Power reduction shroud for a hard disk drive
REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 08/266,729 filed on Jun. 27, 1994, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to disk drive data storage systems. More particularly, the present invention relates to a high capacity, Winchester-type disk drive employing a substantially circumferential shroud proximate a disk therein to reduce the electrical power consumed by the disk drive. 
     BACKGROUND OF THE INVENTION 
     Over time, Winchester-type fixed disk drives have evolved from large computer peripheral devices having large rotating storage disks and hydraulic head positioning mechanisms into disk drives having very small, fully enclosed packages for inclusion entirely within a housing of small computing systems, such as workstations, personal computers, and portable or laptop computers. Coupled with the miniaturization of disk drives, disk diameters have been reduced from 24 inches to as small as 1.8 inches. 
     Generally, the external package width and length dimensions of a disk drive define what is known in the art as the &#34;form factor&#34; of the disk drive. While disk drive form factors have progressively decreased, the aerial data storage density of the storage disk has increased dramatically. As such, physically very small disk drives provide the same or greater user data storage capacity than characterized much larger disk drives of only a few years ago. 
     The reduction of disk drive form factors has permitted direct integration of disk drives into portable or laptop computers. However, a constraint that confronts a developer of such portable computers is the limited amount of power that is available from the power pack, usually a rechargeable battery. Since a disk drive typically consumes a large fraction of the total available power in a portable computer, a disk drive which consumes less power for a given amount of storage capacity is desirable. 
     Furthermore, environmental concerns about energy conservation have made it desirable to reduce the power consumed by high-capacity disk drives used in desktop computer systems. Since the operation of disk drives significantly contributes to the total power used by a computer, a reduction in disk drive power consumption would in turn reduce the total power used by the computer. 
     High capacity, contemporary disk drives typically include multiple disks arranged in a commonly journalled stack. A plurality of transducer heads, positioned by a transducer head actuator assembly, are used to access data stored on the surfaces of the disks. Although disk drives containing multiple disks advantageously store significant quantities of data, it has been observed that such disk drives consume more power than disk drives containing a single disk. The higher power consumption is due to increased torque needed to change the momentum of a larger mass of air proximate (between) the multiple disks. The frictional drag between the disk surfaces and the air mass is known as a windage loss. In addition, the power consumption of a disk drive containing multiple disks is particularly increased when the disks are rotated at high speed, e.g. 7200 rpm. Thus, it would be advantageous to confine and control the mass of air proximate the rotating disks in an effort to reduce the power consumption of a disk drive. 
     One effort to confine and control the air mass proximate the disks in a disk drive having multiple disks is disclosed in U.S. Pat. No. 4,280,155 issued Jul. 21, 1981. Specifically, this patent discloses apparatus for controlling airflow turbulence within a large disk drive, e.g., a disk drive having disks of about eight inches in diameter. The disclosed apparatus is a cover assembly that encloses the entire disk drive assembly. The cover assembly encloses the disk drive assembly in a housing that surrounds about 270° of the disks&#39; circumference. Furthermore, to control airflow turbulence, the disks are spaced from one another by 0.9 inches. In addition, the &#39;155 patent also discloses using vanes, in a fan-like configuration attached to the rotating disk mounting hub of the disk drive and operating in combination with the enclosure, to reduce the temperature within the disk drive by controlling and directing air flow through the drive. 
     Moreover, the characterization and control of airflow between and near disks in disk drives was investigated and disclosed in E. Lennemann, &#34;Aerodynamic Aspects of Disk Files&#34;, IBM J. Res. Develop., November, 1974, pp. 480-488. Therein, airflow phenomena were described as forming particular patterns within the drive depending upon the number of disks and actuator arm position over the disk(s). 
     Therefore, a need exists in the art for an economical means of reducing the amount of total power consumed during operation of a disk drive, especially, a disk drive containing multiple disks. 
     SUMMARY OF THE INVENTION WITH OBJECTS 
     A general object of the present invention is to provide an improved high performance disk drive which overcomes limitations and drawbacks of the prior art. 
     Another general object of the present invention is to provide a Winchester-type fixed disk drive with a reduced operating current. 
     A specific object of the present invention is to incorporate a shroud proximate the disk(s) in a disk drive in order to control and confine the air mass proximate the disk(s) and lower overall power consumption of the disk drive. 
