Burnish head design with multiple pads on side rail

A disc burnishing head includes an array of burnishing pads and a first and second side rail projecting from a bottom surface of a slider body. The side rails each have an inside surface facing the burnishing pads and an outside surface facing outward. The outside surface of at least the first side rail is serrated. The serrations define a plurality of teeth and notches on the outside surface of the first side rail for cutting, cleaning, and conditioning defects from the surface of a disc.

BACKGROUND

The present invention relates to disc drive systems and more particularly to a method and apparatus for burnishing asperities or irregularities from the surface of a disc.

In data processing systems, magnetic disc drives are used frequently as data storage devices. Data is written onto a rotating magnetic disc by an adjacent read-write head for later retrieval by the same head. The read-write head is located on a slider body, which is mounted to one end of a translatable arm that moves the head in a generally radial direction across the surface of the disc. As the disc spins, the read-write head flies above or below the surface of the disc, with the distance between the head and the surface of the disc depending on the rotational speed of the disc, the elastic force of the arm's suspension, and the shape and surface features of the slider body.

With the disc spinning at thousands of revolutions per minute (rpm), any unwanted interaction between the head and the disc surface can cause both short-term and long-term operational problems. This interaction can range from a thermal asperity to a full head crash. Consequences of contact or near-contact can include a failed read or write process, a temporary performance loss of the read-write head, a permanent defect on the disc surface, or total failure of the drive. These defects must be reduced or removed to provide sufficient clearance for the read-write head throughout the life of the product. Therefore, steps must be taken during the manufacturing process to flatten the disc surface as completely as possible, thereby improving product life and avoiding catastrophic head crashes. Typically, this is done by a burnish process after the disc media is fabricated.

During burnishing, the disc is rotated and the arm with the attached burnishing head is translated across the disc surface between an inner and outer diameter. The burnishing head is designed to fly close to the disc so as to physically contact defects protruding from the disc surface. The head is typically designed with burnishing pads and side rails on a contact surface projecting toward the disc to cut asperities and deflect loose particles as the disc rotates.

In combination with burnishing, a glide testing apparatus is also used to verify that the disc has been burnished sufficiently to meet quality and reliability requirements. The flying height of the glide head is typically lower than the operating height of the read-write head in the final product. The purpose of the lower flying height is to ensure removal of defects with the goal of improving quality and extending the useful life of the drive. A piezoelectric or thermal sensor or similar sensing means on the glide head is triggered each time that it encounters a defect on the surface. A control device electrically connected to the sensing means and the translator mechanism records the location of each defect in memory.

The distance between the disc and read-write head has necessarily decreased with advances in disc drive technology. The read-write head in modern disc drives flies nearly in contact with the disc at all times during normal operation. Therefore, to burnish each operative surface of the disc well below the design clearance of the read-write head, the burnishing methods and the burnishing head must also be improved to meet the increased demands of discs with higher data density.

SUMMARY

A burnishing head for burnishing and cleaning the surface of a disc includes a slider body having a top mounting surface, bottom surface, burnishing pads, and first and second side rails, which project from the bottom surface of the slider body. The side rails each have an inner surface and outer surface, with at least the first side rail having a serrated outer surface.

A disc burnishing apparatus includes a burnishing head, a rotation mechanism for rotating a disc, and a translation mechanism for sweeping the burnishing head across the surface of a disc as the disc is rotated. The burnishing head includes a slider body, an array of burnishing pads, and first and second side rails, at least one of which has a serrated outer surface.

DETAILED DESCRIPTION

A more efficient burnish process for data storage media such as magnetic discs can reduce the cost of manufacturing by decreasing the number of burnishing cycles necessary on a single machine to achieve the desired clearance. Alternatively or in tandem with a decreased number of cycles, cost savings may also be seen by reducing the number of machines necessary to maintain an adequate rate of production, thereby decreasing the required capital investment. The gains in burnishing efficiency and resulting reduction in clearance may also be leveraged by increasing the recording density of discs, which have the ultimate effect of increasing data storage capacity of disc drives. One method of improving the burnishing process is through the use of burnishing heads with improved cutting efficiency and loose particle deflection and retention.

