Shape memory alloy actuator and use thereof

Abstract

The invention relates to an actuator (1) for reversibly producing a translational actuation movement, comprising: an actuation element (2) made of a shape memory alloy, the actuation element being designed to perform a length contraction when heated to a temperature above a transformation temperature range; a superheating collector (3) for absorbing solar thermal radiation, having a collector housing (7), which surrounds a superheating volume which can be heated to a temperature above the transformation temperature range by means of the solar thermal radiation, and having a collector opening (8); wherein a first end (9) of the actuation element (2) is fastened to the collector housing (7) and a second end (10) of the actuation element (2) is arranged so as to be translationally movable, such that the actuation element (2), in an activated length-contracted state at a temperature above the transformation temperature range, is accommodated completely in the superheating volume and, in a non-activated length-relaxed state at a temperature below the transformation temperature range, has partly exited the collector housing (7) through the collector opening (8).

Description

[0001] Shape memory alloy actuator and use thereof

[0002] The invention relates to an actuator for reversibly generating a translational actuating movement, comprising an actuating element made of a shape memory alloy, which is designed to perform a length contraction when heated to a temperature above a transition temperature range. Furthermore, the invention relates to a use of an actuator according to the invention.

[0003] An actuator is a system that converts non-mechanical energy into mechanical work, specifically into a positioning movement (working stroke) and a working force. Actuators with a positioning element made of a shape memory alloy, also called a shape memory alloy actuator (SMA actuator), can be thermally induced to activate, meaning they react to a change in temperature. A shape memory alloy (SMA) is a functional material. It is often referred to as a memory alloy because, after an apparently plastic deformation by heating, it can seemingly "remember" a shape previously imprinted through heat treatment. This shape transformation is based on a temperature-dependent phase transformation of two different crystal structures of the shape memory alloy: the cold phase (martensite) and the hot phase (austenite).Through a phase transformation, which involves the conversion of heat into mechanical energy and takes place within a material-specific transformation temperature range, both crystal structures can transition into one another. In the cold phase (martensite), the SMA material is in a more deformable form with a lower modulus of elasticity than in the stiffer warm phase (austenite). When the shape memory alloy is in the cold phase and heated, the crystal structure begins to change and transform into austenite. The temperature at which this phase transformation begins is called the austenite start temperature (A). s). The temperature at which this phase transformation is completed is called the austenite finish temperature (Af). In the warm phase (austenite), the SMA material returns to its original imprinted shape, generating a tensile force that can be used as a working force for an actuator. In addition, a length contraction of the SMA material occurs, which can be used as an actuating movement or working stroke for an actuator. When the shape memory alloy is cooled from the warm phase, it transforms back into martensite. The starting temperature for this phase transformation is called the martensite start temperature (M s), the final temperature at which this phase transformation is complete is called the martensite finish temperature (Mf). The transformation temperature range is defined as the temperature range between the martensite finish temperature (Mf) and the austenite finish temperature (Af). An elongated actuator made of a shape memory alloy therefore exhibits austenite and an activated, length-contracted state at a temperature above the transformation temperature range, and martensite and a non-activated, length-relaxed state at a temperature below the transformation temperature range.

[0004] There is a need for actuators of this type that can be activated autonomously by solar radiation or sunlight.

[0005] JPA 60-116880 A specifies an actuator for a rotary actuating movement that can be activated by solar radiation. The actuator has an actuating element made of a shape memory alloy that rotates in a housing as an endless loop. The actuating element undergoes a continuous cycle of heating in an open housing area exposed to solar radiation and cooling in a shaded housing area. Consequently, the rotary movement of the actuating element continues until sufficient solar radiation is no longer available. This actuator is therefore unsuitable for executing a defined, translational actuating movement.

