US 20060018075 A1
One or more pairs of magnet assemblages (14 and 16) are provided with magnetized segments (21-30) arranged in a Halbach-like array. The magnet assemblages (14 and 16) define a gap (18) through which magnetic data storage media (12) pass in a direction (20) across the segments (21-30). The magnetized sides (36) of the magnet assemblages (14 and 16) face each other thereby creating strong magnetic fields which degauss the magnetic data storage media (12) passing through the gap (18).
1. An apparatus for erasing magnetic storage media comprising:
at least one pair of magnet assemblages;
each magnet assemblage comprising at least three segments;
each segment having a direction of magnetization approximately perpendicular to the longest dimension of the segment;
at least one magnet assemblage arranged such that the segments are aligned adjacently with the direction of magnetization of each successive segment rotated by approximately 90 degrees relative to the previous segment wherein the direction of magnetization for a segment repeats every fifth segment if the magnet assemblage includes five or more segments; and
a gap defined by each pair of magnet assemblages such that a magnetic field created by each assemblage exists at least partially in the gap.
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19. An apparatus for erasing magnetic storage media comprising:
at least two pairs of magnet assemblages;
each magnet assemblage comprising at least three segments;
each segment having a direction of magnetization approximately perpendicular to the longest dimension of the segment;
each magnet assemblage arranged such that the segments are aligned adjacently with the direction of magnetization of each successive segment rotated by approximately 90 degrees relative to the previous segment wherein the direction of magnetization for a segment repeats every fifth segment if the magnet assemblage includes five or more segments;
a gap defined by each pair of magnet assemblages such that a magnetic field created by each assemblage exists at least partially in the gap; and
at least one of the at least two pairs of magnet assemblages arranged with the segments of the first magnet assemblage aligned at 90 degrees relative to the segments of the second magnet assemblage and with the segments of both magnet assemblages at a 45 degree angle relative to a magnetic storage media path through each gap defined by each pair of magnet assemblages.
20. The apparatus of
21. The apparatus of
at least one additional pair of magnet assemblages disposed on the magnetic storage media path;
each magnet assemblage of the at least one additional pair comprising at least three segments;
each segment of the magnet assemblages of the at least one additional pair having a direction of magnetization approximately perpendicular to the longest dimension of the segment;
each magnet assemblage of the at least one additional pair arranged such that the segments are aligned adjacently with the direction of magnetization of each successive segment rotated by approximately 90 degrees relative to the previous segment wherein the direction of magnetization for a segment repeats every fifth segment if the magnet assemblage includes five or more segments; and
the at least one additional pair of magnet assemblages arranged in attraction.
This invention relates generally to magnetic degaussers and more particularly to permanent magnet magnetic degaussers for erasing magnetic data storage devices.
Magnetic degaussing systems of various kinds are known in the art. Typically, magnetic fields of varying strength and direction are applied to the item to be degaussed forcing the magnetization within the object to change thereby destroying any patterns therein. Magnetic degaussing systems have become increasingly important with the increasing use of magnetic data storage. Data stored magnetically can remain on the storage medium for long periods of time after its use. For example, a computer disk's data can be retrieved even after a user has “erased” the data from the disk because the old data will not be changed until new data is written over that segment of the disk. If another person were to obtain the disk, that person may be able to access information from that disk.
In the art of bulk degaussing of magnetic data storage media, electrically powered degaussing systems are commonly used. For example, laminated steel cores of extruded “U” shapes in association with electrical windings are generally recognized as one configuration suitable for erasure of magnetic data storage media. Similarly, “E” shaped cores may be used. Pairs of such cores are often configured opposite each other with like poles facing, although single sided and offset configurations are also known in the art. Although such configurations are suitable for some situations, these systems have the disadvantage of needing a power source to create the fields necessary for magnetic data storage media erasure.
More recently, the discovery and improvement of rare earth permanent magnets have made the generation of magnetic fields of strengths suitable for bulk media erasure using permanent magnets practical. Such permanent magnets can be arranged with steel elements into magnetic circuits that act much like their electric counterparts. The weight requirements of permanent magnet systems are about equal to the electric systems. Further, the zero power input required by permanent magnets offsets higher production costs as compared to electric systems.
