An androgynous fastener for autonomous robotic assembly of high performance structures is disclosed herein. The androgynous fastener is lightweight and facilitates assembly through simple actuation with large driver-positioning tolerance requirements. The androgynous fastener provides a high-strength, reversible mechanical connection and may be used in high strength-to-weight ratio structural systems, such as lattice structure systems. The androgynous fastener resists tensile and shear forces upon loading of the lattice structure system thereby ensuring that the struts of the lattice structure system govern the mechanical behavior of the system. The androgynous fastener eliminates building-block orientation requirements and allows assembly in all orthogonal build directions. The androgynous fastener may be captive in building-block structural elements thereby minimizing the logistical complexity of transporting additional fasteners. Integration of a plurality of the androgynous fasteners into a high performance, robotically managed, structural system reduces launch energy requirements, enables higher mission adaptivity and decreases system life-cycle costs.

TECHNICAL FIELD

The present invention generally relates to androgynous fasteners.

BACKGROUND AND DESCRIPTION OF RELATED ART

On-orbit assembly of structures allows for space missions that are reliant on large scale infrastructure. Such large scale infrastructure includes space stations, wide aperture transceivers and exoplanetary habitats. On-orbit fastening of modular structural components ranges in size and complexity from demonstration trusses to modules for the International Space Station (ISS). For these applications, assembly ConOps complexity and mission adaptivity benefits from the genderless or androgynous connectors or fasteners. The International Berthing and Docking Mechanism (IBDM) is an example of the ability to work with positional tolerances that are coupled to the capabilities of the Attitude Determination and Control Systems of the components to be connected. At small scales, most space structure assembly experiments in the literature include an original ConOps that includes an astronaut on an Extra Vehicular Activity (EVA) manipulating parts of the system, with tolerances necessarily befitting human dexterity with EVA gloves. This relationship between the design parameters of fastener systems and the control parameters of intended actuation mechanisms is also studied in modular reconfigurable robotics. Like on-orbit coupling mechanisms, the state of the art in reconfigurable robotics transitioned from gendered designs to androgynous fasteners. It is widely recognized that the adaptability and robustness of a robot design relies on high misalignment tolerance in the coupling interfaces. Recent efforts to apply robotics and automation to structural systems for aerospace applications are focused on high performance structural systems with relatively simple robots. This requires fastener mechanisms to employ design principles similar to the IBDM in order to relax the positioning requirements of the assembly robots. Unlike self-reconfiguring modular robotics, the structural connection in discrete lattice materials has high structural efficiency requirements, i.e. the stiffness and loading capacity per given mass. For space applications, the Automated Reconfigurable Mission Adaptive Digital Assembly Systems (ARMADAS) robots must construct a structure that is competitive with current state of the art lightweight structures. For this reason, the connection between building-block lattice elements cannot afford self-actuation due to the mass of the associated mechanisms. Instead, the fastening actuation is designed to be provided by the assembling robots. The mass of the fastening mechanism between building blocks must be minimized, since any nonstructural mass has a parasitic effect on specific properties like modulus and strength, but must maintain geometric features to make robotic fastening reliable with large misalignment tolerances. Because this application calls for actuation that is moved between fasteners, geometric features must ensure not only alignment between fasteners and building-blocks, but also alignment between the fasteners and the robotic driver providing fastener actuation.

Conventional or traditional male-female fasteners are available and include bayonet connectors, shear pins (inserted orthogonal to the net tensile loading directions), press and interference fit connectors, as well as conventional nuts and bolts. However, one significant disadvantage of these conventional fasteners when used to attempt structural connections between building-blocks of a structural system is the requirement for a particular orientation of the building-blocks. Changing or adjusting the orientation of the building blocks to accommodate a fastener is not always feasible and may be impossible in such applications. Another disadvantage of these conventional or traditional fasteners is the complexity in using these fasteners in a captive position in the building blocks that are to be structurally connected together.