[0006] US 8,938,965 B1 discloses an actuator with an actuating element made of a shape memory alloy that can be activated by solar radiation. The actuating element is directly exposed to solar radiation and, when sufficiently heated by the solar radiation, undergoes a linear length contraction. This closes a flap that separates the actuating element from the solar radiation and shades it. In the shade, the actuating element cools down again and is elongated again by a biasing spring that acts as a return element, and the flap opens again. Since the actuating element is directly exposed to solar radiation, the length contraction and thus the activation of the actuator is directly dependent on the intensity of the solar radiation or the ambient temperature, and a sudden actuating movement occurs because almost the entire actuating element is exposed to solar radiation.This actuator is therefore not very practical for control applications where a cascading or temporally slowed or temporally defined control movement or an activation of the actuator with a lower dependence on the ambient temperature or the intensity of the solar radiation is required.

[0007] The object of the present invention is to provide an improved actuator of the generic type which can be activated completely autonomously by solar radiation.

[0008] To achieve this object, the invention has the features of patent claim 1. Accordingly, an actuator according to the invention for reversibly generating a translational actuating movement comprises an actuating element made of a shape memory alloy, wherein the actuating element is designed to perform a length contraction when heated to a temperature above a transition temperature range, and an overheating collector for absorbing solar thermal radiation. The overheating collector has a collector housing enclosing an overheating volume that can be heated by solar thermal radiation to a temperature above the transition temperature range, and a collector opening.A first end of the actuating element is fixed to the collector housing and a second end of the actuating element is arranged to be translationally movable such that the actuating element is completely received in the superheat volume in an activated length-contracted state at a temperature above the transformation temperature range and has partially exited the collector housing through the collector opening in a non-activated length-relaxed state at a temperature below the transformation temperature range.

[0009] The particular advantage of the invention is that solar thermal radiation, or solar radiation, can be used both as a switching signal and as an energy source to activate the actuator to execute a translational actuating movement. Advantageously, the actuator according to the invention activates completely autonomously when needed and can be operated in an energy-self-sufficient, emission-free, and low-noise manner. Furthermore, electrical components for the actuator can be completely dispensed with, which significantly simplifies the design and manufacture of the actuator.

[0010] To execute the adjustment movement, the adjustment element must be heated to a temperature above the transformation temperature range of the shape memory alloy. The superheat collector is designed to absorb solar radiation to heat the superheat volume to a corresponding temperature. When the temperature rises to a temperature above the transformation temperature range, the part of the adjustment element accommodated in the superheat collector undergoes a structural transformation from martensite to austenite, which is associated with a length contraction, i.e., a shortening of the adjustment element.

[0011] The shape memory alloy is preferably designed such that the phase transformation from martensite to austenite occurs in a transformation temperature range that lies above the typical maximum ambient temperatures at a site of use. This ensures that the austenite formation of the SMA material of the actuating element, which is responsible for activating the actuator, takes place exclusively in the overheat collector, thus preventing sudden length contraction. A special feature of the actuator according to the invention is that, in the non-activated state of the actuating element, a large portion of the SMA material of the actuating element is located outside the overheat collector.Heating of the part of the actuating element accommodated in the overheating collector by solar radiation (partial activation) consequently leads to this part experiencing a length contraction under the application of a tensile force, thus drawing further SMA material of the actuating element through the collector opening into the overheating volume. With sufficient solar radiation, this process occurs continuously and autonomously until the actuating element is completely contracted in length or activated and is completely accommodated in the overheating collector. The translational movement resulting from the length contraction of the actuating element can be used as an actuating movement of the actuator according to the invention. In addition, the actuating element provides a tensile force, which can be used as an actuator force of the actuator according to the invention.The tensile force in the activated, length-contracted state of the actuator is greater than in the non-activated, length-relaxed state.

[0012] The actuator returns to its length-relaxed shape in the non-activated state upon cooling to a temperature below the transition temperature range automatically by gravity or a return element. This allows for the exploitation of a two-way effect, i.e., the actuator performs a reciprocal translational actuating movement, or a reversible actuating cycle, during the change of shape from the non-activated to the activated state and back.

