Note: Descriptions are shown in the official language in which they were submitted.
CA 022190~7 1997-11-26
THREE-DIMENSIONAL ACTIVE, COMPOSITE
MEMBRANE, TYPICALLY SMA ACTUATED
BACKGROUND OF THE II~VENTION
1. Field o~ the Invention
The present invention relates to flexible
membranes which can be deformed by an actuating
mechanism, for instance ~or use on airplane wings ~or
the de-icing thereof.
2. Description of the Prior Art
As it is well known in the art, Shape
Memory Alloys (hereinafter referred to aS SMA's)
exhibit the ability to change shape and create force
through a reverse martensitic phase transformation
when energy is supplied to the SMA material.
Unfortunately, this ability cannot be efficiently
induced during the so-called "education pro,~ess" in
more than one direction. This means that, cLepending
on the shape and "education process", a piece made of
SMA will exhibit the highest dimensional
transformation and force production performances only
in the longituclinal, transversal, racial or
circumferential direction, but never ~or any
combination of thereof whatsoever. Furthermore the
highest performances (i.e. highest level in
dimensional transformation or ~orce production) are
available in the longitudinal direction of
monocristal wires. Many solutions to present problems
in different technical fields such as aircraft de-
icing, special gaskets, joints, valves, process
controls, active turbulence-control of fluid flow,
automation, robotics etc., could be simplified or
enhanced if elements capable to reversibly change,
locally or globally, their own three-dimensional
configuration (shape) were available.
CA 022190~7 1997-11-26
SUMMARY OF THE INVENTION
It is there~ore an aim o~ the present
invention to provi~e an active composite membrane
which can be actuated to de~orm in different selected
three-dimensional patterns.
It is also an aim of the present invention
to provide an composite membrane capable of changing
its shape when actuated typically by Shape Memory
Alloy (SMA) components, but also other by appropriate
mechanical actuators.
It is a ~urther aim of the present
invention to provide a three-dimensional active
composite membrane, ~ormed of two layers of polymer
and of a rein~orcement wire net therebetween,
actuated at different three dimensional ]?atterns
(shapes) by an external Shape Memory Alloy (SI~A) wire
net, or other types o~ mechanical actuators 1_o which
it is attached.
As presented hereinabove, a piece made of
SMA cannot exhibit the same rate o~ de~ormation or
force production in more than one direction. The
composite membrane of the present invention amplifies
(by elastic buckling) the actuator's displacement in
a direction perpendicular to its sur~ace (i.e. to its
at rest plane). Therefore, if the composite membrane
of the present invention is attached to a SMA wire
net, the above-mentioned limits of the SMA can be
overcome. When ~)roperly activated, the linear
deformations of t:he wires o~ the SMA net are
amplified by the elastic buckling of the
rein~orcement elements embedded in the composite
membrane of the present invention. The direct result
is a controlled modification of force production or
de~ormation (or both) along the third direction, i.e.
along a normal to the membrane's plane.
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Therefore, in accordance with the present
invention, there is provided a composite membrane
comprising two elastic outer layers and an
reinforcement member therebetween and having edges
thereof attached through one of said outer la.yers to
edges o~ an outer ',hape Memory Alloy actuating net,
said actuating net having an area similar to that o~
said rein~orcement member and smaller than that of
said outer layers, ~3aid actuating net being driven to
contraction or exl_ension by direct heat thereby
causing a normal deflection o~ said reinforcement
ember and thus of said outer layers.
Also in accordance with the present
invention, there is provided a composite membrane
made out of two polymer layers and an embedcled wire
net o~ any geometrical configuration hereafte:r called
reinforcement ~eature, said rein~orcement feature
having its edges attached through one of the polymer
layers to the edges of an outer one-way or two-way
Shape Memory Alloy wire net of geometrical compatible
con~iguration hereafter called actuator feature, said
actuator feature having the same area as t:he said
reinforcement feature, is smaller than the membrane,
it is centered to the middle of the membrane, and is
driven to contraction or extension by direct heat.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature
of the invention, reference will now be made to the
accompanying drawings, showing by way of illustration
a preferred embodiment thereo~, and in which:
Fig. la is the simpli~ied schematic
representation of a cross sectional elevati.on o~ a
three-dimensional active, composite membrane attached
to a SMA wire net. actuator in accordance with the
present invention;
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Fig. lb is a schematic elevation of the
membrane and SMA actuator, including an enlarged
representation in cross section of one possible
attachment system o~ the membrane to its SMA
actuator;
Fig. 2a is a simplified isometric view o~
membrane de~ormation when X-direction wires o~ the
SMA wire net are driven in contraction by heat;
Fig. 2b is a simplified three-dimensional
mesh representation o~ membrane de~ormation when both
X and Y-directions wires of the SMA wire net are
driven in contraction by heat;
Figs. 3a and 3b are schematic
representations o~ some possible con~igurations o~
the rein~orcement net and/or of the SMA wire net;
Fig. 4a i's a simpli~ied isometric view with
an additional detaiLl view of one embodiment o~ the
invention used as an ice prevention or de-icing
device ~or airplanes;
Fig. 4b is a perspective three-dimensional
mesh representation of the membrane's shape when
actuated on a leading edge of an airplane wing's;
Figs. 5a and 5b are respectively simplified
vertical and detailed horizontal cross sectional
representations o~ another embodiment o~ the present
invention used as an immersed pumping device;
Figs. 6, 6a and 6b are simplified isometric
views o~ a still ~urther embodiment o~ the present
invention used to reduce the afterbody drag o~ an
aircra~t's ~uselage; and
Fig. 7 illustrates a side, bottom and
detailed perspective views of the fluid flow control
device described Ln the U.S. Patent No. ~L,718,620
issued on January ]2, 1988 adapted with an embodiment
o~ the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Generally, the present invention relates to
composite membranes and, more particularly, to
composite membranes that can change their shape when
actuated by Shape Memory Alloys (SMA) components or
any other appropriate mechanical actuator.
