Patent Publication Number: US-2023151918-A1

Title: Coupling device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Great Britain Patent Application No. 2116850.5 filed on Nov. 16, 2021, titled Coupling Device, the entire contents of which are hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     This invention relates to releasable mechanical couplings such as may be used to secure a cargo pod, package or other jettisonable item to an aircraft, for example to secure a cargo pod to a cargo delivery UAV. The invention is however of more general applicability, and can be used in a wide variety of circumstances where a releasable, easily mated, reliable, fixed mechanical connection is needed, for example between: a vehicle and a load (e.g. an ISO container and a flat bed truck or ship&#39;s cargo deck); between a vehicle and a fixed location (e.g. a submarine ROV and a docking fixture, or subsea work station); between two structures or objects (e.g. between stacked ISO containers on a cargo ship); between two vehicles or vehicle parts (e.g. between a tractor and trailer, between railway rolling stock, or between stages of a rocket); or between a machine and a replaceable/exchangeable machine tool (e.g. a machine platen and a mould or press tool), to name a few of a myriad of possible uses. 
     BACKGROUND OF INVENTION 
     GB859458 and US3883097 disclose ball lock releasable mechanical couplings of the kind in which locking balls are lockingly projectable from and retractable into apertures circumferentially distributed about a tubular member which itself projects from one of the parts or objects to be releasably coupled to another. The balls are releasably locked in their projecting position by a suitably profiled plunger slidable within the bore of the tubular member. In their projecting position, the balls are received in a circumferential groove or corresponding series of circumferentially spaced apertures formed in the side wall of a socket. This socket is formed in or attached to the other part or object to be coupled, for reception of the projecting tubular member. In each case the plunger is movable to its unlocked position by a powered actuator, such as by pyrotechnically generated or pneumatic gas pressure acting on a piston coupled to the plunger. The piston (or other suitable powered actuator) and the plunger may be integrally formed or connected to one another either directly or via a kinematic linkage. U.S. Pat. Nos. 4,523,731 and 3,596,554 disclose further examples of coupling mechanisms in which a plunger similarly moves between two different operative positions, so that the same profiled surface of the plunger interacts with locking balls, with movement of the plunger between the two positions in one direction moving the balls from a radially retracted, unlocked position to a radially extended, locking position, and movement of the plunger between the two positions in the other direction allowing the balls to move from their locking position back to their unlocked position. 
     To maintain the mechanical connection between the two releasably coupled parts or objects in normal use, the plunger may be biased towards its locked position. In any event, after the coupling has been released by operation of the powered actuator, the balls might be returned by the plunger to their projecting, locked positions. Therefore, to allow the releasable coupling to be made up or remade, in GB859458 manual means are provided for at least temporarily moving the plunger to the released position. Such means could also allow the manual release of the coupling independently of powered release. A manual release mechanism can be useful to circumvent the powered actuator when desired; but it can also present a serious safety hazard. Correct engagement and locking of the disclosed couplings is not completely straightforward either and requires some knowledge or training. Forcefully attempting to make up the couplings without ensuring that the plunger is in the correct, released, position could result in damage to the couplings, and even render them inoperative. 
     BRIEF STATEMENT OF THE INVENTION 
     To mitigate such problems, the present invention provides a coupling mechanism for securing a first object to a second object, the coupling mechanism comprising: a well formed in or securable to the first object; a lug formed on or securable to the second object, the lug being removably insertable in the well along an insertion axis; a shuttle movable within the lug along the insertion axis; first resilient biasing means arranged to bias the shuttle away from a base of the well when the lug is inserted in the well; a plurality of locking elements each movable radially in the lug with respect to the insertion axis, between a retracted position allowing free insertion and withdrawal of the lug into and from the well, and an extended position in which the locking element projects into a recess formed in a side wall of the well so as to lock the lug in the well; each locking element being both movable from the retracted position and retainable in the extended position by a first surface profile of the shuttle; 
     wherein the coupling mechanism comprises a movable stop having: a first position in which the biased movement of the shuttle along the insertion axis is limited so that the locking elements interact with the first surface profile of the shuttle, and a second position in which the biased movement of the shuttle along the insertion axis is extended to cause the locking elements to interact with a second surface profile of the shuttle whereby the locking elements move from their extended position to their retracted position, thereby allowing withdrawal of the lug from the well and disconnection of the first and second objects. 
