Patent Publication Number: US-2021190042-A1

Title: Rotor blade clamping tool

Description:
The present invention relates to a rotor blade clamping tool for lifting a wind turbine rotor blade, the clamping tool including a first clamping element adapted to be arranged at a first side of the rotor blade, a second clamping element adapted to be arranged at a second side of the rotor blade, and a clamping mechanism connecting the first clamping element and the second clamping element and being adapted to open the clamping tool for insertion of the rotor blade between the first and second clamping elements and close the clamping tool for clamping the rotor blade between the first and second clamping elements, at least one of the first and second clamping elements including a first balancing lever and a second balancing lever, each balancing lever being arranged pivotally about a pivot axis and having a first end flexibly connected with a corresponding first rotor blade contacting surface and a second end flexibly connected with a corresponding second rotor blade contacting surface. 
     WO 2012/095112 A1 (Liftra) discloses a tool for handling wind turbine rotor blades. The tool comprises a connecting arrangement having means for connection to a wire connected to a crane or hoist for hoisting the tool and a rotor blade held by the tool. The tool further comprises gripping means for engagement of the blade surface, wherein the gripping means has two cooperating claw-shaped sets of gripping organs driven by actuators, where each set of gripping organs comprises a first claw shaped organ and a second claw shaped organ, which together in engaged position encloses the blade surface around the entire circumference of the blade. However, as the cradle support extends beyond the structural core of the rotor blade into the more fragile area near its trailing edge, any mishandling is more likely to cause blade damage. 
     WO 2018/054440 A1 (Liftra) discloses a rotor blade clamping tool having a first clamping element adapted to be arranged at a first side of the rotor blade and a second clamping element adapted to be arranged at a second side of the rotor blade. Each one of the first and second clamping elements includes a first balancing lever and a second balancing lever, each balancing lever being arranged pivotally about a pivot axis and having a first end flexibly connected with a corresponding first rotor blade contacting surface and a second end flexibly connected with a corresponding second rotor blade contacting surface, wherein the first and second rotor blade contacting surfaces are arranged end to end and form a common rectangular elongated rotor contacting surface. The first and second balancing levers of each clamping element are arranged side by side in parallel configuration, but mutually slightly angled about their longitudinal axes so that the common rectangular elongated rotor contacting surfaces of the respective first and second balancing levers may contact the respective side of the rotor blade surface on different positions along the chord line and conform to the angle of the surface at that particular position. 
     EP 2 345 811 A1 discloses a clamp for clamping a blade for a wind turbine. The clamp comprises a first contact surface adapted to contact a portion of a back surface of the blade and a second contact surface adapted to contact a portion of a front face of the blade. The first and second contact surfaces of the clamp may be displaced relative to each other to allow removably receiving a blade therebetween. The first and second contact surfaces have an elongated rectangular shape and are each formed on a levelling piece having a wedge shaped form so that the contact surfaces may conform to the tapering shape of the rotor blade. However, it may be a disadvantage that the wedge shaped form of the levelling pieces has to be adapted to the specific shape of the rotor blades in question. As many different shapes of rotor blades exist, many different levelling pieces may have to be produced. 
     EP 3 372 549 A1 A discloses a C-gripper for arranging at a cross-member or at a suspension element and a cross-member having at least one such C-gripper for transporting loads. The height of the C-gripper is adjustable. 
     The object of the present invention is to provide a rotor blade clamping tool better suitable for handling heavy rotor blades of many different shapes. 
     In view of this object, the at least one of the first and second clamping elements includes a main balancing lever being arranged pivotally about a main pivot axis and having a first end on which the corresponding first balancing lever is arranged pivotally about a corresponding first pivot axis and a second end on which the corresponding second balancing lever is arranged pivotally about a corresponding second pivot axis, and first and second balancing levers arranged on the same main balancing lever are aligned in their longitudinal direction. 
     In this way, by clamping the rotor blade exclusively in the lengthwise direction of the blade by means of four separate rotor blade contacting surfaces arranged successively in the lengthwise direction and by automatically adapting the angle of each single rotor blade contacting surface to the angle of the rotor blade surface at the respective particular position, the clamping tool may carry the rotor blade directly on the spar cap/shear web and thereby avoid the more fragile areas away from the structural core of the rotor blade. Thereby, very heavy rotor blades of different shapes may be handled by the clamping tool. 
     In an embodiment, the four separate rotor blade contacting surfaces of the at least one of the first and second clamping elements are adapted to be arranged successively in the lengthwise direction of the rotor blade. 
