Patent GB-686272-A (GB)
Title: Improvements in balancing machines
IPC: G01M1/22
Filed: 1950-10-10
Abstract: 686,272. Testing balance of rotary bodies electrically. TELEFONAKTIEBOLAGET L.M. ERICSSON. Oct. 10, 1950 [Oct. 13, 1949; Oct. 15, 1949], No. 24710/50. Class 40 (i). In a system for determining the unbalance of a rotor R mounted for free lateral vibration, pickoffs G1, G2 of e.g. electro-dynamic type, associated with the respective shaft. ends are connected. across respective resistors ra, rb and adapted to be connected in turn by a switch CD through an amplifier FS to one coil of a wattmeter W, the .other coil of which may be connected by a switch H to one or other of reference generators SA, SB coaxial with the rotor R and driven therewith by a motor DM. A measurement e.g. in plane A of the rotor is effected by connecting pick-off G1 to the wattmeter and rotating the stator of the operative reference generator e.g. SA until the wattmeter reading is a maximum when the meter reading is a measure of the out-of-balance magnitude and the angular position of the generator stator read off on a scale YA indicative of the angular position of the out-of-balance forces. Generator SB is similarly used for measurements in plane B of the rotor. Since out-of-balance forces in either plane A, B will affect measurements made in the other plane, the voltage derived from the operative pick-off G1 or G2 is compensated by injecting in series therewith a portion of the other pick-off voltage. To this end the mid-points of resistors ra, rb are short circuited and wipers ga, gb adjusted about either side of the respective mid-points according to the magnitude and sense of the compensation required. According to the invention ga, gb are set without using a balanced rotor as follows. With a switch O1, 02 in its normal (neutral) position and wipers ga, gb set to the mid-points a1, b1 respectively, measurement is effected in plane A of an unbalanced' rotor. The stator SA of generator GA is first turned until the wattmeter W reading is a maximum. Then switch O1, O2 is moved to its lower position in which the output of the other reference generator GB is fed over lines N3, N4 across the resistor ra. The stator SB of generator GB and resistor r4 are then adjusted to cancel out the pick-off voltage from G1, indicated by zero deflection of the wattmeter. A weight is now placed on the rotor in the correction plane B and the consequential meter deflection reduced to zero by adjusting gb. This adjustment of gb suffices for all rotors of the same series as that under test. Contacts ga are adjusted in an analogous manner i.e. with G2 and GB conected to the wattmeter, 'and switch O1, O2 normal the stator of GB'is adjusted for maximum deflection. The switch 01, 02 is then moved to its upper position and the stator of SA and rs then adjusted until the deflection is reduced to zero. A weight is then added to the rotor in plane A and the consequential meter deflection reduced to zero by adjusting ga. In modified arrangements, the resistors r3, r4 are replaced by potentiometers Fig. 2 (not shown), and the balancing voltages derived from the reference generators over these potentiometers may be fed in series with the pick-up outputs Fig. 3 (not shown) rather than in parallel as in Fig. 1. The short-circuited points a1, b1 may be at other than the mid-points of the resistors ra, rb.