Patent Publication Number: US-8118264-B2

Title: Shape memory alloy actuator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of and claims priority to pending application Ser. No. 10/771,489 entitled AIRCRAFT SYSTEMS WITH SHAPE MEMORY ALLOY (SMA) ACTUATORS AND ASSOCIATED METHODS filed on Jun. 29, 2007, the entire contents of which is incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure is directed generally to aircraft systems with shape memory alloy (SMA) actuators, and associated methods. 
     BACKGROUND 
     Shape memory alloys (SMA) form a group of metals that have useful thermal and mechanical properties. If an SMA material such as Nitinol is deformed while in a martensitic state (low yield strength condition) and then heated to its transition temperature to reach an austenitic state, the SMA material will resume its austenitic shape. The rate of return to the austenitic shape depends upon the amount and rate of thermal energy applied to the component. 
     SMA actuators have proven useful in a wide variety of contexts, including aircraft-related contexts, to actuate particular devices. However, the SMA actuators have, in at least some instances, proved challenging to control. In other instances, the integration of SMA actuators has proved challenging. Accordingly, there exists a need in the art for improved techniques for integrating SMA actuators into aircraft systems, and controlling such actuators 
     SUMMARY 
     Aspects of the present disclosure are directed to aircraft systems with shape memory alloy (SMA) actuators, and associated methods. An aircraft system in accordance with a particular embodiment includes an airfoil and a deployable device coupled to the airfoil with a hinge. The hinge has a load path supporting the deployable device relative to the airfoil. The system can further include an SMA actuator coupled between the airfoil and the deployable device, with the actuator being moveable along a motion path different than the hinge load path between a first position with the deployable device deployed relative to the airfoil, and a second position with the deployable device stowed relative to the airfoil. In particular embodiments, the deployable device can include a secondary trailing edge device that depends from a primary trailing edge device. In further particular embodiments, the deployable device can include a noise-reduction hinge tab that deploys from a helicopter rotor. 
     In still another embodiment, the system can include an activatable link positioned between the actuator and the deployable device, with the link having an engaged configuration in which motion of the actuator is transmitted to the deployable device, and a disengaged configuration in which motion of the actuator is not transmitted to the deployable device. For example, in a particular embodiment, the activatable link includes a clutch. In another embodiment, the activatable link includes a rotary spline having first spline elements and second spline elements, with the first and second elements rotatable relative to each other over a first angular range, and rotating together over a second rotational range. 
     Other aspects are directed to methods for operating an airfoil. One method includes supporting a deployable device relative to an airfoil with a hinge having a hinge load path, and moving the deployable device relative to the airfoil by activating an SMA actuator coupled between the airfoil and the deployable device. Activating the actuator can include moving the actuator along a motion path different than the hinge load path. A method in accordance with another embodiment includes using a selectively activatable link to engage an SMA actuator with the deployable device and move the deployable device during a first mode of operation, and disengage the SMA actuator from the deployable device during a second mode of operation, while the actuator is activated. 
     The features, functions and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is partially schematic, isometric illustration of an overall system that includes an aircraft with one or more deployable devices installed in accordance with an embodiment of the disclosure. 
         FIG. 2A  is a partially schematic, bottom isometric illustration of a deployable device and an SMA actuator configured in accordance with an embodiment of the disclosure. 
         FIG. 2B  is a partially schematic top isometric illustration of an embodiment of the arrangement shown in  FIG. 2A , along with additional components. 
         FIG. 3  is a partially schematic, isometric illustration of a connection arrangement between an SMA actuator and a deployable device in accordance with an embodiment of the disclosure. 
         FIG. 4  is a partially schematic, cross-sectional illustration of an embodiment of the connection arrangement shown in  FIG. 3 . 
         FIG. 5  is a partially schematic, plan view illustration of an SMA actuator coupled to a deployable device with an activatable link in accordance with an embodiment of the disclosure. 
