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김종혁(Jong Hyeok Kim),홍예선(Yeh Sun Hong) 유공압건설기계학회 2017 드라이브·컨트롤 Vol.14 No.4
In this study, the force tracking performance of the single-rod and double-rod type EHAs (Electro-Hydrostatic Actuators) was compared by computer simulation and experiments. The force-controlled EHAs exhibit non-linear behavior that are significantly dependent on operation conditions. The investigation focused on localizing the parameters that provide significant rise to the non-linearity. For this, the single-rod and double-rod type EHAs were mathematically expressed to derive their linear models. In parallel, they were modeled by a commercial simulation program including non-linear properties based on experimental results. It was shown that the dependency of the bulk modulus of oil with entrapped air on working pressure dominated the non-linearity in force control performance in case of the double-rod type EHA. The force control of the single-rod type EHA was influenced by much more elements. Besides the asymmetrical piston geometry and the non-linear bulk modulus of oil, its pilot-operated check valves made it dependent not only on the magnitude of reference input but also on its direction.
김종혁 ( Kim Jong Hyeok ) 역사문제연구소 2007 역사문제연구 Vol.- No.18
When the country was newly opened to the world, Incheon became one of the most visible cities in Korea. The primary reason of its growth, and its becoming of the biggest port in the country, was because its location which was closer to the capital than any other harbors in the country. As a result of Incheon`s growth, the Gyeongin-ro line of the Joseon dynasty period, which connected Cheolgot-po(which was the diverging point of the Ganghwa-ro line) and the center of Incheon(the center of regional affairs to be exact), was transformed into a new road connecting Yeongdeung-po and the `country-opener` ports(`개항장`). And during the Japanese occupation period, the road was redirected to pass not Seonghyeon(which it used to go over) but the Weontongi hill, because of its potential connection to the Gyeongin railway. The Gyeongin-ro road of the Japanese occupation period featured almost exactly the same route of the 46th state road of today(which is also referred to as Gyeongin-ro). The road`s characteristic was that, unlike other trunk lines, it was a completely new route compared to the traditional paths(and intersections) that were taken in the earlier periods. To be prepared for the running of automobiles, the Gyeongin-ro was renovated as a 1st class road during the Japanese occupation period, and when horse wagons and cars started to regularly run on the road, the time that had usually been taken between Seoul and Incheon was significantly reduced, to less than half a day. Later, the roads were widened, well covered, and more straightened, and electrical measures were developed for the vehicles. These changes all contributed to the even more reducing of the time. These changes eventually resulted in the expansion of the boundaries which had defined the range of people`s ordinary and casual life. They also peaked the people`s imagination and curiosity of the unknown. It was nothing short of an opportunity for the residents in the region, to expand their perception of space and views of the world, which was also to experience the coming of modernity.
EHA의 정밀 힘제어를 위한 펌프 속도 제어기의 강인 내부루프 보상
김종혁(Jong-Hyeok Kim),홍예선(Yeh-Sun Hong) 유공압건설기계학회 2018 드라이브·컨트롤 Vol.15 No.4
Force-controlled electro-hydrostatic actuators have to exhibit high backdrivability, to quickly compensate for force control errors caused by externally disturbed rod movement. To obtain high backdrivability, the servomotor for driving the hydraulic pump, should rotate exactly to such a revolution to compensate for force control errors, compressing or decompressing cylinder chambers. In this study, we proposed a modified velocity control structure, including a robust internal-loop compensator (RIC)-based velocity controller, for the servomotor to improve backdrivability of a force-controlled EHA. Performance improvement was confirmed experimentally, wherein sinusoidal velocity disturbance was applied to the force-controlled EHA, with constant reference input. Its dynamic force control errors reduced effectively, with the proposed control scheme, compared to test results with a conventional motordriver, for motor velocity control.