Abstract:
Active material actuator assemblies are provided that enable simplified control systems and faster actuator cycle times. A movable member is provided that has multiple active material components operatively connected to it. The active material components are separately selectively activatable for moving the movable member. Movement of the movable member via activation of a first of the active material components triggers activation of the second active material component to further move the movable member. Alternatively or in addition, previously activated active material components are protected from undesired stretching during activation of another active material component or, when desired, an active material component may be reset via activation of another of the active material components in order to prepare it for subsequent activation.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to active material actuator assemblies. 
       BACKGROUND OF THE INVENTION 
       [0002]    Active materials include those compositions that can exhibit a change in stiffness properties, shape and/or dimensions in response to an activation signal, which can be an electrical, magnetic, thermal or a like field depending on the different types of active materials. Preferred active materials include but are not limited to the class of shape memory materials, and combinations thereof. Shape memory materials, a class of active materials, also sometimes referred to as smart materials, refer to materials or compositions that have the ability to remember their original shape, which can subsequently be recalled by applying an external stimulus (i.e., an activation signal). As such, deformation of the shape memory material from the original shape can be a temporary condition. 
       SUMMARY OF THE INVENTION 
       [0003]    Active material actuator assemblies are provided that enable simplified control systems and faster actuation cycle times. In one aspect of the invention, a movable member is provided that has multiple active material components operatively connected to it. The active material components are separately selectively activatable to actuate and thereby move the movable member. Movement of the movable member via activation of a first of the active material components triggers activation of the second active material component to further move the movable member. The activation may be accomplished via activation mechanisms, such as electrical contact strips, that are positioned so that an electrical circuit that activates the second active material component is completed by movement of the movable member in response to the activation of the first active material component. In the case of fluid heating, flow redirecting mechanisms such as spool valves can be arranged so that actuation of the first movable member moves a spool valve to complete another fluid circuit and thereby trigger activation of the second active material component to further move the movable member. Because activation of the second active material component is physically linked to movement of the movable member via the first active material component, control system algorithms to activate the second active material component are not necessary, potentially reducing costs. 
         [0004]    In another aspect of the invention, multiple active material components operatively connected to a movable member are each separately selectively activatable in repeating series for sequential actuation for moving the movable member and are configured such that a previously activated one of said active material components is not reset (e.g., stretched) by actuation of a currently activated active material component. Accordingly, the previously activated component is given time to reduce its resistance to resetting (e.g., to cool) before it is reset and reactivated and thus does not provide resistance during actuation of the currently activated component, increasing efficiency of the actuator assembly. 
         [0005]    In another aspect of the invention, multiple active material components operatively connected to a movable member are each separately selectively activatable in repeating series for moving the movable member and are configured such that a subsequently activated one of said active material components is at least partially reset by actuation of a currently activated one of said active material components. When it is time for the subsequently activated active material component to be activated, it has been wholly reset by one or more of the previously activated active material components to its preactivation state (e.g., a martensite phase in an SMA) in preparation for activation. This “resetting” is physically accomplished via actuation of at least one active material component and therefore additional control system algorithms to reset the active material components are not necessary, potentially reducing costs. Additionally, because the resetting is mechanically accomplished, resetting may be more exact than one accomplished via a control system relying on feedback with its associated inaccuracies. 
         [0006]    The active material actuator assemblies provided herein may function as rotational motors that are more efficient than previous stepping motors that use four shape memory coil springs pulling a biased pin from four different directions to achieve rotation by actuating the SMA springs sequentially. In known stepping motors, only a relatively small force is applied by the springs. Additionally, in such designs after contraction of a spring, it is still relatively hot compared to the ambient temperature and will apply large resistance to the pulling by the next spring compared to the resistance it applies when its temperature is close to ambient (i.e., when in the martensite phase). Finally, there is a waste of the amount of stretch each spring is subjected to since each spring is overstretched by the opposite one and only part of the stretch is used to pull the pin and turn the shaft. The cooperative resistance reduction and resetting mechanism in the rotational motors proposed here can also be used to avoid overstretch such that the full amount of stretch an active material component is subject to is used to do useful work and rotate the shaft. 
         [0007]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic, partially cross-sectional illustration of a first embodiment of a telescoping active material actuator assembly; 
           [0009]      FIG. 2  is a graph of load displacement versus time for the active material actuator assembly of  FIG. 1 ; 
           [0010]      FIG. 3  is a graph of load holding force versus time for the active material actuator assembly of  FIG. 1 ; 
           [0011]      FIG. 4  is a schematic, partially cross-sectional illustration of a second embodiment of a telescoping active material actuator assembly with movable members having bellows; 
           [0012]      FIG. 5  is a schematic, partially cross-sectional illustration in partially fragmentary view of a third embodiment of a telescoping active material actuator assembly having automatic sequential activation; 
           [0013]      FIG. 6  is a schematic illustration of an exemplary embodiment of a locking mechanism for use on any of the actuator assemblies of  FIGS. 1 ,  4  and  5 ; 
           [0014]      FIG. 7  is a schematic perspective illustration of a fourth embodiment of an active material actuator assembly; 
           [0015]      FIG. 8  is a schematic perspective illustration in cross-sectional view of the actuator assembly of  FIG. 7 ; 
           [0016]      FIG. 9  is a schematic fragmentary, cross-sectional view of the actuator assembly of  FIGS. 7 and 8  with some of the active material components activated and the movable members locked together; 
           [0017]      FIG. 10  is a schematic perspective illustration of another embodiment of an active material actuator assembly; 
           [0018]      FIG. 11  is a schematic rear view illustration of the active material actuator assembly of  FIG. 10 ; 
           [0019]      FIG. 12  is a schematic illustration in fragmentary, partially rotated view of the cam lobe and pulleys of  FIGS. 10 and 11  taken along the arrows shown in  FIG. 11 ; 
           [0020]      FIG. 13  is a schematic end view illustration of another embodiment of an active material actuator assembly; and 
           [0021]      FIG. 14  is a schematic perspective illustration of the active material actuator assembly of  FIG. 13  showing an opposing end. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    A number of exemplary embodiments of active material actuator assemblies within the scope of the invention are described herein. The active material actuator assemblies all utilize active material components that may be, but are not limited to, a class of active materials called shape memory materials. Exemplary shape memory materials include shape memory alloys (SMAs), electroactive polymers (EAPs) such as dielectric elastomers, ionic polymer metal composites (IPMC), piezoelectric polymers and shape memory polymers (SMPs), magnetic shape memory alloys (MSMA), shape memory ceramics (SMCs), baroplastics, piezoelectric ceramics, magnetorheological (MR) elastomers, composites of the foregoing shape memory materials with non-shape memory materials, and combinations comprising at least one of the foregoing shape memory materials. For convenience and by way of example, reference herein will be made to shape memory alloys and shape memory polymers. The shape memory ceramics, baroplastics, and the like can be employed in a similar manner as will be appreciated by those skilled in the art in view of this disclosure. For example, with baroplastic materials, a pressure induced mixing of nanophase domains of high and low glass transition temperature (Tg) components effects the shape change. Baroplastics can be processed at relatively low temperatures repeatedly without degradation. SMCs are similar to SMAs but can tolerate much higher operating temperatures than can other shape-memory materials. An example of an SMC is a piezoelectric material. 
         [0023]    The ability of shape memory materials to return to their original shape upon the application of external stimuli has led to their use in actuators to apply force resulting in desired motion. Smart material actuators offer the potential for a reduction in actuator size, weight, volume, cost, noise and an increase in robustness in comparison with traditional electromechanical and hydraulic means of actuation. However, most active materials are capable of providing only limited displacement, limiting their use in applications requiring a large displacement, whether linear or rotational. The invention described herein solves this problem. 
         [0024]    SMAs 
         [0025]    Shape memory alloys are alloy compositions with at least two different temperature-dependent phases. The most commonly utilized of these phases are the so-called martensite and austenite phases. In the following discussion, the martensite phase generally refers to the more deformable, lower temperature phase whereas the austenite phase generally refers to the more rigid, higher temperature phase. When the shape memory alloy is in the martensite phase and is heated, it begins to change into the austenite phase. The temperature at which this phenomenon starts is often referred to as austenite start temperature (A s ). The temperature at which this phenomenon is complete is often called the austenite finish temperature (A f ). When the shape memory alloy is in the austenite phase and is cooled, it begins to change into the martensite phase, and the temperature at which this phenomenon starts is often referred to as the martensite start temperature (M s ). The temperature at which austenite finishes transforming to martensite is often called the martensite finish temperature (M f ). The range between A s  and A f  is often referred to as the martensite-to-austenite transformation temperature range while that between M s  and M f  is often called the austenite-to-martensite transformation temperature range. It should be noted that the above-mentioned transition temperatures are functions of the stress experienced by the SMA sample. Generally, these temperatures increase with increasing stress. In view of the foregoing properties, deformation of the shape memory alloy is preferably at or below the austenite start temperature (at or below A s ). Subsequent heating above the austenite start temperature causes the deformed shape memory material sample to begin to revert back to its original (nonstressed) permanent shape until completion at the austenite finish temperature. Thus, a suitable activation input or signal for use with shape memory alloys is a thermal activation signal having a magnitude that is sufficient to cause transformations between the martensite and austenite phases. 
