Study On The Sensing Characteristics Of A Ball-disc Rotational Micro-gyroscope

As an important component in areas like inertial navigation,the gyroscope is widely used in systems such as weapons,ships and aircraft etc.Vibration gyros based on micro-electromechanical systems(MEMS)are cheap and small in size,and are widely applied in consumer products and tactical level weapon systems.But shortcomes like low linear velocity of the mass due to their vibration working mode makes it difficult to further improve their performance.Rotational micro gyros can obtain higher linear velocity of the rotors,while,due to problems like large relative processing error and difficulty in guaranteeing spinning stability of the rotors,their performances are still not as good as MEMS vibrating gyros.In order to improve the performances of micro gyros,we proposed a ball-disc rotational micro gyro structure with a small volume,low cost,simple structure and potential to achieve high precision.It has obvious differences compared with existing gyros on structure and working principle,which makes existing theoretical models cannot be applied to the analysis and optimization of this gyro.Thus,theoretical researches related to the modeling,analysis and optimization on gyro's sensitive structure are carried out,and gyro prototypes are developed on these bases.The structure of the gyro is proposed,and its working principle researched.Characteristics such as ball-disc rotor,direct drive of a permanent magnet rotor and fluid suspended support make the porposed gyro obviously different from existing ones.According to the symmetry of the gyro structure,a differential capacitance detection structure is adopted to detect the tilt angle of the rotor.A mathematical model of the differential capacitance as a function of rotor's tilt angle and structural size parameters is established.It is used to study the relationship between the structure parameters and static sensing characteristics of the sensing structure of the gyro,which provides guidance to the optimization design of the sensitive structure.A dynamics model of the sensitive structure of the gyro is established,and its dynamic characteristics and dynamic responses are studied.The model describes the radial movement of the rotor as a function of the input angular velocity,and reveals the relationship between the structural sensitivity and the structural parameters.Studies have found that,due to the magnetic equivalent elastic restraint on the rotor from the driving structure,the gyro has a self-balance effect,enabling it to work in open-loop condition.The principle and characteristics of the magnetic equivalent elasticity are studied,and the approximation of the elastic coefficient of the gyro system is obtained using a numerical method.On these bases,the relationship between magnetic elasticity coefficient and structural size parameters is studied,and a method is put forward to adjust the damping coefficient.According to these researches,fine adjustment of the damping state of the gyro from significantly under-damped to critically damped state is achieved,which can effectively improve the dynamic characteristics of the gyro.Mechanical errors are important factors that affect the accuracy of a gyro.Thus,we studied the relationship between the gyro noise and several dominating mechanical errors,and the law of how these errors influence the noise level is obtained.These errors not only increase the noise on drive and nutation frequencies,but also increase the random noise by destroying the match of the differential detection structure.Through comparison,rotor disc concentricity,ball-disc assembly error and magnetization direction error of the rotor are found more important,and should be strictly controlled and adjusted.Among these errors,as the concentricity error of the rotor disc will seriously affect the stability of the rotation of the rotor,balance adjustment of the rotor is needed.However,the ball-disc rotor is too small and has no shaft structure,which makes existing conventional balance adjustment devices unable to be used on it.Thus,a new balance adjustment method is proposed.During the adjusting procedure,the concentricity error of the disc is measured and marked by a tool microscope,and the disc is grinded quantitatively.Experimental results show that this method can significantly improve the rotational stability and device performance of the gyro.Based on above-mentioned research results,gyro prototypes were designed and developed.Test on the dynamic responses of the gyro proved the validity of the dynamics model built above.Using the results of the sensing characteristics researches,structural parameters optimization design of the gyro was carried out.Tests on the gyros before and after optimization show that after optimization the structure sensitivity grows to 21 times of the original value,with nonlinear reduced from the original 5.4% to 0.85%.This result verified the correctness of the static sensing characteristics research of the gyro.Through structure optimization,the measured resolution of the gyro has been improved from the original 0.17 o/s to 0.1 o/s,and the bias stability of the proposed gyro has also been improved from more than 50 °/h to about 0.5 °/h,with greater potential of performance improvement by improving the machining accuracy,increasing working speed and realizing closed-loop detection.