Patent Publication Number: US-2013243598-A1

Title: Bearing and wind turbine containing the bearing

Description:
CROSS-REFERENCE 
     This application claims priority to German patent application no. 10 2011 082 811.7 filed on Sep. 16, 2011, the contents of which are fully incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention generally relates a bearing comprising a linear motor and a wind turbine containing such a bearing. 
     BACKGROUND 
     For wind turbines, the speed at which a rotor of the particular wind turbine rotates is influenced by a change of the angle of attack of one or more rotor blades of the particular rotor of the wind turbine. In this case, the angle of attack of the particular rotor blades can be set such that a stall results, whereby a force generated by oncoming air brakes the rotor and/or its rotor blades. In this case, for example the rotor can come to a stop. This process is also referred to as an active stall. Herein, a change in the angle of attack means that the rotor blades are rotated about their longitudinal axis, relative to the oncoming air, i.e. to present a smaller contact surface to the wind or gusts. 
     For wind turbines, it is often therefore useful to provide a suitable possibility to change the angle of attack of the rotor blades, in order to limit the power output of the particular system and to protect the system from overload. The angle, though which the rotor blades are rotated in order to control the power output of the wind turbine, typically falls in the range between a few degrees and up to 25° or more. In emergency situations, however, the rotor blades are often rotated 90°, in order to stop the rotor as described above. 
     A change in the angle of attack of the rotor blades can be achieved in a different way. In the case of somewhat smaller wind turbines having an output of up to 300 kW, wherein typical values fall in the area of approximately 100 kW, mechanical systems are often utilized, in which the change of the angle of attack is effected by centrifugal forces. In the case of medium-sized wind turbines, which typically have an output in the range between approximately 300 kW and 500 kW, hydraulic systems are used to adjust the angle of attack. In larger wind turbines, which typically have an output of more than 500 kW, electrical systems are used to adjust the angle of attack. 
     Electrical systems for tracking the angle of attack of a rotor blade often have the positive effect that the power output of the wind turbine can be controlled and monitored more accurately. In addition, the overall service life of the components of a wind turbine can often be increased, since load peaks can be prevented, if necessary. Electrical systems also have the advantage over hydraulic systems that the danger of a leak of hydraulic fluids is eliminated. 
     Newer wind turbines having an output power of over 500 kW are typically equipped with electrical systems for adjusting and/or tracking the angle of attack of the rotor blades, since the angle of attack of the individual rotor blades can, in the case of a wind turbine having more than one rotor blade, be individually controlled via electric motors. As a result, installation space can be saved in the interior of the rotor housing. 
     In this context, double-row large size angular contact ball bearings are often used as angle-of-attack or pitch bearings. In this case, one of the bearing rings has gear teeth, via which the electric drive is connectable with the bearing ring. The inner ring is often connected to the corresponding rotor blade so as to rotate therewith, so that it has corresponding gear teeth on its inner side. 
     A comparatively large torque is often required to adjust the angle of attack of the rotor blades. For this reason the electric drive typically has a one-step or multiple-step planetary gearing or also a worm gearing, which is disposed between the electric motor and a pinion engaged with the particular rolling-element bearing ring. 
     The manufacturing of a bearing ring with appropriate gear teeth, however, represents a major challenge due to the tolerances to be maintained, the material properties that are required and must be maintained in the area of the gear teeth (e.g. hardness and toughness) and other properties. The manufacturing of the appropriate gear teeth with such large bearing rings therefore includes a process that is typically expensive. 
     SUMMARY 
     A need therefore exists in the art to provide an improved bearing capable, e.g., of adjusting the angle of attack of a rotor blade of a wind turbine. In addition or in the alternative, a need exist to provide an improved bearing that is preferably simpler to manufacture than conventional bearings used for this purpose. 
     It is therefore an object of the present teachings to disclose improved bearings containing linear motors as well as wind turbines containing the same. 
     According to one aspect of the present teachings, a bearing capable of, e.g., adjusting an angle of attack of a rotor blade of a wind turbine, comprises a first bearing ring that is rotatable relative to a second bearing ring. The first bearing ring comprises, as a slider (translator) of a linear motor, a plurality of magnetic field sources disposed adjacent to one another around at least one part of its circumference, wherein the magnetic field sources are formed such that each two adjacently disposed magnetic field sources generate a magnetic field with alternating polarity. The second bearing ring comprises, as a stator of the linear motor, a group of at least two coils disposed adjacent to each other around at least one part of its circumference. 
     According to another aspect of the present teachings, a wind turbine comprises a rotor and a rotor blade as well as a bearing according to any embodiment disclosed herein. The bearing is preferably disposed between the rotor and the rotor blade such that the rotor blade is mechanically connected to the first bearing ring so as to rotate therewith and the rotor is mechanically connected with the second bearing ring so as to rotate therewith, thereby making possible a change of the angle of attack of the rotor blade. 
     According to these aspects of the present teachings, by using a linear motor, it is no longer necessary to form gear teeth on the bearing rings, as was required in conventional bearings for wind turbines. Therefore, the linear motor can be embodied directly as part of the first and second bearing rings. That is, according to the present teachings, a conventional electric motor having a corresponding transmission is replaced by a direct drive motor. This can make possible not only a sufficiently high torque and a good controllability and monitorability, but can also make superfluous the use of a transmission and the backlash connected with it. 
