Cheol Hoon Park

Korea Institute of Machinery and Materials, Sŏul, Seoul, South Korea

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Publications (74)58.56 Total impact

  • Cheol Hoon Park · Tae Gwang Yoon · Jun Young Park

    No preview · Article · Dec 2015
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    ABSTRACT: The development of long-duration mobile energy sources suitable for mobile robots or small-sized unmanned vehicles is an area of active research. The micro gas turbine generator (MTG) is a promising solution for this purpose because it has both a high energy density and a high power density. A 500W class MTG is under development. The design of the MTG can be divided into two main parts. One part consists of the motor/generator and compressor, whereas the other part consists of the combustor, turbine, and recuperator. The 500W class MTG is designed to operate at an extremely high speed of 400,000 rpm, with a turbine temperature of over 700 °C, to improve the efficiency. Because the magnetism of the NdFeB permanent magnet for the motor/generator would degrade if it were exposed to temperatures over 150-200 °C, thermal insulation between the two parts is needed to reduce the heat transfer from the combustor and turbine. The motor/generator is also cooled by the inlet air flow driven by the compressor. This study presents the results of an experiment designed to verify whether the thermal insulation and air flow are effective enough to keep the temperature of the motor/generator part below 100 °C. From the rotating test, performed with the aid of a high-temperature test rig, it was confirmed that a temperature of less than 50 °C could be maintained in the motor/generator part, under the condition of 1.0 bar compressed air supply.
    No preview · Conference Paper · Jul 2014
  • Cheol Hoon Park · Sang Kyu Choi · Sang Yong Ham

    No preview · Article · Jun 2014
  • Cheol Hoon Park · Sang Kyu Choi · Sang Yong Ham
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    ABSTRACT: Magnetic bearings are oil-free bearings that are widely employed in turbo machineries such as turbo refrigerant compressors in order to eliminate lubrication systems, avoid contamination, and increase efficiency. We have developed a 145 refrigerant ton (RT)-class turbo refrigerant compressor using homopolar-type radial hybrid magnetic bearings (HMBs) and thrust magnetic bearings. The thrust magnetic bearing comprises a thrust HMB and a permanent magnet that generate downward forces to overcome high upward thrust forces of 2000 N at 21 000 rpm. A test rig and controller for the compressor with magnetic bearings were fabricated, and rotordynamics such as the unbalance response and axial displacement were investigated. Rotordynamics analyses using the finite element method predicted that the 1st bending mode is located at a high frequency with sufficient margin from the operating speeds. Further, the zero-to-peak displacement caused by the unbalanced response was sufficiently small. The rotor was stably supported with few vibrations across the entire range of the operational speeds. Our results demonstrate that the advantages of oil-free bearings can be easily exploited in turbo machineries such as turbo refrigerant compressors by adopting HMBs.
    No preview · Article · Jan 2014 · Mechanics and Industry
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    ABSTRACT: Satellites provide a lot of information and essay roles in the areas of defense and space observations. The precise distances to the satellites are measured by emitting and retro-reflecting a laser. For such surveys, satellite laser ranging (SLR) systems have been developed in different forms and for different areas. The structural integrity of the tracking mount is essential for it to be able to track a high-speed satellite precisely, overcoming the various external and internal disturbances and operating conditions. In this study, the analysis of a tracking mount was performed for weight, wind loads, and inertia loads in order to verify its soundness. The results of the comparison between aluminum and steel were analyzed in order to select the optimal material for the fork and main housing part. In addition, the natural frequency and mode shape were predicted. Optimal material selection and structural integrity will also be verified using static analysis.
    Preview · Article · Oct 2013
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    ABSTRACT: This Note proposes a novel radial-thrust combo metal mesh foil bearing (MMFB). Although MMFBs have advantages such as higher stiffness and damping over conventional air foil bearings, studies related to MMFBs have been limited to radial MMFBs. The novel combo MMFB is composed of a radial top foil, thrust top foils, and a ring-shaped metal mesh damper-fabricated by compressing a copper wire mesh-with metal mesh thrust pads for the thrust bearing at both side faces. In this study, the combo MMFB was fabricated in half-split type to support the rotor for a micro gas turbine generator. The manufacture and assembly process for the half-split-type combo MMFB is presented. In addition, to verify the proposed combo MMFB, motoring test results up to 250 000 rpm and axial displacements as a function of rotational speed are presented.
