Patent GB-695639-A (GB)
Title: Improvements in or relating to balance testing machines
IPC: G01M1/22
Filed: 1950-07-18
Abstract: 695,639. Testing balance of rotary bodies. GISHOLT MACHINERY CO. July 18, 1950 [July 26, 1949], No. 17920/50. Class 106 (ii). A vibration pick-up device for use with a balance-testing machine, comprises a verticallymounted torsional spring rigidly attached to the device, weights adjustable along a rod, a hub rigidly attaching the rod to the spring so that the weights may oscillate the spring, electric switching means in the pick-up actuated by the said oscillations, and a stroboscopic lamp actuated by the switching means and cooperating with a number-band embracing the rotating body under test, the whole permitting the degree and position of unbalance in the workpiece to be determined by a measurement of the amplitude of the oscillations and by an inspection of the number-band under the stroboscopic lamp. The vibration pick-up. Fig. 1 is a plan view of the pick-up with its cover removed and Fig. 2 is a vertical sectional view. A threaded rod 12 supporting adjustable inertia weights 10 and 11 is secured to a vertical flat spring 14 clamped at its ends to the casing of the pick-up. An arm 17 with an upturned end 117 extends from the spring 14 into the casing. A reed 19, (see also Fig. 11), is secured at one end to the arm 17 by an electrically-insulated bracket 20 and touches at its remote end the upturned end 117. The reed 19 and the arm 17 oscillate with the spring 14. The amplitude of the oscillations of the reed 19 are measured by an adjustable contact 32. This contact 32 is mounted on, but electrically insulated from, the end of a centring lever 30 (see also Fig. 13), pivoted at 31 to a ratio bar 28, Fig. 15, which is itself pivoted at 29 to the casing of the pick-up device. The free end of the ratio bar 28 is pulled by a spring 36 into engagement with a ratio-pin 35, Fig. 1. The ratio-pin 35 in its zero position above the centre of a gear-wheel 55 extends from a cylindrical ratio-slide 38, Fig. 2, having a screw-threaded extension 39, the ratio-slide 38 moving endwise in a ratioblock 51 having a long slot 71 through which the ratio-pin 35 extends. The ratio-block 51 is fixed to the wheel 55 and this wheel may be turned through a pinion 56 by a knob 57, Fig. 8, having a pointer 59 moving over a scale 60 on the cover 9. A graduated ratio-nut 41 engaging the threaded extension 39, enables the ratio-slide to be moved relatively to the ratioblock 51. The zero position of the ratio-pin 35 is fixed by a pin 40 in the ratio-block 51 and by a screw 61 so adjusted that when the ratio-block 51 is rotated counter-clockwise to engage it, the centre line of the slot 71 is parallel with and in the same vertical plane as the centre line A-A of Fig. 1. The centring- lever 30 may be moved relatively to the ratiobar 28 and engaging at its end the centring- lever 30. Of the electrical leads 47, 48, 49, Fig. 2, the lead 47 is grounded to the casing and is therefore connected to the arm 17, the lead 48 is connected by a wire 22 to the reed 19, and the lead 49 is connected by a wire 26 to the adjustable contact 32. The leads 47, 48 and 49 are connected to a circuit controlling a stroboscopic lamp. Operation of the pick-up device. Ordinarily two or more of the devices are mounted rigidly at convenient points preferably, though not necessarily, on the bearing members 74, Fig. 9, of the balance-testing machine in which the workpiece 64 undergoing test is revolving on its axis, the two devices picking up the vibration of such bearing or bearings due to the unbalancing factors in two or more correctionplanes in which the unbalancing factors are present. For some workpieces which are relatively thin, such as gears, discs, and the like, only one pick-up device is needed. In Fig. 9, two pick-up devices are shown attached to the bearing-members of the workpiece. The inertia-weights 10 and 11 are chosen and adjusted on their respective threaded members 12 and 13 so that one of each of the devices 72 and 73 may determine the position and amount of unbalance in each of two previously chosen correction-planes 75 and 76 respectively, and such that the device 72 is responsive to unbalance in the correction-plane 75, but not to unbalance in plane 76, and that the device 73 is responsive to unbalance in correction-plane 76 but not to unbalance in plane 75. The bearing members 74, Fig. 10a, of the balancetesting machine are each supported on spherical balls, each of said balls 91 (Figs. 10 and 10a), resting in a concave spherical segment of the frame 69. The bearing members 74 each have two corresponding spherical segments in an inverted relationship to those of the frame 69. These bearing members 74, being supported on balls, have a rolling action that is the equivalent of a pendulum suspension. The natural period of oscillation of the bearing members 74 is determined by the radii of curvature of the seats for balls 91. A high natural frequency may be