Method and device for quality-optimised and output-optimised production of dielectric elastomer actuators
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-05-17
- Publication Date
- 2026-04-08
AI Technical Summary
Dielectric elastomer actuators often suffer from defects during production, leading to reduced yield and potential electrical breakdowns due to thickness fluctuations and impurities, which can result in permanent short circuits and unusable actuators, especially in multi-layer systems.
A method involving testing dielectric strength with a controlled test voltage, locating defects optically, and repairing them using a curable adhesive or repair film to ensure the dielectric elastomer actuator film meets the necessary field strength requirements for actuator operation.
This method effectively detects and repairs defects during production, enhancing the reliability and yield of dielectric elastomer actuators by ensuring they meet the required dielectric strength, preventing electrical breakdowns and enabling their use in actuator and sensor applications.
Smart Images
Figure EP2024063804_05122024_PF_FP_ABST
Abstract
Description
[0001] Method and device for the quality and yield-optimized production of dielectric elastomer actuators
[0002] Technical area
[0003] The invention relates to a method and a device for producing dielectric elastomer actuators (DEA).
[0004] Technical background
[0005] Similar to piezoelectric actuators, elastomer actuators enable a change in mechanical properties by applying an electrical voltage. Typically, such elastomer actuators are formed with a dielectric, elastic polymer layer in the form of a film or similar, often with a silicone-based polymer material, sandwiched between two opposing, electrically conductive electrode surfaces. The electrode surfaces are also elastically deformable and can be formed, for example, with a polymer matrix into which electrically conductive particles are incorporated. Suitable materials for the electrically conductive particles include conductive carbon black, metal dust, or carbon nanotubes.
[0006] The elastomer actuators are controlled by a voltage applied to the opposing electrode surfaces. The resulting electric field leads to an electrostatic force of attraction between the two electrode surfaces, which acts on the elastic polymer layer, thereby deforming it and reducing its thickness, while simultaneously increasing its surface area due to material displacement. In recent years, such elastomer actuators have attracted attention because they can replace conventional compressed air-controlled, piezoelectric, or magnetically controlled actuators thanks to their energy-efficient and low-noise operation with sustainable materials that, for example, do not contain rare earths.
[0007] In order to achieve a deformation significant for actuator purposes, it is necessary to apply voltages in the lower kilovolt range to a typical thickness of polymer layers in the range between 20 and 200 pm in order to achieve electric field strengths in the range of 100 V / pm.
[0008] Due to thickness variations or embedded impurities, local defects may occur during the manufacturing of such elastomer actuators. These defects can cause electrical breakdown at typical operating voltages or reduce the breakdown field strength, making it impossible to achieve the field strengths required for operation.
[0009] A breakdown through the dielectric layer leads to a defect, which causes a permanent electrical short circuit and thus prevents use for actuator and sensor purposes. Especially when such electrical elastomer actuators are designed as multilayer systems made of stacked elastomer actuator foils, the yield of such elastomer actuators can be significantly reduced, since even a single defect can render the entire elastomer actuator unusable.
[0010] It is therefore an object of the present invention to provide a method for producing an elastomer actuator film which enables the detection and repair of such defects in the early phase of the production of such elastomer actuators and can be reliably used for further processing.
[0011] Disclosure of the invention
[0012] This object is achieved by the method for producing a dielectric elastomer actuator film according to claim 1 and a corresponding device according to the independent claim. Further embodiments are specified in the dependent claims.
[0013] According to a first aspect, a method for producing a dielectric elastomer actuator with an elastomer actuator film is provided, comprising the following steps:
[0014] Providing the elastomer actuator film comprising a dielectric elastic polymer layer coated on one side with a conductive electrode layer;
[0015] Testing a breakdown strength of the elastomer actuator film by applying a test voltage to form a field strength in the dielectric layer that is below a breakdown field strength of the material of the dielectric layer;
[0016] Localizing at least one breakthrough point using an optical method;
[0017] Repairing the at least one localized breakthrough point by applying a curable adhesive and / or applying a repair film to a side of the dielectric layer opposite the electrode layer.
