阅读说明：本技术 基于电活性材料的致动器设备 (Electroactive material based actuator device ) 是由 E·G·M·佩尔塞斯 M·T·约翰逊 D·A·范登恩德 A·R·希尔格斯 于 2020-01-17 设计创作，主要内容包括：一种致动器设备具有离子电活性材料致动器单元(50)。所述离子电活性材料致动器单元包括整体膜(52),其中,第一致动电极(54)和第二致动电极(56)在所述整体膜(52)上。在所述致动电极(54、56)之间施加DC驱动信号以引起从所述整体膜(52)的一个部分朝向所述整体膜(52)的另一部分的电荷迁移。另外,在所述整体膜(52)的第一表面上提供紧密间隔的测量电极对(64、66),其间距小于在测量电极(64、66)之间的位置处的所述整体膜(52)的厚度(h)的10倍。使用局部表面效应阻抗变化作为信号测量的基础,以用于提供与所述设备的致动状态有关的反馈。(An actuator device has an ion electroactive material actuator unit (50). The ion electroactive material actuator unit comprises a monolithic membrane (52), wherein a first actuation electrode (54) and a second actuation electrode (56) are on the monolithic membrane (52). Applying a DC drive signal between the actuation electrodes (54, 56) to cause charge migration from one portion of the bulk film (52) toward another portion of the bulk film (52). In addition, a pair of closely spaced measurement electrodes (64, 66) is provided on the first surface of the monolithic film (52), with a spacing that is less than 10 times the thickness (h) of the monolithic film (52) at a location between the measurement electrodes (64, 66). Using the local surface effect impedance change as a basis for signal measurement for providing feedback on the actuation state of the device.)

1. An actuator apparatus comprising:

an ionic electroactive material actuator cell (50) comprising a monolithic membrane (52), wherein a first actuation electrode (54) and a second actuation electrode (56) are on the monolithic membrane for receiving a DC drive signal to cause charge migration from one portion of the monolithic membrane (52) towards another portion of the monolithic membrane (52); and

a pair of measurement electrodes (64, 66; 54a, 54b) on a first surface of the monolithic film for measuring an impedance of the monolithic film between the measurement electrodes, the impedance being indicative of an actuation level of the actuator device, wherein the measurement electrodes are spaced apart at a spacing (d) that is less than 10 times a thickness (h) of the monolithic film (52) at locations between the measurement electrodes (64, 66; 54a, 54 b).

2. Actuator according to claim 1, wherein the spacing (d) is less than 5 times the thickness (h) of the monolithic film (52) at a location between the measurement electrodes (64, 66; 54a, 54b), preferably less than 2 times the thickness, preferably less than 1 time the thickness.

3. The actuator of claim 1 or 2, wherein the first actuation electrode (54) and the second actuation electrode (56) are on opposing first and second surfaces, respectively, of the monolithic membrane (52).

4. An actuator device as claimed in any one of claims 1 to 3, wherein the actuator device comprises:

a DC signal source (58) for applying the DC drive signal between the actuation electrodes (54, 56);

a measuring signal source (60) for applying a measuring signal to the measuring electrode pair (64, 66; 54a, 54 b); and

a measuring device (62) for measuring an electrical parameter derived from the measurement signal.

5. The actuator device of claim 4, wherein the measurement signal source (60) is coupled to the pair of measurement electrodes (64, 66; 54a, 54b) and the DC signal source (58) is coupled to the first actuation electrode (54) and the second actuation electrode (56).

6. The actuator device of claim 4, wherein:

the measurement electrode (64, 66) is provided in a channel (100) formed in the first actuation electrode (54), thereby being electrically isolated from the first actuation electrode; or

The measurement electrode (64, 66) is provided in a separate channel (90) formed between physically separate first and second portions of the first actuation electrode (54), thereby being electrically isolated from the first and second portions; or

The measurement electrodes (64, 66) are provided in separate channels (90) formed between the first actuation electrode (54) and the second actuation electrode (56).

7. The actuator device of claim 6, wherein the measurement electrode comprises separate first (54a) and second (54b) portions of the first actuation electrode (54).

8. The actuator device of claim 7, wherein:

the separated first and second portions (54a, 54b) together form an interlocking comb structure; or

The measurement electrodes include a first set of electrically connected first portions of the first actuation electrodes (54) and a second set of electrically connected second portions of the first actuation electrodes (54), wherein the first and second sets are interleaved.

9. The actuator device of claim 7 or 8, wherein the measurement signal source (60) is coupled to the pair of measurement electrodes (54a, 54b) and the DC signal source (58) is coupled to the first portion (54a) of the first actuation electrode (54) and to the second actuation electrode (56).

10. An actuator device as claimed in any of claims 1 to 9, wherein the actuator device comprises a plurality of pairs of measuring electrodes.

11. The actuator device of any one of claims 1 to 10, wherein the actuator device further comprises a controller (88) for controlling the actuator unit based on the measured electrical parameter.

