In-process measurement of the orientations of fibers and the moisture contents of wood by using near infrared spectroscopy

木材被广泛用于不仅保持细胞结构，而且保持其庞大形状的状态。近红外光谱(NIRS)可以作为一种很有前途的技术来分析这类材料的物理状态和化学成分。木材含水率和纤维取向的在线测量是木材内控加工系统中不可缺少的信息。利用带有探测器的近红外激光光源，进行了以下实验：(1)测试了不同水分含量的样品的透射光功率。结果表明，透射光随含水率的增加而增大。(2)考察了不同取向纤维样品的透射光功率。透射光的功率随纤维取向和激光入射角度的不同而不同。(3)测试了不同含水率和不同纤维取向的试件的最大可测深度。现在，为设计具有足够输出的仪器提供了数据。讨论了最佳波长的选择标准。当使用光谱的二阶导数时，可以得到更好的结果。

Wood is widely used in a state where not only cellular structure but also its bulky shape is retained. Near infrared spectroscopy (NIRS) may be called for as a promising technique to analyze the physical state of such materials as well as the chemical composition. This study deals with the inprocess measurement of the moisture content and the orientation of fibers, which are the indispensable information in the nemerically controlled machining system for wood.1. By the use of a near infrared laser light source with a detector, the following experiments were carried out.(1) The power of the transmitted light from the specimens with various moisture contents was examined. It was revealed that transmitted light increased with increasing moisture content.(2) The power of the transmitted light from the specimens with various orientations of fibers was examined. The power of the transmitted light varies characteristically with the orientation of fibers and the angle of incidence of laser beam.(3) Maximum limit of measurable depth of the specimens with various moisture content and orientations of fibers was examined. Now, the data to design the instrument with enough output is available.2. The criteria for the selection of the optimum wavelength were discussed. The better result is obtained when the second derivatives of a spectrum are used.