DEVICE FOR ADJUSTING THE PITCH OF THE BLADES OF A WIND TURBINE AND A METHOD FOR STOPPING THE ROTATION OF THE MAIN SHAFT

Abstract: The present invention relates to a device and a method for adjusting the pitch of wind turbine blades. Adjusting may be a controlling of the pitch in a situation during normal operation of the wind turbine or may be an alteration of the pitch in a fail-safe situation. Activatable driving means being a pitch motor is used for controlling the pitch. A so-called negative brake mechanism is used for altering the pitch in a fail-safe situation and thereby braking the rotation of the main shaft. The fail-safe braking takes place by means of introducing a difference in rotation of a synchronising shaft or a back-up brake wheel in relation to the main shaft. The difference in rotation of the synchronising shaft or the brake wheel is transferred to an angle gear or a worm gear that transfers the rotation to pivot joints onto which the blades are mounted and thereby altering the pitch of the blades.

Description: DEVICE FOR ADJUSTING THE PITCH OF THE BLADES OF A WIND TURBINE AND A METHOD FOR STOPPING THE ROTATION OF THE MAIN SHAFT The present invention relates in a broad aspect to a device and a method for adjusting the pitch of a wind turbine and for stopping the rotation of the blades of a wind turbine. In a limited aspect the invention relates to a device and a method for controlling the pitch angle of a wind turbine blade of a wind turbine having a main shaft rotatably connected to a base part of the wind turbine, at least one blade connected to a hub and the hub being 0 connected to the main shaft, the connection between the blade and the hub enabling rotation of the blade in relation to the hub about a longitudinal axis of the blade, and the connection between the hub and the main shaft also enabling rotation of the blades and the hub about a longitudinal axis of the main shaft, pitch angle altering means connected to the at least one blade for altering the pitch angle of said blade. 5 BACKGROUND FOR THE INVENTION AND INTRODUCTION TO THE INVENTION. In one aspect, the present invention relates to a method of adjusting the angular position of at least one blade of a wind turbine, the said wind turbine comprising a angle gear and 0 a motor for the rotation of a drive wheel of the angle gear and drive pinions of the angle gear for turning at least one blade at an angle, this at least one blade being turned at an angle by the drive pinions, the said drive pinions being rotated by the drive wheel, and the drive wheel being rotated by the motor relative to the main shaft. The invention also relates to a first embodiment of a mechanism for controlling the pitch of at least one blade 5 of a wind turbine relative to a wind direction parallel to a longitudinal main shaft of the wind turbine, the said mechanism comprising a motor for rotating drive wheels in the angle gear around a longitudinal blade shaft via drive wheels of the angle gear. The invention also relates to a second embodiment of a mechanism for controlling the pitch of at least one blade of a wind turbine relative to a wind direction parallel to a longitudinal 0 main shaft of the wind turbine, the said mechanism comprising a motor for rotating worm wheels in a worm gear around a longitudinal axis of the blade via drive wheels of the worm gear. Furthermore the invention relates to a wind turbine having such a mechanism. In another aspect, the present invention relates to a method of stopping the complete 5 rotation of the main shaft of a wind turbine comprising a motor to rotate a drive pinion of a angle gear via a drive wheel of the said angle gear, the said drive pinion being meant to turn at least one blade of the wind turbine around its longitudinal axis. The invention also relates to a mechanism for stopping the complete turning of a main shaft of a wind turbine comprising a motor to rotate a drive pinion in a angle gear via a drive wheel, the said angle gear being meant to pitch at least one blade around a longitudinal axis. Furthermore the invention relates to a wind turbine provided with such a mechanism. DE 42 21 783 describes a device for setting the pitch angle of wind turbine blades. The device comprises an electromotor mounted inside a fixed bearing. Surrounding the fixed bearing a longitudinal axis of rotation has been installed. On the rotational shaft blades have been installed which can be set at an angle relative to the main shaft and relative to a wind direction parallel to the longitudinal main shaft. The motor adjusts the pitch of the blades through a angle gear. The longitudinal main shaft rotating and the pitch of the blades being correct, the motor must rotate at the same speed of rotation as the main shaft to maintain the correct pitch of the blades. This is a major disadvantage. First, it requires very accurate control of the dynamic relations between motor and main shaft, i.e. the rotational speed of the motor in relation to the rotational speed of the main shaft. Second, the motor has to operate continuously to maintain the correct blade pitch. This results in extensive wear of the motor and entails large energy consumption for operating the motor. Furthermore it is necessary to control the speed of rotation variably and continuously relative to the variations in the speed of rotation of the main shaft, and the motor control risks being constantly somewhat behind compared with the main shaft, and consequently an optimal pitch angle of the blades cannot always be obtained. Furthermore, the device is not capable of stopping or limiting the rotation of the main shaft in a controlled manner in case the motor cannot rotate because of e.g. current failure of the motor shaft rotation. The main shaft will, however, stop rotating after a while, since the blades once the motor no longer rotates synchronously with the main shaft will soon be pitched at angular positions which are not optimal for the main shaft rotation. The blades will then reach a stable pitch characterised by the main shaft not rotating at the said pitch. Other prior art wind turbines achieve stopping the rotation of the main shaft by pitching the blades by means of individual motors at each blade. Pitching the blades in this way may have the same technical effect as the above-mentioned procedure and the main shaft stops so that the main shaft either effects no rotation at all or only rotates very slowly in its positive direction of rotation. The object of the present invention is to provide a mechanism which does not suffer from the above mentioned disadvantages, and which will thus to a larger extent be able to establish and maintain the correct pitch of the blades, whether the control is sufficiently precise or not, and without major wear to the gear motor and the pitch motor, or high energy consumption for operating the pitch motor. It is also an object to provide a mechanism which involves very few components and therefore is mechanically stabile and easy to maintain and service. The present object is in a first embodiment of the invention achieved by a method characterised by the rotation of a drive wheel relative to the main shaft being brought to a standstill once the blades have reached the altered pitch. The present object is in a second embodiment of the invention achieved by a method characterised by the rotation of a back-up brake wheel relative to the main shaft being brought to a standstill once the blades have reached the altered pitch. Bringing the rotation of the drive motor or the back-up brake wheel to a standstill relative to the main shaft while the said main shaft is rotating under normal operational conditions provides several advantages. Firstly, the wear of the pitch motor will be substantially reduced compared with a method continuing the rotation of the pitch motor rotation shaft also under normal operational conditions when correct pitch of the blades has been estab- lished. Furthermore, continuously monitoring the speed of rotation of the drive motor or the brake wheel relative to the speed of rotation of the main shaft is no longer necessary. Finally, the drive motor or brake wheel is used exclusively for controlling the pitch of the blades and is not used simultaneously for maintaining a speed of rotation of the drive wheel relative to the speed of rotation of the main shaft, a function which entails further technical control difficulties. A mechanism according to the first embodiment of the device acroding to the invention is characterised in at least a part of the synchronising shaft being aligned with and extends along or parallel with a central axis of the rotatably connected main shaft, so that upon activation of the driving means a difference in angular rotation between the synchronising shaft and the rotatably connected main shaft is introduced, as the pitch angle altering means is/are adapted to convert the angular rotation difference into a rotation of the at least one blade along its longitudinal axis, whereby the pitch angle of the at least one blade is/are altered by activating the driving means and wherein the activatable driving means is located at a front part of the main shaft, the pitch altering means being located at a front end of the main shaft and the synchronising shaft(s) extends from the rear to the front end of the main shaft, the synchronising shaft(s) extends through the interior of the main shaft. A mechanism according to the second embodiment of a device according of the invention is characterised by the back-up brake wheel being provided with a rotating portion of a brake, a fixed portion of the brake being mounted on a stationary part of the wind turbine, and the brake being directed to slowing down the