JP3557913B2

JP3557913B2 - Electric discharge machine

Info

Publication number: JP3557913B2
Application number: JP25488298A
Authority: JP
Inventors: 卓司真柄
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1998-09-09
Filing date: 1998-09-09
Publication date: 2004-08-25
Anticipated expiration: 2018-09-09
Also published as: JP2000084737A

Description

【０００１】
【発明の属する技術分野】
この発明は、単純形状の電極を利用して、被加工物の放電加工を行う放電加工装置の改良に関するものである。
【０００２】
【従来の技術】
従来の放電加工装置を図１２１によって説明する。図１２１において、１は電極、２は被加工物、３は電圧値を可変できる可変電源、４は電流制限用の抵抗値を可変できる可変抵抗、５はパルス電圧を供給するためのスイッチング素子、６はスイッチング素子５のスイッチングを制御するスイッチング制御回路、７は静電容量を可変できる可変コンデンサ素子、８は電極１と被加工物２で形成される加工間隙（以下、極間という。）の浮遊静電容量、９は極間における放電の発生を、電圧の立ち下がりにより検出する放電検出回路である。
【０００３】
次に、上記のように構成された放電加工装置の動作を図１２及び図１３によって説明する。スイッチング制御回路６によりスイッチング素子５をオンすることにより、可変電源３によって決定される電圧が、電極１と被加工物２の間に形成される極間に供給される。放電検出回路９は、極間に放電が発生して、極間の印加電圧が所定の電圧レベルより低くなったことを条件に放電を検出し、検出値をスイッチング制御回路６に送る。
【０００４】
スイッチング制御回路６は放電の発生から所定の時間だけスイッチング素子５のオン状態を維持してオン時間ｔｏｎのみ電流パルスを流した後、スイッチング素子５をオフ時間ｔｏｆｆだけ休止させることにより図１２に示す電流が極間に流れる。以上の電源制御を行うことにより放電加工が進行する。
【０００５】
【発明が解決しようとする課題】
しかしながら、上記のように構成された放電加工装置は、図１４に示すように途中で、電流パルスが遮断することがある。かかる現象は、パルス切れと言われ、電極１の消耗の増加、加工速度が低下する。
【０００６】
パルス切れは、（１）電流パルスの波高値が小さいほど、すなわち制限抵抗Ｒが大きいほど、（２）回路がキャパシティブであるほど、すなわちコンデンサ７の静電容量および極間浮遊容量８が大きく、回路のインダクタンスが小さいほど、生じ易いことが知られているので、パルス切れが発生しにくい回路定数の組合せを選択している。
【０００７】
しかしながら、加工の面積が大きいか、あるいは加工中に加工面積が増大すると、極間に形成される浮遊静電容量８が増大し、最適な回路定数の組合せを選択しても、パルス切れの頻度が高くなる。例えば、１０，０００ｍｍ^２程度以上の加工面積にて５μｍＲｍａｘ以下の面粗さの仕上加工領域の加工の場合、パルス切れの防止が困難となり、パルス切れにより電極１の消耗が著しく増大するなど、加工精度の劣化を招き、加工効率が低下し、加工速度が増大するという問題点があった。
【０００８】
この発明は上記のような課題を解決するためになされたもので、電流パルス切れが多発しても、電極消耗を低減するとともに、加工速度の低下を防ぐ放電加工装置を提供することを目的とする。
【０００９】
【課題を解決するための手段】
第１の発明に係る放電加工装置は、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、上記電極を上記電圧発生手段の陰極にすると共に、上記被加工物を上記電圧発生手段の陽極に切り換える電圧極性切換え手段と、上記静電容量検出手段の検出値に基づて上記電圧切換え発生手段を用いて上記電極及び上記被加工物の電圧極性を切り換える制御手段とを備えたことを特徴とするたものである。
【００１０】
第２の発明に係る放電加工装置は、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成すと共に、電圧値を可変できる可変電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、この静電容量検出手段の検出値に基づき上記可変電圧発生手段の発生する電圧値を変更する制御手段とを備えたことを特徴とするものである。
【００１１】
第３の発明に係る放電加工装置は、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、上記電極と上記被加工物との間隙に流れる電流の波高値を変更する波高値変更手段と、上記静電容量検出手段の検出値に基いて上記波高値変更手段により上記間隙に流れる電流を制御する制御手段とを備えたことを特徴とするものである。
【００１２】
第４の発明に係る放電加工装置は、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、上記電極と上記被加工物との間隙の静電容量値を変更する可変静電容量手段と、上記静電容量検出手段の検出値に基づいて、上記可変静電容量手段の静電容量値を変更する制御手段とを備えたことを特徴とするものである。
【００１３】
第５の発明に係る放電加工装置は、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記電極と上記被加工物との間隙の平均電圧値を定める平均電圧基準手段と、この平均電圧基準手段に基いて上記平均電圧が基準値になるように制御する平均電圧制御手段と、上記極間の静電容量を検出する静電容量検出手段と、この静電容量検出手段の検出値に基づて上記平均電圧基準手段の電圧値を変更制御する制御手段とを備えたことを特徴とするものである。
【００１４】
第６の発明に係る放電加工装置の静電容量検出手段は、間隙の電圧の立ち上がり時間を計測する計測手段であることを特徴とするものである。
【００１５】
【実施の形態】
実施の形態１．
この発明の実施の形態を図１及び図２によって説明する。図１はこの発明の一実施の形態を示す放電加工装置の回路図、図２はパルス電圧の立ち上がり時間を計測する回路図である。図中、従来と同一符号は同一又は相当部分を示し、説明を省略する。図１において、可変電源３は電圧極性切り換え手段としての切り換え部２０を介して可変抵抗４の一端と、被加工物２、可変コンデンサ７の一端などに接続されている。切り換え部２０は可変電源３の極性を切り換えるもので、接点Ａ，Ａと接点Ｂ，Ｂとから成り、一方の接点Ａ，Ａ（Ｂ，Ｂ）が閉成している時は、他方の接点Ｂ，Ｂ（Ａ，Ａ）が開放するように構成されている。
【００１６】
３０は極間の静電容量を静電容量検出手段としての、極間のパルス電圧の立ち上がり時間を計測する計測回路、５０は計測回路３０の検出値に基づいて、例えば、電圧立ち上がり時間の増加によって切り換え部２０を動作して、可変電源３の極性を切り換えて電極１の極性を陰極にすると共に、電圧電源３の電圧を減少するように制御する電源制御器である。
【００１７】
ここで、計測回路３０が極間静電容量Ｃの代わりに電圧の立ち上がり時間を計測するのは、極間静電容量に対応して電圧立ち上がり時間ｔｒが変化するからである。極間静電容量Ｃと電圧の立ち上がり時間ｔｒ（ｔｒ_１、ｔｒ_２…ｔｒｎ）との間には、以下の（１）〜（３）が得られ、下式を解くことで、電圧立ち上がり時間から極間静電容量が求まる。
Ｖｒ_１＝Ｅ・（１−ｅ^{−ｔ１／ＲＣ}）（１）
