Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR COMPOSITE TAPE DISPENSING
Technical Field
The present invention relates to an apparatus for dispensing composite tape,
and more particularly, to an apparatus for laying down prepreg tapes with
precision.
The apparatus can lay down prepreg onto a molding structure having a contoured
surface or a flat surface along a linear or non-linear path.
Background
In composite technology, a resin preimpregnated web or tape may be used to
construct the particular component desired. Prepreg materials consist of
aligned
reinforcing fibers (typically carbon, glass, or aramid fibers) that are pre-
impregnated
with a polymer and used as an intermediate product in the molding of composite
structures. Very often these fibers are collimated in a unidirectional
configuration
forming tape-like products that are typically 12 to 60 inches (30.5 to 152.4
cm) wide.
The composite structure is built up of successive layers of the tape applied
to
a working surface such as, for example, a molding tool, mandrel, or any
surface
used to form composite parts. When building up a composite wind blade, wind
blade
spar, or wing structures, for example, from prepreg tapes, long lengths (i.e.,
greater
than 40 meters) of prepreg tape are laid down on a molding tool with great
precision.
Precise filament alignment is required to achieve the desired composite
properties.
In addition, uniform compaction of the prepreg tape during the laminate build-
up is
required to minimize entrapped air, which can cause voids in the cured
composite
laminate. Very slight misalignment of fiber orientation can cause significant
loss of
critical engineering properties. For example, 5 to 10 degrees off orientation
can
cause a 10 to 20% loss in composite modulus of elasticity. Voids in the
composite
can also result in lower composite properties. Greater than 2% voids can cause
significant loss of inter-laminar shear strength and can act as sites for
damage
growth in the composite during service life.
Composite wind blade spars are often straight-sided laminates of varying
thickness, for example, from approximately 0.1 inch (0.25 cm) to over 1.5
inches
(3.81 cm) thick. They are typically laid up mold surfaces that can range from
flat to
varying degrees of concave or convex curvature. For example, the wind blade
spar
may be flat at the tip and curved at the root. This configuration further adds
to the
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complexity of laying down prepreg tapes with extreme precision. Hand layup of
these spars with prepreg tapes is extremely difficult and time consuming, and
assuring precision is even more difficult. The alternate extreme to hand layup
involves the use of automated tape laying machines. These types of machines
have
been developed for over two decades, primarily for aerospace structures. While
these machines are designed to lay down prepreg tapes with extreme precision,
these machines are very expensive and overly complex for wind blade spars.
Summary
The present invention is directed to an apparatus that is capable of laying
down a wide prepreg product for a structure having in-plane curvature, while
significantly reducing the effects of wrinkling on the inner radius.
In one aspect of the invention, there is provided an apparatus to apply a
resin
impregnated tape to the surface of a molding tool, the apparatus including: an
upper
frame rotatably mounted to a base frame, the upper frame having mounted
thereon
and rotatable therewith a spool holding assembly for holding a spool of resin
impregnated tape wound thereon, a tape compaction assembly including a
compaction roller configured to conform to the surface of the molding tool for
compacting the resin impregnated tape onto the surface of the molding tool,
and a
tape tensioning system for exerting tension on the resin impregnated tape. The
base
frame includes a tracking system for tracking the surface of the molding tool,
the
base frame being reciprocally movable with respect to the surface of the
molding
tool.
In one embodiment, the spool holding assembly includes an alignment system
for laterally aligning the spool of prepreg tape relative to the surface of
the molding
tool.
In one embodiment, the compaction roller includes a plurality of contiguous
disks supported on an axle, the disks having a central bore diameter that is
greater
than the outer diameter of the axle.
In one embodiment, the upper frame rotates at least 1800 on the base frame
to permit changing the direction of application of the resin impregnated tape
on the
surface of the molding tool. The apparatus may further include a turntable
coupled
to the upper frame and the base frame to permit rotation of the upper frame on
the
base frame.
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In one embodiment, the tape tensioning system includes an actuated disk
brake. The disk brake may be manually or automatically actuated.
In one embodiment, the molding tool includes at least one rail and the
tracking
system includes at least two guide rollers that engage the at least one rail.
The surface of the molding tool may include at least one of a convex contour
and a concave contour.
