• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.817-825
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• 2007

During thirty years, deterministic chaos has moved center stage in many areas of applied mathematics. One important stimulus for this, particularly in the early 1970s, was work on nonlinear aspects of the dynamics of plant and animal populations. There are many situations, at least to a crude first approximation, by a simple first-order difference equation. Past studies have shown that such equations, even though simple and deterministic, can exhibit a surprising array of dynamical behavior, from stable points, to a bifurcating hierarchy of stable cycles, to apparently random fluctuations. But higher-order spectral analyses of such behavior are usually not considered. Higher-order spectra of a signal contain important information that is not present in its power spectrum. So, if we find the spectral pattern and get information from it, it will be able to be used effectively in so many fields. Hence, this paper uses auto bicoherence and bicoherence residue which are sort of bispectrum. Applying these to behavior of logistic difference equation, which is typical chaotic signal, the phenomenon of phase coupling and the appearance of frequency band can be analyzed. Such information means that bispectral analysis is useful to detect nonlinearity of signal.

• The Journal of Korea Robotics Society
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• v.8 no.2
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• pp.92-103
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• 2013

Humanoid robot is the most intimate robot platform suitable for human interaction and services. Biped walking is its basic locomotion method, which is performed with combination of joint actuator's rotations in the lower extremity. The present work employs humanoid robot simulator and numerical optimization method to generate optimal joint trajectories for biped walking. The simulator is developed with Matlab based on the robot structure constructed with the Denavit-Hartenberg (DH) convention. Particle swarm optimization method minimizes the cost function for biped walking associated with performance index such as altitude trajectory of clearance foot and stability index concerning zero moment point (ZMP) trajectory. In this paper, instead of checking whether ZMP's position is inside the stable region or not, reference ZMP trajectory is approximately configured with feature points by which piece-wise linear trajectory can be drawn, and difference of reference ZMP and actual one at each sampling time is added to the cost function. The optimized joint trajectories realize three phases of stable gait including initial, periodic, and final steps. For validation of the proposed approach, a small-sized humanoid robot named DARwIn-OP is commanded to walk with the optimized joint trajectories, and the walking result is successful.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.93-100
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• 1998

The basic systems of spatial structures such as shells, membrane, cable-nets and tensegrity structure have been developed to create the large spaces without column. These structures may have large freedom in scale and form, and especially tensegrity structures are received much attention from the view points of their light weight and aesthetics. But There re some difficulties concerning structural stability, surface formation and construction method. One of the way to solve these problems reasonably is a combination of tensile members and rigid members. A structural system based on this concept is referred to as the "HTS ( Hybrid Tension Structure )". This is a type of flexible structural system which is unstable initially, because the cable material has little initial rigidity. As cable - dome hybrid structures is a type of HTS, the initial stress for the self- equilibrated system having stable state have to be introduced. To determine initial stress having stable state, the shape finding analysis is required before the stress - deformation analysis. In this paper, the primary objective is to derive the nonlinear finite element formula of cable and truss members considering geometric nonlinearity for shape finding of cable-dome, and to propose the method to decide the initial stress by the shape analysis of cable-dome hybrid structure with the self-equilibrated state.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.112-112
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• 2013

Well-defined surfaces of single-crystalline solid materials are starting points of self-organizationof nanostructures and chemical reactions controlled in nanoscale. Although highly ordered atomicarrangement can be obtained on semiconductor surfaces, they can be maintained only in vacuumand not in air or in aqueous environment. Since single-crystalline metal oxide surfaces arechemically stable and no further oxidation occurs, their atomic structures can be utilized fornanofabrication in liquid processes, nanoelectrochemistry and nanobiotechnology. Sapphire is oneof the most stable metal oxides and its crystalline quality is excellent, as can be applied to electronicdevices that require ultralow defect densities. We recently found that chemical phase separationoccurs on sapphire surfaces by annealing processes and the formed nanodomains exhibit specificproperties in air and in water [1,2]. In our experiments, highly selective and controllable adsorptionof various protein molecules is observed on the phase-separated surfaces though the materials andcrystallographic orientations are identical [3,4]. Planar lipid bilayers supported on thephase-separated sapphire surface also exhibit a specific formation site selectivity [5]. Chemicalnanodomains appear on other metal-oxide surfaces, such as well-ordered titania surfaces. Wedemonstrate that surface chemistry of the nanodomains can be characterized in aqueousenvironment using atomic force microscopy equipped with colloidal tips and then show adsorptionand desorption behaviors of various proteins on the phase-separated surfaces.

