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Experimental Investigation of Laser Spot Welding of Ni and Au-Sn-Ni Alloy
Lee, Dongkyoung The Korean Welding and Joining Society 2017 대한용접·접합학회지 Vol.35 No.2
Many microelectronic devices are miniaturizing the capacitance density and the size of the capacitor. Along with this miniaturization of electronic circuits, tantalum (Ta) capacitors have been on the market due to its large demands worldwide and advantages such as high volumetric efficiency, low temperature coefficient of capacitance, high stability and reliability. During a tantalum capacitor manufacturing process, arc welding has been used to weld base frame and sub frame. This arc welding may have limitations since the downsizing of the weldment depends on the size of welding electrode and the contact time may prevent from improving productivity. Therefore, to solve these problems, this study applies laser spot welding to weld nickel (Ni) and Au-Sn-Ni alloy using CW IR fiber laser with lap joint geometry. All laser parameters are fixed and the only control variable is laser irradiance time. Four different shapes, such as no melting upper workpiece, asymmetric spherical-shaped weldment, symmetric weldment, and, excessive weldment, are observed. This shape may be due to different temperature distribution and flow pattern during the laser spot cutting.
Experimental Investigation of Laser Spot Welding of Ni and Au-Sn-Ni Alloy
Dongkyoung Lee 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.2
Many microelectronic devices are miniaturizing the capacitance density and the size of the capacitor. Along with this miniaturization of electronic circuits, tantalum (Ta) capacitors have been on the market due to its large demands worldwide and advantages such as high volumetric efficiency, low temperature coefficient of capacitance, high stability and reliability. During a tantalum capacitor manufacturing process, arc welding has been used to weld base frame and sub frame. This arc welding may have limitations since the downsizing of the weldment depends on the size of welding electrode and the contact time may prevent from improving productivity. Therefore, to solve these problems, this study applies laser spot welding to weld nickel (Ni) and Au-Sn-Ni alloy using CW IR fiber laser with lap joint geometry. All laser parameters are fixed and the only control variable is laser irradiance time. Four different shapes, such as no melting upper workpiece, asymmetric spherical-shaped weldment, symmetric weldment, and, excessive weldment, are observed. This shape may be due to different temperature distribution and flow pattern during the laser spot cutting.
Investigation of Laser Ablation on Acrylonitrile Butadiene Styrene Plastic Used for 3D Printing
Dongkyoung Lee 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.1
Microrobotic devices have been widely investigated as promising alternatives to convent biomedical technologies. Microrobotic devices having spatially complex structures such as the helical structures has generally been manufactured by using three-dimensional (3D) printing technologies. However, due to the limitations of the extrusion and lamination processes, microrobotic devices can be constructed with low degree of precision and can have poor surface roughness under the 3D printing technologies. This may cause undesirable damages to the human body tissues. Furthermore, 3D printing requires long processing time due to postprocessing to remove unwanted body parts. To improve surface quality and shorten processing time, this research uses laser machining. Before directly applying laser machining to fabricate microrobotic devices, understanding laser ablation characteristics on Acrylonitrile Butadiene Styrene (ABS), which is a common material used for 3D printing, is necessary. Laser ablation characteristics on this material are investigated with a variation of laser parameters such as a scanning speed and the number of scanning passes. An ablation depth prediction model is suggested. Laser ablation on ABS shows a high aspect ratio (~327.2). Furthermore, color changes around the ablation zone can be utilized for the indication to estimate the absorbed laser energy indirectly.
이성구(Sung-Goo Lee),이호원(Ho-Won Lee),좌동경(Dongkyoung Chwa),홍석교(Suk-Kyo Hong) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
본 논문에서는 비전 시스템으로부터 획득된 인공적 표적을 인식하여 이동로봇과의 상대적인 위치와 자세정보를 추정하고 이동로봇의 위치 안정화 제어 알고리즘을 설계한다. 제안된 상대적 위치추정 및 안정화 알고리즘은 기존의 이동로봇의 위치를 추정하여 목표점과의 상대적 관계를 연산하는 방법에 비해 이동로봇의 위치추정 오차가 이동로봇의 제어 성능에 미치는 영향이 없어 도킹 시스템과 같은 다양한 응용분야에 적용가능하다.
Decentralized behavior-based formation control of multiple robots considering obstacle avoidance
Lee, Giroung,Chwa, Dongkyoung Springer-Verlag 2018 Intelligent service robotics Vol.11 No.1
<P>This paper proposes a decentralized behavior-based formation control algorithm for multiple robots considering obstacle avoidance. Using only the information of the relative position of a robot between neighboring robots and obstacles, the proposed algorithm achieves formation control based on a behavior-based algorithm. In addition, the robust formation is achieved by maintaining the distance and angle of each robot toward the leader robot without using information of the leader robot. To avoid the collisions with obstacles, the heading angles of all robots are determined by introducing the concept of an escape angle, which is related with three boundary layers between an obstacle and the robot. The layer on which the robot is located determines the start time of avoidance and escape angle; this, in turn, generates the escape path along which a robot can move toward the safe layer. In this way, the proposed method can significantly simplify the step of the information process. Finally, simulation results are provided to demonstrate the efficiency of the proposed algorithm.</P>
Control Strategy for Modifiable Bipedal Walking on Unknown Uneven Terrain
Lee, Woong-Ki,Chwa, Dongkyoung,Hong, Young-Dae The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.6
Previous walking pattern generation methods could generate walking patterns that allow only straight walking on flat and uneven terrain. They were unable to generate modifiable walking patterns whereby the sagittal and lateral step lengths and walking direction can be changed at every footstep. This paper proposes a novel walking pattern generation method to realize modifiable walking of humanoid robots on unknown uneven terrain. The proposed method employs a walking pattern generator based on the 3-D linear inverted pendulum model (LIPM), which enables a humanoid robot to vary its walking patterns at every footstep. A control strategy for walking on unknown uneven terrain is proposed. Virtual spring-damper (VSD) models are used to compensate for the disturbances that occur between the robot and the terrain when the robot walks on uneven terrain with unknown height. In addition, methods for generating the foot and vertical center of mass (COM) of the 3-D LIPM trajectories are developed to realize stable walking on unknown uneven terrain. The proposed method is implemented on a small-sized humanoid robot platform, DARwIn-OP and its effectiveness is demonstrated experimentally.
Robust Swing Up and Balancing Control of the Acrobot Based on a Disturbance Observer
Sanghyob Lee,Myunghwan Eom,Dongkyoung Chwa 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
This paper proposes robust swing up and balancing control scheme of the acrobot system based on a disturbance observer. The partial feedback linearization and LQR control method are fast and effective way to control the nominal acrobot system. However, these control method does not guarantee the robustness. Also, the limit cycle phenomenon which appears in the acrobot system around the desired unstable equilibrium point can be assumed a sinusoidal signal. Therefore, disturbance observer for the sinusoidal disturbance is applied to develop the compensation scheme which minimizes the effect of the disturbance. The proposed control strategy was verified through the simulation results.