EthoHand: A dexterous robotic hand with ball-joint thumb enables complex in-hand object manipulation

Abstract

Abstract-Our dexterous hand is a fundmanetal human feature that distinguishes us from other animals by enabling us to go beyond grasping to support sophisticated in-hand object manipulation. Our aim was the design of a dexterous anthropomorphic robotic hand that matches the human hand's 24 degrees of freedom, under-actuated by seven motors. With the ability to replicate human hand movements in a naturalistic manner including in-hand object manipulation. Therefore, we focused on the development of a novel thumb and palm articulation that would facilitate in-hand object manipulation while avoiding mechanical design complexity. Our key innovation is the use of a tendon-driven ball joint as a basis for an articulated thumb. The design innovation enables our underactuated hand to perform complex in-hand object manipulation such as passing a ball between the fingers or even writing text messages on a smartphone with the thumb's end-point while holding the phone in the palm of the same hand. We then proceed to compare the dexterity of our novel robotic hand design to other designs in prosthetics, robotics and humans using simulated and physical kinematic data to demonstrate the enhanced dexterity of our novel articulation exceeding previous designs by a factor of two. Our innovative approach achieves naturalistic movement of the human hand, without requiring translation in the hand joints, and enables teleoperation of complex tasks, such as single (robot) handed messaging on a smartphone without the need for haptic feedback. Our simple, under-actuated design outperforms current state-ofthe-art prostheses or robotic and prosthetic hands regarding abilities that encompass from grasps to activities of daily living which involve complex in-hand object manipulation.

Sparse Eigenmotions derived from daily life kinematics implemented on a dextrous robotic hand

“…Indeed, our sparse code explained more of the variance in natural hand movements than correlation patterns or principle components as derived by classic PCA [1]. We set out here to explore how these results from human kinematics and computational neuroscience play out when we embody them in a robotic system -a novel dexterous robotic hand with a ball-jointed thumb [2].…”

“…We build our work on sparse coding [1] and translate these data-driven models into mechanical implementations on a novel hand [2]. We present a novel approach towards the naturalistic control of dexterous robotic and prosthetic hands by projecting natural motor behaviour in an artificial hand.…”

“…These Sparse EigenMotions (SEMs)[1] form a sparse symbolic code that encodes continuous hand motions. We mechanically implemented the common SEMs on our novel dexterous robotic hand [2] in open-loop control. We report that without processing any feedback during grasp control, several of the SEMs resulted in stable grasps of different daily life objects.…”

The Making of a 3D-Printed, Cable-Driven, Single-Model, Lightweight Humanoid Robotic Hand

“…One cable actuates each finger, but the thumb has an additional cable for adduction motion ( Figure 6D). Previous tests on those low DOFs robotic hands already show that six or seven DOFs are good enough for most grasping gestures (Slade et al, 2015;Konnaris et al, 2016).…”

“…For robotic hands, "ball joints" can be used for simulating a joint with more than one DOF, such as a wrist's joint or a thumb's joint. EthoHand (Konnaris et al, 2016) has a ball-jointed thumb, which is controlled by three motors and six tendons ( Figure 5G). As part of the 3D model, our robotic hand integrates the "ball joint" mechanism to the robotic hand's palm (Figures 5D,E).…”