CN118036303A

CN118036303A - Yarn-level simulation method and system for flower-type weft knitted fabric

Info

Publication number: CN118036303A
Application number: CN202410196564.0A
Authority: CN
Inventors: 汝欣; 彭来湖; 郑诗怡; 胡旭东; 史伟民
Original assignee: Zhejiang Sci Tech University ZSTU
Current assignee: Zhejiang Sci Tech University ZSTU
Priority date: 2024-02-22
Filing date: 2024-02-22
Publication date: 2024-05-14

Abstract

The invention discloses a yarn-level simulation method and a system of a flower-type weft-knitted fabric, belonging to the technical field of fabric simulation, wherein the method comprises the following steps: establishing a coil model; establishing a mapping relation between a rectangular grid and each coil control point in the coil model, and establishing a grid coil model based on the mapping relation; fitting a fabric yarn central line corresponding to the grid coil model to obtain a fabric geometric model; introducing a motion vector to calculate the position variation of each coil control point in the coil model, and determining the position of the control point of the fancy weft knitted fabric by combining the grid coil model and the motion vector; establishing a geometric model of the fancy weft-knitted fabric comprising different coil types; establishing a fabric physical model; calculating a stable position of the control point based on a yarn dynamics equation; adjusting the fabric geometric model to obtain a target fabric geometric model; the visualized target fabric geometry model is compared with the actual fabric sample. And the prediction simulation accuracy is improved, and the cost is reduced and the efficiency is improved.

Description

Yarn-level simulation method and system for flower-type weft knitted fabric

Technical Field

The invention belongs to the technical field of fabric simulation, and particularly relates to a yarn-level simulation method and system of a flower-type weft-knitted fabric.

Background

Knitted fabrics have soft hand feeling and strong air permeability, are popular among the public, and various colors are used for fabric production with the improvement of the aesthetic of users. However, in the knitting process, the yarn is restrained by the loom to generate tension, after the loom is relaxed, the external restraint is released, the knitted fabric is deformed, and particularly the knitted fabric formed by the colored tissue is unstable and easy to deform. For example, when forming a float stitch, the amount of yarn used is significantly less than in other parts, and the shrinkage of the yarn after the external restraint is released is different from that in other parts, resulting in a change in fabric density. However, the patterns of the fabric are varied, and various patterns can be generated by combining different tissue structures according to different arrangements. Therefore, the finally woven fabric is often quite different from the size, pattern and the like designed by a designer, and the design needs to be repeated to obtain an ideal fabric.

In the prior art, the simulation method for the fancy weft-knitted fabric is complex and has poor accuracy, so that the research and development cost of the fabric product is high, the efficiency is low, and the quality of the produced fabric is poor.

Disclosure of Invention

The invention provides a yarn-level simulation method and system for a flower-type weft-knitted fabric, which aims to solve the technical problems of high research and development cost, low efficiency and poor quality of produced fabrics of the fabric products caused by complex and poor accuracy simulation methods for the flower-type weft-knitted fabric in the prior art.

First aspect

The invention provides a yarn-level simulation method of a flower-type weft-knitted fabric, which comprises the following steps:

S101: respectively establishing a coil model comprising a plurality of coil control points according to a coil basic unit, wherein the coil basic unit comprises looping, arc suspending, floating and loop transferring, and the control points comprise a plurality of arc settling control points and a plurality of needle arc braiding control points;

S102: establishing a mapping relation between a rectangular grid and each coil control point in the coil model, and establishing a grid coil model based on the mapping relation;

S103: fitting a three-time Catmull Rom spline curve to the central line of the fabric yarn corresponding to the grid coil model to obtain a fabric geometric model;

s104: introducing a motion vector to calculate the position variation of each coil control point in the coil model, and determining the position of the control point of the fancy weft knitted fabric by combining the grid coil model and the motion vector;

S105: establishing a geometric model of the fancy weft-knitted fabric comprising different coil types;

S106: establishing a fabric physical model according to stress information of the fancy weft-knitted fabric by combining with a yarn dynamics equation, wherein the stress information comprises bending stress, tensile stress, collision force and global damping force;

S107: taking data corresponding to the geometric model as input, and calculating the stable position of the control point after a plurality of time step iterations by combining the motion vector and the fabric physical model;

S108: adjusting the fabric geometric model according to the stable position of the coil control point to obtain a target fabric geometric model;

s109: and (3) visualizing the target fabric geometric model, and comparing the visualized target fabric geometric model with an actual fabric sample to determine whether the fabric geometric model is consistent with the actual fabric sample.

Second aspect

The invention provides a yarn-level simulation system of a flower-type weft knitted fabric, which comprises a processor and a memory for storing executable instructions of the processor; the processor is configured to invoke the memory-stored instructions for performing the yarn-level simulation method of the fancy weft knit in the first aspect.

Compared with the prior art, the invention has at least the following beneficial technical effects:

In the invention, the complex fancy weft knitted fabric is classified by establishing the grid-coil models of four basic coil units, namely looping, arc suspending, floating and loop transferring, so that the analysis flow is simplified, and the accuracy of the simulation result is improved. The method comprises the steps of realizing structural change description of coils through motion vectors, generating a fabric control point model through arrangement and combination of coil units, fitting control points through three Catmull Rom spline curves, obtaining a geometric center line with a tandem structure, improving fitting effect, representing a pattern structure through the geometric model, automatically identifying coil information and motion vectors of the coil structure, color, shrinkage and the like as simulation input, outputting a target fabric geometric model, calculating stress deformation of the fabric through a yarn-level physical model, accurately describing stress deformation conditions of the yarn in the production process, calculating positions of the control points, finally iterating to obtain stable deformed fabric, providing simulation data base, improving simulation result accuracy, forming an efficient and automatic fabric simulation method, improving the prediction effect of the yarn in-machine, enabling the produced fabric to conform to the design structure of the fabric, saving time and raw material cost of repeated design, and improving quality of the produced fabric.

