Suction cup grasping a stone (Image: Tianqi Yue)

A new robotic suction cup which can grasp rough, curved, and heavy stone, has been developed by scientists at the University of Bristol.

The team, based at Bristol Robotics Laboratory, studied the structures of octopus biological suckers, which have superb adaptive suction abilities enabling them to anchor to rock.

In their findings, published in the journal PNAS, the researchers show how they were able create a multi-layer soft structure and an artificial fluidic system to mimic the musculature and mucus structures of biological suckers.

Suction is a highly evolved biological adhesion strategy for soft-body organisms to achieve strong grasping on various objects. Biological suckers can adaptively attach to dry complex surfaces such as rocks and shells, which are extremely challenging for current artificial suction cups. Although the adaptive suction of biological suckers is believed to be the result of their soft body’s mechanical deformation, some studies imply that in-sucker mucus secretion may be another critical factor in helping attach to complex surfaces, thanks to its high viscosity.

“The most important development is that we successfully demonstrated the effectiveness of the combination of mechanical conformation — the use of soft materials to conform to surface shape, and liquid seal — the spread of water onto the contacting surface for improving the suction adaptability on complex surfaces,” said Lead Author Tianqi Yue. “This may also be the secret behind biological organisms’ ability to achieve adaptive suction.”

Their multi-scale suction mechanism is an organic combination of mechanical conformation and regulated water seal. Multi-layer soft materials first generate a rough mechanical conformation to the substrate, reducing leaking apertures to just micrometers. The remaining micron-sized apertures are then sealed by regulated water secretion from an artificial fluidic system based on the physical model, thereby the suction cup achieves long suction longevity on diverse surfaces but with minimal overflow.

“We believe the presented multi-scale adaptive suction mechanism is a powerful new adaptive suction strategy which may be instrumental in the development of versatile soft adhesion,” said Yue.

“Current industrial solutions use always-on air pumps to actively generate the suction however, these are noisy and waste energy.

“With no need for a pump, it is well-known that many natural organisms with suckers, including octopuses, some fishes such as suckerfish and remoras, leeches, gastropods, and echinoderms, can maintain their superb adaptive suction on complex surfaces by exploiting their soft body structures.”

The findings have great potential for industrial applications, such as providing a next-generation robotic gripper for grasping a variety of irregular objects.

The team now plans to build a more intelligent suction cup, by embedding sensors into the suction cup to regulate suction cup’s behavior.

Here is an exclusive Tech Briefs interview with Yue, edited for length and clarity.

Tech Briefs: What was the biggest technical challenge you faced while developing this suction mechanism?

Yue: The biggest challenge is how to make the suction cup stay on complex surfaces for a long time without a vacuuming pump. A suction cup will lose its functionality on rough and curved surfaces due to the leakage. In this study, we overcame this challenge by mimicking an octopus sucker’s biological structures and working principles.

Tech Briefs: Can you explain in simple terms how it works?

Yue: The suction cup works like an octopus sucker. For a long time, it has been believed that the superb suction of octopus suckers stems from the flexible muscles. However, our research has found that besides this, the mucus also plays an important role in its suction to irregular surfaces.

In simple terms, the suction cup we designed uses a multi-layered soft material composed of sponge-like elastomer and silicone pad to mimic the flexible muscle of the octopus, achieving sealing on irregular surfaces at a larger scale, reducing leakage gaps to the micron level. Furthermore, by mimicking the octopus' mucus with water, liquid sealing is achieved for the smaller-scale micron-level gaps, enabling the suction cup to adhere for a long time on rough and highly curved surfaces.

Octopus suckers (Image: Tianqi Yue)

Tech Briefs: How soon could we see this implemented in robotics? What about other industrial applications?

Yue: The practical industrial application requires further optimization of the suction cup's design, for example, the structure, materials, and control theory to lower the cost, but this will not take a long time. Other industrial applications could be healthcare and underwater robots, for example, developing painless surgical suction tools and underwater robotic grippers.

Tech Briefs: The article says, “The team now plans to build a more intelligent suction cup, by embedding sensors into the suction cup to regulate suction cup’s behavior.” Can you talk about the intelligent suction cup? What are your plans with regards to the sensors?

Yue: In this study, we just mimicked the adaptive suction ability of octopus suckers. Actually, octopus suckers are versatile organs which undertake perceive and control functionalities. Our ongoing research aims to make artificial suction cups as versatile as octopi suckers. The optional choice is embedding stretchable strain sensors into the suction disc, so the electrical signal provides the suction cup deformation for us to perceive its physical interaction with the environment.

Tech Briefs: Going from the prior question is: How is it coming along? Are there any updates you can share?

Yue: Our technology on intelligent suction cups allows a regular cheap suction cup to autonomously grip objects, and in the meantime, perceive the surface roughness, wetness and contacting force. This technology will help reduce the industrial robotic grippers' system complexity and cost.

Tech Briefs: Do you have any advice for engineers/researchers aiming to bring their ideas to fruition (broadly speaking)?

Yue: Natural science and engineering science are inseparable. I often get engineering inspiration from research in natural sciences. So, keeping my eyes on biology, environmental science, physics, and chemistry helps me to get interesting engineering ideas.