     By omitting a transmission, gear teeth wear that typically occurs over time can also be avoided. Such gear teeth wear could occur in previously-known embodiments having a gear-based transmission, with the result that precise adjustability could no longer be ensured. In such a case, a very costly replacement was often necessary with conventional bearings, which can preferably be avoided through the use of a bearing according to the present teachings. 
     Likewise, by using a bearing according to the present teachings, installation space can be saved in the interior of the wind turbine, for example in the interior of the rotor housing, since the additional mechanical components, in particular a corresponding transmission, can be omitted. 
     A bearing according to the present teachings can be embodied as a rolling-element bearing, which has a plurality of rolling elements disposed between the first bearing ring and the second bearing ring and in contact with raceways of the first and second bearing rings. Thus the bearing can, for example, be a single row or a multiple row bearing, for example a double row four point bearing. 
     In other exemplary embodiments, the bearing can, however, also be a sliding bearing. Regardless of the type of bearing implemented, a bearing according to the present teachings can further include a lubrication system as an optional component. 
     In an exemplary embodiment of a bearing, the coils of the group of coils and the magnetic field sources of the plurality of magnetic field sources may disposed such that the coils face the magnetic field sources. This configuration makes possible an improved coupling or interaction of the magnetic field or of the magnetic flux of the magnetic field sources with the coils by reducing the distance between the coils and the magnetic field sources. 
     In an exemplary embodiment, adjacent coils of the group of coils can also have a matching winding orientation. In such a case, all of the coils in the group can have the same winding orientation. In other embodiments, however, an alternating winding orientation can be implemented for adjacent coils. Independent of the winding orientation, the coils can be connected in series or in parallel. 
     In a bearing according to the present teachings, the plurality of magnetic field sources can be disposed substantially completely around the circumference of the first bearing ring. Thus it can be possible to enable a large displacement for the bearing. Likewise it can also be possible that the bearing can rotate over any preferred angular range, including even more than 360°. 
     In other exemplary embodiments of a bearing, the plurality of magnetic field sources can also be disposed around the circumference of the first bearing ring, in a predetermined angular range with respect to the midpoint of the first bearing ring, to which angular range a further predetermined angular range directly connects, in which no magnetic field sources are disposed. 
     In such a bearing, the predetermined angular range can encompass at least 75°. Thus it can be possible to use the angle of attack of the rotor blade not only for regulating the power output, but also, in the case of an emergency situation, the angle of attack of the rotor blade can also be rotated so far that the probability of significant damage to the wind turbine due to strong winds can be reduced. In other exemplary embodiments, the bearing can be formed such that the predetermined angular range encompasses at least 90°, in order to make possible a further turning of the rotor blade, i.e. a larger change of its angle of attack, in order to further reduce the risk of damage. 
     In such a bearing, the predetermined angular range can encompass an angular range corresponding to the sum of at least 90°, for example 100° or 120°, and a minimum angular range in which the group of coils is disposed with respect to a midpoint of the second bearing ring. In this way, rotation of the rotor blade, and thus an adjustment of its angle of attack, to at least 90° can optionally be ensured, so that the rotor can be turned fully “out of the wind,” in order to reduce or completely prevent the above-mentioned damage due to the occurrence of gusts or high winds. 
     In such a bearing, the further predetermined angular range can correspond to a minimum angular range, in which the group of coils is disposed with respect to a midpoint of the second bearing ring. In other exemplary embodiments, the further predetermined angular range can also comprise a multiple of, for example two-fold or three-fold, the predetermined angular range. The use of a linear motor thus makes possible a frugal implementation of the necessary magnetic field sources in comparison with a conventional electric motor. This not only allows for a reduction in cost for the manufacture of a bearing according to the present teachings, but also allows the manufacturing to be simplified. 
     In a bearing according to the present teachings, the group of coils can be disposed such that a ratio of an angle, at which two adjacent coils of the group of coils are disposed with respect to a midpoint of the second bearing, to a further angle at which two adjacent magnetic field sources are disposed with respect to a midpoint of the first bearing ring, falls between 0.6 and 0.95 or between 1.05 and 1.4. This allows a compact construction of the linear motor to be implemented and/or a torque development and/or a responsiveness of the linear motor optionally to be improved. In other exemplary embodiments the above-mentioned ratio can also fall for example in the range between 0.8 and 0.95, or between 1.05 and 1.25, or also between 0.85 and 0.95 or between 1.05 and 1.15. In this case, the required installation space can optionally be used more efficiently and/or the responsiveness and/or the torque development can be further improved. 
     In another exemplary embodiment, the total number of coils on the second bearing ring is may be different from the number of magnetic field sources on the first bearing ring. In further exemplary embodiments, the total number of coils on the second bearing ring is thus less than a third, a fourth, a fifth, or a seventh of the total number of magnetic field sources on the first bearing ring. But here also, in other embodiments a suitable different ratio of the total number of coils and magnetic field sources can be implemented. 
     In a bearing according to the present teachings, the group of coils can be disposed with respect to a midpoint of the second bearing ring in an angular range of not more than 30°. Thus it can be possible to further spatially restrict the use of magnetic field sources and/or further increase the possible movement path of the linear motor. Thus a simpler and/or more cost-effective manufacture of a bearing according to the present teachings can optionally be made possible. 
     In such a bearing, a further angular range can connect directly to the angular range; in the further angular range, no coils are disposed on the second bearing ring, and the further angular range encompasses at least 30°. In other exemplary embodiments, the further angular range can encompass at least 45°, at least 75°, at least 90°, at least 100° or at least 120°. Thus in a further exemplary embodiment, each plurality of magnetic field sources can optionally be associated with exactly one group of coils. 
