DEVICE AND METHOD FOR PERFORMING RETROFITTING PROCESS ON A WIND TURBINE BLADE

A device for aligning a tool at a predetermined orientation with respect to a target surface of a wind turbine blade, the device comprising: a suction cup having an outer sealing element for sealing against the target surface; an inner sealing element located radially inward of the outer sealing element for sealing against the target surface, a suction cavity being defined between the outer sealing element and the inner sealing element; and a tool guide located radially inward of the inner sealing element, wherein the tool guide defines a tool access passage.

TECHNICAL FIELD

The invention relates to a device for aligning a tool with an object or workpiece so that a process can be carried out on a surface of that workpiece. The device has particular utility for surfaces of wind turbine blades where drilling processes may need to be performed on the blade, for example to install components of a lightning protection system.

BACKGROUND

Wind turbines blades are usually designed with in-built lightning protection systems which enable them to manage the energy discharged into the blade during a lightning strike in an effective way that avoids damage occurring to the blade. Typically a lightning protection system will include discrete bolt-like receptor elements that penetrate the blade shell. Such receptor elements comprise a metallic head that is left exposed at the blade surface and an elongate connection shaft that extends through the blade shell into the blade interior to be connected to a down conductor. As well as receptor elements, it is known for lightning protection systems to also incorporate metallic mesh-like surface protection layers and receptor elements in the form of metallic blade tips.

An example of a lightning protection system is shown in the Applicant's International patent application WO2015/055215, which describes a wind turbine blade including a surface protection layer embedded in the blade surface. The blade includes a series of receptor elements that are exposed at the blade surface, and which establish an electrical contact with the surface protection layer and extend through the blade shell to connect to a down conducting system. Such a protection system is cost effective to manufacture and effective in operation. Installation of the receptor elements takes place once the main blade structure has been completed, in a so-called post-finishing process. To install the receptor elements, holes must be drilled into the blade shell at a precise location in order that the shanks of the receptor elements engage with the connector bases in the blade interior. Furthermore, the holes must be drilled in a predetermined orientation with respect to the blade surface to ensure that the correct path through the blade shell is followed. Usually the hole needs to be drilled so that it extends along a path that is perpendicular to the blade surface at the mouth of the hole, although other angles may be required.

Supporting a drill in an accurate position and maintaining precise alignment off the drill bit during the drilling process is challenging. Supportive jigs are known, but such jigs tend to be large, heavy and unwieldy structures. It is against this background that the embodiments of the invention have been devised.

SUMMARY OF THE INVENTION

Embodiments of the invention provide a device for aligning a tool at a predetermined orientation with respect to a target surface of a wind turbine blade, the device comprising: a suction cup having an outer sealing element for sealing against the target surface; an inner sealing element located radially inward of the outer sealing element for sealing against the target surface, a suction cavity being defined between the outer sealing element and the inner sealing element; and a tool guide located radially inward of the inner sealing element, wherein the tool guide defines a tool access passage.

The invention provides a simple and robust device for aligning a tool to a target surface of a workpiece, such that processing of the workpiece can be undertaken at a predetermined orientation.

The tool guide may be an annular element, and may include a guide insert receivable in the tool access passage. The inner sealing element may be a sealing ring.

The outer sealing element and the tool guide may be concentric.

The device may include a rigid body portion, and the outer sealing element may extend from the rigid body portion.

The outer sealing element and/or the inner sealing element may be flexible so as to be able to accommodate irregularities and curvature of the target surface. This assists in providing a more effective seal between the suction cup and the workpiece.

The suction cup and, thus, the outer sealing element, may be circular in plan profile. Alternatively, the suction cup and, thus, the sealing element, may have a stadium or oval shape in plan profile. Different general shapes of the suction cup and outer sealing element allow for use of the device in different applications or scenarios. For example, a stadium shaped suction cup and sealing element is advantageous because it allows the device to be used in narrower spaces than would be possible with a more rounded shape. Furthermore, the oval shape lends itself for use on surfaces having greater curvature.

The device may include means for evacuating the suction cup. The means for evacuating the suction cup may include a port for connection to a vacuum source.

