Abstract:
A disc drive spindle motor having improved acoustic properties for use in a disc drive data storage system is provided. In one embodiment, the disc drive spindle motor a base, a stationary member, a rotor and a stator. A bearing interconnects the rotor with the stationary member and allows the rotor to rotate about the stationary member. The stator includes a plurality of teeth extending from a back iron. At least one stiffening member is coupled to the stator, joining the teeth at an end opposite the back iron. The stiffening member substantially reduces vibrations in the stator thereby reducing acoustic noise generated by the motor.

Description:
This application claims benefit of U.S. Provisional Application No. 60/273/003, entitled STATOR RING MASS/STIFFENER FOR IMPROVED ACOUSTICS, filed Mar. 1, 2001 by Herndon et al., which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of stator assemblies of the type used in concert with high-speed spindle elements. More specifically, the invention relates to stator assemblies utilized in a disc drive system. 
     BACKGROUND OF THE INVENTION 
     Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle. The information is accessed by means of read/write heads generally located on a pivoting arm that moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information. 
     During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside a hub that supports the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted by means of two ball or hydrodynamic bearing systems to a motor shaft disposed in the center of the hub. Generally, such motors include a stator comprising a plurality of teeth arranged in a circle. Each of the teeth support a plurality of coils or windings that may be sequentially energized to polarize the stator. A plurality of permanent magnets are disposed in alternating polarity adjacent the stators. As the coils disposed on the stators are sequentially energized in alternating polarity, the magnetic attraction and repulsion of each stator to the adjacent magnets cause the spindle to rotate, thereby rotating the disc and passing the information storage tracks beneath the head. 
     As the coils on the stator are sequentially energized to generate the rotational force, the stators begin to vibrate. Additionally, tolerance stacks across the drive components result in gaps therebetween in a direction along the spindle axis. The energization of the coils produces a solenoid effect in this direction that causes the drive components to move in response to the motor switching, thereby creating an axial vibration. When the resonant frequency of these components, including the stator, is near the switching frequency of the motor, there is little damping of vibrations. Such vibrations, whether in the form of structural mechanical resonances or the forced response of a thin surface member, tend to produce acoustic noise that is irritating to many users and conveys the appearance of an inferiorly constructed unit. 
     Thus, the problem presented is to minimize the vibrations and noise contribution produced by the stator during motor operation. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a disc drive spindle motor having improved acoustic properties is provided. In one embodiment, the disc drive spindle motor includes a base, a stationary member, a rotor and a stator. A bearing interconnects the rotor with the stationary member and allows the rotor to rotate about the stationary member. The stator includes a plurality of teeth supported from a stationary support member. The teeth have a plurality of coils wound thereover. At least one stiffening member is coupled to the stator, joining the teeth at an end opposite the stationary support member. The stiffening member substantially reduces and/or tunes vibrations in the stator thereby reducing acoustic noise generated by the motor. 
     In another aspect of the invention, a disc drive storage system having a stiffened stator is provided. In one embodiment, the disc drive storage system generally includes a housing, a stator, a rotatable member and at least one data storage disc that is coaxially attached to the rotatable member. The housing includes a base that has a stationary member attached thereto. The stationary member is coaxial with a central axis of the base. The rotatable member is interface by a bearing with the stationary member. The stator, also coaxial with the rotatable member, includes a plurality of teeth extending from an annular support member. At least a first annular stiffening member is bonded between the ends of the teeth which minimizes and/or tunes the vibration and acoustic noise contribution of the stator during the system&#39;s operation. 
