JP3668201B2 - Disk storage device and head positioning control method - Google Patents

Description

【００２６】
ここで、Ｐは制御対象８１の伝達特性であり、Ｃは追従コントローラ８０の伝達特性である。また、Ｗは外乱の位置変動特性（８５）であり、外乱値（Ａ）から目標位置変動（ｒ）までの伝達特性を示す。この目標位置変動（ｒ）は、外乱によりドライブの筐体やディスク１が変形し、追従コントローラ８０により追従するトラックが移動するために発生する。更に、Ｋは外乱の加速度変動特性（８６）であり、外乱値（Ａ）から等価的に制御値（ｕ）に加わる外乱の加速度値（ｄ）までの伝達特性を示す。
【００２７】
ヘッド位置誤差（ｅ）に対して外乱（Ａ）の影響を抑制するためには、前記式（１）の分子の項が零になるように、外乱ＦＦコントローラ８８の伝達特性Ｆを下記式（２）に示すように設定すればよい。
【００２８】
【数２】

【００２９】
なお、同システムは、外乱フィードフォワード制御系により、外乱（Ａ）による追従コントローラ８０からの制御入力値（ｕ）に対する影響を補償する方式でもよい。この場合、外乱検出（加速度値Ａ）からヘッド位置誤差（ｅ）までの伝達関数は、前記式（１）の右項の分子が「Ｗ−ＫＰ−ＦＰ」になる。また、外乱ＦＦコントローラ８８の伝達特性Ｆは、前記式（２）の右項の分母が「Ｐ」になる。
【００３０】
次に、図２を参照して、外乱ＦＦコントローラ８８の伝達特性（Ｆ）を決定するためのパラメータ同定方法を説明する。同方法は、いわゆる最小２乗法を利用したものである。図２は、ＦＦコントローラ８８に相当する同定対象２０１（伝達関数Ｂ）と、パラメータ同定器２０２（伝達関数Ｑ）とを要素とする。
【００３１】
パラメータ同定器２０２は、同定対象２０１を離散システムとして、同定対象２０１の入力（ｕ）と出力（ｙ）との関係から伝達特性を推定する。この関係は、下記式（３）のように表現される。
【００３２】
【数３】

【００３３】
ここで、ａはパラメータ同定器４２の出力側の係数パラメータであり、ｂはその入力側の係数パラメータである。ｋは離散システムのステップ数である。
【００３４】
さらに、未知パラメータベクトルθと、入出力ベクトルζ（ｋ）を下記式（４）のように定義する。
【００３５】
【数４】

【００３６】
この定義から、前記式（３）は下記式（５）のように表現できる。
【数５】

【００３７】
ここで未知パラメータの推定値を、時刻（ｋ−１）における推定値を使用して、下記式（６）に示すような同定モデルを計算できる。
【００３８】
【数６】

【００３９】
同定誤差は、下記式（７）により表現できる。
【数７】

【００４０】
最小２乗法によるパラメータベクトルθの推定は、時刻ｋまでの測定データｙ（ｋ），ζ（ｋ）を用いて、下記式（８）に示すような評価関数により算出できる。
【００４１】
【数８】

【００４２】
パラメータベクトルθを決定する方法には、推定値の計算に過去の全データを必要とするオフライン同定と、離散システムの同定ステップ毎に逐次的に推定するオンライン同定がある。外乱ＦＦコントローラ８８の伝達関数（Ｆ）の決定においては、データ量の少ない後者が望ましい。
【００４３】
具体的には、次数（２ｎ＋１）の正方行列Γ（ｋ）を使用して、各同定ステップ毎に下記式（９）を計算する。
【００４４】
【数９】

【００４５】
Γ（ｋ）の初期値は、正の定数（γ）と単位行列（Ｉ）とから、「Γ（０）＝γＩ」となる。
【００４６】
【数１０】

【００４７】
以上のような原理により、パラメータ同定器２０２は、図４または図５のフローチャートに示すような同定処理ステップ（ここではｋ）を実行して、外乱ＦＦコントローラ８８の伝達関数（Ｆ）を推定する。
【００４８】
パラメータ同定器２０２は、同定対象２０１の入力（ｕ）と出力（ｙ）とを取得する（ステップＳ１またはＳ１０）。以下、パラメータ同定器２０２は、前記式（４）の計算を実行する（ステップＳ２またはＳ１１）。次に、前記式（６）及び式（７）の計算を実行する（ステップＳ３またはＳ１２）。さらに、前記式（１０）の計算を実行する（ステップＳ４またはＳ１３）。そして、各同定ステップ毎に前記式（９）の計算を実行する（ステップＳ５またはＳ１４）。
【００４９】
ここで、パラメータ同定器２０２は、同定ステップのカウント数（Ｎ）が十分大きい定数（Ｓ）より大きいならば同定処理を終了する（ステップＳ６のＹＥＳ）。そうでなければ、パラメータ同定器２０２は、同定ステップを続行する（ステップＳ６のＮＯ，Ｓ７）。また、パラメータ同定器２０２は、パラメータ推定値の前サンプル（ｋ−１）との変化量（変化度ｖ）に基づいて、同定処理の終了を判定してもよい（図５の方式）。即ち、パラメータ同定器２０２は、下記式（１１）を計算する（ステップＳ１５）。
【００５０】
【数１１】

【００５１】
パラメータ同定器２０２は、変化度（ｖ）が定数（ｚ）よりも十分小さくなれば、同定処理を終了する（ステップＳ１６のＹＥＳ）。そうでなければ、パラメータ同定器２０２は、同定ステップを続行する（ステップＳ１６のＮＯ，Ｓ１７）。
【００５２】
次に、図６及び図７に示すように、パラメータ同定器２０２の入力側（ｂ）にフィルタ２０４（入力フィルタＨ）を設けた場合、及びその出力側（ａ）にフィルタ２０５（出力フィルタＪ）を設けた場合のパラメータ同定方法を説明する。
【００５３】
各フィルタ２０４，２０５は前記式（３）で示す離散システムそのものであり、伝達特性は、下記式（１２）のように表現される。
【００５４】
【数１２】

