Abstract:
A tape drive with a tape guiding assembly guides tape past the read/write head along a tape path. First and second inner guide rollers are disposed along the tape path on opposite sides of the read/write head and adjacent to the read/write head. First and second outer guides are disposed along the tape path on opposite sides of the read/write head. The inner guides are positioned off-centered with respect to the nominal tape path, while the outer guides are centered on the nominal tape path. The inner guides are adjustable in height and in radial direction to adjust the off-center position of the inner guides, as well as the tape wrap and penetration of the read/write head into the tape.

Description:
RELATED APPLICATIONS 
   This application claims priority to provisional application 60/350,077, filed on Jan. 15, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to the field of tape drives, and more particularly, to a tape guiding assembly in a tape drive. 
   BACKGROUND OF THE INVENTION 
   In a tape drive, a tape is transported from a supply reel to a takeup reel along a tape path. Along the tape path, and between the reels, the tape is wrapped on a read/write head for recording and playback. In order to achieve very high track density data on a tape, lateral motion of the tape at the read/write head needs to be constrained. In other words, at the interface of the read/write head and the tape, it is undesirable to allow the tape to wander laterally from the desired tape path. 
   Another consideration in guiding the tape is the wrap angle and penetration of the read/write head. In order to achieve reliable recording and playback, the wrap angle and penetration at the read/write head needs to be properly aligned. 
   For addressing these problems, certain systems have used compliant tape guides to constrain the tape motion , but the compliant guides need to be very soft for thinner tapes, and resonance is difficult to eliminate. Other prior art systems use tapered or crowned rollers to control the tape motion, but the effects of these special shaped rollers become less efficient when thinner tape is used. 
   Other attempts at constraining the tape edges have used alternate edge guiding by fixed flanges. A concern with such solutions is the wearing of the tape edge by the fixed flanges. Another solution uses alternate edge guiding, but with flanged rollers. However, such an arrangement aligns two groups of rollers to two reference surfaces respectively.  
   SUMMARY OF THE INVENTION 
   There is a need for a system to guide tape in a tape drive that effectively constrains lateral motion of the tape at the read/write head without wearing the edges of the tape. There is also a need for a tape guide assembly that provides tape wrapping alignment in addition to the tape guiding function. 
   These and another needs are met by embodiments of the present invention, which provide a tape guiding assembly for a tape drive comprising a takeup reel that receives tape from a supply reel and means for constraining the motion of the tape. In certain embodiments of the invention, the means includes four guides that are serially positioned along a tape path between the takeup reel and a supply reel. The four guides, in these embodiments, include two outer guides and two inner guides that are symmetrically disposed along the tape path on opposite sides of a read/write head. The two outer guides are centered at a nominal tape path and the two inner guides are positioned off-centered from the nominal tape path. 
   With the present invention, alternate edge guiding is achieved without the definition of two reference surfaces for each roller. In certain embodiments, the guides are adjustable rollers that may be adjusted both in the vertical and radial directions. 
   The earlier stated needs are also met by embodiments of the present invention which provide a tape drive with a tape guiding assembly that guides tape past a read/write head along a tape path. The tape guiding assembly comprises first and second inner guides disposed along the tape path on opposites of the read/write head and adjacent to the read/write head. First and second outer guides are disposed along the tape path on opposite sides of the read/write head and further from the read/write head than the first and second inner guides. The first and second inner guides are positioned off-centered with respect to a nominal tape path and the first and second outer guides are centered on the nominal tape path. In certain embodiments of the present invention, the first and second outer guides are fixed in position while the first and second inner guides are adjustable in height to adjust off-center positioning of the inner guides with respect to the nominal tape path. In still further embodiments of the invention, the first and second inner guides of the tape drive are adjustable in radial direction to adjust tape wrap and penetration of the read/write head into the tape.  
   The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic depiction of the top view of a portion of a tape guide assembly constructed in accordance with embodiments of the present invention. 
       FIG. 2  is a side view of the tape guide assembly of  FIG. 1 , depicting exemplary roller positions relative to a nominal tape position. 
       FIG. 3  shows the tape guiding assembly of  FIG. 2 , with the tape guiding assembly constraining tape motion when the tape leaves the supply reel from a high position. 
       FIG. 4  is similar to  FIG. 3 , but depicts the constraining of the tape when the tape leaves the supply reel from a low position. 
       FIG. 5  is a top, perspective view of an adjustable guide roller constructed in accordance with embodiments of the present invention. 
       FIG. 6  is a bottom, perspective view of the adjustable guide roller of  FIG. 5 . 
       FIG. 7  is a perspective view of a portion of a tape drive constructed in accordance with embodiments of the present invention, particularly depicting the tape guiding assembly. 
       FIG. 8  is an exploded view of the adjustable roller assembly of the present invention. 
       FIG. 9  is a perspective view illustrating a tape guiding assembly with tape being guided. 
       FIG. 10  is a cross-section of an exemplary embodiment of a tool for adjusting the roller height and penetration of the guide roller assembly of  FIGS. 5 and 6 . 
