JP2004276188A

JP2004276188A - Control device and method for micropore electric discharge machine

Info

Publication number: JP2004276188A
Application number: JP2003072905A
Authority: JP
Inventors: Yoshinori Nishimoto; 吉範西本
Original assignee: Toto Ltd
Current assignee: Toto Ltd
Priority date: 2003-03-18
Filing date: 2003-03-18
Publication date: 2004-10-07

Abstract

<P>PROBLEM TO BE SOLVED: To provide a micropore electric discharge machining control device, impairing the machining speed, preventing machining disability due to bending of an electrode, and improving the machining limit depth in micropore electric discharge machining taking conductive material such as metal as a workpiece, in particular in the micropore electric discharge machining where the conductive ceramic to which machining liquid cannot be injected is machined using a bar-like solid fine line electrode. <P>SOLUTION: This control device of the micropore electric discharge machine is composed of: an interpole proportional voltage detecting means; a voltage comparing means; an electric discharge state deterioration detecting means; and an electric discharge stabilization control means for instructing a shaft movement control means to perform the operation of expanding the distance of the interpole interval at least one time within 10 μm in response to a signal from the electric discharge state deterioration detecting means and instructing the shaft movement control means to perform jump operation when the discharge state deterioration signal of the electric discharge state detecting means continues. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、被加工物に微細穴を加工する放電加工の制御装置及び方法に関する。
【０００２】
【従来の技術】
放電加工は、放電現象を媒体として高精度・微細形状の加工が容易であることなど多くの特色を持つと共に、非接触加工である。このために、工具電極と被加工物との間に形成される極間隔を常に放電発生に適した距離に保持することが必要になる。
細穴放電加工では、加工の進行に従って工具電極と被加工物とが除去される量に応じて常に極間隔を追い込まなければならないが、極間隔の加工屑やガスの発生、放電面形状の変化などに対応して放電加工中の極間隔の距離を一定に保つためには、一般的には工具電極と被加工物との極間隔に発生する極間電圧に比例した信号の平均値を制御入力として極間隔の距離が一定になるように工具電極の駆動を制御する方法がとられている。これが、放電加工に関する書物に見られるいわゆるサーボ送り制御といわれるものである。
【０００３】
ところが、細穴放電加工では放電加工によって生成される加工屑が極間隔の加工部に残留しやすく排出されにくい。加工屑は工具電極と被加工物の極間隔に多量に介在すると、加工する必要のない箇所で放電現象が発生したり、１箇所で集中的にアーク現象を生じさせて加工に異常を生じさせたり、工具電極と被加工物が加工屑を介して短絡して加工が進まなくなったりして、加工が進展しなくなる。
このため、直径０．１ｍｍ以上の工具電極が使用できる場合には、パイプ電極を使用して、電極内部に流路を設けて加工液を加工している穴底へ供給し、加工屑の排出を促す。ところが、直径０．１ｍｍ以下の工具電極を使用しなければならないような微細穴を加工する場合には、直径０．１ｍｍ以下のパイプ電極の製作自体が非常に困難であり、さらにパイプ電極の内径が小さくなればなるほど、加工液圧を高くしなければ加工液噴出による加工屑排出の効果が上がらなくなり、設備および消耗品である工具ともに非常に高価なものになってしまうという問題があった。
【０００４】
そこで、工具電極をジャンプ動作させて加工屑排出の効果を得ることが考えられる。ジャンプ動作の説明を図８に示す。放電加工中、加工屑が発生した状態５０では、放電加工中には穴内に加工屑が発生するため、ジャンプ動作途中であり工具電極を穴入口近くまで後退させた状態５１のように瞬間的に工具電極を穴入口付近まで後退させることにより加工屑を排出し、その直後に瞬間的に工具電極を加工していた元の位置付近に戻すことによって加工液を穴底に押し込む。このような工具電極の一連の瞬間的な往復運動がジャンプ動作である。
【０００５】
このジャンプ動作を行うタイミングについては、一定時間間隔に行うという方法も考えられる。しかし、目標とする加工深さに応じてあらかじめジャンプ動作を行う穴加工深さ位置を設定する方がより効果的である。例えば、穴加工深さが深くなるに従って、ジャンプ動作を行う穴加工深さ位置の間隔を短くするという設定方法である。なお、放電加工では被加工物を加工する際に工具電極も消耗するため、工具電極が放電開始後に進んだ距離よりも穴加工深さは小さい値になってしまう。そのため、あらかじめ実験によって加工深さに応じた工具電極の消耗量を求めておき、工具電極位置を検出後、工具電極消耗量を計算に加えて加工深さを演算する。
これによって、細線電極、特に加工液を噴出させることができない棒状の中実細線電極を用いた放電加工において、加工屑排出を促進し、加工速度を上げ、加工限界深さも大きくすることができる（例えば、特許文献１参照。）。
【０００６】
また、細穴放電に限定しない発明としては、位置検出器により電極の動きを検出し、サーボ制御によって、電極と被加工物との極間隔の距離が広がる動作と狭める動作の周期を計数し、この周期が指定値以上になったら放電不安定状態と判断し、一定時間間隔でのジャンプ動作に加えて放電不安定状態から抜け出すためのジャンプ動作を行い、加工屑の排出を促進し、放電を安定させることが出来る方法が開示されている（例えば、特許文献２参照。）。
【０００７】
【特許文献１】
特開平９−７６１２６号公報（第１図）
【特許文献２】
特開平６−７１５１７号公報（第１図）
【０００８】
【発明が解決しようとする課題】
しかしながら、特許文献１記載の予め設定した加工深さのタイミングでジャンプ動作を行う場合には、実際の加工状態を反映して、制御を行うことができないという問題があった。ジャンプ動作中は、加工は休止状態であるため、加工速度を考慮すると出来る限り少ない方がよいが、予めジャンプ動作タイミングを設定する場合には、余裕を見て多めに設定してしまうので、加工速度的には効率的とは考えられない。特に導電性セラミックスのように絶縁性粒子と導電性粒子が混合して形成される材料の場合、絶縁性粒子と導電性粒子の分布が必ずしも均一とは限らず、同じワークでも場所によって加工の進行具合が異なることもあり、ジャンプ動作タイミングをあらかじめ最適に設定することは難しい。
