Abstract:
An apparatus includes a hub, a first disk, a second disk, and a spacer. The hub is supported for relative rotation about a stationary component. The first disk is mounted to the hub with a first dynamic resonance mode associated therewith. The second disk is mounted to the hub with a second dynamic resonance mode associated therewith. The spacer is positioned between the first disk and the second disk, wherein the spacer is operable to cause the first dynamic resonance mode to be different from the second dynamic resonance mode.

Description:
BACKGROUND 
       [0001]    Disk drive capacity has been increasing by reducing the spacing between the tracks. Radial motion that does not follow a repeating pattern is known as a non-repetitive run out. A servo system needs to move the head instantaneously to stay on-track and avoid read/write errors even for non-repetitive run out. 
         [0002]    Servo systems may tend to amplify relative radial motion between the head and data tracks at higher frequencies. This relative radial motion may be further amplified by air circulation within the drive, also known as windage. Windage may amplify the radial motion, and may be further increased in systems with more than one disk. 
       SUMMARY 
       [0003]    An apparatus includes a hub, a first disk, a second disk, and a spacer. The hub is supported for relative rotation about a stationary component. The first disk is mounted to the hub with a first dynamic resonance mode associated therewith. The second disk is mounted to the hub with a second dynamic resonance mode associated therewith. The spacer is positioned between the first disk and the second disk, wherein the spacer is operable to cause the first dynamic resonance mode to be different from the second dynamic resonance mode. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0004]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. 
           [0005]      FIG. 1  shows a cross sectional view of a fluid dynamic motor in which embodiments of the present invention can be implemented. 
           [0006]      FIG. 2  shows the effect of windage on the disks coupled to the fluid dynamic motor with a spacer, in accordance with embodiments of the present invention. 
           [0007]      FIG. 3  shows a cross sectional view of a fluid dynamic motor with tapered ring spacer in accordance with one embodiment. 
           [0008]      FIG. 4  shows a cross sectional view of a fluid dynamic motor with different spacer chamfers in accordance with one embodiment. 
           [0009]      FIG. 5  shows a cross sectional view of a fluid dynamic motor with a lobed ring spacer in accordance with one embodiment. 
           [0010]      FIG. 6  shows a cross sectional view of a fluid dynamic motor with a knee shaped ring spacer in accordance with one embodiment. 
           [0011]      FIG. 7  shows a cross sectional view of a fluid dynamic motor with two spacer rings in accordance with one embodiment. 
           [0012]      FIG. 8  shows a cross sectional view of a fluid dynamic motor with different disk diameters in accordance with one embodiment. 
           [0013]      FIG. 9  shows a cross sectional view of another fluid dynamic motor with different disk thickness in accordance with one embodiment. 
           [0014]      FIG. 10  shows a fluid dynamic motor with upper and the lower disks with different diameters and different thicknesses in accordance with one embodiment. 
           [0015]      FIGS. 11A and 11B  show vibration measurement of the top and the bottom disks in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. While the embodiments will be described in conjunction with the drawings, it will be understood that they are not intended to limit the embodiments. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a thorough understanding. However, it will be recognized by one of ordinary skill in the art that the embodiments 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 embodiments. 
         [0017]    For expository purposes, the terms “axially” or “axial direction” refer to a direction along a centerline axis length of a shaft, e.g., along centerline axis  101  of shaft  140  in  FIG. 1 , and “radially” or “radial direction” refer to a direction perpendicular to the centerline axis  101 . The term “horizontal” as used herein refers to a plane parallel to the plane or surface of an object, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms such as “above,” “below,” “bottom,” “top,” “side,” “higher,” “lower,” “upper,” “over,” and “under” are referred to with respect to the horizontal plane. 
         [0018]    Embodiments of the present invention provide methods and systems for reducing relative radial motion between the head and a given data track. Embodiments described herein are particularly effective at reducing relative radial motion at certain frequencies, e.g., 1000 Hz or higher, that do not follow a repeating pattern but are not limited thereto. For example, radial motion of the disk and data tracks caused by a phenomenon known as windage is reduced. Accordingly, amplitudes of disk modes are reduced, thereby enabling the track density to increase. 
