Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
  • H02N11/00—Generators or motors not provided for elsewhere; Alleged perpetua mobilia obtained by electric or magnetic means
  • H02N11/006—Motors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
  • H10N30/204—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
  • H10N30/2047—Membrane type
  • H10N30/2048—Membrane type having non-planar shape
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/88—Mounts; Supports; Enclosures; Casings
  • H10N30/886—Additional mechanical prestressing means, e.g. springs

Definitions

• the invention relates to an actuator comprising a frame, with an aperture and a polymer attached to the frame.
• Electro-active polymers and their use in connection with actuators for converting electrical energy to mechanical energy and vice versa are known from various disclosures, such as WO 2005/081676, US 2004/263028, US 6812624, and US 6545384.
• the basic principle of the solution is that an elastomeric polymer is sandwiched between two compliant electrodes. When a voltage difference is placed across the top and bottom electrodes, the polymer is squeezed in thickness and stretched in area by the electric field pressure. This basic principle is applied to various actuators as disclosed in the disclosures mentioned above.
• WO 2004/092581 discloses a bimorph actuator.
• the actuator comprises a substrate on top of which a film of a shape memory alloy material is deposited.
• the substrate is a polymer film.
• An object of the invention is to provide a new type of an actuator.
• the actuator of the invention is characterized in that the polymer is attached to the frame such that it extends over the aperture and is attached to the frame from its edges, that the frame is elastic and springy and that the material of at least one of the polymer and frame is such that it can be influenced to change its physical dimensions and/or state of tension, whereby influencing at least one of the polymer and frame causes the frame to make an out-of-plane movement.
• the idea of the disclosed structure is that polymer is attached to a frame comprising an aperture.
• the frame is elastic and springy, whereby the frame and the polymer form a spring and counter-spring structure.
• the material of at least one of the polymer and frame is such that it can be influenced to change its physical dimensions and/or state of tension and influencing at least one of the polymer and frame causes an out-of-plane movement in the actuator.
• the structure of such an actuator is simple and yet the movement of the actuator is rather large.
• the polymer is an electro-active polymer, whereby the polymer is sandwiched between compliant electrodes and the polymer is influenced by applying a voltage difference across the electrodes.
• the polymer is pre-stretched before the frame is attached to the polymer, whereby the polymer causes the frame to change its form from that it had before it was attached to the polymer. Influencing at least one of the polymer and frame causes the frame to move to the form it had before the polymer was attached to the frame.
• the frame comprises a first spring force and the pre-stretched polymer comprises a second spring force opposite to the first spring force.
• the actuator is spring- loaded, and controlling the spring force of at least one of the frame and the polymer causes a rather wide, strong and fast movement of the actuator.
• the frame is planar before it is attached to the polymer, and the pre-stretched polymer draws the frame out-of-plane.
• Influencing at least one of the polymer and frame causes the actuator to move towards the planar form.
• the movement of the actuator is controlled.
• the frame is made stiff at certain parts preferably by arranging stiffening parts in the frame, such that the form of the actuator and the path of the movement is accurate.
• the stiff frame pieces also help to improve the pre- strain such that the polymer becomes larger and thinner, which improves the actuation properties of the actuator, when the active polymer material is a dielectric elastomer.
• Figure 1a schematically shows a top perspective view of a transducer before application of voltage
• Figure 1 b schematically shows a top perspective view of a transducer after application of voltage
• Figure 2 schematically shows a top view of a frame
• Figure 3 schematically shows a top view of an actuator before application of voltage
• Figure 4 schematically shows a side view in cross-section along line A - A in Figure 3;
• Figure 5 shows the actuator of Figure 4 after application of voltage
• Figure 6 schematically shows a top view of a second frame
• Figure 7 schematically shows a top view of a third frame.
• Figures 1a and 1 b illustrate a basic principle utilized in connection with the actuator.
• Reference numeral 1 denotes a polymer for conversion between electrical energy and mechanical energy.
• a first electrode 2 and a second electrode 3 are attached to the electro-active polymer 1 on its top and bottom surfaces, respectively, to provide a voltage difference across a portion of the polymer 1.
• the electrodes 2 and 3 and the electro-active polymer 1 together form a transducer.
• the polymer 1 deflects with a change in electric field provided by the first and second electrodes 2 and 3. As the polymer 1 changes in size, the deflection may be used for producing mechanical work.
• Figure 1 b is a top perspective view illustrating the transducer including deflection in response to a change in electric field.
