Patent GB-643986-A (GB)
Title: Improvements in or relating to automatic rotor-balancing apparatus
IPC: G01C25/00
Filed: 1946-09-20
Abstract: 643,986. Automatic control systems. SPERRY GYROSCOPE CO., Inc. Sept. 20, 1946, No. 28275. Convention date, Sept. 20, 1945. [Class 38 (iv)] [Also in Groups XIX, XXIII and XXXVIII] Automatic rotor-balancing apparatus comprises means for rotating a rotor in a support at a predetermined speed, a pair of electrical pick-ups for producing signals from the vibration of the rotor and a pair of material-removers controlled by the said signals and arranged at or near the ends of the rotor. Piezo-electric crystal pick-ups 42, 42<SP>1</SP>, Fig. 6, arranged on opposite sides of the axle of the rotor 1 to be balanced, are connected one to a thermionic valve amplifier 45 and the other to two valves 43, 44 which are alternately biassed off by a relay 48 operated by a multivibrator 47. The outputs of the valves 43, 44 and 45 are connected to a mixer stage 46 in such a way that, when the valves 45 and 43 are operating, their outputs are combined in phase so that the oscillation of the rotor due to dynamic unbalance is measured and, when the valves 45 and 44 are operating, their outputs are combined in antiphase in order to measure the static unbalance. The stage 46 includes a phase-shifting circuit, which is initially adjusted for any one type of rotor, and the output from this stage is passed through a filter 57, a power amplifier 50 having automatic volume control, and a switch 51 to electromagnetically-controlled grinding plungers 521, 531 (see Group XXIII) arranged on diametrically opposite sides of the rotor, one at the top and one at the bottom. The switch 51, which is controlled by a multivibrator 55 synchronized with the multivibrator 47, causes the plungers 52<SP>1</SP>, 53<SP>1</SP> to operate simultaneously or in antiphase according to whether the relay 48 is set for measuring dynamic or static unbalance respectively. A meter and/or cathode-ray oscilloscope may be connected in the circuit before the filter 57 to indicate the amplitude and phase of the unbalance. The rotor field winding 5, Fig. 4, is energized by the depression of a push-button 6 which operates a switch 7 provided with a holding relay 8. The end of the rotor 1, Fig. 5, has a darkened sector so that a beam of light from a source 22, reflected by the rotor and received by a photoelectric cell 14 gives rise to a substantially square-wave output which is applied to the control grid of an amplifier valve 23, the screen grid of which is connected to a time-delay circuit incorporating a neon tube 24 so that the valve 23 does not conduct until a critical speed has been attained. After amplification by a valve 27, the signal from the photo-electric cell is applied directly, and through a circuit 30 which shifts its phase through 180 degrees at a critical frequency corresponding to the desired speed of rotation of the rotor, to a phasesensitive amplifier 28, the output of which is a D.C. voltage of one polarity or the other according to whether the speed of the rotor is above or below the desiredvalue. This D.C. voltage is connected, through a low-pass filter 34, to an amplifier 35, the output of which is connected to a speed-control relay 11<SP>1</SP> in series with the high-impedance coils 38, Fig. 4, of saturable reactors. The relay 11<SP>1</SP> operates, when the desired rotor speed is attained, to connect the rotor field winding 5 through the low-impedance coils 40 of the saturable reactors which thereafter maintain the rotor speed constant under the control of the D.C. voltage derived from the photo-electric cell. After two cycles in which no error signals arise due to unbalance, a trigger circuit 58, Fig. 6, operates the switch 7 to reverse the polarity of one of the three phases of the supply and thus to stop the rotor. A further circuit 59, not described, then releases the holding relay 8 for the switch 7.