12. Actuator device according to claim 11, wherein the controller comprises a processor (90), a digital-to-analog converter (94) for providing the DC drive signal to the DC signal source, and an analog-to-digital converter (92) for providing the measured electrical parameter signal, and the device further comprises an AC voltage source as the measured signal source (60).

13. The actuator device of any of claims 1 to 12, wherein the electroactive material actuator unit (50) is a current driven actuator, and the device further comprises a current limited DC voltage source as a DC signal source.

14. The actuator device of any of claims 1 to 13, wherein the first actuation electrode (54) is an anode for a DC drive signal and the second actuation electrode (56) is a cathode for a DC drive signal.

15. The device of any one of claims 1 to 14, wherein the electroactive material actuator unit (50) is an ionic polymer metal composite actuator.

Technical Field

The present invention relates to actuator devices utilizing electroactive materials (e.g., electroactive polymers).

Background

KARLThe article "Electrical model for a self-sensing polymeric-metallic composite activating devices with patterned surface electrodes; electrochemical model for a self-sensing ionic polymer-metal composite activated devices with patterned surface electrodes "(smart materials and structures, IOP publishing ltd., bristol, uk, volume 20, No. 12, 2011, 11/22/p 124001) discloses a concept to create a self-sensing ionic polymer-metal composite (TPMC) actuation device with patterned surface electrodes, where the actuator and sensor elements are separated by a grounded shielding electrode. The sensor strip has a U-form surrounding the actuator electrode. The resistance of the sensor strip is related to its bending curvature due to device actuation. The resistance between the terminals at the opposite ends of the sensor strip is measured. The shield electrodes are connected to a common ground of the circuit to eliminate cross talk between the actuator and the sensor.

US 2003067245 discloses an electroactive polymer sensor configured such that a portion of the electroactive polymer is deflected in response to a change in a parameter being sensed. The electrical energy state of the polymer is related to the deflection state. Changes in electrical energy or changes in electrical impedance of the active area due to deflection may then be detected by sensing electronics in electrical communication with the active area electrodes. Such changes may include changes in the capacitance of the polymer, changes in the resistance of the polymer, and/or changes in the resistance of the electrodes, or combinations thereof. An electronic circuit in electrical communication with the electrode detects the change in the electrical property. If, for example, a change in the capacitance or resistance of the transducer is measured, electrical energy is applied to electrodes comprised in the transducer and a change in an electrical parameter is observed.

US 2017365770 discloses an electromechanical actuator comprising a support and a deformable element comprising a portion anchored to at least one anchoring zone of the support and a moving portion, the deformable element comprising: an electroactive layer; a reference electrode disposed on a first side of the electroactive layer; an actuation electrode disposed on a second side of the electroactive layer, the second side opposite the first side. The deformable element comprises a capacitive device for measuring deformation of the deformable element, said device being formed at least in part by a capacitive stack comprising: a measurement electrode on the second side of the electroactive layer, a measurement portion of the reference electrode located facing the measurement electrode, and a portion of the electroactive layer interposed between the measurement electrodes.

JP 2006129541 discloses a polymer actuator device having an internal field detection function for detecting a displacement state of an actuator itself. The electrolytic displacement portions composed of the conductive polymer layer and the counter control electrode are opposed to each other through the electrolyte portion composed of the polymer solid electrolyte layer, and the internal field detection electrode is formed in contact with the electrolytic displacement portions, so that the displacement state produced by the electrolytic displacement portions can be measured as a change in conductivity. With this arrangement, the displacement state of the entire apparatus can be monitored.

Electroactive polymers (EAPs) are a new class of materials within the field of electrically responsive materials. EAP's can be used as sensors or actuators, or can be easily manufactured in various shapes, allowing for easy integration into a wide variety of systems.

Materials have been developed with properties (e.g., actuation stress and strain) that have improved significantly over the past decade. The technical risk has dropped to a level acceptable for product development, making EAP's increasingly interesting commercially and technically. Advantages of EAP include low power consumption, low profile, flexibility, noiseless operation, accuracy, high resolution possibilities, fast response time, and cyclic actuation.

The enhanced properties and special advantages of EAP materials make them suitable for new applications. Based on the electrical actuation, the EAP device can be used in any application where a small amount of movement of a component or feature is desired. Similarly, the technique can be used to sense small movements.

The use of EAPs enables functions that were previously impossible to achieve or offers great advantages in conventional sensor/actuator solutions due to the relatively large combination of deformation and force in a small volume or thin profile, as compared to conventional actuators. EAP also provides noiseless operation, accurate electronic control, fast response, and a wide range of possible actuation frequencies (e.g., 0-20 kHz).

Devices using electroactive polymers can be subdivided into field-driven and ion-driven types of materials.

Examples of field-driven EAPs are dielectric elastomers, electrostrictive polymers (e.g., PVDF-based relaxed polymers or polyurethanes), and Liquid Crystal Elastomers (LCEs).

