Abstract:
An electrically releasable form of hook and loop fastener ( 10 ) allows one half of the fastener to release from the other half without applying direct physical force to either half. The hook elements ( 21 ) of the fastener are formed of a shape-memory alloy material ( 27 ) such as commercially available Ninitol. Release of the hook half ( 14 ) of the fastener from the loop half ( 12 ) is accomplished by passing an electrical current through the shape-memory alloy material to straighten the hooks ( 21 ) so that they release their engagement with the loops ( 18 ). The flow of electricity through the hook half energizes the Ninitol material ( 27 ) to change its shape, either expanding or contracting in length; the change in shape is made to act against another length of material ( 28 ) that remains fixed in length or changes shape in an opposite direction so as to cause the hook shape to straighten toward a rod shape. Upon termination of the flow of electrical energy, the hooks return ( 21 ) to their hook shape, ready for re-engagement with the loops ( 18 ) upon conventional mating of the two halves of the fastener. Release and re-engagement can be repeated, substantially indefinitely.

Description:
[0001]     This invention relates generally to hook and loop fasteners of the type that are well known and commercially available under the Trademark VELCRO. More specifically, the invention relates to hook and loop fasteners in which the two halves of such a fastener can be released from engagement with each other via external means without the application of direct, external physical force.  
         [0002]     Hook and loop fasteners have been well known in the fastener art for many years and they have been used successfully in many and widely diverse applications. The secure engagement of one half to the other and the substantial force required to separate the two halves appear to have contributed significantly to the popularity of this type of fastener. However, the force that must be applied to achieve separation of the two halves, the brief but finite time required to achieve separation, and the incremental or progressive nature of the separation process, have been found to make the separation process difficult and/or unsatisfactory in some instances.  
         [0003]     The inherently incremental nature of the known separation process, requiring the two halves to be progressively “peeled” apart, can make the use of hook and loop fasteners unsatisfactory and/or extremely difficult in applications that lack sufficient clearance for a peeling or tilting motion. Similarly, the finite time required to “peel” one half from the other sometimes precludes the use of hook and loop fastenings when relatively “instant” separation, such as the separation of snap fasteners, is required. Hook and loop fasteners designed for “heavy duty” applications with substantial holding force can require similarly substantial separation forces. Separation forces under these circumstances may exceed the physical ability of certain users, thereby further limiting the application of these worthwhile fastening devices.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention is directed to providing a hook and loop fastener in which the time and force required to separate the two mating halves are reduced to a minimum. This invention is further directed to providing hook and loop fasteners that can be fabricated readily using available materials and known techniques. Another advantage of the hook and loop fastener of this invention is that disengagement of the two halves can be automated if desired. Further, disengagement can even be accomplished remotely, without direct application of external physical force.  
         [0005]     Hook and loop fasteners in accordance with this invention can be fabricated in generally conventional manner, but, commercially available “shape-memory” alloy material such as Nitinol must be used to form at least part of the hook elements. Shape-memory alloy material comprises a key element of the hook and loop fastener of this invention.  
         [0006]     An important aspect of shape-memory alloy material, also known as “muscle wire,” is that it is electrically responsive so as to change its shape when an electrical current flows through it. More specifically, shape-memory alloy material in wire form can be made to contract in length in response to the flow of electricity through the wire. This invention relies on this property of shape-memory alloy wire to allow the two halves of the hook and loop fastener to disengage from each other by passing electrical energy through the hook portion of the fastener. That is, the hooks are caused to straighten so as to loose their “hook” shape when an electrical potential is applied.  
         [0007]     By selectively applying electrical energy to cause the hooks to assume a straight-line “memory” shape, the characteristic interlocking engagement of the hooks with the loops is released, and the two halves of the fastener are, in effect, instantly disengaged from each other. In light of this disclosure, it can now be seen that the application of electrical energy to a suitably constructed hook and loop fastener can be made to cause disengagement of the loop portion of such a fastener from the hook portion without the application of external physical force. That is, if desired, disengagement of the fastener assembly can be effected from a remote location using electrical energy only. In this regard, it will be understood that physical displacement generally will be required to achieve actual separation of the two halves of a fastener. In many applications such displacement can be achieved through the force of gravity alone, after the hook elements are “straightened.” However, in view of this disclosure, it will be apparent to those having ordinary skill in this art that various different arrangements can be employed utilizing the disengagement method and apparatus of this invention to achieve physical separation of two fastener halves.  
