• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.498-501
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• 2000

Air dynamic bearings are inherently unstable in dynamic behavior due to the varying angle of a force produced and the nonlinear characteristics of stiffness. In this study, such dynamic behavior is obtained and compared with experimental results. A body axis coordinate system is employed to avoid the change of a moment of inertia. FDM is used to calculate the pressure distribution on the bearing surface and then the force acting on the rotor was calculated by integrating the pressure distribution. By integrating accelerations which are calculated from the equations of motion using the 4th order Runge-Kutta method, the pose of the bearing at each time step is obtained.

• 한국정밀공학회지
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• 제15권5호
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• pp.137-144
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• 1998

A mathematical model for investigating the form generation mechanism in the centerless thrufeed grinding process is described. The length of the contact line and the magnitude of the grinding force between the grinding wheel and workpieces vary with the change of the axial location of the current workpiece during grinding. Thus, a new coordinate system and a grinding force curve of previous and/or following workpieces are introduced to treat the axial motion. Experiments and computer simulations were carried out using three types of cylindrical workpiece shapes. To validate this model. simulation results are compared with the experimental results.

• 한국정밀공학회지
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• 제8권4호
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• pp.107-117
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• 1991

The dynamic stability problem of nonconservative system is one of the important problems. In this study, flexible missile with mass variation is regarded as a free Timoshenko beam subjected to a controlled follower force. The stability was studied numerically through the finite element method. Through the study, the obtained results are as follows: [1] Without force direction control (1) In the case of no mass reduction, the existence of concentrated mass increases critical follower force. (2) Mass reduction rate of the beam slightly effects on the change of critical follower force. [2] With force direction control (1) Shear deformation parameter S contributes insignificantly to the force at instability when $S{\geq}10^4$. (2) With mass variation, increase of concentrated mass increases critical follower force at instbility. (3) The type of promary instability is determined by the sensor location.

• 대한기계학회논문집B
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• 제20권2호
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• pp.641-648
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• 1996

Thermophoretic particle deposition on a circular cylinder in a uniform laminar air flow was numerically investigated using a control volume method based on the generalized non-orthogonal coordinate system. Variation of air properties due to the change of temperature was taken into account. Effects of variable property on the distribution of heat transfer and deposition rates of particle were discussed. A new correlation of thermophoretic particle deposition on a circular cylinder was proposed in the present study.

• Ocean and Polar Research
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• 제23권2호
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• pp.161-172
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• 2001

A model-to-model comparison is attempted between Princeton Ocean Model (POM) and Miami Isopycnic Coordinate Ocean Model (MICOM) as a first step to extend our knowledge of models' performances in studying the East Sea circulation. The two models have fundamentally different numerical schemes and boundary conditions imposed on these models are not exactly the same each other. This study indicates that MICOM has a critical weak point in that it does not reproduce the shallow surface currents properly while it handles the thermohaline processes and associated movements of intermediate and deep waters efficiently. It is suggested that the mixed layer scheme needs to be modified so that it can match with inflow boundary conditions in order to reproduce the surface currents properly in MICOM. POM reproduces the surface current pattern better than MICOM, although the surface currents in POM appear to undergo the unrealistic seasonal variation and have exaggeratedly large vertical scale. These defects seem to arise during the process of adapting POM to the East Sea, and removing these defects is left as a future task.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 1998년도 Proceedings of International Symposium on Remote Sensing
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• pp.116-121
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• 1998

Global land related datasets such as land use, land cover, vegetation cover percentage, forest cover percentage, are part of important global geospatial environmental datasets for global change studies. Since land cover varies place by place, continental production of dataset is a usual approach. Western academically developed countries have some projects to describe land cover related information in digital form using remote sensing technology in African, American continent and Oceania. In this paper, the author introduce his initiative to coordinate Asian scientists in order to develop land related dataset of Asia for our better understanding of the environment of Asia and for contribution to the development of global dataset. This paper explains activities by Land Cover Working Group (LCWG) of the Asian Association on Remote Sensing(AARS), Data and Information System(DIS) sub-committee of Japan national committee for the International Geosphere and Biosphere Program(IGBP), and the International Society for Photogrammetry and Remote Sensing(ISPRS) Working Group IV/6 on Global databases supporting environmental monitoring.

• 한국정밀공학회지
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• 제22권10호
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• pp.107-113
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• 2005

This paper presents a method to reduce errors in registration, which is used in transformation coordinate system of the multiple measuring data. In general, the ICP algorithms and feature-based approaches are used for registration. In order to measure wrap-around object, it is necessary to change the scanning direction or set-up of the object. A fixture is made to reduce registration errors caused by inaccurate center point of tooling balls, providing the more accurate registration method. And, the motorized fixture controls rotation and tilting to get precise the measuring data and registration. The proposed motorized fixture and registration method have advantages in accurate registration and precise measurement, compared with the conventional methods.

• 한국산업융합학회 논문집
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• 제17권3호
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• pp.184-193
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• 2014

Machine vision systems is applied for various industries such as optimize your spending, automate your production and maximize your efficiency. This research is effective for most optimal light condition of machine vision that technology was applied bald outside human visual acuity. Image processing converts a target image captured by a CCD camera into a digital signal and then performs various arithmetic operations on the signal to extract the characteristics of the target, such as points, lines, circles, area and length. The mathematical concepts of convolution and the kernel matrix are used to apply filters to signals, to perform functions such as extracting edges and reducing unwanted noise. This research analyze and compares matching ratio with reference image and search for optimal lighting condition in accuracy that user wants coming input image according to brightness change of lighting.

• Journal of Power Electronics
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• 제14권5호
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• pp.1028-1037
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• 2014

To optimize controller design and improve static and dynamic performances of three-phase four-leg inverter systems, a compound control method that combines state feedback and quasi-sliding mode variable structure control is proposed. The linear coordinate change matrix and the state variable feedback equations are derived based on the mathematical model of three-phase four-leg inverters. Based on system relative degrees, sliding surfaces and quasi-sliding mode controllers are designed for converted linear systems. This control method exhibits the advantages of both state feedback and sliding mode control. The proposed controllers provide flexible dynamic control response and excellent stable control performance with chattering suppression. The feasibility of the proposed strategy is verified by conducting simulations and experiments.

• 전자공학회논문지B
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• 제29B권10호
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• pp.59-68
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• 1992

In this paper, we proposed coordinator description and ambiguity on the hybrid controller for position/force control of robot manipulator. When the hybrid controller is desiged based on the PID control conception, the parameter sharing problem must be considered. However, selection problem of coordinate system on n-DOF robot manipulator control is unsolved. Moreover, contact force on object and change of shape make another problems. And it is very difficult to figure out the accurate mathematical model of manipulator on account of ambiguity and nonlinearity of actuator. Therfore, we design a new hybrid controller, FPID(Fuzzy PID). For verifying the validity of the controller, we tried computer simulation of this system. As a result, we can get remarkable improvement of overdamping and overshooting. Also we can solve compicance problem effectively. Furthermore, ambiguity problem is solved by adding control knowledge based compensator. So robust controller can be acheived, too.