Elevators began as simple rope or chain hoists. An elevator is essentially a platform that is either pulled or pushed up by a mechanical means. A modern day elevator consists of a cab (also called a "cage" or "car") mounted on a platform within an enclosed space called a shaft or more correctly a "hoistway". In the past elevator drive mechanisms were powered by steam and water hydraulic pistons.
In a "traction" elevator, cars are pulled up by means of rolling steel ropes over a deeply grooved pulley, commonly called a sheave in the industry. The weight of the car is balanced with a counterweight. The friction between the ropes and the pulley furnishes the traction which gives this type of elevator its name.
Hydraulic elevators use the principal of hydraulics to pressurize an above ground or in-ground piston to raise and lower the car. Roped Hydraulics use a combination of both ropes and hydraulic power to raise and lower cars. Recent innovations include permanent earth magnet motors, machine room-less rail mounted gearless machines, and microprocessor controls.
Which technology is used in new installations depends on a variety of factors. Hydraulic elevators are cheaper, but installing cylinders greater than a certain length becomes impractical for very high lift hoistways. For buildings of much over seven stories, traction elevators must be employed instead. Hydraulic elevators are usually slower than traction elevators.
In 1853, Elisha Otis introduced the safety elevator, which prevented the fall of the cab if the cable broke. The design of the OTIS safety is somewhat similar to one type still used today. It consists of knurled roller(s) that lock the elevator to its guides should the elevator descend at an excessive speed, which is monitored by a governor device. The first electric elevator was built by Werner von Siemens in 1880. The safety and speed of electric elevators were significantly enhanced by Frank Sprague.
Modern Elevator Construction
Today, elevators are built under strict supervision of the Building Codes. Model Codes which are the standard in most US jurisdictions require compliance with the American Society of Mechanical Engineers' (ASME) standards for the installation, maintenance, and inspection of elevators. In Canada, the governing authority is the CSA (Canadian Standards Association). In addition other related standards are likely required to be complied with as specified by Local Authorities Having Jurisdiction.
Today, all new elevators are computer-controlled and microprocessor based. This allows the elevator system to place cabs where they are most needed in the interest of smooth running, with behavior based on analysis of building use called "Traffic Studies." Computer control also permits greater control of access to various floors of a building after hours and on weekends. Methods of access control include card readers, keys, and access codes entered into the control panel of the elevator.
Source: WikiPedia - Elevator History
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