Patent Publication Number: US-2022227481-A1

Title: Actuation systems for control surfaces for aircraft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Patent Application No. 21305049.5 filed Jan. 18, 2021, the entire contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to control surfaces for aircraft which are in hinged connection with the aircraft&#39;s wings or stabilizers, and in particular, actuation systems for those control surfaces. 
     BACKGROUND 
     It is known that the design and innovation in the field of aircraft wings and stabilizers is leading to a decrease in thickness of those wings and stabilizers. Such a decrease leads to those wings and stabilizers having an increased efficiency. A consequence of the decrease in thickness is that there is a decreasing amount of space within the wings and stabilizers within which aircraft systems can be located. One such system is an actuation system for a control surface. Such systems will include at least an actuator and an associated hydraulic system, and are typically located in a void in the wing or stabilizer to which the control surface is hinged. 
     A known approach to limiting the space required for an actuation system for a control system is to arrange the actuator to act in a direction approximately parallel to the leading or trailing edge of the control surface, and to employ a bell crank or substantially L shaped lever and a push/pull rod to transmit movement/force from the actuator to the control surface. This arrangement keeps the actuation system close to the edge of the wing or stabilizer with the result that the void required to house the actuation system can be minimised. 
     SUMMARY 
     According to a first aspect of the present disclosure there is provided an actuation system for a control surface for an aircraft in which the aircraft comprises a wing or stabilizer to which a control surface is hinged, the wing or stabilizer comprises a sub-structure, and the control surface has a trailing edge, in which the actuation system comprises a first, second, third and fourth actuator, a first and second bell crank, and at least one push pull rod system, each of the first and second bell cranks comprises a first and a second crank arm, the first and second crank arms intersect with and are joined to each other at an intersection, the first and second crank arms extend from the intersection at an angle to each other, the first bell crank is pivotally connected to the sub-structure by a first pivot extending through the first bell crank&#39;s intersection, and the second bell crank is pivotally connected to the sub-structure by a second pivot extending through the second bell crank&#39;s intersection, the first and third actuators have first and second ends, the first ends of the first and third actuators are connected to the sub-structure, the second end of the first actuator is connected to the first crank arm of the first bell crank at a first connection position, the second end of the third actuator is connected to the first crank arm of the first bell crank at a third connection position, the second and fourth actuators have first and second ends, the first ends of the second and fourth actuators are connected to the sub-structure, the second end of the second actuator is connected to the first crank arm of the second bell crank at a second connection position, the second end of the fourth actuator is connected to the first crank arm of the second bell crank at a fourth connection position, and in the first bell crank the distance between the first connection position and the first pivot is greater than the distance between the third connection position and the first pivot, and in the second bell crank the distance between the second connection position and the second pivot is greater than the distance between the fourth connection position and the second pivot. 
     It is to be understood that all dimensions that are between connection positions and pivots referenced herein are, unless otherwise specified, dimensions between the geometric centres of the connection position and the pivot connecting the bell crank with the substructure. 
     In an embodiment of any of the above embodiments, the first and second crank arms and the intersection of a bell crank are all portions of a single continuous element that forms the bell crank. In such embodiments, the first crank arm is the portion of the bell crank that extends between the pivotal connection of the bell crank to the substructure and the connection of the bell crank with the second ends of the first and third or second and fourth actuators; and the second crank arm is the portion of the ball crank that extends between the pivotal connection of the bell crank to the substructure and the connection of the bell crank with a push pull rod system. The outside perimeter of the bell crank, in the plane in which the bell crank rotates may have, but not be limited to, a substantially L, J or triangular shape. 
     In an alternative embodiment of any of the above embodiments the first and second crank arms are separate arms that extend from the intersection with the first and second crank arms extending from the intersection in different directions. 
     In such embodiments, the first and second crank arms may be integral with each other (for example a single casting or single piece of material, or they may be connected to each other at the intersection using appropriate connection means. Appropriate connection means include, but are not limited to nuts and bolts, adhesive, or welding. 
