Abstract:
An automated tape head assembly for a multiple axis tape laying machine includes a tape supply reel and a tape compaction roller. Tape from the supply reel passes through the space between the two independent structures of the supply reel and compaction roller defining a tape path that substantially maintains a zero Gaussian curvature of the tape. The tape path is a curved path referred to as a compliance loop that results from a substantially or partially unrestrained curved path between the supply reel and the compaction roller. This structure allows the compaction roller to shift laterally and vertically with respect to the supply reel while the supply reel is in a fixed position with respect to the tape head assembly generally. This structure also allows the compaction roller to roll, steer, and follow the fiber tape&#39;s natural path, all with significant independence from the supply reel.

Description:
This present application is a continuation-in-part of U.S. Application Ser. No. 60/581,948, filed Jun. 22, 2004, which is incorporated herein by reference as is set forth in its entirety. 
    
    
     This application relates generally to machines that utilize a tape head to lay down composite strips on a surface and, more specifically to machines that utilize a single tape head or multiple tape heads simultaneously to lay fiber tape onto a contoured surface or mandrel. 
     BACKGROUND 
     Because of the nature of a tape, especially a stiff fiber tape, existing tape heads maintain a tape trajectory from the tape supply reel to the point of application onto a tool that does not allow the tape to move significantly out of a single plane. Existing tape head designs are comprised of (1) a tape supply reel; (2) a tape driving and cutting device; (3) a compaction roller or shoe that impresses the tape on to the surface of the part in process; and (4) a tape backer take-up reel. In these prior implementations, these four items are mounted to a common rigid structure such that their relative positions are fixed. 
     A number of designs have provided limited independent freedom of motion of the compaction roller with respect to the other three elements described above. Some of the prior art designs have passive compliance built into the compaction roller or to the compaction roller rotational shaft support, while others have a controlled position displacement by means of a motor or linear actuator. The designs with compliance of the compaction roller provide this feature to allow tension control across the tape width and allow limited steering of the tape or to impart a correcting force to keep the tape tracking down the centerline of the compaction roller. 
     One example provides for a tape head where the compaction roller can articulate about an axis normal to the compaction roller tangent surface at the intended work surface contact point. This example also provides for an accumulation of fiber tape such that the compaction roller can perform rapid motions to accommodate surface normal vector changes without having to respond with the entire tape head structure immediately. However, the compaction roller work surface contact point is fixed in the plane of the supply reel so that lateral displacements of compaction roller require the entire structure to be displaced. Further, the necessary apparatus and control system requires numerous controls and actuators. The tape accumulation mechanism induces sharp bends in the tape and given the large dimensions of the entire assembly would not be advantageous for a multiple tape head system where close location of adjacent tape heads may be necessary. 
     During tape lay-down a tape head assembly is steered and oriented to keep the compaction roller&#39;s axis normal to the direction of travel and, normal to the work surface as the compaction roller lays tape along the tape center line. These motions require the entire mass and the entire volume of this structure to be accelerated, moved and decelerated imposing large demands for motor power and volume clearance around the tape head structure. The inertia is both translational and rotational for the tape head mass plus the rotational inertia of the supply reel. The supporting structure must also be larger and more massive to accurately place the tape head relative to the tool or mandrel surface. The fact that the tape reel must be moved generally with the compaction roller limits the size of this reel and accordingly the amount of tape that can be laid down on a part between tape re-loads. 
     Another example discloses a method to lay down fiber tape that utilizes multiple tape heads each laying down a single fiber tape in coordination with the other tape heads and a rotating mandrel tool to fabricate a single large fuselage section. This multiple head fiber tape machine provides for a considerable reduction in the time required to fabricate a large fuselage section. However, since it utilizes a prior art tape head design, the size of the fiber tape supply reel and its replenishment must be offset by the demands for space, as each tape head must be articulated during the lay-up process and be accessible for replenishment. The result is a very large heavy support structure required to maintain the tight positional tolerances between heads and limited tape head packing density during operation, limiting the number of heads that can be engaged in the lay-up process simultaneously. 
     A still further example exhibits a method and apparatus to provide a tape head that does not have to be rotated at the termination of each tape pass. This is accomplished by having two or more tape reels where, in one example, the two reels are at opposite sides of the compaction roller. While eliminating the need to perform the large rotations between the termination of one pass and the start of another, this design increases the overall weight and space required and the rotational moment of inertia. A support structure and motion control means would have to be larger and more powerful to accommodate this type of design. 
