Note: Descriptions are shown in the official language in which they were submitted.
HAMD.002
'7~
MAGNETIC ~EADING REFERENCE
SYSTEM FOR MILITARY VEHICLES
The present invention relates to a magnetic heading
reference system and a gun positîon system for military
vehiclesO
A need exists and has existed for a substantial
period of time for an adequate magnetic heading reference
system, i.e., "compass, tl for use in military vehicles,
such as tanks. It is believed that this need was first
recognized during World War II as evidenced by a Depart-
ment of the Army Equipment Board Report dated January 1946.
~ o provide an adequate compass system for a tank
poses special problems due to the extremely high "mag-
netic signature" of the tank. The magnetic signature may
be defined as the aggregate error generated by the total
magnetized material in the tank, and the magnitude of the
error varies with the relationship of the turret to the
body of the tank. If one attempted to use a float-type~
self-contained compass (the so-called "wet" compass~ in a
tank, the magnetic signature of the tank body would cause
the compass to produce erroneous heading rPadings. Fur-
ther, it is believed that, with a wet compass, it would
be virtually impossible to adequately provide compensa-
tion for the magnetic signature~
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Compass system for tanks have been proposed which
involve obtaining heading information from outside the
zone of influence of the magnetic signature and trans
mitting the heading information to an indicator in the
tank. One such system includes a transmitter, which is
mounted at the top of a mast, which is connected to the
body of the tank. While this technique opera~es to re-
duce the effects of the magnetic signature of the tank,
it creates other problems. For example~ the mast can
interfere with firing, especially when located on the
front of the tank. Also, the mast is susceptible to being
damaged or destroyed through rotation of the turret of the
tank with the gun in a lowered position. Moreover, the
height of the mast could significantly alter the silhouette
of the tank, thereby making it more readily identifiable
by the enemy. Thus, this approach has not solved the
long-standing problem.
Quite apart from the problem of compensating for the
magnetic signature of the tank: a "wet" compass is prone
to produce heading errors above and below the seventieth
parallels. These type errora are due to the declination
of the earth's flux lines as they converge on the magnetic
poles.
~5
Tanks typically utilize information received from
spotter planes and forward observers to position the gun
of the tank to engage targets. Once the tank has fired a
round at the target, it is often the case that its location
will be observed by enemy spotter planes or enemy forward
observers. It is, therefore, advantageous, if not abso-
lutely necessary, for the tank to change its location after
firing a round. In order for the tank to be able to engage
the same target rom its new location, the gun must be
repositioned at that new location.
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No gun control system for a tank has heretofore been
available which continuously maintains the gun aimed in the
direction of a given target, regardless of the direction of
travel of the tank. The foregoing deficiencies and short-
comings of the prior art have been overcome by the presentinvention.
In accordance with the present invention, a trans-
mitter for a magnetic heading system is provided for use
with a vehicle having a body which is capable of assuming
any magnetic heading and a turret which is mounted on the
body and which may be rotated 360 in azimuth independently
of the body.
A significant feature of the present invention is
that the transmitter is adapted to be or is located on the
turret of the vehicle or tank. Moreover, with the present
invention, the indication of the magnetic heading of the
tank is not altered by rotation of the turret. In other
words, with t:he present invention, the indication of the
magnetic heading changes only when the vehicle changes
heading, even though the turret might have rotated while
the vehicle was travelling at a given heading.
~5 In accordance with an embodiment of the present
invention, the transmitter includes sensing means for
producing heading information to an indicator in the
vehicle. The sensing means preferably includes a winding
which is movably disposed in the transmitter and which is
maintained in alignment with the fore/aft axis of the
vehicle at all times. The sensing means further includes
a magnet to sense the north south flux lines of the earth.
The magnet is movably disposed in the transmitter in the
center of the winding, and the position of the magnet with
respect to the winding generates information indicative of
the heading of the vehicle.
An embodiment of the transmitter of the present
invention further includes means for detecting tha-t the
turret of the vehicle has rotated with respect to the body
of the vehicle. Inormation based on the detected rota-
tion is used to maintain the winding of the sensing meansin alignment with the direction of travel of the vehicle.
Thus, the position of ~he sensing magnet with respect to
the winding is not affected by rotation of the turret, and
the integrity of the heading information is maintained.
In an alternate embodiment of a transmitter used in
a magnetic heading reference system a fixed delta winding
may be mounted on the vehicle turret with a first movable
magnet disposed in the center of the fixed winding. A
receiver having a rotata~le delta winding and a second
movable magnet disposed therein may be located inside the
vehicle and electrically connected to the fixed external
winding. The second movable magnet inside the vehicle
will be responsive to changes in vehicle heading which
induce a change in the currents in the first fixed wind-
ing. The second magnet to be located inside the tank will
preferably be magnetically connected to a visual display
of the tank heading. The rotatable winding within the
vehicle will be mechanically connected to a servo motor
having a control loop responsive to turret motion. Thus,
in this alternate embodiment vehicle heading is maintained
despite rotation of the vehicle turret. The alternate
embodiment of the magetic heading reference system differs
from the first embodiment in that the alignment correction
system controls the delta winding inside the vehicle,
based on turret rotationO
In accordance wi~h the present invention, a gun
position controller for a vehicle oE the type heretofore
described is also provided. This control system is also
adapted to be mounted in the turret of the vehicle. The
S direction of the gun with respect to magnetic north will
be displayed on an indicator. As the turret is rotated
to bring the gun to a new position, the rotation will be
detected, and the indicator will be changed to display the
new direction of the gun. By providing the co~mander with
this information, the gun control system will enable the
tank commander to maintain magnetic bearing ~o target,
regardless of the magnetic heading of the vehicle itself.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is an exploded front view of a mechanical
configuration of a transmitter in accordance with the
present invention.
FIG. 2 is a schematic diagram in block diagram
form of a portion of the transmitter illustrated in
FIG. 1.
FIGS. 3 and 3a are pictorial diagrams of a tank which illus-
trates various asp~cts o the prese~t invention, a~pearing with FIG. 1.
FIG. 4 is a schematic in block diagram forilt of a
gun position controller in accordance with the present
invention.
FIG. 5 is a schematic diagram in block diagram form
of the magnetic heading reference system of the present
invention.
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FIG. 6 is a pictorial diagram of a tank which is used
to illustrate various aspects of the alternate embodiment
of the invention shown in FIG. 5.
DESCRIPTION OF SPECIFIC EMBODIMENTS
; It will be appreciated that the present invention can
take many forms and embodiments. Some embodiments of the
invention are described and illustrated so as to give an
understanding of the invention. It is no~ intènded, how-
ever, that the illustrative embodiments set orth herein
should in any way limit the scope of the invention.
The description of the invention herein is made with
respect to military tanks. However, it will be appre-
ciated that the invention may be utilized in any type
vehicle having a turret which is rotatable with respect
to the body of the vehicle.
With reference to FIG. 1, one mechanical configura-
tion of transmitter 100 in accordance with the present
inven~ion i6 illustrated. Transmitter 100 comprises a
magnetic assembly including sensing magnet 101 and damping
cup 103. Sensing magnet 101 is mounted on vertical shaft
104, and is free to rotate 360 in azimuth. To minimize
friction, shaft 104 is journalled between two precision
jewels tnot shown) and rests on another jewel (not shown)~
Damping cup 103 is a circular metal cup of aluminum
or other suitable non-ferrous material, and remains fixed.
Damping cup 103 surrounds sensing magnet 101, and approxi-
mately one-half of sensing magnet 101 is enclosed by damp-
ing cup t03, thereby allowing for a suitable air gap
between sensing magnet 101 and damping cup 103. Eddy
currents between damping cup 103 and sensing magnet 101
.? ~' 7
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provide the necessary damping to prevent oscillation and
overshoot of the magnet when it rotates to sense magnetic
north.
Still referring to FIG. 1, transmitter 100 further
includes delta winding 102, which is centered slightly
below the magnet assembly. Delta winding 102 is enclosed
in non-ferrous housing 105, and is journalled on a verti-
cal shaft having suitable slip rings to transmit elec-
tronic inputs ~o the coil and electronic outputs from the
coil. Delta coil 102 and housing 105 are able to rotate
360 in azimuth.
Delta winding 102 and the rotating type transformers
hereinafter ~escribed are preferably activated by the
application of a 26-volt, 400-cycle AC input, which is
illustrated as "AC input" in the drawings (for example,
see FIG. 2). In the case of a tank, that AC input is
preferably obtained by converting the 24-volt DC battery
voltage of the tank to the specified AC input. Apparatus
for making that DC to AC conversion is well known and,
accordingly, is not shown or described herein.
Still referring to FIG. 1, a transmitter in accor~
dance with the present invention further includes balanc-
ing balls 112a and 112b for neutralixing heavy magnetic
errors in the vehicle. Each balancing ball 112a and 1l2b
comprises magnets centered in balls of a suitable non-
ferrous material. Balancing balls 112a and 112b are
3C mounted on extended shafts so that compensation is pro-
vided in the same azimuth plane as that of sensing magnet
101~ Balancing balls 112a and 112b can be adjusted 360
in azimuth by means of screw slots located above the dust
cover. The balls are adjusted in conjunction with each
other to obtain neutralization of heavy magnetic errors of
the vehicle.
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After major errors are neutralized, small magnetic
errors in the vehicle may be compensated by means of poly-
plane compensator assembly 113, which comprises two mounted
magnets with suitable gearing. As shown in FIG. 1, poly-
plane compensator assembly 113 is connected to holding plate1 1 1 .
Referring now to FIG. 2, sensing magnet 101 is con-
stantly aligned with the earth's magnetic flux lines, since
it is free to rotate 360~ in azimuth. Sensing magnet 101
maintains its alignment with the earth's magnetic flux
lines, regardless of the heading of the tank.
When an ~C input is provided to delta winding 102,
electronic signals are generated therein and delta wind-
ing 102 produces a magnetic field. The magnetic field of
delta winding 102 is unbalanced due to the position of
sensing magnet 1 01, and second harmonic voltages are
produced in the three legs of delta winding 1020 These
second harmonic voltages are transmitted to delta winding
( 211 in indicator 210. The signals in receiver delta coil
\ 211 producè a magnetic field which causes receiver magnet
214 to assume an orientation identical to sensing magnet
101. Compass rose 212 responds to the orientation of
receiver magnet 214 to display magnetic heading of the
tank. Preferably, indicator 210 is an indicator similar
to the type described in U.S. Patent 3,875,676 to Hamilton.
With reference now to FIG. 3a, suppose that the body
300 o~ a tank is travelling in the direction indicated by
arrow 303 and that magnetic north is in the direction
shown. Turret 301 is positioned so that gun 302 is
pointed in direction indicated by arrow 305.
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Referring now to both ~IGS.3 and 3a~ suppose furtler
that a target to be engaged requires the rotation of turret
301 such that gun 302 is pointed in the direction of arrow
306. Prior to this rotation: (1) delta winding 102 is
aligned with the direction of travel oE the tank as indi-
cated by arrow 304; (2) the output signals from turret
position transformer 201 an~ control transformer 107 are in
phase; and (3) AC motor 109 is in an idle state. Turret
position transformer 201 and control transformer 107 are
rotating-type tran~formers, whose AC input is provided by
the DC-~C converter referred to above.
When the turret rotates to point gun 302 in direction
- 306, the a~imuth ring of the tank rotates, and that rota-
tion is coupled to the input of turret position ~rans-
former 201 via gearing 203. At this ~ime, the phase of
the signal at the output of turret position transformer
201 is changed and is accordingly out of phase with the
signal at the output of con~rol transformer 107. Thus, an
error signal based on the phase difference is produced at
the output of phase detector 202. That error signal is
amplified by servo amp 108, which drives AC motor 109. AC
motor 109 via gearing 110 rotates delta winding 102 and
housing 105 to keep delta winding 102 aligned with tank
body 300. The rotation of AC motor 109 is also trans-
ferred to the shaft input of control transformer 107 via
gearing 110. The rota~ion of the shaft inpu~ of control
transformer 107 operates to change the phase of the output
of control transformer 107 to bring it into conformity
with the phase of the output of turret position trans-
former 201. When phase comparison is obtained, rotation
of plate 106 ceases.
/77
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Those skilled in the art will of course appreciate
that correction of the phases of the output signals of
turret position transformer 201 and control transformer
107 does not occur instantaneously. However, it would
appear to one observing the operation that alignment is
maintained at all times.
Now suppose that the tank, having fired a round in
the direction 306, changes its heading to the direction
1Q indicated by arrow 307. In accordance with the present
invention, gun position information is provided to enable
the tank commander to keep gun 302 positioned on target in
direction 306, when the tank assumes that new heading.
Now referring to FIG. 4, there is illustrated a
schematic diagram of a gun position system in accordance
with the present invention~ As shown, it comprises phase
detector 400, servo amp 401, AC motor 402, control trans-
former 404, and indicator 405, together with suitable
~earing 403. When there is no rotation of the turret:
(1) the output signals from turret position transformer
201 and con~rol transformer 404 are in phase; and t2) AC
motor 402 is in an idle state.
When the tank starts to change its heading from
direction 303 to direction 307 (FIG. 3), the phase of the
output signal of turret position transformer 201 (FIG. 2)
is ~hanged, since a rotation of the shaft input of the
turret position transformer occurs. As shown, the output
of turret position transformer 201 is fed to one input of
phase detector 400, and the output of control transformer
404 is fed to the other input of phase detector 400. An
error signal is generated at the output of phase detector
400 due to the phase difference, and this error signal is
amplified by servo amp 401 to drive AC motor 402~ Via
gearing 403, the phase of the output of control trans-
former 404 is hrought into conformity with the phase o~
the outpu~ of turret position transformer 201.