     The stop is movable relative to the lug whereby, with the objects disconnected, it can be moved or set to the first position. This can also, where necessary, move the shuttle along the insertion axis to the position in which its first surface profile interacts with the locking elements. The lug is therefore set or returned to a condition in which inserting it into a corresponding well will cause each locking element to automatically lock into the associated recess in the well side wall. Following disconnection of the coupling mechanism, there is no need for any manual intervention to re-set the coupling mechanism ready for reconnection. For example, the stop can be moved from the first position to the second position (by a powered actuator or manually) when it is desired to disconnect the first and second objects, and the stop can be biased towards the first position so that the coupling mechanism is then automatically re-set ready for reconnection again. Or if a fail-safe condition demands disconnection of the coupling, the stop can be biased towards the second position and the powered actuator or manual means arranged to hold the stop in the first position against this bias. Or the stop can be moved between the first and second positions by a double acting powered actuator, e.g., a double acting powered actuator having two rest conditions corresponding to the first and second positions of the stop. 
     The movable stop may comprise a body slidable within the lug between the first and second positions and which can be selectively held at the first position and at the second position. 
     The shuttle is biased away from the base of the well by the first resilient biasing means. Thus, as the lug is inserted into the well, the first resilient biasing means acts on the shuttle. The first surface profile of the shuttle moves the locking elements outwards relative to the insertion axis and into contact with the well side wall. 
     Reaction from the locking elements onto the first surface profile also moves the shuttle together with the lug at this point. This causes compression of the first resilient biasing means as the lug continues to move into the well. When the locking elements draw level with the recessed part of the well side wall, they are pushed outwards into locking engagement therewith by the first surface profile. The shuttle can then move under the influence of the first resilient biasing means, outwardly of the well and inwardly of the lug, so that the first surface profile can hold the locking elements locked in the recessed part of the well side wall. 
     The first surface profile may comprise a slope which, with the coupling mechanism under a separation force or load and the movable stop moved towards the second position, allows the shuttle to be moved by the first resilient biasing means so that the locking elements interact with the second surface profile. The coupling mechanism will thereby uncouple reliably when under load, upon movement of the movable stop from the first position to the second position. 
     The coupling mechanism may comprise second resilient biasing means arranged to bias the shuttle away from the movable stop. These second resilient biasing means can still allow the stop to limit the biased movement of the shuttle along the insertion axis (e.g., by the movable stop abutting the shuttle). The locking elements therefore interact with the first surface profile when the lug is inserted into the well, and thus the locking elements hold the lug locked in the well. However, as the stop is moved towards the second position, the first resilient biasing means may cause the shuttle initially to “follow” stop, until the locking elements interact with the second surface profile of the shuttle and escape from the recessed part of the well side wall. The second resilient biasing means may then allow the stop to move away from the shuttle (creating a gap between these two parts) before the stop reaches the second position. When the locking elements have been released from within the well by interaction with the second surface profile, they are no longer subject to any radially inwardly directed reaction forces and therefore do not offer any significant resistance to movement of the shuttle along the insertion axis. Thus, when the lug has separated from the well and the stop is moved back to the first position, the gap now existing between the movable stop and the shuttle is not eliminated. Instead, the second resilient biasing means can apply a force on the shuttle outwardly along the insertion axis which is sufficient to move the shuttle so that the first surface profile (instead of the second) interacts with the locking elements. The coupling mechanism is thus automatically set or re-set, ready for automatic locking engagement by simple insertion of the lug into the well. 
     The first resilient biasing means may act between the shuttle and a plunger extending outwardly from the lug in the direction of the insertion axis. This can provide a robust construction in which the first resilient biasing means is internal to the lug, where it has greater protection from accidental damage. 
