BRL/Pisa/IIT SoftHand: A Low-cost, 3D-Printed, Underactuated, Tendon-Driven Hand with Soft and Adaptive Synergies

TL;DR

The paper addresses the challenge of affordable, adaptable robotic hands by integrating soft and adaptive synergies into a low-cost, 3D-printed, tendon-driven design. It introduces the BRL/Pisa/IIT SoftHand, featuring a novel three-tendon, single-actuator layout, modular phalanges, and palm-tendon routing that enables both soft and adaptive grasping. Kinematic simulations with empirical joint relations validate the grasping workspace, while experiments demonstrate grasping of diverse objects and holding forces around $19.8$ N, supporting effective synergy-driven manipulation. The work emphasizes manufacturability and openness, offering CAD and fabrication instructions for home-printer production and an open-source release for broader adoption and further refinement.

Abstract

This paper introduces the BRL/Pisa/IIT (BPI) SoftHand: a single actuator-driven, low-cost, 3D-printed, tendon-driven, underactuated robot hand that can be used to perform a range of grasping tasks. Based on the adaptive synergies of the Pisa/IIT SoftHand, we design a new joint system and tendon routing to facilitate the inclusion of both soft and adaptive synergies, which helps us balance durability, affordability and grasping performance of the hand. The focus of this work is on the design, simulation, synergies and grasping tests of this SoftHand. The novel phalanges are designed and printed based on linkages, gear pairs and geometric restraint mechanisms, and can be applied to most tendon-driven robotic hands. We show that the robot hand can successfully grasp and lift various target objects and adapt to hold complex geometric shapes, reflecting the successful adoption of the soft and adaptive synergies. We intend to open-source the design of the hand so that it can be built cheaply on a home 3D-printer. For more detail: https://sites.google.com/view/bpi-softhandtactile-group-bri/brlpisaiit-softhand-design

Figures (7)

• Figure 1: The design overview of the BRL/Pisa/IIT SoftHand, indicating modular components and general dimensions. The right exploded figure shows the main components of a single modular finger. The purple boxes represent the three finger joints (see Fig. \ref{['fig2']} for more details).
• Figure 2: Tendon Layout: The left tendon (in red) routes motion to the joints of thumb and index finger; the middle tendon (yellow) routes motion to the joints of middle and third fingers; the right tendon (green) routes motion to the joints of just the little (pinky) finger.
• Figure 3: Side and top views of the modular fingertip and middle phalanx, showing the tendon layout (red line), elastic band (blue box) and phalanx connecting rod (purple box).
• Figure 5: The left figure shows the finger kinematics simulation and the right figure shows the corresponding finger kinematics in a real experiment
• Figure 7: (a) The BRL/Pisa/IIT SoftHand grasping various objects with different shapes to show its soft and adaptive synergies. (b) The BRL/Pisa/IIT SoftHand grasping various objects with different shapes to show its grasping ability. Videos of these experiments are included in the supplementary video files.