Abstract:
A system for burnishing a disc includes a slider having burnish pads. The burnish pads are disposed on air bearing surface of the slider and extends therefrom. The burnish pad includes a burnish face which configured to burnish a surface of the disc and blow away burnished asperities.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of an earlier filed co-pending provisional application Ser. No. 60/075,007, filed Feb. 17, 1998, entitled “THERMAL BURNISH AIR BEARING CONFIGURATION—STREAM LINE PAD AAB.” 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to disc drive systems. More specifically, the present invention relates to an apparatus for burnishing asperities or surface irregularities on a disc surface. 
     In data processing systems, magnetic disc drives are often used as storage devices. In such devices, read/write heads which are located on a slider (or an air bearing) are used to write data on or read data from an adjacently rotating disc. The head is located either above or under the disc and isolated therefrom by a thin film of air. The thickness of the thin film of air depends on the disc&#39;s rotational speed and the shape of air bearing surface. During drive operation, the fly height of the head continuously changes as the head pitches and rolls with the varying topography of the disc. If the quality of the disc or the read/write head is poor, occasional rubbing or sharp contact may occur between the disc and the head. Such contact may damage the head or the disc, or cause loss of valuable data. 
     With increasing magnetic recording density, the head fly height (or slider clearance) becomes lower and lower. In other words, the contact frequency between disc and head becomes larger. A fly height of as low as 0.7μ″ is currently used in magneto-resistance reading. To prevent damage to either the disc or head for such low slider clearance, it has been recognized that the surface of the disc should be very flat and free of any bumps. 
     Various attempts have been made to provide increasing assurance that undesirable contact between a head and a recording disc does not occur. Rigid manufacturing and quality specifications for both the recording disc and the head have been instituted. One such attempt in the disc industry is to glide test all discs. If a bump or asperity is found on the surface of the disc, the bump must be burnished out by a thermal burnishing air bearing. 
     The burnishing air bearing helps to produce the highest quality media at every level. Thus, there is a need to provide an efficient burnishing air bearing design which has high production yields, low to zero noise in the burnish process, and relatively flat fly heights with nearly zero roll. 
     SUMMARY OF THE INVENTION 
     A disc burnishing system has burnish pads located on the air bearing surface. The air bearing surface provides aerodynamic life to the slider body in response to air flow thereunder. The burnish pad is located on the trailing end of slider and extends therefrom. The burnish pad includes a burnish face which is shaped to behave like a knife at the same time to reduce particle accumulation thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an apparatus for burnishing a disc surface in accordance with the present invention. 
     FIG. 2 is a bottom perspective view of a burnishing air bearing in accordance with the present invention. 
     FIG. 3 is a bottom plan view of a burnishing air bearing in accordance with the present invention. 
     FIG. 4 is a bottom plan view of a burnish pad in accordance with the present invention. 
     FIG. 5 is a stream line diagram depicting air flow under a burnishing air bearing in accordance with the present invention. 
     FIG. 6 is a stream line diagram depicting air flow around burnish pads of the present invention. 
     FIG. 7 is a graph depicting fly height versus slider speed for a 3.5 gmf preloaded burnishing air bearing. 
     FIG. 8 is a graph depicting fly height versus slider speed for a 6.0 gmf preloaded burnishing air bearing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram of disc burnishing system  10  in which the burnishing air bearing of the present invention is particularly useful. System  10  includes spindle motor  12 , actuator  14 , suspension assembly  16 , burnishing slider  17  and controller  20 . 
     Spindle motor  12  is operably coupled to controller  20  and includes spindle  22  which detachably couples to a disc  24 . Upon energization, spindle motor  12  causes spindle  22  and disc  24  to rotate. 
