Coanda Jet Actuators
The Coanda Effect is a hydrodynamic effect in which fluids, flowing at high speed, tends to follow continuous surfaces. It has long been studied , and it’s effects on aerodynamic lift continue to be explored. In addition, it has been used as a method in which to switch the direction of a high speed air jet.
Our group has developed a switch which utilizes this effect to switch the direction of flow of a high speed water jet. This water jet is used as a thrust force for an underwater robot. By changing the direction of this thrust jet, the direction and speed of the motions of an underwater robot can be controlled.
Eccentric Mass Steering
Traditional orientation control in underwater robots requires pairs of outboard thrusters or water jets. While effective, these sorts of actuation schemes can become complex once 3-DOF rotations are required. These are also unsuited to sensitive environments, due to their large protruding parts, as well as violently rotating propellers. In addition, they require 2 actuators per rotational degrees of freedom.
We have developed a steering system which uses a 2-axis gimbal for motions of large eccentrically placed mass. This allows for easy control of two rotational degrees of freedom using fewer actuators (one per degree of freedom).
It functions by changing the hydrostatically stable orientation of the robot dynamically. Since the stable orientation is passively stable (due to hydrostatic effects), this system has the rare combination of passive stability as well as the ability for unlimited rotations about any axis.
Combined with a spherical outer shape, we have developed a robot that can rotate about two axis without any translational motion (“turning in place”), using only components internal to the vehicle.
This is useful for the positioning of sensors onboard the body of the robot. In the case of Nuclear Reactor inspection, this is a camera, use for visual inspection of weld lines, sensors, etc. However, this can truly be applied to any other component which requires precise pointing.
Localization Using Visible Light Fields
A common problem in underwater robotics is that of wireless communication. Unfortunately, radio transmission is impossible beyond several meters, due to the conductivity of water. In addition, SONAR based communication systems are lacking in bandwidth. For this reason, visible light communications have become increasingly popular, due to the ability for visible light to permeate far into water, as well as it’s support for high data rates.
One problem, however, is that line of sight, and precise alignment is needed in order to maintain a data link. This group researches localization techniques using the visible light itself to determine position and orientation of a body equipped with a visible light modem. In this way, we hope to create, using these dual use systems (both communication and localization), robust networks for long range, high data rate communication systems underwater.