JP5453640B2 - Electric discharge machine - Google Patents
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Description
本発明は、一般的な放電加工機を用いてマイクロ加工を行う場合に、給電電極を配置し、非接触給電による静電誘導により、回路に生じるインダクタンスや浮遊容量の影響をなくし、より微小な放電エネルギーにより、微細な表面加工を行う事が可能な放電加工装置に関する。 In the present invention, when micro machining is performed using a general electric discharge machine, a feed electrode is arranged, and the influence of inductance and stray capacitance generated in the circuit is eliminated by electrostatic induction by non-contact power feeding, thereby making the finer The present invention relates to an electric discharge machining apparatus capable of performing fine surface machining with electric discharge energy.
微細な加工に応用されるマイクロ放電加工では、加工がマイクロになるほどコンデンサの容量を小さくしなければならない、しかし、現実の加工機では、図１に示すような、プラス側とマイナス側の配線間、電極ホルダと加工テーブル間、工具電極と工作物間などに浮遊容量が存在し、そこに充電された電荷が、回路に接続された、本来のコンデンサ電荷とともに極間に放電される。従って、マイクロの領域ほど浮遊容量が支配的となるので、配線をなるべく短くしたり、ホルダやテーブルを絶縁体で作ったりするなどの工夫が必要であった。 In micro electric discharge machining applied to fine machining, the capacity of the capacitor must be reduced as the machining becomes micro. However, in an actual machining machine, as shown in FIG. 1, between the plus and minus wires There are stray capacitances between the electrode holder and the processing table, between the tool electrode and the workpiece, and the charge charged there is discharged between the electrodes together with the original capacitor charge connected to the circuit. Accordingly, since the stray capacitance becomes dominant in the micro area, it is necessary to devise such as shortening the wiring as much as possible and making the holder and the table with an insulator.
そのため、浮遊容量の影響を削減し、放電加工による面粗さを向上させる方法として、メイン電源と補助電源を装備し、仕上げ加工時は、補助電源から供給される電流がメイン電源への電流の流れ込みを阻止するダイオードを設け、ダイオードに逆バイアスの所定電圧を供給する逆バイアス用電源を備え、メイン電源供給線の浮遊容量の影響を大幅に低減する方法（特許文献１）や、放電加工装置内の電源装置及びパルス制御部における浮遊容量に蓄積された、電気エネルギーによる電極と工作物との極間での放電を抑制する、抵抗を設ける方法（特許文献２）や、又は、第一、第二の放電エネルギーを発生させる、２つの電源をもち、小さい放電エネルギーの給電線に設けた開閉手段を調節することで、電極−被加工物間の浮遊容量を低減させる方法（特許文献３）が知られている。しかし、このような浮遊容量を削減する技術でも、最小表面粗さは０．４μｍ程度であった。 Therefore, as a method to reduce the effect of stray capacitance and improve surface roughness by electrical discharge machining, a main power supply and an auxiliary power supply are installed. During finishing, the current supplied from the auxiliary power supply is the current to the main power supply. A method of providing a diode for preventing inflow, including a reverse bias power source for supplying a predetermined reverse bias voltage to the diode, and greatly reducing the influence of stray capacitance of the main power supply line (Patent Document 1), or an electric discharge machining apparatus A method of providing resistance (Patent Document 2) that suppresses the discharge between the electrode and the work piece caused by electrical energy accumulated in the stray capacitance in the power supply device and the pulse control unit, or first, Reduces the stray capacitance between the electrode and workpiece by adjusting the opening and closing means provided on the power supply line with low discharge energy, which has two power sources that generate the second discharge energy The method (Patent Document 3) it is known to. However, even with such a technique for reducing stray capacitance, the minimum surface roughness is about 0.4 μm.
また、給電経路を短くし、インダクタンスの影響をなくすため、工具電極に筒状ガイドを機械的に固定し、放電過程に影響しないように大きな間隙を有する放電加工機（特許文献４）が知られているが、間隙を大きく設定する方法が知られているが、この場合では、工具電極と工作物間の放電エネルギーを小さく制御することはできないと考えられる。 Also, there is known an electric discharge machine (Patent Document 4) in which a cylindrical guide is mechanically fixed to a tool electrode and a large gap is provided so as not to affect the discharge process in order to shorten the power feeding path and eliminate the influence of inductance. However, a method for setting the gap large is known, but in this case, it is considered that the discharge energy between the tool electrode and the workpiece cannot be controlled small.
一般的な放電加工機を使用してより微細な加工が可能となる放電加工装置を提供する。 Provided is an electric discharge machining apparatus capable of performing finer machining using a general electric discharge machine.
本発明者等は、給電電極と工具電極の間において電子の移動が無く、給電電極と工具電極間で形成される容量と、工具電極と工作物間の容量のみで、放電エネルギーを決定することで、回路に生じる浮遊容量により最小限界放電エネルギーが決定される従来のマイクロ放電加工機にくらべ、微細な加工を行うことが可能であると考えた。 The present inventors have no movement of electrons between the power supply electrode and the tool electrode, and determine the discharge energy only by the capacity formed between the power supply electrode and the tool electrode and the capacity between the tool electrode and the workpiece. Therefore, we thought that it was possible to perform fine processing compared to the conventional micro electric discharge machine in which the minimum critical discharge energy is determined by the stray capacitance generated in the circuit.
すなわち、本発明は
（１）微小な極間距離を隔てて配置された、工具電極と工作物に、パルス電圧を印加し、前記極間に放電エネルギーを発生させ、前記工作物を加工する放電加工装置において、
前記工具電極が同一軸線上で結合され、前記工具電極と共に軸回転可能に絶縁支持された工具電極給電部と、
前記工具電極給電部に対して一定間隙をもって対向配置した給電電極と、
前記給電電極と前記工作物とが結線されたパルス電源と、
を有し、
前記パルス電源から電圧を印加し、前記給電電極より前記工具電極給電部に静電誘電給電することにより、前記工具電極給電部と対向する前記給電電極間の距離及び対向する面積の少なくとも一方を調整して形成される容量Ｃ１Ａと、前記工具電極と前記工作物間の間隙で形成される容量Ｃ２Ａと、に基づいて、前記放電エネルギーを決定し、
前記工具電極と一定間隙の対向面を保有して配置した電圧測定プローブの検出線と、前記工作物と、が結線された電圧検出回路からなる、前記工具電極と前記工作物との極間電圧を測定する測定装置を装備することを特徴とする、放電加工装置。
That is, the present invention is (1) a discharge for machining a workpiece by applying a pulse voltage to a tool electrode and a workpiece, which are arranged with a small inter-electrode distance, to generate discharge energy between the electrodes. In processing equipment,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A power supply electrode disposed opposite to the tool electrode power supply section with a constant gap;
A pulse power source in which the feeding electrode and the workpiece are connected;
Have
A voltage is applied from the pulse power supply, and electrostatic power is fed from the power supply electrode to the tool electrode power supply unit, thereby adjusting at least one of a distance between the power supply electrodes facing the tool electrode power supply unit and an opposing area. The discharge energy is determined on the basis of the capacitance C 1A formed by the capacitor C 2A formed by the gap between the tool electrode and the workpiece ,
A voltage between the tool electrode and the workpiece, comprising a voltage detection circuit in which a detection line of a voltage measurement probe arranged to hold the opposed surface of the tool electrode with a fixed gap and the workpiece are connected. An electrical discharge machining apparatus equipped with a measuring device for measuring the temperature .
（２）微小な極間距離を隔てて配置された、工具電極と工作物に、パルス電圧を印加し、前記極間に放電エネルギーを発生させ、前記工作物を加工する放電加工装置において、
前記工具電極が同一軸線上で結合され、前記工具電極と共に軸回転可能に絶縁支持された工具電極給電部と、
前記工具電極給電部に一方の端子が接触したコンデンサと、
前記コンデンサの他方の端子と前記工作物とに結線されたパルス電源と、
を有し、
前記パルス電源から電圧を印加し、前記コンデンサと前記工具電極給電部の容量結合により給電を行い、前記コンデンサの容量Ｃ３Ａと、前記工具電極と前記工作物間の間隙で形成される容量Ｃ４Ａと、に基づいて、前記放電エネルギーを決定することを特徴とする、放電加工装置。
(2) In an electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, to generate discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A capacitor with one terminal in contact with the tool electrode power supply unit;
A pulse power source wired to the other terminal of the capacitor and the workpiece;
Have
A voltage is applied from the pulse power source, and power is supplied by capacitive coupling of the capacitor and the tool electrode power supply unit. The capacitor C 3A and the capacitance C 4A formed by the gap between the tool electrode and the workpiece are provided. And the electric discharge machining apparatus, wherein the electric discharge energy is determined.
