Actuator with shape memory alloy elements

Abstract

An actuator (1) has two end pieces (3, 4) spaced apart in the direction of an actuator main axis (2), a preload arrangement which applies a preload force pressing the connecting pieces (3, 4) apart in the direction of the actuator main axis (2), and two contraction elements (8) which run along the actuator main axis (2) between the connecting pieces (3, 4), which are formed on the basis of a shape memory alloy (18) and can be controlled to shorten their free lengths (15) between the connecting pieces (3, 4). The contraction elements (8) running between the connecting pieces (3, 4) are arranged axially and / or rotationally symmetrically to one another with respect to the actuator main axis (2) and run at equal angles to a reference plane to which the actuator main axis (2) is a surface normal. Parallel to the reference plane, the connecting pieces (3, 4) have rectangular floor plans (34).The contraction elements (8) are band-shaped, each extend parallel to a main extension plane, and have widths (14) parallel to the reference plane. The two contraction elements (8) are secured to the connecting pieces (3, 4) across their widths (14) on two mutually parallel sides (35) of their outlines (34). The widths (14) of the contraction elements (8) amount to at least 50% of the side lengths (37) of the two mutually parallel sides (35) of the outlines (34) of the connecting pieces (3, 4).

Description

TECHNICAL FIELD OF THE INVENTIONThe invention relates to an actuator having two connecting pieces spaced apart from one another in the direction of an actuator main axis, a prestressing arrangement which applies a prestressing force which presses the connecting pieces apart in the direction of the actuator main axis, and having contraction elements which run along the actuator main axis between the connecting pieces and are designed on the basis of a shape memory alloy and can be actuated to shorten their lengths between the connecting pieces. More specifically, the present invention relates to an actuator having the features of the preamble of independent claim 1.Furthermore, the invention relates to a device for clamping and releasing a bolt, having a clamping sleeve for receiving a portion of the bolt and having such an actuator which is arranged such that the clamping sleeve is relieved when its contraction elements are controlled to shorten their lengths between the connecting pieces.PRIOR ARTAn actuator having the features of the preamble of independent claim 1 is known from DE 10 2021 103 203 B3. The actuator has two end pieces which are elastically supported against one another in the direction of an actuator main axis by a compression spring and a wire made of a shape memory alloy which is tensioned between the end pieces along the actuator main axis and can be controlled to change length. The wire has at least six contiguous length sections, which are tensioned next to one another in each case along the actuator main axis between the end pieces, whereby the arrangement of the end pieces is stabilized with respect to relative tilting. Preferably, the wire has at least 12, more preferably at least 24 and even more preferably at least 36 contiguous length sections, which are each tensioned along the actuator main axis between the end pieces. In this case, the arrangement of the length sections tensioned between the end pieces is preferably rotationally symmetrical with respect to the actuator main axis as many times as length sections tensioned between the end pieces. Specifically, the length sections are tensioned between points of the end pieces which are arranged along a circular arc-shaped circumference of the respective end piece running at a distance around the actuator main axis. In this case, the wire can be guided around between its length section via hooks which are arranged on the peripheries of both end pieces. Angles of the length sections of equal size to a reference surface to which the actuator main axis is a surface normal are preferably 90°, and the length sections tensioned between the end pieces are preferably arranged at distances from the actuator main axis which lie in a range from one to three times their length between the end pieces. The wire is controlled to a thermally induced shortening by applying an electrical voltage between its ends. The compression spring is dimensioned such that it stretches the wire again as soon as the wire cools down below the transition temperature of its shape memory alloy again. The known actuator is provided in particular for the purpose of loading a clamping sleeve into a receptacle in a base body, wherein the force with which the clamping sleeve is loaded into the receptacle is reduced to its shortening by actuating the wire. A bolt tensioned in the clamping sleeve is thus released.DE 10 2019 100 679 A1 discloses a shape memory actuator arrangement which comprises a wire-shaped shape memory element, a first deflection body and a second deflection body. The deflecting bodies are arranged spaced apart from one another. The wire-shaped shape memory element is wound multiple times around the first deflection body and the second deflection body and forms an actuator arrangement between them. At least one wire holder region on the respective deflection body and the sections of the wire-shaped shape memory element contacting the wire holder region are embedded in a casting compound. The potting compound is electrically insulating and thus isolates the individual windings of the wire-shaped shape memory element from one another. Preferably, potting pots are assigned to both deflection bodies, wherein the potting compound mechanically couples the respective deflection body to the respective potting pot for the transmission of