Patent GB-655151-A (GB)
Title: Apparatus for determining the magnitude and position of the unbalance of a rotor, particularly a rotor of a gyroscope, for the purpose of balancing such rotor
IPC: G01M1/22
Filed: 1944-09-07
Abstract: 655,151. Electric control systems. AKTIEBOLAGET AEROTRANSPORT. Sept. 7, 1944, No. 17132. Convention date, Aug. 10, 1943. [Class 40 (i)] [Also in Group XIX] Apparatus for determining the magnitude and position of the unbalanced mass of a rotor in rotation comprises a frame in which the rotor is mounted for testing, the frame being suspended so that it vibrates in response to the unbalanced forces produced when the rotor is rotated in the frame, the frame being connected to two or more piezo-crystal or other transducers spaced less than 180 degrees from one another, each crystal being connected to a corresponding plate in a cathode-ray tube, the plates being orientated around the axis of the tube in the same way as the crystals are arranged round the frame, the trace on the tube thus forming a circle, or portion of a circle, of radius proportional to the amount of unbalance, means being provided to produce a reference potential which affects the trace to indicate the angular position of the unbalanced mass. The rotor 2, Fig. 1, under test is journalled in a frame 4 fixed at each end by a clamp 6 to a ring 5 connected to a stand 9 by four equally-spaced rods 7. The outer end of each rod 7 carries a metal plate 8 bearing against a respective piezo-electric crystal a, b, c or d mounted in a sleeve 12, initial pressure between the plate and the crystal being provided by a spring 14 and adjusting screw 13. One pair of crystals b, d (Fig. 3), is connected through amplifiers 15, 17 and filter 19 to a pair of deflecting amplifiers 15, 17 and filter 19 to a pair of deflecting elements B, D in a cathoderay tube 21, the other pair of crystals a, c being similarly connected to another pair of deflecting elements A, C. The elements B, D, and A, C are spaced around the tube 21 in a manner corresponding to the spacing of the crystals b, d and a, c around the frame 4. The potentials generated by the vibrations of the frame 4 cause a circular deflection of the cathode-ray having a diameter related to the amount of out-of-balance of the rotor. A change-over switch is provided to connect the tube to the two pairs of crystals at the other end of the frame 4. To determine the position of the out-of-balance mass, the rotor under test has bright and dark parts from the former of which light from a source 22 is reflected to a photo-electric cell 24 connected through an amplifier 25 and filter 26 to an impulse generator 27 which supplies a sharp impulse to a grid 28 in the cathode-ray tube at a known point in each rotation of the rotor 1. This causes the cathode-ray trace to become momentarily brighter, the position of the bright spot Z giving an indication of the position of the out-of-balance mass in the rotor. The bright and dark surfaces may be provided on a graduated cap which is slipped on the end of the rotor being tested. A second cathode-ray tube 33 may be used to indicate the speed of the rotor, a known frequency being applied to one pair of plates 34 and the impulses controlled by the photo-electric cell 24 to another pair of plates 35. Two, three or six crystals may be used, and the crystals may be replaced by condensers or coils. In an alternative arrangement, Fig. 6, impulses from two pairs of crystals a, c and b, d are passed through a common amplifier 57 and filter 38. The crystal pairs a, c and b, d are connected respectively to pairs 49, 50 and 51, 52 of thermionic valves in a preamplifier 39, both valve pairs being connected to the main amplifier 57. The outputs from the valve pairs are alternately suppressed by impulses from an oscillator 40. The output from the main amplifier 57 passes to valves 60, 61 the outputs of which are alternately suppressed by the oscillator 40 and are connected to pairs of plates A, C and B, D of a cathode-ray tube 21. The arrangement is such that, when the output from the crystals a, c is passing through the amplifier 39, the output from the main amplifier 57 is passing to the plates A, C and similarly for the crystals b, d and plates B, D. Timelag devices 64, 65 are interposed before the plates A, C and B, D. Reference impulses originated by the bright surface of the rotor control a device 46 which injects suppressing impulses into the main amplifier 57 and thus causes the cathode-ray trace 67, Fig. 5, to swing towards the centre of the screen at the known point in the rotation of the rotor. Alternatively, the reference impulses may be arranged to deflect the cathode-ray outwards or the ray may normally be suppressed and be operative only at the moment of receipt of the reference impulse, giving a trace 69 of the kind shown in Fig. 8, the angular position of the trace indicating the position of the out-ofbalance mass and the position of the outer radial edge of the trace giving the amount of the said mass. The speed of the rotor is indicated by observing bright spots 70 on the trace controlled by a grid 28 which is supplied with impulses of a known frequency from an oscillator.