• deflection refers to any displacement, expansion, contraction, torsion, linear or areal strain, or any other deformation of a portion of the polymer 1.
• the change in electric field corresponding to the voltage difference produced by the electrodes 2 and 3 produces mechanical pressure within the polymer 1.
• the different electrical charges produced by the electrodes 2 and 3 are attracted to each other and provide a compressive force between the electrodes 2 and 3, and an expansion force on the polymer 1 in planar directions 4 and 5, causing the polymer 1 to compress between the electrodes 2 and 3 as well as stretch in the planar directions 4 and 5.
• the electrodes 2 and 3 are compliant and change their shape with the polymer 1.
• the configuration of the polymer 1 and the electrodes 2 and 3 provides increasing polymer 1 response with the deflection. More specifically, as the transducer deflects, the compression of the polymer 1 brings the opposite charges of the electrodes 2 and 3 closer and the stretching of the polymer 1 separates similar charges in each electrode.
• the transducer continues to deflect until mechanical forces balance the electrostatic forces driving the deflection.
• mechanical forces include elastic restoring forces of the polymer 1 material, the compliance of the electrodes 2 and 3, and any external resistance provided by a device and/or load coupled to the transducer.
• the resultant deflection of the transducer, as a result of the applied voltage, may also depend on a number of other factors, such as the dielectric constant of the polymer 1 and the size of the polymer 1.
• the electro-active polymer 1 can be pre-strained.
• a pre-strain of a polymer may be described in one or more directions as a change in dimension in that direction after pre-straining relative to the dimension in the direction before pre-straining.
• the pre-strain may comprise elastic deformation of the polymer 1 and may be formed, for example, by stretching the polymer in tension and fixing one or more of the edges while stretched.
• the pre-strain improves conversion between electrical and mechanical energy.
• the pre-strain allows the electro-active polymer 1 to deflect more and provide greater mechanical work when converting electrical to mechanical energy.
• Figure 2 shows a frame 6.
• the frame 6 is elastic and springy.
• the frame 6 is made, for example, from a polyethylenetereftalate PET foil.
• the thickness of the foil may vary, for example, between 50 and 500 ⁇ m.
• the material of the frame 6 may also be another suitable springy and elastic material. However if the frame is rather thin, the elastic modulus of the material does not have to be rather low.
• the required elastic properties of the material and the structure of the frame also depend on the elastic properties of the polymer.
• An aperture 7 is formed into the foil by removing the center of the foil, for example, with a sharp cutter.
• the stiffening pieces 8 are glued to the frame 6.
• the stiffening pieces 8 may be made, for example, from the same material as the frame 6. Thus, the parts where the stiffening pieces are situated are more rigid because the total thickness of the frame is greater in those parts.
• Parts of the frame may be made stiff also by making the frame 6 thicker in some parts or by using stiffening wires or rods, or by using another suitable method.
• the foil of the electro-active polymer material 1 is shown in Figure 2 in broken lines.
• the foil of the electro-active polymer material 1 can be, for example, a polyacrylic pressure-sensitive adhesive tape having a trade name VHB 4910 and manufactured by a company called 3M.
• the electro -active polymer is preferably a dielectric elastomer. Suitable materials are, for example, silicone, polyurethane, polyacrylate, natural rubber, latex, isoprene, etc. It is preferable, that the material has a rather large possible strain. If the material is not adhesive as such, glue must be added between the frame and the polymer.
• the electro-active polymer 1 sheet is pre-stretched, and the frame 6 is glued on to the pre-stretched polymer 1 sheet.
• the polymer 1 can be pre-stretched five times by five times such that a pre-strain of 400% by 400% is achieved.
• the pre-strain may be, for example, up to 600% by 600%.
• the actuator will also work with a considerably lower pre-strain.
• the frame 6 is glued to the pre-stretched film of the polymer material 1 in a planar manufacturing step.
• a flat foil frame piece is placed on top of the pre-stretched glue tape of the polymer material 1. The gluing is allowed to proceed slowly and completely with little or no intervention.
• compliant electrodes 2 and 3 can be made, for example, by percolating carbon black or metal particles in a matrix of rubber or grease. Another suitable method for making compliant electrodes can also be used. For example, it is possible to use metal film electrodes, which have the advantage that they can be made self-healing.
• the electrodes 2 and 3 are connected to an electric power source by copper wires, for example.
• an actuator 9 takes the form illustrated in Figures 3 and 4.
• the actuator 9 When the stretched polymer 1 is released, the actuator 9 is left to find its lowest energy state. If the frame 6 is provided with no stiffening pieces 8, the form of the actuator probably becomes quite complex and asymmetrical. In one experiment the actuator had a shape having two waves along the rim, and the actuator was quite curved. The stiffening pieces 8 selectively impede the bending motion in certain parts of the frame. This provides the feature that the motion of the actuator is directed so more practical actuator applications are achieved.
