ACTUATOR DEVICE BASED ON AN ELECTROACTIVE MATERIAL

Abstract

An actuator device has an ionic electroactive material actuator unit includes a unitary membrane with first and second actuation electrodes on the unitary membrane. A DC drive signal is applied between the actuation electrodes to cause migration of charges from one part of the unitary membrane towards another part of the unitary membrane. In addition, a pair of closely spaced measurement electrodes is provided on the first surface of the unitary membrane. In particular, the measurement electrodes are spaced apart by a spacing which is less than ten times the thickness of the unitary membrane at a location between the measurement electrodes. A local surface-effect impedance change is used as the basis of a signal measurement, for providing feedback relating to the state of actuation of the device.

Claims

1. An actuator device comprising: an ionic electroactive material actuator unit comprising a unitary membrane, with first and second actuation electrodes on the unitary membrane for receiving a DC drive signal to cause migration of charges from one part of the unitary membrane towards another part of the unitary membrane; and a pair of measurement electrodes on a first surface of the unitary membrane for measurement of an impedance of the unitary membrane between the measurement electrodes, the impedance representing an actuation level of the actuator device, wherein the measurement electrodes are spaced apart by a spacing which is less than ten times the thickness of the unitary membrane at a location between the measurement electrodes.

2. The actuator device as claimed in claim 1, wherein the spacing is less than five times, less than two times, or less than one times the thickness of the unitary membrane at a location between the measurement electrodes.

3. The actuator device as claimed in claim 1, wherein the first and second actuation electrodes are on opposite first and second surfaces, respectively, of the unitary membrane.

4. The actuator device as claimed in claim 1, wherein the actuator device further comprises: a DC signal source for applying the DC drive signal between the first and second actuation electrodes; a measurement signal source for applying a measurement signal to the pair of measurement electrodes; and a measurement device for measuring an electrical parameter resulting from the measurement signal.

5. The actuator device as claimed in claim 4, wherein the measurement signal source is coupled to the pair of measurement electrodes, and wherein the DC signal source is coupled to the first and second actuation electrodes.

6. The actuator device as claimed in claim 4, wherein: the measurement electrodes are provided in a channel formed in the first actuation electrode, thereby electrically isolated from the first actuation electrode; or the measurement electrodes are provided in a separating channel formed between first and second physically separate portions of the first actuation electrode, thereby electrically isolated from the first and second physically separate portions; or the measurement electrodes are provided in a separating channel formed between the first and second actuation electrodes.

7. The actuator device as claimed in claim 6, wherein the measurement electrodes comprise first and second separate portions of the first actuation electrode.

8. The actuator device as claimed in claim 7, wherein: the first and second separate portions together form an interlocking comb structure; or the measurement electrodes comprise a first set of electrically connected first portions of the first actuation electrode, and a second set of electrically connected second portions of the first actuation electrode, wherein the first and second sets are interleaved.

9. The actuator device as claimed in claim 7, wherein the measurement signal source is coupled to the pair of measurement electrodes, and wherein the DC signal source is coupled to the first portion of the first actuation electrode and the second actuation electrode.

10. The actuator device as claimed in claim 1, wherein the actuator device comprises a plurality of pairs of measurement electrodes.

11. The actuator device as claimed in claim 1, wherein the actuator device further comprises a controller for controlling the ionic electroactive material actuator unit based on a measured electrical parameter.

12. The actuator device as claimed in claim 11, wherein the controller comprises a processor, a digital to analog converter for providing the DC drive signal to a DC signal source, and an analog to digital converter for providing a measurement electrical parameter signal, and wherein the actuator device further comprises an AC voltage source as a measurement signal source.

13. The actuator device as claimed in claim 1, wherein the ionic electroactive material actuator unit is a current-driven actuator, and wherein the actuator device further comprises a current-limited DC voltage source as a DC signal source.

