• Tribology and Lubricants
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• 제33권5호
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• pp.214-219
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• 2017

Abrasive fluidized bed machining (AFBM) is similar to general abrasive fluidized machining (AFM) in that it can perform polishing of the outer and inner surfaces of a 3-dimensional shape by the flow of particles. However, in the case of AFM, the shear force generated by the flow of the particles causes material removal, while in AFBM, the abrasive particles are suspended in the chamber to form a bed. AFBM can be used for deburring, polishing, edge contouring, shot peening, and cleaning of mechanical parts. Most studies on AFBM are limited to metals, and research on application of AFBM to plastic materials has not been performed yet. Therefore, in this study, we investigate the effect of rotating speed of the specimen and the air flow rate on the material removal characteristics during AFBM of polyacetal with a horizontal AFBM machine. The material removal rate (MRR) increases linearly with increase of the rotating speed of the main shaft because of the shear force between the particles of the fluidized bed and the rotation of the workpiece. The reduction in surface roughness tends to increase as the rotating speed of the main shaft increases. As the air flow rate increases, the MRR tends to decrease. At a flow rate of 70 L/min or more, the MRR remains almost constant. The reduction of the surface roughness of the specimen is found to decrease with increasing air flow rate.

• 한국운동역학회지
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• 제15권4호
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• pp.181-189
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• 2005

To know the proper impact posture and changes for the various clubs, changes of impact variables according to the change of golf club length was investigated. Swing motions of three male low handicappers including a professional were taken using two high-speed video cameras. Four clubs iron 7, iron 5, iron 3 and driver (wood 1) were selected for this experiment. Three dimensional motion analysis techniques were used to get the kinematical variables. Mathcad and Kwon3D motion analysis program were used to analyze the position, distance and angle data in three dimensions. Major findings of this study were as follows. 1. Lateral position of the head remained more right side of the target up to 3.5cm compared to the setup as the length of the club increased. 2. Left shoulder raised up to 5cm and right shoulder lowered up to 2.5cm compared to setup. The shoulder line opened slightly (maximum 11 degrees) to the target line. 3. Forward lean angle of the trunk decreased up to 4 degrees (more erected) compared to setup. 4. Side lean angle of the trunk increased compared to setup and increased up to 16 degrees as the club length increased. 5. The pelvis moved to the target line direction horizontally and opened up to 31 degrees. Right hip moves laterally to the grip position at the setup. 6. Flexion of the left leg maintained almost constantly but the right leg flexed up to 11 degrees compared to setup. 7. Left arm is straightened but the right arm flexed about 20degrees compared to straight. 8. Center of the shoulders were in front of the knees and toes of the feet. 9. Hands moved to the left (8.7cm), forward (5.7cm) and upward (11.6cm) compared to the setup. This is because of the rotation of pelvis and shoulders. 10. Shaft angle to the ground was smaller than the lie angle of the clubs but it increased close to the lie of the clubs at impact.

• 문화기술의 융합
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• 제6권1호
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• pp.515-520
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• 2020

본 연구에서는 4절 평행 링크의 설계와 실제 구현에 대한 것으로 평행 4절 링크는 한축의 회전을 다른 축의 회전 운동으로 전달하기 위한 기본적인 기구학적 메카니즘으로 널리 이용되고 있다. 그런데 평행 4절 링크는 운동 도중에 전환점에서 위상 역전이 발생하는 문제가 발생하여 실제 구현에서는 이를 고려하여 설계하여야 한다. 링크 역전을 방지하기 위해서는 추가적인 위상 역전 억제용 링크를 옵셋을 두어 붙이는 2중 평행 사변형 형태의 링크를 제작하면 되는 것으로 일부 알려져 있으나 실제 제작하여 실험한 결과 전환점에서 운동이 부드럽지 않은 현상이 발생하였다. 본 연구에서는 이 문제를 해결하기 위해 위상 역전 방지를 위한 옵셋을 주는 링크외에 보조적으로 평활한 운동을 위한 링크를 추가시켜 피동축이 구동축을 따라 회전할 때에 특정지점에서 위상 역전이 발생하지 않고 평활한 운동을 수행하는 것을 확인 할 수 있었다.

