Actuator subassembly controlled by a shape memory alloy wire, system comprising a plurality of such subassemblies and control method for such a system

Abstract

The invention relates to an actuator sub-assembly (100) controlled by a shape memory alloy wire (130, 130') in a so-called antagonistic configuration, to a system comprising a plurality of such sub-assemblies and to a control method for such a system.

Description

[0001] The present invention relates to actuator subassemblies controlled by shape memory alloy (SMA) wires, systems comprising multiple such subassemblies, and methods for controlling such systems.

[0002] Generally speaking, using SMA wire as an actuation element offers various advantages in terms of weight, power consumption, and cost compared to other actuation systems, thanks to the ability of properly trained SMA wire to shorten when heated (most typically through the Joule effect of a suitable current source).

[0003] The aforementioned advantages of SMA cables, and more generally SMA technology, have been utilized in various technical fields, such as in camera module actuators as described in US 10514593, or in bidirectional discrete actuators as described in EP 3877650, or in bistable inertial actuators as described in international patent applications WO 2021 / 197980 and PCT / EP2022 / 054601, or in fluid valves and fluid valve subassemblies as described in international patent application PCT / EP2022 / 061170 (all of the above applications are in the name of the applicant), or in multi-segment spines with integrated actuation as described in US 20100295417, or in foldable structures as described in US 9205593.

[0004] Generally, SMA-based actuators require a return mechanism that acts in opposition to the SMA actuation element to ensure bidirectional movement of the movable object. The return mechanism can be another active element or a passive elastic element in a so-called counter-configuration, such as a linear or helical spring in various embodiments of the plug actuator described in US 2012 / 104292, and the other active element, such as an SMA component that reacts relative to the first SMA actuation element. Examples of SMA-based counter-components in actuators are given in the aforementioned US 10514593, EP 3877650, EP 3908753, US 4544988, and US 2012 / 151913.

[0005] Another feature commonly understood in SMA-based actuators is the possibility of bistable mechanical control (as described, for example, in the aforementioned international patent applications WO 2021 / 197980 and PCT / EP2022 / 054601).

[0006] The object of this invention is to overcome the limitations of known technologies by utilizing an SMA actuator based on an antagonistic configuration and a bistable SMA wire. A first aspect of the invention relates to an actuator subassembly comprising: a quadrilateral frame having four corner connectors; a movable element disposed corresponding to the center of the quadrilateral frame and connected to the quadrilateral frame via a deformable arm; a first shape memory alloy wire fixed to two opposing corner connectors and in contact with a first surface of the movable element; and a second shape memory alloy wire fixed to two additional opposing corner connectors and in contact with a second surface of the movable element, the second surface being opposite to the first surface.

[0007] In the most common implementation, the first surface is the upper surface of the movable element, and the second surface is the lower surface of the movable element.

[0008] It is important to emphasize that the phrase "corresponding to the center of the frame" is interpreted in the context of the actual device in terms of its manufacturing tolerances. Therefore, although an ideal alignment between the center of the frame and the center of the movable element is desirable, the system can still function even if the axis of symmetry of the movable element (if it exists) does not lie at the intersection between the planes containing the first and second shape memory alloy wires, but rather the movable element as a whole intersects such a plane at the intersection point.

[0009] The present invention will be further illustrated by the following figures, in which:

[0010] · Figure 1A This is a top schematic representation of an actuator sub-assembly according to a first embodiment of the present invention;

[0011] · Figure 1B and Figure 1C yes Figure 1A A schematic cross-sectional view of the actuator subassembly along line AA in its two stable positions;

[0012] · Figure 2A It includes multiple bases Figure 1A A top-view schematic representation of the system of actuator sub-assemblies;

[0013] · Figure 2B yes Figure 2A A schematic cross-sectional view of the system along line A-A';

[0014] · Figure 3A This is a top schematic representation of a system including multiple actuator sub-assemblies according to the second embodiment;

[0015] · Figure 3B and Figure 3CIt consists of actuator sub-assemblies in different equilibrium / stability states. Figure 3A A schematic cross-sectional view of the system along line A-A';

[0016] · Figure 3D yes Figure 3A A schematic cross-sectional view of the system along line B-B'; and

[0017] · Figure 4A and Figure 4B This is an electronic schematic diagram of the upper SMA wire and the lower SMA wire, which are suitable for separately controlling a system comprising twenty-four actuator sub-assemblies according to the invention.

[0018] It should be noted that in some cases, the sizes and proportions of the various elements shown in the figures have been altered to aid in understanding the drawings, particularly, but not exclusively, with reference to the SMA wire diameter and the thickness of the elastically deformable arm. Furthermore, devices 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 essential for understanding the invention.

[0019] exist Figure 1A The diagram shows a top view of an actuator subassembly according to a first embodiment of the present invention, while... Figure 1B and Figure 1C Two cross-sectional views of the actuator subassembly are shown. The actuator subassembly 100 includes a quadrilateral frame 110, particularly a square frame, having four fixing elements 120, 120', 120”, 120”' corresponding to its corners, wherein the opposing elements 120', 120”' along the first diagonal are used to fix the first shape memory alloy wire 130, while the opposing elements 120 and 120” along the other diagonal are used to fix the second shape memory alloy wire 130'.

[0020] The shape memory alloy wires 130 and 130' are in a so-called antagonistic configuration, meaning that the shape memory alloy wires 130 and 130' apply forces to a component in opposite directions. In this example, the component is a movable element 160, over which the wires 130 pass and below which the wires 130' pass. The upper surface of the movable element 160 has a guide 1310 for holding the first SMA wire 130 in place, while the second SMA wire 130' is held in a guide (not shown) formed on the lower surface of the movable element 160, to which a plunger 170 is connected, with the second SMA wire 130' passing between the plunger 170 and the lower surface of the movable element 160.

[0021] The first SMA wire 130 is located above the frame 110, while the second SMA wire 130' is located below the frame 110, and they are located on different planes. When the frame 110 has the preferred square shape shown in the figure, they are orthogonal to each other, which is different from the configuration shown in US10514593, EP 3877650, EP 3908753, US2012 / 151913 and US 4544988 mentioned above.

[0022] Specifically, US2012 / 151913 illustrates two pairs of SMA wires in an antagonistic configuration, each SMA wire connected to two adjacent corners of a parallelepiped frame, which differs from the present invention, in which each of the two SMA wires is connected to an opposite corner of a quadrilateral frame. US 4544988 has a frameless structure in which the diagonal SMA wires are connected to adjacent corners in a similar manner to those in US2012 / 151913. Furthermore, the aforementioned US2012 / 0104292 has an embodiment in which the two antagonistic SMA wires are substantially in the same plane, i.e., their two ends are connected to the same opposite walls of the component cover.

[0023] The use of SMA wires in an opposing configuration, simultaneously located in mutually orthogonal or nearly mutually orthogonal planes, prevents the movable structure from tilting when switching between two stable positions of the actuator. The SMA wire plane is defined as the plane containing the SMA wire and its corner connectors, and this substantial orthogonality between the SMA planes is achieved by connecting the SMA wires to the opposite corners of the quadrilateral frame such that their planes intersect at an angle of 90° ± 20°. This configuration cannot be achieved by the adjacent SMA wire connections described in US2012 / 151913 and US 4544988, nor by SMA wires in an opposing configuration that are substantially in the same plane, as described in US2012 / 104292.

[0024] This aspect is particularly relevant when the movable element material is not rigid and may deform upon repeated actuation of the SMA wires. Furthermore, a substantially orthogonal arrangement simplifies operations for heating the two wires to adjust flow and switch timing. When the attachment points are not perfectly aligned, placing the two wires under stress in the same direction can create a tilting moment, and this occurs when the planes of the SMA wires are substantially parallel but not perfectly parallel, as is the case in real-world devices. The configuration with opposing wires mentioned above in US2012 / 104292 is particularly prone to this problem.

[0025] On the other hand, the movable structure in US2012 / 151913 prevents tilting or twisting by fitting it tightly into channels formed in the inner surface of its parallelepiped frame, which carries the risk of hindering smooth passage between two stable positions. A similar arrangement is also disclosed in US 4544988, which provides guide rails for guiding the movement of the movable structure between two stable positions, the movable structure being connected to its frame not even by elastically deformable arms but solely by the SMA wire itself.

[0026] like Figures 1A to 1C As shown, the invention is not limited to any particular shape or geometry of the movable element 160, as long as the movable element 160 has two opposing surfaces that can be used for robust contact with the anti-SMA wires 130, 130'. The plunger 170 is connected to the movable element 160 to adapt the actuator subassembly for use in fluid or analytical devices such as test microplates comprising a large number of test cells or test traps (the possible numerical range is wide, and typically includes 6 to 1536). Such devices are well known and widely available, see, for example, the paper “Fully integrated rapid microfluidic device translated from conventional 96-well ELISA kit” by M. Jalal Uddin et al., Scientific Reports, Vol. 11, Article No. 1986 (2021).

