Knotting/Unknotting Manipulation of Deformable Linear Objects

Abstract

Here, we propose a planning method for knotting/unknotting of deformable linear objects. First, we propose a topological description of the state of a linear object. Second, transitions between these states are defined by introducing four basic operations. Then, possible sequences of crossing state transitions, i.e. possible manipulation processes, can be generated once the initial and the objective states are given. Third, a method for determining grasping points and their directions of movement is proposed to realize derived manipulation processes. Our proposed method indicated that it is theoretically possible for any knotting manipulation of a linear object placed on a table to be realized by a one-handed robot with three translational DOF and one rotational DOF. Furthermore, criteria for evaluation of generated plans are introduced to reduce the candidates of manipulation plans. Fourth, a planning method for tying knots tightly is established because they fulfill their fixing function by tightening them. Finally, we report knotting/unknotting manipulation performed by a vision-guided system to demonstrate the usefulness of our approach.

Planning for Unraveling Deformable Linear Objects Based on Their Silhouette

“…Moreover, segments touch the outer region are referred to as outer segments, and segments do not touch as inner segments (Wakamatsu et al, 2006). In Fig.6-(a-2), the left terminal segment is an inner segment.…”

“…Unknotting manipulation, i.e., the inverse of knotting manipulation, has been also studied. We have realized automatic planning and execution of knotting/unknotting manipulation (Wakamatsu et al, 2006). Ladd and Kavraki developed an untangling planner for mathematical knots represented as closed piecewise linear curves (Ladd & Kavraki, 2004).…”

“…Fig.3 shows examples of crossings with a subsequence to which operations UO II and AO III are applicable but with locations to which they can not be applied. Any knot can be unknotted by applying operations UO IV alone (Wakamatsu et al, 2006). Note that the state transition graph shown in Fig.2 includes unknotting processes consisting of only UO IV operations.…”

“…The untightenable knot is unknotted when its both endpoints are pulled away from each other. We can check whether a knot is tightenable or untightenable from its crossing state description (Wakamatsu et al, 2006). Fig.4-(a-1) illustrates the silhouette of a knot with 3 crossings.…”

A Human-Robot Collaborative Reinforcement Learning Algorithm

“…Most previous work on knot problems refers mainly to tying and untying tasks that involve strings or cords (e.g., [43,44]) or manipulating deformable objects (e.g., [45,46]). The task described in this paper is different in that the robot manipulator does not grasp a string or rope, but instead grasps a plastic bag, which is closed by tying the plastic handles of the bag into a knot.…”