Mechanical Properties Analysis Of Yarn Strand-Machine Element In Tufting Carpet Machine

With the improvement of living standards of modern society, higher demands for carpet yield and quality were put forward by consumers, main focus on yield and color patterns of carpet. With the development of tufting industry, the enterprises have raised the demands for high efficiency, high speed tufting machine. Thus, digital tufting carpet loom which can achieve more8pile heights and jacquard resolution of1st needle and big pattern cycling of full scale, has been researched and developed by the college of mechanical engineering of Donghua University and others enterprises. It had successfully solved some crucial technologies, for example, group control and decoupling of multi-electronic rollers, path planning and allocation of yarn strand and jacquard methods of online compounding, etc.The process of Jacquard tufting carpet is very complex. The yarn strand after passing the yarn tube, electronic roller, guide yarn roller and multi-layer yarn guides, was threaded with needle which penetrating through backing fabric. The feeding length and tension of single yarn strand have an important influence on the pile height of loop.Aimed at the process of big pattern cycle of full scale tufting carpet, the viscoelasticity and nonlinear transversal vibration of high diner yarn strand, the mechanical properties between yarn and machine part, the interaction between needle and nonwoven etc., were researched in this dissertation.Since the viscoelasticity of yarn strand has very important effect on vibration analysis, feeding length, tension control and eliminating start-up marks. Firstly, according to experimental conditions, the optimal viscoelastic model and its parameters were determined by applying nonlinear LMF into experimental results of yarn strand based on the combination of theoretical modeling and experimental analysis. The results showed that the linear viscoelastic model fits well the mechanical experimental curves, and could be employed to analyze the vibration characteristics of yarn during the tufting. At the same time, the methods for eliminating start-up marks on carpet surface were researched in theoretical. So, four mechanical models were proposed to characterize the creep behavior of carpet yarns after dynamic loading. The constitutive equations for characterizing creep properties after dynamic loading were derived by applying Laplace's transformation. The parameters of the model were obtained by fitting the mechanical model with the experimental results using the Marquardt algorithm for nonlinear regression. A control program was written for the INSTRON tensile tester to carry out dynamic loading of the yarn between two force levels. When comparing the experimental creep curve with the fitted curve from the mechanical model, it is clear that the four-parameter model is a suitable model to describe the creep behavior during tufting machine stoppage since it has the highest coefficient and the lowest residual sum of square. The elongation of carpet yarns during carpet machine stoppage under constant stress can be calculated by applying the theoretical model. Thus, the start-up marks when the carpet machine restarts can be eliminated by adjusting the feeding length according to the calculated elongation.Secondly, the yarn strand was controlled by all kinds of parts, for example jacquard roller, tension roller and other parts with different speeds during jacquard tufting system. A complex coupling system was composed between yarn strand and controlling parts. Since the influence of shaft eccentric of roller, reciprocating motion of needle and transient velocity of electronic roller, the yarn strand will vibrate and the tension will be varied, which has an influence on pile height. The constitutive relation which has been verified in chapter2nd was used for charactering the viscoelasticity of yarn strand, a partial differential equation governing the transverse vibration was derived from the Newton's second law, in which geometric nonlinearity and material nonlinearity were all taken into account. The first-order Galerkin method was used for separating time variable from space variable, and the fourth order Runge-Kutta method was used to solve the governing non-linear differential equation and analyze the dynamic behavior of the system. Furthermore, the effect of transport speed, amplitude of the tension perturbation, the damping coefficient and frequency of the periodic perturbation on the dynamic vibration behavior were analyzed. Based on above analysis, we can conclude that the main method for decreasing amplitude of vibration and vibration of tension is increasing damping coefficient, for example, increasing friction coefficient of jacquard roller.Meanwhile, the dynamic tension of yarn strand between two rollers has effect on accuracy of pile height due to transient velocity of the electronic roller. For simplification, assuming that the yarn strand is linear elasticity with a circular cross section. The dynamic tension fluctuations of yarn strand during transmitted between the electronic roller and drag roller were theoretical analyzed. A mathematical model describing tension fluctuation of yarn strand was derived by applying theorem of moment of momentum and material balance to electronic roller and yarn strand. The dynamic tension is obtained by applying Laplace's transformation and