What is needed is an androgynous fastener that provides the desired performance required for robotic assembly of structural systems comprising building-block lattice elements and also minimizes or eliminates the problems and disadvantages associated with conventional or traditional fasteners.

SUMMARY OF THE INVENTION

Embodiments of an androgynous fastener for autonomous robotic assembly of high performance structures are disclosed herein. The androgynous fastener is configured for autonomous robotic assembly of building block-based lattice structural components. The androgynous fastener facilitates assembly through simple actuation with large driver-positioning tolerance requirements, while producing a reversible mechanical connection with high strength and stiffness per mass. The androgynous fastener may be used in high strength-to-weight ratio structural systems, such as discrete building block-based systems that may be reconfigured and/or scaled and which provide system lifecycle efficiency. The androgynous fastener is lightweight and can be robotically installed into a structural system. The androgynous fastener is capable of resisting the tensile and shear forces upon loading of the lattice structure system thereby ensuring that the struts of the lattice structure system govern the mechanical behavior of the system. The integration of the androgynous fasteners into a high performance, robotically managed, structural system reduces launch energy requirements, enables higher mission adaptivity and decreases system life-cycle costs.

The androgynous fastener disclosed herein eliminates building-block orientation requirements and allows for assembly in all orthogonal build directions. The androgynous fastener is configured so that it may be captive in the building-block structural elements thereby minimizing the logistical complexity of needing to carry additional fasteners for assembly. The androgynous fastener provides a mechanically reversible connection to allow reconfiguration. The androgynous fastener also allows ease of robotic activation with low activation force and high holding strength, as well as low robotic motion complexity (i.e., low degrees of freedom with a low number of states being desired).

In some embodiments, the androgynous fastener comprises a head having a first side portion having a plurality of teeth for engaging a primary tool for maneuvering the androgynous fastener. The head further comprises an opposite second side portion. A conical frustum structure extends from and is contiguous with the opposite second side portion of the head. The conical frustum structure has an angle θ1and a slanted length. The conical frustum structure has a pair of diametrically opposed exterior surfaces and a central axis that is coincident with a central axis of the androgynous fastener. The conical frustum structure has a first plurality of threads thereon that extend along the slanted length and are adjacent to one of the exterior surfaces. The conical frustum structure has a second plurality of threads thereon that are diametrically opposed to the first plurality of threads and extend along the slanted length. The second plurality of threads is adjacent to the other exterior surface of the conical frustum structure. The androgynous fastener further comprises a pair of diametrically opposed arms extending from the opposite second side portion of the head. Each arm is contiguous with the conical frustum structure and adjacent to a corresponding one of the first and second plurality of threads. Each arm has an exterior portion and an interior portion. The interior portions of the arms face each other. Each interior portion comprises a plurality of arm threads and is configured so that the plurality of arm threads taper at a thread taper angle θ2.

In some embodiments, an androgynous fastener comprises a substantially circular head having a first side portion having a plurality of teeth for engaging a primary tool for maneuvering the androgynous fastener. The substantially circular head further comprising an opposite second side portion. The head further comprises a recessed portion and a wall portion contiguous with and extending about the recessed portion. The teeth are contiguous with the recessed portion and the wall portion. The wall portion is angulated with respect to the recessed portion by a degree of angulation such that the recessed portion and wall portion cooperate to form an alignment cone to facilitate alignment of the tool with the teeth. The androgynous fastener further comprises a conical frustum structure extending from the opposite second side portion of the head. The conical frustum structure has an angle θ1and a slanted length. The conical frustum structure has a pair of diametrically opposed exterior surfaces and a central axis that is coincident with a central axis of the androgynous fastener. The conical frustum structure has a first plurality of threads thereon which extend along the slanted length and are adjacent to one of the exterior surfaces of the conical frustum structure. The conical frustum structure has a second plurality of threads thereon that are diametrically opposed to the first plurality of threads and which extend along the slanted length. The second plurality of threads is adjacent to the other exterior surface of the conical frustum structure. The androgynous fastener further comprises a first arm extending from the opposite second side portion of the head. The first arm being contiguous with the conical frustum structure and adjacent to the first plurality of threads. The first arm has an exterior portion and an interior portion. The interior portion comprises a plurality of first arm threads. The interior portion of the first arm is configured so that the plurality of first arm threads taper at a thread taper angle θ2, wherein the thread taper angle θ2is a complementary angle of angle θ1of the conical frustum structure. The androgynous fastener further comprises a second arm extending from the opposite second side portion of the head and diametrically opposed to the first arm. The second arm is contiguous with the conical frustum structure and adjacent to the second plurality of threads. The second arm has an exterior portion and an interior portion that faces the interior portion of the first arm. The interior portion of the second arm comprises a plurality of second arm threads. The interior portion of the second arm is configured so that the plurality of second arm threads taper at the thread taper angle θ2.

