WO2022156834A1

WO2022156834A1 - Temperature actuator

Info

Publication number: WO2022156834A1
Application number: PCT/CZ2021/000052
Authority: WO
Inventors: Michael VALÁŠEK
Original assignee: České vysoké učení technické v Praze
Priority date: 2021-01-25
Filing date: 2021-11-08
Publication date: 2022-07-28
Also published as: EP4291778A1; CZ309254B6; CZ202126A3

Abstract

The invention concerns a temperature actuator comprising movable elements consisting of shape memory alloys and its subject matter consists of a system of at least two SMA elements (1) arranged in succession to one another, activated by various transformation temperatures. SMA elements (1) do a positive and/or negative shift, they are separated from one another by connecting elements (2) and consist of rod-like elements and/or bending elements and/or spiral (spring) elements.

Description

Temperature Actuator

Technical Field of the Invention

The invention concerns a temperature actuator comprising movable elements with a shape memory.

State-of-the-art

A drive of a temperature actuator using metals, or to be precise Shape Memory Alloys - SMA, is highly advantageous thanks to its size and compactness and its energy demands because it draws energy from the environment heat leading to a temperature change. It has a wide utilization in many various fields. However, a great problem is that an actuator has just two positions between which switches over after achieving a transformation (threshold, transition) temperature. So this is only a two-stage actuator. Continuous actuators working in a transformation temperature interval of a shape memory alloy using electrical heating and feedback control have been created, however, a temperature range of their acting is limited to one transformation temperature environment and they require a controlled source of thermal energy, so they cannot use only the environment heat.

An aim of this invention is an actuator which approximates the prescribed continuous dependency of a deviation and a force in dependence on a temperature by a demanded number of discrete states, in which a switch-over from one state (position) to the other occurs.

Subject Matter of the Invention

A subject matter of a temperature actuator comprising movable elements with a shape memory according to this invention consists in a system of at least two SMA elements arranged in succession to one another, activated by various transformation temperatures with a possible positive and/or negative shift. In some case, SMA elements are divided one from another by connecting elements between end parts of which a SMA element and an additional spring is arranged; the end part of an adjoining connecting element reaches between the additional spring and SMA element. SMA elements can consist of rod-like and/or bending elements and/or spiral (spring) elements. A spiral (spring) element consists of a SMA spring placed in a frame and divided from an additional spring by a separating element, whereas a sliding element passes through the SMA spring and the additional spring, or a spiral (spring) element consists of at least two SMA springs placed in a frame between which an additional spring is arranged, which is divided from SMA springs by separating elements, whereas a sliding element passes through the SMA springs and the additional spring. The SMA elements system is possibly connected to a rotational element through a draw element or consists of a SMA spring placed in a frame and connected to a rotational element that passes through the SMA spring.

In some case the SMA elements system forms a bending actuator arranged in a hollow of a pliable body and can be possibly arranged in/on the pliable body. Particular SMA elements can possibly be begirded by an electrical resistance wire connected to a computer controlled electric voltage source.

The advantage of a temperature actuator according to this invention is the approximation of a demanded course of a deviation and acting force of the actuator depending on the temperature by comprising always at least two SMA elements and each of these SMA elements produces a different shift in one direction or a different rotation around one axis of rotation, possibly at different transformation temperature.

Overview of Figures in Drawings

The attached Figures show diagrams and schematic depictions of the temperature actuator parts according to this invention, where

Fig. 1 depicts diagrams of a course of a deviation and acting force of the actuator depending on a temperature,

Fig. 2 to 5 depict particular embodiments of a part of a slide actuator,

Figs. 6 to 8 depict alternative embodiments of a part of a slide actuator,

Figs. 9 and 10 depict other alternative embodiments of a part of a slide actuator, Fig. 11 depicts diagrams of a course of a deviation and acting force of the alternative embodiment of the actuator depending on the temperature,

Figs. 12 and 13 depict alternative embodiments of a part of a slide actuator,

Figs. 14 and 15 depict embodiments of rotational actuators,

Fig. 16 depicts a bending actuator,

Fig. 17 depicts an embodiment of a spatial actuator,

Fig. 18 depicts the embodiment of the actuator as depicted in Fig. 2, the temperature of which is controlled by an electrical resistance wire,

Fig. 19 depicts another alternative of a slide actuator.

