Research On The Application Of Laser Tracker In Measurement Of Large Aspheric Mirror

Large aspheric mirror with its excellent optical properties,has been applied more and more in astronomical observation,space target recognition and other fields.In the grinding stage of large aspheric mirror manufacturing,the profile measurement method is usually used for surface detection.Limited by the range of measurement,it is too difficult for the traditional CMM(Coordinate Measuring Machine)to meet the requirement of large aspheric mirror.However laser tracker has a lot of advantages in the large scale testing,such as large measurement range,fast response,and providing in-position measurement which could effectively avoid the risk of moving large mirror.There are obvious advantages for laser tracker in the detection of large aspheric surface.Researching on the application of laser tracker in the measurement of large aspheric surface,to increase the efficiency in the grinding stage testing and improve the accuracy of the laser tracker,meeting the requirement of the large diameter aspheric mirror surface detection from the forming stage to rough polishing stage and providing guidance for further processing.Furthermore,the technique would achieve the goal of large aspheric mirror in-situ measurement,which will effectively improve the detection efficiency,and avoid the risk of transport.This thesis focuses on researching the application of commercial laser tracker in the measurement of large aspheric mirror grinding stage,and the error distribution of the laser tracker detection system has been analyzed,especially the angle errors,and a method to correct the angle errors is proposed.By calibrating angle error and polynomial fitting,the distribution of laser tracker's angle measurement error can be achieved for calibration.The main research includes the following aspects:1 The system structure of the laser tracker are investigated,and it's working principle is also described.The influence of angle error in the vertical detection system is discussed.The systematic error of the laser tracker has been analyzed.And the influence of different errors on the measurement accuracy is discussed,and error analysis model is established.2 Based on the analyzing of angle error of the laser tracker in the vertical detection system,a method to correct the angle errors is proposed.By calibrating angle error and polynomial fitting,the distribution of laser tracker's angle measurement error can be achieved for calibration.The sampling scheme in the calibration experiment is discussed;two kinds of sampling method are put forward to calibrating different frequency angle error.And the influence of sampling position error and random error in the calibration experiment is discussed.A vertical detection platform is built to measure the laser tracking error,and the distribution of the angle error can be obtained,using S polynomial fitting and inverse solution.3 The automatic detection technology of large aspheric mirror,using the laser tracker in the grinding stage of is studied.The two-dimensional translation mechanism is designed and developed to realize the automatic tracking of the SMR(sphere mounted reflector,SMR)by the laser tracker.The correlation between the tracker and the two-dimensional transform system is developed,to achieve the automatic detection of the large aspheric mirror by the laser tracker.Through the experiment,the error of position caused by the angle errors is acquired.In an 4m aperture mirror detection,the result of the laser tracker are consonant with non-contact probes by calibration.The results show that the root mean square deviation is less than 10%.