Abstract:
A nut assembly includes a base plate and a nut. The base plate includes a bearing surface with bore for the passage of a bolt or the like therethrough. The nut includes a bearing surface engaged with the bearing surface of the base plate. The said nut includes a bore engageable with a bolt or the like passing through the bore of the base plate. The base plate may include foot members disposed around the bore of the base plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application claims the benefit of Provisional Application No. 60/397,008, filed Jul. 19, 2002, and titled SELF-ALIGNING NUT PLATE. 

   FIELD OF THE INVENTION 
   The present invention relates generally to fasteners and more specifically to a self-aligning nut plate for installation on contoured surfaces. 
   BACKGROUND OF THE INVENTION 
   One of the most common mechanical fastening methods is the bolted joint. In this type of joint, a first object and a second object are pulled together by means of an externally-threaded bolt mated to an internally-threaded nut. Generally, the bolt passes through a hole in each of the two objects, with the inner face of the bolt head seating against the outer surface of one of the objects and the inner face of the nut seating against the outer face of the remaining object. Often, a washer will be placed under either one or both of the bolt head and/or nut in order to protect the surface of the objects. 
   The bolted joint has enjoyed a great deal of success as a fastening method, and has been employed in all manner of mechanical devices and structures. Where a bolted joint is anticipated as the preferred method of attachment, one or both of the objects to be secured together will be “counter-bored” or “spot-faced” on one or both of the faces mating with the bolt and nut so as to provide a pair of flat, parallel surfaces suitable for maximum mechanical integrity. 
   One rationale behind the counter-boring and spot-facing operations is that bolts are generally very strong in pure tension. As bending loads are imparted to a bolt, however, strength may be reduced. While pure tension loading imparts a uniform stress across the cross-sectional area of the bolt, bending load represents a concentration of tensile load on one side of the bolt, and a corresponding concentration of compressive loading on the opposite side. In severe cases of misalignment, a bolt may experience a sufficient bending load that mechanical failure occurs. 
   In order to prevent the impartation of bending load to mechanical fasteners, a number of methods have been devised for creating and maintaining a parallel geometry. These methods include the introduction of shims in between the fastener head and a non-parallel surface in order to create a parallel geometry. Each of these methods has a number of drawbacks. For example, where shims are used, there is the potential that one or more shims may come loose at an inopportune time. Further, the use of shims requires that maintenance personnel maintain extremely close attention to the type and number of shims used during disassembly and reassembly. 
   SUMMARY OF THE INVENTION 
   The present invention provides a nut assembly incorporating a base plate having a planar surface, a central bore through the planar surface, a spherical bearing surface disposed around the central bore and a plurality of feet disposed about the central bore. The nut assembly also includes a captive nut having a bolt hole in the center thereof and a bearing surface having a spherical profile. The captive nut is held in engagement with the spherical bearing surface of the base plate. 
   More particularly, the present invention may provide a nut assembly incorporating a generally-triangular base plate having a planar top surface, a planar bottom surface, and a central bore passing from the top surface to the bottom surface. The base plate has a bearing surface, having a spherical profile, disposed around the top edge of the central bore, and three feet, each of which is disposed about the central bore at one corner of the generally-triangular base plate. The nut assembly also includes a captive nut, disposed on the top side of the base plate, having a bore through the center thereof, and a bearing surface, having a spherical profile, disposed against the bearing surface of the base plate. 
   The present invention may provide a nut assembly incorporating a cage having a substantially-planar top surface, a central fastener bore, and three outboard feet, disposed regularly about the central fastener bore. The nut assembly incorporates a seat washer having a substantially-planar bottom surface, disposed against the top surface of the cage, and an inner bearing surface having a spherical profile. The nut assembly incorporates a captive nut having a central fastener hole and a lower bearing surface having a spherical profile. Finally, the nut plate assembly incorporates a lock ring, disposed against a top surface of the captive nut so as to retain the captive nut within the cage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a nut plate and bolt assembly in accordance with one embodiment of the present invention. 
       FIG. 2  is a perspective view of a nut plate and bolt assembly in accordance with one embodiment of the present invention. 
       FIG. 3  is a top view of a nut plate in accordance with one embodiment of the present invention. 
       FIG. 4  is a side view of a nut plate in accordance with one embodiment of the present invention. 