Drawings

The above features, technical features, advantages and implementation of the present invention will be further described in the following description of preferred embodiments with reference to the accompanying drawings in a clear and easily understood manner.

FIG. 1 is a schematic flow chart of a yarn-level simulation method of a flower-type weft knitted fabric provided by the invention;

FIG. 2 is a schematic diagram of a looping structure of a weft knit fabric of the present invention;

FIG. 3 is a schematic view of the structure of the suspension loops, floats and loop transfer of a pattern weft knitted fabric provided by the invention;

FIG. 4 is a cubic Catmull Rom spline curve of adjacent control points and fitted yarn geometric center lines provided by the invention;

FIG. 5 is a schematic view of a loop up-shift, loop shift right-shift and left-shift provided by the present invention;

FIG. 6 is a schematic diagram of a geometric modeling flow provided by the present invention;

FIG. 7 is a schematic view of different color coils according to the present invention;

FIG. 8 is a schematic illustration of the force applied to a yarn in a weaving process provided by the present invention;

FIG. 9 is a schematic diagram showing a comparison of the coil before and after deformation;

FIG. 10 is a schematic diagram showing a comparison of the coil before and after deformation according to another embodiment of the present invention;

FIG. 11 is a comparison of selected samples and simulation results provided by the present invention;

FIG. 12 is a graph of the profile comparison of selected samples and simulation results provided by the present invention.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will explain the specific embodiments of the present invention with reference to the accompanying drawings. It is evident that the drawings in the following description are only examples of the invention, from which other drawings and other embodiments can be obtained by a person skilled in the art without inventive effort.

For simplicity of the drawing, only the parts relevant to the invention are schematically shown in each drawing, and they do not represent the actual structure thereof as a product. Additionally, in order to simplify the drawing for ease of understanding, components having the same structure or function in some of the drawings are shown schematically with only one of them, or only one of them is labeled. Herein, "a" means not only "only this one" but also "more than one" case.

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

In this context, it should be noted that the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected, unless explicitly stated or limited otherwise; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

In addition, in the description of the present invention, the terms "first," "second," and the like are used merely to distinguish between descriptions and are not to be construed as indicating or implying relative importance.

Example 1

In one embodiment, referring to fig. 1 of the specification, a schematic flow chart of a yarn-level simulation method of a fancy weft knitted fabric provided by the invention is shown. Referring to fig. 2 of the drawings, there is shown a schematic diagram of a looping structure of a weft knitted fabric according to the present invention. Referring to fig. 3 of the drawings, there is shown a schematic diagram of the structure of suspension loops, floats and loop transfer of a flower-type weft knitted fabric according to the present invention.

In fig. 2, (a) represents a real fabric made of plain knitting and (b) represents a mesh stitch model of plain knitting. The yarn passes through the knitting arc of the old loop needle and is sleeved on the settling arc of the next loop to form a loop, and the yarn is divided into a front loop and a back loop according to the direction of the string sleeve. From the fabric samples, 9 control points were used to construct the loop structure, as shown in fig. 2 (b), P ₀、P₁、P₇、P₈ corresponds to the sinker loop and P ₂～P₆ corresponds to the needle sinker loop.

In fig. 3, (a) represents a real fabric made up of suspended arcs, (b) represents a real fabric made up of floating threads, (c) represents a real fabric made up of loop-transferred threads, (d) represents a mesh-coil model of suspended arcs, (e) represents a mesh-coil model of floating threads, and (f) represents a mesh-coil model of loop-transferred threads. The suspension loops (fig. 3 (a)) are open structures formed by direct upward stretching of the yarn from the old stitch loops. The float (fig. 3 (b)) is a horizontal structure formed at the front or rear of the previous row of stitches, since the knitting needles are not hooked on the yarn, and the float pattern is constructed by 3 control points in one grid, and the operation of crossing a plurality of columns is achieved by continuously combining the float patterns. The transfer (fig. 3 (c)) is a structure in which the loops are serially sleeved on another column to the left or right, and thus the sinker and needle loops of the transfer are on different columns. The mesh coil models thereof are respectively established according to the structures of the suspension arcs, the floats and the loop transfer (fig. 3 (d), (e) and (f)), and the loop transfer model illustrating the transfer of one needle is called a standard loop transfer model.

S101: a coil model including a plurality of coil control points is built from the coil base units, respectively.

The coil basic unit comprises looping, arc suspending, floating and loop transferring, and the control points comprise a plurality of arc settling control points and a plurality of needle arc braiding control points.

