Flexible sensors based on continuous fiber composite materials, their fabrication methods and applications

Abstract

This invention discloses a flexible sensor based on continuous fiber composite materials, its preparation method, and its applications. Using continuous fibers and flexible thermoplastic resins such as TPU and TPE as raw materials, it is integrally printed using FDM (Fused Deposition Modeling) technology. The multifunctional flexible sensor produced by this invention is low-cost, highly efficient, and convenient; it can be shaped arbitrarily, allowing for customized patterns; the produced sensor can be used without encapsulation; and large deformations can be achieved through structural design, improving strain rate and sensitivity. This multifunctional flexible sensor can not only serve as a basic sensor but also as a flexible wearable sensor.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically relating to a flexible sensor based on continuous fiber composite materials, its preparation method, and its application. Background Technology

[0002] Wearable sensors can be used to monitor and capture human activities, fulfilling the function of continuously monitoring human vital signs. At the same time, because these sensors are applied to the human body, they need to meet skin requirements and have the characteristics of high sensitivity, reliability and sustainability. Wearable sensor systems composed of flexible and stretchable materials are widely used in medical health, human-computer interaction and biomedicine.

[0003] Currently, the fabrication process of wearable sensors is quite complex, requiring a wide variety of materials and involving intricate manufacturing processes. Furthermore, the manufactured sensors need to be packaged before they can be used. The production cycle is long, hindering mass production and resulting in relatively high costs. Additionally, these sensors are typically designed as a thick, small rectangle, limiting their ability to undergo large deformations and personalization; they can only perform a single sensing function. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a flexible sensor based on continuous fiber composite material, its preparation method and application, in order to address the shortcomings of the prior art, and to solve the technical problems of complex sensor preparation process, high production cost, inability to be customized, and inability to achieve large deformation.

[0005] The present invention adopts the following technical solution:

[0006] This invention relates to a method for fabricating a flexible sensor based on continuous fiber composite materials, comprising the following steps:

[0007] S1. Continuous fibers and flexible thermoplastic resin are fed into the 3D printing head. The continuous fibers are impregnated and coated with the molten resin inside the nozzle of the 3D printing head to form a composite filament.

[0008] S2. The composite filament impregnated in step S1 is extruded from the nozzle outlet. Then the resin matrix cools and solidifies and adheres to the upper layer of the specimen. According to the cross-sectional profile and filling information, the print head is driven to move along the set path. The composite filament is extruded from the nozzle and stacked to form a single-layer solid.

[0009] After the single-layer solid printing in step S2 is completed, repeat the above printing process to obtain a flexible sensor based on continuous fiber composite material.

[0010] Specifically, in step S1, the flexible thermoplastic resin is heated and melted inside the 3D printing head, and the molten flexible thermoplastic resin is fed into the nozzle under the thrust of the filament for impregnating and coating continuous fibers.

[0011] Specifically, in step S2, the printing temperature is controlled at 170–290°C, the printing speed at 10–40 mm / s, and the substrate temperature at 45–70°C.

[0012] Specifically, in step S2, the nozzle diameter is 1-3 mm.

[0013] Specifically, in step S2, the interlayer thickness of a single-layer entity is 0.25–0.28 mm, the minimum path spacing is 0.6 mm, and the compensation length is 0.8–1 mm.

[0014] Specifically, two sections of filament, each 5 to 10 cm long, are reserved at the start and end of printing, and 0.8 to 2 cm of filament is sintered at the starting position.

[0015] Furthermore, the exposed continuous fibers after sintering are coated with silver paste.

[0016] Another technical solution of the present invention is a flexible sensor based on continuous fiber composite material, comprising continuous fibers, wherein a flexible thermoplastic resin is disposed on the outside of the continuous fibers.

[0017] Specifically, the multifunctional flexible sensor has a multi-stable structure.

[0018] Another technical solution of the present invention is to apply a flexible sensor based on continuous fiber composite material to wearable devices.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] This invention relates to a method for fabricating flexible sensors based on continuous fiber composite materials. The required sensor pattern can be pre-set and printed without any additional processing. This avoids the need for material processing before fabrication, post-processing of the sensor after fabrication, and sensor packaging. The fabrication process is simple, and the produced sensor can directly contact the human body.