【０００９】
また、特許文献２記載の工具電極側と被加工物側との間に形成される極間隔の距離を広げる動作と狭める動作の周期を計数し、指定値以上になった時に放電状態不安定状態になったと判断する方法では、通常の型彫り放電ではタイミングとしては最適かもしれないが、微細穴放電加工の場合にはタイミングが遅い危険性がある。極間隔の距離を広げる動作には、放電自体は正常であるが、極間隔の距離が狭く放電頻度が高いと判断して極間隔の距離を広げる場合と、短絡や１点での集中放電などの異常放電による場合との２種類がある。後者の場合、極間隔の距離を広げる動作と狭める動作の周期の観察により、放電状態の不安定化を判断する方法では、微細穴放電加工では手遅れになる場合がある。微細穴放電加工では、穴底まで加工液が浸透しにくく、穴が深くなるほど加工屑が排出されにくくなる。
【００１０】
従って、加工が進むにつれて異常放電が発生する確率が高くなり、特に加工屑を介した短絡や１箇所でアークが集中して放電するなどのような異常放電はサーボ送り制御などにより数μｍ程度の微小距離の後退運動では正常な放電への復帰が簡単に出来ない場合もある。さらに、絶縁性粒子と導電性粒子を混合して形成される導電性セラミックスの場合、異常放電が続くと穴底に絶縁性粒子の割合が高くなる傾向があり、ついには放電自体が発生しなくなってしまう。従って、異常放電により極間隔の距離が広がった場合には、極間隔の距離を広げた直後の放電状態が重要であり、これを見過ごした場合、極間隔の距離を広げる動作と狭める動作の周期に異常が認められる前に、すでに微細穴放電加工が不可能な状態に陥っている危険性がある。
【００１１】
本発明は、上記課題を解決するものであり、金属などの導電材料を被加工物とする微細穴放電加工、特に加工液を噴出させることが出来ない棒状の中実細線電極を使用して導電性セラミックスを加工する微細穴放電加工において、加工速度を損なわず、電極曲がりによる加工不能を防止し、加工限界深さを向上する微細穴放電加工制御装置を提供することを目的とする。
【００１２】
【課題を解決するための手段および作用・効果】
上記目的を達成するために請求項第１項記載の発明は、細い棒形状または細いパイプ形状の工具電極と被加工物との間に形成される極間隔に、加工用電源から電圧を印加して放電を発生させるとともに、前記工具電極と前記被加工物を軸移動制御手段から指令を与えることによって相対移動させて前記被加工物の細穴加工を行う微細穴放電加工装置において、前記工具電極と前記被加工物との極間隔に発生する極間電圧に比例したアナログ電圧を検出する極間比例電圧検出手段と、前記アナログ電圧を短絡または放電状態を示す値に設定された基準電圧と比較して論理信号を出力する電圧比較手段と、前記論理信号により短絡または異常放電の状態であることを検出する放電状態悪化検出手段と、前記放電状態悪化検出手段からの放電状態悪化信号により少なくとも１回以上、１０μｍ以内の微小距離だけ前記工具電極と前記被加工物との相対距離を広げる動作を行うように軸移動制御手段に指令するとともに、前記放電状態悪化検出手段による放電状態悪化信号が継続する場合にジャンプ動作を前記軸移動制御手段に指示する放電安定化制御手段とにより構成されることを特徴とする。
【００１３】
電圧比較手段は、極間比例電圧検出手段のアナログ電圧と基準電圧を比較することによって、正常放電、短絡、および異常放電の全てを検出する。そして、放電状態悪化検出手段は電圧比較手段からの信号から短絡と異常放電を抽出し、これを放電状態悪化信号とする。放電状態安定化制御手段は放電状態悪化検出信号により軸移動制御制御手段に対して、まず微小距離後退を指示し、最小労力での正常復帰を試みる。もし、この微小距離後退によって正常放電状態に復帰しなければ、穴底での加工液浸透が十分ではなく、加工屑も多くなっていることが推測され、放電状態安定化制御手段は加工不能などの不具合が発生する前兆とみなす。この不具合が発生する前兆とみなされたタイミングのみで放電状態安定化制御手段が軸移動制御手段に対してジャンプ動作を指示することにより、加工時間的には不利であるジャンプ動作をできるかぎり少なく、必要な回数だけ行うことができる。
【００１４】
従って、本発明によれば、微細穴放電加工において、実際の放電状態に応じて必要な回数だけジャンプ動作を行い、加工速度を損なわず、加工液を穴底へ浸透させ、加工屑の排出を促進させるために加工限界深さを向上させることが出来る。
【００１５】
請求項第２項記載の発明は、前記放電状態悪化検出手段が、前記電圧比較手段からの出力論理信号の放電検知連続時間を計測する計時手段から成り、あらかじめ設定した時間以上に放電検知が継続した場合に放電状態悪化検出信号を出力することを特徴とする。
【００１６】
放電状態悪化検出手段は、電圧比較手段からの正常放電、短絡および異常放電の全ての検出信号から短絡または異常放電を抽出するのに、放電検知連続時間の計測を行う。この場合、放電状態悪化検出までの遅れ時間としては計時手段での放電状態悪化とみなす設定時間のみとなる。
【００１７】
従って、本発明によれば、放電状態悪化状態を高い応答性で検出することが出来き、安定して放電加工を行うことができる。
【００１８】
請求項第３項記載の発明は、前記放電状態悪化検出手段が、前記電圧比較手段からの出力論理信号を平滑しアナログ信号に変換する電圧平滑手段と、前記アナログ信号があらかじめ設定した閾値に達したときに放電状態悪化検出信号を出力する第２の電圧比較手段から構成されることを特徴とする。
【００１９】
放電状態悪化検出手段は、電圧比較手段からの正常放電、短絡および異常放電の全ての検出信号から放電状態悪化検出信号が短絡または異常放電を抽出するのに電圧平滑手段と第２の電圧比較手段とで構成する。正常放電の場合は電圧比較手段の出力は論理反転が瞬時的なパルス波形であり、一方短絡または異常放電の場合は論理反転の時間が長いので、電圧平滑手段で平滑することによって両者を選別するためのアナログ信号を出力することができ、さらに第２の電圧比較手段で両者の選別基準を設けて論理信号化する。
特に、極間隔に電圧を印加する回路がコンデンサと抵抗から構成される電源回路である場合には、放電発生から充電期間中において極間比例電圧検出手段の出力アナログ電圧値と基準電圧値が等しくなる時間よりも大きく、充電時間よりも小さい範囲で電圧平滑手段の平滑時定数を出来る限り小さい値にすることによって応答性を高めることが出来る。さらに、放電状態が悪化しているときに、一時的に正常放電に復帰したように見えてすぐに悪化状態に戻るような場合もあるが、電圧平滑手段では入力の瞬時的な変化は出力に影響を与えにくいため出力は放電悪化状態を維持することが出来る。
【００２０】
従って、本発明によれば、放電状態悪化時に瞬時的に正常になり、再度放電状態が悪化してしまうような場合でも放電状態悪化判定を継続させることが出来き、安定して放電加工を行うことができる。
【００２１】
請求項第４項記載の発明は、前記極間比例電圧検出手段の出力を入力とし、前記電圧比較手段への入力と並列に、前記工具電極と前記被加工物との極間隔の距離が一定になるように前記軸移動制御手段を制御するための制御入力信号として極間比例電圧の平均値を出力する極間比例電圧平滑手段を有することを特徴とする。
【００２２】
正常放電のときには極間比例電圧の平均値を制御入力として放電安定化制御手段が極間隔の距離を一定になるように軸移動制御手段に対して制御出力を行う、いわゆるサーボ送り制御を行い、短絡または異常放電のときには放電状態悪化検出信号により微小距離後退やジャンプ動作などの制御を行う。
【００２３】
従って、本発明によれば、極間隔の距離を一定に保つためのサーボ送り制御と併用することが可能となり、安定して放電加工を行うことができる。
【００２４】
請求項第５項記載の発明は、前記ジャンプ動作において電極下端と加工穴底が最も離れた時に、電極下端が少なくとも被加工物上面より上に出ないことを特徴とする。
【００２５】
ジャンプ動作において、瞬時的に極間隔を広げて、再度元の極間隔に戻すという工程の中で、もし最も極間隔が広がっている状態のときに工具電極下端が被加工物穴入口よりも上に出ているような場合、次の工程の元の極間隔に戻す工程の中で、芯ブレなどの影響により被加工物穴入口にひっかかる可能性がある。微細穴加工用の工具電極は微細で一般的に非常に曲がりやすいため、被加工物穴入口にひっかかると、そのまま工具電極自体がたわみ、工具電極を穴内部に通すことが出来なくなり、加工不能に陥ってしまう。
