• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.2
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• pp.165-173
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• 1998

When an automatic course-keeping is concerned, as is quite popular in modem navigation, the closed-loop steering system consists of autopilot device, power unit (or telemotor unit), steering gear, magnetic or gyro compass and ship dynamics. In order to estimate automatic steering system of ships in open seas. we need to know the characteristics of each component of the system, and also to know the characteristics of disturbance to ship dynamics. In this paper, I provide calculation method of imposing irregular disturbance to autopilot navigation system of the ship in open seas, and also show calculation examples about fishing boat. The disturbance consists of the irregular wave and the fluctuating component of wind. Finally, The disturbances are calculated in terms of equivalent yaw angular velocity. Each spectrum and time history of disturbance are reasonably evaluated.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.700-703
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• 1997

A robust controller for a 6 DOF magnetically levitated fine manipulator is presented. The proposed controller consists of following two parts : a model reference controller (MRC) and a H$_{\infty}$ controller (HIC). First, the MRC stabilizes the motion of the manipulator. Then, the motion of the manipulator follows that of the reference model. Second, the HIC minimizes errors generated from the MRC due to noise and disturbance since the HIC is a kind of robust controller. The experiments of position control and tracking control are carried out by use of the proposed controller under the conditions of free disturbances and forced disturbances. Also, the experiments using PID controller are carried out under the same conditions. The results from above two controllers are compared to investigate the control performances. As the results, it is observed that the proposed controller has similar position accuracy but better tracking performances comparing to the PID controller as well as good disturbance rejection effect due to the robust characteristics of the controller. In conclusion, it is verified that the proposed controller has the simple control structure, the good tracking performances and good disturbance rejection effect due to the robust characteristics of the controller..

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.1
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• pp.51-57
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• 1998

In order to minimize vibration problems of rotating machinery rotors have been assembled through balancing machines. Since perfect balancing is impossible, residual unbalances cause serious vibration while the rotor is in high speed region. To minimize unbalance effects of magnetic bearing systems (AMB) during rotation on-line balancing methodology was studied. Unbalances were considered as disturbances of the system. The disturbance observer was used to estimate unbalance force from measurable state and input variables. Balancing inputs computed according to LQR and outputs of the observer were applied to eliminate unbalances during high speed rotation of the AMB. the effectiveness of the on-line balancing was verified through numerical simulations.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1643-1651
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• 2002

Magnetic levitation systems are required to have a large operating range in many applications. As one method to solve this problem, Time Delay Control (TDC) is applied to a single-axis magnetic levitation system in this paper A reduced-order observer is utilized to estimate states excluding measurable states in the control law. The system consists of a square air-core solenoid and a circular permanent magnet attached on a plastic ball. Theoretical magnetic forces of the system are obtained on the basis of the location of the magnet around the solenoid. The magnetic levitation force is obtained by the experiment, and then compared with the theoretical one. As the results of the control experiments, the nonlinear controller (TDC : 1-2 ㎜) has a larger operating range than the linear controller (PD control : 1-1.4 ㎜), and is superior to linear. control in the robustness to the modeling uncertainty and the performance of the disturbance rejection.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.127-130
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• 1991

A magnetic levitation system with hybrid magnets, which is composed of permanent magnets and electromagnets, consumes less power than the conventional attraction type system. A parallel complementary controller on the lift controller is proposed to reduce the sensitivity for parameter variation and force disturbance. Simulation and experiment show that the lift system has robustness to force disturbance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.5
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• pp.1209-1216
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• 2010

It has increased that peripheral disturbance(blood flow, nerve, Raynaud's phenomenon) and finger rheumatoid arthritis which is caused by the diabetic complications. To improve these pain issues, we proposed new method for the Finger Disease Therapy(FDT). In this paper, we manufactured solenoid cylindrical coil which was only for the FDT using a variable micro-electromagnetic. Also, we designed the Finger Disease Therapy System(FDTS) which could select three stimulation modes(N_pulse, S_pulse, N/S_pulse) and frequency(0.25hz, 0.5hz, 1hz). We used a Teslameter to measure magnetic flux inner solenoid, and measured magnetic flux as distance(0 ~ 3cm) inner solenoid with stimulation modes and frequency. In the results, magnetic flux was the highest in center of solenoid(0cm) for all stimulation modes. Also, the highest magnetic flux was measured as N_pulse(294.3mT), S_pulse(293.8mT) in 1Hz and N/S_pulse (275.4mT) in 0.25Hz, respectively. Therefore, we developed the FDTS using various pattern and intensity for finger diseases therapy, and checked therapy clinic application possibility of the FDTS as measuring magnetic flux inner solenoid.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.12
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• pp.689-697
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• 2005