14. The actuator device as claimed in claim 1, wherein the first actuation electrode is the anode for the DC drive signal and the second actuation electrode is the cathode for the DC drive signal.

15. The actuator device as claimed in claim 1, wherein the ionic electroactive material actuator unit is an ionic polymer metal composite actuator.

16. An actuator device comprising: an ionic electroactive material actuator unit comprising a unitary membrane, with first and second actuation electrodes on the unitary membrane, wherein the first and second actuation electrodes, in response to receiving a DC drive signal, cause migration of charges from one part of the unitary membrane towards another part of the unitary membrane; and a pair of measurement electrodes on a first surface of the unitary membrane to measure an impedance of the unitary membrane between the measurement electrodes, the impedance representing an actuation level of the actuator device.

17. The actuator device as claimed in claim 16, wherein the first and second actuation electrodes are on opposite first and second surfaces, respectively, of the unitary membrane.

18. The actuator device as claimed in claim 16, wherein the first and second actuation electrodes are on same side of the unitary membrane.

19. The actuator device as claimed in claim 16, wherein the measurement electrodes are spaced apart by a spacing which is less than the thickness of the unitary membrane at a location between the measurement electrodes.

20. The actuator device as claimed in claim 19, wherein the spacing between the measurement electrodes lies in a range of 10 μm to 20 μm, and wherein the thickness of the unitary membrane lies in a range of 10 μm to 500 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

[0058] FIG. 1 shows a known electroactive polymer device which is not clamped;

[0059] FIG. 2 shows a known electroactive polymer device which is constrained by a backing layer;

[0060] FIG. 3 shows a current driven ionic electroactive polymer device;

[0061] FIG. 4 shows one possible actuation and measurement system;

[0062] FIG. 5 shows a first example of an electroactive material actuator device in accordance with the invention;

[0063] FIG. 6 shows a second example of an electroactive material actuator device in accordance with the invention;

[0064] FIG. 7 shows electrode signals present in the device of FIG. 6;

[0065] FIG. 8 shows a drive circuit and feedback system for the electroactive material actuator device of FIG. 5;

[0066] FIG. 9 shows a first electrode design for the electroactive material actuator device of FIG. 5;

[0067] FIG. 10 shows a second electrode design for the electroactive material actuator device of FIG. 5;

[0068] FIG. 11 shows a drive circuit and feedback system for the electroactive material actuator device of FIG. 6;

[0069] FIG. 12 shows a first electrode design for the electroactive material actuator device of FIG. 6;

[0070] FIG. 13 shows a second electrode design for the electroactive material actuator device of FIG. 6

[0071] FIG. 14 shows a third electrode design for the electroactive material actuator device of FIG. 6;

[0072] FIG. 15 shows a fourth electrode design for the electroactive material actuator device of FIG. 6; and

[0073] FIG. 16 shows a further design with all electrodes on one side of the membrane.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] The invention will be described with reference to the Figures. It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the device, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the device of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0075] The invention provides an actuator device which has an ionic electroactive material actuator unit comprising a unitary membrane with first and second actuation electrodes. In various embodiments, the first and second actuation electrodes are on opposite first and second surfaces, respectively, while in the embodiment of FIG. 16, the actuation electrodes are one the same side of the unitary membrane. A DC drive signal is applied between the actuation electrodes. In addition, a pair of closely spaced measurement electrodes is provided on the first surface of the unitary membrane; either surface may be the first surface. A local surface-effect impedance change is preferably used as the basis of a signal measurement, for providing feedback relating to the state of actuation of the device.

[0076] FIG. 5 shows a first example of an electroactive material actuator device in accordance with the invention.

[0077] It comprises an ionic electroactive material actuator unit 50 comprising a unitary membrane 52 with first and second actuation electrodes 54, 56, which in this example are on opposite first and second surfaces, respectively, of the unitary membrane 52.

