JP3889229B2 - Eddy current sensor and disk device using the eddy current sensor - Google Patents

Description

【００３７】
被検査体１１における交流磁界Ｈ（ｘ）は、被検査体１１に渦電流Ｉｅを発生させる。渦電流Ｉｅによって、被検査体１１の表面から垂直に磁気インピーダンス効果素子１５に向って、反磁界Ｈｄが発生する。ここで、渦電流Ｉｅによる磁気双極子が面垂直に現れると考えると、その磁極の強さはμＩｅに比例し、長さは被検査体１１の厚さｄが、渦電流Ｉｅの表皮深さδより薄い場合はｄ、厚い場合はδと考えられる。
ここで、渦電流Ｉｅの表皮深さδは、（数２）で表される。
【００３８】
【数２】

【００３９】
ただし、ρは被検査体１１の電気抵抗率、μは被検査体１１の面垂直透磁率、ωはコイル１２に与えられた交流電流Ｉ_ac1の角周波数である。
この磁気双極子の双極子モーメントｍは（数３）又は（数４）で表される。
【００４０】
【数３】

【００４１】
【数４】

【００４２】
磁気インピーダンス効果素子１５に印加される反磁界Ｈｄは（数５）または（数６）で表される。
【００４３】
【数５】

【００４４】
【数６】

【００４５】
ここで、Ｎはコイル１２の巻数、ａはコイル１２の半径である。
【００４６】
本発明では、（数５）または（数６）を基礎にして、渦電流センサと被検査体との距離ｘを求めるときには距離ｘのみを、被検査体の厚さｄを求めるときには厚さｄのみを、変数とするようにして渦電流センサを設計する。
【００４７】
また、非接触型トルクセンサや応力センサを構成するときには、μのみを変数とするようにして渦電流センサを設計する。
【００４８】
磁気インピーダンス効果素子とは、微小交流電流をワイヤー状、リボン状、または薄膜状に形成された磁性線に印加することによって生じるインピーダンスによる出力電圧が外部印加磁界によって変化することを基本原理としている素子である。
【００４９】
図２は、図１で示された渦電流センサに用いられた磁気インピーダンス効果素子１５の斜視図である。図２の磁気インピーダンス効果素子１５は、結晶化ガラス、Ａｌ₂Ｏ₃など絶縁性の非磁性材料からなる基板２１上に、軟磁性材料をスパッタ法や蒸着法などによって、薄膜形成することにより形成された感磁部２２、および感磁部２２の両端部にＣｕなどの導電性材料により形成された電極部２３，２３によって構成されている。感磁部２２は、一つの実施例において、略長方形状または線状にパターン形成されている。或いは、感磁部２２は、出力を大きくするためにＵ字型またはジグザグ状などにパターン形成されてもよい。
【００５０】
感磁部２２は、例えば、組成式がＦｅ_71.4Ａｌ_5.8Ｓｉ_13.1Ｈｆ_3.3Ｃ_4.5Ｒｕ_1.9（ａｔ％）で表される、ｂｃｃ−Ｆｅの結晶粒を主体とし、ｂｃｃ−Ｆｅの周囲にＨｆＣの結晶粒が存在する結晶粒径５〜３０ｎｍの微結晶軟磁性合金薄膜である。この軟磁性合金は、透磁率が高く、外部磁界に対する感度も良好であり、また耐環境性にも優れるものである。
【００５１】
なお、基板２１は結晶化ガラス、Ｓｉ、ＳｉＯ₂、Ａｌ₂Ｏ₃、ホウケイ酸ガラスなどで形成されている。
【００５２】
電極部２３はＣｕ、Ａｌ、Ｎｉ、Ｔｉ、Ｃｒなどの導電性材料からなる。
なお、本実施の形態では、感磁部２２は単層の軟磁性薄膜として形成されているが、感磁部２２は図２の形態に限るものではなく、例えば、絶縁層を介して複数層の軟磁性薄膜が積層されたものでもよい。また、感磁部２２は、軟磁性薄帯を含むものでもよい。
【００５３】
図２の磁気インピーダンス効果素子１５に電極部２３，２３から素子長手方向（Ｘ方向）に駆動交流電流Ｉ_ac2を与え、感磁部２２を素子幅方向（Ｙ方向）に励磁する。
【００５４】
この状態で、外部磁界Ｈｅｘが素子長手方向に印加されると、駆動交流電流Ｉ_ac2が感磁部２２の表面近くを流れようとする「表皮効果」が変化し、感磁部２２のインピーダンスが変化する。感磁部２２のインピーダンス変化を、電極部２３，２３間の電圧の変化として取り出す。
【００５５】
図２に加えて図１を参照して磁気インピーダンス効果素子１５の作用を説明する。コイル１２の内部において中心軸（巻き中心）Ｃａ上に、感磁部２２の中心が位置している。図１において、磁気インピーダンス効果素子１５に交流電源１６からＭＨｚ帯域の交流電流Ｉ_ac2を印加している状態で、磁気インピーダンス効果素子１５の感磁部２２の素子長さ方向に外部磁界Ｈｅｘが印加されると、感磁部２２の両端に素材固有のインピーダンスによる出力電圧Ｅｍｉが発生し、出力電圧Ｅｍｉの振幅が外部磁界Ｈｅｘの強度に対応して数１０％の範囲で変化する。出力電圧Ｅｍｉは、電極部２３，２３を介して取り出される。
【００５６】
本実施の形態の渦電流センサのように、磁気センサとして、感磁部２２の素子長手方向の延長線上に被検査体１１が位置するようにコイル１２の中心軸Ｃ上に設置された磁気インピーダンス効果素子を用いると、感磁部２２両端の電圧変化を測定するだけで、反磁界Ｈｄを測定することができるので、渦電流センサの小型化が非常に容易になる。
【００５７】
また、磁気インピーダンス効果素子１５は、１０^-5Ｏｅ程度の高分解能を有する微弱磁界センサが得られるという特性や、数ＭＨｚ以上の励磁が可能であるために数百ＭＨｚの高周波励磁を振幅変調のキャリアとして自由に使用でき、磁界センサとして使用するときに、遮断周波数を１０ＭＨｚ以上に設定することが容易であるという特性や、消費電力を１０ｍＷ以下にすることができるという特性を持つ。
【００５８】
磁気インピーダンス効果素子１５の磁界検出感度は、例えば磁気抵抗効果素子の数十倍〜数百倍と、高感度である。
【００５９】
なお、磁気センサとして磁気インピーダンス効果素子１５を用いて反磁界Ｈｄの大きさを測定するときには、コイル１２に与えられる渦電流発生用の交流電流Ｉ_ac1の周波数と、磁気インピーダンス効果素子１５に与えられる駆動交流電流Ｉ_ac2の周波数が異なることが必要である。
【００６０】
また、磁気インピーダンス効果素子における、外部磁界依存性のインピーダンス変化の直線性を向上させるために、磁気インピーダンス効果素子の感磁部に直流のバイアス磁界を与えることが有効である。
【００６１】
図３は、磁気インピーダンス効果素子の磁気インピーダンス効果特性を示すグラフである。
【００６２】
磁気インピーダンス効果素子を用いて感磁部に駆動交流電源から駆動交流電流を与えた状態で、外部磁界Ｈｅｘを、磁気インピーダンス効果素子の素子長手方向に印加する。印加した外部磁界Ｈｅｘの大きさを変化させつつ、出力電圧Ｅｍｉを測定すると図３のようなグラフが得られる。
【００６３】
図３の磁気インピーダンス効果特性を示すグラフは、外部磁界Ｈｅｘの大きさがＨｐ₊あるいはＨｐ_-であるときの出力電圧Ｅｍｉの値を示す点を頂点とする双峰形状をなしている。また、Ｈｐ₊とＨｐ_-の絶対値の大きさは、ほとんど等しい。
【００６４】
図３をみると、外部磁界Ｈｅｘの大きさがＨｐ₊、あるいはＨｐ_-に近づくにつれて、出力電圧Ｅｍｉの変化率が大きくなっている。すなわち、外部磁界Ｈｅｘの検出感度は、外部磁界Ｈｅｘの大きさがＨｐ₊あるいはＨｐ_-付近にあるときに良好になる。一方、外部磁界Ｈｅｘの大きさが０付近であるときの、出力電圧Ｅｍｉの変化率は小さく、外部磁界Ｈｅｘの検出感度が低い。
【００６５】
したがって、磁気インピーダンス効果素子を磁気センサとして用いるときには、外部磁界Ｈｅｘ＝０付近における外部磁界Ｈｅｘの検出感度を良好にするために、磁気インピーダンス効果素子の感磁部の素子長手方向に、例えば、大きさＨ_B1あるいは、Ｈ_B2の直流のバイアス磁界を印加して、磁気インピーダンス効果特性を示すグラフを、外部磁界Ｈｅｘの軸方向にシフトさせ、出力電圧の変化率が大きい部分が、外部磁界Ｈｅｘ＝０の軸上に来るようにすることが好ましい。
【００６６】
磁気インピーダンス効果素子の感磁部に直流のバイアス磁界を印加する方法として、本実施の形態では、図１のように、磁気インピーダンス効果素子１５の周囲に巻回されている、被検査体１１に渦電流Ｉｅを発生させる交流磁界Ｈを発生させるためのコイル１２に流されている交流電流Ｉ_ac1に、直流電流Ｉ_dcを重畳させることにより、直流のバイアス磁界Ｈ_Bを発生させて、磁気インピーダンス効果素子１５の感磁部の素子長手方向に印加することができる。
【００６７】
このように、本発明では、被検査体１１に渦電流Ｉｅを発生させるためのコイルと、磁気インピーダンス効果素子１５の感磁部に直流バイアス磁界をかけるためのコイルを一つのコイル１２で兼用することができるので、渦電流センサの小型化が可能になる。
【００６８】
磁気インピーダンス効果素子の感磁部には、前述のような、軟磁性薄膜を用いることが好ましいが、Ｃｏ−Ｆｅ−Ｓｉ−Ｂ系のアモルファスのワイヤーを用いてもよい。しかし、アモルファスワイヤーは、交流電流を流すための配線材を接続するための電極部の形成が困難であること、数十μｍの径のワイヤーは、曲がりやすく、素子の位置合わせが困難であること、または、壊れやすいことといった問題点もある。
【００６９】
磁気インピーダンス効果素子の感磁部を、軟磁性薄膜や軟磁性薄帯で構成すると、前記感磁部を任意の厚さや幅、長さで形成することを可能にし、上記の問題点を解決することができるので好ましい。
【００７０】
磁気インピーダンス効果素子１５の感磁部２２は、上述した軟磁性材料以外の軟磁性材料を用いて形成することができる。
【００７１】
ただし、磁気インピーダンス効果素子１５の感磁部２２を、１ＭＨｚ〜数百ＭＨｚの高周波領域における透磁率μが高く、磁歪定数λが小さい軟磁気特性を備えた強磁性体の薄膜を有するものとして形成するために、感磁部２２は以下に示すような微結晶軟磁性合金薄膜を有することが好ましい。
【００７２】
１．組成式が、Ｔ_100-d-e-f-gＸ_dＭ_eＺ_fＱ_gで表され、ｂｃｃ−Ｆｅ、ｂｃｃ−ＦｅＣｏ、ｂｃｃ−Ｃｏの１種または２種以上の結晶粒と元素Ｍの炭化物もしくは窒化物の結晶粒を主体とした平均結晶粒径３０ｎｍ以下の微結晶軟磁性合金薄膜。
【００７３】
ただし、元素Ｔは、Ｆｅ、Ｃｏのうちどちらか一方あるいは両方を含む元素であり、元素Ｘは、Ｓｉ、Ａｌのうちどちらか一方あるいは両方を含む元素であり、元素Ｍは、Ｔｉ、Ｚｒ、Ｈｆ，Ｖ，Ｎｂ，Ｔａ，Ｍｏ，Ｗから選ばれる１種または２種以上の元素であり、元素Ｚは、Ｃ、Ｎのうちどちらか一方あるいは両方を含む元素であり、Ｑは、Ｃｒ，Ｒｅ，Ｒｕ，Ｒｈ，Ｎｉ，Ｐｄ，Ｐｔ，Ａｕから選ばれる１種または２種以上の元素であり、ｄ、ｅ、ｆ、ｇはａｔ％で、０≦ｄ≦２５、１≦ｅ≦１０、０．５≦ｆ≦１５、０≦ｇ≦１０の関係を満足するもの。
【００７４】
２．組成式が、Ｔ_{100-p-q-e-f-g}Ｓｉ_pＡｌ_qＭ_eＺ_fＱ_gで表され、ｂｃｃ−Ｆｅ、ｂｃｃ−ＦｅＣｏ、ｂｃｃ−Ｃｏの１種または２種以上の結晶粒と元素Ｍの炭化物もしくは窒化物の結晶粒を主体とした平均結晶粒径３０ｎｍ以下の微結晶軟磁性合金薄膜。
【００７５】
ただし、元素Ｔは、Ｆｅ、Ｃｏのうちどちらか一方あるいは両方を含む元素であり、元素Ｍは、Ｔｉ、Ｚｒ、Ｈｆ，Ｖ，Ｎｂ，Ｔａ，Ｍｏ，Ｗから選ばれる１種または２種以上の元素であり、元素Ｚは、Ｃ、Ｎのうちどちらか一方あるいは両方を含む元素であり、Ｑは、Ｃｒ，Ｒｅ，Ｒｕ，Ｒｈ，Ｎｉ，Ｐｄ，Ｐｔ，Ａｕから選ばれる１種または２種以上の元素であり、ｐ、ｑ、ｅ、ｆ、ｇはａｔ％で、８≦ｐ≦１５、０≦ｑ≦１０、１≦ｅ≦１０、０．５≦ｆ≦１５、０≦ｇ≦１０の関係を満足するもの。
【００７６】
これらの軟磁性合金薄膜はスパッタ法や蒸着法などの薄膜形成手段によって好ましく形成されるものであり、等方的でかつ軟磁気特性の良好な軟磁性合金薄膜を提供できるので、磁気インピーダンス効果素子の小型化や高性能化を容易にすることができる。
【００７７】
ただし、本発明に用いる磁気インピーダンス効果素子の感磁部をここに示した組成以外の軟磁性合金薄膜を用いて形成してもかまわない。
【００７８】
磁気インピーダンス効果素子は、薄膜プロセスを用いて製造することができるので、磁気センサの大きさを非常に小さくできる。従って、被検査体表面の狭い範囲で発生する反磁界を正確に測定することができ、渦電流センサと被検査体のある１点との距離、被検査体の厚さ、または被検査体の透磁率などをピンポイントで正確に測定することが可能になる。
【００７９】
なお、磁気センサは、必ずしも、図１のコイル１２の中心軸Ｃａ上に位置しなければならないものではなく、コイル１２から所定位置離れた場所に設置されてもかまわない。
【００８０】
たとえば、図１に示すように、磁気インピーダンス効果素子１７をコイル１２から所定位置離れた場所に設置したとする。図１では、磁気インピーダンス効果素子１７の配線は省略している。
【００８１】
磁気インピーダンス効果素子１７は、コイル１２に流されるコイル１２の中心軸Ｃａから被検査体１１表面におろされた垂線（中心軸Ｃａの同軸線Ｃ）との交点Ｃ１、すなわち交流電流Ｉ_ac1によって被検査体１１に誘起された交流磁界Ｈによって発生した渦電流Ｉｅの中心からの距離がｒで、磁気インピーダンス効果素子１７と交点Ｃ１を結ぶ直線と同軸線Ｃとの角度がθとなる位置に設置されている。
【００８２】
ただし、一つの磁気インピーダンス効果素子１７からの出力のみで、距離ｒと角度θのそれぞれを正確に検出することはできない。したがって、検出誤差を小さくするためには、角度θはできる限り小さいことが好ましい。最も好ましいのは、θ＝０度、すなわち磁気インピーダンス効果素子がコイル１２の中心軸Ｃａ上又は同軸線Ｃ上に設置されることである。
【００８３】
磁気インピーダンス効果素子などの磁気センサが、コイル１２の中心軸Ｃａまたは同軸線Ｃ上に設置されると、すなわち、前記コイルの巻き中心と前記磁気センサの検出部の中心とが同一線上に位置していると、渦電流センサと被検査体のある１点との距離、被検査体の厚さ、または被検査体の透磁率などを正確に測定することが容易になるので好ましい。
【００８４】
このとき、磁気センサが、図１の磁気インピーダンス効果素子１５のように、コイル１２内部の中心軸Ｃａ上に設置されていると、コイル１２から被検査体１１までの距離と被検査体１１から磁気センサまでの距離が等しくなるので、検出された反磁界Ｈｄの大きさから、渦電流センサと被検査体のある１点との距離、被検査体の厚さなどを求めるための計算が簡易化されるのでより好ましい。
【００８５】
または、２つ以上の渦電流センサを用いて、距離ｒと角度θを検出してもよい。
【００８６】
本発明では、交流磁界Ｈを発生させるコイル１２と、被検査体１１からの反磁界Ｈｄを直接検出する磁気センサとが独立している。
【００８７】
従って、被検査体１１の浅い表面を検査する場合に、渦電流Ｉｅの表皮深さδを浅くするために交流電流Ｉ_ac1の周波数を数ＫＨｚ〜数十ＭＨｚ帯の高周波領域にしたときでも、コイル１２の浮遊容量による変位電流のため、検出精度が低下するという問題を低減することができる。
【００８９】
図４（参考例）では、交流電源１３から交流電流Ｉａｃが与えられて交流磁界Ｈを誘起し、この交流磁界Ｈによって金属板である被検査体１１に渦電流Ｉｅを発生させる交流磁界発生手段であるコイル１２と、磁気センサである磁気インピーダンス効果素子１５とが、被検査体１１を介して対向している。なお、図１では、コイル１２の中心軸Ｃａを点線で示し、コイル１２の中心軸Ｃａの同軸線Ｃを一点斜線で表している。
【００９０】
図４に示される本発明の一つの実施の形態においては、コイル１２は絶縁材料で被覆された銅線を所定の巻数にて巻回して形成されたものであり、磁気インピーダンス効果素子１５は、コイル１２の中心軸Ｃａの同軸線Ｃ上に設置されている。すなわち、コイル１２の中心軸Ｃａの同軸線Ｃ上に、感磁部２２の中心が位置している。交流電源１３からコイル１２に交流電流Ｉ_ac1が与えられて、交流磁界Ｈが誘起される。被検査体１１における交流磁界Ｈは、被検査体１１に渦電流Ｉｅを発生させる。渦電流Ｉｅによって、被検査体１１の表面から垂直に磁気インピーダンス効果素子１５に向って、反磁界Ｈｄが発生する。磁気インピーダンス効果素子１５に印加される反磁界Ｈｄの大きさを検出し、反磁界Ｈｄの大きさから磁気インピーダンス効果素子１５と被検査体１１との距離、被検査体１１の厚さ、または被検査体１１の透磁率などを求める。
【００９１】
図４の渦電流センサにおいても、磁気インピーダンス効果素子１５に交流電源１６からＭＨｚ帯域の交流電流Ｉ_ac2を印加している状態で、磁気インピーダンス効果素子１５の感磁部（図４では図示せず）の素子長さ方向に反磁界Ｈｄが印加されると、感磁部両端のインピーダンスが変化する。感磁部両端のインピーダンス変化を、感磁部両端に取付けられた電極（図４では図示せず）を介して出力電圧Ｅｍｉの変化として取り出し、出力電圧Ｅｍｉの変化から磁気インピーダンス効果素子１５に印加された反磁界Ｈｄの大きさを求める。
【００９２】
なお、磁気センサとして磁気インピーダンス効果素子１５を用いて反磁界Ｈｄの大きさを測定するときには、コイル１２に与えられる渦電流発生用の交流電流Ｉ_ac1の周波数と、磁気インピーダンス効果素子１５に与えられる駆動交流電流Ｉ_ac2の周波数が異なることが必要である。
【００９３】
前述のように、磁気インピーダンス効果素子１５の感磁部には、素子長手方向の直流のバイアス磁界を印加することが好ましい。本実施の形態では、図４のように、磁気インピーダンス効果素子１５の周囲に巻回されているコイル１９に直流電源１８から直流電流Ｉｄｃを流すことにより、直流のバイアス磁界を発生させて、磁気インピーダンス効果素子１５の感磁部の素子長手方向に印加することができる。
【００９４】
図５は、本発明のディスク装置の実施の形態を示す側面図であり、光ピックアップ装置に搭載された光ヘッドがディスクの最外周に位置している状態を示している。
【００９５】
光ピックアップ装置３１には、キャリッジ３２上にＤＶＤ用の光ヘッド３３が設けられている。なお、図５には図示しないがキャリッジ３２上にはＣＤ用の光ヘッドも設けられている。キャリッジ３２は、光ディスクＤの径方向へ延びる駆動軸３４とガイドバー（図示せず）によって光ディスクＤの径方向に移動自在に支持されている。駆動軸３４とガイドバーは平行に設けられ、駆動軸３４の両端とガイドバーの両端は、支持体３５ａ，３５ｂによって支持されている。支持体３５ａは光ディスクＤの回転中心よりもＸ軸方向でキャリッジ３２と反対側へずらして設けられ、支持体３５ｂは光ディスクＤの外周縁部近傍に設けられている。また支持体３５ａ，３５ｂは、光ピックアップ装置３１の図示しない機構シャーシ上に固定されている。
【００９６】
前記駆動軸３４の一端にはスレッドモータ３６が設けられており、スレッドモータ３６の回転駆動力によってキャリッジ３２がディスクＤの半径方向へ移動させられる。このとき光ヘッド３３は、光ディスクＤの内周と外周との間を前記ガイドバーに支持されて光ディスクＤに対して水平状態を保ちながら移動させられる。
【００９７】
支持体３５ａには、光ディスクＤの回転中心側へ突出する固定部３７が設けられ、この固定部３７には光ディスクＤを回転駆動させるためのスピンドルモータ３８が設けられる。スピンドルモータ３８には、垂直上方へモータ軸３９が突出して設けられており、このモータ軸３９の先端に光ディスクＤを載置するターンテーブル４０が設けられる。
【００９８】
これにより、光ピックアップ装置３１にＤＶＤ用の光ディスクが装填され、ターンテーブル４０に載置されると、光ヘッド３３側が作動し、またＣＤ用の光ディスクが装填され、ターンテーブル４０に載置されると、前述した図示しないＣＤ用の光ヘッド側が作動する。
【００９９】
なお、それぞれのＤＶＤ用の光ヘッド３３とＣＤ用の光ヘッドには、それぞれの対物レンズをディスク面に平行な方向へ微動させるトラッキング補正手段と、前記対物レンズをディスク面と垂直な方向へ微動させるフォーカシング補正手段が設けられている。
【０１００】
図５に示された本発明の一つの実施の形態では、図１に示された直流電流Ｉｄｃが重畳された交流電流Ｉ_ac1が与えられるコイル１２とコイル１２の中心軸Ｃａ上に設置された磁気インピーダンス効果素子１５を有する渦電流センサ１０ａ、１０ｂを、ディスクＤの記録面Ｄ１に対向させ、かつディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置している。なお、本実施の形態では、渦電流センサ１０ａ、１０ｂは光ヘッド３３上に搭載されている。
【０１０１】
ディスクＤには、レーザ光を反射するために金属層が形成されている、この金属層は例えばＡｌを用いて厚さ１００〜２００ｎｍで形成されている。従って、ディスクＤに、渦電流センサ１０ａ、１０ｂから交流磁界が与えられると、前記金属層に渦電流が発生し、さらに反磁界が生じる。すなわち、渦電流センサ１０ａ、１０ｂを用いて、渦電流センサ１０ａとディスクＤとの距離Ｚ_１及び渦電流センサ１０ｂとディスクＤとの距離Ｚ_２とをそれぞれ測定することができる。さらに距離Ｚ_１と距離Ｚ_２の差の変化を検出することにより、記録中、又は再生中のディスクＤの半径方向の傾きを検出することができる。
