Research On Three-dimensional Measurement In Small Space By Eddy Current Sensor

With the development of the industrial manufacturing technology,the requirement of local precision of parts is gradually improved.Therefore,three-dimensional measurement in small space with complex structures plays an important role.For example,in order to ensure the precision of parts,it is important to ensure the precision of the tooling.Therefore,it is necessary to measure the three-dimensional displacement field of the key features on the tooling.In order to overcome the problems of complex structure,large measurement range,limited installation space,non-destructible coating,and occlusion of key features on the tooling,the eddy current displacement sensor is used to conduct local measurement of each key feature on the tooling.The eddy current displacement sensor has the advantages of small size which makes it easy for installation,non-contact measurement which means that there is no need to damage the coating of the assembly tooling,and high measurement accuracy.All those advantages enable the eddy current displacement sensor to meet the requirements of high precision measurement in complex and small space.Therefore,this paper will study the method of using eddy current displacement sensor to realize three-dimensional space measurement.The basic working principle of eddy current displacement sensor is described and the equivalent circuit of eddy current displacement sensor is analyzed theoretically.The characteristic function of eddy current displacement sensor is analyzed and a polynomial fitting method based on least square method is established to obtain the characteristic function.The calibration system is set up,and the results of linear fitting and polynomial fitting are compared and analyzed through experiments,which lays a theoretical foundation for obtaining necessary parameters of the eddy current displacement sensor.The electromagnetic filed simulation modeling of eddy current displacement sensor is realized through ANSYS Maxwell software.During the relative displacement measurement process of eddy current displacement sensor,factors such as different tilt angles of the target,the different size of the incentive frequency inside the coil,the different hole location in the target,and the different spacing between the two coils have influence on the eddy current field distribution and the eddy current density.All those factors are analyzed in this paper.A three-dimensional information measurement method based on eddy current displacement sensor is proposed.Two necessary parameters of eddy current displacement sensor for three-dimensional measurement are analyzed theoretically and physically.A method for calculating the necessary parameters based on space vector relationship and optimization is designed.The plane datum conversion method is designed to compensate the datum deviation in the measurement theory.The indirect evaluation method of the proposed measurement method is designed and the experiment system platform is constructed.The experiments study the characteristic functions of six eddy current displacement sensors,and it is found that the characteristic functions obtained by the polynomial fitting method based on least square method is closer to the actual calibration data of eddy current displacement sensor than those obtained by the linear fitting method.The characteristic function shows that the necessary parameters are exist and it is necessary to obtain them.The two necessary parameters are obtained by experiments and the three-dimensional information measurement experiments based on the eddy current displacement sensor are carried out.Furthermore,the results of verification experiments show that the average measurement precision of three-dimensional measurement method can reach 0.0212 mm,and the mean square error can reach 0.0127 mm,proving that the measurement precision of the proposed measurement method can meet the requirements of industrial measurement.The result of data analysis shows that the mean value of optimization error of the six sensors is reduced from 5.6140 mm which is based on the displacement datum conversion method to 0.0688 mm which is based on the plane datum conversation method.