     In a bearing according to the present teachings, the coils of a group of coils can be disposed on a common yoke. In this way the efficiency of the linear motor and thus the achievable torque can optionally be improved. 
     In such a bearing, only the coils of one group of coils, i.e. the coils of exactly one single group of coils, are disposed on the common yoke. In this case, the efficiency of the linear motor can optionally be further increased, since any possible interference or overlapping with magnetic fields of other coils can preferably be avoided. 
     The common yoke can, for example, be manufactured from a magnetically soft material. In this case, a further increase in efficiency of the linear motor is optionally possible through a better channeling of the magnetic field lines through the yoke. 
     According to another aspect of the present teachings, the bearing may include a plurality of groups of coils disposed, for example at regular intervals, around the first bearing ring, wherein no coils are disposed between each two adjacent groups of coils in an angular range of at least 30° around the circumference of the second bearing ring. The first bearing ring can then comprise a further plurality of magnetic field sources that are adjacently disposed around a part of the circumference of the first bearing ring, wherein the magnetic field sources of the further plurality of magnetic field sources are formed such that each two adjacently disposed magnetic field sources generate a magnetic field with alternating polarity. By providing a second group of coils and a corresponding further plurality of magnetic field sources, i.e. a second linear motor, a further increase of the torque of the linear motor can optionally be achieved. 
     In such an exemplary embodiment, due to a minimum ensured displacement of the linear motor, i.e. a minimum change region of the angle of attack of the rotor blade from for example 90° or more, it can be advisable or even necessary to utilize at most three groups of coils or at most two groups of coils. 
     In bearings according to the present teachings, the magnetic field sources of the plurality of magnetic field sources can each comprise a permanent magnet, for example a NdFeB permanent magnet, and/or a coil. If a permanent magnet is used, a simpler manufacture of a bearing is made possible, since an electrical connection of the magnetic field sources can then be omitted. If a coil is used as the magnetic field source, a better controllability of the linear motor can optionally be achievable. A guiding or conduit for the electric cable that connects the coils is in this case often unproblematic, since the maximum rotational angle through which the bearing must be able to pivot is typically substantially less than 360°. Moreover a combination of the two options described above is also possible, wherein one or more coils are used to strengthen the magnetic field generated by one or more permanent magnets. 
     The magnetic field sources can optionally comprise a magnetically soft material for channeling the magnetic field lines. In this case, a more precise matching of the magnetic field sources to the geometry of the bearing can optionally occur, whereby the efficiency of the linear motor can optionally be increased. 
     In bearings according to the present teachings, the first bearing ring can be an inner ring of the bearing and the second bearing ring can be an outer ring of the bearing. This configuration represents the configuration that is most often used in wind turbines. Of course in other exemplary embodiments the first bearing ring can also be the outer ring of the bearing, while the second bearing ring can be the inner ring of the bearing. 
     Moreover the possibility exists, of course, of also using a bearing according to the present teachings such that one or both bearing rings, i.e. the first and the second bearing ring, carry out rotational or translational motion with respect to a further component. The use of the terms “stator” and “slider (translator)” in this context simply reflect the usage of common terminology in the context of linear motors, but, however—in particular with regard to the use of the term “stator”—do not indicate any fixing of a stationary arrangement of the particular bearing ring. Thus a bearing ring according to the present teachings can also optionally be used such that the second bearing ring is considered to be rotating. 
     A “midpoint” of a bearing ring is in this context understood to be a (any) point on an axis of the bearing, a rotational axis of the bearing, an axis of symmetry, or a rotational axis of the particular bearing ring. 
     An “angle” or “angular range” in the context of the above or below description is further understood to be an angle that represents a minimum angle or a minimum angular range, as long as something else is not required by the context or is explicit mentioned. Thus for example if groups or other objects encompass an angle or are disposed in an angular range, then “angle” or “angular range” is understood to be the smallest numerical value of the corresponding angle or angular range. Multiples of 360° are in general only rarely considered, such as correspondingly large angles, which optionally encompass bisecting lines, planes, or other geometric objects with one another. 
     Two objects are said to be “adjacent” if no additional object of the same type is disposed between them. Objects are “immediately adjacent” if they border each other, i.e. for example are in contact with each other. 
     A friction-fit connection results from static friction, a materially-bonded connection results from molecular or atomic interactions and forces, and an interference-fit connection results from geometric connection of the respective connecting partners. The static friction thus presupposes in particular a normal force component between the two connecting partners. 
     As already described above, bearings according to the present teachings can for example be used in connection with a wind turbine. They can therefore be implemented as large size bearings, large size rolling-element bearings, or large size sliding bearings. Due to their pivoting range typically being limited to less than 360°, they are also referred to as pivot bearings. 
     However, it should be understood that the present bearings may be advantageously utilized in any applications other than wind turbines, where a pivoting of the bearing rings relative to each other is desirable. 
     Further objects, embodiments, advantages and designs of the present teachings will be explained in the following, or will become apparent, with the assistance of the exemplary embodiments and the appended Figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic illustration of a linear motor. 
         FIG. 2  shows a cross-sectional illustration through a bearing according to the present teachings. 
         FIG. 3  illustrates two objects disposed adjacently at an angle. 
         FIG. 4  shows a schematic view of a bearing according to the present teachings. 
         FIG. 5  shows a schematic view of a further bearing according to the present teachings. 
