Patent Application
20050115116
The present application relates to an article of footwear having a hinged joint.
In many sports, as for instance, cross-country skiing, as much force as possible is to be transferred between the human body and a surface with a view to generating speed. Basically, the magnitude of the forces is determined by the physical capacity of the human body, but at high speed the surface may produce reactive forces which exceed the man-generated forces. The body's main task will then be to resist these forces. In any event, technique and equipment determine how great a portion of the forces is transmitted.
Thus, body-equipment-surface create a three-part system. This system will be explained in more detail with reference to cross-country skiing, although the principle will also apply to other activities. In the following explanation, ski poles and clothing will be disregarded.
The equipment for cross-country skiing traditionally consists of boots, bindings and skis. In order for these components to perform their force transfer task optimally, two requirements must be met:
materials must be as rigid as possible if force is not to be lost in undesirable deformations.
form, materials selection and mechanisms must be selected so that the two other main components in the system, body and surface, can behave as normally or as effectively as possible.
Requirements A and B are often conflicting, and optimal compromises must be made. Let us take the surface as a specific example first. It is advantageous that the snow should not subjected to large, local deformations. A curved, but completely rigid ski will transfer greatest forces in the front end and the tail of the ski on kick or push-off, with the result that these parts become buried in the snow. A ski which distributes force evenly along its whole length is more expedient. There is general agreement on the following fundamental design choices in order to obtain such a ski:
If we approach the equipment from the body instead, flexion of toe joints is an essential movement in cross-country skiing. This flexion is advantageous because, in particular in the classical diagonal technique, it gives a force transfer sequence which is physiologically correct and normal, not so very different from the force transfer sequence in running. Therefore, up until now it is the solution from running that designers have chosen to copy when designing cross-country skiing boots, namely to form boots in flexible materials which allow the degree of flexion required.
However, cross-country skiing has more in common with other skiing disciplines than with running because running is fundamentally different as regards one essential point: the boots forms the interface with the surface. An important degree of freedom in ski design is the possibility of shaping the “underlying surface” of the boot, namely the top surface of the ski. This possibility does exist in running. Therefore, in addition to 1) transferring force, a running shoe must also 2) cushion and distribute forces to avoid unwanted deformations of the foot, and 3) provide information about the position of the foot relative to the underlying surface. The last point is essential for body control and balance.
The same requirements apply in the case of the equipment in cross-country skiing, but here tasks 2 and 3 can and should primarily be performed by the ski, because it forms the interface with the surface. As mentioned before, the front end and the tail of the ski must be flexible in order to satisfy point 2 above (described in more detail in the figures below). However, points 1 and 3 are best met if the central part of the ski, the binding and the boot form a rigid unit.
The explanation for this is that in most cross-country skiing techniques, in both skating and classical styles, force will seldom be distributed evenly across the ski when it is to be transferred from the surface. More force will pass through one of the edges. This is always the case in skating, on hard snow in particular (described in more details in the figures below). Even in the classical diagonal technique, variables such as track direction, lateral inclination of the track and an uneven snow consistency will contribute to a large degree of unpredictability. Therefore, in classical style too, the ski will often be subjected to a torque which is not taken up by the torsional twisting in the front end and tail of the ski.
A rigid boot, in combination with a rigid fastening to the ski, can transfer a large torque to the foot, which can rapidly fine-adjust its position to reestablish necessary balance and control. A soft boot, on the other hand, will when subjected to some load be pressed together between the most loaded ski edge and the corresponding side of the foot (described in more detail in the figures below). This compression and tensile strain will in addition be supplemented by a torsional strain, because most of the force is as a rule transferred through the rear part of the foot, whilst the boot is only held in place at the front by the fastening.
Thus, two important requirements for the design of cross-country skiing equipment can be formulated: choice of dimensions and materials which transfer great force, and adjustment to the body and its movements—with particular emphasis on allowing flexion of toe joints. The manner in which attempts are made to meet this last requirement in today's solutions does not fulfil the first requirement in a satisfactory manner, because the equipment is in tly deformed. This in turn results in undesirable movements of the body. In the following it will also be shown that inhibition of some desirable movements is also a consequence.
There is less flexion of the toe joint in the skating technique than in the classical skiing technique. Therefore, more rigid boot soles have gradually come into use in skating on the grounds that the soles are “torsion-proof”.
The reason that “torsion-proof” is written in inverted commas here is that a completely torsion-proof plate, e.g., a boot sole, which cannot be twisted, can never be bent either. So the existing boot soles are by no means torsion-proof. The same is true of the form around the heel. And even if this were in fact completely torsion-proof per se, it could still be twisted relative to the boot's point of attachment, i.e., the binding, via the non torsion-proof sole.
Nor does a short, bendable segment under the toe joint, in an otherwise rigid plate, give complete torsional rigidity of the sole. The torsional rigidity could be increased by allowing the length of this segment to be close to zero, but then another problem arises: the sole will not be able to elongate. Since the sole of the foot becomes longer on flexion of the toe joint, the foot will then either move upwards in the boot and lose contact with the sole, or be pressed against the toe and heel cap and be deformed in an undesirable manner.
