Guidance and control of the EAVE submersible

The EAVE path and position controller has the task of guiding the submersible through the water during an inspection task. The path that EAVE is to take is defined by a) its location relative to the axis set defined by the sonar transponders with and in the horizontal plane, b) its depth determined from pressure measurements, c) its heading, d) its speed, and e) the time it is to maintain a particular activity. A list of commands is given to the controller before a mission is begun. The list can include such functions as: a) go to a depth, while holding the present heading and, if required, holding the present location: b) rotate to a specific compass heading, and go clockwise or counterclockwise at some maximum rotation rate (allows for a slow or fast "look around"); c) go to a specific location at the same depth while going frontwards, backwards, or sideways at some maximum speed; d) go in a particular direction at some speed for a certain length of time; e) hover for a specific length of time. From two (or more) successive commands to go to a specfic target point, the controller determines the line in space that EAVE must follow. The navigation routines provide the controller with the present location, heading, and speed of the vehicle relative to the transponder coordinate system. The controller then determines the off-track distance, the distance from the next target point, and the difference between the desired and actual heading. These differences are used to create a speed command. If this speed is greater than the maximum speed requested in the command list, the maximum speed from the list is used as the command speed. This speed is compared to the actual speed, and the thrusters are then adjusted to correct actual vehicle speed. To assure that the vehicle will home in on the track and on the final target point even in the presence of small drift currents, an integral control term is added to the speed command for depth, lateral, and forward motion. The terms are added to each control function separately when the difference between the desired position and the actual position for that motion is less than a meter. The controller is designed to allow the addition of a similar term- to the heading control if it is found to be necessary during trials. All controller parameters such as gains and limits at which certain functions begin to operate can be modified in the field.