Study Of Yarn Tension Sensor Based On SAW Device

In the21st century, Sensor Technology has become the focus of the world.Sensor Technology is the basis of technology revolution, information society andintellectual society, which is widely applied to many fields. In recent years, theelectromechanical integration textile equipment, based on Sensor Technology, hasattracted widely attention and deeply research with the technical innovation of textileindustry. The yarn tension sensor, an important part of textile machinery, becomes thefocal point of the textile equipment research.Normally, in each process of yarn and fabrics production, yarn tension is one ofthe most important factors, which directly determines the production and quality ofyarn and fabrics products. So how to accurately measure the yarn tension will becomean urgent task. In order to reflect the yarn tension as really as possible and effectivelycontrol the yarn tension, this work has developed a novel SAW (surface acoustic wave)yarn tension sensor. The design theory and structural optimization method of the SAWyarn tension sensor is studied. The research contents and innovations are as follows:(1) A novel SAW yarn tension sensor was developed. The sensor is designed asan oscillator, which exhibits excellent advantages such as simple structure, smallvolume and good stability. The sensor was fabricated on a42.75°Y-X quartz substrate.Since the temperature coefficient of the substrate is zero, the sensor needs notemperature compensation device. The IDT (Interdigital Transducer) of the oscillatorsbased on delay lines was designed. The design parameters of IDT was given,including the period of IDT, the pair number of IDT, the aperture, the metallizationratio, the thickness of metallic films and the weighting of IDT. The fabricationprocesses of the SAW yarn tension sensor are described. The structure design andworking principle of the SAW yarn tension sensor is presented. The linear regressionmathematical model between the output frequency shift of the SAW yarn tensionsensor and the yarn tension is built, which is solved by the method of least square.(2) Anovel optimal sensitivity design scheme for the SAW yarn tension sensor isproposed based on finite element method. The function relationship between thesensitivity of the SAW yarn tension sensor and the strain rate of the SAW yarn tensionsensor substrate is derived, and the concept of the substrate strain rate is presented.The linear regression mathematical model between the sensitivity of the SAW yarn tension sensor and the strain rate of the SAW yarn tension sensor substrate isestablished using linear regression analysis method and finite element analysismethod. The monotonicity of this model shows that the greater the strain rate of theSAW yarn tension sensor substrate is, the higher the sensitivity of the yarn tensionsensor is. Therefore, according to the conclusion, the theory, which can improvesensor sensitivity through increasing the substrate strain rate, was given. Based on thetheory, the scheme was given to obtain the best substrate strain rate through changingthe substrate size flexibly. In order to obtain the biggest substrate strain rate, thestress-strain finite element analysis models of12different size SAW yarn tensionsensors are built. According to the results of finite element simulation analysis models,the multiple liner regression mathematical model between the SAW yarn tensionsensor substrate strain rate and its size is established. Based on this model, a linearprogramming model was proposed to solve the substrate size corresponding to thebest substrate strain rate. The linear programming results show that the maximumsensitivity will be achieved when the SAW yarn tension sensor substrate length is19mm and its width is3mm. The SAW yarn tension sensor with the size of19×3mmwas fabricated. Experimental results show that the sensitivity of the sensor can reach3114Hz/g, confirming that the sensitivity optimization design scheme is effective andapplicable.(3) The influence of the IDT position on the SAW yarn tension sensor sensitivitywas investigated. It starts from analyzing the tension-strain behaviour of the SAWyarn tension sensor substrate along the SAW propagation direction. Through studyingthe influence of the IDT position on the SAW yarn tension sensor sensitivity, thefunction relationship between the two is gained. The multiple liner regressionmathematical model between the SAW yarn tension sensor sensitivity and the IDTposition is established using multiple linear regression analysis method. Throughanalyzing the correspondence between the mathematical model monotonicity and itspartial derivative sign, it’s found that the sensitivity of SAW yarn tension sensor willincrease with increase in the distance from the left margin of the piezoelectricsubstrate to the left-most of the input and output IDT or decrease in the distance fromthe top of the piezoelectric substrate to the top edge of the input and output IDT.(4) A SAW yarn tension sensor based constant strain rate substrate structure wasdeveloped. According to the finite element simulation model of the substratestress-strain, the distribution characteristics of the SAW yarn tension sensor substratestrain rate are analyzed in detail when the yarn tension acts on the piezoelectric substrate. The influence of the sensor substrate strain rate distribution on the IDTstress-strain properties is investigated. In order to avoid such influence, the constantstrain rate substrate structure is proposed. On the base of both consideration ofsubstrate size and IDT position, the optimal design scheme of the constant strain ratesubstrate structure is presented. A mathematical model is built to solve the designparameters of the constant strain rate substrate, and its solution based on improveddichotomy is given. The SAW yarn tension sensor with the constant strain ratesubstrate was fabricated. Experimental results show that the sensitivity of the sensor is585Hz/g with a maximum relative error of3.16%and a linearity of±0.64%.Compared with the SAW yarn tension sensor based on conventional substratestructure, the SAW yarn tension sensor using constant strain rate substrate showshigher accuracy level and better linearity, but its sensitivity will decrease significantly.