Abstract:
An aircraft includes an electromechanical actuator and a decoupling device. A form-fit between a drive element and a linkage point outside of the actuator element can be reversibly decoupled and recoupled. The decoupling device allows the actuator element to run freely in the event of a malfunction, which effectively prevents a jam.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to European Patent Application 13004215.3-1752, filed Aug. 27, 2013, the entire disclosure of which is herein expressly incorporated by reference. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention relate to aviation technology. In particular, exemplary embodiments of the present invention relate to actuator technology for aerodynamically active elements of an aircraft. Furthermore, exemplary embodiments of the present invention relate to an actuator element with a reversible decoupling device, an actuator arrangement as well as an aircraft, particularly an airplane or helicopter. 
     Actuators are used in aircraft to mechanically move aircraft elements and to change their position or location. For airplanes, these are for example rudder surfaces or wing elements to influence the lift behavior of the airplanes. For helicopters, this can pertain for example to the various rotor blade positions by means of a swashplate. 
     Such actuators are conventionally designed as hydraulic elements, since this technology has been mastered for a long time and is less prone to faults. In the event of a malfunction, conventional hydraulic actuators can usually still be moved; in other words, they are not jammed in the event of a malfunction. 
     Due to the increased electrification of aircraft, it is desired to replace hydraulic actuators, which possibly require a hydraulic system running throughout the entire aircraft, with electric actuators. These can be supplied in a purely electrical manner, wherein such electrical lines are normally simpler to install and maintain in an aircraft than hydraulic lines. In addition, the electrical transmission of power or energy makes a weight decrease possible compared to a hydraulic system. Generating movement by such an electric actuator can now also be executed solely electrically, for example using a suitable drive by means of an electric motor; or however, a local hydraulic system can be provided at the actuator, particularly a hydraulic system arranged in the actuator system, the hydraulic system having to also be supplied with electrical energy only from the outside. 
       FIG. 1 a    depicts a schematic illustration of an electromechanical actuator. 
     As illustrated in this example, two motor elements  1  are linked to drive unit  8  of actuator element  3 , using a suitable linkage consisting of a motor shaft  2   a  and a suitable transmission  2   b . Drive unit  8  is changeable in its length I, particularly in its distance between the two linkage points  5   a,b , so that a length change of drive unit  8  of actuator element  3  modifies the distance between linkage points  5   a,b . By means of a suitable restraint between elements, a moving or tilting of an aerodynamically active structure is possible. Drive unit  8  consists of a first drive element  8   a  and a second drive element  8   b , constructed, for example, as a ball screw drive  8  with a ball nut  8   b  and a ball spindle  8   a . By rotating ball spindle  8   a , ball nut  8   b  can be displaced on it, so that the rotation of ball spindle  8   a  provides a length change of drive unit  8  and thus of actuator element  3  or a change in the distance between linkage points  5   a,b . In the event of a defect of an actuator element, particularly for mission-critical aerodynamically active surfaces, one must ensure that these can at least still be moved despite the defect. In the event that an actuator element fails, depending on actual use, usually a certain redundancy is provided. In the case of tail units or rudders, a second actuator element can be arranged in a force-parallel manner to the first one for example so that the position change of the aerodynamically active surface can be detected by one of the two actuator elements or also by both together. 
     Now should an actuator element of the two parallel actuator elements fail, then the other one can at least maintain the function. However, particularly relevant in this context are defects of actuator elements that subsequently no longer allow a length change to be executed; for example the breaking of the ball of the ball screw drive can possibly jam the ball spindle and the ball nut against each other so that a length change of the actuator element is no longer possible. In such a case, control of the aerodynamically active surface can also not be executed by the parallel-arranged actuator element. In a worst case scenario, the aircraft would thus no longer be controllable and would possibly crash. To keep electromechanically actuator elements changeable in their length at least by an external force, including in a malfunction situation, decoupling devices or decoupling mechanisms can be integrated into the actuator elements, which remove the blockage in a malfunction by decoupling the jammed actuator element and thereby ensure that the aerodynamically active surface remains movable and controllable by the force effect of the parallel-arranged element. 
