On planar grasping with snake robots: Form-closure with enveloping grasps

This paper describes the conditions that a snake robot must meet in order to be able to grasp an object with a circular cross-section. The type of grasp is of the enveloping type, and the conditions to guarantee a grasp with form-closure using three contacts, the minimum number of contacts possible, are presented. The first contribution of this paper is the description of the conditions where form-closure is possible, depending on the radius of the object. The second contribution is the description of two workspaces that help to decide whether the object is within reach of the snake robot, and if it is graspable. This analysis is scale and unit independent, therefore, it is applicable to a wide range of scenarios. These results can also be extended to other redundant open-chained robots using enveloping grasps.