Abstract:
During the manufacture an aircraft, a tool-carrying rail is removably attached to a rail-side surface of the aircraft with a vacuum cup. The tool-carrying rail includes a longitudinal axis to mount a tool. The vacuum cup is stiffened along a first axis transverse to the longitudinal axis of the tool-carrying rail and the vacuum cup is stiffened along a second axis parallel to the rail-side surface of the aircraft. To removably attach the tool-carrying rail, a perimeter of the vacuum cup is removably sealed to the rail-side surface of the aircraft against vacuum loss and a point on the rail is rigidly positioned with respect to a point on the rail-side surface of the aircraft. In addition, a vacuum source is coupled to a spatial volume occupying all of a space between the vacuum cup and the rail-side surface of the aircraft and the tool is slidably positioned along the longitudinal axis of the tool-carrying rail.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of and is a divisional application to U.S. patent application Ser. No. 10/854,209, filed on May 27, 2004, now U.S. Pat. No. 7,134,649 titled “CONFORMAL VACUUM CUP APPARATUS AND METHOD,” the disclosure of which is incorporated herein by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates generally to manufacturing tools and automation. More particularly, the present invention relates to attachment of rail-mounted machine tools to work surfaces. 
   BACKGROUND OF THE INVENTION 
   Portable, vacuum-cup-attached systems for drilling or fastening sections of aircraft fuselage or wing structures, as well as for other manufacturing operations, for other vehicle types, and for static structures, have been developed previously, but have generally been most practical for use only on workpiece areas where the contour is zero or very small in the longitudinal direction of the device. For example, some prior art vacuum cup systems could be attached readily along the flight direction of a cylindrical or otherwise highly curved fuselage, particularly where the fuselage has a long, essentially straight extent (i.e., a contour near zero), but attaching such a system to the fuselage in the circumferential direction, or fore-and-aft along a curving wing rib, would tend sometimes to produce uncertain results. 
   Prior art systems that use small numbers of large vacuum cups have been used, but have tended to be unable to conform smoothly to severe contours. Prior art systems with large numbers of small vacuum cups can follow a contour to some extent, but tend to be limited in the available retaining force by the necessity of having physical clearance around each vacuum cup, and by the limited available length-to-width ratio of an individual cup. 
   Prior art rail-mounted machine tool systems can possess the capability to advance a tool attached to a rail using a motor and gear apparatus integrated with the tool. Measurement apparatus, likewise integrated with the tool, allows the position of the tool to be determined with considerable precision. Nonetheless, prior art systems tend to be limited in their ability to conform to generalized surfaces, being best suited to positioning along low-contour paths. 
   Accordingly, it would be desirable to provide a method and apparatus that provides attachment of a rail system that can conform to surfaces with comparatively large contour in the longitudinal direction of traversal by the rail system and by tools carried thereon. 
   SUMMARY OF THE INVENTION 
   The conformal vacuum cup described in some embodiments comprises a resilient cup member having a series of rigid stiffener elements oriented next to each other along the longitudinal axis of a rail system. A rail can be supported by attachment to the stiffener elements. The stiffener elements can be spaced away from the rail, in a representative embodiment, using standoff pins attached to the stiffener elements and to the rail. Between each pair of stiffener elements is a gap sufficient to allow the rail to flex over a comparatively sharply curved contour without interference. A group of stiffener elements assembled in a mold can be overmolded with an elastomeric material such as urethane, which overmolding encloses all of the stiffener elements and adds a circumferential lip to establish the vacuum cup. The vacuum cup so formed can have kerf shapes formed into the gaps between adjacent stiffener elements to permit substantial motion between the stiffener elements despite the presence of the overmolded elastomer. The above standoff pins can protrude from top and/or bottom surfaces of the overmolded elastomer. 