Torsional rigidity, bending rigidity and compressive/tensile rigidity are all interdependent factors in a solid body, and together they have nine components in the three spatial directions. However, in this problem description we have concentrated on the lack of torsional rigidity in the longitudinal direction, because this is most disadvantageous and can be seen to be a provoking cause of related problems. We shall briefly mention two:
Together, the lack of torsional, bending and compressive/tensile rigidity in today's boot means that the boot is not able to give the foot the necessary support below the ankle. Thus, it is more difficult to balance, especially in skating. Today this is compensated for by making ski boots higher than ankle-height, or by hinging a supporting cuff coaxial with the upper ankle joint (talar). Such solutions give better balance, but will be detrimental to mobility and/or force transfer in cross-country skiing:
To sum up, the binding systems (boot and binding) for cross-country skiing that are used today have the following weaknesses:
All three problems can be traced back to the flexible boot as the basic main solution. The choice of part-solutions will determine which of the last two problems occur most.
If materials and/or dimensions of a boot shell are selected so that the shell is non-deformable, the behaviour of the she be controlled by means of mechanisms. A rigid shell with mechanical joints will only move in the directions and distances and with the resistance allowed by the joints.
The right choice of location, orientation and number of degrees of freedom and the degree of resistance for each joint is essential if the shell, at all times and optimally, is
If loss of friction in the joints and micro-deformations of the foot are not taken into account, this type of footwear will in theory be able to transfer all force between the body and the surface.
If the article of footwear is to be locked mechanically to other equipment, it may be seen as an extension of the body. The same principles for efficient movement and joint design apply.
The weaknesses of today's systems listed above are remedied according to the invention which relates to an article of footwear, characterised in that it consists of a forward portion and a rear portion which are articulated to each other about an axis which is almost coincidental with the metatarsophalangeal joint in the hallux when the foot is located in the article of footwear.
Preferred features of the present invention are set forth in dependent claims 2-5, 7 and 9-13.
The invention will be described in more detail with reference to the attached figures, wherein:
If the heel is pressed down and (3) is in contact with (1) (a turn of 0° in (2b) and (1b)), the mechanism will also be locked in all other directions, because (2) and the parts of (1) and (3) that are in contact are completely rigid and non-deformable. For extra secure sideways locking between (1) and (3), the cross-sections of these components have vertical shapes which complement each other in this position (as in today's flexible solutions).
When the turns in (1b) and (2b) are greater than 0°, both (1) and (3) will only move relative to (2) in one-axis rotation. Components and joints must therefore be designed so that the joint turns in (1b) and (2b) can be at least as great as is natural for the foot, and natural in relation to the surface. (2b) must be located and oriented coincident with the bending axis of the toe joint, so that this largest movement in the sole of the foot is allowed to be made as normal inside the shell. The movements of the boot shell are thus controlled by this movement in a predictable manner. Other movements in the sole of the foot are so small that they are taken up by the flexibility of a soft inner boot. (1b) must be located and oriented so that (1) via (2) and (3) moves in an expedient manner when the foot makes a normal kick or push-off movement for the skiing technique in question.
The rigid boot shell transfers all force between the foot and the underlying surface. This gives greater force utilisation than today and thus contributes directly to greater speed.
It also gives static support to the sole of the foot in all other direction than about the axes of rotation (1b) and (2b), i.e., it helps to prevent undesirably large turns in twisting and side movements of the sole of the foot, and helps to relieve joints and muscles which attempt to prevent such turns. The shell therefore contributes indirectly to higher speed because the body is spared fro force unnecessarily. Any force saved can instead be used in the kick.
In addition to the shell providing static support, the elastic part of the resistance in (2b) and (1b) will give dynamic assistance to the foot movements in that some of the force in the working phase of the movements (kick) is stored in the articulation and is given back to the foot or ski in the quite phase (recovering foot and ski).
To permit (1b) to be opened and the components (1) and (2) to be separated, the system must comprise a locking mechanism consisting of several elements. Some of these must be allocated to (2), whilst the others can either be incorporated directly into (1), or into a separate binding housing component (4) which is fixed to (1).
Either element A or B has an external cylindrically symmetric surface and can rotate relative to a closed, cylindrical cavity in one of the main components. Since the other main component is fixed to this element via the unit AB, this main component and AB rotate together. The axis of rotation (1b) will thus be defined by the centre axis of the cylindrically symmetric surface. The most optimal orientation of (1b) is not necessarily horizontal and perpendicular to the longitudinal axis of the ski, but probably quite close to this.
Desired rotational motion between boot and ski is obtained by incorporating one or more resistance elements M (
Rotational resistance can in principle be adjusted in two ways: by replacing M with resistance elements having different resistance characteristics or by adjusting the pretension in M. One or both ways can be used in the system. The design of elements to be replaced or pretensioned will depend on the resistance principle selected, see the preceding paragraph. In principle, s hanisms do not need to be allocated to the same main component as M.