Certain features and advantages of the present invention have been generally described in this summary section. However, additional features, advantages and embodiments are presented herein or will be apparent to one of ordinary skill of the art in view of the drawings, specification and claims hereof. Accordingly, it should be understood that the scope of the invention shall not be limited by the particular embodiments disclosed in this summary section.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed invention. As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “has”, “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article or apparatus that comprises a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, method, article or apparatus. Also, as used in the specification including the appended claims, the singular forms “a”, “an” and “the” include the plural. Any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. All ranges of numerical values are inclusive.

Reference in the specification to “an exemplary embodiment”, “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrases “an exemplary embodiment”, “one embodiment” or “embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

As used herein, terms such as “vertical”, “horizontal”, “top”, “bottom”, “upper”, “lower”, “middle”, “above”, “below” and the like are used for convenience in identifying relative locations of various components and surfaces relative to one another in reference to the drawings and are not intended to be limiting in any way.

Referring toFIGS.1-2, there is shown androgynous fastener20in accordance with an exemplary embodiment. Androgynous fastener20meets strength requirements and structural requirements associated with operational axial tensile and shear loads and loads arising during torquing and installation. Androgynous fastener20meets these strength and structural requirements while minimizing mass. Androgynous fastener20facilitates robotic assembly and allows successful fastener activation with the lowest required positioning precision of the robotic driver bit and the lowest driving torque for a given fastener strength

Androgynous fastener20comprises head22that is configured for engagement with a robotic driver bit150which is shown inFIGS.7and8and discussed in the ensuing description. In operation, driver bit150rotates androgynous fastener20in order to connect it to another identical androgynous fastener20so as to form a mechanical coupling or mechanical connection. Head22is configured to efficiently transfer torque from robotic drive bit150to androgynous fastener20. Head22has a substantially circular shape and has perimetrical edge23, recessed portion24and wall portion26. Wall portion26extends about recessed portion24. Recessed portion24has a substantially flat portion28. Wall portion26is angulated with respect to recessed portion24by a predetermined degree of angulation. The geometrical characteristics and configuration of head22cooperate to facilitate radial alignment of the robotic drive bit150with head22. Specifically, angulated wall portion26provides a basic alignment feature in the form of a cone, which is referred to herein as the “alignment cone”. The angle of the alignment cone is determined by the degree of angulation of wall portion26. In some embodiments, the degree of angulation of wall portion26is maximized to about 45° in order to allow a greater radial tolerance.

