Valve control system

Abstract

A hydraulic elevator is employed having the usual call buttons at the respective floors and selector buttons for all floors located in the elevator cab. When a button is pushed to select a floor to which the cab is to travel, up or down, as the case may be, the cab starts moving slowly in the selected direction. During initial movement a cam on the cab triggers components in an electric circuit which, by motivating hydraulic valving causes the cab initially to accelerate to a selected rate of travel after which travel proceeds at the selected rate to a slow down point. At that point another component is triggered and the valving causes the cab to decelerate for a selected interval of travel, after which the cab moves slowly to the level to which it was called. The invention here disclosed is one of a balanced electric bridge circuit which is made constantly sensitive to the rate of travel of the cab by use of a stationary tape extending for the full height of the vertical hoist way. The tape has in it a series of perforations through which light passes from a light emitting diode to a photodetector. Fluctuations in the amount of light caused by changes in speed of travel of the elevator cab causes a constant rebalancing of the resistance conditions in one side or the other of an electric bridge circuit whereby to constantly return the travel of the cab to the selected rate, the deviations being so quickly compensated for as to be unnoticed by the occupants of the cab.