Modeling And Simulation Of Tubular Weft Knitted Fabric Based On Surface Division

With the continuous development of the weft-knitting industry,the requirements for the three-dimensional visualization of weft-knitted fabrics in the weft-knitting CAD technology are getting higher and higher.The existing CAD technology research of weft knitting is basically based on the simulation of simple organization and loop unit.There are relatively few studies on the three-dimensional simulation modeling of weft knitted fabrics and the use of CAD technology to guide production.Therefore,further research on the three-dimensional simulation modeling of weft knitted fabrics is of great significance to the development of weft knitted CAD technology.On the basis of weft knitting technology,starting from the surface of tubular weft knitted fabric,a model building method based on surface division is proposed.The method is mainly divided into two parts.The first part is the division of the curved surface of the tubular weft knitted fabric.Firstly,the basic weft-knitted structure and the knitting forming process are analyzed,and on this basis,an overall plan for modeling cylindrical weft-knitted fabrics is proposed.At the same time,the modeling tool(NURBS)of tubular weft knitted fabric surface and its related properties are introduced.According to the characteristics of the weft-knitting machine and the weft-knitted fabric,the curved surface of the tubular weft knitted fabric is divided equally in the axial and circumferential directions.The tubular weft knitted fabric surface is constructed by NURBS.According to the mapping relationship between the parameter domain and the curved surface,a method of equal chord length division is proposed,and the grid division of the tubular weft knitted fabric surface is realized by combining examples.The second part is to establish a tubular weft knitted fabric model based on the results of the surface division.Firstly,a grid-loop model is proposed based on the grid and knitted loops.And select the value points on the actual loop image according to the geometric structure of the loop.Then reverse the control point to get the relationship between the control point and the width and height of the loop.Combining this relationship with the parameter domain mesh obtained by surface division,the control point parameters required by the grid-loop model are established in the surface parameter domain.And map back to the surface of the tubular weft knitted fabric.Next,a grid-loop model is established on the curved surface,and the tubular weft knitted fabric model is established through the arrangement and distribution of the grid-loop model.Verify the feasibility of this modeling method through 3D printing.Finally,the loop length is calculated according to the micro-element method,and the difference between the theoretical and actual loop lengths is compared through experimental analysis,which provides a reference for using the weaving parameter of the loop length to guide production.In order to better display the three-dimensional model of the tubular weft knitted fabric,it is simulated by Open GL.The coordinates of type value points on the model are obtained through the coordinates of control points.According to the idea of rendering settings and coordinate transformation in Open GL,a loop model constructed by the arrangement of cylinders is established.And completed the three-dimensional simulation and interaction of the tubular weft knitted fabric model under the QT framework,and the simulation results are good.