Research On High Precision Automatic Measurement Of Free-form Surface

Free-form surface is widely used in aerospace,precision manufacturing,biomedical and other fields because of its high degree of design freedom,excellent optical performance and excellent dynamic characteristics.it is of great scientific research value and production significance to realize efficient and high-quality manufacturing of free-form surface.Automatic and high-precision measurement of free-form surface is the key to improve its production efficiency and manufacturing quality.The surface change of free-form surface is complex and lack of characteristic structure.when measuring the free-form surface,the existing high-precision measurement methods will face the problems that it is difficult to design the measurement path and determine the spatial position and attitude of the parts to be tested.As a result,the measurement process requires a lot of manual operation,and the measurement experience and operation level of operators will directly affect the measurement efficiency and data accuracy.In order to realize the high-precision automatic measurement of free-form surface,a surface shape cognitive measurement method is proposed in this paper.a compound measurement system is constructed by combining large field of view sensor with high precision sensor,and the measuring part is measured quickly by large field of view sensor.the geometric information of the surface shape of the part to be measured is obtained from the large field of view point cloud by point cloud processing method,and the scanning path of the high precision sensor is designed automatically according to this information.Finally,the highprecision sensor is used to sample the measured surface with high precision,and the high-quality 3D point cloud is obtained to realize the high-precision automatic measurement of free-form surface.Based on this measurement method,a systematic and comprehensive research is carried out on the design and construction of composite measurement system,the unification of multi-sensor coordinate system,automatic measurement path planning and so on.The main research contents and achievements are as follows:(1)A multi-axis composite measurement system with the combination of large field of view grating projection and line structured light sensor is designed and built.the grating projection sensor is used to quickly recognize the surface shape of the part to be tested.the line structured light sensor can measure the surface profile of the measuring part with high speed and high precision.(2)The characteristic structure device is designed,and combined with the spatial rigid body transformation theory and optimization method,the unified calibration of the grating projection measurement coordinate system and the linear structure measurement coordinate system is realized,so that the grating projection measurement data can be accurately transformed into the linear structured light measurement coordinate system.(3)A point cloud extraction method is designed,which combines multi-step point cloud denoising method with RANSAC point cloud segmentation algorithm to achieve high performance-to-noise ratio extraction.(4)An automatic path planning method of line structured light measurement based on surface shape cognition is proposed,which can automatically design the threedimensional scanning path of complex surface when the surface model and spatial position and pose of the part to be tested are unknown,and realize the high-precision automatic measurement of the surface of the part to be tested.