The device may be configured such that misalignment of a tool received in the tool guide with respect to the target surface of the workpiece causes the device to disengage from the workpiece. The device may be configured such that misalignment of a tool received in the tool guide with respect to the target surface of the workpiece results in an audible noise that alerts a user of the device to the misalignment of the tool. In this way, a user of the device can be confident of processing the workpiece at the intended predetermined orientation.

The device may be configured such that a longitudinal axis of a tool received in the tool guide is perpendicular to the target surface of the workpiece when the device is attached to the target surface, in use.

Alternatively, the device may be configured such that a longitudinal axis of a tool received in the tool guide is at an oblique angle to the target surface when the device is attached to the target surface, in use.

The inner sealing element may be located on the tool guide. Or, the inner sealing element may be located between the outer sealing element and the tool guide.

The workpiece may comprise a wind turbine blade and the tool may comprise a drill bit of a drill.

Embodiments of the invention provide a device for aligning a tool at a predetermined orientation with respect to a target surface of a workpiece. The device comprises: an outer sealing element configured to establish a seal with the target surface; an inner sealing element configured to establish a seal with the target surface; a chamber defined between the outer sealing element and the inner sealing element when the device is engaged with a target surface; means for removing air from the chamber; wherein the inner sealing element extends about a tool guide member.

A further aspect of the invention provides a method of guiding a tool with respect to a surface of a workpiece. The method comprises: applying a device in accordance with the device described in the preceding paragraphs to the surface of the workpiece; establishing a negative pressure in the suction cup of the device; bringing a tool into engagement with the tool guide of the device; using the tool on the workpiece.

In some embodiments, the workpiece may be a wind turbine blade and the tool may be a drill bit of a drill. In these embodiments, the step of using the tool on the workpiece may comprise drilling a hole in the wind turbine blade for receiving a component of a lightning protection system. The drilled hole may extend into the wind turbine blade perpendicularly with respect to the target surface at a mouth of the hole. Alternatively, the drilled hole may extend into the wind turbine blade at an oblique angle with respect to the target surface at a mouth of the hole.

The method may comprise locating the device on the workpiece by means of a pre-drilled locating hole.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

DETAILED DESCRIPTION

The present invention relates to a device for aligning a tool at a predetermined orientation with respect to a target surface of a wind turbine blade.

As discussed above, wind turbine blades having lightning protection systems require receptor elements to be installed at specific locations on the blade, and having specific orientations to the blade surface. For this, receptor-receiving holes having a specific orientation to the blade surface at the mouth of the hole are required. In one envisaged embodiment of the invention that will be described below, the alignment device is used for aligning a drill bit to a target surface of a workpiece in the form of a wind turbine blade, for drilling receptor-receiving holes at a specified orientation. In this embodiment, the drill bit is aligned such that the drilled holes extend perpendicularly to the surface of the wind turbine blade at the mouth of the hole, although this orientation may not be required in all embodiments of the invention.

To assist the reader and provide context for the invention, a wind turbine blade having a lightning protection system on which the alignment device may be used will first be described, before turning our attention to the alignment device itself.

With reference toFIG. 1, a wind turbine blade2incorporates a lightning protection system3. The blade2is formed from a blade shell4having two half-shells. The half-shells are typically moulded mainly from fibre reinforced plastic (known as ‘FRP’) that comprises fibre fabric, often glass-fibre, embedded in a cured resin matrix.

The blade2comprises a root end6, at which the blade2would be attached to a rotor hub of a wind turbine, a tip end8, a leading edge10and a trailing edge12. A first outer surface14of the blade2defines an aerodynamic profiled surface that extends between the leading edge10and the trailing edge12. The blade2also includes a second surface also extending between the leading edge10and trailing edge12, which is not shown in the plan view ofFIG. 1, but which is indicated as reference numeral16inFIG. 2.

Turning to the lightning protection system3, this is based on a ‘zoning’ concept in which the blade2is demarcated in a longitudinal or ‘span-wise’ direction into regions or ‘zones’ depending on the probability of receiving a lightning strike in that region. A similar principle is described in WO2013/007267.