【００５５】
ここで、図６に示すように、入力側（ｂ）にフィルタ２０４（入力フィルタＨ）が設けられた場合、パラメータ同定器２０２は、下記式（１３）に示すような伝達関数を同定する。
【００５６】
【数１３】

【００５７】
また、図７に示すように、出力側（ａ）にフィルタ２０５（出力フィルタＪ）が設けられた場合、パラメータ同定器２０２は、下記式（１４）に示すような伝達関数を同定する。
【００５８】
【数１４】

【００５９】
以上のように、パラメータ同定器２０２は、入出力側にフィルタ２０４（Ｈ）及び２０５（Ｊ）を配置することにより、同定対象２０１（Ｂ）に加わる入出力信号を使用しながら、同定対象２０１（Ｂ）とは異なる離散システムの伝達関数を同定することができる。
【００６０】
一般的に、最小２乗法によるパラメータ同定では、同定対象２０１の周波数特性によって収束速度が異なり、積分要素に近い周波数要素を持つ場合には収束時間が非常に大きくなる。同定対象２０１の情報は、低い周波数要素では比較的予想が容易である。従って、既知の情報を使用して同定入出力フィルタ２０４，２０５を構成し、高い周波数要素だけパラメータ同定器２０２で推定することは、実用上で有効な方法である。
【００６１】
また、パラメータ同定では、前記式（３）に示す離散システムの次数によって演算処理量が決まり、パラメータ推定個数の２乗で演算量が増大する。そこで、既知の同定対象２０１の情報を、同定用の入出力フィルタ２０４，２０５に加えて、未知の同定対象２０１の特性だけを同定することで次数を減らし、演算量を削減することが可能である。
【００６２】
ここで、同定対象２０１（Ｂ）の既知部をＢｍとし、また未知部をＢｎとして、下記式（１５）に示すように、同定対象２０１の伝達関数Ｂを定義する。
【００６３】
【数１５】

【００６４】
入力側にフィルタ２０４（Ｈ）が設けられた場合には、下記式（１６）に示すような関係となる。
【００６５】
【数１６】

【００６６】
また、出力側にフィルタ２０５（Ｊ）が設けられた場合には、下記式（１７）に示すような関係となる。
【００６７】
【数１７】

【００６８】
従って、パラメータ同定器２０２は、同定対象２０１の未知部Ｂｎだけを推定できる。既知部Ｂｍが安定である場合には、前記式（１６）に示すように、入力側にフィルタ２０４（Ｈ）を設けた方法が有効である。一方、既知部Ｂｍが不安定で、かつ「１／Ｂｍ」が安定になる場合には、前記式（１７）に示すように、出力側にフィルタ２０５（Ｊ）を設けた方法が有効である。
【００６９】
（パラメータ同定器を含むヘッド位置決め制御システム）
図８は、前述のようなパラメータ同定方法を実行するパラメータ同定器８３を含むシステムの要部を示すブロック図である。
【００７０】
同システムは、外乱観測部８２により観測（検出）された外乱値（加速度値Ａ）が、同定用の入力フィルタ８４（伝達関数Ｈ）を介してパラメータ同定器８３の入力側に印加される構成である。さらに、パラメータ同定器８３の出力側には、ヘッド位置と目標位置（Ｒ）との位置誤差（ｅ）を示す信号が印加される。
【００７１】
ここで、同定対象である外乱フィードフォワード制御系（外乱ＦＦコントローラ８８）は、追従コントローラ８０から出力される制御値（ｕ）を補償する方式のシステムを想定する。同システムにおいて、入力フィルタ８４の伝達関数Ｈは、下記式（１８）に示すように表現できる。
【００７２】
【数１８】

【００７３】
この式（１８）、前記式（１３）及び同システムの外乱（Ａ）から位置誤差（ｅ）までの伝達関数「（Ｗ−ＫＰ）／（１＋ＣＰ）」から、下記式（１９）に示すような関係式が求められる。
【００７４】
【数１９】

【００７５】
即ち、この演算結果（Ｑ）は、外乱ＦＦコントローラ８８の伝達特性Ｆ（Ｆ＝（Ｗ−ＫＰ）／Ｐ）と一致する。前記式（１８）において、追従コントローラ８０の伝達関数Ｃは既知である。また、制御対象８１の伝達関数Ｐも、ディスクドライブにおいては、外乱の加速度変動特性Ｋや外乱の位置変動特性Ｗと比較して、容易に取得可能な値である。
【００７６】
また、外乱フィードフォワード制御系（外乱ＦＦコントローラ８８）により、位置誤差（ｅ）を補償する方式のシステムでは、入力フィルタ８４の伝達関数Ｈは、下記式（２０）に示すように表現できる。
【００７７】
【数２０】

【００７８】
この式（１８）、前記式（１３）及び同システムの外乱（Ａ）から位置誤差（ｅ）までの伝達関数「（Ｗ−ＫＰ）／（１＋ＣＰ）」から、下記式（２１）に示すような関係式が求められる。
【００７９】
【数２１】

