- Email: [email protected]
teramet
OPTICAL ELASTOHYDRCKlYNAMICS MULTIPLE-BEAM
interferometric
methods have
been used to measure the shape of point elastohydrodynamic contact in rolling contact bearings. In a paper ‘Optical elastohydrodynamics’, given at the Institution of Mechanical Engineers in February, Dr A. Cameron (Imperial College) discussed optical design, in particular collimator design, choice of reflecting layer and laser sources for the technique. If oil is drip-fed onto a ball, loaded against a glass plate, (such as shown in Fig.) an elastohydrodynamic film is generated whose thickness can be measured by interference. The glass plate normally used is optical crown, free of striae, and flat to 1 fringe per 12. 5cm2 with a 20%-reflectivity chromium layer on its lower side to give good fringe visibility. (Experiments at high temperatures needed a quartz disc.) The balls had a surface finish better than lnin centre line average with a reflectivity of 60% in oil. Sources used for these experiments were a mercury discharge lamp and a He-Ne laser. With the laser it was found necessary to coat glass-air surfaces with anti-reflection coatings. This may prevent use of the higher power argon ion laser, and the wider spacing of krypton laser frequencies may ease the coating problem. The field stop is imaged by the field and aperture lenses, at about unit magnification, onto the interference plane and controls the size of the illuminated area. The aperture stop, placed at the focus of the aperture lens, controls the degree of collimation and intensity of illumination. Careful collimation made it possible to measure the 30th fringe order. Prof. H. H. Hopkins designed the collimator. ADJ
microscope,
Qbject
lens of microscope
consisting of the measuring head and a 58-cm wide remote electronics unit, costs E980 ex-works, with a delivery of about 3 months. Special versions may be required for specific applications and Cambridge Consultants are able to undertake special designs and one-off production orders to meet such needs. A version is being developed that can control, as well as indicate, inaccuracies in thickness making Teramet a complete tool control system. It is possible that novel applications of the Teramet exist which have not yet been examined, and both NPL and Cambridge Consultants will be glad to give advice. Cambridge Consultants Ltd, Bar Hill, Cambridge CB38EZ.
STRAIN MEASUREMENT FRINGES
IN WELDS USING MOIRE
WHEN MEASURING STRAINS close to the welds in the region of stress, it is desirable to measure over the smallest gauge length (fringe spacing) possible. Because gauge length varies inversely as the accuracy (related directly to the mismatch between the two gratings) a compromise has to be made depending on the particular application. J. Cargill, (NCRE, Dunfermline) in a recent paper indicated that by using a grating pitch of 0.001 and mismatch of 1.005 he could measure strains as small as lOO+/in. He described the method of photo-engraving a line grating on the surface of the test piece, subjecting it to strain (welding) and subsequently making a clear plastic replica. An intriguing feature of the technique is the use by Cargill of his own mismatch gratings. These can be produced by allowing light from a 0. Olin slot in a pinhole camera to pass through a standard 1000 lines/ in grating 100in away. At q2in from the grating the resulting diffraction pattern is allowed to produce a mismatch grating of 1.005 on a suitable photographic film and by using the reversal processing technique, good sharpness of line is achieved. JKD
EUROPEAN OFFICE FOR BADRON
Apparatus for measuring thickness of elastohydrodynamic film (between ball and plate) by interference method.
50 Champs Elysees, Paris is the address of Hadron’s European office. Hadron is the US distributor for CGE products (Compagnie Generale d’Electricite) which include high-power laser systems. One of the systems at the French Atomic Energy Commission Laboratories at Limeil yielded the first reliable production of fusion neutrons in quantity last September. A later system is being installed by Hadron in New York for shared use on a commercial basis.
