Electrically conductive elastic composite yarn and method of making and knitted strain sensor

Abstract

This invention provides a conductive elastic composite yarn, its preparation method, and a knitted strain sensor, belonging to the field of flexible strain sensor technology. This invention prepares intrinsically elastic conductive elastic composite yarn from the material source, overcoming the defect of poor conductive path stability. By mechanically combining the elastic core yarn and the conductive outer yarn through rope braiding or covering processes, the composite yarn structure can be precisely controlled, achieving effective regulation of the mechanical and electrical properties of the conductive elastic composite yarn. After using this conductive elastic composite yarn to prepare a knitted strain sensor, the sensor's sensitivity was significantly improved, proving that the knitting structure is significant for optimizing sensor performance. This "yarn-fabric" design approach helps to further optimize sensor performance.

Description

Technical Field

[0001] This invention belongs to the field of flexible strain sensor technology, specifically relating to a conductive elastic composite yarn, its preparation method, and a knitted strain sensor. Background Technology

[0002] With the rapid development of smart wearable technology, flexible strain sensors have shown broad prospects in fields such as human health monitoring, sports rehabilitation, and human-computer interaction. Compared with traditional rigid electronic sensors, flexible sensors based on textiles have attracted much attention due to their excellent wearing comfort, breathability, and mechanical compatibility with human skin. Among many textile structures, knitted fabrics, with their unique topological configuration formed by interlocking coils, possess inherent high elasticity, stretchability, and body fit, and are considered an ideal flexible substrate for constructing wearable sensing systems.

[0003] The key to constructing a knitted strain sensor lies in effectively integrating sensing functionality with fabric elasticity. Current mainstream technologies can be broadly categorized into three types: First, coating or depositing conductive materials (such as conductive polymers or nanoparticles) on the fabric surface to form a sensitive layer. However, these coatings often suffer from poor adhesion to the substrate and are prone to cracking or peeling after repeated deformation. Second, introducing readily available conductive yarns (such as metal wires or carbon fibers) into the elastic fabric through embroidery. However, modulus mismatch between the conductive yarn and the elastic substrate can easily lead to interface separation, and the embroidery process may damage the uniformity and comfort of the elastic fabric. Third, employing a yarn-addition knitting process, where elastic and conductive yarns are fed in simultaneously during the knitting process, allowing the conductive yarn to cover the surface of the elastic yarn in a stable form, thus directly constructing the sensing unit during fabric formation. This method effectively integrates the sensing unit with the fabric structure and is considered a highly promising technological direction.

[0004] However, the yarn-adding process faces challenges in practical applications. It heavily relies on precise matching of yarn specifications, meticulous control of yarn feeding tension, and the high-precision coordination of a dedicated yarn guide. A stable and uniform covering relationship between the two yarns must be maintained throughout the entire process of yarn padding, bending, and loop formation. Any minute fluctuations can easily lead to the conductive yarn being exposed, shifted, or unevenly covered, affecting the consistency of sensor performance and the stability of the conductive path. Summary of the Invention

[0005] The purpose of this invention is to provide a conductive elastic composite yarn, its preparation method, and a knitted strain sensor. This invention prepares the conductive elastic composite yarn from the source material using rope braiding or covering processes. The resulting composite yarn has conductivity and elasticity, and the knitted strain sensor woven from this conductive composite yarn has a stable conductive path.

[0006] To achieve the objectives of this invention, the following technical solutions are provided: A conductive elastic composite yarn includes an elastic core yarn and a conductive outer sheath yarn disposed on the surface of the elastic core yarn; the disposal includes weaving or covering. The density of the elastic core yarn is 324~756 dtex; the density of the conductive outer yarn is 63~126 dtex.

[0007] Preferably, the elastic core yarn is thermoplastic polyurethane elastic yarn or rubber yarn; The conductive outer yarn is a conductive polymer fiber yarn or a conductive metal-plated fiber yarn.

[0008] Preferably, the conductive polymer fiber yarn comprises polypyrrole-nylon composite fiber yarn and / or poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) modified nylon fiber yarn; The metal-coated fiber yarn includes one or more of silver-plated nylon fiber yarn, silver-plated polyester fiber yarn, and copper-plated nylon fiber yarn.

[0009] Preferably, the diameter of the conductive elastic composite yarn is 0.4~1.1mm.

[0010] The present invention also provides a method for preparing the conductive elastic composite yarn described in the above technical solution, comprising the following steps: The conductive elastic composite yarn is obtained by weaving the elastic core yarn and the conductive outer yarn through a rope braiding process. Alternatively, the conductive outer yarn can be wrapped around the surface of the elastic core yarn through a coating process to obtain the conductive elastic composite yarn.

[0011] Preferably, the mesh count of the weaving is 140 to 200 meshes, the number of weaving spindles is 8 or 16, and the weaving angle ranges from 30° to 78°.

[0012] Preferably, the coating includes single coating, double coating, or cross coating.

[0013] The present invention also provides a knitted strain sensor, comprising a substrate, a non-conductive region, and a conductive region; the conductive region is knitted from the conductive elastic composite yarn described in the above technical solution or the conductive elastic composite yarn prepared by the preparation method described in the above technical solution.

[0014] Preferably, the conductive area of ​​the knitted strain sensor is single-sided jacquard, single-sided inlay, double-sided jacquard, or double-sided inlay.

[0015] Preferably, when the conductive area of ​​the knitted strain sensor is single-sided jacquard or double-sided jacquard, the number of horizontal rows of the conductive area is 2 to 4, and the number of vertical rows is 12 to 36. When the conductive area of ​​the knitted strain sensor is single-sided or double-sided intarsia, the number of longitudinal rows of the conductive area is 2 to 4, and the number of transverse rows is 18 to 54.

[0016] This invention provides a conductive elastic composite yarn, comprising an elastic core yarn and a conductive outer yarn disposed on the surface of the elastic core yarn; the disposal includes weaving or covering; the density of the elastic core yarn is 324~756 dtex; the density of the conductive outer yarn is 63~126 dtex. This invention prepares intrinsically elastic conductive yarn from the source of materials, and mechanically combines the elastic core yarn and the conductive outer yarn through rope braiding or covering processes, allowing precise control of the yarn structure and effective regulation of the mechanical and electrical properties of the conductive yarn. Results from embodiments of this invention show that, using a 756 dtex core yarn, a 90 dtex outer yarn, and a 170-mesh rope braiding process, the conductive elastic composite braided yarn produced by this invention exhibits significantly better overall sensing performance (conductive path stability and consistency) than commercially available elastic yarns within a wide strain range of 15%~90%, and also demonstrates superior wide-strain sensing performance compared to commercially available products.

[0017] This invention also provides a knitted strain sensor, comprising a substrate, a non-conductive region, and a conductive region; the conductive region is woven from the conductive elastic composite yarn described above or the conductive elastic composite yarn prepared by the above-described technical solution. By making the conductive elastic composite yarn into a knitted fabric, the sensitivity of the knitted strain sensor is significantly improved, demonstrating that the structure of the knitted yarn is significant for optimizing the performance of the knitted sensor. The "yarn-fabric" design approach helps to further optimize the sensor's performance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figures 1-2 The resistivity response curves of the conductive elastic composite braided yarn in Embodiment 1 of the present invention are shown at 60% strain and 90% strain, respectively. The specifications of the conductive elastic composite braided yarn are 756 dtex core yarn, 90 dtex outer yarn, and 170 mesh. Figure 3 The static resistance characteristics of the jacquard knitting strain sensor in Embodiment 2 of the present invention; Figure 4 The static resistance characteristics of the intarsia knitted strain sensor in Embodiment 2 of the present invention; Figures 5-7 This illustrates the variation law of the sensitivity coefficient of the strain sensor for jacquard knitting with different tissue structures in Embodiment 2 of the present invention.

[0020] Figures 8-10 This is the variation law of the sensitivity coefficient of the strain sensor with different weave structure inlaid knitting in Embodiment 2 of the present invention; Figure 11 The results of a 50-cycle tensile test of the C2W36 jacquard knitting strain sensor in Embodiment 2 of the present invention are shown. Figure 12 The results of the 50-cycle tensile test of the W2C54 intarsia knitted strain sensor in Embodiment 2 of the present invention are shown. Detailed Implementation

[0021] This invention provides a conductive elastic composite yarn, comprising an elastic core yarn and a conductive outer yarn disposed on the surface of the elastic core yarn; the outer yarn may be woven or covered. The density of the elastic core yarn is 324~756 dtex; the density of the conductive outer yarn is 63~126 dtex.

[0022] In this invention, the density of the elastic core yarn is 324~756 dtex, and in specific embodiments it can be 324, 376, 424, 450, 564, 650 or 756 dtex; the density of the conductive outer yarn is 63~126 dtex, and in specific embodiments it can be 63, 90 or 126 dtex.

[0023] In this invention, the elastic core yarn is thermoplastic polyurethane elastic yarn or rubber yarn; the thermoplastic polyurethane elastic yarn can be spandex yarn; the conductive outer yarn is conductive polymer fiber or conductive metal-plated fiber; the conductive polymer fiber includes polypyrrole (ppy)-nylon composite fiber and / or poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) modified nylon fiber; the metal-plated fiber includes one or more of silver-plated nylon fiber, silver-plated polyester fiber and copper-plated nylon fiber, and in a specific embodiment it can be silver-plated nylon fiber.

[0024] In this invention, the diameter of the conductive elastic composite yarn is 0.4~1.1 mm, and in specific implementations, it can be 0.461, 0.532, 0.573, 0.642, 0.78, 0.866 or 1.008 mm; the static resistance of the conductive elastic composite yarn is 50~150Ω / m; and the maximum sensitivity coefficient (GF) is 3~15.8.

[0025] The present invention also provides a method for preparing the conductive elastic composite yarn described in the above technical solution, comprising the following steps: The conductive elastic composite yarn is obtained by weaving the elastic core yarn and the conductive outer yarn through a rope braiding process. Alternatively, the conductive outer yarn can be wrapped around the surface of the elastic core yarn through a coating process to obtain the conductive elastic composite yarn.

[0026] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0027] This invention does not impose any special limitations on the rope braiding process; any rope braiding process known to those skilled in the art can be used. In a specific embodiment, an MB-16A1S high-speed braiding machine is used for braiding.

[0028] In this invention, the mesh count of the weaving is 140 to 200 meshes, and in specific embodiments it can be 150, 170 or 200 meshes; the number of weaving spindles is 8 or 16 spindles; the weaving angle ranges from 30° to 78°, and the rotation speed is 95 to 98 r / min.

[0029] In a specific embodiment of the present invention, the rope braiding process specifically includes the following steps: S1. Wind the conductive outer yarn onto the braiding bobbin of the MB-16A1S high-speed braiding machine to complete the conductive outer yarn winding operation; MB-16A1S high-speed braiding machine process parameters: speed is 900rpm, winding length is set to 500mm, and the number of braiding spindles is 8 or 16. S2. Install the above-mentioned wound braided bobbin (spindle) into the corresponding position of the MB-16A1S high-speed braiding machine to complete the threading process of the spindle and the elastic core yarn. The process parameters of the MB-16A1S high-speed braiding machine are: spindle speed of 95r / min and segment length of 500mm. After starting the braiding machine, the conductive outer yarn is spirally braided onto the surface of the elastic core yarn through 8 or 16 spindle braiding heads to obtain a conductive elastic composite braided yarn.

[0030] This invention does not impose any special limitations on the coating process; any coating process well known to those skilled in the art can be used. In a specific embodiment, a coating machine from Weifang Jiatian Textile Co., Ltd. is used for coating.

[0031] In this invention, the coating includes single coating, double coating, or cross coating.

[0032] In a specific embodiment of the present invention, the single-coating process includes the following steps: Elastic core yarn threading: The elastic core yarn is introduced into the drafting mechanism through the feeding roller. After drafting, it passes through the center of the hollow spindle through the yarn guide, keeping the core yarn axis aligned with the center of the hollow spindle; (Correction: Adjust the threading sequence, move the drafting mechanism forward, and ensure that the core yarn is drafted and shaped before wrapping). Installation of conductive outer yarn: Fix one bobbin of conductive outer yarn to the yarn frame on the outside of the hollow spindle, and introduce the conductive outer yarn into the winding channel of the hollow spindle through the yarn guide hook; Coating molding: Start the coating machine, the hollow spindle rotates at high speed, set the speed to 3000~8000 r / min, and drive the conductive outer yarn to wind around the surface of the moving elastic core yarn in a spiral trajectory, forming a single layer of conductive coating on the surface of the elastic core yarn, and obtaining conductive elastic composite coated yarn; the coverage of the conductive coating layer is ≥90%.

[0033] In a specific embodiment of the present invention, the double-coating process includes the following steps: Elastic core yarn threading: Thread the yarn according to the revised single-bundle process described above; (Revision: Synchronize the threading sequence of the single-bundle process to avoid perpetuating errors). Synchronous dual-yarn feeding: Two bobbins with wound conductive outer yarn are fixed on the yarn frame outside the hollow spindle. The two conductive outer yarns are introduced into the winding channel of the hollow spindle through independent yarn guide hooks. The two conductive outer yarns are wound synchronously on the surface of the elastic core yarn in the same spiral direction and at the same spacing. The feeding speed ratio of the two conductive outer yarns is 1:1. The yarn tension of the two bobbins with wound conductive outer yarn is the same or the tension difference is ≤0.2cN / dtex. Covering process: The process is carried out according to the modified single-covering process described above. The difference is that, at the same core yarn travel speed, the twist is reduced by 20-30% compared to the single-covering process described above, and the covering angle is 35°-45°.

[0034] The conductive coating layer prepared by the double-coating process of this invention has a parallel structure, which can reduce the static resistance of the conductive outer yarn.

[0035] In a specific embodiment of the present invention, the cross-coating process includes the following steps: A double-spindle reverse hollow spindle covering machine is selected (the two hollow spindles can be independently adjusted in speed and rotate in opposite directions), and conductive yarn bobbins are installed on the upper and lower spindles respectively; Elastic core yarn threading: The elastic core yarn is passed sequentially through the feeding roller, drafting mechanism, lower spindle hollow channel, and upper spindle hollow channel, keeping the core yarn axis aligned with the center of the two hollow spindles, and the core yarn travel speed is set to match the covering machine; Double-layer reverse winding: Lower spindle (inner layer): Conductive yarn is wound in a clockwise direction, with a wrapping angle of 40°~50° and a twist of 200~250 twists / meter; Top spindle (outer layer): The conductive yarn is wound counterclockwise, with a wrapping angle of 30°~40° and a twist of 150~200 twists / meter (the outer layer twist is lower than the inner layer to avoid reverse winding and yarn twisting). Tension coordination control: The tension of the elastic core yarn is slightly higher than that of the conductive outer yarn, with a difference of 0.3~0.5 cN / dtex; the tension of the inner and outer conductive outer yarns is kept consistent, with a tension difference of ≤0.1 cN / dtex, to avoid uneven stress on the double-layer winding that could cause yarn shift; (Supplement: refine the outer layer tension requirements to improve structural stability).

[0036] Post-forming treatment: After the coating is completed, the conductive elastic composite coated yarn blank is heated and shaped by hot air setting at a temperature of 60~80℃ for 20~30s. After setting, it is naturally cooled to room temperature to avoid sudden cooling affecting the elasticity of the core yarn.

[0037] The present invention also provides a knitted strain sensor, comprising a substrate, a non-conductive region, and a conductive region; the conductive region is knitted from the conductive elastic composite yarn described in the above technical solution or the conductive elastic composite yarn prepared by the preparation method described in the above technical solution.

[0038] In this invention, the conductive area of ​​the knitted strain sensor is single-sided jacquard, single-sided inlay, double-sided jacquard, or double-sided inlay.

[0039] In this invention, when the conductive area of ​​the knitted strain sensor is single-sided jacquard or double-sided jacquard, the number of rows in the conductive area is 2 to 4 and the number of columns is 12 to 36; when the conductive area of ​​the knitted strain sensor is single-sided intarsia or double-sided intarsia, the number of columns in the conductive area is 2 to 4 and the number of rows is 18 to 54.

[0040] In this invention, the non-conductive region is a commercially available elastic cord; the density of the elastic cord is 1008 dtex.

[0041] To further illustrate the present invention, the conductive elastic composite yarn, its preparation method, and the knitting strain sensor provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1 Twenty-seven different specifications of conductive elastic composite yarns (braided yarns) were prepared using a rope braiding process according to the parameters shown in Table 1. The specific steps are as follows: Pre-winding: Evenly wind commercially available silver-plated nylon filaments onto the bobbins of the MB-A1 high-speed braiding machine using a single-spindle high-speed winding machine. Then remove the spindles from the MB-16A1S high-speed braiding machine to complete the threading process of the MB-A1 high-speed braiding machine. Next, install the spindles of the MB-16A1S high-speed braiding machine in the correct position and set the process parameters of the MB-A1 high-speed braiding machine: speed of 900 rpm and winding length of 500 mm. Repeat this winding step until all 8 spindles have completed the winding of the silver-plated nylon filaments.

[0043] Weaving Stage: Spindles fully wound with silver-plated nylon filaments are installed one by one into their corresponding positions on the MB-16A1S high-speed braiding machine, completing the threading process between the spindles and the spandex core yarn. Based on the weaving mesh parameters set in the orthogonal experiment in Table 2, the core process parameters of the equipment are simultaneously configured: spindle speed 95 r / min, segment length 500 mm. After starting the equipment, the silver-plated nylon filaments are spirally and evenly wrapped around the surface of the spandex core yarn through 8 braiding heads, forming a "core-sheath" composite structure. The spandex core yarn acts as the "core layer," primarily providing excellent elastic recovery for the rope, corresponding to the core yarn linear density variable in the three factors. The silver-plated nylon filaments act as the "sheath layer," tightly wound around the outside of the core yarn to construct a continuous conductive path, corresponding to the outer yarn linear density variable in the three factors. Together with the weaving mesh number, these two elements constitute the key dimensions affecting the performance of the elastic conductive rope. After all 27 sets of elastic conductive rope samples corresponding to the orthogonal experiments were prepared, systematic structural and mechanical-electrical performance tests were carried out on them. The data were analyzed by combining the three-factor level settings to screen out high-performance conductive elastic braided wires.

[0044] The specific steps for performance testing of conductive elastic composite braided yarn are as follows: The procedure was performed according to GB / T 10685—2007 "Textiles - Fiber Diameter Test Method (Microscopic Method)". The specific steps were as follows: The elastic conductive rope was cut into 10cm long test samples. A Dino·lite AM7013MZT digital microscope was used to observe each sample at three different locations, measuring the diameter D and weaving angle respectively. θ Each parameter was measured three times, and the average value was taken to reduce random errors, ultimately characterizing the regularity of its "core-sheath" composite structure.

[0045] The core evaluation indicators for the force-electric performance test include static conductivity stability, sensitivity coefficient, and reproducibility in cyclic use. The scheme is formulated with reference to GB / T 12703.4-2010 "Evaluation of Electrostatic Properties of Textiles - Part 4: Resistivity" and FZ / T 70006-2022 "Test Method for Tensile Elastic Recovery Rate of Knitted Fabrics," specifically divided into two parts: First, static resistance testing, using a 34461A digital multimeter, connecting the positive and negative test terminals to both ends of a 10cm long sample, adjusting to the resistance test function, and measuring the initial static resistance value R0 to evaluate its initial conductivity stability; Second, a single tensile test, using an HZ-1007E material testing machine, setting the clamping distance to 10cm and the tensile speed to 15mm / min, clamping both ends of the sample in the center and allowing it to straighten naturally, with the multimeter probe simultaneously clamping both ends of the sample, starting the instrument to stretch to 15% strain, and recording the force, displacement, and resistance changes during the stretching process in real time, calculating the sensitivity coefficient GF according to the formula shown in Equation 1: Formula 1; In Equation 1, This is the change in resistance. To quantify its strain-resistance response characteristics.

[0046] The test results are shown in Table 1.

[0047] Table 1 Performance parameters of 27 types of elastic conductive composite braided yarns

[0048] use ( An orthogonal experimental design was used, with factor levels shown in Table 2. The experimental results and analysis are shown in Table 3.

[0049] Table 2 Factors and Levels in Orthogonal Experiment

[0050] Table 3. Results of ANOVA for Sensitivity Coefficient

[0051] Note: This indicates significance at the 0.05 level. The above analysis of variance results show that the core yarn linear density has the most significant impact on the sensitivity coefficient, with an optimal level of 756 dtex. The outer yarn linear density is the second most significant, with an optimal level of 90 dtex. The mesh count, however, has no significant impact on the sensitivity coefficient.

[0052] Mesh count has a significant impact on the apparent structure and morphology of yarn. As shown in Table 4, as the mesh count increases from 140 mesh to 200 mesh, the yarn diameter decreases from 0.866 mm to 0.651 mm. Too small a diameter can cause the yarn to easily bend and tangle during subsequent knitting processes, affecting weaving efficiency and sensor consistency; too large a diameter, on the other hand, limits its application in fine fabrics.

[0053] Table 4. Structural parameters of "756dtex spandex-90dtex silver-plated nylon" composite braided yarn at different mesh counts.

[0054] To balance the knitting flexibility and applicability of the yarn, this invention selects 170 mesh yarn for the subsequent knitted sensor. This mesh size corresponds to a suitable yarn diameter, ensuring both good softness and elasticity while providing sufficient structural stability for subsequent processing. The final yarn specifications determined for the knitted strain sensor are: 756 dtex core yarn, 90 dtex outer yarn, and 170 mesh.

[0055] Figures 1-2The resistance response curves of the conductive elastic composite braided yarn in Embodiment 1 of the present invention under different strains show that the change in its sensitivity coefficient with strain is consistent with the data in Table 7, further demonstrating that it has superior wide strain sensing potential compared to commercially available products.

[0056] Example 2 Fabrication and performance testing of knitted strain sensors: Using an SK280 silver-flute braiding machine, the conductive area of ​​the sensor was braided with the conductive elastic composite braided yarn (756 dtex core yarn, 90 dtex outer yarn, 170 mesh) obtained in Example 1, while the non-conductive area was braided with 1008 dtex elastic yarn. Two types of sensors were fabricated: 1) Jacquard knitting strain sensor: The strain axis is based on the transverse direction. The number of transverse rows (C) in the conductive area are 2, 3, and 4, and the number of longitudinal rows (W) are 12, 24, and 36, corresponding to lengths of approximately 3, 6, and 9 cm. The non-conductive area consists of 20 longitudinal rows on each side and 16 transverse rows on each side.

[0057] 2) Intarsia knit strain sensor: The strain axis is based on the warp direction. The number of warp rows W in the conductive area is 2, 3, and 4, and the number of rows C is 18, 36, and 54, corresponding to lengths of approximately 3, 6, and 9 cm. The non-conductive area consists of 30 rows vertically and 11 warp rows horizontally.

[0058] The specific steps for testing the structure and performance of the knitted strain sensor are as follows: The study tested the influence of structural features of a knitted strain sensor on its mechanical-electrical properties, and compared the differences between the yarn-level properties of the elastic conductive rope and the fabric-level properties of the sensor. The testing consisted of two parts: structural performance testing and mechanical-electrical performance testing.

[0059] Structural performance testing focuses on characterizing the coil structure and thickness distribution of the knitted sensor to ensure the consistency of structural parameters. First, the turn spacing and turn height are tested using a Dino·lite AM7013MZT digital microscope. Three typical locations are selected in the conductive area of ​​each sensor sample to observe and measure the turn spacing A and turn height B. The average value is used to characterize the regularity of the coil structure. Second, thickness testing is performed using a thickness gauge to measure the thickness at multiple points in both the conductive and non-conductive areas of the sensor. Data is recorded and the differences are calculated to assess the potential impact of structural thickness uniformity on sensing performance.

[0060] The force-electric performance testing method is consistent with that of the elastic conductive rope, but the test parameters are adjusted according to the structural characteristics of the fabric sensor. The core evaluation focuses on the sensing stability in practical applications, and includes three parts: First, static resistance testing, using a 34461A digital multimeter, connecting the wires to the two ends of the reserved wire in the conductive area of ​​the sensor, measuring the initial static resistance value R1, and comparing it with R0 of the elastic conductive rope to analyze the influence of knitting on conductivity; Second, single tensile testing, using an HZ-1007E material testing machine, setting the initial clamping distance according to the length of the conductive area of ​​the sensor (3cm, 6cm, 9cm), the tensile speed 15mm / min, clamping the sample in the center and keeping it in a naturally straight state, and simultaneously measuring the resistance change with the multimeter. Single tensile tests are performed with the strain set to 90%, and the force, displacement, and resistance data are recorded in real time to analyze the response characteristics within different strain ranges; Third, reciprocating tensile testing, the operation procedure is the same as the single tensile test, the tensile speed is set to 500mm / min, and the test is repeated 100 times to evaluate the performance stability of the sensor under long-term cyclic tensile conditions.

[0061] Experimental results: (1) Structural feature analysis The sensing performance of knitted strain sensors is largely influenced by their microstructural characteristics. As shown in Tables 5 and 6, the introduction of conductive yarns significantly alters the fabric thickness. In jacquard weaves, the fabric thickness initially increases and then decreases with the increase in the number of warp rows of conductive regions; for example, in a 3-warp configuration, the thickness decreases from 2.536 mm with 24 warp rows to 2.459 mm with 36 warp rows. This change is closely related to the bending morphology and coverage of the conductive yarns in the fabric. The conductive yarns form complex spatial configurations in the fabric, and their bending wave height and width directly affect the stability of the conductive pathway. Similarly, in intarsia weaves, the introduction of conductive regions also significantly increases the fabric thickness, and the thickness change becomes more pronounced with the increase in the number of warp rows, reflecting the different constraints imposed by different weave structures on the spatial distribution of conductive yarns.

[0062] Table 5 Thickness of Jacquard Knitted Strain Sensor

[0063] Table 6 Thickness of Intarsia Knitted Strain Sensor

[0064] (2) Static resistance characteristics The static resistance characteristics of a knitted strain sensor are the core foundation of its sensing performance. The variation of resistance under different structural parameters directly affects the stability of the sensor's signal response. Figures 3-4 The static resistance characteristics of sensors with different tissue structures are demonstrated. In jacquard tissues (such as...) Figure 3In the example shown), as the number of rows of conductive regions increases from 2 to 4, the number of parallel conductive paths increases accordingly, leading to a significant decrease in static resistance. This change stems from the increase in the number of interlacing points of the conductive yarns; more interlacing points mean a denser conductive network, thus reducing the overall resistance. Simultaneously, the increase in the number of warp rows leads to an increase in resistance because longer conductive paths increase the resistance to electron transport. For intarsia structures (such as...), Figure 4 As shown in the figure, the static resistance variation pattern is consistent with that of jacquard weave, but the overall resistance value is generally higher than that of jacquard weave, and the fluctuation range with the change of the number of warp rows is more obvious. A comparison of 54 rows of samples from intarsia weave shows that when the number of warp rows increases from 2 to 4, the increase in resistance is greater than that in jacquard weave with the same parameter. This is because in intarsia weave, the conductive elastic composite braided yarns exist in independent blocks, lacking continuous conductive paths. Electron transmission needs to cross more yarn contact interfaces, and the superposition of contact resistance makes its overall resistance higher. Increasing the number of warp rows further amplifies the influence of these contact interfaces, thus making the resistance fluctuation range more significant.

[0065] To further verify the stability of this pattern, samples with 2 rows and 36 columns in jacquard and 2 columns and 54 rows in marquetry were selected and static resistance tests were repeated 5 times. The results showed that the fluctuation range of the resistance value was extremely small and the coefficient of variation was less than 0.03, indicating that the variation pattern of the static resistance has good repeatability.

[0066] Overall, the static resistance of the knitted strain sensor exhibits a clear regulation pattern with respect to structural parameters. This pattern is closely related to the connectivity of the conductive network, the length of the conductive path, and the contact resistance. This conclusion provides a key basis for subsequent optimization of the sensor's structural parameters and performance adaptation.

[0067] (3) Sensitivity performance mechanism In jacquard structures (such as) Figures 5-7As shown in the figure, the sensitivity coefficient exhibits two core trends with structural parameters: First, when the number of rows is fixed, increasing the number of columns significantly increases the maximum sensitivity coefficient. Taking a jacquard weave with 2 rows as an example, when the number of columns increases from 12 to 36, the maximum sensitivity coefficient increases significantly from 7.23 to 8.10, showing a clear upward trend. Second, when the number of columns is fixed, increasing the number of rows leads to a gradual decrease in the maximum sensitivity coefficient. When the number of columns is fixed at 36, increasing the number of rows from 2 to 4 results in a gradual decrease in the maximum sensitivity coefficient from 8.10 to 7.33. The underlying mechanism of this phenomenon is that increasing the number of warp rows extends the actual length of the conductive yarn in the fabric. When stretched, the original crimped configuration of the yarn is straightened more fully, which not only changes the orientation of the conductive fibers but also amplifies the changes in the number of contact points, contact area, and contact pressure between fibers, resulting in a significant increase in the change in resistance. On the other hand, too many cross rows will result in an excessive number of yarn interlacing points in the conductive area. When stretched, these interlacing points are prone to irreversible slippage, which disperses the concentrated control effect of stress on the conductive network, leading to a weakening of the increase in the change in resistance and a decrease in the sensitivity coefficient.

[0068] In inlaid tissue (such as) Figures 8-10 As shown in the figure, the change pattern of its sensitivity coefficient is highly consistent with that of jacquard weave, but the increase in value is more significant. When the number of longitudinal rows is fixed, the increase in the number of transverse rows has a more obvious effect on improving the sensitivity coefficient. Taking the intarsia weave with 2 longitudinal rows as an example, when the number of transverse rows increases from 18 to 54, the maximum sensitivity coefficient increases from 7.58 to 8.65, an increase of 14.1%, which is significantly higher than the increase of about 11.9% for jacquard weave under the same parameters. The mechanism of this difference is that the principal axis of strain in intarsia weave is in the longitudinal direction. Increasing the number of transverse rows directly lengthens the conductive path in the strain direction, making it easier to amplify the influence of structural deformation on the conductive network, and the increase in resistance change is more significant. When the number of transverse rows is fixed, the mechanism of the decrease in sensitivity coefficient caused by increasing the number of longitudinal rows is consistent with that of jacquard weave, both of which are due to the excessive interlacing points dispersing the stress effect.

[0069] Reproducibility and stability mechanisms Figures 11-12 This demonstrates the sensor's performance in 50 cycles of tensile testing (Note: Figure 11 and Figure 12The upper line graph shows the trend of cyclic tensile performance within the corresponding region. The jacquard 2×36 sensor exhibits excellent signal reproducibility, with high overlap in its resistance change curves and resistance fluctuation of less than 3% after 50 cycles. This stability stems from its uniform conductive network structure, where the slippage and contact state changes of the conductive yarns show good consistency during cyclic tensile testing. The intarsia 2×54 sensor has a reproducibility error of less than 5%, but its stability is slightly inferior to the jacquard structure. This is related to the stress concentration at the boundaries of conductive blocks in the intarsia structure. During cyclic tensile testing, microscopic damage can easily occur at the boundaries of conductive blocks, leading to slight changes in contact resistance. However, both sensors demonstrate long-term stability that meets the requirements of practical applications.

