WO2025202911A1 - Dielectric elastomer actuator deformation mapping - Google Patents

Abstract

A Dielectric Elastomer Actuator has first and second DEA electrodes coupled to electroactive polymer at least one of the DEA electrodes includes a plurality of boundary electrodes configured to detect a localised change in resistivity on the at least one DEA electrode, or detect a localised change in capacitance between the DEA electrodes.

Description

DIELECTRIC ELASTOMER ACTUATOR DEFORMATION MAPPING

FIELD

The present disclosure relates to deformation or pressure sensing and/or mapping and has particular application to dielectric elastomer devices, commonly referred to as dielectric elastomer actuators (DEAs).

Use of the term dielectric elastomer actuator in this document is intended to include, where appropriate, dielectric elastomer devices that perform a generation functions, which are sometimes known as dielectric elastomer generators (DEGs).

BACKGROUND

Dielectric elastomer actuators commonly use flexible conductive electrodes to apply an electric potential to the electroactive material from which they are constructed. A dielectric elastomer actuator (DEA) is a form of soft robotic actuator that induces deformation with an applied electric field. Although commonly used as an actuator, this technology offers versatile applications as an energy generator or sensor and provides attractive features such as high energy density, large displacements, and fast response times.

DEAs have been used to mimic biological muscles in many applications, because of the technology's likeness to biological muscle in terms of elasticity, energy density, and various potential shapes/topologies.

DEAs have been proven to produce strains larger than 1600% which is significantly larger than that of regular biological muscle. However, large DEA strains can often be at the cost of actuator instability and a low effective force. DEAs have a high work and power density comparable to that of biological muscle and have been found experimentally to have energy densities of around 3.4 J.g and theoretically an order of magnitude more.

Self-sensing DEAs for closed-loop control have been proposed, but these simply look at the one-dimensional deformation of a DEA using the overall capacitance of the DEA in order to determine a state of the DEA. Multi-degree-of-freedom (multi-DOF) DEA topologies have been created allowing for a broader range of applications. The complex actuation mechanisms present in multi-DOF DEA topologies give rise to the question of having more resolute sensor data for such topologies to aid with their control.

SUMMARY

In an aspect a Dielectric Elastomer Actuator (DEA), is provided comprising: an electroactive polymer; a first DEA electrode and a second DEA electrode; the first and second electrodes being coupled to the electroactive polymer and being configured to apply or receive electric energy to from the electroactive polymer, and wherein at least one of the DEA electrodes includes a plurality of boundary electrodes.

Optionally, the boundary electrodes are configured to detect a localised change in resistivity on the at least one DEA electrode, or detect a localised change in capacitance between the DEA electrodes.

Optionally, the at least one DEA electrode has a selected resistivity characteristic.

Optionally, the at least one DEA electrode is piezoresistive.

In an aspect a Dielectric Elastomer Actuator (DEA), is provided comprising: an electroactive polymer; a first DEA electrode and a second DEA electrode; the first and second electrodes being coupled to the electroactive polymer and being configured to apply or receive electric energy to from the electroactive polymer, and wherein at least one of the DEA electrodes is configured to be piezoresistive and the other is configured to be not piezoresistive, or at least less piezoresistive.

Optionally, the at least one DEA electrode includes a plurality of boundary electrodes. In an aspect, a Dielectric Elastomer Actuator (DEA), is provided comprising: an electroactive polymer; a first DEA electrode and a second DEA electrode; the first and second electrodes being coupled to the electroactive polymer and being configured to apply or receive electric energy to from the electroactive polymer, and wherein the DEA further comprises a deformation or pressure mapping sensor.

Optionally, the electroactive polymer is provided between the first and second DEA electrodes.

Optionally, the apparatus is further configured to detect a localised change in resistivity on the at least one DEA electrode.

Optionally, the apparatus uses the change in resistivity on at least one DEA electrode to estimate a load event magnitude.

Optionally, the DEA further comprises apparatus configured to detect a localised change in capacitance between the first and second DEA electrodes.

