Research On Non-contact Scanning Measurement Method Of Optical Surface

With the continuous progress of optical element design and processing technology,highprecision optical products are gradually applied in high-tech fields such as space optics,optical communication,UV lithography and so on.In order to effectively reduce geometric aberration,improve imaging quality and replace the combination of traditional optical elements,the optical system is miniaturized and lightweight.On the one hand,optical products are developing towards higher precision surface shape,on the other hand,they are developing towards microstructure,non rotational symmetry and complex surface shape,which also puts forward higher requirements for measurement.At present,the main methods of surface measurement are scanning interferometry and non-contact interferometry.Compared with other measurement methods,non-contact scanning measurement has the advantages of comprehensiveness,flexibility and nondestructive testing.It is not only suitable for all stages of optical processing,but also suitable for the measurement of optical surfaces with various diameters and shapes.However,at present,the non-contact scanning measurement method has some shortcomings,such as difficult to quickly measure complex curved surfaces,the contradiction between probe accuracy and range,and the system accuracy is affected by platform motion error.Aiming at the shortcomings of the above non-contact scanning measurement,this thesis puts forward the corresponding solutions.A non-contact scanning measurement system with strong universality and high precision is developed.The main research contents of this thesis are as follows:（1）The advantages and disadvantages of the existing non-contact scanning measuring instrument are analyzed,and a non-contact scanning measuring scheme based on planar guide rail technology is proposed,which can be applied to the measurement of complex curved surfaces.In order to reduce the influence of the traditional measurement system based on the poor rigidity of the guide rail and the superposition of the mechanical measurement system.In order to solve the problem of small measuring range of high-precision probe,surface tracking technology is adopted when measuring the curved surface whose vector height exceeds the measuring range of probe.In the surface shape tracking technology,the laser ruler is used as the high-precision displacement sensor for the probe to track the displacement,and the external hardware trigger technology is used to solve the difficulty of synchronous acquisition of multi axis position information and probe data,so as to ensure the accuracy of measuring large vector height curved surface.（2）When measuring the curved surface whose vector height exceeds the measuring range of the probe,according to the two different surface tracking requirements,two tracking schemes are developed: the scheme of using high-precision laser ruler,active tracking and synchronous acquisition technology for measuring conventional optical curved surface;The scheme of using flexure hinge platform and adaptive tracking control technology is used to measure complex surfaces（microstructure array,etc.）with large curvature change and changeable curvature center,which can improve the speed of probe tracking and scanning complex surfaces.（3）For the developed measurement platform,the research on error analysis,off-line compensation and uncertainty evaluation are carried out systematically.The off-line compensation method is used to suppress the influence of motion error on the measurement accuracy.For curved surfaces with different diameters and vector heights,the extended uncertainty of the system is in the range of 50～150nm（2σ）.（4）Based on the principle of multi probe error separation,a new virtual multi probe straightness error separation algorithm is proposed for the straightness error of guide rail,which can separate the straightness error in real time and online,and eliminate the parabolic cumulative error of zero error in the traditional multi probe method.Aiming at the motion error of the turntable,an error separation method of virtual parallel two-point method is proposed to separate the motion error of the turntable in real time and online,which solves the problem of harmonic suppression in the traditional multi-point method.（5）Several optical surfaces: aspheric surface,ellipsoidal surface,microstructure array and unpolished grinding surface are measured respectively.The key technologies such as probe extension,surface shape tracking,synchronous acquisition and error compensation are verified,and the measurement repeatability is tested.The experimental results show that the developed measurement system can meet the measurement requirements of sub micron accuracy of optical surface.