[0070] Comparative Example 1 Commercially available flexible conductive wires are sourced from Suzhou TechSilver Fiber Technology Co., Ltd.

[0071] Table 7 Sensitivity coefficient results of conductive elastic composite braided wire and commercially available elastic conductive wire in Example 1.

[0072] As shown in Table 7, within a wide strain range of 15% to 90%, the overall sensing performance of the conductive elastic composite braided yarn (756 dtex core yarn, 90 dtex outer yarn, 170 mesh) of the present invention is significantly better than that of commercially available elastic conductive yarn.

[0073] In summary, the conductive elastic composite braided wire prepared by this invention has the following advantages: 1) High sensitivity: The maximum sensitivity coefficient (GF(max)) of the conductive elastic composite braided wire of this invention is much higher than that of commercially available products under various strains. At 30% strain, the GF(max) of the conductive elastic composite braided wire of this invention is as high as 4.111, while that of commercially available products is only 0.681, representing a sensitivity improvement of more than 5 times.

[0074] 2) Superior stability and reliability: The minimum sensitivity coefficient (GF(min)) of the conductive elastic composite braided yarn of this invention is always positive, and it still maintains a significant response of 0.327 under 90% strain. In contrast, commercially available products show a negative GF(min) (-0.085) at 60% strain, indicating that their conductive path is unstable or has failed, resulting in poor reliability.

[0075] 3) Performance advantages over a wide strain range: The conductive elastic composite braided yarn of the present invention exhibits excellent and stable high sensitivity (GF(max) between 3.0 and 4.1) at different strain levels, while the sensitivity of commercially available products (GF(max) is only 0.681 at most) is generally at a low level.

[0076] The present invention also provides a knitted strain sensor woven from the conductive elastic braided composite yarn. After the conductive elastic braided composite yarn is made into a knitted fabric, the sensitivity of the knitted strain sensor is significantly improved, proving that the knitted structure is of research significance for optimizing the sensor performance. The design concept of "yarn-fabric" helps to further optimize the sensor performance.

[0077] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A conductive elastic composite yarn, characterized in that, It includes an elastic core yarn and a conductive outer yarn disposed on the surface of the elastic core yarn; the disposal includes weaving or covering. The density of the elastic core yarn is 324~756 dtex; the density of the conductive outer yarn is 63~126 dtex.

2. The conductive elastic composite yarn according to claim 1, characterized in that, The elastic core yarn is thermoplastic polyurethane elastic yarn or rubber yarn; The conductive outer yarn is a conductive polymer fiber yarn or a conductive metal-plated fiber yarn.

3. The conductive elastic composite yarn according to claim 2, characterized in that, The conductive polymer fiber yarn includes polypyrrole-nylon composite fiber yarn and / or poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) modified nylon fiber yarn; The metal-coated fiber yarn includes one or more of silver-plated nylon fiber yarn, silver-plated polyester fiber yarn, and copper-plated nylon fiber yarn.

4. The conductive elastic composite yarn according to claim 1, characterized in that, The diameter of the conductive elastic composite yarn is 0.4~1.1mm.

5. The method for preparing the conductive elastic composite yarn according to any one of claims 1 to 4, characterized in that, Includes the following steps: The conductive elastic composite yarn is obtained by weaving the elastic core yarn and the conductive outer yarn through a rope braiding process. Alternatively, the conductive outer yarn can be wrapped around the surface of the elastic core yarn through a coating process to obtain the conductive elastic composite yarn.

6. The preparation method according to claim 5, characterized in that, The mesh count of the weaving is 140 to 200 meshes, the number of weaving spindles is 8 or 16, and the weaving angle ranges from 30° to 78°.

7. The preparation method according to claim 5, characterized in that, The coating includes single coating, double coating, or cross coating.

8. A knitted strain sensor, characterized in that, It includes a substrate, a non-conductive region, and a conductive region; the conductive region is woven from the conductive elastic composite yarn according to any one of claims 1 to 4 or the conductive elastic composite yarn prepared by the preparation method according to any one of claims 5 to 7.

9. The knitted strain sensor according to claim 8, characterized in that, The conductive area of ​​the knitted strain sensor is single-sided jacquard, single-sided inlay, double-sided jacquard, or double-sided inlay.

10. The knitted strain sensor according to claim 8, characterized in that, When the conductive area of ​​the knitted strain sensor is single-sided jacquard or double-sided jacquard, the number of horizontal rows of the conductive area is 2 to 4, and the number of vertical rows is 12 to 36. When the conductive area of ​​the knitted strain sensor is single-sided or double-sided intarsia, the number of longitudinal rows of the conductive area is 2 to 4, and the number of transverse rows is 18 to 54.

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