• Journal of Information Technology Applications and Management
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• 제15권1호
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• pp.261-270
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• 2008

Wireless Mesh Networks (WMNs) have emerged as one of the new hot topics in wireless communications. WMNs have been suggested for use in situations in which some or all of the users are mobile or are located in inaccessible environments. Unconstrained transmission in a WMN may lead to the time overlap of two or more packet receptions, called collisions or interferences, resulting in damaged useless packets at the destination. There are two types of collisions; primary collision, due to the transmission of the stations which can hear each other, and hidden terminal collision, when stations outside the hearing range of each other transmit to the same receiving stations. For a WMN, direct collisions can be minimized by short propagation and carrier sense times. Thus, in this paper we only consider hidden terminal collision while neglecting direct collisions. To reduce or eliminate hidden terminal collision, code division multiple access (CDMA) protocols have been introduced. The collision-free property is guaranteed by the use of spread spectrum communication techniques and the proper assignment of orthogonal codes. Such codes share the fixed channel capacity allocated to the network in the design stage. Thus, it is very important to minimize the number of codes while achieving a proper transmission quality level in CDMA WMNs. In this paper, an efficient heuristic code assignment algorithm for eliminating hidden terminal collision in CDMA WMNs with general topology.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권12호
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• pp.3152-3165
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• 2012

Wireless sensor networks (WSN) often employ asynchronous MAC scheduling, which allows each sensor node to wake up independently without synchronizing with its neighbor nodes. However, this asynchronous scheduling may not deal with collisions due to hidden terminals effectively. Although most of the existing asynchronous protocols exploit a random back-off technique to resolve collisions, the random back-off cannot secure a receiver from potentially repetitive collisions and may lead to a substantial increase in the packet latency. In this paper, we propose a new collision resolution algorithm called Transient Coordinator (TC) for asynchronous WSN MAC protocols. TC resolves a collision on demand by ordering senders' transmissions when a receiver detects a collision. To coordinate the transmission sequence both the receiver and the collided senders perform handshaking to collect the information and to derive a collision-free transmission sequence, which enables each sender to exclusively access the channel. According to the simulation results, our scheme can improve the average per-node throughput by up to 19.4% while it also reduces unnecessary energy consumption due to repetitive collisions by as much as 91.1% compared to the conventional asynchronous MAC protocols. This demonstrates that TC is more efficient in terms of performance, resource utilization, and energy compared to the random back-off scheme in dealing with collisions for asynchronous WSN MAC scheduling.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.184-189
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• 2002

Collision free task planning for dual-arm robot which perform many subtasks in a common work space can be achieved in two steps : path planning and trajectory planning. Path planning finds the order of tasks for each robot to minimize path lengths as well as to avoid collision with static obstacles. A trajectory planning strategy is to let each robot move along its path as fast as possible and delay one robot at its initial position or reduce speed at the middle of its path to avoid collision with the other robot.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.244-249
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• 2001

Collision free task planning for dual-arm robot which perform many subtasks in a common work space can be achieved in two steps : path planning and trajectory planning. Path planning finds the order of tasks for each robot to minimize path lengths as well as to avoid collision with static obstacles. A trajectory planning strategy is to let each robot move along its path as fast as possible and delay one robot at its initial position or reduce speed at the middle of its path to avoid collision with the other robot.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 추계학술대회논문집 - 한국공작기계학회
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• pp.113-118
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• 2000

Collision free task planning for dual-arm robot which perform many subtasks in a common work space can be achieved in two steps : path planning and trajectory planning. Path planning finds the order of tasks for each robot to minimize path lengths as well as to avoid collision with static obstacles. A trajectory planning strategy is to let each robot move along its path as fast as possible and delay one robot at its initial position or reduce speed at the middle of its path to avoid collision with the other robot.

• 전자공학회논문지 IE
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• 제47권2호
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• pp.66-72
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• 2010

자율적인 다중이동 로봇환경에서는 현시점에서 목표점까지 장애물과 충돌없이 연결하는 최적 경로를 설정하는 것은 필수불가결하며 매우 중요하다. 실제 많은 이동로봇은 주위 장애물에 대하여 주어진 정보 없이 미지의 환경에서 자율적 이동이 가능해야 한다. 따라서 본 논문에서는 다중이동 로봇환경에 적합한 새로운 형태의 충돌회피 최적경로에 대한 방법을 연구한다. 잘 알려진 포텐셜필드 방법을 이용하여 다중이동 로봇의 전역경로를 계획하고, 퍼지로직 시스템을 이용하여 각 로봇에 근접하는 혹은 경로를 가로막는 장애물과의 충돌을 피하기 위한 지역경로를 계획한다. 제안된 방법의 성능 및 정확성을 검증하기 위해 다양한 모의실험을 진행하여 결과를 검증하고 이의 결과를 토의한다.

