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Huh, Joo-Youl,Han, Sang-Uk,Park, Chang-Yong 대한금속재료학회 2004 METALS AND MATERIALS International Vol.10 No.2
The effect on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints, caused by adding Bi to eutectic Sn-3.5Ag solder alloy, was examined at the aging temperatures of 150℃ and 180℃. The Cu_(6)Sn_(5) layer growth was significantly enhanced, but the Cu₃Sn layer growth was slightly retarded by the addition of Bi, resulting in significant growth enhancement of the total (Cu_(6)Sn_(5)+Cu₃Sn) IMC layer with increasing Bi addition. The IMC layer growth in the Bi-containing solder joints was accompanied by the accumulation of Bi ahead of the Cu₃Sn layer that resulted in the formation of a liquid layer at the Cu_(6)Sn_(5)/solder interface. A kinetic model was developed for the planar growth of the Cu_(6)Sn_(5) and Cu₃Sn layers in the solder joints, accounting for the existence of interfacial reaction barriers. Predictions from the kinetic model showed that the experimental results could be well explained by the hypothesis that the formation of a Bi-rich liquid layer at the Cu_(6)Sn_(5)/solder interface reduces the interfacial reaction barrier at the interface.
Path Planning for Autonomous Mobile Robot Based on Safe Space
Jong-Hun Park,Uk-Youl Huh 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.5
Path planning is essential for the autonomous navigation of mobile robots. Researchers have been working on ensuring the safe navigation of mobile robots; however, it is impossible to secure the absolute safety of a mobile robot without environmental information. Nevertheless, passive safety of a mobile robot can be secured. With the aim of ensuring safe path planning of a mobile robot, a safety space is proposed in this work by using the parameters of stopping distance and hazard point. Mobile robots should formulate path plans to bypass crossroads or corner areas where their field of view is limited, and they should also be capable of reducing their movement speed to secure safe driving. We demonstrate through extensive simulations that the developed SGPP (safe global path planning) method outperforms the classical A<SUP>*</SUP> and PRM (probabilistic roadmap) algorithms. It improves the navigation time and length of the robot path in comparison to the PRM algorithm and reduces the navigation time by up to 26% compared to the classical A<SUP>*</SUP> algorithm for safe navigation. In addition, results of an experiment conducted on a real robot show that the SGPP method finds a safe path with limited velocity for safe navigation.
Seong-Ryong Chang,Uk-Youl Huh 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.2
Path planning algorithms are used to allow mobile robots to avoid obstacles and find ways from a start point to a target point. The general path planning algorithm focused on constructing of collision free path. However, a high continuous path can make smooth and efficiently movements. To improve the continuity of the path, the searched waypoints are connected by the proposed polynomial interpolation. The existing polynomial interpolation methods connect two points. In this paper, point groups are created with three points. The point groups have each polynomial. Polynomials are made by matching the differential values and simple matrix calculation. Membership functions are used to distribute the weight of each polynomial at overlapped sections. As a result, the path has G<SUP>2</SUP> continuity. In addition, the proposed method can analyze path numerically to obtain curvature and heading angle. Moreover, it does not require complex calculation and databases to save the created path.