The main task of this step is to decompose the structure of the fancy weft knitted fabric into various stitch types and to build a corresponding control point model for each stitch type. By building the stitch model according to the stitch basic unit, the detail and special structure of the fancy weft knitted fabric can be more accurately captured, and different stitch types correspond to different control point layouts, so that the appearance and texture of the knitted fabric can be more truly simulated. By introducing multiple sinker loop control points and multiple needle plaiting loop control points, finer control of the fabric structure can be achieved, which helps to accurately simulate various flower-type knitting effects, including fabric textures and shapes of different stitch types, during simulation. By considering different coil basic units, the method can adapt to the structural difference of various flower-type weft-knitted fabrics, and the modeling mode enables the simulation method to be more universal, so that the method is applicable to flower-type weft-knitted fabrics of different types and styles. Through careful coil modeling, the simulation accuracy is improved, and the simulation result is more close to the actual fancy weft-knitted fabric.

S102: and establishing a mapping relation between the rectangular grid and each coil control point in the coil model, and establishing a grid coil model based on the mapping relation.

In one possible implementation, the mapping relationship is specifically:

P_i＝k_x,iwx+k_y,ihy+k_z,ilz

Wherein k _x,i、k_y,i、k_z,i represents the proportionality coefficients of the control point P _i in the directions of the x axis, the y axis and the z axis in different coil models, x, y and z represent unit vectors in the directions of the x axis, the y axis and the z axis respectively, w represents the width of one grid, namely the circle distance, h represents the height of one grid, namely the circle height, and l represents the thickness of the grid in the direction of the z axis.

Referring to tables 1 to 5, specific values of the scaling factor of each coil model control point are shown.

TABLE 1 front face looping control Point coordinates and corresponding front face looping scaling factor

TABLE 2 reverse face looping control Point coordinates and corresponding reverse face looping scaling factor

TABLE 3 suspension arc control Point coordinates and corresponding suspension arc scaling factor

TABLE 4 float control Point coordinates and corresponding float scaling factors

TABLE 5 transfer control Point coordinates and corresponding transfer scaling factors

In particular, the effect of this mapping relationship is to map control points in the coil model to corresponding locations on the rectangular grid. By such mapping, an efficient fusion of the coil model and the mesh can be achieved in the simulation. Such a mapping relationship is critical for establishing an accurate simulation model, so that the simulation result is more real and reliable.

Referring to fig. 4 of the drawings, there is shown a cubic catmul Rom spline curve of adjacent control points and the fitted yarn geometric center line provided by the present invention.

In fig. 4, as shown in fig. 4 (a), P _k(s) is a cubic Catmull Rom spline curve between adjacent control points P _k、P_k+1, P _k(s) is calculated by four control points P _k-1～P_k+2, fig. 4 (b) is a geometric center line of a yarn in a certain time step, since the position of the control point will be updated once in iteration, the time step t needs to be introduced into an expression to obtain a geometric center line expression in any time step in the whole simulation process, and in this case, emphasis is placed on a knitted fabric composed of a single yarn to reduce the influence of deformation related to yarn twist, so that after the geometric center line is obtained, the yarn surface is obtained by scanning in a circular section without twisting treatment, and the section diameter is the yarn diameter.

S103: and fitting the central line of the fabric yarn corresponding to the grid coil model through three Catmull Rom spline curves to obtain the fabric geometric model.

Wherein a cubic catmul Rom spline is a smooth mathematical curve interpolation method, typically used to fit a smooth curve over a given set of control points. Such a curve consists of a series of cubic polynomial segments, each segment being defined by two adjacent control points. These cubic polynomials meet some conditions of smoothness and continuity, ensuring a smooth transition of the curve at the junction point. The cubic catmul Rom spline ensures smoothness between adjacent control points, avoiding discontinuities and folds of the curve. This is critical for simulating the true motion trajectory of the yarns of a fabric, especially in fancy weft-knitted fabrics, where the trajectory of the yarns can be very complex. The cubic Catmull Rom spline curve is continuously differentiable, meaning that the first and second derivatives of the curve are continuous throughout the curve. This is very helpful in accurately describing the bending and curvature variations of the fabric yarns, as this information is critical to simulating the appearance of fancy weft knitted fabrics. The cubic catmul Rom spline curve can be interpolated by a given control point, ensuring that the curve passes through all given control points. This is useful for deriving the shape of the fabric yarn centerline from actual data, as it retains the key features that are actually observed. By using a three-time Catmull Rom spline curve to fit the center line of the fabric yarn, the bending and shape change of the yarn in space can be more accurately simulated, so that the simulation result is more real and more close to the actual situation. The continuity and micromanipulation of the cubic catmul Rom spline ensures smooth transitions of the fabric geometry model obtained during simulation, avoiding unnatural jumps and discontinuities. By interpolation and fitting of the center line of the fabric yarn, the motion characteristics of the yarn can be captured more accurately, and the simulation precision and accuracy are improved.

After the grid coil model is established, three times of Catmull Rom (C-R) spline curve control points are selected for fitting, so that a smooth yarn geometric center line capable of being controlled locally is obtained. Compared with the Bezier curve which does not have locality, the position of a control point is changed by the C-R spline curve to only influence the curve between the control point and the adjacent control point, compared with the characteristic of NURBS curve approximation fitting, the algorithm of C-R spline interpolation fitting can be used for arbitrarily controlling the points on the curve, and because a geometric model of fancy tissues needs to be established, compared with single plain and rib tissues, the structure is more complex, the geometric center line needs to be precisely controlled, and therefore, the C-R spline curve which can directly control each point on the curve is selected, and the fitting accuracy is improved.

In one possible implementation, S103 specifically includes:

s1031: fitting the fabric yarn centerlines of adjacent control points:

wherein b _i(s) represents a basis function, s represents a basis function factor, and i represents a control point index;

S1032: determining the fabric yarn centerline P _k (s, t) at any time t:

Wherein P _i (t) represents the control point position at time t;

s1033: and splicing the central lines of the yarns of the fabric at any time in sequence to obtain the geometric model of the fabric.

