SYSTEM OPERATION – Steering Modes
Page 47 of 80
3.3.5 Digital FFU
FFU steering control is a closed loop system that compares a commanded
rudder position with an actual rudder position and moves the rudder
accordingly to cause the rudder to follow up to the commanded position.
FFU steering control allows the operator to dial in a desired rudder
position and then let the steering control system take care of placing the
rudder at the desired position.
A digital FFU input devices uses an incremental optical encoder to provide
the rudder position command signal. The signal generated by this
encoder is called a Rudder Order Signal. The rudder order signal is
connected to the MCP. Digital FFU input devices do not provide a
physical representation of the rudder order signal. The MCP is capable of
outputting a signal to drive a Rudder Order Indicator (ROI) which will
continuously display the rudder position commanded by the digital FFU
input.
When DIGITAL FFU mode is selected the current rudder position is
initialized as the starting digital FFU command, therefore when this mode
is selected the rudder will not change its position. Once this mode has
been selected the encoder signals will modify the digital FFU command as
the encoder is turned. Since an incremental input device does not have
any built in hard stops, the number of turns of the device which will
represent a hard over to hard over command can be programmed through
the DSC setup program. Each time DIGITAL FFU mode is selected the
system will re-initialize the current rudder position.
Prior to selecting DIGITAL FFU mode, the ROI signal will display the
current rudder position. Once DIGITAL FFU mode has been initialized the
ROI will begin to change its angle depending on how the digital FFU input
device is turned.
Systems including a digital FFU input device and a NFU input device can
be configured through the DSC setup program to operate these two
modes of steering control in a seamless transfer arrangement. This
means that the operator can use either the Digital Helm or the NFU jog
lever without the having to expressly select the mode using an input
selector button.
One form of digital FFU input device is a Digital Helm. This device
combines power steering control and backup manual steering control in
the same helm unit. The Digital Helm operates like a normal manual helm
pump and at the same time contains a digital optical encoder that rotates
as the helm is turned. The hydraulic lines of the Digital Helm are
Doc No.: MAN01504, 20-02-06 DSC 100 & MCP 100 Manual
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