GB1496760A - Directional guidance of a movable object - Google Patents

Abstract

1496760 Optical guidance LILLEY-WADDINGTON Ltd 17 Dec 1974 [17 Sept 1973] 43576/73 Heading H4D In the construction of a tunnel 22, Figs. 1, 2, the tunnelling shield 20, advanced by means of hydraulic rams 1-12 is guided by means of a laser beam 30 and a photoelectric target 32 mounted on the shield, the target incorporating a reference point such as to give output signals indicative of the deviation of the incident beam from the point and the shield from its correct position, which signals may be fed to an indicator or used to activate one or more of the rams. The target 32 is mounted on means enabling the correction of any roll of the shield. Fig. 4 shows the target in detail wherein the four square selenium cells or silicon photo-diodes are arranged with their edges abutting and at 45 degrees to the vertical to constitute top (T), bottom (B), left (L) and right (R) detector elements. An alternative arrangement of the detector elements is shown in Fig. 8. The detectors are mounted for horizontal and vertical movement relative to the target plate 36 and shield by horizontal-cursor 38 moving over the plate, and vertical cursor 12 moving along the horizontal cursor. The laser beam may impinge at 52. A transparent screen 60, Fig. 7, carrying radial opaque lines may be placed over the detectors to ensure that as the spot 52 moves further away from the centre of the detector a larger signal is given by the element. The signals from the elements are fed to the valves controlling the rams and also to a C.R.T. display, Fig. 5, wherein symbols 1-12 arranged around the C.R.T. screen represent the rams and the numbered concentric diamonds on the screen represent various distances of the spot 52 from the detector centre. The bright-up spot 54 corresponding to spot 52 indicates that rams 7 and 8 should be actuated to correct the displacement.