Translatory actuation unit having a dielectric elastomer actuator

Abstract

The invention relates to a translatory actuation unit (1, 100), comprising: - a dielectric elastomer actuator (DEA) (3, 103), which can be brought from a non-activated state to an activated state by application of an electric voltage, with a length change occurring in at least one deflection direction (A) between two connection points; - an actuation element (5, 105) for providing an actuation travel and / or an actuation force in a translatory actuation direction (S); - a linear transmission (4, 104), which connects the DEA (3, 103) to the actuation element (5, 105) with a step-down transmission ratio or a step-up transmission ratio; - a spring device, which is mechanically coupled to the DEA (3, 103) and / or to the linear transmission (4, 104), the spring device (6, 106) having an at least partially negative spring constant characteristic, so that in the activated state a deflection in the deflection direction (A) is supported with a greater force or a smaller force counteracts the deflection than in the non-activated state.

Description

[0001] Translational position sensor with a dielectric elastomer actuator

[0002] Technical area

[0003] The invention relates to position sensors for electromechanical actuation, in particular to position sensors with dielectric elastomer actuators (DEA).

[0004] Technical background

[0005] A dielectric elastomer actuator is constructed with a flat, highly elastic dielectric polymer layer sandwiched between two flexible and conductive electrodes. The polymer layer material can be or contain natural or synthetic rubber, silicone, or acrylic. The electrodes are typically constructed using carbon composites and / or Meta II structures.

[0006] By applying a high electrical voltage to the electrodes, an electric field is created through the dielectric polymer, exerting an electrostatic force (Maxwell force) between the electrodes, compressing the polymer layer. This reduces its thickness and causes expansion in the surface direction through material displacement. This effect can be used for electromechanical actuators to generate a translational travel or actuating force.

[0007] Due to their low weight, DEAs are suitable for use in position sensors for robotics applications, servo drives, valve controls, and similar applications. Furthermore, DEAs can maintain various positions with very low energy loss during static operation. DEAs can also be operated dynamically up to several kHz, for example, to drive pumps or sounders.

[0008] One possible approach for applying a DEA in an electromechanical actuator is to couple the DEA with a linear gearhead to adapt the DEA's force-travel characteristic curve with a transmission or reduction ratio that can be configured by designing the linear gearhead. Such DEA ​​actuators are typically designed for a specific load situation. Using such an electromechanical actuator for applications with varying load situations requires either a design of the actuator for the most demanding application, resulting in it being oversized for less demanding applications, or a separate design of the actuators for each application, resulting in a large number of different actuator types, increasing costs and manufacturing effort in mass production.In addition, the travel ranges of linear gears with reduction ratios are generally too small for many applications.

[0009] The object of the present invention is to provide an improved translational actuator with a DEA that is applicable and adaptable for various applications with different load requirements. Furthermore, an improved translational actuator with a DEA that also has a sufficient travel range when used with a reduction gear is to be provided.

[0010] Disclosure of the invention

[0011] This object is achieved by the translational actuator according to claim 1 and a method for adapting the translational actuator to different load requirements according to the independent claim.

[0012] Further embodiments are specified in the dependent claims.

[0013] According to a first aspect, a translational actuator is provided, comprising: a dielectric elastomer actuator (DEA) that can be brought from a non-activated state to an activated state by applying an electrical voltage and a change in length occurs in at least one deflection direction between two terminals; an actuating element for providing an actuating path and / or an actuating force in a translational actuating direction; a linear gear that connects the DEA to the actuating element with a reduction or a transmission;a spring device which is mechanically coupled to the DEA and / or to the linear gear and / or comprises the linear gear, wherein the spring device has an at least partially negative spring constant characteristic, so that in the activated state of the DEA its deflection in the deflection direction is supported with a greater force or the deflection is counteracted by a smaller force than in the non-activated state;

[0014] In particular, a first connection of the DEA can be fixed in a stationary manner with respect to the position sensor, e.g. on its housing.

[0015] Such a position sensor enables the realization of a high actuating force while at the same time providing a comparatively large actuating range for a DEA.