         FIG. 6  is a partially schematic, side elevation view of a deployable device coupled to an SMA actuator with a rack and pinion arrangement in accordance with another embodiment of the disclosure. 
         FIG. 7  is a top isometric illustration of a rotor blade that includes multiple deployable devices in accordance with an embodiment of the disclosure. 
         FIG. 8  is a partially schematic, isometric illustration of the deployable devices shown in  FIG. 7 . 
         FIG. 9  is a partially schematic, isometric illustration of an SMA actuator and associated connections with the deployable devices shown in  FIG. 8 . 
         FIGS. 10A-10D  illustrate phases of operation of the actuator arrangement shown in  FIGS. 7-9 . 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure is directed generally toward aircraft systems with shape memory alloy (SMA) actuators, and associated methods. Several details describing structures and/or processes that are well-known and often associated with aspects of the systems and methods are not set forth in the following description for purposes of brevity. Moreover, although the following disclosure sets forth several embodiments of representative aspects of the disclosure, several other embodiments can have different configurations or different components than those described in this section. For example, other embodiments may have additional elements and/or may delete several of the elements described below with reference to  FIGS. 1-10D . 
       FIG. 1  illustrates an aircraft  105  that can form a portion of an overall aircraft system  100 . The aircraft  105  includes a fuselage  101 , wings  110 , horizontal stabilizers  102 , and a vertical stabilizer  103 . Any of these components can include deployable devices, but for purposes of illustration, selected deployable devices are described further below in the context of trailing edge devices mounted to the wings  110 . The wings  110  can each include a leading edge  111 , a trailing edge  112 , and one or more trailing edge devices  118  (e.g., flaps  113 , ailerons, or flaperons) carried at the trailing edge  112 . The trailing edge devices  118 , which are themselves deployable relative to the wing  110 , can include further deployable devices that are driven by SMA actuators, as described in further detail below. For purposes of illustration, the following discussion is provided in the context of a trailing edge flap  113 . In other embodiments, some or all aspects of the components described below can be applied to other trailing edge devices  118 , and/or other non-trailing edge devices. 
       FIG. 2A  is a bottom isometric illustration of the aft portion of one of the trailing edge flaps  113  shown in  FIG. 1 . For purposes of illustration, portions of the external skin of the trailing edge flap  113  are removed. The trailing edge flap  113  includes a deployable device  120  (e.g., a “mini” or other secondary trailing edge device) that is carried toward the aft edge of the trailing edge flap  113 . The trailing edge flap  113  accordingly includes a deployable device receptacle  115  that receives the deployable device  120  in a stowed position. An SMA actuator  122  is coupled to the deployable device  120  to move it between its deployed position (shown in  FIG. 2 ) and its stowed position. Accordingly, the SMA actuator  122  can be connected between one or more flap brackets  114  carried by the trailing edge flap  113 , and one or more device brackets  121  carried by the deployable device  120 . 
       FIG. 2B  is a top isometric illustration of the arrangement shown in  FIG. 2A , along with additional components. These components can include return springs  135  (shown schematically) that bias the deployable device  120  toward either the stowed or deployed position (generally the stowed position). The arrangement can also include one or more thermoelectric modules  143  coupled to the SMA actuator  122  with thermally conductive couplings  144  (e.g., copper straps) to cool the actuator  122 . One or more position sensors  145  can be used for diagnostic purposes to identify the position of the deployable device  120 . 
       FIG. 3  is a partially schematic illustration of the aft portion of the trailing edge flap  113 , and the forward portion of the deployable device  120 . As shown in  FIG. 3 , a hinge pin  123  passes through, and is rotatable relative to, a plurality of flap brackets  114 . The hinge pin  123  can be fixedly clamped to the device brackets  121 . Accordingly, the hinge pin  123  can rotate with the deployable device  120 , and rotate relative to the trailing edge flap  113 . In other embodiments, this arrangement can be reversed. In any of these embodiments, the SMA actuator  122  can be carried within an axially extending opening of the hinge pin  123  to drive the deployable device  120  relative to the trailing edge flap  113 . Further details of a representative embodiment for arranging the SMA actuator  122  and the hinge pin  123  are described below with reference to  FIG. 4 . 
