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Morphable Biorobotics Lab focuses on soft robotics, particulary using biomimicry as a key design approach where inspiration is drawn from nature. My project was under the Octopus Subteam, which focuses on building an octopus inspired soft robot for minimally invasive underwater sampling that includes both locomotion and gripping capabilities.

Bio-Inspired Soft Gripper

Rigid grippers often damage fragile objects during underwater tasks, while human divers face safety and precision limits. Building on the original Soft Balloon Actuators (SBAs), I worked on a design that spiralled inward during inflation to passively self-align around objects. Qualitative testing showed the SBAs could safely conform to irregular shapes and secure delicate samples without damage. With their low-cost, adaptable design, SBAs offer a promising alternative for underwater manipulation.

Note : All information has been disclosed with permission from MBL.

How does it work?

Fluid is pumped through attached tubing to inflate the SBA, enabling it to passively wrap around and grip the object.

Context

Existing solutions face significant challenges: traditional robotic rigid grippers often apply excessive force that can harm delicate structures, while human divers face limitations related to safety, endurance, and environmental conditions. These limitations highlight a pressing need for more effective, gentle, and adaptable manipulation technologies.

Problem

To solve this, a soft gripper was designed to effectively manipulate objects in underwater environments, however the existing design didn't always grip the object so it had to manually be adjusted.

Solution

Soft ballon actuators (SBA’s) are are attached to the ends of a soft robot to allow manipulation / gripping of different objects. They are made out of a flexible material so when a fluid is pumped in, the structure expands / bends in a certain controlled manner, enabling the gripping of an object.

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Fabrication Process

The actuator is fabricated using TPU and Teflon. They are layered and heat pressed under a specific temperature and pressure. The ballons are formed by using Teflon shaped circles in between two TPU layers, to create the small pockets that can be inflated. The 2D layers were made on Adobe Illustrator and laser cut.

Testing and Design Iteration

Different designs were tested to achieve the spiral actuation mechanism as intended. This involved changing the 2D file on Adobe Illustrator.

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Design 1

I initially explored modifying the shape of the actuator's arm to evaluate its impact on gripping capability. However, after qualitative testing, these changes did not result in noticeable performance improvements. This led me to identify that the core limitation was not the material shape itself, but the way the actuator wrapped around the object, as it failed to engage sufficient surface area for a secure grip.

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Design 2

To address this, I explored allowing the actuator arms to move inward toward the center of the object, which significantly improved gripping performance.

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Design 3

Building on this insight, I drew inspiration from the way an octopus arm spirals around objects. I redesigned the Teflon constraint circles to alter the inflation behavior of the balloons, inducing a controlled spiral motion during actuation.

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Design 4

By combining both inward convergence and spiral actuation, I arrived at a design that demonstrated effective and repeatable gripping. Further refinements were made to tune the degree of spiraling, ensuring enough wrap for stability without over-constraining the motion which was seen for this iteration.

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Final Design

This design allows the SBA arms to curl inward while simultaneously spiraling, maximizing surface contact with the object and improving overall gripping performance.

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Qualitative Testing

An attempt was made to pick up objects of varying sizes to compare the performance of the new design with the original design. The new design made object pickup significantly easier, as it passively conformed to and gripped the object with minimal manual adjustment as seen in this video with the rubber duck.