Elevator - A Vertical Transportation I

Date:2016-11-16

An you already know before, most modern elevators are propelled by elevator motors, with the aid of a counterweight, through a system of cables and sheaves (pulleys). By opening the way to higher buildings, the elevator played a decisive role in creating the characteristic urban geography of many modern cities, and promises to fill an indispensable role in future city development.

The practice of lifting loads by mechanical means during building operations goes back at least to Roman times. The Roman architect-engineer Vitruvius in the 1st century BC described lifting platforms that used pulleys and capstans, or windlasses, operated by human, animal, or water power. Steam power was applied to such devices in England by 1800. In the early 19th century, a hydraulic lift was introduced, in which the platform was attached to a plunger in a cylinder sunk in the ground below the shaft to a depth equal to the shaft’s height. Pressure was applied to the fluid in the cylinder by a steam pump. Later, a combination of sheaves was used to multiply the car’s motion and reduce the depth of the plunger. All these devices employed counterweights to balance the weight of the car, requiring only enough power to raise the load.

Prior to the mid-1850s, these principles were primarily applied to freight hoists. The poor reliability of the ropes (generally hemp) used at that time made such lifting platforms unsatisfactory for passenger use. When an American, Elisha Graves Otis, introduced a safety device in 1853, he made the passenger elevator possible. Otis’ device, demonstrated at the Crystal Palace Exposition in New York, incorporated a clamping arrangement that gripped the guide rails on which the car moved when tension was released from the hoist rope. The first passenger elevator was put into service in the Haughwout Department Store in New York City in 1857. Driven by steam power, it climbed five stories in less than a minute and was a pronounced success.

Improved versions of the steam-driven elevator appeared in the next three decades, but no significant advance took place until the introduction of the electric motor for elevator operation in the mid-1880s and the first commercial installation of an electric passenger elevator in 1889. This installation, in the Demarest Building in New York City, utilized an electric motor to drive a winding drum in the building’s basement.

The introduction of electricity led to two further advances: in 1894, push-button controls were introduced, and in 1895, a hoisting apparatus was demonstrated in England that applied the power to the sheave (pulley) at the top of the shaft. The weights of the car and counterweight sufficed to guarantee traction.

By removing the limitations imposed by the winding drum, the traction-drive mechanism made possible taller shafts and greater speeds. In 1904, a “gearless” feature was added by attaching the drive sheave directly to the armature of the electric motor, making speed virtually unlimited.

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