Journal of the Korean Society for Precision Engineering

Study on Phase and Tip-tilt Control Using Adaptive SPGD Algorithm for Coherent Beam Combining: Hyeong Min Yoon, Sangmin Lee, Jae Woo Jung, Kang Hee Lee, Jae Heon Jung, Chang Hwan Kim, Byunghyuck Moon, Eunji Park, Ki Hyuck Kim, Seongmook Jeong, Jun Young Yoon; J. Korean Soc. Precis. Eng. 2025;42(12):1079-1087.
Published online December 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.034

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Coherent Beam Combining (CBC) is a promising technique for enhancing laser output power by accurately aligning the phase and position of multiple laser beams. The Stochastic Parallel Gradient Descent (SPGD) algorithm is commonly used in CBC systems due to its simplicity and scalability. However, its dependence on fixed control parameters can result in slow convergence rates and diminished control stability. To overcome these challenges, this study introduces an adaptive SPGD algorithm that dynamically adjusts the perturbation amplitude and learning rate based on the real-time value of the objective function. This approach accelerates convergence during the initial stages by increasing control inputs when the objective function value is low, while ensuring stability as the function nears its maximum in later stages. Numerical simulations of 7-channel and 19-channel CBC systems revealed that the adaptive SPGD algorithm reduced average iteration counts by 26.4% and 18.1%, respectively, compared to the basic SPGD. Furthermore, the overall control performance improved, achieving high beam combining efficiency with reduced total computation time. This proposed algorithm serves as a straightforward yet effective enhancement to the conventional SPGD method, improving both convergence speed and stability.

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Tape-casting Process Electrochemical Characteristic Test for Fabrication of LST-GDC for Anode Supported SOFCs: Min Ji Kim, Chunghyun Kim, Young-Beom Kim; J. Korean Soc. Precis. Eng. 2025;42(11):937-942.
Published online November 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.073

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In this study, we developed a composite anode support composed of La-doped SrTiO₃ (LST) and Gd-doped CeO₂ (GDC) using a tape casting process for solid oxide fuel cells (SOFCs). By adjusting the pore former content in the slurry, we constructed a bilayered structure consisting of a porous anode support layer (ASL) and a dense anode functional layer (AFL) with the same material composition. The number of tape-cast sheets was controlled to tailor the overall thickness, and lamination followed by co-sintering at 1250^oC resulted in a mechanically robust bilayer. We characterized the microstructural evolution concerning sintering temperature and pore former content using SEM, while XRD confirmed the phase stability of LST and GDC. The measured electrical conductivity at 750^oC ensured sufficient electron transport. To enhance interfacial adhesion and suppress secondary phase formation, we introduced a GDC buffer layer and a pre-sintering treatment prior to electrolyte deposition. A full cell with a YSZ electrolyte and LSCF cathode achieved a stable open circuit voltage of approximately 0.7 V and demonstrated continuous operation at 750^oC. These findings highlight the suitability of LST-GDC composite anodes as thermochemically stable supports, potentially enabling direct hydrocarbon utilization in intermediate-temperature SOFCs.

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Resistant Characteristics of AAO-Based Thin Film Solid Oxide Fuel Cells Using Ni-GDC Anode by GLAD Method: Jaewon Yoo, Myung Seok Lee, Yang Jae Kim, Suk Won Cha; J. Korean Soc. Precis. Eng. 2023;40(4):335-340.
Published online April 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.135

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In this study, we fabricated thin film solid oxide fuel cells on nanoporous anodic aluminum oxide (AAO) substrate for low-temperature operation using the all-through sputtering method. To deposit up to a three-micrometer thick anode with both porosity and electrical conductivity, we used the glancing angle deposition and co-sputtering methods. For the anode materials, we used nickel gadolinium-doped-ceria (Ni-GDC) mixed ionic and electronic conductor (MIEC), which improved hydrogen oxidation reaction reactivity at the anode side. TF-SOFCs were successfully operated at 500℃, and 223.6 mW/cm² was their highest measured maximum power density. We conducted structural and electrochemical analyses to figure out cells’ unique resistant characteristics; ohmic resistance through the anode thin film and polarization resistance of reaction area near the narrowed anode pores. We found how the anode thin film thickness affects the current collecting performance and the anode reactivity, and their effects were qualitatively and quantitatively compared.

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Improvement of Electrolyte Layer Coating Quality Using Statistical Optimization: Seongyong Kim, Changwoo Lee; J. Korean Soc. Precis. Eng. 2019;36(2):149-153.
Published online February 1, 2019; DOI: https://doi.org/10.7736/KSPE.2019.36.2.149

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Slot-die coating technique has become a subject of interest owing to its mass and large area production characteristics. To date, numerous research on the fluid dynamics of coated solution and experimental decision of the coating conditions to improve quality of coated layer have been conducted. However, few studies have been done on the optimization of slot-die coater geometry owing to the high cost associated with its fabrication. In this study, we optimize the geometry of the slotdie coater using computational fluid dynamics. We used a statistical optimization technique (Box-Behnken design). In the optimization process, we determined the significant factors that affect the velocity variation of coated fluid in the transverse direction. An optimal geometry was derived using a desirability test which is generally used to evaluate the suitability of a selected geometry value based on the maximization of the velocity uniformity. Experimental results presenting the uniformity of the coated layer in the transverse direction improved from 4.7% to 1.4%.

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Development and Case Studies of a Function-Based Method for Geometric Tolerance Design: Ho Jae Ahn, Hyunjune Yim; J. Korean Soc. Precis. Eng. 2018;35(4):433-442.
Published online April 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.4.433

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In order to help design engineers to adopt the Geometric Dimensioning & Tolerancing (GD&T), this paper develops a stepby-step method for tolerance design based on the function of the product and its parts. The procedure of this method consists of (1) analysis of functions using Key Characteristics (KC) and Datum Flow Chain (DFC), (2) selection of datum features, and (3) the selection of geometric tolerance types based on the functions. The rules and guidelines for the two latter steps are given and explained in detail, in order that the design engineer can understand the reasons for the rules and use them effectively. The method presented in this paper differs from other previous work, as it is based on the functions, whereas we note that previous work typically focuses on the automation of the tolerancing task without due consideration of functions. The paper also illustrates the developed method through two case studies: an axle-wheel assembly model and a simplified refrigerator model. This geometric tolerance design method is not complete yet in the coverage of various tolerances, e.g. size tolerances and profile, but may assist the beginning design engineer developing a mastery over GD&T.

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An Advanced Prediction Technology of Assembly Tolerance for Vehicle Door
Nam-Yeoung Jeoung, Jin-Hyung Cho, Hyun-Seung Oh, Sae Jae Lee
Journal of Society of Korea Industrial and Systems Engineering.2018; 41(4): 91. CrossRef