【０１０２】
また、渦電流センサは、ディスクＤの記録面Ｄ１側に対向する位置ではなく、図５に示される渦電流センサ１０ｃ、１０ｄのように、ディスクＤの記録面Ｄ１の反対面Ｄ２に対向させられ、かつディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置されてもよい。なお、本実施の形態では、渦電流センサ１０ｃ、１０ｄはそれぞれ固定支持部４１及び４２を介して図示しない機構シャーシ上に固定されている。渦電流センサ１０ｃ、１０ｄを用いて、渦電流センサ１０ｃとディスクＤとの距離Ｚ_３及び渦電流センサ１０ｄとディスクＤとの距離Ｚ_４とをそれぞれ測定することができる。距離Ｚ_３と距離Ｚ_４の差の変化を検出することにより、記録中、又は再生中のディスクＤの傾きを検出することができる。
【０１０３】
渦電流センサ１０ｃ、渦電流センサ１０ｄは、それぞれディスクＤの最外周部付近、最内周部付近に設置されている。渦電流センサ１０ｃと渦電流センサ１０ｄとのディスクＤの半径方向の距離が大きくなると、ディスクＤの半径方向の傾きを精度よく検出できるようになる。
【０１０４】
図５では、渦電流センサをディスクＤの記録面Ｄ１側に２個設けているが、３個以上の渦電流センサが、ディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置されてもよい。また、渦電流センサをディスクＤの反対面Ｄ２側に３個以上の渦電流センサが、ディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置されてもよい。
【０１０５】
また、渦電流センサは、キャリッジ３２上に設置されてもよいし、また、キャリッジ３２の移動を妨げない場所であれば、ピックアップ装置と接触しない任意の場所においてディスクＤに対向するように固定されていてもよい。
【０１０６】
また、複数個の渦電流センサの全てをディスクＤの記録面Ｄ１側に対向させて設置してもよいし、また、複数個の渦電流センサの全てをディスクＤの反対面Ｄ２側に対向させて設置してもよい。
【０１０７】
或いは、複数個の渦電流センサのうち一部をディスクＤの記録面Ｄ１側に対向させて設置し、残りの渦電流センサをディスクＤの反対面Ｄ２側に対向させて設置してもよい。
【０１０８】
図５では、渦電流センサ１０ａ及び１０ｂ、又は渦電流センサ１０ｃ及び１０ｄは、ディスクＤの記録面Ｄ１又は反対面Ｄ２に対向させられ、かつディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置されている。
【０１０９】
本発明では、渦電流センサを、ディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置するだけでなく、図６に示される渦電流センサ１０ｅ及び１０ｆのように、ディスクＤのタンジェンシャル方向（Ｙ方向）に所定の距離を開けて設置することができる。渦電流センサ１０ｅとディスクＤとの距離及び渦電流センサ１０ｆとディスクＤとの距離をそれぞれ測定し、その差の変化を検出することにより、記録中、又は再生中のディスクＤのタンジェンシャル方向の傾きを検出することができる。
【０１１０】
渦電流センサ１０ｅ及び１０ｆは、キャリッジ３２の移動を妨げない場所であれば、任意の場所においてディスクＤに対向するように固定されてよい。
【０１１１】
また、ディスクＤの半径方向（Ｘ方向）に所定の距離を開けて設置された渦電流センサ１０ｃ及び１０ｄによって検出されたディスクＤの半径方向の傾きの値と、渦電流センサ１０ｅ及び１０ｆによって検出されたディスクＤのタンジェンシャル方向の傾きの値とをベクトル的に組み合わせることによってディスクＤの全ての方向の傾きを検出することができる。
【０１１２】
また、図５において、渦電流センサ１０ａ、１０ｂ、１０ｃ、または１０ｄを設置する位置を、光ヘッド３３に対して所定の位置とすると、渦電流センサ１０ａ、１０ｂ、１０ｃ、又は１０ｄとディスクＤとの距離を測定することによって、ディスクＤと光ヘッド３３との距離Ｚ₅を検出することができる。
【０１１３】
本実施の形態のディスク装置では、磁気インピーダンス効果素子を用いた渦電流センサ１０ａ及び１０ｂ、１０ｃ及び１０ｄ、又は１０ｅ及び１０ｆによって、ディスクＤとの距離を検出し、さらにディスクＤの傾きを検出するので、従来のように光学的手段を用いてディスクＤの傾きを検出するものに比べると、装置の組付けに高い精度が要求されず、また、調整工程も、基本的に、基準となる距離を測定したときの磁気インピーダンス効果素子の出力強度を調節するだけでよい。
【０１１４】
従って、本発明では、製造工程を簡略化できる。また、ディスク装置が故障した時でも、本発明では、調整工程が簡略化されているため、修理が容易になるという利点も有する。
【０１１５】
また、渦電流センサとディスクＤとの距離を測るときに、ディスクＤに交流磁界を印加して渦電流を発生させ、反磁界を測定するという非常に単純な工程しか含まれないので、ディスクＤとの距離及びディスクＤの傾きの測定精度が上がる。
【０１１６】
また光ヘッドは、上記のように２つに限られるものではなく、光ヘッド３３のみを１つだけ搭載してもよくあるいは３つ以上搭載してもよい。
【０１１７】
本実施の形態では、本発明の一例として、ＤＶＤ用光ヘッドとＣＤ用光ヘッドとを搭載しているディスク装置について説明した。ＣＤ用光ヘッドには、再生専用タイプのＣＤ−ＲＯＭ用再生ヘッド、追記タイプ又は書換タイプのＣＤ−Ｒ又はＣＤ−ＲＷ用再生及び記録ヘッドなど、ＤＶＤ用光ヘッドには、再生専用タイプのＤＶＤ−ＲＯＭ用再生ヘッド、追記タイプ又は書換タイプのＤＶＤ−Ｒ又はＤＶＤ−ＲＡＭ用再生及び記録ヘッドなど様々なタイプのものがあり、これらを適宜組合わせて構成することができる。
【０１１８】
またＣＤやＤＶＤに対応したディスク装置に限らず、ＭＯ、磁気ディスクに対応したディスク装置など、金属層や磁性層などの導電体層を有するディスク型記録媒体に対応したディスク装置に本発明を適用してもよい。
【０１１９】
なお、図１や図４に示された実施の形態の渦電流センサでは、磁気インピーダンス効果素子１２の感磁部の素子長手方向に印加する直流のバイアス磁界として、コイル１２に流される交流電流Ｉ_ac1に重畳された直流電流Ｉ_dcによって誘起される直流磁界や、コイル１９に流された直流電流Ｉ_dcによって誘起された直流磁界を用いている。
【０１２０】
このほかに、図７（参考例）に示されるように、磁気インピーダンス効果素子１５の感磁部の素子長手方向にバイアス磁界Ｈ_Ｂが印加されるように、硬磁性材料からなるハードバイアス用磁石５０，５０を設置してもよい。
【０１２１】
なお、ディスク装置の光ヘッド３３に設けられているトラッキング補正手段と、フォーカシング補正手段は、例えば、巻線コイルの内部或いは周辺に硬磁性体が設けられ、巻線コイルに電流を流して、巻線コイルと硬磁性体の相対位置を変化させるフォーカスアクチュエータである。上述した磁気インピーダンス効果素子のハードバイアスとして、フォーカスアクチュエータに用いられている硬磁性体を用いることもできる。
【０１２２】
【実施例】
本発明の一つの実施例として、図１に示された渦電流センサ１０を形成し、渦電流センサ１０の磁気インピーダンス効果素子１５と、被検査体１１として用いたＤＶＤとの距離を変化させたときの磁気インピーダンス効果素子１５の出力電圧Ｅｍｉの変化量を調べた。
【０１２３】
コイル１２の半径ａをａ＝０．７ｍｍ、コイル巻数ＮをＮ＝１２００ターン、交流電源１３が供給する交流電流Ｉ_ac1の大きさをＩ_ac1＝２．２ｍＡ、交流電流Ｉ_ac1の周波数ｆをｆ＝４ＭＨｚとした。また、ＤＶＤの導電体層であるＡｌ層の厚さｄはｄ＝０．１５μｍであり、Ａｌ層の透磁率μをμ＝４π×１０^-7（＝μ₀）、電気抵抗率ρをρ＝２．５×１０^-6Ω・ｍとした。
【０１２４】
初期状態として、渦電流センサ１０の磁気インピーダンス効果素子１５とＤＶＤのＡｌ層までの基準距離を１．６５ｍｍとした。ＤＶＤでは保護層の厚さが０．６ｍｍであるので、磁気インピーダンス効果素子からＡｌ層までの距離が１．６５ｍｍであるとき、磁気インピーダンス効果素子とＤＶＤの保護層表面までの距離は１．０５ｍｍである。
【０１２５】
磁気インピーダンス効果素子１５とＤＶＤのＡｌ層との距離ｘを基準距離から変化させたときの、磁気インピーダンス効果素子１５の出力電圧Ｅｍｉの変化を調べた。結果を図８に示す。
【０１２６】
ＤＶＤの規格では、そり角で±０．４°の許容範囲が与えられる。ＤＶＤの半径は６０ｍｍなので、ＤＶＤをターンテーブルに設置したとき、ＤＶＤの中心と最外周の高さ位置の差は、最大で約６０×ｔａｎ０．４°＝０．４（ｍｍ）である。従って、渦電流センサをＤＶＤの傾きを検出するために用いるときには、基準距離から±０．４ｍｍの範囲の距離の変化を検出できればよいと考えられる。
【０１２７】
図８から、磁気インピーダンス効果素子１５とＤＶＤのＡｌ層との距離が、基準距離１．６５ｍｍから±０．４ｍｍの範囲では、磁気インピーダンス効果素子の出力電圧の変化量が求められると、磁気インピーダンス効果素子１５とＤＶＤのＡｌ層との距離の値が一義的に求められる。すなわち、本発明の渦電流センサを用いて、ＤＶＤなどのディスク型記録媒体の記録時、又は再生時にディスク型記録媒体の傾きを検出するディスク装置を構成することができることがわかる。
【０１２８】
実際のディスク装置において、磁気インピーダンス効果素子とＤＶＤのＡｌ層との距離の値を求めるときには、図８のグラフに示されたような、磁気インピーダンス効果素子とＤＶＤのＡｌ層との距離と磁気インピーダンス効果素子の出力電圧の変化量との関係をテーブル化したものを用いてもよいし、磁気インピーダンス効果素子の出力電圧の変化量から反磁界の大きさを求め、前述した（数５）または（数６）を用いて求める距離を算出するなどの方法がある。
【０１２９】
図９は渦電流センサを用いたディスク装置に搭載される第１の光ピックアップ装置の実施の形態を示す斜視図、図１０は図９に示す第１の光ピックアップ装置の平面図、図１１は第１の光ピックアップ装置の動作を示しており、図９の矢視ＡＡ方向の正面図、図１２は第２の光ピックアップ装置の実施の形態を示す斜視図であり、図５のディスク装置をより具体的に示すものである。図１３は第２の光ピックアップ装置の動作を示しており、図１２の矢視ＢＢ方向の断面図である。
【０１３０】
図９ないし図１１に示す第１の光ピックアップ装置６０では、前記キャリッジ３２に設けられた支持ベース６１上に前記光ヘッド３３が設けられている。前記支持ベース６１は、前記キャリッジ３２とともにターンテーブル４０に載置された光ディスクＤの半径方向（図９ではＸ１−Ｘ２方向）に自在に移動できるように支持されている。なお、図９においては図示Ｚ１方向に光ディスクＤの記録面が位置する関係となっている。
【０１３１】
前記支持ベース６１上には、固定部側となる基台６２が固設されている。前記基台６２には、図示Ｙ１−Ｙ２方向に平行に延びる４本の弾性支持部材６３，６３，６３，６３が片持ちはり状態で固定されており、その先端にはレンズ６４を有する光学支持体６５が設けられている。すなわち、前記各弾性支持部材６３は、主として図示Ｘ方向（ディスクの半径方向）及びＺ方向（フォーカシング方向）に弾性変形可能であり、光学支持体６５は各弾性支持部材６３によって弾性的に支持されている。よって、光学支持体６５は、ディスクの半径方向及びフォーカシング方向に可動することが可能である。
【０１３２】
前記基台６２と光学支持体６５との間には、２つのボビン６６，６７が図示Ｘ方向に並設されている。ボビン６６，６７の周囲（図示Ｚ軸回り）には、被覆銅線を所定の巻数にて巻回したフォーカス用の駆動コイル６８，６９が形成されている。またボビン６６，６７の図示Ｙ２側の側面には、所定の巻数で巻回されたトラッキング用の駆動コイル７０，７１が固設されている。なお、前記ボビン６６，６７は、支持ベース６１に固設されており固定部側を成している。
【０１３３】
前記光学支持体６５の図示Ｙ１側の面には、ヨーク部材７２，７３が固設されている。したがって、光学支持体６５は、前記ヨーク部材７２，７３とともに図示Ｘ方向およびＹ方向に可動することができ、ＭＭ（movinng Magnet）方式のピックアップ装置として駆動する。
【０１３４】
前記ヨーク部材７２，７３は、例えば鉄などからなる薄板状の磁性体を折り曲げ又は接合などの手段により、４面を囲うように設けられた磁性体によって磁気回路（閉磁路）が形成されている。前記ヨーク部材７２，７３を形成する４面の磁性体うち、図示Ｚ方向に延びる一方の磁性体（図示Ｙ１側の磁性体）７２ａ，７３ａが、前記フォーカス用の駆動コイル６８，６９の内部に貫通させられており、且つその内面には永久磁石７４，７５が固設されている。
【０１３５】
前記永久磁石７４，７５の図示Ｙ２側の磁極をＮ極とすると、このＮ極と、前記前記ヨーク部材の一方の磁性体７２ａ，７３ａと対向する他方の磁性体７２ｂ，７３ｂとの間がギャップであり、このギャップを介して磁気回路（磁路）が形成されている。そして、前記Ｎ極から生じた磁束は、前記ギャップ内を通り前記他方の磁性体７２ｂ，７３ｂからその内部に入り込み、キャリッジ３２と平行に延びる上部側の磁性体および下部側の磁性体の内部を通ってヨーク部材７２，７３の前記一方の磁性体７２ａ，７３ａに達し、ここから永久磁石７４，７５のＳ極に戻るという経路をたどる。
【０１３６】
前記トラッキング用の駆動コイル７０，７１は、駆動コイル７０，７１を形成する４辺のうち、ともにＺ方向に延びる内側の一辺７０ａ，７１ａのみが前記ヨーク部材７２，７３の内部に位置し、これに対向する外側の一辺７０ｂ，７１ｂは前記ヨーク部材７２，７３の外部に位置するように配置されている。
【０１３７】
上記光ヘッド３３では、ギャップ内を通る磁束が、フォーカス用の駆動コイル６８，６９ではボビン６６，６７の図示Ｙ２側の側面の被覆導線のみを鎖交し、トラッキング用の駆動コイル７０，７１では、前記内側の一辺７０ａ，７１ａ側の被覆導線のみを鎖交するように設定されている。
【０１３８】
また前記支持ベース６１上には、上述の渦電流センサ１０ａ，１０ｂが前記レンズ６４を挟みその両側に設けられている。そして、渦電流センサ１０ａと渦電流センサ１０ｂとを結ぶ仮想線Ｌ１−Ｌ１上にレンズ６４の光軸Ｏ−Ｏが位置するように設定されている。
【０１３９】
なお、渦電流センサ１０ａ，１０ｂの近傍には、上記図１や図４に示すような磁気インピーダンス効果素子１５の感磁部の素子長手方向に直流バイアス磁界を与えるコイル１２やコイル１９などが設けられていたり、あるいは図９に示すように磁気インピーダンス効果素子１５の感磁部の素子長手方向にバイアス磁界Ｈ_Bが印加するハードバイアス用磁石５０，５０が設置されている。
【０１４０】
第１の光ピックアップ装置６０では、前記渦電流センサ１０ａ，１０ｂにより、レンズ６４と記録中、又は再生中のディスクＤとの距離（ディスクＤと光ヘッド３３との距離Ｚ_５）が測定される。
【０１４１】
各弾性支持部材６３には、光学支持体６５およびヨーク部材７２，７３の重量が作用しているため、非駆動状態においては各弾性支持部材６３の先端が図示Ｚ２方向に撓んだ状態にある。よって、予めディスクＤの傾き角度に対する渦電流センサ１０ａ，１０ｂの出力差と、フォーカス用の駆動コイル６８，６９に流す電流の差に対するレンズ６４の光軸Ｏ−Ｏの傾き角度とを調べ、初期状態としておくことが好ましい。
【０１４２】
ディスクＤに面振れが生じて傾いた場合には、前記渦電流センサ１０ａ，１０ｂからは、その傾き角度に比例した出力電圧がそれぞれ出力され、この間の差電圧を得ることができる。よって、ディスクＤの傾きは、前記初期状態からの変化量として把握することができ、フォーカス用の駆動コイル６８，６９には前記変化量に比例した電流が与えられる。
【０１４３】
これにより、磁界中のフォーカス用の駆動コイル６８，６９の被覆導線には、フレミングの左手の法則に従う力が、前記駆動電流の向きに応じて図示Ｚ１又はＺ２方向に生じる。
【０１４４】
そして、図１１に示すようにフォーカス用の駆動コイル６８，６９に異なる向きの電流を与えると、例えば一方の駆動コイル６８（ヨーク部材７２）側では、図示Ｚ１方向の力が働き、他方の駆動コイル６９（ヨーク部材７３）側では、図示Ｚ２方向の力が作用するため、光学支持体６５にその重心Ｇを中心とする偶力が作用するため、レンズ６４の光軸Ｏ−Ｏを傾かせることができる。そして、光学支持体６５のねじれは、４本の弾性支持部材６３との釣り合う位置に設定される。なお、フォーカス用の駆動コイル６８，６９に与える電流と光軸Ｏ−Ｏの傾き角度は、４本の弾性支持部材６３のねじれ剛性によって決定される。したがって、予め与える電流の大きさ及び向きとレンズ６４の光軸Ｏ−Ｏの傾き角度を測定しておき、比例係数を求めておくことが好ましい。
【０１４５】
また、ディスクＤの傾斜角度と、レンズ６４の光軸Ｏ−Ｏの傾き角度との差が０になるようなフィードバック制御を行うことが好ましい。これにより、外乱の影響を受け難くすることができる。さらには、キャリッジ３２が半径方向に移動するときの振動などに起因するレンズ６４の傾き角度のずれを補正することもできるようになる。
【０１４６】
そして、キャリッジ３２が半径方向に移動しディスクＤの傾斜角度が変化しても、これに追従してレンズ６４を傾かせてディスクＤの傾斜角度とレンズ６４の光軸Ｏ−Ｏの傾き角度との差を０とすることができる。
【０１４７】
なお、前記第１のピックアップ装置６０の実施の形態では、渦電流センサ１０ａ，１０ｂが光ヘッド３３上に搭載されているものを示したが、これに限られるものではないことは上述の通りである。すなわち、図５に示すように、渦電流センサ１０ｃ、１０ｄがそれぞれ固定支持部４１及び４２を介して図示しない機構シャーシ上に固定されており、渦電流センサ１０ｃとディスクＤとの距離Ｚ₃及び渦電流センサ１０ｄとディスクＤとの距離Ｚ₄とをそれぞれ測定するものであってもよい。
【０１４８】
図１２および図１３には、光ディスクＤの半径方向（図示Ｘ１−Ｘ２方向）に延びる駆動軸３４とガイドバー８０および光ヘッド３３を搭載したキャリッジ３２などから構成される第２のピックアップ装置９０が示されている。
【０１４９】
前記駆動軸３４の軸回りには螺旋状の送り溝３４ａが形成されている。またキャリッジ３２のＹ２側には、軸受穴３２ａ，３２ｂが穿設されており、前記駆動軸３４が挿通されている。前記軸受穴３２ａ，３２ｂの内面には、前記駆動軸３４の送り溝３４ａに噛み合う雄ねじ部（図示せず）が形成されている。またキャリッジ３２の他方のＹ１側には、Ｕ字形状の軸受部３２ｃ，３２ｄが形成されており、この軸受部３２ｃ，３２ｄ内に前記ガイドバー８０が入り込んでいる。すなわち、前記キャリッジ３２は、駆動軸３４とガイドバー８０に支持されており、前記駆動軸３４がスレッドモータにより回転駆動させられると、前記送り溝３４ａと雄ねじ部との間に生じる送り力により、光ディスクＤの半径方向に自在に移動することが可能とされている。なお、前記キャリッジ３２には、レンズ９２などを搭載した光ヘッド３３が設けられている。
【０１５０】
前記駆動軸３４とガイドバー８０の図示Ｘ２方向の端部は、機構シャーシ上に設けられた支持受け部材８１，８２に支持され、且つ図示しない弾性部材により図示Ｚ２方向に加圧されている。よって、駆動軸３４およびガイドバー８０は、常に支持受け部材８１，８２に圧接させられている。
【０１５１】
一方、前記駆動軸３４とガイドバー８０の図示Ｘ１方向の端部は、支持手段８３により支持されている。前記支持手段８３の図示Ｙ１−Ｙ２方向の端部の下面には、図示Ｘ１−Ｘ２に延びるＵ字溝８３ａ，８３ｂが形成されている。前記駆動軸３４とガイドバー８０の図示Ｘ１方向の端部は、前記Ｕ字溝８３ａ，８３ｂに挿通されており、且つ図示しない付勢手段によって常に図示Ｚ１方向に付勢されている。またＵ字溝８３ａ，８３ｂの両側部には、取付け穴８３ｃ，８３ｃが穿設されている。前記取付け穴８３ｃの板厚方向の中間には段差部８３ｄが設けられており、段差部８３ｄより下側（図示Ｚ２側）の取付け穴８３ｃ２が、段差部８３ｄより上側（図示Ｚ１側）の取付け穴８３ｃ１よりも細い内径寸法で形成されている。
【０１５２】
前記支持手段８３の取付け穴８３ｃには、取付けねじ８５が挿通される。取付けねじ８５の外径寸法は、前記下側の取付け穴８３ｃ２の内径寸法よりも細く形成されており、その長さ寸法は支持手段８３の板厚寸法よりも十分に長いものが使用されている。そして、取付けねじ８５の外周面と下側の取付け穴８３ｃ２の内周面との間にはわずかな隙間余裕が設けられており、前記支持手段８３は取付けねじ８５に沿って図示Ｚ１−Ｚ２方向に移動可能とされている。
【０１５３】