[0016] Furthermore, the linear gear can be designed bidirectionally and have a first coupling point and a second coupling point, wherein the first coupling point is detachably connectable to a second connection of the DEA and the second coupling point is detachably connectable to the actuating element, and wherein the second coupling point is detachably connectable to a second connection of the DEA and the first coupling point is detachably connectable to the actuating element.

[0017] One idea behind the above translational actuator is to couple the DEA to a bidirectionally usable linear gear. The linear gear can be detachably provided within the actuator. The linear gear can be mechanically connected to both the DEA and the actuator element via a first coupling point and a second coupling point, which are preferably movable along a longitudinal direction with a step-up or step-down ratio and coupled to one another.

[0018] Due to the additional detachability of the coupling points, depending on the installation position, both a step-up and a step-down ratio can be achieved with the same components, especially with the same linear gear. In particular, the extension of the stroke achievable by the DEA due to the negative spring constant characteristic of the spring device makes it possible to achieve a step-down ratio where the travel of the actuator is shorter than that of the DEA, but is still sufficient for downstream applications.

[0019] The releasability can be achieved in a manner known per se by a positive and / or non-positive connection, such as a screw connection, a plug connection, a snap-in connection and the like. In order to sufficiently extend the required adjustment travel of the DEA, particularly in the case of a reduction gear, so that a significant adjustment travel of the actuating element can be provided despite the reduction gear, the DEA is preloaded in the elongation direction, i.e. in the direction of expansion of the DEA, by means of a spring device, wherein the spring device has a negative spring constant characteristic in the working range of the translational actuator. The negative spring constant characteristic defines a travel-dependent spring force which acts on the DEA and, with increasing deflection (activation) of the DEA, increasingly supports the deflection more and counteracts the deflection less than in the undeflected, i.e. non-activated state.The spring device thus represents a negative preload mechanism for the mechanics of the actuator.

[0020] While an increase in the actuator stroke is also easily achieved with a (lossless) gear, the spring device with a negative spring constant characteristic simultaneously achieves an increased yield of mechanical work, or cyclically repeatable mechanical energy, from the DEA. This improves the efficiency and energy yield of the DEA (during static operation). An actuator optimized in this way for efficiency and energy has precisely one actuating force-travel characteristic curve, which can be adapted to the load using a (downstream and, if possible, lossless) gear (while maintaining the optimized efficiency and performance).

[0021] The spring device can be provided with a buckled-beam mechanism that is mechanically coupled to the DEA in such a way that the deflections, both in the deactivated and activated states of the DEA, lie in a range of negative spring constant characteristics, in which a spring constant of the spring device is negative relative to a deflection of the DEA. The buckled-beam mechanism corresponds, for example, to a snap spring arrangement that can assume two bistable states. In the transition region between the bistable states, after the transition of a tipping point, there is a region in which the spring characteristic has a negative spring constant characteristic and thus exhibits a decreasing spring force with increasing deflection.The range of the negative spring constant characteristic is configured such that it encompasses the position of the DEA in the non-activated state and the position in the activated state with maximum deflection of the DEA. This means that the design is such that the working range in which the spring device has a negative spring constant characteristic encompasses the adjustment range of the DEA. The linear gear can be provided with a linkage gear in which at least three rod elements are pivotally connected to one another at coupling points so that all angles between the rod elements change when the actuator moves, with two of the coupling points being mounted so that they can be translationally displaced, in particular in the direction of deflection. The rod elements can be pivotally mounted at the coupling points and at the fastening point so that no moment can be absorbed.As a result, the rod elements form two triangles with the displacement axis of the coupling points, the interior angles of which change when one of the coupling points is moved (which also causes the other coupling point to move).

[0022] Alternatively or additionally, the linear gear can have a first linkage arrangement with first rod elements arranged to form a flat quadrilateral, which are connected to one another at corners of the quadrilateral and are pivotable in the surface direction of the quadrilateral, wherein a second linkage arrangement with two second rod elements is provided, which forms a further flat quadrilateral of different size with two of the first rod elements of the first linkage arrangement, which has corners at which the rod elements are pivotable relative to one another, wherein the rod elements are dimensioned such that three corners of the linkage arrangements lie in a row and form a fastening point and the first and second coupling points.

