This invention relates to improvement in a discharge pulse generator used with an electric discharge machine, a laser oscillator, a particle accelerator, etc., for example, for supplying power between a pair of electrodes.
FIG. 17 is a circuit diagram to show the configuration of a discharge pulse generator in a related art and shows an example of a discharge pulse generator of an electric discharge machine. In FIG. 17, numeral 1 denotes an electrode, numeral 2 denotes a workpiece, numeral 3 denotes a DC power supply, numeral 4 denotes a resistor, numeral 5 denotes a capacitor (capacitance C), and L denotes an inductance existing in wiring. A charging circuit made up of the DC power supply 3 and the resistor 4 is connected to the capacitor 5. The electrode 1 and the workpiece 2 are immersed in a work liquid such as water or oil (not shown).
When the voltage of the capacitor 5 is raised by the above-mentioned charging circuit and the work liquid in the gap between poles of the electrode 1 and the workpiece 2 electrically break down, energy stored in the capacitor 5 flows into between the poles of the electrode 1 and the workpiece 2. Discharge current Ig at this time becomes a damped vibration waveform caused by LC oscillation, as shown in FIG. 18.
In FIG. 18, t denotes a time, first current i1 is a current of a half cycle of the resonance frequency of LC oscillation, next current i2 is a current of the opposite polarity to that of the current i1, and current i3 is a current of the opposite polarity to that of the current i2; such several vibration currents flow into between the above-mentioned poles. The pulse width of the first current i1 is a short pulse (T1), but the pulse width where the several vibration currents stop becomes considerably long (T) and discharge continues to occur meanwhile, forming one discharge pulse as a whole. If electric discharge machining is executed using such a discharge pulse generator in the related art, machining based on the pulse T having the comparatively long pulse width rather than machining based on the short pulse T1 is executed and thus it is difficult to finely work on the workpiece 2; this is a problem.
In the discharge pulse generator in the related art as in FIG. 17, bipolar discharge current flows as in FIG. 18. Thus, if setting is made so that electrode consumption lessens in one of the polarities, current always flows also into the direction in which electrode consumption is much, and the electrode consumption grows and thus it becomes difficult to work with high accuracy; this is a problem.
FIG. 19 is a circuit diagram to show the configuration of another discharge pulse generator in a related art disclosed in Japanese Patent Laid-Open No.266133/1995. In the figure, numeral 1 denotes an electrode, numeral 2 denotes a workpiece, numeral 3 denotes a DC power supply, numeral 4 denotes a resistor, numeral 6 denotes a transistor, numeral 7 denotes control means, numerals 8a and 8b denote coaxial cables each with one end side open (characteristic impedances are Z0a and Z0b respectively), and numerals 9a and 9b denote matching impedances connected to the coaxial cables 8a and 8b (impedances are Za and Zb respectively).
FIG. 20 shows an example of discharge current Ig between poles of the electrode 1 and the workpiece 2 in the discharge pulse generator in the related art in FIG. 19. FIG. 20(a) shows the discharge current Ig when the impedances Za and Zb are equal to the characteristic impedances Z0a and Z0b, and FIG. 20(b) shows the discharge current Ig when the impedances Za and Zb are halves the characteristic impedances Z0a and Z0b respectively. In the figure, t denotes a time. If the matching impedances are equal to the characteristic impedances as in FIG. 20(a), the discharge current Ig becomes a pulse-like current waveform with no vibration, but if the matching impedances differ from the characteristic impedances as in FIG. 20(b), the discharge current becomes a vibration-like current waveform as the discharge current in the discharge pulse generator in FIG. 18.
That is, the discharge pulse generator in the related art in FIG. 19 can provide a pulse-like discharge current waveform with no vibration only if the matching impedances are equal to the characteristic impedances of the coaxial cables, and therefore the peak value of the discharge current lowers to a half as the matching impedances are connected; this is a problem.
Since the matching impedances are fixed, if the voltage of the DC power supply 3 is constant, the peak value of the discharge current pulse cannot be changed; this is a problem.
The invention is intended for solving the problems as described above and it is an object of the invention to provide a discharge pulse generator that can raise the peak value of a discharge current pulse.
It is an object of the invention to provide a discharge pulse generator for making it possible to set the peak value of a discharge current pulse to any desired value.
It is an object of the invention to provide a discharge pulse generator fitted for micromachining and capable of decreasing electrode consumption if the discharge pulse generator is used for electric discharge machining.
According to the invention, there is provided a discharge pulse generator for supplying power between a pair of electrodes, comprising at least one distribution constant line of a predetermined length being connected at one termination to the electrodes, charging means being connected to the above-mentioned distribution constant line for charging the capacitance of the above-mentioned distribution constant line, rectification means being connected to an opposite termination of the above-mentioned distribution constant line in a direction in which no current flows relative to voltage of the above-mentioned charging means, and a resistor being connected in series to the above-mentioned rectification means and having a resistance value equal to the characteristic impedance of the above-mentioned distribution constant line.
