• 한국지반환경공학회 논문집
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• 제24권1호
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• pp.51-60
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• 2023

수직 시추와 다르게 방향성 시추작업에서 발생하는 드릴스트링(drill string) 변형, 케이싱(casing) 마모, 키 씨팅(key seating) 등의 문제를 방지하기 위해서는 시추 궤도 내에서 발생하는 토크(torque)와 드래그(drag)가 최소화되어야 한다. 토크와 드래그의 크기는 시추 궤도 형태, 이수(mud), 드릴스트링의 종류 그리고 킥오프 지점(KOP, kick-off point)과 같은 매개변수들에 의해 결정되기 때문에 시추 궤도 설계 과정에서 고려하여 설계하여야 한다. 본 연구에서는 가장 일반적인 방향성 시추 궤도인 빌드-홀드(Build-hold) 형태의 시추 궤도에 킥오프 지점이 각기 다른 시추 궤도를 선정하였고, 분포하중 모델(analytical friction model)을 이용하여 각 구간내에서의 분포하중을 계산하여 궤도 전체에 대한 토크와 드래그를 계산하였다. 또한 매개변수에 따른 분석 값을 비교하여 분포하중이 최소로 발생하는 최적의 시추 궤도를 선정하였다. 분석결과 분포 하중을 최소화하기 위해서는 윤활성이 높은 이수를 사용, 궤도 형태에 따른 알맞은 킥오프 지점과 가능한 최소의 도그-래그를 지정하여 설계하는 것이 효과적임을 알 수 있었다. 이러한 결과는 분포하중을 최소화하기 위한 모든 방향성 시추 궤도 설계에 사용된다.

• 한국항공우주학회지
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• 제37권1호
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• pp.42-54
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• 2009

비행체의 최적궤적문제에서는 최적화의 수렴성 및 효율성을 위해 3자유도 운동역학모델이 이용되며, 비선형 추종제어를 위해서는 6자유도 비선형 운동모델이 이용된다. 따라서, 3자유도 운동역학모델을 통해 획득한 최적궤적을 비선형 추종제어의 기준궤적으로 사용하는 경우에 두 모델간의 상이성으로 인한 문제가 발생하게 되며 성능이 보장하지 못한다. 본 논문에서는 이러한 두 모델간의 차이를 완화시키기 위한 새로운 최적궤적 생성 방법을 제안하였으며, 성층권비행선의 실제 구속조건과 성능조건 및 제트 스트림을 고려하여 최적궤적을 생성하고 기존 결과와 비교함으로써 제안한 방법의 장점을 검증하였다.

• 로봇학회논문지
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• 제8권2호
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• pp.92-103
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• 2013

Humanoid robot is the most intimate robot platform suitable for human interaction and services. Biped walking is its basic locomotion method, which is performed with combination of joint actuator's rotations in the lower extremity. The present work employs humanoid robot simulator and numerical optimization method to generate optimal joint trajectories for biped walking. The simulator is developed with Matlab based on the robot structure constructed with the Denavit-Hartenberg (DH) convention. Particle swarm optimization method minimizes the cost function for biped walking associated with performance index such as altitude trajectory of clearance foot and stability index concerning zero moment point (ZMP) trajectory. In this paper, instead of checking whether ZMP's position is inside the stable region or not, reference ZMP trajectory is approximately configured with feature points by which piece-wise linear trajectory can be drawn, and difference of reference ZMP and actual one at each sampling time is added to the cost function. The optimized joint trajectories realize three phases of stable gait including initial, periodic, and final steps. For validation of the proposed approach, a small-sized humanoid robot named DARwIn-OP is commanded to walk with the optimized joint trajectories, and the walking result is successful.

• 한국항해항만학회지
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• 제42권2호
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• pp.87-96
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• 2018

A trajectory control system plays an important role in controlling motions of marine vehicle when a series of way points or a path is given. In this paper, a sliding mode control (SMC)-based trajectory tracking controller for marine vehicles is presented. A small-sized unmanned ship is considered as a control object. Both speed and heading angle of a ship should be controlled for tracking control. The common point of related researches was to separate ship's speed and heading angle in control methods. In this research, a new control law from a general sliding mode theory that can be applied to MIMO (multi input multi output) system is derived and both speed and heading angle of a ship can be controlled simultaneously. The propulsion force and rudder force are also applied in modeling stage to achieve accurate simulation. Disturbance induced by wind is also tackled in the dynamics considering robustness of the proposed control scheme. In the simulation, we employed a way-point method to generate ship's trajectory and applied the proposed control scheme to ship's trajectory tracking control. Our results confirmed that the tracking error was converged to zero, thus demonstrating the effectiveness of the proposed method.

