Abstract:
A tape path having an implicit squeeze bearing. In such a tape path, one end of the tape is wound upon a first reel, the tape extends around one or more guides, briefly comes into close proximity with itself at the outer wrap of the tape wound upon the first reel, and is wound upon a second reel. By coming within close proximity with itself, the tape forms an implicit squeeze bearing which damps tape tension variation, inhibits the transmission of vibrations from one reel to the other, and eliminates the entrapment of entrained air without any additional rollers or other components. The tape path is suitable for use in a peripheral storage device, such as a magnetic tape drive, and is compatible with a variety of tape cartridge configurations.

Description:
This application is a continuation of application Ser. No. 07/689,396, filed Apr. 22, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a tape path which minimizes the components required to control tape tension, vibrations, and winding disturbances. More particularly, the invention is a tape path having an implicit squeeze bearing. 
     2. Description of the Related Art 
     Magnetic tape drives typically use a reel-to-reel tape transport design, or &#34;tape path&#34;, for controllably advancing the tape past an adjacent tape head. The tape head includes one or more magnetic transducers for writing to and/or reading from the tape. The tape is wound upon 2 reels, one reel at each end. The tape is advanced by rotation of such reels. One problem in reel-to-reel tape paths is tape velocity and tension variation. Variations in tape velocity and tension cause vibration. Tape vibration can be characterized according to the propagation velocity of the vibratory mode, the length and geometry of the vibration transmission path, and the terminating conditions of the vibration transmission path. Tape vibration modes include shear waves, longitudinal waves, out-of-plane resonant bands, and other path resonances. Such vibration in the tape can disrupt the head-tape interface, and thus effects the overall operation of the drive. PG,4 
     Existing tape drives control tape tension and vibration in several ways. The IBM 3420 Magnetic Tape Drive and the IBM 3850 Mass Storage Subsystem employ a combination of rollers and vacuum columns for such a purpose. For example, see U.S. Pat. No. 3,912,144. The IBM 3480/3490 Magnetic Tape Subsystem uses a tape tension transducer in a closed loop tension servo control configuration, as disclosed in U.S. Pat. Nos. 4,406,906 and 4,389,600. These and other drives may also use compliant members or tension arms to control tape tension and dampen vibration. U.S. Pat. Nos. 4,456,160, 4,182,472, 3,806,574, 3,175,780, and 3,004,728 disclose various aspects of tape control, such as guiding rollers and flanges. All of the aforementioned controls use devices ancillary to the reels and tape, which adds both expense and complexity to the tape path. 
     Another problem in reel-to-reel tape paths is air which is entrained in the windings of tape as it is wound upon a reel. The entrained air is trapped into pockets and can result in abrupt tape slippage and changes in tape tension which not only disrupt the head-tape interface, but can also result in catastrophic damage to the tape. The consequences of entrained air depend upon such parameters as the material properties of the tape, the design of the reels and guides used in the tape path, and the winding rate and geometry. Entrained air can be prevented by winding the tape in a vacuum, but such is expensive and inconvenient. U.S. Pat. No. 4,830,303, 4,576,344, and 3,405,884 disclose rollers which are used to control the entrainment of air. Again, rollers are ancillary to the reels and tape and are therefore undesirable. U.S. Pat. No. 3,967,789 also refers to the entrainment of air in a tape winding mechanism. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is the principal object of this invention to improve tape paths. 
     Another object of this invention is a tape path which minimizes the components required to damp tape tension variation and inhibit the transmission of tape vibration. 
     Still another object of this invention is a tape path which minimizes the components required to eliminate winding disturbances, such as air entrained into and trapped within the tape windings. 
     These and other objects of this invention are accomplished by a tape path having an implicit squeeze bearing. In such a tape path, one end of the tape is wound upon a first reel, the tape extends around one or more guides, briefly comes into close proximity with itself at the outer wrap of the tape wound upon the first reel, and is wound upon a second reel. By coming into close proximity with itself, the tape forms an implicit squeeze bearing which damps tape tension variation, inhibits the transmission of vibrations from one reel to the other, and reduces the entrapment of entrained air without any additional rollers or other components. Because vibration is minimized, additional components otherwise required to control tape tension are eliminated. The tape path is suitable for use in a peripheral storage device, such as a magnetic tape drive, and is compatible with a variety of tape cartridge configurations. 
