Improvements in apparatus for use in determining the principal axis of inertia of a body

Abstract

Abstract 586,976. Determining dynamic unbalance. VICKERS-ARMSTRONGS, Ltd., and WALLIS, B. N. Aug. 21, 1944, No. 15965. [Class 106 (ii)] In apparatus for determining the dynamic unbalance of a rotary body, the latter is suspended or supported with ability to swing or rock about a fixed pivotal axis in such a manner as to be free also to oscillate about an axis perpendicular to the said pivotal axis under the 'influence of the differential momentum of any dynamically unbalanced masses in the composition of the body, means being provided for detecting and measuring the amplitude of any such oscillation. As shown, a fly-wheel 21 under test is secured to a vertical strip 18 having a cylindrical head 181 through which passes a horizontal pivot 16 resting upon adjustable pallets borne by two aligned halves of a gantry 10. A hand winch operating blocks and tackle 23 is provided to assist in lifting the body under test. A lever 25 is attached to the head 181 for the purpose of swinging the test piece about the horizontal pivot 16. A tube 26, also secured to the head 181, carries a permanent magnet 34 in the field of which are placed a pair of coils 27, one on each side of the strip 18, so that when the fly-wheel rotates about its axis, as allowed by torsion of the strip 18, a current is induced in the coils 27, which is measured by a mirror galvanometer 29. A lamp 36, carried by the magnet 34, is arranged to throw a beam of light on to a screen 37 upon which are marked horizontal lines to indicate the desired range of swing of the test piece about the horizontal pivot. In use, a series of stations I, II, III, &c. are marked on the test piece (Fig. 2) and, when the latter has been adjusted so that the first station is adjacent to a pointer 40, it is swung through the desired range by the lever 25 and the peak current indicated by the galvanometer is observed. This procedure is repeated for other stations and the galvanometer readings so obtained are plotted as ordinates against the angular positions (station numbers) as abscissµ. The peaks on the curve indicate the angular position of the out-ofbalance masses and their weight and position with respect to the central plane perpendicular to the axis of the test piece may be calculated from the amplitude of the curve. When counter-weights have been attached, the experiment is repeated and, unless correction has been exact, another curve of smaller amplitude will be obtained. The vectors representing the amplitudes of the first and second curves respectively are then drawn in the form of a vector diagram, from which the true counterweights and their positions may be ascertained.

Inventors

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