Examples of ion-driven EAPs are conjugated polymers, Carbon Nanotube (CNT) polymer composites, and Ionic Polymer Metal Composites (IPMC).

Field-driven EAPs are actuated by electric fields through direct electromechanical coupling, while the actuation mechanism of ionic EAPs involves diffusion of ions. Both classes have multiple family members, each with its own advantages and disadvantages.

Fig. 1 and 2 show two possible modes of operation of an EAP device. The device comprises an electroactive polymer layer 14 sandwiched between electrodes 10, 12 on opposite sides of the electroactive polymer layer 14.

Figure 1 shows the device unclamped. The voltage is used to expand the electroactive polymer layer in all directions as shown.

Fig. 2 shows a device designed such that the expansion occurs in one direction only. The device is supported by a carrier layer 16. The voltage is used to bend or flex the electroactive polymer layer.

The nature of this movement results from the interaction between the expanded active layer and the passive carrier layer when actuated. To obtain an asymmetric bend about the axis as shown, molecular orientation (film stretching) may be applied, forcing movement in one direction.

The expansion in one direction may be caused by an asymmetry in the electroactive polymer or may be caused by an asymmetry in the properties of the carrier layer or may be caused by a combination of both.

The electrodes in fig. 1 and 2 create an electric field for a field-driven device.

Fig. 3 shows an example of a current-driven ion apparatus. The actuation mechanism involves the diffusion of ions. Fig. 3 shows the structure of an Ionic Polymer Metal Composite (IPMC). There are fixed anions 30, mobile cations 32 and water molecules 34, the water molecules 34 attaching to the cations to form hydrated cations. These movements are in response to applied actuation signals.

EAP actuators are typically formed as bending actuators. They may be clamped at a first edge from which the actuator protrudes. The protruding portion then bends in response to actuation, and the actuation member is, for example, a distal tip. The dual clamping arrangement is clamped at opposite edges and it flexes in response to actuation. The actuating portion is now for example in the middle of the structure.

EAP can also be used as sensors using piezoelectric or pressure induced ion diffusion based readout. This sensing is based on the fact that the contact pressure causes a voltage output.

There is a desire to improve the versatility (particularly the mode of operation) of responsive material based actuators, for example to precisely control the level of deformation.

When using ionic electroactive polymer actuators in the human body, ionic electroactive polymer actuators have the distinct advantage that they can be operated with low voltages. Especially when such actuators are used in miniaturized devices, i.e. Interventional Medical Devices (IMDs), e.g. catheters and guidewires, the measurement and control system should be very small. There is typically no room to locate the external feedback system.

The invention particularly relates to an ion electroactive polymer actuator. There is a particular need for an ion electroactive polymer actuator in order to achieve more accurate actuation control.

It is known that when such an actuator is activated, the impedance of the ionic electroactive polymer changes, and this can be probed by an electrical signal without compromising or changing the actuation level. The impedance is a measure for the deflection level. This common sensing method is known but is accompanied by disadvantages. The feedback may be based on an ionic electroactive polymer sandwiched between two electrodes, a DC low voltage source and an AC low voltage source in line with an ammeter.

Fig. 4 shows an example of a possible circuit, wherein the top image shows the non-actuated state and the bottom image shows the actuated state.

The actuator is operated by an AC source 40 and a DC source 42 in parallel and connected to the electrodes of an actuator 44. Ammeter 46 measures the current flowing between AC source 40 and DC source 42.

In the top image, the DC source 42 is off and no DC voltage is applied. The AC source 40 applies a voltage in conjunction with a sufficiently high frequency, in which case the ion electroactive polymer actuator 44 shows no observable deflection. Since the cations are distributed over a batch of electroactive polymers, the electrical impedance is relatively low and the ammeter measures the AC current. From the AC voltage and current, the electrical impedance of the electroactive polymer can be determined.

In the bottom image, the DC source 42 is turned on and a DC voltage is applied to the actuator, which deflects in response to the DC voltage. In parallel, the AC source 40 applies a voltage in conjunction with a sufficiently high frequency, in which case the ionic electroactive polymer actuator 44 will also not show the additional deflection observable by means of the AC source. The batch of electroactive polymer is deprived of mobile cations and the electrical impedance is relatively high because the cations have migrated to the cathode of the actuator. The ammeter measures only low AC current.

The problem with this basic approach is that the electrical signal needs to be made very small to avoid heating of the device. Since the impedance variations are also small, it is difficult to accurately measure the sensing signals, and these small signals are prone to noise (especially at large distances) and to interference by relatively large DC signals (which can complicate the measurement results).

Disclosure of Invention

Accordingly, there is a need for improved feedback and control systems for ion electroactive polymer actuators.

The object of the present invention is to at least partly meet the aforementioned needs. This object is at least partly achieved by the device according to independent claim 1. The dependent claims provide advantageous embodiments.

