Patent Abstract:
A coupling for mechanically connecting modular tubular struts of a positioning apparatus or space frame, comprising a pair of toothed rings ( 10, 12 ) attached to separate strut members ( 16 ), the teeth ( 18, 20 ) of the primary rings ( 10, 12 ) mechanically interlocking in both an axial and circumferential manner, and a third part comprising a sliding, toothed collar ( 14 ) the teeth ( 22 ) of which interlock the teeth ( 18, 20 ) of the primary rings ( 10, 12 ), preventing them from disengaging, and completely locking the assembly together. A secondary mechanism provides a nesting force for the collar, and/or retains it. The coupling is self-contained and requires no external tools for installation, and can be assembled with gloved hands in demanding environments. No gauging or measured torque is required for assembly. The assembly can easily be visually inspected to determine a “go” or “no-go” status. The coupling is compact and relatively light-weight. Because of it&#39;s triply interlocking teeth, the connection is rigid. The connection does not primarily rely on clamps, springs or friction based fasteners, and is therefore reliable in fail-safe applications.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application No. 60/643,617, which was filed Jan. 12, 2005. 

   FEDERALLY SPONSORED RESEARCH 
   The United States government has rights in this invention pursuant to Contract No. DE-AC03-76SF00098 between the United States Department of Energy and the University of California, for the operation of Lawrence Berkeley National Laboratory. 

   BACKGROUND OF THE INVENTION 
   This invention relates to the mechanical connection of modular structural elements, such as those of a positioning apparatus or space frame. More particularly, the invention relates to the design of disconnectable couplings functioning as a means to this end. 
   In the context of designing a positioning apparatus, the need arises to design structural elements of same that are rigid, therefore permitting accuracy of placement. Such an apparatus must also transmit mechanical power in order to execute placement, e.g. as in the case of an articulated robot arm. Positioning per se implies using an apparatus to move an object in a given linear direction and/or rotate it. Thus, an active structural element of a positioning apparatus must be able to transmit linear force as well as rotational force, commonly called torque. 
   Further, in the context of designing a positioning apparatus that can be readily assembled from or disassembled into a set of modular components, the coupling design used in connecting these components to each other must reliably transmit torque as well as linear force, with mechanical precision. Here, this kind of coupling will be called a “Torque Coupling”, not to be confused with a conventional power coupling or clutch. 
   To maintain positional accuracy, a Torque Coupling must be capable of being accurately and repeatably assembled, and it must be capable of transmitting linear force and/or torque without mechanical slippage, either linear or rotational. These requirements distinguish the design of a Torque Coupling from that of a conventional power coupling or clutch, such as used in the drive shaft of a motor. In fact, for reasons of practicality the latter are deliberately designed to accommodate misalignment, rendering them unsuitable for true kinematic applications. 
   As it happens, a parallel context exists for which a Torque Coupling is suitable, that of a collapsible Space Frame, i.e. a space frame which can readily be assembled from or disassembled into modular elements. Here, the term “Space Frame” means a rigid assembly of predominantly linear struts, connected to each other at their ends. Rigidity is obtained by the organization of the assembly into a two or three dimensional system of triangles, since the triangle is the only fundamentally rigid shape that can be formed by linear struts. These triangles need not be regular. 
   By their nature, Space Frames are both rigid and lightweight, making them suitable for applications requiring both physical stability and economy of material (i.e. mass), such as bicycle frames, telescope mirror supports, space stations, booms of construction cranes, truss-type bridges, and various types of scientific apparatus. 
   Because of the intrinsic geometry of a Space Frame, its component struts can only be subjected to linear (tensile/compressive) or rotational (torsional) forces—but not bending—as the entire assembly is subject to a variety of loads. Therefore, the fundamental requirements of a Torque Coupling connecting strut components in a Space Frame are the same as for a positioning apparatus, i.e., the Torque Coupling must be capable of being accurately and repeatably assembled, and must reliably transmit linear and/or rotational force without mechanical slippage. 