Referring to fig. 5 of the drawings, there is shown a schematic view of loop up-transfer, loop transfer right-transfer and left-transfer provided by the present invention.

In fig. 5, P _i denotes the control point position of the standard coil, P _i' denotes the control point position of the coil after one row of upward movement, and P _i "denotes the control point position of the coil after two rows of upward movement (the same applies to the looping).

As can be seen from fig. 5, the closed coils of the previous row cannot achieve a normal series of loops due to the existence of the suspended arcs and floats, and are elongated in the longitudinal direction to form a coil structure spanning one or more rows, which is actually formed by a loop formation variation. Likewise, the transfer loops vary in the lateral direction, forming a coil structure that spans one or more columns. The shape of the coil is related to the position of the needle-knitted arc string cover, and when the coil is elongated, the mesh where the needle-knitted arc is located is moved upward in the y-axis direction on the basis of the looping pattern as shown in fig. 5 (a). When the coil moves left and right, the mesh on which the needle arcs are located is moved left or right in the x-axis direction on the basis of the standard loop transfer model, as shown in fig. 4 (b). We therefore represent the change of the stitch loops from their initial position to their relative movement position by the motion vector MV (ax, ay), and the changed stitch model is obtained by standard stitches. The current index grid position is M (i, j), the initial needle arc position is the grid unit where the standard coil needle arc is located, for example, the initial needle arc position of the looping needle is M (i+1, j) shown in (a), the initial needle arc position of the right shift loop needle is M (i+1, j+1) shown in (b), and i and j are the row and the column where the grid is located respectively. Δx represents the number of rows of the coil needle arcs moving longitudinally, which is only a positive number, and Δy represents the number of columns of the coil needle arcs moving laterally, which is a negative number when moving left and a positive number when moving right. The motion vector of the standard coil is mv= (0, 0).

S104: and introducing a motion vector to calculate the position variation of each coil control point in the coil model, and determining the position of the control point of the fancy weft-knitted fabric by combining the grid coil model and the motion vector.

Wherein the motion vector is a vector describing the change in position of the object in space, and contains displacement information of the object from one position to another, and the motion vector is used for calculating the change in position of a loop model control point in the fancy weft knitted fabric. By introducing the motion vector, the motion track of the coil in the space can be better captured, so that the simulation of the fancy weft-knitted fabric is more accurate and lifelike, and the real simulation capability of the fabric structure is improved.

In step S104, a motion vector is introduced to calculate the amount of positional change of each coil control point in the coil model, including longitudinal and lateral movements, and changes in coordinate components in x, y, z-axis directions, the calculation of the motion vector being based on the type of the current coil basic unit and the situation of surrounding coil basic units.

It should be noted that a calculation mode of a motion vector is adopted to accurately describe the position change of the loop model control point in the fancy weft knitted fabric. The method comprises the steps of firstly calculating the motion vector of the current coil basic unit according to the types of surrounding coil basic units, and considering different situations such as left shift, right shift, arc suspension shift and the like. Then, by combining the mesh coil model and the calculated movement vector, the position change of the control point of the fancy weft knitted fabric in the three-dimensional space including the longitudinal and transverse movements and the change of the coordinate components is determined. The process not only realizes the accurate control of the fabric structure, but also considers the moving modes of different coil types, improves the adaptability and the accuracy of simulation, and ensures the consistency and the integrity of the whole simulation model. Through S104, the appearance and the structure of the fancy weft-knitted fabric can be more finely simulated, and the authenticity and the reliability of the simulation result are enhanced.

In one possible implementation, S104 specifically includes:

s1041: and calculating the motion vector of the current coil basic unit, namely the position change quantity of the current coil basic unit according to the types of the surrounding coil basic units.

In one possible implementation, S1041 specifically includes:

S1041A: determining a current index grid position:

M(i,j)

Wherein i and j represent the row index and column index of the current grid, respectively;

S1041B: determining initial vectors of a standard coil and a current coil basic unit, wherein the standard coil is a coil basic unit type with unchanged type, and the current coil basic unit is a coil basic unit type after needle movement:

The initial vector of the standard coil is: mv= (0, 0);

the initial position of the left shift transfer needle knitting arc is as follows: m (i+1, j-1);

the initial position of the right shift transfer needle knitting arc is as follows: m (i+1, j+1);

The initial position of the knitting needle of the loop is: m (i+1, j);

S1041C: under the condition that the current coil basic unit is in a left-shift loop transferring mode, the motion vector of the current coil basic unit is (delta x, delta y) = (0, 0), under the condition that the coil type of a grid where a needle knitting arc is located is recognized as a suspension arc or a floating line, the motion vector of the current coil is delta y-1, the needle knitting arc position after movement is M (i+1, j-1+delta y), and under the condition that the needle knitting arc position after movement is still a suspension arc or a floating line, the motion vector of the current coil is delta y-1-1;

Under the condition that the current coil basic unit moves rightwards, the motion vector of the current coil basic unit is delta y+1, the moved needle knitting position is M (i+1, j+1+delta y), and under the condition that the moved needle knitting position is still a suspension arc or a floating line, the motion vector of the current coil is delta y+1+1;

under the condition that the current coil basic unit moves in a suspended arc, the motion vector of the current coil basic unit is deltax+1, the moved needle knitting position is M (i+1+deltax, j), and under the condition that the moved needle knitting position is still in a suspended arc or a floating line, the motion vector of the current coil is deltax+1+1.

