Patent Application
20090324147
Disc drive memory systems store digital information that is recorded on concentric tracks of a magnetic disc medium. At least one disc is rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. One type of motor has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and a sleeve, while maintaining alignment of the spindle to the shaft. Because rotational accuracy is critical, recent disc drives utilize a motor having fluid dynamic bearings (FDB) between the shaft and sleeve to support a hub and the disc for rotation. In a hydrodynamic bearing, a lubricating fluid such as gas or liquid provides a bearing surface between a fixed member and a rotating member of the disc drive.
Disc drive memory systems are being utilized in progressively more environments besides traditional stationary computing environments. Recently, disc drive memory systems are incorporated into devices that are operated in digital cameras, digital video cameras, video game consoles, personal music players, in addition to portable computers. As such, performance and design needs have intensified.
Storage density has increased, and the size of the storage system has decreased. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage discs. For example, to achieve increased storage densities the transducing head must be placed increasingly close to the surface of the storage disc. This proximity requires that the disc rotate substantially in a single plane. A slight wobble or run-out in disc rotation can cause the surface of the disc to contact the transducing head. This is known as a “crash” and can damage the transducing head and surface of the storage disc resulting in loss of data. Thus, the bearing assembly which supports the storage disc is of critical importance.
Because the two surfaces which form the gap of the hydrodynamic bearing are not mechanically separated, the potential for surface impact exists. Such impacts could occur when the motor supported by the bearing is at rest, or even more damaging, when a shock to the system occurs while the motor is either stopped or spinning. Over time, such impacts could wear down a region on one of the bearing surfaces, altering the pressure distribution and reducing bearing efficiency or induce catastrophic failure due to surface damage like galling. Moreover, particles could be generated by the scraping of one side against the other, which particles would continue to be carried about by the fluid. Such particles could build up over time, scraping the surfaces which define the hydrodynamic bearing, or being expelled into the region surrounding the motor where they could easily damage the disc recording surface.
Additionally, because of the trend for high speed applications in the disc drive industry, power is also a significant factor for optimized performance. A fluid bearing may consume 20% to 30% of the total power of a disc drive, depending on the type of drive. Although the fluid bearing (utilizing a liquid) is robust, at low temperatures and higher speeds, the liquid bearing consumes significant power. Gas bearings are typically utilized for lower power consumption, but conventional gas bearings are especially vulnerable to wear and impact during start-up and stop, as compared to liquid bearings. The gas bearing gap is typically in the range of 0.5 to 5 microns, whereas the liquid bearing has a larger gap with greater tolerance.
The present invention provides a system and method for reduced power consumption and reduced wear in a spindle motor. The spindle motor includes a fluid dynamic bearing containing gas defined between a stationary component and a rotatable component. A liquid layer is coated on at least a portion of at least one of the rotatable component surface and the stationary component surface. The liquid layer is formed from a liquid having a predetermined concentration, and formed having a predetermined thickness. The predetermined thickness is accomplished utilizing at least one of a predetermined dwell time, withdraw velocity and bearing surface roughness. These and various other features and advantages will be apparent from a reading of the following detailed description.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
Exemplary embodiments are described with reference to specific configurations. Those of ordinary skill in the art will appreciate that various changes and modifications can be made while remaining within the scope of the appended claims. Additionally, well-known elements, devices, components, methods, process steps and the like may not be set forth in detail in order to avoid obscuring the invention.
A system and method are described herein for providing reduced power consumption and reduced wear in a spindle motor. The spindle motor includes a fluid dynamic bearing containing gas defined between a stationary component and a rotatable component. A liquid layer is coated on at least a portion of at least one of the rotatable component surface and the stationary component surface, for resisting wear resistance to these surfaces. The liquid layer is formed from a liquid having a predetermined concentration, and formed having a predetermined thickness. The predetermined thickness is accomplished utilizing at least one of a predetermined dwell time, withdraw velocity and bearing surface roughness, as described below. The present invention improves bearing performance. As compared to fluid bearings, the gas bearing of the present invention reduces power consumption. The liquid layer can last for the life of the disc drive, has a low surface energy, high temperature resistance, and has a tendency to spread over the surface even after numerous bearing surface touch downs.
It will be apparent that features of the discussion and claims may be utilized with disc drives, low profile disc drive memory systems, spindle motors, various fluid dynamic bearing design motors including hydrodynamic and hydrostatic motors, and other motors employing a stationary and a rotatable component, including motors employing conical bearings. Further, embodiments of the present invention may be employed with a fixed shaft or a rotating shaft. Also, as used herein, the terms “axially” or “axial direction” refers to a direction along a centerline axis length of the shaft (i.e., along axis 260 of shaft 202 shown in
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
A flex assembly provides the requisite electrical connection paths for the actuator assembly while allowing pivotal movement of the actuator body 126 during operation. The flex assembly (not shown) terminates at a flex bracket for communication to a printed circuit board mounted to the bottom side of disc drive 110 to which head wires are connected; the head wires being routed along the actuator arms 124 and the flexures 122 to the heads 120. The printed circuit board typically includes circuitry for controlling the write currents applied to the heads 120 during a write operation and a preamplifier for amplifying read signals generated by the heads 120 during a read operation.
