Patent Abstract:
A tape guide that has textured surface over which the tape passes. The textured surface has a surface roughness exceeding the flying height of the tape above the surface. This new irregular surface topography reduces the air bearing and allows limited contact between the tape guide and the tape while minimizing tape distortion that can occur with other surface topographies.

Full Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to tape drives and, more particularly, to flanged tape guides that have an irregular surface to reduce the air bearing between the tape and the surface of the hub.  
       BACKGROUND OF THE INVENTION  
       [0002]     Information is recorded on and read from a moving magnetic tape with a magnetic read/write head positioned next to the tape. The magnetic “head” may be a single head or, as is common, a series of read/write head elements stacked individually and/or in pairs within the head unit. Data is recorded in tracks on the tape by moving the tape lengthwise past the head. The head elements are selectively activated by electric currents representing the information to be recorded on the tape. The information is read from the tape by moving the tape longitudinally past the head elements so that magnetic flux patterns on the tape create electric signals in the head elements. These signals represent the information stored on the tape.  
         [0003]     Data is recorded on and read from each of the parallel tracks on the tape by positioning the head elements at different locations across the tape. That is, head elements are moved from track to track as necessary to either record or read the desired information. Movement of the magnetic head is controlled by an actuator operatively coupled to some type of servo control circuitry. Tape drive head positioning actuators often include a lead screw driven by a stepper motor, a voice coil motor, or a combination of both. The carriage that supports the head is driven by the actuator along a path perpendicular to the direction the tape travels. The head elements are positioned as close to the center of a track as possible based upon the servo information recorded on the tape.  
         [0004]      FIG. 1  illustrates generally the configuration of a tape drive  10  typical of those used with single spool tape cartridges. Referring to  FIG. 1 , a magnetic tape  12  is wound on a single supply spool  14  in tape cartridge  16 . Tape cartridge  16  is inserted into tape drive  10  for read and write operations. Tape  12  passes around a first tape guide  18 , over a magnetic read/write head  20 , around a second tape guide  22  to a take up spool  24 . Head  20  is mounted to a carriage and actuator assembly  26  that positions head  20  over the desired track or tracks on tape  12 . Head  20  engages tape  12  as tape  12  moves across the face of head  20  to record data on tape  12  and to read data from tape  12 . Referring to  FIGS. 2 and 3 , roller guide  28  includes disc shaped flanges  30  and an annular hub  32 . Flanges  30  and hub  32  may be machined as a single integral part or as three separate parts bonded together. In either case, flanges  30  function to keep tape  12  at the proper angle as it passes across head  20 . If the tape is presented to the head at too great an angle, then the read and write elements in the head may be misaligned to the data tracks. Flanges  30  are also needed to help keep tape  12  properly packed on take up spool  24 .  
         [0005]     As the tape is pulled over the guides, a film of air is created between the outside surface  34  of hub  32  and tape  12 . This film is often referred to as an air bearing. The air bearing allows the tape to move with low friction very rapidly back and forth between flanges  30 . Consequently, high frequency tape movement can occur when the edge of the tape bumps abruptly against flanges  30 . Read/write head positioning systems have difficulty following such high frequency tape movement. It would be desirable to reduce this air bearing and thereby increase the friction between the tape and the hub to slow the movement of the tape back and forth between the flanges. Slowing the tape in this manner would allow the head positioning system to better follow the tape as it wanders back and forth between the guide flanges.  
         [0006]     One technique that has been used to reduce the air bearing is creating an irregular topography on the surface of the hub. This technique is described in U.S. patent application Ser. No. 09/597,882. In one version of this technique, described in the &#39;882 application, a series of comparatively deep grooves are formed in the surface of the hub to reduce the air bearing. In another version, comparatively high raised areas are formed on the surface of the hub. It has been discovered that these surface topographies can leave imprints on the tape which may, under some conditions, distort or otherwise damage the tape.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to a tape guide that has a textured roughness exceeding the flying height of the tape above the surface. This new irregular surface topography reduces the air bearing and allows limited contact between the tape guide and the tape while minimizing tape distortion that can occur with other surface topographies.  
         [0008]     Surface texture is the repetitive or random deviation from the nominal surface that forms the three dimensional topography of the surface. Surface texture includes roughness, waviness, lay and flaws as those terms are defined in the American National Standard ANSI/ASME B46.1-1985 which is incorporated herein by reference. Surface roughness consists of the finer irregularities of the surface texture. Surface roughness, for purposes of this Specification and Claims, is measured and quantified by the Roughness Average R a  defined in section 3.9.1 of ANSI/ASME B46.1-1985. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a top down plan view of a single spool tape drive.  
         [0010]      FIGS. 2 and 3  are elevation and plan views of a conventional roller tape guide.  
         [0011]      FIG. 4  is an elevation view of a roller tape guide constructed according to one embodiment of the present invention in which a circumferential texture is applied to the surface of the hub.  
