Abstract:
A reusable self-aligning precision latch, including a latch body for mounting a latch assembly, and an interface cone. A lead screw, coupled to the latch body on one end, pivots at an interface on the latch body allowing for self-alignment. A drive cam having a plurality of surfaces and positioned on the lead screw engages a plurality of linkage assemblies such that at least two links are driven. A flexure ball assembly clamped by the plurality of linkage assemblies to the latch body with a pivoting clamp plate such that all clamping forces between the pivoting clamp plate and the latch body are equalized. A motor for closing and opening the self-aligning precision latch by turning the lead screw to apply and release, respectively, the clamping forces between the pivoting clamp plate and the latch body.

Description:
FIELD OF THE INVENTION 
   This invention relates generally to actuated mechanical interlock mechanisms and, more particularly, to high reliability, high stability latching of deployable optical metering structures. 
   BACKGROUND OF THE INVENTION 
   To extend the range of astronomical telescopes, it is necessary to increase the effective aperture. This implies that larger diameter primary mirrors must be employed. The current state of the art has reached the practical size limit of monolithic mirrors. As a result, segmented primary mirrors that include multiple mirrored petals around a monolithic mirrored center segment have been devised. A space borne telescope employing segmented primary mirrors will require deployment once in orbit. Linear, stable, high stiffness precision latches, with high reliability values, should be used to interlock the metering structure, once the mirror is deployed, to maintain mirror performance. The probability of latch failure during system deployment has to be minimized to ensure mission success. Conventional latching technology, discussed in greater detail below, does not address the need for high stiffness, linearity, and precision in latches that are used for interlocking deployable space telescopes. Furthermore, latch technology, as used in satellite antennae, does not meet optical tolerance requirements. Satellite antennae latches often suffer from repeatability and stability problems that are typically two orders of magnitude below optical system requirements. 
   Conventional latching mechanisms are categorized either as a retaining type or a mating type latch mechanism. Retaining type latch mechanisms are preset in the latched position and released in their operating state. Examples of this type are illustrated in U.S. Pat. No. 4,682,804 issued Jul. 28, 1987 to William B. Palmer, et al., titled “Releasable Coupling Assembly and U.S. Pat. No. 4,508,296 issued Apr. 2, 1985 to Keith H. Clark, titled “Hemispherical Latching Apparatus.” These retaining latch mechanisms are used to retain payloads during transport, preventing damage due to shock and vibration. Remote release of the latch allows the payload to be removed from the support structure. High reliability and preload are their key performance features; not linearity, stability, or high stiffness precision. 
   Mating latch mechanisms are illustrated in U.S. Pat. No. 4,431,333 issued Feb. 14, 1984 to Joseph A. Chandler, titled “Apparatus For Releasably Connecting First And Second Objects In Predetermined Space Relationship and U.S. Pat. No. 4,905,938 issued Mar. 6, 1990 to Matthew Braccio et al. These mating latch mechanisms have male couplings that mate with female sockets. Latching occurs after the halves are mated and serve to connect two bodies after contact. These are used to grapple satellites for repair or connection of trusses where only low tolerance alignment is necessary. Again, no consideration is given to linearity, stability, or high stiffness, repeatability and precision of the connection. Consequently, there exists a need for latching mechanisms that are linear, stable, repeatable, and have high stiffness and precision. 
   SUMMARY OF THE INVENTION 
   The aforementioned need is met according to the present invention by providing a reusable self-aligning precision latch, including a latch body for mounting a latch assembly, and an interface cone as described herein. A lead screw, coupled to the latch body on one end, pivots at an interface on the latch body allowing for self-alignment. A drive cam having a plurality of surfaces and positioned on the lead screw engages a plurality of linkage assemblies such that at least two links are driven. A flexured ball assembly clamped by the plurality of linkage assemblies to the latch body, with a pivoting clamp plate, such that all clamping forces between the pivoting clamp plate and the latch body are equalized. A motor for closing and opening the self-aligning precision latch by turning the lead screw to apply and release, respectively, the clamping forces between the pivoting clamp plate and the latch body. 
   Briefly stated, the foregoing and numerous other features, objects and advantages of the present invention will become readily apparent upon review of the detailed description, claims and drawings set forth herein. These features, objects and advantages are accomplished by providing a high stability, high reliability ball-in-cone type latch mechanism designed specifically for large deployable optical systems. 