       FIG. 1 b    depicts an example of such an actuator element. Ultimately, the embodiment of  FIG. 1 b    differs from  FIG. 1 a    only by the provision of a decoupling device  6 . Decoupling device  6  thereby not only decouples the two drive elements  8   a,b  from each other; instead, a decoupling is undertaken in such a manner that a decoupling of the contact points  5   a,b  results, wherein one of the contact points is also essentially connected in a decoupled state with both drive elements of the drive unit, while the connection of a drive element to the second contact point  5   b  is released. The length of an actuator element can hereby change regardless whether a mechanism of the drive unit, for example the first drive element  8   a  to the second drive element  8   b , is jammed. 
     One aspect of the present invention provides a special design of a reversible decoupling device for an electromechanical actuator element. 
     According to a first embodiment of the present invention, an actuator element has a drive unit with a first drive element and a second drive element, wherein the first drive element and the second drive element functionally interact in such a manner to effect a change in length of the actuator element, wherein the actuator element has a decoupling device, wherein the actuator element has two linkage points, whose span can be set by the length change of the actuator, wherein one of the drive elements is connected in an essentially direct-action manner with the other linkage points, wherein the span of the two linkage points in a coupled state of the decoupling device can be adjusted by the actuator element and wherein the span of the two linkage points in the decoupled state of the decoupling device can be changed by subjecting the linkage points to an external force. The decoupling device has a decoupling mechanism with a drive element, a form-fitting element, and a retaining element, wherein the retaining element is set up to take a first position in which the form-fitting element is in a closed state, and wherein the retaining element is set up to assume a second position in which the form-fitting element is in an open state. The drive element is set up to displace the retaining element between the first position and the second position, whereby the form-fit of the form-fitting element can be reversibly released and fixed, wherein the decoupling mechanism functionally decouples the output piston from a drive element of the actuator element in such a manner that the change in length of the actuator element is made possible independent of the drive unit, particularly without any functional decoupling of the first drive element and second drive element. 
     According to another embodiment of the present invention, an actuator arrangement includes at least two actuator elements according to the present invention, wherein the at least two actuator elements are arranged in a force-parallel manner so that a length change of the actuator arrangement can be effected by an actuator element alone or by both actuator elements simultaneously. 
     According to another embodiment of the present invention, an aircraft, particularly an airplane or helicopter, includes an actuator arrangement according to the present invention and/or an actuator element according to the present invention. 
     Conventional actuator elements for actuating aerodynamically active elements have either no decoupling device or one that possibly provides only an irreversible decoupling or a decoupling that can only be re-coupled with great effort. Since electromechanical actuator elements with a decoupling device that control aerodynamically active elements may involve mission-critical elements, which in a malfunction could possibly result in the aircraft crashing, regular testing of a decoupling device and thus the simulation of the malfunction is desirable to ensure correct operation in the event of a malfunction. Electromechanical actuator elements, which cannot be re-coupled with little effort are thus possibly not testable at periodic intervals. It cannot be assured that a conventional decoupling device functions properly in an emergency, thereby ensuring that the flyability of an aircraft is maintained. 
     In contrast to this, the present invention provides an actuator element with a decoupling device, which after actuation can be transferred back into a coupled state in a simple manner. An actuator with such a reversible decoupling device can now be regularly inspected for proper functioning, for example during a comprehensive test prior to operating an aircraft. During the test, the decoupling device can thus be triggered under load the actuator element can thus be decoupled, whereby the worst-case scenario of the flight operation can be reconstructed. At the end of the test run, the still function-capable actuator element can simply be re-coupled and thereby makes its normal operating mode available. 
     Thus, according to the present invention an output piston is coupled with a drive unit of the actuator element in such a manner that the output shaft is connected in a form-fitting manner to a drive element of the drive unit. This represents the normal operating mode. The drive unit has a first drive element and a second drive element, which functionally interact in such a manner that the drive unit can provide a length change of the actuator element. The form-fitting coupling of the output piston to one of the drive elements provides for the length change of the actuator element. The two linkage points of an actuator element, which ultimately represent the effective length of the actuator element, can thus be arranged on the output piston on the one hand and on the actuator element itself on the other, for example on its housing. Thus, a linkage point is rigidly connected to the housing of the actuator element, while the second linkage point is linked via the output piston and is thereby connected to the drive unit. The output piston can be subjected to a translation movement, whereby the actuator element can be adjusted in its length. 
     In a coupled state of the decoupling device, the output piston is now connected to the drive unit or a drive element of the same in a form-fitting manner. In the event of a malfunction or decoupling, the form-fit between the output piston and the drive element of the drive unit may be released. In this way, the actuator element may experience a decoupling from the drive unit and output piston so that the length of the actuator element can be adjusted from the outside by means of a comparatively small amount of supplied power. In the event of a malfunction, in which the actuator element is thus decoupled, this, despite its defect, does not represent a jammed device, which could possibly lead to a negative influence on the controllability of an aircraft. 