   Previously, designs such as the Bicycle Torque Coupling (BTC) of Smilanick, U.S. Pat. No. 5,431,507, utilized a pair of cylindrical fittings bonded to mating strut ends. These fittings each had a set of teeth that interlocked with each other as the two fitting halves were clamped together. This interlocking prevented mechanical slippage due to rotational force. The two fittings were clamped together by a captive threaded casing, or “nut”, that slid over one fitting and screwed onto external threads on the other fitting. This nut contained external notches used for tightening with a specialty wrench. The BTC is produced commercially by the S and S Machine Co. of Roseville, Calif., and is used to attach collapsible bicycle frames together. 
   The BTC-type design presents several problems in certain applications involving a positioning apparatus. First, it is possible to assemble the two fittings together such that the teeth actually touch at their tips instead of interdigitating. In this position it is also possible to engage a few threads of the nut and hold the assembly together, giving the impression that the assembly has been correctly assembled, even though it&#39;s actually at risk of failing in torsion. Also, this mis-assembly will cause the positioning apparatus as a whole to be mis-aligned. As mentioned, it cannot be readily determined by visual inspection whether a BTC-type coupling has been incorrectly assembled in this manner. Therefore it is problematic to validate an assembly with many couplings, e.g. a field application. Therefore the BTC and similar designs are unreliable in fail-safe applications, i.e. applications in which failure would be a high-consequence event. 
   Second, an external wrench is required to assemble a BTC-type coupling. This tool can be misplaced or lost, rendering emergency assembly or disassembly problematic. Worse, in an installation where loose items can cause catastrophic damage by falling into sensitive equipment, an external wrench requires tethering, which can complicate assembly. Furthermore, an external wrench may be difficult to use in environments where the apparatus must be assembled in difficult or hostile environments requiring a technician to wear gloves. Also, an external wrench in the hands of an assembly technician yields unpredictable results in terms of the tightened condition of a BTC-type nut unless a torque wrench is used, but the latter would be quite cumbersome and would require the concurrent use of a dedicated workstation to hold and secure the coupling during tightening. 
   Third, even when correctly assembled, it is not possible to determine by visual inspection whether a BTC-type nut has been properly tightened or is in fact loose, a condition that also renders failsafe operation problematic. 
   Fourth, the use of a threaded nut in a BTC-type design represents, ultimately, a reliance on the frictional forces induced in the threads of the coupling as they are twisted to elastically comply with each other. This is actually a form of clamping, in which the nut functions as a spring, of sorts, due to its elastic character. The reliance on friction, springs or clamping as an attachment scheme is fundamentally unreliable in environments requiring immersion in highly viscous (and therefore lubricating) fluids, such as encountered in a certain class of underground neutrino detectors. Also, friction-based attachments schemes are undermined by vibration, regular or intermittent, e.g. shocks induced by dropping, etc. In industry, nuts installed in mechanically hostile environments typically have some kind of a secondary, positive, mechanical lock to prevent them from backing out. However, these extra parts add complexity, and therefore increase installation difficulty, including the risk of lost parts, or of parts dropped into peripheral instrumentation, possibly resulting in catastrophic damage. 
   Fifth, the BTC-type threaded nuts are bulky in order to incorporate a set of female threads, as well as to have sufficient structural integrity to withstand assembly wrenching forces. This bulk increases the overall weight of an assembly. It also increases the maximum cross-section of a strut assembly, reducing clearances through any bulkhead. 
   Sixth, assembly of a threaded BTC-type nut assembly is time-consuming, because the thread engagement must be carefully started and then turned several times, a wrench must be used, and the wrench force must be gauged somehow, possibly requiring the use of a dedicated assembly workstation and torque wrench. 
