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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to an improved autosteering system, and more
particularly relates to improvements in an auto-steering system for
navigation in which a known feedback control circuit automatic controls
rudder angles in accordance with signals from a known sensor circuit.
In auto-steering systems for navigation, the condition of various
environmental factors influencing navigation such as navigation course,
wind heading and/or tideway are sensed by a sensor circuit which produces
corresponding signals. These signals are accepted by a control circuit
which automatically controls the rudder angle using a feedback control. In
order to carry out this control operation, the control circuit must be
retained in approximately the zero-condition when the control circuit is
inoperative. If this condition is not met, the rudder control can
malfunction since turning of the rudder is carried out relative to the
standard rudder angle position which is deviated from the true zero-point
position, i.e. the neutral axis coinciding the stern direction of the boat
equipped with the auto-steering system. As a result of this disorder in
the rudder control operation, it is quite impossible, when any malfunction
occurs in the system, to confirm whether the system malfunction is caused
by any disorder or disorders in the rudder mechanism and/or the sensor
circuit or the system malfunction is caused by absence of the zero-point
calibration of the control circuit.
BRIEF DESCRIPTION OF THE OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is one object of the present invention to enable successful
and easy zero-point calibration of the rudder angle control circuit for
auto-steering systems.
It is another object of the present invention to enable easy confirmation
and discrimination of the causes it malfunctions in the entire system.
In accordance with one preferred aspect of the present invention, the
auto-steering system includes a reference input circuit to be selectively
coupled to the control circuit via an interposed switching mechanism.
During the normal rudder angle control operation, the control circuit is
connected to the sensor circuit as in the conventional systems. For the
zero-point calibration, the control circuit is connected to the reference
input circuit so that the rudder should be registered at the neutral axis
by the reference input signal.
In the case of auto-steering systems, the rudder angle is selected and
fixed by the operation of the rudder control circuit. However, when any
malfunction occurs in the steering system including the control circuit,
the resultant actual rudder angle is not always the same as the selected
rudder angle. For this reason, it is advantageous to provide an indicator
for visually indicating the actual rudder angle so that the operator can
take any positive action on the steering system in order to compensate
deviation of the actual rudder angle from the selected rudder angle.
In the case of conventional indicators for this purpose, a rudder angle
oscillator is mechanically coupled to the rudder mechanism. The oscillator
adjusts the resistance of a variable resistor incorporated in an indicator
circuit (such as a bridge circuit) such that the actual rudder angle is
visually indicated on the indicator activated by the indicator circuit.
With this construction of the conventional rudder angle indicators,
accuracy in indication is greatly influenced not only by the operational
error in the control system but also by the operational error in the
rudder angle oscillator. The combined effect of these operational errors
considerably lowers the accuracy in the rudder angle indication. In
addition, relatively complicated circuit construction of the conventional
indicators leads to high production cost and increased maintenance
troubles.
It is the other object of the present invention to enable automatic visual
indication of the actual rudder angle with an accuracy of a level almost
equal to that in the feedback control operation.
It is a further object of the present invention to provide a visual rudder
angle indicator whose circuit construction is very simple.
In accordance with another preferred aspect of the present invention, an
indicator circuit is coupled to the feedback line of a rudder angle
control circuit and the feedback signal is used for activating a rudder
angle visual indicator. In this case, however, direct attachment of the
indicator circuit to the feedback line of the control circuit tends to
cause disorder in the rudder angle control operation through introduction
of disturbances and noises into the control circuit, thereby seriously
lowering the accuracy in the rudder angle control operation.
In accordance with the other preferred aspect of the present invention, the
above-described indicator circuit is given in the form of a high input
impedance circuit which operates with extremely small electric current.
On a boat equipped with an auto-steering system, it is standard procedure
to include means for to manually carrying out the steering operation in
addition to the means for automatically steering the vessel utilizing a
rudder angle control circuit. For this manual steering operation, a main
steering unit incorporating the rudder angle control circuit is
accompanied by a remote steering unit coupled thereto by a cord or cords
and incorporating a manual steering circuit. Output from this manual
steering circuit can be adjusted as desired by operator's turning an
adjuster knob providing on the remote steering unit.