[0018] In the following, a dielectric elastomer actuator film is defined as a dielectric elastic polymer layer coated on one or both sides with electrically conductive material, which can be designed in particular as a film or other flat material. At least one electrode layer is applied to the dielectric layer. The elastomer actuator film is a flat structure with a thickness of preferably between 20 μm and 500 μm, and particularly preferably between 20 μm and 50 μm. Suitable materials for the dielectric elastic polymer layer include polymers such as polyacrylic, polydimethylsiloxane (silicone), polyurethane, and rubber materials, as well as thermoplastic elastomer gel.
[0019] The electrode layer can be formed by applying an initially liquid electrode material, e.g., by screen printing, dispensing, or the like. After application, the electrode material is cured or solidified so that it is firmly bonded to the dielectric layer. These elastomer actuator films can be further processed into dielectric elastomer actuators (DEA) through appropriate additional steps, either as a monolayer or by stacking, rolling, or folding to form multilayer systems or the like. The electrode material can preferably be formed with electrically conductive particles embedded in a polymer. The electrically conductive particles can comprise conductive carbon black, graphite, CNTs (carbon nanotubes), metal particles, or comparable substances whose concentration / particle density lies above a percolation threshold.
[0020] Since further processing of a defective elastomer actuator film can lead to unusable actuator assemblies, it is necessary to check for defects in the elastomer actuator film during or after production. Due to the materials used, such as elastic polymers such as silicones or the like, with very thin thicknesses of, for example, between 20 and 50 μm, defects are common, leading to a reduction in the breakdown field strength.
[0021] For this reason, the above method provides for the dielectric elastic polymer layer to first be provided with the electrode layer on one side, in particular by applying and curing, in order to form an elastomer actuator film.
[0022] The dielectric strength of the elastomer actuator film can be tested by applying the elastomer actuator film flatly to a flat, electrically conductive test electrode and applying a test voltage between the electrode layer and the test electrode, with the test voltage being selected depending on the thickness of the dielectric layer. For example, the test voltage can be selected such that, at the specified thickness of the dielectric layer, a field strength is established that is lower than the breakdown field strength of the material of the dielectric layer by a safety margin of, in particular, between 10 and 40%, preferably between 20% and 30%.
[0023] Alternatively or additionally, the test voltage can be selected such that the field strength in the dielectric layer is higher than a specified field strength required for subsequent actuator operation, with a safety margin of, in particular, between 10 and 40%. The test voltage can correspond to a direct voltage or an alternating voltage in the frequency range of 0.1 Hz–10 kHz.
[0024] By applying a test voltage between the test electrode and the applied electrode layer of the elastomer actuator film, the electrostatic attraction between the test electrode and the electrode layer leads to a surface contact between the uncoated surface side of the elastomer actuator film on the test electrode and the formation of an electric field through the dielectric layer.
[0025] The test voltage can be selected, as indicated above, so that the resulting field strength through the dielectric layer, in the absence of defects, is below the breakdown field strength, in particular approximately 60-90% of the breakdown field strength of the material. The test voltage can be selected so that the field strength in the dielectric layer reaches the field strength required for an actuator and that a field strength is created within the dielectric layer for which maximum dielectric strength is required. The level of the field strength to be achieved by the test voltage depends on the specific actuator application.
[0026] By applying the test voltage, the elastomer actuator foil is electrostatically attracted to the test electrode, causing the elastomer actuator foil to adhere to the electrode plate and displace any air between them. The voltage between the electrode layer and the test electrode can be continuously increased, particularly in a ramp-like manner, e.g., with a rate of increase of 200V / s - 1000V / s, up to the test voltage. This ensures that air pockets between the test electrode and the elastomer actuator foil can be avoided or reduced when the elastomer actuator foil is tightened.
[0027] At the same time, a current is measured. If a voltage breakdown occurs at a defect, this can be detected by a flowing current whose strength is significantly higher than the expected current through the electrically insulating dielectric layer. If a current above a predetermined current threshold, a so-called defect current, is detected, it is recognized that a defect is present. When testing the dielectric strength of the elastomer actuator film, it can be provided that the test voltage remains applied for a predetermined period of time, e.g., between 5 ms and 100 ms, after a breakdown is detected, or for a predetermined charge flow that depends on the thickness of the elastomer actuator film.