[0013] According to a further development of the invention, a mass body is attached to the translationally movable second end of the actuating element. The mass of the mass body is dimensioned such that the weight of the mass body is smaller than the tensile force of the actuating element in the activated, length-contracted state and greater than the tensile force of the actuating element in the non-activated, length-relaxed state. The mass body is provided to enable the actuating element to be adjusted back from the activated to the non-activated, length-relaxed state. When the actuator is activated, the actuating element contracts, thereby generating a tensile force large enough to lift the mass body against the force of gravity.After solar radiation ceases or due to a drop in temperature, the actuator returns to its inactive state and undergoes a return to its length-relaxed state due to the force of gravity acting on the mass body. The weight of the mass body is therefore chosen to be greater than the tensile force of the actuator in the inactive state.

[0014] According to a further development of the invention, the actuator comprises a restoring element, wherein a restoring force of the restoring element is greater than a tensile force of the actuating element in the activated, length-contracted state and less than a tensile force of the actuating element in the non-activated, length-relaxed state. The restoring force provided by the restoring element opposes the tensile force applied by the actuating element and ensures that the tensioning element can be returned to the length-relaxed state upon cooling to a temperature below the transition temperature range, in which the tensioning element is preferably arranged predominantly outside the overheat collector.Advantageously, the actuator can be mounted independently of gravity thanks to the return element and therefore also horizontally oriented or vertically upside down, i.e. with the collector opening pointing upwards, i.e. facing the ground.

[0015] The return element is preferably a preload spring, in particular a spiral spring and / or disc spring and / or leg spring and / or sheet metal spring, or a spring assembly with two or more preload springs.

[0016] Advantageously, the actuator according to the invention can be reset without noise and emissions via the mass body or the preload spring as a return element.

[0017] In principle, while maintaining the invention, other alternative embodiments for the return element are also conceivable, such as an electric motor or an actuating cylinder.

[0018] For this gravity-based reset by means of the mass body, the actuator according to the invention is preferably oriented vertically or at an angle to the horizontal so that the weight of the mass body can counteract the tensile force of the actuating element. For this purpose, the collector housing of the overheating collector is oriented so that the collector opening faces downward, i.e., toward the ground.

[0019] According to a further development of the invention, the actuating element is designed as a wire, a wire rope, a wire bundle, or a stranded wire, and is preferably wound spirally or is a spiral spring. Advantageously, this wire-shaped design of the actuating element allows the actuator according to the invention to be designed in a compact form, and the actuating element can be manufactured cost-effectively.

[0020] In the form of a wire wound into a spiral or helical spring, the actuator has a large surface area for heat transfer in a small space, which allows the actuator to be advantageously designed with a reduced cross-section or wire diameter, requiring less thermal radiation than with a thick wire with a large diameter. Furthermore, predetermined spring characteristics can be developed for the actuator.

[0021] Of course, the adjusting element can also be designed as a sheet metal or thin-film element or a differently shaped three-dimensional element while maintaining the inventive idea.

[0022] According to a further development of the invention, the actuator further comprises a linear guide for the actuating element. The linear guide is intended to guide the actuating element in such a way that it executes a defined translational actuating movement with as little friction as possible.

[0023] The linear guide is preferably designed as an elongated guide wire. A first end of the guide wire is arranged at the level of the first end of the actuating element on the collector housing of the overheating collector, and a second end of the guide wire is arranged outside the collector housing. This creates a linear guide for the actuating element that is easy to install and cost-effective to manufacture. The actuating element is preferably wound spirally around the guide wire. The term "guide wire" is to be understood broadly and can, in particular, also include a wire rope, a wire bundle, a stranded wire, or the like.

[0024] According to a further development of the invention, the mass body has an opening through which the guide wire is guided. Advantageously, the mass body forms an element movable along the guide wire, via which the actuating element is guided in a translationally displaceable manner along the guide wire.

