Safety Devices
Today the typical elevator has a safety system made up of the following components: a speed-sensing device known as a governor; a clamping device, or safety, mounted under each end of the car frame that, when activated, grips the guide rail; a tension sheave (pulley) at the shaft bottom, or pit; and a steel governor (safety) rope.
The governor rope makes a complete loop around the governor sheave and the tension sheave in the pit. Because the rope is fastened to and travels with the car, the governor sheave rotates at a speed corresponding to the speed of the car.
If the hoist ropes break or the car overspeeds, the governor activates a device that grips the governor rope. The pull of the governor rope triggers the safeties, which apply clamping force to the guide rails and bring the car to a safe stop.
Safety devices are also built into elevator doors. When the doors open, the car is prevented from moving away from the landing. However, the car will keep itself level as the load changes due to passengers entering or leaving the elevator.
A "safety shoe" mounted on the doors will prevent the doors from closing on passengers or objects in the doorway. The safety shoe will gently strike the object, retract, and cause the doors to reopen. Another safety feature is a light-ray device, which is often used along with safety shoes. This device causes a door reversal whenever the light ray is broken by a passenger entering or leaving the car.
All elevators are equipped with alarm buttons in case of an emergency. Many also have telephones that passengers can use to call for assistance.
Controlling the Elevator
In the 1950's, automatic elevators began to replace people known as elevator operators. Today microprocessors control many elevator functions, including speed and energy consumption. Today's elevators include braille buttons and voice announcements of stops. Both features are helpful to those who have vision problems.
Under development are systems that respond to and can predict how and when people will be moving within a building. These systems assign elevator cars to destinations before actual demand and reduce passenger waiting times. Elevators of the future will be equipped with laser devices that scan a floor to "see" if passengers are waiting there. If so, the elevator will stop for them; if not, it will continue on.
Elevator Improvements and Designs
The increasing height of skyscrapers has led architects and engineers to design elevators that are faster and more efficient. If an elevator stopped on every floor of a 100-story building, it would take a very long time to reach the top. Thus, most skyscrapers designed today have sky lobbies -floors where people switch from express elevators to local elevators.
Express elevators provide fast, nonstop service from the ground floor to the sky lobbies. Once at a sky lobby, passengers take local elevators to their desired floors. This decreases the amount of time people spend waiting for and riding the elevators.
The Petronas Towers, the world's second tallest buildings, located in Malaysia, are 88 stories high. Each tower has a sky lobby on the 41st floor. With this design, the elevators take up only half the floor space that would be necessary for the same number of elevators running from the ground floor to the top floor.
Double-deck elevators are another way to move people efficiently in tall buildings. New York's Citicorp Tower has 20 double-deck elevators. The double-deck elevator consists of two elevator cabs, one on top of the other in a single car frame. The lower cab serves only odd-numbered floors, beginning at the ground, or first, floor. The upper cab serves only even-numbered floors. A double-deck elevator can handle twice as many passengers as an ordinary elevator.
Some elevators are enclosed by glass; called observation elevators, they enable passengers to enjoy the view as they ride. Glass-enclosed elevators are found in many hotels, malls, and landmarks, such as the Seattle Space Needle and the Eiffel Tower.
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