• 연구논문집
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• s.28
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• pp.73-87
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• 1998

A pneumatic control system of compressed air as a working fluid has a variety of advantages such as low price, high respondence, non-explosion and good control performance and thus has many applications in the field of automobile, electronic and semiconductor industry. However, it has a difficulty in contolling a precise position due to quick response of system and compressibility of working fluid and. in particular, shock stress may occur due to an external load, resulting in fracture of a cylinder cap unless cushion device is equipped in the linear actuator. To avoid this, a cushion device should be installed for damping effect of the external load and the supply pressure as well as for decreasing shock stress and vibration caused by high speed rotation. Previous studies include dimensionless analyses and computer simulations of cushion capability and experiments of horizontally-mounted cylinder performances. A new attempt is experimentally made in this study using a vertically-mounted cylinder under an operation condition of 4, 5 and 6 (bar) as supply pressure and 40, 70 and 100 (kgf) as external load. It turns out that the cushion pressure is mainly a function of the external load rather than the supply pressure. The cushion characteristics was also revealed in the meter-in circuit.

• Land and Housing Review
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• v.10 no.3
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• pp.33-41
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• 2019

This study examines the distributions of daylight illuminance in a small office space under clear and cloudy sky conditions. Three shading conditions using Venetian blinds were applied for the analysis of daylight illuminance. Computer simulations using the Lightscacpe were conducted for the daylight conditions applied to the office space. Results indicate that the illuminance differences between clear and cloudy sky for south-facing conditions were greater than those for north-facing conditions. The differences in December and June were the greatest and smallest, respectively. For the north-facing conditions, the daylight illuminance at 10:00, 12:00 and 14:00 in June and September under the cloudy sky was higher than those under the clear sky conditions. For all daylight conditions, the biggest amount of illuminance reduction occurred when the shading device conditions were changed from the no blind to the 45 degree blinds. As the distance from window increased, the shading effect that occurred when the shading device conditions were changed from the horizontal blind to the 45 degree blinds increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.9
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• pp.737-740
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• 2009

SiC power device possesses attractive features, such as high breakdown voltage, high-speed switching capability, and high temperature operation. In general, device design has a significant effect on the switching characteristics, In this paper, we demonstrated that the switching performance of DMOSFETs are dependent on the with Channel length ($L_{channel}$) and Current Spreading Layer thickness ($T_{CSL}$) by using 2-D Mixed-mode simulations. The 4H-SiC DMOSFETs with a JFET region designed to block 800 V were optimized for minimum loss by adjusting the parameters of the JFET region, CSL, and epilayer. It is found that improvement of switching speed in 4H-SiC DMOSFETs is essential to reduce the gate-source capacitance and channel resistance. Therefore, accurate modeling of the operating conditions are essential for the optimizatin of superior switching performance.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.11
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• pp.785-789
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• 2013

Silicon Carbide (SiC) is the material with the wide band-gap (3.26 eV), high critical electric field (~2.3 MV/cm), and high bulk electron mobility (~900 $cm^2/Vs$). These electronic properties allow attractive features, such as high breakdown voltage, high-speed switching capability, and high temperature operation compared to Si devices. In general, device design has a significant effect on the switching and electrical characteristics. It is known that in this paper, we demonstrated that the switching performance and breakdown voltage of IGBT is dependent with doping concentration of p-base region and drift layer by using 2-D simulations. As a result, electrical characteristics of SiC-IGBT deivce is higher breakdown voltage ($V_B$= 1,600 V), lower on-resistance ($R_{on}$= 0.43 $m{\Omega}{\cdot}cm^2$) than Si-IGBT. Also, we determined that processing time and cost is reduced by the depth of n-drift region of IGBT was reduced.

• Journal of IKEEE
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• v.19 no.2
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• pp.210-218
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• 2015

In this paper an auto-switching energy harvesting circuit using vibration and thermoelectric energy is proposed. Since the maximum power point of a thermoelectric generator(TEG) output and a vibration device(PEG) output is 1/2 of their open-circuit voltage, an identical MPPT controller can be used for both energy sources. The proposed circuit monitors the outputs of the TEG and PEG, and chooses the energy source generating a higher output voltage using an auto-switching controller, and then harvests the maximum power from the selected device using the MPPT controller. The proposed circuit is designed in a $0.35{\mu}m$ CMOS process and its functionality has been verified through extensive simulations. The designed chip occupies $1.4mm{\times}1.2mm$ including pads.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2171-2175
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• 2011

The objective of this paper is to discuss technologies on assessing reliability of arc detectors by composing a system that generates and simulates occurrence of arc caused by loss of contact between pantographs and contact wires in a laboratory condition. In order to establish the arc simulator, a device that generates light having the bandwidth of arcs that occur between carbon-metal. The simulator was designed under conditions of EN 50317 and simulations were conducted using the developed device. According to the results, it was possible to conduct certification tests following regulations of international standards and the precision of the simulator was satisfactory. The proposed arc detector assessment system is expected to enhance precision of current collection quality performance assessment methods at high-speed lines and conventional lines while being referred as fundamental technologies for development of detectors suiting international conditions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.2
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• pp.514-535
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• 2019

Information-centric networks operate under the assumption that all network components have built-in caching capabilities. Integrating the caching strategies of information centric networking (ICN) with wireless virtualization improves the gain of virtual infrastructure content caching. In this paper, we propose a framework for software-defined information centric virtualized wireless device-to-device (D2D) networks. Enabling D2D communications in virtualized ICN increases the spectral efficiency due to reuse and proximity gains while the software-defined network (SDN) as a platform also simplifies the computational overhead. In this framework, we propose a joint virtual resource and cache allocation solution for latency-sensitive applications in the next-generation cellular networks. As the formulated problem is NP-hard, we design low-complexity heuristic algorithms which are intuitive and efficient. In our proposed framework, different services can share a pool of infrastructure items. We evaluate our proposed framework and algorithm through extensive simulations. The results demonstrate significant improvements in terms of visiting latency, end user QoE, InP resource utilization and MVNO utility gain.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.4
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• pp.49-56
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• 2021

This paper describes the modeling and simulation of a four-axis dedicated robot that can attach and detach a workpiece on a computer numerical control (CNC) lathe. The robot was modeled as a Scarab robot for compatibility with CNC lathes. The advantages of such a robot are that an actuator with a small capacity can be used for the robot and the degrees of freedom of the robot can be reduced to four. For the simulation of the four-axis dedicated robot, a regular kinematic equation and an inverse kinematic equation were derived. Simulations were performed with these equations from the position of the loading device to the chuck position of the lathe before machining and from the chuck of the lathe to the position of the loading device after machining. The simulation results showed that the four-axis dedicated robot could be operated accurately, and they provided the joint angle of each motor (θ1, θ2, and θ3).

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.3
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• pp.205-213
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• 2021

Due to the advantage of reducing the voltage applied to the switch semiconductor, the input series and output parallel combination is widely used in systems with high input voltage and large output current. On the other hand, the LLC converter is widely used as a high-efficiency power converter, and when connected by ISOP combination, there is a possibility that input voltage imbalance may occur due to a mismatch of passive devices. To avoid damaging the switching device, this study analyzed the DC-link voltage imbalance of a high-capacity supply using an ISOP LLC converter. In addition, the case where DC-link unbalance control was applied and the case not applied was analyzed respectively. Based on this analysis, an initial start-up algorithm was proposed to prevent input power semiconductor device damage due to DC-link over-voltage. The effectiveness of the proposed algorithm has been verified through simulations and experiments.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.364-368
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• 2021

We developed a highly efficient organic photovoltaic (OPV) cell with a poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)]:[6,6]-phenyl-C71-butyric acid methyl ester active layer for harvesting lower-intensity indoor light energy to power various self-powered sensor systems that require power in the microwatt range. In order to achieve higher power conversion efficiency (PCE), we first optimized the thickness of the active layer of the OPV cell through optical simulations. Next, we fabricated an OPV cell with optimized active layer thickness. The device exhibited a PCE of 12.23%, open circuit voltage of 0.66 V, short-circuit current density of 97.7 ㎂/cm², and fill factor of 60.53%. Furthermore, the device showed a maximum power density of 45 ㎼/cm², which is suitable for powering a low-power (microwatt range) sensor system.