Dish-Shaped Thin Beads: A Novel Bead Shape for Wire-Driven Variable Stiffness Mechanisms

In recent years, there has been much research on soft robots with variable stiffness mechanisms. There are various methods for achieving switching stiffness, one of which is the wire method. This consists of multiple segments with through holes, and a wire passed through the center. This method has an advantage in that the stiffness can be increased to the point where the segment material is about to break, and the time required for stiffness switching is very short. However, there have been few studies on methods to shorten the distance between segments, and the size of the whole body is problematic. In this study, we propose a novel bead shape for use in wire-driven variable stiffness mechanisms. This bead is shorter than the distance between beads, and less than half the bead radius, which is the limit of the conventional bead distance. Various theoretical bead design models are developed, and a prototype of the proposed mechanism is fabricated. The usefulness of the proposed bead shape is demonstrated experimentally by measuring the radius of curvature and holding torque, including comparisons with conventional beads. Finally, the characteristics revealed by the experiments are discussed, and future works and applications under development are presented.