Specification

The invention is about an electroactive polymer transducer, and about a switching device with an electroactive polymer transducer.

The present invention relates generally to electroactive polymer devices that convert between electrical energy and mechanical energy. More particularly, the present invention relates to an electroactive polymer transducer.

In many applications, it is desirable to convert between electrical energy and mechanical energy. Exemplary applications requiring conversion from electrical to mechanical energy include robotics, pumps, speakers, sensors, microfluidics, shoes, general automation, disk drives, and prosthetic devices. These applications include one or more transducers that convert electrical energy into mechanical work— on a macroscopic or microscopic level. Exemplary applications requiring conversion from mechanical to electrical energy include sensors and generators.

New high-performance polymers capable of converting electrical energy to mechanical energy, and vice versa, are now available for a wide range of energy conversion applications. One class of these polymers, electro active elastomers, is gaining wider attention. Electroactive elastomers may exhibit high energy density, stress, and electromechanical coupling efficiency.

Electroactive polymers are a class of polymer material which, when applied in the form of a flat configuration such as a film, under the influence of an electrostatic field will contract in thickness and expand in area.

The main advantage of the electroactive polymer transducer technology is the improved efficiency in the energized state with respect to conventional, for example electromagnetic, transducers which are today used in electrical switching devices such as contactors or circuit breakers. This improved efficiency not only reduces the electric power required to operate the transducer, which is also an environmental benefit, but more importantly significantly reduces the amount of heat dissipated by the transducer, so that external heat management systems are no longer required, and thus overall system costs are reduced.

Additional benefits of using electroactive polymer transducer, also called dielectric elastomer actuators, include their potentially low production costs and strategic independence from raw materials such as copper and ferromagnetic materials, which are widely used in state-of-the-art electrical drives. Finally, the inherent compliance of the electroactive polymer transducer may introduce damping into the mechanism which could aid in the suppression of the contact bouncing phenomena well-known in the art.

Electroactive polymer (EAP) transducers, also called dielectric elastomer actuators (DEA) are compliant variable capacitors consisting of a thin elastomeric film coated on each side with a compliant electrode.

The application of an electric field across the electrodes results in electrostatic attraction force between the opposite charges on opposing electrodes and repulsive forces between the like charges within each electrode. These forces generate stress on the film causing it to contract in thickness and expand in area, as illustrated in Figure 1 .

US 201 1 /0025170 A1 shows an electroactive polymer device with a rolled electroactive polymer configuration.

US 7,538,472 B2 shows a programmable shim for manufacturing and assembly lines, with an actuator that may employ electroactive polymers.

US 7,548,010 B2 shows an actuator for large displacements and rotations with an actuator element formed of an electroactive polymer.

It has been proposed that an EAP-based actuator comprises an electroactive polymer in a stacked configuration.

As shown in Figure 2, the stacked configuration consists of a multitude of dielectric elastomer actuator films layered on top of each other with electrode connections alternating between high voltage and ground level. The thickness of each layer is reduced upon application of the voltage, and an overall reduction in stack height is achieved. When the stack is coupled to an external load, the actuation mechanism can be harnessed to perform mechanical work.

An actuator or transducer with a stacked EAP configuration can perform actuation in one direction, starting from the rest state, the neutral position, when the stack is not energized. Actuation energy comes only from the electrical energizing energy applied as a DC voltage.

It is therefore the object of the present invention to propose an electroactive polymer transducer which can be actuated in more than one direction, and which shows increased energy efficiency.

The object of the invention is achieved with an electroactive polymer transducer according to claim 1 .

So the electroactive polymer transducer according to the invention comprises a first stack configuration and a second stack configuration, each stack configuration having a multitude of electroactive polymer layers, layered on top of each other, with electrodes disposed between adjacent layers of electroactive polymer, whereby the electrodes of each stack configuration are alternately interconnected to form an in- terdigital electrode arrangement with two interdigitally interlaced electrode configurations, whereby each stack configuration has a fixed end and a movable end, whereby a first fixed end is the fixed end of the first stack configuration and a second fixed end is the fixed end of the second stack configuration, and whereby the first and the second fixed ends are fixed relatively to each other, whereby a first movable end is the movable end of the first stack configuration and a second movable end is the movable end of the second stack transducer, and whereby the first and second movable ends are coupled together to form a coupling zone for coupling to an external load.

