Field of the Invention

The present invention relates to a method for treatment of a surface of an elongated structure, e.g. a wind turbine blade, which method includes abrading the surface and cleaning the surface by removing abrasive dust from the abraded surface, which method comprising the steps of:

- providing an abrasive head which comprises an abrasive housing containing abrasive lamellae of an abrasive sheet, such as abrasive fabric, of which a front side has abrasive properties and which extend from a rotatable base of the abrading apparatus, and which abrasive lamellae are supported on a back side by an elastic support element comprising support brushes having almost the same length as the lamellae, and which abrasive housing is provided with a suction outlet for removal of abrasive dust by activating a suction unit connected with the suction outlet of the abrasive housing, and

- abrading the surface and cleaning the surface by removing abrasive dust from the abraded surface.

Furthermore the invention relates to an apparatus for treatment of a surface of an elongated structure, e.g. a wind turbine blade, according to the above mentioned method, which apparatus includes an abrasive head which comprises an abrasive housing containing abrasive lamellae of an abrasive sheet, such as abrasive fabric, of which a front side has abrasive properties and which extend from an rotatable base of the abrading apparatus, and which abrasive lamellae are supported on a back side by an elastic support element comprising support brushes having almost the same length as the lamellae, and which abrasive housing is provided with a suction outlet for removal of abrasive dust.

Background of the Invention

The invention is specifically developed in connection with abrading/polishing the surface on wind turbine blades. However, the method and the apparatus according to the invention may also be used in surface treatment of other elongated structures, for example concrete elements or metal pipes.

In the following the invention will be explained in connection with the surface treatment of wind turbine blades.

Earlier it was known to abrade large structures, such as wind turbine blades and panels for aircrafts with hand-held power tools.

The hand-held power tools have unfortunate and hazardous impacts on operators, like e.g. white fingers, static electricity, repetitive work, and massive quantities of dust. Also, the operators have an unsafe environment as they need to work from platforms, ladders, and lifts in order to reach all surface parts of such larger structures.

Earlier wind turbine blades were abraded with the wind turbine blades lying with a flat side oriented largely horizontally and according to a principle known from grind- ing/polishing of floors. However, increasingly it has been desired to place the blades with the flat side standing vertically. Therefore, it is not possible that the force of gravity produces contact pressure to effect the abrading. It has therefore also been suggested to use hand-held tools. However, besides the above mentioned drawbacks, this is a slow procedure in the case of large wind turbine blades.

Therefore in recent years there have been several examples of using abrading plants with abrading tools mounted on a support to be moved across the surface to be abraded and wherein the movement of the support is effected with a robotic arm which is controlled by control means.

From WO 2012/003828 it is known to conduct sanding by means of an automatic abrading arrangement comprising an abrading drum mounted on a robotic arm, and where control means are used e.g. for positioning the drum on the surface to be abraded, in order to control the force by which the drum is pressed towards the surface, and to control the velocity and pattern by which the drum is moved with respect to the surface. In this arrangement an abrasive head is provided which comprises an abrading cylinder enclosed in a shielding housing provided with a suction outlet for removal of dust and a motor for driving the rotation of the abrasive head.

The abrasive head is provided with abrasive lamellae of an abrasive sheet, such as an abrasive fabric of which the front side has abrasive properties and which extend substantially radially from an elongated core. The abrasive lamellae are supported on the back side by an elastic support element comprising support brushes having almost the same length as the lamellae.

The cylinder is during operation of the abrading arrangement rotated so that the front side of the abrasive lamellae is moved across the surface to be abraded. Sufficient surface pressure is established due to the effect of the support brushes. In known manner, the support brushes have a length being shorter than the length of the abrasive lamellae, whereby the outer end of the abrasive lamellae may fold over the outer end of the brushes, whereby it is possible to increase the active area of the abrasive lamellae and to increase the surface pressure of the abrasive lamellae against the surface to be abraded.

The core of the cylinder may be equipped with undercut grooves for retaining the flexible sanding strips comprising the abrasive lamellae as well as the brushes. The grooves may be straight along the longitudinal direction of the core or be helical or spiral shaped.

This arrangement has shown to be effective in abrading the surface of large structures, such as elongated structures, e.g. wind turbine blades.

Even though the shielding housing is provided with a suction outlet which is connected with a suction unit for removal of dust, it has shown that it is necessary to effect a further process to remove dust from the surface in order to clean it sufficiently for a following coating treatment.

