What don’t our robots do that fish do? Just about everything: fish have ways of sensing, navigating, and moving underwater, according to Maarja Kruusmaa, professor of biorobotics at Tallinn University of Technology in Estonia, that none of our robots have.
Maarja’s team—an international one, comprising biologists and engineers from the Italian Institute of Technology, Riga Technical University in Latvia, the University of Verona in Italy, and the University of Bath in the United Kingdom—is designing a biomimetic lateral line and a robotic fish to take advantage of the new sensory capabilities the lateral line creates. We’ve discussed some of them: identifying the position of swimming companions in a school of fish at night, the location and proximity of an approaching predator, and the efficiency of self-generated water movement. All of these functions are beyond the scope of any single sensor currently made by humans. By building a biomimetic lateral line, Maarja and her team are betting that their robotic fish will be able to teach us land lubbers about physical structure in the aquatic world that we can’t comprehend ourselves.
When I visited Maarja’s biorobotics laboratory in spring 2009 I was struck by the ambition of the FILOSE (robotic FIsh LOcomotion and SEnsing) project.[179] The biomimetic lateral line will be placed on a self-propelled robotic fish (Figure 8.1) that controls its swimming performance by varying both neural control variables, like the frequency of its tail beat, and the mechanical properties of the body, such as stiffness.[180] The robotic fish will have to learn how the patterns of flow sensors distributed around its body relate to the external flow patterns and the detection of underwater objects; the FILOSE engineers have used a digital simulation to show that this is possible. This work is funded by the European Commission under their Seventh Framework Programme, which pursues the “European Union’s Lisbon Strategy to become the ‘most dynamic competitive knowledge-based economy in the world.’”[181]
FIGURE 8.1. The FILOSE fish robot at Tallinn University of Technology. Professor of biorobotics Maarja Kruusmaa monitors the FILOSE fish robot in the flow tank, as seen on the right. This is an early developmental stage of the robot, driven by an external motor located above the tank, inputting power via the metal shaft. The large tail is an example of the KISS principle in action: it is a single piece of rubber acting as a robust actuator and rudder for the payload that sits in the rigid head. The biomimetic lateral line will be installed along the length of the FILOSE fish. The FILOSE project is multinational, with Professor Kruusmaa directing. The work is funded by the European Commission through their Seventh Framework Programme. Image on the left by John Long. Image on the right by Maarja Kruusmaa.
In the United States the National Science Foundation is funding work on fish to uncover novel ways to create highly maneuverable underwater vehicles. Malcolm McIver, professor of mechanical engineering at Northwestern University in Illinois, leads a team of engineers and biologists, including George Lauder of Harvard, studying the precision maneuvering of the black ghost knife fish.[182] Knife fish are so called because of their tapered and stiff body. Unlike other fish, knife fish don’t bend their bodies to swim; instead, they ripple a long, thin fin that runs along their belly. This fin enables them to do something unusual among fishes: move vertically without having to point upward. By building a biomimetic robot, Malcolm’s team has shown how this happens and that the function, once understood as a mechanical principle, can be used by engineers building underwater vehicles, even if those vehicles are otherwise unfish-like.
Using a process he calls “biologically derived design,” James Tangorra, assistant professor of mechanical engineering and mechanics at Drexel University, builds robotic bluegill sunfish with George and Melina. Interested in efficient and novel propulsion, they focus on fins and their internal structures—thin, bifurcated rods called rays. In each of the sunfish’s two pectoral fins, fourteen fin rays are independently controlled to bend, cup, and curl the fin. This level of structural control, which occurs dynamically during swimming, is unprecedented in engineering systems. By building fish-inspired robotic structures, the team has learned something new about real fish fins in the process: they bend using a novel structural mechanism involving the shearing of two parallel struts connected at one end.[183] With any flexible, animated structure, like a fin or a whole undulating body for that matter, neural control of its motion becomes the next frontier, as Melina explained when asked about design challenges facing her team and others building robotic fish: “we need to incorporate some sort of realistic understanding of sensation and sensory processing—taking in the sensory input and processing multiple inputs to, in a sense, decide on a motor output.”
The FILOSE fish, the robotic knife fish, and the robotic sunfish fins projects show how fish inspire engineers. Engineers are also building robotic fish in China, France, Indonesia, Japan, Korea, Singapore, and the United Kingdom.[184] Among most of these fish-inspired projects we see three different approaches for getting started: (1) identify a function of a fish or function within a fish that is novel to engineering and can be reduced to a mechanical or mathematical principle, (2) identify a behavior of a fish or system of fish that is novel to engineering and can be reduced to an algorithm, or (3) identify a structure of a fish that is novel to engineering and can be duplicated in other materials. Clearly, novelties in aid of applications are what roboteers fish for.
For Frank Fish—who we met in the last chapter and who, funded by the US Office of Naval Research, heads a multi-institutional building of a robotic manta ray—nautical engineers’ interest in fish has been constant and longstanding. “It all comes down to four words,” he explained, “speed, maneuverability, efficiency, and stealth.” But there’s more to the story than just that: when I asked Frank why so many engineers were building robotic fish, without hesitation he said, “Because the Navy is funding them.”[185]
The US Navy, through the Office of Naval Research (ONR), has been funding work on fish and dolphins since the office’s inception in 1946, leveraging academic research to help engineers understand aquatic propulsion.[186] Having had two ONR research grants in the 1990s with my mathematics collaborator from Lafayette College, Rob Root, I’ve benefited from the Navy’s interest in fish and robotic fish.
179
Full disclosure: I am hired by the European Commission as an outside expert evaluator of the FILOSE project, which the EC funds as part of their Seventh Framework Programme.
180
For the latest on FILOSE Fish, see this paper: M. Kruusmaa, T. Salumae, G. Toming, A. Ernits, and J. Ježov, “Swimming Speed Control and On-board Flow Sensing of an Artificial Trout,”
182
Work on the fish and the biomimetic robot is explained in: O. M. Curet, N. A. Patankar, G. V. Lauder, and M. A. MacIver, “Aquatic Manoeuvering with Counter-Propagating Waves: A Novel Locomotive Strategy,”
183
For more on their robotic fish fin, see: Chris Phelan, James Tangorra, George Lauder, and Melina Hale, “A Biorobotic Model of the Sunfish Pectoral Fin for Investigations of Fin Sensorimotor Control,”
184
If you are interested in other fish-inspired robots, I review the field in “Biomimetics: Robotics Based on Fish Swimming,” in
185
Conversation at the Annual Meeting of the Society for Integrative and Comparative Biology, January 4, 2011.
186
I use the date of 1946 here because that was when President Truman created the ONR to “plan, foster and encourage scientific research in recognition of its paramount importance as related to the maintenance of future naval power, and the preservation of national security.” The Navy, however, considers ONR to have been started earlier, in 1923, as the Naval Research Laboratory. See their timeline at www.onr.navy.mil/About-ONR/History-ONR-Timeline.aspx.