【００２６】
従って、本発明によれば、ジャンプ動作により、工具電極が被加工物穴入口にひっかかり、工具電極が曲がって穴の中に供給されなくなるという不具合を防止することが出来る。
【００２７】
【発明の実施の形態】
以下、本発明の形態により添付図面を参照して説明する。
【００２８】
図１は本発明に係る細穴放電加工機の制御装置の構成図を示す。
加工用電源１は、直流電源２、抵抗３、およびコンデンサ４から構成される。
図１では直流電源２の負極は工具電極５に接続され、直流電源２の正極は被加工物６に接続されるが、工具電極５や被加工物６の材質により極を逆に配線する場合もある。工具電極５と被加工物６との極間隔は、水や放電油などで満たされる。また、工具電極５は上下左右に動作する軸移動駆動手段７に接続されており、少なくとも５００ｒｐｍ以上の回転数で回転可能であることが好ましい。
【００２９】
直流電源２が直流電圧を印加すると、コンデンサ４に電荷が充電され、コンデンサ４の端子間電圧が徐々に上昇する。コンデンサ４の端子間電圧が、工具電極５と被加工物６との間の極間隔の放電開始電圧を超えたとき、工具電極５と被加工物６との間で放電が発生する。
このプロセスの工具電極５と被加工物６との極間電圧の変化を極間比例電圧検出手段８で検出する。極間比例電圧検出手段８の例としては、十分高い抵抗値の抵抗分圧によって、実際に発生する電圧を分圧して検出する方法などがある。
【００３０】
一般的な放電加工機では、極間比例電圧検出手段８で検出された極間比例電圧を極間比例電圧平滑手段１２により平均化し、放電安定化制御手段１１に入力し、放電安定化制御手段１１では工具電極５と被加工物６との極間隔の距離が一定になるように軸移動制御手段１３に指令を送り、軸移動駆動手段７を制御する。
なお、極間比例電圧平滑手段１２は例えば抵抗器とコンデンサから構成される平滑回路などが用いられる。
【００３１】
本発明では、極間比例電圧検出手段８の検出値を、極間比例電圧平滑手段１２への入力に加えて電圧比較手段９を経由した放電状態悪化検出手段１０への入力を並列に設けることによって、放電状態悪化に応じてジャンプ動作を行うことを特徴とする。電圧比較手段９はコンパレータＩＣ回路と基準電圧設定素子で構成され、極間比例電圧と基準電圧との比較によって論理信号を出力し、放電状態悪化検出手段１０に入力する。放電状態悪化検出手段１０では放電状態悪化があらかじめ設定された時間継続した場合に異常を示す論理信号を異常放電信号として放電安定化制御手段１１に出力する。放電安定化制御手段１１は主にモータコントローラ回路で構成される。
【００３２】
異常放電信号が入力された放電安定化制御手段１１では、まずモータドライバ回路とモータ位置検出回路などで構成される軸移動制御手段１３に１〜１０μｍ程度の微小距離の後退指令を出力する。軸移動制御手段１３の動作結果は放電安定化制御手段１１にフィードバックされており、異常放電による後退動作完結も放電安定化制御手段１１に通知される。後退動作完結後も放電状態悪化検出手段１０からの異常放電信号が継続されている場合には、放電安定化制御手段１１は軸移動制御手段１３に対してジャンプ動作指令を出力する。
ジャンプ動作指令を受けた軸移動制御手段１３は、工具電極をジャンプ動作させることにより異常放電を回避し、加工限界深さを向上させることが出来る。
【００３３】
図２は本発明の実施に係る放電状態悪化検出手段１０を計時手段１６により構成する例を示す図である。計時手段１６の例としては、発振回路、カウンタ回路、ラッチ回路の構成がある。
また、図３は放電状態悪化検出手段１０を計時手段１６で構成した場合の極間比例電圧検出手段８から電圧比較手段９、放電状態悪化検出手段１０を経由した放電安定化制御手段１１までの各手段の出力信号波形を示す。電圧比較手段９は、極間比例電圧検出手段８の出力波形２０と基準電圧値２１を比較し、極間比例電圧検出手段８の出力波形２０が基準電圧値２１以下になっている期間、電圧比較手段９の出力論理信号２２をＨＩＧＨの状態にする。
【００３４】
ここで、基準電圧値２１は、放電状態または短絡を示すと実験的に求められた値であり、放電時の電圧下降ピーク値２４よりも少なくとも１０Ｖ以上大きい値を基準電圧に設定している。
【００３５】
正常な放電の場合、極間比例電圧は瞬時的に基準電圧を下回り、短絡または異常放電の場合には、異常期間中基準電圧を下回った状態を継続する。つまり、正常放電時には電圧比較手段９の出力波形２２はパルス幅の短い方形波を示し、異常放電時には電圧比較手段９の出力波形２２はＨＩＧＨの状態が継続する波形となる。
【００３６】
そこで、計時手段１６では、電圧比較手段９の出力論理信号２２がＨＩＧＨの状態になっている時間を計測し、ＨＩＧＨ状態が２５で示されるあらかじめ設定された時間以上継続した場合に、計時手段１６の出力論理信号２３をＬＯＷからＨＩＧＨにする。計時手段１６は出力論理信号ＨＩＧＨの状態を電圧比較手段９の出力論理信号２２がＬＯＷになるまで継続する。計時手段１６の出力論理信号２３は放電悪化検出信号として、次段の放電安定化制御手段１１に使用される。
つまり、計時手段１６の出力論理信号がＨＩＧＨの状態のとき、放電状態が悪化していると放電安定化制御手段１１は判定する。
【００３７】
図４は本発明の実施に係る放電状態悪化検出手段１０を平滑手段１７と第２の電圧比較手段１８により構成する例を示す。また、図５は放電状態悪化検出手段１０を平滑手段１７と第２の電圧比較手段１８で構成した場合の極間比例電圧検出手段８から電圧比較手段９、放電状態悪化検出手段１０を経由した放電安定化制御手段１１までの各手段の出力信号波形を示す。
【００３８】
平滑手段１７の平滑時定数は一般的なサーボ送り制御のために設置される極間比例電圧平滑手段１２の平滑時定数よりも小さい値にする。これにより、電圧比較手段９の出力論理信号２８の状態変化に対する追従性を高めることが出来る。
つまり、正常放電のときには電圧比較手段９の出力２８はパルス幅の短い方形状パルスとなり、ＨＩＧＨの状態になる期間は瞬時的でＬＯＷの期間が十分に長いため平滑手段１７の出力３０の上昇幅は小さく、異常放電のときは電圧比較手段９の出力２８がＨＩＧＨの状態を継続するために平滑手段１７の出力３０は大きく上昇する。第２の電圧比較手段１８では、平滑手段１７の出力３０の上昇があらかじめ設定された値以上に達した状態を判定し、第２の電圧比較手段１８の出力論理信号３１をＬＯＷからＨＩＧＨにして放電状態の悪化を示す。異常放電の状態から正常放電に復帰すると、電圧比較手段９の出力論理信号２８はＬＯＷになり、平滑手段１７の出力３０も下降し、第２の電圧比較手段１８の出力論理信号３１はＨＩＧＨからＬＯＷに戻り、正常放電を示す。第２の電圧比較手段１８の出力論理信号３１は放電状態悪化検出信号として、次段の放電安定化制御手段１１に使用される。
【００３９】
なお、極間比例電圧の平均値により極間隔の距離を制御するサーボ送り制御を行っている場合、極間比例電圧の平均値を、電圧比較手段９と平滑手段１７を介さずに、第２の電圧比較手段１８の入力として使用することも可能である。しかしながら、この場合、異常放電に対する応答性は悪くなるので、好ましくは図４の構成が望ましい。
また、図３、図５の倫理信号の値は一例であり、論理が逆になってもよい。
【００４０】
本発明の実施に係る微細穴放電加工機の制御装置の動作フローチャート例を図６に示す。
この動作フローチャート例は極間比例電圧検出手段８の出力を放電状態悪化検出に利用する電圧比較手段９と放電状態悪化検出手段１０への入力に加えて、極間比例電圧平滑手段１２を並列に設置してサーボ送り制御を併用して行うための１つの例を示すものである。
放電加工スタート（Ｓｔｅｐ１）により、工具電極は加工開始位置に移動する（Ｓｔｅｐ２）。加工用電源１の電圧供給が開始（Ｓｔｅｐ３）されるとともに、工具電極送りも開始される（Ｓｔｅｐ４）。その後、電極下端がワーク表面近傍に達すると、放電加工が開始する。
【００４１】
放電状態としては極間比例電圧検出手段８で検出される極間比例電圧を極間比例電圧平滑手段１２と、電圧比較手段９に入力し、それぞれ極間比例電圧平均値と放電状態悪化検出信号を得る。