Based on an example according to an aspect of the present invention, there is provided an actuator apparatus including:

an ion electroactive material actuator unit comprising a monolithic membrane, wherein a first actuation electrode and a second actuation electrode are on the monolithic membrane for receiving a DC drive signal to cause charge migration from one portion of the monolithic membrane towards another portion of the monolithic membrane; and

a pair of measurement electrodes on a first surface of the monolithic film for measuring an impedance of the monolithic film between the measurement electrodes, the impedance representing an actuation level of the actuator device, wherein the measurement electrodes are spaced apart at a spacing (d) that is less than 10 times a thickness (h) of the monolithic film in a vicinity of the measurement electrodes.

The device enables sensing of the actuation level of the device by measuring impedance based on closely spaced measurement electrode pairs on the same side of the monolithic membrane. Actuation of the device causes charge migration from one side of the bulk film towards the other, so impedance measurements (which may be based on measurements of current at known voltages, or vice versa) are most sensitive at the surface of the bulk film. Actuation causes mobile cations from the anode to be depleted, and these mobile cations are collected at the cathode. The impedance changes relatively greatly so that a low measurement current or voltage is required to obtain a meaningful measurement voltage or current at or through the impedance. This minimizes undesirable heating effects. The measurement of impedance mainly involves the measurement of surface effects rather than volume effects.

The concept of "monolithic film" indicates that the electroactive polymer actuator material does not have a conductive polymer layer separate from the polymer solid electrolyte layer disclosed in JP 2006129541. Because the present invention employs such an integral membrane, the actuation electrodes may be on opposite sides of the membrane, or if desired, on the same side of the membrane, as described below with respect to FIG. 16, some of which are not possible in the two-layer structure of JP 2006129541.

The spacing is preferably less than 5 times the thickness (h) of the monolithic film in the vicinity of the measuring electrode, preferably less than 2 times the thickness, preferably less than 1 time the thickness.

The first and second actuation electrodes may be on opposing first and second surfaces of the monolithic film, respectively. However, they may also be on one side, for example in the form of interdigitated electrodes.

The actuator apparatus preferably further comprises:

a DC signal source for applying the DC drive signal between the actuation electrodes;

a measurement signal source for applying a measurement signal to the pair of measurement electrodes; and

a measuring device for measuring an electrical parameter derived from the measurement signal.

The apparatus thus comprises a suitably designed integral actuator membrane and a signal source and measuring means for actuating the integral membrane and providing position sensing feedback.

The measurement electrode is provided in a channel formed in the first actuation electrode, thereby being electrically isolated from the first actuation electrode. In this case, the first side of the monolithic membrane has at least one of the actuation electrodes and a pair of measurement electrodes formed in the isolated channel region. The measurement electrodes are closely spaced and therefore do not require large channels in the actuation electrode, thus minimally impeding the actuation function.

The measurement electrode may alternatively be provided in a separate channel formed between physically separate first and second portions of the first actuation electrode, thereby being electrically isolated from the first and second portions. In this way, the first actuation electrode is formed by physically separate but electrically connected parts, wherein the measurement electrode is in the spacing between these actuation electrode parts.

If the actuation electrodes are on the same side of the overall film, the measurement electrodes may be provided in separate channels formed between the first actuation electrode and the second actuation electrode.

In these embodiments, the measurement signal source is coupled to the pair of measurement electrodes, and the DC signal source is coupled to the first actuation electrode and the second actuation electrode. Thus, DC drive and sensing are separate independent functions.

In a different set of examples, the measurement electrode includes separate first and second portions of the first actuation electrode. In this way, the first actuation electrode itself is used as a measurement electrode pair by providing a pair of narrowly spaced portions.

In one example, the separated first and second portions together form an interlocking comb structure. The gap then defines a serpentine track. In another example, the measurement electrodes include a first set of electrically connected first portions of the first actuation electrodes and a second set of electrically connected second portions of the first actuation electrodes, wherein the first and second sets are interleaved. The first and second portions may comprise straight lines, in which case the measurement gap is formed as a set of lines.

In these examples, the measurement signal source is coupled to the measurement electrode pair, and the DC signal source is coupled to the first portion of the first actuation electrode and the second actuation electrode. In this way, a DC drive signal is provided between one of the actuation electrode portions and the opposite actuation electrode, while a DC drive signal and a superimposed measurement signal are provided between the other of the actuation electrode portions and the opposite actuation electrode. The voltage across the gap is the measurement signal.

There may be a plurality of measurement electrode pairs, for example for measuring actuation responses at different locations.

The device preferably further comprises a controller for controlling the actuator unit based on the measured electrical parameter. Thus, the measurements serve as a feedback control mechanism to allow the device to be actuated to a desired actuation level with increased accuracy.

The controller may comprise a processor, a digital to analogue converter for providing a DC drive signal to the DC signal source and an analogue to digital converter for providing an electrical parameter measurement signal.