         [0019]    Several disk modes may get excited by windage pressure fluctuations acting on their surfaces. Lower order modes occurring at lower frequencies may result in larger motions that adversely impact the servo system&#39;s ability to track. Some disk modes may be referred to as 0,0 mode (also known as the umbrella mode) and 0,1 mode (also known as the tilting mode). In the umbrella mode, the disks become umbrella-shaped, for example due to windage, and in the tilting mode the disks on the opposite sides of the disk outer edge move in the axial direction out of phase with one another. In other words, in tilting mode the outer edges of the disks on each side move in opposite directions, which is modulated by the rotational speed and manifested in two vibration modes. 
         [0020]    Referring now to  FIG. 1 , a cross sectional view of a fluid dynamic motor is shown, in which embodiments can be implemented. The fluid dynamic motor  100  includes a sleeve  110 , a hub  120 , a base  130 , a shaft  140 , magnets  150 , and a stator  160 . Axial direction  101  shows a centerline axis. Data storage disks (not shown) may be rotated at high speeds during operation using the magnets  150  and the stator  160 . Magnets  150  may be mounted on the hub  120  and may interact with the stator  160  to cause rotation of the hub  120  relative to the stator  160 . The magnets  150  may be magnetized to form two or more magnetic poles. 
         [0021]    The fluid dynamic bearing motor  100  includes stationary component(s) as well as rotatable component(s) that define a fluid dynamic journal bearing and a thrust bearing therebetween. The rotatable component may include the hub portion  120  and the shaft  140  while the stationary component may include the sleeve  110 . For example, the hub  120  and shaft  140  may be coupled with one another to form a single unitary piece, such that they rotate together about the centerline axis  101 . Alternatively, the hub  120  and the shaft  140  may be originally formed from a single piece of material. The interface between the shaft  140  and the sleeve  110  may define the fluid dynamic journal bearing while the interface between the hub  120  and the sleeve  110  may define the thrust bearing. 
         [0022]    It is appreciated that the rotatable component may be the sleeve  110  while the stationary components may include the hub  120  and the shaft  140 . The sleeve  110 , the hub  120 , the shaft  140 , the magnets  150 , and the stator  160  are coupled to and housed in the base  130 . 
         [0023]    The disks are supported on a hub and their rotation is supported by the fluid dynamic bearing to dampen axial and tilting motions. In other words, the axial and tilting motions of disk modes may transfer energy to the supporting motor&#39;s fluid dynamic bearing. The axial and tilting motions may be exacerbated in systems with more than one disk, for example from windage pushing and pulling on the upper and lower surfaces of the disks at the same time. In order for dampening to occur, the axial and tilting motions of the individual disks should cause axial, radial, or tilting of the hub  120  and shaft  140  with respect to the sleeve  110 . Accordingly, some of the kinetic energy is dissipated in the bearing and transformed into heat. 
         [0024]    However, higher order disk vibration modes in multi-disk system may cancel each other out. The cancelation occurs if the vibration modes are substantially identical in frequency and amplitude but of opposite direction. In other words the cancelation causes substantially a net zero relative motion between hub and shaft with respect to sleeve. With substantially net zero relative motion, the bearing may not dampen the disks vibration modes. For example, trapped air between the disks undergoes pressure fluctuations and forces the disks to move in unison but in opposite directions. Accordingly, the deflection force couples within the hub and not through the fluid dynamic bearing as intended. Thus, the disk vibration resulting from the axial and tilting movements is not dampened. In other words, higher order disk vibration modes couple directly to the spindle hub, bypassing the fluid dynamic bearing, thereby increasing the likelihood of read/write errors. 
         [0025]    Referring now to  FIG. 2 , effect of windage on the disks coupled to the fluid dynamic motor with a spacer is shown, in accordance with one embodiment. The fluid dynamic motor  100  may be coupled to an upper disk  210  and a lower disk  220 . The fluid dynamic motor  100  may include a spacer ring  201  that is coupled to the upper disk  210  and the lower disk  220  and is further coupled to the hub  120 . It is appreciated that showing of only an upper and a lower disk is for illustration purposes only and not intended to limit the scope. For example, three or more disks may be coupled to the fluid dynamic motor. In this example, a tilting mode is illustrated caused by the windage force. As described above, disk rotation at high frequencies, e.g., between 1000 Hz to 5000 Hz, may cause the upper disk  210  outer edges to move in opposite directions. Similarly, disk rotation at high frequencies may cause the lower disk  220  outer edges to move in opposite directions. It is noteworthy that the upper disk  210  and the lower disk  220  move in opposite directions of one another. As such, the fluid dynamic bearing is bypassed if unaddressed. 
         [0026]    It is appreciated that at the umbrella mode, the upper disk  210  outer edges may move in the same direction, e.g., move up, while the lower disk  220  outer edges may move in the opposite direction of the upper disk  210  outer edges, hence move down in this instance. As such, at the umbrella mode the fluid dynamic bearing is also bypassed if unaddressed and may result in read/write errors. 
         [0027]    Embodiments of the present invention implement a structure by which axial movement of disks in unison is reduced, thereby attenuating the disk resonances and dampening axial and tilting motions. Accordingly, disk densities may safely be increased without increasing read/write errors. 
         [0028]    Referring now to  FIG. 3 , a cross sectional view of a fluid dynamic motor with tapered ring spacer in accordance with one embodiment is shown. It is appreciated that components that are the same and operate the same as those in the previous figures are numbered with the same element number and their description is not duplicated at each subsequent figure. 
         [0029]    The fluid dynamic motor  300  according to one embodiment includes a spacer ring  310 . The spacer ring  310  is tapered and couples to the hub  120 . The spacer ring  310  is also connected to the upper disk  210  and the lower disk  220 . Having a tapered ring  310  causes the upper disk  210  and the lower disk  220  to deflect at different radia resulting in disk vibration modes that are different. Therefore, windage excitation may move the upper and the lower disks independently and not in unison. Accordingly, energy from tilting or axial motions may be dissipated in the motor&#39;s fluid dynamic bearing, resulting in dampening, because the tilting or axial motions by the upper  210  and lower disks  220  do not cancel each other out. 
         [0030]    In other words, having a tapered spacer ring  310  changes the boundary conditions of the upper disk  210  and the lower disk  220 , thereby shifting the natural frequencies of the upper  210  and lower disk  220  apart such that they vibrate out of phase. As such, tilting and/or axial motions of the upper disk  210  and the lower disk  220 , whether due to windage or some other force, do not occur in unison. In other words, shaping the spacer ring  310  such that the outer edge contacts the upper disk  210  at a different location in comparison to the lower disk  220  effectively changes the diameter of the upper  210  and the lower disk  220 , thereby reducing their tendency to move in opposite directions at the same time. 
         [0031]    Referring now to  FIG. 4 , a cross sectional view of a fluid dynamic motor with different spacer chamfers in accordance with one embodiment is shown. The fluid dynamic motor  400  includes a spacer ring  410 . The spacer ring  410  is coupled to the hub  120  and further connected to the upper  210  and the lower disk  220 . The spacer ring  410  has an upper chamfer  412  that is sized differently than the lower chamfer  414 . Having a spacer ring  410  with its chamfers sized differently causes the upper disk  210  and the lower disk  220  to deflect independently and not in unison. Accordingly, energy from tilting or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting or axial motions by the upper  210  and lower disks  220  do not cancel each other. 
         [0032]    Accordingly, having different spacer chamfers for a spacer ring  410  changes the boundary conditions of the upper disk  210  and the lower disk  220 , thereby shifting the natural frequencies of the upper  210  and lower disk  220  apart such that they vibrate out of phase. As such, tilting and/or axial motions of the upper disk  210  and the lower disk  220 , whether due to windage or other influence, do not occur in unison. In other words, shaping the spacer ring such that the outer edge contacts the upper disk  210  at a different location in comparison to the lower disk  220  effectively changes the diameter of the upper  210  and the lower disk  220 , thereby reducing their tendency to uniformly move in opposite directions. 
         [0033]    Referring now to  FIG. 5 , a cross sectional view of a fluid dynamic motor with a lobed ring spacer in accordance with one embodiment is shown. The fluid dynamic motor  500  includes a spacer ring  510 . The spacer ring  510  is coupled to the hub  120  and further connected to the upper  210  and the lower disk  220 . The spacer ring  510  is lobed. Having a lobed spacer ring  510  causes the upper disk  210  and the lower disk  220  to deflect independently and not in unison. Accordingly, energy from tilting and/or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting and/or axial motions by the upper  210  and lower disks  220  do not cancel each other. 