     Specifically, a disk drive, in accordance with a preferred embodiment of the invention includes a head and disk assembly which contains a spindle motor for rotating a disk hub at a constant angular velocity and at least one rotating disk mounted to the hub. The disk extends radially from the hub. Additionally, the head and disk assembly includes a rotary voice coil actuator assembly, located adjacent the rotating disk, for supporting and selectively positioning transducer heads over the surface of the disk. Such selective transducer head positioning enables the heads to access data stored on the disk. The disk drive further includes a base with a peripheral sidewall surrounding the base such that the sidewall defines an interior space. The head and disk assembly is supported by the base and is contained within the interior space. A cover generally fits over the peripheral sidewall to enclose and seal the head and disk assembly within the interior space. To control and confine the air mass proximate the disk, the disk drive contains a shroud that is positioned substantially circumferentially around the disk. Such control and confinement of the air mass near the disk reduces the power consumption of the spindle motor. Additionally, by lowering the power consumption, such a shroud also lowers the operating temperature of the disk drive. Typically, the shroud is a vertical wall extending between the base and cover and is positioned at a distance of approximately 40 mils from an edge of the disk. To facilitate access to the disk by the actuator assembly, the shroud typically does not fully circumscribe the disk, i.e., the shroud contains a gap such that approximately 320 degrees of the disk circumference is encompassed by the shroud. 
     These and other objects, advantages, aspects and features of the present invention will be more fully understood and appreciated upon consideration of the following detailed description of a preferred embodiment, presented in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the Drawings: 
     FIG. 1 shows a top plan view of a head and disk assembly, incorporating aspects and principles of the present invention, and highlighting an embodiment of the invention; 
     FIG. 2 shows a cross-sectional view of the head and disk assembly, taken along line 2--2 of FIG. 1; 
     FIG. 3 is a graph showing motor run current vs. shroud angle; and 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     FIG. 1 depicts an enlarged top plan view of a disk drive 100 incorporating one embodiment of the invention. FIG. 2 depicts a cross-sectional view, along line 2--2, of the disk drive 100 shown in FIG. 1. The reader will best understand the invention by simultaneously viewing FIGS. 1 and 2 while reading the following disclosure. 
     The disk drive contains a head and disk assembly 102 supported by a base 104 preferably formed as a precision injection aluminum casting. The head and disk assembly 102 may contain one or more commonly journalled disks 106, with five or ten disk arrangements preferred. The following discussion describes the preferred embodiment of the invention as being installed in a disk drive having multiple disks, e.g., a full height (1.6&#34;) micro-Winchester fixed disk drive having e.g. ten data storage disks of 95 millimeters (3.5&#34;) diameter, such as a model Grand Prix manufactured by Quantum Corporation of Milpitas, Calif. However, those skilled in the art will realize that the invention is useful in disk drives having any number of disks. 
     The head and disk assembly 102 includes a plurality of rotating disks 106 mounted to a spindle hub 108. Specifically, the disks are sequentially stacked upon a disk mounting flange 210 of the hub 108. Spacers 212 are positioned between successively stacked disks 106 such that the lower surface of a higher-mounted disk is separated from the upper surface of a lower-mounted disk by a predetermined distance in order to allow the transducer head assembly to pass over the disk surfaces. A clamping ring 214 is attached to the hub 108 and maintains the disks in parallel relation to one another. The annular spacers 212 space the disks 106 apart by a predetermined dimension, such as 2 mm, surface to surface. In operation, a conventional brushless DC spindle motor 200 rotates the hub 108 and the ten disks 106 clamped onto the hub 108 at a constant high angular velocity, e.g., 7200 rpm. 
     Each disk 106 is formed of a substrate material such as aluminum or glass which is coated with a magnetic storage medium such as a high Oersted thin film magnetic storage medium. Each of the disks contains a plurality of concentric data tracks formed in the magnetic storage medium. A conventional rotary voice coil actuator assembly 110, located adjacent the disk, supports a transducer head assembly 112 which &#34;flies&#34; over the surface of the disk. Operating in a conventional manner, the actuator assembly 110 selectively positions the transducer head assembly 112 over a specific data track on the disk to enable the transducer heads 114 within the transducer head assembly to access (read or write) the data within the data tracks. Conventional electronics (not shown) are provided for processing the data, for controlling the position of the actuator assembly, and for controlling the spindle motor. These electronics are connected to the head and disk assembly via ribbon cable 116. 
     More specifically, affixed to the base 104 is a continuous peripheral sidewall 118 which defines an interior space 202 that contains the disk and head assembly 102. A stamped aluminum cover 204 fits over the sidewalls 118 of the base casting 104. Those skilled in the art will appreciate that cover 204 could be manufactured of another suitable material such as steel alloy or composite. The cover 204 is securely attached to the sidewalls 118 by six screws to enclose the head and disk assembly within the interior space. In addition, the disk drive 100 contains a gasket 206, located between the cover 204 and the distal edge of the sidewalls 118, for providing a hermetic seal between the sidewalls 118 and the cover 204, and to provide a fully enclosed and sealed interior space for the head and disk assembly. 