In order to increase the removal of dust, several actions have been taken. The suction capacity has been increased. The velocity of the movement of the cylinder across the surface to be abraded has been changed. The rotational speed of the cylinder, and thereby the tangential movement of the front side of the lamellae over the surface to be abraded due to the rotation of the cylinder, has been changed. However, even though a number of actions have been conducted in order to solve the problem with remaining dust on the surface, it has hitherto not lead to a satisfactory result and have caused a separate dust removal after the abrading procedure.

The abrading of the wind turbine blade is considered to be a relatively clean process, which is effected in an area of the production facility which is a “clean” area, where there is no need for the operator to use protective equipment. The separate process of removing the dust is considered to be a dusty process, which may not be effected in a “clean” area. Therefore, there has been a need to transfer the wind turbine blade to a “dusty” area of the production facility, and after the cleaning the wind turbine blade is again transferred to the “clean” area in order to effect the finishing coating treatment. The transfer is time consuming.

There has been a desire to be able to conduct all processes of the surface treatment in the “clean” area.

Therefore there is a need for modification of the prior art system and to provide a method and an apparatus which overcome the drawbacks of the prior art system and makes it possible in an effective way to effect the abrading and the removal of dust.

Object of the Invention

The object of the present invention is to provide a method and an apparatus which overcome the drawbacks of the prior art system and makes it possible in an effective way to effect the abrading and the removal of dust.

It is a further object of the invention to provide such method and apparatus in a way where only minor modifications are needed for an abrading arrangement described in W02012/003828. Description of the Invention

The object is obtained with a method described by way of introduction and which is peculiar in that the method further comprises the steps of

- providing at least one brush head which comprises a brush housing containing a rotatable brush base having brushes extending from the surface of the rotatable brush base, and which brush housing is provided with a suction outlet for removal of abrasive dust, and

- arranging the at least one brush head in relation to the abrasive head for a simultaneously movement of the abrasive head and the at least one brush head,

- abrading the surface or a part thereof in an abrading step by rotating the rotatable base, whereby the front side with the abrasive properties is abrading the surface of the elongated structure while moving the abrasive head across the surface of the elongated structure, and simultaneously

- brushing the surface or a part thereof in a cleaning step by rotating the rotatable brush base, whereby the brushes brush the surface while activating a suction unit connected with the suction outlet of the brush housing and thereby removing abrasive dust from the abraded surface while moving the abrasive head and the brush head across the surface of the elongated structure thereby performing a surface treatment by simultaneously abrading and cleaning the surface of the elongated structure.

The apparatus according to the invention is peculiar in that the apparatus furthermore comprises at least one brush head which comprises a brush housing containing a rotatable brush base having brushes extending from the surface of the rotatable brush base, and which brush housing is provided with a suction outlet for removal of abrasive dust, and that the at least one brush head is arranged in relation to the abrasive head for a simultaneously movement of the abrasive head and the at least one brush head.

The suction outlets of the housings may be connected to a common suction unit or may be connected to different suction units. The suction outlets of the housings may provide identical or different suction effect.

There may be provided a brush head at one side of the abrasive head. Alternatively a brush head may be provided on opposite sides of the abrasive head. In this situation the treatment may be effected in two opposite directions as a brush head may always be arranged behind the abrasive head as seen in direction of the movement of the abrasive head during the treatment.

Alternatively the at least one brush head may be arranged at a side of the abrasive head as seen in direction of the movement of the abrasive head during the treatment. Hereby the cleaning is effected on a path adjacent to the path being abraded.

In a further alternative, brush heads may be arranged both at the side and in front or behind the abrasive head. Hereby the abrasive head may be moved in any desired path where a brush head will be arranged behind the abrasive head as seen in direction of the movement of the abrasive head during the treatment.

The diameter of a cylinder for the abrasive head and a cylinder of the brush head may have identical diameter and/or length. Alternatively, cylinders having different dimensions may be used for the abrasive head and the brush heads.

When more brush heads are used, they may be arranged on opposite side or same side of the abrasive head as seen in direction of the movement of the abrasive head during the treatment.

Cylinders in brush heads may rotate in same or in different direction in relation to each other or in relation to the rotation of the cylinder in the abrasive head.

A brush head may be arranged on a shaft connected to the abrasive head for a swinging around said shaft and thereby making it possible to arrange the brush head before or after the abrasive head as seen in direction of the movement of the abrasive head during the treatment.