     The second resilient biasing means may act between the plunger and the stop. This is mechanically advantageous, as then the second resilient biasing means can be compressed by insertion of the lug into the well to reduce or eliminate the gap between the shuttle and the stop. The stop can therefore positively retain the first surface profile in interactive engagement with the locking elements. Moreover, with this arrangement the second resilient biasing means doesn&#39;t oppose operation of the first resilient biasing means. 
     The movable stop may comprise a (bistable) mechanism able to selectively hold it stably in either of its first and second positions. For example, the movable stop may comprise cam and a cam follower. Thus, with an appropriate cam profile, the movable stop may be self-locking in its first and second positions. Other appropriate known bistable mechanisms are available within the ordinary competence of the skilled person, for example overcentre-(toggle-) type mechanisms, latching mechanisms with multiple detents, worm-and-wheel drive mechanisms, etc. 
     The movable stop may be connected to a powered actuator or to manual actuation means either directly or by a kinematic linkage. This may enable the powered actuator or manual actuation means to be positioned at any convenient location on or in the second object (for example at a desired location in a cargo pod or vehicle), independently of the position of the lug thereon. 
     The coupling mechanism may comprise a plurality of the wells and a corresponding plurality of the lugs, each lug provided with movable stops and kinematic linkages as described above and connected in common to the powered actuator or manual actuation means. A single powered actuator or manual actuation means (or combinations thereof acting in parallel to provide redundancy in case of failure) may therefore simultaneously power and control the coupling and uncoupling of a number of spatially distributed lugs provided on the second object, with a corresponding number of complementary wells spatially distributed on the first object. A strong, stable, adaptable, versatile, and reliable power operated releasable mechanical coupling device may therefore be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention and some of its further optional features and advantages are described below with reference to illustrative embodiments shown in the drawings, in which: 
         FIG.  1    is a partly “see-through” perspective view showing the main components of a coupling mechanism embodying the invention; 
         FIG.  2    is a diagrammatic cross-sectional view showing a first in a sequence of stages of operation of the mechanism of  FIG.  1   , as a second object (e.g., a suspended cargo pod) is loaded onto, or offered up for mechanical connection with, a first object (e.g., a UAV); 
         FIG.  3    is another diagrammatic cross-sectional view showing a second in the sequence of stages of operation of the mechanism of  FIG.  1   , as the second object is loaded onto, or offered up for mechanical connection with, the first object; 
         FIG.  4    is another diagrammatic cross-sectional view showing a third in the sequence of stages of operation of the mechanism of  FIG.  1   , as the second object is loaded onto, or offered up for mechanical connection with, the first object; 
         FIG.  5    shows the mechanism of the preceding figures in a locked state, so that the first and second objects are mechanically locked together; 
         FIG.  5   a    is an enlarged illustration of a portion of the mechanism shown in  FIG.  5   ; 
         FIG.  6    is similar to  FIGS.  2 - 5   , but shows a first in a sequence of stages during release of the mechanism, for separation of the first and second objects; 
         FIG.  7    is similar to  FIGS.  2 - 5   , but shows a second in the sequence of stages during release of the mechanism, for separation of the first and second objects; 
         FIG.  7   a    is an enlarged illustration of a portion of the mechanism shown in  FIG.  7   ; 
         FIG.  8    is similar to  FIGS.  2 - 5   , but shows a third in the sequence of stages during release of the mechanism, for separation of the first and second objects; and 
         FIG.  9    shows a further embodiment of the invention, comprising a larger assembly of several coupling mechanisms each similar or identical to those shown in the preceding figures, interconnected by kinematic linkages so that all are operated in common by a single powered actuator. 