Optionally, the apparatus uses the change in capacitance to estimate a load event magnitude.

Optionally, the apparatus is further configured to use the localised changes in capacitance and resistivity to provide an estimate of shear stress.

Optionally, the apparatus is further configured to energise the DEA electrodes to produce a movement of the electroactive polymer. The movement may comprise for example a contraction or electrostriction.

Optionally, the apparatus is further configured to receive or harvest electric energy from the DEA electrodes in response to a movement of the electroactive polymer. Optionally, the apparatus is further configured to sense localised changes in capacitance or resistivity while energising or receiving energy from the electroactive polymer.

In an aspect apparatus for sensing a state of a DEA having an actuation electrode which includes a plurality of boundary electrodes is provided, the apparatus comprising a circuit configured to receive signals from the boundary electrodes to detect a localised change in capacitance in the DEA.

Optionally the circuit is configured to inject an AC signal, or a combination of AC and DC signals.

Optionally, the apparatus further comprises a processor configured to estimate a load event magnitude from the detected change in capacitance.

Optionally, the processor is further configured to detect a localised change in resistivity on the actuation electrode.

Optionally, the processor is further configured to use the localised changes in capacitance and resistivity to provide an estimate of shear stress.

Optionally, the apparatus is further configured to energise the DEA to produce a movement of the DEA.

Optionally, the apparatus is further configured to receive or harvest electric energy from the DEA in response to a movement of the DEA.

Optionally, the apparatus is further configured to sense localised changes in capacitance or resistivity while energising or receiving energy from the DEA.

In an aspect a method of sensing a state of a DEA is provided, comprising: Injecting and receiving signals from boundary electrodes to detect a localised change in capacitance in the DEA.

Optionally, the method further comprises estimating a load event magnitude from the detected change in capacitance between the DEA electrodes.

Optionally, the method further comprises detecting a localised change in resistivity of an electrode of the DEA.

Optionally, the method further comprises estimating a shear stress of the DEA from the localised changes in capacitance and resistivity.

Optionally, the method further comprises energising the DEA to produce a movement of the DEA.

Optionally, the method further comprises receiving or harvesting electric energy from the DEA in response to a movement of the DEA.

Optionally, the method further comprises sensing localised changes in capacitance or resistivity while energising or receiving energy from the DEA.

Further aspects will be apparent from the description below.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1 , 1 .1 , 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

DRAWING DESCRIPTION

Examples or embodiments of apparatus and methods for DEA state sensing, which includes pressure or deformation sensing/mapping and/or control will now be described with reference to the accompanying drawings, in which:

Figure 1 is a diagram of a known DEA;

Figures 2 is a diagram of a DEA;

Figure 3 is an exploded view of Figure 2;

Figure 4 shows examples of DEA electrodes;

Figure 5 shows detection apparatus connected to the DEA of Figure 2;

Figures 6 and 7 illustrate detection performed by the apparatus of Figure 5;

Figure 8 is a flow chart showing a detection method;

Figure 9 shows the DEA of Figure 2 undergoing a localised deformation;

Figure 10 shows a cross-section through AA of Figure 9;

Figure 1 1 shows the deformation of Figure 10 in more detail;

Figure 12 shows examples of detected conductance images; Figure 13 is a diagram of a system including the DEA of Figure 2;

Figure 14 is also a configuration of a system including the DEA and EIT related hardware

Figure 15 shows an architecture for simultaneous DEA actuation and EIT mapping which includes a limiting means;

Figure 16 shows energy generation sequence in which a DEA is used as a generator (DEG) in response to a localised compressive load;

Figure 17 is a diagram of an architecture of a DEA-EIT pressure mapping and actuator device with an exploded view of the DEA stack and including an energy harvest circuit;

Figure 18 shows a diagram of force application to a DEA to test performance of the disclosed sensing system;

Figure 19a and 19b show test results for application of force (Fest) and sensed or measured (Fmeas) for 5-30% strain centre loading events at Lo in Figure 18, for 8 wt% CBSR (Fig 19a) and 9 wt% CBSR (Fig 20a);

Figure 20 shows a diagram of an application of the disclosed system in which an EIT sensor input DEA controls an optical lens;

Figure 21 shows a diagram of an application of the disclosed system in which pressure mapping is performed on a sensitive skin for a DEA propelled jellyfish soft robot.