rotation of the back-up brake wheel in relation to the main shaft synchronously with the rotation of the main shaft, and by the continued rotation of the main shaft turning the at least one blade in a situation when it is desirable that the pitch of the blades is altered to a pitch angle differing from an operationally optional pitch angle. Mounting a brake further provides the advantage that static relations between pitch motor, main shaft, angle gear or worm gear and blades are not to be maintained by the motor operating as a brake to maintain static relations, these relations between main shaft, angle gear or worm gear and blades being instead maintained by a brake to relieve the motor when a correct pitch of the blades has been established and the motor therefore is not operating. In a further aspect of the present invention, the purpose of the present invention is to bring the main shaft to a standstill in connection with a novel mechanism for regulating the pitch of the blades in normal operation. A preferred embodiment of the invention is characterised by the blades being permitted to turn in a positive and negative direction when the drive wheel synchronising shaft is stopped, allowing the main shaft to rotate alternately in a forward and a reverse direction of rotation. Bringing the rotation of the main shaft to a standstill is a novel feature, partly by the mechanism controlling the pitch of the blades being new, and partly by the main shaft coming automatically to a standstill in case of current failure of the motor controlling the blade pitch, the so-called pitch motor. Stopping takes place in such a way that the main shaft is not brought to a complete halt, but allowed to rotate around a point of equilibrium. This method of the invention allows the main shaft to rotate alternately and partly in a forward and partly in a reverse direction of rotation. This means that the main shaft bearings and the rotation collar bearings are in motion and therefore will not fail because of any unilateral static load nor because of any dynamic spot load when the main shaft and the rotation collars are completely stopped, nor will they be insufficiently greased by the slow turning of the main shaft in a positive direction of rotation only. A mechanism according to the second embodiment of the invention to be employed by the method is characterised by a back-up brake wheel being provided with a movable portion of a brake, a fixed portion of a brake being mounted to a stationary part of the wind turbine, and a drive wheel of the synchronising shaft being in engagement with the back-up brake wheel, and by the brake being meant to secure the drive wheel of the synchronising shaft relative to the back-up brake wheel in case it is desirable that the pitch of the blades should be placed in a position for stopping the complete rotations of the main shaft. By mounting a brake as defined the rotation of the main shaft can be slowed down in any case of pitch motor failure resulting from a current failure putting the pitch motor out of use. The negative brake will mainly be activated mechanically so that its function is independent of externally applied forces such as electrical current. BRIEF DESCRIPTION OF THE INVENTION The problems discussed above have been solved by means of the present invention which provides a device for controlling the pitch angle of a wind turbine blade of a wind turbine having a main shaft rotatably connected to a base part of the wind turbine, at least one blade connected to the main shaft, the connection enables rotation of the blade about a longitudinal axis of the blade, said pitch controlling device comprises an activatable driving means retained to the rotatably connected main shaft. The activatable driving means is the part of the device according to the invention being activated when the pitch of the wind turbine is to be altered. As indicated, the activatable driving means is only to be activated when the pitch is to be altered, due to the fact, as will become clear from the description below and the accompanying examples of embodiments of the invention, that when the driving means is retained in a motion following the motion of the main shaft, no activation is needed in order to keep the pitch of the blades. In the broad aspect of the invention the pitch controlling device further comprises pitch angle altering means connected to the at least one blade for altering the pitch angle of said blade, and a synchronising shaft connecting the driving means with the pitch angle altering means, at least a part of the synchronising shaft being aligned with and extends along or parallel with a central axis of the rotatably connected main shaft, so that upon activation of the driving means a difference in angular rotation between the synchronising shaft and the rotatably connected main shaft is introduced, as the pitch angle altering means is/are adapted to convert the angular rotation difference into a rotation of the at least one blade along its longitudinal axis, whereby the pitch angle of the at least one blade is/are altered by activating the driving means. In fact, the synchronising shaft or the back-up brake wheel rotates along with the main shaft as long a the pitch angle is not to be altered and therefore if a reference is chosen being the system rotating with the same angular rotation as the main shaft the observer following this reference system will observe the synchronising shaft or the back-up brake wheel standing still. A difference in angular rotation between the main shaft and the synchronising shaft or the back-up brake wheel should therefor in this connection be seen from point of reference fixed to the ground or the base of the wind turbine which is equivalent with the fact that an observer observing the motion of the synchronising shaft or the back-up brake wheel will observe the synchronising shaft or the back-up brake wheel rotating when the stated difference in angular rotation is present. According to a preferred second embodiment of the invention, the pitch altering means comprises a combined worm gear so that a first drive wheel and the second drive wheel are the one and same drive wheel and the first worm wheel of the synchronising shaft and the second worm wheel of the activatable driving means both is in engagement with the one and same drive wheel and the one and same drive wheel being rotatable by both the first worm wheel or the second worm wheel. Obviously, there is the risk of not being able to limit the rotation to the drive wheel and thus to the sprocket and the pivot ring, but a risk of the rotation of the axle of the pitch motor being transferred to a wholly or partly rotation of the synchronising shaft as well and vice versa. Accordingly, if the pitch is to be controlled by the activatable driving means, i.e. the pitch motor, then there is a risk of some or all of the rotation of the axle of the pitch motor will result in a rotation of the synchronising shaft in stead of a rotation of the blades along the longitudinal axis of the blades. This will cause the controlling of the pitch of the blades to take place more slowly than intended or needed or not taking place at all. Also, when a rotation of the synchronising shaft is established in a fail-safe situation, then there is the risk of some or all of the rotation of the synchronising shaft will result in a rotation of the axle of the pitch motor in stead of a rotation of the blades along the longitudinal axis of the blades. This will cause the fail-safe braking to take place to slowly or not taking place at all. In an embodiment of the present invention the pitch controlling device may further comprise preventing means for preventing the pitch altering means from converting the angular rotation difference into a rotation of one or more of the at least one blade when the torque needed to rotate the one or more blade(s) along its longitudinal axis exceed a predetermined torque. This - or these - preventing means is typically applied in order to assure that once a pitch setting of the blades has been provided then for instance the aerodynamic forces acting on the blades will not be able to alter the pitch. The preventing means may be applied by for instance disk brakes, pneumatic means or the like influencing directly or indirectly on the blades possible of being able to rotate along an axis extending substantially in the direction of the blades. However, according to the preferred second embodiment of the invention, the ratio between the worm wheel of the synchronising shaft and the drive wheel is less than 1 :5, preferably is less than 1 :15, preferably is 1:40, and preferably also the ratio between the worm wheel of the activatable driving means and the drive wheel is less than 1 :5, preferably is less than 1:15, preferably is 1:40. When establishing a certain ratio between the worm wheels and the drive wheel of the worm gear it is assured that a rotation of the axle of the pitch motor in order to control the pitch of the blades will not result in a wholly or partly rotation of the synchronising shaft because the torque needed for rotating the synchronising shaft by means of the axle of the pitch motor through the worm gear will be much higher than the torque needed for rotating the pivot ring and the blades. Similarly, it is assured that a rotation of the a synchronising shaft in order to alter the pitch of the blades in a fail-safe condition will not result in a wholly or partly rotation of the axle of the pitch motor because the torque needed for rotating the axle of the pitch motor by means of the synchronising shaft through the worm gear will be much higher than the torque needed for rotating the pivot ring and the blades through