   Accordingly, several objects and advantages of the invention described herein, named the Quick Torque Coupling (QTC), are: 
   First, the QTC eliminates vague and indeterminate conditions of intermediate assembly, such that the assembled condition falls simply into two distinct categories—it is either locked or unlocked. This eliminates the danger of a faulty assembled condition that might fail and/or cause the parent positioning apparatus to be misaligned. Therefore, assembly of the invention is highly reliable and suitable for fail-safe applications, which is an object and advantage. 
   Second, no wrenches, tools or other loose hardware are required for the primary assembly of the QTC. The QTC is self-contained, so there is no risk of not having a tool available for emergency assembly or disassembly. Also, there is no need for a specialized assembly workstation with tethered tools, and there is no danger of dropping either tools or secondary locking hardware into nearby equipment or instrumentation. Therefore, assembly of the QTC is simple and self-contained, which is an object and advantage. 
   Third, the physical engagement of the QTC assembly can be readily inspected by eye, and a “go”/“no-go” status of each coupling can be quickly and easily assessed. Therefore the QTC can be simply and easily tested, which is an object and advantage. 
   Fourth, the QTC locks by direct positive engagement of triply interlocking teeth, eliminating the use of any kind of primary clamping, spring-loaded, or friction based mechanism. Thus, the integrity of the assembled condition of the QTC is fundamentally fail-safe. There is no virtually no danger of unexpected self-disassembly due to the undermining of a threaded coupling by either lubrication and/or vibration or shock. Therefore, the mechanism of the QTC is simple and reliable, which is an object and advantage. 
   Fifth, the QTC eliminates the need for a bulky and heavy captive nut, substituting a low-profile light-weight locking collar. The QTC is therefore relatively compact and light-weight compared to the prior art, such as the BTC, above, which is an object and advantage. 
   Sixth, because the QTC is straightforward, simple, and requires no tools, it is therefore relatively rapid to assemble, compared to the prior art. This reduces installation and maintenance time, which is an object and advantage. 
   Further objects and advantages of the QTC will become apparent from a consideration of the ensuing description and drawings. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a mechanical tubular coupling system comprises primarily a pair of toothed rings attached to strut members, these teeth mechanically interlocking in both an axial and circumferential manner, and a third part comprising a sliding, toothed ring that interlocks the teeth of the first two rings, preventing them from disengaging and completely locking the assembly together. A secondary mechanism of any kind may provide a nesting force for the third ring. 
   In the drawings, closely related figures have the same label number but different alphabetic suffixes. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is an overall view of the invention shown in the disconnected condition, with the upper portion tilted towards the viewer by six degrees; 
       FIG. 1B  is an enlarged detail of  FIG. 1A ; 
       FIG. 1C  is similar to  FIG. 1A , except that the upper portion is tilted away from the viewer by six degrees; 
       FIG. 1D  is an enlarged detail of  FIG. 1C ; 
       FIG. 2A  is similar to  FIG. 1A , except that the invention is shown in the first stage of assembly, with the arrows indicating linear motion or force, and with the front half of the invention cut away to reveal the rear half; 
       FIG. 2B  is an enlarged detail of  FIG. 2A ; 
       FIG. 2C  is similar to  FIG. 2A , except that the rear half of the invention has been cut away instead of the front half, for clarity in rendering foreground detail; 
       FIG. 2D  is an enlarged detail of  FIG. 2C ; 
       FIG. 3A  is similar to  FIG. 2A , except that the invention is shown in the second stage of assembly, with the arrows indicating rotational motion or rotational force (torque); 
