Research On Performances Of Sensor Applied For Force Feedback Magnetic Levitation Control System

The rotor force signals detected by the sensor are the basis of the bearing being activecontrol in force feedback rotor magnetic levitation control system. A force sensor whichconnects inputs with outputs is the feedback link of the force feedback rotor magneticlevitation control system, so it is an important and difficult point of the whole system research.The control precision of force feedback rotor magnetic levitation control system is restrictedby the force sensor used. Only designing the force sensor with the characteristics such as widefrequency response, small error and high stability, force feedback rotor magnetic levitationcontrol system with the characteristics such as high-speed, high-accuracy and high-stabilitycan be ensured. The force sensor is one of premise conditions which can run normally andplay its characteristics in force feedback rotor magnetic levitation control system.Currently, all sensors researched include measuring force bearing, strain force sensor andpiezoelectric force transducer applied for the robot, but they are all not applicable for forcefeedback magnetic levitation control system. So, a2-dimensional force sensor applied forforce feedback rotor magnetic levitation control system should be designed. The2-dimensional force sensor plays a role of support and measurement simultaneously in forcefeedback rotor magnetic levitation control system. It not only can over come the insufficientof magnetic levitation system based on displacement control, but also can simplify thestructure of the whole system which is important for the development of the magneticlevitation control system.On the basis of summarizing the research status of the force sensor both at home andaboard, the force sensor applied for force feedback rotor magnetic levitation control system isdesigned and its performances are analyzed. Firstly, analyzing the requirement of forcefeedback rotor magnetic levitation control system to the property of2-dimensional forcesensor, the research object is determined. Then, structure and spatial arrangement of forcesensitive components are analyzed and optimized, and the design of2-dimensional forcesensor with the characteristics such as high sensitivity, high rigidity, well linearity and strongdecoupling is achieved. Thirdly, under the condition of high frequency, the force electrictransformation relationship of the sensor is given. The coupling relationship among multi-direction force and the influence of the cross sensitivity is analyzed and high frequencyand multi-directions of principle and method are put forward. Finally, the model of theelectromechanical coupling system is established and its dynamic characteristics are studiedwhich can form the completed rotor-support multi-direction dynamic measurement method.The main works accomplished are as follows:(1) The meanings of2-dimensional force sensor choosing the piezoelectric sensors assensitive element are discussed from the performance requirements of force feedback rotormagnetic levitation control system. The circumference symmetrical layout and differentialconnecting mode of the sensitive components are made sure. Considering the characteristicsof the rotor test, the main design points of2-dimensional force sensor components are shownout, the components such as power transmission components, pre-tightening components,shell and the whole sensor structure are designed. The contradiction between sensor carryingcapacity and force measurement is over come which provides an important guarantee torealize force feedback rotor magnetic levitation control. Meanwhile, on the basis of thecharacteristics of main stressed components, the sensor is carried out necessary strength checkby ANSYS modeling and structure parameters of2-dimensional force sensor are made sure.(2) The theory of the2-dimensional force sensor is analyzed and the formula to calculatethe sensitivity of the sensor is derived finally by using ANSYS and influence coefficientmethod. The influence of structure parameters to the sensor sensitivity is studied and itsinfluence law can be received by the analysis of simulation results. The influence problem ofthe cross sensitivity to the sensor measurement accuracy is over come and multi-directions ofprinciple and method are put forward.(3) Because of taking into account the performances between sensor carrying capacityand force measurement concurrently, it is difficult to meet no-distortion measuring conditions.The dynamic models of the mechanical structure and the mechanical structure and measuringcircuit coupling system are established and their amplitude-frequency characteristic arestudied, meanwhile, the dynamics measurement errors of system are analyzed deeply whichshow that the electromechanical coupling lead to the reduction of measurement accuracy.According to the error analysis of the working frequency and adopting amplitude-frequencycharacteristic correction method, the correction function is given and the electromechanical coupling system is amended. The results show that amplitude-frequency error of the couplingsystem modified is less than1%and the coupling system has good dynamic performanceswhich can meet no-distortion measuring conditions.(4) The dynamical model of the2-dimensional force sensor mechanical structure and itsmeasuring circuits coupling system is established. Simulation calculations are carried outrespectively to the step incentive responses and pulse incentive responses of mechanicalstructure and coupling system and their transient response curves are obtained. The influencesof the mechanical structure and its measuring circuits coupling to the dynamic performance ofsystem are analyzed which show that the dynamic performance of designed measuringcircuits can meet the requirements of the force feedback rotor magnetic levitation controlsystem.(5) Proceeding experimental research to pulse incentive responses of mechanicalstructure: dealing with the experimental data by differential method, pulse incentive responsesand cross pulse incentive responses of2-dimensional force sensor structure are abstained andcomparing experimental values with the theoretical values, the results show that the specialstructure design can effectively reduce the cross error; because of electromechanical systemexisting coupling, the performances of electromechanical coupling system are poorer and itserror is larger, so adjusting circuit parameters and modifying dynamic performances, relativesquare integral absolute error, peak error and cross error of mechanical structure modifiedreduce greatly and amendment reduces the error of the measurement circuit and mechanicalstructure coupling.This research features: on the structure, a new sensor applied for magnetic levitation forcefeedback control system is designed. It can over come the contradiction between the forcemeasurement and sensor carrying capacity and provide the basis to realize the force feedbackmaglev control which can ensure the first natural frequency f1nof sensor far higher than2timesworking frequency f02and the influence of cross sensitivity to the sensor precision is over come;the model of the electromechanical coupling system is established and its dynamiccharacteristics is studied which can form the completed rotor-support multi-direction dynamicmeasurement theory; in order to obtain high accuracy measuring, we put the mechanical partand the electrical part as a whole and the coupling system is modified integrally.