Elevator

Today's passenger elevators are not fundamentally different from the Otis original. Practically all are electrically propelled and are lifted between two guide rails by steel cables that loop over a pulley device called a sheave at the top of the elevator shaft. They still employ the counterweight principle. The safety mechanism, called the overspeed governor, is an improved version of the Otis original. It uses centrifugal force that causes a system of weights to swing outward toward the rails should the car's speed exceed a certain limit. Although the travel system has changed little, its control system has been revolutionized. Speed and automation now characterize elevators, with micro-processors gradually replacing older electromechanical control systems. Speeds ranging up to 1,800 ft (550 m) per minute can be attained. Separate outer and inner doors are another essential safety feature, and most now have electrical sensors that pull the doors open if they sense something between them. Most also have telephones, alarm buttons, and emergency lighting. Escape hatches in their roofs serve both for maintenance and for emergency use.

Modern elevators can also be programmed to provide the fastest possible service with a minimum number of cars. They can further be set to sense the weight of a car and to bypass all landing calls when fully loaded. In addition to regular passenger or freight elevators, today's specialized lifts are used in ships, dams, and even on rocket launch pads. Today's elevators are safe, efficient, and an essential part of our daily lives.