The in-house escalator maintenance team atTube Lineshas developed a novel
escalator "smart step" to help the company understand wear and tear
on escalators.
Tube Lines looks after 226 escalators on the Jubilee, Northern
and Piccadilly lines of London Underground and escalators play a
vital role in ensuring passenger journeys run smoothly. With 1.3
million passengers each day, high availability is vital. Between
refurbishments, Tube Lines said it is able to achieve greater than
99% availability on the escalators it maintains, which are in use
20 hours per day.
Steps are designed to last up to 20 years but Ali Albadri, lead
engineer for the smart step project said, "Some steps are lasting
only three years. When there is a problem it is very expensive to
replace." In 2006 Tube Lines replaced over 700 steps in addition to
2000 that were renewed as part of planned refurbishment work.
The reason a step usually lasts just a few years is due to
fatigue cracking caused by the step constantly travelling round the
escalator. If unchecked this could result in unplanned escalator
repairs or station closures and pose a safety risk. This has meant
that the maintenance team has had to run non-destructive testing to
ensure safe operation and plan ad hoc step replacement.
A team of engineers at Tube Lines was set up to look at why
steps cracked. The team found that little was known about the
actual stresses experienced by a working escalator step, eg, those
that result from the differential wear through "stand on the right"
passenger loading. "We needed a way to see what was going on inside
the escalator," said Albadri. The team therefore identified the
need for a diagnostic tool to accurately measure the stresses
experienced in service - the "smart step" concept was born.
The aim of the project was to build a probe that could measure
and record stress on a working escalator, allowing escalator
designers and maintainers to take various measurements while an
escalator was in operation, to verify component life and optimise
component replacement intervals. The team worked with specialists
in data capture and stress analysis to develop a measurement tool
to collect strain data.
It took around six months for Tube Lines to build a prototype
smart step. The step comprises 30 sensors and data logging
equipment fitted within a standard escalator step and can be
operated safely in normal passenger service. The strain gauges are
connected to a high speed data recorder to capture each stress
reading 100 times per second, to build up a full picture of
stresses experienced on the step. Miniature video cameras are
fitted to record the lateral motion of the step within the tracking
system. The recorder can store over 20 hours of data, which is then
downloaded to a laptop computer after the step has been in use for
a full day of operation.
The step has been installed at Colliers Wood station and Tube
Lines is assessing how the device could be used to monitor
escalators continuously, without the need to download data from the
data logger each night. Tube Lines says smart step should result in
maintenance cost savings. By pin-pointing defects at an early
stage, it will allow escalator performance and availability to be
maximised.
Adrian Davey, head of IT at Tube Lines, said, "The challenge now
is to turn smart step into a business solution." Among the issues
he is looking at is how to get data off a moving escalator and how
to use wireless technology underground. Once data is collected it
will need to be loaded into an
SQL Server database at the Tube Lines.
Tube Lines says the smart step technology could be applied
throughout the escalator market and it is in the process of
preparing a patent application. The team has also shared the
findings of the smart step project with colleagues in train
maintenance. This has led to the development of a "smart axle"
being designed and implemented on a Piccadilly Line train. The tool
will be used to determine track forces in order to offer
prospective train builders core data.