[0023] The linear drive can thus be designed using two rod assemblies arranged in quadrangles with pivoting corner joints, where the movement of two adjacent rod elements is mechanically coupled to each other. The rod elements have different dimensions. If one corner of the rod assemblies is fixed in place, for example, to a housing of the translational actuator, another corner located in the longitudinal direction can represent a first coupling point and another corner a second coupling point. The first coupling point can be connected to the DEA, and the second coupling point to the actuator, and vice versa.

[0024] Furthermore, the fastening point on a housing of the actuator can be arranged detachably so that a reversed installation of the linear gear is possible.

[0025] It can be provided that one (or more) spring element(s) with a predetermined spring constant (positive spring constant characteristic) is arranged on one or more of the rod elements between two rod elements pivotally coupled to one another via a corner, so that a moment is caused in the direction of a decreasing angle at the coupling points with respect to the deflection direction, wherein the angular range of possible angles at the coupling points for a deflection of the DEA in the non-activated state and in the activated state at maximum control preferably lies above a limit angle above which the negative spring constant characteristic exists. The limit angle is determined by the mechanical dimensions of the rod elements, the spring constant of the one or more spring elements, and the points of application of the one or more spring elements.

[0026] The connection of the linear gear with a spring element with positive spring constant characteristics enables the realization of a transmission and / or reduction between the DEA and the actuating element as well as a spring effect with negative spring constant characteristics to support the stroke of the DEA in a particularly compact and simple manner.

[0027] Tension, compression and / or torsion springs can be provided as spring elements at the corners between the rod elements or at the coupling points with linear or non-linear characteristics, such as leaf springs, spiral springs, as well as active spring elements with adjustable positive spring constant (e.g. shape memory spring, dielectric elastomer, etc.).

[0028] Alternatively or additionally, a (further) spring element with a predetermined spring constant can be held stationary at one end and arranged at another end on one of the rod elements, so that a moment is caused on the rod element in question in the direction of an increasing angle between the direction of the acting spring force and the longitudinal direction of a section of the rod element in question to the corresponding coupling point, wherein the angular range of possible angles between the rod elements and the direction of the spring force for a deflection of the DEA in the non-activated state and in the activated state at maximum control is below a limit angle below which the negative spring constant characteristic exists.

[0029] Furthermore, the ends of the at least one spring element can be detachably attached to a corresponding attachment point of the respective rod element(s), wherein, in particular, several attachment points are arranged on the respective rod elements in order to detachably attach the ends of the spring element at different distances from a pivot point of the respective rod element. The detachable attachment of the spring element can be achieved by a positive and / or non-positive connection. This allows for variable adjustment of the negative spring constant characteristic.

[0030] Brief description of the drawings

[0031] Embodiments are explained in more detail below with reference to the attached drawings. They show:

[0032] Figure 1 is a schematic representation of a translatory actuator;

[0033] Figures 2a and 2b show a comparison of a DEA with a PBS spring device in the activated and non-activated state and a DEA with an NBS spring device in the activated and non-activated state as well as a representation of resulting characteristic curves;

[0034] Figure 3 shows a representation of a buckled-beam mechanism with a tensioned leaf spring and a corresponding spring characteristic curve;

[0035] Figure 4a and 4b Functional representations of linkage drives as examples for

[0036] Linear gears that provide an increase and a reduction ratio depending on the coupling point at which the DEA engages;

[0037] Figure 5 shows an embodiment of the linear gear as a one-piece component;

[0038] Figure 6 is a perspective view of an exemplary embodiment of a translatory actuator

[0039] Figures 7a to 7c show various configurations of the translatory actuator of Fig. 6; and

[0040] Figure 8 shows an arrangement for the realization of the spring device with the negative

[0041] Spring constant characteristic in the linear gear of Figure 5. Description of embodiments

[0042] Figure 1 shows a schematic representation of a translational actuator 1 that is configurable with respect to travel and force. The translational actuator 1 comprises a housing 2.

