GB698800A - Improvements in or relating to devices for directly measuring and instantaneously recording the angular displacements of a body - Google Patents

Abstract

698,800. Selective signalling systems. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. Feb. 13, 1950 [Feb. 14, 1949], No. 3636/50. Class 40 (i). [Also in Group XL(b)] The orientation of a body S is signalled by causing relative movement between graduated rings Lx, Ly, Lz set mutually at right angles and reading heads Mx, My, Mz to cause the transmission of a corresponding number of impulses to counters. The reading heads may be inductors forming arms of A.C. bridges and having their magnetic circuits varied by graduations of magnetic material on a non-magnetic base or formed by portions of reduced thickness on a magnetic base, Figs. 10 to 14 (not shown). Alternatively the reading heads may be photo-electric and acted on by visible graduation marks on a transparent or, as shown, reflecting base. Optical arrangements. The graduations are illuminated by a lamp 14 acting through the lens system by which they are read and are imaged on a pair of photo-cells Cs, Cc with the aid of a total reflecting prism 6. A third photo cell Cr receives tht image of the end of a lengthened graduation mark indicating the zero position. Operation. As the image of a graduation mark passes photo-cell Cc the output of the cell varies as shown by the heavy line in the upper section of Fig. 8. This voltage is used to trigger a doublestability circuit, the rectangular output of which is differentiated to produce the pips shown in the middle section of Fig. 8. Owing to the different voltages at which the double-stability circuit changes over with rising and falling voltages, the rectangular pulses and their derivatives occur in slightly different positions of the operative graduation according as the graduation is moving from left to right (dotted lines) or right to left (dashed lines). As the graduation passes photo cell Cs, output of the latter takes the form shown by the heavy line in the lower part of Fig. 8 and this after conversion into a rectangular form is used to suppress the pips associated with the right-hand or left-hand side of the graduation. Consequently each time a graduation passes the pair of photocells, a single impulse is produced and this is positive or negative according to the direction of movement of the scale and so steps the counter forwards or backwards.