GB813837A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

813,837. Automatic speed-control systems. GENERAL ELECTRIC CO. Ltd. Nov. 20, 1956 [Nov. 21, 1955], No. 33299/55. Class 38 (4). In a system wherein the speed of a load driven by an electric motor, e.g. a winder cage, is maintained constant over at least a part of its travel by a speed-dependent voltage and a reference voltage from a tapped impedance, the tapping is arranged to be varied in dependence upon the discrepancy between the actual speed and the predetermined speed to eliminate the discrepancy. In the arrangement, Fig. 1 (Prov.), for controlling the speed of a lift motor by a saturable reactor having a control winding 5 responsive to the difference between the reference voltage tapped from a potentiometer 2 and the voltage output from a tachometer generator 4, compensation for variations in the " creep " speed from its predetermined value corresponding to the position of wiper 16 due to load variations, is provided by the connection of a motor 12 in series in a loop in which the tachometer voltage is opposed to the voltage across points 3 and 17 on the potentiometer to drive wiper 16 to a point where the desired speed is attained. For fast speed running the tachometer voltage is compared with the potential on wiper 1 over a contact 10, and at change-over, when control is transferred to wiper 16 by the opening of contacts 10 and the closing of contacts 8, relay 11 is changed over to introduce the " creep control system described when the tachometer voltage drops below that between points 13 and 3. For operation with constant loads, control during the main travel is over contact 7 and the change-over to creep is achieved by a cam in the shaft which opens contact 7 and closes contact 8 whereby the speed is reduced under the control of a torque-limiting circuit until the creep speed is attained. A polarized relay 6 effects connections for driving or braking according to the direction of current flow through the control winding 5. A flywheel motor and a stabilizing winding for the magnetic amplifier are connected in shunt across the tachometer generator. In a modified arrangement described with reference to Fig. 2 Prov., (not shown), the motor 12 is controlled by a polarized relay in response to error and rate-ofchange signals, and in a further modification, Fig. 3 Prov., (not shown), the motor 12 is controlled by a pair of relays operated by the polarized relay which pair of relays serves also to modify the circuit to produce an exaggerated error signal in the control winding. In an alternative arrangement the motor 12 is omitted and the relay is made to connect in an oscillatory manner reference potentials which are above and below that corresponding to the desired speed. An arrangement using geared potentiometers having rolling contacts as described in Specification 800,407, [Group XXXVII], is described with reference to the Figure accompanying the Complete Specification (not shown).