US2862313A - Fabrication of differentially deformable insoles - Google Patents

Description

Dec. 2, 1958 w H JONES 2,862,313

FABRICATION OF DIFFERENTIALLY DEF'ORMABLE INSOLES Filed June 5, 1957 2 Sheets-Sheet 1 FIFTH METATARSAL. SUPPORT AREA Fis 17 IO 7 INVENTOR I W/LL/A/W HE/VRYJO/VES AGENT Dec. 2, 1958 w JONES 2,862,313

FABRICATION OF DIFFERENTIALLY DEFORMABLE INSOLES Filed June 3, 1957 2 Sheets-Sheef 2 AGENT United States Patent i FABRICATION OF DIFFERENTIALLY DEFORMABLE INSOLES William Henry Jones, Montreal, Quebec, Canada, assignor to Canadian Footwear Research Inc., Montreal, Quebec, Canada Application June 3, 1957, Serial No. 663,277

2 Claims. (CI. 36-71) This invention concerns improvements in soles for shoes, and more particularly; concerns a construction of an apertured insole having resilient inserts correlated with the metatarsal support regions of the human foot, and a complementary resilient body associated therewith for controlling load distribution over the metatarsal arch.

In the shoe manufacturing art many comprises are made between a theoretical desired construction on the one hand which will provide a foot with a wholesome and healthy environment and a practical construction on the other hand dictated by the character of available construction materials, style demands, costs and like factors. Soles and insoles of shoes are conventionally fabricated from sheets or slabs of materials of the class having desired rigidity, toughness and porosity, as exemplified by leather and alternative planar materials. As lasted on conventional lasts, a sole is curved simply rather than formed in three dimensions, the axes of curvatures being generally parallel and the sole being bent out of a plane into cylindric form with generally varying radius. With the limited flexure allowed by shoe constructions which attach the upper more or less firmly to the sole edges the curvature of the sole is substantially limited to the cylindric. It will be apparent therefore that-the human foot resting upon the insole of a shoe is provided with a supporting base that is generally an unyielding surface having cylindrical curvatures.

Simple inspection of the underside of a human foot shows that the sole by no means conforms to a series of cylindrical curves generatedabout parallel axes, and in fact when the forward metatarsal joints are bent as occurs in rising up on the toes, there is scant similarity to a surface generated by a line moving parallel to and at varying radius about one or more parallel lines. A fleshy pad of epidermis, dermis, muscle tissue, ligaments and cartilages underlies the ball of the foot, and encases the sesamoid bones that lie below the forward end of the first metatarsal bone. On examining the foot structure in a direction transversely from the ball, the metatarsal arch is apparent, in which the forward ends of the five metatarsal bones are bowed upwardly from the sole. This transverse arch is apparent in each of a series of parallel cross-sections that might be taken of the foot progressive- 1y towards the heel, and the fifth metatarsal bone remains generally horizontal while theothers are inclined upwardly in the direction of the heel. The foot resting upon a flat surface contacts it generally at the forward ends of the first and the fifth metatarsal bones if the foot has a normally developed arch.

. Provided there is no Weakness of the longitudinal arch, the principal other support area of the foot is the base of the Os Calcis or heel bone. In the majority of human feet supported on a flat surface the weight of the body directed downwardly upon'the Talus bone which overlies the 0s Calcis is. applied forwardly of and to one side of the heel pressure. area. Thereby the weight of the foot is distributed almost entirely between. the heel pressure area and the sesamoid bones, and a relatively minor part 2,852,313 Patented Dec. 2, 1958 of the weight is carried by the forward end of the fifth metatarsal bone. On rising to the toes and when the wheight is taken off the heel, the amount of load carried by the fifth metatarsal at its forward end is much increased. The latter condition applies to the foot in highheeled shoes, wherein an attitude of perpetually rising on the toes is maintained, hence the outer metatarsal bone support structure is greatly loaded above the average load sustained in a flat shoe.

