Effect Of Wrapped Structure On The Sensing Performance Of Yarn Strain Sensor

The unique mechanical and physical properties of textiles have became one of the best platforms for wearable sensors.Yarn-type sensor with embeddable,flexible product design features,both as a separate sensor as applied to human physiological activity monitoring,can also be woven into fabric as a sensor device,has attracted widespread attention.Among them,the elastic wrapping yarn structure is one of the preferable solutions to solve the stretchability,reversibility and multi-dimensional stress sensitivity of the yarn sensor.At present,most studies have verified the sensing performance and feasibility of the application of the wrapped yarn sensor,but did not systematically study the relationship between the basic structure parameters of the yarn and the sensor performance.The structural parameters of the wrapped yarns influenced the performance of the yarn strain sensor,which were beneficial to the corresponding yarn forming technology for the sensing performance.Therefore,studying the relationship between the structural parameters and the sensing properties of the wrapped yarns is the key to promote the production and application of the covered yarns strain sensors.According to the structure of the wrapped yarn strain sensor and the yarn forming process,this topic screened the yarn forming method which met the strain sensor.According to the influences of main yarn forming parameters-the degree of wrapping and the number of wrapping on the sensing performance of the yarn strain sensor,expand the sensor forming and performance evaluation.The main research contents are as follows:(1)Analyze the structure and forming requirements of the wrapped yarn strain sensor,modif ied the spinning equipment and determine the forming process of the wrapped yarn.According to the structural requirements of the wrapped yarn strain sensor,the structural princ iple of the wrapped yarn strain sensor was studied and the structure of the wrapped yarn was designed.In this project,the elastic wrapped yarn spinning equipment was constructed and rebuilt.The core yarn adopts the mode of positive yarn feeding,the feeding speed of the core yarn and the winding speed of the yarn was controlled to control the yarn tension.The Outsourcing yarn adopted a radial unwinding method to increase the wrapping tension of the wrapped yarn so that the wrapped yarn was tightly covered.Adjust the ratio of the winding speed to the wrapping speed to control the degree of wrapping.The yarn was successfully spun and coated tightly.The appearance of the spun sample was observed to determine the maximum coverage of the yarn was 40 twists / cm.According to the calculation of the equipment parameters,the spinning process parameters of the wrapped yarn with the wrapping degree from 10 to 40 twists / cm were determined.(2)For the single-layer wrapped yarn strain sensor,the influence of yarn wrapping degree on the sensing performance was studied.Spandex fiber as the core yarn,nylon multifilament yarn for the outsourcing,making degree of 10 to 40 twists / cm single wrapped yarn.The in-situ polymerization method was used to carry out the conduction treatment on the wrapped yarn to prepare a wrapped yarn strain sensor.Yarn repeatedly stretched platform and Agilent 39470 data acquisition cards were used to simultaneously collect the yarn resistance during the drawing process,and observe the surface morphology of the yarns under an optical electron microscope.For the sensitivity of sensor sensing,the resistance change was tested the tensile elongation of the conductive yarn to 100%,the sensitivity was calculated based on the sensitivity formula.The yarn was tested at a constant speed of 2mm / s,resistance acquisition frequency of 250 ms / time.The results showed that the sensitivity of single-layer wrapped yarn strain sensor increases with the degree of wrapping.Under the small strain,as the yarn tension sensitivity increases,when the yarn reaches a certain strain,the yarn tension decreased and the sensitivity began to decrease and gradually stabilizes to a fixed value.For the response repeatability of the sensor,the resistance change of the conductive yarn was tested at a maximum tensile strain of 20% and a cyclic tensile of 100 times.The results showed that with the increase of the coverage,the repeatability of single layer wrapped yarn strain sensor became worse.For the sensitivity threshold of the sensor,the method of strain step reduction was adopted to collect the resistance of the single-layer wrapped yarn strain sensor at a tensile speed of 0.5mm / s and a tensile strain of 5%,2%,1% and 0.5%.The results showed that the single-layer wrapped yarn strain sensor exhibits a significant change in resistance at a strain of 0.5%.(3)For the double-layer wrapped yarn strain sensor,the influence of different wrapping degree on the sensing performance was studied,and the difference between single-layer and double-layer wrapped strain sensors was compared and analyzed.And initially verify the in-body test capability.The single-layer wrapped yarn as the core yarn,nylon multifilament yarn to do the outsourcing yarn,reverse wrapped,to prepared a double covered yarn with the degree of wrapping of 20 to 40 twists / cm.Conductive treatment and testing methods were the same as single-layer wrapped yarns.For the sensitivity of the sensor,the sensitivity of the double-wrapped yarn strain sensor first increased and then decreased,and gradually approached a fixed value,and the sensitivity increased with the increase of the degree of wrapping,which was consistent with the law of double-layer wrapping yarn strain sensor.However,under the same degree of wrapping,the single layer wrapped yarn strain sensor had a higher sensitivity than the double layer.For the repeatability of the sensor,the repeatability of the double-wrapped yarn sensor was better with the increase of the degree of wrapping,which was opposited to that of the singlewrapped yarn sensor.This was mainly due to the fact that when the double wrapped yarn was stretched to the same strain,in the case of a yarn-wrapped yarn sensor,the contact between the outer layer yarn and the inner layer yarn and the core yarn was close and the cohesion force was large,so that the yarn had poor tensile recovery performance.For sensor sensitivity thresholds,when the strain was 0.5%,the double-wrapped yarn sensor produces a uniform response,which was consistent with single-layer wrapped yarn sensors.Therefore,the double-layer wrapped yarn sensor with 40 twists / cm had the best sensing performance with a sensitivity of 5 and good repeatability.It can measure the resistance change with a minimum strain of 0.5%.In order to further verify the in-body detection ability of the sensor,the wrapped yarn strain sensor with the better sensing performance was selected to carry out the experiment of detecting the movement of human limbs.The experiments were performed on the three speeds of slow,medium and fast and full bending and half bending two kinds of movement of the sensor response.The results showed that the sensor response speed increased with the increase of the movement frequency,and the response intensity increased with the bending degree.It showd that when the wrapped yarn sensor was applied to the monitoring of human limbs,it can respond to limb movements of different frequencies and amplitudes and had good practicability and reliability.By studying the relationship between the yarn wrapping degree and the wrapping layer number and the sensing performance of the strain sensor,it was found that the wrapping degree and the wrapping layer mainly affect the response sensitivity and repeatability of the strain sensor,and had little effect on the sensitive threshold va lue.And through in body testing,verified its practicality.However,this subject only aimd at the in-body testing of the wrapped yarn strain sensor,and did not do a deep research on the limb movement detection.In the future research,it also needs to establish the accurate correspondence between its sensitivity and limb movement.