Abstract:
A shape memory alloy actuated device is provided for engaging a movable object. The device may include a first movable component, a shape memory alloy for moving the first component from a first position to a second position, a biasing element configured to expand the shape memory alloy object and apply a continual tensile force to the shape memory alloy object. The device may be configured to allow the first component move between the first position and the second position other than by transferring force to the shape memory alloy object. The device may also be configured to allow the shape memory alloy object to expand and contract when the first component is retained in the first position.

Description:
RELATED APPLICATIONS 
     This application claims the claims priority to, and any other benefit of, U.S. Provisional Patent Application Ser. No. 60/901,257 filed Feb. 15, 2007, the entire disclosure of which is fully incorporated herein by reference. 
    
    
     BACKGROUND 
     Shape memory alloys (SMAs) are metallic alloys that may recover apparent permanent strains when they are heated above a certain temperature. SMAs have two stable states or phases; a hot or austenite state and a cold or martensite state. 
     In the austenite state, the alloy is hard and rigid, while in the martensite state, the alloy is softer and flexible. In the martensite state, the SMA may be stretched or deformed by an external force. Upon heating, the SMA will return to its austenite state and contract or recover any reasonable stretch that was imposed on it. Thus, the SMA recovers with more force than was required to stretch it out. This exerted force upon contraction may be used to perform any number of tasks such as, but not limited to, turning a device on or off, opening or closing a device or object, or actuating a device or object. 
     A variety of problems, however, may occur when an SMA is incorporated in a device to perform one or more of these tasks. For example, SMAs can be damaged if they are inhibited from contracting when heated above their working range of austenite temperatures. In addition, abrupt loading of an SMA, such as short, high peaks of force, can also damage and reduce the longevity of an SMA. For example, an SMA actuator may be used to actuate a latch for a door or a lid. Typically, when the door or lid is closed, it pushes the latch out of the way. Once the door clears the latch, the latch will snap back into position and hold the door closed. Snapping back into position can jerk the SMA, causing a short high peak of force that damages the SMA. Additionally, an SMA that is used in an actuated devices that has two or more positions can droop and become caught or entangled in other parts of the device when the SMA is cooled and elongated but is not stretched taut or placed under tension. 
     SUMMARY OF THE INVENTION 
     In an illustrated embodiment of a device applying at least some of the principles of the invention, an SMA actuated device is disclosed. The SMA actuated device may include a feature that keeps continual tension on the SMA object when the SMA object is in both an austenite state and a martensite state. The SMA actuated device may also include a feature adapted to avoid the SMA object being inhibited from contracting when heated above its austenite transition temperature. The SMA actuated device may also include a feature that isolates the SMA object from forces resulting from the movement of another device component. Various embodiments of the SMA actuated device may include any one or more of these features. 
     In one embodiment a shape memory alloy actuated device is provided for engaging a movable object. The device may include a housing, a first component movable between a first position and a second position relative to the housing where the first component has a first end adapted to engage the movable object when the first component is in the first position. The device may also include a shape memory alloy object for moving the first component from the first component first position to the first component second position, wherein the shape memory alloy object is adapted to expand to a SMA first position and contract to a SMA second position as a function of temperature. A first biasing element may be configured to expand the shape memory alloy object to the SMA first position and apply a tensile force to the shape memory alloy object when the shape memory alloy is in both the SMA first position and the SMA second position. The device may be configured to allow the first component to move between the first component first position and the first component second position other than by transferring force to the shape memory alloy object. The device may also be configured to allow the shape memory alloy object to expand to the SMA first position and contract to the SMA second position when the first component is retained in the first component first position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with the detailed description given below, serve to exemplify embodiments of the invention: 
         FIG. 1  is a perspective view of an exemplary embodiment of an SMA actuated device as disclosed in the application; 
         FIG. 2  is a perspective view a first movable component of the device of  FIG. 1 ; 
         FIG. 3  is a perspective view the second movable component of the device of  FIG. 1 ; 
         FIG. 4  is a perspective view of the third movable component of the device of  FIG. 1 ; 
         FIG. 5  is a close up cross-sectional view of the SMA actuated device of  FIG. 1 ; 
         FIG. 6  is a cross-sectional view of the SMA actuated device of  FIG. 1  in the latched position; 
         FIG. 7  is a cross-sectional view of the SMA actuated device of  FIG. 1  during the SMAs initial contraction; 
         FIG. 8  is a cross-sectional view of the SMA actuated device of  FIG. 1  in the unlatched position; 
         FIG. 9  is a cross-sectional view of the SMA actuated device of  FIG. 1  illustrating the anti jerk and tensioning feature; and 
         FIG. 10 . is a cross-sectional view of the SMA actuated device of  FIG. 1  when the strain relief is engaged. 
     
    
    
     DETAILED DESCRIPTION 
     While various aspects and concepts of the invention are described and illustrated herein as embodied in combination in the embodiments, these various aspects and concepts may be realized in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present invention. Still further, while various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, methods, devices, and so on may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or identified herein as conventional or standard or later developed. Those skilled in the art may readily adopt one or more of the aspects, concepts or features of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated. The embodiments described in the summary and throughout the specification are not intended to limit the meaning or scope of the claims in any way. The terms used in the claims have all of their full ordinary meaning. 