         FIG. 6  shows a schematic view of a further bearing according to the present teachings. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the context of the present description, summarizing reference numbers are used for objects, structures and other components when the respective components or a plurality of corresponding components are described within an exemplary embodiment or within a plurality of exemplary embodiments. Passages of the description which relate to a component are therefore transferable to other components in other exemplary embodiments, to the extent that this is not explicitly excluded or it follows from the context. If individual components are indicated, individual reference numbers are used, which are based on the corresponding summarizing reference numbers. In the following description of embodiments, therefore, identical reference numbers indicate identical or comparable components. 
     Components which occur multiple times in one exemplary embodiment or in different exemplary embodiments can be embodied or implemented identically or differently with respect to some of their technical parameters. It is thus possible, for example, that several components within an exemplary embodiment can be embodied identically with respect to one parameter, but differently with respect to another parameter. 
     Before exemplary embodiments of a bearing and a wind turbine are described in connection with  FIGS. 2 to 6 , a linear motor will first be described in its basic configuration. Thus  FIG. 1  schematically shows a design of a linear motor  100 , as can be used for example in the context of a bearing according to the present teachings. The linear motor  100  has a plurality of magnetic field sources  110 , which are adjacently disposed or formed along a component  120  in such a way that adjacent magnetic field sources  110  generate or provide an alternating polarity with respect to their magnetic field or their magnetic flux. 
     Thus in  FIG. 1 , for ease of illustration, a linear motor or a section of a linear motor  100  is shown, which comprises four magnetic field sources  110 - 1 , . . . ,  110 - 4 . As also shown in  FIG. 1  by the indicators for their polarities (“N” for north and “S” for south), each two adjacent magnetic field sources, for example the magnetic field sources  110 - 1  and  110 - 2 , generate corresponding magnetic fields with different polarity. The same applies for the further magnetic field sources  110  shown in  FIG. 1 . 
     The magnetic field sources  110  are mechanically connected with the component  120 . This connection can occur for example through a materially-bonded connection, a friction fit connection, or an interference fit connection, or also through a combination of two or more of these. Thus the connection can optionally occur through gluing or screws. Depending on the specific implementation, the component  120  can for example comprise a magnetically soft material or also can be manufactured from this material, in order to make possible a channeling of the magnetic field lines of the magnetic field sources  110  in its interior. 
     The linear motor  100  further comprises another component  130 , which can for example be a yoke  140 . The yoke  140  comprises at least one section  150 , which rises above a base section  160  of the yoke  140 . A coil  170  is disposed on the at least one section  150  and can be supplied with an electric current via an appropriate supply line not shown in  FIG. 1 . 
     Thus  FIG. 1  shows a linear motor  100  or a section of the same, which comprises two sections  150 - 1 ,  150 - 2  and two corresponding coils  170 - 1 ,  170 - 2 .  FIG. 1  shows the windings of the coils  170  and their winding orientation, as it depicts the direction of the current flow in the windings of the coils  170  when a current is supplied thereto. Two adjacent coils, i.e. for example the coils  170 - 1  and  170 - 2 , have an identical winding orientation. The coils  170  can be connected in parallel or in series. 
     The coils  170  and the magnetic field sources  110  are disposed such that a gap  180  is present between them, through which the magnetic field lines generated by the magnetic field sources  110  penetrate into the coil  170  or the yoke  140 . Also, the yoke  140  can of course be manufactured from a magnetically soft material or at least comprise it, in order to make possible a channeling of the magnetic field lines in its interior. The width of the gap  180  determines the coupling strength, with which the magnetic field lines of the magnetic field sources  110  couple into the coils  170 . Accordingly, this gap should be designed as small as possible, however large enough that, even in the event of vibrations and other mechanical influences, a collision or contact of the coils  170  with the magnetic field sources  110  is prevented. 
     The magnetic field sources  110  can in principle be realized based on permanent magnets or also based on coils. In the first case the magnetic field sources  110  can for example be implemented based on a neodymium iron boron magnet (NdFeB magnet). Naturally, however, other permanent magnets can also be used. Moreover, of course, the magnetic field sources  110  can likewise be realized based on coils. While with the use of permanent magnets they are mechanically connected with the component  120  and appropriately oriented for the generation of the alternating polarity, in the case of an implementation based on coils, the alternating polarity of adjacent magnetic field sources  110  can be realized by wiring and/or an alternating winding orientation. Of course, combinations of a permanent magnet and a coil can also be implemented in the context of the magnetic field sources  110 . Thus the magnetic field of the permanent magnet can optionally be increased through the use of an additional coil. 
     Independently from this, the magnetic field sources  110  and/or component  120  can comprise a magnetically soft material for channeling the field lines of the magnetic field sources  110 . In this way a better matching of the magnetic field sources  110  to the geometry of the linear motor  100  is optionally achievable. 
     A linear motor  100  represents an electric drive motor, which in contrast to common rotating motors does not displace an object connected to it in a rotating movement but rather in a substantially rectilinear movement (translational movement). At the same time, in principle either an asynchronous—the magnetic field is not fixedly coupled with the movement—or a synchronous mode of operation—for example with a linear stepper motor—is possible. 
     A linear motor  100  follows the same functional principles as a rotary current motor, wherein the original, circularly-disposed electrical excitation windings (stator) are instead disposed on a flat track. The “runner” or translator (slider), which corresponds to the rotor of the rotary current motor, is pulled, in the case of the linear motor, along the movement path by the axially moving magnetic field. Hence the widely-used term “Wanderfeldmachine” (moving field motor). A linear motor  100  can thus be seen as an “unrolled” version of a rotating electric motor. It produces a linear force along its extension or length. 