   ADVANTAGEOUS EFFECT OF THE INVENTION 
   The present invention has the following advantages: a high stability, high reliability, ball-in-cone type latch mechanism designed specifically for large deployable optical systems. The latch mechanism according to the present invention is well suited for use in the deployment of a segmented primary mirror comprising a plurality of petals surrounding a monolithic center segment. Additionally, the present invention provides a precision latch mechanism that can be used to interlock the metering structure of a segmented mirror, once the mirror is deployed to thereby maintain mirror performance. The precision latch mechanism according to the present invention has high repeatability along with linearity, stability, high stiffness and precision as a latch mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 ,  2 , and  3  are perspective illustrations of the latching sequence of the latch mechanism of the present invention in conjunction with an exemplary deployed member and an exemplary reference structure: 
       FIG. 4  is a perspective view of the latch and flexured ball assembly removed from the exemplary deployed member and the exemplary reference structure shown in  FIGS. 1 through 3 ; 
       FIG. 5  is a cross-sectional view of the latch mechanism and flexured ball assembly taken along line  5 — 5  of  FIG. 4 ; 
       FIG. 6  is an exploded perspective view of the spherical bearing assembly; 
       FIG. 7  is an exploded perspective view of the lead screw/cam assembly; 
       FIG. 8  is an exploded perspective view of the flexured ball assembly; 
       FIG. 9  is an exploded perspective view of the linkage assembly; 
       FIG. 10  is an exploded perspective view of the latch and flexured ball assembly of  FIG. 4 ; 
       FIGS. 11   a ,  11   b ,  11   c ,  11   d , and  11   e  are simplified elevational views of the latch and flexured ball assembly (showing only a single linkage assembly) illustrating the four basic kinematic stages of the latch operation; and 
       FIGS. 12   a ,  12   b ,  12   c ,  12   d ,  12   e , and  12   f  are simplified side elevational views of the lead screw/cam assembly in combination with a single coupler link illustrating cam/follower relationship for the six phases of the latching operation. 
   

   To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides a nearly perfect kinematic mount between structural or optical elements and can easily be remotely controlled. Clamping force and drive position feedback can be incorporated to allow controlled closure and continuous force monitoring during and after clamping. A minimum number of moving parts maintains reliability at a value of 0.9994 or better. When in the closed position, the interface consists of a ball captured between two conical surfaces. A novel flexured ball and floating clamp plate is attached to the structure being deployed. The latch base is equipped with a conical seat to accept the ball, and three clamp fingers grip the floating clamp plate once the ball is seated in the socket. A lead screw driven axial cam serves to drive the clamping mechanism into both a clamped and a retracted position. A four bar linkage is formed by the latch cam, coupler link, follower link, and seat. Once the follower link is grounded on the seat, the coupler link acts as a simple lever applying force to the clamp plate. Advantage is taken of the relatively large motion available from a four bar mechanism, as well as the mechanical advantage of a simple lever, once latching is initiated. Large clamping forces generated at the interface by the coupler are reacted at the seat, thereby providing high interface stiffness and linearity. No latching forces are transferred to the optical support structure. High interface clamping forces on the order of thousands of pounds can be achieved with low input torque at the lead screw by choosing appropriate cam angles. Employing a flat cam area at the end of travel eliminates the need for accurate final cam position. Choosing appropriate materials can eliminate thermally induced force variation. End mounting the lead screw in the latch seat with a spherical bearing compensates for part tolerances and equalizes clamp finger force during latching. Lobes on the upper cam surface and lower follower links provide a positive closure in the event that retention springs fail or debris prevents the pawls from moving into position properly. A high level of reliability is obtained by minimizing the number of moving parts. Limit sensors at extremes of cam travel and strain gauges on clamp arms can be provided to monitor operation during the latching procedure. 
