This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-310516, filed Dec. 5, 2008, the entire contents of which are incorporated herein by reference.
1. Field
One embodiment of the invention relates to a storage device with a head slider that floats over a storage medium having a surface coated with a lubricant.
2. Description of the Related Art
In a hard disc drive (HDD), a head slider floats over a magnetic disc when magnetic information is written thereto or read therefrom. At this time, a lubricant is, for example, evaporated and transferred to the medium facing surface of the head slider. If the transferred lubricant is agglomerated on the medium facing surface, a lubricant lump drops onto a surface of the magnetic disc. The lump comes contact with the head slider, and thereby head crash occurs.
Reference may be had to Japanese Patent Application Publication (KOKAI) No. H8-279120, Japanese Patent Application Publication (KOKAI) No. 2003-109340, Japanese Patent Application Publication (KOKAI) No. 2000-348303, Japanese Patent Application Publication (KOKAI) No. 2006-196137, Japanese Patent Application Publication (KOKAI) No. H7-21717, and Japanese Patent Application Publication (KOKAI) No. 2002-175676.
Reference may also be had to Bruno Marchon, Tom Karis, Qing Dai and Remmelt Pit, “A Model for Lubricant Flow From Disk to Slider”, IEEE Transactions on Magnetics, Vol. 39, No. 5, September 2003, pp. 2447-2449, Yansheng Ma and Bo Liu, “Lubricant transfer from disk to slider in hard disk drives”, Applied Physics Letters, 90, 143516, 2007, and Bo Zhang and Akira Nakajima, “Hydrodynamic Lubrication of Slider Air Bearings with the Pumping Effect”, in Proc. Micromechatronics for Information and Precision Equipment, Santa Clara, Calif., June 2006.
As described above, it is well known that the lubricant moves between the magnetic disc and the head slider. However, a method of inhibiting the lubricant from being transferred from the magnetic disc to the head slider has not been disclosed.
A general architecture that implements the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, a storage device comprises a storage medium and a head slider. The storage medium is configured to include a surface coated with a lubricant. The head slider is configured to include a medium facing surface that faces a surface of the storage medium based on the relative movement to the storage medium. The product ph [atm·nm] of air pressure p [atm] defined between the surface of the storage medium and the medium facing surface and a floating amount h [nm] of the medium facing surface defined from the surface of the storage medium satisfies
ph≧0.0129 Mn+71.344
with respect to the molecular weight Mn of the lubricant.
According to another embodiment of the invention, there is provided a method of calculating a transfer amount of a lubricant, comprising calculating a transfer amount of a lubricant on a storage medium to a medium facing surface of a head slider based on the product ph [atm·nm] of air pressure p [atm] defined between a surface of the storage medium and the medium facing surface and a floating amount h [nm] of the medium facing surface defined from the surface of the storage medium.
According to still another embodiment of the invention, a head slider comprises a slider body, a rear rail, a step surface, and an air bearing surface. The slider body is configured to define a medium facing surface. The rear rail is formed at an air outflow end side of the medium facing surface. The width of the rear rail defined in the width direction of the slider body is configured to decrease toward the air outflow end from the air inflow end. The step surface is configured to be defined at the air inflow end side of the rear rail on the rear rail. The air bearing surface is configured to be defined at the air outflow end side of the rear rail on the rear rail and be connected to the step surface through a step difference. At least one of crossing angles between an extension line of the contour of the rear rail defined at a side of the rear rail and the front-rear direction center line of the slider body is larger than the maximum skew angle.
In the housing space, one or more magnetic disks 14 are housed as storage media. The magnetic disc 14 is mounted on the rotation axis of a spindle motor 15. The spindle motor 15 can rotate the magnetic disk 14 at high speed, such as 5400 rpm, 7200 rpm, 10000 rpm, and 15000 rpm. For example, the magnetic disc 14 is configured as a vertical magnetic recording disc. That is, in a recording magnetic film on the magnetic disc 14, a magnetization easy axis is set in the vertical direction perpendicular to a surface of the magnetic disc 14.
In the housing space, a carriage 16 is further housed. The carriage 16 comprises a carriage block 17. The carriage block 17 is rotatably connected to a support shaft 18 extending in the vertical direction. In the carriage block 17, a plurality of carriage arms 19, which extend a horizontal direction from the support shaft 18, are defined. The carriage block 17 may be formed by, for example, extruding aluminum (Al).
