Patent GB-498382-A (GB)
Title: Improvements in or relating to optical testing or measuring apparatus
IPC: G02B21/00
Filed: 1937-06-02
Abstract: 498,382. Optical testing &c. apparatus. KAPELLA, Ltd., WARMISHAM, A., and REASON, R. E. June 2, 1937, Nos. 15281 /37, 25956 /37, and 19535 /38. [Class 97 (i)] Apparatus for testing or measuring plane or curved section profiles of manufactured articles or of appliances used in their manufacture, such as screwthreads or hobs or thread gauges, consists of an illuminating device whereby one or more slits or knife edges are focused on the surface of the object examined to define the section profile, and an optical projecting device for viewing the profile obliquely to the section plane or surface and projecting an accurately focused image thereof. In the simple form shown in Fig. 1, light from a source A passes through a condenser A<1> and over a knife edge A<4>, and is received by an objective A<2> which focuses the knife edge on the object so that the section plane A<5> is defined by the line separating the light and dark parts of the field. The objective A<2> is preferably provided with a diaphragm having a narrow slit aperture A<3>. Diffused light from the object surface is used for oblique projection of the profile on to a screen or photographic plate A<6> by means of a lens A' the nodal planes of which intersect the planes A<5>, A<6> in two parallel lines equidistant from the lens axis. This arrangement gives a distorted image which may be rectified by re-projecting the image A<6> by means of a lens B, Fig. 2, on to a flat screen B<1>. A second, preferably enlarged, photograph of the image B<1> may be obtained in a direction at rightangles to the screen on a plate B<3> by a lens B<2>. Figs. 5 to 7 show a device by which the two flanks of a tooth can be simultaneously illuminated. Two knife edges E<1>, E<2>, formed by the sides of a narrow slit in a flat piece of metal E, are illuminated by the source E<3> and condenser E<4> and are focused by lenses E6, E<6> and a system of reflectors on the flanks F<1>, F<2> of the tooth. The reflecting system associated with the knife edge E<1> comprises a vertical reflector E' deflecting the rays horizontally to a reflector E<8> by which they are directed downwards and inwards to define the part E<9> of the profile. Similarly, reflectors E<10>, E<11> direct rays from the knife edge E<2> on to the part E <12> of the profile. A mask E<13> may be disposed between the lens E<5> and the reflectors, to avoid confusion which might occur from imaging both knife edges on each flank of the tooth. The line E<14>, Fig. 7, is the image of the line E <15>, Fig. 6, so that by moving the plate E parallel to itself along the line E <15>, the point of intersection of the images E<9>, E12 will be moved along the line E<14> to provide adjustment for teeth of the same angle but of different sizes. Fig. 8 shows a device for alternative illumination of one side or the other of the section plane, comprising two sources of light G, G<1> with condensers G<2>, G<3> and knife edges G<4>, G5, a rotatable shutter G<8> being provided to allow light from either source to be received by a prism having a semi-transparent reflecting surface G<7>, and the light reflected or transmitted by this surface being received by the lens G<6> which focuses an image of one or the other knife edge on the surface of the object. Fig. 11 shows means for determining whether two bodies, such as a worm and worm wheel, will mesh properly. A source of light J is used to illuminate the worm J<2> with the wheel J<3> removed, and a source J<1> to illuminate the wheel with the worm removed. The two images are projected, e.g. by the rectifying oblique systems J<5>, J<6>, on to a common surface J<4>. In order to remove interference due to light reflected from parts of the surface of the object, the illuminating beam and the projecting beam may be polarized in planes at right-angles to each other. Specifications 412,179, 498,377, 498,378, 498,419, 498,420, and 498,458 are referred to.