Shape memory alloy wire controlled actuator subassembly, system comprising a plurality of such subassemblies, and control method for such a system

Abstract

The present invention is specific to an actuator subassembly controlled by a shape memory alloy wire, a system comprising a plurality of such subassemblies, and a control method for such a system, the shape memory alloy wire being in a so-called antagonistic configuration.

Description

[Technical Field]

[0001] The present invention is specific to an actuator subassembly controlled by a shape memory alloy (SMA) wire, a system comprising a plurality of such subassemblies, and a method of controlling such a system. [Background technology]

[0002] Generally speaking, the use of SMA wire as an actuation element offers various advantages over other actuation systems in terms of weight, power consumption, and cost, through the ability of appropriately shaped SMA wire to contract when heated, most typically by the Joule effect via an appropriate current supply.

[0003] The above advantages of SMA wire, and more generally SMA technology, have been utilized in various technical fields, for example in the camera module actuator described in US Pat. No. 6,229,999, or in the bidirectional discrete actuator described in US Pat. No. 6,229,999, or in the bistable inertial actuator described in US Pat. No. 6,229,999 and US Pat. No. 6,329,999, or in the fluid valve subassembly described in US Pat. No. 6,329,999 (all of which are in the name of the Applicant), or in the multi-segment spine with integrated actuation described in US Pat. No. 6,329,999, or in the foldable structure described in US Pat. No. 6,329,999.

[0004] Generally speaking, SMA-based actuators require a return means that opposes the action of the SMA actuation component to ensure bidirectional movement of the displaceable article. The return means can be a passive elastic element, such as a linear or coil spring, as in the various embodiments of the plug actuator described in U.S. Patent No. 6,223,999, or another active element, such as an SMA component acting in opposition to the first one, in a so-called antagonistic configuration. Some examples of SMA-based antagonistic components in actuators are given in the aforementioned U.S. Patent Nos. 6,223,999 and 6,223,999, U.S. Patent No. ... and U.S. Patent No. 6,223,999.

[0005] Another feature often appreciated in SMA-based actuators is the possibility of bistable mechanical control, as described in the aforementioned US Pat. Nos. 5,629,999 and 5,729,999. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 10,514,593 [Patent Document 2] European Patent No. 3877650 [Patent Document 3] International Patent Application Publication No. 2021 / 197980 [Patent Document 4] International Patent Application Publication No. 2022 / 184533 [Patent Document 5] International Patent Application Publication No. 2022 / 229247 [Patent Document 6] U.S. Patent No. 20100295417 [Patent Document 7] U.S. Patent No. 9,205,593 [Patent Document 8] US Patent Application Publication No. 2012 / 104292 [Patent Document 9] European Patent No. 3908753 [Patent Document 10] U.S. Patent No. 4,544,988 [Patent Document 11] US Patent Application Publication No. 2012 / 151913 Summary of the Invention [Means for solving the problem]

[0007] The object of the present invention is to overcome the limitations of known technology by using an SMA actuator based on an antagonistic configuration and a bistable SMA wire, and a first aspect thereof is an actuator subassembly comprising a rectangular frame having four corner connectors, a movable element positioned coincident with the center of the frame and connected thereto by an elastically deformable arm, a first shape memory alloy wire fixed to two opposing corner connectors and contacting a first surface of the movable element, and a second shape memory alloy wire fixed to the other two opposing corner connectors and contacting a second surface of the movable element, the second surface facing the first surface.

[0008] In the most common embodiment, the first surface is the top surface of the movable element and the second surface is the bottom surface of the movable element.

[0009] It is important to emphasize that the phrase "coinciding with the center of the frame" must be interpreted in the context of an actual device with its manufacturing tolerances. Thus, while ideal alignment between the center of the frame and the center of the movable element is desirable, the system can function even if the movable element symmetry axis (if any) is not located at the intersection between the planes containing the first shape memory alloy wire and the second shape memory alloy wire, but rather the movable element as a whole intercepts such plane intersection.