The nature of the contact of the unshod human foot walking upon a smooth bed of moistened fine sand or loam earth of relatively uncompacted character may be taken as a highly desirable environment to be simulated in a shoe. As the weight of the foot is brought down upon such support medium, the yielding nature of the compactable sand permits the heel to imprint itself over a relatively broad area while the sole areas under the forward ends of the first and fifth metatarsal bones embed themselves to a lesser extent in proportion to the loading on such areas. As the step is taken to impress an increased load on the metatarsals that part of the sand mass confined beneath and pressed upon by the upwardly bowed sole extending rearwardly between the forward ends of the first and fifth metatarsals is found to accept a significant share of the load, by becoming relatively unyielding. This compacted mass thereby affords a support for the transverse arch. A study of healthy unshod feet of primitive people treading earth paths and sand shows that an important share of the load is taken by the area referred to, and that this area extends heelward for a short distance. A comfortable feel is experienced in barefoot walking on turf or sand loam, and the pressure distribution over the principal and subordinate support areas of the foot on such media is a highly desirable objective to be matched by soles and. insoles of shoes.

In contrast therewith conventional sole and insole constructions provide a platform upon which the three main support areas of the foot bear with relatively limited contact areas and high pressure gradients across such areas. The human foot in a shoe with a firm sole, as the majority of walking shoes are constructed, is in no better position in regard to pressure intensityv and gradient than when standing on a smooth slab or a solid rigid body. The development of callus around such areas is a common ailment while the collapse of the metatarsal arch is a frequent consequence of wearing conventional shoes in walking on pavements and floors.

Heretofore a very great number of forms of arch support, pads, special insoles, and the like modifications of shoe members receiving pressure of the foot have beenevolved for the adjustment of pressure distributions over specific areas of the sole, of a shoe. Specific prior art forms are known wherein an apertured insole or sock liner provides resilient inserts of the character of sponge rubber presented beneath the thee principal contact points. of the foot. The fabrication of such forms as have here-. tofore been proposed presents serious dilficult-ies. in. the lasting of shoes since the aperturing changes the self-support characteristicsof the insole material under the stresses of lasting. Moreover the insertion and attachment of'inserts as previously proposed has been difficult and certain forms have not permitted relatively free insertion and withdrawal of the foot into a shoe so constructed.

The present invention therefore seeks to improve the construction of a shoe so that the pressure gradient (we? the principal support areas and in the area of the transverse metatarsal arch is more nearly uniform and concentrations of pressure are alleviated.

It is another object of the invention to modify a slab sole construction of a shoe to achieve non-uniform resilience over its area and which under pressure ofa human foot is differentially deflectable in accordance with the loads on each of the principal support areas of the sole, and by which the subordinate support areas accept their due share of the load.

Yet another object is the construction of the insole of a shoe to include a sock liner having an upwardly domed resilient projection disposed between the first and fifth metatarsal bones and extending rearwardly and bounded by relatively more deformable resilient portions presented beneath the ends of the first and fifth metatarsal bones.

The present invention has for its principal object to simplify manufacture of a shoe with an apertured insole and to facilitate the making of final adjustments of the several inserts before sealing the sock liner retaining member.

The invention has also the object of arranging a transverse metatarsal arch support body upon an apertured insole in relation to inserts filling the areas under the principal pressure points so as to provide a co-operative load-distributing action and to control the transverse arch curvature of the forward ends of all metatarsal bones as loaded in walking in high heeled shoes.

The following description of the invention is to be read in conjunction with the accompanying figures of drawing whereof certain ones illustrative of human foot structure are included for a better understanding of the relation of the invention thereto; the figures are:

Figure 1, showing in plan view the disposition of bone structure and the principal support areas of the foot;

Figure 2, showing in elevation comparative phantom sections of the foot and embedded in a compactable sand loam and as resulting on an unyielding slab;

Figure 3, diagramming the relation of the apertures and the transverse arch cushions in an insole according to the invention;

Figure 4, a section elevation of a foot in a high-heeled shoe embodying the insole of Figure 3, as designated by the line 44;

Figure 5, a transverse section taken on line 5-5 of the insole of Figure 3;

Figure 6, atransverse section taken on line 6-6 of Figure 3;

Figure 7, a longitudinal section of part of an insole as laid in the flat, taken on line 44 of Figure 3;

Figure 8, an illustration of the manner of retaining punched portions within the apertures of the insole; and,

Figure 9 is a plan view of a perforated sock liner.

Figure l is a self-explanatory drawing, which in conjunction with the other figures of drawing serves to illustrate the weight distribution and proportional loading of areas of the human foot, the body weight being directed downwardly upon the Talus bone.

