Study On Key Techniques Of Ultrasonic Automated Inspection For Curved Surface Parts

Ultrasonic non-destructive inspection was widely used in products all-sided quality control. For the freeform surface parts, how to improve precision, efficiency and the level of automation in ultrasonic inspection is a very important problem. Combined with the actual requirement in the ultrasonic automated inspection, some key techniques and algorithms in relation to ultrasonic measurement, surface reconstruction, ultrasonic inspection path planning and three dimensions ultrasonic surface imaging are systematically studied in this dissertation.In chapter 1, the background of the research work and important significance of the dissertation were discussed. Some crucial techniques involved with the research project, such as surface measurement, surface reconstruction, ultrasonic inspection and etc., were analyzed. The realization blue print of the ultrasonic automated inspection system for curved surface part and detailed research contents of the dissertation were given.In chapter 2, firstly, kinematics modeling of the ultrasonic inspection robot was established and its kinematics analysis was provided, then surface measurement method based on ultrasonic distance measurement theory was studied. In the ultrasonic distance measurement of freeform surface whose CAD model is unknown, it is necessary to estimate position and normal vector of each sampling point in advance. To solve this problem, firstly, initial surface which cursory describing the curved surface part was reconstructed, then surface measurement was carried out with the guiding of the initial surface. Based on the initial surface, adaptive sampling path was generated by recursive dividing initial surface using B-spline knots inserting algorithm. It is shown that this adaptive sampling path generated algorithm can increase ultrasonic distance measurement efficiency.In the chapter 3, surface reconstruction method with profiling measurement data was studied. In the B-spline surface reconstruction with interpolation method, the surface's control points will rapid increase if the cross-sectional curves are uneven. To solve this problem, a new surface reconstruction method based on curve reconstruction with curve's re-sampling points was proposed. This method first reconstructs cross-sectional curves with original measurement points, and resample the cross-sectional curves with common knots array; then reconstructs the cross-sectional curves which have the same knots array with the new sampling points; finally, creates the loft B-spline surface with the new reconstructed cross-sectional curves. It is shown that this method can reduce the surface's control points while maintaining surface reconstruction precision.In the chapter 4, path planning methods were studied to improve inspection efficiency. For the surfaces which parametric lines are uneven, inspection efficiency will be slow if use isoparametric method to generate scan path. To solve this problem, a non-isoparametric path generation algorithm was proposed to generate ultrasonic scan path. This algorithm generates nearly arc-length interval inspection points by using nearly arc-length based parametric redistribution method, it can generate more...