[0078] A DC signal source 58 is used to apply a DC drive signal between the actuation electrodes 54, 56. The actuator unit is a current driven device, and the DC signal source 58 is a current limited voltage source, with controllable voltage thereby to result in different current flowing and hence different actuation levels. The DC signal source can have either polarity, but does not alternate during the driving. The DC signal source could instead be a current source with both a current limiter and a voltage limiter, or even capacitor discharge circuit with current limiter.

[0079] The function of the current limited DC voltage source is to bring the device to a pre-defined voltage state but without exceeding a specific current. The primary reason for this is to avoid damage to the device at excessive currents. Of course, there are several electrical equivalents to achieve the same driving approach.

[0080] By way of example, there may be a peak current limit of 20 mA/cm.sup.2. The desired sustain current depends on the type of ionic EAP.

[0081] A measurement signal source 60 is used to apply a measurement signal. This is preferably an AC signal source for applying an AC voltage. The voltage for the measurement signal is for example below 0.1 V (which is for example less than 10% of the actuation voltage) and with a frequency typically above 1 kHz. The measurement signal is intended to have no, or minimal, influence on the actuation achieved by the DC signal of the DC signal source.

[0082] A current measurement device 62 is provided for measuring an impedance, based on the current resulting from the measurement signal. It has a response time able to measure at the frequency of the measurement signal.

[0083] The measurement signal is applied to a pair of measurement electrodes 64, 66 on the first surface of the unitary membrane. The measurement electrodes 64, 66 are spaced apart by a spacing d which is at most ten times the thickness h of the unitary membrane in the vicinity of the measurement electrodes.

[0084] By this is meant that the thickness is the thickness at the location of the measurement electrodes or at the location of the spacing between the measurement electrodes, since the unitary membrane may not have perfectly uniform thickness over its full area. The spacing is preferably less than 5 times, or two times or even one times the thickness. The spacing is, for example, in the range 10 to 20 μm as this is compatible with processing of relatively large area devices and leaves more area for the actuation electrodes. Thus, “in the vicinity of the measurement electrodes” may mean at a location which is anywhere within the spacing between the measurement electrodes.

[0085] The thickness is for example in the range 10 μm to 500 μm, for example in the range 50 μm to 300 μm.

[0086] Thus, although FIG. 5 shows d less than h as a preferred implementation, advantages are obtained even when d exceeds h. The measurement is still predominantly of the surface effect rather than based on the path which passes twice across the bulk of the device.

[0087] When the distance between the measurement electrodes is decreased, the impedance rate of change will be increased.

[0088] In this design, the current measurement implements an impedance measurement which is in turn a measure of the level of actuation (i.e. bending in the example as shown in FIG. 5).

[0089] The measurement electrodes 64, 66 are on one side of the actuator, and thereby capable of measuring a local impedance change of the actuator close to these electrodes, so measuring an impedance change close to the side of the actuator. The measurement electrodes are for example located on the anode site of the actuator. The area close to these electrodes will be depleted rather quickly from the mobile cations. This will result in a fast impedance change rate. Moreover, since the gap d between the measurement electrodes 64, 66 is small, the change in impedance is relatively large allowing the use of a low AC current and thereby minimizing local heating. A more precise control of the deflection is thereby obtained.

[0090] In the example of FIG. 5, the AC signal source 60 is coupled to the pair of measurement electrodes and the DC signal source 58 is coupled to the first and second actuation electrodes. Thus, the DC driving and AC sensing are separate independent functions and the measurement electrodes are used to form an independent electrical circuit to the circuit used for actuation.

[0091] The measurement electrodes are shown in a gap formed in the actuation electrode 54. As will be described further below, this gap may be a closed channel (i.e. a recess) formed in the first actuation electrode or it may be an open separating channel formed between first and second physically separate portions of the first actuation electrode. In this case, the two electrode portions are electrically connected and have the same applied voltage.

[0092] FIG. 6 shows a second example of an electroactive material actuator device in accordance with the invention.