Gearing 403 is connected directly to the fiducal
ring 406 of indicator 405. Thus, rotation of gearing 403
causes fiducal ring 406 to move to display the position of
the gun with respect to magne~ic ~orth. Such display may
be conveniently effected by employing a marker 407 on
fiducal ring 406.
An alternate embodiment of a magnetic heading refer-
ence system in accordance with the present invention is
generally illustrated in FIGS. 5 and 6. As shown in FIG. 5,
magnetic heading system 500 includes a transmitter device
502, a receiver 504, and a servo controlled correction
system 506.
In the system 500 the transmitter 502 is mounted on
; 20 the turret of the vehicle. The transmitter comprises a
first delta winding 508 which is mounted in a fixed
position in transmitter 502. A north seeking sensing
magnet 510 is disposed within the center of the first
delta winding 508 and is rotatable within the winding.
Movement of the sensing magnet 510 within the delta
winding 508 induces harmonic signals in the form of
currents I1-I3. A change in those currents is repre-
sentative of a change in the heading of the turret.
Such change in turret heading may occur in one of two
ways, as discussed below.
Receiver 504 includes a second delta winding 512
which is located inside the vehicle and which is capable
of rotating through 360~ The delta winding 512 is en-
closed in a manner similar to the transmitter winding of
the embodiment illustrated in FIG. 1. A movable magnet
514 is disposed within the center of the delta winding
512. The delta winding 512 is electrically connected, as
shown, to the delta winding 508 which is fixed to the
turret of the vehicle. The magnet 514 responds to changes
in currents I1~I3 as they are received by the delta wind-
ing 5120
For example, assume that the turret position and the
vehicle heading are aligned and that the vehicle is facing
north. Sensing magnet 510 always points in a northerly
direction. If the heading of the vehicle moves to an
easterly direction and the turret does not rotate, the
relationship of sensing magnet 510 to winding 508 changes,
since winding 508 is fixed. A change in the currents
I1-I3 thus occurs. I'he change in currents I1-I3 will in-
duce a change in magnetic field in the winding 512 that
causes the magnet 514 to rotateO In the receiver, the
magnet 514 is magnetically associated with a visual dis-
play 516 which may be a compass. Thus, the rotation of
magnet 514 causes the needle of the compass 516 to indi-
cate the easterly heading of the vehicle.
Special problems exist when the turret is rotated
with the tank heading remaining the same, and when the
turret is rotating while the tank heading is also chang-
ing. In both instances it is necessary to rotate the
delta winding 512 of the receiver 504 to correct for a
rotation of the turret. Otherwise, a rotation of the
turret position would cause receiver 504 to display an
incorrect change in vehicle heading.
To accomplish the correction for turret rotation, the
control correction system 506 is provided. The control
correction system 506 includes an AC motor 518 mechanically
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connected to the receiver delta winding 512 through a
rotatable shaft 520 and a gearing 522. When the azimuth
ring of the tank rotates, that rotation is coupled to the
input of control transformer 526 via gearing 524. Control
transformer 526 produces an output signal, which is then
suitably amplified by a servo amp 528 which in turn
actuates the ~C motor 518 to drive the delta winding 51~.
Thus, the control correction system 50~ operates to keep
the relative position of magnet 514 and receiver winding
512 the same, even though the turret has rotated.
FIG. 6 illustrates a situation where both the tank
heading and turret position have changed rom a prior
north heading. In the example of FIG. 6 the vehicle has
changed heading from a north heading to a northeast head-
ing while the turret position has changed from a north
heading to an easterly heading. There has thus been a
change in heading of 45, but the turret has rotated 90
from its prior position. Correction system 5U6 operates
in the manner heretofore described to adjust the relative
positions of magnet 514 and winding 512 based on the
additional 45 rotation of the turret.
The alternative embodiment provides certain advan-
tages in extending the longevity of the device since 90%of the precision components found in the FIC,. 1 embodiment
are removed from outside the vehicle and placed inside
offering grea~er protection from weather and extreme
temperatures. Further, since only a north seeking magnet
and a delta winding is fixedly mounted to the turret the
apparatu~ mounted outside the vehicle i5 smaller. Even
with suitable shock mounting and protective covering the
fixed delta winding with movable north seeking magnet
will present a smaller silhouette than the transmitter
illustrated in FIG. 1.
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The foregoing description of the present invention
has been made to comply with the requirements of the
Patent Statute. Those skilled in the art, having the
benefit of the present disclosure, will li~ely be able to
modify the disclosed apparatus to operate in substantially
the same manner to produce substantially the same results
as the disclosed apparatus. The appended claims are in-
tended to cover all such modifications.
