Research On Fast Scanning Method Based On Laser Spot Tracing For Free-Form Surface Confocal Profiler

With the development of science and technology,the requirements for precision and resolution of optical systems are constantly increasing in various scientific research fields,and various new optical components are constantly emerging.Free-form optical components,which contribute to the development of modern optical technology,can effectively simplify the structure of optical systems and correct the aberrations.Thus,the surface accuracy of free-form optical components directly affect the optical systems' imaging quality and optical performance.However,due to the large degree of freedom,asymmetry,and large inclination angle of the free-form surface,the direction of signal light propagation carrying the surface shape information of the component usually deviates from the optical axis of the system and is difficult to be collected by the objective lens.Besides,for the three-dimensional contour measurement of large-caliber free-form optical components,the overall measurement speed is very slow,so how to quickly and accurately complete the three-dimensional contour measurement of freeform optical components is one of the most challenging and urgent problems in the metrology field.Based on the principle of confocal scanning optical imaging,this dissertation utilize the fast transverse scanning resonant mirror and the strategy of simultaneous lateral and axial motion,proposes a fast scanning method for free-form surface contour measurement.In this dissertation,the hardware assembly and software design of contour measurement system are completed,in-depth analysis of several methods of contour filtering is accomplished.The main contents of the dissertation are as follows:(1)Based on the traditional confocal optical scanning imaging theory,chapter 1 constructs a theoretical model of coherent confocal scanning imaging three-dimensional point spread function(3D PSF).In addition,for the contour measurement of largecaliber free-form surfaces,chapter 1 introduces a kind of spot-tracing fast scanning strategy.The feasibility of the scanning strategy is verified by simulation experiments.(2)In order to realize the measurement functions and performance requirements of the measurement system,we designed the confocal scanning measurement light path,and carried out the hardware selection,assembly and debugging of the measurement system are accordingly.The data analysis and processing methods are studied in chapter 3.Based on the Labview software platform,I completed the design of each software module of the system,which ensures the measurement system can meet the contour measurement functional requirements well.(3)In order to further extract the contour of high-precision free-form surface components,this dissertation studies several typical contour filtering methods which are suitable for the spot-tracing fast scanning method.Traditional Gaussian filter,continuation-based Gaussian filter,cubic spline filter and general spline filter are applied to the noisy free-form surface contours.The characteristics of each filter are analyzed according to the simulation experiment results.(4)A single-point envelope detection experiment in the spot-tracing scanning method was carried out to verify the feasibility of the experiment.In addition,the plane mirror contour measurement experiment,the convex spherical mirror contour measurement experiment and the concave aspheric mirror contour measurement experiment in the point-by-point scanning method and spot-tracing scanning method were carried out respectively.The measurement accuracy and measurement speed of the two scanning strategies are compared.