     In accordance with a preferred embodiment of the invention, a shroud is formed about the circumference of the disks. The non-porous shroud is generally a vertical wall that is located proximate edges 208 of the disks 106 and uniformly spaced therefrom. This shroud has three elements: the sidewalls 118 located proximate the edges of the disks for nearly 180 mechanical degrees of the disk edge and multiple shroud elements 120 and 122 are inserted to, in essence, extend the sidewalls to circumscribe approximately another 90 mechanical degrees of the circumference of the disks 106. Thus, the disks are substantially circumscribed with a shroud (vertical wall) spaced a distance A (e.g. 40 mils) from the edges of the disks, as shown in FIG. 2. A gap designated by the angle α in FIG. 1 (approximately 40 mechanical degrees) in the shroud permits the rotary voice coil actuator assembly 110 to move the transducer heads unimpeded over the disks. By incorporating such shrouding about the disks 106, the mass of air which interacts with the spinning disks is controlled and confined. Consequently, as will become apparent from the experimental data discussed below, the addition of shrouding reduces power consumption and the operating temperature of the disk drive. 
     The shrouding elements are typically formed of injection molded plastic pieces or strips of plastic such as Lexan™ or by integral molded portions of the base casting. To maintain the shroud elements 120 and 122 in a fixed, arcuate position, one edge of each element 120, 122 is attached to the base 104 with cement, epoxy, or other bonding material, or by screws, or trapped in place by registration with other structure of the base, such as an arcuate groove. In such a position, the shrouds are located a uniform distance A from the disk edge 208. Additionally, to effectively shroud all the disks 106 within the disk stack, the two shrouding elements 120 and 122 extend between the base 104 and the cover 204. While in the present embodiment the shroud-to-disk distance A is approximately 40 mils, it should be understood that the distance can be optimized for each disk drive as a function of the number of disks, spacing between disks and speed of rotation of the disk stack. 
     Since an object of the present invention is to reduce overall power consumption of the spindle motor 200 and, as a result of reducing the power consumption, reduce the operating temperature of the air and components inside the disk drive 100, various experiments were conducted to verify these effects with regard to the addition of shrouding elements around the disks 106. The details and results of the experiments are detailed below. 
     Experimental Results 
     Experiments were conducted to determine whether the addition of shrouding material positioned circumferentially around the outer edge of the disks (as shown in FIGS. 1 and 2) would reduce the overall power consumption of the disk drive and also reduce the operating temperature of the air and components inside the disk drive. 
     The test was conducted in two phases. A first set of measurements was taken on a disk drive without any shrouding, i.e., control measurements. A second set of measurements was taken from the same disk drive with shrouding elements 120 and 122 added to the disk drive. 
     The equipment used in the experimentation was a Quantum Grand Prix™ (E2 series, &#34;GPE2&#34;) disk drive, powered by a conventional DC power supply and control electronics. An exemplary disk drive architecture is shown in commonly assigned U.S. Pat. No. 5,027,241 to Hatch et al., entitled: Data Head Load Beam for Height Compacted, Low Power Fixed Head and Disk Assembly&#34;, the disclosure thereof being incorporated herein by reference. As configured, the test disk drive improved upon the referenced disk drive of the &#39;241 patent and included ten disks, each being approximately 95 mm in diameter, which were spaced apart on the disk stack with a 2 mm spacing between oppositely facing disk surfaces. In order to achieve the 2 mm spacing, 50% sliders were employed. The disks were rotated at a nominal angular velocity of 7200 rpm. Temperatures measured by thermocouples mounted at specific locations within the disk drive sensed temperature of the outside air, the flexible cable 116, inside sidewall 118 of the base 104, inside air, and the top of actuator assembly 110. 
     The experimental results are shown in the tables below. Table 1 contains the measured temperatures from the disk drive without shrouding, and Table 2 contains the measured temperatures from the same disk drive, with shrouding elements 120 and 122 positioned therein. 
     
                       TABLE 1                                                     
______________________________________                                    
Temperature data from GPE2 disk drive                                     
without shrouding.                                                        
THERMO-    OPERATING DURATION                                             
COUPLE     0      30          1.5       2.5                               
LOCATION   min    min    1 hr.                                            
                              hrs  2 hrs                                  
                                        hrs  3 hrs                        
______________________________________                                    
Outside air                                                               
           22 C.  21 C.  21 C.                                            
                              21 C.                                       
                                   21 C.                                  
                                        21 C.                             
                                             21 C.                        
Flex cable 21 C.  51 C.  55 C.                                            
                              57 C.                                       
                                   58 C.                                  
                                        59 C.                             
                                             59 C.                        
Sidewall   21 C.  47 C.  51 C.                                            