     In an embodiment, the clamping tool is provided with a hoisting attachment arranged so that, during hoisting, the first clamping element is adapted to be arranged at a generally upward side of the rotor blade, and the second clamping element is adapted to be arranged at a generally downward side of the rotor blade, and the distance between the first and second pivot axes of the main balancing lever of the second clamping element is longer than, preferably at least 1.5 times, more preferred at least 2 times, and most preferred about 2.5 times, the distance between the first and second pivot axes of the main balancing lever of the first clamping element. Thereby, the support on the lower side of the rotor blade may be distributed over a longer part of the rotor blade, and thereby the rotor blade may be supported in an even more stable way. 
     In an embodiment, the first clamping element includes the main balancing lever arranged pivotally about the main pivot axis, the second clamping element includes a crossbar arranged on the clamping mechanism and having a first end on which a corresponding first balancing lever is arranged pivotally about a corresponding first pivot axis and a second end on which a corresponding second balancing lever is arranged pivotally about a corresponding second pivot axis, the first and second balancing levers arranged on the crossbar are aligned in their longitudinal direction, and the crossbar is fixed against rotation in relation to the clamping mechanism about any axis extending at least substantially in parallel with the main pivot axis of the first clamping element. Because the crossbar is fixed against rotation in relation to the clamping mechanism about any axis more or less parallel with the main pivot axis of the first clamping element, the wind turbine blade may be held in a fixed orientation in relation to the rotor blade clamping tool. Thereby, the handling of the wind turbine blade by means of the clamping tool may be facilitated. 
     In an embodiment, the clamping tool is provided with a hoisting attachment arranged so that, during hoisting, the first clamping element is adapted to be arranged at a generally upward side of the rotor blade, and the second clamping element is adapted to be arranged at a generally downward side of the rotor blade. 
     In an embodiment, the first rotor blade contacting surface and the second rotor blade contacting surface of each balancing lever has the form of respective longitudinal contact elements being aligned in their longitudinal direction and being arranged at least substantially end to end, but with enough clearance to allow mutual movement, thereby forming a total rotor blade contacting surface of the respective balancing lever. 
     In an embodiment, on the first clamping element, the total rotor blade contacting surface of the first balancing lever and the total rotor blade contacting surface of the second balancing lever are arranged at least substantially end to end, but with enough clearance to allow mutual movement, and, on the second clamping element, the total rotor blade contacting surface of the first balancing lever and the total rotor blade contacting surface of the second balancing lever are spaced at a distance being greater than the length of the total rotor blade contacting surface of the first or second balancing lever of the first clamping element, and preferably greater than 65 percent of, more preferred greater than 70 percent of, and most preferred greater than 75 percent of the combined length, on the first clamping element, of the total rotor blade contacting surface of the first balancing lever and the total rotor blade contacting surface of the second balancing lever. Thereby, the support on the lower side of the rotor blade may be distributed over a longer part of the rotor blade, and thereby the rotor blade may be supported in an even more stable way. 
     In a structurally particularly advantageous embodiment, the main balancing lever of the first clamping element includes a first and a second lever wall arranged in spaced and parallel configuration and being fixed to each other by means of a top plate and a bottom plate, and the corresponding first and second balancing levers extend at least partly between the first and second lever wall. 
     In another embodiment, each main balancing lever of the first and second clamping elements include a first and a second lever wall arranged in spaced and parallel configuration and being fixed to each other by means of a top plate and a bottom plate, and the corresponding first and second balancing levers extend at least partly between the first and second lever wall. 
     In an embodiment, the clamping mechanism connecting the first clamping element and the second clamping element includes a rigid C-formed bracket having a first leg and a second leg, a main bearing bracket for the main balancing lever of the first clamping element is hinged to the first leg of the C-formed bracket and is pivotal in relation to the first leg by means of a clamping actuator, and a main bearing for the main balancing lever of the second clamping element is arranged directly on the second leg of the C-formed bracket. Thereby, the clamping forces between the first clamping element and the second clamping element may be supported by means of a single rigid C-formed bracket which may be designed to a maximum load which may be determined based on the rotor blade to be carried. In this way, it may be avoided that the load is distributed over different brackets which each may have to be designed to a maximum load which may vary according to the way the rotor blade could be handled and therefore may have to be set relatively high. 
