Released on: August 29, 2008, 7:12 am

Press Release Author: Sensor Technology Ltd

Industry: Electronics

Press Release Summary: The University of Texas is working on a new test bed that
will radically improve evaluation of motors for demanding applications. Key to the
researchers' experiments, and at the heart of the test bed is the TorqSense
transducer developed by Sensor Technology.

Press Release Body: Getting the right motor for a demanding application isn\'t
exactly a hit and miss affair, but the performance curves supplied by the
manufacturer can only tell you so much. Beyond that, real world performance
evaluation is needed, and this is where modern test beds come in, offering the
ability to test actuators under a static load (such as a brake) and providing an
important indicator of long term performance and reliability.
Even then, however, the overall picture is limited. Recognising the need for a test
architecture that would look at all possible operating conditions, the Robotics
Research Group (RRG) at the University of Texas set out to design a test bed that
would measure and record an array of physical properties during both dynamic and
non-linear load testing.
The result of the Group\'s work is the Nonlinear Test Bed for Actuators (NBTA), which
is able to simulate real world operation under both linear and non-linear loads.
Flexible enough to accommodate a whole range of prime movers, the test bed comprises
a load motor, a four bar linkage, a brake/clutch and a torque sensor. Each component
is linked to the next via a bellows coupling, with a further bellows coupling used
to connect the torque sensor to the motor under test. All components are held
rigidly against a variety of load profiles by long steel rails, which are secured to
the test bed such as to resist horizontal and vertical forces so that the testing
provides an accurate picture of motor performance. Supporting blocks for the various
mechanical components are height adjustable to support a range of different prime
movers.
In operation, the load motor provides the dynamic test by generating various types
of load, whilst the four bar linkage creates the non-linear periodic load. The load
profiles can be readily defined to simulate real world conditions for the test
motor. An encoder is connected to the motor to provide position, velocity and
acceleration data, while the torque sensor measures the torque between the load
motor and the test motor.
With the torque sensor holding the key both to evaluating the performance of the
test motor and enabling torque control of the load motor, the Group recognised that
selection of this critical product was key to the success of the test bed. The
torque sensor needed to have a torque, speed range and torsional stiffness higher
than the operational range of the test motor. And because the test bed had to test a
range of different motors with different torque-speed curves, the torque sensor also
had to be extremely accurate.
Measuring rotary torque has historically been difficult and expensive because
traditional techniques are invasive to the mechanical systems being measured. So for
an affordable and practical solution would meet these demanding requirements, the
Robotics Research Group turned to Sensor Technology.
Based in Banbury in the heart of Oxfordshire, Sensor Technology has developed a
range of torque sensors based on surface acoustic wave (SAW) technology. The
TorqSense transducers use SAW technology in a novel and patented way to overcome the
problems associated with traditional torque sensors, delivering an inexpensive yet
high performance solution.
The Surface Acoustic Wave based transducer is essentially a 'frequency dependent'
strain gauge that measures the change in resonant frequency caused by an applied
shaft strain. Two SAW devices embedded on a shaft form part of a high frequency
oscillator circuit. When the shaft is twisted, the resulting deformation of the
substrate creates a frequency difference between two embedded SAW devices. The two
frequencies produced by the SAW devices are mixed together to produce difference and
sum signals. The difference signal is a measure of the induced strain due to the
twisting moment, and from this the torque can be derived.
The TorqSense transducers built on SAW technology are designed to operate direct
from a PLC or a PC, removing the need for conventional instrumentation, and will
interface with standard DPMs. TorqSense transducers require minimum shaft length,
have low inertia, no physical contact between shaft and housing, wide bandwidth,
high resolution, high accuracy and excellent magnetic/RF noise immunity.
Evaluation of the NTBA test bed has only just begun, with the Robotics Research
Group currently focusing their efforts on assessing permanent magnet synchronous
motors - a first choice in many robotics applications since they have distinct
advantages over conventional DC motors. Permanent magnet synchronous motors are also
an attractive choice for heavy duty applications because large output can be
obtained during high acceleration and deceleration rates. For the purposes of
evaluating the test bed, permanent magnet synchronous motors have the advantage of
high torque, low speed characteristics, enabling the researchers to give the test
bed a thorough work out.
But the hope is that the test bed will soon be testing a whole range of prime
movers, assessing these motors\' characteristics for demanding applications as
diverse as electric vehicles at one end of the spectrum, or actuating a trim tab in
a submarine at the other.


Web Site: http://www.torqsense.com

Contact Details: Sensor Technology Ltd
PO Box 99605
Raleigh
NC 27624
Ph - 919 954-1004
Fax - 919 954-1009
info@torqsense.com