• 대한기계학회논문집
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• 제18권11호
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• pp.2846-2859
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• 1994

This work deals with kinematic analysis of fault-tolerant 3 degree-of-freedom spherical modules which have force redundancies in its parallel structure. The performance of a redundantly actuated four-legged module with no actuator failure, a single actuator failure, partial and half failure of dual actuator are compared to that of a three-legged module, in terms of maximum force transmission ratio, isotropic characteristics, and fault-tolerant capability. Additionally, a system with an excess number of small floating actuators is considered, and the contribution of these small actuators to the force transmission and fault-tolerant capability is evaluated. This study illustrates that the redundant actuation mode allows significant saving of input actuation effort, and also delivers a fault tolerance.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권7호
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• pp.319-326
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• 2006

This paper proposes a novel fault-tolerant gait for Quadruped robots using energy stability margins. The previously developed fault-tolerant gaits for quadruped robots have a drawback of having marginal stability margin, which may lead to tumbling. In the process of tumbling, the potential energy of the center of gravity goes through a maximum. The larger the difference between the potential energy of the center of gravity of the initial position and that of this maximum, the less the robot tumbles. Hence this difference of potential energy, dubbed as Energy Stability Margin (ESM), can be regarded as the stability margin. In this paper, a novel fault-tolerant gait is presented which gives positive ESM to a quadruped robot suffering from a locked joint failure. Positive ESM is obtained by adjusting foot positions between leg swing sequences. The advantage of the proposed fault-tolerant gait is demonstrated in a case study where a quadruped robot with a failed leg walks on a even slope.

• 자동차안전학회지
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• 제9권4호
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• pp.32-37
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• 2017

For automated vehicles, the integrity and fault tolerance of environment perception sensor have been an important issue. This paper presents radar, vision, lidar(laser radar) fusion-based fault detection algorithm for autonomous vehicles. In this paper, characteristics of each sensor are shown. And the error of states of moving targets estimated by each sensor is analyzed to present the method to detect fault of environment sensors by characteristic of this error. Each estimation of moving targets isperformed by EKF/IMM method. To guarantee the reliability of fault detection algorithm of environment sensor, various driving data in several types of road is analyzed.

• 전자공학회논문지B
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• 제32B권3호
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• pp.1-10
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• 1995

In this paper, a fault-tolerant Mini-MAP system with high reliability is proposed. For fault-tolerance, the LLC sublayer, MAC sublayer, and physical layer of the Mini-MAP system are dualized. The detection of faults, the replacement of the failed network, and the management of the network are three major functions required for the dualization, and they are performed by ESM(Error Supervisory Machine), EMM(Error Management Machine), and NMM(Network Management Machine) of the proposed fault-tolerant Mini-MAP system, respectively. The ring maintenance function of the MAC sublayer is used for the detection of the faults. In the proposed fault-tolerant Mini-MAP system, the data are received from both of the dualized networks and transmitted to the selected one of the two. We analyze the reliability and the MTTF(Mean Time To Failure) of the proposed fault-tolerant Mini-MAP system and show that it has better performance compared to a general Mini-MAP system.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권3호
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• pp.131-140
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• 2005

Fault-tolerant gait generation of a hexapod robot with crab walking is proposed. The considered fault is a locked joint failure, which prevents a joint of a leg from moving and makes it locked in a known position. Due to the reduced workspace of a failed leg, fault-tolerant crab walking has a limitation in the range of heading direction. In this paper, an accessible range of the crab angle is derived for a given configuration of the failed leg and, based on the principles of fault-tolerant gait planning, periodic crab gaits are proposed in which a hexapod robot realizes crab walking after a locked joint failure, having a reasonable stride length and stability margin. The proposed crab walking is then applied to path planning on uneven terrain with positive obstacles. i.e., protruded obstacles which legged robots cannot cross over but have to take a roundabout route to avoid. The robot trajectory should be generated such that the crab angle does not exceed the restricted range caused by a locked joint failure.

• 전자공학회논문지SC
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• 제43권3호
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• pp.16-24
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• 2006

본 논문에서는 비평탄 지형을 보행하기 위한 육족 보행 로봇의 내고장성 걸음새 계획을 제안한다. 본 논문에서 고려하고 있는 고장은 관절고착고장으로 로봇 다리의 관절 하나가 어떤 위치에 고착되어서 보행이 끝날 때까지 움직일 수 없는 상태를 말한다. 기존에 제안되었던 평탄 지형 보행을 위한 내고장성 세다리 걸음새 계획을 바탕으로 본 논문에서는 육족 보행 로봇이 관절고착고장이 발생한 후에도 이차원 착지 불가능 영역이 존재하는 비평탄 지형을 걸을 수 있도록 하는 내고장성 FTL(Follow-The-Leader) 걸음새를 구현한다. 제안된 FTL 걸음새는 고장 난 다리의 착지점에서 로봇이 가질 수 있는 최대한의 보폭을 낼 수 있으며, 기존 내고장성 걸음새보다 착지 불가능 영역을 뛰어넘는 능력이 더 우수하다. 컴퓨터 시뮬레이션을 통해서 제안된 FTL 걸음새의 응용가능성을 검증한다.

• 한국정보통신학회논문지
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• 제26권2호
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• pp.271-277
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• 2022

PBFT(Practical Byzantine Fault Tolerant)는 분산 네트워크 환경에서 비의도적·의도적 결함을 해결하여 합의를 달성할 수 있는 합의 알고리즘으로 높은 성능과 절대적 최종성을 보장할 수 있다. 하지만 합의 과정에서 반복적으로 발생하는 메시지 브로드캐스팅으로 인해 네트워크의 규모가 증가할수록 네트워크 부하도 커진다. PBFT 알고리즘의 특성상 소규모·프라이빗 블록체인에는 적합하지만, 대규모·퍼블릭 블록체인에 적용하기엔 한계가 있다. PBFT는 블록체인 네트워크의 성능에 영향을 끼치기 때문에 산업에서는 PBFT가 제품 및 서비스에 적합한지 테스트할 수 있어야 하며, 학계에서는 PBFT 성능 향상 연구를 위한 통일된 평가지표와 평가 기술이 필요하다. 본 논문에서는 PBFT 계열 합의 알고리즘을 평가할 수 있는 정량적 지표와 평가 프레임워크에 대해 연구한다. 또한 제안한 PBFT 평가 프레임워크를 사용하여 PBFT의 처리량, 지연시간, 내결함성을 평가한다.

• 제어로봇시스템학회논문지
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• 제17권11호
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• pp.1125-1131
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• 2011

This paper presents a control theoretic approach to realizing fault tolerance in asynchronous sequential circuits. The considered asynchronous circuit is assumed to work in space environment and is subject to faults caused by total ionizing dose (TID) effects. In our setting, TID effects cause permanent changes in state transition characteristics of the asynchronous circuit. Under a certain condition of reachability redundancy, it is possible to design a corrective controller so that the closed-loop system can maintain the normal behavior despite occurrences of TID faults. As a case study, the proposed control scheme is applied to an asynchronous arbiter implemented in FPGA.

• 한국정보통신학회논문지
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• 제18권1호
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• pp.63-71
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• 2014

본 논문에서는 Active-Active 방식의 웹서버 이중화 방법에 관해 연구하였다. Rsync과 crontab을 이용하여 웹서버간에 주기적인 복사가 이루어지도록 하여 동일한 상태를 유지시켰다. 로드밸런싱서버가 웹서버를 교대로 실행하여 부하를 분산하고, 빠른 서비스가 제공되도록 하였다. 또한 임의의 웹서버에 장애가 발생하더라도 또 다른 웹서버에 의해 서비스가 계속 유지되도록 하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.1348-1351
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• 1997

The federated Kaman filter(FKF) is being widely used in many multisensor navigatiion systems. It is know that the FKF has advantages of simplicity and fault-tolerance over other decentralized filter techniques. In this paper, optimal and suboptimal FKF configuratiions are mentioned and a covariance analysis technique for the suboptimal FKF is newly presented. The suboptimal FKF configuration, known as No-reset(NR) mode, has better fault tolerance capability than the optimal FKF coniguratioin. In the suggested technique, a suboptimal fusion process of FKF is considered a swell as suboptimal gains of local filters. An upper boun of error covariance for suboptimal FKF is derived. Also, it is mathematically shown that this bound is smaller thanexisting bound in the literatrue. A vehicle-navigaion system is designed using the FKF. In thissystem, a map constraing equation is introduced and used as a measurement equatioin of Kalman filter. Performance analysis is done by the suggested covariance analysis techniques.