| 摘要 |
PURPOSE:To enable to find a displacement of a shielding device, by a method wherein an optical system, consisting of a convex lens and two scale targets crossing the optical axis of said lens at right angles, is mounted, and a center line of an excavation plan is irradiated with light to read a position of light on the targets. CONSTITUTION:A convex lens 5 and a first target 6 are secured to opposite sides of a frame body 8, and a second target 7 is attached between the lens 5 and the target 6 by means of regulating means 9 so that it can move in the axial direction of the convex lens. A measuring device 1 is constituted such that a distance between the convex lens 5 and the first target 6 is equal to the focus distance of the convex lens 5, and the targets 6 and 7 are marked with the degrees in a concentric circle. The measuring device 1 is mounted to a rear end of a shielding device 2 to radiate focusing light from a focusing light generator along a tunnel plan outer line 4. In case the plan center line 4 does not coincide with the center line of the shielding device 24, light on each target is displaced in position, and thereby the displacement of the shielding device is found from said displacement in position. |
