Electrostatically releasable fastening system and method of use

A releasable fastening system comprises a loop portion comprising a loop material, a hook portion comprising a plurality of hook elements, and an actuation device disposed in electrical communication with the loop portion and the hook portion. The actuation device is operable to provide electrostatic charges to the loop material and the hook elements. A method of operating a releasable fastening system comprises contacting a loop portion to a hook portion to form a releasable engagement wherein the loop portion comprises a first electrically conductive sheet and a loop material disposed at the first electrically conductive sheet and wherein the hook portion comprises a second electrically conductive sheet and a hook element disposed at the second electrically conductive sheet, maintaining constant shear and pull forces between the loop and hook portions, and introducing electrostatic charges of opposite polarities to the loop and hook portions to enhance the engagement of the hook and loop portions and of similar polarities to weaken the engagement of the hook and loop portions.

BACKGROUND

This disclosure relates to releasable attachment devices of the type used to fasten, retain, or latch together components of an apparatus or a structure that are to be separated or released under controlled conditions.

Hook and loop type separable fasteners are used to detachably join a plurality of members to each other. These types of fasteners generally have two components disposed on opposing member surfaces. One component typically includes a plurality of resilient hooks while the other component typically includes a plurality of loops. When the two components are pressed together they interlock to form a releasable engagement. The resulting joint created by the engagement is relatively resistant to shear and pull forces, and weak in peel strength forces. As such, peeling one component from the other component can be used to separate the components with a minimal applied force. As used herein, the term “shear” refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relative to each other in a direction parallel to their plane of contact. The term “pull force” refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to move relative to each other in a direction normal to the plane of contact of the parts.

SUMMARY

Disclosed herein is a releasable fastening system. The system comprises a loop portion comprising a loop material, a hook portion comprising a plurality of hook elements, and an actuation device disposed in electrical communication with the loop portion and the hook portion. The actuation device is operable to provide a first electrostatic charge to the loop material and a second electrostatic charge to the hook elements.

In another embodiment, a releasable fastening system comprises a loop portion comprising a loop material, a first electrically conductive sheet on which said loop material is supported or attached, a first insulating layer disposed on said first electrically conductive sheet, and a loop portion support member disposed on said first insulating layer; a hook portion comprising a hook element mechanically engageable with said loop material, a second electrically conductive sheet at which said hook element is supported, a second insulating layer disposed at said second electrically conductive sheet, and a hook portion support member disposed at said second insulating layer; and an actuation device disposed in electrical communication with said loop portion and said hook portion, said actuation device being configured to impart an electrostatic charge of a first polarity to said loop material and a second polarity to said hook elements.

A method of operating a releasable fastening system comprises contacting a loop portion to a hook portion to form a releasable engagement, wherein said loop portion comprises a first electrically conductive sheet and a loop material attached to or disposed on said first electrically conductive sheet, and wherein said hook portion comprises a second electrically conductive sheet and a hook element attached to or disposed on said second electrically conductive sheet; maintaining constant shear forces and constant pull-off forces between said loop portion and said hook portion; introducing a first electrostatic charge to said loop portion; and introducing a second electrostatic charge to said hook portion.

DETAILED DESCRIPTION

Referring now toFIG. 1, one exemplary embodiment of a releasable fastening system is shown generally at10and is hereinafter referred to as “system10.” System10provides for the controlled engagement of hook-and-loop material via an electrostatic mechanism and a method for the attachment of surfaces. The electrostatic mechanism effects the mutual attraction and the mutual repulsion of the hook material and the loop material to selectively enhance passive mechanical engagement and disengagement. In particular, the electrostatic mechanism assists in providing the on-demand remote engagement and disengagement of various facial surfaces including, but not limited to, joints and other points of attachment.

System10comprises a loop portion generally designated12and a hook portion generally designated14. Loop portion12comprises a support16, an insulating layer18disposed on support16, an electrically conductive sheet20disposed on insulating layer18, and a loop material22attached to the electrically conductive sheet20. Hook portion14comprises a support24, an insulating layer26disposed on support24, an electrically conductive sheet28disposed on insulating layer26, and hook elements30attached to the electrically conductive sheet28. The selective engagement and disengagement of hook elements30with loop material22is controlled via an actuation device32disposed in electrical communication with loop portion12and with hook portion14. Dissimilar electrical charges applied to loop material22and to hook elements30from actuation device32effect the electrostatic attraction of loop material22to hook elements30(thus enhancing the engagement of portions12,14), while similar electrical charges applied to loop material22and to hook elements30effect the repulsion of loop material22and hook elements30(thus enhancing the disengagement of portions12,14).