   Referring to  FIGS. 1 through 3 , there are three distinct stages that occur during a deployment operation of a large optical system. A single corner of a typical deployed optical system is illustrated in  FIGS. 1 through 3 . During the first stage as illustrated in  FIG. 1 , the deployed member  10  has attached to it a flexured ball assembly  12 . The flexured ball assembly  12  (shown in greater detail in  FIGS. 4 and 8 ) is in alignment with a latch mechanism  14  (shown in greater detail in  FIGS. 4 and 5 ) which is mounted in a reference structure  16 . Any number of common methods can be used to maintain axial alignment. Latching pawls  18  are driven to their open position, providing clearance for the approaching flexured ball assembly  12 . As deployment proceeds, the flexured ball assembly  12 , makes contact with the latch mechanism  14  as shown in  FIG. 2 . Position sensing of the deployed member  10  is generally provided by an external system (not shown), and indicates when the flexured ball assembly  12  is in its mated position with latch mechanism  14 . At this point the latch mechanism  14  is actuated, which causes the latching pawls  18  to engage the flexured ball assembly  12 , as illustrated in  FIG. 3 . Applying a large force, typically about 1000 pounds, to seat the ball assembly  12 , completes the latching operation. 
   Turning to  FIG. 4 , a more detailed view is shown of the latch  14  and flexured ball assembly  12  removed from their respective structures  10  and  16 . Mounting plate  20  serves as the interface between the latch  14  and the reference structure  16  to which it is mounted. Drive motor  22  moves the latching pawls  18  in and out and supplies clamping force when the latching pawls  18  are in the latched state. The latch mechanism  14  is capable of locking the latching pawls  18  tightly in an open position as well as applying a large clamping force when the latching pawls  18  are in the fully latched position. The latching pawls  18  are supported within a latch body  24  to which mounting plate  20  is integral. 
   Referring next to  FIG. 5 , there is shown a cross-sectional view of the latch mechanism  14  and flexured ball assembly  12  taken along line  5 — 5  of  FIG. 4 . The center portion of latch body  24  provides the clamping force reaction structure as well as the lead screw spherical bearing seat  38   a  (as shown in  FIG. 6 ). The joint stiffness relative to the structure is controlled by the interface stiffness of mounting plate  20 . The actual latch stiffness is controlled by the interface characteristics of the ball seat  28 , clamp plate  30 , and ball  32 . Consequently, the latch mechanism  14  and flexured ball assembly  12  are generally made of a hard material. Although the ball seat  28  is shown as an insert in the latch body  24 , those skilled in the art will conclude that the ball seat  28  may be integral to the latch body  24 . 
   Still referring to  FIG. 5  and also  FIG. 6 , there is a spherical bearing assembly  34  attached to the latch body  24 . The spherical bearing assembly  34  is comprised of a spherical bearing  36 , bearing seat  38   a  centrally located on the bottom of latch body  24 , and bearing cup  38   b  on bearing housing  40 . The geometry of bearing seat  38   a  and bearing cup  38   b  is such that when bearing housing  40  is mounted on the base of the latch body  24  (see  FIG. 6 ), bearing seat  38   a  and bearing cup  38   b  provide a running fit with the spherical bearing  36 . Ball stem  42 , which is integral to lead screw  52 , extends through an axial bore  44  in the bearing housing  40 . The axial bore  44  is sized to clear the lead screw threads and allow up to 18° of tilt on the ball stem  42  in any direction. Material selection for bearing seat  38   a  (integral to latch body  24 ) and bearing cup  38   b  (integral to bearing housing  40 ) are typically hardened  440   c  stainless steel and must be different for the material for spherical bearing  36  (typically hardened M6 tool steel) to prevent micro welding at the contact area, which can occur if the lubricant migrates. Solid lubricants or low friction coatings may also be used on the contacting surfaces. 
