Study On Real Time Measurement System Of Shield Tail Clearance Based On Laser Vision

Shield construction is the most widely used construction method in the construction of subway tunnels.It has been widely used in subway construction due to its advantages of not affecting the normal traffic on the ground and not causing too much influence on the surrounding environment.During construction,the assembly of the segments is completed under the protection of the shield shell.The gap between the inner wall of the shield shell and the outer wall of the segments is called the tail gap of the shield.When the shield machine is advancing forward,the gap between the shield tail will keep changing due to the curvature change of the tunneling route and the fact that the elongation length of each propulsion cylinder is not completely consistent.Too small gap between the shield tail will not only damage the structure of the shield tail,but also cause the tunneling route to deviate from the planned line and cause the project failure.Therefore,real-time measurement of shield tail clearance is very important for the smooth construction of subway tunnel.According to the measurement requirements of shield tail clearance during shield construction,this paper designs a real-time measurement system of shield tail clearance based on laser vision.The main equipment of the system includes image acquisition device,control box,lighting source and computer.Through on-site verification system equipment installation position and after the installation is complete,the system USES image acquisition device inside the camera target area of shield tail clearance for image acquisition,and then using the correlation algorithm and technology of images collected in the key image feature extraction and processing,after calculation will be obtained by the shield tail gap value displayed on the computer monitor of bridge.The main works completed in this paper include:(1)Studied and analyzed the existing shield tail clearance measurement methods and devices,proposed the scheme of shield tail clearance measurement system based on laser vision,completed the selection and design of each hardware part,and carried out the system software design.(2)The image feature extraction and measurement methods of the system are studied,including the extraction method of reference spot and shield tail clearance and the calculation method of shield tail clearance.In order to better complete the extraction of shield tail clearance,this paper applied Mask RCNN network in the extraction of shield tail clearance features.Compared with traditional image processing methods,this method has a better extraction effect on shield tail clearance features.(3)The appropriate imaging of size to ensure the accuracy of image processing to extract the image point when,on this basis,this paper proposes a camera focal length control method based on the oil cylinder stroke feedback,in the target area to be tested object distance changes along with the oil cylinder stroke,by adjusting the camera focal length in the target area to be measured the size of the shield tail clearance imaging unchanged and suitable size.(4)On the basis of(1)to(3),simulation experiment and actual construction site experiment are conducted in the laboratory environment.The experimental results show that the method in this paper is feasible and the measurement error in the site is within 2.2mm.