基于激光测距传感器的树干横截面轮廓检测

利用声波的传播速度构建声学断层图像,已成为一种有效的木材无损检测方法。在实践中发现,树干横截面形状对林木声学断层成像的精度有显著影响。然而,现有研究都是假设树干为圆形的,导致生成的声学断层图像与实际情况不符。为了精确检测原木、活立木的树干横截面形状,研制了一种基于激光测距传感器的树干横截面轮廓检测仪器。采用滚珠丝杆在树干周围建立等边三角形,并利用步进电机驱动激光测距传感器沿滚珠丝杆移动,检测不同位置上树干表面的样本点与滚珠丝杆间的垂直距离,然后通过坐标平移、坐标旋转等坐标转换方法将样本点的测量数据转换到同一个坐标系,最后利用3次样条插值算法对所有样本点进行曲线拟合,可以方便地绘制出待测树干的轮廓。详细介绍了检测仪器的机械系统、电路系统、软件系统的设计方法,并分别采用近似圆形和不规则形状的原木样本进行了实验。实验结果表明,该仪器绘制的树干轮廓与真实情况基本一致,生成的轮廓曲线长度与树干周长之间的相对误差为0.83%。
Acoustic tomography has been proven to be a promising tool for non-destructive testing of standing trees and wooden materials. While reconstructing the acoustic images of the tested samples, the shape of tree stem cross-section is an important factor that significantly influences the accuracy of the nondestructive examination. There are many algorithms developed to implement the image reconstruction with the flight time or propagating time of the acoustic waves. However, in those algorithms, the tree stem cross-section was usually supposed to be circular, which is not often true. As a result, the images can not be fully consistent with the actual situation. In order to accurately measure the cross-section shape of log or standing tree, an automatic instrument was developed using laser distance sensor in this paper. The profile was divided into three segments, which would be measured in three coordinate systems respectively. Driven by the step motor, the laser distance sensor moved along three ball screws one by one, which corresponded the three segments of the tree stem profile. The distance between the sampling points on the stem surface and the ball screw was measured during the movement process of the sensor. Therefore, by using transformation of coordinate translation and rotation, the raw data was converted into the same coordinate system. Finally, the cross-section profile of the tree stem could be plotted using the cubic spline interpolation algorithm. This paper provided the design of the mechanic system, circuit system and software in details. A log sample with a circular shape and a log sample with an irregular shape were utilized in this study to verify the performance of the developed instrument. The experimental results showed that the profile plotted using this instrument was consistent with the actual situation. The error between the length of the constructed curve and the circumference of the tree stem was only 0.83%