Simple solutions with stepless adjustment of pretensioning are recommended because this does not require replaceable parts, and can be done often, e.g., if different snow conditions, style or distance require different resistance in the same ski.
To avoid undesirable deformations of the foot, the correct position of the joint axis (height above sole of foot, length from toe) and its orientation in space (angle to the horizontal axis and perpendicular axis of the ski) are important. In principle, the axis should be coincident with the axis of the toe joint, but certain considerations and reservations are identified and discussed in the following.
The location is of course dependent first and foremost on foot size, so it should be located further back and further up for each boot size. However, the orientation of the toe joint axis varies more unpredictably than, e.g., the axis of the upper ankle joint from person to person. From inside to outside, it appears as a rule to be angled backwards at about 10° and slightly downwards when a person stands on the whole foot.
Two factors make it difficult to determine an average orientation of the toe joint axis, and thus the joint axis of the boot accurately. Firstly, it is a simplification to say that the toe joint axis is one axis, since it passes through all the toes and is surrounded by many small bones and muscles. Thus, it is dynamic and changes orientation relative to the surrounding parts of the sole of the foot. However, the axis can be said to twist upwards and slightly forwards on the outside in the course of a typical bending motion (in running a “typical bending motion” means that 80% of the force passes through the hallux). So, in any case, an average axis for this movement must be chosen. Moreover, there must always be room for the toes during the whole kick movement, so the finest adjustments of the foot's position must be taken up in a soft inner boot (this will be discussed in more detail below).
Secondly, the orientation of the joint must also be seen in connection with the orientation of the fastening, since the rigid forward portion of the boot is a part of both. The movement path of the ski relative to the rear portion of the boot—and thus the force-producing parts of the leg—will be a complex function of the movements in the two joints.
In skating the location and orientation of the fastening axis will probably have limited importance because the boot is only rotated slightly towards the ski, and then after the kick has been made. In the classical diagonal stride, however, we can observe that the knee describes a path that is almost in the vertical plane through the ski axis, whilst the ski is held flat against the surface. This suggests that there should not be much deviation from horizontal axes which are perpendicular to the longitudinal axis of the ski.
The most important change that has been made in relation to today's systems is that the location of the fastening axis has been drawn further back. This is an entirely necessary consequence of the rigid forward portion of the boot, because the last exertion of force in the kick cannot take place via a gradual bending up of the boot sole; the whole of the forward portion of boot will leave the ski at the same time. It is difficult to state when this happens, but the bending will be counteracted by a torque about the fastening axis. It is advantageous that the foot should maintain the large force transfer surfaces in contact as long as possible, but to ensure that this is not too long, we have drawn the fastening axis to the ski quite a lot further back than in today's systems. Thus the torque is smaller and the direction of force transfer after commenced rotation will be more favourable.
In addition, the axis of rotation has been drawn far down, because it will then be possible to transfer force over a larger cylindrical area in the fit between forward part of the boot and ski.
No resistance has been incorporated into (2b) other than the resistance which bending an inner boot, boot sole and a flexible material across the instep gives. In (1b) two resistance elements are incorporated to control resistance.
The rear rigid shell comes up to about the point at which the foot beings to slope inwards. It will therefore prevent sideways movements. A shell of a softer plastic is moulded within this shell. One object of this shell is that it will make allow the boot to be put on by bending the shell out from the foot, but a tightening and closing strap ensures that the shell nonetheless when closed constitutes a closed, relatively torsion-proof form which presses the foot down in the boot. Thus, good support around the whole sole of the foot is obtained.
It is very important that the shell giv but at the same time flexible support under the malleoli. We have solved this by terminating the shell slightly lower and inserting a solid rubber material which moulds to the ankle joint from below. This support is especially important on the outside, because, together with the upper edge of the shell just in front, it gives increasing support and control for the lower ankle joint when it is rotated outwards to perform edging.
The rubber material under the malleoli is a part of a sheath which also passes behind the Achilles' tendon. The sheath is made a little tight so that it must be pulled backwards when the boot is to be put on. Thus, support from behind is also ensured.
With all the rigid support around the lower part of the foot and a completely rigid sole, we have the possibility of doing two important things:
The boot must have a flexible inside for two reasons:
A rigid boot shell has one drawback in comparison with a flexible boot: interior measurements must be dimensioned according to the largest foot measurements among users having the same boot size. The fit will therefore initially be poorer for many. An optimal inner boot solution would be moulding in a foam material as in alpine skiing. A simpler but good alternative which is used in this prototype is to use a standard inner boot in thick warming neoprene, and an individually fitted sole in a harder material which ensures optimal fit and stability under the whole sole of the foot.
The rigid boot according to the invention will give torsional forces on the fastening to the ski which are many times greater than in today's solutions, because none of the forces are lost in longitudinal deformation of the boot sole when the heel is pressed out to the side. A basic principle in the design of the binding part has therefore been to consistently choose solutions and dimensions which are stronger than today's bindings in order to transfer the forces to the ski. The following points show the measures that have been taken.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20012753 | Jun 2001 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NO02/00197 | 6/4/2002 | WO |
