• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.93-98
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• 2001

This paper studies on the design of an ILQ(Inverse Linear Quadratic optimal control) looper control system for hot strip mills. The looper which is placed between each stand plays an important role in controlling strip width by regulating strip tension variation generated from the velocity difference of main work rolls. The mathematical model for looper is firstly obtained by Taylor's linearization of nonlinear differential equations, where it is given as a linear and time invariant state-space equation. Secondly, a looper servo controller is designed by ILQ control algorithm, which is an inverse problem of LQ(Linear Quadratic optimal control) control. By tunning control gain arbitration parameters and time constants, it is shown that the ILQ looper servo controller has the performance that makes well to follow desired trajectories of both strip tension and looper angle.

• 한국정밀공학회지
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• 제17권1호
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• pp.101-109
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• 2000

Mutual torque ripple in a brushless DC motor is the main source of acoustic noise, especially fur motor operation with high speed and torque. This paper presents a method to obtain mutual torque ripple to identify acoustic noise source. Mutual torque ripple can be determined by analyzing phase current shape and magnetic circuit with different lead angles. Current shape is determined by state space model of voltage equation with the use of inductance calculated by FEM, and confirmed by experimental results. Mutual torque ripple is also determined by FEM analysis for the calculated current shape. Acoustic noise experiment reveals that mutual torque ripple with different lead angle is one of the main sources for noise generation in a brushless DC motor.

• 한국소음진동공학회논문집
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• 제18권12호
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• pp.1278-1285
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• 2008

This paper presents an inertia type of piezostack based active mount fur unmanned aero vehicle (UAV) camera system. After identifying the stiffness and damping properties of the rubber element and piezostack a mechanical model of the active mount system is established. The governing equation of mount is then derived and expressed in a state space form. Subsequently, a sliding mode controller which is robust to uncertain parameters is designed in order to reduce the vibration imposed according to the military specification associated with UAV camera mount system operation. Control performances such as acceleration and transmitted force are evaluated through both computer simulation and experimental implementation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
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• pp.5-15
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• 1997

It is the objective of this study that by conducting the serni-solid extrusion using A12024, the effect of various process variables on the quality of extruded product and extrusion force is understood. The results of experiment are compared with those of finite element simulation in order to verify the effectiveness of the developed FE-simulation code. In order to simulate densification in the deformation of serni-solid material, the semi-solid material is assumed to be composed of solid region as porous skeleton following compressible visco-plastic model and liquid region following Darcy's equation for the liquid flow saturated in the interstitial space. Then the flow and deformation of the semi-solid alloy are analyzed by coupling the deformation of the porous skeleton and the flow of the eutectic liquid. It is assumed that initial solid fraction is homogeneous. Yield and plastic potential function presented by Kuhn and constitutive model developed by Gunasekera are used for solid skeleton.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.306-309
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• 2005

This parer describes the tracking control simulation of 6-DOF shaking table with a bell crank structure, which converts the direction of reciprocating movements. For the Joint coordinate-based control which uses lengths of each actuator, the trajectory conversion process inverse kinematics is performed. Applying the Newton-Euler approach, the dynamic equation of the shaking table is derived. To cope with nonlinear problems, time-delay control(TDC) is considered, which has been noted for its exceptional robustness to parameter uncertainties and disturbance, in addition to steady-state accuracy and computational efficiency. If the nominal model is equal to the real system, joint coordinate-based control can be very efficient. However, manufacturing tolerances installation errors and link offsets contaminate the nominal values of the kinematic parameters used in the kinematic model of the shaking table. To compensate differences between the nominal model and the real system. the joint coordinate-based control using acceleration feedback in the Cartesian coordinate space is proposed.

• 한국항공우주학회지
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• 제33권9호
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• pp.56-65
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• 2005

시간유한요소법은 시간영역을 고정시키고 행렬 미분방정식 형태의 공간전파 관계식을 풂으로써 시간과 공간에 대한 동적 해석을 수행하는 방법이다. 이 방법은 공간이산화 유한요소법이나 시/공간 동시이산화 유한요소법에 비해 공간에 관한 자유도가 발생하는 것이 두드러진 특징으로, 이를 이용하여 분포형 구동기의 공간에 따른 특성을 최적화하는 데에 효율적으로 사용될 수 있다. 본 논문에서는 임의의 초기조건을 반영할 수 있도록 구성된 상태변수 벡터를 이용하여 구조물을 시간영역에서 이산화하고, 공간영역에서 전파관계식 및 경계조건을 이용하여 공간전파 관계식을 형성하였다. 이 때 구동기의 공간에 따른 형상 분포는 설계되어야 할 변수의 함수이고, 시간반응은 형상함수를 이용하여 이산화 하였다. 포텐셜 에너지 및 운동에너지를 구조물의 변위제어에 적절한 최적의 성능지수로 설정하고, 이를 최소화하도록 미지의 함수인 구동기의 분포형상을 구하였다. 일반적으로 구조물은 임의의 초기조건에서 외란을 받게 되나, 본 연구에서는 구현가능한 제어법칙을 이용하여 최종시간에서 안정화(rest) 조건을 만족한다고 가정하였다. 구동기 분포형상 최적화를 위해 상태/준상태 방정식을 유도하였다. 서브행렬 재형상화와 시/공간 경계조건을 통해 상태변수와 준상태변수에 대한 Ricatti 미분방정식을 유도하였다. 이를 통해 구동기 분포형상 최적화를 구현하였으며, 수치 시뮬레이션을 통해 적절한 구동기의 분포형상 최적화를 수행할 수 있음을 보였다.