     Further, the terms upper, lower, top, bottom, front, back, upward, and downward are merely references that may be used herein for convenience of explanation and form no structural or use limitation or reference for the invention. 
       FIG. 1 . illustrates an exemplary embodiment of an assembled SMA actuated device  100  as disclosed in the application. The SMA actuated device  100  is adapted to engage a movable object  320 . The SMA actuated device  100  includes an SMA object  315 , a retaining member  325   a  that may be, for example but not limited to, a portion of a housing, a separate component attached to a housing, a first movable component  102 , a second movable component  200 , a third movable component  300 , a first bias element  308 , and a second bias element  310 . 
       FIG. 2  illustrates an exemplary embodiment of the first movable component  102 . The first movable component may be configured in a variety of way. Any structure capable of being moved by an SMA object and capable of engaging a movable object to move, hold or restrict movement of a movable object may be used. In the depicted embodiment, the first movable component  102  is realized as a latch. The first movable component  102  has a tip  322  at one end to engage, lock or hold the movable object  320 . The movable object  320  may be any object that is desired to be held or retained in one position, such as but not limited catch on a door or lid. 
     The exemplary first movable component  102  shown has a generally u-shaped structure with an open cavity and multiple slots and surfaces. The first movable component  102  has a first wall  120  and a second wall  122  extending away from the tip  322  and defining a space or cavity  124  in between. In the depicted embodiment, the first wall  120  and the second wall  122  may extend generally parallel to each other. The first wall  120  has a first opening or slot  105  with a first surface  105   a  and a second surface  105   b . The second wall  122  has a second opening or slot  110  with a first surface  110   a  and a second surface  110   b . The first wall  120  and the second wall  122  includes first retaining surfaces  115   a ,  115   b  and second retaining surfaces  350   a ,  350   b  that are generally perpendicular to the first wall and second wall. 
       FIG. 3  illustrates an exemplary embodiment of the second movable component  200 . The second movable component may be configured in a variety of ways. Any suitable structure capable of attaching to the SMA object to be moved by the SMA object relative to the housing may be used. In the depicted embodiment, the second movable component  200  is realized as a block shaped structure having an opening or slot  205  that extends through the component. The opening or slot  205  has a first surface  205   a  and a second surface  205   b . The opening or slot  205  is adapted to receive the exemplary third movable component  300 . 
       FIG. 4  illustrates an exemplary embodiment of the third movable component  300 . The third movable component  300  may be configured in a variety of ways. Any suitable structure capable of being received in the opening of the second movable component for movement therewith may be used. Thus, other structures movable with respect to the second movable component and engageable therewith may be used. In the depicted embodiment, the third movable component  300  is formed as a generally rectangular prism having a first surface  305   a  and a second surface  305   b . The third movable component  300 , however, may be any suitable shape, such as for example, a cylindrical rod. 
     Referring to  FIGS. 2 and 5 , the SMA actuated device  100  is assembled such that the second movable component  200  is placed into the space or cavity  124  of the first movable component  102  such that the opening or slot  205  is generally aligned with the opening  105  in the first wall  120  and the opening  110  in the second wall  122 . The third movable component  300  is received through the generally aligned openings  105 ,  205  and  110 . The first biasing element  308  is positioned within the space  124  between the first retaining surfaces  115   a ,  115   b  and the second movable component  200 . The second biasing element  310  is positioned around the first movable component  102  between the retaining portions  325   a    325   b  and the second surface  305   b  of the third movable component  300 . In the described embodiment the biasing elements are represented as springs, with the second biasing element  310  being stronger or stiffer than the first biasing element  308 . Any object, however, that provides a biasing force may be used. 
     The SMA object  315  has a first end  335  attached to the second movable component  200  and a second fixed end  330 . The second fixed end  330  of the SMA object  315  and the retaining portions  325   a ,  325   b  do not move with respect to the other components of the SMA actuator (i.e. the other components such as the first, second, and third movable components move relative to the second fixed end  330  and the fixed retaining portions  325   a ,  325   b ). The second fixed end  330  and the retaining portions  325   a ,  325   b  may be fixed to a housing or any other non-moving component. The retaining portions  325   a ,  325   b  may be integrally formed with a housing. 
       FIG. 6 . shows the SMA actuated device  100  in a latched position. The movable object  320  is in a first position, for example, a catch on a door that is closed. The first movable component  102  is in a first position in which the tip  322  holds the movable object  320  in the first position. The first biasing element  308  is biasing the second movable component  200  to its respective first position. The first biasing element  308  is also expanding or elongating the SMA object  315  such that the first end  335  of the SMA object is in its first position. The second biasing element  310  is biasing the third movable component  300  to its first position. When the second movable component  200  and the third movable component  300  are in their respective first positions, there is a small gap  360  between the surface  305   a  on the third movable component and the surface  205   a  on the second movable component  200  and the surfaces  305   a  on the third movable component and the surface  105   a  on the first movable member  102  touch, thus holding the first movable member  102  in a position that engages the movable object  320  to keep the movable object in its first position (e.g. keeps a door closed and latched). 
