BIDIRECTIONAL, LINEAR AND BINARY, SEGMENTED ANTAGONISTIC SERVOMECHANISM-BASED SHAPE MEMORY ALLOY (SMA) ACTUATOR

Abstract

A Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator comprising a main stroke transmitting lever (11 or 18) and a plurality of part-modules (15A or 15B) disposed in a closely spaced arrangement and adapted to undergo a reciprocal translation in a first direction. wherein, the part-modules comprising a plurality of segments having SMA elements (12). The invention provides two configurations arranged in straight and cross configurations of the SMA elements in the part-modules. Further above configuration are arranged in a tight close space however, the cross configuration provides additional 40% compactness. The configurations comprise a S-type long tail or flipped F-type long tail main stroke transmitting lever and plurality of straight or cross configurations part modules, respectively. The novel embodiment can be utilized for micro-positioning of 3D printer filament extruder head, linear and angular displacement applications such as robotic, prosthesis, bi-stable position control, latching-unlatching systems, and other wide engineering applications.

Claims

1. A Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator in straight configuration comprising: a main stroke transmitting lever (11) and a plurality of part-modules (15A) disposed in a closely spaced arrangement and adapted to undergo a reciprocal translation in a first direction; wherein, the part-modules (15A) comprising a plurality of segments having SMA elements (12), further, the segments of the SMA elements are connected between the adjacent part-modules and the main stroke transmitting lever, and each segment of the SMA element extending longitudinally in the first direction; wherein the main stroke transmitting lever undergoes reciprocal translation in the returned direction from the first direction by closely spaced arrangement in opposite/antagonistic configuration by the plurality of part-modules; wherein, the antagonistic configuration of part-modules comprises the plurality of segments of the SMA elements, each segment extending longitudinally generally in the returned direction and segment of the SMA elements connected between two adjacent part-modules and main stroke transmitting lever; wherein, the antagonistic configuration of segment SMA wire elements in series cascading arrangement at both sides of the mechanical lever to provide additive resultant stroke in both forward and reverse direction; wherein, the resultant stroke of the actuator would be used to provide linear and angular or circular motion of actuation; wherein, the present invention of the linear SMA actuator is capable to provide variable stroke displacement from minimum to maximum stroke length with variable magnitude of actuation force in both forward and reserved direction; wherein, Joule heating to the segments of the SMA elements beyond the phase transition temperature causes contraction in the segments of the SMA elements to urge the part-modules to translate the displacement of the main stroke transmitting lever in the first direction, each part-module undergoing a stroke displacement concerning the adjacent part-modules; wherein the stroke transmitting lever provides the motion between the first direction and the reverse direction of full stroke displacement forming a straight configuration; wherein, the full stroke displacement will be achieved maximum 8% strain recovery of the SMA wire contraction; wherein the actuator designed to accommodate the whole length of the SMA wire elements in miniaturize space in segmented length, the segments of the SMA elements (12) are cascaded in series arrangement along with rigid movable strips; wherein, joule heating to the segments of the SMA elements at antagonistic side part-modules beyond the phase transition temperature that causes contraction in the antagonistic side segments of the SMA elements and urge the antagonistic part-modules to translate the displacement of the main stroke transmitting lever in the reverse direction, each antagonistic part-modules undergoing stroke displacement with respect to adjacent part-modules.

2. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 1, wherein the part-modules comprises a plurality of segments of the SMA elements and a plurality of conducting/non-conducting rigid strips S-type of curve ends, if non-conducting material is used, then suitable electrical conductivity needs to provide between the ends; wherein, the strip designed in such a way to move linearly in the first direction and reverse direction through guiding slit with guided pins; wherein the plurality of segments of the SMA elements formed the serial mechanical and electrical connection between the adjacent part-modules and the main stroke transmitting lever S-type with long tail, that combines the stroke displacements of the part-modules in an additive manner; the curved ends of strips are welded with open ends of the segments of the SMA elements to form the series electrical and mechanical connections that produce resultant long stroke displacement in the first direction and the reverse direction.

3. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 1, wherein the part-modules with the segments of the SMA elements create series cascading of electrical conductivity from the first curve end of the part-module to a second curve end of adjacent the part-module and similarly series cascading continues with next set of part-modules first curve end to the adjacent part-module second curve end create first direction cascading link; wherein, identical configuration also develops in opposite/antagonistic side of the main stroke transmitting lever to create reverse direction cascading link to complete the novel embodiment assembly by array formation.

4. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 1, wherein to create series electrical connectivity, first direction and reverse direction, part-modules; the segments of the SMA elements are connected end-to-end by electric arc spot welding technique for passing the electrical current from the first end of the segment of the SMA element to the next end of adjacent part-module to the last segment of the SMA element of adjacent part-module to the fixed anchor point.

5. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 1, wherein the plurality of part-modules are configured in a nested, concentric, telescoping relationship either increasing in width wise or increasing in height wise for maintaining the constant volume that provides design flexibility.

6. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 1, wherein the part-modules on each side of the main stroke transmitting lever in the antagonistic configuration are electrically isolated from each other, however, the part-modules at each side are in series electrically connected encompassing all the plurality of the segments of the SMA elements.

7. The Bidirectional, linear Segmented, Binary Antagonistic Servomechanism-based Shape Memory Alloy (SMA) actuator as claimed in claim 1, wherein the plurality of sub-modules includes a plurality of strips and displacement of each strips are added to the next strip displacement and so on to the last strip that provides the resulting total additive stroke displacement in the first direction stroke and similar stroke displacement obtained in the reverse direction, wherein the actuator can applicable in the bidirectional movement of the 3D printer head.

8. A Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator in a cross-configuration, comprising: a flipped-F-type long tail main stroke transmitting lever 18 and plurality of I-section type part-modules 15B arranged in closely spaced arrangement and undergoes reciprocal translation in a first direction; wherein the cross-configuration part-modules 15B comprises plurality of segments of the SMA element 12, S-type rigid strip 10 and flipped S-type rigid strip 16 combines to form I-section type structure; wherein segments of the SMA elements formed the series cascading configuration through top-side of I-section type part-module 15B extending longitudinal generally in the first direction with adjacent cross-configuration created with part-modules 15B; wherein, joule heating to the top-side series cascading configuration of the segments of the SMA elements beyond the phase transition temperature to contract and urge the I-section type part-modules 15B to translate the displacement at the flipped-F-type main stroke transmitting lever 18 in the first direction, here each I-section type part-modules 15B undergoing the stroke displacement with respect to the adjacent arranged part-modules 15B; wherein in an actuator assembly of cross-configuration, the flipped-F-type long tail main stroke transmitting lever 18 undergoes reciprocal translation in the returned direction from the first direction by the closely spaced arrangement of I-section type part-modules 15B, wherein segments of the SMA elements 12 formed the series cascading configuration through the bottom side of the strip, extending longitudinally generally in the returned direction with adjacent cross-configuration formed by the part-modules 15B; wherein, joule heating to the bottom-side series cascading configuration segments of the SMA elements beyond the phase transition temperature to contract and urge the I-section type part-modules 15B to translate the displacement at the flipped-F-type main stroke transmitting lever 18 in returned direction, here each I-section type part-modules 15B undergoing the stroke displacement with respect to adjacent arranged part-modules; wherein the plurality of I-section type part-modules arranged in close tight spaced which comprises of two conducting/nonconductive rigid strips jointed with a sandwich of the insulating strip 17, and a plurality of segments of the SMA elements 12 welded tightly at the ends of the top-side and bottom-side of I-section part-module stripes, which formed the link of segments of the SMA elements in series cascading arrangement along with flipped F-type; wherein main transmitting module comprised of two strips jointed together with insulating strips for electrical isolation and coupled mechanically to transfer strain during phase transformation; wherein, the loose ends of series connected segments of the SMA elements link terminates at fixed anchor point to complete the mounting; wherein, further includes first ends of the top and bottom series links made of SMA elements are connected to the both ends of the flipped F-type main stroke transmitting lever and remaining ends of top and bottom series link are connected to the fixed anchor points of the main base plate.

9. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 1, wherein actuator provides Max pull/push force of range 2.6 kg; wherein, actuator element(s) length 165 mm (3 segments of 55 mm at each side); wherein, the stroke length (mm)?5 mm (Up to 6, @ 3 elements at each side); wherein, the Actuator element(s) diameter 0.381 mm; wherein, the Number of Actuator element(s) Minimum2 Numbers @ 1 element at each side and Maximum-Multiple of 2 (Up to 6, @ 3 elements at each side) (depending on the required displacement); wherein the Transformation Temperature is of 70-90? C.; wherein, the Stroke length range 2-8 mm (Depending on the no. of actuator element); wherein, the Stroke direction is Bi-direction; wherein, input Voltage 4.2 V DC; wherein, the peak Current ?1 A; wherein the power of 4.2 Watts; wherein the Full Stroke Actuation time is of 1-3 Seconds; wherein the Reset time interval of 1-2 Seconds; wherein the 14. Actuation Control PWM based controller; wherein, SMA actuator is miniaturize in size, capability of efficient rapid heating control module, stroke sensing mechanisms and suitable for accurate position control application by suitable external logical/PC/microcontroller-based control system.

10. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 8, wherein actuator provides Max pull/push force of range 2.6 kg; wherein, actuator element(s) length 165 mm (3 segments of 55 mm at each side); wherein, the stroke length (mm)?5 mm (Up to 6, @ 3 elements at each side); wherein, the Actuator element(s) diameter 0.381 mm; wherein, the Number of Actuator element(s) Minimum2 Numbers @ 1 element at each side and Maximum-Multiple of 2 (Up to 6, @ 3 elements at each side) (depending on the required displacement); wherein the Transformation Temperature is of 70-90? C.; wherein, the Stroke length range 2-8 mm (Depending on the no. of actuator element); wherein, the Stroke direction is Bi-direction; wherein, input Voltage 4.2 V DC; wherein, the peak Current ?1 A; wherein the power of 4.2 Watts; wherein the Full Stroke Actuation time is of 1-3 Seconds; wherein the Reset time interval of 1-2 Seconds; wherein the 14. Actuation Control PWM based controller; wherein, SMA actuator is miniaturize in size, capability of efficient rapid heating control module, stroke sensing mechanisms and suitable for accurate position control application by suitable external logical/PC/microcontroller-based control system.

11. The Bidirectional, Linear and Binary, Segmented Antagonistic Servomechanism-based Shape Memory Alloy (SMA) Actuator as claimed in claim 8, the cross configuration of the part-module provides 40% compact to straight configuration of the embodiment, wherein the actuator can be applicable in the bidirectional movement of the 3D printer head.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] These and other features, aspects, and advantages of the disclosure will become better understood when the following drawing description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0040] FIG. 1 is the drawing of an isometric view illustrating the application of bidirectional segments of the shape memory alloy elements for the micro-positioning of the 3D printer head extruder, as per an embodiment herein.

[0041] FIG. 2 is the diagram that illustrates the orthographic view of the assembly of the main stroke transmitting lever and part-modules on antagonistic/opposite sides of the main stroke transmitting lever to provide bidirectional linear additive stroke and other essential components, as per an embodiment herein.

[0042] FIG. 3 is the diagram illustrating the main stroke transmitting lever, as per an embodiment herein.

[0043] FIG. 4 is the diagram showing the segment of the SMA element, as per an embodiment herein.

[0044] FIG. 5 is the diagram illustrating the assembly of the segments of the SMA element and the main stroke transmitting lever, as per an embodiment herein.

[0045] FIG. 6 is the diagram illustrating the assembly of the S-type part module, as per an embodiment herein.

[0046] FIG. 7 is the exploded assembly view of the straight configuration for the embodiment.