• the frame 6 in Figure 2 has an outer side length of 50 mm and an inner side length of 30 mm the rim width thus being 10 mm.
• the stiffening pieces 8 constitute two of the arms of the frame stiffer. Thus, these arms have a bending modulus, which is much higher than that of the arms denoted by reference numeral 6a.
• the arms 6a having no stiffening pieces 8 form soft hinges. These hinges are springy so that the structure of the actuator 9 becomes inherently spring-loaded.
• the actuator 9 tends to move to the form shown in Figures 3 and 4.
• the voltage difference between the electrodes 2 and 3 may vary for example between 0 kV and 8 kV. The higher the voltage, the flatter the actuator 9. The largest possible actuation strain resides at the position where the actuator 9 becomes flat.
• the bending part i.e. the arms 6a
• the area of the aperture 7 also increases, which results in an increase in the initial amount of elastic energy such that more energy can be released through deformation.
• the actuator 9 bends more open, and as such this actuator 9 shape behaves like a bending segment.
• a smaller frame was more prone to opening.
• the smallest frame also had the largest relaxed bending angle.
• the bending angle may also be varied by changing the width of the bending arms 6a of the frame 6. The wider the bending arms 6a, the stiffer the frame and, therefore the less able to bend.
• Figure 6 shows a shape for the frame 6, which is formed such that two circles of the same size are punched out of a foil with a certain distance between the circles. The remaining notches inside the frame 6 are trimmed with a sharp cutter. The stiffening pieces 8 are formed such that a hole was punched in a square piece and the piece was then cut in half. The foil frame 6 is then glued to the pre-strained polymer 1 and the stiffening pieces 8 are glued to the frame 6.
• Figure 7 shows a structure in which the frame 6 has a circular shape.
• the frame 6 is glued on the pre-strained polymer 1 and the polymer is released and the actuator is left to find its own minimum energy shape.
• the pre-stretched polymer bends the frame such that the outer diameter of the frame 6 decreases.
• the shape of the circular frame 6 comes about as a balance between the contracting stress of the pre- stretched polymer 1 and the bending stress of the frame 6.
• the application of a voltage potential difference between the electrodes 2 and 3 diminishes the compressive effect of the polymer 1.
• the outer diameter of the actuator varies in size between the lowest and highest voltage.
• a side view of such an actuator also shows a size variation from a totally flat object to a curled up object.
• the height of an object may vary, for example, from 0,5 mm to 25 mm.
• the bending of the frame 6 becomes achievable with the elastic energy available in the pre-stretched polymer 1.
• Tuning of the shape and dimensions as the frame 6 results in slight to drastic differences in the self- organized shape of the actuator 9.
• Use of selective stiffening parts of the frame 6 results in a directed actuation output, and shape optimization may result in improved actuation strain properties.
• the circular form of the frame 6 disclosed in Figure 7 provides a shape expansion feature and, for example, the frame shapes disclosed in Figures 2 and 6 provide a bending segment actuator.
• the maximum actuation force achievable is probably equal to the force required to bend the actuator when no polymer 1 is present.
• the initial shape of the frame is flat.
• the frames initially pre-curved to a certain shape thus selectively releasing the bending energy in other parts of the frame. This may selectively stiffen certain part of the frame.
• the polymer 1 is free-standing in the sense that it is not laminated or glued to another strip leaving it free to move with large strains.
• the polymer 1 is fixed to the frame 6 such that it extends over the aperture 7 of the frame 6 and is fixed to the frame 6 only from its edges.
• the polymer 1 is not attached to a substrate that would fix it so that it could not undergo large strains. Because the polymer 1 is free-standing it may store and release substantially larger amounts of elastic energy compared to a polymer that is attached to a substrate.
• the frame may comprise more than one aperture.
• the apertures may have any shape.
• the frame may have any shape and also the stiffening pieces may have any shape.
• the polymer is passive and the frame is active, which means that the frame is influenced for actuating the actuator.
• the bending part 6a of the frame could be made from an active material and the actuator is spring-loaded by the elastomeric polymer.
• the polymer may be, for example, a temperature sensitive elastomer or a light sensitive elastomer. In such a case, the polymer is then influenced by heating it or by light respectively.
• the solution is not restricted to a specific actuation mechanism.
• the polymer can be sensitive to one or more of the following variables: electricity, heat, light, humidity, concentration of specific chemical compounds, magnetism, etc.

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Citations (5)

• 2006
  • 2006-02-24 FI FI20065135A patent/FI119538B/sv active IP Right Grant
• 2007
  • 2007-02-23 WO PCT/FI2007/050098 patent/WO2007096477A1/en active Application Filing

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