[0027] Figures 1A to 1C The actuator subassembly 100 achieves bistable operation via four resilient deformable arms 140, 140', 140”, and 140”'. These four resilient deformable arms connect the movable element 160 to the square frame 110 at the middle position on the side of the frame. Each of the resilient deformable arms 140, 140', 140”, and 140”' has two stable positions: an upper stable position and a lower stable position (e.g., ...). Figure 1B (upper part) and Figure 1C (As shown in the lower part). It should be noted that the alternating actuation of the SMA cables 130, 130' only needs to be sufficient to move the resilient deformable arms 140, 140', 140”, 140”' beyond the snap-on equilibrium position. That is, the total stroke of the movable element 160 is a combination of the pushing effect of the SMA cables and the snapping effect of the deformable arms. Figures 1B to 1C As shown, the flexible arm may 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.

[0028] Preferably, the two SMA wires 130 and 130' have a maximum distance between each other ranging from 2.5mm to 15mm. Figures 1A to 1C In the configuration shown, this corresponds to the height of the movable element 160, as the SMA cables 130 and 130' contact the upper and lower surfaces of the movable element 160, respectively. Preferably, the distance between the frame corner connectors along the frame diagonal is between 25 mm and 100 mm.

[0029] The position of the movable element 160 depends on the last actuated SMA wire, i.e., the lower SMA wire 130' of the plunger 170 in the raised configuration. Figure 1B ) and plunger 170 in a lower configuration upper SMA wire 130 ( Figure 1C It should be noted that the force applied by the resiliently deformable arms 140, 140', 140”, 140”' holds the actuator subassembly in its stable position without actuating the SMA wires 130, 130', thus providing the appropriate SMA wires with power solely for switching the actuator subassembly from one stable position to another.

[0030] Although the actuator sub-assemblies according to the invention can be used as the active part of a standalone actuator, their advantages are fully realized in a so-called matrix configuration, i.e., a configuration in which multiple actuator sub-assemblies are connected together in rows and columns. In this case, a single SMA wire can operate on multiple diagonally aligned actuator sub-assemblies, and adjacent sub-assemblies share one or two common frame corner connectors.

[0031] Figure 2A It shows sixteen according to Figure 1A A top-view schematic representation of such a system 200, consisting of actuator sub-assemblies (four in each row and four in each column). Figure 2B The cross-sectional view shown for a given row, such as along line A-A', illustrates how the four sub-assemblies 201, 202, 203, and 204 that make up the row can be in different states, i.e., the plunger 170 is raised in actuator sub-assemblies 201, 203, and 204, and lowered in actuator sub-assembly 202.

[0032] exist Figures 3A to 3D It shows Figure 2A The above-mentioned variant of the actuator sub-component system, Figures 3A to 3D A system 300 including an actuator subassembly is shown, in which a movable element 360 has a cross-shaped vertical cross section, and resiliently deformable arms 340, 340' are deformable straight elements connecting the movable element 360 to a frame 310, the frame 310 having integrated corner connectors 320, 320', 320", 320"' and 320iv .

[0033] As indicated by Figure 3A Cross-sectional view along line A-A' Figure 3B and Figure 3C As the comparison shows, a specific actuator sub-assembly can be driven by setting a voltage difference between the relative frame corner connectors. Figure 3B In the illustrated case, the second and fourth subassemblies have movable elements 360, which are lowered by actuation of SMA cables 331 and 333 respectively and held in that position by the action of deformable arms. To return them to the upper position, the SMA cables 331' and 333' are lowered by actuation of connectors 320' / 320" and 320"' / 320" respectively. iv Activated by allowing current to pass through, the movable element 360 is pushed upward (e.g., ...). Figure 3C (As shown).

[0034] It is important to emphasize that in these cross-sectional views, such as Figure 2A In the system, SMA components 330, 331, 332, 333, 330', 331', 332', and 333' are all different wires, but a single SMA wire can control multiple actuator sub-assemblies arranged diagonally along the system, such as... Figure 3D As shown, the Figure 3D It is along Figure 3A A schematic cross-sectional view taken from line B-B'. In this case, the lower SMA elements are all part of a single shape memory alloy wire 333', while the upper 330, 331, 332, and 333 are all different SMA wires. In this embodiment, at least one SMA wire connects multiple actuator sub-assemblies, and the number of multiple actuator sub-assemblies is preferably between 6 and 96.