     Such actuator elements are usually provided in the form of an actuator arrangement, which provides for a certain redundancy for controlling or positioning aerodynamically active elements. For example, two actuator elements can be arranged in a force- or effect-parallel manner so that the position and orientation of the aerodynamically active element can be separately effected by each of the actuator elements or however these may interact, whereby a force can be applied by both actuator elements. In the event of a malfunction, i.e., in the event that one of the actuator elements has a defect and is no longer able to function, or in a worst case scenario jammed so that a length change is no longer possible, the decoupling device according to the invention can decouple the actuator element in such a manner that a length change of the actuator element can be effected by an externally applied force. In this case, the defective actuator element could be decoupled and thereby does not represent any restriction regarding the controllability of the aerodynamically effective element for the parallel-arranged second actuator element, besides a slight amount of force expended for changing the length of the defective actuator element. In this way, the controllability of the aerodynamically active surface can continue to remain assured, despite the worst-case scenario of a jamming defect of one of the two actuator elements arranged in an effect- or force-parallel manner. 
     According to a preferred embodiment of the present invention, the drive unit may be designed as a ball screw drive, wherein the first drive element and the second drive element may be designed as a ball spindle and ball nut of the ball screw drive. For adjusting the length change of an actuator element, there are various implementation possibilities. Usually in the aviation segment, a configuration as ball screw drive or roller screw drive is selected, since these are comparatively robust and can transfer large forces in a low-friction and low-wear manner. A ball screw drive thereby normally consists of a spindle as well as a ball nut. Various implementations provide for the moving and rotating of the ball spindle, while a ball nut, secured against rotation, is displaced on the ball spindle. Another embodiment provides for the ball nut to rotate, while the ball spindle thereby completes a translation parallel to the axis of rotation. 
     According to another preferred embodiment of the present invention, the actuator element may also have a motor element, wherein the ball nut can be rotated when using the motor element, by means of which a length change of the actuator element can be executed through the translation of the ball spindle. According to another preferred embodiment of the present invention, the form-fitting element can be engaged with the output piston in a form-fitting manner so that the translation of the ball spindle causes a translation of the output piston. The present invention pertains particularly to an embodiment in which the ball nut rotates, while the ball spindle moves in a translational manner and the length of the actuator element is hereby adjusted. For a preferred decoupling of the drive elements of the drive unit, the decoupling device shall not undo the drive elements themselves if possible since this can possibly not be assured at all times, particularly in the event of a ball screw drive or planetary roller screw drive. To this end, a linkage point is connected to the drive unit, a second linkage point is connected via another element to the other drive element, while the decoupling device or the decoupling mechanism decouples a linkage, particularly a form-fitting one, of a drive element and another element to the linkage point in such a manner that a length-changing capability can be assured by means of an external force on the actuator element in a decoupled state, even if the first drive element and the second drive element are completely jammed, by undoing the connection between the drive element and other element. The decoupling device or the decoupling mechanism can thus be displaced preferably between a first state, a closed state in which the form-fitting element is closed, and a second state, an open state in which the form-fitting element has a released form-fit. 
     According to another preferred embodiment of the present invention, the spindle may be constructed as a hollow spindle, wherein the output piston is arranged inside the spindle. The actuator element of the present invention thus has a drive unit with a ball screw drive, particularly a rotating spindle nut, and a translationally moved spindle, to which an output piston is connected in a form-fitting manner using the decoupling mechanism, wherein the second linkage point is arranged on the output piston. The spindle can thus be constructed as a hollow spindle for example, in whose interior space the output piston is arranged. Without a form-fit of the form-fitting element, the output piston may essentially be freely displaceable inside the spindle, while the output piston in the form-fitted state of the form-fitting element is rigidly connected to the spindle and moves translationally with the spindle when the spindle nut rotates. In a form-fit-released stated, the output piston can be displaced with comparatively little force inside the spindle. 