前記取付けねじ８５は、その先端に形成された雄ねじ部８５ｂが機構シャーシ上に形成された雌ねじ穴８９にそれぞれ螺着固定される。この際、前記取付け穴８３ｃの段差部８３ｄと取付けねじ８５のフランジ部８５ａとの間にスプリングコイル８６，８６が介挿される。よって、支持手段８３は、常に図示Ｚ２方向に付勢された状態で取り付けられている。
【０１５４】
図１２に示すように、前記支持手段８３の下面（Ｚ２側の面）には、切欠き部８３ｅが形成されており、前記切欠き部８３ｅ内には自在に回転するギヤ歯車８７が設けられている。前記ギヤ歯車８７の中心には軸が設けられており、この軸には、図示Ｚ１方向に延びる雄ねじ部８７ａが形成されている。そして、前記雄ねじ部８７ａは、前記支持手段８３の中心に穿設された軸受孔８３ｆの内部に挿通されている。前記軸受孔８３ｆの内面には、前記雄ねじ部８７ａに噛み合う雌ねじ部が形成されており、前記雄ねじ部８７ａと雌ねじ部とのねじ送り作用により、前記支持手段８３が図示Ｚ１−Ｚ２方向に昇降移動させることが可能とされている。よって、前記駆動軸３４とガイドバー８０とは、互いの平行状態を維持したまま支持受け部材８１，８２側を中心として傾斜させることが可能となっている（図１３参照）。
【０１５５】
前記ギヤ歯車８７の近傍には、昇降用の駆動モータ８８が設けられている。前記ギヤ歯車８７は、この駆動モータ８８の駆動力により正転及び逆転方向に回転させられ、これにより支持手段８３が図示Ｚ１−Ｚ２方向に昇降移動させられる。
【０１５６】
なお、第２のピックアップ装置９０における渦電流センサ１０の配置は、上記図５と同様であり、例えば機構シャーシ上に固定されていてもよいし、図１３に示すようにキャリッジ３２上に設置されてもよい。
【０１５７】
渦電流センサを用いることにより、渦電流センサとディスクＤとの距離Ｚ_３及び距離Ｚ_４、あるいは距離Ｚ_１及び距離Ｚ_２をそれぞれ測定することができる（図５参照）。そして、前記距離Ｚ_３と距離Ｚ_４の差の変化、あるいは距離Ｚ_１と距離Ｚ_２の差の変化を検出することにより、図１３に示す記録中、又は再生中のディスクＤの半径方向の傾斜角度αが検出される。さらにはディスクＤと光ヘッド３３との距離Ｚ_５（図５参照）が検出される。
【０１５８】
そして、前記駆動モータ８８に駆動電流を与え、支持手段８３を図示Ｚ１−Ｚ２方向に昇降移動させることにより、駆動軸３４とガイドバー８０の傾斜角度がディスクＤの傾斜角度αと一致するように移動させられる。これにより、第２のピックアップ装置９０に搭載されているレンズ９２の光軸Ｏ−Ｏの傾き角度をディスクＤの傾斜角度αに一致させることができる。よって、ディスクＤの記録面に光ヘッド３３のレンズ９２の焦点が合うフォーカス制御を行なうことが可能である。
【０１５９】
なお、ディスクＤの傾斜角度αとレンズ９２の光軸Ｏ−Ｏの傾き角度との差が０になるようなフィードバック制御を行うことが好ましいことは、上記第１のピックアップ装置６０の場合と同様である。
【０１６０】
【発明の効果】
以上詳細に説明した本発明の渦電流センサでは、交流電流が与えられて交流磁界を誘起し、この交流磁界によって被検査体の導電性部位に渦電流を発生させる交流磁界発生手段と、前記コイルから所定位置離れた場所に設置された磁気センサとが独立している。
【０１６１】
従って、被検査体の浅い表面を検査する場合に、渦電流の表皮深さを浅くするために交流電流の周波数を数ＭＨｚ〜数十ＭＨｚ帯の高周波領域にしたときでも、コイルの浮遊容量による変位電流のため、検出精度が低下するという問題を低減することができる。
【０１６２】
また、前記磁気センサとして磁気インピーダンス効果素子を用いると、渦電流センサの小型化が非常に容易になり、また、反磁界の検出感度が良好になり、被検査体までの距離や被検査体の厚さなどを精度よく測定できる渦電流センサを形成することができる。
【０１６３】
また、本発明では、被検査体に渦電流を発生させるためのコイルと、前述の磁気インピーダンス効果素子にかける直流バイアス磁界を誘起させるためのコイルを一つのコイルで兼用することができるので、渦電流センサの小型化が可能になる。
【０１６４】
また、前記磁気インピーダンス効果素子の前記感磁部を、略長方形の軟磁性薄膜あるいは軟磁性薄帯を含むものとすることにより、渦電流センサの製造が容易になる。
【０１６５】
また、本発明のディスク装置では、前述の磁気センサを用いた渦電流センサによって、記録ヘッド、あるいは再生ヘッド、又は記録及び再生ヘッドとディスク型記録媒体との距離や記録中、又は再生中の前記ディスク型記録媒体の傾きを検出するので、装置の組付けに高い精度が要求されず、また、調整工程も、基本的に、基準となる距離を測定したときの磁気センサの出力強度を調節するだけでよくなるので製造工程を簡略化できる。
【０１６６】
また、本発明の渦電流センサは小型化が容易なので、ディスク装置内に渦電流センサを設置するときに、設置場所の制限を少なくすることができる。
【０１６７】
また、渦電流センサとディスク型記録媒体との距離を測るときに、ディスク型記録媒体の導電層に交流磁界を印加して渦電流を発生させ、反磁界を測定するという非常に単純な工程しか含まれないので、測定精度が向上する。
【図面の簡単な説明】
【図１】本発明の渦電流センサの第１の実施の形態を示す斜視図、
【図２】図１の渦電流センサに用いられる磁気インピーダンス効果素子の斜視図、
【図３】磁気インピーダンス効果素子の磁気インピーダンス効果特性を示すグラフ、
【図４】参考例の渦電流センサの形態を示す側面図、
【図５】本発明のディスク装置の実施の形態を示す側面図、
【図６】本発明のディスク装置の実施の形態を示す平面図、
【図７】参考例の形態の渦電流センサを構成する磁気インピーダンス効果素子の回路図、
【図８】磁気インピーダンス効果素子とＤＶＤのＡｌ層との距離と、磁気インピーダンス効果素子の出力電圧の変化量との関係を示すグラフ、
【図９】渦電流センサを用いたディスク装置に搭載される第１の光ピックアップ装置の実施の形態を示す斜視図、
【図１０】図９に示す第１の光ピックアップ装置の平面図、
【図１１】第１の光ピックアップ装置の動作を示しており、図９の矢視ＡＡ方向の正面図、
【図１２】第２の光ピックアップ装置の実施の形態を示す斜視図、
【図１３】第２の光ピックアップ装置の動作を示しており、図１２の矢視ＢＢ方向の断面図、
【符号の説明】
１０、１０ａ、１０ｂ、１０ｃ、１０ｄ、１０ｅ、１０ｆ 渦電流センサ
１１ 被検査体
１２ コイル
１３、１６ 交流電源
１４ 直流電源
１５ 磁気インピーダンス効果素子
３２ キャリッジ
３３ 光ヘッド
４０ ターンテーブル
６０ 第１の光ピックアップ装置
９０ 第２のピックアップ装置
Ｉｅ 渦電流
Ｈｄ 反磁界
Ｄ ディスク[0001]
BACKGROUND OF THE INVENTION
The present invention uses an eddy current sensor using a magnetic sensor having an excellent sensitivity characteristic for measuring a distance to an object to be inspected including a conductive part, a thickness of the object to be inspected, and the eddy current sensor. The present invention relates to a disk device that detects a distance between a head and a disk type recording medium or an inclination of the disk type recording medium.
[0002]
[Prior art]
A conventional eddy current sensor generates an eddy current by applying an alternating current to an air core coil to induce an alternating magnetic field, and applying the alternating magnetic field to an object to be inspected including a conductive portion, and a demagnetizing field generated by the eddy current. Detects the presence or absence of metal by detecting the decrease in magnetic flux interlinkage with the air core coil due to the decrease in coil voltage, the distance from the air core coil to the object under test, the thickness of the object under test, or the object under test The magnetic permeability of the body was measured.
[0003]
Further, in a disk device for recording / reproducing a disk type recording medium, when the disk (disk type recording medium) is recorded / reproduced, the disk fluctuates in the vertical direction of the recording surface or decenters in the horizontal direction of the recording surface. Sometimes. Tracking control is performed so that the recording / reproducing head always runs on the recording track of the disk even when the disk is run out or decentered. In the case of an optical disc apparatus, the focus control is further performed so that the lens focus of the reproducing head always matches the recording surface of the disc.
[0004]
However, the disc may behave other than surface vibration and eccentricity. In addition, warping occurs during disk formation. In particular, a DVD is easily warped because the thickness of the disk substrate is smaller than that of an optical disk such as a CD. Further, since the recording track width is narrowed as the recording density is increased, the laser beam spot diameter is set to CD or the like by using laser light having a short wavelength and increasing the numerical aperture NA of the objective lens. It is necessary to narrow down considerably when playing. For this reason, the allowable amount of the disc tilt angle (tilt angle) for normal playback is small. Therefore, it is necessary to adjust the angle of the recording / reproducing head by detecting the tilt angle of the disc caused by the warp of the disc during recording / reproducing.
[0005]
In the conventional disk device, when detecting the distance between the recording / reproducing head and the disk or the inclination of the disk, it is detected using optical means. For example, as a device for detecting the tilt of a disk, an LED is disposed facing the recording surface of the disk, and two photodetectors are disposed on both the left and right sides of the LED. When the laser is irradiated from the LED toward the recording surface of the disk, if the disk is tilted, a difference occurs in the intensity of reflected light detected by the two photodetectors. The inclination of the disk is detected by taking the signal difference.
[0006]
[Problems to be solved by the invention]
A conventional eddy current sensor excites an air core coil with alternating current to generate an eddy current in a test object, and detects a decrease in inductance of the air core coil by a demagnetizing field generated by the eddy current.
[0007]
However, with this method, it is difficult to accurately measure the distance between the eddy current sensor and one point on the object to be inspected. Further, when inspecting a shallow surface of an object to be inspected, it is necessary to set the frequency of the alternating current to a high frequency region of several KHz to several tens of MHz in order to reduce the skin depth of the eddy current. Due to the displacement current due to the stray capacitance, there has been a problem that the detection accuracy is lowered.
[0008]
Further, when detecting the distance between the recording / reproducing head and the disk or the inclination of the disk as in the conventional disk apparatus, the apparatus for detecting the distance and the inclination is detected using an optical means. As a result, there is a problem that the manufacturing process of the disk device including the adjustment process becomes complicated, and that the repair when the disk device fails becomes difficult.
[0009]
The present invention has been made to solve the above-described conventional problems. An eddy current sensor that can improve measurement accuracy by using a magnetic sensor, and a recording and / or reproducing head using the eddy current sensor. An object of the present invention is to provide a disk device that can improve the accuracy of detection of the distance and inclination by detecting the distance between the disk and the disk type recording medium or the inclination of the disk type recording medium, and can be easily manufactured and repaired. To do.
[0010]
[Means for Solving the Problems]
  The eddy current sensor of the present invention is an alternating currentI _ac1 Is induced to generate an AC magnetic field, and this AC magnetic field generates an eddy current in the conductive part of the object to be inspected.Coil wound with a predetermined number of turns forAnd a magnetic sensor installed at a predetermined position away from the coil,Is installed on the same side of the object to be inspected,
  The magnetic sensor is a magneto-impedance effect element having a magneto-sensitive part including a soft magnetic material having a magneto-impedance effect, and electrode parts for applying a drive AC current to both ends of the magneto-sensitive part in the longitudinal direction of the element. ,
  DC current I for applying a DC bias magnetic field in the longitudinal direction of the magnetic sensing portion of the magneto-impedance effect element _dc A DC power supply for supplying the AC current I _ac1 Is connected to one of the coils, and the coil includes the alternating current I _ac1 And the DC current I _dc And a superimposed current is givenIt is characterized by this.