[0043] A dielectric elastomer actuator (DEA) 3 is provided in the housing 2. It is rigidly attached to the housing 2 by a first connection 31 and arranged on a linear gear 4 by a second connection 32. The first and second connections 31, 32 are arranged relative to one another in a deflection direction A. Alternatively, a floating mounting of the DEA (mounted on both sides with springs) can also be provided.

[0044] The DEA 3 can be formed in a conventional manner with a layer of an elastic dielectric material, such as an elastomer, such as a silicone film, with a thickness of between 20 μm and 200 μm, for example, on the surface of which electrodes are applied, for example by printing a conductive carbon coating that can be electrically contacted via suitable electrodes. The DEA 3 can be constructed in multiple layers to increase the actuating force when an electrical voltage is applied.

[0045] In an activated state, an electrical voltage, e.g., several hundred volts, is applied to the electrodes of the DEA 3. An electrical voltage at the electrodes of the DEA 3 causes an electric field to form between the electrodes through the dielectric material and induces an electrostatic force of attraction between the electrodes, which compresses the elastic dielectric material. Due to the incompressibility of elastic materials, this causes a change in the length of the dielectric material in one or both surface directions. Preferably, the deflection in one surface direction, referred to as deflection direction A, is brought about by limiting the possible expansion in a surface direction running perpendicular to it.

[0046] The linear gear 4 is preferably designed as a bidirectional gear and has a transmission or reduction ratio between a first coupling point K1 and a second coupling point K2 of the linear gear 4 that is not equal to 1. The bidirectional gear thus makes it possible to form a translatory actuator with a large travel and low actuating force or a small travel and high actuating force, depending on which of the coupling points K1, K2 of the linear gear 4 the second end of the DEA 3 is coupled to.

[0047] The respective other coupling point K2, K1 of the linear gear 4 is mechanically coupled or directly connected to an actuating element 5 for providing a translational stroke / actuating path or an actuating force in an actuating direction S. The actuating element 5 is guided for translational movement in the actuating direction S, wherein the deflection direction A of the DEA 3 preferably runs parallel to the actuating direction S of the guide of the actuating element 5.

[0048] A spring device 6, which has a negative spring constant characteristic and is referred to below as an NBS (negative bias spring) spring device 6, is operatively connected to the second connection 32 of the DEA 3. The negative spring constant characteristic defines a travel-dependent spring force that decreases with increasing deflection. The negative spring constant characteristic is used to assist the deflection of the DEA 3. This means that the spring force difference between the spring force acting during deflection in the non-activated state and the spring force acting in the same direction during deflection in the activated state is negative. In other words, the deflection of the DEA 3 is counteracted by a first low spring force in the activated state and by a second higher spring force of the spring device 6 in the non-activated state.Alternatively, the spring device 6 can also be designed and coupled to the DEA 3 in such a way that in the activated state a first higher spring force acts in the direction of the deflection of the DEA 3 and in the non-activated state a second lower spring force acts in the direction of the deflection of the DEA 3.

[0049] The coupling points K1, K2 enable a detachable connection both with the second connection 32 of the DEA 3 and with the actuating element 6, so that the linear gear can be used as a reduction and as a transmission in the actuator 1 and can be coupled with the DEA 3 and the actuating element 6.

[0050] As shown in conjunction with Figures 2a and 2b based on a comparison of the deflections of a DEA with a spring device with positive spring constant characteristics (PBS spring device) and an NBS spring device, which act in the deflection direction of the DEA 3, one can see the considerably longer travel with the same control of the DEA 3 in conjunction with an NBS spring device 6. Figures 2a show DEAs with a PBS spring device in the activated state PBS-active, with a PBS spring device in the non-activated state PBS-inactive, with an NBS spring device in the non-activated state NBS-inactive and with an NBS spring device in the activated state NBS-active. Figure 2b shows a force-travel characteristic curve of the DEA in the activated state DEA-active and non-activated state DEA-inactive as well as the spring characteristic curve KPBS of the PBS spring device and the spring characteristic curve KNBS of the NBS spring device.The intersection points of the curves KPWS, KNWS with the actuating force-travel characteristic curve of the DEA 3 in the activated and non-activated state correspond to the actuating element positions, AXPBS, AXNBS to the resulting strokes of the DEA 3. It can be seen that the achievable actuating travel (stroke) in the case of the NBS spring device is significantly larger than the achievable deflection with a PBS spring device.

