Acoustically damped disc drive assembly

An acoustically damped disc drive assembly having a housing, the disc drive assembly having internally disposed components capable of generating acoustic vibrations, the housing having a cover comprised of a plurality of plate members, each pair of the plate members having a damping layer disposed therebetween for damping acoustic vibrations imparted to the cover by the internally disposed components. In addition to the damping layer, which is preferably a viscoelastic material compositely bonding such plate members together, an acoustic isolator area may be provided to surround the attachment points of the internally disposed components to the cover in order to provide further damping of the acoustic vibrations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the field of disc drive assemblies, and 
more particularly but not by way of limitation, to improvements in 
housings therefor which incorporate acoustic damping for reducing acoustic 
noise generated by disc drive assemblies. 
2. Brief Description of the Prior Art 
Disc drive assemblies of the type known as "Winchester" disc drive 
assemblies are well known in the industry. The archetype Winchester disc 
drive assemblies incorporated discs fourteen inches in diameter and were 
intended for use with large mainframe computers installed in specially 
constructed computer rooms in which environmental elements such as 
temperature and humidity could be controlled for optimum equipment 
operation. The users of such systems were typically located in locations 
far removed from the system and communicated with the system using 
keyboards and CRT displays, known in combination as remote terminals. 
Because only system maintenance and support personnel were required to 
work directly within the computer room, little consideration was given to 
acoustic noise generated by system elements such as cooling fans and disc 
drive motors. 
However, with the advent of personal computers which are commonly located 
in home and office environments, acoustic noise generation has become a 
significant consideration in system design. In fact, in some marketplaces, 
particularly Europe, the amount of allowable acoustic noise in the 
workplace is strictly regulated by law. 
With restrictions being placed on systems manufacturers, it has become 
common practice for manufacturers, which expect to sell their products 
multinationally, to analyze their intended market and specify their 
systems to meet the strictest requirements demanded in all target 
marketplaces. 
Because most computer system manufacturers do not internally produce their 
own disc drive assemblies, but depend on specialized disc drive 
manufacturers, these system manufacturers have begun to strictly specify 
the amount of acoustic noise that the disc drive assembly itself can 
contribute to the overall system. 
In disc drive assemblies of current technology, the major source of 
acoustic noise is sympathetic vibration of the disc drive housing caused 
by the spindle motor used to spin the discs or by the actuator used to 
move the read/write heads across the discs for data accesses. These disc 
drive assemblies are commonly in the form of a rectangular housing with a 
spindle motor and actuator motor mounted to one internal surface. Recent 
market demands for increased capacity, with accompanying increases in 
precision, have caused disc drive manufacturers to attach the shaft of the 
spindle motor and the pivot shaft of the rotary actuator motor to both the 
top and bottom of the disk drive housing. This has frequently resulted in 
housing surfaces vibrating at resonant frequencies that increase the total 
amount of acoustic noise. 
Several approaches to acoustic noise reduction have been taken by disc 
drive manufacturers. Most involve the addition of compliant isolation 
devices between the noise source (the motors) and the external housing. 
However, such devices add expense to the design and require that space be 
set aside for them within the housing. With market trends toward increased 
capacity and smaller physical drive sizes, manufacturers have been 
understandably reluctant to allow room for these types of noise isolation 
devices in their designs. 
Clearly, a need has long existed for an improved housing for disc drive 
assemblies for reducing acoustic noise generated by disc drive assemblies. 
SUMMARY OF THE INVENTION 
The present invention provides an improved housing for a disc drive 
assembly having internally disposed components generating acoustic 
vibrations, the present invention eliminating or substantially reducing 
the coupling of such acoustic vibrations to the housing. In the present 
invention, the housing has a cover comprising a plurality of plate members 
with damping layers disposed between pairs of plate members, such damping 
layers damping acoustic vibrations imparted to the cover by the internally 
disposed components. The damping layers, preferably of a viscoelastic 
material, are disposed between each pair of plate members and adhesively 
bond the plate members together. 
In some applications, it may be desirable to incorporate acoustic isolator 
areas surrounding attachment points of the internally disposed components 
of the disc drive assembly, such acoustic isolator areas cooperating with 
the viscoelastic damping layers to further damp the acoustic vibrations. 
It is an object of the present invention to provide an improved housing for 
disc drive assemblies to reduce acoustic noise generated by disc drive 
assemblies. 