     In an embodiment, the clamping mechanism connecting the first clamping element and the second clamping element includes a rigid C-formed bracket having a first leg and a second leg, a main bearing bracket for a main balancing lever of the first clamping element is hinged to the first leg of the C-formed bracket and is pivotal in relation to the first leg by means of a clamping actuator, and the crossbar of the second clamping element is arranged on the second leg of the C-formed bracket by means of an exchangeable adapter piece bolted to the crossbar and arranged to maintain a certain angle between a longitudinal direction of the crossbar and an intermediate part of the rigid C-formed bracket connecting the first and second legs of the rigid C-formed bracket. Thereby, as for the embodiment mentioned above, the clamping forces between the first clamping element and the second clamping element may be supported by means of a single rigid C-formed bracket which may be designed to a maximum load which may be determined based on the rotor blade to be carried. In this way, it may be avoided that the load is distributed over different brackets which each may have to be designed to a maximum load which may vary according to the way the rotor blade could be handled and therefore may have to be set relatively high. Furthermore, by means of the exchangeable adapter piece bolted to the crossbar, an angle suitable for the specific wind turbine blade to be handled may be obtained between a longitudinal direction of the crossbar and an intermediate part of the rigid C-formed bracket. Thereby, the rigid C-formed bracket may for instance be handled with its intermediate part extending in an at least substantially vertical direction. Thereby, handling of the wind turbine blade may be facilitated. 
     In an embodiment, the exchangeable adapter piece is connected to the second leg of the C-formed bracket by means of a hinge having a hinge axis extending in the longitudinal direction of the crossbar so that the second clamping element is swingable between an insertion position for insertion of the rotor blade between the first and second clamping elements and a clamping position suitable for clamping the rotor blade between the first and second clamping elements. Thereby, insertion of the rotor blade between the first and second clamping elements may be facilitated. 
     In an embodiment, the second clamping element is swingable between the insertion position and the clamping position by means of a hydraulic actuator. Thereby, operation of the rotor blade clamping tool may be facilitated. 
     In an embodiment, the exchangeable adapter piece is adapted to be locked in the clamping position by means of a locking arrangement connecting the exchangeable adapter piece to the second leg of the C-formed bracket. Thereby, a hydraulic actuator for swinging the second clamping element between the insertion position and the clamping position may be dispensed with or such hydraulic actuator may not need to be dimensioned for carrying the clamping force of the rotor blade clamping tool. 
     In an embodiment, the intermediate part of the rigid C-formed bracket is provided with a transverse bar having opposed ends each being provided with a supporting piece adapted to support a leading edge or a trailing edge of a wind turbine blade held by the rotor blade clamping tool. Thereby, it may further be ensured that the rotor blade is held in a stable position by the clamping tool. 
     In an embodiment, the clamping tool is provided with a hoisting attachment in the form of a hoisting arm having a first end being connected to the clamping mechanism by means of a pivot element and a second end adapted to connect to a cable of a hoisting crane or the like, the pivot element allows pivotal movement of the hoisting arm in relation to the clamping tool about two different axes being at right angles to each other, and the hoisting arm is pivotal about said axes by means of a respective first and second hoist actuator. Thereby, the angle of the clamping tool and thereby the angle of the rotor blade carried by the tool may be varied during handling of the rotor blade so that, for instance, the blade may be positioned correctly in relation to the wind turbine hub when the blade is to be mounted thereon. 
     In a structurally particularly advantageous embodiment, the first leg of the C-formed bracket forms a fork element having a first leg and a second leg carrying a hinge axis therebetween on which the first clamping element is hinged to the first leg of the C-formed bracket, the first end of the hoisting arm is connected to the first leg of the fork element by means of the pivot element, the first hoist actuator is arranged between the second leg of the fork element and the hoisting arm, and the second hoist actuator is arranged between the first leg of the C-formed bracket or a central part of the fork element and the hoisting arm. 
