• Journal of Astronomy and Space Sciences
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• 제25권4호
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• pp.361-374
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• 2008

Recently, satellite formation flying has been a topic of significant research interest in aerospace society because it provides potential benefits compared to a large spacecraft. Some techniques have been proposed to design optimal formation trajectories minimizing fuel consumption in the process of formation configuration or reconfiguration. In this study, a method is introduced to build fuel-optimal trajectories minimizing a cost function that combines the total fuel consumption of all satellites and assignment of fuel consumption rate for each satellite. This approach is based on collocation and nonlinear programming to solve constraints for collision avoidance and the final configuration. New constraints of nonlinear equality or inequality are derived for final configuration, and nonlinear inequality constraints are established for collision avoidance. The final configuration constraints are that three or more satellites should form a projected circular orbit and make an equilateral polygon in the horizontal plane. Example scenarios, including these constraints and the cost function, are simulated by the method to generate optimal trajectories for the formation configuration and reconfiguration of multiple satellites.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.321-324
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• 2003

There are two steps to solve the self-collision avoidance problems for redundant manipulators. First, all links are regarded as cylinders. and then the collisions should be checked among all pairs of the links. Between two cylinders. we can get the collision information derived from the concept or configuration space obstacle in real time. Therefore. it is possible to detect the links where collisions are likely in real time by setting the risk radius which is larger than actual radius. Second. the configuration control points (CCP) should be placed at the ends of the detected links. A cost function is the sum of the distances between the CCPs. To maximize the cost function means the links go far away each other without self-collisions.

• 한국전자통신학회논문지
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• 제15권5호
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• pp.791-798
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• 2020

근래의 무기체계에서 첨단기술이 차지하는 비중은 점차 커지고 있으며, 빠른 기술발전 속도로 인하여 부품의 수명주기가 단축되고 실정이다. 이에 반하여 무기체계는 소요제기단계에서 운영/유지단계까지 오랜 시간이 소모되는 특성이 있다. 이로 인하여, 불가피하게 획득 단계에서 주요부품의 단종이 발생된다. 부품단종은 양산 일정 지연의 지연을 유발할 수 있으며, 나아가 운영유지단계에서는 원활하지 못한 부품 공급으로 운용가용도(Operational Availability)에 나쁜 영향을 미치게 된다. 한편, 사업관리자는 설계, 생산, 운영단계의 총수명주기 비용을 최소화하면서 성능을 극대화할 의무가 있으며, 이를 위해서는 적절한 부품단종관리 계획을 수립하고 이행할 필요가 있다. 본 논문에서는 적절한 부품단종관리를 통하여 절감할 수 있는 회피비용 및 총수명주기비용을 통하여 부품단종관리의 효용성을 분석하였다.

• 대한신경집중치료학회지
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• 제11권2호
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• pp.110-118
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• 2018

Background: The role of clinical pharmacists in medication therapy to improve clinical and economic outcomes has been reported in the literature. This study was conducted to analyze the changes in details of medication interventions before and after the introduction of clinical pharmacists into the care of neurocritical care unit (NCU) patients, and to evaluate the economic effects of clinical pharmacists by calculating the avoidance cost. Methods: A retrospective study was conducted reviewing the electronic medical records from June 2013 to May 2014 (before), and from June 2016 to May 2017 (after). We calculated the number and rates of intervention, the acceptance rates of it, and also reviewed the list of interventions. We calculated avoidance cost if there was no intervention. Results: The monthly mean number of interventions increased from 8.0 (${\pm}5.7$) to 31.7 (${\pm}12.8$) (P<0.001) and the frequency of intervention also increased from 0.8% to 1.6% (P=0.003). The most frequently provided pharmacist intervention was nutritional support before introduction of clinical pharmacists and discussions on the medication plan after. The number of classified interventions was 14 before introduction of clinical pharmacist services and 33 after. The calculated cost avoidance associated with a clinical pharmacists' integration was 77,990,615 won per year. Conclusion: Introduction of clinicals pharmacist into the NCU was associated with increased intervention rates and expanded types of clinical interventions. The cost avoidance achieved by the pharmacists' interventions can be further explored to evaluate if similar expansions of pharmacists' services achieve similar results in other settings.

• 제어로봇시스템학회논문지
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• 제15권1호
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• pp.89-93
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• 2009

This paper deals with obstacle avoidance for unmanned vehicle using stereo system. The "DARPA Grand Challenge 2005" shows that the robot can move autonomously under given waypoint. RADAR, IMS (Inertial Measurement System), GPS, camera are used for autonomous navigation. In this paper, we focus on stereo system for autonomous navigation. Our approach is based on Singh et. al. [5]'s approach that is successfully used in an unmanned vehicle and a planetary robot. We propose an improved algorithm for obstacle avoidance by modifying the cost function of Singh et. al. [5]. Proposed algorithm gives more sharp contrast in choosing local path for obstacle avoidance and it is verified in experimental results.

