• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제32권6호
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• pp.507-511
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• 2019

The purpose of an electric railway system contact wire is to supply electric energy to trains through a contacted pantograph. This energy is then converted into mechanical energy. Recent developments in overhead contact lines include the increase in the tension force up to 34 kN according to train speeds that reach up to 400 km/h with a verified safety. Rigid conductor catenary (R-Bar) for high speeds of up to 250 km/h have been developed in tunnels to save on construction costs. This is significant because minor defects in R-bars in aspects, such as height and stagger affect installation conditions. In this study, we propose the use of a detector that measures the static characteristics to reduce the R-bar installation errors. This detector has been developed to measure the height and stagger of the contact wire using video images.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제19권12호
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• pp.80-86
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• 2020

With the exception of welding activities, it is forbidden to use electricity in shipyards, owing to safety concerns such as the possibility of fire, explosions, and short circuits. In this paper, an automatic chamfering machine using pneumatics is proposed for use in such environments. Customers specify their requirements and the machine derives the corresponding theoretical design conditions. The proposed machine was used to perform 3D modeling, and its suitability and performance were confirmed via cutting experiments of the manufactured device. Two types of sensors may be used in this system: contact and non-contact. In the case of the contact type, an end-stop switch that can recognize the end of the material is installed, and when the machine reaches the end of the material, the end-stop switch is operated to cut off the air pressure. In the non-contact type, four sensors were used: photonic, ultrasonic, metal detection, and encoder. The use of the four sensors was repeated 30 times, and the average error determined. Thus, the optimum sensor was identified.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.480-480
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• 2008

Vacuum circuit breaker(VCB) is now emerging as an alternative of gas circuit breaker(GCB) which uses SF6 gas as insulating material whose dielectric strength is outstanding. But we have to reduce SF6 gas because SF6 gas is one of greenhouse gas and efforts to reduce greenhouse gas are now trend of the world. Therefore, we can say VCB is the optimal alternative of GCB because vacuum is environmentally friendly. The vacuum interrupter is the core part of VCB to interrupt arcing current. There are mainly two methods to extinguish arc. One is radial magnetic field (RMF) method and the other is axial magnetic field (AMF) method. We deals with RMF method in this paper. Compared with AMP, RMF arc quenching method has different principle to extinguish arc. In case of RMF method, pinch effect is much larger than AMF method. Because of pinch effect RMF type contact electrodes have the single large spot which is severly damaged and melted while AMF type contact electrodes have small and multiple spots which are slightly damaged and melted. To prevent contact electrode being damaged and melted from high temperature-arc, RMF method uses Lorentz force to move arc. In this paper we calculated and compared the arc driving force of two cases and we analyzed the force acting on each part of arc by means of commercial finite element method software Maxwell 3D. They have 3petals and we considered two cases. One is the case when fixed(upper) and movable(lower) contacts are in mirror arrangement (Case 1). The other is the case when one of two contacts (movable contact) is revolved at maximum angle as possible as it can be (Case 2). And at each case above, we analyzed arc driving force at two positions, position 1 is the closest to the center of contact and position 2 is near the edge of petal on fixed contact. As a result we could find that Case 2 generated stronger arc driving force than Case 1 at position 1. But at position 2 Case 1 generated stronger arc driving force than Case 2. This simulation method can contribute to optimizing spiral-type electrode designs in a view of arc driving force.

• Tribology and Lubricants
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• 제35권1호
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• pp.16-23
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• 2019

In this study, we aim to analyze the effects of both contact layer properties and surface roughness on contact resistance. The contact has a great influence on performance in terms of electrical conduction and heat transfer. The two biggest factors determining contact resistance are the presence of surface roughness and the surface layer. For this reason we calculated the contact resistance by considering both factors simultaneously. The model of this study to calculate contact resistance is as follows. First, the three representative surface parameters for the GW model are obtained by Nayak's random process. Then, the apparent contact area, real contact area, and contact number of asperities are calculated using the GW model with the surface parameters. The contact resistance of a single surface layer is calculated using Mikic's constriction equation. The total contact resistance is approximated by the parallel connection between the same asperity contact resistances. The results of this study are as follows. The appropriate thickness with reduction effect for contact resistance is determined according to the difference in conductivity between the base layer and surface layer. It was confirmed that the standard deviation of surface roughness has the greatest influence on surface roughness parameters. The results of this study will be useful for selecting the surface material and surface roughness when the design considering the contact resistance is needed.

