• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.147-150
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• 1997

In the study, we consider chua's circuit which is a paradigmatic chaotic system belonging to Lur'e form. It is shown that the dynamic behavior of such a system can be influenced in such a way as to obtain out of chaotic behavior a desired periodic orbit corresponding to an unstable periodic trajectory which exists in the system. This kind of control can be achieved via injection of a single continuous time signal representing the output of the system associated with an unstable periodic orbit embedded in the chaotic attractor We investigate the case when this signal is sampled, i.e. we supply to the system the control signal at discrete time moments only.

• Smart Structures and Systems
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• v.14 no.4
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• pp.643-658
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• 2014

This paper presents the design, modelling and, simulation and experimental results of a shape memory alloy (SMA) actuator based critical motion control application. Dynamic performance of SMA and its ability in replacing servo motor is studied for which the famous open loop unstable balancing ball and beam system direct driven by antagonistic SMA is designed and developed. Simulation uses the mathematical model of ball and beam structure derived from the first principles and model estimated for the SMA actuator by system identification. A PID based cascade control system consisting of two loops is designed and control of ball trajectory for various target positions with settling time as control parameter is verified experimentally. The results demonstrate the performance of SMA for a complicated i.e., under actuated, highly nonlinear unstable system, and thereby it's dynamic behaviour. Control strategies bring out the effectiveness of the actuator and its possible application to much more complex applications such as in aerospace control and robotics.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.307-314
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• 2021

Even though the LCL filters have superior harmonic attenuation ability to L filters, stability has always been an issue. The system could be unstable because of the resonance phenomenon, especially when digital controller is used. Adding a notch filter to the compensator is one approach to solve the problem. Resonance phenomenon can be inhibited by aligning notch frequency to system resonance frequency. However, resonance frequency variation can be obtained because the actual system has a nonstationary characteristic. Therefore, the system could be unstable, where the system parameters are changed when the conventional notch filter is used. An adaptive digital notch filter that stabilizes the system even system parameters are changed. Simulation and experiment results are provided to verify the validity of the proposed adaptive filter.

• Journal of Biomedical Engineering Research
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• v.28 no.5
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• pp.636-646
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• 2007

Adequate postural control depends on the spatial and temporal integration of vestibular, visual, and somatosensory information. Especially, the musculoskeletal function is essential to maintain the postural control. The experimental studies was performed on the muscular activities in the lower extremities during maintaining and moving exercises on an unstable platform with Magneto Rheological(MR) dampers. The unstable platform of the developed system was controlled by electric currents to the MR dampers. A subject executed the maintaining and moving exercises which are presented through the display monitor. The electromyographies of the eight muscles in lower extremities were recorded and analyzed in the time and the frequency domain: the muscles of interest were rectus femoris(RF), biceps femoris(BF), tensor fasciae latae(TFL), vastus lateralis(VL), vastus medialis(VM), gastrocnemius(Ga), tibialis anterior(TA), Soleus(So). The experimental results showed that the muscular activities differed in the four moving exercises and the nine maintaining exercises. For the anterior-posterior pattern, the TA showed highest activities; for the left-right pattern, the TFL; for the 45, $-45^{\circ}$ pattern, the TFL and TA. Also, the rate of the increase in the muscular activities were affected by the condition of the unstable platform with MR dampers for the maintaining and moving exercises. The experimental results suggest that the choice of different maintaining and moving exercises could selectively train different muscles in various intensity. Futhermore, the findings suggested that the training using this system can improve the ability of postural control.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.556-559
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• 1999

In this paper, the Observer Controller IDentification/Eigensystem Realization Algorithm(OCID/ERA) is applied to identify the state space model of a helicopter in hover from a given set of the general input-output data. The objective of this paper is the evaluation of the utility of the OCID/ERA approach to the system identification of a system which has natural unstable mode like a helicopter and to give some guidelines before applying the technique to the real system. As it mentioned above, since a model helicopter is unstable naturally, the closed-loop system identification method(OCID/ERA) using excitation, output and feedback signals of the simulated system is applied.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.122-124
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• 2007

