The Design Of The Optical Axis Measurement System Based On The Characteristics Of Optical Nodal Point

In recent years,optical instruments have developed rapidly,which are widely applied in various fields such as precision detection,military weapons.After the optical system is installated and adjusted,the optical axis needs to be measured to determine the actual position,thereby ensuring the consistency of the optical axis from each mechanism.If the measured optical axis is inconsistent with the actual optical axis position,the centering error will be generated,and the imaging performance will be reduced in the subsequent application of the optical system.Therefore,a method to determine the actual position of the optical axis is proposed in this dissertation.Currently,the actual position of the optical axis is determined according to the measurement of the centering error.Firstly,the existing measurement methods of centering error are investigated,and the advantages and disadvantages of the existing methods are analyzed.On this basis,according to the definition of the optical axis as well as the characteristics of optical nodal point,the line of the nodal point is taken as the optical axis to determine the working principle of the optical axis measurement system.According to the dynamic optical theory,the dynamic optical axis measurement theory based on the characteristics of optical nodal point is researched.When the optical system rotates around the equivalent nodal point at a small angle,the position of the image point remains unchanged;when the object point is located at infinity,the equivalent nodal point coincides with the image nodal point,so that the position of the object nodal point and the image nodal point of the system under test can be determined respectively.The connection between this two points is the optical axis.The datum coordinate system,the nodal point coordinate systems,and the object image coordinate systems are established,and the dynamic optical axis measurement mathematical model is derived by combining the homogeneous coordinate transformation matrix.The composition of the optical axis measurement system mainly includes the following three parts:collimator,rotary table,and microscopic imaging system.The error model of each part is calculated by applying the theory of the small displacement torsor,which provides the basis for the error analysis of the optical axis measurement system.For the system under test with a aperture less than 200mm and a focal length range from20mm to 200mm,the optical design and analysis on the collimator and the microscopic imaging system of the optical axis measurement system.The collimator provides an infinite target for the optical axis measurement system and a reference for the calibration of the initial datum axis.Through the optimization design,an off-axis Newton automatic collimation with a focal length of 2000 mm and the aperture of 200 mm is obtained.To improve the judgement accuracy of the position change of the image point,it is necessary to utilize the microscopic imaging system to amplify the image of the system under the test.In order to meet the demands of different working distance of the system under test,it is necessary to implement a long working distance design for the microscope system.Through the optimization,two optical designs with working distances of 200mm and 100mm,and vertical magnification corresponding to 3~x and 6~x microscopic are obtained..Finally,two optical systems are selected to analyze the accuracy of optical axis measurement based on the characteristics of optical nodal point,and the eccentricity measurement accuracy is less than 10".Then,the optical axis measurement experiments of two optical systems are carried out,and the position coordinates of the optical axis in the reference coordinate system are calculated according to the mathematical model of dynamic centering.It can be seen that the optical axis measurement system based on the characteristics of the optical nodal point provides a new method and mentality for the measurement of the optical axis.