JP4041905B2 - Tracking control device - Google Patents

Description

即ち、補正信号ｃ_１は、振幅差及び時間遅れを生じることなく光スポット位置ｓ_１を直接制御し、補正を行うことができる。
【００６８】
次に、図３を適宜参照しつつ図４に沿って第２の実施形態のトラッキング制御装置の基本的な動作を説明する。図において、トラッキング誤差検出手段１は、光ヘッドが走査を行っているトラックに対するトラッキング誤差信号ｅ_１を検出した後、このトラッキング誤差信号ｅ_１を補正信号生成手段５中の遅延手段１０に入力する（ステップＳ１）。遅延手段１０は、トラッキング誤差信号ｅ_１について光ディスクの１回転周期に相当する時間の遅延を行い、それを補正信号ｃ_１として出力する（ステップＳ２）。
【００６９】
そして、前置補償手段６中の補償手段１１は、補正信号ｃ_１から前置補償信号ｈ_１を生成する（ステップＳ３）、加算手段７は、この前置補償信号ｈ_１を光ヘッドが走査を行っているトラックに対するトラッキング誤差信号ｅ_１に加算する（ステップＳ４）。
【００７０】
次に、安定化補償手段２は、この加算した信号によってトラッキングアクチュエータ３を駆動し、トラッキング制御を行わせる（ステップＳ５）。回転中の光ディスクに対して継続してトラッキング制御を行うために再びステップＳ１に戻り、前述の動作を繰り返す。
【００７１】
これにより、光ディスクの回転数全般に渡っての追従誤差の低減が実現される。
【００７２】
［第３の実施形態］
図５は、本発明の第３の実施形態に係るデジタル制御によるトラッキング制御装置の構成ブロック図である。
【００７３】
図５において、第３の実施形態では、加算手段１８及び安定化補償手段１９をそれぞれデジタル信号処理回路で構成し、トラッキング誤差信号ｅ_１をＡ／Ｄ変換器（ＡＤＣ）１５によってデジタル信号ｅ_１(ｋ)に変換して加算手段１８の一方の入力に与え、安定化補償手段１９の出力デジタル信号をＤ／Ａ変換器（ＤＡＣ）２０によってアナログ信号に変換してトラッキングアクチュエータ３に与えるように構成してある。
【００７４】
即ち、このデジタル制御によるトラッキング制御装置では、トラッキング誤差信号ｅ_１をデジタル信号ｅ_１(ｋ)に変換した後、トラッキング制御装置としての処理を実行する。
【００７５】
図５に示すように、トラッキング誤差検出手段１によって検出されたトラッキング誤差信号ｅ_１は、Ａ／Ｄ変換器（ＡＤＣ）１５にてデジタル信号ｅ_１(ｋ)に変換され、補正信号生成手段５及び加算手段１８に入力される。
【００７６】
ここに、補正信号生成手段５は、記憶手段１６を備える。記憶手段１６は、光ディスクの少なくとも１回転周期に相当する時間のトラッキング誤差信号ｅ_１のデジタルデータｅ_１(ｋ)を記憶する。そして、記憶手段１６は、光ディスクの１周前のトラッキング誤差信号ｅ_１(ｋ)を用いて、サンプリング時刻ｋにおいてｄサンプリング周期に相当する時間だけ進んだ時刻でのトラッキング誤差信号を補正信号ｃ_１(ｋ＋ｄ)として前置補償手段６へ出力する。
【００７７】
また、前置補償手段６は、パルス伝達関数Ｐ_１(ｚ^−１)を持つ補償手段１７を備える。補償手段１７は、記憶手段１６から入力する補正信号ｃ_１(ｋ＋ｄ)をデジタル的に処理し、前置補償信号ｈ_１(ｋ)を出力する。
【００７８】
加算手段１８は、デジタル化されたトラッキング誤差信号ｅ_１(ｋ)と前置補償信号ｈ_１(ｋ)を加算し、その加算結果を安定化補償手段１９に入力する。安定化補償手段１９の出力は、Ｄ／Ａ変換器（ＤＡＣ）２０によってアナログ信号に変換され、トラッキングアクチュエータ３を駆動し、光スポット位置ｓ_１を変化させることによりトラッキング制御を行う。
【００７９】
なお、安定化補償手段１９は、トラッキング制御装置のフィードバック制御系が安定に動作するように振幅と位相の周波数特性の補償を行うと同時に、所望の応答特性を実現するためのパルス伝達関数Ｇ_１(ｚ^−１)を持つ。また、Ｄ／Ａ変換器（ＤＡＣ）２０とトラッキングアクチュエータ３を縦続接続した系は、パルス伝達関数Ｇ_２(ｚ^−１)を持つ。
【００８０】
次に、図５〜図８を参照して第３の実施形態の基本動作を説明する。なお、図６は、第１次の共振モードを持つムービングコイル型トラッキングアクチュエータの回路／運動モデル図である。図７は、記憶手段に記憶された補正信号のデータとサンプリングクロックとの関係模式図である。図８は、第３の実施形態のトラッキング制御装置の基本動作のフローチャートである。
【００８１】
まず、図５〜図７を用いて第３の実施形態のトラッキング制御装置の動作原理を説明する。このデジタル制御系では、補償手段１７のパルス伝達関数Ｐ_１(ｚ^−１)を、トラッキングアクチュエータ３のパルス伝達関数が不安定な零点を持つ場合と持たない場合とに分けて決定する。
【００８２】
いずれの場合も連続系でトラッキングアクチュエータ３の伝達関数を求めた後、それを離散系に変換することによりデジタル制御系における閉ループのパルス伝達関数を得る。さらに、閉ループのパルス伝達関数に基づいて補償手段１７のパルス伝達関数Ｐ_１(ｚ^−１)を決定する。
【００８３】
光ヘッドに用いられる一般的なムービングコイル型のトラッキングアクチュエータは、例えば、文献２『ラジオ技術社、ラジオ技術選書「光ディスク技術」１３４頁』で述べられているように、第１次の共振モードを持つ図６のモデルで表される。図６（ａ）はトラッキングアクチュエータの回路モデルであり、ｖは駆動電圧、ｉは駆動電流、Ｒは抵抗分、Ｌはリアクタンス分である。図６（ｂ）は運動モデルであり、Ｋ_Ｔ，Ｄ_Ｔ，ｍ_Ｔ，ｆ(t)およびｘ(t)は、それぞれ弾性係数、粘性係数、可動部７０の質量、駆動力及び位置を表す。図６（ａ）（ｂ）から、駆動電圧ｖ(ｔ)、駆動力ｆ(ｔ)は、
【００８４】
【数４】

となる。また、推力定数をＫ_ｉとおけば、駆動力ｆ(ｔ)は、
ｆ(t)＝Ｋ_ｉi(t) ・・・ （９）
となる。
【００８５】
そして、式（８）、式（９）を用いて、初期値を０としてラプラス変換を行うことにより、トラッキングアクチュエータ３を電流で駆動した場合の伝達関数Ｇ_２ｉ(ｓ)は、
【００８６】
【数５】

となる。また、トラッキングアクチュエータ３を電圧で駆動した場合の伝達関数Ｇ_２ｖ(ｓ)は、式（７）、式（８）、式（９）を用いて
【００８７】
【数６】

となる。即ち、連続系におけるトラッキングアクチュエータ３のモデルは、電流駆動では２次、電圧駆動では３次の低域フィルタ型になる。
【００８８】
次に、トラッキングアクチュエータ３を駆動する信号を出力するＤ／Ａ変換器（ＤＡＣ）２０は、０次ホールダとして機能することを考慮して、連続系での伝達関数をデジタル制御系のパルス伝達関数Ｇ_２(ｚ^−１)に変換すると、例えば、文献３『コロナ社「基礎デジタル制御」５９頁、表３．５』が示すように、分母と分子の次数差に応じて不安定零点が生じることが知られている。ここで、ｚ＝ｅｘｐ(ｊωＴ_ｓ)である。但し、Ｔ_ｓはサンプリング周期である。
【００８９】
【表１】

【００９０】
表１は、文献３の表３．５を示している。この文献３の表３．５において、トラッキングアクチュエータ３を電流で駆動した場合はｋ＝２となる。電圧で駆動した場合は電圧から電流に変化する過度現象のためにｋの値は１つ増えてｋ＝３となる。そして、いずれの場合も不安定零点が１個以上生じる。一方、図５の安定化補償手段１９のパルス伝達関数Ｇ_１(ｚ^−１)については、不安定零点、不安定極のいずれも持たないように設計を行う。ここで、表１におけるｋは連続系の伝達関数の分母の次数から分子の次数を減じた数値であり、サンプリング時刻を表すｋとは異なる。
【００９１】
前置補償信号ｈ_１(ｋ)に対する光スポット位置ｓ_１の閉ループのパルス伝達関数Ｇ_ｃｌ(ｚ^−１)は、
【００９２】
【数７】

によって表される。なお、式（１２）において、Ａ_ｃ(ｚ^−１)、Ｂ_ｃ(ｚ^−１)は、いずれもｚ^−１の多項式である。また、ｚ^−ｄは、ｄ・Ｔ_ｓ、即ちｄサンプリング周期分の時刻の遅れに相当する。
【００９３】
そこで、式（１２）に基づいて補償手段１７のパルス伝達関数Ｐ_１(ｚ^−１)を下記の手順により定める。まず、閉ループのパルス伝達関数Ｇ_ｃｌ(ｚ^−１)を用いて、Ｐ_１’(ｚ^−１)，Ｐ_１(ｚ^−１)をそれぞれ式（１３）、式（１４）のように定める。
【００９４】
【数８】

【００９５】
【数９】

ここで、式（１３）において、分子のｚ^ｄは、入力に対して出力がｄサンプリング周期分進んだ時刻となることを示す。そこで、Ｐ_１(ｚ^−１)の入力は、ｄサンプリング周期分進んだ時刻における補正信号ｃ_１(ｋ＋ｄ)を用いる。これを図７を用いて説明する。図７において、例えば、光ディスクの１周についてｎ回のサンプリングを行って制御しているものとする。ｍ周目のサンプリングクロックｋに相当する時刻において、（ｍ−１）周目のサンプリングクロック（ｋ＋ｄ）に相当する時刻において記憶された信号を用いる。その他の時刻においても同様の処理を行う。
【００９６】
互いに隣接するトラックは、位置的な相関関係が大きいので、この方法によって等価的にｄサンプリング周期分進んだ時刻における補正信号ｃ_１（ｋ＋ｄ）が得られる。式（１２）と式（１４）によって、補正信号ｃ_１（ｋ＋ｄ）に対する光スポット位置ｓ_１は、
【００９７】
【数１０】

となり、補正信号ｃ_１（ｋ）に対して光スポット位置ｓ_１は、振幅差及び時間遅れを生じることなく追従する。
【００９８】
（Ａ）このように、デジタル制御系においてトラッキングアクチュエータが不安定零点を持たない場合には、式（１４）によりパルス伝達関数Ｐ_１(ｚ^−１)を定めれば、安定な制御系を実現できる。即ち、パルス伝達関数Ｐ_１(ｚ^−１)として、当該フィードバック制御系の入力に対する出力の閉ループのパルス伝達関数Ｇ_ｃｌ(ｚ^−１)の逆数から導出したパルス伝達関数を採用する。
【００９９】
しかし、前述のようにムービングコイル型のトラッキングアクチュエータを使用したトラッキング制御装置では、閉ループのパルス伝達関数Ｇ_ｃｌ(ｚ^−１)は不安定な零点を持つため、式（１２）から直接式（１４）を利用してパルス伝達関数Ｐ_１(ｚ^−１)を定めると、パルス伝達関数Ｐ_１(ｚ^−１)は、不安定な極を持つことになり安定な制御系を構成できない。
【０１００】
（Ｂ）そこで、トラッキングアクチュエータ３のパルス伝達関数が不安定な零点を持つ場合は、次のようにしてデジタル制御系におけるパルス伝達関数Ｐ_１(ｚ^−１)を定める。
【０１０１】
式（１２）のパルス伝達関数Ｇ_ｃｌ(ｚ^−１)において、零点を安定な零点及び不安定な零点に分けて次の式（１６）のように記述する。なお、式（１６）において、Ｂ_ｃ ^＋（Ｚ^−１）は安定な零点、Ｂ_ｃ ⁻（Ｚ^−１）は不安定な零点を含むｚ^−１の多項式である。
【０１０２】
【数１１】

そして、この式（１６）を用いて以下に説明する第１及び第２の２つの方法でパルス伝達関数Ｐ_１(ｚ^−１)を定めて、安定な制御系を構成する。
【０１０３】
第１の方法では、パルス伝達関数Ｇ_ｃｌ(ｚ^−１)の安定な零点のみをパルス伝達関数Ｐ_１(ｚ^−１)の極で相殺する。また、不安定な零点を含むＢ_ｃ ⁻（Ｚ^−１）にはｚ^−１＝１を代入して定数とする。即ち、Ｐ_１’(ｚ^−１)，Ｐ_１(ｚ^−１)をそれぞれ
【０１０４】
【数１２】

【０１０５】
【数１３】

と定める。
【０１０６】
補償手段１７のパルス伝達関数Ｐ_１(ｚ^−１)を式（１８）の形にすることで、パルス伝達関数Ｇ_ｃｌ(ｚ^−１)の安定な零点のみをパルス伝達関数Ｐ_１(ｚ^−１)の極で相殺し、補正信号ｃ_１(ｋ＋ｄ)に対する光スポット位置ｓ_１の応答において安定な制御系が構成される。
【０１０７】
即ち、第１の方法では、式（１２）、式（１６）及び式（１８）により、補正信号ｃ_１(ｋ＋ｄ)に対する光スポット位置ｓ_１の応答は、
【０１０８】
【数１４】