まず、放電状態悪化検出信号より正常放電と異常放電を分別する（Ｓｔｅｐ５、６）。もし、正常放電ならば極間平均電圧より電極移動速度演算を行い、サーボ送り制御により極間隔の距離を一定化するように電極を移動する（Ｓｔｅｐ１３、１４、１５）。また、Ｓｔｅｐ６にて異常放電と判定された場合には、工具電極を微小距離後退（Ｓｔｅｐ７）させた後に、再度放電状態悪化信号を取得（Ｓｔｅｐ８）する。放電状態分岐Ｓｔｅｐ９にて、再度異常放電と判定された場合には、ジャンプ動作（Ｓｔｅｐ１１）を行い、工具電極を大きく短時間に往復運動を行う。その後、加工終了判定（Ｓｔｅｐ１２）を行い、加工終了してなければ、放電状態悪化信号取得（Ｓｔｅｐ５）に戻る。加工終了ならば、工具電極を加工開始位置に戻すなどの加工終了処理（Ｓｔｅｐ１６）を行い、加工を終了（Ｓｔｅｐ１７）する。
【００４２】
図７は本発明の実施に係る極間電圧波形に対しての電極位置軌跡の例を示す図である。この例でもサーボ送り制御を併用している。
正常放電が頻発するような極間電圧波形２０のとき、電極移動速度はゆるやかになり、極間隔の距離を広げようとする。放電頻度が多すぎる場合には微小距離後退することもある。正常放電の頻度が少ない極間電圧波形２１のときは電極移動速度が増し、極間隔の距離を狭めようとする。
異常放電が発生すると、まず電極は微小距離後退するが、微小距離後退後、放電が正常化するのが波形２２であり、異常放電が継続するのが波形２３である。波形２３の場合、加工液の浸透が不足し、加工屑も多いため、加工屑の介しての短絡や１箇所での集中アーク放電などの異常放電が発生しており、不具合が発生しやすい状況と判断してジャンプ動作を行う。
【００４３】
図８は本発明の実施に係る電極ジャンプ動作の説明図である。ジャンプ動作により、電極は少なくとも被加工物表面より下端が下になるように電極消耗率を考慮して計算した位置に移動する。これにより、加工屑を穴から排出する機会を与えることができる。ここで、電極下端が被加工物表面より上に移動してしまうと、微細加工用電極はたわみやすいので、被加工物の穴入口にひっかかってしまうという不具合が発生し、そのまま電極が曲がってしまい加工不能になってしまうことがある。
次に、電極は元の加工位置付近より微小距離上に戻るとともに、加工液を穴底に押し込む働きをする。加工液の穴底への浸透により、再度正常な放電加工を継続しやすい状態に戻すことが出来る。
【００４４】
ジャンプ動作における電極上昇位置についての計算例を示す。
電極下端が被加工物表面近傍に近づき、最初の放電が発生した電極位置をＺ１とする。その後、電極が下降し、ジャンプ動作を開始する直前の電極位置をＺ２とする。電極の下降方向を正方向と定義すると、Ｚ２＞Ｚ１となり、このとき、通常放電間隔は穴の深さより十分小さいので、放電開始点からの電極の送り量は（Ｚ２−Ｚ１）となる。電極は被加工物を加工すると同時に電極自身も消耗する。この消耗する長さは放電開始点からの電極の送り量に比例していると仮定し、放電開始点からの電極の送り量に係数ａを乗算し、ａ（Ｚ２−Ｚ１）とする。つまり、電極を（Ｚ２−Ｚ１）の距離ほど上昇させると、電極下端は被加工物表面よりａ（Ｚ２−Ｚ１）ほど上になってしまう。従って、電極を上昇させたとき、電極下端が被加工物表面より下にある条件は、電極上昇距離をＺ３とすると、
Ｚ３＜（Ｚ２−Ｚ１）−ａ（Ｚ２−Ｚ１）＝（１−ａ）（Ｚ２−Ｚ１）となる。つまり、電極消耗のばらつきを実験的に求め、それを考慮に入れた上で、（１−ａ）より小さい値の係数ｋを求め、ｋ（Ｚ２−Ｚ１）の距離ほど電極を上昇させれば、必ず電極下端は被加工物表面より下にジャンプすることができ、電極が被加工物の穴入り口に引っかかるなどの不具合を回避することができる。
【００４５】
【発明の効果】
本発明は、上記構成により次の効果を発揮する。
請求項１の発明によれば、微細穴放電加工において、実際の放電状態に応じて必要な回数だけジャンプ動作を行い、加工速度を損なわず、加工液を穴底へ浸透させ、加工屑の排出を促進させるために加工限界深さを向上させることが出来る。
請求項２の発明によれば放電状態悪化状態を高い応答性で検出することが出来き、請求項３の発明によれば、放電状態悪化時に瞬時的に正常になり、再度放電状態が悪化してしまうような場合でも放電状態悪化判定を継続させることが出来き、安定して放電加工を行うことができる。
また、請求４の発明によれば、極間隔の距離を一定に保つためのサーボ送り制御と併用することが可能となり、安定して放電加工を行うことができる。
さらに、請求項５の発明によれば、ジャンプ動作により、工具電極が被加工物穴入口にひっかかり、工具電極が曲がって穴の中に供給されなくなるという不具合を防止することが出来る。
本発明は、金属などの導電材料全般に対して有効であるが、特に導電性セラミックスに対する微細穴加工に対して効果が高い。
【図面の簡単な説明】
【図１】本発明の実施に係る微細穴放電加工機の制御装置の構成図である。
【図２】本発明の実施に係る放電状態悪化検出手段を計時手段により構成する例を示す図である。
【図３】本発明の実施に係る計時手段により構成された放電状態悪化検出手段周辺の信号波形例を示す図である。
【図４】本発明の実施に係る放電状態悪化検出手段を平滑手段と電圧比較手段で構成する例を示す図である。
【図５】本発明の実施に係る平滑手段と電圧比較手段により構成された放電状態悪化検出手段周辺の信号波形例を示す図である。
【図６】本発明の実施に係る微細穴放電加工機の制御装置の動作フローチャート例を示す図である。
【図７】本発明の実施に係る極間電圧波形に対しての電極位置軌跡の例を示す図である。
【図８】本発明の実施に係る電極ジャンプ動作の説明図である。
【符号の説明】
１…加工用電源
２…直流電源
３…抵抗
４…コンデンサ
５…工具電極
６…被加工物
７…軸移動駆動手段
８…極間比例電圧検出手段
９…電圧比較手段
１０…放電状態悪化検出手段
１１…放電安定化制御手段
１２…極間比例電圧平滑手段
１３…軸移動制御手段
１６…計時手段
１７…電圧平滑手段
１８…第２の電圧比較手段
２０…極間比例電圧検出手段８の出力波形
２１…電圧比較手段９の基準電圧設定値
２２…電圧比較手段９の出力波形
２３…計時手段１６の出力波形（放電状態悪化検出手段１０の出力波形）
２４…正常放電時の電圧下降ピーク
２５…計時手段１６にて放電状態悪化と判断する時間間隔
２６…極間比例電圧検出手段８の出力波形
２７…電圧比較手段９の基準電圧設定値
２８…電圧比較手段９の出力波形
２９…第２の電圧比較手段１８の基準電圧設定値
３０…電圧平滑手段１７の出力波形
３１…第２の電圧比較手段１８の出力波形（放電状態悪化検出手段１０の出力波形）
４０…正常放電頻度多時極間電圧波形
４１…正常放電頻度少時極間電圧波形
４２…異常放電時極間電圧波形（微小後退で正常放電復帰）
４３…異常放電時極間電圧波形（微小後退でも異常放電継続）
５０…放電加工中、加工屑が発生した状態
５１…ジャンプ動作途中であり工具電極を穴入口近くまで後退させた状態
５２…ジャンプ動作途中であり工具電極を元の加工位置に戻している状態
５３…ジャンプ動作途中であり工具電極を穴入口より上に引き上げた状態
５４…ジャンプ動作途中であり工具電極が穴入口に引っかかり加工不能になった状態[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control apparatus and method for electric discharge machining for machining a fine hole in a workpiece.
[0002]
[Prior art]
The electric discharge machining has many features such as easy machining of high precision and fine shape using the electric discharge phenomenon as a medium, and is a non-contact machining. For this reason, it is necessary to always maintain the pole interval formed between the tool electrode and the workpiece at a distance suitable for generating electric discharge.