In an advantageous embodiment of the invention, the first stack configuration and the second stack configuration have an elongated orientation each, with the fixed end and the movable end positioned at the small sides of the elongated arrangement.

In an advantageous embodiment of the invention, the electrode interconnections are located at long sides of the elongated arrangement positioned oppositely to each other.

In an advantageous embodiment of the invention, the outer surface of the first and the second stack configuration are aligned with each other.

In an advantageous embodiment of the invention, the electrical point of contact to each of the electrode configurations is provided at a long side of the elongated arrangement.

In an advantageous embodiment of the invention, the electroactive polmer based transducer has an electronic control unit electrically connected to each of the points of contact to each of the electrode configurations, configured for alternatingly energizing each of the stack configurations by applying a high DC voltage difference between the two electrode configurations of each of the stack configurations, and for deenergizing each of the stack configurations by switching off the DC voltage difference between the two electrode configurations.

In an advantageous embodiment of the invention, the electroactive polymer based transducer has one electronic control unit to energize and deenergize both the first and the second stack configuration.

In an advantageous embodiment of the invention, the electroactive polymer based transducer has two electronic control units, one for each of the stack configurations, to energize and deenergize each stack configuration separately.

So according to the invention, there is created an electroactive polymer actuator comprising a complementary connection of two electroactive polymer actuators of the stacked dielectric elastomer type. An advantage of the invention lies in the fact that the complementary stack arrangement of the invention enables proportional actuation in two directions from the rest state. A further advantage is that the complementary dual-stack arrangement permits an efficiency gain during switching, since a portion of the stored actuation energy in the energized stack can be recovered when the other stack is energized and used to support energizing the other stack.

An advantageous application of an electroactive polymer transducer according to the invention can be in many fields, for example in robotics, in process automation, in electrical switching devices, etc.

A switching device according to the invention can be for example an electrical switching device comprising a housing, an electrical conductor assembly at least partially within the housing, the electrical conductor assembly including a stationary contact assembly and a movable contact assembly, and a contact actuator operably interfaced with the electrical conductor assembly, the contact actuator comprising an electroactive polymer in a stacked configuration. An electrical switching device according to the invention can be a contactor or a circuit breaker.

Electrical contactors are electrically controlled switches used for opening and closing a power circuit. Conventional contactors rely on an electromagnetic actuator to position a contact carrier which opens or closes the power circuit depending on its location.

The electromagnetic actuators used in the conventional design dissipate energy in the form of heat when the control circuit is energized. In practice, the heat generated by many contactors installed in close proximity within a control cabinet must be actively managed by a cooling system to mitigate damaging temperature levels. This additional cooling equipment incurs additional investment, operating and service costs.

It is a further objective of the present invention to propose an improved electrical switching device with less energy dissipation.

This objective is achieved by an electrical switching device according to claim 9.

An electrical switching device according to the invention comprises an electrical conductor, the electrical conductor assembly including a stationary contact assembly and a movable contact assembly, the movable contact arrangement being separate from the stationary contact arrangement in a first state of open contacts, and the movable contact arrangement being in contact with the stationary contact arrangement in a second state of closed contacts, and a contact actuator operably interfaced with the movable contact assembly, the contact actuator comprising an electroactive polymer transducer in a stack configuration, whereby the stack configuration has a fixed end and a movable end, said movable end forming a coupling zone for being coupled to the movable contact assembly.

The advantage is an electrical switching device which does not generate significant amounts of heat while energized, and therefore total ownership costs is reduced. This is achieved according to the invention in that the contact actuator of the electrical switching device comprises an electroactive polymer in a stacked configuration.

According to this suggestion, dielectric elastomer actuator technology is for the first time applied in the domain of electrical switching devices such as contactors and circuit breakers. For the purpose of the proposed solution, a DEA configuration in form of a stacked configuration has been proposed. Such a configuration has a good balance of output force and stroke capability.