         [0026]    The temperature at which the shape memory alloy remembers its high temperature form (i.e., its original, nonstressed shape) when heated can be adjusted by slight changes in the composition of the alloy and through thermo-mechanical processing. In nickel-titanium shape memory alloys, for example, it can be changed from above about 100 degrees Celsius to below about −100 degrees Celsius. The shape recovery process can occur over a range of just a few degrees or exhibit a more gradual recovery over a wider temperature range. The start or finish of the transformation can be controlled to within several degrees depending on the desired application and alloy composition. The mechanical properties of the shape memory alloy vary greatly over the temperature range spanning their transformation, typically providing shape memory effect and superelastic effect. For example, in the martensite phase a lower elastic modulus than in the austenite phase is observed. Shape memory alloys in the martensite phase can undergo large deformations by realigning the crystal structure arrangement with the applied stress. As will be described in greater detail below, the material will retain this shape after the stress is removed. 
         [0027]    Suitable shape memory alloy materials include, but are not intended to be limited to, nickel-titanium based alloys, indium-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold, and copper-tin alloys), gold-cadmium based alloys, silver-cadmium based alloys, indium-cadmium based alloys, manganese-copper based alloys, iron-platinum based alloys, iron-palladium based alloys, and the like. The alloys can be binary, ternary, or any higher order so long as the alloy composition exhibits a shape memory effect, e.g., change in shape, orientation, yield strength, flexural modulus, damping capacity, superelasticity, and/or similar properties. Selection of a suitable shape memory alloy composition depends, in part, on the temperature range of the intended application. 
         [0028]    The recovery to the austenite phase at a higher temperature is accompanied by very large (compared to that needed to deform the material) stresses which can be as high as the inherent yield strength of the austenite material, sometimes up to three or more times that of the deformed martensite phase. For applications that require a large number of operating cycles, a strain in the range of up to 4% or more of the deformed length of wire used can be obtained. In experiments performed with Flexinol® wires of 0.5 mm diameter, the maximum strain in the order of 4% was obtained. This percentage can increase up to 8% for thinner wires or for applications with a low number of cycles. This limit in the obtainable strain places significant constraints in the application of SMA actuators where space is limited. 
         [0029]    SMPs 
         [0030]    As previously mentioned, other suitable shape memory materials are shape memory polymers (SMPs). “Shape memory polymer” generally refers to a polymeric material, which exhibits a change in a property, such as a shape, a dimension, a shape orientation, or a combination comprising at least one of the foregoing properties in combination with a change in its elastic modulus upon application of an activation signal. Shape memory polymers may be thermoresponsive (i.e., the change in the property is caused by a thermal activation signal), photoresponsive (i.e., the change in the property is caused by a light-based activation signal), moisture-responsive (i.e., the change in the property is caused by a liquid activation signal such as humidity, water vapor, or water), or a combination comprising at least one of the foregoing. 
         [0031]    Generally, SMPs are phase segregated co-polymers comprising at least two different units, which may be described as defining different segments within the SMP, each segment contributing differently to the overall properties of the SMP. As used herein, the term “segment” refers to a block, graft, or sequence of the same or similar monomer or oligomer units, which are copolymerized to form the SMP. Each segment may be crystalline or amorphous and will have a corresponding melting point or glass transition temperature (T g ), respectively. The term “thermal transition temperature” is used herein for convenience to generically refer to either a Tg or a melting point depending on whether the segment is an amorphous segment or a crystalline segment. For SMPs comprising (n) segments, the SMP is said to have a hard segment and (n- 1 ) soft segments, wherein the hard segment has a higher thermal transition temperature than any soft segment. Thus, the SMP has (n) thermal transition temperatures. The thermal transition temperature of the hard segment is termed the “last transition temperature”, and the lowest thermal transition temperature of the so-called “softest” segment is termed the “first transition temperature”. It is important to note that if the SMP has multiple segments characterized by the same thermal transition temperature, which is also the last transition temperature, then the SMP is said to have multiple hard segments. 
         [0032]    When the SMP is heated above the last transition temperature, the SMP material can be imparted a permanent shape. A permanent shape for the SMP can be set or memorized by subsequently cooling the SMP below that temperature. As used herein, the terms “original shape”, “previously defined shape”, “predetermined shape”, and “permanent shape” are synonymous and are intended to be used interchangeably. A temporary shape can be set by heating the material to a temperature higher than a thermal transition temperature of any soft segment yet below the last transition temperature, applying an external stress or load to deform the SMP, and then cooling below the particular thermal transition temperature of the soft segment while maintaining the deforming external stress or load. 
         [0033]    The permanent shape can be recovered by heating the material, with the stress or load removed, above the particular thermal transition temperature of the soft segment yet below the last transition temperature. Thus, it should be clear that by combining multiple soft segments it is possible to demonstrate multiple temporary shapes and with multiple hard segments it may be possible to demonstrate multiple permanent shapes. Similarly using a layered or composite approach, a combination of multiple SMPs will demonstrate transitions between multiple temporary and permanent shapes. 
         [0034]    EAPS 
         [0035]    The active material may also comprise an electroactive polymer such as ionic polymer metal composites, conductive polymers, piezoelectric polymeric material and the like. As used herein, the term “piezoelectric” is used to describe a material that mechanically deforms when a voltage potential is applied, or conversely, generates an electrical charge when mechanically deformed 
         [0036]    Electroactive polymers include those polymeric materials that exhibit piezoelectric, pyroelectric, or electrostrictive properties in response to electrical or mechanical fields. The materials generally employ the use of compliant electrodes that enable polymer films to expand or contract in the in-plane directions in response to applied electric fields or mechanical stresses. An example of an electrostrictive-grafted elastomer is a piezoelectric poly (vinyldene fluoride-trifluoro-ethylene) copolymer. This combination has the ability to produce a varied amount of ferroelectric-electrostrictive molecular composite systems. These may be operated as a piezoelectric sensor or even an electrostrictive actuator. 
         [0037]    Materials suitable for use as an electroactive polymer may include any substantially insulating polymer or rubber (or combination thereof) that deforms in response to an electrostatic force or whose deformation results in a change in electric field. Exemplary materials suitable for use as a pre-strained polymer include silicone elastomers, acrylic elastomers, polyurethanes, thermoplastic elastomers, copolymers comprising PVDF, pressure-sensitive adhesives, fluoroelastomers, polymers comprising silicone and acrylic moieties, and the like. Polymers comprising silicone and acrylic moieties may include copolymers comprising silicone and acrylic moieties, polymer blends comprising a silicone elastomer and an acrylic elastomer, for example. 
         [0038]    Materials used for electrodes of the present disclosure may vary. Suitable materials used in an electrode may include graphite, carbon black, colloidal suspension, thin metals including silver and gold, silver filled and carbon filled gels and polymers, and ionically or electronically conductive polymers. It is understood that certain electrode materials may work well with particular polymers and may not work as well for others. By way of example, carbon fibrils work well with acrylic elastomer polymers while not as well with silicone polymers. 
         [0039]    SMCs/Piezoelectric 
         [0040]    The active material may also comprise a piezoelectric material. Also, in certain embodiments, the piezoelectric material may be configured as an actuator for providing rapid deployment. As used herein, the term “piezoelectric” is used to describe a material that mechanically deforms (changes shape) when a voltage potential is applied, or conversely, generates an electrical charge when mechanically deformed. Preferably, a piezoelectric material is disposed on strips of a flexible metal or ceramic sheet. The strips can be unimorph or bimorph. Preferably, the strips are bimorph, because bimorphs generally exhibit more displacement than unimorphs. 
