Method for manufacturing a component

Abstract

The present invention relates to a method for manufacturing a component in which unidirectionally oriented rigid fibers (2) are applied to the surface of a first substrate (1) and the fibers (2) are covered with a liquid elastomer (3) and dried. Finally, the first substrate (1) is removed, wherein a longitudinal axis of the fibers (2) and a longitudinal axis of the formed elastomer layer are arranged at an angle to each other other than 0° and 90°.

Description

The present invention relates to a method for manufacturing a component. Dielectric elastomer actuators (DEAs) are an actuator technology that utilizes the deformation of dielectric elastomers under the influence of an electric field. Key advantages include large achievable strains, quiet operation, low cost, and their inherent capacitive sensor properties. In their most basic configuration, DEAs consist of an elastic dielectric film onto which two compliant electrodes are applied. When an electric potential is applied to the electrodes, the dielectric film is compressed along the direction of the electric field and expands in the plane perpendicular to the field. Uniaxial movements are often required in soft robotic systems, and several DEA configurations have been designed to enable them. Established configurations for achieving this deformation behavior include stacked actuators, strip actuators, and fiber-stiffened actuators. Stacked actuators consist of multiple stacked DEA layers because the deformation of a single actuator layer would be too small for most applications. In general, stacked actuators can generate large forces due to their large active cross-section.However, laboratory-scale manufacturing processes are complex, and their dimensions cannot be easily adapted to a specific application, as a given deflection can only be achieved by changing the number of actuator layers. Strip actuators, on the other hand, are comparatively easy to manufacture, their dimensions can be freely adapted to application specifications, and they offer the possibility of constructing very compact and flat actuator and sensor systems. Therefore, strip actuators are an advantageous configuration in the development of artificial muscles. However, the strain in the plane of the DEA is biaxial, meaning that for strip DEAs requiring only uniaxial control, the strain perpendicular to the direction of operation is irrelevant. This results in strip DEAs operating at only 50% efficiency. One approach to solving this problem is to introduce anisotropic mechanical stiffness into the actuator by applying uniformly distributed individual fiber stiffening elements perpendicular to the actuator's working direction. However, while a pure shear strain state (no deformation in the transverse direction) is enforced between these stiff elements, the underlying membrane is restricted in its deformation, resulting in a non-uniform strain state when the entire structure is considered. Depending on the area covered by the fibers, the sections between the fibers experience proportionally higher strains, leading to premature strain stiffening. This complicates the prediction of actuator properties and is problematic for use as a capacitive sensor.Furthermore, ensuring a secure bond between the rigid fibers and the actuator's soft substrate presents a technological challenge, ultimately limiting its lifespan. For example, the article by Konstantini et al., "Uni-axial reinforced dielectric elastomer actuators with embedded 3D printed fibers," Smart Mat. Struct. 32 (2023) 125011, describes a method where fibers are glued into pre-molded channels, which is prone to defects. Therefore, surface coverage, fiber geometry, and fiber adhesion must be carefully optimized to achieve a net benefit from adding fibers compared to using simple strip actuators. DE 10 2016 200 148 A1 discloses an electromechanical transducer and a method for manufacturing an electromechanical transducer. Koenigsdorff et al., Anisotropic Carbon Fibre Electrodes for Dielectric Elastomer Actuators, Proceedings of the International Conference and Exhibition on New Actuator Systems and Applications, 2022, ISBN 978-3-8007-5894-4, pp. 97-100, describes a manufacturing approach for anisotropic carbon fiber electrodes. JP S60 - 207 269 A discloses an anisotropic conductive connector. Koenigsdorff et al., Free-standing tubular DEAs for multi-directional bending, SPIE Journals, 2023, Vol. 12482, DOI 10.1117 / 12.2657028, pp. 1-8, discloses a manufacturing approach for free-standing tubular dielectric actuators. The present invention therefore aims to propose a method that avoids the aforementioned disadvantages, thus enabling the simple production of a reliably deformable and long-term stable component. This problem is solved according to the invention by a method according to claim 1. Advantageous embodiments and further developments are described in the dependent claims. In a process for manufacturing a component, unidirectionally oriented rigid fibers are applied to the surface of a first substrate and the fibers are covered with a liquid elastomer. The elastomer is then dried and the first substrate is removed. The described process yields a component in which the fibers are embedded in a dielectric elastomer layer. Due to the stiffness and orientation of the fibers, deformation in a defined direction is enabled, while deformation in other directions is prevented. The resulting component can be used, for example, in actuators. The manufacturing process is simple in its sequence of steps and yet achieves a good bond between the fibers and the elastomer. It can also be provided that after drying (while the elastomer layer still bears the first substrate), the fibers covered with the elastomer are covered with a second substrate. The resulting stack, consisting of the first substrate, the layer of dried elastomer, and the second substrate, is then turned over. Next, the first substrate is removed, and another layer of the liquid elastomer is applied to the side of the elastomer layer that previously held the first substrate. This newly applied elastomer layer is then dried. Finally, the second substrate is removed. The fibers are typically completely covered with the elastomer; that is, after application, no surface area of ​​any of the fibers is free of the elastomer. The elastomer can dry naturally over time in ambient air without additional assistance, or it can be dried in an oven or other heating device. The fibers can be carbon fibers. Carbon fibers are easy to produce and their mechanical properties are suitable for defining the mechanical properties of the component accordingly. Preferably, the fibers exhibit a higher stiffness than the dried elastomer. This allows the stiffness of the manufactured component to be adjusted as desired. The elastomer can be designed as a silicone-based elastomer that is easy to apply and handle. Typically, the first and / or second substrate are designed as a film, i.e., as a flexible, homogeneous sheet of thin material. This simplifies the application and removal of the substrates. The fibers are typically aligned parallel to each other when applied to the surface of the first substrate. This application typically occurs without a force-fit or form-fit connection, but simply by laying them on top. The fibers can be applied to the first substrate at equal distances from each other to define the mechanical properties of the component, but there can also be different distances between individual fibers, at least in pairs. A longitudinal axis of the fibers and a longitudinal axis of the formed elastomer layer are arranged at an angle to each other other than 0°. This tilted arrangement determines the direction along which the finished component should be stretchable. Typically, the two longitudinal axes are perpendicular to each other, so the angle between them is 90°. Here, the longitudinal axis refers to the axis of a body that corresponds to the direction of its greatest extension. The drying of the applied elastomer can be assisted by a rolling process or achieved through the rolling process itself. As a roller passes over the applied elastomer, any remaining liquid is squeezed out. The invention also relates to a component with fibers embedded in an elastomer layer, which is manufactured using a method with the described properties. Exemplary embodiments of the invention are shown in the drawings and are explained below with reference to Figs. 1, 2, 3, 4, 5, 6, 7, 8 to 9. Recurring features are identified by identical reference numerals. Figure 1 shows a perspective top view of a first substrate with fibers arranged on it; Figure 2 shows a view corresponding to Figure 1 during the application of the elastomer and with the elastomer applied; Figure 3 shows a view corresponding to Figure 1 with the second substrate applied; Figure 4 shows a view corresponding to Figure 1 during the removal of the first substrate; Figure 5 shows a view corresponding to Figure 1 during the second application of the elastomer; Figure 6 shows a view corresponding to Figure 1 of a rolling process and release film; Figure 7 shows a view corresponding to Figure 1 of the component with the release film applied; Figure 8 shows a view corresponding to Figure 1 of the component with the release film removed; Figure 9 shows a schematic representation of a dielectric elastomer actuator with the component. Figure 1 shows a perspective view of a substrate 1 in the form of a polyethylene terephthalate (PET) film, with several carbon fibers 2 arranged flat and parallel to each other at equal intervals on a surface of the substrate 1, resulting in a unidirectional orientation of the fibers 2. The fibers 2 merely lie on the surface and are not fixed there by an adhesive bond or any other connection. Figure 2 shows a view corresponding to Figure 1, illustrating how an unkneaded, liquid, silicone-based elastomer 3 is applied to the side of the fibers 2 facing away from the substrate 1 by means of a doctor blade 4. The fibers 2 are ultimately completely covered by the elastomer 3, which encloses the fibers 2. In the state shown in the right part of Figure 2, a dried elastomer layer completely covering the fibers 2 is thus formed on the substrate 1. The squeegee 4 ensures a uniform thickness of the elastomer layer. As shown in Fig. 3, a second substrate 5 is applied to this elastomer layer. The second substrate 5 can be made of the same material as the first substrate 1 and, like the first substrate 1, is in the form of a film. After the application of the second substrate 5, the stack of layers consisting of the first substrate 1, the elastomer layer with the fibers 2, and the second substrate 5 is turned over so that the first substrate 1 is on top. In the next process step shown in Fig. 4, the first substrate 1 is lifted away from the elastomer layer and the fibers 2, so that the fibers 2 are exposed, unless they are enclosed by the elastomer 3. As in the process step shown in Fig. 2, the undiluted elastomer 3 is again applied uniformly in its liquid state to the already formed elastomer layer and the fibers 2 using the doctor blade 4, as shown in Fig. 5, so that at the end of the process the fibers 2 are completely embedded in or encased by the elastomer 3. The two elastomer layers are typically identical in their dimensions, so that, viewed in the thickness direction, the fibers 2 lie centrally in the now formed combined elastomer layer. The combined elastomer layer can be considered, in particular, as a metallurgical bond between the two elastomer layers. A roller 7 can be used to dry the elastomer 3. This roller applies a release film 6 to the elastomer layer and presses out liquid from the elastomer 3, or squeezes out excess elastomer. A rolling process for drying can also be carried out after the elastomer layer production step shown in Fig. 2, or it can be performed only during the formation of one of the two elastomer layers, which then form the combined elastomer layer. The adhesion between the release film 6 and the prepreg, i.e., the elastomer layer with the fibers 3 embedded therein, should be significantly lower than the adhesion between the first substrate 1, which serves as a carrier film, and the prepreg. Otherwise, when the release film 6 is removed, the prepreg may also detach from the first substrate 1. However, it is also possible to omit the release film 6 and squeeze out the excess liquid silicone directly with a roller.However, this method is less suitable for laboratory use, as it can easily lead to contamination of the equipment. Fig. 7 shows the layer stack after the rolling process in the known perspective view with the second substrate 5 below, the combined elastomer layer with integrated fibers 2 and the separating film 6 above. Finally, Fig. 8 shows the layer stack after removal of the separating film 6, wherein in a final step the second substrate 5 is also removed, leaving the elastomer layer with integrated fibers 2. In the illustrated embodiment, the longitudinal axis of the fibers 2 and the longitudinal axis of the combined elastomer layer are parallel to each other, but a tilt between the two longitudinal axes is also possible, or in particular an arrangement in which the two longitudinal axes are perpendicular to each other. The steps shown in Figs. 3-5 are optional and should be carried out if double-sided impregnation of the prepreg is required. This component, also known as prepreg, achieves no strain in the fiber direction, but a uniform strain state perpendicular to the fiber direction, minimal additional mechanical stiffness in the working direction, and long-term stable adhesion between reinforcing fibers and the elastomer 3. The rigid fiber-elastomer prepreg is produced by bonding unidirectionally arranged rigid micrometer fibers to the stretchable elastomer 3. This prepreg can provide good anisotropy for stretchable components while minimizing the impact on stiffness. As a result, in elastomer actuators, the work is concentrated in the desired direction, and in elastomer strain sensors, the capacitance change is quadratically amplified, whereas conventional elastomer actuators exhibit an energy efficiency in the working direction of only about 50 percent, and conventional strain sensors show a small capacitance change in the picofarad range. In the described process, the highly stiff carbon fibers 2 are infiltrated with a soft silicone matrix material, the elastomer 3. After the silicone has cross-linked, the resulting structure can be easily applied to finished actuators to reinforce them. The composite structure consists of the stiff carbon fibers 2, which are continuously distributed in a soft matrix material. This composite layer gives the actuator a high degree of mechanical anisotropy due to the blocked deformation in the fiber direction. Compared to conventional fiber reinforcement, it also offers the significant advantage that movement perpendicular to the fiber direction is hardly restricted, since the stiffness of the composite in this direction is uniform due to the high number of fibers 2.This technology thus offers a promising way to reinforce soft actuators and sensors with minimal additional effort, thereby leveraging the advantages of a pure shear strain state (no deformation in the transverse direction). The prepreg is non-stretchable and incompressible in the fiber direction, while it is stretchable in a direction perpendicular to the fibers. In the discussed embodiment, the prepreg was made from unidirectional carbon fibers and low-stiffness silicone (hardness: Shore 00-30). Fig. 9 shows a schematic view of a dielectric elastomer actuator, in which the component 9 was manufactured using the previously described method. The component 9 is provided with an electrode 8 made of an electrically conductive material on both its upper and lower surfaces. Thus, a plate capacitor of capacitance C with relative permittivity εr, absolute primitiveness ε0, area A and thickness (electrode spacing) d is obtained. The area A and the thickness A can be expressed as follows: with the original length l0, the longitudinal stretch λx, the original width b0, the transverse stretch λy, the original thickness d0, and the transverse stretch λz. The stretch λ = 1 + ε, where ε is the elongation. The change in capacity upon stretching C / C0 can be expressed as follows: where K is a constant. For an incompressible elastic body, the following applies: for elastomers without prepreg. When stretched longitudinally, the following applies: Therefore, the following applies to an elastomer without prepreg: When stretched in the longitudinal direction: And therefore: Thus, the stretchable capacitive sensor, with the addition of the present invention, has a stronger signal.

Claims

Method for producing a component in which unidirectionally oriented stiff fibers (2) are applied to a surface of a first substrate (1) and the fibers (2) are covered with a liquid elastomer (3) and dried, and subsequently the first substrate (1) is removed, wherein a longitudinal axis of the fibers (2) and a longitudinal axis of the formed elastomer layer are arranged at an angle to each other other than 0° and 90°. Method according to claim 1, wherein after drying the elastomer (3) the fibers (2) covered with the elastomer (3) are covered with a second substrate (5) and the stack thus formed is turned over, and subsequently the first substrate (1) is removed and a further layer of the liquid elastomer (3) is applied and dried and finally the second substrate (5) is removed. Method according to claim 1 or claim 2, wherein the fibers (2) are carbon fibers. Method according to one of the preceding claims, wherein the fibers (2) have a higher stiffness than the dried elastomer (3). Method according to any of the preceding claims, wherein the elastomer (3) is a silicone-based elastomer. Method according to one of the preceding claims, wherein the first substrate (1) and / or the second substrate (5) are formed as a film. Method according to one of the preceding claims, wherein the fibers (2) are aligned parallel to each other when applied to the surface of the first substrate (1). Component comprising fibers embedded in an elastomer layer (2) which is manufactured by a method according to one of the preceding claims.

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