In the application case of low-voltage switching devices, electroactive polymer materials in suitable stack configurations will require typically strains of approximately 7%, corresponding to strokes in the range of 1 - 2 mm approximately, at loads of approximately 5 N. This can be achieved with an input voltage applied to the electroactive polymer stack in the range of 1 kV DC voltage, maybe more or less depending on the detailed geometrical and mechanical requirements.

It is known that driving currents for DEA are very low and the device is electrostatic in nature, thus it ideally only consumes power during thickness reduction and not in the holding state. In practice small leakage currents are observed, although they are typically much less than those associated with conventional electromagnetic actuators and therefore increased energy efficiency is still anticipated.

It is a further objective of the present invention to propose an electrical switching device with an improved EAP based actuator.

This objective is achieved by an electrical switching device according to claim 10. According to the invention, an electrical switching device has an electroactive polymer transducer, which has a first and a second stack configuration, whereby the coupling zone is coupled to the movable contact assembly.

According to an advantageous embodiment of the invention, the contact actuator has a contact lever which is coupled to the movable contact assembly, and the contact lever is operably coupled to the coupling zone.

According to an advantageous embodiment of the invention, the switching device has a contact spring arrangement for applying a contact force to the movable contact arrangement in the second state of closed contacts.

According to an advantageous embodiment of the invention, the switching device has a bias spring arrangement pre-loading the stack configuration in the first state of open contacts towards the second state of closed contacts.

According to an advantageous embodiment of the invention, the stack configuration in the first state of open contacts interacts with the contact lever, against the restoring force of the bias spring arrangement, to keep the movable contact assembly separated from the fixed contact assembly.

The invention will now be described in more detail with reference to preferred embodiments of the invention shown in the figures.

It is shown in

Figure 1 : prior art: Operating principle of dielectric elastomer actuator.

Figure 2: prior art: stacked configuration of an electroactive polymeric transducer

Figure 3. operating principle of the complementary stack arrangement according to the invention

Figure 4: a first embodiment of an Electronic Control Unit (ECU) to be used with a electroactive polymeric transducer in complementary stack arrangement according to the invention,

Figure 5: a second embodiment of an Electronic Control Unit (ECU) to be used with a electroactive polymeric transducer in complementary stack arrangement according to the invention,

Figure 6: a third embodiment of an Electronic Control Unit (ECU) to be used with a electroactive polymeric transducer in complementary stack arrangement according to the invention,

Figure 7: Scheme of bidirectional energy transfer system,

Figure 8: a first embodiment of a bidirectional energy transfer system,

Figure 9: a second embodiment of a bidirectional energy transfer system,

Figure 10: a third embodiment of bidirectional energy transfer system,

Figure 1 1 : a first embodiment of an electrical switching device according to the invention, called lever arm design,

Figure 12: a second embodiment of an electrical switching device according to the invention, called slider design,

Figure 13: a third embodiment of an electrical switching device according to the invention, called vacuum interruptor design,

Figure 14: a fourth embodiment of an electrical switching device according to the in- vention, lever arm design with bias spring

Figure one shows the basic operating principle of an electroactive polymer transducer, schematically illustrated in a single sandwich-like cell. A thin film 1 of an electroactive polymer material is coated on both sides with a compliant electrode 2, 2', forming a capacitor structure. With no electric field applied between the electrodes 2, 2', figure 1 a, this is the deactivated state, the film has a thickness dO, and the cell has a width of I0.

The application of an electric field across the electrodes 2, 2', this is the activated state, schematically indicated in figure 1 b by the little arrows 3, results in an electrostatic attraction force between the opposite charges on opposing electrodes 2, 2' and repulsive forces between the like charges within each of the electrodes 2, 2'. These forces generate stress on the film 1 causing it to contract in thickness and expand in area. In figure 1 b, film thickness reduces to d < dO, and cell width increases to l> I0.