（３）微小な極間距離を隔てて配置された、工具電極と工作物に、パルス電圧を印加し、前記極間に放電エネルギーを発生させ、前記工作物を加工する放電加工装置において、
前記工具電極が同一軸線上で結合され、前記工具電極と共に軸回転可能に絶縁支持された工具電極給電部と、
一定間隙をもって前記工作物に対向配置した給電電極と、
前記工具電極給電部と前記給電電極とに結線されたパルス電源と、
を有し、
前記パルス電源から電圧を印加し、前記給電電極より前記工作物に静電誘電給電することにより、前記工作物と対向する前記給電電極の間隙の距離及び対向する面積の少なくとも一方を調整し、前記間隙に形成される容量Ｃ１Ｂと、前記工具電極と前記工作物間の間隙で形成される容量Ｃ２Ｂと、に基づいて、前記放電エネルギーを決定することを特徴とする、放電加工装置。
(3) In an electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, to generate discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A feeding electrode disposed opposite the workpiece with a constant gap;
A pulse power source connected to the tool electrode power supply unit and the power supply electrode;
Have
A voltage is applied from the pulse power source, and electrostatic work is fed to the workpiece from the feeding electrode, thereby adjusting at least one of the distance and the facing area of the feeding electrode facing the workpiece, and a capacitor C 1B is formed in the gap, and a capacitor C 2B is formed at the gap between the workpiece and the tool electrode, on the basis, and determines the discharge energy, the electric discharge machining apparatus.
（４）前記工具電極と一定間隙の対向面を保有して配置した電圧測定プローブの検出線と、前記工作物と、が結線された電圧検出回路からなる、前記工具電極と前記工作物との極間電圧を測定する測定装置を装備することを特徴とする、前記（２）または（３）に記載された、放電加工装置。 ( 4 ) The tool electrode and the workpiece comprising a voltage detection circuit in which a detection line of the voltage measurement probe arranged to hold the opposing surface of the tool electrode and a fixed gap and the workpiece are connected. The electrical discharge machining apparatus according to (2) or (3) , wherein the electrical discharge machining apparatus is equipped with a measurement device that measures an inter-electrode voltage.
（５）前記測定装置は、前記工具電極に対する前記工作物の支持位置を変位する圧電素子を有し、
前記測定装置によって測定した前記工具電極と前記工作物との極間電圧波形に基づいて、前記極間距離が狭すぎて短絡気味であるか、あるいは、広過ぎて開放状態に近いのかを判断し、制御信号を発信し、前記工作物の支持位置を前記圧電素子により変位させることにより調節することで、前記極間間隙を放電が生じ得る適切な値に制御する機能を保有することを特徴とする、前記（１）または（４）に記載された、放電加工装置。
( 5 ) The measurement apparatus includes a piezoelectric element that displaces a support position of the workpiece with respect to the tool electrode,
Based on the voltage waveform between the tool electrode and the workpiece measured by the measuring device, it is determined whether the distance between the electrodes is too short and short-circuited, or too wide and close to an open state. A function of controlling the gap between the electrodes to an appropriate value at which discharge can occur by transmitting a control signal and adjusting the support position of the workpiece by displacing the workpiece by the piezoelectric element, The electric discharge machining apparatus according to (1) or (4) .
（６）前記測定装置は、前記工作物に対する前記工具電極の支持位置を変位するサーボモータを有し、
前記測定装置によって測定した前記工具電極と前記工作物の極間電圧波形に基づいて、前記極間距離が狭すぎて短絡気味であるか、あるいは、広過ぎて開放状態に近いのかを判断し、制御信号を発信し、前記サーボモータを制御して、前記工具電極の支持位置を調節することで、前記極間間隙を放電が生じ得る適切な値に制御する機能を保有することを特徴とする、前記（１）、（４）及び（５）のいずれか１項に記載された、放電加工装置。
( 6 ) The measurement apparatus includes a servo motor that displaces a support position of the tool electrode with respect to the workpiece,
Based on the interelectrode voltage waveform of the tool electrode and the workpiece measured by the measuring device, determine whether the interelectrode distance is too short and short-circuited, or too wide and close to the open state, It has a function of controlling the gap between the electrodes to an appropriate value that can cause discharge by transmitting a control signal, controlling the servo motor, and adjusting the support position of the tool electrode. The electric discharge machining apparatus described in any one of (1), ( 4 ) and ( 5 ).
従来のマイクロ放電加工においては、回路に発生する浮遊容量による影響が支配的であったが、本発明では、静電誘導給電法を採用したことにより、回路のインダクタンスおよび浮遊容量の影響を削減でき、２つの容量比を制御することで、放電エネルギー量が変化し、加工物の表面粗さを制御することが可能になる。また、高速に回転する工具電極給電部への給電ができるため、加工屑の排出が容易に行え、また、工具電極の軸振れを生じさせることなく高精度なマイクロ加工が可能となる。さらに、工具電極とは非接触で、工具電極と工作物間の極間電圧を測定する非接触電圧測定装置から極間電圧を測定し、設定したサーボ基準電位との差より、工作物または、主軸の位置を調整するサーボ制御回路を組み合わせることで、放電加工装置の自動化が可能である。 In conventional micro electrical discharge machining, the influence of stray capacitance generated in the circuit was dominant, but in the present invention, the influence of circuit inductance and stray capacitance can be reduced by adopting the electrostatic induction power feeding method. By controlling the two capacity ratios, the amount of discharge energy changes and the surface roughness of the workpiece can be controlled. In addition, since power can be supplied to the tool electrode power supply section that rotates at high speed, machining waste can be easily discharged, and high-precision micromachining can be performed without causing axial deflection of the tool electrode. Furthermore, the contact voltage is measured from a non-contact voltage measuring device that measures the contact voltage between the tool electrode and the workpiece without contact with the tool electrode. By combining a servo control circuit that adjusts the position of the spindle, the electrical discharge machine can be automated.
帯電している導体（Ａ）に帯電していない導体（Ｂ）を近づければ、導体（Ｂ）には導体（Ａ）の近い側に異種の（Ａが＋であれば−）、遠い側には同種（Ａの＋）の電荷が現れることは知られており、この現象は静電誘導と呼ばれている。 If the uncharged conductor (B) is brought close to the charged conductor (A), the conductor (B) is dissimilar to the side closer to the conductor (A) (if A is +), the far side It is known that the same kind (A +) of charge appears in this, and this phenomenon is called electrostatic induction.
本発明の等価回路の例として、図２のような給電電極・工具電極・工作物を配置した場合。給電電極と工具電極との間において電子の移動が無いため、回路に生じる浮遊容量とインダクタンスを無視することができ、給電電極と工作物に一定周期でパルス電圧Ｖを印加すると、印加電圧Ｖにより、静電誘電現象が生じ、電極内の電子が移動し電荷の偏りが生じる、図２（ａ）。 As an example of the equivalent circuit of the present invention, when a feeding electrode, a tool electrode, and a workpiece as shown in FIG. 2 are arranged. Since there is no movement of electrons between the power supply electrode and the tool electrode, stray capacitance and inductance generated in the circuit can be ignored. When a pulse voltage V is applied to the power supply electrode and the workpiece at a constant period, the applied voltage V In FIG. 2A, an electrostatic dielectric phenomenon occurs, and electrons in the electrode move to cause a bias in charge.
このとき、工具電極と工作物の間の加工間隙において工具電極表面が正、工作物が負に帯電することで極間に電位差が生じ放電が発生する。放電により工作物から工具電極に電子が移動する、図２（ｂ）。 At this time, in the machining gap between the tool electrode and the workpiece, the surface of the tool electrode is positively charged and the workpiece is negatively charged, thereby generating a potential difference between the electrodes and generating electric discharge. Electrons move from the workpiece to the tool electrode due to the discharge, FIG.
次に、印加電圧を０にする。工具電極は放電によって工作物から電子を受入れたことにより負に帯電し、逆に工作物と給電電極は放電により電子を放出したことでともに正に帯電する、図２（ｃ）。 Next, the applied voltage is set to zero. The tool electrode is negatively charged by accepting electrons from the workpiece by discharge, and conversely, the workpiece and the feed electrode are both positively charged by discharging electrons by discharge, FIG. 2 (c).
従って、工具電極が負、工作物が正に帯電していることで極間に電位差が生じ、放電が発生して工具電極から工作物に電子が移動する、図２（ｄ）。このようにサイクルが繰り返されることにより加工が行われる。また、本加工法が図２（ｂ）、図２（ｄ）より両極性放電であることがわかる。 Accordingly, since the tool electrode is negative and the workpiece is positively charged, a potential difference is generated between the electrodes, and a discharge is generated to move electrons from the tool electrode to the workpiece, FIG. 2D. In this way, processing is performed by repeating the cycle. Moreover, it turns out that this processing method is bipolar discharge from FIG.2 (b) and FIG.2 (d).
