基于反投影坐标快速算法的木材CT检测系统研究

Wood CT Detection System Based on Fast Algorithm of Inverse Projection Coordinate

针对木材内部结构复杂、不同树种间密度差异大的特点,提出了一种反投影坐标快速算法,基于此算法构建一套木材无损检测CT成像系统。该系统由X射线发射器、等距平板检测器、旋转载物平台和计算机数据采集成像软件构成。以集成材和小径级原木为试验对象,验证反投影坐标快速算法的可行性。首先采集并修正投影数据;其次根据射线源到旋转中心的距离计算出投影坐标值;最后设置滤波函数并与投影数据作卷积运算,重建木材断层图像。结果表明:应用反投影坐标快速算法,使CT系统图像重建工作平均用时缩短至1 s以内,断层图像分辨率达0.052 mm^2,可显示木材内部裂纹、孔洞等缺陷及节子、年轮、早晚材变化等构造特征,验证了该算法应用于木材无损检测成像系统的有效性。

Nondestructive detection for wood is more difficult than that for other materials because of characteristics of wood itself. According to the characteristics like complex internal structure and wide density differences among different tree species,a fast algorithm of inverse projection coordinates was proposed. A wood nondestructive detection and CT imaging system can be structured on the basis of this algorithm. This system consists of an X-ray emitter,an offset plate detector,a rotating carrier platform,a data acquisition and imaging software. Setting glued laminated timber and small logs as test objects,the feasibility of the algorithm was verified. Firstly,the projection data were collected and corrected,then the projection coordinates can be calculated according to the distance from the source to the center of rotation,and the filtering function was set up and used to calculate the convolution operation with projection data. The wood faultage image was reestablished at last. The result shows that this algorithm can shorten the image reconstruction time of CT system to less than 1 s. Its image resolution can reach0. 052 mm2,and it can also show the internal defects such as holes and cracks,and structural features like wood knots,rings,changes between early wood and late wood,which verify the validity of the algorithm applied to wood nondestructive testing and CT imaging system. This system provides a effective method for wood nondestructive detection.