GB1392325A - Measuring apparatus - Google Patents

Abstract

1392325 Digital measurement of dimensions SIEMENS AG 30 March 1972 [17 May 1971] 14969/72 Heading G1A In measuring the thickness or width of a workpiece by measuring the distance of at least one surface of the work-piece from a reference line, a laser beam is deflected in steps relative to the line by an acoustic-optical deflector to scan over the workpiece and a photo-electric detector receiving reflected light from the workpiece generates a time impulse to read the current deflection angle from which the spacing is digitally calculated. In Fig. 1 the thickness of a workpiece 32 is measured by two laser beams deflected by acousticoptical deflectors 3, 19 away from reference lines 8, 17 on to opposed surfaces of the workpiece. The detectors 7,15 having a narrow field of view defined by apertures 4, 10 and 21, 14, give a pulse when the respective laser beam steps into the small surface area which the photo-detectors are viewing. From the angles alpha and beta, distances 11 and 16 can be calculated which, when subtracted from 18, gives the thickness of the workpiece. In the arrangement of Fig.2 for measuring the width of a workpiece 30 two laser beams from a common laser 23 are directed via prisms 24, 25 to acoustic-optical deflectors 26, 27 which cause the laser beams to scan over respective edges of the workpiece. Photo-detectors 31, 32 give out a timing signal when the respective laser beam leaves or, alternatively, sweeps on to the workpiece. From the time interval between the two time impulses and the known distance b o , width B of the workpiece can be digitally calculated.