According to a further embodiment, the method according to the present invention is peculiar in that the method comprises that the steps of providing the abrasive head and providing the at least one brush head comprise to provide the abrasive housing and the brush housing as a common shielding housing containing both the rotatable base of the abrading apparatus and the at least one rotatable brush base. Hereby it is possible to have an especially technical simple construction as only one shielding housing needs to be arranged, e.g. on a robotic arm, and the suction outlet and piping for connection to a suction unit will also be less complex as compared to the use of different housings for abrasive head and the brush head.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises the steps of

- bringing the abrasive head and the at least one brush head close to the surface to be abraded in such a way that the abrasive lamellae are pushed towards the surface with an essentially constant and predetermined force, and

- bringing the at least one brush head close to the abraded surface in such a way that the brushes are pushed towards the surface with an essentially constant and predetermined force which may differ from the force for the abrasive lamellae.

The positioning of the abrasive head and the at least one brush head in relation to the surface is effected by control means which below will be explained in further details.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises the steps of

- moving the abrasive head and the brush head across the surface following a path in a first direction from a first side edge to a second edge of the elongated structure, -translating the abrasive head and the brush head perpendicular to the first direction, and

-repeating the abrading and cleaning steps for a neighboring path until the elongated structure is treated.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises the step of

- choosing the first direction to be transversal to the longitudinal direction of the elongated structure.

It is preferred to treat the elongated structure in paths being transversal to the longitudinal direction. However it is also possible to effect the treatment in path having an orientation more or less parallel to the longitudinal direction of the elongated structure.

According to a further embodiment the method according to the present invention is peculiar in that the steps of providing the abrasive head and the brush head include providing a robotic arm on which the abrasive head and the brush head are mounted, and which robotic arm is displaceable along the longitudinal direction of the elongated structure and transversal to said longitudinal direction.

Accordingly, the robotic arm may control the movements of the abrasive head and the brush head between the side edges of the elongated structure, and the robotic arm is also moveable in the longitudinal direction of the elongated structure in order to arrange the robotic arm in position for the surface treatment of a neighboring path of the elongated structure.

With the term robotic arm is herein understood a multiple-axis arm having at least 5 degrees of freedom, i.e. that it is able to move the abrasive head and the brush head across the surface of the elongated structure, towards and away from said surface, to tilt the abrasive head and the brush in various planes, and that it is able to rotate the abrasive head and the brush head about an axis substantially normal to the surface of the structure.

The abrasive head and the at least one brush head may be connected with a fixed mutual position. Alternatively, the abrasive head and the at least one brush head may be connected in such a way that they may be moved independently in relation to the surface. Hereby a more flexible positioning of the heads in relation to the surface is possible. The heads may be applied with different distance to the surface and may be arranged with different contact pressure.

The robotic arm is at least a 5-axis arm and most preferred a 6-axis arm, however robotic arms with higher degrees of freedom could also be employed. With a robotic arm having a degree of freedom of 5, 6 or even more, the arm with the abrasive head and the at least one brush head become a more flexible treatment tool that can adjust better to a complex double curved surface of the elongated structure to be abraded and will be able to handle areas around edges, e.g. of a wind turbine blade, more gentle.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises that the rotatable base is chosen as an abrading cylinder, and the abrasive sheets and support brushes are arranged in the cylindrical surface of the cylinder and extends substantially radially from the cylindrical surface of the cylinder and have an extension in the longitudinal direction of the cylinder.

The abrading cylinder in itself is well known, e.g. from a number of prior art documents with various embodiments.

An advantage obtained by employing the abrading cylinder is that a more efficient abrading of a surface may be obtained as compared to the use of abrading discs, and the abrading cylinder is in itself flexible to the shape of the surface and does not need to be perfectly aligned with the surface to perform the abrading of the surface satisfactory. It also readily abrades surfaces of complex shapes such as double-curved surfaces.

A drawback of the abrading cylinder is that it is only efficient when the relative movement of the surface and the abrading cylinder cause the surface to move in the opposite direction of the movement of the abrasive lamellae caused by the rotation of the cylinder, because the movement of the object in that case enhances the movement of the abrasive lamellae with respect to the surface, whereas relative movement of the surface against the direction of the movement of the abrasive lamellae caused by the rotation of the cylinder weakens the abrasive effect on the surface.

Thus, the abrading cylinder is generally applied in abrading apparatuses with a uniform relative movement of the elongated structure with respect to the abrading cylinder.

Furthermore, the abrading cylinder is not particularly suitable for use near edges of structures as the rotation of the cylinder may cause the abrasive lamellae to collide with the edge of the structure in case the axis of rotation of the cylinder is not substan- tially perpendicular to the edge, if the abrading direction of the cylinder is towards the surface of the structure and not towards the edge of the structure. The abrasive lamellae may collide with the edge which has a damaging and life-shortening effect on the lamellae as well a damaging effect on the edge of the elongated structure. This may, however, be avoided by the present combination of an abrading cylinder and a robotic arm, which allow for advanced control of the operational position of the cylinder. Such advanced control may include leaving a marginal edge area without abrading.

