Extrinsic dexterity: In-hand manipulation with external forces

Abstract

Abstract-"In-hand manipulation" is the ability to reposition an object in the hand, for example when adjusting the grasp of a hammer before hammering a nail. The common approach to in-hand manipulation with robotic hands, known as dexterous manipulation [1], is to hold an object within the fingertips of the hand and wiggle the fingers, or walk them along the object's surface. Dexterous manipulation, however, is just one of the many techniques available to the robot. The robot can also roll the object in the hand by using gravity, or adjust the object's pose by pressing it against a surface, or if fast enough, it can even toss the object in the air and catch it in a different pose. All these techniques have one thing in common: they rely on resources extrinsic to the hand, either gravity, external contacts or dynamic arm motions. We refer to them as "extrinsic dexterity".In this paper we study extrinsic dexterity in the context of regrasp operations, for example when switching from a power to a precision grasp, and we demonstrate that even simple grippers are capable of ample in-hand manipulation. We develop twelve regrasp actions, all open-loop and handscripted, and evaluate their effectiveness with over 1200 trials of regrasps and sequences of regrasps, for three different objects (see video [2]). The long-term goal of this work is to develop a general repertoire of these behaviors, and to understand how such a repertoire might eventually constitute a general-purpose in-hand manipulation capability.

Multi-robot grasp planning for sequential assembly operations

“…We show that assuming feasibility of regrasps we can simplify the CSP solutions of manipulation plans significantly. Structures similar to the grasp-placement space [5] or the grasp-graph [6] can be precomputed to satisfy our regrasp feasibility assumption. Our algorithm takes as input a sequence of relative poses of assembly parts.…”

Variable-Grasping-Mode Underactuated Soft Gripper With Environmental Contact-Based Operation

“…Contact with the environment can potentially extend the manipulation capability of robotic hands. Recent studies of motion planning based on this concept are [32]- [35], where motion planning is presented in more detail. Note that motion planning is beyond the scope of this study.…”

In-hand manipulation using gravity and controlled slip

“…Dafle et al presented a strong case for the benefits of extrinsic dexterity for in-hand manipulation [3]. Even though the robot used in the study is equipped with a rather simple gripper, the authors demonstrated that it is still physically possible to reposition the object in the hand of the robot by taking advantage of resources external to the robot's hand such as gravity, use of external objects for support and inertial forces due to the manipulator's acceleration.…”

“…In contrast with [3], our work focuses on one specific manipulation scenario but instead of using discrete preprogrammed actions we design a continuous closed loop control law to move the tool to the target position.…”

“…If, however, the hand has a rather simple kinematic structure, it is perhaps more feasible to employ extrinsic dexterity, i.e. use resources that are external to the robot hand's embodiment [3]. The robot may for instance push the tool against an external object or it may loosen the grip so that the tool falls to a desired position due to gravity.…”