Geometrical instruments – Indicator of direction of force traversing natural media – Magnetic field responsive
Reexamination Certificate
2000-04-24
2002-08-13
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Magnetic field responsive
Reexamination Certificate
active
06430825
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to navigational devices. In particular, the present invention relates to compasses having improved performance which are more easily manufactured.
BACKGROUND OF THE INVENTION
Navigational devices such as compasses are typically used to provide a directional bearing during such activities as camping and hiking. Such compasses typically include either a magnetic thin steel strip pointer or a sintered magnetic pointer. Magnetic thin steel strip pointers typically comprise a stamped thin steel strip which is magnetized and which is mounted to a separate brass or plastic hub. The hub typically receives a press fit jewel bearing which rests upon a pivot upwardly extending from a base. In some applications, the stamped thin steel strip magnet has its opposite ends painted or coated to distinguish between north and south polarities. In other compasses, a disk having direction indicia is secured to the strip, wherein the north indicia is associated with the end of the strip having a south polarity.
Due to the relatively weak sensitivity of such compasses, some compasses alternatively use a sintered magnetic pointer in lieu of the stamped thin steel strip magnetic pointer. To form a sintered magnetic pointer, magnetic metal particles are compressed under extremely high pressures to form a shape which is then heated at extremely high temperatures to molecularly bond the particles together so as to form a solid high volume member which is then magnetized and mounted to a separate hub carrying a press fit jewel bearing. Such sintered pointers have a large thickness and volume due to the manufacturing process requirements. The relatively large volume of such sintered magnets provides a compass with greater magnetic power and sensitivity (i.e., the movement or reaction of pointer in response to movement or rotation of the compass) as compared to the stamped thin steel strip magnetized pointers. However, due to this increased volume, such pointers formed from sintered magnets are large and bulky, increasing the weight and cost of the compass. Moreover, because the magnetic metal particles are only loosely bonded together by the sintering process, sintered magnetic pointers are extremely brittle. In addition, the additional magnetic power offered by such sintered magnetic pointers is to some extent offset by the additional mass and increased inertia of the pointer itself.
Although such conventional compasses are commonly used in a variety of activities, such compasses have several disadvantages. First, compasses having magnetized thin steel strip pointers and compasses having sintered magnetic pointers are expensive in terms of both cost and assembly. With both compasses, the pointer must be assembled to the hub. In addition, the jewel bearing must be press fit into the hub prior to the pointer being rested upon the pivot. Each of the pointer, the hub and the bearing must be manufactured separately, must be separately inventoried and must then be assembled. As a result, such compasses are expensive to manufacture.
Second, the sensitivity or performance of such compasses is frequently inadequate. Although lightweight, the magnetic thin steel strip pointers have limited magnetic power and as a result have limited sensitivity. Though having improved magnetic power and improved sensitivity, sintered magnetic pointers are more expensive to manufacture and are heavy and are bulky, increasing both the size and the weight of the compass.
Third, with such magnetized thin steel strip pointers and such sintered magnetic pointers, it is extremely difficult to provide compasses having a wide range of sensitivities customized for particular applications and consumer budgets. In particular, increasing the magnetic power or sensitivity of such thin steel strip magnetic pointers or such sintered magnetic pointers generally requires increasing the size or mass of the pointer itself. However, increasing the size or mass of the pointer itself also undesirably increases the size and weight of the compass. In addition, each differently sized pointer also generally requires a differently sized compass base or housing as well as differently configured tooling. Purchasing and maintaining such a large inventory of tooling as well as a large inventory of pointers further increases the overall cost of the compass.
Thus, there is a continuing need for a compass and a method for manufacturing such a compass that is lightweight, that can be assembled in less time and that can be provided with a varying sensitivity with a minimal number of changes to the compass itself.
SUMMARY OF THE INVENTION
One embodiment of the invention relates to a compass including a base, a pivot extending from the base along an axis and a pointer. The pointer includes a central portion resting upon the pivot, a first outer portion radially spaced from the axis of the pivot and having a magnetic north polarity and a second outer portion radially spaced from the axis of the pivot and angularly spaced from the first outer portion by 180 degrees. The second outer portion has a magnetic south polarity. The center portion, the first outer portion and the second outer portion are integrally formed as part of a single unitary body including polymeric material.
Another embodiment of the invention relates to a navigational compass device including a base, a pivot extending from the base and a pointer. The pointer includes a bearing support, a bearing coupled to the support and resting upon the pivot, a first wing extending from the bearing support and a second wing extending from the bearing support. The first and second wings have magnetic north and magnetic south polarities, respectively. The bearing support, the first wing and the second wing are integrally formed as part of a single unitary body including a polymeric material.
Another embodiment of the invention relates to a method for making a navigational compass. The method includes providing a base, forming a pivot extending from the base along an axis, mixing a magnetic powder with a fluid polymer, molding the mixture of magnetic powder and fluid polymer so as to form a unitary body having a central portion and first and second opposite portions radially spaced from the central portion, magnetizing the first and second opposite portions so as to have first and second opposite magnetic polarities and resting the central portion upon the pivot. The single unitary body rotates about the axis of the pivot to indicate magnetic north and directions relative thereto.
Another embodiment of the invention relates to a method for making a plurality of navigational compasses having varying sensitivities. The method includes providing a base for each of the plurality of compasses, forming a pivot extending from each base along an axis, mixing a magnetic powder with a fluid polymer for each of the plurality of compasses, varying a ratio of the magnetic powder to the polymeric material for each of the plurality of compasses to provide each of the plurality of compasses with a different sensitivity, molding the mixture of magnetic powder and at least partially fluid polymer so as to form a single unitary body having a central portion and first and second opposite portions radially spaced from the central portion for each of the plurality of compasses, magnetizing the first and second opposite portions so as to have first and second opposite magnetic polarities for each of the plurality of compasses and resting the central portion upon the pivot for each of the plurality of compasses. With the plurality of compasses, the first and second opposite portions rotate about the axis of the pivot to indicate magnetic north and directions relative thereto.
REFERENCES:
patent: 2855696 (1958-10-01), Griswold
patent: 3705334 (1972-12-01), Arens et al.
patent: 3853089 (1974-12-01), Howard
patent: 4357756 (1982-11-01), DeGaeta et al.
patent: 4438568 (1984-03-01), Kramer et al.
patent: 4716655 (1988-01-01), Sakuma
patent: 4930224 (1990-06-01), LeBlanc
patent: 5282318 (1994-0
Bennett G. Bradley
Foley & Lardner
Johnson Outdoors Inc.
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