【００８０】
即ち、この演算結果（Ｑ）は、前記式（２）に示す外乱ＦＦコントローラ８８の伝達特性Ｆと一致する。
【００８１】
図９及び図１０は、当該パラメータ同定器８３と外乱ＦＦコントローラ８８とを含むヘッド位置決め制御システムの構成を示すブロック図である。
【００８２】
図９に示すシステムは、外乱ＦＦコントローラ８８により、追従コントローラ８０から出力される制御値（ｕ）を補償する方式である。また、図１０に示すシステムは、外乱ＦＦコントローラ８８により、位置誤差（ｅ）を補償する方式である。いずれの方式でも、同定終了判定部８７が、パラメータ同定器８３による外乱ＦＦコントローラ８８の伝達特性（Ｆ）の同定処理と、同定後の外乱ＦＦコントローラ８８の制御実行とを制御する構成である。
【００８３】
以下図１１のフローチャートを参照して、図９または図１０に示すシステムの動作を説明する。
【００８４】
ディスクドライブのヘッド位置決め制御（サーボ制御）動作が開始されると、当該システム（即ち、ＣＰＵ７０）は、ヘッドの現在位置と目標位置（Ｒ）との位置誤差（ｅ）及び加速度センサ９（外乱観測部８２）による外乱値（加速度値Ａ）を観測する（ステップＳ２０）。ここで、最初のサンプル（サーボ周期）では、外乱フィードフォワード制御系の同定モードを想定する（ステップＳ２１のＹＥＳ）。
【００８５】
即ち、図９又は図１０に示すように、外乱ＦＦコントローラ８８の出力はオフされた状態で、パラメータ同定器８３の出力はオンされた状態である。追従コントローラ８０は、観測した位置誤差（ｅ）に基づいた追従制御演算を実行し、制御値（ｕ）を算出する（ステップＳ２３）。パラメータ同定器８３は、前述の式（１８）又は式（２０）に示すようなフィルタ演算を実行する（ステップＳ２４のＹＥＳ，Ｓ２５）。そして、パラメータ同定器８３は、図４または図５に示すような同定ステップを実行し、パラメータ同定処理の終了を判定する（ステップＳ２６，Ｓ２７）。
【００８６】
同定処理が終了すると、パラメータ同定器８３は、外乱ＦＦコントローラ８８のパラメータを更新し、新たに外乱に適応する伝達関数（Ｆ）を同定する（ステップＳ２８）。そして、次のサンプルから、外乱ＦＦコントローラ８８の制御実行モードとなり、外乱ＦＦコントローラ８８の出力はオン状態で、パラメータ同定器８３の出力はオフされた状態となる（ステップＳ２９）。
【００８７】
外乱ＦＦコントローラ８８の制御実行モードでは、外乱ＦＦコントローラ８８は制御演算を実行し、外乱（Ａ）による制御値（ｕ）又は位置誤差（ｅ）の変動を補償する（ステップＳ２１のＮＯ，Ｓ２２）。また、外乱ＦＦコントローラ８８の制御実行モードでは、ＣＰＵ７０は、ヘッド位置決め精度の評価を実行し、当該精度が劣化していると判定すると、次のサンプルから同定モードの再実行に移行する（ステップＳ３０，Ｓ３１）。
【００８８】
以上のように同実施形態のシステムによれば、ディスクドライブでの実際上のサーボ制御において、外乱フィードフォワード制御系の伝達関数を決定するためのパラメータ同定モードと、外乱フィードフォワード制御系の制御実行モードとをそれぞれ分離して実行する。従って、ディスクドライブの使用環境または製品毎の機械的ばらつきなどに適応して、外乱に対する外乱フィードフォワード制御系の補償機能を有効にするように、伝達特性（パラメータ）を更新することが可能となる。従って、実際上のディスクドライブの使用環境において、外乱に対するヘッド位置決め精度の向上を安定的に確保することができる。
【００８９】
図３は、当該システムの効果を示すもので、同定パラメータ（特性３００）とヘッド位置決め精度（特性３０１）の時間的変化を示す。ＴＰは、同定判定終了時点を示し、外乱フィードフォワード制御系のパラメータ更新時点を示す。ヘッド位置決め精度の特性３０１は、同定判定終了時点ＴＰから精度が向上したことを示している。
【００９０】
【発明の効果】
以上詳述したように本発明によれば、外乱フィードフォワード制御系を有するヘッド位置決め制御システムを含むディスクドライブにおいて、外乱フィードフォワード制御系の制御実行モードとは分離して、外乱フィードフォワード制御系の伝達特性の同定モードを有する。従って、ドライブの使用時の環境変化や、製品毎の機械的なばらつきに適応するように外乱フィードフォワード制御系の伝達特性を同定することができる。これにより、外乱に対するヘッド位置決め精度の向上を安定的に確保することが可能となる。
【図面の簡単な説明】
【図１】本発明の実施形態に関するディスクドライブの要部を示すブロック図。
【図２】同実施形態に関する外乱フィードフォワード制御系のパラメータ同定方法を説明するための図。
【図３】同実施形態に関するヘッド位置決め制御システムの特性を説明するための図。
【図４】同実施形態に関するパラメータ同定方法を説明するためのフローチャート。
【図５】同実施形態に関するパラメータ同定方法を説明するためのフローチャート。
【図６】同実施形態に関するパラメータ同定方法の第１の変形例を説明するための図。
【図７】同実施形態に関するパラメータ同定方法の第２の変形例を説明するための図。
【図８】同実施形態に関するパラメータ同定器を含むヘッド位置決め制御システムの構成を示すブロック図。
【図９】同実施形態に関するパラメータ同定方法を適用したヘッド位置決め制御システムの構成を示すブロック図。
【図１０】同実施形態に関するパラメータ同定方法を適用したヘッド位置決め制御システムの構成を示すブロック図。
【図１１】同実施形態に関するヘッド位置決め制御システムの動作を説明するためのフローチャート。
【図１２】同実施形態に関するヘッド位置決め制御システムの原理的構成を説明するためのブロック図。
【符号の説明】
１…ディスク
２…スピンドルモータ（ＳＰＭ）
３…ヘッド
４…アクチュエータ
５…ボイスコイルモータ（ＶＣＭ）
６…リード／ライトチャネル
７…マイクロコントローラ
８…ＶＣＭドライバ
９…加速度センサ
１０…加速度信号処理回路
１１…Ａ／Ｄコンバータ
７０…ＣＰＵ
７１…ＲＯＭ
８０…追従コントローラ
８３…パラメータ同定器
８４…フィルタ
８８…外乱フィードフォワード（ＦＦ）コントローラ[0001]
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of disk storage devices, and more particularly to a head positioning control system.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a disk storage device (hereinafter referred to as a disk drive) represented by a hard disk drive, a head positioning control system for positioning a head (magnetic head) at a target position (access target track) on a disk that is a data recording medium. Is provided. The head performs data read / write operations on the disk.
[0003]
The head positioning control system controls the voice coil motor (VCM) of the actuator on which the head is mounted by a feedback control system using a CPU as a controller, and executes head follow-up control with respect to the target position. In such a system, there has been developed or proposed a system provided with a disturbance feedforward control system for suppressing the influence of external vibration and shock (hereinafter referred to as disturbance) applied to the drive.
[0004]
The disturbance feedforward control system calculates a compensation value for suppressing the influence of the disturbance based on the acceleration value of the disturbance detected (observed) by the acceleration sensor provided in the drive. With this disturbance feedforward control system, it is possible to absorb fluctuations caused by disturbances during head follow-up control.
[0005]
[Problems to be solved by the invention]
A head positioning control system including a disturbance feedforward control system can realize a compensation function for a disturbance applied during the drive of the disk drive, and thus can improve the head positioning accuracy.
[0006]
By the way, the performance of the disturbance feedforward control system depends on the setting of the transfer characteristic (F) to be set. Normally, the transfer characteristic F includes the acceleration fluctuation characteristic (transfer characteristic K) of the disturbance, the position fluctuation characteristic due to the disturbance (transfer characteristic W), and the characteristics (stiffness, resonance) of the actuator including the VCM that is the control target (transfer characteristic P). , Attenuation rate) and the like. In addition, in actual disk drives, there are mechanical variations among drive products, acceleration sensor mounting angle, relative angle of head positioning position, direction of external force of disturbance, aging, etc. The transfer function (K, W, P) at varies.
[0007]
However, generally, during the disk drive manufacturing process, the transfer characteristic F of the disturbance feedforward control system is fixedly set and is not updated after product shipment. For this reason, when the disk drive is actually used, the effect of the head positioning accuracy with respect to the disturbance may greatly vary due to mechanical variations and environmental changes among the individual products.
[0008]
Accordingly, an object of the present invention is to improve the head positioning accuracy against disturbance by making it possible to determine the transfer characteristics of the disturbance feedforward control system so as to adapt to environmental changes during use and mechanical variations between products. An object of the present invention is to provide a disk storage device that can be secured stably.
[0009]
[Means for Solving the Problems]
An aspect of the present invention relates to a disk storage device (disk drive) that uses a head positioning control system that performs tracking control by a feedback control system and disturbance compensation by a disturbance feedforward control system. The system includes a parameter identification function for updating the transfer characteristic of the disturbance feedforward control system in accordance with the observed disturbance when the disk storage device is used.
[0010]