         [0041]    One type of unimorph is a structure composed of a single piezoelectric element externally bonded to a flexible metal foil or strip, which is stimulated by the piezoelectric element when activated with a changing voltage and results in an axial buckling or deflection as it opposes the movement of the piezoelectric element. The actuator movement for a unimorph can be by contraction or expansion. Unimorphs can exhibit a strain of as high as about 10%, but generally can only sustain low loads relative to the overall dimensions of the unimorph structure. A commercial example of a pre-stressed unimorph is referred to as “THUNDER”, which is an acronym for Thin layer composite UNimorph ferroelectric Driver and sEnsoR. THUNDER is a composite structure constructed with a piezoelectric ceramic layer (for example, lead zirconate titanate), which is electroplated on its two major faces. A metal pre-stress layer is adhered to the electroplated surface on at least one side of the ceramic layer by an adhesive layer (for example, “LaRC-SI®” developed by the National Aeronautics and Space Administration (NASA)). During manufacture of a THUNDER actuator, the ceramic layer, the adhesive layer, and the first pre-stress layer are simultaneously heated to a temperature above the melting point of the adhesive, and then subsequently allowed to cool, thereby re-solidifying and setting the adhesive layer. During the cooling process the ceramic layer becomes strained, due to the higher coefficients of thermal contraction of the metal pre-stress layer and the adhesive layer than of the ceramic layer. Also, due to the greater thermal contraction of the laminate materials than the ceramic layer, the ceramic layer deforms into an arcuate shape having a generally concave face. 
         [0042]    In contrast to the unimorph piezoelectric device, a bimorph device includes an intermediate flexible metal foil sandwiched between two piezoelectric elements. Bimorphs exhibit more displacement than unimorphs because under the applied voltage one ceramic element will contract while the other expands. Bimorphs can exhibit strains up to about 20%, but similar to unimorphs, generally cannot sustain high loads relative to the overall dimensions of the unimorph structure. 
         [0043]    Suitable piezoelectric materials include inorganic compounds, organic compounds, and metals. With regard to organic materials, all of the polymeric materials with noncentrosymmetric structure and large dipole moment group(s) on the main chain or on the side-chain, or on both chains within the molecules, can be used as candidates for the piezoelectric film. Examples of suitable polymers include, for example, but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), poly S-119 (Poly(vinylamine) backbone azo chromophore), and their derivatives; polyfluorocarbines, including polyvinylidene fluoride (“PVDF”), its co-polymer vinylidene fluoride (“VDF”), trifluorethylene (TrFE), and their derivatives; polychlorocarbons, including poly(vinylchloride) (“PVC”), polyvinylidene chloride (“PVC2”), and their derivatives; polyacrylonitriles (“PAN”), and their derivatives; polycarboxylic acids, including poly (metharcylic acid (“PMA”), and their derivatives; polyureas, and their derivatives; polyerethanes (“PUE”), and their derivatives; bio-polymer molecules such as poly-L-lactic acids and their derivatives, and membrane proteins, as well as phosphate bio-molecules; polyanilines and their derivatives, and all of the derivatives of tetramines; polyimides, including Kapton molecules and polyetherimide (“PEI”), and their derivatives; all of the membrane polymers; poly (N-vinyl pyrrolidone) (“PVP”) homopolymer, and its derivatives, and random PVP-co-vinyl acetate (“PVAc”) copolymers; and all of the aromatic polymers with dipole moment groups in the main-chain or side-chains, or in both the main-chain and the side-chains, and mixtures thereof. 
         [0044]    Further, piezoelectric materials can include Pt, Pd, Ni, T, Cr, Fe, Ag, Au, Cu, and metal alloys and mixtures thereof. These piezoelectric materials can also include, for example, metal oxide such as SiO 2 , Al 2 O 3 , ZrO 2 , TiO 2 , SrTiO 3 , PbTiO 3 , BaTiO 3 , FeO 3 , Fe 3 O 4 , ZnO, and mixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS, GaAs, AgCaSe 2 , ZnSe, GaP, InP, ZnS and mixtures thereof. 
         [0045]    MR Elastomers 
         [0046]    Suitable active materials also comprise magnetorheological (MR) compositions, such as MR elastomers, a class of smart materials whose rheological properties can rapidly change upon application of a magnetic filed. MR elastomers are suspensions of micrometer-sized, magnetically polarizable particles in a thermoset elastic polymer or rubber. The stiffness of the elastomer structure is accomplished by changing the shear and compression/tension moduli by varying the strength of the applied magnetic field. The MR elastomers typically develop their structure when exposed to a magnetic field in as little as a few milliseconds. Discontinuing the exposure of the MR elastomers to the magnetic field reverses the process and the elastomer returns to its lower modulus state. Suitable MR elastomer materials include, but are not intended to be limited to, an elastic polymer matrix comprising a suspension of ferromagnetic or paramagnetic particles, wherein the particles are described above. Suitable polymer matrices include, but are not limited to, poly-alpha-olefins, natural rubber, silicone, polybutadiene, polyethylene, polyisoprene, and the like. 
         [0047]    MSMAs 
         [0048]    MSMAs are alloys, often composed of Ni—Mn—Ga, that change shape due to strain induced by a magnetic field. MSMAs have internal variants with different magnetic and crystallographic orientations. In a magnetic field, the proportions of these variants change, resulting in an overall shape change of the material. An MSMA actuator generally requires that the MSMA material be placed between coils of an electromagnet. Electric current running through the coil induces a magnetic field through the MSMA material, causing a change in shape. 
         [0049]    Exemplary Embodiments of Telescoping Active Material Actuator Assemblies 
         [0050]    Referring to  FIG. 1 , a first embodiment of an active material actuator assembly  10  is illustrated. The active material actuator assembly  10  has multiple movable members  12 ,  14  and  16  and a fixed anchor member  18 . Movable member  14  is referred to in the claims as the first movable member and movable member  16  is referred to as the second movable member. The movable members  12 ,  14  and  16  are preferably concentric bodies, which in cross-section may be circular, rectangular, triangular or any other shape, and are arranged in a “telescoping manner” such that movable member  12  is able to move at least partially in and out of movable member  14 , which can move at least partially in and out of movable member  16 , which can move at least partially in and out of anchor member  18 . In alternative embodiments, the movable members  12 ,  14  and  16  need not be concentric. The telescoping movable members may be aligned to provide linear movement or may have a curved form to cause nonlinear movement, such as along a circumference of a circle. Multiple active material components are utilized to affect the telescoping movement. An active material component  32  is connected at one end to anchor member  18  and at an opposing end to movable member  16 . Active material component  32  is referred to as the first active material component in the claims. The active material component  32  is shown routed through an opening in a proximal face  34  of movable member  16  and connected to a distal face  36  of the movable member  16 , but could alternatively be connected to the proximal face  34 . Active material component  38  is connected at one end to movable member  16  and at an opposing end to movable member  14 . Active material component  38  is referred to as the second active material component in the claims. The active material component  38  is shown routed through an opening in a proximal face  40  of movable member  14  and connected to a distal face  42  of the movable member  14 , but could alternatively be connected to the proximal face  40 . Active material component  44  is connected at one end to movable member  14  and at an opposing end to movable member  12 . The active material component  44  is shown routed through an opening in a proximal face  46  of movable member  12  and connected to a distal face  48  of the movable member  12  but may alternatively be connected to the proximal face  46 . End anchors  52  secure the respective ends of the active material components  32 ,  38  and  44  to the respective movable members and the anchor member. The anchors  52  may be crimped portions of the respective active material components or may be any material capable of restraining an end of the active material component to the respective member, such as a rubber plug, a welded joint or adhesive/epoxy bonded joint. 
         [0051]    In  FIG. 1 , three active material components  32 ,  38  and  44  are shown. Within the scope of the invention, additional movable members connected with additional active material components may be used. Although the active material components  32 ,  38  and  44  are depicted as elongated wires, they may be rods, blocks, springs or any other shape capable of contracting upon activation (or deactivation). Finally, an active material component may consist of multiple discrete active material elements such that multiple active material elements may be connected between a pair of adjacent movable members or between the anchor member  18  and movable member  16 ; i.e., sets of active material components may be used. For example, an additional active material component  19  (shown in phantom) may be connected between the anchor member  18  and the movable member  16  in addition to the single active material component  32 . The active material elements may be in the form of wires or any other geometric shape. 
         [0052]    It should be appreciated that, within the scope of the invention, a single active material component such as an SMA wire may be configured with different regions or segments connecting a movable member to a fixed member having different active material properties such that modulated movement of a load attached to the movable member is achieved between the movable member and the fixed member via the different regions of the single active material component actuating at different times. 
         [0053]    In  FIG. 1 , the movable members  12 ,  14  and  16  are shown at extreme extended positions, each not able to move any further out of the respective adjacent member due to flange-like stops  20 ,  22 ,  24  that extend from the respective movable members  12 ,  14  and  16 , to interfere with an inner surface of the respective adjacent members at openings  26 ,  28 ,  30  in movable members  14 ,  16  and anchor member  18  through which the movable members  12 ,  14  and  16  translate, respectively. The stops  20 ,  22  and  24  are integrally arranged such that movement of movable member  16  to the right via contraction of active material component  32  pulls along movable members  12  and  14 , and movement of movable member  14  to the right via contraction of active material component  38  pulls along movable member  12 . 