During engagement of portions12,14, either portion is biased in the direction of the other portion such that facial surfaces (i.e., surfaces having the loop material or hook elements attached thereto) thereof are disposed in intimate contact with the other. Alternatively, both portions may be simultaneously biased in the direction of the other portion such that intimate contact is maintained between the facial surfaces. The engagement of the facial surfaces creates an interfacial joint that is strong when one of the surfaces is subject to shear or subject to a pull force, but weaker when one of the surfaces is subject to a peeling force. A peeling force is a force that is concentrated in a localized region of adjacently-positioned hook elements and results in the mechanical release of the hook elements from the loop material in the localized region (as opposed to “pull-off,” which is the simultaneous mechanical release of all of the hook elements over the engaged facial surfaces when the facial surfaces are biased in opposing directions and in directions orthogonal to the direction in which the interfacial engagement extends). Continuous application of the peeling force results in a wave-like travel of the release front across the interengaged facial surfaces. The force needed for the application of a peeling force is lower than the force needed for pull-off due to the fact that only a few hook elements at a time are released in the former while all of the hook elements are released simultaneously in the latter. For example, when portions12,14are pressed into facial engagement, hook elements30engage with loop material22such that the close spacing of hook elements30resists substantial lateral movement when subjected to shearing forces in the directions of the plane of interfacial engagement. Similarly, when the engaged facial surfaces are subjected to a force orthogonal to this plane (pull-off forces), hook elements30resist substantial separation of portions12,14. However, when hook elements30are subjected to the peeling force, hook elements30can become more easily disengaged from loop material22. In order to provide a point of leverage for separating portions12,14using a peeling force, either support16or support24is preferably flexible.

Loop material22generally comprises either a random- or ordered arrangement of loops supported or attached to the electrically conductive sheet20. Each loop comprises one or more strands of material capable of maintaining an electrostatic charge configured to define a pile. Materials from which the loops can be configured include, but are not limited to, plastics, fabrics, metals, combinations of the foregoing materials, and the like. Suitable plastics include thermoplastics such as for example polypropylene, polyethylene, polyamide, polyester, polystyrene, polyvinyl chloride, acetal, acrylic, polycarbonate, polyphenylene oxide, polyurethane, polysulfone, and other like thermoplastic polymers.

Hook elements30comprise either a random- or ordered arrangement of hook elements supported or attached to the electrically conductive sheet28. Each hook element30comprises a member fabricated from a material that is capable of maintaining an electrostatic charge and having a shape such that passive mechanical engagement with a loop of loop material22is facilitated upon the pressing together of portions12,14. Materials from which hook elements30can be fabricated include, but are not limited to, plastics, fabrics, metals, combinations of the foregoing materials, and the like. Suitable plastics include thermoplastics such as for example polypropylene, polyethylene, polyamide, polyester, polystyrene, polyvinyl chloride, acetal, acrylic, polycarbonate, polyphenylene oxide, polyurethane, polysulfone, and other like thermoplastic polymers. The shape of each hook element30is preferably that of an inverted “J” although other shapes, for example, mushroom shapes, knobs, anchor shapes, “T” shapes, spirals, or any other mechanical form of a hook-like element may be utilized.

In order to minimize the migration and dissipation of electrostatic charge, insulative coatings are preferably applied to the loops of loop material22, hook elements30, and electrically conductive sheets20,28, as is shown with reference to FIG.2. Insulative coatings, shown at29, are preferably disposed as needed at all exposed surfaces of loop material22, hook elements30, and electrically conductive sheets20,28to prevent migration of charge between the various elements as well as the dissipation of charge to the surrounding environment.

Referring now to bothFIGS. 1 and 2, other exemplary embodiments of hook elements30, in addition to being capable of maintaining an electrostatic charge, may further be formed of a material that provides a shape-changing capability and/or a change in flexural modulus to each individual element. For example, the shape-changing capability and/or a change in flexural modulus of hook elements30may be effected through the use of shape memory alloys, shape memory polymers, piezoelectric materials, magnetostrictive materials (also referred to as magneto-restrictive materials), ionic polymer metal composites, elastic memory composites, electroactive polymers and metal composites, and the like.

Electrically conductive sheets20,28preferably comprise planar members through which opposing charges are respectively communicated to loop material22and hook elements30from actuation device32. Electrically conductive sheets20,28may be uniform in thickness or they may be variously thin or thick. The flexibility or rigidity of each electrically conductive sheet20,28may be determined by the material from which each sheet20,28is fabricated as well as its thickness. Sheets20,28are disposed respectively at insulating layers18,26using adhesives or mechanical mean, e.g., bolts, clamps, or other mechanical fastener. Materials from which electrically conductive sheets20,28may be fabricated include, but are not limited to, metals such as copper, aluminum, silver, alloys such as steel, electrically conductive polymers, combinations of the foregoing materials, and the like.

Insulating layers18,26are disposed at electrically conductive sheets20,28to inhibit the discharge of charge through supports16,24. Materials from which insulating layers18,26can be fabricated include, but are not limited to, ceramics, glass, rubber, non-conductive thermosets and thermoplastic materials (e.g., polyethylene, polytetrafluoroethylene, nylon), combinations of the foregoing materials, and the like.