静電誘電給電を用いた、マイクロ放電加工法の等価回路は、図３（ａ）の開放時、図３（ｂ）の放電時のように表すことができる。電極の内部抵抗をＲ０とし、給電電極と工具電極給電部、ならびに工具電極と工作物の間で形成される容量をＣ１，Ｃ２とし、放電によって生じる極間の電圧降下をツェナーダイオードに置き換えＲとＶｄを用いて表し、放電時の回路は、工具電極が正、工作物が負の放電が生じた場合に対し、工具電極が負、工作物が正の放電が生じた場合は、Ｖｄの符号は反転する。また、図中ａ点での電圧Ｖ（ｔ）とし、ａ点より各回路線に流れ出す電流をＩ１（ｔ）、Ｉ２（ｔ）、Ｉ３（ｔ）とし、電源電圧を数１、Ｔを印加電圧の周期、ｔｏｎをパルス幅とすると。図３で示した等価回路の開放時を数２で、放電時を数３で表わすと、次のようになる。 An equivalent circuit of the micro electric discharge machining method using the electrostatic dielectric power supply can be expressed as when the circuit shown in FIG. 3A is opened and when the electric discharge is shown in FIG. 3B. The internal resistance of the electrode is R 0 , the capacitance formed between the feed electrode and the tool electrode feed section, and the tool electrode and the workpiece is C 1 and C 2, and the voltage drop between the electrodes caused by the discharge is applied to the zener diode The replacement R and Vd are used to represent the circuit during discharge when the tool electrode is positive and the workpiece is negatively discharged, whereas the tool electrode is negative and the workpiece is positively discharged. , V d is inverted. Also, the voltage V (t) at the point a in the figure is assumed, the current flowing out from the point a to each circuit line is I 1 (t), I 2 (t), I 3 (t), and the power supply voltage is given by Is the period of the applied voltage, and t on is the pulse width. The time when the equivalent circuit shown in FIG. 3 is opened is expressed by Equation 2, and the time of discharge is expressed by Equation 3, which is as follows.
開放時は以下の式になる。 When opened, the following formula is used.
放電時は以下の式になる。 When discharging, the following equation is obtained.
これらの式を計算することにより求めた加工間隙の極間電圧波形を図４に、加工間隙を流れる放電電流を図５に示す。印加電圧Ｖは、周期Ｔ＝１１０μｓ、振幅１５０Ｖ、デューティ４５％の単極の矩形波とした。また、また、計算に用いた回路定数はそれぞれＣ１＝１０ｐＦ、Ｃ２＝１ｐＦ，Ｒ＝１００Ωとした。Ｃ１の値は、円筒コンデンサの容量として見積もった。また、放電電圧Ｖｄは２０Ｖに設定し、また、電源の内部抵抗Ｒ０は実際の値を用い、加工間隙の抵抗Ｒは放電電流のピーク値が一般的な微細加工で観察されるオーダと一致するように設定した。また、放電電圧Ｖｄは２０Ｖに設定した。工具電極が帯電していない初期状態からシミュレーションを開始し、第１周期は放電が生じない場合を仮定した。そして、ｔ＝５／４Ｔ、７／４Ｔ、９／４Ｔ、１１／４Ｔにおいて放電が発生したと仮定した。放電後、極間電圧がＶｄ＝２０Ｖとなり電荷が放電され、加工間隙の電流が０Ａとなった瞬間に絶縁が回復すると考え、開放状態の等価回路に切り替えた。図４中に示す（ａ）は開放状態にある領域、（ｂ）は工具電極が正、工作物が負として放電が生じた領域であり、その瞬間に図５に示すように放電電流が流れる。（ｃ）は放電終了後、再び開放状態になった領域であり、（ｄ）は工具電極が負、工作物が正で放電した領域である。図５の（ａ）、（ｂ）、（ｃ）、（ｄ）は図２の（ａ）、（ｂ）、（ｃ）、（ｄ）の各状態と対応している。 FIG. 4 shows a voltage waveform between the machining gaps obtained by calculating these equations, and FIG. 5 shows a discharge current flowing through the machining gap. The applied voltage V was a unipolar rectangular wave with a period T = 110 μs, an amplitude of 150 V, and a duty of 45%. In addition, the circuit constants used for the calculation were C 1 = 10 pF, C 2 = 1 pF, and R = 100Ω, respectively. The value of C 1 is estimated as the capacity of the cylinder capacitor. The discharge voltage V d was set to 20V, also the order using the actual value the internal resistance R 0 of the power supply, the resistance R of the machining gap is the peak value of the discharge current is observed in the general microfabrication Set to match. The discharge voltage V d was set to 20V. The simulation was started from the initial state in which the tool electrode was not charged, and it was assumed that no discharge occurred in the first period. It was assumed that discharge occurred at t = 5 / 4T, 7 / 4T, 9 / 4T, and 11 / 4T. After the discharge, the voltage between the electrodes became V d = 20 V, the charge was discharged, and the insulation was restored at the moment when the current in the machining gap became 0 A, and the equivalent circuit was switched to the open state. 4A is a region in an open state, and FIG. 4B is a region where discharge is generated with the tool electrode being positive and the workpiece being negative, and at that moment, a discharge current flows as shown in FIG. . (C) is an area that is opened again after the end of discharge, and (d) is an area where the tool electrode is negative and the workpiece is positive and discharged. (A), (b), (c), and (d) in FIG. 5 correspond to the states (a), (b), (c), and (d) in FIG.
前記で示したシミュレーションが正しいことを証明するために加工実験を行った。本発明の給電電極が間隙をもって、先端に工具電極が同一軸線上で固定された工具電極給電部の外側に配置された装置の概念図は図６に示す。工具電極給電部はプーリ・ベルトによりＶ字軸受と、鋼球を介して上部の軸受に押付けられながら回転する。軸受にＶ字形状を用いることにより、心振れが極めて小さく、高い回転精度が得られ、高精度な加工が可能となる。給電電極である中空パイプ内に工具電極給電部を挿入した状態で、給電電極を給電電極用Ｖ字軸受に押し付けながら固定した。工具電極給電部と給電電極を、取り付ける際は同心となるよう設定した。静電誘導給電を用い、工具が回転する微細放電加工を行うには、工具電極給電部を装置本体から絶縁する必要がある。そこでＶ字軸受は、工具電極給電部と接する部分に絶縁体であるセラミックを用い、さらに上部軸受の固定部を樹脂製とすることで装置本体から工具電極給電部を絶縁した。ＤＣモータを駆動し、プーリ・ベルトを介して工具電極給電部を回転させる。 In order to prove that the simulation shown above is correct, a processing experiment was conducted. FIG. 6 shows a conceptual diagram of an apparatus arranged outside the tool electrode power supply unit in which the power supply electrode of the present invention has a gap and the tool electrode is fixed to the tip on the same axis. The tool electrode feeding portion rotates while being pressed against the V-shaped bearing and the upper bearing via a steel ball by a pulley and belt. By using a V-shaped bearing, the runout is extremely small, high rotational accuracy is obtained, and high-precision machining is possible. With the tool electrode power supply portion inserted into the hollow pipe as the power supply electrode, the power supply electrode was fixed while being pressed against the V-shaped bearing for power supply electrode. The tool electrode power supply unit and the power supply electrode were set to be concentric when attached. In order to perform fine electrical discharge machining in which the tool rotates using electrostatic induction power feeding, it is necessary to insulate the tool electrode power feeding unit from the apparatus main body. Therefore, the V-shaped bearing uses ceramic which is an insulator at a portion in contact with the tool electrode power supply portion, and further, the tool electrode power supply portion is insulated from the apparatus main body by making the fixing portion of the upper bearing made of resin. The DC motor is driven to rotate the tool electrode power feeding unit via the pulley and belt.
タングステン（φ０．３１）の工具電極は、長さ１２５ｍｍの給電電極に挿入された工具電極給電部(φ３．８)の先端中央部にハンダ付けされている。給電電極は銅パイプ(外径φ６６．３５、内径φ４．５)であり、中空部に工具電極給電部が挿入されている。図７に給電電極と工具電極の断面図を示す。給電電極と工具電極給電部は一定の間隙を持って平行に支持され、工具電極給電部の先端部には、工具電極が固定され、工作物と極間間隙を持って配置した。非接触電圧測定プローブが、工具電極の電荷を測定し、工具電極と工作物間の極間電圧波形をオシロスコープにより測定する。 The tool electrode of tungsten (φ0.31) is soldered to the center of the tip of the tool electrode feed portion (φ3.8) inserted into the feed electrode having a length of 125 mm. The feeding electrode is a copper pipe (outer diameter φ66.35, inner diameter φ4.5), and the tool electrode feeding portion is inserted into the hollow portion. FIG. 7 shows a cross-sectional view of the feeding electrode and the tool electrode. The power supply electrode and the tool electrode power supply unit were supported in parallel with a certain gap, and the tool electrode was fixed at the tip of the tool electrode power supply unit and arranged with a gap between the workpiece and the electrode. A non-contact voltage measuring probe measures the charge of the tool electrode and measures an inter-electrode voltage waveform between the tool electrode and the workpiece with an oscilloscope.