• 제어로봇시스템학회논문지
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• 제10권6호
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• pp.510-518
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• 2004

The PID trajectory tracking controller for robotic systems shows performance limitation imposed by inverse dynamics according to desired trajectory. Since the equilibrium point can not be defined for the control system involving performance limitation, we define newly the quasi-equilibrium region as an alternative for equilibrium point. This analysis result of performance limitation can guide us the auto-tuning method for PID controller. Also, the quasi-equilibrium region is used as the target performance of auto-tuning PID trajectory tracking controller. The auto-tuning law is derived from the direct adaptive control scheme, based on the extended disturbance input-to-state stability and the characteristics of performance limitation. Finally, experimental results show that the target performance can be achieved by the proposed automatic tuning method.

• 한국세라믹학회지
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• 제40권11호
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• pp.1062-1066
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• 2003

Design of a piezoelectric actuator for the ultrasonic motor must ensure that contact point has elliptic trajectory of movement. The new idea of an elliptic trajectory formation of the piezoelectric actuator is investigated in the paper. Shaking beam for the piezoelectric linear ultrasonic motor was introduced to realize this new idea. The principle is based on the excitation of longitudinal and flexural vibrations of the actuator by using two sources of longitudinal mechanical vibrations shifted by $\pi$/2. Mode-frequency and harmonic response analyses of the actuator based on FEM have been carried out. The moving trajectory of the contact point has been defined. Finally, The experimental research of shaking beam has been confirmed an opportunity of the elliptic trajectory reception with the help of one stable mode of the vibrations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 A
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• pp.19-22
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• 2003

This paper proposes an algorithm for navigation of an autonomous mobile robot with vision sensor. For obstacle avoidance, we used a curvature trajectory method. Using this method, translational and rotational speeds are controlled independently and the mobile robot traces a smooth curvature trajectory that consists of circle trajectories to a target point. While trying to avoid obstacles, the robot fan be goal-directed using curvature trajectory.

• 한국기계가공학회지
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• 제6권3호
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• pp.71-76
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• 2007

The fatalities of pedestrian account for about 40.0% of all fatalities in Korea 2005. Vehicle-Pedestrian accident generates trajectory of pedestrian. In pedestrian involved accident, the most important data to inspect accident is throw distance of pedestrian. The throw distance of pedestrian can be influenced by many variables. The variables that influence trajectory of pedestrian can be classified into vehicular factors, pedestrian factors, and road factors. Vehicular factors are the frontal shape of vehicle, impact speed of vehicle, the offset of impact point. Many studies have been done about the relation between impact speed and throw distance of pedestrian. But the influence of the offset of impact point was neglected. The influence of the offset of impact point was analyzed by Working Model, and the trajectory of pedestrian, dynamic characteristics of multi-body were analyzed by PC-CRASH, a kinetic analysis program for a traffic accident. Based on the results, the increase of offset reduced the throw distance of pedestrian. However box type vehicle just like bus, the offset of impact point did not influence the throw distance of pedestrian considerably.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 합동 추계학술대회 논문집 정보 및 제어부문
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• pp.169-172
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• 2002

This paper is concerned with walking trajectory generation by applying the genetic algorithm. The walking trajectory is generated though three via-points and genetic algorithm is employed to find velocity and acceleration at each via-point. Also genetic algorithm is applied for balancing joint trajectory. Fitness function is used for minimizing the trajectory. As a result, new algorithm generated the smooth trajectory. The proposed algorithm is verified by the experiment of biped walking robot developed in our Control laboratory, and we compared the result with the previous walking algorithm. It showed that the new proposed algorithm generated the better walking trajectory.

• ETRI Journal
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• 제43권6호
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• pp.1013-1023
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• 2021

In this study, we propose a practical path planning method that combines the A^* search algorithm and minimum snap trajectory generation. The A^* search algorithm determines a set of waypoints to avoid collisions with surrounding obstacles from a starting to a destination point. Only essential waypoints (waypoints necessary to generate smooth trajectories) are extracted from the waypoints determined by the A^* search algorithm, and an appropriate time between two adjacent waypoints is allocated. The waypoints so determined are connected by a smooth minimum snap trajectory, a dynamically executable trajectory for the quadrotor. If the generated trajectory is invalid, we methodically determine when intermediate waypoints are needed and how to insert the points to modify the trajectory. We verified the performance of the proposed method by various simulation experiments and a real-world experiment in a forested outdoor environment.