Torque Transducers optimise drug delivery.
Critical drug delivery errors are being driven out of
medical practise by advancing intravenous (IV)
medication delivery technologies with smart memories
and optimised drive mechanisms.
ALARIS Medical Systems® develops drug-infusion systems
and patient monitoring equipment for hospitals and other care
facilities around the world and is constantly developing new
technologies and refining existing equipment. Actual drug
delivery is usually performed by a precision pumping mechanism
coupled to a syringe or needle-less equivalent, so at its
international headquarters in Basingstoke, ALARIS is using
the latest techniques to optimise pump drives design.
It has just installed Surface Acoustic Wave (SAW) monitoring
facilities with which it is mapping the performance characteristics
of the many motors its buys in as pump drives so that they can
be optimally matched to specific application requirements.
SAW is a radical new technology encompassed in Torqsenseä,
the world’s first low cost non-contact rotary torque transducers
suitable for OEM applications, just developed with government
backing by Sensor Technology in Banbury.
Rotary torque is difficult to measure by methods that require
physical contact with the drive mechanism, as drag is introduced
which increases the actual torque in the test piece. So Sensor
Technology has harnessed the phenomenon of SAW or Raleigh
waves, which were first observed over 100 years ago and which
form a major part of the destructive force of an earthquake.
Torqsense is in effect a frequency dependent strain gauge, which
measures the change in resonance frequency caused by the
rotary strain in the drive shaft and this frequency signal is then
monitored via an adjacent fixed pick up. Because it is frequency
based it has a wide bandwidth, high immunity to magnetic
fields and high tolerance to electronic interference.
Paul Risborough, Senior Electronics Engineer explains how
ALARIS is using the Torquesense transducer: “Most of our
pumps are driven by stepper motors, which we test by driving
them against a DC motor acting as a brake. To get
comprehensive modelling of a motor we have to be able to
vary the speed from the slowest running right up to stall speed,
so we need a speed range of about 0-1200rpm. We also
subject the test motors to shock loads, sudden reversing
and irregular speed changes, all generated from a PWM
(pulse width modulate) control we made here in the lab.
The Torqsense is mounted between the two motors and faithfully
downloads the instantaneous shaft torque to a computer for
logging, analysis and modelling”.
Commenting further, Paul went on to say “We use a DC Motor
because it is less expensive, simpler, easier and faster than
the dynamometer that would be conventional to use. This is
very much in keeping with the idea of using Torqsense, because
the alternatives were all much more expensive and complicated.”
ALARIS employs about 200 people in Basingstoke and 3000
across the world. Last year, Globally it turned over about £300m
(Over US$ 400m) supplying to over 5000 hospitals and other
medical care providers. In contrast Sensor Technology’s centre
of operations is in Oxfordshire with 20 people and a network of
consultants and distributors worldwide. What both companies have
in common is the desire and commitment to push forward the
technological boundaries in their chosen fields by combining
science, technology and business acumen.
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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
August 2003