The width of the resin impregnated tape applied to the molding tool, in one
embodiment, is within the range of about 11.5 inches (292 mm) to about 60
inches
(152.4 cm).
In a further aspect of the invention, that apparatus further includes a
slitter for
slitting the resin impregnated tape lengthwise into a plurality of strips, the
slitter
mounted on and rotatable with the upper frame. The slitter may include a
plurality of
stationary or rotary knives.
In one embodiment, the plurality of strips of resin impregnated tape is
uniform.
In another embodiment, the width of the plurality of strips of resin
impregnated tape
is non-uniform.
In one embodiment, the apparatus further includes a plurality of accumulator
rollers disposed downstream of the slitter, each accumulator roller being
independently activatable for accumulating and de-accumulating a portion of a
respective strip of resin impregnated tape, the accumulator rollers mounted on
and
rotatable with the upper frame.
In one embodiment, the apparatus further comprising a controller configured
to control at least one of: the placement of the resin impregnated tape on the
surface
of the molding tool; the tension exerted by the tensioning system on the tape;
the
direction in which the tape is applied to the surface of the molding tool; and
the
speed at which the tape is applied to the surface of the molding tool.
In one aspect of the invention there is provided a carriage to apply a resin
impregnated web to the contoured surface of molding tool, the carriage
including: an
upper frame mounted to a base frame, the upper frame having mounted thereon: a
first spool holding assembly for holding a spool of resin impregnated web
wound
thereon, a second spool holding assembly for holding a spool of scrim material
mounted thereon; a web compaction assembly including a compaction roller
configured to conform to concave and convex portions of the surface of the
molding
tool for compacting the resin impregnated web onto the surface of the molding
tool,
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and a web tensioning system for exerting tension on the resin impregnated web.
The base frame includes: a plurality of wheels mounted on the base frame and
supporting the carriage, the wheels engaging the surface of the molding tool
for
propelling the carriage along the contoured surface of the wind blade spar cap
molding tool; and a tracking system for tracking the surface of the molding
tool, the
carriage reciprocally movable with respect to the contours of the surface of
the
molding tool.
In one embodiment, the carriage further includes a nip for joining a layer of
scrim material from the spool of scrim material to the resin impregnated web
prior to
compacting the resin impregnated web onto the surface of the molding tool.
Brief Description of the Drawings
In the annexed drawings, like references indicate like parts or features:
FIG. 1 is a perspective view of an apparatus for laying down prepreg tape
according to an embodiment of the invention.
FIG. 2 is a top view of the apparatus of FIG. 1.
FIG. 3 is a front view of the apparatus of FIG. 1 with a spool of prepreg
material mounted thereon.
FIG. 4 is a side view of the apparatus of FIG. 1 with a spool of prepreg
material mounted thereon.
FIG. 5 is a perspective view of an embodiment of the apparatus for laying
down prepreg tape according to the invention as positioned on a molding tool.
FIG. 6 is a front view of the apparatus of FIG. 5.
FIG. 7 is a perspective view of the apparatus of FIG. 5, illustrating
rotational
motion of the upper frame.
FIG. 8 is a perspective view of an apparatus for laying down prepreg tape that
includes tape slitting and dispensing assemblies in accordance with an
embodiment
of the present invention.
FIG. 9 is a side view of the apparatus of FIG. 8.
FIG. 10 is a top view of the apparatus of FIG. 8.
FIG. 11 is an enlarged top view of the tensioning system of the apparatus of
FIG. 8.
FIG. 12 is a side view of a section of the apparatus of FIG. 8 with a spool of
prepreg material mounted thereon.
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FIG. 13 is a perspective view of the tape alignment assembly of the apparatus
of FIG. 8.
FIG. 14 is a bottom view of the tape positioning assembly of the apparatus of
FIG. 8.
FIG. 15A is a schematic drawing illustrating a prepreg tape dispensed using
conventional apparatus in a linear direction.
FIG. 15B is a schematic drawing illustrating a prepreg tape dispensed using
conventional apparatus in a non-linear direction.
FIG. 16 is a photograph showing a prepreg tape dispensed using
conventional apparatus onto a curved surface.
FIG. 17 is a perspective view of an embodiment of the apparatus including a
scrim dispensing assembly according to the invention
Detailed Description
The apparatus of the present invention is useful for forming composite
laminated structures by applying tape of continuous fibers that have been
preimpregnated with a resin binder onto a surface of a mold, mandrel or tool.
