Method for arranging a plurality of preforms in a wind turbine blade mould

Field of the invention

The present invention relates to a method of manufacturing a wind turbine blade, the method comprising arranging a plurality of preforms in a wind turbine blade mould, to an apparatus for use in the method, and to a preform for a wind turbine blade shell.

Background of the invention

Wind is an increasingly popular clean source of renewable energy with no air or water pollution. When the wind blows, wind turbine rotor blades spin clockwise, capturing energy through a main shaft connected to a gearbox and a generator for producing electricity. Rotor blades of modern wind turbines are carefully designed to maximise efficiency. Modern rotor blades may exceed 80 metres in length and 4 metres in width.

Wnd turbine rotor blades are typically made from a fibre-reinforced polymer material, comprising a pressure side shell half and a suction side shell half, also called blade halves. The cross-sectional profile of a typical blade includes an airfoil for creating an air flow leading to a pressure difference between both sides. The resulting lift force generates torque for producing electricity.

The shell halves of rotor blades are often manufactured using blade moulds. First, a blade gel coat or primer is applied to the mould. Subsequently, fibre reinforcement and/or fabrics are placed into the mould followed by resin infusion. A vacuum is typically used to draw epoxy resin material into a mould. Alternatively, prepreg technology can be used in which a fibre or fabric pre-impregnated with resin forms a homogenous material which can be introduced into the mould. Several other moulding techniques are known for manufacturing wind turbine blades, including compression moulding and resin transfer moulding. The shell halves are assembled by being glued or bolted together substantially along a chord plane of the blade.

As the length of wind turbine blades increases, the cycle time to manufacture such blades is prolonged due to the structure of these blades. Typically, glass layers are unrolled from crane-assisted cradles from rolls going up and down the length of the blade. In between such glass layers, a core material, such as foam, either balsa or another type, is arranged. The number of layers of glass and core that needs to be deposited on respective upwind and downwind shell halves for a >70 meter blade accurately creates a number of challenges for blade manufacturers. Furthermore, the root diameter of such blades poses another challenge, as fabric shifting may cause wrinkles, necessitating costly and time-consuming repairs.

In this regard, the use of preforms becomes increasingly important. A preform is a shaped arrangement of fibres, such as multiple layers thereof, which has been bound and/or consolidated for later use as part of the fibre lay-up in the blade mould. The rationale for using preforms for blade manufacturing is to reduce cycle time in the blade mould. In addition, using preforms may reduce the number of required repairs due to the pre-consolidated structure of the preforms. As blade lengths increase, using preforms for blade lay-up adds efficiency and precision.

Typically, multiple preforms will be used in manufacturing a wind turbine blade, whereas sometimes only one preform is used for each shell. This usually requires large spaces for manufacturing and for storing the preforms. In addition, the manufacturing of preforms of different shapes and sizes can be time-consuming and expensive. Providing moulds for manufacturing preforms can be tedious and costly, which applies even more if preforms of various shapes and curvatures are required. Equipment for handling such various preforms will often take up a large space during storage.

A shell half of a modern wind turbine blade may comprise different preforms of 20 or more slightly different geometries, which provides certain challenges in particular with regard to transferring the different preforms from their respective preform moulds to the blade mould.

It is therefore a first object of the present invention to provide a cost-efficient and effective way of arranging a plurality of preforms for wind turbine blade parts within the blade mould.

It is a further object of the present invention to provide a flexible and efficient apparatus for such processes. It is another object of the present invention to provide an improved method of manufacturing a wind turbine blade using preforms with various geometries.

It is another object of the present invention to provide a preform design that is particularly well suited for such manufacturing processes, and that reduces the formation of wrinkles within the root shell structure.

