Research On Image Reconstruction Algorithm Of Wood Defects Based On Asymmetric Ellipse

In the process of wood growth,there will be holes,decay and other defects due to various reasons,which seriously affect the health of trees,so effective detection of internal defects is of great significance to the protection of trees.Stress wave nondestructive testing technology has been widely used in wood nondestructive testing because of its low cost,easy to carry equipment,high safety,strong applicability and so on.The accuracy of the traditional stress wave imaging algorithm is greatly affected by the number of sensors,and the interpolation range of the existing elliptic space interpolation algorithm is relatively fixed,which is easy to cause large defect area and position deviation of reconstructed trees.In order to further improve the imaging accuracy,a stress wave defect nondestructive testing tomography algorithm based on asymmetric ellipse spatial interpolation is proposed and compared with other ellipse interpolation algorithms to analyze the internal defects of logs.The main work of this paper is as follows:(1)The hardware platform of stress wave data acquisition is established,and the acquisition control interface is built on the computer to realize the control of the beginning and end of data acquisition,the setting of sampling frequency and data storage.(2)in order to improve the reconstruction accuracy,an asymmetric ellipse spatial interpolation method(AETA)is proposed.The algorithm first processes and modifies the velocity obtained by the self-made stress wave detection equipment,and then calculates the velocity value of the ray intersection point and segments the ray according to the intersection point to get the velocity value of each segment.Then estimate the different control coefficients on both sides of the ray,determine the ray influence area,and finally generate the reconstructed image according to the velocity value of the grid element.Using four defect models and three log samples as experimental materials,AETA algorithm is used to reconstruct defects and compared with basic elliptic space interpolation algorithm(BEIA)and weighted elliptic space interpolation algorithm(EBSI).The experimental results show that the results of defect model of AETA algorithm are 4.81%,16.83% and 38.8%higher than those of the other two methods.The log samples increased by 9.55%,11.11% and31.27%,respectively.Therefore,the reconstruction effect of AETA algorithm is better,and the area and size of the defects after reconstruction are more overlapping with those in the model or log samples.(3)the time data of the defect model under 6,8,10 and 12 sensors are obtained by finite element simulation software,and the velocity values are calculated.Three elliptic spatial interpolation algorithms AETA,BEIA and EBSI are used to reconstruct the defect model under different number of sensors.The influence of the number of sensors on imaging and the reconstruction effect of different algorithms are compared and analyzed.The results show that with the decrease of the number of sensors,the defect reconstruction effect becomes worse,and the three parameters and imaging effect of AETA algorithm are better than the other two algorithms.(4)the reconstructed defect image is processed by image segmentation and edge detection in order to reduce the influence of velocity transition region at the boundary between defect and healthy wood on the determination of defect.A variety of imaging algorithms based on elliptic interpolation are compiled by using MATLAB software,and the user interface is established by using GUIDE integrated tools.In the interface,operations such as reading time or speed data,setting wood parameters,selecting imaging algorithms to be used,and displaying reconstructed defect images and ray distribution maps can be realized in a more simple and intuitive way.