     According to another preferred embodiment of the present invention, a form-fit may be provided in the first position of the retaining element between the output piston and the spindle, while in the second position of the retaining element, the form-fit between the output piston and the spindle is released and the output shaft can essentially be freely displaced inside the spindle. In this way, the retaining element enables one to simply switch between a form-fitting state and a non-form-fitting stated of the form-fitting element. The retaining element together with the form-fitting element thereby preferably does not act in the same force direction that may act on the actuator element due to a lengthening or shortening. Particularly preferred is the exertion of a force of the retaining element on the form-fitting element for providing the form-fit essentially vertically to the force provided by the actuator element based on its lengthening or shortening. The force provided by the retaining element can hereby essentially restrict itself to maintaining the form-fit and must not simultaneously be configured in such a stable manner as to resist the force, which the actuator element applies during lengthening or shortening. In this way, the force of the retaining element is decoupled from the force of the actuator element. 
     According to another preferred embodiment of the present invention, the form-fitting element may be constructed as a plurality of ball elements, wherein the output piston has recesses corresponding to the ball elements, wherein the retaining element is constructed as a sleeve element with recesses, wherein the sleeve element can be rotated using the drive element of the decoupling mechanism, wherein the sleeve element is set up in the first position to retain the ball elements in the recesses of the output piston to provide the form-fit between the output piston and spindle, and wherein the sleeve element is set up in the second position to accommodate the ball elements in the recesses of the sleeve element, so that the form-fit is released. The form-fitting elements can thus be displaced between a first, form-fitting position in which they are arranged in the recesses of the output piston and a second form-released position in which they are arranged in the recesses of the sleeve element. The sleeve element may thus execute a comparatively minor rotation and essentially be pivoted between a position in which the recesses of the sleeve element align with the form-fitting elements and a position in which the form-fitting elements are pressed or retained in the corresponding recesses of the output piston. A preferred release under load of the form-fit is hereby also possible, since due to the design of the form-fitting elements as ball elements, no jamming surfaces can occur. As soon as the recesses of sleeve element align with the ball elements, the latter are pressed, due to the form of the ball surface, out of the corresponding recesses of the output piston into the recesses of the sleeve element, and release the form-fit. 
     According to another preferred embodiment of the present invention, the actuator element may also have a housing and a sealing element arrangement, wherein the sealing element arrangement is set up in such a manner that the region of the form-fitting element, retaining element, output piston, and housing are essentially designed in a sealed manner so that in particular the region can be filled with a suitable lubricant. By means of such an arrangement, friction in the decoupling mechanism may be further reduced so that the actuation force of the decoupling mechanism is comparatively low. By means of the sealed design of the region of the sealing element arrangement, the latter may also be designed in an essentially maintenance-free manner. 
     According to another preferred embodiment of the present invention, the actuator element may also have rod seals, wherein when using the rod seals, a sealing effect is essentially provided for the lubricant also during a test. In this way, a test of the decoupling device can be repeatedly performed without possibly risking a function impairment in the event of a malfunction. 
     According to another preferred embodiment of the present invention, one of the linkage points may be arranged on a housing end of the actuator, while the other linkage point is arranged on the external end of the output piston. In this way, the two linkage points, which form the effective length of the actuator element, are arranged on opposite ends of the actuator element, while a simple decoupling of the output piston and elements provided in the actuator element, such as individual drive elements, can continue to be provided by the decoupling device or the decoupling mechanism. 
     According to another preferred embodiment of the present invention, the decoupling device may be decouplable in the course of a test and be re-couplable after completion of the test. A cyclic function test regarding the emergency coupling of the actuator element may hereby be performed and it may in particular be assured that the actuator element or its decoupling device can execute and not block a decoupling, even in a critical malfunction during flight. 
     According to another preferred embodiment of the present invention, the decoupling device may actuate the decoupling mechanism of the actuator element in the event of a defect of a drive unit or the ball screw drive or planetary roller screw drive of an actuator element, so that the actuator element is functionally decoupled, wherein the length change of the actuator arrangement can still be effected by the non-decoupled actuator element. The decoupling device according to the invention thereby ensures that the displaceability of an actuator element is assured from the outside even in the event of a fault, in a worst-case scenario in the event of the first and second drive elements jamming each other, so that the remaining, redundant, parallel-arranged second actuator element can continue to adjust the aerodynamically active element without being negatively influenced by the defective actuator element. 
