• Aerospace Engineering and Technology
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• v.2 no.1
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• pp.54-62
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• 2003

The satellite in space has a tiny size but is subject to the disturbance torques caused by various sources. The presence of environmental disturbance torques significantly affects the orient as well as the orbital motion of satellite. The sources of environmental effects on LEO Satellite attitude dynamics are various. Four of these, gravity gradient, Earth's magnetic field, solar radiation pressure and aerodynamic are dominant and deterministic. In this study, we describe the model of environmental disturbance torques acting on LEO Satellite and the effects of environmental disturbance torques on LEO Satellite attitude dynamics in detail.

• Science of Emotion and Sensibility
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• v.7 no.4
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• pp.19-24
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• 2004

The purpose of this study is to evaluate the possibility of identifying joint damping property through commercially available isokinetic ergometer (BIODEX). The proposed method is to estimate the damping torque of the knee joint from the difference between the external joint torque for maintaining isokinetic movement and the gravity torque of the lower leg. The damping torque was estimated at various joint angular velocities, from which the damping property would be derived. Measurement setup was composed of the BIODEX system with an external force sensor and Labview system. Matlab was used in the analysis of the damping property. The experimental result showed that the small variation in angular velocity due to acceleration and deceleration of the crank arm resulted in greater change of inertial torque than the damping torque. Therefore, the estimation of damping property from the isokinetic movement is difficult.

• Journal of Dental Rehabilitation and Applied Science
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• v.27 no.4
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• pp.343-358
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• 2011

As implant treatment has become popular, lots of different shapes and materials of the implant upper component have been supplied. And there are also diverse reports about failures including loosening of the abutment screw which is one of the most common reason. Purpose : The purpose of this study is to find out how different screw tightening orders and methods influence on screw loosening according to the different connection systems. The upper component was fabricated by casting method. After fabricating master models that are precisely attached to the upper component, 5 experimental models each for the external connection system and internal connection system were fabricated using splinting impression technique. First, to find out the influence of the screw tightening order, screws were tightened in 3 orders; 1-2-3-4, 2-3-1-4, 2-4-3-1. After tightening, removal torque values (RTV) of each group was measured. And also to find out the influence of screw tightening method, a model with 2-3-1-4 screw tightening order was tightened with 30 Ncm at one time(1-step method) and the RTV was compared with the same order group (2-3-1-4) in the 2 step method. In the external connection system, RTV appeared significantly lower in group 2-3-1-4 than group 2-4-3-1 (p<0.05). And also in the internal connection system, the RTV of group 2-3-1-4 appeared significantly lower than that of group 2-4-3-1 and 1-2-3-4 (p<0.05). When comparing the tightening number of the screw without considering the screw tightening order, the first tightened screw appeared significantly higher RTV than the second one in the external connection system (p<0.05), however there was no significant difference from the first tightened screw to the last tightened screw in the internal connection system. And there was no statistically significant difference between the two screw tightening methods in both internal and external connection system. In the comparison of external and internal connection system, each RTV appeared 16.27 Ncm and 14.25 Ncm and appeared as a statistically significant difference (p<0.05). There was a significant difference in RTV measured according to the screw tightening order. The lowest RTV appeared in the groups started tightening from the middle. There was also a significant difference in RTV between the two connection system groups. A further study is needed to find out the influence factors in RTV and also a study is required related to the load condition.

• Journal of Dental Rehabilitation and Applied Science
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• v.31 no.4
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• pp.310-315
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• 2015

Purpose: The purpose of this study was to measure the tightening torque for dental implant in dental laboratory and to analyze of the effects of different tightening torque. Materials and Methods: The tightening torque for dental implant in dental laboratory were measured by digital torque gauge. The length of abutment and analog were measured as tightening torque of manufacturer's instructions and the measured value. And the data were statically analyzed. Results: The mean tightening torque of implant screw in dental laboratory was $1.563{\pm}0.332Ncm$. The external type implant system of total length were showing no significant differences but the internal type implant system had difference significant (P < 0.05) when compared with tightening torque. Conclusion: The implant prosthesis should be made under manufacturer's instructions especially as tightening torque of screw. For the fidelity of implant prosthesis, dental technician should learn how to use the torque gauge.

• Journal of the Korean Magnetics Society
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• v.8 no.6
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• pp.388-394
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• 1998

We designed and fabricated an improved null-type torque magnetometer for measuring magnetic anisotropy of magnetic materials. This torque magnetometer has a measurement range of $~{\pm}15$ dyne.cm, and the range can be controlled. Resolution is ~0.0005 dyne.cm. Noise level is less than 0.01 dyne.cm with one measurement, and less than 0.004 dyne.cm with 10 averaged measuremets. The precision is less than 0.5 %. In contrast to typical null-type torque magnetometers, we placed a small ferrite magnet in the Helmholtz coil, instead of placing coil in the permanent magnet. From this novel sturucture, we can design a geometrically isotropic and relatively light-weight sample rod. Also, we can prevent the effect of input and output lines of coil exposed in the magnetic field in torque meter. Consequently, our novel null-type torque magnetometer can have a better sensitivity, faster response time, and smaller distortion of torque curve than commercially available torque magnetometers.

