Magnetic Tape Cleaner

The present invention relates generally to the cleaning of magnetic media and more particularly, to the honing of magnetic tape to remove dirt and loose oxide.

Magnetic tape is now utilized for storage of digital and analog information in applications ranging from computers to video recordings. In normal use, magnetic tape picks up airborne dirt particles and oxide flakes from its surface. The presence of these contaminants on the tape causes errors in the writing of information to and reading information from the tape. The contaminated areas move the tape away from the read and write heads resulting in a failure to record or playback the intended information.

This problem with accumulation of dirt and oxide has been well recognized in the art. Fixed and rotating single blade devices have been used to hone contaminants from the surface of magnetic tape. A significant problem with single blade devices is heavy blade wear due to the hardness of the oxide coatings on the tape.

A device with multiple honing surfaces has also been used to clean magnetic tape. The use of multiple surfaces reduces the wear problem of single honing surface devices. A rotating cylindrical tube is utilized with a plurality of slots spaced about its circumference. A vacuum line connected to an aperture provided at the base of the tube serves to withdraw the particles cleaned from the tape. A problem with this method is the high expense and complication of fabricating a hollow slotted cylindrical tube of a material sufficiently hard to withstand the abrasion of the oxide coatings on the tape. Another problem with the tube design is that it heats up due to inadequate cooling airflow. The shape of the slot performs the dual functions of defining the honing surface and providing an air conduit for the removal of particles cleaned from the tape. This does not provide an effective means of controlling the flow of air past the tape or through the slot for needed cooling and self cleaning of the honing surface. As a result, the high temperatures generated by friction cause the loose oxide and dirt removed from the tape to become welded to the honing surfaces. This mandates frequent cleaning of the slotted tube design.

The present invention utilizes a cylindrical carrier of a softer, molded material in which hard inserts are set for the honing surfaces. The carrier with inserts is less expensive and more easily fabricated than the slotted tube design. The inserts, acting as honing blades, are set in the circumference of the carrier alternating with baffled airflow openings. The airflow openings extend into the interior of the carrier where they communicate with a vacuum source. During the cleaning operation the pressure differential created by the vacuum source forces the tape against the blades. Leakage of air past the tape flows over the blades, cooling them. The air then travels into the carrier's airflow openings effectively withdrawing the contaminants removed from the tape. The airflow openings and the baffles within the openings are placed and shaped to optimize this airflow. As a consequence, there is less dirt and oxide buildup on the blades and a reduced need for cleaning.

The improved airflow additionally provides a more effective low pressure area between the tape and the carrier. This insures a better contact between the tape and the blades permitting the use of higher tape transport speeds. Consequently, cleaning to be accomplished at more quickly than with the prior art.

In a preferred embodiment the tape cleaner comprises a transport mechanism which moves the tape from reel to reel past, and tangentially in contact with, the rotating cylindrical cleaning element. The cleaning element comprises a carrier structure with a multiciplicity of alternating blades and airflow openings distributed circumferentially around the carrier structure. The blades and airflow openings are of a length wider than the tape to insure the entire recording surface of the tape is brought in contact with the blades. The cleaning element is rotated at a speed so that the tape passing over the cleaning element slips relative to the element. This causes the blades to hone the entire oxide surface of the tape as it passes by the element. The airflow openings are recessed and have baffles which direct the airflow. A vacuum line is connected to an opening below the cleaning element providing a pressure differential between the atmosphere and the airflow openings. The pressure differential forces the tape against the rotating blades insuring good contact therewith. The pressure differential also creates airflow past the blades to cool them and carries the dirt and oxide particles honed from the tape away from the cleaning element.

A feature of the invention is that the cleaning element may be comprised of a softer molded carrier structure with the blades being one or more hard sharp-edged inserts embedded in the circumference of the carrier structure.

FIG. 1 is a top plan view of an embodiment of the cleaning element and transport of this invention.

FIG. 2 is a front elevation view taken along line 2--2 of FIG. 1.

FIG. 3 is a top plan view of the cleaning element of this invention.

FIG. 4 is a side elevation view of FIG. 3.

FIG. 5 is a section view taken along line 5--5 of FIG. 3.

FIG. 6 is a top plan view of element 50 shown in FIG. 5.

Referring to FIG. 1, the apparatus has a tape transport mechanism with a cover plate 10. Supply and takeup reels 20 are rotatably mounted on the cover plate. The reels 20 are reversible so that tape 12 may be moved bi-directionally past a cleaning element 24. The cleaning element 24 is medially disposed between the reels 20 and surrounded by a housing 22.

