Development Of Shield Tail Gap Measurement System Based On Machine Vision

Shield machine is a tunnel construction equipment integrating advanced technology in many fields,such as machinery,electricity,hydraulic,optical,information,and so on.It has the characteristics of fast tunneling speed and high comprehensive benefits.Shield tail gap refers to the gap between the inner wall of shield tail and the outer edge of segment,which is one of the key tunneling parameters of shield machine.In shield construction,shield tail gap changes continuously.If the gap value exceeds the design range,it will increase the propulsion resistance,reduce the tunneling speed,accelerate the wear of the shield tail brush,cause the shield tail seal to fail,and even lead to major safety accidents,like tunnel leakage and ground collapse.Therefore,accurate measurement of shield tail gap is of great significance.Based on machine vision technology,a method of measuring shield tail gap on the basis of prefabricated scale was proposed.A set of non-contact measurement system for shield tail gap was developed according to the requirements of measurement and analysis,and other performance indicators,such as correctness and accuracy.The data acquisition equipment and system control equipment were selected and designed to complete the hardware system construction.With Visual Studio 2017 as the development environment,the C# programming language was used to develop the system software with OpenCV and EmguCV image processing technology to realize the three-layer architecture design.In order to reduce the difficulty of plotting the refabricated scale and improve the calibration accuracy of the system,a portable shield tail gap measurement instrument was designed,and calibration software was developed for continuous and synchronous acquisition of three types of calibration data,including shield tail gap,measurement distance and segment end image.Industrial cameras and laser sensors are used to collect segment end images and measurement distances respectively.Data are processed to realize feature extraction of segment tenon and measurement distance limiting filtering.On this basis,the information of the two is integrated into the image coordinate system of segment end image to realize joint measurement of shield tail clearance.The drawing of prefabricated scale and data self-checking were studied in depth,as well as the solution of minimum shield tail gap and maximum travel difference of propulsion hydraulic cylinder.And the computational model and implementation method were proposed.They are the important theoretical basis of the shield tail gap measurement system.The shield tail gap measurement system was applied to the Tsinghua Yard tunnel project of Beijing-Zhangjiakou high-speed railway.The measurement experiment shows that the data error increases with the increase of measurement distance.And the segmentation principle of prefabricated scale was proposed to improve the measurement accuracy while lowering the workload.Real-time and continuous measurement of shield tail gap were carried out.And statistical analysis results of measured data show that the accuracy of measurement reaches 96.3%,and the maximum absolute error is ±3 mm,and the maximum relative error is 4.1%.They meets the engineering requirements and have a good application effect.Finally,the influence of relevant factors on measurement accuracy was analyzed from 4 aspects: hardware equipment,software algorithm,field installation and external environment,which lays a foundation for the follow-up system optimization and improvement.