[0010] The invention is further explained with the help of the following figures. [Brief explanation of the drawings]

[0011] [Figure 1A] 1 is a schematic diagram of an actuator subassembly viewed from above in accordance with a first embodiment of the present invention; [Figure 1B] 1B is a schematic cross-sectional view of the actuator subassembly of FIG. 1A along line AA in its stable position. [Figure 1C] 1B is a schematic cross-sectional view of the actuator subassembly of FIG. 1A along line AA in its stable position. [Figure 2A]1B is a schematic diagram of a system according to FIG. 1A, seen from above, comprising multiple actuator subassemblies; [Figure 2B] 2B is a schematic cross-sectional view of the system of FIG. 2A taken along line AA'. [Figure 3A] 10 is a schematic diagram of a top view of a system including multiple actuator subassemblies according to a second embodiment. FIG. [Figure 3B] 3B is a schematic cross-sectional view of the system of FIG. 3A along line A-A' with the actuator subassembly in different equilibrium / stable states. [Figure 3C] 3B is a schematic cross-sectional view of the system of FIG. 3A along line A-A' with the actuator subassembly in different equilibrium / stable states. [Figure 3D] 3B is a schematic cross-sectional view of the system of FIG. 3A taken along line BB'. [Figure 4A] FIG. 10 is a diagram of an electronic circuit suitable for controlling the top SMA wires of a system with 24 actuator subassemblies, in accordance with the present invention. [Figure 4B] FIG. 10 is a diagram of an electronic circuit suitable for controlling the lower SMA wires of a system with 24 actuator subassemblies, in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] It should be noted that the sizes and dimensional ratios of the various elements shown in the figures have been modified in some cases to facilitate understanding of the drawings, although not exclusively with reference to the diameter of the SMA wire and the thickness of the elastically deformable arms. Furthermore, the means for supplying current / voltage to the SMA wire are not shown, as they are well known to those skilled in the art and are not necessary for understanding the present invention.

[0013] A schematic top view of an actuator subassembly according to a first embodiment of the present invention is shown in Figure 1A, and two cross-sectional views thereof are shown in Figures 1B and 1C. The actuator subassembly 100 comprises a rectangular frame 110, specifically a square frame, having four fixing elements 120, 120', 120'', 120''', coinciding with its corners, where opposing elements 120', 120''' along a first diagonal are used to fix a first shape memory alloy wire 130, and opposing elements 120 and 120'' along the other diagonal are used to fix a second shape memory alloy wire 130'.

[0014] The shape memory alloy wires 130, 130' are in a so-called antagonistic configuration, meaning that they exert opposing forces on a particular component, the movable element 160, over which wire 130 passes and below which wire 130' passes. The upper surface of the movable element 160 has a guide 1310 to hold the first SMA wire 130 in place, and the second SMA wire 130' is held in a guide (not shown) formed on the lower surface of the movable element 160 to which the plunger 170 is connected, with the second SMA wire 130' passing between them.

[0015] The first SMA wire 130 is above the frame 110 and the second SMA wire 130' is below the frame 110, and they are in different planes that are orthogonal to each other when the frame 110 has the preferred square shape shown in the figures, unlike the configurations shown in the above-mentioned U.S. Patent Nos. 5,629,292; 5,629,293; 5,629,294; 5,629,294; and 5,629,294.

[0016] Specifically, U.S. Patent No. 6,266,649 shows two pairs of SMA wires in an antagonistic configuration, with each SMA wire connected to two adjacent corners of a parallelepiped frame, unlike the present invention, in which two SMA wires are each connected to opposite corners of a rectangular frame. U.S. Patent No. 6,266,649 has a frameless structure with SMA antagonistic wires in similar connections at adjacent corners as U.S. Patent No. 6,266,649. Also, the above-mentioned U.S. Patent No. 6,266,649 has an embodiment with two SMA wires in an antagonistic configuration that are essentially in the same plane, i.e., their two ends are connected to the same opposing walls of the assembly cover.

[0017] The use of SMA wires in an antagonistic configuration that simultaneously lie in mutually orthogonal or nearly orthogonal planes prevents tilting of the movable structure during switching between the two stable positions of the actuator. The SMA wire plane is defined as the plane containing the SMA wire and its corner connectors, and such substantially orthogonal state between the SMA wire planes is achieved by SMA wires connected to opposite corners of a rectangular frame such that the planes intersect at an angle of 90°±20°. Such a state is not achievable by adjacent SMA wire connections in the aforementioned U.S. Pat. Nos. 5,629,299 and 5,749,929, nor by the antagonistic configuration of SMA wires that lie essentially in the same plane in U.S. Pat. No. 5,749,929.