DETAILED DESCRIPTION

In the following description, specific details are given to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, modules, including those in the form of software modules, functions, circuits, etc., may be shown in block diagrams in order not to obscure the embodiments in unnecessary detail. In other instances, well-known modules, structures and techniques may not be shown in detail in order not to obscure the embodiments.

Also, it is noted that the embodiments may be described as a process that is depicted as a flowchart, a flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process is terminated when its operations are completed. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc., in a computer program.

Referring to the drawings, a simple configuration of a DEA 1 is shown by way of example as a circular parallel plate capacitor, which consists of an electroactive polymer such as a thin elastomer sheet or membrane 2 between two compliant conductive electrodes 3, 4, as shown in Figure 1. When a voltage from power supply 5 is applied to the compliant electrodes 3, 4, the electrostatic force arises between the electrodes causing the electroactive polymer comprising the dielectric elastomer (DE) membrane 2 to contract by a decrease in thickness and an increase in area as shown by arrows 6 and 8 respectively. The resulting actuation is controlled by changing the applied voltage. The region encompassing the two compliant electrodes and the DE portion sandwiched between them is called the 'active region'.

Designing a DEA for practical applications is often highly constrained by three key modes of failure as well as the parameters of the constituent components. A common mode of failure is the electromechanical instability of the elastomer. With increasing voltage, the DE compresses until the voltage exceeds the critical point at which dielectric breakdown occurs. At the point of failure, the DE membrane experiences a surge of electrical current, permanently changing the DE insulative properties. The second mode is a loss of tension in the elastomer when an applied voltage is large and the axial force provides an excessively large compression. The stress in the DE may cause the plane to lose tension such that the elastomer no longer actuates as expected, if at all. Often resulting in visible wrinkles in the DE. The third mode is a physical rupture of the elastomer due to stretching beyond the DE's yield strength. A force or pressure sensor may help to avoid failure. A benefit of DEA technology is its potential to be fabricated into various topologies depending of the desired application including, parallel plate, roll, tube, helical, and conical geometries.

A new DEA construction referenced 10 is shown in Figure 2. In this construction, which is shown as an example only, the electroactive polymer 2 is again provided as a membrane or sheet, however it will be understood that a wide variety of topologies are possible (as referred to above), and as indicated in part by the irregular shape of the actuator construction. In some applications or embodiments, the DEA 10 may comprise part of a wearable item, or robotic component, so the topology and number of degrees of freedom may vary. The example of Figure 2 is intended to provide a straightforward example to disclose the construction for ease of comprehension.

In the DEA 10, at least one of the electrodes 3, 4 (in this example electrode 3) is constructed or selected to have a plurality of boundary electrodes 11. Although electrodes 11 are described herein as boundary electrodes, it will be understood that they do not always have to be located at an edge or periphery of the electrode 3, DEA or related device. The boundary electrodes 11 are located at a boundary of the sensing domain. In most of the examples provided herein the sensing domain happens to coincide with a boundary of a DEA electrode such as electrode 3, but in other DEA constructions the sensing domain may comprise only a part of a DEA electrode or similar structure. As will be described further below, the boundary electrodes allow a non-invasive method of pressure mapping without compromising a monolithic piezoresistive material. The construction provides a pressure mapping sensor which has the ability to estimate the magnitude and location of deformation events in a planar piezoresistive material. The hardware required can include a piezoresistive sensor domain with attached boundary electrodes, driver electronics, and a reconstruction processor.