Another object of the present invention, while achieving the before-stated 
object, is to provide an improved housing for disc drive assemblies that 
is inexpensive to manufacture. 
Other objects, features and advantages of the present invention will become 
apparent from the following detailed description when read in conjunction 
with the drawings and appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, shown is a perspective view of a typical disc drive 
assembly 10 having a housing 12 with a cover 14 removed to show the 
relationship between the major internal mechanical components. A spindle 
motor shaft 16, supporting a spindle motor 17, is attached to the housing 
12 within the disc drive assembly 10. Mounted on the spindle motor 17 are 
a number of circular discs 18 coated with a magnetic recording medium. 
Digital information is recorded on the discs 18 in a large number of 
circular, concentric data tracks 20. When power is applied to the disc 
drive assembly 10, the spindle motor 17 rotates the discs 18 at a constant 
high speed. In the example shown, the discs 18 rotate in the 
counter-clockwise direction. 
An actuator motor, shown generally at 22, is also mounted to the housing 12 
and operates under the control of electronic circuitry (not shown) to 
selectively rotate an actuator body 24 about an actuator pivot shaft 26. 
Attached to the actuator body 24 is a plurality of read/write head 
assemblies 28 which are used for data recording and retrieval of 
information from the data tracks 20. 
Disc drives typically have the data tracks 20 on the discs 18 at a density 
greater than 1000 tracks per inch measured radially on the disc surface. 
Furthermore, the actuator motor 22 used to move the read/write head 
assemblies 28 can typically seek to any desired data track 20 in less than 
about 20 miliseconds on the average. This makes the precision and 
stability of the geometric relationship between the discs 18 and 
read/write head assemblies 28 critically important. 
In order to increase the precision and stability of the relationship 
between the discs 18 and the read/write head assemblies 28, both ends of 
the spindle motor shaft 16 and the actuator pivot shaft 26, about which 
the actuator 24 pivots, are secured to the housing 12 and the cover 14. 
As shown in FIG. 1, a plurality of machine screws 30 (some of which are 
shown) are used to fasten the cover 14 to the housing 12 by appropriately 
disposed and mated apertures in the cover 14 and threaded bores in the 
housing 12. One particular screw 32 extends through the cover 14 and into 
a threaded bore in one end of the spindle motor shaft 16, while a second 
screw 34 fastens one end of the actuator pivot shaft 26 of the actuator 
body 24 in a similar manner. With this type of arrangement, when the disc 
drive assembly 10 is completely assembled, tilt between the actuator body 
24 and the spindle motor 17 is minimized. 
Referring now to FIG. 2, shown is a simplified cross-sectional view of a 
prior art disc drive assembly 35, similar to the disc drive assembly of 
FIG. 1. A spindle motor shaft 36 supporting a spindle motor 37 and an 
actuator pivot shaft 38 is shown attached to a housing 39 and a cover 40. 
For clarity, an actuator body supported by the actuator pivot shaft 38 has 
been omitted from FIG. 2. 
The spindle motor shaft 36 is fastened to the housing 39 and to the cover 
40 by screws 42. The actuator pivot shaft 38 is fastened to the housing 39 
and to the cover 40 in a similar manner by screws 44. Further, the cover 
40 is fastened to the housing 39 by screws 46. Mounting the spindle motor 
37 and the actuator (not shown) in this manner provides for minimum 
"wobble" of the spindle motor and the actuator, thus preserving the 
intended geometric relation between the read/write head assembly and the 
discs (both not shown). 
This configuration does, however, present a problem. Because the two motors 
are rigidly attached to both the housing 39 and the cover 40, any 
vibration in the motors will be transmitted to the housing 39 and the 
cover 40. This in turn causes both the housing 39 and the cover 40, which 
are essentially flat plates, to vibrate in sympathy with the motors, 
particularly if the natural frequency of either of the plates is a 
harmonic of the motor vibration. Such vibration can cause amplification of 
the vibrations into acoustic noise at these resonant frequencies. 
It would be desirable, therefore, to isolate the vibration of these motors 
from the flat surfaces of the housing 39 and cover 40 without sacrificing 
the rigidity offered by this configuration. This is achieved using the 
present invention. 
