By Kal Kaur
Basic Bio-mechanics of a Robotic Fish
There may soon be a new type of paraphyletic aquatic life in the World’s waters – the robotic fish, used to track underwater pollution levels and underwater life. Currently, there are many underwater vehicles used to track movement of submarines and to clear waterways, but their size and shape doesn’t exactly blend in with aquatic life.
Autonomous underwater vehicles are also limited to their manoeuvrability and the level of noise created by these tracking systems. When considering locomotion of small fish, these aquatic species can move effectively in an aqueous environment due to their small size, make better use of the water, and make less noise. The lack of noise in a large aquatic environment will also be a survival technique for small fish to help prevent them being tracked by larger prey. Monitoring pollution levels isn’t the only reason why the development of robotic fish technology is important, but also to observe feeding habits and behavioural patterns to help understand the basic science to such life and to use this information in efforts to conserve the environment.
Basic Bio-mechanics of a Robotic Fish
The structural frame to a fish is divided up into specific sections based on function. To begin with, we can take a look at the caudal fin. Zhou C, et al and a team of researchers at the Institute of Automation, Chinese Academy of Sciences, Beijing, demonstrate a novel prototype of a robotic fish. The Caudal fin, also known as the tail to a fish is the driving force for a fish, it’s a what allows the fish to move through water freely. The team have used a tail that moves up and down to help push the fish in a forward direction using a direct current motor. There are also rubber tubes to this prototype that make the frame of the fish’s body (figure 1).
Figure 1. Basic structure to a robotic fish. Source: Zhao C, et al. Design and control of biomimetic robotic fish FAC-I. Published in Kato, N., Kamimura, S. (2008). Bio-Mechanisms of Swimming and Flying: Fluid Dynamics, Biomimetic Robots and Sport Science. Japan: Springer Science and Business Media.
The Caudal fin is only part of the structure to a fish. Fins are also important and fundamental to a fish being able to maintain balance in water. In a protocol design, Zhao C and the research team designed the front end of a fish by creating two pectoral fins that can rotate freely and encompass three degrees of freedom with both fins responding to a step motor. There are three motors to help manoeuvre the robotic fish: motor 1 is attached to a Cardan shaft (a propeller shaft that transmits torque and rotation), and motors 2 and 3 are also attached to a separate Cardan shaft at the opposite end of the structure. Motors 1 and 3 are responsible for moving back and forth to create a left and right movement in the pectoral fin. The pectoral fins begin to roll in order to change the positioning of the robot fish in water.
The application of one robotic fish in a dynamic underwater environment is not going to be able to capture movement range of aquatic life and monitor their behaviour, or even provide sufficient data on oceanic pollution. It is therefore important to use a multi-robotic fish system that can provide large amounts of data at any one time. Shao J et al have created a hardware platform that can support the application of a multi-robotic fish system in monitoring aquatic life. This team have divided the hardware platform into four systems: robotic fish, image capturing, decision making and control, and wireless communication. The image capturing system comprises of an overhead camera that gathers data on the surrounding underwater environment. These images are then transferred to a decision maker as input signals which in response generates control commands wirelessly to the multi-robotic fish system.
Recent press has highlighted a number of research projects currently looking at the application of robotic fish in the management of underwater pollution. A popular example is the SHOAL project which is currently taking the media by storm and is a project managed by the BMT group. The group have been able to engineer a multi-robotic fish system that can work in synchronicity to track pollution in ports. The interesting functional aspect to these fish is their ability to test water for pollutants in-situ. Each fish is built with chemical sensors that are designed to trace the source of the pollution and are able to do this effectively using ultrasonics. The robotic fish can move underwater for eight hours without any assistance from humans. Professor Huosheng Hu and his team at the School of Computer Science and Electronic Engineering, University of Essex are working on building up to five robotic fish that are set to be tested in the port area of Gijon in Northern Spain. The video below describes the radical idea of robotic fish and the benefit of using this technology in monitoring pollution levels in water.
One of the major challenges with robot fish concerns their power supply – such robotic fish need to be designed so that they are not tethered with wires so that they can move freely in deep water. Therefore, efficiency and how well this system can use a power supply will be a hot topic for advancing this research area. Furthermore, robotic fish may have been studies extensively in a lab setting, but being able to monitor how this system interacts and responds to stimuli underwater will be a long stroke.
- Mazumder, S.K. (2011). Wireless Networking Based Control. USA, New York: Springer Science and Business Media, LLC.
- Hailes, S. (2010). Sensors Systems and Software: First International ICST Conference, S-CUBE. Pisa, Italy, September 2009. Revised Selected Papers. USA, New York: Springer Science and Business Media.
- Zhao C, et al. Design and control of biomimetic robotic fish FAC-I. Published in Kato, N., Kamimura, S. (2008). Published in Bio-Mechanisms of Swimming and Flying: Fluid Dynamics, Biomimetic Robots and Sport Science. Japan: Springer Science and Business Media.
- Shao, J, et al. Development of the Multiple Robot Fish Cooperation System. Published in: Ali, M. Advances in Applied Artificial Intelligence: 19th International Conference on Industrial Engineering and Other Applications of Applied Intelligent Systems, IEA/AIE 2006.
- The BMT Group