• Proceedings of the KIPE Conference
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• 전력전자학회 2013년도 추계학술대회 논문집
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• pp.177-178
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• 2013

To implement servo system using LIM, thrust and normal force control must be made in a moment. Thus, vector control is required to control magnetic flux and toque. In this paper, we applied to constant slip frequency vector control method by controlling d-q axis current and presented various simulation results.

• Tribology and Lubricants
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• 제18권1호
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• pp.55-60
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• 2002

In many dynamic systems, there are unwanted oscillation which may arise the reduction of performance. Especially in low sliding speed condition, the stick-slip is an important issue because it because unstable motion as well as inaccurate position control in the system. Most previous works on the stick-slip are, however, only concerned with simple modeling under the condition of constant normal force. The normal force and the amount of hydraulic oil are variable with a cylinder stroke in the telescopic boom. This paper presents the pressure variations during stick-slip with the cylinder of telescope boom. Pressure variations by stick-slip has a similar pattern to that of single mass-spring model. The stick-slip is gradually decreased by means of increased flow rate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.59-62
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• 2005

Small force measurements ranging from 1 pN to $100{\mu}N$, we call it Nano Force, become the questions of common interests of biomechanics, nanomechanics, material researches, and so on. However, unfortunately, quantitative and accurate force measurements have not been taken so far. This is because there ,are no traceable force standards and a calibration scheme. This paper introduces a quantitative force metrology, which provides traceable link to SI (International Systems of Units). We realize SI traceable force ranging from 1 nN to $100{\mu}N$ using an electrostatic balance and disseminate it through transfer standards, which are self-sensing cantilevers that have integrated piezoresistive strain gages. We have been built a prototype electrostatic balance and Nano Force Calibrator (NFC), which is an AFM cantilever calibration system. As a first experiment, we calibrated normal spring constants of commercial AFM cantilevers using NFC. Calibration results show that the spring constants of them are quite differ from each other and nominal values provided by a manufacturer (up to 240% deviation).

• Tribology and Lubricants
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• 제18권1호
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• pp.1-8
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• 2002

Nano adhesion and friction between a $Si_{3}N_{4}$ AFM(atomic force microscope) tip and thin silver films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM and LFM(lateral force microscope) modes in various range of normal loads. Thin silver films deposited by IBAD (ion beam assisted deposition) on Si-wafer (100) and other Si-wafers of different surface roughness were used. Results showed that nano adhesion and friction decreased with the surface roughness. When the Si surfaces were coated by pure silver, the adhesion and friction decreased. But the adhesion and friction were not affected by the thickness of IBAD silver coating. As the normal force increased, the adhesion forces of bare Si-wafer and IBAD silver coating film remained constant, but the friction forces increased linearly. Test results suggested that the friction was mainly governed by the adhesion as long as the load was low.

• Wind and Structures
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• 제32권4호
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• pp.371-391
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• 2021

Tornadoes are the most devastating meteorological natural hazards. Many empirical and theoretical numerical models of tornado vortex have been proposed, because it is difficult to carry out direct measurements of tornado velocity components. However, most of existing numerical models fail to explain the physical structure of tornado vortices. The present paper proposes a new empirical numerical model for a tornado vortex, and its load effects on a low-rise and a tall building are calculated and compared with those for existing numerical models. The velocity components of the proposed model show clear variations with radius and height, showing good agreement with the results of field measurements, wind tunnel experiments and computational fluid dynamics. Normal stresses in the columns of a low-rise building obtained from the proposed model show intermediate values when compared with those obtained from existing numerical models. Local forces on a tall building show clear variation with height and the largest local forces show similar values to most existing numerical models. Local forces increase with increasing turbulence intensity and are found to depend mainly on reference velocity Uref and moving velocity Umov. However, they collapse to one curve for the same normalized velocity Uref / Umov. The effects of reference radius and reference height are found to be small. Resultant fluctuating force of generalized forces obtained from the modified Rankine model is considered to be larger than those obtained from the proposed model. Fluctuating force increases as the integral length scale increases for the modified Rankine model, while they remain almost constant regardless of the integral length scale for the proposed model.

