The Torqstar Torque Sensor
The importance and usefulness of torque measurement in
fastening and other applications has been recognised for
many years, but the challenge in the past has been to
monitor and measure torque both accurately and
economically in the manufacturing environment.Although strain gauge torque transducers provide high
accuracy, their high cost and bulkiness are features which
have limited their use primarily to research and development
laboratories and in quality assurance testing in order to
verify standards. In addition, such transducers require high
maintenance levels, making them unsuitable for mass
integration into manufacturing systems.Low cost methods have been tried to control torque in
the manufacturing environment, including non-direct systems
which, for example, monitor changes in electrical power
consumption. But such methods typically provide poor
resolution and are not accurate enough to be useful.
The new Torqstar sensors meet the challenges for sensors
to be used in manufacturing environments and can now be
designed directly into production equipment. They cost up
to 60% less than comparable strain gauge methods. The
accuracy of the new transducers is within 0.5% of full scale,
comparing favourably with strain gauge units costing almost
five times as much, and they offer a compact size and
rugged construction.
Torqstar transducer fitted
directly in tightening head
for tops and caps on bottles,
tubes, cans and jars.
Both rotary and reaction transducers are available in the
range 6-120 Nm, and units can be readily adapted to a
wide range of applications. A prime example is equipment
for tightening tops and caps on bottles, tubes, cans, and
jars, ensuring that these are tightened to just the right
torque.Another growing application is in monitoring electric motor
efficiency. Worn bearings or over-tight shafts on equipment
such as fans or blowers increases operational costs
significantly. Fitting Torqstar sensors to motors as standard
is now a practical reality.
Monitoring machine tool efficiency is another important
application where Torqstar transducers can important role.
Worn or blunt tools increase machining times and require
more power. This can lead to broken tools, increase in
machine wear and poor quality parts.Torqstar sensors can be integrated into machines to monitor
efficiency and prompt timely tool replacement or sharpening.Further potential applications for these sensors are enhanced
when they are coupled with position or speed encoders, or
rotation counters. In threaded assembly operations such as
bolted joints or bottle capping, these combined technologies
deliver not only accurate and consistent tightening torque,
but can also detect cross-threading or under/over size
threads.
The sensor is made up of two
main components:
A stainless steel shaft,
dimensioned for the appropriate
torque, and a second metal ring,
which fits tightly on the shaft.
Although the ring appears to be
normal steel, it is actually a
special titanium-nickel material
which has the property of being magneto-elastic.Magneto-elastic materials are commonly known as pseudo
magnets. When at rest, they produce no external magnetic
fields, but as soon as their form experiences a change in
shape through applied stress, their magnetic characteristics
change to give a field whose strength is directly proportional
to the applied stress.
The ring of magneto-elastic material is magnetised circum-
ferentially. Without an applied torque, the magnetic field is
contained wholly within the ring. However, as torque is
applied to the shaft, the magnetic field twists within the
ring and field lines intersect with the surface of the ring
in proportion to the amount of torque applied.The size of the magnetic force is measured by means of a
fluxgate magnetometer (FMG), which is an integral part
of the electronics package. The FMG measures and converts
the force to an electrical signal. Unwanted external magnetic
fields are blocked out by the Torqstar enclosure.
From an article from Variohm
For more details, call +44(0) 1327 351004
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