[0018] This aspect is particularly relevant when the moving element material is not rigid and may deform during multiple actuations of the SMA wire. Furthermore, the substantially orthogonal arrangement simplifies the task of heating both wires to coordinate flow and switching timing. If both wires are stressed along the same direction, this can create a tilting moment when the attachment points are not perfectly positioned, which occurs when the planes of the SMA wires are essentially but not perfectly parallel, as in a real device. The aforementioned configuration of Patent Document 8 with antagonistic wires is particularly prone to exposing this problem.

[0019] On the other hand, the movable structure of Patent Document 11 fits snugly into a channel formed on the inner surface of its parallelepiped frame, thereby preventing tilting or twisting that could hinder a smooth transition between two stable positions. A similar arrangement is disclosed in Patent Document 10, which provides guide rails to guide the movement of the movable structure between two stable positions, and the movable structure is connected to its frame only by the SMA wire itself, and not by an elastically deformable arm.

[0020] The present invention is not limited to any particular shape or geometric configuration of the movable element 160, so long as it has two opposing surfaces available for firm contact with the antagonistic SMA wires 130, 130′, as shown in FIGS. 1A-1C. A plunger 170 is connected to the movable element 160 to facilitate use of the actuator subassembly in fluidic or analytical devices, such as test microplates with a large number of test cells or test wells (the range of possible values ​​is very wide, typically between 6 and 1536). Such devices are widely known and in widespread use; see, for example, the article by M. Jalal Uddin et al., “Fully integrated rapid microfluidic device translated from conventional 96-well ELISA kit,” Scientific Reports volume 11, Article number: 1986 (2021).

[0021] 1A-1C achieves bistable operation via four elastically deformable arms 140, 140′, 140″, 140′″ that connect the movable element 160 to the square frame 110 at central locations on the frame sides, each of said elastically deformable arms 140, 140′, 140″, 140′″ having two stable positions, an upper position and a lower position, as shown in FIG. 1B (top) and FIG. 1C (bottom). Note that the alternating actuation of the SMA wires 130, 130′ merely needs to be sufficient to carry the elastically deformable arms 140, 140′, 140″, 140′″ beyond their snap-on equilibrium positions; i.e., the total movement of the movable element 160 is a combination of the effect of the SMA wire pushing and the snapping of the deformable arms. As shown in Figures 1B-1C, the flexible arm can have a first straight, rigid portion 1400 connected to the frame 110 and a second, elastically deformable portion 1410 connected to the movable element 160.

[0022] Preferably, the two SMA wires 130, 130' have a maximum distance between each other comprised between 2.5 mm and 15 mm, which corresponds to the height of the movable element 160 in the configuration shown in Figures 1A-1C, as the SMA wires 130 and 130' are in contact with their upper and lower surfaces, respectively. Preferably, the distance between the frame corner connectors along the frame diagonal is comprised between 25 mm and 100 mm.

[0023] The position of the movable element 160 depends on the SMA wire that was last actuated, i.e., the lower SMA wire 130' for the plunger 170 in the raised configuration (FIG. 1B) and the upper SMA wire 130 for the plunger 170 in the lowered configuration (FIG. 1C). Note that the force exerted by the elastically deformable arms 140, 140', 140", 140'" maintains the actuator subassembly in its stable position without requiring actuation of the SMA wires 130, 130', so power is provided to the appropriate SMA wires only to switch the actuator subassembly from one stable position to the other.

[0024] Although the actuator subassembly according to the invention can be used as the active component of a stand-alone actuator, its advantages are fully exploited in a so-called matrix configuration, i.e., in which multiple actuator subassemblies are connected to each other in rows and columns, where a single SMA wire can operate on multiple diagonally aligned actuator subassemblies, with adjacent subassemblies sharing one or two common frame corner connectors.

[0025] 2A shows a schematic view from above of such a system 200 made up of 16 actuator subassemblies according to FIG. 1A, four in each row and four in each column. A cross-sectional view of a given row, e.g., along line A-A', shown in FIG. 2B, shows how the four subassemblies 201, 202, 203, 204 making up the row can be in different states, i.e., the plunger 170 can be raised in actuator subassemblies 201, 203, 204 and alternatively lowered in actuator subassembly 202.

