A study of radial error propagation and self-servowriting in disk drives

Melkote, Hemant; McNab, Robert J.; Cloke, B.; Agarwal, Vineeta

doi:10.1109/acc.2002.1023212

Cited by 18 publications

(10 citation statements)

References 5 publications

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“…In [2] the error propagation is contained by addition of a correction signal to the PES, derived by suitably filtering the PES measured during the self servowrite period. Modeling of the SSTW process was attempted in our earlier work [1]. A method of containing the propagation by addition of a feedforward signal was recently outlined in [7] with experimental results.…”

Section: A Radial Error Propagationmentioning

confidence: 99%

Modeling and control for self-servowriting in hard disk drives: a repetitive process approach

Melkote

McNab

2006

2006 American Control Conference

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This paper considers modeling and correction signal design for self servowriting in disk drives. Self-servowriting is a process whereby the position and timing burst information are written on the disk surface by using the servo information from a previously written track as a reference (seed) for writing the burst information on a subsequent track, and repeating the process. An obstacle to this process is radial error propagation, whereby the distortion in the successive written tracks builds up. In this paper, a reference correction signal is designed which when added to the position error signal (PES) prevents the radial error propagation. The design of the correction signal is carried out through a repetitive systems approach and does not require several revolutions of track following in order to compute it. The analysis is verified by means of simulations which show the containment of radial error propagation.

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Section: A Radial Error Propagationmentioning

confidence: 99%

Modeling and control for self-servowriting in hard disk drives: a repetitive process approach

Melkote

McNab

2006

2006 American Control Conference

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“…Therefore, a major concentric SSTW control design challenge is to achieve appropriate disturbance attenuation and containment track error propagation levels simultaneously. In order to overcome such challenge, several recent novel control design methodologies have been proposed, including SSTW control design using a 2-Dimensional Roesser model [15] and SSTW control design based on a feedforward control structure [16].…”

Section: B Control Design Of Concentric Sstw Servo Systemsmentioning

confidence: 99%

Control design of concentric self-servo track writing systems for hard disk drives

Nie

Horowitz

2010

Proceedings of the 2010 American Control Conference

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Modern hard disk drives (HDDs) generate the head position error signal (PES) by reading special magnetic patterns called servo patterns, which are written in designated areas on the disk surface known as servo sectors, and measure the position of the head relative to the center of the data track. Servo sectors are typically created during the HDD manufacturing process and are not subsequently overwritten or erased. The process of writing servo sector patterns is known as servo track writing (STW). The accuracy and precision of the servo track writing process plays a crucial role in dictating the ultimate track density and areal storage density of the HDD. There are several mechanisms for performing servo track writing. Conventional servo track writing processes use additional sensing and positioning equipment external to the HDD. In contrast, self-servo track writing processes only use the HDD's reading and writing heads and servo system; thus avoiding many of the manufacturing cost increases and productivity losses associated with conventional servo track writing. This paper presents two novel controller synthesis methodologies for performing concentric self-servo track using a feedforward control structure. In the first methodology, it is assumed that a conventional track-following causal feedback compensator has been designed. A non-causal feedforward compensator, which utilizes the stored error signal that was created while writing the previous track, is subsequently designed using standard H ∞ control synthesis techniques, in order to achieve good disturbance attenuation while preventing the propagation of tracking errors from previous tracks. In the second methodology, both the track-following feedback compensator and the feedforward compensator are simultaneously designed via a mixed H 2 /H ∞ control scheme, which involves the solution of a set of linear matrix inequalities. Simulation results confirm that the two proposed control synthesis methodologies prevent error propagation from the previously written tracks and significantly improve self-servo track writing performance.

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“…In this paper, the learning filter F z ( ) is considered as a FIR filter with three causal terms and two non-causal terms, i.e., 2 1 Consequently, the matrix SF is expressed as,…”

Section: Optimal Control Formulationmentioning

confidence: 99%

“…See Ye et al [1], and Melkote et al [2] among others for further details. Iterative Learning Control (ILC) based control structure (Melkote and McNab [3], Wu and Tomizuka [4]) has been proved to be an effective approach to contain the radial error propagation.…”

Section: Introductionmentioning

confidence: 99%

An Iterative Learning Control design for Self-Servowriting in Hard Disk Drives using L<inf>1</inf> optimal control

Dong

Tomizuka

2009

2009 American Control Conference

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This paper presents an Iterative Learning Controller (ILC) design for Self-Servowriting (SSW) process in Hard Disk Drives (HDDs). In SSW, the position and timing information are written onto the disk surface by referring to the previously written servo information. This process is repeated until the whole disk is completely written. The main issue in this process is Radial Error Propagation (REP), which refers to the accumulation of the written-in errors as tracks are written sequentially. In this paper, an ILC scheme is designed by using the position error information in the previous track to prevent REP and improve the quality of servowriting. Analytic conditions for stability and monotonic convergence are discussed. The learning filter design is formulated as an (or induced L ) optimal control problem, which is solved by optimization programming. Simulation results show that REP is contained and a good quality of servowriting is assured.

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A study of radial error propagation and self-servowriting in disk drives

Cited by 18 publications

References 5 publications

Modeling and control for self-servowriting in hard disk drives: a repetitive process approach

Modeling and control for self-servowriting in hard disk drives: a repetitive process approach

Control design of concentric self-servo track writing systems for hard disk drives

An Iterative Learning Control design for Self-Servowriting in Hard Disk Drives using L<inf>1</inf> optimal control

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