Patent GB-419186-A (GB)
Title: Improvements in and relating to a method of and apparatus for balancing rotating bodies
IPC: G01M1/04
Filed: 1934-02-13
Abstract: 419,186. Testing balance of rotary bodies. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of Thearle, E. L.; 1278, Dean Street, Schenectady, New York, U.S.A.) Feb. 13, 1934, No. 4769. Convention date, Feb. 15, 1933. [Classes 106 (ii) and 106 (iv).] Comprises a method of and means for determining the amplitude and direction of maximum vibration at each of the bearings of the body in three cases : (a) as the body normally is ; (b) with the addition of a known out of balance weight at one end ; and (c) with the addition of a known out of balance weight at the other end. From the six readings taken the necessary corrections to secure balance are calculated. The rotor 1 to be balanced is mounted on the shaft 2 in its usual frame, the pedestals 3 of which carry brackets supporting small generators 4, 5. A single generator may be used and transferred from one pedestal to another as required. A contact device 6 is driven by a flexible shaft 7 from the shaft 2. The generators are connected to the contact device 6 through a switch 8 and galvanometer 9 calibrated in terms of vibration movement of the pedestals. Generators. Each generator 4, 5, Fig. 5, is carried by a bracket 10 rigidly secured to the pedestal. Mounted on a rod or tube 11 secured to the bracket 10 are spaced springs 12. These support the relatively massive magnet 13 of annular form having an annular air gap 14 between the poles. Each spring 12, Fig. 7, has four arms and by means of slits 15 is divided into two parts 16, 16<a> which are secured respectively to the non-magnetic head 17 and to the rod 11. The right hand spring is similarly secured to the head 18 and rod. The axial stiffness of the springs is compensated by a device consisting of two stiff struts 23 having knife edges at the ends located in grooves in blocks 20 carried by the part 18 and a block 22 carried by the rod 11, the blocks 20 being drawn together by two parallel and adjustable springs 24. This device is so adjusted that it assists the relative movement of field structure and rod 11 sufficiently to compensate axial stiffness of the springs 12. Modified arrangements of this compensating device are described. The armature comprises a coil of wire 25 mounted on an insulated annular support 25<a> carried by a spider 25<b> on the rod 11. As the machine pedestal vibrates, the coil moves axially and generates an electromotive force proportional to the velocity of vibration of the pedestal. Contact device. A stub shaft 26a in the casing 26 is driven from the shaft 7 and carries a cam 27 which has a raised surface 27<a> for 180‹ and also a pointer 28 located opposite the middle of the raised surface. A ring member 29 concentric with the shaft 26<a> can be turned through gearing from a handle 37 and carries fixed and movable contacts 31, 32 which are moved into engagement for half a revolution by the cam. A pointer 38 on the ring 29 reads over a fixed scale 39. Operation. A correct balance requires the addition or removal of two masses, one near each end. Four quantities must be determined, the amount and phase of each mass. This is determined in three runs. With the motor run up to a predetermined speed the switch 8 is operated to connect the motor at the end nearest the device 26. The plate 29 is adjusted until reading of the galvanometer is "zero." The pointer 38 gives the phase of maximum vibration. If the contacts are shifted further through 90‹ in the direction of rotation the galvanometer reading will be proportional to the relative amplitude. Thus one rector quantity N is determined. By switching to the other motor a similar quantity F is determined for the far end. A trial weight Wn is applied to the near end and quantities N2, F2 determined. A third run is made with a weight Wf applied to the far end and two quantities N3, F3 determined. From these six quantities the necessary corrections for out of balance can be calculated.