Guide roller with magnet and bushing for stabilizing roller barrel for tape media

Abstract

A tape guide roller having a magnet and a bushing for stabilizing a roller barrel for a tape medium and a tape drive having the guide roller are provided. The tape guide roller has a roller barrel extending about a vertical axis. The tape medium passes across the roller barrel for guiding the tape medium along a tape path. A plurality of magnets positioned relative to the vertical axis provide an axial force for axially stabilizing the tape guide roller.

Description

[Technical Field]

[0001] 1. Field of the Invention A tape guide roller having a magnet and a bushing for stabilizing a roller barrel for a tape medium and a tape drive having the guide roller are provided.

[0002] 2. Description of Related Technology In magnetic storage systems, data is read from and written to magnetic recording media using magnetic read and write elements formed on a tape head. Data is written to the magnetic recording media by moving a magnetic recording transducer over the media to the location where the data is to be stored. The magnetic recording transducer generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning a magnetic read element and then sensing the magnetic field of the magnetic media. The read and write operations may be independently synchronized with the movement of the media to ensure that data can be read from and written to the desired location on the media.

[0003] A tape drive includes a tape guide roller positioned relative to the read / write tape head for guiding and positioning the tape media as it passes over the read / write tape head. The tape guide roller includes a ball bearing within a roller barrel over which the tape media passes. The tape guide roller is one of the major contributors to mechanical disturbances in a tape drive, which increases the standard deviation of the position error signal (PES), thereby resulting in increased read and write errors by the tape head. One technique for reducing the mechanical disturbances introduced by the tape guide roller is to use an air-bearing roller, which requires pressurized air to function.

[0004] Low mechanical disturbance tape guide rollers are further required in tape paths used for servo formatting, i.e., for writing servo patterns to the tape during tape manufacturing. Mechanical disturbances caused by the tape guide rollers during servo formatting lead to disturbances being written into the servo patterns of the tape media / cartridge, which further degrade the standard deviation of the position error signal (PES) during tape drive read and write operations.

[0005] There is a need in the art for improved techniques for mounting tape guide rollers to reduce mechanical disturbances in tape drives. Summary of the Invention

[0006] A tape guide roller having a magnet and a bushing for stabilizing a roller barrel for a tape medium and a tape drive having the guide roller are provided. The tape guide roller has a roller barrel extending about a vertical axis. The tape medium passes across the roller barrel for guiding the tape medium along a tape path. A plurality of magnets positioned relative to the vertical axis provide an axial force for axially stabilizing the tape guide roller. [Brief explanation of the drawings]

[0007] [Figure 1] 1 illustrates one embodiment of a tape drive system in which embodiments may be implemented.

[0008] [Figure 2] 1 illustrates one embodiment in which the tape drive housing has been cut away to reveal the internal components of the tape drive.

[0009] [Figure 3] FIG. 1 illustrates one embodiment of a side view of a tape guide roller.

[0010] [Figure 4]4 illustrates one embodiment of a cross-sectional view of the tape guide roller of FIG. 3.

[0011] [Figure 5] 1 illustrates a cross-sectional view of one embodiment of a tape guide roller.

[0012] [Figure 6] 6 illustrates one embodiment of the roller barrel of the tape guide roller of FIG. 5.

[0013] [Figure 7] FIG. 6 shows a perspective view of the tape guide roller of FIG. 5.

[0014] [Figure 8] 6 illustrates a front view of one embodiment of the tape guide roller of FIG. 5.

[0015] [Figure 9] 10 illustrates an embodiment of the location of the magnet, bushing, and thrust bearing in the tape guide roller. [Figure 10] 10 illustrates an embodiment of the location of the magnet, bushing, and thrust bearing in the tape guide roller. [Figure 11] 10 illustrates an embodiment of the location of the magnet, bushing, and thrust bearing in the tape guide roller.

[0016] [Figure 12] 1 illustrates an embodiment of a thrust bearing. DETAILED DESCRIPTION OF THE INVENTION

[0017] Capacity gains in tape cartridges require improved track density scaling to read ever-increasingly denser tracks. The key to enabling track density scaling is improving the tape drive's track-following performance—reducing the standard deviation of the position error signal (sigma PES) in reading and writing data during track following. Track-following performance can be limited by mechanical disturbances in the tape drive. One of the primary contributors to these disturbances is the tape guide roller, which typically uses ball bearings and generates disturbances over a wide range of frequencies. These disturbances shift to higher frequencies as tape speeds increase, making it more difficult to achieve low-sigma PES at high tape speeds. Disturbances caused by the tape roller guide also vary significantly from roller to roller, most likely due to variations in the bearings themselves and the assembly process.