During the normal automatic steering operation, the rudder angle control
circuit is connected to a sensor circuit and rudder angle is determined
with reference to the output from the sensor circuit. During the manual
steering operation, the rudder angle control circuit is connected to the
above-described manual steering circuit in the remote steering unit. In
order to effect this shifting in the steering mode, the main steering unit
is provided with a main A-M (auto-manual) switch which selectively
connects the rudder angle control circuit to either one of the sensor and
manual steering circuits. The above-described shifting in the steering
mode can be carried out by the operator's operating this main A-M switch
in the main steering unit.
From the viewpoint of the principal purpose of the remote steering, it is
undesirable to require the operator to get to the main steering unit in
order to operate the main A-M switch every time shifting in the steering
mode is required. This problem is particularly undesirable in the case of
small-sized boats on which the operator is always forced to attend to a
variety of highly technical operations for well-controlled and safe
navigation of the boats.
It is a yet further object of the present invention to free the operator on
a boat from the trouble of getting to the main steering unit in order to
shift the steering mode.
In accordance with a further preferred aspect of the present invention, a
subsidiary A-M (auto-manual) switch is provided on a remote steering unit
coupled to a main steering unit incorporating a main A-M switch and both
A-M switches are operationally interlocked to each other.
During navigation by the automatic steering operation, a boat does not
always sail on a straight course even when the rudder is on the neutral
axis coinciding the stern direction. This is often caused by special
operational deviation in the rudder mechanism, wind heading and/or
tideway. In other words, the actual neutral position of the rudder does
not always correspond to the nominal neutral axis of the rudder.
In accordance with a yet further preferred aspect of the present invention,
the manual steering circuit of the remote steering unit includes a
variable resistor adapted for trimming of the zero-point of the circuit
corresponding to deviation of the actual neutral position of the rudder
from the nominal neutral axis coinciding the boat stern direction.
The factors influencing the above-described deviation does not fluctuate
often in practice. Accordingly, it is rather advantageous that the trimmed
state of the manual steering circuit can be provisionally fixed until any
large fluctuation occurs in any of the factors.
In accordance with a yet further object of the present invention, the
manual steering circuit of the remote steering unit can be provisionally
fixed in a trimmed state.
When the manual steering circuit is provided with a variable resistor of a
slide brush type operable by turning an adjuster knob arranged on the
remote steering unit, the operator needs to reset the adjuster knob to the
zero-point after completion of the manual steering. This resetting
operation give the busy operator additional troublesome work.
It is a yet further object of the present invention to free the operator
from the trouble in resetting the manual steering circuit to the
zero-point.
In accordance with a yet further preferred aspect of the present invention,
the manual steering circuit of the remote steering unit is automatically
resettable to the zero-point.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the construction of an embodiment of
the auto-steering system in accordance with the present invention,
FIG. 2 is a circuit diagram, partly in black box, of the auto-steering
system shown in FIG. 1,
FIG. 3 is a circuit diagram of an embodiment of the potentiometer element
used in the auto-steering system shown in FIG. 2,
FIG. 4 is a block diagram showing the construction of another embodiment of
the auto-steering system in accordance with the present invention,
FIG. 5 is a circuit diagram, partly utilizing functional blacks, of the
auto-steering system shown in FIG. 4,
FIG. 6 is a block diagram showing the construction of another embodiment of
the auto-steering system in accordance with the present invention,
FIG. 7 is a circuit diagram, partly utilizing functional blacks, of the
auto-steering system shown in FIG. 6,
FIG. 8 is a circuit diagram of an embodiment of the manual steering circuit
used in the auto-steering system shown in FIG. 7, and
FIGS. 9 and 10 are circuit diagrams of other embodiments of the manual
steering circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 depicts the basic construction of an embodiment of the auto-steering
system in accordance with the present invention. The auto-steering system
includes a control circuit 1 (adapted for controlling the operation of a
rudder mechanism) which is selectively coupled to either a sensor circuit
4 or a reference input circuit 5 via a switching mechanism 3. The control
circuit 1 is operationally coupled to the sensor circuit 4 during the
normal control operation in order to control the operation of the rudder
mechanism 2 in accordance with input signals passed from the sensor
circuit 4, whereby enabling navigation by automatic steering. Prior to
starting the control operation, the control circuit 1 is operationally
coupled to the reference input circuit 5 for the purpose of carrying out
the zero-point calibration as hereinafter described in more detail.
