Embroidered electrocardio sensing fabric with stitch density gradient control and preparation method thereof

Abstract

The invention provides an embroidery electrocardio sensing fabric with a stitch density gradient control function and a preparation method of the embroidery electrocardio sensing fabric. The embroidery electrocardio sensing fabric comprises a flexible fabric substrate layer and an embroidery structure arranged on the flexible fabric substrate layer, the embroidery structure comprises an electrocardio-electrode contact area, a substrate area and a gradient transition area located between the electrocardio-electrode contact area and the substrate area. The gradient transition area is an area extending outwards from the boundary of the electrocardio-electrode contact area to the initial boundary of the base area, and the stitch density of the embroidery structure is gradually transited from a high level close to the electrocardio-electrode contact area to a low level close to the base area; the stitch density refers to the number of needle points in the unit length in the embroidery threading path direction and is used for representing the compactness degree of the embroidery structure; according to the technical scheme, quantitative and controllable design of embroidery stitch parameters can be realized.

Description

Technical Field

[0001] This invention relates to the field of flexible wearable electronics and smart textiles, and in particular to an embroidered electrocardiogram sensing fabric with stitch density gradient control and its preparation method. Background Technology

[0002] Electrocardiography (ECG / EKG) is an important means of detecting cardiac electrical activity. Current ECG monitoring typically uses wet electrodes in conjunction with conductive gel in contact with the skin, which can obtain relatively good signal quality. However, in long-term wear and daily use scenarios, this type of solution still has certain limitations in terms of comfort, convenience, and integration with clothing. For example, conductive gel may cause skin irritation or discomfort, the use is somewhat dependent on proper operating procedures, and changes in electrode adhesion or contact state over time can affect signal stability.

[0003] With the development of wearable electronics and smart textiles, fabric-based dry electrodes have attracted attention due to their softness, breathability, flexibility, and ease of integration with clothing. Existing fabric electrode fabrication methods include coating, printing, weaving, and embroidery. Among these, embroidery has advantages in terms of flexible pattern design, good compatibility with garment manufacturing processes, and easy precise control of the shape and position of the conductive area, making it an important method for realizing fabric electrodes.

[0004] Current embroidery techniques generally treat variations in stitch density as a means of adjusting processing efficiency or local conductivity continuity, failing to recognize the coupling relationship between the spatial continuity and rate of change of stitch density and the mechanical properties of the fabric, as well as the stability of the contact impedance at the electrode edge. Existing embroidered ECG sensing fabrics typically achieve ECG signal acquisition by forming conductive embroidery areas on the fabric surface. To ensure conductivity continuity, related solutions often employ a higher stitch density within the electrode area or differentiate between the electrode area and surrounding areas using different stitch densities. However, the inventors discovered during their research that these solutions still have room for improvement in the following aspects:

[0005] (1) Using uniform or large-area high-stitch-density embroidery in the electrode area and its surrounding area can easily lead to an increase in local stiffness of the fabric, a decrease in softness and breathability, and is not conducive to long-term wear comfort.

[0006] (2) When different stitch densities are set using a simple partitioning method, the stitch density changes abruptly at the boundary between the electrode area and the non-electrode area, which can easily cause discontinuity in the mechanical properties of the fabric and form local stress concentration during wearing, stretching or washing.

[0007] (3) Abrupt changes in the density of needle marks and the distribution of conductive materials in space may also lead to uneven distribution of conductive networks and large changes in contact impedance in the electrode edge area, thereby affecting the stability of ECG signal acquisition.

[0008] In addition, in existing embroidered ECG sensing fabrics, the setting of embroidery stitch density and related process parameters mostly depends on the operator's experience or the default parameters of the equipment, and there is a lack of clear quantitative control rules, which makes it difficult to guarantee the structural consistency and performance repeatability between different products, which is not conducive to large-scale production and quality control.

[0009] The technical problems to be solved by this invention include:

[0010] 1) How to ensure the conductivity required for ECG signal acquisition while also considering the softness of the fabric and wearing comfort;

[0011] 2) How to avoid abrupt changes in needle density at region boundaries to reduce the risks of discontinuous mechanical properties and uneven distribution of conductive networks;

[0012] 3) How to establish a quantifiable and repeatable embroidery parameter control mechanism.

[0013] Unlike methods that simply set density by partitioning or use arbitrary functions for smoothing, the inventors discovered that the spatial continuity of stitch density and its first-order rate of change in the electrode edge region are key factors affecting fabric performance. Specifically, this parameter is coupled with the fabric edge stress gradient, conductive network connectivity, and contact impedance fluctuations. Summary of the Invention

[0014] In view of this, the purpose of this invention is to provide an embroidered electrocardiogram sensing fabric with stitch density gradient control and its preparation method, so as to realize the quantitative and controllable design of embroidery stitch parameters.

[0015] To achieve the above objectives, the present invention adopts the following technical solution: an embroidered electrocardiogram (ECG) sensing fabric with stitch density gradient control, comprising a flexible fabric base layer and an embroidery structure disposed on the flexible fabric base layer; the embroidery structure includes: an ECG electrode contact area, a base area, and a gradient transition area located between the ECG electrode contact area and the base area; the gradient transition area refers to the region extending outward from the boundary of the ECG electrode contact area to the starting boundary of the base area, and its width is the shortest distance between the boundary of the ECG electrode contact area and the starting boundary of the base area; the width W is the nominal transition zone width set by the design; for irregular boundaries, along the outer normal of the boundary... Define a local width and take its nominal value as W; within the gradient transition zone, the stitch density of the embroidery structure gradually transitions from a high level near the ECG electrode contact area to a low level near the base area, thereby forming a continuous or quasi-continuous structural transition between the electrode contact area and the base area; the stitch density refers to the number of needle points per unit length along the embroidery path direction, used to characterize the density of the embroidery structure; the boundary of the ECG electrode contact area refers to the outer contour boundary of the electrode contact area formed by the conductive yarn embroidery in the fabric plane projection; when the electrode contact area is formed by fill embroidery or satin embroidery, the outer edge of the area covered by the conductive stitches is taken as the boundary.

[0016] In a preferred embodiment, the ECG electrode contact area is used to contact human skin to collect ECG bioelectric signals. The ECG electrode contact area is formed by conductive yarn embroidery, and the embroidery stitches include at least conductive stitches formed by conductive yarn, with a stitch density of a first stitch density ρ1, where ρ1 is 8-15 stitches / mm. In a preferred embodiment, the base area is located outside the ECG electrode contact area and uses non-conductive yarn, with a stitch density of a second stitch density ρ2, where ρ2 is 0-3 stitches / mm, and ρ2 = 0 stitches / mm corresponds to no embroidery or skipped stitch processing. In a preferred embodiment, the gradient transition area is set between the ECG electrode contact area and the base area; let d be the shortest distance from any point P in the gradient transition area to the boundary of the ECG electrode contact area, W be the width of the gradient transition area, and let the normalized distance parameter... Where d∈[0,W] and t∈[0,1], then the needle density ρ(d) at point P satisfies: Where f(t) is the normalized transition function, and satisfies f(0)=0 and f(1)=1; a cubic Hermite interpolation polynomial is used as the normalized transition function: .

