• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.412-420
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• 2003

This study describes the merits of PWM control of hydraulic system using high speed on-off valves. Generally, Electro-hydraulic valves can be classified into two classification: valves which are controlled by analog signal and which are controlled by digital. The former includes hydraulic servo valves and proportional valves which require A/D converters as interface to digital computer and too costly and sensitive to oil contamination because of complexity in structures. The latter includes high speed on-off valves which do not require A/D converters because they are normally operated in a pulse width modulation(PWM) method, and are low in price and robust to oil contamination because of their simple structures. The objectives of this study is to analyze the limit cycle which regularly appear in the position control system using 2/2way high speed on-off valves and to give a criterion for the stability of this system. The nonlinear characteristics of PWM and cylinder friction of this system are described by harmonic linearization and the effects of parameter variations to the system stability are simulated.

• The Korean Journal of Zoology
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• v.39 no.2
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• pp.132-138
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• 1996

To learn how maximal locomotory speed of animals is defined in terms of hindlimb structure and muscle contractile function, take-off speed, hindlimb length, thigh muscle mass, shortening velocity and power of the sastrocnemius muscle were measured with one fast species, Rono nigromaculota and one relatively slowresponding species, Bombina orientalis. Take-off speed (m.sec-1) was greater in R. nigromoculata $(2.4\pm0.2SD, $ n: 14) than in the Bombino $(1.6\pm0.1SD, $ n=8). Stvle of the take-off response was a long-iump type in the Rano and a short-ranged hopping in the Bombing. Faster take-off capacity of the ranid frogs was supported by the longer hindlimb length (relative to body length) and the more massive thigh muscles (relative to body mass), compared to the Bombina. Further, the ranids exhibited faster maximal shortening velocity and Breater maximal power generateion than the Bombina [Vmax $(ML.sec-1)=11.79\pm1.69SD$ for the Runa and $9.74\pm1.27SD$ for the Bombina; Pmax $nW.kg-1)=222.42\pm42.42SD$ for the Rono and $169.03\pm34.52SD$ for the Bombinal. With more massive thigh muscles and greater mechanical power, the ranids would generate greater total power and thus higher energy release per unit time to muscle tissues for the burst take-off. As a consequence, biomechanical properties seen in the ranids seem to be more effective for frost take-off than in the Bombina.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1469-1478
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• 1995

PWM control is a kind of nonlinear control. The merits of PWM control of hydraulic equipment are the robustness of the high speed on-off valve and its low price. And it is easily implemented to hydraulic equipments with microcomputer. The high speed on-off valve is directly digitally controlled without any D/A converter. The objectives of this study is to analyze the limit cycle which regularly appear in the position control system using high speed on-off valve, and to give a criterion for the stability of this system. To do this, the nonlinear characteristics of PWM and cylinder friction of this system are described by harmonic linearization and the effects of parameter variations to the system stability are examined theoretically and experimentally. Consequently, the availability of the proposed method is confirmed well.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.369-378
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• 1999

This paper presents position control of an electro-hydraulic servo system whoch is operated by four 2-2way high speed on-off valves with either PWM PID control method or sliding mode control method, The advantages of using high speed on-off valves instead of electo-hydraulic servo valves or electro-hydraulic proportional valves are low price robustness for oil contamination and direct control without a D/A converter. The system consists of load cylinder inertia car potentiometer and external load cylinder. The experiments were carried out under several conditions and the results were compared. As a result the sliding mode method has shown good control performance and the robust and stable positioning of the elector-hydraulic servo system can be achieved accurately.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.2
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• pp.236-243
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• 1999

This study deals with the application of high speed on-off valves to an electro-hydraulic servo indexing system incorporated electro-hydraulic servo valces. Comparing with the electro-hydraulic servo valve the high speed on-off valve has some merits. Which included low price robustness to the oil contamination and dircect control without D/A converter. The considered sys-tem of this study is controlled by pulse width modulation(PWM) of the control law which is pro-duced by a PID controller which is used broadly in industrial equipments. The dynamic character-istics corresponding to variations of system parameters such as inertia moment system gain and supply pressure are investigated by computer simulation and experiment. Consequently the availability of the application of high speed on-off valve to servo indexing system instead of electro-hydraulic servo valve is confirmed.

• The Transactions of the Korea Information Processing Society
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• v.7 no.2
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• pp.437-445
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• 2000

The reuse partitioning system in microcellular networks are dropped performance of system because of increase hand-off of high-speed terminal. In this paper, we propose hand-off algorithm to improve the performance of reuse partitioning system using microcell according to the ratio of traffic distribution between innercell and outercell from resource management of high-speed and slowspeed terminal. Also, we compare to RPS and evaluate the teletraffic performance analysis of high-speed and slow-speed terminal through computer simulations that we derive the hand-off probability, call dropping probability.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.79-86
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• 1995

Frequency response method is used to design hydraulic servo systems and improve its performance. In this study a method is proposed to get simply the frequency response of the electro-hydraulic servo system which use PWM controlled high-speed on-off valves. Firstly, the describing function of the PWM element is derived and tested. It is found that the character- istic of PWM element could be approximated to a saturation characteristic in the range of allowable frequency. And the dynamic characteristic of the valve-cylinder system could be negligible. The working characteristic of high-speed on-off valve is considered as time delay. So simulation is performed in the basis of the reconstructed block diagram. And this method is verified by experiments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2043-2048
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• 2011

High speed drive method for a fuel injector cleaner with current control is presented in this paper. The fuel injector cleaner is used for cleaning the fuel injectors in vehicles when it is clogged with deposit and rust. The fuel injector cleaner cleans the fuel injector by turning on and off the fuel injector rapidly. When the fuel injectors are cleaned, the switching speed is very important. However, when the fuel injector is turned off, the residual current in the fuel injector coil slows down the return action of the plunger in the fuel injector deteriorating performance and speed of the fuel injector cleaner. In this paper, fast turn off operation method of fuel injectors is developed for more effective cleaning. The simulation and experiment results show the validity of the proposed method.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.219-222
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• 2007

The Full-Off Fitting of Movable Bracket using conventional line have received a dynamic contact impact between contact wire and pantograph of electric rolling stock, so this impact cause a rapid vibration of foreword and back near the supporting point of movable bracket. The Full-Off Fitting on Movable Bracket in conventional line differs from that in high speed line. Now conventional line have required a speed up for new electric locomotive and electric car. In speed-up track and big impact place, the Full-Off Fitting and the dropper often get demage. We have done a study of buffering function to solve that problem in conventional line. We have find a need adopting buffer fitting. It is decrease a dynamic impact between contact wire and pantograph of electric rolling stock.

• Proceedings of the KIEE Conference
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• 1996.11a
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• pp.84-87
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• 1996

This paper presents a energy function to reflect the control effect of speed governor which has a cut-off property which means position and rate limit The proposed energy function satisfies the semi-negativeness of its time derivative and well reflects the parameters of speed governor to the energy function. The transient stability analysis by the direct method for the single machine infinite bus system has been conducted with the use of the proposed energy function, which shows that the results by the direct method well agree with that by the conventional time simulation method. This thesis shows a possibility of more accurate stability analysis by taking into account the cut-off property of speed governor's output.