Non-contact Dynamic Measurement Of The Yarn Tension In Winding Process

Yarn tension is a very important parameter in winding process, because its value and scope of the fluctuations will affect the quality and efficiency of the package directly.At present,most of the existed testing equipments are the contact type devices.And these devices will contact directly with the high-speed moving yarn in the process of measurement, which not only affect the result of measurement,but also impact the running state of yarn.To deal with this problem,a method based on the string vibration theory and the image process technology is proposed for non-contact measurement of the yarn tension in winding process.The main contents of the study are as follows:Firstly,regarding the running of the yarn in winding process as a string vibration,the theory formula for the yarn tension was derived,and the principle of non-contact measurement of yarn tension was built.The yarn tension equals to yarn density multiplying the square of the real yarn speed that equals to winding speed plus transverse wave speed.Since winding speed and yarn density are easy to test,transverse wave speed becomes a key factor for measuring the yarn tension.Secondly,the method of testing the yarn waving speed based on the image processing techniques was proposed,and the method was realized. When the yarn reaches to the left or the right end of the winding roll,the yarn will bend due to the sudden change of the running direction.The running state of the yarn was photographed by using the CCD image sensor,the maximum bending points were determined by using the image processing technology subsequently,and the transverse wave speed was finally calculated by coordinating the maximum bending points of two consecutive images.A series of procedures such as gray-scale processing, cut processing,edge extraction,binary conversion were used to extract the coordinates of each point during the image processing.Finally the maximum bending point was obtained by searching the point with the largest distance to the line connecting the beginning point with the end point of the yarn.Thirdly,the test device for the winding yarn tension was designed and built,including the winding machine,continuous image collecting system, dynamic image processing system and graphical user interface.In order to photograph the image dynamically,the HV1303um CCD image sensor was used as the equipment of image collecting system.The image processing programs were written with Matlab language to process the images dynamically.In addition,the GUI(Graphical User Interface) was designed to show the results.Fourthly,Some experiment were taken by using this yarn tension test device to validate the feasibility of this method and research the influence of yarn type,winding speed and yarn linear density on the yarn tension. In addition,the correlation analysis was conducted between the contact and non-contact measurement.The results indicate that the device can detect the winding tension of different kinds of yarns,winding speeds and yarn line density.It is shown that between yarn density and yarn tension are the linear relationship,and between the winding speed and the yarn tension are the quadratic curve relationship.The value of non-contact yarn tension is lower than the contact's under the same experiment condition.Since the method of non-contact measurement and contact measurement are of high correlation,the non-contact method proposed in the thesis can be used instead of the contact measurement.This test method is fit for the yarn tension test during the traverse winding process.And the non-contact dynamic measurement of the yarn tension can be achieved.Both the running states of the yarn and the variations of the yarn tension can be observed in real time.Moreover,it has no effect on the process of the yarn,so it is positive to ensure the quality and efficiency of the winding package.