     
    
    
     DETAILED DESCRIPTION 
     The coupling mechanism  10  shown in  FIG.  1    comprises a housing  12  whose hollow interior forms the well  14 . The housing  12  may be fixedly secured to the first object  16  in any suitable manner, for example by a mounting flange  18  and suitable fasteners (not shown) received in holes  20 . Alternatively, the well  14  may be formed directly in the first object  16 . The lug  22  is shown in  FIG.  1    similarly mounted to the second object  24  by a mounting flange  26  with fastener holes  28 ; although once again this is not essential to the invention. Any suitable mounting method may be used, or the lug  22  may be integrally formed with the second object  24 .  FIG.  1    also shows illustrative examples of the cam and cam follower for the movable stop. In the example shown, the cam takes the form of a cam lever  30  and the cam follower takes the form of a cam follower arm  32 , each pivotally journaled to the lug mounting flange  26 . 
     The lug  22  is insertable into and withdrawable from the well  14  along the insertion axis, marked as A-A in  FIG.  2   . Also visible in  FIG.  2    are the shuttle  34 , the locking elements  36 , and the recess  38  formed in the side wall of the well  14 , into which recess the locking elements  36  will project when moved to their extended position (as further described below, with reference to later Figures of the drawings). In the example shown in the drawings, the locking elements comprise a plurality of separate locking balls  36 , each captively held in a respective “window” in the lug  22 , known as such e.g., from GB859458. However, the locking elements may take any suitable form, e.g., tapered, wedge-shaped, or other suitably shaped elements capable of interaction with the first and second surface profiles of the shuttle  34  and with the recess  38  to provide the required extension and retraction movements. The locking elements  36  may be separate bodies with no resilient links between them, as shown in the drawings. Or they may be mechanically linked, e.g., by mechanical springs or resilient bridging pieces (not shown), including integrally formed resilient bridges; such resilient mechanical links providing either contraction or extension bias, or both, during movement of the locking elements, as required. 
     The shuttle  34  is slidable in a bore  40  running axially through the lug  22 .  FIG.  2    shows the movable stop to comprise (in addition to the cam lever  30  and cam follower arm  32 ): a cam roller  42  journaled to the arm  32 , and a stop body  44  slidable in the bore  40  of the lug  22 . The plunger  46  is also shown, extending outwardly from the lug  22  in the direction of the insertion axis A-A. The plunger  46  is a close sliding fit in an axial bore formed through the shuttle  34 . It has an enlarged head portion projecting from the lug  22 . At the opposite end to the plunger  22 &#39;s head portion, the bore of the shuttle  34  has an inwardly projecting collar. The plunger  46  and shuttle  34  therefore define between them an annular chamber of variable length. The first resilient biasing means in this example take the form of a wave spring (compression spring)  48  housed in this annular chamber to act between the shuttle  34  and the plunger  46 . The plunger  46  may be retained in the shuttle  34  by a circlip (omitted in  FIG.  2    and other drawings, for simplicity), received in a circlip groove  50 . Also, in the illustrative arrangement shown in  FIG.  2   , the stop body  44  and the plunger  46  each contain an axial counterbore. The open ends of the counterbores are mutually adjacent. Each counterbore may therefore accommodate a respective end of the second resilient biasing means, which in this example takes the form of a coil spring (compression spring)  52 . For clarity and simplicity, only the extremities of this coil spring  52  are shown in full in  FIGS.  2  and  8   . Its central portion is indicated in these Figures by dotted lines. In  FIGS.  3 - 7   , the coil spring  52  is omitted altogether, again for clarity and simplicity.  FIG.  2    shows the coupling mechanism in its completely unlocked state, but during an initial stage of forming the locked mechanical connection between the lug  22  and the well  14  in the housing  12 . 
       FIGS.  2 - 4    show a sequence of stages of operation of the illustrative coupling mechanism as the lug  22  is inserted in the well  14  to form the mechanical connection, by appropriate mechanical handling or manipulation of the first and second objects. For example, where the first object ( 16 ,  FIG.  1   ) is a UAV and the second object ( 24 ,  FIG.  1   ) is a cargo pod releasably securable underneath the UAV, the cargo pod may be lifted towards the UAV airframe by independent ground service equipment. In  FIG.  2   , the lug  22  is shown being maneuvered or inserted into the well  12  but has not yet made any physical contact or locking engagement with it. To make the lug  22  easier to guide and manoeuvre into the well  14 , both of these components have complementary tapered or generally frustoconical surface profiles. 
