• 한국가스학회지
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• 제3권2호
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• pp.62-69
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• 1999

본 논문에서는 혼합감도문제를 이용하여 강인한 서보계를 구성함으로서 동위치 제어 시스템의 제어계를 설계하는 방법을 제안하였고, LQG를 이용한 다변수 디지털 서보 제어기 및 H$\infty$ 최적 제어기와의 비교실험을 통하여 제안된 제어기의 유용성을 입증하였다.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1613-1626
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• 2002

This paper presents hybrid control of an active suspension system with a full-car model by using H$\sub$$\infty$/ and nonlinear adaptive control methods. The full-car model has seven degrees of freedom including heaving, pitching and rolling motions. In the active suspension system, the controller shows good performance: small gains from the road disturbances to the heaving, pitching and rolling accelerations of the car body. Also the controlled system must be robust to system parameter variations. As the control method, H$\sub$$\infty$/ controller is designed so as to guarantee the robustness of a closed-loop system in the presence of uncertainties and disturbances. The system parameter variations are taken into account by multiplicative uncertainty model and the system robustness is guaranteed by small gain theorem. The active system with H$\sub$$\infty$/ controller can reduce the accelerations of the car body in the heaving, pitching and rolling directions. The nonlinearity of a hydraulic actuator is handled by nonlinear adaptive control based on the back-stepping method. The effectiveness of the controllers is verified through simulation results in both frequency and time domains.

• Smart Structures and Systems
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• 제25권2호
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• pp.155-167
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• 2020

This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

• Journal of Mechanical Science and Technology
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• 제17권7호
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• pp.999-1010
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• 2003

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulators because hydraulic manipulators have the advantage of electric insulation and power/mass density. Meanwhile an electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of a 6-link electro-hydraulic manipulator system used in the real maintenance task of active electric lines is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust disturbance observers for force control are designed using this information in an H$\_$$\infty$/ framework, and implemented on the two different setups. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved even if the stiffness of environment and the shape of wall change.

• 전자공학회논문지SC
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• 제44권1호
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• pp.59-66
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• 2007

본 논문은 변수 불확실성과 제어기의 곱셈형 섭동을 가지는 특이시스템에 대한 비약성 강인 보장비용 제어기 설계 알고리듬을 제안한다. 제어기가 존재할 조건, 비약성 보장비용 제어기 설계 방법, 제어기에서의 비약성 척도와 보장비용 성능지수를 최소화하는 보장비용의 상한치(upper bound)를 선형행렬부등식 접근방벙으로 제안한다. 또한, 특이치분해와 변수치환 및 슈어 여수정리를 이용하여 구한 충분조건은 구하고자 하는 변수의 견지에서 볼록최적화(convex optimization)가 가능한 선형행렬부등식으로 변형된다. 따라서, 제안한 비약성 강인 보장비용 제어기는 변수 불확실성과 제어기의 곱셈형 섭동을 가지는 폐루프 특시이스템의 점근적 안정성과 보장비용 성능지수를 최소화하고 제어기의 섭동에 대해서도 안정성을 보장한다. 마지막으로, 수치예제를 통하여 제안한 알고리듬의 타당성을 검증한다.

• 전자공학회논문지SC
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• 제42권6호
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• pp.9-14
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• 2005

본 논문은 특이시스템과 곱셈형 섭동을 가지는 제어기에 대한 비약성 $H_{\infty}$ 제어기 설계 알고리듬을 제안한다. 제어기가 존재할 조건과 비약성 $H_{\infty}$ 제어기 설계 방법 및 제어기에서의 비약성 척도를 선형행렬부등식 접근방법으로 제안한다. 또한, 특이치 분해와 변수치환 및 슈어 여수정리를 이용하여 구한 충분조건은 구하고자 하는 모든 변수의 견지에서 볼록최적화(convex optimization)가 가능한 하나의 선형행렬부등식으로 변형된다. 따라서, 제안한 비약성 $H_{\infty}$ 제어기는 점근적 안정성과 폐루프 특이시스템의 $H_{\infty}$ 노옴 유계 및 제어기의 곱셈형 섭동에 대한 안정성을 보장한다. 또한, 제안한 알고리듬을 이용하면 변수 불확실성을 가지는 특이시스템에 대한 강인 비약성 $H_{\infty}$ 제어기 설계 문제에도 쉽게 확장됨을 보인다. 마지막으로, 수치예제를 통하여 제안한 알고리듬의 타당성을 검증한다.

• Journal of Radiation Protection and Research
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• 제46권3호
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• pp.83-97
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• 2021

Background: The lifetime risk of lung cancer incidence due to radiation for nonsmokers is overestimated because of the use of the average cancer baseline risk among a mixed population, including smokers. In recent years, the generalized multiplicative (GM)-excess relative risk (ERR) model has been developed in the life span study of atomic bomb survivors to consider the joint effect of radiation and smoking. Based on this background, this paper discusses the issues of radiation risk assessment considering smoking in two parts. Materials and Methods: In Part 1, we proposed a simple method of estimating the baseline risk for nonsmokers using current smoking data. We performed sensitivity analysis on baseline risk estimation to discuss the birth cohort effects. In Part 2, we applied the GM-ERR model for Japanese smokers to calculate lifetime attributable risk (LAR). We also performed a sensitivity analysis using other ERR models (e.g., simple additive (SA)-ERR model). Results and Discussion: In Part 1, the lifetime baseline risk from mixed population including smokers to nonsmokers decreased by 54% (44%-60%) for males and 24% (18%-29%) for females. In Part 2, comparison of LAR between SA- and GM-ERR models showed that if the radiation dose was ≤200 mGy or less, the difference between these ERR models was within the standard deviation of LAR due to the uncertainty of smoking information. Conclusion: The use of mixed population for baseline risk assessment overestimates the risk for lung cancer due to low-dose radiation exposure in Japanese males.