Designing and Modeling of Tightly Wrapped Twisted Artificial Muscles With Large Stroke and Low Hysteresis

Soft actuator is the key component for soft robots to realize flexible motion. But the difficulty of sensing and control of soft actuators seriously restricts their application. Twisted artificial muscles (TAMs) made from together self-coiling of nylon 6,6 fiber and heating wire are potential to address this challenge due to their extremely high actuating stress and self-sensing ability. However, the together coiled twisted artificial muscles (TCTAMs) have a large self-sensing hysteresis because of the small heating area and the self-coiling process restricts their deformation stroke. Besides, the lack of accurate physical models also blocks the development of the TCTAMs. This article presents a new type of tightly wrapped twisted artificial muscles (TWTAMs) to improve the stroke and reduce the hysteresis. Compared with TCTAMs, the hysteresis of TWTAMs is reduced by 76% and the stroke is improved by 35%. Besides, a physical analytical model based on the self-sensing temperature is established and verified by experiments. This article not only provides a new type of TAMs with large stroke and low hysteresis, but also offers an accurate theoretical analysis model for the performance prediction of TWTAM.