Referring toFIGS.1and2, head22includes bore30that has opening32which is centrally located in recessed portion24. Bore30extends along the central axis34of androgynous fastener20. In an exemplary embodiment, bore30is substantially hex-shaped. In other embodiments, bore30is configured to have other shapes. Bore30provides several functions. First, bore30reduces the overall weight of androgynous fastener20since the material that would have been in the space of bore30would have been subjected to only a minimal load. Second, bore30is configured to receive a secondary tool (e.g. driver bit) that is part of a robotic end effector and thus provides a secondary means of rotating androgynous fastener20in order to fasten it to another identical androgynous fastener20. Head22further includes a pair of openings36in substantially flat portion28of recessed portion24. In an exemplary embodiment, openings are diametrically opposed to each other, wherein opening32of bore30is between openings36. Openings36provide multiple functions. First, openings36provide a means for confirming that two androgynous fasteners20are fully engaged to form a complete mechanical coupling. Specifically, when both androgynous fasteners20are fully connected together to form a mechanical coupling, each opening36of one androgynous fastener20is aligned with a corresponding opening36in the other androgynous fastener20. Such a configuration allows use of an automated line-of-sight sensor to verify that openings36of one androgynous fastener20are aligned with corresponding opening36in the other androgynous fastener20. Another function of openings36is to provide the option of temporarily locking a pair of androgynous fasteners20together when these androgynous fasteners are in the fully engaged position to form a mechanical coupling. Specifically, pins or similar devices may be inserted through openings36of both androgynous fasteners20so that both androgynous fasteners are unable to back out and disengage. The pins may be removed in order to unfasten and release the androgynous fasteners20.

Referring toFIGS.1,3and5A, head22further comprises a plurality of teeth40that are joined or attached to recessed portion24and angulated wall portion26. In an exemplary embodiment, the plurality of teeth40comprises two teeth. However, in other embodiments, there may be more than two teeth40. In an exemplary embodiment, there are two diametrically opposed teeth40. Opening32of bore30is between teeth40. Teeth40are configured to be engaged by robotic driver bit150shown inFIGS.7and8. Specifically, each tooth40has driving surfaces42that are configured to be engaged by robotic driver bit150. The “draft angle” of each tooth40is the angle between driving surface42and the plane of head22. Specifically, the draft angle may be measured between driving surface42and substantially flat portion28of recessed portion24. The draft angle depends upon the axial force from robotic driver bit150and the friction between the robotic driver bit150and teeth40. The friction between robotic driver bit150and the teeth40depends upon the particular material from which the androgynous fastener20is fabricated. The draft angle is chosen to maximize the allowable positional tolerances. It has been found that a draft angle greater than 90° may cause the robotic driver to “cam out” during fastening, but a draft angle less than or equal to 90° reduces this effect and facilitates engagement of robotic driver bit150with head22. Therefore, in an exemplary embodiment, the draft angle is 90° so as to simplify control of robotic drive bit150and eliminate any additional steps for engagement and disengagement. Referring toFIG.5A, the diametrically opposed teeth40maximize the spacing between teeth40so as to provide greater rotational tolerances for driver bit engagement. As used herein, “rotational tolerance” refers to the maximum rotational angle offset that allows androgynous fastener20and driver bit150to engage fully when axial force is applied. The “driver fit” is referred to as the tolerance between the fastener and the driver bit features and may be decomposed into the radial fit and the rotational fit. The radial fit is indicated by the notation RF1and the rotational fit is indicated by the notation RF2. In an exemplary embodiment, the radial fit RF1has a spacing of 3.0 mm. The rotational fit RF2is minimized to allow for a large error in the rotational position of driver bit150. In an exemplary embodiment, the rotational fit RF2is about 50.4°. The driver azimuth angle is maximized so as to allow for the largest tooth height possible which does not cause any interference when the androgynous fastener20is in the unengaged captive position. As used herein, “driver azimuth angle tolerance” refers to the maximum offset angle of driver bit150from the orthogonal position in which driver bit150and androgynous fastener20are still engaged when rotating. The particular structure of head22maximizes the driver azimuth angle tolerance thereby allowing relaxation of the positioning requirements of robotic driver bit150. In an exemplary embodiment, the driver azimuth angle tolerance is about 16.3º.