actuator forces. In this case, the casting compound completely encloses the respective deflection body. The potting pot comprises a fastening element for outputting the actuator forces. In the wire holder region of the respective deflecting body, groove-shaped wire receptacles are formed. A subsection of the actuator arrangement between the first deflection body and the second deflection body can be embedded in an actuator potting element which is connected to the potting compound in a materially bonded manner. The material selected for the actuator potting element is electrically insulating and has sufficient elasticity so that the actuator function is not significantly influenced. In all embodiments of the known shape memory actuator arrangement, a width of the actuator arrangement embedded in the actuator potting element between the deflection bodies is significantly less than 20% of the distance between the deflection bodies. In other words, the known shape memory actuator arrangement is narrow and elongated.DE 195 297 12 A1 discloses a shape memory actuator for an actuating mechanism, for example on space vehicles, which actuator has a heatable actuator made of a shape memory alloy. The control element consists of at least one thin wire arranged in several turns. The turns of the wire are electrically insulated from one another and can be heated by a current flowing through. Specifically, the turns of the wire are electrically insulated from each other by being spaced apart by spacers. In this case, the turns of the wire are guided around mutually movable elements and are fastened positively to these elements.DE 197 303 83 A1 discloses a method for training elements made of shape memory alloy. To carry out the method, an actuator is provided with the elements made of the shape memory alloy, and the actuator is trained in application-compliant fashion as a substantially autonomous unit provided with the untrained elements. An apparatus for carrying out this known method is an actuator with elements made of shape memory alloy. The shape memory alloy elements are wires. Turns of the wires wrap structure elements in a form-fitting manner. In addition to the structural elements to be actuated, removable auxiliary elements are provided. The auxiliary elements comprise a biasing spring in conjunction with a guide tube, which is arranged between deflection bodies and has a low rigidity and serves for shape retention of the turns of the shape memory alloy wire. On the deflection bodies, helical grooves are provided in such a way that a parallel tension is ensured within the windings made of shape memory alloy. In a schematic illustration of the deflection bodies with the helical grooves of a predetermined pitch, the length ratios of which do not correspond to the further figures and details of DE 197 303 83 A1, the windings made of shape memory alloy are distributed over a width running transversely to their longitudinal extents, which width is approximately 60% as large as the distance between the supporting of the windings on the deflection bodies.OBJECT OF THE INVENTIONThe object of the invention is to show an actuator and a device for clamping and releasing a bolt with such an actuator, which are simpler to produce and can be adapted to the respective application.SOLUTIONThe object of the invention is achieved by an actuator having the features of independent claim 1 and a device for tensioning and releasing a bolt with this actuator according to the invention as claimed in claim 18. The dependent patent claims 2 to 17 relate to preferred embodiments of the actuator according to the invention.DESCRIPTION OF THE INVENTIONIn an actuator according to the invention having two connecting pieces spaced apart from one another in the direction of a main axis, a prestressing arrangement which applies a prestressing force which presses the connecting pieces apart in the direction of the actuator main axis, and having two contraction elements which run along the actuator main axis between the connecting pieces and are designed on the basis of a shape memory alloy and can be controlled to shorten their free lengths between the connecting pieces, the contraction elements which run between the connecting pieces are arranged axially and / or rotationally symmetrical with respect to one another with respect to the actuator main axis. To a reference plane to which the actuator main axis is a surface normal, the contraction elements extend at angles of equal magnitude. Parallel to the reference plane, the connecting pieces have rectangular ground planes. The contraction elements are strip-shaped, each extend parallel to a main extension plane and have widths running parallel to the reference plane. The two contraction elements are fixed across their widths on two mutually parallel sides, respectively, of their horizontal planes on the connecting pieces. The widths of the contraction elements amount to at least 50% of side lengths of the two mutually parallel sides of the ground planes of the connecting pieces.The relatively wide contraction members each extend along a straight side edge or flat side surface of each of the two end pieces, and are then fixed to these side edges or side surfaces of the two end pieces, respectively. Thus, the contraction elements can be mounted not only easily on the connecting pieces but also removed again, in order to exchange, for example, the pretensioning arrangement or at least parts of the pretensioning arrangement or the contraction elements themselves. Such an exchange may be useful in order to adapt the actuator to its respective application. In this case, the distance of the end pieces and thus the height of the actuator can be varied via the lengths of the contraction elements between the connection