• Proceedings of the KIEE Conference
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• 2003.07d
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• pp.2325-2327
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• 2003

This thesis is concerned with the control of Arago's disk system using CAN(Controller Area Network). CAN protocol is used widely for the real time control in networked control systems(NCS). A networked control system using CAN is constructed to perform position control of Arago's disk. The mathematical model, of overall system is derived to design an appropriate controller analytical1y. Various operating points of the Arago's disk system in the real time control are chosen as stable region ($45^{\circ}$), marginal1y stable region($90^{\circ}$) and unstable region($120^{\circ}$), and the experiment for the position control of arago's disk system is done for each operating point. The performance of the suggested NCS is verified by experiments. It is shown that the NCS using CAN has stability and excel1ency in real time control.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1742-1745
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• 1997

We have developed a highly responsible probing system for inspection of electrical properties of assemble PCB$_{s}$ (printed circuit boards). However, as the duration of the impact occurring between a probe and a solder joint on PCB is very short, it is very difficult to control the harmful peak impact force and the slip motion of the probe to sufficient level only by its vorce feedback control with high gains. To overcome these disadvantages of the prototype, it needs ot obtain some information of the solder joint in advance before the contact. In addition, to guarantee the reliability of the probing task, the probing system is required to measure several points around the probale target point at high speed. There fore, to meet such requirements, we propose a new noncontaet sensor capable of detecting simultaneously position and normal vectors of the multiple points around the probable target point in real time. By using this information, we can prepare a control strategy for stable contact motion on impact. In this paper, we described measuring priniciple, design, and development of the sensor. The effectiveness of the proposed sensor is verified through a series of experiments.s.

• Journal of Advanced Marine Engineering and Technology
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• v.5 no.1
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• pp.20-27
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• 1981

The alignment of propulsion shaft systems by the fair curve method has been developed over the past twenty years and in recent years its basic problems have been almost solved. At the present time, studies on introducing actual conditions are being undertaken. In a fair curve alignment, its aim is to achieve a stable shaft system which will be relatively insensitive to misalignment or the influence of external factors such as thermal variations due to the sunshine, speed change, etc. The key point of fair curve alignment is the calculations of reactions in the straight support and reaction influence numbers. The present authors have developed those calculating method by the matrix method of the three-moment theorem. The fair curve alignment is based on the analysis of propulsion shaft system which is assumed as a continous beam on multiple support points. The propeller shaft is divided into several elements. For each element, the nodal point equation is derived by the three-moment theorem. Reaction of supporting points of straight shaft and reaction influence numbers are calculated by the matrix calculation of each nodal point equation. It has been found that results of calculation for the model shaft agree well with those of experiment which had been measured by the strain gauge method. Results of calculation for the actual propulsion shafting of the steam turbine had been compared also with those of Det norske Vertas.

• Journal of Korean Association for Spatial Structures
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• v.19 no.4
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• pp.69-76
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• 2019

A stadium roof that uses the pin-jointed spatial truss system has to be designed by taking into account the unstable phenomenon due to the geometrical non-linearity of the long span. This phenomenon is mainly studied in the single-free-node model (SFN) or double-free-node model (DFN). Unlike the simple SFN model, the more complex DFN model has a higher order of characteristic equations, making analysis of the system's stability complicated. However, various symmetric conditions can allow limited analysis of these problems. Thus, this research looks at the stability of the DFN model which is assumed to be symmetric in shape, and its load and equilibrium state. Its governing system is expressed by nonlinear differential equations to show the double Duffing effect. To investigate the dynamic behavior and characteristics, we normalize the system of the model in terms of space and time. The equilibrium points of the system unloaded or symmetrically loaded are calculated exactly. Furthermore, the stability of these points via the roots of the characteristic equation of a Jacobian matrix are classified.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.211-218
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• 1999

The traditional robot manipulators are actuated by continuous range of motion actuators such as motors or hydraulic cylinders. However, there are many applications of mechanisms and robotic manipulators where only a finite number of locations need to be reached, and the robot’s trajectory is not important as long as it is bounded. Binary manipulator uses actuators which have only two stable states. As a result, binary manipulators have a finite number of states. The number of states of a binary manipulator grows exponentially with the number of actuators. This kind of robot manipulator has some advantage compared to a traditional one. Feedback control is not required, task repeatability can be very high, and finite state actuators are generally inexpensive. And this kind of robot manipulator has a fault tolerant mechanism because of kinematic redundancy. In this paper, we solve the inverse kinematic problem of a binary parallel robot manipulator using neural network and test the validity of this structure using some arbitrary points m the workspace of the robot manipulator. As a result, we can show that the neural network can find the nearest feasible points and corresponding binary states of the joints of the robot manipulator

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1790-1795
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• 2004

In this paper, the new password system called SPS(Secure Password System) in order to enhance the security of the system as well as to improve the weakness of the password which is very easy to be disclosed by other people, improving the methods which is identifying the users' legality using the computer system in the multi-users computer. SPS is adopting several strong points such as Easy Embodiment, Low Cost, and most of the good points of the traditional password system. In addition, it makes an easy introduction from the traditional password system. Above SPS has the high stable security in the practical experiments about both the literal attack of the online intruders and the exposure of Clients' password.