In an embodiment, the at least one electrode 3 also has a known or predetermined resistivity characteristic. In an embodiment, the compliant electrode 3 (and/or compliant electrode 4) comprises a piezoresistive material, such as a piezoresistive nanoparticle elastomer composite (PNEC). As is described further below, the boundary electrodes establish boundary conditions to allow electro impedance tomography (EIT) to be used to detect a localised change in impedance, which may comprise a reactance (i.e. capacitance) and/or a resistivity in response to a force being applied to the electrode 3 which causes a deformation of the electrode. In particular, the EIT methodology allows detection of a localised change in resistivity in the sensing domain of electrode 3 and localised change in capacitance between the electrodes 3, 4 in response to the deformation of the electrode 3. The stages required to generate a pressure image using EIT can be simplified into three core stages, data acquisition, image reconstruction, and inverse force model implementation.

As seen in Figure 3, the DEA 10 of Figure 2 is shown in expanded form in which the three layers comprising electroactive material 2, and electrodes 3, 4 are shown separately. In an embodiment the electrode 4 (the lower electrode in Figure 3) comprises a conductive shunt film rather than a piezoresistive elastomer composite and is earthed 9. Although the example of Figure 3 shows an embodiment of the DEA 10 can be constructed as three layers which are joined together, it will be understood that other physical arrangements or manufacturing processes can be used. For example, it will be understood that the DEA 10 can in an embodiment be constructed from a material, such as an appropriate polymer, which has other materials added (for example by doping or impregnation such as using a hydrogel) to selected regions during manufacture to thereby provide regions that form electrodes 3, 4, and/or one or more electroactive regions 2.

Referring to Figures 4(a)-(c), examples of the construction of a DEA are illustrated diagrammatically. In an embodiment the fabrication of the DEA 10 may use a rigid acrylic frame to attach a pre-stretched electroactive elastomer 2. For simplicity in this example, a circular frame 20 is used with the DE at a radial pre-stretch of +10%, i.e. '- r = 1.1 , as this is well within the DE's more predictable linear elastic region. In an embodiment, a circular acrylic frame 20 of 178 mm inner diameter was fabricated from laser cut acrylic of 4 mm thickness to ensure rigidity.

In an embodiment, the elastomer sheet 2 is formed from a relaxed sheet 2 of 4910 VHB tape (3M, Saint Paul, USA) which is then stretched as shown in Figure 4a. To achieve uniform stretch a toroidal hose mechanism 19 can be used as a pre-stretcher annulus. The toroidal mechanism has an axis of rotation along its circumference, giving the ability to roll and stretch the elastomer equiaxia I ly to the desired pre-stretch over a frame 20.

Compliant electrodes (or active area) 3, 4 can be fabricated using acrylic moulds of varying dimensions. In an embodiment the thickness of the electrodes can be selected dependent on the required actuation and/or sensing performance. In an embodiment, thicknesses may for example range from 0.5 mm to 2mm. In an embodiment, electrodes 3, 4 may comprise circular compliant electrodes of 100 mm diameter.

In an embodiment, a compliant electrode 3,4 medium comprises carbon black (CB) powder. In an embodiment, a compliant electrode medium comprises a carbon black silicone rubber (CBSR) composite. Other materials that allow compliant structures having a suitable resistivity characteristic may be used.

In an embodiment either CB or the CBSR composite may be used to make both single (Figure 4(a)) and multiple (Figure 4(c)) circumferential electrode configurations of DEAs. In an embodiment the CB powder used may comprise Vulcan XC-72 powder (Fuel Cell Store, Bryan, USA). In an embodiment the CBSR composite has 8% CB by weight mixed with DragonSkin 10NV silicone rubber (Smooth-On, Macungie, USA). This composite is a piezoresistive medium that is useful for EIT pressure mapping and sensing and is effective for DEA actuation.

In an embodiment, using the liquid silicone rubber, the CBSR composite mixture is formed by combining part A of the silicone solution and 8 wt% CB and mixing (by machine or by hand) for 10 s. The mixture is then placed in the ARV-31 OPCE planetary vacuum mixer (Thinky Inc., Tokyo, Japan) to complete a mixing cycle with 500 RPM for 45 s followed by a cycle with 800 RPM for 45 s. In the same mixing container, part B of the silicone solution is added to the mixture and stirred (which may be done by machine or by hand) for 10 s and immediately the same mixing cycle in the planetary mixer is completed again. After the cycle is completed, the composite is poured into the mould with attached circumferential copper tape boundary electrodes. The CBSR mixture is then placed in an oven at 80 degrees C for 4.5 h to ensure the composite is sufficiently cross-linked.

