A monocular vision and inclinometer combined system for 6DOF measurement of double shield TBM

In order to detect the 6-DOF motions between the two shields of double shield tunnel boring machine (TBM) during excavating process, this paper presents a 6-DOF measurement system combining monocular vision and inclinometer sensors. This technique extends the traditional monocular vision method by adding two inclinometer sensors on the camera and the feature point target of the monocular vision system respectively. Combined measurement model of the system is established and a weighted optimization solution is presented with linear estimation as iterative initial value. A calibration method for the rotation between the inclinometer and the feature point target is elaborated. Through Monte Carlo simulations and comparison experiments of spatial coordinate measurement with total station, the feasibility of the measurement model is validated and the measurement accuracy of the system is evaluated. Compared with the pure monocular vision method, the proposed method greatly improves the measurement accuracy.