[0011]
In the present invention, the means for generating an alternating magnetic field and the magnetic sensor for detecting the demagnetizing field from the object to be inspected are independent.
[0012]
Therefore, when inspecting the shallow surface of the object to be inspected, even if the frequency of the alternating current is set to a high frequency region of several KHz to several tens of MHz in order to reduce the skin depth of the eddy current, the stray capacitance of the coil It is possible to reduce the problem that the detection accuracy is lowered due to the displacement current.
[0013]
  MagnetismQi impedance effect elementThe child isSince it can be manufactured using a thin film process, the size of the magnetic sensor can be very small. Accordingly, it is possible to accurately measure the demagnetizing field generated in a narrow range on the surface of the inspection object, the distance between the eddy current sensor and one point on the inspection object, the thickness of the inspection object, or the inspection object. It becomes possible to accurately measure the permeability and the like pinpoint.
[0015]
  The coil winding center and the coilMagneto-impedance effect elementofMagnetismWhen the center of the part is located on the same line, the distance between the eddy current sensor and one point on the object to be inspected, the thickness of the object to be inspected, or the permeability of the object to be inspected can be accurately measured. Is preferable. At this time,Magneto-impedance effect elementIs the coilinternalWinding centerUpIt is more preferable that it is installed.
[0017]
The magneto-impedance effect element uses a soft magnetic material to form a linear or substantially rectangular thin film-like magnetic sensing part, and applies a drive AC current in the longitudinal direction of the magnetic sensing part to change the voltage across the magnetic sensing part. Since it is possible to measure an external magnetic field simply by measuring, miniaturization is very easy. That is, it is very easy to reduce the size of the eddy current sensor.
[0018]
In addition to the fact that the magneto-impedance effect element can be easily reduced in size, the magnetic field detection sensitivity is high, for example, several tens to several hundred times that of the magneto-resistance effect element.
[0020]
By applying a DC bias magnetic field of a certain magnitude to the magneto-impedance effect element in the longitudinal direction, the linearity of the output voltage change with respect to the change of the external magnetic field can be secured, and the magnetic field detection sensitivity can be improved. This DC bias can be supplied by, for example, a coil wound around the magnetic sensing part of the magneto-impedance effect element.
[0021]
The magneto-impedance effect element is installed at the winding center of the coil, and the magneto-impedance effect element is applied to the coil with an alternating current for inducing an alternating magnetic field that generates an eddy current in a conductive portion of the object to be inspected. When a current superimposed with a direct current for generating a direct current bias magnetic field applied in the longitudinal direction of the element is applied to the magnetic sensing portion of the coil, a coil for generating an eddy current in the object to be inspected, and the above-described magnetic field Since the coil for inducing a DC bias magnetic field applied to the impedance effect element can be used as one coil, the eddy current sensor can be downsized.
[0022]
  In addition, the abovecoilGiven toAboveAC currentI _ac1 And the frequency of the drive AC current applied to the magneto-impedance effect element must be different.
[0023]
In addition, it is preferable that the magnetosensitive portion of the magneto-impedance effect element includes a substantially rectangular soft magnetic thin film or soft magnetic ribbon because manufacturing becomes easy.
[0024]
  The present invention also relates to recording on a disk-type recording medium having a conductor layer.OrRegenerationOr recording and playbackOne or a plurality of the above-mentioned eddy current sensors using the disk-type recording medium as the object to be inspected.Head, orRegenerationHead or recording head and playbackThe magnitude of the demagnetizing field due to the eddy current generated in the conductor layer of the disk type recording medium is set opposite to the disk type recording medium at a predetermined position with respect to the head.Magneto-impedance effect elementBy measuring the disk-type recording medium and the recordingHead, orRegenerationHead or recording and playbackThe distance from the head is detected.
[0025]
  In the present invention, recording is performed by the eddy current sensor using the magnetic sensor described above.Head, or playback head, or recording andSince the distance between the reproducing head and the disk-type recording medium is detected, high accuracy is not required for the assembly of the apparatus and adjustment is required compared to the conventional method in which the distance is detected using optical means. In the process, basically, it is only necessary to adjust the output intensity of the magnetic sensor when the reference distance is measured.
[0026]
Therefore, in the present invention, the manufacturing process can be simplified. In addition, when a disk device breaks down, repairs are often performed at a place other than a well-equipped factory, but in the present invention, the adjustment process is simplified, so that the repair is easy. There are also advantages.
[0027]
  In the present invention, the eddy current sensor may be a radial direction of the disk-type recording medium.OrTangential directionOr the radial direction and the tangential directionA plurality of eddy current sensors are installed at a predetermined distance to each other, and a difference in distance between the plurality of eddy current sensors and the disk-type recording medium is measured.OrIt is possible to detect the tilt of the disc type recording medium during reproduction.
[0028]
  In the present invention, all of the plurality of eddy current sensors are not connected to the recording medium.headUpOrRegenerationheadUpOr recording and playbackOn the head or the recordingHead, orRegenerationHead or recording and playbackOn a pickup device having a carriage on which a head is mounted, it may be fixed so as to face the disk-type recording medium, or all of the plurality of eddy current sensors may be the recording medium.Head, orRegenerationHead or recording and playbackIt may be fixed so as to face the disk type recording medium in a place where it does not come into contact with a pickup device having a carriage on which the head is mounted.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a perspective view showing an eddy current sensor according to a first embodiment of the present invention.
[0030]
In FIG. 1, an eddy current sensor 10 according to the present embodiment includes an alternating current I from an alternating current power supply 13._ac1Is applied to the object 11 to be inspected, which is a metal plate, and an alternating magnetic field H (x) is induced, and the alternating current magnetic field H (x) generates an eddy current Ie in the object 11 to be inspected. And a magneto-impedance effect element 15 which is a magnetic sensor installed on a central axis (winding center) Ca inside the coil 12. In FIG. 1, the central axis Ca of the coil 12 is indicated by a dotted line, and the coaxial line C of the central axis Ca of the coil 12 is indicated by a one-point oblique line.
[0031]
The coil 12 has an alternating current I_ac1AC power supply 13 and DC current I_dcIs connected in series with a DC power source 14 for supplying the power. R is a resistance component. Further, the magneto-impedance effect element 15 is supplied with a driving AC current I from an AC power source 16._ac2Is supplied and the output voltage Emi is taken out.
[0032]
In one embodiment shown in FIG. 1, the coil 12 is formed by winding a copper wire coated with an insulating material at a predetermined number of turns.
[0033]
Further, the entire object to be inspected does not have to be formed of metal, and it is only necessary to have a conductive portion where eddy current is generated.
[0034]
The operation principle of the eddy current sensor shown in FIG. 1 will be described.
AC current I applied to the coil 12_ac1, The distance between the coil 12 and the object 11 to be inspected, x, the electrical resistivity of the object 11 to be inspected ρ, and the surface perpendicular permeability of the object 11 to be inspected μ.
[0035]
First, the alternating current I from the alternating current power source 13_ac1Is given to induce an alternating magnetic field.
The alternating magnetic field H (x) in the device under test 11 is expressed by (Equation 1).
[0036]
[Expression 1]