Even though the use of an abrading cylinder is preferred in most cases the method may alternatively include that the rotatable base is chosen as an abrading disc, and the abrasive sheets extend substantially radially relative to a rotational axis and are arranged in the surface of the disc and with a substantially perpendicular orientation in relation to the surface of the disc.

There may be used a single abrading disc or more abrading discs which are aligned in order to cover a path having a larger width than covered with a single abrading disc. Hereby, it is possible to have abrading disc which may be adapted to abrade surfaces of complex shapes such as double-curved surfaces. The discs in a row may preferably be provided with an overlapping of the strips covered by the discs. The abrading discs may be rotated in same direction or in opposite directions.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises that the rotatable brush base is chosen as a cylinder, and the brushes are arranged in the cylindrical surface of the cylinder and extend substantially radially from the cylindrical surface of the cylinder and have an extension in the longitudinal direction of the cylinder.

A rotatable brush cylinder in itself is well known.

An advantage obtained by employing the brush cylinder is that an efficient brushing of a surface may be obtained as compared to the use of brush discs, and the brush cylinder is in itself flexible to the shape of the surface and does not need to be perfectly aligned with the surface to perform a satisfactory brushing of the surface. It also readily brushes surfaces of complex shapes such as double-curved surfaces. The brush cylinder is generally applied in apparatuses with a uniform relative movement of the elongate structure with respect to the brush cylinder.

Even though the use of a brush cylinder is preferred in most cases, the method may alternatively include that the rotatable base is chosen as a brush disc and the brushes extend substantially radially relative to a rotational axis and are arranged in the surface of the disc and with a substantially perpendicular orientation in relation to the surface of the disc.

There may be used a single brush disc or more brush discs which are aligned in order to cover a path having a larger width than covered with a single brush disc. Hereby it is possible to have brush disc which may be adapted to brush surfaces of complex shapes such as double-curved surfaces. The brush discs in a row may preferably be provided with an overlapping of the paths covered by a single brush discs. The brush discs may be rotated in same direction or in opposite directions.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises that the step of providing an abrasive head includes arranging further brushes between two neighboring abrasive lamellas supported by the support brushes.

This will ensure a more efficient mechanical cleaning of the surface as the further brushes may increase the mechanical removal of dust during the abrading.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises a step of

- abrading a marginal edge area at one or both side edges in the longitudinal direction of the elongated structure while moving the abrasive head and the brush head across the surface following a path parallel to the longitudinal direction of the elongated structure.

The treatment performed while moving the abrasive head and the brush head across the surface following a path transversal to the longitudinal direction of the elongated structure may be used for a larger central surface area of the elongated structure and thereby leaving the marginal edge areas to be treated by the separate treatment while moving the abrasive head and the brush head in the longitudinal direction of the elongated structure.

The treatment of the marginal edge areas may be effected before or after the treatment of the larger central surface area.

This embodiment has the advantage that abrasive dust released to the surroundings is minimized or eliminated which is difficult to obtain, if the abrasive head will move past the edge while moving the abrasive head across the surface following a path transversal to the longitudinal direction of the elongated structure. If the abrasive head will move past the edge, dust may be thrown out when the abrasive head passes the side edge.

According to a further embodiment the method according to the present invention is peculiar in that the method comprises a step of providing control means for controlling the operation of the abrasive head and the operation of the brush head.

The control means may control the operation of the abrasive head and the at least one brush head in a way adapted to let the abrasive head and the at least one brush head be operated according to any desired working pattern for abrading and cleaning the surface of the elongated structure, such as a wind turbine blade.

In case an abrading arrangement described in W02012/003828 is used, then only few modifications in the control means are necessary in order to conduct the method according to the present invention.

The blade may be arranged in a plurality of ways to be treated by the treatment method.

Preferably, arranging the blade comprises the root end of the blade being attached to a suitable fixation arrangement so the blade extends substantially horizontally to be treated while only being supported at the root end of the blade. As another example the blade may be supported by one or more supportive structures arranged underneath the blade in the longitudinal direction of the blade.

It is however naturally understood, that any suitable way of arranging the blade, so it can be abraded and cleaned, may be utilized, and furthermore, e.g. a combination of fixating the root end to a suitable fixation arrangement may be combined with supporting the blade, e.g. underneath the blade at further locations along the blade.