       FIG. 5  is a side section view of a nut plate and bolt assembly in accordance with one embodiment of the present invention. 
       FIG. 6  is a perspective view of a nut plate assembly in accordance with a second embodiment of the present invention. 
       FIG. 7  is a top view of a nut plate assembly in accordance with a second embodiment of the present invention. 
       FIG. 8  is a side view of a nut plate assembly in accordance with a second embodiment of the present invention. 
       FIG. 9  is a side section view of a nut plate assembly in accordance with a second embodiment of the present invention. 
       FIG. 10  is a perspective view of a third embodiment of the present invention. 
       FIG. 11  is a second perspective view of the embodiment shown in  FIG. 10 . 
       FIGS. 12 and 13  are perspective views of a seat washer and captive nut subassembly according to certain embodiments of the present invention. 
       FIG. 14  is a perspective view of a locking pin according to certain embodiments of the present invention. 
       FIG. 15  is a perspective view illustrating a use of a nut plate according to the present invention. 
       FIG. 16  is a top view of the arrangement of  FIG. 15 . 
       FIG. 17  is a sectional view taken along line  17 - 17  of  FIG. 16 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts, which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     FIGS. 1 and 2  are perspective views of a nut plate assembly  100  in accordance with one embodiment of the present invention.  FIGS. 3 ,  4 , and  5  are top, side, and side section views, respectively, of the nut plate assembly of  FIGS. 1 and 2 . Nut plate assembly  100  incorporates a generally-triangular base plate  102  having a substantially planar bottom surface  104  and a substantially planar top surface  106  substantially parallel to bottom surface  104 . Disposed in the center of the base plate  102  is a central bore  107  having a central axis  122  extending substantially orthogonally to the planes of bottom surface  104  and top surface  106 . 
   At each corner of the base plate  102 , a fastener hole  108  passes through the base plate  102 , along a central axis  124  extending substantially orthogonally to the planes of bottom surface  104  and top surface  106 . A raised foot  109  protrudes from the bottom surface  104  around each of the fastener holes  108 . Together, these three raised feet  109  provide three supports for stable registration against three points on either a planar or a non-planar surface. A captive nut  110  is disposed within the center of the nut plate assembly  100 . Captive nut  110  has a threaded hole  128  in the center, for retention of a portion of a fastener, such as the shank  112  of bolt  111 . Head  114  of bolt  111  is of a common type having a hexagonal shape and a size larger than the cross-sectional diameter of shank  112 , but a variety of fasteners may be used in place of bolt  111  without departing from the spirit and scope of the present invention. 
   Captive nut  110  is held in place between the base plate  102  and a nut cage  116 . A set of three nut cage supports  115 , extending from the sides of the base plate  102 , connect the base plate  102  and the nut cage  116 . In the design shown in  FIGS. 1–5 , the nut cage  116  has a hemispherical outer profile, but this shape may vary depending on the application without departing from the spirit and scope of the present invention. 
   As seen most clearly in  FIG. 5 , although the captive nut  110  is held in place between base plate  102  and nut cage  116 , it has a partially-spherical outer profile, so that it is relatively free to rotate about its center point, which lies on or near the central axis  122  of the central bore  107  in the base plate  102 . As can be seen in  FIG. 5 , the central axis  126  of the captive nut  110  may be disposed at a significant angle to central axis  122 . In one embodiment, an angle as large as 10 degrees may be accommodated. As the bolt  111  is tightened into the threaded hole  128  in captive nut  110 , the captive nut bearing surface  130  is brought into engagement with base plate bearing surface  132 , both of which follow a spherical profile. As the captive nut bearing surface  130  begins to exert force against base plate bearing surface  132 , the raised feet  109  exert force on the surface (not shown) against which the nut plate assembly  100  is seated, thereby securing the assembly. 
   With the above-described arrangement, the generally triangular shape of the nut plate assembly  100  allows for a three-point contact against a contoured or non-planar surface. These three points establish a plane against which the nut plate assembly  100  securely registers. With this type of nut plate assembly  100 , it is possible to install fasteners on contoured surfaces without any necessity for shimming during the installation process. Nut plate assembly  100  also allows the mounting of components having flat bases against contoured surfaces without special provisions for mounting fasteners not normal to the contoured surface. 
