Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1247-1
Ankle joint spring element for artificial le~s and
artific~al foot.
2~334~
BACKGROUND OF THE INVENTION
The present invention relates to an ankle joint spring ele-
ment for artificial legs, more particularly to a molded
foamed plastic foot part provided with a metallic reinfor-
cing member.
The invention further relates to an artificial foot for an ~-
artificiaL leg of a molded foamed plastic foot part provided
with a plate-like metallic reinforcing member embedded in its
s~ole region which, within the region of the ball of the foot,
is constructed with a ball-like proceeding bend for assisting ;
the rolling function of the foot and with a - serving in each
case as an elastically yielding or giving shock absorbing or -
cushioning means - a forefoot core and a function core con-
sisting of a tab disposed within the heel region, in which
case the function core and the reinforcing member are rigidly
interconnected and the reinforcing member is comprised of
one or several approximately equally long, superposed leaf
springs which are configured so as to conform to the rolling
profile of the foot.
It has been known for a long time to employ foamed polyure-
thane plastic as material for an artificial foot which pos-
sesses the advantage of having a low weight. As proposed by
way of example in the US-A-3,335,428, the foot part of an
artificial leg may also be formed of an elastic plastic pos-
sessing a different hardness.
Moreover, from the DE-C-354 246, an artificial foot is known
in which, within the region of the sole, a metal bar is em-
bedded. This artificia( foot is intended to make it pos-
sible for a leg or foot amputee to take long strides since
this taking of long strides causes the oblique rearward
displacement of
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the lower leg, thus the resilience of the heel of the foot
resting upon the ground with its entire undersurface. In
addition, it is intended to cause the easy restraightening
up of the lower leg without the same exceeding the vertical
position, while the shifting of the weight of the body in
the forward direction and the raising of the heel is inten- -
ded to be rendered possible by the normal resilience of the -~
metatarsus and the toe portion of the artificial foot. The
resilience or yieldingness is to be achieved by the embed-
ding of a spring plate that passes through the sole and the
heel portion. In order to now be able to bring about the
projection of the lower leg obliquely toward the rear, this
known embodiment of an artificial foot provides a connection
between the rigid lower leg and the spring plate, in which
the lower leg moves from its upright position toward the rear
in the manner of a rocker and, when the weight of the body
is shifted, once more moves forwardly back into the former.
This rocking motion is effected in that the cuneiformly ta-
pe ing, rigid lower leg is seated in a saddle, the one obli-
quity of which is formed by the instep of the artificial
foot and whose counter-obliquity is formed by a bifurcation
of the spring plate. For the further shock absorption, a
compressible wedge-shaped pad, e.g. of soft rubber, is loca-
ted between the bifurcation and the actual spring plate.
In order to avoid an undesirable noise being produced when
the front wedge surface of the lower leg impinges upon the
foot, the forefoot or metatarsus is comprised of a pliant
or readily compressible, at any rate sound-deadening mate-
rial, preferably felt. Also the supporting area of the lower
leg is covered with a cap of this material. In this artifi-
cial foot, the bifurcation of the spring plate is rigidly
connected with the rear wedge-shaped area of the lower leg.
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However, in this case the bifurcation is not sharply bent
aside since a rocking or swinging motion is strived for.
That is why the bifurcation is mounted on the plate so as to
gLide with its knee. Consequently, in this known artificial
foot a steel spring possessing springable properties is inser-
ted which extends into the forefoot. However, in this case,
the important differences in elasticity between metatarsus
and the forefoot have not been taken into account from a
constructional point of view. Moreover, the steel spring em-
ployed here does not make a natural rolling possible; also
the connection problems between the different materials in
the elastic area have not been constructionally solved.