     While the invention is useful in disc drive spindle motors having ball bearings, the invention is particularly useful in hydrodynamic bearing motors to reduce or eliminate pure vibration tones that become more noticeable with lower levels of background vibration. Additionally, the invention may be used to tune the frequency of the stator away from excitation frequencies of other components of the motor. The stiffened stator can have an axial position that is within or below the hub, and can have a radial position that is internal or external to the rotor. The mass of the stiffening member may be tuned to shift the frequency of the stator away from frequencies of other drive components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a top plan view of a disc drive data storage device, in accordance with the invention; 
     FIG. 2 is a sectional view of an isolated hydrodynamic bearing spindle motor in accordance with the invention; 
     FIG. 3 is a plan view of one embodiment of a stator in accordance with the invention; 
     FIG. 4 is a sectional view of the stator shown in FIG. 3, taken along lines  4 — 4 ; 
     FIG. 5 is a sectional view of a ball bearing spindle motor in accordance with the invention; and 
     FIG. 6 depicts one embodiment of a spindle motor in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention comprises a spindle motor for a disc drive data storage device wherein the stator is stiffened and/or tuned to reduce acoustic levels in the storage device. FIG. 1 is a plan view of a typical disc drive  10  wherein the invention is useful. Disc drive  10  includes a housing base  12  and a top cover  14 . The housing base  12  is combined with top cover  14  to form a sealed environment to protect the internal components from contamination by elements from outside the sealed environment. 
     The base and top cover arrangement shown in FIG. 1 is common in the industry. However, other arrangements of the housing components have been frequently used, and the invention is not limited to the configuration of the disc drive housing. For example, disc drives have been manufactured using a vertical split between two housing members. In such drives, that portion of the housing half that connects to the lower end of the spindle motor is analogous to base  12 , while the opposite side of the same housing member, that is connected to or adjacent the top of the spindle motor, is functionally the same as the top cover  14 . 
     Disc drive  10  further includes a disc pack  16  that is mounted for rotation on a spindle motor (not shown) by a disc clamp  18 . Disc pack  16  includes a plurality of individual discs that are mounted for co-rotation about a central axis. Each disc surface has an associated head  20  that is mounted to disc drive  10  for communicating with the disc surface. In the example shown in FIG. 1, heads  20  are supported by flexures  22  that are in turn attached to head mounting arms  24  of an actuator body  26 . The actuator shown in FIG. 1 is of the type known as a rotary moving coil actuator and includes a voice coil motor (VCM), shown generally at  28 . Voice coil motor  28  rotates actuator body  26  with its attached heads  20  about a pivot shaft  30  to position heads  20  over a desired data track along an arcuate path  32 . While a rotary actuator is shown in FIG. 1, the invention is also useful in disc drives having other types of actuators, such as linear actuators. 
     FIG. 2 is a sectional view of a hydrodynamic bearing spindle motor  132  in accordance with the invention. Spindle motor  132  includes a stationary member (shaft)  134 , a hub  136  and a stator  138 . In the embodiment shown in FIG. 2, the shaft is fixed and attached to base  112  through a nut  140  and a washer  142 . The hub  136  is supported by the shaft  134  through a hydrodynamic bearing  137  for rotation about shaft  134 . The bearing  137  includes a radial working surface  146  and axial working surfaces  148  and  150 . The shaft  134  includes fluid ports  154 ,  156  and  158  that supply hydrodynamic fluid  160  and assist in circulating the fluid along the working surfaces of the bearing. 
     The spindle motor  132  further includes a thrust bearing  145  that forms the axial working surfaces  148  and  150  of hydrodynamic bearing  137 . A counterplate  162  cooperates with the working surface  148  to provide axial stability for the hydrodynamic bearing and to position the hub  136  within the spindle motor  132 . An o-ring  164  is provided between the counterplate  162  and the hub  136  to seal the hydrodynamic bearing  137 . The o-ring  164  prevents hydrodynamic fluid  160  from escaping between the counterplate  162  and the hub  136 . If an o-ring is not used, then the counterplate may be laser welded to the hub in order to seal the hydrodynamic bearing. The present invention is useful with this and other forms of hydrodynamic bearings and is not limited to use with this particular configuration. 
     The hub  136  includes a disc carrier member  166  that supports disc pack  16  (shown in FIG. 1) for rotation about shaft  134 . The disc pack  16  is held on disc carrier member  166  by the disc clamp  18  (also shown in FIG.  1 ). A plurality of permanent magnets  170  are attached to the outer diameter of the hub  136 , with the hub  136  and magnets  170  acting as a rotor for the spindle motor  132 . 
