Magnetic marine compass

Details Magnetic marine compass Magnetic marine compass

2002-09-05

2003-12-23

Fulton, Christopher W. (Department: 2859)

Geometrical instruments

Indicator of direction of force traversing natural media

Magnetic field responsive

C033S0010DD, C033S364000

Reexamination Certificate

active

06665944

ABSTRACT:

FIELD OF THE INVENTION
The invention generally relates to magnetic marine compasses and more particularly to magnetic marine compasses that have tilting, self-balancing and no-spin characteristics.
BACKGROUND
A significant issue regarding compasses, whether land-based or marine, is the issue of dip. In certain locations in the globe, due to the position of the compass relative to the north and south poles, the magnet used in compasses will dip toward or away from the ground.
FIG. 1
illustrates the phenomenon of dip. Typical magnetic compasses include a magnet coupled with a compass card. As noted above, at certain latitudes the magnet, and hence the compass card, dip. Specifically,
FIG. 1
shows a two-dimensional representation
10
of a portion of the globe with latitude lines
12
,
14
and
16
. For traditional magnetic compasses, the magnet and the compass card
18
are pivotably mounted on a pin
19
, dip downwardly in areas around latitude line
12
, and dip upwardly in areas around latitude
16
. Around the equator, latitude line
14
, the magnet and compass card
18
dip imperceptibly or not at all. If the dip in certain latitudes is too pronounced, the compass card
18
will be at such an angle that viewing the numbers on the card is rendered difficult.
FIG. 2
shows a more realistic representation of lines of equal dip
24
found on the globe.
Decoupling the magnet from the card is one attempt to introduce self-balancing to compasses. Referring to
FIG. 1
, a compass card
20
does not dip at latitude lines
12
and
14
, but a decoupled magnet
22
does. There are numerous commercially available magnetic compasses with the magnet decoupled from the card. One type is an orienteering magnetic compass. Such a compass is generally used on land by hikers and others to orient themselves with their environment. One manufacturer of orienteering magnetic compasses is Suunto, of Finland, which makes the MC-2G global compass (
FIGS. 4
a
and
4
b
). As shown in
FIG. 4
a
, the orienteering compass
40
includes a compass card
42
, a magnet
44
, a magnet holder
45
with trunnions
46
, a card case
48
, and a pair of jewels
50
,
52
. The magnet holder
45
encircles the bar magnet
44
and the trunnions
46
hold the magnet
44
to the card
42
. The jewels
50
,
52
allow the card
42
and magnet
44
to freely swing.
FIG. 4
b
shows an alternative orienteering compass
60
that includes a bar magnet
62
held to the card
42
via trunnions
46
extending from a magnet holder
64
.
An advantage to the orienteering magnetic compasses
40
and
60
is that the magnet
44
,
62
is decoupled from the card
42
. There are several disadvantages in the use of orienteering compasses in marine environments. One major disadvantage is that to properly function, orienteering compasses must be level, which severely impacts their ability to be used in marine environments. Since orienteering compasses are virtually only land use compasses, their manufacture is less robust than the manufacture of marine compasses. Thus, there has not been a more robust manufacture of a marine compass having a card decoupled from a magnet.
Another form of magnetic compass is a manual-balance type. This type of compass is properly balanced to function within a certain magnetic latitude. Weight is added to the compass card to level the card. However, manual balancing of compasses is labor intensive and time consuming. Further, such manually balanced compasses are capable of functioning in only a limited part of the world.
Another type of magnetic compass is a counter-weight type, which utilizes the weight of the compass card itself to counter the dipping magnetic force and maintain the dipping angle within an acceptable range. One manufacturer of counter-weight types of compasses is C. Plath, which makes the Venus® compass
70
(FIG.
5
). The Venus® compass
70
lessens the dipping by lowering the magnet from the pivot point of the compass card. Thus, the weight of the magnet compensates for the vertical magnetic force causing the dip and allows the card to reach an equilibrium dipping angle with is generally smaller than would have occurred otherwise.
One disadvantage with the counter-weight type of compass is that to provide sufficient moment for the weight of the magnet to counter-balance the dipping force, the magnet must be moved a fairly substantial distance from the pivot point of the card. Referring to
FIG. 3
, the equilibrium equation for a compass card is:
M
=(
W
)(
d
)(sin&THgr;)
where M is the vertical couple or moment, W is the weight of the compass card assembly, d is the depth of the center of gravity, and &THgr; is the dip angle of the compass card. Thus, to move the depth d of the center of gravity Cg of the compass card assembly
30
(including a card
32
and a magnet
34
which pivot about pivot point P), the magnet
34
must be moved away from the card
32
. Such compasses must be taller than other compasses, which adds manufacturing costs and prevents such compasses from being placed in certain locations with limited height.
Another significant issue regarding the use of compasses is that compasses used in marine environments invariably encounter spin. Virtually all compass cards spin under some horizontal vibration frequencies, which are encountered when compasses are mounted on powered vehicles. The difference in inertia between the compass card and fluid within which the compass card is positioned causes relative movement. The relative movement in turn causes contact at the pivot point that leads to friction that drags the compass card in a circular path. Ultimately, the compass card will spin resonantly at some vibration frequencies. Spinning of compass cards inhibits users from properly reading the orientation from the compass.
Rule Industries, Inc., the assignee of this patent application, manufactures a compass under the trademark AQUAMETER® which exhibits no-spin characteristics. The AQUAMETER® compasses, however, lack the ability to self-balance. There are no compasses that exhibit the characteristics of no-spin and self-balance.
SUMMARY
The invention provides a no spin, self-balancing marine compass that includes a pivot assembly, a buoyant-magnetic chamber assembly positioned over the pivot assembly, a reading card assembly surrounding the buoyant-magnetic chamber assembly, a dome encompassing the buoyant-magnetic chamber assembly, the reading card assembly, and the pivot assembly, and fluid within the dome. The buoyant-magnetic chamber assembly is positively buoyant within the fluid, and the buoyant-magnetic chamber assembly, the reading card assembly, and the pivot assembly achieve a near neutral buoyancy within the dome, thereby mitigating spin of the buoyant-magnetic chamber assembly relative to the dome.


REFERENCES:
patent: 1533683 (1925-04-01), Abbot
patent: 1556557 (1925-10-01), Paemelaere
patent: 3805400 (1974-04-01), Giltzow et al.
patent: 4453317 (1984-06-01), Rahn
patent: 6049989 (2000-04-01), Lee
patent: 6493953 (2002-12-01), Rogers

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