Adaptive Measurement of Free-form Surfaces Based on CMM Double Parameter Directions

A kind of adaptive measuring method for free-form surfaces was put forward based on double parameter directions of CMM. At first, a measurable area was generated by boundary points of the surfaces. Then, a few uniform initial scan lines and uniform initial measuring points of each line topology were automatically generated by the measurable area. A B-spline curves were generated by fitting the initial points that automatically measured by the CMM in the U parameter direction and the locations of next point were adaptively predicted by the end curve curvatures. A B-spline surface was fitted by the initial scan line's point cloud, then the next line positions were adaptively determined by the border maximum curvatures of the surfaces in the V parameter direction, and the scanning lines of U parameter direction were measured adaptively, until measurements were completed. Distribution density of the measuring points was determined by the curvature variation characteristics of the measured surfaces. The larger the curvature of the surfaces, the greater the distribution density of the measuring points and the smaller the curvatures of the surfaces, the smaller the distribution density of the measuring points, which guarantees the important feature points not leaking and avoid the data redundancy. The results of measurement experiments for theoretical curves and surfaces show that the measurement precision may reach μm level. The feasibility of the method was verified by an example of a part measurements. © 2017, China Mechanical Engineering Magazine Office. All right reserved.