[0037]
The alternating magnetic field H (x) in the inspection object 11 generates an eddy current Ie in the inspection object 11. Due to the eddy current Ie, a demagnetizing field Hd is generated perpendicularly from the surface of the inspection object 11 toward the magneto-impedance effect element 15. Here, assuming that the magnetic dipole due to the eddy current Ie appears perpendicular to the surface, the strength of the magnetic pole is proportional to μIe, the length is the thickness d of the object 11 to be inspected, and the skin depth of the eddy current Ie. It is considered that d is thinner than δ, and δ is thicker.
Here, the skin depth δ of the eddy current Ie is expressed by (Equation 2).
[0038]
[Expression 2]

[0039]
Where ρ is the electrical resistivity of the device under test 11, μ is the surface perpendicular magnetic permeability of the device under test 11, and ω is the alternating current I applied to the coil 12._ac1Is the angular frequency.
The dipole moment m of this magnetic dipole is expressed by (Equation 3) or (Equation 4).
[0040]
[Equation 3]

[0041]
[Expression 4]

[0042]
The demagnetizing field Hd applied to the magneto-impedance effect element 15 is expressed by (Equation 5) or (Equation 6).
[0043]
[Equation 5]

[0044]
[Formula 6]

[0045]
Here, N is the number of turns of the coil 12, and a is the radius of the coil 12.
[0046]
In the present invention, based on (Equation 5) or (Equation 6), only the distance x is obtained when the distance x between the eddy current sensor and the object to be inspected is obtained, and the thickness d is obtained when the thickness d of the object to be examined is obtained. The eddy current sensor is designed so that only the variable is used.
[0047]
When configuring a non-contact type torque sensor or stress sensor, the eddy current sensor is designed so that only μ is a variable.
[0048]
A magneto-impedance effect element is an element whose basic principle is that an output voltage due to impedance generated by applying a minute alternating current to a magnetic wire formed in a wire shape, ribbon shape, or thin film shape is changed by an externally applied magnetic field. It is.
[0049]
FIG. 2 is a perspective view of the magneto-impedance effect element 15 used in the eddy current sensor shown in FIG. The magneto-impedance effect element 15 in FIG.₂O_ThreeA magnetic sensitive portion 22 formed by forming a thin film of a soft magnetic material on a substrate 21 made of an insulating nonmagnetic material such as a sputtering method or a vapor deposition method, and Cu or the like at both ends of the magnetic sensitive portion 22 It is comprised by the electrode parts 23 and 23 formed with the electroconductive material. In one embodiment, the magnetic sensitive portion 22 is patterned in a substantially rectangular shape or linear shape. Alternatively, the magnetic sensitive part 22 may be formed in a U-shaped or zigzag pattern in order to increase the output.
[0050]
The magnetic sensitive part 22 has, for example, a composition formula of Fe_71.4Al_5.8Si_13.1Hf_3.3C_4.5Ru_1.9This is a microcrystalline soft magnetic alloy thin film having a crystal grain size of 5 to 30 nm, mainly composed of bcc-Fe crystal grains and having HfC crystal grains around bcc-Fe. This soft magnetic alloy has high permeability, good sensitivity to external magnetic fields, and excellent environmental resistance.
[0051]
The substrate 21 is made of crystallized glass, Si, SiO₂, Al₂O_ThreeIt is made of borosilicate glass.
[0052]
The electrode portion 23 is made of a conductive material such as Cu, Al, Ni, Ti, or Cr.
In the present embodiment, the magnetic sensitive part 22 is formed as a single-layer soft magnetic thin film. However, the magnetic sensitive part 22 is not limited to the form shown in FIG. The soft magnetic thin film may be laminated. Further, the magnetic sensitive part 22 may include a soft magnetic ribbon.
[0053]
In the magneto-impedance effect element 15 shown in FIG. 2, the drive AC current I extends from the electrode portions 23, 23 in the element longitudinal direction (X direction)._ac2To excite the magnetosensitive portion 22 in the element width direction (Y direction).
[0054]
In this state, when the external magnetic field Hex is applied in the longitudinal direction of the element, the driving AC current I_ac2However, the “skin effect” that tends to flow near the surface of the magnetic sensing part 22 changes, and the impedance of the magnetic sensing part 22 changes. The impedance change of the magnetic sensing part 22 is taken out as a change in voltage between the electrode parts 23 and 23.
[0055]
The operation of the magneto-impedance effect element 15 will be described with reference to FIG. 1 in addition to FIG. The center of the magnetosensitive portion 22 is located on the central axis (winding center) Ca inside the coil 12. In FIG. 1, a magneto-impedance effect element 15 is connected to an alternating current I in the MHz band from an alternating current power supply 16._ac2When an external magnetic field Hex is applied in the element length direction of the magnetic sensing part 22 of the magneto-impedance effect element 15 while the voltage is applied, an output voltage Emi due to the material-specific impedance is generated at both ends of the magnetic sensing part 22 The amplitude of the output voltage Emi changes within a range of several tens of percent corresponding to the strength of the external magnetic field Hex. The output voltage Emi is taken out through the electrode portions 23 and 23.
[0056]
Like the eddy current sensor of the present embodiment, as a magnetic sensor, a magnetic impedance installed on the central axis C of the coil 12 so that the device under test 11 is positioned on an extension line in the element longitudinal direction of the magnetosensitive portion 22. When the effect element is used, the demagnetizing field Hd can be measured simply by measuring the voltage change at both ends of the magnetic sensing unit 22, so that the eddy current sensor can be very easily downsized.
[0057]
The magneto-impedance effect element 15 is 10^-FiveThe characteristic is that a weak magnetic field sensor having a resolution as high as Oe can be obtained, and since excitation of several MHz or more is possible, high frequency excitation of several hundred MHz can be freely used as an amplitude modulation carrier, and can be used as a magnetic field sensor. Sometimes, it has a characteristic that it is easy to set the cutoff frequency to 10 MHz or more and a characteristic that power consumption can be made 10 mW or less.
[0058]
The magnetic field detection sensitivity of the magneto-impedance effect element 15 is as high as, for example, several tens to several hundred times that of the magneto-resistance effect element.
[0059]
When measuring the magnitude of the demagnetizing field Hd using the magneto-impedance effect element 15 as a magnetic sensor, an AC current I for generating an eddy current applied to the coil 12 is measured._ac1And the drive AC current I applied to the magneto-impedance effect element 15_ac2Need to have different frequencies.
[0060]
In order to improve the linearity of the external magnetic field-dependent impedance change in the magneto-impedance effect element, it is effective to apply a direct-current bias magnetic field to the magnetosensitive part of the magneto-impedance effect element.
[0061]
FIG. 3 is a graph showing the magneto-impedance effect characteristics of the magneto-impedance effect element.
[0062]
An external magnetic field Hex is applied in the element longitudinal direction of the magneto-impedance effect element in a state where the drive AC current is applied from the drive AC power source to the magnetic sensing unit using the magneto-impedance effect element. When the output voltage Emi is measured while changing the magnitude of the applied external magnetic field Hex, a graph as shown in FIG. 3 is obtained.
[0063]
The graph showing the magnetoimpedance effect characteristic of FIG. 3 shows that the magnitude of the external magnetic field Hex is Hp.₊Or Hp_-A bimodal shape having a vertex indicating a value indicating the value of the output voltage Emi at the time of. Hp₊And Hp_-The absolute values of are almost equal.
[0064]
In FIG. 3, the magnitude of the external magnetic field Hex is Hp.₊Or Hp_-As the value approaches, the rate of change of the output voltage Emi increases. That is, the detection sensitivity of the external magnetic field Hex is such that the magnitude of the external magnetic field Hex is Hp.₊Or Hp_-Good when near. On the other hand, when the magnitude of the external magnetic field Hex is near 0, the change rate of the output voltage Emi is small, and the detection sensitivity of the external magnetic field Hex is low.
[0065]
Therefore, when the magneto-impedance effect element is used as a magnetic sensor, in order to improve the detection sensitivity of the external magnetic field Hex in the vicinity of the external magnetic field Hex = 0, H_B1Or H_B2The graph showing the magneto-impedance effect characteristic is shifted in the axial direction of the external magnetic field Hex so that the portion where the output voltage change rate is large is on the axis of the external magnetic field Hex = 0. It is preferable to make it.
[0066]
As a method of applying a DC bias magnetic field to the magnetic sensing part of the magneto-impedance effect element, in the present embodiment, as shown in FIG. 1, the test object 11 wound around the magneto-impedance effect element 15 is applied. AC current I flowing in coil 12 for generating AC magnetic field H that generates eddy current Ie_ac1DC current I_dcIs superimposed on the DC bias magnetic field H._BCan be generated and applied in the element longitudinal direction of the magnetic sensing portion of the magneto-impedance effect element 15.
[0067]
Thus, in the present invention, the coil for generating the eddy current Ie in the object to be inspected 11 and the coil for applying a DC bias magnetic field to the magnetic sensing part of the magneto-impedance effect element 15 are combined with one coil 12. Therefore, the eddy current sensor can be miniaturized.
[0068]
For the magnetic sensing part of the magneto-impedance effect element, it is preferable to use a soft magnetic thin film as described above, but a Co—Fe—Si—B amorphous wire may be used. However, it is difficult to form an electrode part for connecting a wiring material for flowing an alternating current with an amorphous wire, and a wire with a diameter of several tens of μm is easily bent and it is difficult to align elements. There are also problems such as being fragile.
[0069]
When the magnetosensitive part of the magneto-impedance effect element is composed of a soft magnetic thin film or a soft magnetic ribbon, the magnetosensitive part can be formed with an arbitrary thickness, width, and length, thereby solving the above problems. This is preferable.
[0070]
The magnetic sensitive part 22 of the magneto-impedance effect element 15 can be formed using a soft magnetic material other than the soft magnetic material described above.
[0071]
However, the magnetically sensitive portion 22 of the magneto-impedance effect element 15 is formed as having a thin film of a ferromagnetic material having a soft magnetic property with a high magnetic permeability μ and a small magnetostriction constant λ in a high frequency region of 1 MHz to several hundred MHz. Therefore, it is preferable that the magnetic sensitive part 22 has a microcrystalline soft magnetic alloy thin film as described below.
[0072]
1. The composition formula is T_100-defgX_dM_eZ_fQ_gA microcrystalline soft crystal having an average crystal grain size of 30 nm or less mainly composed of one or more kinds of crystal grains of bcc-Fe, bcc-FeCo, and bcc-Co and carbide or nitride crystal grains of the element M. Magnetic alloy thin film.
[0073]
However, the element T is an element including one or both of Fe and Co, the element X is an element including one or both of Si and Al, and the element M is Ti, Zr, One or more elements selected from Hf, V, Nb, Ta, Mo, and W. The element Z is an element including one or both of C and N, and Q is Cr, It is one or more elements selected from Re, Ru, Rh, Ni, Pd, Pt, and Au, and d, e, f, and g are at%, and 0 ≦ d ≦ 25, 1 ≦ e ≦ 10 , 0.5 ≦ f ≦ 15, 0 ≦ g ≦ 10.
[0074]
2. The composition formula is T_100-pqefgSi_pAl_qM_eZ_fQ_gA microcrystalline soft crystal having an average crystal grain size of 30 nm or less mainly composed of one or more kinds of crystal grains of bcc-Fe, bcc-FeCo, and bcc-Co and carbide or nitride crystal grains of the element M. Magnetic alloy thin film.
[0075]
However, the element T is an element containing one or both of Fe and Co, and the element M is one or more selected from Ti, Zr, Hf, V, Nb, Ta, Mo, and W. The element Z is an element containing one or both of C and N, and Q is one or two selected from Cr, Re, Ru, Rh, Ni, Pd, Pt, and Au. P, q, e, f, and g are at%, 8 ≦ p ≦ 15, 0 ≦ q ≦ 10, 1 ≦ e ≦ 10, 0.5 ≦ f ≦ 15, 0 ≦ g Those satisfying the relation of ≦ 10.
[0076]
These soft magnetic alloy thin films are preferably formed by thin film forming means such as sputtering and vapor deposition, and can provide soft magnetic alloy thin films with isotropic and good soft magnetic characteristics. Can be easily reduced in size and performance.
[0077]
However, the magnetosensitive portion of the magneto-impedance effect element used in the present invention may be formed using a soft magnetic alloy thin film having a composition other than that shown here.
[0078]
  MagnetismQi impedance effect elementThe child isSince it can be manufactured using a thin film process, the size of the magnetic sensor can be very small. Accordingly, it is possible to accurately measure the demagnetizing field generated in a narrow range on the surface of the inspection object, the distance between the eddy current sensor and one point on the inspection object, the thickness of the inspection object, or the inspection object. It becomes possible to accurately measure the permeability and the like pinpoint.
[0079]
The magnetic sensor does not necessarily have to be located on the central axis Ca of the coil 12 in FIG. 1, and may be installed at a location away from the coil 12 by a predetermined position.
[0080]
For example, it is assumed that the magneto-impedance effect element 17 is installed at a predetermined position away from the coil 12 as shown in FIG. In FIG. 1, the wiring of the magneto-impedance effect element 17 is omitted.
[0081]
The magneto-impedance effect element 17 is an intersection C1 of a perpendicular line (coaxial line C of the central axis Ca) drawn from the central axis Ca of the coil 12 flowing through the coil 12 to the surface of the inspection object 11, that is, an alternating current I._ac1Is a position where the distance from the center of the eddy current Ie generated by the alternating magnetic field H induced in the inspection object 11 by r is r, and the angle between the straight line connecting the magneto-impedance effect element 17 and the intersection C1 and the coaxial line C is θ. Is installed.
[0082]
However, each of the distance r and the angle θ cannot be accurately detected only by the output from one magneto-impedance effect element 17. Therefore, in order to reduce the detection error, the angle θ is preferably as small as possible. Most preferably, θ = 0 degrees, that is, the magneto-impedance effect element is installed on the central axis Ca or the coaxial line C of the coil 12.
[0083]
When a magnetic sensor such as a magneto-impedance effect element is installed on the central axis Ca or the coaxial line C of the coil 12, that is, the winding center of the coil and the center of the detection part of the magnetic sensor are located on the same line. In this case, it is easy to accurately measure the distance between the eddy current sensor and one point on the object to be inspected, the thickness of the object to be inspected, the magnetic permeability of the object to be inspected, and the like.
[0084]
At this time, if the magnetic sensor is installed on the central axis Ca inside the coil 12 like the magneto-impedance effect element 15 in FIG. 1, the distance from the coil 12 to the device under test 11 and the device under test 11 are determined. Since the distance to the magnetic sensor becomes equal, the calculation for obtaining the distance between the eddy current sensor and one point on the object to be inspected, the thickness of the object to be inspected, and the like from the detected demagnetizing field Hd is simple. This is more preferable.
[0085]
Alternatively, the distance r and the angle θ may be detected using two or more eddy current sensors.
[0086]
In the present invention, the coil 12 that generates the alternating magnetic field H and the magnetic sensor that directly detects the demagnetizing field Hd from the device under test 11 are independent.
[0087]
Therefore, when inspecting the shallow surface of the device under test 11, the alternating current I is used to reduce the skin depth δ of the eddy current Ie._ac1Even when the frequency is set to a high frequency region of several KHz to several tens of MHz, it is possible to reduce the problem that the detection accuracy decreases due to the displacement current due to the stray capacitance of the coil 12.
[0089]
  FIG.(Reference example)Then, an alternating current Iac is applied from the alternating current power source 13 to induce an alternating magnetic field H, and the alternating magnetic field H is a means for generating an eddy current Ie in the inspected object 11 that is a metal plate. A magneto-impedance effect element 15 that is a magnetic sensor is opposed to the object under test 11. In FIG. 1, the central axis Ca of the coil 12 is indicated by a dotted line, and the coaxial line C of the central axis Ca of the coil 12 is indicated by a one-point oblique line.
[0090]