図７の電極部を一般の金型加工に使用されている型彫り放電加工機（ソディック ＡＱ−３５Ｌ、加工範囲Ｘ２６６０ｍｍＹ２５０ｍｍＺ２５０ｍｍ）の主軸に固定した、工作物はアクリル製の加工槽中に固定され、加工槽は加工機の加工テーブル上に置かれた精密変位テーブル上に設置してある。 The electrode part of FIG. 7 is fixed to the main shaft of a die-sinking electric discharge machine (Sodic AQ-35L, processing range X2660 mm Y250 mm Z250 mm) used for general mold processing, and the workpiece is fixed in an acrylic processing tank, The processing tank is installed on a precision displacement table placed on the processing table of the processing machine.
加工機の放電パルス回路を利用したが、放電持続時間が一定であるアイソパルスではなく、一定周期で一定パルス幅の電圧を印加する方式のトランジスタ放電回路を選択した。また、極間に現れる極間電圧波形が従来のものと異なるので、加工機のサーボ送り制御が利用できない。そこで、極間距離の調整と加工送りには放電加工機の送りを使用せず、精密変位テーブルを用いて手動で工作物を上下させることによって加工をおこなった。その際、オシロスコープにより極間電圧波形を目視で観察し、放電が持続するように目盛を調節した。加工条件を表１に示す。 Although the discharge pulse circuit of the processing machine was used, a transistor discharge circuit that applied a voltage with a constant pulse width at a constant period was selected instead of an isopulse with a constant discharge duration. Further, since the voltage waveform between the electrodes appearing between the electrodes is different from the conventional one, the servo feed control of the processing machine cannot be used. Therefore, the machining of the distance between the poles and the machining feed were carried out by manually moving the workpiece up and down using a precision displacement table without using the feed of the electric discharge machine. At that time, the voltage waveform between the electrodes was visually observed with an oscilloscope, and the scale was adjusted so that the discharge continued. Table 1 shows the processing conditions.
非接触電圧測定プローブは、図７のように、工具電極と同心である円環形状であり、給電電極と一定間隔を設け配置してある。工具電極の電圧が変化すると、工具電極と非接触電圧測定プローブの間で電界が生じ、非接触電圧測定プローブに静電誘導現象により電荷が蓄積される。従って、工具電極とプローブ間の容量と検出線の浮遊容量との比で分割された極間電圧が測定でき、オシロスコープで極間電圧波形がモニタできる。 As shown in FIG. 7, the non-contact voltage measuring probe has an annular shape that is concentric with the tool electrode, and is arranged with a certain distance from the feeding electrode. When the voltage of the tool electrode changes, an electric field is generated between the tool electrode and the non-contact voltage measuring probe, and charges are accumulated in the non-contact voltage measuring probe due to an electrostatic induction phenomenon. Therefore, the voltage between the electrodes divided by the ratio of the capacitance between the tool electrode and the probe and the stray capacitance of the detection line can be measured, and the voltage waveform between the electrodes can be monitored with an oscilloscope.
オシロスコープでモニタした極間電圧波形を図８に示す。図中に示す（ａ）、（ｂ）、（ｃ）、（ｄ）の領域は図４の同じ記号の領域に対応している。シミュレーションのように初めて放電が発生した時の波形ではないが、図８より、本発明の加工法は、両極性放電であることがわかる。実際に測定した極間電圧波形、と等価回路の解析により求めた極間電圧波形（図４）は、図４及び図８中の（ａ）、（ｂ）、（ｃ）、（ｄ）時で定性的に傾向が一致している、つまり、本発明の加工法を正しく等価回路で表わすことができ、原理を証明できた。 FIG. 8 shows the voltage waveform between the electrodes monitored with an oscilloscope. Regions (a), (b), (c), and (d) shown in the figure correspond to regions of the same symbol in FIG. Although it is not the waveform when the first discharge occurs as in the simulation, it can be seen from FIG. 8 that the processing method of the present invention is a bipolar discharge. The actual measured inter-electrode voltage waveform and the inter-electrode voltage waveform obtained by analyzing the equivalent circuit (FIG. 4) are shown in FIGS. 4 and 8 at (a), (b), (c), and (d). Qualitatively agree with each other, that is, the processing method of the present invention can be correctly expressed by an equivalent circuit, and the principle can be proved.
工具電極給電部と対向する給電電極と工具電極間の静電容量Ｃ１は、極間の誘電率をε、工具電極給電部外径をａ、給電電極内径をｂ、給電電極長さをＬとすれば、数４により求めることができる。 The capacitance C 1 between the feeding electrode and the tool electrode facing the tool electrode feed section, the dielectric constant of the machining gap epsilon, the tool electrode feeding outer diameter a, a feeding electrode inner diameter b, and the feeding electrode length L Then, it can obtain | require by Formula 4.
ここで、Ｖｃ１、Ｖｃ２は各々Ｃ１、Ｃ２の充電電圧、Ｑ１、Ｑ２は各々Ｃ１，Ｃ２に充電される電荷である。従って給電電極長さＬを短くすると、給電電極と工具電極の間で形成される容量、Ｃ１が小さくなり、Ｖｃ１が大きくなるため、加工間隙の極間電圧Ｖｃ２が小さくなり、放電エネルギーを減少させることができる。パルス電源からの印加電圧が決まり、給電電極の仕様を決めれば数３で静電容量Ｃ１、Ｃ２が決まり、放電電圧が決定される。 Here, V c1, V c2 are each C 1, C 2 of the charging voltage, Q 1, Q 2 are each C 1, charge that is charged to C 2. Accordingly, when the feed electrode length L is shortened, the capacitance C 1 formed between the feed electrode and the tool electrode is reduced, and V c1 is increased, so that the interelectrode voltage V c2 of the machining gap is reduced and the discharge energy is reduced. Can be reduced. When the applied voltage from the pulse power source is determined and the specifications of the power supply electrode are determined, the capacitances C 1 and C 2 are determined by Equation 3, and the discharge voltage is determined.
したがって、回路に生じる浮遊容量により最小限界放電エネルギーが決定される従来型の放電加工機に比べ、本発明では、工具電極に静電誘電給電する方法により、回路に発生するインダクタンスや浮遊容量の影響を削除し、極間に充電された微小な電荷の放電のみで加工するので、微細な加工が可能になり、さらに、非接触で給電が可能なので、回転する工具電極給電部や、気体軸受、磁気軸受等を用いた放電加工が可能となる。 Therefore, compared to a conventional electric discharge machine in which the minimum critical discharge energy is determined by the stray capacitance generated in the circuit, the present invention has an effect of inductance and stray capacitance generated in the circuit by a method of electrostatically feeding the tool electrode. Since it is processed only by the discharge of a minute charge charged between the electrodes, fine processing becomes possible, and furthermore, non-contact power supply is possible, so the rotating tool electrode power supply part, gas bearing, Electric discharge machining using a magnetic bearing or the like becomes possible.
放電エネルギーを小さくするために、工具電極と工作物の間の電圧を下げると、工具電極と工作物間の極間間隙が狭くなる、しかし、極間距離が狭くなるほど加工屑の排出は困難となるため、加工が不安定になる。そこで、本発明の装置においては、給電電極と工具電極給電部が別々に支持され、工具電極がプーリーで回転可能な設計とし、極間距離が狭くても、加工屑の排出が容易に行える構造とした。 If the voltage between the tool electrode and the workpiece is lowered in order to reduce the discharge energy, the gap between the tool electrode and the workpiece becomes narrower. Therefore, processing becomes unstable. Therefore, in the apparatus of the present invention, the power supply electrode and the tool electrode power supply unit are separately supported, the tool electrode is designed to be rotatable by a pulley, and even when the distance between the electrodes is small, the structure can be easily discharged. It was.
給電電極の内径、長さの差異により静電容量Ｃ１がどの位変化するのを計算で求め、結果を表２にまとめてみた。 The amount of change in the capacitance C 1 due to the difference in the inner diameter and length of the feeding electrode was determined by calculation, and the results are summarized in Table 2.
本発明の放電加工装置を用いて、鏡面の出ているブロックゲージ上に、加工条件表３で、数秒間加工を行い、得られた放電痕の大きさを、工具電極を３０００ｒｐｍで回転させた場合と工具電極非回転の場合で、工具回転による効果を比較した。 Using the electrical discharge machining apparatus of the present invention, machining was performed on the mirror gauge block gauge for several seconds in the machining condition table 3, and the size of the resulting electrical discharge mark was rotated at 3000 rpm. The effect of tool rotation was compared between the case and the case where the tool electrode was not rotated.
