颗粒磨圆度计算中棱角关键点的优化选取

磨圆度是在介观层面上描述颗粒轮廓形状的重要参数，它定量描述了颗粒棱角对颗粒轮廓的影响。现有的磨圆度计算方法，不能准确识别颗粒轮廓中的棱角，而且计算量较大。因此，为了提高准确性，减少计算量，本文提出一种优化选取方法用于选取颗粒轮廓角的关键点。首先，将颗粒轮廓变换为极坐标展开曲线，再利用极小值点对曲线进行分段，并使用傅里叶拟合算法对分段后的曲线拟合。其次，选取拟合后轮廓中的凸部位，并依据凸部位的突出程度，挑选出包含棱角圆的凸部位。最后筛选凸部位中用于拟合棱角圆的关键点，并计算出棱角圆的半径用于计算磨圆度。本文使用K-S标准粒子板和其他学者的研究结果对算法进行了验证，实验结果表明，优化选取方法计算出的棱角圆数量的准确率和磨圆度分类的准确率均达到了100%。本文还进一步分析了使用平均滤波算法对颗粒轮廓进行平滑时，不同的滤波参数对轮廓分段的影响，并给出了较优的参数选取范围。

Optimal Selection Algorithm of Key Points of Corners for Calculating Particle Roundness

Roundness is an important parameter to describe the shape of particle contour at the mesoscopic level, and it quantitatively describes the influence of particle corners on the contour. The existing roundness calculation method can not exactly recognize corners of particle contour, and involves a large amount of calculation. To solve these problems, in this paper an optimal selection algorithm is proposed to select the key points of corners of the particle contour. Firstly, the particle contour is transformed into a polar coordinate expansion curve, then the curve is segmented by using the minimum points, and the segmented curve is fitted by using the Fourier fitting algorithm. Secondly, the convex parts in the fitted contours are selected, and those containing the corner circles are selected according to the convexity of the convex parts. Finally, the key points used to fit the corner circles in the convex parts are selected, and the radiuses of the corner circles are figured out in order to calculate the roundness. In this paper, K-S standard particle chart and other scholars'' research results are used to verify the algorithm. The experimental results show that the accuracy of the number of corner circles calculated by the optimization selection method and the accuracy of roundness classification have both reached 100%. Further more, this paper is analyzed the influence of different filtering parameters on contour segmentation when using average filtering algorithm to smooth the particle contour, and the optimized parameter selection range is also given.