Patent GB-1036723-A (GB)
Title: Tunnel construction error-detection and indicating apparatus
IPC: G01C15/00
Filed: 1962-01-31
Abstract: 1,036,723. Optical positioning. LONDON TRANSPORT BOARD, and H. C. P. HAVERS. April 30, 1963 [Jan. 31, 1962], No. 3672/62. Heading H4D. [Also in Division G4] Tunnel construction error detection and indicating apparatus comprises a lantern 1, Fig. 1, including a light source 5 and an optical lens system 6, so arranged as to produce a beam of light X, with a cross-section having two sharply defined edges at right-angles, said lantern being arranged to be positioned on a datum line determined by surveying methods and representative of the theoretically correct path of driving the tunnel, a target 2, adapted to be mounted on a movable member 11, arranged to follow the actual path of driving of the tunnel, and including a horizontal and vertical row of light-sensitive elements, 8 and 9 respectively, the arrangement being such that a predetermined number of such elements as energized by the light beam when the target is correctly positioned with respect to the datum line and a greater or lesser number of such elements are energized when the position of the target diverges from the correct position, to produce output signals indicative of the position of the target with respect to the datum line, and means for amplifying said signals to produce an indication of the degree and direction of divergence of the target, and thus of the movable member, from the theoretically correct path of driving of the tunnel. The outputs from the light sensitive elements 8 are fed to transistor amplifiers and are then combined in adder 10 for application to one input of a recording apparatus 4, to actuate a recording pen and indicate the horizontal tunnelling error. The outputs of elements 9 are similarly treated to actuate a second recording pen to indicate the vertical tunnelling error. The movable member 11 may be a shield having an outer shape conforming to that of the tunnel, and being moved forward as the tunnel progresses. The shield 11 may rotate about its axis and give an erroneous tunnelling error indication. To overcome this, level indicators 12 and 13 are provided, and comprise, Fig. 3 (not shown), a widened section 14 of a U-tube 15, containing an opaque liquid 16, e.g. mercury, having an upper surface within the section 14 for small angles of rotation of the shield 11. The liquid is used to obscure light from a source 17 from falling on a vertical column of light-sensitive elements 18. The outputs of the two indicators are respectively combined with the outputs of the two rows 8 and 9, such that the combined, resulting, horizontal and vertical error signals sent to the two recorder pens indicate the respective position errors of the centre of the shield. The distance apart of the elements in the rows 8 and 9 and in the rows 18 are proportioned according to the position of the target 2 and the distance apart of the indicators 12 and 13. So that the horizontal and vertical tunnelling errors may be related to the corresponding position along the tunnel a distance recording means is provided. This may comprise, mounted on a framework which is moved forward as the tunnelling progresses, a spring- loaded arm in constant contact with the tunnel wall. The contacting part of the arm may be provided with a rubber-faced wheel on a caterpillar drive arranged to actuate a distance switch once for each complete revolution. Alternatively the tunnel wall may be formed with ridges on circumferential grooves at intervals which may actuate the switch arm. The switch may cause a movement of one or both of the recorder pens or a third pen may be provided. When a curve is to be followed in the tunnelling, the theoretical change in output from the rows 8 and 9 may be automatically subtracted from the observed changes as the tunnelling progresses, such that only the actual tunnelling errors will be indicated. To give warning when one of the light-sensitive elements ceases to function, alternate elements in, say, row 8 are separately collected and connected to two circuits, between which a differential relay is connected. This relay gives an alarm when the difference between the two circuit outputs is greater than that equivalent of the output of one element. Ammeters may be provided to give an indication in lieu of or in addition to the recording means. During periods of non- tunnelling the light beam X may be interrupted, giving false readings. A master switch is therefore provided at the recorder input, manually or automatically operable.