    No preview · Article · Oct 2013 · The Review of scientific instruments
  • Dong Il Park · Cheol Hoon Park · Joohan Park · Jinho Kyung · Doohyung Kim
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    ABSTRACT: There are many automation system in the thin film solar cell manufacturing line. Especially, many kinds of robot are used to handle the large solar cell substrate. Handling the large substrate at high speed is an important issue for high productivity. Because the robot handles the large and heavy substrate at high speed, there are some issues such as vibration control and the optimal design of arms and forks. There have been some previous research about the deflection and the compensation of arms and forks. And we also performed the static/dynamic simulation and analyzed the vibration characteristics in the previous research. In the paper, we carried out more specific simulation and compared the result with the basic vibration characteristics. We can establish the exacter simulation model by the comparison between the simulation and the experiment. We applied the vibration control algorithm such as input shaping algorithm to reduce vibration and proved the effect of the vibration control using both simulation and experiment.
    No preview · Conference Paper · Oct 2013
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    Cheol Hoon Park · Sang Kyu Choi · Ji Hoon Ahn · Sang Yong Ham · Soohyun Kim
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    ABSTRACT: Hybrid-type magnetic bearings using both permanent magnets and electromagnets have been used for rotating machinery. In the case of conventional thrust hybrid magnetic bearings supporting axial loads, radially magnetized permanent ring magnets, which have several demerits such as difficult magnetization and assembly, have been used to generate bias flux. In this study, a novel thrust hybrid magnetic bearing using an axially magnetized permanent ring magnet is presented. Because it is easy to magnetize a ring magnet in the axial direction, the segmentation of the ring magnet for magnetization is not required and the assembly process can be simplified. For verifying the performance of the proposed method, a test rig that consists of a proposed thrust magnetic bearing and variable loads is constructed. This paper presents the detailed design procedures and the obtained experimental results. The results show that the developed thrust magnetic bearing has the potential to replace conventional thrust magnetic bearings.
    Preview · Article · Sep 2013 · Journal of Magnetics
  • Cheol Hoon Park · Soohyun Kim · Kyung-Soo Kim
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    ABSTRACT: Centrifuges are devices that separate particles of different densities and sizes through the application of a centrifugal force. If a centrifuge could be operated under atmospheric conditions, all vacuum-related components such as the vacuum chamber, vacuum pump, diffusion pump, and sealing could be removed from a conventional centrifuge system. The design and manufacturing procedure for centrifuges could then be greatly simplified to facilitate the production of lightweight centrifuge systems of smaller volume. Furthermore, the maintenance costs incurred owing to wear and tear due to conventional ball bearings would be eliminated. In this study, we describe a novel vacuum chamber-free centrifuge supported by magnetic bearings. We demonstrate the feasibility of the vacuum chamber-free centrifuge by presenting experimental results that verify its high-speed support capability and motoring power capacity.
    No preview · Article · Sep 2013 · The Review of scientific instruments
  • Cheol Hoon Park · Sang Kyu Choi
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    ABSTRACT: For turbo refrigerant compressor, oil-free bearing has merits that the continuous operation is possible because the lubrication system is not required and the refrigerant is not contaminated by the oil. Magnetic bearing is one of oil-free bearing and recently it started to be applied to a few turbo refrigerant compressors because of easy maintenance thanks to no friction and no wear in bearing. 200RT class turbo refrigerant compressor using oil-free bearing is under development after finishing the development of 145RT compressor. This paper presents the design modification from 145RT compressor and design procedure of hybrid thrust magnetic bearing using both of permanent magnet and electromagnet. Thrust magnetic bearing are designed to support 2,000N thrust force by compressor at 18,000rpm operating speed. The controller for magnetic bearing was designed and the rotordynamic analysis such as critical speed, and unbalance response in case that the rotor is supported by magnetic bearings are simulated by using finite-element method.