     Referring to  FIG. 7 , as the SMA object  315  is heated to its austenite start temperature and begins to contract, the SMA object will pull the second movable component  200  toward the fixed end  330  of the SMA object. As a result, the gap  360  between the surface  205   a  on the second movable component  200  and the surface  305   a  of the third movable component will close and the two components will come into contact. The SMA object  315  may be heated to its austenite temperature in a variety of ways. For example, an electric power source (not shown), such as for example, a battery or an electric main, may be placed in circuit communication with the SMA object  315  in a manner that allows the power source to send an electric current through the SMA object. A control unit may control the application of the electric current through the SMA object. Other means of heating the SMA object, such as heating the air surrounding the SMA object, may be used. 
     Referring to  FIG. 8 , as the SMA object  315  continues to contract, it continues to pull the second movable component  200  toward the fixed end  330  of the SMA object, which also pulls the third movable component  300  toward the fixed end  330  and compresses the second biasing element  310 . As a result of the force from the SMA object  315  compressing the second biasing element  310  and pulling the second movable component and third movable component toward the fixed end  330  of the SMA object, the first biasing element  308  pushes the first movable component  102  toward the fixed end  330  of the SMA object. In  FIG. 8 , the first movable component  102 , the second movable component  200 , the third movable component  300  and the SMA object are illustrated in their respective second positions. Moving the first movable component  102  from the first component first position to the first component second position disengages or releases the movable object  320 . In the depicted embodiment, the movable object  320  is a catch for a door that is spring loaded such that when the first movable component is moved toward the second position, the movable object automatically opens. The movable object, however, does not have to be spring loaded. For example, the first movable component could simply unlock the door. After unlatching, the device  100  may return to the position illustrated in  FIG. 6  (i.e. the components are returned to their respective first positions). 
       FIG. 9  illustrates the SMA actuated device  100  when the first movable component  102  and the third movable component  300  are in their respective second positions but the second movable component and the SMA object are in their respective first positions. This may occur, for example, when the SMA actuated device  100  is initially in the position illustrated in  FIG. 5  and an external force acts on the first movable component  102  to move the first component second position. For example, in an embodiment in which the first movable member is a door latch, when the door is closed, the door may engage and force the latch toward the second position as the door closes. As the movable object  320  pushes the first movable member  102 , the second biasing element  310  is compressed by the third movable component  300  and a gap  345  is formed between the retaining portion  325   b  and retaining surface  350   b  on the first movable component  102  and a gap  355  is formed between the surface  205   a  on the second movable component  200  and the surface  305   a  on the third movable component. As illustrated in  FIG. 9 , even though the SMA object is in an expanded position (i.e. a martensite state in which the SMA object is softer and flexible), the first biasing element  308  applies a tensile force to the SMA object to avoid slack in the SMA object becoming caught or entangled in other parts of the device. The first biasing element  308 , for example, may be configured to keep the SMA object  315  taut when the SMA object is in the first SMA position. Thus, the first biasing element  308  provides a tensioning feature to the device  100 . 
     When the movable object  320  clears the tip  322  of the first movable component  102 , the second bias element  310  biases the first movable component back to the first component first position ( FIG. 6 ). The first movable component  102  may return quickly or snap back to the first position. However, due to the gap  355  ( FIG. 9 ) and the gap  360  ( FIG. 6 ), the first movable component  102  and the third movable component  300  return to their respective first positions, without transferring force to or jerking the SMA object  315 . Thus, the SMA actuated device has an anti-jerk feature that protects the SMA object  315  and allows the first movable component to move between the first component first position and the first component second position other than by transferring force to the SMA object. 
       FIG. 10 . illustrates the SMA actuated device  100  when the first movable component  102  is in the first component first position and the SMA object  315 , the second movable component  200 , and the third movable component  300  are in their respective second positions. This may occur, when the first movable object is held or stuck in the first position. If the SMA object  315  is actuated, the SMA object will pull the second movable component  200  and the third movable component  300  to their respective second positions. As a result, both the first biasing element  308  and the second biasing element  310  are compressed and the surface  305   a  on the third movable component  300  separates from the surface  105   a  on the first movable component. The SMA object  315 , therefore, can expand to the SMA first position and contract to the SMA second position when the first movable component  315  is retained in the first component first position. Thus, the SMA actuated device  100  has a strain relief feature that avoids damage to the SMA object  315  that could result from the SMA object being inhibited from contracting when heated above its austenite transition temperature. 
     The invention has been illustrated by the above description of embodiments, and while the embodiments have been described in some detail, it is not the intent of the applicants to restrict or in any way limit the scope of the invention to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicants&#39; general or inventive concept. The embodiments described in the summary and throughout the specification are not intended to limit the meaning or scope of the claims in any way. The terms used in the claims have all of their full ordinary meaning.