Abstract:
An actuator includes a capturing part, a retained part and a heating element which applies heat to the retained part or the capturing part responsive to selective application of power to the at least one heating element. The capturing part attaches to a first object and has a first coefficient of thermal expansion. The retained part attaches to a second object and has a second coefficient of thermal expansion. The retained part is insertable into the capturing part in a first state of the actuator. The retained part is held in contact with the capturing part via an interference fit to hold the first and second objects proximate to each other in a second state. The retained part is ejected from the capturing part in a third state. Applying heat via the heating element causes a transition between the second and the first or third states of the actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of prior-filed, co-pending U.S. Provisional Application No. 61/530,236, filed on Sep. 1, 2011, the entire contents of which are hereby incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Example embodiments generally relate to releasable electro-mechanical actuators and, more particularly, relate to a release actuator employing components with different coefficients of thermal expansion. 
       BACKGROUND 
       [0003]    Releasable actuators of many kinds have been used to selectively hold parts together. Such actuators may range from very simple to more complex designs and may have many different release mechanisms. Given the wide variance in design and materials that have been employed, it will be appreciated that there is a corresponding wide variance in the costs, reliability characteristics, and performance characteristics of such devices. However, for certain operating environments, reliability and performance cannot be sacrificed. 
         [0004]    For example, submerged applications and/or flight applications (including space flight) may place actuators in critical situations where the cost of failure can be quite high, and the environment can also be quite inhospitable. Instrumentation, satellite payloads, and other equipment that may employ or be used in connection with such actuators may need to be reliably operable, but also operate without introducing significant shock. At the same time, simplicity of design and part economy may also be important. However, production of an actuator balancing all of the design factors mentioned above has been a significant challenge. 
       BRIEF SUMMARY OF SOME EXAMPLES 
       [0005]    Accordingly, some example embodiments include a relatively simple and reliable actuator. Some example embodiments employ two parts that have different coefficients of thermal expansion (CTE). Accordingly, for example, the parts releasably fit together at a first temperature and then, subsequent to changing the temperature, one of the parts may be captured within by the other. Release of the captured part may then be achieved by changing the temperature back. The released part may then be ejected (e.g., via a kickoff spring) and, in some cases, a tell-tale or other indicator of release may be triggered. 
         [0006]    In one example embodiment, an actuator is provided. The actuator may include a capturing part, a retained part and at least one heating element that is disposed to apply heat to the retained part or the capturing part responsive to selective application of power to the at least one heating element. The capturing part is attachable to a first object and is formed of a material having a first coefficient of thermal expansion. The retained part is attachable to a second object and is formed of a material having a second coefficient of thermal expansion. The retained part is insertable into the capturing part in a first state of the actuator. The retained part is held in contact with the capturing part via an interference fit to hold the first and second objects proximate to each other in a second state of the actuator. The retained part is ejected from the capturing part in a third state of the actuator. The first and second coefficients of thermal expansion are different such that applying heat via the at least one heating element causes a transition between the second state of the actuator and either of the first or third states of the actuator. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0007]    Having thus described example embodiments of the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
           [0008]      FIG. 1  is a top perspective view of a capturing part of an actuator according to an example embodiment; 
           [0009]      FIG. 2  is a bottom perspective view of the capturing part of  FIG. 1  according to an example embodiment; 
           [0010]      FIG. 3  is a top perspective view of a retained part of the actuator of  FIG. 1  according to an example embodiment; 
           [0011]      FIG. 4  illustrates a cross section view of the actuator according to an example embodiment; and 
           [0012]      FIG. 5  illustrates an example embodiment of the actuator of  FIGS. 1-4  with optional modifications applied thereto according to another example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Some example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all example embodiments are shown. Indeed, the examples described and pictured herein should not be construed as being limiting as to the scope, applicability or configuration of the present disclosure. Rather, these example embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. 
         [0014]    Some example embodiments may enable the provision of a highly reliable actuator that has a relatively simple construction and few moving parts. The actuator may have very low shock and operate with low power and low current. The actuator may employ a capturing part and a retained part that is to be held by the capturing part. The capturing part and retained part may each have a different coefficient of thermal expansion (CTE) so that temperature changes are used to alternately capture and release the retained part in the capturing part. 
