Study On Structure And Realistic Simulation Of Warp-knitted Laces

Due to the exquisite outlook and top-grade quality,warp-knitted laces are widely used as decorations,home textiles and fashion materials.However,there are two bottlenecks when developing new products,namely the technical complexity and cost-consuming production.For solving this issue,a computer-aided design(CAD)system based on realistic simulation of laces has been developed and remains being improved by scholars which can help directly check simulation results after finishing techniques design and make revisions without making fabric samples.Although the present lace CAD systems can be used for designing and simulating most patterns,they cannot yet efficiently handle any extremely complicated or newly fashionable lace techniques.Meanwhile,simulation results formed by these CAD systems cannot ideally show realistic fabric appearance.Therefore,to meet the immediate needs of designing new laces and to solve the problems in lace simulation,this work conducted a research on building a mathematic model for CAD structure design and presented a simulation method for structural deformation and appearance visualization.The built model and presented approach were used for developing a CAD system for warp-knitted laces.Since the knitting principle and mathematic representation of warp-knitted lace structures are the basis of building CAD design and simulation models,this work primarily studied the basic ground structures,jacquard structures and multibar pattern structures,focuses of which were on Cliptronic jacquard technology,yarn-cutting patterns and lace selvages design.Based on that,a CAD design model was built with mathematic matrixes of threading cycle,lapping data and jacquard bitmap to act as the basis of CAD simulation modeling.Much attention was paid to the representation of Cliptronic jacquard technology with matrixes and an approach of designing jacquard borderline structures.With the mathematic model above,an improved mass-spring model was proposed for simulating lace structural deformation behavior.Roots of lace loops were simplified as mass particles and thus the fabric was referred as a mass matrix.Underlaps and loop legs were treated as structural massless springs to link particles,including ground springs,jacquard springs and pattern springs.Based on that,the resultant elastic force loaded on particles by these springs was calculated according to the Newton's second law and the Hook's law after analyzing factors on causing loops deformation.Motion of particles caused by the elastic forces of springs was solved by using explicit Euler equations.The solution accuracy was converged to first order because of forward difference quotient.System stability was improved by eliminating the velocity variable and computing the particle shift at any time step.Research was also done for solving possible problems of super elasticity and particle collision with two-dimensional oriented bounding boxes,thus ensuring no unreasonable loops penetration.To prove the simulation accuracy of loops deformation based on the mass-spring model,a feature matching method in computer images processing was proposed,based on which the mesh contour features of both real lace image and simulation result were extracted firstly by morphological dilating and eroding algorithms.Afterwards,seven Hu invariant moments of each image were calculated to solve the similarity.Therefore,after tested with a real lace sample and its simulation result,the mass-spring model was proved practical and accurate in simulating lace structural deformation.As to simulating realistic visualization of lace structures,this work took yarns as research targets to conclude HSV color distribution along yarn diameter based on real yarn photographs.While the features of light intensity along the yarn axis,namely the lapping length,were studied by building pattern structures geometries.By using digital image processing technology,meshes of hue,saturation and value of real yarn photographs were extracted and projected on yarn section plane to show features along yarn diameter.Based on least-square method,the projected curves in HSV color mode were then fitted with piecewise linear segments for obtaining featured functions of dull,semi-dull and shinning wrapped yarns.Then to know features along lapping length,an improved BlinnPhong lighting model was adopted and geometries of pattern structures were drawn to solve light intensity along yarn length with piecewise functions.Feature functions along both yarn diameter and length were summed up with tested weights to finally show visual appearance of lace patterns.The solved features in geometric coordinate were transferred to pixels with featured colors for rendering simulation results according to the Gouraud method.A model for visible lapping detection was also proposed when dealing with multi-bar lapping coverage based on an improved depth buffer method.With the above mathematic matrixes of lace structures and simulation models,a CAD simulation system for warp-knitted laces was developed via Visual Studio platform.The system frame and main functions were introduced.The windows of designing technical parameters,views of designing patterns and simulating laces were realized by designing data structures of threading,lapping and jacquard information.This interactive design interface made it possible to efficiently design and simulate warp-knitted laces with better quality,which was proved by three classic lace patterns.The above four steps conducted to finish this work are all for developing an advanced CAD system for designing and realistically simulating laces.Studies on structures and mathematic representation act as the basis,simulation modeling of deformation and visual appearance as the focus,and finally system developing acts as the key purpose,as well as efficiently saving design time and upgrading design quality.The research achievement can be used as a reference for realizing customized production and 3D virtual reality of lace products.