Autonomous Burrowing and Retrieval of Soft Robotic Anchors in Granular Media

Vertical digging into and out of granular media is a challenging task for autonomous systems. Granular media present considerable resistance to vertical penetration due to the high friction forces and large pressure at depths. In this paper, we present a soft robot that is capable of digging into and out of granular media to depths over 10× its body length. Our robot incorporates a vibration motor to locally fluidize the granular media for burrowing, and a soft pneumatic actuator to adjust the volume and hence the density of the robot, allowing it to transition from digging down to digging up. To analyze the performance of the robot, we measure its weight and density, track its location using a motion capture system, and investigate the effect of local fluidization. When the robot is buried and inflated with vibration turned off, it can increase its passive anchoring force by 5.22× (up to 35 N) relative to when the robot is deflated with vibration on. By contrast, by inflating the soft pneumatic bladder and providing vibration the robot is able to actively unburrow.