共焦点レーザ顕微鏡(ＯＬＹＭＰＵＳ製ＬＥＸＴ ＯＬＳ３０００)を用いて、放電痕径を測定した。放電痕の観察結果をまとめたグラフを図９で示す。従来の非回転式工具では給電容量６．６ｐＦまでしか放電が確認できなかったが、今回使用した回転式工具では１．９ｐＦまで給電容量を小さくしても放電痕を得ることができた。また非回転式工具では給電容量１３ｐＦまでしか安定した加工が行えなかったが、回転式工具では７．５ｐＦまで安定した加工が行えた。給電容量が小さいほど充電電圧ＶＣ２が小さくなり、放電エネルギーが小さく、放電が生じる極間間隙は狭くなり、加工屑排出が困難になると考えられるが、工具回転により加工屑の排出性が良好になったため、非回転式工具電極を用いた場合よりも、小さな給電容量１．９ｐＦで放電痕が得られたと考えられる。 The diameter of the discharge mark was measured using a confocal laser microscope (LETY OLS3000 manufactured by OLYMPUS). A graph summarizing the observation results of the discharge marks is shown in FIG. With the conventional non-rotating tool, discharge could only be confirmed up to a power supply capacity of 6.6 pF, but with the rotary tool used this time, discharge traces could be obtained even when the power supply capacity was reduced to 1.9 pF. In addition, the non-rotary tool could only perform stable machining up to a power supply capacity of 13 pF, but the rotary tool could perform stable machining up to 7.5 pF. The smaller the power supply capacity, the smaller the charging voltage V C2 , the smaller the discharge energy, the narrower the gap between the electrodes where discharge occurs, and it will be difficult to discharge the scraps. Therefore, it is considered that the discharge trace was obtained with a smaller power supply capacity of 1.9 pF than when the non-rotating tool electrode was used.
より小さな給電容量で加工をおこなえば、放電エネルギーを小さくできることから加工面の粗さをさらに向上できる可能性がある。しかし最小の放電痕が得られた給電容量１．９ｐＦを使用した場合には、加工面に放電集中がおき加工が進まなかった。これは放電が飛び始める極間間隙は２μｍ以下であり、手動では放電が飛ぶ微小な極間距離を適切に保つことができなかったことが原因であると考えられる。放電集中を防ぐためには、μｍ単位の極間間隙の制御を自動で行う必要がある。 If the machining is performed with a smaller power supply capacity, the discharge energy can be reduced, so that the roughness of the machined surface may be further improved. However, when using a power supply capacity of 1.9 pF with which the minimum discharge trace was obtained, discharge concentration occurred on the machined surface and machining did not proceed. This is considered to be because the gap between the electrodes where the discharge starts is 2 μm or less, and the minute distance between the electrodes where the discharge flies can not be maintained properly manually. In order to prevent discharge concentration, it is necessary to automatically control the gap between the electrodes in units of μm.
極間の状態を把握するため極間電圧の時間平均値（以下，平均極間電圧と呼ぶ）を検出する必要がある。しかし本発明の放電加工装置において極間電圧を測定するために、高速回転する工具電極給電部に直接検出線を接続することは不可能である。そこで、本発明では、非接触電圧測定法を用いて、極間電圧の測定を行う。 In order to grasp the state between the electrodes, it is necessary to detect the time average value of the voltage between the electrodes (hereinafter referred to as the average voltage between the electrodes). However, in order to measure the voltage between the electrodes in the electric discharge machining apparatus of the present invention, it is impossible to connect the detection line directly to the tool electrode power feeding portion that rotates at high speed. Therefore, in the present invention, the interelectrode voltage is measured using a non-contact voltage measurement method.
非接触電圧測定法の原理を、図１０に示す。工具電極近傍に非接触で非接触電圧測定プローブ(検出線を付けた金属)を置く。図１０の場合は工具電極と同心である円環である。そして、工具電極の電圧が変化すると、非接触電圧測定プローブとの間で電界が生じ、非接触電圧測定プローブに静電誘導現象により電荷が蓄積される。
極間電圧は、工具電極とプローブ間の容量ＣＰ（以下，非接触プローブ容量ＣＰと呼ぶ）にかかる電圧ＶＣＰと，検出線間の浮遊容量ＣＳにかかる電圧ＶＣＳとの和で表せ，ＶＣＰ，ＶＣＳともに極間電圧の変化に応じて変化すると考えられる。よって、検出線間の電圧ＶＣＳを測定することにより極間電圧の変化を捉えることが可能となる。ここで捉えた電圧が開放時と短絡時で変化すれば、その電圧を基にして極間間隙のサーボ制御が可能となる。
The principle of the non-contact voltage measurement method is shown in FIG. A non-contact voltage measurement probe (metal with a detection line) is placed in the vicinity of the tool electrode in a non-contact manner. In the case of FIG. 10, it is a ring concentric with the tool electrode. When the voltage of the tool electrode changes, an electric field is generated between the tool electrode and the non-contact voltage measuring probe, and charges are accumulated in the non-contact voltage measuring probe due to an electrostatic induction phenomenon.
The voltage between the electrodes is the sum of the voltage V CP applied to the capacitance C P between the tool electrode and the probe (hereinafter referred to as a non-contact probe capacitance C P ) and the voltage V CS applied to the floating capacitance C S between the detection lines. It can be considered that both V CP and V CS change according to the change of the interelectrode voltage. Therefore, it is possible to capture the change in the interelectrode voltage by measuring the voltage V CS between the detection lines. If the voltage captured here changes between open and short circuits, servo control of the gap between the electrodes can be performed based on the voltage.
非接触電圧測定を行いながら加工する場合、非接触プローブ容量ＣＰが従来の工具電極・工作物間の静電容量Ｃ２に加わるため、放電エネルギーが変化する可能性がある。その結果、加工特性が変化する可能性が考えられる。そこで、その影響について調査した。 When processing while non-contact voltage measurement, since the non-contact probe capacitance C P is applied to the electrostatic capacitance C 2 between the conventional tool electrode-workpiece, there is a possibility that the discharge energy changes. As a result, the processing characteristics may change. Therefore, the effect was investigated.
非接触電圧測定を行った場合と、行わなかった場合で、鏡面の出ているブロックゲージ上に表４に示す加工条件で数秒間加工を行い、得られた放電痕を比較した。このとき用いた給電容量Ｃ１は７．５ｐＦである。 When the non-contact voltage measurement was performed and when it was not performed, processing was performed for several seconds on the mirror gauge block gauge under the processing conditions shown in Table 4, and the obtained discharge traces were compared. Feeding capacity C 1 using this time is 7.5 pF.
共焦点レーザ顕微鏡(ＯＬＹＭＰＵＳ製ＬＥＸＴ ＯＬＳ３０００)を用いて、得られた放電痕径を測定した。測定結果を図１１に示す。非接触電圧測定を行った場合と行わない場合で、得られた放電痕の大きさはほとんど等しいことがわかる。よって、非接触電圧測定を行うことによる放電エネルギーへの影響は、小さいと考えられる。また、今回使用した非接触プローブ容量が０．７５ｐＦと小さいため、影響が小さくなったと考えられる。 The obtained discharge scar diameter was measured using a confocal laser microscope (LETY OLS3000 manufactured by OLYMPUS). The measurement results are shown in FIG. It can be seen that the size of the discharge traces obtained is almost the same when the non-contact voltage measurement is performed and when the non-contact voltage measurement is performed. Therefore, the influence on the discharge energy by performing the non-contact voltage measurement is considered to be small. Moreover, since the non-contact probe capacity | capacitance used this time is as small as 0.75 pF, it is thought that the influence became small.
上記したように、非接触電圧測定法を用いることで、極間電圧の変化を検出することが可能であることがわかった。しかし、静電誘導給電を用いた放電加工では、図８での電圧波形図に示したように、グラウンドを挟んでほぼ同じ大きさの両極性の電圧波形を示すため、極間電圧の時間平均をとると、プラス側とマイナス側で打ち消し合い０近くになってしまう。そのため、極間電圧の時間平均を取る前に絶対値化する必要がある。 As described above, it was found that the change in the interelectrode voltage can be detected by using the non-contact voltage measurement method. However, in the electric discharge machining using electrostatic induction power supply, as shown in the voltage waveform diagram in FIG. If they are taken, they will cancel each other out on the plus side and minus side and become close to zero. Therefore, it is necessary to make the absolute value before taking the time average of the interelectrode voltage.
そこで平均極間電圧を検出するための回路製作を試みた。図１２に今回製作した平均極間電圧検出回路の概念図を示す。まず極間電圧を非接触で検出し、オペアンプを用いた高入力インピーダンスの差動増幅回路へ入力する。ここで使用したオペアンプの入力インピーダンスは１０１２Ωである。差動増幅回路により、適当な大きさに変圧された極間電圧は、絶対値化された後ＲＣ回路を用いて平滑化され、バッファアンプを通して出力される。 Therefore, an attempt was made to produce a circuit for detecting the average interelectrode voltage. FIG. 12 is a conceptual diagram of the average interelectrode voltage detection circuit manufactured this time. First, the voltage between the electrodes is detected in a non-contact manner and input to a high-impedance differential amplifier circuit using an operational amplifier. The input impedance of the operational amplifier used here is 10 12 Ω. The voltage between the electrodes transformed to an appropriate magnitude by the differential amplifier circuit is converted to an absolute value, smoothed using an RC circuit, and output through a buffer amplifier.