Ｖｒ_２＝Ｅ・（１−ｅ^{−ｔ２／ＲＣ}）（２）
ｔｒ＝ｔ_２−ｔ_１（３）
ここで、Ｒは回路の抵抗値（電流制限抵抗）、Ｅは電圧電源３の電圧値、ｔ_１は電圧印加からＶｒ_１までの立ち上がり時間、ｔ_２は電圧印加からＶｒ_２までの立ち上がり時間である。
【００１８】
また、極間静電容量の増大により電極１の極性を通常と逆の陰極にするのは、パルス幅が短い波形の方が電極の消耗が少ないことが知られているからである。例えば、加工面積が１０，０００ｍｍ^２程度以上について、電極１が陽極でパルス切れの頻発する状態で加工をしている時に、電極１の極性を陰極として０．０１〜０．１μＦ程度のコンデンサを極間に付加し、パルス幅が０．１〜０．５μｓ程度と短いコンデンサ電流波形にて加工をした方が電極１の消耗も少なく、加工速度も速いからである。
【００１９】
図２の計測回路３０において、３３、３４は基準電圧設定器、３５、３６は電圧立ち上がり時の電圧を基準電圧と比較するコンパレータ、３７は基準カウントパルス発生器、３８はＡＮＤ回路、３９はＮＡＮＤ回路、４０は電圧立ち上がり時間をカウントするカウンター、４１はカウンター４０の出力を保持するラッチ回路である。
【００２０】
次に、上記のように構成された放電加工装置の動作を図１〜図３を参照して説明する。図３は計測回路の動作を示すタイムチャートである。まず、切り換え部２０の接点Ａ，Ａを閉成すると共に、接点Ｂ，Ｂを開放のままにしてスイッチング制御回路６がスイッチング素子５をオンすることにより、可変電源３の電圧値が電極１と被加工物２の間に形成される極間に供給される。
【００２１】
放電検出回路９は、極間において放電が発生し、電極１と被加工物２の間の印加電圧が所定の電圧レベルより低くなった場合に放電を検出し、検出結果をスイッチング制御回路６に送る。スイッチング制御回路６は放電の発生からスイッチング素子５を時間ｔｏｎのみオンして極間の電圧を図３（ａ）に示すように立ち上げて電流パルスを流した後、スイッチング素子５を時間ｔｏｆｆのみオフさせ、かかるスイッチング動作を繰り返す。
【００２２】
計測回路３０は、基準電圧設定器３３が電圧パルス立ち上がり時における低電圧レベルＶｒ_１をコンパレータ３５に出力し、同様に基準電圧設定器３４は高電圧レベルＶｒ_２をコンパレータ３６に出力している。コンパレータ３５、３６は基準電圧Ｖｒ_１、Ｖｒ_２と極間電圧を比較し、極間電圧がＶｒ_１、Ｖｒ_２より高いときに出力が「Ｈ」となり、コンパレータ３５、３６の出力はＡＮＤ回路３８に送られる。
【００２３】
ＡＮＤ回路３８の出力ａは図３（ａ）に示すように極間電圧がＶｒ１からＶｒ２まで立ち上がり時間ｔｒ_１、ｔｒ_２、ｔｒ_３に相当した幅を持ったパルス電圧を出力する。ＡＮＤ回路３８の出力ａは基準カウントパルス発生器３７の出力とともにＮＡＮＤ回路３９に送られ、パルス列を出力ｂする。なお、立ち上がり時間は、ｔｒ_２＞ｔｒ_１＞ｔｒ_３の関係を有する。
【００２４】
カウンター４０はこのパルス列ｂをカウントし、立ち上がり時間に相当する出力をラッチ回路４１は出力ａの立ち下がりのタイミングで立ち上がり時間ｔｒ_１、ｔｒ_２、ｔｒ_３に対応した出力値Ｅ_１、Ｅ_２、Ｅ_３（Ｅ_２＞Ｅ_１＞Ｅ_３）の信号ｃを出力し、次の電圧印加時間まで保持する。なお、この信号（ｃ）はデジタル量であるが、説明の便宜上、図においてアナログ量として図示してある。
【００２５】
ここで、上記電圧の立ち上がり時間ｔｒ_１（ｔｒ_３）が予め定められた時間ｔｐよりも短いと、すなわち、極間の静電容量が低い場合には、切り換え部２０は、接点Ａ，Ａを閉成、接点Ｂ，Ｂを開放したままの状態において、計測回路３０の出力値Ｅ_２に、ほぼ反比例して可変電源３の出力電圧値を電圧制御器３０により制御することで、図１３に示す電流が極間に流れる。
【００２６】
一方、電圧の立ち上がり時間ｔｒ_２が予め定められた時間ｔｐよりも長いと、すなわち、極間の静電容量が高い場合には、切り換え部２０は、接点Ａ，Ａを開放すると共に、接点Ｂ，Ｂを閉成し、電極１の極性を陰極にして、電源電圧制御器１２は、計測回路３０の出力値Ｅ_２に、ほぼ反比例して可変電源３の出力電圧値を電圧制御器３０により制御することで、図４に示す極間の電圧・電流波形が得られる。
【００２７】
電極１の極性が陰極となり、極間の印加電圧が低くなることにより、放電を継続するには、極間の距離が減少させることから、極間静電容量が増大する。該静電容量の増大により、図４に示すようにコンデンサ放電の後のパルス電流が確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工が行われる。よって、電極消耗が低減するとともに加工速度が増大する。さらに、加工中に加工面積が変化し、パルス切れの発生頻度が増加していくような加工の場合にも、均一なコンデンサ放電電流が得られるよう制御でき、ひいては加工速度、加工精度等を改善できる。なお、上記実施の形態では、電圧立ち上がり時間ｔｒが増加した場合には、電極１の電圧極性を陽極から陰極に切り換えてから、極間の電圧値を減少させたが、該電圧極性を切り換えずに極間の電圧値のみ減少させても良い。
【００２８】
実施の形態２．
この発明の他の実施の形態を図５によって説明する。図５はこの発明の他の実施の形態を示す放電加工装置の回路図である。図５において、６０は極間に流れる電流の波高値を変更する波高値変更手段としての抵抗切り換え部で、抵抗切換え部６０は、可変電源３とスイッチング素子５との間に、抵抗Ｒ１，Ｒ２，Ｒ３がそれぞれ常開接点６０Ｄ，６０Ｅ，６０Ｆを介して接続されており、抵抗Ｒ１，Ｒ２，Ｒ３の抵抗値はＲ１＞Ｒ２＞Ｒ３の関係にある。７０は電圧立ち上がり時間が増大した場合、その立ち上がり時間に応じて常開接点６０Ｄ，６０Ｅ，６０Ｆのいずれかを閉成して、放電電流パルスの波高値を変更制御する抵抗制御器である。
【００２９】
次に、上記のように構成された放電加工装置の動作を図５及び図６によって説明する。極間静電容量が低いと、計測回路３０は、電圧立ち上がり時間ｔｒ_１を検出し、抵抗制御器７０は、常開接点６０Ｆを閉成すると共に、常開接点６０Ｄ，６０Ｅを開放にして抵抗Ｒ３を回路に挿入して電流の波高値をそれほど制限せずに制御する。上記実施の形態１とほぼ同様であるので、説明を省略する。
【００３０】
一方、極間静電容量が増大すると、計測回路３０は、長くなった電圧立ち上がり時間ｔｒ_２を計測するとともに、検出値を抵抗制御器１３に送る。抵抗制御器１３は、常開接点６０Ｄを閉成して抵抗Ｒ１を回路に挿入して電流の波高値を充分に制限して制御する。また、電圧立ち上がり時間ｔｒ_３の場合には、常開接点６０Ｅを閉成すると共に、常開接点６０Ｄ，６０Ｆを開放にして抵抗Ｒ２を回路に挿入して電流の波高値をやや制限して制御する。
【００３１】
極間の電流波高値が低くなることにより、放電を継続するには、極間の距離を減少させることから、極間静電容量が増大する。該静電容量の増大により、図６に示すようにコンデンサ放電の後のパルス電流を確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工が行われる。よって、電極消耗が低減するとともに加工速度が増大する。
【００３２】
なお、上記実施の形態では、電圧立ち上がり時間ｔｒが増加した場合には、極間の電流波高値のみ減少させたが、電極１の電圧極性を陽極から陰極に切り換えてから、該極間の電流波高値を減少させても良い。
【００３３】
実施の形態３．
この発明の他の実施の形態を図７によって説明する。図７は放電加工装置の回路図である。図７において、８０は極間の静電容量を変更する可変静電容量手段としてのコンデンサ切り換え部で、コンデンサ切換え部８０は、極間に、コンデンサＣ１，Ｃ２，Ｃ３がそれぞれ常開接点８０Ｄ，８０Ｅ，８０Ｆを介して接続されており、コンデンサＣ１，Ｃ２，Ｃ３の静電容量値はＣ１＞Ｃ２＞Ｃ３の関係にあり、９０は電圧立ち上がり時間が増大した場合、その立ち上がり時間に応じて常開接点８０Ｄ，８０Ｅ，８０Ｆのいずれかを閉成して、放電電流パルスの波高値を変更制御するコンデンサ制御器である。
