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      • KCI등재

        이동로봇의 분산점 칼만 필터 기반 옥외용 위치평가

        이우석,임종환 한국정밀공학회 2019 한국정밀공학회지 Vol.36 No.2

        This paper proposes a practical method, for evaluating positioning of outdoor mobile robots using Unscented Kalman Filter (UKF). Since the UKF method does not require the linearization process unlike EKF localization, it can minimize effects of errors caused by linearization of non-linear models for position estimation. This method enables relatively high performance position estimation, using only non-inertial sensors such as low-precision GPS and a digital compass. Effectiveness of the UKF localization method was verified through actual experiments and performance of position estimation was compared with that of the existing EKF method. Experimental results revealed the proposed method has better performance than the EKF method, and it is stable regardless of initial error size, and observation period.

      • KCI등재후보

        Enhance Charge Cycle Efficiency of Lead-acid Battery using Solar Power System

        이우석,박한밀,신은수 적정기술학회 2018 적정기술학회지(Journal of Appropriate Technology) Vol.4 No.2

        In developing countries, many areas are not supplied with electricity due to lack of electric power infrastructure, and many others are suffering from unstable power quality and frequent power outages. As an alternative, power supply using renewable energy, such as solar, wind, and small hydro power, is being activated. Among these, the most widely used source is photovoltaic power generation system, which is easy to install and maintain. In developed countries where power supply is smooth, grid connected photovoltaic systems that use conventional electricity together are generally used for the purpose of reducing electricity bill. However, in developing countries, because conventional electricity supply is unstable, independent solar power generation systems using batteries are mainly used. Among these, a solar panel is a semi-permanent product that can be used for more than 20 years, whereas a typical battery is a consumable with a maximum life span of less than five years, accounting for most maintenance cost of solar power systems. In addition, in the case of a lead storage cell, which is readily available in developing countries and therefore is most widely used, lifespan has been drastically reduced depending on environmental conditions such as pre-charge method, temperature, and humidity, which frequently makes it replaced in six months. For these reasons, management methods to extend lifespan of lead storage cell have become an important research topic. In this study, a voltage level was set as a measure value to identify and manage the characteristics of charging and discharging of lead storage batteries, and standardized discharge curves were created using LED lamps that consume the most stable power. Based on this, the discharging characteristics for different kinds of DC and AC products were identified. Also, the proper isolation voltage level to extend the battery lifespan was verified. The study will be used to design an optimized solar power system along with the further study on charging efficiency of solar power systems in developing countries.

      • KCI등재

        정형외과 영역에서 로봇수술

        이우석,정우석 대한정형외과학회 2018 대한정형외과학회지 Vol.53 No.6

        Of the many factors that affect the clinical outcomes of orthopedic surgery, the surgical procedure is the most important. Robotics have been developed to perform the surgical procedures more accurately and consistently. Robotic surgical procedures in the orthopedic field were developed 20 years ago. Some designs of surgical robots have disappeared due to practical problems and complications, and an another design of surgical robots is emerging. To date, the use of robot surgery in arthroplasty is still controversial in terms of the clinical outcomes, practicality, and cost-effectiveness, even though it has been reported to be effective in the alignment and positioning of components in the field of artificial joints. Early robotic surgery was based mainly on active robot surgery according to the scheduled operation without the intervention of the operator. Recently the semi-active system of robotic surgery has been introduced. In a semi-active system, the robot constrains the surgeon to a haptic boundary defined by the computer based on the 3-dimensional imaging preoperative plan, and the operator can change the preoperative plan through real-time feedback during operation. 정형외과 수술의 임상적 결과에 영향을 미치는 요소는 여러 가지가 있지만 수술적 수기가 가장 중요한 요인이며 로봇공학은 술기를 보다 정확하고 일관되게 수행하기 위해 도입되었다. 정형외과 영역에서는 20년 전부터 로봇수술을 사용하였으나 실용성 문제와 합병증의 발생으로 일부 로봇은 도태되었으며 단점을 개선한 로봇이 소개되고 있다. 대부분의 로봇수술은 인공관절수술 분야에서 시행되었고 치환물의 정렬과 위치 선정에서 우수한 것으로 보고되고 있다. 그러나 임상적 결과의 우수성, 실용성, 가성비 등의 측면에서 제한점이 있고 일부 로봇수술에서는 합병증 발생 빈도가 높다는 보고가 있었다. 초기 로봇수술은 수술자의 개입 없이 계획된 수술이 진행되는 능동형 로봇수술이 주를 이루었으나 최근에는 수술과정에서 실시간 피드백을 통해 술자가 술 전 계획을 변경할 수 있고, 햅틱경계 내에서 제한된 골절제를 함으로써 주요 혈관, 신경, 인대 등의 손상을 최소화할 수 있는 반능동형 로봇수술이 소개되고 있다.