FIG. 1Aschematically depicts disc burnishing system10, which performs a burnishing process on a surface of magnetic disc12. Burnishing system10includes disc12to be burnished by burnishing head20. Disc12is rotated around center14in direction16by means of rotation mechanism18. Adjacent to disc12, burnishing head20with serrated side rail22is mounted to translator arm24. Translator arm24comprises swing arm26and suspension system28. Swing arm26is mechanically connected at trailing end36to translation mechanism38. Swing arm26is operably connected at the opposite end to suspension system28. It should be noted that inFIG. 1A, head20and arm24have been magnified relative to disc12.

In this example of suspension system28, load beam30connects elastically to flexure32. Dimple34on load beam30protrudes toward flexure32, permitting head20to move with the topography of disc12. The elastic force of suspension system28counteracts the air pressure pushing burnishing head20away from disc12, resulting in burnishing head20flying at a substantially constant height over the surface. Data may be recorded on both the top and bottom surfaces of disc12, in which case a similar suspension and burnishing head may be provided below disc12and operated in tandem with suspension system28and burnishing head20to burnish the bottom surfaces. Other suspension systems may be substituted for suspension system28.

As disc12rotates in the direction indicated by arrow16, translation mechanism38moves translator arm24in an arc in the direction shown by arrow40. This achieves the desired effect of sweeping burnishing head20across the top or (bottom) surface of disc12between inner radius42and outer radius44. Arm24may be translated continuously during rotation of disc12or in a predetermined distance/time combination such that burnishing is performed in concentric regions of disc12.

FIG. 1Aalso illustrates the types of surface defects that need to be removed by the burnishing process. These defects include asperities46, loose particles48, and contaminants50.

FIG. 1BandFIG. 1Cdepict a side view of disc12, burnishing head20, and translator arm24shown inFIG. 1A. Burnishing head20comprises slider body52mounted to bottom mounting surface53of flexure32, and comprises several features including serrated side rails22and tapered leading edge64.

As seen inFIGS. 1A and 1B, air dragged by the spinning of disc12flows toward and under burnishing head20. Air flowing under side rails22first encounters tapered leading edges64, which are shaped to provide lift. The surfaces of side rails22proximate to disc12act as air bearing surfaces creating lift from the passing air, causing burnishing head20to fly at a substantially constant height over the surface of disc12. Burnishing head20effectively burnishes and cleans the surface of disc12by keeping this height as low as possible without damaging disc12. This allows the features projecting from surface54of burnishing head20to reduce or cut off asperities46, collect contaminants48, and deflect or collect loose particles50located on the surface of disc12.

FIG. 1Cdepicts an exploded view of some of the features of burnishing head20depicted inFIG. 1B. These magnified features include side rail22with serrated outer surface58. Serrated outer surface58with teeth60and notches62improve both the overall cutting and cleaning performance of burnishing head20compared to smooth or non-serrated side wall outer surfaces. Serrated outer surface58provides for increased surface area for reducing and cutting asperities46and more area to deflect and collect loose contaminants48and particles50from the surface of disc12. Serrated outer surface58can take a variety of forms, with teeth and notches of different shapes. Some examples are shown inFIGS. 2A-3C.

FIG. 2Adepicts a bottom perspective view of burnishing head20with rectangular serrations on outer surfaces58of both side rails22. Side rails22and a plurality of burnishing pads66project from surface54of burnishing head20.FIG. 2Adepicts a bottom perspective view of burnishing head20where serrated outer surfaces58define teeth60and rectangular notches62.FIG. 2Bdepicts a bottom perspective view of burnishing head20where serrated outer surfaces define teeth60and triangular notches62. Teeth60and notches62may also have shapes such as trapezoidal (as shown inFIG. 16) other polyhedral and irregular shapes.FIGS. 2A and 2Balso show burnishing pads66with rectangular and triangular cross sections projecting from surface54although other regular or irregular burnishing pad cross sections can also be used. InFIGS. 2A and 2B, side rails22and burnishing pads66have been magnified relative to the remainder of burnishing head20in order to illustrate some of the features and benefits of serrated outer surface58.