       FIG. 3B  is an enlarged detail of  FIG. 3A ; 
       FIG. 3C  is similar to  FIG. 2C , but showing the second stage of assembly of the invention as in  FIG. 3A ; 
       FIG. 3D  is an enlarged detail of  FIG. 3C ; 
       FIG. 4A  is similar to  FIG. 3A , but showing the third stage of assembly of the invention; 
       FIG. 4B  is an enlarged detail of  FIG. 4A ; 
       FIG. 4C  is similar to  FIG. 3C , but showing the third stage of assembly of the invention as in  FIG. 4A ; 
       FIG. 4D  is an enlarged detail of  FIG. 4C ; 
       FIG. 5  is similar to  FIG. 4A , except that the view is orthogonal with respect to the invention; 
       FIG. 5A  is an enlarged detail of  FIG. 5 ; 
       FIG. 5B  is identical to  FIG. 5A , except that only teeth  20  are shown; 
       FIG. 5C  is identical to  FIG. 5A , except that only teeth  18  are shown; 
       FIG. 5D  is identical to  FIG. 5A , except that only teeth  22  are shown; 
       FIG. 6A  is a view of an auxiliary ring  90  which supplies a nesting force; 
       FIG. 6B  is a view of an alternative version  86  of locking ring  14 , incorporating a supplementary flange  88  to facilitate manual operation; 
       FIG. 6C  is a view of an alternative embodiment of the invention, with both auxiliary nesting force ring  90  and modified locking ring  86  in the retracted (unlocked) position; 
       FIG. 6D  is a view of an alternative embodiment of the invention, with both auxiliary nesting force ring  90  and modified locking ring  86  in the extended (locked) position. 
       FIG. 7A  is similar to  FIG. 5A , except that additional geometry  92 ,  94 ,  96  has been incorporated in teeth  18 ,  20  and  22  to provide for a snapping action when they are engaged; 
       FIG. 7B  is similar to  FIG. 7A  except that only teeth  20  are shown; 
       FIG. 7C  is similar to  FIG. 7A  except that only tooth  18  is shown; 
       FIG. 7D  is similar to  FIG. 7A  except that only tooth  22  is shown; 
       FIG. 8A  is a view of an alternative version  114  of ring  14  with extended, flexile teeth; 
       FIG. 8B  is a view of alternative embodiment of the invention, showing alternate versions  1   10 ,  1   12 , respectively, of rings  10 ,  12 , and alternate version  114  of ring  14 , the latter shown disengaged from rings  110 ,  112  (unlocked); 
       FIG. 8C  is similar to  FIG. 8B , except that ring  114  is shown engaged with rings  110 ,  112  (locked); 
       FIG. 9A  is a view of an alternative embodiment of the invention in the disconnected (unlocked) condition, showing alternate versions  116 ,  118 , respectively of rings  10 ,  12 , which have been modified to incorporate an O-ring seal for fluid conveyance; 
       FIG. 9B  is similar to  FIG. 9A , except that the invention is shown connected (locked); 
   

   IDENTIFICATION OF THE REFERENCE NUMBERS 
     10 : First ring; 
     12 : Second ring; 
     14 : Third or locking ring; 
     16 : Strut segments (two shown); 
     18 : Typical tooth of ring  10 ; 
     20 : Typical tooth of ring  12 ; 
     22 : Typical tooth of locking ring  14 ; 
     24 : Circumferential tab of tooth  18 ; 
     26 : Circumferential tab of tooth  20 ; 
     28 : Radial tab of tooth  18 ; 
     30 : Radial tab of tooth  20 ; 
     32 : Typical axial contacting region between teeth  18  and ring  12 ; 
     34 : Typical axial clearance region between teeth  20  and ring  10 ; 
     36 : Typical rotational contacting region between teeth  18  and  20 ; 
     38 : Typical rotational clearance region between bases of teeth  18  and ends of teeth  20 ; 
     40 : Typical rotational clearance region between bases of teeth  20  and ends of teeth  18 ; 
     42 : Typical axial clearance region between ends of teeth  22  and ring  12 ; 
     44 : Typical axial contact region between teeth  22  and teeth  18 ; 
     46 : Typical axial contact region between teeth  22  and teeth  20 ; 
     48 : Typical axial clearance region between ring  14  and radial tabs  28  and  30 ; 
     50 : Typical notch between teeth  18  of ring  10 ; 
     52 : Typical notch between teeth  20  of ring  12 ; 