[0047] FIG. 8 is the diagram illustrating the working stages of the straight configuration of the embodiment in backward position, central position, and forward position, as per an embodiment herein.

[0048] FIG. 9 is the diagram illustrating the exploded assembly of the cross configuration for the embodiment, as per an embodiment herein.

[0049] FIG. 10 is the diagram illustrating the assembly of the I-type section part-module, as per an embodiment herein.

[0050] FIG. 11 is the diagram illustrating the assembly of flipped F-type stroke transmitting lever, as per an embodiment herein.

[0051] FIG. 12 is the diagram illustrating the working stages of the cross configuration of the embodiment in backward position, central position, and forward position, as per an embodiment herein.

[0052] FIG. 13 is the measured stroke displacement with applied PWM current pulses for control heating, as per an embodiment herein.

[0053] FIG. 14 is the repetitive measurement of the full stroke displacement with applied PWM current pulses for control heating for forward and backward motion, as per an embodiment herein.

[0054] FIG. 15 is the measured net load for external work done with applied PWM current pulses for control heating, as per an embodiment herein.

[0055] FIG. 16 is the repetitive measurement of net load with applied PWM current pulses for control heating of the forward and backward motion, as per an embodiment herein; and

[0056] FIG. 17 is the measurement of the net load and total stroke displacement by the embodiment in reiterative cycles, as per an embodiment herein.

[0057] Labels of figures: 1. Printer head base plate, 2. Circular guideway with bush assembly, 3. Extruder Throat, 4. Heater Block, 5. Nozzle, 6. Guide Shaft, 7. Stroke transfer connecting link, 8. Mounting base, 9. Mounting plate, 10. S-type rigid strip(s) (10A-10D), 11. S-type long tail stroke transmitting lever(s) (11A, 11B), 12. Segment(s) of the SMA element (12A-12F), 13. Fastening pin(s), 14. Crimp by metallic ferrule(s) (14A-14B), 15. Part-module(s) (15A, 15B), 16. Flipped S-type rigid strips, 17. Insulating strip, 18. Flipped F-type long tail main stroke transmitting lever, 19. Mounting and guiding slit.

[0058] Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION

[0059] To promote an understanding of the principles of the disclosure, reference will now be made to the various embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the disclosure as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the disclosure and are not intended to be restrictive thereof.

[0060] Reference throughout this specification to an aspect, another aspect or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, appearances of the phrase in an embodiment, in another embodiment, some embodiments, one or more embodiments and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. The terms comprises, comprising, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by comprises . . . a does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0061] Embodiments of the disclosure will be described below in detail with reference to the accompanying drawings.

[0062] The present invention provides a bidirectional, linear and binary segmented antagonistic servomechanism-based shape memory alloy (SMA) actuator, wherein the straight configuration comprising: a main stroke transmitting lever (11) and a plurality of part-modules (15A) disposed in a closely spaced arrangement and adapted to undergo a reciprocal translation in a first direction; wherein, the part-modules (15A) comprising a plurality of segments of the SMA elements (12), further, the segments of the SMA elements (12) are connected between the adjacent part-modules (15A) and main stroke transmitting lever (11), and each segment of the SMA element (11) extending longitudinally in the first direction; wherein the main stroke transmitting lever (11) undergoes reciprocal translation in the returned direction from the first direction by closely spaced arrangement in opposite/antagonistic configuration by the plurality of part-modules (15A); wherein, the antagonistic configuration of part-modules (15A) comprises the plurality of segments of the SMA elements (12), each segment extending longitudinally generally in the returned direction and segment of the SMA elements (12) connected between two adjacent part-modules and main stroke transmitting lever (11);