   Referring to  FIG. 7 , the lead screw/cam assembly  48  is comprised of drive cam  50 , lead screw  52 , having a drive slot  139 , spring element  54 , motor coupling  56 , and motor coupling pin  60 . The drive cam  50  is preferably a hardened  440   c  stainless steel (or material dissimilar to the lead screw  52 ) and is threaded to mate with the lead screw  52  which is preferably made of hardened M6 tool steel. A fine pitch thread, typically  ¼–80 , is employed to provide great mechanical advantage and axial load bearing capabilities. Those skilled in the art will recognize the possibility of employing other thread types such as Acme geometry or a ball screw based on available motor torque, link geometry, and required clamping force. Optimization methods for these mechanisms are well known in the art. For wet lubricated interfaces red brass, beryllium copper, or titanium is employed for the drive cam  50 . Similar materials for the drive cam  50  and coupler links  64  (shown in  FIG. 5 ) may be employed if low friction coatings are applied to mating surfaces. Motor coupling  56  is internally threaded to match the thread of lead screw  52 . Motor coupling  56  is positioned on the lower end of lead screw  52  to serve as a limit or travel stop for drive cam  50  when the latch is in the full open state. Once properly located, motor coupling  56  is pinned in place to prevent rotational and axial movement when contacted by the lower surface of drive cam  50 . The lower surface  58  of the bearing housing  40  serves as an upper limit or travel stop for drive cam  50 . Motor coupling pin  60  serves to lock motor coupling  56  in place on lead screw  52 . The drive cam  50  is kept from rotating as the lead screw  52  turns via three anti-rotation flanges  62  that engage the latch housing  26  (shown in  FIG. 5 ). The latch housing  26  should be made be made from a material dissimilar to drive cam  50  (typically aluminum or magnesium alloy), or a low friction surface treatment may be employed. 
   Still referring to  FIG. 7  and also  FIG. 5 , lead screw  52  extends through drive cam  50 . The bottom of the lead screw  52 , to which is attached motor coupling  56  via drive slot  139 , interfaces with or is otherwise coupled to the drive shaft  68  of drive motor  22  (both are shown in  FIG. 5 ). Drive motor  22  (shown in  FIG. 5 ) is supported from motor mount  72  (shown in  FIG. 5 ) which is attached to the latch housing  26 . An inward radial force is applied to the coupler links  64  (shown in  FIG. 5 ) by a spring element  54 , which is mounted on the lower surface of drive cam  50 . The latch housing  26  also serves as an anti-rotation surface for the drive cam  50  and as a mounting surface for the motor mount  72 . Lead screw/cam assembly  48  resides inside of latch housing  26  and is integral to the spherical bearing assembly  34 . Drive cam  50  engages the actuating arms  76  of coupler links  64  to operate the latch (both are shown in  FIG. 5 ). 
   An exploded view of the flexured ball assembly  12  is shown in  FIG. 8 . The flexured ball assembly  12  comprises a flexured stem  80  including a cylindrical mounting shaft  82 , a clamp plate retaining flange  84 , a clamp plate centering shoulder  86 , and a threaded shank  88 . The cylindrical mounting shaft  82  is typically mounted in an interface block attached to a bipod flexure pair (not shown). Three such bipod flexure pairs constitute an arrangement well known in the art as a kinematic mount. Compliant member  90  is placed on threaded shank  88  and moved down until it meets the clamp plate retaining flange  84 . Clamp plate  30  is placed on the threaded shank  88  and also moved down to meet compliant member  90 . Ball  32  is then threaded onto threaded shank  88  and is tightened against clamp plate centering shoulder  86 . A diametrically located hole  92  is provided in ball  32  to allow the ball  32  to be pinned by drilling a hole through the threaded shank  88  after assembly. The geometry of the clamp plate centering shoulder  86 , clamp plate inner bore  94 , clamp plate conical surface  96 , and ball  32 , is such that compliant member  90  is only slightly compressed, keeping the clamp plate  30  perpendicular to the axis of flexured stem  80 , and clamp plate conical surface  96  in contact with the ball  32 . Clamp plate inner bore  94  is slightly larger than clamp plate centering shoulder  86  allowing the clamp plate  30  to tip about the axis with only a slight force on the edge of the clamp plate  30 . This “floating clamp” feature prevents locking in strains due to deployment mechanism misalignment or part dimensional variations in the latch. Ball  32  and clamp plate  30  are preferably made from hardened  440   c  stainless steel, since they define the clamped interface stiffness. Flexured stem  80  can be of any metal although a 400 series stainless steel is preferred. It is obvious to those skilled in the art that selection of low thermal expansion material may be employed to enhance dimensional stability. 