     54 : Base of typical notch between teeth  22 , corresponding to axial clearance region  48 ; 
     56 : Portion of notch  52  profile corresponding to axial contact region  32  and axial clearance region  42 ; 
     58 : Portion of tooth  18  profile corresponding to axial contact region  32 ; 
     60 : Portion of tooth  20  profile corresponding to rotational clearance region  40 ; 
     62 : Portion of tooth  18  profile corresponding to rotational clearance region  40 ; 
     64 : Portion of tooth  20  profile corresponding to rotational contact region  36 ; 
     66 : Portion of tooth  18  profile corresponding to rotational contact region  36 ; 
     68 : Portion of tooth  20  profile corresponding to rotational clearance region  38 ; 
     70 : Portion of tooth  18  profile corresponding rotational clearance region  38 ; 
     72 : Portion of tooth  20  profile corresponding to axial clearance region  34 ; 
     74 : Portion of notch  50  profile corresponding to axial clearance region  34 ; 
     76 : Portion of tooth  20  profile corresponding to axial contact region  46 ; 
     78 : Portion of tooth  22  profile corresponding to axial contact region  46 ; 
     80 : Portion of tooth  18  profile corresponding to axial contact region  44 ; 
     82 : Portion of tooth  22  profile corresponding to axial contact region  44 ; 
     84 : Portion of tooth  22  profile corresponding to axial clearance region  42 ; 
     86 : An alternate version of locking ring  14  with an integral flange  88 ; 
     88 : The flange of ring  88 , which facilitates manual operation; 
     90 : A ring with integral spring geometry to supply a nesting force to ring  86 ; 
     92 : Provision for a snapping action to occur in regions  36 ; 
     94 : Provision for a snapping action to occur in regions  44 ; 
     96 : Provision for a snapping action to occur in regions  46 ; 
     98 : Portion of tooth  20  in provision for snapping action  92 ; 
     100 : Portion of tooth  20  in provision for snapping action  96 ; 
     102 : Portion of tooth  18  in provision for snapping action  94 ; 
     104 : Portion of tooth  18  in provision for snapping action  92 ; 
     106 : Portion of tooth  22  in provision for snapping action  96 ; 
     108 : Portion of tooth  22  in provision for snapping action  94 ; 
     110 : An alternate version of ring  10  without radial tabs  28 , for use with locking ring  114 ; 
     112 : An alternate version of ring  12  without radial tabs  30 , for use with locking ring  114 ;  114 : An alternate version of locking ring  14  with extended, flexible teeth that protrude inward at their ends to lock rings  110 ,  112  together; 
     116 : An alternate version of ring  10  with an internal o-ring groove  120 ; 
     118 : An alternate version of ring  12  with an integral internal sleeve (o-ring throat)  122 ; 
     120 : The o-ring groove of ring  116 ; 
     122 : The internal sleeve of ring  118 ; 
     124 : O-ring, normally installed in o-ring groove  120 ; 
     126 : Portion of radial tab  28  associated with clearance region  48 ; 
     128 : Portion of radial tab  30  associated with clearance region  48 . 
   DETAILED DESCRIPTION OF THE INVENTION 
   A preferred embodiment of the present invention is illustrated in  FIGS. 1A and 1C , wherein both figures show the disassembled (unlocked) condition of the invention. Two steel or aluminum rings  10  and  12 , each with a circumferential array of teeth  18  and  20  respectively, are welded or brazed to the ends of struts  16  such that their teeth extend axially outward. Other materials and/or joining techniques may be used instead. A locking ring  14  is assembled such that it slides over ring  10  with its teeth facing teeth  10 . Ring  14  has a set of teeth  22 , which engage the teeth  18  and  20  of rings  10  and  12  in the assembled condition. In the embodiment shown, the diameter of the struts  16  is about 3 inches. The wall thickness of the struts is about 1/16 inch, as is that of the ring  14 . The teeth  18  and  20 , of rings  10  and  12  have radial thickness that varies, but are not diametrically solid. 