In one embodiment of the present invention shown in FIG. 4, the coil 12 is formed by winding a copper wire coated with an insulating material with a predetermined number of turns, and the magneto-impedance effect element 15 includes: It is installed on the coaxial line C of the central axis Ca of the coil 12. That is, the center of the magnetic sensing part 22 is located on the coaxial line C of the central axis Ca of the coil 12. AC current I from the AC power source 13 to the coil 12_ac1Is given to induce an alternating magnetic field H. The alternating magnetic field H in the inspection object 11 generates an eddy current Ie in the inspection object 11. Due to the eddy current Ie, a demagnetizing field Hd is generated perpendicularly from the surface of the inspection object 11 toward the magneto-impedance effect element 15. The magnitude of the demagnetizing field Hd applied to the magneto-impedance effect element 15 is detected, and the distance between the magneto-impedance effect element 15 and the object to be inspected 11, the thickness of the object under test 11, or the object to be inspected is determined from the magnitude of the demagnetizing field Hd. The magnetic permeability of the inspection body 11 is obtained.
[0091]
In the eddy current sensor of FIG. 4 as well, the magneto-impedance effect element 15 is connected to the AC current I in the MHz band from the AC power supply 16._ac2When a demagnetizing field Hd is applied in the element length direction of the magnetosensitive part (not shown in FIG. 4) of the magneto-impedance effect element 15 in the state where the magnetic field is applied, the impedances at both ends of the magnetosensitive part change. The impedance change at both ends of the magnetic sensing part is taken out as a change in the output voltage Emi via electrodes (not shown in FIG. 4) attached to both ends of the magnetic sensing part, and applied to the magneto-impedance effect element 15 from the change in the output voltage Emi The magnitude of the demagnetizing field Hd is obtained.
[0092]
When measuring the magnitude of the demagnetizing field Hd using the magneto-impedance effect element 15 as a magnetic sensor, an AC current I for generating an eddy current applied to the coil 12 is measured._ac1And the drive AC current I applied to the magneto-impedance effect element 15_ac2Need to have different frequencies.
[0093]
As described above, it is preferable to apply a DC bias magnetic field in the longitudinal direction of the element to the magnetic sensitive part of the magneto-impedance effect element 15. In the present embodiment, as shown in FIG. 4, a DC bias magnetic field is generated by passing a DC current Idc from a DC power supply 18 through a coil 19 wound around the magneto-impedance effect element 15, thereby generating a magnetic field. It can be applied in the element longitudinal direction of the magnetic sensing part of the impedance effect element 15.
[0094]
FIG. 5 is a side view showing an embodiment of the disk device of the present invention, and shows a state in which the optical head mounted on the optical pickup device is located on the outermost periphery of the disk.
[0095]
The optical pickup device 31 is provided with an optical head 33 for DVD on a carriage 32. Although not shown in FIG. 5, an optical head for CD is also provided on the carriage 32. The carriage 32 is supported by a drive shaft 34 extending in the radial direction of the optical disc D and a guide bar (not shown) so as to be movable in the radial direction of the optical disc D. The drive shaft 34 and the guide bar are provided in parallel, and both ends of the drive shaft 34 and both ends of the guide bar are supported by supports 35a and 35b. The support 35a is provided so as to be shifted from the rotation center of the optical disc D to the opposite side of the carriage 32 in the X-axis direction, and the support 35b is provided in the vicinity of the outer peripheral edge of the optical disc D. The supports 35a and 35b are fixed on a mechanism chassis (not shown) of the optical pickup device 31.
[0096]
A thread motor 36 is provided at one end of the drive shaft 34, and the carriage 32 is moved in the radial direction of the disk D by the rotational driving force of the thread motor 36. At this time, the optical head 33 is supported by the guide bar between the inner periphery and the outer periphery of the optical disc D, and is moved while maintaining a horizontal state with respect to the optical disc D.
[0097]
The support 35a is provided with a fixing portion 37 that protrudes toward the center of rotation of the optical disc D. The fixing portion 37 is provided with a spindle motor 38 for driving the optical disc D to rotate. The spindle motor 38 is provided with a motor shaft 39 protruding vertically upward, and a turntable 40 on which the optical disk D is placed is provided at the tip of the motor shaft 39.
[0098]
As a result, when the optical disk for DVD is loaded into the optical pickup device 31 and placed on the turntable 40, the optical head 33 side is activated, and the optical disk for CD is loaded and placed on the turntable 40. Then, the CD optical head side (not shown) operates.
[0099]
Each DVD optical head 33 and CD optical head has tracking correction means for finely moving each objective lens in a direction parallel to the disk surface, and finely moving the objective lens in a direction perpendicular to the disk surface. Focusing correction means is provided.
[0100]
In one embodiment of the present invention shown in FIG. 5, an alternating current I superimposed with the direct current Idc shown in FIG._ac1And the eddy current sensor 10a, 10b having the magneto-impedance effect element 15 installed on the central axis Ca of the coil 12 are opposed to the recording surface D1 of the disk D and the radial direction (X (Direction) with a predetermined distance. In the present embodiment, the eddy current sensors 10 a and 10 b are mounted on the optical head 33.
[0101]
  A metal layer is formed on the disk D to reflect the laser beam. This metal layer is formed with a thickness of 100 to 200 nm using, for example, Al. Therefore, when an AC magnetic field is applied to the disk D from the eddy current sensors 10a and 10b, an eddy current is generated in the metal layer, and a demagnetizing field is further generated. That is, the distance Z between the eddy current sensor 10a and the disk D using the eddy current sensors 10a and 10b.₁And the distance Z between the eddy current sensor 10b and the disk D₂And can be measured respectively. Further distance Z₁And distance Z₂By detecting changes in the difference betweenDuring,Alternatively, it is possible to detect the inclination of the disk D being reproduced in the radial direction.
[0102]
  Further, the eddy current sensor is not opposed to the recording surface D1 side of the disk D, but opposed to the opposite surface D2 of the recording surface D1 of the disk D as in the eddy current sensors 10c and 10d shown in FIG. And a predetermined distance in the radial direction (X direction) of the disk D. In the present embodiment, the eddy current sensors 10c and 10d are fixed on a mechanism chassis (not shown) via fixed support portions 41 and 42, respectively. The distance Z between the eddy current sensor 10c and the disk D using the eddy current sensors 10c and 10d.₃And the distance Z between the eddy current sensor 10d and the disk D₄And can be measured respectively. Distance Z₃And distance Z₄By detecting changes in the difference betweenDuring,Alternatively, it is possible to detect the tilt of the disk D being reproduced.
[0103]
The eddy current sensor 10c and the eddy current sensor 10d are installed near the outermost periphery and the innermost periphery of the disk D, respectively. When the radial distance of the disk D between the eddy current sensor 10c and the eddy current sensor 10d increases, the inclination of the disk D in the radial direction can be accurately detected.
[0104]
In FIG. 5, two eddy current sensors are provided on the recording surface D1 side of the disk D, but three or more eddy current sensors are installed at a predetermined distance in the radial direction (X direction) of the disk D. May be. Further, three or more eddy current sensors may be installed on the opposite surface D2 side of the disk D at a predetermined distance in the radial direction (X direction) of the disk D.
[0105]
In addition, the eddy current sensor may be installed on the carriage 32, and is fixed so as to face the disk D at any place that does not contact the pickup device as long as the movement of the carriage 32 is not hindered. It may be.
[0106]
Further, all of the plurality of eddy current sensors may be set to face the recording surface D1 side of the disk D, or all of the plurality of eddy current sensors face the opposite surface D2 side of the disk D. May be installed.
[0107]
Alternatively, a part of the plurality of eddy current sensors may be disposed to face the recording surface D1 side of the disk D, and the remaining eddy current sensors may be disposed to face the opposite surface D2 side of the disk D.
[0108]
In FIG. 5, the eddy current sensors 10a and 10b or the eddy current sensors 10c and 10d are opposed to the recording surface D1 or the opposite surface D2 of the disk D, and have a predetermined distance in the radial direction (X direction) of the disk D. Open and installed.
[0109]
  In the present invention, the eddy current sensor is not only installed at a predetermined distance in the radial direction (X direction) of the disk D, but also the tanger of the disk D as in the eddy current sensors 10e and 10f shown in FIG. It can be installed at a predetermined distance in the local direction (Y direction). Recording is performed by measuring the distance between the eddy current sensor 10e and the disk D and the distance between the eddy current sensor 10f and the disk D and detecting the change in the difference.During,Alternatively, the inclination in the tangential direction of the disc D being reproduced can be detected.
[0110]
The eddy current sensors 10e and 10f may be fixed so as to face the disk D at any place as long as the movement of the carriage 32 is not hindered.
[0111]
Further, the radial inclination value of the disk D detected by the eddy current sensors 10c and 10d installed at a predetermined distance in the radial direction (X direction) of the disk D and the eddy current sensors 10e and 10f are detected. It is possible to detect the inclinations of all directions of the disk D by combining the values of the inclinations of the tangential direction of the disk D in vector.
[0112]
In FIG. 5, when the position where the eddy current sensor 10 a, 10 b, 10 c, or 10 d is set to a predetermined position with respect to the optical head 33, the eddy current sensor 10 a, 10 b, 10 c, or 10 d and the disk D , The distance Z between the disk D and the optical head 33 is measured._FiveCan be detected.
[0113]
In the disk device of the present embodiment, the distance from the disk D is detected by the eddy current sensors 10a and 10b, 10c and 10d, or 10e and 10f using the magneto-impedance effect element, and the inclination of the disk D is further detected. Therefore, compared with the conventional one that detects the tilt of the disk D using optical means, high accuracy is not required for the assembly of the apparatus, and the adjustment process is basically a reference distance. It is only necessary to adjust the output intensity of the magneto-impedance effect element when measuring.
[0114]
Therefore, in the present invention, the manufacturing process can be simplified. In addition, even when the disk device fails, the present invention has an advantage that the adjustment process is simplified and repair is easy.
[0115]
Further, when measuring the distance between the eddy current sensor and the disk D, only an extremely simple process of applying an alternating magnetic field to the disk D to generate an eddy current and measuring a demagnetizing field is included. And the measurement accuracy of the distance of the disk D and the tilt of the disk D are increased.
[0116]
Further, the number of optical heads is not limited to two as described above, and only one optical head 33 may be mounted, or three or more optical heads may be mounted.
[0117]
In the present embodiment, as an example of the present invention, a disk device equipped with a DVD optical head and a CD optical head has been described. The optical head for CD is a reproduction-only type reproduction head for CD-ROM, the write-once type or rewritable type CD-R or the reproduction and recording head for CD-RW, and the optical head for DVD is a reproduction-only type DVD. There are various types such as a read head for ROM, a write-once type or a rewritable type DVD-R or DVD-RAM playback and recording head, and these can be combined as appropriate.
[0118]
In addition, the present invention is not limited to disk devices compatible with CDs and DVDs, but is also applied to disk devices compatible with disk-type recording media having conductive layers such as metal layers and magnetic layers, such as disk devices compatible with MO and magnetic disks. May be.
[0119]
In the eddy current sensor according to the embodiment shown in FIGS. 1 and 4, an alternating current I flowing in the coil 12 is applied as a direct current bias magnetic field applied in the element longitudinal direction of the magnetic sensing portion of the magnetoimpedance effect element 12._ac1DC current I superimposed on_dcThe DC magnetic field induced by the coil 19 and the DC current I flowing through the coil 19_dcDC magnetic field induced by is used.
[0120]
  In addition to this, FIG.(Reference example)As shown in FIG. 2, the bias magnetic field H is formed in the longitudinal direction of the magnetic sensing portion of the magneto-impedance effect element 15._BMay be provided with hard bias magnets 50, 50 made of a hard magnetic material.
[0121]
The tracking correction means and the focusing correction means provided in the optical head 33 of the disk device are provided with, for example, a hard magnetic material inside or around the winding coil, and a current is passed through the winding coil to wind the winding. This is a focus actuator that changes the relative position of the wire coil and the hard magnetic material. As the hard bias of the magneto-impedance effect element described above, a hard magnetic material used for the focus actuator can be used.
[0122]
【Example】
As one embodiment of the present invention, the eddy current sensor 10 shown in FIG. 1 is formed, and the distance between the magneto-impedance effect element 15 of the eddy current sensor 10 and the DVD used as the device under test 11 is changed. The amount of change in the output voltage Emi of the magneto-impedance effect element 15 was examined.
[0123]
The AC current I supplied from the AC power source 13 is a radius a of the coil 12 a = 0.7 mm, the number N of coil turns N = 1200 turns._ac1The size of I_ac1= 2.2mA, AC current I_ac1The frequency f was set to f = 4 MHz. The thickness d of the Al layer, which is the conductor layer of the DVD, is d = 0.15 μm, and the permeability μ of the Al layer is μ = 4π × 10^-7(= Μ₀), Electrical resistivity ρ = ρ × 2.5 × 10^-6Ω · m.
[0124]
As an initial state, the reference distance between the magneto-impedance effect element 15 of the eddy current sensor 10 and the Al layer of the DVD was 1.65 mm. Since the thickness of the protective layer in DVD is 0.6 mm, when the distance from the magneto-impedance effect element to the Al layer is 1.65 mm, the distance from the magneto-impedance effect element to the surface of the protective layer of the DVD is 1.05 mm. It is.
[0125]
The change in the output voltage Emi of the magneto-impedance effect element 15 when the distance x between the magneto-impedance effect element 15 and the Al layer of the DVD was changed from the reference distance was examined. The results are shown in FIG.
[0126]
In the DVD standard, an allowable range of ± 0.4 ° is given in the warp angle. Since the radius of the DVD is 60 mm, when the DVD is set on the turntable, the maximum difference between the height of the center of the DVD and the outermost periphery is about 60 × tan 0.4 ° = 0.4 (mm). Therefore, when the eddy current sensor is used to detect the tilt of the DVD, it is considered that it is only necessary to detect a change in distance within a range of ± 0.4 mm from the reference distance.
[0127]
  From FIG. 8, when the distance between the magneto-impedance effect element 15 and the Al layer of the DVD is within the range of the reference distance of 1.65 mm to ± 0.4 mm, the amount of change in the output voltage of the magneto-impedance effect element is obtained. The value of the distance between the effect element 15 and the Al layer of the DVD is uniquely determined. That is, recording on a disc type recording medium such as a DVD using the eddy current sensor of the present invention.Time,Alternatively, it can be seen that a disk device that detects the tilt of the disk-type recording medium during reproduction can be configured.
[0128]
In the actual disk device, when the value of the distance between the magneto-impedance effect element and the Al layer of the DVD is obtained, the distance between the magneto-impedance effect element and the Al layer of the DVD and the magneto-impedance as shown in the graph of FIG. A table showing the relationship with the change amount of the output voltage of the effect element may be used, or the magnitude of the demagnetizing field is obtained from the change amount of the output voltage of the magneto-impedance effect element. There is a method of calculating a distance to be calculated using Equation 6).
[0129]
9 is a perspective view showing an embodiment of a first optical pickup device mounted on a disk device using an eddy current sensor, FIG. 10 is a plan view of the first optical pickup device shown in FIG. 9, and FIG. 9 shows the operation of the first optical pickup device, a front view in the direction of the arrow AA in FIG. 9, FIG. 12 is a perspective view showing an embodiment of the second optical pickup device, and the disk device in FIG. This is more specifically shown. FIG. 13 shows the operation of the second optical pickup device, and is a cross-sectional view in the direction of arrow BB in FIG.
[0130]
In the first optical pickup device 60 shown in FIGS. 9 to 11, the optical head 33 is provided on a support base 61 provided on the carriage 32. The support base 61 is supported so as to be freely movable in the radial direction (X1-X2 direction in FIG. 9) of the optical disc D placed on the turntable 40 together with the carriage 32. In FIG. 9, the recording surface of the optical disc D is positioned in the Z1 direction shown in the figure.
[0131]