The
fibers may consist of carbon, glass, ceramic, metal, and/or polymers. The
resin
binder may be a thermoset or thermoplastic resin.
In one aspect of the invention, an apparatus for laying down a wide,
unidirectional prepreg tape for a structure, and in particular, for a wind
blade, is
provided. The apparatus includes a spool holder for demountably holding a
spool of
a continuous web of prepreg material having a wide width. The apparatus
includes a
mechanism for properly placing the prepreg on the surface of the molding tool.
In
addition, the apparatus includes a rotatably mounted prepreg tape placement
assembly for bi-directional tape placement and compaction.
The width of the prepreg tape product is typically in the range of about 11.5
inches (292 mm) to about 60 inches (152.4 cm). In one embodiment, the width of
the prepreg tape is about 12 inches (30.5 cm) to about 60 inches (152.4 cm),
or
about 11.5 inches (292 mm) to about 15.75 inches (400 mm). In general, it is
advantageous to use wider prepreg tape so as to increase the rate of prepreg
tape
lay down, and thus increase production efficiency. With the apparatus of the
present
invention, it is possible to further increase production rates by providing bi-
directional
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tape placement and compaction. Application of the prepreg material on the
molding
tool may be carried out in the forward direction and in the reverse direction.
Referring to FIGS. 1-3, in one embodiment of the invention, the prepreg tape
laying apparatus is a carriage 10 that includes an upper frame 12 rotatably
mounted
to a base frame 14. Mounted on the upper frame 12 are a prepreg spool holding
assembly 16 and a compaction assembly 18. The base frame 14 includes a
tracking
system 20 to precisely place the prepreg material on the surface of the
molding tool.
The spool holding assembly 16 includes a spindle 22 and spool supports 24
mounted on spindle 22. Spool supports 24 include quick-adjust pins 26 that
contact
the inside of the prepreg spool core to center the spool 80 on the spindle 22.
The
spool holding assembly 16 enables rapid prepreg spool change-out and
positioning.
Spindle 22 is supported at each end by trusses 28 on the upper frame 12.
Referring to FIG. 3, the carriage 10 includes a spool positioning system 30
that includes disk 32 and lateral adjustment bracket 34. The spool positioning
system 30 controls the lateral position of the spool of prepreg material on
the
carriage throughout the prepreg dispensing operation. Disk 32 is fixed to
spindle 22.
The disk 32 is positioned between the arms of a U-shaped bracket 34. A pad 36
coupled to each arm of the bracket 36 contacts the disk 32. Using positioning
handle 31, small lateral (i.e., perpendicular to the direction of tape
application)
adjustments in the alignment of the prepreg tape can be made by laterally
moving
the bracket 34 during tape dispensing as necessary.
The carriage 10 includes a tensioning system 38 for maintaining a suitable
level of tension on the prepreg material during dispensing operation. A
friction
adjuster 40 applies pressure to the disk 32 and pads 36 within the bracket 34
to
establish a baseline resistance to rotation of the prepreg roll during the
dispensing
operation. This adjuster 40 can be either manually operated or automatically
operated based on feedback from tension monitoring sensors (not shown).
The tensioning system 38 includes a spring-loaded arm 42 that provides a
measurement of the tension on the prepreg tape. The force of the spring 44 on
the
spring-loaded arm 42 also compensates for minor fluctuations in force that
result
from the propulsion of the prepreg dispensing carriage 10 and from the
diametric
change of the prepreg material as it is dispensed from the spool. In one
embodiment (not shown), the tensioning system may further include sensors for
tension monitoring and adjustment. Tension roller 47 attached to lateral bar
46
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positions the prepreg tape near the surface of the molding tool in preparation
for the
compaction step.
The compaction assembly 18 acts to press down the prepreg material as it is
dispensed onto the surface of the molding tool. The compaction assembly
applies
compaction pressure regardless of the twist and curvature of the molding tool
surface. A compaction roller 48 is made up of a plurality of thin, heavy
contiguous
disks 50 on a lateral axle 52 with the flat faces of the disks pressed
together. The
disks 50 have a central bore diameter that is larger than the diameter of the
axle 52.