In an embodiment, two types of compliant electrode configuration may be used, as shown in Figure 4. The Figure 4a-4c configurations are illustrated only to show how a DEA which does not include the deformation sensing disclosed herein may be constructed, being used for example for testing basic DEA actuation.

In an embodiment of DEA 10 a conductive rigid or compliant lower electrode 4 may be used with an upper compliant electrode 3 according to Figure 4d which has boundary electrodes 1 1.

The multiple boundary electrode configuration of Figure 4d has the boundary electrodes 1 1 arranged circumferentially located at a boundary of the sensing domain. In an embodiment the circumferential electrode configuration consists of evenly spaced circumferential electrodes. In the example shown there are sixteen spaced circumferential electrodes. The multiple circumferential electrode configuration can be used for both pressure mapping and actuation functionality of the DEA 10. In an embodiment, prior to curing the compliant electrodes in a circular mold, pieces of conductive copper tape are placed into the mold to thereby form the circumferential electrodes. In an embodiment, the width of the circumferential electrodes is 8 mm. In an embodiment, the circumferential electrodes are placed with a 3 x 8 mm area embedded in the compliant electrode circumference edge with the rest of the circumferential electrode protruding for easy access to external electrical connections.

Providing at least electrode 3 as a compliant conductive electrode with multiple boundary electrodes 1 1 allows an EIT approach to be used for deformation and/or pressure mapping, allowing measurements or at least estimates of magnitude and location of feree loads present on the DEA, whether those loads are imposed externally or from actuation of the DEA. Therefore, a non-invasive method of pressure mapping is provided. An example of the detection apparatus 30 which is used to perform the energisation and sensing is shown in Figure 5. In an embodiment the apparatus includes a power supply 31 which includes an AC source configured to provide a supply which can be selectively applied to the boundary electrodes 1 1 by signal or control circuit 32 via conductors 33. In an embodiment the power supply 30 can be additionally provided as a DC source.

In an embodiment an impedance measurement circuit 34 is provided to detect changes in impedance from the applied signals as described further below. In an embodiment a processor 36 processes the detected impedances and provides an output, for example a deformation map that represents a state of the DEA 10, which may be used to determine for example the physical disposition of the DEA in response to an electrical actuation or a physical manipulation of the DEA. It will be understood that the separate circuit modules referred to in Figure 5 may be provided in different combinations, for example as a single device for attachment to DEA 10, or even as a part of DEA 10.

In an embodiment the EIT based implementation can perform at image frame rates higher than 50 Hz or more. Due to the viscoelastic and resistive nature of the sensor, the frequency response can be lower than that of the frame rate of the sensor depending on the piezoresistive sensing domain used.

The stages required to generate a pressure and/or deformation image using EIT can be simplified into three core stages:

1. Data acquisition

2. Image reconstruction

3. Inverse pressure model

Data acquisition involves an excitation drive pattern to be applied to the piezoresistive sensing domain comprising in this example electrodes 3, having boundary electrodes 1 1 . Pairs of boundary electrodes 1 1 are energised by injection of a current or voltage and data gathered by concurrently monitoring the remaining boundary electrodes. The EIT detection process is shown in Figure 8, which now described with reference to Figures 6 and 7. The process begins in step 101 which consists of the injection of a known AC current or voltage 50 having a characterising frequency and magnitude selected based on the properties of the electrode, whereby a voltage at an unenergized boundary electrode will have a magnitude sufficient for reliable detection. The current or voltage 50 is supplied from the power supply 31 through two boundary electrodes 1 1 as shown in Figures 6 and 7, producing an alternating current and voltage distribution across the electrode as indicated graphically by arrows 52 in Figure 7. In an embodiment a drive pattern is used to energise adjacent pairs of electrodes, moving from one adjacent pair to another adjacent pair. This may continue until all pairs have been energised so that data is collected across the sensing domain. In other embodiments other combinations of electrodes may be energised, and in some embodiments not all combinations may need to be energised in order to collect sufficient data for solving the inverse problem. Concurrently all voltages VO-Vn at the other (non-energised) boundary electrodes of the material domain are read as shown in step 102. Then the known current source 50 is applied to the next set of adjacent electrodes, and all of the other adjacent electrode voltages are read once more as shown in step 103. The magnitude and phase relationship of the detected voltages is dependent on the deformation of electrode 3 and the distance between electrode 3 and electrode 4. This process is repeated until it has been deemed there have been sufficient readings for the processor to solve the inverse problem and generate an impedance distribution. Repeating the application of the applied current or voltage 50 around the boundary electrodes 11 at the boundary of the sensing domain allows localised changes in impedance (including resistivity/conductance and capacitance) to be determined. This provides significantly improved information about the state of the DEA for control purposes, including closed loop control.

The data is provided into an EIT optimisation algorithm to generate a map or distribution of the changes in impedance, as shown in step 104. In an embodiment the impedance distribution can comprise both a conductance or resistivity distribution for electrode 3 and a capacitance distribution of the electrode 3 relative to the earthed electrode. In step 105 an inverse model is used by the processor 36 to generate delta force estimates for each mesh element in the map image or images. This allows the data to be converted into a pressure map by the processor, so that a state of the DEA can be determined for control.

As shown in step 106, the steps above are repeated while the DEA is being used or activated so that real time force mapping and estimation is provided for closed loop control of the DEA 10.

In an embodiment the process above may additionally include the injection of a known DC current or voltage from the power supply through two boundary electrodes 1 1 , for example multiplexed with application of the AC supply, to further assist in determining the resistivity/conductance distribution.

Figure 9 diagrammatically illustrates a force applied to the DEA 10. The force is shown as an object 60 applied to electrode 3 in the downward direction toward the electrode 4, causing a localised deformation 62 in the electrode 3.

Figure 10 shows a diagrammatic cross-section through the DEA 10 of Figure 9 taken through plane A-A of Figure 9. The electric field between electrodes 3 and 4 as a result of the applied AC current is shown by lines 64. It can be seen in Figure 10 that the localised region 66 in which the deformation 62 has a smaller separation distance between the electrodes 3 and 4 in that localised region. The reduction in separation distance causes a localised increase in capacitance and the change in capacitance is detected by the method described above.

Turning now to Figure 1 1, it can be seen that the stress state of the DEA 10 can be determined from the data gathered using the method(s) described above. Figure 11 shows a similar situation to that of Figure 10 in which an object 60 has deformed the DEA 10. The localised detected increase in capacitance is shown in the graph of capacitance against distance, and the distance or area 68 across which the deformation occurs can be determined or estimated from the detected localised change in capacitance. The changes in conductance or resistivity that occur in electrode 3 can then be resolved as regions of increased resistance 70 which represent tension in the electrode 3 and reduced resistance 72 which represent compression in electrode 3. From this data a stress state of the electrode 3 and/or the DEA 10 can be determined.

Figure 12 shows examples of EIT conductance images that can be generated using the method(s) above. To form blobs as estimates of the applied loads, post-processing was completed by applying an 85 % threshold mask to the EIT image. These blob images were subsequently analysed using two spatial performance metrics, the centre-of-mass error, ECoM, (Figure 12a) and the shape fit, SF, (Figure 12b). The circle 76 is the actual load area and the dark elements 78 are the load estimate area. The ECoM values were determined by calculating the difference between the CoM of the actual load and the blob representing the load estimate. The SF was determined by calculating the radial mean square error between all of the, n, perimetral nodes of the blob load estimate and the actual load circumference, as taken from the CoM of the actual load area.

