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Feed-forward method for repeatable runout cancellation

a repeatable runout and feedforward technology, applied in the field of magnetic recording devices, can solve the problems of non-repeatable runout, inability of the servo mechanism to completely correct, and inability of the closed loop servo mechanism to adequately correct the misalignment of the transducer

Inactive Publication Date: 2010-09-23
HEADWAY TECH INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention relates to a method for minimizing the effects of repeatable runout (RRO) in a hard disk drive (HDD). The technical effects of this invention include reducing the impact of RRO on the HDD's performance, achieving good performance with a simple algorithm that requires minimal processor resources and data memory space, and significantly reducing the computational convergence time. The method involves applying a feed-forward algorithm that can be easily implemented and requires minimal processor resources. The method also includes a method for compensating for RRO by applying a simple algorithm that can be easily implemented and requires minimal processor resources. The method includes a method for switching between different compensation terms based on the position of the transducer. The invention also includes a method for dividing the surface of the disk into zones and calculating separate corrective data for each zone. Overall, the invention provides a simple and effective solution for minimizing the impact of RRO in HDDs.

Problems solved by technology

Thus, if the signal sent from the transducer indicating its deviation from the centerline is a complicated oscillatory waveform (as a function of deviation vs. servo wedge location), the closed loop servo mechanism will be unable to adequately correct the misalignment of the transducer.
Other reasons for such transducer oscillations include factors such as disk slippage, disk warpage and even poorly written servo data.
The problem caused by RRO is due to the fact that the HDD transducer is trying to follow the motion of that point.
Another source of positional error is called non-repeatable runout (NRRO), which is caused by various random and environmental effects on the motion of the disk and which is not easily eliminated.
However, if the RRO exceeds some predetermined tolerance defined by the manufacturing parameters of the disk drive, then the servo mechanism is incapable of completely correcting for it and the disk drive will not operate properly.
As compared to the method of the present invention to be described below, this previous method was computationally intensive, utilized much storage capacity and was time consuming.
Smith is particularly concerned with correcting for PES outliers, whose extreme values can adversely affect attempts to compensate for RRO.

Method used

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Examples

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Embodiment Construction

[0046]The present invention teaches a method of operating a hard disk drive (HDD) using disks having a plurality of substantially radially concentric annular tracks, in each of which there is embedded servo track information within some number of regularly spaced wedges of small angular width. Note, this number will be denoted “wpr”, for “wedges per revolution”, in the code written below.

[0047]The information stored within these wedges is used to align a read / write transducer relative to a desired radial position on a track (the “target” position). The method of the invention provides a quick and simple mechanism for making repeatable runout (RRO) corrections at each servo wedge location for the chosen disk tracks (e.g. while at a wedge denoted “n”) and computing new such corrections while at that servo wedge and feeding these corrections forward to be accessed and used at the next servo wedge (e.g. a wedge denoted “n+1”). In this way, the PES of the read / write transducer, which inc...

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Abstract

A magnetic hard disk drive includes a method for eliminating that portion of track following error by a read / write transducer that is caused by repeatable runout of the disk tracks. The repeatable runout is eliminated by application of an iterative algorithm that calculates feed-forward correction terms based on gain coefficients iteratively calculated from the amplitude and phase portions of a Bode plot characterizing the system. The corrective coefficients can be inserted into the hard disk drive at a summing junction that redefines the centerline of the track, or at a summing junction that causes the actuator to follow the repeatable runout and make non-repeatable runout corrections relative thereto.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates generally to a magnetic recording device in which there is a rotating magnetic disk on which servo information has been written to guide the positioning of a read / write transducer. More particularly, it relates to such a device wherein the use of the servo information has been optimized to cancel the effects of repeatable runout (RRO).[0003]2. Description of the Related Art[0004]As shown schematically in FIG. 1, a typical magnetic disk (1) mounted on a rotatable spindle (12) in a hard disk drive (HDD) (11) is characterized by radially concentric, annular, circular tracks (17) on which data can be written and from which data is read by means of a read / write transducer (13) mounted on an actuator assembly (14). In order to for the read / write transducer to accurately follow such a circular track while executing reading and writing operations, i.e., to maintain a fixed radial position over the centerl...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): G11B5/596
CPCG11B5/59627
Inventor DROUIN, DAVIDWAHNG, BILLY
Owner HEADWAY TECH INC
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