News Column

Patent Issued for Method of Disc Alignment Using Printed Alignment Marks

August 12, 2014

By a News Reporter-Staff News Editor at Journal of Technology -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Gauzner, Gennady (San Jose, CA); Kuo, David S. (Palo Alto, CA); Hwu, Justin Jia-Jen (Fremont, CA); Wang, Li-Ping (Fremont, CA); Yu, Zhaoning (Mountain View, CA); Lee, Kim Yang (Fremont, CA), filed on December 2, 2009, was published online on July 29, 2014.

The assignee for this patent, patent number 8792201, is Seagate Technology LLC (Cupertino, CA).

Reporters obtained the following quote from the background information supplied by the inventors: "Embodiments of the present invention relate in general to disc shaped recording media, and more particularly to alignment a disc storage media within a disc drive unit.

"Hard disc drives provide prerecorded tracking servo information on data recording surfaces of their magnetic hard discs. This servo information is typically spaced evenly along tracks. Data is recorded between the servo information. In some cases, servo information is radially aligned, and looks like spokes of a wheel.

"During operation, the disc drive magnetic read/write head flies over the spinning discs and reads information from the tracks as the information passes beneath the head. This information includes both data and servo information. The servo information tells the disc drive servo system where the head is in relation to the track in order that the disc drive servo system may adjust the head's radial position to keep the head on track center.

"The servo information may be written onto a disc's surface using a variety of techniques. A newer approach mounts a large number of discs onto a spinstand and writes the servo information onto all of them at the same time. This approach, also known as 'multiple disc write' ('MDW'), is attractive because a number of discs maybe written at the same time. However, this approach also introduces a number of problems because the discs themselves are not assembled onto the disc drive spindle at the time servo tracks are written.

"One of the problems is that the disc must be mounted onto the drive spindle in the same 'orientation' it was written. For example, if the servo tracks were written by a rotary actuator, the servo burst will be arrayed in an arc that follows the arc of the servo-track writer. To read such servo information properly, the disc drive's actuator should be aligned to traverse the same arc as the servo-writer. For this to occur, the discs are mounted in the same orientation for the disc drive's actuator as they were for the servo-writer's actuator. In most cases, this is accomplished by assuring that a disc's 'top' surface when it is mounted in the servo-writer also be the 'top' surface when that same disc is mounted in the disc drive.

"A second problem occurs when two (or more) such prerecorded MDW discs are mounted in a single disc drive. Not only should the arcs of both discs be aligned, but also the tracks themselves should be substantially aligned vertically, that is, the tracks of one disc should be substantially congruent with tracks of the other discs such that they form 'aligned' cylinders. In this manner, the disc drive can switch between a head reading a specific track number on the top surface of the topmost disc, to a head reading the same track number on of the top surface of the next disc in the stack without needing to perform a seek. If the respective tracks were significantly misaligned in some fashion, switching between them without performing a seek or some other alignment technique would not be possible. After a head switch, the drive may need to find out its location. This may even require it to seek a track '0' in order to recover a proper track number.

"A third problem caused by writing servo data while the disc is mounted on a different spindle is track eccentricity. A hard disc's inner diameter has a tolerance specification much looser than the track eccentricity specification of most disc drive servo systems. If the disc is mounted on the disc drive's spindle in a manner that is significantly off center from the way it was written on the servo writer, it could exceed the drive's servo system eccentricity tolerance. While most disc drive servo systems have eccentricity feed forward mechanisms to help increase their eccentricity tolerances, these feed forward systems typically have stroke limits far below the loosest tolerances for hard disc inner diameters.

"Another problem is the angular alignment of the servo spokes from one disc to another. If the angular misalignment is too large, the drive cannot reliably switch heads from one disc surface to another located on a second disc.

"A current practice for achieving such alignment is to bias all the discs in the MDW servo-writer against the servo-writer's spindle so that each of the discs' inner diameters is vertically aligned at a point of contact with the servo-writer's spindle. Thereafter, when these discs are assembled onto a disc drive's spindle, alignment of their inner surface contact points that abut against the disc drive spindle causes them to have the same vertical alignment they had in the MDW servo-writer. Depending on the precision of alignment of the discs in both the MDW servo-writer and in the disc drive, and upon the precision that the respective servo information is written by the MDW servo-writer, the alignment of the inner surface contact points automatically aligns the tracks of respective discs congruently into the same cylinders they had on the servo-track writer.

