| 摘要 |
1,192,874. Control of D.C. motors. ENGLISH ELECTRIC CO. Ltd. 9 May, 1969 [13 May, 1968], No. 22606/68. Heading H2J. A D.C. hoist motor has an armature 10 and field winding 11, and is supplied from source 12 whose current output is limited. A field control unit 17 receives a signal on line 16 which represents the armature voltage, whereby the field excitation is varied in inverse proportion to the armature voltage when the armature current is at a maximum. An isolator 20 receives a signal proportional to the armature current, whilst a tachometer generator 24 is associated with a capacitor 25 to provide a signal representing the acceleration of the motor. A summing amplifier 22 receives the signals on lines 21, 26, and, when the hoist is lowering a load, produces on line 27 a signal representing the armature current required to produce sufficient torque to balance the load torque. In the field control unit 17, the signals on lines 16, 27, are opposed to set a limit below which the motor flux cannot fall. This prevents the load from overhauling the motor. |