Examples of Embodiments of the Invention

Fig. 1 shows a demanded deviation course at the top left-hand side and the actuator acting forces depending on a temperature at the bottom left-hand side. This is a continuous course. Fig. 1 shows a discrete approximation of this continuous course at the top and bottom right-hand side. This approximation is possible on condition that for particular transformation (threshold, transition) values of ti temperature, when a switch-over from one state (shape) into another (memoried) state (shape) occurs, there are corresponding shape memory metals and/or alloys with a given transformation temperature. There is a lot of shape memory metals with various transformation temperatures h on a large scale of transformation temperatures at least from 50 degrees C to 700 degrees C. For example, NiTi has a change of transformation temperature ti by 10 degrees along with a change by 1% of Ti content. A result is an approximation of the curve depicted in Fig. 1 on the left-hand side depending on Fig. 1 on the right-hand side. There are lots of shape memory alloys with different transformation temperatures f.

It is clear from Fig. 1 that the approximation of the course of the dependence of length and force on temperature requires several intervals, at least three for the minimum value, the mean value and the maximum value.

Fig. 2 shows a schematic depiction of a slide actuator that performs the demanded approximation depicted in Fig. 1. This is performed in a way that several SMA elements 1 consisting of rods of SMA material connected through connecting elements 2 form a system with L length attached to frame 3 and acting by F force. Each of these SMA elements 1 has a different transformation temperature f, this means not all of these SMA elements 1 have the same transformation temperature tj. This system of SMA elements 1 comprises particular parts, one of which is depicted in Fig. 3. This part consists of SMA element 1 consisting of a rod with a length di, a cross-section Si and connected to the adjoining members through connecting elements 2.

The aim is to create an actuator that has a prescribed course of L length in dependence on t temperature (Fig. 1). This can be achieved by an actuator comprising a succession of rods of shape memory alloys (Fig. 3), which are activated (transformed) when reaching transformation temperature ti. One rod has a length di and a cross-section Si and a change of its length by ALi=£i+i - F occurs at transformation temperature f (increasing). We can say that SMA element 1 is activated by transformation temperature f. It applies that

ALi = Ti di (1) where Ti stands for a shape constant, which determines a shape memory imposed in SMA element 1. It is obvious that a change of ALi dimension of SMA element 1 is proportional to its di length. This length change occurs only when the actuator does not act by some force. If it has to act also by Fi+i force, then its deformation has to be greater

ALi + ALpi = Ti di (2) by ALFi deformation caused by acting of force Fi+1. The actuator acts by Fi+i = Fi + Fi force given by a relation

AFi = ki AL_Fi (3) where ki stands for a rigidity of SMA element i, which is proportional to the material Young’s modulus and to Si cross-section of SMA element L At acting of AFi force the resulting deformation of SMA element 1 is only ALi, as required. If the system of SMA elements 1 depicted in Fig. 2 reached transformation temperature f, then a change of the inner structure of SMA element z occurs the way that its shape grows by Ti and its rigidity increases by ki. This causes a shift of z element by ALi influenced by acting of an increment of AFi force.

However, the whole issue is more complicated as acting of AFi force increment causes a deformation of other SMA elements 1 in the actuator, thus a deformation of z element has to be

where n stands for a number of SMA elements 1 in the actuator.

However, the entire procedure will require iterations.

An alternative solution of SMA element 1 is depicted in Fig. 4. This is a bending element. SMA element 1 consists of a V-shaped rod with a length d„ a crosssection Si connected to the adjoining members through connecting elements 2. Bending SMA element 1 number z is shape-modified so that it is elongated by Li when reaching transformation temperature h. This is achieved the way that the beam forming SMA element 1_ is of V shape that is gaped more or less during the transformation. A deformation of SMA element 1 after reaching transformation temperature f is plotted with a dashed line in Fig. 4. SMA elements 1 can also be of shapes different than V.

