采用视频引伸计对试样进行轴向拉伸试验时，通过跟踪试样表面两根标线的移动来计算标线之间的距离变化，从而得到试样的拉伸变形。当拉伸时产生非拉伸方向的移动或夹具与试样打滑时，传统标线检测方法会丢失要跟踪的标线、或者偏离标线，引起测量误差。本文在测量材料微应变性能时，采用快速归一化互相关算法对标线进行跟踪，提出了1/8降采样方法来加快矩形框跟踪速度，达到跟踪的实时性要求。同时本文采用双曲正切函数拟合得到亚像素边缘点，在试样表面检测标线边缘，从而完成标线距离的测量。最后本文设计了软硬件系统。实验证明，本系统在保证测量实时性的前提下，实现了亚像素边缘检测。测量最大偏差不超过0.005 mm。%The video extensometer tracks movement of two marked lines on surface of the specimen and calculate the shifted distance of the marked lines in the axial direction tensile experiment. So the displacement of the specimen are derived. During stretching movement in non-axial direction or the skid between the specimen and the fixture will be generated. The traditional line detection method will be failed to track marked lines or deviate from marked lines which will cause test error. In this paper,fast normalized cross-correlation algorithm is used to track movement of marked lines when measurement micro-strain properties of the material. Down-sampling is proposed to speed up tracking sample rectangles to meet requirement of real-time measurement. Furthermore the hyperbolic tangent func⁃tion is used to fit sub-pixel edge points in this paper. And detected edges of marked lines to achieve the measure⁃ment of distance. Hardware and software systems are designed. Experiments show that this system achieves the sub-pixel level edge detection ensuring real-time measurement. The absolute maximum error is less than 0.005 mm.
展开▼
