Abstract:
A flexible rail machine tool couples temporarily to a structure by vacuum cups and positions a tool head at any desired point over an area. The toolhead can perform operations such as drilling, bolt insertion, and acquisition of dimension data. The flexible rail can conform to surface curvature in one or more axes. Tool head perpendicularity to the structure can be sensed and adjusted as needed. The as-attached position of the rail may be compensated for through coordinate transformation, allowing holes, for example, to be placed with substantial precision.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to manufacturing tools and automation. More particularly, the present invention relates to rail-mounted machine tools and automated positioning systems. 
   BACKGROUND OF THE INVENTION 
   Classic aircraft production has, since early in the history of hard-skinned aerostructures, involved making templates and aligning them on fuselage and flight surface skins, then drilling through holes in the templates using hand-held drills to prepare the aerostructure for installation of rivets and screws. Placement of holes in the structure has thus generally been limited to human speeds, and has required extensive inspection. 
   In theory, a massive robotic apparatus could be developed that could autonomously place holes at any location on a workpiece such as an aerostructure, with the robotic apparatus placed, for example, on a monument base separated from the workpiece, and with each hole drilled with accuracy limited by the position sensors in the robotic apparatus. Such apparatus, however, has not been developed or shown to be economically feasible for general use. However, it has been demonstrated that a manufacturing apparatus with some degree of automation, attached directly to a portion of a workpiece under construction, can be practical, where desirable criteria of practicality include accuracy, adaptability, speed, low manufacturing cost, and light weight and compact size for ease of positioning,. 
   For generally flat and/or straight surfaces, which can occur, in a limited number of cases, along the longitudinal axis of a fuselage, a variety of robotic tools can be effective. For example, in an early version, a substantially rigid rail was temporarily attached to a workpiece using common fasteners such as screws. A drill could be moved along the rail, by hand or using a motorized positioner, to successive locations adjacent to the rail, at which locations the drill could be caused to drill a clean, straight hole. The drill could then be advanced until all of the needed holes along that straight line had been drilled. 
   The process and apparatus described above has strengths, namely that a series of holes can be drilled with quite good precision and decent speed, but also has several drawbacks. For example, there must first be correctly located mounting holes to which to attach the rail. Further, installation and removal of the rail may easily mar the workpiece. Also, alignment is critical and may be time-consuming. As well, only a small percentage of needed holes are likely to fall on any one line, so devising the drilling patterns, preparing mounting holes, and repeatedly repositioning the rail can be tedious. In addition, as noted, a rigid rail cannot traverse curves, so the above-described tool could not be positioned circumferentially on fuselages, for example, or typically in any direction other than spanwise on wings. 
   An additional drawback, not only to the apparatus described above but to other apparatus in existence, involves limited excursion range for a drilling component of the apparatus. Typical tools may use two rails to provide a secure base, then translate a toolhead across a workpiece. Even if the toolhead can move between the rails as well as along the rails, no work can be performed outside an excursion envelope established by the two rails. 
   Accordingly, it is desirable to provide a flexible rail machine tool method and apparatus that conforms to a workpiece surface that may have significant curvature, which flexible rail machine tool can drill holes within a work zone on the workpiece. It is further desirable that such a tool be able to traverse a surface along at lease one axis without manual repositioning and to drill holes normal to a surface substantially without manual intervention. It is further desirable that such a tool be able to drill holes outside the excursion envelope defined by the rail system attachment footprint. It is further desirable that such a tool be able to translate desired hole locations from a reference coordinate system to an as-affixed coordinate system. It is further desirable that such a tool be readily mounted and demounted from the workpiece. 
   SUMMARY OF THE INVENTION 
   The foregoing needs are met, to a great extent, by the present invention, wherein, in one embodiment, a flexible rail machine tool method and apparatus is provided that is able to conform to a workpiece surface that has significant curvature and is able to perform machining operations such as drilling holes within a work zone on the workpiece. In another aspect, the flexible rail machine tool method and apparatus is further able to traverse a surface along at lease one axis without manual repositioning and is able to perform machining operations such as drilling holes normal to a surface. In yet another aspect, the flexible rail machine tool method and apparatus is further able to perform machining operations such as drilling holes outside the boundaries of its attachment device. In still another aspect, the flexible rail machine tool method and apparatus is further able to translate desired hole locations from a reference coordinate system to an as-installed coordinate system. In another aspect, the flexible rail machine tool method and apparatus can be readily mounted and demounted from the workpiece. 