Fig. 5 shows a different solution of a slide actuator than that depicted in Fig. 2; this is achieved by using bending SMA elements 1 depicted in Fig. 4. Here the particular SMA elements 1 consist of bending SMA elements 1 depicted in Fig. 4 connected through connecting elements 2.

Fig. 6 shows a solution of a slide actuator with additional spring 5 for a prestress and a safe return of SMA element 1 into an original shape after a decrease below the transformation temperature. SMA element 1 is with additional spring 5 prestressed between end parts of connecting element 2 in Fig. 6. On the contrary, a similar connecting element 2 depicted in Fig. 7 performs a sliding motion of SMA element 1 and its return into the original shape by activation when exceeding the transformation temperature. By interchanging a succession of SMA element 1_ and additional spring 5 a motion of SMA element 1 can be changed into a motion of connecting element 2 into an opposite direction, as evident in Fig. 7.

Fig. 8 shows an entire slide actuator, similar to the actuators depicted in Fig. 2 and Fig. 5, assembled using parts depicted in Fig. 6 and Fig. 7. Connecting elements 2 reach by their end parts into adjoining connecting element 2, so aside from a prestress they also perform a motion transfer between the parts depicted in Fig. 6 and Fig. 7.

Fig. 9 shows a more space-saving solution of SMA element 1 consisting of a rod depicted in Fig. 3. For this purpose in Fig. 9 spiral wound SMA spring 4 is used, which is in a body of frame 3 defined in the appropriate state before the SMA transformation by additional spring 5, also spiral wound, defining clearances before (Fig. 9 at the top) and after the SMA transformation (Fig. 9 at the bottom). Spiral wound springs can be helical cylindrical with a regular helix or with a general spiral. A transformation of the SMA element represented by a spiral wound spring 4 causes ALj move of sliding element 6. Sliding element 6 is placed slidingly in frame 3 and a separating element 14 is firmly fixed to it; separating element 14 is placed between spiral wound SMA spring 4 and additional spiral wound spring 5. Spiral wound SMA spring 4 and also additional spiral wound spring 5 only freely lean on frame 3 and separating element 14. Sliding element 6 moves thanks to their elongation or shortening. The advantage of this solution consists in that spiral wound SMA spring 4 (with a length corresponding to L length in Fig. 2) after being wound around sliding element 6 is shorter than before winding owing to the length of sliding element 6. Thus the needed length of the SMA element is shorter. Spiral wound SMA spring 4 can be replaced by a comparable element, for instance a spiral element, or a spiral conical spring.

However, the solution in Fig. 9 is for one SMA element 1. A substitute for the solution depicted in Fig. 2 with more SMA elements, which are transformed at different transformation temperatures h as depicted in Fig. 1 , using a spiral wound spring is shown in Fig. 10. Spiral wound SMA spring 4 consists of a succession of SMA elements 1 connected through connecting elements 2. At the increasing temperature sliding element 6 is gradually drawn out, while the environment temperature reaches respective transformation temperatures h as depicted in Fig. 1. Particular SMA elements 1 can have a different Li length and different Si crosssection, as plotted in the central part of spiral wound SMA spring 4. A solution with a spiral wound spring as depicted in Fig. 9 can be used also for a negative shift of the actuator at the increasing temperature. Fig. 11 shows a required course of a deviation (and also a course of an acting force that may increase or decrease) depending on a temperature as in Fig. 1. However, this dependence is not monotonous. In Fig. 1 the dependence is only increasing. But in Fig. 11 the dependence is also decreasing in one part. It can decrease both continuously and more times during the whole course. Fig. 11 on the right-hand side describes an approximation of the course shown in Fig. 11 on the left-hand side.