The disks 50 have polished faces and/or friction reducing media on the faces
of the
disks to enable independent movement of each disk. The heavy disks 50 are able
to
move vertically, so that the edge of each disk contacts the prepreg material
to
provide compaction. Adjacent the last disk at each end are retention members
54 on
the axle 52 to maintain the lateral position of the disks 50 and limit their
motion to
rotation about the axle and translation perpendicular to the axle 52. Swing
away arm
56 of the compaction assembly 18 is pivotably mounted on the upper frame 12 at
pivot point 58. The rotational movement of the compaction assembly 18 enables
the
operator to lift the compaction assembly off of the prepreg tape when the
compaction
assembly is not in use. The compaction assembly 18 may optionally include
other
features, including flexible-urethane or pneumatic shaped rollers, and spring
or
pneumatic loaded "fingers"/arms (not shown).
Referring to FIG. 4, as the prepreg material 82 is unwound from the spool 80,
it passes over redirect roller 43 and is then positioned near the surface of
the
molding tool by tension roller 47. The carriage 10 travels across the surface
of the
molding tool in the direction indicated by the arrow. The compaction assembly
18 is
lowered so that compaction roller 48 contacts the prepreg tape 82 and applies
compaction pressure to compress the prepreg tape 82 to the surface of the
molding
tool 60.
Referring to FIGS. 5 and 6, the carriage 10 may be moved over the surface
64 of a molding tool 60 by wheels 70 positioned on each of the four corners of
the
base frame 14. The carriage 10 may be self-propelled using, for example, an
electric motor (not shown). In one embodiment, the carriage 10 is guided by a
rail 62
positioned along the surface of the molding tool 60.
In the illustrated embodiment, the components of the tracking system 20 of
the carriage 10 are integrated into the carriage 10 and are coordinated with
the
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configuration of the molding tool 60 to assure the proper placement of the
prepreg
tape. Typically, the coordination focuses on a specific feature of the final
composite
structure. As an example, the point where the centerline of a wind blade spar
cap
contacts the surface of the molding tool 60 may be used as a "key
characteristic".
Tracking system 20 maintains precise position of the prepreg dispensing
carriage
relative to the key characteristic. Components of the tracking system 20 may
be
embedded in the molding tool surface 64 or in a separate guide rail 62
positioned on
the edges of planar portions 68 of the molding tool at either side of a
central concave
portion 66 of the molding tool 60 as shown in FIGS. 5-7.
The tracking system 20 includes at least one pair of guide rollers 72 mounted
to the end of at least one of the legs 74 of the base frame 14 of the carriage
and
proximate to wheel 70. The pair of guide rollers 72 are space apart so that
they
engage both sides of rail 62 and traverse along the axis of the rail 62. A
second pair
of guide rollers 72 may be mounted to a second leg 74 on the same side of the
base
frame proximate to the second wheel 70. The guide rollers 72 are coordinated
with
the molding tool to provide definitive position of the carriage 10; provide
proper twist
of the carriage 10 to mirror that of the molding tool 60; and maintain contact
of the
carriage 10 to the molding tool 60 along the entire length of the molding
tool.
Tracking guide rollers 72 also help to eliminate pull-off of the carriage
resulting from
forces needed to propel the carriage along the molding tool.
In one alternative embodiment, the one or more rails are positioned under the
molding tool, rather than on the surface of the molding tool. In another
alternative
embodiment, a separate rail is not used to guide the carriage. Instead, the
molding
tool surface itself incorporates key features that are tracked by the carriage
so as to
assure the proper placement of the prepreg material.
The compaction roller 48 exerts a compressive force to the prepreg tape by
contacting the top surface of the structural composite being laminated as the
tape is
deposited on the molding tool. The compaction roller 48, made up of a
plurality of
thin heavy, contiguous disks 50, is able to conform to the contours of the
surface of
the molding tool 64, and in particular, is conformable to the concave portion
66 of the
molding tool so as to reduce the tendency of the tape to wrinkle when applied
to the
concave (or convex) portions of the molding tool surface. With the compaction
roller
48, the prepreg tape can be applied to molding tool surfaces having areas of
varying
degrees of concave curvature, areas having varying degrees of convex curvature
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and areas that are flat. The prepreg tape any also be applied along a non-
linear
path on the molding tool surface.