   In another aspect, a vacuum cup for removable connection between a conformable, tool-carrying rail and a rail-side surface of a workpiece comprises an inner surface of the vacuum cup, an outer surface of the vacuum cup, a plurality of resilient pads joined into a contiguous whole (wherein the area between each pad and the rail-side surface of the workpiece defines a zone), a plurality of stiffener elements (wherein at least one of the plurality of stiffening elements is embedded at least partially within each respective one of the pads, and wherein the stiffener elements are attachable to the rail), and a resilient peripheral seal, joined to the pads and surrounding the periphery of all of the zones between the pads and the rail-side surface of the workpiece. 
   In still another aspect, a vacuum cup for removable connection between a conformable, tool-carrying rail and a rail-side surface of a workpiece comprises an inner surface of the vacuum cup, an outer surface of the vacuum cup, a plurality of resilient pads joined into a contiguous whole, wherein the area between each pad and the rail-side surface of the workpiece defines a zone, a plurality of stiffener elements, wherein one of the plurality of stiffening elements is embedded at least partially within each of the pads, and wherein the stiffener elements are attachable to the rail, and a resilient peripheral seal, joined to the pads and surrounding the periphery of all of the zones between the pads and the rail-side surface of the workpiece, and a plurality of standoff pins attached to the rail, where at least one of one of the standoff pins is attached to a respective one of each of the stiffener elements. 
   In still another aspect, an attachment between a rail with a longitudinal axis and a rail-side surface of the workpiece comprises means for stiffening a vacuum cup along an axis transverse to the longitudinal axis of the rail and parallel to the rail-side surface of the workpiece, means for removably sealing the stiffening means to the rail-side surface of the workpiece against vacuum loss, means for rigidly positioning a point on the rail with respect to a point on the rail-side surface of the workpiece, and means for coupling a vacuum source to a spatial volume occupying all of a space between the means for sealing and the rail-side surface of the workpiece. 
   In yet another aspect, a method for removably attaching a rail with a longitudinal axis to a rail-side surface of a workpiece comprises stiffening a vacuum cup along an axis transverse to the longitudinal axis of the rail and parallel to the rail-side surface of the workpiece, removably sealing a perimeter of the vacuum cup to the rail-side surface of the workpiece against vacuum loss, rigidly positioning a point on the rail with respect to a point on the rail-side surface of the workpiece, and coupling a vacuum source to a spatial volume occupying all of a space between the vacuum cup and the rail-side surface of the workpiece. 
   There have thus been outlined, rather broadly, certain embodiments of the invention, in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
   In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
   As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may be used readily as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view illustrating from beneath a fully compressed conformal vacuum cup according to a preferred embodiment of the invention. 
       FIG. 2  is an oblique view from above with cutaway of a conformal vacuum cup according to the embodiment of  FIG. 1 . 
       FIG. 3  is an exploded view of an end stiffener and associated standoff pins according to the embodiment of  FIG. 1 . 
       FIG. 4  is an exploded view of an intermediate stiffener and associated standoff pins according to the embodiment of  FIG. 1 . 
       FIG. 5  is a section view of a vacuum connection with an intact diaphragm. 
       FIG. 6  is a section view of a vacuum connection with a pierced diaphragm in which a barbed tubing coupling has been installed. 
       FIG. 7  is a side view with cutaway of a conformal vacuum cup installed on a rail and pressed onto a workpiece, according to the embodiment of  FIG. 1 . 
       FIG. 8  is a section view of a groove and kerfs separating two pads according to the embodiment of  FIG. 1 . 
       FIG. 9  is a section view of a groove without kerfs. 
       FIG. 10  is an oblique view from above of a conformal vacuum cup according to an alternative embodiment of the invention. 
       FIG. 11  is a side view of a multiplicity of conformal vacuum cups according to the alternative embodiment of  FIG. 10 , showing attachment to a rail and a curved workpiece. 
   

   DETAILED DESCRIPTION 
   Various embodiments in accordance with the present invention provide vacuum cup apparatus and methods for attachment of devices such as, for example, a rail system used in operations such as drilling series of holes, which holes may be needed for assembling screws or rivets through airplane sheet surfaces into underlying structures. Although described in the context of aircraft manufacturing, various embodiments can also be useful in other manufacturing industries. The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. 