In small-hole electrical discharge machining, the gap between the poles must always be driven in accordance with the amount of tool electrode and workpiece to be removed as the machining progresses. In order to keep the distance between the poles during EDM constant in response to such factors, generally, control the average value of the signal proportional to the pole-to-pole voltage generated between the tool electrode and the workpiece. As an input, a method of controlling the driving of the tool electrode so that the distance between the poles is constant is adopted. This is what is called so-called servo feed control found in books on electric discharge machining.
[0003]
However, in the small hole electric discharge machining, machining waste generated by the electric discharge machining is likely to remain in the extremely spaced machining portions and is hardly discharged. If a large amount of machining waste is interposed between the poles between the tool electrode and the workpiece, discharge phenomena may occur at places where machining is not required, or arcing may occur intensively at one location, causing abnormal machining. In addition, the tool electrode and the workpiece are short-circuited through the processing chips, and the processing does not progress, and the processing does not progress.
For this reason, when a tool electrode having a diameter of 0.1 mm or more can be used, a pipe electrode is used to provide a flow path inside the electrode and supply the machining fluid to the bottom of the hole where the machining is performed, and discharge machining chips. Prompt. However, when machining a fine hole that requires the use of a tool electrode having a diameter of 0.1 mm or less, it is very difficult to produce a pipe electrode having a diameter of 0.1 mm or less. If the machining fluid pressure is not increased, the effect of ejecting the machining swarf will not be enhanced unless the machining fluid pressure is increased, and there is a problem that both the equipment and the consumable tool become very expensive.
[0004]
In view of this, it is conceivable to obtain the effect of discharging machining chips by performing a jump operation of the tool electrode. FIG. 8 illustrates the jump operation. During the electric discharge machining, in the state 50 in which machining chips are generated, since machining chips are generated in the hole during the electric discharge machining, a jump operation is being performed, and the tool electrode is retracted to near the hole entrance. The machining waste is discharged by retracting the tool electrode to the vicinity of the hole entrance, and immediately thereafter, the machining fluid is pushed to the bottom of the hole by instantaneously returning to the vicinity of the original position where the tool electrode was processed. Such a series of instantaneous reciprocating movements of the tool electrode is a jump operation.
[0005]
As for the timing of performing the jump operation, a method of performing the jump operation at regular time intervals may be considered. However, it is more effective to set a hole processing depth position at which a jump operation is performed in advance according to a target processing depth. For example, there is a setting method in which, as the drilling depth increases, the interval between the drilling depth positions where the jump operation is performed is shortened. In the electric discharge machining, since the tool electrode is also consumed when machining the workpiece, the hole machining depth is smaller than the distance that the tool electrode has advanced after the start of the electric discharge. Therefore, the amount of consumption of the tool electrode according to the machining depth is obtained in advance by an experiment, and after detecting the position of the tool electrode, the machining depth is calculated by adding the amount of consumption of the tool electrode to the calculation.
Thus, in electric discharge machining using a thin wire electrode, particularly a rod-shaped solid thin wire electrode which cannot eject a machining liquid, it is possible to promote discharge of machining chips, increase a machining speed, and increase a machining limit depth ( For example, see Patent Document 1.)
[0006]
Further, as an invention not limited to the fine hole discharge, the movement of the electrode is detected by the position detector, and by servo control, the period of the operation of increasing and decreasing the distance between the electrodes and the workpiece is counted, If this cycle exceeds the specified value, it is determined that the discharge is unstable, and in addition to the jump operation at regular time intervals, a jump operation is performed to get out of the unstable discharge state. A method capable of stabilizing is disclosed (for example, see Patent Document 2).
[0007]
[Patent Document 1]
JP-A-9-76126 (FIG. 1)
[Patent Document 2]
JP-A-6-71517 (FIG. 1)
[0008]
[Problems to be solved by the invention]
However, when a jump operation is performed at a timing of a preset processing depth described in Patent Literature 1, there is a problem that control cannot be performed while reflecting an actual processing state. During the jump operation, the machining is in a pause state, so it is better to minimize the machining considering the machining speed.However, when setting the jump operation timing in advance, it is necessary to set a large margin with sufficient margin. It is not considered efficient in terms of speed. In particular, in the case of a material formed by mixing insulating particles and conductive particles, such as conductive ceramics, the distribution of the insulating particles and the conductive particles is not always uniform, and the processing of the same workpiece progresses depending on the location. Since the condition may be different, it is difficult to optimally set the jump operation timing in advance.
[0009]
In addition, the cycle of the operation of widening and narrowing the distance between the poles formed between the tool electrode side and the workpiece side described in Patent Document 2 is counted, and the discharge state becomes unstable when the period exceeds a specified value. In the method of judging that it has become, the timing may be optimal in normal die-sinking electric discharge, but there is a risk that the timing is late in the case of micro-hole electric discharge machining. For the operation to increase the distance between poles, the discharge itself is normal, but when the distance between the poles is narrow and the frequency of discharge is judged to be high, the distance between the poles is widened, or when a short circuit or concentrated discharge at one point occurs. And abnormal discharge. In the latter case, in the method of judging the instability of the discharge state by observing the cycle of the operation of widening and narrowing the distance between the poles, it may be too late in the fine hole electric discharge machining. In micro-hole electrical discharge machining, the machining liquid does not easily penetrate to the bottom of the hole, and the deeper the hole, the more difficult it is to discharge the machining waste.
[0010]
Therefore, as machining proceeds, the probability of occurrence of abnormal discharge increases, and in particular, abnormal discharge such as short-circuiting due to machining chips or arc concentrated at one location is reduced to about several μm by servo feed control or the like. There is a case where it is not easy to return to the normal discharge by the retreating movement of a minute distance. Furthermore, in the case of conductive ceramics formed by mixing insulating particles and conductive particles, if abnormal discharge continues, the proportion of insulating particles tends to increase at the bottom of the hole, and eventually the discharge itself does not occur Would. Therefore, when the distance between poles is widened due to abnormal discharge, the discharge state immediately after the distance between poles is widened is important. There is a risk that the microhole electrical discharge machining is already in an impossible state before the abnormality is recognized.
[0011]
The present invention has been made to solve the above-mentioned problem, and has a conductive material such as a metal. It is an object of the present invention to provide a micro-hole electric discharge machining control device which does not impair the machining speed, prevents machining inability due to electrode bending, and improves the machining limit depth in micro-hole electric discharge machining for processing conductive ceramics.
[0012]
[Means for Solving the Problems and Functions / Effects]
In order to achieve the above object, according to the first aspect of the present invention, a voltage is applied from a machining power supply to a pole interval formed between a thin rod-shaped or thin pipe-shaped tool electrode and a workpiece. In the micro-hole electric discharge machining apparatus for generating electric discharge and performing relative movement of the tool electrode and the workpiece by giving a command from an axis movement control means to perform the fine hole machining of the workpiece, the tool electrode And a pole-to-pole proportional voltage detecting means for detecting an analog voltage proportional to a pole-to-pole voltage generated in a pole-to-pole distance between the workpiece and the workpiece, and comparing the analog voltage with a reference voltage set to a value indicating a short-circuit or discharge state. Voltage comparison means for outputting a logic signal by detecting the state of short-circuit or abnormal discharge by the logic signal; A signal instructs the axis movement control means to perform an operation of extending the relative distance between the tool electrode and the workpiece by a small distance of at least once or less than 10 μm by a signal, and a discharge state by the discharge state deterioration detection means. When the deterioration signal continues, the discharge stabilization control means instructs the axis movement control means to perform a jump operation.
[0013]
The voltage comparison means detects all of the normal discharge, the short circuit, and the abnormal discharge by comparing the analog voltage of the gap voltage detection means with the reference voltage. Then, the discharge state deterioration detection means extracts a short circuit and abnormal discharge from the signal from the voltage comparison means, and uses this as a discharge state deterioration signal. The discharge state stabilization control means first instructs the axis movement control control means to retreat a small distance by the discharge state deterioration detection signal, and attempts to restore the normal state with minimum effort. If it does not return to the normal discharge state due to this minute distance retreat, it is estimated that the penetration of the machining fluid at the bottom of the hole is not enough, and that there is a large amount of machining chips. It is regarded as a precursor to the occurrence of a failure. The discharge state stabilization control unit instructs the axis movement control unit to perform a jump operation only at a timing considered to be a precursor to the occurrence of this problem, so that a jump operation disadvantageous in machining time is performed as little as possible. It can be done as many times as needed.