     FIG. 6  is a perspective view of a nut plate assembly in accordance with a second embodiment of the present invention.  FIGS. 7–9  are top, side and side section views of the nut plate assembly of  FIG. 6  in accordance with a second embodiment of the present invention. Nut plate assembly  200  is constructed of a nut plate cage  202  containing a captive nut  210  seated against a seat washer  230  and retained by a lock ring  222  having a y-shape. 
   Nut plate cage  202  incorporates a base portion having a substantially-planar bottom surface  204 , a substantially-planar top surface  206 , and three fastener bores  208 , each disposed about a bore axis  248 . In one embodiment, the bore axes  208  lie in separate planes coincident with the principal axis  240  of the central bore (not shown) and disposed at 120 degrees to one another. Adjacent to each of the three fastener bores  208  is a foot  244  extending from the fastener bore  208  toward the center of the nut plate cage  202 . Feet  244  are designed to be relatively readily-deformable, in order to conform to the surface against which the nut plate assembly  200  is secured. 
   The nut plate cage  202  has a central bore (not shown) in the bottom thereof to allow for passage of a central fastener through the bottom of the nut plate cage  202 . This bore extends along the principal axis  240  extending from the center of the nut plate cage  202  and generally orthogonally to the planes of the bottom surface  204  and top surface  206 . 
   At three edges of the base portion, a set of bends  214  transition into three substantially-planar cage sides  216  having inner and outer surfaces disposed substantially orthogonally to the bottom and top planes  204  and  206  of the lower portion of cage  202 . In or near the center of each side is a cutout  218 . At the top of each cage side  216 , there is a pair of shoulders  220  shaped and sized to receive a portion of the ring loops  224  of the lock ring  222 . The inner portions of the lock ring  222  incorporate retaining segments  226 , which register against the top surface of the captive nut  210 , preloading it against the seat washer  230 . 
   The captive nut  210  has a hole  232  down its center for accommodation of a fastener (not shown). Depending on the application, the fastener may engage the hole by means of threads, or may be attached by other means. As with nut plate assembly  100  shown in  FIGS. 1–5 , captive nut  210  is held in place by lock ring  222 , but is free to rotate around its center point through a limited range of motion due to the employment of mating surfaces having spherical profiles. The range of motion of the captive nut  210  is limited in part by locking pins  234  extending outward from captive nut  210  and through cutouts  218  in cage sides  216  along pin axes  242 . In the embodiment shown in  FIGS. 6–9 , the pin axes  242  are disposed at approximately 120 degrees to one another. As the captive nut  210  is rotated about an axis, locking pins  234  move within cutouts  218  until the motion of one or more of locking pins  234  is impeded by the edge of the cutout  218  within which it moves. 
   As seen in  FIG. 9 , the bottom bearing surface  250  of captive nut  210  seats against inner bearing surface  252  of the seat washer  230 . The bottom surface  246  of seat washer  230  rests on the top surface  206  of the nut plate cage  202 , but is free to slide across the top surface  206 , so as to accommodate a certain degree of radial misalignment. 
     FIG. 10  is a perspective view of a third embodiment of the present invention.  FIG. 11  is a second perspective view of the embodiment shown in  FIG. 10 . Nut plate assembly  300  is constructed of a nut plate cage  302  containing a captive nut  310  seated against a seat washer  330 . 
   Nut plate cage  302  incorporates a base portion having a substantially-planar bottom surface  304 , a substantially-planar top surface  306 , and three feet  308 . In one embodiment, the centers of the feet  308  lie in separate planes coincident with the principal axis of the nut plate cage  302  and disposed at 120 degrees to one another. Adjacent to each of the three feet  308  is a ridge  344  extending from the foot  308  toward the center of the nut plate cage  302 . In certain embodiments, ridges  344  are designed to be relatively readily-deformable, in order to conform to the surface against which the nut plate assembly  300  is secured. 
   The nut plate cage  202  has a central bore  312  in the bottom thereof to allow for passage of a central fastener through the bottom of the nut plate cage  302 . This bore extends along a principal axis extending from the center of the nut plate cage  302  and generally orthogonally to the planes of the bottom surface  304  and top surface  306 . 
