Robotic Fish

November 3, 2011 - via Emory Univeristy

A team of engineers at Michigan State University is currently researching and developing a biomimetic natatory cybernetic morphon, more clearly, a robotic fish (Smith). Their research is a part of a larger school that attempts to combine the sciences of biology, engineering, and computing. By replicating the processes of natural organisms, it is hoped that more efficient robots can be developed. In their effort to design an efficient aquatic robot, the engineers at MSU have turned to actual fish for inspiration. Living fish are already well suited to aquatic environments, so it is hoped that their anatomy can be used in various underwater robots and vehicles.

MSUToday: Robofish wonder
The robotic fish components are made using a three-dimensional printer, which operates similarly to a two-dimensional paper printer. Different fish parts are drawn using a computer program, and the designs are then printed. Unlike a 2D printer which simply squirts ink onto a piece of paper, the 3D printer spreads a plastic powder. The printer deposits the layers one over another and sculpts the fish parts from bottom to top (Shipman). By changing the type and ratios of the plastics used, the engineers can create accurate colored fish parts of varying flexibilities and densities.

3D printing in action
The fish are propelled by means of an electroactive polymer. An electroactive polymer (EAP) is a polymer (a large molecule with repeating structural units) whose shape and size change when stimulated by an electric field (Bar-Cohen). With the proper application of electricity, usually from a battery, the EAP’s shape can be controlled. Because EAPs can be made to flex, they are occasionally used as artificial muscles. Concerning the robotic fish, an EAP connects a plastic caudal fin to the fish’s body where a battery is located, allowing the fin to oscillate like a real fin.

EAPs are used in robotic fish for at least three reasons. First, EAPs operate quietly (Tan Modeling of Biomimetic Robotic Fish Propelled by An Ionic Polymer-Metal Composite Actuator). Other actuators, like combustion engines, make a considerable amount of noise. Quiet underwater vehicles would be better suited for things like surveillance, military applications, and ecological studies. Second, EAPs can be made smaller than other actuators (Tan). Without the need for a bulky motor, smaller fish can be created. Finally, EAPs can be used underwater (Tan). Unlike electric or gasoline engines, EAPs do not need be waterproofed. As long as the battery is kept dry, the polymer itself can be exposed to water (Bar-Cohen). One interesting attribute of EAPs is that they can generate an electric impulse in response to a physical force (Ihlefeld). This can allow a robotic fish to receive environmental feedback as it moves. Differences in water speed and pressure can stimulate the EAP to send an electric impulse to the fish’s microcontroller, allowing the fish to change its speed and direction accordingly. EAPs are very similar to actual muscles then, complete with feedback mechanisms.

The fish also posses communication capabilities (Tan An Autonomous Robotic Fish for Mobile Sensing). They can communicate not only with their programmers but also with other robotic fish. The robots make use of the ZigBee communication protocol. Compared to other possible protocols like Wi-FiTM and BluetoothTM , ZigBee uses less energy, has better range, and can be used for mesh networking with other robotic fish (Tan).

The robots are equipped with a GPS receiver, digital compass, and temperature sensor. Using GPS and its on board compass, the robots can be set to travel to practically any location on earth (Tan). The only drawback is that the GPS antenna must be positioned above water, preventing the robot from navigating while completely submerged. It must periodically resurface to reorient itself. The developers hope to rectify this problem in the future (Tan). The temperature sensor records the temperature of the water, but it’s main purpose is to set a precedent. If the thermometer works well during trial runs, other more useful sensors can be added in the future (Tan).

For control, the robots are equipped with a microcontroller, essentially a miniaturized computer (Tan). The microcontroller sets the frequency of the vibrations of the fish’s tail and receives feedback from the EAP, managing the robot’s speed and course. Furthermore, it receives position data from the GPS and digital compass. Radio communications, both with the programmers and other robotic fish, are handled by the microcontroller.
The fish are powered by two rechargeable lithium batteries (3.6 V, 750 mAh). The batteries supply 3.3 volts of steady current to power the EAP actuator (Tan).
 
The possible applications of robotic fish are diverse. The fish could be placed into lakes to monitor for traces of industrial waste and aquatic pathogens. Though a stationary sensor can do this, a robotic fish could move to other areas of the lake, effectively giving it unlimited sensing range.

The fish could also be used to explore underwater caverns and shipwrecks. Usually, when an area is too dangerous for humans, explorers use a propeller-driven drone. These machines, however, generate turbulence with their propellers. The turbulence can damage decaying shipwrecks and delicate cave formations, possibly resulting in a cave in of some sort. Robotic fish can prevent such accidents. Real fish swim in and around caves and shipwrecks all the time, their delicate little tails producing almost no turbulence at all. A robotic fish could be sent to explore areas too precarious for humans and drones.

A less noble application includes military use. The robotic fish could be strapped with explosives. With their GPS programming, the fish could be used as stealthy underwater guided weapons.

There is even a possible application in nanotechnology. EAPs are simply chains of atoms. Theoretically, an infinitesimal EAP could be used to propel a nanobot. The nanorobotic fish could be implanted into a person’s body where it could perform various tasks such as administering site-specific drugs and attacking cancer cells.
Of course, the fish can always be displayed in aquariums.
 
Works Cited
Bar-Cohen, Yoseph. “Electroactive Polymers (EAP).” Electrochemistry Encyclopedia. Case Western University, Dec. 2004. Web. 02 Nov. 2011. <http://electrochem.cwru.edu/encycl/art-p02-elact-pol.htm>.
Ihlefeld, Curtis M., and Zhihua Qu. “A Dielectric Electroactive Polymer Generator-actuator Model: Modeling, Identification, and Dynamic Simulation.” NASA ADS. High Energy Astrophysics Division at the Harvard-Smithsonian Center for Astrophysics, 10 Mar. 2008. Web. 02 Nov. 2011. <http://adsabs.harvard.edu/abs/2008SPIE.6927E..23I>.
Matt, Shipman. “What Is 3D Printing? And How Does It Work?” The Abstract. North Carolina State University, 15 June 2011. Web. 02 Nov. 2011. <http://web.ncsu.edu/abstract/technology/3d-printing/>.
Smith, Robin Anne. “Synchronized Swimming: Patrolling for Pollution with Robotic Fish | Guest Blog, Scientific American Blog Network.” Scientific American Blog Network. Scientific American, 19 Sept. 2011. Web. 11 Oct. 2011. <http://blogs.scientificamerican.com/guest-blog/2011/09/19/synchronized-swimming-patrolling-for-pollution-with-robotic-fish/>.
Tan, Xiaobo, Drew Kim, Nathan Usher, Dan Laboy, Joel Jackson, Azra Kapetanovic, Rason Rapai, Beniamin Sabadus, and Xin Zhou. An Autonomous Robotic Fish for Mobile Sensing. Michigan State University, 16 Oct. 2006. Web. 02 Nov. 2011. <http://www.egr.msu.edu/%7Exbtan/Papers/iros06_fish.pdf>.
Tan, Xiaobo, Ernest Mbemmo, Zheng Chen, and Stephan Shatara. Modeling of Biomimetic Robotic Fish Propelled by An Ionic Polymer-Metal Composite Actuator. Michigan State University, 06 Dec. 2007. Web. 02 Nov. 2011. <http://www.egr.msu.edu/%7Exbtan/Papers/ICRA08-FishModel.pdf>.
https://blogs.emory.edu/cs190/2011/11/03/robotic-fish/

External link: https://blogs.emory.edu/cs190/2011/11/03/robotic-fish/

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