• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.687-694
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• 1997

The anisotropy and shape of distributed piezopolymer actuator have advantages over isotropic piezo ceramic materials, since these features of PVDF can be utilized as another design variable in control application. This study is interested in the reduction of sound transmission through elastic plate into interior space by using the PVDF actuator. The plate-cavity system is adopted as a test problem. The vibration of composite plate and the sound fields through plate are analyzed by using the coupled finite element and boundary element method. Some numerical simulations are performed on sound transmission through elastic plates. To investigate the effects of anisotropy and shape of distributed piezopolymer actuator, various kinds of distributed PVDF actuators are applied in sound control simulation for isotropic and anisotropic plates. The PVDF actuators applied are different from each other in their shapes and laminate angles. The results of control simulation show that the control effectiveness of distributed PYDF actuator can be enhanced by using the coupling between shape of actuator and vibration modes of structure and the anisotropy of piezoelectric properties of PVDF.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.503-505
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• 1998

The position control of an induction motor using Feedforward Neural Networks(FNNs) was studied in this paper. A teaching signal was obtained from sliding surface without a particular signal. And the FNNs team through the back propagation algorithm so as to reduce the error between the real position of the motor and the reference value. The structure of a controller was designed simply, for the fast calculating response which is certainly necessary for induction motor position control. And to show the superiority of this controller, 3-phase vector control induction motor whose power capacity is 2.2kw was modeled, and it was simulated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.2
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• pp.124-131
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• 2002

This paper presents the design of an active vibration suppression controller for an air-spring type vibration isolation table. Firstly, isolation system model is constructed considering the isolation table, attached equipment and voice-coil actuator. An active control system is designed based on frequency-shaped sliding mode control theory rewarding high frequency uncertainties with respect to attached equipments on the isolation table. Finally. the performance of the active isolation system is evaluated by simulation under some disturbance conditions which are transmitted from base structure of the isolation system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.835-840
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• 2010

This study develops a variable structure controller using nonlinear surface instead of the fixed, which has been the robustness against parameter variations and extraneous disturbance during the reaching phase. reaching time of the system trajectory is faster than the fixed method. This proposed scheme has better performance than the conventional method in reaching time, parameter variation and extraneous disturbance. The effectiveness of the proposed control scheme is verified by simulation results.

• Journal of the Korean institute of surface engineering
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• v.54 no.1
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• pp.1-11
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• 2021

Porous dendrite structure AuCu alloy was formed using a hydrogen bubble template (HBT) technique by electroplating to improve the catalytic performance of gold, known as an excellent oxygen reduction reaction (ORR) catalyst in alkaline medium. The rich Au surface was maximized by selectively electrochemical etching Cu on the AuCu dendrite surface well formed in a leaf shape. The catalytic activity is mainly due to the synergistic effect of Au and Cu existing on the surface and inside of the particle. Au helps desorption of OH- and Cu contributes to the activation of O2 molecule. Therefore, the porous AuCu dendrite alloy catalyst showed markedly improved catalytic activity compared to the monometallic system. The porous structure AuCu formed by the hydrogen bubble template was able to control the size of the pores according to the formation time and applied current. In addition, the Au-rich surface area increased by selectively removing Cu through electrochemical etching was measured using an electrochemical calculation method (ECSA). The results of this study suggest that the alloying of porous AuCu dendrites and selective Cu dissolution treatment induces an internal alloying effect and a large specific surface area to improve catalyst performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.430.2-430.2
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• 2016

The front transparent conductive oxide (TCO) films in thin fill solar cell should exhibit high transparency, conductivity, good surface morphology and excellent light scattering properties. The light trapping phenomenon is limited due to random surface structure of TCO films. The proper control of surface structure and uniform cauliflower TCO films may be appropriate for efficient light trapping. We report light trapping scheme of ICP-RIE glass texturing by SF6/Ar plasma for high roughness and haze ratio of ITO films. It was observed that the variation of etching time, pattern size and Ar flow ratio during ICP-RIE process were important factors to improve the diffused transmittance and haze ratio of textured glass. The ICP-RIE textured glass showed low etching rates due to the presence of metal elements like Al, B, F and Na. The ITO films deposited on textured glass substrates showed the high RMS roughness and haze ratio in the visible wavelength region. The change in surface morphology showed negligible influence on electrical and structural properties of ITO films. The ITO films with high roughness and haze ratio can be used to improve the performance of thin film solar cells.