     FIG. 1  is an oblique bottom view that shows a fully compressed vacuum cup  10  according to an exemplary embodiment. The vacuum cup  10  has a peripheral sealing lip  12  that is shown deflected as it would be seen from below a transparent workpiece (a workpiece  70  is shown in  FIGS. 7 and 11 ) when vacuum from an external vacuum system (shown in  FIG. 10 ) has been applied to the volume between the cup  10  and the workpiece  70 , and has caused outside air pressure to force the cup  10  against the workpiece  70 . The exemplary vacuum cup  10  comprises two end pads  14  along with three intermediate pads  16 . Each pad  14  or  16  comprises a stiffener (stiffeners  26  and  28  are shown in  FIG. 2 ) encapsulated in the resilient material of the vacuum cup  10 , and further comprises two standoff pins  18  with bottom ends  20  that can directly contact the workpiece when the cup  10  is compressed. The standoff pin tops  22  can be attached to a rail using suitable fastenings (a rail  72  is shown in  FIGS. 7 and 11 ). One or more partial holes  24  that are used to permit vacuum system attachment are shown in each end pad  14  and in more detail in  FIGS. 5 and 6 . 
     FIG. 2  is an oblique cutaway view of the vacuum cup  10  from above. Representative pads  14  and  16  are shown cut away to reveal an end pad stiffener  26  and intermediate pad stiffeners  28  within their respective pads  14  and  16 . Similar stiffeners are fully shown in  FIGS. 3 and 4 . 
     FIG. 3  is an oblique exploded view showing an end stiffener  30  substantially similar to the corresponding stiffener  26  in  FIG. 2 . The stiffener  30  is shown with two standoff pins  18  oriented for insertion. Each of the exemplary standoff pins  18  in  FIG. 3  has a pin top  22  with a chamfer  32  and a female thread  34  for attachment to a rail  72  (shown in  FIGS. 7 and 11 ). A taper section  36  and an interference-fit section  38  on each standoff pin  18  can allow the pin  18  to be pressed substantially permanently into the corresponding hole  40 . A shoulder  42  can provide an integral stop to allow the pin  18  to bear against the stiffener  26  or  30 , with the pin bottom end  20  at a uniform distance from the bottom surface  44  of the stiffener  26  or  30 . Three bores  46  in the end stiffener  30  can be used to provide passage for vacuum connection (shown in  FIGS. 5 and 6 ). 
     FIG. 4  is an oblique exploded view showing an intermediate stiffener  48  substantially similar to the corresponding stiffener  28  in  FIG. 2 . The stiffener  48  is shown with two standoff pins  18  oriented for insertion. Each of the pins  18  in  FIG. 4  has a pin top  22  with a chamfer  32  and a female thread  34  for attachment to a rail  72  (shown in  FIGS. 7 and 11 ). A tapered section  36  and an interference-fit section  38  on each pin  18  can allow the pin  18  to be pressed essentially permanently into the corresponding hole  40 . A shoulder  42  can provide a stop that allows the pin  18  to bear against the stiffener  48 , with the pin bottom end  20  at a uniform distance from the bottom surface  50  of the stiffener  28  or  48 . 
   Returning to  FIG. 2 , the sealing lip  12  is shown relaxed and deflected downward in its rest orientation. Inscribed around most of the perimeter of each of the pads  14  and  16  is a kerf or lower slot  60 . An upper groove or slot  62  is present as well. The two kerfs  60  and one groove  62  together provide some degree of decoupling between each two stiffeners  26 ,  28 ,  30 , or  48 , allowing the stiffeners  26 ,  28 ,  30 , or  48  to draw together or move apart as flexed by the rail  72  (shown in  FIGS. 7 and 11 ) to which they are fastened, and/or to twist relative to each other if so driven by the mounted curve profile of the rail  72 . 
     FIG. 5  is a section through  FIG. 1  at section line  5 - 5 . This shows that the first partial hole  24  in the bottom face  52  of an end pad  14  aligns with a second partial hole  54  in the top face  56 , shown in  FIG. 2 , of the end pad  14 . The two partial holes  24  and  54  are separated by a diaphragm  58 , and may preferably be positioned within one of the bores  46  in the end stiffeners  26  and  30 . 
