Patent GB-869072-A (GB)
Title: Method and apparatus for balancing rotary members
IPC: G01M1/22
Filed: 1957-07-26
Abstract: 869,072. Measuring electrically. BULOVA WATCH CO. Inc. July 26, 1957 [Aug. 9, 1956], No. 23818/57. Class 40 (1). [Also in Groups XXXVI and XL (b)] A balance-wheel is corrected for out-ofbalance by rotating it at an angular velocity, the mean value of which does not vary from revolution to revolution, detecting, e.g. by means of a capacitive pick-up or a photo-electric cell variations of velocity within a revolution to indicate when the centre of gravity lies between the centre of rotation and a cutting-device and operating the cutting device to remove metal to move the centre of gravity towards the centre of rotation, General description and operation (Fig. 1).- As shown, the balance-wheel is supported by its pivot in jewelled bearings 45 carried in arms 46 rotatable about an axis 47. During testing a spring 48 holds the end of one of arms 46 in engagement with stop 49. A solenoid, not shown, advances the entire assembly carrying the balance wheel into the field of coils 50 by means of which is produced a three-phase rotating field which spins the balance wheel. An oscillator feeds a high-frequency signal (Fig. 3a) to arms 46 which are capacitively coupled to the balance wheel through the jewelled bearings. As the wheel rotates balancing pins 44 amplitude modulate the oscillator frequency picked up by electrodes 65 (Fig. 3b). If the wheel is not balanced it moves more slowly as the out-ofbalance position approaches the top. This slowing modulates the output waveform and is used to indicate the extent and position of the unbalance (see below). If the unbalance is excessive a brake 53 is clamped on to the wheel by solenoid 52. When the unbalance is at its lowest position, a further solenoid 54 operates a lever to move the wheel until the brake drops between adjacent pins and a solenoid 63 pushes the wheel and its mounting against the action of spring 48 till one of pins 44 is drilled out to an extent dependent on the unbalance. This process is repeated until the unbalance is below the allowable maximum when the wheel mounting solenoid withdraws the balance wheel and its mounting and it is ejected. Circuit and detailed operation, Fig. 2.-The output of 30 kilocycle oscillator 3 (Fig. 3a) is amplitude-modulated by the rotation of the wheel (Fig. 3b) the varying spacing of the modulating peaks indicating unbalance of the wheel. The signal is demodulated at 5 to give waveform 3c and is then fed through a limiter amplifier 6 which produces square wave output 3d. The square waves control a sawtooth generator 7 to produce waveform 3g which is fed through level regulator 8 to produce waveform 3h. Waveform 3h is obtained from curve 3g across level regulator 8 which consists of a rectifier condenser and discharge resistor. The condenser is charged during the ascending portions of the sawtooth but the voltage across it has not time to fall to zero during the vertical portions of the sawtooth. Thus a direct component of signal 3h remains which is the mean speed signal. Waveform 3h is fed through rectifier 9<SP>1</SP> to ring modulator 10 where it is compared with a standard signal from source 11. The ring modulator is fed with a 20 kilocycle signal from source 9 and the amplitude of the 20 kilocycle output is proportional to the difference between the voltage 3h and that from source 11 to rotate the balance wheel at a substantially constant velocity. The output signal 3h from regulator 8 is also fed to a low-pass filter 15 to produce waveform 3i, the amplitude of which indicates the extent, and the phase the angular position of, the unbalance. When key 40 is operated an impulse is applied to bi-stable circuit 16 which emits a pulse to energize the carriage solenoid 17<SP>1</SP> to move the balance wheel into the rotating field. The output pulse from bi-stable circuit 16 is also applied to a gate circuit 22 and a four second timing unit 18. Unit 18 discharges a capacitor 31 for four seconds and then applies a pulse to one-second timing unit 19. This unit opens gate circuit 30 for one second to allow condenser 31 to charge from waveform 3h after the smoothing to give 3i at 15 and rectification at 29. Thus capacitor 31 acquires a charge proportional to the unbalance. At the end of the one-second period the capacitor charge is applied to gate 13 to which the final pulse from timing circuit 19 is also applied. If the capacitor charge is sufficiently low gate 37 opens, bi-stable circuit 16 is restored and the carriage solenoid 17<SP>1</SP> moves the wheel out of therotating field and, after a delay introduced by mono-stable circuit 39 an ejector solenoid removes the wheel from its support. If the bi-stable circuit 16 is not reset, thus indicating that the unbalance is excessive a circuit 22 connected to circuit 16 is opened after a 0.2 sec. delay imposed by monostable circuit 20 and remains open for one second under the control of timing circuit 21. Output pulses from limiter amplifier 23 having waveform 3k are transmitted through gate 22 to bi-stable circuit 24. Only the trailing edge of the pulse shown as " Flip " in waveform 3m is operative. This " Flip " energizes the brake magnet 52 to stop the balance-wheel at a point determined by the phase of the " Flip." When the bi-stable circuit changes from its first to its second state timing circuits 27 and 34 are energized after a 0.2 second delay imposed by mono-stable circuit 26. Timing unit 27 energizes solenoid 54 for 0.3 sec. to rotate the balance-wheel until the brake-lever falls between two pins while timing unit 34, the length of operation of which is adjusted in accordance with the amount of unbalance, energizes magnet 63 to bring a pin 44 into contact with drill 60 for a period dependent on the unbalance. Timing unit 34 is controlled by oscillator 32, the output of which is controlled in accordance with the charge on capacitor 31. At the end of the drilling period solenoid 63 is de-energized and the balance-wheel moves away from the drill. Timing unit 34 sends a pulse to delay device 36 which restores bi-stable devices 24, 16. Bistable device 24 operates brake magnet 52 so as to release the balance wheel while the impulse supply to timing circuit 18 discharges capacitor 31 and the entire operation is repeated until the wheel is within the approved limit and is then rejected. In a modification (Fig. 7) the light source 130 and lenses 131, 132 image slits 134, 136 on to adjacent pins 44 of the balance wheel. Light passing the pins as they rotate is directed to mirror 138 and from there to photo-cell 140. The output of this cell is amplified and is the waveform shown at Fig. 3c.