A disk storage device according to an aspect of the present invention is a disk storage device having a head positioning control system for positioning the head to a target position on a disk, which is a data recording medium, wherein the head positioning control system includes the head Based on the position error between the current position of the head and the target position, tracking control means for performing positioning control with the actuator mechanism for moving the head as a control target, and disturbance corresponding to vibration or impact applied from the outside are detected. The disturbance detection means, the feedforward control means for executing the feedforward control for suppressing the influence of the disturbance on the control operation of the follow-up control means, and the feedforward control execution mode are separated from each other, The disturbance characteristic value detected by the disturbance detection means and the position error Based on the bets, and and a identification mode means for performing the parameter identification processing to determine the transfer characteristic of the feed-forward control means,
The identification mode means performs a filter operation according to the control object having the disturbance characteristic value as an input and a transfer characteristic of the tracking control means, and based on the filter operation result and the position error, the parameter identification It is configured to perform processing.
[0011]
In the head positioning control system having such a configuration, a process for identifying a parameter for determining the transfer characteristic of the disturbance feedforward control system adapted to the observed disturbance is executed when the disk drive is used. In other words, the parameter identification mode can be executed separately from the control execution mode of the disturbance feedforward control system. Therefore, it is possible to update the transfer characteristics of the disturbance feedforward control system after the product shipment of the disk drive so as to adapt to environmental changes during use and mechanical variations from product to product. Therefore, it is possible to stably ensure the improvement of the head positioning accuracy against the disturbance under the actual use environment.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
(Disk drive configuration)
As shown in FIG. 1, the disk drive of the present embodiment includes a disk 1 that is a data recording medium, a spindle motor (SPM) 2, a head 3 that performs a data read / write operation, and an actuator 4. .
[0014]
The disk 1 is rotated by SPM2. The disk 1 has a large number of concentric tracks 100 on its surface. Each track 100 includes a predetermined number of servo areas 101 arranged at predetermined intervals in the circumferential direction. Servo information used for detecting the position of the head 3 in the head positioning control system is recorded in the servo area 101 during normal read / write operations.
[0015]
The head 3 is normally mounted with a read head and a write head separated on a slider. The actuator 4 mounts the head 3 and moves the head 3 in the radial direction of the disk 1 by the driving force of the voice coil motor (VCM) 5. The VCM 5 is a control object in a narrow sense in the head positioning control system and is a main element of the actuator mechanism.
[0016]
The disk drive further includes a read / write channel 6, a microcontroller 7, a VCM driver 8, and an acceleration sensor 9. The read / write channel 6 includes a signal processing circuit 60 that processes a read signal and a write signal corresponding to servo information or user information read from a read head included in the head 3. The read / write channel 6 includes a position detection circuit 61 that extracts servo information from the read signal and generates a position detection signal for detecting the position of the head 3.
[0017]
The microcontroller 7 includes a microprocessor (CPU) 70 that is a main element of the head positioning control system, and a ROM 71 that stores the program (firmware) and various control parameters. The CPU 70 implements a feedback control system and a disturbance feedforward control system of the head positioning control system by executing a program stored in the ROM 71. The VCM driver 8 generates a drive current corresponding to the control operation amount from the CPU 70 (including the compensation value by the disturbance FF controller) and supplies the drive current to the VCM 5.
[0018]
The acceleration sensor 9 detects the acceleration (disturbance value) of a disturbance (excitation force) corresponding to vibration or impact applied to the disk drive, and outputs the detection signal to the acceleration signal processing circuit 10. The acceleration signal processing circuit 10 amplifies the detection signal from the acceleration sensor 9 and has a noise reduction filter (LPF or the like). The A / D converter 11 converts the acceleration signal into an acceleration value (denoted as A) that is a digital value and outputs the acceleration value to the CPU 70.
[0019]
(Head positioning control system)
The configuration and operation of the head positioning control system according to the embodiment will be described below with reference to FIGS.
[0020]
First, the principle operation of the system will be described with reference to FIG.
[0021]
As described above, this system is realized by the CPU 70. The CPU 70 acquires the current position of the head 3 from the position detection circuit 61 in synchronization with the rotation angle of the disk 1. Further, the CPU 70 constitutes a sample value control system for calculating a control operation amount (referred to as a control value u) input to the control object 81 (VCM 5) at a constant time interval (servo cycle). The drive current value supplied to the VCM 5 is set in advance by the VCM driver 8.
[0022]
In this system, a follow-up controller (transfer function C) 80 constituting a feedback control system outputs a control value calculated at a predetermined servo cycle (sample interval) to a control object 81, and the head position is set to a target position on the disk ( Control to follow R).
[0023]
On the other hand, the disturbance feedforward control system includes a disturbance feedforward controller (hereinafter referred to as FF controller) 88 as a main element. The FF controller 88 acquires the acceleration value (A) of the disturbance (excitation force) observed by the disturbance observation unit 82 (that is, the acceleration sensor 9) at the timing when the current position of the head is obtained.
[0024]
Here, this system is a method of compensating the influence on the position error (e) due to the disturbance (A) by the disturbance feedforward control system. Here, the transfer function from the disturbance detection (acceleration value A) to the head position error (e) can be expressed as the following equation (1).
[0025]
[Expression 1]

