• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.15-22
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• 2006

This paper presents a novel signal tracking algorithm for GNSS receivers using a MLE technique. In order to perform a robust signal tracking in severe signal environments, e.g., high dynamics for navigation vehicles or weak signals for indoor positioning, the MLE based signal tracking approach is adopted in the paper. With assuming white Gaussian additive noise, the cost function of MLE is expanded to the cost function of NLSE. Efficient and practical approach for Doppler frequency tracking by the MLE is derived based on the assumption of code-free signals, i.e., the cost function of the MLE for carrier Doppler tracking is used to derive a discriminator function to create error signals from incoming and reference signals. The use of the MLE method for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited for various GNSS signals with same structure of tracking module. This paper proposes two different types of MLE based tracking method, i.e., an iterative batch processing method and a non-iterative feed-forward processing method. The first method is derived without any limitation on time consumption, while the second method is proposed for a time limited case by using a 1st derivative of cost function, which is proportional to error signal from discriminators of conventional tracking methods. The second method can be implemented by a block diagram approach for tracking carrier phase, Doppler frequency and code phase with assuming no correlation of signal parameters. Finally, a state space form of FLL/PLL/DLL is adopted to the designed MLE based tracking algorithm for reducing noise on the estimated signal parameters.

• Transactions on Control, Automation and Systems Engineering
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• 제4권3호
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• pp.217-223
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• 2002

The paper presents a single constraint equation of the direct kinematic solution of 6-dof (Stewart-Gough) platforms. Many research works have presented a single polynomial of the direct kinematics for several 6-dof platforms. However, the formulation of the polynomial has potential problems such as complicated formulation procedures and discrimination of the actual solution from all roots. This results in heavy computational burden and time-consuming task. Thus, to overcome these problems, we use a new formulation approach, called the Tetrahedron Approach, to easily derive a single constraint equation, not a polynomial one, of the direct kinematics and use two well-known numerical iterative methods to find the solution of the single constraint equation. Their performance and characteristics are investigated through a series of simulation.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제12권3호
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• pp.191-199
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• 2008

This paper proposes a new method for the inverse problem of the three-dimensional reconstruction of the electrical activity of the brain from electroencephalography (EEG). Compared to conventional direct methods using additional parameters, the proposed approach solves the EEG inverse problem iteratively without any parameter. We describe the Lagrangian corresponding to the minimization problem and suggest the numerical inverse algorithm. The restriction of influence space and the lead field matrix reduce the computational cost in this approach. The reconstructed divergence of primary current converges to a reasonable distribution for three dimensional sphere head model.

• International Journal of Precision Engineering and Manufacturing
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• 제3권4호
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• pp.5-14
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• 2002

This paper addresses the challenges of dealing with uncertainties based on interval analysis. An interval approach is proposed on the basis of Boundary Selection Method (BSM) for treating systems of linear interval equations in the presence of columnwise dependencies. An iterative procedure is developed for the problem solving where uncertainties are characterized in the form of interval quantities. An applied example is used to illustrate effectiveness and usefulness of the proposed approach. This new method can be applied for such circumstances that involve finite element analysis of structures, inverse dynamic analysis of mechanisms, and worst case design studies in the presence of the uncertainties.

• 전기학회논문지
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• 제56권4호
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• pp.777-783
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• 2007

In this paper, we present a novel control approach for linear motor-based transfer systems in which friction reduction and enhancement of control performance are considered. In general, in such systems friction effects from rails and wheels, and internal bearings complicate control scheme since in particularly its dynamics are arbitrarily changed due to mass variation, detent force of motor systems, and gaps among stators. Our control approach is achieved to reduce this undesired friction dynamics using fuzzy system. We construct hybrid control approach for this control system which Is composed of a nominal control and a vertical control against friction. Fuzzy parameter vector is optimally determined from iterative simulation experiments. We demonstrate its superiority via numerical simulations comparing with a traditional control method.