【００３４】
次に、上記のように構成された放電加工装置の動作を図７及び図８によって説明する。極間静電容量が低いと、計測回路３０は、電圧立ち上がり時間ｔｒ_１を検出し、コンデンサ制御器９０は、常開接点８０Ｆを閉成すると共に、常開接点８０Ｄ，８０Ｅを開放にしてコンデンサＣ３を極間に挿入して制御する。上記実施の形態１とほぼ同様であるので、説明を省略する。
【００３５】
一方、極間静電容量が増大すると、計測回路３０は、長くなった電圧立ち上がり時間ｔｒ_２，ｔｒ_３を計測するとともに、検出値をコンデンサ制御器９０に送る。コンデンサ制御器９０は、電圧立ち上がり時間ｔｒ_２の場合には、常開接点８０Ｅを閉成すると共に、常開接点８０Ｄ，８０Ｆを開放にしてコンデンサＣ２を回路に挿入して制御する。また、電圧立ち上がり時間ｔｒ_３の場合には、常開接点８０Ｄを閉成すると共に、常開接点８０Ｅ，８０Ｆを開放にしてコンデンサＣ１を極間に挿入して制御する。
【００３６】
電圧立ち上がり時間の増大により、図８に示すようにコンデンサ放電の後のパルス電流が確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工が行われる。よって、電極消耗が低減するとともに加工速度が増大する。
【００３７】
なお、上記実施の形態では、電圧立ち上がり時間ｔｒが増加した場合には、極間の静電容量を増加させたが、電極１の電圧極性を陽極から陰極に切り換えてから、該極間の静電容量を増加させても良い。
【００３８】
実施の形態４．
この発明の他の実施の形態を図９によって説明する。図９はこの発明の他の実施の形態を示す放電装置の回路図である。この実施の形態は平均電圧サーボ方式に応用したもので、平均電圧サーボ方式は、極間の電圧波形より得られる極間電圧の平均値を極間距離と等価とみなすことができる他の状態量として用い、極間電圧の平均値が極間距離に比例することを利用したものである。
【００３９】
図９において、１５は極間静電容量が増大した場合、極間サーボの基準電圧値を減少させると共に、この基準電圧値になるように制御する基準電圧制御器、１６は極間の加工中の平均電圧値を検出する平均電圧検出器、１７は平均電圧検出器１６により検出された値が上記基準電圧値を維持するように、極間の距離を制御する駆動制御器、１８は位置駆動装置である。
【００４０】
次に、上記のように構成された放電加工装置の動作を図９及び図１０によって説明する。極間静電容量が低いと、計測回路３０は、電圧立ち上がり時間ｔｒ_１を検出し、上記実施の形態１とほぼ同様の電源制御を行い、加えて、極間の状態に応じて極間の相対距離が一定となるよう送り制御をしている。すなわち、極間電圧検出器１６は加工中の極間の平均電圧値を検出し、駆動制御器１７は平均電圧検出器１６により検出された平均電圧値に基いて、加工電圧を一定に維持するために、極間を制御する信号を位置駆動装置１８に送る。位置駆動装置１８は駆動制御器１７の指令信号に基づいて、電極１を駆動しながら放電加工が進行する。
【００４１】
一方、極間静電容量が増大すると、計測回路３０は、長くなった電圧立ち上がり時間ｔｒ_２，ｔｒ_３を実施の形態１のように計測するとともに、この検出値を基準電圧制御器１５に送る。基準電圧制御器１５は、計測回路３０の検出値に基づき、極間サーボの基準電圧値を減少すると共に、加工中の平均電圧値を減少するように制御する。
【００４２】
従って、極間基準電圧が低くなることにより、放電を継続するには、極間の距離を減少させることから、極間の静電容量は増大する。かかる静電容量の増大により図１０に示すようコンデンサ放電のあとのパルスが確実に遮断され、コンデンサ放電のみの均一な電流波形による加工が行われる。よって、電極消耗が低減するとともに加工速度が増大する。
【００４３】
なお、上記実施の形態では、電圧立ち上がり時間ｔｒが増加した場合には、極間の基準電圧を減少させたが、電極１の電圧極性を陽極から陰極に切り換えてから、該極間の基準電圧を減少させても良い。
【００４４】
また、上記実施の形態では、極間の静電容量検出手段として、パルス電圧の立ち上がり時間を計測する計測回路３０を用いたが、図１１に示すように、特開平８−２６７３２３号公報に開示された極間の静電容量測定部１００を用いても良い。静電容量測定部１００は、直流を阻止するためのコンデンサ１２１と、交流正弦波を発振する発振器１２２と、比較的小さな抵抗を有する抵抗１２３とを電極１と被加工物２との間に接続している。
【００４５】
また、上記実施の形態による計測回路３０は、電圧Ｖｒ_１からＶｒ_２までの立ち上がり時間を計測したが、極間電圧の印加開始から電圧がＶｒ_２に達するまでの時間を、立ち上がり時間ｔｒとして計測しても良い。かかる場合には、コンパレータ２５、２６を１つにできる。
【００４６】
また、上記実施の形態による計測回路３０は、加工用電圧パルスの立ち上がり時間を計測したが、放電休止の時間中に検出用パルス電圧を印加し、検出用パルス電圧の立ち上がり時間を計測し、制御する構成としてもよい。
【００４７】
【発明の効果】
第１の発明によれば、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、上記電極を上記電圧発生手段の陰極にすると共に、上記被加工物を上記電圧発生手段の陽極に切り換える電圧極性切換え手段と、上記静電容量検出手段の検出値に基づて上記電圧切換え発生手段を用いて上記電極及び上記被加工物の電圧極性を切り換える制御手段とを備えたので、極間の印加電圧を低くして放電を継続させるから、極間距離を減少して極間の静電容量を増大せしめコンデンサ放電後のパルス電流を確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工ができる。よって、電極消耗が低減されると共に、加工速度の低下が防止できるという効果がある。
【００４８】
第２の発明によれば、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成すと共に、電圧値を可変できる可変電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、この静電容量検出手段の検出値に基づき上記可変電圧発生手段の発生する電圧値を変更する制御手段とを備えたので、極間の印加電圧を低くして放電を継続させるから、極間距離を減少して極間の静電容量を増大せしめコンデンサ放電後のパルス電流を確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工ができる。よって、電極消耗が低減されると共に、加工速度の低下が防止できるという効果がある。
【００４９】
第３の発明によれば、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、上記電極と上記被加工物との間隙に流れる電流の波高値を変更する波高値変更手段と、上記静電容量検出手段の検出値に基いて上記波高値変更手段により上記間隙に流れる電流を制御する制御手段とを備えたので、極間の電流波高値を減少して放電を継続させるから、極間距離を減少して極間の静電容量を増大せしめコンデンサ放電後のパルス電流を確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工ができる。よって、電極消耗が低減されると共に、加工速度の低下が防止できるという効果がある。
【００５０】