FIG. 2 depicts a further detailed construction of the auto-steering system
shown in FIG. 1. As shown therein, control circuit 1 includes an amplifier
11 whose output terminal is coupled to the negative input terminal. of a
differential amplifier 12. The output terminal of the amplifier 12 is
coupled to a drive motor 15 via a pair of motor driving circuits 13 and 14
each of which is provided with a kind of low-pass filter in order to cut
off high frequency deviation signals. A potentiometer element 16 is
inserted between the drive motor 15 and the rudder mechanism 2. The output
terminal of the potentiometer element 16 is coupled to the positive
terminal of the above-described differential amplifier 12 via an amplifier
17. Here, the potentiometer-element 16 operates in proportion to the
rotation angle of the drive motor 15 as hereinafter described in more
detail. The amplifier 17 is adapted for negative feed-back of the output
from the drive motor 15. That is, the inputs to the differential amplifier
12 from the amplifiers 11 and 17 are inverse in phase to each other.
The rudder mechanism 2 includes a rudder 21 operationally connected to the
output shaft of the drive motor 15 so that the rudder turns and deviates
from the neutral axis thereof in accordance with the rotation angle of the
drive motor 15, the neutral axis coinciding with the stern direction of
the boat for which the rudder 21 is used. The extent of turning, i.e. the
magnitude of deviation, of the rudder 21 from the neutral axis is
proportional to the distance of movement of the potentiometer-element 16
from the neutral axis as hereinafter described in more detail.
The switching mechanism 3 includes a multi-contact switch 31 which, in the
case of illustrated embodiment, possesses a set of five contacts. One of
the contacts is coupled to the input terminal of the amplifier 11 of the
control circuit 1, the other of the contacts is coupled to a reference
input element 51 of the reference input circuit 5 and remaining contacts
are coupled to elements 41, 42 and 43 of the sensor circuit 4,
respectively.
The reference input element 51 takes the form of an electric circuit
including, for example, a resistor and applies a prescribed magnitude of
reference input signal, e.g. a voltage signal, to the control circuit 1.
The elements 41, 42 and 43 of the sensor circuit 4 are given, for example,
in the form of a navigation course finder, a wind heading finder and a
tideway finder, respectively. Upon sensing factors influencing the
navigation mode of the associated boat such as navigation course, wind
heading and tideway, each of the elements 41, 42 and 43 applies
corresponding signal to the control circuit 1 for determination of the
rudder angle at which the rudder 21 should be registered.
One embodiment of the above-described potentiometer-element 16 is shown in
FIG. 3, in which rotation of the output shaft of the drive motor 15 is
transmitted to a variable resistor 162 via a suitable reduction gear
mechanism 161 so that the movement of the slide arm of variable resistor
162 is proportional to the rotation of the drive motor 15. In other words,
the moving distance of the slide arm of variable resistor 162 should be
proportional to the rotation angle of the drive motor 15 and the moving
direction of the slide arm of variable resistor 162 corresponding to the
rotating direction of the drive motor 15. The correlation is so designed
that the slide arm of variable resistor 162 will travel over distances V
on both sides of the neutral axis thereof, when the rudder 21 turns over
angles .theta. on both sides of the neutral axis thereof. In other words,
a voltage drop 2 V caused by movement of the slide arm of variable
resistor 162 corresponds to a turning angle 2.theta. caused by movement of
the rudder 21. Further, the resistor 162 should be registered at the
neutral axis (the electric potential=V) when the rudder 21 is registered
at the neutral axis (turning angle=0).
In the auto-steering system of the present invention having the
above-described construction, the normal control operation is carried out
in the following fashion.