     The stator  138  is generally formed of a stack of stator laminations  172  and associated stator windings  174 . The stator  138  is generally retained in the base  112  by fasteners, adhesives or other conventional methods. In the embodiment illustrated in FIG. 2, the stator  138  is disposed in a pocket formed in the base  112 . A tab  120  is fastened by a screw  122  to the base  112  and includes a portion that overlies the stator  138  thus retaining the stator  138  in the pocket of the base  112 . In accordance with the invention, the stator  138  is stiffened by at least a first stiffening member  188  coupled thereto. Optionally, one or more additional stiffening members such as a second stiffening member  189  may also be coupled to the stator  138 . 
     FIG. 3 is a plan view of one embodiment of a stator  200  having at least a first stiffening member  280  bonded thereto. FIG. 4 is a sectional view of the stator  200 , taken along lines  4 — 4  of FIG.  3 . The stator  200  includes a stator lamination  202  comprising an annular support member  204  and a plurality of teeth  206   a - 206   l , that extend inward from the support member  204  toward a central axis  207 . The teeth  206   a - 206   l  are disposed about an inner diameter  222  of the stator  200 . A plurality of phase windings  208   a - 208   l  are wound on the stator teeth  206   a - 206   l , respectively, for magnetic communication with an internal rotor (not shown). The phase windings  208   a - 208   l  can have a number of winding configurations. Some examples of phase windings that may benefit from the invention are discussed in U.S. patent Ser. No. 08/469,643, entitled IRONLESS HYDRODYNAMIC SPINDLE MOTOR, filed Jun. 6, 1995 by Dunfield et al., and in U.S. patent Ser. No. 08/400,661, entitled HYDRODYNAMIC SPINDLE MOTOR HAVING DISTRIBUTED WINDINGS, filed Mar. 8, 1995 by Dunfield et al., both of which are commonly assigned and are hereby incorporated by reference in their entireties. 
     A flexible printed circuit (FPC)  210  carries a plurality of conductors  212  that are electrically connected to start and finish winding terminations  214 ,  216 ,  218  and  220 . The terminations  214 ,  216 ,  218  and  220  are electrically connected to the phase windings  208   a - 208   l  in a conventional manner. 
     The support member  204 , stator teeth  206   a - 206   l  and windings  208   a - 208   l  may optionally include an overmold  209 . The overmold  209  is generally a resilient rubber-like or plastic-like material that dampens the vibrational energy of the stator  200 . Each of the stator lamination teeth  206   a - 206   l  remain exposed at an end  236  of the teeth  206   a - 206   l  defined along inner diameter  222  for close communication with the rotor. Generally, overmolded stators can have a number of configurations. One example of an overmolded stator that may benefit from the invention is described in U.S. Pat. No. 5,694,268, entitled SPINDLE MOTOR HAVING OVERMOLDED STATOR, issued Dec. 2, 1997 to Dunfield et al., which is hereby incorporated by reference in its entirety. 
     The first stiffening member  280  is generally adhered between two or more of the teeth  206   a - 206   l  adjacent the ends  236 . The first stiffening member  280  may be a ring or a segment thereof, and in one embodiment is bonded to each of the teeth  206   a - 206   l . The first stiffening member  280  substantially prevents relative movement between the individual teeth  206   a - 206   l , thereby substantially eliminating the resonance modes of the individual teeth  206   a - 206   l . In stators  200  incorporating an overmold, the first stiffening member  280  is generally disposed between the overmold  209  and the end  236  of the teeth  206   a - 206   l  or be optionally encapsulated in the overmold  209 . 
     The first stiffening member  280  may be fabricated from a variety of substantially rigid materials or composites suitable for mechanically coupling the teeth  206   a - 206   l  of the stator  200 . As the teeth  206   a - 206   l  coupled by the first stiffening member  280  vibrate in unison along the central axis  207  in what is known as an umbrella mode, the mass of the first stiffening member  280  (along with any other stiffening members utilized) should be selected to shift (e.g., tune) the umbrella mode away from any motor excitation frequencies. Thus, the rigidity of stiffening member  280  substantially prevents the vibration of the teeth  206   a - 206   l  relative each other unlike the overmold  209  that absorbs vibration between the teeth  206   a - 206   l . Since the frequency of a member (such as the stator  200 ) is a function of the square root of the stiffness divided by the mass, adding mass to the first stiffening member  280  will shift the umbrella mode of the stator  200  to a lower frequency. Accordingly, the mass of the stiffening member  280  (including any other stiffening members) may be selected to move the umbrella mode away from other know excitation frequencies of other motor or drive components. 