Figure 2 shows a schematic example of a stacked arrangement of 20 single cells like the one shown in figure 1 . This is the schematic basic structure of an electroactive polymer based actuator comprising electroactive polymer cells in a stacked configuration. The stacked configuration shown in figure 2 consists of a multitude, here 20, of dielectric elastomer, or electroactive polymer, actuator films, 1 through 1 n with electrodes 2, 2' through 2n, 2n', layered on top of each other. The electrodes are alternately connected between a high voltage source 4 and ground level 5. A Switch 6 is foreseen to switch between energized and deenergized state. Upon application of the voltage, when the switch is closed, an overall reduction of the stack height is achieved, coupled to an overall increase of stack width. When the stack is coupled to an external load, it works like an actuator and can be harnessed to perform mechanical work. An actuator with a stacked configuration as shown in figure 2, can perform actuation only in one direction. Imagine the upper cell with film 1 and electrodes 2, 2' was fixed, then in the activated state the lowest cell with film 1 n and electrodes 2n, 2n' would move upwards, in direction of arrow P.

Looking now at figure 3, this shows the operating principle of the complementary stack arrangement according to the invention. The novel configuration features a stacked ElectroActive Polymer (EAP) actuator 10 having a first section 1 1 and a second section 12. Both sections 1 1 , 12 are complementary sections that are individually actuated. In this configuration, three stable actuator positions are realizable using on- off control in combination with ancillary drive electronics, see partial figures 3a, 3b, 3c.

The first section 1 1 is a first stack configuration 1 1 , and the second section 12 is a second stack configuration 12. Each stack configuration 1 1 , 12 has a multitude of electroactive polymer layers, only one of the layers is highlighted with a reference sign 13 in figures 3a, 3b and 3c for better clearness. The layers 13 are layered on top of each other, with electrodes 14 disposed between adjacent layers 13 of electroactive polymer, whereby the electrodes 14 of each stack configuration 1 1 , 12 are alternately interconnected to form an electrode arrangement with two interlaced electrode configurations 15, 16 and 15', 16'. The interlaced electrode configurations 15, 16, 15', 16' here are designed to form an interdigital structure.

Each stack configuration 1 1 , 12 has a fixed end 17 and a movable end 18, 18'. A first fixed end 17 is the fixed end of the first stack configuration 1 1 , and a second fixed end 17' is the fixed end of the second stack configurationi 2. The first and the second fixed ends 17, 17' are fixed relatively to each other. A first movable end 18 is the movable end of the first stack configuration 1 1 , and a second movable end 18' is the movable end of the second stack transducer 12. The first and second movable ends 18, 18' are coupled together to form a coupling zone 19 for coupling to an external load, such as for example the contact lever of a switch.

The first stack configuration 1 1 and the second stack configuration 12 have an elongated orientation each, with the fixed end 17, 17' and the movable ends 18, 18' positioned at the small sides of the elongated arrangement. The elongated arrangement may be a cylindrical shape, or an elongated cubic shape, for example.

The electrode interconnections are located at long sides of the elongated arrangement positioned oppositely to each other.

The outer surface of the first and the second stack configuration are aligned with each other.

The electrical point of contact to each of the electrode configurations is provided at a long side of the elongated arrangement. In the figure, T1 is the electrical point of contact to the electrode configuration 15, T2 is the point of contact to the electrode configuration 16, T3 is the point of contact to the electrode configuration 15', T4 is the point of contact to the electrode configuration 16'. Figure 3a shows the neutral state. Both stack configurations 1 1 , 12 are deenergized. The coupling zone 19 is in the neutral position. In Figure 3b a state is shown where the lower stack configuration 12 is energized. It increases in diameter, the coupling zone 19 is pulled down, in direction of the arrow P1 .Accordingly, the upper stack configuration 1 1 is elongated, some of the energy applied to the lower stack configuration is stored as elastic energy in the upper stack configuration 1 1 . Figure 3c shows the complimentary state. Here the upper stack configuration 1 1 is energized, the coupling zone 19 moves upward in direction of arrow P2. A part of the energy applied to contract the upper stack configuration 1 1 is stored in the lower stack configuration as elastic energy by elongating the lower stack configuration 12.

