Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
DEVICE FOR_THE RE-EDUCATION OF A LIMB
FIELD OF THE INVEN'rION
The invention relates to the medical or veterinary equipment
sector, and more specifically to a device for the re-education
of limbs comprising a motor element in shape memory alloy. This
device is intended particularly for re~establishing the
0~ articular and/or muscular function of a limb following an
accident, prolonged immobilisation or similar.
In the present text, the term "limb" shall be understood to
describe any part of the human or animal body which comprises a
muscle and/or a joint.
BACKGROUND OF~ THE INVENq~ION
It is a known fact that to recover the articular or muscular
function of a limb that has suffered traumatism or~prolonged
immobilisation, it is necessary to undertake re-education of
this Iatter by subjecting it to programmes of specific
movements.
Generally speaking, the re-education can be performed in two
ways which may~be independent or complementary consisting either
of the participation of a practitioner or of the use of
mechanical apparatus specific to this re-education.
~ owever, in both cases the still convalescent patient must
make frequent visits at appointed times to the practitioner or
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to special premises where the said re-education equipment is
situated.
This therefore results on the one hand in the patient being
fatigued, and on the other hand in time constraints that often
05 are badly suited to occupational activity.
Furthermore, features of the mechanical re-education
apparatus used generally include relatively high cost and
complex apparatus of heavy construction not easy to operate by
the patient alone.
OBJECTS OF THE INVENTION
The object of the invention is therefore to overcome the
disadvantages analysed above by providing a device for the
re-education of a limb that is simple, lightweight, of low cost
and easy to operate by the patient himself.
BRIEF SUMMARY OF THE INVENTION
For this purpose the object of the invention is a device for
the re-education of a limb which, in accordance with the
invention, comprlses at least one motor element made in shape
memory alloy, ~he motor element possessing at least one shape
memory state corresponding to a specific configuration, control
means for bringing the motor element into the said shape memory
state and means of mechanical attachment for securing at least a
part of the motor element to a part of the limb to be
re-educated.
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BRIEF DESCRIPTION OF THE INVENTIOM
In accordance with a preferred embodiment, these attachment
means comprise an envelope accommodating at least a part o~ the
limb to be re-eaucated and containing the motor elements. This
envelope may be formed in particular by a sheath or belt of
05 fabric in the manner of a dressing.
It is known that shape memory alloys have the property of
being capable of undergoing reversible transformation from a
first crystallographic phase state of the austenitic type (high
temperature HT) to a second crystallographic phase state of the
1~ martensitic type (low temperature LT ) and thus being capable of
being educated to assume, under certain ~onditions, a
confi~uration which is termed shape memory state, or memorised
state.
In other words, if an object consisting of such an alloy is
educated in such a way that it memorises a con~igu~ation in the
austenitic phase state (~T), for example, and this object is
subsequently deformed whilst it is in a martensltic phase state
(LT), it remains in its deformed configuration. If this object
is then heated to be brought to a temperature at which its phase
state is austenitic (HT), it tends progressively to re-assume
its non-deformed shape, i.e. the configuration corresponding to
its memorised state.
With such alloys, the transition from one phase state to
another occurs in one dir~ction as in the other within a
temperature zone. The temperature at which the austenitic phase
starts to appear when the alloy is heated is termed TAs and the
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temperature at which the formation of the phase is completed is
termed TAf tTAf~ TAs~. In similar fashion, when the alloy is
cooled, the martensitic phase transformation starting and
finishing temperatures ar0 termed TMs and TMf respectively (TMf
05 ~ TMs).
Generally speaking, it is to be noted that TMs and TMf are
appreciably lower than TAf and TAs respectively, the temperature
zones [TAs, TAf] and [TMs, TMf] being governed by the
composition of the alloy.
It is also to be noted that amongst these alloys, the Ti,
Ni; Ti, Ni, x; and Cn, Al, X~ alloys are particularly
interesting; X being one of the group of metallic doping
additives.
Such alloys and their education procedure are described
particularly in a NASA article SP 5110 published in 1972 and
entitled "55 Nitinol, the alloy with a memory : its physical
metallurgy properties and applications".
The incorporation of one or more motor elements formed of a
shape memory alloy, for example in a dressing intended to~be
intimately attached to a limb to be re-educated, with this
element being subjected to alternate heating and cooling, thus
allows a specific movement of the limb to be effected for the
purpose of its re-education.
Preferably the conductive properties of the alloy will be
~5 used to produce heating of the motor element by the Joule
effect, the control means being thus formed by a simple source of
voltage to the terminals of which the motor element is
connected.