   In accordance with one embodiment of the present invention, a flexible rail machine tool for performing operations on a workpiece comprises a primary rail coupled to the workpiece, a toolhead, an end effector on the toolhead, wherein the end effector is a mechanism that performs a machine tool function, and a first support mechanism attaching and supporting the toolhead with respect to the primary rail, wherein the first support mechanism is situated between a first maximum lateral extent of the toolhead and a second maximum lateral extent of the toolhead. 
   In accordance with another embodiment of the present invention, a flexible rail machine tool for performing operations on a workpiece comprises means for removably coupling a primary rail to the workpiece, means for performing cutting, holding, measuring, heating, and other processing on the workpiece, and means for positioning the means for performing processing with respect to the workpiece. 
   In accordance with yet another embodiment of the present invention, a method for performing machine-tool operations upon a workpiece comprises the steps of positioning a primary rail with respect to the workpiece, spacing the primary rail at a uniform distance with respect to the workpiece, removably coupling the primary rail to the workpiece, fixing a machining tool with respect to the primary rail, and performing cutting, holding, measuring, heating, and other processes on the workpiece using the machining tool. 
   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 readily be utilized 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 first perspective view illustrating a flexible rail machine tool according to a preferred embodiment of the invention configured for drilling between the rails, with external covers shown in place. 
       FIG. 2  is a closer view of the flexible rail machine tool of  FIG. 1 . 
       FIG. 3  is a second perspective view of the flexible rail machine tool according  FIG. 1  configured for cantilever machining, with several covers shown removed. 
       FIG. 4  is a side view of the flexible rail machine tool, with several covers, the frame, and some additional hardware elements omitted, but showing all three rails. 
       FIG. 5  is a perspective view of the flexible rail machine tool from the viewpoint of  FIG. 3 , with some additional frame elements omitted and all rails included. 
       FIG. 6  is an end view of the flexible rail machine tool in  FIG. 1 , with structural devices and housings omitted. 
       FIG. 7  is a perspective view from below the flexible rail machine tool of  FIG. 1 . 
       FIG. 8  is a perspective view showing a reaction foot used in place of a second rail in accordance with an alternate embodiment of the invention. 
       FIG. 9  is a block diagram of the flexible rail machine tool with a variety of end effectors suitable for use with embodiments of the invention. 
   

   DETAILED DESCRIPTION 
   An embodiment in accordance with the present invention provides a rail system for positioning a toolhead above a workpiece that may have significant curvature in one or more axes. Smooth motion of the toolhead on a rail suspension system is achieved in the exemplary embodiment through use of a main rail system comprising one or more relatively long and wide, flat, flexible rails with vee-shaped rail edge faces contacted by mating bearing devices, such as rollers, on the toolhead. Motorized drive of the toolhead along a rail system axis parallel to the rail edge faces—hereinafter the longitudinal axis—in the exemplary embodiment is achieved using a pinion gear on the toolhead and a rack formed into the primary rail. 
   The toolhead may be capable of self-driven motion along and about multiple axes. In addition to having rollers and a motor drive to permit traversing the longitudinal extent of the main rails, the toolhead may be equipped with cross rails, which may preferably be configured at right angles to the main rails, and for which a motor drive that may be separate from the longitudinal motor drive may permit autonomous transverse positioning. In addition, motorized rotation of a chuck or mandrel for machining is a preferable capability. Similarly, a toolhead with a machine tool such as a drill is generally required to plunge the tool into and out of the workpiece using another motor drive. Further, tilting the toolhead to adjust the angle of penetration with respect to the toolhead may be desirable, and may call for yet another motor drive. Additional desirable capabilities may include replacement of one type of machine tool with another, or addition of multiple tools and accessory devices for measuring position, inserting and steadying fastenings from a dispenser into a hole previously prepared, or a variety of other useful operations. 
   For the purposes of this disclosure, the term “end effector” is used as a term of summary, incorporating, for example, “drill” as well as “grinder,” “inserter,” “measuring probe,” and any other suitable functions for which a flexible rail machine tool may be employed. 
   For the purposes of this disclosure, translation along the longitudinal axis of the main rails is also termed X-axis motion. Transverse motion with respect to the main rails, still substantially parallel to the mean surface of the workpiece, is termed Y-axis motion. Stroke motion of the end effector penetrating the workpiece is termed Z-axis motion. Tilting the end effector with respect to the toolhead X-axis, so that the end effector enters the workpiece at an angle with respect to the toolhead, is termed A-axis motion. The exemplary embodiment does not feature tilt of the end effector about the Y-axis, which would be B-axis motion. End effector spindle rotation about the Z-axis is termed C-axis motion. In addition to these motions, there is provision for applying a pressure preload to the workpiece. Also, there is provision for a compensator to make fine adjustments to the orientation of the entire toolhead about the A-axis. 
   Attachment of the primary rail to the workpiece preferably uses vacuum cups with spacing pins. The described rail, which is relatively long, wide, and thin, may be relatively rigid with respect to lateral flexure while allowing bending and twisting to conform to the workpiece. General conformance to contours of the workpiece can be realized with a multiplicity of rigid spacing pins, preferably of uniform height, attached to the rail and drawn against the workpiece. Such height uniformity may promote consistent rail-to-workpiece spacing, which in turn may maximize X-axis positioning accuracy. The holding force can come from any of a variety of sources, one of which is vacuum from an external vacuum source fed to a resilient cup surrounding each spacing pin or group of spacing pins. The use of a sufficiently large total vacuum cup surface area can permit the flexible rail machine tool to be attached to a workpiece at effectively any orientation. 
   The toolhead may include automated position detection for one or more of its motions, so that the location of a tool with respect to the workpiece may be known with good precision. This capability may be extended to include computational correction of position, so that, for example, a detector on a toolhead can identify reference positions on a workpiece and deliver them to a processor that can calibrate its positioning commands to the toolhead, effectively performing coordinate transformation and automatically drilling holes where desired irrespective of initial rail placement uncertainty. 
   Preferred embodiments of the invention will now be further described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. 
     FIG. 1  is an overall perspective view of a flexible rail machine tool  10  comprising a toolhead  12  and resting on a primary rail  22  and a second rail  38  coupling the toolhead  12  to a workpiece  14 . 
     FIG. 2  is an enlarged view of the flexible rail machine tool  10  of  FIG. 1 , further detailing the toolhead  12  and showing the toolhead  12  riding on short segments of the two rails  22  and  38 . It may be observed that the apparatus of  FIG. 2  is shown with multiple covers (including those identified as  16 ,  18 , and  20 ) installed. The primary rail  22 , located near the center of the toolhead  12 , is incised with a gear tooth rack  24 , and is fitted beneath with spacing pins  26  and vacuum cups  28 . The first side frame member  30  provides structural integration for the toolhead  12 . Also visible are vee rollers  32 , a first primary rail roller support arm  34 , and a first primary rail pivot  36 . Vee rollers  32  include a circumferential female vee groove  33  that bears against a male vee groove  23  along the edge of the primary rail  22 . 
   In the foreground of  FIG. 2  is a second rail  38 , which is herein termed a spanned rail, since the placement of the two rails in this configuration spans the reach of the end effector  40 . The spanned rail  38  is, like the center rail  22 , equipped with spacing pins  42  and vacuum cups  44 , of which vacuum cups  44  two are shown in part in  FIG. 1 . A vacuum source  128  is shown schematically, connected by hoses  130  to vacuum cups  28  and  44  to provide attachment force. The spanned rail support mechanism  46  for the spanned rail  38  is shown, comprising spanned rail vee rollers  48  to provide direct support to the spanned rail  38 , a short transverse rail  50  joining the spanned rail vee rollers  48 , spanned transverse vee rollers  52  that allow the toolhead  12  to move independently of the spanned rail  38 , and a spanned support bracket  54  to affix the spanned rail support mechanism  46  to the toolhead  12 . The spanned rail vee rollers  48  include a circumferential female vee groove  49  that bears against a male vee groove  39  along the edge of the spanned rail  38 . and the spanned transverse vee rollers  52  include a circumferential female vee groove  53  that bears against a male vee groove  51  along the edge of the transverse rail  50 . 
   The direct coupling of the primary rail  22  to the toolhead  12  allows free rotation of the toolhead  12  about the A-axis only. The looser coupling of the second rail  38  allows the toolhead  12  to float laterally (in the Y-axis direction) with respect to the second rail  38 , as well as having A-axis rotation and unencumbered X-axis motion. This permits the primary rail  22  to serve as a reference, while the second rail  38  provides stability and support. The second rail  38  is thus permitted to follow a non-parallel path over a complexly curved workpiece  14  without causing binding of the coupling apparatus. 
   The coupling mechanism for the second rail—which, in the exemplary embodiment, is the spanned support bracket  54  shown—has mounting slots  55 . Bolts through such slots  55  can permit adjustments to be made to the stance of the toolhead  12 . Should it be desired to make such stance adjustments dynamically, such as under computer control during operations, a motorized, sensor-equipped actuator can be interposed between the spanned support bracket  54  and the toolhead  12 . 
     FIG. 3  is a third perspective view of the flexible rail machine tool  10  with some covers ( 16 ,  18 , and  20  of  FIG. 2 ) omitted, in which view the spanned rail  38  has been removed and a cantilever rail  56  has been added, equipped with spacing pins  58  and vacuum cups  60 , and attached to the toolhead  12  using a cantilever rail support mechanism  62  comprising cantilever rail vee rollers  64  to provide direct support to the cantilever rail  56 , a short transverse rail  66  joining the cantilever rail vee rollers  64 , cantilever transverse vee rollers  68  that allow the toolhead  12  to move independently of the cantilever rail  56 , and a coupling mechanism—in this exemplary embodiment, a cantilever support bracket  70 —to affix the cantilever rail support mechanism  62  to the toolhead  12 . The cantilever rail vee rollers  64  include a circumferential female vee groove  65  that bears against a male vee groove  57  along the edge of the cantilever rail  56 , and the cantilever transverse vee rollers  68  include a circumferential female vee groove  69  that bears against a male vee groove  67  along the edge of the transverse rail  66 . 
   As in the spanned configuration, the cantilever support bracket  70  shown has mounting slots  72 . Adjustment of bolts through such slots  72  can permit adjustments to be made to the stance of the toolhead  12 . If it should be desired to make such stance adjustments dynamically, such as under computer control during operations, a motorized, sensor-equipped actuator can be interposed between the cantilever support bracket  70  and the toolhead  12 . 
   Switching from spanned to cantilever configuration can permit the end effector  40  to operate near a workpiece edge or in a region of excessive curvature or weaker underlying structural support, thereby extending the capability of the flexible rail machine tool  10 . It will be observed that the attachment hardware for the two configurations may differ, so that conversion from one to the other configuration may require different components in some embodiments, although use of the same components for both may be preferable in other embodiments. 
     FIG. 3  shows additional features of the flexible rail machine tool  10 . The end effector spindle  76  may in some embodiments be powered (C-axis motion) using belt feed  78  from a motor  80 . Advance of the end effector spindle  76  (Z-axis motion) is shown driven by a rotary actuator  82  using a toothed belt  84  from a toothed drive pulley  86  to a pair of toothed driven pulleys  88 , applying torque to drive screws and drive nuts (enclosed within uprights  90 ), and raising and lowering a transverse spindle support arm  92 . 
     FIGS. 4–7  show both the spanned rail  38  and the cantilever rail  56  for reference. Although typical embodiments may use one or the other, use of both may be preferable for some embodiments. 
     FIG. 4  is a side view showing the above features and the mechanism for tilt of the drive spindle  76  (A-axis motion). Tilt can be realized using a tilt actuator  94 , which is connected by a spherical bearing  96  to the end effector  40 . An arced rail  98  allows the spindle  76  to pivot substantially about the point of contact  100  with the workpiece. 
     FIG. 5  is a perspective view showing key elements in their operation orientation. In this view, the transverse (Y-axis) actuator  102  and one of the transverse rails  104  may be seen, along with parts of the two arced rails  98  and the associated tilt actuator  94 . The transverse rail  104  is attached to the toolhead  12  frame, the end units  106  and  108  and intermediate unit  110  of which are visible in part in this view. 
     FIG. 5  also shows more detail of the primary rail  22  with its rack  24 , spacing pins  26 , and vacuum cups  28 . A drive mechanism, which includes a motor and may, depending on embodiment details, include a gear reducer, an encoder, and motor drive electronics, is shown housed in a longitudinal drive housing  112 . A pinion gear is enclosed within a pinion gear shroud  114 . The drive housing  112  and pinion gear shroud  114  form an integrated assembly with a second primary rail roller support arm  116 . 
     FIG. 6  presents substantially the same view as  FIG. 5  with more mounting apparatus omitted. In this view, the first primary rail roller support arm  34  and the second primary rail roller support arm  116 , as well as the third primary rail roller support arm  118 , may be seen, along with the primary rail drive coupling spring  120  that ties the three arms  34 ,  116 , and  118  together. As noted, the first primary rail roller support arm  34  is coupled to the first side frame member  30  by a pivot  36 ; an equivalent pivot can be used to support the third primary rail roller support arm  118 . These two arms can carry the weight of the toolhead  12 , while the second primary rail roller support arm  116  couples the longitudinal axis force from the X-axis drive mechanism to the primary rail  22 . 
   A pitch plane of a rack—corresponding to the pitch line of a planar projection of a circular gear—is the effective plane through which the drive pinion acts in coupling motion between the two components of a rack and pinion. The neutral plane of a flexing object with thickness is a surface, ordinarily within the object, that does not change dimension in a direction of interest during flexure. This may, for example, be the midplane of a flexible slab formed of a material that is substantially uniform in composition in the direction of interest. 
   With proper fabrication, the pitch plane of the machined rack  24  may preferably lie on the neutral plane of the primary rail  22 . As a result, primary rail  22  flexure to conform to workpiece  14  (see  FIG. 1 ) curvature can leave the length of the driven axis substantially unchanged, substantially eliminating this error term from position computations. Thus correlation between the angular position of the pinion gear and longitudinal position of the toolhead  12  on the workpiece  14  may be based on the known surface length of the workpiece  14  without a curvature correction. 
   Torsional limberness in the coupling spring  120  allows twist in the workpiece  14  to be accommodated through twist in the primary rail  22  with minimal torsional loading error on the end effector  40 . Since the primary rail  22  is used as a dimensional reference, the second rail  38  can conform to a portion of the workpiece surface that differs appreciably in orientation, with the reaction function of the second rail  38  substantially unaffected. 
   Alternative embodiments of coupling spring  120  are possible, including for example cables in tension, rods, and a cross-slot in the frame that couples to the second support arm  116 . Each such embodiment allows the X-axis force from the pinion to be coupled to the toolhead  12 . 
     FIG. 7  is a bottom view of a preferred embodiment of the flexible rail machine tool, in which again both the spanned and cantilevered rails are shown. In this view, first and second normalizing sensors  121 A and  121 B, respectively, are shown along with an end effector preload mechanism  122 . The normalizing sensors  121 A and  121 B can be used to detect whether the end effector spindle  76  (see  FIG. 3 ) is oriented normal to the workpiece within an acceptable tolerance range. Assuming that workpiece  14  surfaces are curved essentially uniformly over a range such as the span between the two normalizing sensor  121 A and  121 B, having the displacement of the two sensors  121 A and  121 B approximately equal implies that they are meeting the workpiece  14  surface on either side of a point approximately normal to the end effector spindle  76  axis. This assumption is generally valid over a wide range of surfaces to be worked with machine tools. In use, a processor can accept measurements from the two sensors  121 A and  121 B and generate a correction function, directing the tilt (A-axis) actuator  94  (see  FIG. 4 ) to adjust the end effector  40  angle for normality, that is, perpendicularity, to the workpiece. Y-axis compensation may be required to assure that holes are placed at the desired locations including the normality compensation; this correction can be incorporated into a position control processor algorithm. 
   A second axis of normality can be detected by adding another pair of sensors to measure B-axis error. With suitable transducer placement, one of the B-axis sensors can be sensor  121 A or sensor  121 B, with its measurement used a second time. Adding B-axis motion may require an additional bearing system and actuator. 
   The preload mechanism  122  can apply an initial force to the workpiece approximately equal to a total force to be applied during a machine process such as drilling. As tool force is subsequently applied, the preload  122  can be adjusted to keep the total force substantially constant throughout the tool cycle. 
     FIG. 8  is a perspective view of another embodiment showing a reaction foot  124  with a pneumatic actuator  126  to counter the force applied by the preload mechanism  122  during tool actuation. Although an embodiment of the flexible rail machine tool  10  is shown in  FIGS. 1–7  using rail configurations with at least two sets of vacuum cups, it will be appreciated that it is likewise feasible either to use a reaction foot  124  attached to the toolhead  12  in place of a second rail or to use a second rail without vacuum cups to function as a nontranslating reaction element. 
   Although the flexible rail machine tool  10  is useful for aerospace manufacturing, it will be appreciated that it can also be used for manufacturing and construction in shipbuilding, civil engineering, and other industries. Likewise, the size of the tool disclosed herein is appropriate for aerospace manufacturing, but it will be appreciated that far larger tools may be appropriate for larger construction projects, while very small tools achieving proportional precision and autonomous operation may be desirable for miniature applications. Operation in hostile environments such as under water may similarly be a desirable feature of other embodiments of the invention. Attachment of the apparatus in space or other hard-vacuum environments and to rough or porous surfaces, as well as in other environments not suitable for vacuum use, may require recourse to mechanical clamps or fasteners, or to magnetic or eddy-current coupling devices. 
   The toolhead in the exemplary embodiment is shown configured as a drill. Adaptation of this toolhead to other functions is possible. For example, a drill with multiple bits can include automatic change of bits, whether to drill a variety of sizes of holes or to use several bits for a specified number of holes each, setting aside worn bits until resharpened or discarded. Similarly, tools may include, for example, gauges, fastener inserters, grinders, welders, adhesive applicators, heaters, curing lamps, pressure pads, ultrasonic testers, and any other tools that may be suitable for automated or remotely controlled 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.