Project Description
Abstract
We are studying issues in fluid mechanics, nonlinear control, and sensing that are necessary for the development of self-propelled robot fish.
Motivation & Aims
Fish are very impressive swimmers in many ways, and it is possible that submersible robots that swim like fish might be superior to submersibles using propellors. For example, fish-like robots might be quieter, more maneuverable, and possibly more energy efficient. At the moment we are focusing on carangiform fish: fish with large, high-aspect-ratio tails that swim mostly by moving their tails and keep the rest of their body fairly rigid. Many large, fast fish (e.g. swordfish) fall into this category and they are arguably the easiest to replicate mechanically.
We would like to know how to control a robot "fish" so that it swims
stably and efficiently. Furthermore, we would like to understand the
types of sensing that are required to enable robust and efficient
carangiform propulsion.
Research
Our group's particular approach to fish locomotion is to employ the tools of geometric mechanics. These have been useful in simplifying the control of other kinds of locomotion systems and we hope that they can also be applied to fluid mechanical systems.
In our theoretical analysis and in computer simulations, we are
treating the water around the fish as an ideal fluid, i.e. neglecting
most of the effects of viscosity. We regard the whole problem as
essentially planar and treat the wake of the fish as a sequence of
point vortices in an otherwise irrotational fluid. The validity of
this approximation is largely supported by our experimental results.
We have built a double-jointed "fishtail" suspended in a water tank
which will propel itself and a carriage on rails along the length of
the tank (see Figure 1 for a schematic diagram and photographs of the
system; Figure 2 for visualization of the trailing vortices). The
point of the carriage is that it simplifies the experiment by keeping
the motors, electronics, etc. out of the water. In the near term we
plan to add a rigid body in front of the tail and increase the number
of degrees of freedom of the carriage so that the "fish" can turn,
sideslip, etc.
Figure 1: Left: schematic and photograph of
apparatus side view. Right: Top view Schematic and photograph from
the rear as apparatus swims down the tank.
Figure 2: Visualization of fluid vortex sheet during an
actual experiment
Accurate and robust control of carangiform locomotion will require the robot
to have a reasonable estimate of the complex flow field surrounding its
body. In conventional nonlinear control, one would attempt to make an
complete model for the local fluid mechanics and then build an estimator to
estimate the details of the fluid flow that are necessary for control
algorithm operation. However, in the case of carangiform locomotion, the
model is exceptionally complex. Nature seems to have solved this problem by
evolving a complex sensing system known as the lateral line organ. In the
long term we plan to explore the use of advanced pressure sensors that could
imitate the lateral line sensory organs of fish and provide the same data
about the local water flow that fish use to regulate their swimming. This
problem serves a very rich and complex example of how nature uses sensing to
simplify control design and enhance performance.
Modelling and Experimental Investigation of Carangiform
Locomotion for Control
- Scott D. Kelly, Richard J. Mason, Carl T. Anhalt, Richard M. Murray, and Joel W. Burdick
- 1998 American Control Conference
- (compressed post-script copy).
Construction and Modelling of a Carangiform Robotic Fish
- Richard Mason and Joel Burdick
- 1999 International Symposium on Experimental Robotics
- (post-script copy)
Propulsion and Control of Deformable Bodies in an Ideal Fluid
- Richard Mason and Joel W. Burdick
- 1999 IEEE International Conference on Robotics and Automation
- (post-script copy)
Experiments in Carangiform Robotic Fish Locomotion
Modelling Efficient Pisciform Swimming for Control
- Scott D. Kelly and Richard M. Murray
- International Journal of Robust and Nonlinear Control
- Volume 10, number 4, pages 217-241, 2000
Nonlinear Control Methods for Planar Carangiform Robot Locomotion
Fish
- K. A. Morgansen, V. Duindam, R. J. Mason, J. W. Burdick and
R. M. Murray
- submitted to the 2001 International Conference on Robotics and Automation
- (post-script
copy)
The following movies show the movement of our fish as we apply various gaits. Different sides of the fish are shown: Side view (which shows how the fish propels inself forward), Top view (which shows the movement of the water as the fish flaps its tail) and Back View (which shows an underwater view of the moving tail).
For each movie, two versions are included: a Quicktime version (click
here to get the latest quicktime player) and a Real
version (click here to
get the latest Real player).
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