Research On Touch Slip Detection Based On PVDF Force Sensor

Polyvinylidene fluoride(PVDF)is a piezoelectric thin film with characteristics such as high flexibility and mechanical strength,wide frequency band,low acoustic resistance,good chemical stability and high sensitivity.Therefore,it is very suitable for sensing physical quantities of the human body.The main objective of this study is to identify the contact force and sliding force by PVDF piezoelectric film sensor array.The relationship between the output voltage of the film and the mechanical stress can be obtained by the piezoelectric equation of the piezoelectric material and the force analysis of the film.The array structure is optimized to reflect the magnitude and direction of load force.The experimental characterization of the performance parameters of the array points and the dynamic slip experiments prove the feasibility of using the array structure to identify the touch slip state.The research contents are as follows:1.Theoretical calculation and finite element simulation.According to the piezoelectric equation of piezoelectric material,the relationship between the voltage output of piezoelectric film and the stress in the direction of axis 3 and axis 1 is derived.ANSYS Workbench software was used to analyze the relationship between voltage output and strain and stress on the linear path of piezoelectric film.The piezoelectric thin film array points were analyzed,and the voltage output under different positive pressure was observed.The simulation error is obtained by comparing the calculated value with the simulated value.It is found that the actual voltage of the array point is the superposition of the voltage generated in the axis 1 direction and the axis 3 direction by observing the voltage generated in the axis 1 direction and the axis 3 direction respectively,which proves the correctness of the theoretical calculation.At the same time,it is found that when the piezoelectric film is subjected to positive pressure in the axis 3 direction,the stress will also be generated in the axis 1 direction,and because of the softness of the polymer material,there will be extrusion on the outside edge of the stressed area,resulting in the opposite stress and voltage to the stressed area.2.Array structure design.According to the piezoelectric equation and the physical parameters of PVDF film,the theoretical voltage expression of the array point is obtained.Then according to the theory of uniform load in the center of the circular film,the more specific voltage expression of the array point is obtained.By deducing the relationship between the stress in the axis 3 direction and the stress in the axis 1direction and the distance from the load center,the basis is provided for the design of the array point spacing.The separation distance and arrangement form of array points are obtained by simulation analysis.The sensor array structure is simulated to verify the feasibility of identifying contact force and sliding force.3.Point performance characterization and slip detection of PVDF thin film sensor array.The static performance of the designed and manufactured PVDF piezoelectric film sensor array was characterized through the establishment of an experimental platform with appropriate experimental instruments.The voltage output of the array point under the pressure of 1 N ～ 10 N was mainly explored.The sensitivity of the sensor array point was obtained by fitting the line of the voltage signal with the least square method.The actual sensitivity of the array points is obtained.Through the slip identification test,the obtained multi-channel voltage signal is analyzed.By comparing the voltage value and the difference of the time when the signal value appears,the force path and the force magnitude during the slip process can be determined.