• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.207-209
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• 2005

Recently, the use of IPMSM is coming to be active, in many industrial applications. In sensorless drive of IPMSM, it is important to know the exact information of the initial rotor position, because the wrong estimation of the initial rotor position brings about the decrease of the starting torque, or a temporary reverse revolution, In addition, PMSM is necessary to use the accurate information of the inductance for the precise torque control owing to the reluctance torque. In this paper presents initial rotor position estimation method and, measure method of the each-axis inductance. And to minimize the speed estimations error, the estimated speeds are compensated by using an instantaneous reactive power in synchronously rotating reference frame.

• 대한치과보철학회:학술대회논문집
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• 대한치과보철학회 2001년도 추계학술대회
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• pp.51-51
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• 2001

• 한국지열·수열에너지학회논문집
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• 제16권1호
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• pp.1-8
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• 2020

In this study, a new shape of wind turbine with horizontal axis has been proposed. The proposed wind turbine has two pairs of 3 tiltable blades which minimizes air resistance during the reverse rotational direction. Under a given wind speed, 3D numerical simulations on tiltable blades were performed for various TSRs(tip-speed-ratios). Four cases of rotational position was considered to analyze the torque and wind power generated on the blade surfaces. The results show that the maximum wind power occurs at the TSR of 0.2. Due to the blade tilting, the wind passes through the blade without air resistance at the reverse rotational direction. The torque is mainly caused by pressure differences between the front and rear surface of the blade, and it becomes maximum when the blade is located at the azimuth angle of 330°.

• 한국항공우주학회지
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• 제39권6호
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• pp.498-504
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• 2011

속도와 샤프트각 그리고 피치 변화에 따른 토크 평형상태의 자동회전에서 플래핑 거동 특성과 전진비의 변화를 조사하였다. 속도 증가에 따른 압축성 효과를 모사하기 위해 압축성 Navier-Stokes 솔버로 해석된 2차원 데이터를 Pitt/Peters 유도흐름 이론과 함께 사용하였고 토크 평형상태에 대한 세 변수의 조합을 찾기 위해 과도모사법(TSM)을 이용하였다. 토크 평형상태에서 최대 플래핑각을 속도, 샤프트각, 피치와의 관계로 나타내고 전진비 변화와 비교함으로써 후진깃의 역풍영역 확대가 로터의 자동회전 특성에 관여하는 현상을 정성적으로 고찰하였다.

• 대한치과보철학회지
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• 제51권4호
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• pp.276-283
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• 2013

연구 목적: 본 연구에서는 기성 지대주와 맞춤형CAD-CAM 지대주의 적합성 및 나사 사이의 안정성 대해 알아보고자 한다. 연구 재료 및 방법: 오스템 임플란트 시스템을 이용하였다. 동일회사에서 제작된 기성 지대주(Transfer abutment, Osstem Implant Co. Ltd, Busan, Korea) 및 맞춤형CAD-CAM 지대주(CustomFit abutment, Osstem Implant Co. Ltd, Busan, Korea)와 국내 외주 제작된 맞춤형CAD-CAM 지대주(Myplant, Raphabio Co., Seoul, Korea)를 5개씩 선택, 제작하였으며 나사는 각 회사에서 제공되는 것을 사용하였다. 제조사의 지시에 따라 고정체와 지대주를 30 Ncm으로 조인 후 초기 풀림 토크를 3회 반복 측정한 후 통계 분석하였다(${\alpha}=.05$). 고정체-지대주 연결체를 에폭시 레진에 매몰 후 습식 절삭 및 연마하여 계면 사이의 적합성을 FE-SEM으로 관찰하였다. 결과: 지대주의 초기 풀림 토크 값은 각각 기성 지대주(Transfer abutment)에서 $26.0{\pm}0.30Ncm$, 동일 회사에서 제작된 맞춤형CAD-CAM 지대주(CustomFit abutment)에서 $26.3{\pm}0.32Ncm$, 외주로 제작된 맞춤형CAD-CAM 지대주(Myplant abutment)에서 $24.7{\pm}0.67Ncm$였다. 국내 외주 제작된 맞춤형CAD-CAM 지대주에서 유의적으로 낮은 초기 풀림 토크 값을 보였으며(P=.027), 고정체-지대주 계면에서 변연 간극이 관찰되었다. 결론: 본 실험의 한계 내에서 국내 외주 제작된 맞춤형CAD-CAM 지대주는 동일 회사에서 제작된 기성 지대주나 맞춤형CAD-CAM 지대주에 비해 더 낮은 나사 안정성 및 적합성을 보인다고 볼 수 있다.