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BRIEF DESCRIPTION OF THE DR~WINGS
Further advantages an~ features of the inv~ntion will appear
in the course of the detailed description which follows, of
embodiments given for the purpvse of illustration in association
with the drawings, of which:
0~ - figure 1 is a view in longitudinal section representing
diagrammatically a first embodiment of the device in accordance
with the invention, equipped with its control means and placed on
a finger in a first position;
- figure 2 is a similar view to figure 1, the control means
having been omitted, whilst the finger is in a second position;
- figure 3 is a view in transverse sëction along the line
III-III of figure 2;
- figure 4 is a view in longitudinal section representing
diagrammatically a second embodiment of the device:in a cordance
with the invention which is again equipped with its control means
and placed on a finger in a first position;
- figure 5 is a similar view to figure 4, but partially
representing the device in accordance with the invention and in
a second position;
- figure 6 is a view in transverse section along the line
IV-IV of figure 5;
- figure 7 is a plan view representing diagrammatically and
without a control circuit a third ~mbodiment of the device in
accordance with the invention; and
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- figure ~ is a view in transverse section along the line
VIII~VIII of figure 7.
The detailed description of the invention will be given
within the conte~t of an application to the re-eauaation of the
05 joints of a finger, but it is clear that the invention is not
restricted to the embodiments describ~d or envisaged. In
particular, the device in accordance with the invention may be
used to advanta~e for the r~-education of other limbs, and in
such a case it will possess different configurations which will
1~ ~e made compatible with the shape of the limb on which it is to
be fitted.
DETAILED pESCRIPTION OF THE INVENTION
Referring firstly to figures 1 to 3, a first embodiment is
seen of the device for the re-education of a limb in accordance
with the invention, marked througho~t by the reference number 1.
This device fitted on a finger 2 comprises a sheath ~
enveloping substantially the entirety of the finger to be
re-educated.
This sheath 4, made for example of a woven element,
comprises a motor element 6 in shape memory alloy connected to a
circuit 8 forming the control means.
The motor element 6 is formed of a wi~e in shape memory
a110y educated to have a one way effect and the memorised shape of
which is the straight shape of the motor element 6 represented
in figure 2.
The motor element 6 which is of circular cross-section, is
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encased in an electrically and thermally insulating synthetic
material 10 (figure 3) such as a silicone or the like.
As clearly visible in figures 1 to 3, the motor element 6 is
incorpoxated within a wall of th~ sheath 4 and extends parallel
05 to its longitudinal axis substantially over the entire length of
the sheath.
Of course, in accordance with one embodiment the motor
element may be placed and attached on an outer sur~ace of the
sheath, for example by means of a self-adhesive tape or the
like.
In the embodiment shown, the motor element is located on the
top of the finger when the device is in place on the finger, but
it is to be understood that depending on the education of the
motor element situated in the sheath 4 and the shape of the
section of this element, the device may be placed in such a way
that the motor element is located underneath or on the sides of
the finger.
Moreover, the motor element 6 has a proximal extremity 12
and a distal extremity 14 connected respectively by means of two
conventional electrical connectors 16, 18 to the control circuit
8. It is to be noted that the electrical connectors 16, 18 are
similarly coated with an electrically insulating material, and
preferably this is the same material as that coating the motor
element 6.
The circuit 8 forming the contro1 means comprises in series, a
direct current supply 20, a switch 22, a device 24 for varying
the strength of the voltage circulating in the circuit and
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circuit breaking means 26. The circuit 8 also comprises monitoring
means 28 connected in parallel to the switch 22 and to the
device 24.
Advantageously the drive circuit 8 may be formed using
05 commercially available integrated circuit components, the
monitoring means 28 comprising in particular a microprocessor
_combined with programmable memory. In one embodiment the moni
toring means 28 compr~se timing means for programmin~ and/or
monitoring automatically tile r~-~uuca~i~n cycles.
The operation of the device in accordance with the invention
is as follows:
Firstly it is to be noted that the device descxibed above
only permits, with a one way effect educated motor element, what
is termed "active" re-education. "Active" re-education implies
re-education requiring an effort on the part of the patient who
must attempt to perform a movement without any external aid. In
the example described it involves re-educating the joints of a
finger with the patient being asked to bend his finger.
The finger 2 is encompassed in the sheath 4 which is, for
example, in a position corresponding to the finger extended
position (figure 2), and in the example illustrated has the
memorised shape of the motor element 6. The motor element is at
this moment in a martensitic crystallographic phase state (low
temperature or T C TMs). The patient bends his finger to bring
~5 it into the position shown in figure 1, at the same time
deforming the motor element 6. Once the finger is bent and the
mot~r element deformed, the patient closes the contro1 circuit 8
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by means of the switch 22. This closure causes current to pass
through the motor element and as a consequence causes it to heat
up by the Joule effect, so that the ~emperature of the motor
element rises. ~s soon as this temperature exceeds the
05 temperature TAs, i.e. the temperature at which the austenitic
crystallographic phase (high temperature) starts to form, the
motor element 6 becomes progressively deformed to re-assume its
memorised state (figure 2) as soon as the motor element reaches
a temperature substantially higher than TAf.