       FIG. 4  is a partially schematic, top cross-sectional illustration of embodiments of the system portions shown in  FIG. 3 . As shown in  FIG. 4 , the hinge pin  123  is fixedly attached to the device brackets  121 , and is rotatable within apertures of the flap brackets  114 . For purposes of illustration, bearings (e.g., ball bearings) and/or other features that support the relative rotation of the hinge pin  123  are not shown in  FIG. 4 . The SMA actuator  122  is received in an annular channel  146  of the hinge pin  123  and is attached at one end to an actuator support  125 . The opposite end of the SMA actuator  122  is attached to the hinge pin  123 , e.g., at an actuator/hinge pin connection  124 . When the SMA actuator  122  is heated (e.g., by applying an electrical current to the actuator  122 ), it tends to twist, as indicated by arrow A. Because one end of the SMA actuator  122  is fixed relative to the trailing edge flap  113 , the twisting motion of the SMA actuator  122  rotates the hinge pin  123  relative to the trailing edge flap  113 . This motion in turn rotates the deployable device  120  relative to the trailing edge flap  113 , as indicated by arrow D. In a particular arrangement, the deployable device  120  is in its stowed position when the SMA actuator  122  is inactive (e.g., cooled), and rotates to its deployed position when the SMA actuator is activated (e.g., heated). In other embodiments, the SMA actuator  122  can be configured in the opposite sense. 
     In any of the foregoing embodiments described above with reference to  FIGS. 3 and 4 , the deployable device  120  can be carried and supported relative to the trailing edge flap  113  via a hinge load path, and the deployable device  120  can be moved relative to the trailing edge flap  113  along a motion path that is different, at least in part, than the load path. For example, as shown in  FIG. 4 , the load path supporting the deployable device  120  relative to the trailing edge flap  113  includes the device brackets  121 , the hinge pin  123 , and the flap brackets  114 . The motion path between the deployable device  120  and the trailing edge flap includes the device brackets  121 , the hinge pin  123 , the SMA actuator  122 , and the actuator support  125 . An advantage of this arrangement is that the deployable device  120  will remain attached to the trailing edge flap  113 , even in the unlikely event of a complete failure of the SMA actuator  122 . For example, if the SMA actuator  122  were to fracture in such a way that it no longer provides mechanical continuity between the actuator support  125  and the hinge pin  123 , the flap brackets  114  still provide a continuous load path between the deployable device  120  and the trailing edge flap  113 . The load path provided by the flap brackets  114  can accordingly provide a fail-safe connection between the trailing edge flap  113  and the deployable device  120 . 
     One characteristic of SMA actuators that has proved challenging to designers is the fact that many SMA actuators have different response characteristics over different portions of their actuation ranges. For example, typical SMA actuators may move relatively slowly at the beginning of the actuation range, move more quickly in the middle of the range, and then slow down again toward the end of the range. Another characteristic of many SMA actuators is that, once activated, they require power to remain in their actuated positions. Particular embodiments of systems that address both of these challenges are described below. 
       FIG. 5  is a partially schematic, partial cross-sectional top plan view of the deployable device  120  coupled to the trailing edge flap  113  with one or more activatable links  526  configured in accordance with an embodiment of the disclosure. In this embodiment, two SMA actuators  522  are coupled between the trailing edge flap  113  and the deployable device  120 . In one particular embodiment, each SMA actuator  522  rotates in the same direction when actuated, and accordingly, the two SMA actuators  522  can provide a redundant actuation capability. In other embodiments, each of the SMA actuators  522  can rotate the deployable device  120  in opposite directions. Accordingly, one SMA actuator  522  can be used to deploy the deployable device  120 , and the other can be used to stow the deployable device  120 . In either of these arrangements, the SMA actuators  522  are connected to an actuator support  525  that is fixed relative to the trailing edge flap  113 . The motion of the SMA actuators  522  is then selectively transmitted to the deployable device  120  via two corresponding activatable links  526 . In a first mode of operation, the activatable links  526  transmit motion of the actuators  522  to the deployable device  120 , and in a second mode of operation, they do not, as described further below. 
