Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly ("directly driven") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

In order to extract more energy from the wind, the size of the rotor diameter is increased by increasing the dimensions of the wind turbine blades. To reduce the overall weight of the wind turbine blades, these may generally comprise composite materials and are often manufactured with resin-infused glass fiber composites. The manufacturing of wind turbine blades using composite materials allows them to meet the requirements with respect to size, geometry, and weight. Further, fibers can be aligned with load paths, generating blades with anisotropic mechanical properties and with enhanced mechanical properties. The possibility of fiber alignment allows placing the fibers at the exact position and direction as needed to provide the component with the required stiffness and strength. However, a desired fiber alignment is not currently a fully automated process, and repeatability is challenging.

Although composite materials have significant benefits compared with other structural materials, deposition of fiber mats is a complicated process. Particularly, a mold for a wind turbine blade shell comprises areas with complicated curvatures, including doubly curved surfaces and also including (almost) vertical surfaces. When depositing fiber mats, the fiber mats buckle and display waviness. This is inherent to many manufacturing processes of fiber-reinforced composite parts and significantly affects mechanical properties such as stiffness, strength, and fatigue of the product. Even though this is a specific problem related to wind turbine blade manufacturing, but similar problems may be encountered in other technical fields as well.

To avoid such buckling and waviness, the fibers need to be placed with shear displacement. Shear means that e.g. transverse fibers may not extend along the transverse direction, but rather at an angle.

To control proper fiber deposition, the placement of the fibers is still often carried out by hand. Even if fiber mats may initially be laid out in an automated process, a subsequent manual process is often necessary to avoid the aforementioned buckling and provide products with desired mechanical properties. Inherently in a manual process, the product quality and consistency is difficult to ensure.

A manual process allows a diverse draping of the fiber layers into the production tool and results in composite components with reduced weight and locally optimized mechanical properties. The manual placement and/or alignment of the fiber mats into the production tool results in a very tedious and cumbersome task, with limited reproducible quality and high production cost. <CIT> discloses the features of the respective preambles of claims <NUM> and <NUM>.

For these and other reasons, it is of interest to improve fiber deposition processes and to achieve this through an automatic or semi-automatic process, for which product quality can be highly reproducible and improved.

The present disclosure provides examples of systems and methods that at least partially overcome some of the drawbacks of existing wind turbine blade manufacturing processes.

In a first aspect, an apparatus for deposition of a fiber mat on a surface is disclosed. The fiber mat has a length that extends along a laying direction and a width that extends along a transverse direction. The apparatus comprises a reel for holding a roll of the fiber mat, a first and a second roller at a corresponding first and second transverse position and a fiber mat tension compensator. The first and second rollers are configured for applying traction on the fiber mat to unroll the fiber mat from the reel in the laying direction. Further, the first roller is controlled independently from the second roller. Besides, the fiber mat tension compensator is configured to adjust a tension in the fiber mat along the transverse direction.

According to this first aspect, the apparatus, by controlling the rollers independently, allows to locally modify the alignment of the fibers in the fiber mat, whereas, at the same time, generates a fiber mat deposition substantially free from wrinkles and other surface imperfections. This is achieved by means of the combination of the rollers with the fiber mat tension compensator, which limits the accumulation of fiber downstream of the rollers. This results in a considerable reduction in the manufacturing time as compared to known approaches for fiber mat deposition over three dimensional surfaces. Further, the apparatus significantly reduces the need of manual post-deposition assistance, which at the same time, promotes a highly repeatable final product.

In another aspect, a method for depositing a fiber mat having a length and a width on a surface is provided. A roll of the fiber mat is arranged on a reel, and the method comprises rotating two or more rollers to apply traction to the fiber mat and pull the fiber mat from the reel in a laying direction. During rotation of the rollers, one of the rollers has a different speed than at least one of the other rollers to obtain a shear angle in the fiber mat. Further, the method comprises depositing the fiber mat on the surface, and adjusting the tension along the width of the fiber mat in a portion of the fiber mat between the rollers and the reel.

