Form closure-based path-planning in obstacle-aided locomotion for snake robots

Abstract

Snake robots are hyperredundant manipulators with a wide range of potential applications ranging from search-and-rescue to ocean and outer space exploration. When snake robots use obstacles in the environment to push themselves forward it is referred to as obstacle-aided locomotion (OAL). The problem of finding a path that optimally exploits available obstacles in the environment for OAL currently does not have a general solution. A snake robot in contact with a set of obstacles is fundamentally similar to an object being grasped by a robotic hand. By interpreting the environment-robot contact as a grasp, we can employ the form closure concept for assessing the robustness of a given configuration; if the snake robot’s “grasp” of its environment has continual form closure when following a given path, the robot is guaranteed to not drift off that path. This presents a potential technique for analyzing the path-planning problem for OAL. This paper assesses the form closure of a rigid object on a planar surface by means of a novel method as well as a traditional method based on the grasp matrix. Furthermore, it introduces the notion of a form closure margin as a measure of how much a configuration must change before form closure is lost, and proposes three metrics that quantify this property. Finally, the applicability of the proposed metrics is demonstrated through their application to optimal path-planning for three specific scenarios. The results indicate that the proposed algorithm has strong potential to contribute to robust path-planning for OAL.