Design And Study On The Properties Of Resistance Pressure Sensor Based On Warp Knitted Spacer Fabric

The new type of flexible pressure resistance sensor can sense the pressure signal.When under pressure,the change of the yarn shape or contact area of the sensing part causes the change of the resistance value.They use this principle to convert the pressure signal into an observable electrical signal according to a certain rule for output.Textile science and engineering and electrical,agriculture,medical,mechanics and other disciplines have more and more close connections and integration,which is the inevitable trend of more effective and rapid development of smart clothing.The original smart clothing directly combined traditional fabrics with ordinary electronic devices.Although such smart clothing can give many functions we want to achieve,it reduces the comfort of the fabric.When evaluating the advantages and disadvantages of smart clothing,we should not only pay attention to the functions they have,but more importantly,we hope that they have the same comfort as traditional clothing,mainly including breathability and softness.First of all,the traditional smart clothing has more hardware facilities,which makes the original fabric softness decline.Secondly,the rising product cost has resulted in a low market acceptance capacity.Finally,the washing of traditional smart clothing is difficult and the durability is poor.Therefore,flexible sensors focusing on the comfort of smart clothing are widely concerned by researchers.This topic studies the performance of flexible pressure resistance sensors for the purpose of monitoring the sitting,sleeping and walking posture of the human body.Based on warp knitted spacer fabric,the flexible pressure resistance sensors are designed and knitted,and the effect of the sensing area and spacer fabric performance on the sensor performance is studied.Through compression experiments,this topic analyzes the relationship between the compressive strain and resistance of conductive fabrics.It is hoped that the following research will lay the foundation for the design and preparation of flexible pressure resistance sensors with superior performance.First,select the material of the single-sided conductive layer of the spacer fabric,design and prepare the form of the single-sided conductive layer of the spacer fabric.Select the appropriate conductive yarn and fabric structure and design the sensing area of the single-sided conductive layer of the spacer fabric.In order to facilitate the experiment,the warp knitted single needle bed conductive fabric is pasted on the surface of the spacer fabric for related simulation.Experiments are carried out on ordinary spacer fabrics under the same parameter conditions to study the effect of the area of the conductive area,the resistance measurement direction and the compression method on the resistance-strain curve,and the feasibility of the single-sided conductive layer scheme is determined.Secondly,after determining the feasibility,the conductive yarns are directly knitted on the surface of the warp knitted spacer fabric.Appropriate parameters are selected,and the relationship between the series and parallel resistances of the warp knitted conductive fabric courses and wales is studied.Under the combined action of the thread resistance of the yarn itself and the contact resistance between the yarns,a preliminary resistance model of the warp knitted conductive fabric is established.Study the influence of compression method and conductive area on the strain-resistance sensing performance of the warp knitted spacer conductive fabric.Then,the sensing performance of the pressure resistance sensor of the double-layer warp knitted spacer fabric is studied,and the superimposed experimental scheme of the single-sided conductive layer of the spacer fabric is designed.When using different superimposed experimental methods and compression forms,determine whether the linearity and sensitivity of the flexible piezoresistive sensor meet the requirements,and compare with the single-sided conductive layer solution.Finally,the applicability and practical feasibility of warp knitted spacer fabrics for pressure resistance sensors are obtained.A more complete system is formed for spacer fabric piezoresistive sensors.It provides greater help and practical significance for adding pressure resistance sensing to future cushions,mattresses and insoles and putting them into production.Through the above research,it is found that the experimental compression form has a greater influence on the sensing characteristics of the pressure resistance sensor.In the simulation experiment,when the compression surface is flat,the strain-resistance characteristics are divided into two stages: the resistance decreases slowly with the increase of strain,and then decreases rapidly.When the compression surface is a spherical surface,the strain-resistance characteristics can be divided into three stages: the resistance shows a tendency to decrease slightly first,then rise slowly,and finally decrease sharply.At stage II of the plane compression process and stage III of the surface compression process,the knitted spacer flexible piezoresistive sensors have good linearity.The sensitivity of the sensor when the spherical surface is compressed is significantly higher than that of the corresponding plane compression.Sensing performance is good.Therefore,the compression form of the curved surface should be adopted.First,the curved surface compression can better simulate the arc contact of the human body part to the cushion in actual life.Second,when the spherical curved compression head is used,the sensitivity of the sensor is higher.The sensitivity in the compressed form of the curved surface can determine the measurement direction of the course and the sensing area of 35 mm × 35 mm.The resistances between the wales of fabric loops are connected in parallel,and the initial resistance shows a power function change law with the increase of the number of wales of the fabric.The initial resistance decreases with the increase of the number of wales of the yarn.The resistances between the fabric courses are connected in series,and the initial resistance presents a linear function of positive correlation with the increase of the number of fabric courses;whether it is plane compression or curved surface compression,it can be divided into 4 different levels according to the range of the resistance value.Compared with plane compression and curved surface compression,in the 75% strain region,the resistance change of the warp knitted conductive fabric is too gentle to meet the sensitivity and linearity requirements of the sensor.The resistance of the curved surface compression of warp knitted conductive fabric decreases first and then increases with the increase of strain,and the linearity of the resistance reduction phase is very good.When the conductive area is 39 mm×39 mm,the combined performance of linearity and sensitivity is the best.With the increase of surface compression strain of warp knitted spacer conductive fabric,the contact resistance between upper and lower conductive yarns decreases,and the length resistance increases;during the compression process,the change of contact resistance between upper and lower conductive yarns gradually weakens and tends to be stable,and finally the change of length resistance gradually strengthens and takes the dominant position.No matter whether the contact surface of the sensing area of the pressure resistance sensor is plane or curved surface,there is stage I,which can well meet the linearity and sensitivity of the sensor.In both,the curved surface is the better choice.In the actual life,there are more curved surfaces in the contact process between the cushion fabric and the human body,so it can better meet the actual stress deformation situation.Whether it is a single-layer pressure resistance sensor or a double-layer pressure resistance sensor,the selection of the best position of the sensing area is the top layer of the whole spacer fabric pressure resistance sensor.The double-layer pressure resistance sensor also has a good linearity,and the double-layer pressure resistance sensor is better than the single-layer pressure resistance sensor no matter the strain range of stage I or the sensitivity of the pressure resistance sensor.