     A linear motor is not limited to straight paths in the sense of a mathematical line or line segment. Linear motors  100  can rather also be used for movement along a curved path or line and accordingly can be formed in curved shape. 
     Linear motors  100  can make it possible to directly execute a translational movement. They thus make possible the construction of direct drives, in which a gear reduction or transmission can be omitted. In this field, linear motors have the advantage of high accelerations and correspondingly high forces and torques. High velocities can also optionally be achieved or generated. 
     Linear motors  100  can be implemented both based on conventional conductors as well as based on superconductors. In the latter case, the provision of an appropriate cooling can be advisable, in order to achieve the superconducting state of the affected components. 
     In the linear motor  100  shown in  FIG. 1 , the coils  170  are disposed in the form of a group  190 , wherein each group  190  comprises at least two coils  170 . 
       FIG. 2  shows a cross-sectional representation through a wind turbine according to the present teachings having a bearing  200  according to the present teachings. A wind turbine according to the present teachings comprises a rotor  210  as well as at least one rotor blade  220 , whose respective attachment structures are shown in  FIG. 2 , by which they are connected with the bearing  200  to adjust an angle of attack of the rotor blade  220 . 
     The rotor  210  in this context represents the “stationary component,” and the rotor blade  220  represents the “movable component,” since the rotor blade  220  is designed to be adjustable with respect to its angle of attack relative to the rotor  210  by using the bearing  200 . 
     According to an exemplary embodiment, the bearing  200  is formed as a rolling-element bearing, more specifically as a ball bearing. It thus comprises a first bearing ring  230  and a second bearing ring  240 , between which are disposed a plurality of rolling elements  250 . The rolling elements  250  roll on raceways  260 ,  270  of the two bearing rings  230 ,  240 . 
     The first bearing ring  230 , which is formed as inner ring  280  in the present exemplary embodiment, is screwed onto the rotor  210  via corresponding bores and thus is connected so as to rotate therewith. The second bearing ring  240 , which is embodied as outer ring  290  in the exemplary embodiment shown in  FIG. 2 , also has corresponding bores, in order to be screwable onto the rotor blade  220 , in order to create a connection with the rotor blade  220  that ensures that the rotor blade  220  will rotate with the second bearing ring  240 . Both the rotor  210  and the rotor blade  220  can of course be embodied in a multiple-piece manner, so that for example only corresponding attachment structures for the connection with the bearing  200  according to the present teachings are represented in  FIG. 2 . Naturally, in other exemplary embodiments the rotor  210  and the rotor blade  220  can also be connected, using other connecting techniques, with the corresponding bearing rings  230 ,  240  of the bearing  200 . 
     The first bearing ring  230  is formed as a slider (translator) of a linear motor and thus comprises a plurality of magnetic field sources  110  adjacently disposed around at least one part of its circumference. The magnetic field sources  110  are formed such that each two adjacently disposed magnetic field sources  110  generate a magnetic field or a magnetic flux with alternating polarity. As will be explained in more detail below in the context of  FIGS. 4 ,  5  and  6 , the plurality of magnetic field sources  110  can be substantially completely disposed around the circumference of the first bearing ring  230 , or in a predetermined angular range relative to a midpoint of the first bearing ring  230  around its circumference, to which a further predetermined angular range directly connects, in which no magnetic field sources are disposed. 
     The second bearing ring  240  is formed as stator of a linear motor and accordingly comprises a group  190  (not shown in  FIG. 2 ) of at least two coils  170  disposed adjacently around at least one part of its circumference. Between the magnetic field sources  110  and the coils  170 , corresponding gaps  180  are formed, via which the magnetic fields of the magnetic field sources  110  and the coils  170  interact with each other. 
     In the exemplary embodiment of a bearing  200  shown in  FIG. 2 , the magnetic field sources  110  are thus disposed on the inner ring  280 , and the coils  170  are thus disposed on the outer ring  290 , and they thus form a direct drive for the rotor blade  220 , while circumventing and avoiding a transmission. Of course, in other exemplary embodiments, the roles of the first bearing ring  230  and the second bearing ring  240  can be interchanged with respect to their characterization as the inner ring and outer ring. In such a case the inner ring  280  would be facing the second bearing ring  240  and the rotor blade  220 , while the outer ring  290  would be facing the first bearing ring  230  and the rotor  210 . 
     Although in  FIG. 2  the bearing  200  is shown as a single-row ball bearing according to the present teachings, exemplary embodiments are in no way limited to this type of bearing. Thus corresponding bearings  200  can for example be formed as double or multiple row bearings. Other rolling elements  250  than balls can also be used. Thus, for example, barrel, cylindrical, needle-shaped, or conical rolling elements could be used as rolling elements  250 . Exemplary embodiments can also be implemented based on angular contact ball bearings, for example four point ball bearings. But bearing  200  can also be implemented according to the present teachings as a sliding bearing. 
     Before a view of a bearing according to the present teachings is explained in more detail and described in connection with  FIG. 4 , first it will be explained in connection with  FIG. 3  what is meant by an “angle,” by means of which two objects are adjacently disposed with respect to a midpoint. 