Serrated outer surfaces58shown inFIGS. 2A and 2Bprovide improved burnishing performance as a result of the additional cutting surface area provided by teeth60and notches62. Various surface defects on disc12will come into contact with one or more of these features during the burnishing process. The additional cutting surface areas of teeth60as currently disclosed result in more asperities46being removed per rotation of disc12compared to a burnishing head with straight sided (non-serrated) siderails. With serrated outer surface58, many asperities46can be reduced or cut off by teeth60before reaching burnishing pads66, thereby producing a flatter disc surface with fewer protrusions, thus reducing the potention number of cycles required to complete the burnishing process.

Performance of burnishing head20may be further enhanced by changing the angles at which teeth60and notches62project from side rails22and surface54. In the embodiments shown inFIGS. 2A and 2B, the walls72of notches62are perpendicular to surface54and angle θ equals 90° However, teeth60and notches62need not be symmetric, nor is it required that θ be 90° as shown. Teeth60and notches62may project obliquely from bottom surface54. For example, if θ is less than 90°, teeth60act like a scraper against the surface of disc12, cutting more asperities46. However, if θ is greater than 90°, teeth60act like a broom against the surface of disc12, dragging more particles along as disc12spins. Angles can be adjusted as necessary to meet manufacturing requirements.

Cutting performance can be adjusted by varying the shapes of teeth60and notches62. Changing these shapes alters the angle of attack of each wall of teeth60and notches62, which impacts the cutting performance.

The relative angle of attack of individual teeth60and notches62can also be manipulated by increasing or decreasing the overall angle α at which burnishing head20is mounted relative to translation arm24. Angle α is the angle formed between longitudinal axis68of burnishing head20and longitudinal axis70of translator arm24.FIGS. 2A and 2Bdepict angle α as being aligned, e.g. α=0°, however this angle can be adjusted by up to 45° in either direction to optimize performance of burnishing head20. Cutting surface area can be enhanced for a particular application by changing angle α to increase or decrease the approach angle of head20. In certain embodiments where α≠0°, burnishing head20is configured such that more defects on disc12strike serrated outer surface58first instead of leading edge or pads66. In some embodiments, such as the one illustrated inFIG. 2B, increased cutting surface area is achieved even when α=0° because of triangular teeth60and notches62and the circular motion of disc12.

The cutting performed by serrated outer surface58reduces the dependency on burnishing pads66. The limited surface area available on bottom surface54restricts the available cutting area of burnishing pads66. Serrated outer surface58leaves behind a lower density of asperities46after encountering teeth60and notches62on outer surface58. By the time that asperities46reach burnishing pads66on subsequent rotations of disc12, a higher percentage of remaining asperities46are already cut and overall surface smoothness is improved.

Not only is cutting performance enhanced by serrated side rails, deflection and accumulation of loose particles48and contaminants50(shown inFIG. 1A) is also improved. Similar to the enhanced cutting performance, improved cleaning is achieved due to the greater contact area on outer surface58and plurality of possible contact angles created by teeth60and notches62. Some loose particles48strike side rail22in a similar manner to asperities46. The plurality of contact angles and increased surface area on outer surface58creates more locations to strike particles48and impart enough force to deflect them off the surface of disc12. Removal of particles48is also improved from the presence of notches62.

Serrated outer surfaces58, provide notches62of various shapes at several locations to collect particles48and contaminants50. Notches62can be shaped to act like reservoirs collecting particles48and other contaminants50, preventing buildup in one location. This can allow burnishing head20to be used for a longer cycle time between cleaning. In addition, collecting these defects on outer surface58may allow better flying stability of burnishing head20.

FIGS. 3A-3Cdepict the interaction of various surface defects of disc12with features of the invention.FIG. 3Adepicts a bottom view of burnishing head20with rectangular teeth60and resulting notches62.FIG. 3Ais similar to the embodiment depicted inFIG. 2A.FIG. 3Bdepicts a bottom view of burnishing head20with triangular sawtooth-like teeth60and resulting notches62. The triangular serrations can be any form of triangle, including right, equilateral or isosceles.FIG. 3Bis similar to the embodiment depicted inFIG. 2B.FIG. 3Cdepicts a bottom view of burnishing head20with a combination of rectangular, triangular, and irregular teeth60, along with respective notches62. Teeth60and notches62can be a mix of regular and irregular shapes as depicted, or it can be wholly comprised of irregular shapes. The particular selection of teeth60and notches62can be targeted to best integrate the use of a burnishing head with serrated outer surfaces into the needs of a particular manufacturing process.

