A Bioinspired Multimaterial Soft Robotic Hand

University of Coimbra, Portugal

(A) Multimaterial finger’s soft actuator composed of two silicone layers and internal PET reinforcement. (B) Exoskeleton geometry of a single finger designed to bend in three joints (distal, middle, and proximal). (C) Operation principle where the pneumatic actuator inside a stiffer exoskeleton shell promotes the bending of the finger. (D) Attached to a robot manipulator, the soft robotic hand is capable of grasping and manipulating objects of various shapes, weights, and sizes. (Image: Samuel Alves, University of Coimbra, CEMMPRE, ARISE, Department of Mechanical Engineering)

A research paper by scientists at the University of Coimbra proposed a soft robotic hand comprising soft actuator cores and an exoskeleton, featuring a multimaterial design aided by finite element analysis to define the hand geometry and promote finger’s bendability. The new research paper, published on August 8 in the journal Cyborg and Bionic Systems, presented the development, fabrication, and control of a bioinspired soft robotic hand and demonstrated finite element analysis can serve as a valuable tool to support the design and control of the hand’s fingers.

“Recent research led to impactful achievements in functional designs, modeling, fabrication, and control of soft robots. Nevertheless, the full realization of life-like movements is still challenging to achieve, often based on trial-and-error considerations from design to fabrication, consuming time and resources. Using finite element analysis to support the design process, saving time and resources,” said study author Pedro Neto, a Professor at the University of Coimbra.

The finite element analysis comprising (a) hyperelastic behavior of the soft materials, (b) finite rotation and large strain of the exoskeleton and actuators, and (c) frictional contact between exoskeleton and actuators.

“This integrated solution will make soft robotic hands more available to people, at a reduced cost, avoiding the time-consuming design-fabrication trial-and-error processes,” the authors said. Thus, they proposed a soft robotic hand composed of soft actuator cores and an exoskeleton, featuring a multimaterial design aided by finite element analysis to define the hand geometry and promote finger’s bendability.

Soft robots can be fabricated by using multiple materials and using different manufacturing processes, ranging from silicone molding to 3D printing. 3D-printing methods bring significant benefits in design and fabrication, making it easy to introduce complex geometries within soft robots, accelerating/automating the fabrication process, and reducing its cost.

The team showed that the multimaterial soft actuators are designed and fabricated at a reduced cost and time effort, using standard fabrication processes such as molding and single-step 3D printing. The ON–OFF controller, while simple, keeps the set fingers bending angles stable, even in the presence of leaks. The robotic hand demonstrated dexterity and capability to grasp objects with different shapes, weights, and sizes.

“The reinforcement in a circumferential direction guarantees the actuator’s elongation and consequently the fingers bent when inside the exoskeleton,” said author Samuel Alves. “The robotic hand achieved an interesting dexterity level, being able to grasp objects of different shapes and sizes. Nevertheless, it struggles to grasp heavier objects featuring slippery surfaces, showing a concentrated deformation at the base of the fingers while the thumb motion is constrained.

“In addition, depending on the grasping surface and geometry, there exists mechanical interference between the fingers. Since the soft hand is highly nonlinear, with most variables of interest being coupled between themselves, future work will be dedicated to an indepth analysis of the grasping phenomena together with further standardization of testing benchmarks,” said Alves.

This soft robotic hand is accessible and can be built at a reduced cost, avoiding the time-consuming design-fabrication trial-and-error processes, and inspiring innovation around it.

For more information, contact Ning Xu at This email address is being protected from spambots. You need JavaScript enabled to view it..