[0051] The NBS spring device 6 can, for example, be configured using a clamped (preloaded) leaf spring, such as a snap spring, which is used in a deflection range immediately after the tipping point. In principle, such a spring device can be monostable or bistable and have a non-linear characteristic in which a local maximum and a local minimum are present, between which the actuating force-travel characteristic curve has a negative gradient.

[0052] While an increase in the actuator stroke is also easily achieved using a (lossless) gear, the spring device with a negative spring constant characteristic simultaneously achieves an increased yield of mechanical work or cyclically repeatable mechanical energy from the DEA 3 (quantitatively represented by the areas delimited by the dashed lines between the active / inactive DEA curves in Figure 2b). This improves the efficiency and energy yield of the DEA (during static operation). An actuator optimized in this way for efficiency and energy has precisely one actuating force-travel characteristic curve, which can be adapted to the load using a (downstream and, if possible, lossless) gear (while maintaining the optimized efficiency and performance).

[0053] An example of such a snap spring can be, as shown in Figure 3, a buckled beam spring device in which a leaf spring 31 is fixed to two holding points 32 under compressive preload in a rotationally fixed manner. The spring characteristic curve indicates the course of the spring force as a function of the deflection s. In this arrangement, a spring force initially increases when the leaf spring is deflected transversely to the arrangement direction of the holding points 32, but then, upon exceeding a tipping point (at sK) in an NBS deflection range, exhibits a decreasing spring force with further deflection and can ultimately even become negative. By directly mechanically coupling the buckled beam arrangement to the DEA 3, the DEA 3 can be preloaded in the deflection direction A, so that the buckled beam spring device is in the working range with the negative spring constant characteristic (NBS deflection range).

[0054] In principle, other spring devices with negative spring constant characteristics can also be used with the described actuator.

[0055] The advantage of the negative spring constant characteristic, as shown in conjunction with Figures 2a and 2b, is that a larger travel range can be achieved with the DEA 3. This is particularly useful when using the linear gear 4 in the installation direction as a reduction gear, since the travel range of the actuating element 6 is reduced by the reduction ratio relative to a deflection range of the DEA 3. In this way, a sufficiently large travel range of the actuating element 6 can be achieved even when using the linear gear 4 as a reduction gear.

[0056] The linear gear 4 can be designed in a variety of ways.

[0057] In the present exemplary embodiment, the linear gear 4 can be designed as a linkage gear 7, as is schematically shown in Figures 4a and 4b. The linkage gear 7 has three rod elements 71 of the same or different lengths which are pivotably coupled to one another and are pivotably arranged at a non-displaceable fastening point F and at two coupling points K1, K2 which are preferably guided in translation along an identical displacement axis. The arrangement of the rod elements 71 is such that between the two coupling points K1, K2 or between the fastening point F and one of the coupling points K1, K2, two of the rod elements 71 form a triangle with the displacement axis, the interior angles of which change when the coupling points K1, K2 are displaced.When the coupling points K1, K2 are displaced, the rod elements 71 pivot and are deflected laterally, so that the displacements Axi, Ax2 of the coupling points K1, K2 are linearly dependent on one another. The ratio of the displacements corresponds to a transmission or reduction ratio Axi / Ax2. The ratio of the forces Fi, F2 acting on the coupling points also corresponds analogously to a transmission or reduction ratio F2 / F1.

[0058] Figure 4a shows a linkage mechanism 7 with the attachment point F located between the two ends of one of the rod elements, while the ends of the respective rod element 71 are each connected to one end of another of the rod elements 71. The other ends of the other rod elements 71 correspond to the coupling points K1, K2 and are guided accordingly for translational movement. Thus, the attachment point F is located centrally between the two coupling points K1, K2.