     Thus  FIG. 3  shows a first object  300 - 1  and a second object  300 - 2 , which are adjacently disposed with respect to one another. As was explained previously, this means that a further identical or similar object  300  is disposed between these two objects  300 - 1 ,  300 - 2 . The objects  300  are further oriented to a midpoint  310 , which is marked in the figure with an “X.” Accordingly, the objects  300  each have a chosen direction  320 - 1  and  320 - 2 , which is for example an outer edge, a magnetization, or another characteristic orientation of the particular object  300 . 
     The orientation of the objects  300  towards the midpoint  310  in this case means that their chosen directions  320  are oriented towards the common midpoint  310 . Accordingly, connecting lines  330 - 1  and  330 - 2 , which connect the midpoint  310  with each object  300 , run parallel to the chosen directions  320  of each object  300 . 
     In the case shown in  FIG. 3 , it is a fact that the objects  300  each have just one corresponding chosen direction  320 , which converge towards the common midpoint  310 . In other cases, in which the corresponding chosen directions  320  can be assigned to the objects  300 , but they are not oriented towards the midpoint  310 , the connecting lines  330 , which connect the midpoint  310  and the corresponding object  300 , with the preferred direction  320  of the corresponding object encompass an angle that is the same for all involved objects  300 . The first mentioned case thus represents a special case of the more general, second case, wherein the corresponding angle is 0°. 
     The objects  300  can for example be coils  170  or magnetic field sources  110 . Depending on how the corresponding objects  300  are implemented, corresponding chosen directions  320  can for example be given by their geometric design, i.e. for example by their external shape, or however also by functional features. Thus for example in the case of a magnetic field source  110 , a magnetization or a bare magnetic field generated by the magnetic field source can represent the chosen direction  320 . In this context, angles caused by alternating polarity (angles of approximately 180°) optionally remain unconsidered. Likewise, in the case of a coil  170 , a magnetic field generated or generatable therewith can be used as the chosen direction  320 . Depending on the specific implementation, angles due to wiring and/or a winding orientation (angles of approximately 180°) remain unconsidered. Alternatively or additionally, likewise a geometric design of the coil  170 , for example a surface normal, which is given by the coil windings, can be used. 
     The aforementioned angle is the angle  340 , which the connecting lines  330  enclose with each other. As has been mentioned previously, in this context a midpoint  310  is understood to be a—any, for example disposed in a plane perpendicular to the corresponding structures—point on an axis or axis of rotation of a bearing at  100  according to the present teachings or on a symmetrical or axis of rotation of a bearing ring  230 ,  240 . 
       FIG. 4  shows a view of a bearing  200  according to the present teachings with a first bearing ring  230 , wherein it is—different from the bearing  200  shown in FIG.  2 —an outer ring  290 . Accordingly a second bearing ring  240  is formed as the inner ring  280  of the bearing  200 . A plurality  350  of magnetic field sources  110  is mechanically connected with the first bearing ring  230 . In this exemplary embodiment of a bearing  200 , the magnetic field sources  110  are substantially disposed completely around the circumference of the first bearing ring  230 . Two magnetic field sources  110  disposed adjacently to each other respectively generate a magnetic field with alternating polarity. In  FIG. 4  this is shown by illustration of the magnetic field sources  110  in black and white. The two magnetic field sources  110 - 1  and  110 - 2 , marked with a reference number in  FIG. 4 , are thus correspondingly disposed as has previously been described in connection with  FIG. 1 . 
     The bearing  200  further includes at least one group  190  of coils  170 , of which only one is provided with a reference number in  FIG. 4  in order to simplify the illustration. More specifically, the bearing  200  in  FIG. 4  includes in total four groups  190 - 1 , . . . ,  190 - 4  of coils  170 . The coils  170  of a group  190  of coils  170  are each disposed on a common yoke  140 , on which only the coils  170  of the particular group  190  are disposed. The groups  190  of coils  170  as well as the plurality  350  of magnetic field sources  110  thus form a linear motor  100 - 1 , . . . ,  100 - 4 , as was described in connection with  FIG. 1 . 
     The four groups  190  of coils  170  are identically formed in this exemplary embodiment of a bearing  200 , but are disposed at approximately 90° with respect to one another around a common midpoint  310  of the first and of the second bearing ring  230 ,  240 . They each extend over an angular range  380  of about 22°, which is only drawn in connection with the group  190 - 1  in order to simply the illustration of  FIG. 4 . Of course, in other exemplary embodiments, the groups  190  of coils  170  can also extend over an angular range  380  that deviates from approximately 22°. The groups  190  can also optionally be embodied differently. Each angular range  380  of the individual groups  190  can thus be larger or smaller. 
     The angular range  380  is typically defined as the smallest angular range in which each group  190  of coils  170  can be completely encompassed. Of course in other exemplary embodiments a smaller or larger number of groups  190  of coils  170  can also be implemented. Thus for example only a single group  190  of coils may be encompassed. Likewise, however, two, three, or more than four groups  190  can be provided. 
     In a bearing  200  according to the present teachings, the individual groups  190  of coils  170 —independent of their number—are typically disposed in a minimum angular range  380  of at most 30° with respect to a midpoint  310 . Here the design of the drive of the linear motor  100  now comes into consideration. In other exemplary embodiments the angular range  380  can also be reduced to at most 25°, at most 20° or at most 15°. 
