Design Of A High Precision Non-contact Detecting System For Aspheric Surface

Because of some incomparable features of the aspheric surface such as greater design freedom,the convenience of reducing the system structure and the ability of reducing the aberration,the aspheric surface is more widely used in the optical design.However in our country,the development of high precision and non-contact aspheric testing system is relatively backward,which limits the further popularization and application in minor enterprise and colleges.In order to solve this problem,this paper presents a new method based on laser scanning for measuring the aspheric surface.Scanning the outline of aspheric surface by thin laser beam to obtain aspherical surface shape curve.The work and innovation of the paper mainly include the following aspects:1、Analyzing the merits and drawbacks of various kinds of aspheric measurement system,and considering the operational environment,the actual demand and other factors,choosing a laser scanning measurement scheme at last.The paper analyzes the structure of laser scanning measurement scheme in the past,and proposes a scheme which can increase the measuring range of the system and reduce the complexity of the system by adding a mirror in the optical path and being driven by a straight line and a scanning mechanism.2、In the previous laser scanning,angle measurement is performed by measuring the position of the reflected light beam on the CCD.The size and precision of CCD limits the accuracy of the measurement.In this paper,making the light beam in the center of PSD to measure the angle is put forward for the first time,which improves the measurement accuracy of the system.3、Designing the optical path and selecting suitable optical devices based on the proposed scheme.In LightTools,the modeling of optical path is finished,which is in order to ensure the positions,parameters of each optical elements in the optical path and the range and precision of the scanning mechanism.By analyzing the simulation data,we find that a shrinking beam lens is needed to join the optical path.Parameters of the lens is set according to the simulated data in LightTools.And the shrinking beam lens is optimized in CODEV.4、The mechanical structure of shrinking beam lens and fixed components of reflector is designed.The paper has assembled and debugged the each part of the optical devices after they are machined,chosen suitable aspheric surface to carry out system test,and collected the data of the linear displacement,rotation angle and PSD detection.5、To process the collected data,using iterative algorithm to reproduce the shape of the aspheric surface which is measured.The results are compared with the theoretical results to analyze the measurement accuracy and the causes of error.