     Each activatable link  526  can include a pin  523  connected at one end to a solenoid  527 , and at the other end to a clutch  528  that selectively engages with the neighboring SMA actuator  522 . Pin bearings  530  support the pin  523 , and actuator bearings  531  support the SMA actuator  522 . In a particular embodiment, the pin  523  is slidable relative to the device bracket  122  through which it passes, but is not rotatable relative to the device bracket  121 . For example, the hinge pin  523  can include splines that are slideably received in a corresponding opening in the device bracket  121 . When the clutch  528  is disengaged (as shown in  FIG. 5 ), the motion of each SMA actuator  522  is not transmitted to the deployable device  520 . When the solenoid  527  is activated, the clutch  528  engages, and the motion of the SMA actuator  522  is transmitted to the deployable device  120 . In this manner, the clutch  528  can be disengaged while the SMA actuator  522  is moving slowly (e.g., toward the start and/or end of its motion range), and can be engaged when the SMA actuator is moving more quickly (e.g., in the middle of its motion range). A controller  542  can automatically control the solenoids  527  (and therefore the state of the corresponding clutches  528 ) to take advantage of the quickest portion of the actuator motion range. 
     The controller  542  can also be coupled to a lock  529  that selectively engages the deployable device  120 , or a component fixedly attached to the deployable device  120  (e.g., the device bracket  121 ). Accordingly, the SMA actuators  522  can be used to drive the deployable device  120  to its deployed position, and then the lock  529  can engage the deployable device  120  and prevent (or at least restrict or inhibit) it from returning to its stowed position. The controller  542  can then discontinue power to the SMA actuators  522 , allowing the SMA actuators  522  to return to their “relaxed” state, which does not require power. When the deployable device  120  is to be returned to its stowed position, the lock  529  can be disengaged and the SMA actuators  522  and/or a spring device (e.g., the return springs  135  shown in  FIG. 2B ) can return the deployable device  120  to its stowed position. Further details of a representative arrangement for executing these processes are described with reference to  FIGS. 10A-10D . 
       FIG. 6  illustrates a deployable device  120  driven by an SMA actuator  622  in accordance with another embodiment of the disclosure. In one aspect of this embodiment, the deployable device  120  is carried by a trailing edge flap  113  having a flap lower surface  616  with a gap  615  through which the deployable device  120  emerges when deployed. The deployable device  120  has a guide pin  634  that moves along a guide track  617  carried by the trailing edge flap  113 , forming a sliding hinge arrangement. The deployable device  120  also includes a rack  632  that engages with a pinion  633  carried by the trailing edge flap  113 . A roller or other device (not shown in  FIG. 6 ) can apply a force to the deployable device  120  to keep it engaged with the pinion  633 . In another embodiment, the pinion  633  is positioned below the deployable device  120 , and gravity provides the force described above. In any of these embodiments, the pinion  633  can be connected to, and rotated by, the SMA actuator  622 . Accordingly, when the SMA actuator  622  is activated, it rotates the pinion  633 , which in turn moves the deployable device  120  into and out of the receptacle  615  by engaging with and driving the rack  632 . Any of the foregoing arrangements for selectively actuating the SMA actuator  622  and/or locking the SMA actuator  622  can be included in the arrangement shown in  FIG. 6 . In the unlikely event that the SMA actuator  622  fails, the deployable device  120  can remain secured to the trailing edge flap because the guide pin  634  remains engaged with the guide track  617 . 