   Each coupler link  64  (shown in  FIG. 5 ) is part of a linkage assembly  100  as shown in an exploded view in  FIG. 9 . Each linkage assembly  100  is comprised of a coupler link  64 , follower link  102 , and upper pivot pin  106 . Upper pivot pin  106  inserts through bores  108  in follower link  102  and pivot bore  110  in coupler link  64 . Bores  108  in follower link  102  are sized to allow a press fit of upper pivot pin  106 . Bore  110  in the coupler link  64  is sized as a running fit with upper pivot pin  106 . All surfaces of coupler link  64  are treated with low friction coatings to maintain with low interface friction. High stresses in follower link arm  104  and coupler link  64  in the regions of the bores  108  and  110  require these to be made of a high tensile strength material such as hardened  440   c  stainless steel. Similarly, the pivot pin  106  is precision ground hardened tool steel. Pivot bar  112  maintains alignment of the follower link arms  104  during assembly and provides a pivot surface fitting in circular groves  39  (shown in  FIG. 6 ) in the latch body  24 . Mating circular groves  41  (shown in  FIG. 7 ) on the bearing housing  40  capture the pivot bar  112  when mounted to the latch body  24 . Each coupler link  64  has a latching pawl  18  that applies force to the clamp plate  30  (shown in  FIG. 8 ). When follower links  102  are grounded via nubs  114  on secondary cam  63 , (shown in  FIG. 7 ), each coupler link  64  forms a simple lever, where the lever arms are defined as the distance from the center of the pivot bore  10  to the end of the respective latching pawl  18 , and from the center of the pivot bore  110  to the cam follower  116  at the ends of actuating arms  76 . Tab  118  is provided to allow the coupler links  64  to be drawn into the open position. Tapering of each coupler link  64  provides a sliding surface for residence of spring element  54 , (shown in  FIG. 7 ), and allows the bending stiffness of the coupler link  64  to be controlled. The bending stiffness of coupler link  64  and the amount of deflection produced by drive cam  50  (also, shown in  FIG. 7 ) controls the force applied to the clamp plate  30 . Spring element  54  (shown in  FIG. 7 ) maintains contact of the coupler link  64  with the drive cam  50  throughout operation. Follower link  102  is equipped with nubs  114  that are engaged by the drive cam secondary surfaces  63  (shown in  FIG. 7 ) to insure positive positioning of the follower link  102 . 
   An exploded view of the complete latch of the present invention is shown in  FIG. 10  to illustrate the final assembly procedure. Internal subassemblies including the linkage assemblies  100 , lead screw/cam assembly  48 , and ball seat  28  are assembled onto the latch body  24 . Linkage assemblies  100  are pushed into upper clearance slots  134  in the mounting plate  20  until the pivot bars  112  can seat in the circular grooves  39  (shown in  FIG. 6 ) on the latch body  24 . Pivot bars  112  on follower link  102  (shown in  FIG. 9 ) are positioned in circular grooves  39  of the latch body  24 . Lead screw/cam assembly  48  is then mounted to the latch body  24  via the bearing housing  40 , capturing the three pivot bars  112  between circular grooves  39  and  41 . This creates a running fit between pivot bars  112  and circular grooves  39  and  41 . Ball seat  28  (shown in  FIG. 5 ) is also press fit into the axial bore  126  of latch body  24 . Clearance holes in the bearing housing  40  allow the lead screw/cam assembly  48  to be mounted to the bottom of the latch body  24  with screws. The assembled mechanism comprising the latch body  24  and ball seat  28 , linkage assemblies  100 , and lead screw/cam assembly  48 , is then inserted into latch housing  26 . Upper clearance slots  134  in the mounting plate  20  allow free movement of the linkage assemblies  100 . As the lead screw/cam assembly  48  is moved into place on latch body  24  coupler links  64  (shown in  FIG. 9 ) are interposed between the drive cam  50  surfaces and the spring element  54  (both are shown in  FIG. 7 ). Spring element  54  is placed therein to apply an inward radially directed force to the backs of coupler links  64 . Lower clearance slots  136  in the latch housing  26  allow the lead screw/cam assembly  48  to pivot radially about the spherical bearing  36  (shown in  FIG. 6 ) to accommodate mechanical misalignments during latching. The sides of lower clearance slots  136  provide a reaction surface for the anti-rotation flanges  62  (shown in  FIG. 7 ). Motor mount  72  spaces the drive shaft  68  from the end of lead screw  52  (shown in  FIG. 7 ). Preferably, a drive pin  137  extending from drive shaft  68  fits loosely into a drive slot  139  in the lead screw  52  (both are shown in  FIG. 7 ) to allow angular motion at the spherical bearing  36  (shown in  FIG. 6 ). The entire clamping mechanism is allowed to float within the latch housing  26 , allowing clamping to occur even if debris enters the system. 