• 터널과지하공간
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• 제13권5호
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• pp.389-396
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• 2003

본 연구는 정상류 Navier-Stokes 방정식에 섭동(perturbation) 이론을 적용하여 주기함수 간극에 대한 삼승법칙의 수정에 대해 논하였다. 이를 위해, 주기함수를 진폭과 파장에 대한 무차원 함수로 전환한 뒤 미소 계수에 대한 무차원 유동함수와 연속 방정식을 적용하였다. 이러한 과정을 통해 정상류 Navier-Stokes 방정식의 섭동 근사해를 구하였으며 이를 유한 차분법에 적용하였다. 단일 절리 모델에 대한유한 차분 수치해석을 통해, 수정된 삼승 법칙이 주기함수 간극의 유체 유동에 대한 정상류 Navier-Stokes 방정식의 섭동 근사해와 잘 일치하는 것으로 나타났다. 이를 통해 본 연구에서 제시된 삼승 법칙이 간극 분포에 따른 유체 유동의 평가에 있어 유용하게 적용될 수 있는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제40권3호
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• pp.431-451
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• 2011

Time delay inevitably exists in active control systems, and it may cause the degradation of control efficiency or instability of the systems. So time delay needs to be compensated in control design in order to eliminate its negative effect on control efficiency. Today time delay in linear systems has been more studied and some treating methods had been worked out. However, there are few treating methods for time delay in nonlinear systems. In this paper, an active controller for a nonlinear and hysteretic building structure with time delay is studied. The nonlinear and hysteretic behavior of the system is illustrated by the Bouc-Wen model. By specific transformation and augmentation of state parameters, the motion equation of the system with explicit time delay is transformed into the standard state space representation without any explicit time delay. Then the fourth-order Runge-Kutta method and instantaneous optimal control method are applied to the controller design with time delay. Finally, numerical simulations and comparisons of an eight-story building using the proposed time-delay controller are carried out. Simulation results indicate that the control performance will deteriorate if time delay is not taken into account in the control design. The simulations also prove the proposed time delay controller in this paper can not only effectively compensate time delay to get better control effectiveness, but also work well with both small and large time delay problems.

• 제어로봇시스템학회논문지
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• 제20권7호
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• pp.706-712
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• 2014

The inverters used to drive Brushless DC motors (BLDC) include switching devices such as FETs and the faults in FETs cause severe performance degradation in systems where a BLDC acts as actuator. This paper presents a fault detection and isolation method for the FETs of an inverter for BLDC motor control systems, which is based on the EKF (Extended Kalman filter). Firstly, an equivalent circuit model for a BLDC motor plus its inverter system was derived. Secondly, a state-space equation was established, where the on-resistance of the FETs is expressed as a state variable and the EKF equation estimates the on-resistance. If the estimated resistance differs greatly from the known value, it can be asserted that there is a fault on that FET. Thirdly, the local convergence of the established EKF was proved. Finally, through the experiments, the performance of the proposed method was verified. The results show that the on-resistance is estimated close to the value specified in the FET data sheet in normal operation, whereas the estimated resistance is a much larger value than the normal one in case an FET fault occurs. Therefore, it is confirmed that the proposed fault detection and isolation method works appropriately in real systems.

• 한국항공우주학회지
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• 제43권6호
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• pp.516-525
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• 2015

본 연구에서는 정지 비행과 저속 하강 비행하는 회전익기 로터에 대한 소음을 예측하고 실험값과 비교하여 검증하였다. Ffowcs Williams-Hawkings 방정식을 이용한 소음압 예측 프로그램을 개발하였다. 해석 결과의 검증을 위해서 2가지 풍동 시험 결과를 이용하였다. Boeing 360 모델 로터를 이용하여 정지 비행 조건에서의 저차 주파수 대역의 소음압을 검증하였고, HART II 로터를 이용하여 저속 하강 비행 조건의 중간 주파수 대역의 BVI 소음을 검증하였다. 하중 소음을 예측하기 위해서 정지비행 조건에서는 자유후류기법을 통한 공력계수를 이용하였고, 저속 하강 비행 조건에서는 CFD/CSD 연계해석 결과를 이용하였다. 소음해석 결과 저차 주파수 대역의 소음압과 중간 주파수 대역의 BVI 소음압을 비교적 잘 예측하는 것을 확인하였다. BVI 소음압은 FFT 해석을 통하여 소음 방사 지도를 그려 실험결과와 비교하였다. 비교 결과 시험결과와 비교적 유사하게 예측하는 것을 확인하였다.