A compact two-phase twisted string actuation system: Modeling and validation
This work addresses the need for more compact and efficient actuators in robotics, such as for robotic hands and exoskeletons, but is incremental as it builds on existing models and methods.
The paper tackles the problem of achieving high contraction in compact twisted string actuators by introducing a two-phase system (multi-string twist and overtwist) that achieves 81% contraction, validated through experiments with 2 to 8 string systems and life cycle tests.
In this paper, we propose a compact twisted string actuation system that achieves a high contraction percentage (81%) on two phases: multi string twist and overtwist. This type of system can be used in many robotic applications, such as robotic hands and exoskeletons. The overtwist phase enables the development of more compact actuators based on the twisted string systems. Furthermore, by analyzing the previously developed mathematical models, we found out that a constant radius model should be applied for the overtwisting phase. Moreover, we propose an improvement of an existing model for prediction of the radius of the multi string system after they twist around each other. This model helps to better estimate the bundle diameter which results in a more precise mathematical model for multi string systems. The model was validated by performing experiments with 2, 4, 6 and 8 string systems. Finally, we performed extensive life cycle tests with different loads and contractions to find out the expected life of the system.