[0093] It shows the same DC signal source 58 and AC signal source 60 but with a different electrode arrangement.

[0094] In this design, the measurement electrodes are defined by two electrically isolated portions 54a, 54b of the first actuation electrode, for example a split anode. The first actuation electrode itself is used to define the pair of measurement electrodes, by providing a pair of narrowly spaced portions. The spacing d meets the same rules as outlined above.

[0095] The voltage difference between the second actuation electrode 56 (cathode) and the first portion 54a of the first actuation electrode (anode) is determined by the voltage resulting from the DC signal source 58. The voltage difference between the second actuation electrode 56 and the second portion 54b of the first actuation electrode is determined by the voltage resulting from the DC signal source 58 superimposed with the voltage as delivered by the AC signal source 60. Hence, the voltage difference between the two electrode portions across the gap (with width d) is the voltage as delivered by the AC signal source.

[0096] In principle, the level of actuation at the location of the first and second portions 54a, 54b is different. However, when the frequency of the AC signal is high, the ions only vibrate over a very small distance and no net actuation due to the AC signal will occur, equalizing the level of actuation between the portions 54a, 54b. The time averaged voltage of the first and second electrode portions is equal.

[0097] FIG. 7 shows electrode signals present in the device of FIG. 6. Plot 70 is the voltage between the second actuation electrode (cathode) 56 and the first anode portion 54a, plot 72 is the voltage between the second actuation electrode (cathode) 56 and the second anode portion 54b, and plot 74 is the AC voltage between the two electrode portions 54a, 54b. In this example, the voltage of the DC signal source 58 was chosen to be 1.8 V and the peak to peak difference of the AC voltage provided by the AC signal source 60 was chosen to be 0.4 V.

[0098] The circuits described above both operate using a feedback system which is based on a property change of the electroactive material itself, namely the electrical impedance, and no external measuring sensor is required, such as for example a mechanical displacement measuring device. Only an AC source and current meter is sufficient. Since these are connected via electrical wires, the AC and DC signal sources and the current meter can be placed in a peripheral position with respect to the actuator. This enables the use of optimal miniaturized actuators that can be precisely controlled.

[0099] FIG. 8 shows a drive circuit and feedback system for the electroactive material actuator device of FIG. 5. The device is shown as part of a steerable catheter system (although more generally it may be any interventional medical device such as a guidewire), having a catheter 80 and the actuator device 82 formed at the tip of the catheter for providing steering.

[0100] A first pair of wires 84a, 84b connect the actuator device 82 to the DC signal source 58, and a second pair of wires 86a, 86b connect the actuator device 82 to the AC signal source 60.

[0101] A feedback circuit 88 has the AC and DC signal sources connected as shown in FIG. 5.

[0102] The AC voltage and AC current values are fed into a processor 90 via an Analog to Digital converter 92 and in the processor a software program receives these values as function of time and calculates the electrical impedance of the actuator.

[0103] The AC source 60 is, for example, set to a fixed voltage for the impedance measurement function. The voltage may thus already be known to the processor 90 and hence does not need to be reported, or it may be reported as shown to ensure accurate impedance measurement.

[0104] Via a look up table, the software program determines the deflection of the actuator tip and can also predict a final deflection. If the final deflection will be beyond or below the desired deflection, the voltage of the DC signal source 58 may be adapted, by feeding a signal to the DC signal source 58 via a Digital to Analog converter 94, until the desired deflection of the actuator tip has been obtained.

[0105] These calculations are very fast and for a person operating the device, this happens in real time. Moreover, the operator can manually influence the software program if the deflection has to be changed to another level. The latter for instance may arise when a blood vessel bifurcation has been passed and the tip of the device reaches a straight part of the blood vessel. In more sophisticated systems, the adaption to the desired deflection level can be derived from a 3D image of the blood vessel bed through which the device is traversed.

