GB926506A - Apparatus for measuring curved surfaces - Google Patents

Abstract

926,506. Optical apparatus for examining curved surfaces. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Sept. 18, 1961 [Sept. 16, 1960], No. 31956/60. Class 97 (1). Optical apparatus for examining a curved surface comprises a first optical device adapted to reflect a light beam from a selected point on said surface through a right-angle along a reference line, means for indicating the position of the first optical device on the reference line and a second optical device adapted to reflect a light beam from the selected point through a known angle along the reference line, and means for indicating the position of the second optical device on the reference line. The apparatus is shown as applied to the examination of the paraboloidal surface 3 of a micro-wave aerial which is covered by a radome 4. It comprises a tube 2 attached to a container 7, the tube being mounted in apertures 5, 6 and the container being mounted in an aperture on a frame 8 so that the tube and container may be rotated together. Within the container 7 is an electric motor 17 driving a lead screw 12 to move axially of the reflector a carriage 15 for supporting a pentag prism 16. Also in the container 7 is a telescope 23 which is aligned with the reflector's axis. In order to determine the x co-ordinate of a point P marked on the reflecting surface 3, a right pentag 16 is placed on the carriage and the latter moved axially until an image of point P co-incides with the telescope cross-wires. By means of a suitably calibrated revolution counter 19 and dial 21, the x-co-ordinate of point P can then be read off. The pentag prism is then replaced by an angle pentag, which turns light rays, incident normally on one face thereof, through a known angle 0. Carriage 15 is again moved until the image of point P again coincides with the telescope cross-wires. The reading on the counter 19 and dial 21 then indicates the axial distance from the pole of the reflector at which a line drawn from P at an angle 0 to the reflector's axis will meet this axis, and the y-co-ordinate of point P may then be calculated. In this way, the x- and y-co-ordinates of several points P may be determined and by substitution of these values in the usual equation for a parabola (i.e. y<SP>2</SP>=4ax) it can be seen whether the surface is true and also an average value for the focal distance a can be calculated.