Patent Application
20090092346
The present invention relates to the field of hard disk drive development, and more particularly to resolving evaporation of the lubrication or fluid in a fluid dynamic bearing.
Direct access storage devices (DASD) have become part of every day life, and as such, expectations and demands continually increase for greater speed for manipulating data and for holding larger amounts of data. To meet these demands for increased performance, the mechanical assembly in a DASD device, specifically the Hard Disk Drive (HDD) has undergone many changes.
In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are tracks spaced at known intervals across the disk. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk.
Areal densities of hard disk drives (HDD) in the past have increased at significant rates of 60 percent to more than 100 percent per year. This trend has slowed more recently to approximately 40 percent per year due to technology challenges. Areal densities today are close to 100 Gb/in2. HDDs are being used more often as digital applications in the consumer electronics industry proliferates, requiring much higher capacities and setting new expectation for lower acoustics. All of the above makes fluid dynamic bearing spindle motors attractive for minimizing non repeatable run-out (NRRO), lowering acoustical noise, and improving reliability.
Presently, the transition from ball bearing (BB) spindle motors to fluid dynamic bearings (FDB) is almost complete in the HDD industry. In general, by incorporating FDB motors in HDD designs higher areal densities and much faster spindle speeds are achieved for today's applications. For example, NRRO is the highest contributor to track mis-registration (TMR), thus impacting HDD performance. NRRO is also an inhibitor in achieving higher track densities. Ball bearing motors produce larger NRRO due to the mechanical contact with the inherent defects found in the geometry of the race ball interface and the lubricant film. Ball bearing spindle motors have minimized this issue with tighter tolerances and closer inspections. There is an upper limit beyond which the ball bearing design can no longer overcome the NRRO problem at the higher areal densities. Currently with ball bearings, NRRO has settled in the 0.1 micro-inch range.
By contrast, FDBs generate less NRRO due to absence of contact between the rotor and stator. FDB designs are expected to limit NRRO in the range of 0.01 micro-inch. Other inherent properties of the FDB design are higher damping, reduced resonance, better non-operational shock resistance, greater speed control, and improved acoustics. Non-operational shock improvement is a result of a much larger area of surface-to-surface contact. Noise levels are reduced to approximately 20 dBA, since there is no contributing noise from ball bearings.
However, one problem with FDB is the evaporation of the lubrication or fluid within the bearing. In many instances, evaporation of the lubrication fluid greatly decreases the life of the bearing due to the bearing having insufficient lubricant.
A device for providing an air-gap associated with a portion of a fluid dynamic bearing is disclosed. A sleeve is provided and surrounds a portion of a shaft. The sleeve and the shaft are configured for establishing the air-gap proximal to a portion of the fluid dynamic bearing. In addition, a cap is also provided and coupled to the sleeve. The cap has an outer end proximal to a portion of the fluid dynamic bearing such that the air-gap is provided between the outer end of the cap and the portion of the fluid dynamic bearing, wherein the air-gap forms a labyrinth seal.
The drawings referred to in this description should not be understood as being drawn to scale unless specifically notes.
Reference will now be made in detail to the alternative embodiment(s) of the present invention. While the invention will be described in conjunction with the alternative embodiment(s), it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.
Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.
The discussion will begin with an overview of a hard disk drive and components connected therewith. The discussion will then focus on embodiments of a method and system for forming an air-gap associated with a portion of a fluid dynamic bearing (FDB) in particular. Although the fluid dynamic bearing is shown in a hard disk drive, it is understood that the embodiments described herein are useful in a fluid dynamic bearing regardless of whether the fluid dynamic bearing is a portion of a hard disk drive. The utilization of the fluid dynamic bearing within the HDD is only one embodiment and is provided herein merely for purposes of brevity and clarity.
In general, embodiments of the present invention provide a method and apparatus for forming an air-gap associated with a portion of a fluid dynamic bearing (FDB). For example, one problem with traditional fluid dynamic bearing (FDB) is the evaporation of the lubricant within the bearing. The lubricant becomes hot under the rotational pressure of the motor, and evaporates or turns to a mist. For example, when the motor rotates at a high speed, such as at 15,000 rpm, the lubricant may mist and then migrate to other areas. This results in reduced friction handling capability of the remaining lubricant in the FDB. Once the lubricant's evaporation and migration begins, the amount of lubricant in the FDB lessens, and the time to catastrophic failure also lessens.