     According to another preferred embodiment of the present invention, a conductive connection between the decoupling device and an aircraft can be routed solely to the stationary part of the decoupling device, so that a movement of the moveable part of the decoupling device does not require any movability of the conductive connection. By means of the mechanical transfer of the rotation through the pivoting sleeve from the stationary to the moveable part of the decoupling device or the element, all connections of the element, particularly including all connections of the decoupling device, each comprising connections for power transmission as well as for transmitting sensor signals from/to associated controllers/monitoring units can be attached in the stationary part of the element. In this way, one does away with the need for a special design of the cable harness for compensating for any relative motion that would be associated with additional effort, costs, and potentially reduced reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Further details regarding the embodiments of the invention are addressed below using the attached drawings. 
         FIG. 1 a,b    depicts a schematic illustration of an electromechanical actuator; 
         FIG. 2  depicts a schematic illustration of an electromechanical actuator according to the present invention; 
         FIG. 3 a - c    depicts an exemplary embodiment of the decoupling device according to the present invention in a locked, form-fitting state; 
         FIG. 4 a - c    depicts an exemplary embodiment of the decoupling device according to the present invention in an open state; and 
         FIG. 5  depicts an exemplary embodiment of an actuator arrangement according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a schematic illustration of an electromechanical actuator according to the present invention. Specifically,  FIG. 2  depicts a schematic design of an electromechanical actuator  3 , for example to control the primary flight control elements for helicopters. By way of example, two motor elements  1  are provided here that are connected using motor shaft  2   a  and a suitable transfer  2   b,c  to the second drive element  8   b , constructed as a rotating ball nut of a ball screw drive. Actuator element  3  is modifiable or adjustable in its length l, particularly between the two linkage points  5   a,b  so that a length change of actuator element  3  changes the distance between linkage points  5   a,b . Ball nut  8   b  is schematically depicted as a rotating element, whereby the first drive element  20 , for example a ball spindle, moves upward or downward in the rotating ball nut  8   b  in  FIG. 2 . Ball spindle  20  itself is secured against rotation, for example by providing an anti-rotation element that is installed, for example, at the lower end of drive spindle  20 . The lower linkage point  5   a  can for example be attached to a suitable aircraft structure, while the upper linkage point  5   b  can be attached on the swashplate of a helicopter. 
     During normal operation, output piston  10  is rigidly connected to ball spindle  20 , particularly in a form-fitting manner. Such a rigid or form-fitting connection may be provided by decoupling device  6 . During normal operation, ball nut  8   b  rotates, and hereby ball spindle  20 , as well as output piston  10  by the form-fitting link to output piston  10 , is displaced parallel to the axis of rotation of the spindle nut, whereby actuator element  3  is lengthened or shortened, so that the distance of linkage points  5   a,b  is influenced. In the event that a mechanical defect in the drive unit, particularly between drive element  8   b  and drive element  20 , occurs, output shaft  10  can be released using the decoupling mechanism of decoupling device  6 . Output piston  10  can hereby be displaced inside ball spindle  20 , constructed as a hollow spindle, whereby the effective length or the distance between the linkage points  5   a,b  can be adjusted externally by a force applied on actuator element  3 . This force can be applied, for example, by a second actuator element arranged in a force-parallel or effect-parallel manner. In the event of the form-fit between drive element  20  and output piston  10  being released, actuator element  3  is essentially freewheeling, while the adjustability of an aerodynamically active surface can be provided using a second, redundant, parallel-arranged actuator. 
     With further reference to  FIGS. 3 a - c   , an exemplary embodiment of a decoupling device according to the present invention is depicted in a locked, form-fitting state. 
       FIG. 3 a    depicts a longitudinal cross-section through an actuator element  3  according to the invention, while  FIGS. 3 b  and 3 c    depict cross-sections through planes BB and CC. 
       FIG. 3 a    depicts a decoupling device  6  with a drive unit, having a ball spindle  20 , which is displaced upward and downward by a rotating ball nut not depicted in  FIG. 3 a   . Ball spindle  20  is designed as a hollow spindle and accommodates output piston  10  inside. The sole linkage between ball spindle  20  and output piston  10  is the decoupling mechanism of decoupling device  6 . The decoupling mechanism has form-fitting elements, designed for example purposes as six ball elements  31   a - f , which provide a form-fitting connection and thus a force transfer between ball spindle  20  and output piston  10 . In  FIG. 3 a   , form-fitting elements  31   a - f  are arranged in recesses  67  of output piston  10  and simultaneously mounted in adapter element  32 , which is rigidly connected to ball spindle  20 . In this way, a force transfer results between output piston  10  via form-fitting elements  31   a - f  to adapter element  32  and via this to ball spindle  20 . A translation of ball spindle  20  based on the rotation of the spindle nut, in  FIG. 3 a    upward and downward, thus results directly in a comparable movement of output piston  10 . In a form-fitted state of decoupling device  6  according to  FIGS. 3 a - c   , form-fitting elements  31   a - f  thus grasp into recesses  67  of output piston  10 . Form-fitting elements  31   a - f  are held there by a locking sleeve  33 , which in its arrangement according to  FIGS. 3 a - c   , presses form-fitting elements  31   a - f  into recesses  67  of output piston  10  and keeps them there. Locking sleeve  33  also has recesses  33   a - f , which accommodate form-fitting elements  31   a - f  and loosen the form-fit by the sliding of form-fitting elements  31   a - f  out of recesses  67  of output piston  10 . The state of the opened form-fit is portrayed below by referring to  FIGS. 4 a   - c.    