         [0054]    The active material components  32 ,  38  and  44  are shown in the stretched, extended state prior to activation. In the embodiment of  FIG. 1 , the active material components  32 ,  38  and  44  are SMAs actuated at different respective temperatures which may be achieved by the temperature of the surrounding fluid or by resistive heating serving as an activation signal or trigger. The active material component  32  has the lowest Austenite start temperature, (As) followed by active material component  38  and then active material component  44  (i.e., the active material components are arranged in ascending order of Austenite start temperature (As) from the right). The transformation temperature ranges for each of the active material components  32 ,  38  and  44  may be completely distinct or may overlap. The temperature of the active material components  32 ,  38  and  44  could be increased by radiative heating, resistive heating (see  FIG. 5 ), fluidic (convective) heating (shown as an option in  FIG. 1 ) or any combination of the above. 
         [0055]    Return Mechanism 
         [0056]      FIG. 1  contains three respective biasing springs  54 ,  56  and  58  acting as return mechanisms urging movable members  16 ,  14  and  12 , respectively, to the left (against return to original shape). The biasing springs  54 ,  56  and  58  are optional because certain SMA materials with the reversible shape memory effect have the ability to return completely to their original shape without the application of an external restoring force. Also, a restoring force (bias) could be introduced into a load attached to the movable member  12  (or included in movable member  12 ). Furthermore, within the scope of the invention, a design with only one biasing spring  54  could be used. Any other arrangement that puts biasing springs in opposition to the recovery force (i.e., the contraction force) of the active material components could be used, such as arranging the biasing spring external to the movable members  32 ,  38  and  44  or using one biasing spring with the load for all of the active material components. Additionally, the stops  20 ,  22  and  24  act as overstretch prevention mechanisms as they prevent stretching of the active material components, (due to the return force of the springs  54 ,  56  and  58 , respectively) beyond the length determined by interference of the stops  20 ,  22  and  24  with respective movable members  14 ,  16  and anchor member  18 . 
         [0057]    For purposes of illustration, in the embodiment of  FIG. 1 , it is assumed that activation is passively triggered by radiant heating and that the active material components  32 ,  38  and  44  are exposed to the same surrounding temperature. As the temperature of the active material components  32 ,  38  and  44  increases, the transformation of active material component  32  occurs first. Consequently, movable member  16  is pulled to the right and with it, due to the stops  20  and  22 , movable members  12  and  14 , and therefore the load, all working against the force of biasing spring  54  (if used). 
         [0058]    Modulated Movement 
         [0059]    The total displacement achieved and force acting on the load attached to movable member  12 , due to the recovery force of the active material component  32 , is illustrated by x 1  and F 1  in  FIGS. 2 and 3  respectively. The displacement x 1  is indicated in  FIG. 1  as movement of movable member  12  from a start position  60  to an intermediate position  62 . At the completion of the transformation of active material component  32  (or while transformation of active material component  32  is in progress if the transition temperature ranges of active material components  38  and  32  overlap. This is illustrated by the dashed line in  FIGS. 2 and 3  with the overlap region between active material component  32  and active material component  38  represented by the interval t ov1 . Active material component  38  begins to transform pulling with it movable members  12  and  14 , and therefore the load. This causes an additional displacement of the load of x 2  and the force acting on the load is increased by Δ 2 , illustrated in  FIGS. 2 and 3 . The displacement caused by activation of active material component  38  is indicated in  FIG. 1  by movement of movable member  12  from intermediate position  62  to intermediate position  64 . Similarly as with the transformation of active material component  32 , at the completion of the transformation of active material component  38  (or while the transformation of active material component  38  is in progress if the transition temperature ranges overlap as illustrated in  FIGS. 2 and 3  with the overlap region between active material component  38  and active material component  44  represented by the interval t ov2 ), active material component  44  begins to transform, thereby pulling with it movable member  12  and working against the opposing force of spring  58 . At the completion of the transformation of active material component  44 , there is an additional displacement of the load of x 3  and the force on the load is increased by Δ 3 , illustrated in  FIGS. 2 and 3 . The displacement caused by activation of active material component  44  is indicated in  FIG. 1  by movement of movable member  12  from intermediate position  64  to intermediate position  66  in  FIG. 1 . 
         [0060]    In  FIGS. 2 and 3 , the increments in load displacement (x 1 , x 2  and x 3 ) and in force (F 1 , Δ 2  and Δ 3 ) appear equal for purposes of illustration only, but could be different depending on the characteristics of the active material components  32 ,  38  and  44  and the biasing springs  54 ,  56  and  58  and the kind of load that is attached to the movable member  12 . For example, it may be desirable to select the active material components such that some actuate quickly and achieve a relatively large displacement, followed by later actuation of another active material component to achieve a relatively small displacement. For example, active material components  32  and  38  may actuate at lower temperatures and may be selected to contract a relatively large amount, followed by actuation of active material component  44  which may actuate at a relatively high temperature and contracts a lesser amount. The actuation of the earlier actuated active material components may also occur more quickly than the actuation of the later actuated active material component to achieve a fast initial displacement followed by a slower movement to the final load position. In this way, the earlier actuated active material components accomplish coarse tuning or positioning of the load, while the later actuation fine-tunes the load position. Such an arrangement may simplify a control system designed to control the fixed position of the load. If all but one of the active material components actuate simultaneously to accomplish the coarse turning and the fixed active material component accomplishes fine tuning, the control system need only monitor the position of the load after the coarse tuning (i.e., monitor a single measurement of the initial, relatively large coarse-tuned displacement) to provide feedback for accurate positioning during fine tuning, rather than monitoring a series of displacements by actuation of active material components at different times that achieve the coarse tuning. This avoids the cumulative error associated with a series of discrete control measurements and also simplifies any overall control design. It is to be further appreciated that a load that linearly increases with displacement is assumed in the illustrations of  FIGS. 2 and 3 . 
         [0061]    The distinct or overlapping transformations of the different active material components  32 ,  38  and  44  give rise to a modulated displacement profile of the load connected to movable member  12 . The result is that a larger displacement is obtained than with a single active material component or than with multiple active material components spanning from the distal face  48  of movable member  12  to the portion of anchor member  18  at which active material component  32  is connected. Furthermore, the recovery force is modulated as shown in the illustration of  FIG. 3 . The stress on the active material components  32 ,  38  and  44  continually varies with the actuation of each subsequent active material component (assuming no optional locking/latching mechanisms, as in the description below). It is preferable to ensure that the maximum stress in each active material component does not exceed the value required for acceptable performance. If the surrounding temperature decreases, the active material components  32 ,  38  and  44  will be restored to their martensite phase lengths (i.e., the movable members will return to the positions shown in  FIG. 1 ) due to the load and the biasing force of the respective springs  54 ,  56  and  58  (if used), in order as temperature decreases. 
         [0062]    Preferably the recovery force of active material component  44  is larger than that of active material component  38  which in turn is larger than that of active material component  32 . This is especially useful if locking mechanisms are used after the actuation of each active material component thereby isolating the active material component and allowing the next active material component to have a larger recovery force. 
         [0063]    In  FIGS. 2 and 3 , curves  70  and  72 , shown with solid lines, represent the load displacement profile and the load holding force profile, respectively, for the case where transformation of each active material component is completed before the subsequent one begins. Transformation of active material component  32  begins at time t=0, and is completed at time t=t 1 . There is a hold period until time t=t h1  when the temperature of the active material component  38  reaches its austenite start temperature, at which point transformation of active material component  38  begins and continues until time t=t h1 +t 2 . Again, there is then a hold period until time t=t h2  when active material component  44  reaches its austenite start temperature, at which point transformation of active material component  44  begins and is completed at time t=t h2 +t h3 . The flat sections of curves  70  and  72  describe the hold periods where no transformation is taking place. 
         [0064]    For an embodiment where the compositions of the active material components  32 ,  38  and  44  are such that the transformations overlap, the typical load displacement profile and load holding force profile are illustrated by curves  74  and  76 , respectively. For instance, in  FIG. 2 , the overlap in the transformation of active material component  32  and active material component  38  occurs over time t ov1 . During this time, the rate of transformation of active material component  32  increases as active material component  38  begins to transform. At full transformation of active material component  32  the rate of transformation of active material component  38  continues as described earlier. A similar effect occurs over time t ov2  for the overlap of active material component  38  and active material component  44 . The description above is for illustrative purposes only and the response profile of each active material component, distinctly or during overlap, would generally depend on the composition of the active material component and the heat transfer process between the activation input trigger, whether an actuating field, fluid or current, and the active material component. For instance, the transformation rates shown as constant would generally be nonlinear. 