Referring to
The liquid layer 310 is formed from a liquid having a predetermined concentration, and formed having a predetermined thickness. The predetermined thickness is accomplished utilizing at least one of a predetermined dwell time, withdraw velocity and bearing surface roughness. The predetermined dwell time is the time that either the rotatable component surface or the stationary component surface is situated within the liquid prior to being withdrawn from the liquid. The withdraw velocity is the velocity at which either the rotatable component surface or the stationary component surface is withdrawn from the liquid. The bearing surface roughness is the roughness of either the rotatable component surface or the stationary component surface.
The liquid layer can be formed from a variety of substances. Example substances include PFPE, functional PFPE, phosphazene, phosphate ester, a mixture of PFPE and an additive selected from the group consisting of phosphate ester, triaryl phosphate, trialkyl phosphates, TCP and butylated triphenyl phosphate. Example PFPE substances that can be used by the present invention include Z-Tetraol and Z-Dol (by Solvay Solexis™). The liquid concentration can be diluted if needed, for example utilizing PF5060 (by 3M™), and Vertrel XF. The liquid layer is applied to the bearing surface using either dipping, spraying or wiping. In one example, the bearing surface roughness is established in the range of 10 to 100 nm. The thin liquid layer may be coated to a variety of bearing surfaces, including steel, bronze, DLC, Al2O3, TiC, SiN, SiC, and TiN. The liquid layer can be either bonded or not bonded to the bearing surface. The liquid layer is applied prior to operation of the spindle motor, although the liquid layer may have a tendency to spread over the surface after the bearing is put into operation. The thin liquid layer may be utilized along with a wear resistant carbon coating such as diamond-like coating (DLC). Further, the present invention thin liquid layer may eliminate the need for the use of DLC on the relatively rotatable fluid bearing surfaces.
In an embodiment, the predetermined liquid used to form the liquid layer has a concentration in the range of 0.25% to 5%, and the liquid layer is formed with an increased thickness by at least one of: increasing the liquid concentration, increasing the dwell time, and increasing the withdraw velocity. In an embodiment, the withdraw velocity utilized is at least about 0.5 mm/sec. to achieve a substantially uniform liquid layer thickness. It is to be appreciated that the selection of the liquid layer thickness is dependent on factors including bearing size, bearing surface finish, and bearing operational rotation speed. Also, the hardness of the surface material may be considered. In one example, the surface material utilized is a hardened 440C, with a Rockwell scale Rc, in the range of 58 to 60.
Methods of achieving various liquid layer thicknesses are provided by the present invention. In one example, the predetermined liquid is Z-Tetraol, the predetermined concentration is 1%, the predetermined dwell time is in the range of 5 to 10 seconds, the predetermined withdraw velocity is 4 mm/sec., and the liquid layer predetermined thickness is in the range of 20 nm to 110 nm. In another example, the predetermined liquid is Z-Tetraol, the predetermined concentration is 2%, the predetermined dwell time is in the range of 5 to 10 seconds, the predetermined withdraw velocity is 4 mm/sec., and the liquid layer predetermined thickness is in the range of 60 nm to 125 nm. The liquid layer thickness may even more generally range from about 40 nm to 150 nm. In yet another example, the predetermined liquid is Z-Tetraol, the predetermined concentration is 3.33%, the predetermined dwell time is in the range of 5 to 10 seconds, the predetermined withdraw velocity is in the range of 4 mm/sec. to 6 mm/sec., and the liquid layer predetermined thickness is in the range of 80 nm to 195 nm. The liquid layer thickness may even more generally range from about 60 nm to 225 nm. In yet a further example, the predetermined liquid is Z-Tetraol, the predetermined concentration is 5%, the predetermined dwell time is in the range of 5 to 10 seconds, the predetermined withdraw velocity is 4 mm/sec., and the liquid layer predetermined thickness is in the range of 225 nm to 260 nm. The liquid layer thickness may even more generally range from about 120 nm to 350 nm.
As illustrated in
To preserve the bearing, a suitable pair of components having adjacent surfaces (a surface and a counter surface) are selected for a thin liquid coating. For example, any one of or all of shaft 475, sleeve 485, thrustplate 480, and counterplate 495 may be selected for a thin liquid coating. As shown in
Turning now to
Referring to
Modifications and variations may be made to the disclosed embodiments while remaining within the spirit and scope of the invention. The implementations described above and other implementations are within the scope of the following claims.
