# Patent

## Title
Anti-slip foot assembly

## Abstract

An anti-slip foot assembly for a strut is disclosed. An embodiment of the anti-slip assembly includes a heel pad adapted to resist normal forces applied by the strut, a plurality of independently flexible toes adapted to resist the lateral forces that tend to cause slipping. A foot assembly with retractable cleat system is also disclosed.

## Background
CROSS REFERENCES TO RELATED APPLICATIONS
This application claims the benefit of, and is a continuation-in-part of Applicants' prior utility application Ser. No. 13/451,825, filed on Apr. 20, 2012. This prior application is incorporated herein by reference.


FIELD OF INVENTION
The disclosed technology relates generally to anti-slip strut tips, and particularly, to an environment-engaging “foot” assembly adapted to reduce lateral slipping on rugged terrain.
BACKGROUND
The disclosed technology relates generally to anti-slip strut tips, and particularly, to a surface-engaging “foot” assembly adapted to reduce lateral slipping between the foot and surface.
Axial forces applied from the strut to the foot assembly (and in turn to a surface) have a normal force component and a lateral force component. The normal force is perpendicular to the ground. The lateral force is parallel to the ground.
Unless the axial force from the strut is perfectly perpendicular to the surface, there will be a lateral component that will tend to cause the foot to slip along the surface. The force of friction between the foot assembly and the surface tends to resist slipping.
Many types of prior art feet fail to properly grip rugged terrain (including cracked surfaces, uneven sidewalks, pebbles and small obstacles, inclined surfaces, sand and gravel, and in various puddles of liquid). As a result, these prior art feet may not provide sufficient traction to counteract applied lateral forces, and the strut may slip.
Anti-slip features are desirable when the strut is a component of an ambulatory device, such as a cane, walker, crutch or forearm crutch. Anti-slip is particularly important for the forearm crutch. Typical users suffer from partial paralysis, cerebral palsy, or similar afflictions, and rely on the forearm crutch to support nearly all of their weight throughout the day. Since these devices are used to support significant portions of a user's bodyweight, any slipping between the device and environment can be devastating.
Such slipping can lead to the user's sudden loss of balance and stumbling, and may result in serious injury. Every year, an estimated 10,000 people suffer injuries—from broken bones to concussions—from falling during use of their forearm crutches.
There is a need for a foot assembly with improved gripping properties, especially on rugged terrain.
SUMMARY
The disclosed anti-slip foot assembly provides a deformable surface adapted to securely grip environmental surfaces. A combination of structural design choices and material selection provides an improved contact path between foot and environment. The anti-slip foot assembly may be used as the terminal component of a strut, and in particular, an ambulatory device, to provide confident support, even when used on rugged terrain.
The foot assembly may be attached to any strut that might benefit from non-slip properties. This includes, without limitation, crutch, cane, walker, forearm crutch, hiking pose, prosthetic foot, robotic foot, ladder, outrigger, or chair.
In a preferred embodiment, the anti-slip foot assembly is securable to a forearm crutch. Flexible “toes” surround a central heel pad. The toes are adapted to resist lateral slipping forces, while the heel pad is adapted to resist axial forces from the strut (for example, in the crutch embodiment, to support the user's weight).
The toes are manufactured from an elastomer, allowing them to flex independently of each other. The allocation of forces among the toes may vary depending on nature of the surface they engage. When the foot contacts the ground, and the strut applies a force, the foot assembly first distributes the applied force over the separate toes. If one of the toes encounters an obstacle (such as a pebble), the remaining toes will still engage the ground and provide sufficient contact area for traction.
If the foot assembly comes into contact with a wet surface (for example, a puddle), the foot disperses liquid between the channels of the “toes,” further improving the anti-slip properties.
The disclosed embodiments are illustrative, not restrictive. While specific configurations of the foot assembly have been described, it is understood that the present invention can be applied to a wide variety of strut tip assemblies. There are many alternative ways of implementing the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention are disclosed in the following detailed description and accompanying drawings.
FIG. 1 illustrates an exploded view of a foot assembly embodiment.
FIG. 2 illustrates a side view of a non-slip foot embodiment.
FIG. 3 illustrates a bottom view of a non-slip foot embodiment.
FIG. 4 illustrates a foot assembly with a retractable cleat.
FIG. 5 illustrates a foot assembly contacting a surface obstacle.
FIG. 6a illustrates a top-three-quarters view of a foot assembly.
FIG. 6b illustrates a top view of a foot assembly.
FIG. 6c illustrates a bottom view of a foot assembly.
FIG. 6d illustrates a bottom-three-quarters view of a foot assembly.
FIG. 7 illustrates a cut-away side view of a foot assembly with universal adapter.



