EP1050327A1 - Plastic ski pole - Google Patents

Abstract

The external diameter of the central part (G) of the pole is reduced and its thickness is increased. The pole is covered wit foam sleeve (K) with closed cells which limit the shock effects.

Description

The invention relates to stakes made of synthetic material which, associated with nets, tarpaulins or canvases, absorb energy by their bending and thus allow, in the framework for the exercise of sporting discipline, braking and stopping runners in the event of a fall of these.

Safety requirements in the field of ski racing, as in many sports where high speeds are involved, have increased in strength during the decades 1980 and 1990, precisely as a result of the speeds reached by the skiers during these competitions; for skiing, in particular, a number documents representing the state of the art have been published by the Federation International Ski (F.I.S.); for example, the May meeting report 1976 of the Alpine Tracks Commission of the F.I.S. Vitipeno (Sterzing) in Italy, or still from the brochure published in 1991 by the same F.I.S. and titled "Security in Alpine Skiing Competitions ".

This brochure describes an energy absorption device called "Fence of Security "or" F.I.S. type B "; this device consists of one, two or three lines more or less vertical and generally parallel with nets, canvases or tarpaulins from 1.50 to 2 meters in height; these lines of nets, canvases or tarpaulins are placed above the snow and held vertically, about every two meters, by stakes preferably in polycarbonate, particularly flexible and resistant plastic material; these lines are spaced 3 to 5 meters apart.

This device works in the following way to stop a runner who, having makes a fall followed by a slide, jostles these lines of the net; each of the stakes polycarbonate, made integral with others by means of the net, canvas or tarpaulin to which they are all attached, absorbs, by bending, a certain amount of energy (180 to 300 Joules, depending on the type of stake) and thus participates in the braking of the runner; this braking is carried out on one, two or three lines of "Safety Fence", therefore on a ten meters or more, occurs gradually, i.e. under conditions relatively satisfactory security.

For example, according to the recommendations of the F.I.S., the safety devices must be able to stop an 80 kg skier falling into the devices at a speed of 30 meters / second; this represents an energy of 36,000 Joules; if one does not hold ignore other forces involved during the braking process, especially body friction on snow, so it takes 120 to 200 polycarbonate stakes, quantity which depends on their diameter and thickness, be bent at about 90 ° to get the skier to stop.

In practice, polycarbonate stakes 2.50 m high, of 35 mm in diameter and 3 mm thick, each absorbing an energy of the order of 300 joules when 90% folded. This energy absorption system has been shown overall satisfactory despite a number of drawbacks: firstly significant relative stiffness of the wall of the stakes, which may be the cause of fracture of the fine parts of the limbs hitting these stakes; then a springboard effect lifting the skier's body in its trajectory above the snow; finally the high cost of this safety equipment due to the price of polycarbonate.

The first disadvantage can be explained for the following reason: the forces which are exercised, at the moment of impact, at the points of contact between the body and the "Fence of Safety "(and more particularly at the points of contact between the body and the stakes which constitute the energy absorbing elements), are not likely to cause severe bruising when the skier's chest, pelvis or legs come into contact with the stake (s); it’s a different story, especially for women, when this first contact takes place with the fine parts of the limbs, fingers, wrist, forearm, ankles, etc ... and it may happen that these fine parts of the limbs are broken; the reason is that, during the "Shock" between the member and the stake, the stake, until then motionless, sees, for a very short time which is of the order of 2 hundredths of second for an impact speed of 25 meters per second, the speed of the part of the stake that is struck approximately reach the speed of the body which has just come into contact with him ; the acceleration of this part of the stake is considerable, reaching 1250 m / s / s and, consequently, the forces brought into play, at the point of contact of relatively small surface between the body and stake are considerable; the surface of the stake at the point of impact has a very high rigidity and practically no part of the energy is dissipated by a appreciable deformation of the wall of the stake.

The solution to this problem first consisted in further spreading the stakes of the first line of the net; however, this amounts to increasing the risk of limb fractures; indeed, it is preferable that the braking forces are exerted on a greater number of stakes, therefore on a larger impact surface, while in reducing the number of stakes, on the contrary, contributes to reducing this surface and reduce the braking forces, therefore the efficiency of the device.

