• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.603-606
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• 2000

This dissertation is concerned with ultra-precision profile measurement of aspheric surfaces using contact probing technique. A contact probe has been designed as a sensing device to obtain measuring resolutions in nanometer regime utilizing a leaf spring mechanism and a capacitive-type sensor. The contact probe is attached on the z-axis during measurement while aspheric objects are supported on an precision xy-stage whose lateral motions are monitored by a set of two orthogonal plane mirror type laser interferometers. Experimental results show that the contact probing technique developed in this investigation is capable of providing a repeatability of 50 nanometers with a $\pm$3$\sigma$ uncertainty of 300 nanometers. Thermal disturbance is found the most significant factor that should be precisely controlled for accurate measurement.

• Journal of Navigation and Port Research
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• v.44 no.5
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• pp.423-429
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• 2020

A ship's automatic steering system is the basis for addressing control difficulties related to course-changing and course-keeping during navigation through heading angle control, and is a link in realizing unmanned and autonomous ships. This study proposes a robust RCGA-based linear active disturbance rejection controller (LADRC) design method considering environmental disturbances, measurement noise, and model uncertainties in designing a ship heading controller for use when the ship is sailing. The LADRC consisted of a transient profile, a linear extended state observer, and a PD controller. The control gains in the LADRC with the linear extended state observer were adjusted by RCGAs to minimize the integral of the time-weighted absolute error (ITAE), which is an evaluation function of the control system. The proposed method was applied to ship heading control, and its effectiveness was validated by comparing the propulsive energy loss between the proposed method and a conventional linear PD controller. The simulation results showed that the proposed method had the advantages of lower propulsive energy loss, more robustness, and higher tracking precision than the conventional linear PD controller.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2E
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• pp.78-86
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• 2003

We analyzed the measured acoustic field to explore the characteristics of a horizontal coherence in shallow water. Signal spatial coherence data were obtained in the continental shelf off the east coast of Korea using a horizontal line array. The array was deployed on the bottom of 130 m water depth and a sound source was towed at 26 m depth in the source-receiver ranges of 1-13 ㎞. The source transmitted 200 ㎐ pure tone. Topography and temperature profiles along the source track were measured to investigate the relationship between the horizontal coherence and environment variations. The beam bearing disturbance and array signal gain degradation is examined as parameters of horizontal coherence. The results show that the bearing disturbance is about ± 8° and seems to be affected by temporal variations of temperature caused by internal waves. The array signal gains show degradation more than 5㏈ by the temporal and spatial variations of temperature and by the down-sloped topography.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.8-12
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• 2003

To protect digital communications and broadcasting that are expected to be increasingly used at frequencies above 1GHz, there is a need to determine permissible disturbance limits for frequency bands above 1GHz according to indicates that better correlates with interference level in digital systems. The quality of digital communications is expressed in terms of bit error rate(BER) or throughput. In this regard, it has been reported that degradation of BER or throughput can be estimated from the amplitude probability distribution (APD) of disturbance amplitude. Therefore, if the APD can simply be measured with a high accuracy, APD will be an optimal index for the assessment of interference in digital communications. In this paper, we show that a measurement method using statistic model of APD has compatibility about performance reduction estimation of WLAN. And through approach of this inspection, we propose numeral models about interference effects of peak value and time rate of spurious.

• Journal of KSNVE
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• v.6 no.5
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• pp.567-574
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• 1996

This paper concerns an articulated space robot with flexible links. The equations of its motion are derived by means of the Lagrangian mechanics. Assuming that magnitude of elastic motions are relatively small, the perturbation approach is taken to separate the original equations of motion into linear and nonlinear equations. Th effect the desired payload motion, open loop control inputs are first determined based on the nonlinear equations. One the other hand, in order to reduce the positional errors during the maneuver, vibration suppression is actively done with a feedforward control for disturbance cancellation to some extent. Additionally, for performance robustness against residual disturbance, an LQ control modified to have a prescribed degree of stability is applied based on the linear equations. Measurement equations are formulated to be used for the maximum likelihood estimator to reconstruct states from the original robot equations of motion. Finally, numerical simulations show effectiveness of the proposed control design scheme.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.3-8
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• 1994

This paper presents a practical method of measuring the cutting force milling process by sensing the feed-drive servo motor current,avoiding the use of a dynamomenter. The relation between the cutting force and the servo motor currents is obtained after the feed-drive system of machining center is modelled. In order to measure the cutting force indirectly, the cutting force in the feed-drive system is regrared as a disturbance, and a disturbance estimator is designed using Kalman filter. A horizontal type machining center is used in the experimental study. A comparison is made between the cutting force measured from the dynamometer and the servo motor current.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.330-335
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• 1995

The actuator's response delay, disturbance and measurement noise can often cause a significant error in the target tracking of an underwater vehicle. The first purpose of this paper is error analysis about motion of an underwater vehicle when the closed loop system has actuator and disturbance and noise. The underwater vehicle is simulated for cases of various disturbances. The second purpose is robust controller design for the underwater vehicle with parameter uncertainty. So, two robust control methods are applied for the underwater vehicle. One is standard $H_{\infty}$ control, and the other is time-varying sliding mode control with modified saturation function. Suboptimal design parameters for $H_{\infty}$ control, and design parameters for time-varying switching surfaces are provided Simulations for the two controllers are carried out and their performances are analyzed.lyzed.

• Journal of the Korean Magnetics Society
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• v.11 no.1
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• pp.32-37
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• 2001

Effects of steel-skeletons on the geomagnetic distribution in building have been studied through the simulation and measurement of geomagnetic distribution at floor surface. Geomagnetic distribution was simulated by the finite element method, and the vertical component Z of geomagnetic field on the floor surface was measured with the fluxgate-type magnetometer. Horizontal steel-skeletons have a little effect on the Z distribution, but vertical skeletons disturb severely the Z distribution and result in the localized geomagnetic disturbance. This disturbance becomes weakened by the bypassing soft-magnetic plate and/or floor.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.2
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• pp.12-20
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• 2007

The aiming ability is a key to improve the accuracy performance of the gun pointing system in the ground military vehicle. This paper describes the new detection method of chatter vibration using disturbance acceleration in the pointing structure. In order to analysis the vibration trends of the pointing system occurred while the vehicle driving, acceleration data obtained from vehicle was processed by using data processing algorithm with moving average and Hilbert transform. The specific mode constants of acceleration were obtained from various disturbances. Vehicle velocity, road condition and property of pointing structure were considered as factors which make the change of vibration trend in vehicle dynamics. Finally, back propagation neural networks have been applied to the pattern recognition of the classification of vibration signal in various driving conditions. Results of signal processing were compared with other condition result and analysed.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.54 no.2
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• pp.101-107
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• 2005

The reduced power quality due to some of disturbances on power system has great influence on the efficient and life of load for bad with serious economic loss. The response of load about disturbance needs to analysis quantitatively in detail to improve load characteristics. In this research, a power supply device is developed to supply disturbed power similar to that of power system. The developed device can output a voltage and frequency from 180[V] to 240[V], 55[Hz] to 65[Hz] respectively. The most outstanding feature of this device is a function to be performed steady and dynamic state characteristic experiment on load or appliances. Also, this device is designed to include high accuracy ouput and simple measurement.