Displacement And Strain Monitoring Method Based On Digital Image Processing Technology And Feature

As the important contents of the structural health monitoring (SHM), thereare many methods developed on structural displacement and strain monitoring.However, many limitations should be considered and solved, such as the sensorsshould be fixed on the surface of the structure using the sensors-based method,which may not always work for a real world project because of the installationlimitation. Furthermore, the wired sensor-based monitoring method needs manysignal transmission lines. Although the wireless sensor-based monitoringmethods don't need signal transmission lines, the data signals are vulnerable toenvironmental interference; the measured data are often incomplete and mingledwith obvious noise. The problems of the current digital image processingtechnology based monitoring methods are, the sections of the mainstream targetshave directional characteristics; the structural two-dimension displacement,three-dimension displacement and strain monitoring are studied, respectively; themonitoring system's calibration technology is quite complicated. So thedisplacement and strain monitoring method based on digital image of circulartarget and feature is proposed, in order to solve the above deficiencies.In the vision plane, the structural displacement and strain monitoringmethod based on the digital image of target, that is, the structural two-dimensiondisplacement and strain monitoring. In this method, the circular pattern andcentroid are chosen as the target and image feature, respectively. And then, thedigital image preprocessing, digital image binarization, mathematics morphologyoperator-based image edge detection, further de-noising, image edge finepositioning and image centroid fitting are used to process the target image andextract the image feature. Visual monitoring system calibration based on theknown calibration board is proposed. The structural two-dimension displacementand strain are monitored using the image feature and the system resolution.Finally, the simulation and simple real experiment of displacement and strainmonitoring are carried out. The effectiveness of this method is verified.Out of the vision plane, the structural displacement monitoring methodbased on the digital image of target, that is, the structural third dimension displacement monitoring. In this method, the diameter, which doesn't go throughthe mathematics morphology operator, is chosen as the image feature. Thepolynomial is chosen as the form of fitting equation. And then, the change ofmonitoring distance is calculated by extracted diameter and fitted polynomial;the third dimension displacement can be obtained. Moreover, the influence ofmonitoring environment to this method is researched, and the prerequisite of thismethod is given.For the second story of four-story frame structure, the two-dimension andthe third dimension displacement are monitored and tested, respectively. Thefeasibility of the proposed method is verified by this experiment. Moreover, thefactors which can affect the precision of the two-dimension displacementmonitoring method are analyzed; the system error which can affect the thirddimension displacement method is discussed. Finally, the selection strategy ofeach factor is given for practical application.