[0028] After a breakdown occurs at a defect, the breakdown area is initially very small, but expands as the defect current continues to flow. The voltage breakdown degrades or removes the material of the dielectric layer, resulting in a short circuit in which a current (the defect current) flows from the upper electrode to the lower flat test electrode. This causes the breakdown field strength to be exceeded over an increasingly large area.
[0029] When the flow of a defect current is detected, the breakdown point is usually not yet visible. For this reason, the flow of the defect current is maintained for a predetermined period of time to ensure that the breakdown point enlarges and is then detectable by optical means such as cameras or optical detectors. For example, after the defect current is detected, the current flow can be maintained for a predetermined period of time or until a predetermined amount of charge (time integral of the defect current) has flowed through the polymer layer.
[0030] Furthermore, the localization of breakthrough points can be carried out using optical methods, such as an optical or thermal camera or a laser reflection measurement.
[0031] After the current flow is switched off, the elastomer actuator foil is lifted from the test electrode and examined for visible breakdown points using, for example, an optical detection system. The position of a breakdown point is identified and stored for a subsequent repair step.
[0032] In a subsequent step, a repair is performed at the identified breakdown points. The repair is generally performed on the side of the dielectric layer opposite the electrode layer. The repair may involve applying an adhesive material to fill the breakdown point. When an adhesive, preferably initially liquid, is applied to the breakdown point, it is cured. After application, the adhesive can be cured, preferably using UV light or by thermal treatment.
[0033] The adhesive should, at least after curing, match those of the elastomer actuator film in terms of chemical, electrical, and mechanical properties, or deviate from them by no more than 10% in each case. In addition, the adhesive should exhibit good adhesion to the elastomer actuator film so that it does not detach from the material even at elongations exceeding 100%.
[0034] The adhesive can be applied using a dosing machine, a syringe with a stamp or a spatula, for example.
[0035] Furthermore, to repair the localized breakthrough point, a repair film (or a repair layer) made of dielectric material can be applied after the adhesive has been applied, so that it completely covers the breakthrough point and is firmly connected to the dielectric layer after the adhesive has cured. The repair film should have the same or very similar material properties as the elastomer actuator film, ie with regard to the chemical, electrical and mechanical properties, it should not deviate by more than 10% from the corresponding properties of the elastomer actuator film.The repair film corresponds to a repair piece with an area that is selected to be 10% - 1000%, preferably between 50% - 500%, particularly preferably between 100% and 200% larger than the area of the breakdown point, so that a sufficient overlap can be achieved in the surrounding edge area of the breakdown point to fix the repair film on the dielectric layer.
[0036] If the penetration point is larger, e.g. larger than 0.5 mm 2 After applying the adhesive, a repair film can be applied to the puncture area and pressed evenly, e.g., with a stamp or rod. The repair film can preferably be made of an identical material or a material with comparable properties to the polymer layer. Subsequent curing of the adhesive permanently affixes the repair film to the elastic polymer layer.
[0037] In particular, the material of the repair film can correspond to the material of the dielectric layer, and / or the thickness of the repair film can be equal to, less than, or greater than the thickness of the dielectric layer. The thickness and material of the repair film are designed to increase the dielectric strength in the area of the breakdown point to at least the dielectric strength of the dielectric layer.
[0038] Furthermore, it can be provided that a self-adhesive or adhesive repair film is applied to repair the localized breakdown point so that it completely covers the breakdown point and is firmly connected to the dielectric layer.
[0039] It can be provided that after repairing the at least one localized breakdown point, the process of testing the dielectric strength, locating a breakdown point and repairing is carried out again, in particular with the same test voltage, until no breakdown point is found for the previously selected field strength.
[0040] The elastomer actuator film can then be further processed into an elastomer actuator. Further processing can include, for a single-layer actuator, applying a further electrode layer to the as yet uncoated surface side of the dielectric layer, or forming a multilayer elastomer actuator, for example, by stacking several single- or double-sided coated elastomer actuator films or by rolling two superimposed single-sided coated elastomer actuator films so that an electrode layer of a further section of a second elastomer actuator film rests on a section of a first elastomer actuator film against the uncoated surface side of the first elastomer actuator film. According to a further aspect, a device for producing a dielectric elastomer actuator with an elastomer actuator film can be provided, the device comprising:
[0041] A device for providing the elastomer actuator film comprising a dielectric elastic polymer layer coated on one side with a conductive electrode layer;
[0042] A test device configured to test a dielectric strength of the elastomer actuator film by applying a predetermined test voltage to form a field strength in the dielectric layer that is below a breakdown field strength;
[0043] An inspection unit configured to locate at least one breakthrough point using an optical method;
[0044] A repair device configured to repair the at least localized penetration points by applying curable adhesive and / or a repair film.