pieces.Preferably, the widths of the contraction elements are at least 60%, more preferably at least 75% and often at least 90% of the side lengths of the two mutually parallel sides of the ground planes of the connection pieces. In one embodiment, the widths of the contraction elements are approximately exactly as large as their free lengths between the connection pieces. The free lengths of the contraction elements can, however, also be significantly greater than their widths.Radial distances of the contraction elements from the actuator main axis are generally not less than 20%, preferably not less than 30%, and many times, particularly preferably not less than 70%, of their widths. On the other hand, the radial distances of the contraction elements to the main axis are generally not greater than 100%, preferably not greater than 80% and many times, particularly preferably not greater than 60%, of their widths. In a preferred embodiment, the radial distances of the contraction elements to the actuator main axis are approximately half their widths.The two contraction members may be disposed on the side edges or side surfaces of terminal fittings having square plan views. If the sides of the end-planes of the fittings are of different lengths, then the contraction elements are preferably fixed to the sides with the greater side length, i.e. since there is more space where. In the case of the two contraction elements lying opposite one another across the actuator main axis, a prestressing arrangement arranged between the connecting pieces remains accessible over their distance. For example, with a width of the contraction elements of their free length between the connecting pieces, this is possible without the risk of instability of the actuator with respect to a mutual tilting of the end pieces.The angles of equal size at which the contraction elements extend to the reference plane to which the actuator main axis is a surface normal are preferably right angles, i.e. they are preferably 90°.Each contraction element can be divided in the direction of its width into in particular two partial contraction elements, the partial widths of which sum up to the width of the respective contraction element. Such a subdivision of the contraction elements can be advantageous in order to fix the contraction elements to the connecting pieces over their entire widths. For example, cross members for the contraction elements between the partial contraction elements can be supported on a base structure of the respective connecting piece.Each contraction element can have a strip which runs between the connection pieces and is clamped on the connection pieces or a plate which runs between the connection pieces and is clamped on the connection pieces and is made of the shape memory alloy and whose / or its bandwidth is at least 90%, and preferably at least 95%, of the width of the respective contraction element. Such a strip and in particular such a plate made of shape memory alloy has a high dimensional rigidity in the decisive directions. Thus, the two end pieces are mutually guided with high rigidity by the contraction members fixed thereto.Alternatively or in addition to the shape memory alloy ribbon, each contraction element may comprise at least eight length portions of a shape memory alloy wire extending between the fittings and distributed over at least 90%, and preferably at least 95%, of the width of the contraction element. An advantage of using shape memory alloy wire is that such wire is commercially available in various thicknesses, unlike a shape memory alloy ribbon or plate in trained form. The length sections of the wire of each contraction element preferably run in its main extension plane or parallel to its main extension plane. Preferably, each of the contraction members includes at least 16, and more preferably at least 32, of the length portions of the shape memory alloy wire. The number of length segments of each contraction element can also be much larger and can, for example, reach or even exceed one hundred.Of the length sections of each contraction element, a quarter, a third or half can then be contiguous in each case, such that each contraction element has four, three or two non-contiguous wires made of the shape memory alloy, which can then be connected in parallel when energized for resistive heating up to above the transition temperature of the shape memory alloy.The respectively contiguous wires made of the shape memory alloy can be guided around at the ends of the respective ribbon-shaped contraction element via deflection bodies at the ends. These deflection bodies then pass over the width of the respective strip-shaped contraction element; and in a preferred embodiment of the actuator according to the invention, they are each formed at least on their outer circumference from a thermally and electrically insulating material in order to insulate the individual turns of the wire made of the shape memory alloy both thermally and electrically from the connection pieces and in particular electrically from one another.Each contraction element, in particular each contraction element comprising length portions of a wire made of shape memory alloy, may comprise a plastic matrix in which the length portions of the wire and optionally reinforcing fibers are embedded. The reinforcing fibers are preferably not electrically conductive. With the aid of the plastic matrix, in particular if reinforcing fibers are embedded therein, a shape stiffening of the contraction elements is achieved similar to a band made of the shape memory alloy, although the contraction elements contain economically commercially available wire made of the shape memory alloy. The reinforcing fibers can be aligned in particular in mutually crossing