Study On The Drafting And Autolevelling Process Based On The Discrete Theory

Drafting is a main processing method that decreases the linear density of fiber assembly(i.e.sliver,roving)to meet requirement,involving multiple spinning processes(i.e.drawing,roving,spinning),which has a significant effect on the final yarn quality.The research on the drafting process and its unevenness is always a critical problem,which is directly related to the uniformity of semi-finished products.However,the research about the movement behavior of sliver or fiber assembly is not deep enough.Most of them only give a qualitative description and are lack of quantitative researches,resulting in the shortage of researches on autolevelling of drafting process.For this purpose,this thesis sets up models to simulate the behavior of fibers and the dynamic drafting of strands based on the discrete theory,which gives quantitative data and analyze the mechanism about the irregularity of drafting.The autolevelling model is established to improve the quality of output strands,from the point of the balance of fiber distributions in the drafting zone.This thesis first analyses the dynamical behavior of a single fiber and sets up a basic model of drafting to simulate the drafting process in the discrete system.In order to demonstrate the dynamic drafting,an improved model is established based on the refinement of fiber movements.The studies on the number,ratio and distribution of different kinds of fibers in the drafting zone are used to illustrate the mechanism of irregularities during drafting process.On the basis of these conclusions,an autolevelling model is set up to balance the fiber distributions,vary the roller velocity and decrease the unevenness of output strands.This thesis consists of eight chapters,whose organization is given as follows:Chapter 1 is the general introduction,which introduces the background and significance of the study,the achievements and drawbacks of previous researches on the drafting process,and the method,approach and contents of this research.Chapter 2 is the establishment,simulation and verification of the drafting basic model.Firstly,an approach of modeling and simulation is proposed to simulate the drafting process based on the discrete theory.Under some assumptions,a basic model is set up to simulate the dynamic drafting by analyzing the movement behavior of a single fiber.Then,the model is programmed and simulated by the discrete language GPSSWorld.From the comparison of simulation results and experiment data,the approach and model is validated.Last,the characteristics and advantages,as well as the expandability,of the basic model are illustrated by the simulation.Chapter 3 analyses the influence factors of modeling in the discrete system and indicates the principle of simulation parameters selection,by evaluating the output unevenness as assessment criteria.The ingredient of unevenness of actual strands is classified and the common measurement indexes are compared,so the assessment criteria of output unevenness is confirmed.By comparison between the simulation results and USTER~?Statistics as well as theoretical value of limit unevenness,the ingredient of unevenness in the basic model is explained.The effect of material properties and process parameters on the output unevenness,and the principle of simulation parameters selection are analyzed and discussed.Chapter 4 sets up an improved model to demonstrate the dynamic drafting and study the fiber distributions in the drafting zone by the refinement of fiber movements.The dynamic drafting is shown by simulating the attenuation curves of strands,different kinds of fiber distributions and the fluctuation of fiber number in the cross-section.The improved model is validated by comparison of simulation results and experiment data of drawing.The mechanism of irregularities during drafting process is illustrated by analyzing the number,ratio and distribution of different kinds of fibers in the drafting zone.It provides the theoretical foundation for the establishment of discrete autolevelling model.Chapter 5 sets up an autolevelling mode from the point of balancing the fiber distributions in the drafting zone.By introducing the definition of the fiber flux and indicating the problem of classic autolevelling model,the principle as well as process and advantages of the discrete autolevelling model are illustrated,utilizing the conclusions of the improved model of drafting.In order to simulate different condition of input unevenness,the rectangular wave,sinusoidal wave and random wave are selected as the input unevenness of model.Assuming the number of floating fibers fixed,a simple autolevelling model is established.It is used for the characteristics of different speed coverning method and improvement when the velocities of front and back rollers are changed.Utilizing the buffer ability of floating zone,a discrete autolevelling model is set up to improve the ability of autolevelling.Chapter 6 verifies the discrete autolevelling model by experiments and analyses the causes of thick and thin strands.A drafting system for autolevelling is constructed to vary the velocities of front and back rollers at the same time.The system adopts the human-machine interface to input the drafting process parameters,and uses the programmable logic controller to store the autolevelling model.The programmable logic controller sends the calculations to the two servo motors,which control the velocities of front and back rollers.The discrete autolevelling model is validated by autolevelling experiments.The causes of thick and thin strands are indicated by changing the broken ways of strands and the positions of autolevelling,which provides the theoretical and experimental foundation for the selection of delay time of autolevelling system.This thesis takes advantage of the discrete theory to simulate the fiber movement behavior and the dynamic drafting process,study on the fiber distributions in the drafting zone and the mechanism of output unevenness,and set up a discrete autolevelling model to improve the quality of output strands.Contributions of this research:(1)A new approach is proposed to simulate the drafting process.From the point of the single fiber movement behavior,the drafting process of strands is simulated by adopting the discrete theory.The model is a time-domain model,which can calculate the time of different status of each fiber in the drafting zone and trace the movement of an arbitrary fiber.In addition,the model has good expandability,high efficiency of simulation and multiple types of output results to simulate each drafting process of spinning.(2)It reveals the change of strands in the drafting zone.Most of previous model regard the strand as an object and neglect the change in the drafting zone.This research demonstrates the dynamic drafting process of strands in a drafting zone,and analyses the change of number and distributions of different kinds of fibers in an arbitrary cross-section.By the effect of different drafting parameters on the fiber movement behavior,the mechanism of output unevenness is illustrated.(3)A discrete autolevelling model is set up to decrease the output unevenness,from the point of balancing the fiber distributions.Assuming the number of floating fibers fixed,a simple autolevelling model is set up to illustrate the principle advantages of the model.Utilizing the conclusions of the improved model of drafting,the relationship between the velocities of front and back rollers and fiber distributions in the drafting zone is deduced,and a discrete autolevelling model is established.From the analysis of the causes of thick and thin strands,it provides the theoretical and experimental foundation for the selection of delay time of autolevelling system.(4)The model in this research can give quantitative data of drafting process.Most of previous studies only give a qualitative description about the drafting process.The approach of modeling proposed in this thesis can solve the problem and make the results more practical.This research mainly focuses on the movement of strands and fibers in a drafting zone by the discrete theory.It provides the theoretical foundation for the mechanism of output unevenness and the research on autolevelling,as an example of stochastic model in textile processing.