JP3933390B2 - Optical disc apparatus and focus movement method - Google Patents

Description

【００５７】
ここでｔは時間（ｓｅｃ）、Ｘ（ｔ）は時刻ｔにおける面振れ（ｍ）、Ａは面振れ振幅（ｍ）、Ｂは面振れの角速度（ｒａｄ／ｓｅｃ）を表す。制御対象である駆動コイル３を含むフォーカスアクチュエータの機械的動特性を２次系と仮定し、さらにフォーカスジャンプ中のＸ（ｔ）を２階微分した関数（すなわち駆動コイル３の印加信号と等価）のホールド期間をΔ（ｓｅｃ）と定義する。
【００５８】
なお、この場合のホールドとは、フォーカスアクチュエータの駆動電圧を保持することを意味し、例えば、フォーカスドライブ信号のＬＰＦ出力（ローパスフィルタ出力）を保持することを言う。
【００５９】
また、ホールド期間とはホールドの状態が継続される期間、ホールド値とは、例えば、ある時点にホールドされるフォーカスドライブ信号のＬＰＦ出力の大きさを言う。
【００６０】
時刻ｔにおけるホールド値と、ホールド期間Δ後の時刻ｔ＋Δにおける真値との差（誤差）を、各時間で算出した結果により定められる関数をホールド誤差関数（位置誤差の大きさを表わし長さの次元を有する。以下、単に誤差関数と称する場合もある）として定義する。
【００６１】
面振れＸ（ｔ）を時間で２階微分した関数、すなわち駆動コイル３の印加信号（例えば、フォーカスドライブ信号のＬＰＦ出力）のホールドの形態の例としては、ホールド時に当該信号の値を保持する零次ホールドと、ホールド時の当該信号の値と傾きとを併せて保持する１次ホールドがある。
【００６２】
ここでは、零次ホールドの場合のホールド誤差関数をＥ０、１次ホールドの場合のホールド誤差関数をＥ１とすると、それぞれ次式で表すことができる。
【００６３】
【数２】

【００６４】
【数３】

【００６５】
なお、ホールド誤差関数Ｅ０およびＥ１として表わされた、上記式１および２の導出は以下の通りである。
【００６６】
＜式２の導出＞
【００６７】
【数４】

【００６８】
＜式３の導出＞
【００６９】
【数５】

【００７０】
上記式２および式３を参照すると分かるように、誤差関数は、面振れ振幅Ａ、面振れ角速度Ｂおよびホールド期間Δをパラメータとした時間関数によって表わされる。従って、ホールド誤差（ホールド値と、ホールド期間Δ後の真値との差）について論議するには、システムの使用条件によって上記パラメータがどのような値である場合にホールド誤差がどのくらいになるかといった具体的な数値抜きでは無意味であることが分かる。
【００７１】
例えば、再生ディスクをＤＶＤ−ＤＬ、再生速度を４倍速ＣＬＶ再生の最内周、ジャンプ期間（このジャンプ期間において、ホールド動作が行われ、当該ホールド動作によりアクチュエータの駆動電圧が保持されることから、「ホールド期間」と称する場合もある）を１ｍｓｅｃ、ディスク面振れ振幅Ａを例えば３００μｍ（半波振幅）と設定した場合のディスク面振れＸ（ｔ）とホールド誤差関数Ｅ０およびＥ１との関係を図１に示す。
【００７２】
図１中、波形Ａは面振れＸ（ｔ）であり、振幅は１／１０スケールで表示している。また、波形ＢはＥ０、波形ＣはＥ１である。上記の条件の場合、図１を参照すると分かるように、面振れ３００μｍに対するホールド誤差の最大値は、零次ホールドで約１３μｍ、１次ホールドで約２μｍとなる。
【００７３】
前述のように誤差関数（ホールド誤差関数）は、面振れ振幅Ａ、面振れ角速度Ｂ、ホールド期間Δをパラメータとした時間関数で定義されるので、図１に解析結果を示したような条件に対して、ホールド期間Δならびに面振れの角速度Ｂを小さく変化させたときの結果を図２および図３に示す。
【００７４】
図２（ａ）は、図１と同条件の解析結果（すなわち図１と同内容のもの）、図２（ｂ）はホールド期間Δを１ｍｓｅｃから０．８ｍｓｅｃに小さく設定した解析結果である。
【００７５】
この図２（ａ）と（ｂ）とを対比すると、ホールド期間Δを小さくすれば、ホールド誤差関数ＥＯ、Ｅ１ともに各ホールド誤差関数の振幅が小さくなっている。このことから、ホールド期間を短くすることによってホールド誤差を小さくすることが可能であることが分かる。
【００７６】
図３（ａ）は、図１と同条件の解析結果（すなわち図１と同内容のもの）、図３（ｂ）は再生速度を４倍速から３倍速に減少させた場合の解析結果である。
【００７７】
この図３（ａ）と（ｂ）とを対比すると、面振れの角速度Ｂを小さくすれば、ホールド誤差関数ＥＯ、Ｅ１ともに各ホールド誤差関数の振幅が小さくなっている。このことから、再生速度を遅くすることによってホールド誤差を小さくすることが可能であることが分かる。
【００７８】
上記から、ホールド誤差は、面振れ振幅Ａが一定であっても、ホールド期間や再生速度によって値を大きく変え、再生速度が速いほど、また、ホールド期間が長いほどホールド誤差が大きくなる特性を有する。
【００７９】
より定性的に論議するため、ＤＶＤ−ＤＬの面振れ振幅Ａを３００μｍ（半波振幅）、再生速度を４倍速（ＣＬＶ：最内周）としたときの、ホールド期間Δをパラメータとしたときのホールド誤差関数の振幅における最大値（図４では最大位置誤差と表示している。ただし、半波振幅。以降、最大位置誤差と称する場合もある。）を解析した結果を図４に示す。
【００８０】
図４中、実線が零次ホールドの最大位置誤差、点線が１次ホールドの最大位置誤差、破線がＦＥＳ検出限界である。ＦＥＳは検出ダイナミックレンジが物理的に限られており、例えばＤＶＤ用途の一般的なピックアップでは１０μｍ以下となっているので、ここではＦＥＳ検出限界を１０μｍとしている。
【００８１】
このような条件の場合、ホールドによる最大位置誤差がＦＥＳ検出限界を超えると、ホールド後のフォーカス引込の際にＦＥＳ検出が不可能となりフォーカス引込に失敗するため、最大位置誤差がＦＥＳ検出限界を越えることは避けなくてはならない。
【００８２】
図４を参照すると理解できるように、ホールドによる最大位置誤差は、ホールド期間（図４中、ジャンプ期間と表示）が長いほど大きくなり、その量は１次ホールドが零次ホールドより小さい。
【００８３】
図５に可変パラメータをホールド期間だけでなく、再生速度を１〜４倍まで変化させた場合の、零次ホールドにおける最大位置誤差の解析結果を示す。図５を参照して、最大位置誤差をＦＥＳ検出限界未満にするための以下の関係が導き出される。
【００８４】
・再生速度が２倍を超えると、ジャンプ期間を１．８ｍｓｅｃ未満にする必要がある。
・再生速度が速くなればなるほどジャンプ期間を短くする必要がある。
【００８５】
図６に可変パラメータをホールド期間だけでなく、再生速度を１〜４倍まで変化させた場合の、１次ホールドにおける最大位置誤差の解析結果を示す。図６を参照して、最大位置誤差をＦＥＳ検出限界未満にするための以下の関係が導き出される。
【００８６】
・再生速度が３倍を超えても、ジャンプ期間を２ｍｓｅｃ未満にする必要がない。
・再生速度が４倍になっても、ジャンプ期間を１ｍｓｅｃ以下に設定すれば問題ない。
【００８７】
上述の関係から、フォーカスジャンプ期間における面振れ対策（面振れの影響を抑えつつフォーカスジャンプを確実に行う）として、駆動コイル３の駆動信号をホールドすることで実現することができる。
【００８８】
ホールドの種類は、プレイヤ用途のように再生速度が遅い場合（例えば、ＤＶＤの再生に必要とされる速度のおおよそ１倍以下の再生速度）には零次ホールドで充分であり、コンピュータ用のＲＯＭ用途のように再生速度が速い場合（例えば、ＤＶＤの再生に必要とされる速度のおおよそ１倍より大きい再生速度）は１次ホールドを用いれば良いことが分かる。
【００８９】
２．層間移動信号
層間移動信号は、光源から出射するレーザ光を複数の記録層（情報記録層）を有するディスクの各記録層に集光レンズを介して集光された焦点位置を、フォーカスアクチュエータを駆動することにより、当該アクチュエータに結合する集光レンズを複数の記録層の配列される方向に移動して、結果として、個々の記録層上に集光スポットを移動させるための信号である。
【００９０】
層間移動信号は、加減速パルスとアクチュエータ弾性項無効化信号との和で与えられる（すなわち、図７に示された加算ブロック１９からの出力が相当する）。この層間移動信号は、ここでは、加減速パルス（図７に示された加減速パルス発生ブロック１４からの出力）、アクチュエータ弾性項無効化信号（図７に示されたアクチュエータ弾性項無効化信号発生ブロック２０からの出力）の順で説明を行う。
【００９１】
２-１．加減速パルス
制御対象である駆動コイル３を含むフォーカスアクチュエータの機械的動特性は、バネ支持されているため本来拘束系の２次系であるが、説明を簡単にするためバネ支持のない慣性系の２次系と仮定して説明する。対物レンズ２の位置をｘ（ｔ）とすれば、対物レンズ２の速度は位置の１階時間微分、加速度は位置の２階時間微分で表され、以下の式４、５となる。
【００９２】
【数６】

【００９３】
【数７】

【００９４】
駆動コイル３は、印加信号（印加電流）をアクチュエータ駆動力（加速度）に変換する機能がある。アクチュエータ駆動力と印加電流との間には比例関係があるから、印加信号について考察することはアクチュエータ駆動力（すなわち、加速度の次元）について考察することと等価である。
【００９５】
図８に駆動コイル３（これは、駆動コイル３によって移動される対物レンズ２の移動を考えても同じである）の印加信号（対物レンズ２に与えられる加速度を考えても同じである）に対する速度、位置の関係を示す。
【００９６】
図８中、（Ａ）は加速度、（Ｂ）は速度、（Ｃ）は位置を示す。印加信号の加速パルスを図８（Ａ）のように矩形波で与えると速度は１次関数となり、位置は２次関数となる。
【００９７】
そして、加速パルスと減速パルスとを極性が逆で力積（物理的な力積とは力ｆと力ｆが物体に与えられる時間ｔとの積によって定義されるが、本願においては広義の意味で、フォーカシング装置における力ｆは対物レンズ（集光レンズ）に生じる加速度αに比例することから加速度αと該加速度αが対物レンズに与えられる時間ｔとの積、あるいは加速度αが駆動コイルに与えられる電流ｉに比例することから電流ｉと該電流ｉが駆動コイルに与えられる時間ｔとの積をも含めて力積と定義する）を等しくなるように与えれば、減速パルス印加後の速度が零となることを保証できる。
【００９８】
その理由を以下に説明する。
駆動コイル３の初速度を零とする。このとき、矩形波の加速パルスを印加したときの挙動は以下となる。加速度の大きさをＡ、加速度の与えられる期間（加速期間あるいは加速時間とも称す）をＢとすると、速度は加速度の大きさＡをその傾きとする１次関数となり、加速期間Ｂを経過した後の速度はＡＢとなる。
【００９９】
すなわち、この場合、速度は加速度の大きさＡと加速期間Ｂとの積（力積）で表される。加速パルス印加後の加速度の大きさＡが零である期間は速度ＡＢが保持される。
【０１００】
この速度ＡＢを零とする減速パルスの条件は、加速パルスによって与えられる加速度と逆の方向の加速度を生じるように、この説明の場合では、その極性が加速パルスとは逆（例えば、正極に対して負極）で、減速パルスによって与えられる力積を等しくすれば、減速パルスを印加した後の速度は零となることが分かる。
【０１０１】
この場合、フォーカスアクチュエータはフォーカス方向前後に常に移動しているため、その初動における、例えば静止摩擦については殆ど生じず、強いて言えば動摩擦について考慮する必要があるが、その大きさは加速パルスによって与えられる力の大きさに比べて極めて小さいので、加速パルスと減速パルスの力積の総和が略零となるように、加速パルスの力積を実質的に打消すように減速パルスの力積を与えればよい。
【０１０２】
以上の説明によって、アクチュエータが慣性系の場合は加減速パルス印加後のアクチュエータ速度は零となるが、実際のアクチュエータはバネ支持された拘束系であるため、バネ剛性が強いアクチュエータの場合は無視できない量になるため、これを補正する対策が必要となる。
【０１０３】
２−２．アクチュエータ弾性項無効化信号
図９（Ａ）にバネ支持されたアクチュエータ（図９中のｍ）のモデル図（拘束系アクチュエータのモデル図）、同じく（Ｂ）にバネ性を無視することによって理想化された慣性系アクチュエータ（図９中のｍ）のモデル図（慣性系アクチュエータのモデル図）を示す。同図中のｋは、バネの強さを表す弾性係数（バネ係数）であり、ｆはアクチュエータｍの機構部あるいは駆動コイル３により発生する力を受けて移動する部分に作用する力である。
【０１０４】
図１０の▲１▼は、図９（Ａ）に示したバネ支持されたアクチュエータのブロック図である。アクチュエータ機構部に力ｆが作用すると、位置ｘが変動し、バネによって位置変動量に比例した（比例係数ｋ。ここにおけるｋは正。）反力がアクチュエータ機構部にフィードバックされる。このバネによる影響をキャンセルするために、図１０の▲２▼に示すようにＨ（ｓ）で表される力を加えることを仮定する。ここで、Ｈ（ｓ）は以下の式６により表わされる。
【０１０５】
【数８】

