Abstract:
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.
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