GB785905A - Improvements in or relating to apparatus for controlling the stopping of electrically-driven high-speed lifts and hoists - Google Patents

Abstract

785,905. Control of D.C. motors. S.A.D.E.E.S. (SOC. ANON. DES ETABLISSEMENTS EDOUX-SAMAIN). Jan. 24, 1956 [Feb. 9, 1955; Oct. 20, 1955], No. 2346/56. Class 38 (3). A lift motor 11 is supplied from a generator 13 having its field winding 14 supplied through reverser 15 and rectifier 16 from an A.C. source 17. A resistor 18, connected in series with the rectifier 16, is shunted by contacts 24, 25, the contact 25 opening when the lift car reaches a predetermined position near a floor at which a stop is to be made. The contact 24 is of the timedelay type and is controlled by a coil 23 subjected to the difference between a reference voltage and the motor armature voltage, the reference voltage being equal to the armature voltage when the motor is operating at full speed. Thus, when the contacts 25, 21 are opened simultaneously, the time for the current in the coil 23 to decrease to a value allowing the opening of contacts 24 is dependent upon the difference voltage previously developed across resistor 22, so that the delay period is proportional to the difference between the full speed of the motor and the actual speed obtaining when the contact 21 opens. The insertion of resistor 18 in series with the field winding 14 causes the lift to decelerate to its levelling speed, and this levelling speed is reached at substantially a fixed point in the lift shaft although the motor may not have reached its full speed owing to the lift having been started from a floor adjacent to the floor at which the car is to be stopped. In the case of a long travelling distance, the difference voltage drops to zero, no time-lag is introduced, and deceleration starts as soon as the contact 25 opens. In a modification, the time-delay relay is energized in accordance with the difference between, a voltage proportional to the motor speed and one decreasing according to a predetermined law. The decreasing voltage results from the discharge of a capacitor which is supplied with a constant voltage equal to the full-speed armature voltage until the cage attains a predetermined fixed point in the shaft. The capacitor is then discharged through a circuit connected to the armature terminals and comprising the winding of the time-delay relay, and also through an adjustable potentiometer connected in parallel with the capacitor, Fig. 3 (not shown). The time delay relay thus remains energized until the decreasing voltage across the capacitor equals the existing motor armature voltage, dropping of the relay causing the automatic change to levelling speed.