A kinematic model to constrain slip in soft body peristaltic locomotion

Abstract

Soft body locomotion can enable mobile robots that are compliant to their surroundings. To better understand earthworm-inspired locomotion, recent robots such as our Compliant Modular Mesh Worm Robot with Steering (CMMWorm-S) have been developed. For straight-line locomotion, we have shown that balancing segment extension and retraction to mitigate slip determines control wave strategy. However, to effect a turn, the waves required to eliminate slip are more complicated because they are not periodic but rather change for each segment and for each wave. Here, we geometrically prove that the body cannot be reoriented to a new straight configuration facing a new direction in a single wave without slip and that only if the body is a constant, uniform curvature will periodic control waves not require slip. The segments are represented as isosceles trapezoids in order that the model be generalizable over other types of worm-like robots that embody a positive correlation between diameter reduction and length extension. Examples of simulated orthogonal turns are provided that are motivated by slippage in orthogonal turns demonstrated on our soft robot. Future work will involve calibrating Slip Eliminating Control (SEC) to mitigate slip on the robot.