[0026]
Here, P is the transfer characteristic of the controlled object 81, and C is the transfer characteristic of the tracking controller 80. W is a disturbance position fluctuation characteristic (85), which indicates a transfer characteristic from the disturbance value (A) to the target position fluctuation (r). This target position variation (r) occurs because the drive housing and the disk 1 are deformed by disturbance, and the track tracked by the tracking controller 80 moves. Further, K is a disturbance acceleration fluctuation characteristic (86), which shows a transfer characteristic from the disturbance value (A) to the disturbance acceleration value (d) equivalently applied to the control value (u).
[0027]
In order to suppress the influence of the disturbance (A) on the head position error (e), the transfer characteristic F of the disturbance FF controller 88 is expressed by the following formula (1) so that the numerator term of the formula (1) becomes zero. The setting may be made as shown in 2).
[0028]
[Expression 2]

[0029]
The system may be a system that compensates for the influence of the disturbance (A) on the control input value (u) from the tracking controller 80 by a disturbance feedforward control system. In this case, in the transfer function from the disturbance detection (acceleration value A) to the head position error (e), the numerator in the right term of the equation (1) is “W-KP-FP”. Further, in the transfer characteristic F of the disturbance FF controller 88, the denominator of the right term of the equation (2) is “P”.
[0030]
Next, a parameter identification method for determining the transfer characteristic (F) of the disturbance FF controller 88 will be described with reference to FIG. This method uses a so-called least square method. FIG. 2 includes an identification target 201 (transfer function B) corresponding to the FF controller 88 and a parameter identifier 202 (transfer function Q).
[0031]
The parameter identifier 202 estimates the transfer characteristics from the relationship between the input (u) and the output (y) of the identification target 201 using the identification target 201 as a discrete system. This relationship is expressed as the following formula (3).
[0032]
[Equation 3]

[0033]
Here, a is a coefficient parameter on the output side of the parameter identifier 42, and b is a coefficient parameter on the input side thereof. k is the number of steps of the discrete system.
[0034]
Further, the unknown parameter vector θ and the input / output vector ζ (k) are defined as in the following equation (4).
[0035]
[Expression 4]

[0036]
From this definition, the expression (3) can be expressed as the following expression (5).
[Equation 5]

[0037]
Here, using the estimated value of the unknown parameter as the estimated value at time (k−1), an identification model as shown in the following formula (6) can be calculated.
[0038]
[Formula 6]

[0039]
The identification error can be expressed by the following equation (7).
[Expression 7]

[0040]
The estimation of the parameter vector θ by the least square method can be calculated by an evaluation function as shown in the following equation (8) using the measurement data y (k) and ζ (k) until time k.
[0041]
[Equation 8]

[0042]
As a method for determining the parameter vector θ, there are offline identification that requires all past data for calculation of an estimated value and online identification that is sequentially estimated for each identification step of a discrete system. In determining the transfer function (F) of the disturbance FF controller 88, the latter with a small amount of data is desirable.
[0043]
Specifically, the following formula (9) is calculated for each identification step using a square matrix Γ (k) of order (2n + 1).
[0044]
[Equation 9]

[0045]
The initial value of Γ (k) is “Γ (0) = γI” from the positive constant (γ) and the unit matrix (I).
[0046]
[Expression 10]

