Study On Flexible Pressure/Strain Sensors With Micro-Nano Materials And Structures

"Electronic skin" is multi-functional flexible sensing system,which can be attached to the surface of the robot as a skin or cloth,so that the robot has the tactile sensing function.One of the key points of this technology is to study the high-performance flexible pressure/strain sensor.At present,the research of flexible pressure sensor mainly focuses on improving the sensitivity,but the response range is generally small.The research of flexible strain sensor mainly focuses on the detection of strain in a single direction,and it is unable to distinguish the direction of unknown strain.To solve the above problems,this research mainly studies the flexible pressure sensor with high sensitivity and large response range and the flexible strain sensor with the function of strain direction recognition and multi-directional sensing.The main achievements are as follows:From contact resistance theory,the resistive pressure sensor can maintain high sensitivity when the initial contact area is small and can have large pressure response range when the contact area range is extended.Using the COMSOL Multiphysics simulation software the dualfield coupling analysis of the solid mechanics field and the current field on the sensor are simulated with different microstructure arrangements.The results show that by simultaneously increasing the height and spacing of microstructures,the initial contact area can be kept small and the contact area range can be expanded,so that the sensor has both high sensitivity and large response range which are consistent with the theoretical analysis results of contact resistance.Flexible contact resistance pressure sensors are fabricated by assembling the flexible conductive micro-structure and the flexible interdigital electrode face-to-face.By characterizing the sensitivity and response range of sensors with different microstructure arrangements,the correlation of the theoretical analysis of the contact resistance and the simulation results are verified.When the height and spacing of the microstructure are 80 (?)m and 160 (?)m,respectively,the device has the high-sensitivity response range of 0-3.28 k Pa,which is significantly higher than similar studies(? 2 k Pa).The sensor with the microstructures also has fast response time(< 200 ms)and long-term stability(1000 cycles),can quickly and accurately identify tactile signals of different frequencies and pressures,and can be used for human-machine interface for intelligent robots.Flexible strain sensors are made of MWCNTs/PDMS conductive composite ink through the screen printing and coating process.Four different designs of the strain sensors are printed,embedded and encapsulated by PDMS film.Among them,the sensitivity of the unidirectional strain sensor is 2.13 and 1.37 in the 0-20% and 20%-100% strain range,respectively,which can accurately and stably distinguish 0.5% strain increment.The output signal of the bidirectional strain sensor in the stretching direction will be significantly higher than the output signal perpendicular to the stretching direction,which can be used to distinguish the direction of strain.The omnidirectional strain sensor can output basically the same intensity of strain signals in all directions,and can be used to detect the strain in any direction.The strain rosette measures the strain of three sensors,and the strain value and direction of the unknown strain can be obtained by calculation.These four strain sensors realize the functions of strain direction recognition and multi-directional sensing.When the sensor is attached to the finger and wrist joints,it can detect bending signals of different frequencies,indicating that the sensor can be applied to the field of robot joint motion detection.For the patterning and molding process of flexible strain sensors,a roll-to-roll production process is proposed.This process integrates screen printing and coating processes,which can continuously produce flexible strain sensors in a large area,and can promote the development of sensors from the laboratory to the industrialization direction.