Attached to a front end of each of the carriage arms 19 is a head suspension 21. The head suspension 21 extends forward from the front end of the carriage arm 19. A flexure is attached to a front end of the head suspension 21. A gimbal spring is defined in the flexure. Due to the action of the gimbal spring, a flying head slider 22 may change its posture with respect to the head suspension 21. As will be described later, a head device, i.e., an electromagnetic transducer device, is mounted on the flying head slider 22.
When an air flow is produced on a surface of the magnetic disk 14 by rotation of the magnetic disk 14, positive pressure, i.e., buoyancy, and negative pressure act on the flying head slider 22 by the action of the air flow. When the buoyancy, the negative pressure, and a pressing force of the head suspension 21 are in balance, the flying head slider 22 can keep floating with relatively high rigidity during the rotation of the magnetic disc 14.
When the carriage 16 rotates around the support shaft 18 while the flying head slider 22 is floating, the flying head slider 22 can move along a radial line of the magnetic disc 14. As a result, the electromagnetic transducer device on the flying head slider 22 can traverse a data zone between the innermost recording track and the outermost recording track. Thus, the electromagnetic transducer device on the flying head slider 22 is positioned on a target recording track.
A power source such as a voice coil motor (VCM) 23 is connected to the carriage block 17. By the action of the VCM 23, the carriage block 17 can rotate around the support shaft 18. Such rotation of the carriage block 17 enables reciprocation of the carriage arm 19 and the head suspension 21.
As can be seen from
To read out magnetic information, a sense current is supplied from the head IC 26 to the reading element of the electromagnetic transducer device. For example, a reading element of a CPP structure is used as the reading element. Similarly, in order to write magnetic information, an electric current is supplied from the head IC 26 to the writing element of the electromagnetic transducer device. For example, a single magnetic pole head element is used as the writing element. A current value of the sense current is set to a certain value. An electric current is supplied to the head IC 26 from a small-sized circuit substrate 28 arranged in the accommodation space or a printed circuit board (PCB) (not illustrated) attached to an under side of a bottom plate of the base 13.
The flying head slider 22 faces the magnetic disc 14 with the medium facing surface, i.e., a floating surface 34. A flat base surface 35, i.e., a reference surface, is defined on the floating surface 34. When the magnetic disc 14 rotates, an air flow 36 works on the floating surface 34 from the front end toward the rear end of the slider body 31.
A piece of front rail 37 which rises from the base surface 35 is formed on the floating surface 34 at the upstream of the air flow 36, i.e., at the air inflow side. The front rail 37 extends in the slider width direction along the air inflow end of the base surface 35. Similarly, a rear center rail 38 which rises from the base surface 35 is formed on the floating surface 34 at the downstream of the air flow 36, i.e., at the air outflow side. The rear center rail 38 is arranged at the center in the slider width direction. The rear center rail 38 extends from the slider body 31 to the device built-in film 32.
An air bearing surface (ABS) 39 is defined on the top surface of the front rail 37. The air inflow end of the air bearing surface 39 comes into contact with a step surface 42 of the front rail 37 through a step difference 41. The step surface 42 is at a level one step lower than the air bearing surface 39. The step surface 42 is defined at the air inflow end side of the front rail 37. The air bearing surface 39 is defined at the air outflow end side of the front rail 37.
Similarly, an ABS 43 is defined on the top surface of the rear center rail 38. The air inflow end of the air bearing surface 43 comes into contact with a step surface 45 of the rear center rail 38 through a step difference 44. The step surface 45 is at a level one step lower than the air bearing surface 43. The step surface 45 is defined at the air inflow end side of the rear center rail 38. The air bearing surface 43 is defined at the air outflow end side of the rear center rail 38.
The air flow 36 generated by the rotation of the magnetic disc 14 is received by the floating surface 34. At this time, because of the presence of the step differences 41 and 44, a relatively high positive pressure, i.e., buoyancy, is generated on the air bearing surfaces 39 and 43. Further, high negative pressure is generated behind, i.e., at the rear of the front rail 37. The floating posture of the flying head slider 22 is determined by balance of the buoyancy and the negative pressure.