となり、低周波領域において光スポット位置ｓ_１は補正信号ｃ_１(ｋ)に時間遅れを生じることなく追従する。また、トラッキング制御装置の安定性も保たれる。
【０１０９】
次に、第２の方法では、パルス伝達関数Ｐ_１’(ｚ^−１)，Ｐ_１(ｚ^−１)は、それぞれ下記の式（２０）、式（２１）のように定める。なお、式（２０）、式（２１）において、Ｂ_ｃ ⁻（Ｚ）は、多項式Ｂ_ｃ ⁻（Ｚ^−１）においてｚ^−１をｚによって置き換えたものである。
【０１１０】
【数１５】

【０１１１】
【数１６】

この第２の方法では、式（１２）、式（１６）及び式（２１）によって補正信号ｃ_１(ｋ＋ｄ)に対する光スポット位置ｓ_１の応答は、
【０１１２】
【数１７】

となる。
【０１１３】
ここで、Ｂ_ｃ ⁻（Ｚ）とＢ_ｃ ⁻（Ｚ^−１）は、互いに複素共役となることから、光スポット位置ｓ_１は補正信号ｃ_１(ｋ)に対してすべての周波数で時間遅れを生じることなく追従する。また、トラッキング制御装置の安定性も保たれる。
【０１１４】
次に、図５を適宜参照しつつ図８に沿って動作を詳細に説明する。図において、トラッキング誤差検出手段１は、光ヘッドが走査を行っているトラックに対するトラッキング誤差信号ｅ_１を検出する。このトラッキング誤差信号ｅ_１は、Ａ／Ｄ変換器（ＡＤＣ）１５によってデジタル信号ｅ_１(ｋ)に変換された後、補正信号生成手段５及び加算手段１８に入力される。
【０１１５】
補正信号生成手段５は、例えばメモリを使用した記憶手段１６の所定記憶領域にトラッキング誤差信号ｅ_１(ｋ)を逐一格納するとともに、光ディスクの１周前のトラッキング誤差信号ｅ_１(ｋ)を用いて、時刻ｋにおいてｄ・Ｔｓに相当する時間だけ進んだ時刻でのトラッキング誤差信号を演算し（ステップＳ１１）、それを補正信号ｃ_１(ｋ＋ｄ)として記憶手段１６の別の記憶領域に格納する（ステップＳ１２）。
【０１１６】
そして、補正信号生成手段５は、光ディスクの１回転前に記憶された補正信号ｃ_１(ｋ＋ｄ)があるかどうかを判断し（ステップＳ１３）、なければ補正信号＝０とし（ステップＳ１４）、記憶された補正信号ｃ_１(ｋ＋ｄ)があればそれを読み出し（ステップＳ１５）、前置補償手段６に与えて前置補償信号ｈ_１(ｋ)を出力させる（ステップ１６）。
【０１１７】
ここに、前置補償手段６を構成する補償手段１７は、上記第１及び第２の方法で定めたパルス伝達関数Ｐ_１(ｚ^−１)を持つように構成される。即ち、Ｄ／Ａ変換器（ＤＡＣ）２０の０次ホールド機能とトラッキングアクチュエータ３の伝達関数によって得られるパルス伝達関数Ｇ_２(ｚ^−１)が不安定な零点を持たない場合、補償手段１７は、そのパルス伝達関数Ｐ_１(ｚ^−１)が式（１４）となるように構成される。また、パルス伝達関数Ｇ_２(ｚ^−１)が不安定な零点を持つ場合、補償手段１７は、そのパルス伝達関数Ｐ_１(ｚ^−１)が式（１８）あるいは式（２１）となるように構成される。
【０１１８】
次いで、加算手段１８では、補償手段１７の出力から得られる前置補償信号ｈ_１(ｋ)とトラッキング誤差信号ｅ_１(ｋ)とを加算し、安定化補償手段１９に出力する（ステップ１７）。
【０１１９】
安定化補償手段１９は、フィードバック制御系を安定化すると同時に所望の応答特性を実現するためのパルス伝達関数Ｇ_１(ｚ^−１)を持つ。安定化補償手段１９の出力は、Ｄ／Ａ変換器（ＤＡＣ）２０によってアナログ信号に変換されトラッキングアクチュエータを駆動することによって光スポット位置ｓ_１を制御する（ステップ１８）。
【０１２０】
回転中の光ディスクに対して継続してトラッキング制御を行うためには再びステップＳ１１に戻り、以上の動作を繰り返す。これにより、光ディスクの回転数全般に渡っての追従誤差の低減が実現される。
【０１２１】
［第４の実施形態］
図９は、本発明の第４の実施形態に係るデジタル制御によるトラッキング制御装置の構成ブロック図である。
【０１２２】
第４の実施形態のデジタル制御によるトラッキング制御装置では、第３の実施形態において、補正信号生成手段５を、パルス伝達関数Ｑ_１(ｚ^−１)を持つ第１の演算手段２５、パルス伝達関数Ｑ_２(ｚ^−１)を持つ第２の演算手段２６、加算手段２７及び記憶手段１６によって構成し、前置補償手段６をパルス伝達関数Ｐ_１(ｚ^−１)を持つ補償手段２９、遅延量ｚ^−ｄを持つ遅延手段３０及び減算手段３１によって構成してある。
【０１２３】
補正信号生成手段５では、第１の演算手段２５には、Ａ／Ｄ変換器（ＡＤＣ）１５が出力するトラッキング誤差信号ｅ_１(ｋ)が入力され、第２の演算手段２６には、前置補償信号ｈ_１(ｋ)が入力される。また、加算手段２７は、２つの演算手段２５，２６の出力を受けて仮想的なトラック位置を記憶手段１６に出力する。記憶手段１６は、補正信号ｃ_１(ｋ＋ｄ)を前置補償手段６に出力する。
【０１２４】
前置補償手段６では、補正信号ｃ_１(ｋ＋ｄ)が補償手段２９と遅延手段３０とに入力され、補償手段２９と遅延手段３０の出力が減算手段３１に入力され、減算手段３１から前置補償信号ｈ_１(ｋ)が出力される。
【０１２５】
要するに、第４の実施形態では、Ａ／Ｄ変換後のトラッキング誤差信号ｅ_１(ｋ)及び前置補償手段６の出力ｈ_１(ｋ)を補正信号生成手段５に入力して補正信号ｃ_１(ｋ＋ｄ)を生成し、それを前置補償手段６に入力して前置補償信号ｈ_１(ｋ)を得る。加算手段１８は、前置補償信号ｈ_１(ｋ)をトラッキング誤差信号ｅ_１(ｋ)と加算して安定化補償手段１９に入力する。Ｄ／Ａ変換器（ＤＡＣ）２０は、安定化補償手段１９の出力をアナログ信号に変換し、トラッキングアクチュエータ３を駆動する。
【０１２６】
次に、図９を参照して第４の実施形態の基本動作を説明する。第４の実施形態は、上記第３の実施形態において説明したトラッキングアクチュエータ３のパルス伝達関数が不安定な零点を持つ場合と持たない場合のデジタル制御系におけるパルス伝達関数Ｐ_１(ｚ^−１)を定める方法の他の例（第３の方法）を実現するものである。
【０１２７】
Ａ／Ｄ変換器（ＡＤＣ）１５によってデジタル化されたトラッキング誤差信号ｅ_１(ｋ)は、第１の演算手段２５及び加算手段１８に入力される。また、第２の演算手段２６には、前置補償信号ｈ_１(ｋ)が入力される。
【０１２８】
第１の演算手段２５は、入力されたトラッキング誤差信号ｅ_１(ｋ)に対して次の式（２３）で表されるパルス伝達関数Ｑ_１(ｚ^−１)の出力を求め、この結果を加算手段２７の一方の入力に与える。
【０１２９】
【数１８】
Ｑ₁(ｚ^-1)＝１＋Ｇ₁(ｚ^-1)Ｇ₂(ｚ^-1) ・・・ （２３）
また、第２の演算手段２６は、入力された前置補償信号ｈ_１(ｋ)に対して次の式（２４）で表されるパルス伝達関数Ｑ_２(ｚ^−１)の出力を求め、この結果を加算手段２７の他方の入力に与える。
【０１３０】
【数１９】
Ｑ₂(ｚ^-1)＝Ｇ₁(ｚ^-1)Ｇ₂(ｚ^-1) ・・・ （２４）
加算手段２７は、第１及び第２演算手段２５、２６の出力を加算し、次の式
【外１】