Thus, when the blade is arranged in the supportive structure, it may result in the blade deflecting from its ideal shape due to e.g. gravity. For example, if the blade is arranged in the supportive structure by the root being attached to a fixation arrangement, the tip end/free end of the blade will deflect downwards.

In general, the deflection of the blade is dependent on among others, the elasticity of the blade, the size of the blade, the orientation of the blade (e.g. orientation of the leading and trailing edges of the blade), and others.

Also, the blade may deflect in different ways dependent on the blade orientation when e.g. rotating the blade around the longitudinal direction of the blade.

It is preferred that the apparatus for effecting the method comprises control means which facilitate taking such deviations and/or blade deflections into consideration during the abrading and cleaning process.

Thus, it is preferred that the apparatus comprises a deviation handling arrangement for automatically handling and/or compensating for deviations, such as the above mentioned deflections due to the arrangement of the blade to be treated. The deviation handling arrangement gathers information from more data sources.

Accordingly, sensors may be arranged on a support of the heads, e.g. robotic arms and/or vertical columns. These sensors may be contactless distance sensors using laser light or ultrasonic means for providing an input to the control system in order for the control system to determine the actual shape of the blade. According to a further embodiment, the apparatus according to the invention is peculiar in that at the surface, preferably at each end, of the abrasive head and of the brush head there is provided spacing controlling discs safeguarding that the abrasive lamellae and the brushes are not pressed too hard against the surface which is treated.

By using the spacing controlling discs, there is achieved a particularly simple way of ensuring that the abrasive lamellae and the brushes are never pressed too hard against the treated surface. The spacing controlling discs may thus be used in combination with the above mentioned control of the contact pressure. The pressure may in a simple way be adjusted different for the lamellae in the abrasive head and the brushes in the brush head.

By dimensioning the dimension of the spacing controlling discs relative to the dimension of the abrasive lamellae and the brushes, it is ensured that a maximum contact pressure for the abrasive lamellae and the brushes is never exceeded. Too hard pressure against the surface to be treated will thus never occur. The spacing controlling discs are made of a soft material which does not damage the surface, e.g. rubber or plastic.

The spacing controlling discs may be adjustable to adapt to different distance between the surface to be treated and the brushes or the abrasive lamellae.

According to a further embodiment, the apparatus according to the invention is peculiar in that the processing tool includes two abrading cylinders arranged for mutual counter rotation.

Particularly when abrading windmill blades it is important that abrading or polishing cylinders that work beyond a leading edge and trailing edge in a way such that abrading is done away from the windmill blade.

A processing tool with two abrading cylinders will thus be adapted so that the abrading cylinder, which is moved beyond a leading or trailing edge, is rotated in direction away from the wind turbine blade. It is possible to mount two abrading cylinders in separate guides in an abrasive head. Alternatively, they can be placed in a common guide where the guide supports an arm which is pivotably suspended at its centre, and which at each end supports the abrading cylinders.

A plant for treatment may comprise two robotic arms which each is carrying an abrasive head and at least one brush head and which is mounted on each their vertical column which is displaceable along an elongated structure, e.g. a wind turbine blade. The vertical columns may be connected by a horizontal crossbar and supported on wheels so as to be displaceable along the elongated structure on a set of tracks laid out horizontally on the floor.

In this way the plant will be provided with a U-shaped mounting frame that extends above an upper edge of the elongated structure, e.g. a wind turbine blade. The U- shaped mounting frame may thus make it possible to perform surface treatment on two oppositely directed surfaces of the elongated structure. Hereby may be achieved a more rapid surface treatment with a simultaneous treatment of both flat sides of a wind turbine blade.

According to a further embodiment, the apparatus according to the invention is peculiar in that the abrasive housing and the brush housing are provided in form of a common shielding housing containing both the rotatable base of the abrading apparatus and the at least one rotatable brush base. With such apparatus the advantages explained above in relation to the method will be obtained.

Description of the Drawing

In the following embodiments of the present invention will be further explained with reference to the accompanying drawing, in which

Fig. 1 shows a prior art robotic arm equipped with an abrading cylinder,

Fig. 2 is a prior art example of an abrading cylinder within a shielding housing,

Fig. 3 is a prior art example of a working pattern for abrading of the surface of an elongated structure,

Fig. 4 shows a first view of the prior art use for abrading a wind turbine blades,

Fig. 5 shows a second view of the prior art use for abrading a wind turbine blade, Fig. 6 shows a partially schematic view of an abrasive head and two brush heads and a surface to be treated by a method according to the present invention,

Fig. 7 shows a partially schematic view of the abrasive head and the two brush heads seen according to the arrows VII - VII in Fig. 6,

Fig. 8 shows a partially schematic view of the abrading cylinder and the surface shown in Fig. 6 during abrading,

Fig. 9 shows a partially schematic view of the brush cylinders and the surface shown in Fig. 6 during cleaning,

Fig. 10 shows a schematic view of an apparatus according to the present invention, and

Fig. 11 shows a partially schematic view of a further embodiment for an abrasive head and two brush heads and a surface to be treated by a method according to the present invention.

