Study On Thermal Characteristics And Thermal Deformation Compensation Of Giant Magnetostrictive Actuator

Giant magnetostrictive material(GMM)is a new type of functional material controlled by magnetic,which can realize bidirectional conversion of electromagnetic and mechanical energy.The giant magnetostrictive actuator(GMA)which core element is the GMM,has excellent characteristics such as high displacement precision,fast response speed,simple structure and so on.It has broad application prospects in the field of precision and ultra precision machining,active vibration control,fluid machinery and other engineering fields.However,due to inherent characteristics of GMM such as hysteresis characteristics,eddy current characteristics,temperature characteristics,which seriously affect the GMA output characteristics,reduce its performance,limits its development in the field of precision,ultra-precision drive equipment.In this paper,in order to improve the accuracy of GMA,expand its application in the field of precision and ultra-precision machining,the eddy current loss characteristics,nonlinear constitutive behavior of GMM and temperature characteristics,thermal compensation control method and nonlinear multi-field coupled constitutive model were studied.The GMA with thermal compensation function was developed.In this paper,the mathematical model of the classical eddy current loss considering the eddy current effect and the radial magnetic field distribution was established based on the Maxwell electromagnetic equation and the eddy current effect.the excess eddy current loss of the giant magnetostrictive material was discussed by the concept of micro magnetism,the concept of MO(Magnetic Object).A mathematical model of excess eddy current loss considering the effect of stress was established.On the basis of thermodynamic theory and energy conservation law,under the co-coupling of magnetic field,stress and temperature,GMM nonlinear constitutive coupled model with hysteresis and eddy current loss was established.So based on the momentum theorem,a nonlinear multi-field coupled dynamic model of precision micro-displacement GMA was established by explaining the nonlinear constitutive behavior of the material and its strong coupling interaction with the dynamic behavior of the system.And the validity of the nonlinear dynamic model was verified by experiments.The finite element method was used to analyze the magnetic field and temperature distribution of GMA,studied and analyzed thermal deformation compensation control method of GMA.On the basis of the requirements of GMA and the internal temperature distribution,GMA with thermal compensation function was designed by thermal expansion compensation method.Finally,a GMA performance test system was established,the compensating structure of GMA,the displacement characteristic,the temperature characteristic and the pre-load characteristic were studied by experiments.The experimental results show that the temperature of GMA can reach 87.4?,which continuous operation 120 mins under 3A DC excitation,and 150 Hz is the boundary point of two kinds of heat sources inside GMA.The compensating structure has better compensation effect at low temperature(less than 45 ?).The optimal preload of GMA is 18 MPa.The displacement of GMA is not completely linear with the excitation current,The output displacement of GMA is 81.6?m and 54.1?m when the excitation currents 4A and 2A are respectively.The results provide an effective new method for controlling the temperature characteristics and thermal deformation of GMA,and it is of great significance to improve the working precision of GMA and promote its further application in precision and ultra precision machining.