the worm gear. Furthermore, these preventing means may also serve a safety purpose. In this case the preventing means may prevent the blades from being turned when a difference in rotation is introduced between the main shaft and the synchronising shaft, and a preventing means may be applied to each blade. Such a utility may be very important for instance when risk of blocking the turning of the blades for instance by ice or other deposits is present. In a preferred embodiment of the invention the present invention when serving a safety purpose, the preventing means is constituted by a friction clutch. The activatable driving means may preferably be a motor, such as an electromotor, a hydraulic driven motor or a pneumatic driven motor and the pitch altering means is preferably comprised of an angle gear or a worm gear with a drive wheel being rotated by the synchronising shaft and drive pinions or a worm wheel for turning the at least one blade at an angle. In a preferred embodiment of the pitch controlling device according to the present invention, the activatable driving means is/are located at a hub, alternatively at a foremost part of the main shaft and the pitch altering means is being located also at the hub or at a foremost end of the main shaft of the wind turbine. In order to connect the controlling device and the altering means the synchronising shaft of which there may be more than one extends from the rear to the front end of the main shaft or from the back-up brake wheel to the altering means. Even though it may be advantageous to let the synchronising shaft(s) extend at the exterior of the wind turbines hub it is presently preferred that the synchronising shaft(s) extends through the interior of the hub so that the shaft is protected against external effects and influences. In an embodiment where more than one synchronising shaft is utilised each of these shafts may be connected to a blade so that each blade is pitched by one shaft only. Also in this embodiment the shafts may advantageously extend through the interior of the wind turbines hub. In another and presently most preferred embodiment of the present invention both the activatable driving means and the pitch altering means are located at a front part of the main shaft. Most preferably the activatable driving means and at least the synchronising shaft(s) are located in the hub of the wind turbine. A preferred brake applied in the above mentioned embodiment of the present invention is a brake wherein the part being able to rotate is a brake disc and the part of the brake being unable to rotate is a brake calliper having a brake shoe or alternatively wherein the part of the brake being able to rotate is a brake calliper having a brake shoe mounted on the synchronising shaft or on the back-up brake wheel and the part of the brake being unable to rotate is a brake ring mounted on the main shaft or on the a stationary part of the wind turbine, respectively. In another aspect it is desirable to be able to fix - or limit - the rotation of the main shaft when the wind turbine has been stopped. This is achieved as the synchronising shaft(s) or the hub may be provided with a part of a brake being able to rotate and a part of the brake being unable to rotate is mounted on a stationary part of the wind turbine such as on the chassis. Preferably different types of brakes are used in the embodiments of the present invention and in general when a fail safe brake is to be applied braking force is applied by means of springs, pneumatic oil pressure or similar mechanically applied static force and is released by means of electric, hydraulic, mechanic or any other kind of applied dynamic force and when a controlling brake is to be applied braking force is applied by means of electric, hydraulic, mechanical or any other kind of applied dynamic force. Power has to be supplied to the activatable driving means and in case this means is an electrical motor electrical current to that is preferably supplied by at least one slipring mounted concentrically with the main shaft and connected to a power supply. The same methodology may also be applied in case a pneumatic driven motor constitutes the activatable driving means and in this case the slipring will be designed to transfer fluids instead of electrical current. In another preferred embodiment of the pitch controlling device according to the present invention the electrical current to the activatable driving means is preferably supplied by a power source contained in the main shaft or the main shaft being a part of the a power source. This power source may be a battery being charged for instance by induction. The use of a battery is especially useful when only few - and perhaps small - alterations of the blades pitch is introduced since the activatable driving means only consumes power when activated and then there is time available for recharging the battery. In still a preferred embodiment of pitch controlling device according to the present invention the wind turbine comprises a multi-pole generator having a rotor constituting the main shaft of the wind turbine. In an embodiment of the invention where the wind turbine is being equipped with a multi- pole the generator is preferably being connected aligned with at the rear end of the wind turbine. In another aspect the present invention according to the first embodiment relates to a method for controlling the pitch angle of a wind turbine using the pitch controlling device according to present invention. In the method aspect the pitch angle is controlled by introducing, by activating the activatable driving means, a difference in angular rotation between the synchronising shaft(s) and the main shaft by activating the driving means transferring this difference in angular rotation to the pitch angle altering means, deactivating the driving means. Even though the step as described above may be viewed upon as succeeding steps this is normally not the case as these steps are executed in a mechanical device wherein no or at least very little delay is aimed at. The sequence of steps rather expressed the way the altering of the pitch is initiated and the way the "information" is passed on to the blades. Also, "transferring" may be viewed upon as the action of the angle gear or the worm gear, for instance, when being active i.e. the teeth of the gear move relative to each other on the effect of the difference in rotation between the synchronising shaft or the back-up brake wheel and the main shaft. Actually, the alteration of the pitch angle is determined by the operation of the activatable driving means as this means is the one effecting the difference in rotation between the synchronising shaft and the main shaft. The "predetermined amount" may suitable be expressed in terms of radians and the like and as the gearing for instance in the gear transferring is known - if such a gear is used as pitch altering means - the difference in rotation and rotation of the blades also is known which may be expressed as a transferring function giving a functional relationship between for instance the turning of the blade per revolution of the driving means (in case a motor is used), whereby it is an easy task to determine the number of revolutions the driving means has to perform in order to turn the blade a predetermined amount. After the pitch angle of the blades has been set the method according to the present invention may further comprise the step of retaining the angular position of the synchronising shaft or the back-up brake wheel relative to the angular position of the main shaft, in order to assure that no further turning of the blade will be accomplished. If this step is included in the method, the pitch altering process must be initiated by releasing or securing, respectively, the synchronising shaft or the back-up brake wheel relative to the main shaft otherwise a difference in angular rotation between the main shaft and the synchronising shaft(s) or between the back-up brake wheel and the main shaft may occur. During normal operation of the wind turbine, i.e. when the turbine is being operated in production mode, and in particular the during normal application of the method for controlling the pitch angle, the pitch angle is controlled so that the pitching of the blades is between +2° and -10°, primarily between +1° and - 5°. In yet another aspect the present invention relates to a method for stopping the rotation of the blades of a wind turbine. The method applies the method of controlling the pitch angle of wind turbine blade according to the present invention and the stopping is provided by retaining the synchronising shaft to a stationary part of the wind turbine. In order to for instance motioning the bearing in which the main shaft is sitting the main shaft is allowed to turn in either positive or negative direction when the synchronising shaft is being retained to a stationary part of the wind turbine. Typical and preferred values of the angle which the main shaft is allowed to turn in either positive or negative direction when the synchronising shaft is being retained to a stationary part of the wind turbine is given by pitching the blades between 0° to -20° primarily -10° to -15°, when the wind turbine is operating in a so-called negative stall mode. When the wind turbine is operating in a so-called positive pitch mode the angle the main shaft is allowed to turn in either positive or negative direction when the synchronising shaft is being stopped is given by pitching the blades around -1° to +90°, such as between 0° to 65° primarily 0° to 40°. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in greater detail in the following by reference to the enclosed drawing in which fig. 1 and fig. 2 shows a first embodiment and an alternative embodiment, respectively of the pitch controlling means according to the present invention in which the pitch control motor is situated in the front of the wind turbines main shaft and is controlling and altering the pitch of the lades by means of an angle gear, and fig. 3-6 shows a second embodiment of the pitch controlling means according to the present invention in which the pitch control motor is situated in the hub of the wind turbine and is controlling and altering the pitch of the blades by means of a worm gear. DETAILIED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 and Fig. 2 illustrate a part of a drive mechanism of a wind turbine, Fig. 1 showing a first embodiment where a main shaft 1 of the blades is integrated in the main shaft of transmission, and Fig. 2 showing an alternative first embodiment however being almost the same as the one showed in fig. 1 as described below. Each of the two embodiments technically operates in the same way in relation to the invention. The drive mechanism comprises a longitudinal main shaft 1 of a rotor. The rotor has a hub 2 which is secured to the front end 3 of the main shaft and which faces a wind direction W. On the hub blades 4 are mounted which in the embodiment of the drive mechanism 5 shown extend perpendicularly to an axis of rotation A of the longitudinal main shaft 1. The main shaft 1 is supported by bearings 5 that in Fig. 1 and fig. 2 are shown mounted in a chassis 7. In an alternative embodiment of the present invention (not shown) the generator is a multi-pole generator and blades 4 of the wind turbine are connected to the rotor of that generator. Thereby the main shaft 1 is either not present or is constituted by 10 the shaft of the generator. In both cases the transmission connecting the generator to the mains shaft is not present. The blades 4 are mounted rotatably on the hub so as to be able to rotate around an axis B perpendicular on the longitudinal main shaft 1. In alternative embodiments the blades 4 15 and the axis B may extend at an angle differing from a right angle relative to the axis of rotation A, e.g. in turbines where the blades have been submitted to so-called "coning" relative to the main shaft to create a greater distance between the blades and the turbine tower, and where the blades form an obtuse angle with the axis of rotation A. 20 A synchronising shaft 12 having a gear wheel 13 extends through the interior of the main shaft 1 from a rear end 9 of the main shaft 1 to the front end 3 of the main shaft 1. The synchronising shaft 12 is provided at the front with a conical gear wheel 14 forming a drive wheel in an angular gear 15. Other conical gear wheels 16 forming drive pinions of the angular gear engage with the drive wheel 14. The drive pinions 16 of the embodiment of 25 the hub as shown connected through shafts 17 to cylindrical gear wheel 18 forming a drive wheel and engaging with a pivot joint 19 forming part of the blades 4. The motor 11 is mounted onto the front end 3 of the main shaft 1 , and the synchronising shaft 12 may extend from the front end 3 and further forwards into the hub. A drive shaft 30 20 of a motor 11 has been mounted onto the synchronising shaft, this being an electromotor in the embodiment shown. The motor is a pitch motor for controlling a so- called pitch angle of the blades 4 relative to the wind direction W. Via the drive wheel 14, the drive pinions 16, the drive wheels 18 and the pivot joint 19 and by means of the motor 11 the synchronising shaft 12 can rotate the blades 4 around the axis B. 35 The shafts 17 are according to the preferred embodiment shown in Fig 1 indicated as being rigid parts, however provided with friction clutches 30 In order for these shafts 17 to be able to adapt to for instance inaccuracies provided during manufacturing, environmentally governed changes of the geometry of the shafts 17 and/or the changes in geometry of other parts of the wind turbine, the shafts 17 are preferably provided means for adapting to such changes. Examples of such means could be to design the shafts as splines (a shaft being comprises of two parts longitudinal s deable engaged with each other) provide the shafts 17 with cardan joint or combinations thereof As mentioned, in fig 1 and fig 2 the shafts 17 of the pitch controlling means according to the present invention further comprises a friction clutch 30 mounted on at least one of the shafts 17, in the embodiment shown on both of the shafts 17 shown The purpose of these friction clutches 30 is to assure a possibility to rotate at least one of the blades in case of one of the blades being prevented from being rotated along its longitudinal axis, i e that if a blade unintentionally is locked in its pitch angle position then it will still be possible to rotate the remaining un-locked blades This is achieved by the friction clutch 30 being able to transmit a certain amount of torque applied to the shaft 17 through the angular gear 15 When the torque applied to the friction clutch 30 exceed that maximum torque which the clutch 30 is able to transmit, an inner part 17A of the shaft 17 will still be able to rotate whereas the outer part 17B of the shaft 17 will not rotate Alternatively, the inner part 17A of the s aft 17 may be left out in case where friction clutch 30 is directly connected to the gear 15 In a preferred embodiment the friction clutch 30 is constituted by two discs forced against each other along abutment surfaces of the discs for instance by use of springs Typically, layers enhancing friction coat the abutment surfaces In another preferred embodiment the friction clutch 30 is a clutch type wherein spring loaded ratchet co-operating with a toothed nm in such a way that the spring will force a ratchet into a groove defined by teeth in the nm until the force acting on ratchet from the tooth and resulting from the torque applied exceed the force of the spring The use of the above-described clutches 30 may be applied in the cases where a controllable recovery of the mutual angular position of the two parts 17A and 17B of the shafts 17 is desirable This situation could occur in cases where the reason for the blades being prevented from rotation along its longitudinal axis is for instance ice blocking the gear constituted by the gear wheel 18 and the pivot joint 19. Such a recovery system my be comprised of means measuring the angular position of the two parts 17A and 17B of the shaft 17 and retaining means for retaining the outer part 17B of the shaft 17 in a fixed position. As the outer part 17B is retained in a fixed position then a rotation of the inner part 17A of the shaft will change the mutual angular position of the two parts 17A and 17B of the shaft 17. By rotating the inner part 17A, retaining the outer part 17B and measuring the angular position of the two parts 17A and 17B then the predetermined mutual angular of the two parts 17A and 17B will be recovered. Alternative to a friction clutch, a clutch could be a connection means having a part which is destroyed such as a small pin breaking if the force applied to this part exceeds a maximum force, whereby a connection between the gear 15 and the gear wheels 18 is no longer present. As the torque needed to rotate a blade around its longitudinal axis B is generally well defined or at least can be estimated the dimensioning of the friction clutches and the alternative clutches can be chosen based on this torque. In the embodiment shown a single common pitch motor 11 is provided which via a common synchronisation shaft 12 and the angular gear 15 controls the pitch angle of all blades 4 simultaneously. Alternatively it is possible to provide each blade 4 with its own drive shaft instead of a common synchronising shaft 12, its own drive wheel 14 and its own pitch motor 11. It is also possible to submit only a few of the blades 4 to a pitch control by a common pitch motor 11 , common synchronisation shaft 12 and angular gear 15, and to have the other blades 4 be controlled individually. The individual pitch motors may either be placed according to prior art in the hub 2 or may be placed at the rear end 9 of the main shaft 1 having drive shafts extending through the interior of the main shaft 1. The pitch motor 11 of the embodiment shown is an electromotor, but alternatively it may be a hydraulic motor or a pneumatic motor. Current for the pitch motor may be supplied via a number of sliprings (not shown) so as to provide electrical energy to the pitch motor 11 indirectly from an external source of electrical energy through the slip rings. The pitch motor may also be powered by a battery (not shown) incorporated in the main shaft so as to supply electrical energy from the generator or the battery directly to the pitch motor. The battery may then indirectly be charged by an external source of energy. Alternatively a generator may be incorporated as a part of the main shaft in such a way that the generator by rotation of the main shaft can supply electrical energy directly for charging the battery. Furthermore, the motor and/or the battery may be powered by induction. Even though it is possible to keep track of the present pitch setting of the blades through recording all changes made to the pitch angle, it may be advantageous to be able to detect the actual pitch setting. This detection of the pitch setting is suitable performed by a detecting means positioned at the hub providing a signal corresponding to the pitch of the blades. The pitch may be detected for one blade thereby representing the pitch setting of all the blades of the wind turbine or the pitch may be detected for each individual blade whereby it will be possible to detect if one or more