[0106] In this way, a precise and fast control of the deflection is achieved. In this manner, the deflection of the actuator can be controlled to avoid an unintentional piercing of a blood vessel wall by the actuator tip due to bending. For example, in the case of attempting to traverse a chronic total occlusion a timely feedback may be generated to prevent a too large deflection which may pierce the blood vessel wall.

[0107] FIG. 9 shows a first electrode design for the electroactive material actuator device of FIG. 5. It shows the measurement electrodes 64, 66 provided in a separating channel 90 formed between first and second physically separate portions 54a, 54b of the first actuation electrode, thereby electrically isolated from the first and second portions 54a, 54b.

[0108] FIG. 10 shows a second electrode design for the electroactive material actuator device of FIG. 5. It shows the measurement electrodes 64, 66 provided in a channel 100 formed in the first actuation electrode 54 thereby electrically isolated from the first actuation electrode. The channel 100 is closed so just forms an indentation or recess into the main area of the electrode.

[0109] The aspect ratio of the actuator can be adapted to any shape required for a particular application.

[0110] FIG. 11 shows a drive circuit and feedback system for the electroactive material actuator device of FIG. 6. The device is again shown as part of a steerable catheter system, having a catheter 80 and the actuator device 82 formed at the tip of the catheter for providing steering.

[0111] A first pair of wires 84a, 84b connect the device 82 to the DC signal source 58 with one of the wires connecting also to the AC signal source 60, and a second wire 86 provides the second connection of the device 82 to the AC signal source 60.

[0112] The feedback circuit 88 has the AC and DC signal sources connected as shown in FIG. 6. As in FIG. 8, the AC voltage and AC current values are fed into a processor 90 via an Analog to Digital converter 92 and in the processor a software program receives these values as function of time and calculates the electrical impedance of the actuator. This arrangement provides the same functionality and advantages as described above with reference to FIG. 8.

[0113] FIG. 12 shows a first electrode design for the electroactive material actuator device of FIG. 6. The measurement electrodes comprise first and second separate portions 54a, 54b of the first actuation electrode. In this example the portions are rectangles forming a linear gap 120 across which the measurement signal is measured.

[0114] FIG. 13 shows a second electrode design for the electroactive material actuator device of FIG. 6. The measurement electrodes comprise a first set of electrically connected first portions 54a of the first actuation electrode and a second set of electrically connected second portions 54b of the first actuation electrode, wherein the first and second sets are interleaved. This forms a set of parallel linear gaps 120 so that the measurement function is distributed over the actuator area. The measurement gaps thus cover a larger part of the actuator generating a larger sensing signal.

[0115] FIG. 14 shows a third electrode design for the electroactive material actuator device of FIG. 6. The first and second separate portions together form an interlocking comb structure.

[0116] FIG. 15 shows a fourth electrode design for the electroactive material actuator device of FIG. 6. It shows two pairs of measurement electrodes, formed by gaps 120a and 120b, so four portions 54a-54d of the first actuation electrode. This enables independent feedback measurement from multiple locations. Detection of local actuation may be interesting when the actuator is locally blocked and this can be recorded with a multitude of electrode pairs.

[0117] There may similarly be multiple pairs of measurement electrodes for the design of FIG. 5. When multiple measurement electrode pairs are used, multiple current measurement circuits are of course required.

[0118] The aspect ratio of the actuator can again be adapted to every shape required for a particular application.

[0119] The examples above all show actuation electrodes on opposite sides of the unitary membrane. FIG. 16 shows an example with the actuation electrodes 54, 56 and the measurement electrodes 64, 66 on the same, single, side of the unitary membrane.

[0120] FIG. 16A shows a cross sectional view and FIG. 16B shows a plan view. The two actuation electrodes 54, 56 are formed as interdigitated comb electrodes. The pair of measurement electrodes follow a meandering path in the space between the two actuation electrodes.

