GB719250A - Improvements in and relating to control systems for electric lifts and the like - Google Patents

Abstract

719,250. Control of D.C. motors. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd., and JENSEN & CO., Ltd., G. K. March 25, 1953 [April 18, 1952], No. 9822/52. Class 38(3) [Also in Group XXXV] A high-speed passenger lift 1 is driven by a Ward-Leonard set 5, 6 having automatic speed control dependent on the difference between the voltage of a tacho-generator 15 (on the lift drive shaft) and a reference voltage from a potentiometer 17 which is cam operated in accordance with the position of the lift to give maximum speed between floors and optimum acceleration and retardation at decking levels. The error voltage is applied through an amplifier 12, which may comprise grid controlled rectifiers to the generator field 9. For multi-floor operation the cam 24 may be a spiral type as described with reference to Fig. 5 (not shown). Modifications. The reference potentiometer may be replaced by a variable inductance or capacity coupling, or a profiled light screen and a photo-cell. Acceleration. A capacitor 40 shorted by a contact BR3 when the lift is at rest, charges up to provide a reference voltage giving rapid acceleration when the lift starts, and before the potentiometer 17 has been moved from the decking position. Blocking rectifiers 38, 39 provide that whichever voltage is larger i.e. that from potentiometer 17 or the capacitor 40, will be used as a reference voltage, and the potentiometer takes over as the lift leaves the decking level. Lift operation. (i) Starting from rest the car switch causes the motor supply circuit to be closed and contact BR3 to be opened so that the lift accelerates as described above. (ii) Passing floors:-When potentiometer 17 is moved to the maximum speed setting by cam 24, it is held there by magnet HC while the car-switch is closed, enabling the lift to pass floors at maximum speed. (iii) Stopping: -On release of the car-switch the potentiometer follows the cam to reduce speed as decking level is approached. When the car reaches decking level limit switch FSU or FSD is opened by cam 34 or 35 to cause the motor supply circuit and the brake " holding off " magnet OCB to be de-energized. The control circuit is described in greater detail with reference to Fig. 2 (not shown).