         [0015]    The simple construction may provide reliability and simplicity while still keeping costs relatively low. Some embodiments may be used in connection with low power heating elements to enable remote actuation of the actuator. The reliability and performance of the actuator may make it well suited for use in relatively harsh environments such as on aircraft, spacecraft, satellites, submarines, and/or the like. The actuator may therefore provide a reliable mechanism by which to deploy equipment, instruments and/or the like. Moreover, some embodiments may further employ a release indicator (or tell-tale) to reliably indicate to a remotely located operator that the equipment, instruments and/or the like that are deployed via the actuator have been successfully ejected from their docked position. 
         [0016]      FIG. 1  is a top perspective view of a capturing part of an actuator according to an example embodiment.  FIG. 2  is a bottom perspective view of the capturing part of  FIG. 1  according to an example embodiment.  FIG. 3  is a top perspective view of a retained part of the actuator of  FIG. 1  according to an example embodiment.  FIG. 4  illustrates a cross section view of the actuator according to an example embodiment. It should be appreciated that although the actuator of  FIGS. 1-4  shows a substantially cylindrically shaped retained part, any suitable shape could be employed in connection with other example embodiments for both the retained part and the capturing part. 
         [0017]    Referring now to  FIGS. 1-4 , an actuator  10  of an example embodiment will be described. The actuator  10  may include a capturing part  20  that is configured to releasably hold a retained part  30  based on temperature changes applied to the actuator  10 . The actuator  10  may operate to selectively release a piece of equipment, instrument or other component responsive to remote actuation of the actuator  10  (e.g., based on initiation of the temperature change). In an example embodiment, as shown in  FIG. 4 , the capturing part  20  may be mounted to a platform  12  or surface. Meanwhile, the retained part  30  may be coupled to a mount  14  that may connect to the piece of equipment, instrument or other component. When the actuator  10  is actuated remotely, the retained part  30  may be released from the capturing part  20  such that the capturing part  20  remains fixed in contact with the platform  12 , but the retained part  30  is released and, in some cases, separated or ejected from the capturing part  30  so that the piece of equipment, instrument or other component attached to the mount  14  is free to move away from the platform  12 . 
         [0018]    In an example embodiment, remote actuation of the actuator  10  may be accomplished by initiating a temperature change, as mentioned above. The temperature change may actuate the actuator  10  due to the fact that, in some embodiments, the capturing part  20  and the retained part  30  may be made of materials that each have a different CTE. Accordingly, in some embodiments, such as the example embodiment that will be described in connection with the example of  FIGS. 1-4 , the retained part  30  may be made of a material having a low CTE and the capturing part  20  may be made of a material having a high CTE. In some example embodiments, the material having a low CTE may be titanium (e.g., 6AL4V titanium). However, other materials with a low CTE could alternatively be employed. In some example embodiments, the material having the high CTE may be aluminum (e.g., 6061-T6 aluminum). However, other materials with a high CTE could alternatively be employed. 
         [0019]    The low CTE characteristic of the retained part  30  may cause the retained part  30  to be relatively insensitive to temperature changes (at least in relation to expansion and/or contraction of the material used to form the retained part  30 ). Meanwhile, the material with the high CTE (i.e., the capturing part  20 ) may be heated to enable the retained part  30  to fit within a reception sleeve  40  of the capturing part  20 . Responsive to cooling of the capturing part  20 , the retained part  30  may be fixed within the reception sleeve  40  by an interference fit between the capturing part  20  and the retained part  30 . Thereafter, responsive to heating of the capturing part  20 , the reception sleeve  40  may release the retained part  30 . 
         [0020]    In this regard, for example, the high CTE of the capturing part  20  may cause the material of the capturing part  20  (and therefore also the reception sleeve  40 ) to expand as the capturing part  20  is heated. Accordingly, an internal diameter (Dl) of the reception sleeve  40  may increase slightly responsive to heating of the capturing part  20 . When the reception sleeve  40  expands in diameter, the retained part  30  may be insertable into the reception sleeve  40  without contact, or at least with relatively small or minimal contact, between the reception sleeve  40  and the retained part  30 . Thus, for example, an external diameter (D 2 ) of the retained part  30  may be smaller than the internal diameter (D 1 ) of the reception sleeve  40  when the reception sleeve  40  is heated above a threshold temperature. However, when the reception sleeve  40  is cooled to below the threshold temperature, the internal diameter (Dl) of the reception sleeve  40  may decrease to more closely approach the external diameter (D 2 ) of the retained part  30  to create an interference fit therebetween if the retention part  30  is inserted into the reception sleeve  40  prior to the cooling taking place. 
