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조형래,홍금식 釜山大學校生産技術硏究所 1996 生産技術硏究所論文集 Vol.51 No.-
본 논문은 병렬형 매니퓰에이터의 구동부에 입력되는 힘과 상판으로 출력되는 힘과 모우멘트의 전달특성을 연구하였다. 이러한 전달특성을 연구하기 위하여 상관좌표계의 원점을 기준으로한 힘과 모우멘트 벡터로 구성되는 행렬을 힘과 모우멘트의 2부분으로 분리한 후 특이값 분해를 통하여 힘 및 모우멘트의 조종성능, 민감도, 방향성 등을 해석하였다. 이렇게 해석된 결과들은 병렬형 매니퓰레이터의 설계변수의 한 지침으로 사용되어질 수 있다. This paper presents how the input forces through the prismatic joints of the Stewart platform manipulator are transmitted to the upper plate. The matrix containing unit vectors along the legs and moment vectors about the origin of platform based on the plucker coordinate system is splitted into two parts to consider the force and moment transmissions, respectively. Manipulability and sensitivity were investigated in accordance with the changes of radius of platform and angle between legs. Acquired results could be useful in-determining design parameters like radius of platform, angle between joints in the base and platform, etc.
Classification of somatosensory cortex activities using fNIRS
Hong, Keum-Shik,Bhutta, M. Raheel,Liu, Xiaolong,Shin, Yong-Il Elsevier 2017 Behavioural brain research Vol.333 No.-
<P><B>Abstract</B></P> <P>The ability of the somatosensory cortex in differentiating various tactile sensations is very important for a person to perceive the surrounding environment. In this study, we utilize a lab-made multi-channel functional near-infrared spectroscopy (fNIRS) to discriminate the hemodynamic responses (HRs) of four different tactile stimulations (handshake, ball grasp, poking, and cold temperature) applied to the right hand of eight healthy male subjects. The activated brain areas per stimulation are identified with the <I>t</I>-values between the measured data and the desired hemodynamic response function. Linear discriminant analysis is utilized to classify the acquired data into four classes based on three features (mean, peak value, and skewness) of the associated oxy-hemoglobin (HbO) signals. The HRs evoked by the handshake and poking stimulations showed higher peak values in HbO than the ball grasp and cold temperature stimulations. For comparison purposes, additional two-class classifications of poking vs. temperature and handshake vs. ball grasp were performed. The attained classification accuracies were higher than the corresponding chance levels. Our results indicate that fNIRS can be used as an objective measure discriminating different tactile stimulations from the somatosensory cortex of human brain.</P>
Hong, Keum-Shik,Khan, Muhammad Jawad Frontiers Media S.A. 2017 Frontiers in neurorobotics Vol.11 No.-
<P>In this article, non-invasive hybrid brain–computer interface (hBCI) technologies for improving classification accuracy and increasing the number of commands are reviewed. Hybridization combining more than two modalities is a new trend in brain imaging and prosthesis control. Electroencephalography (EEG), due to its easy use and fast temporal resolution, is most widely utilized in combination with other brain/non-brain signal acquisition modalities, for instance, functional near infrared spectroscopy (fNIRS), electromyography (EMG), electrooculography (EOG), and eye tracker. Three main purposes of hybridization are to increase the number of control commands, improve classification accuracy and reduce the signal detection time. Currently, such combinations of EEG + fNIRS and EEG + EOG are most commonly employed. Four principal components (i.e., hardware, paradigm, classifiers, and features) relevant to accuracy improvement are discussed. In the case of brain signals, motor imagination/movement tasks are combined with cognitive tasks to increase active brain–computer interface (BCI) accuracy. Active and reactive tasks sometimes are combined: motor imagination with steady-state evoked visual potentials (SSVEP) and motor imagination with P300. In the case of reactive tasks, SSVEP is most widely combined with P300 to increase the number of commands. Passive BCIs, however, are rare. After discussing the hardware and strategies involved in the development of hBCI, the second part examines the approaches used to increase the number of control commands and to enhance classification accuracy. The future prospects and the extension of hBCI in real-time applications for daily life scenarios are provided.</P>
Existence of Initial Dip for BCI: An Illusion or Reality
Hong, Keum-Shik,Zafar, Amad Frontiers Media S.A. 2018 Frontiers in neurorobotics Vol.12 No.-
<P>A tight coupling between the neuronal activity and the cerebral blood flow (CBF) is the motivation of many hemodynamic response (HR)-based neuroimaging modalities. The increase in neuronal activity causes the increase in CBF that is indirectly measured by HR modalities. Upon functional stimulation, the HR is mainly categorized in three durations: (i) initial dip, (ii) conventional HR (i.e., positive increase in HR caused by an increase in the CBF), and (iii) undershoot. The initial dip is a change in oxygenation prior to any subsequent increase in CBF and spatially more specific to the site of neuronal activity. Despite additional evidence from various HR modalities on the presence of initial dip in human and animal species (i.e., cat, rat, and monkey); the existence/occurrence of an initial dip in HR is still under debate. This article reviews the existence and elusive nature of the initial dip duration of HR in intrinsic signal optical imaging (ISOI), functional magnetic resonance imaging (fMRI), and functional near-infrared spectroscopy (fNIRS). The advent of initial dip and its elusiveness factors in ISOI and fMRI studies are briefly discussed. Furthermore, the detection of initial dip and its role in brain-computer interface using fNIRS is examined in detail. The best possible application for the initial dip utilization and its future implications using fNIRS are provided.</P>
Vortex-induced vibrations and control of marine risers: A review
Hong, Keum-Shik,Shah, Umer Hameed Elsevier 2018 Ocean engineering Vol.152 No.-
<P><B>Abstract</B></P> <P>This paper reviews the dynamics and vibration control techniques for marine riser systems. The riser pipes are modeled as Euler-Bernoulli beams that vibrate under the effects of ocean loads and the movements of the surface vessel, resulting in hybrid ODE-PDE equations. Chronological development of such hybrid models is first discussed, and their approximated ODE models for simulation are examined. Theoretical and experimental techniques for instability and fatigue analyses on the riser systems are also summarized. To increase the fatigue life against ocean currents, passive vibration suppression devices (e.g., strakes and spoilers) were mounted on the surface of the riser. Whereas to tackle the instability problem caused by sea waves, active control techniques utilizing the movements of the vessel were employed. In Conclusions, as future riser technologies, seven research issues are identified.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A review on the dynamics and vortex-induced vibration control methods of marine riser systems. </LI> <LI> The focuses are on mathematical formulations, analyses, and controls (both active and passive methods) of marine risers. </LI> <LI> Identification of future research topics in the area of dynamics and vibration control of marine riser systems. </LI> </UL> </P>