         [0008]     In the disclosed embodiment of the invention, a two-part hook and loop fastener assembly of conventional configuration is formed using electrically conductive flexible material for part of the hook elements. More specifically, in the hook element half of the fastener, the hook elements are formed at least in part, of electrically conductive shape-memory alloy material such as Nitinol. It is known that Nitinol in wire or narrow strip shape, can be made to contract in length in response to the flow of electrical current. This invention contemplates the use of this kind of shape-memory alloy wire or strip. Although expansion or contraction of the material is possible, contraction is believed to be the more commonly available and therefore preferable characteristic.  
         [0009]     It will be understood readily by those having ordinary skill in this art, that wires or strips made of materials having an expansion or contraction characteristic can be joined in parallel relationship with another “inert” material to form a single element, similar to the bimetallic element of a conventional thermostat. Such an element can be made to distort in a desired manner when one of the two materials contracts or expands. The hook elements of the fastener of this invention are constructed accordingly. That is, the hook-shaped elements are formed of a length of shape-memory material joined in parallel relationship with an inert material, the combination being formed to have the desired hook shape. Accordingly, a normally hook-shaped element having the contracting shape-memory material positioned along the outer curved circumference of the hook shape will tend to straighten into a straight-line or “rod” shape when the flow of electricity through the shape-memory “muscle wire” causes the outer circumference of the hook to shorten from its un-energized length. Shortening the outer circumference of the hook has the effect of “opening” the hook shape by straightening it toward a “rod” shape as the inner and outer circumferences of the hook approach equality in length. Thus, the usual, or non-memory form of the hooks corresponds to the conventional “hook” shape used in hook and loop fasteners, whereas the energized, “memory” shape of the normally hook-shaped elements is that of a substantially straight line or rod, free of any significant hook shape.  
         [0010]     It can be seen readily that the substantially straightened rods on the first half of the fastener, free of any reversely bent “hook” shape, will disengage from and be free of locking or fastening engagement with the loop elements of the second half of the fastener. The formed, hook-shape elements are transformed into their straight rod “memory” condition by the flow of electricity through the shape-memory alloy wire material in accordance with the known characteristics of such materials.  
         [0011]     In accordance with this invention, the base surface material of the hook half-portion of the fastener preferably will be electrically conductive. Hooks cut and formed of lengths of stock made of two materials joined in the manner herein identified can be produced and anchored in generally upright orientation to a desired base surface using suitable, known fabrication techniques. Techniques for achieving the necessary electrical connection between the shape-memory alloy portion of each hook and the electrically conductive base surface material can be chosen similarly. The choice of techniques used for this purpose will be decided, in most instances, based upon economic considerations.  
         [0012]     Economic considerations are expected to affect in like manner, the choice of techniques used to facilitate the flow of electricity through the shape-memory alloy material. For example, with the hook portion of the fastener fabricated in accordance with the preceding observations, the loop half of the fastener may be formed of suitable electrically conductive material so that electricity can be made to flow through the hook elements in an electrical path extending from the hook half of the fastener to the conductive material of the loop half-portion.  
         [0013]     As an alternative to establishing an electrical path from the hooks to the loops, each hook element may be formed of two separate, electrically-conductive lengths of material that are electrically coupled to each other at the open end of the hook; in this manner, the electrical path through each hook element extends through one of the lengths of material from its base end to its free end and through the other length of material from its free end to its base end. Separate electrical connections to the base end of each of the two lengths of material can be established by various means such as, for example, forming the base surface of the hook portion from a composite sheet material having a first conductive layer and a separate conductive layer separated by an electrically insulating layer, with one of the conductive elements of a hook coupled to the first conductive layer and the other conductive element of the hook coupled to the second conductive layer.  
