Study On Key Problems Of Automated Ultrasonic Inspection For Curved Surface Composite Parts

Nowadays ultrasonic non-destructive inspection method is widely used for detecting internal flaws in materials and very significant in products all-sided quality control. With large use of parts of complex surfaces in many fields such as aviation, shipping, automobile and medicine, how to design an ultrasonic detection system with flexibility, high precision, high efficiency and acceptable cost is a frontal research to realize automated ultrasonic inspection for the complex surface parts in recent years. Combined with the actual requirements in the automated ultrasonic inspection and its realization scheme, some key problems and algorithms in relation to automated such as dynamic modeling, ultrasonic inspection trajectory planning, the loclization of template in ultrasonic inspection for multi-parts and sensitivity compensation and wave tracking in various thickness of curved surface parts 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, dynamic modeling, ultrasonic inspection trajectory planning, trajectory reliability of multi-parts based on testing templet and sensitivity compensation and wave tracking in various thickness of curved surface parts and etc. In finial part of this chapter, detailed research contents and chapters arrangement were given.In chapter 2, the kinematic equation of ultrasonic inspection system was presented and its dynamic modeling was set up. Firstly the 5-DOF automatic ultrasonic system for curved surface work-pieces was treated as the research subject, kinematic was analysed by using D-H denotation and transfer matrices. The direct and inverse solution was given.Then the recursive relation of the velocity and joint's force between each link of ultrasonic system was deduced. Finally the dynamic modeling of ultrasonic inspection system was set up by Newton-Euler recursive method.In chapter 3, the trajectory plannning in ultrasonic automatic inspection for curved surface work-pieces was studied. According to the features of ultrasonic inspection for curved surface work-pieces, planning the trajectory of the inspection system rightly was key to realize the ultrasonic inspection for flaws. Firstly, the methods of measurement,reconstruction and sampling points generation for curved surface work-pieces was given. Then onsidering the dynamic characteristic of ultrasonic inspection quintic polynomial and 4-3-4 polynomial were respectively adopted to optimize run time of the trajectory of inspection system to solve the point to point and continuous trajectory between points with the constraints in kinematics and dynamics. The method guaranteed the ultrasonic detector to keep stable and rapid to acquire the signal. Finally, experiments showed the validity of algorithm for trajectory planning, which is also the according to improve the performance of ultrasonic inspection system.In chapter 4, the loclization of template in ultrasonic inspection for multi-parts was studied. One kind of graduation match localization algorithm was proposed: firstly the coordinate whose origin was surrounding box's center was established on both testing work-pieces and template separately to make the orient of testing work-piece to trend the template one. Then the center of mass matching was used to cause actual pose of testing work-piece to tally basically with the template. Finally the final localization was completely realized through the entireness mass matching, in which the shortest distance from the space point to the curved surface was searched. Finally all levels of match precision were analyzed through the simulation and the C scanning example was given to confirm this graduation match localization algorithm feasibility. This algorithm can be also applied in the other surveying domains beside ultrasonic inspection.In chapter 5, the sensitivity compasation and waveform tracking in ultrasonic inspection for curved surface workpieces with varying thickness was studied. For the difficulties in sensitivity adjustment of automated ultrasonic inspection caused by the Surface-based composite materials for the workpiece with high decay rate and uneven thickness changes, the principle of ultrasonic C Scanning for workpieces with varying thickness and sensitivity compensation were firstly introduced. Then the method based on BP NN was proposed to access the mapping between the sensitivity of ultrasonic inspection and the surface locations. The method was used to the real-time control and compensation of sensitivity and applied to propose an algorithm to track the bottom waveform of ultrasonic inspection. Finally, scanning examples were given to validate the method satisfy the inspect needs, which was greatly increasing the automation and accuracy of ultrasonic inspection for similar workpieces.In the chapter 6, main results and conclusions of this dissertation were systematically summarized; the prospects and study emphases of the future research work were discussed and forecast.