【０１０６】
このＨ（ｓ）は、アクチュエータがバネ支持されていない場合に上記加減速パルスが印加された時の位置変動にアクチュエータのバネ係数（弾性率）を乗算した量を模擬した出力として定義できる。
【０１０７】
Ｈ（ｓ）はアクチュエータ弾性項を無効化（相殺あるいはキャンセル）する電磁気力（無効化電磁気力Ｈ（ｓ）と称する）であり、これを発生させるための指令信号はアクチュエータの弾性項を無効化するための信号（アクチュエータ弾性項無効化信号と称す）として与えられる。
【０１０８】
無効化電磁気力Ｈ（ｓ）が印加されると、バネ係数による影響がキャンセルされるため、図１０の▲３▼に示すようにバネ係数ブロックｋを無視することができる。この無効化電磁気力Ｈ（ｓ）を印加することによって図９（Ａ）に示した拘束系アクチュエータを図９（Ｂ）に示すバネ支持のない慣性系アクチュエータのように動作させることが可能となる。
【０１０９】
アクチュエータ弾性項無効化信号は、バネ支持されていない場合におけるアクチュエータに加減速パルスが印加された場合の位置変動に比例した信号であるから、アクチュエータ位置を観測する必要があるが、アクチュエータの絶対位置を測定する位置センサがないため、演算によって決定すればよい。
【０１１０】
例えば、図１１（Ｂ）に示すような加減速パルスをアクチュエータに印加した場合のアクチュエータ位置変動は、厳密に言えば図８（Ｃ）に示すように、加減速パルスの印加時は２次関数的に増加、加減速パルスの大きさが零である期間（零期間）は１次関数的に増加する特性をしているが、これを図１１（Ｃ）に示すように単なる１次関数として模擬しても誤差は殆んど生じず、簡便に信号が得られる。
【０１１１】
このようなアクチュエータ弾性項無効化信号を加減速パルスに加算してアクチュエータを駆動すると、アクチュエータ弾性項が無効化され、本来拘束系であるアクチュエータを慣性系のように扱えるため、図１１（Ａ）に示すように加減速パルスの印加後の速度を略零に保証でき、結果として安定なフォーカスジャンプの条件２を満足することができる。
【０１１２】
フォーカス制御ループの位相補償ブロック前段に設けられたフォーカス制御ループスイッチ、前記位相補償ブロック後段に設けられたフォーカスジャンプ選択スイッチ、フォーカス制御信号のノイズ成分除去機能を有するノイズ除去用ローパスフィルタブロック、フォーカスジャンプ直前の上記ローパスフィルタ出力をホールドする手段、対物レンズを層間距離分移動させる層間移動信号を構成するアクチュエータ弾性項無効化信号発生手段と加減速パルス発生手段を有し、さらに加減速パルスを生成する加減速パルス発生手段は、フォーカスエラー信号に基づいて生成したフォーカスアクチュエータを加速あるいは減速する矩形波を出力し、出力モードとして加速パルス、零期間、減速パルスの３つを持ち,フォーカスジャンプ期間の加減速パルスの力積総和が零となる特徴を有している。
【０１１３】
さらにアクチュエータ弾性項無効化信号発生手段は、アクチュエータがバネ支持されていない場合に上記加減速パルスが印加された時の位置変動にアクチュエータのバネ係数（弾性率）を乗算した量を模擬し出力する。上記構成によって、安定なフォーカスジャンプが実現する。
【０１１４】
上記の解析結果および説明を基に、様々な場合に対応した実施の形態を以下に説明する。
【０１１５】
実施の形態１．
本実施の形態は、プレイヤ用途におけるＦＥＳの正極性と負極性の波形特性が等しい場合における適用例を述べる。
【０１１６】
図７に本実施の形態のブロック図を示す。図７において、７は位相補償ブロック８の前段に設けられたフォーカス制御ループスイッチ、１２はホールドブロック、１４は加減速パルス発生ブロック、１９は加減速パルス発生ブロック１４の後段に設けられた加算ブロック、２０はアクチュエータ弾性項無効化信号発生ブロックである。
【０１１７】
図７中、他の構成要素は従来例で説明したブロックと同様であるから、その説明を省略し、フォーカス制御ループスイッチ７、ホールドブロック１２、加減速パルス発生ブロック１４ならびに加算ブロック１９、アクチュエータ弾性項無効化信号発生ブロック２０についてそれらの動作について概要の説明を行う。
【０１１８】
図２０に示した従来の装置では、フォーカスジャンプ中のＦＥＳを位相補償ブロック８に入力し、さらに位相補償ブロック８出力をＬＰＦ１１に入力し、ＬＰＦ１１出力を面振れ補正信号としていた。
【０１１９】
ところが、フォーカスジャンプ中のＦＥＳは非線型であり、また実際的な面から、ピックアップの光学系によってはＦＥＳの不感帯が発生する場合が多い。例えば、フォーカスエラー信号特性カーブである、いわゆるＳカーブの上下振幅が非対称であったり、不要な瘤があったりすると、これが制御信号の検出系における外乱となってＬＰＦ１１の出力結果が乱される（例えば、設計値以外のタイミングずれを引き起こす）結果となる。
【０１２０】
図７に示す本実施の形態はこれを解消するために、フォーカスジャンプ期間中は加減速パルス発生ブロック１４に位相補償ブロック８の前段に設けられたフォーカス制御ループスイッチ７を切り、フォーカスジャンプ中の非線型なＦＥＳが後段の面振れ補正信号生成段１１および１２に伝達しない構成とした。
【０１２１】
さらに、ジャンプ期間中の面振れ補正信号を、ホールドブロック１２により生成するようにしたので、上記の解析で示したように面振れによる誤差を小さく抑えることが可能な構成とした。
【０１２２】
なお、ホールドブロック１２は、特に限定は無いが、ここでは構成が簡単な零次ホールドとする。この場合、先に述べたような解析から、再生速度が遅いアプリケーション、たとえばＤＶＤプレイヤ等に適用されることになる。
【０１２３】
また、さらにアクチュエータ弾性項無効化信号発生ブロック２０ならびに加算ブロック１９を加え、アクチュエータの機械特性（可動部のバネ支持弾性率）によらず擬似的に慣性系アクチュエータと同等の動特性に補正することが可能な構成とした。
【０１２４】
フォーカスジャンプにおいて、上記フォーカス制御ループスイッチ７ならびにホールドブロック１２を制御信号であるホールドブロック１２を制御する信号、スイッチ７およびフォーカススイッチ９を制御する信号を出力するのは、加減速パルス発生ブロック１４において行う。
【０１２５】
加減速パルス発生ブロック１４は、例えばシステムコントローラ等の上位制御部からフォーカスジャンプ指令を受けると、ＦＥＳに基いて加減速パルス切替えタイミングを作成する。
【０１２６】
加減速パルスは、出力モードとして加速パルスが与えられるモード、零期間モード（加速パルスあるいは減速パルスが与えられないモード）、減速パルスが与えられるモードの３つのモードを有する。
【０１２７】
加速パルスおよび減速パルスの各パルスは矩形波で与えられ、パルスの与え方で言うならば、加速パルス、零期間（パルスが与えられない）、減速パルスの順に状態遷移する。
【０１２８】
さらに、先に説明したように、加速パルスと減速パルスは極性が反対で力積を等しく設定する(図８参照)。以下に加減速パルスの切替えタイミングの生成について説明する。
【０１２９】
図１２は、アクチュエータがバネ支持の無い慣性系と仮定した場合において、加減速パルス切替えタイミングを固定値にした場合に生じる不具合を示したものである。
【０１３０】
図１２中（Ａ）は印加パルスとしての加減速パルスが与えられる様子を示したものであり、電流感度が平均値のフォーカスアクチュエータを層間距離４０μｍ移動させる設定となっている。
【０１３１】
図１２中（Ｂ）はフォーカスアクチュエータ位置を示す。図１２（Ｂ）の実線はフォーカスアクチュエータの電流感度平均値でのアクチュエータ位置を示すものである。
【０１３２】
実際のフォーカスアクチュエータの電流感度は、多少のばらつきが必ずあり、一般的には平均値に対して±３ｄB程度である。この場合、図１２（Ａ）の加減速パルスによって駆動される際のアクチュエータ位置のばらつきは、図１２（Ｂ）の点線で示す範囲となる。
【０１３３】
この電流感度ばらつきによる位置変動はおおよそ±１６μｍとなり、ＦＥＳの検出限界である±１０μｍより大きくなるため、ジャンプ後のフォーカス引き込みに失敗する恐れがある。
【０１３４】
本実施の形態では、この問題を解消するため、ジャンプ動作中のＦＥＳに基づいて加減速パルスの状態遷移タイミングを決定する構成とした。図１３にアクチュエータが慣性系アクチュエータと仮定した場合における、本発明の加減速パルスの状態遷移タイミングを示す。
【０１３５】
図１３（Ａ）はフォーカスアクチュエータ位置、（Ｂ）はＦＥＳ、（Ｃ）は加減速パルスを示す。図１３（Ｂ）に示すように、ＦＥＳの零点（ゼロクロス点）からヒステリシスを持たせた値を加速パルス終端閾値、同様に加速パルス終端閾値とは逆極性のヒステリシスを持たせた値を減速パルス始端閾値とする。
【０１３６】
加速パルスは、例えば上位制御部から出力されるジャンプ指令後に直ちに印加されるが、その終端タイミング（加速パルスの印加が終了される時点）はＦＥＳが上記加速パルス終端閾値以下になった時点とする。
【０１３７】
加速パルスの印加が終わると、加速パルスおよび減速パルスのいずれもが与えられない零出力の状態である零期間となり、さらにＦＥＳが減速パルス始端閾値以下になれば、減速パルスを印加開始し、当該減速パルスの終端タイミング（減速パルスの印加が終了される時点）は加速パルスと力積の絶対値が等しくなるタイミングに設定する。
【０１３８】
このようにすれば、アクチュエータの電流感度によらず、加速パルスによって現在層（その時点で焦点が形成されている層。これに対して焦点を別な層に形成する、いわゆるジャンプする先の層を目的層と称する。）からの脱出が保証され、さらに減速パルスの印加タイミングが目的層近傍となることが保証される。
【０１３９】
このように構成することで、図１３（Ａ）に示すようにアクチュエータ電流感度がばらついても、所定の目標位置に位置誤差なく焦点位置が移動（ジャンプ）し、さらに移動後の速度を零にすることが可能となる。
【０１４０】
以上は、アクチュエータが慣性系アクチュエータであると仮定した場合において成り立つが、実際のアクチュエータはバネ支持された拘束系アクチュエータである。
【０１４１】
例えば、アクチュエータのバネ剛性（弾性率）が小さい場合においては、上記の構成で充分実用化に耐えるが、バネ剛性が大きいアクチュエータにおいては、このバネ剛性を考慮に入れたジャンプ動作（フォーカスジャンプ）を実現する必要があり、上記に述べた加減速パルス以外の補正を行う必要が生じる。
【０１４２】
本実施の形態では、この問題を解消するため、アクチュエータ弾性項無効化信号発生ブロック２０と、これを加減速パルスに加算する加算手段１９を設置した。
【０１４３】
アクチュエータ弾性項無効化信号発生ブロック２０は、バネ支持されていない慣性系アクチュエータに加減速パルスが印加された場合のアクチュエータ位置変動にアクチュエータバネの弾性係数を乗じた信号を模擬したものであり、本実施の形態の場合、図１３（Ａ）に弾性係数ｋを乗じたものとなる。
【０１４４】
図１１にアクチュエータ弾性項無効化信号を説明する図を示す。図１１（Ｂ）は加減速パルス、（Ａ）は慣性系アクチュエータのときのアクチュエータ位置（推定値）であり、（Ｃ）は（Ａ）に弾性係数ｋを掛けた信号の模擬信号である。
【０１４５】
図１１（Ｃ）の模擬信号は、その傾きが弾性係数ｋと比例した一次関数で表され、結果として、減速パルス終端における力はｋＷ（Ｗは層間距離＝４０μｍ）となる。
【０１４６】
厳密に言えば、図１１（Ｃ）は２次関数として記述することが望ましいが、１次関数として定義しても誤差はほとんど無いため、実用上問題無い。この図１１（Ｃ）に示した模擬信号を図１１（Ｂ）に示すような加減速パルスに加算ブロック１９において加算することによって、バネによって拘束された拘束系アクチュエータはバネによって拘束されない慣性系アクチュエータと同様の動特性となる。
【０１４７】
ここでＦＥＳの正極性と負極性の波形特性が等しいと仮定する。
この場合は、加速パルス終端閾値および減速パルス始端閾値の絶対値を等しく設定し、かつ、加速パルスと減速パルスのパルスの高さ（振幅）の絶対値を等しく設定すれば（但し、極性は逆）、移動後の位置誤差をも零にすることが可能となる。
【０１４８】
上記条件の下では、前述したフォーカスジャンプが安定に実現する２つの条件を満たしているため、確実なフォーカスジャンプを実現できる。
【０１４９】
実施の形態２．
実施の形態１では、ＦＥＳの正極性と負極性の波形特性が等しい場合に有効なフォーカスジャンプ装置・方法について述べたが、実施の形態２では、ＦＥＳ検出特性がアンバランスな場合についても対応できるフォーカスジャンプ装置・方法について述べる。
【０１５０】
図１４に等速でフォーカスサーチ（対物レンズ２をディスクの配列方向に等速で移動させて焦点位置を検出する動作）を行った場合のＦＥＳを示す。図１４に示すものは、ＦＥＳの正極性と負極性との各検出特性がアンバランスになっている。
【０１５１】
このようにＦＥＳの検出特性がアンバランスな場合、以下のような問題が発生する。
【０１５２】
すなわち、実施の形態１に説明した方法では、減速パルスの始端タイミングを図１４中のａもしくはｂの領域内にある波形に基き作成するので、減速パルスの開始タイミングがＦＥＳ検出特性のアンバランスによる影響を受けてしまう。
【０１５３】
従って、このような場合には、減速パルスの印加後における、速度が零となることは保証されるが、ＦＥＳが零となることは保証できなくなる。
【０１５４】
これを解決するため、本実施の形態においては、上記減速パルスを印加した後に発生するＦＥＳアンバランスに起因する残留ＦＥＳを補正するため、実施の形態１に述べた加減速パルス印加の後、さらに補正パルスを印加してＦＥＳを零とした上でフォーカス引込を行うように構成した。
【０１５５】
本実施の形態２のブロック図を図１５に示す。１５は加減速パルス印加結果判定ブロックである。他の構成は前記実施の形態１において既に説明を行った構成・動作と同様なので説明を省略する。
【０１５６】
加減速パルス印加結果判定ブロック１５は、入力としてＦＥＳ、ならびに加減速パルス発生ブロック１４からの減速パルスの印加が終了したことを示す印加終了タイミングをもらう。
【０１５７】
加減速パルス印加結果判定ブロック１５は、加減速パルス発生ブロック１４に対して、加減速パルスの印加の後に発生する補正加減速パルス生成指令を発生させる。
【０１５８】
加減速パルス印加結果判定ブロック１５ならびに加減速パルス発生ブロック１４の動作を図１６、図１７を用いて説明する。
【０１５９】
図１６は、アクチュエータの弾性項が無視できる場合における本実施の形態の動作を説明する図である。
【０１６０】
図１６中（Ａ）は、フォーカスアクチュエータ位置、（Ｂ）はＦＥＳ、（Ｃ）は加減速パルスであり、それぞれフォーカスジャンプ中の時間変化を示す。
【０１６１】
図１６（Ｂ）から判るように、図１６に示すものはＦＥＳの負極側の出力特性が大きい事例である。フォーカスジャンプ指令を上位制御部から受けると、加減速パルス発生ブロック１４は、加速パルスを発生させる。
【０１６２】
加速パルスの終端は、ＦＥＳが加速パルスの終端タイミング生成閾値を横切る時点とする。この場合、併せて加速パルス印加時間Ｔ０を計測しておく（加速パルスが印加される都度計測する）。
【０１６３】
減速パルス始端タイミング生成閾値を横切るまで、加減速パルスは零期間とする。続いて、ＦＥＳが減速パルス始端タイミング生成閾値を横切る時点からＴ０の期間、減速パルスを印加する。
【０１６４】
なお、このとき、減速パルスの振幅は加速パルスの振幅と等しく設定する（印加する極性は逆極性）。次に減速パルス印加終了時のＦＥＳを観測して、その観測された値を残留ＦＥＳとする（図中、該当値ＦＥＳ＝Ｘ０）。
【０１６５】
続いて、観測された残留ＦＥＳが１／２（すなわち、ＦＥＳの値がＸ０／２）になるまで、残留ＦＥＳが減少する方向に補正加速パルスを印加する。このとき、補正加速パルスの印加時間Ｔ１を計測しておく（補正加速パルスが印加される都度計測する）。
【０１６６】
補正加速パルス印加直後、補正加速パルスと逆方向の補正加速パルスと等しい振幅の補正減速パルスをＴ１の期間印加する（補正加速パルス、補正減速パルスを総称して補正加減速パルスと称す）。
【０１６７】
上記のように構成すれば、加減速パルスならびに補正加減速パルスの力積の総和は零となるため、フォーカスジャンプ終了時におけるアクチュエータの速度が零となることが保証され、また、ＦＥＳについても略零が保証される。これにより、フォーカスジャンプを安定に実現する２つの条件を満たすため、確実なフォーカスジャンプが実現する。
【０１６８】
以上の説明は、アクチュエータの弾性項が無視できる程度に小さい例（慣性系アクチュエータの場合）について述べたが、アクチュエータの弾性項が大きく無視できない場合（拘束系アクチュエータの場合）においては、図１５のアクチュエータ弾性項無効化信号発生ブロック２０ならびに加算ブロック１９を用いてアクチュエータの弾性項を無効化することによって、拘束系アクチュエータであっても慣性系アクチュエータと同様の取り扱いができる。
【０１６９】
この場合のアクチュエータ弾性項無効化信号の挙動を図１８に示す。本例は加速パルスおよび補正加速パルスの両極性が等しい場合である。この場合、加速パルスおよび減速パルスを印加している期間（補正加減速パルス印加期間と称す）において、実施の形態１と同様にアクチュエータ弾性項無効化信号は時間とともに比例して増加する。
【０１７０】
さらに、補正加減速パルス印加期間中においてもアクチュエータ弾性項無効化信号は連続性を失わず、かつその増加率を保ったまま増加する（図１８（Ｃ）参照）。
【０１７１】
このようにアクチュエータ弾性項無効化信号を設定すれば、アクチュエータ弾性項無効化信号は図１８（Ａ）のアクチュエータ位置（信号）を模擬する結果となるため、アクチュエータの弾性項は無効化され、補正化減速パルスを印加した後のアクチュエータ速度を略零に設定することが可能となる。
【０１７２】
従って、上記のように構成すれば、アクチュエータの弾性項が大きい場合（拘束系アクチュエータ）においても、アクチュエータ弾性項は無効化され、加減速パルスならびに補正加減速パルスの力積の総和は零となるため、アクチュエータの速度が零となることが保証され、また、ＦＥＳについても略零が保証される。これにより、フォーカスジャンプを安定に実現する２つの条件を満たすため、確実なフォーカスジャンプが実現する。
【０１７３】
図１７は同じくアクチュエータ弾性項が無視できる場合において、図１６とＦＥＳアンバランス特性が逆、すなわち正極性が負極性より相対的に大きい事例の動作を説明する図である。図１６の説明と全く同様の動作で、図１６と同様に、速度零、ＦＥＳも略零が保証され、安定なフォーカスジャンプが実現できる。
【０１７４】
アクチュエータの弾性項が大きい場合においては、図１９（Ｃ）に示すアクチュエータ弾性項無効化信号を印加すればよい。図１９（Ｂ）に示す例は、加速パルスと補正加速パルスの極性とが逆極性の場合である。
【０１７５】
この場合、加減速パルス印加期間においては、実施の形態１と同様にアクチュエータ弾性項無効化信号は時間とともに比例して増加し、さらに補正加減速パルス印加期間中において前記無効化信号は連続性を失わず、かつその増加率を逆極性にする（図１９（Ｃ）参照）。
【０１７６】
このようにアクチュエータ弾性項無効化信号を設定すれば、アクチュエータ弾性項無効化信号は図１９（Ａ）のアクチュエータ位置信号を模擬する結果となるため、アクチュエータの弾性項は無効化され、補正化減速パルスを印加した後のアクチュエータ速度を略零に設定することが可能となる。
【０１７７】
従って、上記のように構成すれば、アクチュエータ弾性項が大きい場合（拘束系アクチュエータ）においても、アクチュエータ弾性項は無効化され、加減速パルスならびに補正加減速パルスの力積の総和は零となるため、アクチュエータの速度が零となることが保証される。
【０１７８】
また、ＦＥＳについても略零となることが保証される。従って、フォーカスジャンプを安定に実現する２つの条件を満たすため、確実なフォーカスジャンプを実現することができる。なお、上記各実施の形態の説明においては、２つの記録層を有するＤＶＤ−ＤＬにおいて説明したが、記録層をさらに有する（例えば半透明の記録層を２層以上有する場合）多層のディスクを用いても、同様に採用することが可能であり、必ずしも２層の記録層を有するディスクに適用されるものに限定されない。
【０１７９】
【発明の効果】
この発明は、以上説明したように構成されているので、以下に示すような効果を奏する。
【０１８０】
本発明に係るフォーカス移動装置は、複数の記録層を有するディスクのいずれかの記録層上に光源からの出射光を集光して集光スポットを形成する集光レンズを前記複数の記録層の配列される方向に移動するアクチュエータと、該アクチュエータを駆動して前記集光レンズの位置を移動させることにより前記集光スポットの位置を前記記録層の内の一の記録層の位置より他の記録層の位置に変位させるに際し、前記集光スポットの位置を前記一の記録層の位置より移動させるための駆動信号に基づく力積および前記集光スポットの位置を前記他の記録層上に停止させるための駆動信号に基づく力積の総和が略零となるように前記各駆動信号を出力するアクチュエータ駆動手段とを備えることを特徴とするので、移動後のフォーカスエラー信号を零とすることができるとともに移動後の集光レンズと他の記録層との間の相対速度を零とすることができ、安定で確実なフォーカス移動を実現できる。
【０１８１】
また、アクチュエータ駆動手段から出力される、集光スポットの位置を一の記録層の位置より移動させるための駆動信号および他の記録層上に停止させるための駆動信号は、振幅値の絶対値が等しく、極性が逆であって、印加時間が等しいことを特徴とするので、一の記録層の位置より移動させるための駆動信号に基づく力積および他の記録層上に停止させるための駆動信号に基づく力積の総和を容易に略零とすることができ、移動後のフォーカスの安定性を確実に実現できる。
【０１８２】
また、集光レンズの移動直前における焦点制御信号をホールドした補間信号および層間移動信号の和を集光スポットの位置を一の記録層の位置より移動させるための駆動信号とすることを特徴とするので、フォーカスの移動に際し面振れの影響を排除することができ、安定で確実なフォーカス移動を実現できる。
【０１８３】
また、層間移動信号は、一の記録層の位置と他の記録層との間の距離に対応する加減速パルスまたは該加減速パルスとアクチュエータ弾性項無効化信号との和によって与えられることを特徴とするので、層間移動信号をより単純な形で与えることができる。
【０１８４】
また、加減速パルスの印加後に補正加減速パルスを印加することを特徴とするので、フォーカスエラー信号特性が非対称である場合にも安定で確実なフォーカス移動を実現できる。
【０１８５】
また、アクチュエータ弾性項無効化信号は、集光レンズの移動位置を模擬した信号であることを特徴とするので、より安定でより確実なフォーカス移動を実現できる。
【０１８６】
本発明に係るフォーカス移動方法は、複数の記録層を有するディスクのいずれかの記録層上に、光源からの出射光を集光して集光スポットを形成する集光レンズを該集光レンズを移動させるためのアクチュエータを駆動して前記複数の記録層の配列される方向に移動させ、これにより前記集光スポットの位置を前記記録層の内の一の記録層の位置より他の記録層の位置に変位させるに際し、前記集光スポットの位置を前記一の記録層の位置より移動させるための駆動信号に基づく力積および前記集光スポットの位置を前記他の記録層上に停止させるための駆動信号に基づく力積の総和が略零となるように前記各駆動信号を与えることを含むことを特徴とするので、移動後のフォーカスエラー信号を零とすることができるとともに移動後の集光レンズと他の記録層との間の相対速度を零とすることができ、安定で確実なフォーカス移動を実現できる。
【０１８７】
また、アクチュエータを駆動する際の、集光スポットの位置を一の記録層の位置より移動させるための駆動信号および他の記録層上に停止させるための駆動信号は、振幅値の絶対値が等しく、極性が逆であって、印加時間が等しいことを特徴とするので、一の記録層の位置より移動させるための駆動信号に基づく力積および他の記録層上に停止させるための駆動信号に基づく力積の総和を容易に略零とすることができ、移動後のフォーカスの安定性を確実に実現できる。
【０１８８】
また、集光レンズの移動直前における焦点制御信号をホールドした補間信号および層間移動信号の和を集光スポットの位置を前記一の記録層の位置より移動させるための駆動信号とすることを特徴とするので、フォーカスの移動に際し面振れの影響を排除することができ、安定で確実なフォーカス移動を実現できる。
【０１８９】
また、層間移動信号は、一の記録層の位置と他の記録層との間の距離に対応する加減速パルスまたは該加減速パルスとアクチュエータ弾性項無効化信号との和によって与えられることを特徴とするので、層間移動信号をより単純な形で与えることができる。
【０１９０】
また、加減速パルスの印加後に補正加減速パルスを印加することを特徴とするので、フォーカスエラー信号特性が非対称である場合にも安定で確実なフォーカス移動を実現できる。
【０１９１】
また、アクチュエータ弾性項無効化信号は、集光レンズの移動位置を模擬した信号であることを特徴とするので、より安定でより確実なフォーカス移動を実現できる。
【図面の簡単な説明】
【図１】 面振れを有するディスクに対し、フォーカス制御信号をホールドした時に生じる位置誤差を説明するための説明図である。
【図２】 面振れを有するディスクに対し、フォーカス制御信号をホールドした時に生じる位置誤差を説明するための説明図である。
【図３】 面振れを有するディスクに対し、フォーカス制御信号をホールドした時に生じる位置誤差を説明するための説明図である。
【図４】 零次ホールド時の、ジャンプ期間対最大位置誤差を説明するための説明図である。
【図５】 ホールド種類による、ジャンプ期間対最大位置誤差の比較を説明するための説明図である。
【図６】 １次ホールド時の、ジャンプ期間対最大位置誤差を説明するための説明図である。
【図７】 実施の形態１におけるフォーカスジャンプ装置を示すブロック図である。
【図８】 フォーカスアクチュエータの印加パルスに対する動作を説明するための説明図である。
【図９】 アクチュエータの機械特性を説明するための説明図である。
【図１０】 アクチュエータ弾性項無効化信号の原理を説明するための説明図である。
【図１１】 フォーカスジャンプ時のアクチュエータ弾性項無効化信号を説明するための説明図である。
【図１２】 固定加減速パルス印加時の、アクチュエータ感度ばらつきによる位置誤差を説明するための説明図である。
【図１３】 加減速パルス印加タイミングをＦＥＳ振幅基準に設定した場合のアクチュエータの動作を説明するための説明図である。
【図１４】 ＦＥＳ検出特性がアンバランスな事例を説明するための説明図である。
【図１５】 実施の形態２におけるフォーカスジャンプ装置を示すブロック図である。
【図１６】 実施の形態２の動作を説明するための説明図である。
【図１７】 実施の形態２の動作を説明するための説明図である。
【図１８】 実施の形態２におけるアクチュエータ弾性項無効化信号を説明するための説明図である。
【図１９】 実施の形態２におけるアクチュエータ弾性項無効化信号を説明するための説明図である。
【図２０】 従来のフォーカスジャンプ装置を示すブロック図である。
【図２１】 従来のフォーカスジャンプ装置を示すブロック図である。
【図２２】 フォーカスジャンプの主要な技術課題を説明するための説明図である。
【符号の説明】
３ フォーカスアクチュエータ駆動コイル、７ フォーカス制御ループスイッチ、８ 位相補償ブロック、９ 切替えスイッチ、１１ ローパスフィルタブロック、１２ ホールドブロック、１３ 加算ブロック、１４ 加減速パルス発生ブロック、１５ 加減速パルス印加結果判定ブロック、１９ 加算ブロック、２０ アクチュエータ弾性項無効化信号発生ブロック。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to, for example, a DVD in which a plurality of recording layers are laminated, and more particularly to a focus moving apparatus and method for condensing and controlling a light spot on a predetermined recording layer.
[0002]
[Prior art]
Many applications have been filed for a configuration for reproducing an arbitrary recording layer in an optical disc having a multilayer recording layer such as a DVD. For example, Japanese Patent Application Laid-Open No. 10-124883 describes a method of jumping from a recording layer currently under focus control to an arbitrary recording layer (hereinafter referred to as focus jump).
[0003]
FIG. 20 shows a block diagram thereof. In short, what is shown in FIG. 20 is a configuration in which a functional block necessary for a focus jump is added to a general focus control loop.
[0004]
During the focus jump, the focus control loop is cut by the focus jump selection switch 9 provided at the subsequent stage of the phase compensation block 8, and instead of the focus control signal, the current layer (the layer where the focused spot is formed at that time) The acceleration / deceleration signal of the focus actuator that moves the light spot focusing position is applied to the target layer (focus jump destination layer).
[0005]
This acceleration / deceleration signal is composed of an acceleration pulse for exiting the focus actuator from the current layer and a deceleration pulse for bringing the target layer into a focusable position.
[0006]
FIG. 21 is a block diagram showing a focus jump device described in Japanese Patent Application Laid-Open No. 10-124883. In FIG. 21, 100 is a light emitting optical system including a semiconductor LD as a light source, 1 is, for example, a DVD 2 layer (hereinafter referred to as DVD-). (Referred to as DL) disk, 2 is an objective lens, 3 is a focus actuator drive coil rigidly connected to the objective lens 2 and installed in a magnetic circuit, 4 is a half mirror, 5 is a photoelectric conversion element, and 6 is a focus error detection block , 8 is a phase compensation block, 9 is a changeover switch, 10 is a driver amplifier, 11 is a low-pass filter block (hereinafter abbreviated as LPF block), 13 is an addition block, and 14 is an acceleration / deceleration pulse generation block.
[0007]
Disc 1, objective lens 2 (condensing lens), focus actuator drive coil 3 (sometimes simply referred to as drive coil 3), half mirror 4, photoelectric conversion element 5, focus error detection block 6, phase compensation block 8 and driver The amplifier 10 has a general focus control loop configuration. In the conventional apparatus described in the above publication in order to realize a focus jump, the changeover switch 9, the LPF block 11, the addition block 13 and the acceleration / deceleration pulse generation block 14 are provided. The added configuration is adopted.
[0008]
Hereinafter, general focus control will be briefly described. In order to reproduce the information recorded on the recording layer (information recording layer) of the disc 1, the laser light emitted from the light emitting optical system 100 must always be focused on the recording layer of the disc 1 by the objective lens 2. Don't be. In order to realize this, it is necessary to control the position of the objective lens 2 at a predetermined relative position with respect to the disk 1. That is, in the DVD-DL as described above, the recording layer is composed of two films (two layers), a high reflectance film (for example, an aluminum film) and a translucent reflective film (for example, a gold film). , The focused spot is controlled to form a focal point in each of the layers.
[0009]
The disc 1 has warpage, and the allowable amount of warpage is set to ± 300 μm or less, for example. As the disc 1 having such a warp rotates, the disc surface (or recording layer) of the disc 1 moves up and down with respect to a virtual rotation plane perpendicular to the rotation axis by the warp of the disc 1 (hereinafter referred to as the disc 1). Therefore, follow-up control of the objective lens 2 is essential.