         [0021]    In an example embodiment, one or more heating elements  50  may be placed in contact with a body  60  of the capturing part  20  to apply heat to the capturing part  20  when the heating elements  50  are energized by a power source (not shown). The heating elements  50 , which are visible in  FIG. 2 , are shown as being disposed on a bottom portion of the body  60 . However, it should be appreciated that any number of heating elements  50  could be disposed any suitable location on the capturing part  20 . 
         [0022]    The heating elements  50  may be embodied in any suitable manner. However, in an example embodiment, the heating elements  50  may be embodied as a pair of 50 W thick film power resistors. Such resistors may be capable of delivering a peak temperature of between about 115° C. to about 135° C., which may generate, for example, a temperature rise of between about 40° C. to about 50° C. to cross a predetermined temperature threshold for switching the actuator  10  between actuated and not actuated states. Using two heating elements  50  (or more) may provide for redundancy to increase reliability. The heating elements  50  may be affixed to the body  60  via fasteners, glue or other adhesive materials (preferably non-insulating), or via mating of surfaces machined to engage one another. When energized, the heating elements  50  may apply heat to the body  60 , which may be transmitted to sidewalls  70  that form the reception sleeve  40 . As shown in  FIG. 1 , the sidewalls may extend from the body  60  in a direction substantially perpendicular to a plane in which the body  60  lies. Moreover, the sidewalls  70  may form a hollow cylinder having a shape substantially matching that of a plug body  80  of the retained part  30 . Thus, for example, the sidewalls  70  may form a cup-like shape in combination with the body  60  into which the retained part  30  may be insertable for selective retention and release based on the temperature of the capturing part  20  as controlled via the heating elements  50 . 
         [0023]    Although the retained part  30  may be machined, molded or otherwise manufactured to be a single, solid cylindrical object or plug, some embodiments may modify the structure of the retained part  30  to impart certain characteristics that may be desirable for some embodiments. In this regard, for example, some applications it may be desirable to cause separation of the retained part  30  from the capturing part  20  when the actuator  10  is actuated. To achieve such separation, a spring (e.g., kickoff spring  90 ) may be compressed when the retained part  30  is fully seated in the capturing part  20 . Thus, for example, the kickoff spring  90  may be mounted to the body  60  within the reception sleeve  40 . As shown in  FIG. 4 , the insertion of the retained part  30  into the reception sleeve  40  may compress the kickoff spring  90  against the body  60  so that when the interference fit between the reception sleeve  40  and the retained part  30  is relaxed, the kickoff spring  90  may release and exert a spring force to push the retained part  30  out of the reception sleeve  40 . To provide sufficient space for the kickoff spring  90  to be accommodated, the plug body  80  may have a cavity  82  disposed at a central portion thereof. The inclusion of the cavity  82  may make the retained part  30  more cup-like in its shape instead of being a solid cylindrical object. 
         [0024]    Additionally or alternatively, the retained part  30  may be manufactured to include at least two separate parts that may be joined together. For example, as shown in  FIG. 4 , the plug body  80  may be formed as a hollowed out, substantially cylindrically shaped component with the cavity  82  extending completely through the axis of the retained part  30 . A plug back  84  may be provided at one end of the plug body  80  to fill a portion of the cavity  82  and provide an interface with the mount  14 . The plug back  84  may be mounted to the plug body  80  via screws or other fasteners and a portion of the plug back  84  may actually contact the kickoff spring  90 . In some cases, the plug body  80  may be installed at a high temperature and retained within the reception sleeve  40  at a lower temperature prior to the plug back  84  being coupled to the plug body  80 . By installing the plug body  80  without the plug back  84 , the plug body  80  may be carefully installed without pushing against the force of the kickoff spring  90 . Pushing against the force of the kickoff spring  90  while installing the retained part  30  into the reception sleeve  40  may cause wavering or additional movement other than in the axial direction (e.g., a lateral load). Such wavering or movement other than in the axial direction may cause galling between the surfaces of the reception sleeve  40  and the retained part  30  (e.g., at the periphery of the plug body  80 ). Additionally, the taper of the interior of the plug body  80  may reduce the likelihood of the kickoff spring  90  hanging up on the plug body  80  when the actuator  10  is actuated. 