Referring to FIG. 7, the upper frame 12 is rotatably secured to base frame 14
by turntable 76, which enables rotating the prepreg material by 180 degrees
without
removing the dispensing carriage 10 from the molding tool 60. The turntable 76
allows the prepreg material to pass through the center of the apparatus 10
during the
dispensing operation. The locking member 78, when engaged, prevents rotational
movement of the upper frame 12 relative to the base frame 14, and establishes
the
proper location of the prepreg spool for each direction of dispensing on the
molding
tool 60.
The apparatus of the present invention may further include means for guiding
the prepreg lay down to assure controlled fiber alignment. The operation of
the
carriage assembly 10 may be controlled by a controller (not shown). For
example,
the carriage may be connected to a controller that is configured to control
the
placement of the prepreg tape, the tension on the tape, the direction in which
the
prepreg tape is applied to the surface of the molding tool and the speed at
which the
prepreg tape is laid down.
The carriage assembly 10 may apply the prepreg material tape starting from
either end of the molding tool 60 and may start and stop according to
predetermined
ply locations. A cutter may be used to automatically cut the ply. In one
embodiment,
the carriage assembly 10 may include a laser guide (not shown) for determining
the
ply locations.
In one embodiment, the carriage assembly may be removably coupled to a
spool loading station.
In another aspect of the invention, there is provided an apparatus that
includes a slitter and accumulator, the apparatus capable of laying down
strips of
prepreg material formed from a wide prepreg tape product for a structure
having in-
plane curvature, while significantly reducing the effects of wrinkling on the
inner
radius. The initial width of the prepreg tape product may be in the range of
about 12
inches (30.5 cm) to about 60 inches (152.4 cm).
When building up a composite structure from prepreg tapes, the tapes are
usually laid down in straight line directions. Because the tape is being
unrolled from
a single spool, the fibers cannot stretch in the lay-down process and cannot
slide
relative to one another. As a result, these prepreg tapes cannot be laid down
in an
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in-plane curvature geometry without creating wrinkling or puckering on the
inner
radius.
Referring to FIG. 15A, a prepreg tape 200 dispensed using conventional
apparatus in a linear direction has a plurality of aligned reinforcing fibers
202 that are
pre-impregnated with a polymer. When the tape 200 is applied to a flat, linear
surface, the tape lies smoothly without wrinkling or puckering. FIG. 15B
illustrates a
prepreg tape 200 dispensed in a non-linear, curved direction using
conventional
apparatus. The tape 200 lies smoothly along the outer edge 204 of the curved
surface. However, along the inner edge 206, wrinkles 208 are formed.
FIG. 16 is a photograph of a 7 inch (17.8 cm) wide strip of prepreg laid down
to an in-plane radius of curvature of 130 feet (39.6 m) using a conventional
apparatus. The wrinkling and puckering 208 on the inner radius 206 can be
clearly
seen. This wrinkling creates a loss of orientation of fiber direction and
results in loss
of composite mechanical properties in this region. Carbon fiber composites are
particularly sensitive to loss of compression strength due to such loss of
fiber
orientation.
Referring to FIGS. 8-10, another exemplary embodiment of the prepreg tape
dispensing apparatus of the present invention is illustrated. The apparatus
comprises a movable carriage 10 that includes a spool holding assembly 16 for
demountably holding a spool 80 of a continuous web of prepreg tape material 82
having a wide width. As previously described, this embodiment of the carriage
10
includes an upper frame 12 rotatably mounted to a base frame 14. Mounted on
the
upper frame 12 are a prepreg spool holding assembly 16 and a compaction
assembly 18. The base frame 14 includes a tracking system 20 to precisely
place
the prepreg material on the surface of the molding tool. The carriage assembly
10
includes turntable 76 which enables upper frame 12 to rotate relative to base
frame
14, such that application of the prepreg tape material on the molding tool 60
may be
carried out in the forward direction and in the reverse direction.
As the prepreg material tape 82 is unwound from the spool 80, it is advanced
to a slitter 90 where it is slit into a plurality of strips 84 of prepreg
material. The slitter
90 may include, for example, a plurality of stationary knives 92 or rotary
knives. The
number of strips and the width of the individual strips 84 depend on the
degree of
non-linearity of the surface of the molding tool 60 to which the strips 84 are
applied.
For example, the strips 84 may be uniform in width or may have different
widths to
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accommodate the non-linear path of the molding tool 60. While the description
of
the apparatus herein refers to a molding tool, it is to be understood that the
prepreg
material may be applied to the surface of a mold, mandrel, or any other
surface used
to form the composite structure in the prepreg dispensing operation.
In another embodiment, the strips 84 are slit during manufacture of the wide
prepreg web prior to being wound on a single spool. The spool 80 of pre-slit
strips is
then mounted on the spool holding assembly 16.
The carriage 10 includes a mechanism for taking up the difference in length of
the individual strips 84 resulting from the non-linear path of the molding
tool 60. In
one embodiment, an accumulator 94 is used. Accumulator 94 includes a plurality
of
rollers 96, each strip of prepreg 84 having an associated roller that is
independently
extendable and retractable as needed to manage the excess length of the
individual
strip resulting from the non-linear path on the molding tool 60. The
accumulator
rollers 96 maintain tension in the individual strips 84 so that the individual
strips 84
are smoothly applied to the molding tool 60. Extension and retraction of the
rollers
96 of the accumulator 94 may be effected by a plurality of actuators 98
coupled to
the rollers 96. In one embodiment, the actuators 98 include air cylinders.
Referring to FIG. 11, the carriage 10 includes a tensioning system 38 that
includes a brake disk 32 fixed to spindle 22, and pneumatically actuated brake
pads
100 that apply friction to the disk 32 under programmed control.
Referring to FIGS. 12 and 13, as the prepreg material 82 is unwound from the
spool 80, it is advanced to a slitter 90 where it is slit into a plurality of
strips 84 of
prepreg material. The prepreg strips 84 travel over the rollers 96 of the
accumulator
94, the path each strip independently controlled to manage any excess length
of the
individual strip resulting from the non-linear path on the molding tool 60 to
which the
strip is applied. From the accumulator rollers 96, the strips proceed to guide
rollers
102 which position the strips near the surface of the molding tool. The
compaction
roller 48 contacts the prepreg strips 84 and applies compaction pressure to
compress the prepreg strips 84 to the surface of the molding tool 60. The
surface of
the molding surface 60 may include concave and/or convex areas having varying
degrees of curvature, and/or flat areas. Although the path of the individual
prepreg
strips 84 on the surface of the molding tool may be nonlinear or curved, the
apparatus 10 is able to lay down the strips with little or no wrinkling of the
prepreg
layers and/or gaps between the strips on the mold.
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FIGS. 12-14 illustrate the steps involved in the positioning the tape on the
molding tool. Before being slit into strips 84, the tape 82 is guided by the
threading
guide 104 along the tape path as shown in FIG. 12, with the slitter 90
inactivated.
The tape 82 is clamped or held to the surface of the mold tool 60. The slitter
90 is
then activated and the carriage 10 begins to move forward (in the direction
indicated
by the arrow), pulling the tape 82 until the slit portion of the tape (i.e.,
the strips 84)
have extended past the compaction roller 48. The tape 84 is then cut laterally
and
the carriage 10 advances out of the way so the tape just laid down can be
pulled up
and discarded. The carriage 10 then moves to the programmed start position for
the
next layer to be applied, and the compaction roller 48 is lowered to begin
adhering
the prepreg strips 84 to the molding tool surface 64. From this point, the
prepreg
strips 84 are aligned by the crowned accumulator rollers 96 and the crowned
guide
roller 102. As the carriage 10 transitions from straight portions of the
molding
surface 64 to swept portions, or from one radius of sweep to another, the
cross
carriage 106 is shifted laterally by the cross carriage drive motor 104 to
keep the
center of the tape aligned with the center of the molding surface. In this
embodiment, the amount of shift is previously input as offset data points into
a table
in the controller 112. This same cross carriage 106 is used to move the
carriage an
additional or lesser distance as needed to track the tape 82 coming off the
spool 80,
as detected by the web edge sensor 110. This is done to provide a degree of
compensation for tape not evenly wound on the spool 80, or tape 82 that has
shifted
on the spool 80 during transport.
The operation of the carriage assembly may be controlled by a controller 112.
For example, the carriage 10 may be connected to a controller 112 that is
configured
to control the placement of the prepreg tape 82 or strips 84, the tension on
the tape
or strips, the direction in which the prepreg tape or strips are applied to
the surface of
the molding tool 60 and the speed at which the prepreg tape or strips are laid
down.
The carriage assembly 10 may apply the prepreg material tape 82 or strips 84
starting from either end of the molding tool 60 and may start and stop
according to
predetermined tape or strip locations. A cutter, such as an ultrasonic knife
(not
shown) may be used to automatically cut the tape or strips. In one embodiment,
the
carriage assembly may include a laser guide for determining the tape or strip
ply
locations.
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The prepreg tape material 82 on the spool 80 may have a liner or backing
layer adhered to the prepreg tape 82. In one embodiment, the liner or backing
layer
of the prepreg material is removed from the underside of prepreg web prior to
laying
down the tape 82 or individual strips 84 of prepreg material, and is taken up
on liner
take-up roll. In one embodiment (not shown), the prepreg material web 82
includes
a liner on the upper surface of the web that is removed prior to laying down
the web.
The carriage assembly may further include means for detecting incomplete
removal
of the liner or backing from the prepreg material web.
In one embodiment, the carriage assembly 10 may be removably coupled to a
spool loading station.
Referring to FIG. 17, another exemplary embodiment of the prepreg tape
dispensing apparatus of the present invention is illustrated. The apparatus
includes
a scrim dispensing assembly 210 that include a spindle 212 supported at each
end
by mounting bracket 214 on upper frame 12. Spool supports 226 mounted on
spindle 212 contact the inside of the spool of scrim material 224.
A layer of scrim material 216 may be unwound from spool 224 and joined to
prepreg material 82 as it is being unwound from prepreg spool 80 by passing
the
layer of scrim material 216 and the prepreg material 82 through nip rollers
218, 220
just prior to lay down of the prepreg material. The prepreg material 82 with
the scrim
material applied thereto forms a scrim reinforced prepreg 222 that is then
positioned
near the surface of the molding tool 60 by tension roller 47. As the carriage
10
travels across the molding tool 60, the compaction roller 48 contacts the
scrim
reinforced prepreg 222 and applies pressure to compress the prepreg tape to
the
surface of the molding tool 60.
The application of the scrim layer to the prepreg material just prior to lay
down
of the prepreg material provides a path for air evacuation between a first
prepreg
layer and a second prepreg layer subsequently laid down over the first layer
of
prepreg. Mounting the spool of scrim material directly on the cart provides
greater
flexibility as it is not always necessary and/or desirable to use a prepreg
material
having a scrim layer. In some instances, it is desirable to lay down a prepreg
layer
with no scrim and in other instances, a scrim reinforced prepreg layer is
desirable.
The scrim material includes yarns arranged in a grid or an open mesh and
may be made of any suitable material. Examples of yarn materials include
thermoplastic yarns, glass yarns, cellulose-based yarns and aramid yarns.
Suitable
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materials for the scrim include polyester such as polyethylene terephthalate
and
polybutylene terephthalate and copolymers thereof, polyamide such as nylon 6,
nylon 66, nylon 10, nylon 11 and nylon 12, polyethersulphone, polypropylene,
viscose staple yarn, meta and para-aramid, fiberglass, jute, flax, cotton and
combinations of two or more thereof. Polyester scrim materials are
commercially
available, for example, from Dextex Inc. of Georgia (U.S.A.), a subsidiary of
James
Dewhurst.
The strands of the scrim may be in the range of about 40 to about 300 denier,
or about 50 to about 150 denier, or about 50 to about 100 denier. The spacing
of the
warp and weft threads may be in the range of about 1 per inch to 10 per inch
(1 to 10
per 2.54 cm), or about 2 per inch to about 4 per inch (2 to 4 per 2.54 cm). In
one
embodiment, the spacing of the warp threads is 2 per inch (2 per 2.54 cm) and
the
spacing of the weft threads is 1 per inch (1 per 2.54 cm).
The scrim material, in one embodiment, is constructed of polyester threads
having straight warp threads and weft threads that are "wavy" or sinusoidal.
In another embodiment, the scrim material is constructed of polyester fibers
having a round cross-section arranged in a grid of fibers at 0 approximately
3/8 inch
(9.53 mm) apart and fibers at +/-45 spaced 15/16 inch (23.82 mm) apart. Such
scrim material is commercially available from Bellingroth GmbH & Co. (Germany)
under the trade name Bafatex.
EXAMPLE
A four wheeled cart was constructed to hold a spool of prepreg material
having an outside diameter of up to 32 inches (81.3 cm) and an inside diameter
of 12
inches (30.5 cm), and having a length of approximately 1800 feet (549 m). A
600
millimeter wide web of prepreg was slit into twelve strips of 2 in. (50.8mm)
in width
with stationary knives mounted on the cart.
Approximately three spools of prepreg material were used to construct a wind
turbine spar cap. The spools were loaded onto the cart by an overhead crane or
forklift.
The problem of wrinkling was reduced by laying down narrower prepreg strips
from a given radius of curvature. An analysis of this was done for the 130
feet (40
meter) radius of curvature and is shown in Table 1 below. As can be seen for
this
particular analysis, when strips are approximately 2.0 inches (5.0cm) wide,
the
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wrinkling area is reduced to approximately 8% of the baseline for 24 inch (61
cm)
wide prepreg strip.
Table 1
Wrinkle area for a 600mm wide strip on a 40 meter radius
number of strips ay. Width mm av width in. wrinkle area %
1 600.00 23.62 4.181 100.0 Baseline
2 300.00 11.81 2.090 50.0
3 200.00 7.87 1.394 33.3
4 150.00 5.91 1.045 25.0
5 120.00 4.72 0.836 20.0
6 100.00 3.94 0.697 16.7
7 85.71 3.37 0.597 14.3
8 75.00 2.95 0.523 12.5
9 66.67 2.62 0.465 11.1
10 60.00 2.36 0.418 10.0
11 54.55 2.15 0.380 9.1
12 50.00 1.97 0.348 8.3 Target
13 46.15 1.82 0.322 7.7
14 42.86 1.69 0.299 7.1
15 40.00 1.57 0.279 6.7
16 37.50 1.48 0.261 6.3
17 35.29 1.39 0.246 5.9
18 33.33 1.31 0.232 5.6
19 31.58 1.24 0.220 5.3
20 30.00 1.18 0.209 5.0
21 28.57 1.12 0.199 4.8
22 27.27 1.07 0.190 4.5
23 26.09 1.03 0.182 4.3
24 25.00 0.98 0.174 4.2
25 24.00 0.94 0.167 4.0
26 23.08 0.91 0.161 3.8
27 22.22 0.87 0.155 3.7
28 21.43 0.84 0.149 3.6
29 20.69 0.81 0.144 3.4
30 20.00 0.79 0.139 3.3
31 19.35 0.76 0.135 3.2
32 18.75 0.74 0.131 3.1
33 18.18 0.72 0.127 3.0
34 17.65 0.69 0.123 2.9
35 17.14 0.67 0.119 2.9
36 16.67 0.66 0.116 2.8
37 16.22 0.64 0.113 2.7
38 15.79 0.62 0.110 2.6
39 15.38 0.61 0.107 2.6
40 15.00 0.59 0.105 2.5
41 14.63 0.58 0.102 2.4
While this exemplary lay-up could be achieved by using a prepreg product
that consisted of 2-inch (5.1 cm) wide strips, production and packaging of
individual
prepreg strips would add significant cost over starting with a 24 inch (61.0
cm) wide
prepreg product on a single spool.
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The apparatus and process of the present invention is particularly useful for
the construction of wind turbine components. However, the apparatus and
process
can also be used for, for example, in the construction of structural and
aerodynamic
components for airplanes, helicopters, automobile bodies, rail cars, marine
crafts
and the like.
Although the invention has been shown and described with respect to a
certain embodiment or embodiments, it is obvious that equivalent alterations
and
modifications will occur to others skilled in the art upon the reading and
understanding of this specification and the annexed drawings. In particular
regard to
the various functions performed by the above described elements (components,
assemblies, devices, compositions, etc.), the terms (including a reference to
a
"means") used to describe such elements are intended to correspond, unless
otherwise indicated, to any element which performs the specified function of
the
described element (i.e., that is functionally equivalent), even though not
structurally
equivalent to the disclosed structure which performs the function in the
herein
illustrated exemplary embodiment or embodiments of the invention. In addition,
while a particular feature of the invention may have been described above with
respect to only one or more of several illustrated embodiments, such feature
may be
combined with one or more other features of the other embodiments, as may be
desired and advantageous for any given or particular application.
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