Shape memory alloy wire controlled actuator subassembly, system including a plurality of such subassemblies, and control method for such a system - Patents.com

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, most typically through the ability of a suitably 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, are utilized in various technical fields, for example in a camera module actuator as described in US Pat. No. 5,399,663, or in a bidirectional discrete actuator as described in US Pat. No. 5,499,663, or in a bistable inertial actuator as described in US Pat. No. 5,499,623 and US Pat. No. 5,523,636, or in a fluid valve subassembly as described in US Pat. No. 5,523,663 (all of which are in the name of the Applicant), or in a multi-segment spine with integral actuation as described in US Pat. No. 5,523,636, or in a foldable structure as described in US Pat. No. 5,523,636.

[0004] Generally speaking, SMA-based actuators require a return means opposing 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 US Pat. No. 6,233,633, 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 US Pat. No. 6,233,633 and US Pat. No. 6,233,633, ... and US Pat. No. 6,233,633.

[0005] Another feature often appreciated in SMA-based actuators is the possibility of bistable mechanical control, as described in the aforementioned US Pat. Nos. 5,993,333 and 5,943,636. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Pat. 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] US 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. Pat. 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 as well as a bi-stable SMA wire, the first aspect of which 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 being opposite to 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 blocks such a plane intersection.

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

[0011] [Figure 1A] FIG. 2 is a schematic diagram of an actuator subassembly viewed from above in accordance with a first embodiment of the present invention. [Figure 1B] FIG. 1B is a schematic cross-sectional view of the actuator subassembly of FIG. 1A along line AA in its stable position. [Figure 1C] FIG. 1B is a schematic cross-sectional view of the actuator subassembly of FIG. 1A along line AA in its stable position. [Figure 2A]FIG. 1B is a schematic diagram of a system including multiple actuator subassemblies according to FIG. 1A viewed from above. [Figure 2B] FIG. 2B is a schematic cross-sectional view of the system of FIG. 2A taken along line AA'. [Figure 3A] FIG. 13 is a schematic diagram of a top view of a system including multiple actuator subassemblies according to a second embodiment. [Figure 3B] 3B is a schematic cross-sectional view along line A-A' of the system of FIG. 3A with the actuator subassembly in different equilibrium / stable states. [Figure 3C] 3B is a schematic cross-sectional view along line A-A' of the system of FIG. 3A with the actuator subassembly in different equilibrium / stable states. [Figure 3D] FIG. 3B is a schematic cross-sectional view of the system of FIG. 3A taken along line BB'. [Figure 4A] FIG. 13 is a diagram of an electronic circuit suitable for controlling the upper SMA wires of a system with 24 actuator subassemblies in accordance with the present invention. [Figure 4B] FIG. 13 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 PREFERRED EMBODIMENTS

[0012] It should be noted that in order to facilitate understanding of the drawings, the sizes and dimensional ratios of the various elements shown in the figures have been modified in some cases, without making exclusive reference in particular to the diameter of the SMA wire and the thickness of the elastically deformable arms. Moreover, 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 view from above of an actuator subassembly according to a first embodiment of the present invention is shown in Fig. 1A, and two cross-sectional views thereof are shown in Fig. 1B and Fig. 1C. The actuator subassembly 100 comprises a rectangular frame 110, in particular a square frame, having four fixing elements 120, 120', 120'', 120''' coinciding with its corners, the opposing elements 120', 120''' along a first diagonal are used to fix a first shape memory alloy wire 130, and the 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 forces in opposite directions on a particular component, which is the movable element 160, over which the wire 130 passes and under which the 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, and the second SMA wire 130' passes between them.

[0015] A first SMA wire 130 is above the frame 110 and a 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 U.S. Pat. Nos. 5,293,333, 5,396,621, 5,491,792, 5,523,103 and 5,631,200 discussed above.

[0016] In particular, US Pat. No. 6,299,663 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. US Pat. No. 6,299,663 has a frameless structure with SMA antagonistic wires in similar connections to adjacent corners as in US Pat. No. 6,299,663. Also, the above-mentioned US Pat. No. 6,299,663 has an embodiment with two SMA wires in an antagonistic configuration that are essentially in the same plane, i.e., their two tips are connected to the same opposite walls of the assembly cover.

[0017] The use of SMA wires in an antagonistic configuration that are simultaneously in mutually orthogonal or nearly orthogonal planes prevents the movable structure from tilting while switching between the two stable positions of the actuator. The SMA wire plane is defined as the plane that contains the SMA wires and their corner connectors, and such a substantially orthogonal condition between the SMA wire planes is achieved by SMA wires connected to opposite corners of a rectangular frame such that their planes intersect at an angle of 90°±20°. Such a condition is not achievable by adjacent SMA wire connections in the aforementioned US Pat. No. 5,999,433 and US Pat. No. 5,999,433, nor by antagonistic configuration SMA wires that are essentially in the same plane in US Pat. No. 5,999,433.

[0018] This aspect is particularly relevant when the moving element material is not stiff and may deform during multiple actuations of the SMA wire. Moreover, 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 parallel but not perfectly parallel, as in a real device. The above-mentioned configuration of US Pat. No. 6,233,999 with antagonistic wires is particularly prone to exposing this problem.