• The Journal of Advanced Prosthodontics
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• v.6 no.6
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• pp.427-433
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• 2014

PURPOSE. Surface color is one of the main criteria to obtain an ideal esthetic. Many factors such as the type of the material, surface specifications, number of firings, firing temperature and thickness of the porcelain are all important to provide an unchanged surface color in dental ceramics. The aim of this study was to evaluate the color changes in dental ceramics according to the material type and glazing methods, during the multiple firings. MATERIALS AND METHODS. Three different types of dental ceramics (IPS Classical metal ceramic, Empress Esthetic and Empress 2 ceramics) were used in the study. Porcelains were evaluated under five main groups according to glaze and natural glaze methods. Color changes (${\Delta}E$) and changes in color parameters (${\Delta}L$, ${\Delta}a$, ${\Delta}b$) were determined using colorimeter during the control, the first, third, fifth, and seventh firings. The statistical analysis of the results was performed using ANOVA and Tukey test. RESULTS. The color changes which occurred upon material-method-firing interaction were statistically significant (P<.05). ${\Delta}E$, ${\Delta}L$, ${\Delta}a$ and ${\Delta}b$ values also demonstrated a negative trend. The MC-G group was less affected in terms of color changes compared to other groups. In all-ceramic specimens, the surface color was significantly affected by multiple firings. CONCLUSION. Firing detrimentally affected the structure of the porcelain surface and hence caused fading of the color and prominence of yellow and red characters. Compressible all-ceramics were remarkably affected by repeated firings due to their crystalline structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.2
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• pp.327-333
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• 2003

Most of shape defects in steel strip are originated from the structure of rolling mill itself. For instance, strip crown occurs when the work roll is deformed by the bending moment induced on roll chocks. To get rids of the shape defects, it is necessary to increase the stiffness of rolling mill. The structure change of back-up roll is one of alternative ways to increase the mill stiffness without facility revamping from 4 high mill to 6 high mill. In this research work, the new back-up roll was developed and can be used in any type of 4 high mill to reduce the strip shape defects. The developed back-up roll consists of sleeve, arbor and phase angle adjusting system for arbor. The circumference of arbor is specially machined to adapt the strip width change during rolling. The experimental cold rolling test was done to prove the effectiveness of newly developed back-up roll. The experimental rolling results show that the new back-up roll has more powerful performance in reducing the shape defects than conventional back-up roll. It was also found that the new back-up roll has higher stability for shape control. In addition to, the only sleeve surface needs to be reground and changed in most cases, so that the maintenance cost can be greatly reduced.

• Journal of Institute of Control, Robotics and Systems
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• v.22 no.5
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• pp.320-325
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• 2016

This paper presents a robust finite-time sliding mode control (SMC) scheme for unknown disturbance and unmodeled nonlinear friction and dynamics in the robotic manipulator. A finite-time SMC (FSMC) surface and finite-time sliding mode controller are constructed to obtain faster error convergence than the conventional infinite-time based SMC. By adding prescribed constraint control term to a finite-time SMC to compensate for unknown disturbance and uncertainties, a robust control scheme can be designed as well as faster convergence control. In addition, simpler controller structure is built by using feed-forwarding upper bound coefficients of each manipulator dynamic parameters instead of model-based control or adaptive observer to estimate unknown manipulator parameters. Simulation and experimental evaluations highlight the efficacy of the proposed control scheme for an articulated robotic manipulator.

• ETRI Journal
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• v.36 no.5
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• pp.847-855
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• 2014

We developed a highly refractive index planarization layer showing a very smooth surface for organic light-emitting diode (OLED) light extraction, and we successfully prepared a highly efficient white OLED device with an embossed nano-structure and highly refractive index planarization layers. White OLEDs act as an internal out-coupling layer. We used a spin-coating method and two types of $TiO_2$ solutions for a planarization of the embossed nano-structure on a glass substrate. The first $TiO_2$ solution was $TiO_2$ sol, which consists of $TiO_2$ colloidal particles in an acidic aqueous solution and several organic additives. The second solution was an organic and inorganic hybrid solution of $TiO_2$. The surface roughness ($R_a$) and refractive index of the $TiO_2$ planarization films on a flat glass were 0.4 nm and 2.0 at 550 nm, respectively. The J-V characteristics of the OLED including the embossed nano-structure and the $TiO_2$ planarization film were almost the same as those of an OLED with a flat glass, and the luminous efficacy of the aforementioned OLED was enhanced by 34% compared to that of an OLED with a flat glass.