DETAILED DESCRIPTION AND PREFERRED EMBODIMENT
The following is a detailed description of exemplary embodiments to illustrate the principles of the invention. The embodiments are provided to illustrate aspects of the invention, but the invention is not limited to any embodiment. The scope of the invention encompasses numerous alternatives, modifications and equivalent; it is limited only by the claims.
Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. However, the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured.
TERMINOLOGY


    
    
        a. Friction—is not used in its strict tribological sense, but in broader definition, encompassing traction as well as any force or combination of forces that tend to resist sliding motion between two bodies.
        b. Traction—is the physical process in which a tangential force is transmitted across an interface between two bodies resulting in stoppage of relative motion between the bodies.
    
    


FIG. 1 illustrates an exploded view of an anti-slip foot assembly embodiment.
Overview. A preferred embodiment of the foot assembly includes three flexible toes 101 surrounding a heel pad 103. The foot is bolted to an adapter 105, which is in turn secured to a strut 107. A fastener 109 runs through a washer 111 and then through the foot and the adapter 105, securing the two components together. The strut 107 includes a threaded end 113. The adapter 105 includes a socket threaded to accept the threaded end 113 of the strut 107. This embodiment is securable to the ground-engaging end of a forearm crutch. In such circumstances, the foot assembly is sometimes referred to as a “ferrule.” In other embodiments, the design may be secured to any strut that may benefit from anti-slip properties.
Tread. The ground-engaging face 115 of the toes is covered in a tread pattern. In the preferred embodiment, the peripheral edges 117 of the toes are also covered in a tread pattern. The tread pattern further increases anti-slip properties on rough terrain.
Toes—Function. The toes 101 are designed to securely engage a surface and prevent lateral slip. The toes 101 also absorb initial shock upon impact with the ground. If one of the toes 101 encounters an obstacle, it can flex independently to allow the remaining toes to firmly engage the ground.
Channels. Channels 119 between the toes allow liquid to disperse from beneath the foot. When the foot is used on a puddle or wet surface, the channels allow liquid to flow away from the toe-ground contact area. In other embodiments, the individual toes touch each other, without channels in between.
Size. In the preferred embodiment, the height of the foot assembly is about 1.5 inches, the widest circumference at the toes is 9.3 inches, and the narrowest circumference of the foot assembly is 4.8 inches. However, other embodiments may take different sizes. For example, the foot assembly may be miniaturized for tiny robotic appendages, or scaled up for industrial uses, such as outriggers.
Material. In the preferred embodiment, the toes are manufactured from an material with an elastic modulus of between 0.2 and 0.4 GPa, and with sufficient toughness (tear-resistance) to withstand cyclical engagement with rugged outdoor surfaces. Acceptable materials include, without limitation, elastomers such as a purlyurethane blend; an isoprene; a polyisoprene; a natural rubber; a silicone; a butyl rubber (IIR, BIIR, or CIIR) or a cross linkage of EPDM rubber and polypropylenesantoprene.
Heel Pad. The preferred embodiment includes a heel pad 104 arranged at a center of the foot. The pad is designed to support axial forces on the strut. A surface-engaging face of the heel pad 121 includes a tread pattern.
Material. The central heel pad is manufactured from an elastomer such as natural rubber, an isoprene, a silicone or a santoprene.
FIG. 2 illustrates a side view of an anti-slip foot assembly embodiment. The toes 101 are covered in a bottom tread patter 115 and a side tread pattern 117. The toes are separated by channels 119.
FIG. 3 illustrates a bottom view of an anti-slip foot assembly embodiment. Three toes 101 surround a heel pad 103. Channels 119 separate the toes 101. The width of the toes 301 is between 1⁄4 and 1 inch. In another embodiment, the toe width is between 1⁄3 to 1/10 of the outer circumference of the foot assembly. The lower face of the toes may be curved up away from the lower plane of the heel pad.
Toe flexibility may be reduced by adding a bridge 303 from the toe's inner face 305 to the heel pad 103.
Retractable Spike Assembly. In another embodiment, the foot assembly includes a retractable cleat assembly.
FIG. 4 illustrates an alternate embodiment with a retractable spike assembly. In this embodiment, a plurality of retractable cleats 401 are provided on the bottom of an internal “power screw” or “rack and pinion” arrangement 403. This embodiment may be particularly useful for strut tips that are used on both icy and non-icy surfaces. On icy surfaces, the cleats may be extended for improved traction. On other surfaces, the cleats are retracted to minimize wear.
The outer face 405 of the foot assembly may be rotated relative to the strut 407. An inner face of the foot assembly is threaded. When the foot assembly is rotated, the cleats 401 below the lower face of the foot assembly, or retract the cleats into the foot assembly housing 409.
Material. The retractable cleats may be manufactured from a metal such as stainless steel or aluminium alloy. The power screw housing may be manufactured from a polycarbonate plastic material.
FIG. 5. FIG. 5 illustrates a perspective view of an anti-slip foot assembly embodiment in use. A first toe 503 of the foot assembly has come into contact with an obstacle 501 (for example, a pebble). The first toe 503 flexes independently to conform to the contours of the surface obstacle 501. The remaining toes 505 remain securely engaged to the ground surface. This provides improved traction, even on rugged terrain.
FIG. 6.
Press-Fit Strut Socket. FIGS. 6a and 6b illustrate a slip-on or press-on embodiment of an anti-slip foot. This embodiment allows the foot to be mounted onto a strut by receiving an end of the strut into a press-fit strut socket. Examples of such a strut may include, without limitation, a crutch, cane, walker, forearm crutch, hiking pole, prosthetic foot, robotic foot, ladder, outrigger or chair.
Tri-lobed Opening. FIGS. 6a and 6b illustrate a universal sized opening 601 that will accommodate multiple sizes of devices. Strut-socket opening 601 is a tri-lobed stretchable opening which converges slightly in diameter as it gets deeper into the foot. In a preferred embodiment, the strut-socket opening 601 is 2 inches deep. In other embodiments, the opening may be deeper or shallower, as necessary to sufficiently secure the anti-slip foot to the strut.
Toe-Heelpad Bridges. FIG. 6c also illustrates the use of two bridges 303 from the toe's inner face 305 to the heal pad 103. The use of two bridges may help decrease the independent flexibility of the toes. The width, material, and number of bridges may be adjusted to further increase or reduce the ability of the toes to flex independently of each other and of the central heel-pad.
Universal Adapter. FIG. 7 illustrates an embodiment of the anti-slip foot with a universal adapter for receiving a strut.
A universal adapter 701 may include an end with a mounting peg 702 insertable into the strut socket of the anti-slip foot. The mounting peg insertable into the strut socket that may be secured by, for example, a press-fit connection, by glue, by screws or other well-known fasteners.
The universal adapter 701 (or mounting peg) can take any form that allows for mounting of the FIG. 7 assembly to a device requiring a non-slip foot. Adaptor 701 may be permanently bonded or glued to an non-slip foot. An upper face of the adapter may include a threaded end for threadably securing the adapter to a strut. In another embodiment, the universal adapter may be molded as part of the strut itself. In another embodiment, the upper face may be securable to a strut by any other known mechanism.
Although embodiments have been described in detail, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative, not restrictive.