[0019] On the other hand, the movable structure of US Pat. No. 6,299,633 is prevented from tilting or twisting, which would risk impeding the smooth transition between the two stable positions, by fitting it snugly into a channel formed on the inner surface of its parallelepiped frame. A similar arrangement is disclosed in US Pat. No. 6,299,633, which provides guide rails to guide the movement of the movable structure between the two stable positions, said movable structure being 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, as long as it has two opposing surfaces available for firm contact with the antagonistic SMA wires 130, 130', as shown in Figures 1A-1C. A plunger 170 is connected to the movable element 160 to facilitate the use of the actuator subassembly in fluidic devices or analytical instruments, such as test microplates with a large number of test cells or test wells (the possible numerical range is very wide, typically comprised between 6 and 1536). Such devices are widely known and widespread, see for example the article "Fully integrated rapid microfluidic device translated from conventional 96-well ELISA kit" by M. Jalal Uddin et al., Scientific Reports volume 11, Article number: 1986 (2021).

[0021] 1A-1C achieves bistable movement via four elastically deformable arms 140, 140', 140'', 140''' connecting the movable element 160 to the square frame 110 at central positions 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). It should be noted that the alternating actuation of the SMA wires 130, 130' only 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 wires 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, corresponding 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 faces, 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 which SMA wire 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 an active component of a stand-alone actuator, its advantages are fully exploited in a so-called matrix configuration, i.e. in which several actuator subassemblies are connected to each other in rows and columns, where a single SMA wire can run on several diagonally aligned actuator subassemblies, adjacent subassemblies sharing one or two common frame corner connectors.

[0025] Figure 2A shows a schematic view from above of such a system 200 made up of 16 actuator subassemblies according to Figure 1A, four in each row and four in each column. The cross-sectional view of a given row, for example along line A-A', shown in Figure 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 FIG. 2A is shown in FIGS. 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 having integrated corner connectors 320, 320', 320'', 320''', and 320iv.

[0027] As shown by comparison of Figures 3B and 3C, which represent cross-sectional views along line A-A' in Figure 3A, it is possible to actuate a particular actuator subassembly by setting up a voltage difference between opposing frame corner connectors. In the case illustrated in Figure 3B, the second and fourth subassemblies have a 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 arm. To return it to the upper position, SMA wires 331' and 333' are activated by passing a current through it via connectors 320' / 320'' and 320''' / 320iv, respectively, so that the movable element 360 is pushed upwards as shown in Figure 3C.

[0028] In these cross-sectional views, as in the system of Fig. 2A, the SMA elements 330, 331, 332, 333, 330', 331', 332', 333' are all different wires, 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, which is a schematic cross-sectional view taken along line B-B' in Fig. 3A. In this case, the lower SMA elements are all parts of a single shape memory alloy wire 333', and the upper SMA elements 330, 331, 332, 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 invention, it is important to be able to separately control the voltage applied to any 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, the SMA wire or SMA wire section in the case of SMA wires connecting more actuator subassemblies, 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 wires on the top and / or bottom of multiple actuator subassemblies provides significant manufacturing and cost benefits. To achieve this, it is important to prepare a layout where there are two adjacent frame corner connectors in each subassembly connected to a ground wire, with each of the opposing frame corner connectors connected to a respective hardware switch that toggles between an actuated voltage and an isolated state. The toggle electrical switch can preferably be realized with a solid semiconductor, relay, or electromechanical switch. This can be achieved using the same continuous SMA wire, or even separate SMA wires attached to a common connector that is conductive, making them like a single wire, while maintaining no current flow to adjacent frames.

[0031] It should also be noted that the system frame is fabricated such 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 wire is used for two adjacent rows of actuator subassemblies, simplifying the electrical scheme. The system operates using two separate switching ground wires, i.e. the ground potential must be switchable from ground1 / ground2 to no potential (open) and ground1 and ground2 must be two separate ground levels separated from each other (galvanically separated).

[0033] It should be emphasized that while the above solutions do not allow for exactly 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 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 a 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, whereby 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 a 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, whereby 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 invention allows selective control (opening and closing) of test wells in analytical instruments, the number of test wells being typically 6, 12, 14, 48, 96 and 384, as specified by the Biomolecular Sciences Society as ANSI standards according to ANSI / SBS1-2004, ANSI / SBS2-2004, ANSI / SBS3-2004, ANSI / SBS4-2004.

[0036] The invention is not limited to a particular SMA wire size, although wires having diameters between 30 μm and 200 μm are preferably used, and similarly, the 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 denotes an SMA wire, the actuation of which imparts movement to a displaceable element in an opposing direction. [Explanation of symbols]

[0038] 100, 201-204 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 movable element, 170 plunger, 200, 300 system, 410, 420 circuit diagram, 1310 guide, 1400 first straight rigid portion, 1410 second elastically deformable portion

Claims

1. An actuator subassembly comprising: - a quadrilateral frame having four corner connectors; - a movable element disposed at the center of the quadrilateral frame and connected thereto by an elastically deformable arm; - a first shape memory alloy wire fixed to two of the corner connectors disposed at opposite positions among the corner connectors; - a second shape memory alloy wire fixed to the other two opposite corner connectors, wherein two wire planes each including a shape memory alloy wire having its associated corner connector intersect at an angle of 90° ± 20°; 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 such that the two shape memory alloy wires are arranged in an antagonistic configuration to exert forces in opposite directions on the movable element.

2. The actuator subassembly according to 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. The actuator subassembly according to claim 1 or 2, wherein a maximum distance between the first shape memory alloy wire and the second shape memory alloy wire is included between 2.5 mm and 15 mm.

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

5. A system comprising a plurality of actuator subassemblies according to claim 1, arranged in a matrix configuration having adjacent subassemblies sharing a common corner connector whose upper and lower portions are insulated from each other, 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 insulated state.

6. A method of controlling the system according to claim 5, wherein the operation of a specific shape memory alloy wire is realized by setting a voltage difference between the opposing corner connectors to which the wire is fixed.

7. The actuator subassembly according to claim 1, wherein the quadrilateral frame is square-shaped.

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

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