Modeling of the twisted string actuation system with multiple strings

Abstract

Much research in recent years has focused on twisted string actuation (TSA) systems due to their structural simplicity with a high transmission ratio. Nevertheless, most of the TSA applications with multiple strings have been based on conventional models, which commonly cover only overlap twists between strings, not individual twists in a single string. Therefore, the conventional model-based prediction of the total contraction of the TSA with multiple strings is likely to deviate from the measured contraction. In this thesis, a model is proposed considering the kinematics of both overlap twists and individual twists, which simultaneously occur in the twist of the TSA with multiple strings, as well as the effect of stiffness and offsets between strings on the total contraction of the TSA with multiple strings. A comparative study with the conventional model was conducted in terms of the root-mean-square error (RMSE) after both the conventional and proposed models were optimized so that their RMSEs were minimized. The results confirm that better accuracy in the total contraction, as well as the well-fitted trend of the contraction for the whole experimental trials, were achieved in the proposed model.