Fabrication and performance testing of twisted pneumatic artificial muscle actuators

Twisted fiber-based artificial muscles have emerged as a research hotspot in recent years owing to their high power-to-weight ratio and flexibility. However, their widespread application in soft robotics is constrained by inherent limitations, namely small actuation strain and low output force. In this study, a twisted pneumatic muscle actuator was fabricated by integrating Nylon 66 fiber-based artificial muscles with polyvinyl chloride (PVC) tubing, via sequential forming processes including cold drawing, twisting, and heat curing which effectively enhances the actuator’s output force and displacement. The effects of air pressure, winding rod core diameter, and external load on the output performance of the twisted pneumatic muscle were systematically investigated. An elbow joint robot was designed, and the application of the proposed actuator in this robotic system was experimentally studied. The results show that when fabricated using a 5 mm winding rod core, the twisted pneumatic muscle with a 2.5 mm inner diameter post cold drawing achieves a 61% increase in deformation under pneumatic actuation, attaining an actuation strain of 58%. When multiple twisted pneumatic muscles of this type are connected in parallel to drive the elbow joint, a maximum joint rotation of 54.8° is realized within 5 seconds. The artificial muscle developed in this work exhibits a fast response speed and enables effective flexion and extension movements of the elbow joint.