     Locking sleeve  33  is, using drive element  50  and if applicable a suitable translation, twistable or rotatable and thus transferable between a position in which form-fitting elements  31   a - f  are pressed into recesses  67  of output piston  10 , and a position in which recesses  33   a - f  are arranged in such a manner that form-fitting elements  31   a - f  can slide out of recesses  67  of output piston  10 . Locking sleeve  33  thus retains form-fitting elements  31   a - f  in the first position in the form-fit. 
     Two rotation sealing elements  34   a,b , two disk elements  35   a,b  and two covers  36   a,b  are provided and connected to locking sleeve  33  and together result in the sleeve arrangement. Locking sleeve  33  and pivoting sleeve  41  are connected to each other by a shaft-hub connection  42 , which restricts the relative freedom of rotation, yet allows a relative axial movement between output piston  10 , spindle  20 , adapter element  32 , form-fitting elements  31   a - f  and sleeve arrangement on the one hand, and drive element  50 , gear element  40  including gear wheels  43 , pivoting sleeve  41 , bearings  45   a,b  and housing  44   a,b  on the other. In the form-fitting state of decoupling device  6 , the sleeve arrangement shifts inside pivoting sleeve  41 , which is held inside housing  44   a,b  by roller bearings  45   a,b . In an advantageous design of the invention, drive element  50 , gear element  40  including gear wheels  43 , pivoting sleeve  41 , bearing  45   a,b  and housing  44   a,b  may be fixed in a translational manner to linkage point  5   a  and thus for example to the fuselage of the aircraft. The same applies also for all required connections, particularly electrical power and sensor connections between the decoupling device and the fuselage. 
     With further reference to  FIGS. 4 a - c   , an exemplary embodiment of the unlocking device according to the present invention in an open state is depicted. 
     To decouple decoupling device  6 , thus to open the form fit, drive element  50 , for example an electric motor or alternatively a duplex-electric motor with two redundant motor elements on a motor shaft, is supplied with operating power. The resulting rotation of drive element  50  can be intensified, for example, by a two-stage spur gear  40  or alternatively by a single- or multi-stage planetary gear or a combination of planetary and spur gear stages or another suitable gear mechanism. Gear wheel  43  of the second reduction stage is connected to pivoting sleeve  41 , which transmits the rotation to the sleeve arrangement. When a certain force, applied by drive unit  50 , is reached or exceeded, the resistance of the form fit, the static friction of the rotation sealing element  34   a,b  and the static friction between locking sleeve  33  and form-fitting elements  31   a - f  is overcome. Drive element  50  thus pivots gear wheel  43  from the position depicted in  FIG. 3 c    into the position depicted in  FIG. 4 c   , whereby recesses  33   a - f  are arranged in the region of form-fitting elements  31   a - 31   f  and these can slide out of recesses  67  of output shaft  10 . Ball elements  31   a - f  are thus unblocked by the movement of the sleeve arrangement. In doing so, gear wheel  43  may be in contact with the housing wall, as depicted in  FIG. 4 c   , which may simultaneously represent an end position by contacting the housing. Such regions in the housing may be lined by a damping material, such as silicone gel for example. 