The deformation of a sand loam earth mass having a smoothed plane surface designated A by the foot in taking a step to impress the body weight thereon may be understood from Fig. 2, wherein the solid line contour denotes the foot outline under the distributed loading effected. The dotted line A denotes the displaced surface of the earth mass. It will be seen that forwardly of the heel support area of Fig. 1 there is an inclined slope of relatively broad extent conforming to the foot contour which contribute support. Both in front of and rearwardly of the ball of the foot a domed body of loam is formed by compaction and due to the sinking of the sesarnoid area. There is thereby created a broadened support area tending to hold up the transverse arch for some distance heelward of the line joining the forward support points of Fig. 1.

There is also shown in Fig. 2 the effect on the foot of stepping on a smooth rigid slab support. The loading at each of the principal support points of Fig. 1 is concentrated over relatively small areas'of the foot, and the deflection of the heel and ball as indicated-by the dashed outline of the foot shows considerable lateral A stretching due to high gradient of pressure across such areas.

An embodiment of the invention particularly described with reference to Figs. 3 and 4 includes an improved insole 10 which may be realized as a single piece of leather or other suitable flexible non-resilient material and may include a shaped fibre 'base laminate 11 under the arch and heel. That part of the insole which underlies the ball of the foot is apertured by punching out ovoidal or elliptical bodies 12 and 13, in place of which cushioning bodies 14 and 15 are received. The thickness of the latter bodies will generally be substantially twice the thickness of the insole into which these are set. The bodies preferably comprise a rubber sponge of fine cellular character although numerous combinations of materials having desired resilience might be employed. The heel area of the insole supports a tapered cushion 16 of soft spongy rubber cemented to the upper side. Lying immediately adjacent between the inserts 14 and 15 and extending rearwardly therefrom is a yielding upwardly bulged cushion body 17 cemented to the insole and to the edges of the inserts. This cushion is formed preferably of a sponge rubber more dense than that used in forming the inserts and having a bulk modulus of the order of at least two and one half times that of the insert material. The inserts are cemented to the sole 18.

In the manufacture of a shoe having an improved insole according to the invention, the insole body 10 is prepared as by cutting it out with a clicker die shaped to the outline required, to the heel and arch portions whereof may be applied suitable stiffening devices. The blank insole is then placed between dies of the type including shaped punches reciprocable toward a corresponding apertured sole plate in the apertures of which spring-loaded followers are slidable vertically to apply restoring forces to return the sheared-out bodies to their orignal positions in a sheet of stock, when the punches move clear. Numerous prior art mechanisms of a type suitable to carry out this step are known and it is believed this step will be sufliciently understood by practitioners in the art without further elaboration.

The insole with its separable sheared portions 12 and 13 is removed as a unit from the die bed and one or more strips of adhesive tape such as 19, 20 are placed in bridging relation across the insole 10 to hold the free ovoid portions during further handling, as shown in Fig. 8.

The areas which are punched out correspond to the bearing points of the ball of the foot and underlie the joints at the forward ends of the first and fifth metatarsal bones. In general the outer edge of the aperture which lies nearest to the edge of the insole will be spaced inwards about 7 inch. The areas are elongate ovoids and generally are directed in line respectively with the first and the fifth metatarsal bones of the foot. The ovoids may be shaped irregularly if desired, however a preferred plan form has a major axis approximately twice the length of the minor axis, and the inner edge of each aperture extends to the joint of the adjacent metatarsal but does not substantially underlie it.

The construction of the shoe is carried out substantially identically as for the conventional unmodified shoe, the placing of the inserts 14, 15, and the cushions 16, 17 being efiected near the end of the fabrication prior to the cementing down of the sock liner 21. In carrying out one modern constructional procedure the insole with its punched slugs held in place is secured as by tacking to the underside of a wooden last, after which the lasting machine pulls the upper over the last, the edges being secured by cementing and tacking to the insole margins. In this operation the strength of the insole is a critical factor in assuring freedom from buckling and wrinkling. It has been found that a single broad aperture is disadvantageous and impractical and moreover that the retention of the sheared plugs is essential to successful results in modern manufacturing operations. The parts of the shoe are built up on the last, the shank is attached and lasting allowances are trimmed. The outsole is cemented to the insole when the upper is adequately bonded and the tacks used to hold the insole in place have been removed.