Figure 13 illustrates a system for closed loop control of DEA 10, which includes an energisation module or circuit 80 that can apply or receive electric energy to or from the DEA 10, dependent on the output of detection apparatus 30. In an embodiment the apparatus 30 may operate at a DC bias for example to allow it to perform detection concurrently with the DEA 10 being energised. In another embodiment the detection apparatus is multiplexed with energisation of the DEA.

Figure 14 illustrates an example of a closed loop system similar to the system of Figure 13 but showing more detail. In this example, a control device 81 communicates with the DEA excitation device 82 and measurement device 86. The Excitation device 82 comprises a microcontroller 83, output voltage supply 84 and high voltage amplifier 85 the output of which is connected to electrodes 3, 4 via switching network 87. Network 87 also provides connectivity between the boundary electrodes 11 and the measurement/detect circuit 34. Circuit 34 comprises a microcontroller 88 which communicates with control device 81, an excitation source for supplying an AC and or DC source which is controllably injected via network 90. Network 90 also receives the signals from the non-energised boundary electrodes which signals are detected by voltmeter 91 and applied to demodulation and sampling circuit 92. Simultaneous actuation and pressure mapping involves an excitation voltage is applied to the DEA whilst completing EIT to the grounded DEA electrode. To ensure that the EIT electronics are able to operate during transients or dielectric breakdown events, an intermediary limiter 100 may be provided as shown in Figure 15. In the example shown, the limiter comprises one or both of a 20 V Zener diode array 102 and a current limiting resistor, Rn_m. When the DEA is switched on, the compliant electrodes charge. During this charging period a voltage will be developed on the HV and low-voltage EIT electrode characterised by the charging capacitance, CDEA, the HV source resistance, Rnm, and the multiplexer on resistance, Ron- The resistance of the DEA is lumped in with R|j_m. In the configuration shown in Figure 15, a voltage divider is created between the Rnm resistor and the multiplexer, R_on, on-resistance to ensure the voltage seen at the multiplexer input pin is sufficiently low.

During a compressive load event to an actuated DEA-EIT device, the DE thickness is decreased which increases the concentration of charge in the strain area. Both factors increase the likelihood of dielectric breakdown within the material. Feedback from the sensor disclosed herein may be used to decrease the actuation voltage if the device receives a strain that is likely to cause a dielectric breakdown. If breakdown does occur, the sensor disclosed herein enables the mapping of dielectric breakdown locations and sizes The force mapping disclosed herein has been found to be successful with decreasing degrees of mapping error with increasing compliant DEA electrode thickness. A compliant electrode of 2mm thickness, or at least 2mm thickness, provided superior results to thinner electrodes.

As described above, a dielectric generator (DEG) can arise in the DEA-EIT device when a load is applied. A DEG may be incidentally or deliberately created during simultaneous DEA-EIT operation. This effect will take place when the DEA experiences sufficiently large external strains and DEA voltage switching at specific times. This DEG sequence is shown in Figure 16 and is explained as five distinct stages. In the figure, Ci is the initial capacitance of the DEA, Cii is the 'primed' capacitance of the DEA, the positive and negative signs, + and -, on the compliant electrode represent electrical charge, and the cylinder represents a load applicator. The typical operation of a DEG consists of the five main stages described below and is exemplified in Figure 16. Note that the changes in electrostatic force due to loads are ignored.

State A: the DEA has an initial capacitance of Ci, is deformation free, and has zero voltage applied across the compliant electrodes.

State B: the DEA is compressed and deformed with a localised change(s) in thickness of the DE, Az, increasing the DEA capacitance to Cii. Work is done on the DEA by the compressive load storing elastic potential energy in the strained DE.

State C: An applied voltage, Vi, across the compliant electrodes generates electrical charge. Charging the electrodes gives electrical potential energy to the DEA as it is now a charged capacitor.

State D: The DEA is unloaded and returns to its original state with capacitance, Ci, while maintaining the same charge Q causing the voltage to increase to V. When the load is released the elastic potential energy, Us, is used as the DEA returns to a relaxed state. In parallel, the increase in voltage on the DEA increases the electrical potential energy.

State A*: The DEA is discharged into the energy harvesting circuit returning the charge and voltage values across the DEA to zero, returning to State A.