   At three edges of the base portion, a set of bends  314  transition into three substantially-planar cage sides  316  having inner and outer surfaces disposed substantially orthogonally to the bottom and top planes  304  and  306  of the lower portion of cage  302 . In or near the center of each side is a cutout  318 . At the top of each cage side  316 , there is a pair of safety wire holes  320  shaped and sized to receive a portion of a safety wire (not shown). 
   The captive nut  310  has a hole  332  down its center for accommodation of a fastener (not shown). Depending on the application, the fastener may engage the hole  332  by means of threads, or may be attached by other means. Captive nut  310  is held in place by locking pins  334 , but is free to rotate around its center point through a limited range of motion due to the employment of mating surfaces having spherical profiles. The range of motion of the captive nut  310  is limited in part by locking pins  334  extending outward from captive nut  310  and through cutouts  318  in cage sides  316 . In the embodiment shown in  FIGS. 10–11 , the axes of locking pins  334  are disposed at approximately 120 degrees to one another. As the captive nut  310  is rotated about an axis, locking pins  334  move within cutouts  318  until the motion of one or more of locking pins  334  is impeded by the edge of the cutout  318  within which it moves. 
     FIGS. 12 and 13  are exploded perspective views of a seat washer and captive nut subassembly according to certain embodiments of the present invention. As seen in  FIGS. 12 and 13 , seat washer  310  is defined by a substantially-planar washer bottom surface  346 , a spherical washer inner bearing surface  352 , a substantially-planar washer upper surface  354 , a substantially-conical washer outer chamfer  356 , and a substantially-cylindrical washer outer surface  358 . 
   Captive nut  330  is defined by a substantially-cylindrical central bore  332 , a spherical lower bearing surface  350 , a substantially-spherical upper surface  360 , a substantially-cylindrical outer surface  362 , three substantially-cylindrical locking pin bores  364 , and a substantially-conical chamfer  366 . Each of the locking pin bores  364  is profiled to mate with a locking pin  334 . In certain embodiments, the locking pins  334  may be retained in the locking pin bores  364  by threads, while other embodiments may make use of an interference fit or some form of adhesive. 
   As can be seen in  FIGS. 12 and 13 , lower bearing surface  350  of the captive nut  310  interfaces with, and is supported by, inner bearing surface  352  of the seat washer  330 . The bottom surface  346  of the seat washer  330 , in turn, interfaces with, and is supported by, upper surface  306  of the nut cage  302  of nut plate assembly  300  shown in  FIGS. 10 and 11 . With this design, the nut plate assembly  300  is able to accommodate angular misalignment through the spherical interface between captive nut  310  and seat washer  330 , as well as radial misalignment through the planar interface between the seat washer  330  and the nut cage  302 . 
     FIG. 14  is a perspective view of a locking pin according to certain embodiments of the present invention. Locking pin  334  is defined by a substantially-cylindrical pin body  370  having two flats  372  disposed on one end thereof and a locking nub  374  on the opposite end thereof. The locking nub  374  can be employed to impinge on the end of a fastener inserted in the central hole  332  of the captive nut  310  in order to capture the fastener securely within the captive nut  310 . For example, in applications wherein a threaded fastener engages a threaded captive nut  310 , the locking nub  374  may be positioned to interfere with, and thereby prevent, any rotary motion of the threaded fastener with respect to the captive nut  310 . 
   Referring now to  FIGS. 15–17 , there is illustrated the use of a nut assembly according to the present invention to connect a component  501  to a complexly contoured panel  503 . Component  501  includes a tubular member  505  and a planar flange  507 . In the manner well known to those skilled in the art, flange  507  includes a plurality of bolt holes. A component sub-base  509  is disposed between flange  507  and panel  503 . Sub-base  509  has a flat top surface and a bottom surface that is contoured to match the contour of panel  503 . 
   A plurality of bolts  511  pass through holes in flange  507 , sub-base  509  and panel  503 . Each bolt  511  is threadedly engaged with a nut assembly  513 . Each nut assembly  513  is of the type described with reference to  FIGS. 10–14 . As illustrated in  FIG. 17 , nut  515  rotates with respect to nut plate base  517  into axial alignment with bolt  511 . The feet of base  517  engage the surface of panel  503 . The feet and base  517  may deform to the contoured surface upon installation, thereby eliminating the need for shimming. Nut plate washer  519  allows nut  515  to float under loaded conditions. 
   Although preferred embodiments of the invention have been described in detail, it will be understood by those skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.