[0121] This actuator design could switch from a flat surface texture (non-activated) to either a corrugated surface texture (if there is no substrate) or alternatively a wavy shape with alternative bending directions (if there is a rigid substrate), when viewed in the cross section of FIG. 16A.

[0122] The measurement electrodes are able to determine the state of actuation of the actuator by measuring the change of impedance of the region between the actuator electrodes.

[0123] There may also be a single separate measurement electrode so that one of the actuator electrodes functions as one of the pair of measurement electrodes (as is also the case in FIG. 6). The impedance is then measured between the one additional measurement electrode and the electrode where mobile carriers are removed.

[0124] In all designs above, the cathode and anodes may be switched when a deflection in the opposite direction is required. An electrical impedance change can still be measured over the special electrodes, only in this case a fast decrease in impedance is measured.

[0125] It is also possible to provide measurement electrodes on both sides of the unitary membrane. In this case, an increase of electrical impedance may be measured at the anode side and a decrease at the cathode side. The difference between these values may constitute an even faster response when a certain threshold is determined due to noise.

[0126] In fact, the impedance between the measurement electrodes is determined by the impedance of the ionic electroactive material but also by the impedance of the air. In the case that the impedance is dominantly determined by the resistance (i.e. the real part of the impedance), the AC signal source in the electric circuits could be replaced by a DC source.

[0127] However, in general AC sensing signals, for measuring an imaginary impedance component (inductance/capacitance) have a better signal to noise ratio, especially when the AC signal can be isolated via an electrical filter (i.e. lock-in amplifier).

[0128] The choice between the designs of FIGS. 5 and 6 will depend on requirements of particular designs. For instance, FIG. 5 may be preferred when a high precision is required, since the DC and AC electrical circuits can be independent from each other and hence can be optimized. FIG. 6 may be preferred when there is limited space for electrical wires.

[0129] Note that several actuators may be integrated into an interventional medical device over the length of the device. For instance, three actuators may be provided and for each actuator a similar scheme is used as described above, for example based on FIG. 6 to reduce the number of wires. In this case, for actuation the actuators can have one common line and each require one return line to be able to actuate them separately. For the sensing part an additional wire per actuator is required. This constitutes a total of 7 wires.

[0130] The approach of FIG. 5 would also allow one common line for actuation and one common line for AC sensing, constituting a total of 8 wires that is needed to connect the actuators. Alternatively, when a proper addressing system is used, the number of lines may be reduced. This is especially useful if an increasing number of actuators is in demand. With individually controlled actuators the IMD device can make more complicated bends which is useful to traverse tortuous blood vessels.

[0131] In all examples, the electroactive material actuator is based on an ionic (current driven) electroactive polymer material.

[0132] Examples of ionic-driven EAPs are conjugated polymers, carbon nanotube (CNT) polymer composites and Ionic Polymer Metal Composites (IPMC).

[0133] The sub-class conjugated polymers includes, but is not limited to polypyrrole, poly-3,4-ethylenedioxythiophene, poly(p-phenylene sulfide), polyanilines.

[0134] The materials above can be implanted as pure materials or as materials suspended in matrix materials. Matrix materials can comprise polymers.

[0135] To any actuation structure comprising electroactive material (EAM), additional passive layers may be provided for influencing the behavior of the EAM layer in response to an applied drive signal.

[0136] The actuation arrangement or structure of an EAM device can have one or more electrodes for providing the control signal or drive signal to at least a part of the electroactive material. Preferably the arrangement comprises two electrodes. The EAM layer may be sandwiched between two or more electrodes. This sandwiching is needed for an actuator arrangement that comprises an elastomeric dielectric material, as its actuation is among others due to compressive force exerted by the electrodes attracting each other due to a drive signal. The two or more electrodes can also be embedded in the elastomeric dielectric material. Electrodes can be patterned or not.

[0137] It is also possible to provide an electrode layer on one side only for example using interdigitated comb electrodes.