For the normal control operation, the switch 31 is set so as to connect the
amplifier 11 to one of the elements, e.g. the navigation course finder 41,
of the sensor circuit 4. The signal, e.g. the voltage signal, from the
sensor circuit 4 is passed to the differential amplifier 12 via the switch
31 and the amplifier 11 and, depending on the polarity thereof, actuates
either one of the motor driving circuits 13 and 14, the polarity of the
signal determining the turning direction of the rudder 21 about the
neutral axis (turning angle 0). Upon this actuation, the drive motor 15 is
driven for rotation in the clockwise or counterclockwise direction
depending on the polarity of the above-described signal. Then, the
above-described potentiometer element 16 operates in proportion to the
rotation angle of the drive motor 15 in order to apply a feedback signal
to the differential amplifier 12 via the amplifier 17. Here, the feedback
signal is inverse in phase to the signal from the amplifier 11.
As the rudder 21 completes turning over a turning angle corresponding to
the signal from the sensor circuit 4, the input signal from the amplifier
11 and that from the amplifier 17 become identical to each other in their
absolute values retaining inverse phases. Thus, the two inputs offset each
other to make the output from the differential amplifier zero and the
drive motor 15 ceases its rotation. In other words, the drive motor 15
rotates over a rotation angle corresponding to the input signal from the
amplifier 11 only in order to determine the rudder angle.
As the change in navigation course is completed and the resultant actual
navigation course of the boat coincides the course determined on the basis
of the input signal from the sensor circuit 4, the signal from the sensor
circuit 4 becomes zero and, accordingly, the input signal to the
differential amplifier 12 from the amplifier 11 becomes zero, also. In
this case of the example shown in FIG. 3, the electric potential of the
input signal from amplifier 11 assumes V volts. At this stage of the
process, the rudder 21 is off the stern direction, i.e. the neutral axis
of the boat after completing the change in the navigation course and the
potentiometer element 16 now generates a signal corresponding to this
deviation of the rudder 21 from the neutral axis, which is again
proportional to the rotation angle of the motor 15. This signal is again
passed to the differential amplifier 12 via the amplifier 17. As described
already, this signal is inverted in phase and the input signal from the
amplifier 11 is now zero (i.e., V volts). Therefore, the drive motor 15
rotates over a rotation angle corresponding to the input signal from the
amplifier 17 in the direction opposite to that before the change in the
navigation course and thereby the rudder 21 turns towards the neutral
axis.
Upon registration of the rudder 21 at the neutral axis the drive motor 15
ceases the rotation and, accordingly, the rudder 21 ceases the turning.
That is, the boat sails straightly along the selected navigation course.
It will be well understood that the above-described process is fully that
of the ordinary negative feedback operation.
For the zero-point calibration, it is first assumed that the rudder 21 is
located fairly on the neutral axis and, therefore, the variable resistor
162 in FIG. 3 is registered at the neutral axis (electric potential=V
volts) also.
The switch 31 is set so that the amplifier 11 is connected to the reference
input element 51 of the reference input circuit 5 and a reference input
signal of a prescribed magnitude, e.g. an electric potential V, is applied
to the differential amplifier 12 via the amplifier 11. Concurrently with
this, the potentiometer-element 16 applies an inverted input signal of an
electric potential -V to the differential amplifier 12 via the amplifier
17. Thus, the input signals from both amplifiers 11 and 17 offset to each
other, the output signal from the differential amplifier 12 becomes zero,
the drive motor 15 does not start to rotate and the rudder 21 retains its
position on the neutral axis.