     SMA actuator arrangements having characteristics similar at least in part to the embodiments described above can be coupled to other types of airfoils, and/or can have different arrangements in other embodiments. For example,  FIGS. 7-10D  illustrate portions of a rotor blade  710  having deployable devices  720  arranged in accordance with one such embodiment. Beginning with  FIG. 7 , the rotor blade  710  can include two deployable devices  720 , e.g., a first deployable device  720   a  which is visible in  FIG. 7 , and a second deployable device  720   b  described below with reference to  FIG. 8 . The deployable devices  720  can be deployed from the rotor blade  710  to reduce rotor noise, for example, during hover operations in environments having stringent noise attenuation requirements. The deployable devices  720  can be operated with rotary SMA actuators, as is described further below. 
       FIG. 8  is a partially schematic, isometric illustration of the first and second deployable devices  720   a ,  720   b  and associated hardware, removed from the rotor blade  710  shown in  FIG. 7 . The deployable devices  720   a ,  720   b  are supported relative to the rotor blade  710  with blade brackets  714 . Return springs  735  can return the deployable devices  720   a ,  720   b  to their stowed positions without the need for simultaneously activating a corresponding SMA actuator, as is described further below. 
       FIG. 9  is another isometric view of the arrangement shown in  FIG. 8 , with the first deployable device  720   a  removed to expose internal features of the arrangement. The arrangement includes a single SMA actuator  722  that is free to rotate with respect to the blade brackets  714 . The SMA actuator  722  is coupled toward opposing ends to corresponding drivers  736  (including a first driver  736   a  that is visible in  FIG. 9  and a second driver  736   b  that is not visible in  FIG. 9 ). A connector shaft  737  provides the connection between the SMA actuator  722  and the drivers  736   a ,  736   b . The connector shaft  737  also extends through the blade brackets  714  so that if the SMA actuator  722  fails, the corresponding deployable device is still carried in position relative to the rotor blade  710  ( FIG. 7 ). 
     In a particular embodiment, each driver  736  includes a spline  738  having at least one first spline element  739  that selectively engages with a corresponding spline element carried by one of the deployable devices  720   a ,  720   b . As the SMA actuator  722  twists about its longitudinal axis, the first and second drivers  736   a ,  736   b  rotate in opposite directions. During at least a portion of this relative movement, the drivers  736   a ,  736   b  move the corresponding deployable devices  720   a ,  720   b  in opposite directions. The motion of the two devices  720   a ,  720   b  is coordinated by a motion coordinator  750 . In a particular embodiment, the motion coordinator  750  can include first and second opposing coordination arms  751   a ,  751   b , each of which is carried by a corresponding one of the deployable devices  720   a ,  720   b  (e.g., the second coordination arm  751   b  is carried by the second deployable device  720   b ). Each coordination arm  751   a ,  751   b  includes a rack  752  that engages with a centrally located pinion  753 . When one of the deployable device,  720   a ,  720   b  moves, the pinion  753  transmits the motion to other deployable device  720   a ,  720   b  so as to move the other deployable device by the same amount in the opposite direction. 
       FIGS. 10A-10D  are partially schematic, cross-sectional illustrations of the rotor  710 , showing the SMA actuator  722  and the second driver  736   b  of  FIG. 9A  during various phases of operation. As shown in  FIG. 10A , the second driver  736   b  includes a spline  738  having a first spline element  739 . As the SMA actuator  722  twists, the first spline element  739  rotates as indicated by arrow A until it engages a corresponding second spline element  740  carried by the second deployable device  720   b  ( FIG. 10B ). If the first driver  736   a  ( FIG. 9 ) has not yet engaged with a corresponding second spline element carried by the first deployable device  720   a  ( FIG. 9 ), then in a particular embodiment, the SMA actuator  722  continues to twist without further rotating the second driver  736   b . When, for both the first and second drivers  736   a ,  736   b , the first spline element  739  engages the corresponding second spline element  740  (as shown in  FIG. 10C ), continued twisting by the SMA actuator  722  causes the first deployable device  720   a  and the second deployable device  720   b  to rotate away from each other, as indicated by arrows D. This motion is coordinated by the motion coordinator  750  described above with reference to  FIG. 9 . 