[0045] Brief description of the drawings
[0046] Embodiments are explained in more detail below with reference to the attached drawings. They show:
[0047] Figure 1 shows a cross-sectional view through an elastomer actuator film;
[0048] Figures 2a and 2b show cross-sectional views of exemplary elastomer actuators;
[0049] Figure 3 is a schematic representation of an apparatus for producing elastomer actuators with a single-sided electrode layer;
[0050] Figure 4 is a flow chart illustrating the process for manufacturing the elastomer actuator;
[0051] Figure 5 shows a cross-sectional view of a repair site. Description of embodiments
[0052] Figure 1 shows a schematic representation of an elastomer actuator film 1 with a dielectric, elastic polymer layer 2, which is formed in a flat manner. The dielectric layer 2 has a thickness of preferably between 20 pm and 200 pm, in particular between 20 pm and 50 pm. Rubber materials, polyurethanes, polyacrylates, or silicones, among others, can be used for the dielectric layer. The material of the dielectric layer 2 preferably has a dielectric strength of more than 100 V / pm.
[0053] An electrode layer 3, which is essentially electrically conductive, is applied to one or both sides of the dielectric layer (as shown). The electrode layer can be electrically conductive particles embedded in a polymer matrix with a particle concentration above the percolation threshold. The particles can, in particular, contain conductive carbon black, graphite, CNTs (carbon nanotubes), and / or metal. The particles can be embedded in the polymer matrix, wherein the polymer preferably corresponds to the material of the dielectric layer 2 or can contain it. In general, the material of the electrode layer 3 can have the same or higher elasticity as that of the dielectric layer 2.
[0054] The material of the electrode layers 3 can be provided as a liquid or viscous material that can be cured by suitable treatment. Using suitable application methods, the liquid or viscous material of the electrode layers is applied, for example, using screen printing methods, in particular using a printing roller. The applied material of the electrode layer is then cured or dried by thermal treatment, UV irradiation, or in another way to form the electrode layer 3.
[0055] Figures 2a and 2b show cross-sectional views of possible elastomer actuators that can be formed with elastomer actuator films coated on one side. Figure 2b shows a multilayer actuator 10 formed by stacking several elastomer actuator films 1 coated on one side. With the exception of an outer elastomer actuator film 1, the outer sides of the electrode layers 3 each rest against the uncoated surface side of the dielectric layer 2 of a respective adjacent elastomer actuator film 1. The electrode layers 3 are alternately assigned to a polarity of a control voltage U, so that a voltage is generated across the dielectric layers to generate an electric field strength. The resulting electrostatic attractive force compresses the dielectric layer 2 (reduces its thickness), and the areal extent of the multilayer actuator 10 increases.
[0056] Figure 2b shows a further embodiment of a spiral-shaped elastomer actuator 20. An arrangement of two superimposed, one-sidedly coated elastomer actuator films is rolled to form an alternating arrangement of electrode layers 3 and the electrical layers 2. The use of two superimposed elastomer actuator films creates two electrodes that can be charged with different electrical potentials, allowing control using a control voltage. Upon control, the resulting electrostatic force of attraction causes a change in length in the axial direction A of the spiral arrangement.
[0057] Figure 3 shows a manufacturing device 30 for producing an elastomer actuator film 1 from a dielectric layer 2 and one or more electrode layers 3. The elastomer actuator film serves to form an elastomer actuator, in particular as a multilayer actuator or as a spiral-shaped elastomer actuator. The manufacturing method is described using the manufacturing device 30. A corresponding flow diagram is shown in Figure 4.
[0058] In step S1, the manufacturing device 30 for producing the elastomer actuator film receives as starting material a dielectric elastic polymer layer in the form of a flat elastomer actuator film 31. The elastomer actuator film 31 can be stretched and, for example, prestressed and inserted into a holding frame 32.
