361,544. Testing balance of rotary bodies. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. -(Assignees of Stephenson, H. M. ; 1002, Northwood Boulevard, Fort Wayne, Indiana, U.S.A.) Oct. 22, 1930, No. 31733. Convention date, Oct. 22, 1929. [Class 106 (ii).] Comprises a frame mounted on a base and free to vibrate in one plane, means carried by the frame for supporting the body, means for rotating the body on the supporting means, means for applying vibratory impulses to the frame in the said plane and means for varying the strength of the impulses and the plane through the body in which they are applied. A frame comprising longitudinal bars 2, 3 braced together is mounted to swing in a horizontal plane on a pivot 9. The frame carries two driving and support units 13, 14 the distance between which may be varied to accommodate different lengths of rotor to be balanced. The parts of these units are shown displaced for clearness. Each unit comprises two shafts 19, 20 carrying rollers 21 at one end and pulleys 21a at the other end. The shafts are rotatably mounted in the ends of arms 17, 18 which are mounted on a shaft 29 parallel to the shafts 2, 3 and midway between them. The arms may be adjusted by a right- and left-handed screw 27 so that the rollers 21 may be accommodated to different sizes of rotor shafts. A central shaft 24 passes through the arms and is driven by a belt from a motor 32 and transmits the drive through pulleys 34, 33, 21a to the rollers 21. The two units 13, 14 are connected together in spaced relationship by a rod 36 which is fixed to the cross-bar 15 of the unit 14 and secured to the cross-bar 15 of unit 13 by a set-screw 37. The cross-bars 15 are notched at the ends to engage the side-bars 2, 3. When the set-screw 7 of the bearer 6 is clamped the rod 3 is slightly flexed inwards and the bars 15 are clamped. In balancing it is necessary to have two planes of correction, and a guide-bar 38 is provided with stops 39 which are adjusted so that first one and then the other correction plane is brought over the pivot 9 merely by sliding the units 13, 14. Mounted in a bearing yoke 5 is a shaft 40 provided with a chuck 41 for connection to the body to be balanced. Splined on the shaft is a cylinder 42 of nonmagnetic material provided with an inset spiral strip 43 of magnetic material. Located below the cylinder is an electromagnet 44 carried by a yoke 45 and having thin wide poles 46 twisted so that they correspond with the pitch of the spiral 43 and are located one on each side of the cylinder. The yoke 45 is guided longitudinally and may be traversed by means of a rack 50 and pinion 49. The magnet is in circuit with a source of power 53, an ammeter 54 and adjustable resistance 55. A vibration meter 56 has its feeler against one side-bar 3. In use, the units 13, 14 are adjusted to receive the rotor 57 on the rollers 21 and is connected to the shaft 40. One correction plane is then brought over the pivot 9 and the thumbscrew clamped. The motor 32 is started and the magnet 44 energized. The spiral 43 is brought during rotation into line with one or other polepiece and as it passes an impulse in the horizontal plane is given to the frame first in one direction and then in the other. The plane through the body 57 which is horizontal at the time of the impulses can be varied by traversing the polepieces longitudinally of the machine. A position is found in which the impulses are given in the same plane and oppose the unbalanced forces. This is indicated by a minimum vibration of the frame. By adjusting the resistance the imparted impulses can be made exactly equal to those due to out of balance when vibration will cease. By stopping the machine and rotating the rotor until the strip 43 is in line with one pole the plane of unbalance will be located and by reading the ammeter, the amount can be determined. The same operation is now performed for the other plane of correction. A preliminary check may be made to determine the nature of the unbalance. If during rotation, the magnet is unenergized, and the thumb-screw is loosed, and the bearings slid from one extreme position to the other, the reading shows zero vibration at one point, the body is only out of static balance. This may be corrected in the plane found as above. If during the preliminary movement no change in the amplitude of vibration is indicated, the body is out of balance dynamically only and can be corrected by determination of one plane. If there is change of amplitude but no passing through zero vibration both forms of unbalance are present and correction in two planes is necessary.