[0018] The described embodiments provide an improved technology for tape guide roller components, placing passive magnetic bearings on the tape guide roller to provide axial stability of the roller in combination with bushings for axels extending through the roller barrel to provide radial stability. Further embodiments may utilize thrust bearings positioned below the axels extending through the roller barrel. It has been found that utilizing some combination of magnet, bushing, and thrust bearing components improves track-following performance and provides lower sigma PES than has been achieved with ball-bearing rollers. Furthermore, the use of magnets, bushings, and / or thrust bearings has been found to have track-following performance comparable to tape guide rollers using air-bearing rollers, which are substantially more expensive to manufacture than the described embodiments of magnetic bearings, bushings, and / or thrust bearings.

[0019] In one embodiment, the tape guide roller is implemented using a passive magnetic bearing (PMB) combined with a thrust bearing. In a further embodiment, the tape guide roller is implemented with a passive magnetic bearing combined with a bushing that may include synthetic sapphire / ruby / corundum and a thrust bearing. The described embodiments provide improved track-following performance over current ball-bearing rollers and with a performance profile comparable to that achieved by air-bearing tape guides. However, the described embodiments can be manufactured at a much lower cost than air-bearing rollers.

[0020] 1 illustrates one embodiment of a tape drive 100 for reading and writing to a magnetic tape 102 of a magnetic tape cartridge 104. The magnetic tape cartridge 104 comprises a length of magnetic tape 102 wound on one or two reels 106, 108. By way of example, the magnetic tape cartridge 102 may comprise a single reel tape, such as that conforming to the Linear Tape Open (LTO) format. An example of a tape drive 100 is the International Business Machines Corporation TS1160 tape drive. Other implementations of the tape cartridge 102 and tape drive, such as LTO-type tape drives, may also be used.

[0021] The tape drive 100 may further include one or more controllers 110 for operating the tape drive 100 according to commands received from a host system 112 at an interface 114. The controller 110 includes logic and / or one or more microprocessors, along with memory for storing information and program information for operating the microprocessors. The tape drive 100 may comprise a standalone unit or may comprise part of a tape library or other subsystem. The tape drive 100 may be coupled to the host system 112 directly, through a library, or over a network, and may utilize a Small Computer Systems Interface (SCSI), a Fiber Optic Channel interface, or the like at the interface 114.

[0022] The tape cartridge 104 may be inserted into the tape drive 100 and loaded by a mechanism in the tape drive 100, causing one or more read and / or write elements on the tape head 118 to read and / or write information in the form of signals from the magnetic tape 104 as the tape is moved longitudinally by one or more motors 120, which rotate the reels 106, 108. Tape guide rollers 130 guide the tape 104 across the tape head 118 to stabilize the positioning of the tape 104 relative to the head 118 and reduce position error signals (PES). Magnetic tape typically includes multiple parallel tracks or groups of tracks. In some formats, such as the LTO format described above, the tracks are arranged in a serpentine, back-and-forth, wrap pattern, as known to those skilled in the art.

[0023] The recording system may include a servo control system 122 for electronically switching to different sets of read and / or write elements on the tape head 118 and / or for seeking on the tape 102 and moving the tape head 118 laterally to position the read and write elements at and track the desired wrap or wraps. The servo control system 122 may also control the operation of the motor 120 through a motor driver 124 and in response to commands from the controller 110.

[0024] The controller 110 also utilizes a buffer 126 and a recording channel 128 to provide a data flow and formatter for data to be read from and written to tape. The controller 110 may contain program code in a memory device that is loaded into a processor and executed to perform the operations of the tape drive. Alternatively, some or all of the functionality of the controller 110 may be implemented as microcode or firmware in a hardware device within the tape drive 100, such as an Application Specific Integrated Circuit (ASIC). The buffer 126 may comprise any suitable volatile or non-volatile memory device known in the art.

