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K. T. Yoon(윤경택),Y. M. Choi(최영만) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
In the wearable exoskeletons for assisting lower limbs during human walking, strategy for assisting eccentric muscle contractions can effectively save human metabolic energy by replacing the negative joint biological power used for braking body. This technique provides deceleration torque to the lower limb joint in the negative work phase during gait cycle, removing portion of kinetic energy that is naturally dissipated by the muscle. The braking torque is provided from the back-electromotive force of an electromagnetic generator, which is amplified through a gear transmission. This configuration has the advantage that Watts of power are generated while providing deceleration assistance simultaneously. In this study, experimental evaluation of the wearable knee exoskeleton for assisting eccentric muscle contraction is introduced. Our knee exoskeleton prototype provides 8 Nm of braking torque while generating 3 W of electrical power within a gait cycle with a device efficiency of 66%. In the treadmill-walking test, kinematics and muscle activities of lower limbs were observed according to the assist torque level change. In addition, we confirmed that the exoskeleton provides accurate assistance even when the kinetics of the lower limb joints change according to the slope of the ground.
W. K. Lee(이원규),K. T. Yoon(윤경택),Y. M. Choi(최영만) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
In order to assist the human knee joint motion effectively, a biomechanical wearable device should perform the function of propulsion and braking of the knee joint that changes within gait cycle at the correct time. In this study, a twisted string transmission (TST) driven motor-generator system capable of assisting both propulsion and braking the knee joint during gait cycle is proposed. A twisted string transmission amplifies effectively both propulsion and braking torque through high transmission ratio and has advantages of compactness, lightness, and compliance. In this system, the human knee joint is connected to an BLDC motor and a generator by the TST. An one-way clutch bearing is installed at the generator shaft to disengage it from the TST during knee flexion phase. In the knee flexion phase, the motor generates propulsion assistance torque proportional to knee joint torque. The generator produces electricity while assisting braking of the knee joint during knee extension phase through reaction torque. From model-based parametric study, the string parameters and an electrical load of generator circuit were determined to maximize device efficiency. Finally, a testbed of the TST driven motor-generator system was built and performances of the system were evaluated through experiments.
J. Jung(정재환),K. T. Yoon(윤경택),Y. M. Choi(최영만) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
The magnetic spring has been used as a gravity compensator in ultra-precision positioning system or vibration isolator system for semiconductor process, which has a simple structure and can be used in vacuum without mechanical contact. The Halbach array magnetic spring, designed to have quasi-zero stiffness, generates a large levitation force for its volume, and improves control and isolation performance by having a resonance-free characteristic. In many previous studies, the magnetic springs were modeled using surface current model. However, there exists an error in estimating stiffness when compared with finite element model due to inconsideration of permanent magnet reluctance. Furthermore, the geometric tolerances of Halbach array magnetic spring greatly affect the uncertainty of stiffness and force. In this study, a magnetic model considering the magnetic permeability of permanent magnet is proposed. Additionally, tolerance analysis was performed by parametric study and Monte-carlo simulation. Compared with the conventional magnetic model, the stiffness characteristics of the magnetic spring modeled by the proposed magnetic model is closer to that of the finite element model. From the results of tolerance analysis, the dominant tolerance parameters that determines the uncertainty in performance were identified. Through Monte-carlo simulation with 5,000 iterations, statistical estimations of performance variation were obtained.