     Thus, in many exemplary embodiments of a bearing  200 , a further angular range  400  of the second bearing ring  240 , in which no coils are disposed and is therefore free from coils, is directly connected to the angular range  380  of the second bearing ring  240 , in which a group  190  of coils  170  is completely disposed. This further angular range  400  of the second bearing ring  240  often extends at least over 30°, at least over 45°, at least over 75°, at least 90°, at least 100°, or at least 120°. 
     As has already been described above in connection with  FIGS. 1 and 2 , the magnetic field sources  110  can each comprise a permanent magnet, for example a NdFeB magnet, or also a coil. Of course magnetic field sources  110  can likewise embody a combination of both techniques, wherein for example a magnetic field generated by a permanent magnet is amplified with the help of a coil. 
     On the one hand, to make possible a good responsiveness of the linear motor  100  with its magnetic field sources  110  and its coils  170  and on the other hand also a good torque development or force development, the groups  190  of coils  170  can be disposed in such a way that a ratio of an angle, at which two adjacent coils  170  of a group  190  of coils  170  are disposed relative to the midpoint  310 , to a further angle, at which to adjacent magnetic field sources  110  (for example the magnetic field sources  110 - 1  and  110 - 2 ) are disposed relative to the midpoint  310 , falls between 0.6 and 0.95 or between 1.05 and 1.4. In other exemplary embodiments, the ratio can likewise fall between 0.8 and 0.95 or between 1.05 and 1.25, or also between 0.85 and 0.95 or between 1.05 and 1.15. Of course other ratios can also be implemented in exemplary embodiments. This can for example be of interest when the linear motor  100  is embodied as a stepper motor. 
       FIG. 5  shows a view of a further bearing  200  according to the present teachings. The bearing  200  from  FIG. 5  differs from the bearing  200  shown in  FIG. 4  with respect to several points. Thus the magnetic field sources  110  are also adjacently disposed here around at least one part of the circumference of the first bearing ring  230 , wherein two adjacently disposed magnetic field sources  110  accordingly also generate a magnetic field with alternating polarity. This is also represented again by illustration of the magnetic field sources  110  in black and white. The two magnetic field sources  110 - 1  and  110 - 2 , provided with a reference number in  FIG. 5 , are thus disposed as was already described previously in connection with  FIG. 1 . 
     However, in this case, the plurality  350  of magnetic field sources  110  is only disposed in a predetermined angular range  360 , to which a further predetermined angular range  370  connects, in which no magnetic field sources  110  are disposed. In other words the further predetermined angular range  370  is free of magnetic field sources. In the exemplary embodiment of a bearing  200  shown in  FIG. 5 , the predetermined angular range  360  extends over approximately 90°. Since the bearing  200  in  FIG. 5  has a plurality of magnetic field sources  110 , the further predetermined angular range  370  correspondingly extends over approximately 270°. In other exemplary embodiments of a bearing  200 , the predetermined angular range can also be formed smaller or larger. In many exemplary embodiments however, it is useful to implement a predetermined angular range that encompasses at least 75°. 
     The bearing  200  further has only one group  190  of coils  170 , of which for simplicity of illustration in  FIG. 5  only one is provided with a reference number. The coils  170  of the group  190  of coils  170  are disposed on a common yoke  140 , on which only the coils  170  of the group  190  are disposed. The group  190  of coils  170  and the plurality  350  of magnetic field sources  110  form a linear motor  100 , as has been described in connection with  FIG. 1 . 
     In this case, the group  190  of coils  170  extends over an angular range  380  of approximately 22°. Of course in other exemplary embodiments the group  190  of coils  170  can also extend over an angular range  380  that deviates from approximately 22°. This can be larger or also smaller. To make possible an overlap in the angular range between the magnetic field sources  110  and the coils  170 , the bearing illustrated in  FIG. 5  thus has an effective displacement of approximately 68° (=90°−22°). In other words the effective displacement results from the difference of the predetermined angular range  360  and the angular range  380 , over which the coils  170  of the group  190  of coils  170  extend. 
     To make possible, for example, a displacement of 90°, it can be advisable to dispose the magnetic field sources  110  over a predetermined angular range  360 , which corresponds to the sum of 90° and a minimum angular range  380 , in which the group  190  of coils  170  is disposed relative to a midpoint  310  of the second bearing ring  240 . The midpoint  310  of the second bearing ring  240  coincides here with the midpoint of the first bearing ring  230 . In other words, it can be advisable to dispose the plurality  350  of magnetic fields  110  over a predetermined angular range  360 , which comprises at least the sum of the intended displacement (in degrees) and the angular range  380 , over which the group  190  of coils  170  extends. 
     In order to be able to optionally reduce the number of the magnetic field sources  110 , it can therefore be useful to restrict the angular range  380  to at most 30°, at most 25°, at most 20° or at most 15°. Thus in an exemplary embodiment of a bearing  200 , the group  190  of coils  170  extends over an angular range  380  between 10° and 15°. 
     In the exemplary embodiment of a bearing  200  shown in  FIG. 5 , the further predetermined angular range  370 , in which no magnetic fields sources are disposed, encompasses more than twelve-fold the angular range  380 , in which the group  190  of coils  170  is encompassed. In other exemplary embodiments, another multiple can be implemented, for example a one-fold, a two-fold, or a three-fold. Of course this ratio is not restricted to integer ratios. By reducing this ratio, a further linear motor  100  can optionally be implemented. 