directions with diagonal course to the lengths of the contraction elements between the connection pieces.Alternatively or additionally to direct electrical, i.e. resistive heating of strips or wires made of the shape memory alloy, indirect heating can also be realized in the actuator according to the invention in that each contraction element has at least one heating element arranged adjacent to the shape memory alloy. This heating element can also be an electric heating element which can be controlled in response to a temperature increase by applying an electric voltage between its ends.The heating elements separate from the shape memory alloy and tapes, plates or wires formed therefrom have the advantage that the cross section of the tapes, plates or wires can be increased as required for forces to be applied by the contraction elements without having an effect on the direct resistive heating of the tapes, plates or wires. The relative arrangement of the heating elements to the strips, plates or wires made of the shape memory alloy can be fixed in the actuator according to the invention simply by embedding the heating elements and the strips or wires together in the plastic matrix. In this case, thermal insulation effected by the plastic matrix can be used. The thermal insulation delays the dissipation of the thermal energy introduced with the aid of the heating elements and thus accelerates the heating of the shape memory alloy to above its transition temperature.In the actuator according to the invention, the shape memory alloy is preferably one which, when the temperature rises above its transition temperature, reduces the length of the contraction elements between the connecting pieces. In this case, the prestressing force of the prestressing arrangement can be dimensioned or prestressed in such a way that it again stretches the contraction elements as soon as the shape memory alloy cools down below its transition temperature again. The shape memory alloy can, however, also be a two-way shape memory alloy which automatically stretches when its temperature falls below its transition temperature.In a preferred embodiment of the actuator according to the invention, a compression spring of the prestressing arrangement is supported on one of the end pieces via an abutment, the relative position of which is adjustable with respect to the one of the end pieces in the direction of the actuator main axis. By a linear displacement of the abutment relative to the one of the end pieces in the direction of the actuator main axis, a prestress of the compression spring can be varied and, for example, increased to such an extent that the compression spring again stretches the contraction elements as soon as the shape memory alloy cools down below its transition temperature again.The adjustability of the relative position of the abutment with respect to the one of the end pieces can be realized in concrete terms by means of adjusting screws aligned along the actuator main axis. Preferably, three adjusting screws are provided in a rotationally symmetrical arrangement around the actuator main axis. With these three adjusting screws, the abutment can be displaced linearly with respect to the connecting piece without the need for the additional linear guide for the abutment with respect to the connecting piece. If all three adjusting screws are designed identically, it is sufficient to rotate all three adjusting screws by an identical angle in the same direction of rotation. However, by different turning of the adjusting screws, an angular adjustment of the abutment relative to the connecting piece can also be carried out, for example in order to compensate for an end face of the compression spring which does not run exactly normal to the actuator main axis. Furthermore, the adjusting screws can also be loosened to such an extent that the compression spring can be exchanged without the need for further dismantling of the actuator according to the invention if free access to the compression spring is possible between the contraction elements.In a further preferred embodiment of the actuator according to the invention, the prestressing arrangement has clamping wires running along the actuator main axis between two further connecting pieces. The two further connecting pieces are arranged on two cantilever arms, which each extend away from one of the connecting pieces along the actuator main axis and cross in the process along the actuator main axis, so that a sequence of the further connecting pieces along the actuator main axis is interchanged with respect to the connecting pieces rigidly connected to them via the cantilever arms. In this case, the tension wires can be formed from a superelastic shape memory alloy. The fact that the shape memory alloy of the tension wires is superelastic means that the tension wires are in a superelastic state when the actuator is intended to be used and when its contraction elements are actuated to shorten the length that stretches the tension wires. For this purpose, the shape memory alloy of the tension wires is somewhat above their transition temperature, and during the length of the tension wires, the shape memory alloy is transferred from its high temperature phase into its low temperature phase, in which the tension wires are longer, to growing proportions.In the last-described embodiment of the actuator, the increase in the distance of the further connecting pieces in the direction of the actuator main axis resulting from the reduction in the length of the contraction elements can also be tapped and used. Furthermore, means can be provided for controlling the tension wires to shorten their length by increasing the temperature of their shape memory alloy above their transition temperature. In particular, the