However, by utilizing the cap/sleeve implementation described herein, the possibility for evaporation and migration is significantly reduced. In other words, the pressure adjusting capabilities of the fluid dynamic bearing is maintained via the air-gap while the possibility of evaporation and migration into areas other than the FDB is significantly decreased.
With reference now to
The dynamic performance of HDD 110 is a major mechanical factor for achieving higher data capacity as well as for manipulating this data faster. The quantity of data tracks 136 recorded on disk surface 135 is determined partly by how well magnetic head 156 and a desired data track 136 can be positioned to each other and made to follow each other in a stable and controlled manner. There are many factors that will influence the ability of HDD 110 to perform the function of positioning magnetic head 156, and following data track 136 with magnetic head 156. In general, these factors can be put into two categories; those factors that influence the motion of magnetic head 156; and those factors that influence the motion of data track 136. Undesirable motions can come about through unwanted vibration and undesirable tolerances of components. Herein, attention is given to motor-hub assembly 130, which attaches to base casting 113, and in particular, attention is given to the fluid dynamic bearing inside motor-hub assembly 130.
With reference now to
In one embodiment, shaft 210 is the rotating portion of the FDB. In operation, the fluid area within the FDB is not a sealed environment but is instead vented to atmospheric pressure. The reasons for venting the FDB are numerous and well-known in the art, but one important reason for the venting is related to the operational environments within which the FDB is located. For example, the FDB may be part of a hard drive that is used at sea level, on an aircraft, at higher elevation, and the like. As such, there is a need to have an air-gap to allow the air-pressure within the FDB to equalize.
In one embodiment, sleeve 205 is coupled with a rotatable shaft motor. In another embodiment, cap 215 has an outer end 235 proximal to shaft 210 such that air-gap 220 is formed between the outer end of cap 215 and shaft 210. Cap 215 is stationary, while sleeve 205 rotates about shaft 210. Cap 215 may be made from any metal having stable thermo expansion characteristics able to endure operations within a defined range, such as a spindle motor rotating between 10,000 to 17,000 r.p.m.
Referring now to
In one embodiment, sleeve 310 is coupled with tied motor shaft 330. In another embodiment, cap 305 has an outer end 360 proximal to a portion of sleeve 310 such that air-gap 315 is formed between the outer end 350 of cap 305 and sleeve 310. Cap 305 is stationary and is next to sleeve 310 which is rotating.
In another embodiment in which sleeve 310 is coupled with tied motor shaft 330, cap 320 has an outer end 355 proximal to shaft 330 such that air-gap 325 is formed between the outer end 355 of cap 320 and shaft 330. Cap 320 is rotating and is next to shaft 330 which is stationary.
In one embodiment, tied motor shaft 330 may be associated with two labyrinth seals, both displaying the air-gap 315 as depicted in
With reference now to 402 of
Referring now to 404 of
In one example of the present technology, sleeve 205 is coupled with a rotatable shaft motor. Furthermore, one embodiment provides cap 215 having an outer end 235 proximal to shaft 210 such that air-gap 220 is formed between the outer end 235 of cap 215 and shaft 210.
In another example of the present technology, sleeve 310 is coupled with shaft 330 of a tied shaft motor. Furthermore, one embodiment provides cap 305 having an outer end 350 proximal to a portion of sleeve 310 such that air-gap 315 is formed between the outer end 350 of cap 305 and sleeve 310. Another embodiment provides cap 320 having an outer end 355 proximal to shaft 330 such that air-gap 325 is formed between the outer end 355 of cap 320 and shaft 330.
Thus, embodiments of the present invention provide a method and apparatus for forming an air-gap associated with a portion of a fluid dynamic bearing. Additionally, embodiments described herein, decrease the migration of lubricant within an FDB, thereby maintaining and/or lengthening the expected life-span of the FDB.