     FIG. 6  is a section view of a barbed tubing coupling  64  inserted into a vacuum cup  10 . After the diaphragm  58  has been pierced, for example using an ordinary sewing needle, a barbed coupling  64  of suitable size can be inserted into the second partial hole  54 . The barbed coupling  64 , preferably carrying a single barb on each end as shown, preferably passes through the pierced diaphragm  58  and uses the pierced diaphragm  58  as a locking element to retain the barbed coupling  64 . Various options may be preferable in some applications, such as using multiple-barb ends on the barbed coupling  64  or passing the barbed coupling  64  through the pierced diaphragm  58  and the first partial hole  24 , although preferably not extending the barbed coupling  64  so far through the bore  46  as to extend beyond the pin bottom end  20  and contact the workpiece  70 . The top of the barbed tubing coupling  64  is shown to be set at a right angle  66 . The right angle  66  shown may be preferable to allow a vacuum line  68  to deliver vacuum to the vacuum cup  10  without a sharp bend in the line  68 . Other angles and other fitting styles may be preferable in some applications. 
   Returning once more to  FIG. 1 , the multiplicity of partial holes  24  in the end pads  14  can be used to provide optional vacuum connections. In some embodiments it may be preferable to plumb all vacuum cups  10  individually back to a common manifold. This can permit a manifold with valving to apply vacuum systematically, for example applying vacuum first to vacuum cups  10  located near mid rail, then sequentially activating cups outward toward both ends. 
   Experimentation has shown that for at least some combinations of materials and dimensions, a pierced diaphragm  58  may leak substantially no air when no barbed coupling  64  has been installed in it. This can allow the vacuum cup  10  in which the pierced diaphragm  58  exists to hold vacuum acceptably. By extension, a vacuum cup  10  may remain usable with multiple diaphragms  58  that are unused but have been pierced. 
   Since the baseline configuration for the exemplary embodiment employs a common area below the entire vacuum cup  10 , vacuum drawn at a first pierced partial hole  24  can be extended out through a second pierced partial hole  24  (as shown in  FIG. 10 ). Another barbed tubing coupling  64  can be added to connect the vacuum source to a second vacuum cup  10  without using a manifold port at the vacuum source for every vacuum cup  10 . Providing an ample number of partial holes  24  in the embodiment permits a variety of options for distributing vacuum in a rail-mounted machine tool system with a vacuum cups  10  of a single design. The availability of additional partial holes  24  can permit the addition of sensors, gauges, and the like as well as additional vacuum cups  10 . 
   Continuing in  FIG. 1 , the standoff pins  18  are shown surrounded by the elastomer of the pads  14  and  16 . The pin bottom ends  20  can be domed with a radius roughly equal to the elastic deformation of the workpiece  70  effected by the pressure stemming from the applied vacuum plus a portion of the weight of the rail-mounted drilling system. If the elastic deformation of the workpiece  70  can be shown to be negligible, then a satisfactory pin bottom end  20  shape may be achievable with a flat face square to the workpiece and a smooth edge roundoff. The pin bottom end  20  shape, radius of curvature, and size may preferably be chosen to at least minimize scuffing or marring of the workpiece  70 . 
     FIG. 7  is a side view with a partial cutaway, revealing the structure of a vacuum cup  10  pressed against a workpiece  70  and attached to a rail  72  with studs  74 , nuts  76 , and washers  78 . The lip  12  is flexed upward from its rest position as a result of application of vacuum. In  FIG. 7 , a flat workpiece  70  is contacted by the standoff pins  18 , causing the rail  72  to assume a flat shape, parallel to the workpiece  70 . 
