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Suncheol Kwon,Youngjin Na,Yunjoo Kim,Jung Kim 제어로봇시스템학회 2013 제어로봇시스템학회 국제학술대회 논문집 Vol.2013 No.10
This study investigated the characteristics of human responses to different amounts of SEMG-based assistive torque. A power assistive device provided proportional torque with respect to the estimated human torque using surface electromyography (SEMG). Seven participants performed self-paced elbow flexion tests under five conditions, each having the different proportion of the assistance. We computed the variability of the angle and angular velocity of the elbow joint to quantify relative stability of the assisted movements. Power spectral density of the angular acceleration of the joint was also computed to characterize the power and bandwidth of the movements in the frequency domain. From the experiments the variability gradually increased with the amount of the assistive torque and it indicated that the movements in response to increased assistive torque became relatively more unstable. In addition, the power and bandwidth of the movements were gradually increased although subject’s physical efforts for the movements were decreased. This study can be used as a cornerstone to determine the amount of SEMG-based assistive torque for maintaining smooth and natural human movements.
Movement Stability Analysis of Surface Electromyography-Based Elbow Power Assistance
Kwon, Suncheol,Kim, Yunjoo,Kim, Jung IEEE 2014 IEEE Transactions on Biomedical Engineering Vol.61 No.4
<P>The use of power assistive devices that use surface electromyography (SEMG) signals may be limited by the noisy nature of SEMG signals. The aim of this study was to investigate the variation in human movement stability while the amount of SEMG-based assistive power was changed. A robotic device provided a torque that was proportional to the torque estimated by SEMG for assisting human movements, and 12 volunteers participated in the elbow flexion experiments. The maximum finite-time Lyapunov exponent (MFTLE), the average logarithmic rate of the divergence of neighboring trajectories, and the variability of the kinematic data were used to quantify the stability of the assisted elbow movements. The stability provided by the MFTLE decreased as the amount of assistive torque increased with respect to the amount of human torque. The kinematic variability increased with the increase in assistive torque. Therefore, by ensuring that the amount of SEMG-based assistive torque is less than the amount of human torque, the assistance may provide relatively natural movements. This study is the first to quantify movement stability as SEMG-based assistive power is applied. This study can provide a foundation for determining the appropriate amount of SEMG-based assistive power.</P>
Kwon, Suncheol,Park, Hyung-Soon,Stanley, Christopher J.,Kim, Jung,Kim, Jonghyun,Damiano, Diane L. IEEE 2012 IEEE Transactions on Biomedical Engineering Vol.59 No.5
<P>Individuals with cerebral palsy have neurological deficits that may interfere with motor function and lead to abnormal walking patterns. It is important to know the joint moment generated by the patient's muscles during walking in order to assist the suboptimal gait patterns. In this paper, we describe a practical strategy for estimating the internal moment of a knee joint from surface electromyography (sEMG) and knee joint angle measurements. This strategy requires only isokinetic knee flexion and extension tests to obtain a relationship between the sEMG and the knee internal moment, and it does not necessitate comprehensive laboratory calibration, which typically requires a 3-D motion capture system and ground reaction force plates. Four estimation models were considered based on different assumptions about the functions of the relevant muscles during the isokinetic tests and the stance phase of walking. The performance of the four models was evaluated by comparing the estimated moments with the gold standard internal moment calculated from inverse dynamics. The results indicate that an optimal estimation model can be chosen based on the degree of cocontraction. The estimation error of the chosen model is acceptable (normalized root-mean-squared error: 0.15-0.29, R: 0.71-0.93) compared to previous studies (Doorenbosch and Harlaar, 2003; Doorenbosch and Harlaar, 2004; Doorenbosch, Joosten, and Harlaar, 2005), and this strategy provides a simple and effective solution for estimating knee joint moment from sEMG.</P>
Suncheol Kwon,Jung Kim IEEE 2011 IEEE transactions on information technology in bio Vol.15 No.4
<P>A current challenge with human-machine cooperation systems is to estimate human motions to facilitate natural cooperation and safety of the human. It is a logical approach to estimate the motions from their sources (skeletal muscles); thus, we employed surface electromyography (SEMG) to estimate body motions. In this paper, we investigated a cooperative manipulation control by an upper limb motion estimation method using SEMG and joint angular velocities. The SEMG signals from five upper limb muscles and angular velocities of the limb joints were used to approximate the flexion-extension of the limb in the 2-D sagittal plane. The experimental results showed that the proposed estimation method provides acceptable performance of the motion estimation [normalized root mean square error (NRMSE) <;0.15, correlation coefficient (CC) >;0.9] under the noncontact condition. From the analysis of the results, we found the necessity of the angular velocity input and estimation error feedback due to physical contact. Our results suggest that the estimation method can be useful for a natural human-machine cooperation control.</P>
Real-time Motion Intention Estimation Based using Surface Electromyography for Collision Avoidance
Suncheol Kwon,Jung Kim 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
Collision avoidance has been a significant issue to guarantee human??s safety in the robot workspace. This paper presents real-time motion intention estimation based collision avoidance method using surface electromyography (sEMG). An ANN algorithm was used to estimate the upper limb motions of a subject from sEMG signals on five muscles, and the robot was controlled to keep the safety distance from the estimated motion in order to avoid the collision. The proposed method was evaluated through comparison tests with using a goniometer in real-time, and the experimental results showed a reasonable performance of collision avoidance and simultaneous response of the robot with human movements. These promising results can be useful for collision avoidance and safe human-robot interaction.
Suncheol Kwon,Jung Kim 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
This paper presents the preliminary results of a joint angle prediction method for the upper arm and forearm motions using surface electromyogram(sEMG) signals. An artificial neural network ANN) was used to match the relationship between sEMG and upper limb motion in the vertical plane. The sEMG signals from the four sites were fed into the ANN and captured motion data were used as references. The prediction method was tested on one subject through drawing experiments. The performance was evaluated by a root mean squared error(RMSE) and the result was comparable to previous studies (RMSE < 0.02 rad). These results imply that the method is useful for the natural interaction between a human and a cooperative machine.
물리적 인간-로봇 상호작용 시스템을 위한 안전 조인트의 개발
권순철(Suncheol Kwon),장동준(Dongjune Chang),김정(Jung Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
To achieve a safe joint, passive compliant elements such as springs and dampers are preferred to active elements because they can provide fast and reliable performance. However, nonlinear stiffness adjustment of springs is difficult. In this study, a safe joint using the differential gear instead of elastic elements is proposed in order to reduce human injuries in the robotic workspace. If a manipulator linked with one of the output shafts is restrained by external loads, the shaft will not rotate and another shaft will rotate with two times of an input speed; so humans who collide against the manipulator can be safe with the proposed joint. In addition, after the remove of external loads, the proposed joint can work immediately toward target angles. The experimental results show that the proposed joint provides sufficient safety and fast responses. The joint can be applied to a lot of manipulator which require safe interaction with humans.