     The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention, as illustrated in the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of a magnetic tape drive according to the invention. 
     FIG. 2 is a schematic diagram of a magnetic tape path, using the IBM 3480/3490 Magnetic Tape Cartridge, according to the invention. 
     FIG. 3 is an isometric view of a magnetic tape path, without the tape itself, according to FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now more particularly to the drawing, like numerals denote like features and structural elements in the various figures. The tape path of the invention will be described as embodied in a magnetic tape drive. Referring to FIG. 1, a schematic diagram of a magnetic tape drive 1 is shown. Drive 1 includes a tape path 2, which is that portion of drive 1 in contact with a magnetic recording tape 3. Tape 3 may be any flexible magnetic recording tape; the composition of the tape is not relevant to the subject invention. A suitable tape is disclosed in U.S. Pat. No. 4,467,411, hereby incorporated by reference. 
     Tape 3 is wound at one end upon a first tape reel 4 and wound at the other end upon a second tape reel 5. Reels 4 and 5 are mechanically driven to rotate in either direction, as required to position the desired portion of tape 3 in close proximity adjacent to a magnetic tape head 6. Head 6 includes one or more magnetic transducers capable of magnetically writing data to and/or reading data from tape 3. The type of head is not relevant to the subject invention, a suitable head s disclosed in U.S. Pat. No. 4,685,005, hereby incorporated by reference. 
     Data (including analog or digitally encoded audio, visual, or any computer related data) is recorded in one or more tracks on tape 3 using any available recording format. The position of tape 3 relative to head 6 is maintained by tape guides 7 and 8. The type of guides is not relevant to the subject invention, a suitable hydrostatic air bearing guide is disclosed in Garcia et al, Compliant Guide Assembly with High Wear Resistance Contact Pads, IBM Technical Disclosure Bulletin, Vol. 29, No. 5, October, 1986, pp. 2126-27, hereby incorporated by reference. 
     The operation of reels 4 and 5 and head 6 is managed by controller 9 to controllably write data to and/or read data from tape 3. The electrical and mechanical connections to controller 9, the operation of controller 9, and additional components in path 2 are not relevant to the invention. Sample information is available in U.S. Pat. Nos. 4,467,411, 4,406,425, and 4,389,600, all of which are hereby incorporated by reference. 
     Vibration and entrained air are controlled by a squeeze bearing 10. A squeeze bearing may take many forms, as disclosed for example in Watrous, Squeeze Bearing with Sleeve Member having Slit Corners, IBM Technical Disclosure Bulletin, Vol 27, No. 7A, December, 1984, pp. 3916-17 and Hendriks, Digital Tactile Sensor, IBM Technical Disclosure Bulletin, Vol. 27, No. 4A, September, 1984, p. 2191, but generally includes a thin layer of a gas (such as air) used to support a solid physical element. Here, squeeze bearing 10 is an &#34;implicit&#34; squeeze bearing in that it is formed by allowing tape 3 to come within close proximity of itself--no ancillary devices are used. For example, as tape 3 is wound from reel 5 to reel 4, the tape exits reel 5 where it comes within close proximity of the outer wrap of tape previously wound (further along its length) upon reel 4, before looping around guides 7 and 8 and being spooled upon reel 4. In the reverse direction, tape 3 exits reel 4, is looped around guides 8 and 7, comes within close proximity of the outer wrap of tape still wound upon reel 4, and is spooled upon reel 5. 
     In actual operation, squeeze bearing 10 does not allow tape 3 to contact itself. At normal operating velocities of tape 3, a thin film of air is formed between the two surfaces of the tape. Such an air bearing supports a portion of tape 3 (that portion entering or exiting reel 5). The two surfaces have identical velocities, thereby precluding wear of either surface. As used herein, the term &#34;squeeze bearing&#34; refers to the gas film between the surfaces of the tape, depending upon the velocity of the tape. When tape 3 is motionless or moving at low velocities, the squeeze bearing collapses and the tape actually contacts itself. In either condition, the tape applies a force to itself. The amount of force applied depends upon the winding rates, tensions, and geometries. The &#34;close proximity&#34; of the tape to itself refers to either condition. 
     Squeeze bearing 10 has several benefits. The squeeze bearing film acts so as to damp tape tension variation. The squeeze bearing region also acts to inhibit vibration from reel 5 from being transmitted along the tape to the area of head 6. The force applied to the outer wrap of tape 3 on reel 4 acts similar to a simple roller to exhaust the entrained air otherwise entrapped between the wound wraps of the tape on reel 4. The force determining parameters can be selected to control the air film thickness to within the range of surface asperity heights, thereby securing each sequential wrap of tape in place and preventing slippage or damage to the tape. Using typical 1/2 inch or 8 mm magnetic tape, a series of frequency response measurements made at tape velocities ranging from 1 to 5 meters per second and at 2.2 and 3.6 ounces tape tension indicated the squeeze bearing becomes effective in the 1 to 2 meters per second range. In addition, when the tape is motionless, reel 5 has little effect on tape tension. Finally, the short unsupported tape length between the squeeze bearing and reel 5 assists in stacking tape on reel 5. 
     Typical reel-to-reel tape paths wind the tape on each reel with the recording side (the side on which data is recorded and therefore the side facing the transducing head) of the tape facing in toward the center of the respective reel. The tape drive shown in FIG. 1 is configured such that the recording side of the tape on one reel faces in toward the center of the reel and that on the other reel faces away from the center of the reel. As shown, the recording side of the tape wound on reel 5 faces in toward the center of such reel and the recording side of the tape wound on reel 4 faces away from the center of such reel. If desired, such configuration could be changed. For example, the recording side of the tape wound on both reels could be made to face in toward the center of the respective reel. Such is accomplished by winding tape 3 in from the upper left side of reel 5 by rotating reel 5 counterclockwise (as shown, tape 3 winds into the reel from the upper right side by rotating reel 5 clockwise), and by adjusting the position of reel 5 so as to maintain the existence of squeeze bearing 10. The characteristics of some tapes and tape cartridges may provide environmental, shipping, and long term storage advantages to particular configurations, the details of which are not part of the subject invention. 
     Many reel-to-reel tape paths include the transducing head on the same side of the tape as the tape guides. In addition, one or both of the reels may be packaged into a tape cartridge. In the embodiment shown in FIG. 1, head 6 is on the opposite of side tape 3 from guides 7 and 8, and reels 4 and 5 and guides 7 and 8 can be packaged into a single tape cartridge so long as accommodation is made to provide air for the air bearing of guides 7 and 8. If non-air bearing guides are used, no such accommodation is required. Head 6 is not part of the cartridge, but is mounted in drive 1 and mated with tape 3 upon insertion of the cartridge. The configuration of the cartridge, including the location of the reels and guides, and the opening therein to allow for the mating of head 6 and tape 3, is not part of the subject invention except as specified herein. 
     Referring to FIG. 2, an embodiment is shown in which head 16 is located on the same side of tape 13 as guides 17 and 18 and the tape cartridge only includes reel 15. Reel 14, head 16, and guides 17 and 18 are not part of the cartridge, but are mounted in drive 11. Upon insertion of the cartridge into drive 11, the end of tape 13 is removed from reel 15 and threaded through the tape path and onto reel 14. A guide 20 may be used, if required, to adjust the position of tape 13 between reels 14 and 15. As shown, guide 20 is included in drive 11, but such may also be included in a tape cartridge with reel 5. The dashed line indicates the changing position of tape 13, including its outer most wrap about reels 14 and 15 as it is transferred between reels over time. The recording side of tape 13 always faces toward the center of reels 14 and 15. A suitable cartridge is an IBM 3480/3490 Magnetic Tape Cartridge, but ay compatible cartridge could be used as the cartridge configuration is not part of the subject invention except as specified herein. FIG. 3 shows the embodiment of FIG. 2 in more detail. Reel 15 has been removed for convenience, thereby revealing cartridge mounting hub 21. Tape 13 is thus also not shown. Head 16 is shown in mounting bracket 22. Further description of a tape cartridge and threading apparatus suitable for such an embodiment is shown in U.S. Pat. No. 4,334,656, hereby incorporated by reference. 
     While the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in detail may be made therein without departing from the spirit, scope, and teaching of the invention. For example, the invention has been described as practiced in a magnetic tape drive, but could be practiced in other applications, such as an optical tape drive, or in the path of any flexible web. Accordingly, the invention disclosed herein is to be limited only as specified in the following claims.