At transformation temperature ti a negative shift has to occur. A solution of a negative shift using SMA element is shown in Fig. 12 using a spiral wound spring. Spiral wound SMA spring 4 is defined in a body of frame 3 in the appropriate state before SMA transformation by additional spiral wound spring 5 defining clearances before (Fig. 12 at the top) and after the SMA transformation (Fig. 12 at the bottom). Spiral wound SMA spring 4 is placed in the body of frame 3 so that its extension leads to an insertion of sliding element 6, thus to a negative shift. In Fig. 12 spiral wound SMA spring 4 is placed in the body of frame 3 on the opposite side than depicted in Fig. 9.

The solution shown in Fig. 12 is again only for one SMA element for one transformation temperature f. Its enhancement to more SMA elements can be performed analogically to the solution in Fig. 10 with more SMA elements 1 in spiral wound SMA spring 4.

A solution of the actuator for more positive shifts and more negative shifts in the dependence of the actuator shift on the temperature is shown in Fig. 13. It is carried out in a way that all SMA elements leading to a positive shift at the transformation temperature are gathered into a succession of SMA elements j_ in left spiral wound SMA spring 4 and all SMA elements 1 leading to a negative shift at the transformation temperature are gathered into a succession of SMA elements 1 in right spiral wound SMA spring 4. Both of spiral wound SMA springs 4 are separated by additional spiral wound spring 5. Spiral wound SMA spring 4 and additional spiral wound spring 5 are separated by separating elements 14. One of them is firmly fixed to sliding element 6 and the other is moveable towards it. Spiral wound SMA spring 4 and additional spiral wound spring 5 only freely lean on frame 3 and separating elements 14.

The actuators described above are slide actuators. However, rotational actuators can be created as well. A rotational SMA actuator is shown in Fig. 14. Rotor 7 placed in frame 3 is rotated using a momentum acting through a pulling element (a belt, a toothed belt, a chain, a rope) 10 by slide SMA actuator depicted in Fig. 2. Pulling element 10 is prestressed by additional spring 5. The slide SMA actuator depicted in Fig. 5, Fig. 8, Fig. 10 or Fig. 13 can be used instead of the slide SMA actuator depicted in Fig. 2.

Another arrangement of rotational SMA actuator is shown in Fig. 15, where spiral wound SMA spring 4 is a torsional spring that rotates rotor 7 in a way that it is firmly fixed to frame 3 and to separating element 14, which is fixed to rotor 7. Elongation or shortening of SMA elements 1 at the transformation rotates rotor 7.

More complicated SMA actuators can also be created. Fig. 16 shows a bending SMA actuator. It consists of pliable body 8 with a hollow in which SMA elements 1 connected through connecting elements 2 are placed. During their transformation their memory deformation bends pliable body 8 into a required shape dependent on the temperature course. Such a temperature controlled shape of pliable body 8 can be spatial and highly complicated.

Fig. 17 shows still a more general case of a SMA actuator. SMA elements 1 are placed on or inside pliable body 9; SMA elements 1 are attached to pliable body 9 through connecting elements 2. During their transformation their memory deformation deforms pliable body 9 into a required shape dependent on the temperature course. A deformed shape of pliable body 9 is plotted with a dashed line in Fig. 17 on the right-hand side. Such a temperature controlled shape of pliable body 9 can be spatial and highly complicated. SMA elements 1 together form various angles (they are coaxial or parallel or concurrent or nonparallel and nonintersecting, they are of various orientation) and they are indirectly interconnected through pliable body 9 or directly connected through connecting elements 2. Thus SMA elements 1 can form systems of SMA elements 1 as depicted in Fig. 2 or on/inside pliable body 9 there can be placed a slide SMA actuator depicted in Fig. 5, Fig. 8„ Fig. 10 or Fig. 13 or a rotational SMA actuator depicted in Fig. 14 or Fig. 15 or a bending SMA actuator depicted in Fig. 16.

The temperature can be both a real temperature of SMA actuators external environment and a temperature controlled artificially, e.g. by electrical heating. Fig. 18 shows an example of a slide SMA actuator depicted in Fig. 2, the temperature of which is artificially controlled by electrical resistance wire 11 passing around SMA elements 1 from voltage source 12 controlled by computer 13. The artificially controlled temperature can be at all SMA elements 1 or only a part of them.