     At the end of the relative motion between the first and second deployable devices  720   a ,  720   b , a lock  729  can deploy a lock element  741 , as indicated by arrow L 1 , to hold the deployable devices  720   a ,  720   b  in their deployed positions or at least inhibit motion of the deployable devices  720   a ,  720   b . With the lock element  741  in this first or locked position, the SMA actuator  722  can unwind or relax, as indicated by arrow R in  FIG. 10D . At the same time, the deployed lock element  741  can maintain the first and second deployable devices  720   a ,  720   b  in their deployed positions. When it is desired to retract the deployable devices  720   a ,  720   b , the lock element  741  can retract to a second or unlocked position, as indicated by arrow L 2  in  FIG. 10D . The return springs  735  (one of which is visible in  FIG. 10D ) can then return the deployable devices  720   a ,  720   b  to the configuration shown in  FIG. 10A . 
     One feature of several of the foregoing embodiments is that the motion path and load path between the deployable device and the structure from which it depends are separate. An advantage of this arrangement is that the SMA actuator can fail, without causing the deployable device to separate from the structure that carries it. In a particular arrangement, the SMA actuator can be housed, at least in part, in an axial channel of a hinge pin that connects the deployable device to an associated support structure. This configuration can provide the added advantage of a nested, compact arrangement. 
     Another feature of at least some of the foregoing embodiments is that the SMA actuator can be selectively coupled to and decoupled from the deployable device, for example, with a clutch, a selectively engaged spline, or other arrangement. An advantage of these arrangements is that the deployable device can be selectively coupled to the SMA actuator during particular motion phases of the SMA actuator. For example, the deployable devices can be coupled to the SMA actuators only during those portions of the SMA actuator&#39;s motion that are at or above a selected threshold speed. This arrangement can avoid low speed deployment or retraction of the deployed devices. 
     Still another feature of at least some of the foregoing embodiments is that they can include a selectively deployable lock that keeps the deployed device in a particular position (e.g., a stowed position) even if the SMA actuator is unpowered. This arrangement can reduce the amount of power consumed by the SMA actuator. It can also reduce the time required to reposition the deployed device. For example, when the deployed device is provided with a return spring or other return mechanism, it can move to the stowed position more quickly than if the return motion were controlled by the cooling rate of the SMA actuator. 
     Representative materials suitable for manufacturing SMA actuators in accordance with any of the embodiments described above include Nitinol. In a particular embodiment, the Nitinol can be 55% by weight nickel and 45% by weight titanium. In a further particular embodiment, the Nitinol can have an equi-atomic composition, with 50% nickel molecules and 50% titanium molecules. Suitable materials are available from Special Metals Corp. of New Hartford, N.Y., and Wah Chang of Albany, Oreg. The material is then machined, heat treated and trained. The resulting structure can display shape memory effects, including a two-way shape memory effect. Further details of suitable manufacturing processes and resulting structures are included in pending U.S. Application Publication US2005-0198777, assigned to the assignee of the present application and incorporated herein by reference. Other suitable materials include Nitinol with 57% or 60% nickel by weight, and/or nickel/titanium alloys with additional constituents (e.g., palladium and/or platinum) to increase the transition temperature, and/or to attain other material properties. 
     From the foregoing, it will be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made in other embodiments. For example, the SMA actuators and couplings described above can have other features and arrangements in other embodiments. The SMA actuators can be used to drive devices other than the mini trailing edge devices and rotor tabs described above, including other secondary trailing edge devices that are attached to a primary trailing edge device (e.g., a double-slotted trailing edge device). In still further embodiments, the SMA actuators can have an actuation motion path other than the rotary or twisting motion path described above (e.g., a linear motion path). 
     Certain aspects described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, the lock arrangement described above with reference to  FIGS. 7-10D  can be modified and incorporated into the device shown in  FIG. 5 . Further, while advantages associated with certain embodiments have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages. Accordingly, embodiments of the disclosure are not limited except as by the appended claims.