The advantages of this configuration are that energy is not consumed when the actuator is maintained in the central position, and that energy can be recovered when switching between the two extreme positions, improving the overall system efficiency. This is because when changing from the state of figure 3b to the complimentary state of figure 3c, the elastic energy stored in the upper stack configuration 1 1 in figure 3b is recovered and supports the contraction of the upper stack configuration 1 1 when transforming from the state of figure 3b to the state of figure 3c.

The main advantage of the proposed complementary dielectric elastomer - or elec- troactive polymer - stacked actuator arrangement technology is the improved efficiency with respect to conventional singly connected stacked dielectric elastomer actuators, for use in three-position relays and switches. This improved efficiency not only reduces the electric power required to operate the device, which by itself is an environmental benefit, but more importantly significantly reduces the amount of heat dissipated by the device so that external heat management systems are no longer required, and thus overall system costs are reduced. Additional benefits of using dielectric elastomer actuators include their potentially low production costs and strategic independence from raw materials such as copper and ferromagnetic materials, which are widely used in state-of-the-art electromagnetic actuators. Finally, the inherent compliance of the elastomer-based actuator may introduce damping into the mechanism which could aid in the suppression of the contact bouncing phenomena well- known in the art. The proposed novel configuration features a stacked ElectroActive Polymer (EAP) actuator having two complementary sections 1 1 , 12 that are individually actuated. In this configuration, three stable actuator positions are realizable, see figures 3a, 3b, 3c, using on-off control in combination with ancillary drive electronics. The

advantages of this configuration are that energy is not consumed when the actuator is maintained in the central position and that energy can be recovered when switching between the two extreme positions, improving the overall system efficiency.

For energizing an electroactive polymer transducer according to the invention, there is provided an electronic control unit electrically connected to each of the points of contact to each of the electrode configurations, configured for alternatingly energizing each of the stack configurations by applying a high DC voltage difference between the two electrode configurations of each of the stack configurations, and for deenergizing each of the stack configurations by switching off the DC voltage difference between the two electrode configurations. The Electronic Control Unit serves for converting an input voltage applied to the electroactive polymer transducer into the required high DC voltage DC for the electroactive polymer stack

configuration.

The two stacked sections 1 1 , 12 can be powered by one Electronic Control Unit.

An electroactive polymer transducer according to claim 6, having one electronic control unit to energize and deenergizer both the first and the second stack

configuration. The two stacked sections 1 1 , 12 can in an alternative embodiment also be powered by two Electronic Control Units capable of controlling the voltage of each individual stack section 1 1 , 12 separately.

The different options for designing an electronic control unit for controlling the complementary electroactive polymer stack transducer are now explained with reference to the figures 4 to 10.

The proposed system consists of a complementary connection of two electroactive polymer (EAP) actuators 1 1 , 12 of the stacked dielectric elastomer type. The two stacked sections 1 1 , 12 are powered by one or two electronic control units (ECU) capable of controlling the voltage of each individual stack section 1 1 , 12. Different options can be considered for the electronic control unit:

First option is to provide an independent step-up converter 20, 21 and driving circuit 22, 23 for each stack section 1 1 , 12, see figure 4. This is a simple ECU configuration. It consists of two individual step-up converters 20, 21 connected to the EAP stack sections 1 1 , 12 by means of two independent driving circuits 22, 23. In such a configuration the EAP energy is simply discharged into a resistor 25, 26 when the EAP has to be quickly discharged, without regard for energy recovery.

Second option is to provide a single step-up converter 20' with independent driving circuits 22', 23' without energy storage, see figure 5. The second proposed ECU configuration consists of a single step-up converter 20' connected to the two different EAP stack sections 1 1 , 12 by means of two independent driving circuits 22', 23'. The system complexity is slightly reduced but the overall efficiency remains similar to the first configuration since the energy stored in the two EAP stack sections 1 1 , 12 is simply dissipated into the resistors 25, 26 connected in parallel to the stack sections.

