Study On Design And Mechanical Modeling Of Distributed Flexible Tactile Sensor Array

With the development of the intelligent prosthesis,the applications of tactile sensing technology have attracted wide attention.Tactile sensor arrays can provide intelligent prosthesis with distributed three-axis contact force information,improving the environmental perception ability of the amputee.At present,the distribution density and sensitivity of the tactile sensing elements integrated on the intelligent prosthetic hand are relative low,which cannot realize high density and high sensitive perception of distributed tactile force.Besides,the flexibility,sensitivity,and the ability of three-axis force measurement of the existing tactile sensor arrays cannot fully meet the requirements of the intelligent prosthesis.Thus,a novel tactile sensor array structure need to be designed,aiming to realize sensitive measurement of the three-axis contact force.By using mechanical modeling,the sensing performance of the tactile sensor arrays can be analyzed and the sensor's structure can be optimized.In this dissertation,theoretical analysis and experimental research are carried out.The tactile sensor array embedded with truncated pyramids as dielectric layer is designed and fabricated.The mechanical modeling and structure optimization of the sensor array are conducted.Also,the sensing performance of the sensor array mounted on curved surface will also be studied,followed by the experiment research.This work was supported in part by the National Basic Research Program(973)of China under Grant 2011CB013303 and National Natural Science Foundation of China under Grant 51105333.In order to realize tactile sensing of intelligent prosthetic hands,a capacitive tactile sensor unit embedded with solid PDMS(polydimethylsiloxane)dielectric layer is designed.For the mechanical modeling of the multi-layer structure of the sensor unit,the ananlytical model of the capacitive tactile sensor unit embedded with solid PDMS dielectric layer is established.Using the developed model,the capacitance changes of the sensor unit under different loading conditions are analyzed.To improve the accuracy of the predicted deformation,the sub-region modeling method is proposed,and then the modified analytical model of the sensor unit is developed.Based on the analysis,conclusions can be made that though the tactile sensor unit embedded with solid PDMS dielectic layer features large measurement range,the sensitivity and the ability of three-axis force measurement still cannot meet the requirement of sensitive three-axis contact force measurement of the intelligent prosthetic hand.To improve the sensitivity of the tactile sensor array and realize three-axis force detection,the distributed flexible tactile sensor array embedded with truncated pyramids as dielectric layer is designed.The structure of the designed truncated pyramids dielectric layer can increase the sensitivity of the tactile sensor array effectively.The structure of the four capacitors and the bump can enable three-axis force measurement.Then,the three-axis force decoupling model is developed to realize the three-axis force measurement of the tactile sensor array.To realize the contact force sensing performance optimization of the designed capacitive tactile sensor array,the analytical model of the tactile sensor array embedded with truncated pyramids dielectric layer is developed.Based on the developed model,the structural effects of the truncated pyramids dielectric layer and the PDMS bump on the contact force sensing performance of the sensor unit are alalyzed.Then the structural parameters of the tactile sensor unit are optimized.To analyze the curved surface effect on the contact force sensing performance of the tactile sensor mounted on prosthetic hand,the analytical model of the tactile sensor unit mounted on curved surface is developed.Based on the developed model,the initial capacitance changes of the sensor array caused by the bending are analyzed,and the contact force sensing performance of the sensor unit mounted on curved surface is studied.To reduce the complexity of the fabrication procedure and enhance the connection strength of the multi-layers of the designed capacitive tactile sensor array,each layer of the sensor array are fabricated seperately,followed by the multi-layer encapsulation.The key process steps of the sensor's fabrication are designed and analyzed.Based on the determined process parameters,the fabrication of the tactile sensor array is completed.Aiming to investigate the contact force sensing performance of the fabricated sensor array and to validate the proposed analytical models in this dissertation,the scanning circuits for the flexible capacitive tactile sensor array is developed.The platform for evaluating the contact forec sensing performance of the sensor array and the real-time contact force display system are established.The static forces calibration,the measurement of contact distribution,and the measurement of dynamic response speed of the tactile sensor unit are conducted.The contact force sensing performance of the sensor array mounted on curved surface is studied by experiment.The tactile sensor array is mounted on a prosthetic hand for contact force detection,and the experiment results demonstrate that the developed tactile sensor array can be utilized to measure three-axis contact force in intelligent prosthetic hand application.