     Slider  17  is suspended above disc  24  by suspension assembly  16 . Suspension assembly  16  is coupled to actuator  14  such that upon energization of actuator  14 , suspension assembly  16  causes slider  17  to move over the surface of disc  24 . When disc  24  rotates, slider  17  will fly above disc  24  on a small film of air (air bearing). The height at which slider  17  flies over disc  24  is controlled by various factors including, the preload force of suspension assembly  16 , the aerodynamic characteristics of slider  17 , and the rotational speed of disc  24 . Varying these parameters will vary the fly height of slider  17  over disc  24 . 
     Controller  20  is coupled to actuator  14  and spindle motor  12 . Thus, controller  20  is able to control the location of slider  17  over disc  24 , and by varying the energization signal to spindle motor  12 , the fly height of slider  17  over disc  24 . 
     FIG. 2 is a bottom perspective view of slider  17  showing air bearing surface  18  in accordance with the present invention. Slider  17  includes body  26 , first rail  28 , second rail  30  and stream line burnish pads  32 . Body  26  includes upper surface  34 , and lower surface  36 . Both first and second rails  28 , 30  are disposed on and extend from lower surface  36  of body  26 . First rail  28  includes first rail air bearing surface  38 , and second rail  30  includes second rail air bearing surface  40 . 
     Those skilled in the art will appreciate that first and second rails  28  and  30  and leading edge  41  are shaped to create a negative air pressure in areas between first rail  28  and second rail  30 . Although described with respect to a negative pressure air bearing, the present invention may be practiced with any air bearing. A negative pressure air bearing is merely preferred because the negative pressure air bearing provides faster take off, higher stiffness, less altitude sensitivity, and less velocity sensitivity than other air bearing designs. Further, for thermal burnish applications, a low pitch and nearly zero negative roll are required. By employing a slider with nearly zero negative roll, such as air bearing  18 , the outside rail of the slider will be the active rail and thus the disc surface may be effectively burnished, especially the outer radial disc surface. Further, a low pitch slider, such as air bearing  18  provides enhanced stability which facilitates effective burnishing. 
     As can be seen in FIG. 2 first rail  28  and second rail  30  preferably include recessed trailing portions  42 , and  44  respectively. Recessed portions  42  and  44  preferably lie within a plane, which is between the plane of air bearing surfaces  38 ,  40  and bottom surface  36 . Stream line burnish pads  32  are preferably disposed on recess portions  42 ,  44  and extend therefrom. Additionally, stream line burnish pads  32  preferably extend from recessed portions  42 ,  44  a sufficient distance such that stream line burnish pads  32  in the same plane as, or slightly pass through, the plane defined by air bearing surfaces  38 ,  40 . Thus, stream line burnish pads  32  can be extended slightly further from lower surface  36  of body  26  than first rail  28  and second rail  30 . Considering pitch angle, when air bearing  18  flies, stream line burnish pads  32  are positioned nearest disc  24  and thus are generally the only locations which make physical contact with the surface of disc  24 . 
     FIG. 3 is a bottom plan view of slider  17  in accordance with the present invention. As can be seen, air bearing  18  is preferably symmetric about dashed line  45  such that a given air bearing may be used as either an up or down burnishing air bearing. Using a symmetric design improves the manufacturing yield of the thermal burnishing air bearing of the present invention. For example, if the radially outer pad is used for burnishing, the slider may also be used in the up position if outer pads are damaged. However, it should be noted that the present invention may be practiced with non-symmetric designs. 
     As can also be seen in FIG. 3, stream line burnish pads  32  preferably have multiple curved surfaces forming essentially elliptical pads with a semi-circular portion removed. 
