GB1244848A - Optical comparators - Google Patents

Abstract

1,244,848. Profile projection apparatus. PILKINGTON PERKIN-ELMER Ltd. and M. H. FREEMAN. Sept.23, 1968 [Sept.26, 1967], No.43841/67. Heading G2A. [Also in Division G1] Orange light B2 from a lamp 15, Fig.1, is passed through a condenser 16 and over a master work piece 10M and is reflected by a partially reflecting mirror 13 on to a screen 14. At the same time green light B1 from a lamp 11 is passed through the mirror and over a test piece 10 to also illuminate the screen 14 so that overlapping shadows of the pieces 10M and 10 are cast on the screen. Thus, green or orange fringe areas indicate respectively either that the master article 10M is larger or smaller than the article 10 under test. The relative magnifications of the shadows is adjusted by a hand wheel 23 moving a support 18. In a modification the different beams are polarized in mutually perpendicular planes or circularly polarized in opposite senses. In Fig.2 (not shown) and Fig. 3, light from a lamp 24 is split by a plate 26 with a dichroic coating which passes wavelengths above 540 m and reflects wavelengths below 540 m so that transmitted beams B1, B2 of distinctive colours are emitted by the device 26. These beams are passed over the master and test pieces 32, 34 and are re-combined where they coincide by a further dichroic coated plate 28, shadows of the articles or pieces being thrown on to a screen (29) behind the lamp 24. Discrepancies between the articles are determined as from their colour fringes described for Fig. 1. In Fig.4 (not shown) a dichroic coated beam splitting mirror 38 and two ordinary mirrors 39, 40 are employed, an orange beam B3 and a blue/green beam 34 resulting. These beams and a re-combined beam are directed over articles 43, 45 and through a lens 41 on to a screen 42. If the articles are rotatably supported then corresponding sections of the articles may be compared. The screens 14, 29 and 42 are preferably translucent to allow observation to be made on that side remote from the incident beams.