Most of the world is covered by oceans, which are unfortunately heavily polluted. One strategy for dealing with the piles of trash found in these highly sensitive ecosystems – especially around coral reefs – is to use robots to master the cleanup. However, existing underwater robots are mostly bulky with rigid bodies, unable to explore and take samples in complex and unstructured environments, and noisy due to electric motors or hydraulic pumps. For a more suitable design, scientists at the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart looked to nature for inspiration. They configured a jellyfish-inspired, versatile, energy-efficient and nearly noise-free robot the size of a hand. Jellyfish-Bot is a collaboration between the Physical Intelligence and Materials Robotics departments at MPI-IS. “Multi-Purpose Robotic Platform Like Jellyfish for Effective Underwater Propulsion and Manipulation” published in Science Advances.
To build the robot, the team used electro-hydraulic actuators that conduct electricity. Actuators function as artificial muscles that move the robot. Surrounding these muscles is a cushion of air and soft and rigid components that stabilize the robot and make it waterproof. In this way, the high voltage flowing through the actuator cannot touch the surrounding water. The power supply periodically provides electricity through thin wires, causing the muscles to contract and expand. This allows the robot to swim gracefully and create eddies under its body.
“As the jellyfish swims upward, it can trap objects along its path because it creates currents around its body. In this way, it can also accumulate nutrients. Our robot also circulates water around it. This function is useful for collecting objects such as trash particles. It can then transport waste to the surface, where it can then be recycled. It can also collect fragile biological samples such as fish eggs. Meanwhile, there was no negative impact on the surrounding environment. Interaction with aquatic species is gentle and almost noise free”, explained Tianlu Wang. He is a postdoctoral fellow in the Department of Physical Intelligence at MPI-IS and first author of the publication.
His co-author Hyeong-Joon Joo of the Robotic Materials Department continues: “70% of marine debris is estimated to sink to the ocean floor. Plastic makes up over 60% of this waste, taking hundreds of years to decompose. Therefore, we saw an urgent need to develop robots to manipulate objects such as garbage and transport them to the top. We hope underwater robots can one day help clean up our oceans.”
Jellyfish-Bots are able to move and trap objects without physical contact, operating alone or in some combination. Each robot works faster than any other similar invention, reaching speeds of up to 6.1 cm/s. Moreover, Jellyfish-Bot only requires a low input power of around 100 mW. And it’s safe for humans and fish if the polymer material that insulates the robots is torn apart one day. Meanwhile, the noise from the robot is indistinguishable from the background level. In this way the Jellyfish-Bot interacts gently with its environment without disturbing it – just like its natural counterpart.
The robot consists of several layers: some stiffen the robot, others serve to keep it afloat or isolate it. The polymer layer further functions as a floating skin. Electrically powered artificial muscles known as HASEL are embedded in the middle of the different layers. HASEL is a plastic bag filled with liquid dielectric partially covered by electrodes. Applying a high voltage across the electrodes charges them positively, while the water around them is negatively charged. This creates a force between the positively charged electrodes and the negatively charged water which pushes the oil in the pouch back and forth, causing the pouch to contract and relax – much like a real muscle. HASEL can sustain the high electrical pressure generated by charged electrodes and is protected from water by an insulating layer. This is important, because HASEL muscles have never been used to build underwater robots.
The first step was to develop a single-electrode Jellyfish-Bot with six fingers or arms. In a second step, the team divided the single electrode into separate groups to drive them independently.
“We achieved the object of gripping by making four of the arms act as propellers, and the other two as grippers. Or we just move part of the arm, to point the robot in a different direction. We also looked at how we could operate a collection of multiple robots. For example, we took two robots and let them take masks, which is very difficult for just one robot. Two robots can also work together in carrying heavy loads. However, at this point, our Jellyfish Bot needs cables. This is a weakness if we really want to use it someday in the ocean”, said Hyeong-Joon Joo.
Perhaps the cables that power robots will soon be a thing of the past. “We aim to develop wireless robots. Fortunately, we have achieved the first step towards this goal. We have included all functional modules such as battery and wireless communication components to enable wireless manipulation in the future,” continued Tianlu Wang. The team installed the buoyancy unit on top of the robot and the battery and microcontroller on the bottom. They then took their invention for a swim in Stuttgart’s Max Planck campus pool, and successfully steered it. But so far, they have been unable to direct the wireless robot to change course and swim the other way.
Knowing the team, it didn’t take long to achieve this goal.
tags: inspired bio
The goal of the Max Planck Institute for Intelligent Systems is to investigate and understand the organizing principles of intelligent systems and the perception-action-learning loop that underlies them.