Another advantage of permanent magnet systems includes the use of individual elements, which may be off-the-shelf items, rather than trying to fabricate large elements or permanently magnetizing a single large shape. For example, it is known that a total of eight 2-inch by 2-inch by 1-inch neodymium-iron-boron (NeFeB) blocks, magnetized in the 1-inch direction, can be adhered by magnetic attraction onto steel plates as groups of four blocks thereby forming two 2-inch by 8-inch poles, a classic “U” shape magnet of 8-inch depth. Two such “U” shapes can be configured with like poles facing in repulsion across a gap suited to passage of 1-inch thick magnetic media. Such an assemblage can apply a magnetic field with good uniformity and at least 6000 gauss to every point in a common form factor for magnetic data storage media passing through that field. It is understood that at least a second passage of a magnetic storage medium through the field with a different orientation between the storage medium and the magnetic field is necessary to impart the desired change within the storage medium to affect magnetic data storage erasure.
Despite the advantages of these known permanent magnet systems, certain drawbacks exist. For instance, magnetic data storage media are being developed with increasing magnetic coercivities such that much stronger fields must be applied to completely erase the media. As such, the 6000 gauss strength achieved by known permanent magnet bulk degaussing systems is marginal with respect to the emerging media's coercivities.
Attempts to increase the strength of the known permanent magnet bulk degaussing systems by scaling up the systems, however, quickly lead to diminishing returns. Such scaling of prior art includes stacking off-the-shelf elements in their direction of magnetization, placing elements side by side on the steel plates, stacking and placing elements, or substituting larger custom-made elements or magnets for the off-the-shelf elements. It is generally recognized in the art of bulk degaussing that worst case field strength drives performance and that a measure of nonuniformity in field strength can be tolerated. It is also known that attempts to furnish field strengths sufficient for erasure of magnetic storage media with higher coercivities using various prior art facing “U” arrangements would require at least a correspondingly increased amount of NeFeB or other magnetic material plus thick steel components needed to complete the required magnetic circuit. Such a system would result in an unacceptable degree of field strength nonuniformity across the gap. In particular, the diminishing returns from prior art scaling using NeFeB elements arise due to flux leakage from NeFeB elements to each other and into the steel plates where media cannot be placed to affect erasure.
Additionally, any such scaling results in larger volume, increased weight, and greater cost. It is well known that in the assembly of the prior art permanent magnet systems, regions of both magnetic attraction and magnetic repulsion will arise between various elements and members. For example, magnets are attracted to steel plates and to each other when stacked with unlike poles facing. Conversely, placing magnets adjacent to each other with the same magnetic direction causes repulsion, as does placing like poles facing each other across a gap. To counter such forces, framework members must be added. In the prior devices, a thick steel plate serves a dual role as a required component of the magnetic circuit and as one of the framework members, but other members generally must be of nonmagnetic materials to avoid undesirable magnetic circuit paths or unnecessary magnetic field fringing effects. In particular, prior devices require an attraction-countering member between unlike poles, which experiences extreme compressive force, and this member cannot be magnetic steel. These structural requirements only become aggravated with the scaling of the prior permanent magnet devices.
The above needs are at least partially met through provision of the permanent magnet bulk degausser described in the following detailed description, particularly when studied in conjunction with the drawings, wherein:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.
With reference to
The segments 21-25 and 26-30 are aligned adjacently within each magnet assemblage 14 and 16 with the direction of magnetization of each successive segment rotated by approximately 90 degrees relative to the previous segment. More specifically, the direction of magnetization across successive segments rotates in the same direction so that the direction of magnetization repeats within a magnet assemblage only every fifth segment. This magnetization arrangement is commonly known as a Halbach array. In a variation on the traditional Halbach array, segments 22 and 24 of magnet assemblage 14 with directions of magnetization approximately perpendicular to the gap 18 have two rows of permanent magnets, whereas segments 21, 23, and 25 with directions of magnetization approximately parallel to the gap 18 have one row of permanent magnets.
The traditional Halbach array ascribed to Klaus Halbach, as conventionally illustrated in two dimensions in
Preferably each segment 21-30 includes a plurality of permanent magnets arranged in at least one row such that each permanent magnet in the segment has a direction of magnetization pointing in the same direction, substantially perpendicular to the length of the row. The preferred permanent magnet element 40 as illustrated in
One should understand that in three dimensions, such elements or segments depicted as having a square cross section may be square plates, cubes, or rods. Similarly, other permanent magnetic materials may be used. For example, SmCo blocks have aspect characteristics similar to NeFeB and can substitute for it. Also, a particular element size is not necessary. For instance, various segments 21-25 or 26-30 within a magnet assemblage 14 or 16 may have varying sizes and/or shapes. Alternatively, each segment can be an integral permanent magnet with a magnetization in a direction substantially perpendicular to the segment's longest dimension. Also, a complex fixture could magnetize a single large block into a one-piece magnet assemblage with several differently magnetized segments of the block.