Supports16,24at which loop portion12and hook portion14are respectively disposed may be rigid or flexible depending upon the application in which system10is intended to be used. Suitable materials for fabricating supports16,24include plastics, fabrics, and the like. For example, suitable plastics include thermoplastics such as for example polypropylene, polyethylene, polyamide, polyester, polystyrene, polyvinyl chloride, acetal, acrylic, polycarbonate, polyphenylene oxide, polyurethane, polysulfone, and other like thermoplastic polymers. Adhesives may be applied to surfaces of the supports (preferably opposite the surfaces at which the insulating layers are disposed) for application of releasable fastening system10to an apparatus or structure. Alternatively, releasable fastening system10may be secured to an apparatus or structure by bolts, by welding, or any other mechanical securement means. It should be noted that, unlike traditional hook and loop fasteners that typically require at least one support to be flexible so that a peeling force can be applied for separation of the hook and loop fastener, both supports16,24could be fabricated from a rigid or inflexible material in view of the remote releasing capability provided.

InFIG. 3, the engagement of loop portion12and hook portion14of system10is shown. The passive mechanical engagement of portions12,14is effected by the biasing of loop portion12and hook portion14together such that the “J” portions of hook elements30are disposed or entangled with loop material22. After or during the passive engagement of loop material22and hook elements30, the actuation device32is powered and supplies a positive charge40to either the loop material22or the individual hook elements30and a negative charge44to the other of the hook elements30or the loop material22to cause the electrostatic attraction of loop material22and hook elements30, thereby increasing the bond strength between portions12,14, e.g., the shear forces, pull-off forces and peel forces marginally increase.

Referring now toFIG. 4, actuation device32and its relationship to electrically conductive sheets20,28is shown. In one exemplary embodiment, actuation device32is configured to supply an electrical current to electrically conductive sheets20,28. By applying a voltage, the loop material22and the hook elements30are electrostatically charged to effect the electrostatic attraction or repulsion of the loop material22and the hook elements30. The electrical signal may be delivered in conjunction with other types of signals (e.g., a magnetic signal, a heat signal, a pneumatic signal, a mechanical actuation mechanism, or a combination of the foregoing signals and mechanisms) that provide a shape-changing capability or a change in flexural modulus in the hook elements to more easily cause the hook elements to engage with the loop material. The type of signal employed is dependent upon the particular material from which the hook elements and/or the loop material is fabricated.

Actuation device32preferably comprises a first power source50and a second power source54. Each power source50,54is preferably a direct current (DC) power source disposed in electrical communication with its respective electrically conductive sheet20,28. Switching devices60,62(e.g., transistors) are preferably disposed at the anodes of their respective power sources50,54to switch the releasable fastening system between three operating states. Switching device64is preferably disposed intermediate switching device62and electrically conductive sheet28.

In a first operating state of actuation device32as shown inFIG. 5, switching devices60,64, are closed while switching device62is open. Such a combination results in loop material22and hook elements30being charged to opposite polarities to effect their mutual attraction (shown by arrows66). Loop portion12and hook portion14are then mechanically biased together to effect their engagement. The mutual attraction of loop material22and hook elements30, in addition to the mechanical engagement of loop material22with hook elements30, enables hook elements30to be more uniformly and completely engaged with loop material22, thereby facilitating the engagement of the releasable fastening system10.

In a second operating state of releasable fastening system10also shown inFIG. 5, switching devices60,62,64are initially open and neither loop material22nor hook elements30are charged. Loop portion12and hook portion14are biased together to passively engage loop material22and hook elements30. The loops and hook elements30are then charged to opposing polarities by closing switching devices60,64(as in the first operating state) to more uniformly and completely engage hook elements30with loop material22. Switching devices60,64are then opened because a continuous charge is not required to maintain the mechanical engagement of loop material22and hook elements30.

An operating state of actuation device32in which releasable fastening system10is disengaged is shown in FIG.6. Loop material22and hook elements30may be disengaged by maintaining switching devices60,62in the closed position while keeping switching device64open. Such a configuration results in the disposition of similar polarities with respect to loop material22and hook elements30. In the exemplary embodiment shown, the similar polarities are positive. By maintaining similar polarities across loop portion12and hook portion14, the repulsion (as indicated by arrows68) can be effected, thereby facilitating the disengagement of releasable fastening system10.

The releasable fastening system as described above is extremely versatile and can be utilized in a wide variety of applications. For example, the releasable fastening system can be employed to releasably attach two or more automotive structural elements together. Welded and adhesively bonded “rigid” attachments provide fixed load paths. By applying or removing an electrostatic charge to the components of a system, however, load paths can be selectively created or eliminated. The selective creation of a load path may provide an additional force to maintain the integrity of a structure subjected to a stressing force, and the selective elimination of the load path may be used to provide for the controlled failure of a structure when subjected to a stressing force. Other examples include providing a mechanism for opening and closing apparatus such as trunks, doors, glove box, and the like. The releasable fastening system may also be employed for releasable on-demand attachment mechanisms such as for releasable attachment for batteries, fuels cells, cargo containers, vehicle interior and exterior components, and the like. Moreover, the releasable fastening systems can be configured such that an energy source is not required to maintain engagement of the joint. Energy, i.e., the signal supplied by the actuation device, can be used to provide separation, thereby minimizing the impact on energy sources during use of the releasable fastening system.

While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.