         [0012]      FIG. 5  is a detail view of a portion of the roller guide of  FIG. 4  showing the texture in more detail.  
         [0013]      FIG. 6  is an elevation view of a roller tape guide constructed according to another embodiment in which a cross hatched texture is applied to the surface of the hub.  
         [0014]      FIG. 7  is a detail view of a portion of the roller guide of  FIG. 6  showing the texture in more detail.  
         [0015]      FIG. 8  is an elevation view of a roller tape guide constructed according to another embodiment in which a sputter texture is applied to the surface of the hub.  
         [0016]      FIG. 9  is a detail view of a portion of the roller guide of  FIG. 8  showing the texture in more detail.  
         [0017]      FIG. 10  is an elevation view of a roller tape guide constructed according to another embodiment in which a laser texture is applied to the surface of the hub.  
         [0018]      FIG. 11  is a detail view of a portion of the roller guide of  FIG. 10  showing the texture in more detail.  
         [0019]      FIG. 12  is an elevation view of a roller tape guide constructed according to another embodiment in which a machined texture is applied to the surface of the hub.  
         [0020]      FIG. 13  is a detail view of a portion of the roller guide of  FIG. 12  showing the texture in more detail. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     As noted above,  FIG. 1  illustrates generally the configuration of a tape drive  10  typical of those used with single spool tape cartridges. Referring again to  FIG. 1 , a magnetic tape  12  is wound on a single supply spool  14  in tape cartridge  16 . Tape cartridge  16  is inserted into tape drive  10  for read and write operations. Tape  12  passes around a first tape guide  18 , over a magnetic read/write head  20 , around a second tape guide  22  to a take up spool  24 . Head  20  is mounted to a carriage and actuator assembly  26  that positions head  20  over the desired track or tracks on tape  12 . Head  20  engages tape  12  as tape  12  moves across the face of head  20  to record data on tape  12  and to read data from tape  12 .  
         [0022]     A tape guide constructed according to one embodiment of the present invention is shown in  FIGS. 4-5 . Referring to  FIGS. 4-5 , each roller guide  38  includes disc shaped flanges  40  and an annular hub  42 . Tape  12  rides on the outer surface  44  of hub  42 . Each flange  40  extends radially past outer surface  44  of hub  42 . When roller guide  38  is installed in tape drive  10 , for example as guides  18  and  22  in  FIG. 1 , hub  40  rotates on a fixed pin or axle that extends from the tape drive chassis or other suitable support through the center of hub  40 . Ball bearings or like are preferred to reduce friction and minimize wear between hub  40  and the pin or axle on which it turns. Flanges  40  and hub  42  may be machined as a single integral part or as separate parts bonded together  
         [0023]     A circumferential texture  46  is applied to the outer surface  44  of hub  42  to bleed air from between tape  12  and hub surface  44 . Circumferential texture  46  includes a series of shallow grooves or scratches similar to that achieved by placing sand paper with the desired grit size against a turning roller with no lateral motion.  
         [0024]     In an alternative embodiment shown in  FIGS. 6-7 , a cross hatched texture  48  is used. Cross hatched texture  48  includes an array of crossing scratches similar to that achieved by moving sand paper back and forth over a slowly turning roller. In the embodiment shown in  FIGS. 8-9 , a sputter texture  50  is applied to hub surface  44 . Sputter texture  50  includes an array of small bumps similar to that achieved by sputter depositing a texture material on to the guide. In  FIGS. 10-11 , a laser texture  52  is applied to hub surface  44 . Laser texture  52  includes an array of surface irregularities produced by melting and recrystallizing tiny areas on hub surface  44  similar to that achieved with techniques used to produce laser textured recording disks. In  FIGS. 12-13 , a machined texture  54  is applied to hub surface  44 . Machined texture  54  includes a series of ridges or knobs similar to a knurled surface formed at the correct scale to match the desired surface roughness.  
         [0025]     In each of the above described embodiments, the surface texture is designed to allow some contact of the tape with the guide by reducing the air bearing. A texture with a surface roughness exceeding the expected flying height of tape  16  above hub surface  44  is necessary to allow some tape to guide contact. For example, for ½ inch type data storage tapes that have a nominal tape width of 12.65 mm moving at about 4.1 m/s with 1N tension, the tape “flies” on an air bearing about 1.3 microns above the surface of the hub. Hence, for this type of tape and operating configuration, the surface roughness of texture  46 - 54  should be at least 1.3 microns. Although the roughness may be varied as necessary to allow optimum tape to guide contact to achieve the desired damping of lateral movement of the tape, it is expected that textures having a surface roughness of 1-3 microns will have an effect similar to the grooved surface described in the &#39;882 application but without any significant risk of distorting the tape.  
         [0026]     While the invention has been shown and described with reference to the surface textures shown in  FIGS. 4-13 , other suitable textures may be possible. It should be understood, therefore, that variations of and modifications to the textures shown and described may be made without departing from the spirit and scope of the invention which is defined in following claims.

Technology Classification (CPC): 6