         [0065]    Referring again to  FIG. 1 , if active convective (fluid) heating were used instead of passive radiant heating, openings  80 ,  81 ,  82  and  83  would be provided in the respective anchor member  18 , and in movable members  14 ,  16  and  12 . Arrows A illustrate the direction of fluid flow through the openings  80 ,  81 ,  82  and  83  for the general case where the same fluid flows past the different active material components  32 ,  38  and  44  at the same time. Alternatively, if resistive electrical heating is used, the right end of each active material component could be connected to an electric lead, e.g., a positive electric lead, and the left end would be connected to the opposite electric lead, e.g., a negative electric lead, (i.e., at the anchors  52 ) with suitable insulation. Current could be supplied to the different active material components  32 ,  38  and  44  in series or parallel, at the same time or in a defined sequence, depending on the desired force/displacement profile. 
         [0066]    Referring to  FIG. 4 , another embodiment of an active material actuator assembly  110  is illustrated. The active material actuator assembly  110  includes movable members  112 ,  114 , and  116 , anchor member  118  and active material component  132 ,  138  and  144  operable in like manner as similarly numbered components in  FIG. 1 . A load  119  is connected to movable member  112  such that it is moved therewith. Each of the movable members  112 ,  114  and  116  form a frame around an intermediate resilient portion which in this embodiment is bellows  113 ,  115  and  117 , respectively. The bellows  113 ,  115  and  117  are made of a suitable material, such as hydroformed metal, and are attached by any suitable means to the movable members  112 ,  114  and  116 , respectively. The bellows are a flexible material that compresses in width as the active material components  132 ,  138  and  144  contract and the movable members  112 ,  114  and  116  move to the right. Biasing springs  154 ,  156  and  158  may be placed in compression within respective movable members  116 ,  114  and  112  to oppose the restoring force of the active material components  132 ,  138  and  144 . The biasing springs could alternatively be placed in a similar position as springs  54 ,  56  and  58  in  FIG. 1 . As an alternative to the biasing springs  154 ,  156  and  158 , the required bias could be built into all of the bellows  113 ,  115  and  117  or only into bellows  117  to function as a return mechanism resisting the first-activated active material component  132 . Alternatively, the active material components used could have reversible shape memory effect in lieu of the biasing springs or bellows. 
         [0067]    Automatic Activation 
         [0068]    Automatic activation mechanisms could be integrated with the invention so that, assuming active activation, the activation input (i.e., actuating field, fluid or current), is transferred to a succeeding active material component when the preceding active material component reaches a predetermined level of change in a property such as a predetermined level of strain (e.g., a percentage of the maximum possible strain, for safety and/or durability), or when transformation is complete in order to maximize the output of the actuator assembly. That is, movement of a first moveable member via an activation input to a first active material component causes an activation input to a second active actuation mechanism to activate a second active material component. As illustrated in  FIG. 5 , an active material actuator assembly  210  with movable members  212 ,  214 ,  216  and anchor member  218  includes an extension  290  on movable member  216  configured to contact extension  291  on anchor member  218 . (Movable member  212  is shown fragmented, but connects to a load similarly to movable member  112  of  FIG. 4 .) At the completion (or at a predetermined level) of the transformation of active material component  232 , the extension  290  fits into and contacts extension  291 . This action allows the electric circuit (between positive electric lead  292  and negative electric leads  293 ) for active material component  238  to be completed, thereby allowing current to flow through the active material component  238  to cause its transformation to the austenite phase. Various ways could be used to ensure that the electric supply is well insulated from the rest of the active material actuator assembly  210 , for instance, by using a male/female connection system on the extensions  290  and  291 . In other alternative embodiments, the contact between the extension  290  and extension  291  need not directly complete the actuating electric circuit but can be used to trigger the sending of a signal to a control system (not shown) to supply current for the activation of active material component  238  in the case where this is desired. Similar extensions could be added between movable members  214  and  216 , to cause automatic activation of active material component  244 . In the case of active activation via convective heating, the contacting extensions could each have a hollowed conduit to allow the transfer of heating fluid through the conduits to heat a subsequent active material component when the extensions contact one another. For example, one end of one extension could cause a valve or orifice on the second extension to open, thereby allowing fluid flow which can be routed over the active material component. 
         [0069]    Locking Mechanism and Releasing Mechanism 
         [0070]    A locking mechanism or mechanisms could be integrated in an active material actuator assembly to lock adjacent movable members to one another to thereby achieve holding of the movable members in an actuated position during a power-off condition. In  FIG. 6 , an active material actuator assembly  310  (shown only in part, but similar to any of the active material actuator assemblies of  FIGS. 1 ,  4  or  5 ), optional locking mechanism  394  connects movable member  316  to anchor member  318  at the completion of the transformation or at the required level of transformation (i.e., actuation) of an active material component (not shown) connected between movable member  316  and anchor member  318 , where these features operate as like numbered components in the active actuator assembly  210 , i.e., of  FIGS. 1 ,  4  or  5 . Similar mechanisms could be used between other pairs of adjacent movable members in the actuator assembly  310 . More flexibility is obtained in the level of load holding force obtained at each phase (i.e., at the time period associated with contraction of each active material component) since the total force at each stage could be more than the specified limiting force of the active material component in the preceding stage, as the previously activated active material component is isolated by the locking mechanism. For example, the load holding force could be greater than the specified limiting force of the active material component that connects movable member  316  to anchor member  318  after locking of the locking mechanism  394  as the load is then borne by the locking mechanism  394 . Any suitable locking mechanism could be used, including those described with respect to other active actuator assembly embodiments herein. For instance, in the assembly  310  shown in  FIG. 6 , the arm  395  is attached to the movable member  316  and the extension  396  is attached to the anchor member  318 . As the transformation to the fully austenite phase of an active material component connected between movable member  316  and anchor member  318  progresses, movable member  316  is free to translate. Locking occurs when the arm  396  fits into the notch  397  in arm  395  as shown. During the movement to the left of movable member  316  (in the forward transformation to the martensite phase), the locking mechanism  394  is releasable via an upward force (indicated by arrow C) applied to downward extension  389  on extension  396 , compressing spring  399  and thereby pivoting arm  396  about pivot point B to allow its release from the notch  397 . 
         [0071]    Exemplary Embodiment of An Alternative Active Material Actuator Assembly 
         [0072]    Referring to  FIG. 7 , another active material actuator assembly  410  utilizes a “train carts on a railroad” approach to achieve large linear displacement. The active material actuator assembly  410  includes movable members  412 ,  414  and  416 , a fixed member  417  and an anchor member  418 , all of which are linearly aligned on a base member  421 . The movable members  412 ,  414  and  416  slide or roll with respect to the base member  421 , similar to train cars on a railroad track. Although only three movable members are included in the actuator assembly  410  of  FIGS. 7-9 , it should be understood that only two movable members or more than three may alternatively be used. The fixed member  417  and the anchor member  418  are secured to and do not move with respect to the base member  421 . The interface between the movable members  412 ,  414 ,  416  and the base member  421  could be any shape and configuration. In cross section, the base member  421  could be circular, oval, rectangular, triangular, square, etc., as long as the movable members  412 ,  414  and  416  are configured with a mating shape to partially surround the base member. The interface can also be in a dove-tailed shape as shown in  FIG. 7 . As an alternative approach, the base member  421  could have multiple slots, one for each movable member. It is therefore very easy to prevent overstretching and release each movable member at the appropriate location, as the distal end of a slot will always be the desired location for release of a movable member. 