本発明者等は、図３のＣ１とＣ２の容量の違いによる、極間電圧Ｖc２への影響を調べた。図１３はＣ１の容量をＣ２の１０倍にした場合の極間電圧を、図１４はＣ１の容量をＣ２の容量と等しく設定した場合の極間電圧を計算したグラフである。 The present inventors examined the influence on the interelectrode voltage V c2 due to the difference in capacitance between C 1 and C 2 in FIG. Figure 13 is a machining gap voltage in the case where the capacity of the C 1 to 10 times the C 2, FIG. 14 is a graph obtained by calculating the inter-electrode voltage when the capacity of C 1 was set equal to the capacitance of C 2.
このグラフより、極間電圧Ｖc２はコンデンサ容量Ｃ１とＣ２の比により異なり、図１３のＣ１／Ｃ２が１０の場合は、図１４のＣ１／Ｃ２が１の場合より、ＶＣ２の値は２倍以上大きくなることが分かる。このことは、工具電極と工作物の加工間隙の電圧を大きくし、放電エネルギーを増大したい、粗削りの場合は、Ｃ１の容量をＣ２より大きく設定し、微小な放電エネルギーで工作物の表面を加工するが必要とするマイクロ加工の場合では、Ｃ１の容量を下げることで、放電エネルギーを適切なレベルまで小さくすることが可能となる。但し、Ｃ１を下げすぎると、加工間隙の電圧が小さくなり過ぎて放電が生じにくくなる事が分かる。 From this graph, the machining gap voltage V c2 is different from the ratio of the capacitance C 1 and C 2, in the case of C 1 / C 2 is 10 in FIG. 13, from the case C 1 / C 2 in FIG. 14 is 1, It can be seen that the value of V C2 is more than twice as large. This increases the voltage of the machining gap of the tool electrode and the workpiece, would like to increase the discharge energy, in the case of roughing, the capacitance of C 1 is set larger than C 2, the surface of the workpiece with small discharge energy processing the but in the case of micromachining in need, by reducing the capacity of the C 1, it is possible to reduce the discharge energy to an appropriate level. However, excessively lowering the C 1, the discharge be less likely to occur is understood voltage of the machining gap becomes too small.
これまで極間間隙の制御は工作物をのせた精密変位テーブルを手動で上下させて行っていたが、手動では適切な極間間隙が保持できず、放電集中の発生による粗さのバラツキが見られ、さらなる微細加工は困難であった。そこで工作物を圧電テーブルに取り付け、極間間隙のサーボ制御を行い、加工特性の向上を図った。図１５に制御系の概念図を示す。 Until now, the gap between the poles was controlled by manually moving the precision displacement table with the workpiece up and down manually, but the appropriate gap between the poles could not be maintained manually, and there was a variation in roughness due to the occurrence of discharge concentration. Further microfabrication has been difficult. Therefore, the workpiece was mounted on a piezoelectric table and servo control of the gap between the poles was performed to improve the machining characteristics. FIG. 15 shows a conceptual diagram of the control system.
まず極間電圧を、給電電極に並列に設置したリング状の非接触電圧測定プローブで検出し、オペアンプを用いた高入力インピーダンスの差動増幅回路へ入力する。そして差動増幅の出力を絶対値化して平均した極間電圧と、任意に設定できるサーボ基準電圧の差をとり、圧電素子ドライバへ入力する。圧電素子ドライバでは入力された電圧を増幅し圧電素子へ出力する。圧電素子は入力された電圧に応じて変位する。こうして平均極間電圧とサーボ基準電圧の差から圧電テーブルの変位量が決定され、極間間隙の制御をサーボ化できる。 First, the voltage between the electrodes is detected by a ring-shaped non-contact voltage measuring probe installed in parallel with the feeding electrode, and input to a differential amplifier circuit having a high input impedance using an operational amplifier. Then, the difference between the voltage between the electrodes obtained by averaging the differential amplification outputs as an absolute value and the servo reference voltage that can be arbitrarily set is calculated and input to the piezoelectric element driver. The piezoelectric element driver amplifies the input voltage and outputs it to the piezoelectric element. The piezoelectric element is displaced according to the input voltage. Thus, the displacement amount of the piezoelectric table is determined from the difference between the average inter-electrode voltage and the servo reference voltage, and the control of the inter-electrode gap can be servoed.
サーボ送り方式では、平均極間電圧と、作業者が任意に設定できる基準サーボ電圧を比較し、両者が一致するように極間距離が制御される。前記の平均極間電圧検出回路の出力を用いて、以下に示す圧電テーブル・サーボ送り制御回路を作製し、実験を行った。 In the servo feed method, the average inter-electrode voltage is compared with a reference servo voltage that can be arbitrarily set by the operator, and the inter-electrode distance is controlled so that they match. A piezoelectric table / servo feed control circuit shown below was fabricated using the output of the average interelectrode voltage detection circuit, and an experiment was conducted.
図１６に実験装置の概要を示す。圧電テーブルは弾性ヒンジで支持され、一方向のみ駆動できる構造である。圧電テーブル上に加工槽と工作物を固定して、圧電テーブルを上下方向に駆動することで、極間間隙の調整を行った。図１５に示した、圧電テーブル・サーボ制御の概念図で、平均極間電圧と、任意に設定できるサーボ基準電圧の差を、圧電素子ドライバへ入力する。圧電素子ドライバでは入力された電圧を増幅し圧電素子へ出力する。圧電素子は入力された電圧に応じて変位する。こうして平均極間電圧とサーボ基準電圧の差から圧電テーブルの変位量が決定され、極間間隙制御をサーボ化できる。圧電テーブルに入力可能な０〜１５０Ｖの範囲での変位は最大１８μｍであった。マイクロ放電加工における極間間隙は数μｍ以下のため、１８μｍの変位量は極間間隙制御には十分な大きさである。 FIG. 16 shows an outline of the experimental apparatus. The piezoelectric table is supported by an elastic hinge and can be driven in only one direction. The gap between the electrodes was adjusted by fixing the machining tank and the workpiece on the piezoelectric table and driving the piezoelectric table in the vertical direction. In the piezoelectric table / servo control conceptual diagram shown in FIG. 15, the difference between the average inter-electrode voltage and the servo reference voltage that can be arbitrarily set is input to the piezoelectric element driver. The piezoelectric element driver amplifies the input voltage and outputs it to the piezoelectric element. The piezoelectric element is displaced according to the input voltage. Thus, the displacement amount of the piezoelectric table is determined from the difference between the average inter-electrode voltage and the servo reference voltage, and the inter-electrode gap control can be servoed. The maximum displacement within the range of 0 to 150 V that can be input to the piezoelectric table was 18 μm. Since the gap between the electrodes in micro electric discharge machining is several μm or less, the displacement of 18 μm is large enough for controlling the gap between the electrodes.
また、同様に主軸・サーボ制御は、加工機内部の放電検出基板上で平均極間電圧と任意に設定されたサーボ基準電圧を比較し、両者が一致するようにサーボ制御をすればよい。よってサーボ制御するためには、前記の平均極間電圧検出回路の出力を、加工機内の放電検出基板へ入力できれば良い。 Similarly, the spindle / servo control may be performed by comparing the average inter-electrode voltage with an arbitrarily set servo reference voltage on the discharge detection board inside the processing machine, and performing servo control so that the two coincide. Therefore, in order to perform servo control, it is only necessary to be able to input the output of the average interelectrode voltage detection circuit to the discharge detection substrate in the processing machine.
しかし非接触電圧測定では浮遊容量の影響により短絡時でも検出される電圧が０Ｖにはならない。前記の平均極間電圧検出回路の出力は、例えば、開放時で＋６Ｖ、短絡時で＋２Ｖとなるのに対し、放電検出基板への入力電圧は、開放時の−５Ｖから、短絡時の０Ｖまでの範囲でなければならない。そこで開放時に−５Ｖ、短絡時に０Ｖを出力するように、平均極間電圧検出回路の出力を反転増幅し、さらにオフセット電圧を加える。 However, in the non-contact voltage measurement, the voltage detected at the time of a short circuit does not become 0V due to the influence of stray capacitance. The output of the average inter-electrode voltage detection circuit is, for example, + 6V when open and + 2V when short-circuited, whereas the input voltage to the discharge detection board is from -5V when open to 0V when short-circuited Must be in the range. Therefore, the output of the average inter-electrode voltage detection circuit is inverted and amplified so that -5V is output when open and 0V is output when short-circuited, and an offset voltage is further applied.
上記の圧電テーブルを用いた、サーボ送り制御と、加工軸のサーボ送り制御を併用した協調サーボ制御を行うことも可能である。加工機主軸よりも圧電テーブルの方が周波数応答性が高いため、極間の制御は主に圧電テーブルによってなされ、圧電テーブルの変位が上限または下限をこえないように加工機主軸による極間間隙制御を行えば良い。 It is also possible to perform cooperative servo control using the above-described piezoelectric table in combination with servo feed control and machining axis servo feed control. Because the frequency response of the piezoelectric table is higher than that of the machine tool spindle, control between the poles is mainly performed by the piezoelectric table, and the gap between the poles is controlled by the machine tool spindle so that the displacement of the piezoelectric table does not exceed the upper or lower limit. Just do it.
