Study On Flexible Pressure Sensitive Film And The Array Of Pressure Sensor

Flexible pressure sensor is a flexible sensor used to measure the pressure of a variety of complex surface pressure changes in real-time,generally composited by the flexible substrate material,flexible electrode,flexible pressure-sensitive film,according to the combination,it can be divided into single point pressure sensor and the array of pressure sensors.The single-point pressure sensor is mainly aimed at the point target and can be used to accurately measure the pressure change of a single point of the small position.The flexible array pressure sensor is mainly aimed at the surface target and is suitable for detecting the pressure and distribution status of the surface on the complex object.In this paper,the pressure sensitive film based on TPU(thermoplastic polyurethane)and highly conductive carbon black composites was designed and fabricated to study the sensitivity,stability,repeatability,response time,creep resistance of the pressure-sensitive film.The flexible single-point pressure sensor and the array pressure sensor are designed based on the flexible pressure-sensitive film.Then,the conditioning circuit is designed and manufactured.Finally,the corresponding software of the host computer is developed by using the Labview software.The software is able to realise acquisition,calibration,optimization,processing,storage and display.In this paper,we first explored the conductive mechanism of 0-3-type flexible pressure-sensitive film composites,including the commonly used conductive composite materials additive effect: seepage model theory and tunneling theory,as well as conductive composite material multiplication effect: piezoresistive effect(positive pressure resistance and negative pressure resistance effect),the formation and failure process of the internal conductive network of pressure sensitive film were analyzed.Then,the performance characterization methods of pressure sensitive film were introduced.Furthermore,the preparation process of flexible pressure-sensitive film was studied by specific experiments,including the selection of flexible matrix materials,the selection of conductive materials and the selection of other nano-modified materials,and the selection of organic solvents.In this paper,thermoplastic polyurethane(TPU)was used as the matrix material,high conductive carbon black as the conductive material and ITO nanoparticles as the modified materials,and the pressure sensitive film was prepared by casting method.The initial resistance change of the pressure-sensitive film under different carbon black doping concentration was studied.According to the percolation model theory,the seepage threshold of the conductive composite was 10% wt and the percolation area was 10% wt-12% wt.The compressive properties of the compressive films were measured at several different doping concentrations,and the optimal concentration of TPU and high conductive carbon black was 12% wt.Finally,the surface shape of the pressure sensitive film was determined by various performance characterization methods.Appearance,sensitivity coefficient,repeatability,response time and other performance parameters were tested.In order to improve the dispersion effect of the conductive material on the matrix material,the effect of doping ITO nanoparticles and SiO2 nanoparticles on the reproducibility and consistency of the pressure sensitive film was compared.Through the above work,a flexible,pressure-sensitive film with good thickness of 200?m was prepared.The sensitivity and response time(<100ms)were greatly optimized,and the ability of dynamic monitoring of pressure change was realized.Then,a single point pressure sensor,a bending strain sensor and a 4×4 array type pressure sensor were prepared by using the pressure sensitive film.Finally,the back-end signal conditioning circuit and the host computer software of single point and array pressure sensor are designed to convert the change of the resistance of the pressure-sensitive film into the amount of voltage change which is easy to measure.Single-point pressure sensor's back-end circuit using the inverted operational amplifier mcp6001 sensor resistance changes into voltage signals,the AVR microcontroller built-in analog conversion from the serial port sent to the host computer for data processing and display;array pressure sensor's back-end conditioning circuit using AVR single-chip control CD4051 digital analog switch to achieve the array of pressure sensor line scanning,the multi-point problem into easy to deal with a single point of the problem,the collected voltage data sent to the host computer through the serial data processing and display.Aiming at the unavoidable resistance cross coupling problem in array resistance measurement,a new method of eliminating the cross coupling between sensor units of array pressure sensor is proposed by improving the sensor structure.Finally,using the Labview monitoring and development software developed the corresponding host computer software,to achieve the sensor signal's reading and display.