S1042: determining the positions of control points of the fancy weft-knitted fabric by combining the grid coil model and the motion vector:

Wherein Δx >0 represents the number of columns of longitudinal movement of the coil needle winding, Δy represents the number of columns of transverse movement of the coil needle winding, wherein (P _ix,P_iy,P_iz) represents the coordinate components of the ith control point in the directions of x axis, y axis and z axis, and (P _ix',P_iy',P_iz') represents the coordinate components of the ith control point after movement in the directions of x axis, y axis and z axis.

It should be noted that the needle arc starts to move from the initial position according to the movement vector, and the movement vector of the coil is calculated according to the type of the surrounding coil. The translation matrix is defined according to the width and height of the motion vector and the rectangular grid, P _i is the initial coil control point, and the position P _i' of the moved coil control point is calculated. The coil settling arc is fixed, and the motion vector of the control point is (0, 0). All control point positions of the fancy fabrics can be derived based on the standard coil grid-coil model and the motion vector.

Referring to fig. 6 of the specification, a schematic diagram of a geometric modeling flow provided by the present invention is shown.

S105: a geometric model is established comprising fancy weft-knitted fabrics of different stitch types.

The geometric model refers to a design drawing or pattern expression of the fancy weft-knitted fabric, and is specifically represented by a matrix, wherein the matrix represents the structure of the whole fancy weft-knitted fabric, different elements correspond to different grid cells, and information such as coil types, colors, static lengths and the like of all parts is reflected. The geometric model is a powerful tool, and the design of the fancy weft-knitted fabric is expressed in a clear and visible mode, so that more control and flexibility are provided for a designer, and meanwhile, a foundation is provided for subsequent simulation and cooperation.

Referring to fig. 7 of the specification, a schematic diagram of coil structures with different colors provided by the invention is shown;

It should be noted that, for convenience of use and convenience of computer program analysis of knitting patterns, we use color as a logo to represent a geometric model, and squares in the geometric model are pattern topologies represented by color values RGB, each of the squares of one coil type, and fig. 7 lists squares of different colors, RGB values, and their corresponding coil structures.

To describe, store and read the coil information on the geometric model, a two-dimensional matrix of the geometric model is built, the coil information on the square being denoted c (i, j). The coil information comprises a coil type, a coil color and a coil static length, and the coil type, the coil color and the coil static length are correspondingly related to the color value of the square lattice. According to the schematic diagram, traversing the corresponding m×n two-dimensional rectangular grid, identifying the coil information of the corresponding grid unit M (i, j), calculating a motion vector, and outputting a grid coil model. And (3) calculating coordinates of all control points by defining space coordinates of the grid, fitting to generate a smooth yarn center line, and finally obtaining the three-dimensional surface of the knitted fabric.

By the above method, creating an arbitrary fabric pattern becomes a problem of tiling squares into a pattern. By constructing the pattern using this representation, it is possible to simplify the design and modification of the knitting pattern and ensure the production of an effective knitting pattern, which builds the basis for the later simulation.

In one possible implementation, S105 specifically includes:

S1051: establishing a two-dimensional matrix C of the fancy weft knitted fabric by taking the rectangular grid as a unit;

C(i,j)

wherein i=1, 2, …, m, m represents the number of rows of the geometric model, j=1, 2, …, n, n represents the number of columns of the geometric model, wherein the number of rows of the geometric model and the number of columns of the geometric model are respectively equal to the number of rows and the number of columns of the fancy weft-knitted fabric;

S1052: distributing coil colors of each coil type, and binding the coil types, the coil colors and the coil static lengths with corresponding two-dimensional matrix positions;

s1053: traversing each matrix grid in the two-dimensional matrix of the fancy weft-knitted fabric, calculating corresponding coil motion vectors, fitting the yarn center line of the fabric, and obtaining the three-dimensional surface of the knitted fabric, namely a geometric model C' of the fancy weft-knitted fabric:

Referring to fig. 8 of the specification, a schematic diagram of the stress of the yarn in the weaving process is shown.

Fig. 8 shows a schematic view of various energy generated by the stress of the yarn, and of course, the knitted fabric is subjected to the above energy changes, and also has factors such as influence due to twisting of the yarn and shearing force, but the influence of these factors is small, and is not considered herein.

S106: and (3) combining with a yarn dynamics equation, and establishing a fabric physical model according to stress information of the fancy weft-knitted fabric.

The stress information comprises bending stress, tensile stress, collision force and global damping force.

In one possible embodiment, the fabric physical model is specifically:

Wherein T _k represents the yarn section kinetic energy, U _k represents the yarn section internal energy, i.e. the vector sum of the yarn tensile stress and bending stress, and f _k represents the external force to which the yarn section is subjected, including the collision force and the global damping force.

Specifically, by using a yarn dynamics equation, stress information such as bending stress, tensile stress, collision force, global damping force and the like of the fancy weft knitted fabric is considered, and a physical model of the fabric is established, and can be used for describing movement and deformation of the fabric under the action of external force. By combining with yarn dynamics equations, various stress information is considered, so that the established physical model is more in line with the movement and deformation of the actual fancy weft-knitted fabric, and the authenticity and accuracy of the model are improved. S106, stress information of various aspects is considered, including bending stress, tensile stress, collision force and global damping force, and the comprehensive consideration enables the model to be comprehensive and complex, and the real physical behaviors of the fancy weft-knitted fabric can be captured. And after the physical model is established, subsequent simulation and analysis can be more easily carried out, the performances of the fancy weft-knitted fabric under various conditions can be predicted, and powerful support is provided for design and engineering decision-making.

In general, a more detailed and comprehensive physical model is established for the fancy weft-knitted fabric by combining a yarn dynamics equation and considering various stress information, so that the simulation accuracy and practicability are improved.

It should be noted that, on the basis of geometric modeling, another emphasis on simulation of the fancy weft-knitted fabric is to build a physical model. The knitted fabric is formed by hooking yarns into loops by crochets, and the longitudinal loops are mutually sleeved in a stringing way and the transverse loops are continuous. Yarns are subjected to a number of different forces, both internal due to deformation of the yarn itself and external due to yarn-to-yarn contact. The knitting needles pull the yarns to form loops in the weaving process, and the yarns have bending stress; simultaneously, a certain pulling force is applied to the yarn in the weaving process, and the yarn has elasticity, so that external restraint is released after the yarn is taken off, and the yarn generates tensile stress; in the deformation process, collision force can be generated when yarns are contacted with each other; the whole piece of fabric generates global damping when doing deformation motion.

S107: and taking data corresponding to the geometric model as input, carrying out stress analysis on the fabric physical model, and calculating the stable position of the control point after a plurality of time step iterations by combining the motion vector.

It should be noted that, by obtaining the rest length and setting the rest length of the coil, the initial shape of the coil in the static state can be considered more accurately, thereby improving the accuracy of the force analysis. And various physical parameters such as the stretching coefficient, the bending coefficient, the damping coefficient, the collision coefficient and the like of the yarns are considered, so that the stress analysis is more comprehensive and more real. By iterative calculation, the time evolution process of the control point can be obtained, and the stable control point position is obtained, which is necessary for simulating the dynamic behavior of the fancy weft-knitted fabric. The data of the geometric model is analyzed, and the force analysis is carried out on the fancy weft knitted fabric by combining with a yarn dynamics equation, so that various physical parameters and shapes in a static state are considered, and a foundation is provided for subsequent simulation and emulation.

The method is characterized in that a physical model is established according to stress analysis of yarns, positions of yarn control points are solved based on Lagrange dynamic equations, deformation effects of the fabric are obtained through iteration, and deformation simulation of the fancy weft-knitted fabric is achieved.

In one possible implementation, S107 specifically includes:

S1071: obtaining static lengths l _rest of different loops of the fancy weft knitted fabric in a static state, and storing the static lengths into loop information in a corresponding geometric model;

S1072: analyzing an initial model of the fancy weft-knitted fabric according to the geometric model, and setting a loop static length, a yarn stretching coefficient, a bending coefficient, a damping coefficient and a collision coefficient of each loop type;

S1073: the positions of all control points are displayed and solved by using a yarn dynamics equation;

S1074: calculating the iteration positions P (t+deltat) of the control points of all the control points in each yarn segment after one time step of iteration until stable control points are obtained, and stopping the iteration:

where Δt represents a time step length.

The initial simulation model of the knitted fabric was in an ideal state, and the yarns constituting the stitches were in a stretched state, and at this time, all the stitches in the knitted fabric had an ideal shape, but were in an unstable state. In order to simulate the resting shape of the knitted fabric after it is taken off, a resting length of the input stitch is required. The static length of the coil after various tissues were taken off-machine by measuring the fabric sample before the simulation started and stored in the coil information. At the beginning of the simulation, an initial model is precipitated according to a schematic diagram of a schematic maker, and the static length of the coil and the tensile coefficient, bending coefficient, damping coefficient and collision coefficient of the yarn are set. After the start of the simulation, the loops try to return from the stretched state to the rest state, and as the different stitches set the corresponding loop rest lengths, different shrinkage forces are generated inside the yarns of the different stitches, and these forces act on the control points constituting the yarns. And displaying and solving the positions of the control points by using a yarn dynamics equation to realize the shrinkage of the yarns and the deformation of the fabric. With known yarn segments, the positions of all control points of the yarn are calculated to iterate one time step later, thus obtaining new yarn positions, iterating repeatedly until a deformation stable fabric model is generated.

In one possible embodiment, S1074 specifically includes:

S1074A: judging whether to stop iteration or not by the yarn shrinkage L (t) _ratio:

wherein l (0) and l (t) respectively represent the sum of yarn lengths corresponding to each coil at time step 0 and time step t;

S1074B: and under the condition that the yarn shrinkage difference value of the continuous time steps is in the preset yarn shrinkage change range, determining to obtain the stable control point, and stopping iteration.

According to the experimental results, in the shrinkage rate change process of the plain stitch in the simulation process, it can be seen that after the simulation is started, the shrinkage rate of the yarn is obviously reduced and the volatility is reduced after a certain time step, and finally the plain stitch is stabilized in a smaller range, and the fluctuation is the result that the physical properties such as yarn shrinkage, collision and the like jointly act on the knitted fabric model.

