VII. CONCLUSIONS AND FUTURE WORK
A multi-body dynamic model was developed for an underwater glider that includes both longitudinal and lateral
actuators as well as the buoyancy actuator. Building on
prior results in glider steady motion analysis, a motion
control system was developed to control glide path angle
and turn rate. The control system includes model reference
controllers for the servo-actuators, to allow saturation effects
to be easily incorporated. The glide path angle and turn
rate controllers are single-input, single-output PID loops.
The control parameters were tuned using a nonlinear simulation that includes actuator magnitude and rate limits. The
controller’s effectiveness was demonstrated in simulation.
Although the motion control system developed here allows
one to implement general guidance strategies, our aim is
to enable closed-loop tracking of time-suboptimal glider
paths that can be generated in real time using existing
results for nonholonomic mobile robots. These Dubins-like
paths accommodate turn rate and turn acceleration limits,
which are essential aspects of underwater glider motion. For
underwater gliders travelling at constant speed and maximum
flight efficiency, minimum arclength paths are minimum
energy paths. Closed-loop guidance, such as a line-of-sight
strategy, is required because only approximate solutions for
steady turning motion are available and because model and
environmental uncertainty is inevitable. The motion control
system developed here is a necessary step toward convergent
path following.
Acknowledgements. This work was supported by the
Office of Naval Research under grant number N00014-08-
1-0012. The authors gratefully acknowledge the input of the
anonymous reviewers.