A Capacitive-type Testing Device For Suspension Stability Of Magneto-rheological Fluids

The suspension stability of magnetorheological fluid(MRF)is a key factor to ensure its effective operation for a long time,and is currently one of the bottlenecks that limits its extensive engineering applications.The sedimentation process of MRF is: the influence of gravity on the suspension term results in a change in the volume fraction distribution.The volume fraction of suspended particles is positively related to the permittivity of MRF,and there is a direct relationship between the dielectric constant and the capacitance value.In view of the above reasons,the dielectric constant of the MRF is monitored by a specific capacitance sensor to obtain the time history of the suspended particle sedimentation rate and particle concentration distribution.Aiming at the problem of suspension stability in engineering applications of MRF,a capacitive magnetic rheological fluid suspension stability test device is studied.Two types of capacitive sensors are designed.The mechanical system,motion control system and capacitance data acquisition system of the test device are developed,and a set of test device prototype is made.The test results are compared with the inductive test device's,to achieve the quantitative characterization and comprehensive evaluation of the MRF suspension stability.The specific research work is as follows:The engineering application prospects of MRF are briefly summarized.The reasons for static settlement of MRF are analyzed from the force mechanism of suspension elements,and the methods for improving the suspension stability of MRF are summarized.The current research status and methods of evaluating the suspension stability of MRF are listed.Problems with the test device are categorized as,and the research content and significance of this paper are proposed.The process of magnetorheological fluid settling is a process of changing the volume fraction of the levitated term,which is used to establish a model of the relationship between the volume fraction of MRF levitate and the dielectric constant of MRF.The value of the capacitance caused by the settlement of MRF is obtained.The conclusion of fluctuations shows that the process of settling of MRF is accompanied by fluctuations in capacitance.The requirement of a capacitance-based MRF suspension stability test device is proposed and the overall layout design is completed.The test principles of the ring-mandrel and the faced-double-arc type capacitance sensors are presented.The theoretical analysis of these two sensors is performed,in which the eccentricity error of the ring-mandrel type is particularly analyzed.ANSYS is used to simulate the measured electric fields of the two structures,and their advantages and disadvantages are compared and analyzed.Based on the theoretical analysis of two types of capacitive sensors,a ring-mandrel type and a faced-double-arc type capacitive sensor are designed.According to the technical requirements of the test device,the drive motor and the drive screw are selected;The mechanical system of the test device is designed;the technical problems of test tube sealing,test tube clamping,screw movement and so on are solved;The motor drive system module and data acquisition module are designed;The test device components are made,assembled and adjusted;The interface programming of the host computer is performed;Then joint debugging,calibration and calibration of each module are carried out to complete the manufacture of the MRF test device.Six kinds of MRF samples with different volume fractions are prepared,which are tested continuously.Compare the data of the ring-mandrel type capacitance method and the inductance method test.The trend of the two methods is the same.The comparison between the ring-mandrel type capacitance method and the faced-double-arc type capacitance method shows that the former structure is better.Compare with the visual mudline observation method,the high degree of agreement between the two shows that the capacitance method is feasible for evaluating the suspension stability of MRF.The equipment error is analyzed to facilitate the follow-up improvement work.