[0025] 2 illustrates one embodiment of a tape drive 200 showing the internal components within a cutout 201 of a tape drive housing 202. The tape drive 200 includes a housing 202, a tape cartridge 204 inserted into an opening 206 in the tape drive 200. The cartridge includes a supply reel 208 having tape media accessed by a take-up reel 210, which feeds the tape media 212 over tape guide rollers 214a, 214b, 214c, 214d to guide the tape 212 over a tape head 216 for reading from and writing to the tape media 212.

[0026] FIG. 3 illustrates one embodiment of a tape guide roller 300, such as one of guide rollers 214a, 214b, 214c, and 214d of FIG. 2 and guide roller 130 of FIG. 1. Tape guide roller 300 has a housing 301 and includes an axle 302 or shaft extending along a vertical axis extending through the center of roller barrel 304. Housing 301 is shaped to expose the entire surface of roller barrel 304 over which tape media 212 passes. Roller barrel 304 forms a grooved surface 306 over which tape media 212 passes. Grooved surface 306 improves traction between tape media 212 and roller barrel 304. Groove 306 may include ridges that form a spiral across roller barrel 304 or may be parallel.

[0027] FIG. 4 shows a cross-sectional view of the tape guide roller 300 of FIG. 3 taken along vertical cross section 310 in FIG. 3. Inside the roller barrel 304 are two opposing pairs of magnets: upper ring magnets 312a, 314a and two opposing lower ring magnets 312b, 314b. Between each pair of magnets 312a, 314a and 312b, 314b are open spaces 320a, 320b, respectively. Each pair of opposing magnets 312a, 314a and 312b, 314b may have opposite polarities. In an alternative embodiment, each pair of magnets 312a, 314a and 312b, 314b may form concentric rings. The ring magnets 312a, 314a and 312b, 314b may comprise axial-radial passive magnetic bearings. The magnets 312a, 312b, 314a, 314b provide axial stability for the axel 302 and roller barrel 304 to reduce position error signals (PES).

[0028] Each pair of opposing magnets includes an outer magnet 312a, 312b and an inner magnet 314a, 314b. The outer magnets 312a, 312b are mounted to outer support structures 316a, 316b, respectively. The inner magnets 314a, 314b are mounted to inner support structures 317a, 317b, respectively. The inner support structures 317a, 317b are attached to the axel 302 and barrel 304, connecting the axel 302 to the barrel 304. When the axel 302, to which the barrel 304 is fixed, rotates, the barrel 304 rotates. The rotating axel rotates the inner magnets 314a, 314b.

[0029] Outer magnets 312a, 312b are fixed to outer support structures 316a, 316b and may not rotate relative to axel 302 and barrel 304. Inner magnets 314a, 314b rotate relative to outer magnets 312a, 312b, respectively, when axel 302 rotates. Outer magnets 312a, 312b are fixed to outer support structures 316a, 316b, respectively, which are not connected to axel 302, and may not rotate.

[0030] The upper end of axel 302 extends through upper bushing 318a and is supported by upper bushing support 319. Lower bushing 318b may be fixed to the structure. Both bushings 318a, 318b may be non-rotating and may comprise synthetic sapphire, synthetic ruby, corundum, or other materials with high hardness, low friction and wear, and a very smooth surface that can be achieved by polishing. A lubricant may be applied between axel 302 and bushings 318a, 318b.

[0031] FIG. 5 provides a cross-sectional view of a further embodiment of a guide roller 500 having a housing 501, an interior space 502 for an axel (not shown), a roller barrel 504, an upper bushing 506a, and a lower bushing 506b (through which the axel extends into the interior space 502). There is also a pair of opposing upper 510a, 510b ring passive magnetic bearings and a pair of opposing lower 512a, 512b ring passive magnetic bearings. In FIG. 5, the upper magnets 510a, 510b are positioned above the upper end of the roller barrel 504 relative to the vertical axis, and the lower magnets 512a, 512b are positioned below the lower end of the roller barrel 504. Each pair of opposing magnets includes an outer magnet 510a, 512b and an inner magnet 510b, 512a. The outer magnets 510a, 512b are fixed to the roller housing / outer support structure (located above and below the outer magnets 510a, 512b, respectively) and may not rotate relative to the axel and barrel 504 located in the inner space 502. The inner magnets 510b, 512a are attached to an axel (not shown) within the inner space 502 and barrel 504. The inner magnets 510b, 512a rotate relative to the outer magnets 510a, 512b, respectively, when the axel within the inner space 502 and barrel 504 rotates. Distances shown between components in the figures are in millimeters (mm).

[0032] 6 shows an embodiment in which the grooves in roller barrel 504 have spaced ridges, which may be parallel or spiral. A close-up 520 shows the ridges 522 that form the grooves in barrel 504. In one embodiment, grooves 522 are spaced apart at a distance of 0.05 mm, and roller barrel 500 has a diameter of 20 mm, where distances in the figure are in millimeters (mm).

[0033] 7 provides a perspective view of the guide roller 500 of FIG. 5 with the housing 601 shown transparent and the opening 603 exposing the roller barrel 604, upper bushing 606, and upper 610a, 610b and lower 612a, 612b ring passive magnetic bearings. The opening 603 in the housing 601 exposes a large surface area of ​​the roller barrel 604 for participation in the passage of tape media.

[0034] FIG. 8 shows a front view of the guide roller 600 of FIGS. 5, 6, and 7 showing the housing 601, the roller barrel 604, the two upper magnets 610a, 610b, the two lower magnets 612a, 612b, the tip of the axel 602, and the opening 603 in the housing 601 that exposes the surface of the roller barrel 604 that engages the tape media.

[0035] Figure 9 shows one embodiment of the positioning of magnets within a tape guide roller 900 relative to an axel 902. There are two upper magnets 904a, 904b with opposite polarities, and two lower magnets 906a, 906b with opposite polarities, and bushings 908a, 908b, such as those arranged in Figures 3, 4, 5, 7, and 8.

[0036] FIG. 10 shows an alternative embodiment of magnet placement within a tape guide roller 1000 relative to an axel 1002. There is one set of magnets 1004a, 1004b with opposite polarity at the upper end of the tape guide roller 1000. Bushings 1008a and 1008b radially stabilize the axel 1002. To further stabilize the axel 1002, a thrust bearing 1010 may be positioned below the lower end of the axel 1002. The thrust bearing 1010, consisting of a hemisphere / sphere surrounding a flat surface, may comprise the same material as the bushings 1008a, 1008b, such as synthetic sapphire / ruby, or corundum, to engage the lower end of the axel 1002, or may be composed of a steel ball or tip on a brass or steel flat, or a steel shaft with a polished flat on a steel, (synthetic) sapphire, ruby, or corundum ball or hemisphere. The thrust bearings may be lubricated or non-lubricated. In a further embodiment, two pairs of axial magnets, e.g., passive magnetic bearings, as shown in Figure 9, may be present along with a thrust bearing at the lower end of the axel 1002, as shown in Figure 10. The thrust bearings 1010 provide axial stability for the axel 1002.

[0037] Further embodiments may vary in the placement and number of magnets and the polarity of the magnets arranged, and may optionally include a thrust bearing at the upper end of the axel. For example, Figure 11 shows an alternative magnet and thrust bearing configuration for a guide roller 1100 with an axel 1102 and an axial-radial passive bearing magnet with a stack of concentric ring magnets including five inner PBM magnet rings 1104 and four outer PBM magnet rings 1106, and a thrust bearing 1108. Magnets 1104 and 1106 have the same polarity.

[0038] 12 shows one embodiment of a thrust bearing 1200 that includes an inner ball 1202 constructed from a material such as synthetic sapphire, synthetic ruby, or corundum. The axle end contacts the ball portion 1202 of the thrust bearing 1200 and may fit through an opening in a bushing 1204 of the thrust bearing 1200.

[0039] The above-described embodiments utilizing magnets, bushings, and thrust bearings have been found to provide axial and radial stability, thereby substantially reducing read / write detection of position error signals (PES) during tape operation.

[0040] In the above embodiment, a magnet and bushing are used. In alternative embodiments, a magnet or bushing alone may be used to provide stability to reduce the position error signal.

[0041] The present invention may be a system, method, and / or computer program product implemented in the controller 110, including a guide roller, a tape drive, and a method for implementing the guide roller.

[0042] In the described embodiment, the variables i, n, etc., when used in conjunction with different elements, may refer to the same or different instances of that element.

[0043] The terms "an embodiment," "embodiment," "embodiments," "the embodiment," "the embodiment," "the embodiments," "one or more embodiments," "some embodiments," and "one embodiment" mean "one or more (but not all) embodiments of the present invention," unless expressly specified otherwise.

[0044] The terms "including," "comprising," "having," and variations thereof mean "including, but not limited to," unless expressly specified otherwise.

[0045] An enumerated list of elements does not imply that any or all of these elements are mutually exclusive, unless expressly specified otherwise.

[0046] The singular forms "a," "an," and "the" mean "one or more" unless expressly specified otherwise.

[0047] Devices that are in communication with each other are not necessarily in continuous communication with each other unless explicitly specified otherwise. In addition, devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries.

[0048] A description of an embodiment having several components in communication with each other does not imply that all such components are required. To the contrary, a variety of optional components are described to illustrate the wide range of possible embodiments of the present invention.

[0049] Where a single device or article is described herein, it will be readily apparent that more than one device / article (whether or not they cooperate) may be used in place of the single device / article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device / article may be used in place of more than one device or article, or that a different number of devices / articles may be used in place of the number of devices or programs shown. The functionality and / or features of a device may alternatively be embodied by one or more other devices not explicitly described as having such functionality / features. Thus, other embodiments of the present invention need not include the device itself.

[0050] The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto. The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Claims

1. a tape guide roller for guiding a tape medium to a read or write head for reading or writing from or to the tape medium, a roller barrel extending about a vertical axis, the tape medium passing across the roller barrel for guiding the tape medium to a tape path; and a plurality of magnets positioned relative to the vertical axis to provide an axial force for axially stabilizing the tape guide roller; A tape guide roller comprising:

2. The magnet has at least one pair of opposing rings of passive magnetic bearings extending about the vertical axis and having opposite polarities, and the tape guide roller an axle extending through the roller barrel 2. The tape guide roller of claim 1, further comprising: each pair of passive magnetic bearing rings spaced apart on said vertical axis by a distance.

3. The roller barrel has an upper end and a lower end relative to the vertical axis, and the magnet is a first pair of magnets positioned along the vertical axis closer to the upper end of the roller barrel than to the lower end; and a second pair of magnets positioned along the vertical axis closer to the lower end of the roller barrel than to the upper end; The tape guide roller of claim 1 , wherein

4. 4. The tape guide roller of claim 3, wherein the first pair of magnets is positioned above the upper end of the roller barrel on the vertical axis and the second pair of magnets is positioned below the lower end of the roller barrel on the vertical axis.

5. an axel extending along the vertical axis through the roller barrel and the first pair of magnets and the second pair of magnets, the axel having upper and lower ends relative to the vertical axis; a first bushing positioned above the first pair of magnets on the vertical axis, wherein the axle extends through the first bushing; and a second bushing positioned below the second pair of magnets on the vertical axis, wherein the accelerator extends through the second bushing.

4. The tape guide roller of claim 3, further comprising: said first and second bushings radially stabilize said tape guide roller.

6. 6. The tape guide roller of claim 5, wherein the first and second bushings are constructed from a material that is a member of a set of materials that includes synthetic sapphire, synthetic ruby, and corundum.

7. an axel extending through the roller barrel along the vertical axis; a first inner support structure coupled to the shaft and the roller barrel; a first inner magnet coupled to the first inner support structure; a first outer support structure; a first outer magnet coupled to the first outer support structure; a second inner support structure coupled to the shaft and the roller barrel; a second inner magnet coupled to the second inner support structure; a second outer support structure; and a second outer magnet coupled to the second outer support structure; 2. The tape guide roller of claim 1, further comprising: said first and second inner support structures located along said vertical axis between said first and second outer support structures.

8. the roller barrel has an upper end and a lower end relative to the vertical axis, the magnet is positioned closer to the upper end of the roller barrel than to the lower end of the roller barrel, and the tape guide roller is an axel extending through the roller barrel and the magnet along the vertical axis, the axel having upper and lower ends relative to the vertical axis; and a thrust bearing positioned below the lower end of the axel on the vertical axis and in contact with the lower end of the axel The tape guide roller of claim 1 further comprising:

9. a first bushing positioned above the magnet along the vertical axis, wherein the axle extends through the first bushing; and a second bushing positioned along the vertical axis between the magnet and the thrust bearing; The tape guide roller of claim 8 further comprising:

10. 1. A tape drive for performing read or write operations on a tape medium, comprising: a read or write head for reading from or writing to said tape medium; a tape guide roller for guiding the tape medium relative to the read or write head; The tape guide roller is a roller barrel extending about a vertical axis, the tape medium passing across the roller barrel for guiding the tape medium to a tape path; and a plurality of magnets positioned relative to the vertical axis to provide an axial force for axially stabilizing the tape guide roller; 1. A tape drive comprising:

11. The magnet includes at least one pair of opposing rings of passive magnetic bearings having opposite polarities extending about the vertical axis, and the tape guide roller an axle extending through the roller barrel 11. The tape drive of claim 10, further comprising: each pair of rings of the passive magnetic bearings being spaced apart a distance on the vertical axis.

12. The roller barrel includes an upper end and a lower end relative to the vertical axis, and the magnet is a first pair of magnets positioned along the vertical axis closer to the upper end of the roller barrel than to the lower end; and a second pair of magnets positioned along the vertical axis closer to the lower end of the roller barrel than to the upper end; 11. The tape drive of claim 10, comprising:

13. The tape guide roller an axel extending along the vertical axis through the roller barrel and the first pair of magnets and the second pair of magnets, the axel having upper and lower ends relative to the vertical axis; a first bushing positioned above the first pair of magnets on the vertical axis, wherein the axle extends through the first bushing; and a second bushing positioned below the second pair of magnets on the vertical axis, wherein the accelerator extends through the second bushing.

13. The tape drive of claim 12, further comprising: the first and second bushings radially stabilize the tape guide roller.

14. 14. The tape drive of claim 13, wherein the first and second bushings are constructed from a material that is a member of a set of materials that includes synthetic sapphire, synthetic ruby, and corundum.

15. The tape guide roller an axel extending through the roller barrel along the vertical axis; a first inner support structure coupled to the shaft and the roller barrel; a first inner magnet coupled to the first inner support structure; a first outer support structure; a first outer magnet coupled to the first outer support structure; a second inner support structure coupled to the shaft and the roller barrel; a second inner magnet coupled to the second inner support structure; a second outer support structure; and a second outer magnet coupled to the second outer support structure; 11. The tape drive of claim 10, further comprising: a first support structure and a second support structure, the first and second inner support structures being located along the vertical axis between the first and second outer support structures.

16. the roller barrel includes an upper end and a lower end relative to the vertical axis, the magnet is positioned closer to the upper end of the roller barrel than to the lower end of the roller barrel, and the tape guide roller comprises: an axel extending through the roller barrel and the magnet along the vertical axis, the axel including upper and lower ends relative to the vertical axis; and a thrust bearing positioned below the lower end of the axel on the vertical axis and in contact with the lower end of the axel 11. The tape drive of claim 10, further comprising:

17. a tape guide roller for guiding a tape medium to a read or write head for reading or writing from or to the tape medium, a housing, a roller barrel extending about a vertical axis, the tape medium passing across the roller barrel for guiding the tape medium to a tape path; and a plurality of magnets positioned relative to the vertical axis to provide an axial force for axially stabilizing the tape guide roller; and an opening in the housing exposing a surface of the roller barrel for engaging the tape medium; The tape guide roller has

18. The magnet includes at least one pair of opposing rings of passive magnetic bearings having opposite polarities extending about the vertical axis, and the tape guide roller an axle extending through the roller barrel 20. The tape guide roller of claim 17, further comprising: each pair of passive magnetic bearing rings spaced apart on the vertical axis by a distance.

19. The roller barrel includes an upper end and a lower end relative to the vertical axis, and the magnet is a first pair of magnets positioned along the vertical axis closer to the upper end of the roller barrel than to the lower end; and a second pair of magnets positioned along the vertical axis closer to the lower end of the roller barrel than to the upper end; 20. The tape guide roller of claim 17, comprising:

20. an axel extending along the vertical axis through the roller barrel and the first pair of magnets and the second pair of magnets, the axel having upper and lower ends relative to the vertical axis; a first bushing positioned above the first pair of magnets on the vertical axis, wherein the axle extends through the first bushing; and a second bushing positioned below the second pair of magnets on the vertical axis, wherein the accelerator extends through the second bushing.

20. The tape guide roller of claim 19, further comprising: the first and second bushings radially stabilize the tape guide roller.

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