Mecanismo antitravamento para redutores harmônicos : aplicação em atuadores de próteses ativas de membro inferior
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Data
2026-01-30
Autores
Fiorezi, Guilherme Gomes
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Universidade Federal do Espírito Santo
Resumo
Actuators are essential for the operation of a wide range of robotic systems across various modern industries. These actuators are usually equipped with gear reducers directly coupled to the motors and, depending on their type, may be more or less affected by overload events. Harmonic drives, despite their many advantages, are among the most susceptible to overloads and may, in many cases, experience the so-called ratcheting phenomenon. In such events, the actuator may lock and potentially lead to reducer failure. For this reason, torque limiters are widely employed in industrial systems; however, commercial torque limiters typically fully decouple the actuator from the output when activated. As a result, in addition to their excessive size, these devices do not address issues that may arise during their actuation in medical devices, such as prostheses, where complete decoupling can lead to user falls due to loss of controllability. In this context, this work presents a design methodology for an anti-lock mechanism that maintains partial coupling between the actuator motor and the output through springs, providing passive overload absorption and compliant behavior. The proposed methodology addresses the calculation of the desired maximum torque and the torsional stiffness after mechanism actuation. For practical application and demonstration, a mechanism is designed for the ankle joint of the UFES Robotic Leg prosthesis. The anti-lock mechanism is tested on a bench setup to verify the theoretically obtained values and with a human subject performing four activities of daily living to validate the concept and evaluate the impacts of incorporating the mechanism. Overall, the results indicate that the designed mechanism, using the proposed methodology, meets the established design requirements, allowing movements to be performed in a manner very similar to that observed prior to its installation on the prosthesis. The prototype weighs 229 g, has an average torque limit of 60.91 Nm, an average torsion stiffness of 241 Nm/rad, and about ±10° of angular displacement. Some results require manufacturing the parts again to confirm the true origin of the discrepancies; however, other minor differences between the modeling and experimental results can be reduced through improvements in the modeling, such as the inclusion of the effects of torsional springs after a better understanding of their influence.
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Palavras-chave
Limitador de torque , Redutor harmônico , Antitravamento , Torque limiter , Harmonic drive , Strain wave gear , Anti-lock , Robotic prosthesis , Prótese robótica