         [0073]    With regard to  FIG. 7 , the movable members  412 ,  414  and  416  are connected to the anchor member  418  via respective active material components  444 ,  438  and  432 , respectively. The movable members  414  and  416  and the fixed member  417  have a set of aligned openings therethrough that allow active material component  444  to pass through to connect at a distal end to the movable member  412  and at a proximal end to the anchor member  418 , as illustrated. Movable member  416  and fixed member  417  have another set of aligned openings that allow active material component  438  to pass through to connect at a distal end to movable member  414  and at a proximal end to anchor member  418 . Finally, fixed member  417  has yet another opening therethrough that allows active material component  432  to pass through to connect at a distal end to movable member  416  and at a proximal end to anchor member  418 . The ends of each active material component  432 ,  438  and  444  are crimped (or attached by any other suitable means such as welding or adhesive bonding) to maintain positioning. In an alternative design, the active material components  432 ,  438  and  444  connect a respective extension (e.g., a rod or bar) extending from the respective movable member to an extension (e.g. a rod or bar) extending from the anchor member  418  rather than passing through openings in the movable members and the fixed member. To avoid bending and to increase fatigue life, the crimped ends of the active material components  432 ,  438 , and  444  at the anchor member  418  are able to slide rightward during actuation. It is preferred that the bending momentum on the actuator assembly  410  induced by the active material components  432 ,  438  and  444  is minimized by design choice of active material composition, cross-sectional area of the active material components and the structural strength of the base member  421 , the movable members  412 ,  414 ,  416 , fixed member  417  and anchor member  418 . The active material components  432 ,  438  and  444  are shown in extreme extended positions, in a martensite phase, in which the movable members  412 ,  414  and  416  will not move further to the left. The movable members  412 ,  414  and  416  can either roll (via wheel(s) attached to respective movable member with or without bearings), slide or slide and roll on the base member  421  and are separated from each other by predetermined distances according to design. Optionally, multiple anchor members may be utilized so that the proximal ends of the active material components  432 ,  438  and  444  can be at different longitudinal locations with respect to the base member  421 . A load or force that is to be moved by the active material actuator assembly  410  is either formed by the movable member  412  or is mechanically linked to a distal side of it. The load or force may be a weight or spring configured to act as a return mechanism (i.e., to create a force biased against contraction of the active material components  412 ,  414  and  416 ). 
         [0074]    When active material component  444  is activated (by supplying electrical current, as will be discussed below), the recovery or contraction force of the active material component  444  is greater than the total resistance of the load, and the movable member  412  is pulled to the right toward movable member  414 . When movable member  412  moves close to movable member  414 , they lock together via a locking mechanism such as that described in detail with respect to  FIG. 8 . Next active material component  438  is activated to bring movable members  412  and  414  (locked together) to movable member  416 . When movable member  414  is close to movable member  416 , they lock together by locking mechanism such as that described with respect to  FIG. 8 . Similarly, when active material component  432  is then activated, locked-together movable members  412 ,  414  and  416  move to the right and movable member  416  is locked to the fixed member  417  by a locking mechanism as described with respect to  FIG. 8 . 
         [0075]    Locking Mechanism, Releasing Mechanism and Overstretch Prevention Mechanism 
         [0076]    With reference to  FIGS. 7 and 8 , each movable member  412 ,  414 ,  416  includes a locking mechanism. Locking mechanism for movable member  412  includes latch  495 A, pin  497 A and spring  499 A. Latch  495 A is able to enter a slot formed in movable member  414  and go further with pin  497 A passing through due to a slotted keyhole  496 A (see  FIG. 7 ) in the front with a width slightly wider than the diameter of a pin  497 A retained in an opening within the movable member  414 . When movable member  412  touches movable member  414 , the keyhole  496 A in latch  495 A is exactly under the pinhead (i.e., a double-flanged head) of pin  497 A. With a little more shrinking of the active material component  444  (see  FIG. 7 ), the latching pin  497 A will move downward due to the slope of ramped key  498 A and the biasing force of spring  499 A, to fall within the keyhole in latch  495 A. The uppermost flange on the pin  497 A is larger than the bottom hole of movable member  414  and thus rests above it to ensure that the pin  497 A rests in the latch  495 A to latch movable members  412  and  414  together. Movable member  414  (with movable member  412  latched to it) is locked to movable member  416  in like fashion as active material component  438  contracts, and movable member  416  (with movable members  412  and  414  locked to it) is locked to fixed member  417  in like fashion. 
         [0077]    The releasing of the latches is in exactly the reverse order and will be described with respect to the release of movable member  412  from movable member  414 . When movable members  412  and  414  are pulled leftward in  FIGS. 7 and 8  together by the load after actuation when conditions allow active material component  444  to return to its martensite phase, latching pin  497 A touches the slope in the key  498 A, rides up the slope, and the pin  497 A is moved upward until it slides into an upwardly extending stopper portion of the ramped key  498 A. The stopper portion acts as an overstretch prevention mechanism, preventing further movement to the left. At this point, the bottom of the lower flange of the double-flanged head of the pin  497 A (see  FIG. 9  for a view of the double-flanged head) is flush with the top of the latch  495 A and therefore releases it. Similar latches, latching pins and ramped keys are utilized between movable members  414  and  416  and between movable member  416  and fixed member  417 . 
         [0078]    The release of a movable member by releasing the latch must be done when the movable member is at the pre-contraction (original stressed) position. Otherwise, the active material component attached to the movable member may not be stretched enough for next activation and a more distal movable member (activated just prior) will not be able to lock to it. Therefore, the keys  498 A- 498 C are positioned in base member  421  at the desired start position of the movable members  412 ,  414  and  416  or the position of fixed member  417 . 
         [0079]    Since the latching pins  497 A and  497 B move together with the respective movable members  414  and  416 , they should not be blocked by keys  498 B and  498 C, respectively, when moving in the proximal direction. For example, in the fully locked position, the bottom of pin  497 A should be slightly higher than that the top of key  498 B.  FIG. 9  illustrates that the shank portion of the pins  497 A,  497 B, and  497 C have respectively longer lengths and the keys  498 A,  498 B and  498 C are in order of descending height (key  498 A not shown in  FIG. 9 ) so that the more distal movable member, will pass over the more proximal keys during return to the pre-contraction position. The sum length of each locking pin  497 A- 497 C and its matching ramped key  498 A- 498 C is the same for movable members  414  and  416  and fixed member  417 . Alternatively, to reduce the overall height in comparison with actuator assembly  410 , movable members with different widths can be used with keys offset along a horizontal transverse direction such that the keys can be of same height. 
         [0080]    Although only one locking mechanism is shown here, any other existing mechanisms or new mechanisms can be adapted for use with any of the active material actuator assemblies described herein, such as a solenoid-based locking mechanism, a smart materials-based locking mechanism, a safety belt buckle-type latch design, or a toggle on-off design such as in a child-proof lock/release for doors or drawers or in a ball point pen. For example, the cart may have a keyhole, such as a T-shaped slot on a surface facing an adjacent cart. The adjacent cart may have a latch designed to fit in the upper portion of the T-shaped slot (i.e., the horizontal portion of the T-shape) and slide into the lower portion (i.e., the vertical portion of the T-shape) when the cart with the latch moves along a ramped track toward the cart with the T-shaped slot to lock the two carts to one another. The slope of the ramped track is designed to cause the relative vertical displacement between the two carts that enables latching and releasing of the latch from the T-shaped slot. 
         [0081]    Other examples of locking and release mechanisms include a locking mechanism having a latch on one movable member that is configured to slide into a slot of an adjacent movable member. A separate release member can be actuated to push the latch out of the slot, thus releasing the two movable members from one another. The release member may be a roller attached to the end of a spring. The latch rolls along the roller when released, thus avoiding direct contact with the adjacent movable member during its release and reducing friction associated with the release movement. 
         [0082]    Holding Mechanism 
         [0083]    Power off holding is desirable for either full displacement (when the most proximal movable member  416  is locked to the fixed movable member  417 ) or at discrete displacement when a movable member is locked to the next movable member. Power off holding means utilizing a holding mechanism to hold a movable member at a post-activation contracted position, when the activation input is ceased (e.g., when the power is off if resistive heating is used or if temperature cools below the Austenite start temperature in the case of convective or radiant heating). For the embodiment shown in  FIG. 8 , the key  497 A can be lowered down to lock movable members  412  and  414  together. By moving a sliding block  484  underneath the base member  421  along the longitudinal direction, the keys  498 A- 498 C will move off of raised bumps  485  on block  484  and be lowered down due to spring force exerted by springs  499 A- 499 C. With the keys  498 A- 498 C in a lowered position, even though the locking pin  497 A of movable member  414  slides on the slope of key  497 A during return of the active material component  438  to the martensite phase, key  497 A will not be able to push the locking pin  497 A far enough up in order for the lower surface of the lower flange of the pinhead to clear the keyhole opening in latch  495 A. Moving the sliding block  484  will cause holding of the movable members at the key associated with the most proximal of the movable members which have been moved or at the fixed member  417  if all of the movable members have already been moved to the right when the sliding block  484  is moved. To cancel the holding in order to release the movable members, the sliding block  484  can be moved back so that all the keys  497 A-C are pushed up. The vertical displacement of the keys via the sliding block  484  is small and the horizontal movement of the sliding block  484  can be achieved via many mechanisms, such as an electronic solenoid or a short SMA wire. 