     In regard to a released form-fit according to  FIGS. 4 a - c   , external forces can now press on the actuator arrangement of form-fitting elements  31   a - f  outwardly in a radial direction into recesses  33   a - f  of locking sleeve  33 . Elastic C-rings  37   a - f  may be provided inside the openings of adapter element  32  for decelerating the movement of form-fitting elements  31   a - f  C-rings  37   a - f  may apply a certain force on form-fitting elements  31   a - f , whereby these are maintained in position and in particular can no longer slide back automatically into recesses  67  of output piston  10 . Sleeves  38   a - f  may hold the C-rings in the holes (not labeled) of adapter element  32 , whereby sleeve  39  may provide an axial support in an overhang region of the sleeve arrangement in a decoupled state. By means of the released form-fit, a force transfer of the drive unit on to output piston  10  is prevented; instead, output piston  10  can be displaced inside ball spindle  20  designed as a hollow spindle so that actuator element  3  runs freely or can have its length changed by a force acting from the outside. After decoupling, form-fitting elements  31   a - f  may be held by C-rings  37   a - f , sleeves  38   a - f  and sleeve  39  in recesses  33   a - f  of locking sleeve  33 . 
     Such a decoupling may now take place within the scope of a regular test prior to a flight to ensure that decoupling device  6  functions properly in the event of a malfunction. Decoupling device  6  according to the invention thereby allows decoupling under load. 
     After decoupling has occurred, now the length of actuator element  3  can be adjusted from the outside, for example by a redundant actuator element arranged in parallel. The externally acting length change thereby displaces output piston  10  inside ball spindle  20 . 
     To allow coupling of the decoupling device after a possible test, the position of output piston  10  may be adjusted using the redundant, parallel-arranged actuator element in such a manner that recesses  67  in output piston  10  are arranged in the region of form-fitting elements  31   a - f . Drive element  50  may now displace locking sleeve  30  in the opposite direction, thus from a position as depicted in  FIG. 4 c    into a position as depicted in  FIG. 3 c   . Form-fitting elements  31   a - f  are hereby displaced out of recesses  33   a - f  of locking sleeve  33  back into recesses  67  of output piston  10 . Locking sleeve  33  secures form-fitting elements  31   a - f  in recesses  67  of output piston  10  and thereby restores the form-fitting state. Output piston  10  and/or ball spindle  20  can be secured by suitable means against a relative rotation, for example by a pin in a recess. 
     A preferred embodiment of decoupling device  6  according to the invention uses a suitable lubrication, for example oil, grease or similar in the region of form-fitting elements  31   a - f . To do so, rod seals  11   a,b  can be provided, which keep the lubricant in the lubricant space, particularly for only a defined axial relative motion between output piston  10  and ball spindle  20 . Particularly during a test, the axial motion after decoupling may be smaller than a defined limit, which is determined by rod seals  11   a,b , since otherwise a re-lubrication of decoupling device  6  may be necessary. In the event of a mechanical defect, it may be irrelevant whether the lubricant leaves the assigned space, since after an actually occurring defect, actuator element  3  must be replaced and overhauled on a regular basis. 
     Alternatively, the complete space inside the housing of actuator element  3  may be filled with a lubricant, for example synthetic oil. In this case, sealing elements  11   a,b ,  34   a,b  may be dispensed with. Alternatively, permanent lubrication solutions are conceivable as well as suitable coatings. 
     By a suitable lubrication, less wear as well as a longer service life of the mechanical components as well as a low actuating force may result. Each component in the actuator element according to the invention may be individually lubricated, for example the unlocking device, the ball screw drive, or alternatively a planetary roller screw drive, and a possibly provided gear. By splitting up and limiting the individual lubrication volumes, a subsequent fault transfer, for example micrometallic particles of the gear that trigger a defect in the ball screw drive, can be avoided. Lubricants may also diminish a rapid movement of the form-fitting elements, particularly during the decoupling process. 
     The decoupling device according to the invention is thereby advantageously attached rigidly in or on the housing of the electromechanical actuator element, whereby a robust and reliable energy transfer by mechanical components is provided from a fixed position to the moving components of the drive unit. By means of the mechanical transmission, flexible cables, which are possibly subject to premature ageing, may be dispensed with. 
     With additional reference to  FIG. 5 , an exemplary embodiment of an actuator arrangement according to the present invention is depicted. 
       FIG. 5  depicts an embodiment for example purposes of the controller of a swashplate of a helicopter, with three actuator arrangements  70  arranged between the aircraft structure  72   a  and an aerodynamically active element  72   b . Aerodynamically active element  72   b , the swashplate of a helicopter, thereby allows the stationary and cyclic influencing of the angle of attack of the rotor blades so that the helicopter may assume a movement direction corresponding to the control. Swashplate  72   b  is thus supposed to be adjustable in three axes of freedom, wherefore these are essentially controlled freely by three actuator arrangements  70 . Each actuator arrangement  70  has in turn two actuator elements  3 , which are arranged in a force-parallel or effect-parallel manner. The adjustment of the effective lengths of the actuator arrangement  70  can thus be executed by both actuator elements  3  simultaneously or also by only one single actuator element  3 . 