         [0025]    Prevention of galling may generally increase the lifetime and reusability of the actuator  10 . Thus, for example, the retained part  30  may be reused in connection with the same capturing part  20  numerous times. However, in some cases, different retained parts may be used with a single capturing part over different actuation operations, or different capturing parts may be used with a single retained part over different actuation operations so long as galling is minimized so that the surfaces are relatively unmodified by each use. 
         [0026]    A number of anti-galling techniques may be employed. For example, in some embodiments, the capturing part  20  may be coated with a hard coat anodized treatment and the retained part  30  may be coated with a titanium anodizing treatment. Although the sidewalls  70  forming the reception sleeve  40  may be formed to have an internal surface that extends along its entire length to be substantially perpendicular to a surface of the body  60  (or a plane in which the body  60  lies). In some cases, a top portion of the interior of the sidewalls  70  may be tapered and/or a bottom portion of the plug body  80  may be tapered as shown in  FIG. 4  to reduce the potential for galling when the plug body  80  is installed into the reception sleeve  40 .  FIG. 5  illustrates a cross sectional view of a portion of the interface between the sidewalls  70  and the plug body  80 . 
         [0027]    As can be seen from  FIG. 5 , the plug body  80  may include a tapered portion  92  that extends around a periphery of a leading edge of the plug body  80  as the plug body  80  is installed into the reception sleeve  40 . Meanwhile, the sidewalls  70  also include a tapered portion  94  at a top portion of the sidewalls  70  facing the reception sleeve  40 . It should be appreciated that some embodiments may only employ one of the tapered portions ( 92  and  94 ) instead of employing both. However, other example embodiments may employ both or even neither of the tapered portions ( 92  and  94 ). When one or more of the tapered portions ( 92  and  94 ) are employed, alignment of the retained part  30  and the capturing part  20  may be enhanced, to further facilitate reduction of galling. 
         [0028]      FIG. 5  illustrates an example embodiment of the actuator of  FIGS. 1-4  with optional modifications. Of note the modifications shown in  FIG. 5  may be utilized independently of one another or in combination in alternative embodiments.  FIG. 5  (which is not necessarily drawn to scale with respect to the representation of electrical contacts therein) illustrates an example embodiment in which a tell-tale or release indicator is employed. In this regard, for example, some embodiments may employ relatively simple circuitry to facilitate the provision of a confirmation signal when the actuator  10  is actuated to release the retained part  30 . As shown in  FIG. 5 , the release indicator may be embodied by a first electrical contact  96  and a second electrical contact  98 . In some embodiments, the first and second electrical contacts  96  and  98  may be disposed to be spaced apart from each other. However, insertion of the plug body  80  into the reception sleeve  40  may cause the first and second electrical contacts  96  and  98  to make contact with each other and close a simple circuit. When the circuit is closed, a feedback circuit may either provide no indication to a remote operator or may provide an indication that the actuator  10  has not been actuated (i.e., that the retained part  30  is being retained in the capturing part  20 ). However, when the actuator  10  is actuated so that the retained part  30  is ejected from the capturing part  20 , the circuit may be opened. Opening of the circuit may cause the feedback circuit to cease to provide the indication that the actuator  10  has not been actuated, or may actually trigger a positive indication that the actuator  10  has been actuated. 
         [0029]    In an example embodiment, to further prevent or minimize galling, the internal surface of the sidewalls  70  and the external surface of the plug body  80  may also be machined or otherwise manufactured to have no or minimal surface imperfections. In some cases, machining tolerances for the retained part  30  and the reception sleeve  40  may be about +/−0.00015 inches to provide an interference fit between the two of about 0.0006 inches (nominal outer diameter to inner diameter). 