The second disadvantage indicated above consists in the “springboard” effect of the device, effect which is explained by the change in the direction of the forces in question during the process of penetration of the runner's body into the absorption device of energy; indeed, one of the necessary characteristics of the stake as part of the energy absorption device, called a security fence, is to have a diameter and a wall thickness sufficient to withstand bending forces without breaking or without present after a shock, at the point of bending, permanent deformations, such as a pronounced ovalization of the cross section of the stake with approximation of the two opposite walls or even, the deformation being even greater than an ovalization, a crushing of the section of the tube whose wall is divided into two more or less lines

To avoid that after a shock, the stakes, because they have been the subject of a permanent deformation, can no longer play their role in the event of the occurrence of a compared to the diameter of the tube; it has been determined, relatively empirically, that for a stake 35 mm in diameter, the thickness of 3 mm gave results satisfactory, so that after a shock the stakes would lift themselves up and the entire enclosure regained the relative verticality it originally had.

Tests carried out with stakes of lesser thickness, showed that subjected to the same bending forces, these stakes were permanently deformed.

However, given the rigidity of a safety fence post in polycarbonate of Makrolon type or similar, with an outside diameter of 35 mm and a thickness of 3 mm, we see that this stake, driven at its lower part in a snow supposedly compact and frozen forming an indeformable hypothesis, the stake being theoretically perpendicular or slightly inclined with respect to the surface of the snow, this stake, when subjected, to about thirty centimeters above the level of snow, at a force exerted perpendicular to its long axis, has a radius of curvature of this longitudinal axis from its embedding point which, in practice, is not less than 450 mm; schematically shown in Figure 1 a stake 2,500 mm high security fence; it is recessed at its base, on a length of 200 mm in snow and is subject to about 300 mm above the snow surface at a directional force parallel to the snow surface; this one, on the sketch is considered to be horizontal which, in practice, is not the case; so too on the sketch, the vectors representing the different forces are not proportional to these forces.

At the start of the post bending process, the post force, represented by the vector a , which opposes the penetration of the body into the device, is exerted in a direction opposite to the penetrating force, represented by the vector. A ; on the other hand, as the stake bends, and while the force of penetration of the skier's body represented, at its successive points of application, by the vectors A, B, C, D is always exerted, with very little difference, in a direction theoretically parallel to the surface of the snow and perpendicular to the long axis of the stake as placed before the impact, the component of the penetration force which effectively acts to bend the stake gradually decreases as the post bends to represent only the force corresponding to the weight of the runner at the end of the process; this force is shown diagrammatically by the vectors B ', C' and D '; on the other hand, the direction of the reaction force of the stake increases, as the stake bends; it is represented schematically by the sectors a, b, c, d, and is exercised in a direction which gradually changes as the flexion takes place; directly opposite at the start of the process, it is oblique, then applied perpendicularly, and upwards, with respect to the axis of penetration of the body into the security fence; this ascending force therefore results in lifting the body in question; it has happened that the effect of this vertically directed force has been highlighted, the security fence then having, in addition to its retarding effect, a “springboard” effect with the result of projecting the body along an oblique trajectory, the lifting above the surface of the snow and possibly passing it over the second safety fence line if it has been positioned too close to the first line.

The springboard effect is accentuated due to the diameter of 35 mm and the thickness of 3 mm of the stakes most generally used to obtain sufficient energy absorption; due to the relative rigidity which results therefrom; the bending of the tube only intervenes, as indicated in FIG. 2, from the moment when the force which is exerted on it perpendicular to its longitudinal axis at a point of application P sufficiently distant from the upper point of embedding Q in snow, distance which depends on the section of the stake and which is all the more distant from P as the diameter and the thickness of the stake are important; in other words, the stake bends all the closer to point Q the smaller the diameter of the stake; this is true, even if the thickness of the stake is significantly increased; with stakes 35 mm outside diameter and 3 mm thick as they are commonly used, the longitudinal axis of the stake between its point of embedding Q in snow and the point of application of the force of penetration when this point is between 300 mm and 500 mm and the deflection of the stake has occurred, this longitudinal axis has a curvature, near the embedding point, whose radius R1 is at least 450 mm, which has as a result of lifting the skier's body all the way above the snow level.

To schematize the reasons for the springboard effect, it results from the strength of reaction of the stake to the force of penetration of the runner's body into the device of energy absorption and the importance of the bending radius of the stake, which depends on the diameter and thickness of this stake, the two being obviously closely linked.

The third drawback noted is that of the high price of the stakes polycarbonate which represent two or three times the price of the same stake made from polyvinyl chloride; some thought they could find a way to limit spending safety items, using polyvinyl chloride stakes; however, these much cheaper, presented great dangers; polyvinyl chloride stakes lacking impact resistance, lack of resilience, broke, in the event of impact, in forming sharp and possibly sharp shards which were likely to cause serious injuries.