     In an embodiment of the above embodiment, in the first bell crank the ratio of the distance between the first connection position and the first pivot and the distance between the third connection position and the first pivot is around 4:7; and in the second bell crank the ration of the distance between the second connection position and the second pivot and the distance between the fourth connection position and the second pivot is around 4:7. In an alternative embodiment, in the first bell crank the ratio of the distance between the first connection position and the first pivot and the distance between the third connection position and the first pivot is around 4:7; or in the second bell crank the ration of the distance between the second connection position and the second pivot and the distance between the fourth connection position and the second pivot is around 4:7. 
     The advantage of the different distances between the connection positions and the pivot on a bell crank is that the two actuators each have a different lever arm around the pivot connecting the bell crank and the sub-frame. This allows the actuators to be of different specifications and hence of different size and weight. The use of four actuators also has the advantage that the overall dimensions of each of the four actuators (especially the outer diameter of the actuators) is smaller than if only two actuators (one attached to each ball crank) were used. 
     In an embodiment of any of the above embodiments the second crank arms of the first and second bell cranks are each connected to a push pull system, and each push pull system is also connected to the control surface. 
     In some embodiments each push pull system comprises push pull rod, one end of the push pull rod is connected to the control surface and the other end is connected to a second crank arm. 
     In some alternative embodiments of the present disclosure there is only one push pull system to which the second crank arms of both of the first and second bell cranks are connected. In these embodiments the push pull system is adapted to translate the rotational movement of the second crank arms of the first and second bell cranks into a combined linear movement which can be transmitted to the connection between the push pull system and the control surface. In some embodiments the push pull system comprises at least one push pull rod, and one end of a push pull rod is connected to the control surface. 
     In an embodiment of any of the above embodiments at least one connection between the first ends of the first, second, third and fourth actuator and the sub-frame, and/or between the second ends of the first and third actuator and the first bell crank, and/or between the second ends of the second and fourth actuator and the second bell crank, and/or between the second crank arm of the first and second bell cranks and the push pull system, and/or between the push pull system and the control surface, is a connection which allows the connected elements to rotate relative to each other. This ability to rotate relative to each other allows the various elements to adjust their relative alignment as the bell cranks rotate. In some embodiments, the or each connection is a pivotal connection which allows one or both of the connected elements to rotate about the connection, for example a pin or shaft. 
     In an embodiment of any of the above embodiments the first bell crank is configured so that there is an angle of greater than 0 and less than 360 degrees between a line extending from the first connection position to the first pivot and a line extending from the third connection position to the first pivot; and the second bell crank is configured so that there is an angle of greater than 0 and less than 360 degrees between a line extending from the second connection position to the second pivot and a line extending from the fourth connection position to the second pivot. In an alternative embodiment of any of the above embodiments the first bell crank is configured so that there is an angle of greater than 0 and less than 360 degrees between a line extending from the first connection position to the first pivot and a line extending from the third connection position to the first pivot; or the second bell crank is configured so that there is an angle of greater than 0 and less than 360 degrees between a line extending from the second connection position to the second pivot and a line extending from the fourth connection position to the second pivot. It is to be understood that the lines between connection positions and pivots are between the geometric centres of the connection of the connection positions and the pivot. 
     In an embodiment of any of the above embodiments the angle between the lines is an included angle of greater than 0 degrees and less than 90, 80, 70, 60 or 45 degrees. The angle allows the actuators connected to a bell crank to have different orientations. The angle also allows movement of the second end of each actuator to be in a direction close to tangential to the arc swept out by the connection position for that actuator when the bell crank rotates around its pivot. This increases efficiency in the transmission of the movement/force from the actuators to the bell crank. The angle between the lines may also assist in preventing the actuators from colliding/interfering with each other as they reorientate when the bell crank is pivoting around its pivot. 
     In an embodiment of any of the above embodiments the first crank arm of one or both of the first and second bell cranks is comprised of a first and a second arm. This can lead to a lighter bell crank with the same mechanical characteristics than a bell crank where the first crank arm is solid and large enough to have connection positions with a desired angle between the above referenced lines. 
     In an embodiment of any of the above embodiments the first and third actuators are so orientated relative to the trailing edge of the control surface that the second ends of the first and third actuators move away from the first ends of those actuators in a direction which includes an element of movement in a first direction along the trailing edge of the control surface, and the second and fourth actuators are so orientated relative to the trailing edge of the control surface that the second ends of the second and fourth actuators move away from the first ends of those actuators in a direction which includes an element of movement in a direction along the trailing edge of the control surface which is opposite to the first direction along the trailing edge. 
