• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.180-188
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• 2003

In the precision motion device, the frictional problem by mechanical friction causes serious effects on the system performance. Various researches have been executed to solve this problem, but classical fluid lubrication method has some disadvantages in precision motion under clean environment. Therefore, the magnetic bearing and contact-free systems have been focused on with its pollution-free characteristics. In this paper, we treat modeling and analysis of electromagnets not only for magnetic bearing but also fer contact-free electromagnetic actuators. Three types of electromagnet for various applications are modeled and analyzed by magnetic circuit theory and the validity is verified by experiments.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.91-98
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• 2003

In the field of precision manufacturing demanding high positioning performance, the mechanical friction in positioning device deteriorates the quality of the product and increases the cost of production for positioning devices. Therefore, we propose a contract-free linear actuator using active magnetic bearing. The structure and operating principle of the proposed system are explained, and the magnetic forces are analyzed by magnetic circuit theory to design magnetic bearings and linear actuator. With the derived equation of motion, the stability is identified. Experimental results are presented to show the feasibility.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.97.3-97
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• 2002

This paper presents the vibration characteristics of an intelligent cantilever beam in contact with a fluid using a PZT actuator and PVDF film. The dynamic behaviors of a flexible beam-water interaction system are examined. The effect of the liquid level on free vibration of the composite beam in a partially liquid-filled circular cylinder is investigated. The coupled system is subject to an undisturbed boundary condition in the fluid domain. It was found that the coupled natural frequencies decreased with the fluid level for the identical composite beam due to added mass effect. In case of the free-free boundary condition, the natural frequency gently decreased at fluid water level betw...

• International Journal of Precision Engineering and Manufacturing
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• v.7 no.4
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• pp.28-33
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• 2006

Various precision engineering studies have attempted to remove mechanical friction, which causes the performance of a system to deteriorate, from precision positioning devices. Since the classical fluid lubrication method has some disadvantages in clean environments, attention has been focused on magnetic bearings and contact-free systems with their pollution-free characteristics. In this paper, f electromagnets are modeled and analyzed, not only for magnetic bearings but also for contact-free electromagnetic actuators. Three types of electromagnets that are appropriate for various applications were considered using magnetic circuitry theory. The results were experimentally validated.

• Proceedings of the PSK Conference
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• 2003.10b
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• pp.236.1-236.1
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• 2003

Evaluation of solid surface properties is very important for formulation of solid dosage form, specially insoluble drugs. The contact angle of insoluble drugs was measured by the penetration rate into powder bed using Washburn equation and wicking method. From the measured contact angle data, the surface free energy value of pharmaceutical powders ${\gamma}$s was divided and analysized into the polar component, ${\gamma}$s$\^$p/ and the dispersion component, ${\gamma}$s$\^$d/. Furthermore, the data was interpreted for acid part, ${\gamma}$s$\^$+/ and base part, ${\gamma}$s$\^$$\square$/ of surface free energy. (omitted)

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.209.2-209.2
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• 2015

Two dimensional layered materials, such as transition metal dichalcogenides (TMDs) family have been attracted significant attention due to novel physical and chemical properties. Among them, molybdenum disulfide ($MoS_2$) has novel physical phenomena such as absence of dangling bonds, lack of inversion symmetry, valley degrees of freedom. Previous studies have shown that the interface of metal/$MoS_2$ contacts significantly affects device performance due to presence of a scalable Schottky barrier height at their interface, resulting voltage drops and restricting carrier injection. In this study, we report a new device structure by using few-layer graphene as the bottom interconnections, in order to offer Schottky barrier free contact to bi-layer $MoS_2$. The fabrication of process start with mechanically exfoliates bulk graphite that served as the source/drain electrodes. The semiconducting $MoS_2$ flake was deposited onto a $SiO_2$ (280 nm-thick)/Si substrate in which graphene electrodes were pre-deposited. To evaluate the barrier height of contact, we employed thermionic-emission theory to describe our experimental findings. We demonstrate that, the Schottky barrier height dramatically decreases from 300 to 0 meV as function of gate voltages, and further becomes negative values. Our findings suggested that, few-layer graphene could be able to realize ohmic contact and to provide new opportunities in ohmic formations.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.272-279
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• 2001

The objective of this paper is the investigation of the relationships between the surface roughness and film evaporative characteristics of the surface. For example, when the droplet of liquid is in contact with the solid surface, its behavior strongly depends on the surface characteristics. The material properties and geometry - profile shape, waviness, roughness - of the surfaces have strongly influenced on the wettability of the droplet. To investigate the effect of the surface roughness on the film evaporation, firstly, the characteristics of wettabilities were studied according to contact angle and surface tree energy of specimens with various roughness heights. Secondly, the experimental test were carried out on capacities of the tubes diversly roughened by using different kinds of emery papers. Finally, the relationships between the film evaporation characteristics and surface roughness were explained by means of the correlation of contact angle and surface free energy with surface roughness and the influences of surface tree energy on the heat transfer performance.

• Structural Engineering and Mechanics
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• v.30 no.1
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• pp.21-36
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• 2008

The static response of a finite beam resting on a tensionless Pasternak foundation and subjected to a concentrated vertical load is assessed in this study. The concentrated vertical load may be applied at the center of the beam, or it may be offset from the center. The tensionless character of the foundation results in the creation of lift-off regions between the beam and the foundation. An analytical/ numerical solution is obtained from the governing equations of the contact and lift-off regions to determine the extent of the contact region. Although there is no nonlinear term in the equations, the problem shows a nonlinear character since the contact region is not known in advance. Due to that nonlinearity, the essentials of the problem (the coordinates of the lift-off points) are calculated numerically using the Newton-Raphson technique. The numerical results are presented in figures to illustrate the behaviours of the free-free and pinned-pinned beams under symmetric or asymmetric loading. The figures illustrate the effects of the shear foundation parameter and the symmetric and asymmetric loading options on the variation of the contact lengths and the displacement of the beam.

• Transactions of Materials Processing
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• v.24 no.3
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• pp.199-204
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• 2015

Electromagnetic Forming is a high speed forming technology which uses electromagnetic (Lorentz’s) forces to shape sheet metal parts. In the current study the effect of the tool-sheet interaction during electromagnetic forming on formability enhancement is investigated using FEM. The decrease in void volume fraction by having the sheet contact with die helps to improve formability. The main purpose of the current study was to predict improvement of formed sheets whether the sheet contacts or does not contact the die under experimental conditions and 3-D finite element analysis. The results show that fractures caused by the voids in the forming sheet appear only in some specific cases and the bulge height of the conical shape was shorter than the height with a free bulge. For the same height conditions, however, the formability was improved for the conical-shaped die when there is sheet contact with the die.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1078-1081
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• 2004

A robot manipulator is usually operated in two modes: free motion and constraint motion depending on whether the robot comes into contact with the environment or not. At the moment of contact, impact occurs, and sometimes, it possibly degrade the robot's performance by vibration and at worst, shortens its lifetime. In this article, a new proposed algorithm is described by introducing a command signal modification method on the basis of impedance control and a validity of the proposed algorithm is demonstrated by showing a simulation and an experiment.