Study On Shape Measurement Technology Which Used On Non-contact Laser Ultrasonic Testing

With the rapid development of industry,the application scope of laser ultrasonic nondestructive testing technology is more and more broad.Now,the object of laser ultrasonic nondestructive testing is no longer confined to the work-piece with regular shape such as plane and cylinder.In aerospace,nuclear power and other industrial fields,laser ultrasonic nondestructive testing technology is usually needed to make a series of detection work for curved surface work-piece with free-form surface.In order to solve the problem of laser ultrasonic automatic detection for complex curved surface work-pieces,National Bureau of Quality Inspection has launched the development of automatic detection equipment for curved surface work-piece at high temperature based on laser ultrasonic technology.Under the background of automatic detection system development for complex curved surface part with laser ultrasonic technique,a scheme for reconstructing 3D model of object based on monocular camera with multi contour occlusion technique to extract the object normal vector is adopted in this paper.In this paper,an image acquisition system based on CMOS,lens,automatic turntable and computer is established.The internal and external parameters calibration of the system is completed by using the method of Zhang calibration and mathematical calculation.Automatic collection of multi view image sequence of target object is completed by computer control.The collected image sequence is processed with the method of binarization,denoising filter and removing the small area.And the contour data of the object in the image is extracted.The data of multi angle contour sequence and its corresponding optical center point achieved unity in the world coordinates through coordinate transformation.According to the principle of body intersection methods,approximate 3D model of target object is obtained in Rhino.Theoretical and experimental research on the problem regarding the size of the obtained 3D model based on body intersection method is larger than the target object actual size is carried out.The linear changing principle of model size and distance between optical center and object is obtained.And a reverse reduction method based on scale factor between model size and object actual size to restore the resulting model to the actual size of the target object is proposed.The principle of this method is verified by experiment.The target surface normal vector is extracted from the reduced 3D object model through the point coordinate analysis method.The feasibility of the paper scheme is verified with two objects which shapes are from simple to complex as the experimental objects.In the end,the control problem of the probe scan azimuth of laser ultrasonic testing system based on measured point vector is described.This paper promotes the combination of 3D reconstruction technique and laser ultrasonic nondestructive testing technology.It would solve the problem of probe scanning azimuth,and this provides a basis for the development of laser ultrasonic complex curved surface automatic detection system.