   Although rings  10  and  12  each have a set of interlocking teeth  18  and  20  respectively, each extending axially and spaced at angular intervals, the design of teeth  18  and  20  are distinct. Teeth  18  have a compound tab at the end of the tooth that protrudes both circumferentially  24  and radially outward  28 . Teeth  20  have a circumferential tab  26  at its end, and a radial tab  30  at its base that protrudes outward. In the embodiment shown, rings  10  and  12  each have twenty teeth  18  and  20 , respectively. Each tooth  18  and  20  is approximately ¼ inch long, and is spaced at regular angular intervals, although a regular interval is not required, per se. For example, some angular irregularity may be desirable to control the engagement orientation of the coupling halves of the invention. 
   The first assembly step is shown in  FIGS. 2A through 2D . Rings  10 , 14  and one strut  16  form the upper half of the invention. Ring  12  another strut  16  form the lower half. The two halves are aligned axially, and then pushed into contact with each other as indicated by the opposing arrows. These arrows represent linear motion or force. Detail  FIGS. 2B and 2D  show the interaction of a pair of teeth  18  and  20  in this state, viewed from opposite sides. The two rings contact at regions  32  between the ends of teeth  18  and notch bases  56 . To prevent over-constraint, clearance is provided at the complementary regions  34  between the ends  72  of teeth  20  and notch bases  74 . 
   The second assembly step is shown in  FIGS. 3A through 3D . The two halves of the invention are twisted together until the circumferential tabs  24  and  26  engage and interdigitate with each other, as indicated by the opposing arrows. These arrows represent rotational motion or rotational force (torque). Teeth  18  and  20  contact each other at regions  36 . The surfaces of tabs  24  and  26  at regions  36  are oriented to create a wedging action in cooperation with the surfaces at regions  32 . The collective wedging action of all tabs  24  and  26  axially aligns and centers rings  10  and  12  with respect to each other, and locks them together. The halves of the invention then possess only one degree of freedom, namely the reverse (inverse) of the assembling twist. They can no longer move axially, or be offset, or be further twisted with respect to each other. 
   The third and final assembly step is shown in  FIGS. 4A through 4D . Locking ring  14  is pushed axially by hand or by a secondary mechanism of any kind, which is fixed to the upper half of the invention. An example of such a mechanism is illustrated as ring  90  in  FIGS. 6A through 6D . The end of ring  90  opposite the teeth is welded or fixed to strut  16 , leaving the other end free to spring-load locking ring  86 . In this example, ring  86  is the same as ring  14  except that it has a flange to permit manual operation. A nesting force is thus created on ring  14  with respect to the upper half of the invention. This action and reaction are indicated by the opposing arrows in  FIGS. 4A  though  4 D, which represent linear motion or force. The teeth  22  of ring  14  then engage and interdigitate with the radial tabs  28  and  30  respectively, of teeth  18  and  20 . Teeth  22  have a wedge shape, and radial tabs  28  and  30  together form a cooperating wedge shape. Teeth  22  are designed to exactly fill the gap between teeth  18  and  20  resulting from assembly step two, and axial contact occur at regions  44  and  46 . To prevent over-constraint, clearance  42  is provided between the ends of the teeth  22  and notch bases  56 , and clearance  48  is provided between notch bases  54  and radial tabs  28  and  30 . The geometry of this triple interlocking state is designed such that teeth  22  create a wedging action as they engage radial tabs  28  and  30 . 
   Once teeth  22  engage radial tabs  28  and  30 , the single remaining degree of freedom remaining after step two is eliminated, and the assembly is completely locked together. Motion between the two assembly halves is positively and physically blocked by the presence of solid material (the triply interlocking teeth). Thus, no unreliable clamping, spring loading, or friction-based attachment of any kind is utilized in this primary locking action. 