• Clinics in Shoulder and Elbow
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• 제7권1호
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• pp.41-45
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• 2004

In adhesive capsulitis of the shoulder of no response to nonoperative treatment, an arthroscopic capsular release and manipulation improves range of motion and pain relief. We performed an arthroscopic examination in the stiff shoulder, of which she had no response to nonoperative treatment, after the conservative treatment of a clavicular shaft fracture by motorcycle-driver traffic accident. We found the intra-articular 'rotator interval bridging scar adhesion' between subscapularis tendon and antero-superior glenoid fossa under the rotator interval which was no adhesion and contracture itself. We performed the scar adhesion removal and synovectomy, maintaining the rotator interval. We recommended nonsteroidal anti-inflammatory drug for postoperative pain relief and continuous active and passive range of motion (ROM) exercise to gain motions. Preoperatively, active and passive range of motion were 70° for forward elevation, 60° for abduction and especially 0° for external rotation. After postoperative 2 months, active ROM were 150° for forward elevation, 130° for abduction and 80° for external rotation. After postoperative 6 months, passive and active ROM were full. UCLA score improved from preoperative 9 points to postoperative 29 points.

• International Journal of Precision Engineering and Manufacturing
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• 제6권1호
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• pp.51-58
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• 2005

The development of the high-efficiency machine-tools equipment and new cutting tool materials with high hardness, heat- and wear-resistance has opened the way to application of high-speed cutting process. The basic argument of using of high-speed cutting processes is the reduction of time and the respective increase of machining productivity. In this sense, the spindle units may be regarded as one of the most important units, directly affecting many parameters of high-speed machining efficiency. One of the possible types of spindle units for high-speed cutting is the air-bearing type. In this paper, we propose the mathematical model of the dynamic behavior of the air-bearing spindle. To provide the high-level of speed capacity and spindle rotation accuracy we need the adequate model of "spindle-bearings" system. This model should consider characteristics of the interactions between system components and environment. To find the working characteristics of spindle unit we should derive the equations of spindle axis movement under the affecting factors, and solve these equations together with equations which describe the behavior of lubricant layer in bearing (bearing stiffness equations). In this paper, the three influence coefficients are introduced, which describe the center of spindle mass displacement, angle of shaft rotation around the axes under the unit force application and that under the unit torque application. These coefficients are operated in the system of differential equations, which describes the spindle axis spatial movement. This system is solved by Runge-Kutta method. Obtained trajectories and amplitude-frequency characteristics were then compared to experimental ones. The analysis shows good agreement between theoretical and experimental results, which confirms that the proposed model of air-bearing spindle is correctis correct

• 한국기계가공학회지
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• 제16권6호
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• pp.69-74
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• 2017

In the current machining industry, machining precision is necessary and machining is being carried out. In this ultra-precision machining industry, the fixation of the workpiece is very important and the degree of machining depends on the degree of fixation of the workpiece. In ultra-precision machining, various methods, such as using a vise chuck or the like and using bolt nut coupling, are used for fixing a workpiece to an existing machine tool. In particular, when the precision gripping force of the jig is insufficient during machining of the ultra-precision mold parts, the machining material shakes due to the vibration or friction, and the machining precision is lowered. In the ultra-precision machining of power transmission parts, such as gears, the accuracy of the product is then determined. In addition, the amount of heat generated during machining has a significant effect on the machining accuracy. This is because the vibration value changes according to the grasp force of the jig that fixes the workpiece, and the change in the calorific value due to the change in the main shaft rotation speed of the ultra-precision machining. The increase in the spindle rotation speed during machining decreased the heat generation during machining, and the machining accuracy was also good, and it was confirmed that the machining heat changed according to the fixed state of the workpiece and the machining accuracy also changed. In this study, we try to optimize the driving part of the power vise by using structural analysis, rather than the power vise, using the basic mechanical-type power unit.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.115-121
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• 2008

