• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1464-1469
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• 2003

In this paper, fault tolerant mechanisms are presented for a servo manipulator system designed to operate in a hot cell. A hot cell is a sealed and shielded room to handle radioactive materials, and it is dangerous for people to work in the hot cell. So, remote operations are necessary to handle the radioactive materials in the hot cell. KAERI has developed a servo manipulator system to perform such remote operations. However, since electric components such as servo motors are weakened with radiation, fault tolerant mechanisms have to be considered. For fault tolerance of the servo manipulator system, hardware and software redundancy has been considered. In the case of hardware, radioactive resistant electric components such as cables and connectors have been adopted and motors driving a transport have been duplicated. In case of software, a reconfiguration algorithm accommodating one motor's failure has been developed. The algorithm uses redundant axes to recover the end effector's motion in spite of one motor's failure.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.707-711
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• 1999

In this paper, an algorithm of fault tolerant gaits for a quadruped robot is proposed for the purpose of tolerating a locked joint failure. The robot can continue its walking after a locked failure occurs to a joint of a leg by the proposed algorithm. In particular, a periodic gait is proposed as a special form of the proposed algorithm and its existence and efficiency are analytically proven.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.2
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• pp.80-86
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• 2010

We propose a spacecraft attitude estimation algorithm using a federated unscented Kalman filter. For nonlinear spacecraft systems, the unscented Kalman filter provides better performance than the extended Kalman filter. Also, the decentralized scheme in the federated configuration makes a robust system because a sensor fault can be easily detected and isolated by the fault detection and isolation algorithm through a sensitivity factor. Using the proposed algorithm, the spacecraft can continuously perform a given mission despite navigation sensor faults. Numerical simulation is performed to verify the performance of the proposed attitude estimation algorithm.

• Journal of the Korea Society for Simulation
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• v.3 no.1
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• pp.89-98
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• 1994

In this paper, a criteria for selecting an appropriate load redistribution algorithm is devised so that a fault-tolerance distributed system can operte at its optimal efficience. To present the guideline for selecting redistributing algorithms, simulation models of fault-tolerant system including redistribution algorithms are developed using SLAM II. The job arrival rate, service rate, failure and repair rate of nodes, and communication delay time due to load migration are used as parameters of simulation. The result of simulation shows that the job arrival rate and the failure rate of nodes are not deciding factors in affecting the relative efficiency of algorithms. Algorithm B shows relatively a consistent performance under various environments, although its performance is between those of other algorithms. If the communication delay time is longer than average job processing time, the performance of algorithm B is better than others. If the repair rate is relatively small or communication delay time is longer than service time, algorithm A leads to good performance. But in opposite environments, algorithm C is superior to other algorithms.

• Journal of Internet Computing and Services
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• v.9 no.5
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• pp.185-193
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• 2008

An MTBF(mean time between failures) of large scale parallel systems is known to be only an order of several hours, and large computations sometimes result in a waste of huge amount of CPU time, However. the MPI(Message Passing Interface), a de facto standard for message passing parallel programming, suggests no possibility to handle such a problem. In this paper, we propose an application-level fault tolerant computation system, purely on the basis of the current MPI standard without using any non-standard fault tolerant MPI library, that can be used for general scientific synchronous parallel computation.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.2
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• pp.204-210
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• 1988

The residue number system offers the possibility of high-speed operation and error detection/correction because of the separability of arithmetic operations on each digit. A compact residue arithmetic module named the self-checking pulse-train residue arithmetic circuit is effectively employed as the basic module, and an efficient error detection/correction algorithm in which error detection is performed in each basic module and error correction is performed based on the parallelism of residue arithmetic is also employed. In this case, the error correcting circuit is imposed in series to non-redundant system. This design method has an advantage of compact hardware. Following the proposed method, a 2nd-order recursive fault-tolerant digital filter is practically implemented, and its fault-tolerant ability is proved by noise injection testing.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1853-1856
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• 2003

This paper considers the problem of longitudinal control of a platoon of automotive vehicles on a straight lane of a highway and proposes control laws in the event of loss of communication between the lead vehicle and the other vehicles in the platoon. Since safety plays a key role in the development of an Automated Highway System, fault-tolerant control is vital. In this paper, we develop a control algorithm in vehicle platooning and prove that this control algorithm is stable for certain class of faults such as parameter uncertainties. The performance of the controller is demonstrated through a series of simulations incorporating various vehicles and AHS faults. Results of simulation shows that the vehicles have good performance in spite of simple automotive and AHS failure, such as actuator failure,that is to say, engine input failure, communication failure between lead vehicle and the another vehicles.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.2
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• pp.271-277
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• 2022

PBFT (Practical Byzantine Fault Tolerant) is a consensus algorithm that can achieve consensus by resolving unintentional and intentional faults in a distributed network environment and can guarantee high performance and absolute finality. However, as the size of the network increases, the network load also increases due to message broadcasting that repeatedly occurs during the consensus process. Due to the characteristics of the PBFT algorithm, it is suitable for small/private blockchain, but there is a limit to its application to large/public blockchain. Because PBFT affects the performance of blockchain networks, the industry should test whether PBFT is suitable for products and services, and academia needs a unified evaluation metric and technology for PBFT performance improvement research. In this paper, quantitative evaluation metrics and evaluation frameworks that can evaluate PBFT family consensus algorithms are studied. In addition, the throughput, latency, and fault tolerance of PBFT are evaluated using the proposed PBFT evaluation framework.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.8
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• pp.1977-1983
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• 1998

An algorithm-based fault tolerant scheme for the vector convolution is proposed employing the positive and negative checksum vectors that are defined in this paper based on the encoder vector. The proposed scheme is implemented on the aray processor, and then the amount of redundancy is examined thrugh the complexity analysis.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2467-2470
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• 2003

In this paper, fault tolerant mechanisms are presented for a servo manipulator system designed to operate in a hot cell. A hot cell is a sealed and shielded room to handle radioactive materials, and it is dangerous for people to work in the hot cell. So, remote operations are necessary to handle radioactive materials in the hot cell. KAERI has developed a servo manipulator system to perform such remote operations. However, since electric components such as servo motors are weak to radiations, fault tolerant mechanisms have to be considered. For fault tolerance of the servo manipulator system, hardware and software redundancy have been considered. In case of hardware, radioactive resistant electric components such as cables and connectors have been adopted and motors driving a transport have been duplicated. In case of software, a reconfiguration algorithm accommodating one motor's failure has been developed. The algorithm uses redundant axis to recover the end effector's motion in spite of one motor's failure.