Summary of the invention The present invention addresses one or more of the above-discussed objects by providing a method of manufacturing a wind turbine blade, the method comprising providing a plurality of preforms for a wind turbine blade, a blade mould comprising a mould cavity for manufacturing a shell part of a wind turbine blade, an engaging member attached to at least one cable and being adapted for movement over the mould cavity while attached to the at least one cable, a plurality of cable support members disposed on or adjacent to the blade mould, each of the cable support members being adapted for supporting a respective cable, at least one cable actuator in communication with at least one of the cables and configured to move the engaging member over the mould cavity, wherein the method further comprises the steps of a) engaging at least one of the plurality of preforms with the engaging member, b) raising the engaging member with the engaged preform by means of the cable actuator, c) moving the engaging member with the engaged preform over the mould cavity by means of the cable actuator, d) arranging the engaged preform within the mould cavity, and e) disengaging the preform from the engaging member, wherein steps a) to e) are carried out repeatedly for arranging a plurality of preforms within the mould cavity.

It was found that this method reduces the cycle time and significantly increases the speed of manufacturing blades. Advantageously, the preforms can be moved in the method of the present invention with six degrees of freedom, i.e. the preform is free to change position as forward/backward (surge), up/down (heave), left/right (sway) translation in three perpendicular axes, combined with changes in orientation through rotation about three perpendicular axes, i.e. yaw (normal axis), pitch (transverse axis), and roll (longitudinal axis).

In a preferred embodiment, at least 10 preforms, such as at least 20 or at least 30 preforms are used in the method of the present invention. Advantageously, at least 10 preforms, such as at least 20 or at least 30 preforms are used per shell half, i.e. per upwind shell half or downwind shell half. Typically, the preform is a fibrous composite preform. In a preferred embodiment, each preform comprises a fibre material, such as fiberglass, carbon, or aramid. Preferably, each preform also comprises a binding agent. In a particularly preferred embodiment, each preform comprises at least three layers, an upper fibre layer, a core or foam layer, and a lower fibre layer. In some embodiments, the preform may comprise carbon fibres. It is preferred that the preforms are substantially rectangular with the largest dimension extending in a spanwise direction, or length direction, when arranged in the blade mould.

It is preferred that the blade mould is a mould for a shell half of a wind turbine blade, such as an upwind shell half or a downwind shell half. Thus, the shell part is typically an upwind shell half or a downwind shell half. The blade mould can be over 80 meters long. Prior to arranging the preforms within the mould cavity, the mould cavity may be coated with a mould release product and/or a gel coat.

Typically, the engaging member is a member configured to engage a top surface of a preform, i.e. a substantially planar or curved top surface which, when arranged in the mould cavity, faced upwards. The engaging member may comprise one or more hooks, pins or suction cups to engage with a surface of the preform, i.e. to lift the preform into the mould cavity.

In a preferred embodiment, the engaging member is attached to a plurality of cables, preferably four cables extending in four respective directions with an angle of approximately 90 degrees between neighbouring cables as seen in a top view. This advantageously allows moving the engaged preform with six degrees of freedom, i.e. forward/backward, up/down, left/right translation in three perpendicular axes, combined with changes in orientation through rotation about three perpendicular axes, i.e. yaw, pitch, and roll. Thus, each preform can be arranged optimally even with complex mould cavity geometries. The cable support members are preferably cable support towers or vertically extending masts, such as telescoping masts. It is preferred that the cable support members are arranged in respective assemblies of four cable support members in a square-shaped or rectangular-shaped arrangement, with one cable support member in each corner of the square or rectangle.

It is preferred that the plurality of cable support members is disposed adjacent to the blade mould. In a particularly preferred embodiment, two cable support members are disposed on either side of the mould, adjacent to the mould, i.e. two cable support members adjacent to the leading edge side of the mould, and two cable support members adjacent to the trailing edge side of the mould.

The cable actuator may comprise a motor winch for controlling the respective cable’s length and tension. Typically, one end of each cable is reeled around a rotor twisted by a motor.

In the step of engaging at least one of the plurality of preforms with the engaging member, the engaging member preferably grasps, grips or sucks the preform into engagement, before raising the engaging member with the engaged preform by means of the cable actuator. The engaged preform is then moved, for example from a preform preparation station, over the mould cavity by means of the cable actuator. Each preform is then successively arranged within the mould cavity, for example starting at the root end thereof. For example, three or more preforms can be arranged between the leading edge and the trailing edge of the mould cavity at the root end, followed by three or more preforms arranged between the leading edge and the trailing edge of the mould cavity, closer to the tip.

