Disk Pack Bottom Cover With Magnetic Latch

This invention relates in general to a disk pack container and more particularly pertains to an improved arrangement for the magnetic latching of the bottom cover of the container.

Magnetic disks are widely used in electronic data processing systems for the storage and retrieval of information. To protect the magnetic disks, the disks are enclosed in dustproof housings having latchable bottom covers. The disks and their housings are known as disk packs. When it is desired to use a disk, the bottom cover is removed from the housing to enable read-write heads to be brought into close proximity to the information surfaces of the disk while the disk is being rotated. In one type of disk pack having but a single disk in it, a handle on the housing is provided to facilitate carrying of the disk pack. This handle and attendant mechanism also control the unlatching of the bottom cover by separating the magnetic elements joining the bottom cover to the rest of disk pack.

It has been conventional to construct the disk pack housing by injection molding of a synthetic plastic material. Because of their high flux density, Alnico magnets have been employed as the primary element of the magnetic latching device, and the magnets have been secured to the bottom cover by embedding them in the molded material of the bottom cover. In forming the bottom cover, the magnets are held in place within the mold by their magnetic force. This has caused some difficulty because on occasion weak magnets have damaged the molds by falling from their proper locations during the injection molding operation. Furthermore, this method requires a relatively lengthy molding cycle to insure that the magnets remain in their proper position. It should also be noted that because of a scarcity of cobalt, the price of the Alnico magnets has become prohibitive.

FIG. 1 is a top plan view of the prior art bottom cover and shows the symmetrical disposition of the magnets of the latching device;

FIG. 2 is a horizontal view of the prior art bottom cover of FIG. 1 with a portion of the rim of the cover broken away to show one of the embedded Alnico magnet assemblies.

FIG. 3 is a fragmentary horizontal sectional view showing the preferred embodiment of bottom cover constructed in accordance with the present invention;

FIG. 4 is a top plan view of the retainer ring employed in the embodiment of the invention shown in FIG. 3;

FIG. 5 is a horizontal sectional view taken along the section line 5--5 of FIG. 4;

FIG. 6 is a perspective view of the magnet and pole piece assembly employed in the present invention;

FIG. 7 is a fragmentary cross sectional view taken along section line 7--7 of FIG. 3; and

FIG. 8 is a side view of an alternative form of pole piece that may be used in the magnet assembly.

FIGS. 1 and 2 depict a conventional disk pack bottom cover 1 formed by the injection molding of a synthetic non-magnetic plastics material. The cover is of circular configuration and has an upturned rim 2 whose upper edge 2A is inwardly stepped. Spaced around the inside periphery of the rim are ribs 3 which form slight inward protrusions. At the center of the lid is a post 4 that extends upwardly from the floor. As shown in FIG. 2, the post is braced laterally by buttresses 5 which are symmetrically arranged around the post. Disposed on the floor of the cover are receptacles 7 in which are secured permanent magnet assemblies formed by steel cups 8 containing permanent magnets 9. As shown in FIG. 1, the four permanent magnet assemblies are disposed symmetrically about post 4 in alignment with the buttresses 5. Each permanent magnet assembly is made by pressing an Alnico magnet into the steel cup so that the bottom face of the magnet is brought into contact with the bottom of the steel cup. A non-magnetic liner is interposed between the side wall of the steel cup and the permanent magnet to provide a lateral gap that prevents the magnetic flux of the magnet from being short circuited through the magnetic cup. The non-magnetic liner is formed, for example, by electro-plating the side wall of the cylindrical magnet with pure nickel. The steel cup, in the assembly, acts as one pole piece with the exposed upper surface of the magnet providing the opposite pole. As shown in FIG. 2, the steel cup 8 has an external circular groove 8A. During molding of the bottom cover, the plastic material flows into the circular groove and upon solidifying locks the steel cup in the receptable 7.

The bottom cover latches to the housing of the disk pack in the manner shown in the copending application of David E. Butz, Ser. No. 969,073, filed Dec. 13, 1978 and assigned to the assignee of the present application. Briefly, a steel plate having a central aperture through which the post 4 passes, is lowered into contact with the permanent magnets 9 of the bottom cover. The steel plate is magnetically attracted to the permanent magnets, and this engagement latches the bottom cover to the housing of the disk pack container. To disengage the bottom cover from the housing, the steel plate is raised, while the bottom cover is prevented from following the movement of the steel plate by downward pressure applied to the central post 4 and the peripheral edge 2A of the bottom cover.

The improved magnetic latching arrangement for the bottom cover of this invention is depicted in FIGS. 4-8. An annular retaining ring 20 is molded from a non-magnetic plastic material that is preferably the same material used for the bottom cover, typically polycarbonate. The retaining ring, as indicated in FIG. 5, provides an inverted U-shaped channel 21 that extends around the ring. The bottom edges 21A of the inner and outer sides 21B and 21C of the channel carry beads 22 to facilitate ultrasonic welding of the retaining ring to the cover.

Groups of parallel slits 23 are provided in the retaining ring. The slits are arranged in groups of three, and the groups are symmetrically spaced around the retaining ring. While three groups of slits are depicted in FIG. 4, it will be apparent that fewer or more groups may be employed, depending upon the desired strength of the magnetic latch. Further, it will be apparent that each of the groups may have fewer or more than three slits. Protruding through the slits, are plates 24 of a readily magnetizable material such as iron or steel. As shown in FIG. 6, the plates are provided with a shoulder 24A at each end. Between plates is interposed a permanent magnet 25 made of a magnetic ferrite material embedded in a rubbery synthetic material. The plates on either side of the permanent magnet acts as pole pieces with one plate being a North pole and the other plate being a South pole. In a three plate assembly, the magnets are arranged to make the middle plate of one magnetic polarity and the outer two plates of the opposite magnetic polarity.

As shown in FIG. 7, the pole pieces 24 extend through the slots in the retaining ring. The slots are somewhat shorter in length than the longest dimension of the plates 24, and the shoulders 24A lie beneath the top wall 30 of the channel and prevent the pole pieces from being pulled through their respective slots. Consequently, when a pole piece is pulled upwardly, the lifting force is transmitted by the shoulders 24A to the retaining ring and therethrough to the bottom cover.

An alternative form of pole piece 26 is depicted in FIG. 8 in which the pole piece shoulders are defined by lateral tabs 26A and 26B protruding from the ends of the pole piece. The pole piece 26 is symmetric in form so that either edge 26C or 26D of the pole piece can extend through the slot in the retaining ring.

To aid in maintaining the magnetic assemblies in place within the retaining ring 20, the interior U-shaped channel of the ring is provided with lugs 27, 28 and 29 as shown in FIG. 4. The lugs insure that the pole pieces 24 are kept in close contact with the interposed permanent magnets 25. Other means, of course, can be employed to keep the pole pieces and interposed permanent magnets in close contact. For example, they may be held together by rivets, adhesive, clips, tape, potting material, etc.

In assembling the bottom cover of this invention, the pole piece and magnet assemblies are placed in position within the retaining ring, and the retaining ring is then ultrasonically welded to the bottom cover. The retaining ring thereby becomes an integral part of the bottom cover as depicted in FIG. 3. The assembly procedure avoids the difficulty of having the magnets present during the injection molding of the bottom cover and shortens the molding cycle.