NL2002895C - Activatable device, actuator comprising such device and method for activating such device. - Google Patents

Description

Activatable device, actuator comprising such device and method for activating such device

The invention relates to an activatable device and to an actuator comprising the device.

5 The invention further relates to a method for activating an activatable device.

Activatable devices of the type comprising a shape memory alloy are increasingly used in a number of applications. Such an activatable device typically comprises a deformable body, provided with a member of a shape memory alloy. Shaping of aero-10 elastic surfaces, such as aircraft wings or automotive spoilers, during use to control their aerodynamics and deforming hydrofoils to generate and/or control lift and thrust arc typical examples. In other applications, stresses are introduced into a construction to influence the mechanical behaviour thereof, without any noticeable external deformation of the deformable body. Examples include increasing the maximum 15 allowable buckling load of a slender structure, or reducing vibrations in a construction. Yet another application is so-called self-healing of constructions. In this application, a shape memory alloy, embedded in a material, is activated to generate (local) stresses to open up an ampul holding a hardenable resinous medium that, upon release, flows into damaged parts of the material.

20

The known activatable device in general comprises a deformable body and, embedded therein, a member of a shape memory alloy having a transition temperature. The activatable device comprises heating means for activating the shape memory alloy member. Heating the member to exceed its transition temperature causes a phase change 25 of the shape memory alloy, for instance from a martensitic crystal structure to an austenitic crystal structure, and a corresponding change in shape. Since the shape memory alloy member is embedded in the deformable body of the known device, it is in intimate contact therewith and therefore is able to transfer its deformation directly to the surrounding body, which, as a result also deforms from a first position wherein the 30 temperature of the shape memory alloy is below its transition temperature to a second position, wherein the temperature of the shape memory alloy is above its transition temperature or stresses are introduced into the construction to influence the mechanical behaviour thereof, without any noticeable external deformation of the deformable body.

2 A disadvantage of the known activatable device is that its response time is too long for a number of applications, in particular in applications wherein the device has to be activated cyclically.

5 An object of the present invention is to provide an activatable device with a decreased response time relative to the known device, in particular under cyclic activation and deactivation.

The invention thereto provides an activatable device, comprising a deformable body, 10 provided with a member of a shape memory alloy having a transition temperature, heating means for heating the member to above its transition temperature and thereby activate the device by deforming the body, and cooling means for cooling the member, wherein the body comprises at least one cavity that is accessible to the cooling means and moreover holds the shape memory alloy member. The invention is based on the 15 insight that it is not necessary to completely embed the shape memory alloy member in the deformable body in order to adequately transfer the members deformation to the surrounding body. The member indeed may be fixed to the deformable body in at least two spaced apart positions only to cause the body’s deformation as a result of the deformation of the member. It has been found that such form of stress transfer from 20 member to body is adequate to impart deformation to the body and thereby activate the device, in particular also under cyclic activation. Since the at least one cavity is accessible to the cooling means and moreover holds the member substantially free-floating, the cooling means may readily contact the members surface. This intimate contact between member and cooling means leads to improved heat exchange to and 25 from the member and as a result to a faster response time.

With substantially free-floating is meant that the member is not embedded in the deformable body, but is held in the at least one cavity such that the major part of the members surface, preferably more than 50%, more preferably more than 75%, and most 30 preferably more than 90% is accessible to the cooling means. On the other hand the member is fixed to the deformable body in at least two spaced apart positions, to be able to impart its deformation to the deformable body. With deformable body is meant a body that is able to deform, but will not always deform in certain applications. The 3 extent of deformation generally depends on its stiffness relative to the forces that the shape memory alloy member exerts on the body.

In a first embodiment of the invention, the cooling means comprise a coolant selected 5 from the group consisting of a gas, a fluid, and a gel. Such coolants readily flow through the space between the member and the at least one cavity holding the member, and have good heat dissipation properties. The gas is preferably air or nitrogen, both of which show good cooling properties, and whereby the latter is particularly preferred for cyclic activation purposes at relatively high frequencies.

10

In another preferred embodiment, the at least one cavity comprises at least one opening. Providing the cavity or cavities of the deformable body with at least one opening, and preferably with a plurality of openings, not only allows for easy access to the cooling means and in particular the coolant, but also allows to circulate the coolant inside the 15 cavity or cavities. The opening(s) may be accessible from the exterior of the activatable device. In another embodiment, the deformable body comprises multiple cavities within the deformable body, at least some of the cavities comprising openings that connect different cavities to each other.

20 The coolant may be a stationary coolant within the cavity. The coolant however is preferably forced into and through the at least one cavity by separate driving means, such as a pump or ventilator, or as a result of environmental conditions. Indeed, if the activatable device has a relative velocity with respect to a surrounding medium, such as air or water, the surrounding medium may function as coolant in flowing through the at 25 least one cavity, thereby transporting heat away from the member and out of the activatable device. In a preferred embodiment, the element comprises driving means for driving the coolant through the at least one cavity. Using driving means, the coolant is forced along the member independently of the environmental conditions, thereby effectively transporting heat away from the member and out of the activatable device 30 when desired. This leads to shorter cooling times, wherein cooling of the member becomes less influenced by the temperature of the surrounding body.

In another preferred embodiment of the invention, the at least one cavity is a channel and the member is elongated, whereby the member extends in the longitudinal direction 4 of the channel and is fixed to at least one channel wall in at least two spaced apart positions. The present embodiment is particularly useful for activating devices through bending the deformable body. Activating the activatable device using the elongated member of the present embodiment allows to accurately deform the body into a 5 preferred shape. Another advantage of using an elongated member is the fast response time. The two spaced apart positions may be within the deformable body, but at least one of them may also be part of an external object, to which the body may be connected.

10 The at least two positions in which the member is fixed to the deformable body may be chosen as desired. Their position within the body will trigger different deformation modes of the deformable body. Indeed, depending on their position, and upon activating the member, the deformable body may actually compress, elongate, twist, bend etcetera or show a combination of such deformation modes. In certain applications the 15 deformable body may not show any appreciable deformation. Instead, the member will deform and incur large stresses into the body.

In a preferred embodiment, the activatable device comprises a body in the form of a bending beam or bending plate, the body comprising at least one member extending at a 20 distance from the neutral axis of the body. As a result, activating the member will bend the deformable body and thereby activate the activatable device. Deformable bodies of the present embodiment may advantageously be used in aerodynamic and hydrodynamic applications.

25 In another preferred embodiment, the deformable body in the form of a bending beam or bending plate comprises at least one first channel, extending on a first side of the neutral axis for receiving a first member, and at least one second channel extending on a second side of the neutral axis for receiving a second member, the second side being different from the first side. By activating the first member and the second member 30 altematingly, bending directions of the deformable body may be controlled such that the stress in a specific region of the deformable body changes from tension to compression, and vice versa. Preferably, the deformable body in the form of a bending beam or bending plate is relatively thin, which requires little effort to deform and thus low energy for a given preferred deformation. With relatively thin is meant that the ratio of 5 the length of the body to its thickness is more than 5, preferably more than 10 and most preferably more than 20.

The member may be heated in various ways, for example by radiation. Preferably, the 5 shape memory alloy is electrically conductive and the heating means comprise a source of electrical energy, which is electrically connected to the member for forming an electrical circuit with the member. Heating the member via an electrical current is cheap, reliable and fast.

10 The activatable device according to the invention may advantageously be used in an actuator, which actuator further comprises control means for the heating means and/or the cooling means. As the response time of the activatable device according to the invention is shorter than that of the activatable device known hitherto, the actuator according to the invention is able to respond fast as well, and is therefore preferably 15 used in applications, requiring such fast response times.

Particularly preferred applications require cyclic activating of the actuator. Examples of such applications include control of vibrations of constructions, introducing stresses into a construction to increase its maximum allowable buckling load. Another preferred 20 application is the use of the actuator in a wing. Such a wing can effectively make use of an actuator according to the invention, whereby movable parts such as flaps, slats, ailerons or even chevrons and nozzles are controlled using the actuator according to the invention. The wing may for example be part of an aircraft, spacecraft, wind turbine blade or a hydrofoil.

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In a preferred embodiment, the deformable body of the actuator according to the invention forms a part of the wing. This safes weight and results in a fast and substantially continuous deformation of the wing.

30 Tn still another preferred embodiment, the deformable body of the actuator according to the invention forms a part of the trailing edge of the wing, and more preferably substantially forms the trailing edge of the wing. In such embodiments, the actuator according to the invention can effectively be used to deform the wing, and in particular 6 its trailing edge. As a result, a wing is provided that allows flexible deformation patterns.

The invention also relates to a method for activating a device according to the invention, 5 the method comprising heating and/or cooling the member by the heating and/or cooling means respectively, such that the temperature of the member passes the transition temperature of the members shape memory alloy, whereby the cooling means are provided in the at least one cavity of the deformable body. The advantages of this method correspond to the advantages of the activatable device according to the 10 invention as mentioned above.

The temperature of the member may be changed such that the phase of the shape memory alloy of the member changes between austenite and martensite. Preferably, the temperature of the member is changed such that the shape memory alloy changes 15 between phases selected from the group: austenitic - rombolic, rombolic - austenitic, martensite - rombolic, rombolic - martensite. These transitions require less change in temperature and as a result less power consumption is needed and a preferred deformation is achieved in less time. Another advantage is the improved fatigue properties of the activatable device, when changing between the mentioned phases. The 20 rombolic phase is also called the R-phasc.

In some applications the activatable device only needs to deform once. Such applications are for example the self-healing application as explained above. Another application is to improve the impact properties of a construction, by introducing stresses 25 into the construction such that during impact the stresses within the construction will not exceed the yield stress of the material. It may also be that the activatable device is repeatedly deformed, by at least two times passing a transition temperature of the member. In this way use is made of the so-called two-way shape memory effect. Hereby is meant that the member takes a known shape corresponding to a first phase 30 (martensitic, R-shape or austenitic) with a first temperature and a known shape corresponding to a second phase differing from the first phase with a second temperature. This method can be used advantageously in an actuator according to the invention.

7

Another preferred method is characterized in that the cooling means are actively driven through the at least one cavity. With such method, cooling can be performed even faster than without using driving means, thereby emphasizing the advantages of the invention.

5 In still another preferred embodiment of the method, the heating and/or cooling is performed cyclically, causing a cyclic deformation of the deformable body. Although the frequency of such cyclic deformation may be chosen between wide limits, it is preferred to deform the deformable body (and thereby activate the actuator) with a frequency of between 0.05 and 10 Hz, more preferably of between 0.1 and 5 Hz, and 10 most preferably of between 0.2 and 2 Hz. The actuator according to the invention can be used advantageously for the mentioned frequencies, as it allows for rapid cooling of the member.

The invent ion will now be described in more detail, by way of example, with reference 15 to the accompanying figures, in which: figure 1 schematically shows a perspective view on an activatable device according to the invention; figure 2a shows a side view of the activatable device according to figure 1, in undeformed condition; 20 figure 2b shows a side view of the activatable device according to figure 1, in a first deformed condition; figure 2c shows a side view of the activatable device according to figure 1 in a second deformed condition; figure 2d shows a cross-section of the activatable device according to figure 1, along 25 line A-A of figure 2a; figure 3 a schematically shows a cross-section of a rotor blade of a wind turbine according to the invention, figure 3b shows a detailed view of the rotor blade according to figure 3a.

30 With reference to figure 1, a perspective view on an activatable device 1 is shown. The activatable device 1 is made from nylon and manufactured by a moulding process. The element has a length L, width w and height h. The activatable device 1 comprises a deformable body 2. A number of four cavities in the form of channels (3a,3b,3c,3d) extend within the body 2 along the length L of the body 2. Channels (3 a,3b) are located 8 nearby the lower surface 2a of the body 2, and below the neutral axis thereof. Channels (3c,3d) are located nearby the upper surface 2b of the body 2, and above the neutral axis thereof. The channels (3a,3b,3c,3d) comprise openings 4 at the side walls 5 of the body 2. Elongated members of shape memory alloy (6a,6b,6c,6d) extend within the channels 5 (3a,3b,3c,3d) and are fixed to the body 2 at the side walls 5. The fixation is achieved by locally adhering the members (6a,6b,6c,6d) to the channel walls 5 nearby the openings 4. Since the members (6a,6b,6c,6d) are only fixed to the body at the side walls 5 thereof, the members (6a,6b,6c,6d) extend substantially free floating into their respective channels (3a,3b,3c,3d). As the body 2 is isotropic, the members (6a,6b) 10 extend below the neutral plane (not shown) of the body 2, whereas the members (6c,6d) extend above the neutral plane (not shown) of the body 2. The channels (3a,3b,3c,3d) comprise air as a coolant, which coolant readily accesses the space between the members (6a,6b,6c,6d) and the walls of the channels (3a,3b,3c,3d).

15 The heating means 7 comprise a source of electrical energy and is connected to the members (6a,6b,6c,6d) via electrical conductors 8. The heating means 7 comprise four switches (9a,9b,9c,9d), having a first position for closing an electrical circuit with the members (6a,6b,6c,6d) and a second position for interrupting the electrical circuit. Each member (6a,6b,6c,6d) can form a separate electrical circuit with the heating means 7 20 using the switches (9a,9b,9c,9d), respectively. It should be clear that other arrangements for the heating means are possible.

A suitable method for activating the element 1 is as follows. Members (6a,6b,6c,6d) are all below their transition temperature, and as a result the alloys of the members have a 25 martensite crystal structure, which is the starting condition (see also figure 2a). Bringing switches (9a,9b) in their first position will close the electrical circuit with the members (6a,6b). As a result, the members (6a,6b) will heat and pass their transition temperature, wherein the alloy of the members will transfer from their martensite phase into their R-phase. As a result of this phase change, the members will deform as they will take a 30 different crystal structure and as the members (6a,6b) are fixed to the side walls 5 of the body 2, the body 2 will also deform (see also figure 2b). Bringing the switches (9a,9b) in their second position will interrupt the electrical circuit between the members (6a,6b) and the heating means 7. As the channels (3a,3b) are filled with a coolant, and this coolant is readily accessible to the members (6a,6b), in particular is in direct contact 9 with their surface, the members (6a,6b) will cool off within a short period of time, thereby passing their transition temperature, causing a phase change of the alloy of the members (6a,6b), which will take their martensite crystal structure again. The body 2 will then also return to its starting condition (see also figure 2a) in a short time. A 5 similar method applies for activating the members (6c,6d), which will deform the body 2 according to figure 2c.

Figure 2a shows a side view of the activatable device 1 according to figure 1, in undeformed condition, which is the starting condition. All four members (6a,6b,6c,6d) 10 have a martensite crystal stmcture.

Figure 2b shows the activatable device 1 in a first deformed condition, wherein the members (6a,6b) have their rombolic crystal structure, as explained above. Due to the transfer of the alloy from its martensite crystal structure to its rombolic crystal structure, 15 the members (6a,6b) will shorten. The region above the neutral plane (not shown), i.e. nearby the upper surface 2b of the body 2, will undergo compressive stresses, whereas the region below the neutral plane (not shown), i.e. nearby the lower surface 2a of the body 2, may undergo tensile stresses. It is also possible to further heat the members (6a,6b), which will cause a phase change of the members (6a,6b) from their R-phase 20 into their austenitic phase. This may deform the body 2 of the activatable device 1 even more, resulting in increased compressive stresses near the upper surface 2b of the body 2.

Figure 2c shows a side view of the activatable device 1 wherein the body 2 is deformed 25 in the opposite direction of the body 2 shown in figure 2b. The members (6c,6d) have their rombolic crystal stmcture. Due to the transfer of the alloy from its martensite crystal stmcture into its rombolic crystal stmcture, the members (6c,6d) will now shorten. The region below the neutral plane (not shown), i.e. nearby the lower surface 2a of the body 2, will undergo compressive stresses, whereas the region above the 30 neutral plane (not shown), i.e. nearby the upper surface 2b of the body 2, may undergo tensile stresses. It is also possible to further heat the members (6c,6d), which will result in a change of the members (6c,6d) from their R-phase into their austenitic phase. This may deform the body 2 of the activatable device 1 even more, resulting in increased compressive stresses near the lower surface 2a of the body 2.

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Figure 2d shows a cross-section along line A-A of the activatable device 1 according of figure 2a, along line A-A of figure 2a. In addition to the body 2, the channels (3a,3b,3c,3d) and the members (6a,6b,6c,6d), a neutral plane 10 is shown. This is the 5 plane within the body 2, in which compression or tensile stresses will not occur as a result of a pure bending.

With reference to figure 3a, a schematic cross-section of a rotor blade 50 of a wind turbine according to the invention is shown. The rotor blade 50 comprises a leading 10 edge 51 and a trailing edge 52. An activatable device 55 according to the invention forms the trailing edge 52, The activatable device 55 is rigidly fixed to the upper surface 57 and lower surface 58 of the rotor blade 50, by a fixation element 59.

Figure 3b shows a detailed view of the rotor blade 50 according to figure 3a. The 15 activatable device 55, preferably made of nylon, comprises a deformable body having channels 60a, which extend below the neutral axis (not shown) and channels 60b, which extend above the neutral axis of the deformable body. Members (61 a,61 b) extend within the channels (60a,60b) substantially free floating, and are fixed nearby a first edge 62 and a second edge 63. The channels (60a,60b) are filed with air and comprise openings 20 64. The members (61a,61b) arc electrically conductive and connected to heating means 65. The heating means 65 function similar to the heating means 7 as explained in figure 1. Activating members 61a respectively 61b will deform the deformable element 55 downward and upward, respectively.

25 The invention is not limited to the embodiments as shown in the figures. For example, the activatable device according to the invention may also be fixed to the trailing edge, thereby forming an extension of the trailing edge, instead of actually forming the trailing edge.

Claims (15)

1. Activeerbare inrichting, omvattende: een deformeerbaar lichaam, voorzien van een element uit een 5 vormgeheugenlegering, die een overgangstemperatuur bezit, opwarmmiddelen voor het opwarmen van het element tot boven zijn overgangstemperatuur en daarmee de inrichting te activeren door het deformeren van het lichaam, en afkoelmiddelen voor het koelen van het lichaam, 10 waarbij het lichaam ten minste één holte omvat, die toegankelijk is voor de afkoelmiddelen en tevens het clement uit een vormgeheugenlegering houdt.1. Activable device, comprising: a deformable body, provided with an element from a shape memory alloy, which has a transition temperature, heating means for heating the element above its transition temperature and thereby activating the device by deforming the body, and cooling means for cooling the body, wherein the body comprises at least one cavity that is accessible to the cooling means and also keeps the lenght from a shape memory alloy. 2. Activeerbare inrichting volgens conclusie 1, met het kenmerk dat de afkoelmiddelen een koelmiddel omvatten, gekozen uit de groep bestaande uit gas, 15 vloeistof, gel.2. Activable device as claimed in claim 1, characterized in that the cooling means comprise a cooling agent selected from the group consisting of gas, liquid, gel. 3. Activeerbare inrichting volgens conclusie 1 of 2, met het kenmerk dat de ten minste één holte ten minste één opening omvat.Activable device according to claim 1 or 2, characterized in that the at least one cavity comprises at least one opening. 4. Activeerbare inrichting volgens één der voorgaande conclusies, met het kenmerk dat de inrichting aandrijfmiddelen omvat voor het door de ten minste één holte drijven van het koelmiddel.4. Activable device as claimed in any of the foregoing claims, characterized in that the device comprises drive means for driving the coolant through the at least one cavity. 5. Activeerbare inrichting volgens één der voorgaande conclusies, met het 25 kenmerk dat de ten minste één holte een kanaal vormt en dat het element langwerpig is, waarbij het element zich in longitudinale richting van het kanaal uitstrekt en waarbij het element met ten minste één kanaalwand is verbonden op ten minste twee op onderlinge afstand gelegen posities.5. Activable device as claimed in any of the foregoing claims, characterized in that the at least one cavity forms a channel and that the element is elongated, the element extending in longitudinal direction of the channel and wherein the element with at least one channel wall is connected at at least two spaced-apart positions. 6. Activeerbare inrichting volgens conclusie 5, met het kenmerk dat de inrichting een als een buigbalk of buigplaat gevormd lichaam omvat, welk lichaam ten minste een zich op afstand van de neutrale as van het lichaam uitstrekkend element omvat.An activable device as claimed in claim 5, characterized in that the device comprises a body shaped as a bending beam or bending plate, which body comprises at least one element extending at a distance from the neutral axis of the body. 7. Activeerbare inrichting volgens één der voorgaande conclusies, met het kenmerk dat de geheugenlegering elektrisch geleidend is en dat de opwarmmiddelen een bron van elektrische energie omvatten, welke elektrisch geleidend is verbonden met het element voor het vormen van een elektrische schakeling met het element. 5An activable device according to any one of the preceding claims, characterized in that the memory alloy is electrically conductive and that the heating means comprise a source of electrical energy, which is electrically conductively connected to the element for forming an electric circuit with the element. 5 8. Actuator, omvattende een activeerbare inrichting volgens één der voorgaande conclusies en besturingsmiddelen voor de opwarmmiddelen en/of de afkoelmiddelen.8. Actuator, comprising an activatable device as claimed in any of the foregoing claims and control means for the heating means and / or the cooling means. 9. Vleugel, omvattende een actuator volgens conclusie 8 voor het deformeren van 10 ten minste een deel van het oppervlak van de vleugel.9. Wing, comprising an actuator according to claim 8 for deforming at least a part of the surface of the wing. 10. Vleugel volgens conclusie 9, met het kenmerk dat het deformeerbare lichaam van de actuator een onderdeel van de vleugel vormt.A wing according to claim 9, characterized in that the deformable body of the actuator forms a part of the wing. 11. Vleugel volgens conclusie 10, met het kenmerk dat het deformeerbare lichaam van de actuator in hoofdzaak de achterrand van de vleugel vormt.A wing according to claim 10, characterized in that the deformable body of the actuator substantially forms the rear edge of the wing. 12. Werkwijze voor het activeren van een activeerbare inrichting volgens één der conclusies 1 - 7, omvattende het dusdanig opwarmen en/of afkoelen van het element 20 door respectievelijk de opwarmmiddelen en/of de afkoelmiddelen, dat de temperatuur van het element de overgangstemperatuur van de geheugenlegering van het element passeert, waarbij de afkoelmiddelen zijn voorzien in de ten minste één holte van het deformeerbaar lichaam.12. Method for activating an activatable device as claimed in any of the claims 1-7, comprising heating and / or cooling the element 20 in such a way that the heating means and / or the cooling means respectively, that the temperature of the element exceeds the transition temperature of the element. memory alloy of the element passes, wherein the cooling means are provided in the at least one cavity of the deformable body. 13. Werkwijze volgens conclusie 12, met het kenmerk dat de afkoelmiddelen actief door de ten minste één holte worden gedreven.A method according to claim 12, characterized in that the cooling means are actively driven through the at least one cavity. 14. Werkwijze volgens conclusie 12, met het kenmerk dat het opwarmen en/of afkoelen cyclisch wordt uitgevoerd, waarmee een cyclische deformatie van het 30 deformeerbare lichaam wordt veroorzaakt.14. Method as claimed in claim 12, characterized in that the heating and / or cooling is carried out cyclically, whereby a cyclic deformation of the deformable body is caused. 15. Werkwijze volgens conclusie 14, met het kenmerk dat het cyclisch deformeren van het deformeerbare lichaam plaatsvindt met een frequentie tussen 0.05 en 10 Hz, bij voorkeur tussen 0.1 en 5 Hz en met de meeste voorkeur tussen 0.2 en 2 Hz.Method according to claim 14, characterized in that the deformable body is cyclically deformed at a frequency between 0.05 and 10 Hz, preferably between 0.1 and 5 Hz and most preferably between 0.2 and 2 Hz.