blade is not synchronised with the remaining blades. In both case signals originating from the (these) detecting means have to be transferred to a controlling mean being typically a computer controlling the overall performance of the wind turbine. This computer is usually situated retained to the stationary part of the wind turbine, if the computer is not situated far away from the wind turbine in a controlling centre controlling more than one wind turbine, and therefor the signals are transferred from the rotating parts to the stationary parts via telemetry, via slip rings or the like. A movable section of a brake mechanism in the form of a brake disks 22 is mounted on the synchronising shaft 12. Around the brake disk 22 fixed sections of brake mechanisms are mounted in the form of a number of brake calliper 23, 24. The brake calliper 24 is fixed relative to the chassis 7 and will therefore not rotate with the main shaft 1 , the main shaft 1 being rotatably seated relative to the chassis 7. The brake calliper 24 provides a brake mechanism termed the negative brake. Alternatively to mounting the brake disks 22a and 22b on the synchronising shaft 12 and the brake shoes 23,24 on the main shaft 1 respectively the gearbox 6, it will be possible to mount one or both brake shoes 23, 24 on the synchronising axle 12 and to mount brake rings (not shown) corresponding to the brake disks 22a and 22b on the main shaft 1 respectively the gearbox 6. In this way the brake shoes 23, 24 will provide the movable part of the brake and the brake rings will provide the fixed part of the brake. The negative brake 22, 24 is meant to maintain the synchronising shaft 12 relative to the chassis 7 so that the blades 4 will automatically tilt relative to the hub 2 when the main shaft 1 rotates relative to the chassis 7, as the synchronising shaft 12 is secured relative to the chassis 7. This will be the case if on account of an operational breakdown such as an interruption of the control current to pitch motor 11 it becomes desirable to stop the rotation of the main shaft 1 to avoid that the operation of the wind turbine falls below the optimal level. In case of failure it may be desirable to stop the rotation of the main shaft to avoid an overload on the mechanical parts such as the main shaft 1 , the angle gear 15 or the gear motor. However, generally in the case described it will be desirable to stop the rotation of the main shaft to prevent the speed of rotation rising above a predetermined level. The negative brake 22, 24 in this case provides a so-called fail-safe brake by the blades 4 being tilted around the longitudinal axis B of the blades 4 when the main shaft 1 is rotating. The effect of the negative brake 22, 24 is provided by springs 25 or other means not requiring any external dynamically applied electric or hydraulic energy for exerting a force. When the negative brake 22, 24 is not in operation as a fail-safe brake the springs 25 are secured in a prestressed state by means of a hydraulic or electric power source (now shown) requiring control current to operate. As soon as the control current drops, the hydraulic or electric power source stops operating, the load on the springs 25 stops, and the spring force is triggered, having the effect of a relative rotation of the blades and an alteration of the pitch of the blade by means of the negative brake 22, 24. If the blades 4 rotate relative to the hub 2, they will at some point in time be placed in an angular pitch position that entails that the wind W will no longer be able to drive the blades 4 sufficiently to move the main shaft 1. The main shaft 1 will then stop its rotation. Prior to that time the blades 4 will generally have rotated so much relative to the hub 2 that the blades are placed in an angular position which will make the main shaft 1 rotate in reverse direction of rotation. Before the main shaft 1 stops its rotation, the main shaft will therefore have rotated partly around equilibrium alternately in a forward direction and a reverse direction of rotation. When the main shaft 1 has found its position of equilibrium the main shaft 1 may then be brought to a complete standstill by means of a transmission brake (not shown) which in this case acts as a parking brake for the main shaft 1. The transmission brake (not shown) is normally a disk brake secured to a shaft in a gearbox (not shown) and having a brake calliper (not shown) which is secured to the gearbox, thus slowing down the main shaft 1 relative to the gearbox. In certain cases it may be advantageous to let the main shaft 1 continue its partial rotation alternately in forward and reverse directions of rotation since the bearings 5 of the main shaft 1 will be kept in motion when the wind turbine has been slowed down by a fail-safe brake, i.e. stopped at an operational breakdown as a result of a failure of control current to the pitch motor 11. In that case the blades 4 will be pitched at a different pitch angle than the optimal pitch angle until there is no more rotational energy in the forward direction of rotation to rotate the main shaft 1. The extent of the different pitch angle at which there is no more rotational energy depends on the actual design of the blades 4 and on the actual mounting of the blades 4 on the hub 2. In the following concrete values for pitch angles will be stated in different operational cases, but the method and the mechanism of the invention can be used to control the rotation and slowing down of the main shaft both in turbines using positive pitch control and in turbines using negative pitch control. By positive pitch control is meant control by turning the leading edge of the blade against the wind and by negative pitch control is meant control by turning the trailing edge of the blade against the wind. For a given configuration of the blades 4 and for a given mounting of the blades on the hub 2 the second pitch angle may be e.g. between -5° and -25°. Should the blades 4 start a reverse rotation, the blades 4 will find a different pitch angle until there is no more rotational energy in the reverse direction of rotation to rotate the main shaft 1. The blades 4 will find a pitch angle of equilibrium which is different from the optimal pitch angle, depending on the actual configuration of the blades 4 and the actual mounting of the blades 4 on the hub 2, e.g. a pitch angle of -5° to -25°, where the main shaft 1 will rotate partly and alternately in a forward direction and a reverse direction of rotation at a very low speed of rotation. In that case the main shaft will not be slowed down by any transmission brake. When the main shaft 1 has been brought to a standstill and in the case mentioned above when the main shaft is then slowed down by a transmission brake (not shown), the blades 4 will be pitch controlled to a given pitch angle depending on the actual design of the blades 4 and on the actual mounting of the blades 4 on the hub 2, in order to reduce the axial load on the hub 2, the main shaft 1 and the bearings 5. For a given design of the blades 4 and a given mounting of the blades 4 on the hub 2 the pitch angle may be e.g. - 100°. When the pitch motor 11 once the main shaft 1 has been slowed down by the transmission brake has pitch controlled the blades to e.g. -100°, a positive brake (see later) will be used to maintain the angular pitch of the blades. For the sake of security an end stop may be provided at about -120°. In normal operation the blades 4 will be pitch controlled so as to achieve maximum production of electric energy. To prevent the blades 4 from being erroneously pitch controlled in the positive direction, the blades 4 of may be provided with an end stop in the positive direction at a pitch angle of e.g. +2°, but the extent of the pitch angle depends on the actual design of the blades 4 and on the actual mounting of the blades 4 on the hub 2. By normal slowing down in connection with other failures than control current failure the blades 4 will be pitch controlled by the pitch motor at an angular position which depends on the actual design of the blades 4 and on the actual mounting of the blades 4 on the hub 2. For a given design of the blades 4 and a given mounting of the blades 4 on the hub 2, the pitch angle may be -10°. Then the negative brake 22a, 24 will automatically slow down the synchronising shaft 12 so that the main shaft 1 finds its equilibrium where the rotation of the main shaft 1 ceases. The main shaft 1 may then rotate partially and alternately in a forward or a reverse direction of rotation at reduced speed of rotation. The negative brake 22a, 23 in this case does not act as a real fail-safe brake, but as a parking brake for the synchronising shaft 12, but the main shaft 1 will, as mentioned, be able to rotate alternately in a forward direction and a reverse direction of rotation. Alternatively a transmission brake can be used to slow down the main shaft 1 simultaneously with the synchronising shaft 12 being slowed down by the negative brake 22, 24 or by a positive brake. By normal slowing down in connection with high wind speeds the blades 4 will be pitch controlled by the pitch motor 11 to a natural so-called parking position of the blades of e.g. -15°, but depending on the actual design of the blades 4 and on the actual mounting of the blades 4 on the hub 2, a trailing edge (not shown) of the blades 4 being turned against the wind (active stall), and the rotation of the main shaft 1 stopping very rapidly. Then a transmission brake can slow down the main shaft 1 and the blades 4 will be pitch controlled at a forced socalled feathering position of the blades of e.g. -90° to reduce the axial loads on the hub 2, the main shaft 1 , and the bearings 5. When the