Artificial foot having ankle flexible mount

[57] ABSTRACT

An artificial foot including an improved ankle and foot mount is attached to a conventional stump mounted artificial leg. A coil spring extends downwardly from rigid attachment to the artificial limb in the vicinity of the ankle at the upper end and attaches rigidly to a plate in the plane of the sole of the foot at the lower end. The sole plate, extending from the heel to the ball of the foot, cantilevers from the coil spring to emulate natural foot action during walking. A second sole plate support, capable of accommodating both tension and compression as well as side to side foot motion, extends from a mount on the sole plate at the ball of the artificial foot upwardly at an angle to a mount on the ankle of the artificial limb. This provides improved toe action of the artificial limb. Provision is made for mounting either a spring or a variable resistance shock absorber to act in combination with the second spring to imulate natural foot motion.

Claims, 8 Drawing Figures

<img file="US3754286A_D0001.tif" />

Patented Aug. 28, 1973

3,754,286

<img file="US3754286A_D0002.tif" />

Patented Aug. 28, 1973

3,754,286

Sheets-Sheet 2

<img file="US3754286A_D0003.tif" />

<img file="US3754286A_D0004.tif" />

FIG_6

3,754,286

ARTIFICIAL FOOT HAVING ANKLE FLEXIBLE MOUNT

This invention relates to artificial limbs and more particularly to an improved mount for an artificial foot to an artificial leg which provides motion approaching that of the lost limb.

Heretofore artificial limbs have hinged the foot to the limb along a hinge axis taken through the ankle. Two major deficiencies result. First such limbs have been incapable of flexing side-to-side about an axis taken parallel to the plane of the sole from the toe to the heel. If for example the wearer of an artificial limb steps on either a sloped surface, a small irregularity such as a pebble, or turns rapidly, slipping commonly results. For this reason many wearers of artificial limbs have restricted mobility.

Secondly, such limbs transmit through the hinge the shock of the heel coming down on the ground. Such shock can cause irritation to the wearer, typically at the mount of his leg stump to the artificial leg, seriously inhibiting the use of the artificial limb.

It is an object of this invention, therefore, to provide an artificial limb which permits flexure of the foot in the vicinity of the ankle along an axis parallel to the sole taken from the toes to the heel of the foot. Accordingly, at least one coil spring is attached to the ankle of an artificial limb at its upper end, attached to the sole of an artificial foot at its lower end and allowed to flex in columnar flexure therebetween.

An advantage of this mounting of the artificial foot to the ankle is that improved walking on uneven or sloped surfaces results.

Yet another advantage of this mounting is that damping of the shock of the heel striking the ground during brisk walking results.

Yet another object of this invention is to provide improved toe resistance combined with the foregoing artifical limb features. According to this aspect of the invention, a support capable of permitting side to side motion is mounted from the sole of an artificial foot in the vicinity of the ball of the artificial foot to the ankle.

An advantage of this toe to ankle support is that in one form of the invention it can be a spring. This spring acts under tension when the heel of the artificial foot strikes the ground during walking and acts under compression when the weight of the wearer is on the toe of the artificial limb during walking.

An advantage of this second ankle to ball of foot mounted spring is that when it acts in compression improved toe action of the foot relative to the ankle results.

An additional advantage of this second spring is that when it acts in tension, improved heel action of the artificial limb results.

Yet another advantage of this second ankle to ball of the foot mounted coil spring is that it does not interfere with the side-to-side flexure of the limb along about an axis taken from toe to heel of an artificial limb.

Yet another object of this invention is to disclose a shock absorber mount included in combination with the second spring extending from the ankle to the ball of an artificial foot. This shock absorber, is provided with a variable resistance with respect to its stroke, first provides restrictive and slow damping responsive to walking and thereafter with the passage of time provides an accelerated release.

An advantage of this shock absorber is that a natural foot action is more closely emulated by the variable resistance release of the shock absorber.

Other objects, features and advantages of this invention will be more apparent after referring to the following specification and attached drawings in which:

FIG. 1 is a side elevation section of the spring mount of this invention with the rubber form shown cut away;

FIG. 2 is a view from the bottom of the artificial limb looking towards the top illustrating the mounting of the artificial limb;

FIG. 3 illustrates the mount of the artificial limb in the vicinity of the ankle;

FIG. 4a is a rear elevation section of the wearer of the artificial limb walking away from the viewer and simultaneously stepping on a rock to illustrate pivotal movement of the sole of the limb about an axis taken from toe to heel of the shoe of the wearer;

FIG. 4b is a side elevation section of the view shown in FIG. 4a;

FIG. 5 is a side elevation section of the artificial limb shown in FIG. 1 with a variable resistant shock absorber mounted to the artificial limb;

FIG. 6 is a side elevation section of the variable resistant shock absorber illustrating how varying resistance is achieved with respect to the stroke of the shock absorber; and,

FIG. 7 is a side elevation section of the artificial limb shown in FIG. 1 with a sled bar mounted between the ankle and toe.

Referring to FIGS. 1-3 and with specific reference to FIG. 1 an artificial limb is shown broken off in the vicinity of the ankle A. The improved foot and ankle mount is shown mounted to the artificial limb in the vicinity of its ankle A.

In its simplest form the invention includes an ankle plate 14, a mounted coil spring 16, and a sole plate 18. Coil spring 16 is welded to ankle plate 14 at its upper end, to sole plate 18 at its lower end, and thus forms a cantilevered type support for the protruding toe relative to the ankle A. Sole plate 18 extends from the ball of the foot at 20 to the heel of the foot 22. As shown here plate 18 curves upwardly in an arcuate fashion in the vicinity of the heel 22 so as to conform to the rounded part of the heel.

As in most conventional artificial foot constructions a surrounding rubber 25 is poured and cured in a mold which restricts it to the shape of a foot so that sole plate 18, spring 16, and ankle plate 14 are all encased within the artificial limb. Typically, rubber 25 is conformed to the shape of the foot of the wearer.

Referring to FIG. 2, the bottom of sole plate 18 may be viewed. Typically, this plate is apertured at a large aperture 30 so as to provide exposure through the sole of the foot and the center of the coil spring to the bottom side of ankle plate 14. This permits a wrench or the like to tighten a nut 33 on a bolt 35 to effect rigid attachment of the ankle plate 14 to the ankle A of an artificial limb. Additionally, sole plate 18, typically made of a relatively heavy steel, is provided with one or more cut-outs 37 to lighten its weight.

Spring 16 is selected along certain defined parameters. Typically, the spring is selected to a diameter which is slightly smaller than the width of the foot in the vicinity of ankle A. Secondly, the compressive force of the spring is selected so that the full weight of the wearer being placed on the foot will result in ap3,754,286 proximately one-fourth of an inch compression of the spring. In the case of a 185 pound man, when full weight is placed on spring 16 compression of onefourth of an inch will result. Finally, the spring is selected to provide a columnar resistance so that side-toside bending of plate 18 about an axis 40 taken from the ball of the foot at 20 to the heel of the foot at 22 is resisted but nevertheless permitted, (see FIGS. 4α and 4b.)

It can be thus seen that sole plate 18 is in effect cantilevered to ankle 14 by the spring action of spring 16.

In addition to spring 16, sole plate 18 at its ball portion 20 is mounted by a second coil spring 45 to ankle plate 14. Typically sole plate 20 is provided with a first spring mount 46 and ankle plate 14 provided with a second spring mount 47. Typically, mounts 46 and 47 are rigidly connected to the sole plate 18 and ankle plate 14 respectively by welding. Spring 45 is mounted between the mounts so as to be capable of acting both in tension and in compression. For resistance of bending moments, paired half-rounded shafts 49 and 50 and extending from mounts 46 and 47 respectively are confronted at their respective flat surfaces within spring 45 so as to provide some columnar rigidity to spring 45. It should be noted that tilting of sole plate 18 about axis 40 (see FIG. 2) extending from toe to heel of the artificial foot in the plane of the sole is permitted by second spring 45.

Having set forth the mechanics of this artificial limb, attention can now be directed to its dynamics with respect to FIGS. 4α and 4b. Referring to these figures, a wearer of the limb is shown stepping on a pebble, an unacceptable obstacle for most prior art artificial limbs. As can be seen, plate 18 is shown tilting about an axis 40 parallel to the plane of the sole plate just as a natural foot would conform to the presence of pebble 18. The artificial foot conforms to the presence of the pebble.

Additionally, it will be noted that since there is no hinge in the vicinity of the ankle when the weight of the wearer is placed on the artificial foot in the vicinity of sole plate 18 at heel 22 two effects will occur. First, spring 16 will serve to absorb the shock. Secondly, sole plate 18 will pivot about its point of attachment to spring 16 placing spring 45 under tension. Further improved damping of the foot motion will result.

Additionally, when the weight on the artificial limb is shifted, as by walking, so that a portion of the weight is placed at sole plate 18 in the vicinity of the ball of the foot at 20 both spring 16 and spring 45 will come under compression. Improved toe action results.

Referring to FIGS. 5 and 6, an additional embodiment of this invention is illustrated. As shown a shock absorber and spring combination 60 is mounted between mounts 46' on sole plate 18 at the ball of the foot 20 and mount 47' on the leading portion of ankle plate 14. A coil spring 62 capable of acting in both tension and compression is concentrically wound about an inner shock absorber 64. Shock absorber 64 is shown in section at FIG. 6 and includes a conventional cylinder 65 closed at one end, a piston 66 mounted for sliding movement interior of the cylinder 65 and a rod 67 which attaches to mount 47' at ankle plate 14. A second mount 68 at the closed end of the cylinder attached to mount 46' effecting attachment of the unit to sole plate 18 in the vicinity of the ball of the foot at 20.

Cylinder 65 has a goove 70 of variable dimension described in its sidewalls. From the neutral position of the piston shown at 66 goove 70 is provided with a narrow portion 71 which restricts fluid flow from one side of piston 66 to the other side of piston 66. At the lower portion 72 of the groove 70 the groove expands in dimension and accelerated stroke of piston 66 with decreased resistance is provided.

It can thus be seen on movement of mount 47' towards mount 46', as when the weight of the wearer is on the ball of the foot a controlled movement will result. First, there will be a general resistance of the shock absorber 64 to rapid pivotal movement of the ball of the foot 20 towards the ankle plate 14. Thereafter, and with the increasing passage of time cylinder 66 will pass downwardly and towards the wider portion 72 of the channel 70. Fluid will escape from one side of the piston to the other side with greater rapidity. Accelerated movement with decreased resistance will result.

Since the return of the foot to a neutral position in rapid fashion is usually desired, a one way valve 80 can be provided in pistons 66 permitting rapid return of the fluid from the upper portion of cylinder 65 to the lower portion of cylinder 65.

It can be seen at once that the shock absorber 64 of variable resistance when incorporated with the spring action of spring 62 provides improved foot motion. Initially and under conditions of brisk walking resistance emulating that of the natural foot muscles in the vicinity of the ball of the foot will be provided. However, where the wearer stands for relatively long periods of time with the weight on the ball of the foot, sole plate 18 will conform gradualy to the plane of the ground on which the wearer of the limb is walking. This will produce a natural and stabilizing foot action.

Referring to FIG. 7, the simplest form of the ankle to sole plate support is illustrated. A bar 80 is shown having to balls 82 and 83 mounted at either end. These balls are captured in and held securely to ball joint mounts 46 and 47 at the sole plate and ankle respectively. Since the ball joint mounts encompass more than one-half a sphere, the balls are held securely against both tension and compression. As is apparent bar 80 while maintaining the distance between the ankle and sole plate at 20 constant will permit the desired side-to-side motion of the sole plate relative to the ankle.

It will of course be realized that numerous modifications can be made to my invention without departing from the spirit and scope thereof. Specifically, varying springs or combinations of vertically aligned springs could be used in substitution for spring 16. Moreover, a fluid shock absorber alone, a spring alone, or both combined can be used between the mounts at the sole plate in the vicinity of the ball of the foot at the lower end and the ankle plate at the upper end. Likewise, other modifications can be made to my invention without departing from the spirit and scope thereof.