It's not a new idea. Using controlled expansion and contraction to
deliver movement provides the motive force behind every living creature.
But what is new is the way technology is now emulating physiology in the
most diverse of applications from animatronics to architecture
The 'fluidic muscle' (FM) puts a new slant on pneumatic actuation. Its
construction involves wrapping a flexible, hermetically sealed rubber
hose with stretch-resistant fibres arranged in a rhomboid pattern, to
produce a highly robust yet extensible 3D grid, terminated by machined
aluminium couplings. When compressed air enters the hose, the grid
pattern deforms and generates a powerful axial pulling force, simple
pressure changes resulting in repeatable, positioning capabilities.
Direct comparisons with traditional pneumatic cylinders are not
practical, but it is worth noting that the FM's weight is just one tenth
that of a metal cylinder of equal diameter, yet the force is typically
ten times as great. Low weight means low inertia, so the FM is
particularly useful for dynamic applications such as robot grippers. The
FM is also unaffected by stiction, so it is capable of smooth,
controlled, slow movements. When rapid actuation is required, however,
the intrinsic end-position cushioning effect of the muscle is a useful
benefit.
Animatronics is perhaps one of the more obvious applications areas for
this technology, however, at the other end of the applications scale,
large variants of the same FM deployed in animatronic characters have
been used by Festo to provide automated tensioning stanchions for the
company's 'Airtecture' structures - pneumatically (as opposed to
mechanically) pre-tensioned membrane constructions.
Classical air-supported buildings are sealed from the atmosphere and
feature a slightly raised internal pressure, which causes the membrane to
stretch and form the inside of the building. Air locks near the entrances
maintain this positive pressure when a door is opened. Airtecture, on the
other hand, works with a much higher air pressure in the supports but
allows normal atmospheric pressure conditions inside the structure.
Festo's Airtecture exhibition building, for example, employs 330
individual air-inflated, 'Y'-shaped chambers as primary supports. Fluidic
Muscles anchor these inflated support chambers, the largest generating
forces of up to 6kN. The FM pressures are precisely controlled in a
closed loop arrangement, involving load cells and strain gauges, to
compensate for thermal expansion and contraction of the construction
materials. When the controller is linked to a weather station, the FMs
provide optimal rigidity under all atmospheric conditions.
Thanks to its fully sealed construction, the FM is resistant to most
forms of dry, gaseous or liquid contamination, so it offers a lot of
potential for applications that might otherwise compromise the
performance of conventional pneumatic actuators. Such applications range
from sub-sea vehicle arm actuation and floodgate control to valve
actuation in aggressive environments. The FM is equally at home operating
in a vacuum, which opens up a whole new applications area beyond the
reaches of the earth's atmosphere.
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Back to Fluid Power Special September 2002