At this moment, the control circuit can be switched off by the
patient or, should the occasion arise, by the monitoring means so that
the motor element cools down and its crystallographic phase
state passes from the austenitic state to the initlal
martensitic state. At this moment a new cycle can be initiated.
It may easily be understood therefore that in a first phase
the patient makes an effort to bend his finger and that in a
second phase the motor element 6 solid with the sheath 4 forces
the finger into a straight position~
A repetition of this cycle a large number of times enables
the patient to pexform, without ex$ernal aid, simply and at his
own speed, the re-education of his afflicted limb.
In the embodiment represented in figures 1 to 3, a wire
in alloy Ti - Ni of the 50-50 type has been used, the wire
being of diameter D = 2 mm approximately and the circuit being
powered by a supply of about 3 volts. This has enabled a motive
force Fm of the order of 3.5 N to be obtained.
For information, with the alloy used the following phase
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transition temperatures are obtained:
TAs = 60C; TAf = 90C; TMs = 60C; TMf = 40C.
Of course the force that is supplied by the motor element to
the limb to be re-educated may ~ary according to the limb one
05 wishes to re-ed~cate and in this respect it is to be noted that
this motive force is substantially proportional to the
dimensions of the motor element used. It is therefore self
evident that to obtain the same motive force, it is possible to
replace a single motor element by a number of motor elements of
smaller dimensions and acting in the same way.
To prevent the patient feeling uncomfortable as a result of
an excessive temperature in the heating up of the motor element,
between the motor element and the sheath it is possible to
provide an additional layer made of thermally insulating
material (not shown).
Referring now to figures 4 to 6, a second embodiment is
shown of a device in accordance with the invention in which the
elements identical with those described previously are given the
same reference numbers.
In this second embodiment, the device 1 comprises two motor
elements 40, 42 formed of a shape memory alloy and made in the
manner of a strip of substantially rectangular cross-section.
These two motor elements encompassed in an electrically and
thermally insulating material are incorporated in diametrically
opposed walls of the sheath 4 and the latter is placed on the
finger in such a way that they are respectively located under
and on top of the finger. As already described in the first
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embodiment, each element 40, 42 is connected through the
intermediary of electrical connectors to a control circuit 44.
This control circuit 44 differs from the circuit described in
association with figures 1 and 2 by comprising means 46 for
05 alternately energising motor element 40 and motor element 42.
These means 46 are formed by a f1ip-f1Op connected
on the one hand to the power supply 20 and on the o~hex hand to
the electrical connector 18 of each motor element, the rocker
switch 46 being furthermore connected to the monitoring means 28.
The two motor elements 40, 42 are in this case one way effect
educated and possess different memorised shapes in the sense
that for example, the memorised shape (high temperature or
austenitic phase) of the motor element 40 is bent or "crooked"
(figure 4j whereas the memorised shape of the motor element 42
is straight (figure 3~.
Thus when the motor elements 40, 42 are energised
alternately, they act in opposite directions so that an
alternating movement of the finger between its bent positlon
(figure 3) and its extended position can be obtained.
With this suitable control of the device, it is thus
possible to undertake in a simple way a re~education that may be
termed "passive", i.e. without the patien~ providing any effort
to initiate these movements.
In this case, the monitoring means 28 a~e programmed so that
the motor elements 40, 42 are energised systematically in
succession and never simultaneously~
It is similarly understood that these monitoring means 28
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comprise timing means like those described in association with
figures 1 to 3 for performing ~e-education cycles aaapted to
each patient.
O~ course, passive re-education with the aia of such a
OS device can be performed by replacing the two . one way effect
educated motor elements 40, 42 by a single motor element in
alloy with two way.~effects educated shape.memory.
Finally referring to figures 7 and 8, a third embodiment is
seen of the device in accordance with the invention in which a
single motor element 6 is incorporated in a strip of fabric 48
provided on one of its faces with an adhesive material 50 in the
manner of a dressing. The motor element ~ is of course connected
to a control circuit (not shown~ of the type of that described in
association with figures 1 to 3.
In accordance with one embodiment, the adhesive material 50
can be replaced by other means of being attached to the limb to
be re-educated, such as in particular by straps with buckle
fasteners, straps with Velcro fastening, or simllar.
It is to be noted that advantageously such an embodiment
permits the same device to be fitted on limbs of different
shapes, sizes and sections.
It is to be noted that in all the embodiments described
above, the control circuit preferably includes a fuse forming
circuit-breaking means 26 for the event of a short-circuit
occurring in the device.
Finally, it will be noted that such a device has the
advantage of being capable of being used in an autonomous
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manner, i.e. without any association with a fixed point of
reference such as a building or similar, and whatever the
location of the limb to be re~educated~
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