NBS Shortcuts: escalators
Austin Williams looks at variable speeds and the leisurely development of escalator technology in this NBS Shortcut
There are estimated to be 7,100 installed escalators in the UK, supplied and maintained by what the Office of Fair Trading calls ‘the big four’ -ThyssenKrupp, Kone, Schindler and Otis.
At a visitor centre in Essen, Germany, designed by Rem Koolhaas’ Office for Metropolitan Architecture (OMA), a subsidiary of ThyssenKrupp Elevator (with the unfortunate, Carry On-esque name ThyssenKrupp Fahrtreppen) claims to have installed the longest escalators in the world. Located at Zollverein, the former colliery-turned-UNESCO World Heritage Site, the escalators are around 60m long and rise 23m vertically. But don’t believe the hype: the escalator in London’s Angel Tube station as long. The Tyne Pedestrian Tunnel escalator (installed in 1951 and still working) is even longer, at 61m with a 25.8m vertical rise.
For OMA’s Seattle Public Library, which opened in 2004, Koolhaas specified ‘bright chartreuse’ escalators; at Zollverein, they are merely bright orange. But a lick of paint and an increase in length doesn’t alter the fact that there haven’t really been any major changes to the form and function of the escalator since Otis and Charles D Seeberger jointly won first prize at the Paris Exhibition in 1900.
Seeberger bought George A Wheeler’s earlier moving-walkway patent, and merged the word ‘scala’ (which means ‘step’ in Latin) with Otis’ own ‘elevator’. An escalator, after all, is essentially just an angled conveyor belt pulling a series of steps in a constant loop. At the top and bottom, these steps are aligned to form level landings for easy access and dismounting. But there have been constant improvements to the technology over the years and the Holy Grail of commercially viable, variable-speed escalators seems to be just around the corner. (Actually, spiral escalators, which can travel round corners, are already installed at Caesars Palace casino in Las Vegas).
In 2003, a new variable-speed travelator - a trottoir roulant rapide (TRR), known commercially as the ‘Gateway’ - was trialled at Montparnasse Metro station in Paris, and more recently, Pearson International Airport in Toronto, Canada, has had one installed. French manufacturer CNIM - which also supplies the escalators to London Underground - has safely and successfully accelerated ‘pedestrians’ from the usual 0.75m/s travelator speed up to 2.25m/s over a 200m track. This is the equivalent of 8km/h (which is less than the initial trial speeds of 10km/h because there were too many accidents), and more than twice normal walking speed. It is also half the average speed of a double-decker bus in London. If these TRRs were installed across the city at pavement level, running for the bus could become a thing of the past.
Stepping on to a fast-moving travelator is fairly hazardous, so the Montparnasse high-speed system uses small rollers instead of the traditional comb plate (the top and bottom landings that demarcate the start of the ride). Stepping on to the rollers, passengers are pulled along by holding the handrails. You are advised not to walk, so that your feet glide over a transition plate and on to the speeding travelator, thus accelerating from the rollers’ speed of 0.75m/s to 2.25m/s. CNIM believes that for distances of around 500m, the system will compete with the shuttle network.
There’s a long list of patents pending by those waiting to improve on the Gateway’s success. Mitsubishi is trying to vary the speed without relying on transition plates by using larger diameter pulleys at the escalator’s edges, which force the rollers supporting the steps to take
wide turns, slowing them down. NKK has an ingenious travelator system that expands as it moves from normal- to variable- to high-speed zones.
Variable-speed controls can also be energy saving, by reducing the nominal speed of an escalator to around 0.2m/s when it is not being used. This is now being added as standard to manufacturers’ specifications. The Kowloon-Canton Railway system in Hong Kong has travelators that detect when passengers are not using it, slowing it down by 30 per cent. This reduces electricity consumption by 56 per cent. The escalators at Zollverein in Essen are self-starting, and are activated by passengers walking past a
Escalators have to be designed so that they don’t slow down when people step on to them, i.e. when the load increases. This is known as torque control. In some manufacturing industries, conveyor belts have computer-operated, direct torque-control devices that calculate the torque needed 40,000 times per second. Thus, incredibly fast reaction times - and greater efficiency and reduced wear - can be maintained in the system. Escalators have not yet reached that level of sophistication, but torque-control devices ensure that the power adjusts to cater
for variable load.