Another solution to reduce expenses was sought by the use of poles also made of polyvinyl chloride which, about ten centimeters above the snow, had a groove, all around their circumference, reducing the thickness of the stake by about 50%; in case of impact the stake broke so relatively regular there; however, it provided very little energy, therefore did not play its role of energy absorption in the braking device.

The use of polycarbonate stakes, in preference to stakes polyvinyl chloride likely to break under strong impact, forming splinters sharp, sharp and therefore dangerous, led to an increase in the fence line polycarbonate, prescribed for its qualities of impact resistance and flexibility, being of a cost several times higher than the polyvinyl chloride stake.

To give an order of magnitude, we can say that a fence line of safety constituted by a net 2 meters high, by poles of polychloride of vinyl 2.50 m high, 35 mm in diameter with a thickness of 3 mm, and by the accessories for stakes for hanging the net, tarpaulin or canvas, costs 100 units of account, whereas, if polycarbonate is used for the manufacture of stakes the total cost of closing increases to around 150 units of account.

The object of the present invention is to reduce the various drawbacks of the energy absorption device as described above, i.e. to reduce the forces brought into play at the interface point between the members and the stakes, thus reducing the possibilities of fractures, to mitigate the springboard effect of the security fence and to offer a cheaper device.

The stake object of the invention consists of a tubular central part, core of the stake, with a diameter of about 25 mm, but which may vary, depending on the material used and the thickness of this core in relatively large proportions around this dimension; the diameter of the core will, however, be less than the diameter of 35 mm adopted up to now for stakes, the thickness of this core possibly being, on the other hand, larger, 3.5 mm or even 4 mm; it can also be in the form of a full profile, generally called a “rush”, profile which may also not show any circular section, but be hexagonal, oval, square, etc ...

The tests carried out show that the amount of energy absorbed, holds mainly accounts for the section of the tubular profile; it is much the same when bending a tube, whether it is a polyvinyl chloride tube or polycarbonate with an external diameter of 35 mm with a thickness of 3 mm or a tube polyvinyl chloride or polycarbonate with a diameter of 28 mm with a thickness of 4 mm; on the other hand the radius of curvature of a tube of 35 mm, thickness 3 mm, with a force permanently applied at 1 meter above the point of embedding the tube and exercising, always perpendicular to the longitudinal axis of the tube, this radius of curvature R1, considered in the part of the tube between the upper point of the fitting and a point located 350 mm above this point is of the order of 450 mm, whereas, for a tube with the same characteristic but with a diameter of 28 mm and a thickness of 4 mm, the radius of curvature R2 considered in the same zone of the tube is limited to 225 mm; this radius is only 150 mm for a stake of 24 mm outside diameter and 3 mm thick; it is therefore advantageous to use a stake having a core of smaller diameter possible to reduce the bending radius to a minimum and therefore the "springboard" effect which is a direct consequence.

In Figure 3 there is shown a stake J 35 mm in diameter and a 3 mm thick and an L stake 24 mm in diameter and 3 mm thick; Mon and the other are subjected to 1 meter from their point of embedding at the same force Z directed from top to bottom, force which is the result of the weight of the body penetrating the absorption device of energy.

It therefore follows that, subjected to the same force having the same point application and the same direction, the tube bends more and has an area that has its lower part very significantly reduces the springboard effect, since the second tube is curve more than the first; the adoption of a smaller diameter stake presents therefore a great advantage.

This central part of the stake can be either polychloride of vinyl or polycarbonate, the characteristic of the present invention being mainly that the core of smaller diameter and possibly of greater thickness absorbs while bending an amount of energy which is close to that absorbed by a larger tube diameter but of lesser thickness and that the radius of curvature in the neighboring part of the point of embedding is smaller and therefore the "springboard" effect is found decreases.

In practice, and taking into account the second characteristic described below, you can even use a central core, tube or rod, whose cross-sectional area transverse and the energy absorption capacity by bending are reduced compared to those of the reference polycarbonate tube of 35 mm outside diameter and 3 mm thick; indeed, the sleeve, object of the second characteristic of the present invention, also, by flexing, absorbs an amount of energy which can compensate for the amount of energy by which that absorbed by the central part of the stake has been reduced due to reducing its diameter.

