Myeong-Jong Yu

AN EXTENDED ROBUST H∞ FILTER DESIGN FOR SDINS IN-FLIGHT ALIGNMENT

Abstract In this paper, a robust filter for an in-flight alignment (IFA) is presented to effectively eliminate system errors in the case where a strapdown inertial navigation system (SDINS) has large initial attitude errors. First, an extended robust H ∞ filter is proposed for a general nonlinear uncertain system. We also analyze the characteristics of the proposed filter, such as an H ∞ performance criterion, using the Lyapunov function method. Analysis results show that the proposed filter has robustness against disturbances, such as process and measurement noises, and against parameter uncertainties. Then the IFA for the SDINS is designed using the presented filter. Simulation results demonstrate that the proposed filter effectively improve the performance.

Response characteristics of a MEMS resonant accelerometer to external acoustic excitation

In this paper, we present resent works on acoustic response of a MEMS resonant accelerometer. We analyzed why the resonant accelerometer reacted to external acoustic noise theoretically and showed how to reduce the acoustic response characteristics experimentally. The resonant accelerometer consists of a proof mass and a dual ended tuning fork. It behaves in the manner of a differential mode by arranging a pair of accelerometers. The mode shape of accelerometer was analyzed to find out the input mode frequency by using a finite element method(FEM) simulation. Experimental results revealed that the accelerometer reacted to the external acoustic excitation only at the input mode frequency. We showed experimentally that the accelerometer had the susceptibility of 70dB against an acoustic noise. And the results indicated that an acoustic absorber and a metal case applied to the IMU had the reducing effects of 20dB in external acoustic response.

Design and Fabrication of a Superconducting Relative Gravimeter With a Planar Spring

The relative gravimeter is in high demand to improve the performance of a navigation system. Therefore, we designed, fabricated, and tested a superconducting relative gravimeter. The proposed gravimeter features a superconducting planar spring, an electromagnetic levitation, and a superconducting quantum interference device (SQUID) sensor. The advantages of the superconductor include being able to enable the device with exceptional stability and having an extremely low noise. The coupling spring with electromagnetic levitation can also offer a low resonant frequency for better sensitivity. The device consists of a niobium mass-spring vibrometer having a planar spring, a levitation coil, and a SQUID sensor. The vibrometer was designed by conducting the mathematical analysis and the mechanical- electromagnetic finite element analysis simulation. Both the electrodischarge machining process and the high vacuum-thermal process were applied to fabricate superconducting structures. Experiments to store and discharge a persistent current in the levitation coil were carried out at 4.2 K cryogenic condition to confirm the numerical prediction. An experimental setup with a precision linear actuator was used to verify the relationship between induced inductance and displacement. The test result indicates that the gravimeter can measure the fine movement of the levitation mass by reading a SQUID output and the scale factor is ~28 mV/um.

Analysis of compensation for a g-sensitivity scale-factor error for a MEMS vibratory gyroscope

In this paper, we present recent work on the g-sensitivity error of the MEMS vibratory gyroscope. Generally, the g-sensitivity error has been ignored in the use of commercial MEMS vibratory gyroscopes, but it deserves our attention if we are to achieve tactical grade performance for military applications. First, we mathematically show the reason the g-sensitivity error occurs as an additional scale-factor error during the use of MEMS vibratory gyroscopes. Then, we estimate the g-sensitivity error using FEM simulation and verify it by experiment using a centrifugal machine. Consequently, we propose a compensation model to accommodate the g-sensitivity error of a gyroscope and confirm the theoretical prediction with experimental results.

Design of SDINS Rapid Initial Alignment Technique Robust to the Pyro-shock in Multi-Launch Rocket System

In this paper, a SDINS(Strapdown Inertial Navigation System) rapid initial alignment technique robust to the pyro-shock in multi-launch rocket system is proposed. The proposed method consists of three steps. Firth, transfer alignment is performed to estimate misalignment between MINS(Master INS) and SINS(Slave INS), and the estimated misalignment is written in the memory when transfer alignment is completed. Next, the pre-filtering process is performed to get rid of the acceleration error induced by launcher vibration. Finally, the horizontal alignment is performed to compensate misalignment variation caused by pyro-shock. We verified the performance of the proposed alignment method comparing with the conventional transfer alignment method. The simulation shows that the proposed initial alignment technique improves alignment performance.