• 한국지능시스템학회논문지
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• 제15권5호
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• pp.527-532
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• 2005

본 논문에서 불확실한 근사화 오차 유계 추정을 이용한 불확실한 비선형 계통에 대한 적응 퍼지 슬라이딩 모드 제어기를 제안하였다. 계통 출력이 기준 출력을 추종하기 위해 시스템의 불확실성은 결론부 파라미터의 적응 알고리즘에 의해 온라인으로 조정되는 IF-THEN 규칙을 가지는 퍼지 시스템에 의해 근사화하였다. 또한 근사화 오차가 미지의 상수에 의해 유계된다는 가정 하에 리아프노프 합성법으로 근사화 오차 유계 추정 알고리즘을 제안하였다. 전체 제어 시스템은 제어기내의 모든 신호가 균등 유계이고 추종오차가 점근 안정함을 보장한다. 제안한 적응 퍼지 슬라이딩 모드 제어기의 성능을 도립진자 계통에 대한 컴퓨터 모의실험을 통해 입증하였다.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.137-156
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• 2013

In this paper, a meshfree shell adaptive procedure is developed for the applications in the sheet metal forming simulation. The meshfree shell formulation is based on the first-order shear deformable shell theory and utilizes the degenerated continuum and updated Lagrangian approach for the nonlinear analysis. For the sheet metal forming simulation, an h-type adaptivity based on the meshfree background cells is considered and a geometric error indicator is adopted. The enriched nodes in adaptivity are added to the centroids of the adaptive cells and their shape functions are computed using a first-order generalized meshfree (GMF) convex approximation. The GMF convex approximation provides a smooth and non-negative shape function that vanishes at the boundary, thus the enriched nodes have no influence outside the adapted cells and only the shape functions within the adaptive cells need to be re-computed. Based on this concept, a multi-level refinement procedure is developed which does not require the constraint equations to enforce the compatibility. With this approach the adaptive solution maintains the order of meshfree approximation with least computational cost. Two numerical examples are presented to demonstrate the performance of the proposed method in the adaptive shell analysis.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1998년도 춘계학술대회 학술발표 논문집
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• pp.39-42
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• 1998

This paper proposes an adaptive fuzzy control scheme for a class of continuous-time nonlinear dynamic systems for which an explicit linear parameterization of the uncertainty is either unknown or impossible. In order to improve robustness under approximation errors and disturbances the proposed scheme includes deadzone in adaptation laws which varies its size adaptively. The assumption of known bounds on the approximation errors and disturbances is not required since those are estimated using adaptation laws. The overall adaptive scheme is proven to guarantee uniform ultimate boundedness in the Lyapunov sense.

• 한국통신학회논문지
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• 제22권6호
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• pp.1178-1184
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• 1997

Encoding of segment contours is a critical part of a region-based coding system especially at low bit rates where the contour information occupies a majority of the bit rate. When approximating contours with polygons, a fixed upper bound on the distortion is set for the approximation process. Instead of using this fixed bound, adaptive approximation bound for a lossy coding of contourts is proposed in this paper. A function representing the relative importance of the contour segmentis defined to take into account the spatial content of the image. By using this function, the contour can be approximated adaptively. This allows a more general approach than the methods with the fixed distortion measure. The effectiveness of the adaptive contour coding approach is verified through experiments.

• 한국정밀공학회지
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• 제25권12호
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• pp.89-99
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• 2008

In this paper, the position tracking control problem of the servo system with nonlinear dynamic friction is issued. The nonlinear dynamic friction contains a directly immeasurable friction state variable and the uncertainty caused by incomplete parameter modeling and its variations. In order to provide the efficient solution to these control problems, we propose the composite control scheme, which consists of the robust friction state observer, the FNN approximator and the approximation error estimator with sliding mode control. In first, the sliding mode controller and the robust friction state observer is designed to estimate the unknown internal state of the LuGre friction model. Next, the FNN estimator is adopted to approximate the unknown lumped friction uncertainty. Finally, the adaptive approximation error estimator is designed to compensate the approximation error of the FNN estimator. Some simulations and experiments on the servo system assembled with ball-screw and DC servo motor are presented. Results show the remarkable performance of the proposed control scheme. The robust friction state observer can successfully identify immeasurable friction state and the FNN estimator and adaptive approximation error estimator give the robustness to the proposed control scheme against the uncertainty of the friction parameters.