[0014]
Therefore, according to the present invention, in micro-hole electric discharge machining, a jump operation is performed a required number of times in accordance with an actual electric discharge state, and a machining fluid permeates a hole bottom without impairing a machining speed, thereby discharging machining chips. In order to accelerate, the processing limit depth can be improved.
[0015]
According to a second aspect of the present invention, the discharge state deterioration detecting means comprises time measuring means for measuring a discharge detection continuous time of an output logic signal from the voltage comparing means, and the discharge detection continues for a predetermined time or more. In such a case, a discharge state deterioration detection signal is output.
[0016]
The discharge state deterioration detection means measures a discharge detection continuous time to extract a short circuit or abnormal discharge from all detection signals of normal discharge, short circuit and abnormal discharge from the voltage comparison means. In this case, the delay time until the detection of the deterioration of the discharge state is only the set time regarded as the deterioration of the discharge state by the timer.
[0017]
Therefore, according to the present invention, the discharge state deterioration state can be detected with high responsiveness, and electric discharge machining can be stably performed.
[0018]
The invention according to claim 3 is characterized in that the discharge state deterioration detecting means smoothes an output logic signal from the voltage comparing means and converts it into an analog signal, and the analog signal reaches a preset threshold value. And a second voltage comparing means for outputting a discharge state deterioration detection signal when the signal is detected.
[0019]
The discharge state deterioration detection means includes a voltage smoothing means and a second voltage comparison means for extracting a short circuit or an abnormal discharge from the detection signals of the normal discharge, short circuit and abnormal discharge from the voltage comparison means. It consists of In the case of a normal discharge, the output of the voltage comparison means has a pulse waveform in which the logic inversion is instantaneous, whereas in the case of a short circuit or abnormal discharge, the time of the logic inversion is long. And a second voltage comparing means that provides a selection criterion for the two to make a logical signal.
In particular, when the circuit that applies the voltage between the poles is a power supply circuit composed of a capacitor and a resistor, the output analog voltage value of the pole-to-pole proportional voltage detection means is equal to the reference voltage value during the charging period from the occurrence of discharge. Responsivity can be improved by setting the smoothing time constant of the voltage smoothing means to a value as small as possible within a range longer than the predetermined time and shorter than the charging time. Further, when the discharge state is deteriorating, there may be a case where it seems that the discharge has temporarily returned to the normal discharge, and the degraded state is returned immediately. Since the influence is hardly exerted, the output can maintain the discharge deterioration state.
[0020]
Therefore, according to the present invention, even when the discharge state deteriorates instantaneously and the discharge state deteriorates again, the discharge state deterioration determination can be continued, and the electric discharge machining is stably performed. be able to.
[0021]
According to a fourth aspect of the present invention, the output of the pole-to-pole proportional voltage detection means is input, and the distance between the tool electrode and the workpiece is constant in parallel with the input to the voltage comparison means. And an inter-electrode proportional voltage smoothing means for outputting an average value of the inter-electrode proportional voltage as a control input signal for controlling the axis movement control means.
[0022]
During normal discharge, the discharge stabilization control means performs control output to the axis movement control means so that the average value of the interpole proportional voltage becomes a control input and the distance between the poles becomes constant, so-called servo feed control, When a short circuit or abnormal discharge occurs, control such as a retreat of a minute distance or a jump operation is performed by a discharge state deterioration detection signal.
[0023]
Therefore, according to the present invention, it is possible to use together with the servo feed control for keeping the distance between the poles constant, and to stably perform the electric discharge machining.
[0024]
According to a fifth aspect of the present invention, when the lower end of the electrode and the bottom of the processing hole are farthest apart from each other in the jump operation, the lower end of the electrode does not protrude at least above the upper surface of the workpiece.
[0025]
In the jump operation, the pole gap is instantaneously increased and returned to the original pole gap again.If the pole gap is widened, the lower end of the tool electrode is higher than the workpiece hole entrance. In the following step of returning to the original pole interval in the next step, there is a possibility that the workpiece may be caught at the entrance of the workpiece hole due to the influence of center runout or the like. Since the tool electrode for micro hole drilling is fine and generally very easy to bend, if it gets caught at the workpiece hole entrance, the tool electrode itself bends as it is, making it impossible to pass the tool electrode through the hole, making machining impossible I fall.
[0026]
Therefore, according to the present invention, it is possible to prevent a problem that the tool electrode is caught in the workpiece hole entrance by the jumping operation and the tool electrode is bent and is not supplied into the hole.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0028]
FIG. 1 is a configuration diagram of a control device for a small-hole electric discharge machine according to the present invention.
The processing power supply 1 includes a DC power supply 2, a resistor 3, and a capacitor 4.
In FIG. 1, the negative electrode of the DC power supply 2 is connected to the tool electrode 5, and the positive electrode of the DC power supply 2 is connected to the workpiece 6, but the poles are reversed depending on the material of the tool electrode 5 and the workpiece 6. There is also. The gap between the tool electrode 5 and the workpiece 6 is filled with water, discharge oil, or the like. Further, it is preferable that the tool electrode 5 is connected to a shaft moving driving means 7 which moves up, down, left and right, and is rotatable at a rotation speed of at least 500 rpm or more.
[0029]
When the DC power supply 2 applies a DC voltage, the capacitor 4 is charged with electric charge, and the voltage between the terminals of the capacitor 4 gradually increases. When the voltage between the terminals of the capacitor 4 exceeds the discharge starting voltage at the pole interval between the tool electrode 5 and the workpiece 6, discharge occurs between the tool electrode 5 and the workpiece 6.
A change in the voltage between the tool electrode 5 and the workpiece 6 in this process is detected by the gap voltage detecting means 8. As an example of the pole-to-pole proportional voltage detecting means 8, there is a method of detecting a voltage that is actually generated by dividing a voltage that is actually generated by a resistor voltage having a sufficiently high resistance value.
[0030]
In a general electric discharge machine, the inter-electrode proportional voltage detected by the inter-electrode proportional voltage detection means 8 is averaged by the inter-electrode proportional voltage smoothing means 12 and input to the discharge stabilization control means 11. At 11, a command is sent to the axis movement control means 13 to control the axis movement drive means 7 so that the distance between the poles between the tool electrode 5 and the workpiece 6 becomes constant.
The inter-pole proportional voltage smoothing means 12 uses, for example, a smoothing circuit including a resistor and a capacitor.
[0031]
In the present invention, in addition to the input of the detection value of the interelectrode proportional voltage detection means 8 to the input to the interelectrode proportional voltage smoothing means 12, the input to the discharge state deterioration detection means 10 via the voltage comparison means 9 is provided in parallel. Accordingly, a jump operation is performed according to the deterioration of the discharge state. The voltage comparison means 9 is composed of a comparator IC circuit and a reference voltage setting element, outputs a logic signal by comparing the inter-pole proportional voltage and the reference voltage, and inputs the logic signal to the discharge state deterioration detection means 10. When the discharge state deterioration continues for a preset time, the discharge state deterioration detection means 10 outputs a logic signal indicating an abnormality to the discharge stabilization control means 11 as an abnormal discharge signal. The discharge stabilization control means 11 is mainly composed of a motor controller circuit.
[0032]
The discharge stabilization control unit 11 to which the abnormal discharge signal has been input first outputs a retreat command of a minute distance of about 1 to 10 μm to the axis movement control unit 13 including a motor driver circuit and a motor position detection circuit. The operation result of the axis movement control unit 13 is fed back to the discharge stabilization control unit 11, and the completion of the retreat operation due to the abnormal discharge is also notified to the discharge stabilization control unit 11. If the abnormal discharge signal from the discharge state deterioration detecting means 10 continues even after the retreat operation is completed, the discharge stabilization control means 11 outputs a jump operation command to the axis movement control means 13.