【０１３１】
【数２０】

【外２】

記憶し、光ディスクの1周前に記憶された信号を用いて、時刻ｋにおいてｄ・Ｔ_ｓ進んだ時刻に相当する信号を補正信号ｃ_１(ｋ＋ｄ)として補償手段２９及び遅延手段３０に出力する。
【０１３２】
具体的には、記憶手段１６は、図７に示したように、ｍ周目のサンプリングクロックｋに相当する時刻においては、（ｍ−１）周目のサンプリングクロックｋ＋ｄに相当する時刻において記憶された信号を補正信号ｃ_１(ｋ＋ｄ)として出力する。
【０１３３】
この補正信号ｃ_１(ｋ＋ｄ)に対して、補償手段２９は、式（１４）、式（１８）あるいは式（２１）のいずれかで表されるパルス伝達関数Ｐ_１(ｚ^−１)の演算を行う一方、遅延手段３０は、ｄ・Ｔ_ｓに相当するｄサンプリング周期分の時間遅延を行う。減算手段３１は、補償手段２９の出力から遅延手段３０の出力を減算し、次の式（２６）によって表される前置補償信号ｈ_１(ｋ)を発生し、加算手段１８及び第２の演算手段２６に対して出力する。
【０１３４】
【数２１】
ｈ₁(ｋ)＝Ｐ₁(ｚ^-1)ｃ₁(ｋ＋ｄ)−ｚ^-dｃ₁(ｋ＋ｄ) ・・・ （２６）
加算手段１８は、この前置補償信号ｈ_１(ｋ)とトラッキング誤差信号ｅ_１（ｋ）を加算し、安定化補償手段１９に出力する。安定化補償手段１９の出力は、Ｄ／Ａ変換器（ＤＡＣ）２０を介してトラッキングアクチュエー夕３を駆動し、光スポット位置ｓ_１の制御を行う。
【０１３５】
これにより、以上の各実施形態と同様に、光ディスクの回転数全般にわたっての追従誤差の低減が実現される。
【０１３６】
［第５の実施形態］
図１０は、本発明の第５の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。
【０１３７】
図１０では、説明を容易にするため、図５または図９に示したトラッキング制御装置における記憶手段１６に関係する部分のみを取り出してある。その他の部分は、それぞれ図５または図９と共通である。
【０１３８】
図１０に示すように、第５の実施形態では、第２〜第４の実施形態における記憶手段１６を、ｎ個のメモリ素子４０と加算手段４１および乗算手段３９によって構成するものである。メモリ素子４０は、例えば演算を行うデータのビット数に対応する複数のＤ−フリップ・フロップによって構成し、サンプリングクロック毎に縦続接続されている前段のメモリ素子の出力データを取り込むと共に、１クロック前に記憶していた値を縦続接続されている後段のメモリ素子に対して出力する。ｎ番目のメモリ素子４０の出力は乗算手段３９に入力される。乗算手段３９は入力されたデータに対して、｜ｗ｜＜１であり、ｗ＝０を含む適切な係数を乗算する。乗算手段３９の出力は加算手段４１に接続されており、入力信号と加算された信号を１番目のメモリ素子に入力する。補正信号ｃ_１(ｋ＋ｄ)は、（ｎ−ｄ）番目のメモリ素子４０の出力から取り出す。
【０１３９】
第５の実施形態によれば、記憶手段１６に学習効果を持たせることができるので、追従誤差をより小さくすることが可能となる。
【０１４０】
［第６の実施形態］
図１１は、本発明の第６の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。
【０１４１】
図１１では、説明を容易にするため、図５または図９に示したトラッキング制御装置における記憶手段１６に関係する部分のみを取り出してある。その他の部分は、それぞれ図５または図９と共通である。
【０１４２】
図１１に示すように、第６の実施形態では、第２〜第４の実施形態における記憶手段１６を、高速のＣＰＵまたはデジタル・シグナル・プロセッサ（ＤＳＰ）などの演算素子４３及びこの演算素子４３とデータバス４４、アドレスバス４５を介して接続されたメモリ４６によって構成したものである。
【０１４３】
演算素子４３は、トラッキング制御装置のクロックに同期して入力信号を時系列的に取り込んでメモリ４６上に記憶し、その記憶した入力信号に対して光ディスク１回転分の遅延を行った後、補正信号ｃ_１(ｋ＋ｄ)を出力する。
【０１４４】
または、演算素子４３は、トラッキング制御装置のクロックに同期して入力信号を時系列的に取り込んでメモリ４６上に記憶し、その記憶した入力信号に対して、例えば移動平均処理、最小二乗法などの統計的な信号処理を行った後、補正信号ｃ_１(ｋ＋ｄ)を出力する。
【０１４５】
第６の実施形態によれば、光ディスク上に傷やゴミなどがあってトラッキング誤差信号が得られない期間が生じても、トラッキング外れが生じる可能性を低くすることができる。
【０１４６】
なお、メモリ４６に記憶するデータは、光ディスク１周分に相当する入力信号でも、光ディスクの複数回の回転によって得られた入力信号でも良い。
【０１４７】
［第７の実施形態］
図１２は、本発明の第７の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。なお、第７の実施形態は、ＣＬＶ方式、ＺＣＬＶ方式、ＣＡＶ方式、ＺＣＡＶ方式に対応するトラッキング制御装置の原理構成を示し、具体的には、例えば第８、第９の各実施形態のように構成される。
【０１４８】
図１２では、説明を容易にするため、図５または図９に示したトラッキング制御装置における記憶手段１６に関係する部分のみを取り出してある。その他の部分は、それぞれ図５または図９と共通である。
【０１４９】
図１２に示すように、第７の実施形態の記憶手段１６では、入力信号やトラッキング制御装置のクロックに加え、光ディスクの半径方向における光ヘッド位置情報と光ディスク回転角度情報が入力される。
【０１５０】
次に、第７の実施形態のトラッキング制御装置の基本動作を説明する。まず、走査中のトラックに対するトラッキング誤差信号を用いて演算した補正信号を入力信号として、光ヘッド位置情報、光ディスク回転角度情報と共にトラッキング制御装置のクロックに同期して記憶手段１６に記憶する。光ヘッド位置情報は、光ヘッドが走査を行っているトラックの光ディスク上での半径位置を知るために用いる。
【０１５１】
次に、光ディスクの少なくとも１回転前の時刻において記憶手段１６に記憶された補正信号のうち、現在の光ヘッド位置及び光ディスクの回転角度に対応した補正信号を出力信号として読み出す。
【０１５２】
この補正信号を前置補償手段６に入力して前置補償信号を出力し、前置補償信号を走査中のトラックに対するトラッキング誤差信号に加算し、加算後の信号を用いてトラッキング制御を行う。
【０１５３】
［第８の実施形態］
図１３は、本発明の第８の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。なお、第８の実施形態は、ＣＬＶ方式、ＺＣＬＶ方式、ＣＡＶ方式、ＺＣＡＶ方式の対応するトラッキング制御装置の具体的構成例を示す。
【０１５４】
図１３では、説明を容易にするため、図５または図９に示したトラッキング制御装置における記憶手段１６に関係する部分のみを取り出してある。その他の部分は、それぞれ図５または図９と共通である。
【０１５５】
図１３に示すように、第８の実施形態では、第２〜第４の実施形態における記憶手段１６を、高速のＣＰＵまたはデジタル・シグナル・プロセッサ（ＤＳＰ）などの演算素子４７及びこの演算素子４７とデータバス４４、アドレスバス４５を介して接続されたメモリ４８によって構成したものである。
【０１５６】
図１３に示すように、第８の実施形態の記憶手段１６における演算素子４７には、入力信号やトラッキング制御装置のクロックに加え、光ディスクの半径方向における光ヘッド位置情報と光ディスク回転角度情報が入力される。
【０１５７】
次に、図１３，図１４を参照して第８の実施形態のトラッキング制御装置の動作を説明する。なお、図１４は、第８の実施形態のトラッキング制御装置の基本動作のフローチャートである。
【０１５８】
図において、演算素子４７には、光ヘッドが走査を行っているトラックに対するトラッキング誤差信号が入力信号として入力されるとともに、光ディスクの半径方向における光ヘッド位置情報及び光ディスク回転角度情報が入力される。
【０１５９】
演算素子４７は、光ヘッドが走査を行っているトラックに対するトラッキング誤差信号を検出した後、この信号を用いて補正信号を演算し（ステップＳ３１）、補正信号を光ヘッド位置情報と光ディスク回転角度情報と共にメモリ４８に記憶する（ステップＳ３２）。光ヘッド位置情報は光ヘッドが走査を行っているトラックが光ディスク上で半径上のいずれの位置にあるかを知るために用いる。
【０１６０】
具体的には、演算素子４７は、光ヘッド位置情報及び光ディスク回転角度情報を用いてメモリアドレスを一意に決定し、そのアドレスにトラッキング制御装置のクロックに同期して入力信号を時系列的に取り込んでメモリ４８上に記憶し、その記憶した入力信号に対して光ディスク１回転分の遅延を行い、光ヘッド位置情報と光ディスク回転情報と共にメモリ４８に記憶する。
【０１６１】
または、演算素子４７は、光ヘッド位置情報及び光ディスク回転角度情報を用いてメモリアドレスを一意に決定し、そのアドレスにトラッキング制御装置のクロックに同期して入力信号を時系列的に取り込んでメモリ４８上に記憶し、その記憶した入力信号に対して、例えば移動平均処理、最小二乗法などの統計的な信号処理を行い、光ヘッド位置情報と光ディスク回転情報と共にメモリ４８に記憶する。
【０１６２】
次に、演算素子４７は、現在の光ヘッド位置情報と光ディスク回転角度情報に対応する補正信号がメモリ４８に記憶されているかを判断し（ステップＳ３３）、記憶されていなければ補正信号＝０とし（ステップＳ３４）、記憶されていれば、メモリ４８から現在の光ヘッド位置と光ディスク回転角度に対応する補正信号ｃ_１(ｋ＋ｄ)を読み出す（ステップＳ３５）。
【０１６３】
このとき、ステップ３５では、読み出すべき補正信号の光ヘッド位置情報及び光ディスク回転角度情報と記憶されている補正信号の光ヘッド位置情報及び光ディスク回転角度情報が一致しない場合は、一番近い光ヘッド位置情報及び光ディスク回転角度情報を持つ補正信号を用いて補間処理を行った後、それを補正信号ｃ_１(ｋ＋ｄ)として出力する。
【０１６４】
そして、補正信号ｃ_１(ｋ＋ｄ)を前置補償手段に入力して前置補償信号を加算手段に出力し（ステップＳ３６）、この前置補償信号を光ヘッドが走査を行っているトラックに対するトラッキング誤差信号に加算させる（ステップＳ３７）。
【０１６５】
次に、この加算された信号を用いてトラッキング制御を行う（ステップＳ３８）。回転中の光ディスクに継続してトラッキング制御を行うためには再びステップＳ３１へ戻り、前述の動作を繰り返す。
【０１６６】
なお、メモリ４８に記憶するデータは、光ディスク１周分に相当する入力信号でも、光ディスクの複数回の回転によって得られた入力信号でも良い。
【０１６７】
次に、図１５は、光ヘッド位置情報及び光ディスク回転角度情報を検出する方法を説明する図である。図１５において、スピンドルモータ５１に取り付けられて回転する光ディスク５０を光ヘッド５３から出射される光スポット５４が走査する。光ヘッド５３は、リニアモータなどの光ヘッド移動機構５５に取り付けられており、光ディスク５０の半径方向に移動する。
【０１６８】
例えば、ＤＶＤ−ＲＡＭを用いた光ディスク記録装置においては、光ディスク５０上に予め記録されているヘッダを光学的に読み出し、アドレス復号手段５７によってアドレス信号を生成する。クロック再生手段５８は、光ディスク５０上に形成されているグルーブの蛇行信号を光学的に読み出し、例えばＰＬＬ回路を用いてクロック信号を再生する。
【０１６９】
このように得られたアドレス信号を用いると、光ヘッド５３が光ディスク５０上で走査しているトラックの位置がわかるので、それを光ヘッド位置情報検出手段５９を用いて光ヘッド位置情報に変換し出力する。また、光ディスク回転角度検出手段６０は、アドレス信号を回転角度の原点信号として用いてクロック信号を計測し、光ディスク回転角度情報を出力する。
【０１７０】
これらの手段のほか、光ヘッド位置情報は、例えば、光ヘッド移動機構５５に取り付けられたリニアエンコーダなどの位置検出手段５６によっても得られる。また、光ディスク回転角度情報は、例えば、スピンドルモータ５１に取り付けられたロータリーエンコーダなどの回転角度検出手段５２によっても得られる。上記第７、第８の各実施形態で用いる光ヘッド位置情報及び光ディスク回転角度情報は、前述のいずれの手段を用いて取得しても良い。
【０１７１】
第８の実施形態によれば、光ヘッド位置情報と光ヘッド回転速度情報を用いるので、光ディスクの半径によって１回転の周期が変化するＣＬＶ方式や、ＺＣＬＶ方式を用いた記録・再生の装置において追従誤差を低減できる。
【０１７２】
［第９の実施形態］
図１６は、本発明の第９の実施形態に係るデジタル制御によるトラッキング制御装置で用いる光ディスクの概念図である。なお、第９の実施形態は、ＣＬＶ方式、ＺＣＬＶ方式、ＣＡＶ方式、ＺＣＡＶ方式の対応するトラッキング制御装置の具体的構成例を示す。
【０１７３】
第９の実施形態は、第８の実施形態において、光ヘッド位置情報をその数値に従って複数の範囲に分類し、同一の範囲内では１種類の補正信号ｃ１（ｋ＋ｄ）を用いるものである。
【０１７４】
図１６に示すように、第９の実施形態の光ディスク５０は、中心からの半径によってｎ個の領域に分割される。中心からの半径ｒは、
【０１７５】
【数２２】
ｒ_j≦ｒ≦ｒ_j+1 （ｊ＝１，２，・・，ｎ） ・・・ （２７）
によって表される。
【０１７６】
光ディスク５０では、近接したトラック同士は偏心及びトラックの蛇行の傾向などが類似している。したがって、このように領域を分割して式（２７）で表される各領域内では、光ディスク１周分の補正信号ｃ_１（ｋ＋ｄ）のみを用いることで、補正信号ｃ_１（ｋ＋ｄ）のデー夕を記憶するためのメモリ容量を減らすことができる。
【０１７７】
なお、第８、第９の各実施形態において、光ヘッド位置情報及び光ディスク回転角度情報を用いてメモリアドレスを一意に決定する方法は、これら２つの情報を用いてアドレスを決定する方法でも、これら２つの情報を用いて対応するメモリアドレスを割り当てるための変換テーブルを予めメモリ４８に記憶しておき、この変換テーブルを用いる方法でも同様の動作が得られる。
【０１７８】
また、第１〜第９の各実施形態において、トラッキング誤差を検出する方法は、一般に広く使われている３ビーム法、プッシュプル法、ヘテロダイン法、位相差検出法でも良い。さらには、光ディスク上に予め形成されたピットの反射光を用いて検出する方法、グルーブからの回折光を用いて検出する方法、予め記録されたトラッキング誤差検出用の信号を用いて検出する方法のいずれを用いても良い。
【０１７９】
さらに、第３の実施形態（図５）、第４の実施形態（図９）では、補正信号生成手段５、前置補償手段６、加算手段１８及び安定化補償手段１９をそれぞれ個別のブロックとして示したが、これらは高速のＣＰＵまたはデジタル・シグナル・プロセッサなどの演算ユニットとメモリの組み合わせで実現できることはもちろんである。
【０１８０】
また、安定化補償手段１９の出力をＤ／Ａ変換器（ＤＡＣ）２０によってアナログ信号に変換しトラッキングアクチュエータ３を駆動する構成としているが、安定化補償手段１９の出力をパルス幅変調手段（ＰＷＭ）に入力し、その出力パルスによってトラッキングアクチュエータ３を駆動しても全く同様な動作を実現できる。
【０１８１】
また、第１〜第９の各実施形態において使用する安定化補償手段２あるいは安定化補償手段１９は、ロバスト安定化補償器を使用できることはもちろんのこと、一般に広く使われている位相進み遅れ補償型の補償器、ＰＩ型の補償器あるいはＰＩＤ型の補償器でも良いことは当然である。
【０１８２】
さらに、第１〜第９の各実施形態において使用するトラッキングアクチュエータ３は、図６に示した第１次の共振モードを持つムービングコイル型のアクチュエータの他に、例えば第２次、第３次など高次の共振モードを持つムービングコイル型のアクチュエータも使用できるのはもちろんである。また、ムービングコイル型以外にも、例えば圧電型、リニアモータ型、スイングアーム型、あるいはこれら複数のものを組み合わせた複合型のアクチュエータでも良いことは当然である。これらのいずれの形式のトラッキングアクチュエータを用いたトラッキング制御装置に対しても同様に本発明を実施できることはいうまでもない。
【０１８３】
そして、上記各実施形態は、光ディスク記録装置のみならず、光ディスク再生装置、光ディスク記録再生装置及び光テープ記録装置のトラッキング制御系にも適用可能である。また、フォーカス制御装置にも同様の構成で適用可能である。その場合、トラッキング誤差検出手段、トラッキングアクチュエータに代えて、それぞれフォーカス誤差検出手段、フォーカスアクチュエータを用いる。
【０１８４】
【発明の効果】
以上説明したように、本発明によれば、少なくとも光ディスクの１周前のトラッキング誤差信号に振幅と位相の補償をした信号を生成し、それとトラッキング誤差信号とを加算した信号により、光スポット位置を制御するようにしたので、装置の安定性を確保しつつ光ディスクの回転数全般に渡って追従誤差を低減することができる。また、記憶手段に学習機能を持たせることができるので、追従誤差を一層小さくすることができる。また、ＣＬＶ方式、ＺＣＬＶ方式などを用いた光ディスクの記録・再生において、追従誤差を低減することが可能となり、メモリ容量も低減できる。
【０１８８】
したがって、本発明に係るトラッキング制御装置によれば、狭いトラックピッチを持つ大容量の光ディスクに対しての安定した記録・再生が可能となる。また、高速で回転する光ディスクに対してもトラッキング制御が可能となりデータ転送レートの向上が行える。
【図面の簡単な説明】
【図１】本発明の第１の実施形態に係るフィードバック制御装置としてのトラッキング制御装置の原理構成ブロック図である。
【図２】光ディスクの回転数に対するトラッキング制御装置の追従誤差特性の比較図である。
【図３】本発明の第２の実施形態に係るアナログ制御によるトラッキング制御装置の構成ブロック図である。
【図４】本発明の第２の実施形態のトラッキング制御装置の基本動作のフローチャートである。
【図５】本発明の第３の実施形態に係るデジタル制御によるトラッキング制御装置の構成ブロック図である。
【図６】第１次の共振モードを持つムービングコイル型トラッキングアクチュエータの回路モデル／運動モデルを示す図である。
【図７】記憶手段に記憶された補正信号のデータとサンプリングクロックとの関係模式図である。
【図８】本発明の第３の実施形態のトラッキング制御装置の基本動作フローチャートである。
【図９】本発明の第４の実施形態に係るデジタル制御によるトラッキング制御装置の構成ブロック図である。
【図１０】本発明の第５の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。
【図１１】本発明の第６の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。
【図１２】本発明の第７の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。
【図１３】本発明の第８の実施形態に係るデジタル制御によるトラッキング制御装置で用いる記憶手段の構成図である。
【図１４】本発明の第８の実施形態のトラッキング制御装置の基本動作フローチャートである。
【図１５】光ヘッド位置情報及び光ディスク回転角度情報を検出する方法を説明する図である。
【図１６】本発明の第９の実施形態に係るデジタル制御によるトラッキング制御装置で用いる光ディスクの概念図である。
【図１７】従来の一般的に用いられているトラッキング制御装置の構成ブロック図である。
【図１８】繰り返しトラッキング制御により追従性能を改善する従来のトラッキング制御装置の構成ブロック図である。
【符号の説明】
１ トラッキング誤差検出手段
２ 安定化補償手段
３ トラッキングアクチュ工一夕
５ 補正信号生成手段
６ 前置補償手段
７ 加算手段
１０ 遅延手段
１１ 補償手段
１５ Ａ／Ｄ変換器（ＡＤＣ）
１６ 記憶手段
１７ 補償手段
１８ 加算手段
１９ 安定化補償手段
２０ Ｄ／Ａ変換器（ＤＡＣ）
２５ 第１の演算手段
２６ 第２の演算手段
２７ 加算手段
２９ 補償手段
３０ 遅延手段
３１ 減算手段
３９ 乗算手段
４０ メモリ素子
４１ 加算手段
４３ 演算素子
４４ データバス
４５ アドレスバス
４６ メモリ
４７ 演算素子
４８ メモリ
５０ 光ディスク
５１ スピンドルモータ
５２ 回転角度検出手段
５３ 光ヘッド
５４ 光スポット
５５ 光ヘッド移動機構
５６ 位置検出手段
５７ アドレス復号手段
５８ クロック再生手段
５９ 光ヘッド位置情報検出手段
６０ 光ディスク回転角度検出手段
７０ 可動部
７２ 遅延手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tracking control apparatus used for recording / reproducing of an optical disc.
[0002]
[Summary of Invention]
The present invention relates to a tracking control apparatus used for recording / reproducing of an optical disc. According to the present invention, a signal obtained by delaying a tracking error signal in a feedback control system constituting a tracking control device for a time corresponding to a period corresponding to one round of an optical disc is an inverse number of a closed loop transfer function of an output with respect to an input of the feedback control system. It is added to the tracking error signal in the feedback control system via a precompensation means having a transfer function.
[0003]
Alternatively, the present invention provides a closed loop of an output with respect to an input of the feedback control system, wherein a signal obtained by performing arithmetic processing on the tracking error signal stored for a time corresponding to a plurality of rotation cycles of the optical disc is recorded. It is added to the tracking error signal in the feedback control system via a precompensation means having a transfer function that is the reciprocal of the transfer function.
[0004]
As a result, the tracking error due to eccentricity caused by the optical disk and the optical disk rotation mechanism and the like is reduced without reducing the stability of the tracking control device, and the followable optical disk rotation speed is improved.
[0005]
[Prior art]
A tracking control device used for recording / reproducing of an optical disc is configured by a feedback control system. FIG. 17 is a configuration block diagram of a conventional tracking control device. As shown in FIG. 17, the feedback control system of this tracking control device includes a tracking error detection means 1, a transfer function G₁Stabilization compensation means 2 with a transfer function G₂The tracking actuator 3 having
[0006]
In the feedback control system of this tracking control device, the track position t on the optical disk₁And the light spot position s controlled by the tracking actuator evening 3.₁Is detected by the tracking error detection means 1, and the tracking error signal e₁Is input to the stabilization compensator 2.
[0007]
The stabilization compensator 2 has a tracking error signal e so that the tracking controller has a desired response characteristic and performs a stable operation.₁Compensates the frequency characteristics of the amplitude and phase of the signal and outputs it. The output signal of the stabilization compensation means 2 drives the tracking actuator evening 3, and the light spot position s₁To control.
[0008]
As a technique for improving the follow-up performance of such a feedback control system, for example, as described in Reference 1 “Section 4.10 of“ Dynamics and Control of Information Equipment ”published by Yokendo, edited by the Japan Society of Mechanical Engineers”. A method of repeated tracking control is known.
[0009]
FIG. 18 is a block diagram showing the configuration of a tracking control apparatus using this repetitive tracking control method. As shown in FIG. 18, in the feedback control system of this tracking control device, in the configuration shown in FIG. 17, an addition means 7 is provided between the tracking error detection means 1 and the stabilization compensation means 2, and the addition means 7 Output the transfer function e^-LsAccordingly, a delay means 72 for returning to the input of the adding means 7 is provided.
[0010]
In this repetitive tracking control method, the tracking error signal e₁Is added to the output of the delay means 72 by the adding means 7 and the control signal f₁Is output. Control signal f₁Are input to the delay means 72 and the stabilization compensation means 2.
[0011]
The delay means 72 receives the control signal f₁Is delayed by a time corresponding to the rotation period L of the optical disk, and the tracking error signal e is sent to the adding means 7.₁And the control signal f₁Is output.
[0012]
The stabilization compensation means 2 controls the control signal f so that the tracking control device has a desired response characteristic and performs a stable operation.₁Compensates the frequency characteristics of the amplitude and phase of the signal and outputs it. The output signal of the stabilization compensation means 2 drives the tracking actuator 3 and the light spot position s.₁To control.
[0013]
As a result, the tracking error that could not be corrected before one rotation of the optical disk is corrected in advance, so that the follow-up performance is improved.
[0014]
[Problems to be solved by the invention]
Incidentally, in order to record high-quality image data on an optical disk medium for a long time, it is required to increase the recording density of the optical disk and increase the data transfer rate.
[0015]
In order to increase the recording density, it is necessary to use a short wavelength light source and to reduce the light spot diameter by increasing the numerical aperture of the objective lens. This reduces the mark length recorded on the optical disc and uses a narrow track pitch to reduce the area occupied by data per bit.
[0016]
In order to cope with this narrow track pitch, the tracking control device is required to have a sufficiently small tracking error compared to the track pitch. For example, in the case of a CD-ROM, the allowable value of the tracking error is ± 0.1 μm or less for a track pitch of 1.6 μm, and in the case of a DVD-ROM, it is ± 0.02 μm or less for a track pitch of 0.74 μm. The following error must be
[0017]
In order to increase the data transfer rate in the optical disk recording apparatus, it is required to reduce the bit length recorded on the optical disk and simultaneously increase the rotation speed of the optical disk.
[0018]
By the way, the tracks on the optical disk are concentric or spiral. Further, the optical disc has an eccentricity that occurs in the manufacturing process. Further, the spindle motor for rotating the optical disc and the mounting portion for attaching the optical disc to the spindle motor are also eccentric. Since the worst value of the eccentricity is the sum of these, when the track on the optical disk is viewed from the light spot of the optical head, the eccentricity is about ± 100 μm. Due to this eccentricity, the track position, which is the target value of the tracking control device, becomes a periodic function that changes as the optical disk rotates.
[0019]
Therefore, in order to cope with the high-speed rotation of the optical disk, the light spot position must follow the track position on the eccentric optical disk as described above at a high speed. For this purpose, it is necessary to increase the mechanical resonance frequency of the tracking actuator used in the optical head and simultaneously increase the bandwidth of the tracking control device.
[0020]
There are methods to increase the mechanical resonance frequency of the tracking actuator, such as reducing the mass of the moving part and increasing the elastic modulus. However, either method has its limitations, and the upper limit of the mechanical resonance frequency of the tracking actuator that is currently realized. Is about 100 Hz.
[0021]
On the other hand, widening the bandwidth of the tracking control device improves the follow-up performance with respect to high-speed rotation of the optical disc, but reduces the suppression characteristics against disturbances such as noise and vibration.
[0022]
For the above reason, in the tracking control apparatus using only the feedback control system as shown in FIG. 17, the light spot is high-speed with respect to the track on the optical disk rotating at high speed while satisfying the required tolerance of the tracking error. It was difficult to follow the position.
[0023]
On the other hand, the tracking control apparatus using the repetitive control method shown in FIG. 18 as described in Document 1 shows excellent tracking performance for periodically changing inputs. However, if it is a periodic component, it has the property of trying to suppress the error to an infinitely high frequency, which may cause problems in the stability of the tracking control device and may be vulnerable to non-periodic disturbances. Widely known.
[0024]
Further, in a method in which an optical disk rotates at a constant angular velocity (CAV method: Constant Angular Velocity or ZCAV method: Zoned Constant Angular Velocity), iterative control using delay means 72 having a constant delay amount as shown in FIG. Good. However, a method of rotating at a constant linear velocity as in a CD (CLV method: Constant Linear Velocity), or a radius of an optical disk as in a DVD-RAM is divided into several regions, and a substantially constant line in the region. In the method of rotating at a speed (ZCLV method: Zoned Constant Linear Velocity), the cycle of one rotation changes depending on the radius of the optical disk, and therefore it is not possible to perform repetitive control by the method shown in FIG.
[0025]
The present invention has been created to solve such problems. The stability of the tracking control device is ensured, and the follow-up performance with respect to the track on the optical disk rotating at high speed is improved. The CLV method and the ZCLV method are provided. Thus, it is an object of the present invention to provide a tracking control device that is stable and has high tracking performance even when the period of one rotation changes depending on the radius of the optical disk.
[0026]
[Means for Solving the Problems]
  In order to achieve the above object, a tracking control apparatus according to claim 1 generates a tracking error signal corresponding to a difference between a track position on an optical disc and a light spot position emitted from an optical head. An error signal generating means, and the tracking error signal is stored in the storage means over a time corresponding to a plurality of rotation cycles of the optical disc, and at least one of a moving average process and a least squares method is used for the stored signal A correction signal generation means for generating a correction signal by performing a calculation process for extracting a signal corresponding to a tracking error signal before one rotation period, and compensating for the amplitude and phase of the generated correction signalPrefacePrecompensation means for generating a compensation signal by a predetermined pulse transfer function; the tracking error signal;PrefaceAdding means for generating a drive signal obtained by adding the compensation signal, and control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal;
