Elevator systems are key parts of any high-rise building. For structures over five stories high, stairs are not a practical way of ascent. Since ancient times, lift systems have been in use, but they only became popular after the invention of the safety elevator by American inventor Elisha Otis.
Although there are many kinds of elevators, high-rise buildings are typically designed with traction elevators in mind. Smaller buildings often contain hydraulic elevators that rise and fall on a platform and are powered by pressurized liquids. This article focuses on the parts of traction elevators.
Traction elevators require a motor to work. This is usually an Alternating Current electric motor placed in a machine room at the top of the shaft. This provides a high degree of power at high speed. The speed of the motor would be too fast to pull an elevator safely, so it is reduced using a series of gears. Worm gears are typically seen as the most efficient way of reducing speed while retaining torque in elevator applications. They are low efficiency but can resist very high shock loads. They are often used in very high torque applications. Elevator specialists like ATIS will always check for any misalignment of worm drives when auditing the safety of a system.
The elevator car itself is suspended on cables attached to the motor. Most modern elevator cars have similar features. Sliding doors are equipped with sensors that can detect movement and prevent the car from moving off when people are entering or exiting. Passengers often choose floors themselves using a button menu. In the early days of safety elevator operation, this job was done by a professional attendant.
Elevator cars are equipped with several safety devices. Automatic brakes extend in the event of a cable snapping. An intercom system is usually provided so that passengers can talk to an operative in case of an emergency. The cables holding elevator cars are typically rated as being able to carry 125 percent of the total possible capacity of the car.
Traction elevators use counterweights to avoid strain on the electric motor pulling the car up the shaft. Counterweights descend as the car ascends, making use of gravity to produce kinetic energy. Counterweights typically weigh the same as an elevator car that is 40 percent full. The most modern elevator systems use regenerative drives to produce electricity from the heat developed by falling counterweights.
One of the most important safety features of any elevator system is the automatic governor, which is usually housed in the machine room at the top of the shaft. Governors are heavy flywheels connected to the cable as it spools in and out. If the cable spools out too quickly, heavy braking arms are released using a centrifugal force, slowing the flywheel and, therefore, slow the elevator. This mechanical braking is not vulnerable to any digital malfunction and is an essential failsafe.