The measurement signal source may comprise an AC voltage source. The measured electrical parameter may be an AC current resulting from applying an AC voltage to a local impedance of the bulk film in the vicinity of the gap. Alternatively, if the current is applied by a measurement signal source, the measured electrical parameter may be a voltage. The electroactive material actuator unit is a current driven actuator and for this purpose the DC signal source may comprise a current limited DC voltage source controllable to vary the flowing current.

In a preferred example, the first actuation electrode is an anode for a DC signal source and the second electrode is a cathode for the DC signal source. Thus, when the device is actuated, the impedance change involves charge transfer between the cathode and the anode. This provides a strong and fast response impedance change in response to actuation of the device.

The electroactive material actuator unit may be an ionic polymer metal composite actuator.

Drawings

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

figure 1 shows a known electroactive polymer device which is not clamped;

fig. 2 shows a known electroactive polymer device constrained by a backing layer;

FIG. 3 shows a current-driven ionic electroactive polymer apparatus;

FIG. 4 shows one possible actuation and measurement system;

figure 5 shows a first example of an electroactive material actuator apparatus according to the invention;

figure 6 shows a second example of an electroactive material actuator apparatus according to the invention;

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

FIG. 8 illustrates a drive circuit and feedback system for the electroactive material actuator apparatus of FIG. 5;

figure 9 shows a first electrode design for the electroactive material actuator apparatus of figure 5;

figure 10 shows a second electrode design for the electroactive material actuator apparatus of figure 5;

figure 11 shows a drive circuit and feedback system for the electroactive material actuator apparatus of figure 6;

figure 12 shows a first electrode design for the electroactive material actuator apparatus of figure 6;

FIG. 13 shows a second electrode design for the electroactive material actuator apparatus of FIG. 6

Figure 14 shows a third electrode design for the electroactive material actuator apparatus of figure 6;

figure 15 shows a fourth electrode design for the electroactive material actuator apparatus of figure 6; and is

Fig. 16 shows an additional design with all electrodes on one side of the membrane.

Detailed Description

The present invention will now be described with reference to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, 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 apparatus of the present invention will become better understood with regard to 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.

The present invention provides an actuator device having an ion electroactive material actuator unit comprising a monolithic membrane having a first actuation electrode and a second actuation electrode. In various embodiments, the first and second actuation electrodes are on opposing first and second surfaces, respectively, whereas in the embodiment of FIG. 16, the actuation electrodes are on the same side of the monolithic membrane. A DC drive signal is applied between the actuation electrodes. Additionally, a closely spaced pair of measurement electrodes is provided on the first surface of the monolithic membrane; either surface may be the first surface. The local surface effect impedance change is preferably used as a basis for signal measurement for providing feedback on the actuation state of the device.

Fig. 5 shows a first example of an electroactive material actuator device according to the invention.

The electroactive material actuator device comprises an ionic electroactive material actuator unit 50, the ionic electroactive material actuator unit 50 comprising a monolithic membrane 52, the monolithic membrane 52 having a first actuation electrode 54 and a second actuation electrode 56, in this example the first actuation electrode 54 and the second actuation electrode 56 being on opposite first and second surfaces, respectively, in the monolithic membrane 52.

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, the voltage of which is controllable, resulting in different flowing currents and thus different actuation levels. The DC signal source can have either polarity, but will not alternate during driving. The DC signal source can alternatively be a current source with both a current limiter and a voltage limiter, or can even be a capacitor discharge circuit with a current limiter.

The function of the current limited DC voltage source is to bring the device into a predefined voltage state, but not to exceed a certain current. The main reason for this is to avoid damaging the equipment under excessive current. Of course, there are several electrical equivalents that can implement the same driving method.

For example, there may be 20mA/cm²The peak current limit of (2). The desired sustain current depends on the type of ionic EAP.

The 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 used for the measurement signal is for example below 0.1V (which is for example less than 10% of the actuation voltage) and its frequency is typically above 1 kHz. The measurement signal is intended to have no or minimal effect on the actuation effected by the DC signal of the DC signal source.

A current measuring device 62 is provided for measuring the impedance based on the current derived from the measurement signal. It has a response time that can be measured at the frequency of the measurement signal.

A measurement signal is applied to a pair of measurement electrodes 64, 66 on a first surface of the bulk film. The measuring electrodes 64, 66 are spaced apart at a distance d which is at most 10 times the thickness h of the entire film in the vicinity of the measuring electrodes.

This means that the thickness is the thickness at the location of the measuring electrodes or at the location of the spacing between the measuring electrodes, since the entire film may not have a completely uniform thickness over its entire area. The spacing is preferably less than 5 or 2 or even 1 times the thickness. The pitch is for example in the range of 10 μm to 20 μm, since this is compatible with the handling of relatively large areas of the device and leaves more areas to the actuation electrodes. Thus, "in the vicinity of the measuring electrodes" may mean at a position located anywhere within the spacing between the measuring electrodes.