     In  FIG.  3   , the lug  22  is shown inserted further into the well  14  (in comparison to  FIG.  2   ), to the point at which the plunger  46  has just made contact with the base  54  of the well  14 . From this point on in the insertion sequence, further movement of the lug  22  into the well  14  in the direction of the insertion axis A-A, will cause compression of the second resilient biasing means (coil spring  52 ,  FIG.  2   ), which has one end braced against the base  54  of the well  14  via the plunger  46 , and the other end braced within the stop body  44 . During the insertion sequence of  FIGS.  2 - 4   , the stop body  44  is held and locked stationary within (to advance together with) the advancing lug  22 , by the cam roller  42  and a constant radius lobe  56  of the cam lever  30 . The stop body  44  and the movable stop  30 ,  32 ,  42 ,  44  are then in the first position, in which the biased movement of the shuttle  34  along the insertion axis A-A is limited so that the locking elements  36  interact with the first surface profile of the shuttle  34 . The axial limits of this first surface profile are indicated by the references a and b in  FIG.  5   a   . Immediately or soon after the plunger  46  encounters the base  54  of the well  14 , the locking elements  36  will begin to ride up along an adjacent sloping surface  58  forming part of the first surface profile of the shuttle  34 . At this time the shuttle  34  is held stationary relative to the plunger  46  against the circlip in the groove  50  by the first resilient biasing means (wave spring)  48 , which is able to overcome the weight of the locking elements  36  and any slight frictional forces between them and the apertures which house them in the lug  22 . The locking elements  36  are therefore cammed radially outwards by the surface  58  until they encounter the inner wall of the well  14 . Further advancement of the lug  22  into the well  14  then causes the locking elements  36  to be cammed radially inwards again by the sloping surface of the well  14  as this approaches the correspondingly sloped surface of the lug  22 . At this point the plunger  46  is stationary within the well  14 , so the locking elements  36  now push the shuttle  34  along the plunger  46  to compress the first resilient biasing means (wave spring)  48 . 
     As the locking elements  36  draw level with the recess  38  in the well side wall, the wave spring  48  (first resilient biasing means) has been compressed close to its solid condition. This is the configuration of the locking mechanism shown in  FIG.  4   . The wave spring  48  is therefore able to expand and drive the shuttle  34  back inwards along the plunger  46  so that the sloping surface  58  cams the locking elements into the recess  38 . Under the continued influence of the wave spring (first resilient biasing means)  48 , the shuttle then snaps into place behind the locking elements  36 , so that a locking surface  60  on the shuttle (which locking surface makes up the remainder of the first surface profile) rests radially inward of each locking element  36 . The locking elements are therefore lockingly retained in the recess  38 . The lug  22  is therefore lockingly held in the well  14 . This is the condition of the locking mechanism  10  shown in  FIG.  5   . In fact, for reasons explained later, the surface  60  may be provided with a slight reverse camber or taper in comparison to the camber or taper of surface  58 , as represented by the angle α shown in  FIG.  5   a    (which is an enlarged view of the relevant portion of  FIG.  5   ). Loads tending to pull the lug  22  out of the well  14  will therefore (as explained later) cause the locking elements  36  to exert a small net force on the shuttle  34  along the insertion axis A-A in this pull-out direction. However, during insertion of the lug  22  into the well  14  as shown in  FIGS.  2 - 5   , the plunger  46  has been pushed into the lug  22  against the bias of the second resilient biasing means (coil spring)  52 . This is sufficient to eliminate the gap  62  which exists between the shuttle  34  and the stop body  44  when the locking mechanism is set in its unlocked state but primed ready for locking insertion into the well  14  (see  FIG.  2   ). Therefore, in the locked state as shown in  FIG.  5   , when the shuttle  34  snaps into place behind the locking elements  36 , it rests against and is supported by the stop body  44 , which in turn is locked in place by the cam roller  42  and the cam lever  30 . The shuttle  34  therefore cannot move along the axis A-A in the lug pull out direction and the locking elements  36  are held stably in their locking position projecting into the recess  38 . 