Throughout the present disclosure a fiber mat may be regarded as encompassing any piece of cloth of fabric comprising fibers. The fibers may be arranged in strands or rovings. The fiber may be natural or synthetic fibers and particularly may be any type of fiber suitable for fiber reinforced composites, and more particularly may be glass fibers or carbon fibers. The fibers may have a variety of different orientations e.g. the fiber mats may be uniaxial, biaxial, multi-axial or different. The fibers may be woven with different types of weaves or may be unwoven.

Throughout this disclosure, the term "shear angle" should be understood as the angle that is defined between the fibers of the mat and their original, intended direction. transverse fibers may have a shear angle that is the deviation between the original direction of the fibers (i.e. <NUM>° orientation to the length of the fiber mat, <NUM>° orientation to the length of the fiber mat, or others) and the actual direction of the fibers. As an example, the shear angle for fibers arranged at <NUM>° orientation with respect to the length of the fiber mat may be defined as the actual direction of the fibers with respect to the <NUM>° direction.

Since the fibers in a fiber mat may not be tightly connected, in examples the shear angle may be modified across the fiber mat. A positive angle of shear would be understood as a local rotation of the fibers with respect to the intended direction in counterclockwise direction, and a negative angle of shear as a local rotation of the fibers in a clockwise direction.

Reference now will be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims.

<FIG> illustrates a conventional modern upwind wind turbine <NUM> according to the so-called "Danish concept" with a tower <NUM>, a nacelle <NUM> and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub <NUM> and three blades <NUM> extending radially from the hub <NUM>, each having a blade root <NUM> nearest the hub and a blade tip <NUM> furthest from the hub <NUM>.

The wind turbine blade <NUM> comprises a blade shell comprising two blade shell parts or half shells, a first blade shell part <NUM> and a second blade shell part <NUM>, typically made of fiber-reinforced polymer. The wind turbine blade <NUM> may comprise additional shell parts, such as a third shell part and/or a fourth shell part. The first blade shell part <NUM> is typically a pressure side or upwind blade shell part. The second blade shell part <NUM> is typically a suction side or downwind blade shell part. The first blade shell part <NUM> and the second blade shell part <NUM> are fastened together with adhesive, such as glue, along bond lines or glue joints <NUM> extending along the trailing edge <NUM> and the leading edge <NUM> of the blade <NUM>. Typically, the root ends of the blade shell parts <NUM>, <NUM> has a semi-circular or semi-oval outer cross-sectional shape.

<FIG> is a schematic diagram illustrating a cross sectional view of an exemplary wind turbine blade <NUM>, e.g. a cross sectional view of the airfoil region of the wind turbine blade <NUM>. The wind turbine blade <NUM> comprises a leading edge <NUM>, a trailing edge <NUM>, a pressure side <NUM>, a suction side <NUM> a first spar cap <NUM>, and a second spar cap <NUM>. The wind turbine blade <NUM> comprises a chord line <NUM> between the leading edge <NUM> and the trailing edge <NUM>. The wind turbine blade <NUM> comprises shear webs <NUM>, such as a leading edge shear web and a trailing edge shear web. The shear webs <NUM> could alternatively be a spar box with spar sides, such as a trailing edge spar side and a leading edge spar side. The spar caps <NUM>, <NUM> may comprise carbon fibers while the rest of the shell parts <NUM>, <NUM> may comprise glass fibers.

<FIG> is a schematic diagram illustrating an exemplary mold system for molding a blade shell of a wind turbine blade. The mold system <NUM> comprises a first mold <NUM> and a second mold <NUM>. The first mold <NUM> is configured for manufacturing a first blade shell part of a wind turbine blade, such as an upwind shell part of the wind turbine blade (forming the pressure side). The second mold <NUM> is configured for manufacturing a second blade shell part of the wind turbine blade, such as a downwind shell part of the wind turbine blade (forming the suction side). Surfaces <NUM> and <NUM> are mold surfaces for depositing fibers.