According to the invention, there is provided a discharge pulse generator for supplying power between a pair of electrodes, comprising at least one distribution constant line of a predetermined length being connected at one termination to the electrode, charging means being connected to the above-mentioned distribution constant line for charging the capacitance of the above-mentioned distribution constant line, rectification means being connected to an opposite termination of the above-mentioned distribution constant line in a direction in which no current flows relative to voltage of the above-mentioned charging means, a resistor being connected in series to the above-mentioned rectification means and having a resistance value equal to the characteristic impedance of the above-mentioned distribution constant line, and a constant voltage source being connected in series to the above-mentioned rectification means.
According to the invention, there is provided a discharge pulse generator for supplying power between a pair of electrodes, comprising at least one distribution constant line of a predetermined length being connected at one termination to the electrode, charging means being connected to the above-mentioned distribution constant line for charging the capacitance of the above-mentioned distribution constant line, rectification means being connected to an opposite termination of the above-mentioned distribution constant line in a direction in which no current flows relative to voltage of the above-mentioned charging means, a resistor being connected in series to the above-mentioned rectification means and having a resistance value equal to the characteristic impedance of the above-mentioned distribution constant line, voltage detection means for detecting voltage of the above-mentioned resistor, voltage polarity determination means for determining the polarity of the voltage of the above-mentioned resistor detected by the above-mentioned voltage detection means, and charging stop means f or stopping charging of the above-mentioned charging means if the above-mentioned voltage polarity determination means determines that the polarity of the voltage is opposite to polarity just before discharge.
In the discharge pulse generator, at least one of the above-mentioned distribution constant lines is a repetition circuit of discrete capacitors and inductors forming characteristic impedance equal to the characteristic impedance of the above-mentioned distribution constant line.
In the discharge pulse generator, at least one of the above-mentioned distribution constant lines is implemented as a parallel body of a capacitor being connected in parallel to the above-mentioned rectification means and the above-mentioned resistor and an inductor and a resistor being connected in series to the capacitor and characteristic impedance based on the capacitor and the inductor and a resistance value of the resistor of the parallel body are equal to the characteristic impedance of the above-mentioned distribution constant line.
In the discharge pulse generator, the above-mentioned charging means is implemented as a series body of a DC power supply, a resistor, and switching means and control means for turning on/off the switching means is provided.
In the discharge pulse generator, the above-mentioned charging means is made up of a series body of a DC power supply, a resistor, and a diode connected in a charging direction and switching means connected in parallel between the resistor and the DC power supply of the series body and control means for turning on/off the switching means is provided.
In the discharge pulse generator, a current adjusting resistor is connected in series to the termination of the above-mentioned distribution constant line to which the electrode is connected.
In the discharge pulse generator, the predetermined length of the above-mentioned distribution constant line is set so that the propagation time of the above-mentioned distribution constant line becomes a half any desired discharge current pulse width generated between the poles.
According to the invention, there is provided a discharge pulse generator, for use with a wire electric discharge machine for supplying discharge energy between poles of a wire electrode and a workpiece, relatively moving the wire electrode and the workpiece by positioning means, and working on the workpiece, for generating the discharge energy, the above-mentioned discharge pulse generator comprising a first distribution constant line and a second distribution constant line being connected at one terminations in parallel, an upper feeding part connecting an opposite termination of the above-mentioned first distribution constant line for supplying power to the wire electrode, a lower feeding part connecting an opposite termination of the above-mentioned second distribution constant line for supplying power to the wire electrode, charging means being connected to the above-mentioned first distribution constant line and the above-mentioned second distribution constant line for charging capacitances of the above-mentioned first distribution constant line and the above-mentioned second distribution constant line, rectification means being connected to the one terminations of the above-mentioned distribution constant lines in a direction in which no current flows relative to voltage of the above-mentioned charging means, and a resistor being connected in series to the above-mentioned rectification means and having a resistance value equal to the characteristic impedance of the above-mentioned distribution constant line.
The discharge pulse generator according to the invention is configured as described above and the discharge current rises rapidly and a discharge current pulse of a single pulse of the same polarity is generated. Thus, for example, to use the discharge pulse generator for electric discharge machining, the discharge pulse generator is fitted for micromachining and can decrease electrode consumption.
The peak value of the discharge current can be set to any desired value.
Further, the discharge pulse generator can produce group discharge at a predetermined repetitive frequency according to the very simple configuration and thus, for example, to use the discharge pulse generator for electric discharge machining, the workpiece can be worked on with higher accuracy and higher quality at higher speed.