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United States Patent m [in Patent Number: 5,021,905
Sieger  Date of Patent: Jun. 4,1991
U.S. Patent June 4, 1991 Sheet 1 of 2 5,021,905
 DISK DRIVE ENCLOSURE FOR MINIMIZING STRESSES AND A VIBRATION DAMPING SEAL THEREFOR
 Inventor: Roger R. Sieger, Meridian, Id.
 Assignee: Hewlett-Packard Company, Palo Alto, Calif.
 Appl. No.: 434,653
 Filed: Not. 13,1989
 Int. CI.' G11B 17/02; Gl IB 33/14
 U.S. CI 360/97.02; 360/97.01
 Field of Search 360/97.01, 97.02;
 References Cited
U.S. PATENT DOCUMENTS
3,925,584 12/1975 Suzuki et al 428/344 X
4,092,687 5/1978 Butsch 360/97.02
4,199,646 4/1980 Hori et al 428/344
4,249,221 2/1981 Cox et al 360/97.02
Primary Examiner—John H. Wolff
Attorney, Agent, or Firm—E. F. Oberheim
A disk drive in which the base and the cover are interconnected in spaced positions to provide a marginal, peripheral gap between confronting or adjacent faces or edges thereof. The gap is bridged, closed and sealed by means of a pressure sensitive adhesive tape, a viscoelastic tape, which is energy adsorbing to damp disk drive vibrations.
9 Claims, 2 Drawing Sheets
DISK DRIVE ENCLOSURE FOR MINIMIZING STRESSES AND A VIBRATION DAMPING SEAL THEREFOR
FIELD OF THE INVENTION
This invention relates to the sealing of a hard magnetic disk drive enclosure.
BACKGROUND OF THE INVENTION 10
Disk drive enclosures are sealed to prevent the entry of contamination that would damage the internal head/disk interface. Hard disk drives are manufactured in clean environments and are sealed prior to moving them into normal user environments. The internal disk parts, 15 such as the disk stack assembly and the moveable actuator which mounts the magnetic heads and which moves the magnetic heads over the surfaces of the disk, are usually assembled onto some form of a base which is part of the main frame of the disk drive. After all of the 20 parts are in place, a protective cover is installed. Thereafter, the cover and the base are sealed to prevent the entry of contaminants into the enclosure.
The magnetic heads inside the disk drives housings must be accurately positioned over data tracks in order 25 to read back data that has previously been written. If drive parts, forming part of the disk stack and the magnetic head suspension assembly, or the main frame, or the cover, change size and/or shape in a changing thermal environment, positional misregistration between 30 the magnetic heads and the pre-written data tracks, can occur which degrade the performance of the disk drive. Disk drive structural parts are manufactured of materials that are elastic and substantially rigid with respect to the application to which they are put. Structural rigid- 35 ity of the parts is needed to ensure adequate dimensional accuracy and stability. Unfortunately, the inherently poor damping qualities of these elastic parts cause headto-disk positioning errors when the drive is subjected to vibrational inputs. The disk stack assembly which is 40 rotatably mounted on a fixed spindle is often a significant source of input excitation energy that, combined with the undamped drive structure, is a frequent manufacturing problem.
At the time the disk drive cover is installed, accord- 45 ing to conventional practice, the drive is sealed by pressing the cover against a compliant gasket which is often made of an elastomeric material. This gasket is compressed between the cover and the base. This form of sealing poses several problems: 50
In order for a typical gasket to seal a drive, significant pressure must be applied to the gasket. If this pressure remained constant throughout the life of the disk drive, there would be no resulting drive distortion, and no head-to-disk track misregistration. But in reality, the 55 pressure that is applied by the gasket does not remain constant. The material of the gasket relaxes and the pressure reduces over a period of time and exposure to adverse temperatures. Since the stiffness and dimensions of gaskets also change with temperature, drives 60 also usually develop undesirable head-to-disk mistracking as a function of temperature due to the gasket imposed stress changes which affect the position relationship between the cover and the base.
Gaskets are difficult to clean adequately for use in the 65 disk drive. Structural parts of the drive are usually cleaned in an aggressive solvent that cannot be used on the gasket material. Less effective, alternate cleaning
processes usually are required for gaskets. Residual contamination on gaskets can cause damage to the delicate head/disk interface inside a disk drive and reduce the reliability of the disk drive.
Gaskets of this type do not lend themselves to automated assembly processes, so usually they are manually placed into position. Because of this, and inherent defects in the composition and/or surface condition of gaskets and their mating surfaces, the consistency and degree of sealing that is achieved is often unsatisfactory.
DISCLOSURE OF THE INVENTION
Problems of the type encountered in the prior art are overcome in the provision of a disk drive structure in which the cover, when installed, is not pressed against the base. Either the cover or the base or both may have side walls, the ends of which are disposed in confronting, or adjacent, but not touching relationship. In one practical embodiment of this invention, four posts are employed which are mounted at one end of each thereof on the base and which at each of their upper ends receive the top plate of the cover. These posts provide flexibility between the base and the top cover connections. They allow the base and the cover to assume minutely different physical dimensions without imposing any large stresses at the post interfaces. In such an arrangement, the posts are permanently attached to the base and the cover is fastened by screws to the top of each post as well as to the top of the disk spindle and the support for the magnetic head actuator suspension assembly. A disk drive structure in which the top of the disk spindle and the top of the support for the actuator are also attached to the cover which incorporates structural flexibility, and materials having low matched thermal coefficients of expansion for achieving positional predictability, is described in a copending application of the applicant U.S. Ser. No. 07/434,661 filed on the same date as this application, entitled Thermally Predicable Disk Drive Mechanism and assigned to the assignee of this invention.
With the present arrangement, in which the cover and the base do not contact one another, there are no large initial stresses applied to the drive parts tending to permanently displace any of them from the physical relationship among the parts which existed at the time data was recorded on the disks. The drive is sealed by employing a viscoelastic tape seal which does not apply stress to the drive parts. The tape is pressed onto the cover and the base, bridging the gap therebetween in a substantially unstressed condition. Since there are nominally no initial stresses, there are no stress changes over time or temperature. The tape seal is intentionally made of a viscoelastic material which does not generate any significant stress on the drive parts as a result of stiffness changes with changes in temperature, as compressed gaskets do.
By adding a constraining layer (a thin layer of stiff backing material such as aluminum) to the outer face viscoelastic seal material, a high degree of resonant damping is achieved in the overall drive structure. Relative motion between the cover and the base of the drive is damped by the viscoelastic coupling that the seal offers. This added damping greatly reduces the natural ringing of the structure as well as its sensitivity to vibration by sources such as the bearings in rotating disk stack assembly of the disk spindle in the drive.