Detailed Description of the Invention

Figs. 1-5 show examples of the abrading arrangement described in W02012/003828.

An abrading arrangement of the prior art may be used for the method according to the present invention for treatment of a surface by abrading and cleaning. What is needed is to provide at least one brush head and arranging the at least one brush head in relation to the abrasive head for a simultaneously movement of the abrasive head and the at least one brush head and to amend the control means in order to ensure the simultaneously movements of the heads.

The abrading arrangement 1 shown in Fig. 1 comprises a 6-axis articulated robotic arm 2 on which is mounted an abrasive head 3 having an abrading cylinder 4 enclosed in a shielding housing 5 provided with a suction outlet (not shown) for removal of dust and a motor (not shown) for driving the rotation of the abrading cylinder 4. The base 6 of the robotic arm 2 is in Fig. 1 mounted on a vertical column 7 equipped with parallel, vertical tracks 8 on which the base 6 is displaceable arranged in the vertical direction so as to enable abrading of a surface 1 of a wider extent in the vertical direction than the robotic arm 2 itself allows for. The abrading cylinder 4 shown in Fig. 2 has abrasive means which comprise abrasive lamellae 9 of an abrasive sheet, such as abrasive fabric, of which the front side 10 has abrasive properties and which extend substantially radially from an elongated core 11 of the cylinder. The abrasive lamellae 9 are supported on the back side by an elastic support element comprising support brushes 12 having almost the same length as the lamellae 9.

The abrading cylinder 4 is during operation of the abrading arrangement rotated so that the front side 10 of the abrasive lamellae 9 is moved across the surface 1 to be abraded, the direction of rotation are indicated by the curved arrows R on Fig. 2.

The tangential movement of the front side 10 of the lamellae 9 over the surface 1 to be abraded due to the rotation of the abrading cylinder 4 defines the abrading direction of the cylinder 4 indicated with straight arrow AD.

The core 11 of the abrading cylinder 4 shown in Fig. 2 is equipped with helical or spiral shaped undercut grooves for retaining the flexible sanding strips comprising the abrasive lamellae 9 as well as the brushes 12, but the grooves may in another embodiment of the present invention be straight along the longitudinal direction of the core 11.

In a particular embodiment of the present invention, the control means for controlling the operation of the abrading arrangement are adapted to let the abrading cylinder operate according to the working pattern illustrated in Fig. 3 for abrading the surface 1 of an elongated structure 13 having a first edge 14 and a second edge 15, both extending generally in the longitudinal direction of the elongated structure 13, such as a wind turbine blade. The first edge 14 and the second edge 15 are not necessarily parallel to each other but are substantially so as depicted in Fig. 3.

The part of the working pattern described in details herein start at the letter "S" on Fig. 3.

The abrading cylinder 4 is in abrading engagement with the surface 1 of the elongated structure 13 starting at a position at the first edge 14 and moving towards the second edge 15 at a first velocity, and where the cylinder 4 is oriented so that the abrading direction is against the direction of movement of the abrasive head 3, indicated with the straight arrows M in Fig. 3. The reason to have the direction of movement M to be opposite the abrading direction AD of the cylinder 4 is that, it is in that way avoided that the abrasive lamellae 9 collide with the first edge 14 which has a damaging and life-shortening effect on the lamellae 9 as well as damaging effect on the edge 14 of the structure. However, when the direction of movement M is opposite the abrading direction AD, the abrading action on the surface 1 is less efficient, and the speed of the movement of the abrasive head 3 must be reduced to obtain a satisfactory finish of the surface 1, for which reason the extent of these parts of the working pattern, generally referred to with the letter "B" in Fig. 3, has been minimized.

