Abstract:
A data storage cartridge includes a length of magnetic tape wound on a pair of tape reels within a housing to define a tape path. A tape guide disposed along a portion of the tape path includes a top and bottom flange. Each flange is resilient so that it acts to resiliently guide an edge of the tape. This minimizes violent crashes of a tape edge against the tape guide. Each flange may have a plurality of spaced resilient finger guides for directly contacting the edges of the tape. The finger guides serve to independently exert a force on the edges of the tape, thereby guiding the tape.

Description:
TECHNICAL FIELD 
     This invention relates to guiding magnetic storage tape along a tape path, and more specifically to compliant-type tape guides. 
     BACKGROUND ART 
     Tape cartridges for tape carrying digital data on a number of tracks across a magnetic tape are well known. There are generally three types of such data storage cartridges. Single reel cartridges comprise a spool of tape which is provided to a user along with a leader block positioned at one end thereof. In operation, the user places the spool in a drive mechanism which functions to thread the tape for receipt by another reel. The tape is transported between the two reels and data is read and/or written. The drive mechanism is responsible for providing guiding of the tape as it passes by a head such as, for example, a transducer. The drive mechanism also functions to provide tape tension by, for example, servoing the reels as they change their diameters during the read/write process. 
     Dual reel data cartridges, also called “hub-driven” cartridges, include two or more spools or “hubs” integral to the cartridge. Placement of the hubs within the cartridge itself obviates the time and effort required for tape threading and, therefore, permits significantly faster access over conventional single reel cartridges. The internal placement of the hubs further permits the use of an external protective covering or shell which functions to protect the hubs and the tape from contaminants during both storage and use. In operation, respective drive motors engage the spools. In further contrast to the aforementioned, single reel cartridges, dual reel data cartridges also include tape guiding means for guiding the tape past the head or transducer. Typically, the guiding means comprises one or more rigid flanges such as fixed guides or pins. See, for example, U.S. Pat. No. 5,870,924 to Fahimi et al. which discloses a tape bearing surface usable as a front guide assembly. 
     Belt-driven data cartridges, like dual reel cartridges, incorporate the tape within the cartridge itself and include two or more spools or hubs. Unlike, dual reel cartridges, belt-driven data cartridges further include an elastic drive belt operative to engage the tape at the respective tape-spool peripheries and provide tape tension. More specifically, tape cartridges of this type include a cartridge shell that defines an enclosure, and a pair of tape reels supported within the enclosure. A length of magnetic tape extends along a tape path within the enclosure. Each end of the tape is wound onto one of the reels. Like dual reel cartridges, the tape moves past suitable guides or flanges and across an opening in an edge of the cartridge into which a read/write head or transducer protrudes to tension the tape and write or read data when the cartridge is inserted into a recording/reproducing machine. 
     Regardless of the type of data cartridge used, the process for reading and writing data remains substantially the same. That is, data is written across all or substantially all of each respective track. Data is read, however, from only a portion of each track. In this manner, allowances can be made for read errors resulting from shifts in the magnetic tape. As those skilled in the art will recognize, such shifts, called track misregistrations (TMRs) may be caused by numerous events, such as, for example, slamming of a tape edge against a fixed flange (reference edge), tolerance differentials between one or more tape guides and the data cartridge substrate, etc. Any one or more of these events may result in a TMR. 
     In prior art data cartridges where tracks were written linearly on magnetic tapes, a small number of relatively wide data tracks (10 or less) were used. Conventional methods for tape edge guiding were, therefore, generally sufficient. As long as the tape was maintained within a predetermined critical area, data could be written and read consistently. 
     Advances in tape manufacture, coupled with the desire to read and write more information on individual cartridges, however, has altered the control scenario dramatically. Presently, data cartridges have substantially more data tracks (100 or more), each of which is substantially narrower (micrometers in width) than prior art linear written tracks. As a result, much tighter control is necessary to prevent TMR events. 
     To ensure that the cartridge tapes are properly positioned so that each of the very narrow individual tracks having data are appropriately positioned as they cross the read/write head, it is necessary that the tapes be guided precisely along their paths of travel. Closed loop systems have, therefore, been used for positioning data storage cartridge tapes. Such servo systems incorporate servo tracks written on magnetic tapes which are followed by a tracking head. The servo tracking head operates to control the position of the head or transducer to ensure that it is properly aligned with the tape. As TMRs cause the tape to move, the servo tracking head causes the head to move in step thus maintaining the head within the critical read area of the tape. 
     Although servo systems have greatly addressed the problems associated with TMR events, they have created new control problems of their own. As indicated above, such servo systems function to sense and address TMRs by following movement of written servo tracks on the magnetic tapes. Conventional read/write heads, however, have limited bandwidth. Therefore, they are not capable of following very fast motions such as those which result from reflections (“slamming”) of the magnetic tape off of a fixed tape guide. As a result, “servo off track” events occur wherein the servo system is unable to properly align the head with the tape. As a result, the head must back up and again attempt to perform the read or write function. This “servo transient” event is undesirable as it results in unnecessary use of system resources and increases the time required for the read/write process. 
     To address servo transient errors, spring-loaded pads have been proposed for use as bottom flanges on each of the front guide assemblies. These flanges are typically comprised of thin foils which apply a light load (approximately 2 grams nominal per pad or 4 grams edge force) as the tape runs between the front guide assembly. 
     A dual reel data cartridge incorporating the above spring loaded pads is shown in FIG.  1  and designated generally by reference numeral  10 . Cartridge  10  defines an enclosure, not shown, in which a pair of reels  12  and  14  are supported for free rotation about substantially parallel axis. A length of magnetic tape  16  is moved along a tape path established by front guides  18  and  20 . The opposite ends of tape  16  are connected to reels  12  and  14 . Guides  18  and  20  each include pads  22  which, as indicated above, are thin foils which function to apply a light load on the bottom edge of tape  16  in order to register it against the respective top flanges  24  and  26  of guides  18  and  20 . 
     It has been found, however, that these “compliant guides” do not prevent off-track events due to rapid tape movement. Moreover, the high edge force required to address steering effects resulting from tolerance differentials between the hubs  12  and  14  and the base plate  28  results in excessive wear on the tape edge, particularly, the fixed edge, here top edge  30 . Furthermore, violent crashes of the tape edge against the fixed edge can damage the tape. 
     SUMMARY OF THE INVENTION 
     The present invention provides a data storage cartridge having an improved tape guide which overcomes the above-noted problems of durability, tape misregistration, servo off-track events, and servo transient events. 
     In carrying out the above object, there is provided a data storage cartridge including a cartridge housing. The storage cartridge further includes one or more (e.g., two) tape reels rotatably mountable within the housing. A length of magnetic recording tape is wound on the reel or reels such that a portion of the recording tape extends from one reel to the other along a tape path. The improved tape guide is disposed along a portion of the tape. The tape guide comprises a vertical guide wall to provide a surface for slidably engaging the tape as the tape is guided along the tape path portion. 
     The tape guide has upper (top) and lower (bottom) resilient reference flanges for supporting respective edges of the tape being guided. By having both flanges be resilient, instead of just one flange, violent crashes of the tape edge against a fixed flange, which might otherwise occur, are greatly reduced. In one embodiment, each of the flanges includes a plurality of spaced resilient finger guides affixable thereto for directly contacting the edges of the tape. Each finger guide is operative to independently exert a force on the edges of the tape. In a preferred embodiment, the finger guides extend from a flat sheet which may be semi-circular in shape or any other suitable shape. Each of the finger guides is operative to exert a gentle force on the tape edge which is preferably less than 1 gram and more preferably less than 0.5 grams, and most preferably, less than 0.2 grams per finger. The plurality of finger guides may include 2, 3, 5, 10, or 17 or more finger guides. In one embodiment, only one of the flanges has a plurality of finger guides. 
     The invention also includes a tape guide for guiding a length of magnetic data storage tape. The tape guide has top and bottom resilient reference flanges, which may include a plurality of spaced finger guides on at least one of the flanges for exerting a force on the edges of the tape. The tape guide may be present in a cartridge, in a drive, in a servowriter, etc. These and other objects, features, and advantages of the present invention will be more readily apparent with reference to the following drawings wherein like reference numerals correspond to like components. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective diagram of a prior art dual reel data cartridge incorporating a compliant front guide assembly; 
     FIGS. 2 and 3 are perspective diagrams of a dual reel data cartridge incorporating the tape guide of the present invention; 
     FIG. 4 is an exploded perspective view of the tape guide of the present invention; and 
     FIG. 5 is a perspective view of the guide fingers of the tape guide of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 2 and 3 of the drawings, a tape cartridge indicated generally at  32  is provided for carrying data. Like the prior art cartridge shown in FIG. 1, cartridge  32  defines an enclosure (not shown) in which a pair of reels  12  and  14  are supported for free rotation about spaced and substantially parallel axis. A length of magnetic tape  16  is moved along a tape path established by suitable guides as explained below. The opposite ends of tape  16  are connected to reels  12  and  14 . 
     The cartridge shown in FIGS. 2 and 3 is a dual reel cartridge also called a “hub-driven” cartridge. While dual reel cartridge  32  is shown for exemplary purposes, the tape guide of the present invention may be used in any suitable data cartridge including, without limitation, single reel cartridges and belt driven cartridges, as well as equipment such as tape drives, tape servo writers, etc., where it is desired to provide improved tape guidance. Cartridge  32  includes a base plate  28  made of aluminum, or other suitable material, and a cover (not shown) made of a clear or translucent polymer or other suitable material to form the tape cartridge enclosure. The cover is removably fastenable to base plate  28  with conventional snap fasteners (not shown). Screw bosses (not shown) may be provided as needed for attachment of parts to the base plate  28  and/or a suitable cover. 
     A path for the magnetic tape  16  is defined with respect to the reels  12  and  14  by the use of one or more tape guides  36  made according to the teachings of the present invention and explained herein. The guides  36  position the tape properly in the region where the tape is engaged with a transducer or read/write head. 
     Base plate  28  is a relatively rigid plate, generally made of aluminum or other suitable material to provide support. Tape guide  36  is held in place by any select one of a number of known fasteners. For example, screws may be mounted in apertures in the base plate  28  (not shown) and securely held in place in the base plate  28  at the desired locations. Alternatively, tape guide  36  may be mounted to base plate  28  by any suitable method such as, for example, ultrasonic welding, resistance welding, staking, etc. 
     Tape  16  is guided by tape guide  36  along a portion of its path of movement between reels  12  and  14 . Tape guide  36  has an upright guide wall  38  that has a surface generally perpendicular to the base plate  28  when installed. Tape guide  36  includes upper and lower flanges  40  and  42  defining respective reference support shoulders  44  and  46  to position the upper and lower edges of tape  16 . 
     According to the present invention, each of the upper and lower flanges  40  and  42  are resilient. In other words, tape guide  36  is a compliant tape guide where both the upper and lower flanges are resilient or compliant. This allows both flanges to independently maintain contact with both edges of the tape, thereby minimizing the likelihood of violent crashes between the edge of the tape opposite that which contacts a flexible flange and the respective flange. 
     Tape guide  36  may comprise a plurality of resilient finger guides  48  for exerting a force on respective top and bottom edges of tape  16 . Finger guides  48  are designed to directly contact the tape edges, in contrast to prior art guides which contact a foil or other unitary surface, which in turn contacts the tape edges. Thus, in the case of the prior art guides, because the springs contact a foil, the tape is guided not by the individual springs, but rather by the foil. According to the present invention, each finger guide  48  is operative to directly contact the tape edge to apply a force on the tape edge. This allows tape guide  36  to better guide tape  16 , thereby improving guiding while minimizing wear on the tape edges. 
     The force required to guide tape  16  without damage may vary with the application. In a preferred embodiment, a force of less than 1 gram per finger is sufficient. More preferably, the force per finger guide should be less than 0.5 grams, still more preferably less than 0.2 grams, and in certain circumstances, even less than 0.1 grams. There are at least 2 finger guides per flange, and more preferably at least 3. It is still more preferable to have at least 5 finger guides and, more preferably, more than 10. There may be as many as 17 or more finger guides, as shown in FIG.  5 . Preferably, each finger guide should act independently of the other finger guides. 
     Tape guide  36 , and in particular finger guides  48 , may be made from any suitable material including without limitation, plastic, ceramic, metal or any combination thereof in any suitable manner including extrusion, shearing, stamping, etching, forming, etc. In a preferred embodiment, however, finger guides  48  are made of stainless steel or other suitable metal in a stamping or etching process or any other suitable manner. If formed in a stamping process, it will be desirable to affix the finger guides with the rolled or “burr” edge facing away from the tape as the radius edge will be flatter. 
     As shown in FIGS. 3-5, in the preferred embodiment, finger guides  48  extend from a flat sheet which is substantially semi-circular in shape. However, it is recognized that any suitable shape may be used. Finger guides  48  may also be combined with or incorporated within other tape guides including without limitation, elongated tape guides, multi-piece tape guides or any other guide assembly used within a data cartridge, a servo writer, a drive mechanism or any other equipment where it is desired to provide tape edge guiding. 
     A portion of finger guides  48  may be affixable to tape guide  36  to form respective top and bottom flanges. Alternatively, finger guides  48  may be removably or permanently affixed to existing flanges. Any suitable attachment method may be used including without limitation screws  49  through plates  50  and  52  for attachment to base plate  28 . 
     Any number, size, length, width, or shape of finger guides may be used depending on the application. All other variables being the same, the narrower the individual finger guides  48 , the less edge force will be applied. Consequently, the thickness and/or rigidity of the fingers will need to be adjusted accordingly. Finger guides  48  may be the same thickness or one of the guides may be thicker to function as a reference edge. If the same or substantially the same thickness is used, adjustments will need to be made in the coding of the applicable drivers to determine the proper reference edge. Still further, the individual fingers  48  of each guide may have different lengths, widths, etc., depending on the desired edge force. 
     Finger guides  48  may also have various shaped pads  53  for contact with the respective edges of tape  16 . Although shown herein as rectangular, pads  53  may, for example, be round, oval, square, triangular, etc. The individual pads  53  may also have varying widths and sizes depending on the desired force to be applied and the resiliency desired for proper tape guidance. One or more finger guides  48  and/or pads  53  may also be coated, deposited, or formed with suitable inks, polymers, dyes, or other material to provide additional support or dampening or to protect the finger or tape edge during use. Finger guides  48  may also be individual wires. 
     Tape guide  36  need not have finger guides but it must have resilient flanges or shoulders for guiding both edges of the tape. While both flanges should be resilient, one flange may be less resilient than the other, in which case the less resilient flange can act as a “reference” flange for guiding the tape.