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balmoralbalmoral asked in what decade did elevators become automated, ( self-leveling), without the need of an operator?
And got the following answer:
1880's. The history of power elevators in the U.S. began in 1850, when a crude freight hoist operating between two adjacent floors was installed in a New York City building. In 1853, at the New York Crystal Palace exposition, the American inventor and manufacturer Elisha Otis exhibited an elevator equipped with a device called a safety to stop the fall of the car if the hoisting rope broke. In this event a spring would operate two pawls on the car, forcing them into engagement with racks at the sides of the shafts so as to support the car. This invention gave impetus to elevator construction. Three years later the first passenger elevator in the U.S., designed by Otis, was installed in a New York City store. In these early elevators, a steam engine was connected by belt and gears to a revolving drum on which the hoisting rope was wound. In 1859 an elevator raised and lowered by a vertical screw was installed in the Fifth Avenue Hotel in York City. In the 1870s the rope-geared hydraulic elevator was introduced. The plunger was replaced in this type by a relatively short piston moving in a cylinder that was mounted, either vertically or horizontally, within the building; the effective length of the stroke of the piston was multiplied by a system of ropes and sheaves. Because of its smoother operation and greater efficiency, the hydraulic elevator generally replaced the type with a rope wound on a revolving drum. The electric motor was introduced in elevator construction in 1880 by the German inventor Werner von Siemens. His car, carrying the motor below, climbed its shaft by means of revolving pinion gears that engaged racks at the sides of the shaft. An electric elevator was constructed in Baltimore, Maryland, in 1887, operated by an electric motor turning a revolving drum on which the hoisting rope was wound. Within the next 12 years, electric elevators with worm gearing connecting the motor and drum came into general use except in tall buildings. In the drum elevator the length of the hoisting rope, and therefore the height to which the car can rise, are limited by the size of the drum; space limitations and manufacturing difficulties prevented the use of the drum mechanism in skyscrapers. The advantages of the electric elevator, however, including efficiency, relatively low installation costs, and virtually constant speed regardless of the load, spurred inventors to search for a way of using electric motive power in skyscrapers. Counterweights creating traction on electrically driven sheaves solved the problem. Since the introduction of electric motive power for elevators, various improvements have been made in motors and methods of control. At first, single-speed motors only were used. Because a second, lower speed was desirable to facilitate leveling the car with landings, low-speed auxiliary motors were introduced, but later several systems were devised for varying speed by varying the voltage supplied to the hoisting motor. In recent years devices for automatic leveling of cars at landings are commonly used. Originally the motor switch and the brakes were operated mechanically from the car by means of hand ropes. Soon electromagnets, controlled by operating switches in the car, were introduced to throw the motor switch and to release a spring brake. Push-button control was an early development, later supplemented by elaborate signal systems.