providing that the input braking moment is a step response. The amplitude, frequency and damping coefficient of yarn tension fluctuation are obtained. The result shows that the braking moment has an important influence on the yarn strand tension fluctuations. At the same time, the effect of the length of yarn strand between electronic rollers to drag rollers on natural frequency and damping coefficient of fluctuation of yarn strand tension are analyzed. The dynamic response of yarn strand was researched by theoretical analysis, which has established theoretical foundations for stabilizing tension of yarn and improving the accuracy of pile height.Thirdly, the tension of yarn strand in tufting zone has an influence on the pile uniformity and pattern effect of carpet, which is difficult to predict and detect during tufting process. Thus, it is a vital important to design tension controlling part, stabilize tension, improve carpet quality of developing model for calculating tension. Traditional detecting and computing of tension were based on classical Euler's or Capstan formula, which omitting the influence of bending rigidity and power-law friction. In chapter4th, a more effective modified capstan formula was developed by taking both the bending rigidity of the yarn strand and a power-law friction (in place of the Amonton's law) into consideration. During the analyses, the power-law exponent was used as the indicator for the nonlinear friction behavior, whereas the capstan radius ratio was used as the parameters reflecting the bending rigidity. At same time, both ends tension of yarn wrapped around roller was tested by dynamic tension-meter in actual conditions and the tension ratio could be obtained. The experimental results of tension ratio were compared with classical capstan ones and modified ones. It is show that the modified curve has a good agreement with the experimental one. So, it is essential to consider the bending rigidity and power-law friction of yarn strand when designing the structure of electronic roller and dragging roller. Also, the modified model for tension calculation will provide theoretical support for more precise control of yarn strand tension, pile height and improving resolution of single needle.Fourth, the essence of tufting process is the cooperation between reciprocating movement of needle and front and back movement of looper, which is the basic motion of tufting. During tufting process, main resistance is the force acting on needle bar, which equal to the sum of backing resistance and inertia force when the needle penetrate the backing. The needle force will affect its state of motion, optimal designning of transmission mechanism and improvement of spindle speed, etc. Due to cann't calculate the resistance acted on needle, safety coefficient was selected too much for ensuring the strength of the component during practices. Thus, it will not only waste material but also result of structure bulkiness. In addition, the unstable force acting on needle will result in inconsistent with high and low of pile. In the final section, a FE model of needle penetrating nonwoven has been developed in ABAQUS(?) software, based on the geometrical characteristic of needle and materials properties of nonwoven fabric. For simplication, assuming the deformation of nonwoven is linear elasticity when the needle penetrates the nonwoven, a user-defined subroutine VUMAT for characterizing the constitutive relation of the nonwoven fabric and the damage evolution was compiled and connected with a commercial software package ABAQUS/Explicit to calculate the penetration force and simulate the contact damage process of nonwoven fabric. Results of the theoretical analysis were compared with the needle penetration force which was tested by sensor mounted in needle bars of tufting machine. It was found that there is an approximate agreement of the penetration force during tufting between FEA calculations and experimental result, the maximum error is11%. Thus, the nonwoven model and the VUMAT combined with the ABAQUS/Explicit can precisely calculate the impact force acting on needle. The verified FE model could be put into analysis of needle penetration force at high RPM (Revolutions per Minute). Meanwhile, it is vital importance to calculate the needle force, optimal designing of transmission mechanism and improve revolution of the spindle.This thesis was aim at process of digitial tufting carpet machine, the accurately controll of feeding length and tension of yarn strand were taken as goal. The viscoelasticity of yarn strand, nonlinear transversal vibration, the mechanical properties between yarn and machine part, the interaction between needle and nonwoven etc., were researched and the model for controlling the tension of yarn strand was developed. The movement properties and the interaction characteristics were revealed by studying tufting process. Thus, the mechanism for controlling yarn strand tension could be revealed. Problems of controlling yarn tension during tufting process of different pile height were resolved. A FE model of needle penetrating nonwoven has been developed in ABAQUS(?) software, calculating the penetration force acting on needle. All these have provided theoretical foundation for producing carpet of high resolution and big pattern cycle of full scale. In addition, it has a great theoretical value and the actual production significance for improving efficiency.