第４の発明によれば、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記間隙の静電容量を検出する静電容量検出手段と、上記電極と上記被加工物との間隙の静電容量値を変更する可変静電容量手段と、上記静電容量検出手段の検出値に基づいて、上記可変静電容量手段の静電容量値を変更する制御手段とを備えたので、極間の静電容量を増大せしめコンデンサ放電後のパルス電流を確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工ができる。よって、電極消耗が低減されると共に、加工速度の低下が防止できるという効果がある。
【００５１】
第５の発明によれば、対向する電極と被加工物との間隙にパルス状電圧を印加して放電加工を成す電圧発生手段と、上記電極と上記被加工物との間隙の平均電圧値を定める平均電圧基準手段と、この平均電圧基準手段に基いて上記平均電圧が基準値になるように制御する平均電圧制御手段と、上記極間の静電容量を検出する静電容量検出手段と、この静電容量検出手段の検出値に基づて上記平均電圧基準手段の電圧値を変更制御する制御手段とを備えたので、極間基準電圧が低くすることにより、放電を継続するには、極間の距離を減少させることから、極間の静電容量は増大してコンデンサ放電後のパルス電流を確実に遮断し、コンデンサ放電のみの均一な電流波形により被加工物の加工ができる。よって、電極消耗が低減されると共に、加工速度の低下が防止できるという効果がある。
【００５２】
第６の発明によれば、第１から第５の発明の何れかの効果に加え、静電容量検出手段は、間隙の電圧の立ち上がり時間を計測する計測手段としたので、簡易に極間の静電容量を検出できるという効果がある。
【図面の簡単な説明】
【図１】この発明の一実施の形態を示す放電加工装置の回路図である。
【図２】図１に示す計測回路図である。
【図３】図２に示す計測回路の動作を示すタイムチャートある。
【図４】図１の放電加工装置による極間の電圧波形図及び電流波形図である。
【図５】この発明の他の実施の形態を示す放電加工装置の回路図である。
【図６】図５の放電加工装置による極間の電圧波形図及び電流波形図である。
【図７】この発明の他の実施の形態を示す放電加工装置の回路図である。
【図８】図７の放電加工装置による極間の電圧波形図及び電流波形図である。
【図９】この発明の他の実施の形態を示す放電加工装置の回路図である。
【図１０】図９の放電加工装置による極間の電圧波形図及び電流波形図である。
【図１１】この発明の他の実施の形態を示す極間の静電容量検出回路図である。
【図１２】従来の放電加工装置の構成を示す図
【図１３】図１２の放電加工装置による極間の電圧波形図及び電流波形図である。
【図１４】図１２の放電加工装置によるパルス切れ発生時における極間の電圧波形及び電流波形図である。
【符号の説明】
１電極、２被加工物、３可変電源（可変電圧発生手段，電圧発生手段）、１５基準電圧制御器（平均電圧基準手段，平均電圧制御手段）、２０切り換え部（電圧極性切換え手段）、３０計測回路（静電容量検出手段）、６０抵抗切り換え部（波高値変更手段）、８０コンデンサ切換え部（可変静電容量手段）。[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electric discharge machining apparatus for performing electric discharge machining of a workpiece using a simple electrode.
[0002]
[Prior art]
A conventional electric discharge machine will be described with reference to FIG. In FIG. 121, 1 is an electrode, 2 is a workpiece, 3 is a variable power supply capable of varying a voltage value, 4 is a variable resistor capable of varying a resistance value for current limitation, 5 is a switching element for supplying a pulse voltage, Reference numeral 6 denotes a switching control circuit for controlling the switching of the switching element 5, reference numeral 7 denotes a variable capacitor element capable of changing the capacitance, and reference numeral 8 denotes a processing gap (hereinafter referred to as a gap) formed between the electrode 1 and the workpiece 2. The floating capacitance 9 is a discharge detection circuit that detects the occurrence of discharge between the electrodes by detecting the fall of the voltage.
[0003]
Next, the operation of the electric discharge machine configured as described above will be described with reference to FIGS. When the switching element 5 is turned on by the switching control circuit 6, the voltage determined by the variable power supply 3 is supplied between the electrodes formed between the electrode 1 and the workpiece 2. The discharge detection circuit 9 detects the discharge on condition that the discharge occurs between the electrodes and the applied voltage between the electrodes becomes lower than a predetermined voltage level, and sends the detected value to the switching control circuit 6.
[0004]
The switching control circuit 6 maintains the ON state of the switching element 5 for a predetermined time from the occurrence of the discharge, supplies a current pulse only for the ON time ton, and then pauses the switching element 5 for the OFF time toff, as shown in FIG. Current flows between the poles. By performing the above power supply control, electric discharge machining proceeds.
