Patent GB-585440-A (GB)
Title: Improvements in or relating to machines for testing the balance of rotatable bodies
IPC: G01L1/16
Filed: 1944-12-21
Abstract: 585,440. Indicating unbalance of rotary bodies. GYRO-BALANCE CORPORATION. Dec. 21, 1944, No. 25626. Convention date, Dec. 22,1943. [Class 40 (i)] [Also in Group XIX] Apparatus for testing the balance of a rotary member comprises means for rotating the member in axially spaced bearings, a plurality of pressure-sensitive elements disposed at each bearing and angularly displaced around the axis of rotation, and means connected with the pressure-sensitive elements for rendering intelligible the pressure impulses sustained by them due to unbalance in the rotary member. In a preferably right-angled V-groove 21, Fig. 3, in a massive base 20, piezo-electric crystals Q1, Q2 support the bearings 22 of the shaft 15 of the rotary member under test. A . similar arrangement may be provided at the opposite bearing. One of the crystals at each bearing serves to indicate the magnitude and phase of the out-of-balance vector at that bearing when corrections are applied to compensate for the effect at that bearing of another out-of-balance vector referred to the opposite bearing. In Fig. 8, the alternating current from a piezo-electric crystal QLI caused by the out-of-balance vector at the left-hand bearing is fed through a pre-amplifier PALI to the grid of a valve CFLI. The cathode load resistance RC of each valve is equal to the - reciprocal of its mutual conductance and also to the anode load resistance RA. The output at the cathode is therefore equal, but opposite in phase to the output at the anode, and a voltage divider connected across each valve enables attenuated signals of desired strength to be added to the main signals ELI and ERI which are derived from the cathodes. Thus, the signal ELI from the crystal QLI is fed to an amplifier AL together with corrective signals FRI, FRII derived from crystals QRI and ;QRII at the right-hand bearing. Similarly, the signal ERI from the piezo-electric crystal QRI at the right-hand bearing is corrected by attenuated signals FLI, FLII and fed to an amplifier AR. A visual indication of the amplified signals from each bearing is provided by a cathode-ray tube in which a time-proportioned voltage is applied to the horizontal deflection system of a frequency equal to that of the rotation of the rotary member, the unbalance signal causing the vertical deflection, Fig. 12. To start and govern the scanning of the horizontal deflecting saw-tooth voltage, a spot painted on the periphery of the rotary member could be detected by a photo-electric cell. The amplitude A, Fig. 12, of the resulting wave-form would then represent the magnitude of the out-of-balance vector at the bearing under consideration and the displacement of the peak from the origin would indicate the angular displacement of the vector from the painted spot. Separate amplifiers AL, AR and cathode-ray tubes for each bearing could be provided or one set only could be used in conjunction with a switch-over device (Fig. 9, not shown). In another embodiment, the signals from each of the two crystals at each bearing, being 90 degrees out of phase, are compounded to give a circular indication on a cathode-ray tube (Fig. 13). In the apportioning network for this embodiment, two voltage dividers are connected across each of the four valves CFLI &c., Fig. 10, since each crystal now supplies a main signal, e.g. ELI, and two attenuated corrective signals, e.g. FLIa, FLIb, for adding to each of the signals from the two crystals at the opposite bearing. The corrected signals pass through amplifiers ALI, ALII, &c., and influence the deflecting plates of cathoderay tubes CTL, CTR. A single cathode-ray tube could be employed in conjunction with a switch-over device (Fig. 11, not shown). A spot painted on the rotary member can be arranged to produce a protuberance P, Fig. 13, on the circular trace by known electrical connections. Thus, the radius of the circular trace is proportional to the magnitude of the out-of-balance vector at the bearing under observation, and the position of the protuberance P indicates the angular displacement of the vector in relation to the painted spot on the rotor.