An Inhomogeneous Structured Eversion Actuator

Soft actuators are free from any rigid, bulky, and hard components. This is greatly beneficial towards achieving compliant actuation and safe interactions in robots. Inspired by the eversion principle, we develop a novel soft actuator of the inhomogeneous cross-section that can linearly extend and achieve a large payload capability. The proposed soft actuator is a hollow sleeve, made from an airtight fabric, and features a top part of cylindrical shape and a bottom part of a conical shape. Unlike conventional eversion robots that extend unilaterally from the tip, in this proposed actuator the top cylindrical part and the bottom conical part are partially folded inwards so that the two tips are attached together. When pneumatic pressure is applied, the cylindrical part everts increasing in length while the conical section reduces in length folding inwards. The actuator achieves linear strains of 120% and can generate a force 84 N at a low pressure of 62 kPa. We develop a theoretical model to describe the force and strain characteristics of the actuator during eversion from conical shape to cylindrical shape. The results showcase a step towards large strain, high force actuators for safe and compliant robots.