[0005]
[Problems to be solved by the invention]
However, in the electric discharge machine configured as described above, the current pulse may be interrupted on the way as shown in FIG. Such a phenomenon is referred to as a pulse break, which increases the consumption of the electrode 1 and decreases the processing speed.
[0006]
The pulse cutoff is (1) as the peak value of the current pulse is smaller, that is, as the limiting resistance R is larger, and (2) as the circuit is more capacitive, that is, as the capacitance of the capacitor 7 and the stray capacitance 8 between the poles are larger. It is known that the smaller the inductance of the circuit is, the more likely it is to occur. Therefore, a combination of circuit constants in which pulse breakage is less likely to occur is selected.
[0007]
However, if the processing area is large or the processing area increases during the processing, the floating capacitance 8 formed between the poles increases, and even if an optimal combination of circuit constants is selected, the frequency of pulse cut-offs does not increase. Will be higher. For example, 10,000mm ² In the case of machining a finish machining area having a surface roughness of 5 μm Rmax or less with a machining area of about or more, it is difficult to prevent a pulse break, and the pulse 1 significantly increases the consumption of the electrode 1, resulting in deterioration of machining accuracy, There is a problem that the processing efficiency is reduced and the processing speed is increased.
[0008]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an electric discharge machining apparatus that reduces electrode consumption and prevents a reduction in machining speed even when current pulses are frequently cut. I do.
[0009]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an electric discharge machining apparatus comprising: a voltage generating means for applying a pulsed voltage to a gap between an opposing electrode and a workpiece to perform electric discharge machining; and a capacitance for detecting a capacitance of the gap. Detecting means, the electrode being a cathode of the voltage generating means, a voltage polarity switching means for switching the workpiece to an anode of the voltage generating means, and a voltage polarity switching means based on a detection value of the capacitance detecting means. A control means for switching the voltage polarity of the electrode and the workpiece using voltage switching generation means.
[0010]
According to a second aspect of the present invention, there is provided an electric discharge machining apparatus which performs a discharge machining by applying a pulse-like voltage to a gap between an opposing electrode and a workpiece, and a variable voltage generating means capable of changing a voltage value; It is characterized by comprising: capacitance detecting means for detecting capacitance; and control means for changing a voltage value generated by the variable voltage generating means based on a detection value of the capacitance detecting means. .
[0011]
According to a third aspect of the present invention, there is provided an electric discharge machining apparatus, comprising: a voltage generating means for applying a pulsed voltage to a gap between an opposing electrode and a workpiece to perform electric discharge machining; and a capacitance for detecting a capacitance of the gap. Detecting means, a peak value changing means for changing the peak value of the current flowing in the gap between the electrode and the workpiece, and the peak value changing means based on the detected value of the capacitance detecting means, Control means for controlling the flowing current.
[0012]
According to a fourth aspect of the present invention, there is provided an electric discharge machining apparatus comprising: a voltage generating means for applying a pulsed voltage to a gap between an opposing electrode and a workpiece to perform electric discharge machining; and a capacitance for detecting a capacitance of the gap. Detecting means, variable capacitance means for changing a capacitance value of a gap between the electrode and the workpiece, and static capacitance of the variable capacitance means based on a detection value of the capacitance detecting means. Control means for changing the capacitance value.
[0013]
According to a fifth aspect of the present invention, there is provided an electric discharge machining apparatus comprising: a voltage generating means for applying a pulsed voltage to a gap between an opposing electrode and a workpiece to perform electrical discharge machining; and an average of a gap between the electrode and the workpiece. Average voltage reference means for determining a voltage value; average voltage control means for controlling the average voltage to be a reference value based on the average voltage reference means; and capacitance detection for detecting the capacitance between the electrodes. Means, and control means for changing and controlling the voltage value of the average voltage reference means based on the detection value of the capacitance detecting means.
[0014]
The electrostatic capacitance detecting means of the electric discharge machine according to the sixth invention is a measuring means for measuring a rise time of a voltage in the gap.
[0015]
Embodiment
Embodiment 1 FIG.
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram of an electric discharge machine according to an embodiment of the present invention, and FIG. 2 is a circuit diagram for measuring a rise time of a pulse voltage. In the figure, the same reference numerals as those in the related art indicate the same or corresponding parts, and the description will be omitted. In FIG. 1, a variable power supply 3 is connected to one end of a variable resistor 4, a workpiece 2, and one end of a variable capacitor 7 via a switching section 20 as voltage polarity switching means. The switching unit 20 switches the polarity of the variable power supply 3 and includes contacts A, A and contacts B, B. When one of the contacts A, A (B, B) is closed, the other contact is used. B, B (A, A) are configured to be open.
[0016]
Reference numeral 30 denotes a measurement circuit that measures the rise time of the pulse voltage between the poles as capacitance detection means using the capacitance between the poles, and 50 denotes, for example, an increase in the rise time of the voltage based on the detection value of the measurement circuit 30. The power supply controller operates the switching unit 20 to switch the polarity of the variable power supply 3 to make the polarity of the electrode 1 a cathode and to reduce the voltage of the voltage power supply 3.
[0017]
Here, the measurement circuit 30 measures the rise time of the voltage instead of the inter-electrode capacitance C because the voltage rise time tr changes in accordance with the inter-electrode capacitance. The interelectrode capacitance C and the voltage rise time tr (tr ₁ , Tr ₂ ... Trn), the following (1) to (3) are obtained, and by solving the following equation, the interelectrode capacitance can be obtained from the voltage rise time.
Vr ₁ = E · (1-e ^{-T1 / RC} (1)
Vr ₂ = E · (1-e ^{-T2 / RC} ) (2)
tr = t ₂ -T ₁ (3)
Here, R is the resistance value of the circuit (current limiting resistance), E is the voltage value of the voltage power supply 3, t ₁ Is Vr from the voltage application ₁ Rise time until t ₂ Is Vr from the voltage application ₂ It is the rise time until.
[0018]
Further, the reason why the polarity of the electrode 1 is changed to a cathode opposite to that of a normal electrode by increasing the interelectrode capacitance is that it is known that a waveform having a shorter pulse width consumes less electrode. For example, the processing area is 10,000mm ² When the electrode 1 is being processed in a state where the pulse is frequently cut off at the anode, a capacitor of about 0.01 to 0.1 μF is added between the poles with the polarity of the electrode 1 as the cathode, and the pulse width is reduced. This is because machining with a capacitor current waveform as short as about 0.1 to 0.5 μs reduces the consumption of the electrode 1 and increases the machining speed.
[0019]
In the measurement circuit 30 of FIG. 2, 33 and 34 are reference voltage setting devices, 35 and 36 are comparators for comparing the voltage at the time of voltage rise with the reference voltage, 37 is a reference count pulse generator, 38 is an AND circuit, and 39 is a NAND circuit. The circuit, 40 is a counter for counting the voltage rise time, and 41 is a latch circuit for holding the output of the counter 40.