• The Journal of Advanced Prosthodontics
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• 제14권1호
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• pp.22-31
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• 2022

PURPOSE. The purpose of this study was to investigate the misfit and screw preload at the implant abutment connection of implant supported fixed dental prosthesis with cantilever (ICFDP) manufactured using different digital manufacturing techniques and to compare the screw preload before and after cyclic loading. MATERIALS AND METHODS. Mandibular jaw model with four intra-foraminal implants was scanned using digital scanner. Stereolithography file was used to design a framework with nonengaging (NE) abutments and 10 mm cantilever distal to one terminal implant. Five frameworks were constructed using combined digital-conventional techniques (CAD-cast), and five frameworks were constructed using three-dimensional printing (3DP). Additional CAD-cast framework was constructed in a way that ensures passive fit (PF) to use as control. Scanning electron microscope (SEM) measured the implant abutment connection misfit. Sixty screws were used on the corresponding frameworks. Screws were torqued and pre-cyclic loading reverse torque value (RTV) was recorded. Frameworks were subjected to 200,000 loading cycles with a loading point 9 mm from the center of terminal implants adjacent to the cantilever and post-cyclic loading RTVs were recorded. RESULTS. Microscopic readings showed significant differences between frameworks. PF demonstrated the lowest measurements of 16.04 (2.6) ㎛ while CAD-cast demonstrated the highest measurements of 29.2 (3.1) ㎛. In all groups, RTVs were significantly lower than the applied torque. Post-cyclic loading RTV was significantly lower than pre-cyclic loading RTV in PF and 3DP frameworks. Differences in RTVs between the three manufacturing techniques were insignificant. CONCLUSION. Although CAD-cast and three-dimensionally printed (3DP) both produce frameworks with clinically acceptable misfit, 3DP might not be the technique of choice for maintaining screw's preload stability under an aggressive loading situation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.464-469
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• 2001

This work provides the biomechanical evaluations of a manual wheelchair with a bi-directional driving system. The new propulsion strategy can be accomplished by employing a special gear system that converts the oscillatory motion of a handrim into the unidirectional output motion of a wheel. A main feature of the forward. backward propulsion is to supply continuous driving torque without break. Motion. analysis has been performed through 2-dimensional image processing for measuring the kinematic properties of the upper arm and fore arm. Then, the inverse dynamics analysis has been done for obtaining the joint torques, the handrim forces and input/output powers. Results show that the output power by the forward. reverse propulsion is almost twice as much as that by conventional propulsion. Also, the new propulsion is expected to reduce the fatigues and injuries at arm joints by employing more muscle groups for movement. In conclusion, the forward. reverse propulsion can greatly improve the performances of manual wheelchairs by providing better mobility as well as by guaranteeing several advantages from a biomechanical viewpoint. Future development of a manual wheelchair optimized for the bi-directional propulsion will further improve the propulsion performances.

• Journal of Biosystems Engineering
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• 제4권1호
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• pp.1-23
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• 1979