[0021] Furthermore, flexible thermoplastic resin is heated and melted inside the 3D printing head. The molten flexible thermoplastic resin is then fed into the nozzle under the thrust of the filament to impregnate and coat continuous fibers. This allows the formation of a composite filament composed of thermoplastic resin-coated carbon fibers directly in the printer nozzle, avoiding the series of complex chemical treatments required for composite material preparation in other sensor production processes.

[0022] Furthermore, the printing temperature setting allows the thermoplastic resin to completely melt inside the nozzle, thereby completely coating the carbon fiber to form a composite filament. Slower printing speeds are generally used in the test piece printing process, which can result in relatively high precision of the printed test pieces. Faster printing speeds are generally used to control the movement of the printer nozzles before the actual printing begins, which can save time. The substrate temperature setting facilitates better forming of the composite material.

[0023] Furthermore, the nozzle diameter determines the diameter of the composite material to a certain extent. Different nozzles can be used to obtain composite materials of different diameters, and the most suitable composite material diameter can be selected according to the different uses of the sensor.

[0024] Furthermore, the thickness of a single-layer solid is set to 0.25-0.28mm. If the thickness of the single-layer solid is too small, it will cause wire breakage. If the thickness of the single-layer solid is too large, it will cause the composite material to fail to adhere to the substrate. If the path spacing is set too small, it will cause different paths to stick together. The compensation length is set to make the connection of the pattern boundary more stable.

[0025] Furthermore, reserving filament material at the start and end of printing and sintering it at the starting position aims to expose a small amount of carbon fiber, which is beneficial for resistance measurement.

[0026] Furthermore, the purpose of coating the exposed carbon fibers at the sintering location with silver paste is to make the resistance measurement more stable.

[0027] A flexible sensor based on continuous fiber composite material is available. It has low cost, simple manufacturing process, and can be put into use without complicated post-processing and packaging. In addition, the sensor can achieve personalized pattern customization and can undergo large deformation.

[0028] In summary, the preparation method of this invention is low-cost, efficient, and convenient; it can be arbitrarily shaped to achieve personalized pattern customization; the prepared sensor integrates stress, strain, and temperature measurement and can be put into use without packaging; and large deformation can be achieved through structural design to improve strain rate and sensitivity; it can not only be used as a basic sensor but also as a flexible wearable sensor.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the sensor structure of the present invention;

[0031] Figure 2 This is a schematic diagram showing the sensor of the present invention reaching a deformation of 140%.

[0032] Figure 3 This is a schematic diagram of the sensor of the present invention as a strain sensor;

[0033] Figure 4 This is a schematic diagram showing the resistance change of a strain sensor under different strains.

[0034] Figure 5 This is a schematic diagram of the sensor of the present invention as a pressure sensor;

[0035] Figure 6 This is a schematic diagram showing the resistance change of a pressure sensor under different pressures.

[0036] Figure 7 This is a schematic diagram showing the temperature changes at different temperatures when the sensor of the present invention is used as a temperature sensor. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0041] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0042] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0043] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0044] This invention provides a flexible sensor based on continuous fiber composite material. The composite material is made of continuous fiber and flexible thermoplastic resin and is produced using FDM technology. The production method is simple and low-cost, and it can be arbitrarily shaped to achieve personalized customization. Large deformation and sensitivity can be achieved through structural design. It can monitor the resistance changes under different strains, pressures and temperatures to achieve multi-functional sensing. Moreover, the data acquisition and processing are relatively simple.

[0045] This invention discloses a method for fabricating a flexible sensor based on continuous fiber composite materials, comprising the following steps:

[0046] S1. Continuous fibers and flexible thermoplastic resin are fed into the 3D printing head through a filament feeding motor. They are heated and melted inside the 3D printing head. The molten resin is fed into the nozzle under the thrust of the filament. The continuous fibers are fed into the 3D printing head through the fiber guide tube. They pass through the entire 3D printing head and are impregnated and coated by the molten resin inside the nozzle to form a composite filament.

