McKibben Muscle with Elastic Thread Embedded in Parallel Extending Range of Motion of Muscle-Driven Robots

The McKibben muscle, widely employed in antagonistic drive robots, exhibits approximately 20% contraction under pneumatic pressure but lacks crucial passive extensibility. Previous attempts to achieve passive extensibility resulted in reduced overall contraction ratios due to the series connection of elongation and contraction sections. This study proposes a novel artificial muscle design that achieves extension through external force by arranging extensible and contractile components in parallel. The proposed design incorporates a composite thread consisting of an elastic thread and an inextensible thread connected in series, arranged parallel to a conventional McKibben muscle. This configuration yields an artificial muscle capable of approximately 16% contraction and over 40% extension under external force when relaxed. The simplicity of this design facilitates straightforward integration into robotic systems. To demonstrate the efficacy of the proposed artificial muscle, we applied it to a tensegrity robot, exemplifying an antagonistic drive system. This application showcases the potential of our design to enhance the performance and versatility of soft robotic systems.