[0017] In a preferred embodiment, the maximum rate of change of stitch density along the shortest distance d direction within the gradient transition region satisfies:

[0018] Where ρ is in needles / mm and d is in mm; the upper limit of the rate of change corresponds to the variation in the distance between adjacent needle points not exceeding the allowable elastic deformation range of the embroidery thread under the needle speed and thread tension conditions of conventional embroidery equipment, thereby avoiding the risk of local stiffness abrupt changes or stitch loosening in the gradient boundary region; where... This represents the rate of change of stitch density with distance, used to limit the variation in stitch density between adjacent positions within the transition zone; in an implementation where the gradient transition zone is discretized into n levels, the center-to-center distance between adjacent levels is set to... The needle density difference between adjacent layers is Then the following conditions are met: .

[0019] In a preferred embodiment, the embroidery stitches in the gradient transition zone are formed by a mixture of conductive and non-conductive yarns, with the proportion of conductive yarn α(d) gradually decreasing along the direction away from the ECG electrode contact area, and satisfying the following: ,in, α1 represents the proportion of conductive yarn on the side closer to the ECG electrode contact area, and α2 represents the proportion of conductive yarn on the side closer to the base area.

[0020] In a preferred embodiment, the embroidered structure includes at least two ECG electrode contact areas for forming a differential electrode pair or multi-lead electrode array for ECG signal acquisition; the spatial layout of the multiple ECG electrode contact areas can be set according to the standard ECG lead positions; the embroidered ECG sensing fabric also includes a conductive lead area, which connects the ECG electrode contact areas to the connection terminal of an external signal processing circuit.

[0021] This invention also provides a method for preparing an embroidered electrocardiogram (ECG) sensing fabric with stitch density gradient control. The method for preparing the embroidered ECG sensing fabric with stitch density gradient control includes the following steps:

[0022] S1: Select a fabric substrate and fix it to the workbench or embroidery frame of the embroidery machine. Mark the center position of the ECG electrode contact area on the fabric substrate. Determine the electrode layout according to the position of the human ECG leads. Using the boundary of the ECG electrode contact area as a reference, plan the spatial range of the gradient transition area and the base area outward in sequence.

[0023] S2: Establish a planar coordinate system with the center of the ECG electrode contact area as the origin; define the shortest distance d from any point P(x,y) in the gradient transition area to the boundary of the ECG electrode contact area; set relevant parameters for stitch density, including: stitch density ρ1 in the ECG electrode contact area is 8-15 stitches / mm; stitch density ρ2 in the base area is 0-3 stitches / mm; width W of the gradient transition area is 3-15mm; establish a stitch density distribution function; establish a conductive yarn proportion distribution function; (6) generate embroidery stitch paths for each area according to the stitch density distribution function, wherein the stitch spacing s(d) and stitch density ρ(d) satisfy When ρ(d)>0, the needle spacing is generated according to s(d)=1 / ρ(d); when ρ(d)=0 is calculated, no embroidery stitch path is generated in the corresponding area or skipped stitch processing is used. At this time, the needle spacing is no longer calculated according to s(d)=1 / ρ(d).

[0024] S3: Generate embroidery program file; including: using embroidery design software to convert the embroidery pattern into a program file that can be recognized by a computer numerical control embroidery machine; the program file or its generation process contains a layer parameter table or needle point sequence data calculated by the function, so that different devices can reproduce the same density gradient distribution when importing the same parameterization rule; the program file contains the stitch path, stitch density parameters, thread changing or mixing instructions, and stitch sequence for each functional area; for gradient transition areas, the continuous stitch density function is discretized into 3 to 8 levels, each level corresponds to an embroidery subroutine, and the connection between levels is achieved through automatic thread changing or mixing instructions;

[0025] S4: Yarn material preparation and installation; including: preparing conductive yarn, preferably silver-plated nylon yarn or silver-plated fiber yarn, with a linear density of 50-300D and a resistivity of no more than 10Ω / cm, and checking the uniformity and continuity of the yarn; preparing non-conductive yarn, the non-conductive yarn being selected to match the fabric base material, and its color being coordinated with or contrasting with the base; fixing the fabric base to the embroidery frame of the CNC embroidery machine, with the embroidery frame tension controlled at 50-80N / m; installing the conductive yarn at the first needle position of the embroidery machine, and installing the non-conductive yarn at the second needle position; using multiple needle positions when multiple yarns are required;

[0026] S5: Perform embroidery processing; including: importing the embroidery program file generated in S3 into the computer numerical control embroidery machine; setting embroidery process parameters, including needle speed of 600-800 stitches / minute, bobbin tension of 30-50 cN, top thread tension of 60-80 cN, and adjusting the presser foot pressure according to the thickness of the fabric base; performing embroidery processing according to the preset sequence; monitoring embroidery quality, including checking the evenness of stitches, whether there are skipped stitches or broken threads, and whether the tension is appropriate;

[0027] S6: Post-processing; including: trimming, trimming and cleaning loose threads on the back of the fabric; hot pressing and shaping, placing the embroidered fabric in a hot pressing device at a temperature of 100-150℃, a pressing time of 5-30s, and a pressing pressure of 0.1-0.5MPa, to make the embroidery structure smoother and improve the bonding stability between the conductive yarn and the fabric substrate; quality inspection, inspecting the embroidered ECG sensor fabric, including contact resistance testing of the ECG electrode contact area, impedance testing when in contact with simulated skin, mechanical performance testing, air permeability testing, and appearance inspection. Once qualified, the embroidered ECG sensor fabric is obtained.

[0028] In a preferred embodiment, in S2, when the ECG electrode contact area is circular, the shortest distance d from point P to the boundary of the ECG electrode contact area is calculated as follows: Where r is the distance from point P to the center of the electrode area, and R is the radius of the ECG electrode contact area; when the ECG electrode contact area is rectangular or square, its boundary is set to... Then the shortest distance d from point P(x,y) to the boundary of the electrode contact area is: ,in: When the boundary of the electrode contact area is an arbitrary closed curve, the distance d is defined as the minimum Euclidean distance from point P to that boundary curve. In this invention, when the ECG electrode contact area is rectangular or square, a fabric plane rectangular coordinate system is established. The boundary of the electrode contact area in this coordinate system can be represented as an interval. ,in:

[0029] Electrode contact area in The minimum boundary coordinates of the direction, i.e., the left boundary of the electrode. coordinate;

[0030] Electrode contact area in The maximum boundary coordinates of the direction, i.e., the right boundary of the electrode. coordinate;

[0031] Electrode contact area in The minimum boundary coordinates of the direction, i.e., the lower boundary coordinates of the electrode. coordinate;

[0032] Electrode contact area in The maximum boundary coordinates of the direction, i.e., the upper boundary of the electrode. coordinate.

[0033] For any point , and Representing points respectively Relative to the boundary of the electrode contact area direction and The excess distance in the direction (non-negative projected distance) is used to calculate the point. The shortest Euclidean distance to the boundary of the rectangle. Specifically:

[0034] The meaning is:

[0035] when At time, point exist The direction is located between the left and right boundaries of the electrode, therefore ;

[0036] when At time, point Located to the left of the left boundary, therefore (Horizontal distance to the left boundary);

[0037] when At time, point Located to the right of the right boundary, therefore (Horizontal distance to the right boundary).

