Patent GB-399845-A (GB)
Title: Improvements in and relating to the balancing of rotating members
IPC: G01M1/30
Filed: 1932-01-13
Abstract: 399,845. Phase-difference measurements. TAYLOR, M. K. and FERRANTI, Ltd., Hollinwood, Lancashire. Jan. 13, 1932, No. 1068. [Class 37.] Electrical methods are used to measure the characteristics of the vibrations due to out-ofbalance forces in apparatus for testing the balance of rotors. The flyer 1, Fig. 1, is mounted on air bearings 2, 2 in resilient supports 3, 3. Helices 4, 4 of say solder are applied one at each end of the flyer. Each bearing is connected by rods 5, 5 to electric generators 6, 6 of such type that the voltage rises when the displacement of the..bearings increases and these voltages are measured in a voltmeter V. A high resistance potentiometer p may be inserted in the circuit to safeguard the voltmeter. An air turbine 7 drives the flyer, and a tool similar to a lathe tool is used to remove some of the lower spiral 4. If the speed exceeds the critical the solder in being removed from the right place and the increase of speed is rapid and may be heard in the head phones H. Cutting is continued until the voltmeter reads zero when only a hum is heard in the head phones. The switch s is now moved over and the top spiral 4 treated similarly. In a second form, shown in Fig. 2, for balancing small motors, the armature shaft 11 of the motor 10 is fitted at each end with a spiral 12 either on the shaft or as shown on added metal discs 13, 13. A condenser plate 14 capable of being slowly rotated by hand is placed near a key way 15. The table 17 is mounted on two springs 18, 18 having insulated metal plates 19, 19 mounted on a rigid insulated base 20. Vibrations transmitted to the table vary the capacity of the two condensers formed, by the table and insulated plates. These condensers are connected one at a time with a switch s to a thermionic amplifier formed by a circuit including valves 21, 22. The condensers charged by a battery 23 cause varying potentials to be developed across the resistances 24, 25 which are fed to the grids of the valves. Both outputs are now passed through transformers 26, 27 the secondary of the latter being connected in series with the control grid of a tetrode, pentrode or other suitable valve by way of a grid leak and condenser 28 and to the cathode of the valve by way of the screen biassing battery 29. The secondary of transformer 26 is connected in series with the screen grid and by way of battery 29 to the cathode. A suitable voltmeter 30 is placed across the secondary of the transformer 26. In the anode circuit is a milliammeter 31 which indicates any out of balance with respect to the position of condenser plate 14, the voltmeter 30 indicating the degree. In action, as the locating condenser 14 is slowly rotated, an angle is formed at which a maximum anode current flows giving the angle of out-of-balance and indicates the radial displacement on the disc at which it is necessary to remove solder. The tool is applied at this radius. The other end is now treated in the same manner until the. voltmeter reads zero. The first end is now treated again. It may be quicker to use a trial and error method by cutting and bringing the voltage from each end successively down to zero. Electromagnetic devices may be used instead of electrostatic using magnetic generators such as moving iron or moving coil loudspeaker movements or carbon or other microphones. For the phase locator a small condenser used as described is best or a locating cam may be put in the shaft operating a suitable generator to give the required reference point, or a rotating carbon contact may be used. In addition to the above methods of indicating phase relationship, an oscillographic system may be employed, preferably a cathode ray tube in which are four of the time base (on one pair of plates or coils) is synchronized with the rotation frequency by means of the neondiode time base described in the " Proceedings of the Physical Society," Vol. 43, pages 502- 511, 1931, and the oscillations from the vibration and impulse detectors are mixed and applied to the other pair of plates or coils so that the position of the impulse with respect to the vibration may be quickly viewed on the oscillograph screen. In a modification, the vibration potentials are transmitted by way of a transformer to the screen grid of a pentode valve while the kill potentials are transmitted by way of a second transformer to the control grid of the same valve. The output is measured by a milliammeter. Specification 18260/04, [Class 110, Rotary engines &c.], is referred to.