[0025] The shape memory alloy of the actuator is preferably a nickel-titanium alloy (NiTi). Depending on the expected ambient or operating temperatures, ternary shape memory alloys such as NiTiCu, NiTiFe, NiTiHf, NiTiZr, NiTiNb, NitTiCr, NiTiV, or higher-alloyed alloys, such as quaternary shape memory alloys, can also be used for the actuator. Such shape memory alloys based on the alloying elements nickel and titanium advantageously exhibit high tensile strength and elongation at break, along with good corrosion resistance and a long service life.

[0026] Of course, while maintaining the inventive idea, alternative alloy compositions for the adjusting element are conceivable.

[0027] One use of the actuator according to the invention provides for the actuator to be used to extend a sun protection element, in particular a sun sail or a sun awning. The actuator is advantageously activated as a result of solar radiation, so that when shading is required by a sun protection element, the actuator can be automatically activated to extend the sun protection element. Furthermore, the resettable actuator allows the sun protection element to be retracted autonomously when not needed, for example, during heavy cloud cover or at night.

[0028] Further advantages, features, and details of the invention can be gathered from the further subclaims and the following description. The features mentioned therein may be essential to the invention individually or in any combination. The drawings serve merely as examples to clarify the invention and are not limiting in nature. They show: Fig. 1 is a schematic side view of a first embodiment of an SMA actuator according to the invention with an SMA element in the non-activated state,

[0029] Fig. 2 is a schematic side view of the SMA actuator according to the invention according to Fig. 1 with the SMA element in the partially activated state,

[0030] Fig. 3 is a schematic side view of the SMA actuator according to the invention according to Fig. 1 with the SMA element in the fully activated state,

[0031] Fig. 4 is a schematic side view of a second embodiment of an SMA actuator according to the invention with an SMA element in the fully activated state,

[0032] Fig. 5 is a schematic side view of the SMA actuator according to the invention according to Fig. 4 with the SMA element in the partially activated state,

[0033] Fig. 6 is a schematic side view of the SMA actuator according to the invention according to Fig. 4 with the SMA element in the non-activated state,

[0034] Fig. 7 is a schematic side view of a third embodiment of an FGL actuator according to the invention with an FGL element in the non-activated state,

[0035] Fig. 8 is a schematic side view of the SMA actuator according to the invention according to Fig. 7 with the SMA element in the partially activated state and

[0036] Fig. 9 is a schematic side view of the SMA actuator according to the invention according to Fig. 7 with the SMA element in the fully activated state.

[0037] Fig. 1 to Fig. 9 show various embodiments of an actuator 1 according to the invention for performing a translational actuating movement. The actuator 1 comprises, as essential functional components, an actuating element 2 made of a shape memory alloy (SMA) and an overheat collector 3 with a collector housing 7, which

[0038] Superheating volume, and a collector opening 8 through which the adjusting element can be passed.

[0039] The adjusting element 2 is elongated and has a first end 9, which is fixed to the collector housing 7 of the overheating collector 3 and is permanently arranged in the overheating volume. A second end 10 of the adjusting element 2, opposite the first end 9, is arranged or mounted for translational movement and can pass through the collector opening 8.

[0040] The overheating collector 3 is designed to absorb solar thermal radiation (solar radiation) in order to heat the overheating volume enclosed by the collector housing 7 and the part of the actuating element 2 accommodated therein to a temperature above a transformation temperature range of the shape memory alloy of the actuating element 2.

[0041] A first embodiment of the actuator 1 according to the invention is shown in Figs. 1 to 3. The actuating element 2 is designed here as a spirally wound or helically wound wire, i.e., as a spiral spring or helical spring. The collector housing 7 has a substantially can-shaped form and is open on one side in the area of ​​the collector opening 8.

[0042] To guide the actuating element 2 along a defined translational movement direction, the actuator 1 provides a guide wire 6 as a guide line around which the actuating element 2 is wound. A movably mounted, spherical mass body 4 is also attached to the movable second end 10 of the actuating element 2, which provides an opening through which the guide wire 5 is guided.

