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:

A- providing an abrasive head which comprises a housing containing abrasive lamel- lae 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 abrasive head and which abrasive lamellae are supported on a back side by an elastic support element compris- ing support brushes having almost the same length as the lamellae and which housing is provided with a suction outlet for removal of abrasive dust,

B- bringing the abrasive head close to the surface to be abraded in such way that the abrasive lamellae is pushed towards the surface with an essentially constant and pre- determined force,

C- rotating the rotatable base in a first direction whereby the front side with the abra- sive properties is abrading the surface of the elongated structure while moving the abrasive head across the surface following a path in a first direction from a first edge to a second edge, which first direction is transversal to the longitudinal direction of the elongated structure.

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 meth- od, which apparatus includes abrading the surface and cleaning the surface by remov- ing abrasive dust from the abraded surface, which apparatus comprises an abrasive head which comprises a 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 abrasive head and which abrasive lamellae are supported on a back side by an elastic support element comprising support brushes having al- most the same length as the lamellae and which 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/poli shing the sur- face 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 ex- ample concrete elements or metal pipes.

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

Earlier it was known to abrade large structures such as wind turbine blades, 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 the need to work from platforms, ladders and lifts in order to reach all surface parts of such larger structures.

Earlier wind turbine blade where abraded with the wind turbine blade 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 abrad- ed and wherein the movement of the support is effected with an 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 dram on the surface upon which the drum is to be abraded, to control the force by which the drum is pressed towards the surface, and to control the velocity by which the drum is moved with respect to the surface.

In this arrangement an abrasive head is provided which comprise 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 abrading 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 sub- stantially 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 man- ner the support brushes has a length being shorter than the length of the abrasive la- mellae 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 flex- ible sanding strips holding 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 wind turbine blades.

Even though the shielding housing is provided with a suction outlet which is connect- ed 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 sufficient for a fol- lowing 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 remain- ing 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 overcomes 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 overcomes 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 WO2012/003828. 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

- abrading the surface or a part thereof in an abrading step by rotating the rotatable base in a first direction whereby the front side with the abrasive properties is abrading the surface of the elongated structure while moving the abrasive head across the sur- face following a path transversal to the longitudinal direction of the elongated struc- ture, and

- brushing the surface or a part thereof in a cleaning step by rotating the rotatable base in an opposite direction whereby the support brushes brush the surface and thereby remove abrasive dust from the abraded surface while moving the abrasive head across the surface following a path transversal to the longitudinal direction of the elongated structure.

Hereby the treatment of the elongated structure is effected in a way where the paths for abrading and brushing are longer and the number of changes of direction for the movement of the abrasive head is smaller which may decrease the treatment time.

Thus the present invention makes it possible to effectively clean the surface with the same abrasive head used for the abrading simply by reversing the rotation of the rotat- able base to be opposite the abrading direction and move the abrasive head in the op- posite direction along the same path which just has been abraded.

Hereby the support brushes will mechanically act on the surface and remove remain- ing dust particles on the abraded surface. The dust particles are removed through the suction outlet for removal of abrasive dust during the abrading step. Accordingly, there is effected a vacuum and mechanical cleaning whereby it has shown that the surface of the elongated structure is ready for a finishing surface treatment like a coat- ing or painting.

During the cleaning step the abrasive head may be controlled according to same con- trol principles used for the abrading step and the same motor for driving the rotatable base for the abrading step may also be used for the rotation of the rotatable base dur- ing the cleaning step. It is possible to perform the abrading steps for the total surface of the elongated sur- face before performing the cleaning steps or alternatively the abrading steps and the cleaning steps may be performed alternately.

The apparatus according to the invention is peculiar in that the rotatable base is ar- ranged for being rotated with the abrasive lamellae in the abrading direction or with the lamellae in the direction opposite of the abrading direction.

The rotatable base is rotated so that the front side of the abrasive lamellae is moved across the surface to be abraded. The tangential movement of the front side of the la- mellae over the surface to be abraded due to the rotation of the rotatable base defines herein the abrading direction.

For a rotatable base in form of a cylinder the abrading direction will be a direction substantially perpendicular to the longitudinal direction of the cylinder. For a rotatable base in form of a disc the abrading direction will be circular.

The path to be abraded and cleaned will normally be a strip formed area extending transversal to the longitudinal direction of the elongated structure and extending be- tween the side edges of the elongated structure.

The strip formed area may extend from one side edge to the other side edge. Alterna- tively, the strip formed area may have an extension almost to the side edges and leav- ing a side edge area at each side edge which is not abraded and/or cleaned. In the latter situation the side edge area needs to be manually cleaned and/or abraded.

