GB2290561A - Trampoline net - Google Patents

Abstract

A highly air-permeable trampoline walk net structure is formed of a first set of individually tensioned parallel cables (204) intersected by and interwoven with a second set of individually tensioned cables (206) aligned perpendicular to the first set. Each intersection between cables of the first and second sets is left entirely free of extraneous constraints, e.g., knots or swages. The required tensioning may be provided by individual elastic elements, e.g., helical springs (214) attachable to a peripheral support (202a, 202b). The peripheral support may be mounted at a selected height relative to ground to provide a horizontal, highly air-permeable support net. It may be mounted above a means for causing a vertical air flow for free-fall simulation. <IMAGE>

Description

AN AIR-PERMEABLE SUPPORT NET Field of the Invention This invention relates to air-permeable nets, and more particularly to an air-permeable support net in which each intersecting cable is individually tensioned and entirely free of extraneous constraints such as knots or swages.

Backqround of the Prior Art Numerous types of trampoline walk nets are known, which are formed with plural openings which permit ambient air to flow from one side to the other.

Typically, such nets are formed with a flexible, strong, peripheral element which is simultaneously hooked to a larger rigid support element by a plurality of generally radial elastic connections. Intersecting cables in prior art structures are knotted to each other, especially when the cables are made of a material such as nylon, rayon, or other such non-metallic but strong tensile material.

When either monofilament or multifilament metal strands are used, it is standard to provide metal swages at the intersections, principally to eliminate relative slip between intersecting cables.

While the above-described conventional structure may be suitable for recreational trampoline nets, there are particular applications in which the net must be highly air-permeable, long lasting, and very strong. Examples include nets utilized in vertical air tunnels and the like, where a very high speed, substantial ad deliberately induced air flow must pass with minimal hinderance from the net strands. Yet, such a net must also f-ully support workmen who need to walk across the cross-section of the wind tunnel to arrange test items in the flow region when the flow is turned off.

As will be appreciated, the presence of cross-strand swages or knots will block off part of the crosssectioned area available to the air-flow and will impose a significant flow impedance. The faster the speed of the air flow, the most significant will be the consequence of such an impedance. The extra surface area normal to the flow due to the presence of the various swages will also cause physical distortion of the net, increase turbulence, interfere with laminarity of the flow, and increase the costs of operating a wind tunnel in which such a net is present.

There is, however, yet another very significant problem that arises in having a net formed of metal cables with rigid metal swages at the cable intersections. This is best understood with reference to Figs. 6 and 7, which respectively illustrate two types of commonly utilized net swages. As best seen in Fig. 6, when a person steps directly on or very close to a swage 600 at an intersection, the generally downwardly acting weight W will cause local deformation of the net disposition. Thus, when a weight W presses downward just behind the center of a swage 600, one or all of the intersecting cable elements 602, 604, 606 and 608 will experience significant bending at the end of a corresponding swage arm 610.Consequently, at a location such as 612, where a cable experiences significant bending distortion relative to a rigid swage arm 610, there will be quite large stresses developed locally in the cable material. Before long, such localized stressing will cause physical destruction of the cable and, most important, because the intersecting cables are all swaged to each other the entire net must be discarded. This is expensive, results in significant down-t-ime in operating with such a net, and constitutes a significant burden on the net user. This problem is general, regardless of the type of swage used.

Fig. 7 illustrates another commonly utilized type of swage, one in which there are two + shape elements pressed to a cable intersection from opposite sides, with one of the swage elements being locally deformed to cramp on to the other across the thickness of the intersecting cables. Even with such a structure, the imposition of a weight W will tend to cause stress in a cable element 702 to rise to significant levels at the end of a swage arm 710. Note, by comparing Figs. 6 and 7, how the type of swage illustrated in Fig. 7 may pose more of a flow impediment to a flow directed upward through the net. In short, the presence of swages is undesirable for a number of reasons.

There is, therefore, a long-felt need for an airpermeable support net which allows efficient flow of air through the net openings while providing safe, reliable, affordable, and durable support to persons who may have reason to walk on the net.

This problem is particularly acute in an application which is becoming increasing common, i.e., in connection with outdoor free-fall simulators. These are systems in which a high-speed vertical air flow, with minimal turbulence, is to be provided to support a properly dressed person in simulated free-fall. Such a structure is often referred to in the relevant art as an "airodium". Such systems are particularly suitable for training parachutists, free-fall enthusiasts, paratroops, and the like. The person experiencing free-fall, depending on the speed of the air flow and his or her weight and air resistance, generally flies a few feet above an air-permeable support net stretched horizontally, preferably with a safety screen disposed beneath, below which is rotated an air-driving propeller.