<FIG> schematically illustrates an apparatus <NUM> for deposition of a fiber mat <NUM> on a surface according to one example. The apparatus <NUM> comprises a reel <NUM> for holding a roll <NUM> of the fiber mat <NUM>. Said fiber mat <NUM> has a length that extends along a laying direction and a width that extends along a transverse direction. Further, the apparatus <NUM> comprises a first roller <NUM> at a first transverse position and a second roller <NUM> at a second transverse position. The first and second rollers <NUM>, <NUM> are configured for applying traction on the fiber mat <NUM> to unroll the fiber mat <NUM> from the reel <NUM> in the laying direction. Additionally, the first roller <NUM> is controlled independently from the second roller <NUM>. The apparatus <NUM> further comprises a fiber mat tension compensator <NUM> configured to adjust a tension in the fiber mat <NUM> along the transverse direction.

In order to control a shear angle, the rollers <NUM> and <NUM> may be controlled independently, in particular the rotational speed may be controlled independently. If one of the rollers rotates faster than the other one, the fast roller may exert more traction on the fibers, thus creating a shear angle. If one of the rollers rotates faster than the other one, fiber material could accumulate between the other roller and the reel <NUM>. If the rollers have a different velocity profile the tension compensator <NUM> may be used to adjust tension along the transverse direction due to previous differences in rotating speed of each of the roller <NUM>, <NUM>. In the shown example, the fiber mat tension compensator <NUM> may be used to adjust a length of a trajectory between the reel and the rollers to avoid accumulation of material at one of the rollers.

The apparatus <NUM> allows depositing fiber mat <NUM> on a surface in a fast and efficient manner, and allows replicating fiber mat depositions during different runs. Thus, the apparatus <NUM> may increase the repeatability of the results achieved during the manufacturing of composite components. Further, since the first roller <NUM> is controlled independently from the second roller <NUM>, the apparatus <NUM> can modify the shear angle between fibers during deposition in a continuous manner. This allows adapting the shear angle between fibers according to the particularities of the surface where the fiber is to be deposited and severely reduces fiber imperfections such as wrinkles. Further, thanks to the mitigation in fiber imperfections during deposition, operators may not need to brush the deposited fiber, or less than before and therefore, further imperfections due to the operators standing on the fiber mat are also avoided.

The example in <FIG> shows that the apparatus <NUM> may further comprise a frame <NUM> for carrying the reel <NUM>, the first and second rollers <NUM>, <NUM> and the fiber mat tension compensator <NUM>. Said frame <NUM> may be displaceable along the laying direction to facilitate fiber mat deposition. Similarly, said frame <NUM> may comprise sub-frames for each component, i.e. the reel <NUM>, the first and second rollers <NUM>, <NUM> and the fiber mat tension compensator <NUM>, and the sub-frames may be at least partially displaceable between each other.

Additionally, <FIG> shows that the fiber mat tension compensator <NUM> may be arranged between the reel <NUM> and the first and second rollers <NUM>, <NUM>. The shear angle variation that can be achieved when depositing the fiber mats depends inter alia on a distance between the reel, and the rollers and on a tension that the fiber mat tension compensator <NUM> can apply.

In the example illustrated in <FIG>, the fiber mat tension compensator <NUM> comprises a fiber mat contact surface <NUM> and an actuator. The actuator is configured to modify the position of at least a portion of the fiber mat contact surface <NUM> along a vertical direction. In some examples, the actuator may comprise several independent components to locally modify the position of the fiber mat contact surface <NUM>. In the example illustrated in <FIG>, the actuator comprises two movable connections at the two ends of the fiber mat contact surface <NUM> respectively. The fiber mat contact surface <NUM> in this example is the outer surface of a cylinder.

The movable connections in <FIG> are linked to respective spring type elements. The length of the springs may be controlled to determine the vertical position of the ends of the cylinder, and therewith the inclination of the cylinder. But other arrangements may also be employed. For example, the movable connections may be arranged within a vertical guide, or may be directly connected to a guiding system operable by the actuator. The movable connections may be substantially below or above the fiber mat and may allow displacing either end of the cylinder upwards or downwards, and define an inclination of the cylinder, and thereby a tension along the transverse direction. In other examples, the actuator may comprise hydraulic pistons, pneumatic pistons, servomotors, cams or worn screws assemblies to control the position of the fiber mat contact surface <NUM>. Further, other number and distribution of the same could be applied.

In some examples the fiber mat tension compensator <NUM> may comprise a cylinder as a fiber mat contact surface <NUM>. The cylinder may be a freely rotating cylinder, a fixed cylinder or a cylinder with controlled rotation. Other type of surfaces can be used as a fiber mat contact surface <NUM>. In some examples, the fiber mat contact surface <NUM> may comprise two or more portions that can be independently adjusted in height. In some other examples, the fiber mat contact surface <NUM> may be a compliant surface that is capable of modifying the surface shape. Compliant surfaces may have the actuator integrated below the surface to reduce space.

In the present disclosure, a vertical direction should be understood as a direction substantially perpendicular to the laying direction and the transverse direction.

In examples, the surface upon which the fiber mats may be deposited may be an inside surface of a mold for the manufacturing of a shell of a wind turbine blade, but it is clear that the herein disclosed systems and methods may be used for the manufacture of other products, in particular fiber-reinforced composite products, i.e. spar caps. After a mat has been deposited in the mold, further mats be deposited next to the mat, and on top of it. Depending on the shape and e.g. the curvature of mold, the appropriate shear angle may be defined. With the apparatus according to the example of <FIG>, the corresponding shear angle may be used for deposition in an automated and precise manner.

<FIG> also illustrates that the fiber mat tension compensator <NUM> may adjust fiber mat tension along the transverse direction in response to a change in speed of at least one of the rollers <NUM>, <NUM>. Thus, by adjusting the fiber mat tension locally, i.e. in a portion of the fiber mat <NUM>, the fiber mat tension compensator <NUM> avoids the accumulation of fiber behind the rollers <NUM>, <NUM>. As previously discussed, the tension compensation may actuate to adjust to varying speed of the rollers <NUM>, <NUM>.

The example in <FIG> also shows that one or more of the first and second rollers <NUM>, <NUM> may be arranged on a shaft <NUM>. In examples, the rollers <NUM>, <NUM> and the shaft <NUM> define a rotatable connection. Further, the shaft <NUM> may be substantially perpendicular to the laying direction and to the transverse direction This allows modifying an angle defined between the laying direction and the rotation direction of the rollers <NUM>, <NUM>. Changes in this angle can improve the deposition of fiber mat, for example in configurations where the apparatus <NUM> is tilted and gravity acting on the fiber mat <NUM> interferes with achieving a homogenous fiber mat distribution.

Furthermore, in some examples, one or more of the first and second rollers <NUM>, <NUM> may be configured to be translated along the transverse direction. This allows using the apparatus <NUM> with fiber mats of different widths. Further, translating the rollers <NUM>, <NUM> along the transverse direction allows controlling the point of maximum shear angle e.g. in examples with three or more rollers wherein the apparatus <NUM> generates a non-constant shear angle along the transverse direction of the fiber mat <NUM>.

In examples, the reel <NUM> may comprise a drive for rotating a shaft of the reel <NUM> to control a tension of the fiber mat <NUM> on the reel <NUM>. This allows for a more precise fiber mat deposition, as will be discussed in relation with <FIG>. Other methods for controlling the tension in the fiber mat roll <NUM> on the reel <NUM> can be envisaged as well, e.g. rollers or other elements exerting pressure on the outer surface of the fiber mat roll.

In the example of <FIG>, the overall tension on the fiber mat <NUM> is maintained substantially constant between the two rollers <NUM>, <NUM> and the reel <NUM>. Further, <FIG> shows that an additional roller <NUM> may be employed to limit the transmission of shear angle caused by the two rollers <NUM>, <NUM>. Thus, the additional roller <NUM> may comprise a substantially high friction surface to prevent any spanwise variations in the fiber mat <NUM> to reach the reel <NUM>. Additionally, the apparatus <NUM> may comprise two side rollers <NUM>, <NUM> located one at each side of the fiber mat tension compensator <NUM> and configured to limit the vertical displacement of the fiber mat <NUM> caused by the fiber mat tension compensator <NUM> in a longitudinal direction.

<FIG> illustrate four different examples of two rollers <NUM>, <NUM> applying traction on the fiber mat <NUM>. In <FIG>, the first fiber mat end <NUM> corresponds to the fiber portion that is closest to the reel <NUM> whereas the second fiber mat end <NUM> corresponds to the fiber portion that is closest to the deposition surface. <FIG> illustrates a first example wherein the pretension exerted by the reel <NUM> and the fiber mat tension compensator <NUM> is balanced with the traction produced by the rollers <NUM>, <NUM>. In <FIG>, both rollers are rotating at the same speed, and therefore the shear angle <NUM> is zero.

<FIG> illustrates a second example wherein the pretension exerted by the reel <NUM> and the fiber mat tension compensator <NUM> is too high compared with the traction produced by the rollers <NUM>, <NUM>. This causes the fibers directly beneath the rollers <NUM>, <NUM> to advance faster along the laying direction than the rest, and promotes an undesired pattern in the fiber mat <NUM> with negative and positive shear angles <NUM> along the transverse direction.

<FIG> illustrates a third example wherein the pretension exerted by the reel <NUM> and the fiber mat tension compensator <NUM> is too low and the material has a high longitudinal stiffness. In this case, the rollers may appear to be dragging the fiber mat, and again this results in an undesired pattern in the fiber mat <NUM>.

Lastly, <FIG> illustrates a fourth example wherein the pretension exerted by the reel <NUM> and the fiber mat tension compensator <NUM> is unbalanced along the transverse direction. In the example, the tension may be balanced with the traction produced by the second roller <NUM> but it is too high compared with the traction produced by the first roller <NUM>. This leads to a portion of the fiber mat being deposited with the desired shear angle <NUM> (zero in this case) and a portion of the fiber mat being deposited with an undesired shear angle <NUM>.

<FIG> schematically illustrates a fiber mat tension compensator <NUM> acting on a fiber mat portion between the rollers <NUM>, <NUM> and the reel <NUM> (not shown in <FIG>). As in <FIG>, the first fiber mat end <NUM> corresponds to the fiber mat portion that is closest to the reel <NUM> whereas the second fiber mat end <NUM> corresponds to the fiber mat portion that is closest to the rollers <NUM>, <NUM> and deposition surface. In the illustrated example in <FIG>, the type of fiber mat tension compensator <NUM> substantially coincides with the one illustrated in <FIG>, nevertheless the following discussion is also valid for other alternatives that could be applied. The fact that the rollers <NUM>, <NUM> can be independently controlled means that, if a different velocity profile is assigned to each of the rollers <NUM>, <NUM>, the fiber mat portion below each of them will travel at a different speed. Therefore, at a given time after operation, a certain amount of fiber mat may be accumulated behind the roller <NUM>, <NUM> that has been rotating with a lower average speed.

To mitigate the effects of this fiber accumulation, the fiber mat tension compensator <NUM> may use one or more actuators, e.g. pistons, with more than one independent component to adjust the tension of the fiber mat along a transverse direction and more specifically, the fiber mat tension compensator <NUM> balances the tension difference between the reel <NUM> and the first and second rollers <NUM>, <NUM>. This is shown in <FIG>, wherein a first independent component (not shown) lifts a portion of the fiber mat contact surface to compensate the difference in fiber mat length behind the rollers <NUM>, <NUM>. Doing so, the fiber mat tension compensator <NUM> adjusts a length of a path of the fiber mat <NUM> between the reel <NUM> and the first and second rollers <NUM>, <NUM> as a function of the transverse position.

<FIG> schematically shows a portion of the fiber mat <NUM> below the rollers <NUM>, <NUM>. Note that this figure shows a situation that can correspond with the scenario previously discussed in <FIG> or similar. In this figure, the second roller <NUM> is rotating at a higher speed than the first roller <NUM>. This can be derived from the orientation of the fibers, and more precisely from the positive magnitude of the shear angle <NUM> of the fibers.

<FIG> is a flow diagram of an example of a method <NUM> for depositing a fiber mat <NUM> on a surface. The fiber mat <NUM> of the method <NUM> has a length and a width, and a roll <NUM> of the fiber mat <NUM> is arranged on a reel <NUM>. In particular, <FIG> shows that the method <NUM> comprises, at block <NUM>, rotating two or more rollers <NUM>, <NUM> to apply traction to the fiber mat <NUM> and pull the fiber mat <NUM> from the reel <NUM> in a laying direction. Further, at block <NUM> of the method <NUM>, one of the rollers <NUM>, <NUM> has a different speed than at least one of the other rollers <NUM>, <NUM> to obtain a shear angle <NUM> in the fiber mat <NUM>. Further, the method <NUM> also comprises, at block <NUM>, depositing the fiber mat <NUM> on the surface. Additionally, the method also comprises, at block <NUM>, adjusting tension along the width of the fiber mat <NUM> in a portion of the fiber mat <NUM> between the rollers <NUM>, <NUM> and the reel <NUM>.

In some examples, the depositing <NUM> the fiber mat is carried out in a mold for the manufacture of a shell of a wind turbine blade <NUM>. Further, in some examples, the method <NUM> may also comprise brushing a deposited fiber mat <NUM> to reduce fiber mat surface irregularities. The brushing step can be performed manually or automatically.

In some further examples, the rollers <NUM>, <NUM> at block <NUM> of the method <NUM> are rotated in accordance with individual speed profiles, and the individual speed profiles are determined in a simulation of a lay-up process.

Further, the method <NUM> may also comprise infusing the fiber mats <NUM> with resin and curing the resin. Particularly, vacuum assisted resin transfer molding may be used. After curing, a half blade shell may be obtained.

<FIG> is a flow diagram of an example of another method <NUM> for laying fiber mat <NUM> in a mold for a shell of a wind turbine blade <NUM>. The method <NUM> comprises, at block <NUM>, determining a desirable shear angle <NUM> in the fiber mat <NUM>. Besides, the method <NUM> comprises unrolling <NUM> the fiber mat <NUM> from a reel <NUM> as the reel <NUM> is displaced along the mold. Further, the method also comprises, at block <NUM>, depositing the fiber mat <NUM> in the mold in a laying direction at a first transverse position, and applying a second traction in the laying direction at a second transverse position to obtain the desirable shear angle <NUM> in the fiber mat <NUM>. Additionally, the method <NUM> also comprises, at least partially compensating <NUM> a tension in the fiber mat <NUM> along the transverse direction.

In some examples, at block <NUM> of the method <NUM>, the first traction and the second traction may be applied by a first and a second roller <NUM>, <NUM> respectively. Further, the first roller <NUM> may have a first rotational speed and the second roller <NUM> may have a second rotational speed, and the two speeds may be different from each other.

In some further examples, block <NUM> of the method <NUM> may comprise adjusting a length of a path of the fiber mat <NUM> between the reel <NUM> and the first and second rollers <NUM>, <NUM>.

In any of the examples disclosed herein, the fiber mat may comprise glass fiber or carbon fiber.

Claim 1:
An apparatus (<NUM>) for deposition of a fiber mat (<NUM>) on a surface, the apparatus (<NUM>) comprising:
a reel (<NUM>) for holding a roll (<NUM>) of the fiber mat (<NUM>), the fiber mat (<NUM>) having a length and a width, wherein the length extends along a laying direction and the width extends along a transverse direction;
a first roller (<NUM>) at a first transverse position and a second roller (<NUM>) at a second transverse position for applying traction on the fiber mat (<NUM>) to unroll the fiber mat (<NUM>) from the reel (<NUM>) in the laying direction, wherein the first roller (<NUM>) is configured to be controlled independently from the second roller (<NUM>); and
a fiber mat tension compensator (<NUM>) configured to adjust a tension in the fiber mat (<NUM>) along the transverse direction, characterized in that
at least one of the first and second rollers (<NUM>, <NUM>) is configured to be translated along the transverse direction.