How do escalators work?

An escalator is a variation on a conveyor belt. An electric motor turns a pair of chain loops, and those chains pull a series of steps in a constant cycle. Tracks guide the step wheels so each step stays level on the slope and flattens into a platform at the top and bottom. The handrails run off the same drive so they move at the speed of the steps. [1] [2]

The truss is a welded steel frame spanning the upper and lower landings, and it carries everything else. The drive machine, usually an electric motor and gearbox at the top, turns the main drive shaft. Two step chains, one on each side, pass around sprockets on that shaft at the top and around a tension carriage at the bottom. [3]

One popular explainer says a typical escalator uses a 100 horsepower motor. The IEEE source adds that modern drives use AC induction or permanent-magnet synchronous motors with variable-frequency drives, which allow soft starting and more efficient running when traffic is light. [1] [2]

Each step has two sets of wheels that ride on two separate tracks. The upper wheels are attached to the rotating chains and are pulled along by the drive gear. The other wheels simply follow along their own track. Because the tracks are spaced so that the steps never tilt, each step remains horizontal. Near the ends the tracks level off, and the steps flatten into a platform. Grooves in each step let it fit together with the steps in front and behind during this flattening. Hackaday describes the same idea: controlling the vertical distance between the two tracks lets the steps lie flat or stand up. [1] [4]

The IEEE source describes this as a four-point roller and track system. It gives typical inclination angles of 27.3 to 35 degrees and rated speeds of 0.45 to 0.65 meters per second for public installations. [2]

A handrail is a looped rubber belt driven from the same motor system, set to move at the same speed as the steps to steady riders. IEEE notes that standards tightly specify how far handrail speed may deviate from step speed. [1] [2]

At each landing a comb plate has teeth that mesh with the grooves in the step treads and guide feet off the moving surface. Hackaday notes that the comb keeps large objects out of the machinery, and that many escalators have a sensor that stops the machine if something unexpected enters it. A brake holds the escalator, with an auxiliary brake on taller or heavier units, and emergency stop buttons are placed within passengers' reach. [3] [4]

HowStuffWorks says escalators are poorer than elevators at lifting people dozens of stories but better at moving people a short distance, because of their high loading rate. Once an elevator is full, others must wait for it to return, while on an escalator there is room for another rider as soon as one steps on. The National Elevator Industry guide says escalators can rise from 4 feet to over 100 feet. [1] [5]