[0038] The meaning is the same as above:

[0039] when hour ;

[0040] when hour (Vertical distance to the lower boundary);

[0041] when hour (Vertical distance to the upper boundary).

[0042] Therefore, point The shortest distance to the boundary of the rectangular electrode contact area can be expressed as:

[0043]

[0044] in This indicates taking the maximum value of each term within the parentheses, thus ensuring... and All are non-negative quantities, and at point... When falling within the rectangular projection area, the distance in the corresponding direction is 0.

[0045] In a preferred embodiment, in S5, the layered embroidery method of the gradient transition area is as follows: the gradient transition area is divided into n levels along the distance direction, where n is 3 to 8, and the center distance of the i-th level is: The corresponding stitch density ρᵢ and conductive yarn ratio αᵢ are respectively: Let ,but The embroidery machine completes the embroidery of each level in sequence from the outside to the inside or from the inside to the outside. The proportion of conductive yarn is adjusted between levels by automatic thread changing or mixing.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. Achieving quantitative and controllable design of embroidery stitch parameters: This invention establishes a clear functional relationship between stitch density and spatial position, enabling the stitch density to change continuously according to spatial distance, thereby achieving quantitative control of embroidery parameters, reducing reliance on manual experience, and improving process consistency and repeatability.

[0048] 2. Achieving a smooth transition between electrical and mechanical properties: By quantitatively controlling the stitch density and its spatial variation rate within the gradient transition zone, and ensuring the continuous variation of the conductive yarn proportion with spatial position, abrupt changes in the conductive network at the electrode edge and uneven contact impedance are reduced, thereby mitigating the risk of stress concentration caused by sudden changes in local stiffness. Contact impedance stability can be characterized by the fluctuation amplitude of electrode-skin impedance over time or the number of stretching cycles under simulated skin conditions. Mechanical continuity can be characterized by the tensile stress distribution in the edge region, the stitch integrity rate after cyclic stretching, or the resistance change rate. Preferably, the fluctuation amplitude can be expressed using standard deviation or peak-to-peak value. The resistance change rate can be defined as (resistance after cycles - initial resistance) / initial resistance × 100%.

[0049] 3. Helps improve the durability and stability of embroidery structures: Under repeated stretching, bending or washing conditions, it helps reduce the risk of embroidery thread loosening, breakage or fabric delamination in the boundary area, and helps maintain stable electrical properties;

[0050] 4. Balancing ECG signal acquisition performance with wearing comfort: The electrode contact area maintains a high needle density to meet acquisition requirements, while the base area has a low density and a continuous transition through the transition area, improving overall softness, breathability and tactile consistency.

[0051] 5. Reduce the amount of conductive material used and improve economic efficiency: The conductive yarn is concentrated in the electrode contact area and adjacent area, and the conductive yarn is reduced or eliminated in the substrate area, thereby reducing material costs and shortening processing time;

[0052] 6. The process implementation method is highly compatible with the existing garment manufacturing system: it can be directly applied to conventional CNC embroidery and garment production processes;

[0053] 7. It can meet the performance requirements of ECG signal acquisition applications: Under the conditions shown in the embodiment, ECG signal quality with typical characteristic waveforms and relatively stable quality can be obtained.

[0054] 8. Under the same fabric substrate and conductive yarn conditions, compared with a gradient-free or abrupt partition structure, the gradient control structure of the present invention can reduce the contact impedance fluctuation amplitude of the electrode edge region under cyclic stretching or repeated washing conditions, and has a higher conductivity network integrity retention rate. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the overall structure of the embroidered electrocardiogram sensing fabric of the present invention;

[0056] Figure 2 This is an enlarged schematic diagram of the structure of a single ECG electrode region of the present invention, showing the relative positional relationship of the ECG electrode contact area, gradient transition area and base area;

[0057] Figure 3 This is a schematic diagram illustrating the trend of needle density variation in the gradient transition region of this invention.

[0058] Figure 4 This is a schematic diagram of the structure when the gradient transition region of the present invention is discretized into multiple levels;

[0059] Figure 5 This is a schematic diagram of the circular dual-electrode embroidered electrocardiogram sensing fabric in Embodiment 1 of the present invention;

[0060] Figure 6 This is a schematic diagram of the square three-electrode embroidered ECG sensing fabric in Embodiment 2 of the present invention;

[0061] Figure 7 This is a schematic diagram of the process flow for the preparation method of the present invention.

[0062] Explanation of markings in the diagram: 1—Fabric substrate; 2—ECG electrode contact area; 3—Gradient transition area; 4—Base area; 5—Conductive lead area; 6—Connecting end; 7—Conductive yarn; 8—Non-conductive yarn. Detailed Implementation

[0063] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0064] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0065] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0066] This invention provides an embroidered electrocardiogram sensing fabric with stitch density gradient control, referenced Figure 1-7 The invention includes a flexible fabric substrate 1 and an embroidered structure disposed on the flexible fabric substrate 1. The embroidered structure includes: an ECG electrode contact area 2, a base area 4, and a gradient transition area 3 located between the ECG electrode contact area 2 and the base area 4. In this invention, stitch density refers to the number of stitches per unit length along the embroidery path, used to characterize the density of the embroidery structure; the gradient transition area 3 refers to the area extending outward from the boundary of the ECG electrode contact area 2 to the starting boundary of the base area 4, and its width is the shortest distance between the two boundaries. The width W is the nominal transition zone width set by the design; for irregular boundaries, a local width can be defined along the outer normal direction of the boundary and its nominal value can be taken as W. Within the gradient transition area 3, the stitch density of the embroidery structure gradually transitions from a higher level near the ECG electrode contact area 2 to a lower level near the base area 4, thereby forming a continuous or quasi-continuous structural transition between the ECG electrode contact area 2 and the base area 4. The boundary of the ECG electrode contact area 2 refers to the outer contour boundary of the electrode contact area formed by conductive yarn embroidery in the plane projection of the fabric; when the ECG electrode contact area 2 is formed by fill embroidery or satin embroidery, the outer edge of the area covered by the conductive stitches is used as the boundary.

[0067] The ECG electrode contact area 2 is used to contact human skin to collect ECG bioelectric signals. The ECG electrode contact area 2 is formed by embroidery of conductive yarn, and its embroidery stitches include at least conductive stitches formed by conductive yarn, and its stitch density is a first stitch density ρ1, where ρ1 is 8 to 15 stitches / mm.

[0068] The base area 4 is located outside the ECG electrode contact area 2. It is embroidered with non-conductive yarn or without embroidery. Its stitch density is the second stitch density ρ2, where ρ2 is 0 to 3 stitches / mm. ρ2 = 0 stitches / mm corresponds to no embroidery or skipped stitches.

[0069] The gradient transition region is located between the ECG electrode contact area 2 and the base region 4. Let d be the shortest distance from any point P within the gradient transition region to the boundary of the ECG electrode contact area 2, and W be the width of the gradient transition region. Let the normalized distance parameter... Where d∈[0,W] and t∈[0,1], then the needle density ρ(d) at point P satisfies:

[0070]

[0071] Where f(t) is the normalized transition function, satisfying f(0)=0 and f(1)=1. It should be emphasized that the stitch density gradient control of this invention is not only reflected in the continuous change of density values, but also in the constrained control of the spatial rate of change of stitch density, thereby achieving synergistic optimization between electrical and mechanical properties of the embroidery structure. Preferably, the gradient control simultaneously satisfies: continuous density at the endpoints, continuous (or zero) rate of change at the boundaries, and a constrained rate of change within the transition zone, thereby reducing stress concentration and contact impedance fluctuations in the edge region. The above-mentioned stitch density gradient can be structurally expressed as follows: Figure 3 The diagram illustrates the continuous trend of change and is intended to show the spatial distribution characteristics of needle density gradually decreasing from the ECG electrode contact area to the basal region within the gradient transition zone, rather than to define a specific mathematical function.

[0072] Regarding the selection criteria for the normalized transition function f(t): In the preferred embodiment of this invention, a cubic Hermite interpolation polynomial is used as the normalized transition function.

[0073]

[0074] The use of this function is based on the following technical considerations:

[0075] (i) Satisfy the endpoint constraints: f(0)=0, f(1)=1, to ensure that the stitch density is equal to ρ1 and ρ2 at both ends of the transition zone, so as to achieve continuous connection of density values;

[0076] (ii) Achieving continuity of the first derivative: f′(0)=0, f′(1)=0, making the rate of change of stitch density at the boundary zero, avoiding abrupt changes in stitch density at the boundary position, thereby reducing the discontinuity of fabric mechanical properties and the risk of stress concentration.

[0077] (III) Calculation simplicity and engineering feasibility: The cubic polynomial form is simple and easy to program in embroidery CAD software, which facilitates parameter adjustment in engineering applications;

[0078] (iv) Avoid excessive oscillation: The cubic polynomial is monotonically increasing in the interval [0,1], and there will be no oscillation phenomenon. This ensures that the stitch density changes monotonically and continuously along the spatial position, which meets the requirements of actual embroidery process.

[0079] The key to this invention lies in the fact that the normalized transition function f(t) satisfies the endpoint constraints f(0)=0 and f(1)=1, and preferably satisfies the condition that the first derivative at the boundary is continuous and zero, f′(0)=0 and f′(1)=0, to ensure that the rate of change of stitch density at the boundary is continuous and avoids abrupt changes. Based on this, f(t) can be a polynomial function, a piecewise smooth function, or a sigmoid function, etc. The cubic Hermite interpolation polynomial is preferred due to its simple calculation and ease of embedding into embroidery CAD / program files. Experimental and engineering verification shows that, under the same gradient width and endpoint stitch density conditions, using linear or piecewise functions that do not satisfy the condition that the first derivative at the endpoint is zero is more likely to lead to stress concentration in the gradient boundary region and instability of the conductive network, while functions that satisfy the endpoint derivative condition can effectively reduce the above risks.

[0080] Furthermore, the width W of the gradient transition zone is 3–15 mm, preferably 5–10 mm. The determination of this width range is based on the following considerations: when W < 3 mm, the transition zone width is too narrow, making it difficult to achieve a sufficient number of density gradient layers (typically requiring 3–8 layers), resulting in excessive density differences between adjacent layers and poor transition effect; when W > 15 mm, the transition zone occupies too much space, making it difficult to deploy multiple electrodes within a limited garment area and increasing the amount of conductive yarn used; the preferred range of 5–10 mm ensures a smooth transition while also considering space utilization and material economy.

[0081] As one of the key technical features of this invention for achieving a smooth transition of stitch density, the spatial rate of change of stitch density along the shortest distance direction is limited within the gradient transition region to avoid abrupt changes in local mechanical properties. The maximum rate of change of stitch density along the shortest distance d direction within the gradient transition region satisfies:

[0082] Where ρ is in needles / mm and d is in mm. The upper limit of the rate of change corresponds to the variation in the distance between adjacent needle points not exceeding the allowable elastic deformation range of the embroidery thread under the needle speed and thread tension conditions of conventional embroidery equipment, thereby avoiding the risk of local stiffness abrupt changes or stitch loosening in the gradient boundary region. This upper limit can be adjusted according to the elasticity of the fabric substrate, the tension of the embroidery thread, and the target contact resistance fluctuation threshold. 2 needles / mm² is a preferred example that balances workability and edge stability. It represents the rate of change of stitch density (stitches / mm) with distance (mm), and is used to limit the range of stitch density variation between adjacent positions within the transition zone.

[0083] In the implementation where the gradient transition region is discretized into n levels, the center distance between adjacent levels is set to... The needle density difference between adjacent layers is Then the following conditions are met:

[0084]

[0085] In embodiments that satisfy the above-mentioned rate of change limit, the combination parameters of ρ1, ρ2 and W can be selected accordingly.

[0086] Furthermore, the embroidery stitches in the gradient transition zone are formed by a mixture of conductive and non-conductive yarns, with the proportion of conductive yarn α(d) gradually decreasing along the direction away from the ECG electrode contact area, and satisfying the following:

[0087]

[0088] in, α1 is the proportion of conductive yarn on the side closer to the ECG electrode contact area, ranging from 60% to 90%; α2 is the proportion of conductive yarn on the side closer to the base area, ranging from 10% to 30%.

[0089] The above methods are all based on the discrete characteristics of embroidery needle points. By controlling the needle position, stitching, or coverage ratio, the proportion of conductive yarn can be statistically and repeatably adjusted, thereby satisfying the gradient control requirement of α(d). In some implementations, one or more of the following methods can be used to achieve repeatable control of the proportion of conductive yarn α(d):

[0090] (A) Periodic thread change / needle position alternation method: Within the same level, the needle position is switched according to a fixed period M so that the ratio of the number of needle points of conductive stitches to non-conductive stitches approximately satisfies α; for example, when M=10, when α=70%, it can be set that 7 out of every 10 needle points are embroidered with conductive yarn and 3 are embroidered with non-conductive yarn.

[0091] (B) Sub-region area ratio method: Divide the same level into several sub-regions, and make the area ratio of the conductive part regions α while ensuring that the needle density ρ is basically the same.

[0092] (C) Double stitching superposition method: First, a bottom layer of stitches is generated with non-conductive yarn, and then a second stitching superposition is performed with conductive yarn according to the target α coverage ratio.

[0093] Furthermore, in the actual embroidery process, the gradient transition zone can be discretized into 3 to 8 layers. For the circular ECG electrode contact area, each layer can be set as a concentric ring structure; the stitch density and conductive yarn ratio of each layer are determined by the gradient function based on the distance from the center of the layer to the boundary of the ECG electrode contact area, wherein the stitch density decreases by 10% to 25% and the conductive yarn ratio decreases by 10% to 20% between adjacent layers.

[0094] Furthermore, the conductive yarn is selected from one or more of the following: silver-plated fiber yarn, stainless steel fiber yarn, silver-plated nylon yarn, carbon fiber yarn, and conductive polymer composite yarn; the linear density of the conductive yarn is 50-300D, and the resistivity is not greater than 10Ω / cm, preferably not greater than 5Ω / cm.

[0095] Furthermore, the non-conductive yarn is selected from one or more of cotton yarn, polyester yarn, nylon yarn, spandex yarn or viscose yarn, and preferably is the same as or similar to the material of the fabric base to ensure the consistency of the overall hand feel of the fabric.

[0096] Furthermore, the shape of the ECG electrode contact area 2 is circular, elliptical, square, or polygonal, and its area is 100-2000 mm², preferably 300-800 mm².

[0097] Furthermore, the embroidery pattern of the ECG electrode contact area 2 is selected from one or more of satin embroidery, filler embroidery, or flat stitch embroidery.

[0098] Furthermore, the embroidery structure includes at least two ECG electrode contact areas 2 for forming differential electrode pairs or multi-lead electrode arrays for ECG signal acquisition; the spatial layout of the multiple ECG electrode contact areas can be set according to the standard ECG lead positions.

[0099] Furthermore, the embroidered ECG sensing fabric also includes a conductive lead area, which connects the ECG electrode contact area to the connection terminal of the external signal processing circuit. The conductive lead area is formed by embroidery with conductive yarn at a stitch density of 3 to 6 stitches / mm, preferably using a single stitch or double stitch stitching method to reduce the rigidity of the local fabric.

[0100] Furthermore, the fabric base is selected from knitted fabrics, woven fabrics or nonwoven fabrics, with a weight of 80-250 g / m², preferably 120-180 g / m²; in some embodiments, the fabric base is preferably a pure cotton or cotton / polyester blended fabric with good breathability.

[0101] In this invention, the range of values ​​for the first stitch density ρ1, the second stitch density ρ2, and the gradient transition region width W is determined based on a comprehensive consideration of factors such as conductivity continuity, fabric softness, embroidery processability, and actual wearing requirements.

[0102] The first stitch density ρ1 is used to ensure that the conductive yarns in the ECG electrode contact area form a continuous conductive network to meet the requirements of ECG signal acquisition for contact stability; the second stitch density ρ2 is used to reduce the embroidery density in the base area, thereby reducing the impact on the overall softness and breathability of the fabric; the gradient transition area width W is used to achieve a gradual change in stitch density within a limited space to avoid abrupt changes in stitch density at the junction of the ECG electrode contact area and the base area.

[0103] The above parameter range represents the preferred implementation range that enables the implementation of the technical solution of this invention and achieves the corresponding technical effects. Without departing from the technical concept of this invention, appropriate adjustments can be made according to the specific fabric material, embroidery equipment, and application requirements.

[0104] The present invention also provides a method for preparing the above-mentioned embroidered electrocardiogram sensing fabric, comprising the following steps:

[0105] S1: Base fabric preparation and zoning planning: Select the fabric base and fix it on the workbench or embroidery frame of the embroidery machine. Mark the center position of the ECG electrode contact area on the fabric base. Determine the electrode layout according to the position of the human ECG leads. Based on the boundary of the ECG electrode contact area, plan the spatial range of the gradient transition area and the base area outward in sequence.

[0106] S2: Embroidery Pattern Design and Density Function Establishment

[0107] (1) Establish a plane coordinate system with the center of the ECG electrode contact area as the origin;

[0108] (2) Define the shortest distance d from any point P(x,y) in the gradient transition region to the boundary of the ECG electrode contact area;

[0109] (3) Set the relevant parameters of needle density, including: the needle density ρ1 in the ECG electrode contact area is 8 to 15 needles / mm; the needle density ρ2 in the base area is 0 to 3 needles / mm; the width W of the gradient transition area is 3 to 15 mm;

[0110] (4) Establish the needle density distribution function: Let ,but

[0111]

[0112] in .

[0113] (5) Establish the distribution function of the proportion of conductive yarn: Let ,but

[0114]

[0115] Among them, α1 is 60%–90%, and α2 is 10%–30%;

[0116] (6) Generate the embroidery stitch path for each region based on the stitch density distribution function, wherein the stitch spacing s(d) and stitch density ρ(d) satisfy the following conditions: In some implementations, the stitch spacing in the ECG electrode contact area is 0.07–0.12 mm, and the stitch spacing in the gradient transition area gradually increases from 0.08–0.15 mm to 0.25–0.5 mm along the direction away from the electrode area. When ρ(d) > 0, the stitch spacing is generated according to s(d) = 1 / ρ(d); when ρ(d) = 0 is calculated, no embroidery stitch path is generated in the corresponding area or skipped stitch processing is used, and the stitch spacing is no longer calculated according to s(d) = 1 / ρ(d).

[0117] S3: Embroidery program file generation

[0118] (1) The embroidery pattern is converted into a program file that can be recognized by a computer numerical control embroidery machine using embroidery design software; the program file or its generation process contains a hierarchical parameter table or needle point sequence data calculated by the function, so that different devices can reproduce the same density gradient distribution when importing the same parameterization rule;

[0119] (2) The program file contains the stitch path, stitch density parameters, stitch change or stitch mixing instructions and stitch sequence for each functional area;

[0120] (3) The program file may be in DST, PES, EXP or JEF format;

[0121] (4) For the gradient transition zone, the continuous stitch density function can be discretized into 3 to 8 levels, each level corresponds to an embroidery subroutine, and the connection between levels can be achieved through automatic thread changing or thread mixing instructions.

[0122] S4: Yarn Material Preparation and Installation

[0123] (1) Prepare conductive yarn, preferably silver-plated nylon yarn or silver-plated fiber yarn, with a linear density of 50 to 300D and a resistivity of no more than 10Ω / cm, and check the uniformity and continuity of the yarn.

[0124] (2) Prepare non-conductive yarn, wherein the non-conductive yarn is selected from yarns that match the material of the fabric base, and its color can be coordinated with or contrast with the base.

[0125] (3) Fix the fabric base to the embroidery frame of the computer numerical control embroidery machine, and control the tension of the embroidery frame at 50-80 N / m;

[0126] (4) Install the conductive yarn in the first needle position of the embroidery machine and the non-conductive yarn in the second needle position; multiple needle positions can be used if multiple yarns are required.

[0127] S5: Perform embroidery processing

[0128] (1) Import the embroidery program file generated in step S3 into the computer numerical control embroidery machine;

[0129] (2) Set the embroidery process parameters, including needle speed of 600-800 stitches / minute, bottom thread tension of 30-50 cN, top thread tension of 60-80 cN, and embroidery presser foot pressure according to the thickness of the fabric base;

[0130] (3) Perform embroidery processing according to a preset sequence. In some embodiments, the embroidery processing sequence includes: first completing the embroidery of the base area or skipping the embroidery of the base area; then completing the embroidery of each level of the gradient transition area from the outside to the inside. The embroidery machine automatically switches the needle position according to the program to achieve mixed embroidery of conductive yarn and non-conductive yarn; then completing the embroidery of the ECG electrode contact area; and finally completing the embroidery of the conductive lead area. During the embroidery process, a continuous threading mode is preferred to maintain electrical continuity between different functional areas.

[0131] (4) Monitor the quality of embroidery, including checking the evenness of stitches, whether there are skipped stitches or broken threads, and whether the tension is appropriate.

[0132] S6: Post-processing

[0133] (1) Trimming treatment: Trim the loose threads and loose threads on the back of the fabric and clean up the floating threads;

[0134] (2) Hot pressing shaping treatment: The embroidered fabric is placed in a hot pressing device. The hot pressing temperature is 100-150℃, the hot pressing time is 5-30s, and the hot pressing pressure is 0.1-0.5MPa, so as to make the embroidered structure smoother and improve the bonding stability between the conductive yarn and the fabric substrate.

