GB866100A - Improvements in or relating to interferometer optical systems - Google Patents

Abstract

866,100. Photo-electric position determination. LINK AVIATION Inc. Aug. 23, 1957 [Sept. 12, 1956], No. 26710/57. Class 40(3) [Also in Group XX] In an interferometer for measuring the movement of a measuring head 10 relative to an anvil 11, collimated light from a source 1 is split at 4 into two beams 6, 8 which are reflected by prisms 7, 9 before re-combination at 12. On plate 4 is a coating 5 producing a #/4 phase difference between the two halves of split beam 6, # being a selected wavelength, to cause interference in each half 13, 14 of the re-combined beam. Thus, as prism 7 attached to measuring head 10 moves, the intensity of each half beam 13, 14 varies cyclically, the variation in half beam 13 lagging or leading that of half beam 14 according to the direction of the movement of prism 7 and head 10. To measure this movement, the beam 13, 14 is passed through prism 15 and dividing lenses 16 so that the two halfbeams of the selected wavelength pass through apertures in plate 17 on to photo-tubes 18, 19 respectively. The out of phase outputs of these tubes are fed through amplifiers 32, 33, triggers 34, 35 and inverters 36, 37 to a reversible electronic counter 38 which records the number of complete cycles in the intensity variations, this number being commensurate with the distance moved by measuring head 10. Fractions of cycles are measured by a cathode-ray tube 44 to which the photo-tube outputs are also fed via amplifiers 40, 47 and inverters 42, 43. U.S.A. Specification 2,604,004 is referred to.