     To release the locking mechanism  10  and separate the first and second objects  16 ,  24  from one another, the cam lever  30  is pulled in the direction of arrow A as shown in  FIG.  6   . For example, the cam lever  30  may be connected to a powered actuator, or may be actuated in any other suitable way, including by manual means. For example, at its simplest, such manual actuation means may comprise a suitable knob or handle (not shown) directly formed by, connected to, or mounted on the cam lever  30 . Alternatively, the manual actuation means, or powered actuator may be connected to the cam lever  30  by a kinematic linkage (not shown). Powered actuation and/or the use of a kinematic linkage allows the lug  22  to be positioned at some distance from the operator if required. For the purposes of illustration, the cam roller  42  is shown separated from the cam lever  30  in  FIG.  6    but in practice as inertial, weight, friction and damping effects will be negligible, the cam roller  42  will in fact remain in contact with the cam lever under the influence of the second resilient biasing means (coil spring)  52 . The cam roller will therefore drop down off the lobe  56  and onto a smaller radiused portion  64  of the cam lever  30 &#39;s cam profile. Again, under the influence of the second resilient biasing means (coil spring)  52 , the stop body  44  will follow the cam roller  42  and move along the insertion axis A-A away from the well  14 . This is the situation shown in  FIG.  7   . 
     For illustrative purposes,  FIG.  7    shows the shuttle  34  still in its locked position, with a relatively large gap opened up between the adjacent surfaces of the shuttle  34  and the stop body  44 . However, in practice in most cases the shuttle will remain in contact with and move in unison with the stop body  44  during the initial part of the stop body  44 &#39;s movement along the insertion axis A-A away from the well  14 . This is due at least in part to the influence of the first resilient biasing means (wave spring)  48  on the shuttle  34 . However, it may also be partly due to any separation forces acting between the first and second objects  16 ,  24  also acting on the reverse cambered locking surface  60  of the shuttle  34  via the locking elements  36 . Such a separation force may arise for example from the weight of the second object  24  if it is suspended from the first object  16  via the coupling mechanism  10 . As can be seen from the enlarged portion of  FIG.  7    shown in  FIG.  7   a   , the eccentric loading p, q (arising from the separation load) at the corresponding contact patches between each locking element  36  and the housing  12  and lug  22  respectively, imposes a moment on the locking element  36  which in turn generates a further contact force pair r at a contact patch between the locking element and the lug  22 , and a still further contact force pair s at a contact patch between the locking element and the locking surface  60  of the shuttle  34 . As the locking surface  60  is at an angle α to the insertion axis A-A, although radial components of the contact forces s will cancel each other out, axial components of these forces will sum to act on the shuttle  34 , pushing it away from the well  14  along the insertion axis A-A. This force may counteract any tendency for the shuttle  34  to jam under the radial forces imposed on it by the locking elements  36 . 
     When the shuttle  34  reaches the circlip in the groove  50 , it ceases to move along the plunger  46 . The stop body  44  however continues to move away from the plunger  46  under the influence of the second resilient biasing means (coil spring)  52 . A gap  66  therefore opens up between the shuttle  34  and the stop body  44 . This is the situation shown in  FIG.  8   . In this Figure together with  FIG.  7   a   , it can also be seen that due to movement of the movable stop  30 ,  32 ,  42 ,  44 , the locking elements  36  no longer interact with the first surface profile of the shuttle  34 , but now interact with the second surface profile of the shuttle  34 . The axial limits of this second surface profile are indicated by the references b and c in  FIG.  7   a   . The second surface profile includes a groove  68  of part circular or other cross-section of complementary shape to the locking elements  36 . This groove  68  extends circumferentially of the shuttle  34 . With the plunger  46  in contact with the base  54  of the well (see  FIG.  7   ) and the shuttle  34  against the circlip in groove  50  (see  FIG.  8   ), the shuttle groove  68  lies adjacent to the locking elements  36 . Pulling the lug  22  from the well  14  therefore can now cam the locking elements  36  out of their position extending into the recess  38 , so that they retract into the shuttle groove  68 , and allow the lug  22  to be fully withdrawn from the well  14 . This is the configuration of the coupling mechanism  10  shown in  FIG.  8   . 