angular position of e.g. -90° has been established, the negative brake 22, 24 will slow down the synchronising shaft 12 to maintain the pitch angle of -90°. The negative brake 22, 24 is preferably maintained in an activated state by mechanical means 25 such as coil springs or dish springs, the negative brake 22, 24 having to operate without the use of hydraulic, electric or pneumatic energy if the fail-safe brake action is to be established as a result of control current failure to the wind turbine. The negative brake 22, 24 thus provide, as mentioned, a so-called fail-safe brake. The negative brake may be maintained in a non-activated state by hydraulic, electric or pneumatic means. The stopping (or slowing down) of the main shaft 1 was described above with respect to negative pitch control but as mentioned earlier the method may just as well be used when the turbine is working in a positive pitch control mode. In general the method as described above basically the same in case the turbine is working in a positive pitch control mode and therefore the description of the negative pitch control mode is also applicable in the positive pitch control mode now considering the pitching of the blades 4 to proceed in the opposite direction. In this case the blades 4 will find a pitch angle of equilibrium which is different from the optimal pitch angle, depending on the actual configuration of the blades 4 and the actual mounting of the blades 4 on the hub 2, e.g. a pitch angle of -1 ° to + 90°, where the main shaft 1 will rotate partly and alternatively in a forward direction and reverse direction at a very slow speed of rotation. In that case the main shaft 1 will not be slowed down by any transmission brake. The blades 4 of the wind turbine have typically cross sections made up by airfoil profiles being asymmetrically so as to design the turbine to produce as much effect as possible with lowest possible loss. The alternatively rotation of the main shaft 1 occurring in general may be replaced by a more steady state in which the blades 4 stays in a substantial fixed position relative to the wind turbine. When asymmetric profiles are used the initiation of positive pitch control will turn the blades which in turn slow down of the rotation of the main shaft 1 until the substantial steady state is reached. When the turbine is working in the positive pitch control mode, the end stop provided must be provided accordingly to the maximum and/or minimum allowable pitch angle the blade must be able to adjusted to. In another embodiment, as indicated in Fig. 1 , of the present invention the pitch motor 11 together with the transmission comprised of the drive shaft 20 of the pitch motor is situated in the hub. The transmission may preferably be mounted to the main shaft but the drive shaft 20 may also advantageously, as shown, be directly connected to the synchronising shaft 12 eventually through a transmission 45 (referring to Fig. 1 and 2). In general a transmission between the shaft of pitch motor 11 and the synchronising shaft 12 is preferred as the torque of torsion the motor has to overcome may become very large - in large turbine (2-3Mw) the torque may become so large that the gear need is as high as 1 to 300. Suitable choice of transmissions are planet transmissions, cylinder transmissions, cyclo reducers or the like. In the transmission used for transferring a difference in rotational speed between the main shaft 1 and the synchronising shaft 12, the drive wheel 14 is penetrated by the synchronising shaft 12 as it has to proceed through the centre of the main shaft 1 and to the end 3 of the main shaft 1 and into the hub. In an actual design of the drive wheel it does not necessarily has to be penetrated, as this wheel may be an integral part of the synchronising shaft 12. In this embodiment of the present invention the negative brake 22, 24 is situated at the rear of the main shaft 1 and a positive brake may preferably be an integral part of the pitch motor 11 either as a separate brake (not shown) or as the motor acting as a brake. A positive brake is meant to maintain the synchronising shaft 12 relative to the main shaft 1 so as to prevent the blades from pitching around the axis B. A positive brake will be activated by hydraulic, electric or pneumatic means once the pitch motor 11 has rotated the synchronising shaft 12 and thereby through the angle gear 15 tilted the blades 4 to a desired pitch of the blades 4. To avoid unnecessary load on the pitch motor 11 the pitch motor will not be used to maintain a desired blade pitch, but a positive brake will be activated to maintain the established pitch of the blades 4. Transferring of power and control signal to and from the pitch motor is provided by the slip rings indicated in Fig. 1 and by the reference numeral 35 referring to a slip ring situated in the rear of the main shaft 1 and 40 referring to a slip ring situated in the front of the main shaft. As described above the control signal may also be transferred by telemetric so as to render superfluous the slip rings used for that purpose. Figs. 3-6 are perspective views of a second embodiment of a mechanism for a device according to the invention. The mechanism also comprises the main shaft 1 of which a foremost part 3 is partly shown and a hub 2 mounted to the foremost part 3 of the main shaft 1. The hub 2 is provided with pivot joints 19, that constitute part of the blades (not shown) by mounting each of the blades to one of the pivot joints. Each of the pivot joints 19 is mounted in a bearing 31. The inner circumference of the pivot joint 19 is provided with a cogging 32. Along a circumference of the foremost part 3 of the main shaft 1 a back-up brake wheel 33 is mounted. The brake wheel 33 is mounted by means of a bearing 34 that is secured to the hub 2 or to the foremost part 3 of the main shaft 1. The bearing 34 is preferably a roller ball bearing but other types of bearings may be used. Onto the brake wheel a rotatable part of a brake 36, in the embodiment shown a brake disc, is mounted. A fixed part 37 of the brake, in the embodiment shown a brake calliper with a brake shoe (not shown), is mounted to a stationary part (not shown) of the wind turbine in relation to the main shaft 1 and the hub 2 such as onto a chassis of the nacelle. The brake 36,37 is a negative brake functioning as a fail-safe brake, i.e. the brake will establish alteration of the pitch angle of the blades in case the dynamically applicable force to the pitch motor 11 is disconnected. The back-up brake wheel 33 is provided with a cogging 38 on the outside periphery of the wheel. A synchronising shaft 39 extend inside the hub 2 from the part of the hub 2 being mounted to the foremost part 3 of the main shaft 1 and further forwards into the hub 2 to a worm gear 41 which is mounted in the hub 2. A proximal end 42 of the synchronising shaft 39 is provided with a sprocket 43 with a cogging 44 which is in engagement with the cogging 38 of the back-up brake wheel 33. Accordingly, if the back-up brake wheel 33 is rotating in relation to the hub 2 and thereby also in relation to the main shaft 1 , then the synchronising shaft 39 will be rotated by the brake wheel 33. A distal end 46 of the synchronising shaft 39 extend into the worm gear 41 and the distal end 46 of the synchronising shaft 39 is provided with a worm wheel (not shown) being a driving wheel of the worm gear. In the embodiment shown the gear 41 is a worm gear. As mentioned, the distal end 46 of the synchronising shaft 39 is provided with a worm wheel (not shown) driving a drive wheel (not shown) of the worm gear. The drive wheel has an axle (not shown) extending out of the worm gear and towards the pivot joint 19 onto which the blade (not shown) is mounted. The axle is provided with a sprocket 47 having a cogging 48 being in engagement with the cogging 32 on the inner circumference of the pivot joint 19. A rotation of the synchronising shaft 39 will result in a rotation of the worm wheel at the distal end 46 of the synchronising shaft. Accordingly, the rotation of the worm wheel of the synchronising shaft will result in a rotation of the drive wheel in the worm gear, of the sprocket 47 on the axle of the drive wheel, and of the pivot joint 19 and the blades, thereby altering the pitch of the blades. However, the drive wheel of the worm gear may also be driven by another worm wheel (not shown) being a driving wheel of the worm gear, namely a worm wheel of a pitch motor 11 and provided on an outgoing axle 49 of the pitch motor. The worm wheel that is provided on the axle 49 of the pitch motor 11 is also capable of driving the drive wheel of the worm gear. Accordingly, an activation of the pitch motor being the activatable driving means will result in a rotation of the worm wheel on the axle of the pitch motor. Accordingly, the rotation of the worm wheel on the axle of the pitch motor wil result in a rotation of the drive wheel, of the sprocket 47 on the axle of the drive wheel, and of the pivot ring and the blades, thereby controlling the pitch of the blades. Thus, the drive wheel constitutes a common drive wheel of the worm wheels of the synchronising shaft and the axle of the pitch motor. The ratio between the worm wheel of the synchronising shaft and the drive wheel, respectively, and the ratio between the worm wheel of the pitch motor and the drive wheel, respectively, is at least below 1 :5, preferably less than 1 :15, most preferably as low as 1 :40. This ensures a proper "locking effect" between the worm wheels and the drive wheel of the worm gear. The locking effect ensures that a rotation of the axle of the pitch motor only results in a rotation of the pivot joint and thus the blades in order to control