【作者】 李雄兵；

【导师】 周晓军；

【作者基本信息】 浙江大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 超声无损检测方法广泛应用于材料的内部缺陷探测,实现曲面工件的自动超声检测,是近年来国内外超声无损检测领域研究的前沿课题。本文结合曲面工件自动超声检测项目的实际需要和具体实现方案,对系统研制过程中的曲面自动测量、检测路径校验、A波数据压缩以及C扫描图像缺陷识别与评估等关键技术进行了系统深入的研究。第一章阐述了课题的背景和研究的重要意义,分析了曲面工件超声检测、曲面测量等相关技术的国内外研究现状,最后给出了本论文主要的研究内容和章节安排。第二章对超声检测中曲面自动测量方法进行了研究,从机械手运动学建模、声束自动对正和测量点自动规划三个方面系统地介绍了该方法的实现。在声束自动对正的实现中,首先通过实验建立声束入射角与表面波时域特征值之间关系,根据机械手调整前后的二个入射角解算出转动关节需要偏转的角度。在测量点自动规划的实现中利用已测点的三维坐标定量分析曲面曲率的大小,并根据曲率越大测量点布置越密的原理进行测量点自动规划。接着阐述了测量数据经过曲面重建、路径规划生成了超声检测路径的过程。最后通过实验从效率和精度两个方面验证了本章曲面自动测量方法的有效性,并分析了该方法可推广的其他应用领域。第三章对曲面工件超声检测过程中的路径校验问题进行了研究。超声路径规划不当会导致碰撞、水声距不合理的现象,本章给出了一种分级检验方法:首先利用包围盒算法和几何求交算法剔除大量被检对象分离的情况,然后将可能干涉的三维对象正投影到二维平面中,空间碰撞问题就转化为平面碰撞问题,只需计算投影图是否有重叠就可精确判断是否干涉。工程应用验证了该方法的有效性,它也适用于产品装配和数控加工中复杂曲面和圆柱体之间的碰撞干涉快速检查。第四章对超声检测中的A波数据压缩问题进行了研究。将A波数据分解成波形沿、波形和波间距等特征的组合,在此基础上提出了一种基于特征A波数据压缩模型和算法:首先确定波形和波间距的起点和终点,然后根据阈值求解每波形中相邻波形沿的交点,将波形分解成两个或者两个以上的波形沿,最后构造一条最佳直线来拟合波形沿,在实时压缩时可以通过调整压缩参数达到预定的压缩性能指标。构建了压缩算法性能评价指标,通过压缩试验表明该方法能在2%以内的重构误差下达到100以上的压缩比。最后分析了特征压缩的结果在超声C扫描成像和缺陷性质判别中的应用。第五章对曲面工件超声C扫描图像的缺陷识别与评估进行了研究。首先介绍了超声C扫描图像的成像原理及其数学表示,给出了一种C扫描图像缺陷识别与评估的方法和流程。为提高缺陷成分标记的效率,本章采用了一种基于辅助表的区域标记方法,在第一次标记时利用辅助表记录等价标记号,标记完毕后去除重复记录、进行等价分析、补全记录和重新分配标记号,在第二次扫描时修正C扫描图像缺陷标记号并通过试验验证了该方法的有效性;为获得边缘清晰而且轮廓完整的缺陷边缘,提出基于边界元运算的C扫描图像边缘跟踪算法,简化了跟踪过程。第六章对曲面工件自动超声检测系统进行了需求分析,然后介绍了系统的硬件组成。接着从软件工程的角度出发,对系统软件功能进行总体结构设计和详细设计。最后通过检测实例对曲面工件超声检测的基本流程进行了介绍。最后对全文工作进行了总结,并对将来进一步的工作作出展望。更多还原

【Abstract】 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.更多还原