     Then if the cam lever  30  is returned to the first position as shown in  FIG.  2   , the remainder of the movable stop comprised by the cam follower arm  32 , cam roller  42  and stop body  44  is likewise moved to the first position as shown in  FIG.  2    as the cam roller  42  moves back onto the lobe  56 . The second resilient biasing means (coil spring  52 ) acting via the plunger  46  and circlip in the groove  50  is strong enough to push the shuttle  34  past the locking elements  36 , whereby the locking elements no longer interact with the second surface profile of the shuttle  34  but once again interact with the first surface profile of the shuttle  34 . In particular, the locking elements move out of the shuttle groove  68 , and back behind the sloping surface  58  of the shuttle  34 . The locking mechanism  10  is therefore returned to the configuration shown in  FIG.  2   , in which it is set in its unlocked state, but primed ready for locking insertion into the well  14 . Use of the locking mechanism  10  is therefore straightforward and relatively fool proof for the operator. With the coupling mechanism  10  locked, moving the cam lever  30  from the position shown in  FIG.  5    to the position shown in  FIG.  6   , uncouples the coupling mechanism  10 . Then moving the cam lever  30  back to the position shown in  FIG.  1    (i.e., the same position as shown in  FIG.  5   ) automatically re-sets the coupling mechanism  10  to automatically lock by simply inserting the lug  22  into the well  14 . 
     On the other hand, if the coupling mechanism  10  is operated by:
         (a) inserting the lug  22  into the well  14  with the movable stop (cam lever  30 , cam roller  42 , cam follower arm  32 , and stop body  44 ) in the position shown in  FIG.  8   ,   (b) holding the lug in the well (e.g., using ground handling equipment in the case of a lug attached to a cargo pod being connected beneath a UAV), and then   (c) moving the cam lever  30  to the position shown in  FIG.  5   ,       

     this will still result in correct locking engagement of the coupling mechanism  10 . The cam lobe  56  will drive the stop body  44  towards the well  14  via the cam roller  42 , compressing the second resilient biasing means (coil spring  52 ) and initially eliminating the gap  66 . Continued movement of the stop body  44  towards the well  14  then urges the shuttle  34  further into the well  14 . The locking elements  36  are thereby cammed out of the groove  68  and into the recess  38 , whereupon the locking surface  60  on the shuttle  34  and the lobe  56  on the cam lever  30  hold the locking elements  36  in the recess  38 . 
     The coupling mechanism therefore comprises a movable stop having a first position in which the locking elements interact with the first surface profile of the shuttle, and a second position in which the biased movement of the shuttle along the insertion axis is extended to cause the locking elements to interact with a second surface profile of the shuttle whereby the locking elements move from their extended position to their retracted position. Thus, in the illustrated embodiments, the shuttle  34  transitions between three different operative states: a fully “up” position relative to the remainder of the lug, as shown in  FIGS.  2 - 4   ; a mid- or locking position as shown in  FIG.  5   , and a fully “down” position, as shown in  FIG.  8   . As the shuttle  34  transitions between the fully up and the mid-positions, its first surface profile a-b ( FIG.  5   a   ) interacts with the locking balls  36 . As the shuttle  34  transitions between the mid-position and the fully down position, its second surface profile b-c ( FIG.  7   a   ), separate and distinct from the first surface profile a-b, interacts with the locking balls  36  whereby the locking elements move from their extended position to their retracted position. 
     In the prior art, in contrast, the plunger interacting with the locking balls (or like elements) transitions between only two operative positions and the locking balls interact with only a single surface profile of the plunger. There is no third operative position of the plunger and hence no second or further surface profile (distinct from the first) which allows movement of the locking elements from their extended position to their retracted position. 