    
    
     
       The invention will now be explained in more detail below by means of examples of embodiments with reference to the very schematic drawing, in which 
         FIG. 1  is a perspective view of a rotor blade clamping tool according to the invention, 
         FIG. 2  is a perspective view of the rotor blade clamping tool of  FIG. 1 , seen from a different angle, 
         FIG. 3  is a cross-section of the rotor blade clamping tool of  FIG. 1  along a plane extending through both legs of a C-formed bracket of the tool, 
         FIG. 4  is a cross-section of the rotor blade clamping tool of  FIG. 1  along a plane extending through the main balancing levers of both the first and second clamping elements, 
         FIG. 5  is a side view of the first clamping element of the rotor blade clamping tool of  FIG. 1 , 
         FIG. 6  is a longitudinal cross-section through first clamping element of  FIG. 5 , 
         FIG. 7  is a longitudinal cross-section through part of the first clamping element of  FIG. 5 , seen in perspective, 
         FIG. 8  is a top view of a rotor blade contacting element of the first clamping element of  FIG. 5 , 
         FIG. 9  is a perspective cross-sectional view of the rotor blade contacting element of  FIG. 8 , 
         FIG. 10  is a cross-sectional view through the rotor blade contacting element of  FIG. 8 , 
         FIG. 11  is a perspective view of the rotor blade clamping tool of  FIG. 1 , carrying a rotor blade, 
         FIG. 12  is a perspective view of another embodiment of the rotor blade clamping tool according to the invention, carrying a rotor blade, 
         FIG. 13  is a perspective view of yet another embodiment of the rotor blade clamping tool according to the invention, whereby the second clamping element is in a clamping position, 
         FIG. 14  is a side view of the rotor blade clamping tool of  FIG. 13 , whereby the second clamping element is in the clamping position, 
         FIG. 15  is a perspective view of the rotor blade clamping tool of  FIG. 13 , whereby the second clamping element is in an insertion position, 
         FIG. 16  is a side view of the rotor blade clamping tool of  FIG. 13 , whereby the second clamping element is in the insertion position, 
         FIG. 17  is an end view of the rotor blade clamping tool of  FIG. 13 , whereby the second clamping element is in the clamping position, 
         FIG. 18  is an end view of the rotor blade clamping tool of  FIG. 13 , whereby the second clamping element is in the insertion position, 
         FIG. 19  is a cross-sectional view of the rotor blade clamping tool along the line XIX-XIX of  FIG. 14 , whereby the second clamping element is in the clamping position, 
         FIG. 20  is a cross-sectional view of the rotor blade clamping tool along the line XX-XX of  FIG. 16 , whereby the second clamping element is in the insertion position, 
         FIG. 21  is a perspective view of an exchangeable adapter piece, 
         FIG. 22  is an end view of the exchangeable adapter piece of  FIG. 21 , and 
         FIG. 23  is a side view of the exchangeable adapter piece of  FIG. 21 . 
     
    
    
       FIGS. 1 and 2  show an embodiment of a rotor blade clamping tool  1  according to the present invention, for lifting a wind turbine rotor blade  2 .  FIGS. 13 to 20  illustrate another embodiment of the rotor blade clamping tool  1  according to the present invention. The clamping tool includes a first clamping element  3  adapted to be arranged at a first side  5  of the rotor blade  2  and a second clamping element  4  adapted to be arranged at a second side  6  of the rotor blade, as illustrated in  FIG. 11 . A clamping mechanism  7  connects the first clamping element  3  and the second clamping element  4  and is adapted to open the clamping tool  1  for insertion of the rotor blade  2  between the first and second clamping elements  3 ,  4  and close the clamping tool  1  for clamping the rotor blade  2  between the first and second clamping elements  3 ,  4 . 
     In this embodiment, each one of the first and second clamping elements  3 ,  4  includes a main balancing lever  16 ,  17  being arranged pivotally about a main pivot axis  18 ,  19  and having a first end  20  on which a corresponding first balancing lever  8  is arranged pivotally about a corresponding first pivot axis  10  and a second end  21  on which a corresponding second balancing lever  9  is arranged pivotally about a corresponding second pivot axis  11 . Each balancing lever  8 ,  9  has a first end  12  flexibly connected with a corresponding first rotor blade contacting surface  14  and a second end  13  flexibly connected with a corresponding second rotor blade contacting surface  15 . As seen, those first and second balancing levers  8 ,  9  which arranged on the same main balancing lever  16 ,  17  are aligned in their longitudinal direction. 