[0035] Regarding the method of operating the system according to the invention, it is important to be able to independently control the voltage applied to any one of the frame corner connectors, such that, through a suitable voltage difference between the opposing frame corner connectors, the shape memory alloy element (in the case of SMA wire connecting more actuator sub-assemblies, the shape memory alloy element being an SMA wire or an SMA wire portion) is actuated (shortened), thereby changing the actuator sub-assembly to another stable position. Needless to say, no current is supplied to the opposing SMA element until the need arises to switch the actuator sub-assembly back to its previous stable position.

[0036] Using the same wire for the top and / or bottom planes of multiple actuator subassemblies offers significant manufacturing and cost benefits. To achieve this, it is important to prepare a layout in which, in each subassembly, there are two adjacent frame corner connectors connected to a ground wire, and each of the opposing frame corner connectors is connected to a corresponding hardware switch that toggles between an activation voltage and an isolation state. The switching electrical switch can preferably be implemented using solid-state semiconductors, relays, or electromechanical switches. This will use the same continuous SMA wire to maintain no current flowing into adjacent frames, or individual SMA wires attached to a conductive common connector will also make them resemble a single wire.

[0037] It was also noted that, such as Figures 1B to 1C , Figure 2B , Figures 3B to 3D As shown in the cross-sectional view, the system frame is constructed such that the upper and lower portions of each connector are isolated from each other (e.g., by making the frame a double-layer PCB).

[0038] exist Figure 4A and Figure 4B The diagram shows a preferred electronic schematic for supplying power to the SMA elements of a system comprising twenty-four actuator sub-assemblies arranged in a 6x4 matrix. It can be observed that a common ground wire is used for two adjacent rows of actuator sub-assemblies, thus simplifying the electrical scheme. The system operates by using two separate switching ground wires; that is, the ground potential must be able to switch from ground 1 / ground 2 to no potential (open circuit), and ground 1 and ground 2 must be two separate ground levels that are isolated from each other (currently separated).

[0039] It should be emphasized that, using the above solution, it is impossible to operate every actuator sub-component in the system at exactly the same time. However, considering that the minimum operating delay is in the millisecond range and does not affect the system performance, such a delay can be applied under the condition of correct operation of the electrical switch, so that simultaneous actuation (i.e., state change) can be achieved from an operational perspective.

[0040] In more detail, Figure 4A Schematic diagram 410 is used to control the first (upper) SMA wire. The pins used to control the SMA wire or SMA wire section of each sub-assembly are the upper left pin and the lower right pin, thus, in Figure 4A Pins 7 and 29 are missing because no wire will be attached to pins 7 and 29. Similarly, Figure 4B Schematic diagram 420 is used to control the second (lower) SMA wire. The pins used to control the SMA wire or SMA wire section of each sub-assembly are the upper right pin and the lower left pin, thus, in Figure 4BPins 1 and 35 are missing because there is no wire connected to pins 1 and 35.

[0041] As already mentioned in the details of the actuator subassembly, one preferred application is within an analytical apparatus. In this respect, the control method applied to the system according to the invention allows for the selective control (opening and closing) of test traps in the analytical apparatus, the number of which is typically 6, 12, 14, 48, 96, and 384, and is designated as an ANSI standard by the Society for Biomolecular Sciences according to ANSI / SBS 1-2004, ANSI / SBS 2-2004, ANSI / SBS 3-2004, and ANSI / SBS 4-2004.

[0042] This invention is not limited to a specific SMA wire size, although wires with a diameter between 30 μm and 200 μm are preferred. Similarly, this invention is not limited to a specific material for SMA wires, but Ni-Ti based alloys, such as nickelitanol, are preferred.

[0043] Finally, regarding methods for operating and controlling the counter-wire, this information is known to those skilled in the art, see, for example, the paper “An accurately controlled antagonistic shape memory alloy actuator with self-sensing” by Wang et al., published in Sensors, Vol. 12, pp. 7682–7700, 2012. It is important to emphasize that the term “counter-wire” refers to an SMA wire whose actuation causes the displaceable element to move in the opposite direction.