       FIG. 11  is a schematic depiction, similar to  FIG. 2 , of a side view of an alternative embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention addresses problems related to the constraining of tape motion, and aligning tape wrapping and penetration of the read/write head of a tape drive.  The present invention achieves this by constraining the lateral motion of the tape and aligning the wrap angle and penetration of the read/write head through the use of four guides that implement alternate edge guiding of the tape. This alternate edge guiding is accomplished with rollers without the definition of two reference surfaces for each roller. The rollers can be adjusted in their off-center position with respect to a nominal tape path, as well as in the radial direction to adjust the tape guiding and tape wrapping alignment. 
     FIG. 1  depicts a schematic top view of the tape guiding assembly employed in the tape drive in accordance with embodiments of the present invention. The tape drive is indicated schematically as reference numeral  10 , and in  FIG. 1 , only portions of the tape guiding assembly  12  are depicted. 
   Magnetic tape  24  is guided between a supply reel  14  and a takeup reel  16 . The supply reel  14  is part of a tape cartridge, while the takeup reel  16  is permanently located within the tape drive  10 . 
   The tape guiding assembly  12  has four guides: two outer guides  18  and two inner guides  20 . The two outer guides  18  are fixed guides and do not adjust in either the vertical or radial directions. The two inner guides  20 , which are closer to the read/write head  22  than the two outer guides  18 , are adjustable in both the vertical and radial directions in certain embodiments of the present invention. In its top view, the direction of adjustability of the inner guides  20  in the radial direction is indicated by arrows  28 . This causes the inner guides  20  to be moved further into and out of the tape path  26 . The movement of the inner guides  20  in the radial direction causes an adjustment of a desired penetration of a tape  24  by the head  22 , as well as the wrap angles, and the symmetry of the tape wrapping at the read/write head  22 . 
     FIG. 2  depicts a schematic side view of the tape guiding assembly  12  in accordance with embodiments of the present invention. A nominal tape path  30  is depicted for transferring tape between the supply reel  14  and the takeup reel  16 . In this embodiment, the outer guides  18  and the inner guides  20  are all guide rollers. However, the outer guides  18  are considered to be fixed guides, while the inner guides  20  are formed as adjustable guide roller assemblies, and will be described in more detail later. 
   The outer guides  18  are centered at the nominal tape path  30 , providing a clearance of L 1  on each side (i.e., top and bottom) of the tape  24 . The outer guides  18  are not adjusted with respect to the nominal tape path  30 .  
   The inner guides  20  are adjustable in the directions indicated by arrows  32  vertically to clamp the tape  24  at the alternating edges. The adjustment is made to the inner guides  20  to clamp the tape at the alternating edges with an interference of L 2 . In the depicted embodiment of  FIG. 2 , each of the rollers of the inner guides  20  and the outer guides  18  have flanges. 
   Referring to  FIGS. 3 and 4 , it becomes apparent that in the tape moving direction  36 , when the tape  24  comes off the supply reel  14  in either a high position or a low position, the rollers forming the inner guides  20  and the outer guides  18  act to constrain the tape motion in a vertical direction. The contact edges  34  contact the tape  24  to constrain the tape motion. 
   Because the lateral motion of the tape  24  at the read/write head  22  has been constrained, a higher track density of data on the tape  24  can be achieved. The amount of interference L 2  depends upon the strength of the tape  24 . It is important for the tape edge not to be damaged, so that the height adjustment (i.e., the off-center positioning of the inner guides  20 ) is made to constrain the tape motion but not damage the tape edge. 
   In the embodiments of  FIGS. 3 and 4 , the inner guide  20  closer to the supply reel  14  is off-centered above the nominal tape path  30  while the inner guide  20  that is closer to the takeup reel  16  is off-centered below the nominal tape path  30 . In other embodiments of the invention, these positions are reversed so that, the inner guide  20  closer to the supply reel  14  is positioned off-centered below the nominal tape path  30 , and the inner guide  20  closer to the takeup reel  16  is positioned off-centered above the nominal tape path  30 . 
   In still other embodiments, both of the inner guides  20  are positioned off-centered above the nominal tape path  30 , and in other embodiments, both of the inner guides are off-centered below the nominal tape path  30 . 
   For applications where the tape is preferred to fly and slip through the guides, the inner guides  20  are provided with a smooth surface-finish. For applications where the tape is preferred not to fly over the guides, the inner guides  20  have a rough surface-finish, a porous surface-finish, or a grooved surface-finish. In a grooved surface-finish, helical grooves are preferred to prevent tape imprint. 
   An exemplary embodiment of an adjustable guide roller assembly  38  that may be used as the inner guides  20 , is depicted in  FIGS. 5 and 6 .  FIG. 5  shows a top,  perspective view of the adjustable guide roller assembly  38 . A guide roller  40 , having flanges  41  at its top and bottom axial extents, has a central opening  44  in which ball bearings  42  are provided. In preferred embodiments of the invention, two ball bearings  42  are provided, although only the top ball bearing  42  is depicted in  FIG. 5 . Within the central opening  44  of the guide roller  40 , an eccentric shaft  46  is mounted. A pre-load washer  48  is fixed to the shaft. A bearing pre-load spring  50  will pre-load both the ball bearings  42 . 
   A tapped hole  52  is provided in the top of the eccentric shaft  46 . The tapped hole  52  allows for adjustment of the positioning of the adjustable guide roller assembly  38 , as will be described later. 
     FIG. 6  depicts a bottom perspective view of the adjustable guide roller assembly  38 . The bottom of the eccentric shaft  46  can be seen. A shaft biasing washer  54  is provided and serves at least two functions. The shaft biasing washer  54  is a shoulder type washer, where the shoulder supports the lower ball bearing  42 , visible in  FIG. 6 . The other portion of the washer  54  acts as a seat for the eccentric shaft biasing spring  60 , (only seen in  FIG. 7 ). The lower portion of the eccentric shaft  46  rests in a precision hole of the base plate (not shown) of the tape guide  10 . 
     FIG. 7  depicts the adjustable guide roller assembly  38  mounted on the base plate  90 . A mounting plate  56  is supported by two posts  58  connected to the base plate  90 . 
   The bottom of the eccentric shaft  46  is guided into the precision hole of the base plate  90  and is biased in the upward direction using eccentric shaft biasing spring  60 . The eccentric shaft  46  rests against a height setting nut  62 . When the height setting nut  62  is rotated, the shaft  46  moves up or down, the shaft  46  moving by the same amount as the nut  62  since the shaft  46  is biased against the nut  62 . The attachment of the guide roller  40  to the eccentric shaft  46  causes the guide roller  40  to also move upwardly or downwardly with the shaft  46 . 
     FIG. 8  shows an exploded view of the mounting of the adjustable guide roller assembly  38 . A penetration setting clip  68  is provided with two wings  69  (one of which is illustrated) that are opposed to each other. The penetration setting clip  68  is secured to the eccentric shaft  46 . A penetration setting bracket  66  is provided that has slots  71  (one of which is illustrated) which mate with the two wings  69  of the penetration setting clip  68 . The penetration setting bracket  66  has four protrusions that are used to rotate the  penetration bracket  66 . Upon rotation of the penetration setting bracket  66 , the eccentric shaft  46  rotates since the penetration setting clip  68  is secured to the eccentric shaft  46 . Because the guide roller  40  is mounted on the eccentric portion of the shaft  46 , the guide roller  40  translates into and out of the plane of the tape  24 . 
     FIG. 9  shows tape drive  10  with tape  24  extending over a portion of the tape guiding assembly  12 . 
   An exemplary embodiment of a tool  70  to adjust the height of the adjustable guide roller assembly  38  and the penetration of the guide roller  40  into the tape  24  is depicted in  FIG. 10  in cross-section. The tool  70  includes an outer shell  80  with a hex tool nut end for interacting with the height setting nut  62 . Hence, the bottom of the outer shell  80  forms a hexagonal cross-section tool  72 . 
   An inner shell  76  is employed to adjust the wrap angle and penetration by setting the eccentricity of the guide roller  40 . A spring  78  biases the inner shell  76  with respect to the outer shell. A knob  84  is employed to manually change the wrap angle setting using an eccentric-set tool  74  at the end of the inner shell  76 . 
   A through-hole  82  through the inner shell  76  provides access for a screw into the tapped hole  52  in the eccentric shaft  46 . The screw  86  can be tightened from the top through the through-hole  82 . 
   In operation of the tool  70 , the operator engages the tool  70  to the adjustable guide roller  40 . The operator then holds the inner shell  76  and rotates the outer shell  80  to adjust the height of the guide roller  40 . The operator then holds the outer shell  80  and rotates the inner shell  76  while pushing it down to adjust the penetration of the guide roller  40 . Finally, the screw  64  is loaded from the top through the through-hole  82  to tighten the adjustable guide roller assembly  38 . 
   An alternative embodiment of the present invention, depicted in  FIG. 11 , provides tapered rollers  88  instead of flanged rollers. Tapers or fillets at the end of the rollers are used to guide the tape at the alternate edges. Such embodiments are especially desirable if the tape edge is subject to wear. In still further embodiments of the invention, fixed posts and flanges are employed instead of rollers. This embodiment is not depicted in the Figures, but is readily understood by one of ordinary skill in the art. Also, in other embodiments of the invention, rollers may be used that are not adjustable in height, but rather are fixed in the positions described (i.e., the outer guides being centered on the  nominal tape path, and the inner guides being off-centered with respect to the nominal tape path). 
   With the present invention, an advantageous tape guiding assembly for a tape drive is provided that allows alternate edge guiding by using rollers, without the definition of two reference surfaces. Further, the invention accomplishes both tape guiding and tape wrapping alignment by adjustment of two inner guide rollers near the read/write head in both vertical and radial directions. 
   Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.