SUB-MM METROLOGY/TERAMET D. GABOR
THE TERAMET, a device for sensing and measuring the position of a surface, is now available from Cambridge Consultants Ltd. Described by Dr N. W. B. Stone in Optics Technology, February 1970, pp 8- 12, the Teramet is an interferometer using sub-mm waves, designed to measure distances and monitor metal thickness. The version described in the article and shown mounted on a lathe in Fig. 3 of the article,
Dr Dennis Gabor, well-known throughout the world for his work on holography, was awarded the CBE in the New Year’s Honours List. He has also been honoured in the U.S. where he received the IEEE Medal of Honour on 25 March at the Annual Banquet. Dr Gabor has already been awarded the Romford medal (Royal Society), the 1968 Michelson Medal
Optics
Technology
May 1970
115
interferometric
methods have
been used to measure the shape of point elastohydrodynamic contact in rolling contact bearings. In a paper ‘Optical elastohydrodynamics’, given at the Institution of Mechanical Engineers in February, Dr A. Cameron (Imperial College) discussed optical design, in particular collimator design, choice of reflecting layer and laser sources for the technique. If oil is drip-fed onto a ball, loaded against a glass plate, (such as shown in Fig.) an elastohydrodynamic film is generated whose thickness can be measured by interference. The glass plate normally used is optical crown, free of striae, and flat to 1 fringe per 12. 5cm2 with a 20%-reflectivity chromium layer on its lower side to give good fringe visibility. (Experiments at high temperatures needed a quartz disc.) The balls had a surface finish better than lnin centre line average with a reflectivity of 60% in oil. Sources used for these experiments were a mercury discharge lamp and a He-Ne laser. With the laser it was found necessary to coat glass-air surfaces with anti-reflection coatings. This may prevent use of the higher power argon ion laser, and the wider spacing of krypton laser frequencies may ease the coating problem. The field stop is imaged by the field and aperture lenses, at about unit magnification, onto the interference plane and controls the size of the illuminated area. The aperture stop, placed at the focus of the aperture lens, controls the degree of collimation and intensity of illumination. Careful collimation made it possible to measure the 30th fringe order. Prof. H. H. Hopkins designed the collimator. ADJ
microscope,
Qbject
lens of microscope
consisting of the measuring head and a 58-cm wide remote electronics unit, costs E980 ex-works, with a delivery of about 3 months. Special versions may be required for specific applications and Cambridge Consultants are able to undertake special designs and one-off production orders to meet such needs. A version is being developed that can control, as well as indicate, inaccuracies in thickness making Teramet a complete tool control system. It is possible that novel applications of the Teramet exist which have not yet been examined, and both NPL and Cambridge Consultants will be glad to give advice. Cambridge Consultants Ltd, Bar Hill, Cambridge CB38EZ.
STRAIN MEASUREMENT FRINGES
IN WELDS USING MOIRE
WHEN MEASURING STRAINS close to the welds in the region of stress, it is desirable to measure over the smallest gauge length (fringe spacing) possible. Because gauge length varies inversely as the accuracy (related directly to the mismatch between the two gratings) a compromise has to be made depending on the particular application. J. Cargill, (NCRE, Dunfermline) in a recent paper indicated that by using a grating pitch of 0.001 and mismatch of 1.005 he could measure strains as small as lOO+/in. He described the method of photo-engraving a line grating on the surface of the test piece, subjecting it to strain (welding) and subsequently making a clear plastic replica. An intriguing feature of the technique is the use by Cargill of his own mismatch gratings. These can be produced by allowing light from a 0. Olin slot in a pinhole camera to pass through a standard 1000 lines/ in grating 100in away. At q2in from the grating the resulting diffraction pattern is allowed to produce a mismatch grating of 1.005 on a suitable photographic film and by using the reversal processing technique, good sharpness of line is achieved. JKD
EUROPEAN OFFICE FOR BADRON
Apparatus for measuring thickness of elastohydrodynamic film (between ball and plate) by interference method.
50 Champs Elysees, Paris is the address of Hadron’s European office. Hadron is the US distributor for CGE products (Compagnie Generale d’Electricite) which include high-power laser systems. One of the systems at the French Atomic Energy Commission Laboratories at Limeil yielded the first reliable production of fusion neutrons in quantity last September. A later system is being installed by Hadron in New York for shared use on a commercial basis.
SUB-MM METROLOGY/TERAMET D. GABOR
THE TERAMET, a device for sensing and measuring the position of a surface, is now available from Cambridge Consultants Ltd. Described by Dr N. W. B. Stone in Optics Technology, February 1970, pp 8- 12, the Teramet is an interferometer using sub-mm waves, designed to measure distances and monitor metal thickness. The version described in the article and shown mounted on a lathe in Fig. 3 of the article,
Dr Dennis Gabor, well-known throughout the world for his work on holography, was awarded the CBE in the New Year’s Honours List. He has also been honoured in the U.S. where he received the IEEE Medal of Honour on 25 March at the Annual Banquet. Dr Gabor has already been awarded the Romford medal (Royal Society), the 1968 Michelson Medal
Optics
Technology
May 1970
115