Patent GB-494687-A (GB)
Title: Improvements in or relating to optical projection apparatus
IPC: G02B21/00
Filed: 1937-04-29
Abstract: 494,687. Screw - thread gauges. KAPELLA, Ltd., and PHILLIPS, A. C. April 29, 1937, No. 12259. [Class 106 (ii)] [Also in Group XX] Apparatus for testing screw threads and the like comprises two optical systems for projecting simultaneously images of two portions of the object, each system having a member or members rotatable about a part of the optical axis so that the object points of the systems may be adjusted along two circular arcs without altering the relative positions of the images on the screen. As shown in Fig. 2 the object is supported between centres B<4> on a table B adjustable for focusing and each of the optical systems located side by side comprising arms D, E connected to a rotatable shaft C<1> the arm D carrying a projection lens D<1> and mirrors D<2> D<3> to project an image to the screen D<6> via the fixed mirrors D<4>, D<5>, the arm E being connected to the illumination unit shown in Fig. 3. Each unit comprises a lamp F<1> and condenser F<2> carried on a base E<2> pivoted to the arm E and to an arm G<1> detachably connected to a rotatable shaft G parallel to the shaft C<1>, the base also carrying a slidable frame F<5> supporting a rotatable mirror F<3> directing the light upwards on to the object. When the shaft C<1> rotates to project different portions of the object the lenses D<1> describe a circular arc and the bases E<2> remain parallel to the plane containing the shafts G, C<1> so that the images remain stationary on the screen each system being locked in its appropriate position by a cam lever C<2>. The arms E and G<1> are detachably connected to the shafts C'G to permit removal of the illumination unit. To permit the surfaces of objects to be examined auxiliary illuminating units may be detachably secured to the upper arms D to illuminate the object in parallel light, the lower units being removed. To permit the projection lenses to be moved for focusing the modification shown in Figs. 7, 8 may be employed. The lens H is pivoted at J<2> to an arm J pivoted at J to a frame H<2> carried by a rotatable shaft H<3> corresponding to the shafts C<1>. Links J<1> are also pivoted to the lens and frame and the mirrors J<4>, J<5> pivoted on the axes J<2>, J<3> are connected by a link J<6>. A lever K pivoted at K<1>, Fig. 8, to the mirror J<5> is engaged at one end by a fixed pivot K<2> and at the other by a spherical pivot K<3> on the arm J, so that as the arm J is moved for focusing by the head K<5>, the axis of the lens H remains constant in direction and the mirrors are rotated by the arm K at half the rate at which the arm J rotates so as to maintain the image in position on the screen. A clamp C<2> may be provided. The two systems may be inter-connected to be adjustable together so that the line joining the object points remains parallel to the line joining the axes of rotation, or the systems may be moved independently. To permit the distance between the axes of rotation to be varied the apparatus shown in Fig. 11 may be employed. The shafts M<2>, N<2> are rotatable in carriages M<3> N3 sliding in rails M<4> and pressed towards adjustable stops by a compression spring P<7>. Each shaft carries a pulley P, P' over which passes a cable guided by three pairs of idlers P<2>, P<3>, P<4>. Rotation of the pulley P<2> by a worm wheel <p8> causes the cable to rotate the systems simultaneously in opposite directions. Clutches may be provided on the pulleys P, P<1> to permit separate rotation of the system which may be clamped by clamps M<5>. N<5>. The apparatus may be arranged so that parts of the two images are superimposed on the screen to assist the testing of screw threads. In a further modification the centres B<4>, Fig. 2, are so supported as to be bodily removable to be replaced by a glass plate bearing suitable scales to permit the examination of flat objects such as needles. The projection screen may also be detachable to permit attachment of drawings or other marks thereto.