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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.