Patent GB-937171-A (GB)
Title: Means for indicating alignment or position of mobile machines or appliances especially tunnelling machines
Inventor: COLLINS SYDNEY PATRICK
IPC: G01C7/06
Filed: 1960-08-31
Abstract: 937,171. Optical aligning apparatus; mirror mountings. EDMUND NUTTALL & CO. (LONDON) Ltd. June 19, 1961 [Aug. 31, 1960], No. 30053/60. Class 97 (1). A device for indicating the alignment of a machine or appliance which is driven along a predetermined path comprises a reflector mounted on the machine or appliance so as to reflect on to a screen also mounted on the machine or appliance a beam of light, which is projected towards a point on the predetermined path or is projected parallel to that path, whareby the position of the light spot on the screen provides an indication of the alignment of the machine or appliance. The invention is described as applied to a tunnelling shield which is advanced by stages into the earth by the operation of thrust jacks, the earth being progressively removed from the front of the shield. As shown, light projected parallel to the central axis of the tunnel is reflected by an inclined mirror 11, Figs. 5 and 6, through a target screen 12 to a mirror 13 and thence via mirrors 14, 15, 16, 17 and 18 to a viewing screen 19 provided with a graduated scale. Any deviations of the tunnelling shield from alignment with the tunnel axis will be shown up by movement of the light spot from the zero point on the screen 19. The mirrors and screen are mounted on a frame 22 suspended from the tunnelling shield by horizontal crosspieces which are attached to the frame and engage in arcuate slots 24 whereby the frame is adjustable circumferentially so as to compensate for any angular displacement or rolling of the shield itself. Such angular adjustment is effected by operation of a rack and pinion 25, 26, Fig. 6, and correction effected by means of a liquid-containing U-tube 29, to the liquid level of which a mark on the frame is brought. The light beam may be projected from a target box having a cruciform slot and one quarter of its face in the form of a coloured transparent plate. In this case, the target screen 12 may also have a cruciform slot of similar size to the slot in the target box and a diagonal square opposite to that of the target box in the form of a transparent coloured screen. When the tunnelling shield is correctly aligned, the viewing screen will then show a white image of cruciform shape but any deviation from such alignment will reveal a coloured strip or strips on the viewing screen. Alternatively, the light may be projected from a target box having a cruciform slot in an otherwise opaque screen, and there is mounted, on the tunnelling shield, a transparent target including a coloured transparent cruciform strip. The mirrors may be mounted on the frame as shown in Fig. 7, in which the mirror backing plate 30 is held to the frame by screws 33, there being interposed between the backing plate and the frame a soft rubber cushion 31 and, if desired, copper tube spacers. The mirror 34 may be attached to the backing plate 30 by aluminium clips 35, screws 33 and hard rubber cushions 36, Fig. 9. In order to guide the machine or appliance along a curved path, a fixed target or light source is provided at 51, Fig. 13, and between this and the mirror 54 on the appliance 53a there is a target, which is movable between ' positions such as 57a and 57b by traversing gear provided on the appliance so that the light spot is projected always to fall on the zero point of the viewing screen when the shield is correctly aligned. Another method of aligning the tunnelling shield with its circular path is described and involves the use of two light sources which subtend a constant angle at any point on the major arc of the circular path, there being interposed between the light sources and the mirror a screen which may be opaque with two slits or may be transparent with two coloured strips, the distance apart of the slits or strips subtending the same angle at the viewing screen as the light sources. This screen is movable until the two light beams emitted and passing through the slits or strips in the screen coincide on the viewing screen. In this case the position of these coincident images relative to the zero point on the viewing screen indicates any variation in alignment of the shield.