A controlled flow of hot or cold liquids or gases, also controlled by computer 13, can be used instead of electrical heating.

A time behavior of temperature propagation in the external environment can also be considered instead of a homogenous heating of the whole external environment of the SMA actuator. A succession of SMA elements 1 corresponding to particular transformation temperatures ti then determines a time behavior of a deformation of the SMA actuator and subsequently even of pliable body 9.

Fig. 19 shows that SMA elements 1 depicted in Fig. 2 can be connected together directly without connecting elements 2.

SMA elements 1 can be of various shapes, not only a rod or a V-shaped beam. SMA element 1 only have to be memory-modified so that at achieving transformation temperature f it can be deformed as needed, e.g. elongated, shortened, bent etc. So at achieving transformation temperature f SMA elements 1 can be elongated or shortened in accordance with the memory modification.

Additional springs 5 can be replaced by SMA elements 1 with a movement opposite to original SMA elements L

All variants described above can be combined one with another.

The artificially controlled temperature can be computer controlled.

The advantage of the above described solutions of the temperature actuator is that it approximates the required course of a deviation and acting force depending on the temperature within a large scale of temperatures even without a thermal energy controlled source and for varied and complicated types of actuator motions.

Vztahove znacky

• 1 - SMA prvek

• 2 - spojovaci prvek

• 3 - ram

• 4 - SMA pruzina

• 5 - doplnkova pruzina

• 6 - posuvny prvek

• 7 - rotor (rotacni prvek)

• 8 - poddajny nosnik (ohybovy prvek)

• 9 - teleso memci tvar

• 10 - f emen (ozubeny f emen, fetez, lano)

• 11 - elektricky odporovy drat

• 12 - zdroj elektrickeho napeti

• 13 - pocitac

• 14 - oddelovaci prvek

Claims

Patent Claims

1 . A temperature actuator comprising movable elements consisting of shape memory alloys, characterized in that it consists of a system of at least two SMA elements (1) arranged in succession to one another, with positive and/or negative shift and separated one from another by connecting elements (2), activated by at least three different transformation temperatures.

2. A temperature actuator according to Claim 1, characterized in that SMA elements (1) consist of rod-like and/or bending elements and/or spiral (spring) elements.

3 . A temperature actuator according to the Claims mentioned above, characterized in that SMA element (1) and additional spring (5) are arranged between end parts of connecting element (2).

4. A temperature actuator according to the Claims mentioned above, characterized in that an end part of adjoining connecting element (2) reaches between SMA element (1) and additional spring (5).

5. A temperature actuator according to the Claims mentioned above, characterized in that a spiral element forms SMA spring (4) placed in frame (3) and separated from additional spring (5) by separating element (14), whereas sliding element (6) passes through SMA spring (4) and additional spring (5).

6. A temperature actuator according to the Claims mentioned above, characterized in that a spiral element consists of at least two SMA springs (4) placed in frame (3); between SMA springs (4) additional spring (5) is arranged and separated from SMA springs (4) by separating elements (14), whereas sliding element (6) passes through SMA spring (4) and additional spring (5).

7. A temperature actuator according to the Claims mentioned above, characterized in that a system of SMA elements (1) is connected to rotational element (7) through pulling element (10) or forms SMA spring (4) placed in frame

(3) and connected to rotational element (7), which passes through SMA spring

(4).

8. A temperature actuator according to the Claims mentioned above, characterized in that a system of SMA elements (1) forms a bending actuator arranged in a hollow of pliable body (8).

9. A temperature actuator according to the Claims mentioned above, characterized in that a system of SMA elements (1) is arranged in pliable body (9).

10. A temperature actuator according to the Claims mentioned above, characterized in that particular SMA elements (1) are begirded by electrical resistance wire (11) connected to electrical voltage source (12) controlled by computer (13).