The use of barley seeder attached to rotary tiller in the rural area has a significant meaning not only for the solution of labor peak season, but also for the increase of land utilization efficiency. The facts that presently being used barley seeders are all based on the mechanical principles of the reverse rotation, center drive and are all using forward rotating tine, which is used to be easily and heavily worn out when it rotates reversely, raise problem of recommending them to rural area in Korea. Therefore, the main objective of the study was to develop new type of rotary tine attachable to barley seeders. To attain the objective the following approaches were applied. (1) The kinematic analysis of reverse rotating barley seeders. (2) The studies on the soil bin and artificial soil. (3) The comparative experiment on the power requirement of prototype tine. The results obtained from the studies are summarized as follow: 1. The kinematic analysis of barley seeder attached to rotary tiller: The following results were obtained from the kinematic analysis for deriving general formulae of the motion and velocity characterizing the rotary tine of barley seeders presently being used by farmers. a) The position vector (P) of edge point (P) in the rotary tine of reverse rotating, center drive was obtained by the following formula. $$P=(vt+Rcos wt)i+Rsin wt j+ \{ Rcos \theta r sin \alpha cos (wt- \beta +\theta r) +Rsin \theta r sin \alpha sin (wt-\beta + \theta r) \} lk $$ b) The velocity of edge point $(P^')$ of reverse rotating, center drive rotary tine was obtained by the following formula. $$(P^')=(V-wR sin wt)i+(w\cdot Rcoswt)j + \{ -w\cdot Rcos \theta r\cdot sin \alpha \cdot sin (wt-\beta +\theta r) + w\cdot Rsin \theta r\cdot sin \alpha \cdot cos (wt- \beta + \theta r \} k $$ c) In order to reduce the power requirement of rotary tine, the angle between holder and edge point was desired to be reduced. d) In order to reduce the power requirement, the edge point of rotary tine should be moved from the angle at the begining of cutting to center line of machine, and the additional cutting width should be also reduced. 2. The studies on the soil bin and artificial soil: In order to measure the power requirement of various cutting tines under the same physical condition of soil, the indoor experiments Viere conducted by filling soil bin with artificially made soil similar to the common paddy soil and the results were as follows: a) When the rolling frequencies$(x)$ of the artificial soil were increased, the densIty$(Y)$ was also increased as follows: $$y=1.073200 +0.070780x - 0.002263x^2 (g/cm^3)$$ b) The absolute hardness $(Y)$ of soil had following relationship with the rolling frequencies$(x)$ and were increased as the rolling frequencies were increased. $$Y=37.74 - \frac {0.64 + 0.17x-0. 0054x^2} {(3.36-0.17x + 0.0054x^2)^3} (kg/cm^3)$$ c) The density of soil had significant effect on the cohesion and angle of internal friction of soil. For instance, the soil with density of 1.6 to 1.75 had equivalent density of sandy loam soil with 29.5% of natural soil moisture content. d) The coefficient of kinetiic friction of iron plate on artificial soil was 0.31 to 0.41 and was comparable with that of the natural soil. e) When the pulling speed of soil bin was the 2nd forward speed of power tiller, the rpm of driving shaft of rotary was similar to that of power tiller, soil bin apparatus is indicating the good indoor tester. 3. The comparative experiment on the power requirement of prototype tine of reverse rotating rotary: According to the preliminary test of rotary tine developed with various degrees of angle between holder and edge pcint due to the kinematic analysis, comparative test between prototype rotary tine with $30 ^\circ $ and $10 ^\circ$ of it and presently being used rotary tine was carried out 2nd the results were as follows: a) The total cutting torque was low when the angle between holder and edge point was reduced. b) $\theta r$ (angle between holder and edge point) of rotary tine seemed to be one: of the factors maximizing the increase of torque. c) As the angle between holder and edge point ($\theta r$) of rotary tine was $30 ^\circ $ rather than $45 ^\circ $, the angle of rotation during cutting soil was reduced and the total cutting torque was accordingly reduced about 10%, and the reduction efficiency of total cutting torque was low when the angle between holder and edge point ($\theta r$) of rotary tine was $10 ^\circ $, which indicates that the proper angle between holder and edge point of rotary tine should be larger than $10 ^\circ $ and smaller than $30 ^\circ $ . From above results, it could be concluded that the use of the prototype rotary tine which reduced the angle between holder and edge point to $30 ^\circ $, insted of $45 ^\circ $, is disirable not only decreasing the power requirements, but also increasing the durabie hour of it. Also forward researches are needed, WIlich determine the optimum tilted angle of rotary brocket, and rearrangement of the rotary tine on the rotary boss.

• 한국지반공학회지:지반
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• 제3권4호
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• pp.31-40
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• 1987

얕은 지반의 현장탐사와 다짐도의 측정등에 적합한 나선탐사시험을 개발하여 그 시기결과를 표준 관입시험, 도추관입시험, 현장밀도시험 등 기존의 현장시험결과와 비교, 분석하였다. 나선탐사설험은 다른 현장시광에 비하여 경제적이며 1인이 쉽게 시험할 수 있는 장점이 있다. 흙의 물성치는 택 사기를 지반에 관입시키는데 필요한 토오크로 나타내며 본 연구결과, 표준관입시험 및 원유관입시 험의 결과와 잘 일치하고 표준관입시험과의 상관관계는 흙의 종류에 따른 유관성이 낮으나 도유관 입시험과의 경우, 유관성이 높다. 또한 나선탐사시험은 상대다짐또와 다짐지반의 현장밀도의 측정 에도 정도가 높다. 한펀 지반의 평균정립(D50)이 증가함에 따라 나선탐사시험의 역포전비는 감소하는 특성을 보인다.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1185-1201
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• 2018

This paper presents a sensorless direct torque control (DTC) combined with sliding mode approach (SM) and space vector modulation (SVM) to achieve mainly a high performance and reduce torque and flux ripples of a parallel-connected two five-phase permanent magnet synchronous machine (PMSM) drive system. In order to increase the proposed drive robustness and decrease its complexity and cost, the rotor speeds, rotor positions, fluxes as well as torques are estimated by using a sliding mode observer (SMO) scheme. The effectiveness of the proposed sliding mode observer in conjunction with the sliding mode control based DTC is confirmed through the application of different load torques for wide speed range operation. Comparison between sliding mode control and proportional integral (PI) control based DTC of the proposed two-motor drive is provided. The obtained speeds, torques and fluxes responses follow their references; even in low and reverse speed operations, load torques changes, and machines parameters variations. Simulation results confirm also that, the ripples of the torques and fluxes are reduced more than 3.33% and 16.66 %, respectively, and the speed overshoots and speed drops are reduced about 99.85% and 92.24%, respectively.