  The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. The transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut off. ( z-1), it has a pulse transfer function represented by the following equation (18).,
    P ₁ ( z ^-1 ) = Ac (z ^-1 ) / {Bc ⁺ (Z ^-1 ) Bc ⁻ (1)}... (18)
  Where Gcl ( z ^-1 ) = Z ^-D Bc ⁺ (Z ^-1 ) Bc ⁻ (Z ^-1 ) / Ac (z ^-1 )
            Ac (z ^-1 ): Gcl ( z ^-1 ) Pole term
            Bc ⁺ (Z ^-1 ): Gcl ( z ^-1 ) Stable zero term
            Bc ⁻ (Z ^-1 ): Gcl ( z ^-1 ) Unstable zero term
            Bc ⁻ (1): Gcl ( z ^-1 ) Z ^-1 = 1 and constant
              Turned into
            d: Equivalent lead sampling number
  The pulse transfer function uses the response of the light spot position as the correction signal to Gcl. ( z-1) P1 ( z-1 ) Gcl when calculating by multiplication ( z-1 ) And the DC gain of the pre-compensation means is set to Gcl. ( z ^-1 ) To match the inverse of DC gainIt is characterized by that.
[0027]
  According to a second aspect of the present invention, there is provided a tracking control device that generates a tracking error signal corresponding to a difference between a track position on an optical disc and a light spot position emitted from an optical head, and the light The position information of the optical head and the rotation angle information of the optical disk in a state where the head follows the track on the optical disk are stored in the storage means together with the tracking error signal or the signal obtained as a result of performing the arithmetic processing on the tracking error signal. The stored optical head position information and optical disk rotation angle information are both stored after the time corresponding to the rotation period of at least one rotation of the optical disk is stored, and the optical head is currently scanning the optical disk. When these two pieces of information coincide with each other, the tracking error signal already stored, And correction signal generating means for outputting a resultant signal subjected to arithmetic processing to the tracking error signal as a correction signal,
  Compensation of amplitude and phase of generated correction signalPrefacePrecompensation means for generating a compensation signal by a predetermined pulse transfer function; the tracking error signal;PrefaceAdding means for generating a drive signal obtained by adding the compensation signal; and control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal;
  The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. The transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut off. ( z-1), it has a pulse transfer function represented by the following equation (18),
    P ₁ ( z ^-1 ) = Ac (z ^-1 ) / {Bc ⁺ (Z ^-1 ) Bc ⁻ (1)} ... (18)
  Where Gcl ( z ^-1 ) = Z ^-D Bc ⁺ (Z ^-1 ) Bc ⁻ (Z ^-1 ) / Ac (z ^-1 )
            Ac (z ^-1 ): Gcl ( z ^-1 ) Pole term
            Bc ⁺ (Z ^-1 ): Gcl ( z ^-1 ) Stable zero term
            Bc ⁻ (Z ^-1 ): Gcl ( z ^-1 ) Unstable zero term
            Bc ⁻ (1): Gcl ( z ^-1 ) Z ^-1 = 1 and constant
              ,
            d: Equivalent lead sampling number
  The pulse transfer function uses the response of the light spot position as the correction signal to Gcl. ( z-1) P1 ( z-1 ) Gcl when calculating by multiplication ( z-1 ) And the DC gain of the pre-compensation means is set to Gcl. ( z ^-1 ) To match the inverse of DC gainIt is characterized by that.
[0028]
  The tracking control device according to the invention described in claim 3 is:Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disk and the light spot position emitted from the optical head, and the tracking error signal corresponds to a plurality of rotation cycles of the optical disk An operation for storing in the storage means over time and applying a statistical method of moving average processing or least square method to the stored signal to extract a signal corresponding to the tracking error signal before one rotation period Correction signal generating means for performing processing to generate a correction signal, pre-compensation means for generating a pre-compensation signal that has compensated the amplitude and phase of the generated correction signal by a predetermined pulse transfer function, and the tracking error Adding means for generating a drive signal obtained by adding the signal and the pre-compensation signal; And control means for scanning the target track on the optical disk to the light spot,
  The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. The transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut off. ( z-1), it has a pulse transfer function represented by the following equation (21).,
    P ₁ ( z ^-1 ) = Ac (z ^-1 ) Bc ⁻ (Z) / [Bc ⁺ (Z ^-1 ) {Bc ⁻ (1)} ² ] (21)
  Where Gcl ( z ^-1 ) = Z ^-D Bc ⁺ (Z ^-1 ) Bc ⁻ (Z ^-1 ) / Ac (z ^-1 )
            Ac (z ^-1 ): Gcl ( z ^-1 ) Pole term
            Bc ⁺ (Z ^-1 ): Gcl ( z ^-1 ) Stable zero term
            Bc ⁻ (Z ^-1 ): Gcl ( z ^-1 ) Unstable zero term
            Bc ⁻ (1): Gcl ( z ^-1 ) Z ^-1 = 1 and constant
              Turned into,
            d: Equivalent lead sampling number
  The pulse transfer function uses the response of the light spot position as the correction signal to Gcl. ( z ^-1 ) ・ P ₁ ( z ^-1 ) Gcl when calculating by multiplication ( z ^-1 ) Cancel the poles and stable zeros of,Furthermore, the product of the closed-loop pulse transfer function makes the phase difference zero at all frequencies, and the DC gain of the pre-compensation means is expressed as Gcl. ( z ^-1 ) To match the inverse of DC gainIt is characterized by that.
[0029]
  The tracking control device according to the invention of claim 4Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disk and the light spot position emitted from the optical head, and the optical head in a state of following the track on the optical disk The position information of the optical head and the rotation angle information of the optical disk are stored in a storage means together with a tracking error signal or a signal obtained as a result of performing arithmetic processing on the tracking error signal, and corresponds to at least one rotation period of the optical disk. When the stored optical head position information and optical disk rotation angle information both coincide with these two pieces of information at the present time when the optical head is scanning on the optical disk, the information is already stored. The tracking error signal, or the result of performing arithmetic processing on the tracking error signal A correction signal generating means for outputting the obtained signal as a correction signal, a pre-compensation means for generating a pre-compensation signal that has compensated the amplitude and phase of the generated correction signal by a predetermined pulse transfer function, and Adding means for generating a drive signal obtained by adding a tracking error signal and the pre-compensation signal; and control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal;
  The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. The transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut off. ( z-1), it has a pulse transfer function represented by the following equation (21).,
    P ₁ ( z ^-1 ) = Ac (z ^-1 ) Bc ⁻ (Z) / [Bc ⁺ (Z ^-1 ) {Bc ⁻ (1)} ² ] (21)
  Where Gcl ( z ^-1 ) = Z ^-D Bc ⁺ (Z ^-1 ) Bc ⁻ (Z ^-1 ) / Ac (z ^-1 )
            Ac (z ^-1 ): Gcl ( z ^-1 ) Pole term
            Bc ⁺ (Z ^-1 ): Gcl ( z ^-1 ) Stable zero term
            Bc ⁻ (Z ^-1 ): Gcl ( z ^-1 ) Unstable zero term
            Bc ⁻ (1): Gcl ( z ^-1 ) Z ^-1 = 1 and constant
              Turned into,
            d: Equivalent lead sampling number
  The pulse transfer function uses the response of the light spot position as the correction signal to Gcl. ( z ^-1 ) ・ P ₁ ( z ^-1 ) Gcl when calculating by multiplication ( z ^-1 ) And the product of the closed-loop pulse transfer function makes the phase difference zero at all frequencies, and the DC gain of the precompensation means is Gcl. ( z ^-1 ) To match the inverse of DC gainIt is characterized by that.
[0030]
  The tracking control device according to the invention described in claim 5 is:Claim 3 or 4In the tracking control device described inThe correction signal generating means divides the optical head position information into a plurality of areas according to the radius of the optical disk, information on the area to which the position of the optical head belongs when the optical head follows a track on the optical disk, and The rotation angle information of the optical disk at the time is stored in a storage means together with a tracking error signal for a time corresponding to one rotation period of the optical disk or a signal obtained as a result of performing arithmetic processing on the tracking error signal. At the present time when scanning is performed, it is determined to which of the divided areas the position of the optical head belongs, and the tracking error signal corresponding to the rotation angle information of the optical disk in that area, or the tracking error signal Reading out the signal obtained as a result of the arithmetic processing from the storage means as a correction signalIt is characterized by that.
[0032]
  Claim6The tracking control device according to the invention described in claim 1 to claim 15In the tracking control device according to any one of the above, the signal stored in the storage means is sequentially updated according to the rotation of the optical disk.
[0036]
  The present inventionAccording to the above, it is possible to control the light spot position by generating a signal obtained by compensating the amplitude and phase of the tracking error signal at least one round before the optical disc and adding the tracking error signal. Accordingly, it is possible to reduce the tracking error over the entire number of rotations of the optical disk while ensuring the stability of the apparatus.In addition, the storage means can have a learning function. Therefore, the tracking error can be further reduced. In addition, even when there is a period in which a tracking error signal cannot be obtained due to scratches or dust on the optical disk, the possibility of occurrence of tracking failure can be reduced. Further, in the recording / reproducing of an optical disc using the CLV method, the ZCLV method, etc., it becomes possible to reduce the tracking error and also reduce the memory capacity.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
  [First Embodiment]
  FIG. 1 is a block diagram showing the configuration of a tracking control apparatus according to the first embodiment of the present invention. First embodimentThe present inventionIt shows the principle configuration of the tracking control device according toYes,The second to ninth embodiments shown below are based on the first embodiment.
[0041]
As shown in FIG. 1, the tracking control apparatus of the first embodiment is provided with an adding means 7 between the tracking error detecting means 1 and the stabilization compensating means 2 in the configuration shown in FIG. The correction signal generating means 5 and the precompensation means 6 having the transfer function P1 are arranged in this order on the path for introducing one input (the output of the tracking error detecting means 1) to the other input of the adding means 7. It is.
[0042]
The correction signal generation means 5 is a tracking error signal e detected by the tracking error detection means 1.₁Tracking error signal e detected at least before one rotation of the optical disk₁Correction signal c based on₁Is generated.
[0043]
The pre-compensation means 6 receives the correction signal c₁Precompensation signal h based on₁Is output to the other input of the adding means 7.
[0044]
Also in the first embodiment, the stabilization compensator 2 has the amplitude and phase of the feedback control system that is formed by the tracking error detector 1, the adder 7, the stabilization compensator 2 and the tracking actuator 3. Frequency characteristics are compensated for, and stable feedback control is realized. This also applies to the following second to ninth embodiments.
[0046]
Next, the basic operation of the tracking control apparatus of the first embodiment will be described with reference to FIG.
[0047]
In FIG. 1, the track position t₁And light spot position₁Is detected by the tracking error detection means 1, and the tracking error signal e is detected.₁Get. Tracking error signal e₁Is branched into two, one being input to the adding means 7 and the other being input to the correction signal generating means 5.
[0048]
The correction signal generation means 5 is a tracking error signal e detected at least before one rotation of the optical disk.₁Correction signal c using₁Is output. The precompensation means 6 has a transfer function P₁Therefore, the correction signal c₁Compensation of the frequency characteristics of the amplitude and phase of the pre-compensation signal h₁Output as.
[0049]
This pre-compensation signal h₁Is the tracking error signal e by the adding means 7.₁And the frequency characteristic of the amplitude and phase of the signal (drive signal) obtained as a result is compensated by the stabilization compensator 2 and input to the tracking actuator 3 to drive the light spot position s.₁To control.
[0050]
As described above, in the first embodiment, in addition to the tracking error signal for the track on which the optical head is scanning, the pre-compensation signal is generated using the tracking error signal detected at least before one rotation of the optical disk. In addition, since tracking control is performed using a signal obtained as a result of calculation using the pre-compensation signal and the tracking error signal, the tracking error can be reduced. This will be specifically described below.
[0051]
First, the transfer functions of the stabilization compensation means 2 and the tracking actuator 3 are respectively expressed as G₁, G₂It is determined. From FIG. 1, the input / output relationship of the tracking error detecting means 1 is
t₁-S₁= E₁              ... (1)
It is. Further, the spot position s controlled by the tracking actuator 3₁Is
(E₁+ H₁) G₁G₂= S₁    ... (2)
It is.
[0052]
As described above, since the optical disk, the spindle motor, and the optical disk mounting portion are decentered, the track position on the rotating optical disk with respect to the light spot of the optical head is a function that changes periodically. Furthermore, adjacent tracks have a large positional correlation.
[0053]
Therefore, the precompensation signal h is based on the tracking error that cannot be suppressed at least before one rotation.₁Is generated. Further, it can be understood that the follow-up error can be reduced by performing correction in the next rotation using this signal.
[0054]
Here, the track position at the m-th rotation of the optical disk is expressed as t._{1, m}S_{1, m}, Tracking error signal e_{1, m}, H_{1, m}Is described. Tracking error signal e before the (m−1) th rotation of the optical disk_{1, m-1}Precompensation signal h obtained using_{1, m-1}Is used, the light spot position s at the m-th rotation_{1, m}Is
s_{1, m}= (E_{1, m}+ H_{1, m-1}) G₁G₂ ... (3)
It becomes. By repeating this operation, t_{1, m}= S_{1, m}Can be realized. In the following second to ninth embodiments, specific means and configurations for realizing this at high speed and stably are described. According to these embodiments, a tracking error characteristic as shown in FIG. 2 is obtained.
[0055]
FIG. 2 is a comparison diagram of the tracking error characteristics of the tracking control apparatus with respect to the rotational speed of the optical disk obtained by the present invention. In FIG. 2, (a) is a tracking error characteristic obtained by the tracking control apparatus of the present invention, and (b) is a tracking error characteristic obtained by a conventional tracking control apparatus.
[0056]
As shown in FIG. 2, the tracking error is an allowable value e.₀In the conventional tracking control device, the following rotation speed is the rotation speed N as shown in FIG.₁Although the following, in the tracking control device of each embodiment of the present invention, as shown in FIG.₂Is expanded to. That is, according to each embodiment of the present invention, it can be understood that the tracking error can be reduced over the entire rotation speed of the optical disk.
[0057]
  [Second Embodiment]
  FIG. 3 is a block diagram showing the configuration of the tracking control device by analog control according to the second embodiment of the present invention.It is.
[0058]
As shown in FIG. 3, the second embodiment includes a delay unit 10 as the correction signal generation unit 5 and a compensation unit 11 as the pre-compensation unit 6. Others are the same as in the first embodiment.
[0059]
The delay means 10 includes a tracking error signal e₁Correction signal c obtained by delaying time corresponding to one rotation period of the optical disk₁Is output. Compensation means 11 provides a correction signal c₁Precompensation signal h with amplitude and phase compensation applied to₁Is output.
[0060]
Next, the operation of the second embodiment will be described with reference to FIGS. FIG. 4 is a flowchart of the basic operation of the tracking control device of the second embodiment.
[0061]
First, the operation principle of the tracking control apparatus of the second embodiment will be described with reference to FIG. The transfer function of the compensation means 11 is P₁(s), the transfer functions of the stabilization compensation means 2 and the tracking actuator 3 are respectively represented by G₁(s), G₂This is represented by (s).
[0062]
When the connection between the compensation unit 11 and the addition unit 7 is disconnected with respect to the feedback control system formed by the tracking error detection unit 1, the addition unit 7, the stabilization compensation unit 2 and the tracking actuator 3, the input to the addition unit 7 is performed. Signal h₁Light spot position with respect to₁Transfer function G_cl(s) is obtained by the following equation (4).
[0063]
[Expression 1]
G_cl(s) = G₁(s) G₂(s) / {1 + G₁(s) G₂(s)} (4)
Therefore, the pre-compensation means 6 has a transfer function P of the compensation means 11.₁(s) is
[0064]
[Expression 2]
P₁(s) = {1 + G₁(s) G₂(s)} / G₁(s) G₂(s) ... (5)
It is realized to satisfy. That is, the pre-compensation means 6 has a transfer function that is the inverse of the closed-loop transfer function of the output with respect to the input of the feedback control system.
[0065]
And the compensation means 11 of the pre-compensation means 6 is the transfer function P shown in the equation (5).₁According to (s), the correction signal c₁The frequency characteristics of the amplitude and the phase are corrected with respect to the signal and output to the adding means 7 for tracking control.
[0066]
At this time, the correction signal c₁Light spot position s₁Is expressed by the following equation (6) from the equations (4) and (5).
[0067]
[Equation 3]

