Design and theory of operation
20169223D 3-1
3 DESIGN AND THEORY OF OPERATION
3.1 General system description
An autopilot is an apparatus that controls the rudder of a vessel in
order to maintain a selected heading. There are different design
principles for such an apparatus, but they all basically operate as
shown in Fig. 3-1. This diagram shows that the vessel's heading is
supplied from the compass to a detector circuit. The detector will
sense when the vessel is off course and to what side. The detected
signal is amplified and directed to energize either the port or
starboard solenoids, i.e. make the rudder move one way or the other.
COMPASS
DET AMP
FB
FEEDBACK
UNIT
STBD. TRIGGER
PORT TRIGGER
SOLENOID
SOLENOID
RUDDER
HEADING
RUDDER POSITION
Fig. 3-1
Autopilot principle diagram
In order to stop the rudder movement, a feedback signal is produced
by the feedback unit. The feedback signal will be compared with the
compass signal and when there is a balance between the two, the
solenoid will be de-energized. The rudder has now been moved to a
position that makes the vessel turn. This turn is picked up by the
compass and causes a new unbalance between the feedback signal
and the error signal which energizes the opposite solenoid. Now the
rudder will start to move back towards the previous position, and the
feedback signal will again cancel out the unbalance and de-energize
the solenoid to stop the rudder.
By utilizing digital technology to perform the function of an
autopilot, the typical block diagram will be slightly changed. Even
so, the basic operation should be recognized on Fig. 3-2.
As we know, a microprocessor can only do what it has been
programmed to. This is called software. The program can be either
fixed or partly adjustable to adapt the microprocessor to the
individual type of vessels.
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