[0047]
Based on the principle as described above, the parameter identifier 202 executes an identification process step (here, k) as shown in the flowchart of FIG. 4 or 5 to estimate the transfer function (F) of the disturbance FF controller 88. .
[0048]
The parameter identifier 202 acquires the input (u) and output (y) of the identification target 201 (step S1 or S10). Hereinafter, the parameter identifier 202 performs the calculation of the formula (4) (step S2 or S11). Next, the calculation of the formula (6) and the formula (7) is executed (step S3 or S12). Further, the calculation of the formula (10) is executed (step S4 or S13). And the calculation of said Formula (9) is performed for every identification step (step S5 or S14).
[0049]
Here, if the identification step count number (N) is greater than a sufficiently large constant (S), the parameter identifier 202 ends the identification process (YES in step S6). Otherwise, the parameter identifier 202 continues the identification step (NO in step S6, S7). Further, the parameter identifier 202 may determine the end of the identification process based on the amount of change (degree of change v) from the previous sample (k-1) of the parameter estimated value (the method in FIG. 5). That is, the parameter identifier 202 calculates the following formula (11) (step S15).
[0050]
[Expression 11]

[0051]
If the degree of change (v) is sufficiently smaller than the constant (z), the parameter identifier 202 ends the identification process (YES in step S16). Otherwise, the parameter identifier 202 continues the identification step (NO in step S16, S17).
[0052]
Next, as shown in FIGS. 6 and 7, when the filter 204 (input filter H) is provided on the input side (b) of the parameter identifier 202, and the filter 205 (output filter J) is provided on the output side (a). ) Will be described.
[0053]
Each of the filters 204 and 205 is a discrete system itself represented by the above formula (3), and the transfer characteristic is expressed as the following formula (12).
[0054]
[Expression 12]

[0055]
Here, as shown in FIG. 6, when the filter 204 (input filter H) is provided on the input side (b), the parameter identifier 202 identifies a transfer function as shown in the following equation (13).
[0056]
[Formula 13]

[0057]
As shown in FIG. 7, when the filter 205 (output filter J) is provided on the output side (a), the parameter identifier 202 identifies a transfer function as shown in the following formula (14).
[0058]
[Expression 14]

[0059]
As described above, the parameter identifier 202 arranges the filters 204 (H) and 205 (J) on the input / output side, thereby using the input / output signal applied to the identification target 201 (B) while identifying the identification target 201. A transfer function of a discrete system different from (B) can be identified.
[0060]
In general, in the parameter identification by the least square method, the convergence speed varies depending on the frequency characteristics of the identification target 201, and the convergence time becomes very long when the frequency element is close to the integral element. The information of the identification target 201 is relatively easy to predict at low frequency elements. Therefore, it is a practically effective method to configure the identification input / output filters 204 and 205 using known information and estimate only high frequency elements by the parameter identifier 202.
[0061]
In parameter identification, the amount of calculation processing is determined by the order of the discrete system shown in Equation (3), and the amount of calculation increases by the square of the estimated number of parameters. Therefore, by adding the information of the known identification target 201 to the input / output filters 204 and 205 for identification and identifying only the characteristics of the unknown identification target 201, the order can be reduced and the amount of calculation can be reduced. is there.
[0062]
Here, assuming that the known part of the identification target 201 (B) is Bm and the unknown part is Bn, the transfer function B of the identification target 201 is defined as shown in the following equation (15).
[0063]
[Expression 15]

[0064]
When the filter 204 (H) is provided on the input side, the relationship is as shown in the following equation (16).
[0065]
[Expression 16]

[0066]
Further, when the filter 205 (J) is provided on the output side, the relationship is as shown in the following equation (17).
[0067]
[Expression 17]

[0068]
Therefore, the parameter identifier 202 can estimate only the unknown part Bn of the identification target 201. When the known part Bm is stable, a method of providing a filter 204 (H) on the input side is effective as shown in the equation (16). On the other hand, when the known part Bm is unstable and “1 / Bm” is stable, the method of providing the filter 205 (J) on the output side is effective as shown in the above equation (17). .
[0069]
(Head positioning control system including parameter identifier)
FIG. 8 is a block diagram showing a main part of a system including a parameter identifier 83 for executing the parameter identification method as described above.
[0070]
In this system, the disturbance value (acceleration value A) observed (detected) by the disturbance observation unit 82 is applied to the input side of the parameter identifier 83 via the identification input filter 84 (transfer function H). It is. Further, a signal indicating a position error (e) between the head position and the target position (R) is applied to the output side of the parameter identifier 83.
[0071]
Here, the disturbance feedforward control system (disturbance FF controller 88) to be identified is assumed to be a system that compensates the control value (u) output from the follow-up controller 80. In this system, the transfer function H of the input filter 84 can be expressed as shown in the following equation (18).
[0072]
[Expression 18]

[0073]
From this equation (18), the equation (13), and the transfer function “(W−KP) / (1 + CP)” from the disturbance (A) to the position error (e) of the system, the following equation (19) is obtained. Is required.
[0074]
[Equation 19]

[0075]
That is, the calculation result (Q) matches the transfer characteristic F (F = (W−KP) / P) of the disturbance FF controller 88. In the equation (18), the transfer function C of the tracking controller 80 is known. Further, the transfer function P of the control object 81 is also a value that can be easily obtained in the disk drive as compared with the acceleration fluctuation characteristic K of the disturbance and the position fluctuation characteristic W of the disturbance.
[0076]
Further, in a system in which the position error (e) is compensated by the disturbance feedforward control system (disturbance FF controller 88), the transfer function H of the input filter 84 can be expressed as shown in the following equation (20).
[0077]
[Expression 20]

[0078]
From this equation (18), the equation (13), and the transfer function “(W−KP) / (1 + CP)” from the disturbance (A) to the position error (e) of the system, the following equation (21) is obtained. Is required.
[0079]
[Expression 21]