Referring to
As illustrated in
The magnetic disc 14 has a surface coated with a lubrication film 51. The thickness of the lubrication film 51 is set to, for example, about 1 nm. The lubrication film 51 is made of, for example, a lubricant such as perfluoropolyether (PFPE). As illustrated in
The inventor analyzed the movement of the lubricant molecules 52 and the air molecules 53 between the floating surface 34 and the surface of the magnetic disc 14. The direct simulation Monte Carlo (DSMC) technique was used for the analysis. For implementation of the analysis, first to third models were set. In the first to third models, molecular weights Mn of the lubricant molecules 52 were set to 2510, 4500, and 6500, respectively. In all the models, the lubricant molecule 52 was assumed as a hard sphere. A ratio of a nitrogen (N2) molecule to an oxygen (O2) molecule of the air molecule 53 was set to, for example, 80[%]:20[%].
As a result of analysis through the DSMC technique, as illustrated in
As the air pressure p increases, the number of the air molecules 53 between the floating surface 34 and the surface of the magnetic disc 14 increases. Therefore, it is considered that as the air pressure p increases, the lubricant molecules 52 are likely to collide with the air molecules 53. As a result, the reaching rate a of the lubricant molecules 52 to the floating surface 34 decreases. Thus, transfer of the lubricant molecules 52 to the floating surface 34 is inhibited. On the other hand, as the floating amount h increases, the number of the air molecules 53 between the floating surface 34 and the surface of the magnetic disc 14 increases. Therefore, it is considered that as the floating amount h increases, the lubricant molecules 52 are likely to collide with the air molecules 53. The reaching rate a of the lubricant molecules 52 to the floating surface 34 decreases. As a result, transfer of the lubricant molecules 52 to the floating surface 34 is inhibited.
The inventor formulated the reaching rate a based on the analysis result through the DSMC technique. The reaching rate α is expressed by Equation (1) as follows:
where C is a constant term. It can be understood from Equation (1) that the reaching rate α is in inverse proportion to a sum of the product ph and a predetermined constant term C. As the product ph is set to be smaller than the constant term C, the reaching rate α gradually approaches 1. It can be understood from Equation (1) that when the product ph is larger than the constant term C, the reaching rate α is in inverse proportion to the product ph. That is, as the product ph, i.e., the air pressure p or the floating amount h, increases, the reaching rate a decreases. Therefore, it becomes clear that it is important in reducing the reaching rate α to set the product ph to be equal to or more than the constant term C.
As can be seen from
A relationship between the molecular weight Mn and the constant term C was calculated. As a result, as illustrated in
C=0.0129 Mn+71.344 (2)
As described above, since it is necessary to set the product ph to be equal to or more than the constant term C, the following Equation (3) is derived:
ph≧0.0129 Mn+71.344 (3)
A relationship between the floating amount h and the air pressure p illustrated in
In
As described above, in the HDD 11, the product ph of the floating amount h and the air pressure p between the floating surface 34 and the surface of the magnetic disc 14 is set to a value equal to or more than a predetermined value. As a result, transfer of the lubricant molecules 52 to the floating surface 34 is inhibited. Therefore, the flying head slider 22 can stably float for a long time. Further, a new component does not need to be added to the flying head slider 22 to prevent the lubricant molecules 52 from being transferred to the floating surface 34. Thus, extra cost is not required. The presence of the air molecules 53 is considered in calculating the product ph. Therefore, a transfer amount of the lubricant molecules 52 transferred to the floating surface 34 is calculated with higher accuracy compared to conventional technologies.
According to the flying head slider 22a, if the flying head slider 22a is arranged at any radial direction position on the magnetic disc 14, the air flow 36 flowing in toward the rear center rail 38 works on the step surface 45 and the air bearing surface 43. That is, the air flow 36 works on the air bearing surface 43 through both a step difference between the base surface 35 and the step surface 45 and a step difference between the step surface 45 and the air bearing surface 43. As a result, sufficiently high positive pressure, i.e., buoyancy, is generated in the air bearing surface 43 at any radial direction position on the magnetic disc 14. Therefore, high air pressure p is generated between the floating surface 34 or the air bearing surface 43 and the surface of the magnetic disc 14. Thus, transfer of the lubricant molecules 52 to the floating surface 34 is inhibited.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Number | Date | Country | Kind |
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2008-310516 | Dec 2008 | JP | national |