Patent GB-650263-A (GB)
Title: Improvements in or relating to balancing machines
IPC: G01M1/22
Filed: 1948-01-26
Abstract: 650,263. Testing balance of crank-shafts &c. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Jan. 26, 1948, No. 2340. Convention date, March 23, 1939. [Class 40 (i)] [Also in Group XIX] A machine for analysing the amount of unbalance of a rotor 5, such as a crank-shaft, having four preselected balancing points on the surface thereof, the unbalance components of which are to be determined, the first two, 1 and 4, of these points being in one axial plane and the second two, 2 and 3, being in a separate axial plane, comprises yieldable mountings 6, 7 for the rotor so as to allow free oscillation thereof in at least one plane as a result of unbalance, electromagnetic means 16, 17 generating current proportional to the unbalance, an electromagnetic potentiometer network for yielding a first resultant current nullified with respect to the current component caused by unbalance at (for example) point 1, means for yielding a second resultant current component nullified with respect to the current components caused by unbalance at points 2 and 3, and means for combining the first and second resultant currents thereby to yield an indication of the unbalance at point 4. The full circuit is shown in Figs. 3A and 3B (not shown). In the simplified circuit shown in Fig. 5 for measuring the unbalance at point 1, the pick-up 'coils 16, 17 are connected to a potentiometer network B<SP>1</SP> including reversing switches 67, 74, 99 and resistors 59<SP>1</SP>, 59. The currents from the coils are amplified at A<SP>1</SP>, and supplied to the voltage moving coil 85 of a wattmeter. The stationary current coil 87 of the watt-meter is connected with the stator of a sine wave generator 57 coupled to the rotor 5. The stator has two windings 90 degrees apart, and it can be rotated to alter the phase change of the output, and so give an indication of the position of unbalance in the rotor 5. With the stator voltage 90 degrees out-of-phase with the pick-up voltages from points 2 and 3, the watt-meter reading is zero, and the effect of unbalance at these points is nullified. A potentiometer contact 63<SP>1</SP> can be adjusted to take a fraction of the larger of the two pick-up voltages (e.g. that from coil 17), and the reversing switches operated to subtract one of the pick-up voltages from the other, so that the voltage of only one pick-up appears across the resistor 63, the other being nulled. The unbalance due to point 4 has thus been nulled, and therefore the voltage remaining is caused by unbalance at point 1. If the watt-meter is calibrated in terms of resistor 63, it can read this unbalance voltage directly. Preferably, however, a nulling generator 100, always in phase with generator 57, is used to produce a bucking voltage which is opposite to that due to point 1 across the resistor 63. By adjusting a nulling potentiometer 78 until the watt-meter reading is zero, the potentiometer setting is a record of the unbalance of point 1. To measure the unbalance of other points, further different networks, nulling potentiometers, and generators are used to avoid waste of time in changing adjustments. For example, to read the unbalance of point 2 (or point 3), generators 58 and 137 (not shown) are used instead of generators 57 and 100, respectively. For point 4, the generators 57 and 100 are used. A generator 25 (not shown) for eliminating initial unbalance and calibrating of the machine, has four windings spaced 90 degrees apart, and it is possible to obtain by potentiometers and switches a voltage from each winding varying in amount and reversible in direction. Two windings can be put in series with each pick-up coil 16, 17, to null or compensate the voltages from the latter. The generator 25 is only used when a perfectly balanced rotor or crank is not available, and an unbalanced rotor or crank 5 is placed in the machine for the purposes of initial calibration. The amplifier circuit includes four valves, employs negative feed-back, and is designed to eliminate undesired oscillations and so that a change in phase shift due to changing amplitude of voltage at frequencies ranging from 300 to 3600 cycles per minute is very small. A resistor and switch for each pick-up coil 16, 17 allow the choice of either of two proportions of the pick-up voltage, so that the sensitivity can be varied. In use, when a balanced rotor is provided, or after the voltages produced in the pick-up 16, 17 have been compensated by the generator 25 as described above, the network is adjusted to prohibit the passage of undesirable voltages before the actual rotor to be tested is substituted in the machine. This involves the placing of trial weights at the points 1, 2, 3, and 4 in turn, and adjusting the generators, potentiometers, and reversing switches so that four circuits will give independent indications of unbalances at the four locations. These adjustments are necessary each time a different type of crank-shaft is to be tested. U.S.A. Specification 2,165,024 is referred to.