     DEFINITIONS 
     Composite tape lay down heads are utilized to fabricate structural components that are comprised of multiple plies or lamina of unidirectional fiber tapes either pre-impregnated with an adhesive resin or infused with an adhesive resin after lay-up assembly. The fabrication is carried out by adding successive strips of fiber tape onto a rigid contoured support mold structure or contoured mandrel known as the tool which usually defines one surface of the finished part. Normally strips of composite tape are laid down side-by-side until the surface of the part is fully covered. One layer of generally parallel tape is known as a lamina. Successive lamina are laid down each on top of the preceding lamina, usually at a different angle of orientation to adjacent lamina. The surface upon which a tape is being applied is known as the work surface. The finished part which is comprised of many lamina is known as a laminate. 
     When the lay-up procedure is completed, the finished part, while still on the tool, is normally placed in a pressure and temperature controlled chamber known as an autoclave to aid in the consolidation of the part and cure the resin adhesive. 
     Each strip of fiber tape can be applied to the tool surface along any direction. However, the path that the tape is to follow must not cause kinking or buckling of the tape. This constraint is known as natural path and this type of path on a contoured surface will have continuous zero geodesic curvature. 
     In a number of applications such as parts of the aerodynamic surfaces as used on aerospace vehicles, some of the lamina cover only a portion of the part surface and these are usually associated with thicker sections of the laminate known as doublers where load concentrations are expected to be higher. One or a number of tape heads are manipulated relative to the surface of the tool by automatic machinery or a gantry system. The relative motion between the tape head and the tool may include the motion of the tool, such as in the case of a rotating mandrel with a contoured surface. In the specific case of a resin impregnated fiber tape, a wax paper tape known as a backer is usually releasably adhered to one side of the tape. The backer function is to prevent the tape from adhering to itself while in roll form. This backer is relatively easy to peel away from the fiber tape as the backer is not utilized in the part but is discarded. 
     It is important to distinguish between the type of tape head addressed by the present invention from other methods of laying down composite materials such a fiber placement, yarn placement and filament winding. A fiber, a yarn or a filament are in general geometrically one dimensional and can follow a straight line trajectory or a series of straight line trajectories along their paths from their supply source to the point of application, making turns if need be by means of pulleys or smooth rigid curved guides. 
     A tape as manipulated in the present invention is a flat two dimensional ribbon with intrinsic geometric constraints. For example a flat tape does not allow twisting along a straight trajectory without inducing significant shear in the tape causing for example a striated fibrous tape to splay, split apart or buckle. In general the vectors normal to the tape surface at any two points along the tape&#39;s length must be in the same plane unless the tape&#39;s path includes an untensioned space curve such that the zero Gaussian curvature of the tape be preserved. 
     SUMMARY 
     The present invention solves the above problems by mechanically separating a prior art tape head into two independent parts. Each part may be articulated independently, or one with respect to the other. The tape from a supply reel passes through the space between the two independent structures, taking a path that substantially maintains the zero Gaussian curvature of the tape, and allows smooth but substantially out of plane bending on the tape. 
     Unidirectional carbon fiber tapes are extremely stiff along their length, but are in general somewhat fragile due to the their filament and uncured adhesive composition. Filament metrics must be respected as the tape may splay or split if even small amounts of shear or bending are imparted along the tape trajectory. If the Gaussian curvature of the tape is maintained near to zero then the tape will not be subjected to detrimental shear forces. Further, if the bending that the tape is subjected to is moderate, then the tape and backer will retain their fiber and bond integrity. These tape path limitations may easily be met if the tape is allowed to travel in a substantially or partially unrestrained curved path between the supply reel and the compaction roller. 
     A substantially or partially unrestrained curved path may take the form of a C-shaped half circle, an S-shaped path, or may take the form of part of a helix. In all forms the tape&#39;s Gaussian curvature remains substantially close to zero. This curved path can be referred as a compliance loop. 
     A motorized feed roller located on a supply reel frame pulls tape from the supply reel and pushes the tape into the compliance loop. Another motorized feed roller located on the compaction roller structure pulls tape from the compliance loop. These two motors must manage the amount of tape in the loop, and do so by combining feedback from velocity and position sensors measuring the amount of tape passing through each end of the loop, and by sensing the loop depth by means of contact or non-contact sensors such as ultrasonic or optical distance measuring sensors. This type of tape path curve has been used for many years by motion picture cameras and projectors and is normally referred to as film loop or storage loop. The film loop provides for a small amount of un-tensioned film between the supply reel and the frame exposure mechanism on the camera. A similar loop is also maintained between the frame exposure mechanism and the film take-up reel. The frame exposure mechanism requires very high accelerations and frequent starts and stops while both the supply and take-up reels are in smooth continuous motion. 
