Geodesic
Development of a Lever-Based Twisted String Actuator for Exoskeleton Systems
Russian journal of nonlinear dynamics, Tome 20 (2024) no. 5, pp. 827-844

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The development of exoskeleton technologies has garnered increasing interest from industrial companies, particularly in the context of active exoskeletons that are powered by an external energy source. A key component in these systems is the actuation device, which plays a pivotal role in their overall performance. Among the various actuation mechanisms, the twisted string actuator (TSA) has emerged as a promising candidate for wearable robotic systems. The TSA mimics the behavior of human muscles but offers higher efficiency, making it an attractive solution for exoskeleton applications. This study introduces a novel lever-based transmission mechanism designed to adapt TSAs to human joints that require torque, rather than a linear force. To support this approach, we developed a mathematical model that accurately describes the dynamics of the proposed mechanism. A series of experiments were conducted to validate the model, confirming its reliability. In addition to the theoretical work, we integrated the lever-based TSA into an exoskeleton and tested its effectiveness in reducing muscle loads. The experiments focused on squatting exercises, where significant reductions in muscle activity were observed, demonstrating the exoskeleton’s potential for easing physical strain on users. The accuracy of the lever-based TSA model was further confirmed by the experiments in predicting the generated force and the actuation angles achieved. The estimated error between the sensor data and the models predictions were 1.64 MAE (degrees) for the revolute joint angle and 1.79 MAE (Newtons) for the tension force of the string. Moreover, the results showed that the lever-based TSA provided the necessary torques for the hip joint, aligning well with the natural movement of the human body. This makes it easier to control and adapt the system in practical exoskeleton applications, enhancing its usability and effectiveness.
Keywords: exoskeletons, twisted string actuator, actuating mechanisms
Mots-clés : transmission ratio 
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     author = {A. D. Kirilin and V. A. Skvortsova and V. V. Koshman},
     title = {Development of a {Lever-Based} {Twisted} {String} {Actuator} for {Exoskeleton} {Systems}},
     journal = {Russian journal of nonlinear dynamics},
     pages = {827--844},
     publisher = {mathdoc},
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     number = {5},
     year = {2024},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ND_2024_20_5_a7/}
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A. D. Kirilin; V. A. Skvortsova; V. V. Koshman. Development of a Lever-Based Twisted String Actuator for Exoskeleton Systems. Russian journal of nonlinear dynamics, Tome 20 (2024) no. 5, pp. 827-844. http://geodesic.mathdoc.fr/item/ND_2024_20_5_a7/