Third option is to provide a single step-up converter 20" with independent driving circuits 22", 23" with energy storage 24, 24', 24", see figure 6. Here a more flexible ECU is proposed. In such a configuration an ECU topology consisting of a single step-up converter 20" is proposed together with an energy storage solution. Three energy storage topologies 24, 24', 24" can be imagined: one 24' before the step-up converter 20", one 24 after this stage, or 24" directly in parallel to the stack sections 1 1 , 12.

The choice of the circuit should be done based on the voltage level, the amount of energy to be stored / transferred and the expected savings.

Regardless of which ECU configuration is employed, the complementary actuator system is capable of three stable output positions as shown in figure 3, where mechanical work is performed on the external mechanical system via the motion of the central stack coupling zone 19.

Three different ECU examples are proposed hereafter using a bidirectional energy transfer system to store the EAP energy in a storage device 24a consisting for instance in a capacitor bank or in a combination of capacitor bank plus battery. The bidirectional energy transfer system could simply consist in a switch connected in series with a diode and an inductance as shown in the figure below. The two parallel circuit branches provide the bidirectional system capabilities, see figure 7.

The first example offers relatively high flexibility but at the expense of more compli- cated topology, see figure 8. Two ECUs are connected to the two complementary stack sections 1 1 , 12. The bidirectional energy transfer provides the interface between the EAPs and an energy storage device 24a. By suitably controlling the overall system, the following operations are possible:

Firstly, the two electronics control units 27, 28 can be used to regulate the voltage across the stacks 1 1 , 12, for example performing position or speed control.

Secondly, the two bidirectional energy transfer systems 29, 30 can be controlled to save the exceeding energy during the discharge process of the two EAP stack sections 1 1 , 12.

Thirdly, the energy can also be transferred from one EAP to the other in case of alternative operations.

The second example, see figure 9, is based on the same idea but focuses on a more specific application. No energy storage solution is implemented. The energy is transferred from one stack section 1 1 to the other 12 by means of the bidirectional interface 29.

The two EAPs 1 1 , 12 can be controlled to perform the following operations:

Firstly, the two ECUs 27, 28 can regulate the voltage across the two EAP stack sections 1 1 , 12.

Secondly, the bidirectional interface 29 can be controlled in order to charge one EAP stack section 1 1 and simultaneously discharge the other 12. Alternative compression and relaxation of the two stack sections 1 1 , 12 is therefore possible without using a passive element like a parallel resistor for discharging purposes;

Thirdly, in case fast discharging of both stack sections 1 1 , 12 is required ,a passive element such as a resistor would need to be included in parallel to the two EAP stack sections.

The main benefit of the described solution is to combine a relatively simple solution in terms of topology with a rather good efficiency especially when alternative operations of the two stack sections 1 1 , 12 are considered.

The third alternative consists of only one ECU 27' with an energy storage solution, see figure 10. The ECU 27' is connected in parallel to the energy storage 24"'. The bidirectional interface 29', 30' is responsible for transferring the energy from the stor- age device 24"', such as a capacitor or battery, to the EAP stack sections 1 1 , 12 and vice versa. The overall system can operate as follows:

Firstly, the ECU 27' can regulate the voltage across the energy storage 24"'.

Secondly, the energy can be transferred from the storage 24"' to the two EAP stack sections 1 1 , 12 and back by means of the two bidirectional interfaces. 29', 30'

In such a solution the EAP voltage level cannot be independently regulated for the two stack sections.

Now looking at figures 1 1 to 14.

An electrical switching device 40 is shown, comprising an electrical conductor assembly, the electrical conductor assembly including a stationary contact assembly 41 and a movable contact assembly 42, the movable contact arrangement 42 being separate from the stationary contact arrangement 41 in a first state of open contacts, see figures 1 1 a, 12a. The movable contact arrangement 42 is in contact with the stationary contact arrangement 41 in a second state of closed contacts, see figures 1 1 b and 12b. There is further a contact actuator 43 operably interfaced with the movable contact assembly 42. The contact actuator 43 comprises an electroactive polymer transducer 44 in a stack configuration, whereby the stack configuration has a fixed end 45 and a movable end 46, said movable end 46 forming a coupling zone for being coupled to the movable contact assembly 42.