Additionally, it is understood that assembling the invention from individual blocks can introduce acceptable minor field imperfections due to surface roughness, size and shape tolerance, and the common practice of plating NeFeB material. Similarly, introduction of thin nonmagnetic elements such as shims between permanent magnet elements 40 or segments 21-25 or 26-30 may introduce some acceptable field imperfections. Likewise, relatively thin and magnetically soft ferromagnetic materials introduced as shims between permanent magnet elements 40 or segments 21-25 or 26-30 would hardly disturb the fields.
The harmonic content above the fundamental as seen in
Alternatively, Halbach-like arrays of more or less than five segments can be utilized. For example, a mirror-imaged pair of three-segment (as illustrated in
In one such alternative embodiment illustrated at
The alternative embodiment of
In addition to the field strength and uniformity advantages of the various embodiments, there is much less need for steel elements and framing materials when compared to prior permanent magnet devices. Contrary to the prior permanent magnet devices, steel is not required for any supporting members or magnetic circuit elements. Also, any such shielding of the small magnetic flux leakage of the various embodiments would only be needed for certain applications such as against compass interference in airborne or other mobile applications. Typically, thin steel also suffices to shield against the slight magnetic flux leakages arising from imperfections in magnet element dimensions and magnetization. In applications where shielding is not a factor, nonmagnetic materials having better strength to weight characteristics can alternatively be used for framing. Additionally, the repulsive or attractive forces between the magnet assemblages of the various embodiments are generally reduced in comparison to prior conventional degaussers. Thus, less extensive framing support is needed.
In alternative embodiments, the overall size of the degausser 10 can be manipulated. For instance, a data processing operation that depends on erasing a large quantity of microminiaturized hard disk drives could benefit from a drastically scaled down version of the invention. In one example, it is now feasible to issue a personal digital assistant (PDA) for each patient entering a hospital. Also, each PDA may include an apparatus for removeably connecting an inexpensive 5 mm thick 4G Byte disk drive. The PDA could conveniently accompany a patient anywhere in the hospital (except places like MRI imagers) to capture all diagnostic and treatment information on the one drive. Medical records by law, however, must be protected. Thus, by using a physically smaller embodiment of the invention, such small drives can be erased after their use by being passed through the degausser 10. The large variety of NeFeB blocks available off the shelf other than the preferred permanent magnets raises many possibilities for configurations of the invention.
Also, Halbach arrays are known with magnetization angles of less than 90 degrees between segments. Use of multiple thin plate magnet segments with such reduced angular magnetization yield some further optimization for certain applications. Such approaches trade off some loss at additional contact surfaces between segments for improved harmonic content of the magnetic field profile.
In yet another embodiment, a pair of mirror-imaged permanent magnet assemblages 80 and 82 as illustrated in
In still another embodiment, gap adjustability can be introduced to trade off field strength against media thickness capacity. Frame structures for manipulating the magnet assemblages to adjust the gap width and to offset the assemblages are known, and an example of such a frame structure 90 is illustrated in
Crank 108 and lower pinion gear 110 rigidly attach to each other and rotatably attach to upper plate 94. Lower spur gears 112 and tall upper pinion gears 114 also rigidly attach to each other and rotatably attach to upper plate 94. Upper spur gears 116 attach rigidly to the partially threaded rods 104. Turning crank 108 causes lower pinion gear 110 to turn lower spur gears 112 that turn tall upper pinion gears 114, thereby causing upper spur gears 116 and rods 104 to turn. Threaded portions 106 of rods 104 act on upper plate 94 to selectively raise or lower it, thus affecting the gap 18 between magnet assemblages 14 and 16 for the passage of various magnetic storage media with different thicknesses.
The form of gap adjustment shown in
Similarly, many prior art applications may be used with the various embodiments to impart the sufficient exposure of the magnetic storage media to varying fields necessary to accomplish complete erasure. As noted above, when trying to erase magnetic storage media, simply providing a simple linear media path through a single magnetic field direction is generally recognized as requiring further media-field variation, such as two passes through the magnetic field combined with a rotation of the media or field. Such actions can be performed by a human operator, or by the use of mechanisms known in the art. Also, various mechanisms can impart a raster-scan-like motion to the magnetic media path to accomplish full magnetic exposure of media volume to a smaller magnetic field volume.
Alternatively, two or more pairs of permanent magnet assemblages can provide fields of varying direction along a media path 20. In one embodiment, one pair of magnet assemblages is mirror-imaged across the gap with magnetic sides in repulsion such as the degausser in
In yet another embodiment illustrated in
This embodiment can be further modified to add cross-gap magnetic fields, forming a “universal” configuration that erases horizontal and perpendicular hard disk drive media in one pass and no media rotation. For example, to the configuration of
Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept.