Formation Simulation Of Weft-Knitted Fabrics Based On Yarn Dynamics

The shape of weft knitted fabrics will deform during the knitting process due to the influence of materials,composite structures,and knitting technological.For fabrics knitted with different structures,their steady shapes after knitting process always deviate from designed shapes due to the unbalanced force between the internal loops,such as sweaters,scarves,and knitted knee pads,which are common in daily life.Therefore,this paper proposes a method that can accurately simulate the appearance of a weft knitted fabric and its overall shape after knitting by building the geometric and physical model of weft knitted fabrics,which can predict their true shape after molding,and be used to guide actual production and improve production efficiency.First,we established the geometric model of weft knitted fabric.The weft knitted fabric is represented by mesh-loop units and a series of control points are calculated to control the yarn direction of the weft knitted fabric.The control points are fitted using a cubic Catmull-Rom spline curve to describe the geometric centerline of the yarn;The three-dimensional surface of the yarn is constructed based on the Frenet frame.Secondly,we established the physical model of weft knitted fabric.The continuous yarns constituting the weft knitted fabric are divided into yarn segments,and each segment is regarded as an elastic rod with a certain elastic modulus;Based on the Euler-Lagrange equation,the dynamic equation of yarn is constructed,and the tensile and bending deformation of yarn is analyzed.The corresponding energy and force equations are established;A global damping is set for the system to stabilize the deformation of the weft knitted fabric.Thirdly,we simulate the knitting process of weft knitted fabric.The BMP images are used as design input diagrams of the simulation,and mapped to the initial simulation model of the weft knitted fabric.Then,iterative simulation is carried out to solve the dynamic equation of each time step and update the geometric modeling of knitted fabric.In response to the penetration problem of yarn under force during the simulation process,this paper first uses OBB bounding boxes to perform preliminary collision detection on the yarn,and then uses discrete spheres to represent the yarn for further collision detection and calculate the collision force.After obtaining a stable simulation model of knitted fabrics,the contour of the knitted fabric is extracted through image processing methods,and the contour is described using image moments.A metric for evaluating the similarity of knitted fabric contours is proposed.Finally,we design and develop the simulation system for weft knitted fabric formation according to the simulation scheme of weft knitted fabric formation.Two different types of weft knitted fabrics were designed and simulated using this system,and the accuracy of the simulation results was evaluated.This paper focuses on the problem of deviation between the actual shape and design shape of weft knitted fabrics after forming.A simulation study of weft k nitted fabrics is conducted,and a weft knitted fabric forming simulation system is developed.It can predict the true shape of weft knitted fabrics after forming,reduce the number of samples,and shorten the production cycle,which has important practical significance.