It is next assumed that, at the timing of the zeropoint calibration, the
rudder 21 is off the neutral axis and located at the position deviated
from the neutral axis by a turning angle .theta./2. Under this situation,
the variable resistor 162 is located at the position of the electric
potential 1.5 V. The switch 31 is set so that the amplifier 11 is
connected to the reference input element 51 of the reference input circuit
5 and a reference input signal of an electric potential V is applied to
the differential amplifier 12 via the amplifier 11. Concurrently with
this, the potentiometer-element 16 applies an inverted input signal of an
electric potential -1.5 V to the differential amplifier 12 via the
amplifier 17. Thus, the output signal from the differential amplifier 12
is given in the form of an electric potential difference -0.5 V between
the input signals from both amplifiers 11 and 17. This output signal from
the differential amplifier 12 actuates the drive motor 15 for rotation
over a rotation angle in order to turn the rudder 21 towards the neutral
axis. As the rudder 21 is registered at the neutral axis, the feedback
signal of an electric potential -V from the amplifier 17 offsets the
reference input signal of an electric potential V from the amplifier 11,
the output signal from the differential amplifier 12 becomes zero, the
drive motor 15 ceases rotation and the rudder 21 is registered at the
neutral axis. In other words, deviation of the rudder 21 from the neutral
axis is corrected and the zero-point calibration is completed.
In the foregoing embodiment, the turning ambit of the rudder 21 is selected
over angles .theta. on both sides of the neutral axis, the moving ambit of
the variable resistor 162 is selected over voltages V on both sides of the
neutral axis and the magnitude of the reference input signal is fixed to
an electric potential V. However, relative magnitudes of the three values
can be adjusted variously in accordance with the practical conditions
under which the auto-steering system in accordance with the present
invention is used. In conclusion, the relationship in magnitude should be
fixed so that the potentiometer-element 16 generates an output signal of a
magnitude corresponding to the neutral axis thereof when the rudder 21 is
located on the neutral axis and the inverted feedback signal from the
potentiometer-element 16 offsets the reference input signal, thereby
making the output signal from the differential amplifier zero.
In accordance with the present invention, zero-point calibration of the
control circuit in the auto-steering system can be carried out at any time
by a simple switching operation. Thus, the control circuit is always kept
in a fairly zero-point calibrated state. When any malfunction occurs in
the auto-steering system, the cause for the malfunction can be very
reliably located by simply checking the sensor circuit and the rudder
mechanism. Therefore, there is no danger that a disorder or disorders in
these parts will be confused with a disorder in the control circuit
itself.
A modified embodiment of the auto-steering system in accordance with the
present invention is shown in FIG. 4, in which the control circuit 1 is
accompanied by an indicator circuit 6 adapted for visual indication of the
actual rudder angle and advantageously given in the form of a high input
impedance circuit for the minimum disturbance on the feedback signal in
the control circuit.
One embodiment of the construction of the indicator circuit 6 is shown in
more detail in FIG. 5, in which the indicator circuit 6 includes a
differential amplifier 61, an indicator 63 and a variable resistor 64
adapted for zero-point calibration. One input terminal of the differential
amplifier 61 is coupled to the feedback line of the control circuit 1 and
the other terminal thereof is coupled to a variable resistor 64 via a
brush 67. The output terminal of the differential amplifier 61 is coupled
to the indicator 63 via a variable resistor 62 adapted for moving ambit
adjustment of the indicator hand.
The indicator 63 is preferably so adjusted that the indicator hand should
be registered at the zero-point at the middle of the indicator scale when
the rudder 21 is located fairly on the neutral axis. As an exceptional
case which is rather rare in practice, the zero-point of the indicator
scale may be more or less deviated from the midway position when the
turning direction of the rudder 21 is limited to one side of the neutral
axis for any reason.
For the zero-point calibration, the control circuit 1 is kept in the
inoperative state. A voltage V/2 is applied to a terminal 66 and a voltage
V is applied to a terminal 65. Upon this condition, the variable resistor
64 is adjusted such that the indicator hand points to the middle of the
indicator scale. When the indicator 63 is accompanied by no special
mechanical deviation, this zero-point calibration can be attained by
simply registering the brush 67 at the middle of the entire length of the
resistor 64. However, since it is quite usual that the indicator 63 has
some mechanical deviation, correct zero-point adjustment cannot be
attained in practice simply by registering the brush 67 at the middle of
the entire resistor length.