Such an arrangement, choice of a tube of smaller diameter having possibly a greater thickness, would not eliminate either of the two disadvantages noted above, know the brittleness by lack of resistance of the polychloride tube vinyl which breaks under the impact of forming dangerous fragments and on the other hand the creation of considerable forces at impact points between the stake and a limb, forces likely to cause fractures of the members of the runners.

The second characteristic of the stake object of the present invention is that this semi-rigid central core which, by bending, absorbs a certain amount of energy, is covered with a foam sheath or sleeve, preferably cell polyolefin closed so that this foam does not fill with water which, frozen, would deprive the sheath of foam of its plasticity.

The thickness of the foam sleeve may preferably be between 8 and 25 mm, thus bringing the total outside diameter of a stake up to 70 mm, although the thickness of the foam sleeve is not, in itself, a characteristic of the invention; this foam sleeve has a density which is on average 25 Kilos / M3 but which may vary depending on the technical specification of the stake; the higher the density high the less the shock absorbing effect but the greater the absorption capacity energy will be important; the greater the thickness of the sleeve, the higher the density of the foam constituting it may be low, the maximum efficiency in terms of safety being obtained by a thick and low density sleeve; such a sleeve however which would bring the outside diameter of the stake to a high value of 100 or 150 mm for example would make the use of stakes in the field less easy, if only because of the larger volumes of stakes to be transported to their place of use; the this patent does not exclude the possibility of using such relatively large stakes diameters, the interest of the organizer of speed sport competition, skiing in particular, being, however, to have light stakes and of reasonable size.

We will take into account for the sizing of the foam sleeve, term of thickness and density, since the post must be able to straighten completely after bending; gold, a foam sleeve, isolated from the central core, retains permanent deformation after bending and does not regain its exact shape of origin by the effect of its internal forces alone; the denser the foam, the more easy, however, for the sleeve to regain its original shape under the combined action of its internal forces and forces of the soul with which it is associated; the stake in its structure and its composition is designed by establishing a compromise between the characteristics of its two components, core and sleeve, so that, taking into account the intended use, (for example a very flexible stake, therefore absorbing little energy, for the first line of device, or, on the contrary, a more rigid stake, therefore absorbing more energy, for the second or third line that the runner will hit at a reduced speed compared to his initial speed of penetration of the device due to the energy absorbed by the first line of the device) this stake has a satisfactory energy absorption capacity while that the thickness and density of the foam sleeve associated with the core provides good safety by reducing the forces generated by the “shock” and at the same time ensuring a effective recovery of the stake in its original position after a shock in the device security.

The foam sleeve covering the stakes makes it possible to reduce very appreciably the drawbacks of the current security fence system; indeed, the foam having a high compressibility will deform under the effect of the shock of a body against the stake; whereas the impact surface between a limb, wrist for example, and a polycarbonate or polyvinyl chloride stake is very reduced, due to plasticity very small wall of such tubes, when these tubes, even if their diameter is reduced, are covered with a foam sleeve, the surface of the sleeve deforms and the member which the strike is applied to a very significantly increased surface; forces resulting from shock is proportionately reduced and the risk of trauma is reduced especially.

What is true for the member who hits the stake is also true for the stake which is struck by the member; experience proves that a tube of polyvinyl chloride which shatters with "glass" shatter when subjected to impact test, is not broken when surrounded by a foam sleeve of appropriate thickness.

For this reason it is possible to use, for the core of the stake object of the present invention, a polyvinyl chloride tube whose plasticity will be similar to that of a polycarbonate tube, thanks to the choice and percentage of plasticizer in the composition of the raw material.

The price of polyvinyl chloride being much lower than that of polycarbonate, the price of the stake and that of the energy absorption device will be found significantly decreased.

It is specified that polycarbonate is mentioned to refer to a material with high resilience and great flexibility and that the core of the stake can be made of any plastic material having these characteristics; similarly it is refers to polyvinyl chloride as a presenting material, with adjuvants suitable, high flexibility but lower resilience than that of polycarbonate; for the realization of the central core, polycarbonate and polyvinyl chloride can be replaced by any other material having similar mechanical characteristics and possibly by a spiral wire spring.