[0080]
That is, the calculation result (Q) matches the transfer characteristic F of the disturbance FF controller 88 shown in the equation (2).
[0081]
9 and 10 are block diagrams showing the configuration of the head positioning control system including the parameter identifier 83 and the disturbance FF controller 88.
[0082]
The system shown in FIG. 9 is a system in which the disturbance FF controller 88 compensates the control value (u) output from the follow-up controller 80. Further, the system shown in FIG. 10 is a system in which the position error (e) is compensated by the disturbance FF controller 88. In any method, the identification end determination unit 87 controls the identification process of the transfer characteristic (F) of the disturbance FF controller 88 by the parameter identifier 83 and the control execution of the disturbance FF controller 88 after the identification.
[0083]
The operation of the system shown in FIG. 9 or 10 will be described below with reference to the flowchart of FIG.
[0084]
When the head positioning control (servo control) operation of the disk drive is started, the system (that is, the CPU 70) detects the position error (e) between the current position of the head and the target position (R) and the acceleration sensor 9 (disturbance observation). The disturbance value (acceleration value A) by the unit 82) is observed (step S20). Here, in the first sample (servo cycle), the disturbance feedforward control system identification mode is assumed (YES in step S21).
[0085]
That is, as shown in FIG. 9 or FIG. 10, the output of the disturbance FF controller 88 is turned off, and the output of the parameter identifier 83 is turned on. The follow-up controller 80 executes follow-up control calculation based on the observed position error (e), and calculates a control value (u) (step S23). The parameter identifier 83 executes a filter operation as shown in the above-described equation (18) or equation (20) (YES in step S24, S25). Then, the parameter identifier 83 executes an identification step as shown in FIG. 4 or 5 and determines the end of the parameter identification process (steps S26 and S27).
[0086]
When the identification process is completed, the parameter identifier 83 updates the parameter of the disturbance FF controller 88 and newly identifies a transfer function (F) adapted to the disturbance (step S28). Then, from the next sample, the disturbance FF controller 88 enters the control execution mode, the output of the disturbance FF controller 88 is on, and the output of the parameter identifier 83 is off (step S29).
[0087]
In the control execution mode of the disturbance FF controller 88, the disturbance FF controller 88 executes control calculation to compensate for fluctuations in the control value (u) or the position error (e) due to the disturbance (A) (NO in step S21, S22). . Further, in the control execution mode of the disturbance FF controller 88, the CPU 70 evaluates the head positioning accuracy, and when determining that the accuracy has deteriorated, the CPU 70 shifts to the re-execution of the identification mode from the next sample (step S30). , S31).
[0088]
As described above, according to the system of the embodiment, in the actual servo control in the disk drive, the parameter identification mode for determining the transfer function of the disturbance feedforward control system and the control execution of the disturbance feedforward control system The mode is executed separately. Therefore, it is possible to update the transfer characteristic (parameter) so as to enable the compensation function of the disturbance feedforward control system with respect to the disturbance in accordance with the use environment of the disk drive or the mechanical variation of each product. . Therefore, it is possible to stably ensure an improvement in head positioning accuracy against disturbances in an actual disk drive use environment.
[0089]
FIG. 3 shows the effect of the system, and shows temporal changes in the identification parameter (characteristic 300) and the head positioning accuracy (characteristic 301). TP indicates the end point of the identification determination, and indicates the parameter update point of the disturbance feedforward control system. A head positioning accuracy characteristic 301 indicates that the accuracy has improved since the end point TP of the identification determination.
[0090]
【The invention's effect】
As described above in detail, according to the present invention, in the disk drive including the head positioning control system having the disturbance feedforward control system, the disturbance feedforward control system is separated from the control execution mode of the disturbance feedforward control system. It has a transfer characteristic identification mode. Therefore, the transfer characteristic of the disturbance feedforward control system can be identified so as to adapt to environmental changes during use of the drive and mechanical variations among products. As a result, it is possible to stably ensure improvement in head positioning accuracy against disturbance.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main part of a disk drive according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining a parameter identification method for a disturbance feedforward control system according to the embodiment;
FIG. 3 is a view for explaining characteristics of a head positioning control system according to the embodiment;
FIG. 4 is a flowchart for explaining a parameter identification method according to the embodiment;
FIG. 5 is a flowchart for explaining a parameter identification method according to the embodiment;
FIG. 6 is a view for explaining a first modification of the parameter identification method according to the embodiment;
FIG. 7 is a view for explaining a second modification of the parameter identification method according to the embodiment;
FIG. 8 is a block diagram showing a configuration of a head positioning control system including a parameter identifier according to the embodiment.
FIG. 9 is a block diagram showing a configuration of a head positioning control system to which the parameter identification method according to the embodiment is applied.
FIG. 10 is a block diagram showing the configuration of a head positioning control system to which the parameter identification method according to the embodiment is applied.
FIG. 11 is a flowchart for explaining the operation of the head positioning control system according to the embodiment;
FIG. 12 is a block diagram for explaining the basic configuration of a head positioning control system according to the embodiment;
[Explanation of symbols]
1 ... disk 2 ... spindle motor (SPM)
3 ... Head 4 ... Actuator 5 ... Voice coil motor (VCM)
6 ... Read / write channel 7 ... Microcontroller 8 ... VCM driver 9 ... Acceleration sensor 10 ... Acceleration signal processing circuit 11 ... A / D converter 70 ... CPU
71 ... ROM
80 ... Tracking controller 83 ... Parameter identifier 84 ... Filter 88 ... Disturbance feedforward (FF) controller

Claims (16)