The variable resistor 62 determines the maximum moving ambit of the
indicator hand, i.e. the maximum voltage magnitude to be applied to the
indicator 63. Here, it should be noted that the moving angle of the
indicator hand does not always coincide with the actual rudder angle. The
moving angle of the indicator hand is proportional to the actual rudder
angle only. So, when the maximum moving angle of the indicator hand is
once selected, it is necessary to set the indicator scale in accordance
with the maximum moving angle so selected. In one example of this setting,
the maximum moving angle of the indicator hand is fixed to .+-.60 degrees
for the maximum rudder angle of .+-.90 degrees. In this case, the actual
rudder angle is of .+-.45 degrees when the maximum moving angle of the
indicator hand is .+-.30 degrees, respectively.
In the case of the above-described embodiment, the feedback signal in the
control circuit is directly utilized as an input for actuating the
indicator and, therefore, visual indication of the rudder angle can be
carried out with an accuracy equal to that in the control operation. The
indicator circuit is very simple in the construction thereof. Use of the
high input impedance circuit for the indication successfully avoids
undesirable disturbance on the feedback signal processed in the control
circuit.
A further modified embodiment of the auto-steering system in accordance
with the present invention is shown in FIGS. 6 and 7, in which the system
is adapted for remote steering of the boat, too. That is, the main
steering unit M including the control circuit 1 for the rudder is
accompanied by a remote steering unit R via a suitable electric wire or
wires. In the drawings, the contacts of switches marked as "AUT" are used
for automatic steering whereas those of switches marked as "MAN" are used
for manual steering using the remote steering unit R.
As shown in FIG. 6, the main steering unit M includes a main A-M
(auto-manual) switching mechanism 7 inserted between the switching
mechanism 3 and the control circuit 1, the mechanism 7 being adapted for
switching between the automatic and manual steering of the boat for which
the auto-steering system in accordance with the present invention is used.
The control circuit 1 in the main steering unit M is coupled to the remote
steering unit R via the above-described main A-M switching mechanism 7.
As shown in FIG. 7, the remote steering unit R includes a subsidiary
(auto-manual switch 81) having two contacts AUT and MAN and a manual
steering circuit 80 having three terminals X, Y and Z. The manual steering
circuit 80 includes a variable resistor 82 whose resistance can be
adjusted as desired by manually operating a knob not shown.
One practical embodiment of the variable resistor 82 takes the form of a
slide type variable resistor such as shown in FIG. 8.
The main A-M switching mechanism 7 includes a main A-M switch 71 having two
input contacts AUT and MAN, the first contact AUT is coupled to the output
contact of the switching mechanism 3 and the second contact MAN is coupled
to the terminal Y of the manual steering circuit 80, i.e. the slide brush
terminal in the case of the resistor construction shown in FIG. 8. The
output contact of the main A-M switch 71 is coupled to the input terminal
of the amplifier 11 in the control circuit 1 (see FIG. 2). A relay 72 is
inserted between the contact AUT of the subsidiary A-M switch 81 and the
electric source of a potential V in an arrangement operable on the main
A-M switch 71. When the relay 72 is active, the automatic steering contact
AUT of the switch 71 is closed whereas the manual steering contact MAN is
closed when the relay 72 is inactive.
The terminal Z of the manual steering circuit 80 is coupled to an electric
source of a potential V and the terminal X is to an electric source of a
potential -V.
For the automatic steering, the automatic steering contact AUT of the
subsidiary A-M switch 81 is closed in order to activate the relay 72 and,
upon activation of the relay 72, the automatic steering contact AUT of the
main A-M switch 71 is closed. Thus, the amplifier 11 of the control
circuit 1 is connected to the sensor circuit 4 via the switch mechanisms
71 and 3 for the normal control operation. When the actual navigation
course of the boat is fairly on the initially selected one, the output
signal from the sensor circuit 4 is zero. When the actual navigation
course of the boat is off the initially selected one, a corresponding
signal is output from the sensor circuit 4.
For the manual steering operation, the manual steering contact MAN of the
subsidiary A-M switch 81 is closed in order to make the relay 72 inactive
and the manual steering contact MAN of the main A-M switch 71 is closed.
Now, the amplifier 11 of the control circuit 1 is disconnected from the
sensor circuit 4 and connected to the slide brush terminal Y of the manual
steering circuit 80 (see FIG. 8). As described already, the X-terminal of
the variable resistor 82 is kept at an electric potential-V and the
Z-terminal at an electric potential+V. A pair of resistors R1 and R2 are
inserted between the both terminals X and Z in series connection and the
connection point between the resistors R1 and R2 is grounded. Thus, a
bridge output is obtained between the slide brush terminal Y and the
above-described grounded connection point. In the case of the manual
steering operation, the resistance of the variable resistor 82 is set by
the manual operation on the adjustor knob (not shown). Turning of the
rudder is carried out in accordance with the above-described bridge output
from the manual steering circuit 80.
As described already, the manual steering circuit 80 includes the manually
adjustable variable resistor 82 adapted for setting the input to the
control circuit 1 during the manual steering operation. However, a boat
will not always sail in a straight direction even when the rudder is
located on the neutral axis meeting the stern direction of the boat. Such
deviation from the straight sailing is caused by mechanical deviation
special to the rudder mechanism, wind heading and/or tideway. In other
words, the actual neutral position of the rudder does not always meet the
nominal neutral axis thereof.
An arrangement shown in FIG. 9 is proposed in order to compensate the
deviation of the above-described kind. In the illustrated construction, an
additional variable resistor 83 adapted for trimming is inserted in series
between the variable resistor 82 and the Z-terminal. By adjusting the
resistance of the additional variable resistor 83, the zero-point of the
manual steering circuit 80 is fixed in accordance with the deviation of
the actual rudder neutral position from the nominal rudder neutral axis.
In accordance with the above-described embodiment, the steering mode of the
boat can be freely shifted from automatic to manual and vice versa. In
addition, since the main A-M switch of the main steering unit is
operationally locked to the subsidiary A-M switch of the remote steering
unit, the above-described shifting in the steering mode can fairly be
carried out by simply operating the adjustor knob arranged on the remote
steering unit in the hand of the operator.
FIG. 10 depicts a further modified embodiment of the auto-steering system
in accordance with the present invention in which zero-point resetting of
the manual steering circuit is carried out quite automatically. In this
case, the resistor element 821 is accompanied by a slide brush 822 movable
over the entire length thereof and the slide brush 822 is associated with
a pair of springs 823 and 824 which urge the slide brush 822 to move in
opposite directions along the resistor element 821. The strength of the
springs 823 and 824 should be so selected that when no external force is
imposed upon the slide brush 822, the spring forces balance to each other
and the slide brush 822 is registered at the zero-point on the resistor
element 821, which corresponds to registration of the rudder at the
neutral axis. When external force is imposed upon the slide brush 822 by
operating the adjuster knob (not shown), the slide brush 822 deviates from
the above-described zero-point while overcoming the spring force. When the
external force acting on the slide brush 822 is cancelled, that is, the
operator's hand on the adjuster knob is removed, the slide brush 822 quite
automatically resumes its initial zero-point position on the resistor
element 821 due to the repulsion of the springs 823 and 824.
In accordance with this embodiment, zero-point resetting of the manual
steering circuit can be carried out quite automatically simply by
operator's detaching the adjuster knob on the remote steering unit after
shifting of the steering mode, thereby considerably simplifying the remote
steering operation and freeing the operator from trouble in the resetting
work.
In a further variant of the auto-steering system in accordance with the
present invention, it is employable to combine the zero-point trimming
construction shown in FIG. 9 with the automatic zero-point resetting
construction shown in FIG. 10.
Further, in the case of the zero-point trimming construction shown in FIG.
9, the above-described factors causing the deviation of the actual rudder
neutral position from the nominal rudder neutral axis do not in general
fluctuate so often. So, once the zero-point trimming is completed, it is
rather advantageous to provisionably fix the trimmed state of the manual
steering circuit. For this effect, the additional variable resistor 83
shown in FIG. 9 may be accompanied by a suitable mechanism for
provisionally fixing the selected resistance.
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