• Transactions of the Korean Society of Mechanical Engineers
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• 제12권2호
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• pp.206-214
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• 1988

To improve the surface waviness in the peripheral milling, the feedrate is controlled so that the cutting force measured in the normal direction to the workpiece is constant. A discrete time first order model between the feedrate and the tool deflection is derived for the control. It has been shown by the analysis that the tool deflection is directly related to the feedrate and largely affects the surface waviness during cutting. The experimental results shown that the surface waviness is drastically improved by the proposed methods.

• Proceedings of the KSR Conference
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.1248-1253
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• 2005

The study is indispensable for the dynamic behaviors because this Cable-stayed long span bridge ; has a more flexible structure than normal bridge can have weaknesses which are impact factor, deflection and defectives etc. This study analyze the dynamic behavior by an analysis of the moving constant train force on railway with Midas/Civil that is a commercial finite element analysis tool about Extradosed PSC Bridge. Also it will be checked the dynamic behavior features and standard of the dynamic capability.

• Journal of the Institute of Electronics and Information Engineers
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• 제50권3호
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• pp.16-22
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• 2013

A general characterization procedure based on the extraction of a 2n-port admittance matrix corresponding to n uniform coupled lines on the multi-layered substrate using the Finite-Difference Time-Domain (FDTD) technique is presented. In this paper, the frequency-dependent normal mode parameters are obtained from the 2n-port admittance matrix to analyze multi-layered asymmetric coupled line structure, which in turn provides the frequency-dependent propagation constant, effective dielectric constant, and line-mode characteristic impedances. To illustrate the technique, several practical coupled line structures on multi-layered substrate have been simulated. Especially, embedded conductor structures have been simulated. Comparisons with Spectral Domain Method are given, and their results agree well. It is shown that the FDTD based time domain characterization procedure is an excellent broadband simulation tool for the design of multiconductor coupled lines on multilayered PCBs as well as thick or thin hybrid structures.

• Proceedings of the KIEE Conference
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• 대한전기학회 1991년도 하계학술대회 논문집
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• pp.641-644
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• 1991

Constant slip frequency operation of linear infliction motor is essential for the stable levitation. Control scheme for the constant slip frequency with general purpose frequency inverter is proposed, Speed sensing scheme with proximitity switch for the speed feedback is also proposed. Optimal slip frequency, at which normal force is equal to 0, is selected by the experiment. This slip frequency is a comand to the controller. It shows good characteristic during acceleration and deceleration.

• Korean Journal of Applied Biomechanics
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• 제27권2호
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• pp.117-124
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• 2017

Objective: The purpose of this study was to examine the effect of changes in degrees of freedom of the fingers (i.e., the number of the fingers involved in tasks) on the task performance during force production and releasing task. Method: Eight right-handed young men (age: $29.63{\pm}3.02yr$, height: $1.73{\pm}0.04m$, weight: $70.25{\pm}9.05kg$) participated in this study. The subjects were required to press the transducers with three combinations of fingers, including the index-middle (IM), index-middle-ring (IMR), and index-middle-ring-little (IMRL). During the trials, they were instructed to maintain a steady-state level of both normal and tangential forces within the first 5 sec. After the first 5 sec, the subjects were instructed to release the fingers on the transducers as quickly as possible at a self-selected manner within the next 5 sec, resulting in zero force at the end. Customized MATLAB codes (MathWorks Inc., Natick, MA, USA) were written for data analysis. The following variables were quantified: 1) finger force sharing pattern, 2) root mean square error (RMSE) of force to the target force in three axes at the aiming phase, 3) the time duration of the release phase (release time), and 4) the accuracy and precision indexes of the virtual firing position. Results: The RMSE was decreased with the number of fingers increased in both normal and tangential forces at the steady-state phase. The precision index was smaller (more precise) in the IMR condition than in the IM condition, while no significant difference in the accuracy index was observed between the conditions. In addition, no significant difference in release time was found between the conditions. Conclusion: The study provides evidence that the increased number of fingers resulted in better error compensation at the aiming phase and performed a more constant shooting (i.e., smaller precision index). However, the increased number of fingers did not affect the release time, which may influence the consistency of terminal performance. Thus, the number of fingers led to positive results for the current task.