[0026] A variation of the above-described actuator subassembly system of Figure 2A is shown in Figures 3A-3D, which show a system 300 comprising an actuator subassembly in which a movable element 360 has a cross-shaped vertical cross section and elastically deformable arms 340, 340' are deformable linear elements connecting the movable element 360 to a frame 310 that has integrated corner connectors 320, 320', 320'', 320''', and 320iv.

[0027] As shown by a comparison of Figures 3B and 3C, which represent cross-sectional views along line A-A' in Figure 3A, it is possible to drive a particular actuator subassembly by establishing a voltage difference between opposing frame corner connectors. In the case illustrated in Figure 3B, the second and fourth subassemblies have movable element 360 that is lowered via actuation of SMA wires 331 and 333, respectively, and held in that position by the action of the deformable arms. To return it to its upper position, SMA wires 331' and 333' are activated by passing current through it via connectors 320' / 320" and 320'" / 320iv, respectively, resulting in movable element 360 being pushed upward as shown in Figure 3C.

[0028] In these cross-sectional views, SMA elements 330, 331, 332, 333, 330', 331', 332', and 333' are all different wires, as in the system of FIG. 2A, but it should be emphasized that a single SMA wire can control multiple actuator subassemblies arranged along the system diagonal, as shown in FIG. 3D, a schematic cross-sectional view taken along line B-B' in FIG. 3A. In this case, the bottom SMA elements are all portions of a single shape memory alloy wire 333', and the top SMA elements 330, 331, 332, and 333 are all different SMA wires. In this embodiment, at least one SMA wire connects multiple actuator subassemblies, the number of which is preferably comprised between 6 and 96.

[0029] With regard to the method of operating the system according to the present invention, it is important to be able to separately control the voltage applied to either of the opposing frame corner connectors so that an appropriate voltage difference between the opposing frame corner connectors will cause the shape memory alloy element, or in the case of SMA wires connecting more actuator subassemblies, the SMA wire or SMA wire section to be actuated (shortened) to change the actuator subassembly to another stable position. Of course, no current is supplied to the antagonistic SMA element until it is necessary to return the actuator subassembly to its previous stable position.

[0030] Using the same wire on the top and / or bottom of multiple actuator subassemblies offers significant manufacturing and cost benefits. To achieve this, it's important to design a layout where each subassembly has two adjacent frame corner connectors connected to a ground wire, with each opposing frame corner connector connected to a respective hardware switch that toggles between an activated voltage and an isolated state. The toggle electrical switches can be implemented with solid-state semiconductors, relays, or electromechanical switches. This can be achieved using the same continuous SMA wire, or separate SMA wires attached to a common connector that is conductive enough to make them appear as a single wire, maintaining zero current flow to adjacent frames.

[0031] It should also be noted that the system frame is fabricated so that the top and bottom of each connector are isolated from each other, as shown in the cross-sectional views of Figures 1B-1C, 2B, and 3B-3D (e.g., by fabricating the frame as a double-layer PCB).

[0032] A preferred electrical circuit diagram for powering the SMA elements for a system with 24 actuator subassemblies arranged in a 6x4 matrix is ​​shown in Figures 4A and 4B. It can be observed that a common ground line is used for two adjacent rows of actuator subassemblies, simplifying the electrical scheme. The system operates using two separate switching ground lines; that is, the ground potential must be switchable from Ground 1 / Ground 2 to no potential (open), and Ground 1 and Ground 2 must be two separate ground levels that are galvanically isolated from each other.

[0033] It should be emphasized that although the above solutions do not allow for the precise simultaneous operation of each and every actuator subassembly in the system, simultaneous actuation (i.e., state change) can be achieved from an operational standpoint by applying minimal operational delays with appropriate operation of the electrical switches, considering that such delays are on the order of milliseconds and do not affect the performance of the system.

[0034] More specifically, circuit diagram 410 in Figure 4A is for controlling the first (top) SMA wire, and the pins for controlling the SMA wire or SMA wire portion of each subassembly are the top left pin and bottom right pin, so pins 7 and 29 are missing in Figure 4A because they would not have wires attached to them. Similarly, circuit diagram 420 in Figure 4B is for controlling the second (bottom) SMA wire, and the pins for controlling the SMA wire or SMA wire portion of each subassembly are the top right pin and bottom left pin, so pins 1 and 35 are missing in Figure 4B because they would not have wires attached to them.