    No preview · Chapter · Jan 2013
  • Jong-Seok Lee · Cheol Hoon Park · Touradj Ebrahimi
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    ABSTRACT: Local optimization techniques such as gradient-based methods and the expectation-maximization algorithm have an advantage of fast convergence but do not guarantee convergence to the global optimum. On the other hand, global optimization techniques based on stochastic approaches such as evolutionary algorithms and simulated annealing provide the possibility of global convergence, which is accomplished at the expense of computational and time complexity. This chapter aims at demonstrating how these two approaches can be effectively combined for improved convergence speed and quality of the solution. In particular, a hybrid method, called hybrid simulated annealing (HSA), is presented, where a simulated annealing algorithm is combined with local optimization methods. First, its general procedure and mathematical convergence properties are described. Then, its two example applications are presented, namely, optimization of hidden Markov models for visual speech recognition and optimization of radial basis function networks for pattern classification, in order to show how the HSA algorithm can be successfully adopted for solving real-world problems effectively. As an appendix, the source code for multi-dimensional Cauchy random number generation is provided, which is essential for implementation of the presented method.
    No preview · Chapter · Jan 2013
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    Yuxi Hou · Iickho Song · Hwang-Ki Min · Cheol Hoon Park
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    ABSTRACT: Owing to the singularity of the within-class scatter, linear discriminant analysis (LDA) becomes ill-posed for small sample size (SSS) problems. Null-space-based LDA (NLDA), which is an extension of LDA, provides good discriminant performances for SSS problems. Yet, as the original scheme for the feature extractor (FE) of NLDA suffers from a complexity burden, a few modified schemes have since been proposed for complexity reduction. In this brief, by transforming the problem of finding the FE of NLDA into a linear equation problem, a novel scheme is derived, offering a further reduction of the complexity.
    Full-text · Article · Jun 2012 · IEEE transactions on neural networks and learning systems
  • Cheol Hoon Park · Dong Il Park · Tae Kwang Yoon
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    ABSTRACT: A beam type solar cell substrate transport robot is under development to meet the high demand to increase the productivity of solar cell. In order to reduce the tact time and increase the productivity, the accurate position control with vibration rejection technique becomes more important as the size of solar cell substrate becomes larger. This paper is focusing on the beam type substrate handling robot. The flexible modes of the beam in the fork are predicted by FE analysis and they are verified by the experiment using impact test. After constructing the simulation model including flexible mode, the motion simulation is conducted by using MATLAB/Simulink. The vibration due to the flexible mode during the motion is predicted, and the vibration attenuation after applying input shaping is evaluated. The motion simulation results which input shaping is applied show that the vibration due to the flexible mode could be noticeably attenuated.
    No preview · Conference Paper · Jan 2012
  • Dong Il Park · Cheol Hoon Park · Yijun Yoo
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    ABSTRACT: Nowadays, automation system using robot is very important to increase productivity in mass production system. Especially, solar cell manufacturing line is composed of many types of robots such as cassette robot and several glass handling robots for high productivity. Because solar cell substrate is three to five times heavier than LCD glass substrate, handling a heavy substrate is the main issue in the solar cell manufacturing process. Therefore, position precision, transfer speed and vibration control of glass are the main issues. In the paper, hybrid type substrate handling robot used in the vacuum environment is introduced and its performance is analyzed.
    No preview · Conference Paper · Jan 2012
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    ABSTRACT: In this study, we have proposed and implemented a design for the tracking mount and controller of the ARGO-M (Accurate Ranging system for Geodetic Observation – Mobile) which is a mobile satellite laser ranging (SLR) system developed by the Korea Astronomy and Space Science Institute (KASI) and Korea Institute of Machinery and Materials (KIMM). The tracking mount comprises a few core components such as bearings, driving motors and encoders. These components were selected as per the technical specifications for the tracking mount of the ARGO-M. A three-dimensional model of the tracking mount was designed. The frequency analysis of the model predicted that the first natural frequency of the designed tracking mount was high enough. The tracking controller is simulated using MATLAB/xPC Target to achieve the required pointing and tracking accuracy. In order to evaluate the system repeatability and tracking accuracy of the tracking mount, a prototype of the ARGO-M was fabricated, and repeatability tests were carried out using a laser interferometer. Tracking tests were conducted using the trajectories of low earth orbit (LEO) and high earth orbit (HEO) satellites. Based on the test results, it was confirmed that the prototype of the tracking mount and controller of the ARGO-M could achieve the required repeatability along with a tracking accuracy of less than 1arcsec.
