Patent GB-498899-A (GB)
Title: Improved method of and apparatus for determining the unbalance of rotors, and enabling them to be correctly balanced
IPC: G01M1/22
Filed: 1937-07-16
Abstract: 498,899. Electric signalling systems. SPERRY GYROSCOPE CO., Inc. July 16, 1937, No. 19784. Convention date, July 18, 1936. [Class 40 (i)] [Also in Group XIX] The phase of an alternating E.M.F. of electromagnetic means sensitive to the vibrations due to unbalance of a rotor is varied and combined directly in opposition to a reference E.M.F. corresponding to the speed of the rotor, the angular position of the electromagnetic means from a reference point and the magnitude of its E.M.F. being measured to give the position and magnitude of the unbalanced mass in the rotor. Extending upwards from a bench 1 are pillars 2 on which is adjustably supported a frame 3. An electromagnetic pick-up 5 has a hollow stem 6 bearing in the frame 3 and having fixed to it a dial 8 co-operating with a stationary pointer 10. The armature 12 of the pick-up pivots on a transverse pin 13 and is provided with a winding 14 connected by leads 15 passing through the stem 6 to the primary of a transformer 16. The coupling between the armature 12 and bearing housing 18 comprises the pointed end 17 of the armature engaging a slight depression in the housing. Upper and lower housings 18, 18<1> are clamped to a spider frame 20 the lower part of which is secured at three points 120‹ apart to the inner ends of leaf springs 25 rigidly secured to an annular base member 26. The springs being at the level of the lower bearing there is little or no vibration at this end. A lamp 28 directs a beam through a lens 29 upon the upper surface of the rotor 19 the beam being reflected to a photo-electric cell 30, the output of which is connected to the primary of the transformer 31. The secondary is connected through leads 32 to a band-pass filter 33 the output of which is connected through leads 36 to a voltmeter 37 or to a cathode-ray oscillograph which is used if the wave forms supplied from the photo-cell and pick-up are unlike. The transformer 16 is connected through an attenuator 38 to leads 32, and by adjusting the knob 39, the effective resistance of the attenuator is varied and hence the voltage from the pick-up may be reduced as desired. The filter 33 serves to cut out voltage of frequency other than fundamental motor frequency arising from vibration due to causes other than out of balance. In use, each rotor is provided with a black spot 43. The pick-up and indicator 8 are initially set angularly with respect to the point at which the light beam strikes the rotor so that when the unbalanced weight at the upper end coincides with the centre of the spot 43, the zero on the dial coincides with the pointer 10. This is accomplished by placing a weight at the centre of the spot, speeding up the rotor to test speed and turning the pick-up so that meter 37 reads zero. The disc 8 is now adjusted with respect to the pick-up so that the zero on the disc coincides with pointer 10 and the nut 44 is tightened up. A rotor is inserted by releasing the clamps and placing the trunnions in bearings carried by the housings 18 18<1> and reclamping. An air nozzle 26<1> serves to rotate the rotor. In order to determine the magnitude of unbalance, the lamp 28 is turned off and the meter 27 read. In order to locate the position, the knob 39 is adjusted so that the output of the pick-up is the same as the output of the photo-cell 30, the setting of the knob being another measure of the unbalanced weight. The lamp 28 is turned on, and the disc 8 turned until the meter 37 indicates zero showing that the pick-up voltage is 180‹ out of phase with that from the photo-cell. The reading of the scale 11 measured in the direction of rotation gives the position of the unbalanced weight with respect to the centre of the black spot. The rotor is now turned upside down and the test repeated for the other end.