[0063] The present invention as illustrated in FIG. 1 and FIG. 2, provides an embodiment of the invention which includes a 3D printer head comprises a printer head base plate 1 that holds all supporting accessories and components including a mounting plate 9 of the novel linear actuator to provide exact linear motion of the nozzle 5. The printer head components; A circular guideway assembly 2 having a bush assembly (which includes bush holder 2A and bush 2B) is attached to the printer head base plate 1 to provide a frictionless linear motion to the extruder assembly (4 and 5). The circular guideway assembly 2 guides an extruder throat 3 in linear motion. The mounting base 8 is attached to the printer head base plate 1 by grub screws. In an embodiment, an S-type main stroke transmitting lever 11 is connected with the extruder assembly (4 and 5) by a stroke transfer connecting link 7. The use of a guide shaft 6 provides an external support to the extruder assembly movement and controls linear motion. The guide shaft 6 is fabricated with a stiff, high-strength metal rod; press fitted to the printer head base plate 1. A Teflon bush (not shown) is fixed in the stroke transfer connecting link 7 to provide frictionless motion of the guide shaft 6. The extruder throat 3 works as a guiding path of the printing material/filament to the heater block 4 for the melting of print material. It is also precisely mated width wise with the circular guideway assembly 2 to provide stiffness and linear movement to the extruder assembly (4 and 5). A Teflon tube is pre-filled in the extruder throat 3 to avoid sticking of melted filament. The extruder throat 3 is further connected to the heater block 4, which is fabricated with a metallic material to melt the feed filament and maintain the flow of melted material for the printing process. The extruder throat 3, and the heater block 4 are connected by self-threading. The lower side of the heater block 4 is attached to the nozzle 5 to pass melted material for printing. A hole on the heater block 4 has the provision of fixing an electric heater element (not shown) and a thermocouple (not shown). The stroke transfer connecting link 7, made of a high-strength and thermal insulator material, creates the link between the main stroke transmitting lever 11 and the heater block 4. The invention provides the movement to attach circular guideway assemblies 2 having the Teflon bush, and the connected assembly of heater block 4 and the nozzle 5. It is the part that directly connects the actuator assembly to the heater block 4. It is now joined with the heater block 4 with the help of the tiny screws (not shown). The mounting base 8 holds the complete assembly of the invented linear actuator by a mounting plate 9.

[0064] The present invention as illustrated in FIG. 2, provides an embodiment of the invention which describes the front view of the complete assembly as shown in FIG. 1. The long tail S-type main stroke transmitting lever 11 is connected with the part-modules 15A via the segment of the SMA elements 12 crimped by metallic ferrules 14. The crimping end 14A of the SMA element 12A is welded on the mounting plate 9, and the other end 14B is welded on the end of actuator strip 10A. The pattern follows on the other side also, where the crimping end 14B of the SMA element 12F is welded on the mounting plate 9, and another end 14A is welded on the end of actuator strip 10D. The S-type main stroke transmitting lever 11 is associated in series with other S-type rigid strips (10A-10D) and SMA wire elements (12A-12F) in such that they form the complete links of SMA wire segments. The S-type main stroke transmitting lever 11 and S-type rigid strips (10A-10D) are mounted on the mounting plate 9 with the help of metallic fastening pins 13 (13A-13J). S-type strips 10A and 10B provide backward direction movement to the S-type main stroke transmitting lever 11 whereas S-type strips 10C and 10D provide forward direction movement to the S-type main stroke transmitting lever 11. All the strips (10 and 11) of the embodiment are fixed on the mounting plate 9 with mounting and a guiding slit 19 by the fastening pins 13, in such a way to maintain close tolerance and frictionless sliding.

[0065] The present invention as illustrated in FIG. 3, provides an embodiment of the invention which describes the various parts of the S-type main stroke transmitting lever 11 in which two strips 11A and 11B are attached to each other with a sandwiched insulating strip 17 to maintain electrical insulation with high strength between them.

[0066] The present invention as illustrated in FIG. 4 provides an embodiment of the invention which shows a segment of the SMA element 12, which is to be welded at the ends of the S-type main stroke transmitting lever 11 and S-type rigid strips 10 with the help of the crimped metallic ferrule 14. The interconnection in the series electrical connection of the segments of the SMA elements 12 forms the complete link of the SMA wire actuation. When heating current flows through them, total length changes, which is directly transferred to the S-type main stroke transmitting lever 11 for stroke displacement.

