Grasping by spiraling: reproducing elephant movements with rigid-soft robot synergy

The logarithmic spiral is observed as a common pattern in several living beings across kingdoms and species. Some examples include fern shoots, prehensile tails, and soft appendages like octopus arms and elephant trunks. In the latter cases, spiraling is also used for grasping. Motivated by how this strategy simplifies behavior into kinematic primitives and combines them to develop smart grasping movements, this work focuses on the elephant trunk, which is more deeply investigated in the literature. We present a soft arm combined with a rigid robotic arm to replicate elephant grasping capabilities. In our system, the rigid arm ensures positioning and orientation, mimicking the role of the elephant’s head, while the soft manipulator reproduces trunk motion primitives of bending and twisting under proper actuation patterns. The synergy between rigid and soft components replicates 9 distinct elephant grasping strategies, enabling adaptation to various object shapes and sizes while reducing control complexity.