     FIG. 4 is an enlarged bottom plan view of one of thermal burnish pads  32 . Thermal burnish pad  32  includes curved leading edge  46 , first curved lateral edge  48 , curved trailing edge  50 , and second curved lateral edge  52 . Curved leading edge  46  is connected to first curved lateral edge  48  and second curved lateral edge  52  which are each connected to curved trailing edge  50 . Preferably, curved leading edge  46  and curved trailing edge  50  have the same curvature. Additionally, first curved lateral edge  48  preferably has a curvature that is less than that of curved leading edge  46  and curved trailing edge  50 . Further, it is also preferred that second curved lateral edge  52  have a curvature which is different than that of curved leading edge  46 , first curved lateral edge  48  and curved trailing edge  50 . Moreover, leading edge  46 , first curved lateral edge  48  and trailing edge  50  are concave with respect to center  53 , while second curved lateral edge  52  is convex with respect to center  53 . 
     The curvatures of stream line burnish pad  32  are preferable because they provide enhanced aerodynamic characteristics to the stream line burnish pads  32  of the present invention. Once stream line burnish pad  32  contacts an irregularity on the disc surface, it cuts or otherwise mechanically removes a portion, if not all of the surface irregularity. The removed portion is preferably carried away immediately otherwise the removed portion can begin dragging on the disc surface with the pad. If this happens, the disc itself may be damaged and electric noise may enlarge or even be created. By providing curvature to edges  46 - 52  of the stream line burnish pad  32 , air flow around the stream line burnish pad  32  will cause the burnish debris to be swept away immediately upon separation from the disc surface. This is because the air velocity stream line will follow the pad curvature as will be described more fully with respect to FIGS. 5 and 6. 
     FIGS. 5 and 6 are stream line diagrams showing air flow under air bearing surface  18  taken along the length and width of slider  17  of the present invention. For clarity, the leading edge of air bearing  18  would be on the left side of FIG. 5, and the trailing edge, including stream line burnish pads  32  would be on the far right side of FIG.  5 . As can be seen in FIGS. 5 and 6, air flowing under air bearing  18  will flow around the curved leading edge  46  of stream line burnish pads  32 . Thus, debris which is mechanically removed from the disc surface by stream line burnish pads  32  will be blown clear. Such debris will not drag across the disc surface. 
     FIG. 7 is a chart depicting air bearing fly height for varying linear air bearing speed for a 3.5 gmf preload. FIG. 7 shows that for a speed of approximately 375 inches per second (ips), the outer rail trailing edge (ORTE) of the head will fly at approximately 0.8138 microinches from the disc surface. Additionally, at 375 ips, the inner rail trailing edge (IRTE) will fly at a distance of approximately 0.9848 microinches from the disc surface. FIG. 7 also shows the minimum fly height (H MIN ). As can be seen in FIG. 7, as the linear speed of the air bearing is increased, the fly height increases as well. However, for a given increase in linear speed, the outer rail trailing edge will increase its fly height more than the inner rail trailing edge. 
     FIG. 8 is a chart of fly height versus air bearing linear speed for an air bearing with a 6.0 gmf preload. FIG. 8 shows a comparison of fly heights for the outer rail of the air bearing contrasted with the fly height of the inner rail. As can be seen in FIG. 8, at a linear speed of approximately 400 ips the outer rail trailing edge flies at approximately 0.5861 microinches while the inner rail trailing edge flies at approximately 0.6884 microinches. Additionally, at a slider speed of approximately 600 ips, the outer rail trailing edge flies at approximately 0.6448 microinches while the inner rail trailing edge flies at about 0.6949 microinches. Thus, it can be seen that at a 6.0 gmf preload, the inner rail trailing edge flies at a relatively flat profile over speed variations from approximately 400 ips to approximately 600 ips, while the outer rail trailing edge varies its fly height from about 0.5861 microinches to about 0.6448 microinches over comparable speed variations. 
     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 spirit and scope of the invention. For example, although the present invention has been described with respect to burnishing magnetoresistive discs, the present invention may be practiced upon magneto-optical or optical discs as well. Sliders of the present invention may be fabricated using any desired technique photolithographic masking and ion milling, chemical etching or reactive ion etching. Any number, shape or position of pads may be used. The pads should be of a material sufficiently hard to reduce wear of the pad over extended use.