Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
2001-05-24
2002-09-24
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
Reexamination Certificate
active
06456455
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a vibration damped spacer article, the spacer article preferably having good force (torque and/or pressure and/or stress) retention and the ability to provide damping to an adjacent rotatable storage article on a disk drive assembly. The present invention provides a damped spacer article that preferably has a sufficient force retention to prevent significant rotatable storage article movement during use. The present invention also provides a disk drive having rotatable spacer article(s) and the damped spacer article(s) positioned thereon.
BACKGROUND OF THE INVENTION
Periodic or random vibrations or shocks can excite the resonant frequencies in a rotatable storage article (such as the disk(s) in a disk drive), which can be problematic due to the resultant formation of undesirable stresses, displacements, fatigue, and even sound radiation. Such undesirable vibrations or shocks are typically induced by external forces and can be experienced by a wide variety of articles and under a variety of conditions. For example, resonant vibrations can cause excessive vertical displacement of an optical disk's surface during operation, which may lead to poor laser focus. Proper laser focus is a key to optimum write/read characteristics, signal quality, and tracking ability.
Various techniques have been used to reduce vibrational and shock effects (stresses, displacements, etc.) on rotatable storage articles. Three basic techniques to reduce vibration and shock effects include:
1) adding stiffness or mass to the rotatable storage article so that the resonant frequencies of the rotatable storage article are not excited by a given excitation source,
2) isolating the rotatable storage article from the excitation source so the vibrational or shock energy does not excite the rotatable storage article's resonant frequencies, and
3) damping the rotatable storage article so that given excitations from the excitation source do not result in excessive negative effects at the resonant frequencies of the rotatable storage article.
An isolation technique for limiting vibration transmission is described in U.S. Pat. No. 4,870,429. A single-sided or double-sided optical disk structure is described that includes two sheets of substrate bonded to each other with a foam spacer interposed between the two substrates to restrict or isolate the vibrations caused by external forces. The spacer is made from an elastomeric foam material and is positioned between the two substrates to restrict the transmission of such forces (e.g., vibrations or shocks). The thickness of the spacer is stated to be preferably not less than 0.2 mm, more preferably not less than 0.4 mm, because, when the thickness is too small, the effect of the spacer to restrict or isolate forces is not exhibited sufficiently. Such a system adds to the overall size of the rotatable storage article and may be impractical where close positioning of the article to other structures is desired.
Two types of surface or external damping treatments that can be used to reduce shock or vibration impact on rotatable storage articles are: (1) free layer damping treatments; and (2) constrained layer damping treatments. Both of these damping treatments can provide high levels of damping to a structure, i.e., dissipation of undesirable vibrations, without sacrificing the stiffness of the structure. The use of viscoelastic materials as exterior surface damping treatments is described in EP 0507515. Examples of additional surface or external damping techniques are described, for example, in U.S. Pat. Nos. 2,819,032; 3,071,217; 3,078,969; 3,159,249; and 3,160,549. However, all of the aforementioned damping techniques can add complexity and expense to the design of the rotatable storage article, limit the amount of exterior article surface available for data storage, and can increase the overall size of the article.
U.S. Pat. No. 5,725,931 discloses a constrained layer damper having slits ban and/or cutouts therein, which constrained layer damper provides improved damping performance. The constrained layer damper is useful for damping rotatable storage media, such as compact disks.
U.S. Pat. No. 5,691,037 and WO 96/21,560 disclose vibration damped laminate articles having improved force (torque and/or pressure and/or stress) retention, a method of making one article type, and novel tools used to make the one article type. The first laminate comprises at least one layer of damping material between at least two substrate layers. At least one deformation area is present in the laminate where the substrates are plastically deformed such that they are closer together than in non-deformed areas of the substrate and the damping material has less mass than in a non-deformed area of the article. The deformation area provides areas of good force retention for an attachment device attached thereto. The second laminate, which is not deformed, contains an additive of sufficient modulus, diameter and loading in its vibration damping layer to provide improved force retention. Spacer articles for disk drives are not discussed.
U.S. Pat. No. 5,538,774 provides a method for internally damping a rotatable storage article that is subject to resonant vibrations. The rotatable storage article, although capable of providing good damping, requires a redesign of the rotatable storage article to include the internal damping material, which can be costly to manufacture.
The typical method of providing spacing between disks in a disk drive type application involves the use of solid spacers between the disks. These spacers can be made from many materials, including aluminum, ceramics, stainless steel, rigid plastics, etc. These spacers, however, provide minimal vibration damping.
As the read and write tracks per inch (TPI) and the recording density of disks increase, there is a need to improve the vibration damping of disks economically and simply to implement the disks in existing and future disk drives. With new recording head technology, higher TPIs are possible (10,000-100,000 TPI and above). This now makes vibrations in disks more important to reduce, as vibrations in disks can reduce the TPI that can be reliably read and written. In the past, the spacers have been used to space the disks apart and provide some isolation or improved thermal expansion properties to prevent disks, such as ceramic disks, from breaking.
For example, U.S. Pat. No. 5,663,851 discloses a disk drive spindle hub assembly for a hard disk drive that includes a spindle hub with a stack of information storage disks journaled about the spindle hub in a spaced-apart, vertically aligned relation. Annular spacers are positioned between adjacent information storage disks in order to space the disks apart in the vertically aligned relation of the spindle hub. A disk clamp is configured to concentrically clamp the stack of information storage disks in axial alignment with the spindle hub. A dummy disk comprising an arrangement of a metal plate, a damping portion, and a polyester film is disposed between the disk clamp and the storage disk in order to absorb spurious vibrations and minimize stress concentrations and disk distortion when the storage disks are mounted for rotation within the hard disk drive.
Newer drive rotation speeds of 7,200 and above revolutions per minute (RPMS) plus increased shock requirements (500 to 1,000 or more g of force) require a high force retention in the spindle assembly to prevent disks from slipping or shifting on the spindle. Shipping or shifting can cause data location to be lost or degraded, hindering read/write performance and/or drive reliability.
U.S. Pat. No. 5,367,418 discloses a hub assembly that incorporates O-rings that can absorb external loads applied in either an axial or radial direction relative to the hub.
U.S. Pat. No. 5,590,004 discloses a resilient clamping member positioned between a spindle flange and the upper side of a disk, with a compliant element supported by the spindle rim and contacting the lower side o
Bushman Richard P.
Johnson Brian L.
Jung Michael A.
McCutcheon Jeffrey W.
Morse Thomas L.
3M Innovative Properties Company
Davis David
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