   To better understand the functions of the individual latch parts, it is necessary to understand the basic kinematic stages of the latching operation. These are illustrated schematically in  FIGS. 11   a, b, c, d , and  e , by showing only one linkage assembly  100  on the latch housing  26 . It is assumed the flexured ball assembly  12  is seated in the latch housing  26  when the latching operation begins. The first stage, illustrated in  FIG. 11   a , shows latching pawl  18  in its widest position allowing clamp plate  30  of the flexured ball assembly  12  to easily move into the latch. Drive cam  50  on the lead screw  52  pulls the coupler link  64  into its lowest position. Contact between the drive cam  50  and coupler link  64  is maintained by the radially inward force from spring element  54 . A four bar linkage is formed by the drive cam  50 , lead screw  52 , coupler link  64 , and follower link  102  in this stage. At the second stage, shown in  FIG. 11   b , drive cam  50  has moved up on lead screw  52  toward the latch housing  26  to a point where nubs  114  almost contact secondary cam surface  63 . Further upward motion of the drive cam  50  initiates contact of the secondary cam  63  with the nubs  114  on follower link  102 . Even further upward motion forces follower link  102  into the position illustrated in  FIG. 11   c . At this third stage, drive cam  50  has moved further up on lead screw  52  toward the latch housing  26  allowing nubs  114  to move down the curved surface of secondary cam  63 , preventing the follower link  102  from moving back to a previous position. At this point the clamp plate  30  is considered captured. Although no force is being applied, the flexured ball assembly  12  cannot move out of the capture range of the latch. Grounding of the follower link  102  on secondary cam  63  via the nubs  114  degenerates the four bar linkage into a simple lever that is activated in the final latching stage by the drive cam  50 . 
   The end of the fourth stage of the latching process is illustrated in  FIGS. 11   d  and  11   e . Here, the drive cam  50  has moved nearly to its final position on the lead screw  52 . Movement of the coupler link  64  along the drive cam  50  initiates contact of latching pawl  18  with the clamp ring  30  and applies the full clamping force. In the final clamped position, illustrated in  FIG. 11   e , the cam  50  has moved to its final position on lead screw  52  and a full clamping force is applied. 
   Drive cam  50  is designed to have six distinct operating regions as illustrated in  FIGS. 12   a, b, c, d, e , and  f . The first state is shown schematically in  FIG. 12   a  where coupler link  64  and follower link  102  are fully retracted, putting the latch in its open position. The top of drive cam  50  is equipped with a flange  140  having a lip  142  that prevents tab  118  from leaving upper cam surface  144  as it is pulled down by lead screw  52 . Spherical bearing assembly  34  reacts to an initial upward force from the lead screw  52 , while spring element  54  applies a radially directed force on coupler link  64 . It is not necessary for cam follower  116  to be in contact with the surface of drive cam  50 . Secondary cam follower  160  at the end of nub  114  contacts the top portion of secondary cam surface  63 . In the event that spring element  54  does not have enough force to push follower link  102  and coupler link  64  into position, for example, if debris is in the interface, secondary cam surface  63  of cam  50  can force them into position. The second state is shown schematically in  FIG. 12   b ; where drive cam  50  has slightly moved up on the lead screw  52  to a point where tab  118  is still in contact with upper cam surface  144 , but has moved in radially from lip  142  to allow cam follower  116  to make positive contact with cylindrical surface  146  on drive cam  50 . Contact between coupler link  64  and cylindrical surface  146  is maintained by spring element  54  and contact between the secondary cam surface  63  and the secondary cam follower  160 . A slight downward force is applied to the spherical bearing assembly  34  by lead screw  52 . 
   The third state is shown schematically in  FIG. 12   c ; where drive cam  50  has moved up further along lead screw  52 . Cam follower  116  has moved from the cylindrical surface  146  to the steep tapered surface  148  on drive cam  50 , while tab  118  is no longer in contact with any surface. Spherical bearing  34  reacts only to a light upward force and spring element  54  maintains a radially directed force on coupler link  64 . Latching pawl  18  (shown in  FIGS. 11   a – 14   e ) closes on the clamp plate  30  (shown in  FIGS. 11   a – 11   e ) during this stage. When cam follower  116  reaches the end of the steep tapered surface  148 , the latching pawl  18  is in contact with the clamp plate  30 . Secondary cam follower  160  has moved down the secondary cam surface  63 . The four bar linkage degenerates into a simple lever at this stage since the follower link  102  is grounded to the secondary cam  63  via the nubs  114  of follower link  102 . 
