A New Spiral-Type Inflatable Pure Torsional Soft Actuator

Abstract Soft robot has become a hot topic recently due to its distinct advantages over traditional rigid robots such as high deformability and good impact resistance. However, the coupled deflections of flexile materials bring challenges to soft robotic research in many aspects such as kinematic modeling, dynamic analysis, and control. Besides, unwanted deformations might enlarge external dimensions of soft robots, causing a reduction in the efficiency and bringing about unexpected or harmful contacts with surrounding environments that will significantly affect the robots' performance. In this study, we propose a new inflatable soft actuator driven by two spiral chambers twined with fibers for the first time. A key feature of this actuator is that it possesses a pure and high-efficient torsional motion with no bending and extension movements when works without load, which reduces the difficulties of theoretical analysis and control to some extent. Kinematic model is established by combining virtual work principle and elastic strain energy function for nonlinear flexible materials. The new soft torsional actuator module is carefully designed and fabricated, of whi