Synchronizing multiple steering inputs to marine...

Details Synchronizing multiple steering inputs to marine... Synchronizing multiple steering inputs to marine...

1999-12-29

2001-11-06

Swinehart, Ed (Department: 3617)

Ships

Steering mechanism

Remote control steering excluding manual operation

Reexamination Certificate

active

06311634

ABSTRACT:

TECHNICAL FIELD
This invention relates to marine autopilots and “fly by wire” steering systems employing incremental rudder commands and a rudder servo that accepts them.
BACKGROUND OF THE INVENTION
Several marine equipment suppliers are now manufacturing “fly by wire” steering and/or engine control systems for marine vessels. Such systems have merit because they simplify the installation and reduce the costs associated with auxiliary control stations. For example, flying bridge and portable remote control stations are simpler to install with wiring than with the plumbing and cabling associated with hydraulic- and cable-actuated control systems.
However, fly by wire systems are not without their problems. Transferring control among multiple helms and an autopilot requires some sort of synchronization of the multiple possible steering commands to each other and to the actual rudder position. (The descriptions presented in this application refer, for purposes of convenience, to a rudder of a marine vessel, although they are also applicable to any marine vessel controllable turning moment generator such as an outboard or outdrive steering angle actuator.) Without synchronization, when control is transferred from one steering input. device to another, the rudder actuator attempts to “jump” to the newly commanded position, creating what is referred to as a control “bump.” These problems result from a traditional steering systems paradigm, in which an absolute wheel angle causes a corresponding rudder angle, e.g., a centered (between helm stops) helm rotation angle causes a zero rudder deflection, and a large helm rotation angle (at the helm stop) causes a fully deflected rudder in a corresponding direction.
FIG. 1
represents operational control states found in typical prior art autopilot systems in which a helmsman must steer to a desired heading and press a button to place the autopilot (AP) in an engaged state
10
. To place the autopilot in a disengaged or standby state
12
, the helmsman must press a standby button, or in some cases, disengage a clutch or turn the helm. Some prior autopilots will revert to engaged state
10
if the helmsman steers back to the original heading. Many prior autopilots further include a power steering feature in which the rudder angle or heading setpoint can be controlled by a handheld remote control or by a knob on the autopilot control panel.
FIG. 2
represents a typical prior art hydraulic steering system in which a helm
22
rotates a helm pump
24
, and an autopilot pump motor
26
rotates an autopilot pump
28
. Either autopilot pump motor
28
or helm pump
22
can supply fluid to a steering cylinder
30
that actuates a rudder
32
. No bump occurs in such a steering system if the autopilot system is engaged when autopilot pump motor
26
is stopped (i.e., starting rudder command equals the current angle of rudder
32
). Likewise, no bump occurs when the autopilot is disengaged because rudder
32
simply responds to rotations of helm pump
24
. Moreover, if the autopilot is engaged while helm
22
is rotating, the normal response is for the autopilot to correct by causing autopilot pump
28
to subtract fluid from steering cylinder
30
to compensate for fluid added by rotation of helm pump
24
. Because of the hydraulically coupled synchronization of such steering systems, there are many known techniques by which helm
22
can automatically override the autopilot. It should be noted that when steering cylinder
30
reaches its stops, helm
22
is also stopped. Of course, steering system
20
may have multiple helms and autopilots hydraulically coupled to steering cylinder
30
. With suitable electronic inputs to the autopilot, autopilot pump
28
is usable as a power steering device.
There are previously known non-hydraulic techniques for synchronizing helms and autopilot systems. Referring to
FIGS. 3 and 4
, U.S. Pat. No. 5,107,424 for CONFIGURABLE MARINE STEERING SYSTEM (“Bird et al.”) describes an example of a prior fly by wire steering system 40 having multiple steering devices 42 that are selectable by an input selector 44. To prevent steering angle bumps in steering system 40 when input selector 44 selects a different one of steering devices 42, the newly selected device is first electronically initialized to the current rudder angle. Moreover, mechanical stops associated with steering devices 42 were eliminated so that any newly selected steering device can simply add to or subtract from the rudder position commanded by the previously selected steering device. Accordingly, synchronization among steering devices 42 in steering system 40 employs continuously rotatable, incremental steering devices in combination with steering device initialization.
Bird et al. recognized that incremental steering commands can accumulate to an indefinitely large number. Therefore, each input device limits its output to the maximum deflection of the rudder.
FIG. 4
shows that a limiter 50 in controller 46 prevents a rudder actuator 48 from being commanded beyond its mechanical stops. A rudder angle transducer 52 closes the steering servo loop.
Bird et al. implemented helms 54 and 56 with incremental optical encoders driving associated pulse-counting up/down accumulators. However, whenever one of helms 54 or 56 is selected, its up/down accumulator must be reset to zero, making each of helms 54 and 56 yet another initialized device.
What is needed, therefore, is a marine vessel fly by wire steering system that automatically and seamlessly transfers steering control among multiple steering devices, which may include one or more autopilots or helms, without necessarily requiring manual steering device selection.
SUMMARY OF THE INVENTION
An object of this invention is, therefore, to provide a marine steering system for synchronizing inputs from multiple steering devices.
Another object of this invention is to provide a marine steering system having a variable steering ratio that is a function of vessel speed.
A further object of this invention is to provide a marine steering system having a fully automatic autopilot engage/disengage feature that allows a helmsman to set autopilot controlled course changes via the helm.
Still another object of this invention is to provide an apparatus that stops helm rotation when the rudder is at full deflection.
A preferred embodiment of a marine vessel steering system of this invention includes one or more incremental steering devices, a control panel, and an autopilot that are electrically connected to a command processor. The steering system further includes an autopilot attitude controller and an incremental servo for actuating the rudder.
There are many control and interlinking possibilities for the steering system. In one implementation, the autopilot may be engaged or disengaged by pressing buttons alternately on the control panel or on emergency disengaged by rotating an incremental helm a small amount. Course changes may be set in the autopilot by employing a course selection dial or by pressing course change command buttons on the control panel.
In another implementation, an incremental helm is employed as a course selector for the autopilot. A course selection controller is implemented within the command processor and the autopilot attitude controller. Upon engagement of the autopilot, the heading set therein is the current heading at the instant of engagement plus any change of heading received from the helm after engagement. The course selection controller employs a helm increment summer and a washout filter that are both initialized to zero upon engagement. The output of the washout filter follows short-term course changes but forgets them over a longer time. A disengage threshold block receives the output of the washout filter and causes the autopilot to disengage if the output exceeds a predetermined threshold. Accordingly, the course selection controller allows a helmsman to make occasional course changes without the autopilot automatically disengaging, but if the helmsman rotates the helm at a rate and

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