The electroactive polymer transducer 44 can have a first and a second stack configuration as described above. Here in the figures 1 1 to 14 for clarity purposes only on of the stacks is shown. The coupling zone 19 is coupled to the movable contact assembly 42.

The contact actuator has a contact lever 47 which is coupled to the movable contact assembly 42, and whereby the contact lever 46 is operably coupled to the coupling zone 19.

In the embodiment shown in figure 14, there is a contact spring arrangement 48 for applying a contact force to the movable contact arrangement 42 in the second state of closed contacts. In the embodiment shown in figure 14, there is also a bias spring arrangement 49 pre-loading the stack configuration 43 in the first state of open contacts towards the second state of closed contacts.

The stack configuration 43 in the first state of open contacts interacts with the contact lever 47, against the restoring force of the bias spring arrangement 49, to keep the movable contact assembly 42 separated from the fixed contact assembly

Two representative concepts for the implementation of an electroactive polymeric (EAP) transducer in electrical contactors are provided in Figure 1 1 and Figure 12. In each case the arrangement is shown for contactors that are normally open, however similar normally closed configurations are also realizable. These embodiments also indicate the use of return springs to disengage the contacts when the EAP is discharged, however embodiments which utilize the inherent stiffness of the elastomer actuator to disengage the contacts are also possible. In all cases, the ancillary electrical apparatus to energize and de-energize the EAP are not shown.

In the first embodiment, see figure 1 1 , the electromagnetic actuator present in conventional designs has been replaced by a stacked EAP. Upon activation by a suitable applied voltage, the stack contracts and acts on a lever arm. The lever arm acts on the contact carriage in a manner that engages the electrical contacts.

Upon de-energizing the EAP, the return springs, or inherent stiffness of the EAP stack, disengage the contacts and open the load circuit.

In the second embodiment, see figure 12, the motion of the contact carrier is constrained by a slot or other general guiding feature to maintain its orientation. The EAP acts directly on the carrier without the use of the lever arm. The carrier is guided by the housing on opposing sides to maintain the carrier orientation while facilitating ease of assembly.

The concept of applying EAP to electrical switches is not limited to contactors. An additional variation illustrating an embodiment for use in circuit breaker arrangements typical in medium- and high-voltage products is provided in Figure 13. In this arrangement, a stacked DEA is employed to drive the movable contact of a conventional vacuum interrupter 50. The schematic is not to scale, and the benefits of using EAP here include potential cost savings and that the inherent compliance of the elastomer-based actuator may introduce damping into the mechanism which could aid in the suppression of the contact bouncing phenomena well-known in the art.

In order to actuate a stacked electroactive polymer transducer, such as it has been proposed to use as contact actuator in an electrical switching device, a sufficiently high electrostatic field is required. To generate the electrostatic field, a sufficiently high voltage in the range of 1 kV, maybe more, maybe less, depending on the geometry and the required mechanical properties such as strain-, stroke-, force requirements, will have to be applied to the electrodes of the electroactive polymer stack configuration.

List of reference signs thin film

n thin film

electrode

' electrode

n electrode

n' electrode

electric field

high voltage source

ground

switch

0 stacked EAP actuator

1 first section

2 second section

3 layer

4 electrode

5 electrode configuration

5' electrode configuration

6 electrode configuration

6' electrode configuration

7 fixed end

7' fixed end

8 movable end

8' movable end

9 coupling zone

0 step-up converter

0' step-up converter

0" step-up converter

1 step-up converter

2 driving circuit

2' driving circuit

3 driving circuit

3' driving circuit

4 energy storage

4' energy storage

4" energy storage

4"' energy storage

4a energy storage

5 resistor

6 resistor

7 electronic control unit

7' electronic control unit

8 electronic control unit

9 bidirectional energy transfer system9' bidirectional energy transfer system0 bidirectional energy transfer system0' bidirectional energy transfer system0 electrical switching device

1 stationary contact assembly

2 movable contact assembly contact actuator

electroactive polymer transducer fixed end

movable end

contact lever

contact spring

bias spring

vacuum interruptor