[0138] A substrate can be part of the actuation arrangement. It can be attached to the ensemble of EAP and electrodes between the electrodes or to one of the electrodes on the outside.

[0139] The electrodes may be stretchable so that they follow the deformation of the EAM material layer. This is especially advantageous for EAP materials. Materials suitable for the electrodes are also known, and may be selected from the group consisting of thin metal films, such as gold, copper, or aluminum or organic conductors such as carbon black, carbon nanotubes, graphene, poly-aniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), e.g. poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Metalized polyester films may also be used, such as metalized polyethylene terephthalate (PET), for example using an aluminum coating.

[0140] The materials for the different layers will be selected for example taking account of the elastic moduli (Young's moduli) of the different layers.

[0141] Additional layers to those discussed above may be used to adapt the electrical or mechanical behavior of the device, such as additional polymer layers.

[0142] There are many uses for electroactive material actuators and sensors. In many applications the main function of the product relies on the (local) manipulation of human tissue, or the actuation of tissue contacting interfaces. In such applications EAP actuators provide unique benefits mainly because of the small form factor, the flexibility and the high energy density. Hence EAPs can be easily integrated in soft, 3D shaped and/or miniature products and interfaces. Examples of such applications are:

[0143] Skin cosmetic treatments such as skin actuation devices in the form of EAP based skin patches which apply a constant or cyclic stretch to the skin in order to tension the skin or to reduce wrinkles;

[0144] Respiratory devices with a patient interface mask which has an EAP based active cushion or seal, to provide an alternating normal pressure to the skin which reduces or prevents facial red marks;

[0145] Electric shavers with an adaptive shaving head. The height of the skin contacting surfaces can be adjusted using EAP actuators in order to influence the balance between closeness and irritation;

[0146] Oral cleaning devices such as an air floss with a dynamic nozzle actuator to improve the reach of the spray, especially in the spaces between the teeth. Alternatively, toothbrushes may be provided with activated tufts;

[0147] Consumer electronics devices or touch panels which provide local haptic feedback via an array of EAP transducers which is integrated in or near the user interface;

[0148] Catheters with a steerable tip to enable easy navigation in tortuous blood vessels. The actuator function for example controls the bending radius to implement steering, as explained above.

[0149] Another category of relevant application which benefits from EAP actuators relates to the modification of light. Optical elements such as lenses, reflective surfaces, gratings etc. can be made adaptive by shape or position adaptation using EAP actuators. Here the benefits of EAP actuators are for example the lower power consumption.

[0150] Some examples where asymmetric stiffness control is of interest are outlined below.

[0151] Actuators may be used in valves, including human implantables such as prosthetic heart valves or valves in organ-on-chip applications or microfluidic devices. For many valves, an asymmetric behavior is desired: compliant and large displacement in a direction with the flow, and stiff in a direction against the flow. Sometimes high actuation speed is required to close a valve quickly.

[0152] A flexible display actuator is desired in some applications, for example in smart bracelets. When the flexible display moves to another position or shape for better reading or visual performance, a large displacement is required. When the display is in its rest position, the display actuator must be stiff to hold its position firmly.

[0153] There are also applications in noise and vibration control systems. Using stiffness variation, it is possible to move away from resonance frequencies and hence reduce vibrations. This is useful for example in in surgery robotic tools where precision is important.

[0154] Soft robotics (artificial muscle systems supporting the human body) for example is used to support or hold a body part in a certain position (e.g. against gravity), during which stiffness is required. When the body part moves in the opposite direction resistance is not required and low stiffness is desirable.

[0155] A segmented catheter application may also benefit from variable stiffness. For example, when the catheter tip bends around a corner, it is desired that the segment just behind the tip is temporarily compliant such that the rest of the catheter follows the tip.

[0156] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Measures recited in mutually different dependent claims may be advantageously combined. Any reference signs in the claims should not be construed as limiting the scope.