   The fourth state is shown schematically in  FIG. 12   d ; where drive cam  50  has moved further up along lead screw  52 . Cam follower  116  has moved to the end of the steep tapered surface  148  on drive cam  50 . Secondary cam follower  160  is now contacting the side of secondary cam surface  63  preventing follower link  102  from releasing clamp plate  30  (shown in  FIGS. 11   a – 11   e ) even if a dislodging force is encountered on any of the three pawls. Spherical bearing assembly  34  still reacts only to a light upward force and spring element  54  is no longer needed to keep follower link  102  and coupler link  64  in position. 
   The fifth state is shown schematically in  FIG. 12   e ; where drive cam  50  has moved further up along lead screw  52  almost to its final position. Cam follower  116  has moved from the steep tapered surface  148  to a shallow tapered surface  150  on drive cam  50 . Displacement due to drive cam&#39;s  50  motion bends the coupler link  64  applying a high load on the clamp ring  30  (not shown). Spherical bearing  34  assembly reacts to a high downward force substantially greater than spring element  54 . When cam follower  116  reaches the end of the shallow tapered surface  150  the latching pawls  18  (shown in  FIGS. 11   a – 11   e ) generate the maximum force on clamp plate  30 . Use of a shallow taper gives a large mechanical advantage while clamping, thereby reducing the required motor torque for a desired clamping force. 
   The final state is shown schematically in  FIG. 12   f ; where drive cam  50  has reached its final position on lead screw  52 . Cam follower  116  has moved from the shallow tapered surface  150  to a lower cylindrical surface  152  on drive cam  50 . No changes in reaction forces are seen, since the coupler link  64  has experienced no further deflection on the lower cylindrical surface  152  than that seen at the end of the shallow tapered surface  150 . This eliminates the need to have a precise stopping point for the drive motor  22 , and allows motor slip to occur with out changing the clamping force. 
   The invention has been described with reference to one or more preferred embodiments. However, it will be appreciated that a person of ordinary skill in the art can effect variations and modifications, without departing from the scope of the invention. 
   PARTS LIST 
   
       
         10  deployed member 
         12  flexured ball assembly 
         14  latch mechanism 
         16  reference structure 
         18  latching pawl 
         20  mounting plate 
         22  drive motor 
         24  latch body 
         26  latch housing 
         28  ball seat 
         30  clamp plate 
         32  ball 
         34  spherical bearing assembly 
         36  spherical bearing 
         38   a  bearing seat 
         38   b  bearing cup 
         39  circular grooves 
         40  bearing housing 
         41  mating circular grooves 
         42  ball stem 
         44  axial bore 
         48  lead screw/cam assembly 
         50  drive cam 
         52  lead screw 
         54  spring element 
         56  motor coupling 
         58  lower surface of bearing housing  40   
         60  motor coupling pin 
         62  anti-rotation flange 
         63  secondary cam 
         64  coupler link 
         68  drive shaft 
         72  motor mount 
         76  actuating arm 
         80  flexured stem 
         82  cylindrical mounting shaft 
         84  clamp plate retaining flange 
         86  clamp plate centering shoulder 
         88  threaded shank 
         90  compliant member 
         92  hole 
         94  clamp plate inner bore 
         96  clamp plate conical surface 
         100  linkage assembly 
         102  follower link 
         104  follower link arm 
         106  upper pivot pin 
         108  bore 
         110  pivot bore 
         112  pivot bar 
         114  nubs 
         116  cam follower 
         118  tab 
         126  axial bore 
         134  upper clearance slot 
         136  lower clearance slot 
         137  drive pin 
         139  drive slot 
         140  flange 
         142  lip 
         144  upper cam surface 
         146  cylindrical surface 
         148  steep tapered surface 
         150  shallow tapered surface 
         152  lower cylindrical surfaced 
         160  secondary cam follower