FIG. 3 is a diagrammatical, cross-sectional view of a cover 50 for a 
housing of a disc drive assembly illustrating the present invention. The 
configuration shown consists of an inner plate member 52 and an outer 
plate member 54 coupled by a viscoelastic damping layer 56. As shown, the 
inner plate member 52 includes attachment bosses 58A for mounting the 
cover 50 to a housing (not shown), a mounting boss 58B for attaching the 
top of the spindle motor shaft (not shown) to the inner plate member 52, 
and another mounting boss 58C for attaching the top of the rotary actuator 
pivot shaft (also not shown) to the inner plate member 52, such attachment 
preferably achieved by appropriately disposed apertures (not shown) 
through such bosses. Thus, vibrations of the spindle motor (not shown) and 
the actuator (also not shown) will be coupled to the inner plate member 52 
at the mounting bosses 58B and 58C, respectively. The outer plate member 
54 acts as a non-structural "dead mass" component that is effectively 
isolated from the vibration sources by the viscoelastic damping layer 56. 
Co-pending U.S. patent application Ser. No. 673,967, filed Mar. 22, 1991 
and assigned to the assignee of the present invention, is incorporated 
herein by reference and discloses a scheme for acoustic isolation of 
vibration sources from plate members by the inclusion of an acoustic 
isolator in the plate member in the area surrounding the attachment point 
of the vibration source. Similar acoustic isolators can be incorporated 
into the laminated cover of the present invention, as will be described 
below. 
FIG. 4 is a diagrammatical representation in cross section of another 
embodiment of a cover 60 of the present invention. In the embodiment shown 
in FIG. 4, an outer plate member 62 serves as a "dead mass" acoustic 
damping component as discussed above in relation to FIG. 3. A viscoelastic 
damping layer 64 serves to attach the outer plate member 62 to an inner 
plate member 66 which again includes attachment bosses 68 for attaching 
the cover 60 to a housing (not shown), and mounting bosses 70, 72 for 
attaching the spindle motor shaft (not shown) and the actuator pivot shaft 
(not shown), respectively. However, in the embodiment shown in FIG. 4, the 
inner plate member 66 includes an acoustic isolator 74 surrounding the 
mounting boss 70 for the spindle motor shaft. The acoustic isolator 74 
acts, as disclosed in the previously cited patent application, to further 
isolate the motor vibration sources from the remainder of the inner plate 
member 66, reducing to an even greater extent the amount of vibration 
which can pass from the inner plate member 66 through the viscoelastic 
damping layer 64 to the outer plate member 62. In this configuration, the 
outer plate member 62 can be inexpensively formed from sheet metal, while 
the inner plate member 66 can be cast and then machined to provide the 
required precision support for the spindle motor and actuator. 
FIG. 5 shows a diagrammatical representation of another embodiment of a 
cover 80 made in accordance with the present invention. In this 
embodiment, the functions of attaching the cover 80 to a housing (not 
shown) and of mounting the tops of the spindle motor shaft and actuator 
pivot shaft have been divide between an inner plate member 82 and an outer 
plate member 84. That is, the inner plate member 82 includes attachment 
bosses 86 for attaching the cover 80 to the housing, while the outer plate 
member 84 incorporates mounting bosses 88A, 88B for mounting the spindle 
motor shaft and actuator pivot shaft (both not shown). The inner plate 
member 82 includes cutouts 90A, 90B to permit attachment of the internal 
components to the outer plate member 84, and the inner and outer plate 
members 82, 86 are joined by a viscoelastic damping layer 92. 
FIG. 6 shows yet another embodiment of the present invention in which the 
attachment and mounting roles of the two plate members have been reversed 
from the embodiment shown in FIG. 5. That is, an inner plate member 94 of 
a cover 96 includes mounting bosses 98A, 98B for mounting the tops of the 
spindle motor shaft and actuator pivot shaft (neither shown), while an 
outer plate member 100 is formed to include attachment bosses 102 for 
mounting the cover 96 to a housing (not shown). In this embodiment, the 
vibration sources, the spindle motor and the actuator, are isolated from 
the outside of the housing of the disc drive assembly by a viscoelastic 
damping layer 104 disposed between the inner and outer plate members 94, 
100. 