• International Journal of Aeronautical and Space Sciences
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• 제11권4호
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• pp.351-359
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• 2010

This paper proposes a linear system control algorithm with collision avoidance in multiple satellites. Consideration of collision avoidance is augmented by adding a weighting term in the cost function of the original tracking problem in linear quadratic control (LQC). Because the proposed algorithm relies on a similar solution procedure to the original LQC, its inherent advantages, including gain-robustness and optimality, are preserved. To confirm and visualize the derived algorithm, a simple example of two-vehicle motion in the two-dimensional plane is illustrated. In addition, the proposed collision avoidance control is applied to satellite formation flying, and verified by numerical simulations.

• 한국문헌정보학회지
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• 제39권2호
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• pp.35-55
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• 2005

본 연구는 목록 아웃소싱의 타당성 분석을 시도하였으며, 아웃소싱으로 인해 발생하는 부가가치를 정보경제학에 기초한 직접편익, 가치연결의 효과로 분류하여 분석하는 경제성 분석모형을 적용하였다. 직접편익은 비용절감과 비용회피로 가치연결 효과는 목록 품질의 향상정도로 측정하였다. 분석결과, 목록 아웃소싱의 종합적인 타당성은 입증되지 않았으며, 이는 납품업체들의 전문성 결여로 품질제어를 하는데 사서의 시간이 많이 투입되어 실제적인 비용절감에 효과가 거의 없는 것이 가장 근 요인인 것으로 나타났다. 이렇게 현실적인 타당성이 미흡한 상태에서 목록 아웃소싱을 무리하게 이용할 경우 운영비용의 절감과 봉사기능의 제고라는 기본 취지를 달성하는 것이 불가능할 것이다.

• Journal of Information Processing Systems
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• 제16권6호
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• pp.1324-1342
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• 2020

Various modified algorithms of rapidly-exploring random tree (RRT) have been previously proposed. However, compared to the RRT algorithm for collision avoidance with global and static obstacles, it is not easy to find a collision avoidance and local path re-planning algorithm for dynamic obstacles based on the RRT algorithm. In this study, we propose boundary-RRT*, a novel-algorithm that can be applied to aerial vehicles for collision avoidance and path re-planning in a three-dimensional environment. The algorithm not only bounds the configuration space, but it also includes an implicit bias for the bounded configuration space. Therefore, it can create a path with a natural curvature without defining a bias function. Furthermore, the exploring space is reduced to a half-torus by combining it with simple right-of-way rules. When defining the distance as a cost, the proposed algorithm through numerical analysis shows that the standard deviation (σ) approaches 0 as the number of samples per unit time increases and the length of epsilon ε (maximum length of an edge in the tree) decreases. This means that a stable waypoint list can be generated using the proposed algorithm. Therefore, by increasing real-time performance through simple calculation and the boundary of the configuration space, the algorithm proved to be suitable for collision avoidance of aerial vehicles and replanning of local paths.

• 제어로봇시스템학회논문지
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• 제18권12호
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• pp.1132-1138
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• 2012

The MPC (Model Predictive Control) is one of the techniques that can be used to control an unmanned vehicle. It predicts the future vehicle trajectory using the dynamic characteristic of the vehicle and generate the control value to track the reference path. If some obstacles are detected on the reference paths, the MPC can generate control value to avoid the obstacles imposing the inequality constraints on the MPC cost function. In this paper, we propose an obstacle modeling algorithm for MPC with inequality constraints for obstacle avoidance and a method to set selective constraint on the MPC for stable obstacle avoidance. Simulations with the field test data show successful obstacle avoidance and way point tracking performance.

• 한국자동차공학회논문집
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• 제22권3호
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• pp.241-249
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• 2014

This paper presents a path planning algorithm of an autonomous vehicle (ADAM III) for collision avoidance in the presence of multiple obstacles. Under the requirements that a low-cost GPS is used and its computation should be completed with a sampling time of sub-second, heading angle estimation is proposed to improve performance degradation of its measurement and a hierarchical structure for path planning is used. Once it is decided that obstacle avoidance is necessary, the path planning consists in three steps: waypoint generation, trajectory candidate generation, and trajectory selection. While the waypoints and the corresponding trajectory candidates are generated based on position of obstacles, the final desired trajectory is determined with considerations of kinematic constraints as well as an optimal condition in a term of lateral deviation. Finally the proposed algorithm was validated experimentally through field tests and its demonstration was performed in Autonomous Vehicle Competition (AVC) 2013.