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

Thus, although fig. 5 shows d less than h as a preferred embodiment, advantages can be obtained even if d exceeds h. The measurement is still mainly surface effects, not based on a path that passes twice in the volume of the device.

As the distance between the measurement electrodes decreases, the rate of change of impedance will increase.

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

The measuring electrodes 64, 66 are on one side of the actuator and are thus able to measure local impedance changes of the actuator close to these electrodes and thus close to the actuator. The measuring electrode is located, for example, on the anode region of the actuator. The regions close to these electrodes will be depleted of mobile cations rather quickly. This will cause a fast rate of change of impedance. Furthermore, because the gap d between the measurement electrodes 64, 66 is small, the change in impedance is relatively large, allowing the use of low AC currents and minimizing local heating. Thereby a more precise control of the deflection is obtained.

In the example of fig. 5, an AC signal source 60 is coupled to the pair of measurement electrodes, and a DC signal source 58 is coupled to the first actuation electrode and the second actuation electrode. Thus, DC drive and AC sensing are separate independent functions, and the measurement electrodes are used to form an independent circuit for the circuit for actuation.

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

Fig. 6 shows a second example of an electroactive material actuator device according to the invention.

It shows the same DC signal source 58 and AC signal source 60 but with different electrode arrangements.

In this design, the measurement electrode is defined by two electrically isolated portions 54a, 54b of the first actuation electrode (e.g., a split anode). The first actuation electrode itself serves to define the pair of measurement electrodes by providing a pair of narrowly spaced portions. The spacing d follows the same rules as described above.

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 derived 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 a voltage derived from a DC signal source 58 superimposed with a voltage delivered by an AC signal source 60. Thus, the voltage difference between the two electrode portions across the gap (having width d) is the voltage delivered by the AC signal source.

In principle, the level of actuation at the location of the first portion 54a and the second portion 54b is different. However, when the frequency of the AC signal is high, the ions vibrate only over a very small distance and no net actuation due to the AC signal occurs, equalizing the actuation level between the portions 54a, 54 b. The time-averaged voltages of the first electrode portion and the second electrode portion are equal.

Fig. 7 shows the 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, 54 b. In this example, the voltage of the DC signal source 58 is selected to be 1.8V, and the peak-to-peak difference of the AC voltage provided by the AC signal source 60 is selected to be 0.4V.

Both of the above-described circuits operate using a feedback system based on changes in the properties of the electroactive material itself (i.e., electrical impedance) and do not require external measurement sensors, such as, for example, mechanical displacement measurement equipment. Only an AC source and current meter will suffice. Since these devices are connected via wires, the AC signal source and the DC signal source and the current meter can be placed in peripheral positions with respect to the actuator. This enables the use of an optimally miniaturized actuator that can be precisely controlled.

Fig. 8 shows a drive circuit and feedback system for the electroactive material actuator apparatus of fig. 5. The device is shown as part of a steerable catheter system (but more generally it may be any interventional medical device, e.g. a guide wire) having a catheter 80 and an actuator device 82 formed at the catheter tip for providing steering.

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.

The feedback circuit 88 has an AC signal source and a DC signal source connected as shown in fig. 5.

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

The AC source 60 is set to a fixed voltage for an impedance measurement function, for example. Thus, the processor 90 may already know the voltage and therefore need not report the voltage, or may report the voltage as shown to ensure accurate impedance measurements.

Via a look-up table, the software program determines the deflection of the actuator tip and can also predict the final deflection. If the final deflection will exceed or fall below the desired deflection, the voltage of the DC signal source 58 can be adjusted by feeding a signal to the DC signal source 58 via the digital-to-analog converter 94 until the desired deflection of the actuator tip has been obtained.

These calculations are very fast and occur in real time to the person operating the device. Furthermore, if the deflection has to be changed to another level, the operator can manually influence the software program. This may occur, for example, when a bifurcation has been passed through a vessel and the tip of the device reaches a straight section of the vessel. In more complex systems, adjustments to the desired deflection level can be derived from 3D images of the vascular bed traversing the device.

In this way, accurate and fast control of the deflection is achieved. In this way, the deflection of the actuator can be controlled to avoid situations where the actuator tip inadvertently pierces the vessel wall due to bending. For example, in the case of an attempt to traverse a chronic total occlusion, feedback may be generated in time to prevent excessive deflection that may puncture the vessel wall.

Fig. 9 shows a first electrode design for the electroactive material actuator apparatus of fig. 5. It shows the measurement electrodes 64, 66, the measurement electrodes 64, 66 being provided in separate channels 90 formed between the physically separate first and second portions 54a, 54b of the first actuation electrode, thereby being electrically isolated from the first and second portions 54a, 54 b.

Figure 10 shows a second electrode design for the electroactive material actuator apparatus of figure 5. It shows the measurement electrodes 64, 66, the measurement electrodes 64, 66 being provided in a channel 100 formed in the first actuation electrode 54, thereby being electrically isolated from the first actuation electrode. The channel 100 is closed and thus forms only a recess or groove into the main area of the electrode.

