Study On Key Problems Of Automated Ultrasonic Inspection For Complex Surface Parts

Ultrasonic non-destructive inspection methods are widely used for detecting internal flaws in materials. It's a frontal research to realize automated ultrasonic inspection for the complex surface parts in recent years. Combined with the actual requirement in the automated ultrasonic inspection, some key techniques and algorithms in relation to automated ultrasonic measurement, ultrasonic inspection path checking, A-wave data compression and flaw recognition and evaluation of C-scan image 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 ultrasonic inspection, surface measurement and etc., were analyzed. Finial in this chapter, detailed research contents and chapters arrangement were given.In chapter 2, an automated surface measurement method based on ultrasonic was presented, it's key techniques, kinematic modelling,sound beam auto-alignment and measurement points planning, were introduced in details. In sound beam auto-alignment, a relation model between angle of incidence and time-domain eigenvalue of reflect wave signal was proposed. Angles between cradle heads and normal direction of survey point could be figured out according to two associated angles of incidence; In measurement points planning, surface's curvature was analysed by 3-D coordinate of points which were measured, then measurement points were automated planned according to the surface's curvature. Lots of experiments showed the validity of the method from survey ing inefficiency and accuracy, It can also be applied to other surveying domains besides ultrasonic inspection.In chapter 3, path checking in ultrasonic automatic inspection for complex surface parts was studied. Collision and abnormal water depth may occur if inspection path is planned irrationally, a hierarchy method of path checking was proposed. Firstly algorithms of bounding box and geometric intersection were used to remove most cases where components were separated. Then triaxial components which may collide were projected onto diaxial plane. Finally collision interferes were accurately identified according to orthographic projections overlap or not. The engineer application results showed that the method can meet the efficiency and accuracy requirements of the ultrasonic inspection, It can also be applied to the cases of assembly and NC machining, where needs rapid collision detection between cylinder and complex curved components.In chapter 4, A-wave data compression in ultrasonic inspection was studied. A-wave data was disassembled into features such as wave slope, waveform and wave gap, an A-wave data compression algorithm based on these features was presented: Firstly figured out the range of each waveform and wave gap. Then proposed a method to get the intersection points of wave slopes among each waveforms. Finally constructed an optimal line to fit the wave slope. Compression algorithm performance evaluation parameters were provided, engineering applications show that the algorithm based on features is effective, the data reconstruction error is less than 2% even when the compression ratio reaches 100. Finally in this chapter, the applications of compression results in ultrasonic C imaging and flaw property discrimination were introduced.In chapter 5, a method on flaw recognition and evaluation of C-scan image was proposed, imaging theory and mathematical expression of C-scan images was firstly introduced. To improve efficiency of flaw component labeling, assistant table was used to save equivalent label at the first scanning, after some disposal processes to assistant table, such as wiping off repeated records, equipollence analysis, adding records and redistributing labels, c-scan image elements was relabeled at the second scanning, applications testify the validity of the method. To detect clear-cut and intact flaw edge, an algorithm base on edge element was proposed, simplifying the process of tracking edge.In the chapter 6, firstly, the hardware and software components of the automated ultrasonic inspection system for complex surface parts were introduced. Then, system software functions were designed based on software engineer. Finally, a complete inspection example was given.In the chapter 7, main results and conclusions of this dissertation were systematical summarized, the prospects and study emphases of the future research work were discussed and forecast.