GB642916A - An improved apparatus for testing the balance of rotating bodies - Google Patents

Abstract

642,916. Electric indicating systems. AVERY, Ltd., W. & T., and BINNS, A. Oct. 19, 1947, No. 19369. [Class 40 (i)] [Also in Group XIX] Apparatus for testing the balance of rotating bodies comprises a two-phase generator adapted to be driven at the same speed as the body to be tested, either of the phase voltages of which can be selected by switch mechanism to be compared on a centre zero wattmeter with the phase voltage of a current generated by a pair of pick-ups operated by the unbalance oscillations of the test body, the current from the pick-ups being proportioned by means of a potentiometer to accord with the positions of pre-selected planes of correction on the body being tested. The body a to be tested is driven by a motor k, and is freely mounted on bearings b secured to the upper ends of flexible metal strips fixed to a slidable carriage. The oscillations of the bearings actuate pick-ups f, f <SP>1</SP> in the fields of permanent magnets, and the combined currents are supplied to a wattmeter j. Two-phase current, with phases at 90 and 270 degrees, generated by an alternator h coupled to the shaft of the body a, is also supplied to the wattmeter. With this twophase system, two readings are necessary at each end of the body a which are obtained by a multiple four-point switch comprising switch portions p<SP>1</SP>, p<SP>2</SP> and p<SP>3</SP>. The portions p<SP>2</SP>, p<SP>3</SP> control, respectively, the pick-ups f, f<SP>1</SP> and the portion p<SP>1</SP> the phase of the alternator h. Switches s, s<SP>1</SP> are for changing the polarity of the pick-up currents which is dependent upon the position of the node of oscillation of the body a. The current from the two pick-ups isproportioned by potentiometers r, r<SP>1</SP>. Variable resistances specially calibrated so that the meter will read in the desired units may be incorporated in the circuit. In operation, a standard balanced body similar to the body a is first placed in the machine. A weight is added to the right-hand end of the body which is then rotated, and the potentiometer r<SP>1</SP> adjusted for zero reading on the wattmeter. The weight is then removed and applied to the left-hand end of the body, and the potentiometer r adjusted for zero reading on the wattmeter. The test body a is now placed in the machine, and readings of the wattmeter noted for two positions at each end of the body. A disc q on the driving shaft n has four graduations - thereon at 90 degrees apart indicating the positions of correction for the test body.