[0010]
In this case, the object to be controlled is the objective lens 2, the tracking target is the recording layer of the disk 1, and the control type is relative position control with respect to the disk 1 (hereinafter sometimes simply referred to as position control).
[0011]
The position control of the objective lens 2 is realized by feeding back a signal based on a relative position error signal between the objective lens 2 and the disc 1 (a signal corresponding to a deviation from the focal length between the two) to the objective lens driving means. It is possible to use a very general focusing device well known so far (for example, a focusing device employing an astigmatism method).
[0012]
The objective lens driving means, which is a configuration necessary for driving (moving) the objective lens 2 to the optimum position (position where a condensed spot can be formed on the recording layer of the disk 1), is mainly described below. Including.
[0013]
For example, the configuration for detecting the relative position with respect to the disc 1 (the focal length of the objective lens 2 and the distance between the disc 1 and the objective lens 2) includes the half mirror 4 and the photoelectric conversion element 5 in FIG. The light beam (laser light) emitted from the light emitting optical system 100 is incident on the disk 1, and the half mirror 4 guides the reflected light from the disk 1 toward the photoelectric conversion element 5.
[0014]
In the photoelectric conversion element 5, an electrical output corresponding to a relative position from an output from a position detection photodetector (for example, a two-divided photodetector) incorporated in the photoelectric conversion element 5 (sometimes simply referred to as a relative position). Get. As the photoelectric conversion element 5, a quadrant detector or the like frequently used in a method of detecting a focus error signal well known as a so-called astigmatism method is used.
[0015]
Further, an error signal between the relative position and a predetermined relative position (this error signal is a difference between a signal output from the photoelectric conversion element 5 and an electric signal having a predetermined value) can be obtained.
[0016]
The objective lens driving means includes a focus error detection block 6 as a means for generating Focus Error Signal (FES), and a focus control loop by compensating the phase of the output output from the focus error detection block 6. A phase compensation block 8 as a phase compensation unit for stabilization and a drive coil 3 as a drive unit for changing the position (focus position) of the objective lens 2 to be controlled are included.
[0017]
The phase compensation block 8 is generally constituted by a phase advance filter that advances the phase of a band near 1 kHz.
[0018]
The drive coil 3 is rigidly connected to the objective lens 2 and moves the objective lens 2 in a direction perpendicular to the surface of the disk 1 (surface on which the recording layer extends) by passing a drive current through the drive coil 3. Have
[0019]
The drive control of the objective lens is performed by controlling the drive current based on a focus control signal that is an output from the phase compensation block 8, and the laser light is recorded on the recording layer of the disk 1 by the operation described above. A control system for condensing light is realized.
[0020]
Next, a method of focus jumping (jumping the position of the objective lens 2 in the focus control direction) in the conventional apparatus will be described.
[0021]
The signal applied to the drive coil 3 at the time of focus jump is given by the sum of the surface shake interpolation signal, which is the output from the LPF block 11, and the output signal from the acceleration / deceleration pulse generation block 14, and the addition of these two signals is This is performed in the addition block 13.
[0022]
In this case, when the focus control is performed by the selection switch 9, the focus control signal that is the output of the phase compensation block 8 is selected, and when the focus jump is performed, the focus jump signal output from the addition block 13 is selected. To do. Thereby, state transition (state switching) between the focus control state and the focus jump state is controlled.
[0023]
The LPF block 11 is set so that the cutoff frequency is higher than the disk rotation frequency, and has a function of extracting only the disk surface shake component of the focus control signal.
[0024]
Further, the acceleration / deceleration pulse generation block 14 includes, for example, an acceleration pulse that is a rectangular wave for acceleration based on a focus jump command output from an upper block such as a system controller that controls the entire apparatus, and a rectangular wave for deceleration. Is generated, and switching from the acceleration pulse to the deceleration pulse is performed at the zero cross timing of the FES during the focus jump.
[0025]
The deceleration pulse ends when the FES is in focus (when the FES zero-crosses), and at the same time, the changeover switch 9 switches to focus control and is given when the focus pull-in operation is completed. The jump operation ends.
[0026]
[Problems to be solved by the invention]
The necessary condition for realizing a stable and reliable focus jump can be determined by whether or not the focus control loop is pulled in immediately after the focus jump operation.
[0027]
The conditions for the focus control loop to be stably pulled in are that the FES detected from the recording layer (target layer) at the target position during the focus pull-in operation is near zero, and the relative speed between the disk 1 and the objective lens 2. Is close to zero.
[0028]
If you organize these two conditions,
Condition 1. The FES after the jump operation is zero.
Condition 2. The relative speed between the objective lens 2 and the disc 1 after the jump operation (hereinafter referred to as the post-jump relative speed) is zero.
That is, if the jump operation can be set in this way, a stable and reliable focus jump can be realized.
[0029]
FIG. 22 summarizes the main points of the problem to be overcome in order to realize the focus jump. The contents of FIG. 22 are listed and explained as follows.
[0030]
(1) Since the position detection signal is lost during the focus jump, open loop control is performed.
Reason: The FES detection range (for example, less than 10 μm) is narrower than the interlayer distance (for example, about 40 μm), and there is a focus error dead zone (a range in which a focus error cannot be detected during the focus jump. In the above example, about 20 μm). Exists. Therefore, when the objective lens 2 is in the dead zone due to the focus jump, the open loop control is performed.
[0031]
{Circle around (2)} The disk that is the tracking target has surface runout, but it is necessary to apply focus servo even in such a state.
Reason: Even during the focus jump, the relative position and relative speed between the disc 1 and the objective lens 2 change due to the surface shake of the disc 1. Therefore, if the jump is performed without taking the surface shake of the disc 1 into consideration, Condition 1 and Condition 2 (In reality, it is more difficult to satisfy the condition 2).
[0032]
For example, the conventional focus jump apparatus and method described in Japanese Patent Laid-Open No. 10-124883 is limited to a pickup having no dead zone as shown in the above (1), and is generally used with a dead zone. It is difficult to directly apply what is described in the above publication to a simple pickup.
[0033]
Furthermore, in the prior art disclosed in the publication, the countermeasure against the surface shake of the above (2) is taken, but the FES obtained during the focus jump is non-linear, and the non-linear component of such FES is Since it is input to the LPF block 11 as a disturbance, there is a problem in that the surface shake interpolation signal is affected.
[0034]
Further, in the prior art disclosed in the publication, the acceleration / deceleration pulse, which is the output of the acceleration / deceleration pulse generation block 14, is set by paying attention only to the FES position (that is, here, the zero cross timing of the FES). Therefore, it cannot be guaranteed that the relative speed between the objective lens 2 and the disk 1 under condition 2 is zero.
[0035]
Therefore, when the focus is pulled in after the focus jump, the objective lens 2 causes overshoot and the like, thereby increasing the signal reading time. In the worst case, there is a problem that the focus pull-in fails.
[0036]
The present invention has been made to solve the above-described problems. Even in a disk with large surface runout, even when the reproduction speed is high, and even when the mechanical elastic modulus of the focus actuator is large. An object is to obtain a stable focus jump method.
[0037]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is constituted by the following means.
[0038]
A focus moving device according to the present invention includes a condensing lens for condensing emitted light from a light source to form a condensing spot on any recording layer of a disc having a plurality of recording layers. An actuator that moves in the direction of arrangement, and the position of the condensing lens is moved by driving the actuator to move the position of the condensing spot from the position of one of the recording layers to the other recording layer. When displacing to the position of the layer, the impulse based on the drive signal for moving the position of the focused spot from the position of the one recording layer and the position of the focused spot are stopped on the other recording layer. Actuator driving means for outputting each of the driving signals so that the sum of impulses based on the driving signals is substantially zero.
[0039]
Also, the drive signal for moving the position of the focused spot from the position of one recording layer and the drive signal for stopping on the other recording layer, which are output from the actuator driving means, have absolute values of amplitude values. Equal, opposite in polarity and equal in application time.
[0040]
The sum of the interpolation signal holding the focus control signal immediately before the movement of the condenser lens and the interlayer movement signal is used as a drive signal for moving the position of the condensed spot from the position of one recording layer. .
[0041]
The interlayer movement signal is given by an acceleration / deceleration pulse corresponding to a distance between the position of one recording layer and another recording layer or a sum of the acceleration / deceleration pulse and an actuator elastic term invalidation signal. And
[0042]
The correction acceleration / deceleration pulse is applied after the acceleration / deceleration pulse is applied.
[0043]
The actuator elastic term invalidation signal is a signal simulating the moving position of the condenser lens.
[0044]
The focus moving method according to the present invention includes a condensing lens that condenses light emitted from a light source to form a condensing spot on any recording layer of a disc having a plurality of recording layers. The actuator for moving is driven to move in the direction in which the plurality of recording layers are arranged, and thereby the position of the condensing spot is set to be different from the position of one recording layer in the other recording layers. When shifting to a position, an impulse based on a drive signal for moving the position of the focused spot from the position of the one recording layer and a position for stopping the position of the focused spot on the other recording layer Including the drive signals so that the sum of impulses based on the drive signals is substantially zero.
[0045]
Also, when driving the actuator, the absolute value of the amplitude value of the drive signal for moving the position of the focused spot from the position of one recording layer and the drive signal for stopping on the other recording layer are equal. The polarity is opposite and the application time is equal.
[0046]
Further, the sum of the interpolation signal holding the focus control signal immediately before the movement of the condensing lens and the interlayer movement signal is used as a drive signal for moving the position of the condensing spot from the position of the one recording layer. To do.
[0047]
The interlayer movement signal is given by an acceleration / deceleration pulse corresponding to a distance between the position of one recording layer and another recording layer or a sum of the acceleration / deceleration pulse and an actuator elastic term invalidation signal. And
[0048]
The correction acceleration / deceleration pulse is applied after the acceleration / deceleration pulse is applied.
[0049]
The actuator elastic term invalidation signal is a signal simulating the moving position of the condenser lens.
[0050]
DETAILED DESCRIPTION OF THE INVENTION
Basic description of embodiments of the present invention
Focus jump jumps (records) the focal position of the objective lens from the current recording layer (sometimes referred to as the current layer) to which focus control is currently applied to the target recording layer (sometimes referred to as the target layer). The focus position is changed between layers), and the target layer is required to have a function of performing focus control instantaneously or within a very short time. Although DVD-DL is described here, a disc such as DVD-DL is a disc having a plurality of recording layers (in the case of DVD-DL, it has two recording layers) as described above. On one of the recording layers, the emitted light emitted from a light source such as a semiconductor laser is condensed by a condenser lens (objective lens) to form a condensed spot. In DVD-DL, a highly reflective film and a semi-transparent reflective film are formed in layers, and focus control is, so to speak, moving the condenser lens using an actuator or the like in the direction in which the recording layers are arranged. Is achieved.
[0051]
From the viewpoint of focus control, this function is a special operation (mode) in which the focus control loop is cut off (completely) (open loop) during a focus jump, and then the focus control loop is closed (closed loop) suddenly after the focus jump ends. It can be said that.
[0052]
That is, during the focus jump, the FES signal is lost, and in order to ensure stable focus pull-in after the end of the focus jump, a follow-up operation is performed even when the focus jump is in progress. Thus, a surface deflection interpolation signal is required instead of the FES signal.
[0053]
Accordingly, the focus jump signal energized to the drive coil 3 during the focus jump includes a disc surface shake interpolation signal and a focus so that the disc surface shake during the focus jump period can be followed and interpolated. The position moves the interlayer distance from the current layer (one recording layer of the plurality of recording layers) to the target layer (the other recording layer with respect to one recording layer of the plurality of recording layers), What is necessary is just to give based on the sum with the acceleration-deceleration pulse from which the speed at the time of the stop becomes zero. The surface shake interpolation signal and acceleration / deceleration pulse required for such a focus jump signal will be described in detail below.
[0054]
1. Surface runout interpolation signal
Let's theoretically describe the surface shake interpolation signal that gives the function of following the surface shake regardless of the FES signal during the focus jump.
[0055]
As described for the conventional apparatus, the disc surface runout (following target in this case) appears periodically because the disc with warpage rotates, and when this is treated as a function, it is expressed by a periodic function. it can. Here, in order to simplify the explanation, it is assumed that the surface deflection of the disk is given by the following sine wave.
[0056]
[Expression 1]

