Research On Detection Technology Of Large-aperture Infrared Optical Lens Based On Three-coordinate Measurement

When large aperture infrared lens is widely used in the system of high resolution and high sensitivity infrared camera,to ensure the imaging quality of the system,studying how to realize high precision measurement of large aperture infrared lens is very important.In the field of optical testing,the center thickness,refractive index and curvature radius on both sides of the lens are the four basic parameters which will influence the performance of lens.In the system of infrared camera,the accuracy of curvature radius is one of the most important factors affecting the imaging performance of large aperture infrared lens,and it is measured throughout the entire process of lens production.The common lens curvature radius measuring instruments mainly include spherometer,optical template,profiler and interferometer.At present,the commonly used lens curvature radius measuring methods can measure curvature radius of small aperture infrared lens with a high measuring precision.However,they are generally deficient in measuring range and flexibility when measuring the large aperture infrared lens.CMM has the advantages of generality,large measuring range,high measuring precision,measurement method is simple and flexible,etc.Researching on using CMM to measure the curvature radius of large aperture infrared lens have significant application value,for it can make up the deficiency that the present common curvature radius measurement methods have.Firstly,the infrared optical lens curvature radius measuring method which is based CMM is discussed from four aspects of content in this paper as follows: the selection of measuring probe,the clamping of the lens under test,establishment of the measurement coordinate system and the choice of sampling strategy,and a kind of curvature radius measurement scheme based on “three-ring sampling” is developed.Secondly,according to the CMM curvature radius measurement principle,a measuring standard deviation estimated formula of the method is deduced by using the theory of error,analyzing the source of measurement error,and summarizing the factors which affect the accuracy of measurement.Besides,the measuring range and precision of the method are analyzed by means of MATLAB.Finally,the feasibility of the “three-ring sampling” measurement scheme and the correctness of the standard deviation estimation formula are verified through the experimental measurement of the infrared lenses whose aperture are 160 mm and 280 mm respectively.The results show that CMM can measure curvature radius of large aperture infrared lens(?>200mm),and the minimum standard deviation of the measurement can reach micron scale.The size of the lens,kinds of the sampling strategy,times of the measurement and the measuring accuracy of CMM are the main factors that will affect the accuracy of the measurement,and because the standard deviation estimated formula can reflect the impact of these factors,it can provide a theoretical basis for making a reasonable measurement scheme.