In this paper, an application of a decentralized $H_{\infty}$ controller(DHC) to multiple controlled-permanent magnet(CMAG) magnetic levitation(Maglev) systems is presented. The designed DHC using two Riccati equations iteratively has simpler structure and needs less computational loads than conventional centralized $H_{\infty}$ controller. A target plant is a hybrid-type CMAG system with permanent magnet and coil, and its mathematical model is firstly derived to design the DHC. To implement the designed algorithm, a real Maglev vehicle system including digital controller, chopper, sensor, etc., is manufactured. To compare the performances of the DHC method with an observer-based state feedback control(OSFC), the input tracking and disturbance rejection characteristics are experimentally tested. As performance indices(PI), integral of squared error(ISE), integral of absolute error(IAE), integral of time multiplied by absolute error(ITAE) and integral of time multiplied by squared error(ITSE) are used. From the experimental results, it can be seen that the input tracking and disturbance rejection performances of the DHC are better than those of the conventional controller.

• Journal of the Korean Institute of Navigation
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• v.12 no.1
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• pp.55-69
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• 1988

The sensing part of the remote-indicating magnetic compass has to be placed where the ship's magnetic effects are minimum, in order that the compass may remain usable under the varying magnetic conditions likely to be experienced on board the ship. In this paper the model of the overall ship's magnetism is built using Vacquier's method frequently used in determining the geomagnetic anomaly, on the assumption that the steel ship generate the magnetic disturbance in the geomagnetic field. It was found that the values of the magnetism observed on board approximate to those of the magnetism calculated from the captioned model, under the condition that the ship's material isominated by the permanent magnetism. And on the basis of the above model, it was feasible to locate the place of the minimum magnetic field by computer calculation.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.2
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• pp.40-46
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• 2004

Magnetic bearing has been adopted to support a rotor by electromagnetic force without mechanical contact and lubrication process. The recent growth of magnetic bearing applications in many industrial fields requires more accurate design of bearing-rotor system. Due to external forces and uncertainties of magnetic bearing system the actual performance and stability my be worse than it is designed. This paper describes the governing equations of rotor magnetic bearing systems and/or the designing of robust controller via standard $H_{\infty}$ control problem. The system stability and response characteristics are studied by simulations and verified with experimental results.

• Journal of Astronomy and Space Sciences
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• v.19 no.1
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• pp.75-88
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• 2002

The climatological characteristics of the polar ionosphere is examined in terms of the ionospheric conductance and electric field. For this purpose, 109 days of measurements from the Sondrestrom incoherent scatter radar are utilized. By combining these two quantities, it is possible to deduce the overhead ionospheric current distributions. The ionospheric current density thus obtained is compared with the corresponding ground magnetic disturbance. Also examined is the effect of the field-aligned current on the ground magnetic disturbance, particularly on the D component Several interesting climatological characteristics about the ionosphere over the Sonderstrom are apparent from this study. (1) The conductance distribution is mainly due to solar EUV radiation during day-time On the other hand, the conductance distribution during the night-time is very low. (2) The conductance distribution one. the polar cap region during the day-time is controlled mostly by the solar EUV radiation, while it is extremely low during night-time wish the Hall and Pedersen conductances being 1.6 and 1.2 siemen, respectively (3) The region of the maximum N-S electric field tend to locate in the dayside sector. The E-W component of the electric field is stronger than that over Chatanika (4) The E-W auroal inospheric current (J/sub E/) is more important in the sunlit hemisphere than the night hemisphere. And a strong southward current is noted in the prenoon sector (5) There is a significant correlation between the overhead ionospheric current and the simultaneously observed ground magnetic disturbance. However, the assumption for the infinite sheet current approximation is far from realistic, underestimating the current density. And the correlation between ${\Delta}H$ and J/sub E/ is higher than the one between ${\Delta}D$ and J/sub N/ , indicating that field-aligned current affects significantly ${\Delta}D$.