         [0084]    An alternative holding mechanism is illustrated in  FIG. 7  with respect to movable member  412 . The alternative holding mechanism includes a pawl  486  and a ratchet portion  487  of the base member  421 . The pawl  486  allows the movable member  412  to be held at any position. To release the movable member  412 , the pawl  486  is pulled away (either rotated upward or pulled upward) from the ratchet portion  487  by a mechanism (not shown) such as an electronic solenoid or a short SMA wire. 
         [0085]    Automatic Activation 
         [0086]    The active material actuator assembly  410  can automatically mechanically activate the active material components sequentially to eliminate control logic and therefore reduce the cost. To realize this, the proximal ends of the active material components  432 ,  438  and  444  at the anchor member  418  are all connected to the negative pole of the electric current supply, such as a battery (supply not shown) and the positive pole of the electric current supply is connected to separate electrical contact strips  491 A,  491 B and  491 C each located on the base member  421  between movable members (see  FIG. 7 ). The bottom of each movable member  412 ,  414  and  416  has its own specific electrical contact strip running fore and aft (in the same direction that the movable members  412 ,  414  and  416  move) that is aligned with a specific electrical contact strip on the base member  421 . For example, referring to  FIG. 7 , movable member  412  has electrical contact strip  490 A (shown with dashed lines) on a bottom surface thereof that is aligned with electrical contact strip  491 A (also referred to herein as a first active material activation mechanism) on the base member  421 . Movable member  414  has an electrical contact strip  490 B on a bottom surface thereof that is aligned with electrical contact strip  491 B (also referred to herein as a second active material activation mechanism) on the base member  421 . Movable member  416  has an electrical contact strip  490 C (shown with dashed lines) on a bottom surface thereof that is aligned with electrical contact strip  491 C on the base member  421 . The active material component connected to each distal movable member always maintains electrical contact with the electrical contact strip on the bottom of the movable member it is attached to. When a switch (not shown) is turned on to allow power flow from the electric current supply, active material component  444  will be in a closed circuit (the circuit including the electrical contact strip  490 A, the electrical contact strip  491 A, the active material component  444  and the power leads) causing active material component  444  to contract and move movable member  412  toward movable member  414 . After movable members  412  and  414  lock together, further movement of movable member  412  will cause electrical contact strip  490 A to be out of contact with electrical contact strip  491 A on the base member  421  and will cause the electrical contact strip  490 B at the bottom of movable member  414  to be in contact with electrical contact strip  491 B on the base member  421 . At this point, active material component  444  is in open circuit and active material component  438  is in closed circuit. Thus, an activation input to the second movable member, i.e., power from the electric current supply attached to the power leads, activates the active material component  438  to move the movable member  414  (and movable member  412  locked thereto). This “automatic activation” of the next active material component via movement of the previous movable member will be repeated until the movable member  416  reaches fixed member  417 . By using a contact switch on movable member  417 , the power can be turned off. 
         [0087]    By locking each locking mechanism as each respective active material component  444 ,  438 , and  432  contracts, the load operatively attached to the first movable member or the first movable member itself has a travel distance equaling the sum of the respective gaps (i.e., the open space along base member  421 ) between movable members  412  and  414 , between movable members  414  to  416  and between movable member  416  and fixed member  417 . To return the load back toward the distal end of base member  421 , the holding mechanism is first released (i.e., sliding member  484  is moved) if it was utilized, and the latch  495 C is released from the locking pin  497 C. As the active material component  432  is cooled and applies less resistance to stretching, the force of the returning mechanism also referred to as the load (e.g., a dead weight, a constant spring, a linear spring, a strut) is able to pull all the movable members  412 ,  414  and  416  toward the distal end of the base member  421 . When movable member  416  is closer to its designed pre-contraction position, the latching between latch  495 B and locking pin  497 B is released by ramped key  498 B and therefore movable member  416  can be detached from movable members  412  and  414 . Similarly, movable member  414  will detach from movable member  412  and stop at the designed pre-contraction location due to the ramped key  498 A. 
         [0088]    Large displacement can be achieved by the active material actuator assembly  410 , as many movable members can be added. The surface area between the movable members and the base member  421  (on which the movable members slide, roll or roll and slide) can be minimized to reduce friction losses. Finally, the returning force of the load can be matched very easily by a load holding force profile as the size or number of active material components, the composition and/or the transformation temperatures can be different for different movable members. Therefore, any returning mechanism such as strut, dead weight, linear spring, constant spring etc. can be chosen for convenience and performance. To have proper fatigue life and for safety and reliability, it is important that the active material components are not over-stretched by the returning mechanism. 
         [0089]    In the embodiment shown in  FIG. 8 , all of the movable members  412 ,  414  and  416 , and the fixed member  417  have same sized components (the body of movable member or fixed member, the latches  495 A- 495 C, the setscrew at the top of each movable member  412 ,  414 ,  416  and fixed member  417  to adjust the tension of springs  499 A- 499 C) as shown in movable members  412 ,  414  and  416 , as well as components of varying dimension (locking pin  497 A and ramped key  498 A) as shown in and discussed with respect to  FIG. 9 . 
         [0090]      FIG. 9  shows movable member  412  locked to movable member  414  which is locked to movable member  416 . Key  498 B acts as a power off holding mechanism as it is raised by bump  485  to interfere with pin  497 B.  FIG. 9  illustrates the positioning just prior to automatic activation of active material component  432  (not shown in this cross-section) to move moveable member  416  to lock to fixed member  417 . 
         [0091]    Exemplary Embodiments of Other Active Material Actuator Assemblies 
         [0092]    Referring to  FIG. 10 , an active material actuator assembly  510  includes a movable member in the form of a shaft  512  that is rotatable about a center axis  513 . The shaft  512  is concentric with an opening of a base member  517  and rotates therein. Optionally, a bearing may be placed between the shaft  512  and the base  517  to aid rotation. Referring to  FIG. 11 , on an opposite side of the base  517 , a cam lobe  519  is connected for rotation with the shaft  512 . Referring again to  FIG. 10 , an extension member, which may be referred to herein as a pin  521  extends from the shaft  512  such that it is offset from and parallel with the center axis  513 . Multiple active material components  532 ,  538 ,  539  and  544 , shown in the form of wires (but which may be belts, straps, strips, thin plates, chains or other shapes), have one end attached to the pin  521 . Active material component  532  is bent over pulley  523 A and further bent over pulley  525 A and extended toward the bottom of the base  517  where an end is attached to retaining pin  527 A. Active material component  538  is bent over pulley  523 B and extends toward the bottom of the base  517  where it attaches at an end to retaining pin  527 B. Active material component  539  is bent over pulley  523 C and extends toward the bottom of base  517  where it attaches to retaining pin  527 C. Active material component  544  is bent over pulley  523 D and further bent over pulley  525 B and extends toward the bottom of base  517  where it attaches to retaining pin  527 D. As an alternative to the pulleys  523 A-D and  525 A-B, gears may be used with the active material components  532 ,  538 ,  539  and  544  (or at least a nonactive wire portion connected thereto) being in the form of chains. The pulleys  523 A- 523 D (or gears if used instead of pulleys) are also referred to herein as sliding elements. 
         [0093]    By bending the active material components  532 ,  538 ,  539  and  544  via pulleys  523 A-D and  525 A-B to extend in a common direction, packaging size is greatly reduced, with only one long dimension (the distance between the pulleys and the retaining pins at the bottom of the base member  517 ) accommodating the length of the active material components. Optionally, to avoid fatigue degradation due, directly or indirectly, to bending of the active material components, regular metal wires (or belts, strips, etc.) having long fatigue life may be used for any portion experiencing bending and active material composition may be used only for the portion from the respective pulleys  525 A,  523 B,  523 C and  525 B to the retaining pins  527 A-D (i.e., the portion that remains straight throughout the actuation cycle). 
         [0094]    The base member  517  has multiple slots  529 A,  529 B,  529 C and  529 D extending therethrough. Extension portions of the pulleys  523 A,  523 B,  523 C and  523 D extend through the respective slots  529 A,  529 B,  529 C and  529 D so that a portion of each pulley is in contact with a cam surface  531  of the cam lobe  519 . 
