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전극 개수에 따른 근전도 기반 휴먼-컴퓨터 인터페이스의 정확도에 대한 연구
이슬비(Seulbi Lee),지영준(Youngjoon Chee) 한국HCI학회 2015 한국HCI학회 논문지 Vol.10 No.2
NUI(Natural User Interface)는 사용자의 자연스러운 동작이나 동작 시 발생하는 생체 신호를 해석하여 기계에 명령을 내리는 것을 말한다. 물리적인 변화가 있어야 사용이 가능한 가속도 센서나 영상 기반의 NUI와는 달리 특정 동작과 관련된 근육의 표면 근전도(surface Electromyogram, sEMG)를 측정하면 실제 움직임이 발생하지 않아도(isometric contraction) 동작 의도를 예측할 수 있다. 본 연구에서는 근전도 기반으로 손목 동작 의도를 분류할때 전극 개수에 따른 정확도를 확인하고, 키보드 등에 적용 가능한 인터페이스 기술을 제안한다. 손목의 동작 중 신전(extension, up), 굴곡(flexion, down), 외전(abduction, right), 내전(adduction, left)의 네 가지 동작 의도를 분류하는 실험을 진행하였다. 50ms 간격으로 계산된 제곱평균제곱근(Root Mean Square, RMS)을 특징으로 사용하였고, 동작 의도 인식을 위해 역전파 알고리즘으로 학습한 다층 퍼셉트론 분류기를 사용하였다. 전극 쌍의 개수를 네개(91.9%), 세 개(87.0%), 두 개(78.9%)로 줄여가며 정확도를 확인했다. 전극 쌍의 개수가 네 개에서 두 개로 줄었을 때 정확도는 약 13% 감소하였다. 두 쌍의 전극만 사용하는 경우의 분류 정확도를 높이기 위하여 직전의 RMS를 특징에 추가하였다. 150 ms 이전까지의 정보를 사용하였을 때, 분류 정확도가 78.9%에서 83.6%로 4.6% 증가하였다. 전극 쌍의 개수가 감소함에 따라 정확도는 감소하였지만, 이전 데이터를 함께 사용한 경우 부분적으로 증가 시킬 수 있음을 확인하였다. NUI (Natural User Interface) system interprets the user’s natural movement or the signals from human body to the machine. sEMG (surface electromyogram) can be observed when there is any effort in muscle even without actual movement, which is impossible with camera and accelerometer based NUI system. In sEMG based movement recognition system, the minimal number of electrodes is preferred to minimize the inconvenience. We analyzed the decrease in recognition accuracy as decreasing the number of electrodes. For the four kinds of movement intention without movement, extension (up), flexion (down), abduction (right), and adduction (left), the multilayer perceptron classifier was used with the features of RMS (Root Mean Square) from sEMG. The classification accuracy was 91.9% in four channels, 87.0% in three channels, and 78.9% in two channels. To increase the accuracy in two channels of sEMG, RMSs from previous time epoch (50-200 ms) were used in addition. With the RMSs from 150 ms, the accuracy was increased from 78.9% to 83.6%. The decrease in accuracy with minimal number of electrodes could be compensated partly by utilizing more features in previous RMSs.
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이슬비 ( Seulbi Lee ),오충광 ( Chunggwang Oh ),허재홍 ( Jaehong Heo ) 인문사회 21 2021 인문사회 21 Vol.12 No.6
The purpose of this study was to investigate whether Nunchi, known to promote the mental health of members of Korean society, enhances the mental health of Koreans through rejection sensitivity (RS). The proposed model was the fully mediated model that Nunchi would enhance mental health in the mediation of RS. To verify this model, data were collected from 310 colleges students (male 129, female 181) and analyzed by the SEM. Results showed that the model fit the data, suggesting that Nunchi, which diverts attention to external situations and interprets the situation realistically, could be beneficial for the mental health such as subjective wellbeing and psychological problems. And Nunchi could be used as the intervention in psychotherapy. In future research, it is necessary to examine whether the model fit varies with individual cultural orientation. And it seems that additional studies on mediating variables are needed.
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금속 적층제조된 대형 실린더 부품의 열변형에 미치는 적층 높이 및 재료 특성 영향에 관한 해석
이슬비(Seulbi Lee),방태양(Tae Yang Bang),김우종(Woojong Kim),강민철(Mincheol Kang),최윤석(Yoon Suk Choi) 대한용접·접합학회 2021 대한용접·접합학회지 Vol.39 No.3
The laser powder bed fusion technique involves depositing layers by selectively melting a material. This leads to rapid melting and solidification, followed by repeated reheating and remelting. The complex thermal hysteresis and resultant thermal gradient inevitably cause thermal stress and distortion in additively manufactured products. The thermal stress and distortion lead to dimensional inaccuracies, defects such as delamination and cracking, and finally, adverse effects on the product life. In this study, a thermomechanical analysis of a large cylinder (hollow shape, with a height of 750 mm, an outer diameter of 500 mm, and a thickness of 20 mm) was performed using the finite element method to investigate the effects of building height and material properties on thermal distortion. Specifically, the evolution of thermal distortion was systematically interpreted with the thermal hysteresis. Depending on the building height of the cylinder, the thermal hysteresis was influenced by the bed plate and the thermal effect of the predeposited and postdeposited layers. In addition, the thermal distortion tendencies of Ti-6Al-4V and Inconel 718 metal powders were examined based on the material properties, particularly thermal diffusivity. The maximum thermal distortion occurred at approximately 100 mm below the top surface of the cylinder for both materials. Moreover, the thermal distortion of the Ti-6Al-4V was more significant than that of Inconel 718 because of the lower thermal diffusivity of the former.
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