         [0030]    In some embodiments, to avoid or reduce heat transfer from the capturing part  20  to the platform  12 , the body  60  may be separated from the platform  12  by spacers  100 . The spacers  100  may be made of an insulating material and may be threaded (e.g., via helicoils) to enable the platform  12  to be affixed to the body  60  (e.g., via a screw or other fastener engaging the spacer  100  to the body  60  and another screw or fastener engaging the spacer  100  to the platform  12  as shown in  FIG. 4 ). In some embodiments, Vapor Deposited Aluminum (VDA) tape may be used to coat portions of the body  60  to reduce or minimize energy loss from radiation. However, other strategies may be employed to reduce or minimize parasitic heat loss in other embodiments as well. 
         [0031]    In some cases, it may be desirable to minimize the amount of energy required for release. Minimizing the mass of components forming the reception sleeve  40  and minimizing the surface area of overlap (i.e., the interface area) between the retained part  30  and the capturing part  20  may assist in reducing the amount of energy required for release since a smaller change in temperature may initiate a release. To minimize, or at least reduce, the amount of energy required for release (or ejection) of the retained part  30 , the plug body  80  of the retained part  30  may be provided with one or more ridges  110  provided on a surface of the periphery thereof. Two are shown in  FIG. 5 . However, any number of ridges  110  may be provided in alternative embodiments. The ridges may be engaged by a surface of the sidewalls  70  when the sidewalls contract responsive to cooling thereof in order to form the interference fit between the sidewalls  70  and the ridges  110 . The ridges  110  may continuously extend all the way around the periphery of the plug body  80 , or they may be discontinuous and only extend along one or more portions of the plug body  80 . The ridges  110  may further be provided with any desired width and/or height of extension off of the surface of the periphery of the plug body  80 . The height, width and other characteristics of the ridges  110  (if employed) may be selected to provide a desired amount of holding force generation by the interference fit when the retained part  30  is being held in place by the captured part  20 . Furthermore, in some cases, the ridges  110  may be provided on internal portions of the sidewalls  70  instead of being provided on the plug body  80 . 
         [0032]    As indicated above, the retained part  30  may be insertable into (or may be withdrawn from) the reception sleeve  40  when the capturing part  20  is heated above a particular temperature. This condition may be referred to as a first state of operation of the actuator  10 . Thereafter, when the retained part  30  has been inserted into the reception sleeve  40  and the capturing part  20  is cooled, the internal diameter (D 1 ) of the reception sleeve  40  may decrease slightly until an interference fit may be established between the reception sleeve  40  and the retained part  30 . The establishment of the interference fit responsive to the removal of the heat source and/or cooling of the capturing part  20  may transition the actuator  10  into a second state (e.g., an engaged state). The tolerances of the internal diameter (D 1 ) of the reception sleeve  40  and the external diameter (D 2 ) of the retained part  30  may be very closely controlled in order to achieve desired characteristics for the actuator  10 . For example, if more holding force is desired prior to actuation of the actuator  10 , a surface area of contact area between the reception sleeve  40  and the plug body  80  of the retained part  30  may be increased. Thereafter, responsive to heating of the capturing part, the interference fit may be disestablished (e.g., due to an increase in diameter of the reception sleeve) and the retained part  30  may be ejected from the actuator  10  in a third state of the actuator  10 . 
         [0033]    Thus, for example, the retained part  30  may be mounted to an object that is deployable into an environment (e.g., space, undersea, etc.) and the capturing part  20  may be heated and cooled, and thereafter reheated, to enable the retained part  30  to be installed into the capturing part  20 , retained therein, and subsequently ejected to separate the object from another object (e.g., a space vehicle, a submerged vehicle and/or the like) that provides a host platform for the capturing part  20 . The capturing part  20  may be insulated from the host platform (e.g., via spacers) so that heat that is remotely and/or selectively applied to the capturing part  20  to affect actuation of the actuator  10  may not be communicated to the host platform. 
         [0034]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe exemplary embodiments in the context of certain exemplary combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. In cases where advantages, benefits or solutions to problems are described herein, it should be appreciated that such advantages, benefits and/or solutions may be applicable to some example embodiments, but not necessarily all example embodiments. Thus, any advantages, benefits or solutions described herein should not be thought of as being critical, required or essential to all embodiments or to that which is claimed herein. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.