• Journal of Institute of Control, Robotics and Systems
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• v.9 no.2
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• pp.159-167
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• 2003

This study suggests the hybrid fault diagnosis method of signed digraph (SDG) and partial least squares (PLS). SDG offers a simple and graphical representation for the causal relationships between process variables. The proposed method is based on SDG to utilize the advantage that the model building needs less information than other methods and can be performed automatically. PLS model is built on local cause-effect relationships of each variable in SDG. In addition to the current values of cause variables, the past values of cause and effect variables are inputted to PLS model to represent the Process armies. The measured value and predicted one by dynamic PLS are compared to diagnose the fault. The diagnosis example of CSTR shows the proposed method improves diagnosis resolution and facilitates diagnosis of masked multiple-fault.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.454-457
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• 1995

In optical disc system, tracking actuator is consisted of coarse actuator and fine tracking actuator. This, two-stage actuator, requires many devices and two servos for large stroke and precisional displacement. These complicate configuration increases moving mass. So dynamic characteristics become bad, that is, sensitivity of high frequency gain decrease. In this paper, frequency performance is willing to be better as so one dimensional tracking actuator is designed. In order to investigate the performance of the proposed tracking actuator, the Bode diagram is plotted with Dynamic analyzer and friction characteristic is explained. Finally, tracking error performance is ins investigated into 0.1 .mu.m resolution with MATLAB simulation.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.4
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• pp.72-78
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• 2004

In this paper, a development of an inductive position sensor is described. The sensor is similar to a radial magnetic bearing in that the sensor stator is shaped like a heteropolar magnetic bearing and is driven by a switching amplifier. A demodulation filter extracts the gap information from the switching current ripples. A prototype sensor exhibits the resolution of $0.43\mum$ and the dynamic bandwidth of about 800Hz. The dynamic performance can be improved by increasing the switching frequency. However, the eddy current effects become noticeable at high switching frequency, thus limiting the improvement of the bandwidth.

• Wind and Structures
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• v.5 no.2_3_4
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• pp.369-378
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• 2002

The application of Large Eddy Simulation (LES) in a curvilinear coordinate system to the flow around a square cylinder is presented. In order to obtain sufficient resolution near the side of the cylinder, we use an O-type grid. Even with a curvilinear coordinate system, it is difficult to avoid the numerical oscillation arising in high-Reynolds-number flows past a bluff body, without using an extremely fine grid used. An upwind scheme has the effect of removing the numerical oscillations, but, it is accompanied by numerical dissipation that is a kind of an additional sub-grid scale effect. Firstly, we investigate the effect of numerical dissipation on the computational results in a case where turbulent dissipation is removed in order to clarify the differences between the effect of numerical dissipation. Next, the applicability and the limitations of the present method, which combine the dynamic SGS model with acceptable numerical dissipation, are discussed.

• Journal of Communications and Networks
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• v.8 no.4
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• pp.432-441
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• 2006

As the community antenna television (CATV) networks becomes ubiquitous, instead of constructing an entirely new broadband network infrastructure, it has emerged as one of the rapid and economic technologies to interconnecting heterogeneous network to provide broadband access to subscribers. How to support ubiquitous real-time multimedia applications, especially in a heavy traffic environment, becomes a critical issue in modern CATV networks. In this paper, we propose a time guaranteed and efficient upstream minislots allocation algorithm for supporting quality-of-service (QoS) traffic over data over cable service interface specification (DOCSIS) CATV networks to fulfill the needs of realtime interactive services, such as video telephony, video on demand (VOD), distance learning, and so on. The proposed adaptive fast expansion algorithm and the loading statistics with dynamic swapping algorithm have been shown to perform better than that of the multimedia cable network system (MCNS) DOCSIS.

• Proceedings of the IEEK Conference
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• 2002.06b
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• pp.133-136
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• 2002

This paper discusses the design of a sample-and -hold amplifier(SHA) that has a 12-bit resolution with a 100 MS/s speed. The sample-and-hold amplifier uses the open-loop architecture with hold-mode feedthrough cancellation for high accuracy and high sampling speed. The designed SHA is composed of input buffer, sampling switch, and output buffer with additional amplifier for offset cancellation Hard Ware. The input buffer is implemented with folded-cascode type operational transconductance Amplifier(OTA), and sampling switch is implemented with switched source follower(SSF). A spurious free dynamic range (SFDR) of this circuit is 72.6 dB al 100 MS/s. Input signal dynamic range is 1 Vpp differential. Power consumption is 65 ㎽.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1166-1174
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• 2000

In this paper, we introduce a positioner based on magnetic levitation to eliminate the friction which is the most severe effect to limit high resolution on the micro level. Differently from existing electromagnetic device, the proposed positioner consists of air core solenoid and permanent magnet. Although the combination produces small magnetic force, it is suitable for realizing micro motion repeatedly without the accumulation of error because there is no hysteresis caused by ferromagnetic materials, no eddy current loss, no flux saturation. First, the approximate modeling of stiffness and damping effects between the magnetic elements is made and verified experimentally. Then, we have formulated the dynamic equation of one d.o.f magnetic levitation positioner using linear perturbation method and discussed the necessity of optimization for the chief design parameters to maximize the stability performance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.189-193
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• 2001

The performance of printer can be determined by the printing speed, noise level, printing quality which includes the resolution, regularity of printed matter and etc. Among them, printing quality mostly depends on the irregularity of the line spacing and dot size. The irregular line spacing and dot size in laser beam printer are mainly from the jitter which comes from the vibration of Organic Photo Conductive(OPC) drum and the Laser Scanning Unit(LSU). Jitter due to the vibration of LSU appears as high-frequency component which occurs 100-300$\mu\textrm{m}$ interval in printed matter and the causes of it can be estimated as the vibration of polygon motor, case, reflecting mirror and etc. In this paper, vibration characteristics of the LSU under development are investigated and the strategy for improvement of the dynamic characteristics is established and its validity is demonstrated.

• Journal of Ship and Ocean Technology
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• v.8 no.2
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• pp.20-28
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• 2004

A dynamic-thermodynamic sea ice model with 50-km spatial and 24-hour temporal resolution is used to investigate the spatial and long-term temporal variability of the sea ice cover the Arctic Basin. The model satisfactorily reproduces the averaged main characteristics of the sea ice and the sea ice extent in the Arctic Basin and its decrease in early 1990th. At times model allows to suppose partial recovery of sea ice cover in the last years of twenty century. The employment of explicit form for description of ridging gives opportunity to assume that the observed thinning is the result of reduction the intensity of ridging processes and to estimate long-term variability of probability the ridge free navigation in the different parts of the Arctic Ocean including the North Sea Route area.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.83-86
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• 2004

Carbon nanotube (CNT) tips in tapping mode atomic force microscopy (AFM) enable very high-resolution imaging, measurements, and manipulation at the nanoscale. We present recent results based on experimental analysis that yield new insights into the dynamics of CNT probe tips in tapping mode AFM. Experimental measurements are presented of the frequency response and dynamic amplitude-distance data of a high-aspect-ratio multi-walled (MW) CNT tip to demonstrate the non-linear features including tip amplitude saturation preceding the dynamic buckling of the MWCNT. Surface scanning is performed using a MWCNT tip on a SiO$_2$ grating to verify the imaging instabilities associated with MWCNT buckling when used with normal control schemes in the tapping mode. Lastly, the choice of optimal setpoints for tapping mode control using CNT probe tip are discussed using the experimental results.