     In an embodiment of any of the above embodiments the first and third actuators and the second and fourth actuators are so deployed that movement of the second ends of the first and third actuators away from their first ends is movement in substantially the opposite direction to movement of the second ends of the second and fourth actuators away from their first ends. 
     The above embodiments allow the first and second bell cranks to be located next to each other on the sub-frame and to be caused to rotate in opposite directions when the second ends of all of the actuators are moving in the same direction relative to their first ends, that is when the piston of each actuator is extending or retracting. 
     In an embodiment of any of the above embodiments the first and second actuators have the same specifications as each other, and the third and fourth actuators have the same specifications as each other. This allows the forces acting on the first and second bell cranks to be equal when the pistons of each actuator are all extending or all retracting. 
     In an embodiment of any of the above embodiments the stall load of each of the first and second actuators is greater than the stall load of each of the third and fourth actuators. In some embodiments the stall load of each of the third and fourth actuators is about half the stall load of each of the first and second actuators respectively. 
     In an embodiment of any of the above embodiments the first, second, third and fourth actuators are specified so that the stall load for each actuator is selected to produce the same surface stall hinge on the control surface for each actuator. The surface stall hinge and the stall load for an actuator are related by the gear ratio between the actuator and the surface. 
     In an embodiment of any of the above embodiments at least one of the first, second, third and fourth actuators is a hydraulic two way actuator. 
     In an embodiment of any of the above embodiments the actuator system further comprises first, second and third hydraulic manifold blocks, in which each of the first, second, third and fourth actuators are hydraulic two way actuators, the first actuator is in hydraulic communication with the first hydraulic manifold block, the second actuator is in hydraulic communication with the second hydraulic manifold block, and the third and fourth actuators are in hydraulic communication with the third hydraulic manifold block. 
     This configuration is desirable because it uses only three hydraulic manifold blocks rather than four to control four actuators. This configuration is advantageous because: it results in weight savings and a reduced number of parts; the use of three hydraulic manifolds (and thus the three hydraulic systems typically found in an aircraft) makes the actuation system safer and allows the aircraft not to use some safety features of the aircraft such as damping of the control surface; and the use of three hydraulic manifolds rather than two allows each hydraulic manifold to be thinner than if only two manifolds were used. A further advantages is that the load distribution between the first and second, and third and fourth actuators is uniform. 
     In an embodiment of any of the above embodiments the first, second and third hydraulic manifold blocks all have the same specification. This is advantageous because it limits the number of spare parts that need to be held in case of maintenance or breakdown of the actuator system of the present disclosure. This arrangement is possible because the arrangement of the third and fourth actuators having a connection position closer to the pivot of the bell crank than the first and second actuators allows the second ends of the third and fourth actuators to travel less distance and to travel more slowly than the second ends of the first and second actuators. Furthermore, because the third and fourth actuators have a smaller stall load than the first and second actuators, the outer diameter of the third and fourth actuators is smaller than that of the first and second actuators and thus the cross sectional area of the third and fourth actuators is smaller than that of the first and second actuators. All of these factors have the effect that the rate of flow of hydraulic fluid required for the third and fourth actuators is lower than that required for the first and second actuators. This allows the third hydraulic manifold to serve two actuators and remain of the same size and specification as the first and second hydraulic manifolds. 
     In an embodiment of any of the above embodiments the actuators of the actuation system are such that the first and second actuators each have an external diameter of 70 mm and a stall load of around 5000 Nm, and the third and fourth actuators each have an external diameter of 60 mm and a stall load of around 2500 Nm with the actuators having a nominal available hydraulic pressure of 4000 psi (27.579 MPa). 
     According to a second aspect of the present disclosure there is provided an aircraft comprising a control surface and a control surface actuation system according to the first aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be further described and explained by way of example with reference to the accompanying drawings in which 
         FIG. 1  shows an aircraft; 
         FIG. 2  shows a schematic representation of an embodiment of an actuation system according to the present disclosure; 
         FIG. 3A  shows a detail of the actuation system of  FIG. 2 ; and 
         FIG. 3B  shows a detail of an alternative actuation system according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , an aircraft  2  has a fuselage  4 , a pair of wings  6 , a pair of horizontal stabilizers  8  and a vertical stabilizer  10 . Each of the wings  6 , horizontal stabilizers  8  and a vertical stabilizer  10  comprise at least one control surface  6   c ,  8   c , and  10   c  respectively. 