    No preview · Article · Jan 2012 · Advances in Space Research
  • Cheol Hoon Park · Dong il Park · Hyun Min Do
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    ABSTRACT: According to high demand of market for the solar cell, there are active researches to increase the productivity of solar cell. The automated process line to produce solar cell can consist of various types of solar cell substrate handling robots such as cassette transfer robot, glass handling robot and vacuum robot. In order to reduce the tact time and increase the productivity, accurate position control with vibration rejection technique is becoming more important for the solar cell substrate handling robots. This paper is focusing on the substrate handling robot in vacuum environment and presents the design process for its controller. The simulation model for vacuum robot was constructed by using Matlab/SimMechanics and trajectory tracking performance was simulated by using Matlab/Simulink. The motion control simulation for vacuum robot is performed based on the tact time and the results are presented.
    No preview · Article · Jan 2011
  • Cheol Hoon Park · Dong Il Park · Hyun Min Do
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    ABSTRACT: The automated solar cell process line is composed of various types of solar cell substrate handling robots such as cassette transfer robots, glass handling robots and vacuum robots. This paper is focusing on the beam type solar cell substrate transport robot and presents the design procedure for motion simulation model. The simulation model for beam type robot is constructed by using Matlab/Simulink and SimMechanics. The trajectory is generated based on the one tack time motion and the tracking performance using the simulation model is predicted as well.
    No preview · Conference Paper · Jan 2011
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    Jong-Seok Lee · Cheol Hoon Park
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    ABSTRACT: We propose a novel stochastic optimization algorithm, hybrid simulated annealing (SA), to train hidden Markov models (HMMs) for visual speech recognition. In our algorithm, SA is combined with a local optimization operator that substitutes a better solution for the current one to improve the convergence speed and the quality of solutions. We mathematically prove that the sequence of the objective values converges in probability to the global optimum in the algorithm. The algorithm is applied to train HMMs that are used as visual speech recognizers. While the popular training method of HMMs, the expectation-maximization algorithm, achieves only local optima in the parameter space, the proposed method can perform global optimization of the parameters of HMMs and thereby obtain solutions yielding improved recognition performance. The superiority of the proposed algorithm to the conventional ones is demonstrated via isolated word recognition experiments.
    Full-text · Article · Sep 2010 · IEEE TRANSACTIONS ON CYBERNETICS
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    Sung Hwan Won · Iickho Song · Sun Young Lee · Cheol Hoon Park
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    ABSTRACT: A class of recurrent neural networks is proposed and proven to be capable of identifying any discrete-time dynamical system. The application of the proposed network is addressed in the encoding, identification, and extraction of finite state automata (FSAs). Simulation results show that the identification of FSAs using the proposed network, trained by the hybrid greedy simulated annealing with a modified cost function in the training stage, generally exhibits better performance than the conventional identification procedures.
    Full-text · Article · Sep 2010 · IEEE Transactions on Neural Networks
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    ABSTRACT: Various passive and/or active antirolling devices have been used for suppressing the rolling motion of ships in the ocean. In this study, a maglev-type active mass driver (AMD) is developed for controlling the rolling motion of a shiplike structure. No friction is generated during the motion of this maglev-type AMD, as the moving mass is floated by the magnetic levitation force and displaced by the propulsion force generated by the linear motor. For verifying the feasibility of the proposed method, a small AMD having a moving mass of approximately 4.0 kg is constructed and used in a small-scale model of a catamaran. This paper presents the detailed design procedures and obtained experimental results. Our results show that the developed maglev-type AMD has the potential for use in controlling the rolling motion of ships and other oceanographic vessels.
    Full-text · Article · May 2010 · The Review of scientific instruments