• Journal of the Korean Society for Precision Engineering
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• v.32 no.9
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• pp.773-779
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• 2015

The laser Powder Bed Fusion (PBF) system is currently recognized as a leading process. Due to the various materials employed such as thermoplastic, metal and ceramic composite powder, the application's use extends to machinery, automobiles, and medical devices. The PBF system's surface quality of prototypes and processing time are significantly affected by several parameters such as laser power, laser beam size, heat temperature and laminate thickness. In order to develop a more elaborate and rapid system, this study developed a new PBF system and sintering process. It contains a 3-axis dynamic focusing scanner system that maintains a uniform laser beam size throughout the system unlike the $f{\theta}$ lens. In this study, experiments were performed to evaluate the effects of various laser scanning parameters and fabricating parameters on the fusion process, in addition to fabricating various 3D objects using a PA-12 starting material.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.155-159
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• 2009

Crack-controlled method which utilizes the dynamic energy such as explosives and propellent gases have been applied to the development of mineral resource and oil and civil engineering. It is necessary to consider the fracture processes associated with the material properties and external forces to control crack propagation using borehole pressure. To investigate the influence of the applied borehole pressure waveform on the crack propagation in rock masses having different material properties, a no-free surface model was used, consisting of a borehole in rock with a continuous boundary. Loading rates ranging from 1 to 100MPa/${\mu}s$ with different rock mass properties was employed to investigate the loading rate dependency of fracture patterns in the rock mass.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.171-176
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• 2005

In the information storage development, the trend of the storage device is to increase the recording density. Among such an effort, near-field probe recording is spotlighted as a method of high increasing recording density. For the successfully embodiment of storage device, the actuating mechanism of near-field probe is essentially designed. In this paper, we suggest the slider similar with conventional HDDs and design the slider using near- field probe for the purpose of applying the slider in order to control gap between probe and media. The most important object of slider design is to guarantee the flying ability and stability. For achievement of these design objects, we perform two step of optimal design process. The media is mod! eled as random displacement, which is only considered roughness of disk surface. The design slider is analyzed with dynamic state in assumed media. At this process, the optimal model is confirmed to stable flying stability.

• Transactions of the Society of Information Storage Systems
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• v.2 no.1
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• pp.65-70
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• 2006

In the information storage development, the trend of the storage device is to increase the recording density. Among such an effort, near-field probe recording is spotlighted as a method of high increasing recording density. For the successfully embodiment of storage device, the actuating mechanism of near-field probe is essentially designed. In this paper, we suggest the slider similar with conventional HDD and design the slider using near-field probe for the purpose of applying the slider in order to control gap between probe and media. The most important object of slider design is to guarantee the flying ability and stability. For achievement of these design objects, we perform two step of optimal design process. The media is supposed to model as random displacement, which is only considered roughness of disk surface. The design slider is analyzed with dynamic state in assumed media. At this process, the optimal model is confirmed to stable flying stability.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.9
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• pp.768-773
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• 2005

A new approach for human foot modelling and last design based on the cross sectional method is presented in this paper. The proposed last design method utilizes the dynamic trimmed parametric patches for the foot 3D data and last 3D data. The cross section a surface of 3D foot for the 3D last, design modeling of free form geometric last shapes. The proposed last design scheme wraps the 3D last data surrounding the measured 3D foot data with the effect of deforming the last design rule The last design rule of the FFD is constructed on the FFD lattice based on foot-last shape analysis. In addition, the control points of FFD lattice are constructed with cross sectional data interpolation methods from the a finite set of 3D foot data. The deformed 3D last result obtained from the proposed FFD is saved as a 3D dxf foot data. The experimental results demonstrate that the last designed with the proposed scheme has good performance.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.2
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• pp.203-212
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• 2002

Active magnetic hearings allow much high surface speed than conventional ball bearings and therefore greatly suitable for high speed cutting. This paper describes a design and test of an active magnetic bearing system with 16-pole radial magnets. The spindle is originally designed for a CNC lathe and driven by outer motor with 5.5 kW power and maximum speed 10,000 rpm. Considering static load condition and geometric restrictions, radial magnet is designed 16-pole type for smaller outer diameter of the spindle system. Dynamic system characteristics such as natural frequency, critical speed, stiffness, damping and system stabilities are simulated with a rigid rotor model including direct feedback controller. The designed spindle system is realized with digital PIDD controller to compensate phase lag of PWM amplifier and magnet coils. With levitation and step response experiment the control system characteristics are tested, and the spindle is rotated up to 10,000 rpm stab1y.