As shown inFIGS. 3A-3C, defects striking outer surface58are partially or completely cleared by teeth60and notches62. The use of serrated outer surfaces58on rails22increases the opportunities for reduction or removal of asperities46. Asperities have a chance of striking various edges of teeth60and notches62at a plurality of different angles instead of a single wall at a single angle. This cutting effect is depicted inFIGS. 3A-3Cfor three different embodiments of teeth60and notches62.

Similarly, particles48are also more likely to be deflected away or captured in notches62when compared to a straight outer edge. The greater surface area provided by serrated outer surfaces58also acts to deflect some particles48, while collecting others in notches62. Contaminants50also have more potential locations to be collected on outer surface58in the form of notches62, which provides enhanced cleaning capacity.

While burnishing pads66perform significant cutting tasks during burnishing, increased cutting efficiency and cleaning efficiency cannot be realistically achieved simply by increasing the number of burnishing pads66. Air must be free to pass in the voids between burnishing pads66or else the flying stability of burnishing head20is sacrificed. In each of the figures, burnishing pads66are arranged in a matrix pattern on the bottom of burnishing head20to balance cutting efficiency and flying stability of burnishing head20. Though pads66are depicted as diamond shapes in the drawings, burnishing pads66may be any single shape or combination of shapes depending on the application.

With serrated outer surfaces58of rails22, more defect cutting, deflecting of particles, and capturing of particles and contaminants occurs on outer surface58. As such, particles48and contaminants50are trapped or collected before they can become trapped under burnishing head20. Limiting the number of trapped particles between burnishing pads66and between burnishing pads66and side rails22maintains consistent air flow over the air bearing surfaces of side rails22. This results in a more consistent flying height, and in even more efficient cutting and cleaning. In addition, the enhanced cleaning capacity results in fewer loose particles, which minimizes possible damage to disc12. High speed contact with burnishing pads66or the air bearing surface of side rails22can result in embedding of particles48into the surface, causing permanent damage to disc12.

Table 1 below illustrates the improvement in burnishing efficiency achieved with burnishing heads with serrated side rails versus burnishing heads with non-serrated side rails.

TABLE 1Comparison of burnishing performed by serrated andnon-serrated side rails.Head TypeSerrated railsNon-serratedGlide Yield69%39%Mean Hard Hit Count/100 surfaces1.114.53Mean Soft Hit Count/100 surfaces2.1923.76Mean Glide Noise/100 surfaces0.4610.764
The data show a significant improvement in reducing defects by the burnishing head with serrated side rails, as can be seen by the increase in glide yield and the decrease in the various defects. Glide yield is a measure of discs passing a glide test after a defined burnishing process. The mean hard hit count per 100 surfaces is a measure of the average number of times that a glide head physically contacted an asperity during testing. The mean soft hit count per 100 surfaces is the average number of times that an asperity was high enough to affect the glide head but not high enough to make physical contact. The mean glide noise is the relative amount of background noise that the glide head measures over the entire disc surface. As shown in Table 1, burnishing heads having serrated side rails clearly show improved burnishing efficiency in all typical measurements over burnishing heads with non-serrated side rails.

Certain shapes and arrangements of teeth and notches on the side rails of burnishing head20will exhibit better surface cleaning, while other arrangements will exhibit better cutting efficiency. The needs of a particular burnishing application will determine the selection of the shape and arrangement of notches and teeth to balance cutting and cleaning requirements and optimize the overall disc manufacturing process. Several other factors that affect burnishing include variations in initial disc quality, disc rotation speed, disc material, and burnishing material, and angle α formed by burnishing head axis68and translation arm axis70. These factors may also be taken into account in the design of the serrated side rails for a particular burnishing application.

The relative proportion of each defect can also affect the choice of shapes used on outer surface58. Discs with more particles48and contaminants50are burnished better if outer surface58has larger notches62, which act to collect these defects. In contrast, larger teeth60with more cutting area will more effectively burnish discs with more asperities46. While complex shapes may increase both cutting and cleaning efficiency, the costs of fabricating such shapes on a micron or submicron scale may also increase.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention as claimed. The implementations described above and other implementations are within the scope of the following claims.