Shape memory alloy based actuator subassembly and valve including the same

Abstract

The invention relates to an SMA wire-based actuator subassembly (10) for controlling the displacement of a movable plunger (12) by means of an SMA wire (14) and a return spring (15), to a composite actuator subassembly structure comprising two said subassemblies as well as to valves and to valve systems comprising these valves.

Description

[0001] The present invention relates to a shape memory alloy (SMA) wire based actuator sub-assembly, a valve comprising the same and uses thereof.

[0002] An area where the advantages given by the use of SMA wires have long been recognized is in the control of fluid valves, as described in US patents No. 3,835,659 and No. 4,973,024, where a valve element is driven by a SMA wire against the action of a biasing element. These advantages are particularly relevant in specific applications of microfluidic valves and so-called “lab-on-a-chip” applications, such as described in the paper “Electronic control of elastomeric microfluidic circuits with shape memory actuators” by Vyawahare et al. published on Lab Chip, 2008, 8, 1530-1535.

[0003] Improved SMA based valves are constantly evolving, as for example described in European patent EP 3894728 in the name of the Applicant. JP 2006 / 125445 and US 10337635 disclose various forms of SMA based valves, where a SMA wire acts against a biasing element on a plunger which carries a diaphragm which closes an inflow passage. Depending on the arrangement of the biasing element, the valve can be a normally open valve as in JP 2006 / 125445, or a normally closed valve as in US 10337635. The current for the SMA wire actuation is supplied through an electrical connector positioned close to the SMA wire holder, i.e. on the opposite side of the valve with respect to the plunger tip carrying the diaphragm.

[0004] Despite the widespread recognition of the advantages of SMA based valves, one of the improvements that has not been properly addressed relates to systems and applications where multiple valves need to be individually controlled and actuated. Applications that benefit from these multiple valve systems are for example high-end pneumatic mattresses, pneumatic top layer mattresses, comfort seats for cinemas, cars, aircrafts, wheelchairs.

[0005] An example of a SMA based system capable of multiple actuations independently is given in international patent application WO 2023 / 017158 in the name of the Applicant, where multiple controls of a SMA based actuator are achieved by means of a specific SMA wire configuration, i.e. a series of SMA wires in antagonistic configuration. This system can achieve the goal of selective actuation with a SMA based solution, but the specific SMA wiring configuration spans different elements and therefore individual maintenance is not possible.

[0006] Systems with multiple valves still need to be improved in two different aspects: on one hand the ease of adding a valve to a support module and on the other hand the possibility of easily replacing one or more of such modules without the need of lengthy operations on the whole system. The present invention overcomes these main drawbacks, wherein a first aspect of the invention consists in an actuator sub-assembly comprising the features recited in claim 1 and a valve comprising one or more such actuator sub-assemblies as recited in claim 13.

[0007] It is important to highlight that, unlike the above mentioned JP 2006 / 125445 and US 10337635, the present invention does not envisage the use of a housing for the actuator sub-assembly, but rather an open structure, i.e. the support structure is a flat planar structure that holds the elements of the actuator sub-assembly, thus making the sub-assembly simpler, cheaper and less voluminous. This also allows for an easy coupling of the support structures of two independent sub-assemblies, or even for the use of a single support structure to carry two independently operating plungers, thus further reducing the volume of the valve.

[0008] Furthermore, unlike the above mentioned prior art, the mutual positioning and related geometrical requirements of the plunger, the coupling means and the electrical terminals, the electrical terminals extending to the same side of the plunger tip, allow for a quick and effective coupling / disconnection of the fluid management and delivery system through a single operation, in which the mechanical, electrical and fluid connection / disconnection are all performed together.

[0009] The present invention will be further disclosed below through a detailed description of some embodiments thereof. In the description reference will be made to the figures of the attached drawings, in which:

[0010] Figure 1 a front view of an actuator sub-assembly according to a preferred embodiment of the present invention is schematically shown,

[0011] Figure 1A is Figure 1 a zoomed view of the dashed area A of

[0012] Figure 2 a perspective top view of a composite actuator sub-assembly structure according to a preferred embodiment of the present invention is schematically shown,

[0013] Figure 3 a perspective top view of a valve according to the present invention is schematically shown,

[0014] Figure 4 a perspective top view of Figure 3 the valve shown in

[0015] For the sake of easier understanding of the figures, the dimensions and the dimensional ratios of the elements have been modified in some cases, in particular and not exclusively relating to the length and diameter of the SMA wire.

[0016] Figure 1 A schematic front view of an actuator sub-assembly 10 according to the application is shown in Figure 1. The largest component of the actuator sub-assembly 10 is its support 11, which presents a coupling surface 110, i.e. a surface that will come into contact with the bottom surface of a retaining element (not shown) at which the actuator sub-assembly 10 is to be fitted / mounted. For the sake of convenience, the coupling surface 110 will define the top / upper portion of the actuator sub-assembly, however such sub-assembly can in a less preferred configuration be located above the retaining element in a so-called upside-down configuration (i.e. in this case the coupling surface 110 will be the bottom portion that will come into contact with the top surface of the retaining element).

[0017] The actuator sub-assembly 10 presents coupling elements 171, 172 that protrude beyond the coupling surface 110, each having an engagement surface 1710, 1720, i.e. a surface that will come into contact with the top surface of the retaining element, said engagement surfaces 1710, 1720 defining a virtual engagement plane E.

[0018] The distance between the support coupling surface 110 and the virtual engagement plane E is comprised between 0.5 mm and 3 mm, preferably between 1 mm and 2 mm, and presents a variation of no more than 10% over the entire coupling surface 110, to ensure a fluid-tight coupling between the actuator sub-assembly 10 and the retaining element. For the sake of clarity, the 10% variation is an absolute requirement, meaning that the difference between the maximum distance and the minimum distance between the support coupling surface 110 and the virtual engagement plane E divided by the maximum distance < 0.1.

[0019] The purpose of this limited variation is to guarantee a proper sealing between the sub-assembly and the retaining element, in order to limit the risk of leakage of the fluid controlled by the valve. This is particularly important in the case where the fluid is a liquid, since the electrical connectors supplying the electrical current to the SMA wire extend to the same top portion where the plunger tip is located. In this respect, the connection between the sub-assembly and the retaining element is made tighter, preferably by providing screw seats 181, 182, 183 in the top portion of the support 11, preferably having top surfaces 1810, 1820, 1830 aligned with the virtual engagement plane E (as shown in Figure 2). Figure 1

[0020] ​The actuator sub-assembly 10 further comprises an SMA wire 14 fixed to the support 11 via two SMA wire retainers 141, 142. The actuation and de-actuation of the SMA wire 14 causes a movement of the movable plunger 12 having a body comprising an elongated portion extending into a guide element 13 present on the support 11. The movable plunger 12 has a tip 121 protruding from the coupling surface 110 and extending above the virtual engagement plane E. Preferably, the plunger tip 121 is interlocked to the body of the movable plunger 12, wherein a central portion of the SMA wire 14 is interposed between the movable plunger tip 121 and the movable plunger elongated portion, i.e. the body of the movable plunger.

[0021] To ensure a stable contact between the SMA wire 14 and the movable plunger body, preferably there is a groove (not shown) on the movable plunger elongated portion facing the movable plunger tip 121, which will ensure mechanical stability without the need of using less preferred permanent fixing means for the SMA wire 14, such as gluing or welding.

[0022] The restoring force of the actuator sub-assembly 10, i.e. the force acting against the SMA wire 14, is provided by an elastic return element, such as a spring 15, which is fitted on the plunger body below the movable plunger tip 121.

[0023] In the embodiment shown in Figure 1 , the support structure 10 further presents two end stops 111, 112 (better shown in Figure 1A ), positioned to engage with corresponding protrusions on the movable plunger 12, such end stops 111, 112 blocking the upward movement caused by the de-actuation of the SMA wire 14 and due to the restoring force of the spring 15.

[0024] The two electrical connectors 161, 162 for supplying current to the SMA wire 14 extend from the SMA wire retainers 141, 142, respectively, to the top portion of the support structure 11. Preferably, the terminal portions 1610, 1620 of the electrical connectors 161, 162 are flexible and extend at a height comprised between the coupling surface 110 and the virtual engagement plane E.

[0025] Preferably, as Figure 1As shown in the figures, the actuator subassembly 10 presents mechanical interlocking portions 171, 172 as connecting means and screws fitted into seats 181, 182, 183; this represents a preferred embodiment in which the protruding mechanical interlocking portions 171 and 172 provide a preliminary manner of fixing and positioning of the actuator subassembly 10 on the retaining element, so as to make the most appropriate and stable fixing easier by means of the screws (not shown) fitted into the screw seats 181, 182, 183. This is a particularly convenient preferred embodiment, especially in the case where a plurality of actuator subassemblies are to be mounted on the same retaining element, but the invention is not limited or in any way to this arrangement and combination of coupling elements, or to additional and alternative fixing means such as gluing or hot riveting, also known as thermoplastic riveting.

[0026] Figure 1A is Figure 1 an enlarged view of the dashed area A of figure 1, which serves to better understand some details of the actuator subassembly 10. More specifically, the details of the plunger 12, the elastic return element 15 and the end stops 111 and 112 can be better observed. It can also be understood that the end stops 111 and 112 limit the upward movement imposed by the elastic return element 15, while the downward end stop 131, which is present on the upper surface of the nose 121 of the guide element 13 facing the movable plunger 12, limits the movement imposed by the actuation of the SMA wire 14.

[0027] Figure 2 A perspective top view of a composite actuator subassembly structure 20 according to a preferred embodiment of the invention is shown in figure 2. The composite actuator subassembly structure 20 comprises two actuator subassemblies 10, 10' as described in figure 1, each having a lower left corner 101, 101' and a lower right corner 102, 102', wherein the corners are identified with the movable plunger nose 121, 121' being observed in the upward position and the movable plunger being in front with respect to the associated support structure. Figure 1

[0028] In other words, in the composite actuator subassembly structure 20, the lower left corner 101 of the actuator subassembly 10 is coupled with the lower right corner 102' of the actuator subassembly 10', and the lower right corner 102 of the actuator subassembly 10 is coupled with the lower left corner 101' of the actuator subassembly 10'. The composite actuator subassembly structure 20 can be obtained by coupling the two different actuator subassemblies 10, 10', for example by means of a clamping or mechanical slide lock, however less preferred solutions such as welding or gluing can be used.

[0029] Alternatively, a single common moulded support is used to mount the SMA wires 14, 14' and the other elements of the composite actuator subassembly structure as previously described.​

[0030] exist Figure 1 and Figure 2 In the illustrated embodiments, and more generally in all embodiments covered by the invention, preferably, the length of the SMA wire 14 is between 40 mm and 130 mm, and most usefully, the elastic reset element 15 is a spring with an elastic constant between 0.05 N / mm and 0.3 N / mm.

[0031] It should be emphasized that, although from a geometric point of view, the SMA wires used preferably have a diameter between 25 μm and 500 μm, the present invention is not limited to a specific type of SMA wire; furthermore, since SMA wires are real objects, they may deviate from a circular cross-section, so the term diameter is intended to be the diameter of the smallest closed circle.

[0032] While this invention is not limited to any specific SMA, Ni-Ti based alloys, such as nitinol, are preferred. Ni-Ti based alloys can alternately exhibit superelastic behavior or SMA behavior depending on their processing. The properties of nitinol and the methods that allow these properties to be achieved are well known to those skilled in the art, see, for example, Dennis W. Norwich's paper "A Study of the Properties of a High Temperature Binary Nitinol Alloy Above and Below its Martensite to Austenite Transformation Temperature" presented at SMST 2010.

[0033] Nickeltinol can be used as is, or its transformation temperature characteristics can be adjusted by adding elements such as Hf, Nb, Pt, and Cu.

[0034] In another aspect, the present invention relates to a valve comprising a printed circuit board (PCB) that at least holds an actuator subassembly 10 according to the invention as previously defined. The PCB has an orifice corresponding to a movable plunger of the actuator subassembly, the orifice being sealed with a compressible sealant, wherein an airtight cap is in airtight contact with the PCB and encloses the plunger, the airtight cap having at least two ports, wherein at least one port is closable by the movable plunger of the actuator subassembly.

[0035] Figure 3 A schematic diagram of such a valve 30 is shown, which includes a composite actuator sub-assembly structure 20 mounted on a retaining PCB 31.Figure 3 In a preferred embodiment, the compound actuator subassembly structure 20 has two different types of PCB connection elements: protruding mechanical interlocking parts 171 and 172 and screw seats. The mechanical interlocking parts 171 and 172 are used to initially position and snap-lock the compound actuator subassembly structure 20 onto the retaining PCB 31, and the screw seats are used to securely lock it in place via screws. This arrangement is very practical when multiple compound actuator subassembly structures 20 must be mounted on the same PCB 31 or when only one compound actuator subassembly structure 20 needs to be replaced, making maintenance of the valve system (i.e., the retaining PCB 31 on which multiple compound actuator subassembly structures 20 are mounted) easier and more practical.