Furthermore, from the DE-C-361 972, an artificial foot provi-
ded with a longitudinal spring element consisting of several
reciprocally stepped leaf springs, whose leaf springs, with
their rearward ends, are secured to the underside of a rigid
block forming the rear foot portion, but separated from the
sole by an intermediate layer, while the front spring ectre-
mities carried downwardly at a suitable double angle, press
directly upon the sole that is expediently covered with a
protective sheet.
In an artificial foot for artificial legs known from the
US-A-2,556,525, in an external foamed plastic molded foot
part, a stiff but flexible plastic portion is embedded which
extends over the entire length of the foot, in which case,
in this stiff but flexible plastic part, a metal insert of
spring steel is embedded. Even though an internal, partially
flexible plastic part with a metal insert of spring steel
is employed in this known artificial foot, it is not possible
in this artificial foot to lay the rolling function onto the
jarring or jolting line predetermined by nature. Despite the
use of a flexible plastic part and of a metal insert of
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spring steel, an adequate mobility in the metatarsophalangeal
articulation, as exists in nature, is not possible. -~
In the DE-A-22 37 758, an ankle joint that is movable every~
where for tubular skeleton artificial limbs is proposed which,
on an axis screwed into a carrier element, possesses a ball- -- -~
and-socket joint, upon which an eyebolt is pressed which, in
a press fit on a commercially obtainable ball-and-socket joint, -
receives the swivelable eye bolt, whose shank, while guided
glidingly and flexibly in a ball-and-socket joint, carries a ~-
closing plate at the end which, fitted in the front and in
the rear with buffer elements, controls the limitation of
movement.
In order to provide an artificial foot for artificial legs
having a rolling resistance predetermined over a long period
of time and a buckling possibility in the metatarsophalangeal
articulation, an artificial foot is proposed in the DE-C-
23 41 887, in which the forefoot elasticity is ensured by
the insertion of a homogeneous elastomer, that is to say, -
an elastic recovery capacity in the forefoot is taken into
consideration which went beyond padding effects formed un-
til that time. It has also already been proposed to make use
of a reinforcing member of two approximately equally long,
superposed leaf springs which are configured so as to cor- -
respond to the rolling profile of the foot.
It is the technical problem of the present invention to de-
velop further the ankle joint spring element stated in the
beginning in such a way that it permits a movement of the
foot along the lines of a prosupination about the longitudi-
nal axis of the foot. It is furthermore the technical prob-
lem of the present invention to develop further an artificial
foot of the known type in such a way that a function mecha-
nism is provided which corresponds to the natural coordina-
ted movement.
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SUMMARY OF THE INVENTION
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The technical problem of the invention is resolved by the
ankle joint spring element described in the Claim 1 which
possesses a U-shaped outline, whose respective legs, when
subjected to a load, can be moved elastically toward each
other. The advantage of this embodiment consists in that a
material-saving section can be employed and the manufacturing
costs thus reduced to a minimum.
Further developments of the ankle joint spring element are
described in the Claims 2 through 9. It is thus provided
in order that the elasticity is increased that the running
out ends of the channel section, preferably with the excep-
tion of the subareas required for the attachment to an accom-
modation space for a leg connection portion, taper in their
material thickness in the direction of the free end. By pre-
ference, the ends of the legs are constructed so as to be
thickened, in a special embodiment provided with bead-like
thickened portions which are formed over the entire width.
With regard to an attachment, e.g. with the aid of a bolt,
these thickened portions supply an adequate mounting or gui-
dance without the risk of material fractures or elastic de-
formations existing.
According to a further embodiment, the ends of the legs are
in each case provided with at least one, preferably two,
drilled holes disposed in a side-by-side arrangement. Owing
to the superposed drilled holes of different legs, one bolt
can be inserted at a time.
A further improvement with respect to the prosupination about
the longitudinal axis of the foot while at the same time ma-
king possible a rotation about the longitudinal axis of the
leg results when the channel section is provided with re-
cesses that exten~ at least over a part of its longitudinal
axis. These recesses consist preferably of elongated slots,
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which, in a further improvement, extend continuously from - -
the first leg across the base up to the second leg of the
channel section.
