Patent GB-511320-A (GB)
Title: Improvements in apparatus for testing the balance of rotors
IPC: G01M1/22
Filed: 1938-06-11
Abstract: 511,320. Testing balance of rotors. SPERRY GYROSCOPE CO., Inc. June 11, 1938, No. 17366. Convention date, June 12, 1937. Addition to 498,899. [Class 106 (ii)] [Also in Group XXXVIII] Comprises apparatus for determining the unbalance of a rotor by electromagnetic means as in the parent Specification and consists in mounting the rotor so that one point of its axis is prevented from vibrating while the vibration of another point of the axis is measured electromagnetically without the rotor contacting with the electromagnetic means. A bedplate 1 mounted upon a table 2 has upwardly and downwardly extending arms 3, 4 printed with slide bearings 5, 5' for shafts 6, 6<SP>1</SP> provided with teeth with which mesh pinions actuated by knobs 7, 7<SP>1</SP>. The shafts 6, 6<SP>1</SP> carrying pointers 8, 8' cooperating with degree scales 9, 9' on discs 10, 10<SP>1</SP> turning with electromagnetic pick-up units 11, 11'. These are similar and each comprises one or more horseshoe magnets 12 having a depending pole 13 of soft iron on which is carried a coil 14. The magnet 12 is adapted to cooperate with an armature 15 comprising a soft iron ring fixed on the rotor frame 16. The pole 13 inserted through the apertured centre of ring 15 and under the rotor unbalance the armature moves in an eccentric path around the pole without contatting with it causing a voltage in coil 14 of the frequency of the rotor speed. The armature is threaded into a vertically adjustable housing carrying a ball bearing for a rotor trunnion. The rotor frame 16 is of spider form having three arms radiating from hubs. Each arm has upper and lower horizontal members 23, 23<SP>1</SP> and connecting member 24. Spool-shaped studs 25, 25<SP>1</SP> are fixedupon outer ends of members 23, 23<SP>1</SP> for engagement in triangular apertures 27, 27' provided in upper and lower supporting leaf springs 26, 26<SP>1</SP>. ,Each set of springs is spaced apart 120 degrees from the next. When a rotor is inserted into the ball bearings, the springs 26. 26<SP>1</SP> are substantially on a level with the upper and lower correction planes " of the rotor. The frame 16 is adapted to be selectively supported at either " correction plane " at will by moving knob 30. This knob is on a vertical shaft having cams engaging slots in blocks adapted to slide in casing 28. The knob 30 is connected by linkages with similar cam shafts block and casings at the outer ends of each set of springs. The sliding blocks carry the outer ends of the springs and the cams are so arranged in phase that when the upper set of blocks and springs are pushed in towards the rotor the lower set are slid outwards. Thus when one set of studs 25<SP>1</SP> engage the narrow part of the triangular slots, the other set engage the inside parts and are free to oscillate. In an intermediate position of the knob, both springs 26, 26<SP>1</SP> engage their studs 25, 25<SP>1</SP> and firmly support the rotor frame at both ends, thus facilitating insertion or removal of the rotor. A switch 44 operated from button 30 selectively connects units 11, 11<SP>1</SP> to leads 45 of an indicating circuit. To obtain a reference voltage a lamp 47 directs a beam on to the underside of the rotor, the reflected light being received by a photo cell 50. The intensity of the light can be varied by turning knob 49 to vary resistance in the lamp circuit, Half of the under surface may be polished and the other half left dull. As the rotor turns the output of cell 50 varies at rotor frequency which is that of the output of unit 11, 11'. The cell 50 is connected by leads 51 to the mixer and attenuator 46. This comprises a transformer 52 with two primary windings connected to leads 45, 51 and a single secondary connected across a potentiometer 53. Leads 54 connect to a band filter 55 connected by leads 56 to an amplifier 57 connected to a voltmeter 59 or cathode ray oscillograph. In use the rotor is inserted and secured. Weights are placed upon the ends of rotor in a common vertical plane through one end of the unpolished surface of the rotor and the air from a nozzle allowed to rotate it. The frame is allowed to pivot in the lower correction frame. At speed, the knob 7 is operated to move the pick-up 11 down so that the pole 13 enters the opening in the armature 15. With lamp 47 turned off the meter 59 is now read to indicate pick-up voltage only. The pick-up 11 is now raised and lamp turned on and knob 49 adjusted so that meter 59 reads as before. The pick-up is now again lowered and angularly adjusted until meter 59 reads zero. The equal output of pick-up and cell are directly out of phase. Indicator 10 is now adjusted angularly so that point 8 reads zero. The scale of 9' is then similarly set. To test balance, the rotor is allowed to pivot in the lower " correction plane" and output of pick-up 11 read on meter 59 with lamp unlit. The pick-up is raised and lamps 47 lit and regulated until output of meter 59 is the same. This corresponds to magnitude of unbalanced weight. The pick-up is now lowered and turned until meter reads zero. The indication of scale 9 gives angular position. The. test is repeated for the other " correction plane."