Both at the start and at the termination of a session of free-fall, such an individual will have to walk on the trampoline net. Furthermore, during a training session, one or two trainers will walk around the periphery of the principal air flow region to guide and teach the trainee who is experiencing simulated free-fall supported by the upward air flow through the net. Such individuals, therefore, will impose repeated loads on the swages at cable intersections of the net. Training sessions may also be provided, depending on the size of the system, for a number of individuals simultaneously, e.g., to train them for free-fall exhibitions.When a number of people engaged in such an activity all walk repeatedly around on the same net, the various cables may be highly stressed again and again at the ends of the swage arms and the potential for breakage of individual cables therefore becomes a matter of serious concern.

One solution that was considered in developing the present invention was to have a woven net free of external constraints at cable intersections wherein the cables are all, at both ends, supported to a common peripheral flexible element that tensions them collectively, i.e., in common. It is believed, however, that such a structure would make it rather difficult to replace a single broken cable and, if the peripheral tensioning element were to fail all the cables would be out of commission simultaneously, i.e., the net would simply collapse.

The present invention arose out of research and development to produce an air-permeable support net particularly suited for use in airodiums as described above. It is explained more fully hereinbelow with reference to accompanying drawing figures.

Summary of the Invention Accordingly, it is a principal object of this invention to provide an air-permeable net which comprises pluralities of intersecting cables which are not constrained relative to each other by extraneous constraints at cable intersections.

It is another object of the present invention to provide an air-permeable support net in which pluralities of intersecting and interwoven cables define square openings which facilitate free flow of air therethrough with low impedance.

Yet another object of this invention is to provide an air-permeable net structure in which intersecting orthogonal sets of cables are free of extraneous constraints at cable intersections and in which each of the cables is individually tensioned and separately connected to a common support so that a broken cable may be disconnected from the support and replaced by a replacement cable quickly and inexpensively.

It is an even further object of this invention to provide an air-permeable net structure in which a peripheral support element supports two sets of orthoginally intersecting and interwoven cables each individually tensioned and releasably mounted to the support.

In another aspect of this invention, it is a principal object of this invention to provide a method of forming an air-permeable net in which individual intersecting cables are individually tensioned and free of extraneous constraints at cable intersections.

Yet another related object of this aspect of the invention is to provide a method of forming an airpermeable net which permits a high speed air flow therethrough with minimal flow impedance, wherein the replacement of individual broken strands can be done very easily.

Accordingly, in a preferred embodiment of this invention there is provided an air-permeable support net which includes a plurality of spaced apart and individually tensioned first cables each oriented parallel to a first direction and a plurality of spaced apart and individually tensioned second cables each oriented to be parallel to a second direction which is perpendicular to the first direction. The second cables are woven in an over and under manner, free of extraneous constraints, to successive intersecting first cables, and vice versa.

In another aspect of the invention there is provided a method of forming a net, comprising the steps of individually tensioning a plurality of first cables, each oriented parallel to a first direction and individually tensioning a plurality of second cables, each oriented parallel to a second direction perpendicular to said first direction with each of said second cables woven free of extraneous constraints in an over and under manner relative to successive intersecting first cables and vice versa.

These and other related objects and aspects of this invention will be better understood with reference to the following detailed description in light of the accompanying drawing figures.

Brief Description of the Drawings Fig. 1 is a vertical cross-sectional view of a static system for generating a controlled, smooth, fast, upward flow of air to permit simulated free-fall exercises, the flow being directed upwardly through a net according to a preferred embodiment of this invention; Fig. 2 is a plan view of the principal elements of a net structure according to a square version of the preferred embodiment; Fig. 3 is a plan view of the principal elements of a twelve-sided version of the preferred embodiment; Fig. 4 is a partial enlarged view showing details of individual cable connections at a corner portion of a net of the preferred embodiment per Fig. 2; Figs. 5(A) and 5(B) are enlarged views of exemplary individual intersections between intersecting cables in the preferred embodiment;; Fig. 6 is a partial perspective enlarged view to explain one type of stressing experienced by cables in a net according to the prior art; and Fig. 7 is a partial perspective view, comparable to Fig. 6, to cable stressing experienced with a different type of swage according to the prior art.