The axis movement control means 13 having received the jump operation command can avoid abnormal discharge by performing the jump operation of the tool electrode, and can improve the machining limit depth.
[0033]
FIG. 2 is a diagram showing an example in which the discharge state deterioration detecting means 10 according to the embodiment of the present invention is constituted by the time measuring means 16. Examples of the timer 16 include an oscillation circuit, a counter circuit, and a latch circuit.
Further, FIG. 3 shows a configuration from the inter-pole proportional voltage detection means 8 to the voltage comparison means 9 and the discharge stabilization control means 11 via the discharge state deterioration detection means 10 when the discharge state deterioration detection means 10 is constituted by the time keeping means 16. The output signal waveform of each means is shown. The voltage comparison means 9 compares the output waveform 20 of the inter-electrode proportional voltage detection means 8 with the reference voltage value 21, and outputs the voltage during the period when the output waveform 20 of the inter-electrode proportional voltage detection means 8 is equal to or less than the reference voltage value 21. The output logic signal 22 of the comparison means 9 is set to HIGH.
[0034]
Here, the reference voltage value 21 is a value experimentally determined to indicate a discharge state or a short circuit, and a value larger than the voltage drop peak value 24 at the time of discharge by at least 10 V is set as the reference voltage.
[0035]
In the case of a normal discharge, the interelectrode proportional voltage instantaneously falls below the reference voltage, and in the case of a short circuit or abnormal discharge, the state in which the voltage falls below the reference voltage continues during the abnormal period. That is, during normal discharge, the output waveform 22 of the voltage comparison means 9 shows a square wave with a short pulse width, and during abnormal discharge, the output waveform 22 of the voltage comparison means 9 becomes a waveform in which the HIGH state continues.
[0036]
Therefore, the time counting means 16 measures the time during which the output logic signal 22 of the voltage comparing means 9 is in the HIGH state, and when the HIGH state continues for a preset time indicated by 25, the time counting means 16 Is changed from LOW to HIGH. The timer 16 continues the state of the output logic signal HIGH until the output logic signal 22 of the voltage comparator 9 becomes LOW. The output logic signal 23 of the timer 16 is used as a discharge deterioration detection signal by the discharge stabilization control unit 11 at the next stage.
That is, when the output logic signal of the timer 16 is in the HIGH state, the discharge stabilization controller 11 determines that the discharge state is deteriorating.
[0037]
FIG. 4 shows an example in which the discharge state deterioration detecting means 10 according to the embodiment of the present invention is constituted by the smoothing means 17 and the second voltage comparing means 18. FIG. 5 shows a case where the discharge state deterioration detecting means 10 is constituted by the smoothing means 17 and the second voltage comparing means 18, and passes from the interelectrode proportional voltage detecting means 8 to the voltage comparing means 9 and the discharge state deterioration detecting means 10. The output signal waveforms of each means up to the discharge stabilization control means 11 are shown.
[0038]
The smoothing time constant of the smoothing means 17 is set to a value smaller than the smoothing time constant of the inter-pole proportional voltage smoothing means 12 provided for general servo feed control. As a result, it is possible to improve the followability to the state change of the output logic signal 28 of the voltage comparison means 9.
In other words, during a normal discharge, the output 28 of the voltage comparing means 9 is a square pulse having a short pulse width, and the HIGH state is instantaneous and the LOW period is sufficiently long, so that the rising width of the output 30 of the smoothing means 17 is large. In the case of abnormal discharge, the output 30 of the voltage comparing means 9 continues to be in the HIGH state, so that the output 30 of the smoothing means 17 rises greatly. The second voltage comparing means 18 determines a state where the rise of the output 30 of the smoothing means 17 has reached a predetermined value or more, and changes the output logic signal 31 of the second voltage comparing means 18 from LOW to HIGH. This shows the deterioration of the discharge state. When the state returns from the abnormal discharge to the normal discharge, the output logic signal 28 of the voltage comparison means 9 becomes LOW, the output 30 of the smoothing means 17 also falls, and the output logic signal 31 of the second voltage comparison means 18 changes from HIGH. Return to LOW, indicating normal discharge. The output logic signal 31 of the second voltage comparison means 18 is used by the next-stage discharge stabilization control means 11 as a discharge state deterioration detection signal.
[0039]
In the case where the servo feed control for controlling the distance between the poles is performed based on the average value of the pole-to-pole voltage, the average value of the pole-to-pole voltage is calculated without using the voltage comparing means 9 and the smoothing means 17. Can also be used as an input to the voltage comparison means 18 of FIG. However, in this case, the response to the abnormal discharge is deteriorated. Therefore, the configuration shown in FIG. 4 is preferable.
Also, the values of the ethics signals in FIGS. 3 and 5 are examples, and the logic may be reversed.
[0040]
FIG. 6 shows an example of an operation flowchart of the control device of the micro-hole electric discharge machine according to the embodiment of the present invention.
In this example of the operation flowchart, in addition to the voltage comparison means 9 and the input to the discharge state deterioration detecting means 10 which use the output of the gap proportional voltage detecting means 8 for detecting the deterioration of the discharge state, the gap proportional voltage smoothing means 12 is connected in parallel. It shows one example for installing and performing servo feed control together.
With the start of electric discharge machining (Step 1), the tool electrode moves to the machining start position (Step 2). The voltage supply of the machining power supply 1 is started (Step 3), and the tool electrode feed is also started (Step 4). Thereafter, when the lower end of the electrode reaches the vicinity of the work surface, electric discharge machining starts.
[0041]
As the discharge state, the inter-electrode proportional voltage detected by the inter-electrode proportional voltage detection means 8 is input to the inter-electrode proportional voltage smoothing means 12 and the voltage comparison means 9, and the inter-electrode proportional voltage average value and the discharge state deterioration detection signal, respectively. Get.
First, normal discharge and abnormal discharge are distinguished from the discharge state deterioration detection signal (Steps 5 and 6). If the discharge is normal, the electrode moving speed is calculated from the average voltage between the electrodes, and the electrodes are moved by servo feed control so as to keep the distance between the electrodes constant (Steps 13, 14, 15). If it is determined in Step 6 that the discharge is abnormal, the tool electrode is retracted by a small distance (Step 7), and then the discharge state deterioration signal is obtained again (Step 8). If it is determined again that the discharge is abnormal in the discharge state branch Step 9, a jump operation (Step 11) is performed, and the tool electrode reciprocates largely in a short time. Thereafter, a machining end determination (Step 12) is performed, and if machining is not completed, the process returns to the discharge state deterioration signal acquisition (Step 5). If machining is completed, machining end processing such as returning the tool electrode to the machining start position (Step 16) is performed, and the machining is ended (Step 17).
[0042]
FIG. 7 is a diagram showing an example of an electrode position trajectory with respect to a voltage waveform between electrodes according to the embodiment of the present invention. In this example, servo feed control is also used.
In the case of the inter-electrode voltage waveform 20 in which normal discharge frequently occurs, the electrode moving speed becomes slow and an attempt is made to widen the inter-electrode distance. If the frequency of discharge is too high, there may be a retreat of a minute distance. In the case of the inter-electrode voltage waveform 21 in which the frequency of normal discharge is low, the electrode moving speed increases, and the distance between the inter-electrodes is reduced.
When an abnormal discharge occurs, the electrode first retreats by a minute distance. After the retreat by a minute distance, the waveform 22 normalizes the discharge, and the waveform 23 indicates that the abnormal discharge continues. In the case of the waveform 23, since the penetration of the machining fluid is insufficient and there is a large amount of machining waste, abnormal discharge such as short-circuiting through the machining waste or a concentrated arc discharge at one place occurs, and a problem is likely to occur. And a jump operation is performed.
[0043]
FIG. 8 is an explanatory diagram of the electrode jump operation according to the embodiment of the present invention. By the jump operation, the electrode is moved to a position calculated in consideration of the electrode wear rate so that the lower end is at least lower than the surface of the workpiece. Thereby, an opportunity to discharge the processing waste from the hole can be provided. Here, if the lower end of the electrode moves above the surface of the workpiece, the electrode for micro-machining tends to bend, causing a problem that the electrode is caught at the hole entrance of the workpiece, and the electrode is bent as it is. Processing may not be possible.