以上述べたサーボ制御方法で、手動による極間間隙制御と同じ条件で加工し、測定した加工面粗さを図１７に示す。同一加工面で２０回測定した平均値は、手動で０．６２μｍＲｚに対して、圧電テーブル・サーボ制御で０．５５μｍＲｚ、主軸サーボ制御で０．７３μｍＲｚ、協調制御で０．８５μｍＲｚであった。しかし同一加工面内で粗さにばらつきが見られるため、極間間隙制御法によらず、粗さはほぼ同じであると考えられる。 FIG. 17 shows the measured machined surface roughness measured by the servo control method described above under the same conditions as the manual gap control. The average value measured 20 times on the same processed surface was 0.55 μmRz by the piezoelectric table servo control, 0.73 μmRz by the spindle servo control, and 0.85 μmRz by the cooperative control, with respect to 0.62 μmRz manually. However, since the roughness is observed in the same processed surface, the roughness is considered to be almost the same regardless of the gap control method.
また，このときの加工速度を図１８に示す。加工速度は手動の極間間隙制御で３７６μｍ３／ｍｉｎであるのに対して、圧電テーブル・サーボ制御で５４９μｍ３／ｍｉｎ、主軸サーボ制御で１１８５μｍ３／ｍｉｎ、協調制御で１３２９μｍ３／ｍｉｎであり、応答性の最も高いと考えられる協調制御で加工速度がもっとも速かった。また、主軸サーボ制御に比べ、より応答性が高いと考えられる圧電テーブル・サーボ制御で加工速度が遅かった。ゲインが高すぎる場合は短絡しやすく加工が不安定になるため、加工速度も遅くなる。以上より、極間間隙制御のサーボ化により、加工形状、加工面粗さは手動による極間間隙制御の場合とほぼ同等であったものの、加工速度を１．５倍から３．５倍速くできた。 Moreover, the processing speed at this time is shown in FIG. Whereas the processing speed is 376μm 3 / min manually interpolar gap control, 549μm 3 / min in the piezoelectric table servo control, in the spindle servo control 1185μm 3 / min, in a cooperative control be 1329μm 3 / min The machining speed was the fastest with the coordinated control that was considered to be the most responsive. In addition, the machining speed was slower with the piezoelectric table servo control, which is considered to be more responsive than the spindle servo control. If the gain is too high, short-circuiting is likely and machining becomes unstable, resulting in a slow machining speed. From the above, the servo control of the inter-electrode gap control has made the machining shape and surface roughness almost the same as the case of manual inter-electrode gap control, but the machining speed can be increased 1.5 to 3.5 times. It was.
給電電極を工具電極給電部に間隙をもって配置する位置に関しては、工具電極給電部を取り囲む円筒形状のほか、工具電極給電部の上部対向面に微小な極間距離を隔てて対向する位置に、給電電極を配置し、給電電極と工具電極給電部の間隙、又は、対向面積を制御することで、放電エネルギーを制御することも可能である。 As for the position where the power supply electrode is arranged in the tool electrode power supply part with a gap, in addition to the cylindrical shape surrounding the tool electrode power supply part, the power supply electrode is supplied to a position facing the upper facing surface of the tool electrode power supply part with a small distance between the electrodes. It is also possible to control the discharge energy by arranging the electrodes and controlling the gap between the power supply electrode and the tool electrode power supply unit or the facing area.
本発明の原理によれば、給電電極と工具電極給電部に間隙を持たせて、静電容量を制御し、放電エネルギーを制御することが出来るが、本発明の原理から考えれば、給電電極を工作物に接近させ、給電電極と工作物に微小な間隙をもたせて、給電電極から工作物への静電容量Ｃ１Ａを調整しても同じ結果が得られるはずである。あるいは、工具電極給電部にコンデンサ端子を接続し容量結合し、コンデンサの電極面積、電極間距離、電極間に介在する物質の誘電率等を選択することで、同様に静電容量を調整することが可能であり、同様に、コンデンサ端子と工作物に容量結合で接続し、静電容量制御し、放電エネルギーを調整することも可能である。装置の概念図を示すと、図１９のように、工具電極給電部側から給電する場合で、給電電極を使用した場合は図１９（ａ）に、コンデンサを使用した容量結合法は図１９（ｂ），工作物側を給電電極で接続する場合の装置を図２０（ａ）に、コンデンサで容量結合する場合を図２０（ｂ）に示す。工作物側に容量結合した場合図２０（ａ）についても工具側から給電する場合と同じ等価回路で表せることから．両者が同じ性能を示すことを確認するため、実際に加工を行った。 According to the principle of the present invention, it is possible to provide a gap between the power supply electrode and the tool electrode power supply unit to control the capacitance and control the discharge energy. it is close to the workpiece, by remembering small gap to the workpiece and the feed electrode, adjusting same result even when the electrostatic capacitance C 1A to workpiece from the feed electrode should be obtained. Alternatively, the capacitance can be adjusted in the same way by connecting a capacitor terminal to the tool electrode power supply unit and capacitively coupling it, and selecting the electrode area of the capacitor, the distance between the electrodes, the dielectric constant of the substance interposed between the electrodes, etc. Similarly, it is also possible to connect the capacitor terminal and the work piece by capacitive coupling, control the electrostatic capacity, and adjust the discharge energy. The conceptual diagram of the apparatus is as shown in FIG. 19, when power is supplied from the tool electrode power supply side, and when the power supply electrode is used, FIG. 19A shows the capacitive coupling method using a capacitor. FIG. 20 (a) shows an apparatus when the workpiece side is connected by a feeding electrode, and FIG. 20 (b) shows a case of capacitive coupling with a capacitor. When capacitive coupling is performed on the workpiece side, FIG. 20A can also be represented by the same equivalent circuit as when power is supplied from the tool side. In order to confirm that both showed the same performance, it processed actually.
そこで、給電電極、工具電極間に生じる静電容量Ｃ１Ａに代わり、給電用に市販のコンデンサＣ３Ａをテーブル越しに工作物へ接続し、表５の条件で加工を行った。工具電極はタングステン軸を用い、極間間隙の制御は、工作物を載せた精密変位テーブルを手動で上下させて行った。図２１（ａ）は給電電極を工作物側に近接した場合でＣ１Ｂ容量２７ｐＦと、（ｂ）工具側に近接した場合でＣ１Ａ容量２８ｐＦに設定した場合とで、極間電圧波形を比較した図である。 Therefore, instead of the electrostatic capacitance C 1A generated between the power feeding electrode and the tool electrode, a commercially available capacitor C 3A for power feeding was connected to the workpiece through a table, and processing was performed under the conditions shown in Table 5. The tool electrode used a tungsten shaft, and the gap between the electrodes was controlled by manually moving the precision displacement table on which the workpiece was placed up and down. And C 1B capacitor 27pF in FIG. 21 (a) when in close proximity to the feeding electrode to the workpiece side, in the case of setting the C 1A capacitance 28pF when close to (b) tool side, comparing the machining gap voltage waveform FIG.
図２１より、給電電極の位置が異なると、極間電圧の値はことなるが、開放時、放電時とも同じようなパターンの波形が見られ、また、図２２に、Ｃ１Ａ容量とコンデンサ容量Ｃ１Ｂを変化させ、数秒間加工をおこない、給電容量と得られた放電痕直径を測定すると、給電容量が大きいほど放電痕直径が大きくなることがわかり、マイクロ加工では、給電容量を調整することで、表面あらさを制御できることが分かる。図２３に、工作側にＣ１Ｂ給電容量２７ｐＦでマイクロ加工した工作物の例を示す。 From FIG. 21, when the position of the feeding electrode is different, the value of the voltage between the electrodes is different, but the waveform of the same pattern is seen at the time of opening and discharging, and FIG. 22 shows the C 1A capacity and the capacitor capacity. changing the C 1B, performs several seconds machining, measuring the discharge traces diameter obtained as a feeding capacity, can see that the more feed capacity larger discharge crater diameter is large, the micro-machining, by adjusting the feeding capacity It can be seen that the surface roughness can be controlled. 23 shows an example of a workpiece that is microfabricated with C 1B feeding capacity 27pF to work side.
以上の結果より、給電用の静電電極を工具電極側と工作物側のどちらかに接する位置に取り付けても，同程度の大きさの放電痕が得られ、また、非接触で極間電圧を検出し、圧電テーブルを用いれば、工具電極と工作物の極間間隙をサーボ制御できることが分かった。
また、工具電極として、金属ワイヤを使用して工作物の切断等に使用されている、ワイヤ放電加工は、図２４に示すように、工作物をはさんで、上下の位置で給電子をワイヤに押し付けて給電を行っているが、給電子の磨耗による加工特性の劣化、浮遊容量やインダクタンスの影響による、最小放電エネルギー限界値や、放電電流波形の立ち上がりの遅れを生じる。
Based on the above results, even when the electrostatic electrode for power supply is attached at a position in contact with either the tool electrode side or the workpiece side, the same level of discharge trace is obtained, and the contact voltage is non-contact. It was found that the gap between the electrode between the tool electrode and the workpiece can be servo controlled by using the piezoelectric table.
