A Geometry-Centered Review of Bending Actuators Across Multiple Actuation Technologies

Bending actuators are key components in soft robotics and other engineering applications where compact, reversible, and biomimetic motion is required. Although many bending actuators have been identified, the literature remains fragmented, with most studies organized by material type, activation principle, or application domain. This review adopts a configuration-based perspective and classifies bending actuators by geometric architecture rather than by actuation technology. Representative actuators from the literature were analyzed and grouped according to geometric mechanisms that convert input energy into curvature. The analysis reveals that diverse actuator technologies repeatedly rely on a set of recurring configuration families, including laminated, tubular, internal chambers, rolled, origami/kirigami, articulated, and hybrid structures. By emphasizing geometry, the proposed taxonomy clarifies the structural origins of bending motion and enables cross-technology comparison of bending actuators.