[0067] The present invention as illustrated in FIG. 5, provides an embodiment of the invention which shows the S-type main stroke transmitting lever 11 (FIG. 3) arranged with the segment of the SMA elements (FIG. 4) in such a way that the total displacement from each segment of the SMA elements 12 can transfer to the next part-module SMA segment. The open ends of the segment of the SMA elements 12 are further connected to the S-type rigid strip 10 (part-modules shown in FIG. 6).

[0068] The present invention as illustrated in FIG. 6, provides an embodiment of the invention which shows the S-type part module 15A, which is connected in plurality with the S-type main stroke transmitting lever 11. The S-type part module is assembled with the S-type rigid strip 10 and the segment of the SMA elements 12.

[0069] The present invention as illustrated in FIG. 7, provides an embodiment of the invention which represents an exploded view of the printer head assembly and the complete assembly of linear actuator straight configuration of SMA segments, some of which are in multiple numbers, can be seen in a periodic manner for a connected functioning. The placement of different components such as the S-type rigid strips 10, the S-type main stroke transmitting lever 11, segments of the SMA elements 12, the mounting plate 9, and the fastening pins 13 etc. can be seen in this assembly diagram with all the associated parts, as well as their functioning can be related to each other.

[0070] The present invention as illustrated in FIG. 8 provides an embodiment of the invention which depicts the different working stages of the straight configuration of the linear actuator. Mainly three different working stages are shown and explained in the figure. In the first stage, a backward direction (say negative) additive displacement (?3?l) observe first side links made of three SMA elements, which is caused by applying pulling force generated in other side links made by three SMA element via the S-type main stroke transmitting lever 11. The SMA elements 12A, 12B, and 12C exhibit expansion by the recovery bias force applied due to contraction in the SMA elements 12D, 12E, and 12F; net resulting stroke displacement obtain ?3?l by the S-type main stroke transmitting lever 11. Similarly, the third stage (rightmost corner) shows a positive displacement of ?3?l because the segment of the SMA elements 12D, 12E, and 12F exhibit expansion with respect to bias force applied due to contraction of the SMA elements 12A, 12B, and 12C by the external stimuli. The central geometry is kept at a free position at which no force is acting on any side of the segment of SMA elements 12. The overall total displacement is a summation of individual displacements ?l produced by individual segments of SMA elements (12A-12C and 12D-12F).

[0071] The present invention as illustrated in FIG. 9 provides an embodiment of the invention which shows an assembly of the cross design configuration of the linear actuator in compact design, which provides bidirectional stroke displacement for linear and binary actuation applications. The cross configuration design is 40% compact than the straight configuration of the embodiment. The mounting plate 9 accommodates segments of the SMA elements 12A and 12F welded one end on the anchor at the surface. The other ends of the segments of the SMA elements 12A and 12F are welded on the S-type rigid strip 10A and flipped S-type rigid strip 16A, which are separated by the sandwiched insulating strip 17. Similarly, the rest of the segments of the SMA elements 12B, 12E, 12C, and 12D are attached to strips 10B, 16B, 11B, and 11A. All these strips are attached to the mounting plate 9 by the fastening pins (13A-13F). The SMA elements 12D, 12E, and 12F create forward direction series electrical link and the SMA elements 12A, 12B and 12C create backward direction series electrical link of the SMA. The movement starts by contraction and expansion in the forward and backward SMA elements 12 links when electrical stimuli is applied to either of the link that translates the strain recovery to stroke transmitting lever for net stroke displacement of the embodiment.

[0072] The present invention as illustrated in FIG. 10 provides an embodiment of the invention which shows the isometric view of cross configuration I-section type part-module 15B. The I-section part-module 15B comprising of S-type rigid strips 10 and the flipped S-type rigid strips 16 pasted together with sandwiching of the insulating strip 17 to make I-section type of strip. The segments of the SMA elements 12 are attached at one ends of S-type rigid strips 10 and the flipped S-type rigid strips 16 of the I-section type to develop the complete cross configuration design part module of the embodiment. The part-module 15B is attached with flipped F-type long tail main stroke transmitting lever 18 to create assembly of the embodiment. The role of the sandwich insulating strip 17 is to provide insulation between the top-bottom strips and these strips are maintained the electrical continuity among the top-top side strips and bottom-bottom side strips of attached part-modules. The cross configuration design of the embodiment is highly compact than the straight configuration (FIG. 2). The I-section part-module 15B ensures the motion in forward and backward direction of the flipped F-type main stroke transmitting lever 18 in one direction according to applied control signals.

[0073] The present invention as illustrated in FIG. 11, provides an embodiment of the invention which shows the flipped F-type main stroke transmitting lever 18 used to transfer the stroke displacement with actuation force for external work/actuation, in association of attached part-modules 15B. The segments of the SMA elements 12 are attached at the ends of individual strips at the I-section part-module 15B and the F-type main stroke transmitting lever 18 to build the embodiment (FIG. 9). When there is a contraction in one of the complete links made by the segment of the SMA elements in association with the F-type main stroke transmitting lever 18, it moves in forward direction, and when there is a contraction in other complete link made by the segment of the SMA elements, the flipped F-type main stroke transmitting lever 18, it moves in the backward direction. The tail end of flipped F-type main stroke transmitting lever 18 can be attached for actuation of external work.

[0074] The present invention as illustrated in FIG. 12, provides an embodiment of the invention which shows the working stages of cross configuration design linear actuator. Three distinct stages are shown and explained in the figure. In the first stage, a backward direction (say negative) additive displacement (??l) observe in top series link made of three SMA elements, which is caused by applying pulling force generated in bottom series link made of three SMA element via the flipped F-type main stroke transmitting lever 18. The segment of the SMA elements 12A, 12B, and 12C illustrate a contraction with respect to external stimuli resulting in a net negative movement of ?3?l to the flipped F-type main stroke transmitting lever 18. Similarly, another geometry at the rightmost corner shows a positive displacement of 3?l because the segment of the SMA elements 12D, 12E, and 12F shows a contraction with respect to external stimuli. Second and central geometry is kept at an accessible position where no force is acting on any side of the Segment of the SMA elements 12. The total displacement is a summation of the individual's displacements (?l) produced by group of three segment of the SMA elements, 12A, 12B, 12C in backward (negative) direction and group of three SMA elements in opposite side, 12D, 12E, 12F, produced displacement in forward (positive) directions.

[0075] In another embodiment, the operation of the invented linear actuator is controlled by pulses of electrical energy or train of Pulse Width Modulation (PWM) control signal with a suitable electrical power source. The magnitude of applied electrical power regulates different parameters such as total stroke length displacement, net actuation force generation, response time, operating speed, and working bandwidth of the embodiment. These parameters are also directly related to the dimensions (length and diameter) of employed SMA wire. The overall volumetric dimensions of the assembly depend on the number of part-modules used, and each part-module stroke length contributes to yielding total stroke length in an additive manner and net actuation force by the invention. Therefore, the number of part-modules develop by segmenting the whole length designed SMA wire. The total resultant stroke length represents by SL defined by

SL.sub.f=?.sub.i=1.sup.n?l.sub.i(1)

SL.sub.b=?.sub.i=1.sup.n?l.sub.i(2) [0076] where f is forward and b is backward stroke length of part-module, and i=1, 2, . . . n (segments of the SMA elements in part-module) At equilibrium, the total stroke length (SL) by part-module is

SL.sub.f=?SL.sub.b(3)