An adequate support, while at the same time providing an
adequate elasticity is achieved when the width of the chan-
nel section amounts to approximately û.4 to 0.6 times the
length. By preference the channel section is, when regarded
in a view from the top, substantially rectangular. If a tita-
nium-aluminum alloy is employed as material for the channel
section, it is possible to construct the ankle joint spring
element so as to possess a low weight. The previously des-
cribed ankle joint spring element is preferabLy incorporated
into an artificial foot of the type described in the beginning,
in which it serves as a connection between a reinforcing mem-
ber and an accommodation space of a leg connection portion
which is connected to a leg of the channel section. The leaf
springs or spring used in the artificial foot consist(s) of
carbon fiber or of titanium or of a titanium alloy.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiment examples of the invention are illustrated in the
drawings. Thus
i 9. 1 shows a perspective view of an ankle joint spring
element, and
i 9. 2 shows a cross-section through an artificial foot.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The reinforcing member 10 depicted in Fig. 1 possesses a
bend 11 within the region of the ball of the foot 12 of the
artificial foot which is configured in conformity with the
rolling profile of the foot. The reinforcing member 10 is ~
embedded in a forefoot core 13 as well as in a tab 14 ~;
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2103~41
located in the heel region. The function core comprising the
components 1û,13 and 14 is surrounded by a molded foamed plas-
tic part 15 which, in its rearward portion, has a hoLlow
space for accommodating articulations or fastening elements.
The downwardly directedshoulder 11 is constructed in such a
way that the rolling function is laid onto the front tri-
section line (metatarsophalangeal line). In this connection,
a forefoot core 13 comprised of an elastomer is vulcanized
onto the bend 11 of the reinforcing member 10, which, in its
Lower terminating line, corresponds to the external configu-
ration of the ball of the foot. Owing to the foam-enveloped
structure, the forefoot core 13 is completely resistant to
aging so that the rolling resistance is inalterably prede-
terminable over a protracted period of time. The tab 14 is
attached by vulcanization in the heel portion in a corres-
ponding fashion.
At its rear end, the reinforcing member 10 constructed in
the form of a leaf spring is connected to the ankle joint
spring element 16 according to the invention in the form of
a channel section. The base of the channel section points in
the direction of the toes or the free ends of the channel
section legs point toward the heel. The channel section 16,
which is depicted in greater detail in Fig. 2, possesses
thickened portions 17 which extend across the entire width
b. In these thickened portions 17, drilled holes 18 or 19
disposed in a side-by-side arrangement are to be found in ~ -
said thickened portions 17, which are arranged superposedly ~
in such a fashion that bolts 20 which can be gathered from ;
Fig.1, can be inserted through respective superposed drilled
holes of the two legs. This bolt 20 is screwed together with ;~
an accommodation space of a leg connection part or is other-
wise rigidly connected. The channel section 16 is further
provided with slots 21 that reach as far as into the area of
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the thickened portions 17 which extend continuously from the
one free leg across the base up to the end of the other free
leg. Thse slots, here two slots 21, are carried parallel to
each other and parallel to the non-depicted longitudinal
axis. The channel section is constructed in such a way that,
if possible, both legs but at least one leg, exhibit(s) a
reduction in thickness 22 toward the free end, whereby the
elasticity of the free leg is increased in the area. As can
be gathered from Fig.1, between the free legs of the channel
section 16, soft polyurethane foam 23 is inserted. The leaf
spring serving as reinforcing member 10 is constructed of
carbon fiber or titanium.
The depicted artificial foot possesses the advantage that it
makes smooth movements possible which merge into each other.
For different foot sizes it is possible in each case to use
different channel section spring systems, in which connection
the dimensioning of the channel sections permits a resistance
which is matched precisely with the requirements of the move-
ment. Over and above that, specific flexibilities enter into
the construction via the elaongated slots 21.