On the other hand, the foam sleeve itself absorbs energy by its plastic deformation during bending of the stake, to obtain a capacity of determined energy absorption, corresponding, for example, to that of a stake polycarbonate 35 mm and 3 mm thick, we can limit the dimension of the core central, taking into account the energy absorption capacity provided by the sleeve. The stake object of the present invention therefore makes it possible to provide solutions to the various drawbacks reported: the shocks are less violent due to the damping effect of the foam sleeve and the risk of fracture are reduced; the springboard effect is also limited due to the use of a flexible core of smaller diameter which decreases the bending radius of the longitudinal axis of the stake which lies closer to the snow surface; the price of the stake can, finally, be reduced since it is possible, of a part to replace polycarbonate with cheaper polyvinyl chloride and other share to reduce the section of the central core used and consequently its price, by putting at take advantage of the energy absorption capacity of the foam sleeve to reach the level of energy absorption capacity desired for the stake.

The manufacture of these stakes poses no particular problem; so the foam sheath having a theoretical inside diameter equal to the outside diameter of the core central, with a slight tolerance in addition, assembly can be done by threading the core central inside the foam sleeve, when the stake is made in three time, the first concerning the manufacture of the core by extrusion, the second concerning the manufacture of the sleeve also by extrusion and the third the assembly of the two elements; he is however possible to provide a co-extrusion according to the technique used for the manufacture of electrical cables, the various protection and insulation sheaths of cables being successively extruded, one after the other and on top of each other, as part of a same production line.

FIG. 4 represents a stake of energy absorption device consisting of a central core E of relatively small transverse dimension, 22 mm in diameter, polyvinyl chloride or polycarbonate; this soul is a rush full of 2.50 meters high with a blunted bottom part over 250 mm to facilitate the installation of the stake in the ground or in the snow; a polyolefin foam sleeve F with cells 50 mm outside diameter, 22.5 mm inside diameter and 2 meters high covers the soul over almost its entire height; figure 5 represents a stake consisting of a central tubular core G of 25 mm outside diameter and 3 mm thick polycarbonate or polyvinyl chloride; a plastic tip H is attached to the lower part of the stake; at its base, over a height of 100 mm; at its base, the central core is not covered by the foam sleeve K, 25.5 mm in diameter inside and 60 mm in outside diameter, so as not to interfere with the installation of the stake in the snow and to allow the hanging of the net, the tarpaulin or the canvas associating the stakes between them; FIG. 5 represents the stake with a foam sleeve of 2 meters and the Figure 6 with a foam sleeve which protects the central core only over a height of 1250 mm which is considered sufficient taking into account the height above the snow that the runner's body is supposed to have when it hits the stake and taking into account the location of the safety device line of which this stake.

FIG. 7 represents a traditional stake J made of polycarbonate or polyvinyl chloride, about 35 mm in diameter, with a foam sleeve protecting only its lower part, while in FIG. 8, the sleeve offers a protection over most of the height of the stake above ground level or the snow ; in Figure 7 the foam sleeve is cylindrical and open only at its two ends; it was threaded on the stake, while the sleeve of figure 8 is split along its longitudinal axis, the stake being inserted inside the sleeve from the side of the latter, by temporary deformation resulting in a widening of the lateral slit of the muff ; these sleeves are removable and can be used to reduce the effects of impact on existing polycarbonate or polyvinyl chloride stakes; they can have any height determined according to security requirements; he can exist an annular space N between the stake and the sleeve.

Claims (9)

Stakes for energy absorption and stop devices animated speed runners, these stakes, fixed in the ground or snow at their lower part and associated with each other by means of a net, a canvas or a tarpaulin of these stakes, absorb by their bending part of the kinetic energy of the sportsman for the slow down and possibly stop for a distance compatible with safety requirements, these stakes are characterized in that they consist of a longitudinal central core in flexible and elastic semi-rigid material and a foam sleeve capable of deformation under the effect of an impact, the central core and the protective sleeve having, together, mechanical characteristics such that the stake takes up a neighboring position from its original position after a shock that caused it to flex. Stakes according to claim 1, characterized in that the central core is consisting of a plastic rod with great elasticity. Stakes according to claim 1, characterized in that the core is constituted by a tubular profile of synthetic material having great elasticity. Stakes according to claims 1, 2 and 3 characterized in that the core flexible is made of polycarbonate or similar material with high elasticity and good resilience. Stakes according to claims 1, 2 and 3 characterized in that the core flexible is made of polyvinyl chloride or similar material having a large elasticity but less impact resistance than the stakes according to claim 4. Stakes according to claim 1, characterized in that the core is constituted by a metal spiral spring. Stakes according to claim 1, characterized in that the sleeve foam is removable Stakes according to Claims 1 to 7, characterized in that the sleeve protective foam covers the core over most of its height. Stakes according to Claims 1 to 7, characterized in that the sleeve synthetic foam covers only the lower part of the stakes.

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