• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.12
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• pp.778-788
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• 2000

Chopper and sensors failures resulting from electric shock and mechanical vibration generated by rail irregularities are the serious problem deteriorating the performance in the electromagnetic suspension systems. Thus, this paper proposes a fault-tolerant control scheme with a dynamic compensator for the failure of the choppers, gap sensors and acceleration sensors in electromagnetic suspension system. The advantage of the proposed control method are demonstrated through simulation and experimental results for the levitation characteristics when the failures of the chopper and sensors occur, respectively.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.2
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• pp.141-148
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• 2012

This paper proposes fault tolerant gaits of a quadruped robot with feet of flat shape. Fault tolerant gaits make it possible for a legged robot to continue static walking against a leg failure. In the previous researches, it was assumed that a legged robot had feet that have point contact with the surface. When the robot is endowed with feet having flat shape, fault tolerant gaits can show better performance compared with the former gaits, especially in terms of the stride length and gait stability. In this paper, fault tolerant gaits of a quadruped robot against a locked joint failure are addressed in straight-line motion and crab walking, respectively.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.7
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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.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.3
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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.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.1
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• pp.10-19
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• 1990

A fault tolerant control system, in which a digital back-up controller system is added on the existing analog control system, is developed for enhancing reliability of boiler control system in power plant. The digital back-up controller system(DBCS) has a multi-processor structure with capabilities of fault diagnosis, back-up control, self test, and graphic monitoring. Specifically, switching mechanism composed of expandable modules is designed so that back-up controller takes over any faulty control loops and the number of back-up control loops is determined as that of simultaneous faults. A process simulator that simulates the boiler analog control system is developed for safety test and performance evaluation prior to real plant application. DBCS is installed at the Ulsan thermal power plant, and fault tolerant control performance is assured under the faults that some controller modules are pulled out.

• 연구논문집
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• s.30
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• pp.79-92
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• 2000

Chopper and sensors failures resulting from electric shock and mechanical vibration generated by rail irregularities are the serious problem deteriorating the performance in the electromagnetic suspension systems. Thus, this paper proposes a reliable output feedback control scheme for the electromagnetic suspension systems in the present of chopper, gap sensor and acceleration sensor failures. The designed controller is an extended version of a novel design technique which has the design method of the output feedback controller using dynamic compensator. The benefits of this scheme are demonstrated through the simulation and experimental results for proposed controller against chopper, gap sensor and acceleration sensor failures of electromagnetic suspension system.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.12
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• pp.689-695
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• 2003

Fault-tolerance is an important design criterion for robotic systems operating in hazardous or remote environments. This paper addresses the issue of tolerating a locked joint failure in gait planning for hexapod walking machines which have symmetric structures and legs in the form of an articulated arm with three revolute joints. A locked joint failure is one for which a joint cannot move and is locked in place. If a failed joint is locked, the workspace of the resulting leg is constrained, but hexapod walking machines have the ability to continue static walking. A strategy of fault-tolerant tripod gait is proposed and, as a specific form, a periodic tripod gait is presented in which hexapod walking machines have the maximum stride length after a locked failure. The adjustment procedure from a normal gait to the proposed fault-tolerant gait is shown to demonstrate the applicability of the proposed scheme.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.595-601
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• 2009

A flight control system for high reliability consists of complicated redundant structures. This redundancy can improve fault tolerant characteristics of system. So, a system manager is able to choose a suitable structure using analyzed quantitative data of various redundant structures. In this paper, we analyzed redundant characteristics and reliability. We defined necessary mathematical model for analysis tool. Then we compose a reliability block diagram analysis tool applying such defined analysis model using Simulink blocks. Finally we verified the analysis tool using a commercial tool.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.3
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• pp.6-12
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• 2011

Electric vehicles and robots are real-time distributed control systems composed of multiple drive subsystems using micro controller units. Each control subsystem should be modular, compact, power saving, interoperable and fault tolerable in order to be incorporated into the networked real-time distributed control system. Under the networked real-time distributed control the synchronization problem can be occurred to the position and orientation tracking control due to the load variance, mismatch and time delay between the multiple drive subsystems. This paper suggests two types of position synchronization control of the single link manipulators. One of them is composed of cross controller, Kalman filter and disturbance observer, and the other uses the generation of target trajectories to minimize the gradient vector of the scalar function which is composed of the sum of square errors between the reference input vector and the output vectors. The availability of the proposed control schemes is shown through the control experiments.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.51 no.5
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• pp.175-181
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• 2002

In this paper, fault tolerant digital governor is designed to realize ceaseless controlling and to improve the reliability of control system. Designed digital governor huts duplex I/O module and triplex CPU module and also 2 out of 3 voting algorithm and self diagnostic ability. The Processor module of the system(SIDG-3000) is developed based on 32 Bit industrial microprocessor, which guaranteed high quality of the module and SRAM for data also SRAM for command are separated. The process module also includes inter process communication function and power back up function (SRAM for back-up). System reliability is estimated by using the model of Markov process. It is shown that the reliability of triplex system in mission time can be dramatically improved compared with a single control system Designed digital governor system is applied after modelling of the steam turbine generator system of Buk-Cheju Thermal Power Plant. Simulation is carried out to prove the effectiveness of the designed digital governor system