Figure 17 shows an example of an architecture of a DEA-EIT pressure mapping and actuator device with an exploded view of the DEA stack and including an energy harvest circuit 1 10. Figures 18-19 show performance of the disclosed sensing system. Figure 18 shows a diagram of force application to a DEA, and Figures 19a and 19b show the measurements obtained for force applied at Lo in Figures 18.

Figure 20 shows a diagram of an application of the disclosed system in which an EIT sensor input DEA controls an optical lens, and Figure 21 shows a diagram of an application of the disclosed system in which pressure mapping is performed on a sensitive skin for a DEA propelled jellyfish soft robot.

In this specification, where reference has been made to external sources of information, including patent specifications and other documents, this is generally for the purpose of providing a context for discussing the features of the present invention. Unless stated otherwise, reference to such sources of information is not to be construed, in any jurisdiction, as an admission that such sources of information are prior art or form part of the common general knowledge in the art.

As used herein the term "and/or" means "and" or "or", or both. As used herein "(s)" following a noun means the plural and/or singular forms of the noun. The term "comprising" as used in this specification means "consisting at least in part of". When interpreting statements in this specification which include that term, the features prefaced by that term in each statement all need to be present, but the other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

Claims

1 . A Dielectric Elastomer Actuator (DEA), comprising: an electroactive polymer; a first DEA electrode and a second DEA electrode; the first and second electrodes being coupled to the electroactive polymer and being configured to apply or receive electric energy to from the electroactive polymer, and wherein at least one of the DEA electrodes includes a plurality of boundary electrodes configured to detect a localised change in resistivity on the at least one DEA electrode, or detect a localised change in capacitance between the DEA electrodes.

2. The DEA of claim 1 , wherein the at least one DEA electrode has a selected resistivity characteristic.

3. The DEA of claim 1 or claim 2, wherein the at least one DEA electrode is piezoresistive.

4. The DEA of any one of the preceding claims wherein the DEA further comprises a deformation or pressure mapping sensor.

5. The DEA of any one of the preceding claims, wherein the electroactive polymer is provided between the first and second DEA electrodes.

6. The DEA of any one of the preceding claims, wherein the apparatus uses a change in resistivity to estimate a load event magnitude.

7. The DEA of any one of the preceding claims, wherein the apparatus uses a change in capacitance to estimate a load event magnitude.

8. The DEA of any one of the preceding claims, wherein the apparatus is further configured to detect the location of a load event from a localised change in resistivity of the at least one electrode, or a localised change in capacitance between the electrodes.

9. The DEA of any one of the preceding claims, wherein the apparatus is further configured to use the localised changes in reactance and resistivity to provide an estimate of shear stress.

10. The DEA of any one of -the preceding claims, wherein the apparatus is further configured to energise the DEA electrodes to produce a movement of the electroactive polymer.

1 1 . The DEA of any one of -the preceding claims, wherein the apparatus is further configured to receive or harvest electric energy from the DEA electrodes in response to a movement of the electroactive polymer.

12. The DEA of claim 10 or 1 1 , wherein the apparatus is further configured to sense localised changes in capacitance or resistivity while energising or receiving energy from the electroactive polymer.

13. A method of sensing a state of a DEA having a DEA electrode which includes a plurality of boundary electrodes, the method comprising: applying signals to energise selected boundary electrodes and receiving signals from unenergised boundary electrodes to detect a localised change in impedance in the DEA or a localised change in resistivity in the DEA electrode.

14. The method of claim 13, further comprising estimating a load event magnitude from the detected change.

15. The method of claim 14, further comprising estimating a shear stress of the DEA from the localised changes.

16. The method of any one of claims 13 - 15, further comprising energising the DEA to produce a movement of the DEA.

17. The method of any one of claims 13 - 15, further comprising receiving or harvesting electric energy from the DEA in response to a movement of the DEA.

18. The method of claim 16 or 17, further comprising sensing localised changes in capacitance or resistivity while energising or receiving energy from the DEA.