• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.111-116
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• 2001

A practical scheme to reduce failure of the PCB(Printed Circuit Board) of a monitor is introduced using deformed mode shape under mechanical shock. When the monitor is given critical shock loads, cracks are commonly initiated at the tip of a hole on the PCB. Accordingly, a deformed mode shape of the PCB is obtained using a FEM code to define a weak point on the PCB under mechanical shock, and then the position and direction of the hole is determined to prevent the failure at the critical mode shape. Also, the stress intensity factor around the weak point on the PCB is calculated to check the possibility of fracture by normal tensile stress. In conclusion, present research is useful to assist the practical design of components-layout on the PCB.

• Proceedings of the KIEE Conference
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• 2008.04c
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• pp.190-192
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• 2008

GNSS(Global navigation Satellite system) is the system which determines the users' position using the navigation satellites. The position determination using GNSS has to be always Possible to appling GNSS to railway system widely. Especially, to apply GNSS to the safety-critical application, such as train control system, the satellite's visibility has to be always secured. This study describes the necessity of visibility analysis and the method. And also the visibility analysis of the stand-alone GNSS and the integration GNSS are performed and the applicability of GNSS for train control application is analysed.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.4
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• pp.14-20
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• 2012

A properly determined separation minima applied in Air Traffic Management(ATM) is critical for safe and efficient aircraft operations. The separation minima is primarily determined by the accuracy performance of surveillance system, and, due to the stringent aviation safety standard, the position accuracy of the surveillance system must be estimated with a high level of reliability. This study proposed a method for estimating the position accuracy of surveillance system with a relatively small amount of data by finding upper confidence limit instead of maximum likelihood values of unknown parameters. Through the proposed method, it is possible to determine a required separation minima with a more reliability in the face of data scarcity which often occurs when we implement a new surveillance system such as Automatic Dependent Surveillance-Broadcast (ADS-B).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.290-294
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• 1995

In master-slave teleoperation system, time delay may be a critical problem because a task is performed over a distance. Even if the system is stable without time delay, time delay can make the system unstable. In this paper a new control scheme applicable to the system with time delay would be proposed,which is based on the conventional position-position feedback type controller. The stability of this control system is proved using scattering theory, and is compared with the conventional ones. By performing the simulation of a one-d.o.f master-slave system, the validity of the proposed algorithm is verified.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.53 no.12
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• pp.739-750
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• 2004

In case while M(modulation index) is more than 0.7, the spectrum of motor voltage and current of a conventional two-phase SRP-PWM scheme are not reduced considerably. To solve the problems of a conventional two-phase SRP-PWM, this paper proposes a two-phase SRP-PWM(DZSRP-PWM) with double zero vector mode which zero vector is selected as V(111) in case of M >0.7, and zero vector is selected as V(000) if M < 0.7. For the validity of the proposed method, the PSIM simulations and experiments were achieved. And the simulation and experiment results show that the voltage and current harmonics all over the modulation index are spread to a wide band area.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.317-324
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• 2001

This study deals with high power Nd:YAG laser welding of thin steels for small pressure vessels. Full penetration welding at the overlap joint was performed so as to assure sufficient weld strength. Results showed that mid-depth weld size reduced drastically with increasing the travel speed. Position of focus had little effect on the bead formation even though short focal system was used. However, the shape factor and the bead width had closely related with the position of focus. Based on the microstructural inspection, acceptable weld was obtained when the overlap clearance was controlled up to 20% of the base metal thickness. In the case that the joint contained more clearance than the critical value, both the tensile shear strength and the tear strength were reduced. Results also demonstrated that shielding gases were proved to play a key role as far as the bead formation characteristics was taken into consideration. Blowing dry air through 5mm in diameter nozzle produced narrower bead cross-section than that of argon or nitrogen shielding.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.4
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• pp.446-454
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• 2011

In terms of the anatomy and mechanics of the human foot, a flexible robot foot with toes and heel joints is designed for a bipedal walking robot. We suggest three design considerations in determining foot design parameters which are critical for walking stability. Those include the position of the frontal toe, the stiffness of toes and heels, and the position of the ankle joint. Compared with the conventional foot with flat sale, the proposed foot is advantageous for human-like walking due to the inherent structural flexibility and the reasonable parameter values. Simulation results are provided to determine the design parameters and also show that the proposed foot enables smaller energy consumption.

• Journal of Information Technology Applications and Management
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• v.20 no.4
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• pp.293-313
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• 2013

Preproject phase is an important but often ignored research area in information systems field although it has an undeniable importance for successful project. The purpose of this study is to identify factors affecting project performance in preproject phase and to find empirically critical factors among them. After deriving 9 factors through literature review including clear project definition, project leader position, staffing efforts, preproject team expertise, preproject knowledge scope, preproject partnering, top-management support, resource sufficiency, and project climate, the study investigate the influence of those factors on project performance. The study results reveal that clear project definition, project climate, resource sufficiency, pre-project knowledge scope, project leader position have significant impact on project process satisfaction, a measure of project performance, but the other factors do not. Based on the empirical results, the study discuss academic and practical implications.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.9
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• pp.158-165
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• 2000

Reverse engineering is reproducing products by directly extracting geometric information from physical objects such as clay model wooden mock-up etc. The fundamental work in the reverse engineering is to acquire the geometric data for modeling the objects. This research proposes a novel method for data acquisition aiming at unmanned fast and precise measurement. This is come true by the sensor fusion with CCD camera using structured light beam and touch trigger sensor. The vision system provides global information of the objects data. In this case the number of data and position allocation for touch sensor is critical in terms of the productivity since the number of vision data is very huge. So we applied wavelet transform to reduce the number of data and to allocate the position of the touch probe. The simulated and experimental results show this method is good enough for data reduction.

• Smart Structures and Systems
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• v.7 no.5
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• pp.349-363
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• 2011

To assess the performance of a structure requires the measurement of global and relative displacements at critical points across the structure. They should be obtained in real time and in all weather condition. A Global Navigation Satellite System (GNSS) could satisfy the last two requirements. The American Global Position System (GPS) provides long term acquisitions with sampling rates sufficient to track the displacement of long period structures. The accuracy is of the order of sub-centimetres. The steel building which hosts the authors' laboratory is the reference case-study within this paper. First a comparison of data collected by GPS sensor units with data recorded by tri-axial accelerometers is carried out when dynamic vibrations are induced in the structure by movements of the internal bridge-crane. The elaborations from the GPS position readings are then compared with the results obtained by a Finite Element (FE) numerical simulation. The purposes are: i) to realize a refinement of the structural parameters which characterize the building and ii) to outline a suitable way for processing GPS data toward structural monitoring.