According to a specific embodiment the method according to the present invention is peculiar in that the method further comprises the steps 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 across the surface following a path parall el to the longitudinal direction of the elongated structur e, and

- brushing the marginal edge area at one or both side edges in the longitudinal direc- tion of the elongated structure whereby the support brushes brush the surface and thereby remove abrasive dust from the abraded surface while moving the abrasive head across the surface following a path parallel to the longitudinal direction of the elongated structure.

The treatment performed while moving the abrasive 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 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.

According to a further aspect of the present invention the method comprises the steps of

- abrading the surface or a part thereof in an abrading step by rotating the rotatable base in a first direction whereby the front side with the abrasive properties is abrading the surface of the elongated structure while moving the abrasive head across the sur- face following a path parallel with the longitudinal direction of the elongated struc- ture, and

- brushing the surface or a part thereof in a cleaning step by rotating the rotatable base in an opposite direction whereby the support brushes brush the surface and thereby remove abrasive dust from the abraded surface while moving the abrasive head across the surface following a path parallel with the longitudinal direction of the elongated structure.

Hereby the treatment may also include treatment of marginal edge areas of the elon- gated structure. According to a further embodiment the method according to the present invention is peculiar in that the method comprises the steps of

B- bringing the abrasive head close to the surface to be abraded in such way that the abrasive lamellae is pushed towards the surface with an essentially constant and pre- determined force,

C- rotating the rotatable base in the first direction whereby the abrading step is per- formed while moving the abrasive head across the surface following a path in a first direction from a first edge to a second edge,

E- reversing the rotation of the rotatable base,

F- bringing the abrasive head close to the abraded surface in such way that the support brushes are pushed towards the surface with an essentially constant and predetermined force,

G- moving the abrasive head across the surface following the same path in the oppo- site direction from the second edge to the first edge whereby the cleaning step is per- formed,

I- translating the abrasive head along the longitudinal direction of the elongated struc- ture with a distance corresponding to the width of the path and repeating steps B to G for a neighboring path until the elongated structure is treated or alternatively repeating the abrading steps for the elongated structure before perform- ing the cleaning steps.

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

D- moving the abrasive head away from the surface in such way that there is no con- tact between the abrasive lamellae and the surface, which step is effected before the reversion step and

H- moving the abrasive head away from the surface in such way that there is no con- tact between the support brushes and the surface, which step is effected before the translating step.

In case an abrading arrangement described in WO2012/003828 is used then only few modifications in the control means are necessary in order to conduct the method ac- cording to the present invention. The blade may be arranged in a plurality of ways to be abraded by the abrading ar- rangement.

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 abraded by the abrading arrangement 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 by the abrading arrangement may be utilized, and fur- thermore 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 loca- tions along the blade.

Thus, when the blade is arranged in the abrading arrangement, 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 abrading arrangement by the root being attached to a fixation ar- rangement, the tip end/free end of the blade will deflect downwards.

In general, the deflection of the blade is dependent of 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 abrading arrangement comprises control means which facilitates taking such deviations and/or blade deflections into consideration during the abrading process and the cleaning process.

Thus, it is preferred that the abrading arrangement 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 abraded. The deviation handling arrangement gathers information from more data sources.

According to a further embodiment the method according to the present invention is peculiar in that step A includes providing a robotic arm on which the abrasive head is mounted and which robotic arm is displaceable along the longitudinal direction of the elongated structure.

Accordingly the robotic arm controls the movements of the abrasive head between the side edges of the elongated structure and the robotic arm is also moveable in the longi- tudinal direction of the elongated structure in order to arrange the robotic arm in posi- tion for the surface treatment of a neighboring path of the elongated structure.

With the term robotic arm is herein understood a multiple-axis aim having at least 5 degrees of freedom, i.e. that it is able to move the abrasive head across the surface of the elongated structure, towards and away from said surface, to tilt the abrasive head in various planes and that it is able to rotate the abrasive head about an axis substan- tially normal to the surface of the structure, so that the abrading direction may be re- versed by a 180° rotation of the abrasive head.

The robotic arm is at least a 5-axis arm and most preferred a 6-axis arm, however ro- botic arms with higher degrees of freedom could also be employed. With a robotic aim having a degree of freedom of 5, 6 or even more, the arm with the abrasive head becomes a more flexible abrading tool that can adjust better to a complex double curved surface of the elongated structure to be abraded and will be able to handle are- as around edges more gentle.

According to a further embodiment the method according to the present invention is peculiar in 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 from 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 satisfac- tory. It also readily abrades surfaces of complex shapes such as double-curved surfac- es.

A drawback of the abrading cylinder is that it is only efficient when the relative movement of the surface and the abrading cylinder causes 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 abrasive heads with a uniform rela- tive 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 lamel- lae 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 extends substantially radially relative to a rotational axis and are ar- ranged 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 with 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 step C comprises the steps of alternating the abrading direction of the rotated cylinder during the movement of the abrasive head across the surface follow- ing the path in the first direction from the first edge to the second edge whereby the abrading direction of the cylinder is in the same direction or in direction opposite of the movement of the abrasive head from the first edge to the second edge.

It is necessary to reverse the rotational direction of the cylinder when changing from the abrading step to the cleaning step. Then it is possible to change the use of the brushes from support brushes to be active cleaning brushes or vice versa.

However, during one pass from the first edge to the second edge during the abrading step it is possible to alternate the abrading direction in relation to the direction of the movement of the abrasive head. Hereby the abovementioned problems with damage of the side edges of the elongated structure may be eliminated.

According to a further embodiment the method according to the present invention is peculiar in that step A includes arranging further brushes between two neighboring abrasive lamellas.

This will ensure a more efficient mechanical cleaning of the surface as the number of brushes may be increased. According to a further embodiment the method according to the present invention is peculiar in that steps C and G involves that the path abraded and brushed extend to a position close to first edge and the second edge, thereby leaving a marginal edge area at the first and the second edge which is not abraded and brushed.

As explained above there might be a risk of damaging the edges. This risk is eliminat- ed when the abrading starts and stops in a small distance from the edges.

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 control- ling the operation of the abrasive head.

The control means may control the operation of the abrading arrangement in a way- adapted to let the abrading cylinder be operated according to any desired working pat- tern for abrading and cleaning the surface of the elongated structure having a first edge and a second edge both extending generally in the longitudinal direction of the elongated structure, such as a wind turbine blade.

According to a further embodiment, the apparatus according to the invention is pecu- liar in that at the surface, preferably at each end, of the abrasive head there is provided spacing controlling discs safeguarding that the abrasive lamellae are not pressed too hard against the surface which is abraded.

By using the spacing controlling discs, there is achieved a particularly simple way of ensuring that the abrasive lamellae are never pressed too hard against the treated sur- face. The spacing controlling discs may thus be used in combination with the above- mentioned control of the contact pressure.

By dimensioning the dimension of the spacing controlling discs relative to the dimen- sion of the abrasive lamellae, it is ensured that a maximum contact pressure for the abrasive lamellae is never exceeded. Too hard pressure against the surface to be abraded will thus never occur. The spacing controlling discs are made of a soft mate- rial which does not damage the surface, e.g. rubber or plastic. Furthermore, the spacing controlling discs may ensure that the brushes are pressed towards the surface during the cleaning step.

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

According to a further embodiment, the plant according to the invention is peculiar in that the rotatable base is arranged for being rotated in opposite rotational directions while the abrasive head is in a fixed position in order to change the position of the abrasive lamellae in relation to the abrading direction.

With this embodiment the motor which drives the rotatable base shall be of a con- struction which is reversible, or a reverse gear may be used between a motor and the rotatable base. When changing between abrading and cleaning the orientation of the rotation of the abrasive head is reversed. This embodiment makes it possible that the abrasive head is supported with same orientation in its support. Hereby it is possible to make use of a robotic arm being of a more simple construction and having fewer de- grees of freedom.

According to a further embodiment, the apparatus according to the invention is pecu- liar in that the processing tool includes two abrading cylinders arranged for mutual counter rotation. Particularly when abrading wind turbine blades, it is important that abrading cylinders that work beyond a leading edge and trailing edge in a way such that abrading is done away from the wind turbine blade.

An abrasive head with two abrading cylinders will thus be adapted so that the abrad- ing 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. 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 in a way.

There might be arranged more than one abrasive head. There may be arranged more abrasive heads at one side of the elongated structure or there may be arranged abrasive heads on opposite sides of an elongated structure, e.g. a wind turbine blade in order to reduce the total time used for the surface treatment.

A plant for treatment may comprise two robotic arms which are each carrying an abra- sive head and which are 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.

Description of the Drawing

In the follownng 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 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 surface shown in Fig. 6 during abrading,

Fig. 8 shows a partially schematic view of the abrasive head and the surface shown in Fig. 6 during cleaning,

Fig. 9 shows a partially schematic view of an abrasive head comprising an abrading disc and a surface to be treated by a method according to the present inven- tion, Fig. 10 shows a schematic view of an abrading disc of the abrasive head shown in Fig. 9,

Fig. 11 shows a more detailed schematic sectional view through an abrasive head shown in Fig. 9,

Fig. 12 shows a partially schematic view of the abrasive head and the surface shown in Fig. 9 during abrading and

Fig. 13 shows a partially schematic view of the abrasive head and the surface shown in Fig. 9 during cleaning.

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 amending the control means in order to ensure that the rotation of the abrading cyl- inder may be reversed in relation to the abrading direction.

The abrading arrangement 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 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 cylinder 4 defines the abrading direction of the cyl- inder 4 indicated with straight arrow AD.

The core 11 of the cylinder 4 shown in Fig. 2 is equipped with helical or spiral shaped undercut grooves for retaining the flexible sanding strips holding 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 op- erated 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 extend- ing 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 detail herein start at the letter "S" on Fig.

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 have a damaging and life-shortening effect on the lamellae 9 as well a damaging effect on the edge 14 of the structure. However, when the direction of movement M is opposite the abrading direc- tion 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 is lifted away from the structure 13 so that the cylinder 4 disengages the sur- face 1 of the structure 13 and the abrasive head 3 is turned around at the position indi- cated in Fig. 3 with the letters "TU" so that the abrading direction AD of the cylinder 4 is reversed. Now, the abrasive head 3 is lowered towards the structure 13 until the cylinder 4 engages the surface 1 with a sufficient force and the movement of the abra- sive head 3 across the surface 1 of the structure towards the second edge 15 is contin- ued. 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 overlap- ping 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 di- rection 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 direc- tion 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 of the present invention is 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 sup- ported 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 and cleaning 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 abrad- ed/cleaned simultaneously by the abrasive heads 3 earned by the robotic aims 3, 3'. The arrangement is displaced along the blade on the tracks 17 so that the whole sur- face of the blade may be abraded and cleaned. 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 approxi- mate the predefined ideal shape of the blade 13. A set of sensors (not shown) are ar- ranged on the robotic arms 2, 2' and/or on the vertical columns 7, 7', in particular con- tactless 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 situation between the abrading step and the cleaning step where the abrading cylinder 4 with the abrasive lamellae 9 are lifted free of the surface 1.

Fig. 7 illustrates the situation during the abrading step. The abrasive lamellae 9 sup- ported 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.

However, according to the present invention a cleaning of the path which has just been abraded shall be cleaned before starting abrading of the neighboring path. There- fore, the abrading head 3 is not translated when the second edge 15 is reached.

Instead there is effected a reversing the rotation of the rotatable base in order to re- verse the rotation of the cylinder for establishing a rotation opposite to the abrading direction. This is effected after the abrasive head 3 is lifted away from the structure 13 so that the cylinder 4 disengages the surface 1.

Thereafter the abrasive head 3 is brought close to the abraded surface in such way that the support brashes 12 are pushed towards the surface with an essentially constant and predetermined force. Then the abrasive head 3 is moved across the surface 1 following the same path in the opposite direction from the second edge 15 to the first edge 14 whereby the support brushes 12 brush the surface 1 and thereby remove abrasive dust from the abraded surface in the path.

Hereafter the abrasive head 3 is moved away from the surface 1 in such way that there is no contact between the support brashes 12 and the surface 1.

After this the abrasive head 3 is translated along the longitudinal direction 18 of the wind turbine blade with a distance corresponding to the width of the path.

Thereafter the neighboring path is abraded as described above.

Fig. 8 illustrates the situation during the cleaning step. The brushes 12 will be in con- tact with the surface 1 whereas only the passive back side of the abrasive lamellae 9 may be in contact with the surface 1 as the cylinder rotates in counter clockwise direc- tion.

Fig. 9 illustrates a different embodiment of the abrasive head being of a circular form and in the situation between the abrading step and the cleaning step where the abrasive head is lifted free of the surface 1.

Figs. 10 and 11 illustrate more details of the abrasive head of Fig. 9. The abrasive head comprises an abrading disc 19. The disc 19 has radially orientated lamellae 9 and support brushes 12 arranged in the flat surface of the disc 19. The disc 19 enclosed in a shielding housing 5’ provided with a suction outlet 23 for removal of dust and a mo- tor (not illustrated) for rotating of the abrading disc 19. The shielding housing 5’ com- prise a bowl formed screen portion 21 which along a circumferential wall is provided with shielding brushes 22 which ensures a good contact with the surface of the elon- gated structure 13 and ensures that dust is maintained inside the housing for extraction via the suction outlet 23.

The abrading disc 19 is provided with suction holes 20 for removal of dust. In the em- bodiment illustrated the suction holes 20 are arranged along radially orientated lines between neighbouring lamellae 9. The suction holes may be arranged in other suitable form.

Fig. 12 illustrates the situation during the abrading step. The abrasive lamellae 9 sup- ported 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 disc 19 rotates in di- rection of the arrow.

Fig. 13 illustrates the situation during the cleaning step. The brushes 12 will be in con- tact with the surface 1 whereas only the passive back side of the abrasive lamellae 9 may be in contact with the surface 1 as the cylinder rotates in direction of the arrow.