Once arranged accurately in the mould cavity, the preform can be disengaged. The preform may be released in step e) in a blade mould in a substantial horizontal orientation, a substantially vertical orientation or some intermediate orientation between vertical and horizontal.

Steps a) to e) are carried out repeatedly for arranging a plurality of preforms within the mould cavity, for example 5 or more times, such as 10 or more, or 20 or more times. It is preferred that a software with vision inspection control is used to ensure the accuracy of preform placement. Step a) can advantageously be carried out at a preparation station at one or more preforms are kept for transferring the preform(s) to the blade mould for moulding a shell part, such as an upwind or downwind shell half, of a wind turbine blade. Alternatively, the one or more preforms may be located within a stockpile of preforms, or within their respective preform moulds where the preforms were formed, prior to step a).

The wind turbine blade shell part is preferably a shell half of a blade, such as a pressure side shell half or a suction side shell half. In some embodiments, the method of manufacturing a wind turbine blade part may involve arranging preforms in a prefab mould with subsequent infusing of resin and curing for manufacturing sub parts for later blade assembly. In some embodiments, the wind turbine blade part is a root laminate, a main laminate or a part thereof. In another embodiment, the blade part is a blade half. In other embodiments, the blade part is a full blade.

Typically, a resin infusion step is carried out once all of the preforms have been arranged in the blade mould. Advantageously, the resin infusion step comprises vacuum assisted resin transfer moulding. In a preferred embodiment, the resin dissolves the binding agent of the preform. Other embodiments involve chemical binding, for example for epoxy or thermoset resins. The resin for injecting the preform during the manufacturing of wind turbine blade parts, such as a root laminate, may be an epoxy, a polyester, a vinyl ester or another suitable thermoplastic or duroplastic material. In other embodiments, the resin may be a thermosetting resin, such as epoxy, vinyl ester or polyester, or a thermoplastic resin, such as nylon, PVC, ABS, polypropylene or polyethylene.

Preferably, the preform to be used in the present methods is a consolidated arrangement of material comprising fibres, such as glass fibres, and a binding agent. The preform will typically be used for manufacturing a blade half of a wind turbine blade. The preforms can be used in a subsequent blade moulding process as part of the fibre lay-up in the blade mould, such as a blade half mould. The preforms used according to the present invention can be placed within the root region of a blade mould, thus constituting part of the root laminate. The root region may correspond to a region of the blade having a substantially circular or elliptical cross-section. However, the preforms could also be used for other parts and regions of a wind turbine blade, such as trailing edge or leading- edge reinforcements or adhesive flanges. Alternatively, the preforms could be used for a full blade layup. The method of manufacturing a wind turbine blade part of the present invention may comprise laying up additional material, such as fibre material, in the blade mould together with the preforms. In a preferred embodiment, steps a) to e) are carried out at least 10 times for arranging at least 10 preforms within the mould cavity.

In a preferred embodiment, moving the engaging memberwith the engaged preform over the mould cavity comprises retracting or extending the cables by means of the cable actuator. Typically, this will be achieved by winding or unwinding the cable from a rotor that is twisted by a motor. In a preferred embodiment, each cable has a corresponding cable actuator, wherein the cable actuator winds or unwinds the cable from a spool driven by the cable actuator

In a preferred embodiment, a cable actuator is provided at each of the cable support members, the cable engaged with the actuator at a proximate end and attached to the engagement member at a distal end of the cable. Where the cable support member takes the form of a vertically extending mast, such as telescoping mast, a cable actuator may be arranged at the top of the mast. In another embodiment, the cable actuator is disposed on or within the engagement member.

In a preferred embodiment, each cable further comprises an attachment to a respective one of the plurality of cable support members, such that the engaging member is configured to traverse above the mould cavity by extending or retracting the cable relative to the respective support member.

In a preferred embodiment, each of the cable support members comprises a cable actuator. In a preferred embodiment, the cable support member is a cable support tower.

In a preferred embodiment, the engaging member is a gripping device, such as a needle gripper. In other embodiments, the engaging member may comprise one or more suction cups.