     The present invention takes an important step further by providing for relative translational and rotational displacements to occur as the tape moves through the compliance loop from the supply reel to the compaction roller. In general the present assembly provides for a significant decrease in the mass of the parts of the tape head that must make numerous position and track adjustments along a single tape course. It now becomes clear that maneuvering the compaction roller is much less demanding of the volume of space required as compared to the prior art. Further, the motion control system driving the compaction roller, comprised of motors, transmissions and amplifiers, can now be substantially reduced in size and cost. 
     Another advantage of the present assembly is that it allows a very large tape supply reel to be used since the supply reel may be remote (for instance at least about 10 to 100 times the width of the tape) and does not need to have its axis aligned with the compaction roller. In a multi-head system, the present invention allows for mounting a number of supply reel structures on a common frame, this frame can move relative to the work surface. Each supply reel structure is provided with only a steering rotation of the supply reel axis with respect to the common frame. Each supply reel would also have an associated compaction roller structure that could make translational and rotational orientation movements relative to the common frame. 
     The present invention provides for the compaction roller to perform the following motions independently of the supply reel:
         Advance and retreat along the tape path sufficiently to allow tape cutting while the supply reel remains in translational motion relative to the tool surface;   Roll about the tape centerline sufficiently to maintain the tool surface normal;   Pitch about the compaction roller contact point with the work surface, where the pitch axis of rotation would be parallel to the compaction roller shaft axis, to maintain the compaction roller structure normal to the work surface;   Shift laterally and vertically so that the compaction roller can maintain tape centerline and maintain natural path constraints as required while traveling over varying surface features on the tool; and   Shift laterally to allow the tape head access to a reasonable candidate tape centerline that may not be directly below the tape carriage centerline.       

     All of these motions are on the order of two or three times the width of the tape and, for the motion normal to the tool or work surface, displacements of up to four or five times the width of the tape are practical. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation schematic view of a tape head assembly in accordance with the present invention. 
         FIG. 2  is a front elevation schematic view of the tape head assembly shown in  FIG. 1 . 
         FIG. 3A  is a front elevation view of a pair of tape head assemblies identical to the one shown in  FIGS. 1 and 2 . 
         FIG. 3B  is a side elevation view a pair of tape head assemblies each identical to the one shown in  FIGS. 1 and 2  in an alternative configuration to that shown in  FIG. 3A . 
         FIGS. 4A and 4B  are top elevation and perspective views respectively of a single supply wheel structure and compaction roll structure shown at three successive locations as a tape head passes over a ramp on a work surface. 
         FIGS. 5A and 5B  are top elevation and perspective views respectively of a supply rail structure and compaction roller structure of six tape heads mounted on six locations on a single carriage simultaneously addressing six separate tape courses on a work surface. 
         FIGS. 6A ,  6 B and  6 C are top elevation, perspective and side views respectively of a supply reel structure and compaction roller structure illustrating a single tape with an S-shaped tape path addressing a laterally displaced tape course. 
         FIGS. 7A and 7B  are to plan and side elevation respectively of a supply reel structure and compaction roller structure on a single tape head with a helical-shaped tape path addressing a laterally displaced tape course. 
     
    
    
     DETAILED DESCRIPTION 
     In one example, an automatic tape head assembly for a multiple axis tape laying machine for depositing tape in courses upon a work surface comprises a tape supply reel and a tape compaction roller. The tape compaction roller comprises a tape feed puller and a tape cutter. The tape supply reel and tape compaction roller are independently movable relative to the work surface and with respect to each other. The tape fed from the supply reel to the compaction roller and a tape travel path there between is maintained at substantially zero Gaussian curvature. The tape travel path between the supply reel and the compaction roller may be greater than a straight line between the supply reel and compaction roller. The tape head assembly may further comprise a backer reel rotatable around a third axis and a backer travel path between the compaction roller and the backer reel. The backer travel path may be greater than a straight line between the compaction roller and the backer reel. The movement of the supply reel and compaction roller is accomplished by independent positioning motors, and the positioning motors may be controlled by a common controller. The supply reel may unwind tape and feed it to the compaction roller in a continuous motion. The length of the tape travel path may vary during operation of the tape laying machine. The tape travel path may have a generally C-shaped curve, a generally S-shaped curve, or a generally helical-shaped curve. 
     The following example shown in the attached drawings is merely one alternative of the present invention. Of course those of skill in the art may take the teachings herein and develop further and additional variations based on the teachings herein. 