[0057]
Here, t represents time (sec), X (t) represents surface vibration (m) at time t, A represents surface vibration amplitude (m), and B represents angular velocity (rad / sec) of surface vibration. Assuming that the mechanical dynamic characteristic of the focus actuator including the drive coil 3 to be controlled is a secondary system, and further, a function obtained by second-order differentiation of X (t) during the focus jump (that is, equivalent to the applied signal of the drive coil 3) Is defined as Δ (sec).
[0058]
Note that holding in this case means holding the driving voltage of the focus actuator, for example, holding the LPF output (low-pass filter output) of the focus drive signal.
[0059]
Further, the hold period is a period during which the hold state is continued, and the hold value is, for example, the magnitude of the LPF output of the focus drive signal held at a certain time.
[0060]
A function defined by the result of calculating the difference (error) between the hold value at time t and the true value at time t + Δ after the hold period Δ is a hold error function (representing the size of the position error and the length (Hereinafter sometimes referred to simply as an error function).
[0061]
As an example of the function of second-order differentiation of the surface shake X (t) with respect to time, that is, the form of holding the applied signal of the driving coil 3 (for example, the LPF output of the focus drive signal), the value of the signal is held at the time of holding. There is a zero-order hold and a first-order hold that holds both the value and slope of the signal at the time of holding.
[0062]
Here, when the hold error function in the case of zero-order hold is E0, and the hold error function in the case of first-order hold is E1, each can be expressed by the following equations.
[0063]
[Expression 2]