     As illustrated in  FIGS. 7, 9 and 10 , the flexible connection between each end  12 ,  13  of the balancing levers  8 ,  9  and the corresponding rotor blade contacting surface  14 ,  15  has the form of a ball joint  51  with limited movement. The ball joint  51  is formed by a connection element  52  having a partly spherical head  53  arranged in a cylindrical bore  54  having a conical bottom  55 . A shaft  56  of the connection element  52  is arranged in a cylindrical bore  57  formed in the corresponding end  12 ,  13  of the corresponding balancing lever  8 ,  9 , and the cylindrical bore  54  in which the partly spherical head  53  of the connection element  52  is arranged is formed on the corresponding first or second longitudinal contact element  22 ,  23  forming the corresponding rotor blade contacting surface  14 ,  15 . The shaft  56  of the connection element  52  is adjustable in the longitudinal direction of the cylindrical bore  57  of the corresponding balancing lever  8 ,  9  by means of a not shown screw inserted into a threaded hole  58  in the end of the shaft  56  of the connection element  52 . Furthermore, rotation of the shaft  56  of the connection element  52  in the cylindrical bore  57  is prevented by means of a key  59  fitting corresponding keyways of the shaft  56  of the connection element  52  and the cylindrical bore  57 . The partly spherical head  53  is maintained flexibly in the cylindrical bore  54  against the conical bottom  55  by means of a rubber ring  60  arranged above the head  53 . Furthermore, the movement of the ball joint  51  is limited by means of a pin  64  inserted through a corresponding bore extending through the partly spherical head  53 . The ends of the pin  64  are arranged in corresponding opposite grooves  65  formed longitudinally in the wall of the cylindrical bore  54  formed in the corresponding first or second longitudinal contact element  22 ,  23  so that the pin  64  extends generally in the longitudinal direction of the corresponding longitudinal contact element  22 ,  23 . In this way, the rotation of the ball joint  51  is limited to certain angles of rotation about the longitudinal axis of the shaft  56  and about an axis extending at right angles to the longitudinal axis of the shaft  56  and extending at right angles to the longitudinal direction of the corresponding longitudinal contact element  22 ,  23 . 
     As seen in  FIGS. 1 to 4, 11 and 13 to 20 , the clamping tool  1  is provided with a hoisting attachment  36  arranged so that, during hoisting, the first clamping element  3  is arranged at a generally upward side  5  of the rotor blade  2 , and the second clamping element  4  is arranged at a generally downward side  6  of the rotor blade  2 . Generally, according to the present invention, the four separate rotor blade contacting surfaces  14 ,  15  of the first and second clamping elements  3 ,  4  are adapted to be arranged successively in the lengthwise direction of the rotor blade. As seen, in the embodiment illustrated in  FIGS. 1 to 4 and 11 , the distance between the first and second pivot axes  10 ,  11  of the main balancing lever  17  of the second clamping element  4  is longer than the distance between the first and second pivot axes  10 ,  11  of the main balancing lever  16  of the first clamping element  3 . Preferably, the distance between the first and second pivot axes  10 ,  11  of the main balancing lever  17  of the second clamping element  4  is at least 1.5 times, more preferred at least 2 times, and most preferred about 2.5 times, the distance between the first and second pivot axes  10 ,  11  of the main balancing lever  16  of the first clamping element  3 . 
     As seen in  FIGS. 5 to 8 , the first rotor blade contacting surface  14  and the second rotor blade contacting surface  15  of each balancing lever  8 ,  9  has the form of respective longitudinal contact elements  22 ,  23  being aligned in their longitudinal direction and being arranged substantially end to end, but with enough clearance to allow mutual movement, thereby forming a total rotor blade contacting surface  24 ,  25  of the respective balancing lever  8 ,  9 . Each longitudinal contact element  22 ,  23  is provided with a contact surface formed by a suitable material, such as rubber or the like, for achieving a suitably high friction between the longitudinal contact element  22 ,  23  and the surface of the rotor blade. Alternatively, the contact surface may in fact by formed by one piece of flexible material extending over all contact elements  22 ,  23  belonging to the respective main balancing lever  16 ,  17 . Said contact surface may suitably be formed with ribs and/or grooves or the like therein in order to obtain better grip. 
     In the embodiment illustrated in  FIGS. 13 to 16 , the first clamping element  3  includes a main balancing lever  16  arranged pivotally about the main pivot axis  18  just as in the embodiment illustrated in  FIGS. 1 to 4 . However, in the embodiment illustrated in  FIGS. 13 to 16 , the second clamping element  4  includes a crossbar  66  arranged on the clamping mechanism  7  and having a first end  67  on which a corresponding first balancing lever  8  is arranged pivotally about a corresponding first pivot axis  10  and a second end  68  on which a corresponding second balancing lever  9  is arranged pivotally about a corresponding second pivot axis  11 . The first and second balancing levers  8 ,  9  arranged on the crossbar  66  are aligned in their longitudinal direction. Furthermore, the crossbar  66  is fixed against rotation in relation to the clamping mechanism  7  about any axis extending at least substantially in parallel with the main pivot axis  18  of the first clamping element  3 . Because the crossbar  66  is fixed against rotation in relation to the clamping mechanism  7  about any axis more or less parallel with the main pivot axis  18  of the first clamping element  3 , the wind turbine blade may be held in a fixed orientation in relation to the rotor blade clamping tool  1 . Thereby, the handling of the wind turbine blade by means of the clamping tool  1  may be facilitated. 