[0059] A further embodiment of a linkage transmission is shown in Figure 4b, wherein a coupling point K2 is arranged between the attachment point F and the corresponding other of the two coupling points K1. The rod element 71, pivotally connected to the attachment point F at one end, is pivotally connected between its two ends to another of the rod elements 71, the other end of which is connected to the second coupling point K2.

[0060] In both linkage drives, a mechanical coupling of the coupling points K1, K2 takes place with a fixedly positioned attachment point, which corresponds to a reduction or a transmission.

[0061] A possible further embodiment of the linear gear, which does not require any translationally guiding bearings, is shown in Figure 5. A square linkage gear 8 can be seen with four first rod elements 81, which are connected to one another as a flat square to form a first rod arrangement 82, so that the ends of the rod elements 81 form corners at which the rod elements 81 can be pivoted relative to one another in a pivoting direction that lies in the surface direction of the square. The corners 85 of the first rod arrangement 82 are provided by flexible connecting elements 86, for example made of a flexible plastic (e.g. thermoplastic polyurethane) or the like, which have a smaller cross-section than the rod elements 81 and which are strip-shaped in order to permit pivoting preferably only in the surface direction of the first rod arrangement 82. Alternatively, corresponding joints can also be provided.

[0062] A first corner of the first linkage arrangement 82 can be provided with a first holding arrangement 83, which forms the first coupling point K1. A second corner 85 opposite thereto, which forms the attachment point F, can be provided with a fastening device 84 for stationary fastening of the quadrilateral linkage mechanism 8, e.g., for attaching it to the housing 2.

[0063] The first rod assembly 82 can be coupled to a second rod assembly 90 having two second rod elements 87 pivotally connected to one another via a third corner 88. These second rod elements 87 are pivotally connected to two first rod elements 81 of the first rod assembly 82, which are connected to the second corner, and are pivotably attached via further flexible connecting elements 89 at a distance from the second corner 85, so that upon adjustment of the first rod assembly 82, the interior angles of the second rod assembly 90 change accordingly. The third corner can be connected to a second holding assembly 89, which represents a second coupling point K2.

[0064] The second rod elements 87 can be shorter than the first rod elements 81, thus forming a linear gear that implements a reduction between the first and second coupling points K1, K2. The first rod elements 81 and the second rod elements 87 can each be provided with a length such that the quadrilateral linkage is symmetrical with respect to the axis passing through the attachment point F and the coupling points K1, K2.

[0065] Fastening point F, first coupling point K1 and second coupling point K2 lie on one axis and in an actuator 1 this axis can run parallel to the deflection direction A of the actuating movement of the DEA 3 and the actuating direction S of the longitudinally guided actuating element 6.

[0066] Figure 6 shows a schematic perspective view of a possible embodiment of a position sensor 101, which essentially corresponds to the mode of operation of the generally described position sensor 1 of Figure 1 and has a buckled beam mechanism of Figure 3 and a linear gear 104 of Figure 5 as a spring device 106.

[0067] The housing 102 and the actuating element 105 guided on the frame of the housing 102 can be seen. Furthermore, the DEA 103 is fastened to the housing 102 by its first connection. A second connection of the DEA 103 is detachably connected, e.g., via a screw connection, plug connection, or another type of positive and / or non-positive detachable connection, to a coupling point K2 of a linear gear 104. Furthermore, the actuating element 105 is detachably connected, here for example via a screw connection, to one of the coupling points K1 of the linear gear 104.

[0068] Figures 7a and 7c show top views of various configurations of the actuator of Figure 6. In the illustrations of Figures 7a and 7c, the linear gear is arranged in different installation positions between the actuator 105 and the DEA 103. Depending on the installation position of the linear gear 104, an increase or decrease ratio can be realized. The fastening device of the linear gear can also be arranged detachably on different sides of the frame of the housing 102 for the various configurations, in particular by means of a screw connection.

[0069] As shown in Figure 7b, the connection point of the actuator 105 and the second connection of the DEA 103 can be connected directly to each other without a linear gear in order to achieve a direct drive of the actuator 105 by the DEA 103.