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.171-179
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• 2003

In this paper a neural network-based fault tolerant control system for aircraft sensor and actuator failures is considered. By exploiting flight dynamic relations a set of neural networks is constructed to detect sensor failure and give alternative signal for the faulty sensor. For actuator failures another set of neural networks is designed to perform fault detection, identification, and accomodation which returns the aircraft to a new stable trim. Integrated system is simulated to show the performance of the system with sensor and control surface failures.

• Journal of the Korean Institute of Intelligent Systems
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• v.22 no.2
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• pp.174-180
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• 2012

This paper proposes a decentralized adaptive output-feedback controller design for nonlinear interconnected systems with unknown time delays. The interaction terms with unknown delays are related to all states of subsystems. The time-delayed functions are compensated by using appropriate Lyapunov-Krasovskii functionals and function approximation technique. The observer dynamic surface design technique is employed to design the proposed memoryless local controller for each subsystem. In addition, we prove that all signals in the closed-loop system are semiglobally uniformly bounded and control errors converge to an adjustable neighborhood of the origin.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.16-22
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• 2004

Unsteady vortex shedding behind a rectangular cylinder near a wall influences both increasing of drag and dynamic stability of heavy vehicle, bridge or building. Incompressible Averaged Navier-Stokes equation with modified ${\varepsilon}-SST$ turbulence model is adapted for investigating the flow field between the rectangular cylinder and the wall. In case the vortex shedding happens, not only the averaged maximum velocity is higher than other cases, but the position of the maximum velocity is closer to the lower surface of rectangular cylinder. On this study, it is confirmed that the vortex shedding behind a rectangular cylinder can be suppressed by the passive control method added by horizontal and vertical fences to the lower surface of rectangular cylinder.

• Physical Therapy Korea
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• v.9 no.2
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• pp.1-17
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• 2002

The purpose of this study was to identify the differences of the static and the dynamic balance reactions in the flexion syndrome (FS) and the extension syndrome (ES) group of the patients with chronic lowback pain (LBP) and healthy subjects. Twenty subjects were included in each group. By using EquiTest 5.02, the static balance was measured by the equilibrium score and the strategy score of sensory organization test (SOT), while the dynamic balance was measured by the latency of motor control test (MCT) and the sway energy of adaptation test (ADT). Oswestry Disability Index (OSI) was used to measure level of the disability in patients with chronic LBP. The equilibrium scores, the strategies of SOT, and thelatencies of MCT of three groups were compared with one way ANOVA, while the sway energy of ADT was compared with repeated measures one way ANOVA. The results of this study showed that the equilibrium scores and the strategy scores of SOT were significantly lower in patients with chronic LBP than in healthy subjects. The equilibrium scores and the strategy scores of SOT were significantly differences between the FS and ES groups in condition 5 (support surface was sway-referenced and visual information waseliminated by eye closure), and 6 (support surface was sway-referenced and visual information was altered by sway-referencing). The FS group showed delayed average reaction time at large posterior translation, however, the ES group showed delayed average reaction time at large anterior translation, Even though the sway energy of the patients with chronic LBP were greater than that of healthy subjects during the toe down (plantar flexion rotation), the values between the FS and ES groups didn't show any significant difference. The disability level showed highly correlation with the equilibrium score of the condition 5. As the results, the FS and ES groups divided by the their symptoms and signs in patients with chronic LBP showed different balance reaction. Therefore, more accurate evaluation and balance treatments are needed to focus on their symptoms and signs in patients with chronic LBP.