     The clamping tool  1  illustrated in  FIGS. 13 to 16  is provided with a hoisting attachment  36  arranged so that, during hoisting, the first clamping element  3  is adapted to be arranged at a generally upward side  5  of the rotor blade  2 , and the second clamping element  4  is adapted to be arranged at a generally downward side  6  of the rotor blade  2 . 
     Furthermore, as seen in  FIGS. 1, 2, 4 and 13 to 16 , on the first clamping element  3 , the total rotor blade contacting surface  24  of the first balancing lever  8  and the total rotor blade contacting surface  25  of the second balancing  9  lever are arranged substantially end to end, but with enough clearance to allow mutual movement, whereas, on the second clamping element  4 , the total rotor blade contacting surface  24  of the first balancing lever  8  and the total rotor blade contacting surface  25  of the second balancing lever  9  are spaced at a distance D indicated in  FIG. 4 . As further indicated, the total rotor blade contacting surface  24 ,  25  of the first or second balancing lever  8 ,  9  of the first clamping element  3  has a length L. In the illustrated embodiment, D is approximately 5/3×L. Furthermore, as seen, the combined length, on the first clamping element  3 , of the total rotor blade contacting surface  24  of the first balancing lever  8  and the total rotor blade contacting surface  25  of the second balancing lever  9  is slightly more than 2 L. According to the invention, it is preferred that D is greater than 65 percent of, more preferred greater than 70 percent of, and most preferred greater than 75 percent of said combined length of 2 L. 
     As seen in  FIGS. 5 to 7 , the main balancing lever  16  of the first clamping element  3  includes a first and a second lever wall  26 ,  27  arranged in spaced and parallel configuration and being fixed to each other by means of a top plate  28  and a bottom plate  29 , and the corresponding first and second balancing levers  8 ,  9  extend at least partly between the first and second lever wall  26 ,  27 . 
     As seen in  FIGS. 1 to 4 , the clamping mechanism  7  connecting the first clamping element  3  and the second clamping element  4  includes a rigid C-formed bracket  30  having a first leg  31  and a second leg  32 . A main bearing bracket  33  for the main balancing lever  16  of the first clamping element  3  is hinged to the first leg  31  of the C-formed bracket  30  and is pivotal in relation to the first leg  31  by means of a clamping actuator  35 . A main bearing  34  for the main balancing lever  17  of the second clamping element  4  is arranged directly on the second leg  32  of the C-formed bracket  30 . 
     In the embodiment illustrated in  FIGS. 13 to 16 , the clamping mechanism  7  connecting the first clamping element  3  and the second clamping element  4  includes a rigid C-formed bracket  30  having a first leg  31  and a second leg  32 . A main bearing bracket  33  for a main balancing lever  16  of the first clamping element  3  is hinged to the first leg  31  of the C-formed bracket  30  and is pivotal in relation to the first leg  31  by means of a clamping actuator  35 . The crossbar  66  of the second clamping element  4  is arranged on the second leg  32  of the C-formed bracket  30  by means of an exchangeable adapter piece  69  bolted to the crossbar  66  and arranged to maintain a certain angle between a longitudinal direction of the crossbar  66  and an intermediate part  70  of the rigid C-formed bracket  30  connecting the first and second legs  31 ,  32  of the rigid C-formed bracket  30 . The exchangeable adapter piece  69  is bolted to the crossbar  66  in that the exchangeable adapter piece  69  is provided with a number of bolt holes  82  on a flange  84  of the exchangeable adapter piece  69  corresponding to bolt holes  83  of the crossbar  66 . The flange  84  is further provided with a protrusion  85  matching a not shown corresponding recess of the crossbar  66 . 
     The exchangeable adapter piece  69  is connected to the second leg  32  of the C-formed bracket  30  by means of a hinge  71  having a hinge axis extending in the longitudinal direction of the crossbar  66  so that the second clamping element  4  is swingable between an insertion position for insertion of the rotor blade  2  between the first and second clamping elements  3 ,  4  as illustrated in  FIGS. 15, 16, 18 and 20  and a clamping position suitable for clamping the rotor blade  2  between the first and second clamping elements  3 ,  4  as illustrated in  FIGS. 13, 14, 17 and 19 . The hinge  71  is formed by insertion of a hinge pin  79  into hinge holes  80  of the second leg  32  of the C-formed bracket  30  and of the exchangeable adapter piece  69 , respectively. 