After the last is removed from the shoe, the shearedout plugs are manually lifted out by pulling off tapes 19, 20. Each of the metatarsal pads 14, are then cemented on its underside and aifixed in an aperture against the exposed outsole 18. The body 17 which has been cut to conform to the plan outline of the inserts 14, 15 is cemented on its base and positioned against the inserts before it is pressed down against the insole. Similarly, heel cushion 16 is cemented down.

A sock liner 21 which is preferably a thin split leather member with smooth side up and cut to conform to the shape of the insole is preferably pierced over the forward ends of the first and fifth metatarsals and over the heel cushions. The sock liner is then cemented down over the insole and cushions.

The sock liner may be formed as a composite structure whereof each of the pierced areas is realized in any very soft pliant material and the pieces are taped to the main body of the liner or its underside.

An alternative to the foregoing completed shoe construction may omit thebody 17 until the final fitting of the customers foot, at which time a body may be specifically shaped from .a blank form, as by shaving and wire wheel scratching.

A material found to be particularly suitable for use as inserts 14, 15 comprises a sheet sponge rubber stock in a thickness of 4 inch sold under the trade name Airfoam, made by the Goodyear Rubber Company of Akron, Ohio. A sample of this material tested under compressive loading was observed to have a modulus of elasticity of approximately 12, or in other words, its defiection rate was 12 pounds per inch per inch for a column cross-section of one square inch. Values considerably above this amount may be also useful, particularly where the weight of the person to be supported is above normal. Moreover the thickness of the insert may be varied somewhat. For example, in a mans shoe construction where an intermediate sole lies between the insole and the outsole the extra layer may be also apertured in correspondence with the apertures of the insole and thicker insert bodies of appreciably firmer material may be inserted into the deeper opening provided.

A material found satisfactory for pad 17 in one practical embodiment of a Womens shoe, to serve as support for the transverse metatarsal arch, was formed from a porous red rubber having a modulus of elasticity in compression lying in the range from about 35 to about 60, which is the rate of load application in pounds to deflect a column of one square inch cross section one inch per inch of length. Various maximum heights of cushion ranging from about 4 inch to inch have been successfully employed. It will be understood that the form of the cushion is not necessarily limited to a body symmetric about a center line. The maximum thickness portion should preferably underlie the forward ends of the second, third and fourth metatarsal bones, and should continue heelward to about the midlength positions of these bones, at which the thickness will have tapered to zero. The edges of the cut-outs or indentations formed in the pad are preferably tapered to a thickness such that the insert bodies 14 and 15 protrude slightly above the edges of body 17.

The method of constructing shoes with apertured sole members having inserts placed in the apertures is not restricted solely to shoes having the openings described. Numerous other arrangements may be chosen, and the invention extends moreover to a single broad opening under the metatarsal bone group, the insole being fixed to the last with the slugs or slugs which have been sheared out in the punching operation replaced into their former positions. It is within the scope of the invention to substitute metal pads having numerous hooks or teeth extending therefrom to hold the slug and the blank in their original relations, in lieu of the adhesive strips 19, 20, such metal pad being removed after the lasting is completed.

I claim:

1. In a shoe having an outsole, the combination of a planar insole member formed with a pair of openings underlying the forward ends of the first and the fifth metatarsal bones of the foot, a pair of resiliently deformable insert bodies thicker than said insole member removably fitting each opening to protrude upwardly therefrom, a resilient metatarsal pad having a pair of marginal indentations registrable with said pair of insert bodies and removably secured to said insole member, said pad having an upwarly domed convex face extending between said inserts and tapering toward the heel and having a maximum height greater than the protruding height of said insert bodies.

2. The combination as in claim 1, wherein said resilient metatarsal pad comprises a sponge body having a bulk modulus of elasticity not less than about two and one-half times the bulk modulus of elasticity of said insert bodies.

References Cited in the file of this patent I UNITED STATES PATENTS 1,481,133 Gr-ossman Jan. 15, 1924 1,670,811 Jones :May 22, 1928 1,675,711 Jones July 3, 1928 1,741,419 Jones Dec. 31, 1929 1,841,942 Fenton Jan. 19, 1932 1,977,693 Page Oct. 23, 1934 2,253,429 Hess Aug. 19, 1941 2,323,579 Vigorith July 6, 1943 FOREIGN PATENTS 511,720 Great Britain Aug. 23, 1939

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