Referring toFIGS.7and8, there is shown an exemplary embodiment of robotic driver bit150that may be used to rotate androgynous fastener20in order to connect the androgynous fastener20to another identical androgynous fastener to form a mechanical coupling. Robotic driver bit150also is configured to pull androgynous fastener20in a reverse axial direction in order to disassemble the mechanical coupling. Robotic driver bit150comprises base portion152having a central bore154for receiving a rotatable shaft (not shown) of a robotic end effector (not shown). Robotic driver bit150includes head engagement portion156that is contiguous with base portion152. Head engagement portion156is configured to engage head22of androgynous fastener20and comprises surface158and tooth engaging structure160for engaging one of teeth40. Tooth engagement structure160comprises sides162and164which are substantially perpendicular to surface158and configured to contact driving surfaces42of teeth40. Tooth engagement structure160includes top portion side166which has beveled portion167. The angle of beveled portion167is configured to substantially match the angle of angulation of wall portion26of head22. Tooth engagement structure160includes overhanging portion168, the purpose of which is discussed in the ensuing description. Similarly, head engagement portion156further comprises tooth engagement structure170. Tooth engagement structure170comprises sides172and174which are substantially perpendicular to surface158and configured to contact driving surfaces42of teeth40. Tooth engagement structure170includes top portion176and beveled portion177. The angle of beveled portion177is configured to substantially match the angle of angulation of wall portion26of head22. Tooth engagement structure170includes overhanging portion178, the purpose of which is discussed in the ensuing description.

Referring toFIGS.1-4and5A, head22further includes slot-like openings50in perimetrical edge23of head22. In an exemplary embodiment, slot-like openings50are diametrically opposed to each other. Each slot-like opening50extends through wall portion26and also under a corresponding one of teeth40. Slot-like openings50allow driver bit150to disassemble a mechanically coupling formed by a pair of androgynous fasteners20. Each slot-like opening50creates a pocket in which a corresponding portion of driver bit150is positioned during disassembly of the mechanically coupling. Specifically, each overhanging portion168and178of driver bit150is configured to fit into a corresponding slot-like opening50. Once driver bit150rotates androgynous fasteners20to the open position (counter-clockwise), the driver bit150is pulled backward in the axial direction. Since overhanging portions168and178are positioned within slot-like openings50, the movement of driver bit150backward in the axial direction pulls androgynous fasteners20apart along the axial direction thereby disengaging androgynous fasteners20from each other. The extension of slot-like openings50through perimetrical edge23of head22also facilitates fabrication of androgynous fastener20by injection molding.

As shown inFIGS.1,2,4and5B, head22further includes opposite second side portion54and centrally located structure56contiguous with and extending from opposite second side portion54. Centrally located structure56has the geometric shape of a modified right circular cone wherein with the portion of the cone having the vertex is cut off so as to form a frustum or conical frustum. The angle θ1of the conical frustum is the same as the angle of the unmodified right circular cone. In an exemplary embodiment, the θ1is twenty degrees (20°) (. Centrally located structure56is referred to herein “conical frustum structure56”. Central axis58of conical frustum structure56is coincident with the central axis34of androgynous fastener20. Bore30longitudinally extends through conical frustum56and the longitudinally extending axis of bore30is coincident with central axis58of conical frustum structure56. Conical frustum structure56has a slanted length and a pair of separate exterior surfaces60and61. In an exemplary embodiment, exterior surfaces60and61are diametrically opposed to each other. Conical frustum structure56has a first plurality of threads62thereon which extend along the slanted length and are adjacent to exterior surface60. Conical frustum56has a second plurality of threads64thereon that are adjacent to exterior surface61. In some embodiments, threads62and64are joined or attached to conical frustum structure56and in other embodiments, threads62and threads64are integral with conical frustum structure56. In an exemplary embodiment, the first plurality of threads62and the second plurality of threads64are diametrically opposed. In an exemplary embodiment, each thread62and64is configured as a saw tooth buttress style thread. It has been found that the saw tooth buttress shape of the threads yields less friction than other thread shapes and requires relatively less torque to engage and thus facilitates robotic actuation. Another desirable effect of a saw tooth buttress thread is that for high and unidirectional loads, the face of the thread, which is bearing the load, is perpendicular to the load direction. Each plurality of threads62and64has a predetermined number of threads and each thread has predetermined thread angle. In an exemplary embodiment, the predetermined number of threads is three (3) and the predetermined thread angle is thirty degrees (30°). It has been found that a thread angle of about thirty degrees (30°) allows for a higher surface area of contact.