         [0014]     In brief, means are provided for making electrical connections to the two ends of the electrical path, however constituted, so that ultimately, an electrical potential difference is imposed between the ends of the shape-memory alloy portion of each hook. When an electrical potential difference is imposed, the current flowing through the shape-memory alloy material of the hook elements will cause them to assume their shortened, or extended, “memory” condition, thereby straightening and disengaging the hook elements from the loop elements so as to release the two halves of the fastener from each other. Generally, the straightened condition of the hook elements will be maintained by the flow of electricity. If an electrical path is established between the two halves of the fastener, it is apparent that current flow will be interrupted as soon as the two halves have separated. Alternatively, if the electrical path is established within the hooks independently of the loops, then current flow will continue until it is deliberately interrupted as by a switch or the like. Within the field of shape memory material technology, choosing materials having a longer or shorter “recovery time” will determine how long the hooks will remain in substantially straightened condition following the interruption of electrical current flow.  
         [0015]     It can now be seen that release of the two fastener halves from engagement with each other can be accomplished without application of any external physical force whatsoever, and accordingly, release can be controlled remotely and, if desired, automatically. All that is required is the application of electrical energy to cause current flow through the muscle wire portion of each hook element in the hook portion of the hook and loop fastener assembly. Preferably, a switch or other suitable means of controlling current flow is connected in series with the electrical path that includes the hook portion of the assembly, so that current flow through the path can be enabled or interrupted, selectively and substantially at will.  
         [0016]     These and other features, and advantages of this invention will be made more apparent to those having skill in this art, by reference to the following specification considered in conjunction with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a simplified, partial side elevation view of the two halves of a hook and loop fastener assembly in accordance with this invention;  
         [0018]      FIG. 2  is a partial side elevation view of the hook and loop fastener halves of the assembly of  FIG. 1 , shown in engaged relationship;  
         [0019]      FIG. 3  is a partial side elevation view of the hook and loop fastener assembly of  FIG. 1 , showing the appearance of the fastener in response to the flow of electricity therethrough;  
         [0020]      FIG. 4  is a simplified side view of the hook and loop fastener of this invention showing details of a corresponding electrical circuit; and  
         [0021]      FIG. 5  is a simplified side view of another embodiment of the hook and loop fastener of this invention showing a modified electrical circuit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     In the following description, certain specific details of the disclosed embodiment such as circuits, interconnections, materials and techniques, etc, are set forth for purposes of explanation rather than limitation, so as to provide a clear and thorough understanding of the present invention. However, it should be understood readily by those skilled in this art, that the present invention may be practiced in other forms and embodiments which do not conform exactly to the details set forth herein, without departing significantly from the spirit and scope of this disclosure. Further, in this context, and for the purposes of brevity and clarity, detailed descriptions of well-known apparatus, circuits and methodology have been omitted so as to avoid unnecessary detail and possible confusion.  
         [0023]     Referring now to the drawings, the hook and loop fastener assembly  10  of  FIG. 1  may be seen to comprise a loop half-portion  12  and a mating, hook half-portion  14 . Loop half-portion  12  in this case incorporates loop base surface  16  having a plurality of loop elements  18  extending substantially normally therefrom. The mating hook half-portion  14  of assembly  10  incorporates a hook base surface  20  having a plurality of hook elements  21  extending substantially normally therefrom.  
         [0024]     The shape and overall function of loop elements  18  are typical of the conventional structure of the loop half-portions and loop elements of known hook and loop fasteners; accordingly, these aspects of this structure will not be described in detail herein. In this regard, it should be noted that each loop element  18  is characterized by an open center portion  26  defined by the surrounding “loop” shape. And, it should be understood further that loop elements  18  may be formed and attached to loop base  16  in various, well known manners, such as a mass of interconnected helical loops of fibrous material fastened to the base  16 , as shown in the drawings or, individual loop shapes may formed integrally with the material of loop base  16  by known fabricating and/or molding processes.  
         [0025]     In turn, each hook element  21  of hook portion  14  extends from a fixed end  22  to a free end  23  at the open end  25  of hook shape  24 , remote from fixed end  22 . Fixed end  22  is attached to and extends from hook base surface  20 . In the conventional manner of hook and loop fasteners, hook-shapes  24  extend into and between loop elements  18  when hook portion  14  is urged into opposed, substantially abutting relationship with loop portion  12 . When the two fastener half-portions  12 ,  14  are urged toward each other, at least some of the hook shapes  24  at the free ends  23  of hooks  21  pass through and become entangled in the open portions  26  of loops  18  as shown in  FIG. 1 , thereby “locking” the two halves  12 ,  14  of fastener assembly  10  together, in a well-known manner.  