Claims

1. An actuator sub-assembly (100; 201, 202, 203, 204) comprising: - a quadrilateral frame (110; 310) having four corner connectors (120, 120', 120", 120"'; 320, 320', 320", 320"', 320 iv ) ; - a movable element (160; 360) placed in correspondence of the center of the quadrangular frame (110; 310) and connected to the quadrangular frame (110; 310) by elastically deformable arms (140, 140', 140", 140"'; 340, 340'); - a first shape memory alloy wire (130; 330, 331, 332, 333) fixed on two opposite ones of the corner connectors; and - a second shape memory alloy wire (130'; 330', 331', 332', 333') fixed on the other two opposite corner connectors so that two wire planes intersect at an angle of 90° ± 20°, each wire plane containing a shape memory alloy wire and the relative corner connector of the shape memory alloy wire, the first shape memory alloy wire (130; 330, 331, 332, 333) being in contact with a first surface of the movable element (160; 360) and the second shape memory alloy wire (130'; 330', 331', 332', 333') being in contact with a second surface of the movable element (160; 360), the second surface being opposite to the first surface so that the two shape memory alloy wires are arranged in an antagonistic configuration in which they exert a force on the movable element (160; 360) in opposite directions.

2. The actuator subassembly (100; 201, 202, 203, 204) according to claim 1, wherein a plunger (170) is connected to the second surface of the movable element (160; 360) and the second shape memory alloy wire (130') passes between the plunger (170) and the second surface of the movable element (160; 360).

3. The actuator subassembly (100; 201, 202, 203, 204) according to any one of claims 1 and 2, wherein, The maximum distance between the first shape memory alloy wire (130; 330, 331, 332, 333) and the second shape memory alloy wire (130'; 330', 331', 332', 333') is comprised between 2.5 mm and 15 mm.

4. The actuator subassembly (100; 201; 202; 203; 204) according to any one of claims 1 and 2, wherein, The distance between the corner connectors (120, 120', 120", 120"'; 320, 320', 320", 320" ', 320 iv ) along the frame diagonal comprises between 25 mm and 100 mm.

5. The actuator subassembly (100; 201; 202; 203; 204) according to claim 3, wherein, The distance between the corner connectors (120, 120', 120", 120"'; 320, 320', 320", 320" ', 320 iv ) along the frame diagonal comprises between 25 mm and 100 mm.

6. The actuator subassembly (100; 201; 202; 203; 204) according to claim 1, wherein, The quadrangular frame (110; 310) is square shaped.

7. A system (200; 300) comprising a plurality of actuator subassemblies (100; 201, 202, 203, 204) according to any one of claims 1 to 6, arranged in a matrix configuration, wherein, Adjacent sub-assemblies share a common corner connector, the upper and lower parts of the common corner connector being isolated from each other, each sub-assembly having two adjacent corner connectors connected to a ground line and each of the opposite corner connectors being connected to a respective hardware switch that switches between an activation voltage and an isolated state.

8. The system (200; 300) according to claim 7, wherein A common ground line is used for two adjacent rows of actuator sub-assemblies and when the system comprises at least two separate common ground lines, each of the at least two separate common ground lines is a separate ground level, each common ground line being isolated from the other common ground lines and being switchable from a ground potential to a no potential.

9. The system (200; 300) according to claim 8, wherein At least one of the first shape memory alloy wires (330, 331, 332, 333) is in contact with an upper surface of a plurality of diagonally aligned movable elements (160; 360) and at least one of the second shape memory alloy wires (330', 331', 332', 333') is in contact with a lower surface of the plurality of diagonally aligned movable elements (160; 360).

10. The system (200; 300) according to claim 8 or 9, wherein The plurality of first shape memory alloy wires (330, 331, 332, 333) are parallel to each other and the plurality of second shape memory alloy wires (330', 331', 332', 333') are parallel to each other.

11. The system (200; 300) according to claim 7, wherein The hardware switch is implemented using solid state semiconductors, relays or electromechanical switches.

12. The system (200; 300) according to claim 9, wherein The number of movable elements (160; 360) in contact with individual shape memory alloy wires (330, 331, 332, 333) and (330', 331', 332', 333') is comprised between 6 and 96.

13. A method of controlling a system (200; 300) according to any one of claims 7 to 12, wherein, Actuation of a particular shape memory alloy wire (330, 331, 332, 333) and (330', 331', 332', 333') is achieved by a voltage difference set between opposing corner connectors having the wire fixed thereon.

14. The method of claim 13, wherein, The method is employed to control selective opening and closing of test wells in an analytical device.

15. The method of claim 14, wherein, The number of test wells is comprised between 6 and 384. The number of test wells is comprised between 6 and 384.

Images