Referring toFIGS.1-4and5B, androgynous fastener20further comprise extending arms70and72that are joined or attached to conical frustum structure56. In some embodiments, extending arms70and72are integral with conical frustum structure56. In an exemplary embodiment, extending arms70and72are diametrically opposed to each other. Extending arm70comprises interior portion74, exterior portion76and lengthwise edges78and80. Interior portion74is configured to have a plurality of threads82thereon. Similarly, extending arm72comprises interior portion84, exterior portion86and lengthwise edges88and90. Interior portion84is configured to have a plurality of threads92thereon. As shown inFIG.2, interior portions74and84face each other and have the same number of threads. In an exemplary embodiment, interior portions74and84have three (3) threads82and92, respectively. In an exemplary embodiment, each thread82and92is configured as a saw tooth buttress style thread. Each thread82and92is configured to have a predetermined thread angle θ3. As used herein, “thread angle” refers to the angle θ3between adjacent thread surfaces. In an exemplary embodiment, the thread angle θ3is about thirty degrees (30°). Threads82and92are configured to have a predetermined pitch. As used herein, “pitch” of the threads refers to the axial distance D1(seeFIG.4) between the crests of adjacent threads. In an exemplary embodiment, the pitch is about 1.9 mm. When two androgynous fasteners20are engaged to form a mechanical coupling, the three threads of an arm (e.g. arm70or72) of one androgynous fastener20engage the three threads (e.g. threads62or64) on conical frustum structure56of the other androgynous fastener20. This results in a total of six threads being engaged. It has been found that a thread pitch of 1.9 mm in conjunction with the engagement of six threads facilitates distribution of the load across more surfaces and prevents the possibility of shear failure on a single thread.

Referring toFIGS.2,3,12and13, arm70further comprises tab member95that is attached to exterior portion76. Tab member95has portion96that extends beyond lengthwise edge78. Similarly, arm72further comprises tab member98that is attached to exterior portion86. Tab member98has portion99that extends beyond lengthwise edge88. The purpose of tab members95and98is discussed in the ensuing description.

As shown inFIGS.2-4, interior portion74of arm section70is configured so that threads82are in a tapered arrangement based on a predetermined thread taper angle θ2. Similarly, interior portion84of arm section72is configured so that threads92are in a tapered arrangement based on the predetermined thread taper angle θ2. The thread taper angle θ2is the complementary angle of angle θ1of conical frustum structure56. It has been found that the thread taper θ2contributes to the minimization of the mass of androgynous fastener20. In an exemplary embodiment, the thread taper θ2is about seventy degrees (70°). As discussed in the foregoing description, in an exemplary embodiment, angle θ1of conical frustum structure56is twenty degrees (20°). Since the exemplary thread taper angle θ2is seventy degrees (70°), angles θ1+θ2are complementary angles (i.e. θ1+θ2=90°). Referring toFIG.4, the notation D2refers to the external diameter which is the maximum diameter of the overall thread features. Androgynous fastener20is configured to have a maximum allowable external diameter D2based on the unit-cell geometry so as to provide a maximum contact area. In an exemplary embodiment, the external diameter D2is about 15.9 mm.

Referring toFIG.6, there is shown Table I which provides a summary of the exemplary parameter values and performance metrics of androgynous fastener20. It is to be understood that the parameter values and performance metrics shown in Table I pertain to an exemplary embodiment and that in other embodiments, these parameters and performance metrics may vary.