[0064]
[Equation 3]

[0065]
The derivations of the above equations 1 and 2 expressed as hold error functions E0 and E1 are as follows.
[0066]
<Derivation of Formula 2>
[0067]
[Expression 4]

[0068]
<Derivation of Equation 3>
[0069]
[Equation 5]

[0070]
As can be seen by referring to the above formulas 2 and 3, the error function is represented by a time function using the surface shake amplitude A, the surface shake angular velocity B, and the hold period Δ as parameters. Therefore, in order to discuss the hold error (the difference between the hold value and the true value after the hold period Δ), what is the value of the above parameter depending on the usage conditions of the system? It turns out that it is meaningless without specific numerical values.
[0071]
For example, the playback disc is DVD-DL, the playback speed is the innermost circumference of the quadruple speed CLV playback, the jump period (the hold operation is performed in this jump period, and the drive voltage of the actuator is held by the hold operation. The relationship between the disc surface runout X (t) and the hold error functions E0 and E1 when the disc holdout amplitude A is set to, for example, 300 μm (half wave amplitude) is set to 1 msec. It is shown in 1.
[0072]
In FIG. 1, the waveform A is a surface runout X (t), and the amplitude is displayed on a 1/10 scale. Waveform B is E0 and waveform C is E1. In the case of the above condition, as can be seen with reference to FIG. 1, the maximum value of the hold error with respect to the surface runout of 300 μm is about 13 μm for the zero-order hold and about 2 μm for the first-order hold.
[0073]
As described above, the error function (hold error function) is defined by a time function using the surface shake amplitude A, the surface shake angular velocity B, and the hold period Δ as parameters, so that the conditions shown in FIG. On the other hand, FIG. 2 and FIG. 3 show the results when the hold period Δ and the angular velocity B of the surface shake are changed small.
[0074]
2A shows an analysis result under the same conditions as in FIG. 1 (that is, the same content as in FIG. 1), and FIG. 2B shows an analysis result in which the hold period Δ is set small from 1 msec to 0.8 msec.
[0075]
2A and 2B are compared, if the hold period Δ is reduced, the amplitude of each hold error function is reduced in both the hold error functions EO and E1. From this, it can be seen that the hold error can be reduced by shortening the hold period.
[0076]
3A shows an analysis result under the same conditions as in FIG. 1 (that is, the same content as in FIG. 1), and FIG. 3B shows an analysis result when the playback speed is reduced from 4 × speed to 3 × speed. .
[0077]
3A and 3B are compared, if the angular velocity B of the surface shake is decreased, the amplitudes of the hold error functions are reduced in both the hold error functions EO and E1. From this, it can be seen that the hold error can be reduced by reducing the reproduction speed.
[0078]
From the above, the hold error has a characteristic that even if the surface vibration amplitude A is constant, the value greatly varies depending on the hold period and the reproduction speed, and the hold error increases as the reproduction speed increases and the hold period increases. .
[0079]
In order to discuss more qualitatively, the hold period Δ when the surface vibration amplitude A of DVD-DL is 300 μm (half-wave amplitude) and the reproduction speed is quadruple speed (CLV: innermost circumference) is used as a parameter. FIG. 4 shows the result of analyzing the maximum value of the amplitude of the hold error function (shown as the maximum position error in FIG. 4; however, it is a half-wave amplitude. Hereinafter, it may be referred to as the maximum position error).
[0080]
In FIG. 4, the solid line indicates the maximum position error of the zero-order hold, the dotted line indicates the maximum position error of the primary hold, and the broken line indicates the FES detection limit. The detection dynamic range of FES is physically limited. For example, in a general pickup for DVD use, the detection dynamic range is 10 μm or less. Therefore, the FES detection limit is set to 10 μm here.
[0081]
Under such conditions, if the maximum position error due to holding exceeds the FES detection limit, FES detection becomes impossible at the time of focus pull-in after holding, and focus pull-in fails, so the maximum position error exceeds the FES detection limit. That must be avoided.
[0082]
As can be understood with reference to FIG. 4, the maximum position error due to the hold increases as the hold period (shown as a jump period in FIG. 4) becomes longer, and the amount of the first-order hold is smaller than the zero-order hold.
[0083]
FIG. 5 shows the analysis result of the maximum position error in the zero-order hold when the variable parameter is changed not only in the hold period but also in the reproduction speed from 1 to 4 times. Referring to FIG. 5, the following relationship for deriving the maximum position error below the FES detection limit is derived.
[0084]
If the playback speed exceeds twice, the jump period must be less than 1.8 msec.
-The faster the playback speed, the shorter the jump period.
[0085]
FIG. 6 shows the analysis result of the maximum position error in the primary hold when the variable parameter is changed not only in the hold period but also in the reproduction speed from 1 to 4 times. With reference to FIG. 6, the following relationship for deriving the maximum position error below the FES detection limit is derived.
[0086]
-Even if the playback speed exceeds three times, the jump period need not be less than 2 msec.
-Even if the playback speed is quadrupled, there is no problem if the jump period is set to 1 msec or less.
[0087]
From the above relationship, it can be realized by holding the drive signal of the drive coil 3 as a countermeasure against the surface shake during the focus jump period (a focus jump is reliably performed while suppressing the influence of the surface shake).
[0088]
As for the type of hold, when the playback speed is slow as in a player application (for example, a playback speed that is approximately one time less than or equal to the speed required for DVD playback), zero-order hold is sufficient. It can be seen that when the playback speed is high as in the application (for example, a playback speed higher than about one time required for DVD playback), the primary hold may be used.
[0089]
2. Interlayer movement signal
The inter-layer movement signal is obtained by driving a focus actuator by focusing a laser beam emitted from a light source on each recording layer of a disk having a plurality of recording layers (information recording layers) via a condenser lens. This is a signal for moving the condensing lens coupled to the actuator in the direction in which the plurality of recording layers are arranged, and as a result, moving the condensing spot on each recording layer.
[0090]
The interlayer movement signal is given as the sum of the acceleration / deceleration pulse and the actuator elasticity term invalidation signal (that is, the output from the addition block 19 shown in FIG. 7 corresponds). Here, the interlayer movement signal includes an acceleration / deceleration pulse (output from the acceleration / deceleration pulse generation block 14 shown in FIG. 7), an actuator elasticity term invalidation signal (actuator elasticity term invalidation signal generation shown in FIG. 7). The description will be made in the order of output from the block 20).
[0091]
2-1. Acceleration / deceleration pulse
The mechanical dynamic characteristic of the focus actuator including the drive coil 3 to be controlled is a secondary system of a restraint system because it is supported by a spring, but a secondary system of an inertia system without a spring support for simplicity of explanation. It is assumed that the system. Assuming that the position of the objective lens 2 is x (t), the speed of the objective lens 2 is represented by the first-order time derivative of the position, and the acceleration is represented by the second-order time derivative of the position.
[0092]
[Formula 6]

