How Do Elevators Work?
Perhaps the best way to illustrate how elevators work is to take a virtual trip to the surprisingly well-fortified WiseGEEK offices on the 65th floor of a modern office building. As you first enter the lobby, you’ll notice a bank of elevators clustered together. What you’re actually seeing is one set of doors and a call button. When you press that call button, a command is sent to a computer controlling all of the elevators. The computer determines which of the elevators is moving in a downward direction and is closest to the ground floor. When the selected elevator car reaches the ground floor, the computer commands the electric motor at the top of the elevator shaft to stop gradually. Once the computer senses that the elevator’s door and the lobby door are at the same level, it commands electrically powered arms to retract both doors. At this point, you may enter the elevator car itself. By pressing the button numbered “65,” you have now sent an order to the computer controlling all
Elevator installation is a mature business, yet change is under way as office space and energy get pricey. Most buildings that are taller than four stories use traction elevators. A motor at the top of the shaft turns a sheave—essentially a pulley—that raises and lowers cables attached to the cab and a counterweight. Gears connect the motor and sheave in slower systems. Faster elevators are gearless; the sheave is coupled directly. Either way, the machinery typically fills an entire room above or beside the top of the shaft, occupying what could be prime penthouse space. But innovations are allowing builders to squeeze the equipment into the head of the shaft itself or against a side wall. “We are steadily shifting to gearless, machine room–less designs,” says Jeff Blain, senior project manager at Schindler Elevator in New York City. Some companies are using permanent-magnet gearless motors, which are smaller than traditional designs but have become just as powerful. And Otis Elevator
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