[0135] (3) Quality inspection: The embroidered ECG sensing fabric is inspected, including contact resistance test of ECG electrode contact area, impedance test when in contact with simulated skin, mechanical performance test, air permeability test and appearance inspection. The embroidered ECG sensing fabric is obtained after passing the inspection.

[0136] Furthermore, in step S2, when the ECG electrode contact area is circular, the shortest distance d from point P to the boundary of the ECG electrode contact area can be calculated as follows:

[0137]

[0138] Where r is the distance from point P to the center of the electrode area, and R is the radius of the ECG electrode contact area. When the ECG electrode contact area is rectangular or square, its boundary is set as... Then the shortest distance d from point P(x,y) to the boundary of the electrode contact area is:

[0139]

[0140] in: When the boundary of the electrode contact area is an arbitrary closed curve, the distance d is defined as the minimum Euclidean distance from point P to the boundary curve, which can be obtained by automatically calculating the nearest boundary point using embroidery CAD / pattern making software.

[0141] Further, in step S5, the layered embroidery method of the gradient transition area is as follows: the gradient transition area is divided into n levels according to the distance direction, where n is 3 to 8, and the center distance of the i-th level is...

[0142]

[0143] The corresponding needle density ρ i and the proportion of conductive yarn α i They are respectively: ,but

[0144]

[0145] The embroidery machine completes the embroidery of each layer in sequence from the outside to the inside or from the inside to the outside. The proportion of conductive yarn is adjusted between layers by automatic thread changing or mixing.

[0146] Furthermore, in step S6, for application scenarios that require integration with clothing, the post-processing also includes edge sealing or locking of the embroidered area, as well as softening or antibacterial treatment as needed.

[0147] The following is a detailed explanation of the embroidered ECG sensor fabrics for round and square electrodes:

[0148] Example 1: Circular dual-electrode embroidered ECG sensing fabric

[0149] The embroidered ECG sensing fabric of this embodiment includes a fabric substrate 1 and an embroidered structure disposed on the fabric substrate 1. The embroidered structure includes two ECG electrode contact areas 2, gradient transition areas 3 disposed around the periphery of each ECG electrode contact area, a base area 4 located outside the gradient transition area, and a conductive lead area 5 for electrical connection.

[0150] Fabric base 1 is made of cotton / spandex knitted fabric with a weight of approximately 150g / m² and an overall size of approximately 200mm × 150mm. The fabric base has good softness and elasticity, making it suitable for close-fitting wear.

[0151] Each ECG electrode contact area 2 is a circular structure with a diameter of approximately 25 mm. The ECG electrode contact area 2 is embroidered with conductive yarn to form conductive stitches, with a stitch density of ρ1 (approximately 12 stitches / mm). The conductive yarn is silver-plated nylon yarn with a linear density of approximately 150D and a resistivity of approximately 3 Ω / cm. The embroidery pattern uses a satin embroidery technique to create a uniformly covered and stable conductive surface.

[0152] A gradient transition zone 3 is arranged around the periphery of the ECG electrode contact area 2, with a width W of approximately 8 mm. The shortest distance from any point within the gradient transition zone to the boundary of the ECG electrode contact area is denoted as d. Let the normalized distance parameter t = d / 8, then the needle density ρ(d) within the gradient transition zone is determined according to the following relationship:

[0153]

[0154] Meanwhile, the proportion of conductive yarn α(d) in the gradient transition zone gradually decreases along the direction away from the ECG electrode contact area, and the relationship is as follows:

[0155] In actual embroidery processing, to facilitate CNC embroidery program generation and thread changing control, the gradient transition zone is discretized into four concentric ring levels. Each level uses its center distance as an approximate parameter, as shown in the table below:

[0156]

[0157] The base area 4 is located outside the gradient transition area 3 and is used to maintain the overall softness and breathability of the fabric. The base area 4 is not subject to additional embroidery treatment or is only treated with low-density non-conductive embroidery, and its stitch density is the second stitch density ρ2, which is approximately 0 stitches / mm.

[0158] The conductive lead area 5 is formed by embroidery using the conductive yarn and is used to connect the ECG electrode contact area 2 and the connection end 6. The stitch density of the conductive lead area 5 is approximately 4 stitches / mm, and the stitching method can be single stitch or double stitch to reduce local fabric rigidity while ensuring electrical continuity.

[0159] The preparation method of this embodiment can be performed according to the aforementioned steps S1 to S6. The process parameters such as embroidery equipment type, embroidery frame tension, needle speed, thread tension, and presser foot pressure can be selected and set within the preferred range given in the specification.

[0160] Under the example test conditions of this embodiment (including contact resistance test, simulated skin impedance test, cyclic stretching test, wash durability test, breathability test, and ECG signal acquisition test), compared with the structure without gradient transition or the structure with uniform high stitch density, the gradient transition structure shows a significant improvement trend in durability, wearing comfort, and edge structure stability.

[0161] Example 2: Square three-electrode embroidered ECG sensing fabric

[0162] This embodiment provides an embroidered electrocardiogram (ECG) sensing fabric with stitch density gradient control, including a fabric substrate 1 and an embroidery structure disposed on the fabric substrate 1. The embroidery structure includes three ECG electrode contact areas 2, gradient transition areas 3 respectively disposed around each ECG electrode contact area, a base area 4 located outside the gradient transition area, and conductive lead areas 5 and connection terminals 6 for connection with external signal processing circuits.

[0163] (I) Fabric substrate 1 is made of polyester woven fabric with a weight of approximately 120 g / m² and a substrate size of approximately 250 mm × 200 mm. The fabric substrate has good dimensional stability and is suitable for precise positioning and batch processing of multi-electrode structures.

[0164] (II) ECG electrode contact area; In this embodiment, three ECG electrode contact areas 2 are provided to form a three-lead ECG monitoring electrode array. Each ECG electrode contact area 2 is a square structure with a side length of approximately 20 mm and an area of ​​approximately 400 mm². 2 The three ECG electrode contact areas are arranged in an equilateral triangle on the fabric plane, with the center-to-center distance between adjacent electrodes being approximately 100 mm.

[0165] The ECG electrode contact area 2 is formed by embroidering conductive yarn to create conductive stitches, with a stitch density of the first stitch density ρ1, where ρ1 is approximately 10 stitches / mm. The embroidery pattern uses a fill embroidery method to obtain a more uniform conductive coverage and a stable contact area.

[0166] (III) Conductive and non-conductive yarns; The conductive yarn is a stainless steel fiber blended yarn with a stainless steel fiber content of approximately 30%, a linear density of approximately 200D, and a resistivity of approximately 5Ω / cm. The non-conductive yarn is a polyester yarn of the same or similar material as the fabric base, used for mixed embroidery in the gradient transition zone or for optional decorative embroidery in the base zone.

[0167] (IV) Gradient transition zones 3 are respectively arranged around the periphery of each ECG electrode contact area 2, and their width W is approximately 10 mm.

[0168] The needle density ρ(d) at any point P within the gradient transition region is determined by the shortest distance d from that point to the boundary of the corresponding ECG electrode contact area, where d ∈ [0, W]. Let t = d / W, then the needle density distribution function is:

[0169]

[0170] Wherein, ρ1 is approximately 10 stitches / mm; ρ2 is the stitch density in the base area, which can be 0 to 3 stitches / mm in this embodiment, for example, 0 stitches / mm to maintain the softness of the base.

[0171] The proportion of conductive yarn α(d) in the gradient transition zone gradually decreases along the direction away from the ECG electrode contact area, and the relationship is as follows:

[0172]

[0173] Among them, α1 is approximately 0.75 (i.e., 75%), and α2 is approximately 0.15 (i.e., 15%).

[0174] To facilitate CNC embroidery processing, this embodiment discretizes the gradient transition zone 3 into 4 levels, with each level set sequentially from the inside out along the distance direction. Example parameters are as follows:

[0175]

[0176] (V) The base area 4 is located outside the gradient transition area 3 and is used to maintain the overall softness and breathability of the fabric. The base area 4 is embroidered with non-conductive yarn at low density or is not embroidered at all, with a stitch density ρ2 of 0 to 3 stitches / mm. In this embodiment, the base area 4 is not embroidered.

[0177] (VI) The conductive lead area 5 is used to connect the contact areas 2 of each ECG electrode to the connection end 6. The conductive lead area 5 is formed by embroidery of conductive yarn, and its stitch density can be selected as 3 to 6 stitches / mm, for example 4 to 5 stitches / mm. The stitching method can be single stitch or double stitch.

[0178] Comparative Example 1: Abruptly Partitioned Embroidered ECG Sensing Fabric with No Gradient Transition

[0179] Comparative Example 1 provides an embroidered ECG sensing fabric, whose fabric substrate material, conductive yarn type, embroidery equipment and basic process parameters are consistent with those of Example 1, except that the stitch density gradient control structure described in this invention is not used.

[0180] Specifically, in Comparative Example 1, the same cotton / spandex knitted fabric as in Example 1 was used as the fabric base, with a weight of approximately 150 g / m² and a base size of approximately 200 mm × 150 mm. The ECG electrode contact area adopted the same circular structure as in Example 1, with a diameter of approximately 25 mm, and was embroidered using the same silver-plated nylon conductive yarn (linear density of approximately 150D, resistivity of approximately 3 Ω / cm).

[0181] In Comparative Example 1, the stitch density of the ECG electrode contact area is set to a first stitch density ρ1, for example, approximately 12 stitches / mm; the base area is located outside the ECG electrode contact area, and is embroidered with non-conductive yarn at low density or without embroidery, with a stitch density of a second stitch density ρ2, for example, approximately 0 stitches / mm. The ECG electrode contact area and the base area are directly adjacent in space, with no gradient transition area between them, and the stitch density abruptly changes at the boundary of the regions.

[0182] Except for the absence of a stitch density gradient transition zone, Comparative Example 1 is consistent with Example 1 in terms of embroidery pattern type, needle speed, thread tension, embroidery frame tension, conductive lead area structure, and post-processing.

[0183] Under the same test conditions (including contact impedance test under simulated skin contact conditions, cyclic tensile test and washing durability test), the embroidered ECG sensing fabric prepared in Comparative Example 1 is more prone to local stress concentration in the electrode boundary area, and the continuity of the conductive network decreases more significantly during repeated mechanical deformation, resulting in increased contact impedance fluctuation amplitude, which is not conducive to maintaining stability during long-term ECG signal acquisition.

[0184] The reason is that, due to the lack of continuous transition control of stitch density, the stitch density changes abruptly at the junction of the electrode area and the base area, resulting in obvious mechanical discontinuity in the embroidery structure in this area, which makes it easier to induce local structural instability during stretching, bending or washing.

[0185] Comparative Example 2: Uniform high stitch density embroidered ECG sensor fabric

[0186] Comparative Example 2 provides another embroidered ECG sensing fabric, whose fabric substrate, conductive yarn type, embroidery equipment and processing conditions are consistent with those of Example 1. The difference is that a uniform high stitch density embroidery structure is used in the electrode-related area and its surrounding area.

[0187] Specifically, in Comparative Example 2, the shape, size, and position of the ECG electrode contact area are the same as in Example 1; conductive yarn is used for embroidery in the ECG electrode contact area and a certain range around it, and the embroidery stitch density is basically consistent in space, for example, it is set to about 12 stitches / mm. No gradient control is performed on the stitch density, and no gradient transition area with continuous transition characteristics is set.

[0188] Except for the different spatial distribution of stitch density, Comparative Example 2 is consistent with Example 1 in terms of fabric substrate material, linear density of conductive yarn, resistivity, embroidery pattern type, needle speed, thread tension and post-processing.

[0189] Under the same test conditions, compared with Example 1, the embroidered ECG sensing fabric prepared in Comparative Example 2 forms a uniform high-stitch-density embroidery structure over a larger area, resulting in a significant increase in local fabric stiffness, a decrease in air permeability and tactile consistency, and a significant increase in the amount of conductive yarn used.

[0190] The reason is that while uniform high stitch density embroidery can ensure electrical continuity, it does not constrain the rate of change of stitch density in the electrode edge area, making it difficult to achieve a comprehensive balance between electrical performance, mechanical performance and wearing comfort.

Claims

1. An embroidered electrocardiogram sensing fabric with stitch density gradient control, characterized in that, The system includes a flexible fabric base layer and an embroidered structure disposed on the flexible fabric base layer. The embroidered structure includes: an ECG electrode contact area, a base area, and a gradient transition area located between the ECG electrode contact area and the base area. The gradient transition area refers to the region extending outward from the boundary of the ECG electrode contact area to the starting boundary of the base area, and its width is the shortest distance between the boundary of the ECG electrode contact area and the starting boundary of the base area. The width W is the nominal transition zone width set by the design. For irregular boundaries, a local width is defined along the outer normal direction of the boundary and its nominal value is taken as W. Within the transition zone, the stitch density of the embroidery structure gradually transitions from a high level near the ECG electrode contact area to a low level near the base area, thus forming a continuous or quasi-continuous structural transition between the electrode contact area and the base area. The stitch density refers to the number of needle points per unit length along the embroidery path, used to characterize the density of the embroidery structure. The boundary of the ECG electrode contact area refers to the outer contour boundary of the electrode contact area formed by the conductive yarn embroidery in the fabric plane projection. When the electrode contact area is formed using fill embroidery or satin embroidery, the outer edge of the area covered by the conductive stitches is used as the boundary.

2. The embroidered ECG sensing fabric with stitch density gradient control according to claim 1, characterized in that, The ECG electrode contact area is used to contact human skin to collect ECG bioelectric signals. The ECG electrode contact area is formed by embroidery with conductive yarn, and the embroidery stitches include at least conductive stitches formed by conductive yarn, with a stitch density of a first stitch density ρ1, where ρ1 is 8 to 15 stitches / mm.

3. The embroidered ECG sensing fabric with stitch density gradient control according to claim 1, characterized in that, The base area is located outside the contact area of ​​the ECG electrode, and is made of non-conductive yarn. Its stitch density is the second stitch density ρ2, where ρ2 is 0 to 3 stitches / mm. ρ2 = 0 stitches / mm corresponds to no embroidery or skipped stitch processing.

4. The embroidered ECG sensing fabric with stitch density gradient control according to claim 1, characterized in that, The gradient transition region is located between the ECG electrode contact area and the base region; let d be the shortest distance from any point P within the gradient transition region to the boundary of the ECG electrode contact area, and W be the width of the gradient transition region; let the normalized distance parameter... Where d∈[0,W] and t∈[0,1], then the needle density ρ(d) at point P satisfies: Where f(t) is the normalized transition function, and satisfies f(0)=0 and f(1)=1; a cubic Hermite interpolation polynomial is used as the normalized transition function: .

5. The embroidered ECG sensing fabric with stitch density gradient control according to claim 1, characterized in that, The maximum rate of change of stitch density along the shortest distance d direction within the gradient transition region satisfies: Where ρ is in needles / mm and d is in mm; the upper limit of the rate of change corresponds to the variation in the distance between adjacent needle points not exceeding the allowable elastic deformation range of the embroidery thread under the needle speed and thread tension conditions of conventional embroidery equipment, thereby avoiding the risk of local stiffness abrupt changes or stitch loosening in the gradient boundary region; where... This represents the rate of change of stitch density with distance, used to limit the variation in stitch density between adjacent positions within the transition zone; in an implementation where the gradient transition zone is discretized into n levels, the center-to-center distance between adjacent levels is set to... The needle density difference between adjacent layers is Then the following conditions are met: .

6. The embroidered ECG sensing fabric with stitch density gradient control according to claim 1, characterized in that, The embroidery stitches in the gradient transition zone are formed by a mixture of conductive and non-conductive yarns, with the proportion of conductive yarn α(d) gradually decreasing away from the ECG electrode contact area, and satisfying the following: ,in, α1 represents the proportion of conductive yarn on the side closer to the ECG electrode contact area, and α2 represents the proportion of conductive yarn on the side closer to the base area.

7. The embroidered ECG sensing fabric with stitch density gradient control according to claim 1, characterized in that, The embroidered structure includes at least two ECG electrode contact areas for forming differential electrode pairs or multi-lead electrode arrays for ECG signal acquisition; the spatial layout of the multiple ECG electrode contact areas can be set according to the standard ECG lead positions; the embroidered ECG sensing fabric also includes a conductive lead area, which connects the ECG electrode contact areas to the connection terminal of an external signal processing circuit.

8. A method for preparing an embroidered electrocardiogram sensing fabric with stitch density gradient control, characterized in that, The preparation of the stitch density gradient controlled embroidered electrocardiogram sensing fabric according to any one of claims 1-7 comprises the following steps: S1: Select a fabric substrate and fix it to the workbench or embroidery frame of the embroidery machine. Mark the center position of the ECG electrode contact area on the fabric substrate. Determine the electrode layout according to the position of the human ECG leads. Using the boundary of the ECG electrode contact area as a reference, plan the spatial range of the gradient transition area and the base area outward in sequence. S2: Establish a planar coordinate system with the center of the ECG electrode contact area as the origin; define the shortest distance d from any point P(x,y) in the gradient transition zone to the boundary of the ECG electrode contact area; Set relevant parameters for stitch density, including: stitch density ρ1 in the ECG electrode contact area is 8-15 stitches / mm; stitch density ρ2 in the base area is 0-3 stitches / mm; width W of the gradient transition area is 3-15mm; establish a stitch density distribution function; establish a conductive yarn proportion distribution function; (6) generate embroidery stitch paths for each area according to the stitch density distribution function, wherein the stitch spacing s(d) and stitch density ρ(d) satisfy When ρ(d)>0, the needle spacing is generated according to s(d)=1 / ρ(d); when ρ(d)=0 is calculated, no embroidery stitch path is generated in the corresponding area or skipped stitch processing is used. At this time, the needle spacing is no longer calculated according to s(d)=1 / ρ(d). S3: Generate embroidery program file; including: using embroidery design software to convert the embroidery pattern into a program file that can be recognized by a computer numerical control embroidery machine; the program file or its generation process contains a layer parameter table or needle point sequence data calculated by the function, so that different devices can reproduce the same density gradient distribution when importing the same parameterization rule; the program file contains the stitch path, stitch density parameters, thread changing or mixing instructions, and stitch sequence for each functional area; for gradient transition areas, the continuous stitch density function is discretized into 3 to 8 levels, each level corresponds to an embroidery subroutine, and the connection between levels is achieved through automatic thread changing or mixing instructions; S4: Yarn material preparation and installation; including: preparing conductive yarn, preferably silver-plated nylon yarn or silver-plated fiber yarn, with a linear density of 50-300D and a resistivity of no more than 10Ω / cm, and checking the uniformity and continuity of the yarn; preparing non-conductive yarn, the non-conductive yarn being selected to match the fabric base material, and its color being coordinated with or contrasting with the base; fixing the fabric base to the embroidery frame of the CNC embroidery machine, with the embroidery frame tension controlled at 50-80N / m; installing the conductive yarn at the first needle position of the embroidery machine, and installing the non-conductive yarn at the second needle position; using multiple needle positions when multiple yarns are required; S5: Perform embroidery processing; including: importing the embroidery program file generated in S3 into the computer numerical control embroidery machine; setting embroidery process parameters, including needle speed of 600-800 stitches / minute, bobbin tension of 30-50 cN, top thread tension of 60-80 cN, and adjusting the presser foot pressure according to the thickness of the fabric base; performing embroidery processing according to the preset sequence; monitoring embroidery quality, including checking the evenness of stitches, whether there are skipped stitches or broken threads, and whether the tension is appropriate; S6: Post-processing; including: trimming, trimming and cleaning loose threads on the back of the fabric; hot pressing and shaping, placing the embroidered fabric in a hot pressing device at a temperature of 100-150℃, a pressing time of 5-30s, and a pressing pressure of 0.1-0.5MPa, to make the embroidery structure smoother and improve the bonding stability between the conductive yarn and the fabric substrate; quality inspection, inspecting the embroidered ECG sensor fabric, including contact resistance testing of the ECG electrode contact area, impedance testing when in contact with simulated skin, mechanical performance testing, air permeability testing, and appearance inspection. Once qualified, the embroidered ECG sensor fabric is obtained.

9. The method for preparing an embroidered electrocardiogram sensing fabric with stitch density gradient control according to claim 1, characterized in that, In S2, when the ECG electrode contact area is circular, the calculation of the shortest distance d from point P to the boundary of the ECG electrode contact area is as follows: Where r is the distance from point P to the center of the electrode area, and R is the radius of the ECG electrode contact area; when the ECG electrode contact area is rectangular or square, its boundary is set to... Then the shortest distance d from point P(x,y) to the boundary of the electrode contact area is: ,in: When the boundary of the electrode contact area is an arbitrary closed curve, the distance d is defined as the minimum Euclidean distance from point P to the boundary curve.

10. The method for preparing an embroidered electrocardiogram sensing fabric with stitch density gradient control according to claim 1, characterized in that, In S5, the layered embroidery method of the gradient transition area is as follows: the gradient transition area is divided into n levels according to the distance direction, where n is 3 to 8, and the center distance of the i-th level is: The corresponding needle density ρ i and the proportion of conductive yarn α i They are respectively: ,but The embroidery machine completes the embroidery of each level in sequence from the outside to the inside or from the inside to the outside. The proportion of conductive yarn is adjusted between levels by automatic thread changing or mixing.

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