• 한국경영과학회지
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• 제23권4호
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• pp.97-109
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• 1998

In this paper, we propose a new approach to solve stochastic fluid flow models applied to the analysis of ceil loss of an ATM multiplexer. Existing stochastic fluid flow models have been analyzed by using linear differential equations. In case of large state space, however. analyzing stochastic fluid flow model without numerical errors is not easy. To avoid this numerical errors and to analyze stochastic fluid flow model with large state space. we develope a new computational algorithm. Instead of solving differential equations directly, this approach uses iterative and numerical method without calculating eigenvalues. eigenvectors and boundary coefficients. As a result, approximate solutions and upper and lower bounds are obtained. This approach can be applied to stochastic fluid flow model having general Markov chain structure as well as to the superposition of heterogeneous ON-OFF sources it can be extended to Markov process having non-exponential sojourn times.

• Journal of Mechanical Science and Technology
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• 제15권7호
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• pp.831-838
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• 2001

Torque ripple control of brushless DC motor has long been the main issue of the servo drive systems in which the speed fluctuation, vibration and acoustic noise need to be minimized. The vast majority of the methods for suppressing the torque ripple require the Fourier series analysis and either the iterative or least mean square minimization. In this paper, a novel approach based on the d-q-0 reference frame that achieves ripple-free torque control with maximum efficiency is presented. The proposed method optimizes the reference phase current waveforms including even the case of 3-phase unbalanced condition, and the motor winding currents are controlled to track the optimized current waveforms by the delta modulation technique. As a results, the proposed approach provides a simple and yet effectine means for obtaining the optimal motor excitation currents. The validity and applicability of the proposed control scheme are verified through simulations and experimental investigations.

• 한국기계연구소 소보
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• 통권18호
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• pp.131-136
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• 1988

A small-deflected beam can be easily solved by assuming a linear system. But a large-deflected beam can not be solved by superposition of the displacements, because the system is nonlinear. The solutions for the large-deflection problems can not be obtained directly from elementary beam theory for linearized systems since the basic assumptions are no longer valid. Specifically, elementary theory neglects the square of the first derivative in the beam curvature formula and provides no correction for the shortening of the moment-arm cause by transverse deflection. These two effects must be considered to analyze the large deflection. Through the correction of deflected geometry and internal axial force, the proposed new approach is developed from the linearized beam theory. The solutions from the proposed approach are compared with exact solutions.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
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• pp.270-273
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• 2007

In this paper, a SAR-despeck1ing approach of adaptive iteration based a Bayesian model using the lognormal distribution for image intensity and a Gibbs random field (GRF) for image texture is proposed for noise removal of the images that are corrupted by multiplicative speckle noise. When the image intensity is logarithmically transformed, the speckle noise is approximately Gaussian additive noise, and it tends to a normal probability much faster than the intensity distribution. The MRF is incorporated into digital image analysis by viewing pixel types as states of molecules in a lattice-like physical system. The iterative approach based on MRF is very effective for the inner areas of regions in the observed scene, but may result in yielding false reconstruction around the boundaries due to using wrong information of adjacent regions with different characteristics. The proposed method suggests an adaptive approach using variable parameters depending on the location of reconstructed area, that is, how near to the boundary. The proximity of boundary is estimated by the statistics based on edge value, standard deviation, entropy, and the 4th moment of intensity distribution.

• 한국CDE학회논문집
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• 제8권2호
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• pp.84-89
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• 2003

Axiomatic Design Theory is one of the most useful design methodologies which uses Functional Requirements(FRs) and Design Parameters(DPs) to make human designers more creative, to reduce the random search process, to minimize the iterative trial-and-error process, and to determine the best design among those proposed. In this research, we show how to develop a CAD system for an automotive rubber machinery using the axiomatic design approach to illustrate the effectiveness of the theory and we suggest a better way to select FRs and DPs in axiomatic design approach which can help designers to select them more effectively, objectively, and easily.