Abstract:
A high speed disk drive utilizing a vibration absorber, coupled between a center base and a retaining frame via a plurality of vibration transfer-dampers, to absorb vibration of data readout head and data storage disk, thereby reducing vibration of both data readout head and outer housing of disk drive, allowing high speed data readout from the data storage disk.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a high speed data storage disk drive, and more particularly to a disk drive having a vibration damper for more accurate data access at high speed rotation. 
     2. Background of the Invention 
     Data storage disks such as optical compact disks (CD) have become popular data storage media, being capable for storing large amounts of data at a relatively low cost per datum. A typical CD-ROM can store about 640 MBytes of data, and the new Digital Versatile Disks (DVD) can store more than 2.5 GBytes of data. A disk drive comprising a data pickup head is used to read data from the compact disks. The data pickup head must align precisely to the recording tracks of the compact disks to accurately read data. 
     A disadvantage of the optical disks has been the low data transfer rate of the disk drives. Earlier CD-ROM drives had a data transfer rate of about 150 KBytes/sec. By increasing the rotation speed of the optical compact disk, it is possible to increase the data transfer rate. Presently, 32× speed CD-ROM drives have been developed. The 32× speed CD-ROM drive is capable of rotating a disk at a speed which is thirty-two times the speed of a conventional audio CD. When a disk rotates at high speed, any imbalance on the disk itself will result in an increase in the vibration of the disk drive. 
     A perfect disk has its center of mass exactly at the geometrical center of the disk. Due to manufacturing errors, the center of mass of a CD-ROM disk typically vary by 0-6 g-mm from the center (where 1 g-mm equals to 1 gram of mass located 1 mm from center). This is tolerable for 16× or slower speed CD-ROM drives. But for a 32× or higher speed CD-ROM drive with a disk rotating at approximately 8000 rpm (revolutions per minute), the vibration due to an imbalance will likely result in reading errors arising from the inability of the data pick-up head to align precisely with the recording tracks on the disk. The vibration will also be translated to the housing of the CD-ROM drive, and further on to the computer housing, resulting in an annoying vibration noise of the drive unit. 
     One conventional method of reducing vibration is to use a heavy metal frame to stabilize the pickup head and data storage disk. As the disk drive speed increases, the weight of the base of the disk drive motor must also be increased. However, to reduce the vibration to an acceptable level, the weight required for a 33× speed disk drive would be about 3 times the weight of normal disk drives. 
     Another method that has been proposed is to use vibration absorbers, such as soft rubber pads to absorb vibration. FIG. 1 shows a schematic drawing of the damping mechanism of a prior art disk drive comprising a center base and a retaining frame. The center base supports a motor and a data pickup head. The retaining frame is connected to an outer housing. Rubber pads are inserted between the retaining frame and the center base to absorb and reduce vibration (the details of the motor and pickup head are not shown). 
     Vibration absorbers with different damping coefficients have different vibration damping properties. Typically, soft rubber pads have been used to dampen high frequency vibration, whereas hard rubber pads are used to dampen low frequency vibration. 
     FIG.  2 ( a ) show the vibration amplitude of the center base at different motor rotation frequencies when soft damping pads are used in a prior art disk drive. FIG.  2 ( b ) show the vibration amplitude of the retaining frame at different motor drive frequencies when soft damping pads are used in a prior art disk drive (“f 0 ” refers to the normal operation frequency of the disk drive). The soft damping pads are made from a material which will have a resonant frequency lower than the operation frequency of the motor drive. As can be seen, when soft damping pads are used, the vibration level of the retaining frame is greatly reduced, while the vibration amplitude of the center base remains quite high (a vertical scale of one corresponds to the vibration amplitude of a stand-alone center base (i.e., not coupled to the retaining frame) of a prior art disk drive operating at frequency f 0 ). 
     FIG.  2 ( c ) show the center base vibration amplitude versus motor drive rotation frequency curve when hard damping pads are used in a prior art disk drive. FIG.  2 ( d ) show the retaining frame vibration amplitude versus motor drive rotation frequency curve when hard damping pads are used in a prior art disk drive. The hard damping pads are made from a material which will have a resonant frequency higher than the operation frequency of the motor drive. As can be seen, when hard damping pads are used, the vibration level of the center base can be reduced somewhat, while the vibration amplitude of the retaining frame becomes quite high. 
     As can be seen, using damping pads cannot satisfactorily reduce the vibration caused by high speed rotation of disks with center of mass located away from the geometrical center. 
     SUMMARY OF THE INVENTION 
     What is needed, therefore, is a method and device for reducing vibration of a high speed disk drive without unduly increasing overall weight. 
     The present invention is a disk drive for reading data from a data storage disk, the disk drive comprising a center base, a retaining frame, a vibration absorber, a first plurality of vibration transfer-dampers, and a second plurality of vibration transfer-dampers. The first plurality of vibration transfer-dampers, and a second plurality of vibration transfer-dampers. The center base supports the motor and the data storage disk. The retaining frame retains the vibration absorber and the center base. The first plurality of vibration transfer-dampers are coupled to the retaining frame and the vibration absorber for damping and transferring vibrations. The second plurality of vibration transfer-dampers are coupled to the center base and the vibration absorber, for transferring and damping vibrations of the center-base to the vibration absorber, thereby reducing the vibration of the center base. 
     One advantage of the present invention is to provide a cost-effective method of reducing vibration in high speed disk drives caused by disk imbalances, resulting in more reliable read/write operations. 
     Another advantage is that the vibration noise incurred on the outer housing is reduced, thereby lowering the vibration noise level during disk drive operation. 
    
