Icy Control

How ISE achieves complex control over a vehicle that will leave, collect data and return as directed has much to do with its Automatic Control Engine (ACE) software. The sub’s main operations involve sensing its position and heading, and making corrections to get back on target if it’s off, in terms of thrust, roll, yaw and pitch. The sub matches its course to what it has been programmed to have, using sensors that detect currents combined with a French-made inertial navigation system – gyros that measure spin of the earth and provide a heading and accelerometers to give position over time. This is combined with actuators and software in between.

The sub’s other main operation is detecting any of 82 possible faults (problem scenarios), such as a high temperature reading or an instrument ceasing to give data, says Crees. The sub has 12 possible responses for each of the 82 scenarios, which range from ‘ignore’ to ‘surface immediately.’ 

Getting the sub to return to mission start/end point would be fairly straightforward if that point were a land-based dock, but when it’s a hole in an ice floe, this point will have drifted. An acoustic homing beacon, detected by the sub’s hydrophone array, does the trick. However, Crees points out “This only works if the sub successfully returns to where it started. We can communicate acoustically with it only for 4 km, so it’s completely on its own most of the time.”

As with any robot, when the sub has seemingly done something unexpected, it usually turns out that it has actually done what it has been told to do. “For example, in a task we call ‘final approach,’ the sub homes in on a point and stops,” says Crees. “But during testing in this case (in Vancouver’s Burrard Inlet), we later realized that we’d also given it a speed and travel time, and the point that instruction took it to was inside the radius that we’d given it as the point to stop, so it didn’t go anywhere.”

Ultimately, getting the hardware and software to work together so that the sub would accomplish any given mission file was all about modularity. “We reconfigure rather than recompile our code when we make changes, so that the software is built in modular layers,” Crees says. “Similarly, the sub’s sensor systems are also independent of each other.”

This means that if something goes wrong with a wet cable from a sensor coming into the dry pressure hull, it’s not going to cause other issues. “It’s like a problem with a robot hand versus a human hand,” says Crees. “You can disconnect a robot’s hand fairly easily and fix it or put a new one back on, but a human hand is totally integrated, and therefore much more complex to fix."
www.ise.bc.ca