Re~erence is now made to Figs. la and lb
wherein one embodiment o~ the present invention is
presented. It cclnsists of a composite rnaterial
membrane M attached to a rectangular one-way type
Shape Memory Alloy rLet ~which represents the external
actuator ~eature). More particularly, the membrane
consists o~ two layers (100) o~ elastic material
(e.g. elastomer) rein~orced by a rectangular wire net
(110) sandwiched therebetween, which provides to the
membrane the desire(1 sti~ness. The rein~orcement net
(110), having a s~Laller sur~ace then the membrane, is
located between the elastic layers ~100). The edges
o~ the reinforcement net (110) are attached to an
external SMA net (120) by attachment elemen1s (115)
and (116). The flexible ribbon (115) that passes
through the lower layer (100) is bonded or riveted to
the reinforcement net (110) and to the transitional
member (116) to which the external actuator (120) is
also attached by any appropriate means (bond, screws,
rivets, etc.), as presented in detail in Fig. lb.
Due to t:he reintorcement net (1]0), the
de~ormations induced by the SMA net (12CI), when
actuated, will be uni~ormly distributed over the
entire rein~orced area of the membrane M. The SMA net
(120) is made up o~ knitted SMA wires, individually
connected to an appropriate electrical power supply.
Theretore, any combination of actuated and non-
actuated wires o~ the SMA net (120) is available. For
instance, i~ the X-direction wires o~ the SMA net
(120) are actuated, the SMA wire net (120) will
contract itsel~ along the X-direction and will pull
on the corresponding edges of the rein~orcement net
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(110) The reinforcement net (110) cannot contract
itsel~ so the only possibility ~or it to accommodate
the new X-dimension o~ the SMA net (120) is to bend
upward (i.e in the Z-direction), as represented in
Fig. 2a. The non-rein~orced zones o~ the elastic
membrane (100) generate the bias ~orce ~or membrane
shape recovery once the one-way type SMA net (120) is
deactivated.
If the SMA wire net (120) is activated in
both directions (i.e. the X and Y direction w-res) at
the same time, a more complex three-dimensional shape
will result, as pres,ented in Fig. 2b. Furtherrnore, if
selected wires of the SMA net (120) are actuated
sequentially, a corresponding dynamic modi~icaLtion o~
the three-dimensional shape o~ the membrane M will
result. The shape, grid size and grid orient~tion of
the SMA nets (120) with respect to the shape, grid
size and grid orientation o~ the rein~orcement net
(110) are essential design parameters that go~ern the
membrane's per~ormances. Parameters such as
elasticity modulus and thickness o~ the elastomer
layers (100), maLterial and stiffness of the
reinforcements (110), etc., are also to be considered
in the design process of the composite membrane M.
Dif~erent net (reinforcement and actuator) shapes are
represented in Fig. 3.
Another embodiment of the present invention
makes use of a two-way type SMA wire net. In this
case, the bias force is no longer needed as the SMA
net is capable to perform by itself the entire cycle
(contraction and extension) while being driven by
temperature changes. Therefore, the layers (100) o~
the composite membrane M can be made of plastic
polymer and the reinforcement wire net (110) can
extend to the membrane's edges.
