Diver navigation system

An underwater navigation device wherein a flux gate compass provides head difference signals, a doppler navigation sonar provides drift angle signals, which signals are combined by a summer to provide steering correction signals that are displayed by a steering null meter.

BACKGROUND OF THE INVENTION 
This invention relates to navigation devices and more particularly to 
apparatus for providing improved underwater navigation capability to 
swimmer-divers, small submersibles, or the like. 
Swimmer-diver navigation has been materially aided with the introduction of 
devices utilizing doppler effects of sonar to provide accurate data as to 
direction and speed of travel over the bottom. U.S. Pat. No. 3,810,080 to 
E. K. Hunter provides a good example of such a device which also 
incorporates for the diver's use a magnetic steering compass and a drift 
meter. The latter provides to the diver a visual indication of the amount 
of lateral drift he is experiencing, due to cross currents in the water. 
While that device automatically gives the diver a quantitative drift 
indication, the amount of heading correction that he must effect to make 
his desired course good will require a mental computation that depends 
upon his skill and experience. In practice, making the necessary heading 
correction is made more difficult by the fact that each change in either 
heading or drift produces a resultant change in the other. 
Moreover, it has been found that swimmer-divers using the navigation device 
of U.S. Pat. No. 3,810,080 experience difficulty in accurately reading the 
magnetic steering compass thereof while swimming and also watching the 
drift meter which is close to, but separate from the compass. 
Accordingly, it is desirable to provide an underwater navigation device or 
system having a single, null type indicator that will tell the user 
whether he is actually heading in the proper direction to make good a 
predetermined desired course in spite of transverse currents and, if not, 
what steering correction he must effect to make the course good. 
SUMMARY OF THE INVENTION 
With the foregoing in mind, it is a principal object of the invention to 
provide an improved underwater navigation device which will enable the 
user to more accurately make good a predetermined course over the bottom 
in spite of currents transverse thereto. 
Another important object is the provision of a navigation aid that will 
provide a single null type indication of when the user in pursuing the 
proper heading to compensate for drift. 
Yet another object is the provision of a navigation aid that automatically 
combines factors of heading and drift angle to provide a quantitative and 
directional indication of the necessary steering corrections required. 
Still another object of the invention is the provision of a navigation 
device or system having the foregoing features and which can readily be 
incorporated in a swimmer-diver manipulated unit. 
A further object is the provision of a navigation device for underwater use 
that is reliable, accurate, and does not require auxilliary units such as 
beacons, transponders and the like. 
Other objects and many of the attendant advantages will be readily 
appreciated as the subject invention becomes better understood by 
reference to the following detailed description, when considered in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a navigation device embodying the invention is 
indicated generally at 10 and is carried by suitable support structure in 
the form of a vehicle or housing represented by the dot-and-dash line 12. 
The device 10 comprises a compass 14, which in this preferred embodiment 
is of the pivoted card magnetic type, that can be used in positioning the 
housing 12 on a predetermined course heading during preparations for use 
which will later be more completely described. 
The device 10 further comprises an oscillator 16 which operates at a 
substantially fixed A.C. frequency of 400 Hz. The 400 Hz frequency of 
oscillator 16 is applied, as shown by flow line 18, as an energizing input 
signal to an earth inductor or flux gate 20. The flux gate 20 is 
conveniently of the type comprising an excitation winding associated with 
three delta connected induction windings. The flux gate 20 is connected, 
as shown by lines 22, to a variable control transformer 24, conveniently 
comprising three star connected inductors and having a rotatable resolver 
winding mechanically connected to a course setting crank 26. The output of 
the control transformer 24, represented by line 30, is in the form of a 
second harmonic A.C. signal of 800 Hz, and is applied via line 30 as one 
input to a phase detector 32. The latter may conveniently be in the form 
of a phase sensitive rectifier network. 
The 400 Hz output of oscillator 16 is also applied, as shown by line 36 to 
a frequency doubler 38 which produces as an output, line 40, an 800 Hz 
signal as a reference input to the phase angle detector 32. 
The output of the phase angle detector 32 is in the form of a D.C. voltage, 
line 42, analogous of heading differences relative to a predetermined 
heading selected by adjustment of the control transformer 24 by means of 
crank 26 in a manner and for a purpose which will be made apparent as this 
description precedes. The aforedescribed combination of oscillator 16, 
earth inductor or flux gate 20, control transformer 24, frequency doubler 
38, and phase detector 32 will be recognized as the basic arrangement of 
an earth inductor compass. Such compasses are well known and the full 
theory of operation thereof need not be dealt with here. Suffice it to say 
that with the flux gate 20 in a desired heading position relative to the 
earth's magnetic field, the rotor or resolver winding of the control 
transformer 24 can be rotated by crank 26 to a position where the phase 
angle of the 800 Hz second harmonic output signal 30 will match the phase 
angle of the 800 Hz reference signal 40. In that condition there is a zero 
voltage output signal 42 from the phase detector 32, and the compass is 
then "set" for the desired heading. Thereafter changes in heading in one 
direction or the other will cause a corresponding change in phase angle of 
the signal 30 that will produce a heading difference signal 42 in the form 
of the mentioned D.C. analog voltage and which is a positive voltage for 
differences in one direction and negative for differences in the other 
direction. 
The heading difference D.C. analog voltage output 42 is applied as one 
input to a D.C. voltage summing amplifier 44. A second voltage input to 
the summing amplifier 44 is derived from a doppler navigation sonar 50, 
the output 52 of which is analogous to drift angle .theta. of the vehicle 
or housing 12 carrying the device 10. The sonar 50 is of conventional well 
known construction of the type that comprises orthogonal sets of 
hydrophones and projectors directed toward the bottom being traversed, 
together with suitable resolver circuitry for providing the drift angle 
representing signal 52. The drift angle .theta., as will be understood by 
those skilled in the art to which the invention pertains, is a function of 
the lateral component of current acting on the vehicle or 
housing-swimmer-diver combination, and of the heading and forward speed 
thereof. Thus, if a heading of 090.degree. were steered with a cross 
current 72, an uncorrected track 76 would be traveled. The signal 52 will 
be a positive voltage for drift angles .theta. to one side of the device 
heading and a negative voltage for drift angles to the other side. 
The summing amplifier 44 provides a D.C. voltage output, line 54, that is 
analogous of the algebraic sum of heading difference signal 42 and the 
drift angle signal 52. The output 54 of the summing amplifier is applied 
to a steering null meter 56, which in the preferred embodiment comprises a 
zero centering microammeter having a movable needle or pointer 58 and a 
center reference mark or index 60. 
The analog voltage signals 42 and 52 are so scaled, and the polarities so 
selected, that the algebraic sum thereof is zero whenever the heading 
difference of the device 10 is just sufficient to offset or compensate for 
the drift angle. In this condition the desired course is being made good. 
MODE OF OPERATION 
Referring now additionally to FIG. 2, consider that a swimmer-diver desires 
to utilize a navigation device of this invention, carried for example in 
steerable housing 12, to travel a desired course 70 of 090.degree. from 
point A to point B, there being a current, represented by vector 72, 
having a component 74 acting transversely of the desired course. With the 
device stationary, e.g., resting on the bottom, the user points or heads 
it in the desired direction as determined by the magnetic compass 14. The 
crank 26 of the control transformer 24 is then operated in a predetermined 
direction, e.g., clockwise, if the pointer 58 is to the left of the index 
60, until the pointer is centered on that index. If the pointer were to 
the right of the index, the crank is turned counter-clockwise until the 
pointer is centered. The earth inductor or flux gate compass portion of 
the device 10 is thereby set for the desired course to be made good. 
Following the mentioned directional procedures avoids the possibility of 
introducing a reciprocal heading due to the ambiguity of two zero 
positions of the control transformer rotor. 
Now, the user can begin moving the housing 12 and included device 10 toward 
point B, but instead of steering by the magnetic compass 14 which was used 
in setting the earth inductor or flux gate compass by crank 26, the user 
steers by maintaining a zero or null reading on the steering null meter 
58. This is done by watching the needle or pointer 58. If the pointer 
points to the left of the index 60, the user turns to the left until the 
pointer re-centers on the index. If, however, the pointer points to the 
right of the index, the user steers to the right to re-center the pointer. 
By so doing, a heading will be pursued that compensates for the currents 
acting on the system, and the desired course will be made good. It should 
be noted that, when there is a cross current, the magnetic compass heading 
actually pursued or steered will be to one side of the desired course set 
into the device, and the user should not steer by that compass, but only 
by the null meter. 
It will be appreciated from the foregoing that the user is relieved of the 
difficult task of continuously monitoring separate instruments, namely a 
magnetic compass and a drift meter, and can avoid mentally combining the 
readings thereof. 
Obviously, other embodiments and modifications of the subject invention 
will readily come to the mind of one skilled in the art having the benefit 
of the teachings presented in the foregoing description and the drawing. 
It is, therefore, to be understood that this invention is not to be 
limited thereto and that said modifications and embodiments are intended 
to be included within the scope of the appended claims.