[0070] In the illustrated embodiment, the NBS spring device 106 is designed as a buckled beam device in which a preloaded leaf spring is clamped in the frame of the housing 102. This has a spring plate in the form of a leaf spring that is firmly clamped under preload between two opposite legs of a housing frame surrounding the actuator. During deflections of the DEA 103 in the non-activated state and in the activated state with maximum control, the spring plate is deformed in such a way that a W is formed, i.e., so that the setting positions of the activated state and the non-activated state of the DEA 103 lie in the range of a negative spring constant characteristic of the spring device 106 with respect to an increasing deflection of the DEA 103.

[0071] Instead of the buckled-beam device, the spring device 106 can also be designed in combination with the linkage mechanism 104, as shown, for example, in connection with Figures 4a, 4b, and 5, in that two adjacent or opposite rod elements 81 of the linkage mechanism 104 are preloaded via a preloaded tension spring or compression spring, such as a coil spring, as a spring element with a positive spring constant characteristic with a spring force in the direction of a decreasing angle between the rod elements 81 or between the axis and one of the rod elements 81. Furthermore, spring elements can be mounted between mutually opposite joints.This leads to a spring characteristic of the entire arrangement which, in a certain working range (travel range), has a varying spring constant dependent on the travel with a negative spring constant with respect to the increasing deflection of the DEA 103 upon its activation.

[0072] Such an arrangement is shown as an example in Figure 8. The tension spring 111, as a spring element with a positive spring constant characteristic, is arranged between the rod elements 81 of the linkage 8, which are adjacent to the first coupling point K1, so that the tension spring 111 exerts a force in the direction of a decreasing angle between the respective rod elements 81. The tension spring is fastened to a respective attachment point 112 between the ends of the corresponding rod elements 81. If the angle between the respective rod elements 81 exceeds a limit angle, which depends on the distance between the attachment points 112 and the spring constant of the tension spring 111, the entire arrangement has a negative spring constant characteristic, i.e. with respect to the coupling points K1, K2, the counterforce decreases with increasing stroke of the DEA 103 (increasing angle enclosed by the triangle consisting of spring element 111 and rod elements 81).

[0073] Alternatively, the spring element with the positive spring constant characteristic can also be connected at one end to a stationary (housing-fixed) mounting point. Another end of the spring element can then engage one of the rod elements 81 in such a way that the angle between the direction of the spring force and the path of the rod element 81 changes when the linear gear is adjusted.

[0074] In principle, there are many possibilities for arranging one or more spring elements with a positive spring constant characteristic within the linkage mechanism, as long as they act in the direction of a decreasing angle between a rod element at each of the coupling points K1, K2 and the translational direction of movement of the respective coupling point K1, K2. The point of application of the spring element(s) can be arranged directly on the rod element connected to the respective coupling point K1, K2, or can act on it indirectly, so that the spring element exerts a force in the direction of a decreasing angle between the rod element at the respective coupling point and the axis of the direction of movement of the respective coupling point.

[0075] Thus, in the above quadrilateral linkage mechanism, alternatively or additionally, a further spring element 113 can be designed as a compression spring parallel to the axis of the coupling points K1, K2, which is arranged between two of the rod elements 81 and also has the effect of reducing the angle between the respective rod element at the coupling points and the axis of translational movement of the coupling points.

[0076] A plurality of attachment points 112 can be provided on the respective rod elements 81, to which the tension spring 111 is selectively attached in order to influence the limit angle and adjust the characteristics of the actuator. The attachment points 112 can be provided, for example, as openings or protruding pins in / on the rod elements 81. By positively attaching the ends of the tension spring 111 to a selected attachment point on the rod elements 81, the negative spring constant characteristic is selected to realize the increased travel range. The further the selected attachment points 112 are spaced from each other, between which the tension spring 111 is inserted, the greater the spring force acting between them, so that the achievable force difference between the positions in an activated and deactivated state of the spring device is increased.

[0077] Alternative or additional spring elements can be arranged to adjust the spring constant characteristics of the spring device.