"A conventional way to align the discs onto both the servo-track writer and disc drive spindles so that the same portion of the disc inner surface contacts each is to mark the discs with a laser prior to their being loaded onto the MDW servo-writer. However, the laser marking tools are expensive and bulky, they require substantial clean room space and different tools are required to mark glass and nickel phosphorus/aluminum substrates. Finally, the use of a laser marking tool can adversely impact drive reliability in a number of ways.

"One approach to solving these problems with using laser markings was to record the alignment marks magnetically when the servo track data is written. Commonly assigned U.S. Pat. Nos. 7,221,528 and 6,940,678 describe the use of magnetic alignment marks, also referred to as magnetic index marks (MIMs), to indicate the location on a magnetic recording surface of a magnetic hard disc where the disc abuts against the spindle of a multiple-disc servo writer. MIMs are especially well suited for use with magnetic media in which the disc head can be used to write the alignment marks.

"Patterned magnetic media refers to hard disc recording media produced using techniques to achieve higher recording density by printing individual grains onto the magnetic media. Using these techniques, a data bit can be stored on a single grain, resulting in greater disc storage density. More specifically, Discrete Track Recording (DTR) or Bit Patterned Media (BPM) processes can be used to imprint islands (tracks for DTR) onto a substrate of a data storage disc. To produce the islands, a template is formed. Once the template is created, it can be used in a process to produce patterned media.

"It is appreciated that analogous alignment problems persist for patterned magnetic media. Producing alignment marks with lasers is undesirable for the reasons set forth above. Moreover, producing MIMs is impractical for patterned magnetic media in which data is encoded magnetically using nanolithography techniques. Thus, there has been a need to produce alignment marks for printed magnetic media."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Accordingly, what is needed is a mechanism and method for aligning a disc media within a hard drive unit. More specifically, what is needed is a mechanism and method for aligning a template pattern of a disc media such that it is centered about the center of a spindle of the hard drive unit. Embodiments of the present invention provide these advantages.

"Embodiments of the present invention provide a method for proper alignment of a disc media within a hard drive unit such that the concentric tracks of a template pattern are centered about a spindle of the hard drive unit. The method includes providing alignment marks on a disc media, and aligning the template relative to a disc substrate where the substrate includes a spindle hole. The template defines a template pattern comprising an alignment mark to be positioned with respect to a center of the spindle hole. The positioning of the template pattern with respect to the spindle hole center is determined based on determining a radial direction between the center of the spindle hole and the alignment mark. The method further includes offsetting a center of the template pattern with respect to the spindle hole center along the radial direction by an amount determined by subtracting from the radius of the spindle hole a radius of a spindle expected to be disposed in the spindle hole during a drive assembly process.

"The method also includes outlining, using the template pattern, a substrate pattern to be etched on a surface of the substrate and etching the substrate pattern onto the surface according to the outline so that pattern is transferred to the disc substrate according to the alignment process described above.

"Embodiments of the present invention also include the disc media produced by the above process. The disc produced includes rings of bit patterns or tracks eccentric around the disc spindle hole, whereupon when the disc is assembled on a spindle it can be abutted against the spindle at an angular orientation determined by the PIM, causing the rings to be concentric around the spindle, even though they are eccentric around the spindle hole of the disc.

"Further embodiments of the present invention include the method of using the pattern etched onto the disc media for alignment of the disc media within a hard drive unit. Embodiments further include a hard drive unit constructed using the disc media embodiment."

For more information, see this patent: Gauzner, Gennady; Kuo, David S.; Hwu, Justin Jia-Jen; Wang, Li-Ping; Yu, Zhaoning; Lee, Kim Yang. Method of Disc Alignment Using Printed Alignment Marks. U.S. Patent Number 8792201, filed December 2, 2009, and published online on July 29, 2014. Patent URL:

Keywords for this news article include: Seagate Technology LLC.

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Source: Journal of Technology

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