The present invention relates to the field of hard disk drive development, and more particularly to resolving particulate contamination 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 evenly 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 sleeve 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 contamination of the lubrication or fluid within the bearing. Basically, particulate contamination of the lubrication fluid greatly decreases the life of the bearing.
A fluid dynamic bearing with a modified air-gap is disclosed. One embodiment provides a clamp adjacent to the fluid dynamic bearing, the clamp for clamping at least one disk with respect to the fluid dynamic bearing. In addition, a cap is also provided proximal to a shaft of the fluid dynamic bearing, the cap having an outer end proximal to the clamp such that an air-gap is provided between the outer end of the cap and the clamp.
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 a fluid dynamic bearing (FDB) with a modified air-gap 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 a fluid dynamic bearing with a modified air-gap. For example, one problem with traditional fluid dynamic bearing (FDB) is the contamination of the lubrication or fluid within the bearing. As particulate works through the gap between the cap and the shaft of the FDB, the fluid is contaminated causing the fluid to retain more heat thereby causing further internal contamination. This results in additional fluid contamination and reduced friction capability of the fluid in the FDB. In other words, once the fluid contamination begins, the time to catastrophic failure is significantly reduced.
However, by utilizing the cap/clamp implementation described herein, the possibility for contaminating the fluid within the FDB is significantly reduced without requiring any modification to other components of the fluid dynamic bearing. In other words, the pressure adjusting capabilities of the fluid dynamic bearing is maintained via the new air-gap while the possible contamination of the fluid within the FDB are 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 general, clamp 210 is utilized to hold at least one disk in place around the FDB 200 while cap 220 is used as a cover to reduce the ability for particulate to enter into the fluid within the FDB. Shaft 230 refers to the stationary or non-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.
Referring now to
Referring now to
In addition to server class hard drives and desktop hard drives, mobile hard disk drives also use fluid dynamic bearing motors due to the high areal densities that are being achieved with today's technology. Desktop and mobile HDD track densities today are exceeding 100,000 tracks per inch (100 kTPI), which can compound the issues of NRRO. Incorporating FBD motors in the design of desktop and mobile hard drives solves many of the issues of NRRO.
Fluid Dynamic Bearing motors provide improved acoustics over traditional Ball Bearing spindle motors. The source of acoustic noise in the HDD is the dynamic motion of the disk, actuator and spindle motor components. The sound components are generated from the motor magnet, stator, bearings, and disks. These sound components are all transmitted through the spindle motor to the HDD base casting and top cover. Eliminating the bearing noise by use of fluid dynamic bearing spindle motors reduces one area of the noise component that contributes to acoustic noise. In addition, the damping effect of the lubricant film further attenuates noise contributed from the spindle motor components. This results in lower acoustic noise from HDDs employing fluid dynamic bearing spindle motors. Industry data has shown a 4 dBA or more decrease in idle acoustic noise or some HDD designs.
With reference now to 402 of
Referring now to 404 of
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Thus, embodiments of the present invention provide a method and apparatus for forming a fluid dynamic bearing with a modified air-gap. Additionally, embodiments described herein, decrease the contamination of the fluid within the FDB without requiring a modification or change in the viscosity of the fluid in the fluid dynamic bearing. Furthermore, embodiments described herein, provide a fluid dynamic bearing with a modified air-gap without modifying the manufacturing or structure of any components other than the clamp or cap within the fluid dynamic bearing design.