A core engine for pre-cooled turbojet engines is designed and its component performances are examined both by CFD analyses and experiments. The engine is designed for a flight demonstration of precooled turbojet engine cycle. The engine uses gas hydrogen as fuel. The external boundary including measurement devices is set within $23cm{\times}23cm$ of rectangular cross section, in order to install the engine downstream of the air intake. The rotation speed is 80000 rpm at design point. Mixed flow compressor is selected to attain high pressure ratio and small diameter by single stage. Reverse type main combustor is selected to reduce the engine diameter and the rotating shaft length. The temperature at main combustor is determined by the temperature limit of non-cooled turbine. High loading turbine is designed to attain high pressure ratio by single stage. The firing test of the core engine is conducted using components of small pre-cooled turbojet engine. Gas hydrogen is injected into the main burner and hot gas is generated to drive the turbine. Air flow rate of the compressor can be modulated by a variable geometry exhaust nozzle, which is connected downstream of the core engine. As a result, 75% rotation speed is attained without hazardous vibration and heat damage. Aerodynamic performances of both compressor and turbine are obtained and evaluated independently.

• 융합정보논문지
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• 제7권2호
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• pp.59-65
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• 2017

창의적 모듈형 완구의 동작 구현을 위하여 동작을 기록하고 또한 읽어서 반복 동작하는 방식의 움직임이 요구된다. 이 때 완구 동작용 모터 출력축에는 전위차계를 사용하여 절대 회전각을 읽어서 제어를 수행하게 된다. 하지만 전위차계의 감지 영역의 불안정한 부분이 일정 영역에 존재하게 되는데 이로 인한 모터 제어의 불안정을 가져올 수 있다. 본 논문에서는 2개의 전위차계를 한 축에 장착시켜 안정된 영역을 각각 읽어서 1회전 절대각을 찾는 알고리즘을 제안한다. 그리고 다중 회전을 수행 시 필요로 하는 보정 알고리즘에 대해서도 기술하였다. 제안된 방식은 실제 토포보 모듈라 완구에 적용하여 동작을 기록하고 반복 동작을 수행하여 효과적으로 동작됨을 보였다. 아울러 다 회전 동작을 기록하고 동작 시켜 제안된 방식의 유용성을 제시하였다. 향 후 다양한 동작을 통하여 기록과 재생의 기능을 확대해 나갈 것이다.

• 제어로봇시스템학회논문지
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• 제10권3호
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• pp.286-293
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• 2004

This paper presents the result of a study on the starter control for a turbo generator. Because a starter in gear box type turbo-generator system is composed of gearbox and brush DC motor, it should be replaced with High Speed Generator(HSG)) in HSG type Turbo-generator. There-ore, it is necessary to design a new starting algorithm and starter. In gearbox type system, brush DC motor is rotated to the designed speed using low voltage-high current battery power. After brush DC motor speed is increased to several times by gearbox, gas turbine engine can be rotated to designed starting speed. If we implement a starter with High Speed Generator(HSG), it is necessary to drive high-speed generator to high-speed motor. High-speed generator with permanent magnet on rotor has a low leakage inductance fur driving high-speed rotation, and it is necessary high DC link voltage for inverter when High-speed generator is driven to high speed. This paper presents result of development of the boost converter for converting high voltage DC from low battery voltage and design of the inverter for controlling a high frequency current to be injected to motor winding. Also, we show performance of the designed starter by driving the turbo generator.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.385-395
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• 2017

A new digitized decoupled dual-axis micro dynamically tuned gyroscope with three equilibrium rings (TMDTG) is proposed which can eliminate the constant torque disturbance (CTD) caused by the double rotation frequency of a driving shaft with a micro dynamically tuned gyroscope with one equilibrium ring (MDTG). A mechanical and kinematic model of the TMDTG is theoretically analyzed and the structure parameters are optimized in ANSYS to demonstrate reliability. By adjusting the thickness of each equilibrium ring, the CTD can be eliminated. The digitized model of the TMDTG system is then simulated and examined using MATLAB. Finally, a digitized prototype based on FPGA is created. The gyroscope can be dynamically tuned by adjusting feedback voltage. Experimental results show the TMDTG has good performance with a scale factor of $283LSB/^{\circ}/s$ in X-axis and $220LSB/^{\circ}/s$ in Y-axis, respectively. The scale factor non-linearity is 0.09% in X-axis and 0.13% in Y-axis. Results from analytical models, simulations, and experiments demonstrate the feasibility of the proposed TMDTG.