When the abrasive head 3 has been moved away from the first edge 14, the abrasive head 3 may be lifted away from the structure 13, so that the cylinder 4 disengages the surface 1 of the structure 13, and the abrasive head 3 is turned around at the position indicated in Fig. 3 with the letters "TU", so that the abrading direction AD of the cylinder 4 is reversed. Now, the abrasive head 3 may be lowered towards the structure 13, until the cylinder 4 engages the surface 1 with a sufficient force, and the movement of the abrasive head 3 across the surface 1 of the structure towards the second edge 15 is continued. In this part of the working pattern, generally referred to with the letter "A" in Fig 3, the direction of movement M and the abrading direction AD of the cylinder 4 is the same direction, the abrading action is therefore more efficient and the speed of the movement of the abrasive head 3 can be considerably higher than in the B parts of the working pattern.

In Fig. 3 the parts A, B of the working pattern are depicted with a minor distance in between for the sake of clarity. However, the parts A, B are in the present embodiment abutting or are overlapping, e.g. 1 to 3 centimeters so that the whole of the surface 1 is abraded by the cylinder 4. In an alternative embodiment, the parts A, B are overlapping in the longitudinal direction of the structure 13 with half the width of the cylinder 4 so that each area of the surface will be abraded twice by the cylinder 4. The areas around the edges 14, 15 may only be partly abraded by the cylinder 4 and require a manually controlled abrading to obtain the correct finish. According to the prior art, the treatment only comprises abrading. According to this prior art, the following step will be performed after the second edge 15 is reached by the abrasive head 3.

The head is translated substantially one width of the cylinder 4 in the longitudinal direction of the elongated structure 13, the translation being indicated generally by the arrows in Fig. 3 referred to with the letters "TL". The sequence of working patterns is now repeated starting from the second edge 15 and moving towards the first edge 14 of the elongated structure 13, where a part B of the working pattern, where the direction of movement M is opposite the abrading direction AD, ends with a turning TU of the abrasive head and is continued with a part A, where the direction of movement M is the same as the abrading direction AD, etc.

A particular embodiment and use are shown in Figs. 4 and 5, where two robotic arms 2, 2', each carrying an abrasive head 3, are mounted on each their vertical column 7, 7', which are connected by a horizontal crossbar 16 and supported on wheels so as to be displaceable along an elongated structure 13 on a set of tracks 17 laid out horizontally on the floor.

This arrangement is particularly suitable for abrading the surface of an elongated structure in the form of a wind turbine blade 13, where the two flat sides between the leading edge 14 and the trailing edge 15 of the blade 13 can be abraded simultaneously by the abrasive heads 3 carried by the robotic arms 3, 3'. The arrangement is displaced along the blade on the tracks 17, so that the whole surface of the blade may be abraded. In order to facilitate a compensation for the twist of the blade 13 along an axis in its longitudinal direction 18, the blade 13 is supported, so that it may be rotated around its axis for the blade 13 to be substantially horizontally oriented at the position of the vertical columns 7, 7'.

The control system controlling the operation of the arrangement shown in Figs. 4 and 5 comprises a predefined set of data defining the ideal three-dimensional shape of the finished blade 13, and the control system is adapted for controlling by means of the robotic arms 2, 2' the position of the abrasive heads 3, the force with which they are pressed towards the surface 1 of the blade 13, and the speed with which they are moved across the surface 1 so as to process the surface 1 of the blade 13 to approximate the predefined ideal shape of the blade 13. A set of sensors (not shown) are arranged on the robotic arms 2, 2' and/or on the vertical columns 7, 7', in particular contactless distance sensors using laser light or ultrasonic means for providing an input to the control system in order for the control system to determine the actual shape of the blade 13.

Fig. 6 illustrates the abrasive head 3 and two juxtaposed brush heads 19 and the surface 1 to be treated.

Fig. 6 illustrates the situation where the abrasive head 3 with the abrasive lamellae 9 and the brush heads 19 with brushes 20 are lifted free of the surface 1.

Each of the brush heads 19 comprises a brush housing 21 containing a rotatable brush base in form of a rotatable core 22 provided with brushes extending from the cylindrical surface of the rotatable brush core 22. The brush core is cylindrical and accordingly, the brush core 22 and the brushes 20 constitute a brush cylinder 23.

The brush housing 21 is connected with a suction outlet 24 for removal of dust which is removed from the surface 1 by the mechanical action of the brushes 20. Furthermore, a motor (not shown) is established for driving the rotation of the brush cylinder 23.

The brush cylinder 23 is during operation of the system rotated so that the brushes are moved across the surface to be brushed. The direction of rotation is indicated by curved arrows in Fig. 6. The direction of the rotation of the brush cylinders 23 may be orientated in the opposite direction, and the brush cylinders 23 may also be rotated in opposite directions. The brushes 20 effect a tangential movement over the surface 1 to be cleaned due to the rotation of the brush cylinder 23. Hereby, a mechanical action is effected on the surface which removes dust, which remains on the surface 1 by a combined mechanical action and the suction action through the suction outlet 24.