Here, the blade2is divided into three zones for the purposes of lightning protection—these are illustrated inFIG. 1as zones A, B and C. Zone A extends from the root end6of the blade to approximately 60% of the blade length in the span-wise direction. In this zone, the blade2has a low risk of a lightning strike and so will be expected to receive a low incident of strikes at low current amplitudes, and low total charge transfer, which is acceptable for blade structural impact. In this example, the blade2is not equipped with any external lightning protection within this zone.

Zone B extends from the end of zone A to approximately 90% of the blade length in a span-wise direction. In this zone the blade2has a moderate risk of lightning strike and is expected to withstand moderately frequent direct lightning strike attachments having increased impulse current, peak current and total charge transfer. Accordingly, the blade2is provided with a first lightning protection sub-system in the form of a surface protection layer20.

Finally, zone C extends from the end of zone B to the tip end8of the blade2. In this zone the blade2is subject to a high likelihood of lightning strikes and is expected to withstand peak current amplitudes of in excess of 200 kA and total charge transfer in excess of 300 coulomb and, moreover, a high incident of strikes. To provide the required level of protection for the blade, zone C includes two further lightning protection sub-systems, namely an array of receptors22and a blade tip assembly24. Both the receptor array22and the blade tip assembly24are electrically connected to a down conducting system26, comprising first and second down conductors28,30running along the length of the blade2from the tip end8to the root end6, generally being arranged adjacent the leading edge10and trailing edge12of the blade2, respectively.

As has been mentioned, the surface protection layer20is in zone B and comprises an electrically conductive layer that is integrated into both the upper half-shell and the lower half-shell of the blade2. The conductive layer may be a metallic screen or mesh, and preferably a mesh/screen in the form of an expanded metal foil, e.g. an expanded aluminium foil, that acts to attract lightning strikes over a large area of the blade and which is connected to the down conducting system26in a manner that will be described. The surface protection layer20is connected to the down conductors28,30by a plurality of connector arrangements40. In some arrangements, four connector arrangements40are included on the blade2, two being adjacent the leading edge10of the blade and two being adjacent the trailing edge12of the blade2. Other arrangements are possible.

FIG. 2shows a leading edge connector arrangement40in more detail. The connector arrangement40includes a block-like connector component42that forms part of the down conducting system and which is shaped to fill the volume in the relatively deep profile of this region of the blade2and provide an electrical connection to a first connector element44associated with the leeward surface14and a second connector element46associated with the windward surface16.

The connector component42comprises first and second connector bases48,50that are encapsulated by an insulating member52that is generally annular in form. The connector bases48,50are conductive, preferably brass for its high conductivity, corrosion resistance, and suitability for drilling, although other metals or alloys are acceptable. The insulating member52is moulded directly to the connector bases48,50and so serves to suppress the initiation of ionization and streamers during highly charged environmental conditions, which thereby guards against a lightning strike directly onto the connector bases48,50rather than on a connector element44,46. The insulating member52is formed of a suitable polymer having a high dielectric strength, for example polyurethane.

The first connector element44electrically couples the surface protection layer20on the leeward surface14to the first connector base48. Similarly, the second connector element46couples the surface protection layer20on the windward surface16to the second connector base50. The connector elements44,46are identical so only one of them shall be described in detail. The first connector element44is in the form of a bolt having a head44aand a shank or stem44b. Stainless steel is typically used for the bolt, although other conductive materials, particularly metals, are also acceptable. The shank44bextends through the blade2and engages with the first connector base48by way of cooperating screw threads, and the head44ais arranged to lie flush with the surrounding surface of the surface protection layer20. The connector element44is installed in the blade after the blade has been fabricated and removed from its mould. Holes120or drillings are formed through the blade skin from the exterior surface to the interior surface and into the receptor base48, and are preferably perpendicular to the blade surface. Following formation of the hole120, the connector element44is inserted into the hole120and screwed into or otherwise engaged with the receptor base48to make the electrical connection. An identical arrangement is provided to couple the surface protection layer20on the windward surface16to the second connector base50.

As has been mentioned above, the head of the connector element44defines an electrical coupling or interface between the surface protection layer20and the respective connector component42. In particular, the connector element electrically couples the surface protection layer20at the outer surface of the blade to the down conductor28in the interior of the blade.

