Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Leg – Knee
Reexamination Certificate
2001-08-22
2003-01-21
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Leg
Knee
C623S044000
Reexamination Certificate
active
06508843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a knee joint of an artificial limb.
2. Description of the Related Art
A conventional knee joint of an artificial limb includes a single axis. Such single axis based knee joint is structurally simple, but the single axis must be set rearward of a leg in order to prevent knee from bending the moment an ankle comes into contact with a ground level, and an ankle load is applied to an artificial limb. As a result, movement of the artificial limb becomes unnatural. Thus, a knee joint structure adopting a four-joint link mechanism is often employed. In the four-joint link mechanism, a virtual center axis during an idle leg phase can be set upward of the link mechanism, thus providing excellent control properties. A description will be given by referring to the accompanying drawings.
FIG. 1
is a diagram of a knee joint employing a conventional four-joint link mechanism. The knee joint is composed of a link mechanism that comprising four links
101
,
102
,
103
, and
104
. Upper link
101
is fixed to a thigh support part
110
of an artificial limb. Lower link
103
is linked with a foot part
111
of the artificial limb. A stopper
105
for preventing angle formed by the upper link
101
and the front link
102
from extending over a predetermined angle is provided at the upper link
101
. The stopper
105
stops knee stretching. During the idle leg phase, a cross point between an extension line of the front link
102
and that of the rear link
104
is defined as a virtual rotation center axis P
101
. In the example of
FIG. 1
, a link mechanism is constructed so that an initial position of the virtual rotation center axis P
101
is positioned far above and at the rear of the link mechanism.
Thus, lines of action F
101
and F
102
of a load during ankle landing at a moment when the idle leg phase goes to a leg grounding phase, i.e., when a foot part
111
comes into contact with a ground level GL extend forward of the virtual rotation center axis P
101
, and never come rearward. Thus, knee is not bent during ankle landing, by which walking is stable. The line of action F
101
indicates a case in which a stretched muscle of a thigh joint of a physically handicapped person wearing an artificial limb is strong, and the line of action F
102
indicates a case in which the stretched muscle of the thigh joint is weak. Next, lines of action of a load when walking is advanced, and a toe leaves the ground level GL, i.e., during toe take-off are defined as F
103
and F
104
. The line of action F
103
indicates a case in which the bent muscle of the thigh joint of the physically handicapped person is strong, and the line of action F
104
indicates a case in which the bent muscle of the thigh joint is weak. The line of action F
103
when the bent muscle is strong passes through the rear of the virtual rotation center axis P
101
, and thus, knee bending takes place during toe take-off, enabling smooth walking. However, in the case where the bent muscle is weak, the line of action F
104
passes through front of the virtual rotation center axis P
101
. Thus, knee bending cannot be done, and smooth toe take-off cannot be done.
On the other hand, as shown in
FIG. 2
, in a four-joint link mechanism constructed so that the virtual rotation center axis P
102
is positioned to be comparatively forward, during toe take-off, the line of action F
103
in the case where the bent muscle is strong and the line of action F
104
in the case where the bent muscle is weak as well pass through the rear of the virtual rotation center axis P
102
. Thus, knee bending taken place, enabling smooth toe take-off. However, when the ankle is landed, in the case where the stretched muscle is strong, the line of action F
101
passes through the sufficient front of the virtual rotation center axis P
102
, and thus, there is no worrying about knee bending. However, in the case where the stretched muscle is weak, the line of action F
102
passes through the vicinity of the virtual rotation center line P
102
. Thus, knee bending sometimes takes place, and walking may become unstable.
SUMMARY OF THE INVENTION
In this way, in the knee joint using the four-joint link mechanism, the prevention of knee bending during ankle landing and smooth knee bending during toe take-off become a matter of antinomy. Thus, it has been necessary to design a moderate link mechanism between the mechanism of FIG.
1
and that of
FIG. 2
, which is extremely drawn, according to the muscle power of the physically handicapped person wearing the artificial limb or it has been necessary for the physically handicapped person to master how to use the stretched muscle during ankle landing or how to use the bent muscle during toe take-off according to the characteristics of the link mechanism of the provided artificial limb through training.
In order to mitigate the above described matter of antinomy, U.S. Pat. No. 5,181,931 proposes that a length of one link of the four-joint links is contracted due to a load. However, this apparatus requires a sliding portion for contracting and extending the length of the link, and a mechanism becomes more complicated as compared with a pure link mechanism in which a movable part is formed of an axis that is a joint. Thus, there has been a problem in view of cost efficiency or durability.
Accordingly, it is an object of the present invention to provide a knee joint structure of an artificial limb having excellent stability when an ankle is landed, being capable of absorbing shock during ankle landing and smooth knee bending during toe take-off, and capable of improving appearance during walking, by employing a pure link mechanism with its simple mechanism, which a physically handicapped person with wide range of muscle power can use without requiring special training.
Actuation
When thus formed, in the idle leg phase shown in
FIG. 3
, an auxiliary front link
3
and a lower link
4
are widened to be pressed by means of an elastic element
8
, and is pressed against a second stopper
7
. The auxiliary front link
3
and lower link
4
operate integrally. Thus, a link mechanism operates as if it were a four-joint link. A knee can swing universally when a first cross point P
10
is defined as a virtual rotation center axis. The knee stretch position is restricted by a first stopper
6
. When the knee is bent, the virtual rotation center axis moves along a single dotted line from the first cross point P
10
. When the knee is bent, and the knee joint is bent as one sits on the floor with one's knee being bent, the link mechanism is deformed as indicated by a double dotted line. Then, the virtual rotation center axis moves along the single dotted line to the cross point P
11
. The above actuation is identical to that of a conventional four-joint link knee joint structure.
Now, actuation at a moment when the ankle of the foot part
11
is landed on the ground level GL after the idle leg phase has moved to the leg grounding phase will be described with reference to FIG.
4
. When the angle is landed on the ground level GL, and a weight is applied, the line of action of such load is obtained as the line of action F
1
or F
2
according to whether the stretched muscle of the thigh joint of the physically handicapped person wearing the artificial limb is strong or weak. Here, the lines of action F
1
and F
2
both pass through the rear of a second cross point P
20
. Thus, a force is applied to the lower link
4
, such that an angle formed by the auxiliary front link
3
and lower link
4
is reduced against the elasticity of the elastic element
8
, and the elastic element
8
is compressed. Then, the angle formed by the auxiliary front link
3
and lower link
4
is reduced, and the auxiliary front link
3
leaves the second stopper
7
. As a result, an interval between axes
22
and
24
is reduced, and an angle formed by a main front link
2
and a rear link
5
is reduced as compared with a case of the idle leg phase shown in FIG.
3
.
Blanco Javier G.
Imasen Engineering Corporation
Willse David H.
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