obtained by the use of short radii of curvature of the seats. When the workpiece or rotor 64 is rotated at a speed above the resonant or natural period of the bearing members and of the inertia-weights 10 and 11 about their pivot spring 14 the inertiaweights 10 and 11 are forced to oscillate at the frequency initiated by the rotation of the unbalanced rotor 64. The ratio-block 51 is set at zero position (see Figs. 1 and 8), by turning the knob 57 (Fig. 8) clockwise to zero so that the ratio-block 51 rests against the end of the stopscrew 61. The ratio-nut 41 is turned counterclockwise until the ratio-slide 38 (Fig. 2), rests against stop-pin 40. As the inertia-weights oscillate about the spring pivot 14 in a clockwise direction from central or neutral position the arm 17 leaves contact with the reed 19, proceeds to its maximum and is stopped from further twisting in that direction due to the resisting force in the twisted spring 14 balancing the inertia force in the weights 10 and 11 set up by the initiating oscillation of the entire mass. The oscillation of the mass then starts in the opposite direction, the inertia-force is reduced, and the twisted spring 14 starts to return the weights 10 and 11 and arm 17 toward their zero or neutral position. As this portion of the oscillation cycle continues the inertia-force becomes zero and the inertiaweights 10 and 11 and associated arm 17 return to zero or neutral position at which point the arm 17 contacts the reed 19. At this instant the electrical circuit which flashes the stroboscope light 67 is completed and the light 67 flashes illuminating a number on a numberband 68 temporarily attached circumferentially to the workpiece or rotor 64. In the manner above described, the next half cycle of the oscillation of the inertia-weights 10 and 11 and associated arm 17 continues, the weights now continuing their counter-clockwise rotation about the pivot spring 14 to a maximum, then returning to neutral or zero position. During this half of the cycle the arm 17 carries the associated reed 19 with it, breaking the contact of the reed 19 with the contact-plate 32. At zero position the reed 19 is again in contact instantaneously with both the upturned end 117 of arm 17 and the contact-plate 32, thus causing the stroboscope light to again flash illuminating a number on the number-band 68. The centring-screw 44 is then adjusted so that the instantaneous contact takes place at zero or neutral position. This is easily determined by observing the numbers on the number-band 68. This band is numbered in twenty equal divisions and its length is just equal to the circumference of the portion of the rotor 64 on which it is mounted; thus zero and 10 on the mounted number-band 68 are diametrically opposite, as are 1 and 11, 2 and 12, and so on. The centring-screw 44 is adjusted until two such diametrically opposite numbers are illuminated alternately, such as 1 and 11, 4 and 14, and so on, the particular number being determined by the location about the circumference of the unbalance in the particular correctionplane being tested. The electrical circuit is so arranged that either of the alternately flashing numbers may be switched off. Then the number remaining and appearing may indicate the heavy side of the rotor 64 in the correctionplane being tested or the light side. When the weights 10 and 11 are in oscillatory motion of constant amplitude and the ratio-block 51 is in some predetermined position such as in Fig. 6, the ratio-nut 41 may be turned in such a direction as to move the ratio-pin 35 further from its central position. If such motion be continued a point will be reached in which the reed 19 will not touch the contact-plate 32 and the stroboscopic light will cease to flash. The settings of the ratio-block 51 and the rationut 41 will then give a direct measure of the amplitude of oscillation of the inertia-weights 10 and 11 about their pivot spring 14. The operator may remove or add weight to the rotor 64, according to choice. A workpiece or rotor 64 should be preliminarily balanced by trial and error until it is in balance within reasonable limits, whereupon an unbalance weight of known amount as great as will be expected to be encountered in commercial balancing operations for a workpiece of this type is applied in the left-hand correction-plane 75, Fig. 9. The inertia-weights 10 and 11 on the right-hand device 73 are adjusted longitudinally on their respectively threaded rods 12 and 13 until no indication of unbalance is apparent as evidenced by the manner in which the stroboscope light 67 flashes. When the weights 10 and 11 are not oscillating about their pivot spring 14 the light 67 either does not flash at all, or flashes intermittently, not regularly, as when the inertia-weights are oscillating in cyclic sequence. The known weight is then removed from plane 75 and attached in the right-hand correctionplane 76 and the same procedure followed as with the left-hand device 72 on the left bearing member 74. The kn