[0020]
Next, the operation of the electric discharge machine configured as described above will be described with reference to FIGS. FIG. 3 is a time chart showing the operation of the measurement circuit. First, while the contacts A, A of the switching unit 20 are closed, and the contacts B, B are kept open, the switching control circuit 6 turns on the switching element 5, so that the voltage value of the variable power supply 3 It is supplied between the poles formed between the workpieces 2.
[0021]
The discharge detection circuit 9 detects a discharge when a discharge occurs between the electrodes and the applied voltage between the electrode 1 and the workpiece 2 becomes lower than a predetermined voltage level, and sends the detection result to the switching control circuit 6. send. The switching control circuit 6 turns on the switching element 5 only for a time ton from the occurrence of the discharge, raises the voltage between the electrodes as shown in FIG. It is turned off and the switching operation is repeated.
[0022]
The measurement circuit 30 determines that the reference voltage setting unit 33 has the low voltage level Vr at the time of rising of the voltage pulse. ₁ Is output to the comparator 35, and the reference voltage setting unit 34 similarly outputs the high voltage level Vr ₂ Is output to the comparator 36. The comparators 35 and 36 are connected to the reference voltage Vr ₁ , Vr ₂ And the voltage between contacts, and the voltage between contacts is Vr ₁ , Vr ₂ When it is higher, the output becomes “H”, and the outputs of the comparators 35 and 36 are sent to the AND circuit 38.
[0023]
As shown in FIG. 3A, the output a of the AND circuit 38 has a rise time tr at which the voltage between the electrodes changes from Vr1 to Vr2. ₁ , Tr ₂ , Tr ₃ A pulse voltage having a width corresponding to is output. The output a of the AND circuit 38 is sent to the NAND circuit 39 together with the output of the reference count pulse generator 37, and outputs a pulse train b. The rise time is tr ₂ > Tr ₁ > Tr ₃ Has the relationship
[0024]
The counter 40 counts the pulse train b and outputs an output corresponding to the rising time to the latch circuit 41 at the falling timing of the output a. ₁ , Tr ₂ , Tr ₃ Output value E corresponding to ₁ , E ₂ , E ₃ (E ₂ > E ₁ > E ₃ ) Is output and held until the next voltage application time. Although this signal (c) is a digital quantity, it is shown as an analog quantity in the figure for convenience of explanation.
[0025]
Here, the voltage rising time tr ₁ (Tr ₃ ) Is shorter than the predetermined time tp, that is, when the capacitance between the electrodes is low, the switching unit 20 closes the contacts A and A and keeps the contacts B and B open. , The output value E of the measuring circuit 30 ₂ By controlling the output voltage value of the variable power supply 3 by the voltage controller 30 almost in inverse proportion, the current shown in FIG.
[0026]
On the other hand, voltage rise time tr ₂ Is longer than a predetermined time tp, that is, when the capacitance between the electrodes is high, the switching unit 20 opens the contacts A, A, closes the contacts B, B, and closes the electrodes. 1 as a cathode, the power supply voltage controller 12 outputs the output value E ₂ By controlling the output voltage value of the variable power supply 3 by the voltage controller 30 almost in inverse proportion, the voltage / current waveform between the electrodes shown in FIG. 4 is obtained.
[0027]
Since the polarity of the electrode 1 becomes a cathode and the applied voltage between the electrodes is reduced, and the discharge is continued, the distance between the electrodes is reduced, so that the capacitance between the electrodes is increased. Due to the increase in the capacitance, the pulse current after the discharge of the capacitor is surely interrupted as shown in FIG. 4, and the workpiece is processed with a uniform current waveform of only the discharge of the capacitor. Therefore, the electrode consumption is reduced and the processing speed is increased. Furthermore, even in the case of processing where the processing area changes during processing and the frequency of pulse cuts increases, it is possible to control so that a uniform capacitor discharge current can be obtained, thereby improving the processing speed, processing accuracy, etc. it can. In the above-described embodiment, when the voltage rise time tr increases, the voltage polarity of the electrode 1 is switched from the anode to the cathode, and then the voltage value between the electrodes is reduced. However, the voltage polarity is not switched. Alternatively, only the voltage between the electrodes may be reduced.
[0028]
Embodiment 2 FIG.
Another embodiment of the present invention will be described with reference to FIG. FIG. 5 is a circuit diagram of an electric discharge machine according to another embodiment of the present invention. In FIG. 5, reference numeral 60 denotes a resistance switching unit as a peak value changing means for changing the peak value of the current flowing between the poles. The resistance switching unit 60 includes resistors R1 and R2 between the variable power supply 3 and the switching element 5. , R3 are connected via normally open contacts 60D, 60E, 60F, respectively, and the resistance values of the resistors R1, R2, R3 satisfy the relationship of R1>R2> R3. Reference numeral 70 denotes a resistance controller that closes one of the normally open contacts 60D, 60E, and 60F according to the rise time of the voltage and changes and controls the peak value of the discharge current pulse.
[0029]
Next, the operation of the electric discharge machine configured as described above will be described with reference to FIGS. When the capacitance between the electrodes is low, the measuring circuit 30 detects the voltage rise time tr ₁ Is detected, the resistance controller 70 closes the normally open contacts 60F, opens the normally open contacts 60D and 60E, inserts the resistor R3 into the circuit, and controls the current peak value without much limiting. . Since it is almost the same as the first embodiment, the description is omitted.
[0030]
On the other hand, when the capacitance between the electrodes increases, the measuring circuit 30 determines that the voltage rising time tr has become longer. ₂ And sends the detected value to the resistance controller 13. The resistance controller 13 closes the normally open contact 60D, inserts the resistance R1 into the circuit, and controls the peak value of the current sufficiently to control. Also, the voltage rise time tr ₃ In the case of (1), the normally open contact 60E is closed, the normally open contacts 60D and 60F are opened, and the resistor R2 is inserted into the circuit to control the current peak value slightly.
[0031]
In order to continue the discharge by decreasing the current peak value between the electrodes, the distance between the electrodes is reduced, so that the capacitance between the electrodes is increased. Due to the increase in the capacitance, the pulse current after the discharge of the capacitor is surely cut off as shown in FIG. Therefore, the electrode consumption is reduced and the processing speed is increased.
[0032]
In the above embodiment, when the voltage rise time tr is increased, only the peak value of the current between the electrodes is reduced. However, after the voltage polarity of the electrode 1 is switched from the anode to the cathode, the current between the electrodes is reduced. The peak value may be reduced.
[0033]
Embodiment 3 FIG.
Another embodiment of the present invention will be described with reference to FIG. FIG. 7 is a circuit diagram of the electric discharge machine. In FIG. 7, reference numeral 80 denotes a capacitor switching unit as a variable capacitance means for changing the capacitance between the poles. The capacitor switching unit 80 includes capacitors C1, C2, and C3 between the poles, which are normally open contacts 80D, The capacitors C1, C2, and C3 have a capacitance relationship of C1>C2> C3, and when the voltage rise time is increased, 90 is normally set according to the rise time. A capacitor controller that closes one of the open contacts 80D, 80E, and 80F to change and control the peak value of the discharge current pulse.