Next, the electrode functions to return a small distance from the vicinity of the original processing position and to push the processing liquid to the bottom of the hole. By the penetration of the machining fluid into the bottom of the hole, it is possible to return to a state where normal electric discharge machining can be continued easily.
[0044]
4 shows a calculation example of an electrode rising position in a jump operation.
The electrode position where the lower end of the electrode approaches the vicinity of the surface of the workpiece and the first discharge occurs is denoted by Z1. Thereafter, the electrode is lowered and the electrode position immediately before the start of the jump operation is defined as Z2. If the descending direction of the electrode is defined as the positive direction, Z2> Z1. At this time, since the normal discharge interval is sufficiently smaller than the depth of the hole, the feed amount of the electrode from the discharge start point is (Z2-Z1). The electrode itself wears out at the same time as the workpiece is processed. Assuming that the consumed length is proportional to the electrode feed amount from the discharge start point, the electrode feed amount from the discharge start point is multiplied by a coefficient a to obtain a (Z2-Z1). That is, when the electrode is raised by a distance of (Z2-Z1), the lower end of the electrode is higher by a (Z2-Z1) than the surface of the workpiece. Therefore, when the electrode is lifted, the condition that the lower end of the electrode is below the surface of the workpiece is as follows, assuming that the electrode lifting distance is Z3.
Z3 <(Z2-Z1) -a (Z2-Z1) = (1-a) (Z2-Z1). That is, if the variation in electrode wear is determined experimentally, and taking that factor into account, a coefficient k smaller than (1-a) is determined, and the electrode is raised by a distance of k (Z2-Z1). In addition, the lower end of the electrode can always jump below the surface of the workpiece, thereby avoiding such a problem that the electrode is caught in the hole of the workpiece.
[0045]
【The invention's effect】
The present invention has the following effects by the above configuration.
According to the first aspect of the present invention, in micro-hole electric discharge machining, a jump operation is performed a required number of times in accordance with an actual electric discharge state, a machining liquid is permeated into a hole bottom without impairing a machining speed, and machining chips are discharged. In order to promote the processing, the processing limit depth can be improved.
According to the second aspect of the present invention, it is possible to detect the deteriorated state of the discharge state with high responsiveness. In such a case, the determination of the deterioration of the discharge state can be continued, and the discharge machining can be stably performed.
According to the fourth aspect of the present invention, it is possible to use together with the servo feed control for keeping the distance between the poles constant, and to stably perform the electric discharge machining.
Further, according to the fifth aspect of the present invention, it is possible to prevent a problem that the tool electrode is hooked on the workpiece hole entrance by the jumping operation and the tool electrode is bent and is not supplied into the hole.
The present invention is effective for all conductive materials such as metals, but is particularly effective for processing fine holes in conductive ceramics.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a control device of a micro-hole electric discharge machine according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example in which a discharge state deterioration detection unit according to an embodiment of the present invention is configured by a time measurement unit.
FIG. 3 is a diagram showing an example of a signal waveform around a discharge state deterioration detecting means constituted by a time measuring means according to an embodiment of the present invention.
FIG. 4 is a diagram showing an example in which the discharge state deterioration detecting means according to the embodiment of the present invention is constituted by a smoothing means and a voltage comparing means.
FIG. 5 is a diagram showing an example of a signal waveform around a discharge state deterioration detecting means constituted by a smoothing means and a voltage comparing means according to the embodiment of the present invention.
FIG. 6 is a diagram illustrating an example of an operation flowchart of a control device of the micro-hole electric discharge machine according to the embodiment of the present invention.
FIG. 7 is a diagram showing an example of an electrode position locus with respect to a voltage waveform between electrodes according to the embodiment of the present invention.
FIG. 8 is an explanatory diagram of an electrode jump operation according to the embodiment of the present invention.
[Explanation of symbols]
1. Processing power supply
2: DC power supply
3 ... resistance
4: Capacitor
5. Tool electrode
6 ... Workpiece
7. Axis moving drive means
8. Means for detecting proportional voltage between contacts
9 ... Voltage comparison means
10 ... discharge state deterioration detection means
11 ... Discharge stabilization control means
12... Inter-pole proportional voltage smoothing means
13. Axis movement control means
16 ... Timekeeping means
17: voltage smoothing means
18. Second voltage comparing means
20: output waveform of the inter-pole proportional voltage detection means 8
21: Reference voltage set value of voltage comparison means 9
22: output waveform of voltage comparison means 9
23: output waveform of the timing means 16 (output waveform of the discharge state deterioration detecting means 10)
24: Voltage drop peak during normal discharge
25: Time interval for determining that the discharge state is deteriorated by the timer 16
26 output waveform of the inter-pole proportional voltage detection means 8
27: Reference voltage set value of voltage comparison means 9
28 output waveform of voltage comparing means 9
29: Reference voltage set value of second voltage comparison means 18
30 output waveform of voltage smoothing means 17
31: output waveform of the second voltage comparing means 18 (output waveform of the discharge state deterioration detecting means 10)
40: Normal discharge frequency multi-hour inter-electrode voltage waveform
41: Voltage waveform between electrodes when normal discharge frequency is low
42: Voltage waveform between electrodes during abnormal discharge (normal discharge is restored by minute retreat)
43: Voltage waveform between electrodes during abnormal discharge (abnormal discharge continues even if it is slightly retracted)
50: State in which machining chips were generated during electric discharge machining
51: A state in which the tool electrode is retracted to near the hole entrance during the jump operation
52: A state in which the tool electrode is returned to the original machining position during a jump operation.
53: A state in which the tool electrode is raised above the hole entrance during the jump operation
54: A state in which machining is not possible because the tool electrode is caught in the hole entrance during the jump operation

Claims

A voltage is applied from a machining power source to a pole interval formed between a thin rod-shaped or thin pipe-shaped tool electrode and a workpiece to generate a discharge, and the tool electrode and the workpiece are pivoted. In a micro-hole electric discharge machine that performs relative hole movement by giving a command from a movement control means to perform fine hole machining of the workpiece,
A pole-to-pole proportional voltage detection unit that detects an analog voltage that is proportional to a pole-to-pole voltage generated in a pole interval between the tool electrode and the workpiece,
Voltage comparing means for comparing the analog voltage with a reference voltage set to a value indicating a short circuit or a discharge state and outputting a logic signal;
Discharge state deterioration detection means for detecting a short circuit or abnormal discharge state by the logic signal,
In accordance with the discharge state deterioration signal from the discharge state deterioration detection means, the axis movement control means is instructed to perform an operation of increasing the relative distance between the tool electrode and the workpiece by a minute distance of at least once or less than 10 μm. And a discharge stabilization control means for instructing the axis movement control means to perform a jump operation when the discharge state deterioration signal by the discharge state deterioration detection means continues. Control device.

The discharge state deterioration detection means includes time measurement means for measuring a discharge detection continuous time of the output logic signal from the voltage comparison means, and outputs a discharge state deterioration detection signal when discharge detection continues for a preset time or more. The control device for a micro-hole electric discharge machine according to claim 1, wherein

The discharge state deterioration detecting means smoothes an output logic signal from the voltage comparing means and converts the output logic signal into an analog signal, and outputs a discharge state deterioration detection signal when the analog signal reaches a preset threshold value. 2. The control device for a micro-hole electric discharge machine according to claim 1, further comprising a second voltage comparing means.

The output of the interpole proportional voltage detection means is input, and the axis movement control means is controlled in parallel with the input to the voltage comparison means so that the distance between the tool electrodes and the workpiece is constant. 4. The control device for a micro-hole electric discharge machine according to claim 1, further comprising an inter-electrode proportional voltage smoothing means for outputting an average value of the inter-electrode proportional voltage as a control input signal for controlling.

The thin hole electric discharge machine according to claim 1, wherein the lower end of the electrode does not protrude at least above the upper surface of the workpiece when the lower end of the electrode is farthest away from the bottom of the machining hole in the jumping operation. Control method.