Design and Development of a Soft Actuator for a Robot Inspired by the Octopus Arm

The octopus provides roboticists with a good example of a completely compliant structure that can however reach good levels of stiffness and then exert forces on its environment. With no rigid structures, the octopus can deform its body and fit small apertures, its arms can bend in all directions and they can even elongate. The peculiar muscular Structure of the octopus arm, named muscular hydrostat, acts in fact as a modifiable skeleton, providing stiffness when and where needed. A key point in imitating this muscular structure is that the muscular hydrostat creates a sort of antagonistic mechanism between different muscle fibres. As a consequence, the arm movements are given by a combination of contractions of part of the muscles and passive stretching of the other muscles. On one side, this reduces the contraction requirements for the single muscle; on the other side, the contractile structure must be compliant and passively stretchable. The contractile units proposed here are built with EAP (Electro-Active Polymer) technology, with a particular geometry that increases the contraction range and force, by using soft materials. Contraction tests on prototypes of the contracting units show a very good similarity with a theoretical model and support the starting hypothesis on the possibility of building a robotic octopus-like arm based on an artificial muscular hydrostat.