,a confocal spectral model was proposed to study and analyze the impact of optical components such as light sources,optical fibers,and lenses on chromatic confocal measurement system,providing guidance for device parameter selection.Aiming at the problem of low signal-to-noise ratio in the measurement of weakly reflective samples such as glass and water using a chromatic confocal measurement system,APC(Angled Physical Contact)end face optical fiber was used instead of commonly used PC(Physical Contact)end face optical fiber to improve signal-to-noise ratio of the measurement.Aiming at the design issues of dispersion probes in the system,the specific design idea and process of dispersion probes using ZEMAX were discussed,providing a reference for designing and optimizing new dispersion probes.Aiming at the problem of extracting spectral peak wavelengths,a segmented threshold parabolic fitting algorithm was proposed to extract spectral peak wavelengths.This algorithm maintains the accuracy and stability of commonly used Gaussian and parabolic fitting algorithms,and can achieve multi-peak wavelength extraction that is difficult to deal with by commonly used fitting algorithms.After completing device selection and dispersion probe design,a set of optical fiber chromatic confocal measurement system was built.The experimental calibration results show the system has a range of 1.52 mm in the wavelengths range of 435 to 683 nm and an axial measurement accuracy of 0.25μm.The performance of the system is superior to the systems designed by some scholars,indicating that the proposed method can effectively solve the specific problems encountered in the process of building the system.2.A parallel plate model based on wavefront aberration minimization was proposed to correct the parallel plate model based on edge ray tracing.By measuring the thickness of the cover glass and comparing with the results measured by scanning electron microscope,it is proved that the proposed correction method can effectively improve the accuracy of the thickness measurement results.The chromatic confocal measurement system was used to monitor the evaporation of a sessile water droplet evaporating in different environments.A spherical cap model was proposed to based on the parallel plate model for correction of the thickness measurement error caused by the lensing effect of sessile water droplet.The change of the contact angle of sessile water droplet with time was calculated using the spherical cap model,demonstrating the potential application of chromatic confocal technique in dynamic monitoring of liquids.3.Using Lab VIEW,a two-dimensional electronically controlled scanning platform and a spectrometer joint control program for measuring surface topography of objects was developed.The experiments measured the surface topography of coins,concave spherical mirrors,and other samples.Based on the normalized response spectrum calculated by ZEMAX,the optical artifacts,surface tilt,and height measurement errors in surface topography measurement were analyzed.For optical artifacts,a blind area recognition program is set to eliminate them.For surface tilt,the tilting coefficients in the X direction and the Y direction were calculated to eliminate them.For height measurement errors,an error table related to tilt angles and wavelengths can be obtained by measuring a standard sample for correction.These error processing methods have promoted the development of high-precision surface topography measurement technology based on chromatic confocal technique. |