Detailed Description of the Preferred Embodiments To fully appreciate a particularly beneficial use of the present invention, reference may be had to Fig. 1, which illustrates in schematic form an airodium structure 100 for providing simulated free-fall experience to a person 1000. The airodium structure 100 has the form of a strong but readily erectable frame comprising a plurality of upward support elements 102 and 104, and bracing elements 106, which together support an extended horizontal structure at a selected height above ground 108. The system includes an engine 110 for driving a drive shaft 112 connected to a gear box and transmission 114 to rotate a vertical shaft to which is mounted a rotating propeller 116. An electrical motor (not shown) may be substituted for an internal combustion engine and may be quieter and less polluting.

Rotation of propeller 116 (as indicated by the short arrows) causes a forced, high-speed, upward flow of air which flows from the surroundings to a region below the propeller and is then driven by the propeller 116 upward past a flow-straightening vane structure 118 mounted to upward support elements 102, 102. Immediately above vane structure 118 may be provided a safety screen 120 of intersecting steel rods, typically spaced about 9 inches apart, to ensure against inadvertent and harmful access by the legs of person 1000 to rotating propeller 116 in the event of catastrophic structural failures.

Just above safety screen 120 is provided an airpermeable support net structure 122 which is the subject of this invention.

In the system per Fig. 1, immediately surrounding the principal upward air flow region is disposed an array of wedge-shaped foam cushions 124 to protect person 1000 against physical harm in the event he or she should drift away from the principal upward air flow through the airpermeable support net structure 122. Under normal operation, before and after provision of the desired air flow, person 1000 would walk on the intersecting strands of net structure 122. Surrounding the foam elements 124 is a region 126 where observers and/or trainers may be positioned as appropriate. The system may be operated from an operating console 128. The focus of the present invention is, of course, on the air-permeable trampoline net structure. However, the present applicant hereby expressly incorporates from his copending and contemporaneously filed U.S. Patent Application Serial No. , titled "MEANS FOR LINEARIZING AN OPEN AIR FLOW", relevant details of the structure and functioning provided therein of the vane structure in the airodium per Fig. 1 hereof as necessary to understand the structure and functioning of the present invention.

Figs. 2 and 3 respectively illustrate, in plan view, a four-sided square net structure 200 and a twelve-sided net structure 300. Other than the different overall shapes, both of these structures share many significant structural and functional features.

As best seen in Fig. 2, for a square net structure 200 there is provided a peripheral support 202, preferably made of tubular steel, I-beams, strong wooden beams or the like. This corresponds to the outer peripheral portion of the air-permeable support net structure 122 as described in relation to Fig. 1 earlier.

In Fig. 2, this peripheral support 202 is shown only schematically. Persons of ordinary skill in the mechanical arts may be expected to select the necessary materials, cross-sectional dimensions, and other details of peripheral support 202 in accordance with the particular application at hand. It is necessary only that peripheral support 202 be physically strong enough to support the cable strands where each cable strand is connected thereto under all foreseeable loading conditions with appropriate allowance made for a comfortable factor of safety.

In the square net structure per Fig. 2, there is provided a first plurality of parallel cables 204 (shown vertically in Fig. 2) and a second set of parallel cables 206 which intersect the first set 204 at right angles.

Each cable, in each of sets 204 and 206, is preferably made of the same material and to the same dimensions so as to have the same physical strength.

Each cable is individually supported at both of its distal ends to the peripheral support 202. As discussed more fully hereinbelow, there are absolutely no knots or swages at any intersections between the intersecting and interwoven sets of cables 204 and 206.

Referring now to Fig. 3, it will be appreciated that except for the different geometry of peripheral support 302 there is much in common with the previously described structure per Fig. 2. Thus, there is provided a first set of parallel cables 304 (shown vertically oriented in Fig. 3), and a second set of parallel cables 306, orthogonally intersecting the same, all of cables 304 and 306 being individually supported to peripheral support 302.

Certain differences become apparent from a direct comparison of the differently shaped structures per Figs.

2 and 3. Thus, one readily apparent difference is that each of cables 204 and 206 in the square-shaped net has its own unique mount 208 to support 202. By contrast, in the twelve-sided net structure per Fig. 3, some of the cables have unshared mounts 308 at peripheral support 302. Depending on the overall size of the peripheral support 302 and the desired spacing between adjacent cables, either 304, 304, or 306, 306, it may be desirable to mount the respective ends of two intersecting cables 304 and 306 to a common mount 310. This is shown only schematically in Fig. 3, and this figure is not drawn to a very precise engineering scale, but persons of ordinary skill in the art are expected to readily understand this.

