GB772326A - Device on electrically-driven elevators for stopping exactly at floor level - Google Patents

Abstract

772,326. Automatic speed control systems. INVENTIO AKT.-GES. Aug. 9, 1955 [Aug. 12, 1954], No. 22897/55. Class 38 (4). [Also in Group XXXVII] When a lift cage is descending and approaching a floor level at which a stop is to be made, at the position a the hoisting motor HM is disconnected by switch S4 and an induction regulator J is energized by closure of switch S<SP>1</SP>. At the same time, a roller R having a lever arm H coupled to the rotor of the induction regulator which is mounted on the cage is brought into contact with a control cam C positioned near the floor. A switch S2 in the output circuit of a tachometer generator T is also closed, and, to initiate a braking operation, a switch in the excitation circuit of an eddy-current brake WB is likewise actuated. The rectified voltage at the terminals K of the induction regulator is, at first, equal to the opposing voltage of the tachometer generator, so that the grid of valve V is at zero potential and the brake WB is not excited. As the lift approaches the floor, the deflection of arm H reduces the secondary voltage of the induction regulator so that the voltage at terminals K becomes less than the tachometer voltage and the grid potential of the valve V is lowered. The resultant decrease in the anode current of the valve increases the excitation of the eddy-current brake derived from valve amplifier Th. The lift is thus retarded until the tachometer voltage is again equal to that at terminals K. When the secondary voltage of the induction regulator becomes zero the lift is stopped, the switches S1, S2 are opened, and a magnetic brake B is applied. For the opposite direction of travel, the switches S3, S5, become effective. In a modification,the induction regulator is replaced by a transformer with a tapered shield between its primary and secondary coils, Fig. 2 (not shown). As the lift approaches a floor, the shield is withdrawn from the magnetic circuit of the transformer, so reducing the coupling between the windings and the secondary voltage. In another arrangement a shield passes between the plates of a capacitor connected in a bridge circuit with three other capacitors, Fig. 3 (not shown). One diagonal of the bridge circuit is connected to a source of alternating-current and the other diagonal is connected through a rectifier to the terminals K. A further embodiment has a sliding contact near the floor co-operating with a potentiometer on the cage so that the output of the potentiometer reduces when the cage approaches the floor.