         [0026]     In accordance with established prior art practice, separation of half-portions  12 ,  14  can be achieved by applying sufficient physical force in opposite directions to pull the two parts away from each other. Separation in this manner “unbends” the resiliently flexible hook shapes  24  until they straighten enough to slip out of the open centers  26  of loops  18 . This is the conventional and well-known method of operation of hook and loop fasteners. With proper selection of known and available materials, the hook and loop fastener of this invention will separate in accordance with the prior art as well as in accordance with the invention herein disclosed.  
         [0027]     In accordance with this invention, loop portion  12  may formed of electrically conductive material so that an electrical current path can be established incorporating hooks  21  and loop half portion  12 . That is, loop half portion  12  having base surface  16  with a plurality of loop elements  18  extending in substantially normal relationship therefrom, may be formed as a unitary structure of electrically conductive material. Alternatively, if desired, loop half portion  12  can be made of a non-conductive material that has been coated with a conductive material, provided that problems involving abrasion and eventual wearing away of the conductive coating are overcome satisfactorily. And as will be disclosed herein, loop portion  12  may remain entirely non conductive in accordance with another embodiment of the invention. A consistent requirement for each form of loop portion  12  is a reasonable flexibility of the loops  18  as well as base surface  16  so that engagement and disengagement of the mated halves  12 ,  14  of the fastener assembly  10  can be accomplished as intended.  
         [0028]     The structure and function of hook portion  12  defines the significant aspects of this invention, in that hook elements  21  are constructed so as to straighten in response to the flow of electrical current through the hook. In accordance with this invention, at least part of each hook element  21  is formed of shape-memory alloy material such as Nitinol, which is frequently identified as “muscle wire”. It is a known characteristic of shape-memory material that it may be made so as to expand or contract in response to electrical energy. In wire form, shape-memory material accordingly may either shorten or elongate in response to the application of an electrical potential. In this invention, generally flexible and electrically conductive shape-memory wire is incorporated into hook elements  21  in the hook shape shown in  FIGS. 1 and 2 . Hook elements are configured, as explained in the following, so that when an electrical potential is applied between the free end  23  and the fixed end  22  of element  21 , the element will substantially straighten from the hook shape  24 , shown in  FIGS. 1 and 2 , to the generally straight-rod shape extending between fixed ends  22  and free ends  23  of hook elements  21 , as shown in  FIGS. 3 and 4 .  
         [0029]     Hook elements  21  of this invention utilize the expansion/contraction characteristics of shape-memory wire to alter the shape of the elements from the usual hook shape to a substantially straight rod shape in response to the flow of electrical energy. This is accomplished in a manner akin to the operation of a thermal bimetallic element responding to heat energy.  
         [0030]     As shown most clearly in  FIG. 2 , the composite body of each hook element  21  comprises a first length of flexible shape-memory wire or strip material  27 , coupled in side-by-side parallel relationship with a second length of preferably different flexible material  28 . In repose, that is in the absence of electrical energy, the composite body maintains its “hook” shape. Upon application of an electrical potential difference between the fixed end  22  and the free end  23  of shape-memory length  27 , expansion or contraction of length  27  acts against the relatively fixed-length curvature of material length  28  to cause the curvature to straighten into or near straight-rod shape. The straightening need only be enough to permit hooks  24  to loose their “grip”, that is their engagement within the open centers  26  of loops  18 .  
         [0031]     Specifically if “muscle wire” of the type that contracts in response to electrical energy is being used for element  27 , hook elements  21  will be configured so that shape memory material length  27  is positioned proximate the outer curved edge of hook shape  24 ; then, the length of material  27 , representing the outer circumference of the curved hook shape  24 , will grow shorter in response to the flow of electricity, while the dimension of inner length  28  will remain unchanged. Accordingly, hook shape  24  will straighten as the dimensions of its inner and outer circumferences approach equality.  
         [0032]     With reference to expansion and/or contraction of the shape memory material, it should now be recognized that shape-memory wire or strip that elongates in response to electrical energy, can be adopted for use in place of, or in combination with, material that contracts, by using the shape-memory material for the inner curvature portion of hook shape  24  instead of, or in combination with, the outer curvature portion. A combined use of expansion-type material for the inner curvature of the hook shape, with contraction-type material for the outer curvature of the hook shape, may be particularly effective when added force is required for heavy duty applications or when particularly stiff flexible materials are employed.  
