Double Helical Soft Pneumatic Actuator Capable of Generating Complex 3D Torsional Motions

This letter presents a novel tube-type pneumatic helical actuator generating complex 3-dimensional torsional motions. Inspired by the molecular structure of DNA, this actuator is fabricated by combining two helical contraction actuators, introduced in our previous research, in parallel and covered by a sleeve. By controlling the air pressure and top rotation angle of each helical actuator, this double helical actuator can realize bidirectional screwing, curving, and mixture of screwing and curving in a 3-dimensional space. Qualitative working principles of these patterns are analyzed, and two mathematical models are introduced to estimate the helical diameter change in one motion and coordinate change of the tip point in another motion according to the air pressure. The models were validated through experiments. Finally, taking advantage of its shape-controllable features with a vast range of workspace, the effectiveness as an application to a flexible manipulator for inspection in narrow spaces is investigated and its validity is experimentally verified.