[0036] Valve 30 includes an airtight cover 32 having a first port 331, a second port 332, and a third port 333. Most commonly, this configuration is used to set pressure in an auxiliary device; therefore, in this case, the first port is connected to a pressurized fluid line, the second port is connected to an environment for depressurization, and the third port is a drive port connected to the device. The airtight cover 32 also includes connecting portions 181' and 182' positioned corresponding to screw seats 181 and 182.

[0037] To better understand the interaction between PCB 31 and the composite actuator sub-assembly structure 20, Figure 4 It shows Figure 3 A perspective view of the embodiment without the airtight cover 32.

[0038] like Figure 4 As shown, valve 30 includes a pressure sensor 34. It should be emphasized that the pressure sensor 34 is not an essential element of the invention, but rather a preferred feature to improve the performance of valve 30. The invention, in its assembled state and therefore relating to valves and valve systems, requires the presence of a compressible sealant layer 41 to simultaneously seal the orifice between the PCB 31 and the composite actuator subassembly structure 20, and preferably extends to cover the plunger tip 121. In a preferred embodiment, this layer also extends below the hermetic cap 32 to facilitate a hermetic seal compared to other methods (i.e., soldering). It should be emphasized that, for the sake of readability of the drawings and understanding of the underlying structure, the boundaries of the sealant layer 41 are shown only via embossed lines.

[0039] Preferably, the compressible sealant has a thickness between 0.2 mm and 2.7 mm (as measured in the uncompressed / free region) and most usefully employs an elastomeric material, preferably selected from silicone or rubber.

[0040] although Figure 3A valve is shown having two actuator subassemblies, or more precisely a valve having a composite actuator subassembly structure 20 comprising two actuator subassemblies 10, 10', but a valve having a single actuator subassembly 10 (i.e. a single plunger located under the air-tight cover 32) can also be implemented.

[0041] The single actuator subassembly solution can be used to implement a two-way valve or a three-way valve, however for a three-way valve the preferred solution is to have two actuator subassemblies per valve, preferably coupled together in a composite actuator subassembly structure, so that the two plungers controlling the valve ports respectively are present in the same air-tight cover to set the state of the third (outlet) port present in the air-tight cover.

[0042] In the case where two plungers are present in the same valve, such as Figure 4 The maximum distance of the two plungers, defined as the distance between the centers of the plunger tips, is preferably comprised between 5 mm and 20 mm, as shown in

[0043] As shown in Figure 3 and Figure 4 A same PCB can mount multiple actuator subassemblies according to the present invention, in order to implement a valve system, and in this respect, it can be observed in Figure 3 that the (optional) pressure sensors 34',... 34 n Most usefully, the maximum number of valves on a same PCB is 48, the more valves the higher the advantages of the present invention in terms of assembly and maintenance, even if such advantages exist considering that a single valve is mounted per PCB.

[0044] The valves and valve systems according to the present invention are most usefully used to control fluid pressure or flow, where the most common fluids are liquids such as oil, water or are generally gases such as air.

[0045] As already mentioned, in the most useful applications of the valves and valve systems according to the present invention, there are high-end pneumatic mattress, pneumatic top layer mattress, comfort seats for cinemas, cars, aircraft, wheelchair seats, but the valves and valve systems according to the present invention can also be employed to control fluid (say for example, air, water, oil) reservoirs; although the present invention is not limited to these applications, other exemplary fields of application are in the automotive field, such as in windshield wipers, or in vehicle seat adjustment by air flow regulation, the general operating principle of which is described in US patent 7,517,279.

Claims

1. An actuator subassembly (10) comprising: - a support structure (11) having a support coupling surface (110) beyond which one or more coupling elements (171, 172) protrude, each presenting an engagement surface (1710, 1720), the support coupling surface (110) defining a top portion of the actuator subassembly (10) and the engagement surfaces (1710, 1720) defining a virtual engagement plane E, - a movable plunger (12) mounted on the support structure (11), the movable plunger (12) having a tip (121) protruding from the support coupling surface (110) and extending above the virtual engagement plane E, - the movable plunger (12) having a body comprising an elongated portion extending into a guide element (13) present on the support structure (11), - a shape memory alloy wire (14) the extremities of which are fixed to two shape memory alloy wire retainers (141, 142) mounted on the support structure (11) and the central portion of which is connected to an intermediate portion of the movable plunger (12) to cause displacement of the movable plunger (12) upon actuation of the shape memory alloy wire (14), - an elastic return element (15) acting in opposition to the shape memory alloy wire (14), - two electrical connectors (161, 162) extending respectively from the shape memory alloy wire retainers (141, 142), characterized in that the distance between the support coupling surface (110) and the virtual engagement plane E is comprised between 0.5 mm and 3 mm, preferably between 1 mm and 2 mm, with a variation of no more than 10% over the entire coupling surface (110), and in that the two electrical connectors (161, 162) extend to the top portion of the support structure (11).

