• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.470-473
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• 1996

This paper presents an iterative learning control scheme for industrial manipulators. Based upon the frequency-domain analysis, the input update law of the learning controller is given together with a sufficient condition for the convergence of the iterative process in the frequency domain. The proposed learning control scheme is structurally simple and computationally efficient since it is independent joint control depending only on locally measured variables and it does not involve the computation of complicated nonlinear manipulator dynamics. Moreover, it is capable of canceling the unmodeled dynamics of the manipulator without even the parametric model. Several important aspects of the learning scheme inherent in the frequency-domain design are discussed and the control performance is demonstrated through computer simulations.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.138-141
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• 2001

In this paper, a VBF(variable bandwidth filter) is suggested and analyzed in time-frequency domain. There are four kinds of VBF, which are low-pass VBF, high-pass VBF, band-pass VBF and band-stop VBF. The proposed VBF can extract the components of signals within variable instantaneous bandwidth at a specific time instant. Instantaneous bandwidth is estimated in time-frequency domain. The VBF is represented by rational form in extended Fourier frequency domain.

• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.336-338
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• 2006

One of the important topics concerning the safety of electrical and electronic system is the reliability of the wiring system. The Time-Frequency Domain Reflectometry(TFDR) is a state-of-the-art system for detection and estimation of the fault on a wiring/cable. The purpose of this paper is to implement a Labview based TFDR Real Time system though the instruments of PCI extensions for Instrumentation(PXI). The TFDR Real Time system consists of the five parts: Reference signal design, signal generation, signal acquisition, algorithm execution, results diplay part. In the signal generation and acquisition parts we adopt the Arbitrary Waveform Generator(AWG) and Digital Storage Oscilloscope(DSO) PXI modules which offer commonality, compatibility and easy integration at low cost. And execution of the PXI modules not only is controlled by the Labview programing but also the total system process is executed by the Labview application software.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.4 s.97
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• pp.155-162
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• 1999

Input shaping technique has been used as a simple method of controlling the residual vibration of a flexible manipulator. With the conventional methods previously proposed by several authors, the frequency range that shows a good performance is restricted. When the designed frequency being different from the natural frequency of a system, the performance of control degrades remarkably. This paper introduced a new technique that designs input shaping with robustness in the z-domain.

• Earthquakes and Structures
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• v.15 no.3
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• pp.263-273
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• 2018

Operational modal analysis is being widely used in aerospace, mechanical and civil engineering. Common research fields include optimal design and rehabilitation under dynamic loads, structural health monitoring, modification and control of dynamic response and analytical model updating. In many practical cases, influence of noise contamination in the recorded data makes it difficult to identify the modal parameters accurately. In this paper, an improved frequency domain method called Enhanced Least Square Complex Frequency (eLSCF) is developed to extract modal parameters from noisy recorded data. The proposed method makes the use of pre-defined approximate mode shape vectors to refine the cross-power spectral density matrix and extract fundamental frequency for the mode of interest. The efficiency of the proposed method is illustrated using an example five story shear frame loaded by random excitation and different noise signals.

• Journal of Institute of Control, Robotics and Systems
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• v.5 no.8
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• pp.883-888
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• 1999

To obtain high positioning auccuracy for a long, flex bleman Ipulator, residual vibration must be removed from the tip motion. But it is difficult to control the vibration of low frequency. There are open-loop and closed loop methods in the elimination of the residual vibration. We inroduce input shaping technique has been used as a simple open-loop method of controlling the residual vibration of a flexible manipulator. Design of input shaper in the continuous time domain is complicated. This paper presents a new technique that designs input shaper in the z-domain and analyzes input shaping method in the z-domain. This technique is simple and easy to design input shaper.

• Steel and Composite Structures
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• v.28 no.4
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• pp.509-516
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• 2018

The differential quadrature (DQ) and teaching-learning based optimization (TLBO) methods are coupled to introduce a hybrid numerical method for maximizing fundamental natural frequency of laminated composite skew plates. The fiber(s) orientations are selected as design variable(s). The first-order shear deformation theory (FSDT) is used to obtain the governing equations of the plate. The equations of motion and the related boundary conditions are discretized in space domain by employing the DQ method. The discretized equations are transferred from the time domain into the frequency domain to obtain the fundamental natural frequency. Then, the DQ solution is coupled with the TLBO method to find the maximum frequency of the plate and its related optimum stacking sequences of the laminate. Convergence and applicability of the proposed method are shown and the optimum fundamental frequency parameter of the plates with different skew angle, boundary conditions, number of layers and aspect ratio are obtained. The obtained results can be used as a benchmark for further studies.

• Journal of Communications and Networks
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• v.15 no.5
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• pp.496-503
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• 2013

In an orthogonal frequency division multiplexing system, conventional interpolation techniques cannot correctly balance performance and overhead when estimating dynamic long-delay channels in single frequency networks (SFNs). In this study, classical filter analysis and design methods are employed to derive a complex interpolator for maximizing the resistible echo delay in a channel estimator on the basis of the correlation between frequency domain interpolating and time domain windowing. The coefficient computation of the complex interpolator requires a key parameter, i.e., channel length, which is obtained in the frequency domain with a tentative estimation scheme having low implementation complexity. The proposed complex adaptive interpolator is verified in a simulated digital video broadcasting for terrestrial/handheld receiver. The simulation results indicate that the designed channel estimator can not only handle SFN echoes with more than $200{\mu}s$ delay but also achieve a bit-error rate performance close to the optimum minimum mean square error method, which significantly outperforms conventional channel estimation methods, while preserving a low implementation cost in a short-delay channel.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.227-234
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• 2007

This paper describes a transmission method based on a single carrier with frequency domain equalization (SC-FDE) scheme with cyclic prefix(CP). The SC-FDE has similar features with orthogonal frequency division multiplexing(OFDM). Similar to OFDM, a SC-FDE system is computationally efficient since equalization is reformed on a block of data in the frequency domain. Especially, it has the advantage of low sensitivity to nonlinear distortion compared to OFDM. In this paper, we design a SC-FDE receiver using decision-directed method, and present simulation results.

• Structural Engineering and Mechanics
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• v.22 no.2
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• pp.185-195
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• 2006

Nowadays it is very necessary to generate artificial accelerograms because of lack of adequate earthquake records and vast usage of time-history dynamic analysis to calculate responses of structures. According to the lack of natural records, the best choice is to use proper artificial earthquake records for the specified design zone. These records should be generated in a way that would contain seismic properties of a vast area and therefore could be applied as design records. The main objective of this paper is to present a new method based on wavelet theory to generate more artificial earthquake records, which are compatible with target spectrum. Wavelets are able to decompose time series to several levels that each level covers a specific range of frequencies. If an accelerogram is transformed by Fourier transform to frequency domain, then wavelets are considered as a transform in time-scale domain which frequency has been changed to scale in the recent domain. Since wavelet theory separates each signal, it is able to generate so many artificial records having the same target spectrum.