Patent GB-994895-A (GB)
Title: Improvements relating to a process and device for determining the unbalance in rotating bodies
IPC: G01M1/20
Filed: 1962-02-01
Abstract: 994, 895. Measuring rotary unbalance. W. & T. AVERY Ltd. Feb. 1, 1962 [Feb. 1, 1961], No. 4186/62. Heading G1N. Unbalance of a rotary workpiece is determined by imposing on an electrically deflectable journal, on which the body rotates, a known vibratory excitation at a frequency different from the rotation frequency and combining a voltage indicative of the resultant vibrations of the journal with reference voltages in synchronism respectively with the rotation and excitation frequencies. A separate calibration run is not therefore required. In Fig. 1, a flywheel or tyre 1 is rotated by a motor 3 mounted on a bridge 4 secured to leaf springs 6. The bridge is vibrated by an exciter 8 actuated by A.C. from source 21 through a potentiometer 24. The vibrations are detected by a moving coil transducer 9 and fed to respective Hall generators 14, 28. The field coil 13 of Hall generator 14 is energized from a phase reference generator 12, so that the Hall device is responsive to currents from transducer 9 which are caused by rotary unbalance only, currents caused by the applied excitation being of the wrong frequency. The field coil 27 of Hall generator 28 is supplied from the same source as exciter 8 so this generator responds only to currents due to the applied excitation. The outputs of the two Hall generators are applied to ratiometer 33 and the quotient is indicative of the unbalance. Potentiometer 24 is controlled by currents received from a transducer 37 having a feeler 28 in contact with the contour of the workpiece 1. The device is thus automatically compensated for workpieces of different shapes and sizes. Transducer 9 may have two separate coils or a single coil. A second measurement of the unbalance, at 90 degrees to the first may be made by providing a phase shifter in leads 15 from generator 12, or providing the generator with two windings 90 degrees apart. In the latter case the measuring system may be duplicated to give the measurements simultaneously. Alternatively the stator of generator 12 may be rotated through 90 degrees. To measure unbalance in two planes (Fig. 2) resiliently mounted bridges 52a, 52b carry roller bearings for the workpiece 51. In this case the exciter and transducer for each bridge are combined in a single unit 56, 57 having an exciter winding 56a, 57a and a pick-up winding 56 aa, 57aa (Fig. 3). First Hall generators 113, 114 are supplied with the transducer and exciter supply currents to give outputs indicative of EL + ER<SP>1</SP> and ER + EL<SP>1</SP>, i.e. the excitation applied to one bridge plus the effect on the same bridge of the excitation applied to the other. From these outputs is subtracted the rectified supply voltage, equivalent to EL = ER, leaving ER<SP>1</SP> at output 121 and EL<SP>1</SP> at 123. These voltages are applied to dividers 125, 126 and are divided into the rectified supply voltage to give outputs ER/ER<SP>1</SP> and EL/EL<SP>1</SP> in windings 130 and 131 respectively. Hall generators 134, 135 are supplied with the transducer currents and phase reference generator currents, from generators 59a, 59b, so that their outputs are UL + UR<SP>1</SP> and UR + UL<SP>1</SP>, respectively. By means of leads 140, 142 values UL and UR and subtracted from these respective quantities so that UR<SP>1</SP> and UL<SP>1</SP> are applied to further Hall generators 132, 133, respectively. These gives outputs of UR<SP>1</SP>. ER/ER<SP>1</SP> and UL<SP>1</SP>. EL/EL<SP>1</SP> to indicators 144, 145 and it is shown that these outputs are equivalent to UR and UL. The stators of generators 59a, 59b are rotatable by gearing 59c, 59d, and the shaft of motor 59 (Fig. 2) has a calibrated disc 58a for indicating the angular setting with respect to the rotor windings. Specification 957, 452 is referred to.