GB643963A - Improvements in or relating to fast and slow speed driving means for electric lifts and the like - Google Patents

Abstract

643,963. Control of two motors FOULDS, Ltd., E. A.. and FOULDS, W. G. Feb. 6, 1945, No. 2980. [Class 38(iii)] Driving means for lifts and the like comprises in combination a high speed alternating-current motor, a direct-current levelling motor which is adapted to be rheostatically braked, and switch means for alternative motor operation. An alternating-current motor 14 is supplied from mains 10 and is coupled to a direct-current motor 17. A transformer 15 affords a high voltage supply through a rectifier 16 and a low voltage supply is obtained from a transformer 19 and rectifier 20. The armature of the direct-current motor is shunted by a braking resistance 22 and the coil of a vibratory relay 21, the contacts of which control the high voltage supply to the field 17b which is connected in series with the coil 23a of a relay 23 controlling the supply to the armature 17a. The field 17b is connected in shunt with a discharge rectifier 24. When the lift approaches a selected floor a selector switch cuts off the supply to the alternating-current motor and a levelling switch energizes the field 17b to send a heavy current through the resistance 22 which energizes the relay 21 to break the direct-current field supply Thereafter the relay 21 will make and break until the braking voltage reaches a predetermined low value and the relay 21 is permanently closed whereupon the relay 23 is energized to close the circuit of the armature 17a and the lift is driven at a low speed until it is levelled at the desired floor. In a modification, the relay 21 is an ordinary relay and a low resistance is shunted across the contacts of this relay and the coil 23a.