• Structural Engineering and Mechanics
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• v.55 no.1
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• pp.229-244
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• 2015

H-infinity norm relates to the maximum in the frequency response function and H-infinity control method focuses on the case that the vibration is excited at the fundamental frequency, while 2-norm relates to the output energy of systems with the input of pulses or white noises and 2-norm control method weighs the overall vibration performance of systems. The trade-off between the performance in frequency-domain and that in time-domain may be achieved by integrating two indices in the mixed vibration control method. Based on the linear fractional state space representation in the modal space for a piezoelectric flexible structure with uncertain modal parameters and un-modeled residual high-frequency modes, a mixed dynamic output feedback control design method is proposed to suppress the structural vibration. Using the linear matrix inequality (LMI) technique, the initial populations are generated by the designing of robust control laws with different H-infinity performance indices before the robust 2-norm performance index of the closed-loop system is included in the fitness function of optimization. A flexible beam structure with a piezoelectric sensor and a piezoelectric actuator are used as the subject for numerical studies. Compared with the velocity feedback control method, the numerical simulation results show the effectiveness of the proposed method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.438-444
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• 1997

Recently, optical disk drives are increasingly demanded to have higher speed as well as high information density, especially for applications like CD-ROM drives. To this end, improvement of their optical pick-up structure and control is recognized the very challenging issue. In this paper, the 2-D motion of the pick-up is first analytically modelled to identify the cause and effect of the troublesome cross coupling between auto-focusing and tracking directions. Subsequently, the overall system equations are derived to include the dynamics of the related components in the auto-focusing servo system. While its unmeasurable parameters being estimated by the least square error method, a simple but decent linear model can be obtained within its operating frequency range. To design the high speed and robust positional servo controller, the design specifications are detailed and H$\sub$.inf./ control method is employed based on the simple model. Using the pickup in a commercial 8 fold speed CD-ROM drive as an example, performance of the designed controller is verified by realtime experiments.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1371-1373
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• 2005

Recently, preparing the problems in connection with energy and environment, grid-connected power systems have been intensively researched in the world. In general, the output power of grid-connected inverter (GCI) contains noisy components of inverter switching frequency. Moreover, pre-existing grid voltage disturbances degrade the output power quality. The objective of this paper is to make a GCI output high quality power. A robust current control scheme using neural network is presented in thispaper. To show the feasibility of the proposed scheme, some simulation results are provided.

• The Journal of the Acoustical Society of Korea
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• v.25 no.2E
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• pp.69-73
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• 2006

In this paper, we propose a robust music audio fingerprinting system for automatic music retrieval. The fingerprint feature is extracted from the long-term dynamic modulation spectrum (LDMS) estimation in the perceptual compressed domain. The major advantage of this feature is its significant robustness against severe background noise from the street and cars. Further the fast searching is performed by looking up hash table with 32-bit hash values. The hash value bits are quantized from the logarithmic scale modulation frequency coefficients. Experiments illustrate that the LDMS fingerprint has advantages of high scalability, robustness and small fingerprint size. Moreover, the performance is improved remarkably under the severe recording-noise conditions compared with other power spectrum-based robust fingerprints.

• Nuclear Engineering and Technology
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• v.34 no.5
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• pp.436-444
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• 2002

The robust controller for the nuclear reactor power control system is designed. Since the reactor model is not exact, it is necessary to design the robust controller that can work in the real situations of perturbations. The reactor model is described in the form of transfer function and the bound of each coefficient is determined to set up the linear interval system. By the Kharitonov and the edge theorem, a frequency based design template is made and applied to the determination of the controller. The controller designed by this method is simpler than that obtained by the H$_{\infty}$. Although the controller is designed with the basis of high power, it could be used even at low power.n at low power.