On the support base 61, a base 62 serving as a fixed portion is fixed. Four elastic support members 63, 63, 63, 63 extending in parallel with the Y1-Y2 direction shown in the figure are fixed to the base 62 in a cantilever state, and an optical support having a lens 64 at the tip thereof. A body 65 is provided. That is, each elastic support member 63 is elastically deformable mainly in the X direction (radial direction of the disk) and Z direction (focusing direction) in the drawing, and the optical support 65 is elastically supported by each elastic support member 63. ing. Therefore, the optical support 65 can be moved in the radial direction and the focusing direction of the disc.
[0132]
Two bobbins 66 and 67 are juxtaposed between the base 62 and the optical support 65 in the X direction shown in the figure. Around the bobbins 66 and 67 (around the Z axis in the drawing), focus drive coils 68 and 69 are formed by winding a coated copper wire with a predetermined number of turns. Also, tracking drive coils 70 and 71 wound with a predetermined number of turns are fixedly provided on the side surface of the bobbins 66 and 67 on the Y2 side in the figure. The bobbins 66 and 67 are fixed to the support base 61 and constitute a fixed portion side.
[0133]
Yoke members 72 and 73 are fixed to the surface of the optical support 65 on the Y1 side in the figure. Therefore, the optical support 65 can move in the X direction and the Y direction in the figure together with the yoke members 72 and 73, and is driven as an MM (moving magnet) type pickup device.
[0134]
For the yoke members 72 and 73, a magnetic circuit (closed magnetic path) is formed by a magnetic body provided so as to surround four surfaces by means such as bending or joining a thin plate-shaped magnetic body made of, for example, iron. . Of the four magnetic bodies forming the yoke members 72 and 73, one of the magnetic bodies (magnetic body on the Y1 side) 72a and 73a extending in the Z direction in the figure is placed inside the focus drive coils 68 and 69. Permanent magnets 74 and 75 are fixedly provided on the inner surface thereof.
[0135]
If the magnetic pole on the Y2 side of the permanent magnets 74 and 75 is an N pole, there is a gap between the N pole and the other magnetic bodies 72b and 73b facing the one magnetic bodies 72a and 73a of the yoke member. A magnetic circuit (magnetic path) is formed through this gap. The magnetic flux generated from the N pole passes through the gap and enters the inside of the other magnetic bodies 72b and 73b, and passes through the upper and lower magnetic bodies extending in parallel with the carriage 32. It passes through the path of reaching the one magnetic body 72a, 73a of the yoke member 72, 73 and returning to the south pole of the permanent magnet 74, 75 from here.
[0136]
Of the four sides forming the drive coils 70, 71, only one inner side 70 a, 71 a extending in the Z direction is positioned inside the yoke members 72, 73. The outer sides 70b and 71b opposite to each other are arranged so as to be located outside the yoke members 72 and 73.
[0137]
In the optical head 33, the magnetic flux passing through the gap interlinks only the coated conductors on the side surfaces on the Y2 side of the bobbins 66 and 67 in the focus drive coils 68 and 69, and in the tracking drive coils 70 and 71. The inner conductors 70a and 71a are set so as to interlink only the covered conductors.
[0138]
On the support base 61, the eddy current sensors 10a and 10b described above are provided on both sides of the lens 64. The optical axis OO of the lens 64 is set on an imaginary line L1-L1 connecting the eddy current sensor 10a and the eddy current sensor 10b.
[0139]
In the vicinity of the eddy current sensors 10a and 10b, there are provided a coil 12 and a coil 19 for applying a DC bias magnetic field in the longitudinal direction of the magnetic sensing element of the magneto-impedance effect element 15 as shown in FIGS. Or a bias magnetic field H in the longitudinal direction of the magnetic sensing portion of the magneto-impedance effect element 15 as shown in FIG._BThe hard bias magnets 50 and 50 to which are applied are installed.
[0140]
  In the first optical pickup device 60, the eddy current sensors 10a and 10b are used for recording with the lens 64.During,Or the distance from the disk D being reproduced (the distance Z between the disk D and the optical head 33)₅) Is measured.
[0141]
Since the weights of the optical support 65 and the yoke members 72 and 73 act on each elastic support member 63, the tip of each elastic support member 63 is bent in the Z2 direction in the non-driven state. . Therefore, the output difference of the eddy current sensors 10a and 10b with respect to the tilt angle of the disk D and the tilt angle of the optical axis OO of the lens 64 with respect to the difference in current flowing through the focus drive coils 68 and 69 are examined in advance. It is preferable to be in a state.
[0142]
When the disk D is tilted due to surface vibration, the eddy current sensors 10a and 10b output output voltages proportional to the tilt angles, and a difference voltage therebetween can be obtained. Therefore, the tilt of the disk D can be grasped as a change amount from the initial state, and a current proportional to the change amount is given to the focus drive coils 68 and 69.
[0143]
As a result, a force in accordance with Fleming's left-hand rule is generated in the Z1 or Z2 direction shown in the figure depending on the direction of the drive current on the coated conductors of the focus drive coils 68 and 69 in the magnetic field.
[0144]
Then, as shown in FIG. 11, when currents in different directions are applied to the focus drive coils 68 and 69, for example, on the one drive coil 68 (yoke member 72) side, a force in the Z1 direction shown in the figure acts, and the other drive On the coil 69 (yoke member 73) side, a force in the Z2 direction shown in the drawing acts, and a couple force around the center of gravity G acts on the optical support 65, so that the optical axis OO of the lens 64 is tilted. be able to. The twist of the optical support 65 is set at a position that balances with the four elastic support members 63. Note that the current applied to the focus drive coils 68 and 69 and the inclination angle of the optical axis OO are determined by the torsional rigidity of the four elastic support members 63. Therefore, it is preferable to measure the magnitude and direction of the current applied in advance and the tilt angle of the optical axis OO of the lens 64 to obtain the proportionality coefficient.
[0145]
Further, it is preferable to perform feedback control so that the difference between the tilt angle of the disk D and the tilt angle of the optical axis OO of the lens 64 becomes zero. Thereby, it can be made hard to receive the influence of disturbance. Furthermore, it is possible to correct a deviation in the tilt angle of the lens 64 caused by vibrations or the like when the carriage 32 moves in the radial direction.
[0146]
Then, even if the carriage 32 moves in the radial direction and the tilt angle of the disk D changes, the lens 64 is tilted following this to tilt the disk D and the tilt angle of the optical axis OO of the lens 64. The difference can be zero.
[0147]
In the embodiment of the first pickup device 60, the eddy current sensors 10a and 10b are mounted on the optical head 33. However, the present invention is not limited to this. is there. That is, as shown in FIG. 5, the eddy current sensors 10c and 10d are fixed on a mechanism chassis (not shown) via fixed support portions 41 and 42, respectively, and the distance Z between the eddy current sensor 10c and the disk D is fixed._ThreeAnd the distance Z between the eddy current sensor 10d and the disk D_FourAnd may be respectively measured.
[0148]
12 and 13 show a second pickup device 90 including a drive shaft 34 extending in the radial direction (X1-X2 direction in the drawing) of the optical disc D, a guide bar 80, a carriage 32 on which the optical head 33 is mounted, and the like. It is shown.
[0149]
A spiral feed groove 34 a is formed around the drive shaft 34. Further, bearing holes 32a and 32b are formed on the Y2 side of the carriage 32, and the drive shaft 34 is inserted therethrough. A male screw portion (not shown) that meshes with the feed groove 34a of the drive shaft 34 is formed on the inner surfaces of the bearing holes 32a and 32b. Further, U-shaped bearing portions 32c and 32d are formed on the other Y1 side of the carriage 32, and the guide bar 80 enters the bearing portions 32c and 32d. That is, the carriage 32 is supported by the drive shaft 34 and the guide bar 80, and when the drive shaft 34 is driven to rotate by a sled motor, a feed force generated between the feed groove 34a and the male screw portion It is possible to move freely in the radial direction of the optical disc D. The carriage 32 is provided with an optical head 33 on which a lens 92 and the like are mounted.
[0150]
The ends of the drive shaft 34 and the guide bar 80 in the X2 direction shown in the figure are supported by support receiving members 81 and 82 provided on the mechanism chassis, and are pressed in the Z2 direction by an elastic member (not shown). Therefore, the drive shaft 34 and the guide bar 80 are always in pressure contact with the support receiving members 81 and 82.
[0151]
On the other hand, ends of the drive shaft 34 and the guide bar 80 in the X1 direction shown in the figure are supported by a support means 83. U-shaped grooves 83a and 83b extending in the X1-X2 direction are formed on the lower surface of the end portion in the Y1-Y2 direction of the support unit 83. The ends of the drive shaft 34 and the guide bar 80 in the X1 direction are inserted into the U-shaped grooves 83a and 83b and are always urged in the Z1 direction by an urging means (not shown). Further, mounting holes 83c and 83c are formed on both sides of the U-shaped grooves 83a and 83b. A stepped portion 83d is provided in the middle of the mounting hole 83c in the plate thickness direction, and a mounting hole 83c2 below (step Z2 in the drawing) below the stepped portion 83d is attached above (step Z1 in the drawing) above the stepped portion 83d. The inner diameter is smaller than that of the hole 83c1.
[0152]
A mounting screw 85 is inserted into the mounting hole 83 c of the support means 83. The outer diameter of the mounting screw 85 is formed to be narrower than the inner diameter of the lower mounting hole 83c2, and the length is sufficiently longer than the plate thickness of the support means 83. . A slight clearance is provided between the outer peripheral surface of the mounting screw 85 and the inner peripheral surface of the lower mounting hole 83c2, and the support means 83 extends along the mounting screw 85 in the Z1-Z2 direction shown in the figure. It is possible to move to.
[0153]
The mounting screw 85 has a male screw portion 85b formed at the tip thereof screwed and fixed to a female screw hole 89 formed on the mechanism chassis. At this time, the spring coils 86 and 86 are inserted between the step portion 83 d of the mounting hole 83 c and the flange portion 85 a of the mounting screw 85. Therefore, the support means 83 is always attached in a state of being urged in the Z2 direction shown in the drawing.
[0154]
As shown in FIG. 12, a notch 83e is formed in the lower surface (Z2 side surface) of the support means 83, and a freely rotating gear gear 87 is provided in the notch 83e. ing. A shaft is provided at the center of the gear gear 87, and a male screw portion 87a extending in the Z1 direction is formed on the shaft. The male screw portion 87a is inserted into a bearing hole 83f formed in the center of the support means 83. A female screw portion that meshes with the male screw portion 87a is formed on the inner surface of the bearing hole 83f, and the support means 83 moves up and down in the Z1-Z2 direction shown in the drawing by the screw feeding action of the male screw portion 87a and the female screw portion. It is possible to make it. Therefore, the drive shaft 34 and the guide bar 80 can be inclined with the support receiving members 81 and 82 as the center while maintaining the mutual parallel state (see FIG. 13).
[0155]
A drive motor 88 for raising and lowering is provided in the vicinity of the gear gear 87. The gear gear 87 is rotated in the forward and reverse directions by the driving force of the drive motor 88, whereby the support means 83 is moved up and down in the Z1-Z2 direction shown in the figure.
[0156]
The arrangement of the eddy current sensor 10 in the second pickup device 90 is the same as that in FIG. 5 described above. For example, the eddy current sensor 10 may be fixed on the mechanism chassis or installed on the carriage 32 as shown in FIG. May be.
[0157]
  By using an eddy current sensor, the distance Z between the eddy current sensor and the disk D₃And distance Z₄Or distance Z₁And distance Z₂Can be measured respectively (see FIG. 5). And the distance Z₃And distance Z₄Change in distance or distance Z₁And distance Z₂By detecting the change in the difference between the records shown in FIG.During,Alternatively, the tilt angle α in the radial direction of the disc D being reproduced is detected. Further, the distance Z between the disk D and the optical head 33₅(See FIG. 5) is detected.
[0158]
Then, a drive current is applied to the drive motor 88, and the support means 83 is moved up and down in the Z1-Z2 direction in the drawing so that the tilt angle of the drive shaft 34 and the guide bar 80 coincides with the tilt angle α of the disk D. Moved. Thereby, the inclination angle of the optical axis OO of the lens 92 mounted on the second pickup device 90 can be matched with the inclination angle α of the disk D. Therefore, it is possible to perform focus control in which the lens 92 of the optical head 33 is focused on the recording surface of the disk D.
[0159]
The feedback control is preferably performed so that the difference between the tilt angle α of the disk D and the tilt angle of the optical axis OO of the lens 92 is zero, as in the case of the first pickup device 60. It is.
[0160]
【The invention's effect】
In the eddy current sensor of the present invention described in detail above, an alternating current is induced to induce an alternating magnetic field, and the alternating magnetic field generating means for generating an eddy current in a conductive part of the object to be inspected by the alternating magnetic field, and the coil Is independent of the magnetic sensor installed at a predetermined position away from the sensor.
[0161]
Therefore, when inspecting the shallow surface of the object to be inspected, even if the frequency of the alternating current is set to a high frequency region of several MHz to several tens of MHz in order to reduce the skin depth of the eddy current, it depends on the stray capacitance of the coil. Due to the displacement current, it is possible to reduce the problem that the detection accuracy is lowered.
[0162]
In addition, when a magneto-impedance effect element is used as the magnetic sensor, the eddy current sensor can be miniaturized very easily, the detection sensitivity of the demagnetizing field is improved, the distance to the object to be inspected, the An eddy current sensor capable of measuring the thickness and the like with high accuracy can be formed.
[0163]
In the present invention, the coil for generating an eddy current in the object to be inspected and the coil for inducing a DC bias magnetic field applied to the above-described magneto-impedance effect element can be used as a single coil. The current sensor can be downsized.
[0164]
In addition, when the magnetosensitive portion of the magneto-impedance effect element includes a substantially rectangular soft magnetic thin film or soft magnetic ribbon, the eddy current sensor can be easily manufactured.
[0165]
  In the disk apparatus of the present invention, recording is performed by an eddy current sensor using the magnetic sensor described above.Head, or playback head, or recording andDistance between recording head and disc type recording medium and recordingDuring,Alternatively, since the inclination of the disk-type recording medium being reproduced is detected, high accuracy is not required for the assembly of the apparatus, and the adjustment process is basically performed by the magnetic sensor when the reference distance is measured. Since only the output intensity needs to be adjusted, the manufacturing process can be simplified.
[0166]
Further, since the eddy current sensor of the present invention can be easily miniaturized, when the eddy current sensor is installed in the disk device, it is possible to reduce the restriction of the installation location.
[0167]
Also, when measuring the distance between the eddy current sensor and the disk type recording medium, an alternating magnetic field is applied to the conductive layer of the disk type recording medium to generate an eddy current and measure the demagnetizing field. Since it is not included, the measurement accuracy is improved.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a first embodiment of an eddy current sensor of the present invention,
2 is a perspective view of a magneto-impedance effect element used in the eddy current sensor of FIG.
FIG. 3 is a graph showing magneto-impedance effect characteristics of the magneto-impedance effect element;
[Fig. 4]Reference exampleEddy current sensorForm ofSide view showing the state,
FIG. 5 is a side view showing an embodiment of a disk device of the present invention;
FIG. 6 is a plan view showing an embodiment of the disk device of the present invention,
[Fig. 7]Reference exampleCircuit diagram of magneto-impedance effect element constituting eddy current sensor of form,
FIG. 8 is a graph showing the relationship between the distance between the magneto-impedance effect element and the Al layer of the DVD and the amount of change in the output voltage of the magneto-impedance effect element;
FIG. 9 is a perspective view showing an embodiment of a first optical pickup device mounted on a disk device using an eddy current sensor;
10 is a plan view of the first optical pickup device shown in FIG. 9,
11 shows the operation of the first optical pickup device, and is a front view in the direction of arrow AA in FIG.
FIG. 12 is a perspective view showing an embodiment of a second optical pickup device;
13 shows the operation of the second optical pickup device, and is a cross-sectional view in the direction of arrow BB in FIG.
[Explanation of symbols]
10, 10a, 10b, 10c, 10d, 10e, 10f Eddy current sensor
11 Inspected object
12 coils
13, 16 AC power supply
14 DC power supply
15 magneto-impedance effect element
32 Carriage
33 Optical head
40 turntable
60 First optical pickup device
90 Second pickup device
Ie Eddy current
Hd Demagnetizing field
D disc