[0035] As already mentioned with regard to the construction details of the actuator subassembly, one of the preferred applications is in analytical instruments. In this regard, the control method applied in the system according to the present invention allows for the selective control (opening and closing) of test wells in analytical instruments, the number of test wells typically being 6, 12, 14, 48, 96, and 384, as specified by the Biomolecular Science Society as ANSI standards according to ANSI / SBS1-2004, ANSI / SBS2-2004, ANSI / SBS3-2004, and ANSI / SBS4-2004.

[0036] The present invention is not limited to a particular SMA wire size, although wires having diameters between 30 μm and 200 μm are preferably used.Similarly, the present invention is not limited to a particular material for the SMA wire, although Ni-Ti based alloys such as Nitinol are preferred.

[0037] Finally, with regard to how to manipulate and control the antagonistic wire, this information is known to those skilled in the art, see for example the article "An accurately controlled antagonistic shape memory alloy actuator with self-sensing" by Wang et al., published in Sensors, 12, 7682-7700, 2012. It is important to emphasize that the term antagonistic wire refers to an SMA wire whose actuation imparts movement to a displaceable element in an opposite direction. [Explanation of symbols]

[0038] 100, 201 to 204 actuator subassembly, 110, 310 frame, 120, 120', 120'', 120''', 320, 320', 320'', 320''', 320iv corner connector, 130 first shape memory alloy wire, 130' second shape memory alloy wire, 140, 140', 140'', 140''', 330, 330', 331, 331', 332, 332', 333, 333', 340, 340' elastically deformable arm, 160, 360 moving element, 170 plunger, 200, 300 system, 410, 420 circuit diagram, 1310 guide, 1400 first straight rigid portion, 1410 second elastically deformable portion

Claims

1. 1. An actuator subassembly comprising: a frame having a rectangular shape in top view and four corner connectors; a mobile element located coincident with the center of said rectangular frame and connected thereto by an elastically deformable arm; a first shape memory alloy wire fixed to two of said corner connectors located at opposite positions; a second shape memory alloy wire secured to the other two opposing corner connectors; Equipped with a first wire plane including the first shape memory alloy wire and its associated two corner connectors, which is perpendicular to the plane of the rectangle in a top view, and a second wire plane including the second shape memory alloy wire and its associated two corner connectors, which is perpendicular to the plane of the rectangle in a top view, intersecting at an angle of 90°±20° in a top view; An actuator subassembly, wherein the first shape memory alloy wire contacts a first surface of the movable element, the second shape memory alloy wire contacts a second surface of the movable element, and the second surface faces the first surface so that the two shape memory alloy wires are arranged in an antagonistic configuration exerting opposing forces on the movable element.

2. The actuator subassembly of claim 1 , wherein a plunger is connected to the second surface of the movable element and the second shape memory alloy wire passes therebetween.

3. 3. The actuator subassembly according to claim 1, wherein the maximum distance between the first shape memory alloy wire and the second shape memory alloy wire is comprised between 2.5 mm and 15 mm.

4. 2. The actuator subassembly of claim 1, wherein the distance between the corner connectors along a diagonal of the frame is comprised between 25 mm and 100 mm.

5. 10. A system comprising a plurality of actuator subassemblies according to claim 1 arranged in a matrix configuration with adjacent subassemblies sharing a common corner connector whose upper and lower portions are insulated from one another, wherein each of the subassemblies has two adjacent corner connectors connected to a ground wire, and each of the opposing corner connectors is connected to a respective hardware switch that toggles between an activation voltage and an isolation state.

6. 6. The method of controlling a system as recited in claim 5, wherein actuation of a particular shape memory alloy wire is achieved by establishing a voltage difference between the opposing corner connectors to which the wire is secured.

7. The actuator subassembly of claim 1 , wherein the rectangular frame is square-shaped.

8. The system of claim 5 , wherein the hardware switch that toggles between the activation voltage and the insulating state is a solid-state semiconductor, a relay, or an electromechanical switch.

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