Patent GB-287608-A (GB)
Title: Apparatus for the solution by optical means of data capable of representation in theform of triangles
IPC: G01C3/30
Filed: 1926-12-10
Abstract: 287,608. Barr & Stroud, Ltd., and French, J. W. Dec. 10, 1926. Plane trigonometry calculators. - The solution of data capable of representation in the form of triangles is effected by optical means, the measurements being determined as a result of the movement of an optical image in a field of view. Mechanism is provided whereby the image may be displaced in accordance with polar rectangular or oblique coordinates for the purpose of measuring the position of the image radially or angularly or with reference to co-ordinate axes or other points of reference in the field of view. The displacement and/or rotation of the image in the field of view is effected by optical means such as deviating prisms. The means provided permit the image A, Fig. 1 being set to the required position in the field of view and also enable the distance 6 of the image A from the horizontal axis or the distance 7 from the vertical axis to be determined. A graticule B, Fig. 2 is illuminated by a lamp 10 and an image of the graticule B is formed in the plane 13 by the lens 12. A deviating prism 15 capable of rotational movement about and a translational movement along the optical axis will by its position determine the position angularly and radially of the image A. A second prism 17, having its deviation axis parallel to the axis 4, 5, Fig. 1 and capable of longitudinal movement along the optical axis between the plane 13 and the lens 12, is used to measure the distance 7 by the amount of movement required to bring the image A into coincidence with the vertical line 8, 9. The initial settings of the prisms 15, 17 are such that the image A is at the centre of reference. Should the distance 6 be required to be determined the prism 17 is rotated through 90‹ and appropriately displaced. Instead of rotating the prism 17, an additional prism 20, Fig. 7 with its deviation axis at right angles to that of the prism 17 may be placed between the plane 13 and the eyepiece 14, together with an additional lens 18 functioning in a manner similar to that of lens 12. In order to determine the position of a target 22, Fig. 6, from the gun position 24, when the distance from the target 22 to the rangefinder 23, the rangefinder 23 to the gun 24 and also the angle b are all known, the arrangement shown in Fig. 7 may be used, the prism 27 being capable of rotation as well as translation. The prism 15 is displaced and rotated by amounts corresponding to the distance 21 and the angle b respectively resulting in the image position A, Fig. 8. The prism 27 having been previously arranged with its axis parallel to the diameter 4, 5, is displaced longitudinally to bring the image A into the position 28, the distance A-28 corresponding to the distance 23, 24, Fig. 6. The angle C is obtained by rotation of both prisms 15, 27 until the point 28 lies at 29 in the axis 4, 5. Translation of the prism 20 to bring the image A from the point 29 to the centre of reference 3 will give the required range from the gun to the target. In place of a single prism moving the image in consequence of a translational movement. two prisms capable of relative rotation may be used, whereby the effective deviating power is varied. The direction of the deviation axis is varied by rotating the prisms together. In one modification of the system one part of the optical axis may be at an angle to the other part passing by way of a right-angled prism capable of rotation about an axis at right angles to the plane of the optical axis to produce angular displacement of the image A. Mechanism is described whereby the various movements are effected, some of which are shown in the general arrangement, Fig. 15 of one form of apparatus embodying the optical system shown in Fig. 7. Rotation of the handle 63 by an amount indicated on dial 95 gives a movement of translation to the prism 15, through differential gearing to a wheel 70 and thence through the wheel 72 to the screw 73 on which the prism 15 is mounted. Similarly the prism 27 is translated a distance indicated on the dial 96. The prism 15 is rotated by the handle 75 through gearing shown, the amount being indicated on dial 94. Simultaneous rotation of prisms 15, 27 is effected by the handle 84 indicating on dial 93. Prism 20 is given a motion of translation by the handle 90, the amount being indicated on dial 92. The various data of Fig. 6 are consequently indicated on the dials 92 - - 96.