Patent GB-1160804-A (GB)
Title: Apparatus for Measuring the Spherical Coordinates of a Luminous Point
IPC: E21B47/02
Filed: 1967-07-07
Abstract: 1,160,804. Optical position finding. SOC. D'APPLICATIONS GENERALES D'ELECTRTCITE ET DE MECANIQUE. 7 July, 1967 [22 July, 1966], No. 31,300/67. Heading H4D. The Specification describes apparatus for determining the spherical co-ordinates of a light spot 3, Fig. 1, produced by the projection of a light beam 4, said co-ordinatea being representative of the position of a universally pivotable reflector 5, said reflector in turn being connected to a pendulum 14, the entire arrangement being installed in a drilling pipe 6, whereby the pendulum keeps vertical and the measured light spot co-ordinates indicate any deviation of the drilling pipe 1 from the vertical. For convenience, however, in the following description, the drilling pipe &c. will be assumed fixed vertically and the mirror 5 and pendulum 14 movable. The light beam 4, from source 3, is directed on to the inside surface of an outer hemisphere 7 by means of mirrors 17 and 18. A reflecting meridian strip 8 is provided on said inside surface opposite mirror 18, such that with mirror 5 perpendicular to axis X-X, i.e. horizontal, the light beam is incident on the top end of the strip and is reflected back on itself to be picked up by photo-sensitive means 12. Mirrors 17 and 18 and hemisphere 7 rotate together at speed N such that with mirror 5 respectively (a) horizontal and (b) inclined at angle a to the horizontal, the spot 31 describes relative to fixed space (a) a "latitude" circle, and (b) an inclined circle, and relative to the reflective strip (a) a fixed position (see above) and (b) a crossing movement once per revolution, the "altitude" angle at which the spot crosses the strip (and a pulse is produced by means 12) being 2α below the "altitude" angle of the top of the strip. An inner hemisphere 23 is interposed between mirror 5 and strip 8 and is cut away to form a mask, Fig. 3, having an opaque portion Z 0  and a transparent portion Z T , the edge 28 having an equation The hemisphere 23 rotates in the same direction as hemisphere 7 but with a much lower speed N -. Thus as angle α increases, the strip 8 is R masked by opaque zone Z 0  for less and less time and the number of pulses generated by means 12 increases, substantially linearly with α, thereby giving an indication of the "latitude" of spot 31. Fig. 9 shows hemisphere 23 in which edge 28 has the equation and the number of generated pulses decreases with increasing α. A "mirrored" curve may be substituted for the straight edge 27 to form a symmetrical mask, Fig. 10 (not shown). In the arrangement of Fig. 11 (not shown), the functions of the hemispheres are reversed, i.e. the reflecting surface on the outer hemisphere has the shape of the opaque areas Z 0  of Figs. 3 and 9 and the inner hemisphere is provided with a slot, the mirrors 17 and 18 now rotating at the faster speed with said inner heinisphere. Damping of the pendulum movement may be by liquid 15, Fig. 1, or by a damping magnet, Fig. 11. To determine the azimuth of the vertical plane containing the axis of the mirror 5, the azimuth of strip 8 (slit 108, Fig. 11) at the moment means 12 produces a pulse, is determined. Thus hemisphere 7 is formed with counting slots 44, Fig. 16, and a reference slot 45 in line with strip 8. Light from source 46 passes through the slots and produces pulse outputs from photo-cells 49 and 50. Photo-cell 49 is contacted by means counting the number of slots 44, which count is started with the occurrence of a pulse from means 12, is stopped by a pulse from photo-cell 50, and represents the required azimuth angle. The reflecting surface may be a pool of mercury covered with a damping liquid. Pendulum 14 is then dispensed with.