• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.65-67
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• 1986

The model simplification method of the linear time invariant continuous system is proposed. Using the energy dispersion method the dynamic modes with dominent energy contribution are selected, and the poles of the denomenater are retained. And there is investigated how the dynamic modes affected the system characteristic. The parameters of the numerator are determined by time moment matching method. This method is that the algorithm is simple and also the simplified model found is always stable if the original system is stable, and through examples we assured that this method leads to good results in both transient and steady state responses.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.56-59
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• 2003

As the slab is longer and lighter, it is more sensitive to the external force so that the vibration of slab and noise induced by the slab vibration is bigger than expected in normal slab. The purpose of this study is to investigate how the dynamic characteristic of slab is different from the normal slab through the system identification and tn evaluate the vibration control performance when the damper system is installed. Finally, we was trying to understand by what mechanism the slab noise is induced from the slab vibration. The relationship between the vibration and the noise of slab is shown by the numerical simulation.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.8
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• pp.116-121
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• 2001

The paper presents the dynamic characteristics of a rotor-bearing system supported by an actively controlled hydrodynamic journal bearing. The proportional. derivative and integral controls are adopted for the control algorithm to control the hydrodynamic journal bearing with an axial groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis, which uses the Reynolds condition. The speed at onset of instability of a rotor-bearing system is increased by both proportional and derivative control of the bearing. The proportional control increases the stability threshold without affecting the whirl ratio. However, for the derivative control of the bearing, increase of stability threshold speed is accompanied by a parallel reduction of the whirl ratio. The integral control has no effect on stability characteristics of hydrodynamic journal bearing. The PD-control is more effective than proportional or derivative control. Results 7how the active control of bearing can be adopted for the stability improvement of a rotor-bearing system.

• Journal of Astronomy and Space Sciences
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• v.11 no.2
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• pp.281-295
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• 1994

In this paper, the Variable Structure System(VSS) theory with new continuous switching dynamic equation is used to design an automatic controller for the active nutation damping in momentum bias stabilized spacecraft. In the application of VSS theory to a linearized multivariable system with the nutation damping systems, there exist some disadvantages such as how to determine the switching gains and how to reduce the chattering phenomina and reaching phase in input and state trajectories. To solve these drawbacks, this paper presents the continuous switching dynamic equation instead of the discontinuous switching logics to obtain the sliding mode. The new design approach is much simpler than the VSS theory. And there do not exist chattering phenomina in this method because the obtained control inputs are continuous. Simultaneously the reaching phase is reduced by a suitable choice of design factor.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.3
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• pp.275-284
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• 2004

This paper discusses how to control the compensation voltages in dynamic voltage restorers (DVR). On analyzing the power circuit of a DVR system, control limitations and control targets are presented for the voltage compensation in DVRs. Based on the preceded power stage analysis, a novel controller for the compensation voltages of DVRs is proposed by a feed forward control scheme. This paper discusses also the time delay problems in the control system of DVRs. Digitally controlled DVR systems normally have control delay at amount of one sampling time of the control system and a half of the switching period of the DVR inverter. The control delay in digital controllers increases the dimension of the system transfer function one degree higher, which makes the control system more complicate and more unstable. This paper proposes a guide line to design the control gain, appropriate output filter parameters and inverter switching frequency for DVRs with digital controllers. Proposed theory is verified by an experimental DVR system with a full digital controller.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.620-626
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• 2004

For general nonlinear processes, it is difficult to control with a linear model-based control method and nonlinear controls are considered. Among the numerous approaches suggested, the most rigorous approach is to use dynamic optimization. Many general engineering problems like control, scheduling, planning etc. are expressed by functional optimization problem and most of them can be changed into dynamic programming (DP) problems. However the DP problems are used in just few cases because as the size of the problem grows, the dynamic programming approach is suffered from the burden of calculation which is called as 'curse of dimensionality'. In order to avoid this problem, the Neuro-Dynamic Programming (NDP) approach is proposed by Bertsekas and Tsitsiklis (1996). To get the solution of seriously nonlinear process control, the interest in NDP approach is enlarged and NDP algorithm is applied to diverse areas such as retailing, finance, inventory management, communication networks, etc. and it has been extended to chemical engineering parts. In the NDP approach, we select the optimal control input policy to minimize the value of cost which is calculated by the sum of current stage cost and future stages cost starting from the next state. The cost value is related with a weight square sum of error and input movement. During the calculation of optimal input policy, if the approximate cost function by using simulation data is utilized with Bellman iteration, the burden of calculation can be relieved and the curse of dimensionality problem of DP can be overcome. It is very important issue how to construct the cost-to-go function which has a good approximate performance. The neural network is one of the eager learning methods and it works as a global approximator to cost-to-go function. In this algorithm, the training of neural network is important and difficult part, and it gives significant effect on the performance of control. To avoid the difficulty in neural network training, the lazy learning method like k-nearest neighbor method can be exploited. The training is unnecessary for this method but requires more computation time and greater data storage. The pH neutralization process has long been taken as a representative benchmark problem of nonlin ar chemical process control due to its nonlinearity and time-varying nature. In this study, the NDP algorithm was applied to pH neutralization process. At first, the pH neutralization process control to use NDP algorithm was performed through simulations with various approximators. The global and local approximators are used for NDP calculation. After that, the verification of NDP in real system was made by pH neutralization experiment. The control results by NDP algorithm was compared with those by the PI controller which is traditionally used, in both simulations and experiments. From the comparison of results, the control by NDP algorithm showed faster and better control performance than PI controller. In addition to that, the control by NDP algorithm showed the good results when it applied to the cases with disturbances and multiple set point changes.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1993.06a
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• pp.1137-1140
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• 1993

A dynamic-structure system is one that has the flexibility to change the system configuration automatically so as to operate in an optimal manner. A conceptural model for a dynamic-structure system is presented in this paper. In this model, the interchangeable components of the overall system are grouped together. Their activity levels are evaluated by an intelligent preprocessor that is associated with the group. A knowledge-based task distribution system evaluates the activity levels and makes decisions as to how the components operating below capacity should be shared with workcells that have similar components that are overloaded. Associated decision making can be effected through fuzzy logic and particularly the compositional rule of inference. A simulation example is given to illustrate the application of dynamic structuring.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.9
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• pp.1010-1019
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• 1992

As the dynamics model for industrial robot is a mutural coupling of inertia, centrifugal force, gravity, etc it is very difficult to get solution to the question how it works. To control such complex non-linear features of the manipulator, it is required to develop a lot simpler algorithm on the real time.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.308-313
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• 2005

For a real-time quadruped robot running control, there are many important objectives to consider. In this paper, the running control architecture based on global states, which describe the cyclic target motion, and central pattern is proposed. The main goal of the controller is how the robot can have robustness to an unpredictable environment with reducing calculation burden to generate control inputs. Additional goal is construction of a single framework controller to avoid discontinuities during transition between multi-framework controllers and of a training-free controller. The global state dependent neuron network induces adaptation ability to an environment and makes the training-free controller. The central pattern based approach makes the controller have a single framework, and calculation burden is resolved by extracting dynamic equations from the control loop. In our approach, the model of the quadruped robot is designed using anatomical information of a cat, and simulated in 3D dynamic environment. The simulation results show the proposed single framework controller is robustly performed in an unpredictable sloped terrain without training.

• Structural Engineering and Mechanics
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• v.29 no.5
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• pp.489-504
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• 2008

In piezoelectric flexible structures, the contribution of vibration modes to the dynamic response of system may change with the location of piezoelectric actuator patches, which means that the ability of actuators to control vibration modes should be taken into account in the development of modal reduction model. The spatial $H_2$ norm of modes, which serves as a measure of the intensity of modes to system dynamical response, is used to pick up the modes included in the reduction model. Based on the reduction model, the paper develops the state-space representation for uncertain flexible tructures with piezoelectric material as non-collocated actuators/sensors in the modal space, taking into account uncertainties due to modal parameters variation and unmodeled residual modes. In order to suppress the vibration of the structure, a dynamic output feedback control law is designed by imultaneously considering the conflicting performance specifications, such as robust stability, transient response requirement, disturbance rejection, actuator saturation constraints. Based on linear matrix inequality, the vibration control design is converted into a linear convex optimization problem. The simulation results show how the influence of vibration modes on the dynamical response of structure varies with the location of piezoelectric actuators, why the uncertainties should be considered in the reductiom model to avoid exciting high-frequency modes in the non-collcated vibration control, and the possiblity that the conflicting performance specifications are dealt with simultaneously.