A compact two-phase twisted string actuation system: Modeling and validation

TL;DR

This paper introduces a compact two-phase twisted string actuation system with high contraction efficiency, improved modeling accuracy, and validated performance through experiments and life cycle testing for robotic applications.

Contribution

It presents a novel two-phase twisted string system with an improved radius prediction model and validation, enabling more compact and reliable actuators for robotics.

Findings

Achieved 81% contraction in the proposed system

Validated the model with experiments on 2, 4, 6, and 8 string systems

Performed life cycle tests to estimate system durability

Abstract

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.