[Lex Computer & Tech Group/LCTG] Escalator

[john rudy]

I get a site called QUORA and occasionally it includes some very interesting
information.  I thought that this explanation of an escalator falls into
that category.  My first job out of college was at the Raytheon Shawsheen
plant in Andover that was previously an old mill.  It had a wooden escalator
that broke down frequently.  I was told it was the oldest working escalator
in New England.

John



===============================================






<https://www.quora.com/Why-does-the-handrail-on-an-escalator-always-go-faste
r-than-the-stairs>


<https://www.quora.com/Why-does-the-handrail-on-an-escalator-always-go-faste
r-than-the-stairs> Why does the handrail on an escalator always go faster
than the stairs?



Q: Why does the handrail on an escalator always go faster than the stairs?

First: How can the handrail on an escalator go at the same speed as the
stairs?

The handrail and the steps do not need to be driven in a way that makes them
do a full round at the same time. Nobody cares if the hidden portion of the
handrail belt is longer, and the next time a certain stair emerges, a
completely different portion of the handrail belt travels alongside it. All
that matters is that, at least during the straight portion, they travel at
the same linear velocity.

An escalator is driven by a single motor. The stairs and the handrail belt
are driven by separate wheels, coupled by a chain drive:



Here’s another design, where the handrail belt is actually shorter than the
step chain:



(images from:
<http://www.electrical-knowhow.com/2012/04/escalators-basic-components-part-
two.html>
http://www.electrical-knowhow.com/2012/04/escalators-basic-components-part-t
wo.html)

To match the speeds, two things are relevant: gear ratio of the chain drive,
and the outer diameter of the wheel that drives the handrail belt. Nothing
fancy.

Can the handrail go at exactly the same speed as the stairs?

If the handrail was driven by teeth, like a toothed belt, then yes, it could
run at exactly the same speed. However, it is driven by friction.

Here’s a picture of an escalator handrail drive wheel:



Over time, the rubber on the drive wheel wears out, thus reducing its
diameter. So, over time, the handrail is going to run somewhat slower. If
the rubber wears down to the metal (or if the rubber hardens), it will start
slipping and the handrail will move in a jerky fashion and will be lagging
considerably.

Why would the handrail go faster than the stairs?

Let’s assume that when the rubber on the drive wheel wears down by 3 mm
(1/8″), the handrail lags 80 mm (3″) over the course of 8 m (26 ft).
That’s about 1%.

Some standards require that the speed should not deviate more than 2%. Some
standards specify a load (a force) which should not slow down the handrail.
Now, considering that the drive wheel will wear down, and that some slippage
may occur due to dust and grease, the specification for a brand new drive
wheel is probably adjusted ‘to be on the safe side’, causing the handrail
to run 1-2% faster than the stairs. By targeting the new drive wheel at +2%,
one could get double the service life out of it.

It is possible that the newer materials aren’t wearing down as fast as the
ones used before. A well maintained escalator might therefore always have a
handrail running fast.

Does the handrail always go faster than the stairs?

In different countries there are different standards. And different
manufacturers - some more concerned with service life, others possibly
focused more on passenger comfort. Then there are different designs, some
maintain the handrail speed better than others. So, no, not all people will
agree that the handrail always goes faster than the stairs.

Alternate explanation

Some people suggest that handrails run faster than the stairs for escalators
going up, and slower than the stairs for escalators going down. The idea is
that in case a rider is not paying attention, and is relying on the handrail
for balance, they should fall on the stairs upwards, rather than downwards.

It is possible that this was intentionally done in some installations. It is
also possible that one notices such a difference in installations where the
drive wheels on escalators going up had worn down and were replaced, while
the ones on escalators going down are still the original ones, since they
don’t wear down as much.





John Rudy

781-861-0402

781-718-8334 (cell)

John.rudy at alum.mit.edu <mailto:John.rudy at alum.mit.edu>



13 Hawthorne Lane

Bedford, MA  01730-1047





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