[0034]
Next, the operation of the electric discharge machine configured as described above will be described with reference to FIGS. When the capacitance between the electrodes is low, the measuring circuit 30 detects the voltage rise time tr ₁ Is detected, the capacitor controller 90 closes the normally open contact 80F, opens the normally open contacts 80D and 80E, and inserts the capacitor C3 between the poles to control. Since it is almost the same as the first embodiment, the description is omitted.
[0035]
On the other hand, when the capacitance between the electrodes increases, the measuring circuit 30 determines that the voltage rise time tr ₂ , Tr ₃ And sends the detected value to the capacitor controller 90. The capacitor controller 90 determines the voltage rise time tr ₂ In this case, the normally open contact 80E is closed, the normally open contacts 80D and 80F are opened, and the capacitor C2 is inserted into the circuit for control. Also, the voltage rise time tr ₃ In this case, the normally open contact 80D is closed, the normally open contacts 80E and 80F are opened, and the capacitor C1 is inserted between the poles for control.
[0036]
Due to the increase in the voltage rise time, as shown in FIG. 8, the pulse current after the discharge of the capacitor is reliably cut off, and the workpiece is processed with a uniform current waveform of only the discharge of the capacitor. Therefore, the electrode consumption is reduced and the processing speed is increased.
[0037]
In the above embodiment, when the voltage rise time tr is increased, the capacitance between the electrodes is increased. However, the voltage polarity of the electrode 1 is switched from the anode to the cathode, and then the static between the electrodes is changed. The electric capacity may be increased.
[0038]
Embodiment 4 FIG.
Another embodiment of the present invention will be described with reference to FIG. FIG. 9 is a circuit diagram of a discharge device showing another embodiment of the present invention. This embodiment is applied to the average voltage servo method, and the average voltage servo method uses other state quantities that can be regarded as equivalent to the distance between the poles obtained from the voltage waveform between the poles. And that the average value of the voltage between the electrodes is proportional to the distance between the electrodes.
[0039]
In FIG. 9, reference numeral 15 denotes a reference voltage controller for reducing the reference voltage value of the gap servo when the capacitance between the poles increases, and controlling the reference voltage value to be equal to the reference voltage value. Is a drive controller for controlling the distance between the poles so that the value detected by the average voltage detector 16 maintains the reference voltage value, and 18 is a position drive. Device.
[0040]
Next, the operation of the electric discharge machine configured as described above will be described with reference to FIGS. When the capacitance between the electrodes is low, the measuring circuit 30 detects the voltage rise time tr ₁ Is detected, power control is performed in substantially the same manner as in the first embodiment, and feed control is performed so that the relative distance between the poles becomes constant according to the state of the poles. That is, the inter-electrode voltage detector 16 detects an average voltage value between the poles being processed, and the drive controller 17 maintains the processing voltage constant based on the average voltage value detected by the average voltage detector 16. For this purpose, a signal for controlling the gap is sent to the position driving device 18. The position driving device 18 advances the electric discharge machining while driving the electrode 1 based on a command signal from the drive controller 17.
[0041]
On the other hand, when the capacitance between the electrodes increases, the measuring circuit 30 determines that the voltage rise time tr ₂ , Tr ₃ Is measured as in the first embodiment, and the detected value is sent to the reference voltage controller 15. The reference voltage controller 15 controls the reference voltage value of the gap servo based on the detection value of the measurement circuit 30 so as to decrease the average voltage value during machining.
[0042]
Therefore, in order to continue the discharge by lowering the reference voltage between the electrodes, the distance between the electrodes is reduced, so that the capacitance between the electrodes is increased. Due to the increase in the capacitance, the pulse after the discharge of the capacitor is surely cut off as shown in FIG. Therefore, the electrode consumption is reduced and the processing speed is increased.
[0043]
In the above-described embodiment, when the voltage rise time tr increases, the reference voltage between the electrodes is decreased. However, after the voltage polarity of the electrode 1 is switched from the anode to the cathode, the reference voltage between the electrodes is reduced. May be reduced.
[0044]
In the above embodiment, the measuring circuit 30 that measures the rise time of the pulse voltage is used as the capacitance detecting means between the electrodes. However, as shown in FIG. 11, the measuring circuit 30 is disclosed in Japanese Patent Application Laid-Open No. 8-267323. The capacitance measurement unit 100 between the poles may be used. The capacitance measuring unit 100 connects a capacitor 121 for blocking DC, an oscillator 122 for oscillating AC sine wave, and a resistor 123 having a relatively small resistance between the electrode 1 and the workpiece 2. are doing.
[0045]
Further, the measuring circuit 30 according to the above-described embodiment uses the voltage Vr ₁ To Vr ₂ The rise time was measured until the voltage became Vr from the start of the application of the gap voltage. ₂ May be measured as the rise time tr. In such a case, the number of comparators 25 and 26 can be reduced to one.
[0046]
In addition, the measuring circuit 30 according to the above-described embodiment measures the rise time of the machining voltage pulse, but applies the detection pulse voltage during the time of the discharge pause, measures the rise time of the detection pulse voltage, and performs control. It is good also as a structure which performs.
[0047]
【The invention's effect】
According to the first aspect, voltage generating means for applying a pulsed voltage to the gap between the facing electrode and the workpiece to perform electric discharge machining, and capacitance detecting means for detecting the capacitance of the gap are provided. A voltage polarity switching means for switching the workpiece to an anode of the voltage generation means, and the voltage switching generation based on a detection value of the capacitance detection means. Control means for switching the voltage polarity of the electrode and the workpiece using the means, so that the voltage applied between the electrodes is lowered to continue the discharge. The electric capacity is increased, the pulse current after the discharge of the capacitor is reliably cut off, and the workpiece can be machined by a uniform current waveform of only the discharge of the capacitor. Therefore, there is an effect that the electrode consumption is reduced and a reduction in the processing speed can be prevented.
[0048]
According to the second aspect, a pulse voltage is applied to the gap between the opposing electrode and the workpiece to perform electric discharge machining, and a variable voltage generating means capable of changing the voltage value, and the capacitance of the gap is reduced. Since there is provided a capacitance detecting means for detecting and a control means for changing a voltage value generated by the variable voltage generating means based on a detection value of the capacitance detecting means, the applied voltage between the electrodes is reduced. Since the discharge is continued, the distance between the poles is reduced, the capacitance between the poles is increased, and the pulse current after the discharge of the capacitor is surely cut off. . Therefore, there is an effect that the electrode consumption is reduced and a reduction in the processing speed can be prevented.
