GB707811A - Improvements in or relating to a motor speed control - Google Patents

Abstract

707,811. Automatic speed control systems. GARRETT CORPORATION. March 29, 1950 [April 6, 1949], No. 7841/50. Class 38(4) A speed control for an electric motor having an armature, and a running field and a speed control field comprises a switching device rendered operative by deviation of the motor from desired speed to connect the control field to a control current source, the current in the control field tending to change the voltage applied across the armature. As shown the speed control is applied to a synchronizing system employing two series wound reversible motors 10, 11 for moving the ailerons of an aircraft. The motors 10, 11 have armatures 12, 13 and running fields 14, 15, and 16, 17 respectively, the armature being connected on one side to one side of the power source and on the other to the common leads of the running fields. As well. as being connected to the ailerons the motors 10, 11 are connected through suitable reduction gears to arms 30, 31 of potentiometers 34, 35 which form a bridge circuit which includes the winding 40 of a normally open polarized relay 41. The relay 41 controls the position of a switch contact 45 which is given a negative polarity whilst a manually operated switch 60 connected to the positive side of the power source serves to energize one or other of relays 65, 66 controlling the direction of rotation of the motors through relay operated contacts 75, 76, and 80, 81. Assuming that the switch 60 is thrown to the dotted line position shown the relay 66 is energized and contacts 80, 81 assume the position shown in dotted lines. The motors then rotate under the control of field windings 14 and 16. If the motor 10 speeds up, or the motor 11 slows down the bridge circuit becomes unbalanced so as to energize the polarized relay 41 in a sense to make contact between contacts 45 and 47. As a result (a) an increased current flows through the field 14 and causes an increased drop across the field with a subsequent decrease of voltage applied across armature 12 and (b) the direction of current in field 15 is such that the magnetizing force created thereby is aiding and in the same direction as that in the field 14. Accordingly the motor 10 is slowed down or the motor 11 speeding up the contact 45 of the relay 41 makes contact with contact 46 and as a result of the consequent current flow through fields 16 and 17 the motor 11 is slowed down. The apparatus may be modified by interchanging the bridge leads 38, 39 and applying to the conductor 50 a positive contact of a negative polarity so that the slower of the two motors is made to speed up. By enploying a 'bridge upon a bridge' circuit the control system may be applied to the synchronizing of a group of motors.