[0043] The actuating element 2 and the guide wire 5 are inclined with respect to their longitudinal extent at an angle of incidence a of approximately 30° to the horizontal, whereby the mass body 4, due to gravity or the force of Earth's attraction, exerts a weight force opposite to the internal tensile force of the actuating element 2. In order to be able to move the actuating element 2 from the activated, length-contracted state to the non-activated, length-relaxed state and back, a mass of the mass body 4 is dimensioned such that the weight force of the mass body 4 is smaller than a tensile force of the actuating element 2 in the activated, length-contracted state and greater than a tensile force of the actuating element 2 in the non-activated, length-relaxed state.

[0044] Fig. 1 shows the actuator 1 with the actuating element 2 in the non-activated, length-relaxed state. The actuating element 2 protrudes largely from the superheat collector 3 and is accommodated in the region of the first end 9 in the superheat volume enclosed by the collector housing 7. The actuating element 2 assumes this state at a temperature below the transformation temperature range of the shape memory alloy. This is typically the case under heavy cloud cover or shading, as well as at night when sufficient solar radiation from the sun is not available.

[0045] In Fig. 2, the actuator 2 is in a partially activated transition state. The superheat collector absorbs sufficient solar radiation, causing the portion of the actuator 2 accommodated in the superheat volume to heat to a temperature above the transition temperature range and to enter the activated state. Consequently, this superheated portion of the actuator 2 has experienced a length contraction under the application of a tensile force, causing the mass body 4 to be slightly displaced upwards along the guide wire 5 toward the superheat collector 3.

[0046] In Fig. 3, the actuating element 2 is in the activated, length-contracted state and is completely absorbed into the superheated volume. The actuator 1 is thus activated. The tensile force of the actuating element 2 is greater than in the non-activated state and greater than the opposing weight force of the mass body 4, so that the mass body 4 has been pulled in front of the collector opening 8.

[0047] The distance by which the movable mass body 4 has been displaced as a result of the change in state of the actuating element 2 from the non-activated state according to Fig. 1 to the activated state according to Fig. 3 defines an actuating movement or a working stroke for the actuator 1. Figs. 4 to 6 show a second embodiment of an actuator 1 according to the invention. The actuator 1 here, as usual, has the can-shaped, one-sidedly open overheat collector 3, the elongated actuating element 5 in the form of a spirally wound wire made of a shape memory alloy, and the spherical mass body 4. The actuator 1 or the actuating element 5 are vertically upright here, i.e., oriented perpendicular to the horizontal. The collector opening 8 of the overheat collector 3 points downwards, i.e., towards the ground, so that the weight of the mass body 4 is directed vertically downwards.The weight of the mass body 4 thus causes a gravity-induced return of the actuating element 2 when, as a result of cooling, the latter transitions from the activated, length-contracted state, shown in Fig. 4, to the non-activated, length-relaxed state, shown in Fig. 6. Since the mass body 4 always keeps the actuating element 2 vertical in this embodiment of the actuator 1, a linear guide and a return element can be dispensed with.

[0048] A third embodiment of the actuator 1 according to the invention is shown in Fig. 7 to Fig. 9. The actuator 1 comprises, as usual, the can-shaped and one-sided open overheat collector 3, the elongated actuating element 2 in the form of a spirally wound wire made of a shape memory alloy, the spherical mass body 4 and the guide wire 5. Furthermore, the actuator 1 here comprises an elongated spirally or helically wound pretensioning spring as a return element 6. The pretensioning spring and the actuating element 2 are each wound around the elongated guide wire 5. The actuator 1 is oriented horizontally here, i.e. the actuating element 2 and the return element 6 as well as the guide wire 5 are each oriented parallel to the horizontal with respect to their longitudinal extent.

[0049] The return element 6 is arranged here on a side opposite the actuating element 2 and is attached to the mass body 4 by a movable end. The return element 6 provides a horizontal return force that directly opposes the tensile force of the actuating element 2. Therefore, gravity-based return is not necessary. The return force of the return element 6 is selected such that it is greater than the tensile force of the actuating element 2 in the non-activated, length-relaxed state and smaller than the tensile force of the actuating element 2 in the activated, length-contracted state.