Referring now to Fig. 4, and as generally illustrated in the square net structure per Fig. 3, peripheral support 202 actually comprises a plurality of sides such as 202a, 202b. Each such side is provided, for example, conventional eye-bolts 212, 212 to which are mounted linear helical springs 214, 214 which may have conventional hooked ends or be provided S-hooks for engaging eye-bolts 212, 212. The other end of each such linear helical spring 214 may also be provided with a hooked end 216 or another S-hook for hooking on to a simple conventional loop 218 formed at the distal end of a corresponding cable 204 or 206. Such a loop may be formed by turning back a distal length of the cable and swaging it to the extended portion of the cable. Such swaging does not expose the cable to the type of stresses discussed earlier. A convenient size for a loop may be 1 1/2 - 2 in.

As will be readily appreciated, instead of a linear helical spring such as 214, any conventional alternative, e.g. a bungee-cord, a molded rubber elastic element, or any functional equivalent thereof, may be employed instead. Similarly, persons of ordinary skill in the art will immediately appreciate that by forming each cable to the necessary length between its loop ends, and by appropriate selection of the elastic element, e.g., spring, bungee-cord, etc., 214, the desired precise amount of tensile force can be applied to opposite ends of each cable in the net structure. Any conventional technique for adjusting such a tensile force, e.g., by threading in or out a corresponding eye-bolt 212 relative to the peripheral support element 202a or 202b, such tensioning adjustment can be readily obtained.Such an adjustment can be readily effected in known manner, e.g., simply by rotating the shank of the conventional eye-bolt in or out the corresponding threaded portion of the peripheral support, hence it is not considered necessary to provide detailed illustration of such a commonly known element.

There is always the likelihood that a particular spring, eye-bolt, or cable mount may break, and the corresponding cable come lose or, if heavily loaded, spring out of place. To reduce the likelihood of complications and danger arising from such an eventuality, a safety cable 250 may be loosely passed through the supported loops of the net cables 204, 206, as best seen in Fig. 4. It should be clearly understood that this safety cable 250 is not at any time put in tension during normal use of the net structure and that it does not functionally or structurally correspond to the peripheral flexible element found in conventional nets.

Referring now to Fig. 5(A), it is seen how two intersecting cables 204 (underneath) and 206 (above) according to the present invention are simply woven in over and under manner and are entirely free of all extraneous physical constraints. Another view of two such intersections is shown in Fig. 5(B). In both Figs.

5(A) and 5(B) it is seen how actual physical contact between intersecting cables 204 and 206 is limited to a very small region 260 which can, at most, be a very narrow line or surface area where the materials of the two cables actually touch each other. It will thus be appreciated how the structure of the present invention gives virtually unlimited freedom to each cable to momentarily slide slightly along, to gently bend over, or to do both relative to an intersecting cable at their mutual surface contact at the intersection region 260.

Once an externally imposed load, e.g., the weight of a person walking on the net, is removed the intersecting cables that are relieved of such a load will return to their normal disposition relative to each other as determined by their individual tensioning. Suitable materials for the cables include stainless steel, t monofilament type or comprise a plurality of filaments.

A convenient diameter for such cables for an airodium net is approximately 3/32 in.

Since the material and the dimensions of the cables are selected to allow for an ample factor of safety and to ensure that there is the desired strength and flexibility, the claimed structure thus ensures against the generation of highly stressed repeated bending of a cable at a hard element, e.g., as occurs for cable 602 at the end of swage arm 610 at location 612 in Fig. 6. The selected structure thus ensures durability of each cable far beyond anything possible with the structures taught in the prior art.

Stressed materials inevitably weaken and may fail, however, and the present invention provides yet another advantage. If a particular cable fails or shows signs of wear, the rest of the net structure can be left in place and a replacement cable woven through in place of the old cable, whereafter the replacement cable can be hooked up at its distal end loops to the necessary tensioning element. The safety cable 250 could then be passed through the end loops of the replacement cable to restore its safety function.

Even when a person steps hard on a net structure as taught and claimed herein, because each cable is individually tensioned and physically experiences friction at each of its intersections with intersecting cables, there is entirely adequate retention of spacing between cables. Extensive experimentation has established that when each cable is individually tensioned as taught herein, even with substantial forced air flows through the net structure and simultaneous walking on the net structure by relatively heavy individuals, each of the cables remains in place and the square openings remain substantially unchanged and permit easy, low-impedance, air flow through the net structure.