Note that the upper surface of the head44ais exposed at the blade surface and so can also serve as a receptor element for lightning strikes. The surface protection layer20and, in particular, the electrical connection between it and the connector element44will now be described with reference toFIGS. 3 and 4.

InFIG. 3, the surface protection layer20is shown in exploded view for clarity against a blade mould surface portion80. In this example, the surface protection layer20includes three main components: an outer insulating layer82, an inner insulating layer84and a conductive layer86sandwiched between the insulating layers82,84.

Both the outer insulating layer82and the inner insulating layer84are glass fibre fabric. The outer insulating layer82becomes the outer surface or skin of the blade2once the blade2is fully fabricated. Therefore it is preferred that the outer insulating layer82is a relatively lightweight fabric, for example less than 200 gsm, so as not to inhibit the formation of leaders from the conductive layer86during lightning conditions. The thin outer insulating layer82also reduces the risk of surface damage during a strike. Conversely, since it is desirable to insulate in-board from the surface protection layer20, the weight of the inner insulating layer84is heavier, for example around 600 gsm.

In order to promote a good electrical contact between the conductive layer86and the connector element44, the conductive layer includes reinforced zones, identified inFIG. 3generally as ‘90’. The reinforced zones90serve to strengthen the conductive layer86in localised regions by thickening the metal foil. For example, the conductive layer86may undergo a soldering or casting process to solidify the expanded foil in localised regions. Alternatively, one or more conductive elements in the form of plates, discs or the like are bonded to the conductive layer86in the required zones. Bonding may be by way of brazing for example. The reinforced zone90may improve the robustness of the conductive layer86where it connects to the connecting element44.

In each reinforced zone90, a forming element92is applied to the outer insulating layer82prior to the lay down of the conductive layer86. The forming element shapes the conductive layer86during blade fabrication to provide a recess for receiving a respective connector element44so that the surface protection layer20can be electrically connected to the internal components of the down conducting system26.

In establishing the electrical connection between the surface protection layer20and the down conducting system26, it is important that the connector elements44extend through the blade shell at an angle that is perpendicular to the surrounding region of the surface protection layer20in order that the head44aof the connector element44establishes a robust electrical connection with the surface protection layer20. However, in practice, the fabrication of a wind turbine blade is a labour-intensive process which requires that the drillings for the connector elements44are drilled through the blade shell manually or using a suitable tool to ensure that the drilling are formed as accurately as possible. In such circumstances, the connector element44could be aligned incorrectly thereby compromising the electrical connection between the surface protection layer20and the down conducting system26. This could cause electrical arcing which has the potential to damage both the connector element and the conductive layer, thereby further reducing the effectiveness of the electrical connection to the point of failure. The present invention addresses this issue by providing an alignment device that allows for properly aligned holes to be drilled in the surface of the wind turbine blade for receiving connector elements44of the lightning protection system.

FIG. 4is an enlarged view of region ‘A’ inFIG. 2showing one of the connector arrangements40in greater detail.

Here, the surface protection layer20is shown as defining the leeward surface14of the blade2together with a set of structural blade components96with which the surface protection layer20is integrated during a resin infusion and curing process. The structural blade components96may include further fabric layers, foam core sections and the like, as would be known to a person skilled in turbine blade design, but which will not be described in detail here for the sake of brevity.

The forming element92is an outwardly-tapered annular disc that includes an inner aperture98defining an inner wall100. The forming element is preferably a polymeric part, particularly polyurethane. The forming element92sits in-board of the outer insulating layer82such that the layer82extends over a flat outer face92aof the forming element92and terminates at an aperture101aligned with the inner wall100. Note, however, that the outer insulating layer82may instead terminate at the outer edge of the forming element92.

The conductive layer86is in-board of the outer insulating layer82and is positioned such that a reinforced zone90thereof is in registration with, or ‘superimposed’ on, the aperture98of the forming element92. Here, the reinforced zone90includes first and second metal discs102that are cast onto either side of the conductive layer86and so are integral parts of the surface protection layer20.

The dished or domed shape of the forming element92raises the level of the reinforced zone90so that it defines a recessed base104adjacent the inner wall100of the forming element92. The recessed base104and the inner wall100thereby provide a countersink cavity105for the head44aof the connector element44.