TABLE-US-00001 Specifications of the Actuator S. No. Parameter Range 1. Max pull/push force 2.6 kg 2. Actuator element(s) 165 mm (3 segments of length 55 mm at each side) 3. Stroke length (mm) ~5 mm (Up to 6, @ 3 elements at each side) 4. Actuator element(s) 0.381 mm diameter 5. Number of Actuator Minimum2 Numbers @ element(s) 1 element at each side MaximumMultiple of 2 (Up to 6, @ 3 elements at each side) (depending on the required displacement) 6. Transformation 70-90? C. Temperature 7. Stroke length range 2-8 mm (Depending on the no. of actuator element) 8. Stroke direction Bi-direction 9. Input Voltage 4.2 V DC 10. Peak Current ~1 A 11. Power 4.2 Watts 12. Full Stroke Actuation time 1-3 Seconds 13. Reset time interval 1-2 Seconds 14. Actuation Control PWM based controller

[0077] While specific language has been used to describe the subject matter, any limitations arising on account thereto, are not intended. As would be apparent to a person in the art, various working modifications may be made to the method to implement the inventive concept as taught herein. The drawings and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment.

EXAMPLES

[0078] The experiments were performed to measure the performance of the invented SMA actuator quantitatively. The experimental setup consists of an invented SMA actuator, PC-based controller and data acquisition system, measurement sensors for stroke length (displacement) and net load for external work done, and a regulated power supply with the connected heating module. The joule heating technique is employed for regulating the heating current by the pair of PWM signals generated from a PC-based NI DAQ (National Instrument Data acquisition) system. Generated load was measured by a pair of load cells (LC) of measuring capacity 10 lb from Honeywell Inc., USA. The first end of LC is rigidly mounted at the mounting base 8 and another end is firmly connected to the loose end of the segments of the SMA elements 12. A laser displacement sensor (IL-30 along with IL-100 amplifier from Keyence, Japan) was employed for stroke length (displacement) measurement. The multifunction NI-DAQ card PXIe-6341 was used for data acquisitions.

Example 1

[0079] The first example demonstrates the stroke length (displacement) measurement of the invented bidirectional linear SMA actuator. The PWM controlled heating pulses are applied to both sides of the main stroke transmitting lever part-modules (PM1 & PM2) simultaneously in 37% and 1% of the PWM duty ratio. The conditions of duty ratio are flipped in the next interval to complete one cycle of the forward and backward motion. The total stroke length in the forward and backward direction is measured of 4.8 mm. The measured stroke length and applied control heating pulses for one complete cycle are shown in FIG. 13.

Example 2

[0080] The second example demonstrates the repeatability of 4.8 mm stroke length in forward and backward direction motion of both part-modules (PM1 & PM2) with respect to simultaneously applied heating current pulses as shown in FIG. 14. As part module 2 is activated the device moves in the forward direction and gets stable after reaching to maximum limit. When part module 1 is activated the device moves in the backward direction and gets stable after reaching to maximum limit.

Example 3

[0081] The third example demonstrates the net load measurement from the invented SMA actuator for the external work done. The PWM controlled heating pulses are applied to both the part-modules (PM1 & PM2) simultaneously in 37% and 1% of the PWM duty ratio and the conditions of duty ratio are flipped in the next interval to complete one cycle of forward and backward motion. The total net load in the forward and backward directions is measured of 2.6 kg. The observations of the net load and applied control heating pulses for one complete cycle are shown in FIG. 15.

Example 4

[0082] The fourth example demonstrated the repeatability of measured 2.6 kg net load for external work done in forward and backward motion of both part-modules (PM1 & PM2) with respect to simultaneously applied heating current pulses as shown in FIG. 16. As part module 2 (PM2) is activated, the device moves in the forward direction and generates push force and stable after reaching to maximum limit. When part module 1(PM1) is activated the device moves in the backward direction and generates pull force and stable after reaching to maximum limit in return direction.

Example 5

[0083] In example 5, the combined output measurements of the forward and backward strokes of the developed device are shown. The device can produce 4.75-4.85 mm of total forward and backward stroke length (displacement) with 2.5-2.8 kg net load generated for external pulling and pushing of work done in each cycle of the operation. The results are plotted in FIG. 17.