[0093]
[Expression 7]

[0094]
The drive coil 3 has a function of converting an applied signal (applied current) into an actuator driving force (acceleration). Since there is a proportional relationship between the actuator driving force and the applied current, considering the applied signal is equivalent to considering the actuator driving force (ie, the dimension of acceleration).
[0095]
FIG. 8 shows a drive coil 3 (this is the same even when considering the movement of the objective lens 2 moved by the drive coil 3) with respect to the applied signal (the same applies considering the acceleration given to the objective lens 2). Shows the relationship between speed and position.
[0096]
In FIG. 8, (A) shows acceleration, (B) shows speed, and (C) shows position. When the acceleration pulse of the applied signal is given by a rectangular wave as shown in FIG. 8A, the velocity becomes a linear function and the position becomes a quadratic function.
[0097]
The acceleration pulse and the deceleration pulse are impulses with opposite polarities (a physical impulse is defined by the product of the force f and the time t at which the force f is applied to the object. Since the force f in the focusing device is proportional to the acceleration α generated in the objective lens (condensing lens), the product of the acceleration α and the time t at which the acceleration α is applied to the objective lens, or the acceleration α is applied to the drive coil. If the current i is defined to be equal to the product including the product of the current i and the time t when the current i is given to the drive coil), the speed after application of the deceleration pulse is Can be guaranteed to be zero.
[0098]
The reason will be described below.
The initial speed of the drive coil 3 is set to zero. At this time, the behavior when a rectangular wave acceleration pulse is applied is as follows. Assuming that the magnitude of acceleration is A and the period during which acceleration is given (also called acceleration period or acceleration time) is B, the speed is a linear function with the magnitude of acceleration A as its slope, and after the acceleration period B has elapsed. The speed is AB.
[0099]
That is, in this case, the speed is represented by the product (impulse) of the magnitude A of acceleration and the acceleration period B. The speed AB is maintained during a period in which the acceleration magnitude A after application of the acceleration pulse is zero.
[0100]
In this case, the polarity of the deceleration pulse with zero speed AB is opposite to that of the acceleration pulse (for example, with respect to the positive electrode). If the impulse given by the deceleration pulse is equalized, the speed after the deceleration pulse is applied is zero.
[0101]
In this case, since the focus actuator is always moving back and forth in the focus direction, for example, static friction hardly occurs in the initial motion, and it is necessary to consider dynamic friction, but the magnitude is given by the acceleration pulse. Since the magnitude of the generated force is extremely small, the impulse of the deceleration pulse can be given so as to substantially cancel the impulse of the acceleration pulse so that the sum of the impulse pulse and deceleration pulse is almost zero. That's fine.
[0102]
From the above explanation, when the actuator is an inertial system, the actuator speed after application of the acceleration / deceleration pulse becomes zero. However, since the actual actuator is a restraint system supported by a spring, it cannot be ignored in the case of an actuator with strong spring rigidity. Therefore, measures to correct this are necessary.
[0103]
2-2. Actuator elasticity term invalidation signal
FIG. 9A is a model diagram of an actuator (m in FIG. 9) supported by a spring (model diagram of a restraint system actuator), and FIG. 9B is an inertial actuator idealized by ignoring spring characteristics ( FIG. 10 shows a model diagram m) (model diagram of an inertial actuator) in FIG. In the figure, k is an elastic coefficient (spring coefficient) representing the strength of the spring, and f is a force acting on the moving part that receives the force generated by the mechanism part of the actuator m or the drive coil 3.
[0104]
10 is a block diagram of the spring-supported actuator shown in FIG. When the force f acts on the actuator mechanism, the position x changes, and a reaction force proportional to the amount of position change (proportional coefficient k, where k is positive) is fed back to the actuator mechanism by the spring. In order to cancel the influence of this spring, it is assumed that a force represented by H (s) is applied as shown in (2) of FIG. Here, H (s) is expressed by Equation 6 below.
[0105]
[Equation 8]