     With reference to  FIG. 2 , a schematic view of a control surface  6   c  is shown. The arrangement of  FIG. 2  can equally be applied to control surfaces  8   c  and or  10   c . A number of such arrangements may be present in any wing  6  or stabilizer  8 ,  10 . 
     The control surface  6   c  is connected to a wing  6  via a pair of hinges  12 . The hinges  12  have a common hinge line (not shown) which is substantially parallel to the control surface edge  14 . The control surface  6   c  may rotate about that hinge line. 
     The wing  6  is comprised of an outer skin (not shown) and a sub-frame (not shown). Within the outer skin and mounted onto the sub-frame is an actuator system  16 . The actuator system  16  includes first, second, third and fourth actuators  18 ,  20 ,  22  and  24 , first and second bell cranks  26 ,  28 , and a push pull system  30 . 
     The first actuator  18  is a double acting hydraulic linear actuator with a rear mount  32  which is pivotally connected to the wing&#39;s sub-frame, a cylinder  34 , and a piston  36  which is pivotally connected to the first bell crank  26  at a first connection position by a pivot  38 . The first actuator  18  is powered from a hydraulic manifold block  40  via a first flow line  42  and a second flow line  44 . The hydraulic manifold block  40  is in hydraulic communication with a first hydraulic system which includes a fluid reservoir and hydraulic pumps elsewhere in the aircraft (not shown). 
     The second actuator  20  is a double acting hydraulic linear actuator with a rear mount  46  which is pivotally connected to the wing&#39;s sub-frame, a cylinder  48 , and a piston  50  which is pivotally connected to the second bell crank  28  at a second connection position by a pivot  52 . The second actuator  20  is powered from a hydraulic manifold block  54  via a first flow line  56  and a second flow line  58 . The hydraulic manifold block  54  is in hydraulic communication with a second hydraulic system which includes a fluid reservoir and hydraulic pumps elsewhere in the aircraft (not shown). 
     The third actuator  22  is a double acting hydraulic linear actuator with a rear mount  60  which is pivotally connected to the wing&#39;s sub-frame, a cylinder  62 , and a piston  64  which is pivotally connected to the first bell crank  26  at a third connection position by a pivot  66 . 
     The fourth actuator  24  is a double acting hydraulic linear actuator with a rear mount  68  which is pivotally connected to the wing&#39;s sub-frame, a cylinder  70 , and a piston  72  which is pivotally connected to the second bell crank  28  at a fourth connection position by a pivot  74 . 
     The third and fourth actuators  22 ,  24  are both powered from a hydraulic manifold block  76 . The hydraulic manifold block has a first port which connects with the third and fourth actuators  22 ,  24  via first flow lines  78 ,  82  respectively, and a second port which connects with the third and fourth actuators  22 ,  24  via second flow lines  80 ,  84  respectively. The hydraulic manifold block  76  is in hydraulic communication with a third hydraulic system which includes a fluid reservoir and hydraulic pumps elsewhere in the aircraft (not shown). 
     With reference to  FIG. 3A  and with reference with  FIG. 2 , the first bell crank  26  is comprised of a plate of material  120  (in some examples the bell crank  26  may be a cast material, in some examples the bell crank  26  may be cut from a sheet of plate material). The outside shape or parameter of the plate  120  is configured to surround apertures for receiving pivots  86 ,  38 ,  66  and  108 . The pivot  86  is connected to the sub-frame of the wing  6  and allows the bell crank  26  to rotate clockwise or anti-clockwise about pivot  86 . 
     The apertures for pivots  38  and  66  are both spaced from the aperture for pivot  86  in the same general direction. The directions of pivots  38  and  66  from the pivot  86  are represented by dashed lines  114  for pivot  38  and  116  for pivot  66 . The dashed lines  114  and  116  are rotationally separated by around 38 degrees. Pivot  38  is at a greater distance from pivot  86  than pivot  66 . 