In addition, as shown in FIG. 24, wire electric discharge machining is used for cutting a workpiece using a metal wire as a tool electrode. However, there is a deterioration in processing characteristics due to wear of the power supply, a minimum discharge energy limit value, and a delay in the rise of the discharge current waveform due to the effects of stray capacitance and inductance.
又、給電子にワイヤを接触させることにより、図２５に示すように、ワイヤのワイヤガイド穴中心から偏心を生じ、加工方向を変更した時、あるいは、ワイヤを傾けたりした時に、ワイヤ中心位置がワイヤガイド穴中心に対してズレて、加工精度が低下する問題が明らかになっている。 Further, by bringing the wire into contact with the power supply, as shown in FIG. 25, the center of the wire is eccentric from the center of the wire guide hole, and when the machining direction is changed or the wire is tilted, the position of the wire center is changed. There has been a problem that the machining accuracy is deteriorated due to deviation from the center of the wire guide hole.
しかしながら、図２６に示したように、本発明の非接触給電方法をワイヤ放電加工に用いることにより、給電子の磨耗による加工特性の変化がなくなるので、高価な給電子を交換する必要が無くなり、経済的である。 However, as shown in FIG. 26, since the non-contact power feeding method of the present invention is used for wire electric discharge machining, the machining characteristics are not changed due to the wear of the power supply, so that it is not necessary to replace expensive power supply, Economical.
又、給電電極と工具電極のワイヤが非接触なため、非常に長い、給電線の引き回しによる、浮遊容量の影響が無視できる。更には、給電部が軸対称になるので、給電子を押付けて給電する場合の非軸対称がもたらすワイヤ位置やワイヤ傾き角度の誤差が低減でき、誤差をゼロに出来なくとも、ＮＣデータで補正することも容易になる。 Further, since the wires of the power supply electrode and the tool electrode are not in contact with each other, the influence of stray capacitance due to the very long power supply line can be ignored. Furthermore, since the power feeding section is axisymmetric, errors in the wire position and wire tilt angle caused by non-axisymmetric when feeding by pressing the power supply can be reduced, and even if the error cannot be reduced to zero, it is corrected with NC data. It is also easy to do.
１００ 工具電極給電部
１５０ 工具電極
２００ 給電電極
２５０ 給電用コンデンサ
３００ 工作物
Ｌ 給電電極長さ
Ｐ 非接触電圧測定プローブ
ＰＷ パルス電源
Ｏ オシロスコープ
Ｔ 精密変位テーブル
Ｚ 絶縁テープ
100 Tool electrode feeder 150 Tool electrode 200 Feed electrode 250 Feed capacitor 300 Workpiece L Feed electrode length P Non-contact voltage measurement probe PW Pulse power supply O Oscilloscope T Precision displacement table Z Insulation tape
Claims (6)
前記工具電極が同一軸線上で結合され、前記工具電極と共に軸回転可能に絶縁支持された工具電極給電部と、
前記工具電極給電部に対して一定間隙をもって対向配置した給電電極と、
前記給電電極と前記工作物とが結線されたパルス電源と、
を有し、
前記パルス電源から電圧を印加し、前記給電電極より前記工具電極給電部に静電誘電給電することにより、前記工具電極給電部と対向する前記給電電極間の距離及び対向する面積の少なくとも一方を調整して形成される容量Ｃ１Ａと、前記工具電極と前記工作物間の間隙で形成される容量Ｃ２Ａと、に基づいて、前記放電エネルギーを決定し、
前記工具電極と一定間隙の対向面を保有して配置した電圧測定プローブの検出線と、前記工作物と、が結線された電圧検出回路からなる、前記工具電極と前記工作物との極間電圧を測定する測定装置を装備することを特徴とする、放電加工装置。 In the electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, generating discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A power supply electrode disposed opposite to the tool electrode power supply section with a constant gap;
A pulse power source in which the feeding electrode and the workpiece are connected;
Have
A voltage is applied from the pulse power supply, and electrostatic power is fed from the power supply electrode to the tool electrode power supply unit, thereby adjusting at least one of a distance between the power supply electrodes facing the tool electrode power supply unit and an opposing area. The discharge energy is determined on the basis of the capacitance C 1A formed by the capacitor C 2A formed by the gap between the tool electrode and the workpiece ,
A voltage between the tool electrode and the workpiece, comprising a voltage detection circuit in which a detection line of a voltage measurement probe arranged to hold the opposed surface of the tool electrode with a fixed gap and the workpiece are connected. An electrical discharge machining apparatus equipped with a measuring device for measuring the temperature .
前記工具電極が同一軸線上で結合され、前記工具電極と共に軸回転可能に絶縁支持された工具電極給電部と、
前記工具電極給電部に一方の端子が接触したコンデンサと、
前記コンデンサの他方の端子と前記工作物とに結線されたパルス電源と、
を有し、
前記パルス電源から電圧を印加し、前記コンデンサと前記工具電極給電部の容量結合により給電を行い、前記コンデンサの容量Ｃ３Ａと、前記工具電極と前記工作物間の間隙で形成される容量Ｃ４Ａと、に基づいて、前記放電エネルギーを決定することを特徴とする、放電加工装置。 In the electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, generating discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A capacitor with one terminal in contact with the tool electrode power supply unit;
A pulse power source wired to the other terminal of the capacitor and the workpiece;
Have
A voltage is applied from the pulse power source, and power is supplied by capacitive coupling of the capacitor and the tool electrode power supply unit. The capacitor C 3A and the capacitance C 4A formed by the gap between the tool electrode and the workpiece are provided. And the electric discharge machining apparatus, wherein the electric discharge energy is determined.
極間に放電エネルギーを発生させ、前記工作物を加工する放電加工装置において、
前記工具電極が同一軸線上で結合され、前記工具電極と共に軸回転可能に絶縁支持された工具電極給電部と、
一定間隙をもって前記工作物に対向配置した給電電極と、
前記工具電極給電部と前記給電電極とに結線されたパルス電源と、
を有し、
前記パルス電源から電圧を印加し、前記給電電極より前記工作物に静電誘電給電することにより、前記工作物と対向する前記給電電極の間隙の距離及び対向する面積の少なくとも一方を調整し、前記間隙に形成される容量Ｃ１Ｂと、前記工具電極と前記工作物間の間隙で形成される容量Ｃ２Ｂと、に基づいて、前記放電エネルギーを決定することを特徴とする、放電加工装置。 In the electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, generating discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A feeding electrode disposed opposite the workpiece with a constant gap;
A pulse power source connected to the tool electrode power supply unit and the power supply electrode;
Have
A voltage is applied from the pulse power source, and electrostatic work is fed to the workpiece from the feeding electrode, thereby adjusting at least one of the distance and the facing area of the feeding electrode facing the workpiece, and a capacitor C 1B is formed in the gap, and a capacitor C 2B is formed at the gap between the workpiece and the tool electrode, on the basis, and determines the discharge energy, the electric discharge machining apparatus.
前記測定装置によって測定した前記工具電極と前記工作物との極間電圧波形に基づいて、前記極間距離が狭すぎて短絡気味であるか、あるいは、広過ぎて開放状態に近いのかを判断し、制御信号を発信し、前記工作物の支持位置を前記圧電素子により変位させることにより調節することで、前記極間間隙を放電が生じ得る適切な値に制御する機能を保有することを特徴とする、請求項１または４に記載された、放電加工装置。 The measuring device includes a piezoelectric element that displaces a support position of the workpiece with respect to the tool electrode,
Based on the voltage waveform between the tool electrode and the workpiece measured by the measuring device, it is determined whether the distance between the electrodes is too short and short-circuited, or too wide and close to an open state. A function of controlling the gap between the electrodes to an appropriate value at which discharge can occur by transmitting a control signal and adjusting the support position of the workpiece by displacing the workpiece by the piezoelectric element, The electric discharge machining apparatus according to claim 1 or 4 .
前記測定装置によって測定した前記工具電極と前記工作物の極間電圧波形に基づいて、前記極間距離が狭すぎて短絡気味であるか、あるいは、広過ぎて開放状態に近いのかを判断し、制御信号を発信し、前記サーボモータを制御して、前記工具電極の支持位置を調節することで、前記極間間隙を放電が生じ得る適切な値に制御する機能を保有することを特徴とする、請求項１、４及び５のいずれか１項に記載された、放電加工装置。 The measuring device has a servo motor for displacing a support position of the tool electrode with respect to the workpiece;
Based on the interelectrode voltage waveform of the tool electrode and the workpiece measured by the measuring device, determine whether the interelectrode distance is too short and short-circuited, or too wide and close to the open state, It has a function of controlling the gap between the electrodes to an appropriate value that can cause discharge by transmitting a control signal, controlling the servo motor, and adjusting the support position of the tool electrode. The electric discharge machining apparatus according to any one of claims 1, 4, and 5 .
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