When installed in the blade, the shank44bof the connector element44locates through an opening103through the reinforced zone90and the drilling or bore120in the structural component96. The drilling120extends between an outer shell surface121and an inner shell surface122, and also extends into receptor base48which, in this embodiment, may be threaded for receiving the connector element44.

In this position, the underside surface of the head44aof the connector element44is opposed to the surface protection layer20and serves as a contact face124to make electrical contact with it. In this embodiment, the contact face124makes direct contact with the reinforced zone90, such that the reinforced zone90can be considered to be a contact region for the surface protection layer20. As shown inFIG. 4, the head44makes reliable contact with the recessed base104defined by the reinforced zone90since the two components are substantially planar, so that the head44alies flat on the metal discs102of the reinforced zone90without any air gaps. However, this electrical connection can be compromised by angular misalignment of the shank44bof the connector element.

An alignment device160in accordance with a first embodiment of the invention will now be described with reference toFIGS. 5 to 12.

The alignment device160comprises a suction cup162for attaching the alignment device160to a surface of a workpiece and a tool guide168for guiding a tool170to the surface of the workpiece at a specific orientation. In the described embodiment, the alignment device160is configured for aligning a drill bit170to the surface14of a wind turbine blade2, such that the drill bit170is aligned to produce a drilling or hole120in the wind turbine blade2that extends perpendicularly from the surface14.

The suction cup162may comprise a rigid body portion174having a generally oval shape and an outer sealing element176. In this embodiment, the outer sealing element176is in the form of a flexible sealing skirt and will be referred to as such from now on. Advantageously, the flexible nature of the sealing skirt176in this embodiment allows for irregularities and curvature of the target surface14of the wind turbine blade2to be accommodated, thereby helping to provide a more effective seal between the suction cup162and the wind turbine blade2. However, the skilled person would appreciate that the sealing element176could take other forms in other embodiments of the invention.

The rigid body portion174includes a major outer surface178that faces away from the surface14of the wind turbine blade2in use and a major inner surface180that faces towards the surface14of the wind turbine blade2in use. Here, the terms “inner” and “outer” are intended to indicate the position of the surfaces178,180with respect to the surface14of the wind turbine blade2when the alignment device160is attached to the wind turbine blade2for use. That is to say, the inner surface180of the rigid body portion174is positioned closer to the surface14of the wind turbine blade2than the outer surface178of the rigid body portion174when the alignment device160is attached to the wind turbine blade2.

The outer sealing skirt176extends from a circumferential edge182of the inner surface180of the rigid body portion174to define a sealing rim184of the suction cup162that engages the wind turbine blade2to form an outer seal185in use. The outer sealing skirt176of the suction cup162is formed from a flexible material such as rubber or silicone to enable the suction cup162to deform as necessary to form an effective seal between the suction cup162and the wind turbine blade2. In some embodiments, the outer sealing skirt176may be formed as a moulded component that is stretched over the rigid body portion174to be engaged in its final position. Alternatively, the sealing skirt176may be secured to the rigid body portion174at the circumferential edge182of the rigid body portion174by means of glue or other fastening means. The sealing skirt176may also be ‘over moulded’ onto the rigid body portion174. When the alignment device160is attached to the wind turbine blade2, a suction cavity186is defined between the tool guide168, the outer sealing skirt176and the surface14of the turbine blade2. Two ports in the form of through-holes188are provided in the rigid body portion174of the suction cup162and are located at opposite sides of the tool guide168in use. The through-holes188provide a means for evacuating the suction cavity186of the suction cup162in order to attach the alignment device160to the wind turbine blade2, as will be described in more detail later. It should be noted that although two through-holes188are included in this embodiment of the alignment device160, more or fewer holes188are possible, and this should not be considered limiting. A central aperture189is provided in the rigid body portion for receiving the tool guide168in use.

The alignment device160further comprises means for evacuating the suction cup162in the form of a vacuum pipe assembly192and a vacuum source or pump (not shown). In use, air is evacuated from the suction cavity186through the vacuum ports188via the vacuum pipe assembly192to mount the alignment device160to the wind turbine blade2. The vacuum pipe assembly192can be seen inFIG. 5. It should be understood that whilstFIG. 5shows just one form that the vacuum pipe assembly192may take, many other configurations are possible. For example, in some embodiments a single flexible pipe could be used to couple a single through-hole of the suction cup162to the vacuum pump. The vacuum pipe assembly192comprises a connector194for coupling to the vacuum pump.

Turning now to the tool guide168of the alignment device160, this will be described with particular reference toFIGS. 7 to 10.

The tool guide168is an annular element located radially inward of the outer sealing skirt176. The tool guide is attached to the inner surface180. In this embodiment it includes a sealing element198for creating a seal between the tool guide168and wind turbine blade2, as will be explained later. The tool guide comprises a guide insert200(shown inFIG. 7) receivable in the central aperture189of the suction cup162and a guide insert collar220for receiving a portion of the guide insert200in use. In this embodiment, the circumference of the outer sealing skirt176and the tool guide168are concentric, although this is not essential. Expressed another way, the outer sealing skirt176surrounds, or extends about the tool guide168, both components being centred on the same axis.

Referring toFIG. 7in particular, the guide insert200comprises a cylindrical body portion226provided with a tool access passage in the form of a central aperture228and a circumferential flange230provided at an outer end232of the guide insert200. The guide insert aperture228is sized to receive a 10.5 mm drill bit70in this example, but may be sized to accommodate different sized drill bits or other tools in other examples.

Referring now toFIG. 8, the guide insert collar220is cylindrical in shape and comprises a central aperture234for receiving the guide insert200, an outer surface236that abuts with the inner surface180of the rigid body portion174in use, and an inner surface238that abuts with the wind turbine blade2in use. In this way, the inner surface238of the guide insert collar220is positioned closer to the wind turbine blade surface14than the outer surface236of the guide insert collar220in use.

An annular groove is provided on the inner surface238of the guide insert collar220for receiving the sealing element198, now referred to as the inner sealing element198for clarity. The inner sealing element198may be, for example, a sealing ring in the form of a rubber O-ring. Of course, the inner sealing element198may be formed of another appropriate material, so long as it is suitable for forming an effective seal with the wind turbine blade2. In use, the inner sealing element198is seated in the annular groove of the guide insert collar220and is compressed between the guide insert collar220and the wind turbine blade2to provide an air-tight inner seal245at the interface. Although the inner sealing element198of this embodiment is separate from the guide insert collar220, it should be noted that the inner sealing element198may be formed as part of the guide insert collar220in other embodiments. Alternatively, a surface of the tool guide may itself form the inner sealing element198of the alignment device160.

With reference toFIGS. 9 and 10, when the alignment device160is assembled and ready for use, the vacuum pipe assembly192is attached to the suction cup162at through-holes188, the guide insert collar220is attached to the rigid body portion174of the suction cup162and the inner sealing element198is received in the annular groove of the guide insert collar220. The guide insert200is received in the central aperture189of the suction cup162, such that a leading edge246of the guide insert200is received in the guide insert collar220and the circumferential flange230of the guide insert200abuts with the outer surface178of the rigid body portion174. The guide insert200is received in the central aperture189of the suction cup162, and in the guide insert collar220in a tight fit, to ensure minimal lateral movement or rotation of the guide insert200during operation of a tool170received in the guide insert200, whilst allowing the guide insert200to be received in and removed from the suction cup162by the user without the use of additional tooling. In an example, a locking mechanism may be provided to prevent the rotation of the guide insert200.

The alignment device160has a generally oval or stadium shape. In particular, the suction cup162and, thus, the sealing skirt176have a generally oval or stadium shape in plan profile. An oval shape is advantageous because it allows the alignment device160to be used in narrower spaces than would be possible with a more rounded shape. Furthermore, the oval shape lends itself for use on surfaces having greater curvature, which is especially important for use near the tip end of the wind turbine blade2.

FIG. 10shows the alignment device160attached to the surface14of the wind turbine blade2. Here, the inner sealing element198and outer sealing skirt176are engaged with the blade surface14to form the suction cavity186, and air has been evacuated from the suction cavity186in the direction indicated by arrows248by means of the vacuum pipe assembly192and vacuum pump (not shown inFIG. 10for clarity). The drill bit170is received in the tool access passage228such that a longitudinal axis250of the tool170is perpendicular to the surface14of the wind turbine blade2at the mouth of the hole120for drilling. In this way, the drill bit170is arranged to form a hole120in the wind turbine blade2that extends perpendicularly with respect to the surface14of the wind turbine blade2.

If the drill bit170becomes misaligned from its intended orientation, such that the longitudinal axis250of the tool170is no longer perpendicular to the surface14of the wind turbine blade2as is shown inFIG. 11, the inner seal245formed between the inner sealing element198and the wind turbine blade surface14is broken. This causes air to be drawn into the suction cavity186via the tool access passage228, resulting in an audible hissing noise, and also a loss of suction of the suction cup162which may cause the alignment device160to disengage from the surface14of the wind turbine blade2. In this way, the alignment device160is configured to alert the user when the tool170becomes misaligned such that the user can be confident of processing the workpiece2at the intended orientation with respect to the target surface14.

The method for using the alignment device160to drill a hole120in the surface14of the wind turbine blade2for receiving a connector element44of a lightning protection system3will now be described with particular reference toFIGS. 10 to 12. As has been mentioned already, the alignment device160of this embodiment is configured to enable a hole120to be drilled that extends perpendicularly from the surface14of the blade2. However, the alignment device160may be configured to enable a tool to process a workpiece from a different angle in other embodiments of the invention, according to the intended application. For example, the tool guide168may be adapted such that the aperture228of the guide insert200defines a central aperture that extends at an oblique angle with respect to the surface14of the wind turbine blade2in use.

In a first step, the surface14of the wind turbine blade2is prepared by drilling a small locating hole252having a depth of 3 mm to 5 mm in the surface14of the wind turbine blade2, at the position on the blade2at which the connector element44of the lightning protection system3is required. The locating hole252marks the position at which the connector element44is to be installed on the turbine blade2, and assists in locating the alignment device160in the correct position on the blade2for use. As already noted above, the connector elements44must be installed at a precise location on the blade2in order that the shanks44bof the connector elements44engage with the connector bases48,50in the blade interior. Furthermore, the holes120must be drilled in a predetermined orientation with respect to the blade surface14,16to ensure that the correct path through the blade shell is followed. In this case, the hole120must be drilled so that it extends along a path that is perpendicular to the blade surface14,16at the mouth of the hole120.

To prepare the alignment device160for attachment to the wind turbine blade2, the guide insert200is inserted into the central aperture189of the suction cup162until the circumferential flange230of the guide insert200abuts the outer surface178of the rigid body portion174of the suction cup162and the leading edge246of the guide insert200is received in the aperture234of the guide insert collar220. The guide insert200is now securely held in place in the suction cup162. In this example, the guide insert aperture228is dimensioned for use with a 10.5 mm drill bit170. However, the guide insert200may be dimensioned so as to be usable with different sized drill bits, or with other types of tools. In this way, a single suction cup162may be usable with numerous different guide inserts, each guide insert being tailored for use with a different type and/or size of tool.

Prior to attachment of the alignment device160to the wind turbine blade2, the vacuum pump (not shown) is coupled to the vacuum pipe assembly192and the surface14of the wind turbine blade2and the sealing surfaces of the alignment device160(i.e. the sealing rim184of the suction cup162and the inner sealing element198of the tool guide168) are wiped clean to ensure that they are free from dirt or dust. This ensures that effective inner and outer seals245,185are formed between the alignment device160and the surface14of the wind turbine blade2, and guards against arbitrary loss of suction when the alignment device160is mounted to the blade2.

For attachment, the alignment device160is oriented such that the outer surface178of the rigid body portion174faces away from the surface14of the wind turbine blade2and the inner surface180of the rigid body portion174faces towards the surface14of the wind turbine blade2. A drill bit170is inserted through the guide insert aperture228and the tip of the drill bit170is located in the pre-drilled locating hole252provided on the surface14of the wind turbine blade2, to ensure that the alignment device160is attached at the correct position for use.

