| In the underground subway and tunnel construction,double shield tunnel boring machine(TBM)shows good capabilities while facing terrain of high rock strength and complex rock composition,so it has become the best choice of TBM now.Pure monocular vision is the most popular way for the real-time pose measurement of the front shield currently,but this method has the disadvantages of low accuracy and poor stability.In order to solve this problem,this paper makes in-depth research in monocular vision’s optical feature point model,software and hardware platform and algorithm of camera calibration,and presents a 6-DOF measurement system combining monocular vision and inclinometer sensors.The feasibilities of the measurement system are validated through computer simulation.Afterwards,for the accuracy verification of the proposed system,the experimental platform which can simulate the position and pose variation of double shield TBM’s front shield is established.Compared with the pure monocular vision system,the proposed system highly improves the measurement accuracy and stability.Besides,the system accuracy is better than 3mm when the measurement distance is from 2.5m to 4m,which can satisfy precision measurement requirements for front shield’s position and pose during excavating process.The main research work and innovations are as follows:1.Analyze the development status of monocular vision for pose measurement and shortcomings of monocular vision system when measuring the pose of double shield TBM’s front shield,make clear the research direction and aim of this paper.2.Design the whole structure of the measurement system for the pose of double shield TBM’s front shield,establish a new feature point model of spatial topology according to the structure scheme,complete the design of the hardware system whose core processor is ARM Cortex-A8,select embedded Linux as software platform,finish the application program which contains many functions such as image acquisition and processing,communications,pose calculation and so on.3.Summarize the common methods of camera calibration in the field of large-scale measurement and their merits and demerits,propose a new method of camera calibration which is based on three-axis turntable.MATLAB simulation results validate the feasibilities of the proposed method,and the experimental platform is built to verify the accuracy of this method.4.Present a new method for the pose measurement of double shield TBM’s front shield combining monocular vision and inclinometer sensors.Study the spot labeling and center extraction algorithm.Besides,a calibration method for the rotation between the inclinometer sensor and the feature point target is elaborated in this paper.Through simulation experiments and the experimental platform,validate and analyze measurement precision of the proposed measurement system. |
