GB801239A - - Google Patents

Abstract

801,239. Rotor balancing. GENERAL MOTORS CORPORATION. June 11, 1956 [July 25, 1955], No. 17938/56. Class 40 (1). In a system for measuring the unbalance of a rotor an electrical signal U obtained from the vibrations thereof is harmonically resolved into two components A and B proportional to U sin # and U cos # respectively (# being an arbitrary angle) and these further resolved into signals related to A cos 0, A sin #, B cos 0 and B sin 0 (where 0 refers to the angular position of unbalance) which are combined to give (A cos # + B sin #) and (A sin 0 - B cos #); the angle # is then adjusted so that the second of these quantities is zero, whereupon 0 = # and the sum (A cos # + B sin #) corresponds to the magnitude of unbalance. Signals from vibration of the rotor shaft 11 (Fig. 1) are split up in the resolver 40 which has a manual adjustment (148) of the angle #. The quadrature outputs are passed to transformers 52 and 52<SP>1</SP> with centretapped secondaries, from which the sum and difference outputs are applied to amplitude- and angle-indicators 92 and 96 respectively. The polarities of the outputs are changed twice per revolution of the rotor shaft 11 by means of relay coils 66, 66<SP>1</SP>, 68 and 68<SP>1</SP> operated by cams 106 and 108 driven from shaft 11. Coils 66 and 68<SP>1</SP> are controlled by cam 106 and coils 66<SP>1</SP> and 68 by cam 108 spaced 90 degrees from 106 on the shaft 102. By operating the control 148 until the indication of 96 is zero the reading of 148 gives a measure of the position of unbalance # and the reading of 92 indicates the magnitude of unbalance. If the rotor to be balanced is axially elongated two pick-ups are used with two separate sets of apparatus or with the same one connected to the two in succession. In the case of a belt-driven machine (Fig. 11) the reference point from which the angle # is measured is a white spot from which light is reflected to a photo-cell 179. The pulse from the latter triggers a sawtooth generator whose output is shaped by the usual circuitry to give two square waves in appropriate time-relationship for operation of the relay coils at XX and YY. In an extension of the system (Fig. 10) the amplitude signal is applied via line 190 to a servo amplifier where it is compared with a D.C. standard 196. The resulting error signal actuates a servomotor 200 which controls an attenuator 32 to reduce the amplifier input; the setting of the attenuator then gives a measure of the amplitude of the rotor unbalance. A further servo system 204, 206, 208, 211 may actuate a device 212 such as a driller or welder to remove the unbalance from the rotor. The shaft is rotated via a similar servomotor 222 (driven by the phase signal) so that the device 212 operates on the rotor in the correct position determined by the angle #.