• Tribology and Lubricants
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• 제22권3호
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• pp.137-143
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• 2006

The sliding contact interface of machine components such as bearings, gears frequently operates in lubrication at the inception of sliding failure under high loads, speed and slip. The surface temperature at the interface of bodies in a sliding contact is one of the most important factors influencing the behavior of machine components. Most surface failure in sliding contact region result from frictional heat generation. However, it is difficult to measure temperature rise experimentally. So the calculation of the surface temperature at a sliding contact interface has long been an interesting and important subject for tribologist. The surface temperature rise is related in contact pressure, sliding speed, material properties and lubrication thickness. Though roughness, load, ect all of the condition, are same, film thickness varies with velocity. In this study, surface temperature rise due to frictional heating in lubrication is calculated with various velocities. Surface film shearing and dry solid asperity contact are used to simulate the change of frictional heat in lubricated contact

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제22권2호
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• pp.310-317
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• 2013

In this paper, the contact pressure of the wafer and polishing pad for final polishing process for 300 mm-wafer were investigated through numerical analysis using FEM tool, ANSYS. The distribution of the contact pressure is one of main parameters which affects on the flatness and surface roughness of polished wafers. Two types of polishing head, a hard type head with ceramic disk and a soft type head with air bag were considered. The effects of the deformation and initial shape of table on the contact pressure were also examined. Both heads and tables were modeled as 3D finite element model from solid model, and the material properties of polishing pads and rubber plate for the air-bag head were obtained from tensile tests. The contact pressure deviation on wafer surface was smaller with air bag head than hard type head even when the table had form errors such as convex or concave. From this 3D analysis, it could be concluded that the air-bag head has better uniformity of the contact pressure on wafer. Also, the effects of inner diameter of air bag and radial clearance between wafer and retainer were investigated as view point of contact pressure concentration on the edge of wafer.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.662-665
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• 2008

We experimentally investigate the evaporation characteristics of water droplet on surfaces of various wettabilities in the range of contact angle from 30$^{circ}$ to 150$^{circ}$. When a liquid droplet on a solid surface evaporates, the contact angle generally decreases with time and the evaporation rate varies with the droplet geometry such as the contact angle and the radius of curvature. Experimental data on the contact angle as a function of the droplet volume obtained by digital image analysis techniques cannot be explained by the existing theories. By measuring the temporal evolutions of the droplet radius and contact angle, we find the qualitative difference between the evaporation patterns on the hydrophilic surfaces where the contact radius remains constant initially and those on the superhydrophobic surfaces where the contact angle remains constant. Also, the evaporation rate is observed to depend on the surface material although the currently available models assume that the rate is solely determined by the droplet geometry. Despite the fact that the theory to explain this dependence on the surface remains to be pursued by the future work, we give the empirical relations that can be used to predict the droplet volume evolution for each surface. It is expected that the present study will contribute to interpreting the effect of droplet geometry on the evaporation.

• Journal of Sensor Science and Technology
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• 제28권2호
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• pp.117-120
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• 2019

Graphene is recognized as a promising material for silicon photonics, since it has a wide optical-window that entirely covers the optical communication wavelength region ($1.3{\sim}1.6-{\mu}m$) and extremely high-carrier mobility that makes it possible to fabricate the high-speed photodetectors. However, the maximum absorbance of monolayer graphene is only 2.3%, which limits the photoresponse characteristics of graphene photodetectors. As a result, a low photoresponsivity of graphene photodetector is a critical issue limiting the use of graphene photodetectors in the optical communications field. In this paper, we investigated effects of optically-modulated metal-graphene contact on the photoresponsivity of graphene photodetectors. The optical modulation of the contact resistance mainly determined the photoresponse characteristics of graphene photodetectors. The Ni-contact graphene photodetector which has a characteristic of the significant optical modulation of metal-graphene contact showed a higher photoresponsivity than the Pd-contact device. This work will provide a way to improve the photoresponse characteristics of graphene-based photodetector and contribute to the development of high-speed/high-responsivity graphene photodetector.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.700-705
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• 2003

In this paper, an extended process model is proposed for the application of flexible belt grinding equipment as utilized in robotic grinding. The analytical and experimental results corresponding to grinding force, material removal rate (MRR) and contact area in the robotic grinding shows the difference between the conventional grinding and the flexible robotic grinding. The process model representing the relationship between the material removal and the normal force acting at the contact area has been applied to robotic programming and control. The application of the developed model in blade grinding demonstrates the effectiveness of proposed process model.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제25권9호
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• pp.732-737
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• 2012

This study made a specimen (contact surface size: $45\;mm{\times}0.02\;mm{\times}45{\sim}55\;mm$) with silicon rubber for low voltage cable with 50 phr silica filler. The electrification voltage of electrostatics were measured for different sizes of contact surface with the applied voltage of 10kV and the environmental settings of temperature ($25{\sim}40^{\circ}C$) and humidity (40~80%). The following conclusions were made. The electrification voltage of electrostatics decreased as the humidity increased. The electrification voltage of electrostatics increased as the temperature increased. The larger the surface size, the higher the electrification voltage of electrostatics. The property of the material had more effect on the relaxation time than the humidity.