| With the wide application of optical system in military,aviation,civil and other fields,the requirement of lens center thickness is becoming more and more.But most of the thickness of lens center detection in production are still using traditional contact detection method,the contact detection because of the big disadvantages such as low accuracy,human factors,has been unable to meet the needs of the lens to detect the thickness of the center.Developing a non-contact,non-invasive,fast response of lens center thickness measuring system is of great significance.The main research contents of this paper are as follows:In this paper,the laser triangulation method is used to measure the thickness of lens center.Firstly,based on the principle of laser triangulation,the measuring scheme of the lens center thickness of the direct-facing double CCD laser triangulation method is determined.The theoretical accuracy analysis of the measurement system is completed according to the system measurement scheme.Secondly,according to the design requirements of the measurement system,the required devices are selected to determine the optical structure and mechanical structure of the system.The overall structure of the system,lens clamping structure,camera clamping structure,laser clamping structure and shell are designed.The software of lens center thickness measurement system is designed based on Microsoft Foundation Class（MFC）to realize fast data processing.On this basis,the checkerboard calibration board is used to complete the installation and calibration of the system.Then,the scattering spots on the surface of the lens are simulated,and the standard deviation,variance and range of the extraction results of different spot centering algorithms under different salt-and-pepper noise coefficients are analyzed.The gray center algorithm with better stability is selected as the core algorithm of the system.Through a large number of experiments,the effects of laser wavelength,lens material and measurement environment on the scattered light spot on the lens surface are studied.It is found that 635 nm laser can measure the thickness of K9 material but not quartz material,and 405 nm laser can measure the thickness of quartz material but not K9 material in the ultra-clean chamber.It is also found that 405 nm laser can form a scattering line segment in K9 material.A thickness measurement method based on scattering line segment is proposed,and the thickness measurement of transparent plate is completed through theoretical analysis and experimental verification,which shows the feasibility of the method.Finally,the center thickness of the lens with different surface types and different materials is measured by using the lens center thickness measurement system with different wavelength laser.The measurement range of the system is 1-10 mm,and the standard deviation of measurement is less than 0.01 mm,which meets the tolerance requirements of the lens center thickness.The measurement errors caused by laser energy,beam aperture,image processing algorithm and lens tilt are analyzed. |