2. The actuator subassembly (10) of claim 1, wherein, The coupling elements comprise protruding mechanical interlocking portions (171, 172).

3. The actuator subassembly (10) according to any one of the preceding claims, wherein, The coupling elements comprise screw seating portions (181, 182, 183).

4. The actuator subassembly (10) according to any one of the preceding claims, wherein, Each electrical connector (161, 162) has a flexible portion (1610, 1620) extending to the height between the support coupling surface (110) and the virtual engagement plane E.

5. The actuator subassembly (10) according to any one of the preceding claims, wherein, The length of the shape memory alloy wire (14) is comprised between 40 mm and 130 mm.

6. The actuator sub-assembly (10) according to any one of the preceding claims, wherein, The elastic return element (15) is a spring having an elastic constant comprised between 0.05 N / mm and 0.3 N / mm.

7. The actuator sub-assembly (10) according to any one of the preceding claims, wherein, The support structure (11) has two end stops (111, 112) for limiting the travel of the movable plunger (12) when driven by the elastic return element (15).

8. The actuator sub-assembly (10) according to any one of the preceding claims, wherein, The upper surface of the guide element (13) presents an end stop (131) for limiting the travel of the movable plunger (12) when driven by the shape memory alloy wire (14).

9. A composite actuator subassembly structure (20) comprising two actuator subassemblies (10, 10’) according to any one of claims 1 to 8.

10. The composite actuator subassembly structure (20) of claim 9, wherein, The two actuator subassemblies (10, 10’) are joined together.

11. The composite actuator subassembly structure (20) of claim 10, wherein, The joining of the actuator subassemblies (10, 10’) is achieved by clamping or by mechanical sliders.

12. The composite actuator subassembly structure (20) of claim 9, wherein, The two actuator subassemblies (10, 10’) share a common support structure (11).

13. A valve comprising at least a printed circuit board (31) holding an actuator subassembly (10) according to any one of claims 1 to 8, the printed circuit board (31) having an aperture corresponding to the movable plunger tip (121) of the actuator subassembly, the aperture being sealed by a compressible sealant (41), and the valve comprising a hermetic cover (32) in hermetic contact with the printed circuit board (31) and enclosing the plunger tip (121), the hermetic cover (32) having at least two ports (331, 332), wherein, At least one of the ports can be closed by the plunger tip (121).

14. The valve of claim 13, wherein, The valve further comprises a pressure sensor (34) located below the hermetic cover (32).

15. The valve of claim 13 or 14, wherein, The valve comprises a composite actuator subassembly structure (20) according to any one of claims 9 to 12.

16. The valve of any one of claims 13 to 15, wherein, The number of ports of the hermetic cover (32) is 3.

17. The valve of claim 15, wherein, The maximum distance between the centers of the plunger tips (121, 121’) is comprised between 5 mm and 20 mm.

18. The valve of any one of claims 13 to 17, wherein, The compressible sealant (41) is further interposed between the printed circuit board (31) and the hermetic cover (32).

19. The valve of any one of claims 13 to 18, wherein, The compressible sealant (41) is an elastic material with a thickness comprised between 0.2 mm and 2.7 mm.

20. The valve of claim 19, wherein, The elastic material is chosen from silicone or rubber.

21. A valve system comprising from 2 to 48 valves according to any one of claims 13 to 20.

22. A method for controlling the pressure of a fluid in a device, wherein, The pressure is controlled by a valve system according to claim 21.

23. The method of claim 22, wherein, The fluid is chosen from air, water, oil.

24. The method of claim 22 or 23, wherein, The device is a bed mattress, a top layer mattress, a seat or a fluid reservoir.

25. The method of claim 22 or 23, wherein, The device is an automotive part, preferably a windscreen wiper or a seat adjustment mechanism.

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