tension wires can be controlled for a length reduction in order to lengthen the contraction elements previously controlled for a length reduction by temperature increase and subsequently already cooled back to their starting length.In a device according to the invention for clamping and releasing a bolt with a clamping sleeve for receiving a section of the bolt and an actuator according to the invention, the actuator is arranged such that the clamping sleeve is relieved if the contraction elements of the actuator are controlled to shorten their lengths between the connecting pieces and the clamping sleeve is relieved of a force applied by the compression spring in this way. Such a device for tensioning and releasing a bolt is known in principle, i.e. apart from the configuration of the actuator according to the invention, from DE 102021 103 203 B3.The actuator according to the invention can also be used for the direct clamping and release of structural elements, for example by its one connecting piece resting on one side of a structural element or a plurality of structural elements stacked on top of one another, while on the other side of this structural element or of the stack of structural elements, an anchor element resting on the other connecting piece with a tension bolt passing through the structural element or the stack of structural elements, the one connecting piece and the compression spring, as far as the other connecting piece. In the case of shortened contraction elements, the anchor element has a maximum distance from the one of the end pieces, at which the structural element or the stack of structural elements can be arranged between the one of the end pieces and the anchor element. When the shape memory alloy then cools and the contraction elements elongate again, the structural element or the stack of structural elements is tensioned between the one of the end pieces and the anchoring element. This voltage can be canceled in a targeted manner by actuating the contraction elements to shorten their length between the connecting pieces.Advantageous further developments of the invention are evident from the patent claims, the description and the drawings.The advantages of features and combinations of a plurality of features mentioned in the description are merely exemplary and can be applied alternatively or cumulatively without the advantages necessarily having to be achieved by embodiments according to the invention.With regard to the disclosure content-not the scope of protection-of the original application documents and of the patent the following applies: Further features can be taken from the drawings-in particular the geometries shown and the relative dimensions of a plurality of components with respect to one another and their relative arrangement and operative connection. The combination of features of different embodiments of the invention or of features of different patent claims is likewise possible deviating from the selected relations of the patent claims and is hereby excited. This also relates to features which are illustrated in separate drawings or are mentioned in the description thereof. These features can also be combined with features of different patent claims. Features listed in the patent claims can likewise be omitted for further embodiments of the invention, but this does not apply to the independent patent claims of the issued patent.The features mentioned in the patent claims and the description should be understood in terms of their number such that exactly this number or a greater number than the mentioned number is present, without the need for explicit use of the adverb "at least". Thus, if a compression spring is mentioned, for example, this is to be understood as meaning that exactly one compression spring, two compression springs or more compression springs are present. The features mentioned in the patent claims can be supplemented by further features or be the only features that the subject matter of the respective patent claim has.The reference numerals included in the claims do not represent a limitation on the scope of the subject matter protected by the claims. They are intended merely to make the claims more readily understood.BRIEF DESCRIPTION OF THE FIGURESThe invention is explained and described in more detail below with reference to preferred exemplary embodiments shown in the figures. FIG. 1 is a perspective view of an embodiment of the actuator according to the invention. FIG. 2 is a perspective view of another embodiment of the actuator according to the invention. FIG. 3 is a view basically corresponding to FIG. 2 with some turns of a shape memory alloy wire omitted to show an internal structure of a contraction member of the actuator of FIG. 2. FIG. 4 is a perspective view of the actuator of FIGS. 2 and 3 with a fitting of the actuator omitted to show an adjustment device of the actuator. FIG. 5 is a perspective view of the actuator of FIGS. 2 to 4 viewed from a similar direction to FIG. 4 but showing its two end pieces. FIG. 6 is an exploded view of the actuator of FIGS. 2 to 5 in the same direction of view as that of FIGS. 2 and 3. FIG. 7 is a perspective view of another embodiment of the actuator according to the present invention. FIG. 8 is a view basically corresponding to FIG. 7 with some turns of a wire and a shape memory alloy tension wire omitted to show an internal structure of a contraction member and a biasing assembly of the actuator of FIG. 7. FIG. 9 is a view basically corresponding to FIGS. 7 and 8 with all turns of the shape memory alloy wire and the tension wire omitted to show the internal structure of the contraction member and the biasing assembly of the actuator of FIGS. 7 and 8 ; and FIG. 10 is an exploded view of the actuator of