Development Of Spectral Confocal Displacement Measurement System

With the rapid development of high-end precision manufacturing industry in China,various high-precision displacement sensors emerge in endlessly to ensure the product performance and quality of products.Spectral displacement sensor is a novel highprecision photoelectric displacement sensor.It establishes a one-to-one correspondence between the focusing distance and the wavelength by optical dispersion,which can measure the surface profile and morphology,and the thickness of transparent materials.It can also achieve more multifunctional measurement through the combination of multiple probes,which has the characteristics of non-destructive,non-contact and fast speed.It is widely used in industries,aviation,medical,semiconductor chips and other fields,and has attracted close attention from scholars at home and abroad.This paper is based on the principle of spectral confocal displacement sensor,the dispersion lens is designed and optimized by ZEMAX.Finally,two sets of optimized point-scanning spectral confocal sensing systems and a line-scanning spectral confocal sensing system are designed and built.The working wavelength range of the dispersive lens of the two point scanning sensing systems is 400～700nm,and the measurement ranges are 3.21 mm and 0.9mm,respectively.With a spectrometer with a resolution of 0.7nm,the measurement accuracy of the dispersion lens with a measurement range of 3.21 mm is better than 7μm,the measurement accuracy of the dispersion lens with a measurement range of 0.9mm is better than 0.6μm.The point scanning displacement measurement system is connected by optical fiber coupler,which has simple structure and is conducive to integration.The graphical interface is designed for the measurement system through python programming,which can display the contour information of the measured object in real time and further product it.The plane mirror,semi-transparent mirror and other objects are used as the measured objects for measurement.The experimental results show that the two point scanning measurement systems are suitable for the measurement of different material surfaces,and the measurement accuracy reaches the design expectation.The point scanning confocal displacement sensor needs to be equipped with a precise two-dimensional displacement platform to obtain the surface profile information of the measured object,and the scanning efficiency is low.The line scanning confocal displacement sensor can obtain the three-dimensional morphology of the measured object through one-dimensional scanning.In this paper,a dispersion lens composed of cylindrical lens and spherical lens is designed by ZEMAX.Its working wavelength range is 500～700nm,the axial measurement range is 1.2mm,and the effective contour length is about 1cm.The linear scanning spectral confocal sensor cannot use ordinary spectrometer for signal processing.Therefore,a signal acquisition system with blazed grating as dispersion element is designed by ZEMAX.Finally,a set of coaxial linear scanning spectral confocal displacement sensing system is built.The plane mirror and semi-transparent mirror are used as the measured objects for measurement.The experimental results show that the axial measurement accuracy of the system is 1.57μm,and the resolution is better than 5μm,and the measurement accuracy is high,which has high practical value.And the system is used to restore the three-dimensional surface morphology of self-made objects.