When a net is used in a vertical air tunnel, or in an airodium, e.g., per Fig. 1, yet another advantage is realized. The air propelled upward by rotating propeller 116 inevitably carries with it a swirl component, i.e., velocity components perpendicular to the propeller axis or upward direction. Vane structure 118 is deliberately located and shaped to eliminate most of this swirl and to redirect the flow upward, i.e., aligned with the axis of the propeller. Safety screen 120 has relatively large openings therethrough and commensurately fewer dissecting elongate elements and, generally, plays a relatively small part in removing residual turbulence from the flow.

However, because the square openings of the net, e.g., 200 or 300, are relatively small, preferably about 2 inches-to the side, the intersecting cables do play a contributory role in removing some residual gross turbulence that remain in the upward flow that has passed the vane structure 118 and the safety screen 120. The consequence is that in the region of interest, namely from about one foot to about twenty feet above the intersecting net cables, there is a singularly smooth upward flow of air. Such flows typically are in the range 110 mph. to 140 mph., and the cross-section of such a flow may be of the order of 10 ft. - 17 ft. depending on the size of the propeller and the available power to drive it. The absence of swages at the cable intersections considerably reduces the impedance posed by the net to such a flow, and consequential savings in power to drive the propeller are realized.

In this disclosure, there are shown and described only the preferred embodiments of the invention, but, as aforementioned, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

Claims (17)

WHAT I CLAIM IS:

1. A net structure, comprising: a- plurality of spaced apart and individually tensioned first cables each oriented parallel to a first direction; and a plurality of spaced apart and individually tensioned second cables each oriented parallel to a second direction, wherein said second direction is perpendicular to said first direction, and each of said second cables is woven in an over and under manner free of extraneous constraints relative to successive intersecting first cables and vice versa.

2. The net structure according to claim 1, further comprising: a plurality of tensioning means for applying respective tension forces to each of said first and second cables to individually tension the same.

3. The net structure according to claim 2, further comprising: support means for supporting said plurality of tensioning means, wherein each of said tensioning means comprises an elastically deformable element detachably attached at a first end to a respective one of said first and second cables and at a second end detachably attached to said support means.

4. The net structure according to claim 3, wherein: each cable is formed to have a connection loop at each end, respective tensioning means being connected to apply a selected tension force thereat.

5. The net structure according to claim 4, wherein: each tensioning means comprises a helical spring having a first hook at one end to connect thereat to a loop of a corresponding one of said first and second cables and a second hook at another end to connect to said support means.

6. The net structure according to claim 5, further comprising: tension adjustment means for adjusting a tension applied by said tensioning means to a corresponding one of said first and second cables.

7. The net structure according to claim 1, wherein: said first and second cables are made of the same material and are similar in cross-section.

8. The net structure according to claim 6, wherein: said first and second cables are each formed of a material selected from a group of tension cable materials consisting of stainless steel, galvanized steel, and nylon.

9. The net structure according to claim 3, wherein: said support means comprises a peripheral support element formed to enable adjustable attachment thereat of individual tensioning means.

10. The net structure according to claim 9, further comprising: means for mounting said support means in a horizontal disposition at a selected height above ground.

11. The net structure according to claim 7, wherein: said first and second cables each comprise cable strand about 3/32 inch in cross-sectional diameter.

12. The net structure according to claim 11, wherein: said first and second cables are each formed of a material selected from a group of tension cable materials consisting of stainless steel, galvanized steel, and nylon.

13. A method of forming a woven, air-permeable net, comprising the steps of: individually tensioning a plurality of first cables, each oriented parallel to a first direction; and individually tensioning a plurality of second cables, each oriented parallel to a second direction perpendicular to said first direction, with each of said second cables woven free of extraneous constraints in an over and under manner relative to successive intersecting first cables and vice versa.

14. The method according to claim 12, comprising the further step of: providing peripheral support from which tensioning forces are applied to opposite ends of said first and second cables individually.

15. The method according to claim 14, wherein: said support step comprises attaching elastic elements to corresponding ends of said cables individually.

16. A method of providing a low-impedance support over a vertical air flow, comprising the steps of: individually tensioning a plurality of first cables, each oriented parallel to a first direction; individually tensioning a plurality of second cables, each oriented parallel to a second direction perpendicular to said first direction, with each of said second cables woven free of extraneous constraints in an over and under manner relative to successive intersecting first cables and vice versa; and disposing the intersecting individually tensioned first and second cables substantially horizontally over said vertical air flow to allow low-impedance passage thereof through openings between the intersecting first and second cables while providing support to a load placed thereover.

17. The method according to claim 15, comprising the further step of: providing peripheral support from which tensioning forces are applied to opposite ends of each of said first and second cables individually.