Distributed Sensing for Soft Worm Robot Reduces Slip for Locomotion in Confined Environments

Earthworms are soft-bodied animals with mechanosensory organs that allow them to bend and contort, and adapt to external perturbations. To mimic these attributes of the earthworm on a robotic platform, we designed and constructed a new robot: Distributed-Sensing Compliant Worm (DiSCo-Worm) Robot. DiSCo-Worm is equipped with 36 Force Sensing Resistors (6 per segment) that allow the robot to detect external constraints and 12 flexible stretch sensors (2 per segment) that allow for tracking the shape of the robot. We show the ability of the robot to navigate in constrained spaces using an open-loop, time-based controller and a closed-loop sensory feedback controller. The results indicate that the robot can sense external constraints and its internal state (longitudinal extension of each segment) and use this information to change its state of either expanding in diameter, contracting in diameter or anchoring. Sensory feedback reduces high forces that otherwise result in damage to the robot by stopping actuation shortly after contact. In this way, each segment applies forces 33% to 80% (based on the location of the sensor) of its weight, when locomoting between two parallel surfaces. Using a closed-loop controller, the robot is able to adapt to its environment and almost eliminates forward slip, which accounts for 58% of the total motion in case of open-loop control.