the pitch of the blades in a normal operational condition. It also ensures that a rotation of the synchronising shaft only results in a rotation of the pivot joint and thus the blades in order to alter the pitch of the blades in a fail-safe condition. By choosing among different suitable materials that the worm wheels and/or the drive wheel are made of, then a further locking effect between the wheels may be established. During normal operation of the wind turbine the pitching of the blades will take place by means of the pitch motor. The pitch motor is preferably an electric motor and when providing electric current to the motor the rotation of the worm wheel on the axle of the pitch motor will result in a rotation of the blades along the longitudinal axis of the blade in order to control the pitch angle of the blade to an optimal operational pitch. During fail-safe operation where it is not possible to use the pitch motor for altering the pitch of the blades, perhaps because of the electric current being disconnected, then the back-up brake wheel will result in an alteration of the pitch of the blade. Altering of the pitch of the blades is established in order to slow down or stop the rotation of the main shaft. When a fail-safe condition occurs, the brake calliper with the brake shoes and the corresponding brake disc will start braking the back-up brake wheel. A braking of the brake wheel will result in the brake wheel exhibiting a rotation in relation to the main shaft and in relation to the hub. Thus, a difference in the rotational speed of the brake wheel and the main shaft and hub will occur. This rotation of the brake wheel in relation to the main shaft and the hub will result in rotation of the sprocket on the proximal end of the synchronising shaft. Thus, the rotation will result in rotation of the synchronising shaft itself and of the worm wheel at the distal end of the synchronising shaft. This results in a rotation of the drive wheel of the worm gear and of the pivot joint and the blades along the longitudinal axis of the blades. The rotation of the blades results in an alteration of the pitch in order to pitch the blades into a pitch different than the pitch during normal operation. In the embodiment shown the back-up brake wheel is one complete wheel extending around the entire circumference of the main shaft. However the brake wheel may also be divided into segments of a wheel one segment for each of the blades that must have the ability of the pitch being altered during fail-safe braking. This further implies the need of a separate brake mechanism for each of the brake wheels. The second embodiment shown in figures 3-6 may be provided with alternative features or additional features like the ones mentioned for the first embodiment and the alternative first embodiments shown in figures 1-2 such as the synchronising shaft being provided with as splines (a shaft being comprises of two parts longitudinal slideable engaged with each other). Also the synchronising shaft(s) 39 may be provided with clutches like the ones that the shafts (see fig. 1-2) may be provided with. The invention is described above referring to specific embodiments of a wind turbine. The wind turbine of the embodiment shown has its main shaft parallel to the direction of the wind and its blades extending perpendicularly to the main shaft. The wind turbine is basically an up-wind turbine, but may also be a down-wind turbine. Alternatively to using a gear in connection with the main shaft it will be possible to use a multipole generator using no gear. Furthermore other transmission solutions than those shown may be applied. It will be possible to use particularly the negative brake in other types of wind turbines. The positive brake and the negative brake of the embodiment shown are illustrated as disk brakes with a common brake disk. A brake disk may be used for each of the two brakes, and also other types of brakes than disk brakes may be used for both the positive brake and the negative brake. The equilibrium of the main shaft may be found at other pitch angles than those mentioned. That depends entirely on the type of wind turbine, the form and dimensions of the blade and on the mechanical inertia of the wind turbine in question. Furthermore the actual values of pitch angles indicated in the description are not limitative but only mentioned as examples of given pitch angles. As discussed in the description, the actual values of the pitch angles at which optimal operational conditions can be achieved depend partly on the design of the blades and partly on the way in which they are mounted on the hub.

Claims: CLAIMS 1. A device for controlling the pitch angle of at least one wind turbine blade having a main shaft rotatably connected to a base part of the wind turbine, at least one blade connected to a hub and the hub being connected to the main shaft, the connection between the blade and the hub enabling rotation of the blade in relation to the hub about a longitudinal axis of the blade, and the connection between the hub and the main shaft also enabling rotation of the blades and the hub about a longitudinal axis of the main shaft, pitch angle altering means connected to the at least one blade for altering the pitch angle of said blade, a pitch angle altering means connected to the at least one blade for altering the pitch angle of said blade, and a synchronising shaft connecting the driving means with the pitch angle altering means, at least a part of the synchronising shaft being aligned with and extends along or parallel with a central axis of the rotatably connected main shaft, so that upon activation of the driving means a difference in angular rotation between the synchronising shaft and the rotatably connected main shaft is introduced, as the pitch angle altering means is/are adapted to convert the angular rotation difference into a rotation of the at least one blade along its longitudinal axis, whereby the pitch angle of the at least one blade is/are altered by activating the driving means and wherein the activatable driving means is located at a front part of the main shaft, the pitch altering means being located at a front end of the main shaft and the synchronising shaft(s) extends from the rear to the front end of the main shaft, the synchronising shaft(s) extends through the interior of the main shaft. 2. A pitch controlling device according to claim 2, wherein the pitch altering means comprises preventing means for preventing the pitch altering means from converting the angular rotation difference into a rotation of one or more of the at least one blade when the torque needed to rotate the one or more blade(s) along its longitudinal axis exceed a predetermined torque. 3. A pitch controlling device according to claims 2-4, wherein the pitch altering means comprise(s) an angle gear with a drive wheel being rotated by the synchronising shaft and drive pinions for turning the at least one blade at an angle. 4. A pitch controlling device according to any of the claims 2-7, wherein the synchronising shaft(s) is/are provided with a part of a brake being able to rotate and a part of the brake being unable to rotate is mounted on the main shaft. 5. A pitch controlling device according to any of the claims 2-8, wherein the synchronising shaft(s) is/are provided with a part of a brake being able to rotate and a part of the brake being unable to rotate is mounted on a stationary part of the wind turbine such as on the chassis. 6. A device for controlling the pitch angle of at least one wind turbine blade having a main shaft rotatably connected to a base part of the wind turbine, at least one blade connected to a hub and the hub being connected to the main shaft, the connection between the blade and the hub enabling rotation of the blade in relation to the hub about a longitudinal axis of the blade, and the connection between the hub and the main shaft also enabling rotation of the blades and the hub about a longitudinal axis of the main shaft, pitch angle altering means connected to the at least one blade for altering the pitch angle of said blade, said pitch controlling device being positioned at the foremost part of the main shaft and comprising a back-up braking mechanism constituted by a wheel part being positioned circumferentially along the periphery of the main shaft and being rotatable in relation to the main shaft and the hub and said back-up brake wheel part being provided with braking means and said pitch controlling device also comprising a synchronising shaft connecting the back-up brake wheel part with the pitch angle altering means, said pitch angle altering means being secured to an inner wall of the hub onto which the blades are mounted being capable rotating with the hub and being in engagement with the pivot joint synchronising that upon a braking of the back-up brake wheel a rotation of the synchronising shaft is introduced, the pitch angle altering means being adapted to convert a rotation of the synchronising shaft into a rotation of the at least one blade along its longitudinal axis, whereby the pitch angle of the at least one blade is altered. 7. A pitch controlling device comprising an activatable driving means secured to the hub and being in engagement with the pitch altering means, the engagement enabling rotation of the blade in relation to the hub about a longitudinal axis of the blade when the activatable driving means is activated. 8. A pitch controlling device according to claim 7, wherein the pitch altering means comprises means for preventing the pitch altering means from converting a rotation of the synchronising shaft into a rotation of the activatable driving means. 