         [0095]    Resetting Cooled Active Material Components and Avoiding Stretching of Hot Active Material Components 
         [0096]    The active material components  532 ,  538 ,  539  and  544  can be actuated in that order in a repeating series (or in the reverse order in a repeating series) to move the pin  521  and therefore rotate the shaft  512  to which a load is attached (or which constitutes a load). Both clockwise and counterclockwise rotation can be equally achieved in the actuator  510  by reversing the order of actuation. To avoid overstretching, to decrease resistance to stretching of a just actuated and still hot active material component and to decrease response time, the pulleys  523 A- 523 D are designed to move in the respective slots  529 A- 529 D according to the cam surface  531  (i.e., the cam profile) of the cam lobe  519 , shown in  FIG. 11 . In  FIG. 11 , pulleys  523 C and  523 D are shown on a larger arc of the cam surface  531  and in the farthest position relative to the center axis  513 . In contrast, pulleys  523 A and  523 B are on a smaller arc and in the nearest position relative to the center axis  513 . The pin  521  is nearest to pulley  523 C (see  FIG. 10 ), active material component  539  (referred to in the claims as the first active material component) has just been actuated and it is time to activate active material component  544  (referred to in the claims as the second active material component). During the contraction of active material component  544 , pulley  523 D will sit on the: larger arc and remain a constant distance to the center axis  513 . The pin  521  will be pulled and moved toward pulley  523 D. Pulley  523 C will move toward the center axis  513  because it will be on the smaller arc when pin  521  moves near pulley  523 D. Due to this inward motion of pulley  523 C sliding in slot  529 C toward the center axis  513 , the previously actuated and potentially not yet cooled active material component  539  will not be further stretched and will apply no resistance to the work done (i.e., to the rotation of shaft  512 ) by actuation of active material component  544  provided the portion of active material component  544  (or wire if that portion is not active material) between pulley  523 C and retaining pin  527 C is barely stretched. This portion of active material component  544  between pulley  523 C and retaining pin  527 C will change in length only a minimal amount if it is nearly perpendicular to the longitudinal direction of the slot and if it is much longer than the longitudinal dimension of the slot.  FIG. 10  is schematic in nature and the dimensions are not to scale. Positions and shapes of the slots and positions of the retaining pins are also schematic. In addition, additional pulleys (not shown for simplicity) may slide with pulleys  523 A-D and help with the routing of the active material components. Although pulley  523 B sits on the same smaller arc during this period, the cooled active material component  538  is stretched since pin  521  moves near to pulley  523 D from a position near pulley  523 C. Pulley  523 A increases its distance from the shaft center during this period since the rotating cam  519  causes it to slide in slot  529 A and move to a larger arc, maintaining the length of the active material component  532  between pin  521  and pulley  523 A. When activation of active material component  544  is complete, active material component  532  is in the right position and ready for a subsequent activation. 
         [0097]    Within the scope of the invention, the number of active material components is not limited to four. A rotational motor as in  FIGS. 10 and 11  could haven only three or more than four active material components. Furthermore, the slots  529 A-D are not limited to the shape shown. A center line running the length of each slot does not necessarily pass through the shaft center and need not be straight. 
         [0098]    Automatic Activation 
         [0099]    Sequential automatic activation by the mechanical rotation of the shaft  512  can be utilized to allow the elimination of control logic to activate the active material components  532 ,  538 ,  539  and  544  sequentially and therefore potentially reduce cost. The four individual ends of the active material components connected to pins  527 A through  527 D can be connected to the negative pole of a battery (not shown). Referring to  FIG. 12 , the positive pole of the battery is connected to a switch  589  and then connected to an electrical brush  533  on the cam surface  531  of cam  519 . An electrical contact strip  535  extends partially around the cam surface  531 . The contact strip  535  is in electrical contact with a circular electrical strip  537  on the cam surface  531  that touches the brush  533  at all times. On the surface of each pulley  523 A,  523 B,  523 C and  523 D that touches the cam surface  531 , there is a circular electrical contact strip  541 A,  541 B,  541 C and  541 D, respectively, positioned to be sequentially in contact with the contact strip  535  as the shaft rotates. The circular electrical contact strip  541 A- 541 D on each pulley  523 A- 523 D is electrically connected to the surface area of the pulley that the respective active material component is touching (or that a non-active material portion, e.g., a metal portion of a wire, strip, chain or belt that is connected to an active material portion, as explained above, is touching). All surface areas of the cam surface  531  and of the pulleys  523 A- 523 D are non-conducting except those mentioned above. 
         [0100]    When the switch  589  is closed (i.e., by turning on the actuator assembly  510 ), electrical power runs to the full circle electrical contact strip  537  and to whichever one of the pulleys  523 A- 523 B is then positioned in contact with the contact strip  535  (pulley  523 C in  FIG. 12 ). The active material component connected with that pulley is activated to move the pin  521 . Movement of the pin  521  due to actuation of that active material component, as described above, will rotate the cam  519 , causing the next sequential one of the pulleys to be positioned in contact with the electrical contact strip  535  to activate the active material component connected thereto (and will cause the previously actuated active material component to move out of contact with the contact strip  535 ). The contact strip  535  may extend  90  degrees or so around the cam surface such that only one of the four pulleys  523 A- 532 D is in contact with the contact strip  535  at any given time. Alternatively, the contact strip may extend less than 90 degrees, to allow a longer cooling period between activations, or greater than 90 degrees such that there is some overlap of activation of the active material components. The portion of the cam profile  519  about which the contact strip  535  extends may be longer if only three active material components and corresponding pulleys are used, or shorter if more than four are used. In general, the portion over which the contact strip  535  extends is cam-profile dependent. 
         [0101]    Power off holding of the active material actuator assembly  510  is desirable. It can be realized via the locking mechanism (and corresponding release mechanism) similar to that described with respect to the active material actuator assemblies  410  above or a ratchet mechanism. 
         [0102]    Another embodiment of an active material actuator assembly  610  operating as an incremental rotational motor is shown in  FIG. 13 . A shaft  612  with an extension or pin  621  is concentric with a hole through a cylindrical housing  617  and rotates with or without the help of a bearing. Active material components  632 ,  638 ,  639  and  644  are attached to the biased pin  621  at one end, bent over pulleys  623 A-D and  625 A-D and attached to retaining pins at the other end of the cylindrical housing (pins not shown, but  FIG. 14  shows the active material components in fragmentary view extending toward the pins). The pulleys  623 A-D and  625 A-D sit on sliders  643 A-D that slide in slots  629 A-D of the cylindrical housing  617 . The active material components  632 ,  638 ,  639  and  644  can be activated sequentially and therefore rotate the shaft  612  with respect to the cylindrical housing  617 . Since all the active material components  632 ,  638 ,  639  and  644  are bent (via the pulleys  625 A-D) to extend in the axial direction of the shaft  612 , sufficiently-sized active material components able to achieve large displacement (e.g., active material components of a sufficient length to achieve adequate displacement of the movable member via contraction of each active material component) are enabled while packaging size is minimized. Optionally, to avoid fatigue degradation due to bending of active material components, non-active material portions (e.g., regular metal wire) having long fatigue life can be substituted for any portion of the active material components experiencing bending and active material can be used only in the portion that remains straight throughout the actuation cycle, i.e., the portion nearly parallel to the axial direction of the shaft  612 . 
         [0103]    The sliders  643 A- 643 D ride on a cam lobe  619  of the shaft  612 . The cam profile  631  (shown in the  FIG. 14 ) allows the slider to which the just-actuated active material component is operatively connected to move toward the center of the shaft  612  and therefore prevents being pulled by the next-actuated active material component. The cam profile  631  therefore utilizes the contraction force of the active material components more efficiently (i.e., utilizes the force to turn the shaft rather than to work against restrictive force of the just-actuated active material component), allows more cooling time before stretching of a previously actuated component, and decreases the cycle time of the actuator assembly  610 . The cam profile  631  can also be made to avoid unnecessary overstretching of the active material components. In  FIGS. 13 and 14 , each active material component is only stretched by the opposite actuated active material component (i.e., active material component  644  is stretched when active material component  638  is actuated and vice versa, and active material component  639  is stretched when active material component  632  is activated and vice versa) and the amount of stretch is the same as the amount needed to pull the pin  621  and rotate the shaft  612  when it is actuated. 
         [0104]    Automatic activation is possible which will eliminate the use of control logic to activate wires sequentially and therefore reduces the cost. By providing an electrical contact strip only partially extending around the cam surface similarly to electrical contact strip  535  in the embodiment of  FIG. 12 , the respective active material components will be activated sequentially as the shaft  612  rotates. Power off holding is desirable and it can be realized via a ratcheting or locking and releasing mechanisms, as described with respect to other embodiments herein. 
         [0105]    Note that in the active material actuator assembly  610 , the number of active material components is not limited to four. There could be only three active material components or more than four. The slots  629 A-D are not limited to the configuration shown. The center line of the slots does not necessarily pass through the shaft center and is not necessarily straight. In addition, both clockwise and counterclockwise rotation can be equally achieved in the said mechanism. Moreover, to reduce response time and decrease cooling time while maintaining required force, several thinner SMA components can be used in place of each active material component (e.g., several thinner SMA wires in place of each single SMA wire) to connect the distal end. 
         [0106]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.