• Journal of the Korean Society for Precision Engineering
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• v.21 no.11
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• pp.91-98
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• 2004

TFLIM(Transverse Flux Linear Induction Motor), making its closed magnetic path with the direction of the traveling field orthogonal, had been developed to decrease an edge effect of the general induction motor. To control the levitation force and the thrust force on the secondary part of TFLIM independently, the various methodologies have been presented. When we try to achieve the independent control using only the multi-phase inputs assigned in the stator coils as an approach, in which condition we can minimize the coupling effect between two forces\ulcorner In this paper, we show the qualitative influence of a slip frequency, an ac magnitude, a dc offset superposed in the ac power, and a major parameter of TFLIM on the couple through the computer simulation. And to realize the independent motions between levitation and thrust motion without any auxiliary means fur isolation of the secondary part of TFLIM, the decouple compensator is suggested, including the experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.3 s.96
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• pp.72-77
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• 1999

This paper presents 2-dimensional vibration cutting increases dynamic stiffness of tool support and improves the quality of machined surface in micro-machining. 2-dimensional vibration cutting is generated by two piezo actuators arranged orthogonally. A sine-type voltage is input to one actuator and a phase-shifted sine-type voltage is input the other. Then the vibration device actuates the tool in a 2-D elliptical motion with pulsed cutting force. It is a characteristic of 2-D vibration cutting that some negative thrust force occurs as the direction of friction on a tool rake surface is reversed. It helps not only chip flow smoothly and continuously but also cutting force be reduced. The quality of machined surface by 2-D vibration cutting depends on such parameters as vibration amplitude, frequency, cutting speed, depth of cut, etc. Compared to conventional cutting through tool path simulation and experiments under several conditions, the 2-D vibration cutting is verified to bring forth a great decrease of cutting forces, much better surface roughness and moreover much less burr.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.12
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• pp.986-993
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• 2002

The equations of motion for an automated guide-way transit(AGT) system running on a path with roughness have been derived to investigate dynamic responses and wheel loads of moving vehicles of the AGT system. A vehicle of the AGT system is idealized as three-dimensional model with 11 degree-of-freedom. The computer program is developed to solve the dynamic equations, and anlatical results are verified by comparing the results with experimental oness. Parametric studies are carried out to investigate the dynamic responses of an AGT vehicle according to vehicle speeds, surface roughness, damping and stiffness of suspension systems. The parametric study demonstrates that amplitudes of dynamic responses and the wheel loads have a tendency to increase according to travel speeds, the stiffness of suspension system and surface roughness. On the other hand. those amplitudes tend to decrease according to increase of damping of the suspension system.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.70-77
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• 2006

Stress drops of Brune's single-corner ${\omega}^2$ source model were estimated for the earthquakes (2.0$M3.5{\sim}4.0$ and increase up to $M4.5{\sim}5.0$ above which the level of the stress drop could be assumed to be flat or decrease according to whether the rupture process accompanies buried fault or surface rupturing. The converted data of corner frequency and seismic moment were nicely fitted to the relation of $M_0{\propto}f^3$ but show systematically higher corner frequencies for $M_0>10^15$ Nm. This relationship enables systematic evaluation of a scaling relation between magnitude and stress drop. The inverted level of the stress drop is comparable to the recent studies conducted domestic and abroad. A result of lower stress drop estimated by Jun(1991) is supposed to be due to the use of low frequency spectra and existence of two-comer source model around the Korean Peninsula.

• Advances in nano research
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• v.8 no.1
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• pp.25-36
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• 2020

Rotating systems concern with torsional vibration, and it should be considered in vibration analysis. To do this, the time-dependent torsional vibrations in a single-walled carbon nanotube (SWCNT) under the linear and harmonic external torque, are investigated in this paper. Eringen's nonlocal elasticity theory is considered to demonstrate the nonlocality and constitutive relations. Hamilton's principle is established to derive the governing equation of motion and consequently related boundary conditions. An analytical method, called the Galerkin method, is utilized to discretize the driven differential equations. Linear and harmonic torsional loads, along with determined amplitude, are applied to the SWCNT as the external torques. SWCNT is considered under the clamped-clamped end supports. In free vibration, analysis of small scale effect reveals the capability of natural frequencies in different modes, and this results desirably are in coincidence with another study. The forced torsional vibration in the time domain, especially for carbon nanotubes, has not been done before in the previous works. The previous forced studies were devoted to the transverse vibrations. It should be emphasized that the dynamical analysis of torsion is novel, workable, and at the beginning of the path. The variations of nonlocal parameter, CNT's thickness, and the influence of excitation frequency on time-dependent angular displacement and nondimensional angular displacement are investigated in the context.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.59-69
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• 2019

This paper focuses on the numerical simulation of ice abrasion induced by unbreakable ice floe. Under the assumption that unbreakable floes behave as rigid body, the Discrete Element Method (DEM) was applied to simulate the interaction between a fixed structure and ice floes. DEM is a numerical technique which is eligible for computing the motion and effect of a large number of particles. In DEM simulation, individual ice floe was treated as single rigid element which interacts with each other following the given interaction rules. Interactions between the ice floes and structure were defined by soft contact and viscous Coulomb friction laws. To derive the details of the interactions in terms of interaction parameters, the Finite Element Method (FEM) was employed. An abrasion process between a structure and an ice floe was simulated by FEM, and the parameters in DEM such as contact stiffness, contact damping coefficient, etc. were calibrated based on the FEM result. Resultantly, contact length and contact path length, which are the most important factors in ice abrasion prediction, were calculated from both DEM and FEM and compared with each other. The results showed good correspondence between the two results, providing superior numerical efficiency of DEM.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.12
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• pp.98-104
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• 2020

In this work, a study on the 5-axis machining of ball gear cam is conducted which is a continuation of reference [1]. The ball gear cam used in this study delivers motion in conjunction with the ball supported by the turret. Therefore, it requires carbonizing heat treatment and is usually completed using a 4-axis machining with a carbide ball end mill. If the nose part of the ball end mill is not allowed to participate in the machining, then CBN tools without the nose part can be used. However, machining of certain shapes can be carried out only by contacting the ball in some of the areas on either side which can improve the surface of the machining. This requires a 5-axis machining in order to maintain a constant angle for the processing path. Therefore, in this work, the 5-axis machining method is studied in order to maintain the direction of the cutter axis at a constant angle with the tangent direction of the curve-ball gear cam. Furthermore, the 5-axis machining program for the ball gear cam was developed and the machining experiment was completed and verified.

• Korean Journal of Applied Biomechanics
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• v.32 no.4
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• pp.147-152
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• 2022

Objective: The purpose of this study was to analyze the effects of club head and golf ball kinematics and body alignment according to the swing plane during golf driver swing. Method: Sixteen college golfers participated in this study. Kinematic data of the club head and golf ball were collected using golf swing analysis system (Trackman Ver. 3e). The body alignment variables were collected using 8 motion capture system. An Independent samples t-test was used for comparison between the Out-to-In group and In-to-Out group, and the statistical significance level was set at .05. Results: For the club head related variables, club path and club face angle showed higher values in Out-to-In swing plane than In-to-Out swing plane. For the kinematic variables of the golf ball, the total distance showed a higher value in the In-to-Out swing plane than that of the Out-to-In swing plane. For the body alignment, the In-to-Out swing plane showed higher values than the Out-to-In swing plane for the pelvis rotation angle and trunk rotation angle. Conclusion: This study suggest that it would be more effective to use the In-to-Out swing plane for increasing the total distance during the golf driver swing.

• The Journal of Korea Robotics Society
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• v.16 no.4
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• pp.327-335
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• 2021

In this paper, we propose an embedded robot system based on "ROS2 on Yocto" that can support various robots. We developed a lightweight OS based on the Yocto Project as a next-generation robot platform targeting cloud robotics. Yocto Project was adopted for portability and scalability in both software and hardware, and ROS2 was adopted and optimized considering a low specification embedded hardware system. We developed SLAM, navigation, path planning, and motion for the proposed robot system validation. For verification of software packages, we applied it to home cleaning robot and indoor delivery robot that were already commercialized by LG Electronics and verified they can do autonomous driving, obstacle recognition, and avoidance driving. Memory usage and network I/O have been improved by applying the binary launch method based on shell and mmap application as opposed to the conventional Python method. Finally, we verified the possibility of mass production and commercialization of the proposed system through performance evaluation from CPU and memory perspective.

• The Journal of Korea Robotics Society
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• v.17 no.4
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• pp.417-424
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• 2022

In this paper, the developed trunk cargo unloading automation system is introduced, and the RGB-D sensor-based box loading situation recognition method and unloading plan applied to this system are suggested. First of all, it is necessary to recognize the position of the box in a truck. To do this, we first apply CNN-based YOLO, which can recognize objects in RGB images in real-time. Then, the normal vector of the center of the box is obtained using the depth image to reduce misrecognition in parts other than the box, and the inner wall of the truck in an image is removed. And a method of classifying the layers of the boxes according to the distance using the recognized depth information of the boxes is suggested. Given the coordinates of the boxes on the nearest layer, a method of generating the optimal path to take out the boxes the fastest using this information is introduced. In addition, kinematic analysis is performed to move the conveyor to the position of the box to be taken out of the truck, and kinematic analysis is also performed to control the robot arm that takes out the boxes. Finally, the effectiveness of the developed system and algorithm through a test bed is proved.