[0106]
This H (s) can be defined as an output simulating an amount obtained by multiplying the position fluctuation when the acceleration / deceleration pulse is applied when the actuator is not spring-supported by the spring coefficient (elastic modulus) of the actuator.
[0107]
H (s) is an electromagnetic force that invalidates (cancels or cancels) the actuator elasticity term (referred to as invalidation electromagnetic force H (s)), and the command signal for generating this invalidates the elasticity term of the actuator. Is given as a signal (referred to as actuator elasticity term invalidation signal).
[0108]
When the invalidating electromagnetic force H (s) is applied, the influence of the spring coefficient is canceled, so that the spring coefficient block k can be ignored as shown in (3) of FIG. By applying this invalidating electromagnetic force H (s), the restraint system actuator shown in FIG. 9 (A) can be operated like the inertial system actuator without spring support shown in FIG. 9 (B). .
[0109]
The actuator elasticity term invalidation signal is a signal proportional to the position fluctuation when the acceleration / deceleration pulse is applied to the actuator when it is not supported by the spring, so it is necessary to observe the actuator position, but the absolute position of the actuator Since there is no position sensor for measuring, it may be determined by calculation.
[0110]
For example, when the acceleration / deceleration pulse as shown in FIG. 11 (B) is applied to the actuator, the actuator position fluctuation is strictly a quadratic function when the acceleration / deceleration pulse is applied as shown in FIG. 8 (C). The period during which the magnitude of the acceleration / deceleration pulse is zero (zero period) increases linearly, but this is simply expressed as a linear function as shown in FIG. Even if simulated, almost no error occurs, and a signal can be easily obtained.
[0111]
When the actuator elastic term invalidation signal is added to the acceleration / deceleration pulse and the actuator is driven, the actuator elastic term is invalidated and the actuator which is originally a restraint system can be handled like an inertial system. As shown in FIG. 5, the speed after application of the acceleration / deceleration pulse can be guaranteed to be substantially zero, and as a result, the stable focus jump condition 2 can be satisfied.
[0112]
Focus control loop switch provided before the phase compensation block of the focus control loop, focus jump selection switch provided after the phase compensation block, low-pass filter block for noise removal having a noise component removing function of the focus control signal, focus jump It has means for holding the preceding low-pass filter output, actuator elastic term invalidation signal generating means and acceleration / deceleration pulse generating means for forming an interlayer movement signal for moving the objective lens by the interlayer distance, and further generates an acceleration / deceleration pulse. The acceleration / deceleration pulse generating means outputs a rectangular wave that accelerates or decelerates the focus actuator generated based on the focus error signal, and has three acceleration pulses, zero period and deceleration pulse as output modes. Deceleration The sum of impulse impulses is zero.
[0113]
Further, the actuator elasticity term invalidating signal generating means simulates and outputs an amount obtained by multiplying the position fluctuation when the acceleration / deceleration pulse is applied when the actuator is not supported by a spring by the spring coefficient (elastic modulus) of the actuator. . With the above configuration, a stable focus jump is realized.
[0114]
Based on the above analysis results and description, embodiments corresponding to various cases will be described below.
[0115]
Embodiment 1 FIG.
In the present embodiment, an application example will be described in which the positive and negative waveform characteristics of the FES in the player application are equal.
[0116]
FIG. 7 shows a block diagram of the present embodiment. In FIG. 7, 7 is a focus control loop switch provided before the phase compensation block 8, 12 is a hold block, 14 is an acceleration / deceleration pulse generation block, and 19 is an addition block provided after the acceleration / deceleration pulse generation block 14. , 20 is an actuator elasticity term invalidation signal generation block.
[0117]
In FIG. 7, the other components are the same as the blocks described in the conventional example, so the description thereof will be omitted, and the focus control loop switch 7, hold block 12, acceleration / deceleration pulse generation block 14 and addition block 19, actuator elasticity The operation of the term invalidation signal generation block 20 will be outlined.
[0118]
In the conventional apparatus shown in FIG. 20, the FES during the focus jump is input to the phase compensation block 8, the output of the phase compensation block 8 is input to the LPF 11, and the output of the LPF 11 is used as a surface shake correction signal.
[0119]
However, the FES during the focus jump is non-linear, and from a practical aspect, an FES dead zone often occurs depending on the optical system of the pickup. For example, if the vertical amplitude of the so-called S curve, which is a focus error signal characteristic curve, is asymmetrical or has an unnecessary knob, this becomes a disturbance in the control signal detection system and the output result of the LPF 11 is disturbed ( For example, this causes a timing shift other than the design value.
[0120]
In order to solve this problem, the present embodiment shown in FIG. 7 turns off the focus control loop switch 7 provided in the preceding stage of the phase compensation block 8 in the acceleration / deceleration pulse generation block 14 during the focus jump period, The non-linear FES is not transmitted to the subsequent surface shake correction signal generation stages 11 and 12.
[0121]
Furthermore, since the surface shake correction signal during the jump period is generated by the hold block 12, an error due to surface shake can be suppressed as shown in the above analysis.
[0122]
The hold block 12 is not particularly limited, but here is a zero-order hold with a simple configuration. In this case, the analysis described above is applied to an application with a slow reproduction speed, such as a DVD player.
[0123]
In addition, an actuator elasticity term invalidation signal generation block 20 and an addition block 19 are added, and the dynamic characteristics equivalent to those of the inertial actuator are artificially corrected regardless of the mechanical characteristics (spring supporting elastic modulus of the movable part) of the actuator. The configuration is possible.
[0124]
In the focus jump, the focus control loop switch 7 and the hold block 12 output a signal for controlling the hold block 12, which is a control signal, and a signal for controlling the switch 7 and the focus switch 9 in the acceleration / deceleration pulse generation block 14. Do.
[0125]
The acceleration / deceleration pulse generation block 14 generates an acceleration / deceleration pulse switching timing based on the FES when receiving a focus jump command from a host control unit such as a system controller.
[0126]
The acceleration / deceleration pulse has three modes: a mode in which an acceleration pulse is given as an output mode, a zero period mode (a mode in which no acceleration pulse or deceleration pulse is given), and a mode in which a deceleration pulse is given.
[0127]
Each pulse of the acceleration pulse and the deceleration pulse is given by a rectangular wave, and in terms of the way of giving the pulse, the state transitions in the order of the acceleration pulse, the zero period (no pulse is given), and the deceleration pulse.
[0128]
Further, as described above, the acceleration pulse and the deceleration pulse have opposite polarities and the impulses are set equal (see FIG. 8). The generation of acceleration / deceleration pulse switching timing will be described below.
[0129]
FIG. 12 shows a problem that occurs when the acceleration / deceleration pulse switching timing is set to a fixed value, assuming that the actuator is an inertial system without spring support.
[0130]
(A) in FIG. 12 shows a state in which an acceleration / deceleration pulse is applied as an applied pulse, and is set to move a focus actuator having an average current sensitivity of 40 μm between layers.
[0131]
In FIG. 12, (B) shows the focus actuator position. The solid line in FIG. 12B indicates the actuator position at the current sensitivity average value of the focus actuator.
[0132]
The actual current sensitivity of the focus actuator always varies somewhat, and is generally about ± 3 dB with respect to the average value. In this case, the variation in the actuator position when driven by the acceleration / deceleration pulse in FIG. 12A is in the range indicated by the dotted line in FIG.
[0133]
The position variation due to this current sensitivity variation is approximately ± 16 μm, which is larger than the FES detection limit of ± 10 μm, so that there is a possibility that the focus pull-in after the jump may fail.
[0134]
In this embodiment, in order to solve this problem, the state transition timing of the acceleration / deceleration pulse is determined based on the FES during the jump operation. FIG. 13 shows the state transition timing of the acceleration / deceleration pulse of the present invention when the actuator is assumed to be an inertial actuator.
[0135]
13A shows the focus actuator position, FIG. 13B shows the FES, and FIG. 13C shows the acceleration / deceleration pulse. As shown in FIG. 13B, a value having hysteresis from the zero point (zero cross point) of the FES is a acceleration pulse end threshold value, and similarly, a value having hysteresis having a polarity opposite to that of the acceleration pulse end threshold value is a deceleration pulse. The starting threshold is used.
[0136]
The acceleration pulse is applied immediately after, for example, a jump command output from the host control unit, but its end timing (when application of the acceleration pulse ends) is the time when the FES is equal to or less than the acceleration pulse end threshold. .
[0137]
When the application of the acceleration pulse is finished, a zero period in which neither the acceleration pulse nor the deceleration pulse is given is a zero period, and when the FES falls below the deceleration pulse start threshold, the application of the deceleration pulse is started. The end timing of the deceleration pulse (when the application of the deceleration pulse is completed) is set to a timing at which the absolute value of the impulse pulse and the impulse are equal.
[0138]
In this way, regardless of the current sensitivity of the actuator, the current layer (the layer in which the focal point is formed at that time) is formed by the acceleration pulse. On the other hand, the so-called jump destination layer that forms the focal point in another layer Is called the target layer), and the application timing of the deceleration pulse is guaranteed to be in the vicinity of the target layer.
[0139]
With this configuration, even if the actuator current sensitivity varies as shown in FIG. 13A, the focal position moves (jumps) to the predetermined target position without a position error, and the speed after the movement is reduced to zero. It becomes possible to do.
[0140]
The above is true when it is assumed that the actuator is an inertial actuator, but the actual actuator is a spring-supported restraint actuator.
[0141]
For example, when the spring stiffness (elastic modulus) of the actuator is small, the above configuration can withstand practical use, but for an actuator with a large spring stiffness, a jump operation (focus jump) that takes this spring stiffness into account can be performed. Therefore, it is necessary to perform correction other than the acceleration / deceleration pulse described above.
[0142]
In this embodiment, in order to solve this problem, the actuator elastic term invalidation signal generation block 20 and the adding means 19 for adding this to the acceleration / deceleration pulse are provided.
[0143]
The actuator elasticity term invalidation signal generation block 20 simulates a signal obtained by multiplying an actuator position variation when an acceleration / deceleration pulse is applied to an inertial actuator not supported by a spring by an elastic coefficient of the actuator spring. In the case of the embodiment, FIG. 13A is multiplied by the elastic coefficient k.
[0144]
FIG. 11 is a diagram for explaining the actuator elasticity term invalidation signal. FIG. 11B is an acceleration / deceleration pulse, FIG. 11A is an actuator position (estimated value) for an inertial actuator, and FIG. 11C is a simulation signal of a signal obtained by multiplying (A) by an elastic coefficient k.
[0145]
The simulated signal in FIG. 11C is expressed by a linear function whose slope is proportional to the elastic coefficient k. As a result, the force at the end of the deceleration pulse is kW (W is the interlayer distance = 40 μm).
[0146]
Strictly speaking, it is desirable to describe FIG. 11C as a quadratic function, but there is almost no error even if it is defined as a linear function, so there is no practical problem. The simulation signal shown in FIG. 11C is added to the acceleration / deceleration pulse as shown in FIG. 11B in the addition block 19 so that the restraint system actuator restrained by the spring is an inertia system actuator not restrained by the spring. The dynamic characteristics are the same.
[0147]
Here, it is assumed that the positive and negative waveform characteristics of the FES are equal.
In this case, if the absolute value of the acceleration pulse end threshold and the deceleration pulse start threshold are set equal, and the absolute value of the height (amplitude) of the acceleration pulse and deceleration pulse is set equal (however, the polarities are reversed) ), The position error after the movement can be made zero.
[0148]
Under the above conditions, since the above-described two conditions for realizing the focus jump stably are satisfied, a reliable focus jump can be realized.
[0149]
Embodiment 2. FIG.
In the first embodiment, the focus jump device / method effective when the positive and negative waveform characteristics of the FES are equal is described. However, the second embodiment can cope with the case where the FES detection characteristics are unbalanced. A focus jump apparatus and method will be described.
[0150]
FIG. 14 shows an FES when focus search is performed at a constant speed (an operation for detecting the focal position by moving the objective lens 2 at a constant speed in the disk arrangement direction). In the case shown in FIG. 14, the detection characteristics of the positive polarity and the negative polarity of FES are unbalanced.
[0151]
Thus, when the FES detection characteristics are unbalanced, the following problems occur.
[0152]
That is, in the method described in the first embodiment, the start timing of the deceleration pulse is generated based on the waveform in the region a or b in FIG. 14, and therefore the start timing of the deceleration pulse is due to the unbalance of the FES detection characteristics. It will be affected.
[0153]
Therefore, in such a case, it is guaranteed that the speed becomes zero after application of the deceleration pulse, but it cannot be guaranteed that the FES becomes zero.
[0154]
In order to solve this, in this embodiment, in order to correct the residual FES caused by the FES imbalance that occurs after the deceleration pulse is applied, after the acceleration / deceleration pulse application described in the first embodiment, The focus was pulled in after the correction pulse was applied and the FES was made zero.
[0155]
A block diagram of the second embodiment is shown in FIG. Reference numeral 15 denotes an acceleration / deceleration pulse application result determination block. Other configurations are the same as the configurations and operations already described in the first embodiment, and a description thereof will be omitted.
[0156]
The acceleration / deceleration pulse application result determination block 15 receives FES as an input and an application end timing indicating that the application of the deceleration pulse from the acceleration / deceleration pulse generation block 14 has ended.
[0157]
The acceleration / deceleration pulse application result determination block 15 causes the acceleration / deceleration pulse generation block 14 to generate a corrected acceleration / deceleration pulse generation command generated after application of the acceleration / deceleration pulse.
[0158]
The operations of the acceleration / deceleration pulse application result determination block 15 and the acceleration / deceleration pulse generation block 14 will be described with reference to FIGS.
[0159]
FIG. 16 is a diagram for explaining the operation of the present embodiment when the elastic term of the actuator is negligible.
[0160]
In FIG. 16, (A) is a focus actuator position, (B) is FES, and (C) is an acceleration / deceleration pulse, and each shows a time change during a focus jump.
[0161]
As can be seen from FIG. 16B, the example shown in FIG. 16 is a case where the output characteristics on the negative electrode side of the FES are large. When a focus jump command is received from the host controller, the acceleration / deceleration pulse generation block 14 generates an acceleration pulse.
[0162]
The end of the acceleration pulse is the time when the FES crosses the acceleration pulse end timing generation threshold. In this case, the acceleration pulse application time T0 is also measured (measured every time the acceleration pulse is applied).
[0163]
The acceleration / deceleration pulse has a zero period until the deceleration pulse start end timing generation threshold is crossed. Subsequently, a deceleration pulse is applied for a period of T0 from the time when the FES crosses the deceleration pulse start timing generation threshold.
[0164]
At this time, the amplitude of the deceleration pulse is set equal to the amplitude of the acceleration pulse (the polarity to be applied is opposite). Next, the FES at the end of the deceleration pulse application is observed, and the observed value is set as the residual FES (corresponding value FES = X0 in the figure).
[0165]
Subsequently, a corrected acceleration pulse is applied in a direction in which the residual FES decreases until the observed residual FES becomes 1/2 (that is, the value of FES is X0 / 2). At this time, the application time T1 of the correction acceleration pulse is measured (measured every time the correction acceleration pulse is applied).
[0166]
Immediately after the correction acceleration pulse is applied, a correction deceleration pulse having the same amplitude as the correction acceleration pulse in the direction opposite to the correction acceleration pulse is applied for the period T1 (the correction acceleration pulse and the correction deceleration pulse are collectively referred to as a correction acceleration / deceleration pulse).
[0167]
With the above configuration, the sum of impulses of the acceleration / deceleration pulse and the corrected acceleration / deceleration pulse is zero, so that the actuator speed at the end of the focus jump is guaranteed to be zero. Zero is guaranteed. As a result, the two conditions for stably realizing the focus jump are satisfied, so that a reliable focus jump is realized.
[0168]
In the above description, an example in which the elastic term of the actuator is small enough to be ignored (in the case of an inertial actuator) has been described. However, in the case where the elastic term of the actuator cannot be largely ignored (in the case of a restraint type actuator), FIG. By disabling the elastic term of the actuator using the actuator elastic term invalidating signal generation block 20 and the addition block 19, even the restraint type actuator can be handled in the same manner as the inertial type actuator.
[0169]
The behavior of the actuator elastic term invalidation signal in this case is shown in FIG. In this example, both the acceleration pulse and the correction acceleration pulse have the same polarity. In this case, during the period in which the acceleration pulse and the deceleration pulse are applied (referred to as a corrected acceleration / deceleration pulse application period), the actuator elasticity term invalidation signal increases proportionally with time as in the first embodiment.
[0170]
Further, the actuator elasticity term invalidation signal does not lose continuity even during the application of the corrected acceleration / deceleration pulse, and increases while maintaining the increase rate (see FIG. 18C).
[0171]
If the actuator elasticity term invalidation signal is set in this way, the actuator elasticity term invalidation signal results in simulating the actuator position (signal) in FIG. 18A, so that the actuator elasticity term is invalidated and corrected. It becomes possible to set the actuator speed after applying the control deceleration pulse to substantially zero.
[0172]
Therefore, with the above configuration, even when the elastic term of the actuator is large (constrained actuator), the actuator elastic term is invalidated, and the sum of the impulses of the acceleration / deceleration pulse and the corrected acceleration / deceleration pulse becomes zero. Therefore, it is guaranteed that the speed of the actuator becomes zero, and substantially zero is also guaranteed for FES. As a result, the two conditions for stably realizing the focus jump are satisfied, so that a reliable focus jump is realized.
[0173]
FIG. 17 is a diagram for explaining the operation in the case where the FES unbalance characteristic is opposite to that in FIG. 16, that is, the positive polarity is relatively larger than the negative polarity when the actuator elastic term is negligible. The operation is exactly the same as that described with reference to FIG. 16, and similarly to FIG. 16, the velocity zero and the FES are guaranteed to be substantially zero, and a stable focus jump can be realized.
[0174]
When the elastic term of the actuator is large, an actuator elastic term invalidation signal shown in FIG. The example shown in FIG. 19B is a case where the polarity of the acceleration pulse and the correction acceleration pulse are opposite.
[0175]
In this case, in the acceleration / deceleration pulse application period, the actuator elasticity term invalidation signal increases proportionally with time as in the first embodiment, and the invalidation signal has continuity during the corrected acceleration / deceleration pulse application period. The loss is not lost and the rate of increase is reversed (see FIG. 19C).
[0176]
If the actuator elastic term invalidation signal is set in this way, the actuator elastic term invalidation signal simulates the actuator position signal shown in FIG. 19A. Therefore, the elastic term of the actuator is invalidated and corrected deceleration is performed. The actuator speed after applying the pulse can be set to substantially zero.
[0177]
Therefore, with the above configuration, even when the actuator elastic term is large (restraint actuator), the actuator elastic term is invalidated, and the sum of the impulses of the acceleration / deceleration pulse and the corrected acceleration / deceleration pulse becomes zero. The actuator speed is guaranteed to be zero.
[0178]
Also, it is guaranteed that the FES is substantially zero. Therefore, since the two conditions for stably realizing the focus jump are satisfied, a reliable focus jump can be realized. In the description of each of the above embodiments, a DVD-DL having two recording layers has been described. However, a multi-layer disc having a recording layer (for example, having two or more translucent recording layers) is used. However, it can be similarly adopted, and is not necessarily limited to one applied to a disc having two recording layers.
[0179]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
[0180]
A focus moving device according to the present invention includes a condensing lens for condensing emitted light from a light source to form a condensing spot on any recording layer of a disc having a plurality of recording layers. An actuator that moves in the direction of arrangement, and the position of the condensing lens is moved by driving the actuator to move the position of the condensing spot from the position of one of the recording layers to the other recording layer. When displacing to the position of the layer, the impulse based on the drive signal for moving the position of the focused spot from the position of the one recording layer and the position of the focused spot are stopped on the other recording layer. Actuator drive means for outputting the drive signals so that the sum of impulses based on the drive signals for the operation becomes substantially zero. It is possible to zero can be the relative speed between the condenser lens and the other recording layer after movement to zero, it can be realized reliably focus movement stable.
[0181]
Also, the drive signal for moving the position of the focused spot from the position of one recording layer and the drive signal for stopping on the other recording layer, which are output from the actuator driving means, have absolute values of amplitude values. Since it is equal, the polarity is reversed and the application time is equal, the impulse based on the drive signal for moving from the position of one recording layer and the drive signal for stopping on the other recording layer The sum of impulses based on can be easily made substantially zero, and the stability of the focus after movement can be realized with certainty.
[0182]
The sum of the interpolation signal holding the focus control signal immediately before the movement of the condenser lens and the interlayer movement signal is used as a drive signal for moving the position of the condensed spot from the position of one recording layer. Therefore, it is possible to eliminate the influence of the surface shake when moving the focus, and to realize a stable and reliable focus movement.
[0183]
The interlayer movement signal is given by an acceleration / deceleration pulse corresponding to a distance between the position of one recording layer and another recording layer or a sum of the acceleration / deceleration pulse and an actuator elastic term invalidation signal. Therefore, the interlayer movement signal can be given in a simpler form.
[0184]
Further, since the corrected acceleration / deceleration pulse is applied after the acceleration / deceleration pulse is applied, stable and reliable focus movement can be realized even when the focus error signal characteristic is asymmetric.
[0185]
Further, since the actuator elastic term invalidation signal is a signal simulating the moving position of the condenser lens, more stable and more reliable focus movement can be realized.
[0186]
The focus moving method according to the present invention includes a condensing lens that condenses light emitted from a light source to form a condensing spot on any recording layer of a disc having a plurality of recording layers. The actuator for moving is driven to move in the direction in which the plurality of recording layers are arranged, and thereby the position of the condensing spot is set to be different from the position of one recording layer in the other recording layers. When shifting to a position, an impulse based on a drive signal for moving the position of the focused spot from the position of the one recording layer and a position for stopping the position of the focused spot on the other recording layer Since each of the drive signals is provided so that the sum of impulses based on the drive signals is substantially zero, the focus error signal after the movement can be made zero and the condensed light after the movement The relative speed between the lens and the other recording layers can be zero, it can be realized reliably focus movement stable.
[0187]
Also, when driving the actuator, the absolute value of the amplitude value of the drive signal for moving the position of the focused spot from the position of one recording layer and the drive signal for stopping on the other recording layer are equal. Since the polarity is opposite and the application time is equal, the impulse based on the drive signal for moving from the position of one recording layer and the drive signal for stopping on the other recording layer are used. The total sum of the impulses based on this can be easily made substantially zero, and the focus stability after the movement can be reliably realized.
[0188]
Further, the sum of the interpolation signal holding the focus control signal immediately before the movement of the condensing lens and the interlayer movement signal is used as a drive signal for moving the position of the condensing spot from the position of the one recording layer. Therefore, it is possible to eliminate the influence of the surface shake when moving the focus, and it is possible to realize a stable and reliable focus movement.
[0189]
The interlayer movement signal is given by an acceleration / deceleration pulse corresponding to a distance between the position of one recording layer and another recording layer or a sum of the acceleration / deceleration pulse and an actuator elastic term invalidation signal. Therefore, the interlayer movement signal can be given in a simpler form.
[0190]
Further, since the corrected acceleration / deceleration pulse is applied after the acceleration / deceleration pulse is applied, stable and reliable focus movement can be realized even when the focus error signal characteristic is asymmetric.
[0191]
Further, since the actuator elastic term invalidation signal is a signal simulating the moving position of the condenser lens, more stable and more reliable focus movement can be realized.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining a position error that occurs when a focus control signal is held with respect to a disc having surface deflection.
FIG. 2 is an explanatory diagram for explaining a position error that occurs when a focus control signal is held with respect to a disc having surface deflection.
FIG. 3 is an explanatory diagram for explaining a position error that occurs when a focus control signal is held with respect to a disk having surface deflection.
FIG. 4 is an explanatory diagram for explaining jump period versus maximum position error during zero-order hold;
FIG. 5 is an explanatory diagram for explaining a comparison between a jump period and a maximum position error according to a hold type.
FIG. 6 is an explanatory diagram for explaining jump period vs. maximum position error at the time of primary hold.
FIG. 7 is a block diagram showing a focus jump device in the first embodiment.
FIG. 8 is an explanatory diagram for explaining an operation of the focus actuator with respect to an applied pulse.
FIG. 9 is an explanatory diagram for explaining mechanical characteristics of an actuator.
FIG. 10 is an explanatory diagram for explaining the principle of an actuator elastic term invalidation signal.
FIG. 11 is an explanatory diagram for explaining an actuator elasticity term invalidation signal at the time of a focus jump.
FIG. 12 is an explanatory diagram for explaining a position error due to variation in actuator sensitivity when a fixed acceleration / deceleration pulse is applied.
FIG. 13 is an explanatory diagram for explaining the operation of the actuator when the acceleration / deceleration pulse application timing is set on the basis of the FES amplitude.
FIG. 14 is an explanatory diagram for explaining a case where FES detection characteristics are unbalanced.
FIG. 15 is a block diagram illustrating a focus jump device according to a second embodiment.
FIG. 16 is an explanatory diagram for explaining the operation of the second embodiment;
FIG. 17 is an explanatory diagram for explaining the operation of the second embodiment.
FIG. 18 is an explanatory diagram for explaining an actuator elastic term invalidation signal in the second embodiment.
FIG. 19 is an explanatory diagram for explaining an actuator elastic term invalidation signal in the second embodiment.
FIG. 20 is a block diagram showing a conventional focus jump device.
FIG. 21 is a block diagram showing a conventional focus jump device.
FIG. 22 is an explanatory diagram for explaining main technical problems of focus jump.
[Explanation of symbols]
3 focus actuator drive coil, 7 focus control loop switch, 8 phase compensation block, 9 changeover switch, 11 low-pass filter block, 12 hold block, 13 addition block, 14 acceleration / deceleration pulse generation block, 15 acceleration / deceleration pulse application result determination block, 19 Addition block, 20 Actuator elasticity term invalidation signal generation block.