     The profile of the first stiffening member  280  may be selected to enhance rigidity and should include sufficient surface area to adequately bond the member  280  to the teeth  206   a - 206   l . In one embodiment, the stiffening member  280  is ring-shaped and has a square or rectangular cross section. While the invention is particularly useful in hydrodynamic bearing motors to reduce pure tone vibrations where the background vibration level is relatively low, the invention is also useful in motors having ball bearings to reduce or eliminate the transfer of vibrations from the stator to the base. 
     Optionally, a second stiffening member  282  (and other stiffening members when utilized) is typically configured similar to the first stiffening member  280 . In the embodiment depicted in FIG. 4, the second stiffening member  282  is adhered to the opposite side of the teeth  206   a - 206   l  relative to the first stiffening member  280 . 
     FIG. 5 illustrates one embodiment of a spindle motor having ball bearings, as opposed to a hydrodynamic bearing. The spindle motor  550  includes a shaft  552 , a hub  554  and a stator  556 . The shaft  552  is a stationary shaft that is fixedly attached to a base  558 . The shaft  552  is also attached to the inner races of ball bearings  560  and  562 . The hub  554  is attached to the outer races of bearings  560  and  562  for rotation about the shaft  552 . The hub  554  includes a disc carrying member  564  that carries a plurality of magnetic discs (not shown) for rotation about the shaft  552 . The hub  554  also carries a plurality of permanent magnets  566  that form a rotor for the spindle motor  550 . As in the embodiments described with reference to FIGS. 2-4, the stator  556  includes one or more stiffening members, for example, a first stiffening member  502  and a second stiffening member  504 . 
     FIGS. 2-5 illustrate embodiments in which the stator is positioned external to the hub such that the stiffening members are positioned along the inner diameter of the stator. However, the stiffening members can also be positioned along the outer diameter of the stator. 
     FIG. 6 depicts one embodiment of a spindle motor having stiffening members positioned along the outer diameter of the stator. Spindle motor  610  includes a shaft  612 , a hub  654  and a stator  616 . The shaft  612  is a stationary shaft that is fixedly attached to a base  618 . The hub  654  is rotatably disposed on the shaft  612  having a hydrodynamic bearing  656  disposed therebetween. Alternatively, one or more ball bearings may be utilized in lieu of the hydrodynamic bearing  656 . The hub  654  includes a disc carrying member  620  that carries a plurality of magnetic discs (not shown) for rotation about the shaft  612 . The hub  654  also carries a plurality of permanent magnets  622  that forms a rotor for spindle motor  610 . As in the embodiments described with reference to FIGS. 2-4, stator  616  includes one or more stiffening members, for example, a first stiffening member  602  and a second stiffening member  630 , for reducing vibration and acoustic noise generation of the motor  610 . 
     Integrating the stiffening members to the stator has several advantages. First, the stiffeners link the individual stator teeth by their ends thereby substantially eliminating the resonances of the individual teeth. Additionally, the mass of the stiffening members may be tuned (i.e., selectively increased or decreased) to move the frequency of the stator away from the motor and drive component&#39;s excitation frequencies, thus minimizing the stator&#39;s contribution to vibration and acoustic noise generated by the drive. 
     Although the invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the placement of one or more stiffening members disposed between the teeth of the stator can be configured in a variety of ways and can include a combination of the embodiments discussed above. The embodiments shown in the figures are provided by way of example only. Also, the stiffened stator can be implemented in a variety of stator and base configurations. The stator could be supported directly from the shaft, rather than the base supporting the shaft, and still usefully incorporate the invention. The stiffened stator of the invention can be used in fixed shaft or rotating shaft spindle motors. In a rotating shaft spindle motor, the bearing is located between the rotating shaft and an outer stationary sleeve that is coaxial with the rotating shaft. The stator in such a configuration could be supported either from the base or the interior of the sleeve. The term “base” used herein refers to the base itself or any stationary extension thereof.