Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
2001-07-25
2002-09-24
Nguyen, Hoa T. (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
Reexamination Certificate
active
06456458
ABSTRACT:
BACKGROUND OF INVENTION
1. Technical Field
The present invention relates to spindle motors; in particular to disk-drive spindle motors employing hydrodynamic bearings that generate rotational dynamic pressure in shaft-sleeve interposed lubricant for rotationally bearing the disk-supporting shaft/sleeve.
2. Description of Related Art
Disk drive devices, such as computer hard disk drives, in which spindle motors are employed to drive data-storing disks, are well known. Spindle motors of this type may include hydrodynamic bearing configurations that generate bearing pressure in the lubricating fluid dynamically when the motor spins, thereby stabilizing, for example, a disk-supporting sleeve rotationally against a stationary spindle shaft.
One such motor is disclosed in U.S. Pat. No. 5,504,637. The disclosed motor includes a stationary shaft, a thrust plate fixed endwise to the stationary shaft, and a rotary hub having an annular central recess encompassing the thrust plate and integral with a sleeve surrounding the shaft. The motor further includes a thrust washer fixed over the central recess in the hub, confining the thrust plate in the rotary hub recess. Lubricant is retained in a clearance between the base of the recess and the axially adjacent surface of the thrust plate; the lubricant and the clearance-defining surfaces of the recess and thrust plate form a first hydrodynamic thrust bearing. Axially adjacent, clearance-defining surfaces of the thrust plate and thrust washer, together with lubricant retained in the clearance form a second hydrodynamic thrust bearing.
Herringbone grooves for generating hydrodynamic pressure are formed in a first portion of the cylindrical surface of the shaft. The first portion of the shaft cylindrical surface is surrounded by the radially adjacent inner circumferential surface of the sleeve at an annular micro-gap filled with lubricant. The grooved first portion of the shaft cylindrical surface, the adjacent inner surface of the sleeve, and the lubricant in the micro-gap establish a first radial bearing. Hydrodynamic-pressure-generating herringbone grooves are also formed in a second portion of the shaft cylindrical surface, radially adjacent the inner surface of the sleeve at another annular micro-gap filled with lubricant. The grooved second portion of the shaft cylindrical surface, the adjacent inner surface of the sleeve, and the lubricant in the micro-gap establish a second radial bearing. The hydrodynamic-pressure-generating grooves in the first and second radial bearings generate hydrodynamic pressure when the sleeve rotates relative to the shaft.
The hydrodynamic pressure thus generated in the radial bearings imparts high rigidity to the radial bearings to stabilize sleeve rotation. To stabilize sleeve rotation further, the first and second radial bearings are spaced apart at a predetermined distance, supporting the sleeve to eliminate wobble as it rotates about the shaft.
In a conventional motor of the foregoing type, the first and second radial bearings provide radial stability to the sleeve, maintaining the rotary hub in a vertical orientation with respect to the stationary shaft. Further, the first and second radial bearings maintain the sleeve in a concentric relationship with respect to the stationary shaft during rotation of the rotary hub. The effectiveness of the radial bearings in maintaining the rotary hub in a constant concentric relationship with respect to the shaft depends on the rigidity of each of the radial bearings and the axial distance between their respective centers. The farther apart the first and second radial bearings are, the more stable the rotary hub rotation will be against radial movement with respect to the shaft, since the thrust bearings primarily only restrain axial movement of the rotary hub.
Personal computers, in which disk-drive storage devices driven by conventional motors such as described above are utilized, are continually becoming smaller and thinner. The motors for spinning the hard disk in these disk-drive storage devices are expected to become smaller and thinner as well. Because the radial bearings are essential to the radial support of the rotary hub, however, and because making the distance between the radial bearings as large as possible is advantageous for imparting greater rotational stability to the rotary hub, reducing the axial height of motors employing first and second radial bearings presents difficulties.
Moreover, simply making motor structural components, such as the rotary hub and the thrust plate, thinner in order to reduce the motor axial height makes secure, precision assembly of the motor components to one another difficult. In particular, if the shaft and the thrust plate are not securely fixed to one another, the rotational precision of the motor is negatively affected.
Japanese laid patent application 08331796 (1996) discloses a different type of motor that includes a stationary sleeve encompassing a rotational shaft. In this case as well two axially separated sets of hydrodynamic-pressure-generating grooves are formed in the cylindrical surface of the shaft. The grooved sections of the shaft cylindrical surface and radially adjacent sections of the inner circumferential surface of the stationary sleeve define annular micro-gaps in which lubricant is retained, and together with the lubricant form upper and lower radial hydrodynamic bearings for supporting the rotational shaft.
However, the motor configuration disclosed in this Japanese publication does not utilize the radially extensive surface(s) of a thrust plate to establish hydrodynamic thrust bearing(s) as, in contrast, does the first motor configuration discussed above. Rather, hydrodynamic pressure generation grooves formed on the base-end surface of the shaft and/or the adjacent surface of a plate fixed to the sleeve, and lubricant in the clearance defined between the two surfaces, form a single hydrodynamic thrust bearing. Since the shaft is of diameter that is proportionately smaller than the thrust plate in the first motor discussed above, the grooves formed on the base-end surface of the shaft and/or the adjacent surface of the plate may not be able to generate sufficient thrust hydrodynamic pressure to support adequately the thrust load generated by rotation of the motor. Increasing the diameter of the shaft in order to obtain increased hydrodynamic pressure in the lubricant in the thrust bearing is not a practical consideration for this motor, because an increased shaft diameter in such a motor would result in greater energy loss that would decrease the electrical efficiency of the motor.
U.S. Pat. No. 5,659,445 to Yoshida et al. is directed to improving the lubricating configuration in a recording disk-drive motor. As set forth in the Summary section, Yoshida et al. accomplish this i) by employing tapered lubricant clearances in the thrust and radial dynamic-pressure bearing sections to increase dynamic lubricant pressure, and ii) by containing the dynamic pressure lubricant with a magnetic fluid seal device. Yoshida et al. thus seek to improve bearing and lubricating performance by increasing the dynamic pressure generated in, and at the same time keeping air out of, the radial and thrust bearing sections. The magnetic fluid seal device taught by Yoshida et al. is to prevent air, which has a larger coefficient of thermal expansion/contraction than the lubricant, from entering the bearing sections and destabilizing their performance.
Yoshida et al. thus teach improving motor bearing performance by employing tapered clearances to increase rotational dynamic pressure in the lubricant, which at the same time necessitates containing the lubricant with magnetic fluid seal devices. In turn, the magnetic fluid seal devices taught in every pertinent Yoshida et al. embodiment require a separate thrust plate/member for at least the thrust bearing on the rotor-hub adjacent end.
For example, Yoshida et al. discloses, as shown in
FIG. 18
, a recording-disk rotating device that includes a radial bearing portion
Judge James
Nguyen Hoa T.
Nidec Corporation
Watko Julie Anne
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