| With the intensification of population aging in recent years,the incidence rate of foot diseases,such as diabetes foot,continues to increase.The plantar pressure distribution can reflect the foot injury or pathological changes.Monitoring the plantar pressure can effectively prevent foot diseases.Textile based pressure sensor is widely used in plantar pressure monitoring because of its soft,comfortable,high biocompatibility and combination with foot textile products.Among them,the fabric based piezoresistive sensor is realized by converting the pressure stimulus into a resistance signal.Because of its simple sensing mechanism,easy construction,low manufacturing cost and other advantages,it is an ideal choice for plantar pressure monitoring.At present,the research on fabric based piezoresistive sensor for plantar pressure monitoring focuses on changing the materials of piezoresistive layer and electrode layer to improve the sensing performance.Due to the deformation damage of piezoresistive material under high pressure,the sensing durability and stability of the sensor cannot meet the application requirements,and the performance of the sensor needs to be further optimized from the perspective of fabric structure.In view of the problems of poor durability and stability of fabric based piezoresistive pressure sensor,this topic takes fabric structure as the sensing carrier,and designs a simply supported beam structure based on piezoresistive sensing principle,and develops a piezoresistive sensing array fabric with groove type cavity structure for plantar pressure monitoring,The influence of different yarn arrangement ratios in the fabric sensor array on the sensing performance of the sensing unit and the distribution density of the sensing unit are discussed.The response mechanism of the designed fabric sensor is analyzed through finite element simulation,so as to achieve the balance between the durability and repeatability of the fabric pressure sensor and the whole fabric based structure when monitoring the change of foot pressure.Finally,the actual application test and evaluation of the pressure monitoring insole are carried out.The specific research contents and conclusions are as follows:（1）Based on the processing theory of convex bar weave and fabric weave structure phase,a simply supported beam fabric sensing array based on piezoresistive sensing principle is designed.The sensitivity of this structure can reach 9.12×10-3（N/cm2）-1in the pressure range of 0～75 N/cm2,and the sensing units present uniform and stable sensing performance.In order to realize a fabric structure type pressure sensor with stable sensing characteristics,a convex bar structure is proposed for design based on the principle of simply supported beam mechanics.By analyzing the structural characteristics and formation mechanism of the convex bar structure and determining the operating parameters,a simple supported beam structure sensing array fabric based on the convex bar structure is prepared,and its sensing unit performance and sensing response consistency are evaluated.The experimental results show that the cross convex structure is selected,the low structural phase is designed,and the fabric tightness is designed as Ej=58.07％,When Ew=96.86％,it can show a good convex strip structure characteristics.The sensitivity of the fabric sensing unit is up to 9.12×10-3（N/cm2）-1in the pressure range of 0～75 N/cm2,which meets the monitoring range of human daily plantar pressure and abnormal plantar pressure of diabetes foot patients.In addition,each sensor unit point on the sensor array fabric prepared by weaving process presents uniform sensing performance,which proves that this method can achieve the integrated integration of sensor array fabric.（2）By studying the different yarn arrangement ratio and distribution spacing in the fabric sensor array,the size and distribution density of the sensor unit are determined.It is found that the sensing performance is best when the yarn arrangement ratio of the fabric sensor unit is 10:6and the spacing is6mm.The working mechanism of the sensor unit is clarified through finite element simulation.In order to obtain the specifications of fabric sensor array suitable for plantar pressure monitoring,firstly,the sensing performance is evaluated by designing orthogonal experiments to determine the size of the sensing unit;Secondly,three different distribution distances are set to determine the distribution density of the sensing unit;Finally,for the best sensor array,the finite element simulation analysis is used to verify the pressure sensing principle of the fabric.The experimental results show that the change of fabric structure factors will cause the change of sensing performance.The fabric sensing unit with yarn arrangement ratio of 10:6（insulation area of 25 mm2,conductive area of 22.5 mm2）has the best sensing performance,and its sensitivity can reach 10.41×10-3（N/cm2）-1,the response range is far enough to meet the daily plantar pressure monitoring range（0～150 N/cm2）;The response time is fast（the loading/unloading pressure is 51ms/90ms）,the hysteresis error is only 2.08,the variation of the first and last output amplitude of the resistance in the repeatability test is only 1.1％,and it has good durability（>300 times）,meeting the requirements of the daily plantar pressure monitoring range.Under the original spacing（6mm）,the distribution density of the fabric sensing unit is the best,it has a good single point compression signal response,its response deviation is only 5.07％,and it has a low signal coupling effect,so the final fabric sensing array specification is determined.Through simulation analysis,it is observed that under the action of uniformly distributed pressure,the simply supported beam surface of the sensing unit cavity structure is most sensitive to the application of force,which proves the pressure sensitivity of the simply supported beam structure fabric sensor array.Its axial distribution around the center shows that structural changes can cause changes in the sensing performance,which has certain reference significance for the design of piezoresistive sensor array fabrics.（3）Validate the feasibility of fabric pressure sensor array applied to plantar pressure monitoring,clarify that the fabric sensor array has good sensing response performance under static and dynamic plantar pressure range,and can reflect the plantar pressure distribution state,and verify the feasibility of the prepared fabric sensor array in the application of plantar pressure monitoring.In order to verify the feasibility of the fabric pressure sensor array to monitor the plantar pressure,the pressure monitoring insole was prepared to monitor and analyze the response of the sensor unit under the static and dynamic plantar pressure of the human body.The experimental results show that the fabric sensor array has good sensitivity to static plantar pressure;The dynamic plantar pressure also shows a stable periodic resistance change.The resistance change rates of the two measured units are 92％ and 99％ respectively,which means that they have good dynamic response and strong anti-interference ability;Moreover,it can reflect the pressure distribution of human feet.The distribution of plantar pressure of different subjects can be observed by visualized cloud images,which proves that the prepared fabric sensor array can be used for the monitoring of plantar pressure,and verifies the feasibility of the prepared fabric sensor array in practical applications.Based on the above discussion and analysis,this topic has developed a stable and durable plantar pressure monitoring piezoresistive sensor array fabric from the perspective of fabric structure by applying the principle of simply supported beam mechanics,and realized the integrated integration of sensor array fabric through the combination of fully automatic woven technology and traditional textile and garment processing technology,providing a new tool choice for plantar pressure monitoring such as medical care,sports training,etc,The proposed design method and processing technology can also be used to develop piezoresistive sensing array fabrics in other demand areas. |
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