The vacuum pump is turned on and the alignment device160is applied to the wind turbine blade2by pushing the device160against the surface14of the wind turbine blade2such that the sealing rim184of the suction cup162, the inner surface238of the guide insert collar220and the inner sealing element198are in abutment with the surface14of the wind turbine blade2. In this way, the suction cavity186is formed as a sealed chamber between the outer seal185formed by the outer sealing skirt176and the inner seal245formed by the inner sealing element198. Air is evacuated from the sealed suction cavity186by means of the vacuum pump, such that a negative pressure is established in the suction cup of the device and the alignment device160is held on the blade surface14. Attaching the alignment device160to the wind turbine blade2in this way is advantageous as it allows the user of the alignment device160to have both hands free for subsequent operation of the tool170.

Once the alignment device160is attached to the wind turbine blade2, the guide insert aperture228is checked for alignment with the locating hole252to ensure correct positioning of the alignment device160on the blade2. This may be done by means of a visual inspection. If the alignment device160is not correctly positioned, the alignment device160is removed and the above process is repeated until correct alignment is achieved.

When the alignment device160is properly attached at the correct location on the wind turbine blade2, the drill bit170is inserted into the guide insert aperture228as shown inFIG. 10, and drilled through the surface protection layer20and into the connector base48to form the hole120for receiving the connector element44of the lightning protection system13as shown inFIG. 12. In this embodiment, the hole120is formed having a depth of 12 mm in the connector base48.

The alignment device160is configured such that a tool received in the tool guide168approaches the blade surface14perpendicularly to the blade surface14. In this way, a drill bit170received in the tool guide168of the invention is operable to form the hole120such that it extends below the surface of the blade2at an angle that is perpendicular to the blade surface14.

Once drilling is complete, the drill bit170is removed from the guide insert200. Compressed air may be used to remove any metal swarf or debris from the drilled hole120.

The depth of the drilled hole120may be measured using a vernier gauge to ensure the required depth has been achieved. If the hole120is found to be too shallow, the alignment device160may be re-attached such that further drilling can be effected. Alternatively, a depth probe may be inserted through the guide insert aperture228to measure the depth of the drilled hole120whilst the alignment device160is attached to the wind turbine blade2.

As a further step, once the required hole depth has been achieved, the drill bit170and guide insert200are removed from the central aperture189. A guide insert200suitable for receiving an appropriate thread tap (not shown) is then inserted into the tool guide aperture228, and the thread tap is inserted into the guide insert aperture228. A thread tap wrench may then be used in combination with the thread tap to create a thread in the hole120for receiving the connector element44of the lightning protection system13.

In this embodiment of the invention, a 10.5 mm drill bit170is used and the hole120is drilled through the surface protection layer20and into the connector base48to form a 12 mm deep hole in the connector base48. The required depth of hole and dimension of the drill bit170may vary for different lightning protection systems13and turbine blades2, and for different applications of the alignment device160.

It should be noted that in the unlikely event that the alignment device160detaches from the wind turbine blade2prematurely during the drilling process, the suction cup162and the sealing element198are checked for damage and re-cleaned, the surface14of the wind turbine blade2is re-cleaned, and the vacuum pipe assembly192and any additional piping used to couple the vacuum pump to the vacuum pipe assembly192is checked for damage or blockages before re-attachment.

Whilst an alignment device160having a generally oval or stadium shape has been described above, the skilled person would understand that other possible shapes and configurations of the alignment device160are possible. For example, the alignment device may have a circular shape in plan profile, i.e. the outer sealing element176has a generally round circumference. A different shape of the alignment device allows for use in different applications or scenarios having different space requirements.

As has been described above, the inner sealing element198is located on the tool guide168. However, in another example, the inner sealing element198may not be positioned on the tool guide168and is instead positioned between the outer sealing element176and the tool guide—in this example, the inner sealing element198could effectively be a sealing skirt attached to the inner surface180of the alignment device160.

The inner surface238of the tool guide168that abuts with the wind turbine blade surface14does not have to be a planar surface. Instead, the inner surface238could have a curvature which is designed to specifically match the curvature of the blade surface14in order to provide a better seal.