In a disk storage device having a head positioning control system for controlling the positioning of a head at a target position on a disk, which is a data recording medium,
The head positioning control system includes:
Follow-up control means for performing positioning control on the basis of a position error between the current position of the head and the target position, with an actuator mechanism that moves the head as a control target;
Disturbance detection means for detecting disturbance corresponding to vibration or impact applied from the outside;
Feedforward control means for performing feedforward control for suppressing the influence of the disturbance on the control operation of the tracking control means;
Separately from the execution mode of the feedforward control, a parameter identification process for determining a transfer characteristic of the feedforward control unit is executed based on the disturbance characteristic value detected by the disturbance detection unit and the position error. An identification mode means ,
The identification mode means performs a filter operation according to the control object having the disturbance characteristic value as an input and a transfer characteristic of the tracking control means, and based on the filter operation result and the position error, the parameter identification A disk storage device configured to execute processing .   2. The disk storage device according to claim 1, wherein the disturbance detection unit includes an acceleration sensor that detects acceleration as a disturbance characteristic value. The feedforward control means is configured to generate a compensation signal for absorbing fluctuations generated in the control operation of the follow-up control means due to the disturbance based on an acceleration value corresponding to the disturbance characteristic value. The disk storage device according to claim 1 , wherein: Having an identification end determination means for determining the end of the parameter identification processing by the identification mode means;
The identification end determination means disables the function of the feedforward control means during the execution of the parameter identification process, and updates transfer characteristics and feedforward control to the feedforward control means after the parameter identification process ends. The disk storage device according to claim 1 , wherein the disk storage device is configured to be executable . 2. The feedforward control unit is configured to execute feedforward control for compensating for a variation due to the disturbance from the position error that is an input of the tracking control unit. The disk storage device described. The identification mode means includes
Performing a filter operation according to a transfer characteristic (CP / (1 + CP)) having the disturbance characteristic value as an input and the transfer function P of the controlled object and the transfer function C of the follow-up control means,
The disk storage device according to claim 5, wherein the parameter identification process is executed based on the filter calculation result and the position error . The feedforward control means is configured to execute feedforward control for compensating for fluctuations due to the disturbance from a control operation amount that is an output of the follow-up control means. The disk storage device described. The identification mode means includes
Performing a filter operation according to a transfer characteristic (P / (1 + CP)) that takes the disturbance characteristic value as input and sets the transfer function P to be controlled and the transfer function C of the tracking control means;
The disk storage device according to claim 7, wherein the parameter identification processing is configured to be executed based on the filter calculation result and the position error . A head positioning control method applied to a disk storage device having a head positioning control system for positioning and controlling a head at a target position on a disk as a data recording medium,
The head positioning control system includes:
A follow-up control function for performing positioning control on an actuator mechanism for moving the head based on a position error between the current position of the head and the target position; and
A disturbance detection function for detecting a disturbance corresponding to vibration or impact applied from the outside;
A feedforward control function for performing feedforward control for suppressing the influence of the disturbance on the control operation of the tracking control function;
Separate from the execution mode of the feedforward control, a parameter identification process for determining the transfer characteristic of the feedforward control function is executed based on the disturbance characteristic value detected by the disturbance detection function and the position error. With an identification mode function,
The identification mode function performs a filter calculation according to the control object having the disturbance characteristic value as an input and a transfer characteristic of the tracking control function, and performs the parameter identification process based on the filter calculation result and the position error. The head positioning control method is configured to execute the following. The head positioning control system includes:
Executing the parameter identification process by the identification mode function when executing the identification mode;
Determining the end of identification, which is the end of the parameter identification process;
After completion of the identification, executing a transfer characteristic update for the feedforward control function;
Enabling the feedforward control function after performing the updating step;
The head positioning control method according to claim 9, wherein the head positioning control method is configured to execute processing including : 10. The head positioning control method according to claim 9 , wherein the feedforward control function is configured to execute feedforward control for compensating for a variation due to the disturbance from the position error . The identification mode function is:
Performing a filter operation according to a transfer characteristic (CP / (1 + CP)) having the disturbance characteristic value as an input and the transfer function P of the controlled object and the transfer function C of the follow-up control means,
The head positioning control method according to claim 11, wherein the parameter identification process is configured to be executed based on the filter calculation result and the position error . The feedforward control function, to claim 9, characterized in that it is configured from the calculated control amount to perform a feed-forward control for compensating the variation due to the disturbance by the following control functions The head positioning control method described. The identification mode function is:
Performing a filter operation according to a transfer characteristic (P / (1 + CP)) that takes the disturbance characteristic value as input and sets the transfer function P to be controlled and the transfer function C of the tracking control means;
The head positioning control method according to claim 13, wherein the parameter identification process is executed based on the filter calculation result and the position error . In a disk storage device having a head positioning control system for controlling the positioning of a head at a target position on a disk, which is a data recording medium,
The head positioning control system includes:
Follow-up control means for performing positioning control on the basis of a position error between the current position of the head and the target position, with an actuator mechanism that moves the head as a control target;
Disturbance detection means for detecting disturbance corresponding to vibration or impact applied from the outside;
Feedforward control means for performing feedforward control for suppressing the influence of the disturbance on the control operation of the tracking control means;
Separately from the execution mode of the feedforward control, a parameter identification process for determining the transfer characteristic of the feedforward control unit is executed based on the disturbance characteristic value detected by the disturbance detection unit and the position error. Identification mode means;
An identification end determination means for determining the end of the parameter identification process by the identification mode means,
The identification end determination means includes
During the execution of the parameter identification process, the function of the feedforward control unit is disabled, and after the parameter identification process is completed, the transfer characteristic can be updated and the feedforward control can be performed for the feedforward control unit. A disk storage device configured as described above. A head positioning control method applied to a disk storage device having a head positioning control system for positioning and controlling a head at a target position on a disk as a data recording medium,
The head positioning control system includes:
A follow-up control function for performing positioning control on an actuator mechanism for moving the head based on a position error between the current position of the head and the target position; and
A disturbance detection function for detecting a disturbance corresponding to vibration or impact applied from the outside;
A feedforward control function for performing feedforward control for suppressing the influence of the disturbance on the control operation of the tracking control means;
Separate from the execution mode of the feedforward control, a parameter identification process for determining the transfer characteristic of the feedforward control function is executed based on the disturbance characteristic value detected by the disturbance detection function and the position error. With an identification mode function,
Executing the parameter identification process by the identification mode function when executing the identification mode;
Determining the end of identification, which is the end of the parameter identification process;
After completion of the identification, executing a transfer characteristic update for the feedforward control function;
Enabling the feedforward control function after performing the updating step;
A head positioning control method configured to execute a process including:

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