## Claims

1. An anti-slip foot assembly comprising:
a strut-socket at an upper face of the assembly comprising a stretchable opening for securing a strut therein;
a central heel-pad adapted to resist an axial force from a strut seated within the strut-socket, the heel-pad extending from within the assembly to a bottom surface thereof and comprising a bottom, ground-engaging surface;
a plurality of flexible toes adapted to resist lateral slipping forces from a strut seated within the strut-socket, the toes surrounding the central heel-pad and separated from the heel-pad by one or more channels, each toe comprising:
an outer face extending from the foot assembly and comprising an outer tread pattern;
an inner face; and
a bottom, ground-engaging face comprising a bottom tread pattern,
wherein each toe is separated from the other by one or more channels having a sufficient width and height to allow each toe to be independently flexible, each channel extending through the inner and outer face of the toe; and

one or more bridges extending from the heel-pad to the inner surface of one or more of the toes.

2. The anti-slip foot of claim 1, wherein the number of toes is three.

3. The anti-slip foot of claim 1, wherein the number of toes is four.

4. The anti-slip foot of claim 1, wherein the strut-socket is securable to a strut with a press-fit connection.

5. The anti-slip foot of claim 1, wherein the strut-socket comprises a tri-lobed opening.

6. The anti-slip foot of claim 5, wherein the strut-socket is narrower at the opening than at a base thereof.

7. The anti-slip foot of claim 1 further comprising a mounting peg secured to the strut-socket.

8. The anti-slip foot of claim 7, wherein,
the mounting peg is threadably securable to a strut.

9. The anti-slip foot of claim 7, further comprising a strut, and wherein,
the mounting peg is an integrated component of the strut.

10. The anti-slip foot of claim 1, wherein the heel-pad is aligned to an axis of the strut-socket.

11. The anti-slip foot of claim 1, wherein,
the depth of one of the channels between one of the toes and the heel-pad is at least 1⁄2 of the height of the foot.

12. The anti-slip foot of claim 1, wherein,
the depth of one of the channels between the one of the toes and the heel-pad is at least 1⁄4 of the height of the foot.

13. The anti-slip foot of claim 1, wherein,
the strut-socket is centrally located on the upper face of the foot assembly,
the toes radiate around a lower face of the foot,
the heel-pad is located in the center of the toes, and
the heel-pad is aligned to an axis of the strut-socket.

14. The anti-slip foot of claim 1, wherein
an outer circumference of the anti-slip foot is between 15 and 30 cm.

15. The anti-slip foot of claim 1, wherein
the largest circumference of the anti-slip foot is between 50 and 100 cm.

16. The anti-slip foot of claim 1, wherein
the largest circumference of the anti-slip foot is between 1 and 5 cm.