• Proceedings of the KIEE Conference
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• 2005.10c
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• pp.186-188
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• 2005

BLDC 전동기는 선형적인 토크 대 전류, 속도 대 전압 특성을 갖고 있으며 기계적, 전기적인 잡음이 없고, 가감속 제어가 용이하며, 토크 대 관성의 비가 매우 높아 소형으로 높은 출력을 낼 수 있다는 장점을 가지고 있다. 그러나 전기자 전류의 전환(Commutation)시 고정자 권선의 인덕턴스 성분과 역기전력으로 인해 발생되는 전류 리플은 BLDC 전동기 토크리플의 중요한 원인이 된다. 이에 본 논문에서는 고속 연산이 가능하고 별도의 외부 메모리 없이 칩 하나로 모든 동작을 할 수 있는 TMS320LF2407 DSP칩을 사용, Hard-chopping PWM 방식을 이용하여 전류 리플을 감소시켰으며, 이를 시뮬레이션 및 실험을 통해 증명하였다.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.310-311
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• 2010

하이브리드 자동차(HEV)용 매입형 영구자석 동기 전동기(IPMSM)의 Lookup-Table을 이용한 토크제어는 전류 및 온도 등과 같은 외부 환경에 의한 파라미터 변동으로 인해 전체적인 구동 성능이 떨어지게 된다. 따라서 본 논문에서는 전류 및 자속 값을 이용하여 지령 토크에 대한 전류 지령치를 보상함으로써 출력 토크를 보상하였다. 구동 성능은 시뮬레이션을 통하여 확인하였다

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.10-11
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• 2011

단일 회전자 전동기와 달리 동일한 크기에서 높은 출력 밀도와 높은 토크의 장점이 있는 이중 회전자 구조를 갖는 전동기는 공간적 제약을 받는 전기 자동차, 전기 이륜차 등의 분야에 활발히 연구되고 있다. 이중 회전자 구조를 갖는 전동기는 고 토크 운전을 위해 이중 인버터 운전 방식이 요구된다. 이때, 내부와 외부전동기의 역기전력이 다를 때 이를 고려하지 않고 운전한다면 발생하는 동손이 증가하여 운전효율 저하로 이어진다. 본 논문에서는 이중 회전자 구조를 갖는 3상 BLDC 전동기에서 내부와 외부전동기의 역기전력비(${\alpha}$)와 고정자 저항 비(${\beta}$)를 고려한 전류분배방식을 통해 동손을 최소화하는 최적운전 알고리즘을 제안하였다.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.327-330
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• 2001

본 논문에서는 고압 대전력 3상 유도전동기의 고정자 권선을 이용한 전압원 인버터의 병렬운전 방식을 제안한다. 현재 사용되고 있는 대부분의 4극 이상 대전력 유도전동기는 각 상의 권선이 외부에서 접근이 가능하도록 외부단자가 설치되어 있으며, 이들 외부단자를 이용하여 복수대의 전압원 인버터를 병렬운전하여 대전력 유도전동기를 구동할 수 있다. 이와 같이 고압 대전력 유도전동기를 복수 개의 전압원 인버터를 병렬 운전하여 구동할 경우, 특정 인버터의 고장발생 시 비록 구동 토크는 감소될지라도, 나머지 인버터로 시스템을 계속 구동할 수 있어 시스템의 고장대처능력을 향상시킬 수 있다. 또한 병렬 운전되고 있는 각 인버터의 스위칭 동작에 대해 서로 위상 차를 갖게 함으로서, 등가 스위칭 주파수를 증가시켜 출력 토크 리플 감소와 입력 전류 리플 감소, DC Link 커패시터의 크기 감소와 같은 좋은 특성을 얻을 수 있다. 또한 각 인버터로의 전력의 분산에 의해 시스템에서 발생하는 EMI 영향을 감소시킬 수 있다. 본 논문에서는 제안한 방식을 컴퓨터 시뮬레이션을 통해 특성을 증명하였다.

• Composites Research
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• v.22 no.2
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• pp.30-36
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• 2009

In this paper, we propose the design method for the composite torque link of a landing gear for a helicopter. The composite torque link has to be light weighted and very stiff to keep the shock absorber in the landing gear of helicopter. The configuration and structural shape has to be designed in consideration of the RTM (Resin Transfer Molding) manufacturing process which is adopted to minimize the manufacturing cost. The mechanical properties are obtained through the coupon tests with the specimens made by the same manufacturing process for the composite structure. The optimal design process was performed through iterative modifications of the models which were verified by stress analysis using FEM. The composite torque link has lug-shaped parts and is very thick, so 3D Layered solid elements of ABAQUS were used to get the stress field including the stress components in thickness direction and non-linear static analysis using contact B.C. of rigid-deform condition was used to get the optimal design.