Patent GB-841570-A (GB)
Title: Method and apparatus for the balance centering of rotors
IPC: G01M1/04
Filed: 1956-08-23
Abstract: 841,570. Correcting rotary unbalance. AVERY Ltd., W. & T. (Schenck Maschinenfabrik G.m.b.H., C.). Aug. 23, 1956, No. 25728/56. Class 106 (2). [Also in Group XXXVIII] Apparatus for centre-machining a rotor comprises adjustable bearings for supporting the rotor, electrical means mounted in the housing for measuring the magnitude and phase of the unbalance in selected balancing planes, displacement devices for moving the axis about which the rotor rotates in a phase and by a magnitude determined by the unbalance measurements, and drilling means fixed in the housing for marking the axis of rotation when the unbalance is zero. As shown (Figs. 1a, 2a, 3) a Cardan shaft 104 is mounted between supports 102, 103 each containing a vibration pick-up 102<SP>1</SP>, 1031 and a motor 310 for driving the shaft 104, and a phase-reference generator 311, giving sine and cosine voltage outputs synchronous with the unbalance voltages in the pick-ups. The unbalance voltages and the reference voltages are fed in known manner to watt-meters 115, 116 which indicate the perpendicular components of the unbalance at the left or right-hand bearing, as determined by a switch 140. Motor 310 drives the shaft 104 via sprocket-wheels 325a<SP>1</SP>, 325a<SP>11</SP> and a chain 125, sprocket wheel 325a<SP>11</SP> being attached to a hollow shaft 205 carrying a flange 206a to which the test rotor 104 is bolted. Surrounding the hollow shaft 205 is a cam spindle 212 mounted on bearings or sleeves 209, 210, and having two eccentric cam surfaces 213, 214 which are circular cylinders whose axes are equally inclined to the spindle axis. Each cam surface is located by four hemispheres 217<SP>1</SP>-217<SP>1111</SP>, 218<SP>1</SP>-218<SP>1111</SP>, supported in guides mounted on the fixed housing 105. The upper hemispheres are spring-loaded, and the lower hemispheres are axially adjustable by a knob 111, whereby the axis of shaft 205 is angularly displaced relative to the housing 105. The cam spindle 212 is also coupled to the stator or motor 310 through a differential gear 320 and sprockets 325b<SP>1</SP>, 325b<SP>11</SP>, both the cam spindle 212 and the stator housing of motor 310 being rotatable together by a knob 312. Inside the hollow shaft 205 is a further shaft 128 whose axis is fixed with respect to the housing 105, which carries a centring tool 203. The motor 310 is energized to drive the rotor 104 so that meters 115, 116 indicate the unbalance components. The location of the peaks on cam 212 is changed by rotating the knob 312, which rotates the angle of the phase reference voltages by rotating the housing of the generator 311, until the unbalance component indicated on watt-meter 116 is zero, and meter 115 indicates the magnitude of the unbalance, simultaneously bringing the peaks of cam spindle 212 into the correct phase position to compensate for the inherent unbalance in shaft 104 by displacement of the axis of rotation. Knob 111 is then rotated to produce this displacement until meter 115 also indicates zero. This is performed for the balancing plane at each support, and finally switch 151 is operated to reduce the speed of the motors 310 and energize motor 130 which drives shaft 128 to cause the centring tool 203 to mark the true axis of rotation on the end faces of shaft 104. The apparatus may be used to determine the centre of a disc-shaped rotor, utilising only one support 102, and the displacement mechanism located inside the housing 105 may be oil-filled. The unbalance mass of the cam spindle 212 due to its eccentricity may be mechanically compensated by a pendulum 507 (Fig. 5a) attached to a bearing-plate 510 between the leaf-spring supports 5031, 503<SP>11</SP> by a cross-spring mounting 508. The upper end of the pendulum is displaced by radial movements of the cam surface and produces correspondingly opposing movements of a weight 509 attached to the lower end of the pendulum. Electrical compensation may be effected by a potentiometer fed with an appropriate voltage from generator 311, and opposing the output from the pick-ups 1021, 1031 by an amount determined by the slider which is mechanically attached to the screwproducing axial movement of the cam spindle 212. The mechanical or electrical compensating apparatus may also be used to simulate an unbalance mass which will subsequently be added to the rotor during use. The invention may also be applied to a vertical rotor whose unbalance is analysed into perpendicular components in two axially-spaced planes. As shown (Fig. 7a) a workpiece 604, clamped at 602, is driven by a hollow shaft 702 through gearing 712, 712a and a shaft 621 attached to a motor (not shown). Inside the shaft 702 is the centring tool 721 whose axis is fixed relative to the housing 705. Surrounding the shaft 702 is a cam spindle 912 with four concentric cam surfaces 914<SP>1</SP> each of which is located relative to the housing by four hemispheres 717, those on the left being spring-loaded, and those on the right being individually adjustable axially by knobs 724. The cam spindle 912 is also driven by shaft 621 through gears 713, 713a, at half the speed of shaft 702 and is of square crosssection (Fig. 10), the cam surface members 9141 comprising rings mounted in pairs on spring- plates 904 attached to the surfaces of spindle 912. The upper rings 914<SP>1</SP> are displaced from their central positions in perpendicular directions by their appropriate knobs 724<SP>1</SP> to eliminate unbalance in an upper balancing plane, and then the lower rings are similarly displaced to remove unbalance in a lower balancing plane. The apparatus may be made automatic by using the wattmeter pointers in association with switch contacts to control electric motors rotating the knobs 724. Specifications 715,627, 744,662, 756,168 and 757,765 are referred to.