• 한국대기환경학회지
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• 제27권6호
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• pp.681-691
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• 2011

The size distributions of smoke particles from fire are prerequisite for the studies on fire detection and adverse health effects. Above the flame of the fire, coagulation dominates and the smoke particles grow from 1 to 50 nm up to 100 to 3,000 nm, sizes ranging from the free-molecular regime to the continuum regime. The characteristics of the agglomeration of the smoke particles are well known, independently for each of the free-molecular and continuum regimes. However, there are not many systematic studies in the entire regime by the complexity of the mechanisms. The purpose of this work is to find the characteristics of the development of the size distribution of smoke particles by agglomeration in the entire size range covering the free-molecular regime, via transition regime, to the near-continuum and continuum regime for each variation of parameters such as fractal dimension, primary particle size and dimensionless coagulation time. In this work, the dynamic equation for the discrete-size spectrum of the particles was solved using a nodal method based on the modification of a sectional method. In the calculation, the collision frequency function for the entire regime, which is derived by using the concept of collision volume and general enhancement function, was applied. The self-preserving size distribution for the entire regime is compared with the ones for the free-molecular or continuum regimes for each variation of the parameters.

• 로봇학회논문지
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• 제15권2호
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• pp.100-106
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• 2020

In the agricultural field, interests in research using robots for fruit harvesting are continuously increasing. Dual arm manipulators are promising because of its abilities like task-distribution and role-sharing. To operate it efficiently, the task sequence must be planned adequately. In our previous study, a collision-free path planning method based on a genetic algorithm is proposed for dual arm manipulators doing tasks cooperatively. However, in order to simplify the complicated collision-check problem, the movement between tasks of two robots should be synchronized, and thus there is a problem that the robots must wait and resume their movement. In this paper, we propose a heuristic algorithm that can reduce the total time of the optimal solution obtained by using the previously proposed genetic algorithm. It iteratively desynchronizes the task sequence of two robots and reduces the waiting time. For evaluation, the proposed algorithm is applied to the same work as the previous study. As a result, we can obtain a faster solution having 22.57 s than that of the previous study having 24.081 s. It will be further studied to apply the proposed algorithm to the fruit harvesting.

• 정보처리학회논문지:소프트웨어 및 데이터공학
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• 제11권9호
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• pp.363-370
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• 2022

다중 사물 환경에서 목표 사물만의 정밀한 파지를 위해서는 장애물과의 충돌 회피 지능과 정교한 파지 지능이 필요하다. 이 작업을 위해선 다중 사물 환경 인지, 목표 사물 인식, 경로 설정, 로봇손의 사물 파지 지능이 필요하다. 본 연구에서는 RGB-D 영상 센서를 이용하여 다중 사물 환경과 사물을 인지하고 3D 공간을 매핑한 후, 충돌 회피 경로 탐색 알고리즘을 활용하여 목표 사물까지의 경로를 탐색 및 설정하고, 강화학습을 통해 학습된 사람형 로봇손의 목표 사물 파지 지능을 활용해 최종적으로 시뮬레이션 및 하드웨어 사물 파지 시스템을 구현하고 검증하였다. 사람형 로봇손을 구현한 시뮬레이션 환경에서 5개의 사물 중 목표 사물을 지정하고 파지한 결과 경로 탐색 없는 파지 시스템이 평균 78.8%의 성공률과 34%의 충돌률을 보일 때, 경로 탐색 지능과 결합된 시스템은 평균 94%의 성공률과 평균 20%의 충돌률을 보였다. UR3와 QB-Soft Hand를 사용한 하드웨어 환경에서는 3개의 사물 중 목표 사물을 지정하고 파지한 결과 경로 탐색 없는 파지 시스템이 평균 30%의 성공률과 97%의 충돌률을 보일 때, 경로 탐색 지능과 결합된 시스템은 평균 90%의 성공률과 평균 23%의 충돌률을 보였다. 본 연구에서는 RGB-D 시각 지능, 충돌 회피 경로 탐색, 사물 파지 심층 강화학습 지능의 결합을 통하여, 사람형 로봇손의 목표 사물 파지가 가능함을 제시하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.423-427
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• 1993

A velocity planning method is proposed that ensures collision-free and minimal delay-time motions for two robotic manipulators and auxiliary equipments. Additional path, which makes robot start with possible largest speed, is added to the original prescribed path of one of two robots, and this running start along the additional path reduces delay time introduced to avoid collision between the robots and therefore reduces total traveling time.