Claims (8)

In an optical disc apparatus for reproducing information from a plurality of recording layers on which information is recorded,
  A focus error detection block for generating a focus error signal; and a phase compensation block for performing phase compensation on the focus error signal and outputting a focus control signal, and supplying the focus control signal to a focus actuator A focus control loop for focusing the light spot on the recording layer by controlling the position of the objective lens driven by the actuator so as to be in a predetermined position with respect to an arbitrary recording layer;
  A focus jump device that performs a focus jump that moves and focuses a light spot from one recording layer to another, and
  The focus jump device
  A focus control loop switch provided in a preceding stage of the phase compensation block;
  A low-pass filter block for removing a noise component of the focus control signal;
  A hold block for holding an output signal of the low-pass filter block and outputting an interpolation signal;
  An acceleration / deceleration pulse generation block for generating an acceleration / deceleration pulse;
  An actuator elasticity term invalidation signal generation block for generating an actuator elasticity term invalidation signal having a function of invalidating a mechanical elasticity term of the focus actuator;
  Adding means for adding the interpolation signal, the acceleration / deceleration pulse, and the actuator elasticity term invalidation signal to generate a focus jump signal;
  A focus control loop selection switch that is provided at a subsequent stage of the phase compensation block and selects the focus control signal or the focus jump signal output from the phase compensation block;
  In the focus control mode, the focus control loop selection switch selects the focus control signal and supplies it to the focus actuator;
  In the focus jump mode, the focus control soup switch is turned off, and the focus control loop selection switch selects the focus jump signal and supplies it to the focus actuator.
  The acceleration / deceleration pulse generation block outputs a rectangular wave generated based on the focus error signal to accelerate or decelerate the focus actuator, and has three modes of acceleration pulse, zero period, and deceleration pulse as output modes, The sum of impulses of the acceleration / deceleration pulses is set to zero,
  The actuator elastic term invalidation signal is a signal simulating the movement position of the focus actuator when the light spot moves from one recording layer to another recording layer.
  An optical disc device characterized by the above. 2. The actuator elastic term invalidation signal is given by a linear function proportional to a time from the start of movement from the one recording layer to another recording layer. An optical disk device according to the above. The acceleration / deceleration generation block performs mode transition in the order of the acceleration pulse, the zero period, and the deceleration pulse during a period in which the movement from the one recording layer to the other recording layer is performed, and after the deceleration pulse is applied, Observe the amplitude and polarity of the other recording layer focus error, apply a correction acceleration pulse for a period until the focus error is halved in the direction in which the focus error decreases, and then apply a correction deceleration pulse, 2. The optical disc apparatus according to claim 1, wherein the corrected deceleration pulse is set so that a sum of impulses with the corrected acceleration pulse becomes zero. The actuator elastic term invalidation signal is given by a linear function proportional to the time from the start of movement from the one recording layer to the other recording layer,
  In the generation period of the corrected acceleration pulse and the generation period of the corrected deceleration pulse, if the polarity of the acceleration pulse and that of the corrected acceleration pulse are opposite, the actuator elastic term invalidation signal The number is set so that the continuity is not lost and the rate of increase is reversed.
  The optical disc apparatus according to claim 3, wherein In reproducing information from an optical disc having a plurality of recording layers on which information is recorded,
  Focus control mode using a focus control loop that focuses the light spot on the recording layer by controlling the position of the objective lens to a predetermined position with respect to an arbitrary recording layer, and recording from one recording layer to another The focus jump mode that moves the light spot to the layer and focuses can be switched,
  In the focus jump mode, the focus control loop switch provided before the phase compensation block of the focus control loop is turned off, and the focus control loop selection switch provided after the phase compensation block is switched to switch the focus jump. Select the signal
  The focus jump signal has a function of invalidating an interpolation signal obtained by holding a signal obtained by removing noise from the focus control signal immediately before switching to the focus jump mode, and a mechanical elastic term of the focus actuator. It is given as the sum of actuator elasticity term invalidation signal and acceleration / deceleration pulse,
  The acceleration / deceleration pulse is a rectangular wave generated based on a focus error signal for accelerating or decelerating the focus actuator,
  The acceleration / deceleration pulse output mode includes three modes of acceleration pulse, zero period, and deceleration pulse, and the sum of impulses of the acceleration / deceleration pulse is set to zero,
  The actuator elastic term invalidation signal is a signal simulating the movement position of the focus actuator when the light spot moves from one recording layer to another recording layer.
  A focus moving method characterized by that. 6. The actuator elastic term invalidation signal is a linear function proportional to a time from the start of movement from the one recording layer to another recording layer. The focus movement method described in 1. The acceleration / deceleration generation block performs mode transition in the order of the acceleration pulse, the zero period, and the deceleration pulse during a period in which the movement from the one recording layer to the other recording layer is performed, and after the deceleration pulse is applied, Observe the focus error amplitude and polarity for other recording layers,
  Apply a correction acceleration pulse for a period until the focus error becomes 1/2 in the direction in which the focus error decreases, and then apply a correction deceleration pulse,
  The corrected deceleration pulse is set so that the sum of impulses with the corrected acceleration pulse is zero.
  The focus movement method according to claim 5, wherein: The actuator elastic term invalidation signal is given by a linear function proportional to the time from the start of movement from the one recording layer to the other recording layer,
  In the generation period of the corrected acceleration pulse and the generation period of the corrected deceleration pulse, if the polarities of the acceleration pulse and the corrected acceleration pulse are opposite, the actuator elastic term invalidation signal does not lose continuity, and The rate of increase is set to have a reverse polarity
  The focus movement method according to claim 7, wherein:

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