Patent GB-1454537-A (GB)
Title: Machine guidance
IPC: G01C7/06
Filed: 1973-10-12
Abstract: 1454537 Tunnelling machines JOHN MOWLEM & CO Ltd 11 Oct 1974 [12 Oct 1973] 47695/73 Heading E1F [Also in Divisions G3 and H4] A device such as a tunnelling shield which is to be guided along a laser beam has a target attached to it which comprises two screens spaced along the beam path. The front screen has an aperture on which the beam is incident, and the aperture has light detectors or guides spaced around it; the beam is restricted by passage through the aperture, and strikes the rear screen at a region around which are further detectors or guides. When the device is accurately positioned relative to the beam all the detectors on the front screen are illuminated, but none of those on the rear screen are. The signals from the detectors can be used to effect automatic guidance of the device, or can be displayed for manual control. Roll of the guided device can be compensated for by a pendulum mechanism which moves the target screens relative to the device. Target: the target has two arms 3, 4, Fig. 1, which are pivoted at their ends 5, 6 to a casing (not shown), and which are also linked 7 and the pivot points lie in a line. Screen 9 and 10 are parallel to one another. When pin 7 and the pivot points line in a line. Screen 9 carries an aperture 11 and light guides 13, each leading to a respective photo-detector. Screen 10 carries similar guides 15. The guides 13 are normally illuminated by the laser beam while guides 15 are not. Guidance system: the target of Fig. 1 is attached to a tunnelling shield 49 in Fig. 4, and the shield is pushed forward by twelve rams of which only one, 51, is shown. The rear screen carries twelve light guides corresponding to the rams, while the front screen has four guides. The target is initially set up at the shield edge, on the laser beam, and the rams are actuated by switches 56, also seen in Fig. 5. If the shield deviates from the beam one or more guides on the rear screen are illuminated, and this controls the corresponding rams via amplifiers 60, 61 and relays 57. Lamps 63 on a control box 53, Fig. 5, are also lit corresponding to the illuminated guides, and by operating an override switch 59 manual ram control is possible by moving a control stick 67 towards the lit lamp or lamps, or by operating switches 56. If the target is so far off line that all four front screen guides cease to be illuminated the automatic guidance will be disabled by cut out 64 which operates the override switch 59; cut out 64 has a five second delay before it operates. A hydraulic ram circuit is described, Fig. 7 (not shown). Roll compensation: when the target is attached to the edge of the cylindrical tunnelling device, roll of that device will raise or lower the target relative to the laser beam. Such raising or lowering is detected by a pendulum attached to the target, and the pendulum either moves the target mechanically or by electric motors to compensate the roll. In Fig. 1 the bob 19 pivots about the upper end of shaft 26 during roll, and moves a thread 21 to which it is attached at 25. The thread in turn is attached to arm 3 at 23 and moves that arm; the other arm is also moved via pin 7 and slot 8, so that the screens move vertically to compensate the roll induced raising or lowering of the target. The pivot point of the pendulum is adjustable by knob 29 so that the roll compensation is appropriate to the distance of the target from the shield's axis. In the electrical embodiment of Fig. 3, motion of bob 19 strains one of the wires 32, 33 and slackens the other one. The wires, which are anchored at their ends 35, 36, are connected to a bridge 37, and imbalance in their resistance drives motor 38 and 39 depending on which way the bob moved. The motor drives a threaded shaft 40 via a gear, and a follower 45 on the shaft is moved and in turn moves the thread 21 which is attached to the target arms as above. To ensure that the motor is stopped when the target is back on the beam a light detector 47 placed at the centre of the guides on the rear screen is used to disable the motors when illuminated.