The Research On Outputting The IGES Format File Of Fabric Geometry

It is essential to simulate the fabric geometry accurately and then to saved it as a file for a 3D textile CAD system.In order to share the information between different textile CAD systems the fabric geometry information should be saved according to universal accepted standard.The United States released the first the initial graphics exchange specification Initial Graphics Exchange Specification(IGES)which develops data conversion between different platforms,so did China list IGES in GB14213-2008.The key to save a geometry IGES file is how to decompose the components of geometry properly,represent it by code according to specification then write the float data of components information in the right position of parameter data section to insure the data can be read and shared.Fabric(woven fabric ? knitted fabric and braided fabric)consists of a number of yarns,the point is how to represent the components of yarn in fabric by using IGES file.In this research,the yarn is divided into three parts: the yarn body and two end faces in order to represent complete yarn entity.The cross section of the yarn body is modeled by closed secondary quasi-uniform NURBS curve which modeled by 18 control points,the control line is modeled by cubic quasi-uniform NURBS curve;the two end faces of the yarn also modeled by NURBS surface,setting the U direction in secondary quasi-uniform NURBS curve which was made up of different size ring,and using a quasi-uniform NURBS curve to build the V direction which is along the radius to the center.Then assemble different shape of cross section along the axis direction,thus the NURBS surface model of bending yarn will be modeled.The yarn entity is the geometry invariability which is modeled by NURBS and it can represent the changeable cross section,the yarn can be uniform and changeable to reflect the shape variation ofvarious kinds of fabric.The information can be stored in a particular TXT file.The directory entry section and parameter data section of IGES file record the important information of components.In parameter data section,the data is arranged based on the specification,and then write the directory entry section to record the property information and the number of lines.The main idea is to exchange the information in TXT file to B-Spline curve data and further transform to IGES file in writing yarn information into IGES file.According the specification of IGES,a software is developed under Visual C++ to read the TXT file of yarn and fabric,write the information into IGES file by automatic calculating all the yarn B-Spline surface information.The main problem is how to preserve the information of NURBS surface in writing yarn information into the IGES file.The file can be opened by commonly used 3D design software Rhinoceros and Pro/E,further operation of grid can be aided to the yarn entity with no data missing which proves the outputting of IGES format file of fabric geometry is effective.