[Paper Review] A Novel Design of Soft Robotic Hand with a Human-inspired Soft Palm for Dexterous Grasping

Haihang Wang, Fares J. Abu‐Dakka+3 more|arXiv (Cornell University)|Sep 2, 2020

Soft Robotics and Applications17 references4 citations

TL;DR

This paper presents a novel soft robotic hand with a human-inspired soft palm and hybrid bending soft fingers (HBSF) for dexterous grasping. Actuated by pneumatic pressure, the hand enables splaying, bending, and thumb abduction via a modular soft palm, achieving 32 out of 33 grasp postures in the Feix taxonomy with robust, compliant grasping of diverse objects including fragile and heavy items.

ABSTRACT

Soft robotic hands and grippers are increasingly attracting attention as a robotic end-effector. Compared with rigid counterparts, they are safer for human-robot and environment-robot interactions, easier to control, lower cost and weight, and more compliant. Current soft robotic hands have mostly focused on the soft fingers and bending actuators. However, the palm is also essential part for grasping. In this work, we propose a novel design of soft humanoid hand with pneumatic soft fingers and soft palm. The hand is inexpensive to fabricate. The configuration of the soft palm is based on modular design which can be easily applied into actuating all kinds of soft fingers before. The splaying of the fingers, bending of the whole palm, abduction and adduction of the thumb are implemented by the soft palm. Moreover, we present a new design of soft finger, called hybrid bending soft finger (HBSF). It can both bend in the grasping axis and deflect in the side-to-side axis as human-like motion. The functions of the HBSF and soft palm were simulated by SOFA framework. And their performance was tested in experiments. The 6 fingers with 1 to 11 segments were tested and analyzed. The versatility of the soft hand is evaluated and testified by the grasping experiments in real scenario according to Feix taxonomy. And the results present the diversity of grasps and show promise for grasping a variety of objects with different shapes and weights.

Motivation & Objective

• To address the limitation of rigid robotic hands in handling fragile or irregularly shaped objects due to high contact forces and poor compliance.
• To overcome the oversight in soft robotic hands by integrating a functional, actuated soft palm that enables dynamic finger repositioning.
• To design a hybrid bending soft finger (HBSF) that mimics human-like motion in both bending and lateral deflection for enhanced dexterity.
• To validate the hand’s grasping performance in real-world scenarios using the Feix grasp taxonomy and physical experiments.
• To demonstrate low-cost, lightweight, and safe human-robot interaction through pneumatic actuation and passive compliance.

Proposed method

• Design of a modular soft palm with two actuated parts: one for palm splaying and bending, and another for thumb abduction, both pneumatically actuated.
• Development of the hybrid bending soft finger (HBSF) by combining the chamber network structure of PneuNets with fibre-reinforcement to enhance bending efficiency and force capacity.
• Use of the SOFA physics engine for finite element method (FEM) simulation of HBSF and soft palm actuation to predict motion and force response.
• Fabrication of a 6-finger soft hand prototype using silicone rubber and embedded air chambers, actuated via pneumatic pressure control.
• Implementation of a sequential actuation strategy: palm functions (splaying, bending, thumb abduction) are actuated first to fit the object, followed by finger pressurization.
• Grasping experiments conducted using a Franka Emika Panda robot arm to test grasp stability and repeatability under controlled motion (40 mm/s).

Experimental results

Research questions

• RQ1 Can a soft robotic hand with an actuated, human-inspired soft palm significantly improve grasp dexterity and adaptability compared to rigid or fixed-palm designs?
• RQ2 To what extent can the hybrid bending soft finger (HBSF) replicate human-like motion in both bending and lateral deflection for enhanced grasping versatility?
• RQ3 How well can the soft hand perform across the full spectrum of grasp types defined in the Feix taxonomy, particularly in terms of posture diversity and stability?
• RQ4 What is the performance trade-off between finger segment count and actuation capability in the HBSF design, especially in achieving both bending and deflection?
• RQ5 Can the soft hand achieve safe, compliant interaction with humans and fragile objects while maintaining sufficient grasping force for heavy items?

Key findings

• The soft hand successfully achieved 32 out of 33 grasp postures in the Feix taxonomy, demonstrating high postural dexterity and broad applicability.
• The HBSF with 11 segments achieved optimal performance, enabling both significant bending (up to 68°) and lateral deflection for versatile grasping.
• The soft palm achieved a maximum bending angle of 68° and a thumb abduction angle of approximately 90°, enabling effective repositioning of fingers for complex objects.
• The hand demonstrated robust grasping of a 143 g watering can and a 541 g chair, confirming high grasping force and load capacity.
• The hand exhibited high compliance and safety in human-robot interaction, with no damage to the hand or human subjects during contact.
• The experimental results validated the simulation predictions from the SOFA framework, confirming the reliability of the FEM-based design approach.