    
     The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages and embodiments of the invention will be apparent to those skilled in the art from the following description, accompanying drawings and appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing showing a prior art compact disk drive. 
     FIG.  2 ( a )-( d ) show the relationship between vibration amplitude and operation frequency of the center base and the retaining frame-using damping pads with different damping coefficients in a prior art disk drive. 
     FIG. 3 is a drawing of an embodiment of the present invention. 
     FIG.  4 ( a )-( c ) are plots of vibration amplitude of the retaining frame, the vibration absorber, and the center base versus motor drive frequency. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 3 shows a preferred embodiment of the present invention. A disk drive  300  comprises a retaining frame  302 , a vibration absorber  304 , a first plurality of vibration transfer-dampers  308 , a center base  306 , and a second plurality of vibration transfer-dampers  310 . Disk drive  300  also comprises a data readout head and a motor drive (not shown in the drawing). Typically, the data readout head and the motor drive are mounted on center base  306 . A clamp is coupled to the motor for supporting and securing a data storage disk (not shown). When the motor rotates, the data storage disk rotates accordingly; the data readout head moves over the data storage disk and reads (or writes) data from (or to) the data storage disk. The operation of reading (writing) data from (to) a data storage disk is known in the art. 
     Center base  306  is preferably a plastic frame for supporting the data readout head and the motor drive. Center base  306  is coupled to vibration absorber  304  via the second plurality of vibration transfer-dampers  310 . Typically, the second plurality of vibration transfer-dampers  310  comprises four rubber pads, and are made of a material having a resonant frequency higher than the operation frequency of the motor drive. 
     Vibration absorber  304  is preferably a metal frame with mass larger than center base  306 . Vibration from the rotational motion of the motor drive and data storage disk is transferred to vibration absorber  304  through the second plurality of vibration transfer-dampers  310 . Part of the vibration is dampened by the second plurality of vibration transfer-dampers  310 . 
     Vibration absorber  304  is coupled to retaining frame  302  via a first plurality of vibration transfer-dampers  308 . Typically, the first plurality of vibration transfer-dampers  308  comprises four rubber pads having a resonant frequency lower than the operation frequency of the motor drive. Retaining frame  302  can be metal or plastic, preferably plastic, and is coupled to the housing of the disk driver. 
     FIG. 3 shows another embodiment of the present invention wherein a flap  312 , or plurality of flaps  312 ,  314 ,  316 , and  318  are stably disposed at the edge(s) of vibration absorber  304  to provide wind motion responsive to the vibration motion of the flaps  312  et al. which are in turn responsive to the vibration motion of vibration absorber  304 . The motion of the flaps  312  et al. will provide further damping due to air resistance and also produce thermal dispersion due to the flapping. Another embodiment (not shown) allows non-stable attachment of the flaps  312  et al. through hinges or springs which will provide greater range of flapping motion than that of vibration absorber  304  itself. This will necessarily result in less damping due to air resistance but will increase the thermal dispersion. There are of course other equivalent embodiments such as various non-rectangular shapes (e.g., semicircles), flaps with holes and/or baffles which constitute substantially the same means for optimizing the damping and/or the thermal dispersion in substantially the same way. 
     FIG.  4 ( a ) is a plot of the relationship between vibration amplitude of retaining frame  302  versus motor drive rotation frequency when operation frequency of the motor drive is 6000 rpm. The vertical scale of one corresponds to the vibration amplitude of a stand-alone center base of a disk drive. By utilizing the vibration absorber and vibration transfer-damper assembly; the vibration amplitude of retaining frame  302  is reduced to less than 10% of the stand-alone center base. The operation frequency of 6000 rpm is only an example; the reduction of vibration holds true for other operation frequencies as well. 
     FIG.  4 ( b ) is a plot of the vibration amplitude of vibration absorber  304  versus motor drive rotation frequency. Again, the vertical scale of one corresponds to the vibration amplitude of the stand-alone center base. The vibration amplitude of vibration absorber  304  at the operation frequency of 6000 rpm is almost twice that of a stand-alone center base. The vibration of center base  306  is transferred to vibration absorber  304 . 
     FIG.  4 ( c ) is a plot of the vibration amplitude of center base  306  versus motor drive rotation frequency. Again, the vertical scale of one corresponds to the vibration amplitude of the stand-alone center base. By utilizing the vibration absorber and vibration transfer-damper assembly, the vibration amplitude of center base  306  at the operation frequency of 6000 rpm is reduced to less than 40%. 
     Table 1 is a comparison of vibration of the center base of a CD-ROM drive (for example, the AOpen CD-932E manufactured by Acer Incorporated) utilizing the present invention and vibration of the center base of other CD-ROM drives (e.g., TEAC CD-532E and NEC CDR-1900A). For the vibration magnitude in the Z direction, the AOpen CD-932E produces 0.472 m/s 2  at 6900 rpm and 0.622 m/s 2  at 8000 rpm. In contrast, the vibration magnitude for the TEAC CD-532E is 0.911 m/s 2 , and for the NEC CDR-1900A is 2.220 m/s 2  at 6900 rpm. The Z direction corresponds to the direction perpendicular to the surface of the data storage disk. By reducing vibration in the Z direction, the distance between the data readout head and the data storage disk can remain relatively constant to facilitate accurate data readout. By utilizing the present invention, the AOpen CD-932E is capable of operation at a speed of 8000 rpm, resulting in a data transfer rate 34 times that of an audio CD. By comparison, the highest data transfer rate by the other disk drives is 31 times that of an audio CD. 
     
