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Design and Control of Flexure based XY θz Stage
Dongwoo. Kang,Kihyun Kim,Youngman Choi,Daegab Gweon,Sukwon Lee,Moongoo. Lee 대한기계학회 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.11S
This article presents the design and control of an ultraprecision XY θz stage with nanometer accuracy. The stage has a plane mechanism and symmetric hexagonal structure which consists of a monolithic flexure hinge mechanism with three piezoelectric actuators and six flexures preserving the plane motion. The symmetric design reduces the effect of temperature gradient on the structure. Because the relationship between design variables and system parameters are quite complicated and there are some trade-offs among them, it is very difficult to set design variables manually and optimal design procedure is used. The objective of design is maximizing the 1st resonant frequency to improve the dynamic characteristics. The reason is that the stage must move with heavy load of about 20 ㎏. The higher resonant frequency also makes the stage stiffer and stronger against the dynamic force and moment. This paper describes the procedures of selecting parameters for the optimal design and a mathematical formulation for the optimization problem. The stage was designed to attain ± 10 um in the X- and Y-direction and ±90arcsec in the yaw direction at the same time and have the 1st resonant frequencies of 455.5 ㎐ in X- and Y-direction and 275.3 ㎐ for yaw direction without load. The stage was fabricated according to the optimal design results and experimental results indicate that the design procedure is effective. A conventional PI control results are presented for ultraprecision motion.
Heavy Metal Reduction and Solidification based on CO<sub>2</sub> Uptake using Hydroxide Solutions
( Dongwoo Kang ),( Juhee Son ),( Yunsung Yoo ),( Jinwon Park ) 한국폐기물자원순환학회(구 한국폐기물학회) 2019 한국폐기물자원순환학회 추계학술발표논문집 Vol.2019 No.-
A large amount of municipal solid waste (MSW) is produced daily due to the development of the industry and economy, most of which is utilized, incinerated, and deposited in landfills. In some developed nations in Europe, the utilization of MSW incineration (MSWI) ash as construction material has been studied because of its physical properties, which are similar to that of aggregate. Except for the utilization, most of the produced MSW is incinerated and deposited in landfills. However, landfills are not preferred in nations with confined land areas because they require a large area due to the MSW volume. To decrease the MSW volume, incineration can be used. However, problems occur with respect to the treatment of MSWI ashes. When MSWI ashes are buried, hazardous components, such as heavy metals and othermetal components, can leach out, resulting in groundwater pollution. Because the groundwater can flow over long distances, the environmental and biological problems are not limited to the land close to the landfill area. Hence, the MSWI ash must be stabilized. In this study, we discuss new methods that can be used to treat MSWI fly ashes withhigher heavy metal contents compared with MSWI bottom ashes. By adding 0.5 M ammonium, sodium, and potassium hydroxide solutions to the MSWI fly ash, the leaching of hazardous materials, including heavy metals and other metal cations, is induced. Subsequently, the characteristics of the solution, which has a high pH value, are utilized and a CO<sub>2</sub> uptake procedure is applied to fix the metal cations in the aqueous phase in solids for easier handling. Compared with conventional acid leaching, the heavy metals, which leach out of the MSWI fly ash, can be converted into solids by CO<sub>2</sub> uptake. Further handling is easier and additional wastewater processing is not required. To verify the methodology, the compositions of the untreated MSWI fly ash and MSWI fly ash treated with four types of leaching solution, that is, distilled water, 0.5 M sodium hydroxide aqueous solution, 0.5 M potassium hydroxide aqueous solution, and 0.5 M ammonium hydroxide solution, were analyzed. The heavy metal reduction characteristics were determined using supporting data obtained from different methods such as qualitative XRD and SEM analyses.
Dongwoo Kang,Ju Lee IEEE 2014 IEEE transactions on magnetics Vol.50 No.2
<P>This paper proposes an electromagnetic field computation method using an interpolation method with sigmoid functions. This method is useful for approximating and developing a 3-D electromagnetic field model. Particularly, the authors have been researching a spherical motor for a robotic eye. The spherical motor has a spherical air-gap unlike the radial air-gap motor or the axial air-gap motor. The spherical motor proposed in this paper realizes three degrees-of-freedom movements with only one motor. As the spherical motor has a complicated coil structure, the 3-D FEM would be essential for calculating torque while the rotor is tilted. However, 3-D FEM requires much computation time and a huge memory capacity to store the results. The electromagnetic field is rapidly calculated using an interpolation torque function proposed in this paper. The improvement of the spherical motor due to our method is verified through experiment, the results of which are compared with simulation data.</P>
Kang, Dongwoo,Lee, Eonseok,Kim, Hyunchang,Choi, Young-Man,Lee, Seunghyun,Kim, Inyoung,Yoon, Dukkyun,Jo, Jeongdai,Kim, Bongmin,Lee, Taik-Min American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.115 No.23
Offset printing processes are promising candidates for producing printed electronics due to their capacity for fine patterning and suitability for mass production. To print high-resolution patterns with good overlay using offset printing, the velocities of two contact surfaces, which ink is transferred between, should be synchronized perfectly. However, an exact velocity of the contact surfaces is unknown due to several imperfections, including tolerances, blanket swelling, and velocity ripple, which prevents the system from being operated in the synchronized condition. In this paper, a novel method of measurement based on the sticking model of friction force was proposed to determine the best synchronized condition, i.e., the condition in which the rate of synchronization error is minimized. It was verified by experiment that the friction force can accurately represent the rate of synchronization error. Based on the measurement results of the synchronization error, the allowable margin of synchronization error when printing high-resolution patterns was investigated experimentally using reverse offset printing. There is a region where the patterning performance is unchanged even though the synchronization error is varied, and this may be viewed as indirect evidence that printability performance is secured when there is no slip at the contact interface. To understand what happens at the contact surfaces during ink transfer, the deformation model of the blanket's surface was developed. The model estimates how much deformation on the blanket's surface can be borne by the synchronization error when there is no slip at the contact interface. In addition, the model shows that the synchronization error results in scale variation in the machine direction (MD), which means that the printing registration in the MD can be adjusted actively by controlling the synchronization if there is a sufficient margin of synchronization error to guarantee printability. The effect of synchronization on the printing registration was verified experimentally using gravure offset printing. The variations in synchronization result in the differences in the MD scale, and the measured MD scale matches exactly with the modeled MD scale. (C) 2014 AIP Publishing LLC.
Oxidation resistance of iron and copper foils coated with reduced graphene oxide multilayers.
Kang, Dongwoo,Kwon, Jee Youn,Cho, Hyun,Sim, Jae-Hyoung,Hwang, Hyun Sick,Kim, Chul Su,Kim, Yong Jung,Ruoff, Rodney S,Shin, Hyeon Suk American Chemical Society 2012 ACS NANO Vol.6 No.9
<P>Protecting the surface of metals such as Fe and Cu from oxidizing is of great importance due to their widespread use. Here, oxidation resistance of Fe and Cu foils was achieved by coating them with reduced graphene oxide (rG-O) sheets. The rG-O-coated Fe and Cu foils were prepared by transferring rG-O multilayers from a SiO(2) substrate onto them. The oxidation resistance of these rG-O-coated metal foils was investigated by Raman spectroscopy, optical microscopy, and scanning electron microscopy after heat treatment at 200 °C in air for 2 h. The bare metal surfaces were severely oxidized, but the rG-O-coated metal surfaces were protected from oxidation. This simple solution process using rG-O is one advantage of the present study.</P>