4. CONTROL STRATEGIES
A challenging task within the Search-and-Rescue-Process
is the autonomous approach of the POB by the rescue
vehicle. The entire control process is time-critical and
characterised by different sections from running ahead at
maximum service speed till maintaining a bearing and
constant distance at nearly zero speed. The control task
at the open sea can be realised by cascaded heading and
track controllers which use the model background of a
slim rigid body, explained in Fossen (2002). Additionally,
the drift of the position of the POB has to be taken into
account. After reaching a certain distance to the POB,
2 provides data of different Global Navigation Satellite Systems
GPS, GLONASS, and GALILEO (ready)
3 Short-Range-Device- (SRD) radio modems (433.7 and 869.4MHz)
and Worldwide-Interoperability-for-Microwave-Access- (WiMAX-)
radio modem (5.47GHz)
IFAC MCMC 2012
September 19-21, 2012. Arenzano, Italy
74
Fig. 3. Automation of the rescue vessel
the rescue vessel has to stop and maintain this distance
without endangering the POB until the manual rescue
operation is initiated. These operations at zero speed cannot
be realised with conventional cascaded track control
systems, since special algorithms are necessary. Therefore
a subordinated Multiple-Input-Multiple-Output (MIMO)
speed cascade was integrated into the control system, explained
in Korte et al. (2009) and Rosenwasser and Lampe
(2006). The speed control cascade itself was realised as a
2DoF (Degrees of Freedom) control structure consisting of
a feedforward control structure and a feedback controller.