     The aperture for pivot  108  is spaced from the pivot  86  in the direction indicated by the dashed line  118 . The angle between the direction of dashed line  118  and of dashed line  114  is around 110 degrees. 
     A flange  122  extends around the periphery of the plate  120 . The flange  122  stiffens the plate  120 . 
     The distance between the first connection position (the centre of pivot  38 ) and the centre of the pivot  86  is distance D 1  and the distance between the third connection position (the centre of pivot  66 ) and the centre of the pivot  86  is distance D 3 . D 1  is greater than D 3 . In some embodiments the ratio of D 1  to D 3  is around 4:7. 
     The second bell crank  28  is comprised of a plate of material  124  (in some examples the second bell crank  28  may be a cast material, in some examples the second bell crank  28  may be cut from a sheet of plate material). The outside shape or parameter of the plate  124  is configured to surround apertures for receiving pivots  94 ,  52 ,  74  and  106 . The pivot  94  is connected to the sub-frame of the wing  6  and allows the bell crank  28  to rotate clockwise or anti-clockwise around the pivot  94 . 
     The apertures for pivots  52  and  74  are both spaced from the aperture for pivot  94  in the same general direction. The directions are represented by dashed lines  126  for pivot  52  and  128  for pivot  74 . The dashed lines  126  and  128  are rotationally separated by around 38 degrees. Pivot  52  is at a greater distance from pivot  94  than pivot  74 . 
     The aperture for pivot  106  is spaced from the pivot  94  in the direction indicated by the dashed line  132 . The angle between the direction of dashed line  132  and of dashed line  126  is around 110 degrees. 
     A flange  126  extends around the periphery of the plate  124 . The flange  126  stiffens the plate  124 . 
     The distance between the first connection position (the centre of pivot  52 ) and the centre of pivot  84  is distance D 2  and the distance between the fourth connection position (the centre of pivot  96 ) and the centre of pivot  94  is distance D 4 . D 2  is greater than D 4 . In some embodiments the ratio of D 2  to D 4  is around 4:7. 
     A push pull system  30  is pivotally attached to the second bell crank  28 . 
     With reference to  FIG. 3B  and with further reference to  FIG. 2  a second arrangement for the first and second bell cranks  26 ,  28  is shown. The first bell crank  26  is comprised of first and second arms  90 ,  92  which intersect at the intersection  93 . The first arm  90  is comprised of arms  90   a  and  90   b  which mechanically effectively comprise a single arm  90 . The pistons  36 ,  64  of the first and third actuators  18 ,  22  are fixed to arms  90   a ,  90   b  at the first and third connection positions via pivots  38 ,  66  respectively. The first bell crank  26  is pivotally connected to the wing&#39;s sub-frame via a pivot  86  which extends through the intersection  93 . The distance between the first connection position (the centre of pivot  38 ) and the centre of the pivot  86  is distance D 1  and the distance between the third connection position (the centre of pivot  66 ) and the centre of the pivot  86  is distance D 3 . D 1  is greater than D 3 . In some embodiments the ratio of D 1  to D 3  is around 4:7. 
     The push pull system  30  is pivotally attached to the second arm  92  of the first bell crank  26  by pivot  88 . 
     The second bell crank  28  is comprised of first and second arms  98 ,  100  which intersect at the intersection  101 . The first arm  98  is comprised of arms  98   a  and  98   b  which mechanically effectively comprise a single arm  98 . The pistons  50 ,  72  of the second and fourth actuators  20 ,  24  are fixed to arms  98   a ,  98   b  at the second and fourth connection positions via pivots  52 ,  74  respectively. The second bell crank  28  is pivotally connected to the wing&#39;s sub-frame via a pivot  94  which extends through the intersection  101 . The distance between the second connection position (the centre of pivot  52 ) and the centre of the pivot  94  is distance D 2  and the distance between the fourth connection position (the centre of pivot  74 ) and the centre of the pivot  94  is distance D 4 . D 2  is greater than D 4 . In some embodiments the ratio of D 2  to D 4  is around 4:7. 
     The push pull system  30  is pivotally attached to the second arm  100  of the second bell crank  28  by pivot  96 . 