     In the event of a malfunction, in which for example an actuator element  3  of an actuator arrangement  70  has a defect, a decoupling device according to the invention decouples the drive unit of the defective actuator element  3 , so that the length change of actuator arrangement  70  can be provided solely by the non-defective actuator element  3  of an actuator arrangement  70 . In the event of a malfunction, i.e., in the case of a defect of an actuator element  3 , the functioning of actuator arrangement  70  can hereby be fully assured and thereby the ability to position swashplate  72   b  in its 3 degrees of freedom. In the event of a test of actuator arrangement  70 , one of the actuator elements  3  can be decoupled, while the length change of corresponding actuator element  3  can be provided by the effect-parallel or force-parallel arrangement of the non-decoupled actuator element. Even after decoupling of an actuator element  3  is complete, the second, non-decoupled actuator element can enable a position or length of the decoupled actuator element to be adjusted that allows a re-coupling of the decoupled actuator element  3 . 
     In doing so, a general aspect of the present invention is that the decoupling device according to the invention is constructed in such a manner that the form-fitting elements and the retaining element move translationally with output piston  10  and linkage point  5   b , but that pivoting sleeve  41  ensures that drive unit  50  and gear  40  do not move translationally or rotationally relative to linkage point  5   a . Pivoting sleeve  41  thereby transmits the pivot movement from gear  40  translationally fixed to linkage point  5   a  and the gear unit of decoupling device  50  to form-fitting elements  31 , fixed translationally to the spindle as well as in a coupled state of decoupling device  6  also to output piston  10  and linkage point  5   b , and sleeve arrangement  33 ,  34   a,b ,  35   a,b ,  36   a,b.    
     Since motor element  1 , force transmission element  2   a - c , and the second drive element  8   b  of the element according to  FIG. 2  are also fixed translationally to linkage point  5   a  and this may also be preferred for any sensor systems, particularly to determine force, rotational and translational position as well as temperature, all electrical connections between the actuated element and associated control units in the stationary system may run to linkage point  5   a  and must not compensate a rotational and/or translational relative motion between an actuated element, for example an aerodynamically active surface, and the fuselage of the aircraft. 
     Such relative movements may otherwise be taken into consideration in the design of an associated cable harness and would thereby result in additional complexity, costs, and potentially reduced reliability.  FIGS. 3 a - c    as well as  FIGS. 4 a - c    depict the element in its extended state, in other words for a maximum adjusted distance between linkage points  5   a  and  5   b . In a retracted state of the element, output pistons  10 , spindle  20 , adapter element  32 , form-fitting elements  31   a - f , and sleeve arrangement  33 ,  34   a,b ,  35   a,b ,  36   a,b  would shift up to the lower end of pivoting sleeve  41 , while drive element  50 , gear element  40  with gear wheels  43 , pivoting sleeve  41 , bearing  45 , and housing  44  would remain stationary. 
     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
     LIST OF REFERENCE SIGNS 
     
         
           1  Motor element 
           2   a,b,c  Force transmission 
           3  Actuator element 
           5   a,b  Linkage points 
           6  Decoupling device 
           8  Drive unit/ball screw/ball screw drive 
           8   a  First drive element/drive spindle/ball spindle 
           8   b  Second drive element/spindle nut/ball nut 
           10  Output piston 
           11   a,b  Rod seals 
           20  Ball spindle/spindle 
           31   a - f  Form-fitting elements/ball elements 
           32  Adapter element 
           33  Locking sleeve 
           33   a - f  Recesses in locking sleeve 
           34   a,b  Rotation sealing elements 
           35   a,b  Disk elements 
           36   a,b  Cover 
           37   a - f  C-rings 
           38   a - f  Sleeves 
           39  Sleeve 
           40  Gear 
           41  Pivoting sleeve 
           42  Shaft-hub connection 
           43  Gear wheel 
           44   a,b  Housing 
           45   a,b  Roller bearing 
           50  Drive element/electric motor 
           67  Recesses in output shaft 
           70  Actuator arrangement 
           72   a  Airframe 
           72   b  Aerodynamically active element