Claims (9)

An alternating current I _ac1 is applied to induce an alternating magnetic field, and this alternating magnetic field causes a coil wound with a predetermined number of turns to generate an eddy current in a conductive portion of the object to be inspected, and a predetermined amount from the coil. A magnetic sensor installed at a location away from the position, is installed on the same side of the object to be inspected,
The magnetic sensor is a magneto-impedance effect element having a magneto-sensitive part including a soft magnetic material having a magneto-impedance effect, and electrode parts for applying a drive AC current to both ends of the magneto-sensitive part in the longitudinal direction of the element. ,
A DC power source for supplying a DC current I _dc for applying a DC bias magnetic field in the longitudinal direction of the magnetic sensing element of the magneto-impedance effect element and an AC power source for supplying the AC current I _ac1 are provided in one coil. An eddy current sensor connected to the coil, wherein a current in which the alternating current I _ac1 and the direct current I _dc are superimposed is applied to the coil . Winding around the eddy current sensor according to claim 1, wherein the center of the magnetosensitive portion are positioned on the same line of the magneto-impedance effect element of the coil. The eddy current sensor according to claim 2 , wherein the magneto-impedance effect element is installed on a winding center inside the coil. Eddy current sensor according to any of the frequency of the alternating current I _ac1 applied to said coil, to the frequency of the driving alternating current applied to said magneto-impedance effect element is not different claims 1 3. 5. The eddy current sensor according to claim 1, wherein the magnetosensitive portion of the magneto-impedance effect element includes a substantially rectangular soft magnetic thin film or soft magnetic ribbon. 6. Recording disk type recording medium having a conductive layer, or reproduction, or a disk device for recording and reproducing, according to the disk type recording medium in any one of claims 1 to 5, wherein the object to be inspected One or a plurality of eddy current sensors are installed facing the disk type recording medium at a predetermined position with respect to the recording head, the reproducing head, or the recording head and the reproducing head. By measuring the magnitude of the demagnetizing field caused by the eddy current generated in the conductor layer with the magneto-impedance effect element , the disk type recording medium and the recording head, or the reproducing head, or the recording and reproducing head A disk device characterized by detecting a distance. A plurality of the eddy current sensors are installed at a predetermined distance in the radial direction , the tangential direction , or the radial direction and the tangential direction of the disk type recording medium, and the plurality of eddy current sensors. The disk device according to claim 6 , wherein an inclination of the disk type recording medium during recording or reproduction is detected by measuring a difference between a distance between the disk type recording medium and the disk type recording medium. All of the plurality of eddy current sensors are on the recording head , the reproducing head , the recording and reproducing head, or the recording head, the reproducing head, or the carriage on which the recording and reproducing head is mounted. in the pickup device having a disk device according to claim 6 or 7 it is fixed so as to face the disk-type recording medium. All of the plurality of eddy current sensors are opposed to the disk-type recording medium in a place where they do not contact the recording head, the reproducing head, or a pickup device having a carriage on which the recording and reproducing head is mounted. The disk device according to claim 6 or 7 , wherein the disk device is fixed.

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