• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.3 s.303
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• pp.1-10
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• 2005

This paper proposes a novel fault-tolerant gait planning of a hexapod robot considering kinematic constraints. The failure concerned in this paper is a locked joint failure for which a joint in a leg cannot move and is locked in place. It is shown that the conventional fault-tolerant gait of a hexapod robot for forward walking on even terrain may be fallen into deadlock, depending on the configuration of the failed leg. For coping with such deadlock situation, a novel fault-tolerant gait planning is proposed. It can avoid deadlock by adjusting the position of the foot trajectory, and has the same leg sequence and stride length as those of the conventional fault-tolerant gait. To demonstrate the superiority of the proposed scheme, a case study is presented in which a hexapod robot, having walked over even terrain before a locked joint failure, could avoid deadlock and continue its walking by the proposed fault-tolerant gait planning.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.5
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• pp.34-45
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• 2000

In this paper, a multiagent fault-tolerant supervisory control methodology is proposed for serial production systems under partial observation. To this end, the idea of multiagent control is incorporated with the fault-tolerant supervisory control of discrete event systems. Especially, the concept of mutual fault-tolerance between cascaded processes is established and the unobservable fault identification utilizing the difference information of the controlled results is investigated. Then the synthesis of agent supervisors is formulated based on the proposed concept. A case study of the fault-propagation control of polypropylene prepolymerization and polymerization processes is provided to illustrate the proposed control policy.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.3 s.309
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• pp.16-24
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• 2006

In this paper, fault-tolerant gait planning of a hexapod robot for walking over irregular terrain is presented. The failure concerned in this paper is a locked joint failure for which a joint in a leg cannot move and is locked in place. Based on the previously proposed fault-tolerant tripod gait for walking over even terrain, fault-tolerant follow-the-leader(FTL) gaits are proposed for a hexapod robot with a failed leg to be able to walk over two-dimensional rough terrain, maintaining static stability and fault tolerance. The proposed FTL gait can have maximum stride length for a given foot position of a failed leg, and yields better ditch crossing ability than the previously developed gaits. The applicability of the proposed FTL gait is verified by using computer graphics simulations.

• Journal of KSNVE
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• v.8 no.6
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• pp.1181-1192
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• 1998

This paper describes the performance of a full-authority neural network-based fault tolerant system within a flight control system. This fault tolerant flight control system integrates sensor and actuator failure detection, identification, and accommodation (SFDIA and AFDIA), The first task is achieved by incorporating a main neural network (MNN) and a set of n decentralized neural networks (DNNs) to create a system for achieving fault tolerant capabilities for a system with n sensors assumed to be without physical redundancy The second scheme implements the same main neural network integrated with three neural network controllers (NNCs). The function of NNCs is to regain equilibrium and to compensate for the pitching, rolling. and yawing moments induced by the failure. Particular emphasis is placed in this study toward achieving an efficient integration between SFDIA and AFDIA without degradation of performance in terms of false alarm rates and incorrect failure identification. The results of the simulation with different actuator and sensor failures are presented and discussed.

• Journal of the Korean Institute of Intelligent Systems
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• v.19 no.4
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• pp.457-463
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• 2009

In this paper, a novel foot force distribution algorithm for hexapod walking robots is presented. The considered hexapod robot has fault-tolerant tripod gaits with a failed leg in locked-joint failure. The principle of the proposed algorithm is to minimize the slippage of the leg that determines the stability margin of the fault-tolerant gaits. The fault-tolerant tripod gait has a drawback that it has less stability margin than normal gaits. Considering this drawback, we use the feature that there are always three supporting legs, and by incorporating the theory of Zero-Interaction Force, we calculate the foot forces analytically without resort to any optimization technique. In a case study, the proposed algorithm is compared with a conventional foot force distribution method and its applicability is demonstrated.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.5 s.311
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• pp.19-27
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• 2006

Improvement in gait stability of fault-tolerant gaits for quadruped robots is addressed in this paper. The previously developed fault-tolerant gait gives a quadruped robot the ability to continue its walk against the occurrence of a leg failure. But it has a drawback of having marginal gait stability, which may lead to tumbling when the robot body's center of gravity is perturbed. To overcome such a drawback, a novel fault-tolerant gait is presented in this paper that generates positive stability margin against a locked joint failure, in which a joint of a leg is locked in a known place. Positive stability margin is obtained by adjusting foot positions of supporting legs between leg swing sequences. The advantages of the proposed fault-tolerant gait are discussed by comparing with the previous gait in terms of gait stability, stride length and gait velocity.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10a
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• pp.477-479
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• 2000

최근 대부분의 시스템은 즉각적인 정보를 요구하는 실시간 시스템이다. 실시간 시스템은 오류에 대한 유연적인 대체를 필요로 하는 내고장성 시스템(fault tolerant system)의 개념을 지향한다. 내고장성 시스템은 보다 정확한 시스템 설계가 중요하며, 특히 실시간 시스템에서 필요로 하는 여러 종류의 시간제약에 대한 풍부한 표현력과 명세된 시간에 대한 검증이 중요하다. 본 논문은 특정 시점과 시간 간격, 주기, 이산 시간, 다수의 타이머에 의한 동적 등의 시간 관련 동작을 ATM(Abstract Timed Machine)에 기반으로 명세하고 명세된 시간에 대한 분석을 살펴본다.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.2
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• pp.135-140
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• 2016

Corrective controllers enable fault diagnosis and tolerance for various faults in asynchronous sequential circuits without resort to redesign. In this paper, we propose a static corrective controller in order to decrease the size of the controller. Compared with dynamic controllers, static controllers can be made using only combinational circuits, as they need no inner states. We address the existence condition and design procedures for static corrective controllers that overcome state transition faults. To show the validity and advantage, the proposed controller is applied to an SEU error counter implemented on FPGA.

• Journal of IKEEE
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• v.24 no.3
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• pp.727-734
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• 2020

Fault tolerant corrective control for asynchronous sequential machines (ASMs) with transient faults is discussed in this paper. The considered ASM is vulnerable to a kind of faults whose manifestation may arise during transient transitions of the ASM, leading to transient faults occurring in non-fundamental mode. To overcome adverse effects caused by these faults, we present a novel corrective control scheme that can detect and tolerate transient faults in non-fundamental mode. The existence condition and design algorithm for an appropriate fault tolerant controller is addressed in the framework of corrective control theory. The applicability of the proposed control methodology is demonstrated in the FPGA experiment.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.105-111
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• 2003

Qualification Model of On-board Computer (OBC) for KAISTSAT-4 was developed. The OBC of KAISTASAT-4 has some improved features compared with that of KAISTSAT-3: To reduce weight and size of OBC many logics are implemented by FPGAs, and a network controller is included in OBC to access the satellite network with high speed. Also, the developed OBC has an improved tolerance against SEUs and faults. The OBC was fully tested under simulated space environment with no errors.