Locomotion via Active Suction in a Sea Star-Inspired Soft Robot

Some marine animals, such as sea stars, have developed versatile adhesive appendages that can be used for a variety of behaviors including sticking to surfaces, manipulating objects, and locomoting. These appendages couple reversible adhesion capabilities with muscular structures that can do work on the world while still being soft enough to conform to various surfaces and to squeeze through tight spaces. We took inspiration from the hydraulic tube feet of sea star to create modules consisting of soft active suction discs and soft pneumatic linear actuators. Tube feet convert fluid motion into linear actuation using soft tubes that are constrained radially. In this work, we study the tradeoff between the stiffness of such radial constraints, and the ability of the linear actuators to apply axial forces. The adhesive force of the suction disc is dependent on both the pressure differential between the suction cavity and the environment and the deformation within the body of the disc while it is being loaded. We show that the tube foot modules are capable of creating locomotion over flat surfaces, up small steps, and in a confined space due to the redundancy caused by an array of actuators. We also show that active suction not only enables the use of softer tube foot actuators, but that sensing this active suction line provides feedback to increase the efficiency of locomotion over obstacles.