GB729901A - Improvements relating to balancing machines - Google Patents

Abstract

729,901. Measuring rotor unbalance electrically. SMALL ELECTRIC MOTORS, Ltd. Dec. 4, 1953, No. 33811/53. Class 40 (1). [Also in Group XL (c)] An apparatus for determining the position and magnitude of the unbalance masses of a rotor T (Fig. 1) by supporting it on bearings 1, 2 associated with transducers 5, 6 feeding signals which are combined at 7 to give a signal whose amplitude and phase is indicative of the magnitude and position of the unbalance mass at each support, which signal is fed through a tuned filter 8 and amplifier 9 to an indicator 11, and also to a stroboscope 13 so that the cyclic flashes on the stroboscope indicate the phase of the unbalance mass on indicator 11, is characterized in that the filter circuit 8 is continuously adjusted to the speed of rotation of the test rotor T. The A.C. supply feeding the rotor-driving motor 3 is also fed to a frequencysensitive bridge 14, whereby changes in frequency produce an unbalance current which energizes a motor 16 to rebalance the bridge 14, simultaneously adjusting impedance elements 17 in filter 8 to the new frequency. Methods of modifying the circuits to cope with changes in the relationship between the frequency of the mains supply and the frequency of the signals from the transducers produced by,e.g. a change in gear ratio, are discussed. The frequency-sensitive bridge 14 comprises capacitors 30, 33 (Fig. 2) and resistors 31, 32, an unbalance voltage between the corners 40, 40a due to a change in supply frequency being amplified by valves 36, 36a, 46, 46a to produce a current through the armature 50 of motor 16 which alters resistors 31, 32 to restore balance. The tuned filter 8 comprising two arms of a bridge circuit having a capacitor 88 (Fig. 3) and variable resistor 89 in series in one arm and a capacitor 90 and variable resistor 91 in parallel in the other arm, follows amplifying valves 62, 68, 93, 75 which are supplied with negative feed-back from the bridge circuit. The variable resistors 89, 91 are adjusted by the motor 16 as described above, to tune the circuit 8 to the frequency of the signals from the transducers 5, 6. The selected output signals are amplified at 102, integrated at 114, 115, 116 and rectified by double-diode 119 to be shown on a meter 11, and also feed a trigger valve 110 for flashing the stroboscopic lamp 13. Specification 726,107 is referred to.