[0059] In step S2, liquid or viscous electrode material is applied to one surface of the elastomer actuator film thus fixed, for example, using a screen printing device 33. This material is then cured by a suitable treatment step, such as thermal or UV irradiation. The elastomer actuator films thus formed, clamped in the holding frame 32, are then tested for their dielectric strength in a test device 34 using a plate-shaped test electrode 35.
[0060] For this purpose, in step S3, the holding frame with the produced elastomer actuator foil is placed with the non-coated surface side onto the electrically conductive flat or planar test electrode
[0061] 35 and is applied with a test voltage from a voltage source 37 by means of a suitable contact, such as a conductive stamp 36, which is adapted to the geometry of the electrode and in particular can also be controlled segmentally, which is pressed onto the top side of the electrode layer. The level of the test voltage is selected such that at the nominal values, ie at the nominal thickness of the dielectric layer 2, a field strength between the test electrode
[0062] 36 and the electrode layer 2, which corresponds to a suitably selected test field strength and which, for example, lies within a tolerance of approximately 10-30% below the breakdown field strength. For example, the test voltage can be selected such that a field strength of 100 V / pm is formed for the nominal thickness of the dielectric layer 2.
[0063] When the test voltage is applied, a current flow is simultaneously measured using a current measuring device 38. The current is monitored, and if it is determined that a predefined current threshold is exceeded, a fault and voltage breakdown can be concluded. The breakdown continues until the test voltage is switched off.
[0064] The test voltage can be applied as a ramp-like voltage increase with a rise rate of between 50V / s and 1000V / s in order to apply the elastomer actuator foils to the surface of the test electrode in such a way that as few air pockets as possible remain between the elastomer actuator foil and the test electrode.
[0065] The aim of the test device 34 is to create a breakdown point at a defect that can be detected using optical means. For this purpose, after determining that the current threshold has been exceeded, the test current is applied for a predetermined period of time, e.g., between 10 ms and 200 ms, so that it can be assumed that the breakdown point is visible. Alternatively, the predetermined period of time after the breakdown is detected can also be determined by reaching a predetermined amount of charge flowing after the breakdown is initially detected. The test voltage is then switched off, and the elastomer actuator film is subjected to an optical inspection in an inspection unit 40 in step S4. The optical inspection is performed on the uncoated surface side of the elastomer actuator and can be performed using cameras or laser reflection measurements.Optical inspection locates one or more breakouts. The position of the defect can be determined and saved from the camera image or laser reflection measurement.
[0066] In a subsequent step S5, the dielectric layer on the side not coated with the electrode layer 3 is repaired using a repair device 41. For this purpose, it is first checked whether the area of the breakthrough point is larger than a predetermined breakthrough area of, for example, 0.5 mm 2 If the area is smaller than the predetermined penetration area, a repair can be performed by applying an adhesive that can be cured thermally, using UV light, or by other means. The adhesive can be applied using a syringe or spatula and then cured.
[0067] If the area of the breakthrough point is larger than 0.5 mm 2, in addition to applying the adhesive, a repair film made of a suitable material, for example the material of the dielectric layer, can also be applied. Such a repair site is shown, for example, in Figure 5. Here, a repair site 42 is shown on an elastomer actuator film 43. The repair film 44 is placed on a layer of adhesive 45 and preferably has a thickness that is equal to or less than the thickness of the dielectric layer 2. After the repair film 44 has been applied, the adhesive 45 can be cured in the manner described above. The area of the repair film 44 is preferably selected such that it completely covers the breakthrough point 46 and has an overlap area with the area of the dielectric layer 2 around the breakthrough point 46, which overlap area can be approximately 10 to 1000% of the area of the breakthrough point.
[0068] Instead of the adhesive, a self-adhesive repair film or one that adheres to the surface of the dielectric layer 2 can also be provided. The elastomer actuator thus formed can then be further processed in a conventional manner, i.e., either by applying an electrode layer to the second, still uncoated, surface of the elastomer actuator film 1 or by stacking or winding the single-sided coated elastomer actuator film 1 to form a multilayer actuator or spiral-shaped elastomer actuator.