The aspect ratio of the actuator can be adjusted for any shape required for a particular application.

Fig. 11 shows a drive circuit and feedback system for the electroactive material actuator apparatus of fig. 6. The device is again shown as part of a steerable catheter system having a catheter 80 and an actuator device 82 formed at the tip of the catheter for providing steering.

A first pair of wires 84a, 84b connect the device 82 to the DC signal source 58, wherein one wire of the first pair of wires 84a, 84b is also connected to the AC signal source 60, and a second wire 86 provides a second connection of the device 82 to the AC signal source 60.

The feedback circuit 88 has an AC signal source and a DC signal source connected as shown in fig. 6. As shown in fig. 8, the AC voltage and current values are fed to a processor 90 via an analog-to-digital converter 92, and in the processor a software program receives these values as a 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.

Fig. 12 shows a first electrode design for the electroactive material actuator apparatus of fig. 6. The measurement electrode includes separate first and second portions 54a, 54b of the first actuation electrode. In this example, the first portion 54a and the second portion 54b are rectangles forming a linear gap 120 across which the measurement signal is measured.

Figure 13 shows a second electrode design for the electroactive material actuator apparatus of figure 6. The measurement electrodes include a first set of electrically connected first portions 54a of the first actuation electrodes and a second set of electrically connected second portions 54b of the first actuation electrodes, 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. Thus, the measurement gap covers a larger portion of the actuator that generates a larger sensing signal.

Figure 14 shows a third electrode design for the electroactive material actuator apparatus of figure 6. The separated first and second portions together form an interlocking comb structure.

Figure 15 shows a fourth electrode design for the electroactive material actuator apparatus of figure 6. It shows 2 pairs of measurement electrodes formed by gaps 120a and 120b, thus forming four portions 54a-54d of the first actuation electrode. This enables independent feedback measurements from multiple locations. The detection of local actuation is of great interest when the actuator is locally blocked and this can be recorded with individual electrode pairs.

There may similarly be multiple measurement electrode pairs for the design of fig. 5. When using multiple measuring electrode pairs, of course, multiple current measuring circuits would be required.

The aspect ratio of the actuator can again be adjusted for each shape required for a particular application.

All of the above examples show actuation electrodes on opposite sides of the monolithic membrane. FIG. 16 shows an example with actuation electrodes 54, 56 and measurement electrodes 64, 66 on the same single side of the overall film.

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 measuring electrode pair follows a meandering path in the space between the two actuation electrodes.

This actuator design can be switched from a flat surface texture (inactive) to a corrugated surface texture (if no substrate is present) or alternatively to a wavy shape with alternating bending directions as viewed in the cross-section of fig. 16A (if a rigid substrate is present).

The measuring electrodes are able to determine the actuation state of the actuator by measuring the change in impedance of the area between the actuator electrodes.

There may also be a separate single measuring electrode, so that one of the actuator electrodes serves as one of the pair of measuring electrodes (as is the case in fig. 6). The impedance between one additional measuring electrode and the electrode where the moving carrier is removed is then measured.

In all of the above designs, the cathode and anode can be switched when deflection in opposite directions is required. It is still possible to measure changes in electrical impedance at a particular electrode, only in this case a rapid decrease in impedance is measured.

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

In practice, the impedance between the measurement electrodes is determined not only by the impedance of the ionic electroactive material, but also by the impedance of the air. In case the impedance is mainly determined by the resistance (i.e. the real part of the impedance), the AC signal source in the circuit can be replaced by a DC source.

However, in a general AC sensing signal, measuring the imaginary part of the impedance (inductance/capacitance) may result in a better signal-to-noise ratio, especially when the AC signal can be isolated via an electrical filter (i.e. a lock-in amplifier).

The choice between the designs of fig. 5 and 6 will depend on the requirements of the particular design. For example, when high accuracy is required, fig. 5 may be preferred because the DC circuit and the AC circuit can be independent of each other and can therefore be optimized. Fig. 6 may be preferred when space for the wires is limited.

Note that several actuators may be integrated into the interventional medical device over the length of the device. For example, three actuators may be provided, and for each actuator a similar scheme (e.g., based on the scheme of fig. 6) is used as described above to reduce the number of wires. In this case, the actuators can have a common line for actuation, and each actuator requires a return line to be able to actuate them separately. For the sensing portion, an extra wire is required for each actuator. This constitutes a total of 7 wires.

The method of fig. 5 would also allow one common line for actuation and one common line for AC sensing, making up a total of 8 wires required to connect the actuators. Alternatively, the number of lines may be reduced when using a suitable addressing system. This is particularly useful where more and more actuators are required. With independently controlled actuators, IMD devices are able to make more complex bends, which is useful for traversing tortuous vessels.

In all examples, the electroactive material actuator is based on ionic (current driven) electroactive polymer materials.

