Not Twisting Your Arm: Combining Grasping and Rotation in a Single Robot Hand Mechanism

Vatsal V. Patel, Aaron Dollar

Keywords: design, mechanisms, in-hand manipulation

TL;DR: A robotic hand that combines grasping and wrist-like object rotation capabilities within a single mechanism for more efficient and versatile manipulation of a wide range of everyday objects.

Abstract: Object reorientation plays a vital role in dexterous robot manipulation tasks such as turning doorknobs or aligning a key. For robotic systems, this is most often done with a simple gripper attached to a 3-DOF wrist. But wrists are mechanically-complex, and the wrist axes are often far from the grasped object, resulting in parasitic translations and awkward whole-arm motions. We present the Sphinx robot hand that can both grasp and then rotate a wide range of objects in all three axes about a known fixed point within the hand and close to the object, replicating much of the function of traditional wrists. The mechanism of the hand is such that all the fingers' revolute axes intersect at a common point (independent of object shape, pose, or grasp), and all manipulated poses of objects are at a fixed distance from this point. We detail the spherical parallel design and workspace model of the wrist-like hand, validate its performance especially for lower-DOF robot arms without traditional wrists and show that it can accurately rotate objects over large angles with open-loop control. The Sphinx hand will be made available as open-source hardware through the Yale OpenHand project and experimental results can be seen in the video at: https://youtu.be/EPUDe4hbHBk.

Submission Number: 5