• The Journal of the Acoustical Society of Korea
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• v.38 no.6
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• pp.661-669
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• 2019

High frequency active sonar is appropriate for detecting small targets such as a diver in coast environment. In case of using high frequency active sonar in shallow coastal environment, a false alarm rate is high due to clutters caused by marine biological noise, ship noise, wake, etc. In this paper, we propose an algorithm for target detection which is robust against clutter in active sonar system in shallow coastal environment. The proposed algorithm increases the rate of reduction clutter using calculation of statistical characteristics of signal and a clustering method. The algorithm is evaluated and analysed with sea trial data, as a result, that shows the rate of reducing rate of clutter of 96 % and over.

• The Korean Journal of Applied Statistics
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• v.24 no.6
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• pp.1181-1196
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• 2011

Image fusion is the process of combining information from two or more source images of a scene into a single composite image with application to many fields, such as remote sensing, computer vision, robotics, medical imaging and defense. The most common wavelet-based fusion is discrete wavelet transform fusion in which the high frequency sub-bands and low frequency sub-bands are combined on activity measures of local windows such standard deviation and mean, respectively. However, discrete wavelet transform is not translation-invariant and it often yields block artifacts in a fused image. In this paper, we propose a robust image fusion based on the stationary wavelet transform to overcome the drawback of discrete wavelet transform. We use the activity measure of interquartile range as the robust estimator of variance in high frequency sub-bands and combine the low frequency sub-band based on the interquartile range information present in the high frequency sub-bands. We evaluate our proposed method quantitatively and qualitatively for image fusion, and compare it to some existing fusion methods. Experimental results indicate that the proposed method is more effective and can provide satisfactory fusion results.

• Journal of Powder Materials
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• v.22 no.5
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• pp.331-336
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• 2015

We report on the succesful fabrication of ZnO nanorod (NR)-based robust piezoelectric nanogenerators (PNGs) by using Cu foil substrate. The ZnO NRs are successfully grown on the Cu foil substrate by using all solution based method, a two step hydrothermal synthesis. The ZnO NRs are grown along c-axis well with an average diameter of 75~80 nm and length of $1{\sim}1.5{\mu}m$. The ZnO NRs showed abnormal photoluminescence specrta which is attributed from surface plasmon resonance assistant enhancement at specific wavelength. The PNGs on the SUS substrates show typical piezoelectric output performance which showing a frequency dependent voltage enhancement and polarity dependent charging and discharging characteristics. The output voltage range is 0.79~2.28 V with variation of input strain frequency of 1.8~3.9 Hz. The PNG on Cu foil shows reliable output performance even at the operation over 200 times without showing degradation of output voltage. The current output from the PNG is $0.7{\mu}A/cm^2$ which is a typical out-put range from the ZnO NR-based PNGs. These performance enhancement is attributed from the high flexibility, high electrical conductivity and excellent heat dissipation properties of the Cu foil as a substrate.

• The Journal of the Acoustical Society of Korea
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• v.24 no.8
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• pp.492-497
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• 2005

In this paper, we suggest that the new volume of robust audio watermarking method protects form the MP3 compression attack, mostly used in audio field. Watermarks were inserted at the coefficients repeatedly from low frequencies to high frequencies after DCT transform in commonly used Cox's spread spectrum method. However, our method could be investigated losing frequency when MP3 attacks and make order by small amount of losing frequency and then insert watermarks rightly through statistical analysis. In the result about various sound clips, the suggested method have better performances than Cox's method by preserving watermarks and reducing distortions of the original sounds.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.98-100
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• 2007

This paper proposes a robust digital controller for PWM voltage source inverter using CRA method. The usual inverter controller for the operation of constant voltage and constant frequency consists of a double looped PI controller for the outer voltage controller and the inner current controller, of which the order of characteristic polynomial is high and so the gain tuning is difficult. Considering the limited switching frequency of the devices and sampling frequency of the digital controller, the gain tuning is usually based on the engineering experiences with the try and error method. In this paper, the error-space approach is used to get the system model including the controller with low order, and the characteristic ratio assignment (CRA) method is proposed for the design of robust controller which has the advantage to design the optimal gain to meet the referenced response and overshoot within the limit range. The PSiM simulation and experience results are shown to verify the validity of the proposed controller.