A circular aperture 26 is cut through the top cover plate 10 adjacent to the base of cleaning element 24. Referring now to FIG. 2, a skirt 16 of the cleaning element extends through the aperture 26. The aperture is in communication with a plenum 28 mounted on cover plate 10 opposite to housing 22. The plenum 28 is in communication with a vacuum source 58 through conduit 40. Cleaning element 24 communicates with the vacuum source 58 creating a pressure differential between the atmosphere and the cleaning element 24. This pressure differential forces the tape against cleaning element 24 and creates an airflow which removes dirt and oxide particles cleaned from the tape 12.

Auxiliary vacuum cleaners 18 comprise hollow tubes with small openings on one surface are additionally connected to the vacuum source 58. Vacuum cleaners 18 are medially disposed between the cleaning element and the idle rollers. The openings on the cleaners 18 remove loose dirt and oxide particles from the base side of the tape as it passes by in contact with the cleaners, both before and after the tape's contact with the cleaning element 24.

Turning now to FIGS. 3, 4 and 5, there is seen cleaning element 24 of this invention, which is a cylindrical carrier 56 containing a plurality of honing blades 50, airflow openings 48 and baffles 54. The blades 50 perform the primary cleaning action with regard to the tape 12. Cleaning element 24 rotates presenting a plurality of cleaning or honing surfaces to the tape as the tape moves past the element. Since the tape passes tangentially to the loci of points defined by the rotating blades, the surface of the blades will be worn down evenly, and are thus self sharpening. The number of blades is not critical so long as there is a sufficient number to achieve an even and smooth transport of the tape past the cleaning element.

The blades 50 are fabricated of a hard non-magnetic material such as tungsten carbide or material of similar or greater hardness. The material is sintered, cast or otherwise fabricated, polished, and mounted in the carrier 56. The length of the blades are sufficient so that they will more than cover the width of the magnetic tape to be cleaned. As shown in FIGS. 5 and 6, the preferred longitudinal cross-section of the blades is triangular with a step at each end to provide interlocking surfaces with the carrier.

The carrier 56 is fabricated of a moldable softer and less expensive material than that used for the blades. Material such as thermoset polycarbonite plastic or other suitable injection moldable thermoset plastic may be used for the carrier 56. The carrier is preferably molded with the blades in place. After molding, the carrier and blades are machined to their final configuration.

In the presently preferred embodiment, the carrier 56 is made up of a one piece molded construction generally cylindrically in shape comprising a skirt 66 which defines a cavity 60, above which a center hub 62 extends. A multiplicity of radial ribs 64 extend between the hub 62 and the skirt 66. A blade 50 is imbedded into the end of each rib 64. A portion 68 of the rib 64 extends beyond the imbedded blade 50 to insure its retention within the rib.

The ribs 64 define the airflow openings 48 of the carrier 56. The airflow openings 48 are in communication with the cavity 60. Within each airflow opening 48, attached to the top of the skirt 66 and axially recessed from its outer circumference, a baffle 54 extends upwardly parallel to the axis of the hub 62. The center hub 62, the ribs 64 and the baffles 54 are all of the same height, which is greater than the width of the tape to be cleaned. Baffles 54 are of a shape to efficiently create a pressure differential between the blades 50 and the tape 12 insuring good contact therebetween, direct air past the blades 50 cooling them and creating the airflow necessary to remove contaminants cleaned from the tape. The baffles 54 are semicircular in cross-section with their flat side facing away from the hub 62.

Returning now to FIG. 2, the cleaning element 24 is mounted on an axle 38 passing through hub 62. At the top of the cleaning element, a lock nut 36 engages the exposed portion of the axle 38 and maintains tight engagement between the axle, a cover 32 and the top surface of the cleaning element. The cover 32 functions as an air seal for the top portion of the cleaning element 24. Axle 38 is tightly-fitted in the hub 62 so that rotation of the axle causes rotation of the cleaning element. Axle 38 decreases in diameter as it extends through a sleeve bearing 42 attached to the lower side of the plenum 28. The change in diameter of the axle maintains the position of the axle relative to the bearing 42. The axle terminates in a motor assembly 30. The sleeve bearing 42 and the motor assembly 30 serve to hold the axle in a rotatable position perpendicular to the top cover plate 10.

The cleaning element is driven by the motor assembly 30 in the same or opposite direction as the movement of the tape past the element, at a slightly faster or slower rate than the movement of the tape. For example, the speed of rotation of the cleaning element may be approximately 300 r.p.m. with a differential speed of the tape being about 10% faster or slower than the rotational speed of the cleaning blades 50 on the cleaning element.

The foregoing discloses and describes a preferred embodiment of the present invention. One skilled in the art will readily recognize from such discussion that various changes, modifications and variations may made therein without departing from the spirit and scope of the invention as defined in the following claims.