摘要：

1275045 Measuring small objects SIRA INSTITUTE 5 Sept 1969 [5 June 1968] 26875/68 Heading G1A [Also in Divisions G2-3] To measure a dimension of an object, such as the width of an aperture 2, radiation from a source 1 e.g. a laser is directed at the object and the resulting diffraction or interference pattern formed at a slit 4 is focused on to a rotating radial transmission grating 6, the resulting light signal received at a detector 8 through a diffusing screen 7 being at least part of a Fourier transform response of the intensity distribution in the scanned diffraction pattern image. The axis of the slit 4 is perpendicular to that of the aperture 2 and the grating axis 16 is movable relative to optic axis 17 to provide different scanning spatial frequencies. By measuring the output of the photo-detector, using an instrument 13, at two or more scanning frequencies and extrapolating to zero detector output, the width of the aperture may be determined, since this width is proportional to the spatial frequency at zero detector output Fig. 3 (not shown). Alternatively, readings taken at various spatial frequencies may be compared with readings obtained from a standard object in a gauging process. The apparatus may be designed to operate automatically and reject articles outside a given tolerance. Units 8, 11, 12 and 13 of the detector circuit may be interchanged with an incoherent source of light 1 so as to scan the radiation beam before the diffraction pattern is formed.

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