| With the development of urban rail transportation,the safety of the tunnel condition monitoring is very important,and crack is one of the main diseases tunnel.The traditional tunnel detection technology cannot get cracks depth information,and it is difficult to distinguish the interference problems such as oil stain,water damage and other interference problem.In this thesis,the three-dimensional measurement technology of structured light is used to detect tunnel cracks.By obtaining the three-dimensional information of cracks,the reliable detection of tunnel cracks is realized.A projector was used to project sinusoidal coded grating fringes onto the tested object,and a camera was used to obtain the coded grating fringes of the tested object.After that,phase unwrapping technology was used to unpackage the obtained series of images,and the phase height mapping relationship was used to obtain the three-dimensional information of cracks.In the process of 3D reconstruction of tunnel cracks,it is necessary to calibrate carefully.The principle and process of system calibration of measurement system are analyzed and introduced in detail,and the calibration method of projector is optimized.Finally,the internal and external parameters of camera and projector are obtained.Aiming at the problem of using phase unwrapping technology to unpack images,the phase unwrapping technology of structured light 3D measurement is deeply studied and analyzed.The four-step phase shift method is combined with the least square method,the branch cut method and the multi-frequency heterodyne method to carry out phase unwrapping.The experiment shows that the algorithm combining the four-step phase shift method and the multi-frequency heterodyne method has the highest accuracy.Therefore,in this thesis,a method combining four-step phase shift method and multi-frequency heterodyne method is used to unfold the phase of tunnel crack image,and then three-dimensional reconstruction of tunnel crack is carried out according to the simulation of system calibration data.Considering the length of the tunnel and the non-uniformity of the cracks,several groups of continuous fracture images were taken and spliced by ICP algorithm,and the tunnel cracks were identified by height difference algorithm.The experiment shows that under the influence of oil stains,water stains and other interference factors,the three-dimensional measurement technology of structured light can recognize the three-dimensional information of tunnel cracks,which is of great significance to improve the accuracy of tunnel cracks identification and scientifically guide the maintenance and maintenance of tunnels. |