In all of the above described embodiments, acoustic damping is accomplished 
by the relatively large area of damping material sandwiched between outer 
and inner plate members. This damping material is preferably formed in a 
thin sheet with contact adhesive on both surfaces, thus allowing the 
damping material to act as the attachment mechanism for joining two plate 
members, while acoustically isolating the plate members from each other. A 
suitable damping material available with contact adhesive on both surfaces 
is "SCOTCHDAMP.RTM.", manufactured by the 3M Company. 
Referring now to FIG. 7, shown is another embodiment of the present 
invention. An outer plate member 110 of a cover 111, typically formed from 
sheet aluminum, is provided with attachment bosses 112 for attaching the 
cover 111 to a housing (not shown). The outer plate member 110 is also 
provided with mounting bosses 114A and 114B for attaching a spindle motor 
shaft and an actuator pivot shaft (both not shown) to the cover 111. The 
attachment bosses 112 and the mounting bosses 114A and 114B are formed by 
stamping the outer plate member 110. By stamping the outer plate member 
110, countersinks are created for the heads of the mounting and attachment 
screws (not shown). An inner plate member 116, also typically formed of 
sheet aluminum, is die cut to incorporate cutouts 118 around the 
attachment bosses 112 and mounting bosses 114A and 114B. A viscoelastic 
damping layer 120, disposed between the outer plate member 110 and the 
inner plate member 116, is die cut to match the shape of the inner plate 
member 116. The viscoelastic damping layer 120 is provided with contact 
adhesive on both surfaces to join the outer and inner plate members 110 
and 116. This configuration allows metal-to-metal contact between the 
cover 111 and the housing, thus permitting uniform tightening of the 
screws (not shown) used to mount the cover 111 to the housing, and 
insuring reliable and secure assembly of the cover 111 to the housing. The 
inner plate member 116 hangs from the viscoelastic damping layer 120 and 
acts as a "dead mass" component to damp any vibrations imposed on the 
outer plate member 110 by the spindle motor and actuator. 
FIG. 8 shows a partially exploded perspective view of a cover illustrated 
in accordance with the embodiment shown in FIG. 7. In FIG. 8, a cover 130 
has been inverted to show its innerside, the side which faces the interior 
of the disc drive assembly when mounted on the housing thereof. An outer 
plate member 132 is shown to have a plurality of attachment bosses 134 
which include screw holes 136 for mounting the cover 130 and a housing 
(not shown). The attachment bosses 134 are formed so that contact surfaces 
138 of the attachment bosses 134 are in a coplanar relationship with an 
inner surface 140 of an inner plate member 142 when the cover 130 is 
secured to the housing. The outer plate member 132 also includes a spindle 
motor shaft mounting boss 144, an actuator pivot shaft mounting boss 146, 
and two actuator motor mounting bosses 148, all formed similarly to the 
attachment bosses 134 as described hereinabove. 
The inner plate member 142 is relieved in all four corners to avoid direct 
contact between the plate members 132 and 142 in the areas surrounding the 
attachment bosses 134. Also, the inner plate member 142 is formed with a 
central opening 150 to provide spacing between the cover 130 and various 
internal components of the disc drive assembly (not shown). A viscoelastic 
damping layer 152 is shaped and dimensioned to match the shape and 
dimensions of the inner plate member 142. If desired, the area of the 
outer plate member 132 not mated to the viscoelastic damping layer 152 and 
inner plate member 142 can have additional damping material applied 
thereto. Preferably, both the outer and inner plate members are formed of 
sheet aluminum about 0.030 inch thick, and the viscoelastic damping layer 
152 is formed about 0.002 inch thick. The resulting cover 130 is simpler 
and less expensive to implement than a comparable cast and machined cover, 
as well as being lighter without sacrificing necessary structural 
strength. 
Tests of actual disc drive assemblies incorporating the present invention 
have shown it to be effective in reducing broad-band noise. The results of 
these tests are summarized in FIG. 9, a bar graph showing the maximum and 
average reduction in sound power emitted by a test population of disc 
drive assemblies using varying configurations of the cover of the present 
invention. The differences in the configurations denoted "A" through "E" 
have been summarized in Table I below. The test population for 
configurations A, B, D, and E consisted of four individual disc drive 
assemblies, and the test population for configuration C consisted of two 
disc drive assemblies. In all configurations, the viscoelastic damping 
layer between the outer and inner plate members was a 0.002 inch thick 
layer of SCOTCHDAMP.RTM. SJ-2015, type 1202, and the "Thin Section" noted 
in Table I indicates the presence or absence of a 1.5-inch diameter relief 
surrounding the spindle motor mounting boss. 