In a preferred embodiment, the method further comprises the steps of infusing resin into the plurality of arranged preforms, and curing or hardening the resin in order to form the shell part. In another aspect, the present invention relates to the use of a cable driven robot for manufacturing a wind turbine blade. In a preferred embodiment, said use comprises arranging a plurality of preforms within a mould cavity of a blade mould using the cable driven robot. Preferably, the cable driven robot comprises several flexible cables wherein one end of each cable is reeled around a rotor twisted by a motor, and the other end is connected to an engaging member, such as a gripping device, for engaging a preform. In some embodiments, the cable driven robot is a four-cable-driven parallel robot. In some embodiments, the cable driven robot is an eight-cable-driven parallel robot.

In another aspect, the present invention relates to a wind turbine blade obtainable by the method of the present invention.

In another aspect, the present invention relates to an apparatus for use in a method according to the present invention, the apparatus comprising a blade mould having a mould cavity for manufacturing a shell part of a wind turbine blade, an engaging member and at least one cable, wherein the engaging member is attached to the at least one cable, the engaging member being adapted for movement over the mould cavity while attached to the at least one cable, a plurality of cable support members disposed on or adjacent to the blade mould, each of the cable support members being adapted for supporting a respective cable, and at least one cable actuator in communication with at least one of the cables and configured to move the engaging member over the mould cavity.

In some embodiments, one or more of the cable support members may form a rigid support frame. In a preferred embodiment, the cable actuator comprises at least one motor winch and/or pulley. The apparatus of the present invention may also comprise a computer and a control panel equipped with motor drivers and power supply.

The apparatus of the present invention may also comprise one or more sensors and cameras for enhanced movement control. For example, laser ranging can be used to guide accurate placement of preforms within the mould cavity.

In some embodiments, a programmable logic controller may be used to control the apparatus of the present invention. In a preferred embodiment, the apparatus comprises logic for defining a lay-up area within the mould cavity and driving the actuators and engagement member for arranging a plurality of preforms in a wind turbine blade mould. In a preferred embodiment, the apparatus comprises logic for engaging a preform for the shell part of the wind turbine blade, raising the engaging member with the engaged preform by means of the cable actuator, moving the engaging member with the engaged preform over the mould cavity by means of the cable actuator, arranging the engaged preform within the mould cavity, and disengaging the preform from the engaging member.

In a preferred embodiment, the apparatus comprises at least one rail extending in a substantially spanwise direction of the blade mould. The at least one rail is preferably disposed adjacent to the blade mould. Preferably, the apparatus comprises at least two rails extending in a substantially spanwise direction of the blade mould, wherein a first rail extends along the leading edge of the blade mould and a second rail extends along the trailing edge of the blade mould.

In a preferred embodiment, the cable support members are slidably arranged on a rail extending in a substantially spanwise direction of the blade mould. Thus, the rail may extend essentially along the entire length of the blade mould. In a preferred embodiment, four cable support members together form a substantially quadrangular rigid support frame that is slidably arranged on respective rails extending along either side of the blade mould, wherein a first rail extends along the leading edge of the blade mould and a second rail extends along the trailing edge of the blade mould. The cable support members and/or the rigid support frame may comprise one or more guide members at their respective lower ends to guide the cable support members or the support frame along the rail(s).

In a preferred embodiment, the apparatus comprises four interconnected cable support members wherein pairs of two cable support members are arranged at opposing sides of the blade mould. The four interconnected cable support members are preferably slidably arranged around the blade mould.

In a preferred embodiment, the engaging member is a gripping device such as a needle gripper, preferably a pneumatic needle gripper. The needle gripper preferably comprises a plurality of gripping needles which can be retracted into and extended from a gripper base part or a gripper housing. The gripping member is advantageously suitable for gripping a preform comprising a fabric, one or more fibre materials, and/or other materials that can be penetrated by needles. Useful needle grippers are disclosed in US 2016/0257509 A1 and US 8,104,807 B2.

In another embodiment, the engaging member comprises a vacuum cup. In some embodiments, some of the engaging members are needle grippers, and some of the engaging members are vacuum cups.