     FIG. 8  is a section through the vacuum cup  10  of  FIG. 1 , in which the kerfs  60  and upper groove  62  are shown as they would be with a vacuum cup  10  positioned on a flat workpiece  70 . Where the workpiece  70  surface is curved, the standoff pins  18  (shown in  FIGS. 1 and 2 ) are drawn by the vacuum to conform to that curve, shifting the stiffeners  28  and  30 , and causing the elastomer between the kerfs  60  and the upper groove  62  to flex. This flexure allows the vacuum cup  10  to conform to a workpiece  70  with a relatively sharp curvature, and thus to cause the rail  72  to so conform. Twist in the workpiece  70  can be accommodated as well, with the elastomer flexing as necessary. 
     FIG. 9  is a section through an alternative vacuum cup configuration retaining the upper groove  62  but without kerfs. This configuration may be preferable on some workpieces, for example where curvature is slight or nonexistent along the rail longitudinal axis. 
   Alternative methods for fastening standoff pins to a rail could include welding, brazing, and equivalent metallurgical bonding methods, as well as application of a flange to the top of each standoff pin, which flange could have multiple radially-arrayed holes for rivets or other fastenings. The stud  74 , nut  76 , and washer  78  of the exemplary embodiment can be replaced by other threaded fasteners, such as screws with or without washers, and can be prevented from loosening by application of antivibration materials, upset threads, and other technologies. 
     FIG. 10  is an oblique view of a conformal vacuum cup  10  according to another design. Here, the lip  12  is made wavy instead of straight-edged as in  FIGS. 1-9 . In the embodiment shown, the elastomeric material  80  does not surround the stiffeners  28  and  30  above an attachment shoulder  82 . The embodiment shown has one inlet vacuum line  84  and one outlet vacuum line  86 , with no provision for additional vacuum lines. In this embodiment, a fitting  88  is employed to seal to a threaded hole and connect to a vacuum hose  94  at an approximate right angle.  FIG. 10  further shows in schematic form the use of a vacuum source  92  connected by a vacuum hose  94  to use the vacuum cup  10 . In the embodiment shown, a second fitting  88  connects to a second vacuum hose  86  to carry vacuum to another vacuum cup  10  or to an accessory such as a gauge. 
     FIG. 11  shows multiple samples of the conformal vacuum cup  10  of  FIG. 10  attached to a curved rail  72  using studs  74 , nuts  76 , and washers  78 . Also shown is a convex-curved workpiece  70 . The curvature of the rail  72  requires the flexing of the conformal vacuum cups  10  to accommodate the drawing together of the individual stiffeners  30  and  48  shown in  FIGS. 3 and 4 . 
   The stiffeners  26 ,  28 ,  30 , and  48  described herein can preferably be fabricated from a material with specific physical properties. One such desirable stiffener property is higher flexure resistance than the rail  72  and/or the workpiece  70 , particularly in the thickness used. Another such desirable stiffener property is compatibility with insertion of pins  18 , which compatibility includes adequate malleability to permit pin  18  insertion and similarity in temperature coefficient of expansion to the pins  18 . Another such desirable stiffener property is compatibility with the elastomeric overmolding material, which compatibility includes tolerance of the temperatures at which the molding takes place and chemical compatibility with the overmolding material. Typical materials likely to be suitable include various aluminum and stainless steel alloys, fiber reinforced phenolics, engineering plastics such as PEEK®, and others. 
   Suitable elastomers for the vacuum cup overmolding material include a class of synthetic rubbers known generically as urethanes. Other classes of elastomers, such as vinyls, as well as other formable materials, may, like urethanes, have adequate ranges of durometer values and acceptable physical properties such as tear resistance for repeated use and may exhibit an ability to withstand rough treatment. Urethanes in the preferred range of durometers can in some formulations exhibit a desirable ability to cling to surfaces, which ability may add to the positioning force of the vacuum cups  10 . Vinyls may exhibit significantly lower cling than urethanes, which may be preferable in some embodiments. Other elastomers may likewise exhibit desirable combinations of attributes for specific uses. 
   Forcing air, such as from a compressor, through a vacuum cup system may allow the cups to function as air bearings to make tool repositioning easier and quicker. Specific features such as lip shape, interface surface profile, elastomer material choice, and available air flow rate may inhibit or facilitate such use. 
   The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and, accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.