In the practical application process, in order to improve the simulation efficiency, the difference value of the shrinkage rate of the continuous time step is used as the judgment basis for the stability of the knitted fabric model, and as the set time step is very small, the shrinkage rate difference value of the continuous time step is too small, so that judgment errors are easy to be caused, and whether the difference value of the shrinkage rate of the calculated yarn in the time steps t and t-50 is smaller than or equal to a set threshold value theta:

|L(t)_ratio-L(t-50)_ratio|≤θ

If the difference value of 20 times is smaller than the threshold value, the shrinkage of the tissue is considered to be stable, and when the shrinkage of all tissues in the fabric is considered to be stable, the deformation of the fabric is considered to be stable, and the simulation is ended. In the simulation of the scheme, the threshold value is specifically 10 ^-4.

It should be noted that, the size of the predetermined yarn shrinkage can be set by those skilled in the art according to actual needs, and the present invention is not limited herein.

Referring to fig. 9 of the specification, a comparative schematic diagram of a coil before and after deformation is shown.

Referring to fig. 10 of the drawings, there is shown a comparative schematic diagram of the coil before and after deformation of another coil according to the present invention.

Fig. 9 and 10 are results of simulation experiments, and fig. 9 shows a comparison between an initial model of a flower color tissue and a simulation result: (a), (d) and (g) are geometric models, (b), (e) and (h) are initial models of suspension arcs, floats and loop transfers, and (c), (f) and (i) are simulation results of suspension arcs, floats and loop transfers. Fig. 9 shows a comparison of the initial model and simulation results for three flower structures: (a), (d) and (g) are geometric models, (b), (e) and (h) are initial models, and (c), (f) and (i) are simulation results. Experiments based on Microsoft Visual Studio 2019IDE and OpenGL graphics library, simulation experiments were completed on AMD Ryzen 55600Hwith Radeon Graphics (specifications: 3.30GHz and 16GB RAM) equipment, and the time step of iterative solution was 0.00001s. To clearly show the deformation effect of the basic structure, a comparison of the tuck, float and loop transfer before and after deformation is made as shown in fig. 9. In order to verify that the method can be used for correctly establishing the fancy knitted fabric model and simulating the deformation effects of different flower types, the comparison of the structures of various flower types shown in fig. 10 before and after deformation is made.

S108: and adjusting the fabric geometric model according to the stable position of the coil control point to obtain the target fabric geometric model.

Referring to fig. 11 of the drawings, a comparison of selected samples and simulation results provided by the present invention is shown.

Fig. 11 shows initial models, simulation results and sample physical graphs for 9 cases. The geometric model provided by the method can accurately represent the shape of the fabric, and a good deformation effect can be simulated through the physical model. The scheme designs 9 samples, and weaves experimental samples on a Fengshan computerized flat knitting machine. All fabrics tested were woven on the same flat knitting machine with the same yarn (3 icelandings). In order to obtain the mesh width w and the mesh height h of the initial model, a flat knitted fabric uniform sample is knitted by using the same knitting parameters under the same environment, and the stitch pitch and the stitch height of the flat knitted fabric uniformly distributed are measured. The measured loop height to loop distance ratio was 0.6, yarn radius was 2mm, and an initial model of the fabric was generated by the method of 2.4. The static length l _rest of the coil is measured by a disassembling method according to the actual fabric, in order to simulate the reliability of input, based on plain stitch, the fabrics with evenly distributed suspension arcs, floats and loop transfer are respectively woven under the same weaving parameters, and the static length is measured and averaged. The static length of each coil type and other simulation parameters are specifically 2.28cm of looping static length, 0.5/cm of floating line static length, 3.23/cm of loop moving static length, 1.73/cm of suspension arc static length, 10000gcm ²/s² of stretching coefficient, 0.008gcm ²/s² of bending coefficient, 0.8g/s of damping, 8000 of collision force and 0.006g/cm of mass.

Specifically, visual C++ and OpenGL can be utilized to visualize the designed fancy weft-knitted fabric, the reliability and the accuracy of the simulation method are proved by comparing the simulation result with the outline of an actual sample, the research can be used for the molding simulation of the fancy weft-knitted fabric, the machine unloading effect can be predicted, the time and the raw material cost for repeated design are saved, and the foundation is provided for simulating three-dimensional knitted clothing.

Referring to fig. 12 of the drawings, a profile comparison result graph of selected samples and simulation results provided by the present invention is shown.

In fig. 12, sample is a sample, contour comparison is a contour comparison, and the serial number is the sample serial number.

To verify the accuracy and reliability of our method, the simulation results were compared with experimental samples. The contours of the sample and the simulation result are extracted by an image processing method, and the similarity of the sample and the simulation result is intuitively displayed. In order to describe the profile similarity more accurately, a similarity index S (a, B) is defined, a represents the profile of the sample, B represents the profile of the simulation result, and the more S (a, B) tends to 0 to represent the higher the profile similarity. Table 3 shows the profile comparison graphs and similarity indexes of all the case samples and the simulation results, wherein the dark lines represent the sample profiles, the light lines represent the simulation profiles, and it can be seen that the similarity between the simulation results and the real objects is very high.

It should be noted that, we set up the grid-coil model of four basic coil units of looping, arc suspending, floating and loop transferring, realize the structural change of the coil by moving vector, generate the fabric control point model by the arrangement and combination of the coil units, fit the control point with three Catmull Rom spline curves, and obtain the geometric center line with the tandem structure. The geometric model is used for representing the pattern structure, the coil information and the motion vector of the coil structure, the color, the shrinkage rate and the like are automatically identified as the input of simulation, and the initial model of the knitted fabric is output. In addition, the physical model of yarn grade is used for calculating the stress deformation of the fabric, an explicit method is used for solving a mechanical equation, the position of a control point is calculated, the stable deformed fabric is obtained through iteration, finally, a method for analyzing and verifying the fabric is made, the simulation result is compared with a sample, and the result shows that the fancy weft knitting fabric model established by the method is effective, the deformation effect is close to a real object, and the method has higher precision and vivid flower-shaped effect.