                              53 C.                                       
                                   54 C.                                  
                                        54 C.                             
                                             54 C.                        
Inside air 21 C.  47 C.  52 C.                                            
                              54 C.                                       
                                   55 C.                                  
                                        55 C.                             
                                             55 C.                        
Actuator   21 C.  49 C.  53 C.                                            
                              55 C.                                       
                                   57 C.                                  
                                        57 C.                             
                                             57 C.                        
assembly                                                                  
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                       TABLE 2                                                     
______________________________________                                    
Temperature data from GPE2 disk drive                                     
with shrouding.                                                           
THERMO-    OPERATING DURATION                                             
COUPLE     0      30          1.5       2.5                               
LOCATION   min    min    1 hr.                                            
                              hrs  2 hrs                                  
                                        hrs  3 hrs                        
______________________________________                                    
Outside air                                                               
           22 C.  22 C.  22 C.                                            
                              22 C.                                       
                                   22 C.                                  
                                        22 C.                             
                                             22 C.                        
Flex cable 22 C.  47 C.  52 C.                                            
                              55 C.                                       
                                   56 C.                                  
                                        56 C.                             
                                             56 C.                        
Sidewall   22 C.  43 C.  48 C.                                            
                              50 C.                                       
                                   51 C.                                  
                                        51 C.                             
                                             51 C.                        
Inside air 22 C.  44 C.  48 C.                                            
                              51 C.                                       
                                   52 C.                                  
                                        52 C.                             
                                             52 C.                        
Actuator   22 C.  45 C.  50 C.                                            
                              53 C.                                       
                                   54 C.                                  
                                        54 C.                             
                                             54 C.                        
assembly                                                                  
______________________________________                                    
 
    
     Note that the operating temperatures stabilize after two hours of continuous disk drive operation. Moreover, and quite significant to the present invention, the addition of shrouding elements 120 and 122 proximate the disks reduces the operating temperature of the disk drive by 3 degrees C. 
     In addition to measuring the operating temperature of the disk drive, experiments were also conducted to measure changes in operating current to the spindle motor (motor run current) in response to changes in the amount of shrouding placed around the disks in the Grand Prix™ disk drive. The additional shrouding is measured in mechanical degrees about the disks. The experimental results for motor run current versus mechanical degrees of shrouding are shown in FIG. 3. 
     The line labeled 300 shows changes in the motor run current as shrouding is added while the actuator arm is positioned at the inner diameter of the disk; line 302 shows changes in the motor run current as shrouding is added while the actuator arm is positioned at the outer diameter of the disk. In each case, points 304 and 306 indicate the motor run current of the disk drive without additional shrouding, e.g., with 180 degrees of shrouding produced by the sidewalls of the disk drive. As additional shrouding is added to further circumscribe the disks, the additional shrouding reduces the motor run current. The disks were circumscribed by additional shrouding elements until the motion of the actuator assembly was impeded by the shrouding, e.g., approximately 270 degrees of shrouding. The motor run current with 270 degrees of shrouding is indicated as points 308 and 310. As is clear from this experimental data, the addition of the shrouding elements reduces the motor run current as well as the operating temperature of the disk drive. 
     The foregoing disclosure discussed adding two shroud elements 120 and 122 to a disk drive that presently had sidewalls that partially shrouded the disks. However, those skilled in the art will realize that if the sidewalls of a disk drive are not presently proximate the disks, a single shrouding element can be provided that substantially surrounds the disks for approximately 270 degrees. In this manner, a single shroud, uniformly distanced from the disk edges, can be fashioned to substantially circumscribe the disks with, of course, an opening in the shroud to enable the actuator assembly to position the transducer head assembly over the disks. Such a shroud could be produced as an elongated, rectangular strip of plastic having a width that provides shrouding for at least one of the disks and a length that substantially circumscribes the circumference of the disks. One edge of the shroud (a long edge) would be attached to the base of the disk drive. 
     In a further embodiment of the invention, the two shroud elements, rather than be additional elements that are cemented to the base, can be fashioned during casting of the base and sidewalls as extensions of the sidewalls. Thus, the shroud elements would be formed of cast aluminum as an integral portion of the disk drive base. Additionally, the sidewalls that are proximate the disks could be cast to be a uniform distance from the disks. In this manner, the sidewalls and the extensions would, in combination, form a shroud that is a uniform distance from the disks. 
     By enclosing the rotating disk stack with a confining shroud, positioned at an optimized radial distance from the spinning disks, a reduction in the amount of power required to spin the disks at a high rotational velocity is obtained. A further beneficial result is a corresponding reduction in temperature rise within the disk drive enclosure. 
     Having thus described an embodiment of the invention, it will now be appreciated that the objects of the invention have been fully achieved, and it will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosure and the description herein are purely illustrative and are not intended to be in any sense limiting.