     The exchangeable adapter piece  69  is illustrated in further details in  FIGS. 21 to 23 . 
     In a not illustrated embodiment, the second clamping element  4  is swingable between the insertion position and the clamping position by means of a hydraulic actuator. 
     In the embodiment illustrated in  FIGS. 13 to 20 , the exchangeable adapter piece  69  is adapted to be locked in the clamping position by means of a locking arrangement  72  in the form of a locking pin  77  insertable into a locking hole  78  of the exchangeable adapter piece and a corresponding locking hole  81  of the second leg  32  of the C-formed bracket  30  and thereby connecting the exchangeable adapter piece  69  to the second leg  32  of the C-formed bracket  30 . 
     In the embodiment illustrated in  FIGS. 13 to 20 , the intermediate part  70  of the rigid C-formed bracket  30  is provided with a transverse bar  74  having opposed ends  75  each being provided with a supporting piece  76  adapted to support a leading edge or a trailing edge of a wind turbine blade held by the rotor blade clamping tool  1 . 
     By means of the exchangeable adapter piece  69  bolted to the crossbar  66 , an angle suitable for the specific wind turbine blade to be handled may be obtained between a longitudinal direction of the crossbar  66  and the intermediate part  70  of the rigid C-formed bracket  30 . Thereby, the rigid C-formed bracket  30  may for instance be handled with its intermediate part  70  extending in an at least substantially vertical direction as best illustrated in  FIGS. 14 and 16 . Thereby, handling of the wind turbine blade may be facilitated. In the embodiments illustrated in  FIGS. 1 to 11  and in  FIGS. 13 to 16 , the clamping tool  1  is provided with a hoisting attachment  36  in the form of a hoisting arm  37  having a first end  38  being connected to the clamping mechanism  7  by means of a pivot element  40  and a second end  39  adapted to connect to a cable of a hoisting crane or the like by means of an eyebolt  50 . The pivot element  40  allows pivotal movement of the hoisting arm  37  in relation to the clamping tool  1  about two different axes  41 ,  42  being at right angles to each other, and the hoisting arm  37  is pivotal about said axes by means of a respective first and second hoist actuator  43 ,  44 . Thereby, the angle of the clamping tool  1  and thereby the angle of the rotor blade  2  carried by the tool  1  may be varied during handling of the rotor blade so that, for instance, the blade may be positioned correctly in relation to the wind turbine hub when the blade  2  is to be mounted thereon. 
     The first leg  31  of the C-formed bracket  30  forms a fork element  45  having a first leg  46  and a second leg  47  carrying a hinge axis  48  therebetween on which the first clamping element  3  is hinged to the first leg  31  of the C-formed bracket  30 . The first end  38  of the hoisting arm  37  is connected to the first leg  46  of the fork element  45  by means of the pivot element  40 , the first hoist actuator  43  is arranged between the second leg  47  of the fork element  45  and the hoisting arm  37 , and the second hoist actuator  44  is arranged between a central part  49  of the fork element  30  and the hoisting arm  37 . 
     In an alternative embodiment of the clamping tool  1  illustrated in  FIGS. 1 to 11  and in  FIGS. 13 to 16 , the clamping tool  1  may be adapted to be used in a not shown rotor blade hoisting system for installation and/or deinstallation of a rotor blade on a hub of a wind turbine, wherein the rotor blade hoisting system includes an upper cable support system adapted to be mounted on a top end of the wind turbine, a lower cable support system adapted to be arranged at a lower end of the wind turbine at a distance from the wind turbine, and at least a left and a right cable both adapted to be extended, in spaced relationship, between the upper cable support system and the lower cable support system. In this alternative embodiment of the clamping tool  1  according to the invention, the clamping tool  1  may be adapted to be arranged with the central part of the C-formed bracket  30  above the rotor blade  2 , the first leg  31  of the C-formed bracket to the left, at a first pressure or suction side of the rotor blade, and the second leg  32  of the C-formed bracket to the right, at a second pressure or suction side of the rotor blade. The hoisting attachment  36  may therefore be replaced by means of a left climbing system arranged on the first leg  31  of the C-formed bracket and adapted to climb on the left cable and a right climbing system arranged on the second leg  32  of the C-formed bracket and adapted to climb on the right cable, each of the left and the right climbing systems including at least a first and a second roller adapted to roll on the respective cable and adapted to, when the clamping system is clamped onto the rotor blade, be spaced in a longitudinal direction of the rotor blade so that the first rollers are placed nearer a root end of the rotor blade than the second rollers, and wherein at least one of the first and second rollers of each of the left and the right climbing systems is a motor driven roller. In this alternative embodiment of the clamping tool  1 , it may be preferred that, on both the first and second clamping elements  3 ,  4 , the total rotor blade contacting surface  24  of the first balancing lever  8  and the total rotor blade contacting surface  25  of the second balancing lever  9  are spaced at a distance D indicated in  FIG. 4 . 