         [0034]    In other words, the lobed spacer ring  510  changes the boundary conditions of the upper disk  210  and the lower disk  220 , thereby shifting the natural frequencies of the upper  210  and lower disk  220  apart such that they vibrate out of phase. As such, tilting and/or axial motions of the upper disk  210  and the lower disk  220 , whether due to windage or not, do not occur in unison. The lobed spacer ring  510  contacts the upper disk  210  at a different location in comparison to the lower disk  220  and effectively changes the diameter of the upper  210  and the lower disk  220 , thereby reducing their tendency to move in opposite directions in unison. 
         [0035]    It is appreciated that the spacer ring may have any shape as long as the spacer contacts the upper disk at a different location in comparison to the lower disk. For example, referring now to  FIG. 6 , a cross sectional view of a fluid dynamic motor with a knee shaped ring spacer in accordance with one embodiment is shown. The fluid dynamic motor  600  may include a spacer ring  610 . The spacer ring  610  is coupled to the hub  120  and is further coupled to the upper disk  210  and the lower disk  220 . The spacer ring  610  may be knee shaped such that it contacts the upper disk  210  at a different location in comparison to the lower disk  220 . Having a knee shaped spacer ring  610  causes the upper disk  210  and the lower disk  220  to deflect independently and not in unison. Accordingly, energy from tilting and/or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting and/or axial motions by the upper  210  and lower disks  220  do not cancel each other. 
         [0036]    In other words, the knee shaped spacer ring  610  changes the boundary conditions of the upper disk  210  and the lower disk  220 , thereby shifting the natural frequencies of the upper  210  and lower disk  220  apart such that they vibrate out of phase. As such, tilting and/or axial motions of the upper disk  210  and the lower disk  220 , whether due to windage or not, do not occur in unison. The knee shaped spacer ring  610  contacts the upper disk  210  at a different location in comparison to the lower disk  220  and effectively changes the diameter of the upper  210  and the lower disk  220 , thereby reducing their tendency to move in opposite directions in unison. 
         [0037]    It is appreciated that the spacer ring shapes described herein are exemplary and not intended to limit the scope of the embodiments. For example, the upper portion of the ring spacer may have a non-uniform diameter and the lower portion of the ring spacer may have a uniform diameter. 
         [0038]    Referring now to  FIG. 7 , a cross sectional view of a fluid dynamic motor with two spacer rings in accordance with one embodiment is shown. The fluid dynamic motor  700  according to one embodiment includes an upper spacer ring  710  and a lower spacer ring  720 . The upper spacer ring  710  is coupled to the upper disk  210  and is further coupled to the hub  120 . The lower spacer ring  720  is coupled to the lower disk  220  and is further coupled to the hub  120 . It is appreciated that the upper spacer ring  710  contacts the upper disk  210  at a different location in comparison to the lower spacer ring  720  and that the two spacer rings are separated from one another. 
         [0039]    Having two spacer rings  710  and  720  contacting their respective disks in different locations cause the upper disk  210  and the lower disk  220  to deflect independently and not in unison. Accordingly, energy from tilting and/or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting and/or axial motions by the upper  210  and lower disks  220  do not cancel each other. 
         [0040]    Accordingly, having an upper spacer ring  710  and a lower spacer ring  720  contacting their respective disks in different locations change the boundary conditions of the upper disk  210  and the lower disk  220 . As such, the natural frequencies of the upper  210  and lower disk  220  are shifted apart and the disks vibrate out of phase. As such, tilting and/or axial motions of the upper disk  210  and the lower disk  220 , whether due to windage or not, do not occur in unison. In other words, having two spacer rings shaped such that the outer edge of the upper spacer ring  710  contacts the upper disk  210  at a different location in comparison to the point of contact between the lower spacer ring  720  and lower disk  220  effectively changes the diameter of the upper  210  and the lower disk  220 , thereby reducing their tendency to move in opposite directions in unison. 
         [0041]    Referring now to  FIG. 8 , a cross sectional view of a fluid dynamic motor with different disk diameters in accordance with one embodiment. In this embodiment, the fluid dynamic motor  800  includes an upper disk  810  that has a different diameter than the lower disk  820 . Furthermore, the fluid dynamic motor  800  may include one or more spacers in accordance with one of the embodiments described above. For example, in this embodiment, the fluid dynamic motor  800  includes a lobed spacer  510 . But it is appreciated that the spacer ring may be according to any of the spacers described above, e.g., tapered spacer, different spacer chamfers, etc. 