Master and slave of teleoperation control system through internet or long distance cable must keep stable. If one part becomes unstable or time delay happens in network, the all system can become unstable. Usually stability of teleoperation control system can distinguish by passivity. In this paper, we implemented bilateral teleopcration control system that load passivity controller to keep stability of system. Composed by manipulator that trillion this sricks and horizontal manufacturing that have force reflecting function are available and embodied so that control through wireless LAN may be available. And distinguished stability through an experiment and manufacturing performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2365-2370
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• 2008

In this paper, applications of wavelet neural network controller to position control of nonlinear system are considered. Wavelet neural network is used in the objectives which improve the efficiency of LQR controllers. It is possible to make unstable nonlinear systems stable by using LQR(Linear Quadratic Regulator) technique. And, in order to be adapted to disturbance effectively in this system it uses wavelet neural network controller. Applying this method to the position control of nonlinear system, its usefulness is verified from the results of experiment.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.1 s.94
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• pp.72-80
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• 2005

Recent studies have dealt with brake squeal in terms of the coupled vibration of brake component parts. In this paper, we assemble the mode models derived from FE analysis of the individual components of the drum brake system into the system model by considering the friction interaction of the lining and drum at the interface. The validity of the component models are backed up by the experimental confirmation work. By scrutinizing the real parts of the complex eigen-values of the system, the unstable modes, which may be strong candidate sources of squeal noise, are identified. Mode participation factors are calculated to examine the modal coupling mechanism. The model predictions for the unstable frequencies pointed well the actual squeal noise frequencies measured through field test. Sensitivity analysis is also performed to identify parametric dependency trend of the unstable modes, which would indicate the direction for the squeal noise reduction design. Finally, reduction of the squeal noise tendency through shape modification is tried.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.17 no.2
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• pp.129-138
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• 2013

A spatio-temporal models as systems of ODE which describe two-species Beddington - DeAngelis type predator-prey system living in a habitat of two identical patches linked by migration is investigated. It is assumed in the model that the per capita migration rate of each species is influenced not only by its own but also by the other one's density, i.e. there is cross diffusion present. We show that a standard (self-diffusion) system may be either stable or unstable, a cross-diffusion response can stabilize an unstable standard system and destabilize a stable standard system. For the diffusively stable model, numerical studies show that at a critical value of the bifurcation parameter the system undergoes a Turing bifurcation and the cross migration response is an important factor that should not be ignored when pattern emerges.

• 한국공간정보시스템학회:학술대회논문집
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• 2004.05a
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• pp.75-82
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• 2004

Many researcher's efforts have made a significant advancement of space frame structure with various portion, and it becomes the most outsanding one of space structures. However, with the characteristics of thin and long term of spacing, the unstable behavior of space structure is shown by initial imperfection, erection procedure or joint, especially space frame structure represents more. This kind of unstable problem could not be set up clearly and there is a huge difference between theory and experiment. Moreover, the discrete structure such as space frame has more complex solution, this it is not easy to derive the formulation of design about space structure. In this space frame structure, the character of rise-span ratio or load mode is represented by the instability of space frame structure with initial imperfection, and snap-through or bifurcation might be the main phenomenon. Therefore, in this study, space frame structure which has a lot of aesthetic effect and profitable for large space covering single layer is dealt. And because that the unstable behavior due to variation of inner force resistance in the elastic range is very important collapse mechanism, I would like to investigate unstable character as a nonlinear behavior with a geometric nonlinear. In order to study the instability. I derive tangent stiffness matrix using finite element method and with displacement incremental method perform nonlinear analysis of unit space structure, star dome and 3-ring star dome considering rise-span $ratio(\mu}$ and load $ratio(R_L)$ for analyzing unstable phenomenon.