[0047] S2. The impregnated composite filament is extruded from the nozzle outlet. Subsequently, the resin matrix cools and solidifies rapidly, adhering to the upper layer of the workpiece. The fibers can be continuously pulled out from the nozzle. Under computer control, the XY motion mechanism drives the print head to move according to the set path based on the cross-sectional profile and filling information. The composite filament is continuously extruded from the nozzle and piled up to form a single-layer solid.

[0048] The printing temperature is controlled between 170 and 290°C, depending on the melting point of the flexible thermoplastic resin used; the printing speed range is 10 to 40 mm / s, depending on the printing steps and the required printing precision; the substrate temperature range is 45 to 70°C, which needs to be adjusted according to the adhesion of the composite material and the ambient temperature.

[0049] The nozzle diameter is 1–3 mm, depending on the flexible thermoplastic resin and the number of fibers in the carbon fiber. Different nozzle diameters need to be determined based on different filament materials. The interlayer thickness of a single-layer solid is 0.25–0.28 mm, the minimum path spacing is 0.6 mm, and the compensation length is 0.8–1 mm.

[0050] After the single-layer solid printing in steps S3 and S2 is completed, the Z-axis worktable is lowered by a layer thickness distance, and the printing process is repeated to realize the manufacturing of three-dimensional continuous fiber composite material components.

[0051] Composite filaments can be shaped arbitrarily and can be prepared into various desired shapes and structures.

[0052] The contact between each layer of the solid is the contact between flexible thermoplastic resins.

[0053] Two sections of filament, each 5-10 cm long, are reserved at the start and end of printing. 0.8-2 cm of these sections need to be sintered at the starting position to expose the continuous internal fibers for monitoring electrical signals.

[0054] In this process, silver paste is coated onto the exposed continuous fibers, and then dried with a heat gun to stabilize the resistance while enhancing the conductivity of the continuous fibers.

[0055] This invention is based on FDM 3D printing. After designing the preset sensor structure, printing can be completed under computer control, achieving personalized customization and avoiding many complex production methods. Simultaneously, corresponding structural design allows for large sensor deformation and improved sensitivity. Furthermore, since the external thermoplastic resin coating is an insulating material, it can directly contact the human body, eliminating the need for encapsulation when used as a wearable sensor. Due to the piezoresistive effect of carbon fiber, it can serve as a strain, stress, and pressure sensor. Additionally, as a highly conductive material, carbon fiber exhibits a relationship between resistance and temperature; therefore, the produced continuous fiber composite material sensor can function as a sensor integrating strain, pressure, and temperature.

[0056] Please see Figure 1 The present invention discloses a flexible sensor based on a continuous fiber composite material, comprising continuous fibers disposed inside and flexible thermoplastic resin disposed outside.

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment provides an example of using continuous fiber composite material as a strain sensor:

[0060] 1) In this embodiment, 1K continuous fiber bundles and TPU resin are used as raw materials for 3D printing of continuous fiber composite materials. Based on the material properties, the printing temperature is 170℃, the printing speed is 10mm / s, the substrate temperature is 45℃, the interlayer thickness is 0.25mm, the path spacing is 0.6mm, the nozzle diameter is 1mm, and the compensation length is 0.8mm.

[0061] 2) Determine that the specimen structure used as a stress sensor is a multistable structure, such as... Figure 3 As shown, relevant treatments were performed on the reserved wires at both ends, and the resistance change was measured using a TH2516A resistance meter.

[0062] 3) Connect the specimen end to end to form a ring, wear it on your elbow, and bend your elbow to 30°, 60° and 90° respectively to apply different strains to the specimen. Measure the change in resistance of the specimen under different strains, such as... Figure 2 and Figure 4 As shown, the sensor can be directly used as a wearable device; the resistance of the multifunctional flexible sensor changes differently under different strains, and its resistance increases with the increase of the strain degree, so it can be used as a strain sensor.

[0063] Example 2

[0064] This embodiment provides an example of using continuous fiber composite material as a pressure sensor:

[0065] 1) In this embodiment, 1K continuous fiber bundles and TPU resin are used as raw materials for 3D printing of continuous fiber composite materials. Based on the material properties, the printing temperature is 230℃, the printing speed is 20mm / s, the substrate temperature is 65℃, the interlayer thickness is 0.26mm, the path spacing is 0.6mm, the nozzle diameter is 2mm, and the compensation length is 0.9mm.

[0066] 2) The specimen structure used as a pressure sensor was determined to be a spider web structure, such as... Figure 5 As shown, relevant treatments were performed on the reserved wires at both ends, and the resistance change was measured using a TH2516A resistance meter.

[0067] 3) Fix the specimen on the table and drop the same small ball freely from a distance of 40cm, 60cm, and 80cm from the center of the specimen, applying different pressure changes. Measure the change in resistance of the specimen under different pressures. Figure 6 As shown, it can be observed that the resistance of the multifunctional flexible sensor changes differently under different pressures, and its resistance increases with increasing pressure, thus it can be used as a pressure sensor.

[0068] Example 3

[0069] This embodiment provides an example of using continuous fiber composite material as a strain sensor:

[0070] 1) In this embodiment, 1K continuous fiber bundles and TPU resin are used as raw materials for 3D printing of continuous fiber composite materials. The printing temperature is set to 290℃, the printing speed to 40mm / s, the substrate temperature to 70℃, the interlayer thickness to 0.28mm, the path spacing to 0.6mm, the nozzle diameter to 3mm, and the compensation length to 1mm. A 20cm long section of composite filament is directly dragged out by hand without any structural design. The two ends of the filament are treated, and the resistance change is measured using a TH2516A resistance meter.

[0071] 2) Place the wire on the heating table and heat it from 30℃ to 100℃, in 10℃ increments, holding each temperature for 15 minutes. Measure the resistance at each temperature. Then cool it from 100℃ to 30℃, using the same measurement method as during the heating process. The change in resistance of the specimen is shown in the figure. Figure 7 As shown, it can be observed that the resistance of the multifunctional flexible sensor changes differently at different temperatures, and its resistance decreases as the temperature increases, making it suitable as a temperature sensor.

[0072] In summary, the flexible sensor based on continuous fiber composite material, its preparation method, and its application greatly simplify the sensor preparation process, avoiding complex processes such as composite material production, post-processing, and packaging, while also reducing costs. The sensor pattern has sufficient freedom, allowing for personalized customization, and large deformation can be achieved through structural design. Furthermore, it can monitor the resistance changes of the sensor under different strain, pressure, and temperature variations, and the data acquisition and processing are relatively simple.

[0073] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for fabricating a flexible sensor based on continuous fiber composite materials, characterized in that, Includes the following steps: S1. Continuous fibers and flexible thermoplastic resin are fed into the 3D printing head. The continuous fibers are impregnated and coated with the molten resin inside the nozzle of the 3D printing head to form a composite filament. The flexible thermoplastic resin is heated and melted inside the 3D printing head. The molten flexible thermoplastic resin is fed into the nozzle under the thrust of the filament to impregnate and coat the continuous fibers. S2. The composite filament impregnated in step S1 is extruded from the nozzle outlet. Subsequently, the resin matrix cools and solidifies, adhering to the upper layer of the specimen. According to the cross-sectional profile and filling information, the print head is driven to move along the set path. The composite filament is extruded from the nozzle and stacked to form a single-layer solid. The printing temperature is controlled at 170~290℃, the printing speed is 10~40mm / s, the substrate temperature is 45~70℃, the nozzle diameter is 1~3mm, the interlayer thickness of the single-layer solid is 0.25~0.28mm, the minimum path spacing is 0.6mm, and the compensation length is 0.8~1mm. At the start and end of printing, two sections of filament with a length of 5~10cm are reserved, and 0.8~2cm is sintered at the starting position. After sintering, the exposed continuous fibers are coated with silver paste. After the single-layer solid printing in step S2 is completed, repeat the above printing process to obtain a flexible sensor based on continuous fiber composite material. The flexible sensor has a multi-stable structure; the continuous fiber is carbon fiber, and the flexible thermoplastic resin is TPU.

2. A flexible sensor based on continuous fiber composite material, characterized in that, The flexible sensor based on continuous fiber composite material is prepared according to claim 1, comprising continuous fibers, and the outer surface of the continuous fibers is provided with flexible thermoplastic resin.

3. A wearable device, characterized in that, Including the flexible sensor based on continuous fiber composite material as described in claim 2.

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