[0069] As described above, the process can be carried out in batches with one or more sections of the dielectric foil arranged in the holding frame, in which these can be coated with the electrode material.
[0070] Alternatively, the process can also be carried out on an endless belt of the dielectric layer material.
Claims
Claims 1. A method for producing a dielectric elastomer actuator (10, 20) with an elastomer actuator film (1), comprising the following steps: Providing (S1, S2) the elastomer actuator film (1) comprising a dielectric elastic polymer layer (2) coated on one side with a conductive electrode layer (3); Testing (S3) a breakdown strength of the elastomer actuator film (1) by applying a test voltage in order to form a field strength in the dielectric layer (2) which is below a breakdown field strength of the material of the dielectric layer; Localizing (S4) at least one breakthrough point using an optical method; Repairing (S5) the at least one localized breakthrough point (46) by applying a curable adhesive (45) followed by curing and / or by applying a repair film (44) to a side of the dielectric layer (2) opposite the electrode layer (3).
2. Method according to claim 1, wherein the dielectric strength of the elastomer actuator film (1) is tested by applying the elastomer actuator film (1) flatly to a flat test electrode (36) and applying a test voltage between the electrode layer (3) and the test electrode (36), wherein the test voltage is selected depending on the thickness of the dielectric layer (2) such that a field strength is established in the dielectric layer (2) which is lower by a safety margin of in particular between 10 and 40% than a breakdown field strength of the material of the dielectric layer (2).
3. Method according to claim 1 or 2, wherein when testing the dielectric strength of the elastomer actuator film (1), the test voltage remains applied for a predetermined period of time, in particular between 5 ms and 100 ms, or for a predetermined charge flow after a breakdown has been detected.
4. Method according to one of claims 1 to 3, wherein the localization of breakthrough points (46) is carried out by means of optical means, in particular by means of a camera or a laser reflection measurement.
5. Method according to one of claims 1 to 4, wherein adhesive (45) is applied in particular by means of a syringe, a stamp or a spatula to repair the localized breakthrough point (46).
6. Method according to one of claims 1 to 5, wherein, in order to repair the localized breakthrough point after the application of the adhesive (45), a repair film (44) made of dielectric material is applied so that it completely covers the breakthrough point (46) and after the curing of the adhesive (45) is firmly connected to the dielectric layer (29).
7. Method according to one of claims 1 to 5, wherein for repairing the localized breakthrough point a self-adhesive or adhesively fixed repair film (44) is applied so that it covers the breakthrough point (46) is completely covered and firmly connected to the dielectric layer (29).
8. The method according to claim 6 or 7, wherein the material of the repair film (44) corresponds to the material of the dielectric layer (2) and / or the thickness of the repair film (44) is equal to or smaller than the thickness of the dielectric layer (2).
9. The method according to any one of claims 1 to 8, wherein the provision of the elastomer actuator film (1) comprises applying a conductive electrode material to one or both sides of a film of a dielectric layer (2).
10. The method according to any one of claims 1 to 9, wherein the test voltage is provided as a DC voltage or an AC voltage with a frequency in the range of 0.1 Hz - 10 kHz, wherein, in particular, when the test voltage is applied, it is increased at a rate of increase of between 50 V / s and 1000 V / s up to the test voltage 11. The method according to any one of claims 1 to 10, wherein after repairing the at least one localized breakdown point (46), the method steps of testing the dielectric strength, locating a breakdown point (46) and repairing are carried out repeatedly, in particular with the same test voltage, until no new breakdown point (46) is found.
12. A device for producing a dielectric elastomer actuator (10, 20) with an elastomer actuator film (1), the device comprising: a device (30) for providing the elastomer actuator film (1), which comprises a dielectric elastic polymer layer (2) coated on one side with a conductive electrode layer (3); a test device (34) designed to test a dielectric strength of the elastomer actuator film (1) by applying a test voltage in order to develop a field strength in the dielectric layer (2) that is below a breakdown field strength of the material of the dielectric layer; an inspection unit (40) designed to locate at least one breakdown point (46) using an optical method;a repair device (41) which is designed to repair the at least one localized breakthrough point (46) by exclusively applying a curable adhesive (45) followed by curing and / or by applying a repair film (44) to a side of the dielectric layer (2) opposite the electrode layer (3);