Development Of Capacitive Six-axis Force Sensor For Robot

Six-axis force sensor is the key sensing equipment for the robot to realize flexible and intelligent operation because it can detect arbitrary force in space.It has been widely used in industrial robots,medical robots,space robots,and other intelligent equipment.The most widely used six-axis force sensor is a strain gauge.However,the requirement of the sticking process of the strain gauge is very high,and in the practical application process,the strain gauge is vulnerable to mechanical wear,which affects the measurement results.In this paper,a capacitive six-axis force sensor is researched and developed,and analyzing the common measurement principle of the capacitive six-axis force sensor,then determines the measurement principle based on the combination of the capacitive effect of the parallel plate and the capacitive effect of the vertical plate.The structure of the sensor is designed according to the principle of measurement,and the statics and modal analysis are carried out with the software to determine the dimension parameters of the sensor deformation beam.The capacitor hardware detection circuit and the calibration platform of the six-axis force sensor are designed.Finally,the static characteristics of the capacitive six-axis force sensor are analyzed and the six-axis force sensor is decoupled.The main research contents are as follows:(1)Introducing the research status of the six-axis force sensor at home and abroad,elaborate on the research significance of the subject and the main research content of this paper.(2)Comparing and analyzing measuring principles of various capacitive sensors,analyzing the advantages and disadvantages of sensitivity and theoretical linearity of different measuring principles theoretically,considering the static characteristics and mechanical structure of sensors comprehensively,the measuring principle of the six-axis force sensor is determined based on parallel plate variable-pole capacitance effect and vertical plate variable-pole capacitance effect.(3)Combined with the analysis of the performance of ordinary straight beam,a composite beam structure is proposed as the elastomer of the sensor;Hyper Mesh software is used to analyze the displacement of the dynamic plate when the sensor is subjected to full-range force under different structural parameters of deformed beams.According to the capacitor pole distance-capacitance curve,considering linearity and sensitivity,the optimum range of the capacitor pole plate is selected to find out the applicable structure of the sensor deformation beam.The mechanical structure of the sensor is simulated by Hyper Mesh software,and the static physical characteristics of the sensor are checked to ensure that the designed sensor meets the requirements of the material stress limit.At the same time,the sensor structure is modally analyzed and its first six natural frequencies are obtained to determine its operating frequency band.(4)According to compare the traditional capacitance detection methods,analyzing the advantages and disadvantages of various detection circuits,and finally choose a digital capacitance detection circuit based on AD7147 chip which has a certain anti-interference ability and high integration.In order to improve the linearity and sensitivity of the sensor,a two-layer design and differential arrangement are adopted for partial electrodes of the sensor.Finally,the schematic diagram of the capacitive six-axis force sensor and PCB board is drawn by using Altium Designer software.(5)By using weights as force source,designing a six-axis force sensor calibration platform with low cost and accuracy;and use the experimental platform to calibrate the six directions of the sensor in turn;solve the sensitivity,linearity,repeatability and hysteresis of the six directions of the sensor through MATLAB software according to the collected data.The decoupling matrix of the capacitive six-axis force sensor is solved by ordinary least squares,and the coupling error and relative error in each direction are analyzed.Finally,the designed sensor linearity is less than 3%,repeatability is less than 5%,hysteresis is less than3.5%;relative error of decoupling is 0.381%,1.235%,3.439%,1.880%,0.538%,3.283%,and maximum coupling error in each direction is 4.068%.