FIGS. 7 to 9 looking in the same direction as that of FIGS. 7 to 9.DESCRIPTION OF THE FIGURESThe actuator 1 shown in FIG. 1 has two end pieces 3 and 4 spaced apart from one another in the direction of an actuator main axis 2. The end pieces 3 and 4 are rigid solid plates of square horizontal planes 34 bounded by sides 35 and 36 parallel in pairs, a central opening 5 on the actuator main axis 2 and having three threaded bores 6 in each of their four side faces for receiving fastening screws 7. Two strip-shaped contraction elements 8 extend along and here also parallel to the actuator main axis 2 between the end pieces 3 and 4. For this purpose, as is not shown in FIG. 1, fastening screws 7 engage with their threaded shanks through holding elements 9 and the contraction elements 8 into the threaded bores 6 in the respective side surface and are supported with their screw heads on the holding elements 9. The contraction elements 8 are formed on the basis of a shape memory alloy and, to shorten their lengths, can be controlled between the connection pieces 3 and 4 by heating the shape memory alloy to above its transition temperature. In the opposite direction along the actuator main axis 2, the end pieces 3 and 4 are pressed apart from one another by a compression spring 10 with an engagement protection sleeve of a prestressing device 26. The compression spring 10 is supported on the connecting piece 3 via a support plate 11. The compression spring 10 is supported on the connecting piece 4 via a further support plate 12, wherein it is guided in a guide sleeve 13 fastened to this support plate 12. The compression spring 10 is dimensioned and prestressed between the connecting pieces 3 and 4 in such a way that it again stretches the contraction elements 8 when their shape memory alloy has cooled down below its transition temperature again. Alternatively or additionally, it is a two-way shape memory alloy, so that the contraction elements 8 automatically recover their original length when the transition temperature is undershot. The strip-shaped contraction elements 8 each extend in or parallel to a main extension plane, wherein a width 14 of the contraction elements 8 in a virtual reference plane to which the actuator main axis 2 is a surface normal is here not only just as large as side lengths 37 of the sides 35 of the ground planes 34 of connection pieces 3, 4 but also approximately as large as a free length 15 of the contraction elements between the connection pieces 3 and 4. a dimensional rigidity of the contraction elements 8 results which suppresses not only relative tilting of the end pieces 3 and 4 but also relative displacement of the end pieces 3 and 4 transversely to the actuator main axis 2, at least in the direction of the width 14.The contraction elements 8 can each have a layer structure made of one or more strips or one or more plates made of the shape memory alloy and one or more planar heating elements, which are bonded to one another and / or are embedded together in a plastic matrix. The plastic matrix not only holds the layer structure together, but also thermally isolates it from the outside, so that a heat input through the heating element is used to a large extent for a temperature increase of the strips or plates made of the shape memory alloy in order to exceed their transition temperature. Alternatively or additionally, wires made of the shape memory alloy running along the actuator main axis 2 can also be embedded in such a plastic matrix together with one or more heating elements. Furthermore, the plastic matrix can be reinforced by embedded, preferably non-electrically conductive, reinforcing fibers. These reinforcing fibers may be oriented crosswise diagonally to the width 14 and the free length 15.A clamping element, not shown in FIG. 1, can extend from one of the end pieces 3 and 4 through the adjacent pressure plate 11 or 12 and the compression spring 10 and the opening 5 in the other connection piece 3 or 4 in order to clamp a structural element or a stack of structural elements between the respective other connection piece 3 or 4 and an anchor element fastened to the clamping element and selectively to release them by actuating the contraction elements 8 to shorten their lengths 15 between the connection pieces.This possible application also exists in the actuator 1 shown in the following figures, FIG. 2 shows that the end pieces 3 and 4 of this actuator 1 are each H-shaped within their rectangular horizontal planes 34, deflection bodies 16 being mounted in the free ends of their legs. Wires 17 made of the shape memory alloy 18 of the contraction elements 8 run around the deflection bodies 16, and each of the four wires 17 in total here is wound in a plurality of turns around the respective two deflection bodies 16 on mutually corresponding sides of the end pieces 3 and 4, wherein length sections 19 of the wire 17 made of the shape memory alloy 18 run between the connection pieces 3 and 4 and are distributed in the process over the width 14 of the respective contraction element 8. Each of the four wires 17 according to FIG. 2 correspondingly has a plurality of successive length sections 19. The width 14 of the contraction elements 8 is here likewise approximately as great as their free length 15 between the connecting pieces, i.e. here the free length of the length sections 19 between the deflecting bodies 16.FIG. 3, in which one of the wires 17 is omitted, shows that the deflection bodies 16 each have an insulation body 20 which is guided on a bolt 21 and is provided on its outer periphery with grooves 22. The grooves 22 guide the turns of the respective wire 17 so that its individual length sections 19 run at defined lateral distances from one another. For direct resistive heating of the wire 