[0049]
According to the third aspect, voltage generating means for applying a pulsed voltage to the gap between the facing electrode and the workpiece to perform electric discharge machining, and capacitance detecting means for detecting the capacitance of the gap A peak value changing means for changing a peak value of a current flowing in a gap between the electrode and the workpiece, and a current flowing in the gap by the peak value changing means based on a detection value of the capacitance detecting means. Control means to reduce the peak value of the current between the poles and continue the discharge, so reduce the distance between the poles and increase the capacitance between the poles to ensure the pulse current after discharging the capacitor. The workpiece can be machined by a uniform current waveform of only the capacitor discharge. Therefore, there is an effect that the electrode consumption is reduced and a reduction in the processing speed can be prevented.
[0050]
According to the fourth aspect, voltage generating means for applying a pulsed voltage to the gap between the facing electrode and the workpiece to perform electric discharge machining, and capacitance detecting means for detecting the capacitance of the gap A variable capacitance unit that changes a capacitance value of a gap between the electrode and the workpiece; and a capacitance value of the variable capacitance unit based on a detection value of the capacitance detection unit. Since the control means is provided for changing the capacitance, the capacitance between the electrodes is increased, the pulse current after the discharge of the capacitor is reliably cut off, and the workpiece can be machined with a uniform current waveform of only the discharge of the capacitor. Therefore, there is an effect that the electrode consumption is reduced and a reduction in the processing speed can be prevented.
[0051]
According to the fifth invention, a voltage generating means for applying a pulsed voltage to a gap between the facing electrode and the workpiece to perform electric discharge machining, and an average voltage value of the gap between the electrode and the workpiece. Average voltage reference means to be determined, average voltage control means for controlling the average voltage to be a reference value based on the average voltage reference means, and capacitance detection means for detecting the capacitance between the electrodes, And control means for changing and controlling the voltage value of the average voltage reference means based on the detection value of the capacitance detection means.In order to continue discharging by lowering the gap reference voltage, Since the distance between the poles is reduced, the capacitance between the poles is increased, the pulse current after the discharge of the capacitor is reliably cut off, and the workpiece can be processed with a uniform current waveform of only the discharge of the capacitor. Therefore, there is an effect that the electrode consumption is reduced and a reduction in the processing speed can be prevented.
[0052]
According to the sixth aspect, in addition to the effect of any one of the first to fifth aspects, since the capacitance detecting means is a measuring means for measuring the rise time of the voltage of the gap, the capacitance between the gaps can be easily determined. There is an effect that the capacitance can be detected.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an electric discharge machine according to an embodiment of the present invention.
FIG. 2 is a measurement circuit diagram shown in FIG.
FIG. 3 is a time chart illustrating an operation of the measurement circuit illustrated in FIG. 2;
4A and 4B are a voltage waveform diagram and a current waveform diagram between poles by the electric discharge machine of FIG.
FIG. 5 is a circuit diagram of an electric discharge machine according to another embodiment of the present invention.
6A and 6B are a voltage waveform diagram and a current waveform diagram between the electrodes by the electric discharge machine of FIG.
FIG. 7 is a circuit diagram of an electric discharge machine according to another embodiment of the present invention.
8 shows a voltage waveform diagram and a current waveform diagram between the electrodes by the electric discharge machine of FIG. 7;
FIG. 9 is a circuit diagram of an electric discharge machine according to another embodiment of the present invention.
10A and 10B are a voltage waveform diagram and a current waveform diagram between the electrodes by the electric discharge machine of FIG. 9;
FIG. 11 is a diagram showing a capacitance detection circuit between poles according to another embodiment of the present invention.
FIG. 12 is a diagram showing a configuration of a conventional electric discharge machine.
FIG. 13 is a diagram showing a voltage waveform and a current waveform between electrodes by the electric discharge machine of FIG. 12;
FIG. 14 is a diagram showing a voltage waveform and a current waveform between electrodes when a pulse break occurs in the electric discharge machine of FIG. 12;
[Explanation of symbols]
1 electrode, 2 workpiece, 3 variable power supply (variable voltage generation means, voltage generation means), 15 reference voltage controller (average voltage reference means, average voltage control means), 20 switching unit (voltage polarity switching means), 30 Measuring circuit (capacitance detecting means), 60 resistance switching section (peak value changing means), 80 capacitor switching section (variable capacitance means).

Claims

Voltage generating means for applying a pulsed voltage to the gap between the opposing electrode and the workpiece to perform electric discharge machining,
Capacitance detection means for detecting the capacitance of the gap,
Voltage polarity switching means for switching the electrode to the cathode of the voltage generating means, and switching the workpiece to the anode of the voltage generating means,
Based on the detection value of the electrostatic capacitance detecting means, the polarity of the electrode by using the voltage switching generating means on the cathode when the capacitance is high, switches the polarity of the workpiece to the anode, the voltage Control means for controlling the output voltage of the generation means to decrease ,
An electric discharge machining device comprising:

A variable voltage generating means capable of applying a pulsed voltage to a gap between the facing electrode and the workpiece to perform electric discharge machining and to vary a voltage value,
Capacitance detection means for detecting the capacitance of the gap,
Control means for controlling the voltage value generated by the variable voltage generation means to be low when the capacitance is high, based on the detection value of the capacitance detection means,
An electric discharge machining device comprising:

Voltage generating means for applying a pulsed voltage to the gap between the opposing electrode and the workpiece to perform electric discharge machining,
Capacitance detection means for detecting the capacitance of the gap,
Crest value changing means for changing the crest value of the current flowing in the gap between the electrode and the workpiece,
Based on the detection value of the capacitance detecting means, when the capacitance is high, control means for controlling the peak value changing means to control the current peak value flowing through the gap to be low ,
An electric discharge machining device comprising:

Voltage generating means for applying a pulsed voltage to the gap between the opposing electrode and the workpiece to perform electric discharge machining,
Capacitance detection means for detecting the capacitance of the gap,
Variable capacitance means for changing the capacitance value of the gap between the electrode and the workpiece,
Control means for increasing the capacitance value of the variable capacitance means when the capacitance is high , based on the detection value of the capacitance detection means,
An electric discharge machining device comprising:

Voltage generating means for applying a pulsed voltage to the gap between the opposing electrode and the workpiece to perform electric discharge machining,
Average voltage reference means for determining an average voltage value of the gap between the electrode and the workpiece,
Average voltage control means for controlling the average voltage to be a reference value based on the average voltage reference means;
Capacitance detection means for detecting the capacitance between the electrodes,
Control means for controlling the voltage value of the average voltage reference means to be low when the capacitance is high, based on the detection value of the capacitance detection means,
An electric discharge machining device comprising:

6. The device according to claim 1, wherein the capacitance detecting unit measures a rise time of a voltage of the gap, and determines that the capacitance between the electrodes is high when the voltage is longer than a predetermined time. The electric discharge machining device according to any one of the above.

Voltage polarity switching means for switching the electrode to the anode of the voltage generating means, while the electrode is a cathode of the voltage generating means,
Based on the detection value of the capacitance detecting means, when the capacitance is high, using the voltage switching generating means to switch the polarity of the electrode to the cathode and the polarity of the workpiece to the anode. The electric discharge machining device according to any one of claims 3 to 5.