       FIG.  9    shows a coupling mechanism  100  which includes a kinematic linkage operatively interconnecting four wells  14  and four lugs  22 , which wells and lugs as such may be in accordance with the invention as described above. Other numbers of wells and numbers of complementary lugs may clearly be provided by appropriate adaptation of the arrangement shown, within the ordinary competence of those skilled in the art. Cam levers  30  of the movable stops of each lug  22  are connected to corresponding crank levers  70   a  and  70   b  by connecting rods  72   a   1 ,  72   a   2 ,  72   b   1 , and  72   b   2 . The connections at each end of each connecting rod  72   a   1 ,  72   a   2 ,  72   b   1 ,  72   b   2  may comprise for example a clevis and pivot pin (or other suitable pivot connection) represented diagrammatically in  FIG.  9    by a small solid circle. The crank levers  70   a  and  70   b  are interconnected by a torsion shaft or tube  74  journaled in bearings  76 . These bearings may be mounted to the second object (for example the frame or chassis of a detachable cargo pod, not shown in  FIG.  9   ), together with the lugs  22  and their associated movable stops/cam levers  30 . The wells  14  may be formed in the first object (for example the airframe of a UAV, not shown in  FIG.  9   ) or may be formed in housings  12  attached to the first object. The crank lever  70   a  has an extension  78  at one end. A powered linear actuator  80  is mounted to the second object. A further connecting rod  82  is connected to the linear actuator  80  at one end and to the crank lever extension  78  at its other end, by suitable pivot connections, e.g., devises and pivot pins. Activation of the actuator  80  extends the rod  82  and therefore moves all of the cam levers  30  from their locking to their unlocking position. The lugs  22  are thereby disconnected from their wells  14 , allowing separation of the first and second objects. The actuator  80  may be replaced or supplemented by a manual actuation lever or other suitable manual actuation means for moving the connecting rod  82 , crank levers  70   a ,  70   b  or other parts of the kinematic linkage, to move the cam levers  30  between the locked and released positions as required. The cam levers  30 , connecting rods  72   a   1 ,  72   a   2 ,  72   b   1 ,  72   b   2 ,  82  and/or the torsion shaft  74  may be resiliently biased towards the locking position, for example by suitably arranged mechanical springs operatively connected to the kinematic linkage. The crank lever  70   b  may be provided with an extension, connecting rod, and powered linear actuator similar to those  78 ,  82 ,  80  associated with the crank lever  70   a . The two powered linear actuators can provide redundancy in case one of the actuators should fail. Additionally, or alternatively, powered linear actuators may be connected for direct operation of one or more or all of the cam levers  30 . Additionally, or alternatively, rotary powered actuators can be arranged to move one or more or all of the cam levers  30  and torsion shaft  74  from their locking to their unlocking positions. Where each cam lever  30  has its own associated powered actuator, further elements of the kinematic linkage may be omitted (although presence of the kinematic linkages may help to ensure co-ordinated simultaneous operation of the individual lugs and hence clean release of the coupling). 
     Further variants and modifications will be readily apparent to those skilled in the art. For example, the powered linear actuator  80  may be replaced by a double acting powered linear actuator, in which case the resilient biasing means of the kinematic linkage may optionally be omitted. Alternatively, where a fail-safe condition demands disconnection of the coupling, the linear actuator  80  and at least a part of the further connecting rod  82  may be replaced by resilient biasing means urging the crank lever  70   a  in the unlocking direction. A powered actuator or manual actuation means (linear or rotary) can then be provided for moving the crank lever  70   a  to the locking position when it is desired to maintain the first and second objects mechanically locked together. Corresponding modifications to the other actuator powered arrangements described above can be readily conceived by those skilled in the art in the event that fail safe separation of the objects is required. In any case, the powered actuators may be of any suitable kind, for example electrically, pyrotechnically, pneumatically (gas pressure) or hydraulically (incompressible fluid pressure) operated. Force/torque transmitting components of the above-described kinematic linkage may be partially or wholly replaced by other suitable kinds of force/torque transmitting mechanisms or components, for example by cables, and/or Bowden cables, and/or hydraulic and/or pneumatic arrangements with master and slave cylinders, and/or gears, drive belts, drive chains, etc.