Research On Modeling And Control Of Drafting Processing Draw Frame

Fibre material processing is an important branch of materials processing as well as drawing is an important step of fibre material processing. The autoleveller of draw frame is a self-adjusting system used to control drawn yarn uniformity in fibre processing and has close relationship with each working procedure. In the drafting process of draw frame, the change of uniformity of drawn yarn thickness is a kind of stochastic process, which includes all kinds of uneven and complex waveform. If the effective measures are not adopted to control uniformity of yarn thickness, the yarn will not only include the quondam uniformity, but also add uneven in each working procedure. That will result in low mightiness, high sever rate and bad uniformity of yarn and product quality will be influenced at last. It makes study of autoleveller of draw frame become a very important research direction of fibre material processing field.It is difficult to establish the precise and practical mathematical model and autoleveller of draw frame because of the complicated drafting mechanism and the changeful work circumstance and parameters. The technology which is only mastered by several international companies is kept a secret and not to been opened. Although the autolevellers of draw frame have been designed by many companies in our country, there is a gap between these autolevellers with like iternational produts. Therefore, it is important for our national textile industry to design and develop an autoleveller of draw frame with high performance.On the basis of textile technics theory, dynamics modeling and computer simulation technologies, starting with change of yarn in drafting area, the change of yarn thickness in drafting area is considered as a process of changeable gain and drafting gain curve is introduced for the first time. A variable-drafting model of draw frame is established with block diagram. The simulation output from variable-drafting model of draw frame is compared to real output and influence of different drafting gain curves on variable-drafting model is analyzed. The results show that the variable-drafting model of draw frame in the paper can express actual drafting processing of draw frame relatively. In allusion to the imprecise variable-drafting model of draw frame, an identification model of draw frame is established with dynamic discrete linear model according to real yarn input and output signals of draw frame. The real yarn input and output signals of draw frame are preprocessed and the delay time of the identification system is calculated with the correlation analysis method. The reliability of the identification model is been proved by comparison between output signal from the identification model and real output signal. The result shows the precision of the identification model is better than that of variable-drafting model of draw frame and the identification model is reliable and easy-to-use.Based on study of autoleveller system of draw frame, the working process of draw frame is divided into control procedure and drafting procedure from the point of view of identification in this paper. Controlled quantity of the servosystem and yarn input signal are regarded as input signals of the identification system and yarn output signal is regarded as output signal of the identification system. The identification modeling of draw frame able to be applied in autoleveller system is put forward and transfer functions of control procedure and drafting procedure of draw frame are obtained apart. The open-loop autoleveller system of draw frame is simulated with the identification model. The simulation output signal with autoleveller is compared to the simulation output signal without autoleveller and the result shows open-loop autoleveller system can lower unevenness of yarn. Based on open-loop autoleveller system, a new mixed-loop autoleveller system of draw frame is introduced. A new difference-time control method is applied in mixed-loop autoleveller, in which open-loop feedforward control system and closed-loop feedback control system have different control cycles. This model reliability is been proved with experiments. The quality and quantitative control of yarn and autoleveller effect are improved evidently.The ingredients of autoleveller system of draw frame are analyzed. Chosen principle and result of hardware are indicated. The frame of software is designed from point of view of software engineering, and functions and implementation methods of main program and interrupt program are studied in depth. The autoleveller control system of draw frame in the paper is experimented on draw frame FA398A and results show unevenness of yarn and weight deviation are improved greatly.