In the invention, the complex fancy weft knitted fabric is classified by establishing the grid-coil models of four basic coil units, namely looping, arc suspending, floating and loop transferring, so that the analysis flow is simplified, and the accuracy of the simulation result is improved. The method comprises the steps of realizing structural change description of coils through motion vectors, generating a fabric control point model through arrangement and combination of coil units, fitting control points through three Catmull Rom spline curves, obtaining a geometric center line with a tandem structure, improving fitting effect, representing a pattern structure through the geometric model, automatically identifying coil information and motion vectors of the coil structure, color, shrinkage and the like as simulation input, outputting a target fabric geometric model, calculating stress deformation of the fabric through a yarn-level physical model, accurately describing stress deformation conditions of the yarn in the production process, calculating the positions of the control points, finally iterating to obtain stable deformed fabric, providing simulation data base, improving simulation result accuracy, forming an efficient and automatic fabric simulation method, improving yarn unloading prediction effect, enabling the produced fabric to conform to the design structure of the fabric, saving time and raw material cost of repeated design, and improving quality of the produced fabric.

Example 2

In one embodiment, the invention provides a yarn-level simulation system of a fancy weft-knitted fabric, which is used for executing the yarn-level simulation method of the fancy weft-knitted fabric in the embodiment 1.

The yarn-level simulation system of the flower-type weft-knitted fabric provided by the invention can realize the steps and effects of the yarn-level simulation method of the flower-type weft-knitted fabric in the embodiment 1, and in order to avoid repetition, the invention is not repeated.

The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The foregoing examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims

1. A yarn-level simulation method of a flower-type weft knitted fabric, characterized by comprising:

s103: fitting the central line of the fabric yarn corresponding to the grid coil model through three Catmull Rom spline curves to obtain a fabric geometric model;

s106: establishing a fabric physical model according to stress information of the fancy weft-knitted fabric by combining a yarn dynamics equation, wherein the stress information comprises bending stress, tensile stress, collision force and global damping force;

S107: taking data corresponding to the geometric model as input, and calculating stable positions of the control points after a plurality of time step iterations by combining the motion vector and the fabric physical model;

S109: and visualizing the target fabric geometric model, comparing the visualized target fabric geometric model with an actual fabric sample, and determining whether the fabric geometric model is consistent with the actual fabric sample.

2. The yarn-level simulation method of a fancy weft knitted fabric according to claim 1, wherein the mapping relation is specifically:

P_i＝k_x,iwx+k_y,ihy+k_z,ilz

3. The yarn-level simulation method of a fancy weft knitted fabric according to claim 1, wherein S103 specifically comprises:

s1031: fitting the fabric yarn centerlines of adjacent control points:

S1032: determining the fabric yarn centerline P _k (s, t) at any time t:

Wherein P _i (t) represents the control point position at time t;

4. The yarn-level simulation method of a fancy weft knitted fabric according to claim 1, wherein S104 specifically comprises:

S1041: calculating a motion vector of a current coil basic unit, namely a position change amount of the current coil basic unit according to the types of surrounding coil basic units;

S1042: determining control point positions of the fancy weft knitted fabric by combining the grid coil model and the motion vector:

5. The yarn-level simulation method of a fancy weft knitted fabric according to claim 4, wherein S1041 specifically comprises:

S1041A: determining a current index grid position:

M(i,j)

the initial vector of the standard coil is: mv= (0, 0);

the initial position of the knitting needle is: m (i+1, j);

6. The yarn-level simulation method of a fancy weft knitted fabric according to claim 1, wherein S105 specifically comprises:

s1051: establishing a two-dimensional matrix C of the fancy weft-knitted fabric by taking the rectangular grid as a unit;

C(i,j)

wherein i=1, 2, …, m, m represents the number of geometric model rows, j=1, 2, …, n, n represents the number of geometric model columns, wherein the number of geometric model rows and the number of geometric model columns are respectively equal to the number of rows and the number of columns of the fancy weft-knitted fabric;

s1053: traversing each matrix grid in the two-dimensional matrix of the fancy weft knitted fabric, calculating corresponding coil motion vectors, fitting the central line of the yarn of the fabric, and obtaining the three-dimensional surface of the knitted fabric, namely a geometric model C' of the fancy weft knitted fabric:

7. Yarn-level simulation method of a fancy weft knitted fabric according to claim 1, characterized in that the fabric physical model is specifically:

8. The yarn-level simulation method of a fancy weft knitted fabric according to claim 1, wherein S107 specifically comprises:

s1072: analyzing an initial model of the fancy weft-knitted fabric according to the geometric model, and setting a coil static length, a yarn stretching coefficient, a bending coefficient, a damping coefficient and a collision coefficient of each coil type;

S1073: the yarn dynamics equation is utilized to display and solve the positions of all the control points;

where Δt represents a time step length.

9. The yarn-level simulation method of a fancy weft knitted fabric according to claim 8, wherein S1074 specifically comprises:

10. Yarn level simulation system for a fancy weft knitted fabric, characterized by being adapted to perform a yarn level simulation method for a fancy weft knitted fabric according to any one of claims 1 to 9.