Research On Reconstruction Of Complicated Surface Based On A Few Scattered Points

CMM is the main measure instrument in the reconstruction of complicated surface.For the parts which have the irregular cross-section or concave aperture,it can only get a small amount of scattered data with CMM.How to reduce the error between numerical model and the physical model is one of the difficulties in the digitization of complex surface.Reconstructing of complicated surface based on a few scattered points,it is necessary to reduce points,and to construct the smooth surface which accord with the physical model,it's very important for the precise measurement of data and the method of surface reconstruction,or the surface is not smooth or have great difference with physical model.The methods of reconstruction of complicated surface based on a small amount of scattered data points were studied in this dissertation,one method was that data will be directly used in the reconstruction,and then make inspection and correction of model by automatically check,enable the model reach accuracy.And the other is to get the data corrected using probe radius compensation,then to reconstruct.The main contributions of the dissertation were as follows:1.Data pre-processing technologies such as singular points elimination,data densification and radius compensation were studied.2.The fundamental theory of surface reconstruction was discussed which led to the finding that there were some characteristic in Bezier,B-Spline and NURBS.So NURBS were chosen as the fundamental methods to achieve surface reconstruction, and analyzed the theory and method of curve and surface smoothness.3.The correlative theory of NURBS curve and surface reconstruction was introduced.It presented methods to interpret NURBS curve and surface,including the parameter of data points,confirming of knot vectors,computing basis function and control points,as well as the modification of NURBS surface.4.Taking the reconstruction of impeller for example,previous two methods were applied to reconstructing three-dimensional model,quantitative calculate and analyze of reconstruction surface error,and corresponding colorized error charts and error distribution charts were presented.