• 대한기계학회논문집A
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• 제20권9호
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• pp.2744-2751
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• 1996

In case of limited power supply, a rotating shaft system may not reach its operating speed that is greater than its critical speed, but the speed oscillates with small ampllitude near critical speed. As a result, it is considered that the operating mode plays an important role in the smooth start of machines. In order to investigate the dynamic behaviors of the rotating shaft system at the beginning stage, one has derived the equations of motion whose degrees of freedom is three, two translations and one rotation. The simultaneous differential equations are numerically solved by using runge-Kutta method, and thus the small time step length could be required corresponding to the stability of solution. Three types of operating modes dependent upon the driving torque rate have been numerically investigated according to the maximum displacement of shaft center. The first type of relation is linear, the second type is composed of two linear curves recommended by machine manufacturer, and the last one is the proposed torque curve reflecting the frequency response curve of one degree of freedom system. For the second type of modes, it is found that the optimal range of intermediate speed to the critical speed lies between 0.8 and 0.9. In addition to that, the maximum displacement can be reduced more if the third type of mode is utilized.

• 아태비즈니스연구
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• 제11권2호
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• pp.27-43
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• 2020

Purpose - This study explores the impact of the real estate industry on related industries for the perspective of Chinese steel companies. Design/methodology/approach - The impact of housing prices on the 41 listed steel companies' performance was analyzed by using the panel data model. We used two kinds of housing price indexes that are set in the panel data models to estimate the range of the real estate market, driving the performance growth of steel listed companies. Moreover, the net profit of steel companies is used as the dependent variable. To test the stability of the model, ROA used as a dependent variable for the robustness test. Also, to avoid the time trend of housing prices, this paper selects the growth rate of housing prices as the primary research variable. After Fisher-type testings, there is no unit root problem in both independent and dependent variables. Findings - The results indicated that the rise in the housing price has a positive influence on the steel company performance. When the housing price increases by 1%, the net profit of steel enterprises will increase by 5 to 20 million yuan. Research implications or Originality - In this paper, empirical data at the micro-level and panel model are used to quantify China's real estate industry's driving effect on the iron and steel industry, providing evidence from the microdata level. It helps us to understand further the status and role of China's real estate industry in the economic structure.

• 한국소음진동공학회논문집
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• 제18권4호
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• pp.424-431
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• 2008

Recently, it is required that acoustic transducers for underwater detection and communication sensor have wide bandwidth and low operating frequency. In this research, the new acoustic transducer is proposed. This transducer is tonpilz type, and made of 1-3 piezoelectric composites as a driving parts. The developed transducer is evaluated the TVR(transmission voltage response) and RVS(receiving voltage sensitivity) characteristics around $4{\sim}14\;kHz$ frequency range and is compared to conventional tonpilz transducer made of solid piezoelectric ceramics as a driving parts. The resonance frequency of the developed transducer is decreased by 30% and the -3 dB bandwidth is increased by 90%, compared to conventional transducer with same dimensions. The value of TVR is decreased by 9 dB and The value of RVS is the same at resonance frequency.

• 한국음향학회지
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• 제28권6호
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• pp.491-498
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• 2009

본 논문에서는 수중 음향 압전 트랜스듀서의 고효율, 정전력 구동이 가능하도록 절연 트랜스포머와 체비셰프 필터함수를 이용한 임피던스 정합회로 설계 방안을 제안하였다. 제안된 정합회로는 진동과 무관한 트랜스듀서의 리액턴스 성분을 최소화하고 넓은 동작주파수 범위에서 평탄한 출력 전력 특성을 갖도록 설계되었다. 체비세프 필터함수를 표준 원함수로하는 저역통과 필터를 단종단 제자형 회로로 설계하고 대역통과 주파수변환을 통하여 트랜스듀서의 등가모델과 트랜스포머의 권선비에 적합한 정합회로를 설계하였다. 제안된 기법을 예제 모델 Tonpilz형 압전 트랜스듀서에 대한 가상부하에 적용하고 시뮬레이션과 실험을 통하여 그 결과를 비교함으로써 제안된 기법의 타당성을 검증하였다.

• 한국소음진동공학회논문집
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• 제17권10호
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• pp.967-975
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• 2007

A rotordynamic analysis was performed with a dry vacuum pump, which is a major equipment in modern semiconductor and LCD manufacturing processes. The system is composed of screw rotors, lobes picking air, helical gears, driving motor, and support rolling element bearings of rotors and motor. The driving motor-screw rotor system has a rated speed of 6,300 rpm, and was modeled utilizing a rotordynamic FE method for analysis, which was verified through 3-D FE analysis and experimental modal analysis. As loadings on the bearings due to the gear action were significant in the system considered, each resultant bearing load was calculated by considering the generalized forces of the gear action as well as the rotor itself. Each resultant bearing loading was used in calculating each stiffness of rolling element bearings. Design goals are to achieve wide separation margins of lateral and torsional critical speeds, and favorable unbalance responses of the rotor in the operating range. Then, a complex rotordynamic analysis of the system was carried out to evaluate its forward synchronous critical speeds, whirl natural frequencies and mode shapes, unbalance responses under various unbalance locations, and torsional interference diagram. Results show that the entire system is well designed in the operating range. In addition, the procedure of rotordynamic analysis for dry vacuum pump rotor-bearing system was proposed and established.

• Journal of Biosystems Engineering
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• 제40권4호
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• pp.327-334
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• 2015

Purpose: A falling-type weight sorter equipped with a load cell was developed to sort lightweight dried persimmons. The performance of the sorter was also evaluated. Methods: The electronic weight sorter for dried persimmon comprises a feeder part, a weight-measurement part, an indicator part, a carrier cup, a discharging part, and a driving part. The weight setting and zero-point adjustment are performed digitally for the convenience of users. For the experimental trials, 228 rubber-clay specimens (representative of dried persimmons) in the weight range of 24.73~99.56 g were manufactured for use in experiments to evaluate the performance of the sorter. Results: The average error of the weight measurements from three experimental trials was 1.655%, with a bias of -0.492 g, a root-mean-square error (RMSE) of ${\pm}0.808g$, and a coefficient of determination ($R^2$ ) of 0.997. Conclusions: The load-cell-based electronic dried-persimmon weight sorter developed in this study facilitates effective, precise, and convenient sorting of dried persimmons.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권12호
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• pp.718-724
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• 2004

This study investigates the design factors of Interior Permanent Magnet Synchronous Motor(IPMSM) which is applied to Hybrid electric vehicle as a driving power. Recently, there are many studies of IPMSM for application to Hybrid Electric Vehicle, because IPMSM has characteristics of high torque, high power density and high efficiency which come from reluctance torque due to difference of inductance as well as magnet torque. This study analyzes the inductance and design characteristics of IPMSM by using finite element method and focuses on design and analysis of IPMSM which can operates with high efficiency at low speed range. For this embodiment, magnet shape is changed from conventional block type to arc type without any change of outline dimension of motor and this change of magnet shape makes it possible to increase back EMF and sinusoidal waveform. Analysis results are verified by test of improved and embodied motor. As a test result , increased back EMF and sharply decrease of harmonics are secured and through this contribution of reduced fuel consumption of Hybrid electric vehicle is expected.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.923-928
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• 2003

This paper presents the motion control of a mobile robot with arc sensor for lattice type welding. Its dynamic equation and motion control method for welding speed and seam tracking are described. The motion control is realized in the view of keeping constant welding speed and precise target line even though the robot is driven along a straight line or comer. The mobile robot is modeled based on Lagrange equation under nonholonomic constraints and the model is represented in state space form. The motion control of the mobile robot is separated into three driving motions of straight locomotion, turning locomotion and torch slider controls. For the torch slider control, the proportional integral derivative (PID) control method is used. For the straight locomotion, a concept of decoupling method between input and output is adopted and for the turning locomotion, the turning speed is controlled according to the angular velocity value at each point of the comer with range of $90^{\circ}$ constrained to the welding speed. The proposed control methods are proved through simulation results and the results have proved that the mobile robot has enough ability to apply the lattice type welding line.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.83-93
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• 2002

This paper presents a motion control method and its simulation results of a mobile robot for a lattice type welding. Its dynamic equation and motion control methods for welding speed and seam tracking are described. The motion control is realized in the view of keeping constant welding speed and precise target line even though the robot is driven for following straight line or curve. The mobile robot is modeled based on Lagrange equation under nonholonomic constraints and the model is represented in state space form. The motion control of the mobile robot is separated into three driving motions of straight locomotion, turning locomotion and torch slider control. For the torch slider control, the proportional-integral-derivative (PID) control method is used. For the straight locomotion, a concept of decoupling method between input and output is adopted and for the turning locomotion, the turning speed is controlled according to the angular velocity value at each point of the corner with range of 90$^{\circ}$ constrained to the welding speed. The proposed control methods are proved through simulation results and these results have proved that the mobile robot has enough ability to apply the lattice type welding line.

• 한국자동차공학회논문집
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• 제5권6호
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• pp.175-182
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• 1997

The purpose of this study is to investigate the effects of intake manifold shapes to improve the engine performance in a 3-cylinder LPG engine with a closed loop fuel supply system. To know the flow resistance of intake manifolds with shape, the intake negative pressure of each runner in intake manifolds were measured by using the digital pressure meter at each driving condition. And, the engine torque and power have been measured with an engine dynamometer while adjusting the optimal fuel consumption ratio with a solenoid driver. As 속 results form this experiment, the torque characteris- tics were more improved with the plenum chamber(B type intake manifold) than with the banana type(A type intake manifold). The torque characteristics were improved at mid-engine speed(rpm) range as the inner diameter of the intake manifold became smaller. And also the optimum volume among the examined plenum chamber volume was 0.74 times(590cc) the displacement of the test engine.