• Journal of Institute of Control, Robotics and Systems
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• v.10 no.1
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• pp.15-21
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• 2004

This paper deals with asymptotic stabilization problems for linear systems with time-varying input disturbances. In order to eliminate the influence of a disturbance on the system, a disturbance observer is designed and the time-varying disturbance can be rejected using its estimated value. Since the disturbance observer is kind of low-pass filter, it has inevitably estimation errors. To eliminate the inflences on the performance due to these errors, the additional control is designed based on these estimation errors using a well-known min-max control method. It is shown that the asymptotic stability of the closed-loop system is guaranteed. In general, the min-max control method requires the switching of control inputs and the switching magnitude of the control input is determined by the disturbance estimation error bounds. As the error bounds can be made arbitrarily small by choosing the high gain for the disturbance observer, the control method suggested in this paper can reduce the chattering phenomena as small as possible. Therefore, it has superior performance to the existing ones.

• Journal of the Korean Society of Industry Convergence
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• v.18 no.2
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• pp.129-138
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• 2015

This study describe a new method to control posture and velocity for a wheeled mobile robot using visual feedback control method with a position based visual feedback. To slove the problem of vibration phenomena which were shown in the previous researches using a simple switching function based on a threshold, the proposed visual servo control law introduces the fusion function based on a blending function. The chattering problem and rapid motion of the mobile robot can be eliminated. And we consider the nonlinearity of the wheeled mobile robot unlike the previous visual servo control laws using linear control methods to improve the performances of the visual servo control law. The proposed posture control law using visual servoing is verified by a theoretical analysis and simulation and experimental results.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.5
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• pp.114-122
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• 2006

This paper presents a new control scheme that combines a sliding mode control and a neural network. In the proposed sliding mode control, a continuous control is employed removing the switching phenomena and the equivalent control within the boundary layer is estimated through on-line teaming of the neural network. The performances of the proposed control are compared with off-line neural network and on-line neural sliding mode control by computer simulation. The simulation results show that the proposed control reduces high frequency chattering and tracking error in example of the two link manipulator.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2319-2324
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• 2005

This paper proposes a intelligent gain and boundary layer based sliding mode control (SMC) method for robotic systems with unknown model uncertainties. For intelligent gain and boundary layer, we employ the self recurrent wavelet neural network (SRWNN) which has the properties such as a simple structure and fast convergence. In our control structure, the SRWNNs are used for estimating the width of boundary layer, uncertainty bound, and nonlinear terms of robotic systems. The adaptation laws for all parameters of SRWNNs and reconstruction error bounds are derived from the Lyapunov stability theorem, which are used for an on-line control of robotic systems with unknown uncertainties. Accordingly, the proposed method can overcome the chattering phenomena in the control effort and has the robustness regardless of unknown uncertainties. Finally, simulation results for the three-link manipulator, one of the robotic systems, are included to illustrate the effectiveness of the proposed method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.1
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• pp.31-38
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• 1999

In this paper, we proposed a fuzzy sliding mode controller for a robot manipulator with passive joints. A robot manipulator with passive joints which is not equipped with actuators is a kind of underactuated systerms. The control of underactuated manipulators is more difficult than that of fully-actuated ones. Though the sliding mode control technique has a robust charocteristics to prrarreter uncertainties and external disturbances, the chattering phenomena becorne one of the major problems in application to the real plant. plant.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.6
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• pp.143-157
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• 1994

This paper is concerned with the position control of electrohydraulic servo system under parameter variation. An adaptive sliding mode control which uses the direct parameter estimation scheme, is proposed to design a robust controller for fast and accurate control of the system. It is shown that the adaptive sliding mode control algorithm is robust and effective in attaining fast and accurate position control of system under time-dependent parameter variation. It is also shown experimentally that chattering phenomena in a sliding mode control can significantly be reduced by using boundary layer technique, and that new approach in sliding mode control introducing a term proportional to the distance between the current state and the sliding surface in the control law is effective to obtain fast response and to increase stability of the system. Computer simulation on the dynamic performance of the control system is also presented.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.211-218
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• 2021

This paper addressed the problems of controlling the coupled pitch-roll motions in a marine vessel exposed to the regular waves in the longitudinal and transversal directions. Stabilization of the pitch and roll motions can be regarded as the essential task to ensure the safety of a ship's navigation. One of the important features in the pitch-roll motions is the resonance phenomena, which result in unexpected large responses in terms of pitch and roll modes in some specific conditions. Besides, owing to its inherent characteristics of coupled combination and nonlinearity of restoring terms, the vessel shows various dynamical behaviors according to the system parameters, especially in the pitch responses. Above all, it can be seen that suppression of pitch rate remains the most significant challenge to overcome for ship maneuvering safety studies. To secure the stable upright condition, a quasi-sliding mode control scheme is employed to reduce the undesirable pitch and roll responses as well as chattering elimination. The Lyapunov theory is adopted to guarantee the closed stability of the pitch-roll system. Numerical simulations demonstrate the effectiveness of the control scheme. Finally, the control goals of state convergences and chattering reduction are effectively realized through the proposed control synthesis.

• Journal of The Korean Association For Science Education
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• v.26 no.5
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• pp.660-673
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• 2006

There have been many attempts to determine the value and the role of school laboratory experiment, but it seems hard to find consensus among these attempts from the perspective of education. This difficulty seems mainly due to disagreement on the concept of education, which has caused an instrumental attitude considering the school laboratory only as a means of developing science or pursuing various functions of school. However, the Endogenous Theory of Education (ETE), which claims education as 'a form of life', has recently paved the way for laboratory experiment to be justified as an opportunity of 'educooperation' allowing students to experience the intrinsic values of education in the medium of science. According to this theory, it is not the detailed practicals but the whole context where the laboratory activity is situated that matters in revealing the inherent educational phenomena. Through this new perspective, I observed two biology laboratory classes in a high school and analyzed the pattern of teacher-student and student-student interactions. Some meaningful educooperation was found in students' chattering, which has been traditionally considered as merely noise in the classroom, rather than in teacher-student interactions. This study discusses the reasons for these findings in detail and culminates in suggesting ways for accentuating the educational aspect of school laboratory activity.