17, in which the length sections 19 are connected in series, the wire 17 can be used without additional insulation, because the length sections 19 do not come into electrical contact with one another except via their ends and thus do not electrically short off any part of the respective wire 17.FIG. 4 shows, by omitting the connecting piece 3 of the actuator 1 according to FIGS. 3 and 4 and a different angle of view, an abutment for the compression spring 10, which abutment is formed with free ends of three adjusting screws 24 and the relative position of which is adjustable with respect to the connecting piece 3 omitted in FIG. 4 by rotating the three adjusting screws 24 arranged so as to be distributed rotationally symmetrically about the actuator main axis 2. The adjustability allows both a displacement of the abutment in the direction of the actuator main axis 2 and an angular orientation of the abutment with respect to the actuator main axis 2.Specifically, the adjusting screws 24 engage in internal threads in the one of a perforated disk 23, which is supported on the connection piece 3, not shown here, in the direction of the actuator main axis 2.FIG. 5 shows the actuator 1 with the lower connecting piece 3 from a similar viewing direction as in FIG. 4. By rotating the adjusting screws 24, not only can the prestress of the compression spring 10 be varied, but the compression spring 10 can also be relieved to such an extent that it can be replaced without further dismantling of the actuator 1.The exploded drawing according to FIG. 6 shows an annular channel 25 in the lower connecting piece 3, in which the compression spring 10 supported at the free ends of the adjusting screws 24 is guided laterally. Furthermore, FIG. 6 shows that the connecting pieces 3 and 4 have tubular extensions which engage telescopically one inside the compression spring 10 and whose lumens are aligned with the opening 5.In the embodiment of the actuator 1 illustrated in FIGS. 7 to 10, the two contraction elements 8 are each divided into two partial contraction elements 27 which are arranged next to one another in the direction of the width of the respective contraction element 8. Partial widths 14' and 14'' of the partial contraction elements 27 add to the width 14 of the contraction elements 8, and the subdivision of the contraction elements 8 makes it possible to support the bolts 21, on which the insulating bodies 20 are guided, also between the partial contraction elements 27. Also taking into account the cantilevers 32 and 33, the widths 14 of the contraction elements 8 here are greater than 50% of the side lengths 37 of the sides 35 of the ground planes 34 of the connecting pieces 3 and 4. the cantilevers 32 and 33 extend and overlap along the actuator main axis 2, so that further connecting pieces 30 and 31 at the free ends of the cantilevers 32 and 33 have a reverse sequence along the actuator main axis 2 compared to the connecting pieces 3 and 4 rigidly connected to them. Sections of a tension wire 28 made of a superelastic shape memory alloy 29 run between the further connection pieces 30 and 31. The tension wire 28 is wound directly around bolts 21, which are supported in each case not only at their ends but also in their centers on the further connection pieces 30 and 31. The tensioning wire 28 is prestressed to such an extent that it is in a superelastic state and thus applies a prestressing force which is largely independent of the spacing of the connecting pieces 3 and 4 or of the further connections 30 and 31, that is to say is substantially constant. The prestressing arrangement 26 of this embodiment of the actuator 1 applies a comparatively small prestressing force between the connecting pieces 3 and 4 which is distributed too uniformly over the sides 36 of the further connecting pieces 30 and 31.LIST OF REFERENCE CHARACTERS1 Actuator 2 Actuator main axis 3 Connecting piece 4 Connecting piece 5 Opening 6 Threaded bore 7 Fastening screw 8 Contraction element 9 Holding elements 10 Compression spring 11 Supporting plate 12 Supporting plate 13 Guide sleeve 14 Width 14' Partial width 14" Partial width 15 Length 16 Deflection element 17 Wire 18 Shape memory alloy 19 Length section 20 Insulating body 21 Bolt 22 Groove 23 Perforated disk 24 Adjusting screw 25 Annular channel 26 Prestressing arrangement 27 Partial contraction element 28 Clamping wire 29 Superelastic shape memory alloy 30 Further connecting piece 31 Further connecting piece 32 Extension arm 33 Extension arm 34 Horizontal plan 35 Side 36 Side 37 Lateral lengthReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 103 203 B3 [0003, 0028]DE 10 2019 100 679 A1

[0004] DE 195 297 12 A1

[0005] DE 197 303 83 A1

[0006]

Claims

Actuator (1) having - two connecting pieces (3, 4) spaced apart from one another in the direction of an actuator main axis (2), - a prestressing arrangement () which applies a prestressing force which presses the connecting pieces (3, 4) apart in the direction of the actuator main axis (2), and - two contraction elements (8) which run along the actuator main axis (2) between the connecting pieces (3, 4) and are formed on the basis of a shape memory alloy (18) and can be actuated to shorten their free lengths (15) between the connecting pieces (3, 4), - the contraction elements (8) which run between the connecting pieces (3, 4) being arranged axially and / or rotationally symmetrical to one another with respect to the actuator main axis (2) and running at angles of equal magnitude to a reference plane to which the actuator main axis (2) is a surface normal, characterized - in that the connecting pieces (3, 3, 4) are arranged axially and / or rotationally symmetrical to one another with respect to the actuator main axis (2), The contraction elements (8) may have rectangular ground planes (34) parallel to the reference plane, the contraction elements (8) may be strip-shaped, may extend parallel to a main extension plane and may have widths (14) extending parallel to the reference plane, and the two contraction elements (8) may have widths (14) across their widths (14) on two mutually parallel sides (35), the ground planes (34) of which are fixed to the connection pieces (3, 4), the widths (14) of the contraction elements (8) being at least 50% of side lengths (37) of the two mutually parallel sides (35) of the ground planes (34) of the connection pieces (3, 4).Actuator (1) according to Claim 1, characterized in that the widths (14) of the contraction elements (8) are at least 60% or 75% or 90% of the side lengths (37) of the two mutually parallel sides (35) of the ground planes (34) of the connecting pieces (3, 4).Actuator (1) according to Claim 1 or 2, characterized in that radial distances of the contraction elements (8) to the actuator main axis (2) are not more than 100% or 80% or 60% and / or not less than 20% or 30% or 40% of their widths (14).Actuator (1) according to one of the preceding claims, characterized in that the ground planes (34) of the connecting pieces (3, 4) are square.Actuator (1) according to one of the preceding claims, characterized in that the angles of the contraction elements (8) which are of equal size to the reference surface are 90°.Actuator (1) according to one of the preceding claims, characterized in that each contraction element (8) is divided in the direction of its width (14) into partial contraction elements (), the partial widths (14', 14") of which sum up to the width (14) of the respective contraction element (8).Actuator (1) according to one of the preceding claims, characterized in that each contraction element (8) has a strip of the shape memory alloy (18) which runs between the connection pieces (3, 4) and is clamped on the connection pieces (3, 4) and the strip width of which is at least 90% or 95% of the width (14) of the contraction element (8).Actuator (1) according to one of the preceding claims, characterized in that each contraction element (8) has at least 8 or 16 or 32 length portions (19) of a wire (17) made of the shape memory alloy (18), which run between the connection pieces (3, 4) and which are distributed over at least 90% or 95% of the width (14) of the contraction element (8).Actuator (1) according to Claim 8, characterized in that at least 4 or 8 or 16 length sections (19) of the wire (17) made of the shape memory alloy (18) are contiguous.Actuator (1) according to Claim 9, characterized in that the contiguous length sections (19) are guided around the ends of the respective ribbon-shaped contraction element (8) via deflection bodies (16), wherein the deflection bodies (16) pass through over the width (14) of the respective ribbon-shaped contraction element (8) and are formed on their periphery from a thermally and electrically insulating material.Actuator (1) according to one of the preceding claims, characterized in that each contraction element (8) has a plastic matrix, in which reinforcing fibres are optionally embedded.Actuator (1) according to one of the preceding claims, characterized in that each contraction element (8) has a heating element which is arranged adjacent to the shape memory alloy (18) and can be controlled to increase the temperature by applying an electrical voltage between its ends.Actuator (1) according to one of the preceding claims, characterized in that the shape memory alloy (18) reduces the length of the contraction elements (8) between the connecting pieces (3, 4) when the temperature rises.Actuator (1) according to Claim 13, characterized in that the prestressing force is dimensioned such that it extends the contraction elements (8) again as soon as the shape memory alloy (18) cools down below its transition temperature again.Actuator (1) according to one of the preceding claims, characterized in that the prestressing arrangement has a compression spring (10) which is supported on one of the end pieces (3, 4) via an abutment, the relative position of which with respect to the one of the end pieces (3, 4) is adjustable in the direction of the actuator main axis (2), optionally by means of three adjusting screws (24) aligned along the actuator main axis (2).Actuator (1) according to one of the preceding claims, characterized in that the prestressing arrangement has tension wires running along the actuator main axis (2) between two further connecting pieces, wherein the two further connecting pieces are arranged on two cantilevers which each extend away from one of the connecting pieces (3, 4) along the actuator main axis (2) and in the process cross along the actuator main axis (2), and wherein the tension wires () are preferably formed from a superelastic shape memory alloy ().Actuator (1) according to one of the preceding claims, characterized in that a tension element which is resistant to compression and / or tension extends from the one of the end pieces (3, 4) along the actuator main axis (2) in the direction of the actuator main axis through the other of the end pieces (3, 4), wherein an anchor element is fastened or can be fastened to the free end of the tension element on the side of the other of the end pieces (3, 4) which faces away from the other of the end pieces (3, 4).Device for clamping and releasing a bolt, comprising - a clamping sleeve for receiving a portion of the bolt and - an actuator (1) according to one of the preceding claims, which is arranged such that the clamping sleeve is relieved when its contraction elements (8) are controlled to shorten their lengths (14) between the connection pieces (3, 4).

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