FIGS.9-13illustrate the process for connecting a pair of androgynous fasteners20together to form a mechanical coupling or mechanical connection. In order to facilitate understanding of this process, the androgynous fasteners20that are to be connected together are referred to as “fastener20A” and “fastener20B”. The reference numbers “70A” and “72A” shall refer to the arms of fastener20A, and the reference numbers “70B” and “72B” shall refer to the arms of fastener20B. Furthermore, the threads on arms70and72of both fasteners20A and20B are referred to as “arm threads” and the threads on conical frustum structure56of both fasteners20A and20B are referred to as “frustum threads”.FIG.9illustrates the alignment of androgynous fasteners20A and20B that is required to allow the fasteners20A and20B to be connected together to form a mechanical coupling. Each fastener20A and20B is positioned so that each of its arm sections is aligned with a corresponding one of exterior surfaces60and61of conical frustum structure56of the other fastener. As discussed in the forgoing description, exterior surfaces60and61are the portions of conical frustum structure56that do not have any threads thereon. For example, fastener20A is positioned so that arm70A is aligned with exterior surface61of fastener20B and arm72A is aligned with exterior surface60of fastener20B. Next, as shown inFIG.10, fasteners20A and20B are maneuvered in axial direction toward each other. This may be accomplished by a pair of robotic end effectors (not shown), each of which having driver bit150. Referring toFIG.11, fasteners20A and20B are fully inserted into each other such that arm70A of fastener20A faces exterior surface61of fastener20B and arm section72A of fastener20A faces exterior surface60of fastener20B, and arm72B of fastener20B faces exterior surface60of fastener20A and arm70B of fastener20B faces exterior surface61of fastener20A.

Referring toFIG.12, fastener20A is rotated clockwise and fastener20B is rotated counter-clockwise so that arm threads82of fastener20A engage frustum threads64of fastener20B and arm threads92of fastener20A engage frustum threads62of fastener20B, and arm threads82of fastener20B engages frustum threads64of fastener20A and arm threads92of fastener20B engage frustum threads62of fastener20A. Rotation of the fasteners20A and20B may be accomplished by the aforementioned robotic end effectors. Fasteners20A and20B are rotated until the arm threads of fastener20A are fully engaged with the frustum threads of fastener20B, and the arm threads of fastener20B are fully engaged with the frustum threads of fastener20A. This occurs when fasteners20A and20B reached the maximum rotation as shown inFIG.13. As shown inFIG.13, portion99of tab98on arm72A extends over exterior portion86of arm72B and portion99of tab98on arm72B extends over exterior portion86of arm72A thereby providing further integrity to the mechanical coupling formed by androgynous fasteners20A and20B.

The friction between the interlocking threads of fasteners20A and20B compresses the fasteners20A and20together and through elastic deformation, provides a preloaded joint. The faces of the interlocking threads are perpendicular to the direction of the axial forces thereby providing a higher load capacity.

The particular material from which androgynous fastener20may be fabricated depends upon the particular application and the required performance. Suitable materials include, but are not limited to, reinforced plastics, PEEK, aluminum, copper, nickel, titanium and steel. Androgynous fastener20may be fabricated by any suitable fabrication processes, depending upon the material, the particular application and the required mechanical performance. Such suitable fabrication processes include, but are not limited to,3D printing processes such as FDM, SLA, Polyjet, etc. Other suitable fabrication processes are CNC milling, casting and forging.

Efficient and high-integrity in-orbit assembly of space structures is critical for enabling missions that demand large scale infrastructure. Future space construction will require robots to operate autonomously in extreme environments. Utilizing conventional or traditional fastening components results in complex assembly requirements and intricate robotic systems with multiple points of failure. Androgynous fastener20eliminates the problems associated with conventional or traditional fasteners and achieves both the strength requirements and robotic assembly specifications required for the assembly of any space structure. Androgynous fastener20achieves a high load capacity and large engagement tolerances for robotic driver bits or similar tools.