• 한국산학기술학회논문지
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• 제16권6호
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• pp.3661-3666
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• 2015

본 논문은 MDO에서 적용가능한 근사기법의 활용에 관한 연구를 수행하였다. MDO 통합 설계 시스템을 구축하는데 있어서, 최적화 과정에서 발생하는 수많은 반복 계산, 광범위한 다분야 간 설계 및 CAD/CAE와의 연계를 고려함으로써 발생하는 방대한 계산량 및 데이터의 정보량으로 인해 수반되는 계산 비용을 현저히 줄이지 않고는 통합설계 시스템을 실제로 구축한다 해도 그 효용성은 비현실적일 수밖에 없게 된다. 따라서 본 연구에서는 MDO 통합설계 시스템 프레임워크의 목적을 위해, 필수적으로 선행되어야 하는 다양한 근사기법의 적절한 활용을 통해 MDO에서 적용가능한 근사기법의 활용에 대한 연구를 수행하였다.

• International Journal of Control, Automation, and Systems
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• 제4권2호
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• pp.146-154
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• 2006

In this paper, we propose direct and indirect adaptive fuzzy sliding mode control approaches for a class of nonaffine nonlinear systems. In the direct case, we use the implicit function theory to prove the existence of an ideal implicit feedback linearization controller, and hence approximate it to attain the desired performances. In the indirect case, we exploit the linear structure of a Takagi-Sugeno fuzzy system with constant conclusion to establish an affine-in-control model, and therefore design an indirect adaptive fuzzy controller. In both cases, the adaptation laws of the adjustable parameters are deduced from the stability analysis, in the sense of Lyapunov, to get a more accurate approximation level. In addition to their robustness, the design of the proposed approaches does not require the upper bounds of both external disturbances and approximation errors. To show the efficiency of the proposed controllers, a simulation example is presented.

• International Journal of Control, Automation, and Systems
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• 제5권5호
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• pp.479-491
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• 2007

This paper presents a new adaptive observer design method for a class of uncertain nonlinear systems by using spline approximation. This scheme leads to a simplified observer structure which requires only fixed number of integrations, regardless of the number of parameters to be estimated. This benefit can reduce the number of integrations of the observer filter dramatically. Moreover, the proposed adaptive observer automatically generates the required spline elements according to the varying output value and, as a result, does not requires the pre-knowledge of upper and lower bounds of the output. This is another benefit of our approach since the requirement for known output bounds have been one of the main drawbacks of practical universal approximation problems. Both of the benefits stem from the local support property, which is specific to splines.

• 제어로봇시스템학회논문지
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• 제14권11호
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• pp.1103-1109
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• 2008

Since the flexible joint robots with motor dynamics are represented by the fifth-order nonlinear sγstem, it is difficult and complex to design the controller for electrically driven flexible-joint (EDFJ) robots. In this paper, we propose a simple adaptive control method to solve this problem. It is assumed that the model uncertainties of the robots dynamics, joint flexibility, and motor dynamics are unknown. For the simple control design, the dynamic surface design method is applied, and all uncertainties in the robot and motor dynamics are compensated by using the adaptive function approximation technique. It is proved that all signals in the controlled closed-loop system are uniformly ultimately bounded. Simulation results for three-link EDFJ manipulators are provided to validate the effectiveness of the proposed control system.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1997년도 추계학술대회 학술발표 논문집
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• pp.199-203
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• 1997

In this paper is proposed a new direct adaptive fuzzy controller that dan ve applied for tracking control of a class of uncertain nonlinear SISO systems. It is shown that, in the presence of the perturbations such as fuzzy approximation error and external disturbance, boundedness of all the signals in the system is ensured, while under the assumption of no perturbations, the stability of the overall system in guaranteed. Also, the concept of persistent excitation in the adaptive fuzzy control systems is introduced to guarantee the convergence and the boundedness of adaptation parameter in the proposed controllers. Simulation example shows the effectiveness of the proposed method in the presence of fuzzy approximation error and external disturbance.