TORQUE ABOUT RELIABILITY FOR POWERED WHEELCHAIRS.
A TorqSense transducer is helping ensure the reliability of
powered wheelchairs, scooters, golf buggies and other electric
vehicles, having been incorporated into a dynamometer rolling
road built by PG Drives in Dorset.
PG Drives manufacture black box electronic motor controllers for
chair and vehicle builders around the world. Reliability and robustness
are paramount as their duty cycle is so unpredictable. Even the least
adventurous users are likely to 'go off road' occasionally, get caught
in the rain, tackle a big hill up or down, or find themselves needing to
carry a large load.
The rolling road was built earlier this year to measure the torque between
the motor under test and the inertia network it is driving, which is
simulated by selective use of both passive and active loads. The
orqSense transducer, manufactured by Sensor Technology in Banbury
monitors the motor's performance by constantly measuring the torque
at its output shaft and feeding a data stream out to a computer for logging
and analysis.
TorqSense is a non-contact transducer that uses Surface Acoustic
Waves (SAWs) as frequency dependent strain gauges to measure
changes in resonant frequency in the motor's drive shaft as the test
programme is run. A wireless radio frequency coupling is used to
transfer the data signal to a pick-up head.
The same coupling is used to supply power to the strain gauges,
possible because the gauges are based on piezo technology so
need less than one milliwatt of power. This arrangement does away
completely with the difficulties of fitting slip rings and maintaining their
contact quality throughout an extended test run.
TorqSense embraces all the advantages of SAW technology, including
no load imparted to the drive mechanism under investigation, a
broader signal bandwidth than other analogue based technologies
and elimination of electromagnetic interference.
"We often run arduous test regimes for 10 hours or more until the
battery is flat," says Dr Richard Gears of PG Drives. "We always
have the rig manned for safety. With large currents being generated
and the motor regularly overloaded, we can't risk lights-out overnight
testing."
The procedures can simulate on and off road, every type of surface,
steep gradients, gentle gradients, all sorts of extreme weather, heavy
loads, shock loads and every other anomalous behaviour you can
imagine. Until last year the analysis regime was based on test driving
around the town, but consistency and repeatability were, of course,
impossible to achieve. "The rolling road has been used constantly
since we built it, so its reliability is a much as issue as that of our
controllers in the field. Looking back, I don't how we ever managed
without it."
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For more information, please contact :-
Sensor Technology Ltd.
Tel: +44(0)1295 730746 Fax: +44(0)1295 738966
Email: info@sensors.co.uk
Website: www.sensors.co.uk
March 2006