   As noted, locking ring  14  requires a nesting force to maintain its engagement with teeth  18  and  20 . This nesting force is very small in relation to the ability of the assembly to resist linear and rotational forces and/or deflection. Therefore, the assembly can be considered a kind of mechanical amplifier, in a very broad sense. Any number of types of secondary mechanisms may be employed to supply this nesting force. Examples include clamping or spring loaded devices (such as the ring  90  shown in  FIGS. 6A through 6D ) or friction-based attachment (e.g. screws). While a particular nesting force mechanism for the preferred embodiment has been illustrated, any of a plurality of different design solutions are considered to be well known and within the skill of the art. These include designs that are compact, mechanically simple, low-profile and integral to the assembly, and having no loose parts. 
     FIG. 5   a  shows the triply interlocking state of one set of teeth  18 ,  20  and  22  in a profile view. Related  FIGS. 5B through 5D  preserve this view orientation, showing each of these teeth separately. In this view orientation teeth profiles  18  and  22 , and notch  52  profile are shown simultaneously perpendicular to the drawing plane, and thus the principal axis of the invention. This is also the orientation required to machine them, e.g. using Computer Numerically Controlled (CNC) machining. Any circumferential indexing scheme may be used to machine each profile incrementally around the circumference of each ring  10 ,  12 , or  14 . Teeth profiles  18 ,  20  and  22  are thus designed to concurrently cooperate with each other. For example, surfaces  56  and  58  cooperate to form axial contact regions  32 , surfaces  64  and  66  cooperate to form rotational contact regions  36 , surfaces  80  and  82  cooperate to form axial contact regions  44 , and so forth. It should also be pointed out that although teeth  18  and  22  have simple profiles by design, notch  52  is explicitly designed to cooperate with them, and not tooth  20  per se. For this reason, tooth  20  does not have a simple profile. 
   In an alternative embodiment, radial tabs  28  and  30  of rings  10  and  12  protrude radially inward rather than outward. Thus, in order to engage them, locking ring  14  is internal to rings  10  and  12 , instead of external. 
   In a different alternative embodiment, rings  10  and  12  may be integral with their respective struts  16 , depending on the material selection and fabrication method. That is, ring  10  and strut  16  would comprise a single part, etc. For example, plastic injection molding, and even Micro-Electro-Machining Systems (MEMS) technology would support this topology. Of course, this integration could also be achieved using CNC machining techniques. 
   In a different alternate embodiment illustrated in  FIGS. 7A through 7D , circumferential tabs  24  and  26  may be shaped to snap together instead of or in addition to wedging, and similarly for the interface between teeth  22  and teeth  18 ,  20 . Such an embodiment may obviate the need to supply a separate nesting force to ring  14  (as shown in  FIGS. 6A-6D ). 
   In a different alternative embodiment (not shown), the triply interlocking condition is obtained by the concurrent cooperation of profiles of teeth  20 ,  22  and notches  50  together, rather than teeth  18 ,  22  and notches  52  together. 
   In a different alternative embodiment, illustrated in  FIGS. 8A through 8C , radial tabs  28  and  30  are omitted, transforming rings  10 ,  12  into rings  110 ,  112 . Also, Teeth  22  are elongated so that they may flex, and additional thickness is added on their inside ends, resulting in ring  114 , shown. When ring  114  is translated over engaged rings  110  and  112 , teeth  22  snap into the cavities of the engaged teeth of rings  110 ,  112 , locking them all together. This design may also obviate the need to supply a separate nesting force to ring  14  (as shown in  FIGS. 6A-6D ). 
   In a different alternative embodiment illustrated in  FIGS. 9A and 9B , ring  10  is provided with an integral o-ring groove  120 , transforming it into ring  116 . Also, ring  12  is provided with an integral sleeve (o-ring throat)  122 , transforming it into ring  118 . When rings  116  and  118  are engaged with an o-ring  124  installed in groove  120 , the coupling becomes liquid tight and can be used for fluid conduits, such as casings or risers in the oil industry. 