5 9. A pitch controlling device according to claim 7, wherein the pitch altering means comprises means for preventing the pitch altering means from converting a rotation of the activatable driving means into a rotation of the synchronising shaft. 10. A pitch controlling device according to claim 7 or 8, wherein the activatable driving 10 means is a motor, such as an electromotor, a hydraulic driven motor or a pneumatic driven motor. 11. A pitch controlling device according to claims 7-10, wherein the pitch altering means comprises a first worm gear with a first worm wheel to be rotated by the synchronising 15 shaft and a first drive wheel to be rotated by the first worm wheel for turning the at least one blade at an angle. 12. A pitch controlling device according to claims 7-10, wherein the pitch altering means comprises a second worm gear with a second worm wheel to be rotated by the activatable 20 driving means and a second drive wheel to be rotated by the second worm wheel for turning the at least one blade at an angle. 13. A pitch controlling device according to claims 7-10, wherein the pitch altering means comprises a combined worm gear so that a first drive wheel and the second drive wheel 25 are the one and same drive wheel and the first worm wheel of the synchronising shaft and the second worm wheel of the activatable driving means both is in engagement with the one and same drive wheel and the one and same drive wheel being rotatable by both the first worm wheel or the second worm wheel. 30 14. A pitch control device according to claims 11-13 wherein the ratio between the worm wheel of the synchronising shaft and the drive wheel is less than 1 :5, preferably is less than 1 :15, preferably is 1 :40. 15. A pitch control device according to claims 11-13 wherein the ratio between the worm wheel of the activatable driving means and the drive wheel is less than 1 :5, preferably is less than 1 :15, preferably is 1 :40. 5 16. A pitch controlling device wherein the back-up brake wheel part is a toothed wheel part extending circumferentially around the main shaft and wherein the synchronising shaft is provided with a toothed wheel being in engagement with the back-up brake wheel part so that a rotation of the back-up brake wheel part will impart a rotation of the synchronising shaft. 10 17. A pitch controlling device according to 16 wherein the back-up brake wheel part constitutes a number of segments of a wheel, and wherein the number of segments is the same as the number of blades of the wind turbine, and each of said number of wheel segments being intended for controlling only one blade. 15 18. A pitch controlling device according to 16 wherein the back-up brake wheel part constitutes one complete wheel, and wherein the complete wheel is intended for controlling all blades of the wind turbine. 20 19. A pitch controlling device according to any of claims 1-18 wherein the synchronising shaft(s) is/are provided with a part of a brake being able to rotate and wherein the main shaft is provided with a part of the brake being unable to rotate. 20. A pitch controlling device according to any of claims 1-18 wherein the back-up brake 25 wheel part is provided with a part of a brake being able to rotate and wherein a stationary part of the wind turbine is provided with a part of the brake being unable to rotate. 21. A pitch controlling device according to claim 19 or 20, wherein the part of the brake being able to rotate is a brake disc and the part of the brake being unable to rotate is a 30 brake calliper having a brake shoe. 22. A pitch controlling device according to claim 19, wherein the part of the brake being able to rotate is a brake calliper having a brake shoe mounted on the synchronising shaft and the part of the brake being unable to rotate is a brake ring mounted on the main shaft. 35 23. A pitch controlling device according to claim 22, wherein the part of the brake being able to rotate is a brake calliper having a brake shoe mounted on the synchronising shaft and the part of the brake being unable to rotate is a brake ring mounted on the chassis. 5 24. A pitch controlling device according to claim 20, wherein the part of the brake being able to rotate is a brake calliper having a brake shoe mounted on the back-up brake wheel part and the part of the brake being unable to rotate is a brake ring mounted on the stationary part of the wind turbine. 10 25. A pitch controlling device according to claims 19-24, wherein braking force is released by means of a dynamically applied force such as an electrically, hydraulic or mechanically dynamic force. 26. A brake according to claims 19-26, wherein braking force is applied by means of a 15 mechanically applied static force such as a number of springs. 27. A pitch controlling device according to any of the claims 1-26, wherein electrical current to the activatable driving means is supplied by at least one slipring mounted concentrically with the main shaft and connected to a power supply. 20 28. A pitch controlling device according to any of the claims 1-26, wherein the electrical current to the activatable driving means is supplied by power source contained in the main shaft or the main shaft being a part of the a power source. 25 29. A pitch controlling device according to any of the claims 1-28, wherein the wind turbine comprises a multi-pole generator having a rotor constituting the main shaft of the wind turbine. 30. A pitch controlling device according to any of the claims 1-28, wherein the wind 30 turbine comprises a multi-pole generator being connected aligned with at the rear end of the wind turbine. 31. A method of controlling the pitch angle of blades of a wind turbine by rotating the blades around a longitudinal axis of the blades, which method applies a device according 35 to any of the claims 1-30, comprising the steps of activating the activatable driving means and upon which an activation of the pitch altering means is introduced in order to alter the pitch of the blades by means of the pitch altering means, retaining a rotation of the synchronising shaft relative to the pitch altering means when activating the activatable driving means and when transferring the activation of the activatable driving means to the pitch altering means thereby maintaing the retaining of the rotation of the synchronising shaft relative to the pitch altering means, and de-activating the activatable driving means when the pitch of the at least one blade has been altered to the pitch wanted. 32. Method according to claim 31 wherein retaining the rotation of the synchronising shaft is obtained by introducing a resistance towards rotation from a drive wheel of the pitch altering means to a drive wheel or worm wheel of the synchronising shaft. 33. A method according to claim 31 or 32, wherein the pitch angle is controlled so that the pitching of the blades is between +2° to -10, primarily between +1° to - 5°. 34. A method of controlling the pitch angle of at least one blade of a wind turbine in order to stop the rotation of the hub and of the at least one blade around the longitudinal axis of the main shaft, which method applies a device according to any of the claims 6-30, comprising the steps of braking the back-up brake wheel part relative to the main shaft upon which a rotation of the synchronising shaft is introduced in order to alter the pitch of the blades by means of the pitch altering means, retaining activation of and/or reaction of the activatable driving means relative to the pitch altering means when the rotation of the synchronising shaft is introduced, when braking the back-up brake wheel part and introducing the rotation of the synchronising shaft and the altering of the pitch angle by means of the pitch altering means thereby maintaining the retaining of the activation of and/or the reaction of the activatable driving means relative to the pitch altering means, and releasing the braking of the back-up brake wheel part and thereby stopping the rotation of the synchronising shaft when the pitch of the at least one blade has been altered to the pitch wanted. 35. A method for stopping the rotation of the blades of a wind turbine by applying the method according to any of the claims 31-34, said stopping is provided by retaining the synchronising shaft in relation to the back-up brake wheel part. 36. A method of stopping the rotation of the blades of a wind turbine according to claim 35, wherein the main shaft is allowed to turn in either positive or negative direction when the synchronising shaft is being retained to in relation to the back-up brake wheel part. 37. A method of stopping the rotation of the blades of a wind turbine according to claim 35 and 36, wherein the angle the main shaft is allowed to turn in either positive or negative direction when the synchronising shaft is being retained to the back-up brake wheel part is given by pitching the blades between 0° and -20°, primarily between -10° and -15°. 38. A method of braking the main shaft of a wind turbine, according to claim 36, wherein the angle the main shaft is allowed to turn in either positive or negative direction when the synchronising shaft is being stopped is given by pitching the blades between -1° to +90°, such as between 0° to 65° primarily 0° to 40°. 39. A wind turbine comprising a device according to any of the claims 1-5 or any of the claims 7-10 or any of the claims 19-38. 40. A wind turbine comprising a device according to any of the claims 6-18 or any of the claims 19-38.

Inventors: NIELSEN THOMAS KRAG, VILSBOELL NIELS, NIELSEN, THOMAS, KRAG, VILSBOELL, NIELS
Applicants: NEG MICON A S, NIELSEN THOMAS KRAG, VILSBOELL NIELS, NEG MICON A/S, NIELSEN, THOMAS, KRAG, VILSBOELL, NIELS
Application year: 2000
Main classification: F03D7
IPC codes: F03D7