Examples of ion-driven EAPs are conjugated polymers, Carbon Nanotube (CNT) polymer composites, and Ionic Polymer Metal Composites (IPMCs).

Subclasses of conjugated polymers include, but are not limited to, polypyrrole, poly-3, 4-ethylenedioxythiophene, poly (p-phenylene sulfide), polyaniline.

The materials described above can be implanted as pure materials or as materials suspended in a matrix material. The matrix material can include a polymer.

For any actuation structure that includes an electroactive material (EAM), an additional passive layer may be provided for affecting the behavior of the EAM layer in response to an applied drive signal.

The actuating arrangement or structure of the EAM device can have one or more electrodes for providing a control signal or a drive signal to at least a portion of the electroactive material. Preferably, the arrangement comprises two electrodes. The EAM layer may be sandwiched between two or more electrodes. Such clamping requires an actuator arrangement comprising an elastic dielectric material, since its actuation is due to compressive forces applied by the electrodes attracting each other due to the drive signal, etc. Two or more electrodes can also be embedded in the elastic dielectric material. The electrode may or may not be patterned.

It is also possible to provide the electrode layer on only one side, for example using interdigitated comb electrodes.

The substrate can be part of an actuation arrangement. It can be attached to the entirety of the EAP between the electrodes and the electrode, or to one of the external electrodes.

The electrodes may be stretchable such that they follow the deformation of the EAM material layer. This is particularly advantageous for EAP materials. Materials suitable for use in the electrodes are also known and may be selected from the group comprising: a thin metal film (e.g., gold, copper, or aluminum) or an organic conductor (e.g., carbon black, carbon nanotubes, graphene, Polyaniline (PANI), poly-3, 4-ethylenedioxythiophene (PEDOT) (e.g., poly (3, 4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT: PSS))). Metallized polyester films, such as metallized polyethylene terephthalate (PET), may also be used, such as by using an aluminum coating.

The materials used for the different layers will be chosen, for example, to take into account the elastic modulus (young's modulus) of the different layers.

The additional layers discussed above may be used to tailor the electrical behavior or mechanical properties of the device, e.g., additional polymer layers.

Electroactive material actuators and sensors have many uses. In many applications, the main function of the product relies on (local) manipulation of human tissue or actuation of a tissue contact interface. In such applications, EAP actuators provide unique benefits, primarily due to low profile, flexibility, and high energy density. Thus, EAPs can be easily integrated in soft 3D-shaped and/or miniature products and interfaces. Examples of such applications are:

cosmetic skin care, for example skin-actuated devices in the form of EAP-based skin patches, which apply a constant or cyclic tension to the skin in order to tighten the skin or reduce wrinkles;

a breathing apparatus with a patient interface mask having an EAP based active cushion or seal to provide alternating normal pressure to the skin to reduce or prevent facial redness marks;

electric shaver with self-adaptive shaver head. The height of the skin contact surface can be adjusted using EAP actuators in order to influence the balance between tightness and irritation;

oral cleaning devices, such as air flosses with dynamic nozzle actuators, to improve the reach of the spray, particularly in the spaces between the teeth. Alternatively, the toothbrush may be provided with activated bristles;

a consumer electronics device or touchpad that provides local haptic feedback via an EAP transducer array integrated in or near the user interface;

a catheter with a steerable tip that enables easy navigation in tortuous vessels. As explained above, the actuator functions, for example, to control the bend radius to effect steering.

Another related application that benefits from EAP actuators involves the modification of light. Optical elements such as lenses, reflective surfaces, gratings, etc. can be adapted by shape or position adjustment using EAP actuators. Here, the benefit of EAP is, for example, lower power consumption.

Some examples of interest in asymmetric stiffness control are summarized below.

The actuator may be used in valves, including valves implantable in the human body, such as one or more prosthetic heart valves in an on-chip organ application or microfluidic device. For many valves, asymmetric behavior is desired: with compliance and large displacement in the direction with flow and stiffness in the direction resisting flow. Sometimes high actuation speeds are required to close the valve quickly.

Flexible display actuators are desirable in some applications, such as in smart bracelets. Large displacements are required when the flexible display is moved to another position or shape for better reading or with better visual appearance. The display actuator must be held firmly in place when the display is in its rest position.

As well as applications in noise and vibration control systems. By using stiffness variation, it is possible to move away from the resonance frequency and thus reduce vibrations. This is useful, for example, in surgical robotic tools where accuracy is important.

Soft robots (artificial muscular systems supporting the human body) are for example used to support or support the body in a certain position (e.g. against gravity), during which stiffness is required. When the body part is moved in the opposite direction, resistance is not required and a low stiffness is desired.

Segmented catheter applications may also benefit from variable stiffness. For example, when the catheter tip is bent around a corner, it is desirable that the segment behind the tip be temporarily compliant so that the rest of the catheter follows the tip.

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 word "a" or "an" does not exclude a plurality. Although some measures are recited in mutually different dependent claims, this does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.