Design,Manufacture And Optimization Of Flexible Three Dimensional Force Sensor Based On Piezoresistive Structure

With the development of sensor technology,the flexibility,precision and intelligence of medical devices and prosthetics have become the key problems.As a core sensing component,flexible pressure sensor should meet the multi-dimensional force sensing requirements of various application scenarios.Among them,the flexible three-dimensional(3D)force sensor can detect the magnitude and direction of the force through the structural design of the material,and then realize the fine perception and control of the sensing object.At present,the main challenges that restrict the application of 3D force sensors are the miniaturization and array of devices.In this thesis,two kinds of flexible piezoresistive 3D force sensors based on filled conductive composite materials are fabricated by spraying and laser direct writing.The main research contents are as follows:(1)The film formation and properties of graphene composite were studied.The influence of the viscosity of polyoxyethylene(PEO)solution on the electrospray mode was investigated.The uniform morphology of low viscosity(0.6wt.%)PEO solution ensured the controllability of electrical properties.The influence of spraying process parameters on film forming uniformity and film thickness is analyzed.The heating temperature of flexible substrate is 50℃,and the spraying voltage is 5.5 kV.Finally,the micro morphology,electrical properties and pressure sensitive properties of the graphene-polyoxyethylene(GPEO)films were characterized.The film resistance and bulk piezoresistive properties can be controlled by material ratio and process parameters.(2)Design,manufacture and test of flexible interlocked 3D force sensor.Based on the detection mechanism of piezoresistive sensor,the model of interlocked hemispherical structure and its contact resistance is established,and the effects of graphene concentration and spraying time on the contact resistance of hemispherical films were investigated.The filling concentration of graphene is 60 wt.%,and the spraying time is 40 min,which determined by measuring the contact piezoresistance of the hemispherical structure,the size radius of the interlocked hemisphere was 1 mm and the contact angle was 45°.The normal pressure and shear force of the sensor were tested respectively.The normal sensitivity was 6.33 kPa-1(0-3.0 kPa),the highest tangential sensitivity was 2.43 N-1(0-0.9 N),the response time was 59 ms,and the angular resolution of the tangential force was 30°.(3)Structure optimization and decoupling analysis of flexible 3D force sensor.Based on the performance stability and decoupling difficulty of the interlocked structure,an optimized patterned 3D force sensor structure is proposed,and the detection mechanism of the structure is described.Combined with the finite element analysis of the stress distribution in the deformation process of the flexible matrix,the element location and layout are determined.The performance of piezoresistive unit is tested.The sensor has very low detection limit(8 mg),reasonable response time(310 ms)and cycle stability(1500 times).The detection ability of 3D force sensor is verified.Finally,the decoupling model of 3D force overturning deformation is established.