To advance the automated inspection and maintenance of the inner wall of tunnels, an advanced inspection system aimed at regulating traffic was developed. In this inspection system, a guide frame was installed along the tunnel ceiling wall that is above the protection frame built over the road and resembles a gantry crane. The inspection device was fitted with an inspection guide frame (IGF), which stabilized its movement and improved its accuracy. However, as this protection frame moves along the tunnel, the guide frame should have the capacity to avoid convex obstacles such as the duct fan, the lamp and road traffic signs within the tunnel. Therefore, the entire inspection guide frame is made of variable geometry truss (VGT), which makes it possible to suitably alter the shape of the guide frame whenever necessary and pass it through the tunnel. To enable the guide frame adapt to any shape, the inverse analysis method and mathematical interpolation method were applied. The orientation of each frame was reversely analyzed according to the shape of the obstacle measured using the laser range finder (LRF), and the frame’s actuator was controlled simultaneously. We investigated the construction of a system that can perform a series of tasks such as searching for obstacles and positioning, frame shape simulation, frame shape change, inspection of the device and movement. By applying spline interpolation, we managed to practically determine the shape of the guide frame that would avoid obstacles.

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