[0050] The invention is not limited to the embodiments of the actuator 1 illustrated in the figures. In particular, the components of the actuator 1 can be freely selected within wide limits with regard to their dimensions, shape, number, and arrangement relative to one another.

[0051] Because the actuator 1 according to the invention can be activated autonomously as a result of solar radiation, it can be used in particular for tensioning a sun protection element, for example a sun sail or a sun awning or the like.

[0052] Of course, numerous other possible uses for the actuator 1 according to the invention are conceivable.

[0053] Identical components and component functions are marked with the same reference symbols.

[0054] List of reference symbols

[0055] 1 actuator

[0056] 2 control element

[0057] 3 Overheating collector

[0058] 4 mass bodies

[0059] 5 Guide wire

[0060] 6 Reset element

[0061] 7 Collector housing

[0062] 8 Collector opening

[0063] 9 first end

[0064] 10 second end

[0065] 11 first wire end

[0066] 12 second wire end a angle of attack

Claims

Patent claims 1. Actuator (1) for reversibly generating a translational actuating movement comprising an actuating element (2) made of a shape memory alloy, which is configured to perform a length contraction when heated to a temperature above a conversion temperature range, comprising a superheat collector (3) for receiving solar thermal radiation with a collector housing (7) which encloses a superheat volume that can be heated by the solar thermal radiation to a temperature above the conversion temperature range, and with a collector opening (8), wherein a first end (9) of the actuating element (2) is fixed to the collector housing (7) and a second end (10) of the actuating element (2) is arranged to be translationally movable such thatthat the actuating element (2) in an activated length-contracted state at a temperature above the conversion temperature range is completely contained in the superheat volume and in a non-activated length-relaxed state at a temperature below the conversion temperature range has partially emerged from the collector housing (7) through the collector opening (8).

2. Actuator (1) according to claim 1, characterized in that a mass body (4) is attached to the second end (10) of the actuating element (2), the mass of which is dimensioned such that a weight force of the mass body (4) is less than a tensile force of the actuating element (2) in the activated, length-contracted state and is greater than a tensile force of the actuating element (2) in the non-activated, length-relaxed state.

3. Actuator (1) according to claim 1 or 2, characterized in that the actuator (1) further comprises a restoring element (6), wherein a restoring force of the restoring element (6) is less than a tensile force of the actuating element (2) in the activated, length-contracted state and is greater than a tensile force of the actuating element (2) in the non-activated, length-relaxed state. Actuator (1) according to claim 3, characterized in that the return element (6) is a preload spring, in particular a coil spring and / or disc spring and / or torsion spring and / or sheet metal spring, and / or a spring assembly with two or more preload springs. Actuator (1) according to any one of claims 1 to 4, characterized in that the actuating element (2) is designed as a wire and / or wire rope and / or wire bundle and / or strand, and is particularly preferably wound in a spiral shape. Actuator (1) according to any one of claims 1 to 5, characterized in that the actuator (1) further comprises a linear guide for the actuating element (2).Actuator (1) according to claim 6, characterized in that the linear guide is a longitudinally extended guide wire (5), wherein a first wire end (11) of the guide wire (5) is arranged at the level of the first end (9) of the actuating element (2) on the collector housing (7) of the superheating collector (3) and a second wire end (12) of the guide wire (5) is arranged outside the collector housing (7). Actuator (1) according to claim 7, characterized in that the mass body (4) has an opening through which the guide wire (5) is passed. Actuator (1) according to any one of claims 1 to 8, characterized in that the actuating element (2) in the non-activated, length-relaxed state is arranged outside the superheating volume to at least 50% with respect to its longitudinal extent. Actuator (1) according to one of claims 1 to 9, characterized in that the shape memory alloy of the actuating element (2) is a nickel-titanium alloy.Use of an actuator (1) according to one of claims 1 to 10 for stretching a sun protection element, in particular a sun sail or a sun awning.

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