   In principle, the design of the invention permits the number of teeth  18  or  20  to be chosen freely as a design parameter. For example, the preferred embodiment illustrates a twenty-tooth configuration per ring, spaced at regular angular intervals. However, it should be noted that while this choice is arbitrary, two parameters may constrain it. These are the nominal magnitudes of the axial and circumferential engagement of teeth  18  and  20 . For example, if the axial engagement is on the order of ¼ inch, a circumferential engagement of two inches may be impractical. Also, a three inch diameter strut  16  will support a population of about twenty ¼ inch wide teeth per each ring  10  and  12 . Obviously, more teeth of the same size wouldn&#39;t fit, but a larger population of narrower teeth, or a smaller population of wider teeth might be less efficient in contributing to the total strength and stiffness of the assembly, for various reasons. 
   The preferred embodiment illustrates a regular angular interval of teeth  18  and  20 . This interval need not be regular, or it may be intermittently regular. The choice allows the angular orientation of engagement to be controlled. An example of this would be the field assembly of a positioning arm from a series of segments with couplings on the ends. A controlled assembly alignment would prevent mis-assembly of the arm; the latter would impair its function as a fiducial device. 
   The triply interlocking condition illustrated in  FIGS. 5A through 5D  implies that the profiles of sets of teeth  18  and  22 , and notches  52  need to be simultaneously perpendicular to a reference plane, and particularly the main axis of the invention, but this may not necessarily be so. So, for example, the orientation of axial contact regions  44  and  46  might not be mutually parallel to the same reference surface as for circumferential contact region  36  (in fact they might still function without being mutually parallel to any reference surface). Similar arguments can be made for the other cooperating surfaces without substantially altering the function or intrinsic attributes of the invention. The point is that small variations or permutations in cooperating surfaces (e.g.  32 ,  36 ,  44 ,  46 , etc.) can be made without affecting functionality. 
   A final point of clarification on the function of the wedge geometry of the invention should be made. The Quick Torque Coupling (QTC) is in principle an “exact-constraint” device. This means that it achieves its rigidity by removing exactly six degrees of freedom—three degrees of translation (in X, Y, Z) and three degrees of rotation (in XY, XZ, and YZ). As mentioned, this is to avoid any direct reliance on friction, clamping, or spring loading, because these methods can be unreliable and inaccurate in precision couplings, although they may be used to advantage to supply a secondary, nesting force to the locking ring. Therefore, the function of the wedging action between tabs and teeth as described herein is to sequentially eliminate axial, radial, and circumferential clearance, and therefore motion, between the coupling halves, and is categorically not used to retain the teeth by wedge friction, per se. 
   Accordingly, the reader will see that the invention provides a highly reliable precision coupling for the fast and easy assembly of precision portable positioning devices and space frames. The QTC requires no troublesome external tools to operate—it is completely self-contained. There is no risk of dropping a tool into a sensitive peripheral area, and assembly can be handled with gloved hands in difficult conditions. Because of it&#39;s easily verifiable “go” or “no-go” condition, the QTC eliminates uncertainty at assembly—it is clearly locked or unlocked. No gauging or torque wrenching is required. The QTC is compact and relatively light-weight. Because of it&#39;s triply interlocking teeth, the QTC is rigid. Also, it does not rely primarily on clamps, springs or friction based fasteners, which can fail in demanding situations. 
   While the above description contains many specificities, these should not be construed as limitations on the scope of the invention, but as exemplifications of the presently preferred embodiments thereof. Many other ramification and variations are possible within the teachings of the invention. Applications are also envisioned for tripods, sailboat and antenna masts, telescopes, flag poles, quick release couplings, tent poles, fishing rods, sign posts, MEMS devices, space station structures, and more. 
   Thus the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given above.

Technology Classification (CPC): 5