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Design of a Single-Input, Five-Output Differential Actuation Unit for Underactuated Hands

Hugo Scuderoni, Alessandro Perini, Matteo Russo

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AI summary

Key figure (auto-extracted from paper)

A novel asymmetric planetary gearbox successfully balances torque across five fingers from a single motor, enabling adaptive grasping through pure mechanical intelligence.

underactuation differential gearbox planetary gears robotic hands tendon-driven actuation mechanical design

Problem

Single-motor underactuated hand mechanisms typically actuate only four fingers or suffer from unbalanced force transmission, limiting dexterity and safety. Scaling differential gearboxes to five balanced outputs remains mechanically challenging.

Approach

The authors designed a compact, single-axis asymmetric planetary gearbox with five differential stages, combining numerical optimization with tendon pulley diameter tuning to balance torque distribution across all five outputs.

Key results

Successful synthesis of a balanced one-input, five-output planetary gearbox
Experimental validation of a 3D-printed prototype demonstrating adaptive torque distribution
Quantification of transmission errors due to friction and 3D-printing backlash (up to 32% loss)
Demonstration of robust load redistribution and linear behavior under high-force conditions

Why it matters

Enables reliable, lightweight, single-motor control for five-fingered robotic hands, prostheses, and exoskeletons without sacrificing precision or safety.

Abstract

Robotic hands, prosthetics, and hand exoskeletons struggle with replicating the natural dexterity of human hands: the mechanical intelligence of our muscles can be hardly repli- cated with rigid actuators, while soft mechanisms compromise precision. Underactuated hand mechanisms represent a trade- off between these extremes. However, single-motor solutions, while robust and compact, generally actuate a maximum of four fingers or present critical differences in force transmission between the fingers. Here, we propose a design for a single- input, five-output differential gearbox that delivers balanced transmission thanks to a unique asymmetrical layout. This feature enables adaptive grasp control through mechanical intelligence only, providing the user with a reliable, safe, and lightweight solution for tendon-driven hand mechanisms. A preliminary 3D-printed prototype is presented to demonstrate the concept.

Index terms

Mechanism Design Actuation and Joint Mechanisms Product Design Development and Prototyping