         [0042]    Different diameters for the upper disk  810  and the lower disk  820  cause the upper disk  810  and the lower disk  820  to deflect independently and not in unison. Moreover, having a ring spacer that contacts the upper disk  810  and the lower disk  820  at different locations may further help the disks deflect independently and not in unison. Accordingly, energy from tilting and/or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting and/or axial motions by the upper  810  and lower disks  820  do not cancel each other. 
         [0043]    In other words, the differently sized disks change the boundary conditions of the upper disk  810  and the lower disk  820 , thereby shifting the natural frequencies of the upper  810  and lower disk  820  apart such that they vibrate out of phase. As such, tilting and/or axial motions of the upper disk  810  and the lower disk  820 , whether due to windage or not, do not occur in unison. Further, addition of a spacer ring contacting the upper disk  810  at a different location in comparison to the lower disk  820  further changes the effective diameter of the upper  810  and the lower disk  820 , thereby reducing their tendency to move in opposite directions in unison. 
         [0044]    Referring now to  FIG. 9 , a cross sectional view of a fluid dynamic motor with different disk thickness in accordance with one embodiment is shown. The fluid dynamic motor  900  includes an upper disk  910  and a lower disk  920  that have different thicknesses. For example, the upper disk  910  is thinner in comparison to the lower disk  920 . Different thickness for the disks causes the natural frequencies of the upper disk  910  to separate from the lower disk  920 , which causes them to deflect independent from one another and not to move in unison. As such, the disks couple through the fluid dynamic bearing that dampens the motion in axial and/or tilting directions. It is appreciated that a spacer ring making contact with the upper disk  910  and the lower disk  920  at different locations may further exacerbate independent movements of the upper and the lower disks. It is appreciated that the spacer ring may be in accordance with any of the embodiments described above (in this example, the spacer ring is lobed). Accordingly, energy from tilting and/or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting and/or axial motions by the upper  910  and lower disks  920  do not cancel each other. 
         [0045]    It is further appreciated that independent movements of the upper  1010  and the lower disk  1020  may further be exacerbated by having the upper and the lower disks with different diameters, as shown in  FIG. 10 . As shown by the fluid dynamic bearing  1000 , the upper disk  1010  has a different diameter in comparison to the lower disk  1020 . In this embodiment, the lower disk  1020  has a thickness that is greater than the thickness of the upper disk  1010 . However, it is appreciated that their respective thicknesses may be the same and having different thicknesses is merely exemplary and not intended to limit the scope of the present invention. Moreover, it is appreciated that the ring spacer may be in accordance with any of the embodiments described above (in this example, the spacer ring is lobed). However, it is appreciated that other embodiments may not require a ring spacer since the diameter of the upper and the lower disks are different. Accordingly, energy from tilting and/or axial motions are transferred to the motor&#39;s fluid dynamic bearing because the tilting and/or axial motions by the upper  1010  and lower disks  1020  do not cancel each other. 
         [0046]    It is appreciated that different materials may be used to vary the density and the elasticity of each disk to ensure that the disks do not move in unison. For example, different types of glass, polycarbonate plastic, aluminum, protective acrylic coating, etc., may be used for the upper disk than from the lower disk. The embodiments described above may be combined in any fashion, as desired. For example, any combination of the ring spacers (described above), with different diameters for the disks, with different thicknesses for different disks, different material for the disks, etc., may be used to ensure that the disks do not move in unison and to ensure transfer of energy to the fluid dynamic bearing. 
         [0047]    Referring now to  FIGS. 11A and 11B , a comparison of the vibration measurement between a system without spacers and an exemplary embodiment of the present invention is shown.  FIG. 11A  illustrates vibration measurement when the top and the bottom disks have the same thickness. As can be seen, high vibrations are measured for the tilting and the umbrella modes illustrated by 0,0 and 0,1 mode for frequencies over a 1000 Hz. However, lower vibration measurements are registered for tilting and the umbrella modes for the top and the bottom disks having different thicknesses, as shown by  FIG. 11B . In other words, a fluid dynamic motor in accordance with embodiments herein transfer the tilting and/or axial motions of the disks to the fluid dynamic bearing, thereby dampening the motions. As such, the disk density may be increased. 
         [0048]    The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings.