Research On Flexible Displacement Sensing Characteristics Of Dielectric EAP

As a kind of superelastic insulation material,dielectric EAP(Electro-active Polymer)has the advantages of large strain,good flexibility and light weight,which can not only realize flexible sensing,but also adapt to the shape of the object to be measured without hindering the movement of the measured object.In this paper,based on the capacitive sensing principle of dielectric EAP,the displacement sensing characteristic of dielectric EAP is studied,which has potential application prospect in flexible robot and rehabilitation training.The working principle of the dielectric EAP capacitive displacement sensor is analyzed,and the structure of the sensing cell is designed.Through the capacitance analysis of the single sensitive cell and the double sensitive cell(face to face),the linear relationship of capacitance difference between the facing cell and the displacement is found,which determines the use of differential measurement method to obtain the sensitivity of the sensing cell to improve the sensitivity and linearity of the sensing cell.The influence of the manufacturing and installation errors of the sensing cell on the sensing performance is analyzed.The size of the sensing cell is determined,and the sensing cell is completed.The dielectric constantr? of dielectric EAP material is measured by using the model similar to parallel plate capacitor.The static test is carried out on the sensing cell by measuring device driving inner frame in plane.The data processing and static calibration are done by fitting a straight line and plane using the least square method.The results show that the sensitivity is 63.21 pF/mm(X direction)and 63.08 pF/mm(Y direction)respectively.The capacitance difference of face-to-face sensing element is only linearly related to the displacement in the direction,which is independent of the displacement in the other direction.The influence of the installation error on the calibration is analyzed,and the feasibility of the differential measurement method is proved.The sensitivity of the Z-direction displacement sensor by two sensing cells is 66.44pF/mm.Based on the sensing cell,a two-DOF angular displacement sensor is designed to establish the relationship between the capacitance of the sensor and the angular displacement around X and Y axis.The sensitivity of the sensor is about 111.28pF/(°)and 114.76pF/(°).A four-DOF displacement sensor is developed to detect the displacement of the guide rod in the X and Y directions and the angular displacement around the X and Y axes.The end error of the guide rod is within 0.25%.