[0078] The linear drive is illustrated here as a quadrilateral rod assembly. A linear drive constructed in this way can easily be formed as a single piece, with the rod elements being designed with corresponding flexible joints. These can be easily achieved by providing a reduced thickness or by using an elastic material. In this way, the entire linear drive can be designed as a single piece. To implement a spring device with such a linear drive, a spring element, e.g., in the form of a spiral spring or the like, can be arranged between two adjacent rod elements.

Claims

Claims 1. Translational actuator (1, 100), comprising: a dielectric elastomer actuator (DEA) (3, 103) which can be brought from a non-activated state to an activated state by applying an electrical voltage and which causes a change in length in at least one deflection direction (A) between two terminals; an actuating element (5, 105) for providing an actuating displacement and / or an actuating force in a translational actuating direction (S); a linear drive (4, 104) which connects the DEA (3, 103) to the actuating element (5, 105) with a reduction or a transmission;a spring device which is mechanically coupled to the DEA (3, 103) and / or to the linear drive (4, 104), wherein the spring device (6, 106) has at least a partially negative spring constant characteristic, such that in the activated state a deflection in the deflection direction (A) is supported with a greater force or a lesser force opposes the deflection than in the non-activated state.; 2. Actuator according to claim 1, wherein a first connection of the DEA (3, 103) is fixed in position relative to the actuator.

3. Actuator according to claim 1 or 2, wherein the linear drive (4, 104) is bidirectional and has a first coupling point and a second coupling point, wherein the first coupling point is detachably connectable to a second connection of the DEA (3, 103) and the second coupling point is detachably connectable to the actuating element (5, 105).

4. Actuator according to claim 3, wherein the spring device (6, 106) has a buckled-beam mechanism which is mechanically coupled to the DEA (3, 103) such that the deflections are in a region of negative spring constant characteristic both in the non-activated state and in the activated state, where a spring constant of the spring assembly (6, 106) with respect to a deflection of the DEA (3, 103) is negative. Actuator according to one of claims 3 to 4, wherein the linear drive (4, 104) has a linkage drive in which at least three rod elements are pivotably connected to one another at coupling points, such that during an actuating movement of the actuator all angles between the rod elements change, wherein two of the coupling points are slidably mounted.Actuator according to claim 5, wherein the linear drive (4, 104) has a first linkage arrangement (82) with first rod elements arranged to form a flat quadrilateral, which are connected to one another at the corners of the quadrilateral and are pivotable in the plane direction of the quadrilateral, wherein a second linkage arrangement with two second rod elements is provided, which together with two of the first rod elements of the first linkage arrangement form a further flat quadrilateral of different size, which has corners at which the rod elements are pivotable relative to one another, wherein the rod elements are dimensioned such that three corners of the linkage arrangements are in a row and form a mounting point and the first and the second coupling point. Actuator according to claim 6, wherein the mounting point is detachably arranged on a housing of the actuator.Actuator according to one of claims 5 to 7, wherein at least one spring element with a predetermined positive spring constant is arranged on one of the rod elements and / or between two rod elements pivotably coupled to each other such that a moment in the direction of a decreasing angle is effected at the coupling points with respect to the deflection direction, wherein the angular range of possible angles at the coupling points for a deflection of the DEA (3, 103) in the non-activated state and in the activated state at maximum control lies above a limit angle from which the negative spring constant characteristic is present.Actuator according to one of claims 5 to 8, wherein at least one spring element with a predetermined positive spring constant is arranged at one end on one of the rod elements, such that a moment is exerted on the rod element in the direction of an increasing angle between the direction of the acting spring force and the longitudinal direction of a section of the rod element. at the corresponding coupling point, wherein the angular range of possible angles between the rod elements and the direction of the spring force for a deflection of the DEA (3, 103) in the non-activated state and in the activated state at maximum control lies below a limit angle below which the negative spring constant characteristic exists. Actuator according to claim 8 or 9, wherein the at least one spring element is detachably attached to the relevant rod element(s), wherein in particular several attachment points are arranged on the relevant rod elements in order to detachably attach the spring element at different distances from a corner between the relevant rod elements.

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