       FIG. 12  illustrates an alternative embodiment of the rotor blade clamping tool  1  according to the invention, carrying a rotor blade  2 . According to this embodiment, the clamping tool  1  is carried by means of a different hoisting attachment  36  in the form of a V-formed bracket  61  having an upper end adapted to connect to a cable of a hoisting crane or the like and having a lower end being tiltable in relation to an actuator box  63  arranged on the C-formed bracket  30  about an axis being substantially parallel to the longitudinal direction of the rotor blade  2  by means of tilting actuators  62 . The actuator box  63  is arranged rotatable by means of a not shown actuator on the C-formed bracket  30  about an axis being substantially at right angles to the longitudinal direction of the rotor blade  2  and being substantially horizontal in the illustration. 
     LIST OF REFERENCE NUMBERS 
     
         
         D distance between total rotor blade contacting surface of first and second balancing lever of second clamping element 
         L length of total rotor blade contacting surface of first or second balancing lever of first clamping element 
           1  rotor blade clamping tool 
           2  wind turbine rotor blade 
           3  first clamping element 
           4  second clamping element 
           5  first side of rotor blade 
           6  second side of rotor blade 
           7  clamping mechanism 
           8  first balancing lever 
           9  second balancing lever 
           10  first pivot axis 
           11  second pivot axis 
           12  first end of balancing lever 
           13  second end of balancing lever 
           14  first rotor blade contacting surface 
           15  second rotor blade contacting surface 
           16  first main balancing lever 
           17  second main balancing lever 
           18  first main pivot axis 
           19  second main pivot axis 
           20  first end of main balancing lever 
           21  second end of main balancing lever 
           22  first longitudinal contact element 
           23  second longitudinal contact element 
           24  first total rotor blade contacting surface 
           25  second total rotor blade contacting surface 
           26  first lever wall of first main balancing lever 
           27  second lever wall of first main balancing lever 
           28  top plate of first main balancing lever 
           29  bottom plate of first main balancing lever 
           30  C-formed bracket 
           31  first leg of C-formed bracket 
           32  second leg of C-formed bracket 
           33  main bearing bracket for first main balancing lever 
           34  main bearing for second main balancing lever 
           35  clamping actuator 
           36  hoisting attachment 
           37  hoisting arm 
           38  first end of hoisting arm 
           39  second end of hoisting arm 
           40  pivot element 
           41  first axis of pivot element 
           42  second axis of pivot element 
           43  first hoist actuator 
           44  second hoist actuator 
           45  fork element 
           46  first leg of fork element 
           47  second leg of fork element 
           48  hinge axis of fork element 
           49  central part of fork element 
           50  eyebolt 
           51  ball joint 
           52  connection element 
           53  partly spherical head 
           54  cylindrical bore on longitudinal contact element 
           55  conical bottom 
           56  shaft of connection element 
           57  cylindrical bore in balancing lever 
           58  threaded hole in connection element 
           59  key 
           60  rubber ring 
           61  V-formed bracket 
           62  tilting actuators 
           63  actuator box 
           64  pin 
           65  groove in wall of cylindrical bore 
           66  crossbar 
           67  first end of crossbar 
           68  second end of crossbar 
           69  exchangeable adapter piece 
           70  intermediate part of rigid C-formed bracket 
           71  hinge 
           72  locking arrangement 
           73  cross-sectional contour of a wind turbine blade 
           74  transverse bar 
           75  end of transverse bar 
           76  supporting piece 
           77  locking pin 
           78  locking hole of exchangeable adapter piece 
           79  hinge pin 
           80  hinge hole 
           81  locking hole of second leg 
           82  bolt holes of exchangeable adapter piece 
           83  bolt holes of crossbar 
           84  flange of exchangeable adapter piece 
           85  matching protrusion of exchangeable adapter piece