That is, the correction signal c₁Is the light spot position s without causing an amplitude difference and time delay.₁Can be directly controlled and corrected.
[0068]
Next, the basic operation of the tracking control apparatus of the second embodiment will be described along FIG. 4 with reference to FIG. 3 as appropriate. In the figure, a tracking error detection means 1 is a tracking error signal e for a track scanned by an optical head.₁After detecting the tracking error signal e₁Is input to the delay means 10 in the correction signal generating means 5 (step S1). The delay means 10 includes a tracking error signal e₁Is delayed for a time corresponding to one rotation period of the optical disk, and the correction signal c₁(Step S2).
[0069]
The compensation means 11 in the pre-compensation means 6 receives the correction signal c₁To precompensation signal h₁(Step S3), the adding means 7 sends the pre-compensation signal h₁The tracking error signal e for the track on which the optical head is scanning₁(Step S4).
[0070]
Next, the stabilization compensator 2 drives the tracking actuator 3 with the added signal to perform tracking control (step S5). In order to continuously perform tracking control on the rotating optical disk, the process returns to step S1 again, and the above-described operation is repeated.
[0071]
As a result, it is possible to reduce the tracking error over the entire number of rotations of the optical disk.
[0072]
  [Third Embodiment]
  FIG. 5 is a block diagram showing the configuration of a tracking control apparatus using digital control according to the third embodiment of the present invention.is there.
[0073]
In FIG. 5, in the third embodiment, the adder 18 and the stabilization compensator 19 are each constituted by a digital signal processing circuit, and a tracking error signal e₁Is converted into a digital signal e by an A / D converter (ADC) 15.₁(k) is converted and given to one input of the adding means 18, and the output digital signal of the stabilization compensating means 19 is converted into an analog signal by the D / A converter (DAC) 20 and given to the tracking actuator 3. It is configured.
[0074]
That is, in this tracking control device by digital control, the tracking error signal e₁The digital signal e₁After the conversion to (k), processing as a tracking control device is executed.
[0075]
As shown in FIG. 5, the tracking error signal e detected by the tracking error detecting means 1₁Is a digital signal e in an A / D converter (ADC) 15.₁It is converted into (k) and input to the correction signal generating means 5 and the adding means 18.
[0076]
Here, the correction signal generation means 5 includes a storage means 16. The storage means 16 stores a tracking error signal e for a time corresponding to at least one rotation period of the optical disk.₁Digital data₁Store (k). Then, the storage means 16 stores the tracking error signal e one round before the optical disk.₁Using (k), the tracking error signal at the time advanced by the time corresponding to the d sampling period at the sampling time k is corrected signal c.₁Output to the precompensation means 6 as (k + d).
[0077]
Further, the pre-compensation means 6 has a pulse transfer function P₁(z^-1) Is provided. The compensation unit 17 receives the correction signal c input from the storage unit 16.₁(k + d) is processed digitally and the pre-compensation signal h₁Output (k).
[0078]
The adding means 18 is a digitized tracking error signal e.₁(k) and precompensation signal h₁(k) is added, and the addition result is input to the stabilization compensator 19. The output of the stabilization compensator 19 is converted into an analog signal by a D / A converter (DAC) 20 to drive the tracking actuator 3, and the light spot position s.₁Tracking control is performed by changing.
[0079]
The stabilization compensator 19 compensates the frequency characteristics of the amplitude and phase so that the feedback control system of the tracking controller operates stably, and at the same time, a pulse transfer function G for realizing a desired response characteristic.₁(z^-1)have. In addition, a system in which the D / A converter (DAC) 20 and the tracking actuator 3 are connected in cascade has a pulse transfer function G₂(z^-1)have.
[0080]
Next, the basic operation of the third embodiment will be described with reference to FIGS. FIG. 6 is a circuit / motion model diagram of the moving coil type tracking actuator having the first resonance mode. FIG. 7 is a schematic view of the relationship between the correction signal data stored in the storage means and the sampling clock. FIG. 8 is a flowchart of the basic operation of the tracking control device of the third embodiment.
[0081]
First, the operation principle of the tracking control device of the third embodiment will be described with reference to FIGS. In this digital control system, the pulse transfer function P of the compensating means 17₁(z^-1) Is determined depending on whether the pulse transfer function of the tracking actuator 3 has an unstable zero point or not.
[0082]
In any case, after obtaining the transfer function of the tracking actuator 3 in a continuous system, it is converted into a discrete system to obtain a closed-loop pulse transfer function in the digital control system. Furthermore, the pulse transfer function P of the compensation means 17 based on the closed-loop pulse transfer function.₁(z^-1).
[0083]
A general moving coil type tracking actuator used for an optical head has a first resonance mode as described in, for example, Reference 2 “Radio Technology Company, Radio Technology Selection“ Optical Disc Technology ”page 134”. It is represented by the model shown in FIG. FIG. 6A shows a circuit model of the tracking actuator, where v is a drive voltage, i is a drive current, R is a resistance component, and L is a reactance component. FIG. 6B shows a motion model, and K_T, D_T, M_T, F (t) and x (t) represent the elastic coefficient, the viscosity coefficient, the mass of the movable part 70, the driving force and the position, respectively. 6 (a) and 6 (b), the drive voltage v (t) and the drive force f (t) are
[0084]
[Expression 4]