In some embodiments, the engaging member releasably attaches to the preform upon contact with the top surface of the preform. Preferably, one or more needles of the engaging member penetrate the preform or a layer thereof.

In another aspect the present invention relates to a preform for a wind turbine blade shell, the preform comprising at least two fibre layers and a core material sandwiched between the two fibre layers, wherein the preform has a length of 2-10 metres, a width of 0.5-5 metres and a thickness of 10-100 mm. These dimensions and structural features are found to result in a beneficial trade-off between stiffness vs drapeability, to be able to comply to the shape of the mould when placing the preforms within the mould cavity. As compared to known preforms for wind turbine blades, which are typically quite large and/or do not comprise a core layer the preforms of the present invention, the preforms of the present invention allow for a highly accurate and wrinkle-minimising blade manufacturing process.

It is preferred that the preform is for use in a method according to the present invention. The core material may be one or more of balsa wood, PVC and PET foam. In a preferred embodiment, the core material comprises balsa wood.

According to a preferred embodiment, the preform comprises a stack of upper fibre layers, a stack of lower fibre layers and a core material sandwiched between the two stacks of fibre layers. The stack of upper fibre layers may comprise three or more layers of fibre material. Likewise, the stack of lower fibre layers may comprise three or more layers of fibre material. The fibre material preferably comprises a glass fibre material. In other embodiments, the fibre material comprises a carbon fibre material and/oran aramid fibre material.

In some embodiments, the preform has a length-width ratio of at least 2:1 or at least 3:1. In other embodiments, the preform has a length-width ratio of at least 5:1. The preform will typically include fibre material and a binding agent to form the preform. Preferably, the fibre material and the binding agent are heated using one or more heating devices, such as an oven. Preferably, a binding agent is added to the fibres prior to the heating step. Such binding agent is preferably present in an amount of 0.1-15 wt% relative to the weight of the fibre material. The binding agent may also be present in an amount of 10-20 gram per square meter of glass surface. The fibre material may include fibre rovings, such as glass fibre rovings. The binding agent of the preform can be added simultaneously with the fibres or subsequently to fibre lay-up. The binding agent is preferably present in an amount of 0.1-15 wt% relative to the weight of the fibre material.

The binding agent may also be present in an amount of 5-40, preferably 10-20, gram per square meter of glass surface. In preferred embodiments, the binding agent is present in an amount of 0.5-5 wt%, preferably 0.5-2.5 wt%, relative to the weight of the fibre material. Advantageously, the binding agent is a thermoplastic binding agent. The binding agent may comprise a polyester, preferably a bisphenolic polyester.

In a preferred embodiment, the heating of the fibre material and the binding agent to form the preform takes place at a temperature of between 40 and 160 °C, preferably between 90 and 160 °C. An example of a suitable binding agent for the preform is a polyester marketed under the name NEOXIL 940. Examples include NEOXIL 940 PMX, NEOXIL 940 KS 1 and NEOXIL 940 HF 2B, all manufactured by DSM Composite Resins AG. Another example is a polyester resin marketed under the name C.O.I.M. FILCO® 661 FPG 005, which is a bisphenolic unsaturated polyester resin in powder form. Preferably, the binding agent is a polyester, preferably a bisphenolic polyester. In other embodiments, the binding agent is a hotmelt adhesive or based on a prepreg resin.

According to another embodiment, the binding agent is a thermoplastic binding agent. Typically, the fibre rovings are at least partially joined together by means of the binding agent by thermal bonding. In a preferred embodiment, the binding agent is a binding powder, such as a thermoplastic binding powder. In one embodiment, the preforms of the present invention essentially consist of the fibre material and the binding agent. This means that the preforms contain no more than 10 wt%, preferably not more than 5 wt% or not more than 1 wt%, of material other than fibre material and binding agent relative to the total weight of the preform. According to another embodiment, the preform consists of the fibre material and the binding agent. In another embodiment, the fibre material used for the preforms of the present invention essentially consists of glass fibres. This means that the fibre material contains not more than 10 wt%, preferably not more than 5 wt% or not more than 1 wt%, of material other than glass fibres relative to the total weight of the fibre material. According to another embodiment, the fibre material consists of glass fibres.

