Escalator

Overview

An escalator is a continuously moving staircase that carries pedestrians between floors at a fixed incline, almost always 30 degrees in commercial buildings (35 degrees only on short rises). Unlike an elevator, it has no waiting and no defined capacity limit: a 1000 mm unit running at 0.5 m/s can move on the order of 9,000 people an hour. The visible part is a band of metal steps that emerge flat at the lower landing, rise as a staircase through the incline, then flatten again and disappear under a comb at the top. Everything that makes that happen is hidden inside a steel structure and beneath the floor plates at each end.

The whole machine bears on the Steel Truss, a welded steel space frame that spans between the two floor slabs and rests on support angles at each landing. The truss carries the step band, the machinery and the side balustrades, and its underside is closed by cladding panels.

How it works

Power comes from the Geared Drive Machine, a geared machine at the upper landing. A three-phase induction motor drives a worm-and-helical Worm / Helical Gearbox whose worm stage is self-locking, so the stair cannot run backward under load. The gearbox turns a main shaft carrying the main drive sprocket, which pulls the Step Band through a drive chain. A spring-applied Electromagnetic Brake clamps the shaft whenever power is cut or a fault trips, holding the loaded band in place.

The step band is an endless loop of steps coupled to a pair of heavy roller chains. Each step rides on four rollers: two chain rollers on the axle and two trailing rollers behind. As the rollers follow the fixed Step Guide Track rails, the geometry folds each tread flat at the landings and steps it up through the incline. The chains wrap the drive sprocket at the top and terminal sprockets at the bottom, returning the steps underneath.

Riders hold the moving handrail of the Handrail System. A rubber handrail belt is driven by friction wheels geared off the same main shaft, so it tracks step speed; a spring tensioner keeps it taut and guide profiles steer it around the loop. The side enclosure is the Balustrade, with glass panels, a deck board under the handrail, and a skirt panel beside the steps fitted with a deflector brush to keep feet and clothing out of the step gap.

At each landing the Comb & Landing Plates assembly bridges the moving steps to the fixed floor: a toothed comb plate meshes into the step cleats so nothing is caught, and a landing plate gives solid footing. Running it all is the Control System system, a microcontroller board driving a variable-frequency drive that soft-starts the motor and drops the band to a standby crawl when no one is present. Layered over the control is the Safety Device Set set: switches for a missing or broken step, comb impact, skirt obstruction, handrail-speed deviation and step-chain breakage, any of which drops the brake.