     Each push pull system  30  is comprised of a push pull rod  102  which is pivotally connected to the first or second bell crank  26 ,  28 . The push pull rod  102  extends between its connection to the first or second bell crank  26  or  28  via pivot  108  or  106  and a pivot  110  or  112  which connects the push pull rod  102  with the control surface  6   c . The pivot  110  or  112  is located within the structure of control surface  6   c  in such a position that pushing or pulling the pivot  110  or  112  with the push pull rod  102  causes the control surface  6   c  to rotate about the hinge line of hinges  12 . 
     Each of the connections between the actuators and the sub-frame, between the actuators and the bell cranks, between the push pull rods and the bell cranks, and between the push pull rod and the control surface are all pivotal connections. This allows a reorientation of those various elements relative to each other when the first and second bell cranks  26 ,  28  rotate relative to the sub-frame. 
     When the actuator system  16  is actuated so as to cause push pull rod  102  to push the pivot  110 , a control system (not shown) causes hydraulic fluid to: 
     (i) pass from hydraulic manifold block  40  into the cylinder  34  of the first actuator  18  via first flow line  42  and from the cylinder  34  to the hydraulic manifold block  40  via the second flow line  44 ; 
     (ii) pass from hydraulic manifold block  54  into the cylinder  48  of the second actuator  20  via first flow line  56  and from the cylinder  48  to the hydraulic manifold block  54  via the second flow line  58 ; 
     (iii) pass from hydraulic manifold block  76  into the cylinder  62  of the third actuator  22  via first flow line  78  and from the cylinder  62  to the hydraulic manifold block  76  via the second flow line  80 ; and 
     (iv) pass from hydraulic manifold block  76  into the cylinder  70  of the fourth actuator  24  via first flow line  82  and from the cylinder  70  to the hydraulic manifold block  76  via the second flow line  84 . 
     This flow of hydraulic fluid causes: 
     (a) the pistons  36  and  64  of the first and third actuators  18 ,  22  to cause the first bell crank  26  to rotate in an anticlockwise direction (as seen in  FIG. 2 ) around pivot  86 ; and 
     (b) the pistons  50  and  72  of the second and fourth actuators  20 ,  24  to cause the second bell crank  28  to rotate in a clockwise direction (as seen in  FIG. 2 ) around pivot  94 . 
     The rotation of the first and second bell cranks  26 ,  28  causes the pivots  108  and  106  to move towards the control surface  6   c  and hence push pull rod  102  pushes pivot  110  or  112  causing control surface  6   c  to rotate about the hinges  12  in a first direction. 
     When the actuator system  16  is actuated so as to cause push pull rod  102  to pull the pivot  110 , a control system (not shown) causes hydraulic fluid to: 
     (i) pass from hydraulic manifold block  40  into the cylinder  34  of the first actuator  18  via second flow line  44  and from the cylinder  34  to the hydraulic manifold block  40  via the first flow line  42 ; 
     (ii) pass from hydraulic manifold block  54  into the cylinder  48  of the second actuator  20  via second flow line  58  and from the cylinder  48  to the hydraulic manifold block  54  via the first flow line  56 ; 
     (iii) pass from hydraulic manifold block  76  into the cylinder  62  of the third actuator  22  via second flow line  80  and from the cylinder  62  to the hydraulic manifold block  76  via the first flow line  78 ; and 
     (iv) pass from hydraulic manifold block  76  into the cylinder  70  of the fourth actuator  24  via second flow line  84  and from the cylinder  70  to the hydraulic manifold block  76  via the first flow line  82 . 
     This flow of hydraulic fluid causes: 
     (a) the pistons  36  and  64  of the first and third actuators  18 ,  22  to cause the first bell crank  26  to rotate in a clockwise direction (as seen in  FIG. 2 ) around pivot  86 ; and 
     (b) the pistons  50  and  72  of the second and fourth actuators  20 ,  24  to cause the second bell crank  28  to rotate in an anticlockwise direction (as seen in  FIG. 2 ) around pivot  94 . 
     The rotation of the first and second bell cranks  26 ,  28  causes the pivots  108  and  106  to move away from control surface  6   c  causing push pull rod  102  to pull pivot  110  or  112  causing control surface  6   c  to rotate about the hinges  12  in a second direction opposite to the first direction. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure. 
     Various aspects of the actuation systems disclosed in the various embodiments may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described above. This disclosure is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Although particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the description as a whole.