      • KCI등재

        대역폭 계층 구조의 광대역 음성 부호차기 개발

        이우석,손창용,이영범,박호종 한국음향학회 2004 韓國音響學會誌 Vol.23 No.6

        본 논문에서는 대역폭 계층 구조의 광대역 음성 부호화기 구조와 이를 위한 상위 대역 부호화기를 제안한다. 상위 대역 부호화기는 상위 대역 신호를 다수의 주파수 밴드로 분할하고, 각 밴드 신호를 DCT 변환하여 양자화한다. DCT 계수는 크기와 부호로 분리하여 독립적으로 처리하며, 각각의 특성에 적합한 양자화 방법을 개발하여 성능을 향상시킨다. 또한, 하위 대역의 부호화된 이득 파라미터를 상위 대역의 양자화에 이용함으로써 부호화 성능을 향상시키는 방법을 제안한다. G.729E로 하위 대역을 부호화하고 제안한 부호화기로 상위 대역을 처리하는 대역폭 계층 구조의 광대역 음성 부호화기를 개발하였고, 주관적 음질을 측정하여 24kbps G.722.1보다 우수한 음질을 가지는 것을 확인하였다. In this paper. the structure of bandwidth scalable wideband speech codec and its high-band codec are proposed. In the high-band codec. the signal is divided into frequency bands. and each band is quantized in DCT domain. The DCT coefficients are splitted into magnitude and sign, and each is quantized independently by a specialized method based on its characteristics. In addition. the quantized gain parameter in the low-band codec is utilized in the high-band codec for an enhanced performance. The bandwidth scalable wideband speech codec using G.729E for low-band and the proposed codec for high-band is developed, and it is confirmed that the proposed codec has better subjective performance than 24kbps G.722.1.

      • KCI등재

        회전자 여자제어를 이용한 풍력발전 DFIG의 출력제어

        이우석,오철수 한국조명전기설비학회 1999 조명·전기설비학회논문지 Vol.13 No.3

        풍력발전은 넓은 범위의 속도제어를 요구하며, 권선형 유도발전기를 이용한 DFIG시스템을 이러한목적에 잘 부합한다. 동기속도 이상의 영역에서 풍속에 의한 원동기 속도와 증가에 불구하고 회전자 여자 주파수를 슬립주파수와 다르게 인가하여 DFIG의 속도와 출력 제얼르 다루고 있다. 속도제어와 동작점 이동의 해석을 위하여 토크시뮬레이션을 하였고, 회전자 여자주파수와 전압제어에 의해 출력이 정격값 이하의 안정된 영역에서 제어될 수 있음을 고찰하였다. Wide operating range and speed control is needed for wind power generating and a Doubly Fed Induction Generator(DFlG) has good adaptivity for that purpose. Ths paper investigates speed and output stator power control using a grid connected to a DFlG in super-synchronous speed regions, by control of both magnitude and frequency of the voltage fed to the rotor. For the speed control analysis, torque simulation is perforrred whereby the different slip between qJernting rmtor driving frequency and synchronous frequency of M-G system awlied. To keep the output rating of the generator, the exciting frequency and voltage attenuation are arolied.rolied.

      • KCI등재

        LCS 인공 슬관절을 이용한 슬관절 전치환술

        이우석,한승환,배임돈,한창동,임대의 대한슬관절학회 2001 대한슬관절학회지 Vol.13 No.1

        Purpose: We evaluated the efficiency of low contact stress(LCS) system in total knee arthroplasty by analyzing clinical and radiological results. Materials and Methods: Out of 128 cases who underwent total knee arthroplasty with meniscal bearing type LCS system, eighty one cases who were followed up for more than two years were analysed. Average follow-up period was 32.6 months(24 months-48 months). The diagnoses were six cases of degenerative arthritis, eighteen cases of rheumatoid arthritis, and two cases of avascular necrosis. Clinical analysis were performed by American Knee Society Knee Score and Hospital for Special Surgery(HSS) knee score and radiographic analysis were performed by the Knee Society Roentgenographic Evaluation and Scoring System. Results: Average preoperative flexion contracture was improved from 13.4 degrees preoperatively to 1.2 degrees at final follow-up and average arc of motion was changed from 107 degrees preopeatively to 108 degrees at final follow-up without significant improvement. American Knee Society Knee Score was improved from average 55.2 preoperatively to 88.5 at final follow-up. HSS knee score also showed improvement from average 58.2 to 86.5. Tibio-femoral angle was improved from 6.3 degrees of varus preoperatively to 5.1 degrees of valgus at final follow-up. Radiolucent lines was seen most commonly at zone 1 in anteroposterior radiograph of tibia and in zone 1 in lateral radiograph of femur. Complications such as superficial wound infection, stiffness, and meniscal bearing fracture were seen in four cases. Conclusion: Total knee arthroplasty using LCS system showed satisfactory improvement in flexion contracture, deformity correction. Clinical and radiographic result.

      • KCI등재

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