Patent GB-406772-A (GB)
Title: Improvements in and relating to the balancing of rotary bodies
IPC: G01M1/22
Filed: 1932-09-26
Abstract: 406,772. Testing balance of rotary bodies. FORD MOTOR CO., Ltd., 88, Regent Street, London. Sept. 26, 1932, No. 26722. Convention date, June 17. [Classes 106 (ii) and 106 (iv).] Comprises a method of dynamic balancing in which the body is formed with a dynamically overbalanced portion located in a predetermined angular position or within a predetermined angular range whereby unavoidable variations in forming will change only the amount of overbalance, then ascertaining the amount and angularity of the overbalance and removing it whereby the general angular position of the overbalance may be located so that removal thereof will necessarily occur within a predetermined angular range. The invention is described in connection with the balancing of a crankshaft Fig. 16, with four crank throws 14 each 90‹ apart the two throws on each end being partly counterbalanced by weights 11 forged on the shaft between the throws. Split weights 12 are clamped around each crank pin equal to the weight of the heavy end of the rod plus half the weight of the rod. A pair of flanges 13 one near each end are provided to coact with the weights 11 so as slightly to overbalance the throws and weights 12 so that metal will never have to be removed from the crank-throw side of the shaft. The crank shaft 10 is rotatably mounted in a pair of supports 19 free to vibrate transversely to the axis of the crank shaft. The latter is rotated by a synchronous motor 20, Figs. 5, 6, the armature of which is mounted on a tubular shaft 22 which drives through a universal joint 23 a splined shaft 25 extending back through the shaft 22 the free end being secured to a diaphragm 26, Fig. 7, clamped between discs 27 the outer one having a sleeve 28 adapted to fit over one end of the crank shaft to which it is secured by a spring- pressed key 29 engaging a key-way on the shaft. The motor may be started and stopped from either side of the machine through a shaft 31, switch mechanism 32 and buttons 33. Apair of carriages 35 are slidable in the frame 15 each carriage comprising a pair of truss members 36 secured thereto by spring strips 37. The upper ends are secured to a fulcrum plate 38 by strips 39. A downward extension 40 from the plate 38 is bored to receive in ball and roller bearings a shaft 41 which receives the support 19 which is offset so that the axis aligns with the centre of the flange 13. Each plate 38 is provided with an electric clamp operated by a solenoid 47. To enable the natural period of vibration of the support to be tuned to slightly higher than the frequency of rotation of the shaft, each carriage is provided with four flat springs 48. The intermediate portions of the centre two springs are clamped to opposite sides of the extension 40 each end of these two being adjustably clamped to the ends of the two outer springs. The centre portions of the outer pair of springs are clamped to adjusting screws 50 mounted in brackets 51 integral with the carriage. Indicating mechanism. A beam 52 is fixed to each lower end of the extension 40 and has extending from its ends bars 53 which are connected by a rod 54. A pair of minor trusses 55 are resiliently secured at the bottom by spring strips 57 to a fixed bracket 56 and at the top by spring strips 57 to a minor fulcrum plate 58 connecting the upper ends of the trusses. An arm 59 extends down from the plate 58 the lower end having a vertical slot. A bracket 61 connects each of the lower portions of the truss members with the rod 54. The movement of the target 60 is thus an amplification of the movement of the part 19. Damping. A copper plate 63 attached to the plate 58 moves in a strong magnetic field produced by a core 62 having a winding 64 and constitutes a damping device. Optical projection. A centrally located source of light 67 is focussed on targets 60 by condensers 69. Two telescopes 70 are focused on slots in targets 60. The light traversing the. target is reflected by prisms 71 through a special lens 73 convex in a longitudinal plane only to a prism 74 and is reflected back towards the centre of the machine to an eight-sided mirror 75 driven through an 8 : 1 reduction gear in time with the crankshaft. A suitable arcuate screen 76 is provided upon which the target slot is focused by the telescope. If during a rotation of the crank shaft a target 60 is vibrating a sine wave path will be described on the scale 76 the peak of which after allowing for lag of the damping device, corresponds to the angular position of unbalance. Drive for mirror. The inner end of the motor shaft drives a shaft 78 which in turn through spiral gears 81 drives a shaft 80 which drives through spiral gears 82 the mirror shaft 83. By adjusting the knob 91 and disc 90 the shaft 83 may be moved longitudinally against the influence of a spring which movement owing to the spiral gears being in mesh serves to adjust the phase of the mirror. Null reading. Each telescope is adjusted from a disc 101, Fig. 5, through worm gear 99, 98, and quadrants 97, 95 by which shaft 94 is rocked and arm 93 carrying telescope swung over. The peak of the wave is brought to " zero " line of telescope by manipulating handle 90 and then is lowered to the centre of the scale by using disc 101. The angle and number of inch-ounces may then be read off. Having ascertained these values while the bearing at one end is secured from vibration by its clamp, the opposite end being allowed to vibrate, the operation is repeated for the other end. The shaft is then marked and holes drilled in the flanges 13.