Now referring to Fig. 4 wherein the present
invention is used as an ice-prevention and/or de-
CA 02219057 1997-11-26
icing device for airplanes, the rein~orcement net
inside the membrane M is replaced by several sets of
a plurality o~ str:;ngs or straps (110) parallel to
each other, each set; being positioned parallel to the
leading edge of the wing W The reinforcement
elements (strings or straps) within one set are each
individually attach,ed (clamped) through the lower
elastic layer (100) to their own respective SMA wire
(lZ0), hereina~ter called actuator, located between
the membrane M and the wing surface S. One end o~
each SMA actuator (120) is electrically connected to
a general bus bar l130), while the other end of the
SMA actuators (120) within an actuator set is
electrically connected to a set bus bar (135), as
schematically represented in Fig. 4a. Thus each set
(reinforcement elements and their corresponcLing SMA
actuators) can be independently connected and
activated from the same electrical power supply When
one set is activated, all the corresponding SMA
actuators are heated by the electrical cur~ent and
driven into contraction. So each corresponding
reinforcement element within the activat:ed set
undergoes a buckling deformation in a direction
perpendicular to the wing surface S.
If all the actuator sets (120) are
activated at the same time, the general change in
shape of the membrane M, presented in Fig. 4b will
shed the ice accumulated thereon. If the actuator
sets (120) are actuated sequentially, the membrane M
will undergo a dynamic wave-like deformation that
will prevent the ice accretion on the membrane
surface.
Reference is now made to Fig. 5 wherein the
present invention is used as an immersed pumping
device. In this embodiment of the invent:Lon, the
membrane has a more complex three-dimensional
configuration. In this case, the membrane is
CA 022190~7 1997-11-26
cylindrical, having a star-like cross sectional shape
(in its at rest or deactivated state), as shown in
Fig. 5b. In addition to the reinforcement net (110),
several longitudinal strings or straps (140),
hereina~ter called sti~eners, are placed between the
elastic layers (100) of the membrane at the star
edges. The ends o~ the sti~eners (140) are attached
to the top and bottom rings (150) which are also
embedded in the membrane. The upper and lower collar
rings (160) attached and sealed to the top and bottom
ends of the membrane are attached to each c,ther by
several SMA wires, strings or straps (120),
hereina~ter called actuators. The collar rinc~s (160)
are connected to an electrical power supply. The
lower collar ring (160) lodging an intake one-way
valve (170) is ~ixed and sealed to an outer l-ylinder
(180). The upper collar ring (160) lodging a one-way
transition valve (190) is free to move downward when
the actuators (120) are activated and upward (the
return bias ~orce bleing due to the elasticit~r o~ the
stif~eners) when the actuators (120) are deactivated.
A one-way exhaust valve (200) installed at the top of
the outer cylinder (180) prevents the ~luid back-~low
when the actuators (120) are deactivated. ~hen the
actuators (120) are activated, the volume o~ the
suction chamber (S) increase while the volume o~ the
pressure chamber (E') decreases. Thus the two actions
(suction and pumping) are ~ul~illed within the same
stroke. When the actuators (120) are deactivated, the
~luid ~rom the suction chamber (S) passes through the
one-way trans~er valve (180) into the pressure
chamber (P).
Now turning to Fig. 6 which presents
another possible embodiment of the present invention
used to generate the ridges described U.S. Patent No.
4,718,620 entitled "TERRACED CHANNELS FOR REDUCING
AFTERBODY DRAG", rows of sti~eners (210) are added
CA 022190~7 1997-11-26
to the rein~orcement net (110). The posit:Lon and
orientation o~ the sti~eners (210) with respect to
the grid size and orientation of the reinforcement
net (110) depend on the ridge's characteristics The
SMA wire net is replaced by a plurality o~ SMA wires
(120), hereinafter called actuators, which are
attached to each st:if~ener (210) in a row. A thin
strip (220) o~ appropriate sti~ness is ~ixed along
one of its edges to the upper elastic layer (100) at
one edge o~ each row of sti~eners (210). The width
o~ the strip (220) may or may not exceed the width o~
the corresponding row (to which it is attached). The
ends o~ each actuator (120) within a row are
electrically connected through the row's bus bars to
an electrical power supply. When one row is
activated, each corresponding sti~ener (210) bends
upward (due to the contraction o~ the corresponding
actuator) thereby tilting the strip (220) upwards, as
illustrated in Fig. 6a. Thus each row can
independently generate a ridge wen activated. The
advantage o~ using the present invention in
conjunction with the above-mentioned U.S. Patent
resides in the ~act that the ridges can be
dynamically produced or removed (in function of
flight conditions), by simply activating or
deactivating the appropria-te zones o~ the membrane.
Higher flexibility and performance can be achieved if
the strip (220) is replaced by a row of threads (230)
in a brush-like arrangement, as presented in ~ig. 6b.
In this configuration, the present embodimenl: of the
invention can be used as an active turbulence-control
system of the air~low on the wing upper sur~ace or of
the upswept afterbody, as shown in the Fig. 7.