         [0033]     As suggested previously herein, and as illustrated in  FIG. 4  of the drawings, electrical connector means  30 ,  32  are associated with hook fastener half-portion  14  for imposing an electrical potential difference from an electrical power source  34  between the fixed end  22  and the free end  23  of shape memory material length  27  of hook elements  21 . That is, the source of electricity  34  is connected in series with an electrical on-off control switch  40 , and both source  34  and switch  40  in turn are connected in series, via electrical connector means  32 , 33 , with the electrical path that includes the length of shape memory material  27 , such that the electrical paths represented by hook elements  21  lies between switch  40  and source  34 .  
         [0034]     With reference to the electrical coupling of connector means  32 ,  33 , to hook elements  21 , it should be understood that the “ends” of the electrically conductive material does not necessarily require connections at the actual physical extremities of the material and connections proximate the ends thereof generally will be acceptable for the purposes herein disclosed. The electrical connector means  32 , 33  may be of any suitable and known form of electrical connector, including both separable connectors and terminal connectors. If separable connectors are used it will be understood that only one half of each of two connectors need be coupled to the fastener of this invention, while the remaining half of each separable connector is reserved for establishing electrical connections with external devices, sources and/or equipment.  
         [0035]     To provide for electrical coupling to hooks  21  when length  28  comprises conductive material connected in series with length  28  at the free ends thereof, base  20  of hook portion  14  may comprise a composite having a first conductive sheet or layer  29  separated and electrically insulated from a second conductive sheet  30  by an intermediate insulating sheet or layer  31 . With hook elements  21  mounted to this form of base  20 , apertures  35  formed in top sheet  29  allow extensions of conductive material length  28  to extend through sheet  29  without electrical contact so that they can extend into electrical contact with second conductive sheet  30 . Conductive shape memory length  27  of each hook element  21  similarly contacts sheet  29  directly. Accordingly, electrical connector means  32  coupled to sheet  29  and electrical connector means  33  coupled to sheet  30 , readily allow an electrical potential difference to be imposed between the fixed ends  22  of conductive lengths  27 ,  28  of hook elements  21 .  
         [0036]     In this embodiment of the invention, as shown in  FIG. 4 , a source of electricity  34  is connected in series with an electrical on-off control switch  40  and both source  34  and switch  40  in turn are connected via electrical connector means  32 , 33 , in series with the path defined by lengths  27 ,  28  of hook elements ( 21 ) and conductive sheets  29 ,  30 .  
         [0037]     In the alternative embodiment of the invention illustrated in  FIG. 5 , hook elements  21  incorporate only a single length of conductive material  27 , as previously described herein, and loop elements  18  are formed of electrically interconnected continuous coils of conductive material such as wire that, accordingly, provides an exposed conductive surface for the conductive surface of the hook elements to engage. In this embodiment of the invention, base  20  of hook portion  14  incorporates at least a single sheet of conductive material  29  electrically connected to shape material lengths  27  of hooks  21 , with electrical connector means  32  electrically connected to sheet  29  so that one side of an electrical source  34  may be connected to lengths  27  of hooks  21 . Further, base surface  16  of loop portion  12  may either incorporate a separate single sheet of conductive material  30  electrically coupled to loop elements  18  and to connector means  33 , or, conductive sheet  30  may be avoided entirely and electrical connector means  33  may be connected directly to conductive loops  18 , to complete the electrical connection to the second side of electrical source  34 .  
         [0038]     As in the operation of the embodiment of the invention illustrated in  FIG. 4 , in the embodiment of  FIG. 5  as well, a source of electricity  34  is connected in series with an electrical on-off control switch  40  and both source  34  and switch  40  in turn are connected in series, in this case, with the path defined by hook elements ( 21 ) and loop elements ( 18 ) via electrical connector means  32 , 33 .  
         [0039]     Although a preferred embodiment of the method and apparatus of this invention has been illustrated and described, those having skill in this art will recognize that various other forms and embodiments now may be envisioned readily without departing significantly from the spirit and scope of the invention disclosed herein and set forth in the accompanying claims.