It becomes. Also, the thrust constant is K_iThen, the driving force f (t) is
f (t) = K_ii (t) (9)
It becomes.
[0085]
Then, by using the equations (8) and (9), the Laplace transform is performed with the initial value set to 0, so that the transfer function G when the tracking actuator 3 is driven with a current is used._2i(s) is
[0086]
[Equation 5]

It becomes. Further, the transfer function G when the tracking actuator 3 is driven by voltage._2v(s) is calculated using Equation (7), Equation (8), and Equation (9).
[0087]
[Formula 6]

It becomes. That is, the model of the tracking actuator 3 in the continuous system is a secondary low-pass filter type for current driving and a tertiary for voltage driving.
[0088]
Next, considering that the D / A converter (DAC) 20 that outputs a signal for driving the tracking actuator 3 functions as a zero-order holder, the transfer function in the continuous system is changed to the pulse transfer function of the digital control system. G₂(z^-1), It is known that an unstable zero occurs depending on the difference between the denominator and the numerator, as shown in, for example, Document 3 “Corona“ Basic Digital Control ”, page 59, Table 3.5”. . Where z = exp (jωT_s). However, T_sIs the sampling period.
[0089]
[Table 1]

[0090]
Table 1 shows Table 3.5 of Document 3. In Table 3.5 of Document 3, k = 2 when the tracking actuator 3 is driven with current. When driven by voltage, the value of k increases by one and becomes k = 3 due to an excessive phenomenon that changes from voltage to current. In either case, one or more unstable zeros are generated. On the other hand, the pulse transfer function G of the stabilization compensator 19 of FIG.₁(z^-1) Is designed so that it does not have unstable zeros or unstable poles. Here, k in Table 1 is a numerical value obtained by subtracting the order of the numerator from the order of the denominator of the transfer function of the continuous system, and is different from k representing the sampling time.
[0091]
Precompensation signal h₁Light spot position s with respect to (k)₁Closed-loop pulse transfer function G_cl(z^-1)
[0092]
[Expression 7]

Represented by In formula (12), A_c(z^-1), B_c(z^-1) Are all z^-1Is a polynomial. Z^-DIs d · T_sThat is, this corresponds to a time delay of d sampling periods.
[0093]
Therefore, the pulse transfer function P of the compensation means 17 based on the equation (12)₁(z^-1) Is determined by the following procedure. First, the closed-loop pulse transfer function G_cl(z^-1), P₁’(Z^-1), P₁(z^-1) Are defined as shown in equations (13) and (14), respectively.
[0094]
[Equation 8]

[0095]
[Equation 9]

Here, in the formula (13), z of the molecule^dIndicates that the output has advanced by d sampling periods relative to the input. So P₁(z^-1) Is input as a correction signal c at a time advanced by d sampling periods.₁(k + d) is used. This will be described with reference to FIG. In FIG. 7, for example, it is assumed that sampling is controlled n times for one round of the optical disk. The signal stored at the time corresponding to the sampling clock (k + d) of the (m−1) th cycle is used at the time corresponding to the sampling clock k of the mth cycle. Similar processing is performed at other times.
[0096]
Since adjacent tracks have a large positional correlation, the correction signal c at a time equivalently advanced by d sampling periods by this method.₁(K + d) is obtained. From the equations (12) and (14), the correction signal c₁Light spot position s with respect to (k + d)₁Is
[0097]
[Expression 10]

And the correction signal c₁Light spot position s with respect to (k)₁Tracks without amplitude differences and time delays.
[0098]
(A) As described above, when the tracking actuator does not have an unstable zero point in the digital control system, the pulse transfer function P is expressed by the equation (14).₁(z^-1), A stable control system can be realized. That is, the pulse transfer function P₁(z^-1) As a closed-loop pulse transfer function G of the output with respect to the input of the feedback control system_cl(z^-1The pulse transfer function derived from the reciprocal of) is adopted.
[0099]
However, in the tracking control device using the moving coil type tracking actuator as described above, the closed-loop pulse transfer function G_cl(z^-1) Has an unstable zero, so the pulse transfer function P is directly obtained from the equation (12) using the equation (14).₁(z^-1), The pulse transfer function P₁(z^-1) Has an unstable pole and cannot constitute a stable control system.
[0100]
(B) Therefore, when the pulse transfer function of the tracking actuator 3 has an unstable zero, the pulse transfer function P in the digital control system is as follows.₁(z^-1).
[0101]
Pulse transfer function G of equation (12)_cl(z^-1), The zero point is divided into a stable zero point and an unstable zero point, and is described as the following equation (16). In Equation (16), B_c ⁺(Z^-1) Is a stable zero, B_c ⁻(Z^-1) Is z with unstable zeros^-1Is a polynomial.
[0102]
## EQU11 ##

Then, using this equation (16), the pulse transfer function P can be obtained by the first and second methods described below.₁(z^-1) To establish a stable control system.
[0103]
In the first method, the pulse transfer function G_cl(z^-1Only the stable zero of the pulse transfer function P₁(z^-1) In addition, B including unstable zeros_c ⁻(Z^-1) Is z^-1= 1 is substituted for a constant. That is, P₁’(Z^-1), P₁(z^-1) Each
[0104]
[Expression 12]

[0105]
[Formula 13]

It is determined.
[0106]
Pulse transfer function P of compensation means 17₁(z^-1) In the form of equation (18), the pulse transfer function G_cl(z^-1Only the stable zero of the pulse transfer function P₁(z^-1) To cancel the correction signal c₁Light spot position s with respect to (k + d)₁A stable control system is configured in response.
[0107]
That is, in the first method, the correction signal c is obtained by the equations (12), (16), and (18).₁Light spot position s with respect to (k + d)₁Is the response
[0108]
[Expression 14]

The light spot position s in the low frequency region₁Is the correction signal c₁Follow (k) without any time delay. In addition, the stability of the tracking control device is maintained.
[0109]
Next, in the second method, the pulse transfer function P₁’(Z^-1), P₁(z^-1) Are defined as in the following equations (20) and (21). In the formula (20) and the formula (21), B_c ⁻(Z) is the polynomial B_c ⁻(Z^-1) In z^-1Is replaced by z.
[0110]
[Expression 15]

[0111]
[Expression 16]

In the second method, the correction signal c is expressed by the equations (12), (16), and (21).₁Light spot position s with respect to (k + d)₁Is the response
[0112]
[Expression 17]

It becomes.
[0113]
Where B_c ⁻(Z) and B_c ⁻(Z^-1) Are complex conjugates with each other, so that the light spot position s₁Is the correction signal c₁Follow (k) at all frequencies without any time delay. In addition, the stability of the tracking control device is maintained.
[0114]
Next, the operation will be described in detail with reference to FIG. In the figure, a tracking error detection means 1 is a tracking error signal e for a track scanned by an optical head.₁Is detected. This tracking error signal e₁Is converted into a digital signal e by an A / D converter (ADC) 15.₁After being converted to (k), it is input to the correction signal generating means 5 and the adding means 18.
[0115]
For example, the correction signal generation unit 5 stores a tracking error signal e in a predetermined storage area of the storage unit 16 using a memory.₁(k) is stored one by one and the tracking error signal e one round before the optical disk is stored.₁Using (k), a tracking error signal at a time advanced by a time corresponding to d · Ts at time k is calculated (step S11), and the correction signal c is calculated.₁(k + d) is stored in another storage area of the storage means 16 (step S12).
[0116]
Then, the correction signal generation means 5 is a correction signal c stored before one rotation of the optical disk.₁It is determined whether or not (k + d) is present (step S13). If not, the correction signal = 0 is set (step S14), and the stored correction signal c is stored.₁If there is (k + d), it is read (step S15) and given to the pre-compensation means 6 to give a pre-compensation signal h.₁(k) is output (step 16).
[0117]
Here, the compensation means 17 constituting the pre-compensation means 6 is the pulse transfer function P defined by the first and second methods.₁(z^-1). That is, the pulse transfer function G obtained by the zero-order hold function of the D / A converter (DAC) 20 and the transfer function of the tracking actuator 3.₂(z^-1) Does not have an unstable zero, the compensation means 17 uses the pulse transfer function P₁(z^-1) Is configured as in equation (14). The pulse transfer function G₂(z^-1) Has an unstable zero, the compensation means 17 uses the pulse transfer function P₁(z^-1) Is configured to be expression (18) or expression (21).
[0118]
Next, in the adding means 18, the pre-compensation signal h obtained from the output of the compensating means 17.₁(k) and tracking error signal e₁(k) is added and output to the stabilization compensator 19 (step 17).
[0119]
The stabilization compensation means 19 stabilizes the feedback control system and at the same time a pulse transfer function G for realizing a desired response characteristic.₁(z^-1)have. The output of the stabilization compensator 19 is converted into an analog signal by a D / A converter (DAC) 20 and drives a tracking actuator to drive the light spot position s.₁Is controlled (step 18).
[0120]
In order to continuously perform the tracking control on the rotating optical disk, the process returns to step S11 and the above operation is repeated. As a result, it is possible to reduce the tracking error over the entire number of rotations of the optical disk.
[0121]
  [Fourth Embodiment]
  FIG. 9 is a block diagram showing the configuration of a tracking control apparatus using digital control according to the fourth embodiment of the present invention.It is.
[0122]
In the tracking control apparatus by digital control of the fourth embodiment, in the third embodiment, the correction signal generating means 5 is connected to the pulse transfer function Q.₁(z^-1) Having a first calculation means 25 and a pulse transfer function Q₂(z^-1), The second calculating means 26, the adding means 27, and the storage means 16, and the precompensation means 6 is connected to the pulse transfer function P.₁(z^-1) Compensation means 29 having a delay amount z^-DThe delay means 30 and the subtraction means 31 having
[0123]
In the correction signal generation means 5, the first calculation means 25 has a tracking error signal e output from the A / D converter (ADC) 15.₁(k) is input, and the second computing means 26 receives the pre-compensation signal h.₁(k) is input. The adding means 27 receives the outputs of the two calculating means 25 and 26 and outputs a virtual track position to the storage means 16. The storage means 16 stores the correction signal c₁(k + d) is output to the pre-compensation means 6.
[0124]
In the pre-compensation means 6, the correction signal c₁(k + d) is input to the compensation unit 29 and the delay unit 30, and outputs of the compensation unit 29 and the delay unit 30 are input to the subtraction unit 31, and the precompensation signal h is output from the subtraction unit 31.₁(k) is output.
[0125]
In short, in the fourth embodiment, the tracking error signal e after A / D conversion.₁(k) and output h of the pre-compensation means 6₁(k) is input to the correction signal generating means 5 to input the correction signal c₁(k + d) is generated and input to the precompensation means 6 to input a precompensation signal h₁(k) is obtained. The adding means 18 is a precompensation signal h₁(k) is the tracking error signal e₁Add to (k) and input to stabilization compensation means 19. The D / A converter (DAC) 20 converts the output of the stabilization compensator 19 into an analog signal and drives the tracking actuator 3.
[0126]
Next, the basic operation of the fourth embodiment will be described with reference to FIG. In the fourth embodiment, the pulse transfer function P in the digital control system in the case where the pulse transfer function of the tracking actuator 3 described in the third embodiment has an unstable zero point and does not have the zero point.₁(z^-1) To determine another example (third method).
[0127]
Tracking error signal e digitized by an A / D converter (ADC) 15₁(k) is input to the first calculating means 25 and the adding means 18. Further, the second calculation means 26 has a precompensation signal h.₁(k) is input.
[0128]
The first calculating means 25 receives the input tracking error signal e₁The pulse transfer function Q expressed by the following equation (23) with respect to (k)₁(z^-1) And the result is given to one input of the adding means 27.
[0129]
[Expression 18]
Q₁(z^-1) = 1 + G₁(z^-1) G₂(z^-1(23)
Further, the second calculating means 26 receives the input precompensation signal h.₁The pulse transfer function Q expressed by the following equation (24) with respect to (k)₂(z^-1) And the result is given to the other input of the adding means 27.
[0130]
[Equation 19]
Q₂(z^-1) = G₁(z^-1) G₂(z^-1(24)
The adding means 27 adds the outputs of the first and second calculating means 25 and 26, and
[Outside 1]