TABLE I 
______________________________________ 
Outer Plate 
Inner Plate 
Thin Section 
Configuration 
Thickness Thickness Used 
______________________________________ 
A .050 .030 Yes 
B .050 .030 No 
C .050 .030 Yes 
D .030 .030 Yes 
E .030 .050 Yes 
______________________________________ 
As shown in Table I, the outer plate member was 0.050 inch thick in 
configurations A, B and C, and 0.030 inch thick in configurations D and E. 
The inner plate member was 0.030 inch thick in all configurations except 
E, where it was 0.050 inch thick. 
Configurations A and B were covers made in accordance with the embodiment 
shown in FIG. 6; that is, the outer plate member was used to mount the 
cover to the housing and the spindle motor and actuator pivot shaft were 
mounted to the inner plate member. The difference between configurations A 
and B is that in configuration A, the outer plate member and the 
viscoelastic damping layer were removed in a 1.5 inch diameter area 
surrounding the spindle motor mounting boss, leaving a 0.030 inch "thin 
section". 
Configuration C was made in accordance with the embodiment shown in FIG. 4; 
that is, the attachment bosses for attaching the cover to the housing and 
the mounting bosses for mounting the spindle motor shaft and actuator 
pivot shaft to the cover were all part of the inner plate member, while 
the outer plate member simply floated on the viscoelastic damping layer. 
Configurations D and E were made in accordance with the embodiments shown 
in FIGS. 7 and 8. The cover was attached to the housing via the outer 
plate member, and the spindle motor shaft and the actuator pivot shaft 
were also mounted to the cover via the outer plate member. The inner plate 
member was suspended from the viscoelastic damping layer. Both 
configurations featured a 1.5 inch diameter area removed from the inner 
plate member and the viscoelastic damping layer surrounding the spindle 
motor attachment boss. The only difference in the two configurations was 
the thickness of the inner plate member, 0.030 inch in configuration D and 
.050 inch in configuration E. 
As reflected in FIG. 9, all configurations resulted in significant 
reduction of generated noise levels. What does not show up from the graph 
of FIG. 9, but was evident from the testing, was that the greatest 
reduction in sound level was achieved in those disc drive assemblies that 
were noisiest with a standard cast and machined cover. This means that not 
only did al disc drive assemblies tested benefit from the use of the 
present invention, but that the greatest improvement was achieved on those 
disc drive assemblies that needed improvement the most. 
FIGS. 10A, 10B, 10C, and 10D are graphic representations of the results of 
additional testing carried out on a standard cast and machined cover, and 
on a cover made in accordance with the embodiments of FIGS. 7 and 8 as 
described above. In this testing, a test fixture was created to suspend 
the cover by a very thin wire using one of the mounting apertures. An 
impact hammer generating a fixed input energy stimulus was then used to 
strike the cover. The resultant energy in the cover was then measured. In 
the graphs of FIGS. A-D, the horizontal axis represents time and the 
vertical axis represents the amplitude of the "ringing" resulting from the 
covers being struck. FIGS. 10A and 10B show results for the cover of the 
present invention and FIGS. 10C and 10D show results for standard cast and 
machined covers, with the time scale being altered between FIGS. 10A and 
10B and between 10C and 10D. An examination of the graphs reveals that the 
standard cover rang for a period of time longer than 140 milliseconds 
after being struck, while the vibrations in the cover of the present 
invention were damped to effectively zero amplitude within about 2 
milliseconds of impact, thus showing the superior damping characteristics 
of the present invention. 
While these tests utilized specific plate materials and thicknesses and 
specific damping materials, similar reductions in generated sound levels 
are to be expected utilizing other plate materials and properly selected 
types of damping materials from other manufacturers. For instance, the 
outer or inner plate members of the present invention could be made of 
plastic, fiberglass, ceramic or other rigid material. 
It will be clear that the present invention is well adapted to carry out 
the objects and to attain the ends and advantages mentioned as well as 
those inherent therein. While presently preferred embodiments have been 
described for purposes of this disclosure, numerous changes may be made 
which will readily suggest themselves to those skilled in the art and 
which are encompassed in the spirit of the invention disclosed and as 
defined in the appended claims.