In one embodiment, the binding agent is present in an amount of 1-6 wt% relative to the weight of the fibre material. According to another embodiment, the melting point of the binding agent is between 40° and 220 °C, preferably between 40 and 160 °C. According to another embodiment, the binding agent comprises a polyester, preferably a bisphenolic polyester. In one embodiment of the present invention, each preform essentially consists of the fibre material and the binding agent. According to another embodiment, the fibre material comprises fibre rovings, preferably glass fibre rovings. In other embodiments, the fibre material may comprise carbon fibres or a hybrid material. According to another embodiment, the fibre material comprises a fibre fabric, such as a fibre mat. In another embodiment, a preform may further comprise at least one fibre fabric such as a fibre mat. Fibre rovings may be arranged on top and/or below such fabric.

In other embodiments, the preform comprises one or more threads for keeping the at least two fibre layers and a core material associated.

In a preferred embodiment, the preforms used in the afore-mentioned methods are used as part of the root region of a wind turbine blade, such as the root laminate. The root region may extend up to 40 meters, such as up to 25 meters, from the root end of the blade, as seen in its longitudinal direction. In other embodiments, the root region may extend to the shoulder of the blade +/- 5 meters. However, the preforms could also be used for other parts and regions of a wind turbine blade. In other embodiments, the preforms manufactured according to the afore-mentioned method are used over a length of 10-35% of the total blade length. In another embodiment, the preforms manufactured according to the afore-mentioned method are used in a region of the blade extending between its root end and a shoulder of the blade.

It will be understood that any of the features described above for one aspect of the present invention may be combined with each of the other aspects of the present invention. In particular, features and embodiments described with regard to the method of manufacturing a wind turbine blade may also apply to the apparatus for use in a method according to the present invention and/or to the preform as such.

As used herein, the term “wt%” means weight percent. The term “relative to the weight of the fibre material” means a percentage that is calculated by dividing the weight of an agent, such as a binding agent, by the weight of the fibre material. As an example, a value of 1 wt% relative to the weight of the fibre material corresponds to 10 g of binding agent per kilogram of fibre material.

As used herein, the term “longitudinal” means an axis or direction running substantially parallel to the maximum linear dimension of the element in question, for example a strip member or a preform mould.

As used herein, the term “horizontal” means that the direction of movement is generally parallel with respect to the ground. As used herein, the terms “vertical”, "downwardly" and "upwardly" refer to directions of movement which is generally perpendicular with respect to the ground.

As used herein, the term "proximal" refers to a location with respect to a cable that, during normal use, is closest to the cable support member. By contrast, the term “distal” refers to a location with respect to the cable that, during normal use, is closest to the engagement member.

Detailed description of the Invention

The invention is explained in detail below with reference to embodiments shown in the drawings, in which corresponding components are identified by the same reference numerals, wherein

Fig. 1 shows a wind turbine,

Fig. 2 shows a schematic view of a wind turbine blade,

Fig. 3 shows a schematic view of an airfoil profile through section l-l of Fig. 4, Fig. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

Fig. 5 is a perspective drawing of a blade mould for producing a wind turbine shell part,

Fig. 6 is a perspective exploded view of a preform according to the present invention,

Fig. 7 is a schematic top view of an apparatus according to the present invention, Fig. 8 is a perspective view of an apparatus for use in a method according to the present invention, and

Fig. 9 illustrates several steps of a method according to the present invention.

Detailed Description

Fig. 1 illustrates a conventional modern upwind wind turbine according to the so-called "Danish concept" with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. Fig. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance rfrom the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance rfrom the hub.

A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

Figs. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention. Fig. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use - i.e. during rotation of the rotor - normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively. Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d _f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d _t of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness land the local chord length c. Further, the position d _p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

Fig. 4 shows other geometric parameters of the blade. The blade has a total blade length L. As shown in Fig. 3, the root end is located at position r= 0, and the tip end located at r = L. The shoulder 40 of the blade is located at a position r = L _w , and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius r ₀ and a minimum inner curvature radius /?, which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as Ay, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

As illustrated in Fig. 5, a manufacturing process for manufacturing a blade part, such as a blade half, may involve laying a number of preforms 98a, 98b, 98c in a blade mould 96. For example, the preforms 98a, 98b, 98c are used for a blade section starting from the root end of the blade, such as the root region. The preforms 98a, 98b, 98c are arranged in the blade mould cavity 97, usually together with additional fibre material 94. Then, resin is infused to the blade mould cavity 97, which is subsequently cured or hardened in order to form the blade part, such as a blade half.

Fig. 6 is a perspective exploded view of a preform according to the present invention. The preform comprises one or more upper fibre layers 64, one or more lower fibre layers and a core material 68 sandwiched between the two fibre layers. The preform has a length L of 2-10 metres, a width W of 0.5-5 metres and a thickness T of 10-100 mm. When arranged in the blade mould cavity the length L will typically extend in a spanwise direction, whereas the width Wwill typically extend in the chordwise direction. Fig. 8 is a perspective view of an apparatus 62 for use in a method according to the present invention, and Fig. 7 provides a schematic top view. The apparatus comprises a blade mould 96 having a mould cavity 97 for manufacturing a shell part 52, typically a shell half, of a wind turbine blade. Furthermore, the apparatus comprises an engaging member 70 and four cables 72a-d, wherein the engaging member 70 is attached to each of the cables 72a-d. The engaging member 70 is adapted for movement over the mould cavity 97 while attached to the at least one cable 72a-d. Four cable support members 74a-d, such as cable support towers, are disposed adjacent to the blade mould 96, each of the cable support members 74a-d being adapted for supporting a respective cable 72a-d. In the illustrated first position, the engaging member 70 picks up a preform 98 from a stockpile of preforms. The hatched lines in Fig. 8 illustrate the cables and the engaging member in a second position, in which the engaged preform 98 is arranged in the mould cavity.

As best seen in the schematic top view of Fig. 7, at least one cable actuators 76a-d are each in communication with one of the cables 72a-d, thus being configured to move the engaging member 70 over the mould cavity 97. Each cable 72a-d is engaged with its actuator 76a-d at a proximate end and attached to the engagement member 70 at a distal end of the cable. Each cable actuator winds or unwinds its cable from a spool driven by the cable actuator. Thus, moving the engaging member 70 over the mould cavity will typically comprises retracting or extending the cables 72a-d by means of the cable actuators 76a-d. As illustrated in Fig. 9, the cable support members 74 can be slidably arranged on a rail 78 extending in a substantially spanwise direction of the blade mould 96. The cable support members 74a-d can be interconnected, see Figs 9a-c.

As also illustrated in the sequence of Figs. 9a-c, the method of manufacturing a wind turbine blade may comprise providing a plurality of preforms 98 for a wind turbine blade at a at a preparation station 80. In Fig. 9a, the a first preform 98a is shown as hovering over the blade mould cavity 97, being engaged by the engaging member 70, which is suspended from cables 70. In Fig. 9b, the preform 98a has been arranged in the mould cavity 97 and the engaging member is disengaging the preform 98a. Fig. 9c illustrates a point in time where already four preforms 98a-d have been arranged in the blade mould cavity 97 with the method of the present invention. The invention is not limited to the embodiments described herein and may be modified or adapted without departing from the scope of the present invention.

List of reference numerals

2 wind turbine

4 tower 6 nacelle 8 hub 10 blade 14 blade tip 16 blade root 18 leading edge

20 trailing edge 22 pitch axis 30 root region 32 transition region 34 airfoil region

40 shoulder / position of maximum chord 50 airfoil profile 52 pressure side 54 suction side 56 leading edge

58 trailing edge 60 chord 62 apparatus 64 upper fibre layer 66 lower fibre layer

68 core material 70 engaging member 72 cable 74 cable support members 75 top surface of preform

76 cable actuator 78 rail 80 preparation station 94 fibre material 96 blade mould 97 blade mould cavity

98 preform c chord length d _t position of maximum thickness d _f position of maximum camber d _p position of maximum pressure side camber f camber L blade length r local radius, radial distance from blade root t thickness Ay prebend