       
         
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                                                TEAC 
                 NEC 
                 AOpen 
               
               
                   
                 CD-532E 
                 CDR-1900A 
                 CD-932E 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   Highest motor drive rotation 
                 6900 rpm 
                 6900 rpm 
                 8000 rpm 
               
               
                 speed 
               
               
                 Highest data transfer rate 
                 31× 
                 31× 
                 34× 
               
               
                 (multiple of normal audio 
               
               
                 CD) 
               
               
                 Access time * 
                 96 ms 
                 85 ms 
                 98 ms 
               
             
          
           
               
                   Vibration (m/s 2 ) 
                         0.635 
                 0.677 
                 0.591 
                 0.756 
               
               
                 X 
                 0.650 
                 1.270 
                 0.471 
                 0.628 
               
               
                   
                 0.911 
                 2.220 
                 0.472 
                 0.622 
               
               
                 Y 
                   
                   
                 (6900 
                 (8000 
               
               
                   
                   
                   
                 rpm) 
                 rpm) 
               
               
                 Unbalanced disk 6 g-mm Z 
               
             
          
           
               
                   Noise 
                 49.8 dB 
                 56.2 dB 
                 49.0 dB 
               
               
                   
               
               
                 * Tested with CD-Certify Pro (12/3/1997)  
               
             
          
         
       
     
     While the above is a full description of the, specific embodiments, various modifications, alternative constructions and equivalents may be used. For example, the material of the vibration transfer-dampers between the vibration absorber and the center base, and between the vibration absorber and the retaining frame can be changed. The material and weight of the center base, vibration absorber, and retaining frame can also be adjusted according to practical considerations. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.