This article is part of our exclusive IEEE Journal Review Series in partnership with IEEEX.
The fish is able to quickly glide through the water and turn its head with one movement of its tail. Researchers have tried to achieve similar results using water robots. In fact, one group in China has made progress in using a flexible electromagnetic fin that drives underwater robot at a speed of 405 millimeters – or 1.66 body lengths – per second. The team's robotic swimmer can also make turns within a radius of just 0.86 body lengths.
Fanhao Zhou, Associate Professor State Key Laboratory of Ocean Sounding at Zhejiang University in Zhejiang, China, assisted with the research. Zhou notes that fish are agile, efficient and adaptive, and imitating these qualities with a robot is not an easy task.
“Traditional robotic fins powered by motors They can create a lot of traction, but they are often bulky and rigid,” he says. drivesOn the other hand, they are flexible, but usually too weak to be practical. Our goal was to combine the best of both worlds – a compact drive that is powerful but flexible, like real muscles.”
Creating a new type of fin
So the research team developed a flexible electromagnetic fin with an elastic joint that moves back and forth with little friction. It consists of two small coils and spherical magnets. When alternating current flows through the coils, it creates an oscillating magnetic field that causes the fin to flap back and forth like a fish's tail. When the magnetic field does not oscillate, the fin returns to its neutral position at rest.
In their study, the scientists tested their bionic fin in a swimming pool. Zhe Wang, Ph.D. student in Zhou's lab points out that the team not only successfully piloted the bionic fin in water, but also built a mathematical model relating the electrical input current to the hydrodynamic thrust output. “This means we can predict how the fin will behave underwater simply based on the input current, which is rare in soft robotics,” he says.
The new robotic fish design exhibits different swimming behavior at different fin oscillation speeds. Zhe Wang et al.
In their experiments, the researchers used a high-speed camera and a precision force sensor to measure the fin's trajectory and the thrust it generated, achieving a peak thrust of 0.493. newtonsdespite the fact that the fin weighs only 17 grams.
Zhou notes that the robotic system is small, light and powerful, and will also be easily scalable to multi-fin systems. However, he adds that the current design consumes a lot of energy. “The electromagnetic coils draw a lot of current, so the float time is relatively short,” he explains. “We are exploring ways to reduce energy waste, e.g. [by] optimizing coil geometry, using energy recovery circuits, and employing intelligent control strategies that do not require constant excitation.”
The researchers expect this robotic system could have a range of applications, including possibly underwater exploration, environmental monitoring and inspection, such as safely interacting with coral reefs and sea life.
“Our next step is to study the coordinated movement of multiple fins, which will allow the robot to perform more flexible and realistic swimming behavior,” says Wang. “We are also exploring ways to improve energy efficiencyextend operating time and further miniaturize the system for small autonomous underwater platforms.”
The researchers' bionic fin is described in study published September 4 in IEEE Letters on Robotics and Automation.
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