• Journal of Advanced Marine Engineering and Technology
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• v.23 no.1
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• pp.69-78
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• 1999

In this study a new pattern of pressure control of hydraulic cylinder using high speed On-Off solenoid valve in the electro-hydraulic system has been suggested. The control valve is 3-way high speed On-Off solenoid valve which is operated by PWM(Pulse Width Modulation)control signal. The high speed On-Off solenoid valve has a tendency to induce severe pressure fluctuation in the hydraulic actuator so it has not been used for the purpose of closed loop control with direct pres-sure feedback. In this study closed loop control with direct pressure feedback is enabled by using a digital filter which has linear minimum mean square filter algorithm. Through some experiments it is confirmed that stable pressure control can be realized by the proposed control technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10A
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• pp.980-986
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• 2008

Spatial multiuser access is investigated for the reverse link of multiuser multiple-input multiple-output (MIMO) systems. In particular, we consider two alternative a aches to spatial multiuser access that adopt the same detection algorithm at the base station: one is a closed-loop approach based on singular value decomposition (SVD) of the channel matrix, whereas the other is an open-loop approach based in space-time block coding (STBC). We develop multiuser detection algorithms for these two spatial multiuser access schemes based on the minimum mean square error (MMSE) criterion. Then, we compare the bit error rate (BER) performance of the two schemes and a single-user MIMO scheme. Interestingly, it is found that the STBC approach can provide much better BER performance than the SVD approach as well as than a single-user MIMO scheme.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.3
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• pp.26-30
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• 2001

Controller refinement scheme to improve the performance of a conventional system automatically in frequency domain is proposed. The controller automatic tuning method features using experimental frequency responses of the conventional closed-loop system, the conventional controller, and the improved closed-loop system, instead of poorly modeled plant due to non-linearities and disturbances. The improved closed-loop system characteristics is automatically acquired by the con-ventional closed-loop system characteristics and the proposed performance index in system bandwidth. And the proper controller is realized by least squares approximation in frequency domain. To testify the usefulness of the approach, the path tracking control of robot arm is performed. Experimental results and analytic results are well-matched.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.480-483
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• 1995

Identification of a process in closed-loop control system is an important problem in practice. This paper deals with parameter estimation using input-output data of the process operating in a closed-loop system. It is necessary to determine orders and delay-time to get consistent estimators by least square method for input-output data collected from the process. The authors considered a problem to determine delay-time in the condition that orders were known, in last KACC. So we extend the range to determine orders and delay-time in this paper.

• Current Optics and Photonics
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• v.8 no.2
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• pp.183-191
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• 2024

High-resolution retinal imaging based on adaptive optics (AO) is important for early diagnosis related to retinal diseases. However, in practical applications, closed-loop AO correction takes a relatively long time, and traditional open-loop correction methods have low accuracy in correction, leading to unsatisfactory imaging results. In this paper, a SH-U-net-based open-loop AO wavefront correction method is presented for a retinal AO imaging system. The SH-U-net builds a mathematical model of the entire AO system through data training, and the Root mean square (RMS) of the distorted wavefront is 0.08λ after correction in the simulation. Furthermore, it has been validated in experiments. The method improves the accuracy of wavefront correction and shortens the correction time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.10
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• pp.863-871
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• 2017

LMS (least mean square) algorithm widely used in the AVCS (active vibration control system) of helicopters calculates control input using the forward path transfer function and error signal. If the error signal is sinusoidal, it can be represented as the combination of cosine and sine functions with frequency and phase synchronized with the reference signal. The control input also has the same frequency, therefore control algorithm can be simply implemented if the cosine and the sine amplitudes of the control input are calculated and the frequency and phase of the reference signal are used. Calculation of the control input is implemented as simple matrix operation and the change of the control command is slower than the frequency of the error signal, consequently control algorithm can be operated at lower frequency. The signal processing algorithm extracting cosine and sine components of the error signals are modeled using Simulink and PIL (processor-in-the-loop) mode simulation was executed for real-time performance evaluation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.55-56
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• 2017

In this paper, a wideband loop antenna is designed using a CPW feeding method for indoor digital TV applications. The proposed loop antenna consists of a square loop and two circular sectors which connect the loop with central feed points, and the CPW feed line is inserted in the lower circular sector. The CPW feed line is designed to match with the 75 ohm port impedance for DTV applications, and the ground slots are etched in order to improve the impedance matching in the middle frequency region. The optimized antenna is fabricated on FR4 substrate, and the experiment results show that it operates in the frequency band of 463-1,280 MHz for a VSWR < 2, which assures the operation in the DTV band.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.164-167
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• 1996

This paper presents an off-line P.I.D parameter estimation method during normal operation in power plant. The process parameters are estimated using the recursive least square method. The controller parameters are estimated on the basis of desired characteristics of the dynamic model of the closed-loop control.

• The Journal of the Acoustical Society of Korea
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• v.14 no.3
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• pp.28-36
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• 1995

In this paper, a double loop control model using leaky delay LMS algorithm are proposed for active noise control. The proposed double loop control model estimates the loudspeaker characteristic and the error path transfer function with on-line using only gain and acoustic time delay to reduce computation burden. The control of error signal through double loop control scheme makes the more robust cntrol system. The input signal of filter to estimate acoustic time delay is used difference between input signal of input microphone and adaptive filter output. And also, in nonstationary environments, the leaky delay LMS algorithm is employed to counteract parameter drift of delay LMS algorithm. For practical noise signal, the proposed double loop control model reduces noise level about 12.9 dB.

• Journal of Navigation and Port Research
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• v.32 no.6
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• pp.481-487
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• 2008

Ship's wireless LAN was in the limelight as equipment of ease, cost reduction, various func tion al i ty. In the paper, a dual-bandpass filter for wireless LAN has proposed, which was designed by using dual-mode square loop resonator with square patch in compliance with 2.4 GHz and 5 GHz band of wireless LAN. The dual-bandpass filter could be designed by adjusting sizes of one perturbation element and three of reference elements in compliance with the frequency bands of 2.4 GHz and 5.8 GHz, Furthermore, new dual-bandpass filter was also designed by adjusting stopband of using open stubs in compliance with the frequency bands of 2.4 GHz and 5.2 GHz. The measured results for the fabricated dual-bandpass filters agreed well with the simulated ones, and hence, it was confirmed that the proposed design method is valid.