• Journal of Institute of Control, Robotics and Systems
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• v.7 no.8
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• pp.697-702
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• 2001

The ring laser gyro(RLG) has been used extensively in strapdown inertial navigation system(SDINS) because of the apparent of having wide dynamic range, digital output and high accuracy. The dithered RLG system has dynamic motion at sensor level, caused by the dithering motion to overcome the lock-in threshold. In this case, an attitude error is produced by not only the true coning of the vehicle motion but also the pseudo coning of the sensor motion. This paper describes the definition of the multi-frequency coning motion and its noncommutativity error to reject the pseudo coning error produced by the sensor motion such as the dithered RLG. The simulation results are presented to minimize the multi-frequency coning error.

• Journal of Ocean Engineering and Technology
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• v.29 no.6
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• pp.436-444
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• 2015

A submerged body is sensitive to changes in the roll moment because of the small restoring moment and moment of inertia. Thus, a method for predicting the roll-related hydrodynamic coefficients is important. This paper describes a deduction method for the hydrodynamic coefficients based on the results of a coning motion test. A resistance test, static drift test, and coning motion test were performed to obtain the coefficients in the towing tank of Seoul National University. The sum of the hydrodynamic force, inertial force, gravity, and buoyancy was measured in the coning motion test. The hydrodynamic force was deduced by subtracting the inertial force, gravity, and buoyancy from the measured force. The hydrodynamic coefficients were deduced using the regression method.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.3
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• pp.242-247
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• 1996

In this paper, an optimal coning compensation algorithm for strapdown system is proposed by minimizing the coning error. The proposed algorithm is derived as a generalized form in that it contains the class of the existing coning algorithms and allows the design of optimal algorithm for various combinations of gyro samples. It is shown the magnitude of resulting algorithm errors depends mainly on the total number of gyro samples including present and previous gyro samples. Based on the results, the proposed algorithm enables the algorithm designers to develop the effective coning compensation algorithm according to their attitude computation specifications with ease. In addition, the multirate method which can efficiently implement the algorithm is presented.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.4
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• pp.614-621
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• 2016

Micro-Doppler (MD) shift caused by the micro-motion of a ballistic missile (BM) can be very useful to identify it. In this paper, the MD signatures of three scale-model BMs are investigated using a portable measurement system. The measurement system consists of an X-band 2-by-2 phase comparison mono-pulse radar, and a mechanical device that can impart controlled spinning and coning motions simultaneously to a model to yield the MD signature that replicates the characteristic of each target and the corresponding micro-motion. The coning motion determined the overall period of MD, and the spinning motion increased its amplitude. MD was also dependent on aspect angle. The designed system is portable, and can implement many micro-motions; it will contribute to analysis of MD in various situations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.81-88
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• 2006

In this paper, we analyze a noncommutativity error that is not able to be compensated with integrating gyro outputs in RLG-based INS. The system can suffer from some motion known as RLG dithering motion, coning motion, ISA motion derived by an AV mount and vehicle real dynamic motion. So these motions are a cause of the noncommutativity error, the system error derived by each motion has to be analyzed. For the analysis, a relation between rotation vector and gyro outputs is introduced and applied to define the coordinate transformation matrix and the angular vector.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.261-267
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• 2013

In this paper, wind tunnel test and analytical prediction are compared for result of flapping motion in helicopter forward flight condition. Tests were performed at low speed wind tunnel at Chungnam National University, test section of wind tunnel has 1.8 by 1.8 meter open-jet test section area. According to the results of measured data for aerodynamic performance of model rotor in forward flight. It has to observed the difference of analytical and measured results of power coefficient for fixed thrust coefficient. And calculated and measured data of helicopter rotor flapping angles in forward flight are compared for a model rotor in a wind tunnel. A test was conducted to verify the measured data of coning and lateral/longitudinal flapping angle with predicted values.

• Journal of Astronomy and Space Sciences
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• v.20 no.3
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• pp.205-216
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• 2003

The attitude motion of a spin-stabilized, upper-stage spacecraft is investigated based on a two-body model, consisting of a symmetric body, representing the spacecraft, and a spherical pendulum, representing the liquid slag pool entrapped in the aft section of the rocket motor. Exact time-varying nonlinear equations are derived and used to eliminate the drawbacks of conventional linear models. To study the stability of the spacecraft's attitude motion, both the spacecraft and pendulum are assumed to be in states of steady spin about the symmetry axis of the spacecraft and the coupled time-varying nonlinear equation of the pendulum is simplified. A quasi-stationary solution to that equation and approximate resonance conditions are determined in terms of the system parameters. The analysis shows that the pendulum is subject to a combination of parametric and external-type excitation by the main body and that energy from the excited pendulum is fed into the main body to develop the coning instability. In this paper, numerical examples are presented to explain the mechanism of the coning angle growth and how angular momenta and disturbance moments are generated.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1958-1961
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• 2004

Ring Laser Gyroscopes used as navigational sensors inherently experience a lock-in region, where very low rotational rates are not measurable. Most RLG manufacturers use a mechanical dither motor that applies a small oscillatory rotational motion larger than this region to resolve this problem. Any input acceleration that bends this dithering axis causes flexure error, which is a noncommutative error that can not be compensated by simply using integrated gyro sensor output. This paper introduces noncommutative error equations that define attitude errors caused by flexure errors. In this paper, flexure error is classified as sensor level error if the sensing axis coincides with the dithering axis and as system level error if the two axes do not coincide. The relationship between gyro output and the rotation vector is introduced and is used to define the coordinate transformation matrix and angular motion. Equations are derived for both sensor level and system level flexure error analysis. These equations show that RLG based INS attitude error caused by flexure is directly proportional to time, amount of input acceleration and the dynamic frequency of the vehicle.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.8
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• pp.631-638
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• 2018

In this paper, we propose a method to improve the performance by guidance technique and applying it to the precision guided ammunition. The proposed method is a technique designed to reduce the target error of ammunition by reducing the projectile error without analyzing the motion characteristics of the shot. This technique is applied to the moving average filter technique which is widely used as signal processing technique to reduce the fluctuation of the output of the inboard mounting inertial sensor caused by the rotation and the coning motion of the ammunition. In order to compare the performance of the applied technique including the simple 3D guided control technique and the proposed improvement technique. It is confirmed that the application of this technique improves the accuracy of impact of the cannon - launched ammunition with severe environmental conditions and irregular motion characteristics unlike the missile.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.1-8
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• 2006

A steady prediction method is presented to compute dynamic damping coefficients for axisymmetric projectiles. Viscous flow analysis is essential to the steady method using a zero-spin coning motion in the inertial coordinate frame. The present method is applied to compute the pitching moment and the pitch-damping moment coefficients for the Army-Navy Spinning Rocket. The results are in good agreement with the parabolized Navier-Stokes data, range data, and unsteady prediction data. Predictions for Secant-Ogive-Cylinder configurations are performed to investigate effects of afterbody geometries. To investigate the geometrical effect and flow physics, the longitudinal developments of the coefficients are examined in detail.