The abrasive head 3 is connected with a brush head 19 on each side. Typically, only one brush head 19 is needed. This brush head 19 needs to be arranged at the side of the abrasive head 3 which is directed opposite to the movement of the abrasive head 3 over the surface 1. However, when having two brush heads 19 arranged with one head on each side of the abrasive head it is possible to use the system with a direction of movement for the abrasive head in both directions across the surface 1. Alternatively, only one brush head 19 may be arranged which is displaceable from one side to the other side of the abrasive head 3.

The brush heads 19 may be arranged in a fixed position in relation to the abrasive head 3. However, it is preferred that the brush heads 19 are arranged movable in relation to the abrasive head 3 in order to make a better adaptation to the surface 1 to be brushed.

Fig. 7 illustrates the abrasive head 3 and the brush heads as seen in direction of arrows VII-VII in Fig. 6. Fig. 7 illustrates that the brush heads 19 comprising the brush cylinders are arranged parallel with the abrasive head 3 containing the abrading cylinder.

Fig. 7 is a schematic figure for illustrating the parallel orientation of the heads and accordingly, the cylinders are not illustrated in this figure.

Fig. 8 illustrates the situation during the abrading. The abrasive lamellae 9 supported on the back side by the support brushes 12 will be in contact with the surface 1 with their active front side 10 having abrasive properties as the cylinder rotates in clockwise direction as indicated with a curved arrow.

Fig. 9 shows the brushes 20 from both brush cylinders 23 in contact with the surface 1. Even though both brush cylinders 23 are shown in contact with the surface 1 simultaneously, a typical use will involve that only one brush cylinder is in contact with the surface 1. Between the two brush cylinders 23 an abrading cylinder (not illustrated in Fig. 9) will be arranged.

Alternatively, the two brush cylinders 23 illustrated in Fig. 9 may be arranged at one side of the abrasive head in order to have two brush heads 19 following the abrasive head in order to brush the surface which has been abraded by the abrasive head. Here- by, a more efficient cleaning may be effected compared to the use of only one brush head 19.

In the illustrations in Figs. 6-9 it is indicated that the diameter of the brush cylinders 23 are smaller than the diameter of the abrading cylinder 4. However, the diameter may be identical for the abrading cylinder 4 and the brush cylinders 23. Alternatively, there may be a difference, and typically the brush cylinders will have a diameter which is smaller than the diameter of the abrading cylinder 4 as illustrated in Figs. 6- 9.

The brushes 20 are arranged in the core 22. The brushes may be arranged in a helical or spiral shaped undercut grooves in the core 22. Such undercut grooves may be used for retaining the brushes in the same way which is known for the holding of abrasive lamellae as well as the support brushes. The grooves arranged in the core 22 may be straight along the longitudinal direction of the core 22 as an alternative to the helical or spiral shape.

Fig. 10 shows a schematic view of an apparatus according to the present invention where a brush head 19 is arranged together with an abrasive head 3 on the robotic arm 2 which is mounted on the vertical column 7.

The brush head 19 as well as the abrasive head 3 are connected with suction outlets 24 and 25 which are connected to a common suction unit 26 arranged on a common base unit 27. The base unit 27 is provided with wheels 28 for movement along an elongated structure to be treated.

The brush head 19 is arranged on the abrasive head 3 through an arm 29 which is arranged for a swinging indicated by double-arrow 30 around a shaft 31 attached to the abrasive head 3. Hereby one brush head 19 may be placed on either side of the abrasive head 3 depending on the movement of the abrasive head 3 during an abrasive step.

Fig. 11 shows a view corresponding to Fig. 6. In this embodiment the abrading cylinder 4 and the brush cylinders 23 are arranged in a common shielding housing 32 hav- ing a suction outlet 33 which is connected to a suction unit for removal of dust from the abrading effected by the abrading cylinder 4 and dust from the mechanical action effected on the surface by the brush cylinders 23 which remove dust which remains on the abraded surface.

Typically only one brush cylinder 23 is needed. This brush cylinder 23 needs to be arranged at the side of the abrading cylinder 4 which is directed opposite to the movement of the abrading cylinder 4 over the surface 1. However, when having two brush cylinders 23 arranged with one on each side of the abrading cylinder, it is possi- ble to use the system with a direction of movement for the common shielding housing 32 in both directions across the surface 1.

The brush cylinders 23 and the abrading cylinder 4 will typically have substantially same lengths. Accordingly, they may have a length corresponding to the width of the common shielding housing 32.