     In this case, the angular range  380  is typically defined as the smallest angular range, in which the group  190  of coils  170  can be completely encompassed. With regard to the design of the magnetic field sources  110  as well as the design of the angle, at which two adjacent magnetic field sources  110  and/or two adjacent coils  170  of a group  190  are disposed, reference is made to the embodiments above. The further angular range  400 , in which no coils are disposed on the second bearing ring  240  and is therefore free of coils, thus extends in this exemplary embodiment of a bearing  200  over more than 330°. 
       FIG. 5  thus shows a bearing  200  according to the present teachings, wherein the magnetic field sources  110  are attached to the outer ring  290 , in order to channel the magnetic flux. Accordingly, coils  170  are attached to the inner ring  280 . By applying current to the coils  170 , a turning or rotation of the bearing  200  is thus effected. The magnetic field sources  110  can be formed here from permanent magnets and/or electromagnets, i.e. coils, or can comprise such permanent magnets and/or electromagnets. 
       FIG. 6  shows a further exemplary embodiment of a bearing  200 , which differs in essence from the bearing  200  shown in  FIG. 5  in that this exemplary embodiment now comprises two linear motors  100 - 1  and  100 - 2 . In the exemplary embodiment shown in  FIG. 6 , the two linear motors  100 - 1 ,  100 - 2  are identically embodied, however are disposed at an angle of 180° to each other relative to the midpoint  310 . 
     Thus the first linear motor  100 - 1  includes a first group  190 - 1  of coils  170 , which—analogous to the exemplary embodiment shown in FIG.  5 —are fastened to the inner ring  280 . Accordingly, the plurality  350  of magnetic field sources  110  is in turn connected with the outer ring  290 . 
     However, the bearing  200  shown in  FIG. 6  further includes a second linear motor  100 - 2 . Due to its identical design, it also has a group  190 - 2  of coils  170 , which are also connected with the inner ring  280 , i.e. with the second bearing ring  240 . Moreover, the second linear motor  100 - 2  includes, however, a further plurality  390  of magnetic field sources  110 . The further plurality  390  of magnetic field sources  110  corresponds here, with regard to design and orientation, to the plurality  350  of magnetic field sources  110  of the linear motor  100 - 1 . 
     In other exemplary embodiments of a bearing  200 , the further plurality  390  of magnetic field sources  110  can, however, also be implemented differently. Independent thereof, it includes, however, magnetic field sources  110  adjacently disposed around a part of the circumference of the first bearing ring  230 , wherein the magnetic field sources  110  of the further plurality  390  of magnetic field sources are likewise designed such that each two adjacently disposed magnetic field sources  110  generate a magnetic field with alternating polarity. 
     The two groups  190 - 1  and  190 - 2  of coils  170  are disposed here spaced from each other. More specifically, the second bearing ring  240  thus has a further angular range  400 , which typically encompasses at least 30°, in which no coils  170  are connected with the second bearing ring  240 . 
     In other exemplary embodiments, however, more than the previously mentioned number of linear motors  100  can be implemented, with a correspondingly larger number of groups  190  of coils  170  and a correspondingly larger number of pluralities  350 ,  390  of magnetic field sources  110 . Depending on the specific implementation, in the case of an intended displacement of at least 90°, the number of linear motors  100  implemented is limited, however, to a maximum of three. In this case the groups  190  of coils  170  and/or the pluralities  350 ,  390  of magnetic field sources  110  are each implemented, for example, at an angle of 120° to each other with respect to a midpoint  310 . 
     In other words, in this exemplary embodiment, the linear motors  100 , which are also referred to as linear drives, are now attached on both sides of the bearing  200 . In this way an increase in torque and/or force can be generated. This can for example be advisable, if due to structural requirements a single linear motor  100  can no longer suffice to provide an appropriate torque. 
     Exemplary embodiments of a bearing  200  thus make possible an angle-of-attack bearing for a rotor blade of a wind turbine having a direct drive based on a linear motor concept. 
     Exemplary embodiments of a bearing  200  can thus make possible a simpler manufacture of a bearing and/or space-saving bearing assembly and/or—due to the omitted transmission—a low-backlash angle-of-attack adjustment of a rotor blade of a wind turbine. Exemplary embodiments of a bearing can thus be used in connection with wind turbines which comprise one or more rotor blades  220 . A bearing  200  according to the present teachings can, however, also be used in other systems and machines, wherein a similar adjustment of an angle of attack or a similar angle is advisable. 
     The features disclosed in the above description, the claims and the drawings can be used, individually or in any combination, for the realization of exemplary embodiments in their various designs and—except where the description indicates otherwise—combined with each other in any way. 
     Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above may be utilized separately or in conjunction with other features and teachings to provide improved bearings and wind turbines and methods for manufacturing and using the same. 
     Moreover, combinations of features and steps disclosed in the above detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. 
     All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter. 
     REFERENCE NUMBER LIST 
     
         
           100  Linear Motor 
           110  Magnetic field source 
           120  Component 
           130  Further component 
           140  Yoke 
           150  Section 
           160  Base section 
           170  Coil 
           180  Gap 
           190  Group 
           200  Bearing 
           210  Rotor 
           220  Rotor blade 
           230  First bearing ring 
           240  Second bearing ring 
           250  Rolling elements 
           260  Raceway 
           270  Raceway 
           280  Inner ring 
           290  Outer ring 
           300  Object 
           310  Midpoint 
           320  Preferred direction 
           330  Connecting line 
           340  Angle 
           350  Plurality of magnetic field sources 
           360  Predetermined angular range 
           370  Further predetermined angular range 
           380  Angular range 
           390  Further plurality of magnetic field sources 
           400  Further angular range