Design Of A Rotational Micro-gyro Based On Magnetic Self-restoring Effect And Study On The Detection Method

Gyroscope is an inertial sensor for measuring angular speed.Gyroscope is the core component of inertial systems in vehicles(such as aircraft,submarine,missile),and of modules for angular speed measurement in commercial electronics(such as gamepad,smartphone).Based on sensing principle,mechanical gyroscope is devided into two cat-egories of vibratory gyroscope and rotational gyroscope.Micro-electro-mechanical sys-tems(MEMS)vibratory gyroscope has been used widely in commercial electronics with relatively not very high precision requirement for its advantages of low price,small vol-ume,low power consumption.However,MEMS vibratory gyroscope has unavoidable mechanical cross-talk between vibrations of driving and sensing directions,which restricts further performance development.The bias stability performance of most vibratory gyro-scopes is much larger than 10°/h.Gyroscopes based on precession effect mainly include liquid floated gyroscope of large volume and MEMS suspended gyroscope(magnetically suspended gyroscope,electrostatically suspended gyroscope).In principle,because of high driving speed of the rotational gyroscope,which leads to high moment of inertia of the rotor,precision of rotational gyroscope should be higher than that of vibratory gyro-scope.Liquid floated gyroscope of large volume,mostly used in military products,is of high precision,but with a very high price.For MEMS suspended gyroscope,existence of levitation structure leads to complicated fabrication technology and difficulty in miniatur-ization.Thus,they are not widely used.Furthermore,stability of rotor levitation limits the precision performance of the gyroscope.No MEMS suspended gyroscope with the bias stability performance much better than that of MEMS vibratory gyroscope is reported up till now.To solve the problem of poor stability of rotor levitation in traditional MEMS levi-tated rotational micro-gyroscope and improve the precision of rotational micro-gyroscope,Harbin Institute of Technology(HIT)leads and undertakes the 973 project of“basic re-search of motion interface nano effect of micro/nano inertial device”.Under the support of the project,a rotational gyroscope with a ball-disk shaped rotor supported by a water-film bearing(hereinafter referred to as ball-disk shaped rotational micro-gyroscope)is proposed.The gyroscope solves the problem of low levitation stability in traditional sus-pended gyroscope with the trade-off of a relatively larger volume(length 24 mm,thickness4.8 mm)compared with MEMS gyroscope.Through experiment test and the third party(Tsinghua University)authentication,the bias stability achieves 0.5°/h,which is a lead-ing precision performance in China.Study and fabrication of the gyroscope prototype is an important part of the 973 project.Driving system based on low-damp water-film bearing of the gyroscope is designed.The system adopts brushless direct current motor structure of 12 poles.Through modal analysis,maximum driving speed of the gyroscope is identified.By deriving the analytical expression of the driving torque expressed by magnetic potential and driving angle,the requirement for stable driving is obtained.A close-loop drive system based-on back elec-tromotive force(EMF)detection with a quick and low-power-consumption drive scheme is designed to achieve a faster spinninig speed of the rotor under rated driving power to exhibit better gyroscope performance.To provide a stable support to the rotor with low damp,which enhances gyroscope performace and decreases the driving power consump-tion caused by friction torque from support to the rotor simutaneously,a superhydropho-bic surface is fabricated on the rotor ball and water-film bearing is applied.A method of superhydrophobic surface fabrication on the stainless steel rotor ball is proposed,and the contact angle of the fabricated superhydrophobic surface is 167°,exhibiting excellent superhydrophobic property.Experiments reveal that under the application of water-film bearing,the fabricated superhydrophobic surface can increase the driving speed of 11%under the rated driving current,which improves gyroscope effect.The overall structure of the ball-disk shaped rotational micro-gyroscope is designed with the confirmed driving structure.The sensing principle based on magnetic self-restoring effect is studied.The magnetic torque produced by the effect balances Coriolis torque,which avoides possible unstability of control brought by traditional electromagnetic feed-back system and the mutual magnetic interference between feedback system and driving system.Dynamical equations with the magnetic self-restoring coefficient as the elastic coefficient are constructed,based on which,regulation of step response and impulse re-sponse is studied further.The study has guiding significance to the design of the detection system of precessional angle.On account of the brushless direct current motor driving structure with driving poles allocated at radial directions of the rotor,torque produced by driving magnetic field to precessional rotor,namely,the effect of the driving system to gyroscope sensing principle,is analyzed.A method based on differential capacitance is proposed to detect precessional angle of the gyroscope rotor.Through analytical analysis,modeling and simulation,relationship between differential capacitance under rotor precession,and parameters of electrode di-mension,gap between the electrode and the rotor,is studied.Based on the study,structure of the differential capacitor is designed.Aiming at the problem of nonlinearity in differ-ential capacitance detection,nonlinearity correction algorithm based on multiple support vector regression machine is proposed,and data fusion based on ordered wieghed average operator is conducted to decrease fitting errors in transitional regions of piecewise sec-tions during nonlinearity correction.The detection system is designed.Noise sources of the system are analyzed and related noise reduction measures are proposed.Gyrospsce performance is tested through experiments.Average value and standard variation of mea-surement errors are-0.0055°/s and 0.0295°/s,respectively.And bias stability reaches0.5°/h.