[0131]
[Expression 20]

[Outside 2]

D · T at time k using the signal stored and stored one revolution before the optical disk_sA signal corresponding to the advanced time is corrected signal c₁It is output to the compensation means 29 and the delay means 30 as (k + d).
[0132]
Specifically, as shown in FIG. 7, the storage means 16 is stored at the time corresponding to the sampling clock k + d in the (m−1) th cycle at the time corresponding to the sampling clock k in the mth cycle. The corrected signal c₁Output as (k + d).
[0133]
This correction signal c₁With respect to (k + d), the compensation means 29 has a pulse transfer function P expressed by any one of the equations (14), (18), or (21).₁(z^-1), While the delay means 30 is d · T_sA time delay corresponding to d sampling period is performed. The subtracting means 31 subtracts the output of the delay means 30 from the output of the compensating means 29, and the precompensation signal h expressed by the following equation (26).₁(k) is generated and output to the adding means 18 and the second calculating means 26.
[0134]
[Expression 21]
h₁(k) = P₁(z^-1) c₁(k + d) -z^-dc₁(k + d) (26)
The adding means 18 sends the pre-compensation signal h₁(k) and tracking error signal e₁(K) is added and output to the stabilization compensator 19. The output of the stabilization compensator 19 drives the tracking actuator 3 via a D / A converter (DAC) 20, and the light spot position s.₁Control.
[0135]
As a result, the tracking error can be reduced over the entire number of rotations of the optical disk, as in the above embodiments.
[0136]
  [Fifth Embodiment]
  FIG. 10 is a block diagram of the storage means used in the tracking control device by digital control according to the fifth embodiment of the present invention.is there.
[0137]
In FIG. 10, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. 5 or 9 are taken out for easy explanation. Other parts are the same as those in FIG. 5 or FIG.
[0138]
As shown in FIG. 10, in the fifth embodiment, the storage means 16 in the second to fourth embodiments is constituted by n memory elements 40, an adding means 41, and a multiplying means 39. The memory element 40 is composed of, for example, a plurality of D-flip flops corresponding to the number of bits of data to be operated. The memory element 40 takes in the output data of the preceding memory element connected in cascade for each sampling clock and one clock before The value stored in is output to the subsequent memory element connected in cascade. The output of the nth memory element 40 is input to the multiplication means 39. Multiplication means 39 multiplies the input data by an appropriate coefficient that satisfies | w | <1 and includes w = 0. The output of the multiplication means 39 is connected to the addition means 41, and the signal added with the input signal is input to the first memory element. Correction signal c₁(k + d) is taken from the output of the (n−d) th memory element 40.
[0139]
According to the fifth embodiment, since the storage unit 16 can have a learning effect, the tracking error can be further reduced.
[0140]
  [Sixth Embodiment]
  FIG. 11 is a block diagram of the storage means used in the tracking control device by digital control according to the sixth embodiment of the present invention.It is.
[0141]
In FIG. 11, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. 5 or 9 are taken out for easy explanation. Other parts are the same as those in FIG. 5 or FIG.
[0142]
As shown in FIG. 11, in the sixth embodiment, the storage means 16 in the second to fourth embodiments is replaced with an arithmetic element 43 such as a high-speed CPU or a digital signal processor (DSP) and the arithmetic element 43. And a memory 46 connected via a data bus 44 and an address bus 45.
[0143]
The arithmetic element 43 takes the input signal in time series in synchronization with the clock of the tracking control device and stores it in the memory 46, and after correcting the stored input signal for one rotation of the optical disk, the correction is performed. Signal c₁Output (k + d).
[0144]
Alternatively, the arithmetic element 43 takes in the input signal in time series in synchronization with the clock of the tracking control device and stores it in the memory 46. For the stored input signal, for example, moving average processing, least square method, etc. After performing the statistical signal processing, the correction signal c₁Output (k + d).
[0145]
According to the sixth embodiment, even when there is a period in which a tracking error signal cannot be obtained due to scratches or dust on the optical disk, the possibility of occurrence of tracking failure can be reduced.
[0146]
The data stored in the memory 46 may be an input signal corresponding to one rotation of the optical disc or an input signal obtained by a plurality of rotations of the optical disc.
[0147]
  [Seventh Embodiment]
  FIG. 12 is a block diagram of the storage means used in the tracking control device by digital control according to the seventh embodiment of the present invention.It is. In addition,The seventh embodiment shows a principle configuration of a tracking control apparatus corresponding to the CLV method, the ZCLV method, the CAV method, and the ZCAV method. Specifically, the seventh embodiment is configured as in the eighth and ninth embodiments, for example. The
[0148]
In FIG. 12, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. Other parts are the same as those in FIG. 5 or FIG.
[0149]
As shown in FIG. 12, in the storage means 16 of the seventh embodiment, optical head position information and optical disk rotation angle information in the radial direction of the optical disk are input in addition to the input signal and the tracking control device clock.
[0150]
Next, the basic operation of the tracking control device of the seventh embodiment will be described. First, the correction signal calculated using the tracking error signal for the track being scanned is stored as an input signal in the storage unit 16 together with the optical head position information and the optical disk rotation angle information in synchronization with the clock of the tracking control device. The optical head position information is used to know the radial position of the track on which the optical head is scanning on the optical disk.
[0151]
Next, the correction signal corresponding to the current optical head position and the rotation angle of the optical disk among the correction signals stored in the storage means 16 at the time before at least one rotation of the optical disk is read as an output signal.
[0152]
This correction signal is input to the pre-compensation means 6 to output a pre-compensation signal, the pre-compensation signal is added to the tracking error signal for the track being scanned, and tracking control is performed using the signal after the addition.
[0153]
  [Eighth Embodiment]
  FIG. 13 is a block diagram of the storage means used in the tracking control device by digital control according to the eighth embodiment of the present invention.It is. In addition,The eighth embodiment shows a specific configuration example of the tracking control device corresponding to the CLV method, the ZCLV method, the CAV method, and the ZCAV method.
[0154]
In FIG. 13, only parts related to the storage means 16 in the tracking control apparatus shown in FIG. Other parts are the same as those in FIG. 5 or FIG.
[0155]
As shown in FIG. 13, in the eighth embodiment, the storage means 16 in the second to fourth embodiments is replaced with an arithmetic element 47 such as a high-speed CPU or a digital signal processor (DSP) and the arithmetic element 47. And a memory 48 connected via a data bus 44 and an address bus 45.
[0156]
As shown in FIG. 13, the arithmetic element 47 in the storage means 16 of the eighth embodiment inputs optical head position information and optical disk rotation angle information in the radial direction of the optical disk in addition to the input signal and the tracking control device clock. Is done.
[0157]
Next, the operation of the tracking control apparatus of the eighth embodiment will be described with reference to FIGS. FIG. 14 is a flowchart of the basic operation of the tracking control apparatus of the eighth embodiment.
[0158]
In the figure, the tracking error signal for the track on which the optical head is scanning is input as an input signal to the arithmetic element 47, and optical head position information and optical disk rotation angle information in the radial direction of the optical disk are input.
[0159]
The arithmetic element 47 detects a tracking error signal for the track on which the optical head is scanning, calculates a correction signal using this signal (step S31), and uses the correction signal as optical head position information and optical disk rotation angle information. At the same time, it is stored in the memory 48 (step S32). The optical head position information is used to know which position on the radius of the track on which the optical head is scanning is on the optical disk.
[0160]
Specifically, the arithmetic element 47 uniquely determines the memory address using the optical head position information and the optical disk rotation angle information, and takes the input signal in time series in synchronization with the clock of the tracking control device. Is stored in the memory 48, and the stored input signal is delayed by one rotation of the optical disk and stored in the memory 48 together with the optical head position information and the optical disk rotation information.
[0161]
Alternatively, the arithmetic element 47 uniquely determines a memory address using the optical head position information and the optical disk rotation angle information, and takes in the input signal in time series in synchronization with the clock of the tracking control device to the memory 48. The stored input signal is subjected to statistical signal processing such as moving average processing and least square method, and stored in the memory 48 together with optical head position information and optical disk rotation information.
[0162]
Next, the computing element 47 determines whether or not a correction signal corresponding to the current optical head position information and optical disk rotation angle information is stored in the memory 48 (step S33), and if not stored, the correction signal = 0. (Step S34) If stored, the correction signal c corresponding to the current optical head position and the optical disk rotation angle is stored from the memory 48.₁(k + d) is read (step S35).
[0163]
At this time, in step 35, when the optical head position information and optical disk rotation angle information of the correction signal to be read does not match the optical head position information and optical disk rotation angle information of the stored correction signal, the closest optical head position is determined. After performing an interpolation process using a correction signal having information and optical disk rotation angle information, the correction signal c₁Output as (k + d).
[0164]
And the correction signal c₁(k + d) is input to the pre-compensation means and the pre-compensation signal is output to the addition means (step S36), and this pre-compensation signal is added to the tracking error signal for the track on which the optical head is scanning ( Step S37).
[0165]
Next, tracking control is performed using the added signal (step S38). In order to perform tracking control continuously on the rotating optical disk, the process returns to step S31 again, and the above-described operation is repeated.
[0166]
The data stored in the memory 48 may be an input signal corresponding to one rotation of the optical disc or an input signal obtained by a plurality of rotations of the optical disc.
[0167]
Next, FIG. 15 is a diagram for explaining a method for detecting optical head position information and optical disk rotation angle information. In FIG. 15, a light spot 54 emitted from an optical head 53 scans an optical disk 50 attached to a spindle motor 51 and rotating. The optical head 53 is attached to an optical head moving mechanism 55 such as a linear motor, and moves in the radial direction of the optical disc 50.
[0168]
For example, in an optical disk recording apparatus using a DVD-RAM, a header recorded in advance on the optical disk 50 is optically read and an address signal is generated by the address decoding means 57. The clock reproducing means 58 optically reads the meandering signal of the groove formed on the optical disc 50 and reproduces the clock signal using, for example, a PLL circuit.
[0169]
By using the address signal obtained in this way, the position of the track scanned by the optical head 53 on the optical disk 50 can be known, and this is converted into optical head position information using the optical head position information detecting means 59. Output. Further, the optical disk rotation angle detection means 60 measures the clock signal using the address signal as the rotation angle origin signal and outputs optical disk rotation angle information.
[0170]
In addition to these means, the optical head position information can also be obtained by position detecting means 56 such as a linear encoder attached to the optical head moving mechanism 55, for example. The optical disk rotation angle information can also be obtained by a rotation angle detection means 52 such as a rotary encoder attached to the spindle motor 51, for example. The optical head position information and the optical disc rotation angle information used in the seventh and eighth embodiments may be obtained using any of the above-described means.
[0171]
According to the eighth embodiment, since the optical head position information and the optical head rotational speed information are used, the tracking is performed in a recording / reproducing apparatus using the CLV method in which the period of one rotation changes according to the radius of the optical disk or the ZCLV method. Error can be reduced.
[0172]
  [Ninth Embodiment]
  FIG. 16 is a conceptual diagram of an optical disk used in a tracking control device by digital control according to the ninth embodiment of the present invention.It is. In addition,The ninth embodiment shows a specific configuration example of the tracking control device corresponding to the CLV method, the ZCLV method, the CAV method, and the ZCAV method.
[0173]
In the ninth embodiment, the optical head position information is classified into a plurality of ranges according to the numerical values in the eighth embodiment, and one type of correction signal c1 (k + d) is used within the same range.
[0174]
As shown in FIG. 16, the optical disk 50 of the ninth embodiment is divided into n regions by a radius from the center. The radius r from the center is
[0175]
[Expression 22]
r_j≦ r ≦ r_{j + 1}   (J = 1, 2,..., N) (27)
Represented by
[0176]
In the optical disc 50, the adjacent tracks are similar in the tendency of eccentricity and track meandering. Therefore, the correction signal c for one round of the optical disk is obtained in each area represented by the equation (27) by dividing the area in this way.₁By using only (k + d), the correction signal c₁The memory capacity for storing the data of (k + d) can be reduced.
[0177]
In each of the eighth and ninth embodiments, the method for uniquely determining the memory address using the optical head position information and the optical disk rotation angle information is the same as the method for determining the address using these two pieces of information. A conversion table for assigning a corresponding memory address using two pieces of information is stored in the memory 48 in advance, and the same operation can be obtained by using this conversion table.
[0178]
In each of the first to ninth embodiments, a method for detecting a tracking error may be a generally used three-beam method, push-pull method, heterodyne method, or phase difference detection method. Furthermore, a detection method using reflected light of a pit formed in advance on an optical disc, a detection method using diffracted light from a groove, and a detection method using a tracking error detection signal recorded in advance. Either may be used.
[0179]
Further, in the third embodiment (FIG. 5) and the fourth embodiment (FIG. 9), the correction signal generation means 5, the pre-compensation means 6, the addition means 18 and the stabilization compensation means 19 are each made into individual blocks. Although shown, it goes without saying that these can be realized by a combination of an arithmetic unit such as a high-speed CPU or a digital signal processor and a memory.
[0180]
Further, the output of the stabilization compensator 19 is converted into an analog signal by the D / A converter (DAC) 20 and the tracking actuator 3 is driven. The output of the stabilization compensator 19 is converted to a pulse width modulation means (PWM). ), And the tracking actuator 3 is driven by the output pulse, the same operation can be realized.
[0181]
In addition, the stabilization compensator 2 or the stabilization compensator 19 used in each of the first to ninth embodiments can use a robust stabilization compensator as well as a generally used phase lead / lag compensation. Of course, a type compensator, a PI type compensator, or a PID type compensator may be used.
[0182]
Furthermore, the tracking actuator 3 used in each of the first to ninth embodiments is, for example, a second order, a third order, etc. in addition to the moving coil type actuator having the first order resonance mode shown in FIG. Of course, a moving coil type actuator having a higher-order resonance mode can also be used. In addition to the moving coil type, for example, a piezoelectric type, a linear motor type, a swing arm type, or a composite type that combines a plurality of these may be used. It goes without saying that the present invention can be similarly applied to a tracking control apparatus using any of these types of tracking actuators.
[0183]
The above embodiments can be applied not only to the optical disk recording apparatus but also to the tracking control system of the optical disk reproducing apparatus, the optical disk recording / reproducing apparatus, and the optical tape recording apparatus. Further, the present invention can be applied to the focus control device with the same configuration. In that case, instead of the tracking error detection means and the tracking actuator, a focus error detection means and a focus actuator are used, respectively.
[0184]
【The invention's effect】
  As explained above,The present inventionAccording to the present invention, the optical spot position is controlled by generating a signal obtained by compensating the amplitude and phase of the tracking error signal at least one round before the optical disk and adding the tracking error signal to the tracking error signal. The tracking error can be reduced over the entire number of rotations of the optical disc while ensuring the stability of the optical disc.Further, since the storage unit can have a learning function, the tracking error can be further reduced. Further, in the recording / reproducing of an optical disc using the CLV method, the ZCLV method, etc., it becomes possible to reduce the tracking error and also reduce the memory capacity.
[0188]
Therefore, according to the tracking control device of the present invention, stable recording / reproduction can be performed on a large-capacity optical disk having a narrow track pitch. Also, tracking control can be performed on an optical disk rotating at high speed, and the data transfer rate can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the principle configuration of a tracking control device as a feedback control device according to a first embodiment of the present invention.
FIG. 2 is a comparison diagram of tracking error characteristics of a tracking control device with respect to the rotation speed of an optical disc.
FIG. 3 is a block diagram showing a configuration of an analog control tracking control apparatus according to a second embodiment of the present invention.
FIG. 4 is a flowchart of a basic operation of a tracking control device according to a second embodiment of the present invention.
FIG. 5 is a block diagram showing the configuration of a tracking control apparatus based on digital control according to a third embodiment of the present invention.
FIG. 6 is a diagram showing a circuit model / motion model of a moving coil tracking actuator having a first-order resonance mode.
FIG. 7 is a schematic diagram of a relationship between correction signal data stored in a storage unit and a sampling clock.
FIG. 8 is a basic operation flowchart of a tracking control apparatus according to a third embodiment of the present invention.
FIG. 9 is a block diagram showing the configuration of a tracking control apparatus by digital control according to a fourth embodiment of the present invention.
FIG. 10 is a configuration diagram of storage means used in a tracking control device by digital control according to a fifth embodiment of the present invention.
FIG. 11 is a configuration diagram of storage means used in a tracking control device by digital control according to a sixth embodiment of the present invention.
FIG. 12 is a configuration diagram of storage means used in a tracking control apparatus by digital control according to a seventh embodiment of the present invention.
FIG. 13 is a configuration diagram of storage means used in a tracking control apparatus by digital control according to an eighth embodiment of the present invention.
FIG. 14 is a basic operation flowchart of a tracking control apparatus according to an eighth embodiment of the present invention.
FIG. 15 is a diagram for explaining a method of detecting optical head position information and optical disc rotation angle information.
FIG. 16 is a conceptual diagram of an optical disk used in a tracking control device by digital control according to a ninth embodiment of the present invention.
FIG. 17 is a block diagram showing a configuration of a conventional tracking control device that is generally used.
FIG. 18 is a configuration block diagram of a conventional tracking control apparatus that improves tracking performance by repetitive tracking control.
[Explanation of symbols]
1 Tracking error detection means
2 Stabilization compensation means
3 Tracking Actu Engineering Overnight
5 Correction signal generation means
6 Pre-compensation means
7 Addition means
10 Delay means
11 Compensation means
15 A / D converter (ADC)
16 Memory means
17 Compensation means
18 Adding means
19 Stabilization compensation means
20 D / A converter (DAC)
25 First calculation means
26 Second computing means
27 Adding means
29 Compensation means
30 Delay means
31 Subtraction means
39 Multiplying means
40 memory elements
41 Adding means
43 arithmetic elements
44 data bus
45 Address bus
46 memory
47 arithmetic elements
48 memory
50 optical disc
51 spindle motor
52 Rotation angle detection means
53 Optical head
54 Light Spot
55 Optical head moving mechanism
56 Position detection means
57 Address decoding means
58 Clock recovery means
59 Optical head position information detecting means
60 Optical disk rotation angle detection means
70 Moving parts
72 Delay means

Claims (6)

Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The tracking error signal is stored in a storage unit over a time corresponding to a plurality of rotation periods of the optical disc, and at least one of a statistical method of moving average processing or least square method is applied to the stored signal, Correction signal generation means for generating a correction signal by performing arithmetic processing for extracting a signal corresponding to the tracking error signal before one rotation period;
A precompensation means the amplitude and phase predistortion signal before performing the compensation of the generated correction signal generated by a predetermined pulse transfer function,
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre- compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut is Gcl ( z-1) And a pulse transfer function represented by the following equation (18) :
P ₁ ( z ⁻¹ ) = Ac (z ⁻¹ ) / {Bc ⁺ (z ⁻¹ ) Bc ⁻ (1)} (18)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): Gcl ( z ⁻¹ ) pole term
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (z ⁻¹ ): An unstable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (1): Gcl ( z ⁻¹ ) is a constant with z ⁻¹ = 1 as the unstable zero
Turned into
d: Equivalent lead sampling number
The pulse transfer function cancels the pole of Gcl ( z-1 ) and a stable zero when the response of the light spot position is obtained by multiplying the correction signal by Gcl ( z-1) · P1 ( z-1 ). And the DC gain of the pre-compensation means is matched with the reciprocal of the DC gain of Gcl ( z ⁻¹ ) ,
A tracking control device characterized by that. Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The position information of the optical head and the rotation angle information of the optical disk in a state where the optical head follows the track on the optical disk are stored together with the tracking error signal or the signal obtained as a result of performing arithmetic processing on the tracking error signal. After the time corresponding to the rotation period of at least one rotation of the optical disk has passed, the stored optical head position information and optical disk rotation angle information are both scanned by the optical head over the optical disk. A correction signal generating means for outputting, as a correction signal, a tracking error signal that has already been stored or a signal obtained as a result of performing arithmetic processing on the tracking error signal when the two information coincide with each other at the present time When,
A precompensation means the amplitude and phase predistortion signal before performing the compensation of the generated correction signal generated by a predetermined pulse transfer function,
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre- compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
The pre-compensation means uses the tracking error signal generation means, correction signal generation means, pre-compensation means, addition means, and control means as the predetermined pulse transfer function as a feedback control system that forms a closed loop. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut is Gcl ( z-1). And a pulse transfer function represented by the following equation (18):
P ₁ ( z ⁻¹ ) = Ac (z ⁻¹ ) / {Bc ⁺ (z ⁻¹ ) Bc ⁻ (1)} (18)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): Gcl ( z ⁻¹ ) pole term
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (z ⁻¹ ): An unstable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (1): Gcl ( z ⁻¹ ) is a constant with z ⁻¹ = 1 as the unstable zero
,
d: Equivalent lead sampling number
The pulse transfer function cancels the pole and stable zero of Gcl ( z-1 ) when the response of the light spot position is obtained by multiplying the correction signal by Gcl ( z-1) · P1 ( z-1 ). And the DC gain of the pre-compensation means is matched with the reciprocal of the DC gain of Gcl ( z ⁻¹ ).
A tracking control device characterized by that. Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The tracking error signal is stored in a storage unit over a time corresponding to a plurality of rotation periods of the optical disc, and at least one of a statistical method of moving average processing or least square method is applied to the stored signal, Correction signal generation means for generating a correction signal by performing arithmetic processing for extracting a signal corresponding to the tracking error signal before one rotation period;
Pre-compensation means for generating a pre-compensation signal that has been compensated for the amplitude and phase of the generated correction signal by a predetermined pulse transfer function;
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre-compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut is Gcl ( z-1) , Having a pulse transfer function represented by the following equation (21) :
P ₁ ( z ⁻¹ ) = Ac (z ⁻¹ ) Bc ⁻ (z) / [Bc ⁺ (z ⁻¹ ) {Bc ⁻ (1)} ² ] (21)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): Gcl ( z ⁻¹ ) pole term
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (z ⁻¹ ): An unstable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (1): Gcl ( z ⁻¹ ) is a constant with z ⁻¹ = 1 as the unstable zero
That turned into,
d: Equivalent lead sampling number
When the pulse transfer function obtains the response of the light spot position by multiplying the correction signal by Gcl ( z ⁻¹ ) · P ₁ ( z ⁻¹ ) , the pole of Gcl ( z ⁻¹ ) and a stable zero point are obtained. offset, and further wherein the phase difference is set to zero in the product all the frequencies of the pulse transfer function of the closed loop, to match the DC gain of the pre-compensation means to the inverse of the DC gain of Gcl (z ^-1),
A tracking control device characterized by that. Tracking error signal generating means for generating a tracking error signal corresponding to the difference between the track position on the optical disc and the position of the light spot emitted from the optical head;
The position information of the optical head and the rotation angle information of the optical disk in a state where the optical head follows the track on the optical disk are stored together with the tracking error signal or the signal obtained as a result of performing the arithmetic processing on the tracking error signal. After the time corresponding to the rotation period of at least one rotation of the optical disk is stored, the stored optical head position information and optical disk rotation angle information are both scanned by the optical head over the optical disk. A correction signal generating means for outputting, as a correction signal, a tracking error signal that has already been stored or a signal obtained as a result of performing arithmetic processing on the tracking error signal when the two pieces of information coincide with each other at the present time When,
Pre-compensation means for generating a pre-compensation signal that has been compensated for the amplitude and phase of the generated correction signal by a predetermined pulse transfer function;
Adding means for generating a drive signal obtained by adding the tracking error signal and the pre-compensation signal;
Control means for causing the light spot to scan a target track on the optical disk based on the generated drive signal, and
The pre-compensation unit includes the tracking error signal generation unit, the correction signal generation unit, the pre-compensation unit, the addition unit, and the control unit as the predetermined pulse transfer function as a feedback control system that forms a closed loop. When the transfer function of the output of the light spot position with respect to the input from the pre-compensation means side to the adding means when the connection between the pre-compensation means and the adding means is cut is Gcl ( z-1) , Having a pulse transfer function represented by the following equation (21) :
P ₁ ( z ⁻¹ ) = Ac (z ⁻¹ ) Bc ⁻ (z) / [Bc ⁺ (z ⁻¹ ) {Bc ⁻ (1)} ² ] (21)
^{Here, Gcl (z -1) = z} -d Bc + (z -1) Bc - (z -1) / Ac (z -1)
Ac (z ⁻¹ ): Gcl ( z ⁻¹ ) pole term
Bc ⁺ (z ⁻¹ ): A stable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (z ⁻¹ ): An unstable zero term of Gcl ( z ⁻¹ )
Bc ⁻ (1): Gcl ( z ⁻¹ ) is a constant with z ⁻¹ = 1 as the unstable zero
That turned into,
d: Equivalent lead sampling number
When the pulse transfer function obtains the response of the light spot position by multiplying the correction signal by Gcl ( z ⁻¹ ) · P ₁ ( z ⁻¹ ) , the pole of Gcl ( z ⁻¹ ) and a stable zero point are obtained. Canceling, and the product of the closed-loop pulse transfer function makes the phase difference zero at all frequencies, and makes the DC gain of the pre-compensation means coincide with the reciprocal of the DC gain of Gcl ( z ⁻¹ ) .
A tracking control device characterized by that. The tracking control device according to claim 3 or 4 ,
The correction signal generating means divides the optical head position information into a plurality of areas according to the radius of the optical disk, information on the area to which the position of the optical head belongs when the optical head follows a track on the optical disk, and The rotation angle information of the optical disk at the time is stored in a storage means together with a tracking error signal for a time corresponding to one rotation period of the optical disk or a signal obtained as a result of performing arithmetic processing on the tracking error signal. At the present time when scanning is performed, it is determined to which of the divided areas the position of the optical head belongs, and the tracking error signal corresponding to the rotation angle information of the optical disk in that area, or the tracking error signal Read out the signal obtained as a result of performing arithmetic processing from the storage means as a correction signal ,
A tracking control device characterized by that. The tracking control device according to any one of claims 1 to 5,
The signal stored in the storage means is sequentially updated according to the rotation of the optical disc .
A tracking control device characterized by that.

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