     Referring to  FIG. 1  and  FIG. 2 , an example of an automated tape head assembly is shown. A tape supply reel  2 , rotates on shaft  3 , that is supported by the supply reel structure  4 , pays out tape  25  (shown when reel is full  5  and shown when reel is almost depleted  6 ), is guided over a roller  7 , and descends to the motorized tape supply feed assembly  8 . The feed assembly  8  pushes the tape  25  into the compliance loop  9 . 
     The tape travel path between the feed assembly  8  (a portion of the supply reel structure) and the feed assembly  110  (a portion of the compaction roller structure) is shown as compliance loop  9 . As shown, the tape travel path (compliance loop  9 ) has a C-shaped curve. The tape travel path defines a substantially or partially unrestrained curve that enables a substantially zero Gaussian curvature of the tape. A tape travel path, in order to be substantially or partially unrestrained, must be greater than the distance defined by a straight line between a supply reel and a compaction roller. A tape travel path may also be S-shaped or define a generally helical-shaped curve. 
     Referring again to  FIGS. 1 and 2 , the tape  25  enters the compaction roller structure  11  and is guided into a motorized feed assembly  110  where the backer tape  26  is removed and pushed into its unique compliance loop  13  by an associated motorized feed assembly  115 . The fiber tape  25 , now separated from the backer tape  26  is pushed forward by the pinch feed assembly  110 , through the flying shear cutter assembly  111  and under the compaction roller  112  where it is pressed adherently onto the work surface. The actual roller  112  can alternatively be a shoe or a presser shoe or foot. These alternative constructions are included herein with respect to the term compaction roller. 
     The backer tape  26  passes through guides  10  to motorized puller assembly  14  and then wound onto a motorized take-up reel  15  rotating on a shaft  16 . Paths  18  and  19  show the backer tape&#39;s path as it is wound onto the take-up reel at the start  18  and finish  19  of winding. 
     The entire assembly is mounted on a single carriage  21  that can be moved by servo motor control (not shown) along linear bearings  22  fixed to a support beam  20 . The supply reel structure  2  is mounted on the carriage  21  by means of a rotary bearing  34  whose rotation is positioned by a servo motor  32  and associated pinion and ring gear  33 . The compaction roller structure  11  is moved relative to the supply reel structure  4  by four servo motors— 35 ,  36 ,  130  and  131 . 
     The compaction roller structure  11  is positioned relative to the supply reel structure  4  by the coordinated motion of the following four motors and associated mechanical drive components: servo motor  35  is able to translate the compaction roller structure support  12  parallel to the Z axis  132 , servo motor  36  is able to rotate the compaction roller structure support  12  about an axis indicated by  133 , servo motor  36  is able to rotate the compaction roller structure  11  about another axis indicated by  130  and servo motor  131  is able to rotate the compaction roller structure  11  about the axis indicated by  134 . Lastly the tool surface  200  is able to translate along one axis controlled by a servo motor (not shown). The coordinated motion of all of these motors are able to position the compaction roller structure  11  relative to the supply reel structure  4  and relative to the work surface  200  in all degrees of freedom except pitch. The pitch rotation axis is defined as the vector normal to both the tape course centerline and to the work surface at any point along the tape centerline. Because of the moderate surface contours of the tool experienced in this particular embodiment and to simplify the presentation, the pitch axis was not deemed necessary. And further, the axis required to translate the compaction roller structure in the direction along the tape path at the point of compaction roller contact with the work surface, is not required in this embodiment to simplify the presentation and because the compaction roller structure contains a flying shear so that the tape head can cut while in motion relative to the work surface. 
     Suitable inverse kinematics calculations, well known in the art, that utilize the desired tape course centerline, work surface normal vector and the kinematics relationships of the all of the axis explained above are required to provide the command signals for each of the associated motors. The relative position of the compaction roller structure  11  with respect to the supply reel structure  4  is further governed by the tape and backer compliance loops  9  and  13  respectively. 
     A C-shaped compliance loop  9  (as shown) will require that there be a small but significant steering angle offset between the plane normal to the shaft of the supply reel and the plane of the normal to the shaft of the compaction roller when the compaction roller structure has to be either positioned laterally ( 133  rotated) or rolled at an angle ( 134  rotated) to the supply reel structure. 
     An S-shaped compliance loop does not require the small but significant angle as detailed above, but does impose a tighter bending radius on the tape. The compliance loops  9  and  13  for the tape  25  and the backer  26  respectively are managed by their respective motorized feed assemblies  110  and  14 . 
     The supply reel  2  is managed by a servo motor  30  operating in torque mode so that it can rotate the reel to assist in its startup and apply a resisting torque to manage the tension on the tape and decelerate the reel. The backer reel  15  is managed in a similar manner as the supply reel. However, the backer servo motor  31  is usually applying torque to wind the tape. 
       FIGS. 3A and 3B  show two different arrangements where two tape heads are mounted on to the same carriage  21 , said carriage being able to move along the Y axis beam, translating both tape head supply reel structures  2  in fixed relation to one another along the Y axis. Each supply reel structure may rotate independently relative to the carriage  21  about an axis generally normal to the work surface that each head is to address. 
     When the beam is able to be controllably moved relative to the work surface in the X direction, both of the tape heads are able to apply tape simultaneously due to the fact that the compaction roller assembly of each tape head can be positioned relative to its associated supply reel structure. Each tape head is able to follow generally parallel, but significantly varying courses that, in this embodiment, are on the order of two or three times the width of the tape. 
     Tape head proximity for fixedly mounting the heads to a common carriage is governed by avoidance of collisions between each of the tape heads or any appendage thereof during expected simultaneous movements. 
     Turning now to  FIGS. 4A and 4B , there is shown a supply reel  2  and compaction roller  112  as discussed in more detail earlier herein. The additional tape head structure has been removed for the sake of demonstrating the positional relationship between the supply reel  2  and the compaction roller  112 . In  FIGS. 4A and 4B , the applied tape  201  has been pressed onto the work surface  200 . Three successive locations of the supply reel  2  versus the compaction roller  112  are shown as the tape head passes over a ramp on the work surface  200 . The supply reel  2  moves relative to the work surface  200  at a fixed height along a straight line, while the compaction roller  112  structure makes path changes in the transverse, roll and elevation directions. The tape travel path or compliance loop  9  between the supply reel  2  and compaction roller  112  shows a C-shape. The compliance loop  9  and the relative orientation of the supply reel  2  with the compaction roller  112  allow the compaction roller to enjoy substantial independent movement in relation to the supply reel. 
       FIGS. 5A and 5B  illustrate how an alternative tape head construction could operate. In these figures, the supply reel  2  are all fixed to a single carriage (not shown) to allow the tape head to address six separate strips of applied tape  201  on the work surface  200 .  FIGS. 5A and 5B  demonstrate how this single tape head construction would conceptually operate in an efficient manner. The compliance loops  9  facilitate the independent movement of the compaction rollers  112  with respect to the respective supply reels  2 . 
       FIGS. 6A ,  6 B and  6 C demonstrate various views of a supply reel  2  and compaction roller  112 , and importantly, an S-shaped compliance loop  9 . These figures illustrate how the applied tape  201  is adhered to the work surface  200  by a compaction roller assembly as described. This alternative demonstrates the S-shaped compliance loop between the tape supply  2  and the compaction roller  112 . Of course, as with all of the tape travel path or compliance loop  9  illustrated herein, the size of the compliance loop may vary during operation or by design as a result of the physical characteristics of the tape  25  that is being laid down. 
       FIGS. 7A and 7B  illustrate a supply reel  2  and compaction roller  112  and a helical-shaped compliance loop  9  there between. In these figures, the supply reel  2  is oriented such that the tape  25  will form a helical curve as it feeds from the reel  2  to the compaction roller  112 . The size, curvature, and number of curves of the helical curve that may be formed will vary depending on the operation of the tape head assembly and the type of tape that is being laid down. 
     Generally, with reference to all of  FIGS. 4-7 , the reference coordinate frame shows X, Y, Z as the right hand orthoganal axis, about which U, V, W are the rotational axis, also right hand oriented. The motion of the supply reel  2  relative to the work surface  200  is in the positive X direction. Otherwise, the supply reel  2  maintains a fixed Y and Z position where it is only allowed to rotate about the Z axis. On the other hand, the compaction roller  112  is allowed to articulate in at least four degrees of freedom relative to its associated supply reel  2 . The reel support structure has one degree of freedom—it is able to rotate about the Z axis. The reel support structure can be fixed to a frame that either 1) is able to translate in the X-Y plan relative to the work surface, 2) is able to translate in only the X or Y axis will the work surface is able to translate along the other of the two axes (X or Y), or 3) is stationary, where the work surface is able to translate in the X and Y directions. 
     While the invention has been described with reference to specific embodiments thereof, it will be understood that numerous variations, modifications and additional embodiments are possible, and all such variations, modifications, and embodiments are to be regarded as being within the spirit and scope of the invention.